Premature infants, carnitine

It is clear from this discussion that carnitine is required in humans for the oxidation of long-chain fatty acids. In humans, carnitine is derived from both dietary sources and endogenous biosynthesis. Meat products, particularly red meats, and dairy products are important dietary sources of carnitine. Since biosynthesis can meet all physiological requirements, carnitine is not an essential nutrient. Premature infants are an exception to this rule as they lack a mature biosynthetic system and have limited tissue carnitine stores. As many infant formulas, particularly those based on soy protein, are low in carnitine, premature infants receiving a significant part of their nutrition from such formulas may be susceptible to carnitine deficiency. 

Hepatic steatosis usually is a result of excessive administration of carbohydrates and/or lipids, but deficiencies of carnitine, choline, and essential fatty acids also may contribute. Hepatic steatosis can be minimized or reversed by avoiding overfeeding, especially from dextrose and lipids.35,38 Carnitine is an important amine that transports long-chain triglycerides into the mitochondria for oxidation, but carnitine deficiency in adults is extremely rare and is mostly a problem in premature infants and patients receiving chronic dialysis. Choline is an essential amine required for synthesis of cell membrane components such as phospholipids. Although a true choline deficiency is rare, preliminary studies of choline supplementation to adult patients PN caused reversal of steatosis. 

Carnitine can be synthesized from lysine and methionine, but synthesis is decreased in premature infants. Low carnitine levels can occur in premature infants receiving parenteral nutrition or carnitine-free diets. 

Equally, demonstrating that a compound has a physiological function as a coenzyme or hormone does not classify that compound as a vitamin. It is necessary to demonstrate that endogenous synthesis of the compound is inadequate to meet physiological requirements in the absence of a dietary source of the compound. Table 1.3 lists compounds that have clearly defined functions, but are not considered vitamins because they are not dietary essentials endogenous synthesis normally meets requirements. However, there is some evidence that premature infants and patients maintained on long-term total parenteral nutrition may be unable to meet their requirements for carnitine (Section 14.1.2), choline (Section 14.2.2), and taurine (Section 14.5.3) unless they are provided in the diet, and these are sometimes regarded as... 

In addition to the established vitamins, a number of organic compounds have clear metabolic functions they can be synthesized in the body, but it is possible that under some circumstances (as in premature infants and patients maintained on long-term total parenteral nutrition) endogenous synthesis may not be adequate to meet requirements. These compounds include biopterin (Section 10.4), carnitine (Section 14.1), choline (Section 14.2), creatine (Section 14.3), inositol (Section 14.4), molybdopterin (Section 10.5), taurine (Section 14.5), and ubiquinone (Section 14.6). 

Although carnitine is not generally nutritionally important, it may be required for premature infants, because tbey have a limited capacity to synthesize it. However, there is inadequate evidence to support routine carnitine supplementation of parenteraUy fed premature infants (Cairns and Stalker, 2000). Carnitine depletion occurs in patients undergoing hemodialysis, but there is Utde evidence that supplements are effective in treating the associated dyslipidemia (Raskind and El-Chaar, 2000 Hurot et al., 2002). 

MS/MS analysis of DBS is one model of clinical analysis that has been utilized on millions of infants for 15 years. Each year since its first clinical use in the mid-1990s, there have been substantial improvements such as improved ionization, more sensitive instruments, and a reduction of the actual size of instruments. The profile has expanded to include T4, succinylacetone, and in a few labs, LSD metabolites and steroids. Many of these analyses can be used in other clinical applications and research such as nutrition studies in premature infants or postmortem screening on sudden unexplained deaths in infants or carnitine status in dialysis patients with end-stage renal disease. As additional clinical assays are developed and used, it might be wise for these labs to consider the models of MS/MS, NBS, and the DBS as a reference. 

Premature infants are born with a relative inability to synthesize carnitine, although at birth the plasma concentration of carnitine is higher in pre-term neonates than in term infants (Novak et aL, 1981). It has been suggested that the long chain fatty acids found in intravenous lipid emulsions may not be adequately metabolized because of a relative carnitine deficiency (Penn et al., 1980). Carnitine facilitates the transfer of free fatty acids across the mitochondrial membrane. In its absence, P-oxidation of long chain fatty acids is curtailed, and cellular energy metabolism is... 

Penn, D., Schmidt-Sommerfeld, E., and Wolf, M., 1980, Carnitine deficiency in premature infants receiving total parenteral nutrition. Early Hum. Rev. 4 23. 

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