Browsing by Author "Liu, B."
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Item Chracterisation of the insulinotropic activity of aqueous extracts of Gymnema sylvestre in mouse B-cells and human Islets of Langerhans(Cell. Physio. Biochem, 2009) Anane-Asare, H.; Liu, B.; Al-Romaiyan, A.; Ameil, S.A.; Huang, G.C.; Jones, P.M.; Persaud, S.J.Leaves of the Gymnema sylvestre (GS) plant have been used to treat diabetes mellitus for millennia, but the previously documented insulin secretagogue effects of GS extracts in vitro may be non-physiological through damage to the beta-cells. We have now examined the effects of a novel GS extract (termed OSA) on insulin secretion from the MIN6 beta-cell line and isolated human islets of Langerhans. Insulin secretion from MIN6 cells was stimulated by OSA in a concentration-dependent manner, with low concentrations (0.06-0.25 mg/ml) having no deleterious effects on MIN6 cell viability, while higher concentrations (> or = 0.5 mg/ml) caused increased Trypan blue uptake. OSA increased beta-cell Ca2+ levels, an effect that was mediated by Ca2+ influx through voltage-operated calcium channels. OSA also reversibly stimulated insulin secretion from isolated human islets and its insulin secretagogue effects in MIN6 cells and human islets were partially dependent on the presence of extracellular Ca2+. These data indicate that low concentrations of the GS isolate OSA stimulate insulin secretion in vitro, at least in part as a consequence of Ca2+ influx, without compromising beta-cell viability. Identification of the component of the OSA extract that stimulates regulated insulin exocytosis, and further investigation of its mode(s) of action, may provide promising lead targets for Type 2 diabetes therapy.Item A novel Gymnema sylvestre extract stimulates insulin secretion from human islets in vivo and in vitro(John Wiley & Sons Ltd., 2010) Anane-Asare, H.; Al-Romaiyan, A.; Liu, B.; Maity, C.R.; Chatterjee, S.K.; Koley, N.; Biswas, T.; Chatterji, A.K.; Huang, G.C.; Amiel, S.A.; Persaud, S.J.; Jones, P.M.Many plant-based products have been suggested as potential antidiabetic agents, but few have been shown to be effective in treating the symptoms of Type 2 diabetes mellitus (T2DM) in human studies, and little is known of their mechanisms of action. Extracts of Gymnema sylvestre (GS) have been used for the treatment of T2DM in India for centuries. The effects of a novel high molecular weight GS extract, Om Santal Adivasi, (OSA(R)) on plasma insulin, C-peptide and glucose in a small cohort of patients with T2DM are reported here. Oral administration of OSA(R) (1 g/day, 60 days) induced significant increases in circulating insulin and C-peptide, which were associated with significant reductions in fasting and post-prandial blood glucose. In vitro measurements using isolated human islets of Langerhans demonstrated direct stimulatory effects of OSA(R) on insulin secretion from human ß-cells, consistent with an in vivo mode of action through enhancing insulin secretion. These in vivo and in vitro observations suggest that OSA(R) may provide a potential alternative therapy for the hyperglycemia associated with T2DM.Item Petrology and geochemistry of TTG and K-rich Paleoproterozoic Birimian granitoids of the West African Craton (Ghana): Petrogenesis and tectonic implications(Precambrian Research, 2019-10-14) Sakyi, P.A.; Addae, R.A.; Su, B.; Dampare, S.B.; Abitty, E.; Su, B-C.; Liu, B.; Asiedu, D.K.We conducted petrologic, geochemical and isotopic studies on Paleoproterozoic Birimian granitoids that intrude the Bole-Nangodi Belt in northern Ghana, in southeastern West African Craton (WAC), to constrain the geodynamic evolution of the Birimian Supergroup. The rocks are potassic (K)-rich granitoids (KRGs), tonalities, trondhjemites, granodiorites (TTGs), pegmatite and aplite. The K2O contents of the KRGs are up to 5 wt%, with generally high concentrations of Rb, Ba, Sr, Cr and Ni. They are highly fractionated calc-alkaline I-type granitoids, enriched in LILE and LREE relative to HREE and HFSE. Chondrite-normalized REE diagrams indicate fractionated LREE (average LaN/SmN=5.05) and HREE (GdN/YbN=4.56) patterns, with slight negative Eu anomalies (average Eu/Eu*=0.75). This may indicate an evolved magma source with varying degrees of plagioclase fractionation. The KRGs share similar geochemical characteristics with the TTGs into which they intrude. Both rock types are characterized by Ba and Th enrichment and depletion in Nb‐Ta, Zr‐Hf, and Ti, which are typical characteristics of subduction-related magmas. The pegmatite-aplite association is slightly geochemically different and may have formed at a time later than the KRGs. The ԐNd(2.1 Ga) values range from+0.90 to+1.24 and −0.86 to+1.37 respectively for the TTGs and KRGs, with TDM1 ages of 2.34–2.38 Ga and 2.36–2.53 Ga and TDM2 ages of 2.21–2.24 Ga and 2.22–2.39 Ga respectively. These indicate their juvenile character, possibly a depleted mantle source with minor contributions from a pre-Birimian (or Archean?) crustal material in their source material(s). The TTGs and KRGs are volcanic arc granites (VAG) and syn-collisional (Syn-COLG) granites, with formation temperatures and pressures of ~640–750 °C and ~2–6 kbar respectively. Based on the high temperatures, I-type signature, calc-alkaline nature and other geochemical characteristics, we infer that the TTGs, KRGs and pegmatite-aplite association developed under high oxygen fugacity conditions in an orogenic tectonic setting related to subduction. Thus, our geochemical and isotopic results are consistent with an island arc tectonic setting arising from subduction–accretion processes, which are typical for the Paleoproterozoic terranes of the WAC. These processes may have contributed to the amalgamation of the Columbia (Nuna) supercontinent during the Paleoproterozoic (2.1–1.8 Ga) orogeny.