Should dietary calcium and protein be restricted in patients with nephrolithiasis?

The effects of dietary changes on bone markers in postmenopausal vertebral osteopenia

BACKGROUND & AIMS

Nutrition is one of the most important environmental factors affecting the formation of osteopenia. The purpose of this study was to investigate the effects of dietary changes on bone formation and bone resorption markers of postmenopausal women with vertebral osteopenia.

METHODS

In this study, 108 women with postmenopausal vertebral osteopenia were included. Patients were observed for a month to identify their regular nutritional status. Before intervention, blood and urine samples were taken from all patients. Then, 2-day food consumption records were taken and the patients were divided into 4 groups. Different types of diets (opposite of their regular diets) were prepared for these groups (1: control, 2: reduced-carbohydrate, 3: reduced-protein, 4: reduced-sodium) and followed for 3 months. At the end of follow-ups, blood and urine samples were taken again and changes in osteocalcin (OC) and N-terminal telopeptide (NTX) levels were examined.

RESULTS

According to biochemical analysis, there was a significant decrease (p < 0,001) in OC levels in reduced protein group and an increase (p > 0,05) in reduced carbohydrate group. When NTX levels were assessed, a significant decrease (p < 0.001) in the reduced carbohydrate group and a significant increase in the reduced protein group (p < 0.05) were found.

CONCLUSION

Our findings show that reduced carbohydrate diet protected whereas, reduced protein diet negatively affected bone health. Osteopenic individuals were thought to be able to improve bone health and their quality of life by early dietary intervention.

Vitamin K1 Inhibition of Renal Crystal Formation through Matrix Gla Protein in the Kidney

BACKGROUND AND OBJECTIVES

Vitamin K (VK) plays a major role in modifying the binding of calcium in bones and blood vessels. Understanding the effect of VK on crystal formation in the kidney would contribute to advancing the treatment and prevention of kidney stones.

METHODS

Rats were treated with vitamin K1 (VK1) for 8 weeks. VK1 levels were detected and crystal formation were observed. HK2 cells were exposed to calcium oxalate monohydrate crystals. Apoptosis and cell viability were detected. Crystal deposition was analyzed using atomic absorption assay. The adenovirus vectors expressing matrix Gla protein (MGP) and siMGP were constructed to elucidate the effect and mechanism of VK1 on crystal formation. MGP expression in vivo and in vitro was analyzed by Western blot. The mRNA levels of monocyte chemoattractant protein-1 (MCP-1) and collagen I was measured by semiquantitative RT-PCR.

RESULTS

The concentrations of VK1 in whole blood and kidney tissues rose under treatment with VK1. Crystal formation was inhibited from the second to the 6th week, the frequency and quality of crystal formation decreased significantly, and the location of crystal formation was limited to a greater extent in the rats treated by VK1 compared to the control group. Warfarin treatment in the crystals-exposed HK2 cells significantly increased the number of crystals adhering to cells and the number of apoptotic cells and reduced cell viability. VK1 treatment reversed warfarin's above influence. VK1 inhibited the upregulations of MCP-1 and collagen I in kidney tissues under crystal load. VK1 treatment increased MGP expression in vivo and in vitro, and MGP is necessary for VK1 to play a role in crystal deposition in cells.

CONCLUSIONS

VK1 treatment can inhibit the formation of renal crystals in vivo. VK1 increases MGP expression and functions through MGP to reduce crystal deposition in cells and provide cell protection. Our findings suggest that VK1 treatment could be a potential strategy for the treatment and prevention of nephrolithiasis.

The characteristics of the stone and urine composition in Chinese stone formers: primary report of a single-center results

OBJECTIVE

To assess urine composition in Chinese patients with urolithiasis.

METHODS

Five hundred seven Chinese patients with urolithiasis from our center in southern China were included in this study. Analysis of stone composition was performed using infrared spectrometry. From all patients, 24-hour urine samples were collected for analysis of urinary variables. Some ion activity product risk indices were also calculated.

RESULTS

The major stone constituents in the 507 analyzed stones were as follows: calcium oxalate (78.3%), infection stone components (14.6%), uric acid (3.6%), and calcium phosphate (3.4%). Only 1 stone was composed of cystine (0.2%). Of all patients, 504 (99.4%) had 1 or several urinary metabolic abnormalities. Hypocitraturia was recorded in 93.9%, high sodium excretion in 58.6%, small urine volume in 45.6%, hyperoxaluria in 31.0%, hypercalciuria in 26.0%, hyperuricosuria in 19.3%, and hyperphosphaturia in 2.8%. Moreover, high sodium excretion was more frequent in men than women (59.2% vs 49.3%, P = .027), whereas hypercalciuria was more common in women (34.5% vs 20.4%, P <.001). High levels of urine sodium (187.7 ± 86.9 vs 179.8 ± 107.7 mmol/24h, P = .038) and phosphate (18.26 ± 8.36 vs 15.69 ± 11.14 mmol/24h, P <.001) were found in men than in women. Infection stones were significantly (P <.004) more common in women. Compared with noninfection stone formers, the occurrence of hypomagnesuria (P = .040) was more common in patients with infection stones.

CONCLUSION

The results of urinary risk factors for stone formation in this study might serve as a basis for design of recurrence prevention. It is of interest to note that some of the demonstrated abnormalities differ from that in reports from other countries.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis: report of three Turkish siblings

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), an autosomal recessive renal tubular disorder is characterized by the impaired tubular reabsorption of magnesium and calcium in the thick ascending limb of the loop of Henle. This disease is caused by mutations in the claudin-16 gene (CLDN16), which encodes the tight junction protein, claudin-16. Claudin-16 belongs to the claudin family and regulates the paracellular transport of magnesium and calcium. Here, we report on three Turkish siblings with typical clinical features of FHHNC in association with the homozygous mutation Leu151Phe.

Prevention of Stone Disease

In recent years stone disease has become more widespread in developed countries. At present the prevalence is 5.2 and 15% of men and 6% of women are affected. The increase is linked to changes in lifestyle, eating patterns and obesity which has become very common. The 'metabolic syndrome' includes all the diseases, e.g. hypertension, lipid imbalances, type 2 diabetes mellitus, gout and cardiovascular disease, which are concomitant in the majority of stone formers. Dietary patterns, besides leading to stone formation, also determine stone chemistry. With a diet that is rich in oxalates, calcium oxalate will constitute 75% of stones, struvite 10-20%, uric acid 5-6% and cystine 1%. As approximately 50% of patients with stones suffer recurrences, metabolic and/or pharmacological prophylaxis is recommended.

Physiology of epithelial Ca2+ and Mg2+ transport

Ca2+ and Mg2+ are essential ions in a wide variety of cellular processes and form a major constituent of bone. It is, therefore, essential that the balance of these ions is strictly maintained. In the last decade, major breakthrough discoveries have vastly expanded our knowledge of the mechanisms underlying epithelial Ca2+ and Mg2+ transport. The genetic defects underlying various disorders with altered Ca2+ and/or Mg2+ handling have been determined. Recently, this yielded the molecular identification of TRPM6 as the gatekeeper of epithelial Mg2+ transport. Furthermore, expression cloning strategies have elucidated two novel members of the transient receptor potential family, TRPV5 and TRPV6, as pivotal ion channels determining transcellular Ca2+ transport. These two channels are regulated by a variety of factors, some historically strongly linked to Ca2+ homeostasis, others identified in a more serendipitous manner. Herein we review the processes of epithelial Ca2+ and Mg2+ transport, the molecular mechanisms involved, and the various forms of regulation.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis associated with CLDN16 mutations

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC), an autosomal recessive renal tubular disorder, is characterized by the impaired tubular reabsorption of magnesium and calcium in the thick ascending limb of the loop of Henle and an eventual progression to end-stage renal disease. Recent studies have reported that this disease is caused by mutations in the CLDN16 gene, which encodes the tight junction protein, paracellin-1. Paracellin-1 belongs to the claudin family and regulates the paracellular transport of magnesium and calcium. Here, we report on two Korean siblings with typical clinical features of FHHNC in association with compound heterozygous mutations, G233C and 800delG, in CLDN16. Their parents were asymptomatic heterozygous carriers of the single mutations. This is the first report of FHHNC in Korea, and the mutations reported are novel.

Developments in stone prevention

PURPOSE OF REVIEW

This review focuses on new developments in stone prevention. Unfortunately, no major progress in this field has happened. There is a worldwide lack of randomized and controlled trials, which could confirm our theoretical assumptions and preventive concepts in stone disease. With these preconditions in mind, this review presents the current knowledge of metabolic influences causing the symptom "stone" and the effective measures against it.

RECENT FINDINGS

Modern lifestyle, dietary habits and obesity emerge to be the promoters of idiopathic stone disease. Cross-sectional studies showed significant correlations between these factors and kidney stones with direct implications on our preventive concepts: normalization of body mass index, adequate physical activity, balanced nutrition and sufficient circadian fluid intake. Modern diets containing a lot of animal protein, refined carbohydrates and salt act on the metabolism like an acid load. To overcome these disadvantageous effects, a sufficient supply of potassium and alkali is required. Last but not least, calcium should not be restricted. There is clear evidence from clinical and experimental research that a normal or a high calcium supply is appropriate in calcium stone disease. Only in absorptive hypercalciuria calcium restriction remains beneficial in combination with thiazide and citrate therapy.

SUMMARY

Up to 85% of all stone patients could anticipate lower risk of stone recurrence with elementary reorientation of their lifestyle and dietary habits. Normalizing the major risk factors is easy and cheap. About 15% of patients forming stones require additional specific pharmacological prevention. The specific measures to avoid recurrence of the stone disease are precisely defined.

Characteristics of nanobacteria and their possible role in stone formation

Kidney stone formation is a multifactorial disease in which the defence mechanisms and risk factors are imbalanced in favour of stone formation. We have proposed a novel infectious agent, mineral forming nanobacteria (NB), to be active nidi that attach to, invade and damage the urinary epithelium of collecting ducts and papilla forming the calcium phosphate center(s) found in most kidney stones. Stone formation may proceed in urine supersaturated with calcium phosphate, calcium oxalate and uric acid/urate under the influence of crystallization promoters and inhibitors. Our hypothesis underlines the role of active nidi: even supersaturated urine requires nidi for crystallization to appear.

Effects of an oxalate load on urinary oxalate excretion in calcium stone formers

OBJECTIVE

To investigate the oxalate intake and the effect of an oxalate load on urinary oxalate excretion in calcium stone-forming (CSF) patients.

DESIGN

Prospective study.

SETTING

University-affiliated outpatient Renal Lithiasis Unit.

PATIENTS AND CONTROLS

Seventy (70) CSF and 41 healthy subjects (HS) collected a 24-hour urine sample and were submitted to a 3-day dietary record to determine mean oxalate (Ox), calcium (Ca) and vitamin C intake. Fifty-eight (58) CSF patients were randomly selected to receive milk (N = 28) or dark (N = 30) chocolate as an oxalate load.

INTERVENTION

Administration of either milk (94 mg Ox + 430 mg Ca) or dark chocolate (94 mg Ox + 26 mg Ca) for 3 days. A 24-hour urine sample was obtained before and after the load to determine calcium, oxalate, sodium, potassium, urea, and creatinine.

MAIN OUTCOME MEASURE

Oxalate intake and excretion.

RESULTS

CSF patients presented mean Ox intake of 98 +/- 137 mg/d, similar to that of HS (108 +/- 139 mg/d). Mean Ox and vitamin C intake was directly correlated with Ox excretion only in CSF. The consumption of dark chocolate induced a significant increase in mean urinary Ox (36 +/- 14 versus 30 +/- 10 mg/24 hr) not observed in the milk chocolate group. Thus, a 2-fold increase in Ox intake in this population of CSF patients produced a significant 20% increase in oxaluria, not observed when Ca was consumed simultaneously.

CONCLUSION

The present study suggests that even small increases in Ox intake affect oxalate excretion and the mitigation of urinary oxalate increase by Ca consumption reinforces that Ca and Ox intakes for CSF patients should be in balance. Further studies are necessary to assess whether or not a 20% increase in oxaluria will lead to a higher risk of stone formation.

Recurrent renal stone disease-advances in pathogenesis and clinical management

Kidney stones are common in industrialised nations: up to 15% of white men and 6% of all women will develop one stone, with recurrence in about half these people. Risk factors for formation of stones include urinary promoters (calcium, urate, cystine, and sodium) and urinary inhibitors (magnesium, citrate, and nephrocalcin). Acute renal colic can be precipitated by dehydration and reduced urine output, increased protein intake, heavy physical exercise, and various medicines. Such colic manifests as severe loin pain and can be accompanied by frequent urination, dysuria, oliguria, and haematuria. Documentation of stone characteristics is extremely important: type, size, location, and underlying metabolic abnormalities. Such details can be obtained with a combination of biochemical investigations, microscopic examination of urine under polarised light, and an intravenous pyelogram. Ultrasonography and plain abdominal radiographs are also useful, especially for patients unable to tolerate an intravenous pyelogram. Acute therapy includes complete pain relief, rehydration, and encouragement of diuresis. Long-term management encompasses education of patients with regard to diet and fluid intake, control of calciuria, citrate replacement, and treatment of any underlying urinary-tract infection or metabolic abnormality. Stones smaller than 5 mm normally pass spontaneously, whereas larger stones, as big as 2 cm, are best treated with extracorporeal shock-wave lithotripsy. All physicians should have a clear understanding of the pathogenesis and clinical management (acute treatment and prevention of recurrence) of renal stone disease.

Prevention of nephrolithiasis

The high incidence of recurrence after an initial stone event underscores the need for an effective medical prophylactic program. Dietary modification and drug therapies have long been advocated to reduce the likelihood of stone recurrence. While the efficacy of a high fluid intake has been validated in a randomized trial, the benefit of other dietary measures is based on modulation of urinary stone risk factors and outcomes derived from observational studies. Several drug therapies have been evaluated in a limited number of prospective, randomized trials and efficacy has been demonstrated for thiazides, allopurinol and alkali citrate in some populations of recurrent stone formers. The role of selective versus nonselective therapy for stone prevention awaits further study.