Effects of bepridil on Ca2+ uptake by cardiac mitochondria

Reversal of mitochondrial permeability transition pore and pancreas degeneration by chloroform fraction of Ocimum gratissimum (L.) leaf extract in type 2 diabetic rat model

Introduction: Unmanaged Diabetes Mellitus (DM) usually results to tissue wastage because of mitochondrial dysfunction. Adverse effects of some drugs used in the management of DM necessitates the search for alternative therapy from plant origin with less or no side effects. Ocimum gratissimum (L.) (OG) has been folklorically used in the management of DM. However, the mechanism used by this plant is not fully understood. This study was designed to investigate the effects of chloroform fraction of OG leaf (CFOG) in the reversal of tissue wastage in DM via inhibition of mitochondrial-mediated cell death in streptozotocin (STZ)-induced diabetic male Wistar rats. Methods: Air-dried OG leaves were extracted with methanol and partitioned successively between n-hexane, chloroform, ethylacetate and methanol to obtain their fractions while CFOG was further used because of its activity. Diabetes was induced in fifteen male Wistar rats, previously fed with high fat diet (28 days), via a single intraperitoneal administration of STZ (35 mg/kg). Diabetes was confirmed after 72 h. Another five fed rats were used as the normal control, treated with corn oil (group 1). The diabetic animals were grouped (n = 5) and treated for 28 days as follows: group 2 (diabetic control: DC) received corn oil (10 mL/kg), groups 3 and 4 were administered 400 mg/kg CFOG and 5 mg/kg glibenclamide, respectively. Body weight and Fasting Blood Glucose (FBG) were determined while Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) and beta cell (HOMA-β), and pancreatic tissue regenerating potential by CFOG were assessed. Activity-guided purification and characterization of the most active principle in CFOG was done using chromatographic and NMR techniques. The animals were sacrificed after 28 days, blood samples were collected and serum was obtained. Liver mitochondria were isolated and mitochondrial permeability transition (mPT) was investigated by spectrophotometry. Results: CFOG reversed diabetic-induced mPT pore opening, inhibited ATPase activity and lipid peroxidation. CFOG reduced HOMA-IR but enhanced HOMA-β and caused regeneration of pancreatic cells relative to DC. Lupanol was a major metabolite of CFOG. Discussion: Normoglycemic effect of CFOG, coupled with reversal of mPT, reduced HOMA-IR and improved HOMA-β showed the probable antidiabetic mechanism and tissue regenerating potentials of OG.

Calcium antagonists and Bay K8644 promote depolarization of the rat heart mitochondrial membrane potential. Further evidence for a role in alteration of oxidative metabolism

Studies were carried out using a tetraphenylphosphonium (TPP+)-selective electrode to monitor the effect of selected calcium (Ca2+) antagonists and the dihydropyridine Ca2+ agonist Bay K8644 on membrane potential (psi) associated with isolated rat heart mitochondria. Verapamil and diltiazem (10-500 microM), standard Ca2+ antagonists, produced a depolarization of both liver and heart mitochondria at concentrations > 150 microM. In contrast, nitrendipine (10-200 microM), a dihydropyridine compound, produced a concentration-related inhibition of psi in mitochondria from both sources, effects which were statistically significant at concentrations > 50 microM. Cinnarizine (10-100 microM) and bepridil (10-100 microM) also produced inhibition of heart psi, these effects being particularly noted in the presence of bepridil, where depolarization of the membrane was statistically significant with only 10 microM drug. The results indicate the complexity of action of these drugs at the mitochondrial level. In general, drug actions on psi appear to be correlated with previously reported effects on Ca2+ transportation rather than oxidative phosphorylation associated with rat heart mitochondria. The findings also illustrate that the mitochondrial actions of cardiovascular compounds may be of relevance in situ, particularly during ischaemia/reperfusion when mitochondria become loaded with Ca2+.

Effects of bepridil compared to those of its quaternary analogue on femoral arteries from spontaneously hypertensive rats

The effects of bepridil and its quaternary analogue, methylated bepridil, were studied on femoral arterial strips from spontaneously hypertensive rats (SHR). Methylated bepridil relaxed precontracted strips more rapidly than did bepridil, but bepridil was a more potent vasorelaxant. Both drugs non-competitively inhibited arterial contraction evoked by voltage-dependent or alpha-adrenoceptor-operated Ca2+ influx with bepridil being more potent than methylated bepridil. In the absence of extracellular Ca2+, the contractile responses of Wistar-Kyoto rats (WKY) and SHR arteries to norepinephrine and caffeine were reduced similarly by methylated bepridil and bepridil. It is suggested that the effects of bepridil involve both extracellular and intracellular actions. The altered sensitivity of the contraction mechanism with norepinephrine-releasable Ca2+ to the Ca2+ antagonist may be due to an abnormality in the intracellular vasocontraction process distal to Ca2+ release from storage sites of the SHR blood vessels.

Binding of bepridil to isolated rat heart mitochondria

We investigated mass action of isolated rat heart mitochondria with the calcium antagonist bepridil. At pH 7.20 bepridil in basic form b associates rapidly with the mitochondrial membrane but the amount fixed is higher in non-energized mitochondria than in mitochondria energized by succinate or ATP Mg2+. This effect is related to the dissociation state of the drug since conditions favoring the acidic form bH+ suppress this difference. Tritiated bepridil bound to mitochondrial membrane is only partially displaced by high concentrations of unlabeled drug (greater than or equal to 510(-5) M). No membrane energization effect is noted on this displacement. Binding values of bepridil to mitochondrial membrane (KD 1.710(-5) M; Bmax 23.8 nmol.mg-1 protein) show only low affinity receptor sites. Bepridil binding to the lipid part of the inner membrane surface is postulated. This interaction is used to explain some of the in vitro effects of this calcium antagonist on membrane bound enzyme activities.

Comparative effects of bepridil, its quaternary derivative CERM 11888 and verapamil on caffeine-induced contracture in ferret hearts

1. The effects of bepridil, its quaternary derivative: CERM 11888 (methyl-pyrrolidinium bromide) (10(-7)-10(-5) M), and verapamil (10(-7)-10(-6) M) were compared on caffeine-induced contracture of isolated ventricular trabeculae of the ferret. 2. Bepridil diminished the amplitude of contracture in a concentration-dependent fashion, and this effect was significantly different from that of CERM 11888 which, like verapamil, only reduced the amplitude at the highest concentration used. 3. Bepridil (10(-6) M) significantly shortened the time to peak tension and accelerated the relaxation phase of contracture. This latter effect was different from that of CERM 11888. Verapamil (10(-6) M) also tended to accelerate the relaxation phase. At 10(-5) M these actions of bepridil on the time to peak and relaxation tended to reverse. 4. At all concentrations bepridil and verapamil reduced the rate of repriming of contracture and this effect of bedpridil was significantly different from that of its quaternary derivative which only showed a significant effect at 10(-5) M. 5. These results demonstrate a clear intracellular effect of bepridil in the ferret heart. Verapamil and CERM 11888 had only weak intracellular effects even at high concentrations. 6. Analysis of the results suggests that the main sites of action of bepridil in this model are the sarcoplasmic reticulum and one or two calcium compartments in the sarcolemma.

The anti-ischaemic activity of the novel compound, CERM 11956, compared with that of bepridil and nifedipine in isolated guinea-pig hearts

A comparison between the protective activity of bepridil, its novel derivative, CERM 11956, and nifedipine in isolated electrically paced guinea-pig hearts after 60 min of global ischaemia followed by 30 min of reperfusion has been made. All three compounds exerted a significant anti-ischaemic effect, as indicated by an improved recovery of functional parameters (left ventricular pressure and coronary perfusion), a delayed onset of the ischaemic contracture, and an enhanced recovery of biochemical (CrP, ATP and adenylate energy charge) parameters. The most pronounced anti-ischaemic activity was shown by the compound CERM 11956 at concentrations that displayed only minor negative inotropic activity. From the results it may be concluded that the new bepridil derivative, CERM 11956, is a promising and potent anti-ischaemic compound, which has little influence on haemodynamic parameters.

Effects of bepridil on calcium release from rat heart mitochondria

Bepridil at concentrations above 10 microM, and at pH 7.2 stimulates calcium release from rat heart mitochondria. However this action is different from that of ClCCP, an uncoupler of oxidative phosphorylations, since it is ruthenium red insensitive. At lower concentrations bepridil may inhibit the Na-induced calcium release. The effects of bepridil depend on the pH and indicate that the protonated form of the drug is more efficient on calcium release than the basic form.

Effects on hemodynamics and left ventricular ejection fraction of intravenous bepridil for impaired left ventricular function secondary to coronary artery disease

To define the hemodynamic effects of bepridil in patients with depressed left ventricular (LV) function, 22 patients with an LV ejection fraction (EF) of 0.45 or less were studied before and after 2 mg/kg (n = 11) and 4 mg/kg (n = 11) of intravenous bepridil. Maximal hemodynamic effects were evident between 15 and 30 minutes after drug infusion. After 2 mg/kg, heart rate decreased 9% (p less than 0.01), cardiac index 17% (p less than 0.01), LV dP/dt max 16% (p less than 0.01), stroke work index 14% (p less than 0.01) and mean aortic pressure 8% (difference not significant). Right atrial pressure increased 8% (not significant), pulmonary arterial wedge pressure 24% (p less than 0.01) and systemic vascular resistance 17% (p less than 0.01). After administering 4 mg/kg of bepridil the changes in heart rate, cardiac index, right atrial pressure, LV dP/dt max, mean aortic pressure and systemic vascular resistance were almost identical to those after the smaller dose. The larger dose produced a 40% (p less than 0.01) increase in pulmonary arterial wedge pressure and a 22% decrease in stroke work index (p less than 0.01), but only the change in wedge pressure was significantly greater (p less than 0.01) than that produced by the lower dose. Radionuclide-determined LVEF decreased 6% (p less than 0.05), from 0.33 +/- 0.14 after 2 mg/kg and 11% (p less than 0.05) from 0.27 +/- 0.11 after 4 mg/kg of bepridil. The data indicate that bepridil exerts significant negative inotropic and chronotropic effects in patients with impaired LV function.

Comparison of the effects of bepridil and diltiazem upon globally ischemic rat hearts

Effects of the Ca2+ antagonists, bepridil (20 microM) and diltiazem (2.5 microM), upon ischemia/reperfusion injury were assessed in perfused, working rat hearts. These treatments were equally cardiodepressant in non-ischemic hearts. A lower concentration (5 microM) of bepridil was also assessed. Hearts which were reperfused following 33 min of global ischemia recovered 12.8% of preischemic pressure-rate product and had markedly reduced ATP, total adenine nucleotides, ATP/ADP ratio, and mitochondrial function. Treatment with bepridil before and during ischemia did not improve recovery of cardiac function, tissue energy reserves, or mitochondrial function upon reperfusion with control buffer. Control hearts treated with bepridil had normal levels of high energy compounds. Treatment with diltiazem significantly improved contractile function, and metabolic parameters. Ischemia/reperfusion injury was associated with a doubling of tissue Ca2+ content. Pretreatment with diltiazem, but not bepridil, reduced Ca2+ overload. Bepridil did not directly protect the myocardium from ischemia/reperfusion injury perhaps due to its inability to prevent Ca2+ overload.

Effect of methylated bepridil on slow action potentials in cardiac muscle and vascular smooth muscle

The anti-anginal agent bepridil blocks slow Ca2+ channels in a variety of tissues. Since bepridil accumulates inside cells, the possibility exists that bepridil acts, at least partially, from inside the cell. To test this possibility, we examined the effects of a quaternary ammonium analog of bepridil, methylated bepridil, which presumably would enter the cells less readily, on the Ca2+-dependent slow action potentials of guinea pig papillary muscles (in 25 mM [K+]0) and rabbit pulmonary arteries (in tetraethylammonium chloride). In cardiac muscle, methylated bepridil had little effect on the slow action potentials at low stimulation frequencies (0.5 Hz), but at higher frequencies (1.0 and 2.0 Hz) the slow action potentials were depressed and/or the muscle was unable to follow each stimulation. These effects are similar to those obtained with bepridil, but bepridil was more potent than methylated bepridil. In vascular smooth muscle cells, methylated bepridil inhibited the slow action potentials at a somewhat lower dose than bepridil. We conclude that, in cardiac muscle, bepridil probably has two sites of action, one outside the cell (presumably on or associated with the slow Ca2+ channel) and a second site inside the cell. On the other hand, in vascular smooth muscle cells, bepridil may act only on an external site.

Comparative effects of bepridil and diltiazem on systemic blood pressure and isolated peripheral arteries in spontaneously hypertensive rats

Bepridil and diltiazem were studied for their effects on blood pressure (BP) and heart rate (HR) of spontaneously hypertensive rats (SHR) and on vascular tone of femoral and mesenteric arterial strips from SHR. The drugs (i.v.) reduced BP and HR more markedly in SHR than in normotensive Wistar Kyoto rats (WKY). The effects of bepridil were less pronounced and less prolonged than those of diltiazem. Bepridil relaxed arterial strips precontracted by KCl or prostaglandin F2 alpha to almost the same extent as diltiazem in both SHR and WKY. Bepridil was almost as potent as diltiazem in inhibiting non-competitively the Ca2+-evoked contractions of arteries depolarized in a Ca2+-free, high K+ buffer. alpha-Adrenoceptor agonist-induced contractions accompanied and not accompanied by Ca2+ influx were inhibited more markedly by bepridil than diltiazem under certain conditions. The inhibitions were more marked in SHR than in WKY. Thus, it was suggested that both drugs acted as Ca2+ influx inhibitor to reduce vascular tone. Bepridil inhibited intracellular vasoconstriction mechanisms linked with alpha-adrenoceptors more potently than did diltiazem in SHR. Taken together, these actions can explain the antihypertensive properties of both drugs in SHR.

Effects of bepridil on force development and transmembrane electrical activity of adult canine Purkinje strands: comparison with nisoldipine and lidocaine

Superfusion of a bepridil containing normal Tyrode solution produced a concentration-dependent decrease in force development and shortening of action potential duration in isolated Purkinje strands. At a concentration close to the 50% inhibitory concentration for effects on force development and action potential duration, bepridil blocked 'slow' action potentials in potassium depolarized, isoproterenol-restored Purkinje strands. When the concentration-response relations for decreasing force development and shortening action potential duration were compared to those of nisoldipine and other calcium entry inhibitors, bepridil was the least potent. Bepridil also showed a concentration-dependent effect on the maximum rate of rise of the Purkinje fiber action potential upstroke similar to, though less potent than that of lidocaine. In addition, like lidocaine, bepridil shifted the membrane responsiveness curve of the Purkinje strands to the left. These findings indicate that bepridil produced effects that are consistent with its classification as a calcium entry inhibitor (class IV antiarrhythmic), as well as effects that are 'lidocaine-like' (class I antiarrhythmic).