Regulation mechanism for fatty acid and -ketoglutarate oxidations

Pharmacological targets of metabolism in disease: Opportunities from macrophages

From advances in the knowledge of the immune system, it is emerging that the specialized functions displayed by macrophages during the course of an immune response are supported by specific and dynamically-connected metabolic programs. The study of immunometabolism is demonstrating that metabolic adaptations play a critical role in modulating inflammation and, conversely, inflammation deeply influences the acquisition of specific metabolic settings.This strict connection has been proven to be crucial for the execution of defined immune functional programs and it is now under investigation with respect to several human disorders, such as diabetes, sepsis, cancer, and autoimmunity. The abnormal remodelling of the metabolic pathways in macrophages is now emerging as both marker of disease and potential target of therapeutic intervention. By focusing on key pathological conditions, namely obesity and diabetes, rheumatoid arthritis, atherosclerosis and cancer, we will review the metabolic targets suitable for therapeutic intervention in macrophages. In addition, we will discuss the major obstacles and challenges related to the development of therapeutic strategies for a pharmacological targeting of macrophage's metabolism.

Propionyl-L-carnitine: biochemical significance and possible role in cardiac metabolism

Propionyl-CoA is formed principally during amino acid catabolism. It is then converted chiefly to succinate in a described three-step sequence. Free propionate is formed from propionyl-CoA to a very limited extent, but this anion can participate in a futile cycle of activation and hydrolysis, which can significantly deplete mitochondrial ATP. Free CoA and propionyl-CoA cannot enter or leave mitochondria, but propionyl groups are transferred between separate CoA pools by prior conversion to propionyl-L-carnitine. This reaction requires carnitine and carnitine acetyl transferase, an enzyme abundant in heart tissue. Propionyl-L-carnitine traverses both mitochondrial and cell membranes. Within the cell, this mobility helps to maintain the mitochondrial acyl-CoA/CoA ratio. When this ratio is increased, as in carnitine deficiency states, deleterious consequences ensue, which include deficient metabolism of fatty acids and urea synthesis. From outside the cell (in blood plasma), propionyl-L-carnitine can either be excreted in the urine or redistributed by entering other tissues. This process apparently occurs-without prior hydrolysis and reformation. It is suggested that heart tissue utilizes such exogenous propionyl-L-carnitine to stimulate the tricarboxylic acid cycle (via succinate synthesis) and that this may explain its known protective effect against ischemia.

Switch on and switch off phenomenon of liver gluconeogenic function in lamprey (Lampetra fluviatilis L.) under the influence of season and temperature

The potential activity of pyruvate carboxylase in lamprey liver is the same as in mammals. However, at certain stages of the life cycle this reaction does not take place because of ATP deficiency in mitochondria. Energy charge potential of liver cells ranges from 0.76 to 0.11 throughout a year. Heat adaptation of lampreys leads to a rapid increase of the ATP level and of the NAD+/NADH ratio in liver. The intensity of gluconeogenesis and glycogen levels are also enhanced. Cold reacclimation reverses the effect. A scheme accounting for the temperature changes in energy status of hepatocytes has been proposed.

Studies on the influence of fatty acids on pyruvate dehydrogenase interconversion in rat-liver mitochondria

1. The effect of fatty acids on the interconversion of pyruvate dehydrogenase between its active (nonphosphorylated) and inactive (phosphorylated) forms was measured in rat liver mitochondria respiring in state 3 with pyruvate plus malate and 2-oxoglutarate plus malate and during state 4 to state 3 transition in the presence of different substrates. The content of intramitochondrial adenine nucleotides was determined in the parallel experiments. 2. Decrease of the intramitochondrial ATP/ADP ratio with propionate and its increase with palmitoyl-L-carnitine in state 3 is accompanied by a shift of the steady-state of the pyruvate dehydrogenase system towards the active or the inactive form, respectively. 3. Transition from the high energy state (state4) to the active respiration (state3) in mitochondria oxidizing 2-oxoglutarate or plamitoyl-L-carnitine causes an increase of the amount of the active form of pyruvate dehydrogenase due to the decrease of ATP/ADP ratio in the matrix. 4. No change in ATP/ADP ratio can be observed in the presence of octanoate in mitochondria oxidizing pyruvate or 2-oxoglutarate in state 3 or during state 4 to state 3 transition. Simultanelusly, no significant change in phosphorylation state of pyruvate dehydrogenase occurs and a low amount of the enzyme in the active form is present with octanoate or octanoate plus 2-oxoglutarate. Pyruvate abolishes this effect of octanoate and shifts the steady-state of pyruvate dehydrogenase system towards the active form. 5. These results indicate that fatty acids influence the interconversion of pyruvate dehydrogenase mainly by changing intramitochondrial ATP/ADP ratio. However, the comparison of the steady-state level of the pyruvate dehydrogenase system in the presence of different substrates in various metabolic conditions provides some evidence that accumulation of acetyl-CoA and high level of NADH may promote the phosphorylation of pyruvate dehydrogenase. 6. Pyruvate exerts its protective effect against phosphorylation of pyruvate dehydrogenase in the presence of fatty acids of short, medium or long chain in a manner which depends on its concentration. It is suggested that in isolated mitochondria pyruvate counteracts the effect of acetyl-CoA and NADH on pyruvate dehydrogenase kinase.