Increased sensitivity to 1,25(OH)2D3 in bone from genetic hypercalciuric rats

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.

Calcium oxalate crystal localization and osteopontin immunostaining in genetic hypercalciuric stone-forming rats

BACKGROUND

The inbred genetic hypercalciuric stone-forming (GHS) rats develop calcium phosphate (apatite) stones when fed a normal 1.2% calcium diet. The addition of 1% hydroxyproline to this diet does not alter the type of stone formed, while rats fed this diet with 3% hydroxyproline form mixed apatite and calcium oxalate stones and those with 5% hydroxyproline added form only calcium oxalate stones. The present study was designed to determine the localization of stone formation and if this solid phase resulted in pathologic changes to the kidneys.

METHODS

GHS rats were fed 15 g of the standard diet or the diet supplemented with 1%, 3%, or 5% hydroxyproline for 18 weeks. A separate group of Sprague-Dawley rats (the parental strain of the GHS rats), fed the standard diet for a similar duration, served as an additional control. At 18 weeks, all kidneys were perfusion-fixed for structural analysis, detection of crystal deposits using the Yasue silver substitution method, and osteopontin immunostaining.

RESULTS

There were no crystal deposits found in the kidneys of Sprague-Dawley rats. Crystal deposits were found in the kidneys of all GHS rats and this Yasue-stained material was detected only in the urinary space. No crystal deposits were noted within the cortical or medullary segments of the nephron and there was no evidence for tubular damage in any group. The only pathologic changes occurred in 3% and 5% hydroxyproline groups with the 5% group showing the most severe changes. In these rats, which form only calcium oxalate stones, focal sites along the urothelial lining of the papilla and fornix of the urinary space demonstrated a proliferative response characterized by increased density of urothelial cells that surrounded the crystal deposits. At the fornix, some crystals were lodged within the interstitium, deep to the proliferative urothelium. There was increased osteopontin immunostaining in the proliferating urothelium.

CONCLUSION

Thus in the GHS rat, the initial stone formation occurred solely in the urinary space. Tubular damage was not observed with either apatite or calcium oxalate stones. The apatite stones do not appear to cause any pathological change while those rats forming calcium oxalate stones have a proliferative response of the urothelium, with increased osteopontin immunostaining, around the crystal deposits in the fornix.

Vitamin D receptor gene polymorphism in hypercalciuric children

Idiopathic hypercalciuria is a complex disease resulting from an interaction between environmental and genetic factors. Recently, the relationship between vitamin D receptor ( VDR) alleles and calcium homeostasis has been investigated. This study was conducted to explore the association of VDR gene polymorphism with the risk of absorptive hypercalciuria (AH). We investigated the VDR gene polymorphisms, ApaI, BsmI, and TaqI, in relation to intact parathormone (PTH), osteocalcin, and 25-hydroxyvitamin D in 80 children (42 males, 38 girls) with AH and in 86 healthy children without hypercalciuria. A significant difference in the ApaI genotype was observed between the AH group and the control group ( chi(2)=7.21, P=0.027). The AA genotype was associated with a 3.5-fold increased risk for idiopathic hypercalciuria compared with the Aa/aa genotype (odds ratio 3.5, 95% confidence interval 1.1-11). The BsmI and TaqI polymorphisms did not show any significant association with AH. Serum osteocalcin levels were significantly higher in the group with the AA genotype compared with those with the Aa or aa genotype ( P=0.02, P=0.05, respectively). The results indicate that the ApaI AA genotype of the VDR gene is not only associated with AH but is also related to differences in serum osteocalcin.

Decay-Accelerating Factor Deficiency Increases Susceptibility to Dextran Sulfate Sodium-Induced Colitis: Role for Complement in Inflammatory Bowel Disease

Decay-accelerating factor (DAF or CD55) is expressed on colonic epithelial cells but its function in the mucosa is unknown. In humans, a proportion of DAF-deficient (Cromer INAB) patients develop inflammatory bowel disease (IBD). To evaluate how DAF deficiency may contribute to gut inflammation and thus could play a role in IBD pathogenesis, we compared the severity of dextran sulfate sodium-induced colitis in Daf1 gene-targeted and control mice. Seven days after consuming 3% dextran sulfate sodium in their drinking water, Daf1(-/-) mice suffered markedly greater weight loss (-24.7 +/- 7.5% vs -14.2% +/- 4.9%), exhibited uniformly bloody diarrhea as compared with soft stool in control mice, developed shortened colons, and had larger spleens. Histological examination of distal colons showed massively increased neutrophilic and mononuclear cell infiltration, greater epithelial cell destruction, and increased ulcerations. Cytokine production in organ cultures of colonic explants showed increased levels of IL-12 and IL-6. Fourteen days after switching back to regular water, in contrast to the Daf1(+/+) controls which showed little stool abnormality, all Daf1(-/-) mice continued to have diarrhea. Organ culture cytokine measurements at this time point, i.e., the end of the recovery phase, showed markedly increased levels of IL-10 (6-fold), IL-12 (4-fold), and IL-6 (2-fold), as well as TNF-alpha (>10-fold) compared with the controls. Our findings argue that, as shown for IL-10 in IL-10(-/-) mice and IL-2 in IL-2(-/-) mice, DAF control of complement additionally is important in regulating gut homeostasis and consequently its activity may participate in protecting against IBD.

Repair of full-thickness bowel injury

OBJECTIVE

Colon surgery is more and more often performed in complex situations such as after trauma, under immunosuppression, or in the elderly. Even under optimal conditions, anastomosis fails in certain situations. The objective of this study was to demonstrate the normal phases of bowel healing and to review the local and systemic factors affecting healing with special attention to critical care variables such as major surgery, acute hemorrhage, and infections.

DATA SOURCE

MEDLINE cited and/or published articles.

DESIGN

Review analysis.

RESULTS

Colon healing is a structured cascade of different phases that can be affected by a multitude of local (infection, ischemia) and systemic (diabetes, malnutrition, anemia, hypothermia, trauma) factors. The normal phases of repair, the resulting bursting pressure as an experimental index of healing, and the available published data on local and systemic factors affecting healing are summarized.

CONCLUSION

Several local and systemic factors negatively affect bowel healing; there is still a small portion of patients who fail to heal, suggesting that intrinsic factors need to be analyzed.

Quantitative trait loci for hypercalciuria in a rat model of kidney stone disease

Hypercalciuria is the most common risk factor for kidney stones and has a recognized familial component. The genetic hypercalciuric stone-forming (GHS) rat is an animal model that closely resembles human idiopathic hypercalciuria, with excessive intestinal calcium absorption, increased bone resorption, and impaired renal calcium reabsorption; overexpression of the vitamin D receptor (VDR) in target tissues; and calcium nephrolithiasis. For identifying genetic loci that contribute to hypercalciuria in the GHS rat, an F2 generation of 156 rats bred from GHS female rats and normocalciuric WKY male rats was studied. The calcium excretion was six- to eightfold higher in the GHS female than in the WKY male progenitors. Selective genotyping of those F2 rats with the highest 30% and lowest 30% rates of calcium excretion was performed, scoring 98 markers with a mean interval of 23 cM across all 20 autosomes and the X chromosome. With the use of strict criteria for significance, significant linkage was found between hypercalciuria and a region of chromosome 1 at D1Rat169 (LOD, 2.91). Suggestive linkage to regions of chromosomes 4, 7, 10, and 14 was found. The proportion of phenotypic variance contributed by the region on chromosome 1, with appropriate adjustments, was estimated to be 7%. Candidate genes encoding the VDR and the calcium-sensing receptor were localized to regions on rat chromosomes 7 and 11, respectively, but the suggestive quantitative trait locus on chromosome 7 was not in the region of the VDR gene locus. Identification of genes that contribute to hypercalciuria in this animal model should prove valuable in understanding idiopathic hypercalciuria and kidney stone disease in humans.

Pathogenesis of hypercalciuric nephrolithiasis

The major contribution of hypercalciuria in raising urinary state of saturation with respect to calcium salts and subsequent risk of nephrolithiasis is appreciated. Derangements in the physiological mechanisms that regulate calcium homeostasis and contribute to hypercalciuria have also been identified. New avenues of research are beginning to explore the specific defects that may contribute to hypercalciuria. From such studies, an understanding of the role of certain dietary excesses as contributors to the development of hypercalciuria and, in some cases, attendant bone loss, is beginning. The contribution of genetics to hypercalciuria has provided a powerful means of identifying genes that contribute to the hypercalciuric phenotype in a number of hypercalciuric conditions. Such studies have disclosed that hypercalciuria is probably polygenic in nature and will require a concerted effort to better understand the defects while attempting to develop gene-specific countermeasures.

Calcium oxalate stone formation in genetic hypercalciuric stone-forming rats

BACKGROUND

Over 54 generations, we have successfully bred a strain of rats that maximizes urinary calcium excretion. The rats now consistently excrete 8 to 10 times as much calcium as controls, uniformly form poorly crystalline calcium phosphate kidney stones, and are termed genetic hypercalciuric stone-forming (GHS) rats. These rats were used to test the hypothesis that increasing urinary oxalate excretion would not only increase the supersaturation with respect to the calcium oxalate solid phase, but also would increase the ratio of calcium oxalate-to-calcium phosphate supersaturation and result in calcium oxalate stone formation.

METHODS

To increase urine oxalate excretion an oxalate precursor, hydroxyproline, was added to the diet of male GHS rats. The GHS rats were fed a standard 1.2% calcium diet alone or with 1%, 3% or 5% trans-4-hydroxy-l-proline (hydroxyproline).

RESULTS

The addition of 1% hydroxyproline to the diet of GHS rats led to an increase in urinary oxalate excretion, which did not increase further with the provision of additional hydroxyproline. The addition of 1% and 3% hydroxyproline did not alter calcium excretion while the provision of 5% hydroxyproline led to a decrease in urine calcium excretion. The addition of 1% hydroxyproline led to an increase in urinary calcium oxalate supersaturation, which did not further increase with additional hydroxyproline. The addition of 1% and 3% hydroxyproline did not alter urinary supersaturation with respect to calcium hydrogen phosphate while the addition of 5% hydroxyproline tended to lower this supersaturation. Compared to rats fed the control and the 3% hydroxyproline diet the addition of 5% hydroxyproline increased the ratio of calcium oxalate supersaturation to calcium phosphate supersaturation. Virtually all rats formed stones. In the control and 1% hydroxyproline group, all of the stones were composed of calcium and phosphate (apatite), in the 3% hydroxyproline group the stones were a mixture of apatite and calcium oxalate, while in the 5% hydroxyproline group all of the stones were calcium oxalate.

CONCLUSIONS

The provision of additional dietary hydroxyproline to GHS rats increases urinary oxalate excretion, calcium oxalate supersaturation and the ratio of calcium oxalate-to-calcium phosphate supersaturation, resulting in the formation of calcium oxalate kidney stones. Thus, with the addition of a common amino acid, the GHS rats now not only model the most common metabolic abnormality found in patients with nephrolithiasis, hypercalciuria, but form the most common type of kidney stone, calcium oxalate.

Regulation of matrix metalloproteinases in a model of colonic wound healing in a rabbit

PURPOSE

Matrix metalloproteinases occur in the colon at an anastomosis but not in the normal colon. Matrix metalloproteinase synthesis can be regulated by cytokines, for example interleukin-1 beta and growth factors, such as transforming growth factor beta and basic fibroblast growth factor. The aim of this study was to investigate the regulation of matrix metalloproteinases at an anastomosis by identifying the cell types that synthesize matrix metalloproteinases, examining factors that might regulate their synthesis, determining whether they occur in an active form, and assessing the effect of suture type on these parameters.

METHODS

An anastomosis was formed in the distal colon of rabbits using either polyglactin or polydioxanone and the animals were killed six hours or seven days later. The distribution of matrix metalloproteinases and cytokines and the cell types were assessed by immunohistochemistry. Matrix metalloproteinase-2, matrix metalloproteinase-3, and matrix metalloproteinase-9 were detected also by zymography.

RESULTS

Immunohistochemistry showed that matrix metalloproteinases were restricted to the suture line. Although zymography demonstrated that matrix metalloproteinase-2 was present mainly in an active form, matrix metalloproteinase-9 and matrix metalloproteinase-3 were present in the pro-form. The active form of matrix metalloproteinase-3 occurred more often in the polydioxanone-sutured rabbits. With the exception of matrix metalloproteinase-9, the matrix metalloproteinases were synthesized by fibroblasts. Interleukin-1 beta and transforming growth factor beta were more widespread than in the normal colon and were localized adjacent to the matrix metalloproteinases. Basic fibroblast growth factor was also more widespread postoperatively but occurred deeper in the anastomosis than the matrix metalloproteinases.

CONCLUSIONS

This study has shown that interleukin-1 beta and transforming growth factor beta may regulate the synthesis of the matrix metalloproteinases by fibroblasts and that minor differences that occur in the matrix metalloproteinase profile are dependent on the suture type.

Intestinal fibrosis in human and experimental inflammatory bowel disease

Fibrosis is a serious complication of Crohn disease for which there is no effective therapy. It is unclear why fibrosis, particularly fibrosis of the mucosal layer, develops in Crohn disease and not in ulcerative colitis. Smooth muscle cells, subepithelial myofibroblasts, and fibroblasts have traditionally been considered mediators of fibrosis, but new information points to a role of interstitial cells of Cajal and mast cells. Recent evidence about the role of each of these cell types in fibrosis in Crohn disease or other inflammatory bowel diseases is described. Hypothetical models to describe how altered function of these cells could underlie fibrosis of the mucosa or submucosal layers are presented. Fibrosis is not well characterized in any animal model of inflammatory bowel disease. The merits of several animal models for defining the mechanisms of inflammation-induced intestinal fibrosis are reviewed.

Pulmonary edema fluid from patients with acute lung injury augments in vitro alveolar epithelial repair by an IL-1beta-dependent mechanism

Efficient alveolar epithelial repair is crucial for the restoration of the injured alveolar epithelial barrier in patients with acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). We hypothesized that pulmonary edema fluid from patients with ALI /ARDS would inhibit alveolar epithelial repair as measured in an in vitro epithelial wound-repair model using the human alveolar epithelial-like cell line A549. In contrast to our initial hypothesis, pulmonary edema fluid from patients with ALI/ARDS increased alveolar epithelial repair by 33 +/- 3% compared with pooled plasma from healthy donors (p < 0.01). By contrast, the plasma and the pulmonary edema fluid from patients with hydrostatic pulmonary edema, and the plasma from patients with ALI/ARDS had similar effects on epithelial repair as pooled plasma from healthy donors. Inhibition of interleukin-1beta (IL-1beta) activity by IL-1 receptor antagonist reduced alveolar epithelial repair induced by ALI/ARDS edema fluid by 46 +/- 4% (p < 0.001), indicating that IL-1beta contributed significantly to the increased epithelial repair. In summary, pulmonary edema fluid collected early in the course of ALI/ARDS increased alveolar epithelial repair in vitro by an IL-1beta-dependent mechanism. These data demonstrate a novel role for IL-1beta in patients with ALI/ARDS, indicating that IL-1beta may promote repair of the injured alveolar epithelium.

Effect of acidosis on urine supersaturation and stone formation in genetic hypercalciuric stone-forming rats

BACKGROUND

We have successively inbred over 45 generations a strain of rats to maximize urine calcium excretion. The rats now consistently excrete 8 to 10 times as much calcium as controls and uniformly form poorly crystalline calcium phosphate kidney stones. In humans with calcium nephrolithiasis, consumption of a diet high in acid precursors is often cited as a risk factor for the development of calcium-based kidney stones; however, the effect of this diet on urinary supersaturation with respect to the common solid phases found in kidney stones has not been determined.

METHODS

To determine the effect of the addition of an acid precursor on urine ion excretion, supersaturation, and stone formation, we fed these genetic hypercalciuric stone-forming (GHS) rats 13 g/day of a 1.2% calcium diet with 0.0, 0.5, 1.0, or 1.5% NH4Cl in the drinking water for 14 weeks (N = 8 for each). Urine was collected and analyzed every two weeks.

RESULTS

As expected, the addition of dietary NH4Cl led to a progressive fall in urine pH and urine citrate, while urine ammonium increased. Urine calcium and phosphorus increased, while urine oxalate fell. Increasing dietary NH4Cl led to a fall in supersaturation with respect to CaHPO4 (brushite) and CaOx and a rise in supersaturation with respect to uric acid. In spite of differences in supersaturation, most rats in each group formed stones that contained calcium phosphate and not calcium oxalate.

CONCLUSIONS

Thus, while the provision of additional dietary acids alters urinary ion excretion and lowers supersaturation with respect to CaHPO4 and CaOx, it does not change the character or rate of stone formation in the GHS rats.

Increased vitamin D receptor level enhances 1,25-dihydroxyvitamin D3-mediated gene expression and calcium transport in Caco-2 cells

Altered vitamin D receptor (VDR) level has been proposed to explain differences in intestinal responsiveness to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. We tested whether the enterocyte VDR level influences 1,25(OH)2D3-mediated gene expression and transepithelial calcium (Ca) transport in the human intestinal cell line Caco-2. Cells were stably transfected with a human metallothionein (hMT) IIA promoter-human VDR (hVDR) complementary DNA (cDNA) transgene that overexpressed hVDR in response to heavy metals. In MTVDR clones, induction of 25-hyroxyvitamin D3-24-hydroxylase (24-OHase) messenger RNA (mRNA) expression by 1,25(OH)2D3 (10(-9) M, 4 h) was correlated to metal-induced changes in nuclear VDR level (r2 = 0.99). In MTVDR clones, basal VDR level was 2-fold greater and 1,25(OH)2D3-mediated Ca transport (10(-7) M, 24 h) was 43% higher than in parental Caco-2 cells. Treatment of MTVDR clones with Cd (1 microM, 28 h) increased VDR level by 68%, significantly enhanced 1,25(OH)2D3-mediated Ca transport by 24%, and increased accumulation of calbindin D9K mRNA by 76% relative to 1,25(OH)2D3 alone. These observations support the hypothesis that the enterocyte VDR level is an important modulator of intestinal responsiveness to 1,25(OH)2D3.

1,25-Dihydroxyvitamin D3 hypersensitivity of osteoclast precursors from patients with Paget's disease

Our previous studies suggested that increased osteoclast formation and activity in Paget's disease may be related in part to increased responsiveness of highly purified osteoclast precursors to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. However, the basis for this enhanced sensitivity to 1,25-(OH)2D3 is unclear. To address this question, we examined 24-hydroxylase and 1,25-(OH)2D3 receptor (VDR) messenger RNA (mRNA) expression during human osteoclast differentiation from normal subjects and patients with Paget's disease in response to 1,25-(OH)2D3 as well as VDR content and affinity. Reverse-transcription polymerase chain reaction (RT-PCR) analysis of granulocyte-macrophage colony-forming unit (GM-CFU), the earliest identifiable osteoclast precursor, derived from patients with Paget's disease demonstrated 24-hydroxylase mRNA expression in response to 1,25-(OH)2D3 was induced at concentrations of 1,25-(OH)2D3 that were at least one log less than that required for normal GM-CFU. VDR mRNA and VDR protein were detected in both immature and more differentiated osteoclast precursors, as well as in osteoclast-like multinucleated cells (MNCs). However, VDR expression was lower in MNCs than the mononuclear precursor cells. Osteoclast precursors and MNCs from patients with Paget's disease had levels of VDR expression similar to those of normal subjects but showed increased VDR affinity for 1,25-(OH)2D3. Because the effects of 1,25-(OH)2D3 are in part mediated by induction of expression of RANK ligand on marrow stromal cells, which in turn stimulates osteoclast formation, we examined expression of RANK ligand mRNA by marrow stromal cell lines derived from patients with Paget's disease and normal subjects in response to 1,25-(OH)2D3. RT-PCR analysis showed no difference in sensitivity of marrow stromal cells to 1,25-(OH)2D3 from normal subjects or patients with Paget's disease although the Paget's stromal cells expressed increased basal levels of RANK ligand mRNA. These results show that VDR protein is expressed in early and more differentiated osteoclast precursors, that expression levels of VDR decline with osteoclast differentiation, and that 1,25-(OH)2D3 has direct effects on osteoclast precursors. The enhanced sensitivity to 1,25-(OH)2D3 is an intrinsic property of osteoclast precursors from patients with Paget's disease that distinguishes them from normal osteoclast precursors. Furthermore, our results suggest that an increased affinity of VDR for 1,25-(OH)2D3 may be responsible for the enhanced 1,25-(OH)2D3 sensitivity of osteoclast precursors in patients with Paget's disease compared with normal subjects.

Calcium phosphate supersaturation regulates stone formation in genetic hypercalciuric stone-forming rats

BACKGROUND

Hypercalciuria is the most common metabolic abnormality observed in patients with nephrolithiasis. Hypercalciuria raises urine supersaturation with respect to the solid phases of calcium oxalate and calcium phosphate, leading to an enhanced probability for nucleation and growth of crystals into clinically significant stones. However, there is little direct proof that supersaturation itself regulates stone formation. Through successive inbreeding of the most hypercalciuric progeny of hypercalciuric Sprague-Dawley rats, we have established a strain of rats, each of which excrete abnormally large amounts of urinary calcium and each of which forms calcium phosphate kidney stones. We used these hypercalciuric (GHS) rats to test the hypothesis that an isolated reduction in urine supersaturation, achieved by decreasing urine phosphorus excretion, would decrease stone formation in these rats.

METHODS

Thirty 44th-generation female GHS rats were randomly divided into three groups. Ten rats received a high-phosphorus diet (0.565% phosphorus), 10 a medium-phosphorus diet (0.395% phosphorus), and 10 a low-phosphorus diet (0.225% phosphorus) for a total of 18 weeks. The lowered dietary phosphorus would be expected to result in a decrease in urine phosphorus excretion and a decrease in urinary supersaturation with respect to the calcium phosphate solid phase. Every two weeks, 24-hour urine collections were obtained. All relevant ions were measured, and supersaturation with respect to calcium oxalate and calcium hydrogen phosphate were determined. At the conclusion of the experiment, each rat was killed, and the kidneys, ureters, and bladder were dissected en block and x-rayed to determine whether any stones formed. A decrease in stone formation with a reduction in urinary supersaturation would support the hypothesis that supersaturation alone can regulate stone formation.

RESULTS

Decreasing the dietary phosphorus intake led to a progressive decrease in urine phosphorus excretion and an increase in urine calcium excretion, the latter presumably caused by decreased intestinal calcium phosphate binding and increased calcium absorption. With decreasing dietary phosphorus intake, there was a progressive decrease in saturation with respect to the calcium phosphate solid phase. Fifteen of the 20 kidneys from the 10 rats fed the high-phosphorus diet had radiographic evidence of kidney stone formation, whereas no kidneys from the rats fed either the medium- or low-phosphorus diet developed kidney stones.

CONCLUSIONS

A decrease in urine phosphorus excretion not only led to a decrease in urine supersaturation with respect to the calcium phosphate solid phase but to an elimination of renal stone formation. The results of this study support the hypothesis that variation in supersaturation alone can regulate renal stone formation. Whether a reduction of dietary phosphorus will alter stone formation in humans with calcium phosphate nephrolithiasis remains to be determined.

Genetic hypercalciuric stone-forming rats

In humans, idiopathic hypercalciuria is associated with stone formation. In order to study the mechanisms that are responsible for excess urine calcium excretion, in ways that are difficult or impossible in humans, we have developed a rat model of hypercalciuria. Spontaneously hypercalciuric rats have been successively inbred for over 50 generations to produce a strain in which urine calcium excretion is over 10 times greater than that of controls, and all rats form kidney stones. Analysis of the model has revealed that the rats not only exhibit increased intestinal calcium reabsorption but an independent defect in renal tubular calcium resorption and an increased tendency for bone resorption. These findings closely parallel those in patients with idiopathic hypercalciuria. In the intestine, bone and kidney there is an increased number of vitamin D receptors which are hyperresponsive to 1,25-dihydroxyvitamin D3. Whether the increased number of vitamin D receptors is directly responsible for the hypercalciuria and whether the same abnormality is present in humans with idiopathic hypercalciuria is under investigation. Hypercalciuric rats appear to be an excellent model to provide insights into the mechanisms causing hypercalciuria, and to delineate treatments for stone disease.

Increased dietary oxalate does not increase urinary calcium oxalate saturation in hypercalciuric rats

BACKGROUND

Human calcium oxalate (CaOx) nephrolithiasis may occur if urine is supersaturated with respect to the solid-phase CaOx. In these patients, dietary oxalate is often restricted to reduce its absorption and subsequent excretion in an effort to lower supersaturation and to decrease stone formation. However, dietary oxalate also binds intestinal calcium which lowers calcium absorption and excretion. The effect of increasing dietary oxalate on urinary CaOx supersaturation is difficult to predict.

METHODS

To determine the effect of dietary oxalate intake on urinary supersaturation with respect to CaOx and brushite (CaHPO4), we fed 36th and 37th generation genetic hypercalciuric rats a normal Ca diet (1.2% Ca) alone or with sodium oxalate added at 0.5%, 1.0%, or 2.0% for a total of 18 weeks. We measured urinary ion excretion and calculated supersaturation with respect to the CaOx and CaHPO4 solid phases and determined the type of stones formed.

RESULTS

Increasing dietary oxalate from 0% to 2.0% significantly increased urinary oxalate and decreased urinary calcium excretion, the latter presumably due to increased dietary oxalate-binding intestinal calcium. Increasing dietary oxalate from 0% to 2.0% decreased CaOx supersaturation due to the decrease in urinary calcium offsetting the increase in urinary oxalate and the decreased CaHPO4 supersaturation. Each rat in each group formed stones. Scanning electron microscopy revealed discrete stones and not nephrocalcinosis. X-ray and electron diffraction and x-ray microanalysis revealed that the stones were composed of calcium and phosphate; there were no CaOx stones.

CONCLUSION

Thus, increasing dietary oxalate led to a decrease in CaOx and CaHPO4 supersaturation and did not alter the universal stone formation found in these rats, nor the type of stones formed. These results suggest the necessity for human studies aimed at determining the role, if any, of limiting oxalate intake to prevent recurrence of CaOx nephrolithiasis.

Alendronate decreases urine calcium and supersaturation in genetic hypercalciuric rats

BACKGROUND

The mechanism of excess urine calcium excretion in human idiopathic hypercalciuria (IH) has not been determined but may be secondary to enhanced intestinal calcium absorption, decreased renal calcium reabsorption, and/or enhanced bone demineralization. We have developed a strain of genetic hypercalciuric stone-forming (GHS) rats as an animal model of human IH. When these GHS rats are placed on a low-calcium diet (LCD), urinary calcium (UCa) excretion exceeds dietary calcium intake, suggesting that bone may contribute to the excess UCa excretion. We used the GHS rats to test the hypothesis that bone contributes to the persistent IH when they are fed an LCD by determining if alendronate (Aln), which inhibits bone resorption, would decrease UCa excretion.

METHODS

GHS rats (N = 16) and the parent strain (Ctl, N = 16) were fed 13 g/day of a normal (1.2%) calcium diet (NCD) for seven days and were then switched to a LCD (0. 02%) for seven days. Ctl and GHS rats in each group were then continued on LCD for an additional seven days, with or without injection of Aln (50 micrograms/kg/24 hrs). UCa excretion was measured daily during the last five days of each seven-day period. To determine the effects of Aln on urine supersaturation, the experiment was repeated. All relevant ions were measured, and supersaturation with respect to calcium oxalate and calcium hydrogen phosphate was determined at the end of each period.

RESULTS

UCa was greater in GHS than in Ctl on NCD (7.4 +/- 0.5 mg/24 hrs vs. 1.2 +/- 0.1, GHS vs. Ctl, P < 0.01) and on LCD (3.9 +/- 0.2 mg/24 hrs vs. 0. 7 +/- 0.1, GHS vs. Ctl, P < 0.01). LCD provides 2.6 mg of calcium/24 hrs, indicating that GHS rats are excreting more calcium than they are consuming. On LCD, Aln caused a significant decrease in UCa in GHS rats and brought GHS UCa well below calcium intake. Aln caused a marked decrease in calcium oxalate and calcium hydrogen phosphate supersaturation.

CONCLUSION

Thus, on a LCD, there is a significant contribution of bone calcium to the increased UCa in this model of IH. Aln is effective in decreasing both UCa and supersaturation. The Aln-induced decrease in urine supersaturation should be beneficial in preventing stone formation in humans, if these results, observed in a short-term study using the hypercalciuric stone-forming rat can be confirmed in longer term human studies.

Chronic experimental colitis induced by dextran sulphate sodium (DSS) is characterized by Th1 and Th2 cytokines

Oral administration of DSS has been reported to induce an acute and chronic colitis in mice. The aim of our study was to evaluate if the chronic phase of DSS-induced colitis was characterized by a Th1/Th2 response and how this would relate to mucosal regeneration. Swiss Webster mice were fed 5% DSS in their drinking water for 7 days, followed by 2-5 weeks consumption of water. Control mice received only water. The animals were killed at 3 and 6 weeks after induction. Their colons were isolated for histology and immunohistochemistry, using specific MoAbs for T and B cells, macrophages, interferon-gamma (IFN-gamma), IL-4 and IL-5. Colons were scored for inflammation, damage and regeneration. Two weeks after stopping DSS the colonic epithelium had only partially healed. Total colitis scores were still increased, especially in the distal colon, which was due to more inflammation, damage and less regeneration. In areas of incomplete colonic healing the basal parts of the lamina propria contained macrophages and CD4+ T cells. These CD4+ T cells showed a focal increase of IFN-gamma and IL-4 staining compared with control animals. These findings were still observed 5 weeks after stopping DSS in some mice, albeit less extensive. Chronic DSS-induced colitis is characterized by focal epithelial regeneration and a Th1 as well as Th2 cytokine profile. We postulate that chronic immune activation mediated by both populations of Th cells can interfere with colonic healing and can play a role in the pathogenesis of chronic colitis.

Network of inflammatory cytokines and correlation with disease activity in ulcerative colitis

OBJECTIVE

The inflammatory component of most human inflammatory chronic diseases implicates the production of proinflammatory cytokines. Tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL1beta) seem to play an important role in ulcerative colitis (UC) in relevant experimental models. Moreover, antiTNF therapy seems promising experimentally and clinically. However, these cytokines, and TNFalpha more particularly, are hardly seen in vivo in such patients. The mediators of choice, correlated with disease activities or drug efficacy, remain unclear. To characterize in vivo the network of colonic cytokines in patients with UC, and the contribution of the various cytokines to disease activity we performed this study, using the colonic perfusion method.

METHODS

A 20-cm colon length was perfused. Perfusate samples were collected for cytokine determination by enzyme-linked immnoassays. Nineteen perfusions were performed in mild to moderate UC, including two successive perfusions in four patients. Six healthy control patients and four having Crohn's disease (CD) with rectal involvement were studied. Endoscopic score, leukocyte scintigraphy, and systemic markers of inflammation were simultaneously quantified.

RESULTS

Large amounts of IL1beta, TNFalpha, IL6, and IL8 were produced in UC patients with a highly significant correlation between TNFalpha, IL1beta and IL8 two by two. Multivariate factorial analysis indicated that IL1beta showed the best correlation with disease activity. Locally produced IL6 was strongly associated with circulating platelet counts. Moreover, production of inflammatory cytokines was associated with similar variations of disease activity in the four patients with two successive perfusions performed. The level of inflammatory cytokines in CD was lower than in UC; TNFalpha, IL1beta, and IL6 were not found in any control patients.

CONCLUSION

UC appears to be a chronic inflammatory disease characterized by high production of all four proinflammatory cytokines (IL1beta, TNFalpha, IL6, and IL8). These results suggest that colonic perfusion may be a suitable method to evaluate the local anticytokine properties of new drugs, in correlation with disease activity and systemic markers of inflammation.

Stones and bones: bone resorption and metabolism in stoneformers

Abnormalities of bone metabolism and osteopenia (which may be progressive) are features of idiopathic calcium stone disease. This abnormal bone metabolism may be mediated by increased levels of, or responsiveness to, calcitriol or cytokines, including interleukin-1. Bone resorption may be reduced experimentally with bisphosphonates, but for clinical management an appropriate adjustment of dietary calcium intake may be the method of choice to ameliorate bone loss.

Hyperresponsiveness of vitamin D receptor gene expression to 1,25-dihydroxyvitamin D3. A new characteristic of genetic hypercalciuric stone-forming rats

Hypercalciuria in genetic hypercalciuric stone-forming (GHS) rats is accompanied by intestinal Ca hyperabsorption with normal serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels, elevation of intestinal, kidney, and bone vitamin D receptor (VDR) content, and greater 1,25(OH)2D3-induced bone resorption in vitro. To test the hypothesis that hyperresponsiveness of VDR gene expression to 1,25(OH)2D3 may mediate these observations, male GHS and wild-type Sprague- Dawley normocalciuric control rats were fed a normal Ca diet (0.6% Ca) and received a single intraperitoneal injection of either 1,25(OH)2D3 (10-200 ng/100 g body wt) or vehicle. Total RNAs were isolated from both duodenum and kidney cortex, and the VDR and calbindin mRNA levels were determined by Northern blot hybridization using specific cDNA probes. Under basal conditions, VDR mRNA levels in GHS rats were lower in duodenum and higher in kidney compared with wild-type controls. Administration of 1,25(OH)2D3 increased VDR gene expression significantly in GHS but not normocalciuric animals, in a time- and dose-dependent manner. In vivo half-life of VDR mRNA was similar in GHS and control rats in both duodenum and kidney, and was prolonged significantly (from 4-5 to > 8 h) by 1,25(OH)2D3 administration. Neither inhibition of gene transcription by actinomycin D nor inhibition of de novo protein synthesis with cycloheximide blocked the upregulation of VDR gene expression stimulated by 1,25(OH)2D3 administration. No alteration or mutation was detected in the sequence of duodenal VDR mRNA from GHS rats compared with wild-type animals. Furthermore, 1,25(OH)2D3 administration also led to an increase in duodenal and renal calbindin mRNA levels in GHS rats, whereas they were either suppressed or unchanged in wild-type animals. The results suggest that GHS rats hyperrespond to minimal doses of 1,25(OH)2D3 by an upregulation of VDR gene expression. This hyperresponsiveness of GHS rats to 1,25(OH)2D3 (a) occurs through an increase in VDR mRNA stability without involving alteration in gene transcription, de novo protein synthesis, or mRNA sequence; and (b) is likely of functional significance, and affects VDR-responsive genes in 1, 25(OH)2D3 target tissues. This unique characteristic suggests that GHS rats may be susceptible to minimal fluctuations in serum 1, 25(OH)2D3, resulting in increased VDR and VDR-responsive events, which in turn may pathologically amplify the actions of 1,25(OH)2D3 on Ca metabolism that thus contribute to the hypercalciuria and stone formation.

Increased intracellular Th1 cytokines in scid mice with inflammatory bowel disease

Severe combined immunodeficient (scid) mice engrafted with small pieces of full thickness gut wall from immunocompetent syngenic donors develop a chronic and lethal colitis. Lymphocytes from the lamina propria of engrafted mice were analyzed for phorbol ester/ionomycin-induced cytokine production by intracellular staining. A 4-5-fold increase in the fraction of IFN-gamma-producing CD4+ lamina propria T cells was found in moderately and severely diseased mice when compared to healthy congenic C.B-17 control mice. The number of IL-2-producing T cells was increased by approximately 2-fold when comparing mice suffering from severe disease to healthy control mice. The fraction of TNF-alpha positive CD4+ T cells was increased by a factor of two in both moderately and severely diseased mice. When analyzing Th2 cytokines, it was found that the levels of IL-4-producing CD4+ T cells was not altered in diseased animals, whereas the fraction IL-10-producing CD4+ T cells was reduced by a factor of 20. The combined data showed a 15-25-fold increase in the Th1/Th2 ratio of diseased mice when compared to healthy control mice. No intracellular cytokines could be detected in lymphocytes not treated with phorbol ester/ionomycin. The present data identify a prominent role for Th1-type T helper cells in the immunopathogenesis of gut wall graft-induced inflammatory bowel disease in scid mice.

Defective renal calcium reabsorption in genetic hypercalciuric rats

Idiopathic hypercalciuria is a frequent cause of calcium (Ca) containing kidney stones. We have previously shown that there is increased intestinal Ca absorption in selectively inbred genetic hypercalciuric stone forming (GHS) rats; however, excess Ca excretion persists when the rats are fed a low Ca diet indicating a defect in renal Ca reabsorption and/or increased bone resorption. To determine if GHS rats have a defect in renal Ca reabsorption we performed 14C-inulin clearance studies on parathyroidectomized female GHS and control (Ctl) rats. After three baseline collections, chlorothiazide (CTZ) or furosemide (FUR) was infused and three more collections were obtained. Both GFR and filtered load of Ca did not differ among the groups; however, fractional and absolute excretion (UcaV) of Ca was three times higher in GHS rats. The increased Ca excretion was not diminished by a low Ca diet. Urine flow rate nearly tripled in all rats after either FUR or CTZ. After CTZ, UcaV was decreased to a greater extent in GHS compared to Ctl rats. After FUR, UcaV was increased to a greater extent in Ctl rats compared to GHS rats. These data indicate that GHS rats have a defect in renal Ca reabsorption, in addition to increased intestinal Ca absorption. The effect of CTZ was greater, and that of FUR was smaller, in GHS compared with Ctl rats, suggesting that the defect in renal Ca handling might be at the level of the thick ascending limb.