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Friday, January 9, 2015

The gut microbiota and inflammatory non-communicable diseases: Associations and potentials for gut microbiota therapies

The health of our modern society is being threatened by a plethora of chronic inflammatory non-communicable diseases (NCDs) which share in common, an underlying low-grade inflammation. These include early onset NCDs such as allergy, asthma and some autoimmune diseases and later onset NCDs including cardiovascular disease (CVD), metabolic disease and neurodegenerative disorders. While inflammation and the pathways to disease are multifactorial, the altered gut colonization patterns associated with declining microbial diversity is a central theme, and increasingly implicated in the physiological, immunological and metabolic dysregulation seen in many NCDs. Upon review of the current literature, West et al discuss the relationships between gut colonization and inflammatory NCDs, and gut microbiota modulation strategies for their treatment and prevention (J Allergy Clin Immunol 2015; 135: 3-13).

The critical role of the gut microbiota in immune development has been well documented in germ free animal models, demonstrating the failure of normal maturation and, in particular, failure of the systemic immune regulatory networks that result in both allergic and autoimmune phenomena. Data from several animal models have formed a basis to further explore the role of gut microbiota in early programming of host responses in humans. Collectively, recent literature suggests that the imprinting of human gut microbiota may commence already in utero and is then further shaped by postnatal exposures such as cesarean or vaginal delivery, antibiotics to the mother or infant, breastfeeding, and introduction to solid foods.

Culture independent DNA-based studies have demonstrated associations between reduced gut microbiota diversity and early onset NCDs including atopy, eczema, and asthma. Furthermore, inflammatory bowel disease (IBD), celiac disease, and type 1 diabetes have been shown to be associated with dysbiosis. It is also suggested that the early microbial environment drives more sustained predisposition to low-grade inflammation into adulthood and the propensity for later onset NCDs. Aberrations in the gut microbiota may also have implications for obesity-associated NCDs.

The most widely used approach for treatment and prevention of NCDs has been to administer probiotics. For example, specific probiotics promote favorable intestinal colonization and their fermented products have anti-inflammatory, immunomodulatory, and metabolic effects, although the effects are variable when evaluated in clinical trials. Fecal microbiota transplantation (FMT) is an emerging therapy that has been successful in the treatment of Clostridium difficile infection and possibly IBD. While much remains unknown, multidisciplinary and integrative approaches may ultimately lead to improved strategies to overcome the disease epidemic of modern civilizations. 

Question for the authors:
Most treatment and prevention research focuses on early development and manipulation of the gut microbiota. What is known about treatment of allergic and autoimmune diseases in adults through diet and lifestyle modifications that directly alter the gut microbiota composition?

Most treatment and prevention research focuses on early development and manipulation of the gut microbiota. What is known about treatment of allergic and autoimmune diseases in adults through diet and lifestyle modifications that directly alter the gut microbiota composition?

There is clear evidence that diet impacts gut microbiota composition, however intervention studies aiming at modulating the gut microbiota in adults with allergic or autoimmune disease are scarce.  Dietary patterns such as the Mediterranean diet have been associated with increased asthma control in cross-sectional studies although the effect on gut microbiota composition was not studied. However, there is some support that a Mediterranean-style diet may influence gut microbiota.  In a small pilot study, Marlow et al 2013, examined the effects of a Mediterranean-influenced dietary intervention on inflammatory biomarkers and gut microbiota in eight Crohn’s disease patients. This 6-week dietary intervention resulted in a trend for reduced inflammation and ”normalised” gut microbiota with an increase in Bacteroidetes and the Clostridium clusters, and a decrease in Proteobacteria and Bacillaceae.

Even though most probiotic prevention and treatment studies have targeted a pediatric population, there are also randomized controlled trials with probiotics (although most commonly given as supplements and not incorporated in the diet) for treatment of allergic disease also in adults. The results have been variable, although meta-analyses generally show no benefit of probiotics for treatment of allergic disease.

The impact of lifestyle modifications other than diet in this context is even less studied. Benjamin et al 2012, reported smoking to be associated with an increase in Bacteroides-Prevotella both in patients with active Crohn’s disease and in healthy controls suggesting that smoking may at least partially contribute to the dysbiotic state. Stress is another lifestyle  factor with potential to impact gut microbiota composition via the gut-brain axis, however there is a paucity of studies in the context of allergic and autoimmune disease.

Clearly, there is need for well-designed dietary and life-style intervention studies targeting gut microbiota in both allergic and autoimmune disease.

Thursday, January 8, 2015

The Microbiome in Asthma

Newly developed culture-independent methods for microbial detection are deepening the understanding of their role in lung disease. A persuasive body of evidence suggests that the microbiome of the lower airways differs distinctly in the obstructive lung disease, including asthma. Huang and Boushey provide their perspective on the findings of studies of differences in the airway microbiome in patients with asthma vs. healthy subjects, and of studies of relationships between environmental microbiota, gut microbiota, immune function, and the development of asthma (J Allergy Clin Immunol 2015; 135: 25-30). Additionally, they provide a rationale for approaches involving directed manipulation of the gut and airway microbiome for treatment and prevention of allergic asthma.

Alterations in respiratory tract immune function are at least theoretically linked to the immunomodulatory activity of gut microbiota through the concept of a “common mucosal response”. This proposes that antigen presentation at one mucosal site stimulates migration of lymphoid cells to other mucosal sites, shaping immune responsiveness at those sites as well. Studies in mice provide strong support for the concept that bacterial community composition of the gut can shape developing immune function to foster or protect against allergic sensitization.   Similarly, studies focused exclusively on lung microbiota suggest that establishment of a lung microbiome occurs and is a dynamic process after birth. The authors discuss relationships of gut microbiota in response to viral respiratory infection, and provide findings that bacteria regulate immune defense against viral infections in mouse models. For example, interaction between exposure to allergens and microbial exposure has been seen in inner city children. Surprisingly, children with the highest rates of atopic sensitization and recurrent, presumably virus induced wheeze were found in children exposed to the lowest levels of cockroach, mouse and cat allergen and the lowest levels of bacterial diversity in their first year of life. On the contrary, the lowest rates of atopy and wheezing were found in those who had been exposed to the highest levels of these allergens and bacterial diversity. These results suggest that the bacteria served as a tolerance-inducing adjuvant for allergens.

The authors emphasize that dissecting the role of the microbiome in asthma is challenged by the heterogeneity of the disease at multiple levels. These levels include asthma’s clinical and inflammatory heterogeneity, genetic factors that contribute to asthma risk, and the multiplicity of immune pathways involved in asthma. To progress to clinical studies of oral or aerosol administration of microbiota for treatment and especially for prevention of asthma which will necessarily involve enrollment of pregnant women or of newborn infants will likely require overcoming ethical, legal, and cultural hurdles as high as the scientific ones we currently face.

Question for the authors:
The studies described in your review focus on the early development of the mucosal microbiota. Is there evidence that manipulating the microbiota in adults with allergic asthma may be a potential therapeutic?

We are a long way from human studies of the effects on allergic or asthmatic symptoms of manipulating the microbiota in adults with the condition. So the evidence available is largely from studies of mice, like Karimi et al’s study showing that dietary supplementation with L. reuteri increased Treg cell number and activity and reduced the allergic inflammation induced by allergen challenge in previously sensitized and challenged BALB/c mice (Am J Respir Crit Care Med Vol 179. pp 186–193, 2009).  Nothing comparable has been done in humans with established allergic asthma.

Update on Epigenetics in allergic disease

Chronic inflammatory diseases, including allergies and asthma, are the result of complex interactions between the genetic predisposition and environmental factors.  Epigenetics comprises the umbrella of such biochemical reactions and mechanisms including DNA methylation and chromatin modifications on histones and other structures. In their review, Harb and Renz review the recent developments in this context with emphasis on allergy and asthma research (J Allergy Clin Immunol 2015; 135: 15-24) .

There are many different epigenetic modifications affecting the status of the transcription of genes. For example, epigenetic modifications of T-cells start very early during the activation/differentiation program with naïve non-committed precursors during fetal immune development. DNA methylation is a biochemical process by the addition of a methyl group to the DNA nucleotides cysteine or adenine. This process leads mainly to gene silencing and subsequently to the inhibition of gene transcription. Histones are highly alkaline proteins found in eukaryotic cells nuclei that package and order the DNA into structural units called nucleosomes. Histone modifications range from gene activation to gene silencing and can have some DNA repair functions as well. The authors have previously shown that allergen sensitization and development of the TH2 immune response is closely linked to epigenetic programming of the previously naïve T-cell during development of the effector status. Moreover, house dust mite can also elucidate epigenetic modifications in asthmatic patients. Furthermore, environmental microbes are also considered to play an important role in shaping the immune response particularly early in life. For example, regulatory T-cell function was shown to be more efficient with farming exposure and was associated with demethylation of the FOXP3 promoter in offspring of mothers with farm milk exposure compared to controls. On the other hand,tobacco smoke has also been shown to impact epigenetic programming of different cell types.

There are many studies suggesting that different diet and nutrients exert their effect through epigenetic mechanisms, such as folic acid and vitamin B12 which are prominent methyl donors and can affect the DNA methylation status universally. In addition to that, fish oil is the main source of Omega-3 fatty acids that are precursors of a large number of anti-inflammatory mediators including defensins and resolvins, and recent data provides mechanisms toward an altered expression of NF-KB affecting important inflammatory regulatory pathways through deacetylation. The authors discuss a variety of examples indicating a role of epigenetic alteration as a mechanism linking obesity and the effect on altered gene expression leading to an asthma phenotype. Moreover, stress represents an additional environmental factor through epigenetic modifications, with evidence of altered gene expression that modifies the allergic phenotype.

The authors emphasize that questions remain on the role of different epigenetic regulator mechanisms in various areas. More clinical studies are needed to unmask the exact mechanism of epigenetic modifications and their role in disease development. Other questions relate to the regulation of gene-specific epigenetic modifications and the control of the events through the underlying enzymatic machinery. Reversibility and stability of these effects also require further attention together with the question about the inheritance of different epigenetic marks.

Monday, December 8, 2014

Introducing an environmental assessment and intervention program in inner-city schools

Few studies have comprehensively examined the role the school environment plays in asthma and how effectively changing the environment may reduce morbidity, when adjusting for exposures in the home. In their review, Huffaker and Phipatanakul summarize the importance and common challenges of school-based environmental assessment and intervention studies linked to health effects (J Allergy Clin Immunol 2014; 134: 1232-1237). They discuss the challenges and potential benefits of comprehensive environmental assessment and health outcomes in inner-city schools.

The school environment has been shown to be a significant reservoir for allergens and pollutants. Indoor allergens known to be important in urban home environments may also be important in schools, including cockroach, cat, dog, mouse, dust-mite, and molds. Studies have identified children with asthma in inner-cities have markedly higher levels of mouse allergen in their schools compared to levels in their individual bedrooms. Given the paucity of comprehensive data on school-based environmental interventions and health outcomes, successful home-based strategies currently serve as the model for school-based interventions. For example, practical interventions to reduce environmental exposures at home such as the use of air filtration systems and integrated pest management can be utilized in schools. 

Despite the challenges associated with implementing environmental interventions in schools, evidence supports the importance of school and classroom exposures and health outcomes. School-based interventions have the potential to reduce exposures for many symptomatic children, in contrast to the individual families impacted by home-based interventions. If effective, results from school-based interventional studies could inform public policy change, funding and initiatives. If it can be demonstrated that reduction of classroom-specific exposures leads to improved asthma outcomes, then findings can be translated into efficient and cost-effective strategies to benefit communities of children through improvement of the school environment, where children in America spend the majority of their day.

Establishing School-Centered Asthma Programs

Approximately 36,000 children miss school each day due to asthma which ultimately affects a child’s ability to learn. In fact, according to a U.S National Interview Survey, children with asthma missed three times more school and had a 1.7 times greater risk of having a learning disability compared to well children. Moreover, students attending schools with the highest proportions of low income students are more likely to miss school because of asthma. In their review article, Cicutto et al discuss how asthma and associated causal pathways can have interactive and synergistic effects that result in a complex situation that must be addressed collectively through a coordinated and partnered approach (J Allergy Clin Immunol 2014; 134: 1223-1230). School-centered interventions are thus directed at improving asthma control and reducing asthma-related absenteeism.

Asthma management at schools is important for pediatric pulmonologists and allergists, primary care providers and the whole interdisciplinary team working alongside them to provide quality asthma care. Several studies and systematic reviews demonstrate that students with asthma when supported through school-centered asthma care programs can have improvements in asthma knowledge, confidence in and actual practice of asthma management skills, regular use of preventive asthma medications, reduced school absenteeism, better school performance, and the use of urgent and emergent asthma care. Collectively, available research demonstrates that programs that either provide asthma care directly at-school and/or ensure adequate links between school, family and asthma care provider have achieved a reduction in asthma morbidity. The authors indicate that the synergy created by collaborative and coordinated efforts of schools and asthma care providers assists students and their families to achieve asthma control and reduce associated morbidity.

Future research is needed to determine the cost effectiveness of school-centered asthma programs and how to sustain program implementation once research funding no longer exists. Nonetheless, community asthma care providers are essential to successful asthma management across home and school settings.

Question for the authors:

You emphasize that clinicians must be advocates for appropriate services within inner city schools. What approaches can you suggest clinicians utilize to educate local school administrators?

Schools, especially inner city schools, are very limited in resources that they can devote to health care. Therefore, clinicians can provide a valuable service by partnering with schools in varying ways. The first step would be for the clinician to set up a dialogue with the school nurse that is responsible for a high proportion of the children in their practice.

A multitude of things can be done once this step is taken. First, an understanding of the challenges the nurse faces in delivering medications in school would be a start to the conversation. Many school action plans are not provided to the school nurse and many are not written for the school nurse. Also, availability of and access to rescue medications at school can be a challenge. A dialogue between the school nurse and clinician can help resolve these problems at the core level. Next, steps could be taken to assist the school nurse with education of school staff around medication administration and recognizing symptoms of asthma. The rest will depend on the clinician’s time and interest in improving asthma care in the school setting and developing a sense of community engagement.

Once you do get involved, it is a very rewarding experience. The school nurses really appreciate it, and the clinician will understand the challenges in managing care in the real world setting.

Wednesday, November 5, 2014

Environmental impacts on immune responses in atopy and asthma

Despite the improvement of air quality in the U.S. since the enhancement of the Clean Air Act in 1990, exposures to outdoor and indoor air pollution remain a significant risk factor for both the development of asthma and the triggering of asthma symptoms.   Clinical studies have shown that significant asthma exacerbations were attributable to air pollution exposure, as a result of living in densely populated cities with elevated ambient fine particulate matter (PM2.5) and ozone (O3). In their review, Miller and Peden highlight new data on the effects of pollutant exposure on the innate and adaptive immune responses, genetic and epigenetic modifiers of response to pollutants, and potential interventions to mitigate these effects (J Allergy Clin Immunol 2014; 134(5): 1001-1008).

Several studies have determined that the effects of air pollution are heightened during the prenatal period.  This suggests that there is greater vulnerability of the growing lungs and the developing immune system, thus predisposing towards more airway inflammation later in life.  Similarly, studies suggest that factors such as chronic low-grade inflammation associated with obesity and stress may predispose towards asthma. Furthermore, the authors describe evidence that the mechanism behind these effects alter the innate and adaptive immunity, inducing a heightened immune response. Another emerging area of investigation is the effects of the environment on oxidative stress genes such as glutathione S-transferase (GST) genes as well as genes associated with Toll-like receptors of the innate immune system. Newer mechanistic lines of investigation focus on epigenetic regulation, and identifying asthma genes whose imprinting may be disrupted by environmental exposures.

Pollutant induced asthma exacerbations are less frequent in patients that use inhaled corticosteroids, suggestive that interventions that target acute inflammatory responses are beneficial, however future studies are required to test the efficacy of interventions in this population. Actively minimizing both indoor and outdoor pollutants and government air care regulations could decrease pollutant impacts on allergic lung disease.

Question for the authors:
How has the improved air quality over recent decades relate to the incidence of pollution related asthma exacerbations? 

In studies of both the Atlanta and Beijing Olympic Games, interventions that decreased automotive and point-source combustion were associated with decreased asthma morbidity. Future studies are needed to investigate more thoroughly whether improvements in air quality contribute to fewer asthma exacerbations.   This remains a difficult challenge to show as even the best designed epidemiological studies are unable to prove causality.

Stress and asthma: novel insights on genetic, epigenetic and immunologic mechanisms

In the U.S., ethnic minorities and the economically disadvantaged are disproportionately exposed to chronic psychological stressors such as poverty, discrimination and violence. Recent findings support a causal link between exposure to these stressors at the individual or community level and asthma morbidity. Moreover, current evidence suggests that the relation between stress and asthma is complex and partially mediated or modified by environmental exposures, adherence with treatment, co-morbidities and coping mechanisms.

In a review article, Rosenberg et al discuss recent findings suggesting potential biologic mechanisms for stress-related asthma, including changes in the methylation and expression of genes that regulate behavioral, autonomic, neuroendocrine, and immunologic responses to stress (J Allergy Clin Immunol 2014; 134(5): 1009-1015). For example, there may be susceptibility genes that predispose chronically stressed youth to both post-traumatic stress disorder and asthma. Moreover, recent studies show that low socioeconomic status in early life may program sustained resistance to glucocorticoid signaling, which could undermine the efficacy of steroid therapy in subjects who develop asthma.

The authors emphasize that the development of novel indicators or biomarkers of chronic stress is imperative, given that current stress measures cannot be used in young children or are difficult to implement in large studies. In addition, adequate phenotypic assessment of asthma, accounting for mediators and modifiers of the effects of stress on asthma, and studying the role of stress on treatment responses in vivo are key elements of future longitudinal studies of stress and asthma. Ultimately, further mechanistic insights on stress-related asthma should improve the prevention and treatment of asthma, particularly in vulnerable populations.