ANTIHYPERGLYCAEMIC AND ANTIPEROXIDATIVE ROLES OF ACARBOSE IN TYPE 2 DIABETES MELLITUS ARE POSSIBLY MEDIATED THROUGH CHANGES IN THYROID FUNCTION

Can gallic acid potentiate the antihyperglycemic effect of acarbose and metformin? Evidence from streptozotocin-induced diabetic rat model

This study investigated the influence of dietary phenolic acid- Gallic acid (GA) on the antihyperglycemic properties of acarbose (ACA) and metformin (MET). Streptozotocin-induced diabetic rats were treated (p.o) with ACA, MET, GA and their combinations for 14 days. The effects of the treatments on blood glucose and insulin levels, pancreas α-amylase and intestinal α-glucosidase activities, as well as thiobarbituric acid reactive species (TBARS), thiol and reactive oxygen species (ROS) levels, including antioxidant enzyme activities were investigated. A significant increase in blood glucose, insulin, ROS and TBARS levels, and impaired antioxidant status, as well as elevation in the activities of α-amylase and α-glucosidase observed in diabetic rats were ameliorated in the treatment groups. Hpwever, GA had varying effects on the antidiabetic properties of the drugs. Nevertheless, GA showed more potentiating effects on the antidiabetic effect of MET and these effects were better observed at the lower dose of GA.

Links between Thyroid Disorders and Glucose Homeostasis

Thyroid disorders and diabetes mellitus often coexist and are closely related. Several studies have shown a higher prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. Thyroid hormone affects glucose homeostasis by impacting pancreatic β-cell development and glucose metabolism through several organs such as the liver, gastrointestinal tract, pancreas, adipose tissue, skeletal muscles, and the central nervous system. The present review discusses the effect of thyroid hormone on glucose homeostasis. We also review the relationship between thyroid disease and diabetes mellitus: type 1, type 2, and gestational diabetes, as well as guidelines for screening thyroid function with each disorder. Finally, we provide an overview of the effects of antidiabetic drugs on thyroid hormone and thyroid disorders.

[Pharmacological approaches for correction of thyroid dysfunctions in diabetes mellitus]

Thyroid diseases are closely associated with the development of types 1 and 2 diabetes mellitus (DM), and as a consequence, the development of effective approaches for their treatment is one of the urgent problems of endocrinology. Traditionally, thyroid hormones (TH) are used to correct functions of the thyroid system. However, they are characterized by many side effects, such as their negative effect on the cardiovascular system as well as the ability of TH to enhance insulin resistance and to disturb insulin-producing function of pancreas, exacerbating thereby diabetic pathology. Therefore, the analogues of TH, selective for certain types of TH receptors, that do not have these side effects, are being developed. The peptide and low-molecular weight regulators of thyroid-stimulating hormone receptor, which regulate the activity of the thyroid axis at the stage of TH synthesis and secretion in thyrocytes, are being created. Systemic and intranasal administration of insulin, metformin therapy and drugs with antioxidant activity are effective for the treatment of thyroid pathology in types 1 and 2 DM. In the review, the literature data and the results of own investigations on pharmacological approaches for the treatment and prevention of thyroid diseases in patients with types 1 and 2 DM are summarized and analyzed.

Dietary supplementation of grape skin extract improves glycemia and inflammation in diet-induced obese mice fed a Western high fat diet

Dietary antioxidants may provide a cost-effective strategy to promote health in obesity by targeting oxidative stress and inflammation. We recently found that the antioxidant-rich grape skin extract (GSE) also exerts a novel anti-hyperglycemic activity. This study investigated whether 3-month GSE supplementation can improve oxidative stress, inflammation, and hyperglycemia associated with a Western diet-induced obesity. Young diet-induced obese (DIO) mice were randomly divided to three treatment groups (n = 12): a standard diet (S group), a Western high fat diet (W group), and the Western diet plus GSE (2.4 g GSE/kg diet, WGSE group). By week 12, DIO mice in the WGSE group gained significantly more weight (24.6 g) than the W (20.2 g) and S groups (11.2 g); the high fat diet groups gained 80% more weight than the standard diet group. Eight of 12 mice in the W group, compared to only 1 of 12 mice in the WGSE group, had fasting blood glucose levels above 140 mg/dL. Mice in the WGSE group also had 21% lower fasting blood glucose and 17.1% lower C-reactive protein levels than mice in the W group (P < 0.05). However, the GSE supplementation did not affect oxidative stress in diet-induced obesity as determined by plasma oxygen radical absorbance capacity, glutathione peroxidase, and liver lipid peroxidation. Collectively, the results indicated a beneficial role of GSE supplementation for improving glycemic control and inflammation in diet-induced obesity.

Apigenin (4‘,5,7-trihydroxyflavone) regulates hyperglycaemia, thyroid dysfunction and lipid peroxidation in alloxan-induced diabetic mice

The potential of apigenin (4′,5,7-trihydroxyflavone) in regulating hyperglycaemia, thyroid dysfunction and lipid peroxidation (LPO) has been revealed. While in alloxan-treated diabetic animals, a significant decrease in the concentrations of serum insulin, thyroxine (T4) and triiodothyronine (T3), with a parallel increase in serum glucose and hepatic glucose-6-phospatase (G-6-Pase) activity, was observed, administration of 0.78 mg kg−1 of apigenin for 10 consecutive days increased the levels of serum insulin and thyroid hormones with a parallel decrease in glucose concentration and hepatic G-6-Pase activity. Alloxan-induced elevation in serum cholesterol was also reduced by the compound. With respect to LPO, while in alloxan-treated animals an increase in hepatic LPO and a decrease in the activity of cellular antioxidants, such as catalase (CAT) and superoxide dismutase (SOD), and in glutathione (GSH) content was observed, administration of apigenin to alloxan-treated mice reversed all these changes, suggesting its hepatoprotective potential. Similar effects of apigenin were also observed in most of the parameters in normoglycaemic animals. It appears that apigenin has a potential to regulate diabetes mellitus, as well as disease-induced thyroid dysfunction and lipid peroxidation.

Amelioration of corticosteroid-induced type 2 diabetes mellitus by rosiglitazone is possibly mediated through stimulation of thyroid function and inhibition of tissue lipid peroxidation in mice

We investigated the possible involvement of thyroid hormones and lipid peroxidation in the antidiabetic potential of rosiglitazone (a peroxisome proliferator-activated receptors gamma-agonist) on corticosteroid-induced type 2 diabetes mellitus. Rosiglitazone was administered to dexamethasone-induced hyperglycaemic male mice and the alterations in serum concentrations of thyroid hormones insulin, total cholesterol, triglycerides and fasting glucose were studied. Simultaneously changes in lipid peroxidation, reduced glutathione (GSH) content, superoxide dismutase and catalase activities in renal and cardiac tissues (which are commonly affected in diabetes mellitus), were also investigated. Administration of dexamethasone (1.0 mg/kg/day intramuscularly for 28 days) caused hyperglycaemia with a parallel increase in serum insulin, total cholesterol, triglycerides and tissue lipid peroxidation with a decrease in serum levels of both the thyroid hormones (triiodothyronine, T(3) and thyroxine, T(4)) and in the activity of associated tissue antioxidants such as superoxide, catalase and glutathione. However, rosiglitazone administration (3.2 mg/kg/day orally for 21 days) along with an equivalent amount of dexamethasone reverted most of these changes, including a marked inhibition of tissue lipid peroxidation and an increase in the serum levels of both thyroid hormones. The present findings reveal that the test drug ameliorates corticosteroid-induced type 2 diabetes mellitus through an increase in serum thyroid hormone concentrations and inhibition in tissue lipid peroxidation.

Amelioration of L-thyroxine-induced hyperthyroidism by coumarin (1,2-benzopyrone) in female rats

1. The efficacy of coumarin (1,2-benzopyrone) was examined for the regulation of hyperthyroidism in female rats. 2. Coumarin was administered (10 mg/kg per day for 15 days) to l-thyroxine (L-T(4))-induced hyperthyroid as well as to euthyroid rats and changes in serum concentrations of thyroid hormones and in associated parameters, such as serum cholesterol, activity of hepatic 5'-monodeiodinase (5'DI) and glucose-6-phosphatase (G-6-Pase), glycogen content, bodyweight and daily food consumption, were analysed. Simultaneously, changes in hepatic lipid peroxidation (LPO), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) were also investigated. 3. Although L-T(4) administration increased serum levels of thyroid hormones, the activity of hepatic 5'DI, G-6-Pase and LPO and daily food consumption, it decreased the level of serum cholesterol, hepatic glycogen content and the activities of anti-oxidant enzymes, such as SOD, CAT and GSH. 4. However, simultaneous administration of coumarin for 15 days to a group of hyperthyroid animals reversed most of the aforementioned changes, indicating its potential to ameliorate hyperthyroidism. Moreover, the drug did not increase, but rather decreased, hepatic LPO, suggesting its safe nature. 5. The present findings reveal a positive role for coumarin in the regulation of hyperthyroidism without any hepatotoxicity. It also appears that the test compound inhibits thyroid function at both a glandular level and at the level of peripheral conversion of T(4) to tri-iodothyronine.

Antidiabetic potential of Citrus sinensis and Punica granatum peel extracts in alloxan treated male mice

An investigation on the effects of four different concentrations of peel extract from Citrus sinensis (CS) or Punica granatum (PG) in male mice revealed the maximum glucose lowering and antiperoxidative activities at 25 mg/kg of CS and 200 mg/kg of PG. In a separate experiment their potential was evaluated with respect to the regulation of alloxan induced diabetes mellitus. While a single dose of alloxan (120 mg/kg) increased the serum levels of glucose and alpha-amylase activity, rate of water consumption and lipid peroxidation (LPO) in hepatic, cardiac and renal tissues with a parallel decrease in serum insulin level, administration of 25 mg/kg of CS or 200 mg/kg of PG was found to normalize all the adverse changes induced by alloxan, revealing the antidiabetic and anti peroxidative potential of test fruit peel extracts. Subsequent phytochemical analysis indicated that the high content of total polyphenols in the test peels might be related to the antidiabetic and antiperoxidative effects of the test peels.