KUPFFER CELL ACTIVATION BY HYDROGEN PEROXIDE: A NEW MECHANISM OF PORTAL PRESSURE INCREASE

This study aimed to investigate the effects of reactive oxygen species on the hepatic macrophages, the Kupffer cells (KC), and to identify the relevant targets of vasoconstrictors involved in the regulation of intrahepatic microcirculation and therefore portal pressure. The effects of hydrogen peroxide (H(2)O(2)), xanthine/xanthine oxidase or a thromboxane (TX) analogue (U46619; 0.1 mu M) were tested in sham-operated and fibrotic livers (bile duct ligation over 4 weeks) during isolated rat liver perfusion and in vivo with or without additional KC blockade (gadolinium chloride, 10 mg kg(-1) body weight, 48 and 24 h, i.p.). To investigate downstream mechanisms, a TXA(2) antagonist (BM 13.177; 20 mu M) or a Rho kinase inhibitor (Y27632; 10 mu M) was infused additionally. TXB(2) efflux was measured by enzyme-linked immunosorbent assay. The phosphorylation state of moesin (p-moesin), as indicator for Rho kinase activity, was assessed by Western blot analyses. Portal pressure was dose-dependently increased by H(2)O(2) (maximum, 0.5 mM) and, to a lower extent, by xanthine/xanthine oxidase together with catalase. The portal pressure increase by H(2)O(2) was attenuated by previous KC blockade. TXA(2) efflux increased after H(2)O(2) infusion and was reduced by KC blockade. The TXA(2) antagonist counteracted the H(2)O(2)-induced increase in portal pressure. The Rho kinase inhibitor attenuated portal pressure increase after TXA(2) analogue or H(2)O(2) infusion. Hepatic levels of p-moesin were increased after H(2)O(2) infusion. Reactive oxygen species increased portal pressure via stimulation of TXA(2) production by KCs and a subsequent Rho kinase-dependent contraction of the intrahepatic vasculature. In conclusion, the KCs that are well known to produce H(2)O(2) could also be activated by H(2)O(2). This vicious cycle may best be interrupted at the earliest time point.