Localization of angiotensin-converting enzyme, prolyl endopeptidase and other peptidases in cultured neuronal or glial cells

Inhibition of angiotensin converting enzyme induces mechanical allodynia through increasing substance P expression in mice

Although emerging evidence shows that angiotensin converting enzyme (ACE) is associated with pain, it is not clear whether inhibition of ACE could affect to nociceptive transmission and which mediators are involved in this process. Here we investigated whether administration of the ACE inhibitors, captopril and enalapril increases the expression of substance P (SP) and whether this increase contributes to the induction of mechanical allodynia in mice. ACE was expressed in the lumbar dorsal root ganglion (DRG) and the superficial dorsal horn (SDH) region of the spinal cord in mice. Either intraperitoneal or intrathecal administration of the ACE inhibitors, captopril and enalapril for 10 days significantly increased the paw withdrawal frequency to innocuous mechanical stimuli and the levels of SP in both the lumbar DRG and the SDH region of the spinal cord dorsal horn. In addition, intraperitoneal administration of the SP receptor (neurokinin-1 receptor) antagonist, L-733,060 suppressed mechanical allodynia that was induced by pretreatment of captopril and enalapril. Intraplantar administration of SP for 3 days induces mechanical allodynia, and this effect was reduced by exogenous ACE administration. These findings demonstrate that inhibition of ACE increases the levels of SP in both the lumbar DRG and spinal cord dorsal horn, ultimately contributing to the induction of mechanical allodynia in mice.

ACE activity in blood and brain axis in an animal model for schizophrenia: Effects of dopaminergic manipulation with antipsychotics and psychostimulants

Objectives: Angiotensin I-converting enzyme (ACE) was initially correlated with schizophrenia (SCZ) in studies showing a correlation of ACE increased enzyme activity with memory impairments. Possible role for ACE in SCZ was also suggested by ACE activity interaction with dopaminergic mechanisms to modulate abnormalities of sensorimotor gating. In addition, we have demonstrated higher ACE activity in blood of SCZ subjects, its implication in cognitive performance in SCZ and its power as a predictor for SCZ diagnosis.Methods: ACE activity was determined in the serum and in selected brain regions of an animal model presenting SCZ-like behaviour, before and after the treatment with typical and atypical antipsychotics, and also in the serum of animals receiving the psychostimulants amphetamine/lisdexamphetamine.Results: Dopaminergic manipulations with antipsychotics and psychostimulants influenced the ACE activity, but with no correlation with the animal blood pressure.Conclusions: The validity of measuring ACE activity in animal blood to predict activity in the CNS, as well as the lack of correlation between the activity and blood pressure, before and after the treatment with antipsychotics, were confirmed here. Correlations of the present findings with data from clinical studies also strengthen the value of this animal model for studying several aspects of SCZ.

Suppressive effect of clozapine but not haloperidol on the increases of neuropeptide-degrading enzymes and glial cells in MK-801-treated rat brain regions

MK-801, a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, produces neurotoxicity in adult rodent brain, and causes schizophrenia-like psychosis and cognitive dysfunction. Since neuropeptides and neuropeptide-degrading enzymes play important roles in cognitive function, we examined whether or not MK-801-induced schizophrenia-like psychosis is co-related with the changes of these enzymes in rat brain regions. In the present study, we investigated the effect of systemic treatment with MK-801 (0.5mg/kg) on neuropeptide-degrading enzymes, prolyl oligopeptidase (POP) and thimet oligopeptidase (EP 24.15), and glial marker proteins GFAP and CD11b in rat brain regions. The levels of POP and EP 24.15 activities increased significantly three days after treatment with MK-801 in the posterior cingulate/retrosplenial cortices (PC/RSC). Since atypical neuroleptic clozapine but not typical neuroleptic haloperidol prevents the MK-801-induced schizophrenia-like symptoms, we further examined the pretreated effects of the neuroleptics. Clozapine, but not haloperidol, significantly attenuated MK-801-induced changes in the levels of the neuropeptide-degrading enzymes. Immunohistochemical studies on GFAP and CD11b showed the increase in the PC/RSC of MK-801-treated rat brain and the pretreatment with clozapine suppressed these changes. Double immunostain experiments of EP 24.15 and GFAP antibodies demonstrated some co-localization of the neuropeptidase with astrocytes. The present findings suggest that change of neuropeptidases in the brain is in part correlated with changes of glial cells, and may play an important role in the control of schizophrenia-like psychotic disorders.

Pentylenetetrazol-induced seizures affect the levels of prolyl oligopeptidase, thimet oligopeptidase and glial proteins in rat brain regions, and attenuation by MK-801 pretreatment

The regulatory mechanisms of neuropeptide-metabolizing enzymes often play a critical role in the pathogenesis of neuronal damage. A systemic administration of pentylenetetrazol (PTZ), an antagonist of GABA(A) receptor ion channel binding site, causes generalized epilepsy in an animal model. In the present study, we examined the involvement of prolyl oligopeptidase (POP), thimet oligopeptidase/neurolysin (EP 24.15/16) and glial proteins in PTZ-treated rat brain regions, and the suppressive effect of MK-801, a non-competitive NMDA receptor antagonist, pretreatment for their proteins. The activity of POP significantly decreased in the hippocampus at 30min and 3h, and in the frontal cortex at 3h after PTZ treatment, and pretreatment with MK-801 recovered the activity in the cortex at 3h. The activity of EP 24.15/16 significantly decreased in the hippocampus at 3h and 1 day, and in the cortex at 3h after the PTZ administration, whereas pretreatment with MK-801 recovered the change of the activity. The Western blot analysis of EP 24.15 showed significant decrease of the protein level in the hippocampus 3h after the PTZ treatment, whereas pretreatment with MK-801 recovered. The expression of GFAP and CD11b immunohistochemically increased in the hippocampus of the PTZ-treated rat as compared with controls. Pretreatment with MK-801 also recovered the GFAP and CD11b expression. These data suggest that PTZ-induced seizures of the rats cause indirect activation of glutamate NMDA receptors, then decrease POP and EP 24.15/16 enzyme activities and EP 24.15 immunoreactivity in the neuronal cells of the hippocampal formation. We speculate that changes of those peptidases in the brain may be related to the levels of the neuropeptides regulating PTZ-induced seizures.

Current antipsychotic dose correlates to mononuclear cell counts in the cerebrospinal fluid of psychotic patients

Elevated cerebrospinal fluid (CSF) angiotensin I-converting enzyme (ACE) levels have been evidenced in patients with schizophrenia who have been treated with antipsychotics. In order to explore a possible mononuclear cell origin of CSF ACE, the authors determined CSF ACE and CSF mononuclear cell counts from 25 acutely psychotic patients, who had been drug-free for at least 4 months but started on conventional antipsychotic medication within a few days before sampling. No correlations were found between CSF to serum ACE ratio and CSF mononuclear cell counts. However, CSF total mononuclear cell count, CSF lymphocyte count, and CSF mononuclear phagocyte count evidenced significant positive correlations with current dose of antipsychotic medication expressed as chlorpromazine equivalents. The authors conclude that no indication of a relationship between mononuclear cells and CSF ACE activity was found. Surprisingly, a relationship between chlorpromazine dose and CSF mononuclear cell counts was found, which may indicate drug-related changes in cell-mediated immunity. This finding needs replication and further corroboration in well-designed studies.

Decrease in cytosolic Aspartyl-aminopeptidase but not in Alanyl-aminopeptidase activity in the frontal cortex of the aged rat

To test the neurotoxic hypothesis of excitatory amino acids, we evaluated the possible contribution to the free acidic amino acid pool of Aspartyl-aminopeptidase activity in the frontal cortex of adult (3 month old) and aged rats (3 groups of animals aged 26, 29 and 33 months). Aspartyl-aminopeptidase activity showed a significant decrease in the oldest rats (29 and 33 months old) whereas the activity of Alanyl-aminopeptidase, an unspecific enzyme, did not change with age. These data invalidate the idea that excess free acidic amino acids are released by aminopeptidases in the aged rat but do provide evidence of age-related changes in this enzymatic activity. The possible implications of our findings for general alterations in protein degradation are discussed.

Elevated angiotensin-converting enzyme (kininase II) in the cerebrospinal fluid of neuroleptic-treated schizophrenic patients

Disturbances of water homeostasis have frequently been reported in schizophrenia. Water homeostasis is regulated by arginine vasopressin (AVP), the renin-angiotensin system and natriuretic hormones. The aim of this study was to determine the activity of the central renin-angiotensin system in schizophrenia by measuring levels of angiotensin-converting enzyme (ACE) in the cerebrospinal fluid (CSF) and blood in 14 in-patients with schizophrenia on neuroleptic medication and in 9 healthy volunteers. The levels of CSF ACE were significantly higher in the schizophrenia group. There were no correlations between CSF ACE and gender, age, age at first episode, duration of illness, term of hospitalization or neuroleptic dosage. No correlations between CSF ACE and serum ACE were found in either group. The authors suggest an activated central renin-angiotensin system in schizophrenia at least during antipsychotic drug treatment, which may cause 'psychogenic' polydipsia in some patients. ACE and the brain renin-angiotensin system may also play a role in the regulation of neuron growth and differentiation in schizophrenia.

Neuronal localization of pyroglutamate aminopeptidase II in primary cultures of fetal mouse brain

Pyroglutamate aminopeptidase II is a highly specific membrane-bound ectopeptidase proposed to inactivate thyrotropin releasing hormone (TRH) in brain extracellular space. Its activity was measured in primary cell cultures of fetal brain in an attempt to define its cellular localization. Enzyme activity was detected in hypothalamic or cortical cell membrane fractions from 4- to 12-day-old cultures. When proliferation of nonneuronal cells was abolished by cytosine arabinoside treatment, pyroglutamate aminopeptidase II specific activity was increased as compared to untreated cultures, the opposite was observed for pyroglutamate amino-peptidase I activity. Treatment of cortical cells with the neurotoxic agent glutamate reduced simultaneously pyroglutamate aminopeptidase II and glutamate decarboxylase activities. Glial cell cultures expressed pyroglutamate aminopeptidase I or glutamate synthase activities but not pyroglutamate aminopeptidase II. The data suggest that pyroglutamate aminopeptidase II is predominantly localized in neuronal cells. This is consistent with a role for pyroglutamate aminopeptidase II in TRH-ergic synaptic transmission.

Pharmacological properties of voltage-dependent calcium channels in functional microvessels isolated from rat brain

Voltage-operated calcium channels were studied in rat intracerebral microvessels. The contractile reactivity to KCl-depolarization was assessed by the measurement of internal diameter of superfused microvessels. Dihydropyridine receptor sites associated with calcium channels were identified and characterized using 3H(+)PN 200-110 [isopropyl-4-(2,1,3-benzodiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- -methoxycarbonyl-pyridine-3-carboxylate]. Depolarization induced by high-KCl solution produced a marked reduction of the internal diameter of cerebral microvessels which was associated with the appearance of rhythmic activity. The vessel contraction was reversible and abolished by nimodipine. Binding studies with 3H(+)PN 200-110 revealed the existence of a single class of specific, stereoselective and voltage-dependent binding sites which bound (+)PN 200-110 with a KD of 88 +/- 6.6 pmol l-1 at 37 degrees C in microvessels incubated in NaCl medium. When microvessels were incubated in KCl-medium, the apparent KD value was reduced to 35 +/- 2 pmol l-1. Bmax was not significantly changed. The effect of KCl was not related to concomitant changes in the Na concentration. The potency of various dihydropyridine derivatives in inhibiting 3H(+)PN 200-110 binding was in agreement with their pharmacological potency in smooth muscle preparations. The effect of PN 200-110 and of nimodipine was stereoselective. Ki values of PN 200-110 and of nimodipine were increased in depolarized preparations, while nifedipine's potency was unchanged. Verapamil was only a partial inhibitor of 3H(+)PN 200-110 binding. The effect of diltiazem was stereoselective: the (+)-cis isomer enhanced the binding and the (-)-cis isomer of diltiazem poorly inhibited the binding of PN 200-110. Results showed that isolated cerebral microvessels possess functional voltage-operated calcium channels, which contain potential-modulated receptors for dihydropyridine calcium entry blockers with characteristics similar to those described in other tissues.

Changes in nine enzyme markers for neurons, glia, and endothelial cells in agonal state and Huntington's disease caudate nucleus

Enzymes considered to be markers for neurons (angiotensin converting enzyme, thermolysin-like metalloendopeptidase, alanine aminopeptidase, and glutamate-oxaloacetate transaminase), glia (glutamine synthetase, pyruvate carboxylase, and beta-glucuronidase), and endothelial cells (alkaline phosphatase and plasminogen activator) were measured in caudate nucleus from 10 sudden death controls, eight agonal state controls, and 16 Huntington's disease patients. Glutamate-oxaloacetate transaminase was slightly reduced by agonal state. The four enzymes with a neuronal distribution were all correlatively reduced in Huntington's disease caudate nucleus. Glutamine synthetase activity was reduced and beta-glucuronidase mean activity increased over twofold in Huntington's disease caudate nucleus, with the two enzyme activities being inversely related. Pyruvate carboxylase was markedly affected by agonal state and was very variable in Huntington's disease caudate nucleus. The two endothelial enzymes were unaltered in Huntington's disease caudate nucleus. The findings are indicative of neuronal loss, an increased proportion of altered glia, and also of maintained vasculature in Huntington's disease caudate nucleus. Measurement of enzyme activities can help to delineate the types of cell altered in Huntington's disease.

Peptidase-containing neurons in rat striatum

The effects of surgical lesions on peptidase activity have been studied in the striatonigral system of the rat brain. Knife cuts separating the anterior part of the caudate putamen from the globus pallidus resulted in a decrease in the activity of angiotensin-converting enzyme and alanyl aminopeptidase in both the globus pallidus and substantia nigra. The activity of nigral prolyl endopeptidase and leucyl aminopeptidase was also decreased. An increase in dipeptidyl aminopeptidase and arginyl endopeptidase activity was observed in both the caudate putamen and globus pallidus. These results suggest that the striatal neurons containing angiotensin-converting enzyme or alanyl aminopeptidase project to both the globus pallidus and substantia nigra, and the neurons containing prolyl endopeptidase and/or leucyl aminopeptidase project to the substantia nigra. Dipeptidyl aminopeptidase and arginyl endopeptidase are probably associated with glial function.