Impaired Relaxation in Aorta from Streptozotocin-diabetic Rats: Effect of Aminoguanidine (AMNG) Treatment

Aim The effect of 8 weeks′ streptozotocin (STZ)- induced diabetes and aminoguanidine (AMNG), the inhibitor of advanced glycosylation reaction, treatment on arteriolar reactivity to vasoactive substances was investigated in vitro. Materials and Methods Studies were performed in untreated control rats (n = 10), STZ-induced (60 mg/kg i.v.) diabetic rats (n = 10), AMNG-treated (600 mg/l given in drinking water throughout 8 weeks) control rats (n = 10) and AMNG-treated (600 mg/l given in drinking water, beginning at 72h after STZ and throughout 8 weeks of diabetes) diabetic rats (n = 10). Results are expressed as the mean ±s.e. Relaxant responses are expressed as a percentage (%) relaxation of noradrenaline-induced tone. Statistical comparisons were made by one-way analysis of variance (ANOVA) followed by Tukey–Kramer multiple comparisons test. Results 1. The decreased body weights (205 ± 6 g) and increased blood glucose levels (583 ± 8 mg/dl) of diabetic rats were partially restored by treatment of aminoguanidine (253 ± 6 g, p < 0.05 and 480 ± 14 mg/dl, p < 0.001, respectively). 2. Diabetes caused a 71% deficit in maximal endothelium-dependent relaxation to acetylcholine for noradrenaline precontracted aortas (p < 0.001). AMNG treatment prevented the diabetes-induced impairment in endothelium dependent relaxation (58 ± 8%) to acetylcholine, maximum relaxation remaining in the non-diabetic range (78 ± 4%). 3. Neither diabetes nor treatment affected endothelium-independent relaxation (pD₂ and max. Relax.) to sodium nitroprusside. 4. Vasoconstrictor responses (pD₂ and Max. Contraction) to noradrenaline and KCl were not influenced by the diabetic state and treatment. Conclusion Our data suggest that 8 weeks of experimental diabetes is associated with a decreased endothelium-dependent vasodilatation. AMNG treatment may prevent diabetes-induced endothelial dysfunction. This may be mediated via the prevention of advanced glycosylation end product formation, the enhanced release of vasodilator substances such as prostacyclin, the increased elasticity of blood vessels, the antioxidant activity and inhibitor activity of enzyme aldose-reductase by AMNG.     

Sensory Nerve Innervation of Epineurial Arterioles of the Sciatic Nerve Containing Calcitonin Gene–Related Peptide: Effect of Streptozotocin-Induced Diabetes

The authors have determined that epineurial arterioles of the sciatic nerve are innervated by nonadrenergic, noncholinergic nerves that contribute to the regulation of vasodilation. Using immunohistochemistry, the authors determined that nerves innervating epineurial arterioles contain the neuropeptide calcitonin gene–related peptide (CGRP). Using streptozotocin-induced diabetic rats, the authors demonstrated that CGRP content in sensory nerves innervating epineurial arterioles and vasodilation in response to exogenous CGRP was decreased. In summary, epineurial arterioles of the sciatic nerve are innervated by sensory nerves containing the neuropeptide CGRP. The diabetes-like condition induced by streptozotocin reduces the content of CGRP in these nerves and exogenous CGRPmediated vasodilation. CGRP is likely an important regulator of vascular tone and compromising its function could contribute to nerve ischemia and diabetic neuropathy.     

Effect of Fidarestat and α-Lipoic Acid on Diabetes-Induced Epineurial Arteriole Vascular Dysfunction

In the present study, the authors examined whether treating streptozotocin-induced diabetic rats with the combination of α-lipoic acid and fidarestat, an aldose reductase inhibitor, can promote the formation of dihydrolipoic acid in diabetic animals and thereby enhance the efficacy of α-lipoic acid as monotherapy toward preventing diabetic vascular and neural dysfunction.Treating diabetic rats with the combination of 0.25% α-lipoic acid (in the diet) and fidarestat (3 mg/kg body weight) prevented the diabetesinduced slowing of motor nerve conduction velocity and endoneurial blood flow. This therapy also significantly improved acetylcholine-mediated vasodilation in epineurial arterioles of the sciatic nerve compared to nontreated diabetic rats. Treating diabetic rats with 0.25% α-lipoic acid and fidarestat (3 mg/kg body weight) was equally or more effective in preventing vascular and neural dysfunction than was monotherapy of diabetic rats with higher doses of α-lipoic acid or fidarestat. Treating diabetic rats with the combination of 0.25% α-lipoic acid and fidarestat (3 mg/kg body weight) significantly improved several markers of oxidative stress and increased the serum levels of both α-lipoic acid and dihydrolipoic acid. These studies suggest that combination therapy consisting of α-lipoic acid and fidarestat may be more efficacious in preventing diabetes-induced vascular and neural dysfunction in peripheral tissue compared to monotherapy, which requires higher doses to be equally effective. The effect of this combination therapy may in part be due to the increased production and/or level of dihydrolipoic acid.     

Diabetes abolishes the vascular protective effects of estrogen in female rats

Estrogen is known to exert a protective effect against cardiovascular disease. However, women with diabetes have three times the risk as compared with age-matched non-diabetic women. Our previous study on aortic rings of ovariectomized (OVX) female rats treated with 17-beta-estradiol (E2) demonstrated that the beneficial effect of estrogen is related to the basal release of NO from endothelial cells. In the present study, in order to understand why estrogen protection is abolished in diabetes, we tested vascular responses in OVX, streptozotocin-diabetic female rats and their non-diabetic controls receiving or not E2 replacement. Concentration-response curves to norepinephrine (NE) showed attenuation of the contractile response in E2-treated diabetic, with respect to non-diabetic preparations. This response was further impaired in diabetic, E2-deprived rats. The basal release of NO, as evaluated by concentration-related responses to N(G)-methyl-L-arginine acetate in NE-precontracted aortic rings, was found to be impaired in E2-treated diabetic rats, no further effect being induced by E2 deprivation. The endothelium-dependent relaxation produced by carbachol did not change between groups, whereas the relaxation produced by histamine was enhanced by both diabetes and E2 deprivation. However, E2 treatment counteracted the response to histamine only in preparations from non-diabetic animals. Finally, the relaxation induced by sodium nitroprusside, an endothelium-independent relaxant agent, was comparable between groups. These findings suggest that the lack of protective effects of estrogen in diabetes may be mainly ascribed to the failure of estrogen to reverse the impaired basal release of NO and the abnormal relaxation to histamine, which are observed in the aorta of diabetic rats.     

Integrins mediate mechanical compression–induced endothelium-dependent vasodilation through endothelial nitric oxide pathway

Cardiac and skeletal muscle contraction lead to compression of intramuscular arterioles, which, in turn, leads to their vasodilation (a process that may enhance blood flow during muscle activity). Although endothelium-derived nitric oxide (NO) has been implicated in compression-induced vasodilation, the mechanism whereby arterial compression elicits NO production is unclear. We cannulated isolated swine (n = 39) myocardial (n = 69) and skeletal muscle (n = 60) arteriole segments and exposed them to cyclic transmural pressure generated by either intraluminal or extraluminal pressure pulses to simulate compression in contracting muscle. We found that the vasodilation elicited by internal or external pressure pulses was equivalent; moreover, vasodilation in response to pressure depended on changes in arteriole diameter. Agonist-induced endothelium-dependent and -independent vasodilation was used to verify endothelial and vascular smooth muscle cell viability. Vasodilation in response to cyclic changes in transmural pressure was smaller than that elicited by pharmacological activation of the NO signaling pathway. It was attenuated by inhibition of NO synthase and by mechanical removal of the endothelium. Stemming from previous observations that endothelial integrin is implicated in vasodilation in response to shear stress, we found that function-blocking integrin α₅β₁ or α_vβ₃ antibodies attenuated cyclic compression–induced vasodilation and NO_x (NO⁻₂ and NO⁻₃) production, as did an RGD peptide that competitively inhibits ligand binding to some integrins. We therefore conclude that integrin plays a role in cyclic compression–induced endothelial NO production and thereby in the vasodilation of small arteries during cyclic transmural pressure loading.     

Regulation of acetyl-CoA carboxylase in rat mammary gland. Effects of starvation and of insulin and prolactin deficiency on the fraction of the enzyme in the active form in vivo

The `initial' (I), endogenous phosphatase-activated (A) and citrate-activated (C) activities of acetyl-CoA carboxylase were measured in mammary-gland extracts of pregnant and lactating rats. There was a 10-fold increase in the A and C enzyme activities in the transition from early to peak lactation [cf. data of Mackall & Lane (1977) Biochem. J. 162, 635–642], but there was no significant increase in the ratio of the initial activity to the A and C activities of the enzyme. Starvation (24h) or short-term (3h) streptozotocin-induced diabetes both resulted in a 40% decrease in I/A and I/C activity ratios. In starvation this was accompanied by a decrease in the absolute values of the A and C activities such that the initial activity in mammary glands of starved animals was 45% that in glands from fed animals. Insulin treatment of starved or diabetic animals 60min before killing increased the I activity without affecting the A or C enzyme activities. Removal of the pups for 24h from animals in peak lactation (weaning) resulted in a marked but similar decrease in all three activities such that, although the initial activity was only 10% of that in suckled animals, the I/A and I/C activity ratios remained high and unaltered. Inhibition of prolactin secretion by injection of 2-bromo-α-ergocryptine gave qualitatively similar results to those during weaning. Simultaneous administration of ovine prolactin completely prevented the effects of bromoergocryptine. It is suggested that the initial activity of acetyl-CoA carboxylase in rat mammary gland is regulated by at least two parallel mechanisms: (i) an acute regulation of the proportion of the enzyme in the active state and (ii) a longer-term modulation of enzyme concentration in the gland. Insulin appeared to mediate its acute effects through mechanism (i), whereas prolactin had longer-term effects on enzyme concentration in the gland. A comparison of initial enzyme activities (I) obtained in the present study with rates of lipogenesis measured in vivo [Agius & Williamson (1980) Biochem. J. 192, 361–364; Munday & Williamson (1981) Biochem. J. 196, 831–837] gave good agreement between the two sets of data for all conditions studied except for 24h-starved and streptozotocin-diabetic animals. It is suggested that acetyl-CoA carboxylase activity is rate-limiting for lipogenesis in the mammary gland in normal, fed, suckled or weaned animals but that in starved and short-term diabetic animals changes in the activity of the enzyme by covalent modification alone may not be sufficient to maintain the enzyme in its rate-limiting role.     

Hindlimb unweighting alters endothelium-dependent vasodilation and ecNOS expression in soleus arterioles.

The purpose of this study was to test the hypothesis that endothelium-dependent dilation is impaired in soleus resistance arteries from hindlimb-unweighted (HLU) rats. Male Sprague-Dawley rats (300-350 g) were exposed to HLU (n = 14) or weight-bearing control (Con, n = 14) conditions for 14 days. After the 14-day treatment period, soleus first-order (1A) arterioles were isolated and cannulated with micropipettes to assess vasodilator responses to an endothelium-dependent dilator, ACh (10(-9)-10(-4) M), and an endothelium-independent dilator, sodium nitroprusside (SNP, 10(-9)-10(-4) M). Arterioles from HLU rats were smaller than Con arterioles (maximal passive diameter = 140 +/- 4 and 121 +/- 4 microm in Con and HLU, respectively) but developed similar spontaneous myogenic tone (43 +/- 3 and 45 +/- 3% in Con and HLU, respectively). Arteries from Con and HLU rats dilated in response to increasing doses of ACh, but dilation was impaired in arterioles from HLU rats (P = 0.03), as was maximal dilation to ACh (85 +/- 4 and 65 +/- 4% possible dilation in Con and HLU, respectively). Inhibition of nitric oxide (NO) synthase (NOS) with N(omega)-nitro-L-arginine (300 microM) reduced ACh dilation by approximately 40% in arterioles from Con rats and eliminated dilation in arterioles from HLU rats. The cyclooxygenase inhibitor indomethacin (50 microM) did not significantly alter dilation to ACh in either group. Treatment with N(omega)-nitro-L-arginine + indomethacin eliminated all ACh dilation in Con and HLU rats. Dilation to sodium nitroprusside was not different between groups (P = 0.98). To determine whether HLU decreased expression of endothelial cell NOS (ecNOS), mRNA and protein levels were measured in single arterioles with RT-PCR and immunoblot analysis. The ecNOS mRNA and protein expression was significantly lower in arterioles from HLU rats than in Con arterioles (20 and 65%, respectively). Collectively, these data indicate that HLU impairs ACh dilation in soleus 1A arterioles, in part because of alterations in the NO pathway.     

Enhanced arterial contractility to noradrenaline in diabetic rats is associated with increased phosphoinositide metabolism.

The purpose of this study was to investigate whether the increased contractile responsiveness of aortae from male rats with 12-14 week streptozotocin-induced diabetes to noradrenaline is associated with alterations in phosphoinositide metabolism. The contractile response to noradrenaline (10 microM) in both the presence and absence of extracellular calcium was significantly enhanced in aortae from diabetic rats. No significant differences were found between control and diabetic arteries in the basal incorporation of 32P and [3H]myo-inositol into phosphoinositides, or in the basal accumulation of [32P]phosphatidic acid and [3H]inositol phosphates. However, noradrenaline (10 microM) caused significantly greater breakdown of [32P]phosphatidylinositol 4,5-bisphosphate and formation of [32P]phosphatidic acid and [3H]inositol phosphates in diabetic aortae than in control preparations. The production of [3H]inositol phosphates induced by noradrenaline was selectively reduced by the alpha 1-adrenoceptor antagonist, prazosin, in both control and diabetic tissues. These results indicate that phosphoinositide metabolism in response to noradrenaline via stimulation of alpha 1-adrenoceptors is enhanced in aortae from chronic streptozotocin-diabetic rats. The increase in inositol 1,4,5-trisphosphate and 1,2-diacylglycerol production that presumably results could be responsible, at least in part, for the enhanced contractile response of aortae from diabetic rats to noradrenaline.     

Bone medullary arterioles from ovariectomized rats have smaller baseline diameters but normal eNOS expression and NO-mediated dilation

This study was designed to test the hypothesis that endogenous estrogens decrease the expression of endothelial nitric oxide synthase (eNOS) in resistance-size bone arterioles, thereby reducing endothelium-dependent vasodilator function. Sexually mature female rats were ovariectomized to reduce endogenous estrogens. Age-matched female rats served as controls. Seven to ten days after ovariectomy, bone marrow tissue was collected from the femoral canal. Immuno-histochemistry was performed to detect expression of estrogen receptors, alpha and beta and eNOS. eNOS protein content in medullary bone arterioles was compared using Western blot analysis. Endothelial cell function was assessed by quantitating the dilation of isolated, pressurized bone arterioles in response to acetylcholine. The results indicate that the endothelium of bone arterioles from ovariectomized and control rats express ER-alpha, ER-beta and eNOS. eNOS protein content in the two groups of arterioles did not differ. However, the baseline diameter of arterioles from ovariectomized rats (63+/-4 microm) was significantly smaller than the diameter of arterioles from control rats (75+/-3 microm, p<0.05). The two groups of arterioles dilated equally in response to acetylcholine. L-NAME, an inhibitor of eNOS, almost completely abolished the dilator responses to acetylcholine, but not to sodium nitroprusside. L-Arginine restored acetylcholine-induced dilation after L-NAME treatment. Thus, arteriole dilation to acetylcholine appears to be mediated almost exclusively by NO. The smaller diameter of arterioles from ovariectomized rats suggests that endogenous estrogens exert a significant dilator influence on bone arterioles. However, the dilator influence does not appear to be mediated by an increase in eNOS expression or enhanced NO-dependent vasodilation. These results indicate that estrogens do not decrease eNOS expression or diminish NO-mediated dilation of bone medullary arterioles.     

RhoA/Rho-Kinase and Nitric Oxide in Vascular Reactivity in Rats with Endotoxaemia

RhoA/Rho-kinase (RhoA/ROK) pathway promotes vasoconstriction by calcium sensitivity mechanism. LPS causes nitric oxide (NO) overproduction to induce vascular hyporeactivity. Thus, we tried to examine the role of RhoA/ROK and NO in the regulation of vascular reactivity in different time-point of endotoxaemia. Male Wistar rats were intravenously infused for 10 min with saline or E. coli endotoxin (lipopolysaccharide, LPS, 10 mg/kg) and divided to five groups (n = 8 in each group): (i) Control, sacrificed at 6 h after saline infusion; (ii) LPS1h, sacrificed at 1 h after LPS infusion; (iii) LPS2h, sacrificed at 2 h after LPS infusion; (iv) LPS4h, sacrificed at 4 h after LPS infusion; and (v) LPS6h, sacrificed at 6 h after LPS infusion. LPS1h and LPS2h were regarded as early endotoxaemia, whereas LPS4h and LPS6h were regarded as late endotoxaemia. Indeed, our results showed that LPS reproduced a biphasic hypotension and sustained vascular hyporeactivity to noradrenaline (NA) in vivo. Interestingly, this hyporeactivity did not occur in ex vivo during early endotoxaemia. This could be due to increases of aortic RhoA activity (n = 5, P<0.05) and myosin phosphatase targeting subunit 1 phosphorylation (n = 3, P<0.05). In addition, pressor response to NA and vascular reactivity in early endotoxaemia were inhibited by ROK inhibitor, Y27632. Furthermore, plasma bradykinin was increased at 10 min (24.6±13.7 ng/mL, n = 5, P<0.05) and aortic endothelial NO synthase expression was increased at 1 h (+200%. n = 3, P<0.05) after LPS. In late endotoxaemia, the vascular hyporeactivity was associated with aortic inducible NO synthase expression (n = 3, P<0.05) and an increased serum NO level (n = 8, P<0.05). Thus, an increased RhoA activity could compensate vascular hyporeactivity in early endotoxaemia, and the large NO production inhibiting RhoA activity would lead to vascular hyporeactivity eventually.     

Insulin action and binding in isolated hepatocytes from fasted, streptozotocin-diabetic, and older, spontaneously obese rats

Insulin binding and basal and insulin-stimulated uptake of α-aminoisobutyric acid were measured in isolated hepatocytes from young control rats as well as from older spontaneously obese, 72h-starved, and nonketotic streptozotocin-diabetic rats. Isolated hepatocytes from older spontaneously obese rats are similar to those from younger smaller rats in size, maximal insulin responsiveness, the dose–response relationship for insulin-stimulated aminoisobutyrate uptake, and the number and affinity of insulin receptors. Hepatocytes from 72h-fasted rats have similar numbers of insulin receptors per cell as cells from young control animals, but are significantly smaller, have an enhanced basal rate of aminoisobutyrate uptake, and are insulin resistant with regard to maximal insulin-stimulated uptake of aminoisobutyrate at 0.1mm-aminoisobutyrate. Because of the decreased maximal response to insulin, the concentration of insulin that elicits a half-maximal response of aminoisobutyrate uptake is decreased. Hepatocytes from diabetic animals, like those from starved rats, have significantly greater basal rates of aminoisobutyrate uptake; whereas the maximal absolute insulin response is the same as control cells, the percentage response is smaller. These cells bind significantly more insulin than do control cells. The increase in insulin binding is reflected in a shift to the left of the dose–response curve for insulin-stimulated uptake of aminoisobutyrate. These studies indicate that there is no insulin resistance with regard to uptake of aminoisobutyrate in hepatocytes from older obese rats. Furthermore, the insulin resistance observed in hepatocytes from starved rats occurs despite an increase in the number of receptors per unit surface area and cannot be explained by alterations in the interaction between insulin and its receptor. The enhanced insulin binding per unit surface area, however, is reflected in the shift to the left of the dose–response curve for insulin. This is also true for hepatocytes from diabetic animals, in which insulin binding per cell is increased.     

Systemic Treatment with Vanadium Absorbed by Coprinus comatus Promotes Femoral Fracture Healing in Streptozotocin-Diabetic Rats

The purpose of this study was to analyze the impact of vanadium absorbed by Coprinus comatus (VACC) on fracture healing in streptozotocin-diabetic rats. Forty-five male Wistar rats used were divided into three groups: normal rats (control), diabetic rats, and diabetic rats treated with VACC. A standardized fracture-healing model with a stable plate fixation was established for the rat femoral fracture. After a 4-week stable fixation, callus quality was assessed by microcomputerized tomography and histological and biomechanical examinations. In addition, bone samples were obtained to evaluate the content of mineral substances in bones. Compared with the diabetic group, vanadium treatment significantly increased bone mineral content and biomechanical strength and improved microstructural properties of the callus. The ultimate load was increased by 29.1 % (P?<?0.05), and the total bone volume of callus enhanced by 11.2 % (P?<?0.05) at 4 weeks post fracture. Vanadium also promoted callus bone formation, which caused a 35.5 % increase in the total area of callus. However, VACC did not accelerate the fracture repair process in histological analysis. In conclusion, the current study suggests that systemic treatment with vanadium could promote fracture healing in streptozotocin-diabetic rats.     

Preventive Effect of Dipeptidyl Peptidase-4 Inhibitor on Atherosclerosis Is Mainly Attributable to Incretin's Actions in Nondiabetic and Diabetic Apolipoprotein E-Null Mice

Aim

Several recent reports have revealed that dipeptidyl peptidase (DPP)-4 inhibitors have suppressive effects on atherosclerosis in apolipoprotein E-null (Apoe ^−/−) mice. It remains to be seen, however, whether this effect stems from increased levels of the two active incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP).

Methods

Nontreated Apoe ^−/− mice, streptozotocin-induced diabetic Apoe ^−/− mice, and db/db diabetic mice were administered the DPP-4 inhibitor vildagliptin in drinking water and co-infused with either saline, the GLP-1 receptor blocker, exendin(9–39), the GIP receptor blocker, (Pro³)GIP, or both via osmotic minipumps for 4 weeks. Aortic atherosclerosis and oxidized low-density lipoprotein-induced foam cell formation in exudate peritoneal macrophages were determined.

Results

Vildagliptin increased plasma GLP-1 and GIP levels without affecting food intake, body weight, blood pressure, or plasma lipid profile in any of the animals tested, though it reduced HbA1c in the diabetic mice. Diabetic Apoe ^−/− mice exhibited further-progressed atherosclerotic lesions and foam cell formation compared with nondiabetic counterparts. Nondiabetic and diabetic Apoe ^−/− mice showed a comparable response to vildagliptin, namely, remarkable suppression of atherosclerotic lesions with macrophage accumulation and foam cell formation in peritoneal macrophages. Exendin(9–39) or (Pro³)GIP partially attenuated the vildagliptin-induced suppression of atherosclerosis. The two blockers in combination abolished the anti-atherosclerotic effect of vildagliptin in nondiabetic mice but only partly attenuated it in diabetic mice. Vildagliptin suppressed macrophage foam cell formation in nondiabetic and diabetic mice, and this suppressive effect was abolished by infusions with exendin(9–39)+(Pro³)GIP. Incubation of DPP-4 or vildagliptin in vitro had no effect on macrophage foam cell formation.

Conclusions

Vildagliptin confers a substantial anti-atherosclerotic effect in both nondiabetic and diabetic mice, mainly via the action of the two incretins. However, the partial attenuation of atherosclerotic lesions by the dual incretin receptor antagonists in diabetic mice implies that vildagliptin confers a partial anti-atherogenic effect beyond that from the incretins.     

Nitric Oxide Resistance Reduces Arteriovenous Fistula Maturation in Chronic Kidney Disease in Rats

Background

Autologous arteriovenous (AV) fistulas are the first choice for vascular access but have a high risk of non-maturation due to insufficient vessel adaptation, a process dependent on nitric oxide (NO)-signaling. Chronic kidney disease (CKD) is associated with oxidative stress that can disturb NO-signaling. Here, we evaluated the influence of CKD on AV fistula maturation and NO-signaling.

Methods

CKD was established in rats by a 5/6^th nephrectomy and after 6 weeks, an AV fistula was created between the carotid artery and jugular vein, which was followed up at 3 weeks with ultrasound and flow assessments. Vessel wall histology was assessed afterwards and vasoreactivity of carotid arteries was studied in a wire myograph. The soluble guanylate cyclase (sGC) activator BAY 60–2770 was administered daily to CKD animals for 3 weeks to enhance fistula maturation.

Results

CKD animals showed lower flow rates, smaller fistula diameters and increased oxidative stress levels in the vessel wall. Endothelium-dependent relaxation was comparable but vasorelaxation after sodium nitroprusside was diminished in CKD vessels, indicating NO resistance of the NO-receptor sGC. This was confirmed by stimulation with BAY 60–2770 resulting in increased vasorelaxation in CKD vessels. Oral administration of BAY 60–2770 to CKD animals induced larger fistula diameters, however; flow was not significantly different from vehicle-treated CKD animals.

Conclusions

CKD induces oxidative stress resulting in NO resistance that can hamper AV fistula maturation. sGC activators like BAY 60–2770 could offer therapeutic potential to increase AV fistula maturation.     

Effects of Trientine,a Metal Chelator,on Defective Endothelium-dependent Relaxation in the Mesenteric Vasculature of Diabetic Rats

Diabetes mellitus compromises endothelium-dependent relaxation of blood vessels. This has been linked to the generation of reactive oxygen species (ROS), which neutralise nitric oxide (NO) and interfere with vasodilator function. Experiments using chelators have emphasised the importance of ROS produced by transition metal catalysed reactions. However, particularly for the small arteries and arterioles that control microcirculatory blood flow, NO is not the only endothelium-derived mediator; endothelium-derived hyperpolarizing factor (EDHF) has a major role. EDHF-mediated vasodilation is severely curtailed by diabetes; however, little information exists on the underlying pathophysiology. Deficits in the EDHF system, alone or in combination with the NO system, are crucial for the development of diabetic microvascular complications. To further elucidate the mechanisms involved, the aim was to examine the effects of diabetes and preventive and intervention chelator therapy with trientine on a preparation that has well-defined NO and EDHF-mediated responses, the rat mesenteric vascular bed. In phenylephrine-preconstricted preparations, maximum vasodilation to acetylcholine was reduced by 35 and 44% after 4 and 8 weeks of streptozotocin-induced diabetes, respectively. Trientine treatment over the first 4 weeks gave 72% protection; intervention therapy over the final 4 weeks prevented deterioration and corrected the initial deficit by 68%. These responses depend on both NO and EDHF. When the latter mechanism was isolated by NO synthase inhibition, diabetic deficits of 53.4 (4 weeks) and 65.4% (8 weeks) were revealed, that were 65% prevented and 50% corrected by trientine treatment. Neither diabetes nor trientine altered vascular smooth muscle responses to the NO donor, sodium nitroprusside (SNP). Thus, the data suggest that metal catalysed ROS production makes a substantial contribution to defects in both the EDHF and NO endothelial mechanisms in diabetes, which has therapeutic implications for microvascular complications.     

Effects of trientine,a metal chelator,on defective endothelium-dependent relaxation in the mesenteric vasculature of diabetic rats

Diabetes mellitus compromises endothelium-dependent relaxation of blood vessels. This has been linked to the generation of reactive oxygen species (ROS), which neutralise nitric oxide (NO) and interfere with vasodilator function. Experiments using chelators have emphasised the importance of ROS produced by transition metal catalysed reactions. However, particularly for the small arteries and arterioles that control microcirculatory blood flow, NO is not the only endothelium-derived mediator; endothelium-derived hyperpolarizing factor (EDHF) has a major role. EDHF-mediated vasodilation is severely curtailed by diabetes; however, little information exists on the underlying pathophysiology. Deficits in the EDHF system, alone or in combination with the NO system, are crucial for the development of diabetic microvascular complications. To further elucidate the mechanisms involved, the aim was to examine the effects of diabetes and preventive and intervention chelator therapy with trientine on a preparation that has well-defined NO and EDHF-mediated responses, the rat mesenteric vascular bed. In phenylephrine-preconstricted preparations, maximum vasodilation to acetylcholine was reduced by 35 and 44% after 4 and 8 weeks of streptozotocin-induced diabetes, respectively. Trientine treatment over the first 4 weeks gave 72% protection; intervention therapy over the final 4 weeks prevented deterioration and corrected the initial deficit by 68%. These responses depend on both NO and EDHF. When the latter mechanism was isolated by NO synthase inhibition, diabetic deficits of 53.4 (4 weeks) and 65.4% (8 weeks) were revealed, that were 65% prevented and 50% corrected by trientine treatment. Neither diabetes nor trientine altered vascular smooth muscle responses to the NO donor, sodium nitroprusside (SNP). Thus, the data suggest that metal catalysed ROS production makes a substantial contribution to defects in both the EDHF and NO endothelial mechanisms in diabetes, which has therapeutic implications for microvascular complications.     

Exogenous Nitric Oxide (NO) Interferes with Lead (Pb)-Induced Toxicity by Detoxifying Reactive Oxygen Species in Hydroponically Grown Wheat (Triticum aestivum) Roots

Nitric Oxide (NO) is a bioactive signaling molecule that mediates a variety of biotic and abiotic stresses. The present study investigated the role of NO (as SNP [sodium nitroprusside]) in ameliorating lead (Pb)-toxicity in Triticum aestivum (wheat) roots. Pb (50 and 250 μM) alone and in combination with SNP (100 μM) was given to hydroponically grown wheat roots for a period of 0–8 h. NO supplementation reduced the accumulation of oxidative stress markers (malondialdehyde, conjugated dienes, hydroxyl ions and superoxide anion) and decreased the antioxidant enzyme activity in wheat roots particularly up to 6 h, thereby suggesting its role as an antioxidant. NO ameliorated Pb-induced membrane damage in wheat roots as evidenced by decreased ion-leakage and in situ histochemical localization. Pb-exposure significantly decreased in vivo NO level. The study concludes that exogenous NO partially ameliorates Pb-toxicity, but could not restore the plant growth on prolonged Pb-exposure.     

High-fat diet-induced reduction in nitric oxide-dependent arteriolar dilation in rats: role of xanthine oxidase-derived superoxide anion

Obesity frequently leads to the development of hypertension. We hypothesized that high-fat diet (HFD)-induced obesity impairs the endothelium-dependent dilation of arterioles. Male Wistar rats were fed with normal (control) or HFD (60% of saturated fat, for 10 wk). In rats with HFD, body weight, mean arterial blood pressure, and serum insulin, cholesterol, and glucose were elevated. In isolated gracilis muscle arterioles (diameter: approximately 160 microm) of HFD, rat dilations to ACh (at 1 microM, maximum: 83 +/- 3%) and histamine (at 10 microM, maximum: 16 +/- 4%) were significantly (P < 0.05) decreased compared with those of control responses (maximum: 90 +/- 2 and 46 +/- 4%, respectively). Dilations to the NO donor sodium nitroprusside were similar in the two groups. Inhibition of NO synthesis by N(omega)-nitro-l-arginine methyl ester reduced ACh- and histamine-induced dilations in control arterioles but had no effect on microvessels of HFD rats. The superoxide dismutase mimetic Tiron or xanthine oxidase inhibitor allopurinol enhanced ACh (maximum: 90 +/- 2 and 93 +/- 2%, respectively)- and histamine (maximum: 30 +/- 7 and 37 +/- 8%, respectively)-induced dilations in HFD arterioles, whereas the NAD(P)H oxidase inhibitor apocynin had no significant effect. Correspondingly, in carotid arteries of HFD rats, an enhanced superoxide production was shown by lucigenin-enhanced chemiluminescence, in association with an increased xanthine oxidase, but not NAD(P)H oxidase activity. In addition, a marked xanthine oxidase immunostaining was detected in the endothelial layer of the gracilis arterioles of HFD, but not in control rats. These findings suggest that, in obese rats, NO mediation of endothelium-dependent dilation of skeletal muscle arterioles is reduced because of an enhanced xanthine oxidase-derived superoxide production. These alterations demonstrate substantial dysregulation of arteriolar tone by the endothelium in HFD-induced obesity, which may contribute to disturbed tissue blood flow and development of increased peripheral resistance.     

A GIP Receptor Agonist Exhibits β-Cell Anti-Apoptotic Actions in Rat Models of Diabetes Resulting in Improved β-Cell Function and Glycemic Control

Aims

The gastrointestinal hormone GIP promotes pancreatic islet function and exerts pro-survival actions on cultured β-cells. However, GIP also promotes lipogenesis, thus potentially restricting its therapeutic use. The current studies evaluated the effects of a truncated GIP analog, D-Ala²-GIP_1–30 (D-GIP_1–30), on glucose homeostasis and β-cell mass in rat models of diabetes.

Materials and Methods

The insulinotropic and pro-survival potency of D-GIP_1–30 was evaluated in perfused pancreas preparations and cultured INS-1 β-cells, respectively, and receptor selectivity evaluated using wild type and GIP receptor knockout mice. Effects of D-GIP_1–30 on β-cell function and glucose homeostasis, in vivo, were determined using Lean Zucker rats, obese Vancouver diabetic fatty rats, streptozotocin treated rats, and obese Zucker diabetic fatty rats, with effects on β-cell mass determined in histological studies of pancreatic tissue. Lipogenic effects of D-GIP_1–30 were evaluated on cultured 3T3-L1 adipocytes.

Results

Acutely, D-GIP_1–30 improved glucose tolerance and insulin secretion. Chronic treatment with D-GIP_1–30 reduced levels of islet pro-apoptotic proteins in Vancouver diabetic fatty rats and preserved β-cell mass in streptozotocin treated rats and Zucker diabetic fatty rats, resulting in improved insulin responses and glycemic control in each animal model, with no change in body weight. In in vitro studies, D-GIP_1–30 exhibited equivalent potency to GIP_1–42 on β-cell function and survival, but greatly reduced action on lipoprotein lipase activity in 3T3-L1 adipocytes.

Conclusions

These findings demonstrate that truncated forms of GIP exhibit potent anti-diabetic actions, without pro-obesity effects, and that the C-terminus contributes to the lipogenic actions of GIP.     

Impaired deformability of erythrocytes in diabetic rat and human: investigation by the nickel-mesh-filtration technique

Comprehensive research to quantify the deformability of erythrocytes in diabetic animals and humans has been lacking. The objective of this study was to compare the impairment of erythrocyte deformability in diabetic rats and patients by use of the same rheologic method. Deformability was investigated in streptozotocin-induced diabetic rats and diabetic patients, by using the highly sensitive and quantitative nickel-mesh-filtration technique. Erythrocyte filterability (whole-cell deformability) was defined as flow rate of hematocrit-adjusted erythrocyte suspension relative to that of saline (%). Hematological and biochemical data for diabetic rats did not differ from those for age-matched control rats except for hyperglycemia and malnutrition. Erythrocyte filterability for diabetic rats was significantly lower than that for control rats (69.4 ± 10.1%, n = 8, compared with 83.1 ± 4.2%, n = 8; p < 0.001). Likewise, erythrocyte filterability for diabetic patients was significantly impaired compared with that for controls (87.6 ± 3.4%, n = 174, compared with 88.6 ± 2.1%, n = 51; p = 0.046). Stepwise multiple regression analysis revealed that this impairment was mostly attributable to associated obesity (BMI, p = 0.029) and glycemic stress (HbA1c(JDS), p = 0.046). We therefore conclude that erythrocyte filterability is commonly impaired in diabetic rats and in humans. Moreover, metabolic risk accumulation further impairs erythrocyte filterability, resulting in derangement of the microcirculation.