Recombinant TRAIL induces miorelaxating activity in rat aortas, which is abrogated by the induction of diabetes mellitus

TNF-related apoptosis inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of cytokines, which exist either as type II membrane or as a soluble protein. Although the best-characterized activity of TRAIL is represented by its anti-cancer activity, it has been recently shown that TRAIL serum levels are decreased in patients affected by atherosclerotic cardiovascular disease raising the possibility that circulating soluble TRAIL might also affect vascular biology. In this respect, it has been previously shown that TRAIL induces the in vitro release of nitric oxide by vascular endothelial cells. In order to explore the in vivo relevance of these in vitro findings, we have assessed the vascular reactivity in response to recombinant TRAIL in a more intact paradigm. For this purpose, rings (4mm long) from rat thoracic aorta were obtained by both control (3-month-old male non-diabetic Wistar rats receiving vehicle infusion) and rats in which diabetes mellitus was induced by injecting 40 mg/kg streptozotocin (SZT). After sacrifice of the animals, aortas were harvested, cleaned of connective tissue and vascular reactivity was analyzed in ex vivo immediately after harvest. During submaximal contraction with phenylephrine, incubation of aortic segments in the presence of increasing (up to 1000 ng/ml) concentrations of recombinant human TRAIL, resulted in significant (p<0.01) vaso-relaxation. The effect was dose-dependent and was completely abolished by pre incubation of the rat aortic rings with L-NAME, clearly indicating that the NOS pathway played a key role in mediating the myo-relaxating activity of TRAIL. In parallel, we have investigated whether the induction of diabetes mellitus might affect the relaxating activity of aortic rings in response to TRAIL. Diabetes mellitus was induced by destruction of pancreatic islet cells by treating rats with SZT (40 mg/kg). Non-fasting blood glucose concentrations of both SZT-diabetic rats (SZT, n = 10) and age-matched control non-diabetic rats treated with vehicle (n = 10) were measured at days 5 and 15, when animals were sacrificed with CO2. The loss of insulin secretion triggered stable hyperglycemia, as evaluated by blood glucose measurement: 260±46 and 295±55 in diabetic rats at days 5 and 15 after diabetic induction, respectively, versus 89±8 in control rats. Relaxation to TRAIL was completely abrogated in aortic rings obtained from SZT-induced diabetic rats. To the best of our knowledge, this is the first demonstration that soluble recombinant TRAIL promotes a dose-dependent myo-relaxation activity when added ex vivo to rat aortic rings, thus suggesting that it might play a physiological role in the control of vascular tone regulation. Importantly, such myorelaxating activity was completely abrogated in diabetic rats, as early as 15 days after diabetes mellitus induction by STZ injection. It should be emphasized that diabetic vascular dysfunction is a major clinical problem that predisposes patients to a variety of cardiovascular diseases. In fact, diabetic patients frequently suffer from macroscopic and microscopic vasculopathy and accelerated atherosclerosis. The loss of myo-relaxating activity is a key feature of endothelial dysfunction, which invariably precedes permanent vascular alterations. Taken together with previous data showing that TRAIL significantly counteracts the pro-adhesive activity of inflammatory cytokines on endothelial cells in vitro and displays anti-atherosclerotic activity when injected in vivo in ApoE−/−null mice, our present findings suggest that a therapeutic strategy aimed to restore the miorelaxating response to TRAIL may be suitable for improving the vascular function in diabetes mellitus.