Rhabdomyolysis or crush syndrome is a pathology caused by muscle injury resulting in acute renal failure. The latest data give strong evidence that this syndrome caused by accumulation of muscle breakdown products in the blood stream is associated with oxidative stress with primary role of mitochondria. In order to evaluate the significance of oxidative stress under rhabdomyolysis we explored the direct effect of myoglobin on renal tubules and isolated kidney mitochondria while measuring mitochondrial respiratory control, production of reactive oxygen and nitrogen species and lipid peroxidation. In parallel, we evaluated mitochondrial damage under myoglobinurea in vivo. An increase of lipid peroxidation products in kidney mitochondria and release of cytochrome c was detected on the first day of myoglobinuria. In mitochondria incubated with myoglobin we detected respiratory control drop, uncoupling of oxidative phosphorylation, an increase of lipid peroxidation products and stimulated NO synthesis. Mitochondrial pore inhibitor, cyclosporine A, mitochondria-targeted antioxidant (SkQ1) and deferoxamine (Fe-chelator and ferryl-myoglobin reducer) abrogated these events. Similar effects (oxidative stress and mitochondrial dysfunction) were revealed when myoglobin was added to isolated renal tubules. Thus, rhabdomyolysis can be considered as oxidative stress-mediated pathology with mitochondria to be the primary target and possibly the source of reactive oxygen and nitrogen species. We speculate that rhabdomyolysis-induced kidney damage involves direct interaction of myoglobin with mitochondria possibly resulting in iron ions release from myoglobin's heme, which promotes the peroxidation of mitochondrial membranes. Usage of mitochondrial permeability transition blockers, Fe-chelators or mitochondria-targeted antioxidants, may bring salvage from this pathology.

Oxidative stress-related renal pathologies apparently include rhabdomyolysis and ischemia/reperfusion phenomenon. These two pathologies were chosen for study in order to develop a proper strategy for protection of the kidney. Mitochondria were found to be a key player in these pathologies, being both the source and the target for excessive production of reactive oxygen species (ROS). A mitochondria-targeted compound which is a conjugate of a positively charged rhodamine molecule with plastoquinone (SkQR1) was found to rescue the kidney from the deleterious effect of both pathologies. Intraperitoneal injection of SkQR1 before the onset of pathology not only normalized the level of ROS and lipid peroxidized products in kidney mitochondria but also decreased the level of cytochrome c in the blood, restored normal renal excretory function and significantly lowered mortality among animals having a single kidney exposed to ischemia/reperfusion. The SkQR1-derivative missing plastoquinone (C12R1) possessed some, although limited nephroprotective properties and enhanced animal survival after ischemia/reperfusion. SkQR1 was found to induce some elements of nephroprotective pathways providing ischemic tolerance such as an increase in erythropoietin levels and phosphorylation of glycogen synthase kinase 3β in the kidney. SkQR1 also normalized renal erythropoietin level lowered after kidney ischemia/reperfusion and injection of a well-known nephrotoxic agent gentamicin.

It is generally accepted that mitochondrial production of reactive oxygen species is nonlinearly related to the value of the mitochondrial membrane potential with significant increment at values exceeding 150 mV. Due to this, high values of the membrane potential are highly dangerous, specifically under pathological conditions associated with oxidative stress. Mild uncoupling of oxidative phosphorylation is an approach to preventing hyperpolarization of the mitochondrial membrane. We confirmed data obtained earlier in our group that dodecylrhodamine 19 (C(12)R1) (a penetrating cation from SkQ family not possessing a plastoquinone group) has uncoupling properties, this fact making it highly potent for use in prevention of pathologies associated with oxidative stress induced by mitochondrial hyperpolarization. Further experiments showed that C(12)R1 provided nephroprotection under ischemia/reperfusion of the kidney as well as under rhabdomyolysis through diminishing of renal dysfunction manifested by elevated level of blood creatinine and urea. Similar nephroprotective properties were observed for low doses (275 nmol/kg) of the conventional uncoupler 2,4-dinitrophenol. Another penetrating cation that did not demonstrate protonophorous activity (SkQR4) had no effect on renal dysfunction. In experiments with induced ischemic stroke, C(12)R1 did not have any effect on the area of ischemic damage, but it significantly lowered neurological deficit. We conclude that beneficial effects of penetrating cation derivatives of rhodamine 19 in renal pathologies and brain ischemia may be at least partially explained by uncoupling of oxidation and phosphorylation.

A mitochondria-targeted chimeric compound consisting of a rhodamine derivative linked to a plastoquinone molecule (10-(6'-plastoquinonyl)decylrhodamine, SkQR1) was studied under conditions of acute brain or kidney damage. A protective effect of this compound was demonstrated in a model of focal brain ischemia, rat kidney ischemia/reperfusion, myoglobinuria (rhabdomyolysis, or crush syndrome), and pyelonephritis. We found that a single intraperitoneal injection of SkQR1 diminishes the size of the ischemic zone in the brain and improves performance of a test characterizing neurological deficit in ischemic animals. Control substance not containing plastoquinone appeared to be not neuroprotective. The data show that SkQR1 is a nephroprotectant and neuroprotectant, which can be due to the antioxidative action of this Skulachev cation.

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