Plasma retinol-binding protein (RBP) and transthyretin (TTR): Markers of inflammation-induced hyporetinemia

To assess the combined use of plasma RBP and TTR in interpreting whether low plasma retinol is due to a deficiency of vitamin A (VA) or to inflammation, we have used a rat model and data from a randomized controlled community trial of VA supplementation in post-measles infected children. Plasma retinol, RBP and TTR concentrations were determined in VA-deficient and VA-supplemented rats with and without endotoxin-induced inflammation. Without and with inflammation, plasma RBP averaged 1.6±0.1 μM (mean ± SEM) and 0.5±0.04 μM in marginally VA-deficient rats, and 2.4±0.2 and 1.2±0.1 μM in VA-supplemented rats. Both vitamin A status and inflammation affected plasma RBP (2-way ANOVA, P<0.01); thus VA-deficient rats with inflammation had a significantly lower RBP concentration. However, TTR was only reduced significantly by inflammation. Without and with inflammation, plasma TTR averaged 7.3±0.6 and 4.2±0.3 μM in marginally VA-deficient rats, and 8.3±0.6, and 5.2±0.4 μM in VA-supplemented rats. Therefore, rats with both VA deficiency and inflammation had molar ratios of RBP:TTR which were ∼50% of all other groups. The association between plasma retinol, C-reactive protein (CRP), RBP, and TTR was also assessed in 153 post-measles cases, ages 5 mo-17 y, 2 wk after children received placebo or 200,000 IU of VA. Placebo-treated children with plasma retinol ≤ 0.35 μM and elevated CRP had the lowest RBP:TTR ratios. Thus, the combined analysis of plasma RBP and TTR is helpful in interpreting low plasma retinol during inflammation. [Support: DK09110 (FJR) & DK46869 (ACR).].