Discovery of Kinetic Trapping of Poloxamers inside Liposomes via Thermal Treatment.

Poloxamers, a class of biocompatible, commercially available amphiphilic block polymers (ABPs) comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks, interact with phospholipid bilayers, resulting in altered mechanical and surface properties. These block copolymers are useful in a variety of applications including therapeutics for Duchenne muscular dystrophy, as cell membrane stabilizers, and for drug delivery, as liposome surface modifying agents. Hydrogen bonding between water and oxygen atoms in PEO and PPO units results in thermoresponsive behavior because the bound water shell around both blocks dehydrates as the temperature increases. This motivated an investigation of poloxamer-lipid bilayer interactions as a function of temperature and thermal history. In this study, we applied pulsed-field-gradient NMR spectroscopy to measure the fraction of chains bound to 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) liposomes between 10 and 50 °C. We measured an (11 ± 3)-fold increase in binding affinity at 37 °C relative to 27 °C. Moreover, following incubation at 37 °C, it takes weeks for the system to re-equilibrate at 25 °C. Such slow desorption kinetics suggests that at elevated temperatures polymer chains can pass through the bilayer and access the interior of the liposomes, a mechanism that is inaccessible at lower temperatures. We propose a molecular mechanism to explain this effect, which could have important ramifications on the cellular distribution of ABPs and could be exploited to modulate the mechanical and surface properties of liposomes and cell membranes.

Uptake of HIV testing among aging adults in Agincourt, South Africa: perception of community, social network, and individual characteristics.

This cross-sectional study examined the impact of perception of community, social network and individual variables on the likelihood of voluntary HIV testing of people 40 years and older living in Agincourt, South Africa. The data came from Health and Aging in Africa: A Longitudinal Study of an INDEPTH Community in SA (HAALSI) Cohort from Agincourt. We applied three logistic regression models. Results showed that voluntary uptake of HIV testing was significantly associated with two network factors, namely friendships within the network and frequency of fighting in the network. At the community level, attachment to place was significantly associated with voluntary testing, while at the individual level, education, sexual behaviour, employment and age were significantly associated with the voluntary uptake of HIV testing. The implications of these findings are that age-appropriate interventions must be devised to sensitise older people in Agincourt about HIV risks. Also, leadership at the community level and in social networks must encourage members to consider voluntary testing for their own and community interests.

Priorities and Indicators for Economic Evaluation of Built Environment Interventions to Promote Physical Activity.

BACKGROUND: Built environment approaches to promoting physical activity can provide economic value to communities. How best to assess this value is uncertain. This study engaged experts to identify a set of key economic indicators useful for evaluation, research, and public health practice. METHODS: Using a modified Delphi process, a multidisciplinary group of experts participated in (1) one of 5 discussion groups (n = 21 experts), (2) a 2-day facilitated workshop (n = 19 experts), and/or (3) online surveys (n = 16 experts). RESULTS: Experts identified 73 economic indicators, then used a 5-point scale to rate them on 3 properties: measurement quality, feasibility of use by a community, and influence on community decision making. Twenty-four indicators were highly rated (≥3.9 on all properties). The 10 highest-rated "key" indicators were walkability score, residential vacancy rate, housing affordability, property tax revenue, retail sales per square foot, number of small businesses, vehicle miles traveled per capita, employment, air quality, and life expectancy. CONCLUSION: This study identified key economic indicators that could characterize the economic value of built environment approaches to promoting physical activity. Additional work could demonstrate the validity, feasibility, and usefulness of these key indicators, in particular to inform decisions about community design.