Molecular modeling studies and anti-TB activity of trisubstituted indolizine analogues; molecular docking and dynamic inputs

A series of trisubstituted indolizine analogues has been designed as a result of a fragment-based approach to target the inhibition of mycobacterial enoyl-acyl carrier protein reductase. Anti-tuberculosis (TB) screening of the characterized compounds by a resazurin microplate assay method revealed that ethyl group at second position of indolizine nucleus exhibited activity against susceptible and multidrug-resistant strains of Mycobacterium tuberculosis at concentration of 5.5 and 11.3 μg/mL, respectively. A molecular docking study was also conducted to evaluate the stability of the active compounds, and compound with ethyl substitution at second position of indolizine nucleus showed the highest free binding energy of ΔG ?24.11 (kcal/mol), a low clash score of 3.04, and high lipo score of ?13.33. Indolizine analog with ethyl substitution at second position demonstrated Molecular Mechanics/Generalized Born Surface Area (?23.85 kcal/mol). Two molecular dynamics studies were computed (100 ps and 50 ns) to calculate the relationship between the potential and kinetic energies of the active anti-TB compound with time and temperature. The discovery of this lead may have a positive impact on anti-TB drug discovery.     

Early responses of drought-resistant and -susceptible tomato plants subjected to water stress

Three-week-old seedlings of one drought-susceptible tomato cultivar (Lycopersicon esculentum cv. “New Yorker”) and two drought-resistant species of tomato (Solanum pennellii andLycopersicon chilense) were subjected to various degrees of PEG 8000-induced water stress from ?0.017 to ?1.0 MPa for a duration of 24 h so that their early responses to water stress could be compared. Such a comparison would determine if there was a relationship to root cytokinin levels following sudden induction of water stress in the drought-resistant species. Transpiration rates of leaves were monitored throughout the 24-h period, shoots were evaluated for leaf water potential (LWP), and roots were extracted for levels oft-zeatin riboside (t-ZR) and dihydrozeatin riboside (DHZR) using a monoclonal antibody enzyme immunoassay. Transpiration rates were evaluated gravimetrically by difference every 6 h up to 24 h. Transpiration rate decreased with increasing PEG levels and passage of time in all three species, measured at 6 and 12 h, logarithmically in the case of the twoLycopersicon species and linearly in the case ofSolanum. From 12–18 h (while plants were in darkness), transpiration rate was a function of the level of PEG only and not time in all three species. When light resumed from 18–24 h, only 5.pennellii showed no further decrease in transpiration rate over time with increasing PEG. Drought-susceptibleL. esculentum had a stronger linear decrease in LWP with increasing PEG 8000 concentration than the other two species.L. esculentum also had a higher initial transpiration rate than did either of the drought-resistant species. The two drought-resistant species showed less change in LWP with 5.pennellii having a small decrease andL. chilense having little change. OnlyS. pennellii exhibited a decrease in roott-ZR levels, which may imply a role for root cytokinin within the first 24-h exposure to water stress in this species.L. esculentum exhibited no change in roott-ZR. The levels oft-ZR inL. chilense were less than that ofL. esculentum but showed only a slight decrease with increasing PEG.S. pennellii andL. chilense, although both drought-resistant tomato species, showed different patterns of response with respect to pattern of decline in transpiration rate, LWP, and roott-ZR levels.     

Will an Unsupervised Self-Testing Strategy for HIV Work in Health Care Workers of South Africa? A Cross Sectional Pilot Feasibility Study

Background

In South Africa, stigma, discrimination, social visibility and fear of loss of confidentiality impede health facility-based HIV testing. With 50% of adults having ever tested for HIV in their lifetime, private, alternative testing options are urgently needed. Non-invasive, oral self-tests offer a potential for a confidential, unsupervised HIV self-testing option, but global data are limited.

Methods

A pilot cross-sectional study was conducted from January to June 2012 in health care workers based at the University of Cape Town, South Africa. An innovative, unsupervised, self-testing strategy was evaluated for feasibility; defined as completion of self-testing process (i.e., self test conduct, interpretation and linkage). An oral point-of-care HIV test, an Internet and paper-based self-test HIV applications, and mobile phones were synergized to create an unsupervised strategy. Self-tests were additionally confirmed with rapid tests on site and laboratory tests. Of 270 health care workers (18 years and above, of unknown HIV status approached), 251 consented for participation.

Findings

Overall, about 91% participants rated a positive experience with the strategy. Of 251 participants, 126 evaluated the Internet and 125 the paper-based application successfully; completion rate of 99.2%. All sero-positives were linked to treatment (completion rate:100% (95% CI, 66.0–100). About half of sero-negatives were offered counselling on mobile phones; completion rate: 44.6% (95% CI, 38.0–51.0). A majority of participants (78.1%) were females, aged 18–24 years (61.4%). Nine participants were found sero-positive after confirmatory tests (prevalence 3.6% 95% CI, 1.8–6.9). Six of nine positive self-tests were accurately interpreted; sensitivity: 66.7% (95% CI, 30.9–91.0); specificity:100% (95% CI, 98.1–100).

Interpretation

Our unsupervised self-testing strategy was feasible to operationalize in health care workers in South Africa. Linkages were successfully operationalized with mobile phones in all sero-positives and about half of the sero-negatives sought post-test counselling. Controlled trials and implementation research studies are needed before a scale-up is considered.     

Changes in fish assemblages following 10 years of protection in Tasmanian marine protected areas

Most studies examining effects of marine protected areas (MPAs) on fish assemblages are potentially confounded, either because they are once off comparisons between fished and unfished locations, or because they are snapshot studies over a fixed period. Here we compare long-term changes within fully protected Tasmanian marine reserves with changes at external reference sites on an annual basis over the first ten years of protection. The results highlight the importance of long-term datasets for differentiating changes occurring over differing time scales. Notable results include a statistically significant increase in abundance of Latridopsis forsteri and large fish (> 300 mm) when examined across all reserves relative to controls, and a 10-fold increase in the abundance of large fish and a doubling of per site species richness of large fish within the Tinderbox Marine Reserve relative to controls. Short-term resident species that recruit sporadically show very different patterns in reserves compared to those that recruit regularly and have long-term age-class storage. While several recent reviews have suggested size of MPAs and duration of protection has little influence on the extent of recovery, our results suggest this is not the case and that responses can be slow, complex and species-specific. The extent of localised fishing pressure appeared to have a substantial influence on the degree of change detected, potentially confounding meta-analyses of recovery rates in MPAs if overlooked as a relevant parameter.     

Major metabolic homocysteine-derivative, homocysteine thiolactone, exerts changes in pancreatic beta-cell glucose-sensing, cellular signal transduction and integrity

Homocysteine can be converted to its reactive thioester, homocysteine thiolactone. Cytotoxic properties of these amino thiols have been attributed to protein homocysteinylation, increased oxidative stress, DNA damage and apoptosis. This study used pancreatic BRIN-BD11 beta-cells to examine functional defects caused by acute and long-term exposure to homocysteine thiolactone in comparison with homocysteine. Acute and long-term exposure to both agents caused concentration-dependent inhibitions of glucose-induced insulin secretion while impairing the insulin-secretory responses to alanine, KCl, elevated Ca(2+), forskolin and PMA. Acute exposures also caused significant reduction in the amplitude of KCl-induced membrane depolarisation but no effects on changes of intracellular Ca(2+) induced by alanine or KCl. Cellular insulin content and DNA damage were not altered following culture, however, there were early signs of apoptosis consistent with impaired cellular integrity. In conclusion, exposure to homocysteine thiolactone, like homocysteine, induced beta-cell dysfunction and demise by mechanisms independent of changes in membrane potential and [Ca(2+)](i).     

Characterisation of membrane mimetics on a dual polarisation interferometer

Dual polarisation interferometry (DPI) has been used to characterise the formation of hybrid bilayer membranes (HBM) on a silicon-oxynitride surface. This technique allows the simultaneous determination of multiple physical properties of an HBM, as the HBM is being formed in a single experiment: mass, thickness in the z-direction (normal to the surface), tilt angle of the first layer and refractive index. Decanoic acid was covalently attached to an amine modified silicon-oxynitride sensor chip surface via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride condensation reaction. The decanoic acid layer was 0.92+/-0.12 nm thick, indicating a tilt angle of 57 degrees from surface normal, and possessed a mass of 1.05+/-0.10 ng mm(-2) and a refractive index (RI) of 1.450+/-0.020. Phospholipid vesicles made from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were injected over the fatty acid surface to form an HBM. The DPPC HBM was 4.32+/-0.68 nm thick, with a total mass of 3.18+/-0.60 ng mm(-2) and a RI of 1.404+/-0.007. The DMPC HBM was 2.12+/-0.34 nm thick, with a total mass of 2.25+/-0.51 ng mm(-2), and a RI of 1.435+/-0.007. DPI thus provides an insight into HBM formation and differences between the structural organisation of HBMs of different composition.     

Observations on the incidence and seasonal fluctuations of certain crustacean larvae in the plankton of the South-West Coast of India

The seasonal fluctuations in the incidence of planktonic organisms and the larval forms of certain crustaceans such as crabs, barnacles and post larvae of prawns in the plankton of the south-west coast of India have been followed for a period of three years from 1963. South-west monsoon period is the least productive period for zooplankton in this area. Brachyuran zoeae, post larvae of prawns and barnacle nauplii occur in the plankton throughout the year with distinct peaks for different groups. The zoeae ofUca annulipes occur in the plankton from September to May with a peak during November–December. The zoeae ofPortunus pelagicus are present in the plankton from September to June and their abundance is in February–March. The post larvae ofMetapenaeus affinis are found in the inshore plankton from November to June with the peak in March. The nauplii ofBalanus amphitrite communis occur in the plankton in all the months of the year, the peak incidence has been during November January. The zoeae ofU. annulipes are found to tolerate better the medium saline conditions. Of the ecological factors, salinity of the ambient water and the availability of planktonic food for the larvae seem to influence the seasonal fluctuations of these crustacean larvae in this locality.     

A comparative study of ricin and diphtheria toxin-antibody-conjugate kinetics on protein synthesis inactivation

Kinetic data on toxin and antibody-toxin-conjugate inactivation of protein synthesis have been used to assess the variables which affect the transport of these toxins into the cytosol compartment. First-order inactivation rate constants of protein synthesis (ki) are compared under conditions of known receptor occupancy. The effect of inclusion of toxin B chains, both homologous and heterologous, in antibody-toxin conjugates is observed, and factors which affect toxin lag periods are studied. The results show that the inclusion of B chains in conjugates increases ki values 3-10-fold, but only if the B chain is homologous with the A chain. In spite of the augmentation of antibody-toxin-conjugate ki values by homologous toxin B chain, these ki values are only 1/20 those observed with unmodified toxins on sensitive cells. A further difference noted between toxins and antibody-toxin conjugates is the presence of a dose-dependent lag when toxins, but not antibody-toxin conjugates, effect sensitive cell types. This lag period for ricin can be shortened by alkalinizing the cell medium. The kinetic data can be fit by assuming a processing step interposed between the binding of ricin to surface receptors and the interaction of the A chain with ribosomes which is first-order in toxin concentration and pH-dependent. The time constant of this event is reflected in the dose-dependent lag period. It is proposed that antibody-toxin conjugates do not participate in this processing event and therefore fail to achieve the high entry levels exhibited by unmodified toxins.