Relative hypoxia is essential in wound healing since it normally plays a pivotal role in regulation of all the critical processes involved in tissue repair. Hypoxia-inducible factor (HIF) 1α is the critical transcription factor that regulates adaptive responses to hypoxia. HIF-1α stability and function is regulated by oxygen-dependent soluble hydroxylases targeting critical proline and asparaginyl residues. Here we show that hyperglycemia complexly affects both HIF-1α stability and activation, resulting in suppression of expression of HIF-1 target genes essential for wound healing both in vitro and in vivo . However, by blocking HIF-1α hydroxylation through chemical inhibition, it is possible to reverse this negative effect of hyperglycemia and to improve the wound healing process (i.e., granulation, vascularization, epidermal regeneration, and recruitment of endothelial precursors). Local adenovirus-mediated transfer of two stable HIF constructs demonstrated that stabilization of HIF-1α is necessary and sufficient for promoting wound healing in a diabetic environment. Our findings outline the necessity to develop specific hydroxylase inhibitors as therapeutic agents for chronic diabetes wounds. In conclusion, we demonstrate that impaired regulation of HIF-1α is essential for the development of diabetic wounds, and we provide evidence that stabilization of HIF-1α is critical to reverse the pathological process.

OBJECTIVE—Conjugated linoleic acid (CLA) is a group of dietary fatty acids with antiobesity and antidiabetic effects in some animals. The trans10cis12 (t10c12) CLA isomer seems to cause these effects, including improved insulin sensitivity. Whether such isomer-specific effects occur in humans is unknown. The aim of this study was to investigate whether t10c12 CLA or a commercial CLA mixture could improve insulin sensitivity, lipid metabolism, or body composition in obese men with signs of the metabolic syndrome. RESEARCH DESIGN AND METHODS—In a randomized, double-blind controlled trial, abdominally obese men (n = 60) were treated with 3.4 g/day CLA (isomer mixture), purified t10c12 CLA, or placebo. Euglycemic-hyperinsulinemic clamp, serum hormones, lipids, and anthropometry were assessed before and after 12 weeks of treatment. RESULTS—Baseline metabolic status was similar between groups. Unexpectedly, t10c12 CLA increased insulin resistance (19%; P < 0.01) and glycemia (4%; P < 0.001) and reduced HDL cholesterol (−4%; P < 0.01) compared with placebo, whereas body fat, sagittal abdominal diameter, and weight decreased versus baseline, but the difference was not significantly different from placebo. The CLA mixture did not change glucose metabolism, body composition, or weight compared with placebo but lowered HDL cholesterol (−2%; P < 0.05). CONCLUSIONS—These results reveal important isomer-specific metabolic actions of CLA in abdominally obese humans. A CLA-induced insulin resistance has previously been described only in lipodystrophic mice. Considering the use of CLA-supplements among obese individuals, it is important to clarify the clinical consequences of these results, but they also provide physiological insights into the role of specific dietary fatty acids as modulators of insulin resistance in humans.

Hyperglycemia and hypoxia are suggested to play essential pathophysiological roles in the complications of diabetes, which may result from a defective response of the tissues to low oxygen tension. In this study, we show that in primary dermal fibroblasts and endothelial cells, hyperglycemia interferes with the function of hypoxia-inducible factor-1 (HIF-1), a transcription factor that is essential for adaptive responses of the cell to hypoxia. Experiments using proteasomal and prolyl hydroxylases inhibitors indicate that hyperglycemia inhibits hypoxia-induced stabilization of HIF-1α protein levels against degradation and suggest that mechanisms in addition to proline hydroxylation may be involved. This effect of hyperglycemia was dose dependent and correlates with a lower transcription activation potency of HIF-1α, as assessed by transient hypoxia-inducible reporter gene assay. Regulation of HIF-1α function by hyperglycemia could be mimicked by mannitol, suggesting hyperosmolarity as one critical parameter. The interference of hyperglycemia with hypoxia-dependent stabilization of HIF-1α protein levels was confirmed in vivo, where only very low levels of HIF-1α protein could be detected in diabetic wounds, as compared with chronic venous ulcers. In conclusion, our data demonstrate that hyperglycemia impairs hypoxia-dependent protection of HIF-1α against proteasomal degradation and suggest a mechanism by which diabetes interferes with cellular responses to hypoxia.