In vitro inhibition of cellular immune responses by benzodiazepines and PK 11195. Effects on mitogen- and alloantigen-driven lymphocyte proliferation and on IL-1, IL-2 synthesis and IL-2 receptor expression

Activation of GABA(A) receptors inhibits T cell proliferation

BACKGROUND

The major sites for fast synaptic inhibition in the central nervous system (CNS) are ion channels activated by γ-aminobutyric acid (GABA). These receptors are referred as GABA(A) receptors (GABA(A)R). Recent evidence indicates a role of GABA(A)R in modulating the immune response. This work aimed to discern the role of GABA and GABA(A)Rs in human and mouse T cell activity.

METHODS

Mouse splenocytes or human peripheral blood mononuclear cells (PBMCs) were activated with anti-CD3 antibodies and the proliferation of both CD8+ and CD4+ T cells assessed through flow cytometry. Subsequently, the effects on T cell proliferation of either GABA(A)R modulation by diazepam that is also capable of activating mitochondrial based translocator protein (TSPO), alprazolam and allopregnanolone or inhibition by bicucculine methiodide (BMI) and (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) were assessed.

RESULTS

Positive modulation of GABA(A)Rs either by benzodiazepines or the neurosteroid allopregnanolone inhibits both mouse and human T cell proliferation. GABAergic inhibition of T cell proliferation by benzodiazepines could be rescued by GABA(A)R blocking. Our data suggest that benzodiazepines influence T cell proliferation through both TSPO and GABA(A)Rs activation.

CONCLUSIONS

We conclude that activation of GABA(A)Rs provides immunosuppression by inhibiting T cell proliferation.

Early-stage 11C-Flumazenil PET predicts day-14 selective neuronal loss in a rodent model of transient focal cerebral ischemia

Predicting tissue outcome early after stroke is an important goal. MRI >3 h accurately predicts infarction but is insensitive to selective neuronal loss (SNL). Previous studies suggest that chronic-stage ¹¹C-flumazenil PET (FMZ-PET) is a validated marker of SNL in rats, while early-stage FMZ-PET may predict infarction. Whether early FMZ-PET also predicts SNL is unknown. Following 45-min distal MCA occlusion, adult rats underwent FMZ-PET at 1 h and 48 h post-reperfusion to map distribution volume (V_T), which reflects GABA-_A receptor binding. NeuN immunohistochemistry was performed at Day 14. In each rat, V_T and %NeuN loss were determined in 44 ROIs spanning the hemisphere. NeuN revealed isolated SNL and cortical infarction in five and one rats, respectively. In the SNL subgroup, V_T-1 h was mildly reduced and only weakly predicted SNL, while V_T-48 h was significantly increased and predicted SNL both individually (p < 0.01, Kendall) and across the group (p < 0.001), i.e. the higher the V_T, the stronger the SNL. Similar correlations were found in the rat with infarction. Our findings suggest GABA-_A receptors are still present on injured neurons at the 48 h timepoint, and the increased 48 h V_T observed here is consistent with earlier rat studies showing early GABA-_A receptor upregulation. That FMZ binding at 48 h was predictive of SNL may have clinical implications.

Mouse T cells express a neurotransmitter-receptor signature that is quantitatively modulated in a subset- and activation-dependent manner

Neurotransmitters are known to modulate the course of an immune response by targeting cells in both the innate and adaptive immune systems. Increasing evidence suggests that T cells, by expressing specific neurotransmitter receptors (NR) are directly regulated by them, leading to altered activation and skewed differentiation of the adaptive immune response. Given that gene expression in T cells changes in lineage- and activation-dependent fashion, it is expected that sensitivity to neurotransmitters may also vary along these lines. Here we generate an important resource for further analysis of this tier of immunoregulation, by identifying the distinct profile of NR transcripts that are expressed by peripheral T cells in mice, at different states of activation and differentiation. We find that only about 15% of the total annotated NR genes are transcribed in these T cells and most of them do not change in different subsets of T cells (CD8, CD4 - Naïve vs Memory vs Treg), or even when T cells migrate to different tissues. We suggest that the T cell-expressed NRs, found across all these subsets identifies a core, constitutive NR signature for the T cell lineage. In contrast, a very limited number (<2) of NRs were observed to mark each of the post-activation T cell states, suggesting that very specific neurotransmitter signals are available to modulate T cell responses in vivo in these subsets.

The ligands of translocator protein inhibit human Th1 responses and the rejection of murine skin allografts

The translocator protein (TSPO) ligands affected inflammatory and immune responses. However, the exact effects of TSPO ligands on Th1 responses in vitro and in vivo are still unclear. In the present study, we found that TSPO ligands, FGIN1-27 and Ro5-4864, suppressed the cytokine production in a dose-dependent manner by purified human CD4⁺ T-cells from peripheral blood mononuclear cells (PBMCs) after stimulation. TSPO ligands inhibited the production of interferon γ (IFN-γ) by memory CD4⁺ T-cells and the differentiation of naïve CD4⁺ T-cells into Th1 cells via suppressing the activity of the corresponding transcription factors as indicated by reduced expression of T-bet and down-regulation of STAT1, STAT4 and STAT5 phosphorylation. TSPO ligands suppressed cell proliferation and activation of CD4⁺ T-cells by the inhibition of TCR signal transduction including membrane proteins: Zap, Lck, Src; cytoplasm proteins: Plcγ1, Slp-76, ERK, JNK and the nucleoproteins: c-Jun and c-Fos. In addition, FGIN1-27 inhibited mixed lymphocyte reactions by human or murine cells. After the transplantation of allogeneic murine skin, injection of FGIN1-27 into mice prevented graft rejection by inhibition of cell infiltration and IFN-γ production. Taken together, our data suggest that TSPO ligands inhibit Th1 cell responses and might be novel therapeutic medicine for the treatment of autoimmune diseases and prevention of transplant rejection.

Delayed developmental immunotoxicity of prenatal benzodiazepines

Treatment of pregnant rats with low doses of classical benzodiazepines (BDZ, e.g. 1.25 mg diazepam/kg body weight) or a peripheral type BDZ receptor (PBR) agonist between gestational days 14 and 20 has been shown to result in a long-lasting depression of cellular and humoral immune responses in the offspring. Considerable alterations in mitogen-stimulated cytokine production in rats exposed to diazepam prenatally have now been observed: TNF-alpha liberation by splenocytes of diazepam-exposed rats was reduced at 2 wk of age and increased above control values at 8 wk, and interleukin (IL)-6 was depressed in the offspring at 2 and 8 wk of age. IL-1 was diminished during post-weaning and adult periods in male offspring but only in adult life in female offspring. In contrast, T-cell derived IL-2 was decreased during the postnatal period and normalized in adulthood. Prostaglandin E(2) (PGE(2)), which is known to down-regulate tumour necrosis factor-alpha (TNF-alpha) was increased and interferon-gamma (IFN-gamma), which stimulates TNF-alpha release, was depressed in 2-wk-old offspring that had been treated prenatally. Release of PGE(2) and IFN-gamma was still altered in young adulthood. While the initial action on the foetal immune system remains unknown, an interaction of the drugs with the PBR is suggested by the effectiveness of the PBR agonist and by altered characteristics of PBR (i.e. a decreased B(max) of [(3)H]PK 11195 binding to macrophage membranes of 8-wk-old offspring and an increased Kd of spleen cell membranes of 2-wk-old offspring).

Effects of different doses and schedules of diazepam treatment on lymphocyte parameters in rats

Benzodiazepines (BZD) are widely used for the treatment of anxiety. They enhance GABA-ergic neurotransmission through the binding on specific BDZ recognition sites, within the GABA(A) receptor-ion channel complex. However, recent studies showed that BZD also act on peripheral benzodiazepine receptor sites (PBR) or translocator protein 18 kDa (TSPO). Evidence for a direct immunomodulatory action for BZD emerged from studies that demonstrated the presence of TSPO on immune/inflammatory cells. The present study was designed to analyze the effects of diazepam on rat lymphocyte parameters, specifically on phenotype, cell proliferation and cell death. The effects of both acute and long-term (21 days) diazepam (1 and 10 mg/kg/day) administrations were evaluated. Results showed that diazepam (1 mg/kg) treatment did not change the immune parameters analyzed. However, both diazepam (10 mg/kg) acute and long-term treatments decreased the number of apoptotic cells; they also increased the percentage of T cytotoxic cells; decreased the percentage of B cells and increased the corticosterone serum levels. The induction of functional tolerance was suggested for the highest dose of diazepam (10 mg/kg), but not for the smaller dose (1 mg/kg) used, at least for diazepam effects on corticosterone serum levels. Diazepam effects were discussed as being related to the number of TSPO sites present on immune cells and/or to the increased levels of serum corticosterone observed after the treatments used.

Reduction of acute inflammation in rats by diazepam: role of peripheral benzodiazepine receptors and corticosterone

Carrageenin causes a reproducible inflammatory reaction and remains the standard irritant for examining acute inflammation and anti-inflammatory drugs. High doses of diazepam (10.0-20.0 mg/Kg) were shown to reduce the volume of acute inflammatory paw edema in rats as a response to carrageenin administration. The present experiment was undertaken to investigate the possible roles of peripheral-type benzodiazepine receptors (PBRs) and corticosterone on the anti-inflammatory effects of diazepam. Five experiments were conducted to assess the effects of a single dose (10.0 mg/Kg) of diazepam on carrageenin-induced paw edema (CIPE), pleurisy and increase in vascular permeability in rats. Results showed that: 1. diazepam or Ro5-4864 (a PBR agonist) treatment reduced CIPE values; 2. prior treatment with PK11195 (a non-benzodiazepine PBR antagonist) suppressed the effects of either diazepam or Ro5-4864 on CIPE; 3. diazepam reduced the volume of the pleural exudate in carrageenin-injected rats, as well as its leukocyte count; 4. diazepam treatment reduced the magnitude of the increase in vascular permeability caused by carrageenin; 5. adrenalectomy suppressed the effects of diazepam on CIPE; and 6. diazepam treatment increased the serum concentration of corticosterone. These results suggest a relevant role of PBR and corticosterone on diazepam-induced changes in inflammation. They are discussed in the light of a possible activation of mitochondrial PBRs within the adrenal gland cells by diazepam, thereby increasing the serum levels of corticosterone and thus reducing CIPE.

Effects of nefazodone on the immune system of mice

Mice exposed to a chronic auditory stressor and treated with nefazodone (10 mg/kg/day s.c.), showed a reduction in stress-induced suppression of thymus and spleen cellularity, and in peripheral T-Iymphocyte population. The in vitro blastogenic response of spleen lymphoid cells to mitogen concanavalin A, the in vitro and in vivo activity of phagocytosis, both measured using the zymosan and carbon clearance tests, respectively, were also assessed and nefazodone was found to partially reverse the inhibitory effect of stress on those parameters. Nefazodone did not significantly affect those parameters in unstressed mice. In conclusion, this report provides evidence on the immunoprotective effects of this novel antidepressant drug against the adverse effects of stress in mice.

The peripheral benzodiazepine receptor ligand PK 11195 inhibits arthritis in the MRL-lpr mouse model

OBJECTIVE

Mice of the MRL-lpr strain develop a severe autoimmune arthritic condition when primed with complete Freund's adjuvant. The pathology is similar to that seen in human rheumatoid arthritis. We investigated whether PK 11195, a powerful ligand for peripheral benzodiazepine receptors, would have preventative or therapeutic effects in this model.

METHODS

MRL-lpr mice were primed with complete Freund's adjuvant at 13-14 weeks of age. Daily PK 11195 injections were started on the same day as priming to test for preventative effects. Daily PK 11195 injections were started 10 days after priming to test therapeutic effects.

RESULTS

PK 11195 showed both preventative and therapeutic effects. At 1 mg/kg/day, it inhibited disease onset. At 3 mg/kg/day, it inhibited established disease progression.

CONCLUSION

The evidence suggests that PK 11195 may be the prototype of a new class of anti-inflammatory agents.

Effects of psychotropic drugs on cell proliferation and differentiation

Some of the psychotropic agents widely used for the amelioration of anxiety, depression, and psychosis also show an effect at the cellular proliferation level. Surprisingly little research, however, has been directed to the antitumoral potential of these drugs, alone or in combination with established cancer treatments. Our review of the literature to date has yielded some promising early findings. Ligands active at the benzodiazepine (BZ) receptors have been studied the most extensively and were found to have differential, concentration-dependent effects on the growth and proliferation of both normal and cancer cells. Of the phenothiazines tested, chlorpromazine (CPZ) and perphenazine (PPZ) had the most potent cytotoxic action on fibroblasts and glioma cells. Antiproliferative effects also were noted by these and other agents in leukemic and breast cancer cell lines. Additional psychotropic drugs studied include the atypical antipsychotics, antidepressants, and mood stabilizers, especially lithium. Most of the reported activities were observed in in vitro studies and were achieved at high pharmacological concentrations. Further in vivo studies in well-designed animal models are warranted to determine whether these well-tolerated, relatively inexpensive, and widely available drugs or their derivatives may be added in the future to the armamentarium of cancer pharmacotherapy.

Developmental, neuro and immunotoxic effects of perinatal diazepam treatment in rats

In utero exposure of rats to low dosages of diazepam (1.0-2.0 mg/kg) has been found to result in depression of the cellular and humoral immune responses during adulthood. Behavioral dysfunctions were also reported in infants from mothers with high benzodiazepine (BDZ) intake during pregnancy. The present experiment was undertaken to reconsider the potential action of diazepam during ontogeny in order to obtain further information about developmental processes using a refined methodology. Time-pregnant rats were treated subcutaneously with diazepam (2.0 mg/kg/day,: group E1) or with diazepam vehicle (group C1) from gestational day 14 to 20. Other dams (group E2) received the same BDZ dose from the 1st to the 21st day of lactation (weaning) or were not treated, remaining undisturbed in their home cages (group C2). The following results were obtained for animals perinatally treated with diazepam compared to groups C1 and C2: 1--increased time for testis descent and decreased time for vaginal opening (group E2); 2--no changes in the dates for ear end eye opening, or incisor tooth eruption (groups E1 and E2); 3--increased locomotor activity in the open-field (group E2) and/or in the plus maze (groups E1 and E2); 4--decreased levels of anxiety measured in the plus maze (groups E1 and E2); 5--decreased macrophage spreading and phagocytosis (groups E1 and E2). These results, which occurred in the absence of overt signs of maternal or fetal toxicity, demonstrate developmental, neuro- and immunotoxic effects of perinatal diazepam treatment in rats.

GABA(A) receptors mediate inhibition of T cell responses

We describe the presence of functional GABA(A) receptors on T cells. GABA inhibited anti-CD3 and antigen-specific T cell proliferation in vitro in a dose-dependent manner that was 1) mimicked by the GABA(A) receptor agonist muscimol (but not the GABA(B) receptor agonist baclofen), 2) blocked by GABA(A) receptor antagonists and a GABA(A) receptor Cl- channel blocker (picrotoxin) and 3) enhanced by pentobarbital. These data suggest that GABA(A) receptors mediate this immune inhibition and that these receptors can be modulated in a similar fashion to their neuronal counterparts. Finally, GABA inhibited DTH responses in vivo. Thus, pharmacological modulation of GABA(A) receptors may provide new approaches to modulate T cell responses in inflammation and autoimmune disease.

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).

Stress, neuropsychiatric disorders and immunological effects exerted by benzodiazepines

Psychoneuroimmunology is a growing scientific field which deals with the mutual interplay between nervous and immune systems. In this framework, many data have demonstrated that cytokines (CKs) derived from the periphery are able to cross the blood brain barrier and act upon the central nervous system (CNS) [e.g., the hypothalamic-pituitary-adrenal axis (HPAA)], thus regulating several physiological functions (thermoregulation, sleep, appetite) or damaging the nervous tissue, when released in exaggerated amounts. On the other hand, nervous cells, such as astrocytes and microglial cells also generate proinflammatory CKs which may be detrimental for the CNS. The neuromodulating CK network can be triggered by microorganisms and/or their products (i.e. bacterial endotoxins), but also stressful life events may activate the HPAA, thus affecting the immune system function. This review will place emphasis on some clinical conditions, such as phobia and migraine without aura (MWA), characterized by anxiety disorders. Patients affected by these neuropsychiatric alterations exhibit multiple functional deficits of phagocytes and T lymphocytes which allow penetration of various pathogens into the host. This is also supported by the detection of circulating bacterial endotoxins and the evidence of both spontaneous and induced exaggerated release of proinflammatory CKs in phobic and MWA patients. The possible iatrogenic effects of benzodiazepines (BDZ) on the immune system have been evaluated by in vitro and in vivo studies. In this respect, it emerges that diazepam exerts an inhibitory function on the immune system, while alprazolam behaves as an immunoenhancer. The presence of central and/or peripheral BDZ receptors on immune cells seems to be the key mechanism responsible for the immunomodulation exerted by these drugs.

Benzodiazepines, anxiety and immunity

Experimental and clinical studies suggest that the central and peripheral benzodiazepine (BDZ) receptors together with their ligands form the molecular basis of a novel regulatory network that contributes to the effects of anxiety on immune status. The peripheral-type receptors located on phagocytes and glial cells appear to play a key role in mediating the effects of endogenous and exogenous BDZs both on the defence mechanisms that protect the host against pathogens and on inflammatory reactions that take place within the periphery and the brain in response to injury. In addition, the central-type receptor, which forms part of the gamma-aminobutyric acidA receptor complex, may contribute to the regulation of T-cell function by modulating the activity of the hypothalamo-pituitary-adrenocortical axis or the sympathoadrenal system or both, which, in turn, exert a significant effect on immune function. Thus, anxiogenic BDZs in general suppress the immune response, whereas anxiolytic BDZs may protect the individual from stress-induced immunosuppression.

Peripheral-type benzodiazepine receptor ligands modulate human natural killer cell activity

Following our earlier work, we evaluated the in vitro effect of ligands active at the peripheral-type benzodiazepine receptors on human natural killer cell activity. Peripheral blood mononuclear cells were incubated with benzodiazepine receptor ligands. After 4 h we observed a nonspecific inhibition of natural killer cell activity induced by both peripheral (Ro5-4864 and PK 11195) and central (clonazepam) benzodiazepine receptor ligands; after 24 h, the suppressive activity was specific to peripheral and mixed (diazepam) ligands, and the central-type ligand had no effect. This significant, specific suppression of NK cell activity was completely reversed by the addition of human recombinant interleukin-2 or human leukocyte interferon. Our research provides additional information on the immunomodulatory effects of peripheral-type benzodiazepine ligands. Further studies are needed to clarify the underlying mechanism of natural killer cell inhibition and to determine the clinical implications of these findings.

Impaired host resistance to Trichinella spiralis as a consequence of prenatal treatment of rats with diazepam

In utero exposure of Long Evans rats to low dosages of diazepam has previously been found to result in depression of cellular and humoral immune responses until adulthood, with marked changes in cytokine release by splenocytes and splenic macrophages. In order to assess the significance of these alterations in immune cells with regard to host resistance, we investigated the resistance of adult offspring towards Trichinella spiralis. Time-pregnant rats were treated with diazepam (1.25 mg/kg/day) or vehicle from gestational day 14 to 20. Male offspring were infected with T. spiralis at 2 months of age. This infection model tests the participation of T- and B-cell populations and of macrophages. Prenatally diazepam-exposed animals exhibited an impaired defence towards T. spiralis. The number of muscle larvae was increased as determined in digested carcasses and by morphometric analysis of the tongue. Moreover, antibody titers were altered, i.e., IgG was decreased and IgA was elevated in the prenatally diazepam-exposed group. These results demonstrate an impaired defense towards T. spiralis in adult rats after prenatal exposure to diazepam.