All-trans-retinoic acid (tRA) modulates in human mesangial cells (MC) antioxidant defenses, the expression of interleukin-1beta-induced vascular cell-adhesion molecule-1 (VCAM-1), cyclooxygenase-2 (COX-2), and the retinoic acid-receptor-beta (RAR-beta). The correlation of the serum levels of glycated hemoglobin A1c with tRA in type 2 diabetes mellitus patients led us to hypothesize that tRA and glycated albumin (GA), the main circulating glycated protein, might mutually interact in MC. We studied 1) the influence of tRA on GA effects in cultured MC: an assessment was made on how pre-incubation with tRA modified the effects of GA on intracellular oxidation and on the expression of mRNA and protein of COX-2 and VCAM-1; and 2) the influence of GA on tRA effects in MC: we studied how the induction of RARbeta expression by tRA was modified by GA.
Results: GA dose-dependently increased intracellular oxidation and the expression of the molecules involved in leukocyte infiltration, namely COX-2 and VCAM-1 . Pre-incubation with tRA exacerbated GA effects by up to a three- to four-fold additional increase. In turn, induction by tRA of RAR-beta was fully inhibited by GA. Thus tRA and GA reciprocally influence their effects in MC. It is possible that this interaction may have a pathophysiological or pharmacological role in diabetic nephropathy.