**10. Plant phytochemicals associated with antidiabetic activity**

Photochemicals or phytonutrients are chemical compounds that occur naturally in plants that have protective or disease preventive properties [58]. Each type of fruit or vegetable may contain hundreds of phytochemicals. They have been reported to show multiple beneficial effects in combating diabetes and diabetes related complications [58]. The widest known groups of phytochemicals are the alkaloids, terpenes, and phenolics. Plant constituents such as polysaccharides, peptides, alkaloids, glycopeptides, triterpenoids, amino acids, steroids, xanthone, flavonoids, lipids, phenolics, coumarins, iridoids, alkyl disulphides, inorganic ions and guanidines are reported to have antidiabetic activities [49, 59]. More interestingly, the following phytochemicals are reported to have antidiabetic activity, aminoacids like hypo‐ glycin A and hypoglycin B, alkaloids like catharanthine, leurosine, lochnerine, arecoline and vindoline, pinitol, epicatechin, S-methyl cysteine sulphoxide, S-allyl cysteine sulphoxide, andrographolide, allicin (thio-2-propene-1- sulfinic acid S-allyl ester), shamimin, beta vul‐ garosides I–IV, glycoside of leucopelargonidin and leucodelphinidin, mangiferin, marsupsin, pterosupin, pterostilbene, salacinol, swerchirin, trigonelline, berberine, harmane, norharmane, pinoline, quercetin, chlorogenic acid, hesperidin, naringin, epigallocatechin gallate, charantin, galactonmannan, lactucain C, kaempferol glucosides, caffeoyl glucoside, bakuchiol, swerchir‐ in, thysanolactone, bellidifolin and kolaviron have been documented for potential phytonu‐ trients [60].

*Lawsonia inermis, Moringa oleifera, Psidium guajava, Bauhinia reticulate, Balanites aegyptiaca, Lannea kerstingii, Daucus carota, Zizyphus spina, Anana senegalensis, Eugenia caryophyllata, Blighia*

Some Selected Medicinal Plants with Antidiabetic Potentials

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The leaves of *Mangifera indica* are used as an antidiabetic agent in Nigerian folk medicine. The hypoglycemic activity of *Mangifera indica* has been reported in both rats and mice [63-64]. Aqueous extract of the leaves of *Mangifera indica* were found to possess hypoglycaemic activity against glucose-induced hyperglycaemia but not with normoglycaemic or STZ-induced diabetic rats and mice respectively [63-64]. The hypoglyceamic effect of this plant was thought to be by reduction of intestinal absorption of glucose. Antihyperglycaemic activity of aqueous stem bark extract of *Mangifera indica* was also reported by Ojewole [65]. The extract from the stem bark of *Mangifera indica* administered intraperitoneally in streptozotocin induced diabetics rats produced a significant reduction in blood glucose level in rats Ojewole [65].

In Nigeria, the leaves of *Vernonia amygdalina* Del. (VA) and *Azadirachta indica* A. Juss (AI) have been used traditionally as a remedy against diabetes mellitus [66]. Atangwho et al. [66] reported that significant antidiabetic effect of the combination therapy was achieved when VA and AI were combined. The mechanism of action of the combination therapy was proposed as attenuation of oxidative stress, insulin mimetic action and β-cell regeneration. The presence of flavonoids such as luteolin, luteolin 7-*O-β*-glucuronoside, and luteolin 7-*O-β*-glucoside has been shown to be responsible for the antioxidant activity of *Vernonia amygdalina* [67]. The presence of these flavonoids could therefore contribute significantly to the antidiabetic

Etuk and Mohammed [68] reported that 200 mg/kg of *V. amygdalina, C. procera, C. goratensis* and *M. indica* aqueous extracts produced a significant (p < 0.05) reduction in the blood glucose levels of the rats in alloxan-induced diabetic mellitus. In the same vein, *A. leicarpus, C. arereh* and *G. hirsutum* extracts produced a non-significant reduction (p > 0.05) in blood glucose levels in rats after treatment. Similarly, aqueous extracts of *M. Oleifera, S. occidentalis* and *K. senegal‐ ensis* were found to produce a minimal effect (about 4% reduction) on the alloxan-induced hyperglycemia in rats (Etuk and Mohammed, 2009). In summary, Etuk and Mohammed (2009) reported that 200mg/kg body weight of *Vernonia amygdalina* (67%), *Calotropis procera* (59%), *Cassia gorotensis* (53%) and *Magnifera indica* (35%) extracts produced a significant (p < 0.0.5%) reduction in blood glucose levels in diabetic rats while *Angeissus leiocarpus*(30%), Cassia arereh (19%), *Gossypium hirsutum* (17%), *Khaya senegalensis* (4%), *Senna occidentalis* (4%) and *Moringa*

Previous study showed that aqueous leaves extract of *Psidium guajava* (PG) at 250 mg/kg showed statistically significant hypoglycaemic activity on alloxan-induced diabetic rats [69]. A 4-week supplementation of PG (125 and 250 mg/kg) in streptozotocin (STZ)-induced diabetic rats was shown to protect pancreatic tissues, including islet β-cells, against lipid peroxidation and DNA strand breaks induced by STZ, thereby reducing the loss of insulin-positive β-cells and insulin secretion [70]. More so, PG was found to markedly inhibited pancreatic nuclear factor-kappa B protein expression induced by STZ and restored the activities of antioxidant

enzymes, including superoxide dismutase, catalase, and glutathione peroxidase [70].

*sapida.*

property of *Vernonia amygdalina*.

*oleifera* (4%) produced a nonsignificant (p <0.05%) effect.
