Altered IgG<SUB>4</SUB> renal clearance in patients with inflammatory bowel diseases. Evidence for a subclinical impairment of protein charge renal selectivity

Background.A loss of intestinal glycosaminoglycans (GAGs) has been shown in inflammatory bowel diseases (IBD). Since GAGs are involved in the regulation of renal protein filtration and GAGs disruption is associated with anionic proteinuria, we examined whether changes in the selectivity of renal protein filtration occur in IBD.
Methods.From 46 patients with IBD (17 with Crohn's disease (CD), and 29 with ulcerative colitis (UC)) and 21 healthy subjects, urine and serum samples were obtained. Albumin, total IgG and IgG₄ clearances were measured using sensitive methods. Serum p-ANCA and TNF-α were tested.
Results.Median IgG₄ clearance was 0.041 ml/ min/10^-3 in patients with UC and 0.10 ml/ min/10^-3 in CD patients, both significantly higher than in controls (0.03 ml/min/10^-3) (P&lt;0.03). IgG₄ clearance was above the upper normal limit in 9/17 CD (53%) and in 10/29 UC (34.5%). Eighteen of 19 patients showing abnormal IgG₄ clearance were taking mesalazine. In patients on maintenance oral mesalazine, IgG₄ clearance was higher than that in patients off treatment (0.12 vs 0.03 ml/min/10^-3, P=0.04). No clinical/laboratory sign of renal dysfunction was documented in patients with altered IgG₄ clearance and maintained on mesalazine treatment.
Conclusion.Renal protein charge permselectivity is impaired in 40% of patients with IBD with no overt proteinuria. Our data suggest that altered IgG₄ clearance may represent a subclinical marker of renal involvement in IBD.