Proximal Tubule Secretory Clearance, Injury, and Kidney Viability in Cirrhosis.

Introduction: Cirrhosis affects all structures of the kidney, in particular the tubules, which are responsible for secretion of protein-bound metabolites and electrolyte/water homeostasis. Yet, prevailing assessments of kidney function focus solely on glomerular filtration rate (GFR), which may incompletely reflect these processes. We sought to characterize markers of tubular function, injury, and viability in patients with and without cirrhosis.

Methods: We recruited outpatients undergoing liver transplantation evaluation for a collection of plasma and 24-hour urine, matching by GFR to control participants without cirrhosis. We measured urinary kidney injury molecule-1, a marker of proximal tubular injury, as well as epidermal growth factor (EGF), a marker of viability necessary for tubular epithelial cell proliferation after injury. We also estimated secretory clearance by measuring several highly secreted endogenous metabolites in urine and plasma.

Results: We recruited 39 patients with cirrhosis (mean model for end-stage liver disease 17 ± 4, Child-Pugh 8 ± 2, estimated glomerular filtration rate 66 ± 20 mL/min/1.73 m 2 ) and 58 GFR-matched controls without cirrhosis (estimated glomerular filtration rate 66 ± 21 mL/min/1.73 m 2 ). Urinary kidney injury molecule-1 was 4.4-fold higher than controls (95% confidence interval: 2.9-6.5), and EGF averaged 7.41-fold higher than controls (95% confidence interval: 2.15-25.53). We found that of 8 solutes, 5 had significantly greater kidney clearance in cirrhosis (1.3-2.1-fold higher): indoxyl sulfate, p-cresol sulfate, pyridoxic acid, tiglylglycine, and xanthosine.

Discussion: Cirrhosis was characterized by molecular signs of tubular injury in stable outpatients without acute kidney injury, accompanied by largely preserved tubular secretory clearance and greater signs of tubular viability. Within the limitations of the study, this suggests a phenotype of chronic ischemic injury but with initial preservation of tubular function in cirrhosis.