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The leaves of Garcinia gracilis Pierre, Clusiaceae, have been used as flavouring materials in food, with no previous reports of their biological activities and chemical constituents. In this study, the methanolic extract of G. gracilis afforded three compounds namely apigenin-8-C-α-l-rhamnopyranosyl-(1→2)-β-d-glucopyranoside (1), 5-hydroxymethyl-2-furaldehyde, and vanillic acid. All of the isolates were initially evaluated for superoxide anion radical scavenging activity and α-glucosidase inhibitory effects. Compound 1, which was the major component, showed the most potent activities among these three isolates. Further biological evaluations revealed that compound 1 could prevent the pBR322 plasmid DNA damage induced by the photochemical reaction of riboflavin and protect P19-derived neurons from the oxidative stress condition induced by serum deprivation. It was concluded that the potent biological activities of G. gracilis could be attributed to the synergistic effect of compound 1 with other constituents found in the plant. Keywords: Antioxidant, DNA protective, Flavonoid glycoside, Garcinia gracilis, α-Glucosidase, Neuroprotective

A methanol extract from the whole plant of Dendrobium formosum Roxb. ex Lindl., Orchidaceae, showed inhibitory potential against α-glucosidase and pancreatic lipase enzymes. Chromatographic separation of the extract resulted in the isolation of twelve phenolic compounds. The structures of these compounds were determined through analysis of NMR and HR-ESI-MS data. All of the isolates were evaluated for their α-glucosidase and pancreatic lipase inhibitory activities, as well as glucose uptake stimulatory effect. Among the isolates, 5-methoxy-7-hydroxy-9,10-dihydro-1,4-phenanthrenequinone (12) showed the highest α-glucosidase and pancreatic lipase inhibitory effects with an IC50 values of 126.88 ± 0.66 μM and 69.45 ± 10.14 μM, respectively. An enzyme kinetics study was conducted by the Lineweaver-Burk plot method. The kinetics studies revealed that compound 12 was a non-competitive inhibitor of α-glucosidase and pancreatic lipase enzymes. Moreover, lusianthridin at 1 and 10 μg/ml and moscatilin at 100 μg/ml showed glucose uptake stimulatory effect without toxicity on L6 myotubes. This study is the first report on the phytochemical constituents and anti-diabetic and anti-obesity activities of D. formosum. Keywords: Dendrobium formosum, Glucose uptake, α-Glucosidase, Pancreatic lipase

Recently, our group established a new approach for preparing injectable hydrogels using vinyl-functionalised pH-responsive microgel particles [Liu et al., Soft Matter, 2011, 7, 4696]. pH-responsive microgels swell when the pH approaches the pKa of the particles. Liu et al. used inter-particle crosslinking of vinyl-functionalised microgel particles to prepare hydrogels composed of doubly crosslinked microgels (D-microgels). Here, we combine vinyl-functionalised microgels with added, small-molecule, crosslinkers to prepare high modulus D-microgel/hydrogel (H-X) composites for the first time. The vinyl-functionalised microgel particles used were poly(EA/MAA/BDD)/GM; where, EA MAA, BDD and GM are ethyl acrylate and methacrylic acid, 1,4-butanediol diacrylate and glycidyl methacrylate, respectively. Two added crosslinkers were used to demonstrate the versatility of our approach. They were ethyleneglycol dimethacrylate (EGD) and N,N′-methylenebisacrylamide (BA). We compare the data to control hydrogel composites prepared using non-vinyl-functionalised singly crosslinked microgels (S-microgels). All of the composites showed pH-dependent swelling behaviours and mechanical properties. The storage modulus value for the as-made D-microgel/H-EGD composite was 0.12 MPa and is the highest reported to date for a hydrogel containing pH-responsive microgels. The as-made control S-microgel/H-X composites had high ductilities. Dynamic rheology data were used to determine the effects of vinyl functionalisation on the composite mechanical properties. All of the composites exhibited pH-dependent swelling and a “breathing in” transition occurred. The swollen D-microgel/H-X composites retained their high modulus values upon swelling; although, their ductilities decreased. Because we used two different crosslinkers and pH-responsive microgels containing carboxylic acid groups, the method introduced here for preparing high modulus hydrogel composites should be widely applicable.

The ability to tune the mechanical properties of hydrogel composites through the rational design of their constituents has excellent potential for providing advanced hydrogels for regenerative medicine applications. In this study we investigate the morphology and mechanical properties of a new family of pH-responsive hydrogel composites. They were prepared by adding crosslinking monomers (X) to concentrated dispersions of pH-responsive poly(EA/MAA/BDD) (ethylacrylate, methacrylic acid and butanediol diacrylate) MG particles. These MG/X dispersions formed physical gels. The dispersions were then polymerised to give pH-responsive hydrogel composites containing MGs, which are termed here as MG/H-X. The MG particles swelled strongly when the pH exceeded 6.0. The added crosslinking monomers were either ethyleneglycol dimethacrylate (EGD) or poly(ethylene glycol) dimethacrylate (PEGD). The latter had molecular weights in the range of 330 to 750 g/mol. If X had a molecular weight of 330 g/mol, or more, osmotic deswelling of the MG particles occurred. This strongly affected both the gelation behaviour of the MG/X dispersions and the mechanical properties of the chemically crosslinked MG/H-X hydrogel composites. For these new hydrogel composites X acted in two ways; it directed the morphology through osmotic deswelling of the MG particles and also provided a source of crosslinking. The storage modulus of the hydrogel composites was tuneable over a range of five orders of magnitude. The MG/H-X hydrogel composites showed pH-dependent swelling and mechanical properties. The hydrogel composites could also be prepared using poly(EA/MAA/EGD) and poly(EA/MAA/PEGD550) microgels. The simple method introduced here should enable construction of a wide range of pH-responsive hydrogel composites containing microgels with morphologies that can be tuned at the length scale of the MG particles, i.e., about 100 to 500 nm.