Early elevation of complement-related proteins in metabolic dysfunction-associated steatotic liver disease (MASLD) with normal liver enzymes.

BACKGROUND: Metabolic dysfunction-associated steatotic liver disease (MASLD) affects a quarter of the population. Although multiple studies have investigated the mechanisms underlying steatohepatitis and MASLD progression, little attention has been paid to milder cases, particularly those with normal enzyme levels. Our objective was to evaluate the molecular events in patients with MASLD and normal enzyme levels. METHODS: We performed a proteomic analysis on serum samples from 83 healthy controls and 50 patients with MASLD. The major findings were then validated in serum samples from 35 controls and 60 patients with MASLD and normal liver enzyme levels (MASLD-NLE), as well as a male mouse model with metabolic dysfunction-associated liver steatosis and normal liver enzymes (mice-NLE) induced by a high-fat diet (HFD). RESULTS: Despite having normal enzyme levels, patients with MASLD-NLE exhibited significantly higher levels of ALT, AST, γGGT, hs-CRP, uric acid and creatine compared to controls. Serum proteomics indicated elevated complement-related proteins in patients with MASLD-NLE, evidenced by elevated protein levels of C3 and CFH in both cases using different cutoffs for normal ALT levels. C3 and CFH also showed positive correlations with γGGT, hs-CRP, ALT, and uric acid levels. Additionally, the elevation of C3 and CFH was confirmed in another set of human serum samples, as well as in serum and liver samples of mice-NLE using ELISA. CONCLUSIONS: Our study provides novel evidence that the complement system is already activated in patients with MASLD-NLE, potentially offering new avenues for treating MASLD at an early stage.