Raffaele Girlanda¹, Amrita Cheema², Prabhjit Kaur², Juan-Francisco Guerra¹, Jennifer Riggs², Cal Matsumoto¹, Michael Zasloff², Thomas Fishbein¹

¹Transplant Institute Georgetown University Hospital, Washington, DC, United States; ²Georgetown University School of Medicine, Washington, DC, United States

Background/Aim: Surveillance endoscopy and biopsy are currently standard methods to monitor intestinal transplant recipients and to diagnose rejection. Limits of biopsy include invasiveness, sampling error and cost. Early non-invasive markers of intestinal rejection are needed. Metabolomics is a new approach to analyze the composition in small molecules of biologic samples. In a pilot study we applied metabolomics to the effluent fluid from ileostomy or stool of intestinal transplant recipients to assess the feasibility of metabolomics to identify biomarkers of intestinal allograft rejection.

Patients and Methods: We collected a sample (1ml) of ileostomy fluid or stool from 19 intestinal transplant recipients (8M 11F median age 15 years (1-54) transplanted between 2003 and 2011 (isolated intestine n=16, liver-intestine n=3). At the time of sample collection 16 patients had no rejection (group A) and 3 patients had acute rejection (group B) (grade 2 n=1, grade 3 n=2). Immunosuppression consisted of antibody induction (basiliximab or thymoglobulin) and maintenance with tacrolimus, sirolimus and prednisone. Sample preparation and metabolite extraction was performed as per protocol. UPLC-TOF MS analysis was performed. The data were acquired in duplicate for each sample in positive and negative ionization mode and pre-processed using MassLynx software (Waters Corporation, USA), followed by multivariate data analysis using the SIMCA-P software (Umetrics, Inc.) and the Random Forests algorithms. Madison Metabolomic Consortium Database and the Human Metabolome Database were used to identify detected metabolites.

Results: We detected a total of 347 and 627 metabolites (amino acids, bile acids, fatty acids, metabolites of drugs and others) in the negative and positive ionization mode respectively, with a specified mass range of 50-850 Daltons. There was a significant interclass separation between the non rejection and rejection groups with a factor of change 10x or higher (range 10-10000) in 30/99 and 40/133 of top metabolites interrogated in the two modes, respectively. The metabolomic profile of non-rejectors was homogenous, while the rejection group was heterogeneous, probably due to the small sample size. Identification and characterization of these metabolites and functional pathway analysis is ongoing.

Conclusion: In this pilot study metabolomics proved to be a feasible method to monitor non-invasively intestinal transplant recipient. Our preliminary results show a different ileostomy/stool profile between patients with acute rejection and non-rejectors. Although larger studies are needed, metabolomics appears to be a promising tool to identify biomarkers of intestinal allograft rejection.