Inhibitory effect of IL-8 on insulin action in human adipocytes via MAP kinase pathway

<p>Abstract</p> <p>Background</p> <p>Various cytokines and other compounds are produced in human adipose tissue and might have functions in the adipose tissue. They might be involved in complications associated with obesity and diabetes. Recently, interleukin-8 (IL-8) has been shown to be produced and released from human adipose tissue and/or adipocytes, suggesting IL-8 involvement in some obesity-related health complications. Therefore, we found it of interest to investigate whether IL-8 is involved in the insulin action in human adipocytes.</p> <p>Methods</p> <p>The IL-8 levels in the medium were measured using ELISA. The IL-8 mRNA expression was analyzed using Northern blot analysis. The phosphorylation of Akt was analyzed using Western blot analysis. Furthermore, we examined the effect of IL-8 on the phosphorylation of Akt induced by insulin.</p> <p>Results</p> <p>The level of IL-8 in the medium and the IL-8 mRNA expression after stimulation with either TNF-α, IL-1β, or CRP was significantly enhanced in human adipocytes. It is particularly interesting that IL-8 per se also enhanced IL-8 mRNA expression. The IL-8 induced-IL-8 mRNA expression was inhibited by PD98059 (a MEK inhibitor) or SB203580 (a p38 MAPK inhibitor). The IL-8 inhibited insulin-induced Akt phosphorylation. The inhibitory effect of IL-8 was eliminated by either PD 98059 or SB203580.</p> <p>Conclusion</p> <p>These data suggest that IL-8 is a main adipocytokine producing insulin resistance via the inhibition of insulin-induced Akt phosphorylation in adipocytes. The attenuation of IL-8 action might be a target for prevention of diabetes and its complications.</p

Purification of enzymatically inactive peptidylarginine deiminase type 6 from mouse ovary that reveals hexameric structure different from other dimeric isoforms

The murine peptidylarginine deiminase (PAD) has five isoforms encoded by different genes and partici- pates in a variety of cellular functions through the citrullination of target proteins. The crystal structure of human PAD4 with a dimeric form was previously solved because of the enzyme’s relevance to rheuma- toid arthritis. PAD6, abundant in mouse oocytes and eggs, is believed to take part in early events of embryogenesis, but its biochemical properties are little understood. Here we have purified and charac- terized a recombinant PAD6. A PAD6 cDNA was cloned from mouse ovary RNA and expressed in Escherichia coli through pET29 and pGEX vectors. When benzoyl-L-arginine ethyl ester was used as a substrate, no appreciable activity was detected with a cell homogenate under conditions where a human PAD4 cDNA caused significant activity. Both pro- teins were affinity-purified to near homogeneity. The circular dichroism spectra of PAD6 and human PAD4 were similar in the far ultraviolet region. On molecular sieving, PAD6 was eluted faster than human PAD4. The cross-linking of PAD6 with dime- thyl suberimidate clearly showed six bands on an sodium dodecyl sulfate-polyacrylamide gel. These results indicate that PAD6 can constitute a hexameric structure. The purified PAD6 still showed no enzy- matic activity. This unique structure and loss in enzymatic activity is strongly suggested to favor the formation of egg cytoplasmic sheets as the architectu- ral protein

The Beneficial Effects of Astaxanthin on Glucose Metabolism and Modified Low-Density Lipoprotein in Healthy Volunteers and Subjects with Prediabetes

Astaxanthin (ASTX) is an antioxidant agent. Recently, its use has been focused on the prevention of diabetes and atherosclerosis. We examined the effects of astaxanthin supplementation for 12 weeks on glucose metabolism, glycemic control, insulin sensitivity, lipid profiles and anthropometric indices in healthy volunteers including subjects with prediabetes with a randomized, placebo-controlled trial. Methods: We enrolled 53 subjects who met our inclusion criteria and administered them with 12 mg astaxanthin or a placebo once daily for 12 weeks. Subsequently, their HbA1c levels, lipid profiles and biochemical parameters were determined. The participants also underwent a 75 g oral glucose tolerance test (OGTT), vascular endothelial function test and measurement of the visceral fat area. Results: After astaxanthin supplementation for 12 weeks, glucose levels after 120 min in a 75 g OGTT significantly decreased compared to those before supplementation. Furthermore, the levels of HbA1c (5.64 &plusmn; 0.33 vs. 5.57 &plusmn; 0.39%, p &lt; 0.05), apo E (4.43 &plusmn; 1.29 vs. 4.13 &plusmn; 1.24 mg/dL, p &lt; 0.05) and malondialdehyde-modified low-density lipoprotein (87.3 &plusmn; 28.6 vs. 76.3 &plusmn; 24.6 U/L, p &lt; 0.05) were also reduced, whereas total cholesterol (TC), triglyceride (TG) and high-density lipoprotein-C (HDL-C) levels were unaltered. The Matuda index, which is one of the parameters of insulin resistance, was improved in the ASTX group compared to that before supplementation. Conclusions: our results suggest that ASTX may have preventive effects against diabetes and atherosclerosis and may be a novel complementary treatment option for the prevention of diabetes in healthy volunteers, including subjects with prediabetes, without adverse effects

Pravastatin suppresses the interleukin-8 production induced by thrombin in human aortic endothelial cells cultured with high glucose by inhibiting the p44/42 mitogen activated protein kinase

1. 3-Hydroxy-3-methylglutaryl co-enzyme A reductase inhibitors (statins) prevent the progression of atherosclerosis by lowering cholesterol. However, the effect of statins on the synthesis of pro-inflammatory cytokines from endothelial cells has not yet been fully investigated. Here, we examined the effect of pravastatin, one of the statins, on IL-8 synthesis induced by thrombin in human aortic endothelial cells (AoEC) cultured with high glucose concentrations. 2. Pravastatin significantly decreased the IL-8 synthesis induced by thrombin. 3. Pravastatin inhibited the p44/42 MAP kinase activity induced by thrombin, but did not inhibit the p38 MAP kinase activity. 4. Translocation of ras protein from the cytosol to plasma membrane was inhibited by pravastatin. 5. Pravastatin inhibit the activator protein-1 activity, but did not inhibit the activation of IκB-α. 6. Dominant negative ras inhibited the p44/42 MAP kinase activity induced by PMA. 7. Our results suggest that pravastatin inhibits IL-8 synthesis by blocking the ras-MAP (p44/42) kinase pathway rather than nuclear factor-κB. Pravastatin may prevent atherosclerosis not only by lowering cholesterol levels, but also by suppressing IL-8 synthesis in AoEC through the inhibition of p44/42 MAP kinase, and this may be more beneficial in diabetic patients than in non-diabetics