Further evidence that the microbiome can improve melanoma cancer therapy

T stages of melanoma

Yesterday we discussed a paper that discussed how the microbiome impacted a melanoma cancer therapy.  In the same issue of Science another article was published where researchers from Chicago independently made a similar discovery - that the microbiome itself can impart an anti-tumor effect on melanoma.

The scientists were using a  common mouse model for melanoma between two different laboratories (Taconic Labs and Jackson Labs) when they noted that the cancer progressed much differently between the labs.  The Taconic mice had more aggressive cancer than the Jackson mice.  They hypothesized that one possible difference between the mice in the two labs were their microbiomes.  In fact, when the Taconic mice were given the Jackson mice's microbiomes, the Taconic mice's cancer grew more slowly.  The scientists then attempted to identify which bacteria were having the effect.  They compared the mice's microbiomes and discovered that Bifidobacteria were much more abundant in the Jackson mice.  Upon treating the Taconic mice with strains of Bifidobacterium longum and Bifidobacterium breve the Taconic mice's cancer grew more slowly.  Interestingly, the scientists discovered that the bacteria were likely increasing the activation of T-cells, because mice that had mutated T-cells did not have the microbiome-mediated anti-cancer effect.

This study points to an exciting role of the microbiome in mediating and activating the immune system to attack and destroy some cancers.  The researchers note that there are likely other microbiome bacteria that have this effect, but that they have only identified the Bifidobacteria.  Hopefully the scientists will be able to measure the effect in humans, and observe an association between patient outcome and the presence and absence of certain gut bacteria.

Melanoma cancer therapy’s efficacy may depend on the existence of specific gut bacteria

Ipilimumab is a monoclonal antibody (mAb) that binds to, and activates T-cells. (Technically, the drug binds to the CTLA-4 receptor on T-cells, which decreases T-cell suppression)  It is currently an approved therapy for the treatment of metastatic melanoma.  Unfortunately, activation of the immune system can damage the microbiome, and taking iplimumab often results in adverse side effects in the gut, such as diarrhea.  Scientists from France were studying the effect of the drug on the microbiome when they discovered that its efficacy was actually dependent on the presence of certain gut bacteria.  They published their results in the journal Science.

First, the scientists administered the ipilimumab to three groups of mice that had been given cancer through an established model.  One group of mice had a normal microbiome, the second group was germ-free, and the final group had a normal microbiome, but then were given antibiotics.  Surprisingly, the mAb activated much fewer T-cells and was much less effective in destroying the cancer in the mice that were germ free and had been given antibiotics compared to the normal mice.  In addition, the scientists noted that intestinal inflammation occurred in the normal mice, but less so in the others.  Next, the scientists measured the microbiome changes as a result of administration of the mAb, and observed a rapid decrease in Bacteroidales, Burkholderiales, and an increase in Clostridiales.  The scientists then inoculated cancerous mice with specific bacterial species prior to administration of the drug, and then measured the drug’s efficacy.  Remarkably, specific species, such as Bacteroides thetaiotaomicron were able to reestablish the drug’s therapeutic potential and decrease inflammation.

The microbiome’s complex dynamic with the immune system once again presents itself, this time by modulating the efficacy of ipilimumab.  The scientists did do some work on humans, and they noted that not all human patients suffering from melanoma and taking ipilimumab have those beneficial bacteria in their stool.  The scientists did not discuss whether their existence was associated with the cancer’s progression in humans, although it would be interesting to see.  Ipilimumab is just one of many drugs that use the immune system to attack cancer.  Continued research is needed on the microbiome’s impact on these drugs.

Prebiotics in human breast milk are associated with infant weight

Human breast milk contains nutrients and compounds that are beneficial for infants. Human milk oligosaccharides (HMOs) are a group of important complex carbohydrates that are found in breast milk. These HMOs are important in the developing infant because they serve as a prebiotic, helping to shape the infant’s gut microbiome by facilitating the selection of beneficial bacteria. The link between gut microbiota composition and infant obesity has led to speculation that HMOs might affect certain bacteria that in turn lead to decreased body fat. Because HMO composition of female breast milk varies over the course of lactation, researchers in Oklahoma and California tested to see whether differences in milk HMO content are associated with infant body weight. The results of their study were published in The American Journal of Clinical Nutrition.

Twenty-five mother-infant pairs participated in this study. On average, the mothers were 29.5 years of age and overweight before conception. When the infants were 1 month and 6 months old, the mothers supplied breast milk samples to test for HMO composition. Concurrently, the infants’ body fat composition, weight, and length were measured.

The findings suggest that HMOs are associated with infant body weight, fat mass, and lean mass at both 1 month and 6 months. A diversity of HMOs, such as LNFFPI (lacto-N-fucopentaose I, a sugar), DSLNT (difucosyl-LNT, a sugar), and FDSLNH (fucosyl-disialyl-lacto-N-hexaose, a sugar) accounted for 33% of the fat mass, which was more than other variables such as gender, and mothers’ pregnancy BMI. infant fat mass than did sex, pregnancy BMI.  LNFPI was inversely associated with 1 month old infant weight, while at 6 months it was inversely associated with weight, lean mass, and fat mass. Overall, the presence of a diverse group of HMOs decreased infant body mass.  While this study has its limitations because it does not specifically test the bacterial composition of the gut, it is a first step to identifying an association between HMOs and infant BMI. As obesity remains an epidemic in the United States, perhaps the microbiome is the first place to look towards to prevent the disease. 

Probiotic does not restore gut microbiota function in patients with metabolic syndrome

Insulin resistance may increase the risk for metabolic syndrome

Metabolic syndrome is a condition that often leads to diabetes, heart disease, and even stroke and obesity, a chronic worldwide epidemic is a leading cause of metabolic syndrome (MetS).  It has also been shown that the microbiome may be an important factor in the development of obesity and subsequently, MetS, possibly due to its impact on gut barrier integrity and inflammation. While probiotics have been used as an intervention in several animal studies on obesity and MetS, there have not been sufficient results in humans to show it is having a positive effect.

Despite significant amounts of research, the question still remains if probiotics are having a lasting effect on the gut when administered. It is not clear if taking a probiotic is colonizing in the gut or if it is only providing an acute response during the timeframe it is being administered. A team of scientists published their work showing the effect that Lactobacillus casei Shirota (LcS) had on patients with MetS. The researchers administered LcS to 13 patients with MetS and 15 individuals received no LcS. They sequenced their microbiota composition from stool samples and compared it to healthy controls.

They found that LcS did not have an impact on Bacteroidetes/Firmicutes ratio and that it was slightly higher in the healthy controls. Serum bile acids were similarly not affected by LcS administration. While they did see small microbiota changes, LcS was not able to change the Bacteroidetes/Firmicutes ratio or gut barrier dysfunction, two important staples of metabolic syndrome.

While the small sample size of the patient cohorts may have been a factor in the failure to observe microbiota changes after probiotic administration, it was still important to see that probiotics may not always have the intended consequences we are seeking. In this study, probiotic administration did not provide a benefit to the Metabolic syndrome patients and further studies will be needed to better understand the microbiome implications of probiotics.

The microbiome can protect against metabolic dysregulation brought on by disease

Pathogenic infections can lead to metabolic alterations that result in maladies such as cachexia, or muscle wasting.  Antibiotics can be prescribed to treat a variety of intestinal diseases or inflammatory conditions, but these agents can also disrupt the natural microbiome ecology that could perhaps provide benefits to protecting against metabolic dysregulations.  On top of this, harnessing components of the microbiome with respect disease tolerance is an avenue under continuous exploration.  Within this contextual framework, researchers from The Salk Institute for Biological Studies in La Jolla, CA investigated to see whether components of the microbiome could have a protective effect on metabolic dysregulation brought on by gut trauma and/or infection.   

To initiate the investigation, the researchers used an induced-injury model known as the dextran sulfate sodium (DSS) intestinal injury model to create symptoms associated with inflammatory bowel disease/Crohn’s disease.  DSS was applied to mice in two cohorts procured from two distinct laboratories (Jackson labs [Jax] and UC Berkeley lab [CB]).  This treatment was administered to C57 mice followed by an administration of an antibiotic cocktail of ampicillin, vancomycin, neomycin, and metronidazole (AVNM) to provide remedy for the injury.  The AVNM cocktail had no impact on the severity of DSS in mice procured from Jackson labs, whereas mice procured from UC Berkeley colonies demonstrated significantly less muscle wasting.  This observation led to the hypothesis that microbiota composition differences between both cohorts of mice drove this observation. 

After examining cecal content from AVNM-CB and AVNM-Jax mice, it was determined that the CB mice had a higher composition of E. coli compared to the Jax mice.  Building on the original supposition, the researchers then administered E. coli to Jax mice, and upon DSS administration, they demonstrated significantly less wasting pathology as compared to the vehicle control groups (i.e., DSS treatment without being administered E. coli).  The researchers further investigated whether E. coli had a protective effect in response to infectious microbes in addition to induced-DSS injury, and Jax mice were infected with Salmonella Typhimurium or Burkholderia thailandensis.  There was no significant difference in alterations in host metabolism, caloric uptake, or inflammation between E. coli-administered groups and controls.  However, the E. coli group demonstrated increased signaling in the insulin-like growth factor 1/phosphatidylinositol 3-kinase/AKT pathway in skeletal muscle, a pathway implicated in the prevention of muscle wasting.  This finding effectively provides mechanistic evidence of protecting against muscle wasting. 

Together, these findings provide additional evidence that support the microbiome’s role in tempering inflammatory disease or injury.  Further delineation of molecular pathways associated with these maladies will advance our understanding and treatment of disease.   

There are important differences in the gut mucus of germ free and conventionally raised mice

Mucus is not just produced by snails.

The mucus lining of our intestines are the critical interface between the microbiome and the epithelial cells that make up the intestines.  It provides many essential roles in its interaction with the microbiome, but perhaps most importantly it is a physical barrier that separates microbiome bacteria from the vasculature.  Without it, bacteria can elicit an immune response which results in inflammation that is characteristic of IBDs.  New research out of Sweden shows how mucus changes over time as the result of microbiome colonization.  The results were published in the journal Cell Host and Microbe last week.

The researchers undertook a number of experiments whereby they measured the mucus in germ free and conventionally raised mice.  In general, the conventionally raised mice had thinner, more easily shed mucus in their small intestines that allow for diffusion of nutrients.  This mucus contained antimicrobial peptides that prevented bacteria from passing across it.  The conventional mice’s large intestines’ mucus was thick and stiff and impenetrable to bacteria.  This mucus maintained most of its properties even after the conventionally raised mic were treated with antibiotics.  On the other hand, the germ free mice had thin and stiff mucus in their small intestines, as well as thick, but easily penetrable mucus in their large intestines.  This shows that the conditions under which the mucus develops is important to its eventual structure and function.  After, the scientists inoculated some of the germ free mice with the microbiome of the conventional mice and monitored the mucus over time.  It took an entire 6 weeks for the mucus to finally resemble the mucus of a conventionally raised mice.  In addition, the scientists looked that the glycans that were being formed in the mucus, and also noticed differences between the germ free and conventional mice.  As discussed on this blog previously, these glycans can be important in determining which bacteria colonize the gut.  To that end, the researchers measured the microbiome in the mice and discovered that conventional mice had a higher Firmicutes to Bacteroidetes ratio compared to germ free mice.  In addition, even after the germ free mice had been inoculated with the new bacteria, their microbiomes never truly matched the conventionally raised mice’s.

More than anything, this paper shows us the critical importance that mucus plays in microbiome health, science and research.  It demonstrates the importance of an early life microbiome to the maturation of a healthy mucus that can properly regulate the microbiome.  It also shows a possible negative consequence of antibiotics or dietary compounds can have on the mucus, and by extension the microbiome.  Finally, among many other things, it shows that microbiome research should consider the effect of the mucus on their experiments, especially ones involving germ free mice.