Abstract:
Kidney stone disease has attracted considerable interest among scientists as
one of the most important non-communicable diseases. Approximately 20% of
the population has affected by kidney stones. Kidney stones are collection of
microcrystalline biomineralized materials, mainly containing calcium oxalate
monohydrate (COM) or dihydrate (COD), either alone or combined. Even
though the kidney stone disease is a global health issue, a few therapeutic
protocols are effective to treat kidney stones. The current study investigated
the effect of some selected organic acids on calcium oxalate kidney stone
formation and dissolution in synthetic urine and in supper saturated solutions.
The organic acids used were malic acid, parahydroxybenzoic acid, syringic
acid, caffeic acid and citric acid. Aqueous solutions of CaCl2 and CaC2O4
were combined together at pH 7.3 to prepare the calcium oxalate supper
saturated solutions. To simulate the natural urine conditions for the
experiments, typical standard reference artificial urine solutions were prepared.
Varying amounts of individual organic acids and their mixtures (1-10 mg
range) were separately added to the supper saturated and synthetic urine
solutions. The crystal deposition kinetics were monitored by conductivity
measurements. The formed crystals were characterized by FTIR, XRD, SEM
and redox titrations to determine the structure and the morphology of calcium
oxalate crystals formed. In all experiments, the formed crystals were mainly
consisted of thermodynamically more stable COM. The inhibition activity of
organic acid varies in the order of malic acid (3.2%) < caffeic acid (4%) <
syringic acid (6.2%) < acid mixture (10%) < parahydroxybenzoic acid (10.6%)
and citric acid (18.82%) in synthetic urine solutions. Parahydroxybenzoic acid
showed the second highest inhibition effect compared to the known citric acid
due to the formation of stable calcium salt. However, the percentage inhibition
observed for acid mixtures closely represent the sum of percentage inhibition
showed by individual acids (~10.0% vs 11.4%). That means acid mixtures do
not exhibit synergistic behavior either in synthetic urine or in supersaturated
solutions.
