ORIGINAL ARTICLE 503 Studying inhibition of calcium oxalate stone formation: an in vitro approach for screening hydrogen sulfide and its metabolites _______________________________________________ S. Vaitheeswari 1, 2 , R. Sriram 1, 2 , P. Brindha 1, 2 , Gino A. Kurian 1,2 1 School of Chemical and Biotechnology, SASTRA University, Thanjavur, T. N, India; 2 Vascular Biology Lab, SASTRA University, Thanjavur, T. N, India ABSTRACT ARTICLE INFO ______________________________________________________________ ______________________ Purpose: Calcium oxalate urolithiasis is one of the most common urinary tract disea- ses and is of high prevalence. The present study proposes to evaluate the antilithiatic property of hydrogen sulfide and its metabolites like thiosulfate & sulfate in an in vitro model. Materials and Methods: The antilithiatic activity of sodium hydrogen sulfide (NaSH), sodium thiosulfate (Na 2 S 2 O 3 ) and sodium sulfate (Na 2 SO 4 ) on the kinetics of calcium oxalate crystal formation was investigated both in physiological buffer and in urine from normal and recurrent stone forming volunteers. The stones were characterized by optical and spectroscopic techniques. Results: The stones were characterized to be monoclinic, prismatic and bipyramidal habit which is of calcium monohydrate and dihydrate nature. The FTIR displayed fingerprint corresponding to calcium oxalate in the control while in NaSH treated, S=O vibrations were visible in the spectrum. The order of percentage inhibition was NaSH>Na 2 S 2 O 3 >Na 2 SO 4 . Conclusion: Our study indicates that sodium hydrogen sulfide and its metabolite thio- sulfate are inhibitors of calcium oxalate stone agglomeration which makes them unsta- ble both in physiological buffer and in urine. This effect is attributed to pH changes and complexing of calcium by S 2 O 3 2 -and SO 4 2 - moiety produced by the test compounds. Key words: Urolithiasis; In Vitro Techniques; Calcium Oxalate; Spectrosco- py, Fourier Transform Infrared; Hydrogen Sulfide Int Braz J Urol. 2015; 41: 503-10 _____________________ Submitted for publication: April 17, 2014 _____________________ Accepted after revision: October 18, 2014 INTRODUCTION The incidence of urolithiasis in recent times is alarmingly increasing in both adult and pedia- tric populations (3 per 1000 in men and 2 per 1000 in women) (1, 2). This may be due to the change in lifestyle and dietary intake as diet plays an im- portant role in the pathogenesis of kidney stone (3). Recurrent stone formation is one of the major concerns in this disease where frequent medical cares for the patients are required (4). Even though calcium phosphate and Mg-ammonium phosphate stones are prevalent, calcium oxalate stones are occurring with high incidence (70-80%) (5). This may be due to the relatively high consumption of animal protein and fat and low consumption of carbohydrate in the diet (1). The formation of stones nadir due to calcium oxalate crystal retention in the kidney resulted from the accumulation plasma oxalate, derived from both endogenous and exogenous sources. Experimental evidence indicates that Vol. 41 (3): 503-510, May - June, 2015 doi: 10.1590/S1677-5538.IBJU.2014.0193