Disruption of mitochondrial functions involving mitochondrial permeability transition pore opening caused by maleic acid in rat kidney

Journal of Bioenergetics and Biomembranes - Propionic acid (PA) predominantly accumulates in tissues and biological fluids of patients affected by propionic acidemia that may manifest chronic renal...     

Metabolites from algae with economical impact

In order to survive in a highly competitive environment, freshwater or marine algae have to develop defense strategies that result in a tremendous diversity of compounds from different metabolic pathways. Recent trends in drug research from natural sources have shown that algae are promising organisms to furnish novel biochemically active compounds. The current review describes the main substances biosynthesized by algae with potential economic impact in food science, pharmaceutical industry and public health. Emphasis is given to fatty acids, steroids, carotenoids, polysaccharides, lectins, mycosporine-like amino acids, halogenated compounds, polyketides and toxins.     

3-Methylcrotonylglycine Disrupts Mitochondrial Energy Homeostasis and Inhibits Synaptic Na+,K+-ATPase Activity in Brain of Young Rats

Deficiency of 3-methylcrotonyl-CoA carboxylase activity is an inherited metabolic disease biochemically characterized by accumulation and high urinary excretion of 3-methylcrotonylglycine (3MCG), and also of 3-hydroisovalerate in lesser amounts. Affected patients usually have neurologic dysfunction, brain abnormalities and cardiomyopathy, whose pathogenesis is still unknown. The present study investigated the in vitro effects of 3MCG on important parameters of energy metabolism, including CO₂ production from labeled acetate, enzyme activities of the citric acid cycle, as well as of the respiratory chain complexes I–IV (oxidative phosphorylation), creatine kinase (intracellular ATP transfer), and synaptic Na⁺,K⁺-ATPase (neurotransmission) in brain cortex of young rats. 3MCG significantly reduced CO₂ production, implying that this compound compromises citric acid cycle activity. Furthermore, 3MCG diminished the activities of complex II-III of the respiratory chain, mitochondrial creatine kinase and synaptic membrane Na⁺,K⁺-ATPase. Furthermore, antioxidants were able to attenuate or fully prevent the inhibitory effect of 3MCG on creatine kinase and synaptic membrane Na⁺,K⁺-ATPase activities. We also observed that lipid peroxidation was elicited by 3MCG, suggesting the involvement of free radicals on 3MCG-induced effects. Considering the importance of the citric acid cycle and the electron flow through the respiratory chain for brain energy production, creatine kinase for intracellular energy transfer, and Na⁺,K⁺-ATPase for the maintenance of the cell membrane potential, the present data indicate that 3MCG potentially impairs mitochondrial brain energy homeostasis and neurotransmission. It is presumed that these pathomechanisms may be involved in the neurological damage found in patients affected by 3-methylcrotonyl-CoA carboxylase deficiency.     

Creatine and Antioxidant Treatment Prevent the Inhibition of Creatine Kinase Activity and the Morphological Alterations of C6 Glioma Cells Induced by the Branched-Chain α-Keto Acids Accumulating in Maple Syrup Urine Disease

Accumulation of the branched-chain alpha-keto acids (BCKA), alpha-ketoisocaproic acid (KIC), alpha-keto-beta-methylvaleric acid (KMV), and alpha-ketoisovaleric acid (KIV) and their respective branched-chain alpha-amino acids (BCAA) in tissues and biological fluids is the biochemical hallmark of patients affected by the neurometabolic disorder known as maple syrup urine disease (MSUD). Considering that brain energy metabolism is possibly altered in MSUD, the objective of this study was to determine creatine kinase (CK) activity, a key enzyme of energy homeostasis, in C6 glioma cells exposed to BCKA. The cells were incubated with 1, 5, or 10 mM BCKA for 3 h and the CK activity measured afterwards. The results indicated that the BCKA significantly inhibited CK activity at all tested concentrations. Furthermore, the inhibition caused by the BCKA on CK activity was totally prevented by preincubation with the energetic substrate creatine and by coincubation with the N-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, indicating that deficit of energy and nitric oxide (NO) are involved in these effects. In contrast, other antioxidants such as glutathione (GSH) and trolox (soluble Vitamin E) were not able to prevent CK inhibition. In addition, we observed that the C6 cells changed their usual rounded morphology when exposed for 3 h to 10 mM BCKA and that creatine and L-NAME prevented these morphological alterations. Considering the importance of CK for brain metabolism homeostasis, it is conceivable that inhibition of this enzyme by increased levels of BCKA may contribute to the neurodegeneration of MSUD patients.     

Medium-chain fatty acids accumulating in MCAD deficiency elicit lipid and protein oxidative damage and decrease non-enzymatic antioxidant defenses in rat brain

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most frequent disorder of fatty acid oxidation with a similar prevalence to that of phenylketonuria. Affected patients present tissue accumulation of the medium-chain fatty acids octanoate (OA), decanoate (DA) and cis-4-decenoate. Clinical presentation is characterized by neurological symptoms, such as convulsions and lethargy that may develop into coma and sudden death. The aim of the present work was to investigate the in vitro effect of OA and DA, the metabolites that predominantly accumulate in MCADD, on oxidative stress parameters in rat cerebral cortex homogenates. It was first verified that both DA and OA significantly increased chemiluminescence and thiobarbituric acid-reactive species levels (lipoperoxidation) and decreased the non-enzymatic antioxidant defenses, measured by the decreased total antioxidant capacity. DA also enhanced carbonyl content and oxidation of sulfhydryl groups (protein damage) and decreased reduced glutathione (GSH) levels. We also verified that DA-induced GSH decrease and sulfhydryl oxidation were not observed when cytosolic preparations (membrane-free supernatants) were used, suggesting a mitochondrial mechanism for these actions. Our present data show that the medium-chain fatty acids DA and OA that most accumulate in MCADD cause oxidative stress in rat brain. It is therefore presumed that this pathomechanism may be involved in the pathophysiology of the neurologic symptoms manifested by patients affected by MCADD.     

Inhibition of mitochondrial creatine kinase activity by D-2-hydroxyglutaric acid in cerebellum of young rats

D-2-Hydroxyglutaric aciduria (DHGA) is a neurometabolic disorder biochemically characterized by tissue accumulation and excretion of high amounts of D-2-hydroxyglutaric acid (DGA). Although the affected patients have predominantly severe neurological findings, the underlying mechanisms of brain injury are virtually unknown. In previous studies we have demonstrated that DGA, at concentrations as low as 0.25 mM, significantly decreased creatine kinase activity and other parameters of energy metabolism in cerebral cortex of young rats. In the present study, we investigated the effect of DGA (0.25-5 mM) on total creatine kinase (tCK) activity, as well as on CK activity in cytosolic (Cy-CK) and mitochondrial (Mi-CK) preparations from cerebellum of 30-day-old Wistar rats in order to test whether the inhibitory effect of DGA on CK was tissue specific. We verified that tCK (22% inhibition) and Mi-CK (40% inhibition) activities were moderately inhibited by DGA at concentrations of 2.5 mM and higher, in contrast to Cy-CK, which was not affected by the acid. Kinetic studies revealed that the inhibitory effect of DGA was non-competitive in relation to phosphocreatine. We also observed that this inhibition was fully prevented by preincubation of the homogenates with reduced glutathione, suggesting that the inhibition of CK activity by DGA is possibly mediated by modification of essential thiol groups of the enzyme. Our present results therefore demonstrate a relatively weak inhibitory effect of DGA on cerebellum Mi-CK activity, as compared to that provoked in cerebral cortex, and may possibly be related to the neuropathology of DHGA, characterized by cerebral cortex abnormalities.     

Proline Reduces Creatine Kinase Activity in the Brain Cortex of Rats

Type II hyperprolinemia is an inherited disorder caused by a deficiency of ¹-pyrroline-5-carboxilic acid dehydrogenase, whose biochemical hallmark is proline accumulation in plasma and tissues. Although neurological symptoms occur in most patients, the neurotoxicity of proline is still controversial. The main objective of the present study was to investigate the effect of acute and chronic administration of proline on creatine kinase activity of brain cortex of Wistar rats. Acute treatment was performed by subcutaneous administration of one injection of proline to 22-day-old rats. For chronic treatment, proline was administered twice a day from the 6th to the 21st postpartum day. The results showed that creatine kinase activity was significantly inhibited in the brain cortex of rats subjected to acute proline administration. In contrast, this activity was increased in animals subjected to chronic administration. We also measured the in vitro effect of proline on creatine kinase activity in cerebral cortex of 22-day-old nontreated rats. Proline significantly inhibited creatine kinase activity. Considering the importance of creatine kinase forthe maintenance of energy homeostasis in the brain, it is conceivable that an alteration of this enzyme activity in the brain may be one of the mechanisms by which proline might be neurotoxic.     

Insulinomimetic effects of kaempferitrin on glycaemia and on 14C-glucose uptake in rat soleus muscle

Bauhinia forficata is one of the Bauhinia species mostly used as an antidiabetic herbal remedy in Brazil. Kaempferitrin (kaempferol-3,7-O-(alpha)-L-dirhamnoside) is the predominant flavonol glycoside found in the B. forficata leaves. The aim of the present work was to study the long-term effect of kaempferitrin on glycaemia in diabetic rats, as well as the in vitro effect of this compound on 14C-D-glucose uptake and 14C-leucine incorporation into protein in normal rat soleus muscle. Kaempferitrin was found to have an acute lowering effect on blood glucose in diabetic rats and to stimulate the glucose uptake percentile, as efficiently as insulin in muscle from normal rats. This compound did not have any effect on glucosuria or on protein synthesis in muscle from normal and diabetic animals. However, the protein synthesis in the kaempferitrin-treated groups was maintained at the same level as the respective controls. Thus, the hypoglycaemic effect and the prompt efficiency of the kaempferitrin in stimulating [U-14C]-2-deoxi-D-glucose uptake in muscle -constitute the first evidence to indicate that the acute effect of this compound on blood glucose lowering may occur as a consequence of the altered intrinsic activity of the glucose transporter (Vmax or glucose transporters translocation?) not involving directly the synthesis of new carriers.     

Arginine Administration Decreases Cerebral Cortex Acetylcholinesterase and Serum Butyrylcholinesterase Probably by Oxidative Stress Induction

In the present study we investigated the action of vitamins E and C on the inhibition of acetylcholinesterase and butyrylcholinesterase activities provoked by arginine in cerebral cortex and serum of 60-day-old rats. Animals were pretreated for 1 week with daily intraperitoneal administration of saline (control) or vitamins E (40 mg/kg) and C (100 mg/kg). Twelve hours after the last injection, animals received one injection of arginine (0.8 microM/g of body weight) or saline. Results showed that acetylcholinesterase and butyrylcholinesterase activities were decreased in the arginine-treated rats. Furthermore, pretreatment with vitamins E and C prevented these effects. The data indicate that the reduction of acetylcholinesterase and butyrylcholinesterase activities caused by arginine was probably mediated by oxidative stress. Assuming the possibility that these effects might also occur in the human condition, our findings may be relevant to explain, at least in part, the neurological dysfunction associated with hyperargininemia and might support a novel therapeutic strategy to slow the progression of neurodegeneration in this disorder.