P0445 : Obeticholic acid, an FXR agonist, reduces hepatic fibrosis in a rat model of toxic cirrhosis

Abstract

use of ammonia lowering agent, OP, lowers portal pressure in BDL rats, through reduced HSC activation. Methods: In vitro: Primary humanHSC (hHSC) were cultured. Effects of NH4Cl challenge (0.1–10mM over 24–72hrs) on hHSC to proliferation (BrdU), metabolic activity (MTS assay), viability (Neutral-Red), ultrastructural changes (EM) and gene/protein expression were studied. To test recovery, ammonia treated cells were replenished with glutamine and in separate experiments, pre-treated with L-methionine-sulfoximine (MSO-GS inhibitor) to determine the importance of GS. In vivo: 28-day BDL rats were treated with saline or OP for 5 days and portal pressure measured at termination and tissues were harvested for studies. Results: In vitro: Hyperammonemia in primary hHSC induced time-dependent decreases in proliferation and metabolic activity, whilst inducing cell swelling and a myofibroblast-like phenotype even at 50–100umol/L. Ultrastructurally, ammonia-treated hHSC caused a dose-dependent ER enlargement and this was reversible by replenishing the culture with glutamine. NH3 inhibition of hHSC proliferation was dependent on GS activity as MSO with hyperammonemia induced cell detachment and prevention of recovery suggesting that glutamine is important for hHSC survival. In vivo: BDL rats, with hyperammonemia had increased hepatic expression of pro-fibrogenic hHSC-related genes (a-SMA, PDGFb-R, Myosin IIA/IIB and Coll1), low eNOS activity and DDAH-1 and high portal pressure (14.4±0.8mmHg), all of which were corrected by OP treatment (PP: 11.1±0.3mmHg, P < 0.01). Conclusions: These novel data suggest that hyperammonemia modifies hHSC’s and imparts a swollen myofibroblast phenotype, which is reversible upon ammonia reduction. In vivo ammonia lowering decreases pro-fibrogenic and activated HSC gene and protein expression and lowers portal pressure, highlighting ammonia as a target for portal hypertension therapy and the key role of HSC in this process.