Potential effect of senna italica on glucose transport receptors - translocation go GLUT4 in NIH-3T3-L1 preadipocytes and C2C12 muscle cells

Abstract

Diabetes mellitus is one of the major diseases worldwide that is life threatening and is reaching an epidemic proportion. The most important approach in reducing the burden of the disease worldwide is to search for effective, low cost hypoglycaemic drugs with fewer side effects. Past experimental evidence confirmed the hypoglycemic activity of many indigenous African medicinal plants. S. italica (Fabaceae family) is widely used by traditional healers to treat a number of diseases such as sexually transmitted diseases and other forms of intestinal complications traditionally. The current study was aimed at evaluating the in vitro effects of root and leaf extracts of S. italica on GLUT4 translocation in NIH-3T3-L1 preadipocytes and C2C12 muscle cells. In order to address the aim of the study various methods were undertaken. The roots and leaves of S. italica collected from Zebediela sub-region of the Limpopo province, South Africa, were ground to fine powder and extracted using acetone, methanol, ethyl acetate and n-hexane. The various extracts of the root and leaf material were subjected to fingerprint profiling using TLC plates and different mobile phases (BEA, CEF, EMW and BAW). The chromatograms were visualized with vanillin-H2SO4 reagent, p-anisaldehyde and iodine vapour. The extracts were assayed for the type of secondary metabolites contained in the studied plant parts using chemical text and by TLC analysis. The total phenolic content of the root and leaf material were also evaluated. Evaluation for antioxidant activity was performed using 0.2% DPPH qualitatively and quantitatively with vitamin C as a positive control. Toxicity study was performed on C2C12 muscle cells using the MTT assay, with Curcumin as a positive control and untreated cells as a negative control. The CC50 values of the acetone root and leaf extracts were determined by linear regression. The effect of acetone root and leaf extracts on glucose uptake by C2C12 muscle cells was evaluated, also on western blot and immunofluorescence for NIH-3T3-L1 preadipocytes. The solvents employed for extraction in this study are commonly used to extract various biological active compounds from plants in research settings. Methanol extracted more compounds followed by acetone, then ethyl acetate and n-hexane the least. The constituents extracted by methanol may be mostly sugars, amino acids and glycosides due to the polarity of this solvent. Hydro-alcoholic solvents extract a variety of compounds that are mostly polar. Acetone extracts mostly alkaloids, aglycones and glycosides while n-hexane in general extracts mostly waxes, fats and fixed oils. High yield was obtained with leaf extracts with all the solvent used for extraction as compared to the root. The TLC finger-print showed that good separation was achieved with the methanol and acetone extracts in CEF mobile phase, ethyl acetate extracts in CEF and EMW and n-hexane extracts in BEA respectively, especially with the leaf extract. Most compounds present in S. italica extracts were UV active. Some compounds that were not reactive with vanillin-H2SO4 reagent were shown to be reactive with p-anisaldehyde reagent and iodine vapour which revealed the presence of sugars or aromatic compounds. Chemical analysis for secondary metabolites of the acetone root and leaf extracts revealed the presence of flavonoids, terpenes, tannins, steroids, reducing sugars and alkaloids while glycosides were detected only in the leaf extract. The results obtained using TLC analyses were consistent with the results obtained in the chemical analysis. Thin layer chromatography revealed the presence of glycoflavones in the acetone root extract, alkaloids in the root and leaf extracts; and phytosterols and flavonoid aglycones in root and leaf extracts. The acetone root and leaf extracts revealed the presence of phenols. The leaf extract was shown to contain high total phenolic content as compared to the root. The methanol and acetone root and leaf extracts were shown to possess antioxidant activity. However, the concentration of the activity was higher in the acetone root than in the leaf extract. The least activity was observed with the ethyl acetate root and leaf extracts as compared to other extracts. The n-hexane extracts however, was not shown to contain any antioxidant compounds. Although activity observed with the methanol extracts was comparable to that of the acetone extracts in the quantitative assay, the acetone extracts were shown to possess more antioxidant activity in the qualitative assay. The concentration of extracts increased with increase in scavenging activity. The root extract exhibited a more potent antioxidant activity compared to leaf extract. These extracts were evaluated for their cytotoxicity on normal cells. The highest cytotoxic concentration (CC50) was obtained with the root extract with a CC50 value of 297 635 μg/ml at 48 hrs, followed by CC50 value of 21 544 μg/ml at 24 hrs. The CC50 value of the leaf extract at 24 hrs was 2 904 μg/ml with the least value at 48 hrs. The root extract at 24 and 48 hrs together with the leaf extract at 24 hrs were not toxic to C2C12 muscle cells at the concentration tested in this study. The acetone extracts were shown to possibly enhance proliferation of C2C12 muscle cells at a concentration of 0.001–1000 μg/ml. The non-cytotoxic concentration of 25 μg/ml of the leaf extract in combination with insulin showed more glucose uptake as compared to other extracts as well as the control. Prolonged incubation time was shown to increase glucose uptake with leaf extract while increase in concentration of root extract decreased glucose uptake at 24 hrs. At incubation time of 3 and 24 hrs, glucose uptake results at concentration of 2.5 μg/ml were comparable with that of the root extract, with a similar trend observed at 25 μg/ml, although with decrease in uptake. The qualitative and quantitative fluorescence results showed GLUT4 to be translocated to the cell membrane. The leaf extract at a concentration of 25 μg/ml had more fold as compared to other extracts, indicative that more GLUT4 was translocated at this concentration of the leaf extract. The acetone root and leaf extracts were shown to increase protein expression of GLUT4 at 3 hrs incubation time as compared to other incubation times in insulin-stimulated C2C12 muscle cells. The plant constituents of S. italica was shown to contain a variety of secondary metabolites that maybe be acting alone or in concert with each other to exert the various activities observed in this study. Different solvents used for extraction may be responsible for the extraction of different constituents with antioxidant activity observed in the study. The acetone extracts enhanced proliferation of C2C12 muscle cells at concentrations used in the study. However, there was no significant reduction on viability of normal cells. In addition, the extracts were shown to enhance the differentiation of NIH-3T3-L1 preadipocytes into adipocytes and C2C12 muscle cells into myocytes. These in turn induced the translocation of GLUT4 to the cell membrane and as a consequence facilitate glucose transport. Hence, the differentiation of adipose cells as well as glucose uptake of muscle cells and GLUT4 expression might have been enhanced by constituents contained in the acetone extracts. In conclusion, the acetone leaf extract may have a beneficial role in glucose metabolism of differentiated C2C12 muscle cells. Therefore, further studies are however required to elucidate the molecular mechanism by which the acetone leaf extract of S. italica influences the translocation of GLUT4.