Redox-regulating role of insulin: the essence of insulin effect

It is well-known that insulin acts as an important hormone, controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Over the past few years, intensive insulin therapy has been believed to be benefit for the outcome of diabetic patients, in which the suppression of oxidative stress plays a role. Moreover, insulin is accepted as a key component of glucose-insulin-potassium, a treatment which has been believed to exert significant cardiovascular protective effect via the reduction of oxidative stress. Furthermore, accumulating evidence has suggested that insulin exerts important redox-regulating actions in various insulin-sensitive target organs, implying the systematic antioxidative role of insulin as a hormone. It is time for us to revisit insulin effects, through summarizing and evaluating the novel functions of insulin and their mechanisms. This review focuses on the antioxidative effect of insulin and highlights insulin-induced regulation of various antioxidant enzymes via insulin signaling pathways and the cross talk between key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NF-κB) which are responsible for the transcription of antioxidant enzymes, leading to reduced generation of reactive oxygen species (ROS) and the enhancement of the elimination of ROS.

[Therapeutic target for endothelium-derived hyperpolarizing factor signaling in diabetic vascular complication]

Vascular tone is tightly regulated by endothelium-derived factors. These include relaxing factors (EDRFs) such as nitric oxide (NO), hyperpolarizing factors (EDHFs), and contracting factors (EDCFs). Although EDHF is a prominent vasodilator, particularly in smaller arteries, little attention has been paid to the potential role of EDHF responses in diabetes. EDHF signaling may involve various factors, including several diffusible factors and non-diffusible factors (e.g., gap junctions). It has been demonstrated that the alterations in EDHF relaxation seen in mesenteric arteries from diabetic rats may be attributable to an increase in phosphodiesterase 3 (PDE3) activity, leading to a reduction in the action of adenosine 3',5'-cyclic monophosphate (cAMP), and consequently the activity of protein kinase A (PKA) is decreased in such arteries. Moreover, it has been suggested that the imbalance between EDRFs and EDCFs is present in mesenteric arteries from type 2 diabetic rats and the EDHF relaxation can be partly reversed by suppression of EDCF signaling. Indeed, chronic treatment with metformin, eicosapentaenoic acid, or thromboxane synthase inhibitor can reduce EDCF signaling and normalize EDHF signaling in mesenteric arteries from type 2 diabetic rats. Although the improvement or restoration of EDHF responses has not been the direct subject of any pharmaceutical effort, increasing cAMP/PKA signaling (e.g., by inhibiting PDE3 activity) or reducing EDCFs signaling has potential as an interesting therapeutic target in diabetic vasculopathy.

Olive tree wood phenolic compounds with human platelet antiaggregant properties

Oleuropein and (+)-cycloolivil are natural polyphenolic compounds with a significant radical scavenging activity present in olive tree. We have investigated the antiaggregant effects of oleuropein and (+)-cycloolivil isolated from an ethyl acetate extract of olive tree wood. Oleuropein and (+)-cycloolivil reduced the ability of thrombin to stimulate platelet aggregation. Both compounds reduced thrombin-evoked Ca(2+) release and entry to a similar extent to hydroxytyrosol. This effect was greater in platelets from patients with type 2 diabetes mellitus than in controls. Thrombin-, thapsigargin- and 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-evoked protein tyrosine phosphorylation, which is involved in Ca(2+) signalling and platelet aggregation, is inhibited by oleuropein and (+)-cycloolivil. oleuropein and (+)-cycloolivil are natural oxygen radical scavengers that reduce thrombin-induced protein tyrosine phosphorylation, Ca(2+) signalling and platelet aggregation. These observations suggest that oleuropein and (+)-cycloolivil may prevent thrombotic complications associated to platelet hyperaggregability and be the base for the development of antiaggregant therapeutic strategies.