Computational drug repositioning for ischemic stroke: neuroprotective drug discovery.

Background: A comprehensive approach to drug repositioning will be required to overcome translational hurdles and identify more neuroprotective drugs. Results & methods: Gene Set Enrichment Analysis was applied to identify related pathways and enriched genes. Candidate genes were optimized using ToppGene, ToppGenet and pBRIT. From the perspective of the local structures, gene-domain-substructure-drug relationships were constructed. Using the MCODE algorithm and K-means clustering, 31 functional subnetworks were obtained, and 252 drugs with proposed neuroprotective function were identified. Using computational analysis, 72 substructures with different scores were found to correspond to neuroprotective functions. The protective effects of benidipine and barnidipine were confirmed in vitro. Conclusion: The authors' research has great potential to discover more neuroprotective drugs and obtain more information regarding mechanisms of action and functional substructures.

Small Molecule Inhibitor Screen Reveals Calcium Channel Signaling as a Mechanistic Mediator of Clostridium difficile TcdB-Induced Necrosis.

Clostridioides difficile is the leading cause of nosocomial diarrhea in the United States. The primary virulence factors are two homologous glucosyltransferase toxins, TcdA and TcdB, that inactivate host Rho-family GTPases. The glucosyltransferase activity has been linked to a "cytopathic" disruption of the actin cytoskeleton and contributes to the disruption of tight junctions and the production of pro-inflammatory cytokines. TcdB is also a potent cytotoxin that causes epithelium necrotic damage through an NADPH oxidase (NOX)-dependent mechanism. We conducted a small molecule screen to identify compounds that confer protection against TcdB-induced necrosis. We identified an enrichment of "hit compounds" with a dihydropyridine (DHP) core which led to the discovery of a key early stage calcium signal that serves as a mechanistic link between TcdB-induced NOX activation and reactive oxygen species (ROS) production. Disruption of TcdB-induced calcium signaling (with both DHP and non-DHP molecules) is sufficient to ablate ROS production and prevent subsequent necrosis in cells and in a mouse model of intoxication.

Synthesis and in vitro cholinesterase inhibitory potential of dihydropyridine derivatives.

Twelve derivatives of dihydropyridine derivatives (6-17) were synthesized and evaluated for in-vitro cholinesterases (AChE, BChE) inhibitory activity. All compounds showed potent activity with IC50 values between 0.21±0.003 to 147.14±0.12µM for AChE and among them five compounds showed potent activity with IC50 values 17.16±0.02 to 231.6±0.12µM for BChE when compared with standard Eserine (IC50 = 0.85±0.0001 µM (AChE) & 0.04±0.0001µM (BChE). The most potent compound 11 can be considered as potential lead compound showed an inhibition of 95.35±0.11 and IC50= 0.21±0.003 while compound 7 showed an inhibition of 83.45±0.13 and IC50= 17.16±0.02. It is concluded from structural activity relationship that the presence of nitro group at C-2 and C-4 position of dihydropyridine ring increase the acetyl cholinesterase and butyrylcholinesterase activities of these compounds while presence of -Br and -Cl also enhances the activities.

Bactericidal and immunomodulatory properties of magnetic nanoparticles functionalized by 1,4-dihydropyridines.

BACKGROUND: 1,4-Dihydropyridine (1,4-DHP) and its derivatives are well-known calcium channel blockers with antiarrhythmic and antihypertensive activities. These compounds exhibit pleiotropic effects including antimicrobial activities that rely on their positive charge and amphipathic nature. Use of magnetic nanoparticles (MNPs) as carriers of 1,4-DHP modulates their properties and enables improved formulations with higher efficacy and less toxicity. METHODS: In this study, the antimicrobial and immunomodulatory activities of novel 1,4-DHP derivatives in free form and immobilized on MNPs were determined by evaluating pathogen outgrowth and proinflammatory cytokine release in experimental settings that involve incubation of various 1,4-DHPs with clinical isolates of bacteria or fungi as well as mammalian cell culture models. RESULTS: Conventional immobilization of 1,4-DHP on aminosilane-coated MNPs markedly enhances their antimicrobial activity compared to nonimmobilized molecules, in part because of the higher affinity of these nanosystems for bacterial cell wall components in the presence of human body fluids. CONCLUSION: Optimized nanosystems are characterized by improved biocompatibility and higher anti-inflammatory properties that provide new opportunities for the therapy of infectious diseases.

Crystallization from Supersaturated Solutions: Role of Lecithin and Composite Simulated Intestinal Fluid.

PURPOSE: The overall purpose of this study was to understand the impact of different biorelevant media types on solubility and crystallization from supersaturated solutions of model compounds (atazanavir, ritonavir, tacrolimus and cilnidipine). The first aim was to understand the influence of the lecithin content in FaSSIF. As the human intestinal fluids (HIFs) contain a variety of bile salts in addition to sodium taurocholate (STC), the second aim was to understand the role of these bile salts (in the presence of lecithin) on solubility and crystallization from supersaturated solutions, METHODS: To study the impact of lecithin, media with 3 mM STC concentration but varying lecithin concentration were prepared. To test the impact of different bile salts, a new biorelevant medium (Composite-SIF) with a composition simulating that found in the fasted HIF was prepared. The crystalline and amorphous solubility was determined in these media. Diffusive flux measurements were performed to determine the true supersaturation ratio at the amorphous solubility of the compounds in various media. Nucleation induction times from supersaturated solutions were measured at an initial concentration equal to the amorphous solubility (equivalent supersaturation) of the compound in the given medium. RESULTS: It was observed that, with an increase in lecithin content at constant STC concentration (3 mM), the amorphous solubility of atazanavir increased and crystallization was accelerated. However, the crystalline solubility remained fairly constant. Solubility values were higher in FaSSIF compared to Composite-SIF. Longer nucleation induction times were observed for atazanavir, ritonavir and tacrolimus in Composite-SIF compared to FaSSIF at equivalent supersaturation ratios. CONCLUSIONS: This study shows that variations in the composition of SIF can lead to differences in the solubility and crystallization tendency of drug molecules, both of which are critical when evaluating supersaturating systems.

Characterization of the anxiolytic and sedative profile of JM-20: a novel benzodiazepine-dihydropyridine hybrid molecule.

OBJECTIVES: The aim of this study was to investigate the effects of oral administration of a novel benzodiazepine derivative, JM-20, on the neurological behavior of different rodent models, focusing on the GABAergic effect. We have also investigated the acute toxicity of oral administration of JM-20 in mice. METHODS: Mice or rats received oral administration of JM-20 at 2, 4, 8, and 10 mg/kg to evaluate the sedative/hypnotic, anxiolytic, and anticonvulsant effects, as well as the influence on the stereotyped behavior induced by amphetamine. Diazepam (DZP) was used as a positive control. In addition, the mice received a single oral JM-20 dose of 2000 mg/kg to evaluate the acute toxicity. RESULTS: In a dose-dependent manner, JM-20 (i) increased the number of crossings and decreased the number of rearings in the open-field test; (ii) decreased the aggressive behavior of socially-isolated mice; and (iii) increased the latency period for tonic seizure's onset and the percentage of survival of animals with seizures. Moreover, JM-20 increased the sleeping time induced by barbiturates and the time spent and the number of entries in the open arms of the elevated plus-maze test. In the JM-20 toxicity test, no mortality was observed and only minor signs of toxicity associated with sedation were detected. CONCLUSIONS: These results indicate that JM-20 has an anxiolytic profile similar to DZP and its dihydropyridine moiety did not appear to interfere with the GABAergic activity associated with benzodiazepine. Furthermore, JM-20 did not show significant acute toxic effects in mice.

Discovery of potent selective bioavailable phosphodiesterase 2 (PDE2) inhibitors active in an osteoarthritis pain model. Part II: optimization studies and demonstration of in vivo efficacy.

Selective phosphodiesterase 2 (PDE2) inhibitors are shown to have efficacy in a rat model of osteoarthritis (OA) pain. We identified potent, selective PDE2 inhibitors by optimizing residual PDE2 activity in a series of phosphodiesterase 4 (PDE4) inhibitors, while minimizing PDE4 inhibitory activity. These newly designed PDE2 inhibitors bind to the PDE2 enzyme in a cGMP-like binding mode orthogonal to the cAMP-like binding mode found in PDE4. Extensive structure activity relationship studies ultimately led to identification of pyrazolodiazepinone, 22, which was >1000-fold selective for PDE2 over recombinant, full length PDEs 1B, 3A, 3B, 4A, 4B, 4C, 7A, 7B, 8A, 8B, 9, 10 and 11. Compound 22 also retained excellent PDE2 selectivity (241-fold to 419-fold) over the remaining recombinant, full length PDEs, 1A, 4D, 5, and 6. Compound 22 exhibited good pharmacokinetic properties and excellent oral bioavailability (F=78%, rat). In an in vivo rat model of OA pain, compound 22 had significant analgesic activity 1 and 3h after a single, 10 mg/kg, subcutaneous dose.

Discovery of potent, selective, bioavailable phosphodiesterase 2 (PDE2) inhibitors active in an osteoarthritis pain model, part I: transformation of selective pyrazolodiazepinone phosphodiesterase 4 (PDE4) inhibitors into selective PDE2 inhibitors.

We identified potent, selective PDE2 inhibitors by optimizing residual PDE2 activity in a series of PDE4 inhibitors, while simultaneously minimizing PDE4 activity. These newly designed PDE2 inhibitors bind to the PDE2 enzyme in a cGMP-like mode in contrast to the cAMP-like binding mode found in PDE4. Structure activity relationship studies coupled with an inhibitor bound crystal structure in the active site of the catalytic domain of PDE2 identified structural features required to minimize PDE4 inhibition while simultaneously maximizing PDE2 inhibition.

Transdermal delivery of lercanidipine hydrochloride: effect of chemical enhancers and ultrasound.

The effects of permeation enhancers and sonophoresis on the transdermal permeation of lercanidipine hydrochloride (LRDP) across mouse skin were investigated. Parameters including drug solubility, partition coefficient, drug degradation and drug permeation in skin were determined. Tween-20, dimethyl formamide, propylene glycol, poly ethylene glycol (5% v/v) and different concentration of ethanol were used for permeation enhancement. Low frequency ultrasound was also applied in the presence and absence of permeation enhancers to assess its effect on augmenting the permeation of drug. All the permeation enhancers, except propylene glycol, increased the transdermal permeation of LRDP. Sonophoresis significantly increased the cumulative amount of LRDP permeating through the skin in comparison to passive diffusion. A synergistic effect was noted when sonophoresis was applied in presence of permeation enhancers. The results suggest that the formulation of LRDP with an appropriate penetration enhancer may be useful in the development of a therapeutic system to deliver LRDP across the skin for a prolonged period (i.e., 24 h). The application of ultrasound in association with permeation enhancers could further serve as non-oral and non-invasive drug delivery modality for the immediate therapeutic effect.

Anti-arrhythmic and hemodynamic effects of oxy nifedipine, oxy nimodipine, oxy nitrendipine and oxy nisoldipine.

Our previous studies have established cardio-protective effects of furnidipine and its active metabolites. We therefore decided to compare the influence of oral and intravenous administration of furnidipine, nifedipine, nitrendipine and nimodipine to examine their effects on hemodynamics and arrhythmias. Since dihydropyridines are oxidatively metabolized in the body and the oxidized metabolites are among the final products, we studied the influence of four oxidized dihydropyridines (oxy nifedipine, oxy nimodipine, oxy nitrendipine and oxy nisoldipine) on the same parameters. In vivo model of ischemia- and reperfusion-induced arrhythmias of rats was used. Dihydropyridines were administered 5 mg/kg orally (24 and 1 h before ischemia) or 5 µg/kg intravenously (10 min before ischemia). 20 mg/kg of the oxidized dihydropyridines was given orally (24 and 1 h before ischemia). The dihydropyridines exhibited significant anti-arrhythmic actions after both forms of administration but their influence on blood pressure was differential and contrasting and depended on route of administration. The oxidized dihydropyridines imparted strong protection against lethal arrhythmias while exerting differential influences on blood pressure with oxy nifedipine and oxy nisoldipine being hypertensive and oxy nitrendipine being most normotensive. The differential effects observed with the dihydropyridines after the two routes of administration lend strength to the hypothesis that their metabolites may have a significant role in mediating the actions of the parent drug. The strong anti-arrhythmic action of the oxidized dihydropyridines along with their differential effect on blood pressure could indicate their potential use as cardio-protective drugs in certain groups of patients.

Discovery and evaluation of selective N-type calcium channel blockers: 6-unsubstituted-1,4-dihydropyridine-5-carboxylic acid derivatives.

A structure-activity relationship study of 6-unsubstituted-1,4-dihydropyridine and 2,6-unsubstituted-1,4-dihydropyridine derivatives was conducted in an attempt to discover N-type calcium channel blockers that were highly selective over L-type calcium channel blockers. Among the tested compounds, (+)-4-(3,5-dichloro-4-methoxy-phenyl)-1,4-dihydro-pyridine-3,5-dicarboxylic acid 3-cinnamyl ester was found to be an effective and selective N-type calcium channel blocker with oral analgesic potential.

Search for stroke-protecting agents in endothelin-1-induced ischemic stroke model in rats.

BACKGROUND AND OBJECTIVE: Ischemic stroke may initiate a reperfusion injury leading to brain damage cascades where inflammatory mechanisms play a major role. Therefore, the necessity for the novel stroke-protecting agents whose the mechanism of action is focused on their anti-inflammatory potency is still on the agenda for drug designers. Our previous studies demonstrated that cerebrocrast (a 1,4-dihydropyridine derivative) and mildronate (a representative of the aza-butyrobetaine class) possessed considerable anti-inflammatory and neuroprotective properties in different in vitro and in vivo model systems. The present study investigated their stroke-protecting ability in an endothelin-1 (ET-1)-induced ischemic stroke model in rats. MATERIAL AND METHODS: Male Wistar rats were pretreated (for 7 days, per os) with cerebrocrast (0.1 mg/kg), mildronate (100 mg/kg), or their combination, followed by the intracerebral injection of ET-1. Functional and behavioral tests were carried out up to 14 days after the ET-1 injection. Ex vivo, the number of degenerated neurons and the infarction size in the cerebral cortical tissue were assessed histologically. RESULTS: Cerebrocrast and mildronate effectively normalized ET-1-induced disturbances in neurological status, improved the muscle tone, and decreased the number of degenerated cortical cells. Both drugs also reduced the infarction size, and cerebrocrast showed at least a 2-fold higher activity than mildronate. The combination of both drugs did not cause a more pronounced effect in comparison with the action of drugs administered separately. CONCLUSIONS: The 1,4-dihydropyridine and aza-butyrobetaine structures may serve for the design of novel stroke-protecting agents to prevent severe neurological poststroke consequences.

Desferrithiocin analogue iron chelators: iron clearing efficiency, tissue distribution, and renal toxicity.

The current solution to iron-mediated damage in transfusional iron overload disorders is decorporation of excess unmanaged metal, chelation therapy. The clinical development of the tridentate chelator deferitrin (1, Table 1) was halted due to nephrotoxicity. It was then shown by replacing the 4'-(HO) of 1 with a 3,6,9-trioxadecyloxy group, the nephrotoxicity could be ameliorated. Further structure-activity relationship studies have established that the length and the position of the polyether backbone controlled: (1) the ligand's iron clearing efficiency (ICE), (2) chelator tissue distribution, (3) biliary ferrokinetics, and (4) tissue iron reduction. The current investigation compares the ICE and tissue distribution of a series of (S)-4,5-dihydro-2-[2-hydroxy-4-(polyether)phenyl]-4-methyl-4-thiazolecarboxylic acids (Table 1, 3-5) and the (S)-4,5-dihydro-2-[2-hydroxy-3-(polyether)phenyl]-4-methyl-4-thiazolecarboxylic acids (Table 1, 8-10). The three most effective polyether analogues, in terms of performance ratio (PR), defined as mean ICE(primate)/ICE(rodent), are 3 (PR 1.1), 8, (PR 1.5), and 9, now in human trials, (PR 2.2). At the onset of the clinical trial on 9, no data were available for ligand 3 or 8. This is unfortunate, as 3 has many advantages over 9, e.g., the ICE of 3 in rats is 2.5-fold greater than that of 9 and analogue 3 achieves very high levels in the liver, pancreas, and heart, the organs most affected by iron overload. Finally, the impact of 3 on the urinary excretion of kidney injury molecule-1 (Kim-1), an early diagnostic biomarker for monitoring acute kidney toxicity, has been carried out in rats; no evidence of nephrotoxicity was found. Overall, the results suggest that 3 would be a far superior clinical candidate to 9.

Natural and synthetic antioxidants: an updated overview.

Abstract The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

A new mode of mineralocorticoid receptor antagonism by a potent and selective nonsteroidal molecule.

Limitations of current steroidal mineralocorticoid receptor (MR) antagonists have stimulated the search for a new generation of molecules. We screened for novel nonsteroidal compounds and identified MR antagonists derived from the chemical class of dihydropyridines. Chemical optimization resulted in BR-4628, which displays high in vitro and in vivo MR potency as well as selectivity with respect to the other steroid hormone receptors and the L-type calcium channel. Biochemical studies demonstrated that BR-4628 forms complexes with MR that do not promote the recruitment of transcriptional co-regulators. Docking experiments, using the crystal structure of the MR ligand-binding domain in an agonist conformation, revealed that BR-4628 accommodates in the MR ligand-binding cavity differently in comparison with the classical steroidal MR antagonists. An alanine scanning mutagenesis approach, based on BR-4628 docking, allowed identifying its anchoring mode within the ligand-binding cavity. Altogether, we propose that BR-4628 is a bulky antagonist that inactivates MR through a passive mechanism. It represents the prototype of a new class of MR antagonists.

Synthesis of a library of 5,6-unsubstituted 1,4-dihydropyridines based on a one-pot 4CR/elimination process and their application to the generation of structurally diverse fused nitrogen heterocycles.

Indium trichloride is an efficient catalyst for the sequential four-component reaction between aliphatic amines, ß-ketoesters, α,ß-unsaturated aldehydes, and ethanol to afford 6-ethoxy-1,4,5,6-tetrahydropyridines, which were converted in situ into 5,6-unsubstituted 1,4-dihydropyridines via ethanol elimination in the presence of neutral Al(2)O(3), in a very efficient, one-pot protocol from acyclic, readily available starting materials that involves the generation of two C-N σ and one C-C π bonds. The structural variety of the dihydropyridine library thus generated was extended by base-promoted γ-alkylation of their C-2 position. The application of these 1,4-dihydropyridines to the facile generation of molecular diversity and complexity was demonstrated by employing them as dienophiles for Yb(OTf)(3)-catalyzed imino Diels-Alder (Povarov) reactions leading diastereoselectively to hexahydrobenzo[h][1,6]-naphthyridine derivatives containing three adjacent stereocenters. The synthesis of fused dihydropyridines derived from the pyrido[2,1-a]azepine (homoquinolizine) frameworks was also achieved using a four-component tetrahydropyridine synthesis/ring-closing metathesis/elimination strategy.

Desferrithiocin analogue uranium decorporation agents.

PURPOSE: Previous systematic structure-activity studies of the desferrithiocin (DFT) platform have allowed the design and synthesis of analogues and derivatives of DFT that retain the exceptional iron-clearing activity of the parent, while eliminating its adverse effects. We hypothesized that a similar approach could be adopted to identify DFT-related analogues that could effectively decorporate uranium. MATERIALS AND METHODS: The decorporation properties of nine DFT-related analogues were determined in a bile duct-cannulated rat model. Diethylenetriaminepentaacetic acid (DTPA) served as a positive control. Selected ligands also underwent multiple and delayed dosing regimens. Uranium excretion in urine and bile or stool was determined by inductively coupled plasma mass spectroscopy (ICP-MS); tissue levels of uranium were also assessed. RESULTS: The two best clinical candidates are (S)-4,5-dihydro-2-[2-hydroxy-4-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT-PE (9)], with a 57% reduction in kidney uranium levels on oral (p.o.) administration and (S)-4,5-dihydro-2-[2-hydroxy-3-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-3'-(HO)-DADFT-PE (10)], with a 62% renal reduction on p.o. administration. The majority of the metal excretion promoted by these analogues is in the bile, thus further reducing kidney actinide exposure. CONCLUSIONS: While 9 administered p.o. or subcutaneously (s.c.) immediately post-metal is an effective decorporation agent, withholding the dose (s.c.) until 4 h reduced the activity of the compound. Conversion of 9 to its isopropyl ester may circumvent this issue.

Desferrithiocin analogues and nephrotoxicity.

The syntheses of a series of 4'-O-alkylated ( S)-4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-methyl-4-thiazole-carboxylic acid and 5'-O-alkylated ( S)-4,5-dihydro-2-(2,5-dihydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid ligands are described. Their partition between octanol and water, log P(app), is determined, along with their iron-clearing efficiency (ICE) in both non-iron-overloaded, bile duct-cannulated rodents and in iron-overloaded primates. The ligand-promoted biliary ferrokinetics in rats are described for each of the chelators. Plots of log P(app) versus ICE in a rodent model for both the 4'-O-alkylated 2,4-dihydroxy and 5'-O-alkylated 2,5-dihydroxy series produced an inverse parabola plot with r(2) values of 0.97 and 0.81, respectively. The plots indicate an optimum log P(app)/ICE relationship. Because of the nature of the data spread in the 4'-O-alkylated 2,4-dihydroxy series, it will be used to help assess the origin of nephrotoxicity in desferrithiocin analogues: is toxicity simply related to lipophilicity, ICE, or a combination of these properties?

Reactive oxygen species assay-based risk assessment of drug-induced phototoxicity: classification criteria and application to drug candidates.

We have previously demonstrated that the phototoxic potential of chemicals could be partly predicted by the determination of reactive oxygen species (ROS) from photo-irradiated compounds. In this study, ROS assay strategy was applied to 39 marketed drugs and 210 drug candidates in order to establish provisional classification criteria for risk assessment of drug-induced phototoxicity. The photosensitizing properties of 39 model compounds consisting of phototoxic and non-phototoxic chemicals, as well as ca. 210 drug candidates including 11 chemical series were evaluated using ROS assay and the 3T3 neutral red uptake phototoxicity test (NRU PT). With respect to marketed drugs, most phototoxic drugs tended to cause type I and/or II photochemical reactions, resulting in generation of singlet oxygen and superoxide. There seemed to be a clear difference between phototoxic drugs and non-phototoxic compounds in their abilities to induce photochemical reactions. A plot analysis of ROS data on the marked drugs provided classification criteria to discriminate the photosensitizers from non-phototoxic substances. Of all drug candidates tested, 35.2% compounds were identified as phototoxic or likely phototoxic on the basis of the 3T3 NRU PT, and all ROS data for these phototoxic compounds were found to be over the threshold value. Furthermore, 46.3% of non-phototoxic drug candidates were found to be in the subthreshold region. These results verify the usefulness of the ROS assay for understanding the phototoxicity risk of pharmaceutical substances, and the ROS assay can be used for screening purposes in the drug discovery stage.

Comparative effects of three 1,4-dihydropyridine derivatives [OSI-1210, OSI-1211 (etaftoron), and OSI-3802] on rat liver mitochondrial bioenergetics and on the physical properties of membrane lipid bilayers: relevance to the length of the alkoxyl chain in positions 3 and 5 of the DHP ring.

The 1,4-dihydropyridines OSI-1210, OSI-1211 (etaftoron), and OSI-3802 are compounds with similar chemical structure. They differ by the length of the alkoxyl chain in positions 3 and 5 of the dihydropyridine (DHP) ring and by their pharmacological action characteristics. However, as far as we know, a clear relationship between the effects of these compounds and the length of the alkoxyl chain in positions 3 and 5 of the DHP has not been established. The goal of this study was to compare the influence of OSI-1210, OSI-1211 (etaftoron), and OSI-3802 on rat liver mitochondrial bioenergetics and on the physical properties of membrane lipid bilayers, correlating their actions with the length of the alkoxyl chain in positions 3 and 5 of the DHP ring. Using either glutamate/malate or succinate as respiratory substrates, all the compounds, in concentrations of up to 500 microM, depressed state 3 and uncoupled respiration, respiratory control (RCR) and ADP/O ratios, and phosphorylation rate, whereas state 4 respiration was stimulated. However, the stimulatory effect on state 4 induced by OSI-3802, the compound with the longest chain in positions 3 and 5 of the DHP ring, as well as its inhibitory effects on RCR and ADP/O ratios and phosphorylation rate were more pronounced than that induced by OSI-1210 and OSI-1211 (etaftoron), the compounds with the shortest and intermediate chains, respectively. Moreover, OSI-3802 maximized state 4 stimulation and minimized RCR and ADP/O ratios, and phosphorylation rate at a concentration of 100 microM, whereas low graduate effects were detected with OSI-1210 and OSI-1211 (etaftoron) for concentrations of up to 500 microM. At low concentrations (< or =30 microM), OSI-3802, like its analogue OSI-1212 (cerebrocrast), reduced the phase transition temperature, the cooperative unit size, and the enthalpy associated with the phase transition temperature of dimyristoylphosphatidylcholine (DMPC) membrane bilayers. A good correlation was established between the effects of 200 microM OSI-1210, OSI-1211 (etaftoron), and OSI-3802 on glutamate/malate- and succinate-dependent RCR of rat liver mitochondria and on the enthalpy change (Delta H) for the thermotropic profile of DMPC membrane bilayers at a 0.2 drug/DMPC molar ratio, indicating that the changes induced by these compounds on both mitochondrial membrane integrity and physical properties of DMPC membrane bilayers are strongly related to the length of the alkoxyl chain in positions 3 and 5 of the DHP ring. A putative relationship between membrane physical perturbation, bioenergetics impairment and the molecular characteristics of the compounds will be established as an approach to better understand their differentiated toxicological and pharmacological actions.