Effect of anticonvulsant drugs on peripheral benzodiazepine receptors of human lymphocytes

Diazepam binding inhibitor and dehydroepiandrosterone sulphate plasma levels in borderline personality disorder adolescents

BACKGROUND

Borderline personality disorder (BPD) patients display a complex and heterogeneous clinical phenotype that plausibly implies variable underlying pathogenic mechanisms. A dysregulation of peripheral benzodiazepine receptors has previously been shown in BPD peripheral tissues, implying possible alterations of its ligand, the diazepam binding inhibitor (DBI) or of the downstream products of its activation, i.e. neuroactive steroids.

METHODS

The aim of this work consisted in assessing, by ELISA, fasting plasma levels of DBI and dehydroepiandrosterone sulphate (DHEA-S), including cortisol and the cortisol-to-DHEA-S molar ratio (CDR), in 17 BPD adolescents versus 13 healthy controls, testing the possibility that clinical scales related to depressive or anxious traits (CDI, STAI-Y) or to disease severity (BPDCL) might be associated with a selective dysregulation of these parameters.

RESULTS

DBI plasma levels were unchanged, while DHEA-S ones were significantly increased (approx. 70%) and the CDR decreased in BPD patients. No meaningful correlations with clinical variables emerged.

CONCLUSION

Our results indicate that a dysfunction of the neurosteroid system might be operative in BPD in spite of unchanged DBI plasma levels and that DHEA-S might represent a generalized trait marker for the altered stress response that is associated with this disorder.

Evidence in favour of a role for peripheral-type benzodiazepine receptor ligands in amplification of neuronal apoptosis

The mitochondrial peripheral benzodiazepine receptor (PBR) is involved in a functional structure designated as the mitochondrial permeability transition (MPT) pore, which controls apoptosis. PBR expression in nervous system has been reported in glial and immune cells. We now show expression of both PBR mRNA and protein, and the appearance of binding of a synthetic ligand fluo-FGIN-1-27 in mitochondria of rat cerebellar granule cells (CGCs). Additionally, the effect of PBR ligands on colchicine-induced apoptosis was investigated. Colchicine-induced neurotoxicity in CGCs was measured at 24 h. We show that, in vitro, PBR ligands 1-(2-chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195), 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4- benzodiazepin-2-one (Ro5-4864) and diazepam (25- 50 microM) enhanced apoptosis induced by colchicine, as demonstrated by viability experiments, flow cytometry and nuclear chromatin condensation. Enhancement of colchicine-induced apoptosis was characterized by an increase in mitochondrial release of cytochrome c and AIF proteins and an enhanced activation of caspase-3, suggesting mitochondrion dependent mechanism that is involved in apoptotic process. Our results indicate that exposure of neural cells to PBR ligands generates an amplification of apoptotic process induced by colchicine and that the MPT pore may be involved in this process.

GABAA/central benzodiazepine receptor and peripheral benzodiazepine receptor ligands as inducers of phenobarbital-inducible CYP2B and CYP3A

A sequence critical for phenobarbital (PB) induction, the PB response unit (PBRU), situated upstream of the rat CYP2B1 and CYP2B2 genes, includes two nuclear receptor binding sites, NR1 and NR2. When NR1 and NR2 are mutated PB responsiveness is abolished. While no nuclear receptor for which PB is an agonist ligand has yet been identified, PB is a ligand of GABA(A) receptors and it can displace [(3)H] 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195) from its binding site on the peripheral benzodiazepine receptor (PBR). We assessed CYP2B levels in primary rat hepatocytes following treatment with 10 ligands of either or both of these receptors. All compounds tested were found to be CYP2B1/CYP2B2 inducers and most were CYP3A inducers. Five had not previously been described as CYP2B1/CYP2B2 inducers: bicuculline, flunitrazepam, 4'-chlorodiazepam (Ro5-4864), N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide (FGIN 1-27) and 7-(dimethylcarbamoyloxy)-6-phenylpyrrolo-[2,1-d][1,5]benzothiazepine (DCPPBT). Reporter gene analysis demonstrated that CYP2B induction by these agents and other PBR or GABA(A) receptor ligands is mediated through the PBRU and the NR1/NR2 sites, suggesting a molecular mechanism similar to that for PB induction. The potencies for PBRU-dependent induction by 11 ligands of PBR or the GABA(A) receptor was evaluated. FGIN-127, DCPPBT and PK 11195 exhibited EC(50) values for PBRU-dependent transcription activation about three orders of magnitude higher than the reported affinities of the PBR for these agents, arguing against the involvement of the PBR in PB induction. However the EC(50) values found for the agents tested encourage further investigation on the possible involvement of the GABA(A) receptor in PB induction.

Mechanisms of action of carbamazepine and its derivatives, oxcarbazepine, BIA 2-093, and BIA 2-024

Carbamazepine (CBZ) has been extensively used in the treatment of epilepsy, as well as in the treatment of neuropathic pain and affective disorders. However, the mechanisms of action of this drug are not completely elucidated and are still a matter of debate. Since CBZ is not very effective in some epileptic patients and may cause several adverse effects, several antiepileptic drugs have been developed by structural variation of CBZ, such as oxcarbazepine (OXC), which is used in the treatment of epilepsy since 1990. (S)-(-)-10-acetoxy-10,11-dihydro-5H-dibenz [b,f]azepine-5-carboxamide (BIA 2-093) and 10,11-dihydro-10-hydroxyimino-5H-dibenz[b,f] azepine-5-carboxamide (BIA 2-024), which were recently developed by BIAL, are new putative antiepileptic drugs, with some improved properties. In this review, we will focus on the mechanisms of action of CBZ and its derivatives, OXC, BIA 2-093 and BIA 2-024. The available data indicate that the anticonvulsant efficacy of these AEDs is mainly due to the inhibition of sodium channel activity.

Inhibitory action of 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxam ide (PK 11195) on some mononuclear phagocyte functions

Peripheral benzodiazepine receptors (PBRs) are widely distributed throughout the body, but their functions are unknown. They are found on mononuclear phagocytes, and they are up-regulated in a number of neurological and other disease states. We explored the functional consequences of PBR ligand binding to mononuclear-derived cells using the high-affinity ligands 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxam ide (PK 11195) and 4'-chlorodiazepam (7-chloro-5-(4'-chlorophenyl)-1, 3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one; Ro 5-4864). The functions were the following: respiratory burst; secretion of glutamate, interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha); toxicity of culture supernatants towards SH-SY5Y human neuroblastoma cells; and expression of the inflammatory surface markers HLA-DR and Fcgamma RII (CDw32). PK 11195 inhibited the respiratory burst response, reduced release of glutamate and IL-1beta, and suppressed secretion of products cytotoxic to neuronal cells. Selectivity was suggested by the failure of PK 11195 to influence TNF-alpha secretion or expression of HLA-DR and CDw32. Powerful ligands of PBRs, such as PK 11195, may be useful inhibitors of selective macrophage functions, retarding both local and systemic inflammation. Since PK 11195 readily enters the brain, it may be beneficial in treating central as well as peripheral inflammatory diseases.

Peripheral type benzodiazepine receptor in T lymphocyte rich preparation

Some types of mood disorders and drugs are suggested to affect peripheral type benzodiazepine receptors (PBR), but their mechanisms are unclear. The isolation of pure lymphocytes is requisite for the investigation of the function of PBR on lymphocytes, since platelets and monocytes also have many PBR. The objective of this study was to establish a method of binding assay for PBR using pure T lymphocytes. Mononuclear cells and T lymphocytes were prepared by using a density gradient material and magnetic beads, respectively. The cells were analyzed using flow cytometry and a counting chamber. Binding studies were performed using T lymphocytes from 10 normal volunteers. The T lymphocytes were incubated with [3H]PK11195, harvested on glass fiber filters, and counted with a plate scintillation counter. The binding data were analyzed by the Scatchard method. With the magnetic bead technique, pure T cells were selected that contained only 1.5% monocytes and platelet/cell ratio of 1.4. The Scatchard plot of the data indicated that only one type of specific binding site was involved in the binding. The dissociation constant (Kd) was 3.8+/-1.3nM (mean+/-SD), and the Bmax was 379+/-124 fmol//10(6) cells (mean+/-SD). The density gradient- magnetic beads technique can be used as an appropriate method of preparation of T cells for PBR binding assay.

Benzodiazepine receptor agonists modulate thymocyte apoptosis through reduction of the mitochondrial transmembrane potential

Peripheral-type benzodiazepines have been shown to exert immunological effects. In this study, we examined the effects of the peripheral-type benzodiazepines on murine thymocytes. Murine thymocytes that were incubated with the peripheral-type benzodiazepines underwent apoptosis associated with the collapse of mitochondrial transmembrane potential (delta psi(m)). The drugs stimulated dexamethasone- and etoposide-induced apoptosis with the enhanced collapse of delta psi(m). The central-type benzodiazepines had no effect on either the delta psi(m) or apoptosis. The reduction of delta psi(m) depended on protein synthesis and protein phosphorylation. These results suggest that the immunomodulating effect of benzodiazepines is in part due to the modulation of thymocyte apoptosis associated with the collapse of delta psi(m).

Diazepam binding inhibitor (DBI) in the plasma of pediatric and adult epileptic patients

The polypeptide diazepam binding inhibitor (DBI) displays epileptogenic activity by binding to benzodiazepine receptors. We analyzed DBI concentrations in the plasma of pediatric and adult epileptic patients, as a possible peripheral marker in epilepsy. DBI plasma concentrations are significantly higher (+ 62%, P < 0.001) in adult patients and slightly but significantly higher (+15%, P < 0.01) in pediatric patients, compared to age-related controls. Strikingly, plasma DBI is much higher (+81%, P < 0.001) in generalized epilepsy in adults and in drug-resistant pediatric and adult patients. Based on these findings, plasma DBI may be considered as a peripheral biological marker of epilepsy and, in association with lymphocyte benzodiazepine receptor density, of anticonvulsant drug responsiveness.

Carbamazepine affects neutrophil function through an action on peripheral benzodiazepine receptors

The aims of this study were to assess the possible role of peripheral benzodiazepine receptors (pBZrs)1 in mediating the in vitro effects of carbamazepine (CBZ) on some neutrophil functions in healthy volunteers and to investigate neutrophil function and pBZr expression in patients with epilepsia on CBZ monotherapy for at least 1 year. In vitro CBZ (42-168 microM) concentration-dependently inhibited chemotaxis induced by N-formyl-methionyl-leucyl-phenylalanine (FMLP) or lipopolysaccharide (LPS)-activated human serum. CBZ did not affect random migration, phagocytosis index, phagocytosis frequency, NBT reduction frequency, C. albicans lethality index and resting superoxide production. The pBZr antagonist PK 11195 (1 microM, per se ineffective) reversed the inhibitory effect of CBZ on chemotaxis induced by endotoxin-activated serum or FMLP. The pBZr agonist Ro 5-4864 (10-100 microM) mimicked the effect of CBZ on chemotaxis induced by endotoxin-activated serum or FMLP and had no effect on the other parameters. Neutrophils from epileptic patients on chronic CBZ monotherapy had impaired FMLP- and serum-induced chemotaxis and enhanced expression of pBZrs on neutrophils. These data strongly suggest an involvement of pBZrs in mediating the in vitro effects of CBZ on chemotaxis; furthermore, impairment of the same neutrophil function parameters and overexpression of pBZrs in patients are consistent with the hypothesis of an in vivo interaction of CBZ with pBZrs.

Decreased density of lymphocyte benzodiazepine receptors in drug-resistant epileptic patients

Peripheral benzodiazepine receptors (PBR) may have a role in epilepsy and in mediating antiepileptic drug effects. Since PBR in blood mononuclear cells may be acted on by anticonvulsant drugs, we investigated possible modifications of these receptors in newly diagnosed patients, before and after antiepileptic treatment and in drug-resistant epileptic patients. A significantly lower receptor density, with no difference in affinity, was observed in drug-resistant patients, compared to newly diagnosed patients and to normal age-related controls. We suggest the possible use of PBR as a peripheral marker of drug response.

Modifications of diazepam binding inhibitor and peripheral benzodiazepine receptors in the lymphocytes of epileptic patients

Recent experimental evidence has suggested that peripheral benzodiazepine receptors (PBR) may play a role in epilepsy and antiepileptic drug action. Since PBR are also present in circulating lymphocytes, and may interact with anticonvulsant drugs, this study was designed to look for possible modifications of these receptors and their endogenous ligand diazepam binding inhibitor (DBI) in the lymphocytes of epileptic patients treated with various drugs. PBR levels were 50% to 80% higher in patients treated with carbamazepine, phenobarbital and valproic acid than in controls and untreated epileptics. DBI levels were significantly increased in the lymphocytes of untreated patients, and showed only a slight further increase after anticonvulsant therapy. The possibility that PBR and DBI modifications in the lymphocytes of epileptic patients may be linked to the immunological alterations reported in these patients and/or may represent possible markers of neurochemical modifications in the central nervous system is discussed.