Short Chain Fatty Acids Prevent Glyoxylate-Induced Calcium Oxalate Stones by GPR43-Dependent Immunomodulatory Mechanism

Calcium oxalate (CaOx) stones are the most common type of kidney stones and are associated with high recurrence, short chain fatty acids (SCFAs), and inflammation. However, it remains uncertain whether SCFAs affect the formation of CaOx stones through immunomodulation. We first performed mass cytometry (CyTOF) and RNA sequencing on kidney immune cells with glyoxylate-induced CaOx crystals (to elucidate the landscape of the associated immune cell population) and explored the role of SCFAs in renal CaOx stone formation through immunomodulation. We identified 29 distinct immune cell subtypes in kidneys with CaOx crystals, where CX3CR1+CD24- macrophages significantly decreased and GR1+ neutrophils significantly increased. In accordance with the CyTOF data, RNA sequencing showed that most genes involved were related to monocytes and neutrophils. SCFAs reduced kidney CaOx crystals by increasing the frequency of CX3CR1+CD24- macrophages and decreasing GR1+ neutrophil infiltration in kidneys with CaOx crystals, which was dependent on the gut microbiota. GPR43 knockdown by transduction with adeno-associated virus inhibited the alleviation of crystal formation and immunomodulatory effects in the kidney, due to SCFAs. Moreover, CX3CR1+CD24- macrophages regulated GR1+ neutrophils via GPR43. Our results demonstrated a unique trilateral relationship among SCFAs, immune cells, and the kidneys during CaOx formation. These findings suggest that future immunotherapies may be used to prevent kidney stones using SCFAs.

Genetic Prioritization, Therapeutic Repositioning and Cross-Disease Comparisons Reveal Inflammatory Targets Tractable for Kidney Stone Disease

Background

Formation of kidney stones resulting in urological disorders remains a major cause of morbidity in renal diseases and many others. Innate immunity, mainly inflammasome, has demonstrated a key role in the development of kidney stone disease (or "nephrolithiasis"), but a molecular rationale for therapeutic intervention targeting immunity is far from clear. We reason that identifying inflammatory gene networks underlying disease risk would inform immunotherapeutic targets for candidate drug discovery.

Results

We generated an atlas of genetic target prioritization, with the top targets highly enriched for genes involved in the NF-kB regulation, including interaction neighbors of inflammasome genes. We identified a network of highly ranked and interconnecting genes that are of functional relevance to nephrolithiasis and mediate crosstalk between inflammatory pathways. Crosstalk genes can be utilized for therapeutic repositioning, as highlighted by identification of ulixertinib and losmapimod that are both under clinical investigation as inhibitors of inflammatory mediators. Finally, we performed cross-disease comparisons and druggable pocket predictions, identifying inflammatory targets that are specific to and tractable for nephrolithiasis.

Conclusion

Genetic targets and candidate drugs, in silico identified in this study, provide the rich information of how to target innate immune pathways, with the potential of advancing immunotherapeutic strategies for nephrolithiasis.

[Clinicobiochemical and immunological assessment of polyoxidonium efficacy in the treatment of patients with chronic calculous pyelonephritis]

Of 59 patients with chronic calculous pyelonephritis (CCP) taking preparation therapy for extracorporeal lithotripsy, 29 patients received combined basic treatment (antibacterial drugs, phytotherapy, physiotherapy) plus polyoxidonium (a course of 10 intramuscular 6 mg injections each other day). The rest 30 patients (controls) received basic therapy alone. Polyoxidonium efficacy was assessed by the results of clinical, device and immunological investigations, content of the main phospholipid fractions and cholesterol in red cell membranes. The results of the tests show that polyoxidonium has anti-inflammatory and immunomodulating effects, exhibits activity of peroxidation processes, contributes to normalization of a lipid phase of cell membranes and can be recommended as a component of combined treatment of patients with chronic pyelonephritis and urolithiasis.

Autoimmune Responses to Tamm-Horsfall Protein in the Pathogenesis of Chronic Pyelonephritis

Although the role of bacterial infection as the major determinant in the development of acute pyelonephritis has been well documented for years, the nature of the renal scarring typical of chronic "atrophic" pyelonephritis has been a matter of controversy for at least three decades. In the past, recurrent bacterial infection of the kidney was thought to be responsible for the pathologic entity of "chronic pyelonephritis." However, more recent studies suggest that recurrent bacteriuria, in the absence of some form of obstructive uropathy, rarely produces chronic pyelonephritis. The close association between vesicoureteral reflex and chronic pyelonephritis has also been firmly established and has been observed to occur frequently in the absence of urinary tract infection. However, the mechanism by which vesicoureteral reflux injures the kidney has not been firmly established. A number of observations have suggested that some normal component of urine, particularly Tamm-Horsfall protein, might serve as an antigenic determinant involved in the immunopathogenesis of renal scarring in vesicoureteral reflux. The present studies were designed to investigate the immunopathogenic role of Tamm-Horsfall protein in a rabbit model of tubulointerstitial nephritis, and in a swine model of reflux nephropathy. The immune responses to Tamm-Horsfall protein in patients with recurrent nephrolithiasis were also examined, as were the antigenic similarities between Tamm-Horsfall protein and protein-containing components of uropathic bacteria. The results of these studies indicate that autoimmune responses to Tamm-Horsfall protein may occur after exposure to Tamm-Horsfall protein by intravenous challenge in rabbits, and by urinary reflux in pigs, as well as in recurrent nephrolithiasis in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone involvement in idiopathic hypercalciuria

BACKGROUND

To evaluate bone involvement in idiopathic hypercalciuria, 40 lithiasic patients and 10 controls were studied.

METHODS

According to urinary calcium excretion, patients were first classified as hypercalciuric (Hca, n = 22) and normocalciuric (Nca, n = 18). The Hca patients were then subclassified according to bone densitometry (BMD) as osteopenic (HcaO, n = 10) and non-osteopenic (HCaNO, n = 12). Routine biochemistry, dietary records, bone histomorphometry. and cytokines (IL-1beta, IL-6, and TNF) production by peripheral blood mononuclear cell cultures were studied.

RESULTS

There were no differences in routine biochemistry between Hca and Nca groups, except for urinary calcium. Inadequate nutrition was observed in Hca group, showing high protein (80.9% of the patients), carbohydrate (76.2%) and sodium (90%) intake. Calcium intake was low in Hca (57%) and Nca (83%) groups. IL-6 and TNF were not different between the Hca and Nca groups. IL-1beta levels were significantly high in both groups when compared to controls. IL-6 and TNF were higher in HcaO than Nca. BMD in femoral neck in HcaO was lower than in HcaNO and Nca groups. Eroded surface (ES/BS) increased in 91% of the Hca group and 36% had a mineralization defect. In the HcaO group serum PTH correlated negatively with trabecular bone volume (BV/TV) and positively with ES/BS. 1,25(OH),D3 levels correlated positively with osteoblastic surface. Calcium intake correlated positively with BV/TV and inversely with ES/BS. A negative correlation was observed between IL-6 levels and Z score of the femoral neck.

CONCLUSION

Bone involvement was detected in a young population with nephrolithiasis demonstrating that a strict follow-up is necessary in order to control hypercalciuria.

Oxalate ions and calcium oxalate crystals stimulate MCP-1 expression by renal epithelial cells

BACKGROUND

Crystals of calcium oxalate monohydrate (COM) and excess oxalate ions (OX) stimulate an array of responses inducing localized injury and inflammation in the kidneys. These inflammatory responses are key regulators of development of nephrolithiasis. We propose that monocyte chemoattractant protein-1 (MCP-1), a chemokine with potent chemotactic activity for monocytes/macrophages, is a mediator of local inflammatory responses to COM and OX-induced injury. To test this hypothesis, the effects of COM and OX on the expression of MCP-1 mRNA and protein by NRK52E rat renal tubular cells were investigated.

METHODS

Confluent cultures of NRK52E cells were exposed to COM (33 to 267 microg/cm2) or OX (125 to 1000 micromol/L, estimated free oxalate levels of 65.8 to 540 micromol/L) and catalase (400 or 2000 U/mL), a free radical scavenger that protects the cells against detrimental effects of COM and OX, for 1 to 48 hours under serum free conditions. The conditioned media were collected and total cellular RNA isolated from the cells and subjected to enzyme-linked immunosorbent assay (ELISA) and semiquantitative polymerase chain reaction (PCR) to determine the expression of MCP-1 protein and mRNA, respectively.

RESULTS

NRK52E cells express MCP-1 mRNA and protein, and the level of their expression significantly increases following treatments with COM and OX in a time and concentration dependent manner. MCP-1 mRNA expression and protein production increased more significantly after exposure to COM than to OX. These responses were significantly reduced following treatments with catalase (2000 U/mL).

CONCLUSIONS

NRK52E cells express MCP-1 mRNA and protein, and their levels are altered following COM and OX exposure. Since catalase treatment reduced MCP-1 expression, free radicals may be involved in the up-regulation of MCP-1 production by the epithelial cells. The results suggest that elevated expression of MCP-1, which is often associated with local inflammatory response, may mediate similar reactions including attraction of macrophages seen around the interstitial crystals during the early stages of nephrolithiasis.

Early stage of urolithiasis formation in experimental hyperparathyroidism

PURPOSE

We have previously noted marked acceleration in the proliferative activity of parathyroid cells in rats with spontaneous hypercholesterolemia and secondary hyperparathyroidism. Using this proliferative potential we investigated whether transplantation of these enlarged parathyroids into normal rats would induce hyperparathyroidism and renal stones.

MATERIALS AND METHODS

We used 26-week-old male rats with spontaneous hypercholesterolemia as donors, and 5-week-old normal male Sprague-Dawley rats and rats with spontaneous hypercholesterolemia as recipients. Enlarged parathyroid glands were transplanted into group 1--Sprague-Dawley rats with no treatment, group 2--Sprague-Dawley rats that received FK-506 as an immuno-suppressor, group 3--rats with spontaneous hypercholesterolemia rats that underwent parathyroidectomy plus FK-506 administration and group 4--Sprague-Dawley rats that underwent parathyroidectomy plus FK-506 administration. Parathyroidectomy was performed in recipients before transplantation to ensure a low calcium condition.

RESULTS

Grafts were rejected within 11 and 15 weeks in groups 1 and 2, respectively. In group 3, 78% of the grafts were successful even after 19 weeks. In group 4 graft survival was 30% at 15 weeks with complete rejection at 19 weeks. In group 3 gradually elevated serum parathyroid hormone was observed as well as stone plaques containing calcium oxalate and calcium phosphate in renal tubules located mainly in the corticomedullary junction. An increased number of plaques was associated with higher parathyroid hormone.

CONCLUSIONS

Our study shows that transplanted parathyroid glands function with an immunosuppressive agent and the maintenance of hypocalcemic conditions, and they secrete sufficient parathyroid hormone to demonstrate hyperparathyroidism. Plaque in these kidneys indicates an early stage of urolithiasis caused by hyperparathyroidism.

Changing concepts in the aetiology of renal stones

In the past two decades an increasing number of nephrolithiasis-related urinary proteins have been identified. This paper focuses on two of them, namely prothrombin fragment 1 and bikunin, members of the prothrombin and inter-alpha-trypsin inhibitor families of proteins, respectively. Besides their role as inhibitors of crystallization, these proteins are also involved in inflammation-mediated tissue repair. This is the basis for the concept that the response of renal tissue to injury might play an important role in the aetiology of kidney stones.

Preoperative immune status and lipid peroxidation as risk markers for pyelonephritis attack after percutaneous nephrolithotomy

Pyelonephritis attack after percutaneous nephrolithotomy can be predicted on the basis of immunity parameters and blood level of lipid peroxides.

[The immunological aspects of systemic enzyme therapy in the combined treatment of recurrent nephrolithiasis]

Results are submitted of treatment of 50 patients of different years of age, who were presenting with urolithiasis and concomitant chronic pyelonephritis, using methods of surgical treatment alone and in combination with a drug preparation of systemic enzymotherapy (SE) phlogenzyme. Based on the analysis of the findings obtained a conclusion has been drawn that the SE drug phlogenzyme is an effective medication for correction of disorders of the immune homeostasis in patients with urolithiasis and for prevention of recurrent lithogenesis after surgical interventions in kidneys and ureters.

Autoantibodies and primary Sjögren's syndrome in a hypocitraturic stone population

Primary Sjögren's syndrome may be complicated by distal renal tubular acidosis (dRTA) and hypocitraturia, which are risk factors for calcium stone formation. Approached from a different perspective, in patients with urolithiasis and dRTA, autoantibodies and various autoimmune diseases are not uncommon. In search for signs of autoimmune disease, we analysed antinuclear antibodies and total levels of serum IgG in 197 hypocitraturic stone formers (67 women and 130 men). Antinuclear antibodies were present in 1.5% of the men and in 18% of the women. An isolated increase in serum IgG was found in 9% of the men and in 3% of the women. Anti-SS-A antibodies were analysed in a subgroup of 46 women and were estimated to occur in 16% of all hypocitraturic stone forming women. Four of 4 examined women, but no men, fulfilled the criteria of definite or possible primary Sjögren's syndrome. We recommend the analysis of anti-SS-A antibodies in female hypocitraturic stone formers.

Antibodies to Tamm-Horsfall protein in patients treated with extracorporeal shock wave lithotripsy (ESWL)

The aim of this study was to determine antibodies to Tamm-Horsfall protein in patients with nephrolithiasis treated with extracorporeal shock wave lithotripsy (ESWL). The values of antibodies to Tamm-Horsfall protein were determined by direct enzyme immunoassay. No statistically significant differences (P > 0.05) were observed for the IgG and IgM classes of antibodies between the groups of healthy subjects and patients with nephrolithiasis before, and 30 and 60 days after ESWL. The values of IgA class determined 30 days after treatment were significantly higher (P < 0.05) in patients, which could be due to the stimulation of the immune system. The highest values of antibodies to Tamm-Horsfall protein were obtained in both groups in the test with secondary antibodies directed toward IgM class, implicated at the presence of cross-reactive antibodies. Determination of antibodies to THP subunits isolated form urine of patients with nephrolithiasis should be performed.

[The effect of endovascular helium-neon laser therapy on the immune status of patients with acute calculous pyelonephritis]

Cellular immunity was assessed in 48 patients with acute calculous pyelonephritis exposed to intravenous He-Ne laser therapy. It was found that endovascular He-Ne laser therapy in the study regimens corrects immunological abnormalities arising in acute calculous pyelonephritis.

A case of resistant Goodpasture's syndrome and staghorn calculus--treatment with bilateral nephrectomy

We report the case of a 49-year-old female with severe Goodpasture's syndrome, staghorn calculus, and subacute thyroiditis. Despite the use of a combined therapy with corticosteroid, cyclophosphamide, azathioprine and plasma exchange, we were unable to suppress the disease activity or normalize the anti-glomerular basement membrane (GBM) antibody levels. Disease remission with a parallel reduction in anti-GBM antibody titer was only achieved after sequential bilateral nephrectomy.

[The etiological factors in pyelonephritis occurring against a background of nephrolithiasis]

656 urine and 78 blood samples were examined immunomicrobiologically. No bacterial growth was recorded in 43.8% of urine samples. Opportunistic bacteria were represented by Enterobacteriaceae, nonfermenting gram-negative bacteria with predominance of E. coli, P. mirabilis, P. aeruginosa isolated both in monocultures and in associations in conventional diagnostic titers (1g 5 CFU/ml). Throughout 40 days of the hospital stay microflora continuously changed, but until the discharge the infection persisted. The study of the immunological aspect of anti-infection resistance showed that most of the examinees (73%) at admission with pyelonephritis exacerbation have deficient cellular and humoral defense.

Comparison of 15 monoclonal antibodies against tumor-associated antigens of transitional cell carcinoma of the human bladder

Quantitative urinary immunocytology with our monoclonal antibody (mab) 486p 3/12 proved to be valuable for diagnostic use in bladder-cancer patients' urine, especially in the followup of patients with superficial bladder carcinoma. To evaluate the use of other monoclonal antibodies in bladder cancer, we compared 15 mabs directed against bladder-tumor-associated antigens from seven research groups in a broad panel of cellular and tissue specimens (bladder tumor, prostatic adenoma, and kidney stone). Quantitative evaluation was done in cytocentrifuged preparations and tissue specimens. None of the 15 mabs was bladder-tumor-specific. All 15 stained normal urothelium to some extent and six stained granulocytes. Each of the 15 seemed to identify a different cellular antigen, as can be clearly demonstrated by the staining pattern of different regions in the normal kidney. The sensitivity of quantitative urinary immunocytology in bladder-tumor patients can be improved by using a panel, rather than one mab in bladder-tumor patients, but specificity decreases simultaneously. A main reason for the poor specificity of quantitative urinary immunocytology with all 15 mabs is that false-positive results are obtained with all mabs in kidney-stone patients. Our quantitative urinary immunocytology method is a general tool for the diagnostic use of all mabs in bladder-tumor patients. Mabs that have a high sensitivity might be useful in the followup of patients with superficial bladder carcinoma. None of the 15 mabs (because of their poor specificity) seems to be helpful in quantitative urinary immunocytology for screening a population for bladder carcinoma.

[Effects of urologic surgery on lymphocyte blastogenic response to phytohemagglutinin]

In order to study the effect of urological surgery on the defence system, we have evaluated the postoperative evolution of the lymphocyte blastogenic response to phytohemagglutinin (PHA) in 45 patients. 25 of them were subjected to a transurethral resection (TUR) of a vesical tumour, 10 to a transvesical prostatectomy, 6 to a pyelolithotomy and 4 to a nephrectomy due to renal atrophy secondary to lithiasis. We verified a significant drop in the lymphocyte blastogenic response to PHA at 2-4 hours of transvesical prostatectomy (p less than 0.001) and of pyelolithotomy and nephrectomy (p less than 0.001) which was sustained until the fourth and second day after operation respectively, with subsequent return to normal. However, lymphocyte blastogenic response to PHA did not vary significantly during the postoperative of patients subjected to a TUR of vesical tumours. On the whole, the degree and duration of postoperative immunodepression was dependent on the intensity of the surgical traumatism.

HLA and urolithiasis

Frequencies of persons having particular HLA-A, -B, and -C antigens were compared for 113 urolithiasis clinic patients, a subset of 24 patients who had hypercalcuria , and 225 controls. The frequency of HLA- A30 was significantly elevated among the patients. A suggestion (S afwenberg et al. 1978) that HLA-B27 frequency is elevated among hypercalcuric patients with recurrent kidney stones was not confirmed.

Immunopathogenesis of chronic pyelonephritis

Immunopathologic responses to urinary Tamm-Horsfall protein in the development of chronic pyelonephritis were examined by four different approaches. First, in a rabbit model, tubulointerstitial nephritis developed in 64 of 102 rabbits injected intravenously with urine or rabbit Tamm-Horsfall protein as compared with only one of 17 rabbits in two control groups. Circulating cytotoxic lymphocytes plus immunoglobulin G (IgG) antibodies against Tamm-Horsfall protein were found in 51 percent of challenged (urine or Tamm-Horsfall protein) rabbits with tubulointerstitial nephritis as compared with only 8 percent of those without it (p less than 0.001). Second, in a porcine model of reflux nephropathy, 16 of 21 pigs with pyelographic findings indicative of reflux had elevated serum titers of anti-Tamm-Horsfall protein antibody as compared with 0 of 13 with normal pyelograms. Five of 10 refluxing pigs tested also had circulating lymphocytes that were cytotoxic in the presence of Tamm-Horsfall protein as compared with 0 of 13 with normal pyelograms. Third, in human studies, 12 of 49 patients with recurrent nephrolithiasis demonstrated abnormal elevations in anti-Tamm-Horsfall protein antibody; 13 of 49 had an abnormality in one of two assays of cell-mediated immunity to Tamm-Horsfall protein as compared with 0 of the normal control subjects. These abnormalities were not associated with overt obstruction or bacteriuria, but appeared to be more common in patients with recent onset and active recurrent nephrolithiasis. Lastly, an inhibitor of the binding reaction between human Tamm-Horsfall protein and its IgG antibody was detected in extracts of three uropathic coliforms. The inhibitors were partially purified by chromatographic means. Preliminary immunoautoradiographic studies revealed three or less protein-containing subunits of Escherichia coli that cross-reacted with anti-Tamm-Horsfall protein antibody. These studies suggest that autoimmune responses to Tamm-Horsfall protein may occur after exposure to Tamm-Horsfall protein by intravenous challenge, urinary reflux, or recurrent nephrolithiasis. This autoimmune response to Tamm-Horsfall protein may be the pathogenetic mechanism by which these factors, including bacteriuria, contribute to chronic pyelonephritis.

Concanavalin A-activated suppressor cell activity in peripheral blood lymphocytes of urologic cancer patients

Concanavalin A (Con A)-inducible suppressor cell activity in peripheral blood lymphocytes (PBL) of urologic cancer patients and of appropriate controls with benign urologic disorders was measured concurrently. Although the proliferative responses to Con A of the cancer patients were significantly lower than those of controls, no difference in Con A-induced suppressor cell activity was demonstrated between cancer patients and controls when tested under a variety of conditions. Moreover, regression analysis revealed no correlation between the proliferative response to Con A and suppressor cell activity in either cancer patients or controls. The results indicated that Con A-inducible suppressor cell activity was unaltered in urologic cancer patients and suggested that suppressor cells of the type that can be activated by Con A were not involved in the general immunologic impairment frequently associated with urologic cancer.

Antibody to Tamm-Horsfall protein in patients with urinary tract obstruction and vesicoureteral reflux

Urinary tract obstruction and vesicoureteral reflux, which are often associated with urinary tract infections, may lead to progressive renal damage. Relatively little is known about the pathophysiology of this process, and a need exists for noninvasive methods of its detection in its early stages. Because urine is refluxed into the venous and lymphatic drainage of the kidney in severe vesicoureteral reflux and urinary tract obstruction, an immune response to urinary tract components might play a role in the pathophysiology of progressive renal damage and serve as a serologic marker for its presence. A solid-phase radioimmunoassay for a protein found only in the urine (Tamm-Horsfall protein [THP]) was developed and used to measure antibody to THP in the serum of 60 subjects. Significant elevations of antibody to THP were observed in five of 15 patients with obstruction and infection of the urinary tract and in one of 10 patients with infection alone, when these patients were compared with 12 healthy control subjects. Similar elevations of antibody to THP were not seen in uninfected patients with urinary tract obstruction or in patients with low-grade vesicoureteral reflux or sepsis of nonrenal origin. These results suggest that the measurement of antibody to THP might be useful in the identification of patients with obstruction and infection of the urinary tract.

[Antibody-coaded bacteria in urine sediment of children with urinary tract infections (author's transl)]

In 40 girls and 9 women with recurrent, non-obstructive urinary tract infections, and in 5 patients with nephrolithiasis the site of infection was determined by 108 bladder washout tests. The corresponding sediments were examined for antibody-coaded bacteria using an immunofluorescence test (IFT). The IFT was positive in 18 (72%) of 25 supravesical bacteriurias. Out of 75 vesical bacteriurias 39 infantile and 7 adult (together 61%) specimens contained antibody-coaded bacteria. We think the IFT is of no diagnostic value in localizing recurrent urinary tract infections in girls. For adults such an evaluation is not yet possible due to our small number of cases.

The immunological integrity of matrix substance A and its possible detection and quantitation in urine

There would seem to be no doubt that most stone-forming patients at some time during the course of their disorder excrete substances not present in normal urine. However, considerable doubt must now exist that "Matrix Substance A" is a single antigenic entity or that its presence is confined to the active formation of renal calculi.

The hypercalciurias. Causes, parathyroid functions, and diagnostic criteria

The causes for the hypercalciuria and diagnostic criteria for the various forms of hypercalciuria were sought in 56 patients with hypercalcemia or nephrolithiasis (Ca stones), by a careful assessment of parathyroid function and calcium metabolism. A study protocol for the evaluation of hypercalciuria, based on a constant liquid synthetic diet, was developed. In 26 cases of primary hyperparathyroidism, characteristic features were: hypercalcemia, high urinary cyclic AMP (cAMP, 8.58+/-3.63 SD mumol/g creatinine; normal, 4.02+/-0.70 mumol/g creatinine), high immunoreactive serum parathyroid hormone (PTH), hypercalciuria, the urinary Ca exceeding absorbed Ca from intestinal tract (Ca(A)), high fasting urinary Ca (0.2 mg/mg creatinine or greater), and low bone density by (125)I photon absorption. The results suggest that hypercalciuria is partly secondary to an excessive skeletal resorption (resorptive hypercalciuria). The 22 cases with renal stones had normocalcemia, hypercalciuria, intestinal hyperabsorption of calcium, normal or low serum PTH and urinary cAMP, normal fasting urinary Ca, and normal bone density. Since their Ca(A) exceeded urinary Ca, the hypercalciuria probably resulted from an intestinal hyperabsorption of Ca (absorptive hypercalciuria). The primacy of intestinal Ca hyperabsorption was confirmed by responses to Ca load and deprivation under a metabolic dietary regimen. During a Ca load of 1,700 mg/day, there was an exaggerated increase in the renal excretion of Ca and a suppression of cAMP excretion. The urinary Ca of 453+/-154 SD mg/day was significantly higher than the control group's 211+/-42 mg/day. The urinary cAMP of 2.26+/-0.56 mumol/g creatinine was significantly lower than in the control group. In contrast, when the intestinal absorption of calcium was limited by cellulose phosphate, the hypercalciuria was corrected and the suppressed renal excretion of cAMP returned towards normal. Two cases with renal stones had normocalcemia, hypercalciuria, and high urinary cAMP or serum PTH. Since Ca(A) was less than urinary Ca, the hypercalciuria may have been secondary to an impaired renal tubular reabsorption of Ca (renal hypercalciuria). Six cases with renal stones had normal values of serum Ca, urinary Ca, urinary cAMP, and serum PTH (normocalciuric nephrolithiasis). Their Ca(A) exceeded urinary Ca, and fasting urinary Ca and bone density were normal. The results support the proposed mechanisms for the hypercalciuria and provide reliable diagnostic criteria for the various forms of hypercalciuria.