By Sandy Hemphill, Contributing Writer, BabyMed
Antibiotics are often seen as drugs that work quickly and do little, if any harm. They’ve been taken for granted for generations but they’ve been misused and overused and they do cause problems. One problem misuse causes is the growing number of drug-resistant bacteria (superbugs) that are no longer killed off by the most-often used antibiotics. A new study from Germany indicates they also prevent growth of new brain cells that affect memory and they do it by way of the gut microbiome.
Antibiotics and the Gut Microbiome
Broad-spectrum antibiotics are often used in human medical settings and in agricultural livestock operations. In animals and humans alike, broad-spectrum antibiotics target all bacteria, both the good kind that keeps us healthy and the bad kind that makes us sick. By killing off all or multiple strains of bacteria, the bacterial colonization in the digestive tract is thrown off balance.
One side effect of an off-balance gut microbiome is diarrhea. Doctors frequently advise patients to take probiotics such as plain unflavored yogurt to maintain gut health during a course of antibiotics. The association between digestive distress and antibiotics is well established.
Antibiotics, Memory, and Neurogenesis
The new study from the Max-Delbrueck Center for Molecular Medicine in Berlin expands that association from antibiotic to the gut to the brain. “We found prolonged antibiotic treatment might impact brain function,” said the study’s lead author, Dr. Susanne Asu Wolf.
Wolf first suspected a link between the immune system and growth of healthy brain cells approximately 10 years ago while studying T cells. T cells, so called because they originate in the thymus gland, are a type of white blood cells the immune system launches into action when foreign DNA, such as from a bacterium or virus, is detected in the body.
First Experiment
Wolf and her research team used mice to identify any differences in brain function when the gut microbiome was thriving or depleted, as it would be if the mice were taking antibiotics. In one experiment, some mice were given enough antibiotics to destroy almost all intestinal microbes and some were not given any antibiotics:
- Those getting antibiotics scored poorly on memory tests.
- Microscopic study of their hippocampus showed very little neurogenesis (new brain cell formation). The hippocampus is a part of the brain that processes memory.
- A specific type of white blood cells – Ly6C(hi) – was present in lower than normal levels in the blood, bone marrow, and brain, indicating an immune-system association with antibiotics and neurogenesis.
Second Experiment
A second experiment, focusing on Ly6C(hi), compared memory skills and neurogenesis in a group of untreated mice with healthy gut microbiomes against a group that had their gut microbiomes depleted genetically or by antibiotic use. Again, the mice with low levels of Ly6C(hi) performed poorly on memory tests and exhibited evidence of limited growth of new brain cells.
Memory function improved, however, when the mice with depleted levels of Ly6C(hi) were given more of it. Neurogenesis also returned to healthier levels of activity.
"The magnitude of the action of probiotics on Ly6C(hi) cells, neurogenesis, and cognition impressed me," said Wolf. "For us, it was impressive to find these Ly6C(hi) cells that travel from the periphery to the brain and, if there's something wrong in the microbiome, Ly6C(hi) acts as a communicating cell," she added.
Probiotics and Exercise
The German researchers were able to reverse the neurological impairments of antibiotic-depleted gut microbes by administering probiotics to the mice. The probiotics seeded a return to healthy microbial colonization of the gastrointestinal tracts of the mice.
Fecal transplants have proven effective in restoring gut health in humans with chronic bowel and gastrointestinal disorders. When the researchers tried fecal transplants on the antibiotic-treated mice, their gut microbiomes recovered and flourished but their neurological deficits were not reversed as had occurred with oral probiotic administration.
Some antibiotic-treated mice were allowed to exercise on a wheel in their cages instead of getting probiotics or fecal transplants. Memory function and neurogenesis soon returned to normal with no other interventions except exercise.
Antibiotics and Humans
Although Wolf’s study involved mice only, it suggests similar memory loss and impaired neurogenesis might also occur in humans taking antibiotics over a long period of time. Neurological concerns are never welcome at any age but the study suggests thinking twice about prolonged antibiotic use in young children, when brain growth and development is in full swing, and in the elderly, when memory decline is assumed to be a natural part of the aging process.
Sources:
Wolf, SA, et al. "Ly6C(hi) Monocytes Provide a Link between Antibiotic-Induced Changes in Gut Microbiota and Adult Hippocampal Neurogenesis."PubMed. Cell Reports / Cell (Elsevier BV), 31 May 2016. US National Library of Medicine / National Institutes of Health. Web. 20 June 2016.
"The ABC's of Antibiotics."Virginia Department of Health. APIC / Association for Professionals in Infection Control and Epidemiology, n.d. Web. 20 June 2016.