Nutrient modification of the innate immune response: a novel mechanism by which saturated fatty acids greatly amplify monocyte inflammation.

OBJECTIVE: Monocyte/macrophage inflammation is an important contributor to diabetes and cardiovascular disease. Studies have suggested saturated fatty acids (SFA) induce monocyte inflammation in a Toll-like receptor-4-dependent manner, but recent data suggest SFA do not directly interact with Toll-like receptor-4. The present study tests the novel hypothesis that metabolism of SFA cooperatively amplifies Toll-like receptor-4-mediated inflammation. METHODS AND RESULTS: THP-1 monocytes exposed to 100 micromol/L SFA in vitro for 16 hours followed by 1 ng/mL lipopolysaccharide demonstrated enhanced IL-6 and IL-8 mRNA and protein expression (approximately 3-fold higher than the sum of individual responses to SFA and lipopolysaccharide). SFA had similar effects on THP-1 macrophages and primary human monocytes. This amplified lipopolysaccharide response could be blocked by inhibition of SFA metabolism to ceramide and restored by cell-permeable ceramide. Both SFA and ceramide activated PKC-zeta and the mitogen-activated protein kinases Erk, JNK, and p38. Inhibition of these pathways prevented the SFA-induced increase in cytokine expression. CONCLUSIONS: These results provide evidence for potent amplification of monocyte/macrophage innate immune responses by a novel pathway requiring metabolism of SFA to ceramide and activation of PKC-zeta/mitogen-activated protein kinases. These findings demonstrate how nutrient excess may modulate innate immune system activation and possibly contribute to development of diabetes and cardiovascular disease.

Prolonged exposure to high dietary lipids is not associated with lipotoxicity in heart failure.

Previous studies have reported that elevated myocardial lipids in a model of mild-to-moderate heart failure increased mitochondrial function, but did not alter left ventricular function. Whether more prolonged exposure to high dietary lipids would promote a lipotoxic phenotype in mitochondrial and myocardial contractile function has not been determined. We tested the hypothesis that prolonged exposure to high dietary lipids, following coronary artery ligation, would preserve myocardial and mitochondrial function in heart failure. Rats underwent ligation or sham surgery and were fed normal (10% kcal fat) (SHAM, HF) or high fat diet (60% kcal saturated fat) (SHAM+FAT, HF+FAT) for sixteen weeks. Although high dietary fat was accompanied by myocardial tissue triglyceride accumulation (SHAM 1.47+/-0.14; SHAM+FAT 2.32+/-0.14; HF 1.34+/-0.14; HF+FAT 2.21+/-0.20 micromol/gww), fractional shortening was increased 16% in SHAM+FAT and 28% in HF+FAT compared to SHAM and HF, respectively. Despite increased medium-chain acyl-CoA dehydrogenase (MCAD) activity in interfibrillar mitochondria (IFM) of both SHAM+FAT and HF+FAT, dietary lipids also were associated with decreased state 3 respiration using palmitoylcarnitine (SHAM 369+/-14; SHAM+FAT 307+/-23; HF 354+/-13; HF+FAT 366+/-18 nAO min(-1) mg(-1)) in SHAM+FAT compared to SHAM and HF+FAT. State 3 respiration in IFM also was decreased in SHAM+FAT relative to SHAM using succinate and DHQ. In conclusion, high dietary lipids promoted myocardial lipid accumulation, but were not accompanied by alterations in myocardial contractile function typically associated with lipotoxicity. In normal animals, high dietary fat decreased mitochondrial respiration, but also increased MCAD activity. These studies support the concept that high fat feeding can modify multiple cellular pathways that differentially affect mitochondrial function under normal and pathological conditions.