Does a rise in plasma erythropoietin after high-altitude exposure affect FGF23 in healthy volunteers on a normal or low-phosphorus diet?

BACKGROUND AND AIMS

Data of experimental rodent models suggest that hypoxia with subsequent increase in erythropoietin stimulates the expression of the phosphaturic hormone fibroblast growth factor 23 (FGF23).

METHODS AND RESULTS

To translate the findings of animal studies into human physiology, herein we exposed eight healthy volunteers to high altitude (2656 m above sea level) for four days. The volunteers were randomized on a low-phosphorous diet (n = 4) or a normal phosphorus diet (n = 4). Although high-altitude exposure caused a significant increase in plasma erythropoietin (EPO) (before high-altitude exposure: low phosphorus: median EPO 6.6 mIU/ml [interquartile range (IQR) 6.0; 8.2], normal phosphorus: median EPO 9.0 mIU/ml [IQR 7.9; 11.5]; at day 2: low phosphorus: median EPO 21.3 mIU/ml [IQR 19.5; 23.8], normal phosphorus: median EPO 19.4 mIU/ml [IQR 18.0; 20.8]), there was no consistent increase in plasma c-terminal FGF23 or plasma intact FGF23. We observed only a single, intermittent peak in c-terminal FGF23 levels after 5 h of maximal aerobic exercise.

CONCLUSION

These data do not support a substantial effect of moderate hypoxia alone on the expression of FGF23, but they suggest that combined exercise and high-altitude exposure may temporarily induce FGF23 expression.

Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat

Phosphorus is present in diets as naturally occurring P from raw materials or added as an inorganic salt. However, little is known about postprandial kinetics of P absorption in cats. Here, we describe several studies quantifying postprandial kinetics following the ingestion of diets of varying composition. Briefly, cats were fed a meal consisting of 50 % of their metabolic energy requirement in a randomised crossover design. A pre-meal baseline blood sample was taken via cephalic catheter and repeated measurements taken regularly up to 6 h post-meal to assess the whole blood ionised Ca, plasma P and parathyroid hormone concentrations. A diet containing 4·8 g total P/4184 kJ (1000 kcal), 3·5 g P from sodium dihydrogen phosphate (NaH2PO4)/4184 kJ (1000 kcal) and Ca:P 0·6 caused a marked increase in plasma P from baseline to a peak of 1·976 (95% CI 1·724, 2·266) mmol/l (P <0·001), whereas a diet containing 3·38 g total P/4184 kJ (1000 kcal), no added inorganic P and Ca:P 1·55 resulted in a postprandial decrease in plasma P (P = 0·008). Subsequent data indicate that added inorganic P salts in the diet above 0·5 g P/4184 kJ (1000 kcal) cause an increase in plasma P in cats, while diets below this do not. The data presented here demonstrate that sources of added inorganic P salts cause a temporary postprandial increase in plasma P in a dose-dependent manner, prolonged in diets with Ca:P <1·0. Dietary P derived from natural food ingredients (e.g. meat or vegetable matter) does not appear to have any effect on postprandial plasma P.

The impact of a nutritional intervention based on egg white for phosphorus control in hemodialyis patients

BACKGROUND AND AIMS

Here we describe a dietary intervention for hyperphosphatemia in dialysis patients based on the partial replacement of meat and fish, which are one of the main sources of alimentary phosphorous, with egg white, a virtually phosphorous-free protein source. This intervention aims to reduce phosphorous intake without causing protein wasting.

PATIENTS AND METHODS

As many as 23 hyperphosphatemic patients (15 male and 8 female, mean age 53.0 ± 10.0 years) on chronic standard 4 h, three times weekly, bicarbonate hemodialysis were enrolled in this open-label, randomized controlled trial. Patients in the intervention group were instructed to replace fish or meat with egg white in three meals a week for three months whereas diet was unchanged in the control group.

RESULTS

Serum phosphate concentrations were significantly lower in the intervention group than in controls after three (4.9 ± 1.0 vs 6.6 ± 0.8; p < 0.001) but not after one month of treatment. Phosphate concentrations decreased more from baseline in the intervention than in the control group both after one (-1,2 ± 1,1 vs 0,5 ± 1,1; p = 0.004) and after three (-1,7 ± 1,1 vs -0,6 ± 1,1; p < 0.001) months of follow-up. No change either in body weight or in body composition assessed with bioelectrical impedance analysis or in serum albumin concentration was observed in either group.

CONCLUSION

The partial replacement of meat and fish with egg white induces a significant decrease in serum phosphate without causing protein malnutrition and could represent a useful instrument to control serum phosphate levels in hemodialysis patients. CLINICALTRIALS.

GOV IDENTIFIER

NCT03236701.

Impact of nutritional index on the association between phosphorus concentrations and mortality in haemodialysis patients: a cohort study from dialysis outcomes and practice pattern study in Japan

OBJECTIVES

While maintenance of both phosphorus concentration and nutritional status is a major concern in managing haemodialysis patients, the interaction between these parameters is not well understood. The aim of this study was to assess whether or not nutritional index influences the association between phosphorus concentration and all-cause mortality.

DESIGN

A cohort study.

SETTING

The Dialysis Outcomes and Practice Pattern Study, which included 99 representative dialysis facilities in Japan between 1997 and 2010.

PARTICIPANTS

A total of 6230 adult haemodialysis patients who had spent at least 6 months on haemodialysis.

MAIN PREDICTORS

Six categories based on time-averaged factors of the geriatric nutritional risk index (GNRI; the lowest two and highest tertiles) and phosphorus concentration (<3.5, 3.5 to <6 and ≥6 mg/dL).

PRIMARY OUTCOME MEASURE

All-cause mortality rate.

ANALYSIS

Time-dependent Cox regression adjusting for potential confounders.

RESULTS

During the follow-up period (12 294 person-years), we noted 561 deaths (4.6 per 100 person-years), and both high phosphorus concentrations and low-middle GNRI were separately associated with all-cause mortality. The harmful effect of high phosphorus concentrations on all-cause mortality was stronger in patients with high GNRI than in those with low-middle GNRI. On the other hand, the harmful effect of low phosphorus concentrations was stronger in those with low-middle GNRI than in those with high GNRI. Relative excess risk due to interaction (RERI) between high phosphorus concentrations and low-middle GNRI was -0.57, indicating an antagonistic interaction. We also observed a significant statistical multiplicative interaction between phosphorus concentrations and GNRI (p=0.05 by likelihood ratio test).

CONCLUSIONS

The association between time-averaged serum phosphorus concentration and all-cause mortality differs across the nutritional index. Accordingly, nutritional index should be considered when the impact of phosphorus concentration on mortality in haemodialysis patients is evaluated.

Adiponectin alters renal calcium and phosphate excretion through regulation of klotho expression

The kidney controls systemic calcium and phosphate levels and disturbances of its control mechanisms can lead to a variety of diseases. The insulin-sensitizing adipokine adiponectin is renoprotective and accelerates functional recovery following renal injury. However, unlike other adipokines, adiponectin is reduced in obesity. High adiponectin levels are also correlated with bone loss, suggestive of an additional action in mineral metabolism. Using knockout, wild-type, and adiponectin-overexpressing transgenic mice, we sought to identify the mechanistic basis for adiponectin's ability to regulate calcium and phosphate balance at the level of the kidney. Adiponectin knockout mice exhibited lower serum calcium, lower urinary calcium excretion, and markedly lower serum fibroblast growth factor 23 (FGF23) levels, although circulating klotho concentrations were significantly higher than in wild-type littermates. The transgenic mice exhibited lower bone mass and strength, particularly compared to adiponectin knockout mice. The transgenic mice were hyper-responsive to a 2% phosphate-enriched diet, exhibiting 2-fold higher serum FGF23 and concomitantly higher fractional phosphate excretion. These mice also excreted more calcium with calcium-enriched diet and had less renal klotho protein expression. In contrast, the knockout mice exhibited a smaller increase in FGF23 and maintained elevated klotho levels on both mineral challenges. Kidney-specific adiponectin expression in doxycycline-inducible adiponectin mice and adiponectin addition in vitro confirmed adiponectin's ability to reduce tubular epithelial cell klotho secretion. Thus, adiponectin alters calcium and phosphate balance and renal mineral excretion, in part, through klotho. This work highlights the profound effects of adipose tissue on renal function and has identified a new mechanism by which adiponectin may regulate bone mass.

Phosphorus Regulation in Chronic Kidney Disease

Serum phosphorus levels stay relatively constant through the influence of multiple factors-such as parathyroid hormone, fibroblast growth factor 23, and vitamin D-on the kidney, bone, and digestive system. Whereas normal serum phosphorus ranges between 3 mg/dL to 4.5 mg/dL, large cross-sectional studies have shown that even people with normal kidney function are sometimes found to have levels ranging between 1.6 mg/dL and 6.2 mg/dL. While this may partially be due to diet and the factors mentioned above, total understanding of these atypical ranges of serum phosphorus remains uncertain. Risks for bone disease are high in people aged 50 and older, and this group comprises a large proportion of people who also have chronic kidney disease. Consuming diets low in calcium and high in phosphorus, especially foods with phosphate additives, further exacerbates bone turnover. Existing bone disease increases the risk for high serum phosphorus, and higher serum phosphorus has been associated with increased adverse events and cardiovascular-related mortality both in people with chronic kidney disease and in those with no evidence of disease. Once kidney function has deteriorated to end-stage disease (Stage 5), maintaining normal serum phosphorus requires dietary restrictions, phosphate-binding medications, and dialysis. Even so, normal serum phosphorus remains elusive in many patients with Stage 5 kidney disease, and researchers are testing novel targets that may inhibit intestinal transport of phosphorus to achieve better phosphate control. Protecting and monitoring bone health should also aid in controlling serum phosphorus as kidney disease advances.

Association of serum 25-hydroxyvitamin d levels and vitamin D dietary intake with metabolic syndrome: a case control study

BACKGROUND

Association between the vitamin D deficiency and metabolic syndrome (MetS) has previously been noted and reported to be controversial. The aim of this study was to determine the association of serum 25 (OH) D Level and Vitamin D dietary intake with MetS among Iranian population.

METHODS

This analytical study was conducted on 122 patients with MetS based on the ATPIII criteria and 128 subjects without MetS as control from September 2010 to April 2011. Serum levels of calcium, phosphorus and 25(OH) D were compared between the two groups. A food frequency questionnaire (FFQ) was used to calculate dietary intake. Data were analyzed using Chi- square test, t-test, Mann-Whitney U test and logistic regression analysis.

RESULTS

Serum concentrations of 25 (OH) D, calcium and phosphorus and calcium intake were significantly lower in subjects with MetS compared to the subjects without MetS. 98.4% of subjects with MetS and 88.3% without MetS had Vit. D deficiency and this difference was statistically significant (P=0.005). In regression analysis, lower concentration of serum 25 (OH) D, calcium and phosphorus and lower calcium and diary intake were predictors of MetS.

CONCLUSIONS

Serum 25 (OH) D Level, calcium and phosphorus and calcium intake are associated with metabolic syndrome. However, the mechanism of this association requires further studies.

Proposed biokinetic model for phosphorus

This paper reviews data related to the biokinetics of phosphorus in the human body and proposes a biokinetic model for systemic phosphorus for use in updated International Commission on Radiological Protection (ICRP) guidance on occupational intake of radionuclides. Compared with the ICRP's current occupational model for systemic phosphorus (Publication 68, 1994), the proposed model provides a more realistic description of the paths of movement of phosphorus in the body and greater consistency with experimental, medical, and environmental data regarding its time-dependent distribution. For acute uptake of (32)P to blood, the proposed model yields roughly a 50% decrease in dose estimates for bone surface and red marrow and a six-fold increase in estimates for liver and kidney compared with the model of Publication 68. For acute uptake of (33)P to blood, the proposed model yields roughly a 50% increase in dose estimates for bone surface and red marrow and a seven-fold increase in estimates for liver and kidney compared with the model of Publication 68.

Association between obesity and calcium:phosphorus ratio in the habitual diets of adults in a city of Northeastern Brazil: an epidemiological study

BACKGROUND

Low calcium:phosphorus ratios (Ca:P ratio) in habitual diet have been observed worldwide, and it has been shown to be harmful to the bone health of the population. However, no study associating this ratio with obesity was found. Thus, considering that the intake of calcium and phosphorus will generate a ratio between them, which may be associated with obesity, this research seeks at evaluating the relation between obesity and the Ca:P ratio in the habitual diet of adults.

METHODS

Cross-sectional population-based epidemiological study with stratified and systematic sampling. The sample was composed of 506 adults, aged between 18 and 60 years, of both genders. Information on socioeconomic and demographic conditions was obtained through questionnaires completed during home visits, where anthropometric and dietary evaluations were also conducted.

RESULTS

In the habitual diet consumed by the study subjects, a Ca:P ratio above the median of 0.57 reduced the risk of central obesity based on waist-to-height ratio (WHtR) (OR: 0.61; 95% CI: 0.41 - 0.92). Habitual dietary intake of calcium (OR: 0.65; 95% CI: 0.43 - 0.97) and dairy products (OR: 0.56; 95% CI: 0.37 - 0.84) above the median value (485.4 mg and 0.9 servings, respectively) was found to be a protective factor related to central obesity based on WHtR.

CONCLUSIONS

Values above the median for the Ca:P ratio found in the habitual diet were negatively associated with central obesity based on WHtR. In addition, calcium and dairy consumption were negatively associated with central obesity based on WHtR. Therefore, higher Ca:P ratios contributed to a lower prevalence of central obesity.

[The evaluation of selected parameters of calcium and phosphorus metabolism in children with cow's milk allergy]

THE AIM of this study was to evaluate selected parameters of calcium and phosphorus metabolism in children with CMA treated with the following milk substitute formulas: lactose-containing extensively hydrolyzed wheat protein formula, lactose-free extensively hydrolyzed casein protein formula, as well as soy-based formula.

MATERIAL AND METHODS

The study involved 66 children with CMA aged 2-5 years treated with milk-free diet for at least one year. Group I included 31 children fed with a lactose-containing formula, group II - 35 children treated with lactose-free formula. In all children the mean energy intake and nutritional value of daily food rations were assessed. Serum concentrations of calcium (Ca), phosphorus (P), sodium (Na) and magnesium (Mg) were determined using standard methods. Serum values of 25 hydroxyvitamin D (25-OH D) and parathormone (PTH) were assessed by chemiluminescence, whereas concentrations of biochemical markers of bone formation-bone alkaline phosphatase (BALP), osteocalcin (OC) and bone resorption marker-collagen type I crosslinked C-telopeptide (CTX) were determined by immunoenzymatic methods (ELISA), using specific monoclonal antibodies.

RESULTS

There were no significant differences in the mean dietary supply of calcium, phosphorus, magnesium, sodium, total protein and vitamin C in children from both groups. In the diets of children from group II, the mean content of lactose (0.5±1.0 vs 10.0±6.8 g/d) and 25-OH vitamin D (4.1±2.3 vs 8.5±4.0 ug/d) were significantly lower and dietary fibre content (14.7±3.9 vs 10.4±3.9 g/d) was higher. Calcium and vitamin D dietary supply was lower with respect to nutritional recommendations in all the studied children, whereas the dietary deficiency of vitamin D was higher in children from group II. The mean serum concentrations of evaluated biochemical parameters did not reveal any differences in children from the study groups and were in the normal ranges. There were also no differences in the mean serum concentration of 25-OH vitamin D, ALP, BALP, CTX and PTH in patients from both groups. The mean concentration of OC was significantly higher in group II (71±26.6 ng/ml) than in children from group I (61.1±23.4 ng/ml) <0.01. Positive correlation was found between OC and CTX in both study groups.

CONCLUSIONS

1. In children with CMA basic blood laboratory tests may have limited importance in the evaluation of calcium and phosphorus metabolism. 2. Our results suggest that the disturbances in the balance between bone formation and bone resorption processes may occur in children with CMA treated with lactose-free formulas. 3. In order to assure optimal conditions for achieving adequate bone mass by children with CMA, it is necessary to provide them with regular medical and nutritional care.

Effects of dietary phosphate and calcium intake on fibroblast growth factor-23

BACKGROUND AND OBJECTIVES

Little is known about the influence of dietary phosphate intake on fibroblast growth factor-23 (FGF23) and its subsequent effects on vitamin D levels. This study addresses changes in intact FGF23 (iFGF23) and C-terminal FGF23 (cFGF23), phosphaturia, and levels of vitamin D on high and low phosphate and calcium intake.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Ten healthy subjects adhered to a diet low or high in phosphate and calcium content for 36 hours each with a 1-week interval during which subjects adhered to their usual diet. Serum phosphate, calcium, vitamin D metabolites, parathyroid hormone (PTH), and FGF23 levels (cFGF23 and iFGF23) were measured several times a day. Phosphate, calcium, and creatinine excretion was measured in 24-hour urine on all study days.

RESULTS

Serum phosphate levels and urinary phosphate increased during high dietary phosphate intake (from 1.11 to 1.32 mmol/L, P<0.0001 and 21.6 to 28.8 mmol/d, P=0.0005, respectively). FGF23 serum levels increased during high dietary phosphate/calcium intake (cFGF23 from 60 to 72 RU/ml, P<0.001; iFGF23 from 33 to 37 ng/L, P=0.003), whereas PTH declined. 1,25-dihydroxyvitamin D (1,25D) showed an inverse relation with FGF23.

CONCLUSIONS

Variation in dietary phosphate and calcium intake induces changes in FGF23 (on top of a circadian rhythm) and 1,25D blood levels as well as in urinary phosphate excretion. These changes are detectable the day after the change in the phosphate content of meals. Higher FGF23 levels are associated with phosphaturia and a decline in 1,25D levels.

Vegetarian compared with meat dietary protein source and phosphorus homeostasis in chronic kidney disease

BACKGROUND AND OBJECTIVES

Patients with advanced chronic kidney disease (CKD) are in positive phosphorus balance, but phosphorus levels are maintained in the normal range through phosphaturia induced by increases in fibroblast growth factor-23 (FGF23) and parathyroid hormone (PTH). This provides the rationale for recommendations to restrict dietary phosphate intake to 800 mg/d. However, the protein source of the phosphate may also be important.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a crossover trial in nine patients with a mean estimated GFR of 32 ml/min to directly compare vegetarian and meat diets with equivalent nutrients prepared by clinical research staff. During the last 24 hours of each 7-day diet period, subjects were hospitalized in a research center and urine and blood were frequently monitored.

RESULTS

The results indicated that 1 week of a vegetarian diet led to lower serum phosphorus levels and decreased FGF23 levels. The inpatient stay demonstrated similar diurnal variation for blood phosphorus, calcium, PTH, and urine fractional excretion of phosphorus but significant differences between the vegetarian and meat diets. Finally, the 24-hour fractional excretion of phosphorus was highly correlated to a 2-hour fasting urine collection for the vegetarian diet but not the meat diet.

CONCLUSIONS

In summary, this study demonstrates that the source of protein has a significant effect on phosphorus homeostasis in patients with CKD. Therefore, dietary counseling of patients with CKD must include information on not only the amount of phosphate but also the source of protein from which the phosphate derives.

The relationship between habitual dietary phosphorus and calcium intake, and bone mineral density in young Japanese women: a cross-sectional study

Phosphorus and calcium are essential for bone health. There is a concern that a low calcium/phosphorus intake ratio resulting from low calcium intake coupled with high phosphorus intake may have a negative effect on bone mineral status, especially in Western countries. The objective of this study was to examine cross-sectionally the influence of habitual phosphorus and calcium intake and the calcium/phosphorus intake ratio on the bone mineral density (BMD) in 441 young Japanese women (aged 18-22) whose calcium/phosphorus intake ratio was assumed to be lower than young Western women. We also ascertained the relationship between dietary intake and serum or urinary measurements of phosphorus and calcium. Parathyroid hormone (PTH) and 25-hydroxy vitamin D (25(OH)D) were also examined for 214 of the 441 subjects. Phosphorus and calcium intake and the calcium/phosphorus intake ratio had significant positive correlations with urinary phosphorus. Calcium intake and the calcium/phosphorus intake ratio independently had positive and significant associations with BMD in the distal radius adjusted for postmenarcheal age, body mass index, and physical activity. There were no significant associations with BMD in the lumbar spine and femoral neck. These results indicate that in young Japanese women, phosphorus intake did not have a significantly negative effect on bone mineral density, and calcium intake and calcium/phosphorus intake ratio had a small but significant association only in a site-specific manner with BMD.

Association of dietary phosphorus intake and phosphorus to protein ratio with mortality in hemodialysis patients

BACKGROUND AND OBJECTIVES

Epidemiologic studies show an association between higher predialysis serum phosphorus and increased death risk in maintenance hemodialysis (MHD) patients. The hypothesis that higher dietary phosphorus intake and higher phosphorus content per gram of dietary protein intake are each associated with increased mortality in MHD patients was examined.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Food frequency questionnaires were used to conduct a cohort study to examine the survival predictability of dietary phosphorus and the ratio of phosphorus to protein intake. At the start of the cohort, Cox proportional hazard regression was used in 224 MHD patients, who were followed for up to 5 years (2001 to 2006).

RESULTS

Both higher dietary phosphorus intake and a higher dietary phosphorus to protein ratio were associated with significantly increased death hazard ratios (HR) in the unadjusted models and after incremental adjustments for case-mix, diet, serum phosphorus, malnutrition-inflammation complex syndrome, and inflammatory markers. The HR of the highest (compared with lowest) dietary phosphorus intake tertile in the fully adjusted model was 2.37. Across categories of dietary phosphorus to protein ratios of <12, 12 to <14, 14 to <16, and > or =16 mg/g, death HRs were 1.13, 1.00 (reference value), 1.80, and 1.99, respectively. Cubic spline models of the survival analyses showed similar incremental associations.

CONCLUSIONS

Higher dietary phosphorus intake and higher dietary phosphorus to protein ratios are each associated with increased death risk in MHD patients, even after adjustments for serum phosphorus, phosphate binders and their types, and dietary protein, energy, and potassium intakes.

Phosphorus homeostasis in normal health and in chronic kidney disease patients with special emphasis on dietary phosphorus intake

Elevated serum phosphorus has been identified as a cardiovascular risk factor in chronic kidney disease (CKD) patients and a clear understanding of phosphorus homeostasis is very important for practicing nephrologists. At any particular point, serum phosphorus levels reflect the balance between movements of this mineral from and into the intestine, bone, intracellular space, and kidneys. We briefly review here all these exchanges with a particular emphasis on dietary phosphorus intake. Despite all the oral phosphorus binders currently available in the market, dietary restriction of this mineral remains a cornerstone for the prevention and treatment of hyperphosphatemia. An effective restriction of dietary intake of phosphorus requires prescription of a moderate protein intake (0.9-1.0 g/kg/day) and restricted consumption of highly processed fast and convenience foods. Phosphorus added during food processing is an important source of this mineral because of its magnitude and high bioavailabilty. Moreover, as food manufacturers are not required to label the amount of phosphorus added during food processing, a significant amount of the current daily phosphorus intake remains unaccounted when estimating phosphorus intake in CKD patients. The recent development of low phosphorus-containing food products represents a very useful addition for CKD patients.

Asymptomatic rickets in adolescent girls

OBJECTIVE

Inadequate sunlight exposure and calcium intake during rapid growth at puberty lead to hypocalcemia, hypovitaminosis D and eventually to overt rickets. To determine serum biochemical findings of rickets in healthy 11-15 yr old girls, the effect of sunlight exposure and oral vitamin D supplementation on serum 25- hydroxy vitamin D and calcium administration in girls with abnormal findings during December 2002 through March 2003 in Tehran, Iran.

METHODS

Healthy middle school girls were selected for estimation of vitamin D, calcium and phosphorus intake by a three-day food recall. And measurement of serum calcium, phosphorus, parathyroid hormone, alkaline-phosphatase and 25- hydroxyvitamin D concentration. The girls with abnormal findings divided in two groups. Hypovitaminosis D girls subdivided into two groups, supplementary sunlight exposure and vitamin- D administrated for them and calcium administration for the second group for 20 days.

RESULTS

Of 414 girls, the mean daily vitamin D acquirement and calcium intake were 119 +/- 52 IU and 360 +/- 350 mg among all girls respectively. Mean serum 25-hydroxyvitamin D with two or more abnormal biochemical findings in 15 (3.6%) girls (group I) were 7.8 ng/ml and alkaline phosphatse with normal or low calcium in 29 (7%) girls (group II) was 1187 IU/L. Mean serum calcium was 8.2 mg % in 8 of 29 girls. Serum 25- hydroxyvitamin D before and after sunlight exposure was 7.1 +/- 1.9 ng/ml and 13.9 +/- 2.4 ng/ml and vitamin D administration was 7.4 +/- 1.8 ng/ml (group Ia) and 27.9 +/- 4.2 ng/ml (group Ib) respectively. Serum alkaline phosphatase before and after calcium administration were 1187 IU/L and 666 IU/L respectively.

CONCLUSION

We conclude that low daily calcium intake and vitamin D acquirement are two important problems in Iranian girls during rapid growth at puberty; therefore, for prevention of overt rickets calcium and vitamin D Supplementation appear to be necessary.

Food mineral composition and acid-base balance in preterm infants

BACKGROUND

Due to a transient age-related low renal capacity for net acid excretion, preterm infants fed formula are at a considerable risk of spontaneously developing incipient late metabolic acidosis, clinically characterized by e.g., disturbed bone mineralization and impaired growth.

AIM OF THE STUDY

From acid-base data in blood and urine under different diets of modified human milk or preterm formulas is attempted to explore the impact of food mineral (and protein) composition on renal regulation and systemic acid-base balance in preterm infants.

PATIENTS AND METHODS

Data were collected from 48 infants fed their own mother's milk (28 native human milk, 20 enriched with fortifier) and 34 patients on formula (23 on a standard batch, 11 on a modified batch with reduced acid load). Intake of food was measured and acid-base data were determined in blood and timed-urine (8-12 h) samples.

RESULTS

Differences in mineral composition of the diets led to considerable differences of daily "alkali-intake", without significant effects on non-respiratory (base excess, BE) and respiratory (PCO(2)) acid-base data in the blood. In contrast, a highly significant proportionality between individual dietary alkali intake and daily renal base (Na(+) + K(+)-Cl(-)) excretion was observed (y = 0.32x-0.70, n = 80, r = 0.77, P < 0.0001), irrespective of the type of the diet.

CONCLUSION

Renal base saving mechanisms are normally effective in preterm infants to compensate for differences in dietary acid-base load. Generally, nutritional acid-base challenges can be judged much earlier and more safely by urinary than by blood acid-base analysis. Taking into account the age specific low capacity for renal NAE, the relatively high nutritional acid load of preterm standard formula should be reduced.

Molecular and conventional responses of large rainbow trout to dietary phosphorus restriction

The dietary phosphorus (P) requirement for large fish is difficult to estimate because of insensitivities of known P status indicators. We examined dietary P requirement of large rainbow trout (mean body weight 278 g) using recently identified P-responsive genes (mRNA abundances) as well as conventional serum P and bone P. Fish were fed six diets (varied P contents), and the tissues of intestine, pyloric caeca (PC), kidney, serum and bone were collected at varying time intervals. Serum P responded clearly to dietary P by day 2, but the estimated P requirement based on this variable changed as feeding duration continued. Bone P did not respond clearly until week 7. Among P-responsive genes studied, Na/Pi cotransporter in PC (PC-NaPi) was the most sensitive, and responded in 2 days. Fish-to-fish (within treatment) variance was larger in mRNA than in serum P and bone P levels. Estimated dietary P requirements (%P in dry diet) were 0.45 (based on serum P), 0.45 (based on bone P), 0.36 (based on PC-NaPi), 0.33 (based on intestinal NaPi), 0.71 (based on renal NaPi), and 0.33 (based on mitochondrial Pi carrier). This study is the first to evaluate the potential of genomic approaches in determining nutrient requirements of fish.

The effects of dietary phosphorus deficiency on surface pH and membrane composition of the mucosa epithelium in caprine jejunum

In ruminants, the uptake of inorganic phosphate (P(i)) across the intestinal mucosa epithelium by Na-dependent and Na-independent mechanisms is a main regulatory factor in P homeostasis. The aim of the study was to elucidate to which extent Na-independent mechanisms, including pH effects or composition of mucosal brush-border membranes, could be involved in positive stimulation of P(i) absorptive processes seen under the P deficient condition. Therefore, luminal, surface and intracellular pH of the jejunal epithelial cells in control and P depleted goats were compared and biochemical analyses of membrane phospholipids in the apical membrane of the jejunal epithelium were performed. Dietary P depletion resulted in decreased plasma P(i) levels. While pH in jejunal ingesta was not significantly changed, P depletion resulted in a significantly lower surface pH in the crypt region compared to control animals (7.62 +/- 0.02 vs. 7.77 +/- 0.04, n = 4, P < 0.01). Inhibition of apical Na(+)/H(+)-exchange resulted in an increase of the jejunal surface pH in P depleted animals by 0.07 +/- 0.01 (n = 6, P < 0.01) and 0.05 +/- 0.01 (n = 6, P < 0.01) for the villus and the crypt region, respectively. This increase were inversely correlated with the initial surface pH prior to inhibition. In contrast to surface pH, intracellular pH of the jejunal epithelium and the phospholipid composition of the apical jejunal membrane were not affected by P depletion. Although the data suggest the existence of a Na(+)/H(+)-exchange mechanism at the luminal surface of goat jejunum they do not support the hypothesis that adaptational processes of active P(i) absorption from goat jejunum in response to low dietary P could be based on "non P(i) transporter events".

High-phosphorus diet stimulates receptor activator of nuclear factor-kappaB ligand mRNA expression by increasing parathyroid hormone secretion in rats

The purpose of the present study was to clarify the manner by which the supplementation of high-P diet induces bone loss. Eighteen 4-week-old male Wistar-strain rats were assigned randomly to three groups and fed diets containing three P levels (0.3, 0.9, and 1.5 %) for 21 d. A lower serum Ca concentration was observed in the rats fed on the 1.5 % P diet than in the other two groups. Serum P and parathyroid hormone concentrations and urinary excretion of C-terminal telopeptide of type I collagen were elevated with increasing dietary P levels. Serum osteocalcin concentration was increased in the rats fed on the 1.5 % P diet than in the other two groups. Bone formation rate of the lumbar vertebra was significantly increased in the two high-P groups than in the 0.3 % P group. Osteoclast number was significantly increased with increasing dietary P levels. Bone mineral content and bone mineral density of the femur and lumbar vertebra and ultimate compression load of the lumbar vertebra were decreased with increasing dietary P levels. Additionally, ultimate bending load of the femur was decreased in the rats fed on the 1.5 % P diet than in the other two groups. Receptor activator of NF-kappaB ligand (RANKL) mRNA expression in the femur was significantly higher with increasing dietary P levels. These results suggest that secondary hyperparathyroidism due to a high-P diet leads to bone loss via an increase in bone turnover. Furthermore, an increase in osteoclast number was caused by increased RANKL mRNA expression.

Effects of different phosphorus sources in the diet on bone composition and stability (breaking strength) in broilers

In two fattening trials (in each 100 broilers kept in four groups with 25 animals) as well as in a balance trial (four groups with four broilers in a group) the effects of inorganic phosphorus sources [monocalcium phosphate (MCP), dicalcium phosphate (dihydrate; DCP) and defluorinated phosphate (DFP)] in broiler diets were examined. The four diets contained up to 9 g calcium and 6 g phosphorus per kg and comparable energy and nutrient contents. Controls were fed a commercial diet with Ca-Na-phosphate as inorganic phosphorus source supplemented by phytase. In both fattening trials body weight gain, feed consumption and feed conversion were proved as well as the calcium and phosphorus levels in serum, the breaking strength of tibia or humerus and the femur mineralization (ash content in the fat free dry matter). Furthermore, in the balance trial the retention of calcium and phosphorus was determined by calculation (intake minus excretion) as well as by analysis of body composition. On a high performance level (that was only slightly influenced by the different treatments), the addition of DFP resulted in significantly reduced phosphorus availability (estimated by analysis of the whole carcass: control/MCP/DCP/DFP: 48.6/46.0/45.7/35.5%). The significantly reduced phosphorus level in serum (1.77 +/- 0.20/1.77 +/- 0.24/1.73 +/- 0.28 1.34 +/- 0.33 mmol/l) indicates the lower phosphorus retention in broilers given DFP. Furthermore, the crude ash content (582 +/- 17.6/580 +/- 18.6/563 +/- 15.2/547 +/- 29.7 g/kg fat free DM) and the breaking strength of bones (in right tibia in trial 2: 232 +/- 82.4/227 +/- 51.5/232 +/- 41.7/196 +/- 655 N) were lowest when given DFP. For diagnostic purposes it is of special interest that the phosphorus levels in the serum reflected markedly the different concentrations of available phosphorus in the diet.

Genetic dissection of phosphate- and vitamin D-mediated regulation of circulating Fgf23 concentrations

Fibroblast growth factor-23 (FGF23) is a circulating factor that plays critical roles in phosphate and vitamin D metabolism. The goal of our studies was to dissect the pathways directing the vitamin D-phosphate-FGF23 homeostatic axis. To test the role of diet in the regulation of Fgf23, wild-type (WT) mice were fed either a standard (0.44% phosphorus) or a low-phosphate (0.02%) diet. WT mice on standard diet had a serum phosphate of 9.5 +/- 0.3 mg/dl and an Fgf23 concentration of 99.0 +/- 10.6 pg/ml; mice on the low-phosphate diet had a phosphate of 5.0 +/- 0.2 mg/dl (P < 0.01) and an Fgf23 of 10.6 +/- 3.7 pg/ml (P < 0.01). To genetically separate the effects of phosphate and vitamin D on Fgf23, we examined vitamin D receptor null (VDR(-/-)) mice, which are hypocalcemic and hypophosphatemic secondary to hyperparathyroidism. On standard diets, WT and VDR(+/-) mice had Fgf23 levels of 106.0 +/- 30.7 and 90.6 +/- 17.3 pg/ml, respectively, whereas Fgf23 was undetectable in the VDR(-/-). Animals were then placed on a diet that normalizes serum calcium and phosphorus. This 'rescue' increased Fgf23 in WT to 192.3 +/- 32.5 pg/ml and in VDR(+/-) to 388.2 +/- 89.6pg/ml, and importantly, in VDR(-/-) to 476.9 +/- 60.1 pg/ml (P < 0.01 vs. WT). In addition, renal vitamin D 1-alpha hydroxylase (1alpha-OHase) mRNA levels were corrected to WT levels in the VDR(-/-) mice. In summary, Fgf23 is suppressed in diet-induced hypophosphatemia and in hypophosphatemia associated with secondary hyperparathyroidism. Normalization of serum phosphate by diet in VDR(-/-) mice increases Fgf23. Thus, our results demonstrate that Fgf23 is independently regulated by phosphate and by vitamin D.

Influence of phytase added to a vegetarian diet on bone metabolism in pregnant and lactating sows

The purpose of the study was to find out if the supplementation of phytase to a diet of gestating and lactating sows has any effects on performance and bone parameters of the animals. Forty primiparous gilts were assigned into four groups: group A with phytase [4.2 g total phosphorus (P)/kg (gestation) and 4.5 g total P/kg (lactation)], group B without phytase (with phytase supplementation in diet for rearing) and same P content as group A, group C without phytase and higher P contents [5.0 g total P/kg (gestation) and 5.5 g total P/kg (lactation)] and group D with the same diet as group B (no phytase during the rearing). A 6-phytase was used in this trial (750 FTU/kg diet). The four diets were fed during gestation and lactation. Faeces were collected to determine apparent digestibility of minerals. Blood samples were taken to analyse minerals and bone markers. After weaning the sows were slaughtered and the bones of one hind leg were prepared to measure bone mineral density (BMD) and bone mineral content (BMC) of the tibia. Bone ash and mineral content of the phalanx III were determined. Mean P concentrations in serum decreased during gestation and lactation. But there were no significant differences between the groups. Bone formation marker bone-specific alkaline phosphatase decreased at the beginning of lactation whereas bone resorption marker serum crosslaps increased. The BMD and BMC of the tibia were slightly higher in the groups fed higher concentrations of P and phytase. The ash and mineral contents of the phalanx were the highest for the group fed the highest concentration of P. The apparent digestibility of P increased during gestation mostly in group A (57%--> 69%). In conclusion, high P content and addition of phytase to the diet induced a slightly higher ash content of the bones. It is of high importance, that sows during gestation absorb enough P, to avoid lamenesses and sudden fractures. As not many studies with phytase have been performed during gestation and lactation in sows yet, we can recommend, that phytase as supplement can be used to keep P in the diet at a lower level without negative consequences for bone health.

Sevelamer hydrochloride attenuates kidney and cardiovascular calcifications in long-term experimental uremia

BACKGROUND

In chronic renal failure (CRF), hyperphosphatemia and an elevated calcium-phosphate product are associated with vascular calcification and increased cardiovascular morbidity and mortality. Previous data have demonstrated that 3-month treatment of uremic rats with sevelamer was associated with less nephrocalcinosis compared to calcium carbonate (CaCO3), despite similar control of serum phosphorus, calcium-phosphorus product (Ca x P product), and secondary hyperparathyroidism. There was no evidence of aortic calcification after 3 months of uremia (J Am Soc Nephrol 13:2299-2308, 2002). The present studies explore the influence of sevelamer and CaCO3 on cardiovascular and kidney calcifications in long-term experimental uremia over 6 months.

METHODS

Normal and 5/6 nephrectomized rats (U) were fed a high phosphorus (HP) diet for 6 months. Two phosphate binders, CaCO3 and sevelamer, were administered and their influence on hyperphosphatemia, secondary hyperparathyroidism, kidney/myocardial/aortic calcification, and renal function was compared.

RESULTS

All uremic rats began the study with the same degree of renal failure. Sevelamer was as effective as CaCO3 in reducing serum phosphorus, Ca x P product, and attenuating secondary hyperparathyroidism. Despite similar serum cholesterol levels, rats in the U-HP + sevelamer group had markedly lower calcium deposition in the myocardium and aorta (myocardium, 72 +/- 4 microg/g wet tissue; aorta, 736 +/- 156 microg/g wet tissue) compared to rats in either the U-HP + CaCO3 group (myocardium, 179 +/- 48, P < 0.05; aorta, 1308 +/- 343, P < 0.05) or the U-HP group (myocardium, 98 +/- 10, NS; aorta, 2150 +/- 447, P < 0.05). Dual immunohistochemical analysis for calcium and endothelial cell markers demonstrated that myocardial calcium deposition was intravascular within capillaries. Furthermore, calcium deposition in the kidney of uremic rats treated with sevelamer (582 +/- 111 microg/g wet tissue) was lower than that found in uremic rats treated with CaCO3 (1196 +/- 180 microg/g wet tissue). Sevelamer-treated rats had less deterioration in renal function with an associated lower serum creatinine, higher creatinine clearance, and less proteinuria. There was no difference in overall mortality between the three experimental groups.

CONCLUSION

In long-term experimental CRF, in addition to controlling serum phosphorus and secondary hyperparathyroidism as efficiently as CaCO3, treatment with the phosphate-binder sevelamer attenuates vascular and kidney calcification.

Differential regulation of PHEX expression in bone and parathyroid gland by chronic renal insufficiency and 1,25-dihydroxyvitamin D3

Mutations in the PHEX gene are responsible for X-linked hypophosphatemia, a renal phosphate-wasting disorder associated with defective skeletal mineralization. PHEX is predominantly expressed in bones and teeth and in the parathyroid gland of patients with chronic renal failure and tertiary hyperparathyroidism. The purpose of the present study was to examine the effects of renal insufficiency and 1,25-dihydroxyvitamin D3[1,25(OH)2D3] on the regulation of PHEX expression in rat tibia and parathyroid gland. In rats fed a high-phosphate (Pi) diet, ⅚ nephrectomy elicited a significant increase in the serum parathyroid hormone (PTH) concentration that was associated with a significant increase in the abundance of PHEX mRNA and protein in the tibia and a significant increase in PHEX mRNA in the parathyroid gland. In contrast, 1,25(OH)2D3administration to intact rats fed a control diet elicited a significant decrease in the serum PTH concentration that was accompanied by a significant decrease in PHEX mRNA and protein abundance in the tibia and a significant decrease in PHEX mRNA in the parathyroid gland. In addition, the increases in serum PTH levels and PHEX mRNA in the tibia and parathyroid gland in ⅚ nephrectomized rats fed a high-Pidiet were blunted by 1,25(OH)2D3. Serum PTH concentration was positively and significantly correlated with tibial PHEX mRNA and protein abundance. In summary, we demonstrate that PHEX expression in the tibia and parathyroid gland is increased by chronic renal insufficiency and decreased by 1,25(OH)2D3administration and suggest that PTH status may play an important role in mediating these changes in PHEX expression.

Bone mass changes in vivo during the entire reproductive cycle in rats feeding different dietary calcium and calcium/phosphorus ratio content

The purpose of this study was to quantify in vivo the impact of different dietary Ca contents on the maternal total skeleton and skeletal sub-areas in adult rats during pregnancy and lactation, using DXA. Twenty-four female Wistar rats (approximately 5 months old) were mated and divided into three groups (n = 8) and fed one of the following diets, varying only in Ca content (LCD: 0.14%, NCD: 0.6% or HCD: 1.2%). Pups were adjusted to 8-9 per dam. Maternal ionic calcium and in vivo bone mineral density (BMD) were measured at the beginning, after delivery and after weaning. Regardless of the diet, ionized calcium decreased from onset to weaning ( P < 0.05). At weaning, bone mass decreased 7.3% in NCD, 15% in LCD and 10.5% in HCD from initial values. Total skeleton, whole and proximal tibia and spine BMDs only decreased at delivery in the LCD group ( P < 0.05) but, irrespective of the diet, at weaning, they were lower compared to delivery and initial values ( P < 0.05). LCD group presented the lowest BMD in the proximal tibia and spine regions ( P < 0.05). At birth, pups did not present differences, however, at weaning, LCD pups reached the lowest body weight ( P < 0.05), NCD presented the highest body Ca content ( P < 0.05) and there were no differences between LCD and HCD. This in vivo study showed that regardless of the dietary calcium content, the maternal skeleton is slightly affected by pregnancy but severely affected by lactation. However, the degree of such response appears to depend not only on dietary Ca content but also on dietary Ca/P molar ratio.

A kinetic model of inorganic phosphorus mass balance in hemodialysis therapy

BACKGROUND

There is growing evidence that inorganic phosphorus (iP) accumulation in tissues (dTiP/dt) is a risk factor for cardiac death in hemodialysis therapy (HD). The factors controlling iP mass balance in HD are dietary intake (GiP), removal by binders (JbiP) and removal by dialysis (JdiP). If iP accumulation is to be minimized, it will be necessary to regularly monitor and optimize GiP, JbiP and JdiP in individual patients. We have developed a kinetic model (iPKM) designed to monitor these three parameters of iP mass balance in individual patients and report here preliminary evaluation of the model in 23 HD patients.

METHODS

GiP was calculated from PCR measured with urea kinetics; JdiP was calculated from the product of dialyzer plasma water clearance (K(pwiP)) and time average plasma iP concentration (TACiP) and treatment time (t); a new iP concentration parameter (nTAC(iP), the TACiP normalized to predialysis CoiP) was devised and shown to be a highly predictable function of the form nTAC(iP) = 1 - alpha(1 - exp[-betaK(pwiP). t/ViP]), where the coefficients alpha and beta are calculated for each patient from 2 measure values for nTAC(iP), K(pwiP).t/ViP early and late in dialysis; we measured 8-10 serial values for nTAC(iP), K(pwiP). t/ViP over a single dialysis in 23 patients; the expression derived for iP mass balance is DeltaTiP = 12(PCR) - [K(pwiP)(t) (N/7)][CoiP(1 - alpha(1 - exp[-beta(Kt/ViP)]))] - k(b).Nb.

RESULTS

Calculated nTAC(iP) = 1.01(measured nTAC(iP)), r = 0.98, n = 213; calculated JdiP = 0.66(measured total dialysate iP) + 358, n = 23, r = 0.88, p < 0.001. Evaluation of 10 daily HD patients (DD) and 13 3 times weekly patients with the model predicted the number of binders required very well and showed that the much higher binder requirement observed in these DD patients was due to much higher NPCR (1.3 vs. 0.96).

CONCLUSION

These results are very encouraging that it may be possible to monitor the individual effects of diet, dialysis and binders in HD and thus optimize these parameters of iP mass balance and reduce phosphate accumulation in tissues.

Dietary calcium and phosphorus ratio regulates bone mineralization and turnover in vitamin D receptor knockout mice by affecting intestinal calcium and phosphorus absorption

The effects of the dietary Ca and P ratio, independent of any vitamin D effects, on bone mineralization and turnover was examined in 60 VDRKO mice fed different Ca/P ratio diets. High dietary Ca/P ratio promoted bone mineralization and turnover with adequate intestinal Ca and P transports in VDRKO mice.

INTRODUCTION

To clarify the effects of the dietary calcium (Ca) and phosphorus (P) ratio (Ca/P ratio) on bone mineralization and turnover in null-vitamin D signal condition, vitamin D receptor knockout (VDRKO) mice were given diets containing different Ca/P ratios.

MATERIALS AND METHODS

Five groups of 4-week-old VDRKO mice, 10 animals each, were fed diets for 4 weeks. Group 1 was wild-type littermate mice, fed the diet containing 0.5% Ca and P (Ca/P = 1). Group 2 was the control and was fed a similar diet (Ca/P = 1). Groups 3, 4, 5, and 6 were fed the following diets: 0.5% Ca and 1.0% P (Ca/P = 0.5), 1.0% Ca and 1.0% P (Ca/P = 1), 1.0% Ca and 0.5% P (Ca/P = 2), and 0.5% Ca and 0.25% P (Ca/P = 2).

RESULTS AND CONCLUSIONS

Compared with group 2, serum calcium and phosphorus levels in groups 4-6 significantly increased. Serum parathyroid hormone levels increased in group 3 and decreased in group 5. The amounts of intestinal calcium absorption decreased in groups 3 and 4. Phosphorus absorption increased in group 3 and decreased in groups 4-6. Bone mineral content (BMC) and bone mineral density (BMD) of the femur in group 3 significantly decreased and increased in group 5. In the primary spongiosa of the proximal tibia, the trabecular bone volume (BV/TV) and osteoid thickness (O.Th) in group 3 significantly increased, and decreased in group 6. In groups 5 and 6, the numbers of the trabecular osteoclasts increased. In groups 2 and 4, and the secondary spongiosa was identified in 5 of 10 mice. In group 3, there was no secondary spongiosa in either mouse. Osteoid maturation time (OMT) significantly decreased, and bone formation rate (BFR/BS) increased in groups 4-6. These data indicate that the dietary Ca/P ratio regulates bone mineralization and turnover by affecting the intestinal calcium and phosphorus transports in VDRKO mice. They may suggest the existence of Ca/P ratio-dependent, vitamin D-independent calcium and phosphorus transport system in the intestine.

Phosphorus requirement of finishing feedlot calves

Dietary P supplied to feedlot cattle is important because an inadequate supply will compromise performance, whereas excess P may harm the environment. However, P requirements of feedlot cattle are not well documented. Therefore, 45 steer calves (265.2+/-16.6 kg) were individually fed to determine the P required for gain and bone integrity over a 204-d finishing period. The basal diet consisted of 33.5% high-moisture corn, 30% brewers grits, 20% corn bran, 7.5% cottonseed hulls, 3% tallow, and 6% supplement. Treatments consisted of 0.16 (no supplemental inorganic P), 0.22, 0.28, 0.34, and 0.40% P (DM basis). Supplemental P was provided by monosodium phosphate top-dressed to the daily feed allotment. Blood was sampled every 56 d to assess P status. At slaughter, phalanx and metacarpal bones were collected from the front leg to determine bone ash and assess P resorption from bone. Dry matter intake and ADG did not change linearly (P > 0.86) or quadratically (P > 0.28) due to P treatment. Feed efficiency was not influenced (P > 0.30) by P treatment and averaged 0.169. Plasma inorganic P averaged across d 56 to 204 responded quadratically, with calves fed 0.16% P having the lowest concentration of plasma inorganic P. However, plasma inorganic P concentration (5.7 mg/dL) for steers fed 0.16% P is generally considered adequate. Total bone ash weight was not influenced by dietary P for phalanx (P = 0.19) or metacarpal bones (P = 0.37). Total P intake ranged from 14.2 to 35.5 g/d. The NRC (1996) recommendation for these calves was 18.7 g/d, assuming 68% absorption. Based on performance results, P requirements for finishing calves is < 0.16% of diet DM or 14.2 g/d. Based on these observations, we suggest that typical grain-based feedlot cattle diets do not require supplementation of inorganic mineral P to meet P requirements.

Influence of a low calcium and phosphorus diet on the anabolic effect of human parathyroid hormone (1-38) in female rats

Parathyroid hormone (PTH) or synthetic N-terminal PTH fragments administered intermittently have been established as anabolic agents in animal and human bones. In the present study, the influence of a low calcium diet on the anabolic effect of human PTH(1-38) [hPTH(1-38)] was investigated. Forty-eight 10-week-old female Sprague-Dawley rats were randomly assigned to a diet with a low calcium content (LCa) or a diet with the recommended amount of calcium (RCa). After an adaptation period of 15 days, the rats were randomly assigned to hPTH(1-38) treatment (+LCa/+RCa) or vehicle only (-LCa/-RCa) for an additional 14 days. Total bone mineral density (BMD) values of several bones were determined using quantitative computed tomography and from ratios of ash weight to volume. Biomechanical competence of the fourth lumbar vertebrae and of the right femora was assessed. An anabolic effect could be detected in both PTH-treated groups. However, the bones of the +LCa group showed significantly lower BMD and also a diminished increase in maximal breaking force compared with those of the +RCa group. The study demonstrates that the anabolic effect of hPTH(1-38) is blunted by the LCa diet. This suggests that, during PTH treatment, dietary calcium intake is critical.

Dietary phosphorus and an inflammatory challenge affect performance and immune function of weanling pigs

Ninety-six 3-wk-old pigs (6.3+/-0.12 kg initial BW) were allotted to one of eight treatments based on BW and litter origin to determine the effect of dietary phosphorus and an inflammatory challenge on performance and immune function. Four corn-soybean meal-based treatment diets were formulated to contain 0.16, 0.24, 0.32, or 0.40% available P. Monocalcium-dicalcium phosphate was used as the supplemental P source. The Ca:available P ratio was maintained at 2:1. To challenge the pigs, half of the pigs in each dietary treatment were injected i.m. with E. coli lipopolysaccharide (200 microg/kg of BW) on d 7 and 14. This resulted in a 2 x 4 factorial arrangement of treatments. Average daily gain for the 35-d study was increased linearly (P < 0.01) by increasing supplemental P. Average daily gain and ADFI were decreased (P < 0.05) by lipopolysaccharide injection. Serum P concentrations increased linearly (P < 0.01) with increasing supplemental P. Antibody titers to the injection of sheep red blood cells and ovalbumin on d 21 decreased linearly (P < 0.10) by increasing supplemental P. In vitro blastogenic response of lymphocytes to phytohemagglutinin (PHA) on d 25 was increased linearly (P < 0.05) by increasing supplemental P. Blastogenic response of lymphocytes to pokeweed mitogen on d 25 was not affected. On d 31, skinfold thickness 6 h following an intradermal injection of PHA was increased quadratically (P < 0.07) by increasing supplemental P. There were no P x lipopolysaccharide interactions for any immune response measure. In conclusion, increasing supplemental P increased ADG and enhanced cell-mediated immune response but decreased humoral immune response.

Secondary hyperparathyroidism in severe chronic renal failure is corrected by very-low dietary phosphate intake and calcium carbonate supplementation

The main purpose of our study was to verify the effect of a very-low-protein, low-phosphorus diet, supplemented with essential amino acids and keto analogues and with calcium carbonate, on circulating levels of intact parathyroid hormone (i-PTH) in severe chronic renal failure patients with secondary hyperparathyroidism, not treated with any vitamin D preparation. To this aim, we shifted 21 chronic uremics (12 males, 9 females; age 56 +/- 13 years) with serum creatinine >6.5 mg/dl and i-PTH >150 pg/ml, from a standard low-protein diet (0.6 g/kg/day approximately) to a very-low-protein (0.3 g/kg/day), very-low-phosphorus (5 mg/kg/day) diet supplemented with a mixture of essential amino acids and calcium keto analogues (Ketodiet), calcium carbonate (2-4 g/day), iron, and vitamin B12 preparations. The energy supply of both diets was 30-35 kcal/kg/day. Exclusion criteria were a poor compliance with dietary or supplement prescriptions or signs of autonomic hyperparathyroidism. After 4 +/- 2 months of Ketodiet, the i-PTH serum levels decreased by 49% as a mean (from 441 +/- 233 to 225 +/- 161 pg/ml, p < 0.001); serum phosphorus and alkaline phosphatase decreased, whereas serum calcium increased. The great reduction of serum and urinary urea demonstrated a good compliance with Ketodiet, and no sign of protein malnutrition was observed. These findings confirm that even in severe chronic uremic patients dietary phosphorus restriction and calcium carbonate supplementation lower i-PTH serum levels. This is one of the goals of the dietary treatment that can be safely achieved, provided good compliance both with the dietary prescriptions and with adequate energy and supplement intakes.

Chronic metabolic acidosis in azotemic rats on a high-phosphate diet halts the progression of renal disease

BACKGROUND

Hyperphosphatemia and metabolic acidosis are general features of advanced chronic renal failure (RF), and each may affect mineral metabolism. The goal of the present study was to evaluate the effect of chronic metabolic acidosis on the development of hyperparathyroidism and bone disease in normal and azotemic rats on a high-phosphate diet. Our assumption that the two groups of azotemic rats (acid-loaded vs. non-acid-loaded) would have the same degree of renal failure at the end of the study proved to be incorrect.

METHODS

Four groups of rats receiving a high-phosphate (1.2%), normal-calcium (0.6%) diet for 30 days were studied: (1) normal (N); (2) normal + acid (N + Ac) in which 1.5% ammonium chloride (NH4Cl) was added to the drinking water to induce acidosis; (3) RF, 5/6 nephrectomized rats; and (4) RF + acid (RF + Ac) in which 0.75% NH4Cl was added to the drinking water of 5/6 nephrectomized rats to induce acidosis.

RESULTS

At sacrifice, the arterial pH and serum bicarbonate were lowest in the RF + Ac group and were intermediate in the N + Ac group. Serum creatinine (0.76 +/- 0.08 vs. 1.15 +/- 0.08 mg/dL), blood urea nitrogen (52 +/- 8 vs. 86 +/- 13 mg/dL), parathyroid hormone (PTH; 180 +/- 50 vs. 484 +/- 51 pg/mL), and serum phosphate (7.46 +/- 0.60 vs. 12.87 +/- 1.4 mg/dL) values were less (P < 0.05), and serum calcium (9.00 +/- 0.28 vs. 7.75 +/- 0.28 mg/dL) values were greater (P < 0.05) in the RF + Ac group than in the RF group. The fractional excretion of phosphate (FEP) was greater (P < 0.05) in the two azotemic groups than in the two nonazotemic groups. In the azotemic groups, the FEP was similar even though PTH and serum phosphate values were less in the RF + Ac than in the RF group. NH4Cl-induced acidosis produced hypercalciuria in the N + Ac and RF + Ac groups. When acid-loaded (N + Ac and RF + Ac) and non-acid-loaded (N and RF) rats were combined as separate groups, serum phosphate and PTH values were less for a similarly elevated serum creatinine value in acid-loaded than in non-acid-loaded rats. Finally, the osteoblast surface was less in the N + Ac group than in the other groups. However, in the acid-loaded azotemic group (RF + Ac), the osteoblast surface was not reduced.

CONCLUSIONS

The presence of chronic metabolic acidosis in 5/6 nephrectomized rats on a high-phosphate diet (1) protected against the progression of RF, (2) enhanced the renal clearance of phosphate, (3) resulted in a lesser degree of hyperparathyroidism, and (4) did not reduce the osteoblast surface. The combination of metabolic acidosis and phosphate loading may protect against the progression of RF and possibly bone disease because the harmful effects of acidosis and phosphate loading may be counterbalanced.

Current medical management of secondary hyperparathyroidism

The treatment of secondary hyperparathyroidism (HPT) in patients with chronic renal disease has improved markedly in recent years. The skeletal pain, disabling fractures, tendon ruptures, and myriad other symptoms associated with HPT can now be avoided, and the quality of life of patients with end-stage renal disease is improved. Control of hyperphosphatemia, maintenance of normocalcemia, and appropriate dosing of vitamin D analogues can prevent HPT in many cases. Palatable, nutritious diets should be followed; serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone should be monitored; and treatment regimens should be adjusted accordingly. If prevention fails, and even if severe HPT develops, many of these patients can still be controlled medically with correction of hyperphosphatemia and high doses of intravenous calcitriol. In our experience, only a few patients require surgical parathyroidectomy (usually noncompliant patients or patients whose HPT has been poorly managed from early uremia). The essence to medical management is to correct the two most important pathogenetic factors of HPT, hyperphosphatemia, and calcitriol deficiency. We present the current approach to the management of HPT, with highlights of recent advances.

Dietary phosphorus regulates intestinal transport and plasma concentrations of phosphate in rainbow trout

Intestinal inorganic phosphate transport and its regulation have not been studied in fish. In this study, we initially characterized the mechanisms of intestinal inorganic phosphate transport in rainbow trout (Oncorhynchus mykiss) then determined the effects of dietary phosphorus concentrations on intestinal inorganic phosphate uptake, plasma inorganic phosphate, and intestinal luminal inorganic phosphate concentrations. In 11-g trout, the saturable mechanism of brushborder inorganic phosphate uptake had a Kt= 1.2 mmol l(-1) and a Vmax = 0.22 nmol mg(-1) min(-1), while the diffusive component had a Kd = 0.012 min(-1). Similar kinetic constants were obtained from 51-g trout, suggesting that development or size had little effect on transport. Tracer inorganic phosphate (1.18 mmol l(-1)) uptake was almost completely inhibited (>95%) by 20 mmol l(-1) unlabeled inorganic phosphate. Inorganic phosphate uptake (0.2 mmol l(-1)) was strongly inhibited (approximately 75% inhibition) by phosphonoformic acid, a competitive inhibitor of mammalian inorganic phosphate transport, as well as by the absence of Na+ (approximately 90% inhibition). Northern blot and reverse transcription-polymerase chain reaction indicated that the intestinal inorganic phosphate transporter in trout is not related to the cloned Na+ inorganic phosphate-II transporter of winter flounder. Intestinal luminal and plasma inorganic phosphate concentrations each increased with dietary P concentrations. Intestinal inorganic phosphate, but not proline, absorption rates decreased with dietary phosphorus concentrations. As in mammals and birds, a Na-dependent inorganic phosphate carrier that is tightly regulated by diet is present in trout small intestine.

Relationships between bone mineral density, serum vitamin D metabolites and calcium:phosphorus intake in healthy perimenopausal women

OBJECTIVES

To determine the relationships between serum vitamin D metabolites, bone mass, and dietary calcium and phosphorus in a cohort of 510 healthy Danish perimenopausal women.

DESIGN

A population-based cross-sectional study.

SUBJECTS

A total of 510 healthy women aged 45-58 years, with amenorrhoea for 3-24 months. None of the women was using hormone replacement therapy.

MEASUREMENTS

Measurements of total bone mineral content and regional bone mineral density were performed by dual-energy X-ray absorptiometry. Analyses of serum levels of 25-OHD and 1,25-(OH)2D, intact PTH, ionized calcium and phosphate, as well as biochemical markers of bone turnover in blood and urine. Assessment of calcium and phosphorus intake using dietary records.

RESULTS

A consistent inverse relationship between serum 1,25-(OH)2D and bone mineral content/ density was found in whole-body mineral content (P = 0.001), spine (P = 0.005) and femoral neck (P<0.05). There was a positive relationship between levels of 1,25-(OH)2D and biochemical bone markers, indicating that high levels of 1,25-(OH)2D are accompanied by increased bone turnover. The dietary calcium:phosphorus ratio was inversely related to serum 1,25-(OH)2D (P = 0.04) and positively related to bone mineral density (P<0.0005). No relationships could be detected between levels of PTH, serum ionized calcium and phosphate, and serum vitamin D metabolites.

CONCLUSION

Within normal physiological range, elevated levels of 1,25-(OH)2D were associated with decreased bone mineral density and content, reduced calcium:phosphorus ratio in the diet and increased bone turnover.

Rickets and protein malnutrition in northern Nigeria

The aim of the study was to explore the relationship between protein nutritional status and the development of rickets in children living in northern Nigeria. The diagnosis of rickets in 16 children between the ages of 10 months and 7 years was confirmed using established, and recently developed clinical and biochemical parameters. Twenty-seven children devoid of skeletal stigmata were age- and sex-matched to the rachitic patients. A battery of clinical laboratory and anthropometric measurements designed to assess calcium homeostasis, skeletal growth, the extent of bone remodeling or resorption, and protein nutritional status were performed on all subjects. Our central finding was that although the rachitic children were moderately malnourished, their protein nutritional status was significantly better as measured by the serum prealbumin concentration (15.4 v. 12.5 mg/dl, P = 0.0012) when compared with the severely malnourished children who were devoid of any indication of rickets. This may be due, in part, to the fact that actively growing children are more likely to develop rickets than are children whose linear growth is impeded. Unexpectedly, we found that the mean concentrations of serum 1,25-dihydroxyvitamin D in both the rachitic and control group were higher than any values for the active vitamin D metabolite previously reported in the literature.

Effects of dietary phosphorus and protein in dogs with chronic renal failure

Four diets were formulated to contain: 16% protein and 0.4% phosphorus--diet 1; 16% protein and 1.4% phosphorus--diet 2; 32% protein and 0.4% phosphorus--diet 3; and 32% protein and 1.4% phosphorus--diet 4. Forty-eight dogs were fed diet 1 for 3 months after surgical reduction of renal mass, then were allotted to 4 groups of 12 dogs each, with equal mean values for glomerular filtration rate (GFR). Dog of groups 1-4 were fed diets 1-4, respectively, for 24 months. Data collected from the dogs during and at termination of the study were analyzed statistically for effects of dietary protein, phosphorus (P), time, and interactions between these factors. During the 24 months of study, 24 dogs developed uremia and were euthanatized for necropsy. Necropsy also was performed on the remaining 24 dogs after they were euthanatized at the end of the study. Dog survival was significantly enhanced by 0.4% P diets (vs 1.4% P diets), but survival was not significantly influenced by amount of dietary protein. The 0.4% P diets (vs 1.4% P diets) significantly increased the period that GFR remained stable before it decreased, but dietary protein did not have significant effect. Significant blood biochemical changes attributed to P, protein, and time were identified during the study. Terminally, plasma parathyroid hormone concentration was significantly increased from prediet values in all groups of dogs. Urine protein excretion was not significantly affected by dietary amount of either protein or P, when measured by either timed urine collection or urine protein-to-creatinine ratio.(ABSTRACT TRUNCATED AT 250 WORDS)