Mitochondrial Β-oxidation Pathway Research Articles

Relationships between the functional PPARα Leu162Val polymorphism and obesity, type 2 diabetes, dyslipidaemia, and related quantitative traits in studies of 5799 middle-aged white people

Peroxisome proliferator-activated receptor-α (PPARα) is a nuclear receptor capable of regulating the expression of genes involved in peroxisomal and mitochondrial β-oxidation pathways. The common Leu162Val polymorphism in the gene encoding PPARα has inconsistently shown association with quantitative traits related to obesity, type 2 diabetes, and dyslipidaemia. We genotyped the Leu162Val polymorphism in 1383 patients with type 2 diabetes and 4401 control subjects with normal glucose tolerance (NGT) without showing any association between diabetes and genotype. In addition, the Leu162Val polymorphism was not associated with WHO-defined obesity or dyslipidaemia in case-control settings involving 961 obese and 2563 lean subjects and 1399 dyslipidaemic and 4399 normolipidaemic subjects, respectively. Quantitative trait studies of metabolic variables were carried out in 5799 middle-aged, treatment-naïve subjects showing a difference in fasting serum triglyceride concentrations among homozygous Val-carriers (Leu/Leu + Leu/Val, n = 5782, 1.33 ± 1.35 mmol/l vs. Val/Val, n = 17, 2.22 ± 2.4 mmol/l, p = 0.007). Similarly, Val/Val was associated with increased fasting serum total cholesterol concentrations ( p = 0.01). In conclusion, in a relative large-scale study of middle-aged whites we found no evidence of association between the PPARα Leu162Val polymorphism and obesity or type 2 diabetes. If replicated, the Val162Val variant may, however, confer an increase in fasting levels of serum lipids.

Possible role of avian uncoupling protein in down-regulating mitochondrial superoxide production in skeletal muscle of fasted chickens

Little is known about the precise physiological roles of uncoupling protein 1 (UCP1) homologs (UCP2, UCP3, avian UCP) whose levels are up-regulated during fasting. UCPs in skeletal muscle are thought to play a role in the regulation of lipids as fuel substrates, and/or in controlling the production of reactive oxygen species (ROS). The aim of this investigation, using skeletal muscle from fasted chickens, was to examine alterations in the expression of genes encoding for avian UCP and key enzymes relevant to lipid flux across the mitochondrial β-oxidation pathway. We also clarified whether an increase in avUCP content could be associated with altered ROS production by mitochondria. Transcription levels of avUCP and CPT-I genes were increased 7.7- and 9.5-fold after a 24 h fast and slightly diminished but remained about 5.0- and 7.7-fold higher than baseline levels, respectively, after 48 h of fasting. In contrast, members of the β-oxidation pathway, LCAD and 3HADH, were gradually up-regulated from 12 to 48 h of fasting. This suggests that processes involved in the transfer and oxidation of fatty acids are up-regulated differently during the initial stage of fasting. Analysis of ROS production by lucigenin-derived chemiluminescence showed that the FFA-sensitive portion of carboxyatractyloside-upregulated ROS production was greater in skeletal muscle mitochondria from 24 h-fasted chickens compared with control, which leads us to postulate that ROS production is potentially down-regulated by UCP. The possible involvement of a backlog of fatty acid for oxidation, observed in chickens after a 24 h fast, in a transmembrane gradient of free non-oxidized fatty acids is also discussed.

Possible role of avian uncoupling protein in down‐regulating mitochondrial superoxide overproduction in skeletal muscle of fasted chickens

Little is known about the precise physiological roles of the UCP1-homologues (UCP2, UCP3, avian UCP). The confusing aspect regarding the physiological characterization of these UCP variants is that their expression was enhanced in response to fasting, a peculiar result considering that the enhanced expression of these variants occurred in muscle in the fasted state, a basal metabolic state in which energy expenditure would be expected, instead, to be depressed. The aim of this investigation, using skeletal muscle from fasted chickens, was to examine alterations in the expression of gene encoding for avian UCP. We also examined altered transcription of key enzymes relevant to lipid flux across the mitochondrial β-oxidation pathway, and clarified whether up-regulation of avUCP modulates ROS production by mitochondria. avUCP transcription was increased 7.7-fold after a 24 h fast and diminished about 5.0-fold higher than baseline after 48 h of fasting. CPT-I gene expression was enhanced remarkably after 24 h of fasting and was diminished after 48 h, similar to the results seen for avUCP, while members of the β-oxidation pathway, LCAD and 3HADH, were up-regulated after 24 h of fasting, with levels then increasing linearly with time. ROS analysis with LDCL method exhibited the percentage decreases of mitochondrial ROS production following exposure to palmitate, probably via uncoupling, which were 44 and 86 % at time 0 and 24 h of fasting, respectively. This is the first investigation demonstrating possible regulation of mitochondrial ROS via UCP in chicken skeletal muscle in response to fasting.

Kinetic parameters of hepatic oxidation of cyclic fatty acid monomers formed from linoleic and linolenic acids

Cyclic fatty acid monomers (CFAM) occur from linoleic (CFAM-18:2) or linolenic (CFAM-18:3) acids present in some edible oils as a result of domestic frying or industrial refining. They present adverse effects in pups and weaning rats. In the present work, we studied the importance of hepatic oxidation in the metabolism of CFAM. For this purpose, kinetic parameters of Carnitine Palmitoyl Transferase I (key enzyme of the channeling of the fatty acids into the mitochondrial β-oxidation pathway) and Acyl CoA Oxidase (key enzyme of the peroxisomal oxidation pathway) towards CFAM-18:2 and CFAM-18:3 were calculated on hepatic sub-cellular fractions of rats. For mitochondrial oxidation of CFAM, we observed a lower oxygen consumption and a lower activity of Carnitine Palmitoyl Transferase compared to 18:2w6 and 16:0. For peroxisomal oxidation, CFAM-18:2 showed the same kinetic parameters (Vm and K 0.5) as 18:2w6 and 16:0, used for oxidative controls, whereas CFAM-18:3 presented a lower Vm (-50%). This difference should induce a lower catabolism of CFAM-18:3 in liver. This could contribute to their accumulation and probably to their toxic effect.

Effect of Dietary Conjugated Linoleic Acid on the In Vivo Growth of Rat Hepatoma dRLh-84

We examined the effect of dietary conjugated linoleic acid (CLA) on the growth of injected hepatoma dRLh-84 in Donryu rats. After experimental diets containing 0% or 2% CLA were given to male Donryu rats for 3 wk, dRLh-84 cells were injected into the left lobe of the hepatic capsule, and the experimental diet was continued. The cells formed a solid tumor ≥1 wk after the injection, and thereafter the tumor grew with feeding duration. In a morphological study, this tumor appeared to be a low-differentiated hepatoma, and there was no remarkable difference in the morphology of the tumor between 0% and 2% CLA groups. Tumor weight was significantly higher in the 2% CLA group than in the 0% CLA group throughout the feeding period after the injection. Serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase activities were significantly higher in 2% CLA-injected rats than in 0% CLA-injected rats at 3 wk after the injection. CLA upregulated acyl-CoA oxidase activity, especially 1 wk after the injection. However, dietary CLA did not activate carnitine palmitoyl transferase II, which is a rate-limiting enzyme in the mitochondrial β-oxidation pathway. Natural killer cell activity in the spleen tended to be higher in injected rats, but a significant effect of dietary CLA was not recognized. Serum interferon-γ and tumor necrosis factor-a levels were higher in injected than in sham rats. Moreover, these levels were higher in 2% CLA groups than in the respective 0% CLA groups.

Identification of Four Novel Mutations in Patients with Carnitine Palmitoyltransferase II (CPT II) Deficiency

Carnitine palmitoyltransferase II (CPT II) deficiency, an autosomal recessive disorder of fatty-acid oxidation, presents as three distinct phenotypes (neonatal, infantile, and adult onset). In order to investigate the molecular basis of these three phenotypes, six patients with CPT II deficiency have been studied. All six unrelated patients in this study experienced the clinical symptoms of CPT II deficiency. Three patients had the neonatal form, one had the milder infantile form, and the remaining two had the adult-onset form with “muscular” symptoms only. Their diagnoses were based uponin vitroanalysis of the mitochondrial β-oxidation pathway in fibroblasts and standard enzyme assays. We devised a method to screen the entire coding sequence and flanking splice junction of the CPT II gene. A total of six different mutations have been identified, including four novel mutations. Among them, the previously reported common mutation, S113L, was only found in 3 of 12 variant alleles. Three of the six mutations have been identified in a few unrelated patients, while the remaining three have been found in single families. This study, as well as those by others, indicates genetic heterogeneity in this disease. In addition to tabulating the mutations, the correlation of mutant genotype to clinical phenotype is briefly discussed.