Could it alter the course of diabetes?
By Jennifer Brown
Staphylococcus aureus bacteria have long been recognized as a culprit in sepsis, pneumonia, endocarditis, and many other dangerous and deadly diseases.
But can staph bacteria cause diabetes? A University of Iowa microbiologist and expert on S. aureus thinks it’s a distinct possibility. Moreover, it’s a testable concept he’s eager to investigate.
For the most part, S. aureus bacteria appear to be harmless passengers, riding on our skin and the external surfaces of our bodies. In fact, up to 30 percent of us carry it in our noses. Problems arise, however, when S. aureus penetrates the skin or other tissue planes and invades the bloodstream.
UI researcher Patrick Schlievert (’76 PhD) blames superantigen molecules produced by S. aureus for much of the bacterium’s pathogenicity. Inside the body, these toxins disrupt the immune system and ultimately lead to inflammation— the driver of many diseases, including diabetes.
Schlievert has also shown that gaining weight and gaining staph go hand in hand.
“What we are finding is that as people gain weight, they are increasingly likely to be colonized by staph bacteria— to have large numbers of these bacteria living on the surface of their skin,” he says. “Superantigens can diffuse through the skin, so people who are colonized by staph bacteria are being chronically exposed to the superantigens the bacteria are producing.”
But Schlievert, professor and department executive officer of microbiology, thinks he has a solution—or more accurately, a topical gel—that can help obese individuals shed the bacteria, if not the weight, and possibly alter the course of diabetes.
Microbiomes are us
The microbes we carry with us inside and out, and which vastly outnumber us cell-for-cell and gene-for-gene, have a profound influence on our health and well-being, although the intricate details of the relationship are still being discovered.
As with any ecosystem, disturbing the natural balance of components disrupts the overall health of the system. Studies are increasingly finding that many diseases and chronic conditions affecting humans are associated with alterations to the microbiome.
“It’s all about diversity as the protective, healthy state. A lack of diversity leads to dysbiosis, or an imbalance of bacterial populations,” says John Kirby, PhD, UI professor of microbiology. “The analogy is that if you cut down all the trees in a rainforest, an invasive species will take over. You do not live well without your (normal) bacterial consortium.”
Almost 10 years ago, researchers at Washington University showed that transferring bacteria from obese to lean mice made the lean recipients gain weight, suggesting that a bacterial shift induces obesity. The researchers also showed that obese humans had more of one type of bacteria, firmicutes, and less of another type of bacteria, bacteroidetes, than did lean participants, and this shift could be partially reversed by weight loss. That difference caught Schlievert’s attention, because a major pathogen in the firmicute group is S. aureus, a bacterium that Schlievert has been studying for most of his career. In particular, Schlievert has focused on the pathogenic effects of the superantigens produced and secreted by all strains of S. aureus, which over-stimulate the immune system and cause systemic inflammation.
Schlievert’s work on superantigens dates back to the early 1980s, when he identified the superantigen toxic shock syndrome toxin-1 (TSST-1) as the cause of toxic shock syndrome associated with high-absorbency tampons. Since then, he has identified nearly 20 different superantigens and shown that they cause the deadly effects of various staph infections, including sepsis and endocarditis, a serious infection of heart valves. His research has shown that these molecules are critical for both pathogenesis and colonization of S. aureus, and that 100 percent of the population is unable to mount an immune response to at least one of the main superantigens, meaning that everyone is susceptible to their adverse effects.
“As an infectious disease physician, I know this is one of the more aggressive infections that we treat,” says Pat Winokur, MD (’88 R, ’91 F), UI professor of internal medicine. “And once it has gotten deep-seated into the body, it is difficult to treat.”
Schlievert worked with fellow UI microbiologist Al Klingelhutz, PhD, to demonstrate that staph superantigens interact with fat cells and other components of the immune system to promote inflammation. Knowing that chronic inflammation can lead to insulin resistance, the researchers then showed that prolonged exposure to superantigen TSST-1 causes rabbits to develop the hallmark symptoms of diabetes, including insulin resistance, glucose intolerance, and systemic inflammation.
“We basically reproduce Type 2 diabetes in rabbits simply through chronic exposure to the staph superantigen,” Schlievert says.
In addition to evidence indicating that obesity is associated with a microbiome shift that increases the prevalence of staph bacteria, Schlievert notes that he and his clinical colleagues have documented that obese individuals have increased S. aureus colonization of the skin, and that these bacteria are producing superantigens, which can diffuse through the skin.
“What we are arguing is that when people are chronically colonized, as is the case for people who are obese, then that chronic exposure to the superantigens could be contributing to the diabetes,” Schlievert says.
“What we’d really like to know is what happens to the blood sugar levels and insulin resistance when the bacteria are removed by decolonization.”
Applying ‘controlled burn’
As part of his work on toxic shock syndrome, Schlievert and colleagues screened various compounds for antimicrobial activity and identified glycerol monolaurate (GML) as an interesting candidate. GML has several properties that make it attractive as a treatment for diseases caused by dysbiosis.
In lab experiments, GML selectively kills numerous strains of pathogenic bacteria, as well as some viruses and mycobacteria, without killing strains of lactobacillus and bifidobacteria that are considered beneficial or protective players in the human microbiome.
Traditional antibiotics kill the majority of bacteria present in a fairly non-specific fashion, wiping out beneficial commensal bacteria as well as the pathogenic targets. This “clear-cutting” approach provides a potential opportunity for invasive species that might be more aggressive or more antibiotic-resistant to gain a foothold. A prime example of this is the C. difficile bacteria that can colonize a patient’s gut following a course of antibiotics. Once established, these bacteria are extremely hard to eradicate and can cause severe illness. Interestingly, using fecal transplantation to restore a normal microbiome is proving to be very successful treatment for C. diff infections.
Recalling Kirby’s rainforest analogy to describe dysbiosis, Justin Grobe, PhD, UI assistant professor of pharmacology, says that using GML to remove bacteria might be considered a “controlled burn.”
GML also appears to kill bacteria without promoting resistance, an important feature for any proposed antimicrobial therapy, given the alarming increase in antibioticresistant bacteria.
“I will never say that a bacterium would never be able to develop resistance to a drug. But at this point in time, it’s not obvious that there are ways the organisms could develop resistance (to GML),” Winokur notes.
UI Pharmaceuticals has formulated and produced a GML-containing non-aqueous gel under good manufacturing practices for use in human trials.
Starting this fall, Winokur and colleagues in the Vaccine and Treatment Evaluation Unit plan to test the effectiveness of the GML gel against bacterial vaginosis and candidiasis, a common condition that is another example of dysbiosis.
“This is a very unusual disorder,” Winokur says. “It is not obviously an infection caused by a single organism; it’s more an abnormal collection of bacteria in the vaginal vault. GML is promising because, in the test tube, it seems to kill some of the organisms that are more associated with the symptoms and spares some of the organisms that seem to be more protective of the vaginal vault and the normal bacterial milieu.
“Having something that might be able to not just wipe out everything, but kind of reconfigure the bacterial milieu to a more normal state, would be very attractive,” she adds.
The phase 2 clinical trial will enroll 120 women at the UI and the University of Cincinnati. The trial will probably take close to a year, but for individual participants, the course of treatments is only three days with a follow-up at 28 days to test for recurrence of the dysbiosis, which is a common problem for this condition.
“I think the GML will be a very easy product for the participants to use, and I think it will be very well tolerated,” Winokur says.
Safety and ease of use also make GML a good candidate for testing Schlievert’s theory that abnormally high levels of S. aureus on the skin of obese individuals may contribute to the development of Type 2 diabetes.
Schlievert’s clinical colleagues regard this idea as an interesting concept, but they are not yet convinced that decolonizing people with prediabetes of S. aureus will reduce their blood sugar levels and insulin resistance.
“Always, when you are testing something in people, you need to weigh risk and benefit. In this case, the risk of using GML is very low,” Winokur notes. “You take the best data you have (from lab studies) and you make sure the science supports the likelihood of benefit, and then you go into the clinical trial and you test.”
Schlievert hopes to do just that in the near future. He envisions a trial that would include obese, prediabetic patients; obese individuals with normal glucose metabolism; and lean controls. The study would determine staph colonization of the participants and would test whether decolonization with GML affects glucose metabolism.
“I recognize that people may be skeptical about this idea. But I think we have a way to intercede here and alter the course of diabetes,” he says.
Finding trees in the microbial forest
By Jennifer Brown
As microbiome research has advanced with improved sequencing and bioinformatics capabilities, the picture emerging is one of enormous complexity.
University of Iowa researchers John Kirby and Justin Grobe are sorting through this forest of data to determine how changes to gut microbiota affect energy balance.
Using a novel apparatus, Grobe, assistant professor of pharmacology, can measure total metabolic rate—including oxygen-dependent (aerobic) and oxygen-independent (anaerobic) processes—in an experimental animal. This unique approach has revealed the surprising finding that oxygen-independent processes constitute a relatively large fraction (approximately 10 percent) of the total energy turnover. As human obesity results from small imbalances in energy turnover (much less than 10 percent), this suggests that anaerobic systems and tissues, including the gut microbiota, may represent exciting new targets for obesity therapeutics.
The team is coupling these data with a comprehensive yet challenging metagenomic analysis of microbiome changes associated with obesity to determine how dysbiosis, or the imbalance of bacteria, alters metabolic rate and energy balance.
Using sequencing of the 16S gene, they can identify the bacterial species in a microbiome. Kirby, professor of microbiology, likens this approach to identifying which tree species make up the Amazon rainforest by flying over the canopy and taking a series of photos.
“We’re just taking a snapshot to see who is there, but it doesn’t tell us what they are capable of doing or how species interact,” he says.
The next step, he adds, is metagenomics—sequencing all the bacterial genes—which allows researchers to determine the potential functions of the microbes within the microbiome. Some of that functionality may not even come from the bacterial genes but from the microbes’ own “virome.” Bacteria can be infected by viruses known as bacteriophage or “phage,” which insert their own DNA into the bacterial genome. Kirby and Grobe have evidence that some of the metabolic effects of an altered microbiome stem from these phage.
“Phage don’t have a 16S gene, but they integrate into the bacterial genomes, so when we do the metagenomic sequencing, we’ll see all the phage, too,” Kirby says.
Vu BG, Stach CS, Kulhankova K, Salgado-Pabón W, Klingelhutz AJ, Schlievert PM. “Chronic Superantigen Exposure Induces Systemic Inflammation, Elevated Bloodstream Endotoxin, and Abnormal Glucose Tolerance in Rabbits: Possible Role in Diabetes.” mBio. 2015 Mar- Apr; 6(2): e02554-14.
Mueller EA, Schlievert PM. “Non-Aqueous Glycerol Monolaurate Gel Exhibits Antibacterial and Anti-Biofilm Activity Against Gram-Positive and Gram-Negative Pathogens.” PLoS One. 2015; 10(3): e0120280.