Benzodiazepines have high-affinity binding sites and induce melanogenesis in B16/C3 melanoma cells

Peripheral benzodiazepine receptor TSPO needs to be reconsidered before using as a drug target for a pigmentary disorder

The peripheral benzodiazepine receptor (TSPO/PBR) is highly conserved among different species but with perplexing biochemical functions. Multiple ligands of TSPO show commendable regulatory activities in lots of biological functions, such as neuro-protection, cholesterol transport, and so on. These researches support that TSPO may be a potential target for disease treatment and drug development. Previous studies have shown that its ligands benzodiazepines show a satisfactory effect on melanogenic promotion. However, the potential application of TSPO in drug development for pigmentary disorder needs further investigation. In this study, we confirmed the melanogenesis induction of TSPO ligand, Ro5-4864 in mouse melanoma cell lines, human skin tissue, and zebrafish embryos by inducing melanin synthesis and melanosome transport. Molecular genetics and pharmacological studies showed that TSPO deficiency did not affect melanin production in B16F10 cells and zebrafish embryos, nor did it affect the melanin promotion effect of Ro5-4864. Whether or not TSPO exists, the expression of lots of melanogenesis-related proteins, such as TYR, TRP-1, DCT, Mlph, and Rab27 was upregulated with the Ro5-4864 administration. These results indicated that Ro5-4864 induces melanogenesis in a TSPO-independent manner, which is inconsistent with previous research. This research is a reminder that we need to be very careful during target validation in drug development.

Role of Amine Neurotransmitters and Their Receptors in Skin Pigmentation: Therapeutic Implication

Skin pigmentation can occur due to increased melanin, including melanocyte proliferation, melanin biosynthesis, or melanocyte migration. There are many factors that influence the melanin production process, but the role of neurotransmitters in this process is still unclear. We found that histamine and serotonin influence the different stages of melanogenesis and melanogenesis, which increase melanogenesis. Since then, several related papers have been published, and from these papers, it has been recognised that the role of neurotransmitters in skin-pigment-related diseases needs to be summarised. By introducing the role of neurotransmitters in the regulation of various pigment disorders, including vitiligo and melasma, through this review, many researchers can be expected to try to apply neurotransmitter-related agonists and antagonists as treatments for skin pigment disorders.

Diazepam enhances melanogenesis, melanocyte dendricity and melanosome transport via the PBR/cAMP/PKA pathway

Diazepam is a medicament of the benzodiazepine family and it typically produces a sedative effect. Researchers have revealed that diazepam can induce melanogenesis and produce dendrite-like structures in B16 melanoma cells. However, the associated mechanisms of melanogenesis and phenotypic alterations have mostly remained unknown. In this study, we determined the effects of diazepam on melanogenesis, cellular phenotypic alterations, the location of melanosomes and the expression of relevant proteins in melanocytes using Masson-Fontana ammoniacal silver staining, scanning electron microscopy, immunocytochemistry and western blot analysis. Our results collectively indicated that diazepam had a pivotal role in melanocytes by enhancing melanin synthesis, melanocyte dendricity, melanosome trafficking, and capture at the dendrite tips. These functions might be attributed to the fact that diazepam activated the peripheral benzodiazepine receptor (PBR). This increased intracellular levels of cAMP, which stimulated the phosphorylation of cAMP response element-binding (CREB). As a result, this increased the tyrosinase, microphthalmia-associated transcription factor (MITF), Rab27a, Myosin Va, Rab17 and Cdc42 expression. This caused melanogenesis and melanosome transport. Therefore, our findings may provide a potential strategy for treating anti-hypopigmentation disorders.

Biodegradable Kojic Acid-Based Polymers: Controlled Delivery of Bioactives for Melanogenesis Inhibition

Kojic acid (KA) is a naturally occurring fungal metabolite that is utilized as a skin-lightener and antibrowning agent owing to its potent tyrosinase inhibition activity. While efficacious, KA's inclination to undergo pH-mediated, thermal-, and photodegradation reduces its efficacy, necessitating stabilizing vehicles. To minimize degradation, poly(carbonate-esters) and polyesters comprised of KA and natural diacids were prepared via solution polymerization methods. In vitro hydrolytic degradation analyses revealed KA release was drastically influenced by polymer backbone composition (e.g., poly(carbonate-ester) vs polyester), linker molecule (aliphatic vs heteroatom-containing), and release conditions (physiological vs skin). Tyrosinase inhibition assays demonstrated that aliphatic KA dienols, the major degradation product under skin conditions, were more potent then KA itself. All dienols were found to be less toxic than KA at all tested concentrations. Additionally, the most lipophilic dienols were statistically more effective than KA at inhibiting melanin biosynthesis in cells. These KA-based polymer systems deliver KA analogues with improved efficacy and cytocompatible profiles, making them ideal candidates for sustained topical treatments in both medical and personal care products.

Identification, characterization and potent antitumor activity of ECO-4601, a novel peripheral benzodiazepine receptor ligand

PURPOSE

ECO-4601 is a structurally novel farnesylated dibenzodiazepinone discovered through DECIPHER technology, Thallion's proprietary drug discovery platform. The compound was shown to have a broad cytotoxic activity in the low micromolar range when tested in the NCI 60 cell line panel. In the work presented here, ECO-4601 was further evaluated against brain tumor cell lines. Preliminary mechanistic studies as well as in vivo antitumor evaluation were performed.

METHODS

Since ECO-4601 has a benzodiazepinone moiety, we first investigated if it binds the central and/or peripheral benzodiazepine receptors. ECO-4601 was tested in radioligand binding assays on benzodiazepine receptors obtained from rat hearts. The ability of ECO-4601 to inhibit the growth of CNS cancers was evaluated on a panel of mouse, rat and human glioma cell lines using a standard MTT assay. Antitumor efficacy studies were performed on gliomas (rat and human), human breast and human prostate mouse tumor xenografts. Antitumor activity and pharmacokinetic analysis of ECO-4601 was evaluated following intravenous (i.v.), subcutaneous (s.c.), and intraperitoneal (i.p.) bolus administrations.

RESULTS

ECO-4601 was shown to bind the peripheral but not the central benzodiazepine receptor and inhibited the growth of CNS tumor cell lines. Bolus s.c. and i.p. administration gave rise to low but sustained drug exposure, and resulted in moderate to significant antitumor activity at doses that were well tolerated. In a rat glioma (C6) xenograft model, ECO-4601 produced up to 70% tumor growth inhibition (TGI) while in a human glioma (U-87MG) xenograft, TGI was 34%. Antitumor activity was highly significant in both human hormone-independent breast (MDA-MB-231) and prostate (PC-3) xenografts, resulting in TGI of 72 and 100%, respectively. On the other hand, i.v. dosing was followed by rapid elimination of the drug and was ineffective.

CONCLUSIONS

Antitumor efficacy of ECO-4601 appears to be associated with the exposure parameter AUC and/or sustained drug levels rather than C (max). These in vivo data constitute a rationale for clinical studies testing prolonged continuous administration of ECO-4601.

Increased expression of peripheral benzodiazepine receptor (PBR) in dimethylbenz[a]anthracene-induced mammary tumors in rats

Expression of peripheral benzodiazepine receptors (PBR) has been found in every tissue examined; however, it is most abundant in steroid-producing tissues. Although the primary function of PBR is the regulation of steroidogenesis, its existence in nonsteroidogenic tissues as well as in other cellular compartments including the nucleus suggests that there may be other roles for PBR. Our laboratory reported earlier a significant increase of PBR density in the nucleus of DMBA-induced malignant submandibular glands of rats, suggesting a role of PBR in nuclear events of peripheral tissues. Since then numerous studies have demonstrated the abundance of PBR in tumors. Numerous studies implicate a role for cholesterol in the mechanisms underlying cell proliferation and cancer progression. Based on studies with a battery of human breast cancer cell lines and several human tissue biopsies, Hardwick et al. suggested that PBR expression, nuclear localization, and PBR-mediated cholesterol transport into the nucleus are involved in human breast cancer cell proliferation and aggressive phenotype expression. The purpose of the present study is to confirm this hypothesis by developing an animal breast cancer model and correlating the above events with the breast cancer. Weanling rats were maintained on a diet containing animal protein (casein) for 30 days and then a single dose of DMBA in sesame oil (80 mg/kg) was administered by gavage to the animals. Control animals received the vehicle only. After 122 days of DMBA administration, the animals were sacrificed. All tumors were detected by palpation. B(max) of PBRs was 52.6% and 128.4% higher in the non-aggressive and aggressive cancer tissues, respectively, than that in normal tissues. Cholesterol uptake into isolated nuclei was found to be higher in both non-aggressive and aggressive tumor breast tissue than that in control tissue. There was also corresponding increase in B(max) of PBRs in the nucleus of cancer tissues. Furthermore, the nuclear nucleoside triphosphatase (NTPase) activity was found to be higher in aggressive tumor tissues than that in non-aggressive tumor tissues. In conclusion, these data suggest that PBR ligand binding, and PBR-mediated cholesterol transport into the nucleus may be involved in the development of mammary gland adenocarcinoma, thus participating in the advancement of the disease.

Modulation of cholinephosphotransferase activity in breast cancer cell lines by Ro5-4864, a peripheral benzodiazepine receptor agonist

Changes in phospholipid and fatty acid profile are hallmarks of cancer progression. Increase in peripheral benzodiazepine receptor expression has been implicated in breast cancer. The benzodiazepine, Ro5-4864, increases cell proliferation in some breast cancer cell lines. Biosynthesis of phosphatidylcholine (PC) has been identified as a marker for cells proliferating at high rates. Cholinephosphotransferase (CPT) is the terminal enzyme for the de novo biosynthesis of PC. We have addressed here whether Ro5-4864 facilitates some cancer causing mechanisms in breast cancer. We report that cell proliferation increases exponentially in aggressive breast cancer cell lines 11-9-1-4 and BT-549 when treated with nanomolar concentrations of Ro5-4864. This increase is seen within 24 h of treatment, consistent with the cell doubling time in these cells. Ro5-4864 also upregulates c-fos expression in breast cancer cell lines 11-9-1-4 and BT-549, while expression in non-tumorigenic cell line MCF-12A was either basal or slightly downregulated. We further examined the expression of the CPT gene in breast cancer (11-9-1-4, BT-549) and non-tumorigenic cell lines (MCF-12A, MCF-12F). We found that the CPT gene is overexpressed in breast cancer cell lines compared to the non-tumorigenic cell lines. Furthermore, the activity of CPT in forming PC is increased in the breast cancer cell lines cultured for 24 h. Additionally, we examined the CPT activity in the presence of nanomolar concentrations of Ro5-4864. Biosynthesis of PC was increased in breast cancer cell lines upon treatment. We therefore propose that Ro5-4864 facilitates PC formation, a process important in membrane biogenesis for proliferating cells.

Peripheral type benzodiazepine receptor in human parathyroid glands: up-regulation in adenoma

In this study we report the presence of peripheral benzodiazepine receptors (PBRs) in human parathyroid glands and describe the effect of their benzodiazepine type ligands on parathyroid cell function. PBR binding features in normal parathyroid tissue were characterized and compared to parathyroid adenoma, using a specific and selective ligand for PBR, [3H] 1-(2-chlorophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinoline-carboxamide ([3H]PK11195). Affinity and density of [3H]PK11195 binding sites in homogenate membrane preparations from adenomatous and normal tissues were determined. Parathyroid adenoma showed a statistically significant 2.2 fold increase of [3H]PK11195 binding sites, while the affinity remained unchanged. Our results represent the first evidence of PBRs in parathyroid glands and suggest for them a role in influencing PTH release. A clear trend of PBR up-regulation in parathyroid adenoma was also found.

Effects of peripheral benzodiazepine receptor ligands on proliferation and differentiation of human mesenchymal stem cells

The peripheral benzodiazepine receptor (PBR) has been known to have many functions such as a role in cell proliferation, cell differentiation, steroidogenesis, calcium flow, cellular respiration, cellular immunity, malignancy, and apoptosis. However, the presence of PBR has not been examined in mesenchymal stem cells. In this study, we demonstrated the expression of PBR in human bone marrow stromal cells (hBMSCs) and human adipose stromal cells (hATSCs) by RT-PCR and immunocytochemistry. To determine the roles of PBR in cellular functions of human mesenchymal stem cells (hMSCs), effects of diazepam, PK11195, and Ro5-4864 were examined. Adipose differentiation of hMSCs was decreased by high concentration of PBR ligands (50 microM), whereas it was increased by low concentrations of PBR ligands (<10 microM). PBR ligands showed a biphasic effect on glycerol-3-phosphate dehydrogenase (GPDH) activity. High concentration of PBR ligands (from 25 to 75 microM) inhibited proliferation of hMSCs. However, clonazepam, which does not have an affinity to PBR, did not affect adipose differentiation and proliferation of hMSCs. The PBR ligands did not induce cell death in hMSCs. PK11195 (50 microM) and Ro5-5864 (50 microM) induced cell cycle arrest in the G(2)/M phase. These results indicate that PBR ligands play roles in adipose differentiation and proliferation of hMSCs.

Peripheral-type benzodiazepine receptor ligands: mitochondrial permeability transition induction in rat cardiac tissue

Strong evidence is emerging that mitochondrial permeability transition (MPT) may be important in certain physiological conditions and, above all, in the processes of cell damage and death. Reversible MPT, triggered by inducing agents in the presence of calcium ions, has resulted in the opening of a dynamic multiprotein complex formed in the inner mitochondrial membrane and has caused large-amplitude mitochondrial swelling. In the present work, the exposure of de-energized rat cardiac mitochondria to peripheral benzodiazepine receptor (PBR) ligands (1-(2-chlorophenyl-N-methyl-1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195), 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one (Ro5-4864), and diazepam) produced a dose-dependent and cyclosporin A (CSP)-sensitive loss of absorbance, which was indicative of mitochondrial swelling. By contrast, the addition of a high-affinity central benzodiazepine receptor ligand (clonazepam) was ineffective, even at the highest concentration tested. The ultrastructural changes associated with swelling were similar in mitochondria exposed either to PK 11195 or to calcium. Supporting the apoptotic role of PK 11195-induced swelling, supernatants from mitochondria that had undergone permeability transition caused apoptotic changes in isolated cardiac nuclei. In addition, ultrastructural abnormalities were observed in rat cardiac tissue following in vivo PK 11195 administration, with these abnormalities being prevented by CSP co-administration. These data indicate that PBR ligands induce mitochondrial permeability transition and ultrastructural alterations in isolated cardiac mitochondria as well as in myocardiocytes, suggesting a novel strategy for studying the implication of PBR ligands as apoptosis inducers, through a probable effect on the MPT pore.

The peripheral benzodiazepine receptors: a review

Peripheral benzodiazepine receptors (PBRs) have been identified in various peripheral tissues as well as in glial cells in the brain. This review describes the tissue and subcellular distribution of the PBR in mammalian tissues and analyzes its many putative endogenous ligands. It deals with the pharmacological, structural and molecular characterization of the PBR, the proteins associated with the receptor (VDAC, ANC, PRAX-1) and their roles in cell growth and differentiation, cancer, steroid biosynthesis, and other physiological roles.

Cloning and characterization of PRAX-1. A new protein that specifically interacts with the peripheral benzodiazepine receptor

Using a cytoplasmic domain of the peripheral benzodiazepine receptor (PBR) as a bait in the yeast two-hybrid system, we have isolated a cDNA encoding a new protein that specifically interacts with PBR. We named it PRAX-1, for peripheral benzodiazepine receptor-associated protein 1. PRAX-1 is a 1857-amino acid protein, the sequence of which was structurally unrelated to any known proteins. The gene encoding PRAX-1 is located in the q22-q23 region of the long arm of the human chromosome 17. The PRAX-1 mRNA is 7.5 kilobase pairs, predominantly expressed in the central nervous system, pituitary gland, and thymus. At the protein level, we found the PRAX-1 as a single 220-250-kDa protein in the brain and in many different human cell lines tested using specific antibody raised against PRAX-1. Parallel analysis of the PRAX-1 mRNA and protein expression performed in mouse and rat gave similar results. Immunocytochemistry analysis carried out to define the distribution of the PRAX-1 protein in the rat brain showed that PRAX-1 was prevalent in the mesolimbic system, specially abundant in the CA1 subfield of the hippocampus. Exhibiting several domains involved in protein-protein interaction (three proline-rich domains, three leucine-zipper motifs, and an Src homology region 3-like domain), the PRAX-1 may be looked upon as a new adaptator protein. We show that both the Src homology region 3-like domain and a proline-rich domain in PRAX-1 are required for the interaction with PBR. PRAX-1 is a cytoplasmic protein that also partially colocalizes with PBR in the mitochondria, as determined by confocal microscopy and Western blotting. Altogether our observations support a model of interaction implicating PBR and this newly described protein, PRAX-1. As being the first cytoplasmic protein associated with PBR, PRAX-1 is a new tool that opens new fields for exploring PBR biological roles.

Antiproliferative and differentiating effects of benzodiazepine receptor ligands on B16 melanoma cells

In this study, we evaluated the effect of several ligands active at the central-type and peripheral-type benzodiazepine receptor (BzR) (clonazepam, diazepam, PK11195 and Ro5-4864) on the growth and differentiation of B16 melanoma cells. All tested BzR ligands were able to suppress proliferation of the cells at the micromolar range and in a concentration-dependent manner. However, agents selectively active at the peripheral-type BzR (PK11195 and Ro5-4864) exhibited more potent antiproliferative activity. In addition, the BzR ligands were demonstrated to affect the cell cycle by reducing the percent of cells in the S phase and increasing the percent in the G2/M phase. BzR ligands induced cellular phenotypic alterations, which have been previously shown to be associated with melanoma cell differentiation. These alterations included: marked morphological changes, enhancement of melanogenesis, lipid accumulation and increase in the activity of gamma glutamyl transpeptidase. All BzR ligands induced a marked reduction in the concentration of UTP and most of them did the same in GTP and CTP, while ATP levels were not significantly altered. In summary, BzR ligands (clonazepam, diazepam, PK11195 and Ro5-4864) were found to exert antitumor effects in B16 melanoma cells. These findings encourage further studies of a possible therapeutic potential of BzR ligands in treatment of melanoma.

Drug accumulation in melanin: an affinity chromatographic study

The affinity of several drugs to melanin has been indirectly assessed using an affinity chromatographic approach based on immobilized melanin. Plots of the retention of the drugs on the affinity column versus the number of molecules applied were fitted best by nonlinear, exponential curves characteristic for each drug. These curves reflect the complexity of the binding behaviour, consisting of a variety of hydrogen bonding, hydrophobic or ionic interactions as well as cooperative or anti-cooperative interactions between the drug molecules and melanin. The nonlinear fitting procedure was based on a descriptive function and allowed to discriminate the binding behaviour according to parameter estimates which specified the investigated drugs.

Platelet and lymphocyte benzodiazepine binding in patients with Alzheimer's disease

Peripheral blood cells, such as platelets or lymphocytes, have been studied in the investigation of systemic derangements and central nervous system biochemical changes occurring in several neuropsychiatric disorders. In the present work, assaying platelet and lymphocyte peripheral-type benzodiazepine binding in patients with Alzheimer's disease (AD) and healthy controls, we found a significantly reduced number of cell receptors in patients' platelets and lymphocytes. These results are discussed with reference to central nervous system biochemical abnormalities in AD. Moreover, the lymphocyte binding data may represent an impairment of the immune response in AD, since lymphocyte surface peripheral-type benzodiazepine receptors seem to be related to immune function.

The sequential changes in DNA synthesis, glucose utilization, protein synthesis, and peripheral benzodiazepine receptor density in C6 brain tumors after chemotherapy to predict the response of tumors to chemotherapy

BACKGROUND

Monitoring therapy in patients with brain tumors is very difficult and unreliable. It has been shown that there is no good correlation between tumor sensitivity measured in vitro and in situ tumor response to therapies.

METHODS

Sequential changes in tumor size, number of DNA synthesizing cells (labelling index [LI]), glucose utilization (LCGU), protein synthesis (LCPS), and peripheral benzodiazepine receptor (PBR) density were examined after chemotherapy for seven days. This was done using antibromodeoxyuridine immunohistochemical stain and multiple tracer quantitative autoradiography in a C6 rat brain with an implanted glioma. On Day 10 after inoculation, the rats were divided into 5 experimental groups: (1) a nontreatment group (control Group 1); (2) a group received 5% dextrose intraarterial (IA) administration (control Group 2); (3) a group received 1,3-bis-(2-chloroethyl) nitrosourea (BCNU) intravenous (i.v.) administration (Group 3) (5% dextrose was solvent); (4) a group received BCNU IA administration (Group 4) (5% dextrose was solvent); and (5) a group received sarcosinamide chloroethyl nitrosourea (SarCNU) IA administration (Group 5) (solvent as for the BCNU group).

RESULTS

Three treatments showed a significant decrease (P < 0.003) in tumor growth. The most effective treatment was BCNU IA and SarCNU IA was moderately effective. BCNU i.v. showed no effect on tumor growth when compared with the two control groups. The change in the peak LI correlated well with the peak LCGU. These parameters decreased markedly and significantly in both Group 4 and Group 5 from Day 1 after treatment. The rates of the decrease in these biologic factors also correlated well with a decrease in the tumor growth. The LCPS did not correlate with a decrease in the LI or LCGU. The dissociation constant (Kd) and densities of the receptors PBR (B max) did not change significantly in any of the treatment groups during the observation period.

CONCLUSIONS

From the results presented, we concluded that changes in the LI and LCGU represent the most reliable parameters with which to predict the response or sensitivity of this glial tumor to the treatments applied. These data suggest that if changes in peak LCGU were measured in tumors using positron emission tomography, they might be instrumental in providing in vivo information about the sensitivity of a tumor to a given treatment without the need for repeated tumor biopsy.

Chronological study of peripheral benzodiazepine binding sites in the rat brain stab wounds using [3H] PK-11195 as a marker for gliosis

Chronological studies of the development of the peripheral benzodiazepine receptor sites were undertaken with the goal of evaluating the sensitivity of this marker for the study of the gliosis development in the injured brain. No significant increase in [3H] PK-11195 binding occurred in the rat brain stab wound one day following the puncture. A significant increase in the receptor density (Bmax) from the second day onward was observed. The Bmax reached its highest levels in the grey matter on the sixth day after a 23-gauge needle wound (8.75 +/- 0.09; pmol mg-tissue-1) and on the seventh day after an 18-gauge needle wound (8.98 +/- 0.31 pmol mg-tissue-1). In the white matter, the Bmax was greatest seven days after the wound (3.42 +/- 0.07; pmol mg-tissue-1; 23-gauge needle and 3.56 +/- 0.1 pmol mg-tissue-1 in the 18-gauge needle injury). Between 30 and 60 days after the wound, the Bmax was significantly lower than the Bmax observed between 6 and 14 days. The Bmax in the wound produced with needles was seven to eight times greater than the Bmax in the grey matter of the ipsilateral and contralateral cortices. Histological examination showed that there were no astrocytes or macrophages in the stab wound one day after the lesion. However, the glial fibrillary acidic protein positive cells and macrophages appeared on D3 after an injury. Gliosis, as measured by the PK-11195 binding, was also observed in the remote contralateral cortex. Data shows that PK-11195 binding is a very sensitive method of evaluating brain injury and could be of great value in studying progressive injuries in the living human brain in conjunction with positron emission tomography.

Characterization of peripheral benzodiazepine receptors in rat prostatic adenocarcinoma

Using PK 11195, a high affinity ligand for peripheral benzodiazepine receptors (PBZr), binding sites in isolated mitochondrial (m-fraction) and microsomal fractions (p-fraction) from R-3327 Dunning AT-1 tumors, ventral and dorsolateral prostate were studied. Binding of PK 11195 in both m- and p-fractions from AT-1 tumors, but only in m-fraction from ventral and dorsolateral prostate, was specific, saturable, and of high affinity. The PBZr density in m-fraction from AT-1 tumor was 6-fold and 20-fold higher than that in ventral and dorsolateral prostate, respectively. The receptor density in p-fraction from AT-1 tumors was approximately 25% of that found in the m-fraction. Clear differences were observed in the competition by both diazepam and flunitrazepam for binding sites in m- and p-fractions from tumors. These data indicate that the receptors were not only localized to the mitochondria, but were also present in considerable amounts in the microsomal fractions. The unusually high amounts of receptors in the fast growing anaplastic prostatic tumor suggest their involvement in the regulation of cell proliferation and possibly in tumorigenesis.

A 3D model of the peripheral benzodiazepine receptor and its implication in intra mitochondrial cholesterol transport

A three-dimensional (3D) model of the peripheral benzodiazepine receptor (PBR) has been built using molecular dynamics simulations. The transmembrane domain of the receptor has been modeled as five alpha-helices, which are not long enough to cross the entire bilayer membrane but correspond approximately to only one phospholipid layer. The receptor model has also been tested as a cholesterol carrier, and molecular dynamics simulations have shown that it could indeed accommodate a cholesterol molecule within the five helices. All three known PBR sequences have been modeled, and no significant difference has been found between them.

Triazolobenzodiazepines exert immunopotentiating activities on normal human peripheral blood lymphocytes

Previous studies have demonstrated that benzodiazepines (BDZ) (e.g. diazepam) inhibit immune responsiveness. Since these drugs are largely used in psychiatric patients it is of great importance to verify the existence of different types of BDZ, which are not suppressive for the immune system. In this framework, our results indicate that alprazolam and triazolam, two triazolo-BDZ, do not modify in vitro phagocytosis and killing exerted by normal human polimorphonuclear cells and monocytes. On the contrary, they significantly enhance T lymphocyte-dependent antibacterial activity in normal donors. These data support the concept that triazolo-BDZ and, in particular, alprazolam may represent more appropriate drugs for the treatment of psychiatric patients (e.g. patients with phobic disorders and/or migraine) who display immunodeficits.

Localization of the peripheral-type benzodiazepine binding site to mitochondria of human glioma cells

Subcellular fractionation was performed on human U251 glioblastoma cultures. In all subcellular fractions, the binding of the peripheral benzodiazepine ligand, [3H]PK 11195, correlated with the specific activity of monoamine oxidase (r = 0.95, p less than 0.001) and succinate dehydrogenase (r = 0.93, p less than 0.001), two mitochondrial enzymes. The specific activity of plasma membrane and nuclear markers correlated poorly with the presence of PK 11195 binding sites. These data support the mitochondrion as the primary location of peripheral-type benzodiazepine binding sites (PBBS) in human glioma cells. Mitochondria-rich preparations were then assayed for [3H]Ro5-4964 binding. Six nM [3H]Ro5-4964 failed to specifically bind to human U251 mitochondria, but bound vigorously to mitochondria from rat C6 glioma. These data indicate that the low affinity of Ro5-4864 for PBBS in human glioma cells compared to those in rat is due to interspecies receptor variation rather than impaired drug transport into human cells.

Biochemical, physiological, and pathological aspects of the peripheral benzodiazepine receptor

The PBR is a mitochondrial protein composed of at least two subunits, an approximately 30-kDa subunit that contains the site for BZs and an approximately 18-kDa subunit that binds isoquinoline carboxamide derivatives. Porphyrins and diazepam binding inhibitor are putative endogenous ligands for these receptors, which are under neural and hormonal control. Alterations in the density of PBR seem to be a sensitive indicator of stress: up-regulation after acute stress and down-regulation induced by repeated stress. PBR-specific ligands are involved in the control of cell proliferation and differentiation, and their binding is increased in some cancer tumors. Numerous studies in various endocrine organs have revealed that PBR are located in specific regions or tissues in the organs. Furthermore, PBR densities in various organs subject to hormonal control are regulated by organotropic hormones. At least in some cases, BZ ligands do not exert a specific effect in an organ, but rather modulate the well-documented effects of that particular hormone. To the best of our knowledge, BZ ligand action in peripheral tissues is dependent on recognition of PBR, which may suggest a receptor-mediated action.

Ontogenesis of peripheral benzodiazepine receptors: demonstration of selective up-regulation in rat testis as a function of maturation

Peripheral benzodiazepine receptors (PBR) have been localized to the outer mitochondrial membrane in a variety of organs, where they apparently play a role in steroidogenesis, oxidative processes, and/or growth and development. Previous studies have demonstrated ontogenetic changes in heart and lung PBR, with maximal PBR density at 31 days, as opposed to negligible changes in brain PBR during the prenatal through postnatal periods. The present study was designed to examine the influence of maturation and aging upon PBR binding characteristics. Rats aged 1, 2, 12, 18, and 24 months were sacrificed, and the following organs were removed according to standard protocol: heart, lungs, kidneys, adrenal gland, and testes. Binding studies were performed using [3H]PK 11195 as a radioligand. A 3-fold increase in PBR density was demonstrated in testis during maturation, with maximal values appearing at 18 months, followed by a decline at 24 months. None of the other organs examined showed significant changes in PBR density. No alterations were observed in affinity values for the various organs and ages. Since testicular PBR are putatively involved in testosterone production, these results might reflect critical interactions between PBR and gonadal hormone activity during development.

Characterization of [3H]Ro 5-4864 binding sites in rat vas deferens

The presence of benzodiazepine binding sites in rat vas deferens was detected using [3H]Ro 5-4864 as a radioligand. The binding of [3H]Ro 5-4864 to the mitochondrial sites is saturable, reversible, and temperature and time dependent. The association rate constant (k1) was 8.7 +/- 0.7 x 10(7) M-1 min-1, and the dissociation rate constant (k-1) was 0.031 +/- 0.003 min-1. The dissociation constant (KD) determined by saturation binding was 5.22 +/- 0.56 nM. The density of binding was 4,926 +/- 565 fmol/mg of protein. The Hill coefficient of binding was 0.99 +/- 0.01, an indication that [3H]Ro 5-4864 binds to a single site. The [3H]Ro 5-4864 binding was inhibited competitively by Ro 5-4864 and 2-hydroxy-5-nitrobenzyl-6-thioguanosine and noncompetitively by PK 11195, nitrendipine, alpha,beta-methylene-ATP, and carboxyatractyloside and was not affected by clonazepam, dicyclohexylcarbodiimide, or protoporphyrin IX. Our data indicate that [3H]Ro 5-4864 binding sites are not identical to those labeled by PK 11195. These binding sites are modulated by the ADP/ATP mitochondrial carrier, and an interaction of dihydropyridines and [3H]Ro 5-4864 binding sites in rat vas deferens is suggested.

Peripheral benzodiazepine induces morphological changes and proliferation of mitochondria in glioma cells

Peripheral benzodiazepine (PBD) receptors are localized on the mitochondrial membrane and are highly expressed in brain tumors compared to normal brain. To elucidate the biological role of the PBD receptor on mitochondria, we examined the effect of PBDs on mitochondrial morphology in C6 and T98G glioma cells using rhodamine 123 and quantitative electron microscopy. In cells incubated in serum-free medium alone, mitochondria were distributed in a filamentous pattern throughout the cytoplasm. By contrast, the mitochondria aggregated in the perinuclear region in PK11195 or Ro5-4864 (10 nM) treated cells. Quantitative electron micrography revealed a 250% increased in the number of mitochondria with elongated cristae and a fivefold increase in dividing mitochondria in PK11195-treated cells compared with cells incubated in serum-free medium alone. PBD treatment also resulted in vacuolation within the matrix and mitochondrial swelling. These data suggest that PBDs influence mitochondrial morphology and induce mitochondrial replication in cultured glioma cells.

Brain tumors

Recent advances in experimental tumor biology are being applied to critical clinical problems of primary brain tumors. The expression of peripheral benzodiazepine receptors, which are sparse in normal brain, is increased as much as 20-fold in brain tumors. Experimental studies show promise in using labeled ligands to these receptors to identify the outer margins of malignant brain tumors. Whereas positron emission tomography has improved the dynamic understanding of tumors, the labeled selective tumor receptors with positron emitters will enhance the ability to specifically diagnose and greatly aid in the pretreatment planning for tumors. Modulation of these receptors will also affect tumor growth and metabolism. Novel methods to deliver antitumor agents to the brain and new approaches using biologic response modifiers also hold promise to further improve the management of brain tumors.

Molecular cloning and chromosomal localization of a human peripheral-type benzodiazepine receptor

The sequencing of endopeptidase-generated peptides from the peripheral binding site (PBS) for benzodiazepines, purified from a Chinese hamster ovary (CHO) cell line, produced internal sequence information, and confirmed and extended the NH2-terminal PBS sequence that we previously reported. Since the sequences were highly similar to the corresponding rat PBS sequences, we investigated whether they were also conserved in human PBS. Scatchard analysis of [3H]PK11195 (a derivative of isoquinoline carboxamide) binding and photoaffinity labeling with [3H]PK14105 (a nitrophenyl derivative of PK11195) revealed that CHO PBS and human PBS are closely related. Furthermore a rabbit antiserum raised against three peptides synthesized on the basis of the CHO PBS sequence immunoprecipitate the solubilized U937 PBS and also recognize the human protein in an immunoblot analysis. Based on these results, we screened a U937 cell cDNA library with four oligonucleotide probes derived from the CHO sequence. Two of the probes hybridized with several clones that we isolated and sequenced. One of these, h-pPBS11, is 831 nucleotides and contains a full-length representation of human PBS mRNA. The amino acid sequence of human PBS deduced from the cDNA is 79% identical to that reported for rat PBS, however, human PBS contains two cysteines while rat PBS is characterized by the absence of this amino acid. Using the cDNA of human PBS as a probe, the PBS gene was located in the 22q13.3 band of the human genome.

Imaging peripheral benzodiazepine receptors in brain tumors in rats: in vitro binding characteristics

Peripheral benzodiazepine binding constants for transplanted RG-2 gliomas and HD and LK Walker 256 tumors (metastatic breast carcinoma) were determined in Wistar rats using autoradiography. In addition, Kd and Bmax parameters for peripheral benzodiazepine receptors on RG-2 tumors were directly visualized using digital image analysis of autoradiograms. High specific binding of [3H]PK11195, a selective peripheral benzodiazepine ligand, had excellent topographical correlation to areas of histologically verified tumor. Scatchard analysis suggested a single class of peripheral binding sites with similar binding affinities in RG-2 and LK Walker 256 tumors and normal cortex. Bmax was 20-fold greater in glial tumors and 11.6- and 10.6-fold greater in LK and HK Walker 256 tumors, respectively, compared to normal cortex. The location of metastatic tumors, either intracerebrally or subcutaneously, did not effect their Kd or Bmax values. Kd and Bmax values for RG-2 tumors were similar whether determined densitometrically or by direct visualization with image analysis. Binding parameters within normal brain were difficult to visualize by image analysis due to the low level of specific binding. The ability to label specifically intracerebral tumor cells and to characterize the binding parameters shown in this study suggest that peripheral benzodiazepine receptor ligands could be utilized by PET to analyze directly a variety of tumors in humans.

Peripheral-acting benzodiazepines inhibit the growth of human melanoma cells and potentiate the antiproliferative activity of recombinant human interferons

In this study, we evaluated the effect of a series of peripheral-acting benzodiazepines (BZDs), alone and in combination with recombinant human leukocyte (IFN-alpha A), fibroblast (IFN-beta), or immune (IFN-gamma) interferon (IFN), on the growth of human melanoma cells. Specific peripheral-acting BZDs caused a marked suppression in the proliferation of human melanoma cells. The effect on melanoma cell growth required 72 h exposure to the peripheral-acting BZDs and was not observed if the compounds were removed by 48 h. The relative potency of antiproliferative activity of a series of peripheral-acting BZDs on human melanoma cell growth did not correlate with the reported ability of these agents to bind to peripheral sites on the cell membrane of Friend erythroleukemia cells (FELC), nor did they correlate with the ability of these agents to inhibit [3H]thymidine incorporation in FELC, induce differentiation in FELC, or inhibit neurite outgrowth in nerve growth factor-treated rat pheochromocytoma (PC12) cells. The growth of human melanoma cells was also inhibited by various recombinant human IFNs, with IFN-beta displaying greater antiproliferative activity than IFN-alpha A or IFN-gamma. When the peripheral-acting BZD Ro7-3351, which displays growth inhibitory properties when used alone, was combined with IFN, the antiproliferative activity of the combination was greater than either individual compound exerted independently. The combination of IFN-beta plus Ro7-3351 was more active in suppressing HO-1 melanoma cell growth than other IFN preparations in combination with this peripheral-type BZD. Even when combined with a peripheral-acting BZD, such as Ro5-4608, which displayed only marginal antiproliferative activity against human melanoma cells when applied alone, growth suppression of the combination of this peripheral-type BZD with all three types of IFNs was more than additive. These studies suggest that specific peripheral-acting BZDs, both alone and in combination with recombinant IFNs, display novel antiproliferative activity toward human melanoma cells which may involve a different genetic locus than previously observed in other model cell culture systems.

Psychoneuroimmunology: An area of interest for the psychopharmacologist?

Anecdotal evidence suggesting a causal relationship between psychiatric illness, environmental stress and a malfunctioning immune system goes back to antiquity. Recently, clinical and experimental studies have established the interrelationship between neuro- endocrine regulation, the immune system and abnormalities in central neurotransmission which may be deranged as a consequence of stressful events. This short review is an attempt to assess the evidence implicating altered immune responsiveness in depression and to consider the impact of different types of environmental stress in triggering the immune malfunction. While these findings are of considerable biological importance, it is presently unclear whether the immunological changes are primary or secondary to the disease states.

Specific high-affinity binding of peripheral benzodiazepine receptor ligands to brain tumors in rat and man

Two types of benzodiazepine receptors have been identified in mammalian tissues: a central type which is localized to neuronal elements in the brain, and a peripheral type which is present on glial cells and in tissues outside the central nervous system such as kidney. The authors report an increase in specific binding of peripheral benzodiazepine receptor ligands in certain human brain tumors using computer assisted quantitative image analysis of autoradiograms. Higher densities of binding sites to a 3H-labeled selective peripheral benzodiazepine ligand, PK11195 [1-(2-chlorophenyl-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide] were observed in human gliomas as the malignancy of these tumors increased. Specific binding was also present in some non-glial tumors but little binding was demonstrated in necrotic tissue or normal brain. In in vitro binding studies in rats, there was a significant increase in Bmax (1089.3 +/- 232.2 fmol/mg tissue) in C6 glial tumors and LK Walker 256 metastatic tumors (924.2 +/- 183.7) compared with normal brain (62.1 +/- 12.8 fmol/mg tissue). Binding affinities were, however, similar (Kd = 2.09, 2.17, and 2.04 nmol/l, respectively). These findings suggest that the number of peripheral benzodiazepine receptors are increased in brain tumors. These receptors could be utilized in positron emission tomography to image brain tumors.

Imaging of brain tumors using peripheral benzodiazepine receptor ligands

Peripheral benzodiazepine receptor ligands were utilized to selectively image intracerebrally implanted C6 gliomas, RG-2 gliomas, and Walker 256 metastatic tumors by means of quantitative autoradiography. Intravenous injections of 3H-PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide) or 3H-flunitrazepam in combination with clonazepam revealed high densities of peripheral benzodiazepine binding in glial tumors, with less binding in metastatic tumors. Peripheral binding was displaced by preadministration of excess PK11195. Topographical correlation was excellent between areas of histologically verified tumor and high densities of peripheral benzodiazepine binding. The choroid plexus, ependyma, and pineal gland also showed a moderate level of binding, but there was little binding in other normal brain structures or necrotic tissue. Binding densities were three- to fivefold higher in C6 glial tumors compared to normal cortex. Injection of 3H-flunitrazepam alone, which binds to both central and peripheral receptors, had the advantage of showing normal anatomic structures in addition to a clear definition of tumor topography. The potential value of peripheral benzodiazepine ligands in selectively imaging brain tumors in man with positron emission tomography is discussed.

Properties of benzodiazepine binding sites in peripheral blood lymphocytes

Benzodiazepine (BDZ) binding sites were studied by using 3H-diazepam and 3H-Ro 5-4864 in intact lymphocytes from peripheral blood (PBL), in comparison to kidney and cerebellum. Experiments with 3H-diazepam performed at equilibrium and measuring kinetics revealed that BDZ binding sites are indeed present in rat PBL. The binding is saturable (Bmax 557 fmoles/10(6) cells), with high affinity (KD = 9.3 nM) and reversible. Specific binding sites are also observed by saturation experiments with 3H-Ro 5-4864 (Bmax 175 fmoles/10(6) cells, KD 2.2 nM). In addition, analysis of saturation isotherms obtained with 3H-diazepam indicates that BDZ binding sites are also present in human PBL. Scatchard plot of binding isotherms revealed an apparent single population of sites in all cases. The pharmacological characterization of BDZ binding sites in PBL, as compared with those of kidney and cerebellum, showed that these sites belong to the so-called "peripheral type."

Heterogeneity between rat and calf peripheral-type benzodiazepine binding sites: differential sensitivity to Triton X-100

The effect of various detergents treatment on the specific binding of [3H]PK 11195 (2nM) to peripheral-type benzodiazepine binding sites (PBS) in calf and rat kidney, adrenal gland, and cerebral cortex membranes was studied. At a concentration of 0.025%, Triton X-100 increased [3H]PK 11195 specific binding to calf kidney, adrenal gland, and cerebral cortex membranes by 20-40%. At the same concentration, Triton X-100 scarcely affected specific binding of [3H]PK 11195 to rat cerebral cortex but decreased binding to rat kidney and adrenal gland membranes by 20-30%. At a concentration of 0.05% of Triton X-100, [3H]PK 11195 specific binding to calf kidney, adrenal gland, and cerebral cortex membranes was increased by 10-20%; whereas [3H]PK 11195 specific binding to rat kidney, adrenal gland, and cerebral cortex membranes was decreased by more than 40%. The increase in [3H]PK 11195 specific binding to calf kidney membranes following Triton X-100 (0.05%) treatment was apparently due to an increase in the binding affinity of PBS, since the density remained unaltered; whereas, the decrease in [3H]PK 11195 specific binding to rat kidney membranes was due to a decrease in both binding affinity and density of PBS. On the other hand, the detergents 3- [(3- cholamidopropyl)- dimethylammonio] - 1 - propane sulfonate (CHAPS), Tween 20, deoxycholic acid, and digitonin have a similar effect on [3H]PK 11195 specific binding to PBS in both calf and rat kidney membranes.

Diazepam inhibits phagocytosis and killing exerted by polymorphonuclear cells and monocytes from healthy donors. In vitro studies

The effect of a benzodiazepine (BDZ), diazepam on human polymorphonuclear cell (PMN) and monocyte phagocytosis and killing from healthy volunteers has been evaluated. Diazepam is able to inhibit in vitro both functions exerted by PMN and monocytes at 10(-5) and 10(-6) M concentrations/ 4 x 10(6) phagocytes. 10(-7) M concentration was not effective in all the instances. These results are discussed for their possible clinical implications, since previous studies have shown that in patients with phobic disorder there is evidence for reduced phagocytosis and killing capacities.

Pyruvate dehydrogenase interactions with peripheral-type benzodiazepine receptors

Although peripheral-type benzodiazepine recognition sites have been demonstrated in the brain of various species, the precise identity and function of the peripheral benzodiazepine receptor have not been established yet. In light of the recent demonstration of the mitochondrial localization of this receptor and its potential role in intermediary metabolism, we investigated the relationship between the benzodiazepines and the enzyme pyruvate dehydrogenase (PDH), a component of the mitochondrial membrane. The results obtained in the present study demonstrate a specific interaction between PDH and the ligands for the peripheral-type type benzodiazepine receptor, which might account for their effects on cell growth and differentiation.

Effect of benzodiazepines on the proliferation of mouse spleen lymphocytes in vitro

The effect of several benzodiazepines (clonazepam, diazepam, Ro 5-4864, Ro 15-1788) and two pineal gland indoleamines (N-acetylserotonin, melatonin) on the spontaneous proliferation of mouse spleen lymphocytes was estimated in vitro by the 3 H-thymidine uptake assay. It was found that diazepam and Ro 5-4864 (a selective peripheral-type benzodiazepine receptor ligand) produced the concentration-dependent inhibition of 3 H-thymidine incorporation into the DNA of these cells. Ro 15-1788, a specific central-type receptor ligand, evoked a slight inhibitory effect in a high concentration (10(-4) M), whereas clonazepam did not produce any significant inhibition. When Ro 5-4864 was tested in combination with diazepam, the inhibition of lymphocyte proliferation did not exceed the effect of diazepam given alone. Ro 15-1788 was unable to reverse the inhibitory action of diazepam in the same experimental conditions. Melatonin and its precursor N-acetylserotonin tested in the concentration range of 10(-4)-10(-8) M had no significant influence on the spleen lymphocyte DNA replication in our assay system. These data suggest that diazepam inhibition of lymphocyte proliferation is mediated by peripheral-type sites. Additionally, the fact that melatonin and N-acetylserotonin were unable to affect 3 h-thymidine incorporation argues against any benzodiazepine receptor mediated effect of pineal indoleamines on a cellular proliferation.

Limitations of the benzodiazepine receptor nomenclature: a proposal for a pharmacological classification as omega receptor subtypes

At present, the nomenclature of benzodiazepine (BZ) receptors is based on historical association with the BZ structure. However, it is mainly through the new compounds chemically unrelated to BZ that the central and peripheral subtypes of BZ receptors have been characterized. We therefore propose the nomenclature of a Greek letter omega, as omega 1, omega 2, and omega 3 to designate the central BZ1, BZ2, and peripheral BZ receptors, respectively. Among the several classes of non-BZD drugs with affinity for different receptors, the imidazopyridines provide a valuable tool for the characterization of omega receptor subtypes. Most BZ are nonselective ligands for the central omega 1 and omega 2 receptors, while selectivity for omega 1 receptor subtypes is present in several non BZ chemical series: imidazopyridines (zolpidem), triazolopyridazines (CL 218872), betacarbolines (beta-CCE), and pyrazoloquinolines (CGS 8216). Selective ligands for the omega 2 subtype are not available so far. The so-called peripheral BZ receptor is also present in the central nervous system; therefore, the proposed nomenclature of omega 3 receptors resolves this paradox because it does not designate location and is defined in terms of pharmacological specificity. Selective ligands for omega 3 receptors include the BZ Ro 5-4864, and the isoquinolinecarboxamide PK 11195, while the imidazopyridine alpidem is the ligand with the highest affinity for this receptor subtype.

Inhibition of cell proliferation of human gliomas by benzodiazepines in vitro

The effects of several benzodiazepines (diazepam, clonazepam, Ro 15-1788 and Ro 5-4864) on cell proliferation of 2 human gliomas were estimated in vitro by means of [3H]-thymidine uptake assay. It was found that all tested benzodiazepines suppressed [3H]-thymidine incorporation into the DNA of glioma cells, the effects being stronger in case of peripheral-type benzodiazepine receptor ligands. The results indicated that benzodiazepines might exert an antiproliferative action on glioma tumour cells growth.

Imaging of a glioma using peripheral benzodiazepine receptor ligands

Two types of benzodiazepine receptors have been demonstrated in mammalian tissues, one which is localized on neuronal elements in brain and the other, on glial cells and in peripheral tissues such as kidney. In vivo administration of 3H-labeled PK 11195 [1-(2-chlorophenyl-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide] or [3H]flunitrazepam with 5 mg of clonazepam per kg to rats with intracranial C6 gliomas resulted in high levels of tritiated-drug binding to the tumor as shown by quantitative autoradiography. Pharmacological studies indicated that the bound drugs labeled the peripheral benzodiazepine binding site. Binding to the peripheral benzodiazepine site was confirmed primarily to malignant cells with little binding to adjacent normal brain tissue or to necrotic tissue. Tumor cell binding was completely inhibited by preadministration of the peripheral benzodiazepine blocking agent PK 11195 at 5 mg/kg. The centrally selective benzodiazepine ligand clonazepam had no effect on PK 11195 binding to the tumor cells. When binding to other tumor cell lines grown in nude mice and nude athymic rats was evaluated, little or no peripheral benzodiazepine binding was detected on human pheochromocytoma (RN1) and neuroblastoma (SK-N-MC, SK-N-SH) tumor cells, respectively. However, high densities of peripheral benzodiazepine binding sites were observed on tumors derived from a human glioma cell line (ATCC HTB 14, U-87 MG). The presence of high concentrations of specific peripheral benzodiazepine receptors on glial tumors suggests that human primary central nervous system tumors could be imaged and diagnosed using peripheral benzodiazepine ligands labeled with positron- or gamma-emitting isotopes.

Evidence that the peripheral-type benzodiazepine receptor ligand Ro 5-4864 inhibits beta-endorphin release from AtT-20 cells by blockade of voltage-dependent calcium channels

The demonstrations that Ro 5-4864, a ligand selective for the peripheral-type benzodiazepine (BZD) binding site, inhibited cellular differentiation and proliferation and that occupancy of the peripheral-type BZD binding site likely mediated the observed BZD effects on diverse endocrine tissues suggested that Ro 5-4864 disrupted a common cellular regulatory event. Using a well-characterized anterior pituitary-derived tumor cell line (AtT-20 cells), which synthesizes and secretes adrenocorticotropic hormone (ACTH), beta-lipotropin hormone (beta-LPH), and beta-endorphin (BE), we have investigated the molecular mechanism of action of Ro 5-4864's capacity to alter BE secretion. Ro 5-4864 inhibits basal and induced BE release from AtT-20 cells, through a cyclic AMP-independent mechanism. Ro 5-4864 completely blocked the corticotropin-releasing hormone and forskolin-induced release of BE without altering the concomitant production of cyclic AMP. The addition to AtT-20 cells of CGP 28392, a dihydropyridine that has been demonstrated in other systems to specifically activate voltage-dependent Ca2+ channels, resulted in a cyclic AMP-independent, dose-related increase in BE secretion. This CGP-induced BE release was blocked by increasing concentrations of Ro 5-4864. In contrast to the capacity of Ro 5-4864 to block CGP-induced BE release, Ro 5-4864 lacked the capacity to block enhanced BE secretion due to the calcium ionophore A23187, which increases intracellular Ca2+ levels independent of the voltage-dependent Ca2+ channels. Our findings suggest that Ro 5-4864 inhibits BE secretion from AtT-20 cells through a blockade of the voltage-dependent membrane Ca2+ channels and this mechanism of action may be responsible for Ro 5-4864's diverse effects observed on other cell types.

Enhancement of estradiol-induced DNA synthesis in the anterior pituitary gland by the peripheral-type benzodiazepine receptor ligand Ro 5-4864

The effects of peripheral (Ro 5-4864) and central-type (Ro 15-1788) benzodiazepine receptor ligands on estrogen-induced DNA synthesis in the rat anterior pituitary gland was investigated. As expected, a single injection of estradiol (250 micrograms per rat) significantly increased the uptake of 3H-thymidine by anterior pituitary cells. Additional treatment with Ro 5-4864 potentiated the effects of estradiol on pituitary DNA synthesis. Under the same experimental conditions, no effect of Ro 15-1788 and sodium valproate, a GABA-transaminase inhibitor, was detected. These findings indicate the involvement of peripheral-type benzodiazepine receptors in the control of anterior pituitary cell proliferation.

Benzodiazepine receptor-mediated chemotaxis of human monocytes

Benzodiazepines, which are widely prescribed for their antianxiety effects, are shown to be potent stimulators of human monocyte chemotaxis. The chemotactic effects of benzodiazepine receptor agonists were blocked by the peripheral benzodiazepine receptor antagonist PK-11195, suggesting that these effects are mediated by the peripheral-type benzodiazepine receptor. Diazepam was also active in inducing chemotaxis. Binding studies on purified monocytes revealed high-affinity peripheral benzodiazepine receptors, and the displacement potencies of various benzodiazepines correlated with their relative potencies in mediating chemotaxis. The demonstration of functional benzodiazepine receptors on human monocytes, together with recent evidence of receptor-mediated monocyte chemotaxis by other psychoactive peptides (such as opiate peptides), suggests a biochemical substrate for psychosomatic communication.