Decreased bone mass, damage to bone microarchitecture, excessive skeletal fragility, increased risk of fracture... Osteoporosis, strongly linked to ageing, is on the rise in China, where it represents a major public health issue. The confirmation of a link between osteoporosis and an imbalance of the gut microbiota–as numerous studies suggest–would constitute a major advance in our understanding of the mechanisms involved in the development of the disease and significant progress in the development of preventive and/or curative treatments.

Dissimilar gut microbiota

A group of Chinese researchers compared the intestinal microbiota of 48 patients with primary osteoporosis to that of 48 healthy individuals. Unlike secondary osteoporosis, which is caused by disease, primary osteoporosis has no clearly identifiable cause, with age and menopause being its main risk factors. More diverse overall, the gut microbiota of patients with primary osteoporosis was mainly characterized by a greater abundance of bacteria of the Dialister genus, already suspected of being involved in the loss of bone mass, and associated with an increased level of IL-6, a pro inflammatory substance that promotes bone deterioration. It was also richer in bacteria of the Faecalibacterium genus involved in bone formation, which, conversely, the authors believe likely to be the result of an adjustment by the body to counteract the loss of bone mass.

Soon to be a diagnostic tool?

The researchers subsequently tried to assess whether these differences in the composition of the gut microbiota might serve as a diagnostic marker for osteoporosis. The results showed that an analysis of the gut bacteria of Chinese subjects was able to identify osteoporosis with a high degree of accuracy (over 98%). These significant findings open up new approaches to the prevention and treatment of the disease.

Ultraviolet B (UVB) intensity depends on a number of natural factors, including latitude, altitude, weather conditions, time of day and season, with human behavior and lifestyle playing an indirect role also. A recent study on women living in Vancouver, Canada, who were artificially exposed to UVB suggests that UVB increases diversity and richness of the gut microbiota, contributing to good health.

Gut microbiota influenced by the sun

Researchers replicated the study on Brazilian populations whose lifestyle and living conditions were very different from those of the Canadian women. They compared the gut microbiota of the Canadian city dwellers to that of various hunter-gatherer populations, including the Yanomami, an ethnic group living near the Equator, in a region of the Amazon which receives a high amount of sunlight. For the Yanomami, UVB rays are not blocked by pollution, clothing or sunscreen. Like that of the Canadian women, the gut microbiota of the Yanomami seemed to be modulated by exposure to UVB. It showed common characteristics (greater diversity, an increase in bacteria belonging to the Firmicutes phylum, a reduction in bacteria belonging to the Bacteroidetes phylum) that differentiates them from city dwellers. It was also particularly rich in proteobacteria, a peculiarity not fully understood by the researchers, who suggest that high exposure to UVB, due to the Yanomami’s lifestyle and the unique environmental conditions in which they live, may be responsible.

UVB, a factor to be explored

The authors believe that UVB, whether natural or artificial, merits consideration as a factor capable of influencing the composition of the human intestinal microbiota. They conclude that a more in-depth study that takes latitude, and therefore sun exposure, into account could shed new light on the relationship between the host, host’s health, gut microbiota and environment.

The fine particles and pollutants in the air we breathe not only poison our lungs, but apparently disrupt the intestinal microbiota also. The mechanisms involved remain unknown but according to a recent study involving one hundred young Californians exposed to certain air pollutants, science is beginning to hone in on the culprits.

Ozone has been singled out

After measuring the air quality around the volunteers’ homes and analyzing their gut microbiota, the researchers found that nitrogen oxides (nitrogen monoxide and dioxide from road traffic or energy generation) disrupt the intestinal flora. However, it appears that the most significant damage is caused by ozone, a pollutant formed through reactions between various other pollutants. Ozone reduces diversity within the gut microbiota, thereby disrupting its functioning. The study found that almost 130 bacterial species are affected by ozone, with only 9 influenced by nitrogen oxides.

Metabolism disrupted

High ozone exposure is thought to impact important cellular mechanisms, such as cell growth, insulin secretion or fatty acid synthesis and degradation. Some of these processes may also affect the integrity of the intestinal barrier and the metabolism. The researchers suggest that, through their impact on the gut microbiota, air pollutants may lay the groundwork for metabolic disorders such as type 2 diabetes mellitus or obesity.

Fighting pollution to protect the microbiota

This hypothesis should be evaluated in future epidemiological studies and in studies on animals in order to identify the exact mechanisms whereby pollution impacts the intestinal flora and promotes the onset of diseases among humans. However, these preliminary results are a reminder that pollution is a major public health issue that urgently needs to be addressed.

Often diagnosed at an advanced stage, lung cancer is associated to a high mortality rate. An earlier diagnosis would greatly improve both care and chances of survival. Can gut dysbioses serve as an indicator of lung cancer, as for many other diseases, including other types of cancer?

Specific gut dysbiosis signature as an indicator of the stage of cancer

The gut microbiota of 42 patients with three different types (sidenote: Adenocarcinoma (37 patients), squamous cell carcinoma (3 patients), large-cell carcinoma (2 patients) )  of non-small-cell lung cancer (NSCLC) at an early stage (metastasis had taken place in only 3 patients), and that of 65 healthy control subjects, were analyzed using 16S rRNA sequencing. Intestinal dysbioses were observed in the patients with lung cancer: increased presence of species belonging to the Ruminococcus genus and the Lachnospiraceae and Enterobacteriaceae families, among others, compared to control subjects. Therefore, the composition of the microbiota may change as lung cancer develops. In addition, the composition of the intestinal microbiota was specific of each stage of the cancer, with some bacteria only present in the three patients displaying metastasis.

A diagnostic tool?

In order to develop a non-invasive diagnostic tool for early-stage lung cancer, 13 biomarkers based on OTUs (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 )  were identified. Together, these biomarkers made it possible to accurately predict the presence of lung cancer (97.6% of cases). This model was confirmed in a second cohort (34 patients and 40 control subjects), with its predictive power remaining high (76.4%), although lower than in the initial cohort. From this model it was possible to construct a “patient discrimination index” to identify patients with early-stage lung cancer. Based on a weighted score, the index is easy to use for clinical purposes. Its predictive power in the initial cohort (92.4%) was also higher than that measured in the validation cohort (67.7%). Larger cohorts could improve the model and its predictive power.

Experts have the floor

You’ve surely already heard of microbiota. Did you know they’re essential to the proper functioning of the body? World Microbiome Day is a chance to celebrate them. It aims to raise general awareness about the importance of these microbial communities, highlighting advances in research. Our new MICROREVEAL series is part of this educational goal. On June 27 and for the rest of the year, the series will shine a new light on the diversity of microbiomes. In these video reports, journalist Louise Ekland will interview experts about the influence of the various microbiomes in our bodies.

Focus on the vaginal microbiota

This first episode will focus on the vaginal microbiota. Like Julie, you probably wish to know more about this microbiota which plays a key role in women’s health. Louise interviewed Dr. Jean-Marc Bohbot, andrologist and specialist in urogenital infections.

What infections are linked to an imbalance of the vaginal microbiota? What can be done on a daily basis to preserve this microbiota?

Do we not overestimate the importance of microbiota in the urogenital area?

In recent years we have come to understand the urogenital micro- biota more clearly. We now know that it can be a factor in infections, in urinary disorders related to the menopause and even in tumors. The urogenital microbiota and its disruptions must be taken into account in patient management and probiotics must be part of the therapeutic arsenal. Although probiotics are obviously not our only weapon, they are indispensable, since anti-infectious treatments do not treat the cause of recurrence, i.e. the dysbiosis.

What role do you think probiotics can play today against urinary tract infections?

Urinary tract infections are closely linked to imbalances in three microbiomes: the urinary micro- biota, since urine is not sterile; the vaginal micro- biota, with which the urinary microbiota shares many similarities; and the gut microbiota, from which the pathogens involved in urinary tract infections originate (e.g. E. coli, which passes from the anus to the vulvar vestibule and then to the bladder). Conventional antibiotic treatment is justified for single UTI episodes. On the other hand, for recurrent UTIs (more than four episodes per year), it is essential, after having ruled out functional causes (e.g. a tumor of the bladder), to question the pa- tient about possible disorders of the gut microbiota (constipation, etc.) and/or vaginal microbiota, the latter acting as a protective barrier between the digestive and urinary systems. The prevention of recurrence involves treatment for three to six months with intestinal probiotics administered orally, if a dysbiosis of the intestinal microbiota is present, and/or vaginal probiotics, ideally administered vaginally. These treatments may be combined with the use of cranberry, which reduces the level of E. coli in the bladder.

What about vaginal infections?

There are two types of vaginal infections: endogenous infections resulting from changes in endogenous microorganisms (bacteria or fungi) and exogenous infections contracted during sexual intercourse. For endogenous infections, in the case of a single episode, an antimycotic vaginal suppository or antibiotic treatment may suffice. However, where there is a risk of recurrence, the dysbiosis must be treated for several months with gynecological probiotics. Probiotics also have a role to play in exogenous infections, since the less balanced the vaginal microbiota, the greater the risk of acquiring a sexually transmitted infection (STI), and the higher the risk of an unfavorable outcome. For example, the papillomavirus is four to five times more likely not to be completely eliminated, and progresses more rapidly to potentially cancerous forms, when a dysbiosis exists. It is therefore important to test for an imbalance of the vaginal microbiota in infected women through a simple measurement of acidity (the pH should be between 3.5 and 4.5) and then by vaginal sampling where the pH is above 4.5. Where there is an imbalance, laboratory-tested and clinically approved probiotics should be prescribed. A vaginal dysbiosis also increases the risk of contracting HIV. Although the acidity of lactobacilli helps destroy the virus, an inflammatory state increases the presence of lymphocytes, the cells targeted by HIV.

Lastly, what can we expect from vaginal micro- biota transplants?

The results of just over twenty cases of vaginal microbiota transplants have been published. Al- though these results are interesting, they are not yet conclusive. The idea of treating recurrent bac- terial vaginosis through a microbiota transplant still raises concerns as regards the criteria for selecting donors–particularly since the absence of symptoms does not mean that the donor’s flora is balanced–and the indications for the recipient. It will most likely be known within a year or two whether vaginal microbiota transplants can be used as a last resort.

PROBIOTICS: IMPORTANCE OF BACTERIA AND YEASTS

Since a vaginal microbiota dominated by lactobacilli is considered optimal, vaginal probiotics unsurprisingly contain strains of this genus, which vary depending on the probiotic in question (L. acidophilus, L. crispatus, L. reuteri, L. rhamnosus). A review of 22 commercially available topical vaginal probiotics carried out in early 2019 highlighted their potential for the prevention and treatment of BV, but much less so for the prevention and treatment of vulvovaginal candidiasis.²⁰ None of the studies reported any major safety concerns.

Probiotic strains have never been detected in the vagina beyond the period of administration, suggesting they do not colonize the environment in a sustained manner.

In addition to probiotics for local use, oral probiotics have gained considerable importance. Four strains (L. crispatus, L. gasseri, L. jensenii and L. rhamnosus) out of 127 vaginal lactobacilli studied are noteworthy for their ability, in vitro, to acidify the environment, inhibit the growth of G. vaginalis and C. albicans and survive gastrointestinal transit.²¹

But what about in vivo? Consumed in the form of a yoghurt drink by patients suffering from BV (twice a day for four weeks), these same four strains led to a 100% recovery (Amsel criteria), compared to a 65% recovery in the placebo group.²² In addition to bacteria, certain yeasts may also be of interest, particularly against C. albicans. Saccharomyces boulardii, already used in the prevention and treatment of intestinal infections, naturally secretes capric acid, which modifies the structure of C. albicans, reducing its adhesion capacity, inhibiting its filamentation and hindering its ability to form biofilms.²³

VAGINAL MICROBIOTA TRANSPLANTS: PROMISING FIRST CLINICAL TRIALS

In October 2019, the results of a first exploratory trial testing the transplant of vaginal microbiota from donors as a therapeutic alternative in five patients with symptomatic, untreatable and recurrent BV were published in Nature Medicine.²⁴

Four patients showed a full long-term remission (sometimes requiring several transplants or even a change of donor) up to the end of the follow-up period (5 to 21 months after the transplant), with a marked improvement in symptoms, Amsel criteria and the microscopic appearance of vaginal fluids, as well as the reconstitution of lactobacilli-dominated vaginal microbiota.

The remaining patient is still in incomplete remission, while no adverse side-effects were observed. Accordingly, the researchers recommended further trials evaluating the therapeutic efficacy of vaginal microbiota transplants.

Popular with patients, alternative treatments to antibiotics aim to prevent recurrence and antibiotic resistance. They are in line with the recommendations of health authorities, including the Haute Autorité de Santé (HAS) in France, which works to “encourage the appropriate use of antibiotics in order to reduce bacterial resistance that can lead to therapeutic deadlock”.¹⁵ Cranberries, in the form of a 36 mg/day dose of proanthocyanidin, can be used to prevent the recurrence of UTIs linked to E. coli.¹⁶

The depletion of the urinary microbiota in women susceptible to UTIs has raised the question of whether an intake of microorganisms via probiotics can reduce UTI rates. An ideal probiotic should have the ability to adhere to cells, prevent and reduce the adhesion of pathogens, secrete acids (e.g. lactic acid), hydrogen peroxide and bactericides capable of reducing the growth of pathogens, be free of adverse side-effects (they should not be invasive, carcinogenic or pathogenic) and be capable of forming clumps to produce normal, balanced flora.¹⁷

According to the literature, probiotics have proven effective in the treatment and prevention of urogenital infections.¹⁷ Certain lactobacilli (L. rhamnosus, L. fermentum and L. reuteri) have been shown to have a beneficial effect in treating urinary tract infections.¹⁸ An inhibitory effect on E. coli has been demonstrated in vitro, with certain strains of lactobacilli (L. rhamnosus and L. plantarum) possessing antimicrobial properties against this bacterium.¹⁹

Therefore, the data increasingly suggests that probiotics may be used as a first step in the regulation of urinary microbiota in order to reduce the risk of, or treat, certain urinary infections, particularly since they are safe, better tolerated than antibiotics and frequently requested by patients.¹⁷ However, further clinical trials involving large numbers of patients will be required to obtain clear evidence on the preventive and curative role of probiotics in urinary tract infections.¹⁷

A HEALTHY VAGINAL MICROBIOTA: LOW DIVERSITY AND DOMINATED BY LACTOBACILLI

The vaginal microbiota consists mainly of lactobacilli with a protective role. Despite considerable variability among women, in general, five types of community have been categorized, depending on whether they are dominated by L. crispatus, L. gasseri, L. iners or L. jensenii, or have few or no lactobacilli and a significant quantity of strict anaerobic bacteria (Megasphera, Prevotel- la, Gardnerella and Sneathia) known to be characteristic of bacterial vaginosis.⁸

Therefore, while a high number of microbial communities is usually an indicator of health for several microbiotas (digestive microbiota, etc.), the vaginal microbiota is balanced when it has low diversity and is dominated by one or a few species of lactobacilli. In women of childbearing age, hormones promote the proliferation of lactobacilli. Estrogen levels induce the deposition of large amounts of glycogen, the main source of energy for lactobacilli, on the vaginal walls.⁸ From adolescence to the menopause, high estrogen levels promote colonization of the vagina by lactobacilli which metabolize glycogen, produce lactic acid and maintain intravaginal health by lowering the pH level.

BACTERIAL VAGINOSIS: WHEN G. VAGINALIS DRIVES OUT LACTOBACILLI

Despite more than sixty years of re- search, the etiology of BV remains unknown. Nevertheless, research seems to point more and more to the dysbiosis theory according to which dominant lactobacilli are replaced by polymicrobial flora derived from numerous bacterial genera (Gardnerella, Ato- pobium, Prevotella, etc.). G. vaginalis is in effect present in 90% of symptomatic subjects and 45% of normal subjects, whereas Lactobacillus sp. is found in 70% of apparently healthy subjects and 40% of symptomatic subjects.⁹ Consequently, G. vaginalis has been suspected of being the main pathogen in BV. However, there is long-standing disagreement in this regard, since this virulent bacterium has also been found in virgin girls and in sexually active wo- men with normal vaginal microbiota; in other words, colonization by G. vaginalis does not always lead to BV.¹⁰

An explanation recently put forward may settle the debate: there is not one, but at least thirteen, different species of the genus Gardnerella, some of which may not be pathogenic. A mechanism for the development of the dysbiosis has even been suggested:¹⁰ G. vaginalis, transmitted sexually, spreads itself among healthy vaginal lactobacilli, such as L. crispatus, initiating the formation of a biofilm, a structure that further protects the pathogen from the hydrogen peroxide and lactic acid secreted by the lactobacilli. By reducing the redox potential of the vaginal microbiota, G. vaginalis gradually reduces the lactobacilli population in favor of strict anaerobic bacteria such as P. bivia and A. vaginae. G. vaginalis and P. bivia seem to facilitate each other’s development, the former providing amino acids to the latter and the latter ammonia to the former. Lastly, both pathogens produce an enzyme that destroys the mucus in the vaginal epithelium, facilitating the adhesion of different bacteria associated with BV, such as A. vaginae, and potentially causing a polymicrobial infection.

VULVOVAGINAL CANDIDIASIS: A PROLIFERATION OF CANDIDA

Vulvovaginal candidiasis could be linked to an imbalance of the vaginal microbiota together with a proliferation of the fungus Candida, including C. albicans in 80%-92% of cases,¹¹ and to a lesser extent C. glabrata, C. tropi- calis, C. parapsilosis and C. krusei.¹² Exposure to antibiotics, whether local or systemic, is thought to be one of the main factors leading to vulvovaginal candidiasis.¹³ The reduction of certain bacterial species, lactobacilli or not, that control the replication and virulence of Candida yeasts apparently allows the Chlamydia tractomatis fungi already present in the vagina to multiply and induce infection. Future studies involving new sequencing technologies are needed to characterize in further details the interaction between vaginal microbiota, these yeasts and the occurrence and recurrence of vulvovaginal candidiasis.

HEALTHY VAGINAL MICROBIOTA: A SAFEGUARD AGAINST STIS

The vaginal microbiota also plays an important role in maintaining vaginal health and protecting the host against the acquisition and transmission of sexually transmitted infections. Vaginal microbiota with a small number of bacterial communities and dominated by lactobacilli (in particular Lactobacillus crispatus) are those most associated with vaginal health, whereas increased diversity seems to be associated with lower resilience to imbalances and higher susceptibility to STIs such as herpes (BV increases the risk of herpes and vice versa), papillomavirus (increased prevalence and likelihood of contracting HPV, delayed elimination, increased severity of cervical intraepithelial dysplasia), HIV (increased risk of acquisition and transmission), and other infections (gonorrhea, chlamydia and trichomoniasis).¹⁴