Protective actions of gliclazide on high insulin-enhanced neutrophil–endothelial cell interactions through inhibition of mitogen activated protein kinase and protein kinase C pathways

The association between the metabolic syndrome and alanine amino transferase is mediated by insulin resistance via related metabolic intermediates (the Cohort on Diabetes and Atherosclerosis Maastricht [CODAM] study)

The metabolic syndrome is associated with nonalcoholic fatty liver disease (NAFLD) as well as with insulin resistance, inflammatory adipokines, endothelial dysfunction, and higher plasma levels of nonesterified fatty acids (NEFA), all of which may also affect the development of NAFLD. Therefore, we investigated to what extent the association between the metabolic syndrome and alanine aminotransferase (ALT, as a surrogate of NAFLD) can be explained by different metabolic intermediates of the metabolic syndrome. Cross-sectional analyses were performed in 434 subjects from the Cohort on Diabetes and Atherosclerosis Maastricht study (264 men; mean age, 59.5 ± 7.1 years). We used multiple linear regression analyses to investigate the association between the metabolic syndrome and ALT and the mediation role of potential mediators herein. The mediators considered were insulin resistance (homeostasis model assessment), an inflammatory adipokine score (based on interleukin-6, serum amyloid A, intercellular adhesion molecule, adiponectin, and leptin), an endothelial dysfunction score (based on E-selectin, vascular cell adhesion molecule, and von Willebrand factor), and plasma levels of NEFA. All analyses were adjusted for age, sex, smoking, alcohol consumption, and use of medication. Subjects with the metabolic syndrome (53.7%) had significantly higher levels of ALT (β = 0.67 SD [95% confidence interval, 0.49-0.85], P < .001). Adjustment for insulin resistance attenuated this difference by 77.3% (to 0.15 SD [-0.04 to 0.35]). Attenuation by adipose tissue-associated inflammation, endothelial dysfunction, and NEFA was more modest (20.7%, 13.1%, and 9.5%, respectively). Part of the attenuation by NEFA, but not of the other mediators, was additional to that of insulin resistance. Insulin resistance constitutes a key pathophysiological mechanism in the association between the metabolic syndrome and NAFLD (measured as ALT), which may operate through adipose tissue-associated inflammation and endothelial dysfunction and to a lesser extent through NEFA, which may have an independent role in the development of NAFLD in subjects with the metabolic syndrome.

Gliclazide inhibits differentiation-associated biologic events in human monocyte-derived macrophages

We investigated the in vitro effect of gliclazide on human monocyte-derived macrophage scavenger receptor expression and activity, foam cell formation, and lipopolysaccharide-induced cytokine production. Differentiation of human monocytes into macrophages in the presence of gliclazide (1-10 microg/mL) decreased CD36 expression by 20% to 50%, with maximal effect occurring at 2.5 microg/mL (P<.05). This effect was mimicked by vitamin E (50 micromol/L) and N-acetyl-L-cysteine (10 mmol/L). Incubation of the cells with gliclazide and N-acetyl-L-cysteine also reduced CD36 activity by 30% (P<.02). Despite these effects, neither gliclazide nor vitamin E did affect foam cell formation. In contrast, gliclazide significantly reduced lipopolysaccharide-stimulated macrophage tumor necrosis factor alpha and interleukin 6 secretion (P<.05). Overall, these data indicate that gliclazide, at concentrations in the therapeutic range, may regulate some key biologic events associated with the process of monocyte differentiation into macrophages.

Insulin enhances leukocyte-endothelial cell adhesion in the retinal microcirculation through surface expression of intercellular adhesion molecule-1

The purpose of this study was to evaluate the effects of insulin on leukocyte-endothelial cell adhesion in the retinal microcirculation in vitro and in vivo. Human retinal endothelial cells (HRECs) were cultured in medium with or without insulin, and neutrophils allowed to adhere. Adherent neutrophils were quantified by measuring myeloperoxidase activity. Surface expression of endothelial adhesion molecules were studied with the use of an enzyme immunoassay. Insulin at concentrations of 50 and 100 microU/ml significantly increased neutrophil adhesion to HRECs compared with the control cells (P < 0.01, respectively). Surface expression of intercellular adhesion molecule-1 (ICAM-1) significantly increased when HRECs were exposed to 100 microU/ml insulin, as compared with the control cells (P < 0.05). Anti-ICAM-1 antibody significantly inhibited neutrophils adhesion to HRECs (P < 0.0001). Brown-Norway rats received subcutaneous injection of 0.2 U per 100 g body weight insulin three times. Control rats received the same amount of phosphate-buffered saline. Leukocyte entrapment in the retina was evaluated using acridine orange leukocyte fluorography. The number of leukocytes trapped in the retina of insulin-treated rats was significantly elevated compared with that in the control animals (P < 0.0001). These results suggested that insulin enhances leukostasis in retinal microcirculation. Hyperinsulinemia may be a risk factor of retinal microcirculatory disturbances.