Evaluation of the Effectiveness of Tomato (Solanum lycopersicum L.) Juice in Inhibiting Calcium Oxalate Crystal Formation In Vitro

Abstract : Background: Nephrolithiasis is a major urological problem worldwide with a high recurrence rate, reaching approximately 50% within the first 5–10 years after the initial episode. Around 70–80% of kidney stones consist predominantly of calcium oxalate (CaOx). The imbalance between urinary promoters (calcium, oxalate) and inhibitors (citrate, magnesium) leads to supersaturation and crystal formation. Citrate functions as a strong natural inhibitor, although conventional medical therapy may involve considerable costs and adverse effects. Tomatoes (Solanum lycopersicum L.) are an affordable local commodity containing high levels of citrate and magnesium, and therefore hold potential as a natural antilithiasis agent. Objective: To evaluate the effectiveness of tomato juice in inhibiting calcium oxalate crystal formation using a synthetic urine model. Methods: An in vitro experimental study was carried out using a post-test only design with a control group. Samples were divided into five groups with three replications: Negative Control (no treatment), Positive Control (Potassium Citrate 0.5%), and three treatment groups of Tomato Juice at 25%, 50%, and 100% concentrations. Crystal formation was induced using CaCl₂ and Na₂C₂O₄ in synthetic urine. Absorbance was measured using a UV–Vis spectrophotometer (620 nm) at two-minute intervals for 60 minutes. Measured parameters included Slope of Nucleation (SN), Slope of Aggregation (SA), and percentage of inhibition. Results: Tomato juice demonstrated statistically significant inhibitory activity against CaOx crystallization kinetics (p < 0.05 for SN and SA). The 25% concentration produced the highest inhibition rate (approximately 65%), comparable to the positive control (70%). The 50% and 100% concentrations yielded inhibition values of approximately 38% and 37%, respectively, indicating a dose–response pattern that did not increase proportionally with concentration. Conclusion: Tomato juice effectively inhibited calcium oxalate crystal formation in vitro, particularly during the aggregation phase. The optimal effect was observed at the 25% concentration, suggesting a non-linear dose–response possibly influenced by the balance between citrate content and endogenous oxalate in tomatoes.