Macrophage-mediated inflammation plays an essential role in diabetes-associated nonalcoholic steatohepatitis (NASH) and atherosclerosis. Our previous study has shown that acid sphingomyelinase (ASMase) plays a key role in the synergistic stimulation of inflammatory signaling by saturated fatty acid palmitate and lipopolysaccharide (LPS) in macrophages. In the current study, we assessed the effect of ASMase inhibition on NASH and atherosclerosis induced by lard-based, high palmitate-containing high-fat diet (HP-HFD) in combination with LPS in LDL receptor-knockout (LDLR-/-) mice. LDLR-/- mice were fed HP-HFD for 20 weeks and treated with or without a low dose of LPS and amitriptyline, an inhibitor of ASMase. Metabolic assays showed that amitriptyline reduced bodyweight, lipids and insulin resistance induced by HP-HFD or HP-HFD plus LPS. Histological study and Oil Red O staining of livers showed that while mice fed HP-HFD without LPS treatment had hepatic steatosis and hepatocellular ballooning, LPS further increased steatosis and ballooning by 70%. However, amitriptyline attenuated the effect of HP-HFD or HP-HFD plus LPS by 66%. Immunohistochemistry study showed that while mice fed HP-HFD without LPS treatment had a marked immunostaining of F4/80, a biomarker for macrophages, LPS further enhanced F4/80 immunostaining. However, amitriptyline significantly reduced F4/80 immunostaining. Furthermore, results showed that amitriptyline also attenuated atherosclerosis induced by HP-HFD plus LPS. To elucidate the underlying mechanisms, we found that amitriptyline downregulated proinflammatory cytokines by potently reducing sphingosine 1 phosphate, a bioactive sphingolipid. Taken together, this study showed that ASMase inhibition attenuated both NASH and atherogenesis induced by HP-HFD plus LPS and one of the mechanisms potentially involved in the attenuation is inhibition of S1P production.
Z. Lu: None. Y. Li: None. M.F. Lopes-Virella: None. Y. Huang: None.
U.S. Department of Veterans Affairs (1I01CX001825-01); National Institutes of Health