Hormonal Therapy and Risk of Breast Cancer in Mexican Women

The use of hormonal therapies, including hormonal contraceptives (HC) and postmenopausal hormone replacement therapy (HRT) have been shown to influence breast cancer (BC) risk. However, the variations of these effects among populations and ethnic groups are not completely documented, especially among Hispanic women. We evaluated the association between HC and premenopausal BC risk, and between HRT and postmenopausal BC risk in Mexican women. Data from a Mexican multi-center population-based case–control study ofwomen aged 35 to 69 years were analysed. A total of 1000 cases and 1074 matched controls were recruited between 2004 and 2007. Information on hormonal therapy was collected through a structured questionnaire. Results were analysed using conditional logistic regression models. Overall, HC were used by 422/891 (47.3%) premenopausal women and HRT was used by 220/1117 (19.7%) postmenopausal women. For HC, odds ratios (ORs) for BC were 1.11 (95% confidence interval (CI): 0.82, 1.49) for current users and 1.68 (95% CI: 0.67, 4.21) for ever-users. No clear effect of duration of use was observed. For HRT, the OR for BC was significantly increased in ever users (OR: 1.45; 95% CI: 1.01, 2.08). A non-significant increased risk was observed for combined estrogen/progestin, (OR =  1.85; 95% CI: 0.84, 4.07) whereas no effect was observed for the use of estrogen alone (OR = 1.14; 95% CI: 0.68, 1.91). Our results indicate that, HC had a non-significant effect on the risk of pre-menopausal BC, but suggested that injected contraceptives may slightly increase the risk, whereas HRT had a significant effect on post-menopausal BC in this population. This study provides new information about the effects of HC and HRT on BC risk in a Mexican population, which may be of relevance for the population of Latin America as a whole.     

Influence of Cardiac Decentralization on Cardioprotection

The role of cardiac nerves on development of myocardial tissue injury after acute coronary occlusion remains controversial. We investigated whether acute cardiac decentralization (surgical) modulates coronary flow reserve and myocardial protection in preconditioned dogs subject to ischemia-reperfusion. Experiments were conducted on four groups of anesthetised, open-chest dogs (n = 32): 1- controls (CTR, intact cardiac nerves), 2- ischemic preconditioning (PC; 4 cycles of 5-min IR), 3- cardiac decentralization (CD) and 4- CD+PC; all dogs underwent 60-min coronary occlusion and 180-min reperfusion. Coronary blood flow and reactive hyperemic responses were assessed using a blood volume flow probe. Infarct size (tetrazolium staining) was related to anatomic area at risk and coronary collateral blood flow (microspheres) in the anatomic area at risk. Post-ischemic reactive hyperemia and repayment-to-debt ratio responses were significantly reduced for all experimental groups; however, arterial perfusion pressure was not affected. Infarct size was reduced in CD dogs (18.6±4.3; p = 0.001, data are mean±1SD) compared to 25.2±5.5% in CTR dogs and was less in PC dogs as expected (13.5±3.2 vs. 25.2±5.5%; p = 0.001); after acute CD, PC protection was conserved (11.6±3.4 vs. 18.6±4.3%; p = 0.02). In conclusion, our findings provide strong evidence that myocardial protection against ischemic injury can be preserved independent of extrinsic cardiac nerve inputs.     

Low-oxygen and knock-out serum maintain stemness in human retinal progenitor cells

Using stem and progenitor cells to treat retinal disorders holds great promise. Using defined culture conditions to maintain the desires phenotype is of utmost clinical importance. We cultured human retinal progenitor cells (hRPCs) in different conditions: such as normoxia (20% oxygen), and hypoxia (5% oxygen) with and without knock-out serum replacement (KOSR) to evaluate its effect on these cells. KOSR is known nutrient supplement often used to replace bovine serum for culturing embryonic or pluripotent stem cells, especially those destined for clinical applications. The purpose of this study was to identify the impact of different environmental and chemical cues to determine if this alters the fate of these cells. Our results indicate that cells cultured with or without KOSR do not show significant differences in viability, but that the oxygen tension can significantly change their viability (higher in hypoxia than normoxia). However, cells with KOSR in hypoxia condition expressed significantly higher stemness markers such as C-myc and Oct4 (31.20% and 13.44% respectively) in comparison to hRPCs cultured in KOSR at normoxia (12.07% and 4.05%). Furthermore, levels of markers for retinal commitment such as rhodopsin were significantly lower in the KOSR supplemented cells in hypoxia culture compared to normoxia. KOSR is known to improve proliferation and maintain stemness of embryonic cells and our experiments suggest that hRPCs maintain their proliferation and stemness characteristics in hypoxia with KOSR supplement. Normoxia, however, results in mature cell marker expression, suggesting a profound effect of oxygen tension on these cells.

     

A cell–cell repulsion model on a hyperbolic Keller–Segel equation

Journal of Mathematical Biology - In this work, we discuss a cell–cell repulsion model based on a hyperbolic Keller–Segel equation with two populations, which aims at describing the...     

A unifying conceptual model for the environmental responses of isoprene emissions from plants

Background and Aims

Isoprene is the most important volatile organic compound emitted by land plants in terms of abundance and environmental effects. Controls on isoprene emission rates include light, temperature, water supply and CO₂ concentration. A need to quantify these controls has long been recognized. There are already models that give realistic results, but they are complex, highly empirical and require separate responses to different drivers. This study sets out to find a simpler, unifying principle.

Methods

A simple model is presented based on the idea of balancing demands for reducing power (derived from photosynthetic electron transport) in primary metabolism versus the secondary pathway that leads to the synthesis of isoprene. This model''s ability to account for key features in a variety of experimental data sets is assessed.

Key results

The model simultaneously predicts the fundamental responses observed in short-term experiments, namely: (1) the decoupling between carbon assimilation and isoprene emission; (2) a continued increase in isoprene emission with photosynthetically active radiation (PAR) at high PAR, after carbon assimilation has saturated; (3) a maximum of isoprene emission at low internal CO₂ concentration (c_i) and an asymptotic decline thereafter with increasing c_i; (4) maintenance of high isoprene emissions when carbon assimilation is restricted by drought; and (5) a temperature optimum higher than that of photosynthesis, but lower than that of isoprene synthase activity.

Conclusions

A simple model was used to test the hypothesis that reducing power available to the synthesis pathway for isoprene varies according to the extent to which the needs of carbon assimilation are satisfied. Despite its simplicity the model explains much in terms of the observed response of isoprene to external drivers as well as the observed decoupling between carbon assimilation and isoprene emission. The concept has the potential to improve global-scale modelling of vegetation isoprene emission.