Interaction of low-molecular-weight chitosan with mimic membrane studied by electrochemical methods and surface plasmon resonance

Chitosan has shown its potential as a non-viral gene carrier and an adsorption enhancer for subsequent drug delivery to cells. These results showed that chitosan acted as a membrane perturbant. However, there is currently a lack of direct experimental evidence of this membrane perturbance effect, especially for chitosans with low molecular weight (LMW). In this report, the interaction between a lipid (didodecyl dimethylammonium bromide; DDAB) bilayer and chitosan with molecular weight (MW) of 4200 Da was studied with cyclic voltammetry (CV), electrochemical impedance spectroscopy and surface plasmon resonance (SPR). A lipid bilayer was formed by-fusion of oppositely charged lipid vesicles on a mercaptopropionic acid (MPA)-modified gold surface to mimic a cell membrane. The results showed that the LMW chitosan could disrupt the lipid bilayer, and the effect seemed,to be in a concentration-dependent manner.

Seasonal changes in weight and body composition of yak grazing on alpine-meadow grassland in the Qinghai-Tibetan plateau of China

Forty-five male yaks (born April 2001) were studied to determine how seasonal changes on the Qinghai-Tibetan plateau affected BW and body composition. Thirty yaks were weighed monthly from birth to 26 mo of age to determine seasonal changes in BW. The remaining 15 yaks were allocated randomly to five groups (three yaks per group), designated for slaughter at 13, 15, 18, 22, and 25 mo to measure seasonal effects on body chemical composition. All yaks were grazed on the alpine-meadow grassland of the plateau without any supplementation. All BW and body composition data were calculated on an individual basis. Body weight and body composition data were both compared across seven growth periods spanning 2 yr and defined by season. From April (birth) to December 2001 of the first growing season, yak BW increased (P < 0.01); however, during the subsequent cold season (December 2001 to May 2002), BW decreased (P < 0.01). The second growing season ran from May 2002 (13 mo of age) to October 2002 (18 mo of age), and the second live weight-loss season ran from October 2002 until May 2003. The weight loss experienced by yaks during the first weight loss season was 25.64% of the total weight gain in the first growing season. The weight loss experienced by yaks during the second weight-loss season was 29.73% of the total weight gain in the second growing season. Energy retention in the second growing season was 291.07 MJ, 50.8% of which was consumed during the subsequent cold season. Energy accumulation in the summer (from May to July) and fall (from July to October) of the second growing season did not differ (5.01 and 6.30 MJ/kg of EBW gain, respectively; P = 0.63). The energy mobilized during the second winter (from October 2002 to February 2003) was 16.49 MJ/kg of EBW, and in the second spring (from February to May 2003), it was 9.06 MJ/kg of EBW. These data suggest that the decrease in grazing yak BW during the first cold season is much less than during the second cold season, and that the energy content per unit of BW mobilized is greater (P = 0.02) in winter than in spring. Results from this study demonstrate highly efficient compensatory growth in grazing yaks following the first weight loss period during the first cold season. This benefit could be exploited by herders to improve yak production. Yaks may have developed a type of self-protection mechanism to overcome the long cold seasons in the Qinghai-Tibetan plateau.