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Effects of chronic zidovudine administration on CNS function and virus burden after perinatal SIV infection in rhesus monkeys
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Advances in Neuroimmunology Vol. 4, pp. 233-237, 1994
Pergamon
Copyright © 1994 Elsevier ScienceLtd Printed in Great Britain. All rights reserved 0960-5428/94 $26.00 0960-5428(94)00017--4
Effects of chronic zidovudine administration on CNS function and virus burden after perinatal SIV infection in rhesus monkeys Dianne M. Rausch, 1 Melvyn Heyes: and Lee E. Eiden 1 lSection on Molecular Neuroscience, Laboratory of Cell Biology and 2Section on Analytical Biochemistry, Laboratory of Clinical Science, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
Summary Continuous intravenous administration of zidovudine ( A Z T ) has been reported to improve cognitive function in HIV-infected pediatric patients (Pizzo et al., 1988). The effects of long-term zidovudine treatment in the perinatally infected pediatric population, including antiviral efficacy and effects on cognitive and motor function has not been systematically examined. These questions were addressed in rhesus macaque infants infected at birth with SIVsMM/B670, a primate model for infantile H I V infection and disease (Eiden et al., 1993a). Continuous or intermittent administration of A Z T during the first 6 months following infection resulted in about a doubling of lifespan, a delay in the occurrence of motor impairment, and lower virus burden and quinolinic acid levels in cerebrospinal fluid (CSF) following administration of the antiviral drug.
Introduction The vertical acquisition by infants from infected ticularly pressing clinical cal issue (Kozlowski et
of H I V infection mothers is a parand epidemiologial., 1993; Lobato
et al., 1993). Vertical transmission is now thought to occur both perinatally and in utero, with the former mode of transmission probably more frequent (Wara et al., 1993).
Progressive encephalopathy is an obvious clinical problem in this population (Lobato et al., 1993). Its treatment has implications for understanding the relationship between virus burden, replicative state of the virus in brain, and the viral reservoir function of the brain. Experimental treatment protocols for perinatal infection generally are limited by prior demonstration of safety and efficacy in adults. Examination of immune response to virus infection is also confounded in human infants by the presence of maternal antibodies during the first several weeks of life, and lack of knowledge of the exact time of infection. We have studied the infant rhesus m o n k e y infected intravenously at birth with simian immunodeficiency virus (SIV) as a model for perinatal transmission of H I V in which the effects of lentivirus infection on the developing primate immune and central nervous systems can be studied, and the potential efficacy and safety of antiviral agents can be pre-clinically assessed. 233
234
Advances in Neuroimmunology
Methods
Thirteen animals were inoculated intravenously with SIVsMM/B670within 72 hours of birth. Eight animals received subcutaneous A Z T continuously at a rate of 1-1.25 mg/kg/hour, or four times daily at 6-7.5 mg/kg over 15 min, beginning 1 hour prior to the time of inoculation with virus, and thereafter for approximately the first 6 months of life. The presence of virus, viral antigens, and quinolinic acid in CNS and systemic circulation were monitored during the course of disease. Five uninoculated and untreated animals served as controls for clinical chemical, immunological, virological, and behavioral parameters measured during the study.
Results
All virus-inoculated animals were productively infected, as evidenced by consistent virus detection in co-cultures of monkey peripheral blood mononuclear cells (PBMCs) with human phytohemagglutininstimulated PBMCs. All of the animals in the untreated inoculated group showed a transient p26 antigenemia within 2 weeks of inoculation (peak levels as m e a n + S E M ; 12 + 3 ng/ml). There was a significant reduction in initial antigenemia in the continuous A Z T (2.5 + 1.8 ng/ml), but not in the intermittent A Z T group (4.3 + 2.3 ng/ml). The single non-surviving animal during the first 12 months of life in the continuous A Z T group also had the highest initial peak antigemia (9.7 ng/ml) in that group. Three of the five untreated animals succumbed to SIV disease, with wasting and opportunistic infection, by 1 year. One of eight of the A Z T - t r e a t e d animals succumbed to disease at 1 year. Subsequently, seven of the eight animals in the two A Z T groups succumbed to viral disease, surviving twice as long as non-treated animals (654 vs 331 days, p<0.02).
General health and physical development were normal in the AZT-treated group during the 6 month treatment period, as was neurological development, assessed with a battery of tests measuring motor skill and cognitive performance (Murray et al., 1992; Eiden et al., 1993b). Variations in serum chemistry profiles among the uninfected and untreated, the infected and untreated, and the infected and AZT-treated groups are summarized in Table 1. After this time, abnormal serum chemistry, weight loss and decreased CD4/CD8 ratios were observed in the A Z T treatment group, as in the infected non-treatment group, as a function of the development of AIDS in animals of each group (Table 1; D. Rausch et al., in preparation). Motor and cognitive performance were measured in the eight animals infected with SIV and treated with A Z T , and compared to the five uninoculated and five SIVinoculated, untreated animals. Two of five of the infected, non-treated control animals exhibited transient motor impairment, but succumbed to disease ( < 6 months of age) before initiation of cognitive testing. No animals in the A Z T group exhibited motor impairments relative to controls during the first 6 months of life. Following cessation of A Z T treatment, three of eight of the animals in the A Z T group exhibited transient impairment in motor skill performance and two exhibited impairments in visual discrimination learning. During this time, one of the three remaining animals in the virus-inoculated non A Z T group exhibited transient motor skill impairment, and none were impaired in performance of cognitive tasks. Whether the rate of cognitive impairment in the A Z T group was actually higher than that in the untreated infected group could not be assessed, since two of the animals in the latter group had succumbed to viral disease prior to initiation of cognitive testing at 6 months of age (Table 1). Cerebrospinal fluid sampling was not at-
Effects of c h r o n i c z i d o v u d i n e a d m i n i s t r a t i o n
235
Table 1. Comparison of laboratory, biochemical, viral and behavioral parameters in SIV-infected infants during the A Z T treatment period and after the cessation of treatment
Parameter
0-6 months Virus
P26 serum antigen (peak) 12.31 + 2.47 (mean + SEM) CD4/CD8 (MEAN + SD) 1.73 + 0.57* Hematology/chemistry (mean +_ SD) Hemoglobin 12.5 + 1.3 WBC 9943 _+ 4160 Neutrophils 4372 + 2617 Albumin 3.65 _+ 0.65* Virus isolation ( # animals) PBMC 5/5 CSF 2/2 Quinolinicacid (mean + SD) SERUM ND CSF ND Behaviorimpairments ( # animals) MOTOR 2/5 COGNITIVE NA
7-18 months
Virus + A Z T
Virus
Virus + A Z T
3.14 + 1.3
NA
NA
2.35 + 0.75
1.27 _+ 0.64*
1.51 + 0.73
11.8 6241 2247 4.32
11.6 8945 3166 3.40
12.6 9401 3580 3.79
+ + + +
1.0" 1708" 843* 0.25*
_+ 0.8* _+ 1858 _+ 1663 + .60*
+ 0.8 _+ 3104 _+ 1879 - 0.41"
5/5 ND
5/5 3/3
8/8 1/8 ~ 4/8
ND ND
2650 + 423* 554 + 297*
3688 _+ 707* 84 _+ 46*
0/8 NA
1/3 0/3
3/8 2/8
Blood and CSF were sampled regularly for measurement of the above parameters. The p26 serum antigen levels reported here are an average of the highest measurements obtained from each animal within the first 2 weeks following inoculation. Three of the animals in the A Z T group did not show measurable serum P26 levels until more than 6 months after inoculation. Sampling done from 0-6 months corresponds to the time the A Z T treated animals were receiving the medication, sampling from 7-18 months corresponds to the year following the cessation of A Z T administration. Virus isolation from peripheral blood mononuclear cells (PBMC) was done monthly by co-culturing rhesus PBMC with PHA-stimulated donor human PBMC and assaying culture supernatants every 3-4 days for p26 viral core protein levels. Virus isolation from CSF was done at necropsy prior to 6 months of age, then monthly beginning at approximately 6 months of age. CSF is reported here as positive if virus isolation occurred in two or more consecutive CSF samples. In the A Z T group, only o n e animal was CSF virus-rescue positive within the first 6 months after the cessation of the A Z T infusion, which increased to four animals in the next 6 months. Quinolinic acid was measured from monthly samples of serum and CSF as previously described (Heyes and Markey, 1988). Means and standard deviations were determined in the periods indicated from a sum of the means of the measurements of each animal during that period, compared to the means of measurements of five uninfected, age-matched controls during the same period. Statistical significance was determined using the t-test. The motor and cognitive tasks used have previously been described (Murray et al.~ 1992; Eiden et al., 1993). Testing on the motor skill task was initiated at approximately 10 weeks of age. Testing on the cognitive tasks was initiated at the cessation of the A Z T infusions, when the animals were approximately 6 months of age. Impairment on the behavior tasks indicates performance greater than 2 SD from the mean of the scores of the control uninfected animals on the same tasks during the same period. *Indicates statistical significance (p < 0.05) compared to c o n t r o l uninfected animals. NA, not applicable. ND, not done.
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Advances in Neuroimmunology
tempted in any of the groups prior to age 6 months. However, at the time of cessation of A Z T treatment at 6-7 months of age, frequency of virus rescue from CSF was significantly lower in the A Z T group than in the non-treated infected group, while frequency of virus isolation from peripheral blood was equivalent in both groups. Furthermore, CSF levels of quinolinic acid, while elevated in both groups relative to uninfected animals, were approximately five-fold lower in the A Z T group at this time. Since serum quinolinic acid levels were in fact consistently slightly higher in the A Z T group, these data are consistent with the hypothesis that CSF quinolinic acid in primate lentiviral disease derives from the CNS compartment itself, rather than spillover of circulating quinolinate into CSF due to damage to the blood-brain or blood-CSF barriers (Heyes et al., 1991, 1992; Rausch et al., 1994). Discussion The preliminary examination of the ongoing study described above strongly suggests that continuous subcutaneous A Z T administration is safe and efficacious in significantly increasing lifespan after perinatal infection with SIV in rhesus monkeys. A Z T administration appears to delay the onset of motor impairment in SIV-infected infant macaques, and this correlates with a demonstrably lower virus burden in CSF during the time of A Z T treatment. The SIV-infected neonatal rhesus monkey may be a useful primate animal model for determining minimal perinatal treatment regimens for A Z T and other anti-viral agents, and studying the course of viral disease in the neonatal host. The transmission rate of infant infection by vertical transmission from HIV-infected mothers is currently estimated to be about 25% (Wara et al., 1993, and references therein). A recent Clinical Alert, summarizing results from A C T G Pediatric A I D S clinical Trial 076,
describes a decrease in H I V transmission rate from mother to infant from 25.5 to 8.3% when oral administration of A Z T was initiated at 14-34 weeks of gestation, continued throughout pregnancy, and A Z T oral administration to infants continued for an additional 6 weeks post-partum (Clinical Alert, 1994). The results of this study do not allow the relative effects of maternal and infant A Z T administration to be assessed. It would be of considerable interest to know if A Z T administered several days to a week after infection with SIV, with treatment continued for 6 months or more, afforded the same prolongation of life as A Z T treatment begun coincidentally with virus infection. If so, it would be reasonable based on both clinical and pre-clinical results to attempt A Z T therapy several days after birth in infants of HIV-positive mothers who do not receive A Z T during pregnancy, since current methods of detecting virus infection do not allow positive identification of perinatally infected infants until several days after birth. A Z T treatment results in decreased frequency of virus isolation from CSF, and appears to delay motor impairment, suggesting an association between CSF virus burden and CNS outcome. However, the relationship between CNS virus burden and motor impairment will require actual quantitation of virus burden in brain parenchyma and its correlation with functional impairment. Likewise, CSF levels of quinolinic acid appear to reflect the virus burden in the central nervous system compartment, but precise quantitation of quinolinic acid and virus levels in the brain parenchyma, as well as the systemic circulation, will be required to validate this hypothesis. Study of the efficacy, safety, and penetration to the central nervous system of antiviral agents in the perinatally SIVinfected infant rhesus monkey may represent an important opportunity to optimize infantile H I V encephalopathy/AIDS
Effects of chronic zidovudine administration therapeutics. Understanding primate perinatal cellular and humoral responses to viral infection at birth is also critical to rationally tailoring vaccine development to the HIV-infected infant. Examination of infant antibody responses to perinatal SIV infection should contribute to this effort, and is currently underway.
References
Clinical Alert. Important therapeutic information on the benefit of zidovudine for the prevention of the transmission of HIV from mother to infant. Office of Communications, National Institute of Allergy and Infectious Diseases, February 20, 1994. Eiden, L. E., Rausch, D. M., Cunha, A. D., Murray, E. A., Heyes, M., Sharer, L., Nohr, D. and Weihe, E. (1993a). AIDS and the central nervous system: Examining pathobiology and testing therapeutic strategies in the SIVinfected rhesus monkey. Ann. N Y Acad. Sci. 693: 229-244. Eiden, L. E., Murray, E. M. and Rausch, D. M. (1993b). Motor and cognitive functioning in nonhuman primates infected with simian immunodeficiency virus (SIV). An animal model for neuro-AIDS. In: Neuropsychology of HIV Infection, eds. Martin, A. and Grant, I. Oxford University Press, Oxford. Heyes, M. P. and Markey, S. P. (1988). Quantification of quinolinic acid in rat brain, whole blood and plasma by gas chromatography and negative chemical ionization mass spectrometry. Anal. Biochem. 174: 349-359. Heyes, M., Brew, B. J., Martin, A., Price, R. W., Salazar, A. M., Sidtis, J. J., Yergey, J. A., Mouradian, M. M., Sadler, A. E., Keilp, J., Rubinow, D. and Markey, S. P. (1991). Quinolinic acid in cerebrospinal fluid and serum in HIV infection: Relationship to clinical and neurologic status. Ann. Neurol. 29: 202-209. Heyes, M. P., Saito, K., Crowley, J. S., Davis, L. E., Demitrack, M. A., Der, M., Dilling, L. A., Ella, J., Kruesi, M. J. P.,
237
Lackner, A., Larsen, S. A., Lee, K., Leonard, H. L., Markey, S. P., Martin, A., Milstein, S., Mouradian, M. M., Pranzatelli, M. R., Quearry, B. J., Salazar, A., Smith, M., Strauss, D. E., Sunderland, T., Swedo, S. W. and Tourtellotte, W. W. (1992). Quinolinic acid and kynurenine pathway metabolism in inflammatory and non-inflammatory neurological disease. Brain 115: 1249-1273. Kozlowski, P. B., Sher, J. H., Rao, C., Anzil, P. A., Wrzolik, M. A., Sharer, L., Cho, E.-S., Dickson, D. W., Weidenheim, K. M., Llena, J. F., Nelson, S. J. and Kanzer, M. D. (1993). Central nervous system in pediatric AIDS. Results from neuropathologic pediatric AIDS Registry. Ann. N Y Acad. Sci. 693: 295-296. Lobato, M. N., Caldwell, B., Ng, P., Oxtoby, M. and Consortium, T. P. s. o. D. (1993). HIVencephalopathy in children; characteristics, risks, and survival. The First National Conference on Human Retroviruses and Related Infections, p. 180. Murray, E. A., Rausch, D. M., Lendvay, J., Sharer, L. R. and Eiden, L. E. (1992). Cognitive and motor impairments associated with SIV infection in rhesus monkeys. Science 255: 1246-1249. Pizzo, P. A., Eddy, J., Falloon, J., Balls, F. M., Murphy, R. F., Moss, H., Wolters, P., Brouwers, P., Jarosinski, P., Rubin, M., Broder, S., Yarchoan, R., Brunetti, A., Maha, M., Nusinoff-Lehrman, S. and Poplack, D. G. (1988). Effect of continuous intravenous infusion of zidovudine (AZT) in children with symptomatic HIV infection. New Engl. J. Med. 319: 889-896. Rausch, D. M., Heyes, M. P., Murray, E. A., Lendvay, J., Sharer, L. R., Ward, J. M., Rhm, S., Nohr, D., Weihe, E. and Eiden, L. E. (1994). Cytopathologic and neurochemical correlates of progression to motor/cognitive impairment in SIV-infected rhesus monkeys. J. Neuropath. Exp. Neurol. 53: 00-00. Wara, D. W., Luzuriaga, K., Martin, N. L., Sullivan, J. L. and Bryson, Y. J. (1993). Maternal transmission and diagnosis of human immunodeficiency virus during infancy. Ann. N Y Acad. Sci. 693: 14-19.
Advances in Neuroimmunology Vol. 4, pp. 233-237, 1994
Pergamon
Copyright © 1994 Elsevier ScienceLtd Printed in Great Britain. All rights reserved 0960-5428/94 $26.00 0960-5428(94)00017--4
Effects of chronic zidovudine administration on CNS function and virus burden after perinatal SIV infection in rhesus monkeys Dianne M. Rausch, 1 Melvyn Heyes: and Lee E. Eiden 1 lSection on Molecular Neuroscience, Laboratory of Cell Biology and 2Section on Analytical Biochemistry, Laboratory of Clinical Science, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
Summary Continuous intravenous administration of zidovudine ( A Z T ) has been reported to improve cognitive function in HIV-infected pediatric patients (Pizzo et al., 1988). The effects of long-term zidovudine treatment in the perinatally infected pediatric population, including antiviral efficacy and effects on cognitive and motor function has not been systematically examined. These questions were addressed in rhesus macaque infants infected at birth with SIVsMM/B670, a primate model for infantile H I V infection and disease (Eiden et al., 1993a). Continuous or intermittent administration of A Z T during the first 6 months following infection resulted in about a doubling of lifespan, a delay in the occurrence of motor impairment, and lower virus burden and quinolinic acid levels in cerebrospinal fluid (CSF) following administration of the antiviral drug.
Introduction The vertical acquisition by infants from infected ticularly pressing clinical cal issue (Kozlowski et
of H I V infection mothers is a parand epidemiologial., 1993; Lobato
et al., 1993). Vertical transmission is now thought to occur both perinatally and in utero, with the former mode of transmission probably more frequent (Wara et al., 1993).
Progressive encephalopathy is an obvious clinical problem in this population (Lobato et al., 1993). Its treatment has implications for understanding the relationship between virus burden, replicative state of the virus in brain, and the viral reservoir function of the brain. Experimental treatment protocols for perinatal infection generally are limited by prior demonstration of safety and efficacy in adults. Examination of immune response to virus infection is also confounded in human infants by the presence of maternal antibodies during the first several weeks of life, and lack of knowledge of the exact time of infection. We have studied the infant rhesus m o n k e y infected intravenously at birth with simian immunodeficiency virus (SIV) as a model for perinatal transmission of H I V in which the effects of lentivirus infection on the developing primate immune and central nervous systems can be studied, and the potential efficacy and safety of antiviral agents can be pre-clinically assessed. 233
234
Advances in Neuroimmunology
Methods
Thirteen animals were inoculated intravenously with SIVsMM/B670within 72 hours of birth. Eight animals received subcutaneous A Z T continuously at a rate of 1-1.25 mg/kg/hour, or four times daily at 6-7.5 mg/kg over 15 min, beginning 1 hour prior to the time of inoculation with virus, and thereafter for approximately the first 6 months of life. The presence of virus, viral antigens, and quinolinic acid in CNS and systemic circulation were monitored during the course of disease. Five uninoculated and untreated animals served as controls for clinical chemical, immunological, virological, and behavioral parameters measured during the study.
Results
All virus-inoculated animals were productively infected, as evidenced by consistent virus detection in co-cultures of monkey peripheral blood mononuclear cells (PBMCs) with human phytohemagglutininstimulated PBMCs. All of the animals in the untreated inoculated group showed a transient p26 antigenemia within 2 weeks of inoculation (peak levels as m e a n + S E M ; 12 + 3 ng/ml). There was a significant reduction in initial antigenemia in the continuous A Z T (2.5 + 1.8 ng/ml), but not in the intermittent A Z T group (4.3 + 2.3 ng/ml). The single non-surviving animal during the first 12 months of life in the continuous A Z T group also had the highest initial peak antigemia (9.7 ng/ml) in that group. Three of the five untreated animals succumbed to SIV disease, with wasting and opportunistic infection, by 1 year. One of eight of the A Z T - t r e a t e d animals succumbed to disease at 1 year. Subsequently, seven of the eight animals in the two A Z T groups succumbed to viral disease, surviving twice as long as non-treated animals (654 vs 331 days, p<0.02).
General health and physical development were normal in the AZT-treated group during the 6 month treatment period, as was neurological development, assessed with a battery of tests measuring motor skill and cognitive performance (Murray et al., 1992; Eiden et al., 1993b). Variations in serum chemistry profiles among the uninfected and untreated, the infected and untreated, and the infected and AZT-treated groups are summarized in Table 1. After this time, abnormal serum chemistry, weight loss and decreased CD4/CD8 ratios were observed in the A Z T treatment group, as in the infected non-treatment group, as a function of the development of AIDS in animals of each group (Table 1; D. Rausch et al., in preparation). Motor and cognitive performance were measured in the eight animals infected with SIV and treated with A Z T , and compared to the five uninoculated and five SIVinoculated, untreated animals. Two of five of the infected, non-treated control animals exhibited transient motor impairment, but succumbed to disease ( < 6 months of age) before initiation of cognitive testing. No animals in the A Z T group exhibited motor impairments relative to controls during the first 6 months of life. Following cessation of A Z T treatment, three of eight of the animals in the A Z T group exhibited transient impairment in motor skill performance and two exhibited impairments in visual discrimination learning. During this time, one of the three remaining animals in the virus-inoculated non A Z T group exhibited transient motor skill impairment, and none were impaired in performance of cognitive tasks. Whether the rate of cognitive impairment in the A Z T group was actually higher than that in the untreated infected group could not be assessed, since two of the animals in the latter group had succumbed to viral disease prior to initiation of cognitive testing at 6 months of age (Table 1). Cerebrospinal fluid sampling was not at-
Effects of c h r o n i c z i d o v u d i n e a d m i n i s t r a t i o n
235
Table 1. Comparison of laboratory, biochemical, viral and behavioral parameters in SIV-infected infants during the A Z T treatment period and after the cessation of treatment
Parameter
0-6 months Virus
P26 serum antigen (peak) 12.31 + 2.47 (mean + SEM) CD4/CD8 (MEAN + SD) 1.73 + 0.57* Hematology/chemistry (mean +_ SD) Hemoglobin 12.5 + 1.3 WBC 9943 _+ 4160 Neutrophils 4372 + 2617 Albumin 3.65 _+ 0.65* Virus isolation ( # animals) PBMC 5/5 CSF 2/2 Quinolinicacid (mean + SD) SERUM ND CSF ND Behaviorimpairments ( # animals) MOTOR 2/5 COGNITIVE NA
7-18 months
Virus + A Z T
Virus
Virus + A Z T
3.14 + 1.3
NA
NA
2.35 + 0.75
1.27 _+ 0.64*
1.51 + 0.73
11.8 6241 2247 4.32
11.6 8945 3166 3.40
12.6 9401 3580 3.79
+ + + +
1.0" 1708" 843* 0.25*
_+ 0.8* _+ 1858 _+ 1663 + .60*
+ 0.8 _+ 3104 _+ 1879 - 0.41"
5/5 ND
5/5 3/3
8/8 1/8 ~ 4/8
ND ND
2650 + 423* 554 + 297*
3688 _+ 707* 84 _+ 46*
0/8 NA
1/3 0/3
3/8 2/8
Blood and CSF were sampled regularly for measurement of the above parameters. The p26 serum antigen levels reported here are an average of the highest measurements obtained from each animal within the first 2 weeks following inoculation. Three of the animals in the A Z T group did not show measurable serum P26 levels until more than 6 months after inoculation. Sampling done from 0-6 months corresponds to the time the A Z T treated animals were receiving the medication, sampling from 7-18 months corresponds to the year following the cessation of A Z T administration. Virus isolation from peripheral blood mononuclear cells (PBMC) was done monthly by co-culturing rhesus PBMC with PHA-stimulated donor human PBMC and assaying culture supernatants every 3-4 days for p26 viral core protein levels. Virus isolation from CSF was done at necropsy prior to 6 months of age, then monthly beginning at approximately 6 months of age. CSF is reported here as positive if virus isolation occurred in two or more consecutive CSF samples. In the A Z T group, only o n e animal was CSF virus-rescue positive within the first 6 months after the cessation of the A Z T infusion, which increased to four animals in the next 6 months. Quinolinic acid was measured from monthly samples of serum and CSF as previously described (Heyes and Markey, 1988). Means and standard deviations were determined in the periods indicated from a sum of the means of the measurements of each animal during that period, compared to the means of measurements of five uninfected, age-matched controls during the same period. Statistical significance was determined using the t-test. The motor and cognitive tasks used have previously been described (Murray et al.~ 1992; Eiden et al., 1993). Testing on the motor skill task was initiated at approximately 10 weeks of age. Testing on the cognitive tasks was initiated at the cessation of the A Z T infusions, when the animals were approximately 6 months of age. Impairment on the behavior tasks indicates performance greater than 2 SD from the mean of the scores of the control uninfected animals on the same tasks during the same period. *Indicates statistical significance (p < 0.05) compared to c o n t r o l uninfected animals. NA, not applicable. ND, not done.
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tempted in any of the groups prior to age 6 months. However, at the time of cessation of A Z T treatment at 6-7 months of age, frequency of virus rescue from CSF was significantly lower in the A Z T group than in the non-treated infected group, while frequency of virus isolation from peripheral blood was equivalent in both groups. Furthermore, CSF levels of quinolinic acid, while elevated in both groups relative to uninfected animals, were approximately five-fold lower in the A Z T group at this time. Since serum quinolinic acid levels were in fact consistently slightly higher in the A Z T group, these data are consistent with the hypothesis that CSF quinolinic acid in primate lentiviral disease derives from the CNS compartment itself, rather than spillover of circulating quinolinate into CSF due to damage to the blood-brain or blood-CSF barriers (Heyes et al., 1991, 1992; Rausch et al., 1994). Discussion The preliminary examination of the ongoing study described above strongly suggests that continuous subcutaneous A Z T administration is safe and efficacious in significantly increasing lifespan after perinatal infection with SIV in rhesus monkeys. A Z T administration appears to delay the onset of motor impairment in SIV-infected infant macaques, and this correlates with a demonstrably lower virus burden in CSF during the time of A Z T treatment. The SIV-infected neonatal rhesus monkey may be a useful primate animal model for determining minimal perinatal treatment regimens for A Z T and other anti-viral agents, and studying the course of viral disease in the neonatal host. The transmission rate of infant infection by vertical transmission from HIV-infected mothers is currently estimated to be about 25% (Wara et al., 1993, and references therein). A recent Clinical Alert, summarizing results from A C T G Pediatric A I D S clinical Trial 076,
describes a decrease in H I V transmission rate from mother to infant from 25.5 to 8.3% when oral administration of A Z T was initiated at 14-34 weeks of gestation, continued throughout pregnancy, and A Z T oral administration to infants continued for an additional 6 weeks post-partum (Clinical Alert, 1994). The results of this study do not allow the relative effects of maternal and infant A Z T administration to be assessed. It would be of considerable interest to know if A Z T administered several days to a week after infection with SIV, with treatment continued for 6 months or more, afforded the same prolongation of life as A Z T treatment begun coincidentally with virus infection. If so, it would be reasonable based on both clinical and pre-clinical results to attempt A Z T therapy several days after birth in infants of HIV-positive mothers who do not receive A Z T during pregnancy, since current methods of detecting virus infection do not allow positive identification of perinatally infected infants until several days after birth. A Z T treatment results in decreased frequency of virus isolation from CSF, and appears to delay motor impairment, suggesting an association between CSF virus burden and CNS outcome. However, the relationship between CNS virus burden and motor impairment will require actual quantitation of virus burden in brain parenchyma and its correlation with functional impairment. Likewise, CSF levels of quinolinic acid appear to reflect the virus burden in the central nervous system compartment, but precise quantitation of quinolinic acid and virus levels in the brain parenchyma, as well as the systemic circulation, will be required to validate this hypothesis. Study of the efficacy, safety, and penetration to the central nervous system of antiviral agents in the perinatally SIVinfected infant rhesus monkey may represent an important opportunity to optimize infantile H I V encephalopathy/AIDS
Effects of chronic zidovudine administration therapeutics. Understanding primate perinatal cellular and humoral responses to viral infection at birth is also critical to rationally tailoring vaccine development to the HIV-infected infant. Examination of infant antibody responses to perinatal SIV infection should contribute to this effort, and is currently underway.
References
Clinical Alert. Important therapeutic information on the benefit of zidovudine for the prevention of the transmission of HIV from mother to infant. Office of Communications, National Institute of Allergy and Infectious Diseases, February 20, 1994. Eiden, L. E., Rausch, D. M., Cunha, A. D., Murray, E. A., Heyes, M., Sharer, L., Nohr, D. and Weihe, E. (1993a). AIDS and the central nervous system: Examining pathobiology and testing therapeutic strategies in the SIVinfected rhesus monkey. Ann. N Y Acad. Sci. 693: 229-244. Eiden, L. E., Murray, E. M. and Rausch, D. M. (1993b). Motor and cognitive functioning in nonhuman primates infected with simian immunodeficiency virus (SIV). An animal model for neuro-AIDS. In: Neuropsychology of HIV Infection, eds. Martin, A. and Grant, I. Oxford University Press, Oxford. Heyes, M. P. and Markey, S. P. (1988). Quantification of quinolinic acid in rat brain, whole blood and plasma by gas chromatography and negative chemical ionization mass spectrometry. Anal. Biochem. 174: 349-359. Heyes, M., Brew, B. J., Martin, A., Price, R. W., Salazar, A. M., Sidtis, J. J., Yergey, J. A., Mouradian, M. M., Sadler, A. E., Keilp, J., Rubinow, D. and Markey, S. P. (1991). Quinolinic acid in cerebrospinal fluid and serum in HIV infection: Relationship to clinical and neurologic status. Ann. Neurol. 29: 202-209. Heyes, M. P., Saito, K., Crowley, J. S., Davis, L. E., Demitrack, M. A., Der, M., Dilling, L. A., Ella, J., Kruesi, M. J. P.,
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