Detection of cellular responses to toxicants by dielectrophoresis

The dielectrophoretic (DEP) crossover method has been applied to the detection of cell responses to toxicants. Time and dose responses of the human cultured leukemia (HL-60) line were measured for paraquat, styrene oxide (SO), N-nitroso-N-methylurea (NMU) and puromycin. These toxicants were chosen because of their different predominant mechanisms of action, namely membrane free radical attack, simultaneous membrane and nucleic acid attack, nucleic acid alkylation, and protein synthesis inhibition, respectively. For all treatments, the specific membrane capacitance (C(mem)) of the cells decreased while the specific membrane conductance (G(mem)) increased in dose- and time-dependent manners. The DEP responses correlated sensitively with alterations in cell surface morphology, especially folds, microvilli, and blebs, observed by scanning electron microscopy. The DEP method was more sensitive to agents that had a direct action on the membrane than to agents for which membrane alterations were secondary. The responses to paraquat and SO, which directly damaged the cell membrane, could be detected 15 min after exposure, while those for puromycin and NMU, which acted on intracellular targets, could be detected after 30 min. The detection times and dose sensitivity results showed that the DEP method is much faster and more sensitive than conventional cell and higher organism viability testing techniques. The feasibility of producing small instruments for toxicity detection and screening based on cellular dielectric responses is discussed.     

Determination and variation of three active diterpenoids in Andrographis paniculata (Burm.f.) Nees

Simple and rapid methods have been developed for the extraction and simultaneous determination of the three active diterpenoids, andrographolide (AP1), 14-deoxy-11,12-didehydroandrographolide (AP3) and neoandrographolide (AP4), from various samples of Andrographis paniculata (Burm.f.) Nees. Methanol extracts from the dried leaves, stems and crude products were analysed by isocratic HPLC using a methanol and water mobile phase with monitoring at 220 nm. There was a large variation of the three active diterpenoids in different A. paniculata products obtained from Thai markets. The results indicated that the amounts of these active compounds consumed, based on the recommended daily doses, from materials obtained from the different suppliers will be different. In addition, the stability of these three active compounds was also examined in dry herbs stored at room temperature. The results showed that andrographolide was more stable than the others. In contrast, the content of 14-deoxy-11,12-didehydroandrographolide increased and the neoandrographolide content fluctuated during storage time. The combination of different levels of these compounds in the source materials and the changes during storage could have a significant effect on the efficacy of this traditional herbal medicine in clinical treatment.     

Comparison of Contact Patterns Relevant for Transmission of Respiratory Pathogens in Thailand and the Netherlands Using Respondent-Driven Sampling

Understanding infection dynamics of respiratory diseases requires the identification and quantification of behavioural, social and environmental factors that permit the transmission of these infections between humans. Little empirical information is available about contact patterns within real-world social networks, let alone on differences in these contact networks between populations that differ considerably on a socio-cultural level. Here we compared contact network data that were collected in the Netherlands and Thailand using a similar online respondent-driven method. By asking participants to recruit contact persons we studied network links relevant for the transmission of respiratory infections. We studied correlations between recruiter and recruited contacts to investigate mixing patterns in the observed social network components. In both countries, mixing patterns were assortative by demographic variables and random by total numbers of contacts. However, in Thailand participants reported overall more contacts which resulted in higher effective contact rates. Our findings provide new insights on numbers of contacts and mixing patterns in two different populations. These data could be used to improve parameterisation of mathematical models used to design control strategies. Although the spread of infections through populations depends on more factors, found similarities suggest that spread may be similar in the Netherlands and Thailand.