**7.7.** *Aloe barbadensis*

*Aloe barbadensis* (*Aloe vera*), the acclaimed "miracle plant" has been documented to ameliorate the diabetic condition in human subjects and experimental animals and to probably prevent the onset of hyperglycemia in alloxan intoxicated rabbits [121]. Reports of studies on the effect of aloe vera in experimental and clinical diabetes are available. In general, these reports agreed on the antidiabetic efficacy of *Aloe vera*. Oral administration of *Aloe vera* gel extract at a dose of 300 mg/kg bodyweight per day to STZ-induced diabetic rats for a period of 21 days resulted in a significant reduction in fasting blood glucose, hepatic transaminases (aspartate amino‐ transferase and alanine aminotransferase), plasma and tissue (liver and kidney) cholesterol, triglycerides, free fatty acids and phospholipids and a significant improvement in plasma insulin [122]. Can *et al*. concluded from their study that Aloe gel extract has a protective effect comparable to glibenclamide against hepatotoxicity produced by diabetes if used in the treatment of T2DM [123]. Another research finding showed that orally ingested aloe sterols altered the expressions of genes related to glucose and lipid metabolism, and ameliorated obesity- and diabetes-associated disorders in rats [124].

#### **7.8.** *Vernonia amygdalina*

Alcohol extract of *V. amygdalina* was found to significantly improve glucose tolerance in STZdiabetic rats, decrease fasting blood glucose, show protective effect over pancreatic β-cells and cause a slight increase in insulin level in STZ-induced diabetic rats [125]. The same authors found that *V. amygdalina* increased the expression of GLUT 4 in rat skeletal muscle and its translocation to plasma membrane as well. *V. amygdalina* was also found to significantly inhibit the key hepatic gluconeogenic enzyme, glucose-6-phosphatase. Investigation of the synergistic antidiabetic effect of *V. amygdalina* and other medicinal plants yielded positive results. A study on the synergistic antidiabetic activity of *V. amygdalina* and *Azadirachta indica* [126] showed that compared with single extracts, the combined extract of *V. amygdalina* and *A. indica* promptly lowered blood glucose and maintained a relatively steady level over the study period, in tandem with insulin. The features of diabetic pathology, indicated in the histology of the liver and pancreas, were reversed. The extent of recovery was partial with *V. amygdali‐ na*, better with *A. indica*, and distinct and total with *V. amygdalina* and *A. indica* combined. The beneficial synergistic effect was postulated to be exerted via oxidative stress attenuation, insulin mimetic action and β-cell regeneration. The synergistic postprandial blood glucose modulatory properties of *V. amygdalina*, *Gongronema latifolium* and *Occimum gratissimum* aqueous decoctions has also been reported [127]. It was concluded from the study that the decoction containing the three vegetables was superior in activity to any one or blends of only two, of the three decoctions.

#### **7.9.** *Moringa oleifera*

**7.6. Kolaviron**

150 Antioxidant-Antidiabetic Agents and Human Health

**7.7.** *Aloe barbadensis*

**7.8.** *Vernonia amygdalina*

Kolaviron, a biflavonoid complex isolated from *Garcinia kola* possesses multiple biological activities. Kolaviron demonstrated significant hypoglycaemic effect when administered to alloxan diabetic rabbits. The blood sugar was lowered from 506 mg/100 mL to 285 mg/100 mL at 12 h after the administration of 100 mg/kg kolaviron. Kolaviron also inhibited rat lens aldose reductase (RLAR) activity, with an IC50 value of 5.4 x 10-6 [118]. Adaramoye and Adeyemi reported that fractions obtained from kolaviron reduced blood sugar levels in STZ-diabetic rats within 4 h of oral administration and showed favourable effect on the plasma lipid profile of diabetic animals [119]. In addition to its antidiabetic property, kolaviron showed remarkable protective effects on cardiac, renal and hepatic tissues of STZ-diabetic rats. Many antidiabetic

*Aloe barbadensis* (*Aloe vera*), the acclaimed "miracle plant" has been documented to ameliorate the diabetic condition in human subjects and experimental animals and to probably prevent the onset of hyperglycemia in alloxan intoxicated rabbits [121]. Reports of studies on the effect of aloe vera in experimental and clinical diabetes are available. In general, these reports agreed on the antidiabetic efficacy of *Aloe vera*. Oral administration of *Aloe vera* gel extract at a dose of 300 mg/kg bodyweight per day to STZ-induced diabetic rats for a period of 21 days resulted in a significant reduction in fasting blood glucose, hepatic transaminases (aspartate amino‐ transferase and alanine aminotransferase), plasma and tissue (liver and kidney) cholesterol, triglycerides, free fatty acids and phospholipids and a significant improvement in plasma insulin [122]. Can *et al*. concluded from their study that Aloe gel extract has a protective effect comparable to glibenclamide against hepatotoxicity produced by diabetes if used in the treatment of T2DM [123]. Another research finding showed that orally ingested aloe sterols altered the expressions of genes related to glucose and lipid metabolism, and ameliorated

Alcohol extract of *V. amygdalina* was found to significantly improve glucose tolerance in STZdiabetic rats, decrease fasting blood glucose, show protective effect over pancreatic β-cells and cause a slight increase in insulin level in STZ-induced diabetic rats [125]. The same authors found that *V. amygdalina* increased the expression of GLUT 4 in rat skeletal muscle and its translocation to plasma membrane as well. *V. amygdalina* was also found to significantly inhibit the key hepatic gluconeogenic enzyme, glucose-6-phosphatase. Investigation of the synergistic antidiabetic effect of *V. amygdalina* and other medicinal plants yielded positive results. A study on the synergistic antidiabetic activity of *V. amygdalina* and *Azadirachta indica* [126] showed that compared with single extracts, the combined extract of *V. amygdalina* and *A. indica* promptly lowered blood glucose and maintained a relatively steady level over the study period, in tandem with insulin. The features of diabetic pathology, indicated in the histology of the liver and pancreas, were reversed. The extent of recovery was partial with *V. amygdali‐ na*, better with *A. indica*, and distinct and total with *V. amygdalina* and *A. indica* combined. The

drugs do not offer significant tissue-protective effect in diabetic animals [120].

obesity- and diabetes-associated disorders in rats [124].

*Moringa oleifera* is a popular food plant with multiple medicinal uses including treatment of diabetes [128]. Various parts of the plant have been shown to have antidiabetic potential in several studies. In severely diabetic animals, 200 mg/kg aqueous leaf extract of *M. oleifera* reduced fasting blood sugar by 69.2% after 21 days of treatment and also significantly reduced urine sugar [129]. The progression of diabetes was significantly reduced in STZ-diabetic rats treated with methanol extract *M. oleifera* pods for 21 days with treated animals showing a significant reduction in serum glucose and nitric oxide, with concomitant increases in serum insulin and protein levels [130]. It has also been shown that extracts of the bark of the plant prevented dexamethasone-induced insulin resistance in peripheral tissues [131].

#### **7.10. Pinitol (3-O-methyl-D-chiro-inositol)**

In a study which assessed the effects of pinitol supplementation on glucose tolerance and insulin sensitivity, investigators found that a single dose of pinitol, from a naturally-occurring food ingredient, administered acutely influences indices of whole-body glucose tolerance and insulin sensitivity in healthy subjects. The study showed that consumption of a pinitolenriched beverage, containing a dose of 6.0 g, reduced the increase in glycaemia and insuli‐ naemia provoked by oral carbohydrate over-load when compared with a placebo. They remarked that this dietary intervention would be an effective first-step strategy for treating hyperglycaemia and related insulin resistance states, although future research is warranted to evaluate whether chronic doses of pinitol are effective in subjects with altered glucose metabolism [132]. Inositol phosphoglycans (IPG) have been reported to be important postreceptor mediators of insulin action [133,134] and it was suggested that by acting as insulin's second messenger, pinitol could increase insulin sensitivity.
