In vitro cytotoxic, antioxidative and alpha-glucosidase inhibitory potential of a herbal mixture comprised of Allium sativum and Lagerstroemia speciosa.

BACKGROUND Hyperglycemia induced over production of free radicals in the mitochondrial electron transport chain is now considered as one of the central mechanisms in the pathogenesis of diabetic complications. Allium sativum and Lagerstroemia speciosa contains active principles possessing anti-diabetic and antioxidant properties. This study is aimed at evaluating the evidence that supports this traditional claim and investigates the possible synergistic effect on these herbs when given as a herbal mixture in vitro. AIM The present study investigates the cytotoxic, antioxidant and a-glucosidase inhibitory potential of Allium sativum (ASE), Lagerstroemia speciosa (LSE) and their combinations using in vitro methods. MATERIALS AND METHODS The total phenol, total flavonoid and total tannin content were determined in ASE and LSE. The cytotoxic effects of ASE, LSE and their combination in the ratio of 1:2, 1:1 w/w were evaluated using 3T3 L1 preadipocyte cells. Effect of ASE, LSE and its mixture on intracellular reactive oxygen species (ROS) production were determined by 2', 7'dichlorfluorescein diacetate (DCF DA) staining technique in 3T3-L1 adipocytes. The ability of the herbal extracts and their combination to scavenge super oxide radicals and to inhibit alpha-glucosidase enzyme (a carbohydrate metabolising enzyme) were measured using in vitro methods. RESULTS The total phenols and tannins were expressed as microgram (microg) of gallic acid equivalents/mg of extract (GAE/mg), flavonoids as microg of quercetin equivalents/mg of extract (QE/mg). LSE had significant higher total phenol (300.11 +/- 1.99), flavonoid (53.12 +/- 0.48) and tannin content (118.90 +/- 0.15) compared to ASE which possessed total phenol (159.93 +/- 0.87); flavonoid (9.37 +/- 0.73) and tannin content (80.5 +/- 0.19). The IC50 value, the concentration of the extracts that cause 50% inhibition or cell death was measured as an index of cytotoxicity. The IC50 value was found to be in the following decreasing order: 1:2 mixture (98 microg/ml) > ASE (323.6 microg/ml) > 1:1 mixture (428.1 microg/ml) > LSE (2154 microg/ml). The 1:1 mixture was comparatively less cytotoxic under the tested concentration range (1 x 10(0) pg - 1 x 10(8) pg) than 1:2 combinations. The results observed with lactate dehydrogenase (LDH) release were similar to that of cell viability assay. The 1:1 mixture (DIA-2 hereafter) was considered for further investigations. DIA-2 inhibited the ROS levels, which is evidenced by the decreased DCF fluorescence. DIA-2 could also efficiently scavenge the super oxide radical generated from PMS/NADH-NBT system showing an IC50 value 69.99 microg/ml, the IC50 value of ASE (157.7 microg/ml), LSE (20.43 microg/ml), and ascorbic acid (49.64 microg/ml) used as positive control. The results of in vitro a-glucosidase inhibitory assay showed highest IC50 value with LSE (0.3 microg/ml) and DIA-2 (0.7 microg/ml) than ASE (136.3 microg/ml) and positive control miglitol (651.8 microg/ml). CONCLUSIONS DIA-2 exerts synergistic effect in scavenging the ROS and inhibiting the enzyme alpha-glucosidase in vitro compared to its individual extracts. The possible synergistic therapeutic effects may be due the presence of the antioxidant rich flavonoids, phenols and tannins present in LSE and ASE.