Lannea edulis (Sond.) Engl. commonly known as wild grape is used traditionally for the treatment of diabetes. It is only found in Eastern and Southern Africa. Phytochemical screening, antihyperglycemic and antihyperlipidemic effects of aqueous extracts of L. edulis in alloxan induced diabetic rats were carried out. We report herein the findings of this research work. Lannea edulis crude aqueous extracts were obtained by hot infusion and evaporation method. Phytochemical screening was carried out and subsequently toxicity studies of the aqueous extracts were performed to establish the Lethal Dose 50 (LD₅₀) in albino rats. Alloxan monohydrate was used to induce diabetes in the rats. Lannea edulis positive control group doses of 100, 300, and 500 mg/kg were administered to 3 groups for 14 days. The positive control group was administered 5 mg/kg of glibenclamide. The negative and normal control groups were administered distilled water. To determine fasting blood glucose, blood was drawn on days 0, 1, 3, 5, 7, and 14 while it was drawn on days 0 and 14 for the determination of lipids. Phytochemical screening revealed the presence of flavonoids, saponins, tannins, cardiac glycosides, alkaloids and steroids. L. edulis diabetic positive control groups showed significant (P < 0.05) dose dependent reductions in fasting blood glucose levels. When day 0 mean blood glucose levels were compared to day 3 mean blood glucose levels of their respective groups, the 300 mg/kg L. edulis group showed a 23.3% drop and the 500 mg/kg L. edulis group showed a 52.6% drop. The 100 mg/kg L. edulis diabetic positive control group showed a 25.1% drop by day 5, the day on which it showed statistical significance (P < 0.05) compared to the diabetic control. In addition, administration of aqueous extracts of L. edulis to diabetic rats for 14 days significantly decreased (P < 0.05) the levels of serum total cholesterol, triglycerides, Low Density Lipoprotein (LDL) and Very Low Density Lipoprotein (VLDL) whilst increasing the levels of High Density Lipoprotein (HDL), when compared to the diabetic control group. It was concluded that L. edulis showed significant and dose dependent antihyperglycemic and antihyperlipidemic effects thus confirming its traditional use.

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates a spectrum of toxic and biological effects of 2,3,7,8-tetrachloro dibenzo-p-dioxin (TCDD) and related compounds. Peroxisome proliferator activated receptor alpha (PPARalpha) is a nuclear receptor involved in the maintenance of lipid and glucose homeostasis. In this study we hypothesized that one of the possible mechanisms for the effect of TCDD and its related chemicals on fat metabolism could be through down regulation of PPARalpha functions. We treated Wistar rats with an AhR ligand, Sudan III (S.III), and/or PPARalpha ligand, Clofibric Acid (CA), for 3 days. We analysed the expression of one of the PPARalpha-target gene products, CYP4A protein and its mRNA. We also tested HepG2 cells with the afore-mentioned treatments and evaluated their effects on PPARalpha and RXRalpha protein. Treatment of Wistar rats with S.III was found to down regulates CYP4A protein expression and reduced its induction with CA. It also decreased mRNA expressions of CYP4A1, CYP4A2, CYP4A3 and PPARalpha. In HepG2 cells, PPARalpha and RXRalpha protein expression was decreased by S.III treatment in a dose dependent manner. Our results suggest that AhR has an inhibitory effect on PPARalpha function and a new pathway by which AhR ligands could disturb lipid metabolism.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates a spectrum of toxic and biological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. The peroxisome proliferator-activated receptor alpha (PPARα) is a member of the nuclear receptor super-family of ligand-activated transcription factors and it functions as an obligate heterodimer with retinoid X-receptor alpha RXRα. The aim was to investigate whether the negative cross-talk recently proposed by the present authors between AhR and PPARα on CYP4A and CYP1A has any impact on other cytochrome P450 enzymes. Treatment of male Wistar rats with a PPARα ligand clofibric acid (CA) induced CYP2B1/2 and CYP3A proteins, activities, and the mRNA expression of CYP2B1, CYP2B2, CYP3A1 and CYP3A2, and suppressed CYP2C11 protein, activities and mRNA expression. AhR ligand Sudan III (S.III) treatment decreased basal and CA-induced CYP2B, CYP3A and CYP2C11 protein, activities and mRNA expression. To the best of the authors’ knowledge, this is the first study showing the presence of mutual effects of AhR and PPARα on CYP2B and CYP3A and an additive inhibitory effect on CYP2C11 in the livers of male rats.

Catechol estrogens (CEs), such as 4-hydroxyestradiol (4-OHE₂), undergo redox cycling during which reactive oxygen species (ROS) such as superoxide and the chemically reactive estrogen semiquinone (CE-SQ) and quinone (CE-Q) intermediates are produced. The quinone's putative mutagenicity may be enhanced by ROS and/or reactive nitrogen species. High concentrations of nitric oxide (NO) present during inflammatory conditions may react with to form peroxynitrite (ONOO⁻), a potent oxidant implicated in many pathological conditions. In this study, the possible generation of peroxynitrite from the interaction of CEs and NO and its effect on plasmid DNA and intact cells were investigated. A combination of 4-OHE₂ and NO increased the level of single strand breaks (SSB) in plasmid DNA by more than 60% compared to vehicle controls in a metal-free buffer system. 4-OHE₂ alone or NO alone had no effect. Results obtained from use of different antioxidants and ROS scavengers suggested a role of peroxynitrite in oxidative stress. In cells, 4-OHE₂ or NO alone induced dose-dependent DNA damage as assessed by single cell gel electrophoresis. Co-treatment with 4-OHE₂ and NO had an additive effect at lower doses. Generation of intracellular ROS was measured by the oxidation of carboxy-2′,7′-dichlorofluorescein diacetate to the fluorescent compound carboxy-2′,7′-dichlorofluorescein. NO alone, in oxygenated media, generated little ROS whereas 4-OHE₂ produced approximately 70% increase in fluorescence. When added together 4-OHE₂ and NO, produced a 2-fold increase in ROS. The generation and involvement of peroxynitrite to this increase was implied since uric acid inhibited it. Generation of peroxynitrite was also observed by use of dihydrorhodamine 123. Therefore, we conclude that combined treatments with 4-OHE₂ and NO generated peroxynitrite seen from increased fluorescence and its inhibition by uric acid or combined SOD and catalase treatments. Results reported here suggest a role of peroxynitrite in causing damage to biomolecules when CEs and NO are present simultaneously. This may have biological relevance as high concentrations of NO formed during inflammatory conditions may exacerbate cancers due to estrogens.