In Vivo Evidence for a Vitamin B-6 Requirement in Carnitine Synthesis

Abstract

The purpose of this study was to determine whether there is a requirement for vitamin B-6 (B6) in carnitine synthesis. Rats were fed a B6-deficient (-B6) (0.04 mg pyridoxine [PN]/kg) diet (ad libitum or meal-fed) or a control (+B6) (5.7 mg PN/kg) diet (ad libitum or pair-fed). These diets were fed for 6 wk, then some of the rats were repleted with the +B6 diet for 2 wk. Total acid-soluble carnitine (TCN) and free carnitine (FCN) levels were compared in the plasma, liver, skeletal muscle, heart muscle and urine and rats fed +B6 or -B6 diets. In -B6 rats vs. +B6 rats, TCN levels were significantly lower (P less than 0.05) in the plasma, skeletal muscle, heart muscle and urine, but not in the liver. However, if rats were fasted for 3 d, liver TCN concentration of -B6 rats was significantly lower than that of +B6 rats. After B6-deficient rats were repleted with the +B6 diet, the TCN level in the plasma, liver, skeletal muscle, heart muscle and urine returned to the levels of control rats. Thus, the decrease in TCN and FCN levels with a B6-deficient diet and the increase of these levels after B6 repletion provides evidence for the B6 requirement in the biosynthesis of carnitine.

Vitamin B-6 restriction impairs fatty acid synthesis in cultured human hepatoma (HepG2) cells

“…Similar observations have been reported for vitamin B-6-deficient rats, which exhibited hepatic lipid accumulation (2,36). One proposed mechanism for this finding is that vitamin B-6 deficiency impairs carnitine synthesis (10,19). Cho and Leklem provided in vivo evidence that total carnitine concentrations were lower in plasma, skeletal muscle, and liver in rats with vitamin B-6 deficiency than pair-fed controls (10).…”

“…One proposed mechanism for this finding is that vitamin B-6 deficiency impairs carnitine synthesis (10,19). Cho and Leklem provided in vivo evidence that total carnitine concentrations were lower in plasma, skeletal muscle, and liver in rats with vitamin B-6 deficiency than pair-fed controls (10). If carnitine availability under vitamin B-6-deficient status is rate limiting, it could lead to lower fatty acid oxidation rate and, thus, more fatty acid accumulated in cells cultured with lower PL concentrations.…”

Carnitine biosynthesis in mammals

“…Furthermore, rats maintained on a vitamin B ' -deficient diet showed a significant decrease in carnitine levels in extrahepatic tissues. Moreover, when these rats were fasted for 3 days, liver carnitine levels were significantly lower, as compared with fasted control rats [38]. Repletion of vitamin B ' resulted in normalization of the carnitine levels in all tissues, supporting further the requirement of this vitamin in carnitine biosynthesis [38].…”

Influence of vitamin B6 supplementation on polyunsaturated fatty acids concentration in serum and liver of rats fed a diet restricted in protein

“…In animal studies it was shown that pyridoxal-5 , -phosphate (PLP) is crucial for carnitine biosynthesis [25]. Cho and Leklem [26] observed in rats fed a vitamin B 6 -deficient diet, compared with pair-fed control rats, significantly lower concentration of carnitine in blood plasma, muscles and heart but not in the liver. Refeeding with B 6 supplemented diet reversed the observed effect, which provides evidence for pyridoxine requirement in carnitine biosynthesis.…”