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Title: First-pass splanchnic metabolism of dietary cysteine in weanling pigs

item BAUCHART-THEVRET, CAROLINE - Children'S Nutrition Research Center (CNRC)
item COTTRELL, J - Children'S Nutrition Research Center (CNRC)
item STOLL, BARBARA - Children'S Nutrition Research Center (CNRC)
item Burrin, Douglas - Doug

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2011
Publication Date: 12/1/2011
Citation: Bauchart-Thevret, C., Cottrell, J., Stoll, B., Burrin, D.G. 2011. First-pass splanchnic metabolism of dietary cysteine in weanling pigs. Journal of Animal Science. 89(12):4093-4099.

Interpretive Summary: The use of dietary nutrients for growth and function of the developing gut is an important factor in infant nutrient needs. Cysteine is an especially important amino acid derived from dietary protein, because it is a building block for production of antioxidant proteins in the gut epithelial cells. The aim of this study was to measure the amount of dietary cysteine used for metabolic purposes in the gut and liver using the piglet as an animal model for human infants. We measured metabolism by infusing chemically labeled cysteine into the stomach and blood stream and measuring its uptake into gut and liver tissue, absorption into the blood and conversion to carbon dioxide. We found that most (75%) of the dietary cysteine is absorbed into the blood, but the remainder (25%) is used for gut growth and metabolism. Some of the dietary cysteine absorbed from the gut into the blood is then metabolized by the liver, such that these two organs together consume a substantial amount (40%) of the dietary cysteine, leaving only 60% for rest of the body. We also found that most of the cysteine metabolized by the gut was likely used for production of proteins that function in cell survial and protection. These findings provide quantitative information about the nutrient needs for the gut that cannot be obtained in human studies with infants.

Technical Abstract: Cysteine is a semi-indispensable amino acid in neonates and is synthesized from the essential amino acid methionine by transsulfuration. We previously showed that the gastrointestinal tract (GIT) is a metabolically significant site of methionine transsulfuration to cysteine, yet the metabolic fate of dietary cysteine in the GIT has not been established. Cysteine use by gut epithelial cells may play an important role for maintenance of glutathione synthesis and cellular redox function. Our aim was to quantify the extent of gastrointestinal first-pass cysteine metabolism in young pigs. Four-week-old weanling pigs (n = 10) were fed a liquid milk-replacer diet and given an intragastric (IG) and intravenous (IV) [1-13C]-cysteine infusion on two separate days in a cross-over design. Arterial and portal blood samples were collected for 13C-cysteine 13CO2 isotopic enrichment by mass spectrometry. Our results indicated that dietary cysteine is significantly metabolized during its first-pass splanchnic metabolism, accounting for 40% of dietary cysteine intake. We also showed that intestinal absorption was the major metabolic fate of dietary cysteine, representing about 75% intake, indicating that the GIT utilizes 25% of the dietary cysteine intake. Thus, utilization by the GIT represents about one-half (approx. 53%) of the first-pass, splanchnic uptake of dietary cysteine. Moreover, a substantial proportion of dietary splanchnic cysteine metabolism was consumed by the GIT via non-oxidative pathways. We postulate that synthesis of mucosal epithelial proteins, such as glutathione and mucin, are a major non-oxidative metabolic fate for cysteine in the gut.