Urinary organic acids in infant malnutrition

Abstract

The metabolic derangements in severe protein-energy malnutrition (PEM) are only partially known, due to the limitations of blood collection in these patients. Urinary excretion of organic acids was studied by gas chromatography-mass spectrometry in 39 infants with four types of PEM: 1) upon hospital admission, as soon as eventual infections had been cleared, and salt and water deficits corrected, but before oral feeding was started; 2) after start of protein alimentation; 3) on the day of discharge. All of the patients showed an increased excretion of various organic acids at some point of their hospital stay, regardless of the clinical type of PEM. In nearly half of the malnourished children, results were suggestive of blocks in the pathways of propionate (15.4% with increased methylmalonate and 25.6% with 2- methylcitrate), of fatty acid β-oxidation (30.8% with raised dicarboxylic acids with low or low normal 3-hydroxybutyrate), or of both pathways (12.8%). These abnormalities may have been caused by cofactor deficiencies (biotin, vitamin B12, riboflavin, camitine, niacin). Dicarboxylic acids were excreted in high amounts since the initial sample, probably due to increased mobilization of fatty acids. Increased 2-methylcitrate and methylmalonate excretion was observed more frequently once patients started to be orally fed. The accumulation of potentially toxic acyl-CoA precursors of these compounds could contribute to the known clinical worsening of some malnourished infants after suddenly increased protein intake. Other less specific metabolites, such as 3-hydroxybutyrate, lactate, 4-hydroxyphenyl- lactate, fumarate, succinate, and 4-hydroxyphenylacetate, were also abnormally excreted in some patients. The analysis of urinary organic acids provides a new approach for the metabolic study of PEM and may have diagnostic and therapeutic implications.