calcimycin and malonic-acid

Changes in mitochondrial integrity, reactive oxygen species release and Ca2+ handling are proposed to be involved in the pathogenesis of many neurological disorders including methylmalonic acidaemia and Huntington's disease, which exhibit partial mitochondrial respiratory inhibition. In this report, we studied the mechanisms by which the respiratory chain complex II inhibitors malonate, methylmalonate and 3-nitropropionate affect rat brain mitochondrial function and neuronal survival. All three compounds, at concentrations which inhibit respiration by 50%, induced mitochondrial inner membrane permeabilization when in the presence of micromolar Ca2+ concentrations. ADP, cyclosporin A and catalase prevented or delayed this effect, indicating it is mediated by reactive oxygen species and mitochondrial permeability transition (PT). PT induced by malonate was also present in mitochondria isolated from liver and kidney, but required more significant respiratory inhibition. In brain, PT promoted by complex II inhibition was stimulated by increasing Ca2+ cycling and absent when mitochondria were pre-loaded with Ca2+ or when Ca2+ uptake was prevented. In addition to isolated mitochondria, we determined the effect of methylmalonate on cultured PC12 cells and freshly prepared rat brain slices. Methylmalonate promoted cell death in striatal slices and PC12 cells, in a manner attenuated by cyclosporin A and bongkrekate, and unrelated to impairment of energy metabolism. We propose that under conditions in which mitochondrial complex II is partially inhibited in the CNS, neuronal cell death involves the induction of PT.

Topics: Animals; Antimycin A; Bongkrekic Acid; Brain; Calcimycin; Calcium; Catalase; Cell Survival; Cyclosporins; Dose-Response Relationship, Drug; Drug Interactions; Electron Transport Complex II; Enzyme Inhibitors; Female; In Vitro Techniques; Ionophores; Malonates; Membrane Potentials; Methylmalonic Acid; Mitochondria; NADP; Neurons; Nitro Compounds; Oxygen Consumption; PC12 Cells; Permeability; Propionates; Rats; Rotenone; Tacrolimus; Tetrazolium Salts; Thiazoles; Uncoupling Agents

Calbindin is a 28 kDa calcium-binding protein expressed in restricted neuronal populations in the mammalian brain where it may play a role in protecting neurons against excitotoxic insults. Recent findings indicate that electrical activity and some neurotrophic factors can induce the expression of calbindin in neurons. We now report that brain injury, effected by systemic administration of the excitotoxin kainate or mechanical trauma, induces expression of calbindin in cells of the corpus callosum and subcortical white matter. Immunohistochemical analysis using antibodies to the astrocyte-specific proteins (glial fibrillary acidic protein and S-100 beta) established the identity of calbindin immunoreactive cells as astrocytes. Because brain injury is known to induce the expression of several neurotrophic factors and cytokines, we employed cultures of hippocampal and neocortical astrocytes to test the hypothesis that such factors can induce expression of calbindin in astrocytes. Tumor necrosis factors (TNF alpha and TNF beta), cytokines that are expressed in response to brain injury, induced the expression of calbindin in cultured rat hippocampal and neocortical astrocytes. Two neurotrophic factors, basic fibroblast growth factor and nerve growth factor, did not induce calbindin in astrocytes. TNF-treated, calbindin-expressing astrocytes were resistant to acidosis and calcium ionophore toxicity, suggesting that TNFs and calbindin may serve a cytoprotective role in astrocytes in the injured brain.

Topics: Animals; Astrocytes; Blotting, Western; Brain Injuries; Calbindins; Calcimycin; Cells, Cultured; Cerebral Cortex; Excitatory Amino Acid Agonists; Hippocampus; Immunohistochemistry; Ionophores; Kainic Acid; Lymphotoxin-alpha; Male; Malonates; Rats; Rats, Sprague-Dawley; S100 Calcium Binding Protein G; Tumor Necrosis Factor-alpha

It is well established that calcium ionophore A 23187 induces acrosome reaction (AcR) of uncapacitated spermatozoa in the presence of extracellular Ca2+ ions. In the present study, we have investigated how extracellular energy substrates (glucose, pyruvate, and lactate) affect the ionophore-induced AcR of guinea pig spermatozoa. It was found that 0.3 microM concentration of A 23187 had the maximum effect to initiate AcR of guinea pig spermatozoa. Virtually no spermatozoa underwent their AcR when incubated in substrate-free modified Tyrode's medium containing 0.3 microM A 23187 and 2 mM Ca2+. At least one exogenous substrate is essential for the ionophore-induced AcR of spermatozoa. As for efficacy of the substrates, lactate was more effective than pyruvate and glucose. However, a better result was observed when lactate was added along with pyruvate. Malonate inhibited the ionophore-induced AcR but not the hyperactivated motility of spermatozoa. The mitochondrial electron transport chain blockers rotenone, antimycin, and oligomycin failed to inhibit AcR, although in the presence of these blockers spermatozoa were unable to show hyperactivated motility. These results suggest that the mitochondrial citric acid cycle, not the electron transport chain, is probably the energy source for ionophore-induced AcR of guinea pig spermatozoa.

Topics: Acrosome; Animals; Antimycin A; Calcimycin; Energy Metabolism; Glucose; Guinea Pigs; Lactates; Male; Malonates; Mitochondria; Oligomycins; Pyruvates; Rotenone