Margaret Pearle and Dennis Venable moderated this very interesting session. (Abstract numbers follow the comments.)
J. Kyle Anderson and colleagues began by analyzing the “Effect of Calcium Carbonate Supplementation on Stone Forming Risk in Normal Subjects on a Liberal Oxalate Intake”. He reminded us that low calcium diets do not seem to prevent stones. Past studies in dietary supplementation with calcium implied that stone risk increased. They conducted a 2-phase randomized crossover study on a constant diet with calcium carbonate supplementation at 250 mg 4 times daily. Urine calcium did increase, oxalate did not change and citrate increased significantly. Overall, calcium oxalate saturation ratios did not change. Hence, such supplementation does not seem to increase stone risk. However, one attendee questioned the accuracy of the analysis of dietary oxalate performed and pointed out that bioavailability of oxalate from the diet may vary. #1036
M. R. Cooperberg and associates reviewed data on 339 patients with hyperparathyroidism who also received calcium supplementation. Of these, 21% had a history of stones. After their retrospective analysis, it appeared that such supplements actually lowered the risk of stone formation in these patients. However, on questioning, he noted that they did not have data on amounts or duration of calcium supplementation, and they could not predict when the effects became apparent. He summarized by stating “This is a hypothesis generating study.” #1037
David Kang with his co-workers discussed their findings after “Lemonade-based Dietary Manipulation in Patients with Hypocitraturic Nephrolithiasis”. He pointed out that taking prescription citrates can place a financial strain on the patient and may decrease compliance. So they retrospectively measured effects of lemonade supplementation that provided 5.9 gm citric acid from 2 liters of lemonade per 24 hours, and they documented a group of 12 patients followed for a minimum of 6 months. They compared this group with a matched group taking oral citrate tablets. In both groups, urinary citrate increased significantly, and in the lemonade group, rate of stone episodes and new stone formation decreased but did not reach significance. One could question whether some of the improvement came from increased urinary volume created by lemonade intake, but they stated that these volumes did not differ significantly between the groups. They recommend further prospective randomized studies on this subject. #1038
Effects of uricosuria on calcium oxalate stone formation remain controversial. Prior studies included patients on random diets. Pais et al tested whether 65 calcium oxalate stone formers showed hyperuricosuria while on 3 days of standardized formula diets with no uric acid content. They were compared to a similarly treated group of 61 age-matched non-stone formers by indexing urinary uric acid excretion to creatinine. Hyperuricosuria, under these conditions, was noted in 1-2% of stone formers and controls. Hence, it appears that previously noted differences were related to variable dietary intakes of uric acid precursors. #1039
Asplin and Coe reported their observations on urinary oxalate excretion in 132 patients who received some type of Bariatric Surgery in the recent years. In the past, jejuno-ileal bypass (JIB) was used, but it produced such great hyperoxaluria and calcium oxalate supersaturation that it was abandoned in 1979 or 1980. But they determined that even those treated by modern methods show levels of hyperoxaluria greater (83 mg/d) than that of stone formers (39 mg/d) or normals (34 mg/d). More importantly, their calcium oxalate supersaturation levels of 12.1 exceeded those of even JIB patients (8.9), stone formers (9.0) and, of course, normals (7.3). Hence, we must do prospective studies of stone formation in these patients. #1040
Williams, with others in the “Randall’s Plaque Study Group” presented their anatomic review of “Mapping the Precise Orientation of Attached Stones on the Renal Papilla”. They show that their studied calcium oxalate stones have attachment to the papilla via the calcium phosphate Randall’s Plaque, and that such plaques represent the initial nidus for formation of calcium oxalate stones. #1041
Sagi (presented by A. Haecker) and associates reported on their “New in vitro Model for cystinuria type I by RNAi transfection”. Their cell culture model should lead to further studies on possible gene therapy for cystinuria. #1042
Koul and a number of co-workers presented their similar approach to “A Rational gene therapy for Primary Hyperoxaluria-1 (PH-1): Cloning, cellular transfection and sub cellular localization of AGT-GFP-fusion protein.” They were able to transfect AGT into hepatocyte cultures. They conclude by stating that “this is the first study to attempt recombinant AGT gene therapy for treatment of primary hyperoxaluria-1.” #1043