Image by Volker Brinkmann
Preclinical research suggests that usingantibiotics to deplete the body’s microbiome may prevent acute sickle cell crisis in patients with sickle cell disease (SCD) and could potentially offer the first effective strategy for warding off the disease’s long-term complications, such as organ failure.
The work, published in Nature, may also have implications for other inflammatory blood-vessel disorders, including septic shock.
The study was led by Paul Frenette, MD, of Albert Einstein College of Medicine in Bronx, New York. In 2002, Dr Frenette and his colleagues reported that SCD vessel blockages occur when sickled red cells bind to neutrophils that have adhered to the vessel walls.
“This earlier work indicated that not all neutrophils are the same,” Dr Frenette said. “Some appear to be inert, while others appear overly active in promoting inflammation, which is useful for attacking microbes but causes neutrophils to capture sickled red cells inside vessels.”
“So in the current study, we investigated whether the age of the neutrophils might be influencing whether they become active and pro-inflammatory.”
Neutrophils and SCD
The researchers began by transfusing whole blood into mice and then analyzing young neutrophils (harvested 10 minutes post-transfusion) and aged neutrophils (harvested 6 hours post-transfusion). The neutrophils became more active as they aged, suggesting that neutrophils receive external signals telling them to age.
The investigators were able to trace these “aging” signals to the body’s microbiome. They found the microbiome produces chemicals that cross the intestinal barrier and enter the bloodstream, where they generate the aged, overly active subset of neutrophils that contribute to SCD.
“Since the body’s microbiota seem to ‘educate’ neutrophils to age, we realized that purging those microbes through use of antibiotics might help against SCD,” Dr Frenette said.
To find out, he and his colleagues conducted experiments in a mouse model of SCD. These mice possessed 5 times as many aged neutrophils as healthy control mice.
When the researchers depleted the microbiota of SCD mice using antibiotics, they observed a striking reduction in neutrophils but not in other white blood cells (such as monocytes, T cells, and B cells).
Moreover, giving antibiotics to SCD mice appeared to prevent sickle cell crisis. Interactions between neutrophils and red cells were markedly reduced in microbiota-depleted SCD mice, resulting in improved local blood flow and greatly improved survival in the mice.
“What was most surprising and exciting to us was the effect of antibiotics on chronic tissue damage,” Dr Frenette said.
“We found that the spleen enlargement of SCD mice was significantly reduced in the microbiota-depleted animals, and liver analysis revealed major reductions in liver damage, including inflammation, scarring, and tissue death. This is the first time that anything has been found to have an impact on the organ damage that can be so devastating in SCD.”
Septic shock
The investigators then studied septic shock, another serious blood disorder in which activated, pro-inflammatory neutrophils play a role.
To induce septic shock, the team gave control and microbiota-depleted mice a dose of a bacterial toxin that would normally be lethal.
The control mice had the neutrophil aggregates and clumping of neutrophil DNA that contribute to death from septic shock, but the microbiota-depleted mice were largely free of neutrophil complications and survived.
“Remarkably, we could prevent microbiota-depleted mice from surviving septic shock if we infused them with aged neutrophils but not if we infused the same number of young neutrophils,” Dr Frenette said. “So depleting the microbiota may help against inflammatory blood diseases in addition to SCD.”
SCD patient samples
Finally, the researchers investigated whether their findings in mice might be relevant to humans with SCD.
The team obtained blood samples from 9 healthy children and 34 patients with SCD. Eleven patients were taking penicillin daily to ward off infections, as is recommended for children with SCD who are 5 years of age or younger. The other 23 patients with SCD had been off penicillin for at least 2 months.
Consistent with the findings in mice, children with SCD who were not taking penicillin had many more circulating aged neutrophils than the healthy children.
The investigators then compared neutrophil levels in the 2 groups of children with SCD—those taking penicillin and those not on the drug—and found a much lower number of aged neutrophils in the blood of those who were taking penicillin.
“Daily penicillin for patients with SCD younger than 5 works really well in preventing infections,” Dr Frenette said. “Our study suggests that penicillin and other antibiotics could play an even broader role in potentially benefiting older patients.”
“[W]e hope to carry out a clinical trial to determine whether antibiotics can help patients with SCD by preventing the sickle cell crisis and long-term organ damage associated with the disease.”
