Endothelin-induced changes in blood flow in STZ-diabetic and non-diabetic rats: relation to nitric oxide synthase and cyclooxygenase inhibition

Robust arterial spin labeling MRI measurement of pharmacologically induced perfusion change in rat kidneys

Kidney diseases such as acute kidney injury, diabetic nephropathy and chronic kidney disease (CKD) are related to dysfunctions of the microvasculature in the kidney causing a decrease in renal blood perfusion (RBP). Pharmacological intervention to improve the function of the microvasculature is a viable strategy for the potential treatment of these diseases. The measurement of RBP is a reliable biomarker to evaluate the efficacy of pharmacological agents' actions on the microvasculature, and measurement of RBP responses to different pharmacological agents can also help elucidate the mechanism of hemodynamic regulation in the kidney. Magnetic resonance imaging (MRI) with flow-sensitive alternating inversion recovery (FAIR) arterial spin labeling (ASL) has been used to measure RBP in humans and animals. However, artifacts caused by respiratory and peristaltic motions limit the potential of FAIR ASL in drug discovery and kidney research. In this study, the combined anesthesia protocol of inactin with a low dose of isoflurane was used to fully suppress peristalsis in rats, which were ventilated with an MRI-synchronized ventilator. FAIR ASL data were acquired in eight axial slices using a single-shot, gradient-echo, echo-planar imaging (EPI) sequence. The artifacts in the FAIR ASL RBP measurement due to respiratory and peristaltic motions were substantially eliminated. The RBP responses to fenoldopam and L-NAME were measured, and the increase and decrease in RBP caused by fenoldopam and L-NAME, respectively, were robustly observed. To further validate FAIR ASL, the renal blood flow (RBF) responses to the same agents were measured by an invasive perivascular flow probe method. The pharmacological agent-induced responses in RBP and RBF are similar. This indicates that FAIR ASL has the sensitivity to measure pharmacologically induced changes in RBP. FAIR ASL with multislice EPI can be a valuable tool for supporting drug discovery, and for elucidating the mechanism of hemodynamic regulation in kidneys.

Transplantation of human mobilized mononuclear cells improved diabetic neuropathy

Rodent stem cells demonstrated regenerative effects in diabetic neuropathy via improvement in nerve perfusion. As a pre-clinical step, we explored if human mobilized mononuclear cells (hMNC) would have the same effects in rats. hMNC were injected into Rt. hind-limb muscles of streptozotocin-induced diabetic nude rats, and the grafts were monitored using with MRI. After 4 weeks, the effects were compared with those in the vehicle-injected Lt. hind limbs. Nerve conduction, muscle perfusion and gene expression of sciatic nerves were assessed. Induction of diabetes decreased nerve function and expression of Mpz and Met in the sciatic nerves, which are related with myelination. hMNC injection significantly improved the amplitude of compound muscle action potentials along with muscle perfusion and sciatic nerve Mpz expression. On MRI, hypointense signals were observed for 4 weeks at the graft site, but their correlation with the presence of hMNC was detectable for only 1 week. To evaluate paracrine effects of hMNC, IMS32 cells were tested with hepatocyte growth factor (HGF), which had been reported as a myelination-related factor from stem cells. We could observe that HGF enhanced Mpz expression in the IMS32 cells. Because hMNC secreted HGF, IMS32 cells were co-cultured with hMNC, and the expression of Mpz increased along with morphologic maturation. The hMNC-induced Mpz expression was abrogated by treatment of anti-HGF. These results suggest that hMNC could improve diabetic neuropathy, possibly through enhancement of myelination as well as perfusion. According to in vitro studies, HGF was involved in the hMNC-induced myelination activity, at least in part.

Endothelin and diabetic complications: a brain-centric view

The global epidemic of diabetes is of significant concern. Diabetes associated vascular disease signifies the principal cause of morbidity and mortality in diabetic patients. It is also the most rapidly increasing risk factor for cognitive impairment, a silent disease that causes loss of creativity, productivity, and quality of life. Small vessel disease in the cerebral vasculature plays a major role in the pathogenesis of cognitive impairment in diabetes. Endothelin system, including endothelin-1 (ET-1) and the receptors (ET(A) and ET(B)), is a likely candidate that may be involved in many aspects of the diabetes cerebrovascular disease. In this review, we took a brain-centric approach and discussed the role of the ET system in cerebrovascular and cognitive dysfunction in diabetes.

Enhanced Renal Afferent Arteriolar Reactive Oxygen Species and Contractility to Endothelin-1 Are Associated with Canonical Wnt Signaling in Diabetic Mice

BACKGROUND/AIMS

Canonical Wnt signaling is involved in oxidative stress, vasculopathy and diabetes mellitus but its role in diabetic renal microvascular dysfunction is unclear. We tested the hypothesis that enhanced canonical Wnt signaling in renal afferent arterioles from diabetic mice increases reactive oxygen species (ROS) and contractions to endothelin-1 (ET-1).

METHODS

Streptozotocin-induced diabetes or control C57Bl/6 mice received vehicle or sulindac (40 mg·kg-1·day-1) to block Wnt signaling for 4 weeks. ET-1 contractions were measured by changes of afferent arteriolar diameter. Arteriolar H2O2, O2 -, protein expression and enzymatic activity were assessed using sensitive fluorescence probes, immunoblotting and colorimetric assay separately.

RESULTS

Compared to control, diabetic mouse afferent arteriole had increased O2- (+ 84%) and H2O2 (+ 91%) and enhanced responses to ET-1 at 10-8 mol·l-1 (-72±4% of versus -43±4%, P< 0.05) accompanied by reduced protein expressions and activities for catalase and superoxide dismutase 2 (SOD2). Arteriolar O2 - was increased further by ET-1 and contractions to ET-1 reduced by PEG-SOD in both groups whereas H2O2 unchanged by ET-1 and contractions were reduced by PEG-catalase selectively in diabetic mice. The Wnt signaling protein β-catenin was upregulated (3.3-fold decrease in p-β-catenin/β-catenin) while the glycogen synthase kinase-3β (GSK-3β) was downregulated (2.6-fold increase in p-GSK-3β/ GSK-3β) in preglomerular vessels of diabetic mice. Sulindac normalized the Wnt signaling proteins, arteriolar O2 -, H2O2 and ET-1 contractions while doubling microvascular catalase and SOD2 expression in diabetic mice.

CONCLUSION

Increased ROS, notably H2O2 contributes to enhanced afferent arteriolar responses to ET-1 in diabetes, which is closely associated with Wnt signaling. Antioxidant pharmacological strategies targeting Wnt signaling may improve vascular function in diabetic nephropathy.

Endothelin Blockade in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the most common cause of chronic kidney disease and multiple therapeutic agents, primarily targeted at the renin-angiotensin system, have been assessed. Their only partial effectiveness in slowing down progression to end-stage renal disease, points out an evident need for additional effective therapies. In the context of diabetes, endothelin-1 (ET-1) has been implicated in vasoconstriction, renal injury, mesangial proliferation, glomerulosclerosis, fibrosis and inflammation, largely through activation of its endothelin A (ET_A) receptor. Therefore, endothelin receptor antagonists have been proposed as potential drug targets. In experimental models of DKD, endothelin receptor antagonists have been described to improve renal injury and fibrosis, whereas clinical trials in DKD patients have shown an antiproteinuric effect. Currently, its renoprotective effect in a long-time clinical trial is being tested. This review focuses on the localization of endothelin receptors (ET_A and ET_B) within the kidney, as well as the ET-1 functions through them. In addition, we summarize the therapeutic benefit of endothelin receptor antagonists in experimental and human studies and the adverse effects that have been described.

Amelioration of altered serum, liver, and kidney antioxidant enzymes activities by sodium selenite in alloxan-induced diabetic rats

BACKGROUND

The aim of this study was to evaluate the possible protective effect of sodium selenite on serum, liver, and kidney antioxidant enzymes activities in alloxan-induced type 1 diabetic rats.

METHODS

Forty Sprague-Dawley male rats were randomly divided into four groups; Group one as control, Group two as sham-treated with sodium selenite by 1 mg/kg intraperitoneal (i.p.) injections daily, Group three as diabetic untreated, and Group four as diabetic treated with sodium selenite by 1 mg/kg i.p. injections daily .Diabetes was induced in the third and fourth groups by subcutaneous alloxan injections. After eight weeks the animals were euthanized and livers and kidneys were immediately removed and used fresh or kept frozen until analysis. Before the rats were killed blood samples were also collected to measure glutathione peroxidase (GPX) and catalase (CAT) activities in sera.

RESULTS

Glutathione peroxidase and CAT activities serum, liver, and kidney were all significantly less in the diabetic rats than in the controls. Sodium selenite treatment of the diabetic rats resulted in significant increases in GPX activity in the kidneys and livers, and CAT activity in the sera and livers.

CONCLUSIONS

Our results indicate that sodium selenite might be a potent antioxidant that exerts beneficial effects on both GPX and CAT activities in alloxan-induced type 1 diabetic rats.

Sensitivity of arterial spin labeling perfusion MRI to pharmacologically induced perfusion changes in rat kidneys

PURPOSE

To investigate whether arterial spin labeling (ASL) MRI is sensitive to changes by pharmacologically induced vasodilation and vasoconstriction in rat kidneys.

MATERIALS AND METHODS

Changes in renal cortical blood flow in seven rats were induced by adenosine infusion (vasodilation) and L-NAME injection (vasoconstriction). All imaging studies were performed on a 3 Tesla scanner using a FAIR-TrueFISP sequence for the ASL implementation. The acquisition time for each ASL scan was 6 min. Cortical perfusion rates were calculated using regions of interest analysis, and the differences in perfusion rates during baseline, vasodilation, and vasoconstriction were compared and assessed for statistical significance.

RESULTS

Compared with the baseline, an average of 94 mL/100 g/min increase and 157 mL/100 g/min decrease in cortical perfusion was observed following adenosine infusion and L-NAME administration, respectively. The changes in cortical perfusion were significant between baseline and vasodilation (P < 0.05), baseline and vasoconstriction (P < 0.01), and vasodilation and vasoconstriction (P < 0.01).

CONCLUSION

ASL is sensitive to pharmacologically induced perfusion changes in rat kidneys at doses comparable to current use. The preliminary results suggest the feasibility of ASL for investigating renal blood flow in a variety of rodent models.

ABCG1 deficiency promotes endothelial apoptosis by endoplasmic reticulum stress-dependent pathway

The present study was focused on whether ABCG1 deficiency was involved in endothelial apoptosis and its possible mechanism. Human umbilical artery endothelial cells were transfected with ABCG1 siRNA and/or ABCG1 expression plasmid. We observed that silencing of endothelial ABCG1 reduced cholesterol efflux to HDL and increased intracellular lipid content. Moreover, reduction of ABCG1 promoted endothelial apoptosis and expression of endoplasmic reticulum (ER) stress-related molecules GRP78 and CHOP. In contrast, transfection of ABCG1 overexpression plasmid reversed endothelial apoptosis and intracellular lipid accumulation as well as decreased expression of GRP78 and CHOP in ABCG1-deficient endothelial cells. Furthermore, endothelial apoptosis and ER stress-related molecules were induced by repletion of endothelial cells with cholesterol-loaded cyclodextrin, otherwise endothelial apoptotic response and expression of GRP78 and CHOP were suppressed by depletion of cellular cholesterol in ABCG1-deficient endothelial cells. The present results suggest that reduction of ABCG1 induces endothelial apoptosis, which seems associated with intracellular free cholesterol accumulation and subsequent ER stress.

Amelioration of altered antioxidant enzymes activity and glomerulosclerosis by coenzyme Q10 in alloxan-induced diabetic rats

Coenzyme Q10 is a natural antioxidant and scavenging free radicals. In the present study, we examined antioxidative activities of coenzyme Q10 and possible protective effect of coenzyme Q10 on in vivo and in vitro lipid peroxidation, antioxidant enzymes activity and glomerulosclerosis in alloxan-induced type 1 diabetic rats. Thirty Sprague-Dawley male rats were divided into three groups randomly: group 1 as control, group 2 as diabetic untreatment, and group 3 as treatments with coenzyme Q10 by 15 mg/kg i.p. daily, respectively. Diabetes was induced in the second and third groups by alloxan injection subcutaneously. After 8 weeks, animals were anaesthetized, liver and kidney were then removed immediately and used fresh or kept frozen until their lipid peroxidation analysis. Blood samples were also collected before killing to measure the lipid peroxidation and antioxidant enzymes activity. Kidney paraffin sections were prepared and stained by periodic acid-Schiff method. Glomerular volume and leukocyte infiltration were estimated by stereological rules and glomerular sclerosis was studied semi-quantitatively. Coenzyme Q10 significantly inhibited leukocyte infiltration, glomerulosclerosis and the levels of malondialdehyde (MDA) serum and kidney content in treated group compared with the diabetic untreated group. Coenzyme Q10 significantly inhibited LDL oxidation in vitro. Coenzyme Q10 significantly increased the serum levels of glutathione (GSH) and serum activity of catalase (CAT) and superoxide dismutase (SOD) in treated group compared with the diabetic untreated group. Coenzyme Q10 alleviates leukocyte infiltration and glomerulosclerosis and exerts beneficial effects on the lipid peroxidation and antioxidant enzymes activity in alloxan-induced type 1 diabetic rats.