An intact microbiota is required for the gastrointestinal toxicity of the immunosuppressant mycophenolate mofetil

Giant Gastric Ulcers: An Unusual Culprit

Mycophenolate Mofetil (MMF) is routinely used immunosuppressant in solid organ transplantation is commonly associated with several gastrointestinal (GI) side effects. Here we present a case of giant gastric ulcer of 5 cm from MMF use post cardiac transplant. CASE DESCRIPTION: A 56-year-old male with history of severe ischemic cardiomyopathy post heart transplant was on immunosuppression with MMF, tacrolimus and prednisone for 5 months. He presented with severe epigastric pain and intermittent episodes of melena for 1 month. His pain radiated to back that is worsened with eating. Associated with loss of appetite, vomiting and 16-pound weight loss in 3 months. He never smoked, drank alcohol or used over the counter pain medications. He was profoundly anemic requiring blood transfusions. EGD performed demonstrated very large clean-based ulcer of 5 cm diameter in the body, smaller ulcer of 8 mm diameter in pre-pyloric region and 5-10 small aphthous ulcers in the gastric body and fundus. Gastric biopsies taken from the ulcer were negative for Helicobacter pylori, cytomegalovirus and malignancy. Flexible sigmoidoscopy revealed non-bleeding inflamed internal hemorrhoids. Consequently, MMF was discontinued and switched to azathioprine. He was treated with twice daily proton pump inhibitor therapy with resolution of abdominal pain, improved appetite and weight gain. DISCUSSION: MMF is well known for common GI side-effects such as nausea, diarrhea, vomiting, ulcers, abdominal pain and rarely gastrointestinal bleeding. Few studies reported 3 to 8% incidence of ulcer perforation and GI bleeding within 6 months. Risk of gastroduodenal erosions is nearly 1.83 times for MMF, with the highest lesions associated with MMF-tacrolimus-corticosteroid combination treatment as seen in our patient. Hypothesis is that GI tract is vulnerable because of dependence of enterocytes on de novo synthesis of purines, which is disrupted by MMF. Typically, upper GI mucosal injuries of mucosal irritation leading to esophagitis, gastritis and/or ulcers are seen. Endoscopy is both diagnostic and therapeutic if bleeding gastric ulcers are noted. Minor complications improve with reduction of drug dose or use of enteric coated preparation if feasible. Discontinuation of the drug is main stay in the management of MMF related ulcer disease. Simple medical treatment with either H2-receptor antagonists, proton-pump inhibitors, coating agents, prostaglandins or combination has proven effective in most cases. Considering excellent results with medical management of ulcer, role of surgery is limited.

The gut microbiota in transplant patients

Solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) recipients are at increased risk for developing infections due to underlying immunosuppression. Antibiotic use, and in HSCT recipients, the use of preparative regimens prior to transplantation can deplete gut commensal bacteria, resulting in intestinal dysbiosis. Emerging evidence in transplant patients, particularly HSCT, suggest that disturbances in gut microbiota populations are associated with a number of adverse outcomes. Here, we review the outcomes of HSCT and SOT recipients with gut microbiota imbalance or dysbiosis, explore the nascent field of gut microbiome therapeutic approaches including fecal microbiota transplantation and the use of precision probiotics in HSCT and SOT recipients.

Risk factors for Clostridioides (Clostridium) difficile infection following solid organ transplantation in children

BACKGROUND

Clostridioides (Clostridium) difficile infection (CDI) in pediatric solid organ transplant (SOT) recipients is a growing problem, though CDI risk factors in this population are poorly understood. Our objective was to characterize CDI risk factors in pediatric SOT recipients.

METHODS

This retrospective case-control study, performed at a single freestanding academic children's hospital, included all SOT recipients age 1-22 years who were tested for C. difficile by toxin B gene PCR between August 2009 and August 2017. CDI risk factors were assessed by comparing PCR-positive and PCR-negative cases by generalized linear mixed models.

RESULTS

Between August 2009 and August 2017, 409 SOTs were performed of which 138 (33.7%), 134 (32.8%), 131 (32.0%), and 6 (1.5%) were kidney, liver, heart, and small intestine transplants, respectively. Of 205 SOT recipients were tested for CDI, with 723 C. difficile PCR tests performed among these patients. 68/205 (33%) patients developed CDI at least once during the study period. Median (interquartile range) time to diagnosis of first CDI following SOT was 8.9 (1.2, 19.6) months. CDI was independently associated with calcineurin inhibitor use at time of C. difficile testing (odds ratio [OR] 2.38, 95% confidence interval [CI] 1.08, 5.24, P = 0.03) and systemic antibiotic exposure within 30 days of C. difficile testing (OR 1.74, 95% CI 1.08, 2.79, P = 0.02).

CONCLUSIONS

CDI is a common, relatively late post-transplant complication and independently associated with calcineurin inhibitor and systemic antibiotic exposure. The potential impact of specific immunosuppressive drug and antibiotic selection on CDI risk reduction requires further investigation.

Vancomycin relieves mycophenolate mofetil-induced gastrointestinal toxicity by eliminating gut bacterial β-glucuronidase activity

Mycophenolate mofetil (MMF) is commonly prescribed and has proven advantages over other immunosuppressive drugs. However, frequent gastrointestinal side effects through an unknown mechanism limit its use. We have found that consumption of MMF alters the composition of the gut microbiota, selecting for bacteria expressing the enzyme β-glucuronidase (GUS) and leading to an up-regulation of GUS activity in the gut of mice and symptomatic humans. In the mouse, vancomycin eliminated GUS-expressing bacteria and prevented MMF-induced weight loss and colonic inflammation. Our work provides a mechanism for the toxicity associated with MMF and a future direction for the development of therapeutics.

The carnitine-butyrobetaine-TMAO pathway after cardiac transplant: Impact on cardiac allograft vasculopathy and acute rejection

BACKGROUND

Alterations in the partly microbiota-dependent carnitine-γ-butyrobetaine (γBB)-trimethylamine N-oxide (TMAO) pathway have been linked to the progression of heart failure and atherosclerotic disease. We evaluated if circulating γBB, TMAO, and their common precursors carnitine and trimethyllysine (TML) were dysregulated after heart transplantation and associated with development of cardiac allograft vasculopathy (CAV) and acute rejection.

METHODS

We measured these metabolites in plasma from heart transplant recipients with everolimus-based (n = 32) and standard cyclosporine-based immunosuppression (n = 30) at different time-points and accompanied by assessment of CAV by intravascular ultrasound.

RESULTS

Baseline levels of carnitine, TMAO, and TML were elevated in heart transplant recipients compared with controls, and TML remained elevated throughout the observation period. The microbiota-dependent metabolite γBB increased steadily during 3 years of follow-up, with a similar decrease in its endogenous precursor TML. The increase in γBB and the change in TML were associated with a change in total atheroma volume from baseline to 3 years. Increases in γBB and carnitine levels from baseline to 1 year were associated with an increased frequency of acute rejection within the first year after heart transplant.

CONCLUSIONS

Our study reveals alterations of the carnitine-γBB-TMAO pathway after heart transplant, with increasing levels of γBB being associated with acute rejection and increase in total atheroma volume during 3 years of follow-up. Future studies should clarify whether interactions between dietary factors, immunosuppressive drugs, and the gut microbiota could influence acute rejection and CAV development to delineate mechanisms and potential novel treatment targets.

The gut microbiome and pharmacology: a prescription for therapeutic targeting of the gut-brain axis

New frontiers for host-microbe interactions continue to emerge as our knowledge of the adult gut microbiome in health and disease is continually supplemented and improved. Alterations in the gut microbiota composition in irritable bowel syndrome (IBS) are now linked to symptom severity while population-based evidence linking gut microbiome signatures to depression is an important new landmark. The effects of drugs on gut microbiome composition are also becoming clearer. Meanwhile, preclinical studies have delineated the influence of the gut microbiome at a structural and activity level in distinct brain regions. Bacterial metabolites, such as tryptamine, can activate specific receptors to impact gastrointestinal motility. These recent studies bring into focus the future implications for therapeutic targeting of the microbiome-gut-brain axis.