Amporn Jariyapongskul

Alpha-Mangostin Attenuation of Hyperglycemia-Induced Ocular Hypoperfusion and Blood Retinal Barrier Leakage in the Early Stage of Type 2 Diabetes Rats

The present study examined effects of alpha-mangostin (α-MG) supplementation on the retinal microvasculature, including ocular blood flow (OBF) and blood-retinal barrier (BRB) permeability in a type 2 diabetic animal model. Male Sprague-Dawley rats were divided into four groups: normal control and diabetes with or without α-MG supplementation. Alpha-mangostin (200 mg/Kg/day) was administered by gavage feeding for 8 weeks. The effects of α-MG on biochemical and physiological parameters including mean arterial pressure (MAP), OBF, and BRB leakage were investigated. Additionally, levels of retinal malondialdehyde (MDA), advance glycation end products (AGEs), receptor of advance glycation end products (RAGE), tumour necrosis factor alpha (TNF-α), and vascular endothelial growth factor (VEGF) were evaluated. The elevated blood glucose, HbA1c, cholesterol, triglyceride, serum insulin, and HOMA-IR were observed in DM2 rats. Moreover, DM2 rats had significantly decreased OBF but statistically increased MAP and leakage of the BRB. The α-MG-treated DM2 rats showed significantly lower levels of retinal MDA, AGEs, RAGE, TNF-α, and VEGF than the untreated group. Interestingly, α-MG supplementation significantly increased OBF while it decreased MAP and leakage of BRB. In conclusion, α-MG supplementation could restore OBF and improve the BRB integrity, indicating its properties closely associated with antihyperglycemic, antioxidant, anti-inflammatory, and antiglycation activities.

Microhemodynamic indices to evaluate the effectiveness of herbal medicine in diabetes: A comparison between alpha-mangostin and curcumin in the retina of type 2 diabetic rats

OBJECTIVE This study was aimed to develop microhemodynamic indices to evaluate the effectiveness of herbal medicine in diabetic tissues. METHODS Male Sprague-Dawley rats were divided into four groups: normal control rats (Control), type 2 diabetic rats without (DM2) and with supplementation of alpha mangostin (DM2-MG) or curcumin (DM2-CUR). Alpha-mangostin or curcumin (200 mg/kg BW) were fed followed by i.p. injection of streptozotocin (STZ). Mean arterial pressure (MAP) and retinal blood flow (RBF) were measured and retinal flow resistance (RFR) was calculated. Three indices were developed to evaluate the effectiveness of herbal medicines in RFR-MAP diagram based on experimental data of MAP and RFR in type 2 diabetic rats. These indices are α, β, and γ where α is a ratio of reduction in MAP, β is a ratio of reduction in RFR increasing with MAP increase, and γ indicates a ratio of reduction in RFR. RESULTS The elevated MAP and RFR and decreased RBF were observed in DM2 rats.Interestingly, alpha-mangostin or curcumin supplementation significantly increased RBF while decreased MAP and RFR. Using α, β and γ indices, it was found that alpha-mangostin is more effective than curcumin in type 2 diabetic retina. CONCLUSIONS These microhemodynamic indices may be useful to compare various herbal medicines in different tissues.

Long-term oral vitamin C administration improves cerebral microvascular vasodilatory impairment in diabetes: in vivo evidence using diabetic rats

Background: Many clinical reports have indicated that ascorbic acid (vitamin C) improves vasodilatory impairments in patients with diabetes mellitus, but there is very little in vivo evidence to demonstrate its effectiveness on the brain. Objective: To investigate long-term effects of oral vitamin C administration on the cerebral microvascular vasodilation in diabetes, using streptozotocin (STZ)-induced diabetic rats. Materials and methods: Diabetes was induced in male Wistar Furth rats by a single intravenous injection of STZ (55 mg/kg b.w). Ascorbic acid (vitamin C) was administered in drinking water (1g/l). The rats were divided into control and diabetic groups with or without administration of vitamin C. The cerebral microcirculation was observed at different times (12, 24 and 36 weeks) after vitamin C supplementation, using fluorescence videomicroscopy. Responses of cerebral arterioles to acetylcholine (ACh), adenosine-5 diphosphate (ADP) and nitroglycerine (NTG) were studied by measuring diameters of cerebral arterioles before and after topical application on the cortical surface. Results: The vasodilatory responses of cerebral arterioles to ACh and ADP were significantly decreased in diabetic rats, compared with non-diabetic (control) rats. The response to NTG was not altered in diabetic rats, indicating that the vasodilatory impairment involves at the endothelium. The impaired endothelium-dependent vasodilation was prevented by long-term vitamin C administration. Conclusion: Long-term oral vitamin C administration might be of clinical relevance in improving cerebral microvascular vasodilatory impairment in diabetes.