Infection with the hepatitis C virus causes viral genotype-specific differences in cholesterol metabolism and hepatic steatosis

Abstract

Lipids play essential roles in the hepatitis C virus (HCV) life cycle and patients with chronic HCV infection display disordered lipid metabolism which resolves following successful anti-viral therapy. It has been proposed that HCV genotype 3 (HCV-G3) infection is an independent risk factor for hepatocellular carcinoma and evidence suggests lipogenic proteins are involved in hepatocarcinogenesis. We aimed to characterise variation in host lipid metabolism between participants chronically infected with HCV genotype 1 (HCV-G1) and HCV-G3 to identify likely genotype-specific differences in lipid metabolism. We combined several lipidomic approaches: analysis was performed between participants infected with HCV-G1 and HCV-G3, both in the fasting and non-fasting states, and after sustained virological response (SVR) to treatment. Sera were obtained from 112 fasting patients (25% with cirrhosis). Serum lipids were measured using standard enzymatic methods. Lathosterol and desmosterol were measured by gas-chromatography mass spectrometry (MS). For further metabolic insight on lipid metabolism, ultra-performance liquid chromatography MS was performed on all samples. A subgroup of 13 participants had whole body fat distribution determined using in vivo magnetic resonance imaging and spectroscopy. A second cohort of (non-fasting) sera were obtained from HCV Research UK for comparative analyses: 150 treatment naïve patients and 100 non-viraemic patients post-SVR. HCV-G3 patients had significantly decreased serum apoB, non-HDL cholesterol concentrations, and more hepatic steatosis than those with HCV-G1. HCV-G3 patients also had significantly decreased serum levels of lathosterol, without significant reductions in desmosterol. Lipidomic analysis showed lipid species associated with reverse cholesterol transport pathway in HCV-G3. We demonstrated that compared to HCV-G1, HCV-G3 infection is characterised by low LDL cholesterol levels, with preferential suppression of cholesterol synthesis via lathosterol, associated with increasing hepatic steatosis. The genotype-specific lipid disturbances may shed light on genotypic variations in liver disease progression and promotion of hepatocellular cancer in HCV-G3.

Figure 1

Schematic of the endogenous cholesterol biosynthetic pathway. Cholesterol synthesis involves a complex series of enzymatic reactions from the 2 carbon acetyl CoA to 27 carbon cholesterol. De novo cholesterol biosynthesis takes place in the ER membrane, also the site of HCV replication. The rate limiting step is the activity of 3-hydroxy-3-methylglutaryl (HMG) CoA reductase and the production of mevalonate. The post mevalonate intermediate geranylgeranyl is required for HCV replication. Geranyl that is not used in prenylation is converted to farnesyl and subsequently to squalene, then to lanosterol. From lanosterol, cholesterol biosynthesis can proceed by two routes: via a desmosterol intermediate (Bloch pathway), or via a lathosterol intermediate (Kandutsch-Russel pathway), with flux across the two pathways regulated by ∆24 dehydrocholesterol reductase (DHCR24).

Figure 2

Correlation between intra-hepatocellular lipid content (steatosis) and fasting serum markers of endogenous cholesterol synthesis lathosterol and desmosterol in HCV genotypes 1 (N = 6) and 3 (N = 7).

Figure 3

Correlation between intra-hepatocellular lipid content (steatosis) and fasting serum apoB concentration and triglycerides in HCV genotypes 1 (N = 6) and 3 (N = 7).

Figure 4

Principal component analysis (PCA) of fasting sera in positive electrospray ionisation mode demonstrating separation between HCV genotypes.