Hepatic injury-induced remote kidney injury is associated with impaired hepatic clearance of cell-free hemoglobin.

BACKGROUND AND HYPOTHESIS: Hepatic ischemia-reperfusion (HIR) injury, often extends beyond the primary site and causes damage in distant organs, including the kidney. In particular, concomitant kidney injury occurring alongside with the liver injury represents a significant clinical problem, but this mechanistic understanding remains unclear. Given that the liver is the primary organ responsible for clearing cytotoxic cell-free hemoglobin (CFH) and heme released during hemolysis, we hypothesized that hemolysis and impaired hepatic clearance of these hemolysis-derived products following HIR may contribute to kidney injury.

METHODS

Mice were subjected to HIR, after which liver and kidney injury were evaluated. Some mice were administered with cilastatin, a blocker of megalin, or deferoxamine, an iron chelator and ferroptosis inhibitor. After HIR, hemolysis, hepatic expression of CFH/heme clearance-related genes, and ferroptosis in the kidney were analyzed.

RESULTS

HIR induced liver and kidney damage, accompanied by hemolysis, increased CFH/heme levels, and reduced levels of haptoglobin and hemopexin, key regulators of hepatic CFH/heme clearance, in the liver. HIR caused hemoglobin internalization into proximal tubule cells (PTCs). Furthermore, HIR increased heme oxygenase-1 expression, iron content, and lipid peroxidation in the kidneys, while decreasing glutathione levels, indicating that HIR induces ferroptosis in PTCs. Cilastatin prevented HIR-induced hemoglobin uptake, iron accumulation, and lipid peroxidation in the kidneys, thereby protecting the kidneys. Deferoxamine also protected the kidneys against HIR.

CONCLUSION

These findings demonstrate that HIR-induced remote kidney injury (RKI) is associated with elevated circulating CFH/heme resulting from impaired hepatic CFH/heme clearance and increased hemolysis. This suggests that CFH/heme play as mediators of HIR-induced RKI, and that targeting hemolysis and CFH/heme cytotoxicity may be a strategy to treat and prevent remote organ injury, particularly in the kidneys.