Palmitate induces phenotype changes in monocytes via de novo ceramide synthesis

Ageing is associated with physiological changes such as altered adipose tissue distribution and redox status, elevated metabolic disorder risk and increased free fatty acids. Saturated fatty acids can induce insulin resistance in endothelial cells and monocytes, in part explaining the increase cardiovascular disease risk with elevated fatty acids. The aim of this study is to investigate the effects of the two major physiological fatty acids palmitate and oleate (saturated and monounsaturated fatty acids respectively) on monocyte phenotype. THP-1 monocyte cell surface marker expression, mitochondrial reactive oxygen species, cell viability and caspase-3 were evaluated following 24h treatment with palmitate, oleate or bovine serum albumin. A concentration dependent increase in CD11b (p<0.01), CD36 (p<0.001) and mitochondrial reactive oxygen species (p<0.05) following palmitate but not oleate treatment was determined by flow cytometry. Decreased metabolic viability (p<0.01) was observed with palmitate (300μM), whilst no significant change in caspase-3 was observed. The superoxide dismutase mimetic MnTBAP (200μM) ameliorated the reduced metabolic viability and increased mitochondrial ROS due to palmitate, whilst increased CD11b and CD36 were unaffected. De novo ceramide synthesis inhibitor fumonisin B1 (50μM) prevented the palmitate dependent increase in CD11b (p<0.05) and CD36 (p<0.001). Ceramide converting inhibitors 1S,2R-D-erythro-2-N-myristoylamino)-1-phenyl-1-propanol (d-erythro MAPP 20 μM) and 1-phenyl-2-palmitoylamino-3-morpholino-1- propanol (PPMP 0.05 μM) were used to determine if ceramides or downstream sphingolipids are required for palmitate induced phenotype changes in monocytes. In the presence of MAPP and PPMP, palmitate induced increase in CD11b are sustained suggesting sphingolipids are key players in the observed phenotypic changes. The present study demonstrates in monocytes that palmitate but not oleate increases cell surface marker expression, accompanied by increased mitochondrial ROS and decreased metabolic viability. MnTBap could ameliorate changes in mitochondrial ROS and metabolic viability, but surface antigen expression decreased only by fumonisin B1 suggesting changes require de novo ceramide synthesi.