Gene Polymorphisms and Drug-Drug Interactions Determine the Metabolic Profile of Blonanserin

This study aimed to evaluate the effects of cytochrome P450 3A4 (CYP3A4) gene polymorphism and drug interaction on the metabolism of blonanserin. Human recombinant CYP3A4 was prepared using the Bac-to-Bac baculovirus expression system. A microsomal enzyme reaction system was established, and drug-drug interactions were evaluated using Sprague-Dawley rats. Ultra-performance liquid chromatography-tandem mass spectrometry was used to detect the concentrations of blonanserin and its metabolite. Compared with wild type CYP34A, the relative clearance of blonanserin by CYP3A4.29 significantly increased to 251.3%, while it decreased notably with CYP3A4.4, 5, 7, 8, 9, 10, 12, 13, 14, 16, 17, 18, 23, 24, 28, 31, 33, and 34, ranging from 6.09% to 63.34%. Among 153 tested drugs, nimodipine, felodipine, and amlodipine were found to potently inhibit the metabolism of blonanserin. Moreover, the inhibitory potency of nimodipine, felodipine, and amlodipine varied with different CYP3A4 variants. The half-maximal inhibitory concentration and enzymatic kinetics assay demonstrated that the metabolism of blonanserin was noncompetitively inhibited by nimodipine in rat liver microsomes and was inhibited in a mixed manner by felodipine and amlodipine in both rat liver microsomes and human liver microsomes. When nimodipine and felodipine were coadministered with blonanserin, the area under the blood concentration-time curve (AUC)(0-t), AUC(0-∞), and C max of blonanserin increased. When amlodipine and blonanserin were combined, the C max of blonanserin C increased remarkably. The vast majority of CYP3A4 variants have a low ability to catalyze blonanserin. With combined administration of nimodipine, felodipine, and amlodipine, the elimination of blonanserin was inhibited. This study provides the basis for individualized clinical use of blonanserin. SIGNIFICANCE STATEMENT: The enzyme kinetics of novel CYP3A4 enzymes for metabolizing blonanserin were investigated. Clearance of blonanserin by CYP3A4.4, 5, 7-10, 12-14, 16-18, 23-24, 28, 31, 33, and 34 decreased notably, but increased with CYP3A4.29. Additionally, we established a drug interaction spectrum for blonanserin, in which nimodipine, felodipine, and amlodipine kinetics exhibited mixed inhibition. Moreover, their inhibitory potencies decreased with CYP3A4.4 and 5 compared to CYP3A4.1. This study provides essential data for personalized clinical use of blonanserin.

Deletion of voltage-gated calcium channels in astrocytes decreases neuroinflammation and demyelination in a murine model of multiple sclerosis

The experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis was used in combination with a Cav1.2 conditional knock-out mouse (Cav1.2KO) to study the role of astrocytic voltage-gated Ca++ channels in autoimmune CNS inflammation and demyelination. Cav1.2 channels were specifically ablated in Glast-1-positive astrocytes by means of the Cre-lox system before EAE induction. After immunization, motor activity was assessed daily, and a clinical score was given based on the severity of EAE symptoms. Cav1.2 deletion in astrocytes significantly reduced the severity of the disease. While no changes were found in the day of onset and peak disease severity, EAE mean clinical score was lower in Cav1.2KO animals during the chronic phase of the disease. This corresponded to better performance on the rotarod and increased motor activity in Cav1.2KO mice. Furthermore, decreased numbers of reactive astrocytes, activated microglia, and infiltrating lymphocytes were found in the lumbar section of the spinal cord of Cav1.2KO mice 40 days after immunization. The degree of myelin protein loss and size of demyelinated lesions were also attenuated in Cav1.2KO spinal cords. Similar results were found in EAE animals treated with nimodipine, a Cav1.2 Ca++ channel inhibitor with high affinity to the CNS. Mice injected with nimodipine during the acute and chronic phases of the disease exhibited lower numbers of reactive astrocytes, activated microglial, and infiltrating immune cells, as well as fewer demyelinated lesions in the spinal cord. These changes were correlated with improved clinical scores and motor performance. In summary, these data suggest that antagonizing Cav1.2 channels in astrocytes during EAE alleviates neuroinflammation and protects the spinal cord from autoimmune demyelination.

ISSLS PRIZE in basic science 2023: Lactate in lumbar discs-metabolic waste or energy biofuel? Insights from in vivo MRS and T2r analysis following exercise and nimodipine in healthy volunteers

PURPOSE

To quantitatively assess the dynamic changes of Lactate in lumbar discs under different physiological conditions using MRS and T2r.

METHODS

In step1, MRS and T2r sequences were standardized in 10 volunteers. Step2, analysed effects of high cellular demand. 66 discs of 20 volunteers with no back pain were evaluated pre-exercise (EX-0), immediately after targeted short-time low back exercises (EX-1) and 60 min after (EX-2). In Step 3, to study effects of high glucose and oxygen concentration, 50 lumbar discs in 10 volunteers were analysed before (D0) and after 10 days intake of the calcium channel blocker, nimodipine (D1).

RESULTS

Lactate showed a distinctly different response to exercise in that Grade 1 discs with a significant decrease in EX-1 and a trend for normalization in Ex-2. In contrast, Pfirrmann grade 2 and 3 and discs above 40 years showed a higher lactate relative to proteoglycan in EX-0, an increase in lactate EX-1 and mild dip in Ex-2. Similarly, following nimodipine, grade 1 discs showed an increase in lactate which was absent in grade 2 and 3 discs. In contrast, exercise and Nimodipine had no significant change in T2r values and MRS spectrum of proteoglycan, N-acetyl aspartate, carbohydrate, choline, creatine, and glutathione across age groups and Pfirrmann grades.

CONCLUSION

MRS documented changes in lactate response to cellular demand which suggested a 'Lactate Symbiotic metabolic Pathway'. The differences in lactate response preceded changes in Proteoglycan/hydration and thus could be a dynamic radiological biomarker of early degeneration.

Aging differentially affects LTCC function in hippocampal CA1 and piriform cortex pyramidal neurons

Aging is associated with cognitive decline and memory loss in humans. In rats, aging-associated neuronal excitability changes and impairments in learning have been extensively studied in the hippocampus. Here, we investigated the roles of L-type calcium channels (LTCCs) in the rat piriform cortex (PC), in comparison with those of the hippocampus. We employed spatial and olfactory tasks that involve the hippocampus and PC. LTCC blocker nimodipine administration impaired spontaneous location recognition in adult rats (6-9 months). However, the same blocker rescued the spatial learning deficiency in aged rats (19-23 months). In an odor-associative learning task, infusions of nimodipine into either the PC or dorsal CA1 impaired the ability of adult rats to learn a positive odor association. Again, in contrast, nimodipine rescued odor associative learning in aged rats. Aged CA1 neurons had higher somatic expression of LTCC Cav1.2 subunits, exhibited larger afterhyperpolarization (AHP) and lower excitability compared with adult neurons. In contrast, PC neurons from aged rats showed higher excitability and no difference in AHP. Cav1.2 expression was similar in adult and aged PC somata, but relatively higher in PSD95- puncta in aged dendrites. Our data suggest unique features of aging-associated changes in LTCCs in the PC and hippocampus.

The effect of CYP3A4 genetic polymorphism and drug interaction on the metabolism of istradefylline

AIM

This study investigated into the effect of CYP3A4 genetic polymorphism on istradefylline metabolism. Moreover, the potential drug-drug interaction with istradefylline was determined as well as underlied mechanism.

METHOD

In vitro, enzymatic reaction was performed to determine the kinetic parameters of CYP3A4 and its variants on catalyzing istradefylline. Meanwhile, the rat liver microsomes incubation assay was applied to screen interacting drugs. In vivo, SD rats were used to investigate the selected drug interaction. UPLC-MS/MS was used to detect the metabolite M1.

RESULT

The results demonstrated that the relative clearance rate of CYP3A4.29 decrease significantly compared with CYP3A4.1. But there is no statistically diverse in activities among CYP3A4.1, 2 and 3. The relative clearance rates of the remaining variants are significantly decreased compared with CYP3A4.1. In addition, 148 drugs were screened to determine the potential interaction with istradefylline, among which calcium channel blockers were identified. It's indicated that nimodipine has a significant inhibitory effect on metabolizing istradefylline with IC₅₀ of 6.927 ± 0.372 μM, which via competitive and non-competitive mixed mechanism. In vivo, when istradefylline and nimodipine was co-administered to SD rats, we found the main pharmacokinetic parameters of M1 reduced remarkably, including AUC, MRT, C_max and CL_z/F.

CONCLUSION

CYP3A4 genetic polymorphism and nimodipine affect the metabolism of istradefylline. Thus, the present study provided reference data for clinical individualized medicine of istradefylline.

Nimodipine Attenuates Early Brain Injury by Protecting the Glymphatic System After Subarachnoid Hemorrhage in Mice

The glymphatic system (GS) plays an important role in subarachnoid hemorrhage (SAH). Nimodipine treatment provides SAH patients with short-term neurological benefits. However, no trials have been conducted to quantify the relationship between nimodipine and GS. We hypothesized that nimodipine could attenuate early brain injury (EBI) after SAH by affecting the function of the GS. In this study, we assessed the effects of nimodipine, a dihydropyridine calcium channel antagonist, on mice 3 days after SAH. The functions of GS were assessed by immunofluorescence and western blot. The effects of nimodipine were assessed behaviorally. Concurrently, correlation analysis was performed for the functions of GS, immunofluorescence and behavioral function. Our results indicated that nimodipine improved GS function and attenuated neurological deficits and brain edema in mice with SAH. Activation of the cAMP/PKA pathway was involved in this process. GS function was closely associated with perivascular AQP4 polarization, cortical GFAP/AQP4 expression, brain edema and neurobehavioral function. In conclusion, this study shows for the first time that nimodipine plays a neuroprotective role in the period of EBI after SAH in mice through the GS.

Characterization of the zebrafish (Danio rerio) mineralocorticoid receptor

Comparison between evolutionarily distant receptors can provide critical insights into both structure and function. Sequence comparison between the mineralocorticoid receptors (MR) of the zebrafish (zMR) and human (hMR) reveals a high degree of sequence conservation in the major functional domains. We isolated a zMR cDNA to contrast the transcriptional response to a range of ligands and to establish whether a teleost MR exhibits the amino/carboxyl-terminal interaction (N/C-interaction) previously reported for the hMR. Aldosterone, deoxycorticosterone (DOC) and cortisol induced zMR transcriptional activity with similar efficacy to that observed with the hMR. The hMR antagonist, spironolactone, acted as an agonist with the zMR. The zMR exhibited an N/C-interaction in response to aldosterone but, in contrast to the hMR, cortisol and DOC predominantly stimulated the interaction in the zMR. Conservation of the N/C-interaction between evolutionarily distant MR provides evidence of functional significance.

Chronic benzodiazepine-induced reduction in GABA(A) receptor-mediated synaptic currents in hippocampal CA1 pyramidal neurons prevented by prior nimodipine injection

One week oral flurazepam (FZP) administration in rats results in reduced GABA(A) receptor-mediated synaptic transmission in CA1 pyramidal neurons associated with benzodiazepine tolerance in vivo and in vitro. Since voltage-gated calcium channel (VGCC) current density is enhanced twofold during chronic FZP treatment, the role of L-type VGCCs in regulating benzodiazepine-induced changes in CA1 neuron GABA(A) receptor-mediated function was evaluated. Nimodipine (10 mg/kg, i.p.) or vehicle (0.5% Tween 80, 2 ml/kg) was injected 1 day after ending FZP treatment and 24 h prior to hippocampal slice preparation for measurement of mIPSC characteristics and in vitro tolerance to zolpidem. The reduction in GABA(A) receptor-mediated mIPSC amplitude and estimated unitary channel conductance measured 2 days after drug removal was no longer observed following prior nimodipine injection. However, the single nimodipine injection failed to prevent in vitro tolerance to zolpidem's ability to prolong mIPSC decay in FZP-treated neurons, suggesting multiple mechanisms may be involved in regulating GABA(A) receptor-mediated synaptic transmission following chronic FZP administration. As reported previously in recombinant receptors, nimodipine inhibited synaptic GABA(A) receptor currents only at high concentrations (>30 muM), significantly greater than attained in vivo (1 muM) 45 min after a single antagonist injection. Thus, the effects of nimodipine were unlikely to be related to direct effects on GABA(A) receptors. As with nimodipine injection, buffering intracellular free [Ca(2+)] with BAPTA similarly prevented the effects on GABA(A) receptor-mediated synaptic transmission, suggesting intracellular Ca(2+) homeostasis is important to maintain GABA(A) receptor function. The findings further support a role for activation of L-type VGCCs, and perhaps other Ca(2+)-mediated signaling pathways, in the modulation of GABA(A) receptor synaptic function following chronic benzodiazepine administration, independent of modulation of the allosteric interactions between benzodiazepine and GABA binding sites.

Effect of baicalin and berberine on transport of nimodipine on primary-cultured, rat brain microvascular endothelial cells

AIM

To investigate whether baicalin and berberine affects the transport of nimodipine (NMD) across the blood-brain barrier (BBB).

METHODS

Primary-cultured, rat brain microvascular endothelial cells (rBMEC) were used as an in vitro model of the BBB. When cells became confluent, the steady-state uptake of NMD by rBMEC with or without baicalin and berberine was measured. The effects of baicalin and berberine on the efflux of NMD from rBMEC were also studied.

RESULTS

Baicalin (2-5 microg/mL) increased the uptake of NMD, and baicalin (10-20 microg/mL) decreased the uptake. The steady-state uptake of NMD was higher than that of control group in the presence of 0.01-1 microg/mL berberine, but was lower in the presence of 2-10 microg/mL berberine.

CONCLUSION

The bidirectional effect of baicalin and berberine on the uptake of NMD by rBMEC was found. Higher concentration showed an inhibitory effect, and lower concentration demonstrated an increasing effect.

Single photon emission computed tomography and positron emission tomography imaging of multi-drug resistant P-glycoprotein--monitoring a transport activity important in cancer, blood-brain barrier function and Alzheimer's disease

Overexpression of multi-drug resistant P-glycoprotein (Pgp) remains an important barrier to successful chemotherapy in cancer patients and impacts the pharmacokinetics of many important drugs. Pgp is also expressed on the luminal surface of brain capillary endothelial cells wherein Pgp functionally comprises a major component of the blood-brain barrier by limiting central nervous system penetration of various therapeutic agents. In addition, Pgp in brain capillary endothelial cells removes amyloid-beta from the brain. Several single photon emission computed tomography and positron emission tomography radiopharmaceutical have been shown to be transported by Pgp, thereby enabling the noninvasive interrogation of Pgp-mediated transport activity in vivo. Therefore, molecular imaging of Pgp activity may enable noninvasive dynamic monitoring of multi-drug resistance in cancer, guide therapeutic choices in cancer chemotherapy, and identify transporter deficiencies of the blood-brain barrier in Alzheimer's disease.

Interaction of verapamil with lipid membranes and P-glycoprotein: connecting thermodynamics and membrane structure with functional activity

Verapamil and amlodipine are calcium ion influx inhibitors of wide clinical use. They are partially charged at neutral pH and exhibit amphiphilic properties. The noncharged species can easily cross the lipid membrane. We have measured with solid-state NMR the structural changes induced by verapamil upon incorporation into phospholipid bilayers and have compared them with earlier data on amlodipine and nimodipine. Verapamil and amlodipine produce a rotation of the phosphocholine headgroup away from the membrane surface and a disordering of the fatty acid chains. We have determined the thermodynamics of verapamil partitioning into neutral and negatively charged membranes with isothermal titration calorimetry. Verapamil undergoes a pK-shift of DeltapK(a) = 1.2 units in neutral lipid membranes and the percentage of the noncharged species increases from 5% to 45%. Verapamil partitioning is increased for negatively charged membranes and the binding isotherms are strongly affected by the salt concentration. The electrostatic screening can be explained with the Gouy-Chapman theory. Using a functional phosphate assay we have measured the affinity of verapamil, amlodipine, and nimodipine for P-glycoprotein, and have calculated the free energy of drug binding from the aqueous phase to the active center of P-glycoprotein in the lipid phase. By combining the latter results with the lipid partitioning data it was possible, for the first time, to determine the true affinity of the three drugs for the P-glycoprotein active center if the reaction takes place exclusively in the lipid matrix.

Adhesion forces measured between a calcium blocker drug and its receptor in living cells using atomic force microscope

The adhesion force between the tip of an atomic force microscope cantilever derivatized with nimodipine (a calcium blocker, from the dihydropyridine class, currently used in clinical medicine for hypertension) and living cells of Saccharomyces cerevisiae (unicellular eukaryotes which portray ultrastructural features characteristic of higher eukaryotic cells) was measured. This methodology allowed us to locate (and visualize) pores on the cell surface which may be responsible for calcium transportation in the living cells. The interaction of the cantilever derivatized with the calcium blocker and a pore, which can be a calcium channel, is more intense than a non-derivatized cantilever and the pore. Outside the pore (on the rest of cell surface), a derivatized or a non-derivatized cantilever has the same pattern of adhesion force. The information obtained with this method is very important for the design of new, more potent and less toxic drugs for pharmacological use.

Antioxidant activity of different dihydropyridines

Lacidipine, a dihydropyridine-based calcium antagonist (DHP), has already been demonstrated to possess antioxidant activity and to reduce the intracellular production of reactive oxygen species (ROS). To verify if this effect is a peculiarity of this molecule, or belongs to other DHPs, the activity of lacidipine was compared with those of amlodipine, lercanidipine, nimodipine, and nifedipine. The DHPs were incorporated in bovine aortic endothelial cells (BAECs). Cu(2+)-oxidized LDL (ox-LDL, 5 microM) was incubated with BAECs for 5 min. 2',7'-Dichlorofluorescein (DCF) as expression of intracellular ROS production was measured by flow cytometry. Ox-LDL induced a strong increase in intracellular ROS formation (p<0.001) that was significantly reduced only with lacidipine and lercanidipine (p from <0.05 to <0.01); the effect of lacidipine, however, resulted in being much more evident than lercanidipine (p<0.01); amlodipine, nimodopine, and nifedipine had no effect on ROS formation. The lowest IC50s, i.e. the concentrations determining the 50% reduction of ROS, were obtained with lacidipine (p<0.01). The inhibitory effect of lacidipine on ox-LDL-induced ROS production in endothelial cells is a peculiarity of this molecule through its antioxidant activity.

[Pharmaceutical chemistry of "dipines"]

The paper gives an overview on the pharmaceutical chemistry of of dihydropyridine Ca-antagonists through the chapters of history and preparation, structure and properties, metabolism, therapeutical use and analysis. In the author's concept the paper represents a model for postgraduate education. Consequently, after proper volume-cutting, it covers the complete material for undergraduate courses.

Nimodipine affects the microcirculation and modulates the vascular effects of acetylcholinesterase inhibition

The present investigation was undertaken in order to study whether microvascular effects of the calcium antagonist nimodipine induces changes that can explain an increased detoxification of the highly toxic cholinesterase inhibitor soman. Anaesthetised, tracheotomised and artificially ventilated rats were treated intra-peritoneally (ip) with nimodipine, 10 mg kg(-1) or vehicle followed one hour later by the exposure to 45 microg kg(-1) soman (iv). Nimodipine per se induced a vasodilation in the intestine, myocardium and other muscles. In the abdominal skin soman elicited a significant vasoconstriction that was turned into an increased blood flow after nimodipine pre-treatment. A slight vasoconstriction in diaphragm of soman intoxicated rats was turned into a significant vasodilation by nimodipine pre-treatment. In the intestinal parts no effect of soman was detected. However, in nimodipine pretreated animals soman induced a significant vasoconstriction. The capacity of soman detoxifying processes, i.e. enzymatic hydrolysis and covalent binding to different esterases, is unequally distributed throughout the body. Together with the knowledge of the detoxifying processes of cholinesterase inhibition the results support our theory, that nimodipine alters the peripheral blood flow in a beneficial way resulting in improved detoxification ability.

In vivo evaluation of modified gum karaya as a carrier for improving the oral bioavailability of a poorly water-soluble drug, nimodipine

This work examines the influence of modified gum karaya (MGK) on the oral bioavailability of a poorly water-soluble drug, nimodipine (NM), in comparison with that of gum karaya (GK). A cogrinding method was selected to prepare mixtures of NM and GK or MGK in a 1:9 ratio (NM:GK/MGK). Differential scanning calorimetry (DSC), Fourier transmission infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), solubility studies, and in vitro release studies were performed to characterize the properties of the cogrinding mixtures. No drug-carrier interactions were found, as confirmed by DSC and FT-IR studies. The XRD study revealed that the crystallinity of NM was identical in both the cogrinding mixtures and was decreased when compared to that of physical mixtures or pure NM. The in vitro release rate of NM from both cogrinding mixtures was significantly higher than that of physical mixtures or pure NM. The in vivo study revealed that the bioavailability of NM from pure drug was significantly lower when compared to the cogrinding mixtures. The oral bioavailability was found to be NM powder < cogrinding mixtures of NM and GK < cogrinding mixtures of NM and MGK < NM solution. It can be inferred from the above results that MGK, an economical carrier, could be used for the dissolution enhancement of NM.

Nifedipine and nimodipine competitively inhibit uridine kinase and orotidine-phosphate decarboxylase: theoretical relevance to poor outcome in stroke

Nifedipine and nimodipine, dihydropyridine calcium channel blockers, are commonly used as antihypertensive and antianginal agents in patients at risk for stroke. At least one stroke trial suggests that patients receiving calcium channel blockers at the time of an acute stroke have worse outcomes than those receiving other or no antihypertensive medications. We hypothesize that the poor outcome may not be related to blood pressure changes but instead may be mediated by competitive inhibition of important enzymes of pyrimidine synthesis whose products are needed to repair nerve cell membranes after an acute stroke. Both drugs acted as competitive inhibitors of the only enzymes that are known to synthesize the nucleotide uridine-5'-phosphate: uridine kinase and orotidine-5'-phosphate decarboxylase. Nifedipine produced Ki values of 28 microM for uridine kinase and 105 microM for orotidine-5'-phosphate decarboxylase. Nimodipine produced Ki values of 20 microM for uridine kinase and 18 microM for orotidine-5'-phosphate decarboxylase. For uridine kinase, these inhibitors bound more tightly than the physiologic substrates uridine or cytidine. For the decarboxylase, the inhibitors bound less tightly than the normal physiologic substrate orotidine-5'-phosphate. Additional experiments are needed to determine whether the concentrations of nifedipine or nimodipine, and of cytidine, uridine, and orotidine-5'-phosphate in human brain, are such that this inhibition would affect stroke outcome.

Enzyme kinetics and inhibition of nimodipine metabolism in human liver microsomes

AIM

To study the enzyme kinetics of nimodipine (NDP) metabolism and the effects of selective cytochrome P-450 (CYP-450) inhibitors on the metabolism of NDP in human liver microsomes in vitro.

METHODS

Microsomes from six individual human liver specimens were used to perform enzyme kinetic studies and the kinetic parameters were estimated by Eadie-Hofstee equation. Various selective CYP-450 inhibitors were used to investigate their effects on the metabolism of NDP and the principal CYP-450 isoform involved in dehydrogenation of dihydropyridine ring of NDP in human liver microsomes.

RESULTS

There was an important intersubject variability in NDP metabolism in human liver microsomes. For NDP dehydrogenase activity, the Km value was (36 +/- 11) mumol and the Vm value was (17 +/- 7) mumol.g-1.min-1. The dehydrogenation of dihydropyridine ring of NDP was competitively inhibited by ketoconazole (Ket) and troleandomycin (TAO), and the Ki values for Ket and TAO were 0.59 and 122.2 mumol, respectively. Phenacetin (Pnt), quinidine (Qui), diethyldithiocarbamate (DDC), sulfaphenazole (Sul), and tranylcypromine (Tra) had a little or no inhibitory effects on the dehydrogenation of NDP.

CONCLUSION

The intersubject variability of NDP pharmacokinetics was attributed to the metabolic polymorphism of NDP in liver. Cytochrome P-4503A (CYP3A) is involved in the dehydrogenation of dihydropyridine ring of NDP.

Increase in receptor binding affinity for nimodipine in the rat brain with permanent occlusion of bilateral carotid arteries

The permanent occlusion of bilateral common carotid arteries (2VO) in rats has been shown to cause progressive and long-lasting cognitive deficits which may be due to impairment of memory retention and/or memory recall process. To clarify the function of voltage dependent calcium channels and the receptor binding of nimodipine by chronic cerebral ischemia, we examined specific (+)-[3H]PN 200-110 binding and the effect of oral administration of nimodipine in brain regions and hearts of rats, at 2 weeks to 4 months after permanent 2VO. There was no significant difference in either dissociation constant (Kd) or maximal number of binding sites (Bmax) for (+)-[3H]PN 200-110 in the cerebral cortex, hippocampus, corpus striatum and thalamus between 2VO and sham rats. In addition, in vitro inhibitory effect of nimodipine on cerebral cortical (+)-[3H]PN 200-110 binding in 2VO rats was similar to that in sham rats. Compared to control rats, oral administration of nimodipine to both 2VO and sham rats at 2 months after permanent 2VO brought about a significant increase in Kd values of specific (+)-[3H]PN 200-110 binding in the cerebral cortex, hippocampus, thalamus and myocardium, and the increase in Kd values was much larger in brain regions of 2VO rats than sham rats. However, the increase in Kd values in the myocardium did not differ between 2VO and sham rats. This observation suggests an increased in vivo binding affinity for nimodipine in chronic ischemic brain. In conclusion, the present study has shown that oral administration of nimodipine may cause a greater occupation in vivo of 1,4-dihydropyridine (DHP) calcium channel antagonist receptors in brains of permanent 2VO rats than in sham rats. Thus, nimodipine may be pharmacologically effective in preventing brain dysfunction due to cerebral ischemia in vivo.

Long-term effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate and 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione in the rat basal ganglia: calcification, changes in glutamate receptors and glial reactions

Previous data from our laboratory indicate that 25 mM ibotenic acid induces intracellular calcifications in the rat basal forebrain. Because of the lack of specificity of ibotenic acid for a glutamate receptor subtype, a dose-response study with alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate was undertaken and calcified areas (identified with Alizarin Red staining) as well as astro- and microglial reactions (by autoradiography with [3H]lazabemide and [3H]Ro 5-4864) were quantified at one month post-lesion. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole propionate administered into the globus pallidus induced, in a dose-dependent manner, the formation of calcium deposits and the activation of both glial cells, the microglial reaction being particularly robust. From this study, a dose of 5.4 mM alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate was selected for further experiments. [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate, [3H]dizocilpine maleate and [3H]PN 200-110 binding in vitro were performed to assess autoradiographically whether the tissue damage was associated with changes in glutamate receptors and calcium channel binding sites. In the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-treated animals, the specific binding of [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate was significantly reduced by 28% in the lesioned ventral pallidum, whereas it was unchanged in the globus pallidus and substantia innominata. In these three nuclei, calcifications developed and an increase in both glial markers was measured. In contrast, the binding of [3H]PN 200-110 and [3H]dizocilpine maleate were unaffected. Co-injection of 15 mM 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione, a selective alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate receptor antagonist, prevented the formation of calcium concretions, the microglial reaction and the decrease in [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate binding but it failed to inhibit totally the astroglial reaction induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate. This may suggest that the microglial reaction and calcification take place through different mechanisms from the astrogliosis associated with the neuronal loss. In conclusion, acute administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate in the rat globus pallidus elicits a dose-dependent calcification process associated with a chronic reaction of astrocytes and microglia. alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-induced injury is accompanied by a slight reduction of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors in the ventral pallidum, whereas the binding of N-methyl-D-aspartate and L-type calcium channels receptors remains unchanged in any lesioned nucleus.

Autoradiographic [3H]nimodipine distribution after experimental spinal cord injury in rats

Because of its potential for augmentation of blood flow and protection of neurons after neurological insult, nimodipine has been investigated as a treatment of spinal cord injury (SCI). The results have been inconsistent, possibly because of poor delivery of nimodipine to the injured spinal cord. The following study was designed to determine the delivery of nimodipine to the injured spinal cord. It was also hoped that information about the temporal and spatial pattern of binding of nimodipine after SCI might further elucidate the relationship between calcium channel activation and injury. Fourteen female Wistar rats were divided into three groups: control (n = 3), 30 min post-SCI (n = 6); and 4 h post-SCI (n = 5). The injury was produced by acute clip compression for 1 min at T1. [3H]Nimodipine was administered 5 min after laminectomy in the control group, and at the above-specified times after injury in the SCI groups. The drug was then allowed to equilibrate for 30 min before the animals were killed. The spatial patterns and concentrations of [3H]nimodipine in various segments of the spinal cord were autoradiographically determined. The highest concentrations of [3H]nimodipine were at the injury site after SCI. Also, the mean [3H]nimodipine concentrations in all sites in each animal were higher in the injury groups than in the control group (p < 0.05). This study indicates that delivery of this agent to the injured cord is possible, and provides evidence of widespread Ca2+ channel activation in the first 4 h after injury.

Interactions of cocaine with nimodipine: a brief report

This double blind, placebo controlled study of acute calcium channel antagonist use during cocaine administration in five patients found that 60 mg of nimodipine treatment attenuated the systolic, but not diastolic, blood pressure effects of cocaine. In three subjects, a 90 mg dose of nimodipine showed a greater attenuation than that of 60 mg. Subjective effects of cocaine were not altered by either dose of nimodipine.

Multidrug resistance transporter P-glycoprotein has distinct but interacting binding sites for cytotoxic drugs and reversing agents

P-Glycoprotein, the plasma membrane protein responsible for the multidrug resistance of some tumour cells, is an active transporter of a number of structurally unrelated hydrophobic drugs. We have characterized the modulation of its ATPase activity by a multidrug-resistance-related cytotoxic drug, vinblastine, and different multidrug-resistance-reversing agents, verapamil and the dihydropyridines nicardipine, nimodipine, nitrendipine, nifedipine and azidopine. P-Glycoprotein ATPase activity was measured by using native membrane vesicles containing large amounts of P-glycoprotein, prepared from the highly multidrug-resistant lung fibroblasts DC-3F/ADX. P-Glycoprotein ATPase is activated by verapamil and by nicardipine but not by vinblastine. Among the five dihydropyridines tested, the higher the hydrophobicity, the higher was the activation factor with respect to the basal activity and the lower was the half-maximal activating concentration. The vinblastine-specific binding on P-glycoprotein is reported by the inhibitions of the verapamil- and the nicardipine-stimulated ATPase. These inhibitions are purely competitive, which means that the bindings of vinblastine and verapamil, or vinblastine and nicardipine, on P-glycoprotein are mutually exclusive. In contrast, verapamil and nicardipine display mutually non-competitive interactions. This demonstrates the existence of two distinct specific sites for these two P-glycoprotein modulators on which they can bind simultaneously and separately to the vinblastine site. The nicardipine-stimulated ATPase activity in the presence of the other dihydropyridines shows mixed-type inhibitions. These dihydropyridines have thus different binding sites that interact mutually to decrease their respective, separately determined affinities. This could be due to steric constraints between sites close to each other. This is supported by the observation that vinblastine binding is not mutually exclusive with nifedipine or nitrendipine binding, whereas it is mutually exclusive with nicardipine. Moreover, verapamil binding also interacts with the five dihydropyridines by mixed inhibitions, with different destabilization factors. On the whole our enzymic data show that P-glycoprotein has distinct but interacting binding sites for various modulators of its ATPase function.

Regional activation of L-type voltage-sensitive calcium channels in experimental thiamine deficiency

During pyrithiamine-induced thiamine deficiency (PTD), specific regions of the brain develop histological damage. The basis of this selective vulnerability is unknown but the mechanism may involve a glutamate-mediated excitotoxic process in affected structures, leading to alterations in membrane potential and disturbances in calcium homeostasis. In this study, we have examined the volume of distribution of [3H]nimodipine, an L-type voltage-sensitive calcium channel (VSCC) antagonist, in the brain of the PTD rat. An increase in specific binding of [3H]nimodipine was detected only in the posterior thalamus at the symptomatic stage, immediately following the loss of righting reflexes (P < 0.0001). There was also an increase in nonspecific binding in the medial geniculate and inferior colliculi. Replenishment with thiamine at the symptomatic stage returned [3H]nimodipine binding to normal levels. These findings provide evidence that depolarization and activation of L-type VSCCs occur in the posterior thalamus and may contribute to the appearance of histological lesions in this structure during experimental thiamine deficiency.

In vivo uptake of [3H]nimodipine in focal cerebral ischemia: modulation by hyperglycemia

Cell membrane depolarization and tissue acidosis occur rapidly in severely ischemic brain. Preischemic hyperglycemia is recognized to increase ischemic tissue acidosis and the present studies were undertaken to correlate depolarization and tissue acidosis during acute focal cerebral ischemia and hyperglycemia. We used a dual-label autoradiography method to simultaneously measure the in vivo distribution of [3H]nimodipine and [14C]DMO (5,5-dimethyl-2,4-oxazolidinedione) in brain to identify regions of ischemic depolarization and measure regional net tissue pH. Regional cerebral blood flow (CBF) was measured in separate studies. Measurements were made 30 minutes after combined middle cerebral artery and ipsilateral common carotid artery occlusion in normoglycemic and hyperglycemic rats. Tissue pH in the ischemic cortex was depressed to 6.76 +/- 0.11 in normoglycemic rats (n = 12) and 6.57 +/- 0.13 in hyperglycemic rats (n = 12), with significantly greater acidosis in the hyperglycemic group (P < 0.001). In contrast the ratio of [3H]nimodipine uptake in the ischemic cortex relative to the contralateral nonischemic cortex was significantly greater in normoglycemic (1.83 +/- 0.45) than hyperglycemic (1.40 +/- 0.50) rats (P < 0.05). Within this region of ischemic cortex CBF was 31 +/- 22 mL/100 g in normoglycemic rats (n = 8) and 33 +/- 22 mL/100 g/min in hyperglycemic rats (n = 9). Cerebral blood flow did not differ between these two groups in any region. Thus hyperglycemia reduced the extent of ischemic depolarization within the cortex during the first 30 minutes of focal cerebral ischemia. This effect may be related to the increased tissue acidosis or to other factors that may lessen calcium influx and preserve cellular energy stores in the ischemic cortex of the hyperglycemic rats.

Age-related changes in [3H]nimodipine and [3H]rolipram binding in the rat brain

Ageing is associated with changes in neurotransmission which might be correlated with abnormal calcium metabolism. Because there is evidence that nimodipine can enhance the learning abilities of ageing animals and rolipram can enhance the excitability of neurons, providing a functional basis for cognition-enhancing activity, age-related alterations in the binding of voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic adenosine monophosphate-selective phosphodiesterase (cyclic-AMP PDE) were studied in 3-week- and 6-, 12-, 18- and 24-month-old Fisher 344 rats by use of receptor autoradiography. [3H]Nimodipine and [3H]rolipram were used to label the voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic-AMP PDE, respectively. [3H]Nimodipine binding showed no obvious change in all brain areas of 12- and 18-month-old rats, as compared with 6-month-old animals. In 24-month-old rats, however, [3H]nimodipine binding increased significantly in the striatum and hippocampal CA3 sector. In contrast, [3H]rolipram binding showed no significant change in most brain areas during ageing, except for a transient change only in the hippocampal CA1 sector of 12-month-old animals. [3H]Nimodipine and [3H]rolipram binding showed a significant increase in some brain areas of 3-week-old rats compared with 6-month-old animals. The results indicate that in rats voltage-dependent L-type calcium channels are more susceptible to ageing processes than calcium/calmodulin-independent cyclic-AMP PDE. Our data also demonstrate that voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic-AMP PDE might play roles in developmental processes. These findings might help further elucidation of the relationship between age-related neurological deficits and behavioural pharmacology including cognitive function.

Evaluation of a novel nimodipine delivery system in conscious rats that allows sustained release for 24 h

Methodologies that allow prolonged drug administration in animal models, while minimizing surgery and anesthesia, are an important contribution towards studies in awake conditions. Commercially available drug delivery systems like pellets can be customized for the evaluation of experimental therapies with minimal or no discomfort to animals. Our objective was to evaluate pharmacokinetic and physiologic parameters after subcutaneous implantation of rapid 24 h release nimodipine pellets in rats for their potential use as a delivery system for stroke therapeutics. A day prior to the study Sprague-Dawley rats were anesthetized (halothane, N2O, O2) for femoral vessel cannulation and later returned to their cages. On the day of the study the rats were briefly anesthetized (identical regimen as before), and assigned to two groups: nimodipine (NP) and placebo (PL). NP rats received either 0.5 (n = 4), 1 (n = 3), 2 (n = 2), 4 (n = 2), or 15 (n = 5) mg pellets (Innovative Research of America Inc., Sarasota, FL, USA) and PL, rats (n = 5) received placebo pellets. Nimodipine plasma levels were measured at 1, 3, and 6 h. In addition, the 15 mg NP group was followed at 18 and 24 h. Immediately following decapitation the brain was removed for later determination of nimodipine tissue concentration. The NP 15 mg group showed a significant decline of 10% in MABP from base line to 24 h post implantation (p < 0.001). All NP animals achieved at least 83% of their highest plasma concentration at 1 h and 94% at 3 h. A high degree of correspondence (r2 = 0.95, y = 0.36 + 0.28x, n = 16) between the plasma and brain concentrations of nimodipine was present. Although a significant drop in MABP was observed the drop was no greater than 10% in 24 h. Plasma nimodipine levels for the 15 mg animals were within the cerebrovascular effective range. This is the first report to show that 24 h release nimodipine pellets subcutaneously implanted in rats are a reliable delivery system that allows rapid rise and constant nimodipine plasma levels. Therefore, 24 h release pellets are a suitable alternative to other delivery systems like osmotic pumps.

Responses to calcium and binding of 3H-nimodipine in the atrioventricular node, atria, and ventricles of mature and old male Fischer 344 rats

To determine whether aging alters cardiac calcium dose responses or dihydropyridine receptor density or affinity, we performed (a) calcium (Ca2+) dose-response studies (3-5 mM) in Langendorff perfused hearts from 12 mature (4-7 month) and 12 old (23-27 month) Fischer 344 rats, and (b) quantitative autoradiography experiments with 3H-nimodipine (50-3,000 pM) in 20-microns tissue sections containing the compact AV node from hearts of eight mature and eight old F344 rats. Baseline AA interval, AV conduction time, AV Wenckebach block cycle length, and QRS duration were prolonged in isolated hearts from old compared with mature rats. In contrast, neither left ventricular developed pressure nor peak dP/dt was altered by age. Perfusion with increasing concentrations of Ca2+ produced decreased coronary perfusion (p < 0.001) without age-related alterations in AA intervals, AV conduction times, dP/dt, or left ventricular developed pressure. No age-related differences in AV node 3H-nimodipine binding (Bmax: mature, 1.35 +/- 0.41 fmol/mm2; old, 1.33 +/- 0.43 fmol/mm2) or affinity (Kd: mature, 915 +/- 375 pM; old, 973 +/- 369 pM) were detected. Similarly, no age-related differences in 3H-nimodipine receptor number or affinity were detected in left and right ventricular or atrial tissue. Total protein in atrial and ventricular tissue was unchanged with age. However, left atrial and left ventricular isolated membrane protein was significantly lower in senescent compared with mature rat hearts (left ventricle: mature, 49.4 +/- 8.7 mg/g; old, 40.9 +/- 3.5 mg/g; p < 0.05; left atria: mature, 36 +/- 9 mg/g; old, 28 +/- 3 mg/g; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro binding of [3H]nimodipine and [3H]CGS-19755 to rat brain in focal cerebral ischemia

Focal cerebral ischemia results in increased in vivo binding of calcium channel antagonists to both the L-type voltage sensitive calcium channel (VSCC) and the N-methyl-D-aspartate (NMDA) receptor-linked calcium channel. It was the aim of this study to investigate the effect of focal cerebral ischemia on the in vitro binding of calcium channel antagonists to rat brain. Quantitative autoradiography was used to measure regional in vitro binding of the L-type VSCC antagonist [3H]nimodipine and the competitive NMDA receptor antagonist [3H]CGS-19755 to rat brain following 4 h of irreversible focal cerebral ischemia. [3H]Nimodipine binding to the nonischemic hemisphere was characterized by one binding site with regional binding affinity (KD) estimates ranging from 221 to 482 pM and maximal binding site densities (BMAX) ranging from 13.2 (9.6-17.5) pmol/g tissue (estimate and 95% confidence interval) in CA1 to 32.5 (26.5-39.9) pmol/g tissue in dentate. [3H]CGS-19755 binding to the nonischemic hemisphere was characterized by KD estimates ranging from 59 to 97 nM and BMAX values ranging from 143 (108-192) pmol/g tissue in cortex to 569 (515-641) pmol/g tissue in CA1. For [3H]CGS-19755 a model of two binding sites was applicable in several brain regions. No difference in binding site densities or binding affinities between ischemic and paired nonischemic structures (cortex and striatum) was observed with either ligand. In vitro binding of [3H]nimodipine and [3H]CGS-19755 to ischemic brain failed to identify ischemic-induced changes in calcium channel function previously reported by in vivo binding methods.

In vivo binding of [3H]nimodipine in rat brain after transient forebrain ischemia

We report the regional variation in relative in vivo binding of the L-type voltage sensitive calcium channel (VSCC) antagonist [3H]nimodipine to brain following transient forebrain ischemia in the rat. At 30-min of reperfusion after 20 min of forebrain ischemia, [3H]nimodipine binding was significantly increased in striatum, CA3 and CA4, and dentate relative to binding in sham-operated rats, suggesting that VSCCs were responding to ischemic depolarization. Two h following ischemia, binding in all brain structures returned to normal levels indicating repolarization of cell membranes. At 24 h of recirculation, increased [3H]nimodipine binding was again observed in striatum and dentate. Binding remained elevated in the striatum and dentate, and increased binding became evident in the CA1 region of the hippocampus after 48 h of reperfusion. With the exception of the dentate gyrus, the second rise in [3H]nimodipine binding anticipated or coincided with the observed regional ischemic cell changes. These observations in global cerebral ischemia support previous work indicating that in vivo binding of [3H]nimodipine to the L-type VSCC may be an early and sensitive indicator of impending ischemic injury. Such measurements may be of use in identifying vulnerable brain regions and defining a therapeutic window of opportunity in models of cerebral ischemia.

Blockade by calmodulin inhibitors of Ca2+ channels in smooth muscle from rat vas deferens

1. Effects of three compounds which are used as calmodulin inhibitors (trifluoperazine, W-7 and calmidazolium) on Ca2+ channels were investigated in smooth muscle from rat vas deferens. 2. All three calmodulin inhibitors relaxed the smooth muscle precontracted by a high concentration of KCl (63.7 mM). The order of potency for the relaxation was trifluoperazine > W-7 > calmidazolium. 3. In binding studies using a microsomal fraction of vas deferens, all these calmodulin inhibitors displaced specific [3H]-nimodipine binding. Trifluoperazine and W-7 inhibited the binding at concentrations that relaxed the smooth muscle whereas calmidazolium inhibited at concentrations much lower than those necessary for muscle relaxation. 4. Ba2+ current flowing through voltage-gated Ca2+ channels was measured under whole-cell voltage-clamp conditions in isolated smooth muscle cells. The Ba2+ current was suppressed by the three calmodulin inhibitors in the concentration-range where inhibition of [3H]-nimodipine binding was observed. Neither voltage-dependence nor the inactivation time course of Ba2+ current were affected by these compounds. 5. The results suggest that the calmodulin inhibitors directly block Ca2+ channels in the smooth muscle cells. The channel inhibition by trifluoperazine and W-7, but perhaps not that by calmidazolium, may be responsible for the muscle relaxation observed with these compounds.

Voltage sensitive calcium channels mark a critical period in mouse neurodevelopment

Voltage sensitive calcium channel (VSCC) probes 125I-omega-GVIA Conotoxin (omega-GVIA), (+)-[5-methyl-3H]-PN200-110 (3H-PN200), and 3H-Nimodipine were bound to developing Swiss Webster mouse whole brain from postnatal days 3 to 24. 125I-omega-GVIA binding, thought to be presynaptic, showed a 50% increase between days 11 and 14. 3H-dihydropyridine binding, thought to be postsynaptic, showed spike patterns when measured developmentally. 3H-PN200 binding showed a > 150% increase between days 11 and 15. 3H-Nimodipine binding showed a > 100% increase between days 11 and 14. Depolarization-induced 45Ca fluxes also increased between days 8 and 16 by > 500%. The dramatic increases indicated by these binding data correspond to a critical period described by Himwich (Int. Rev. Neurobiol. 4, 117, 1962) between postnatal days 11 and 14 in Swiss Webster mice; during this critical period, dendrites exhibit rapid outgrowth, sensory modalities come on line, EEG patterns mature, and the cortex reaches adult proportions. We conclude from these data that the increase in VSCC activity parallels a critical period in the development of the central nervous system in Swiss Webster mice.

Reversibility of nimodipine binding to brain in transient cerebral ischemia

Using autoradiography, we have measured the in vivo binding of [3H]nimodipine to brain in a rat model of reversible cerebral ischemia. Ischemia was induced by simultaneous occlusion of the middle cerebral artery (MCA) and ipsilateral common carotid artery by microaneurysm clips. Rats were studied after 15 min of ischemia (ischemic group) or after 45 min of reperfusion following 15 min of ischemia (reperfused group). Regional cerebral blood flow (CBF) was determined autoradiographically using [14C]iodoantipyrine in both ischemic (n = 6) and reperfused (n = 6) groups. During ischemia blood flow in the territory of the MCA was depressed and recovered to normal only in the distal territory of the MCA following reperfusion. [3H]Nimodipine binding in the ischemic group (n = 12) was elevated in ischemic brain regions and declined significantly (p < 0.01) in these regions in the reperfused group (n = 11). The ratio of the volume of cortex showing increased binding to the total volume of the forebrain was 0.113 +/- 0.025 (mean +/- SD) in the ischemic group and declined to 0.080 +/- 0.027 following reperfusion (p < 0.005). In general, infarct was only observed in regions showing persistent elevation of nimodipine binding following reperfusion as determined by histology performed in a separate group of rats (n = 8) after 24 h of reperfusion. We conclude that increased nimodipine binding to ischemic tissue is initially reversible with prompt reestablishment of CBF and is a sensitive indicator of early and reversible ischemia-induced cerebral dysfunction.

Molecular basis for the inhibition of 1,4-dihydropyridine calcium channel drugs binding to their receptors by a nonspecific site interaction mechanism

The "membrane bilayer" pathway (Rhodes, D. G., J. G. Sarmiento, and L. G. Herbette. 1985. Mol. Pharmacol. 27:612-623.) for 1,4-dihydropyridine calcium channel drug (DHP) binding to receptor sites in cardiac sarcolemmal membranes has been extended to include the interaction of amphiphiles within the lipid bilayer. These studies focused on the ability of the Class III antiarrhythmic agents bretylium and clofilium to nonspecifically inhibit DHP-receptor binding in canine cardiac sarcolemma. Clofilium was found to inhibit nimodipine binding with an inhibition constant of approximately 5 microM, whereas bretylium had no effect on nimodipine binding. Small angle x-ray diffraction was then used to examine the differential ability of these two Class III agents to inhibit DHP-receptor binding. The time-averaged locations of bretylium, clofilium, and nimodipine in bovine cardiac phosphatidylcholine (BCPC) bilayers (supplemented with 13 mol% cholesterol) were determined to a resolution of 9 A. The location of bretylium as dominated by its phenyl ring in BCPC bilayers was found to be at the hydrocarbon core/water interface, similar to that of the dihydropyridine ring of nimodipine. The location of clofilium as dominated by its phenyl ring was found to be below the hydrocarbon/core water interface within the hydrocarbon chain region of the bilayer, similar to that of the phenyl ring of nimodipine. The location of the dihydropyridine ring portion of nimodipine has previously been shown by neutron diffraction to be located at the hydrocarbon core/water interface of native sarcoplasmic reticulum, consistent with the small angle x-ray data from model membranes in this paper. Therefore, we speculate that the nonspecific inhibition arises from the interaction of clofilium's phenyl ring with the site on the calcium channel receptor where the phenyl ring portion of nimodipine must interact. The DHP-receptor binding pathway would then involve both nonspecific (membrane) and specific (protein) binding components, both of which are necessary for receptor binding.

In vivo binding of nimodipine in the brain: I. The effect of focal cerebral ischemia

We report the regional variation in [3H]nimodipine binding in vivo during focal cerebral ischemia. After intravenous injection, 30 min of circulation of [3H]nimodipine was sufficient to establish a secular equilibrium of distribution in the brain. Rats sustained left middle cerebral and common carotid artery occlusions for 5 min, and 4, 24, and 48 h (n greater than or equal to 6 epr group). They were decapitated 30 min after injection of 250 microCi of [3H]nimodipine and their brains were submitted to autoradiography. The concentrations of [3H]nimodipine in plasma and brain structures, corrected for metabolism of nimodipine, were used to calculate the regional volumes of distribution (V) in the ischemic left (L) and control right (R) hemispheres. Log (VL/VR) was then defined as the group mean of the logarithms of the left-to-right ratio of V of [3H]nimodipine. In the lateral caudate, binding of [3H]nimodipine on the ischemic side was highest within 5 min of occlusion. Log (VL/VR) in this region for the combined sham-operated and normal control rats and those after 5 min and 4 and 24 h of ischemia were -0.014 +/- 0.025, 0.137 +/- 0.056*, -0.201 +/- 0.367, and -0.049 +/- 0.370 (mean +/- SD, *represents p less than 0.01 compared with controls). By contrast, in the superior frontal cortex, values for log (VL/VR) in the same sequence were -0.016 +/- 0.025, 0.028 +/- 0.056, 0.284 +/- 0.228*, and 0.224 +/- 0.069*, thus showing a significant rise in [3H]nimodipine binding only at 4 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Spin-trapping and antioxidant properties of illuminated and nonilluminated nifedipine and nimodipine in heart homogenate and model system

Nifedipine [1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylic+ ++ acid dimethyl ester] and nimodipine [1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic+ ++ acid 2-methoxyethyl 1-methylethyl ester], incorporated into diheptanoylphosphatidylcholine liposomes, which were used as a drug carrier system, slightly inhibited lipid peroxidation (induced by tert-butylhydroperoxide and Fe2+) in rat heart homogenate. Illumination of nimodipine had no effect on its antioxidant potency, whereas illuminated nifedipine was several times more effective than nonilluminated drug. On illumination, nifedipine converts to 2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridinedicarboxylic acid dimethyl ester (NTP). NTP formed stable radicals when interacting with the rat heart homogenate and dioleoylphosphatidylcholine, as detected by EPR spectroscopy. No radical formation was observed if nonilluminated nifedipine and nimodipine or illuminated nimodipine were used. The spin density of the unpaired electron in the NTP-adduct was centered on the nitrogen derived from its nitroso group. The motion of the NTP-adduct radical was restricted, indicating that the radicals were located in the membrane of the homogenate and not in the buffer system. Only NTP (not nifedipine or nimodipine) was effective in trapping free radicals formed by the thermal or photoinduced decomposition of 2,2'-azobisisobutyronitrile and radicals formed by photolysis of di-tert-butylperoxide. The antioxidant and spin-trapping properties of NTP in our systems were attributed to its nitroso group.

Lack of major effects on mouse brain adenosine A1 receptors of oral carbamazepine and calcium antagonists

Interaction with adenosine A1 receptors is a possible contributory mechanism to the anticonvulsant effects of carbamazepine (CBZ) and the dihydropyridine calcium antagonists. We measured the binding of [3H]cyclohexyladenosine to adenosine A1 receptors in mouse brain stem, cerebellum, and cortex after oral administration of nifedipine, nimodipine (NMD), and CBZ for 7 days and compared the results with binding in control mice. Equilibrium dissociation constant (Kd) and receptor numbers (Bmax) were calculated using Scatchard and saturation isotherm analyses. Mean Kds (SEM) in control brain stem, cerebellum, and cortex were 2.09 (0.31), 2.39 (0.2), and 3.12 (0.28) nM, respectively. Results of Bmax for the same areas were 188 (26), 280 (24), and 449 (54) fmol/mg protein. Nifedipine (p less than 0.005) and NMD (p less than 0.02) raised the Kd of A1 receptors only in the cerebellum, and CBZ increased cerebellar Bmax (p less than 0.05). These minor effects on A1 receptors in CF1 mice, when given in doses previously shown to have anticonvulsant properties in these animals, do not suggest that alteration in A1 receptor activity is an important mechanism for the anticonvulsant effects of these drugs.

Interaction of charged and uncharged calcium channel antagonists with phospholipid membranes. Binding equilibrium, binding enthalpy, and membrane location

The membrane location and the binding mechanism of two Ca2+ channel antagonists, amlodipine and nimodipine, in pure lipid membranes were investigated with deuterium and phosphorus-31 nuclear magnetic resonance, with thermodynamic methods such as high-sensitivity titration calorimetry, and by measuring the membrane surface charge via the zeta-potential. The two drugs exhibit quite different physical-chemical properties. The noncharged nimodipine is strongly hydrophobic, and selective deuteration of the lipid membrane reveals a homogeneous distribution of nimodipine across the whole hydrocarbon layer, but no interaction at the lipid headgroup level. The membrane behavior of the amiphiphilic amlodipine (electric charge z = +1) is distinctly more complex. Deuterium magnetic resonance demonstrates that amlodipine adopts a well-defined position in the bilayer membrane. In particular, the charged ethanolamine side group of amlodipine is located near the water-lipid interface, interacting with the dipoles of the headgroup region according to a nonspecific, electrostatic mechanism and inducing a reorientation of the phosphocholine dipoles toward the water phase. At the level of the hydrocarbon segment, the nonpolar ring system of amlodipine interacts specifically with the cis double bond of the membrane lipid, forming a weak association complex. With increasing amlodipine concentration the deuterium signal of the cis double bond gradually loses intensity, a phenomenon previously observed only in related studies on protein-lipid interactions. The binding equilibrium of amlodipine to phosphatidylcholine membranes was studied by measuring the electrophoretic mobility of lipid vesicles and with a centrifugation assay. Hydrophobic interactions of the nonpolar ring systems and electrostatic repulsions at the membrane surface contribute to the binding energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Nimodipine, a voltage-sensitive calcium channel antagonist, fails to ameliorate light-induced retinal degeneration in rat

A recent study demonstrated the amelioration of light-induced photoreceptor degeneration by flunarizine and suggested that the protective effect achieved by the drug may be due to the inhibition of inositol 1,4,5-trisphosphate-induced calcium release from intracellular stores or the inhibition of calcium entry through putative voltage-sensitive calcium channels. In the current study, we investigated the effect of nimodipine, a specific voltage-sensitive calcium channel blocker, in light-induced retinal degeneration to further define the factors involved in the retinal degenerative process. Morphological, morphometric, and biochemical results demonstrated that nimodipine was ineffective in ameliorating light-induced retinal degeneration, and implied that calcium entry through voltage-sensitive channels is unlikely to be involved in this disease process, and inositol 1,4,5-trisphosphate-induced calcium release from intracellular stores may play a dominant role in light-induced photoreceptor cell damage.

Visualization of nimodipine (NIM) binding sites of rat brain by means of a NIM-colloidal gold complex (1-2)

It is described a new method to visualize the binding sites of the Ca(2+)-antagonist nimodipine (NIM) on brain cryostatic sections. NIM was bridged to colloidal gold sols by a suitable amphophilic detergent, and used according to autoradiographic procedures. A detailed mappage of vascular and neuronal NIM binding sites was allowed by silver-intensification of the NIM-gold complex bound to the nervous tissue. Selective distribution patterns were visualized in the main cerebral and cerebellar areas, suggesting that the drug potentially may act on multiple, different targets in the CNS.

Biotransformation of nimodipine in rat, dog, and monkey

14C-labelled (+/-) 3-isopropyl5-(2-methoxyethyl)1,4-dihydro-2,6-dimethyl-4- (3-nitrophenyl)-pyridine-3,5-dicarboxylate (nimodipine, Bay e 9736, Nimotop; CAS 66085-59-4) was administered orally to rat, dog, and monkey (each 5, 10, or 20 mg/kg) and intraduodenally to rat (5 mg/kg). Urine was collected over a period of 24 h (bile 6 h). Dog bile was obtained from the gall bladder 4 h after oral dosing. Rat plasma was taken 1 h p. appl. of the unlabelled compound and additionally at different times following administration of [14C]nimodipine. The metabolite profiles in the excreta were established by TLC (radioscan/autoradiography). The unchanged drug was neither detectable in urine nor in bile, but was present in rat plasma. Nimodipine was extensively metabolized. 18 metabolites were isolated by LC, HPLC, and preparative TLC and identified by comparison with the reference substances using two-dimensional TLC, HPLC, GC/radio-GC, 1H-NMR-spectroscopy, MS, and GC/MS. About 75% of the renally excreted biotransformation products, more than 50% of the metabolites present in the bile (rat, dog) and approx. 80% of the plasma metabolites (rat only) have been identified. The large number of metabolites was produced by some common biotransformation reactions: dehydrogenation of the 1,4-dihydropyridine system, oxidative ester cleavage, oxidative O-demethylation and subsequent oxidation of the resulting primary alcohol to the carboxylic acid, hydroxylation of the methyl groups at 2- or 6-position, hydroxylation of one methyl group of the isopropyl ester moiety, reduction of the aromatic nitro group, and glucuronidation as phase II-reaction.

Activity of the dihydropyridine calcium channels following cerebral ischemia

With an in-vivo autoradiographic method the binding of 3H-nimodipine (CAS 66085-59-4) and cerebral blood flow (14C-iodoantipyrine method) were measured in rat brain after occlusion of the middle cerebral and common carotid arteries. The dependence of the binding to neuronal cellular membranes on the duration of ischemia can be interpreted as indicator of the tissue's functional state or its responsiveness to therapy with calcium entry blockers. In the two analyzed structures, dorsolateral caudate and overlying sensorimotor cortex, the appearance of infarction is preceded by an activation of the nimodipine binding sites followed by persistent decline of the binding intensity. Binding to nimodipine may therefore be a useful marker of ischemic but salvageable brain tissue.

Effects of dihydropyridines on calcium release from the isolated membrane complex consisting of the transverse tubule and sarcoplasmic reticulum

We have investigated a) the effects of the dihydropyridines (DHPs) nifedipine and nimodipine on depolarization-induced (T-tubule-mediated) Ca2+ release in the vesicles consisting of the complex of the T-tubule and SR, and b) the binding of [3H]nimodipine to these vesicles. These DHPs inhibited the slow but not the fast phase of depolarization-induced release, both of which are mediated via the T-tubule. The DHPs have no effect on caffeine-induced release in which T-tubules are not involved. There are two classes of DHP binding sites: one, with high affinity and small capacity, and another, exhibiting low affinity and a much larger capacity. The inhibition paralleled the low affinity binding of DHP with no correlation with the high affinity binding. These results suggest that the low affinity DHP binding sites located probably in the DHP receptor, rather than the high affinity DHP binding site, are responsible for the inhibition of e-c coupling.

Synthesis of [isopropyl-11C]nimodipine for in vivo studies of dihydropyridine binding in man using positron emission tomography

Nimodipine, an antagonist of the L-type calcium ion channel, was labelled with 11C for in vivo positron emission tomography studies of dihydropyridine binding in the human brain. The synthesis was based on esterification of the corresponding acid (W2100) using [2-11C]isopropyl iodide as the labelling precursor. The effects of different bases, solvent mixtures and reaction temperatures on radiochemical yields were investigated. The synthesis including purification by semi-preparative reversed-phase HPLC, required 60-65 min. Conversion of [2-11C]isopropyl iodide to [isopropyl-11C] nimodipine was of the order of 60-80%. The radiochemical yield (isolated) was 20-25%, based on [11C]carbon dioxide. The specific activity of the isolated product varied from 4-40 GBq/mumol (end-of-synthesis).

AHR-16303B, a novel antagonist of 5-HT2 receptors and voltage-sensitive calcium channels

In vivo and in vitro methods were used to characterize AHR-16303B, a novel compound with antagonistic action at 5-HT2 receptors and voltage-sensitive calcium channels. The 5-HT2 receptor-antagonistic properties of AHR-16303B were demonstrated by inhibition of (a) [3H]ketanserin binding to rat cerebral cortical membranes (IC50 = 165 nM); (b) 5-hydroxytryptamine (5-HT)-induced foot edema in rats (minimum effective dose, (MED) = 0.32 mg/kg orally, p.o.); (c) 5-HT-induced vasopressor responses in spontaneously hypertensive rats (SHR) (ID50 = 0.18 mg/kg intravenously (i.v.), 1.8 mg/kg p.o.), (d) 5-HT-induced antidiuresis in rats (MED = 1 mg/kg p.o.), and (e) platelet aggregation induced by 5-HT + ADP (IC50 = 1.5 mM). The calcium antagonist properties of AHR-16303B were demonstrated by inhibition of (a) [3H]nimodipine binding to voltage-sensitive calcium channels on rabbit skeletal muscle membranes (IC50 = 15 nM), (b) KCl-stimulated calcium flux into cultured PC12 cells (IC50 = 81 nM), and (c) CaCl2-induced contractions of rabbit thoracic aortic strips (pA2 = 8.84). AHR-16303B had little or no effect on binding of radioligands to dopamine2 (DA2) alpha 1, alpha 2, H1, 5-HT1 alpha, beta 2, muscarinic M1, or sigma opioid receptors; had no effect on 5-HT3 receptor-mediated vagal bradycardia; and had only minor negative inotropic, chronotropic, and dromotropic effects on isolated guinea pig atria. In conscious SHR, 30 mg/kg p.o. AHR-16303B completely prevented the vasopressor responses to i.v. 5-HT, and decreased blood pressure (BP) by 24% 3 h after dosing.

Nimodipine binding in focal cerebral ischemia

We investigated the binding properties of the voltage-sensitive calcium channel antagonist nimodipine in a rat model of focal cerebral ischemia. Male Sprague-Dawley rats weighing 250 g underwent occlusion of both the proximal middle cerebral artery and the ipsilateral common carotid artery. 3H-nimodipine (130 Ci/mmol) was infused intravenously and circulated for 30 minutes before the rats were killed at 5 minutes, 4, 24, and 48 hours after occlusion. The brains were removed and examined by autoradiography. We observed a focal increase of nimodipine binding in severely ischemic regions at 5 minutes after occlusion, which also appeared in regions with presumed penumbral blood flow levels at 4 hours after occlusion. We hypothesize that nimodipine binds to activated calcium channels in ischemic tissue. This increased binding depends on the duration and severity of cerebral ischemia. Sequential measurements of nimodipine binding may allow the identification of regions with potentially reversible effects of ischemia and the monitoring of their response to therapy.

Rat cerebral cortical synaptoneurosomal membranes. Structure and interactions with imidazobenzodiazepine and 1,4-dihydropyridine calcium channel drugs

Small angle x-ray scattering has been used to investigate the structure of synaptoneurosomal (SNM) membranes from rat cerebral cortex. Electron micrographs of the preparation showed SNM with classical synaptic appositions intact, other vesicles, occasional mitochondria, and some myelin. An immunoassay for myelin basic protein placed the myelin content of normal rat SNM at less than 2% by weight of the total membrane present. X-Ray diffraction patterns showed five diffraction orders with a unit cell repeat for the membrane of 71 to 78 A at higher hydration states. At lower hydration, 11 orders appeared; the unit cell repeat was 130 A, indicating that the unit cell contained two membranes. Electron density profiles for the 130-A unit cell were determined; they clearly showed the two opposed asymmetrical membranes of the SNM vesicles. SNM membrane/buffer partition coefficients (Kp) of imidazobenzodiazepine and 1,4-dihydropyridine (DHP) calcium channel drugs were measured; Kp's for DHP drugs were approximately five times higher in rabbit light sarcoplasmic reticulum than in SNM. Ro 15-1788 and the DHP BAY K 8644 bind primarily to the outer monolayer of vesicles of intact SNM membranes. Nonspecific equilibrium binding of Ro 15-1788 occurs mainly in the upper acyl chain of the bilayer in lipid extracts of SNM membrane.