Effects of β-adrenoceptor blockers on mitochondrial ATPase activity in guinea pig heart preparations

The effects of cardiac drugs on human erythrocyte carbonic anhydrase I and II isozymes

Cardiovascular diseases are the leading cause of mortality worldwide. In recent years, the relationship between carbonic anhydrase inhibitors and atherosclerosis has attracted attention. In this study, we aimed to determine the in vitro effects of 35 frequently used cardiac drugs on human carbonic anhydrase I (hCA I) and II (hCA II). The inhibitory effects of the drugs on hCA I and hCA II were determined with both the hydratase and esterase methods. The most potent inhibitors observed were propafenone (hCA I: 2.8 µM and hCA II: 3.02 µM) and captopril (hCA I: 1.58 µM and hCA II: 6.25 µM). Isosorbide mononitrate, propranolol, furosemide, and atorvastatin were also potent inhibitors. The inhibitor constant, Ki, value from the Lineweaver-Burk plot for propafenone was 2.38 µM for hCA I and 2.97 µM for hCA II. The tested cardiac drugs showed potent in vitro inhibition of the hCA I and II isozymes. Especially, in patients with atherosclerotic heart disease, these drugs may be preferred primarily due to the beneficial effects of carbonic anhydrase inhibition on atherosclerosis.

Toxic medications in Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disorder characterized by acute bilateral vision loss. The pathophysiology involves reactive oxygen species (ROS), which can be affected by medications. This article reviews the evidence for medications with demonstrated and theoretical effects on mitochondrial function, specifically in relation to increased ROS production. The data reviewed provides guidance when selecting medications for individuals with LHON mutations (carriers) and are susceptible to conversion to affected. However, as with all medications, the proven benefits of these therapies must be weighed against, in some cases, purely theoretical risks for this unique patient population.

Development of an in Silico Profiler for Mitochondrial Toxicity

This study outlines the analysis of mitochondrial toxicity for a variety of pharmaceutical drugs extracted from Zhang et al. ((2009) Toxicol. In Vitro, 23, 134-140). These chemicals were grouped into categories based upon structural similarity. Subsequently, mechanistic analysis was undertaken for each category to identify the molecular initiating event driving mitochondrial toxicity. The mechanistic information elucidated during the analysis enabled mechanism-based structural alerts to be developed and combined together to form an in silico profiler. This profiler is envisaged to be used to develop chemical categories based upon similar mechanisms as part of the adverse outcome pathway paradigm. Additionally, the profiler could be utilized in screening large data sets in order to identify chemicals with the potential to induce mitochondrial toxicity.

Mitochondrial Disorder Aggravated by Propranolol

Although there are indications that beta-blockers affect the skeletal muscle in therapeutic dosages, their influence on mitochondrial disorders is unknown. A 52-year-old woman developed double vision, myalgias, muscle cramps, and hip and thigh muscle stiffness. Clinical neurologic examination revealed ptosis, dysarthria, sore neck muscles, weakness and wasting of the thighs, and generally brisk tendon reflexes. Lactate stress testing was significantly abnormal. Needle electromyography was nonspecifically abnormal and myopathic. Muscle biopsy showed mild myopathic changes, target fibers, and a single COX-negative fiber. Probable mitochondrial disorder was diagnosed. The patient had been on 30 mg of propranolol during 7 years for arterial hypertension. Shortly after discontinuation of the drug, her double vision gradually disappeared, myalgias and muscle cramps gradually resolved, and the patient reported an increase in muscle mass on repeated follow-ups. Long-term administration of propranolol may aggravate a mitochondrial disorder. Discontinuation of propranolol may result in a gradual resolution of these adverse reactions.

Atenolol depresses post-ischaemic recovery in the isolated rat heart

Metabolic events during ischaemia are probably important in determining post-ischaemic myocardial recovery. The aim of this study was to assess the effects of the beta-blocker atenolol and the high energy demand in an ischaemia-reperfusion model free of neurohormonal and vascular factors. We exposed Langendorff-perfused isolated rat hearts to low-flow ischaemia (30 min) and reflow (20 min). Three groups of hearts were used: control hearts (n =11), hearts that were perfused with 2.5 micrograms l-1atenolol (n =9), and hearts electrically paced during ischaemia to distinguish the effect of heart rate from that of the drug (n =9). The hearts were freeze-clamped at the end of reflow to determine high-energy phosphates and their metabolites. During ischaemia, the pressure-rate product was 2.3+/-0.2, 5.2+/-1.1, and 3.3+/-0.3 mmHg 10(3)min in the control, atenolol and paced hearts, respectively. In addition, the ATP turnover rate, calculated from venous (lactate), oxygen uptake and flow, was higher in atenolol (11.2+/-1.7 micromol min-1) and paced (8.1+/-0.8 micromol min-1) hearts than in control (6.2+/-0.8 micromol min-1). At the end of reflow, the pressurexrate product recovered 75.1+/-6.4% of baseline in control vs 54.1+/-9.1 and 48.8+/-4.4% in atenolol and paced hearts (P<0.05). In addition, the tissue content of ATP was higher in the control hearts (15.8+/-1. 0 micromol g(dw)(-1)) than in atenolol (10.5+/-2.6 micromol g(dw)(-1)) and paced (10.9+/-1.3 micromol g(dw)(-1)) hearts. Thus, by suppressing the protective effects of down-regulation, both atenolol and pacing apparently depress myocardial recovery in this model.

Actions of amiodarone on mitochondrial ATPase and lactate dehydrogenase activities in guinea pig heart preparations

The effects of amiodarone on mitochondrial ATPase (EC 3.6.1.3) and lactate dehydrogenase (LDH: EC 1.1.1.27) activities were studied in guinea pig mitochondrial preparations in order to test the hypothesis that amiodarone exerts some of its effects as a result of multiple actions on membrane-bound enzymes and receptors. Amiodarone inhibited the ATPase activity in the range of 10 pM to 10 mM (n = 10) with IC50 values of 56.4 +/- 7.2 microM. However, although the inhibitory action was very significant (P < 0.0001, compared to the control) in the concentration range of 100 pM to 10 microM, the differences in individual enzyme responses showed very weak correlation with drug concentration. In this region, the inhibitory effects were almost constant at approximately 37%. Below 100 pM and above this range however, the concentration-response relationships were steep, reaching total inhibition at approximately 2.5 mM. Amiodarone also exerted concentration-dependent inhibitory effects on lactate dehydrogenase activity. However, over the effective inhibitory concentration range (5-95%) of 7.5 microM to 2.5 mM (n = 8) and IC50 value of 108 +/- 6 microM, its inhibitory potency was twofold weaker than that of its ATPase inhibition. We propose that these actions contribute, at least in part, to the mechanism(s) of some of the pharmacological actions of amiodarone.

Investigation of class I anti-arrhythmic drug actions on guinea-pig cardiac mitochondrial lactate dehydrogenase activity

1. The effects of the Class I anti-arrhythmic drugs quinidine, procainamide, lidocaine, phenytoin and tocainide on mitochondrial lactate dehydrogenase activity were compared in guinea-pig heart preparations. 2. All the tested drugs inhibited the enzyme activity in a concentration-dependent fashion, exhibiting varying profiles in their actions. Lidocaine exhibited inhibitory concentration 20% (IC20) and IC50 values of 0.52 +/- 0.02 mmol/L and 25.6 +/- 0.5 mmol/L, procainamide 6.0 +/- 0.2 mmol/L and 108 +/- 7.2 mmol/L, phenytoin 3.4 +/- 0.06 mumol/L and 0.34 +/- 0.02 mmol/L, quinidine 39.2 +/- 1.2 mumol/L and 9.8 +/- 0.8 mmol/L and tocainide 2.7 +/- 0.3 mmol/L and 44.6 +/- 2.5 mmol/L. 3. According to the IC50 values, this is the order of their inhibitory potencies: phenytoin > quinidine > lidocaine > tocainide > procainamide. This trend is in general agreement with the lipophilicity rank of the drugs. 4. It is concluded, therefore, that inhibition of mitochondrial lactate dehydrogenase is a property shared by most Class I anti-arrhythmic drugs which may depend on their lipophilicity and possibly their membrane stabilizing effects.

Effects of class I antiarrhythmic drugs on mitochondrial ATPase activity in guinea pig heart preparations

1. The effects of three class I antiarrhythmic drugs quinidine, lidocaine and lorcainide on undamaged myocardial mitochondrial ATPase [ATP: phosphohydrolase, EC 3.6.1.3] activity were evaluated in guinea pig heart preparations. 2. All three drugs inhibited the enzyme activity in a concentration-dependent fashion. 3. Lorcainide was the most potent, exerting inhibitory effects in the range of less than 1.0 nM-2.0 mM, with IC20 and IC50 values of 9.4 +/- 0.6 nM and 87.2 +/- 5.5 microM. However, in the range of approx. 10 nM-10 microM, the enzyme response decreased only slightly with increasing lorcainide concentrations. 4. Quinidine and lidocaine, on the other hand, inhibited the enzyme activity in the range of 1.0 microM-100 mM. 5. The IC20 and IC50 values for quinidine were 0.92 +/- 0.04 mM and 4.8 +/- 0.6 mM and for lidocaine were 115 +/- 6 microM and 2.3 +/- 0.3 mM. 6. The results show that all three drugs inhibit mitochondrial ATPase activity and that lorcainide is the most potent. 7. These inhibitory effects may be related to the lipophilicity and membrane stabilizing activity of this class of antiarrhythmic drugs.