Effect of streptozotocin on carnitine and carnitine acyltransferases in rat heart, liver, and kidney

Asymptomatic cardiomyopathy in children and adolescents with type 1 diabetes mellitus: association of echocardiographic indicators with duration of diabetes mellitus and metabolic parameters

This study was designed to determine the relationship of dimensions, wall thickness and function of the left ventricle with diabetes duration, fasting blood glucose, lipid profile, beta-OH-butyrate, free fatty acids (FFA) and carnitine levels in children and adolescents with type 1 diabetes mellitus (DM1) who had no cardiovascular complications. Thirty-five patients with DM1 (18 F/17 M, mean age: 12.0 years) and age matched control children (n = 24) were enrolled in the study. Patients with DM1 were subdivided into Group I (mean DM1 duration 3.5 years, n = 14), and Group II (mean DM1 duration 8.2 years, n = 21). Dimensions, wall thickness and systolic functions of the left ventricle were normal in all patients with DM1. Diastolic functions were normal in Group I. In Group II, peak A wave velocity (AVEL) (p = 0.004), velocity-time integral of A wave (AVTI) (p = 0.007) and isovolumetric relaxation time corrected by heart rate (cIVRT) (p = 0.048) were high, and peak E wave velocity (EVEL) and velocity-time integral of E wave (EVTI) were normal. E/A (p < 0.0001) and EVTI/AVTI (p = 0.001) were low in this group. In Group I, systolic and diastolic blood pressure, HDL-cholesterol and FFA values were normal; total cholesterol (p = 0.047), LDL-cholesterol (p = 0.017), beta-OH-butyrate (p = 0.003), and acetyl carnitine (p = 0.006) levels were high. In Group II, diastolic blood pressure (p = 0.008), total cholesterol (p < 0.0001) and LDL-cholesterol (p < 0.0001) were increased; and total carnitine (p = 0.019), free carnitine (p = 0.002) and HDL-cholesterol (p = 0.039) were decreased. Correlations were detected between total carnitine and AVEL and HR; free carnitine and AVEL, E/A and HR; HbA1c and EVTI/AVTI and cIVRT; LDL-cholesterol and E/A, EVTI/AVTI ratios and cIVRT; HDL-cholesterol and AVEL; FFA and LVDD, IVSD, LVPWD, LVmass and CO; metabolic parameters and DM1 duration and echocardiographic findings such as AVEL, EVEL, EVTI, VmaxAV and CO. In conclusion, left ventricular dimensions, wall thickness and systolic functions were normal in children and adolescents with DM1 who had no obvious cardiovascular complications. Left ventricular diastolic functions were abnormal in patients of Group II. Left ventricular diastolic function abnormalities were associated with glycemic control, free and total carnitine, and LDL- and HDL-cholesterol levels.

Myocardial uptake of iodine-125-labeled 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid is decreased in chronic diabetic rats with changes in subcellular distribution

Iodine-123-labeled 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid (123I-BMIPP) is widely used to detect myocardial metabolic changes, but the preferred energy substrates in the myocardium would be expected to be altered in the presence of metabolic disorders such as diabetes mellitus (DM). We investigated the metabolism of branched-chain fatty acids in the myocardium of rats with DM. Streptozotocin-induced DM rats were examined 48 h (acute; AD) and 6 weeks (chronic; CD) after injection of streptozotocin. Hearts were excised 15 min or 60 min after injection of 0.185 MBq of 125I-BMIPP, followed by homogenization in an EDTA-Tris buffer. The homogenates were subjected to differential centrifugation to obtain the mitochondrial (MF) and cytoplasmic (CF) fractions. Myocardial 125I uptake tended to increase in the AD group, but the change was not significant. Myocardial 125I uptake at 15 min was significantly lower in the CD group than in the control group, even in the insulin-treated rats [control (CC), 4.4+/-0.4; not treated (CDN), 3.3+/-0.5; insulin-treated (CDI), 3.4+/-0.4 x 10(4) cpm/g, p<0.05 in each case]. The 125I count value corrected for the blood count (counts/min (cpm) per g of protein divided by blood cpm) in the MF decreased by 40% at 60 min in the CC group, but increased by 60% in the CDN group. The results of the present study suggest that the myocardial uptake of branched-chain fatty acids is decreased in rats with chronic diabetes, probably as a result of mitochondrial dysfunction.

Carnitine metabolism in chronic liver disease

The liver is a central organ for carnitine metabolism and for the distribution of carnitine to the body. It is therefore not surprising that carnitine metabolism is impaired in patients and experimental animals with certain types of chronic liver disease. In this review, the changes in carnitine metabolism associated with chronic liver disease and the role of carnitine as a therapeutic agent in some of these conditions are discussed.

Levels of carnitines in brain and other tissues of rats of different ages: effect of acetyl-L-carnitine administration

Male Sprague-Dawley rats, aged 2, 5, 16, 20 and 30 months and normally fed, were used for determination of carnitines in the brain, serum, heart, tibial muscle, liver and urine. With respect to 5-month-old animals, those aged 30 months exhibited a statistically significant decrement of total carnitine levels in the brain, serum, heart and tibial muscle, accompanied by a dramatic increment in the liver. This suggests impaired net transport of carnitines from the liver to the blood in old age. Urinary excretion was similar in the two age groups. One group received from 5 months on daily 75 mg/kg acetyl-L-carnitine in drinking water. At 20 months, the treated animals showed levels of brain, heart and serum carnitines similar to those of 5-month-old animals. The recovery of brain, heart and serum carnitines in the old animals treated with acetyl-L-carnitine indicates that intestinal absorption and tissue uptake remain sufficiently efficient in the course of aging. The lower level of brain lipofuscins due to acetyl-L-carnitine treatment may be related to the effect of the compound on acetylcholine metabolism.

Evidence for the extreme overestimation of choline acetyltransferase in human sperm, human seminal plasma and rat heart: a case of mistaking carnitine acetyltransferase for choline acetyltransferase

Detection of choline acetyltransferase (ChAc) in a number of non-neuronal tissues has been extremely overestimated. There are two major types of errors encountered. Type 1 error occurs when endogenous substrates (e.g. L-carnitine) are acetylated by acetyltransferase enzymes (e.g. carnitine acetyltransferase ( CarAc ) ) yielding an acetylated product mistaken for acetylcholine (AcCh). In the past, human sperm and human seminal plasma putative ChAc activity has been extremely overestimated due to Type 1 error. This study demonstrates (1) an endogenous acetyltransferase and substrate activity in human sperm and human seminal plasma forming an acetylated product that is not AcCh but probably acetylcarnitine ( AcCar ); (2) that the addition of 5 mM choline substrate does not significantly increase acetyltransferase activity; (3) that boiled seminal plasma contains an endogenous acetyltransferase substrate which is not choline, but probably L-carnitine. Type 2 error occurs when endogenous carnitine acetyltransferase synthesizes true AcCh, resulting in mistaken evidence for ChAc. This is demonstrated by the fact that the choline substrate Km-value for the neuronal or true ChAc from mouse brain is 0.73 +/- 0.06 mM while the Km-value of choline substrate for purified CarAc from pigeon breast muscle is 108 +/- 4 mM. Type 2 error has occurred for the estimation of putative ChAc in rat heart. The rat heart ChAc was measured in previous studies utilizing a concentration of 30 mM choline substrate. While saturation of neuronal ChAc is observed at 2-5 mM choline, saturation of the rat heart CarAc enzyme is not reached until over 800 mM. Purified CarAc significantly synthesizes AcCh at 30 mM choline. Thus, putative ChAc has been greatly overestimated in the scientific literature for mammalian sperm, human seminal plasma and rat heart.

Improvement of myocardial function in diabetic rats after treatment with L-carnitine

The effects of L-carnitine administration on the severity of diabetes were investigated. Serum glucose, free fatty acids (FFA), triglycerides, and ketones from diabetic and normal rats injected for 2 weeks with 3 g/kg/d of either L-carnitine or saline were assayed. Hearts were analyzed for carnitine and long-chain acyl coenzyme A. L-carnitine treatment to diabetic rats significantly reduced serum glucose, FFA, triglycerides, and ketones. In nondiabetic rats, carnitine increased serum ketones while FFA and triglycerides were decreased. L-carnitine treatment to diabetic rats prevented a decrease in myocardial total carnitine content. Long-chain acyl carnitine increased while long-chain acyl coenzyme A decreased. In another experiment, L-carnitine administration (750 mg/kg/d for 14 days) significantly improved the recovery of cardiac output after 60, 90, and 120 minutes of ischemia in diabetic perfused hearts. These results suggest that L-carnitine therapy may reduce the severity of diabetes mellitus and improve myocardial performance.

A radioisotopic-exchange method for quantitation of short-chain (acid-soluble) acylcarnitines

A reliable and sensitive method for the quantitation of picomole amounts of acetylcarnitine, propionylcarnitine, aliphatic 4-carbon, and 5-carbon acylcarnitines has been developed. The procedure requires the measurement of the amounts of carnitine and acid-soluble carnitine and then the enzymatic exchange of 3H- or 14C-labeled L-carnitine into the acylcarnitine pool using commercial carnitine acetyltransferase, essentially free of acyl-CoA hydrolase activity. After isotopic equilibrium is obtained, the radioactive acylcarnitines are separated using either HPLC or thin-layer chromatography. Procedures for both are described. After separation, the amounts of radioactivity in the acylcarnitines are determined and the amount of individual acylcarnitines can be calculated from the specific activity of the initial total carnitine pool or from the ratio of dpm in the acylcarnitine fraction/dpm in free carnitine X (nanomoles L-carnitine) in the sample. The method has several advantages over current procedures, including rapidity, use of small sample sizes, simplicity, and reliability.

Carnitine content of skeletal and cardiac muscle from genetically diabetic (db/db) and control mice

Portions of diaphragm and heart from genetically diabetic and control mice of three age groups were analyzed for free fatty acid, triglyceride, and carnitine content. Triglyceride levels were increased consistently in both cardiac and skeletal muscle from diabetic animals while the amount of free fatty acids was comparable to that measured in tissue from lean littermates. Free carnitine and total carnitine were decreased in diaphragm and heart from db/db mice throughout the course of the study. While the levels of short-chain carnitine were comparable in tissue from control and diabetic animals, the amount of the long-chain derivative was elevated significantly in both diaphragm and heart in the 18-week-old diabetic mice. The results are discussed with respect to (a) alterations in hepatic carnitine metabolism in this animal model reported previously by this laboratory, and (b) changes in carnitine metabolism which we observed in skeletal muscle from streptozotocin-diabetic animals.

Carnitine and creatine content of tissues of normal and alloxan-diabetic sheep and rats

The concentration of carnitine in liver increased 28-fold and urinary carnitine excretion 5-fold in alloxan-diabetic sheep. In contrast there were no similar increases in alloxan-diabetic rats. The creatine content of liver decreased 3-fold and creatine excretion decreased 2-fold in diabetic sheep. In contrast the creatine content of liver increased nearly 4-fold in diabetic rats with no change in creatine excretion. The marked increased in production of carnitine by the liver of the diabetic sheep appears possible because of decreased production and excretion of creatine.

The effect of electrical stimulation, fasting and anesthesia on the carnitine(s) and acyl-carnitines of rat white and red skeletal muscle fibres

Time courses for the effect of electrical stimulation, fasting and sampling mode (anesthesia vs decapitation) on the quantitative distribution of carnitine and its esters in fast white and fast red skeletal muscle fibres of rats were determined. Both fibre types responded similarly to electrical stimulation with respect to changes in acetyl- and propionylcarnitine, but the time course was very different. The proportion of esterified carnitine decreased with fasting and anesthesia in both fibres compared to the fed decapitated group. This shift in the acylation state of carnitine was mainly due to the decrease of acetylcarnitine levels. The data show that the use of anesthetics may induce significant quantitative changes in specific acylcarnitine levels, presumably reflecting changes in specific acylcoenzyme A levels.