Limited trypsin proteolysis renders carnitine palmitoyltransferase insensitive to inhibition by malonyl-CoA in patients with muscle carnitine palmitoyltransferase deficiency

Carnitine palmitoyltransferase (CPT) was studied in muscle homogenates of two patients with muscle CPT deficiency heterozygous for the Ser-113 Leu mutation in the CPT 11 gene. Total CPT activity was normal in both patients but was almost completely inhibited by malonyl-CoA and Triton X-100 whereas in controls 38% and 58% of total activity remained in the presence of malonyl-CoA and Triton X-100, respectively. The addition of 1 % Tween 20 abolished about half of the activity in patients but not in controls. Preincubation of muscle homogenate with trypsin slightly increased the total activity and rendered the activity greatly insensitive to inhibition by malonyl-CoA in both patients and controls. The data support the view that in patients with muscle CPT deficieny both CPT I and II are active, but that CPT II is abnormally accessible to inhibition by malonyl-CoA.Abbreviations CoA coenzyme A - CPT carnitine palmitoyltransferase     

Contributions of phosphorylation to regulation of OCTN2 uptake of carnitine are minimal in BeWo cells

Physiological functions of organic cation transporters (OCTs) in the placenta include transporting essential nutrients from the maternal to fetal circulations. OCTN2 transports carnitine with high affinity, and the transport of several drugs has also been shown to be mediated by this transporter. In this work, the role of phosphorylation and dephosphorylation mechanisms in regulating OCTN2 was investigated by observing the effects of various activators and inhibitors of kinases and phosphatases on the uptake of carnitine in BeWo cells, a human choriocarcinoma trophoblast cell line frequently used as an in vitro model of the rate-limiting barrier for maternal-fetal exchange. Preincubation with genistein resulted in significant increases in both alkaline phosphatase (ALP) activity and carnitine uptake. Levamisole, an ALP inhibitor, caused a more substantial decrease in carnitine uptake than expected from its corresponding decrease in ALP activity. It was determined that levamisole competitively inhibits carnitine uptake, with a K(i) value of 1.01+/-0.05mM, and this effect has a greater role in decreasing carnitine uptake than any indirect effects of ALP inhibition upon OCTN2 function. Progesterone also competitively inhibited carnitine uptake (K(i)=48.6+/-5.0muM), but had no effect on ALP activity in BeWo cells.     

Clofibrate treatment up-regulates novel organic cation transporter (OCTN)-2 in tissues of pigs as a model of non-proliferating species

Recent studies have shown that treatment of rodents with agonists of peroxisome proliferator-activated receptor (PPAR)-alpha causes an up-regulation of novel organic cation transporter (OCTN)-2, a carnitine transporter, and increases carnitine concentration in the liver. This study was performed to investigate whether such effects occur also in pigs which like humans have a lower expression of PPAR alpha and are less responsive to treatment with PPAR alpha agonists than rodents. An experiment with 18 pigs was performed which were fed a control diet or the same diet supplemented with 5 g clofibrate/kg for 28 days. Pigs treated with clofibrate had higher relative mRNA concentrations of OCTN2 in liver (3.1-fold), skeletal muscle (1.5-fold) and epithelial cells from small intestine (1.8-fold) than control pigs (P<0.05). Pigs treated with clofibrate had also higher concentrations of free and total carnitine in the liver and a higher concentration of free carnitine in skeletal muscle than control pigs (P<0.05). Concentrations of gamma-butyrobetaine, the precursor of endogenous formation of carnitine, in liver, muscle and plasma did not differ between both groups; the activity of gamma-butyrobetaine dioxygenase, the rate limiting enzyme of carnitine synthesis, in the liver was lower in pigs treated with clofibrate than in control pigs (P<0.05). This study shows for the first time that treatment with a PPAR alpha agonist causes an up-regulation of OCTN2 in liver, muscle and enterocytes from small intestine of pigs. This in turn increases carnitine concentrations in liver and muscle probably by enhancing carnitine uptake into cells.     

脂质代谢性肌病16例临床病理分析

目的探讨脂质代谢性肌病的病理,讨论此病与线粒体细胞病的关系。方法对１６例经肌肉活检证实的脂质代谢性肌病进行临床和肌肉病理检查,对油红Ｏ染色片进行形态计量分析。结果１６例病人的肌肉活检显示肌纤维内出现大量的脂肪滴,５例出现不整红边纤维。脂肪滴所占肌纤维的平均面积为（１７±６）％,肌纤维内脂肪滴颗粒平均数为２３７±３７。电镜下脂肪滴在肌纤维内和间质细胞内也明显增多。在８例病人可见线粒体内类结晶样包涵体。结论脂质代谢性肌病为全身系统性疾病。     

肉碱对高脂饲料喂养的半饥饿大鼠脂肪代谢的改善作用

目的:探讨补充外源性肉碱对高脂饲料喂养的半饥饿大鼠脂肪代谢的影响。方法:用限食的方法造成半饥饿大鼠模型,在给予高脂饲料基础上,观察补充肉碱的半饥饿动物2周后血浆肉碱浓度、附睾脂肪垫重量、尿酮体排出、血浆脂肪酶活性、肌肉肉碱棕榈酰基转移酶活性以及甘油三酯分泌及清除速率等指标的变化。结果:补充肉碱的动物血浆游离肉碱浓度显著高于正常对照组和半饥饿对照组;尿酮体排出显著低于半饥饿对照组;血浆脂肪酶活性和肌肉肉碱棕榈酰基转移酶活性显著高于正常对照组和半饥饿对照组;甘油三酯分泌速率也显著高于半饥饿对照组。结论:补充外源性肉碱能够显著提高高脂饲料喂养的半饥饿大鼠血中游离肉碱浓度,加速动物体内脂肪代谢。     

Thermolabile polymorphism of carnitine palmitoyltransferase 2: A genetic risk factor of overall acute encephalopathy

ObjectivesAcute encephalopathy is an acute brain dysfunction after preceding infection, consisting of multiple syndromes. Some syndromes, such as acute encephalopathy with biphasic seizures and late reduced diffusion (AESD), are severe with poor outcome, whereas others, such as clinically mild encephalitis/encephalopathy with reversible splenial lesion (MERS), are mild with favorable outcome. Previous study reported the association of the thermolabile polymorphism in Carnitine Palmitoyltransferase 2 (CPT2) gene and severe syndromes of acute encephalopathy. To further explore the pathogenetic role of CPT2 in acute encephalopathy, we conducted a case-control association study of a typical thermolabile CPT2 polymorphism, rs2229291, in 416 patients of acute encephalopathy, including both severe and mild syndromes.MethodsThe case cohort consisted of 416 patients, including AESD, MERS, and other syndromes. The control subjects were 100 healthy Japanese. rs2229291 was genotyped by Sanger sequencing. Genetic distribution was compared between the patients and controls using Cochran-Armitage trend test.ResultsMinor allele frequency of rs2229291 was significantly higher in AESD (p = 0.044), MERS (p = 0.015) and entire acute encephalopathy (p = 0.044) compared to the controls. The polymorphism showed no significant association with influenza virus, or with outcome.ConclusionsThis study provided evidence that CPT2 is a susceptibility gene for overall acute encephalopathy, including both severe and mild syndromes, and suggested that impairment of mitochondrial metabolism is common to various syndromes of acute encephalopathy.     

Levocarnitine Decreases Intradialytic Hypotension Episodes: A Randomized Controlled Trial

Intradialytic hypotension is common complication in stage 5 chronic kidney disease patients on hemodialysis. Incidence ranges from 15 to 30%. These patients have levocarnitine deficiency. A randomized, placebo‐controlled quadruple‐blinded trial was designed to demonstrate the levocarnitine efficiency on intradialytic hypotension prevention. Patients were randomized into four groups, to receive levocarnitine or placebo. During the intervention period, levocarnitine and placebo was administered 0 and 30 min before each hemodialysis session, respectively. During the trial, 33 patients received 1188 hemodialysis sessions. We identified 239 (21.3%) intradialytic hypotension episodes. The intradialytic hypotension episodes were less frequent in the levocarnitine group (9.3%, 60 IH events) (P < 0.001). Hemodialysis is frequently perplexed by intradialytic hypotension episodes. Levocarnitine supplementation before each hemodialysis session efficiently diminishes the intradialytic hypotension episodes. This is a new application method that must be considered and explored.