Acute Inflammation Induces Hyporetinemia and Modifies the Plasma and Tissue Response to Vitamin A Supplementation in Marginally Vitamin A–Deficient Rats

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Abstract
Plasma retinol is reduced during numerous infections, and inflammation alters the hepatic synthesis of retinol-binding protein (RBP). In this study, we have investigated the effects of endotoxin-induced inflammation on vitamin A (VA) supplementation in a rat model of marginal VA deficiency. Marginally VA-deficient rats received an intraperitoneal dose of lipopolysaccharide (LPS, n = 14) or saline (n = 10); 6 h later, six LPS + VA and six saline + VA rats received 7.1 μmol VA orally. Twenty-four hours after endotoxin administration, rats with inflammation (LPS) had lower plasma retinol, RBP, and hepatic RBP than saline rats (37, 31 and 44%, respectively, P < 0.05). Inflammation did not affect VA concentrations in liver and perirenal adipose tissue, although kidney VA was reduced relative to saline rats. However, urinary VA was not detected. Eighteen hours after VA supplementation, inflammation reduced the plasma unesterified retinol response (P < 0.05) in LPS + VA relative to saline + VA rats, although total VA increased as a result of the presence of retinyl esters in LPS + VA rats. Hepatic esterified retinol concentration was reduced (P < 0.01) in LPS + VA compared with saline + VA rats; however, hepatic unesterified retinol did not differ. Renal total retinol increased in VA-supplemented rats, but urinary retinol excretion, when observed, was low, independently of inflammation. These findings indicate that inflammation-induced hyporetinemia does not necessarily imply a loss of VA, but rather represents a redistribution of tissue VA brought about by a reduced hepatic synthesis of RBP. Practical implications from these collective results are to recommend the determination of both unesterified and esterified retinol to fully assess the plasma response to VA supplementation and to caution the use of VA assessment methodologies that depend on the hepatic synthesis of RBP during acute inflammation.