Abstract 644: Enhanced Innate Immunity Pathways and LPS Induced Vasculopathy in Mice Fed a High Fat Diet
Vasculopathy and cardiovascular collapse are major contributors to sepsis outcomes and are apparently related to activation of innate immunity pathways leading to systemic inflammation and oxidative injury. A key contributor for gram-negative pathogens is the Toll-like receptor-4 (TLR4) signaling pathway. Recent studies have suggested that chronic intake of a high-fat diet (HFD) promotes a state of low level inflammation in humans and animals, which may contribute to cardiovascular disease risk and/or progression. We therefore tested the hypothesis that chronic high fat diet would enhance the systemic and/or vascular response to a low dose LPS challenge in mice. C57BL/6J mice were fed with HFD (16% saturated fat, 1.25% cholesterol) or isocaloric control diet (CD, 5% saturated fat, 0.03% cholesterol) for 4 weeks, followed by a single sub-lethal dose of LPS (0.5 mg/kg, ip,) or saline control and sacrificed at 0.5, 2, 4, 12, or 24 h post treatment (n=5 per group). Plasma lipid levels, cytokines (IL6, TNFα, IFNγ) and serum amyloid A (SAA) were measured. Isolated vascular function was assessed at 24 post-LPS using thoracic aortic segments. TLR4 mRNA and protein levels were detected with RT-PCR and immunohistochemistry, respectively. HFD induced hypercholesterolemia (total cholesterol: 343.5 vs.158.1 mg/dL; LDL cholesterol: 217.5 vs. 113.0 mg/dL, p<0.05) and increased levels of plasma SAA (144.3 vs 1.49 μg/mL, p<0.01), but not cytokines, prior to LPS. Hepatic TLR4 mRNA (3.14-fold, p<0.05) was also induced in HFD mice, as were markers of hepatic injury. LPS induced cytokine responses, SAA induction, and TLR4 expression were enhanced in HFD mice (2- to 4-fold increase relative to control responses). Specific deficits in endothelial vascular responses were also observed in LPS treated HFD tissues, whereas no change was observed for either LPS or HFD alone (acetylcholine vasorelaxant response: 79.1%, 82.4%, 75.6%, and 60.8* for CD, LPS, HFD, LPS+HFD, respectively, *p<0.05). These data demonstrate that HFD induced low-grade inflammatory state can amplify responses to LPS and promote cardiovascular toxicities. This apparent synergy of innate immunity pathway amplification may contribute to the heterogeneous outcomes observed in clinical sepsis.