Unsaturated fatty acids suppress interleukin-2 production and transferrin receptor expression by concanavalin A-stimulated rat Iymphocytes

The proliferation of T-lymphocytes is dependent upon their ability to synthesize and secrete the cytokine, interleukin-2, and to express cell surface receptors for interleukin-2 and transferrin. We have previously reported that certain fatty acids inhibit mitogen-stimulated T-lymphocyte proliferation. We now report that unsaturated fatty acids decrease the concentration of interleukin-2 in the culture medium of such cells by up to 45%. This suggests that unsaturated fatty acids inhibit lymphocyte proliferation by suppressing interleukin-2 production. However, lymphocyte proliferation was only partially restored by addition of exogenous interleukin-2 to cell culture medium in the presence of unsaturated fatty acids, indicating that these fatty acids also affect other processes involved in the control of proliferation. Saturated fatty acids, which also inhibit lymphocyte proliferation, did not affect the interleukin-2 concentration in the culture medium suggesting a different mechanism for their action. Neither saturated nor unsaturated fatty acids affected the expression of the interleukin-2 receptor by mitogenstimulated lymphocytes. In contrast, unsaturated fatty acids decreased expression of the transferrin receptor by up to 50%. These observations suggest that the mechanism by which unsaturated fatty acids inhibit lymphocyte proliferation involves suppression of interleukin-2 production and of transferrin receptor expression. The mechanism for the inhibitory action of saturated fatty acids is not clear

Maximal activities of enzymes involved in adenosine metabolism in muscle and adipose tissue of rats under conditions of variations in insulin sensitivity

AbstractThe maximal activities of 5'-nucleotidase, adenosine deaminase and adenosine kinase were measured in quadriceps or soleus muscle from animals in which the sensitivity to insulin was changed. Most conditions caused no effect on the activities but exercise-training increased the activity of adenosine deaminase and cold exposure increased the activity of 5'-nucleotidase in soleus muscle: in addition, ageing decreased markedly the activities of all three enzymes in both muscles. When the activities are based on mg protein they are much higher in both white and brown adipose tissue than in muscle, suggesting that changes in adenosine concentration may be important in changing insulin sensitivity in adipose tissue whereas changes in adenosine receptor number may be more important in muscle

Alterations in Energy/Redox Metabolism Induced by Mitochondrial and Environmental Toxins: A Specific Role for Glucose-6-Phosphate-Dehydrogenase and the Pentose Phosphate Pathway in Paraquat Toxicity

Parkinson’s disease (PD) is a multifactorial disorder with a complex etiology including genetic risk factors, environmental exposures, and aging. While energy failure and oxidative stress have largely been associated with the loss of dopaminergic cells in PD and the toxicity induced by mitochondrial/environmental toxins, very little is known regarding the alterations in energy metabolism associated with mitochondrial dysfunction and their causative role in cell death progression. In this study, we investigated the alterations in the energy/redox-metabolome in dopaminergic cells exposed to environmental/mitochondrial toxins (paraquat, rotenone, 1-methyl-4-phenylpyridinium [MPP+], and 6-hydroxydopamine [6-OHDA]) in order to identify common and/or different mechanisms of toxicity. A combined metabolomics approach using nuclear magnetic resonance (NMR) and direct-infusion electrospray ionization mass spectrometry (DI-ESI-MS) was used to identify unique metabolic profile changes in response to these neurotoxins. Paraquat exposure induced the most profound alterations in the pentose phosphate pathway (PPP) metabolome. 13C-glucose flux analysis corroborated that PPP metabolites such as glucose-6-phosphate, fructose-6-phosphate, glucono-1,5-lactone, and erythrose-4-phosphate were increased by paraquat treatment, which was paralleled by inhibition of glycolysis and the TCA cycle. Proteomic analysis also found an increase in the expression of glucose-6-phosphate dehydrogenase (G6PD), which supplies reducing equivalents by regenerating nicotinamide adenine dinucleotide phosphate (NADPH) levels. Overexpression of G6PD selectively increased paraquat toxicity, while its inhibition with 6-aminonicotinamide inhibited paraquat-induced oxidative stress and cell death. These results suggest that paraquat “hijacks” the PPP to increase NADPH reducing equivalents and stimulate paraquat redox cycling, oxidative stress, and cell death. Our study clearly demonstrates that alterations in energy metabolism, which are specific for distinct mitochondiral/environmental toxins, are not bystanders to energy failure but also contribute significant to cell death progression

Studies on metabolism in macrophages

A general metabolic profile of macrophages was established by measurement of maximum catalytic activities of enzymes in energy-producing pathways and rates of utilisation of glucose, glutamine, fatty acids and ketone bodies under various conditions. It was found that glucose, glutamine and fatty acids can be used to satisfy the energy requirement of the cell. Although a significant proportion of utilised glutamine or fatty acid was converted to C02 by the macrophage, most glucose was not oxidised and was converted, almost stoichiometrically, to lactate. Utilised fatty acids were not only oxidised by the macrophage, but were incorporated into cellular lipid (mainly triacylglycerol and phospholipid). The triacylglycerol rich macrophage was shown to be able to release fatty acids into the culture medium. The importance of glutamine in macrophages was indicated from the high activity of phosphate-dependent glutaminase. Glutamine is probably metabolised by the following enzymes in macrophages: phosphate-dependent glutaminase, aspartate aminotransferase (or other amino acid aminotransferases), oxoglutarate dehydrogenase followed by enzymes of the TCA cycle and metabolism of oxaloacetate by phosphoenolpyruvate carboxykinase. Pyruvate derived via this pathway may be metabolised via pyruvate dehydrogenase or pyruvate carboxylase. A study of the sub-cellular distribution of some of these enzymes suggested that phosphate-dependent glutaminase has a cytosolic as well as a mitochondrial localisation. Further characterisation suggested that the non-mitochondrial activity could be associated with the plasma membrane. To the author's knowledge, this is the first report of a non-mitochondrial localisation for phosphate-dependent glutaminase. Glutaminase was shown to be activated by phosphate and inhibited by glutamate and 2-oxoglutarate. Significant inhibition of glutaminase occurred only at high concentrations of these compounds. Glucose and glutamine were utilised at very high rates by the macrophage, but were not fully oxidised even though the cells were incubated in aerobic conditions. The significance of these high rates of utilisation to the macrophage is discussed.</p