Is the beneficial effect of calcium channel blockers against cyclosporine A toxicity related to a restoration of ATP synthesis?

Protective effect of schisandrin B against cyclosporine A-induced nephrotoxicity in vitro and in vivo

Schisandrin B (Sch B) is an active ingredient of the fruit of Schisandra chinensis. It has many therapeutic effects arising from its tonic, sedative, antitussive and antiaging activities and is also used in the treatment of viral and chemical hepatitis. The aim of this study was to investigate the protective effects of Sch B on cyclosporine A (CsA)-induced nephrotoxicity in mice and HK-2 cells (a human proximal tubular epithelial cell line). After gavage with Sch B (20 mg/kg) or olive oil (vehicle), mice received CsA (30 mg/kg) by subcutaneous injection once daily for four weeks. Renal function, histopathology, and tissue glutathione (GSH) and malondialdehyde (MDA) levels were evaluated after the last treatment. The effects of Sch B on CsA-induced oxidative damage in HK-2 cells were investigated by measuring cell viability, the release of lactate dehydrogenase (LDH), the level of reactive oxygen species (ROS), and the cellular GSH and ATP concentrations. Cellular apoptosis was assessed by flow cytometry. Treatment with Sch B in CsA-treated mice significantly suppressed the elevation of blood urea nitrogen (BUN) and serum creatinine levels and attenuated the histopathological changes. Additionally, Sch B also decreased renal MDA levels and increased GSH levels in CsA-treated mice. Using an in vitro model, Sch B (2.5, 5 and 10 μM) significantly increased the cell viability and reduced LDH release and apoptosis induced by CsA (10 μM) in HK-2 cells. Furthermore, Sch B increased the intracellular GSH and ATP levels and attenuated CsA-induced ROS generation. In conclusion, Sch B appears to protect against CsA-induced nephrotoxicity by decreasing oxidative stress and cell death.

Role of reduced glutathione efflux in apoptosis of immortalized human keratinocytes induced by UVA

We have investigated the role played by GSH efflux in apoptosis of human HaCaT keratinocytes induced by UVA irradiation. UVA irradiation of HaCaT cells caused a rapid rise in GSH efflux across the intact cell membrane, followed by an increase in apoptosis. GSH efflux was stimulated by glucose and was reduced by the addition of exogenous GSH and intracellular GSH depletion by buthionine sulfoximine, suggesting that GSH transport is active and is influenced by the GSH concentration gradient across the cell membrane. Verapamil and cyclosporin A, blockers of the multidrug resistance-associated protein, decreased UVA-induced GSH efflux. GSH efflux occurred within 2 h of UVA irradiation, suggesting that the stimulation of GSH efflux is due to an increase in the activity of pre-existing multidrug resistance-associated protein transporter carrier. Although inhibition of GSH efflux did not affect caspase activation and DNA fragmentation, it delayed the gradual increase in plasma membrane permeability and reduced phosphatidylserine translocation in HaCaT cells. It is therefore likely that upon UVA irradiation, GSH efflux increased the intracellular oxidative stress without intervention of reactive oxygen species, thus resulting in more phosphatidylserine externalization and membrane rearrangement. These provide targets for macrophage recognition and phagocytosis and thus minimize the potential to invoke inflammation or neoplastic transformation.

Comparison of the effects of cyclosporin a on the metabolism of perfused rat brain slices during normoxia and hypoxia

The authors evaluated and compared the metabolic effects of cyclosporin A in the rat brain during normoxia and hypoxia/reperfusion. Ex vivo 31P magnetic resonance spectroscopy experiments based on perfused rat brain slices showed that under normoxic conditions, 500 microg/L cyclosporin A significantly reduced mitochondrial energy metabolism (nucleotide triphosphate, 83 +/- 9% of controls; phosphocreatine, 69 +/- 9%) by inhibition of the Krebs cycle (glutamate, 77 +/- 5%) and oxidative phosphorylation (NAD+, 65 +/- 14%) associated with an increased generation of reactive oxygen species (285 +/- 78% of control). However, the same cyclosporin A concentration (500 microg/L) was found to be the most efficient concentration to inhibit the hypoxia-induced mitochondrial release of Ca2+ in primary rat hippocampal cells with cytosolic Ca2+ concentrations not significantly different from normoxic controls. Addition of 500 microg/L cyclosporin A to the perfusion medium protected high-energy phosphate metabolism (nucleotide triphosphate, 11 +/- 15% of control vs. 35 +/- 9% with 500 microg/L cyclosporin A) and the intracellular pH (6.2 +/- 0.1 control vs. 6.6 +/- 0.1 with cyclosporin A) in rat brain slices during 30 minutes of hypoxia. Results indicate that cyclosporin A simultaneously decreases and protects cell glucose and energy metabolism. Whether the overall effect was a reduction or protection of cell energy metabolism depended on the concentrations of both oxygen and cyclosporin A in the buffer solution.

Regulation of the renal basolateral transport system for organic anions by calcium channel blockers

Calcium channel blockers have been reported to exert multiple effects on renal tubular function. Therefore, the effects of the calcium channel blockers nifedipine and verapamil on the cellular uptake of tritiated para -aminohippuric acid (PAH) into microdissected non-perfused rabbit kidney S2 proximal tubule segments were investigated to study a possible influence of calcium channel blockers on renal PAH transport. Since the tubules were entirely collapsed, the accumulated radioactivity overwhelmingly reflects the transport across the basolateral membrane. Tubular PAH accumulation was increased by 1 and 10 microm verapamil, and by 1 microm nifedipine, but it was unaffected by lower or higher concentrations of these calcium channel blockers. The increase in PAH accumulation caused by 1 microm nifedipine or 10 microm verapamil was independent from changes in intracellular Ca(2+) and inhibited by staurosporine (1 and 10 n m) a potent inhibitor of protein kinase C (PKC). Our results indicate that the calcium channel blockers nifedipine and verapamil increase the transport of organic anions across the basolateral membrane of proximal tubules, probably by an activation of PKC. Furthermore, the increased tubular PAH transport may disturb the estimation of the renal PAH-clearance.

Oxidant, mitochondria and calcium: an overview

Mitochondria are active in the continuous generation of reactive oxygen species (ROS), (e.g., superoxide), thereby favouring a situation of mitochondrial oxidative stress. Under oxidative stress--for example, ischaemia-reoxygenation injury to cells--mitochondria form superoxide, which in turn is converted to hydrogen peroxide and the potent reactive species, hydroxyl radical. Alternatively, mitochondrial superoxide may react with nitric oxide to form potent oxidant peroxynitrite and as a consequence, mitochondrial function is altered. An increase in the release of calcium from mitochondria by oxidants stimulates calcium-dependent enzymes such as calcium-dependent proteases, nucleases, and phospholipases, which subsequently trigger apoptosis of the cells. In principle, calcium can leave mitochondria by different ways: by non-specific leakage through the inner membrane by "pore formation," by changes in the membrane lipid phase, by reversal of the uniport influx carrier, by the specific calcium/hydrogen (or sodium) antiport system, by channel-mediated release pathways, or by a combination of two or more of these pathways. Additionally, the release of calcium from mitochondria can also occur either by oxidation of internal nicotinamide adenine nucleotides to ADP ribose and nicotinamide or by oxidation of thiols in membrane proteins. Once calcium efflux has been triggered, a series of common pathways of apoptosis are initiated, each of which may be sufficient to destroy the cell. Apoptosis requires the active participation of cellular components, and several genes have been suggested to control apoptosis. The proto-oncogene bcl-2 suppresses apoptosis through mitochondrial effects. Overexpression of bcl-2 in the mitochondrial membrane inhibits calcium efflux, but the underlying mechanisms are not clearly known. Further studies are needed to explore the nature of the apoptosis-inducing pathways, the precise mechanisms of calcium efflux, the molecular partners of bcl-2 oncoproteins at the level of the outer-inner membrane contact sites, the molecular biology of the apoptosis-inducing factor formation and release, and the essential molecular targets of apoptosis-inducing proteases. Clarification of these issues might facilitate the understanding of mitochondrial response on cellular calcium dynamics under oxidant stress.

Ursodeoxycholate protects against ethanol-induced liver mitochondrial injury

The purpose of this work was to examine whether ursodeoxycholate (UDC), a hydrophilic bile salt, could reduce mitochondrial liver injury from chronic ethanol consumption in rats. Animals were pair-fed liquid diets containing 36% of calories as ethanol or isocaloric carbohydrates. They were randomly assigned into 4 groups of 7 rats each and received a specific treatment for 5 weeks: control diet, ethanol diet, control diet + UDC, and ethanol diet + UDC. Respiratory rates of isolated liver mitochondria were measured using a Clark oxygen electrode with sodium succinate as substrate. Mitochondria from rats chronically fed ethanol demonstrated an impaired ability to produce energy. At the fatty liver stage, the ADP-stimulated respiration (V3) was depressed by 33%, the respiratory control ratio (RC) by 25% and the P/O ratio by 15%. In ethanol-fed rats supplemented with UDC, both the rate and efficiency of ATP synthesis via the oxidative phosphorylation were improved: V3 was increased by 35%, P/O by 8%. All the respiratory parameters were similar in control group and control + UDC group. On the other hand, the number and size of mitochondria were assessed by electron microscopy and computer-assisted quantitative analysis. The number of mitochondria from ethanol-treated rats was decreased by 29%, and they were enlarged by 74%. Both parameters were normalized to control values by UDC treatment. These studies demonstrate that UDC has a protective effect against ethanol-induced mitochondrial injury by improving ATP synthesis and preserving liver mitochondrial morphology. These UDC positive effects may contribute to the observed decrease in fat accumulation and may delay the progression of alcoholic injury to more advanced stages.