Bay K 8644, modifier of calcium transport and energy metabolism in rat heart mitochondria: a new intracellular site of action

Are antibacterial effects of non-antibiotic drugs random or purposeful because of a common evolutionary origin of bacterial and mammalian targets?

Purpose

Advances in structural biology, genetics, bioinformatics, etc. resulted in the availability of an enormous pool of information enabling the analysis of the ancestry of pro- and eukaryotic genes and proteins.

Methods

This review summarizes findings of structural and/or functional homologies of pro- and eukaryotic enzymes catalysing analogous biological reactions because of their highly conserved active centres so that non-antibiotics interacted with bacterial targets.

Results

Protease inhibitors such as staurosporine or camostat inhibited bacterial serine/threonine or serine/tyrosine protein kinases, serine/threonine phosphatases, and serine/threonine kinases, to which penicillin-binding-proteins are linked, so that these drugs synergized with β-lactams, reverted aminoglycoside-resistance and attenuated bacterial virulence. Calcium antagonists such as nitrendipine or verapamil blocked not only prokaryotic ion channels but interacted with negatively charged bacterial cell membranes thus disrupting membrane energetics and inducing membrane stress response resulting in inhibition of P-glycoprotein such as bacterial pumps thus improving anti-mycobacterial activities of rifampicin, tetracycline, fluoroquinolones, bedaquilin and imipenem-activity against Acinetobacter spp. Ciclosporine and tacrolimus attenuated bacterial virulence. ACE-inhibitors like captopril interacted with metallo-β-lactamases thus reverting carbapenem-resistance; prokaryotic carbonic anhydrases were inhibited as well resulting in growth impairment. In general, non-antibiotics exerted weak antibacterial activities on their own but synergized with antibiotics, and/or reverted resistance and/or attenuated virulence.

Conclusions

Data summarized in this review support the theory that prokaryotic proteins represent targets for non-antibiotics because of a common evolutionary origin of bacterial- and mammalian targets resulting in highly conserved active centres of both, pro- and eukaryotic proteins with which the non-antibiotics interact and exert antibacterial actions.

Changes in mitochondrial function are pivotal in neurodegenerative and psychiatric disorders: how important is BDNF?

The brain is at the very limit of its energy supply and has evolved specific means of adapting function to energy supply, of which mitochondria form a crucial link. Neurotrophic and inflammatory processes may not only have opposite effects on neuroplasticity, but also involve opposite effects on mitochondrial oxidative phosphorylation and glycolytic processes, respectively, modulated by stress and glucocorticoids, which also have marked effects on mood. Neurodegenerative processes show marked disorders in oxidative metabolism in key brain areas, sometimes decades before symptoms appear (Parkinson's and Alzheimer's diseases). We argue that brain-derived neurotrophic factor couples activity to changes in respiratory efficiency and these effects may be opposed by inflammatory cytokines, a key factor in neurodegenerative processes.

Modification of swelling-contraction-aggregation processes in rat muscle mitochondria by the 1,4-dihydropyridines, cerebrocrast and glutapyrone, themselves and in the presence of azidothymidine

The influence of the 1,4-dihydropyridines (DHPs), water-soluble glutapyrone available as sodium, potassium and ammonium salts of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-DHP-4-carboxamide)glutaric acid, from one side, and a lipophylic cerebrocrast, 2-propoxyethyl 2,6-dimethyl-4-(2-difluoromethoxyphenyl)-1,4-DHP-3,5-dicarboxylate, from the other side, on partially damaged mitochondria of the Wistar rat hindlimb muscle was also studied. The following tests were made: (1) rates of endogenous respiration and substrate (succinate) oxidation and oxidative phosphorylation; (2) rates and amplitudes of high-amplitude swelling and contraction after the addition of ATP, ADP and succinate to the previously swollen mitochondria and (3) rate of reversible self-aggregation of mitochondria isolated in salt media after ATP-induced contraction without and in the presence of azidothymidine (AZT). Cerebrocrast (10-100 microM) partially normalized the endogenous respiration rate and slightly augmented the respiration rate after the addition of succinate and to lesser extent ADP. Cerebrocrast in a concentration-dependent manner (2.5-50 microM) increased (two-fold at 20-50 microM) the active contraction amplitude of swollen mitochondria, induced by single or repeated additions of ATP. The influence of cerebrocrast on the ADP- and succinate-induced contractions was less obvious. Unlike cerebrocrast glutapyrone caused a reduction of the ATP-induced contraction amplitude (two-fold at 0.5-5.0 mM), not impairing the mitochondrial contraction ability in response to ATP or succinate. Pre-exposure to 2.5 mM glutapyrone resulted in at least a 10-fold inhibition of the reversible aggregation rate in the presence of 99 and 198 microM AZT. The results suggest the usefulness of further study of cerebrocrast and glutapyrone in preventing AZT-induced and some other mitochondrial myopathies.

The low-affinity dihydropyridine receptor and Na+/Ca2+ exchanger are associated in adrenal medullary mitochondria

The effect of Ca2+ channel-acting drugs on bovine adrenal mitochondria Ca2+ movements was investigated. Mitochondrial Ca2+ uptake is performed by an energy-driven Ca2+ uniporter with a Km of 20.9 +/- 3.2 microM and Vmax of 148.1 +/- 7.2 nmol 45Ca2+ min-1 mg-1. Ca2+ release is performed through an Na+/Ca2+ antiporter with a Km for Na+ of 4.2 +/- 0.5 mM, a Vmax of 7.5 +/- 0.4 nmol 45Ca2+ min-1 mg-1, and a Hill coefficient of 1.4 +/- 0.2 Ca2+ efflux through the mitochondrial Na+/Ca2+ exchanger was inhibited by several dihydropyridines (nitrendipine, felodipine, nimodipine, (+)isradipine) and by the benzothiazepine diltiazem with similar potencies. In contrast, neither CGP 28392, Bay-K-8644, amlodipine, nor verapamil had any effect on Ca2+ efflux. Nitrendipine at 20 microM modified neither the Km nor the Hill coefficient for Na+, whereas the Vmax was reduced to 2.9 nmol 45Ca2+ min-1 mg-1, thus demonstrating noncompetitive modulation of the Na+/Ca2+ exchanger. None of the Ca2+ channel-acting drugs assayed at 100 microM affected Ca2+ influx through the uniporter. Ca2+ channel blockers inhibited the Na+/Ca2+ antiporter and displaced the specific binding of [3H]nitrendipine to intact mitochondria with Ki values similar to the IC50s obtained for the inhibition of the Ca2+ efflux. Ca2+ channel-acting drugs that did not inhibit the Na+/Ca2+ exchanger (amlodipine, CGP 28392, Bay-K-9644, and verapamil, at concentrations of 100 microM or higher) had no effect on [3H]nitrendipine binding. These results suggest that the adrenomedullary mitochondrial dihydropyridine receptor is associated with the Na+/Ca2+ exchanger.

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+.