J. Jing, N. Isoherranen, C. Yeung, B. Kestenbaum; University of Washington, Seattle, WA

BACKGROUND: Strong evidence has recently been found for altered vitamin A carrier protein, retinol binding protein 4 (RBP4), serum levels in patients with chronic kidney disease (CKD), suggesting that altered vitamin A homeostasis might play a role in CKD development and progression. However, the concentrations of retinoic acid (RA) and vitamin A homeostasis have never been evaluated in CKD patients. The aim of our study was to determine whether vitamin A homeostasis is altered in CKD patients in comparison to healthy subjects.
METHODS: 62 CKD patients and 78 gender, -age, and- BMI- matched healthy subjects from the Seattle Kidney Study and Healthy Kidney Study were included in this study. The eGFR of the CKD patients ranged from 153 to 9 mL/min/1.73m2. Retinal, all- trans-RA (atRA) and13cis-RA were measured in plasma by LC-MS/MS and retinol by HPLC. The dietary vitamin A intake of the CKD patients was assessed by food diaries.
RESULTS: Compared with matched healthy subjects, CKD patients had significantly higher (p<0.0001) plasma retinol and atRA concentration but significantly lower (p<0.0001) plasma retinal and 13cis-RA concentrations. In addition, lower eGFR was associated with higher plasma retinol but there was no association between eGFR and atRA or 13cis-RA concentrations. 13cis-RA/ retinol and total RA/retinol ratio was significantly decreased (p<0.0001) in CKD patients suggesting that RA synthesis is decreased in CKD patients. Vitamin A consumption was not associated with circulating retinoid concentration.
CONCLUSION: Retinoic acid and vitamin A homeostasis are altered in patients with CKD. This may be important for the clinical management of CKD as RA is a signaling molecule that plays a critical role in maintaining health.