Oxalate Nephropathy Pathophysiology and Biochemical Features

Abstract

The importance of oxalate (Ox) in human pathology stems from the very low solubility of its calcium salts in biological fluids. Renal excretion is the exclusive way of Ox removal from the body and the efficiency of renal clearance fixes plasma Ox in the order of μmol/l and plasma saturation with calcium oxalate (βc a O x ) safely low. However urine turns out to be near always supersaturated and this accounts for the outermost prevalence of CaOx nephrolithiasis (NL) in man. This crucial role of the kidney accounts for the risk of Ox deposition within renal tissues whenever Ox generation increases, featuring Oxalate Nephropathy. Moreover when renal function is lost, progressive Ox retention induces systemic oxalosis. Severe hyperoxaluria (HOx) is produced by two variants of a rare inborn defect of Ox metabolism. Biochemical features of 5 patients with type I primary HOx (PHOx) are described and the mechanisms of renal and systemic oxalosis discussed. Crohn’s and other ileal diseases are well known causes of enteric HOx. Intestinal absorption of Ox raises to twofold normal and increases urine Ox in such a way as to yield very high values of βc a ox. Recurrent CaOx stones represent a threat for renal function, namely if renal amyloidosis superimposes. Mild Hox may occur in some 20% of idiopathic CaOx stone-formers (ICaSF). This novel entity is currently under study and is held to represent a heterogeneous syndrome. Renal failure which occurs in less than 20% of ICaSF appears to be poorly related to changes in Ox metabolism.