The Effect of Probiotic Supplement on Urinary D-lactic Acid Level in Newborns Receiving Antibiotic Treatment

Lactic acid exists as two optical isomers, L-lactic acid and D-lactic acid. These isomers are metabolized to or synthesized from pyruvate by the action of isomer-specific enzymes (L-lactate dehydrogenase and D-lactate dehydrogenase). Mammals, including humans, do not possess D-lactate dehydrogenase, and therefore D-lactate production in human tissue is very limited. The endogenous single D-lactate synthesis known in man is carried out by glyoxalase. In this pathway, methylglyoxal is converted into D-lactate by the enzymes glyoxalase-1 and glyoxalase-2. Due to this restricted production, the blood D-lactate level in healthy people is so low that L-lactate is the major physiological enantiomer of lactate in the human body.

The bacterial flora in the human gastrointestinal tract has the ability to produce L and / or D-lactate depending on the amount of L-LDH and D-LDH present. Some strains of bacteria have the enzyme DL-lactate racemase to convert one isomer to another. Therefore, racemization reactions can further increase the amount of D-lactate isomers present in the column. Although there is no D-lactate dehydrogenase enzyme in humans, D-Lactate is metabolized into pyruvate by the enzyme D-2-hydroxy acid dehydrogenase (D-2-HDH), an intramitochondrial flavoprotein with high activity in the liver and renal cortex. The kidney's threshold for D-lactate is much lower than L-lactate and is efficiently excreted in urine as well as metabolic clearance. Thus, under normal conditions, D-lactate produced by tissue metabolism or bacterial fermentation in the gut; It does not cause a clinically significant increase in lactate in blood, urine or feces.

D-lactic acidosis is a well-defined complication of short bowel syndrome due to the combination of altered gastrointestinal tract anatomy and abnormal bacterial flora. Many case reports reported in the literature are associated with short bowel syndrome secondary to various causes. There are studies investigating the effects of fermented formulas and probiotics on D-lactic acid in healthy babies. In these studies, no increased risk for D-lactic acidosis was found in healthy infants fed with probiotic supplemented formulas.

Considering the studies on newborns; In babies with necrotizing enterocolit, it has been shown that urinary D-lactate excretion increased as a result of increased enteric bacterial activity. In another study, plasma D-lactic acid level was found to be high in premature babies with necrotizing enterocolitis. However, more detailed studies on newborns are needed.