Methylmalonic and propionic acidemias: lipid profiles of normal and affected human skin fibroblasts incubated with [1-14C]propionate

Pathophysiological mechanisms of complications associated with propionic acidemia

Propionic acidemia (PA) is a genetic metabolic disorder caused by mutations in the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), which is responsible for converting propionyl-CoA to methylmalonyl-CoA for further metabolism in the tricarboxylic acid cycle. When this process is disrupted, propionyl-CoA and its metabolites accumulate, leading to a variety of complications including life-threatening cardiac diseases and other metabolic strokes. While the clinical symptoms and diagnosis of PA are well established, the underlying pathophysiological mechanisms of PA-induced diseases are not fully understood. As a result, there are currently few effective therapies for PA beyond dietary restriction. This review focuses on the pathophysiological mechanisms of the various complications associated with PA, drawing on extensive research and clinical reports. Most research suggests that propionyl-CoA and its metabolites can impair mitochondrial energy metabolism and cause cellular damage by inducing oxidative stress. However, direct evidence from in vivo studies is still lacking. Additionally, elevated levels of ammonia can be toxic, although not all PA patients develop hyperammonemia. The discovery of pathophysiological mechanisms underlying various complications associated with PA can aid in the development of more effective therapeutic treatments. The consequences of elevated odd-chain fatty acids in lipid metabolism and potential gene expression changes mediated by histone propionylation also warrant further investigation.

Propionate regulates lymphocyte proliferation and metabolism

1. The effect of propionate on lymphocyte proliferation and metabolism was investigated. Lymphocytes obtained from human blood and rat mesenteric lymph nodes were utilized. 2. Propionate at concentrations of 0.04 and 1.0 mmol/l stimulated the amount of [3H]thymidine incorporated either in cultured human T lymphocytes or rat T and B lymphocytes. 3. Concentrations of propionate between 2 and 5 mmol/l caused a marked inhibition of lymphocyte proliferation. 4. This short-chain fatty acid was metabolized by these cells and produced succinate in significant amounts; however, its oxidation was low. 5. Propionate did not alter glucose, glutamine and pyruvate utilization and oxidation in incubated rat lymphocytes but increased the formation of lactate and aspartate. 6. In contrast, propionate inhibited by 50% the synthesis of lymphocyte lipid from [1-14C]acetate at concentrations of 0.5 and 1 mmol/l and reduced by half the incorporation of 3H2O into lipids at 1 and 5 mmol/l. 7. The results suggest that inhibition of lipid synthesis is a possible mechanism leading to reduction of lymphocytes proliferation.

Primary structure and activity of mouse methylmalonyl-CoA mutase

Methylmalonyl-CoA mutase (MCM) is an adenosylcobalamin-dependent enzyme that catalyses isomerization between methylmalonyl-CoA and succinyl-CoA (3-carboxypropionyl-CoA). Genetic deficiency of this enzyme in man causes an often fatal disorder of organic acid metabolism termed mut methylmalonicacidaemia. We report cloning of a mouse MCM cDNA and the characterization of its primary structure and biological function. Mouse MCM in fibroblasts and crude liver extracts exhibits activity and reaction kinetics similar to those of the human enzyme. The predicted amino acid sequence of mouse MCM exhibits 94% identity with its human homologue and considerable identity with a prokaryotic MCM. Transfection of the mouse cDNA into cultured cells constitutes an active apoenzyme and can complement genetic deficiency of the apoenzyme in cells from patients with mut methylmalonicacidaemia. These results establish that mouse MCM is homologous to human MCM in structure and function and provides a basis for using the mouse as a model for studying this enzyme and its deficiency state.

Radiochromatography in pharmaceutical and biomedical analysis

Recent advances in the chromatographic analysis of radiolabelled compounds are discussed, with emphasis on the optimization of radioactivity detection in modern chromatographic techniques. Applications are mentioned only infrequently. The state-of-the-art of common radioactivity detection methods is reviewed, as well as promising new detection principles. The latter include flow-through liquid scintillation counting of reversed-phase column eluates based on post-column extraction and solvent segmentation, flow-through heterogeneous counting using a flow cell constructed from axially aligned scintillation fibres, flow cells especially constructed for the detection of beta-emitting radioisotopes in capillary zone electrophoresis, position-sensitive analysers employed in radio planar chromatography and, finally 14C atom counting (as opposed to 14C decay counting) by accelerator mass spectrometry.