Endothelial inflammation correlates with subject triglycerides and waist size after a high-fat meal

Abstract

A rise in postprandial serum triglycerides (PP-sTG) can potentiate inflammatory responses in vascular endothelial cells (ECs) and thus serves as an independent risk factor for predicting increased cardiovascular morbidity. We examined postprandial triglyceride-rich lipoproteins (PP-TGRLs) in subjects ranging from normal to hypertriglyceridemic for their capacity to alter EC acute inflammatory responses. Cultured human aortic ECs (HAECs) were conditioned with PP-TGRLs isolated from human serum at the peak after a moderately high-fat meal. VLDL particle size increased postprandially and varied directly with the subject's PP-sTG level and waist circumference. PP-TGRL particles bound to HAECs and were internalized via LDL receptor-mediated endocytosis. PP-TGRL alone did not induce an inflammatory response over the range of individuals studied. However, combined with low-dose TNF-α stimulation (0.3 ng/ml), it elicited a net 10-15% increase above cytokine alone in the membrane expression of VCAM-1, ICAM-1, and E-selectin, which was not observed with fasting TGRLs. In contrast to upregulation of ICAM-1 and E-selectin, VCAM-1 transcription and expression varied in direct proportion with individual PP-sTG and waist circumference. The extent of monocyte arrest on inflamed HAECs under shear stress also correlated closely with VCAM-1 expression induced by conditioning with PP-TGRL and TNF-α stimulation. This ex vivo approach provides a quantitative means to assess an individual's inflammatory potential, revealing a greater propensity for endothelial inflammation in hypertriglyceridemic individuals with abdominal obesity.

Shear stress modulates VCAM-1 expression in response to TNF-α and dietary lipids via interferon regulatory factor-1 in cultured endothelium

“…Given the functional significance for VCAM-1 as a biomarker for atherogenesis whose expression lies at the convergence of dietary and hemodynamic factors, we used it as a readout of endothelial inflammation in our experiments. We have previously reported that the changes in VCAM-1 expression elicited by TGRL were IRF-1 dependent and strongly correlated with monocyte recruitment to cultured HAECs under shear flow (36,39,44) over a dose range in TNF-␣ that was significantly affected by IRF-1 suppression or overexpression (36). To shed light on the molecular mechanisms by which hydrodynamic shear stress modulates inflammation associated with hypertriglyceridemia, a custom microfluidic device was used that produces a continuous gradient in shear stress over a monolayer of HAECs, allowing visualization of the focal response to inflammation and shear stress during exposure to dietary TGRL (40).…”

“…Human subjects were recruited according to Institutional Review Board-approved protocols at the University of California-Davis. TGRL were collected and characterized as previously described (36,44). Briefly, venous blood was collected after a 12-h overnight fast and again 3.5 h after a standardized moderately high-fat meal (1,230 calories, 42% from fat and 32% from saturated fat).…”

“…To stimulate inflammation, HAECs were treated with TNF-␣ (0.3 ng/ml, R&D Systems) alone or in combination with TGRL (10 mg/dl ApoB) for 4 h (VCAM-1), 2 h (IRF-1), or 1 h (NF-B). The dose of TNF-␣ represents the ϳEC 50 for VCAM-1 expression as measured by flow cytometry (44). Treatments without TGRL were supplemented with an equal amount of buffer in which the isolated TGRL was suspended (196 mM NaCl and 0.3 mM EDTA) to compensate for any changes in volume and media composition.…”

“…TGRL were categorized as proatherogenic (pro-TGRL) or antiatherogenic (anti-TGRL) defined by their capacity to up-or downregulate VCAM-1 surface expression, respectively, relative to TNF-␣ stimulation under static culture (36). We (36,44) have previously documented that TGRL did not elicit an increase in VCAM-1 from HAECs in the absence of TNF-␣ stimulation regardless of its atherogenic activity in its presence. Similarly, we found that TGRL alone did not mediate activation with shear alone, motivating our focus on the superposition of TGRL and cytokine.…”

“…We (36,44) have recently reported that triglyceride-rich lipoproteins (TGRL) isolated from obese and hypertriglyceridemic subjects after a high-fat meal were proatherogenic to human aortic endothelial cells (HAECs) in that they increased VCAM-1-dependent monocyte adhesion relative to TNF-␣ stimulation (36,44). In contrast, TGRL from subjects with normal serum triglycerides did not upregulate inflammation.…”