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Decreased CSF inositol monophosphatase activity after lithium treatment
Psychiarry Research, 53, 103-105 Elsevier
103
Brief Report Decreased CSF Inositol Monophosphatase Activity After Lithium Treatment One of the hypothesized mechanisms of action for the therapeutic effects of lithium for affective disorders is inhibition of the enzyme inositol monophosphatase (IMPase). In a study that used a recently developed assay, cerebrospinal fluid (CSF) IMPase activity was shown to be significantly decreased after 3 weeks of lithium treatment as compared with placebo in a group of normal volunteers. This first report of IMPase inhibition by lithium in human CSF leaves open the possibility that this may be at least part of the mechanism of action of lithium’s clinical effects. IMPase is a key enzyme of the phosphoinositide second messenger system, which couples neurotransmitter and hormone receptors to cellular response elements. IMPase catalyzes the dephosphorylation of inositol monophosphates, which are recycled to inositol, a precursor for the synthesis of inositol phospholipids. The hormoneand neurotransmitter-linked hydrolysis of inositol phospholipids yields the second messengers diacylglycerol, which leads to activation of protein kinase C, and inositol triphosphate, which leads to intracellular calcium release (Berridge et al., 1989). One of the mechanisms by which lithium therapy is hypothesized to work in affective disorders is inhibition of IMPase, which depletes the pool of inositol available in the central nervous system, thereby reducing the amount of inositol phospholipids (Berridge et al., 1989).
Elsevier Science Ireland Ltd.
In humans, the effects of lithium on IMPase have been studied only in red blood cells. Activity was shown to decrease in normal control subjects (Agam and Livne, 1988) and to a comparable degree in a group of manic-depressive patients after treatment (Moscovich et al., 1990). The recent development of an assay to measure IMPase activity in CSF allowed us to apply this measure in a group of normal volunteers participating in a study of lithium’s effects in older people. Subjects were screened for cardiac, renal, endocrine, neuropsychiatric, and other systemic illnesses before participation. The mean age of the subjects was 65.4 (SD = 10.4) years; there were two women and three men. After a period of at least 3 weeks free of medication, subjects were administered placebo capsules for a 3-week period, followed by 3 weeks of treatment with lithium carbonate in a single-blind manner. Lumbar punctures were done between 9 and 10 a.m., after an overnight fast, in the last few days of each treatment phase. CSF was immediately frozen on dry ice and stored at -70 ‘C. CSF IMPase activity was measured radiometrically in triplicate as described previously (Atack et al., 1993), by an investigator without knowledge of drug condition. Briefly, aliquots (75 ~1) of CSF were incubated in buffer containing inositoll-phosphate (Iris(l)))) assay concentration = 0.1 mM) plus trace amounts of i4C-Ins( 1)P.
104 The reaction was terminated by the addition of 25 ~1 10% trichloroacetic acid. The final assay volume was 150 ~1 (1: 1 dilution of the CSF). Inositol plus 14C-inositol (produced by cleavage of Iris(l))) by IMPase) was separated from unhydrolysed substrate (i.e., Ins(l)P plus W-Ins(l)P) by anion exchange column chromatography. The column flowthrough (which contains inositol/ W-inositol) was collected, scintillation fluid was added, it was counted on a scintillation counter, and the radioactivity was assumed to be proportional to enzyme activity (Atack et al., 1993). The coefficient of variation for the assay for these samples was 1.2%. CSF and serum lithium levels were determined by flame photometry. The mean CSF IMPase activity during the placebo phase was 0.70 (SD = 0.16) nMol/ hour/ml and 0.63 (SD = 0.12) nMol/ hour/ml during the lithium phase. CSF IMPase activity decreased in all subjects after lithium treatment, and analysis using a paired t test showed that this difference was significant (t = 2.89, p < 0.04) (Fig. 1). The mean serum lithium level was 0.8 (SD = 0.14) mEq/l, which is within the therapeutic range used for affective disorders, and the mean CSF Fig. 1. Cerebrospinal fluid inositol monophosphatase activity during placebo and lithium treatment phases 1.n 0
-11
References Agam, G., and Livne, A. lnositol-l-phosphatase of human erythrocytes is inhibited by therapeutic lithium concentrations. P&riufr_r Research, 271217-224, 1988. Atack, J.R.; Rapoport, S.I.; and Varley, C.L. Characterization of inositol monophosphatase in human cerebrospinal fluid. Brain Research,
0 .
Subjrcts (n=s)
lithium level was 0.22 (SD = 0.08) mEq/l. The alteration in enzyme activity that we report is consistent with previous doseresponse data on exogenously added lithium to CSF (Atack et al., 1993). This is the first report to our knowledge of IMPase inhibition by lithium in human CSF. Our subjects were normal controls; studies in patients with manic-depressive and other neuropsychiatric illnesses need to be done to explore how inhibition of the enzyme relates to mood state. A number of theories on lithium’s effects on second messenger systems have been proposed to explain its mechanism of action in affective disorders (Berridge et al., 1989). CSF IMPase activity is about two orders of magnitude less than the activity of the enzyme in the brain, but nonetheless the lithium induced activity alteration most likely reflects that in the brain (Atack et al., 1993). Our results confirm that lithium does indeed inhibit CSF IMPase in humans and leave open the possibility that inhibition of this enzyme is at least part of the mechanism of action of the clinical effects of lithium.
613:305-308,
1993.
Berridge, M.J.; Downes, C.P.; and Hanley, M.R. Neural and developmental actions of lithium: A unifying hypothesis. Cell, 59:41 I-419, 1989. Moscovich, D.G.; Belmaker, R.H.; Agam, G.; and Livne, A. Inositol-1-phosphatase in red blood cells of manic-depressive patients before and during treatment with lithium. Biological
Psychiatry,
27:552-555,
1990.
105 Susan
E. Molchan, M.D.1 Section on Geriatric Psychiatry Laboratory of Clinical Science National Institute of Mental Health National Institutes of Health Bethesda, MD, USA
Trey Sunderland, M.D. Section on Geriatric Psychiatry Laboratory of Clinical Science National Institute of Mental Health National Institutes of Health Bethesda, MD, USA
John
Received
R. Atack, Ph.D. Merck Research Laboratories Neurosciences Research Center Terlings Park, Harlow, Essex, UK
March 16, 1994; revised June 14, 1994.
I. Reprint requests to Dr. S.E. Molchan, NIMH, NIH Clinical Center, Bldg. 10, Rm. 3D-41, 9000 Rockville Pike, Bethesda, MD 20892. USA.
103
Brief Report Decreased CSF Inositol Monophosphatase Activity After Lithium Treatment One of the hypothesized mechanisms of action for the therapeutic effects of lithium for affective disorders is inhibition of the enzyme inositol monophosphatase (IMPase). In a study that used a recently developed assay, cerebrospinal fluid (CSF) IMPase activity was shown to be significantly decreased after 3 weeks of lithium treatment as compared with placebo in a group of normal volunteers. This first report of IMPase inhibition by lithium in human CSF leaves open the possibility that this may be at least part of the mechanism of action of lithium’s clinical effects. IMPase is a key enzyme of the phosphoinositide second messenger system, which couples neurotransmitter and hormone receptors to cellular response elements. IMPase catalyzes the dephosphorylation of inositol monophosphates, which are recycled to inositol, a precursor for the synthesis of inositol phospholipids. The hormoneand neurotransmitter-linked hydrolysis of inositol phospholipids yields the second messengers diacylglycerol, which leads to activation of protein kinase C, and inositol triphosphate, which leads to intracellular calcium release (Berridge et al., 1989). One of the mechanisms by which lithium therapy is hypothesized to work in affective disorders is inhibition of IMPase, which depletes the pool of inositol available in the central nervous system, thereby reducing the amount of inositol phospholipids (Berridge et al., 1989).
Elsevier Science Ireland Ltd.
In humans, the effects of lithium on IMPase have been studied only in red blood cells. Activity was shown to decrease in normal control subjects (Agam and Livne, 1988) and to a comparable degree in a group of manic-depressive patients after treatment (Moscovich et al., 1990). The recent development of an assay to measure IMPase activity in CSF allowed us to apply this measure in a group of normal volunteers participating in a study of lithium’s effects in older people. Subjects were screened for cardiac, renal, endocrine, neuropsychiatric, and other systemic illnesses before participation. The mean age of the subjects was 65.4 (SD = 10.4) years; there were two women and three men. After a period of at least 3 weeks free of medication, subjects were administered placebo capsules for a 3-week period, followed by 3 weeks of treatment with lithium carbonate in a single-blind manner. Lumbar punctures were done between 9 and 10 a.m., after an overnight fast, in the last few days of each treatment phase. CSF was immediately frozen on dry ice and stored at -70 ‘C. CSF IMPase activity was measured radiometrically in triplicate as described previously (Atack et al., 1993), by an investigator without knowledge of drug condition. Briefly, aliquots (75 ~1) of CSF were incubated in buffer containing inositoll-phosphate (Iris(l)))) assay concentration = 0.1 mM) plus trace amounts of i4C-Ins( 1)P.
104 The reaction was terminated by the addition of 25 ~1 10% trichloroacetic acid. The final assay volume was 150 ~1 (1: 1 dilution of the CSF). Inositol plus 14C-inositol (produced by cleavage of Iris(l))) by IMPase) was separated from unhydrolysed substrate (i.e., Ins(l)P plus W-Ins(l)P) by anion exchange column chromatography. The column flowthrough (which contains inositol/ W-inositol) was collected, scintillation fluid was added, it was counted on a scintillation counter, and the radioactivity was assumed to be proportional to enzyme activity (Atack et al., 1993). The coefficient of variation for the assay for these samples was 1.2%. CSF and serum lithium levels were determined by flame photometry. The mean CSF IMPase activity during the placebo phase was 0.70 (SD = 0.16) nMol/ hour/ml and 0.63 (SD = 0.12) nMol/ hour/ml during the lithium phase. CSF IMPase activity decreased in all subjects after lithium treatment, and analysis using a paired t test showed that this difference was significant (t = 2.89, p < 0.04) (Fig. 1). The mean serum lithium level was 0.8 (SD = 0.14) mEq/l, which is within the therapeutic range used for affective disorders, and the mean CSF Fig. 1. Cerebrospinal fluid inositol monophosphatase activity during placebo and lithium treatment phases 1.n 0
-11
References Agam, G., and Livne, A. lnositol-l-phosphatase of human erythrocytes is inhibited by therapeutic lithium concentrations. P&riufr_r Research, 271217-224, 1988. Atack, J.R.; Rapoport, S.I.; and Varley, C.L. Characterization of inositol monophosphatase in human cerebrospinal fluid. Brain Research,
0 .
Subjrcts (n=s)
lithium level was 0.22 (SD = 0.08) mEq/l. The alteration in enzyme activity that we report is consistent with previous doseresponse data on exogenously added lithium to CSF (Atack et al., 1993). This is the first report to our knowledge of IMPase inhibition by lithium in human CSF. Our subjects were normal controls; studies in patients with manic-depressive and other neuropsychiatric illnesses need to be done to explore how inhibition of the enzyme relates to mood state. A number of theories on lithium’s effects on second messenger systems have been proposed to explain its mechanism of action in affective disorders (Berridge et al., 1989). CSF IMPase activity is about two orders of magnitude less than the activity of the enzyme in the brain, but nonetheless the lithium induced activity alteration most likely reflects that in the brain (Atack et al., 1993). Our results confirm that lithium does indeed inhibit CSF IMPase in humans and leave open the possibility that inhibition of this enzyme is at least part of the mechanism of action of the clinical effects of lithium.
613:305-308,
1993.
Berridge, M.J.; Downes, C.P.; and Hanley, M.R. Neural and developmental actions of lithium: A unifying hypothesis. Cell, 59:41 I-419, 1989. Moscovich, D.G.; Belmaker, R.H.; Agam, G.; and Livne, A. Inositol-1-phosphatase in red blood cells of manic-depressive patients before and during treatment with lithium. Biological
Psychiatry,
27:552-555,
1990.
105 Susan
E. Molchan, M.D.1 Section on Geriatric Psychiatry Laboratory of Clinical Science National Institute of Mental Health National Institutes of Health Bethesda, MD, USA
Trey Sunderland, M.D. Section on Geriatric Psychiatry Laboratory of Clinical Science National Institute of Mental Health National Institutes of Health Bethesda, MD, USA
John
Received
R. Atack, Ph.D. Merck Research Laboratories Neurosciences Research Center Terlings Park, Harlow, Essex, UK
March 16, 1994; revised June 14, 1994.
I. Reprint requests to Dr. S.E. Molchan, NIMH, NIH Clinical Center, Bldg. 10, Rm. 3D-41, 9000 Rockville Pike, Bethesda, MD 20892. USA.