The creatine kinase system and pleiotropic effects of creatine

The pleiotropic effects of creatine (Cr) are based mostly on the functions of the enzyme creatine kinase (CK) and its high-energy product phosphocreatine (PCr). Multidisciplinary studies have established molecular, cellular, organ and somatic functions of the CK/PCr system, in particular for cells and tissues with high and intermittent energy fluctuations. These studies include tissue-specific expression and subcellular localization of CK isoforms, high-resolution molecular structures and structure–function relationships, transgenic CK abrogation and reverse genetic approaches. Three energy-related physiological principles emerge, namely that the CK/PCr systems functions as (a) an immediately available temporal energy buffer, (b) a spatial energy buffer or intracellular energy transport system (the CK/PCr energy shuttle or circuit) and (c) a metabolic regulator. The CK/PCr energy shuttle connects sites of ATP production (glycolysis and mitochondrial oxidative phosphorylation) with subcellular sites of ATP utilization (ATPases). Thus, diffusion limitations of ADP and ATP are overcome by PCr/Cr shuttling, as most clearly seen in polar cells such as spermatozoa, retina photoreceptor cells and sensory hair bundles of the inner ear. The CK/PCr system relies on the close exchange of substrates and products between CK isoforms and ATP-generating or -consuming processes. Mitochondrial CK in the mitochondrial outer compartment, for example, is tightly coupled to ATP export via adenine nucleotide transporter or carrier (ANT) and thus ATP-synthesis and respiratory chain activity, releasing PCr into the cytosol. This coupling also reduces formation of reactive oxygen species (ROS) and inhibits mitochondrial permeability transition, an early event in apoptosis. Cr itself may also act as a direct and/or indirect anti-oxidant, while PCr can interact with and protect cellular membranes. Collectively, these factors may well explain the beneficial effects of Cr supplementation. The stimulating effects of Cr for muscle and bone growth and maintenance, and especially in neuroprotection, are now recognized and the first clinical studies are underway. Novel socio-economically relevant applications of Cr supplementation are emerging, e.g. for senior people, intensive care units and dialysis patients, who are notoriously Cr-depleted. Also, Cr will likely be beneficial for the healthy development of premature infants, who after separation from the placenta depend on external Cr. Cr supplementation of pregnant and lactating women, as well as of babies and infants are likely to be of benefit for child development. Last but not least, Cr harbours a global ecological potential as an additive for animal feed, replacing meat- and fish meal for animal (poultry and swine) and fish aqua farming. This may help to alleviate human starvation and at the same time prevent over-fishing of oceans

Effects of hypoxia and pharmacological treatment on enzyme activities in skeletal muscle of rats of different ages

The activities of enzymes related to energy metabolism in the gastrocnemius and soleus muscles in young-adult (4 months), mature (12 months), and senescent (24 months) rats were compared after continuous (72 consecutive h) exposure to normobaric hypoxia or normoxia after the vasodilator naftidrofuryl or saline solution had been given intraperitoneally for 30 consecutive days. The maximum rats (Vmax) of the following enzyme activities in the crude extract and/or the crude mitochondrial fraction of each muscle specimen were evaluated for: the anaerobic glycolytic pathway (hexokinase, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase), the tricarboxylic acid cycle (citrate synthase, and malate dehydrogenase), the electron transfer chain (cytochrome oxidase), and the NAD+/NADH redox state (total NADH cytochrome c reductase). The significance of differences between the enzyme activities at different ages or under different experimental conditions in the two tissue preparations of the two muscles were determined by ANOVA. MCA and ETA2 were used to evaluate the net effects of the experimental conditions. First, aging did not seem to affect the soleus and gastrocnemius muscles in the same way. In the gastrocnemius muscle, the major changes were seen in enzymes of the glycolytic pathway, in the crude extracts. In the soleus muscle, the more striking changes in enzyme activities as a function of aging were found in the crude mitochondrial fraction. We also found that hypoxia caused more important changes in 12-month-old rats than in those of other ages (especially the enzyme activities of the gastrocnemius muscle). Naftidrofuryl modified the effects of hypoxia only sometimes and further investigations are necessary before we can draw any conclusions about the pharmacological activity of naftidrofuryl in hypoxi

Influence du vieillissement sur le métabolisme énergétique cérébral pendant la récupération post-hypoglycémique chez le rat - application pharmacologique

Influence of aging on cerebral energetic metabolism was evaluated during and after severe hypoglycemia in rats respectively 20 (adults), 60 (matures) or 100 (senescents) week-old. Cerebral content of carbohydrates, amino-acids, ammonia, ATP, ADP, AMP, creatine phosphate and creatine was analysed after 20 min insulin induced hypoglycemia and after 20 min hypoglycemic recovery induced by glucose infusion. In the rats of different ages tested, effect of raubasine (0.85 mg X kg-1 i.p. and i.v.), almitrine (2.68 mg X kg-1 i.p. and i.v.) and association almitrine plus raubasine (at the same doses) on post-hypoglycemic recovery was tested. Aging does not affect the cerebral metabolic disorders occurring in severe hypoglycemia, but rather the metabolic changes during the post-hypoglycemic restitution. In fact there is lower restitution of the concentrations of cerebral cortical metabolites in older rats: the concentrations of many amino-acids and adenylate nucleotides remains largely abnormal. Compared with saline treated post-hypoglycemic rats, raubasine decreases by 15 to 20\% cerebral glucose and pyruvate contents in "adults" and "matures" rats and by 10 to 15\% glutamate content in rat of different ages tested. Almitrine decreases by 20\% cerebral glucose concentration in "matures" and "senescent" rats. In this latter group, almitrine decreases lactate and ammonium contents and increases by 23\% glutamine level. In rats of all ages that were submitted to 20 min insulin induced hypoglycemia followed by 20 min glucose induced post-hypoglycemic recovery, the association almitrine plus raubasine decreases by 20 to 30\% cerebral glucose, pyruvate and lactate contents and decreases by 15\% glutamate. In older brains the association almitrine plus raubasine decreases by 50\% cerebral content in ammonium and concomitantly induces an equivalent increase in glutamine content. The effect of the combination almitrine plus raubasine is characterized by an increase in rate of metabolic recovery process in all ages teste

Effets du vieillissement et de divers agents pharmacologiques sur le métabolisme énergétique cérébral au cours de la récupération post-hypoglycémique chez le rat

Severe acute hypoglycaemia with isoelectric electroencephalogram induces a major deterioration of the energy state and amino acid contents of the brain. During post-hypoglycaemia recovery of adult animals, brain glucose concentrations return to normal values, whereas glycogen turnover remains low as aspartate and pyruvate concentrations increase. ATP levels rise, but the adenine-nucleotide pool remains small despite return to normal of ADP and AMP. Brain phosphocreatine levels return to normal values, with reciprocal changes in creatine content. In adult rats one also notes during recovery an increase in brain glutamine and glutamate, whereas the gamma-aminobutyrate returns to normal. Finally, ammonium and aspartate remain below, and alanine remains above normal values. Aging has no effect on cerebral metabolic disturbances induced by hypoglycaemia, but it influences the cerebral metabolic restoration processes that develop during post-hypoglycaemia recovery. The restitution of cerebral metabolites is weaker in mature and senescent rats than in adult rats. In the oldest rats, in particular, the concentrations of most of the amino acids and of adenyl nucleotides remain largely abnormal. The effects of dihydroergocristine, erbunamonine, raubasine, almitrine and of the almitrine-raubasine combination on post-hypoglycaemia recovery were evaluated in adult, mature and senescent rats. During recovery these pharmacological agents exert different effects on glycolytic metabolites, amino acids and energy-rich phosphate

Changes induced by aging and drug treatment on cerebral enzymatic antioxidant system

The age-related modifications of the participants to the cerebral enzymatic antioxidant system (superoxide dismutase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase) were evaluated in four brain regions from male Wistar rats aged 5, 10, 15, 20, 25, 30, and 35 months. Both the specific enzyme activity and the profile of any enzyme tested markedly differ with age according to the region examined: parieto-temporal cortex, caudate-putamen, substantia nigra and thalamus. This inhomogeneous age-related profile of enzyme activities could explain both the controversial data of literature and the different regional vulnerability of the brain tissue to damage with aging. In rats aged 10, 20, or 30 months, the chronic i.p. treatment for two months with papaverine or ergot alkaloids (dihydroergocristine, dihydroergocornine, dehydroergocriptine) suggests that the antioxidant enzyme activities may be influenced according to the agent utilized, the brain region tested, and the age of the animal. In any case, small differences in the drug structure support marked differences in the type and extent of the intervention on the antioxidant enzymatic syste

Relationships between gamma-aminobutyrate and succinate cycles during and after cerebral ischemia

Some metabolites (glycogen, glucose, glucose-6-phosphate, pyruvate, lactate, citrate, alpha-ketoglutarate, succinate, fumarate, malate, glutamate, aspartate, gamma-aminobutyrate, glutamine, alanine, NH+4) were measured in rat cerebral cortex after 5 minutes of complete compression ischemia, as well as after 5, 15, or 30 minutes of recirculation following 5 minutes of ischemia. Complete ischemia induced a drop of glycolytic substrates and intermediates, consistent with the increase of lactate, succinate, alanine, and gamma-aminobutyrate, and with the decrease of malate, fumarate, and alpha-ketoglutarate. These events may be regarded as an expression of the activation of the gamma-aminobutyrate cycle and of the succinate cycle, where succinate itself, in the absence of O2, acts as a terminal electron acceptor. During post-ischemic recovery, cerebral parameters tended to normalize, except for the further increase of alanine and the still higher than normal content of both succinate and gamma-aminobutyrate, as an expression of the possible activation of the gamma-glutamyl and gamma-aminobutyrate cycles during recover

Influence of aging and exogenous substances on cerebral energy metabolism in posthypoglycemic recovery

In rats of different ages, acute severe hypoglycemia with isoelectric EEG induced extensive deterioration of the energy state and gross alteration of amino acid contents. During recovery of adult animals, tissue glucose concentration returned to normal, while the rate of glycogen synthesis was slow, both lactate and pyruvate concentrations increasing above normal. In the recovery period of "adult" rats, the ATP concentration increased but the adenine nucleotide pool remained reduced, even if the ADP and AMP concentrations were close to normal. Phosphocreatine was restored to normal concentrations with reciprocal changes in creatine content. In adult rats, during the recovery there was a rise in glutamate and glutamine concentrations, gamma-aminobutyrate concentration returning to normal value. Ammonia and aspartate decreased below normal, while alanine increased above normal. Aging does not affect the cerebral metabolic derangement occurring in severe hypoglycemia, but rather the metabolic changes that the brain tends to reverse during the posthypoglycemic restitution. In fact, there was lower restitution of the concentrations of cerebral cortical metabolites of "mature" and "senescent" rats in comparison with "adult" ones. Particularly, in older brains the concentrations of many amino acids and adenylate nucleotides remained largely abnormal. The effect of some agents on the posthypoglycemic recovery was tested: (a) dihydroergocristine; (b) eburnamonine; (c) raubasine; (d) almitrine; (e) piracetam. During the posthypoglycemic recovery, these different agents exhibited different interferences on glycolytic metabolites, amino acids and energy-rich phosphates. However, a more limited effect of the tested agents, which decrease with aging, was observe