Fish oil may be important to altering the microbiome, reducing anxiety

Last week we published a blog on the gut-brain axis, and the various associations between brain health and the gut microbiome.  One of the ailments we discussed was depression, which is often studied in mice by inducing early life stress on the mice.  One way to do this is by separating mice from their mothers for hours at a time at a young age.  The Maternal Separation model, as it is known, causes stress and anxiety in these mice, but more importantly, research has shown that it creates a dysbiosis of their gut microbiomes as well.  Many scientists believe the dysbiosis may be implicated in causing some of the stress phenotypes, and so reversing this dysbiosis could have therapeutic value.  Researchers from the University College Cork, in Cork Ireland, experimented with N-3 polyunsaturated fatty acids (PUFAs), like those found in fish oil, in these maternally separated mice, and found they may be important to preventing the dysbiosis.  They published their findings in the journal PLoS ONE.

In the study, the researchers separated mice into two groups, one underwent maternal separation, and the other had a normal upbringing.  Within each group the mice were separated into two more groups, one that received fish oil supplements and the other that didn’t.  Over the course of 17 weeks each groups’ feces were sampled for their microbiomes.  The Maternal separation tended to decrease the bacteroidetes to firmicutes ratio of the mice’s microbiome, which has previously been linked to depression in humans.  Interestingly, supplementation with the fish oil increased this ratio in those maternally separated mice.  In addition, the fish oil also increased the concentration of bacteria that were higher in non-separated mice, such as populations of Rikenella.  Finally, the fish oil increased the amount of butyrate producing bacteria, and as we have seen many times before, butyrate and other short chained fatty acids (SCFAs) are often associated with health.

Overall this study showed that fish oil shifted stressed mice’s microbiome to a more natural state, presumably helping them in the process.  While the scientists did not directly measure stress levels in these mice to support the microbiome connection, hopefully that will be part of a follow up study.  The scientists noted that fish oil is clinically shown to reduce inflammation, and made it a point to connect the stress in the mice to systemic inflammation.  Systemic inflammation is also mediated by the microbiome.  Indeed, people that have inflammation from IBD, for example, do tend to have more stress and anxiety.  In the end, fish oil could make for an interesting prebiotic to shift the microbiome, counteract inflammation, and improve mental health. 

Early life stress implications on the gut microbiome

A growing body of evidence supports the significance of the gut microbiome with respect to behavioral disorders, as mediated by disruption to the gut-brain axis.  Importantly, there is a lack of understanding regarding associations between gut microbiome dysbiosis and behavioral phenotypic outcome.  Traumatic childhood events early-in-life can result in later-in-life behavioral consequences.  Maternal separation (MS) is an example of such an event that is represented with a well-established preclinical (i.e., animals) experimental model for early life stress.  In a recent study, researcher’s sought to investigate the precise role of MS in the induction of changes to the gut microbiomes of mice, and the potential behavior phenotypic consequences brought on by these changes. 

C57 mice were subject to three unique experimental groups: germ-free (GF) mice, specific pathogen-free mice (SPF, i.e. mice with microbiome compositions), and germ-free mice that were eventually subject to recolonization.  Mice were either left alone after birth or exposed to MS 3 days after birth.  Behavior was examined after 8 weeks, and the germ-free group was sacrificed after 9-10 weeks and the SPF group after 16-20 weeks.  The recolonization group was recolonized with microbiota at 12-13 weeks, followed by more behavioral tests and subsequent sacrificed. 

Corticosterone - a major stress hormone - was significantly elevated in both GF and SPF mice that were subjected to MS.  The researchers next wanted to define a relationship between the host microbiome and anxiety-like behaviors weeks after being separated from the mothers.  It was fist observed that MS did indeed alter microbiota composition in SPF mice.  Interestingly, MS-induced anxiety like behavior was observed in SPF mice, but not in GF mice, suggesting that the microbiome played a significant role in the development of these types of behaviors.  The experimenters then recolonized the guts of a subgroup of GF mice.  Indeed, behavior was altered in MS mice whose guts were colonized as compared to the MS mice that remained germ free.  Other physiological indicators demonstrated significant interactions between MS and the presence of gut microbiota, as gut microbiota presence had a significant impact on noradrenaline and serotonin levels. 

All told, the findings in this study suggest microbiome dysbiosis is a critical physiological driving force behind the behavioral phenotypes associated with early life stress events.  It will next be important to begin thinking about translate these preclinical findings in a clinical setting, in hopes of exploring ways to help those in need.

Maternal stress can alter the gut microbiome of progeny, possibly affecting brain development

The composition of the vaginal microbiome has been shown to have major health implications for a female’s health as well as the health of a newborn infant.  During birth, microbiota transfer from the mother to the neonate, which eventually go on to colonize the gut of the child.  It has already been shown that disruptions to the vaginal microbiome can impact microbiota colonization in the gut of a neonate, but downstream implications of this have not been thoroughly explored. 

Researcher’s from University of Pennsylvania set out to examine whether maternal stress in mice, and subsequent changes to the vaginal microbiome, could lead to disruptions in the gut microbiome of their progeny.  Expanding upon this, the researchers further investigated whether these disturbances to the gut impaired metabolism.  This transfer of microbiota occurs during a critical time in brain development, which requires a lot of energy and therefore effective metabolism to fuel this process.  The researchers wanted to identify whether or not maternal stress could disrupt the brain development process by way of alterations to microbiome transfer from the mother to its progeny and a subsequent disrupted metabolic process. 

Male C57 mice and female 129S1 mice were used in this study and were bred to form a hybrid F1 generation.  Stress was administered to the female mice using a well-established behavioral paradigm known as the early prenatal stress model.  Pregnant mice assigned to the EPS-stress group were exposed to a series of stressors (8 in total), but pain was not induce nor did these tests directly influence feeding schedule, weight gain, and litter size. 

Animals were then sacrificed and vaginal lavages were collected to examine bacterial composition between stressed (EPS) and non-stressed groups.  Quantitative PCR was used to characterize the microbiomes of the female mice and their offspring.  Lactobacillus, the predominant bacteria populations in the vagina, was significantly disrupted in the EPS group.  There was a reduction in Lactobacillus in the guts of F1 progeny as well.

Colon and plasma metabolic samples were examined in the F1 hybrid generation by extracting fatty acid metabolites using centrifugation.  Analysis showed that metabolic profiles were significantly different between groups.  Namely, of 29 signature metabolites assessed, 6 were increased and 23 were decreased in EPS progeny as compared to the control groups. 

Brain samples of the F1 hybrid generation were collected and amino acid concentrations were analyzed to assess substrate availability in the developing brain.  The F1 offspring from the EPS group displayed significantly less amino acids.  Interestingly, amino acids in a hypothalamic region of the brain were shown to be deregulated, and these concentrations were much lower in males as compared to females. 

It was interesting to see differences in amino acid availability in the hypothalamus between males and females in light of the fact that there are gender biases in neurodevelopmental disorders such as autism spectrum disorder.  Hopefully future studies can elucidate more on the microbiome to see how it relates to human behavior and brain disease.  

Type 2 diabetes and the microbiome. iHMP blog #4

Universal symbol for diabetes

Nearly 10% of individuals in the United States suffer from type 2 diabetes, and the associated costs are hundreds of billions of dollars.  Several studies have correlated microbiome alterations with the presence of diabetes, and studies in mice have shown that changes in the microbiome can lower glucose levels, putting the mice at risk for diabetes.  The iHMP plans on studying diabetes and its associations with the microbiome through a longitudinal study. 

Specifically the iHMP will be testing the following hypotheses:
1) "Environmental stress causes dynamic changes in specific biological pathways in the human body, and these changes lead to alteration of the human microbiome...including glucose."
2) "Some of the changes may affect the [hosts' gene regulation] leading to...biological alteraions that extend well beyond the time of the stress period"
3) "Different physiological stresses, such as respiratory viral infections and diet changes, may have common effects in both the host and microbiome"
Source

The iHMP will investigate these hypotheses by enrolling a cohort of 60 adults at risk for diabetes.  The study will last 3 years and during these years the researchers expect at least 10 individuals to become diabetic.  They will sample the patients' stool, nasal, urine, skin, tongue, and blood microbiomes every 2-3 months, which will measure a full suite of biologics that include bacteria, lipid content, metabolites, and proteins.  Sampling will also occur during periods of 'stress' that include mental stress as well as illnesses and physical trauma.

As always the results of the study will be made available, and we will be checking in on their progress.

This blog post concludes our series on the iHMP (HMP2).  We hope that anyone reading this will continue to check in on the iHMP progress, as we hope the role of the microbiome in pregnancy, IBD, and diabetes continues to unfold. 

The gut-brain axis - microbiome and depression

Today I will be discussing a review from a little more than a year ago that discusses research that links the microbiome with stress, anxiety, and depression.

First, it should be noted that a 2-way communication between the gut and brain has already been established.  The review goes on to mention studies in mice where not only are germ free mice associated with higher stress responses, but stress and anxiety early in life are associated with long-term changes in the microbiome.  There was efficacy in reducing stress by treating stressed mice with probiotics.  Other studies however have shown germ-free mice to have reduced stress when compared to their counterparts.  In addition, multiple studies showed that inflammation of the gut caused by dysbiosis or a pathogenic gut bacteria increased stress and anxiety levels in mice.

There are many mechanisms by which the microbiome communicates with the brain and may affect the stress levels.  I encourage anyone interested to read the paper to learn more.  In the end, more research is needed to discover just how important the microbiome is to our mental health.