A novel role for uric acid in acute kidney injury associated with tumour lysis syndrome

Abstract

Tumour lysis syndrome (TLS) is a complication associated with the treatment of tumour types with high proliferative rate, large tumour burden or high sensitivity to cytotoxic therapy. The implementation of risk stratification strategies [1], appropriate prophylactic measures, vigilant monitoring of laboratory parameters and active interventions to reduce risk factors has dramatically decreased the incidence of clinically significant morbidity that results in end organ damage and mortality. Despite these advances, 5–6% of atrisk paediatric and adult patients undergoing chemotherapy develop acute kidney injury (AKI), and 40–50% of these patients will require dialysis therapies with associated allcause mortality in excess of 50% [2–4]. Similar outcomes are reported with spontaneous TLS [5]. The lack of standardized definitions and outcome measures has hampered appreciation of the extent of adverse renal outcomes in TLS. Recent adoption of a uniform definition of AKI (increase in serum creatinine of 0.3 mg/dL from baseline or a 50% increase in serum creatinine from baseline values within 48 h) [6] and the recognition that the development of in-hospital AKI have significant implications for long-term mortality [7] underscores the need to understand the mechanisms involved in AKI associated with TLS. Furthermore, the effect of chronic kidney disease (CKD) on renal outcomes in TLS requires a study, as clinical tumour lysis occurs more frequently in patients with pretreatment renal impairment [8]. One study examining risk factors for in-hospital AKI of diverse aetiologies reported that CKD increases the risk of AKI 40-fold with a 20-fold increased risk for dialysis [9]. Here, we will briefly review the current understanding of the pathogenesis of TLS-induced AKI. In particular, a recent literature suggests that AKI and nephropathy are not simply due to intrarenal crystal deposition of urate and phosphate. Mechanism of AKI associated with intrarenal deposition of uric acid crystals TLS is a group of metabolic complications that occur after the treatment of large volume, rapidly proliferating haematological cancers including not only acute leukaemia and aggressive lymphomas but also some solid tumours. Metabolic alterations that result include hyperkalaemia, hyperphosphataemia, hyperuricaemia and hyperuricosuria, hypocalcaemia and consequent AKI. Specifically, AKI associated with TLS has been considered to be exclusively a crystal-dependent process caused by the massive and abrupt release of intracellular metabolites from chemosensitive, rapidly proliferating tumour cells that undergo rapid lysis and release nucleic acid breakdown products, phosphorus and potassium. Both urate and calcium phosphate crystals may cause crystal-dependent injury of the kidney which overwhelms the normal homeostatic mechanism(s) autoregulating normal renal physiology [10]. One of the most important mediators of AKI resulting from TLS is uric acid. When dying cells release DNA and RNA, they are degraded in the liver and other sites with the rapid production of uric acid. Serum uric acid rises acutely, resulting in marked uricosuria. Such cell death and degradation also results in acid generation, often with volume depletion, resulting in acidic urine that decreases the solubility of uric acid. When levels of urinary uric acid exceed its solubility, both micro- and macrocrystal formations occur in the distal tubules and collecting ducts with obstruction of the tubular lumen. The prevention of AKI resulting from TLS includes initiating prophylactic measures prior to and during chemotherapy, including hydration, alkalinization of the urine, use of the xanthine oxidase inhibitor allopurinol, as well as the urate oxidase inhibitor, rasburicase or its derivatives.