1. ACUTE TOCOMIN TREATMENT RESTORES ENDOTHELIUM-DEPENDENT RELAXATION IN AORTAE FROM DIABETIC AND WESTERN DIET FED RATS
SF Ali, JCD Nguyen, TA Jenkins & OL Woodman
School of Medical Sciences, RMIT University, Bundoora, VIC
Introduction: Diseases such as diabetes and metabolic syndrome have been demonstrated to impair endothelial function which can occur as a result of increased superoxide concentrations in blood vessels. The consumption of a high fat western diet has been implicated in the increasing incidence of obesity and type 2 diabetes worldwide. Vitamin E is a family of compounds, consisting of tocotrienols and tocopherols, reported to have beneficial effects on vascular function through their antioxidant activity. Tocotrienols share structural similarities with tocopherols that may have therapeutic benefits, including improvement of vascular endothelial function particularly in pathologies involving oxidant stress such as diabetes and metabolic syndrome. Tocotrienols are also reported to possess superior antioxidant properties compared to tocopherol.
Endothelium-dependent relaxation in aortae from normal and diabetic rats
Aim: To determine the acute effect of tocotrienol rich tocomin (composition: tocotrienol rich fraction:40%, -tocopherol:11% and palm olein:38%) extracted from palm oil on endothelium-dependent and -independent relaxation and superoxide production in aortae from diabetic and western diet fed rats.
Methods: 6-8 week old male Wistar rats were randomly assigned to 2 groups (normal and diabetic). Rats were treated with vehicle (normal) or streptozotocin (50 mg/kg iv) to induce diabetes for 10 weeks. Male Wistar Hooded rats were fed a standard diet (SD AIN93G rodent diet, 7% total fat including 1.05% total saturated fatty acids; Specialty Feeds, Perth, Australia) or western diet (WD SF00-219, 21% total fat including 1.80% total saturated fats and 0.15% cholesterol). Rats were fed ad lib for 7 weeks after which they were placed on a restricted diet (70% of normal consumption for 10 weeks). Acetylcholine (ACh)-induced endothelium-dependent and sodium nitroprusside (SNP)-induced endothelium-independent relaxation was measured in rat aortae using standard organ bath techniques in the presence and absence of tocomin (10-4 mg/mL). Superoxide release from aortic segments was measured using lucigenin-enhanced chemiluminessence.
*p0.05 Rmax Significantly different normal vs diabetic and diabetic vs diabetic + tocomin. pEC50 Significantly different normal vs diabetic and diabetic vs tocomin. Sidaks multiple comparison test. n=4-7.
Diabetes significantly impaired maximum relaxation and sensitivity to acetylcholine. Acute treatment with tocomin® (10-4 mg/mL) significantly improved endothelium-dependent relaxation.
Superoxide production in aortae from normal and diabetic rats
Results: Rats treated with streptozotocin and fed a Western diet.
*p0.05 Significantly different control vs diabetic and diabetic vs diabetic + tocomin and #p0.05, DPI vs without DPI in the same treatment group.
Diabetes significantly increased superoxide release from rat aortae. Acute treatment with tocomin® and flavoprotein inhibitor diphenyliodonium (DPI) significantly reduced superoxide levels in diabetic rat aortae.
Endothelium-dependent relaxation in aortae from standard diet and western diet fed rats
* p<0.05 Significantly different normal vs diabetic and SD vs WD, n=7-10, Sidak’s multiple comparison test.
Bodyweight was significantly reduced in diabetic rats at the end of the experimental period. Bodyweight was significantly increased in the western diet fed rats at the end of the experimental period.
*p0.05 pEC50 Significantly different SD vs WD and WD vs WD + tocomin. Sidak’s multiple comparison test. n=6-8.
A western diet significantly impaired sensitivity to acetylcholine without affecting maximum relaxation. Acute treatment with tocomin® (10-4 mg/mL) significantly improved ACh sensitivity without affecting maximum relaxation.
Superoxide production in aortae from standard and western diet fed rats
* p<0.05 Significantly different normal vs diabetic, n=5-8, Sidak’s multiple comparison test.
Blood glucose (BG) levels were significantly elevated in comparison to normal rats, indicating that diabetes was successfully induced. A Western Diet had no effect on blood glucose levels indicating that a high fat western diet does not induce diabetes.
*p0.05, Significantly different SD vs WD and WD vs WD + tocomin, n=4 Sidak’s multiple comparison test.
Diabetes significantly increased superoxide release from western diet fed rat aortae. Acute treatment with tocomin® and flavoprotein inhibitor diphenyliodonium (DPI) significantly reduced superoxide levels in diabetic rat aortae.
Conclusion: These findings demonstrate that during diabetes there is significant impairment of endothelium-dependent relaxation. Acute treatment of diabetic rat aortae with tocomin (10-4 mg/mL) significantly improved endothelial function in the rat aorta. A high fat western diet also causes endothelial dysfunction and increased superoxide production in rat aortae in the absence of diabetes which can be restored with acute tocomin treatment. Tocomin reduced superoxide levels in the diabetic and western diet fed rat vasculature which is a likely explanation for the improved endothelial function. Further investigation into the mechanism of action of tocotrienols is warranted.
*Significantly different normal vs diabetic, p<0.05, n=7-9, Sidak’s multiple comparison test
Diabetic rats had significantly higher blood glucose levels (BGL) in comparison to control rats, indicating that diabetes was successfully induced. A western diet had no effect on HbA1C levels.
Acknowledgements:
We wish to thank the Nutricia Foundation for financial support and Carotech Inc for the gift of tocomin.