Showing posts with label probiotics. Show all posts
Showing posts with label probiotics. Show all posts

Sunday, May 5, 2013

More on 'Bugs as Drugs'

This morning, I was doing a lazy ramble through my favourite blogs and found a post by Carl Zimmer on 'Bugs as Drugs' - primarily on probiotics. And I just came to realise that there is a very interesting tendency these years of using bugs as drugs in a variety of fields.

We are all very much aware of the worries about the increase in antibiotic resistance in bacterial and other pathogens. Moreover, it appears that sometimes antibiotic treatment leads to imbalance in the intestinal microbiota (dysbiosis); a well-known example is intractable Clostridium difficile infections which can potentially lead to pseudomembranous colitis.

C. difficile infection can lead to pseudomembranous colitis
Earlier this year, an article appeared in the renowned The New England Journal of Medicine on a randomised, controlled treatment study on duodenal infusion of donor faeces for recurrent C. difficile. The researchers found that the infusion of donor faeces was significantly more effective for the treatment of recurrent C. difficile infection than the use of vancomycin, the drug usually recommended in this situation. In fact 15/16 patients had resolution of C. difficile-associated diarrhoea upon first or second infusion; however, it might be worthwhile 'shopping around' for the right donor.

And so, how are these faecal transplants developed and administered? Well, it appears that donors are volunteers who have been through a selection process based on a questionnaire on risk factors of infectious diseases. Then donor faeces is screened for parasites (including Blastocystis and Dientamoeba - yes, it warms my heart to see this so explicitly spelled out in the paper... but I wonder which methods were used - it doesn't say!) and enteropathogenic bacteria. Moreover, blood samples from donors are screened for e.g. HIV, hepatitis and antibodies against e.g. Entamoeba histolytica and Strongyloides. Next, a donor pool is created with repeated screening every 4 months. On the day of infusion, faeces is collected by the donor and immediately brought to the hospital, where it is diluted with 500 mL of sterile saline. The solution is stirred, and the supernatant strained and poured in a sterile bottle. Within 6 h after collection of the faecal sample by the donor, the solution is infused through a nasoduodenal tube (2 to 3 mintues per 50 mL). Patients are subsequently monitored for 2 h. Apparently, this is how it works!

Sunday, August 19, 2012

The Potential Role of Our Microbiome Ecosystems

For those who like these pop-sci articles on the still somewhat conjecture-like but very inspiring theories about the role of our intestinal microbiome in health and disease, here's a link to an article from The Economist (18 AUG 2012):

The Human Microbiome: Me, myself, us

And let me reiterate: We still don't know much about mikro-eukaryotes in all this... do they play a role as well? And how do they cope with different types of microbiomes?

Anyways, enjoy!

Friday, June 22, 2012

More Bits And Pieces On The Microbiome... Or Maybe Mycobiome...

I promised to include some more stuff from some of the many recent publications in Science and Science Translational Medicine on the intestinal microbiome and its potential role in health and disease, and I've chosen two papers that could have broad public interest; for those who need an introduction to the microbiome, please go here (Wikipedia entry).

Because the microbiome has been more or less exclusively synonymous with the "bacteriome" it's very refreshing to discover a paper on fungal diversity in the gut. Like Blastocystis, and other single-celled parasites, intestinal fungi are also micro-eukaryotes, and we are continuously searching for the role of micro-eukaryotes in health and disease.

In general, very little is known about fungi in the intestine, and most clinicians, even mycologists, hardly bother about the fungi that may be present in our intestine, - I think I can say that without offending anyone! Maybe one of the most interesting things in a clinical respect is the fact that antibodies against the yeast Saccharomyces cerevisiae (see below) is a common finding in patients with Crohn's Disease, but relatively uncommon in patients with ulcerative colitis and healthy individuals.

Now, Iliev et al. (2012) start out by confirming the fact that fungi are indeed common commensals and thus a part of our normal intestinal flora. They then showed that colitis chemically induced in mice led to circulating antibodies against S. cerevisiae, which suggested that fungal antigens commonly found in the gut might be responsible for the induction of these antifungal antibodies during colitis.
The innate immune receptor Dectin-1 appears to have a key role in fungal recognition and combating. Therefore the authors wanted to further explore the role of this receptor by studying mice with and without Dectin-1. They found that Dectin-1 deficiency led to increased susceptibility to chemically induced colitis, including weight loss, tissue destruction and cell infiltration by inflammatory cells, etc. Moreoever, evidence was found of fungal invasion of inflamed tissue in the Dectin-1 knockout mice and taken together, their data suggest that Dectin-1 deficiency leads to altered immunity to commensal gut fungi.
To cut a long story short, results from these experiments in mice led the investigators to search for mutations in CLEC1A (the human Dectin-1 gene) in patients with ulcerative colitis, and they found that mutations were significantly more common in patients with severe ulcerative colitis (patients requiring colectomy) than in those with a less aggressive disease progression. This suggests that not only bacteria but also intestinal fungi interact with the intestinal immune system and may thereby influence health and disease. If this can be confirmed by others, this is an example of how biomarkers can predict the disposition towards/progression of disease and the results may have profound consequences for diagnostic strategies (e.g. screening for mutations in the Dectin-1 gene) and therapeutic management of patients with severe ulcerative colitis. Maybe it would have been interesting to know about such mutations in patients with Crohn's Disease as well...

Next, the investigators took to identifying what types of fungi were actually present in the colon of these mice. What may be a little bit controversial is the fact that the authors - by amplification and deep sequencing of  ITS1-2 (genetic marker commonly used to identify and taxonomically group fungi) - appear to have found not only species representing a staggering 50 well-annotated fungal genera in the mouse microbiome, but an additional 100 "novel and/or un-annotated fungi" as well - this does sound like a lot, but somehow the reader is calmed down a bit, when the authors later tell us that 97.3% of all fungi detected in the mouse faeces belonged to only 10 species, with 65.2% of the fungal sequences belonging to Candida tropicalis. So, whether the 100 novel fungi are indeed fungi colonising the intestinal tract is unknown, but they may very well represent fungi "on transit", so to say, acquired from food, drink or environment maybe... we know that fungi are ubiquitous - we inhale fungi every day for instance, and when deep sequencing is applied, it may be possible to trace even fungi only present in very small quantities; also ITS-2 analysis does not tell us whether the sequences are from "intact/live" (i.e. colonising) fungi or from degraded fungi (i.e. ingested); a classic example is Saccharomyces cerevisiae (Brewer's or Baker's yeast), which we may often acquire from food and drink, but which may also colonise (settle and proliferate) our intestines. Contamination of the faecal samples from fungi present in the environment and during processing is also a possibility (one of the reasons why PCR-based diagnostics for fungal infections is a tricky task...). Well so, all of these new species/genera may not necessarily represent the "mouse mycobiome". However, the authors found only few of the fungi in the food that was fed to the mice, so this still may remain a bit of a mystery... it would have been interesting to know whether the fungi detected were yeasts or molds, for instance, and very little information can be extracted from the supplementary material (phylogenetic analysis) accompanying the paper. Anyway, it's all very stimulating and further studies will assist in exploring fungal diversity and, hopefully, the diversity of micro-eukaryotes in general.

Saccharomyces cerevisiae is used in food and drink, but may also colonise our guts.

The next paper is one of many recent papers heralding the implementation of microbiome-based therapies in future personalised and precision medicine, possibly relevant to diseases such as inflammatory bowel disease, obesity and diabetes. Microbiome manipulation, so to say, is key to this concept and includes controlled diet, pre- and probiotic interventions, bariatric surgery (e.g. gastric bypass), faecal transplants (see my recent blog post on feacal bacteriotherapy), helminth therapy (yes!) or ecological engineering. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host, and these may be known to many as lactobacilli or bifidobacteria (or simply "yoghurt"!) that protect us against harmful bacteria by inhibiting their growth and by helping reduce cholesterol levels, synthesise vitamins and sustain immune responses. Prebiotics are non-digestible dietary sugar molecules (oligosaccharides) that can enhance the activity of for instance lactobacilli and bifidobacteria. While the potential benefits of pre- and probitics have been known for many years, it is only with current available technology that we are starting to get a mechanistic understanding of their impact on our bodies.

The article picks up on host-gut microbiota metabolic interactions and the so-called "host-microbe metabolic axes", which include pathways and interactions responsible for gut permeability, formation of blood vessels (angiogenesis) in the gut mucosa, ion transports, sulfation ability of xenobiotics, and many other things; sulfation ability is a key component in metabolising of drugs, for instance. Differences in our individual abilities to sulfate certain compounds give us at least one explanation as to why different people may respond differently two drugs treatment (see previous posts), and our ability to metabolise a common drug such as acetaminophen (paracetamol) can apparently be predicted form our preinterventional excretion of the microbial co-metabolite 4-cresyl sulfate; other gut microbial contributions that can alter the absorption, metabolism, and safety of drugs have been demonstrated recently.

Gastric bypass (Roux-en-Y) is a surgical procedure carried out to delay and reduce the absorption of calories and includes bypassing a large part of the stomach and a part of the small intestine by a procedure known as "stapling". Roux-en-Y appears to be associated with major and stable changes in the microbiota and in many microbially generated compounds, all of which are key components in the host-microbe metabolic axes. "This suggests that the microbiota is an essential part of the "gearbox" that connects the physical effects of bariatric surgery to the resulting beneficial effects."

Gut ecology changes with age, and current investigations seek to define the rationale of and potential for manipulating the microbiome of older people, for instance with pre- and probiotics, to secure higher microbiome diversity (high microbiome diversity appears to be beneficial) and resilience to antibiotics-induced changes in gut flora.

For those of you who nearly choked on "helminth therapy" - I may put up a post in the future on how helminths (and maybe other intestinal eukaryotes such as amoebae?) apparently play a role in the presentation and regulation of diseases such as asthma and inflammatory bowel diseases...

The cells of our intestinal microbiome outnumber our own body cells by 10 to 1. Within the next decade or so we will be able to extract a lot of information about how the bacteria and other "bugs" in our guts influence and contribute to health and disease. Importantly, we may have to realise now more than ever that "germs and bugs" and their actions and interactions can hold the key to a healthy life in ways that we wouldn't think were possible only a few years ago. This means that we should acknowledge that some bacteria and parasites may be a sign of a healthy intestinal environment / a healthy gut function, and that consumption of drugs such as antibiotics may produce shifts in our microbiota that may not necessarily be beneficial.

References:

Iliev ID, Funari VA, Taylor KD, Nguyen Q, Reyes CN, Strom SP, Brown J, Becker CA, Fleshner PR, Dubinsky M, Rotter JI, Wang HL, McGovern DP, Brown GD, & Underhill DM (2012). Interactions between commensal fungi and the C-type lectin receptor Dectin-1 influence colitis. Science (New York, N.Y.), 336 (6086), 1314-7 PMID: 22674328
 
Holmes E, Kinross J, Gibson GR, Burcelin R, Jia W, Pettersson S, & Nicholson JK (2012). Therapeutic modulation of microbiota-host metabolic interactions. Science translational medicine, 4 (137) PMID: 22674556