THE EFFECT OF (L)-CYSTEINE AND (L)-2-OXOTHIAZOLIDINE-4-CARBOXYLIC ACID (OTZ) ON URINARY OXALATE EXCRETION - STUDIES USING A HYPEROXALURIC RAT MODEL

Purpose: To determine the efficacy of (L)-cysteine and (L)-2-oxothiazo lidine-4-carboxylic acid (OTZ) in reducing urinary oxalate excretion u nder hyperoxaluric conditions and to determine whether by inclusion of glycolate in a standard diet, cysteine:glyoxylate adduct can be detec ted in hyperoxaluric rats given either compound. Materials and Methods : Hyperoxaluria (200% above basal) was induced 2 days prior to commenc ement of the studies and maintained throughout. After a 3 days baselin e, animals were randomly allocated to a control or treatment group. St andard diet containing either (L)-cysteine or OTZ was then fed to the treatment groups for 5 days while standard diet alone was fed to the c ontrol groups. Urinary oxalate excretion was subsequently monitored an d average daily rates were then compared with basal values. Plasma and urine were analyzed for adduct. Results: Both (L)-cysteine and OTZ si gnificantly reduced urinary oxalate excretion relative to the basal hy peroxaluric level (28.6 +/- 1.5 mu mol./day). While (L)-cysteine reduc ed oxalate excretion over the 5 day treatment period by only 7.82 +/- 1.39 mu mol./day (27%), OTZ reduced it by 12.34 +/- 1.58 mu mol./day ( 43%). Adduct could not be detected in plasma or urine in this study. C onclusions: This study confirms that both (L)-cysteine and OTZ are eff ective in reducing urinary oxalate excretion under hyperoxaluric condi tions, with OTZ being more effective than (L)-cysteine. These compound s were shown to be 3- to 4-fold more effective in reducing urinary oxa late excretion under hyperoxaluric conditions when compared with the r esults from previous studies under normooxaluric conditions.