Urine glycoprotein crystal growth inhibitors. Evidence for a molecular abnormality in calcium oxalate nephrolithiasis.

One reason that some people are prone to calcium oxalate nephrolithiasis is that they produce urine that is subnormal in its ability to inhibit the growth of calcium oxalate crystals. We have identified in human urine a glycoprotein (GCI) that inhibits calcium oxalate crystal growth strongly, and at low concentrations (10(-7) M); in this study, we have isolated GCI molecules from the urine of normal people and patients with calcium oxalate stones. GCI from stone formers is abnormal in three ways: it contains no detectable gamma-carboxyglutamic acid (Gla), whereas normal GCI contains 2-3 residues of Gla per mole; about half of the GCI in urine of patients inhibits crystal growth 4-20 times less than normal GCI as judged by its performance in a kinetic growth assay, in vitro; at the air-water interface, patient GCI has a film collapse pressure approximately half of normal. GCI molecules from the urine of patients with calcium oxalate nephrolithiasis are intrinsically abnormal, and these abnormalities could play a role in the genesis of stones.

Formation of a single calcium stone of renal origin. Clinical and laboratory characteristics of patients.

Of 859 consecutive patients with calcium renal stones, 182 had formed only one stone before entering our program. Ninety-three (51.1%) had idiopathic hypercalciuria or hyperuricosuria; 36 (19.8%) others had a systemic disorder producing stones. The remainder, 53 (29.1%) patients, had no metabolic disorder. The frequency of hypercalciuria was lower than among patients with multiple stones. Compared with recurrent stone formers, patients with single stones were older when they passed their stones, suffered higher rates of complication such as surgery, cystoscopy, and urinary tract infection, and had a lower frequency of idiopathic hypercalciuria. During treatment, 11% formed a new stone in an average follow-up period of three years, a relapse rate similar to that of multiple stone formers; however, those patients with single stones who did relapse formed new stones at lower rates than multiple stone formers. Compared with recurrent stone formers, patients with solitary stones were more often treated with diet alone. Since there were no substantial differences between solitary and recurrent stone disease, patients who have formed a single stone should be evaluated and they should be treated no differently from other patients with stone disease.

Factors that predict relapse of calcium nephrolithiasis during treatment: a prospective study.

We evaluated 522 patients with idiopathic, recurrent calcium nephrolithiasis using a comprehensive clinical and laboratory protocol, and obtained additional laboratory measurements during their subsequent years of treatment in our program. In 57 patients, a new calcium stone ultimately formed during treatment (relapse), whereas 189 others have been free of recurrence during at least two years (average 4.3 +/- 2.2 [SD] years) of follow-up. Compared with the patients who remained stone-free, the patients with relapse (1) had a shorter interval between the time they entered our program and the time their last recurrent, pretreatment stone formed; (2) excreted more calcium *in mg/kg of body weight pr 24 hours) in their urine during treatment (2.79 +/- 1.08 versus 2.39 +/- 0.98 [SD] for relapse and stone-free); and (3) increased their urine volume less during treatment compared with pretreatment values (delta in liters per 24 hours was -0.02 +/- 0.48 versus 0.23 +/- 0.54 for relapse and stone-free). The two groups were otherwise the same. All comparisons used only data obtained prior to relapse. A discriminant function using only these three characteristics correctly identified 72 percent of patients with relapse and 67 percent of those who remained stone-free.

Effects of low-calcium diet on urine calcium excretion, parathyroid function and serum 1,25(OH)2D3 levels in patients with idiopathic hypercalciuria and in normal subjects.

We have used a low-calcium diet providing only 2 mg/kg (body weight) per 24 hours of calcium to distinguish between "renal" and "absorptive" idiopathic hypercalciuria. Sixteen of 27 hypercalciuric subjects excreted calcium in excess of intake during days seven, eight and nine of he diet, suggesting some element of renal hypercalciuria; however, all patients had low or normal serum PTH and urine cAMP levels. In general, fasting urine calcium was elevated in these 16 subjects and normal in the remaining 11, who conserved calcium more normally. SErum 1,25(OH)2D3 levels were the same in patients and normal subjects, even though PTH levels of the patients were below those of he normal subjects. Urine magnesium excretion and phosphorus excretion were both increased in the patients who excreted calcium in excess of intake. Our findings suggest that renal and absorptive hypercalciuria may not be distinct entities but rather the two extremes of a continuum of behavior. A uniform elevation of intestinal calcium absorption and a variable defect of renal calcium reabsorption could explain our results far better than the hypothesis of distinct absorptive and renal forms of hypercalciuria.

Protein fluorescence measurements within electrospray droplets.

The conformation of cytochrome c molecules within electrospray droplets is investigated by monitoring the laser induced fluorescence of its single tryptophan residue (Trp-59). By increasing the alcohol concentration of the electrosprayed solutions, protein denaturation is induced, giving rise to significant changes in the intensity of the detected fluorescence. Comparison with analogous denaturation experiments in solution provides information about the relative protein conformations and differences between the bulk-solution and droplet environments. Both electrospray-plume and bulk-solution fluorescence measurements using low methanol concentration solutions indicate the presence of folded protein structures. At high methanol content, fluorescence measurements are consistent with the presence of partly denatured or unfolded conformations. At intermediate methanol content, differences are observed between the extent of denaturation in solution and that within the droplets, suggesting electrosprayed proteins have more compact structures than those detected in bulk measurements using solutions of similar composition. This infers that some fraction of the proteins within the droplets have refolded relative to their bulk-solution conformation. Protein denaturation experiments using the low vapor pressure solvent 1-propanol indicate that differences between the droplet and solution measurements are not due to solvent evaporation effects. It is suggested that different droplet conformations are more likely the result of protein diffusion to the droplet surface and effects of the droplet/air interface. To our knowledge, these are the first reported measurements of protein fluorescence within electrospray droplets.

Pathogenesis and treatment of calcium stones.

Calcium stones arise from imbalances between urinary excretions of insoluble salts and water. Idiopathic hypercalciuria and hyperparathyroidism are the calcium disorders usually associated with elevated levels of calcium in the urine. Renal tubular acidosis is associated with a disordered acid-base status that results in low urine citrate. Hypocitraturia itself is a cause of calcium stones because it leaves urine calcium free to complex with either oxalate or phosphate. Elevated urine oxalate is commonly associated with dietary excesses, bowel disease, and, rarely, primary hyperoxaluria. Hyperuricosuria, usually of dietary origin, when reversed can cause a fall in new calcium stones.

Renal stone disease in older adults.

The pathophysiology of stone disorder in older adults, as compared to their younger counterparts, has not been thoroughly investigated. This article examines the differences in serum and urine chemistries between groups that are younger and older than 60 years of age. The principal finding is that stone formation occurs at lower urinary supersaturations in older patients, suggesting that other unexplored factors are significant contributors. The authors then review the possible effect of age on the morbidity of stone disease and the implications of stone disease for the development and management of osteoporosis.

Device for quenching studies on rare gas and metal halide excited complexes.

A device is described in which HgCl * is photolytically produced by optically exciting HgCl(2). The same apparatus can be used to excite other metal and rare gas complexes. The device is small, allowing rapid screening using repetitive pulsing and signal averaging techniques.

The risks of oral contraceptives and estrogen replacement therapy.

PIP: The benefits and risks of both oral contraceptives and estrogen replacement therapy (ERT) are evaluated by summarizing briefly the results of the most evidential studies on breast, ovarian, endometrial, and hepatobiliary cancer, heart attack, stroke and venous thromboembolism. The methods used to estimate risk ratios, prospective random-allocation, double-blind trials, and retrospective case- controlled studies, are explained briefly. The ERT used today resemble sequential oral contraceptives, except that only 10-20 mcg ethinyl estradiol is taken for 25 days, and progestins are used on the last 10 days. Breast cancer risk is not different in pill users from nonusers, based on the U.K. General PRactitioner, Oxford Family Planning, Harvard nurses or U.S. SEER National Cancer Institute studies. Studies on ERT and breast cancer are mixed, but only injected estrogens raised the risks. Ovarian cancer is prevented by pill use in proportion to length of use. No studies were reported for ERT. The risk of hepatic cancer is 3.8 to 7.8 higher in pill users, but the number of cases is so rare that this should not affect prescriptions. Neither pill nor ERT raise the risk of myocardial infarction, and after premature surgical menopause, ERT lowers the risk. Based on studies done in the 1970s, oral contraceptives raise the risk of thrombotic stroke while women are taking them, from 10-13/100,000 to 41/100,000. ERT has no clear association with stroke. Similarly, orals increase the risk of venous thromboembolism, 8-fold in the Oxford Family Planning study published in 1986, although the absolute numbers are very small. ERT had no effects no risk of thromboembolism according to the lipid Research, Framingham and Nachtigall studies.^ieng

A urinary calcium-citrate index for the evaluation of nephrolithiasis.

We have performed a multivariate analysis of urine abnormalities in patients with calcium oxalate nephrolithiasis, in which effects of gender were also considered. The characteristic of patients that most clearly sets them apart from normal people is a high level of urine calcium for any given level of urine citrate. Other urine measurements cannot improve upon the separation between patients and normals provided by urine calcium and citrate, and their abnormal relationship to each other. Normal women have higher urine citrate and lower urine calcium than normal men or patients of either sex; normal men differ from stone forming men only moderately. Direct measurements of supersaturation are not helpful in distinguishing between patients and normals, once calcium and citrate have been considered. From our analysis, we have derived a new index for evaluating the significance of urine calcium and citrate levels that seems to offer a better basis for clinical diagnosis than criteria presently in use.

The financial effects of kidney stone prevention.

Prevention of nephrolithiasis (NL) is now medically feasible and widely recommended. However, diagnosis and treatment of remediable causes of stones requires testing and drugs that impose a cost; this cost is balanced by the presumed reductions in stone related events and medical encounters. In order to assess the balance between these, we have analyzed results from 1092 patients with NL unselected except for having clinical follow-up during treatment. From this population, we have derived the changes in rates of new stones, hospitalizations, cystoscopies, and surgical procedures. From these changes, and assignment of a range of possible dollar costs, we estimate that medical stone prevention will result in an average saving of $2,158 +/- $500 (SEM)/patient/year, which is the difference between an expenditure of $1,068/patient on yearly drugs and testing, and a reduction of $3,226 per patient in medical costs. Medical prevention of NL seems justified on a cost saving basis quite apart from its benefits to patients in terms of reduced morbidity and risk from procedures, obstruction, and infection.

Idiopathic hypercalciuria: the contribution of Dr. Jacob Lemann, Jr.

The original contributions of Jacob Lemann to mineral metabolism, especially calcium metabolism and idopathic hypercalciuria, are reviewed. One group of studies concern acid base balance and calcium loss, showing that acid loads increase calcium loss in the urine. Another group of studies concern the calciuria of glucose or carbohydrate ingestion, with the observation that stone patients, who as a population are enriched with hypercalciuria, respond with more exaggerated calciuria to glucose loads than do normal people. Yet another body of work shows that normal men, when given noncalcemic loads of calcitriol, exhibit two essential features of idiopathic hypercalciuria--hyperabsorptive hypercalciuria and bone mineral loss on a low-calcium diet. The final group of studies presented worked on the problem of thiazide hypocalciuric action, and where the calcium goes that does not appear in the urine, as well as the effects of potassium bicarbonate and sodium loads on mineral balance and acid base status.

An increasing number of calcium oxalate stone events worsens treatment outcome.

Current practice recommends metabolic evaluation of patients who have formed multiple renal stones, but not those with one stone or temporally remote stones. This presumes that recentness and recurrence imply greater risk of new future stones. We hypothesize that number of stones reflects how long patients are permitted to form stones untreated, and that forming more stones, itself, raises risk of future stones despite treatment. Our report is a retrospective analysis of 371 male patients selected from a comprehensive clinical and laboratory data base containing 2,527 patients with nephrolithiasis. Before treatment, number of stone events rises with time of observation, and rate of stone event occurrence is constant or falls. During treatment, relapse is correlated with number of pretreatment stones. Life table analysis showed increasing relapse for patients grouped into those with one, two, and three or more stones. Even though number of stones seems controlled by the interval of observation before treatment, more stones predict higher relapse during treatment. Perhaps by leaving nuclei of crystals as residues, stones appear to promote new stones, and the practice of waiting while patients declare themselves multiple stone formers may not always be the best.

Dependence of upper limit of metastability on supersaturation in nephrolithiasis.

Formation of renal stones requires supersaturation (SS) high enough to induce crystallization; such a SS is referred to as the upper limit of metastability (ULM). The ULM for calcium oxalate (CaOx) or calcium phosphate can be measured by adding oxalate or calcium to urine, respectively, and noting the point at which overt crystallization occurs as evidenced by clouding. In principle, the urine should be more prone to form stone crystals as its SS approaches the ULM, and the SS ULM distance has been used as an index of stone forming potential. In addition, one would expect the ULM and initial SS to be unrelated, as the starting urine SS has no apparent link to the amount of calcium or oxalate that urine can dissolve without leading to crystal formation. However, in rats, we have found a surprising correlation between ULM and SS, such that ULM appears to rise with initial SS, for CaOx, and, to a lesser extent, for brushite (Br), a typical calcium phosphate initial phase. In this study, we measured CaOx and Br ULM, and SS, in urine of 50 patients and 11 normal people, to determine if ULM and SS were correlated, as in rats, and to explore the relationship between SS and ULM. We found the same dependence of ULM on SS as in rats, for both CaOx and Br, and found no differences between patients and normal people with respect to this dependency. However, for Br, patients showed a lower ULM than normals, but the same initial SS, meaning that patients were closer to their crystal formation threshold than normals. Treatments for stones had no apparent effect on the SS-ULM dependency. We conclude that in humans, as in rats, ULM is related to initial SS, and that this relationship is the same in patients as in normals for CaOx, but shifted in a stone forming direction for Br among patients. The ULM-SS interaction is unaffected by contemporary conventional stone treatments, and is more marked for CaOx than Br. The mechanisms of the dependence are unknown. The smaller difference between ULM and initial SS for Br in patients than normal supports prior evidence suggesting a defect in stone patients that could lead to calcium phosphate crystallization, subsequent nucleation of CaOx, and stone disease.

Correspondence between stone composition and urine supersaturation in nephrolithiasis.

Supersaturation (SS) with respect to calcium oxalate monohydrate (COM), brushite (Br) and uric acid (UA), obtained in three 24-hour pretreatment urine samples from patients with stone disease were compared to the mineral composition of stones passed by the same patients to determine whether sparse urine SS measurements accurately reflect the long-term average SS values in the kidney and final urine. Among males and females elevation of SS above same sex normals corresponded to composition. As well, treatments that reduced stone rates also reduced these SS values. The degree of calcium phosphate (CaP) admixture was accurately matched by shifting magnitudes of COM and Br SS. As well, increasing CaP content was associated with falling urine citrate and rising urine pH, suggesting renal tubular acidosis. We conclude that sparse urine SS measurements accurately track stone admixtures, and are a reliable index of average renal and urine SS.