Effects of rifaximin on circulating aged neutrophils in sickle cell disease
Authors: Dibyendu Dutta, Barbara A. Methe, Alison Morris, Seah H. Lim
Journal: American Journal of Hematology (2019)

There is a large therapeutic gap in sickle cell disease (SCD). Hydroxyurea reduces acute sickle cell-related events, but does not appear to protect patients from cardiopulmonary complications,1 which are the major causes of death in SCD patients. The long-term effects of newer agents such as crizanlizumab and l-glutamine on the disease course remain to be determined. The only cure currently available for SCD is allogeneic stem cell transplant (allo-SCT); however, many barriers2 prevent allo-SCT from being readily offered to these patients. Investigations into other therapeutic approaches are, therefore, appropriate. Activated and circulating aged neutrophils (CANs) adhere to vascular endothelium and are pivotal for the pathogenesis of sickle cell vaso-occlusive crisis (VOC). CANs in mice are regulated by intestinal microbiota.3 Treatment of SCD mice with a cocktail of ampicillin, neomycin, metronidazole, and vancomycin (ANMV) induced reduction in CANs and protected the mice from fatal tumor necrosis factor-α-induced VOC.3 Therefore, antibiotic therapy might be a potential therapeutic approach for SCD. It is, however, unclear whether the benefits of the ANMV cocktail were related to its effects on the intestinal microbiota or to the systemic effects of the absorbed ampicillin and metronidazole. Long-term use of the ANMV cocktail might also not be clinically practical and safe. An oral antibiotic that has a good safety track record for long-term use and is capable of reducing CANs would be ideal. The question of whether the benefits of the ANMV cocktail are due to its local effects on the intestinal microbiota or due to the systemic effects of the absorbed components of ANMV may also be answered if the candidate oral antibiotic is also not intestinally absorbed. Rifaximin is a minimally absorbed oral antibiotic and it fits the required safety profile. It has been used for a long term in patients with advanced liver disease.4 Its long-term use is not associated with increased risks for the development of Clostridium difficile infection (CDI), an important consideration in order not to abrogate the protective effects from CDI that SCD patients enjoy.5 To determine whether rifaximin was capable of reducing CANs in SCD, 11 patients (6 males and 5 females) with HbSS received rifaximin 550 mg twice a day (ClinicalTrials.gov Identifier: NCT03719729). The median age was 29 years (range 23-56). Median duration of therapy was 2 months (range 1-4). Five patients were taking hydroxyurea at the time of the study. CANs were measured by multicolor flow cytometry. Neutrophils were gated by Gr-1hi CD115lo SSChi and CANs by CD62Llo CXCR4hi within the neutrophil population. Rifaximin was well tolerated in all patients without significant side effects; in particular, we did not observe CDI during rifaximin therapy. There was a dramatic reduction in CANs after 2-4 weeks of rifaximin therapy (median 12.65% [range 6.07-40.05] vs 4.55% [range 2.63-20.25]) (two-tailed P = 0.0036) (Figure 1A). CANs continued to decrease at the 3-month time point in the two patients whose CANs were analyzed. These results, therefore, indicate rifaximin's ability to reduce CANs in humans and lend support to the notion that the local effects on intestinal microbiota contribute to the beneficial effects of the ANMV cocktail in mice. To gain insight into how rifaximin affected the intestinal microbiome, stool specimens from two of the patients were subjected to 16S rRNA gene sequence analysis. Qualitative assessments of taxonomic composition showed that differences such as rifaximin treatment resulted in an increased abundance in Bacteroides (Figure 1B). In summary, not unlike in SCD mice, CANs in human are also regulated by intestinal microbiota. Our findings provide the first evidence that, instead of the ANMV cocktail, rifaximin monotherapy can effectively reduce CANs that are pivotal for the pathogenesis of VOC. Our findings support rifaximin being investigated in SCD to determine its efficacy in altering the clinical course of the disease. None.