The potential protective effects of fermented extra virgin olive oil on high-fructose diet-induced non-alcoholic steatohepatitis in rats

Abstract Non-alcoholic steatohepatitis (NASH), a progressive form of NAFLD, is strongly associated with high-fructose diets. We investigated whether microbial fermentation could enhance the known hepatoprotective effects of extra virgin olive oil (EVOO) by modifying its bioactive compounds such as squalene and antioxidant potential. This study evaluated the effects of fermented EVOO on NASH induced by a high-fructose diet (HFrD) in rats. EVOO was optimized for fermentation using Yarrowia lipolytica , and the highest squalene level was selected based on GC–MS assessment. Male Sprague–Dawley rats were divided into four experimental groups ( n = 6 per group). One group was fed a balanced diet as the control group, while the other groups were placed on a high-fructose diet to induce steatohepatitis. Among these, one group served as the steatohepatitis group, while the remaining two groups received 10% EVOO and fermented EVOO in their diets, respectively, for six weeks. Liver function, serum glucose, insulin, lipid profiles, hepatic lipids, oxidative stress markers, interleukins-6 and IL-1β, as well as histopathological and immunohistochemical assessments, were conducted. Fermented EVOO, characterized by an increased squalene level, significantly improved liver function parameters (as indicated by lower ALT, AST, ALP, and bilirubin levels, p < 0.05), markedly reduced insulin resistance (HOMA-IR, p < 0.05), and significantly decreased hepatic lipid accumulation (total fat, cholesterol, and triglycerides in liver tissue, p < 0.05) compared to the HFrD group. Additionally, significantly enhanced antioxidant markers (GSH: 190.24 ± 1.32 ng/mg; SOD: 174.34 ± 2.15 U/mg; catalase: 10.56 ± 0.86 ng/mg) compared to HFrD controls (GSH: 81.29 ± 2.01; SOD: 71.02 ± 1.57; catalase: 6.77 ± 0.14), while reducing oxidative stress (MDA: 1.12 ± 0.02 vs 2.21 ± 0.02 nmol/mg) and inflammation markers (IL-6: 6.24 ± 0.98 vs 8.34 ± 0.15 ng/g; IL-1β: 7.84 ± 0.99 vs 9.76 ± 0.13 pg/g; all p < 0.05). Histopathological examination revealed a significant reduction in collagen deposition and marked improvements in immunohistochemical changes. These findings suggest that fermented EVOO confers protective effects against high-fructose-induced hepatic steatohepatitis in rats. This highlights its potential as a dietary intervention for managing NASH. Graphical Abstract