Effects of carnitine coingested caffeine on carnitine metabolism and endurance capacity in athletes

The purpose of this study was to examine whether caffeine (CAF), carnitine (CAR), or CAF+CAR mixture administration affects exercise endurance time via carnitine metabolism. Water (CON), CAF, CAR, or CAF+CAR mixture was administered to five male rugby athletes participating in this study by a randomized double-blind fashion who were made to ride a cycle ergometer for exercise. The CAF effect on exercise endurance time was small, but the CAR trial significantly increased the exercise endurance time compared with CON trial; a further CAF+CAR mixture trial had greater effects on the exercise endurance time than those of a CON, CAF, or CAR trial. A CAR or CAF+CAR mixed trial increased urinary nonesterified carnitine (NEC) and total carnitine (TCAR), but no changes were observed in acid-soluble acylcarnitine (ASAC) and acid-insoluble acylcarnitine (AIAC) excretion. A CAR or CAF+CAR mixed trial resulted in higher levels of plasma NEC, ASAC, and TCAR fractions than the CON and CAF trials did on exhaustion time. Total cholesterol, triglyceride, and free fatty acid in blood were significantly increased at exhaustion time, but they were not affected in the CAF or the CAR trial. These results suggest that carnitine ingestion could promote fat oxidation, resulting in higher endurance performance in athletes, and especially these ergogenic effects of carnitine coingested with caffeine may be greater than those of carnitine alone.

L-Carnitine changes the levels of insulin-like growth factors (IGFs) and IGF binding proteins in streptozotocin-induced diabetic rat

This study investigated the effects of L-carnitine on insulin-like growth factor-I/II (IGF-I/II) and insulin-like growth factor binding proteins (IGFBPs) in streptozotocin (STZ)-induced diabetic rats. Each rat in the three L-carnitine-treated groups was injected subcutaneously with L-carnitine, 50 (D50), 100 (D100), or 200 (D200) mg/kg body weight every other day for four weeks, and animals in normal (N) and diabetic (DM) groups received saline by the same method. Diabetic rats had significantly lower carnitine concentrations in serum and liver compared with normal rats. Total carnitine concentrations were increased dose-dependently by carnitine treatment. Total IGF-I in serum from diabetic rats was increased dose-dependently by carnitine treatment, but was statistically significant only in the D200 group. The expression of liver IGF-I mRNA was lower in diabetic rats than in normal rats and increased by L-carnitine treatment. L-Carnitine treatment of diabetic rats had no effect on the levels of IGF-II in serum, liver, and kidney. Although the levels of IGF-II in serum and kidney of diabetic rats were increased in comparison with normal rats, IGF-II mRNA was not expressed in liver. Diabetic rats had markedly lower IGFBP-3 than normal rats did, and IGFBP-3 was increased by L-carnitine treatment. These results demonstrate that L-carnitine treatment of diabetic rats modulates the IGFs/IGFBPs axis. Especially note-worthy is that L-carnitine at a dose of 200 mg/kg/48 h for four weeks was able to restore serum total IGF-I in STZ-induced diabetic rats to nearly normal levels.

Caffeine as a lipolytic food component increases endurance performance in rats and athletes

Caffeine is one of the famous ergogenic aids in the athletic field. Caffeine has been known to stimulate lipolysis that spares stored glycogen utilization during moderate intensity exercise. Therefore, we investigated the effects of caffeine ingestion on exercise performance in rats and athletes. Rats were administered the caffeine (6 mg/kg) 1 h prior to the exercise then were run on a treadmill at a speed of 20 m/min. They were decapitated at 0 min, 30 min, 60 min of exercise, and exhausted time point. Human subjects ingested the caffeine (5 mg/kg) 1 h prior to the exercise. They exercised on a cycle ergometer at 60% of their VO2max for 45 min, and then the exercise intensity was increased to 80% of their VO2max until exhaustion. Blood and breathing gas samples were collected and calculated every 10 min during exercise. Respiratory exchange ratio of the caffeine trial was significantly lower than that of the placebo trial in the athletes' study (p<0.05). Blood free fatty acid (FFA) levels in studies of both rats and athletes were increased by caffeine ingestion during exercise (p<0.05). Blood lactate levels were also increased during exercise in both rats and athletes (p<0.05). Increased FFA and glycerol concentrations reduced glycogen utilization during exercise compared with placebo group in rats. In addition, endurance time to exhaustion was significantly increased by the caffeine ingestion in both rats and athletes (p<0.05). These results suggest that the caffeine ingestion enhanced endurance performance resulting from spare stored glycogen with increasing lipolysis from adipose tissues and fat oxidation during exercise both in rats and in athletes.

Auto-ADP-ribosylation of NAD glycohydrolase from Neurospora crassa

NAD glycohydrolase (NADase; EC 3.2.2.5) is an enzyme that catalyzes hydrolysis of NAD to produce ADP-ribose and nicotinamide. We recently demonstrated that self-inactivation of NADase from rabbit erythrocytes was due to an auto-ADP-ribosylation. In the present study, a mechanism of self-inactivation of NADase from Neurospora crassa by its substrate was investigated by using intact mycelia of N. crassa and purified NADase, which had molecular characteristics different from mammalian NADases. The results suggested that inactivation of NADase from N. crassa was also due to an auto-ADP-ribosylation. These findings indicate that the auto-modification of NADase is one of the universal phenomena to regulate enzyme functions.

Acetylcarnitine-mediated inhibition of ethanol oxidation in hepatocytes

Carnitine-mediated prevention of ethanol-induced hepatic steatosis is related to the attenuation of ethanol metabolism by carnitine in the intact rat. Although carnitine retards ethanol oxidation in the intact animal, the in vitro activities of ethanol-metabolizing enzymes remain unaltered. Therefore, hepatocytes were targeted to understand the mechanism of carnitine effect on ethanol metabolism. Rat hepatocytes were isolated by a collagenase-perfusion technique and incubated in albumin-containing medium with ethanol in the presence or absence of added carnitine or related compounds. Ethanol oxidation was determined by the loss of ethanol as well as by the products formed. The rate of ethanol oxidation in the presence of carnitine was one-half the rate in the absence of carnitine (14 vs. 25 nmol.min-1.million-1 cells). It took 100 times the concentration of carnitine to equal the maximal inhibition produced by acetylcarnitine and the effect of acetylcarnitine was without a lag time. It is concluded that acetylcarnitine is the mediator of carnitine inhibition of ethanol oxidation.

Acetylcarnitine inhibits alcohol dehydrogenase

Carnitine and acetylcarnitine are used as dietary supplements and as therapeutic agents. Carnitine attenuates ethanol metabolism in intact animals but the in vitro activities of alcohol dehydrogenase (ADH), microsomal ethanol oxidizing system (MEOS) or catalase are not significantly altered by carnitine. Since acetylcarnitine was a far more potent inhibitor of ethanol oxidation than carnitine in hepatocytes, the activities of rat liver ADH and MEOS were determined with or without acetylcarnitine. The activity of ADH, not MEOS, was significantly inhibited by acetylcarnitine at NAD: acetylcarnitine < or = 1. The inhibition is of a competitive nature where acetylcarnitine competes with NAD+ (Ki = 135 mumol.L-1). This finding is unique in that this is the first report of this function of acetylcarnitine and it is a novel interaction between two important nutrients, niacin and carnitine.

Carnitine prolongs the half-life of ethanol in broilers

The object was to determine if carnitine attenuated ethanol metabolism in broilers similar to that reported in the rats. Two groups (n = 5) of 5-week-old broilers were given for 10 days the feed with or without 0.5% L-carnitine supplement. A single oral dose of ethanol on day 8 was followed by serial blood samples which were analysed for ethanol. Another dose of ethanol was given on day 10 and 2 hr later, plasma and liver were collected and analysed for ethanol, total lipid, triglycerides and carnitine. The carnitine supplemented diet prolonged the half-life of ethanol due to attenuation of ethanol metabolism which is similar to that reported earlier in rodents. The increases in plasma and hepatic acylcarnitines indicate that supplementary carnitine lessens the load of free acyl groups in the liver by eventual oxidation or excretion.

Opposite effects of dietary saturated and unsaturated fatty acids on ethanol-pharmacokinetics, triglycerides and carnitines

OBJECTIVE

The objective of this study was to determine the effects of saturated fatty acid (SFA) and unsaturated fatty acid (UFA) diets on ethanol pharmacokinetics. Hepatic ADH and plasma carnitines were also evaluated as possible indicators of the mechanism involved.

METHODS

Sprague-Dawley male rats were fed modified AIN76 diets containing 10% coconut oil (SFA) or corn oil (UFA) for 120 days. A single dose (3 g/kg bw) of ethanol (13% solution) was orally administered using a gastric canula on day 30, 90, 105 and 120. Tail vein blood samples were collected at various intervals following ethanol dose and were analyzed for blood-ethanol concentration (BEC). In an analogous trial rats were given these diets for 70 days and blood samples were collected on day 35 and 63 for triglycerides, cholesterol and carnitine determination. The animals were killed on day 70 to collect liver for ADH determination.

RESULTS

Compared to the UFA group, the SFA group exhibited significantly higher BEC, larger area under the curve, longer half-life of ethanol, and lower rates of ethanol elimination. Plasma carnitines were also higher in the SFA vs UFA group. However, hepatic ADH activity was not different between the groups.

CONCLUSION

Dietary SFA protects liver from alcohol injury by retarding ethanol metabolism, and carnitine may be involved.