Post-transplant proteinuria associated with everolimus: Definition of main features with proteomics

Little is known on both the composition and mechanism(s) of proteinuria associated with the use of mTOR inhibitors, in particular of Everolimus (E). We characterized urinary proteins utilizing an integrated proteomics approach (quantitative essays, 2-DE, MALDI-TOF, Western blot) in 48 renal transplant recipients who were alternatively treated with E (n = 31) or with enteric coated mycophenolic acid (EC-MPA) (n = 17). Twelve E patients (39%) developed high (>3 g/day) or intermediate proteinuria (1-3 g) compared to four (23%) of the EC-MPA group. Urinary proteins (p<0.001), β2 microglobulin (p<0.001) and α1microglobulin (p<0.025) were higher in E than in EC-MPA, appeared more rapidly and were inversely correlated with the day of treatment. Proteomics showed a marked increase of all urinary components in E and EC-MPA patients, major changes involving typical components of glomerular damage (albumin, α1-Zn glycoprotein, α2HS glycoprotein, leucin-richα2-glycoprotein) and specific bio-markers for E (clusters of α1-antitrypsin fragments and monoclonal λ chains). Finally, inter-α-trypsin-inhibitor heavy chain H4 precursor was decreased in E and EC-MPA urine compared to normal urine. In conclusion, E induced massive and generalized proteinuria of mixed glomerular and tubular origin that was correlated with the start of treatment and reached a nephrotic range in few cases. Specific urinary markers reflect renal alterations related to the transplant or specific alterations associated with the drug.