Inhibition of the Na+/H+ exchanger reduces rat hepatic stellate cell activity and liver fibrosis:: An in vitro and in vivo study

Background & Aims: The Na+/H+ exchanger is the main intracellular pH (pH(i)) regulator in hepatic stellate cells (HSCs) and plays a key role in regulating proliferation and gene expression. We evaluated the effect of specific inhibition of this exchanger on HSC proliferation and collagen synthesis in vivo and in vitro. Methods: Rat HSCs were incubated in the presence of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta1 iron ascorbate (FeAsc), and ferric nitrilotriacetate solution (FeNTA) with or without the Na+/H+ exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (EIPA). pH(i) and Na+/H+ exchanger activity, cell proliferation, and type I collagen accumulation were measured by using the fluorescent dye 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein, by immunohistochemistry for bromodeoxyuridine, and by enzyme-linked immunosorbent assay, respectively. In vivo liver fibrosis was induced by dimethylnitrosamine administration and bile duct ligation (BDL) in vats treated or not treated with amiloride. Results: PDGF, FeAsc, and FeNTA increased Na+/H+ exchange activity and induced HSC proliferation. TGF-beta1 had no effect on the Na+/H+ exchanger and was able, as for FeAsc and FeNTA, to induce type I collagen accumulation. EIPA inhibited all the effects determined by PDGF, FeAsc, and FeNTA and had no effect on TGF-beta1-induced collagen accumulation. In vivo, amiloride reduced HSC proliferation, activation, collagen deposition, and collagen synthesis. Conclusions: The Na+/H+ exchanger can play a key role in the development of liver fibrosis and in HSC activation in vivo.