Evidence for activation of inflammatory lipoxygenase pathways in visceral adipose tissue of obese Zucker rats.

Central obesity is associated with low-grade inflammation that promotes type 2 diabetes and cardiovascular disease in obese individuals. The 12- and 5-lipoxygenase (12-LO and 5-LO) enzymes have been linked to inflammatory changes, leading to the development of atherosclerosis. 12-LO has also been linked recently to inflammation and insulin resistance in adipocytes. We analyzed the expression of LO and proinflammatory cytokines in adipose tissue and adipocytes in obese Zucker rats, a widely studied genetic model of obesity, insulin resistance, and the metabolic syndrome. mRNA expression of 12-LO, 5-LO, and 5-LO-activating protein (FLAP) was upregulated in adipocytes and adipose tissue from obese Zucker rats compared with those from lean rats. Concomitant with increased LO gene expression, the 12-LO product 12-HETE and the 5-LO products 5-HETE and leukotriene B4 (LTB4) were also increased in adipocytes. Furthermore, upregulation of key proinflammatory markers interleukin (IL)-6, TNFα, and monocyte chemoattractant protein-1 were observed in adipocytes isolated from obese Zucker rats. Immunohistochemistry indicated that the positive 12-LO staining in adipose tissue represents cells in addition to adipocytes. This was confirmed by Western blotting in stromal vascular fractions. These changes were in part reversed by the novel anti-inflammatory drug lisofylline (LSF). LSF also reduced p-STAT4 in visceral adipose tissue from obese Zucker rats and improved the metabolic profile, reducing fasting plasma glucose and increasing insulin sensitivity in obese Zucker rats. In 3T3-L1 adipocytes, LSF abrogated the inflammatory response induced by LO products. Thus, therapeutic agents reducing LO or STAT4 activation may provide novel tools to reduce obesity-induced inflammation.

Role of 12/15-lipoxygenase in the expression of MCP-1 in mouse macrophages.

Monocyte chemoattractant protein (MCP)-1 plays a key role in atherosclerosis and inflammation associated with visceral adiposity by inducing mononuclear cell migration. Evidence shows that mouse peritoneal macrophages (MPM) express a 12-lipoxygenase (12/15-LO) that has been clearly linked to accelerated atherosclerosis in mouse models and increased monocyte endothelial interactions in both rodent and human cells. However, the role of 12/15-LO products in regulating MCP-1 expression in macrophages has not been clarified. In this study, we tested the role of 12/15-LO products using MPM and the mouse macrophage cell line, J774A.1 cells. We found that 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] increased MCP-1 mRNA and protein expression in J774A.1 cells and MPM. In contrast, 12(R)-HETE, a lipid not derived from 12/15-LO, did not affect MCP-1 expression. 15(S)-HETE also increased MCP-1 mRNA expression, but the effect was less compared with 12(S)-HETE. MCP-1 mRNA expression was upregulated in a macrophage cell line stably overexpressing 12/15-LO (Plox-86 cells) and in MPM isolated from a 12/15-LO transgenic mouse. In addition, the expression of MCP-1 was downregulated in MPM isolated from 12/15-LO knockout mice. 12(S)-HETE-induced MCP-1 mRNA expression was attenuated by specific inhibitors of protein kinase C (PKC) and p38 mitogen-activated protein kinase (p38). 12(S)-HETE also directly activated NADPH oxidase activity. Two NADPH oxidase inhibitors, apocynin and diphenyleneiodonium chloride, blocked 12(S)-HETE-induced MCP-1 mRNA. Apocynin attenuated 12(S)-HETE-induced MCP-1 protein secretion. These data show that 12(S)-HETE increases MCP-1 expression by inducing PKC, p38, and NADPH oxidase activity. These results suggest a potentially important mechanism linking 12/15-LO activation to MCP-1 expression that induces inflammatory cell infiltration.

Insulin and glucose play a role in foam cell formation and function.

BACKGROUND: Foam cell formation in diabetic patients often occurs in the presence of high insulin and glucose levels. To test whether hyperinsulinemic hyperglycemic conditions affect foam cell differentiation, we examined gene expression, cytokine production, and Akt phosphorylation in human monocyte-derived macrophages incubated with two types of oxidized low density lipoprotein (LDL), minimally modified LDL (mmLDL) and extensively oxidized LDL (OxLDL). METHODS AND RESULTS: Using Affymetrix GeneChip arrays, we found that several genes directly related to insulin signaling were changed. The insulin receptor and glucose-6-phosphate dehydrogenase were upregulated by mmLDL and OxLDL, whereas insulin-induced gene 1 was significantly down-regulated. In hyperinsulinemic hyperglycemic conditions, modified LDL upregulated Akt phosphorylation and expression of the insulin-regulated aminopeptidase. The level of proinflammatory cytokines, IL-lbeta, IL-12, and IL-6, and of a 5-lipoxygenase eicosanoid, 5-hydroxyeicosatetraenoic acid (5-HETE), was also increased. CONCLUSION: These results suggest that the exposure of macrophages to modified low density lipoproteins in hyperglycemic hyperinsulinemic conditions affects insulin signaling and promotes the release of proinflammatory stimuli, such as cytokines and eicosanoids. These in turn may contribute to the development of insulin resistance.

Fasting decreases the content of D-chiroinositol in human skeletal muscle.

Two classes of inositol phosphoglycans have been implicated as second messengers of insulin, one that activates pyruvate dehydrogenase and contains D-chiroinositol, and one that inhibits cyclic AMP-dependent protein kinase and contains myoinositol. We examined the effects of a 3-day fast on muscle contents of inositols in healthy humans. An oral glucose tolerance test was performed and a biopsy was obtained from the quadriceps femoris muscle after an overnight fast and after a 72-hour fast. The 72-hour fast significantly increased plasma glucose (1.5- to 2-fold) and insulin (2- to 4-fold) after glucose ingestion versus the values after the overnight fast, indicating the manifestation of peripheral insulin resistance. The 72-hour fast resulted in an approximately 20% decrease in the muscle content of D-chiroinositol (P < 0.02), but no change in the myoinositol content. These data demonstrate that fasting specifically decreases the muscle content of D-chiroinositol in human muscle and this may contribute to the finding that insulin-mediated activation of pyruvate dehydrogenase is attenuated after short-term starvation.