Enhancement of benzodiazepine binding sites following chronic treatment with flumazenil

Continuous Infusion of Flumazenil in the Management of Benzodiazepines Detoxification

An effective approach in the treatment of benzodiazepine (BZD) overdosing and detoxification is flumazenil (FLU). Studies in chronic users who discontinued BZD in a clinical setting suggested that multiple slow bolus infusions of FLU reduce BZD withdrawal symptoms. The aim of this study was to confirm FLU efficacy for reducing BZD withdrawal syndrome by means of continuous elastomeric infusion, correlated to drugs plasma level and patients' compliance. Methods: Seven-day FLU 1 mg/day subcutaneously injected through an elastomeric pump and BZDs lormetazepam, clonazepam, and lorazepam were assessed by HPLC-MS/MS in serum of patients before and after 4 and 7 days of FLU continuous infusion treatment. Changes in withdrawal severity were assessed by using the BZD Withdrawal Scale (BWS). Results: Fourteen patients (mean age ± SD 42.5 ± 8.0 years, 5 male and 9 female), admitted to the hospital for high-dose BZD detoxification, were enrolled in the study. Serum FLU concentrations significantly decreased from 0.54 ± 0.33 ng/ml (mean ± SD) after 4 days of treatment to 0.1 ± 0.2 ng/ml at the end of infusion. Lormetazepam concentrations were 502.5 ± 610.0 ng/ml at hospital admission, 26.2 ± 26.8 ng/ml after 4 days, and 0 at the end of treatment. BWS values decreased during FLU treatment temporal period. FLU was well-tolerated by patients. Conclusions: Elastomeric FLU infusion for BZD detoxification is a feasible administration device to maintain adequate, constant, and tolerated FLU concentrations for reducing BZD withdrawal symptoms.

Anticonvulsive effects of protodioscin against pilocarpine-induced epilepsy

Epilepsy is associated with increased morbidity and mortality together and places a large financial burden on individuals and society. To evaluate the anticonvulsant action of protodioscin (PDSN) in experiments with animals with pilocarpine-induced convulsions. We assessed the activity of PDSN in pilocarpine induced seizures in combination with different agents which are acting via diverse receptors, such as atropine, memantine, nimodipine, diazepam, and flumazenil, to determine the exact receptors responsible for the action of PDSN. Furthermore, the level of antioxidant markers was investigated in the cerebellum and cerebral cortex in mice to define the antioxidant action of PDSN. The effects of PDSN on proapoptotic markers (i.e., Bcl-2, Bax, and caspase-3) was investigated via western blot analysis. PDSN significantly enhanced latency to the first convulsion and survival compared to the group treated with pilocarpine alone. Moreover, PDSN improved animal survival, and subjects experiencing no convulsions. Striatal glutamate and aspartate levels were not modified, and gamma amino butyric acid (GABA) levels increased, as a result of treatment with PDSN. The results suggest that the anticonvulsive action of PDSN is dependent on inhibitory amino acids. PDSN treatment also significantly decreased nitrite levels in the blood and brain cortex compared to the normal control. In the western blot analysis, PDSN exerted its neuroprotective effect via the upregulation of Bcl-2 and downregulation of Bax and caspase-3. The results of this study suggest that PDSN exerts neuroprotective effects via multiple mechanisms.

Glucose hypermetabolism in the thalamus of patients with drug-induced blepharospasm

We examined the difference in cerebral function alterations between drug-induced blepharospasm patients and essential blepharospasm (EB) patients by using positron emission tomography with (18)F-fluorodeoxyglucose. Cerebral glucose metabolism was examined in 21 patients with drug-induced blepharospasm (5 men and 16 women; mean age, 53.1 [range, 29-78] years), 21 essential EB patients (5 men and 16 women; mean age, 53.0 [range, 33-72] years) and 24 healthy subjects (6 men and 18 women; mean age, 57.9 [range, 22-78] years) with long-term history of benzodiazepines use (drug healthy subjects). Drug-induced blepharospasm patients developed symptoms while taking benzodiazepines or thienodiazepines. Sixty-three normal volunteers (15 men and 48 women; mean age, 53.6 [range, 20-70] years) were examined as controls. Differences between the patient groups and control group were examined by statistical parametric mapping. Additionally, we defined regions of interests on both sides of the thalamus, caudate nucleus, anterior putamen, posterior putamen and primary somatosensory area. The differences between groups were tested using two-sample t-tests with Bonferroni correction for multiple comparisons. Cerebral glucose hypermetabolism on both side of the thalamus was detected in drug-induced blepharospasm, EB patients and drug healthy subjects by statistical parametric mapping. In the analysis of regions of interest, glucose metabolism in both sides of the thalamus in the drug-induced blepharospasm group was significantly lower than that in the EB group. Moreover, we observed glucose hypermetabolism in the anterior and posterior putamen bilaterally in EB group but not in drug-induced blepharospasm group and drug healthy subjects. Long-term regimens of benzodiazepines or thienodiazepines may cause down-regulation of benzodiazepine receptors in the brain. We suggest that the functional brain alteration in drug-induced blepharospasm patients is similar to that in EB patients, and that alteration of the GABAergic system might be related to the pathology of both blepharospasm types.

Differential effects of short- and long-term zolpidem treatment on recombinant α1β2γ2s subtype of GABA(A) receptors in vitro

AIM

Zolpidem is a non-benzodiazepine agonist at benzodiazepine binding site in GABA(A) receptors, which is increasingly prescribed. Recent studies suggest that prolonged zolpidem treatment induces tolerance. The aim of this study was to explore the adaptive changes in GABA(A) receptors following short and long-term exposure to zolpidem in vitro.

METHODS

Human embryonic kidney (HEK) 293 cells stably expressing recombinant α1β2γ2s GABA(A) receptors were exposed to zolpidem (1 and 10 μmol/L) for short-term (2 h daily for 1, 2, or 3 consecutive days) or long-term (continuously for 48 h). Radioligand binding studies were used to determine the parameters of [(3)H]flunitrazepam binding sites.

RESULTS

A single (2 h) or repeated (2 h daily for 2 or 3 d) short-term exposure to zolpidem affected neither the maximum number of [(3)H]flunitrazepam binding sites nor the affinity. In both control and short-term zolpidem treated groups, addition of GABA (1 nmol/L-1 mmol/L) enhanced [(3)H]flunitrazepam binding in a concentration-dependent manner. The maximum enhancement of [(3)H]flunitrazepam binding in short-term zolpidem treated group was not significantly different from that in the control group. In contrast, long-term exposure to zolpidem resulted in significantly increase in the maximum number of [(3)H]flunitrazepam binding sites without changing the affinity. Furthermore, long-term exposure to zolpidem significantly decreased the ability of GABA to stimulate [(3)H]flunitrazepam binding.

CONCLUSION

The results suggest that continuous, but not intermittent and short-term, zolpidem-exposure is able to induce adaptive changes in GABA(A) receptors that could be related to the development of tolerance and dependence.

The effects of zolpidem treatment on GABA(A) receptors in cultured cerebellar granule cells: changes in functional coupling

AIMS

Hypnotic zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) action, with preferential although not exclusive binding for α1 subunit-containing GABA(A) receptors. The pharmacological profile of this drug is different from that of classical benzodiazepines, although it acts through benzodiazepine binding sites at GABA(A) receptors. The aim of this study was to further explore the molecular mechanisms of GABA(A) receptor induction by zolpidem.

MAIN METHODS

In the present study, we explored the effects of two-day zolpidem (10 μM) treatment on GABA(A) receptors on the membranes of rat cerebellar granule cells (CGCs) using [(3)H]flunitrazepam binding and semi-quantitative PCR analysis.

KEY FINDINGS

Two-day zolpidem treatment of CGCs did not significantly affect the maximum number (B(max)) of [(3)H]flunitrazepam binding sites or the expression of α1 subunit mRNA. However, as shown by decreased GABA [(3)H]flunitrazepam binding, two-day exposure of CGCs to zolpidem caused functional uncoupling of GABA and benzodiazepine binding sites at GABA(A) receptor complexes.

SIGNIFICANCE

If functional uncoupling of GABA and benzodiazepine binding sites at GABA(A) receptors is the mechanism responsible for the development of tolerance following long-term administration of classical benzodiazepines, chronic zolpidem treatment may induce tolerance.

Differential effects of diazepam treatment and withdrawal on recombinant GABAA receptor expression and functional coupling

Prolonged exposure to benzodiazepines, drugs known to produce tolerance and dependence and also to be abused, leads to adaptive changes in GABA(A) receptors. To further explore the mechanisms responsible for these phenomena, we studied the effects of prolonged diazepam treatment on the recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors, stably expressed in human embryonic kidney (HEK) 293 cells. The results demonstrating that long-term (48 and 72 h) exposure of cells to a high concentration of diazepam (50 microM) enhanced the maximum number (B(max)) of [(3)H]flunitrazepam, [(3)H]muscimol and [(3)H]t-butylbicycloorthobenzoate ([(3)H]TBOB) binding sites, without changing their affinity (K(d)), suggested the up-regulation of GABA(A) receptors. As demonstrated by cell counting and WST-1 proliferation assay, the observed increase in receptor expression was not a consequence of stimulated growth of cells exposed to diazepam. Semi-quantitative RT-PCR and Western blot analysis, showing elevated levels of alpha(1) subunit mRNA as well as beta(2) and gamma(2) subunit proteins, respectively, suggested that prolonged high dose diazepam treatment induced de novo receptor synthesis by acting at both transcriptional and translational levels. The finding that the number of GABA(A) receptor binding sites returned to control value 24 h following diazepam withdrawal, makes this process less likely to account for the development of benzodiazepine tolerance and dependence. On the other hand, the results demonstrating that observed functional uncoupling between GABA and benzodiazepine binding sites persisted after the termination of diazepam treatment supported the hypothesis of its possible role in these phenomena.

The role of transcriptional and translational mechanisms in flumazenil-induced up-regulation of recombinant GABA(A) receptors

The aim of this study was to further elucidate the mechanisms involved in adaptive changes of GABA(A) receptors following prolonged exposure to flumazenil, the antagonist of benzodiazepine binding sites on GABA(A) receptors. The effects of prolonged flumazenil treatment were studied on recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors stably expressed in human embryonic kidney (HEK 293) cells. Using radioligand binding experiments we found enhancement in the maximum number of [(3)H]muscimol labeled binding sites in different preparations of HEK 293 cells. The parallel increase of [(3)H]flunitrazepam binding sites in the membranes was reduced in the presence of actinomycin D and cycloheximide, inhibitors of RNA and protein synthesis, respectively. Chronic flumazenil also raised the steady-state level of mRNA encoding alpha(1) receptor subunit. The results suggest that the up-regulation of GABA(A) receptors, observed after prolonged flumazenil treatment is at least partly due to increased de novo synthesis of receptor proteins at both transcriptional and translational level.

Allosteric uncoupling and up-regulation of benzodiazepine and GABA recognition sites following chronic diazepam treatment of HEK 293 cells stably transfected with alpha1beta2gamma2S subunits of GABA (A) receptors

Benzodiazepines are drugs known to produce tolerance and dependence and also to be abused and co-abused. The aim of this study was to further explore the mechanisms that underlie adaptive changes in GABA(A) receptors following prolonged exposure to these drugs. Human embryonic kidney (HEK 293) cells stably expressing recombinant alpha1beta2gamma2s GABA(A) receptors were exposed for 72 h to a high concentration of diazepam (50 microM) in the absence or presence of other drugs. Radioligand binding studies were used to determine the parameters of [(3)H]flunitrazepam and [(3)H]muscimol binding sites and allosteric interactions between these sites. Prolonged treatment with diazepam increased the maximum number (B (max)) of [(3)H]flunitrazepam and [(3)H]muscimol binding sites in the membranes, and of [(3)H]muscimol binding sites on the surface of HEK 293 cells. There was no change in the affinity (K (d)) of binding sites. The diazepam-induced increase in the B (max) value of [(3)H]flunitrazepam binding sites was reduced by two GABA(A) receptor antagonists, gabazine (1 and 10 microM) and picrotoxin (100 microM). In addition, it was reduced by cycloheximide (5 microg/ml), a protein synthesis inhibitor, and actinomycin D (7.5 microg/ml), an RNA synthesis inhibitor. Flumazenil (5 microM), the antagonist of benzodiazepine binding sites, also up-regulated [(3)H]flunitrazepam recognition sites. Simultaneous treatment with diazepam and flumazenil failed to produce an additive up-regulation. GABA (1 nM - 1 mM)-induced potentiation of [(3)H]flunitrazepam binding to membranes obtained from diazepam (50 microM)-pretreated cells was markedly reduced, suggesting functional uncoupling between GABA and benzodiazepine binding sites. The results suggest that diazepam up-regulated benzodiazepine binding sites on stably expressed GABA(A) receptors by stimulating their synthesis at both the transcriptional and translational levels. A comparable increase of [(3)H]muscimol binding sites expressed on the surface of intact HEK 293 cells suggests that internalisation of surface receptors presumably can not explain the uncoupling.