Exercise-induced stress response as an adaptive tolerance strategy

Prenatal exposure to fine particles and polycyclic aromatic hydrocarbons and birth outcomes: a two-pollutant approach

BACKGROUND

Previous epidemiologic studies have considered the effects of individual air pollutants on birth outcomes, whereas a multiple-pollutant approach is more relevant to public health policy.

OBJECTIVES

The present study compared the observed effect sizes of prenatal fine particulate matter (PM_2.5) and polycyclic aromatic hydrocarbons (PAH) (a component of PM_2.5) exposures on birth outcome deficits, assessed by the single vs. two-pollutant approaches.

METHODS

The study sample included 455 term infants born in Krakow to non-smoking mothers, among whom personal exposures to PM_2.5 and PAH were monitored in the second trimester of pregnancy. The exposure effect estimates (unstandardized and standardized regression coefficients) on birth outcomes were determined using multivariable linear regression models, accounting for relevant covariates.

RESULTS

In the single-pollutant approach, each pollutant was inversely associated with all birth outcomes. The effect size of prenatal PAH exposure on birth weight and length was twice that of PM_2.5, in terms of standardized coefficients. In the two-pollutant approach, the negative effect of PM_2.5 on birth weight and length, adjusted for PAH exposure, lost its significance. The standardized effect of PAH on birth weight was 10-fold stronger (β = -0.20, p = 0.004) than that estimated for PM_2.5 (β = -0.02, p = 0.757).

CONCLUSION

The results provide evidence that PAH had a greater impact on several measures of fetal development, especially birth weight, than PM_2.5. Though in the single-pollutant models PM_2.5 had a significant impact on birth outcomes, this effect appears to be mediated by PAH.

Exercise normalizes altered expression of proteins in the ventral hippocampus of rats subjected to maternal separation

Many studies have reported on the detrimental effects of early life adversity and the beneficial effects of exercise on brain function. However, the molecular mechanisms that underpin these various effects remain poorly understood. The advent of advanced proteomic analysis techniques has enabled simultaneous measurement of protein expression in a wide range of biological systems. We therefore used iTRAQ proteomic analysis of protein expression to determine whether exercise counteracts the detrimental effects of early life adversity in the form of maternal separation on protein expression in the brain. Rat pups were subjected to maternal separation from postnatal day 2 to 14 for 3 h day(-1) or normally reared. At 40 days of age, half of the rats in each group (maternal separation and normally reared) were allowed to exercise voluntarily (access to a running wheel) for 6 weeks and the remainder kept as sedentary control animals. At 83 days of age, rats were killed and the ventral hippocampus was dissected for quantitative proteomic (iTRAQ) analysis. The iTRAQ proteomic analysis identified several proteins that had been altered by maternal separation, including proteins involved in neuronal structure, metabolism, signalling, anti-oxidative stress and neurotransmission, and that many of these proteins were restored to normal by subsequent exposure to voluntary exercise in adolescence. Our data show that a broad range of proteins play a role in the complex consequences of adversity and exercise.

Mimetics of hormetic agents: stress-resistance triggers

Mimetics of hormetic agents offer a novel approach to adjust dose to minimize the risk of toxic response, and maximize the benefit of induction of at least partial physiological conditioning. Nature selected and preserved those organisms and triggers that promote tolerance to stress. The induced tolerance can serve to resist that challenge and can repair previous age, disease, and trauma damage as well to provide a more youthful response to other stresses. The associated physiological conditioning may include youthful restoration of DNA repair, resistance to oxidizing pollutants, protein structure and function repair, improved immunity, tissue remodeling, adjustments in central and peripheral nervous systems, and altered metabolism. By elucidating common pathways activated by hormetic agent's mimetics, new strategies for intervention in aging, disease, and trauma emerge. Intervention potential in cancer, diabetes, age-related diseases, infectious diseases, cardiovascular diseases, and Alzheimer's disease are possible. Some hormetic mimetics exist in pathways in primitive organisms and are active or latent in humans. Peptides, oligonucleotides, and hormones are among the mimetics that activate latent resistance to radiation, physical endurance, strength, and immunity to physiological condition tolerance to stress. Co-activators may be required for expression of the desired physiological conditioning health and rejuvenation benefits.

Air pollution and effects on reproductive-system functions globally with particular emphasis on the Brazilian population

In recent years, numerous studies showed that exposure to environmental air pollutants affected reproductive functions and, in particular, produced adverse effects on pregnancy outcomes, fertility, and fetal health. Epidemiological studies demonstrated that exposure to ambient levels of air pollutants are associated with low birth weight, intrauterine growth retardation, prematurity, neonatal death, and decreased fertility in males. Experimental animal data supported these findings and indicated that female fertility was also disturbed. Although there are various mechanisms of action suggested to show the manner in which air pollutants alter pregnancy and the reproductive systems in both genders, further studies are needed to correlate causal relationships. This information would serve to better understand the underlying physiologic changes in the reproductive system induced by exposure to air pollutants and possibly establish a link between the dose and response of individual or mixture of air pollutants.

Epidemiologic evidence of relationships between reproductive and child health outcomes and environmental chemical contaminants

This review summarizes the level of epidemiologic evidence for relationships between prenatal and/or early life exposure to environmental chemical contaminants and fetal, child, and adult health. Discussion focuses on fetal loss, intrauterine growth restriction, preterm birth, birth defects, respiratory and other childhood diseases, neuropsychological deficits, premature or delayed sexual maturation, and certain adult cancers linked to fetal or childhood exposures. Environmental exposures considered here include chemical toxicants in air, water, soil/house dust and foods (including human breast milk), and consumer products. Reports reviewed here included original epidemiologic studies (with at least basic descriptions of methods and results), literature reviews, expert group reports, meta-analyses, and pooled analyses. Levels of evidence for causal relationships were categorized as sufficient, limited, or inadequate according to predefined criteria. There was sufficient epidemiological evidence for causal relationships between several adverse pregnancy or child health outcomes and prenatal or childhood exposure to environmental chemical contaminants. These included prenatal high-level methylmercury (CH(3)Hg) exposure (delayed developmental milestones and cognitive, motor, auditory, and visual deficits), high-level prenatal exposure to polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and related toxicants (neonatal tooth abnormalities, cognitive and motor deficits), maternal active smoking (delayed conception, preterm birth, fetal growth deficit [FGD] and sudden infant death syndrome [SIDS]) and prenatal environmental tobacco smoke (ETS) exposure (preterm birth), low-level childhood lead exposure (cognitive deficits and renal tubular damage), high-level childhood CH(3)Hg exposure (visual deficits), high-level childhood exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (chloracne), childhood ETS exposure (SIDS, new-onset asthma, increased asthma severity, lung and middle ear infections, and adult breast and lung cancer), childhood exposure to biomass smoke (lung infections), and childhood exposure to outdoor air pollutants (increased asthma severity). Evidence for some proven relationships came from investigation of relatively small numbers of children with high-dose prenatal or early childhood exposures, e.g., CH(3)Hg poisoning episodes in Japan and Iraq. In contrast, consensus on a causal relationship between incident asthma and ETS exposure came only recently after many studies and prolonged debate. There were many relationships supported by limited epidemiologic evidence, ranging from several studies with fairly consistent findings and evidence of dose-response relationships to those where 20 or more studies provided inconsistent or otherwise less than convincing evidence of an association. The latter included childhood cancer and parental or childhood exposures to pesticides. In most cases, relationships supported by inadequate epidemiologic evidence reflect scarcity of evidence as opposed to strong evidence of no effect. This summary points to three main needs: (1) Where relationships between child health and environmental exposures are supported by sufficient evidence of causal relationships, there is a need for (a) policies and programs to minimize population exposures and (b) population-based biomonitoring to track exposure levels, i.e., through ongoing or periodic surveys with measurements of contaminant levels in blood, urine and other samples. (2) For relationships supported by limited evidence, there is a need for targeted research and policy options ranging from ongoing evaluation of evidence to proactive actions. (3) There is a great need for population-based, multidisciplinary and collaborative research on the many relationships supported by inadequate evidence, as these represent major knowledge gaps. Expert groups faced with evaluating epidemiologic evidence of potential causal relationships repeatedly encounter problems in summarizing the available data. A major driver for undertaking such summaries is the need to compensate for the limited sample sizes of individual epidemiologic studies. Sample size limitations are major obstacles to exploration of prenatal, paternal, and childhood exposures during specific time windows, exposure intensity, exposure-exposure or exposure-gene interactions, and relatively rare health outcomes such as childhood cancer. Such research needs call for investments in research infrastructure, including human resources and methods development (standardized protocols, biomarker research, validated exposure metrics, reference analytic laboratories). These are needed to generate research findings that can be compared and subjected to pooled analyses aimed at knowledge synthesis.

Low-dose-radiation stimulated natural chemical and biological protection against lung cancer

Research is being conducted world-wide related to chemoprevention of future lung cancer among smokers. The fact that low doses and dose rates of some sparsely ionizing forms of radiation (e.g., x rays, gamma rays, and beta radiation) stimulate transient natural chemical and biological protection against cancer in high-risk individuals is little known. The cancer preventative properties relate to radiation adaptive response (radiation hormesis) and involve stimulated protective biological signaling (a mild stress response). The biological processes associated with the protective signaling are now better understood and include: increased availability of efficient DNA double-strand break repair (p53-related and in competition with normal apoptosis), stimulated auxiliary apoptosis of aberrant cells (presumed p53-independent), and stimulated protective immune functions. This system of low-dose radiation activated natural protection (ANP) requires an individual-specific threshold level of mild stress and when invoked can efficiently prevent the occurrence of cancers as well as other genomic-instability-associated diseases. In this paper, low, essentially harmless doses of gamma rays spread over an extended period are shown via use of a biological-based, hormetic relative risk (HRR) model to be highly efficient in preventing lung cancer induction by alpha radiation from inhaled plutonium.

Toward an economic analysis of the environmental burden of disease among Canadian children

There have been calls for increased investments in research in Canada to determine the extent of exposure and the associated health effects of environmental risks to child health. When allocating scare public health resources, decision makers often rely on cost-benefit analysis to determine whether specific expenditures will yield significant economic benefits by reducing adverse health outcomes. This article describes the elements required for an economic analysis of the environmental burden of disease among Canadian children. Such analysis would require reviewing the strength of the association between environmental exposures and specific adverse pregnancy outcomes and childhood diseases. Second, it would determine the prevalence of childhood diseases and conditions in order to estimate the total economic and social costs associated with the overall burden of childhood diseases in Canada. The next step is to determine how much of the overall burden of disease among Canadian children can be attributed to environmental exposures. Recent environmental burden of disease analyses in other jurisdictions have led to advancement in methodologies that could support this work in Canada. Finally, the economic and social costs attributable to the environmental burden of childhood diseases in Canada could be estimated. Estimates of the economic costs of environmentally related diseases can then be used to determine the appropriate level of investments in scientific research. This article argues for initial investments in establishing a biomonitoring program of children's and pregnant women's exposure to environmental chemicals, as well as a Canadian longitudinal cohort study on the environmental influences on child health and development.

2-D PAGE analysis of pesticide-induced stress proteins of E. coli

Logarithmically growing batch cultures of Escherichia coli were exposed to sublethal concentrations of pyrethroid and carbamate pesticides of four different technical grades. This induced 17-20 stress proteins, as observed using two-dimensional polyacrylamide gel electrophoresis. An E. coli culture growing exponentially in Luria Bertani medium (cell density approximately 2.3x10(9) cells/ml) was exposed to predetermined sublethal doses of individual pesticides. The cells were harvested after 30 minutes of induction and the stress response was developed in fresh LB medium for three hours under the same growth conditions. Cell pellets were obtained and stored in sonication buffer. Two-dimensional polyacrylamide gel electrophoresis was performed to resolve the proteins. Visualization of the protein spots by rapid silver staining showed 17-20 stress proteins which were absent in the standard protein profile of E. coli. On average 29% of these stress proteins were unique to the pollutant, while the remaining stress proteins overlapped with those of other pesticides. The iso-electric points (PIs) and molecular weights of the proteins were determined by comparing with protein markers with known PIs and molecular weights. Furthermore, upon comparing the pesticide-induced proteins within the same class and between the two different classes (pyrethroid and carbamate), it was apparent that the general nature of the stress remained the same throughout, which indirectly proved that the gene or set of genes responsible for stress expression are also the same, irrespective of the chemical nature of the substituents of the pesticides.

Effect of concentric or eccentric weight training on the expression of heat shock proteins in m. biceps brachii of very well trained males

Increased HSP expression in response to acute exercise is well documented in animal studies, and there is growing evidence that similar responses occur in man. In general, many human exercise studies have investigated the HSP response to low force continuous activity, while the knowledge about the HSP response to high force intermittent type of activity, like weight training, is so far sparse. In addition, most studies have used untrained subjects, and a common observation is that acute low force continuous activity in untrained individuals increases the HSP expression in these individuals. The main scope of this study was to investigate the HSP response in very well trained males subjected to longitudinal high intensity exercise, and if this response was dependent on exercise modality [i.e. eccentric (ECC) or concentric (CON) contractions]. Very well trained males performed progressive strength training consisting of either high force ECC or high force CON elbow flexions 2-3 times a week for 12 weeks. Compared with pre-exercise levels, HSP72 expression decreased by 46.1% (P<0.05) after CON contractions. GRP75 expression was unchanged after ECC or CON contractions, while ubiquitin expression decreased by 19.9% (P<0.02) after ECC contractions. These findings imply that chronic, intensive exercise may attenuate the HSP response in well-trained males.

Particulate air pollution and fetal health: a systematic review of the epidemiologic evidence

BACKGROUND

Research on the potential impact of air pollution on the health of adults and children has grown rapidly over the last decade. Recent studies have suggested that air pollution could also be associated with adverse effects on the developing fetus. This systematic review evaluates the current level of epidemiologic evidence on the association between ambient particulate air pollution and fetal health outcomes. We also suggest further research questions.

METHODS

Using database searches and other approaches, we identified relevant publications published between 1966 and 2001 in English. Articles were included if they reported original data on birthweight, gestational age at delivery, or stillbirth related to directly measured nonaccidental exposure to particulate matter.

RESULTS

Twelve studies met the inclusion criteria. There was little consistency in the evidence linking particulate air pollution and fetal outcomes. Many studies had methodologic weaknesses in their design and adjustment for confounding factors. Even in well-designed studies, the reported magnitude of the effects was small and inconsistently associated with exposure at specific stages of pregnancy.

CONCLUSIONS

The currently available evidence is compatible with either a small adverse effect of particulate air pollution on fetal growth and duration of pregnancy or with no effect. Further research should be directed toward clarifying and quantifying these possible effects and generating testable hypotheses on plausible biologic mechanisms.

Estimating the distribution of lag in the effect of short-term exposures and interventions: adaptation of a non-parametric regression spline model

Information on the distribution of lag duration between exposure or intervention and the subsequent changes in risk can help in assessing the impact of exposure, predicting cost-effectiveness of intervention, and understanding the underlying biological mechanisms. Previous approaches focused more on optimizing the strength of the exposure-disease association than on directly estimating lag duration. We propose an alternative approach applicable to the analysis of the lagged effects of binary exposure variables. The density function of the distribution of lags is estimated based on flexible modelling of changes in hazard ratio of exposed versus unexposed subjects. The methodology is evaluated in a simulation study and is applied to the Framingham data to investigate the lagged effect of smoking cessation on coronary heart disease risk.

Air pollution and emergency room visits due to chronic lower respiratory diseases in the elderly: an ecological time-series study in São Paulo, Brazil

The objective of this study was to investigate the effect of daily air pollution levels (carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter with an aerodynamic profile < or = 10 microns) on morbidity by using the daily number of emergency room visits due to chronic lower respiratory disease (CLRD) in people older than 64 years of age in the city of São Paulo, Brazil, from 1996 to 1998. Generalized additive Poisson regression models adjusted for long-time trend and weather (nonparametric functions), weekdays (dummy variable), and daily number of nonrespiratory admissions were adopted. Ozone and sulfur dioxide were the pollutants statistically associated with CLRD visits. Interquartile range increases in the 6-day moving average of sulfur dioxide (11.82 micrograms/m3) and in the 4-day moving average of ozone(35.87 micrograms/m3) increased CLRD emergency room visits in 18% and 14%, respectively. These results reinforce the idea that air pollution may promote adverse health effects in the elderly.

Low frequency noise and whole-body vibration cause increased levels of sister chromatid exchange in splenocytes of exposed mice

Chronic exposure to low frequency (LF) noise and whole-body vibration (WBV) induces both physiological and psychological alterations in man. Recently, we have shown that long-term occupational exposure to LF noise and WBV produces genotoxic effects in man expressed as an increase in sister chromatid exchange (SCE) levels in lymphocytes. The objectives of the present study were to investigate whether the observed effect could be reproduced in a murine model and, if so, which of the agents, LF noise alone or in combination with WBV, would be instrumental in the SCE induction. SCEs were analyzed in spleen lymphocytes of mice exposed to LF noise alone and in combination with WBV for 300 and 600 hr. An effect at the cell cycle kinetics level was also investigated. The results revealed significant increases in the mean SCE number per cell and in the proportion of cells with high frequency of SCEs (HFCs) in lymphocytes of mice submitted to combined noise and WBV over controls. No significant differences were found between single noise-exposed and control mice. A cell cycle delay was observed exclusively in the noise and WBV exposure groups. In conclusion, we demonstrated that, as in exposed workers, prolonged exposure to the combination of LF noise and WBV determines an increase in SCE level in mice while LF noise alone is not effective in SCE induction.

Effect of air pollution on preterm birth among children born in Southern California between 1989 and 1993

We evaluated the effect of air pollution exposure during pregnancy on the occurrence of preterm birth in a cohort of 97,518 neonates born in Southern California. We used measurements of carbon monoxide (CO), nitrogen dioxide, ozone, and particulate matter less than 10 microm (PM10) collected at 17 air-quality-monitoring stations to create average exposure estimates for periods of pregnancy. We calculated crude and adjusted risk ratios (RRs) for premature birth by period-specific ambient pollution levels. We observed a 20% increase in preterm birth per 50-microg increase in ambient PM10 levels averaged over 6 weeks before birth [RRcrude = 1.20; 95% confidence interval (CI) = 1.09-1.33] and a 16% increase when averaging over the first month of pregnancy (RRcrude = 1.16; 95% CI = 1.06-1.26). PM10 effects showed no regional pattern. CO exposure 6 weeks before birth consistently exhibited an effect only for the inland regions (RRcrude = 1.13; 95% CI = 1.08-1.18 per 3 parts per million), and during the first month of pregnancy, the effect was weak for all stations (RRcrude = 1.04; 95% CI = 1.01-1.09 per 3 parts per million). Exposure to increased levels of ambient PM10 and possibly CO during pregnancy may contribute to the occurrence of preterm births in Southern California.