#2858 Immunohistochemical study reveals increased GLUT1 expression in proximal tubules of patients with acute interstitial nephritis

Abstract

Abstract Background and Aims Interstitial inflammation in acute interstitial nephritis can advance into tubular epithelial cells and produce proximal tubular dysfunction, which may be clinically expressed as renal glycosuria. Previous studies have shown that the presence of renal glycosuria in acute kidney injury is a diagnostic clue for acute interstitial nephritis (AIN) with an excellent specificity. Sodium-independent glucose transporter 1 (GLUT1) is localized in the basolateral membrane of epithelial cells along the entire length of the proximal tubule, mainly in the S3 segment, and it is involved in the transcellular glucose transport. The aim of this study was to examine renal expression of GLUT1 in the proximal tubules of patients with biopsy-proven AIN. Method We identified patients with biopsy-proven AIN. After excluding patients with diabetes mellitus and patients who had received steroid treatment previous to the kidney biopsy, we selected 10 patients with biopsy-proven AIN, and we selected 10 patients with acute tubular necrosis (ATN) matched for age, proteinuria and glomerular filtration rate as the control group. An immunohistochemical study for GLUT1 was performed on the biopsies of patients with AIN and ATN. Staining intensity was graded as 0 (negative), 1+ (weak), 2+ (moderate), and 3+ (strong). GLUT1 expression was defined as focal when <50% of epithelial cells stained positive, and diffuse when >50% of the tissue showed strong staining. Results Renal glycosuria was present in 60% of the selected patients with AIN, with a median glycosuria of 150 mg/dl (IQR 0-162 mg/dl), while only 1 patient (10%) with ATN presented glycosuria (p = 0.037). All patients with AIN showed moderate or strong cytoplasmic GLUT1 staining in the epithelial cells of proximal tubules, which was significantly more intense (2+; 20% vs 11%, 3+; 80% vs 33.3%, p = 0.008) and diffuse (80% vs 22.2%, p = 0.002) than in patients with ATN. There was a tendency for positive correlation between the concentration of glycosuria and the extension of GLUT1 staining (r = 0.316, p = 0.078). Conclusion We found higher expression of GLUT1 in the cytoplasm of proximal tubular cells in patients with AIN in comparison to ATN. These findings suggest that proximal tubular injury plays a key role in the pathogenesis of AIN, leading to renal glycosuria in some cases. We hypothesize that the localization of strong GLUT1 staining in the cytoplasm of proximal tubular cells may indicate a misallocation of GLUT1 from plasma membrane where it is functional and a reversed cell polarity which might account for the observed renal glycosuria.