Christine L. Oltman

Epoxyeicosatrienoic Acids and Dihydroxyeicosatrienoic Acids Are Potent Vasodilators in the Canine Coronary Microcirculation

Cytochrome P450 epoxygenases convert arachidonic acid into 4 epoxyeicosatrienoic acid (EET) regioisomers, which were recently identified as endothelium-derived hyperpolarizing factors in coronary blood vessels. Both EETs and their dihydroxyeicosatrienoic acid (DHET) metabolites have been shown to relax conduit coronary arteries at micromolar concentrations, whereas the plasma concentrations of EETs are in the nanomolar range. However, the effects of EETs and DHETs on coronary resistance arterioles have not been examined. We administered EETs and DHETs to isolated canine coronary arterioles (diameter, 90.0+/-3.4 microm; distending pressure, 20 mm Hg) preconstricted by 30% to 60% of the resting diameter with endothelin. All 4 EET regioisomers produced potent, concentration-dependent vasodilation (EC50 values ranging from -12.7 to -10.1 log [M]) and were approximately 1000 times more potent than reported in conduit coronary arteries. The vasodilation produced by 14,15-EET was not attenuated by removal of the endothelium and indicated a direct action of 14,15-EET on microvascular smooth muscle. Likewise, 14,15-DHET, 11,12-DHET, 8,9-DHET, and the delta-lactone of 5,6-EET produced extremely potent vasodilation (EC50 values ranging from -15.8 to -13.1 log [M]). The vasodilation produced by these eicosanoids was highly potent in comparison to that produced by other vasodilators, including arachidonic acid (EC50=-7.5 log [M]). The epoxide hydrolase inhibitor, 4-phenylchalone oxide, which blocked the conversion of [3H]14,15-EET to [3H]14,15-DHET by canine coronary arteries, did not alter arteriolar dilation to 11,12-EET; thus, the potent vasodilation induced by EETs does not require formation of DHETs. In contrast, charybdotoxin (a KCa channel inhibitor) and KCl (a depolarizing agent) blocked vasodilation by 11,12-EET and 11,12-DHET. We conclude that EETs and DHETs potently dilate canine coronary arterioles via activation of KCa channels. The preferential ability of these compounds to dilate resistance blood vessels suggests that they may be important regulators of coronary circulation.

Attenuation of Vascular/Neural Dysfunction in Zucker Rats Treated With Enalapril or Rosuvastatin

Objective: Obese Zucker rats, animal model for the metabolic syndrome, develop a diabetes‐like neuropathy that is independent of hyperglycemia. The purpose of this study was to determine whether drugs used to treat cardiovascular dysfunction in metabolic syndrome also protect nerve function.

Diet-induced obesity in Sprague–Dawley rats causes microvascular and neural dysfunction

The objective of this study was to determine the effect of diet‐induced obesity (DIO) on microvascular and neural function.

Vascular and neural dysfunction in Zucker diabetic fatty rats: a difficult condition to reverse.

Aim:  We had previously demonstrated that vascular and neural dysfunction in Zucker diabetic fatty (ZDF) rats is progressive. In this study, we sought to determine whether monotherapy of ZDF rats can reverse the vascular and nerve defects.

20-Hydroxyeicosatetraenoic Acid (20-HETE) Metabolism in Coronary Endothelial Cells

We have investigated the role of endothelial cells in the metabolism of 20-hydroxyeicosatetraenoic acid (20-HETE), a vasoactive mediator synthesized from arachidonic acid by cytochrome P450 ω-oxidases. Porcine coronary artery endothelial cells (PCEC) incorporated 20-[3H]HETE primarily into the sn-2 position of phospholipids through a coenzyme A-dependent process. The incorporation was reduced by equimolar amounts of arachidonic, eicosapentaenoic or 8,9-epoxyeicosatrienoic acids, but some uptake persisted even when a 10-fold excess of arachidonic acid was available. The retention of 20-[3H]HETE increased substantially when methyl arachidonoyl fluorophosphonate, but not bromoenol lactone, was added, suggesting that a Ca2+-dependent cytosolic phospholipase A2 released the 20-HETE contained in PCEC phospholipids. Addition of calcium ionophore A23187 produced a rapid release of 20-[3H]HETE from the PCEC, a finding that also is consistent with a Ca2+-dependent mobilization process. PCEC also converted 20-[3H]HETE to 20-carboxy-arachidonic acid (20-COOH-AA) and 18-, 16-, and 14-carbon β-oxidation products. 20-COOH-AA produced vasodilation in porcine coronary arterioles, but 20-HETE was inactive. These results suggest that the incorporation of 20-HETE and its subsequent conversion to 20-COOH-AA in the endothelium may be important in modulating coronary vascular function.

Treatment of Zucker diabetic fatty rats with AVE7688 improves vascular and neural dysfunction.

Aim:  Vasopeptidase inhibitors are drugs that inhibit angiotensin‐converting enzyme and neutral endopeptidase (NEP). The latter is a protease that degrades vasoactive peptides and is increased in diabetes. We have previously shown that treating streptozotocin‐induced diabetic rats, an animal model of type 1 diabetes, with AVE7688, a vasopeptidase inhibitor, improves neurovascular and neural function. In this study, we determined the effect of treating Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes, with AVE7688 on vascular and neural function.

Treatment of Streptozotocin-Induced Diabetic Rats With AVE7688, a Vasopeptidase Inhibitor Effect on Vascular and Neural Disease

In epineurial arterioles, acetylcholine-mediated vascular relaxation is mediated by nitric oxide and endothelium-derived hyperpolarizing factor (EDHF), and both mechanisms are impaired by diabetes. The mediator responsible for the effect of EDHF is unknown. In epineurial arterioles, C-type natriuretic peptide (CNP) has properties consistent with EDHF-like activity. Epineurial arterioles express CNP, and exogenous CNP causes a concentration-dependent vascular relaxation. In streptozotocin-induced diabetic rats, CNP-mediated vascular relaxation in epineurial arterioles is decreased. Since CNP may be a regulator of vascular function, a vasopeptidase inhibitor may be an effective treatment for diabetes-induced vascular and neural disease. Vasopeptidase inhibitors inhibit ACE activity and neutral endopeptidase, which degrades natriuretic peptides. Streptozotocin-induced diabetic rats were treated with AVE7688 (450 mg/kg in the diet), a vasopeptidase inhibitor, for 8–10 weeks after 4 weeks of untreated diabetes. Treatment of diabetic rats corrected the diabetes-induced decrease in endoneurial blood flow, significantly improved motor and sensory nerve conduction velocity, prevented the development of hypoalgesia in the hind paw, and reduced superoxide and nitrotyrosine levels in epineurial arterioles. The diabetes-induced decrease in acetylcholine-mediated vascular relaxation by epineurial arterioles was significantly improved with treatment. These studies suggest that vasopeptidase inhibitors may be an effective approach for the treatment of diabetic vascular and neural dysfunction.

Modification of high saturated fat diet with n-3 polyunsaturated fat improves glucose intolerance and vascular dysfunction.

The ability of dietary enrichment with monounsaturated fatty acid (MUFA), n‐3 or n‐6 polyunsaturated fatty acids (PUFAs) to reverse glucose intolerance and vascular dysfunction resulting from excessive dietary saturated fatty acids is not resolved. We hypothesized that partial replacement of dietary saturated fats with n‐3 PUFA‐enriched menhaden oil (MO) would provide greater improvement in glucose tolerance and vascular function compared to n‐6 enriched safflower oil (SO) or MUFA‐enriched olive oil (OO).

Role of the effect of inhibition of neutral endopeptidase on vascular and neural complications in streptozotocin-induced diabetic rats

We have previously shown that treating streptozotocin-induced diabetic rats, an animal model of type 1 diabetes, with Ilepatril (an inhibitor of neutral endopeptidase and angiotensin converting enzyme (ACE)) improves vascular and neural function. In this study we sought to determine the individual effect of inhibition of neutral endopeptidase and ACE on diabetes-induced vascular and neural dysfunction. After 4 weeks of untreated diabetes, rats were treated for 12 weeks with Ilepatril, Enalapril (ACE inhibitor) or Candoxatril (neutral endopeptidase inhibitor) followed by analysis of neural and vascular function. Diabetes caused slowing of motor and sensory nerve conduction, thermal hypoalgesia, reduction in intraepidermal nerve fiber density in the hindpaw and impairment in vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineural arterioles of the sciatic nerve and to atrial natriuretic peptide and calcitonin gene-related peptide in renal arteries. Inhibition of neutral endopeptidase or ACE improved neural function; however, dual inhibition of neutral endopeptidase and ACE with Ilepatril tended to have the greatest efficacy. Ilepatril and Candoxatril treatment of diabetic rats was more efficacious in improving vascular responsiveness in epineurial arterioles than treatment with Enalapril. Ilepatril, Enalapril or Candoxatril treatment of diabetic rats were all efficacious in renal arteries. These studies suggest that combination therapy may be the most effective approach for treatment of diabetic neural and vascular complications.

Treatment of cardiovascular dysfunction associated with the metabolic syndrome and type 2 diabetes.

UNLABELLED Our previous studies have shown vascular dysfunction in small coronary and mesenteric arteries in Zucker obese rats, a model of the metabolic syndrome, and Zucker Diabetic Fatty (ZDF) rats, a model of type 2 diabetes. Because of their lipid lowering action and antioxidant activity, we predicted that treatment with Rosuvastatin, an HMG-CoA reductase inhibitor (statin) or Enalapril, an angiotensin converting enzyme (ACE) inhibitor would improve vascular dysfunction associated with the metabolic syndrome and type 2 diabetes. METHODS 20-week-old Zucker obese and 16-week-old ZDF rats were treated with Rosuvastatin (25 mg/kg/day) or Enalapril (20 mg/kg/day) for 12 weeks. We examined metabolic parameters, indices of oxidative stress and vascular dysfunction in ventricular and mesenteric small arteries (75-175 microm intraluminal diameter) from lean, Zucker obese and ZDF rats (untreated and treated). RESULTS Endothelial dependent responses were attenuated in coronary vessels from Zucker obese and ZDF rats compared to responses from lean rats. Both drugs improved metabolic parameters, oxidative stress, and vascular dysfunction in Zucker obese rats, however, only partial improvement was observed in ZDF rats, suggesting more aggressive treatment is needed when hyperglycemia is involved. CONCLUSION Vascular dysfunction is improved when Zucker obese and, to a lesser degree, when ZDF rats were treated with Rosuvastatin or Enalapril.