Biomarkers of Calcineurin Inhibitor Nephrotoxicity

Nephrotoxicity limits the use of calcineurin inhibitors (CNI) in transplantation. Currently, CNI dosage is adjusted using serum creatinine and plasma CNI levels to protect the graft from toxic damage from overmedication or rejection from undermedication. Reduced long-term survival of transplanted kidneys indicates the need for a suitable biomarker of CNI toxicity. In a rodent model, we identified a panel of five urinary biomarkers of CNI nephrotoxicity comprising KIM-1, calbindin, clusterin, EGF and E cadherin. KIM-1, calbindin, and clusterin were differentially increased in CNI toxicity compared to controls among nine known biomarkers of kidney damage. EGF and E cadherin were identified by quantitative proteomics applied to pooled CNI toxic rodent urine samples. Kidney tissue mRNA expression confirmed increased KIM-1, calbindin, clusterin and EGF. These and other known damage biomarkers were then measured in a pilot study in human urine samples from consecutive kidney transplant recipients over one year. Serum creatinine did not change with plasma CNI levels highlighting that reliance on serum creatinine to identify CNI toxicity places the graft at risk of toxic damage. In contrast, multiple urinary biomarkers of kidney injury were increased despite apparently acceptable target plasma tacrolimus levels highlighting a need for greater awareness of potential CNI toxicity. The rodent model also showed that metformin ameliorated CNI toxicity. Combining CNI with metformin prevented CNI-associated reduction in inulin GFR and urinary biomarker increases. In exploring the mechanisms of metformin, we observed that CNIs reduced renal PGC 1a (a major regulator of mitochondrial homeostasis) at both mRNA and protein levels. We hypothesised that metformin increased PGC 1a by increasing AMPK. PGC 1a protein and mRNA increased when metformin was added to CNI treatment. Tissue AMPK levels correlated positively with PGC 1a in the CNI and CNI-metformin combination treatment groups indicating that PGC 1a may be mechanistically involved in the metformin therapeutic pathway in ameliorating CNI toxicity. Overall, these studies suggest strategies for both detecting and preventing toxicity and for monitoring clinical protection of human kidneys against CNI-associated injury

Clinical characteristics of study subjects.

<p>Key: Data are median (IQR), or n (%).</p><p>NA: not applicable, eGFR: estimated glomerular filtration rate (Modification of Diet in Renal Disease formula), uACR: albumin: creatinine ratio.</p

Concentration of [A] cystatin C in whole urine, and [B] concentration of mRNA for cystatin C in exosomes.

<p>Samples were taken at 4, 24 and 168[cf. deceased] are shown as triangles. The geometric mean is shown. Significant differences between groups [p<0.05] are denoted by horizontal lines.</p

Concentration of [A] KIM-1 in whole urine 4, 24 and 168 h after renal transplantation.

<p>Samples were taken at 4, 24 and 168-1 was not detected in most subjects. For the transplant patients, the data for those who received kidneys from live donors [cf. deceased] are shown as triangles. The geometric mean is shown. Significant differences between groups [p<0.05] are denoted by horizontal lines.</p

Concentration of 18S RNA in urinary exosomes.

<p>Samples were taken at 4, 24 and 168[cf. deceased] are shown as triangles. The geometric mean is shown. Significant differences between groups [p<0.05] are denoted by horizontal lines.</p

Concentration of [A] IL-18 in whole urine, and [B] concentration of mRNA for IL-18 in exosomes.

<p>Samples were taken at 4, 24 and 168[cf. deceased] donors are shown as triangles. The geometric mean is shown. Significant differences between groups [p<0.05] are denoted by horizontal lines.</p

Concentration of [A] NGAL in whole urine, and [B] concentration of mRNA for NGAL in exosomes.

<p>Samples were taken at 4, 24 and 168[cf.deceased] donors are shown as triangles. Significant differences between groups [p<0.05] are denoted by horizontal lines.</p

Spearman correlations between levels of protein and mRNA biomarkers and the day 7 creatinine reduction ratio at 4, 24 and 168

<p>There were no significant correlations between the day 7 CRR and mRNA for these biomarkers, or between mRNA and protein levels of biomarkers. KIM-1 mRNA was not reliably detected in exosomes.</p

Randomised controlled trial of the impact of haemodiafiltration on uraemic neuropathy: FINESSE study protocol

Introduction: The majority of patients undergoing haemodialysis (HD) show evidence of uraemic neuropathy, a condition with no known disease-modifying treatments. The pathogenesis of uraemic neuropathy is poorly understood, but may be related to cumulative exposure to middle molecules or other solutes such as potassium. It is not known whether haemodiafiltration (HDF) reduces the progression of uraemic neuropathy. Methods and analysis: Filtration In the Neuropathy of End-Stage kidney disease Symptom Evolution (FINESSE) is a multicentre, randomised, open-label, blinded endpoint assessment, controlled trial designed to assess the impact of HDF versus HD on uraemic neuropathy. Maintenance HD patients will be randomised in a 1:1 ratio to receive HDF or HD with high-flux membranes for 4 years. The primary endpoint is the difference in the mean change in Total Neuropathy Score (TNS) - a measure of peripheral neuropathy combining symptoms, signs and nerve conduction velocity - over the study period. Secondary outcomes include change at annual timepoints in the TNS and the Neuropathy Symptom Score; and in morbidity, mortality and safety events. Ethics and dissemination: The FINESSE trial has been approved by the Ethics Review Committee of the Sydney South West Area Health Service (HREC/09/RPAH/268) and of Adventist HealthCare Limited (2012-027). When published in a peer-reviewed journal, it will be the largest and longest reported randomised trial aimed at reducing the incidence and severity of uraemic neuropathy. It will advance the understanding of the natural history of uraemic neuropathy and the influence of convective therapies on both neurophysiological and clinical outcomes. It will also allow refinement of current hypotheses surrounding the pathogenesis of uraemic neuropathy and, most importantly, may lead to improvements in the lives of the many patients affected by this debilitating condition