Release of TNF-alpha from in vitro-stimulated monocytes is negatively associated with serum levels of apolipoprotein B in patients with type 2 diabetes.

Impaired course of inflammation is a likely mechanism behind a number of diabetic complications. The present study was undertaken to investigate lipopolysaccharide-induced production of tumour necrosis factor (TNF)-alpha in monocytes from patients with type 2 diabetes and to assess its relationship with diabetes-associated metabolic abnormalities. Monocytic TNF-alpha mRNA production was lower in the diabetic participants compared to their corresponding controls. Diabetic subjects who had been receiving simvastatin treatment had TNF-alpha mRNA production similar to that of the healthy participants. The release of TNF-alpha from diabetic cells correlated negatively with serum levels of apolipoprotein B (apoB) (R = -0.755, P = 0.001), total plasma cholesterol (R = - 0.702, P = 0.002) and the presence of retinopathy (R = -0.572, P = 0.021). No such associations were found in the control subjects. In a multiple linear regression model, only the level of apoB and diabetes duration demonstrated significant effects on the release of TNF-alpha, with apoB alone accounting for 57% of the variation. We conclude that production of TNF-alpha mRNA in response to the bacterial stimulant is compromised in poorly controlled type 2 diabetes. Lipid abnormalities are associated with the observed defect. Impaired cytokine production represents a significant defect in the functioning of the immune system and may contribute to aberrations in the course of inflammation in the diabetic state.

Advanced glycation end products impair the scavenger function of rat hepatic sinusoidal endothelial cells.

AIMS/HYPOTHESIS: We have previously reported that advanced glycation end products are eliminated from the circulation mainly by scavenger receptor-mediated uptake in hepatic sinusoidal endothelial cells. Our experiments showed that the degradation of AGE-modified protein after endocytosis in hepatic sinusoidal endothelial cells occurs slowly compared with that of other scavenger receptor ligands. The aim of this study was to investigate further the mechanism whereby AGE-modified protein affects the important scavenger function of hepatic sinusoidal endothelial cells. METHODS: Primary cultures of hepatic sinusoidal endothelial cells were pre-incubated with unlabelled ligand, unbound ligand was washed off, and the endocytic capacity was measured by addition of radiolabelled ligand, and immune electron microscopy. RESULTS: Pre-incubation with unlabelled AGE-modified bovine serum albumin reduced subsequent endocytosis of radiolabelled scavenger receptor ligands AGE-modified bovine serum albumin, formaldehyde-treated serum albumin, oxidized low density lipoprotein and acetylated low density lipoprotein by 50, 56, 32 and 20%, respectively. Non-scavenger receptor-mediated endocytosis was not affected by pre-exposure to AGE-modified protein. Pre-incubation with a number of non-AGE-ligands did not affect subsequent endocytosis via any of the major endocytosis receptors in hepatic sinusoidal endothelial cells. Incubation in fresh medium for 6 h after pre-exposure to AGE-modified protein almost completely restored normal scavenger receptor-mediated endocytic activity. Quantitative immune electron microscopy showed that the amount of a newly described scavenger receptor for AGE-modified protein is reduced after pre-incubation with AGE-modified protein. Subcellular fractionation showed that pre-incubation with AGE-modified protein delays intracellular transport of scavenger receptor ligands. CONCLUSION/INTERPRETATION: Endocytosis of AGE-modified protein leads to loss of scavenger receptors and delayed intracellular transport in hepatic sinusoidal endothelial cells.