Mitochondrial dysfunction and lipid alterations in primary sclerosing cholangitis

Indications of mitochondrial dysfunction are commonly seen in liver diseases, but data are scarce in primary sclerosing cholangitis (PSC). Analyzing circulating and liver-resident molecules indirectly reflecting mitochondrial dysfunction, we aimed to comprehensively characterize this deficit in PSC, and whether this was PSC specific or associated with cholestasis.

We retrospectively included plasma from 191 non-transplant patients with large-duct PSC and 100 healthy controls and explanted liver tissue extracts from 24 PSC patients and 18 non-cholestatic liver disease controls. Using mass spectroscopy, we profiled lipids and fatty acids, carnitine, acylcarnitines, and metabolites in the tryptophan-kynurenine-nicotinamide pathway.

Hierarchal clustering of fatty acid levels identified patients with PSC and healthy controls as separate clusters. Compared to healthy controls, PSC patients had increased levels of monounsaturated fatty acids (MUFA) and palmitate (C16:0) in plasma, but reduced levels of long-chain saturated fatty acids (SFAs). These findings were more pronounced in PSC patients with cholestasis. Several n-3 polyunsaturated fatty acids were elevated in PSC but not associated with cholestasis. Acylcarnitine ratios C2/C5 and C2/C3 were elevated while C2/C16 was reduced in PSC, indicating impaired mitochondrial fatty acid oxidation of medium-long chained fatty acids. Levels of intermediates in the tryptophan-kynurenine pathway indicated impaired NAD biosynthesis, suggesting impaired energy supply to mitochondria in PSC.

We found that mitochondrial dysfunction was prominent in PSC and associated with increasing cholestasis. Whether this is merely a marker of liver disease and severity, or an underlying driver and potential therapeutic target in PSC remains to be explored.