The presence of pancreatic cancer is said to modify the bacterial composition of the lingual microbiota. This characteristic dysbiosis could lead to the development of new diagnostic tools.
Pancreatic cancer progresses silently and is diagnosed at a later stage, so much so that today it represents the seventh highest cause of death from cancer worldwide. The identification of specific biomarkers therefore turns out to be a public health priority, to ensure earlier management. The microbiotas and their dysbioses, common in cancer, represent in this regard an innovative research focus. A Chinese team examined the microbial characteristics of the tongues of pancreatic cancer patients. This original approach has its roots in traditional Chinese medicine, according to which the tongue reveals the pathophysiological condition of many organs and the progression of the disease.
Increased diversity in patients
The researchers characterized the bacterial populations of the lingual biofilms of 30 subjects with pancreatic head cancer, and of 25 healthy control subjects. Sequencing of 16S rRNA identified 158 (sidenote:
Operational Taxonomic Unit
groups of organisms usually not cultivated or not identified, classified on the basis of the similarity of the DNA sequencing of a given gene. Frequently used as an equivalent to the concept of species
) in the whole of the cohort, whose distribution proved to be linked to the subjects’ state of health. Pancreatic cancer was in fact accompanied by significantly greater microbial diversity (overabundance of 43 OTUs, including Leptotrichia, Fusobacterium, Rothia, Actinomyces, Corynebacterium, Atopobium, Peptostreptococcus, Catonella, Oribacterium, Filifactor, Campylobacter, Moraxella and Tannerella). Conversely, depletion of Haemophilus, Porphyromonas and Paraprevotella was observed in comparison with healthy subjects. This lingual dysbiosis is liable to impact the composition of the intestinal and pancreatic microbiotas via the bloodstream, promoting immune and inflammatory mechanisms associated to the development of cancer.
Towards an early diagnosis
The team noted that high concentrations of Leptotrichia and Fusobacterium, associated with low levels of Haemophilus and Porphyromonas, made it possible to distinguish between patients and persons in good health. In this respect, the researchers consider that the lingual microbiota could be a biomarker of pancreatic cancer. A basis for contemplating the development of tools that facilitate early diagnosis, even prevention of the disease. This hypothesis nevertheless will warrant confirmation on a larger scale and expansion of the analyses to include intestinal and salivary microorganisms of patients.
According to a Chinese study, the presence of Fusobacterium nucleatum in tumor cells might significantly reduce the efficacy of one of the standard adjuvant chemotherapies for colorectal cancer.
The focus on gut dysbiosis was introduced into oncology research following the observation in a growing number of studies that the intestinal microbiota may play a role in resistance to or potentiation of some anti-cancer treatments. For example, Fusobacterium nucleatum (Fn)–an anaerobic bacterium present in the oral cavity, where it can cause periodontitis–was recently linked to carcinogenesis and the progression of colorectal cancer (CRC).
Impact on cytotoxicity
Tests carried out on colorectal cancer cell lines showed that Fn significantly upregulated expression of BIRC3, a protein that inhibits (sidenote:
Apoptosis
Physiological programmed cell death process
). The latter is one of the presumed mechanisms of action of 5-Fluorouracil (5-Fu), a standard adjuvant chemotherapy for CRC: Fn and 5-Fu would therefore have competing actions in the process of tumor destruction. Additional in vitro and in vivo analyses confirmed that Fn directly reduced thecytotoxicity–therefore the efficacy–of 5-Fu.
Increased risk of relapse
What is the mechanism involved? Stimulation of receptors present on the surface of immune cells (Toll-like receptors 4, or TLR4) by bacteria via membrane wall components. This stimulation activates a signaling pathway, which in turn induces expression of BIRC3 in the cancer cells. These results were confirmed by analyzing biopsies of 94 patients with advanced stage CRC and treated with 5‑Fu: the abundance of Fn was increased in 22.3 % of samples, as was expression of BIRC3 and TLR4. Higher levels of these two indicators were also detected in patients who had relapsed. The researchers consider that Fn and BIRC3 could therefore serve as therapeutic targets to reduce resistance to chemotherapy in advanced-stage CRC.
Other cancers in the line of sight
A previous study demonstrated the potential of treatment with metronidazole to reduce tumor growth in mouse models of CRC: however, further work is needed to confirm that this antibiotic therapy is suitable for blocking chemoresistance to 5-Fu before considering its use in clinical practice. This could also be applicable to other types of cancer since BIRC3 has been associated with chemoresistance to 5-FU in pancreatic cancer and to doxorubicin in breast cancer.
Why do red meat lovers have a higher cardiovascular risk? Probably because of their increased blood TMAO levels, a molecule produced by gut microbiota bacteria, according to a study published in the European Heart Journal.
The gut microbiota has already been shown in animal models to be associated to an increased risk of life-threatening cardiac events. Some gut bacteria have the ability to degrade three substances (choline, phosphatidylcholine and carnitine) found in eggs, and mainly in red meat. The product of this degradation is then transported to the liver, where it is transformed into trimethylamine N‑oxide (TMAO), a highly pro-inflammatory molecule that accelerates the development of (sidenote:
atherosclerosis
Fatty plaques on the inner lining of arteries that lead to blood flow obstruction and blood vessel hardening.
), which is one of the well-known risk factors for cardiovascular diseases. A diet rich in meat, eggs and more generally in TMAO precursors, could thus lead to increased cardiovascular risk.
Comparison of 3 diets
To assess this hypothesis, 113 volunteers were given three diets with the same caloric value containing a quarter of proteins from three different sources: red meat, white meat (poultry) or plant foods (pulses, nuts, seeds). Each participant followed the three diets during four-week periods, separated by “washout” periods lasting from 2 to 7 weeks during which they followed a normal diet. Blood and urine TMAO levels were measured during each of the three diets.
Spare your microbiota an excess of red meat
After a month, blood TMAO levels were three times higher in the “red meat” group than in the other two groups. This increase was caused by the higher production of TMAO by gut bacteria from the carnitine present in red meat, and to the lower excretion of TMAO by the kidney. The good news is that the TMAO increase is completely reversible and disappears quickly once red meat is substituted with white meat or plant proteins. According to the authors, these findings explain the increased risk of cardiovascular diseases and premature death observed in avid eaters of red meat and cold cuts. Changing your diet could be a simple way to preserve your microbiota and prevent this risk.
Wang Z et Bergeron N, Levison BS et al. Impact of chronic dietary red meat, white meat, or non-meat protein on trimethylamine N-oxide metabolism and renal excretion in healthy men and women. European Heart Journal 2019 Feb 14;40(7):583-594.
According to an American team, the progression of tumor cells in pulmonary adenocarcinoma is likely to be fueled by dysbiosis of the pulmonary microbiota via an impairment of the local immune response. New anti-cancer treatments could be directly inspired by these results.
Lung cancer is the most lethal cancer in the world, and pulmonary adenocarcinoma (non-small cell lung cancer) is its most common form. As 70 % of patients suffer from infectious pulmonary complications of bacterial origin, a factor that worsens their prognosis, the role of the pulmonary microbiota in the progression of the disease is a fast-growing research avenue.
Tumor growth and the intestinal microbiota
In order to evaluate the functional importance of commensal intestinal bacteria in the occurrence and progression of the tumor, two lines of genetically modified mice in which a pulmonary adenocarcinoma had been induced were used: one group was composed of mice depleted of all microorganisms (“germ-free”, or GF); the second of mice free from specific pathogenic organisms (“Specific Pathogen Free”, or SPF). 8 to 15 weeks after induction of the tumor, the GF mice seemed protected: slowed tumor growth, fewer high-grade lesions. In addition, quadruple antibiotic therapy (ampicillin, neomycin, metronidazole, vancomycin) administered to SPF mice between 2 and 6.5 weeks post-induction stopped the tumor growth, at both early and advanced stages, and reduced the number of high-grade lesions.
Dysbiosis and local infections boost the cancer
The researchers then characterized the pulmonary microbiota. In mice that developed tumors, the pulmonary flora was more abundant and less diversified than that of healthy mice (overabundance of Herbaspirillum and Sphingomonadaceae). In the mice programmed to develop adenocarcinoma, tumor growth was accelerated by the transplantation of bacteria over-represented in the pulmonary microbiota of tumor-carrying mice. More detailed experiments in animals and humans resulted in the following hypothesis: pulmonary inflammation, associated with the adenocarcinoma and triggered by the local microbiota, is likely to contribute to the activation of the local immune response implemented by a specific category of T cells, called γδ T cells. These cells are highly represented in tumor tissues and are thought to differentiate into γδ T cells producing (sidenote:
Pro-inflammatory mediators
IL-22 and amphiregulin
), which would induce infiltration of tumor-promoting neutrophils. Pulmonary infections would fuel this harmful process by maintaining local dysbiosis. Inactivation of these T cells or their mediators therefore appears as a potential therapeutic target for the future.
Food additives are already known to be bad for our health, but they could also disrupt the gut microbiota and have an impact on behavior, according to a recent study. This hypothesis could very well lead us to reconsider our dietary habits.
They have taken over supermarket shelves and are now impossible to avoid! With their unpronounceable code names, food additives are a manufacturer’s dream: they use and abuse them to improve food texture or as preservatives. Studies in mice have however shown their harmfulness: carboxymethylcellulose (CMC) and polysorbate 80 (P80) alter the composition of the gut microbiota and lead to low-grade chronic gut inflammation that promotes the development of metabolic disorders such as obesity and diabetes mellitus.
Differences between males and females
Curious to know whether these frequently-used emulsifiers had an impact on the brain and the behavior of rodents, the American team who first published these results pursued their work. For 12 weeks, the researchers added CMC or P80 to the drinkable water given to mice subjected to several biological, physiological and behavioral tests. The results not only confirmed the findings from the first study, but they also showed that males and females did not react equally to food emulsifiers. Although all rodents presented a disrupted gut microbiota composition, the impact was different depending on sex.
Anxious males, less sociable females
The consumption of emulsifiers also led to behavioral changes, which were also different based on gender. While males showed signs of anxiety, females became less sociable. The authors are not able to explain these variations yet, but they believe that microbiota disruptions have an impact on behavior through the gut-brain axis. If this hypothesis was confirmed in humans, it might explain how processed food is the cause of many psychological and behavioral disorders observed nowadays.
Holder MK, Peters NV, Whylings J, et al. Dietary emulsifiers consumption alters anxiety-like and social related behaviors in mice in a sex-dependent manner. Scientific Reports. 2019 ; 9:172
Quality of life and depression might be partly linked to the composition of the intestinal microbiota? A study has traced the outlines of a neuroactive intestinal microbiota–or neuromicrobiome–a new, fast-growing research field.
Mental diseases do not just involve cerebral processes alone, as evidenced by the increasing body of research into the gut-brain axis. This is the case for a Belgian-Dutch study which demonstrated a link between quality of life (QoL), depression and composition of the intestinal microbiota.
Intestinal markers of the disease?
The researchers sequenced the genome of intestinal bacteria of two Belgian and Dutch cohorts (1,054 and 1,063 individuals respectively) after collecting the (sidenote:
QoL questionnaire
RAND questionnaire with 36 questions providing a score between 0 and 100
) from the participants (partly diagnosed with depression). By analyzing bioinformatics data, they succeeded in correlating the presence of certain bacteria with depression: by way of example Dialister, Faecalibacterium, and Coprococcus were positively linked to the final QoL score. This would be in line with the fact that two of them produce butyrate, a short chain fatty acid found in lower quantities in depressive people. Another important result: Coprococcus and Dialister were depleted in depressive patients (whether or not they were taking antidepressant treatment) in both cohorts. These two bacterial genera could therefore represent potential “psychobiotics”, i.e. probiotics promoting good mental health.
A wide range of neuroactive agents
The researchers also demonstrated a positive correlation between QoL and synthesis of dihydroxyphenylacetic acid (DOPAC), a metabolite of dopamine, by certain intestinal bacteria. Many other (sidenote:
Compounds
Dopamine, acetylcholine, glutamate, acetate, propionate, butyrate, histamine, kynurenine, p-cresol, among others
) are likely to be involved in gut-brain interactions under the influence of the intestinal microbiota, first and foremost serotonin: potentially produced by the bacteria Akkermansia, Alistipes, and Roseburia, serotonin is the most commonly found molecule in the gastrointestinal tract. GABA (γ-amino-butyric acid, another neurotransmitter capable of inhibiting excess neural impulses in neurons) is also likely to have an important neuroactive role to play, as one of its synthesis pathways was more active in depressive patients in one of the cohorts. These new avenues must be investigated to better characterize the effects of the neuromicrobiome.
Researchers have identified specific gut bacteria that could tell a person’s age with relative precision. Should we expect the creation of a bacterial rejuvenating cocktail in the near future? It does not seem likely…
A wealth of information is hidden within the intestinal flora: diseases, inflammation, antibiotics use, diet… Could it also reflect our age? A team of English-speaking investigators went in search of an answer by analyzing the gut microbiota composition of 1,165 healthy people. They obtained a list of 39 bacterial species that make it possible to classify each sample in three age categories, with a 3.94-year precision. This precision level exceeds that of models developed so far, because this team is not the first to investigate a “microbiotic aging clock”.
Neither aging, nor rejuvenating
Could this mean that some bacteria are rejuvenating while others are associated to an early aging? It is proving difficult to make such a shortcut conclusion: pathogenic bacteria do not seem to be necessarily correlated to aging, while the abundance of bacteria deemed beneficial to our health does seem to extend youth. For instance, larger amounts of Campylobacter jejuni, a bacterium that causes diarrhea, are found in the intestinal flora of younger individuals, and this is not the case in elder people who seem to have acquired protective immunity over time.
Significant generational gap
Another key factor to consider is the major changes in ways of life (diet, sedentary lifestyle, environmental factors…) over the last century. In such a context, it is difficult to tell whether the flora composition of today’s young people will undergo the same changes as their elders. In other words, this calls into question the very principle of microbiotic aging clock… The authors, who are also the founders of a biotech company specializing in the treatment of age-related diseases and extension of human life, recognize this bias. A bacterial “elixir of youth” is still not within reach of our flora–or our supermarket shelves, at least for now…
Galkin F, Aliper A, Putin E, et al. Human Gut Microbiome Aging Clock Based on Taxonomic Profiling and Deep Learning, iScience. 2020 Jun 26;23(6):101199.
Alzheimer’s disease could be the consequence of chronic inflammation of neuronal tissue caused by the colonization of bacteria from the oral microbiota which produce toxic proteins called “gingipains”. Therapeutic applications are already being considered.
A link was already established between Porphyromonas gingivalis, chronic periodontitis and Alzheimer’s disease (AD)–a neurodegenerative disease which affects at least 30 million people worldwide: in mice, it was already recognized that repeated exposure to P. gingivalis triggered periodontitis, which in turn was associated to pathologic neurodegenerative signs typical of AD.
Presence of cerebral markers
Based on this knowledge, an international team analyzed samples of post-mortem cerebral tissue from patients diagnosed with Alzheimer’s and controls. In the material collected from patients, the researchers detected a higher proportion of gingipains, toxic proteins produced by P. gingivalis. These gingipains were also present in the individuals not diagnosed with Alzheimer’s, although in smaller quantities, which could represent an asymptomatic preclinical stage of the disease, according to the authors.
Neurotoxicity at several levels
Furthermore, a strong correlation was observed between the levels of gingipains and those of the Tau protein, whose abnormal accumulation is known to be correlated with neuronal and cognitive decline. In vitro analyses have shown that gingipains cleave Tau proteins and that resulting protein fragments are deposited as insoluble intraneuronal filaments, characteristic of AD. These proteins seem also to be involved in the formation of extracellular plaques of Aβ beta amyloid peptides (1-42), other key lesions observed in AD. According to the researchers, AD is therefore likely to be the result of cerebral colonization by P. gingivalis, which is thought to have migrated from the (sidenote:
Oral cavity
Dependent on brushing, mastication or the use of dental floss, bacteria would enter the circulation, reaching and then crossing the blood brain barrier
) and then to have triggered chronic low-grade inflammation via the action of gingipains.
Gingipain inhibitors on trial
The researchers consider these proteins to be new therapeutic targets. The gingipain inhibitor that they are developing is orally bioavailable. It can diffuse through cerebral tissue and is said to be capable of blocking neurodegeneration. In mice, this molecule significantly reduces P. gingivalis levels in the brain and limits the formation of Aβ plaques with greater efficacy than moxifloxacin (a broad-spectrum antibiotic used as a control), without inducing resistance. A phase-1 clinical trial was completed successfully in October 2018 and demonstrated safety of use in humans. Other phase-II and phase-III trials are programmed for 2019 to test the molecule in Alzheimer’s patients.
Could we prevent and/or cure cow's milk protein allergy by restoring the microbiota of at-risk children? This hypothesis seems to be confirmed by studies published in the Nature Medicine journal.
Cow's milk protein allergy affects a lot of newborns fed with infant formula. It appears as varying gastrointestinal (abdominal pains, diarrhea, vomiting), respiratory (cough, sneezing) and skin (hives, eczema) symptoms, that are more or less specific. Impairment of the gut microbiota due to the increase of C-sections and the decrease in breastfeeding could explain this spreading phenomenon.
The microbiota into question
After observing that the microbiota composition of children allergic to cow’s milk is very different to that of non-allergic children, an American team partnered with researchers from Naples, Italy, to investigate the role of commensal bacterial (naturally present in the intestines) in preventing food allergies. They transplanted either the microbiota of allergic or healthy newborns to germ-free mice. When exposed to cow's milk allergen (beta-lactoglobulin), rodents from the first group all developed an anaphylactic reaction (severe and widespread allergic reaction), while those from the second group did not experience any symptom.
A protective species has been identified
Based on their research, they identified the bacterial species that seems to be associated to a lower risk of allergic reaction: Anaerostipes caccae, a butyrate-producing molecule that ensures good intestinal health. Nevertheless, based on their data it is not clear whether the imbalance of the microbiota composition (“dysbiosis”) is a cause or a consequence of cow’s milk allergy. The results showed that commensal bacteria played a major role in the prevention of food allergies, or at least cow’s milk allergy, and confirm the benefits of developing innovative strategies based on microbiota modulation to prevent and/or treat these diseases.
