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Cerebral phosphorus metabolite abnormalities in opiate-dependent polydrug abusers in methadone maintenance
Psychiatry Research: Neuroimaging Section 90 Ž1999. 143]152
Cerebral phosphorus metabolite abnormalities in opiate-dependent polydrug abusers in methadone maintenance q Marc J. Kaufman a,b,U , Mark H. Pollack c , Rosemond A. Villafuerte a , Thellea J. Kukes a , Stephanie L. Rosea , Jack H. Mendelsonb, Bruce M. Cohena , Perry F. Renshaw a a
Brain Imaging Center, McLean Hospital, 115 Mill St, Belmont, MA 02478, USA Alcohol and Drug Abuse Research Center, McLean Hospital, 115 Mill St, Belmont, MA 02478, USA c Anxiety Disorders Program, Massachusetts General Hospital and Habit Management Institute, Boston, MA, USA b
Received 20 January 1999; received in revised form 5 May 1999; accepted 13 May 1999
Abstract This study evaluated cerebral phosphorus metabolites in opiate-dependent polydrug abusers in methadone maintenance therapy ŽMMT. and determined whether metabolite profiles differed based on treatment duration. Phosphorus magnetic resonance spectroscopy Ž 31 P-MRS. data were acquired with the ISIS volume localization method from a 50-mm thick axial brain slice through the orbitofrontal and occipital cortices. Study subjects included 15 MMT subjects, seven having undergone treatment for an average of 39 " 23 weeks Žmean " S.D.. and eight having undergone treatment for 137 " 53 weeks, as well as an age matched comparison group Ž n s 16.. The methadone dose administered on the study day averaged 70.5" 17.1 mg and was statistically equivalent in short- and long-term subgroups. MMT subjects Ž n s 15. differed from control subjects in percent phosphocreatine Ž%PCr. levels Žy13%., and in both phosphomonoester Ž%PME, q13%. and phosphodiester Ž%PDE, q10%. levels, which likely reflect abnormalities in energy and phospholipid metabolism, respectively. There were no sex effects or group by sex interaction effects on these measures. In short-term MMT treatment subjects, abnormal %PCr Žy18%., %PME Žq20%. and %PDE Žq17%. levels were found compared with control subjects. The only metabolite abnormality detected in long-term MMT subjects was decreased %PCr Žy9%., in spite of continued illicit drug abuse. From
q
Portions of these results have been presented in preliminary form at the International Society for Magnetic Resonance in Medicine, Fifth Scientific Meeting and Exhibition, Vancouver, BC, Canada, 1997, and at the Joint Meeting of the International Society for Neurochemistry and American Society for Neurochemistry, Boston, MA, 1997. U Corresponding author. Tel.: q1-617-855-3469; fax: q1-617-855-2770. E-mail address: [email protected] ŽM.J. Kaufman. 0925-4927r99r$ - see front matter Q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 9 2 5 - 4 9 2 7 Ž 9 9 . 0 0 0 1 7 - 7
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these data, we conclude that polydrug abusers in MMT have 31 P-MRS results consistent with abnormal brain metabolism and phospholipid balance. The nearly normal metabolite profile in long-term MMT subjects suggests that prolonged MMT may be associated with improved neurochemistry. Q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Magnetic resonance spectroscopy; Heroin; Cerebral metabolism; Cerebral blood flow; Brain; Substance dependence
1. Introduction The National Institute on Drug Abuse recently reported a resurgence in opiate abuse and dependence in several major American cities ŽNational Institute on Drug Abuse, 1997.. This trend suggests that more people will require treatment for opiate abuse or dependence in the near future. A highly effective treatment for opiate dependence is methadone. Methadone maintenance therapy ŽMMT. has been shown to be effective in reducing drug use ŽCooper et al., 1983; Tims and Ludford, 1984. and improving psychiatric symptoms ŽMcLellan et al., 1982, 1986; Kosten et al., 1993; Strain et al., 1996., as well as improving overall health ŽBall and Ross, 1991. and quality of life ŽTorrens et al., 1997. in opiate abusers. Accordingly, the National Institutes of Health ŽNIH. has recommended expanded use of MMT for treatment of opiate addiction ŽNational Institutes of Health, 1997.. In spite of the growing problem of opiate abuse and the widespread use of MMT, there has been a paucity of research into the brain effects of opiates and the neurochemical effects of methadone administration. The few published studies of opiates document cerebral metabolic and perfusion abnormalities that persist well beyond the period of acute opiate intoxication and withdrawal ŽLondon et al., 1989; Krystal et al., 1995; Rose et al., 1996; Gerra et al., 1998.. One recent study demonstrated that methadone administration improves cerebral perfusion during opiate withdrawal ŽDanos et al., 1998a.. While cerebral blood flow improvements may contribute to the overall efficacy of MMT therapy, there is currently an incomplete understanding of the biological basis of methadone’s effects. Consequently, additional studies are necessary
to elucidate the biological consequences of opiate dependence as well as to determine the effects of methadone and of newly developed treatments. One non-invasive brain-imaging technique that may contribute to this effort is phosphorus magnetic resonance spectroscopy Ž 31 P-MRS.. 31 PMRS allows measurement of molecular pools associated with brain bioenergetic status and membrane integrity. Bioenergetic status is reflected by levels of adenosine triphosphate ŽATP. Ždetected in the b-nucleoside phosphate b-NP resonance., and in the inorganic phosphate ŽPi . and phosphocreatine ŽPCr. resonances. Because cerebral blood flow is closely coupled to cerebral metabolism ŽRaichle et al., 1976; Sokoloff, 1981., the cerebral perfusion deficits associated with opiate dependence Žsee above. that typically are asymptomatic may be detectable with 31 P-MRS. Indeed, 31 PMRS studies of cocaine- and heroin-dependent polydrug abusers in early withdrawal ŽChristensen et al., 1996. have documented cerebral bioenergetic disturbances. In addition to energy-related molecules, 31 P-MRS spectra also contain phospholipid resonances for phosphomonoesters ŽPME. and phosphodiesters ŽPDE., which are markers for membrane integrity and turnover. The PME resonance arises principally from phosphorylcholine ŽPC. and phosphorylethanolamine ŽPE., which serve as precursors for the phospholipids phosphatidylcholine and phosphatidylethanolamine, respectively ŽGyulai et al., 1984.. The PDE peak consists of a narrow component containing small molecules such as glycerophosphocholine ŽGPC. and glycerophosphoethanolamine ŽGPE., which are lipid catabolites, and a larger broad component from mobile phospholipids ŽMurphy et al., 1989; Kilby et al., 1991; Pettegrew et al., 1994.. Phospholipid abnormali-
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ties have also been documented with 31 P-MRS in cocaine-dependent and heroin-dependent polydrug abusers ŽMacKay et al., 1993; Christensen et al., 1996. and in alcoholics ŽMeyerhoff et al., 1995.. This study used 31 P-MRS to evaluate neurochemical indices in opiate-dependent polydrug abusers in MMT. The study population was primarily opiate-dependent, with minimal cocaine use, and was studied after being in MMT therapy for a minimum of 8 weeks. These criteria were selected in order to avoid the brain blood flow abnormalities known to be associated with heavy cocaine use ŽVolkow et al., 1988; Holman et al., 1991; Strickland et al., 1993; Levin et al., 1995; Kosten et al., 1998. and with withdrawal states ŽHolman et al., 1991; Krystal et al., 1995; Levin et al., 1995; Rose et al., 1996; Danos et al., 1998a; Kosten et al., 1998.. We tested the hypothesis that abnormal cerebral phosphorus metabolite profiles would be observed in opiate-dependent polydrug abusers in prolonged MMT. Because of reported sex differences in the effects of chronic substance abuse ŽLevin et al., 1994., we evaluated whether there were any effects of sex on these measures. Additionally, in light of reported clinical improvements in MMT patients Žsee above., we also tested the hypothesis that the neurochemical profile in the long-term MMT group would be comparable to that in the control group.
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2. Methods 2.1. Subjects Opiate-dependent polydrug abusers Žnine women and six men, aged 40 " 5 years, mean " S.D.. were recruited from an outpatient MMT clinic ŽHabit Management Institute, Boston, MA.. Individuals with a history of alcohol abuse or HIV infection were excluded. Subject weights in the MMT group were normal and were statistically equivalent to weights found in sex-matched control subjects. This group was subdivided into two subgroups based on MMT duration: the shortterm Ž n s 7, 39 " 23 weeks. and the long-term Ž n s 8, 137 " 53 weeks. groups. All medical histories, including random biweekly urine toxicology testing results, were reviewed in order to determine population demographics. As part of the screening procedure, subjects were required to estimate their alcohol use during their lifetime, the past year, the past month, and the past 3 days. Subjects estimated their use with a five level scale: 0, 1]4, 5]10, 11]39, and ) 40 exposures. While more than half of the MMT subjects reported lifetime consumption of more than 40 drinks, none reported having consumed more than 10 drinks in the year prior to the study and none reported having consumed more than four drinks in the month prior to the study. Although two
Table 1 Random urine toxicology results
Methadone Opiates Benzodiazepines Cocaine THC Propoxyphene Amphetamine Darvon Morphine Barbiturates Clean urines §
Short-term MMT Ž n s 7.
Long-term MMT Ž n s 8.
98.1" 2.5 39.1" 32.1 27.3" 39.7 15.4" 30.2 10.3" 22.2 5.5 " 7.6 2.1" 5.6 0.0" 0.0 0.0" 0.0 0.5" 1.4 26.3" 26.3
97.4" 3.5 34.4" 24.6 48.8" 34.0 21.0" 29.5 0.8" 1.5 3.1" 4.5 2.1" 3.0 2.1" 2.3U 1.4" 3.9 1.0" 2.8 26.6" 22.1
Shown are means " S.D. for %positive urine tests on biweekly random screens. methadone-positive samples.
U
F1,13 s 5.8, P- 0.04; § Percentage excludes
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subjects reported having had prior alcohol problems, their self-reported alcohol use was not indicative of current alcohol problems, and their removal did not alter the statistical findings. Accordingly, they have been included in the analyses. Positive urine tests were found more than 10% of the time for methadone Ž98%., benzodiazepines Ž39%., opiates Ž37%. and cocaine Ž18%.. Clean urine screens were found on an average of 26% of the time. These characteristics were statistically equivalent in the short- and long-term MMT groups, with the exception of Darvon-positive urines, of which none were found in the short-term group and 2% were found in the long-term group ŽTable 1.. The methadone dose administered on the scan day was statistically equivalent in the short- and long-term treatment groups and averaged 79 " 15 and 63 " 16 mgrday, respectively ŽNS, unpaired t-test.. A comparison group Žsix women and 10 men, aged 40 " 4 years. without history of substance abuse or neurological or psychiatric disorder was studied with identical procedures. All subjects provided written informed consent and the protocol was approved by the McLean Hospital Institutional Review Board. All subjects provided breath and urine samples immediately prior to scanning to determine recent alcohol or illicit drug exposure. A positive breath alcohol sample ŽAlco Sensor III Breathalyzer, Intoximeters Inc., St. Louis, MO. in any subject was grounds for study exclusion. A positive urine test for illicit drugs ŽTriageTM Test, Biosite Diagnostics, San Diego, CA. was grounds for exclusion only in control subjects, since it was assumed that the MMT group would have ongoing drug use ŽBall and Ross, 1991; Kosten et al., 1993; Strain et al., 1996.. Positive TriageTM testing frequencies for all illicit substances were statistically equivalent in the short-term and long-term MMT groups. 2.2. Imaging Spectra were acquired on a 1.5-T General Electric Signa Scanner using a doubly tuned, linear proton, quadrature phosphorus head coil. An axial whole brain slice of 50-mm thickness ŽFig. 1. was prescribed through the orbitofrontalroc-
Fig. 1. Sagittal image of a control subject with the 50-mm-thick axial spectral slice outlined. The slice was positioned through the orbitofrontalroccipital cortices with the inferior edge just superior to the inferior margin of the frontal lobe.
cipital cortices. Spectra were acquired with the image selected in vivo spectroscopy ŽISIS. volume-localized spectroscopy technique ŽOrdidge et al., 1986.. Acquisition parameters were tip angle s 908, repetition time ŽTR. s 3 s, acquisition delay s 350 ms, number of points s 1024, and spectral widths 2500 Hz. Spectra were processed with VARPROrMRUI, which is a singular value decomposition time-domain fitting software package Žvan den Boogaart et al., 1995.. Seven peaks were semiautomatically fit to Gaussian lineshapes, with 5-Hz exponential line broadening: phosphomonoesters ŽPME., inorganic phosphorus ŽPi ., phosphodiesters ŽPDE., phosphocreatine ŽPCr., and g-, a- and b-nucleoside phosphates ŽFig. 2. by an investigator who was blind to the experimental conditions. The residual after spectrum fitting ŽFig. 2, bottom trace. includes a broad signal component from fast relaxing phosphorus nuclei in bone and phospholipids. This component was automatically excluded from the fitted peaks by the VARPROrMRUI software and displayed as a part of the residual. The total phosphorus signal Žsummation of all seven fitted metabolite peak areas. was statistically equivalent
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across groups. Consequently, the ratio of the area of each peak divided by the total phosphorus area Ž%metabolite. was used for between-group comparisons ŽKlunk et al., 1994.. These measures have been shown to be stable in control subjects, with %metabolite values differing by - 5% in repeat scans ŽChristensen et al., 1996.. The intracellular hydrogen ion concentration, pH, was determined using the method of Petroff et al. Ž1985.. Statistical analyses were performed with ANOVAs testing for treatment group effects Žcontrol vs. MMT subjects., sex effects, and MMT duration effects Žcontrol subjects vs. short- vs. long-term MMT groups. using the Statview software package ŽAbacus Concepts, Inc., Berkeley, CA..
3. Results Phosphocreatine Ž%PCr. levels were reduced in the MMT group when compared with control subjects Žy13%, F1,27 s 16.6, P- 0.001.. No differences in %b-NP levels were noted. The %PME levels were elevated in the MMT group Žq13%, F1,27 s 9.5, P- 0.005.. Similarly, %PDE levels were elevated in the MMT group Žq10%, F1,27 s 6.9, P- 0.02.. No effects of sex or interaction effects of group by sex were noted. Additionally, no associations between self-reports of alcohol use and metabolite levels were found. For the three metabolites found to differ above, we tested whether metabolite differences existed between control subjects and short-term and long-term MMT subgroups ŽFig. 3.. An overall difference was noted for %PCr levels Ž F2,28 s 14.5, P- 0.0001.. Post-hoc evaluation with Scheffe’s ´ F-test revealed %PCr differences between control subjects and both short-term MMT subjects Žy18%, P- 0.0001. and long-term MMT subjects Žy9%, P- 0.05.. The %PCr difference between short- and long-term MMT subjects Žhigher %PCr in long- vs. short-term subjects. approached statistical significance Ž P - 0.07.. With regard to phospholipids, group differences were noted for both %PME Ž F2,28 s 6.6, P0.005. and %PDE Ž F2,28 s 8.0, P- 0.002.. Posthoc testing revealed significant %PME and %PDE level differences only between control
Fig. 2. Phosphorus magnetic resonance spectrum from a control subject. Shown Žfrom top to bottom. are the original, reconstructed, and fitted spectra along with the fitting residual. Spectra were processed with 5-Hz exponential line broadening using a singular-value decomposition time-domain fitting software package ŽVARPRO-MRUI.. PME s phosphomonoesters; Pi s inorganic phosphate; PDE s phosphodiesters; PCr s phosphocreatine; g, a , and b s gamma, alpha and beta nucleoside phosphates ŽNP..
subjects and short-term MMT subjects Žq20% and q17% of control subjects, P- 0.005 and P- 0.002, respectively.. Long-term MMT subjects had significantly lower %PDE levels than shortterm subjects Ž P- 0.05.. However, correlations between treatment duration Žweeks. and %PCr, %PME and %PDE levels did not reach statistical significance in this relatively small sample w r s 0.45 Ž P- 0.10., r s y0.33 Ž P- 0.33. and r s y0.35 Ž P- 0.21., respectivelyx. Additionally, we found no overall group differences in pH, but the short-term MMT group had slightly elevated pH Ž7.07" 0.02. compared to long-term MMT subjects Ž7.03" 0.03. Ž P- 0.02. who were statistically equivalent to control subjects Ž7.05" 0.02..
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Fig. 3. Metabolite levels in control subjects Ž n s 16. and in short- Ž n s 7. and long-term Ž n s 8. methadone maintenance treatment ŽMMT. subgroups. Shown are means " S.D. of percent metabolite measures. Post hoc Scheffe ´ test results: U P0.05 vs. control subjects; UU P- 0.01 vs. control subjects; UUU P - 0.0001 vs. control subjects; †P- 0.05 vs. long-term MMT group.
4. Discussion The present data document cerebral phosphorus metabolite abnormalities in opiate-dependent polydrug abusers in prolonged MMT. The findings suggest the presence of both bioenergetic Ždecreased %PCr. and phospholipid Želevated
%PME and %PDE. abnormalities. Importantly, nearly normal metabolite profiles were found in long-term MMT subjects, suggesting that prolonged MMT is associated with improved neurochemical function. Interestingly, Pezawas and colleagues recently reported normalized brain volumes in long-abstinent opiate abusers maintained either with MMT or morphine, when compared with short-duration abstinent subjects ŽPezawas et al., 1998.. Together, these results suggest that long-term opiate-substitution therapy may be beneficial to brain function and structure. The metabolite profiles described presently in the MMT group differ from those reported in other substance abuse populations. White matter PME and PDE levels were decreased in abstinent cocaine-dependent polydrug abusers ŽMacKay et al., 1993. and PDE levels were decreased in alcoholics ŽMeyerhoff et al., 1995., while ATP levels were reduced and PME levels were increased in cocaine- and heroin-dependent polydrug abusers in early withdrawal ŽChristensen et al., 1996.. Since the present study used the same 31 P-MRS technique as Christensen et al. Ž1996., the metabolite differences between these studies are likely to be attributable to subject demographics Že.g. minimal cocaine use in the present group vs. cocaine dependence in Christensen et al.. rather than to methodological differences. Alternatively, metabolite profile discrepancies might be a function of different states of drug use in the two study populations Že.g. active vs. withdrawing.. The mechanism underlying the present metabolite abnormalities is unknown. However, the abnormal MMT metabolite profile parallels abnormal 31 P-MRS profiles found in several types of brain insults. A PCr reduction and concomitant PME increase were reported in a model of chronic cerebral infarction in rodents ŽHoukin et al., 1989.. While it is unlikely that widespread tissue ischemia is occurring in subjects in the present study, it is abundantly clear that cerebrovascular dysfunction occurs in opiate abusers, including those in treatment ŽHolman et al., 1991; Krystal et al., 1995; Levin et al., 1995; Christensen et al., 1996; Rose et al., 1996; Danos et al., 1998a; Gerra et al., 1998.. Since there is a close
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coupling between cerebral metabolism and blood flow ŽRaichle et al., 1976; Sokoloff, 1981., abnormal perfusion may evoke metabolic dysfunction. Indeed, partial cerebral ischemia in piglets has been shown to acutely reduce PCr levels ŽLaptook et al., 1988.. The presently described PCr reduction may indicate compromised cerebral metabolism, and since phospholipid synthesis is an energy-dependent process, this could also result in increased PME levels. Mild cerebral blood flow reductions not associated with pathological changes or PCr changes also could induce PME changes, as flow reductions of - 50% in rodents have been linked to delayed PME elevations but normal PCr levels Žde la Torre et al., 1992.. With regard to PDE levels, increased %PDE implies acceleration of membrane breakdown processes and perhaps cell loss. This interpretation would be consistent with reported cerebral volume reductions in chronic opiate abusers ŽStrang and Gurling, 1989; Danos et al., 1998b; Pezawas et al., 1998.. However, cell death may not be requisite to the observation of PDE increases, since PDE elevations were found in cultured glial cells exposed to hypertonic media, possibly reflecting either an osmolyte role for PDE or a role in membrane remodeling to protect cells against volume shrinkage ŽFlogel et al., 1995.. The hypertonic conditions in that study also induced an increase in glial cell pH ŽFlogel et al., 1995.. Consequently, the present PDE and pH abnormalities suggest that some form of ongoing osmotic stress might be occurring in short-term MMT subjects. PME and PDE increases have also been noted in vitro in neuronal and glial cell cultures treated with toxic immunosuppressants ŽSerkova et al., 1996. and in vivo in human Alzheimer’s disease and Huntington’s disease, with PDE increments corresponding to the degree of neuropathological change ŽPettegrew et al., 1987.. Thus, the present findings may reflect a combination of neuronal or glial death or dysfunction induced by osmotic stress or other toxic processes. 4.1. Continued drug use and metabolite abnormalities The MMT group as a whole produced clean
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urines only 26% of the time. This is consistent with literature reports documenting a high prevalence of illicit drug use in MMT patients ŽIguchi et al., 1988; Nurco et al., 1988; Stitzer et al., 1992.. Clean urine prevalence was virtually identical in both short- and long-term MMT subgroups, and illicit drug use patterns were also statistically equivalent ŽTable 1.. The urine screen results imply that abstinence is not required in order to have a nearly normal phosphorus metabolite profile. However, biweekly random urine screens, which provide dichotomous data, may not be sensitive for detecting modest reductions in drug use. Consequently, some reductions of drug use might have occurred and might be associated with the nearly normal phosphorus metabolite profile found in the long-term MMT group. Other factors may also play a role in the modulation of cerebral phosphorus metabolite levels, including the pharmacological effects of methadone, which stabilizes systemic opiate levels compared to fluctuating levels typically experienced by untreated opiate abusers, as well as collateral positive effects of improved overall health and quality of life observed in MMT patients ŽBall and Ross, 1991; Torrens et al., 1997.. Future longitudinal studies should help to address questions that remain unanswered by the present study, including whether phosphorus metabolite levels actually change over time in persons retained in long-term MMT, what factors mediate those changes, and whether any such changes are correlated with cognitive or other functional improvements. Future studies may also help to elucidate whether 31 P-MRS measures are biological markers for the degree of brain dysfunction in opiate abusers. Such markers would be particularly valuable if it could be determined that baseline 31 P-MRS measures or measures early in the course of MMT were predictive of treatment outcome, given the high attrition rate associated with MMT treatment ŽBall and Ross, 1991. and the promise of additional treatment options such as buprenorphine ŽO’Connor et al., 1998. or LAAM ŽGlanz et al., 1997.. 4.2. Limitations to the present study There are several limitations to this study which
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merit discussion. First, the 31 P-MRS acquisition from an axial slice of whole brain does not permit anatomical localization of neurochemical findings. Consequently, some regional effects could be obscured, such as differences between gray and white matter or between cortical and subcortical regions. In future studies, more anatomically oriented techniques such as magnetic resonance spectroscopic imaging will be applied, which will assist in the detection of anatomically specific baseline 31 P-MRS abnormalities as well as treatment-associated changes. Second, although our analysis did not reveal sex differences in phosphorus metabolite levels, any effects of sex might have been clouded by the relatively small sample size and unbalanced sample numbers. Future studies will use larger and more gender-balanced subject populations. Third, we did not find statistically significant correlations between treatment durations and %metabolite measures, perhaps as a result of small sample size and moderate variability of %metabolite measures. However, while our division of the MMT group into two subgroups of short- and long-term treatment populations might be considered to be arbitrary, stratification afforded more statistical power than a linear regression model to determine whether phosphorus metabolite differences exist as a function of treatment duration. Fourth, it can be argued that individuals retained in MMT for long treatment periods are atypical since nearly half drop out of treatment within 1 year ŽBall and Ross, 1991., and that any findings in such groups would not be applicable to the general population of opiate abusers. Yet, if a criterion for treatment success is defined as prolonged subject retention, then it is critical to study populations who meet such criteria to determine covariates of these outcomes, and in turn whether those covariates Že.g. 31 P-MRS measures. can be used to optimize treatment in individuals who do not benefit from methadone maintenance therapy. Notwithstanding these limitations, the present results suggest that cerebral phosphorus metabolites are abnormal in opiate-dependent polydrug abusers and may serve as markers for brain changes induced by chronic drug abuse. The data further suggest that the metabolite profile is
nearly normal in long-term MMT subjects, implying that these measures may have clinical utility as markers for positive treatment outcome in opiate-dependent patients.
Acknowledgements We gratefully acknowledge the helpful comments of Scott E. Lukas, as well as the excellent technical assistance of Anne Smith, Eileen Connolly, and Rebekah Kaufman. This work was supported in part by NIDA grants DA 09448 ŽPFR., DA 00329 ŽMJK., DA 11231 ŽMHP., DA 04059 ŽJHM., and DA 00064 ŽJHM.. References Ball, J.C., Ross, A., 1991. The Effectiveness of Methadone Maintenance Treatment: Patients, Programs, Services, and Outcome. Springer-Verlag, New York. Christensen, J.D., Kaufman, M.J., Levin, J.M., Mendelson, J.H., Holman, B.L., Cohen, B.M., Renshaw, P.F., 1996. Abnormal cerebral metabolism in polydrug abusers during early withdrawal: a 31 P MR spectroscopy study. Magnetic Resonance in Medicine 35, 658]663. Cooper, J.R., Altman, F., Brown, B.S., Czechowicz, D., 1983. Research on the Treatment of Narcotic Addiction. State of the Art., NIDA Treatment Research Monograph Series, DHHS Pub. No. ŽADM.83]1281. US Dept. of Health and Human Services, Rockville, MD. Danos, P., Kasper, S., Grunwald, F., Klemm, E., Krappel, C., Broich, K., Hoflich, G., Overbeck, B., Biersack, H.J., Moller, H.J., 1998a. Pathological regional cerebral blood flow in opiate-dependent patients during withdrawal: an HMPAOSPECT study. Neuropsychobiology 37, 194]199. Danos, P., Van Roos, D., Kasper, S., Bromel, T., Broich, K., Krappel, C., Solymosi, L., Moller, H., 1998b. Enlarged cerebrospinal fluid spaces in opiate-dependent male patients: a stereological CT study. Neuropsychobiology 38, 80]83. de la Torre, J.C., Fortin, T., Park, G.A., Butler, K.S., Kozlowski, P., Pappas, B.A., de Socarraz, H., Saunders, J.K., Richard, M.T., 1992. Chronic cerebrovascular insufficiency induces dementia-like deficits in aged rats. Brain Research 582, 186]195. Flogel, U., Niendorf, T., Serkowa, N., Brand, A., Henke, J., Leibfritz, D., 1995. Changes in organic solutes, volume, energy state, and metabolism associated with osmotic stress in a glial cell line: a multinuclear NMR study. Neurochemical Research 20, 793]802. Gerra, G., Calbiani, B., Zaimovic, A., Sartori, R., Ugolotti, G., Ippolito, L., Delsignore, R., Rustichelli, P., Fontanesi, B., 1998. Regional cerebral blood flow and comorbid diagnosis
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users treated with buprenorphine. Journal of Nuclear Medicine 36, 1211]1215. London, E.D., Margolin, R.A., Wong, D.F., Links, J., La France, N.D., Cascella, N.G., Broussolle, E.P.M., Wagner, H.N., Jr., Snyder, F.R., Jasinski, D.R., 1989. Cerebral glucose utilization in human heroin addicts: case reports from a positron emission tomographic study. Research Communications in Substances of Abuse 10, 141]144. MacKay, S., Meyerhoff, D., Dillon, W., Weiner, M., Fein, G., 1993. Alteration of brain phospholipid metabolites in cocaine-dependent polysubstance abusers. Biological Psychiatry 34, 261]264. McLellan, A.T., Luborsky, L., O’Brien, C.P., 1982. Is treatment for substance abuse effective? Journal of the American Medical Association 247, 1423]1428. McLellan, A.T., Childress, A.R., Ehrman, R., O’Brien, C.P., Pashko, S., 1986. Extinguished conditioned responses during opiate dependence treatment: turning laboratory findings into clinical procedures. Journal of Substance Abuse Treatment 3, 33]40. Meyerhoff, D.J., MacKay, S., Sappey-Marinier, D., Deicken, R., Calabrese, G., Dillon, W.P., Weiner, M.W., Fein, G., 1995. Effects of chronic alcohol abuse and HIV infection on brain phosphorus metabolites. Alcoholism: Clinical and Experimental Research 19, 685]692. Murphy, E.J., Rajagopalan, B., Brindle, K.M., Radda, G.K., 1989. Phospholipid bilayer contribution to 31 P NMR spectra in vivo. Magnetic Resonance in Medicine 12, 282]289. National Institute on Drug Abuse, 1997. NIDA Research Report: Heroin Abuse and Addiction. NIH Pub. No. 974165. http:rrwww.nida.nih.govrResearchReportsr HeroinrHeroin.html. National Institutes of Health, 1997. Effective Medical Treatment of Opiate Addiction. NIH Consensus Statement, 15, pp. 1]38. Nurco, D.N., Shaffer, J.W., Hanlon, T.E., Kinlock, T.W., Duszynski, K.R., Stephenson, P., 1988. Relationships between clientrcounselor congruence and treatment outcome among narcotic addicts. Comprehensive Psychiatry 29, 48]54. O’Connor, P.G., Oliveto, A.H., Shi, J.M., Triffleman, E.G., Carroll, K.M., Kosten, T.R., Rounsaville, B.J., Pakes, J.A., Schottenfeld, R., 1998. A randomized trial of buprenorphine maintenance for heroin dependence in a primary care clinic for substance users versus a methadone clinic. American Journal of Medicine 105, 100]105. Ordidge, R.J., Connelly, A., Lohman, J., 1986. A general approach to selection of multiple cubic volume elements using the ISIS technique. Journal of Magnetic Resonance 66, 283]294. Petroff, O.A.C., Prichard, J.W., Behar, K.L., Alger, J.R., den Hollander, J.A., Shulman, R.G., 1985. Cerebral intracellular pH by 31 P nuclear magnetic resonance spectroscopy. Neurology 35, 781]788. Pettegrew, J., Kopp, S., Minshew, N., Glonek, T., Feliksik, J., Tow, J., Cohen, M., 1987. 31 P Nuclear magnetic resonance studies of phosphoglyceride metabolism in developing and
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degenerating brain: preliminary observations. Journal of Neuropathology and Experimental Neurology 46, 419]430. Pettegrew, J.W., Panchalingam, K., Klunk, W.E., McClure, R.J., Muenz, L.R., 1994. Alterations of cerebral metabolism in probable Alzheimer’s disease: a preliminary study. Neurobiology of Aging 15, 117]132. Pezawas, L.M., Fischer, G., Diamant, K., Schneider, C., Schindler, S.D., Thurnher, M., Ploechl, W., Eder, H., Kasper, S., 1998. Cerebral CT findings in male opioid-dependent patients: stereological, planimetric and linear measurements. Psychiatry Research 83, 139]147. Raichle, M.E., Grubb, R.L.J., Gado, M.H., Eichling, J.O., Ter-Pogossian, M.M., 1976. Correlation between regional cerebral blood flow and oxidative metabolism. In vivo studies in man. Archives of Neurology 33, 523]526. Rose, J.S., Branchey, M., Buydens-Branchey, L., Stapleton, J.M., Chasten, K., Werrell, A., Maayan, M.L., 1996. Cerebral perfusion in early and late opiate withdrawal: a technetium-99m-HMPAO SPECT study. Psychiatry Research: Neuroimaging 67, 39]47. Serkova, N., Brand, A., Christians, U., Leibfritz, D., 1996. Evaluation of the effects of immunosuppressants on neuronal and glial cells in vitro by multinuclear magnetic resonance spectroscopy. Biochimica et Biophysica Acta 1314, 93]104. Sokoloff, L., 1981. Relationships among local functional activity, energy metabolism, and blood flow in the central nervous system. Federation Proceedings 40, 2311]2316. Stitzer, M.L., Iguchi, M.Y., Felch, L.J., 1992. Contingent takehome incentive: effects on drug use of methadone maintenance patients. Journal of Consulting and Clinical Psychology 60, 927]934.
Strain, E.C., Stitzer, M.L., Liebson, I.A., Bigelow, G.E., 1996. Buprenorphine versus methadone in the treatment of opioid dependence: self-reports, urinalysis, and addiction severity index. Journal of Clinical Psychopharmacology 16, 58]67. Strang, J., Gurling, H., 1989. Computerized tomography and neuropsychological assessment in long-term high-dose heroin addicts. British Journal of Addiction 84, 1011]1019. Strickland, T.L., Mena, I., Villanueva, M.J., Miller, B.L., Cummings, J., Mehringer, C.M., Satz, P., Myers, H., 1993. Cerebral perfusion and neuropsychological consequences of chronic cocaine use. Journal of Neuropsychiatry and Clinical Neuroscience 5, 419]427. Tims, F.M., Ludford, J.P., 1984. Drug Abuse Treatment Evaluation: Strategies, Progress, and Prospects, NIDA Research Monograph, Vol. 51. DHHS Pub. No. ŽADM.84]1329. US Dept. of Health and Human Services, Rockville, MD. Torrens, M., San, L., Martinez, A., Castillo, C., DomingoSalvany, A., Alonso, J., 1997. Use of the Nottingham Health Profile for measuring health status of patients in methadone maintenance treatment. Addiction 92, 707]716. van den Boogaart, A., Howe, F.A., Rodrigues, L.M., Stubbs, M., Griffiths, J.R., 1995. In vivo 31 P MRS: absolute concentrations, signal-to-noise and prior knowledge. NMR in Biomedicine 8, 87]93. Volkow, N.D., Mullani, N., Gould, K.L., Adler, S., Krajewski, K., 1988. Cerebral blood flow in chronic cocaine users: a study with positron emission tomography. British Journal of Psychiatry 152, 641]648.
Cerebral phosphorus metabolite abnormalities in opiate-dependent polydrug abusers in methadone maintenance q Marc J. Kaufman a,b,U , Mark H. Pollack c , Rosemond A. Villafuerte a , Thellea J. Kukes a , Stephanie L. Rosea , Jack H. Mendelsonb, Bruce M. Cohena , Perry F. Renshaw a a
Brain Imaging Center, McLean Hospital, 115 Mill St, Belmont, MA 02478, USA Alcohol and Drug Abuse Research Center, McLean Hospital, 115 Mill St, Belmont, MA 02478, USA c Anxiety Disorders Program, Massachusetts General Hospital and Habit Management Institute, Boston, MA, USA b
Received 20 January 1999; received in revised form 5 May 1999; accepted 13 May 1999
Abstract This study evaluated cerebral phosphorus metabolites in opiate-dependent polydrug abusers in methadone maintenance therapy ŽMMT. and determined whether metabolite profiles differed based on treatment duration. Phosphorus magnetic resonance spectroscopy Ž 31 P-MRS. data were acquired with the ISIS volume localization method from a 50-mm thick axial brain slice through the orbitofrontal and occipital cortices. Study subjects included 15 MMT subjects, seven having undergone treatment for an average of 39 " 23 weeks Žmean " S.D.. and eight having undergone treatment for 137 " 53 weeks, as well as an age matched comparison group Ž n s 16.. The methadone dose administered on the study day averaged 70.5" 17.1 mg and was statistically equivalent in short- and long-term subgroups. MMT subjects Ž n s 15. differed from control subjects in percent phosphocreatine Ž%PCr. levels Žy13%., and in both phosphomonoester Ž%PME, q13%. and phosphodiester Ž%PDE, q10%. levels, which likely reflect abnormalities in energy and phospholipid metabolism, respectively. There were no sex effects or group by sex interaction effects on these measures. In short-term MMT treatment subjects, abnormal %PCr Žy18%., %PME Žq20%. and %PDE Žq17%. levels were found compared with control subjects. The only metabolite abnormality detected in long-term MMT subjects was decreased %PCr Žy9%., in spite of continued illicit drug abuse. From
q
Portions of these results have been presented in preliminary form at the International Society for Magnetic Resonance in Medicine, Fifth Scientific Meeting and Exhibition, Vancouver, BC, Canada, 1997, and at the Joint Meeting of the International Society for Neurochemistry and American Society for Neurochemistry, Boston, MA, 1997. U Corresponding author. Tel.: q1-617-855-3469; fax: q1-617-855-2770. E-mail address: [email protected] ŽM.J. Kaufman. 0925-4927r99r$ - see front matter Q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 9 2 5 - 4 9 2 7 Ž 9 9 . 0 0 0 1 7 - 7
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these data, we conclude that polydrug abusers in MMT have 31 P-MRS results consistent with abnormal brain metabolism and phospholipid balance. The nearly normal metabolite profile in long-term MMT subjects suggests that prolonged MMT may be associated with improved neurochemistry. Q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Magnetic resonance spectroscopy; Heroin; Cerebral metabolism; Cerebral blood flow; Brain; Substance dependence
1. Introduction The National Institute on Drug Abuse recently reported a resurgence in opiate abuse and dependence in several major American cities ŽNational Institute on Drug Abuse, 1997.. This trend suggests that more people will require treatment for opiate abuse or dependence in the near future. A highly effective treatment for opiate dependence is methadone. Methadone maintenance therapy ŽMMT. has been shown to be effective in reducing drug use ŽCooper et al., 1983; Tims and Ludford, 1984. and improving psychiatric symptoms ŽMcLellan et al., 1982, 1986; Kosten et al., 1993; Strain et al., 1996., as well as improving overall health ŽBall and Ross, 1991. and quality of life ŽTorrens et al., 1997. in opiate abusers. Accordingly, the National Institutes of Health ŽNIH. has recommended expanded use of MMT for treatment of opiate addiction ŽNational Institutes of Health, 1997.. In spite of the growing problem of opiate abuse and the widespread use of MMT, there has been a paucity of research into the brain effects of opiates and the neurochemical effects of methadone administration. The few published studies of opiates document cerebral metabolic and perfusion abnormalities that persist well beyond the period of acute opiate intoxication and withdrawal ŽLondon et al., 1989; Krystal et al., 1995; Rose et al., 1996; Gerra et al., 1998.. One recent study demonstrated that methadone administration improves cerebral perfusion during opiate withdrawal ŽDanos et al., 1998a.. While cerebral blood flow improvements may contribute to the overall efficacy of MMT therapy, there is currently an incomplete understanding of the biological basis of methadone’s effects. Consequently, additional studies are necessary
to elucidate the biological consequences of opiate dependence as well as to determine the effects of methadone and of newly developed treatments. One non-invasive brain-imaging technique that may contribute to this effort is phosphorus magnetic resonance spectroscopy Ž 31 P-MRS.. 31 PMRS allows measurement of molecular pools associated with brain bioenergetic status and membrane integrity. Bioenergetic status is reflected by levels of adenosine triphosphate ŽATP. Ždetected in the b-nucleoside phosphate b-NP resonance., and in the inorganic phosphate ŽPi . and phosphocreatine ŽPCr. resonances. Because cerebral blood flow is closely coupled to cerebral metabolism ŽRaichle et al., 1976; Sokoloff, 1981., the cerebral perfusion deficits associated with opiate dependence Žsee above. that typically are asymptomatic may be detectable with 31 P-MRS. Indeed, 31 PMRS studies of cocaine- and heroin-dependent polydrug abusers in early withdrawal ŽChristensen et al., 1996. have documented cerebral bioenergetic disturbances. In addition to energy-related molecules, 31 P-MRS spectra also contain phospholipid resonances for phosphomonoesters ŽPME. and phosphodiesters ŽPDE., which are markers for membrane integrity and turnover. The PME resonance arises principally from phosphorylcholine ŽPC. and phosphorylethanolamine ŽPE., which serve as precursors for the phospholipids phosphatidylcholine and phosphatidylethanolamine, respectively ŽGyulai et al., 1984.. The PDE peak consists of a narrow component containing small molecules such as glycerophosphocholine ŽGPC. and glycerophosphoethanolamine ŽGPE., which are lipid catabolites, and a larger broad component from mobile phospholipids ŽMurphy et al., 1989; Kilby et al., 1991; Pettegrew et al., 1994.. Phospholipid abnormali-
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ties have also been documented with 31 P-MRS in cocaine-dependent and heroin-dependent polydrug abusers ŽMacKay et al., 1993; Christensen et al., 1996. and in alcoholics ŽMeyerhoff et al., 1995.. This study used 31 P-MRS to evaluate neurochemical indices in opiate-dependent polydrug abusers in MMT. The study population was primarily opiate-dependent, with minimal cocaine use, and was studied after being in MMT therapy for a minimum of 8 weeks. These criteria were selected in order to avoid the brain blood flow abnormalities known to be associated with heavy cocaine use ŽVolkow et al., 1988; Holman et al., 1991; Strickland et al., 1993; Levin et al., 1995; Kosten et al., 1998. and with withdrawal states ŽHolman et al., 1991; Krystal et al., 1995; Levin et al., 1995; Rose et al., 1996; Danos et al., 1998a; Kosten et al., 1998.. We tested the hypothesis that abnormal cerebral phosphorus metabolite profiles would be observed in opiate-dependent polydrug abusers in prolonged MMT. Because of reported sex differences in the effects of chronic substance abuse ŽLevin et al., 1994., we evaluated whether there were any effects of sex on these measures. Additionally, in light of reported clinical improvements in MMT patients Žsee above., we also tested the hypothesis that the neurochemical profile in the long-term MMT group would be comparable to that in the control group.
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2. Methods 2.1. Subjects Opiate-dependent polydrug abusers Žnine women and six men, aged 40 " 5 years, mean " S.D.. were recruited from an outpatient MMT clinic ŽHabit Management Institute, Boston, MA.. Individuals with a history of alcohol abuse or HIV infection were excluded. Subject weights in the MMT group were normal and were statistically equivalent to weights found in sex-matched control subjects. This group was subdivided into two subgroups based on MMT duration: the shortterm Ž n s 7, 39 " 23 weeks. and the long-term Ž n s 8, 137 " 53 weeks. groups. All medical histories, including random biweekly urine toxicology testing results, were reviewed in order to determine population demographics. As part of the screening procedure, subjects were required to estimate their alcohol use during their lifetime, the past year, the past month, and the past 3 days. Subjects estimated their use with a five level scale: 0, 1]4, 5]10, 11]39, and ) 40 exposures. While more than half of the MMT subjects reported lifetime consumption of more than 40 drinks, none reported having consumed more than 10 drinks in the year prior to the study and none reported having consumed more than four drinks in the month prior to the study. Although two
Table 1 Random urine toxicology results
Methadone Opiates Benzodiazepines Cocaine THC Propoxyphene Amphetamine Darvon Morphine Barbiturates Clean urines §
Short-term MMT Ž n s 7.
Long-term MMT Ž n s 8.
98.1" 2.5 39.1" 32.1 27.3" 39.7 15.4" 30.2 10.3" 22.2 5.5 " 7.6 2.1" 5.6 0.0" 0.0 0.0" 0.0 0.5" 1.4 26.3" 26.3
97.4" 3.5 34.4" 24.6 48.8" 34.0 21.0" 29.5 0.8" 1.5 3.1" 4.5 2.1" 3.0 2.1" 2.3U 1.4" 3.9 1.0" 2.8 26.6" 22.1
Shown are means " S.D. for %positive urine tests on biweekly random screens. methadone-positive samples.
U
F1,13 s 5.8, P- 0.04; § Percentage excludes
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subjects reported having had prior alcohol problems, their self-reported alcohol use was not indicative of current alcohol problems, and their removal did not alter the statistical findings. Accordingly, they have been included in the analyses. Positive urine tests were found more than 10% of the time for methadone Ž98%., benzodiazepines Ž39%., opiates Ž37%. and cocaine Ž18%.. Clean urine screens were found on an average of 26% of the time. These characteristics were statistically equivalent in the short- and long-term MMT groups, with the exception of Darvon-positive urines, of which none were found in the short-term group and 2% were found in the long-term group ŽTable 1.. The methadone dose administered on the scan day was statistically equivalent in the short- and long-term treatment groups and averaged 79 " 15 and 63 " 16 mgrday, respectively ŽNS, unpaired t-test.. A comparison group Žsix women and 10 men, aged 40 " 4 years. without history of substance abuse or neurological or psychiatric disorder was studied with identical procedures. All subjects provided written informed consent and the protocol was approved by the McLean Hospital Institutional Review Board. All subjects provided breath and urine samples immediately prior to scanning to determine recent alcohol or illicit drug exposure. A positive breath alcohol sample ŽAlco Sensor III Breathalyzer, Intoximeters Inc., St. Louis, MO. in any subject was grounds for study exclusion. A positive urine test for illicit drugs ŽTriageTM Test, Biosite Diagnostics, San Diego, CA. was grounds for exclusion only in control subjects, since it was assumed that the MMT group would have ongoing drug use ŽBall and Ross, 1991; Kosten et al., 1993; Strain et al., 1996.. Positive TriageTM testing frequencies for all illicit substances were statistically equivalent in the short-term and long-term MMT groups. 2.2. Imaging Spectra were acquired on a 1.5-T General Electric Signa Scanner using a doubly tuned, linear proton, quadrature phosphorus head coil. An axial whole brain slice of 50-mm thickness ŽFig. 1. was prescribed through the orbitofrontalroc-
Fig. 1. Sagittal image of a control subject with the 50-mm-thick axial spectral slice outlined. The slice was positioned through the orbitofrontalroccipital cortices with the inferior edge just superior to the inferior margin of the frontal lobe.
cipital cortices. Spectra were acquired with the image selected in vivo spectroscopy ŽISIS. volume-localized spectroscopy technique ŽOrdidge et al., 1986.. Acquisition parameters were tip angle s 908, repetition time ŽTR. s 3 s, acquisition delay s 350 ms, number of points s 1024, and spectral widths 2500 Hz. Spectra were processed with VARPROrMRUI, which is a singular value decomposition time-domain fitting software package Žvan den Boogaart et al., 1995.. Seven peaks were semiautomatically fit to Gaussian lineshapes, with 5-Hz exponential line broadening: phosphomonoesters ŽPME., inorganic phosphorus ŽPi ., phosphodiesters ŽPDE., phosphocreatine ŽPCr., and g-, a- and b-nucleoside phosphates ŽFig. 2. by an investigator who was blind to the experimental conditions. The residual after spectrum fitting ŽFig. 2, bottom trace. includes a broad signal component from fast relaxing phosphorus nuclei in bone and phospholipids. This component was automatically excluded from the fitted peaks by the VARPROrMRUI software and displayed as a part of the residual. The total phosphorus signal Žsummation of all seven fitted metabolite peak areas. was statistically equivalent
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across groups. Consequently, the ratio of the area of each peak divided by the total phosphorus area Ž%metabolite. was used for between-group comparisons ŽKlunk et al., 1994.. These measures have been shown to be stable in control subjects, with %metabolite values differing by - 5% in repeat scans ŽChristensen et al., 1996.. The intracellular hydrogen ion concentration, pH, was determined using the method of Petroff et al. Ž1985.. Statistical analyses were performed with ANOVAs testing for treatment group effects Žcontrol vs. MMT subjects., sex effects, and MMT duration effects Žcontrol subjects vs. short- vs. long-term MMT groups. using the Statview software package ŽAbacus Concepts, Inc., Berkeley, CA..
3. Results Phosphocreatine Ž%PCr. levels were reduced in the MMT group when compared with control subjects Žy13%, F1,27 s 16.6, P- 0.001.. No differences in %b-NP levels were noted. The %PME levels were elevated in the MMT group Žq13%, F1,27 s 9.5, P- 0.005.. Similarly, %PDE levels were elevated in the MMT group Žq10%, F1,27 s 6.9, P- 0.02.. No effects of sex or interaction effects of group by sex were noted. Additionally, no associations between self-reports of alcohol use and metabolite levels were found. For the three metabolites found to differ above, we tested whether metabolite differences existed between control subjects and short-term and long-term MMT subgroups ŽFig. 3.. An overall difference was noted for %PCr levels Ž F2,28 s 14.5, P- 0.0001.. Post-hoc evaluation with Scheffe’s ´ F-test revealed %PCr differences between control subjects and both short-term MMT subjects Žy18%, P- 0.0001. and long-term MMT subjects Žy9%, P- 0.05.. The %PCr difference between short- and long-term MMT subjects Žhigher %PCr in long- vs. short-term subjects. approached statistical significance Ž P - 0.07.. With regard to phospholipids, group differences were noted for both %PME Ž F2,28 s 6.6, P0.005. and %PDE Ž F2,28 s 8.0, P- 0.002.. Posthoc testing revealed significant %PME and %PDE level differences only between control
Fig. 2. Phosphorus magnetic resonance spectrum from a control subject. Shown Žfrom top to bottom. are the original, reconstructed, and fitted spectra along with the fitting residual. Spectra were processed with 5-Hz exponential line broadening using a singular-value decomposition time-domain fitting software package ŽVARPRO-MRUI.. PME s phosphomonoesters; Pi s inorganic phosphate; PDE s phosphodiesters; PCr s phosphocreatine; g, a , and b s gamma, alpha and beta nucleoside phosphates ŽNP..
subjects and short-term MMT subjects Žq20% and q17% of control subjects, P- 0.005 and P- 0.002, respectively.. Long-term MMT subjects had significantly lower %PDE levels than shortterm subjects Ž P- 0.05.. However, correlations between treatment duration Žweeks. and %PCr, %PME and %PDE levels did not reach statistical significance in this relatively small sample w r s 0.45 Ž P- 0.10., r s y0.33 Ž P- 0.33. and r s y0.35 Ž P- 0.21., respectivelyx. Additionally, we found no overall group differences in pH, but the short-term MMT group had slightly elevated pH Ž7.07" 0.02. compared to long-term MMT subjects Ž7.03" 0.03. Ž P- 0.02. who were statistically equivalent to control subjects Ž7.05" 0.02..
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Fig. 3. Metabolite levels in control subjects Ž n s 16. and in short- Ž n s 7. and long-term Ž n s 8. methadone maintenance treatment ŽMMT. subgroups. Shown are means " S.D. of percent metabolite measures. Post hoc Scheffe ´ test results: U P0.05 vs. control subjects; UU P- 0.01 vs. control subjects; UUU P - 0.0001 vs. control subjects; †P- 0.05 vs. long-term MMT group.
4. Discussion The present data document cerebral phosphorus metabolite abnormalities in opiate-dependent polydrug abusers in prolonged MMT. The findings suggest the presence of both bioenergetic Ždecreased %PCr. and phospholipid Želevated
%PME and %PDE. abnormalities. Importantly, nearly normal metabolite profiles were found in long-term MMT subjects, suggesting that prolonged MMT is associated with improved neurochemical function. Interestingly, Pezawas and colleagues recently reported normalized brain volumes in long-abstinent opiate abusers maintained either with MMT or morphine, when compared with short-duration abstinent subjects ŽPezawas et al., 1998.. Together, these results suggest that long-term opiate-substitution therapy may be beneficial to brain function and structure. The metabolite profiles described presently in the MMT group differ from those reported in other substance abuse populations. White matter PME and PDE levels were decreased in abstinent cocaine-dependent polydrug abusers ŽMacKay et al., 1993. and PDE levels were decreased in alcoholics ŽMeyerhoff et al., 1995., while ATP levels were reduced and PME levels were increased in cocaine- and heroin-dependent polydrug abusers in early withdrawal ŽChristensen et al., 1996.. Since the present study used the same 31 P-MRS technique as Christensen et al. Ž1996., the metabolite differences between these studies are likely to be attributable to subject demographics Že.g. minimal cocaine use in the present group vs. cocaine dependence in Christensen et al.. rather than to methodological differences. Alternatively, metabolite profile discrepancies might be a function of different states of drug use in the two study populations Že.g. active vs. withdrawing.. The mechanism underlying the present metabolite abnormalities is unknown. However, the abnormal MMT metabolite profile parallels abnormal 31 P-MRS profiles found in several types of brain insults. A PCr reduction and concomitant PME increase were reported in a model of chronic cerebral infarction in rodents ŽHoukin et al., 1989.. While it is unlikely that widespread tissue ischemia is occurring in subjects in the present study, it is abundantly clear that cerebrovascular dysfunction occurs in opiate abusers, including those in treatment ŽHolman et al., 1991; Krystal et al., 1995; Levin et al., 1995; Christensen et al., 1996; Rose et al., 1996; Danos et al., 1998a; Gerra et al., 1998.. Since there is a close
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coupling between cerebral metabolism and blood flow ŽRaichle et al., 1976; Sokoloff, 1981., abnormal perfusion may evoke metabolic dysfunction. Indeed, partial cerebral ischemia in piglets has been shown to acutely reduce PCr levels ŽLaptook et al., 1988.. The presently described PCr reduction may indicate compromised cerebral metabolism, and since phospholipid synthesis is an energy-dependent process, this could also result in increased PME levels. Mild cerebral blood flow reductions not associated with pathological changes or PCr changes also could induce PME changes, as flow reductions of - 50% in rodents have been linked to delayed PME elevations but normal PCr levels Žde la Torre et al., 1992.. With regard to PDE levels, increased %PDE implies acceleration of membrane breakdown processes and perhaps cell loss. This interpretation would be consistent with reported cerebral volume reductions in chronic opiate abusers ŽStrang and Gurling, 1989; Danos et al., 1998b; Pezawas et al., 1998.. However, cell death may not be requisite to the observation of PDE increases, since PDE elevations were found in cultured glial cells exposed to hypertonic media, possibly reflecting either an osmolyte role for PDE or a role in membrane remodeling to protect cells against volume shrinkage ŽFlogel et al., 1995.. The hypertonic conditions in that study also induced an increase in glial cell pH ŽFlogel et al., 1995.. Consequently, the present PDE and pH abnormalities suggest that some form of ongoing osmotic stress might be occurring in short-term MMT subjects. PME and PDE increases have also been noted in vitro in neuronal and glial cell cultures treated with toxic immunosuppressants ŽSerkova et al., 1996. and in vivo in human Alzheimer’s disease and Huntington’s disease, with PDE increments corresponding to the degree of neuropathological change ŽPettegrew et al., 1987.. Thus, the present findings may reflect a combination of neuronal or glial death or dysfunction induced by osmotic stress or other toxic processes. 4.1. Continued drug use and metabolite abnormalities The MMT group as a whole produced clean
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urines only 26% of the time. This is consistent with literature reports documenting a high prevalence of illicit drug use in MMT patients ŽIguchi et al., 1988; Nurco et al., 1988; Stitzer et al., 1992.. Clean urine prevalence was virtually identical in both short- and long-term MMT subgroups, and illicit drug use patterns were also statistically equivalent ŽTable 1.. The urine screen results imply that abstinence is not required in order to have a nearly normal phosphorus metabolite profile. However, biweekly random urine screens, which provide dichotomous data, may not be sensitive for detecting modest reductions in drug use. Consequently, some reductions of drug use might have occurred and might be associated with the nearly normal phosphorus metabolite profile found in the long-term MMT group. Other factors may also play a role in the modulation of cerebral phosphorus metabolite levels, including the pharmacological effects of methadone, which stabilizes systemic opiate levels compared to fluctuating levels typically experienced by untreated opiate abusers, as well as collateral positive effects of improved overall health and quality of life observed in MMT patients ŽBall and Ross, 1991; Torrens et al., 1997.. Future longitudinal studies should help to address questions that remain unanswered by the present study, including whether phosphorus metabolite levels actually change over time in persons retained in long-term MMT, what factors mediate those changes, and whether any such changes are correlated with cognitive or other functional improvements. Future studies may also help to elucidate whether 31 P-MRS measures are biological markers for the degree of brain dysfunction in opiate abusers. Such markers would be particularly valuable if it could be determined that baseline 31 P-MRS measures or measures early in the course of MMT were predictive of treatment outcome, given the high attrition rate associated with MMT treatment ŽBall and Ross, 1991. and the promise of additional treatment options such as buprenorphine ŽO’Connor et al., 1998. or LAAM ŽGlanz et al., 1997.. 4.2. Limitations to the present study There are several limitations to this study which
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merit discussion. First, the 31 P-MRS acquisition from an axial slice of whole brain does not permit anatomical localization of neurochemical findings. Consequently, some regional effects could be obscured, such as differences between gray and white matter or between cortical and subcortical regions. In future studies, more anatomically oriented techniques such as magnetic resonance spectroscopic imaging will be applied, which will assist in the detection of anatomically specific baseline 31 P-MRS abnormalities as well as treatment-associated changes. Second, although our analysis did not reveal sex differences in phosphorus metabolite levels, any effects of sex might have been clouded by the relatively small sample size and unbalanced sample numbers. Future studies will use larger and more gender-balanced subject populations. Third, we did not find statistically significant correlations between treatment durations and %metabolite measures, perhaps as a result of small sample size and moderate variability of %metabolite measures. However, while our division of the MMT group into two subgroups of short- and long-term treatment populations might be considered to be arbitrary, stratification afforded more statistical power than a linear regression model to determine whether phosphorus metabolite differences exist as a function of treatment duration. Fourth, it can be argued that individuals retained in MMT for long treatment periods are atypical since nearly half drop out of treatment within 1 year ŽBall and Ross, 1991., and that any findings in such groups would not be applicable to the general population of opiate abusers. Yet, if a criterion for treatment success is defined as prolonged subject retention, then it is critical to study populations who meet such criteria to determine covariates of these outcomes, and in turn whether those covariates Že.g. 31 P-MRS measures. can be used to optimize treatment in individuals who do not benefit from methadone maintenance therapy. Notwithstanding these limitations, the present results suggest that cerebral phosphorus metabolites are abnormal in opiate-dependent polydrug abusers and may serve as markers for brain changes induced by chronic drug abuse. The data further suggest that the metabolite profile is
nearly normal in long-term MMT subjects, implying that these measures may have clinical utility as markers for positive treatment outcome in opiate-dependent patients.
Acknowledgements We gratefully acknowledge the helpful comments of Scott E. Lukas, as well as the excellent technical assistance of Anne Smith, Eileen Connolly, and Rebekah Kaufman. This work was supported in part by NIDA grants DA 09448 ŽPFR., DA 00329 ŽMJK., DA 11231 ŽMHP., DA 04059 ŽJHM., and DA 00064 ŽJHM.. References Ball, J.C., Ross, A., 1991. The Effectiveness of Methadone Maintenance Treatment: Patients, Programs, Services, and Outcome. Springer-Verlag, New York. Christensen, J.D., Kaufman, M.J., Levin, J.M., Mendelson, J.H., Holman, B.L., Cohen, B.M., Renshaw, P.F., 1996. Abnormal cerebral metabolism in polydrug abusers during early withdrawal: a 31 P MR spectroscopy study. Magnetic Resonance in Medicine 35, 658]663. Cooper, J.R., Altman, F., Brown, B.S., Czechowicz, D., 1983. Research on the Treatment of Narcotic Addiction. State of the Art., NIDA Treatment Research Monograph Series, DHHS Pub. No. ŽADM.83]1281. US Dept. of Health and Human Services, Rockville, MD. Danos, P., Kasper, S., Grunwald, F., Klemm, E., Krappel, C., Broich, K., Hoflich, G., Overbeck, B., Biersack, H.J., Moller, H.J., 1998a. Pathological regional cerebral blood flow in opiate-dependent patients during withdrawal: an HMPAOSPECT study. Neuropsychobiology 37, 194]199. Danos, P., Van Roos, D., Kasper, S., Bromel, T., Broich, K., Krappel, C., Solymosi, L., Moller, H., 1998b. Enlarged cerebrospinal fluid spaces in opiate-dependent male patients: a stereological CT study. Neuropsychobiology 38, 80]83. de la Torre, J.C., Fortin, T., Park, G.A., Butler, K.S., Kozlowski, P., Pappas, B.A., de Socarraz, H., Saunders, J.K., Richard, M.T., 1992. Chronic cerebrovascular insufficiency induces dementia-like deficits in aged rats. Brain Research 582, 186]195. Flogel, U., Niendorf, T., Serkowa, N., Brand, A., Henke, J., Leibfritz, D., 1995. Changes in organic solutes, volume, energy state, and metabolism associated with osmotic stress in a glial cell line: a multinuclear NMR study. Neurochemical Research 20, 793]802. Gerra, G., Calbiani, B., Zaimovic, A., Sartori, R., Ugolotti, G., Ippolito, L., Delsignore, R., Rustichelli, P., Fontanesi, B., 1998. Regional cerebral blood flow and comorbid diagnosis
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