Histologic and clinical findings in living donor allografts with long-term stable function

BACKGROUND/AIMS

Protocol biopsy is an important strategy which assesses the histological changes that can occur in the renal allograft and adversely affect its outcome. We aimed to evaluate histological changes in long-term living donor transplants.

METHODS

Elective biopsies were done for 120 live donor renal transplant recipients with well-functioning grafts and no rejection history at least 1 year or more after transplant. All patients had serum creatinine levels <2 mg/dl. The histopathological findings using the chronic allograft damage index score were correlated with different clinical and immunological parameters.

RESULTS

Chronic tubulointerstitial fibrosis was the most prevalent finding (85% of cases), mostly of mild degree. Normal biopsies were reported in only 7.5% of cases, whereas chronic cyclosporine nephrotoxicity was detected in 5.8% of biopsies. Posttransplant hypertension was significantly correlated with glomerulosclerosis, and posttransplant diabetes with glomerulosclerosis, mesangial matrix increase, tubular atrophy and interstitial fibrosis. The main risk factors associated with a high chronic allograft damage index score were DR mismatching, posttransplant diabetes and time of biopsy. All histopathological changes increased with advancing donor age and declining graft function.

CONCLUSION

Elective biopsies showed that histopathological findings do exist even with stable renal function that may pave the way for predicting long-term graft outcome.

Cyclosporine-Induced renal dysfunction

The most practical way to assess and to quantitate the renal function in renal transplant patients is the Cockcroft-Gault equation or an equation used to estimate the glomerular filtration rate (GFR), derived from the Modification of Diet in Renal Disease study. Chronic cyclosporine (CsA) nephrotoxicity causes structural lesions in the kidney and an impairment in the GFR. Determining the composition of the interstitial collagens may be helpful to establish the diagnosis. CsA trough levels are a poor indicator of drug exposure; drug exposure should be quantitated using more accurate methods. Although routine biopsies often show histopathological evidence of structural damage, the excellent kidney graft half-life and the documentation that the creatinine clearance usually remains stable over years in CsA-treated renal transplant patients suggest that its use in kidney transplant patients does not inexorably lead to graft failure. Protocol biopsies show a high incidence of chronic structural CsA toxicity but transplant nephrectomies show that CsA nephrotoxicity as the sole cause of graft loss is extremely rare.

Structural and functional correlations in stable renal allografts

BACKGROUND

Renal functional reserve (RFR) has been proposed as a surrogate marker of renal mass, but its significance in well-functioning renal transplants is controversial. Thus, we used early protocol biopsies to analyze structural and functional correlations in stable grafts.

METHODS

We studied 32 cyclosporine (CsA)-treated stable cadaveric transplants at 5 months. Biopsies were evaluated according to Banff criteria and histomorphometry. Inulin and p-aminohippurate clearances were used to calculate glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). RFR after an amino acid infusion (RFR-AA) and after a combined amino acid and dopamine infusion (RFR-AA-DOPA) was evaluated.

RESULTS

Baseline GFR was 54 +/- 16 mL/min/1.73 m2, and ERPF was 219 +/- 55 mL/min/1.73 m2. RFR-AA was 9% +/- 13%, and RFR-AA-DOPA was 22% +/- 20%. RFR-AA correlated with CsA dose (R = 0.39; P = 0.02), whereas RFR-AA-DOPA correlated with CsA dose (R = 0.36; P = 0.04) and CsA levels (R = 0.40; P = 0.02). The only histological parameter associated with RFR was the presence of arteriolar hyalinosis (AH). Patients showing an AH score of 1 or greater (n = 7) had lower RFR-AA (0% +/- 9% versus 11% +/- 13%; P = 0.02) and lower RFR-AA-DOPA (9% +/- 17% versus 26% +/- 19%; P = 0.03). Multivariate analysis showed that an AH score of 1 or greater, but not CsA dose or levels, was associated with RFR-AA (R = 0.42; P = 0.01). RFR-AA-DOPA was associated with hyaline arteriolar damage (R = 0.43; P = 0.01), as well as CsA levels (R = 0.54; P = 0.006).

CONCLUSION

The presence of AH is the only histological parameter associated with impaired RFR in well-functioning grafts.