Objective: To evaluate the influence of plum-, cranberry-and blackcurrant juice on urinary stone risk factors. Design: Investigations were carried out in 12 healthy male subjects aged 18 -38 y. All subjects received a standardized diet formulated according to the dietary recommendations of the German Society of Nutrition. The subjects provided 24 h urine collections in a control, three loading phases. In each loading phase a neutral mineral water was substituted for 330 ml of the particular juice. Results: Cranberry juice decreased the urinary pH, whereas the excretion of oxalic acid and the relative supersaturation for uric acid were increased. Blackcurrant juice increased the urinary pH and the excretion of citric acid. The excretion of oxalic acid was increased too. All changes were statistically significant. The plum juice had no significant effect on the urinary composition. Conclusion: It is concluded that blackcurrant juice could support the treatment and metaphylaxis of uric acid stone disease because of its alkalizing effect. Since cranberry juice acidifies urine it could be useful in the treatment of brushite and struvite stones as well as urinary tract infection. Sponsorship: Funded by our own Division respectively the University.

Results show that 30-day n-3 fatty acid supplementation effectively decreases urinary oxalate excretion and the risk of calcium oxalate crystallization. The mechanism of the physiological effect may be decreased cellular oxalic acid exchange attributable to an altered fatty acid pattern of membrane phospholipids with concomitant changes in oxalate transporter activity. Calcium oxalate stone formers may benefit from long-term n-3 fatty acid supplementation.

Hippuric acid (HA) originating from the conjugation of benzoic acid with glycine is a physiological component of human urine. Findings suggest that HA inhibits calcium oxalate (CaOx) growth and considerably enhances the CaOx solubility in artificial urine. Thus, it is assumed that HA is a major modifier of CaOx formation. However, only a slight CaOx growth inhibition of 1-8% was also reported. These values were also derived from artificial urine. The key mechanism, which led HA to be of interest in urolithiasis research is the fact that in presence of Ca2+ ions HA can form a hippurate complex. By forming such a complex, Ca2+ concentration in urine decreases, and as a consequence, CaOx formation is inhibited. This study was performed in order to clarify the role of HA in native and artificial urine. Biochemical analyses to calculate the relative CaOx supersaturations and crystallisation experiments using an in-line laser probe were examined. BONN Risk Indices indicating the risk of CaOx crystallisation were calculated from the results of the crystallisation experiments. The results obtained from artificial as well as from native urines showed that HA has no significant effects on CaOx formation. We suggest that HA plays only a minor role as a crystallisation modifier in human urine.

In order to distinguish between normocitraturia and hypocitraturia, the 24 h urine excretion value of citric acid is evaluated in relation to the established limit value of 2.5 mmol/day. We propose changing this widely-used excretion value to a "minimum contribution" of citric acid to the total urine's ionic strength, since the inhibitory effect of citric acid on crystallization depends on citrate anions being available to complex calcium ions or to associate with the crystal surface. A total of 71424 h-urine samples, taken from 74 healthy persons and 58 calcium stone formers, were investigated for pH, citric acid concentration ([CA]), and related relative calcium oxalate supersaturation (RS). Based on the Henderson-Hasselbalch-equation, the individual concentrations of the differently charged citrate anion species in each of the urines were calculated from the urinary pH and [CA]. From the anion concentrations determined, the contribution of the urine's citric acid to the total urine's ionic strength, ISCA, was calculated. Referring to the limit value of 2.5 mmol/day and assuming an average urine volume of 1.5 l/day, a hypothetical concentration limit of 1.67 mmol/l can be obtained. Grouping the samples into "stone-formers" and "non-stone-formers" as well as into three different ranges of RS revealed: (1). that the groups' median [CA]-values were below 1.67 mmol/l, and (2). that [CA] was not inversely associated with the risk of stone formation. Within the pH-range of 5 and 7, the ISCA-values which are related to, for example, [CA]=1.67 mmol/l, vary considerably by a factor of nearly three between 2.48 mmol/l and 6.64 mmol/l. The use of a fixed citric acid excretion level for the distinction of normocitraturia from hypocitraturia does not take into account the different citrate species which actually modify the urine's crystallization behaviour. The proposed ISCA approach takes this fact into consideration. From this parameter, a desirable "minimum impact of citric acid" can be derived. In a first approach, a potential ISCA-limit value, which currently distinguishes between urines indicated by a "normo-protective" impact and those indicated by a "hypo-protective" impact with respect to calcium oxalate precipitation, may be set at 2.48 mmol/l.