O46 – Intestinal bile acids differentially control intestinal cell proliferation
Author(s):
Background: Disruption of intestinal epithelial cell proliferation contributes to gut barrier failure in necrotizing enterocolitis. Certain enteric bacteria convert conjugated, primary bile acids (BAs) into more toxic, unconjugated secondary metabolites. Evidence suggests that while some bile acid metabolites may be beneficial to the intestine, secondary metabolites are injurious and lead to disease. Both the epidermal growth factor receptor (EGFR) and the farnesoid X receptor (FXR) are known molecular targets of bile acids and are thought to have opposing effects on intestinal cell proliferation.
Hypothesis: We hypothesized that BAs differentially modulate intestinal epithelial cell proliferation via specific activation of either EGFR or FXR.
Methods: We examined the effects of bile acids on the proliferation of rat intestinal cells (IEC-6) in vitro and confirmed these effects in a mouse colon cell line (YAMC) using both a crystal violet proliferation assay and a nucleic acid incorporation assay (EdU). Pharmacologic manipulation of both EGFR and FXR were used to determine their molecular contribution. Western blot analysis was used to assess EGFR phosphorylation.
Results: Of all bile acids tested, only taurine-conjugated cholic acid (TCA, a primary bile acid) stimulated intestinal cell proliferation (119.3 ± 3.6 % above baseline) while glycine-conjugated cholic acid and unconjugated cholic acid did not. The TCA-induced increase in proliferation was blocked by the EGFR antagonist AG1478 and by the FXR agonist GW4064. Treatment with TCA stimulated EGFR phosphorylation (Tyr1068) at 6 hours on Western blot analysis. In contrast, the taurine-conjugated secondary bile acid deoxycholic acid had no effect on intestinal cell proliferation, while the unconjugated form (DCA) decreased intestinal cell proliferation (70.8 ± 4.1% below baseline). The inhibitory effects of DCA were abolished in a dose dependent manner by blocking FXR activity with guggulsterone.
Conclusions: These results suggest that specific bile acids can be either beneficial or injurious to intestinal epithelial cell proliferation via differential activation of EGFR and FXR. Since secondary bile acids increase during times of dysbiosis, this suggests a possible mechanism by which an altered microbiome may impair intestinal integrity and lead to disease.
Increased Incidence of Blood Product Transfusions Among Transplant Patients Treated with Linezolid Compared to Daptomycin
Author(s):
Background: Thrombocytopenia is a known complication of prolonged linezolid use although little data exist specifically in the transplant population who may be at higher risk secondary to ongoing immunosuppression. This study evaluates the hematological safety of linezolid for the treatment of infections in transplant recipients compared to transplant patients treated with a control antibiotic, daptomycin.
Hypothesis: The incidences of hematological toxicity are increased in transplant patients treated with linezolid compared to transplant patients treated with daptomycin.
Methods: We performed a retrospective study from 1/08 through 6/12 of transplant inpatients on immunosuppression treated with linezolid (LZD) or daptomycin (DAP) excluding patients: <18 years old, pre-engraftment after HSCT, relapsed cancer, aplastic anemia, or those who had received cytotoxic therapy or antibodies within 30 days preceding treatment. Outcomes included the incidences of anemia, leukopenia, or thrombocytopenia at the end of antimicrobial treatment, and blood product transfusions. Results: The LZD cohort included 126 incidences, while the DAP cohort included 130 incidences of treatment. The demographic and baseline clinical variables were similar between cohorts. DAP cohort were more likely to be treated for blood stream infections (46.15% vs 31.75%; P=.02), while LZD group received more linezolid doses (15.8 vs 9.74; P<0.0001) than daptomycin doses received by the DAP group. LZD patients were more likely to receive red blood cell (68% vs 50.8%; P=0.007) and platelet transfusions (38.4% vs 20.8%; P=0.002) during course of treatment. For patients receiving thrombocytopenic drugs, mycophenolate and/or chemotherapeutic agents, end of treatment (EOT) platelet <150K was not statistically significant in the LZD cohort compared to DAP (54.8% vs 40%; P=0.09). Conclusions: Transplant patients who received linezolid had a higher incidence of blood product transfusions, compared to transplant patients who received daptomycin. Although there was no statistically significant EOT thrombocytopenia between cohorts, LZD patients were more likely to receive platelet transfusion during the course of treatment. The difference may be related to greater drug exposure (number of doses) in the LZD cohort. Clinicians caring for transplant patients should account for the need for blood products when considering the use of linezolid.