The nitric oxide precursor L-arginine reduces expression of hyaluronan synthase in experimental vein bypass grafts.

Background: The success of vascular bypass procedures is limited by the development of intimal hyperplasia (IH). The nitric oxide (NO) precursor, L-arginine (L-ARG) significantly reduces IH in both arteries and experimental vein grafts; however, the precise mechanism has yet to be elucidated. Hyaluronan synthase-1 (HAS-1) is one of the two enzymes believed to be responsible for making hyaluronan, a key component extracellular matrix composition.
Purpose: To determine how L-ARG supplementation affects the gene expression of HAS-1 in experimental vein grafts.
Methods: Thirty-four male New Zealand white rabbits were divided into three groups: control (no operation, regular chow and water, n = 4); L-ARG supplemented (n = 15); and no L-ARG (n = 15). The latter two groups underwent a right interposition carotid bypass using jugular vein. Vein grafts were harvested at 7, 14, and 21 days after surgery. Ribonuclease protection assays were performed using 32P-labeled riboprobes for HAS-1 and 18S rRNA as an internal control and expressed as a ratio (HAS-1/rRNA).
Results: There was a significant rise in HAS-1 expression in the vein grafts 7 (1.57 +/- 0.5), 14 (0.7 +/- 0.2), and 21 days (2.82 +/- 0.7) after grafting compared to control (0.14 +/- 0.08) (P < 0.05). L-ARG-supplemented animals had a significant decrease in HAS-1 expression at 21 days (0.65 +/- 0.1) compared to nonsupplemented vein grafts (2.82 +/- 0.7) (P < 0.02).
Conclusions: These results demonstrate for the first time a significant rise in HAS expression in the early experimental vein grafts. Furthermore, L-ARG supplementation significantly diminishes the expression of HAS at 21 days. These results may represent a potential mechanism by which augmentation of the L-ARG/NO pathway inhibits IH in experimental vein grafts and may ultimately provide for improved therapeutic interventions in alleviating IH.