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Peripheral CNS markers in OCD
202
Peripheral CNS markers in OCD
Marazziti, D., Lensi, P., Ravagli, A., Milanfranchi, A., Rotondo, L., Palego, L. and Cassano, G.B. Institute of Psychiatry, University of Pisa, via Roma 67, 56100 Pisa, Italy Key words: Obsessive-compulsive disorder; Serotonin; Dopamine; Peripheral benzodiazepine receptors; Platelets; 3Himipramine binding sites; Sulphotransferase activity
Introduction
Although several data have shown that serotonin (5HT) is involved in the pathophysiology of obsessive-compulsive disorder (OCD) (Zohar and Insel, 1987), it would be too simplistic to link a complex disorder like OCD to the dysfunction of a single neurotransmitter. Actually, animal and clinical data implicate also dopamine (DA) in the mediation of some repetitive behaviours and this is not surprising in view of the complex relationships between the 5HTergic and the DAergic system. The ease isolation of blood platelets, coupled with the similarities in properties of 5HT uptake to the presynaptic uptake system for 5HT, have led to platelets being used as a biochemical model for the study of plasma membrane-mediated 5HT transport, which is possibly modulated by the 3H-imipramine binding (3H-IMI) sites. In addition, platelets possess two forms of sulphotransferase (ST), called TL and the TS, enzymes involved in the catabolism of dopamine (DA), which similar kinetic characteristics to those present in the brain, which may be used as an index of the DA system (Young et al., 1985). Peripheral benzodiazepine receptors (PBRs), localized in glial cells at the level of the central nervous system (CNS), have been also described in platelets (Verma and Snyder, 1989). The presence of these putative, peripheral CNS markers in platelets, prompted us to measure 3H-IMI binding sites, ST activity and PBRs receptors in a group of OCD patients, as compared to healthy controls, in order to provide information on the possible role of different systems in OCD. Subjects and Methods
We included in the study 30 patients (16 male and 14 female, mean age: 32+_7) affected by OCD, according to DSM III-R criteria, and 30 healthy controls matched for age and sex. All patients were evaluated by means of a specially-designed questionnaire 'Questionario per ii Disturbo Ossessivo-Compulsivo' (Lensi et al., in preparation), based upon a semistructured interview to elicit relevant demographic data, family history, psychopathological features and course of the illness. Both patients and controls were not depressed and were psychotropic drug-free. Sixty ml of venous blood was drawn from fasting subjects between 8 and 9 a.m. Platelet membranes and 3H-IMI binding were performed according to a protocol provided by the WHO, as already described (Marazziti et al., 1989). The ST activity was measured according to the original Foldes and Meek method, modified by Reiter et al. (1983). The sulfate donor was 35S3'-phosphoadenosine-5'-phosphosulphate (35S-PAPS, NEN, England, specific activity: 1.5 Ci/mmol), and p-nitrophenol and DA were respectively the substrates of ST TS and TL forms. The peripheral benzodiazepine receptor was performed according to the method of Garish et al. (1986). 3H-IIVIIand 3H-PK 11195 binding parameters (Bmax in fmol/mg protein, and Kd in nM) were calculated by means of microcomputer programs (EBDA and LIGAND). Proteins were measured according to the Peterson's method (1977). The significance of the difference between the 2 groups was measured by unpaired Student-t test (two-tailed), while the correlation between the biological parameters studied was evaluated according to Pearson's analysis. Results and Discussion
The results showed the presence of a decreased maximum binding capacity 03max, fmol/mg protein) of IMI to platelet
203 membranes in the patients than in the controls (478 + 135 vs 1009 + 231, p < 0.0001), with no change in the dissociation constant (Kd). Both the.two forms of ST (pmol/min/mg protein) were higher in patients than in controls: the TL ST was 41 -+ 19 and 18 -+ 11 (p < 0.0001) and the TS ST was 14 -+ 8 and 7 _+ 4 (p > 0.006), respectively. For peripheral benzodiazepine receptors, the Bmax of 3H-PK 11195 binding to platelet membranes was lower in patients than in controls (3124 -+ 1207 vs 5186 _+ 1111). No correlation between the various parameters studied was detected. The findings of the present research on IMI binding are in agreement with a previous report (Weizman et al., 1986) in adult and adolescent OC patients and suggest a disorder of the 5HTergic system at the presynaptic level which might be due to reduced concentration of 5HT in the synaptic cleft. The data on the increased activity of platelet ST might reflect changes in the metabolism of DA, although a clear-cut correlation with the DAergic system has not been demonstrated as yet (Young et al., 1985). The observed reduced number in peripheral benzodiazepine receptor might be linked to a generalized membrane abnormality as already observed in Alzheimer's dementia, or it might constitute a sign of mithocondria dysfunction, due to the specific location of these receptors. In conclusion, the study of peripheral CNS markers such as those present in blood platelets, although with all the limitations of a model able to reflect only some aspects of the complexity of the central neurons, might be considered a sort of indirect window on the CNS and might be of value for in vivo researches. References
Butler, P.R., Anderson, R.J. and Venton, D.L., 1983, Human platelet phenol sulphotransferase: partial purification and detection of two forms of the enzyme. L Neurochem. 41,630-639. Marazziti, D., Placidi, G.F., Cassano, G.B. and Akiskal, S.H., 1989, Lack of specificity of reduced platelet imipramine binding in different psychiatric conditions. Psychiatry Res. 30, 21-29. Verma, A. and Snyder, S.H., 1989, Peripheral type benzodiazepine receptors. Ann. Rev. Pharmacol. Toxicol. 29, 307-322. Weizman, R., Carmi, M., Hermesh, H., Shahar, A., Apter, A., Tyano, S. and Rehavi, M., 1986, High-affinity imipramine binding and serotonin uptake in platelets of eight adolescent and ten adult obsessive-compulsive patients. Am. J. Psychiatry 143, 335-339. Young jr., W.F., Laws jr., E.R., Sharbrough, F.W. and Weishilboum, R.M., 1985, Human phenol sulfotransferase: correlation of brain and platelet activities. L Neurochem. 44, l 131-l 137. Zohar, L and Insel, T.R., 1987, Obsessive-compulsive disorder: psychobiological approaches to diagnosis, treatment and pathophysiology. Biol. Psychiatry 22, 667-687.
Abstract not received
Peripheral CNS markers in OCD
Marazziti, D., Lensi, P., Ravagli, A., Milanfranchi, A., Rotondo, L., Palego, L. and Cassano, G.B. Institute of Psychiatry, University of Pisa, via Roma 67, 56100 Pisa, Italy Key words: Obsessive-compulsive disorder; Serotonin; Dopamine; Peripheral benzodiazepine receptors; Platelets; 3Himipramine binding sites; Sulphotransferase activity
Introduction
Although several data have shown that serotonin (5HT) is involved in the pathophysiology of obsessive-compulsive disorder (OCD) (Zohar and Insel, 1987), it would be too simplistic to link a complex disorder like OCD to the dysfunction of a single neurotransmitter. Actually, animal and clinical data implicate also dopamine (DA) in the mediation of some repetitive behaviours and this is not surprising in view of the complex relationships between the 5HTergic and the DAergic system. The ease isolation of blood platelets, coupled with the similarities in properties of 5HT uptake to the presynaptic uptake system for 5HT, have led to platelets being used as a biochemical model for the study of plasma membrane-mediated 5HT transport, which is possibly modulated by the 3H-imipramine binding (3H-IMI) sites. In addition, platelets possess two forms of sulphotransferase (ST), called TL and the TS, enzymes involved in the catabolism of dopamine (DA), which similar kinetic characteristics to those present in the brain, which may be used as an index of the DA system (Young et al., 1985). Peripheral benzodiazepine receptors (PBRs), localized in glial cells at the level of the central nervous system (CNS), have been also described in platelets (Verma and Snyder, 1989). The presence of these putative, peripheral CNS markers in platelets, prompted us to measure 3H-IMI binding sites, ST activity and PBRs receptors in a group of OCD patients, as compared to healthy controls, in order to provide information on the possible role of different systems in OCD. Subjects and Methods
We included in the study 30 patients (16 male and 14 female, mean age: 32+_7) affected by OCD, according to DSM III-R criteria, and 30 healthy controls matched for age and sex. All patients were evaluated by means of a specially-designed questionnaire 'Questionario per ii Disturbo Ossessivo-Compulsivo' (Lensi et al., in preparation), based upon a semistructured interview to elicit relevant demographic data, family history, psychopathological features and course of the illness. Both patients and controls were not depressed and were psychotropic drug-free. Sixty ml of venous blood was drawn from fasting subjects between 8 and 9 a.m. Platelet membranes and 3H-IMI binding were performed according to a protocol provided by the WHO, as already described (Marazziti et al., 1989). The ST activity was measured according to the original Foldes and Meek method, modified by Reiter et al. (1983). The sulfate donor was 35S3'-phosphoadenosine-5'-phosphosulphate (35S-PAPS, NEN, England, specific activity: 1.5 Ci/mmol), and p-nitrophenol and DA were respectively the substrates of ST TS and TL forms. The peripheral benzodiazepine receptor was performed according to the method of Garish et al. (1986). 3H-IIVIIand 3H-PK 11195 binding parameters (Bmax in fmol/mg protein, and Kd in nM) were calculated by means of microcomputer programs (EBDA and LIGAND). Proteins were measured according to the Peterson's method (1977). The significance of the difference between the 2 groups was measured by unpaired Student-t test (two-tailed), while the correlation between the biological parameters studied was evaluated according to Pearson's analysis. Results and Discussion
The results showed the presence of a decreased maximum binding capacity 03max, fmol/mg protein) of IMI to platelet
203 membranes in the patients than in the controls (478 + 135 vs 1009 + 231, p < 0.0001), with no change in the dissociation constant (Kd). Both the.two forms of ST (pmol/min/mg protein) were higher in patients than in controls: the TL ST was 41 -+ 19 and 18 -+ 11 (p < 0.0001) and the TS ST was 14 -+ 8 and 7 _+ 4 (p > 0.006), respectively. For peripheral benzodiazepine receptors, the Bmax of 3H-PK 11195 binding to platelet membranes was lower in patients than in controls (3124 -+ 1207 vs 5186 _+ 1111). No correlation between the various parameters studied was detected. The findings of the present research on IMI binding are in agreement with a previous report (Weizman et al., 1986) in adult and adolescent OC patients and suggest a disorder of the 5HTergic system at the presynaptic level which might be due to reduced concentration of 5HT in the synaptic cleft. The data on the increased activity of platelet ST might reflect changes in the metabolism of DA, although a clear-cut correlation with the DAergic system has not been demonstrated as yet (Young et al., 1985). The observed reduced number in peripheral benzodiazepine receptor might be linked to a generalized membrane abnormality as already observed in Alzheimer's dementia, or it might constitute a sign of mithocondria dysfunction, due to the specific location of these receptors. In conclusion, the study of peripheral CNS markers such as those present in blood platelets, although with all the limitations of a model able to reflect only some aspects of the complexity of the central neurons, might be considered a sort of indirect window on the CNS and might be of value for in vivo researches. References
Butler, P.R., Anderson, R.J. and Venton, D.L., 1983, Human platelet phenol sulphotransferase: partial purification and detection of two forms of the enzyme. L Neurochem. 41,630-639. Marazziti, D., Placidi, G.F., Cassano, G.B. and Akiskal, S.H., 1989, Lack of specificity of reduced platelet imipramine binding in different psychiatric conditions. Psychiatry Res. 30, 21-29. Verma, A. and Snyder, S.H., 1989, Peripheral type benzodiazepine receptors. Ann. Rev. Pharmacol. Toxicol. 29, 307-322. Weizman, R., Carmi, M., Hermesh, H., Shahar, A., Apter, A., Tyano, S. and Rehavi, M., 1986, High-affinity imipramine binding and serotonin uptake in platelets of eight adolescent and ten adult obsessive-compulsive patients. Am. J. Psychiatry 143, 335-339. Young jr., W.F., Laws jr., E.R., Sharbrough, F.W. and Weishilboum, R.M., 1985, Human phenol sulfotransferase: correlation of brain and platelet activities. L Neurochem. 44, l 131-l 137. Zohar, L and Insel, T.R., 1987, Obsessive-compulsive disorder: psychobiological approaches to diagnosis, treatment and pathophysiology. Biol. Psychiatry 22, 667-687.
Abstract not received