Antibiotics Disrupt Gut Ecology, Metabolism
Humans carry several pounds of microbes in our gastro-intestinal tracts. Recent research suggests that this microbial ecosystem plays a variety of critical roles in our health. Now, working in a mouse model, researchers from Canada describe many of the interactions between the intestinal microbiota and host, and show that antibiotics profoundly disrupt intestinal homeostasis. The research is published in the April 2011 issue of the journal Antimicrobial Agents and Chemotherapy.
"Intestinal microbes help us digest our food, provide us with vitamins that we cannot make on our own, and protect us from microbes that make us sick, amongst other things," says L Caetano M. Antunes of the University of British Columbia, a researcher on the study. In this study, the investigators used powerful mass spectrometry techniques to detect, identify, and quantify more than two thousand molecules which they extracted from mouse feces. They then administered antibiotics to the mice, to kill off most of their gut microbiota, and analyzed the feces anew.
The second round of mass spectroscopy revealed a very different metabolic landscape. The levels of 87 percent of the molecules detected had been shifted up or down by factors ranging from 2-fold to 10,000-fold.
The most profoundly altered pathways involved steroid hormones, eicosanoid hormones, sugar, fatty acid, and bile acid. "These hormones have very important functions in our health," says Antunes. "They control our immune system, reproductive functions, mineral balance, sugar metabolism, and many other important aspects of human metabolism."
The findings have two important implications, says Antunes. "First, our work shows that the unnecessary use of antibiotics has deleterious effects on human health that were previously unappreciated. Also, the fact that our gut microbes control these important molecules raises the possibility that manipulating these microbes could be used to modulate diseases that have hormonal or metabolic origins (such as inmmunodeficiency, depression, diabetes and others). However, further studies will be required to understand exactly how our microbial partners function to modulate human physiology, and to devise ways of using this information to improve human health."
(L.C.M. Antunes, J. Han, R.B.R. Ferreira, P. Lolic, C.H. Borchers, and B.B. Finlay, 2011. Effect of antibiotic treatment on the intestinal metabolome. Antim. Agents Chemother. 55:1494-1503.)
Anti-HIV Vaginal Gel Promising for Protection in Africa, SE Asia
A new vaginal microbicide gel and drug formulation looks promising for empowering women in developing countries to protect themselves from HIV during intercourse, without having to inform their partners, according to research published in the April 2011 issue of the journal Antimicrobial Agents and Chemotherapy.
HIV infection remains a major risk for women in sub-Saharan Africa and Southeast Asia, and one over which women often have little control due to unequal gender status over much of those regions. Investigators say the gel, the subject of the current research, will be cost-effective for such women, and laboratory studies suggest the gel-drug combination will be safe and effective. ImQuest BioSciences, Inc., the drug's developer, hopes to have the gel-drug combination in human clinical trials in 2012.
One of the drug's most important attributes is that it has two distinct mechanisms of action. IQP-0528, as the drug is known, inhibits the virus' ability to enter human cells, as well as the reverse transcription of the virus' genome into the host genome, "which is required for productive infection of the cell," says Robert Buckheit, of ImQuest BioSciences, of Frederick, MD. In that sense, IQP-0528 is like two drugs in one. Laboratory studies suggest that the product will work very effectively.
The investigators assayed a number of candidate drugs before choosing IQP-0528. Some of the other drugs were chemically unstable, or unstable at pH values to which they would be exposed, or otherwise unstable, says corresponding author Patrick F. Kiser of the University of Utah, Salt Lake City. It was critical for the formulation to be stable at ambient temperatures of sub-Saharan Africa, as refrigeration is not widely available in much of that region.
ImQuest continues to investigate a variety of options for drug, gel, and device formulations. "At present we have gels, intravaginal ring, and biofilm formulations of IQP-0528, in addition to the gel described in the paper, and products developed, which include combinations of IQP-0528 with tenofovir, which was recently found to inhibit the sexual transmission of HIV," says Buckheit. All this is in the interest of developing a product which women can use most easily and comfortably.
Kiser is particularly proud of the "symphony of tools and techniques used in the study. We had virology, human explant studies, chemical and physical stability studies, transport studies, and permeability studies of the drug," he says. "Putting all those things together is not trivial."
(A. Mahalingam, A.P. Simmons, S.R. Ugaonkar, K.M. Watson, C.S. Dezzutti, L.C. Rohan, R.W. Buckheit, Jr., and P.F. Kiser, 2011. Vaginal microbicide gel for delivery of IQP-0528, a pyrimidinedione analog with a dual mechanism of action against HIV-1. Antim. Agents Chemother. 55:1650-1660.)
C. diff Colonization Accompanied By Changes in Gut Microbiota: Study Hints at Probiotics As Treatment
Asymptomatic colonization by Clostridium difficile, absent the use of antibiotics, is common in infants and when it happens changes occur in the composition of the gut microbiota according to research published in the March 2011 issue of the Journal of Clinical Microbiology.
The adult human gut is an ecosystem containing several pounds of bacteria, including hundreds of species and more than 100 trillion (100,000,000,000,000) individuals. A healthy microbial ecosystem protects the host against Clostridium difficile, which frequently colonizes the gut after its ecological balance has been disrupted by broad spectrum antibiotics, says Anne Collignon, of the University Paris Sud, Chatenay-Malabry, France.
Collignon and her colleagues examined the bacterial populations from fecal samples taken from 53 infants, 27 of them negative and 26 positive for C. difficile. Using a variety of analytic methods, her team showed that the C. difficile-negative infants' GI tracts contained the species, Bifidobacterium longum, which was absent from the C. difficile-positive infants, while the latter contained other species not present in the non-colonized guts, including Klebsiella pneumoniae. "We believe that this colonization is linked to an encounter with C. difficile spores, which are frequent in the environment, and a permissive microbiota," says Collignon.
"To reconstitute the ecological balance of the microbiota, and with that, the "barrier" effect, seems a very efficient way to combat C. difficile infections," says Collignon. "Our results suggest that Bifidobacterium species, which are used as probiotics, can participate in that barrier effect against C. difficile. But proof is necessary, for example, in gnotoxenic animal models (germ-free animals challenged with specific bacteria)." But she notes that another team of investigators has shown similar results in elderly people. "It is well known that following use of broad-spectrum antibiotics, the gram positive species decrease dramatically, and the bacteroides increase," she says. "Our study gives some clues to the microbiota composition allowing C. difficile colonization," she concludes in the paper.
Clostridium difficile is the most common cause of antibiotic-associated diarrhea and pseudomembranous colitis in adults, and infections are on the rise. Morbidity and mortality are high, and patients who are treated frequently relapse, as spores persist in the gut. Reconstituting the microbial ecology, with its barrier effect "seems a very efficient way to combat C. difficile infections," says Collignon, and recent studies suggest that this can be accomplished with probiotics and fecal transplantation.
(C. Rousseau, F. Levenez, C. Fouqueray, J. Dore, A. Collignon, and P. Lepage, 2011. Clostridium difficile colonization in early infancy is accompanied by changes in intestinal microbiota composition. J. Clin. Microbiol. 49:858-865.)
Antibiotics Cure Anthrax in Animal Models
In the absence of early antibiotic treatment, respiratory anthrax is fatal. The 2001 bioterrorism attacks in the US killed four people, out of 22 infected (10 of them with respiratory anthrax), despite massive antibiotic administration, probably because therapy did not begin until the disease had reached the fulminant stage. But a multi-agent prophylaxis initiated within 24 hours post-infection prevented development of fatal anthrax respiratory disease, and treatment combining antibiotics with immunization with a protective antigen-based vaccine conferred long-term protective immunity against reestablishment of the disease, according to a study in the April 2011 issue of the journal Antimicrobial Agents and Chemotherapy. This study is the first to characterize the severity of respiratory anthrax that can be cured.
The researchers, all from the Israel Institute for Biological Research, Ness-Ziona, tested both the efficiency of different therapeutic approaches in preventing fatal disease from developing in infected animals, and their ability to cure animals in which the disease had developed into a systemic, septic phase. Rescue remains possible with appropriate agents even if initiated two days after infection.
Treatment initiated 24 hours after infection with any of four antibiotics protected the animals during treatment, but many of the animals died of anthrax after treatment was stopped, the antibiotics conferring degrees of protection ranging from 10-90 percent. Combining antibiotic treatment with a protective antigen vaccine left all animals fully protected even after the end of treatment.
Animals whose treatment was delayed beyond 24 hours post-infection developed varying degrees of bacteremia and toxemia. Treatment with doxycycline cured both sick guinea pigs and rabbits exhibiting low to moderate bacteremia; adding protective antigen vaccine to the mix boosted the level of bacteremia that was curable 10-fold in the guinea pigs and 20-fold in the rabbits. But ciprofloxacin plus a monoclonal anti-protective antigen antibody was still more effective.
In all cases, the surviving animals developed immunity against anthrax via subcutaneous challenge.
"Our results suggest that doxycycline and ciprofloxacin are efficient antibiotics to treat anthrax, not only as post-exposure prophylaxis, but also during the systemic phase of the disease," the researchers write. "Treatment with both antibiotics can cure guinea pigs and rabbits in an advanced stage of systemic anthrax"
(S. Weiss, D. Kobiler, H. Levy, A. Pass, Y. Ophir, N. Rothschild, A. Tal, J. Schlomovitz, and Z. Altboum, 2011. Antibiotics cure anthrax in animal models. Antim. Agents Chemother. 55:1533-1542.)
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