Low-Phosphate Meals Accompanied by a Minimum Dose of CaCO3 Downregulates Pro-inflammation by Reducing CKD-MBD Indicators and Triggers by Decreasing Dietary Phosphate Intake

High dietary phosphate intake and poor adherence to phosphate-binding-therapy elevate the risk of hyperphosphatemia in maintenance hemodialysis (HD; MHD) patients. Therefore, chronic kidney disease-related mineral and bone disorder (CKD-MBD) indicators increase; consequently, risks of CKD-MBDs and inflammation are elevated. This double-blind, randomized control trial intervention study was designed to investigate the possibility of reducing blood CKD-MBD indicators and modulating inflammatory indicators by consuming low-phosphate (LP) meals accompanied by a minimum dose of a calcium-based phosphate binder (CaCO3). MHD patients were recruited and randomly assigned to an LP meal group (LP group) or a control group. After initial data collection, blood collection, and dietary counseling, subjects were asked to consume a washout diet for 1 week. During the washout diet period, subjects consumed their usual diet but took 1 tablet of calcium carbonate (1CaCO3) as a phosphate binder with each meal. After the washout diet period, subjects in the LP group and control group respectively consumed LP meals and regular meals twice a day for 1 week. Meat in the LP meals was boiled before the regular cooking process, but meat in control meals was not. All meals were supplied by a central kitchen so that the contents of phosphate and other nutrients could be identified. In total, 40 MHD patients completed the study program. After 1 week of the dietary intervention, the blood Ca x P product and dietary phosphate had significantly decreased in the LP group compared to the control group (p<0.05). The LP group had significantly lower variations in dietary phosphate intake, blood calcium, Ca x P product, and tumor necrosis factor (TNF)-α than the control group by comparing differences between after the dietary intervention and the baseline (△after intervention - baseline, p<0.05). The increase in dietary phosphate intake (△3rd - 2nd dietary phosphate intake) augmented the increase in the TNF-α level by 6.24-fold (odds ratio [95% confidence interval]: 6.24 [1.12~34.92], p<0.05). These results highlighted the conclusion that LP meals accompanied by a minimum dose of CaCO3 downregulated pro-inflammation by reducing CKD-MBD indicators which was triggered by decreasing dietary phosphate intake.

Hyperphosphatemia increases inflammation to exacerbate anemia and skeletal muscle wasting independently of FGF23-FGFR4 signaling

Elevations in plasma phosphate concentrations (hyperphosphatemia) occur in chronic kidney disease (CKD), in certain genetic disorders, and following the intake of a phosphate-rich diet. Whether hyperphosphatemia and/or associated changes in metabolic regulators, including elevations of fibroblast growth factor 23 (FGF23) directly contribute to specific complications of CKD is uncertain. Here we report that similar to patients with CKD, mice with adenine-induced CKD develop inflammation, anemia and skeletal muscle wasting. These complications are also observed in mice fed high phosphate diet even without CKD. Ablation of pathologic FGF23-FGFR4 signaling did not protect mice on an increased phosphate diet or mice with adenine-induced CKD from these sequelae. However, low phosphate diet ameliorated anemia and skeletal muscle wasting in a genetic mouse model of CKD. Our mechanistic in vitro studies indicate that phosphate elevations induce inflammatory signaling and increase hepcidin expression in hepatocytes, a potential causative link between hyperphosphatemia, anemia and skeletal muscle dysfunction. Our study suggests that high phosphate intake, as caused by the consumption of processed food, may have harmful effects irrespective of pre-existing kidney injury, supporting not only the clinical utility of treating hyperphosphatemia in CKD patients but also arguing for limiting phosphate intake in healthy individuals.

FC 018HIGH DIETARY PHOSPHATE INTAKE AND INTRA-CARDIAC SYNTHESIS OF FIBROBLAST GROWTH FACTOR 23 SYNERGISTICALLY WORSEN CARDIAC FUNCTION

Background and Aims Left ventricular hypertrophy (LVH) is a major complication of CKD and associates with increased levels of the phosphaturic hormone fibroblast growth factor (FGF) 23. FGF23 induces hypertrophic growth of cardiac myocytes in vitro and LVH in rodents, suggesting that FGF23 can directly affect the heart. Besides the bone, cardiac myocytes express FGF23, too, and recent studies demonstrate that its expression is increased in cardiac and kidney injury, suggesting that cardiotoxicity of FGF23 may be at least partly due to the paracrine effects of heart-derived FGF23. However, it is still questioned whether elevated FGF23 per se is able to induce pathologic alterations in the heart or whether additional factors in CKD, such as Klotho deficiency or hyperphosphatemia are required for FGF23 to tackle the heart. By generating a mouse model with cardiac-specific overexpression of FGF23 via myocardial gene transfer using adeno-associated virus (AAV), we elucidated the cardiotoxic properties of elevated FGF23 in (1) unchallenged mice, unbiased of alterations usually associated with CKD, and (2) in the presence of high dietary phosphate intake, mimicking the exposure of enhanced serum phosphate. Method First, an adeno-associated virus that expresses murine Fgf23 (AAV-Fgf23) under the control of the cardiac troponin T promotor was injected subcutaneously into eight-week-old male C57BL/6 wildtype mice. After four months, cardiac function and geometry was assessed by cardiac magnetic resonance imaging (MRI) and echocardiography and heart tissue was analysed by qPCR, immunoblot and histological analyses. The biological activity of AAV-Fgf23-derived cardiac Fgf23 was determined using isolated neonatal rat ventricular myocytes (NRVM) in vitro. Second, AAV-Fgf23 and control mice were fed a 2% high phosphate diet (HPD) or a 0.8% normal phosphate diet (NPD) and cardiac phenotype was investigated after six months. Results AAV-Fgf23 mice showed increased cardiac-specific Fgf23 expression and synthesis of intact Fgf23 (iFgf23) protein in the heart resulting in enhanced circulating iFgf23 compared to control. Serum of AAV-Fgf23 mice stimulated hypertrophic growth of isolated NRVM and induced pro-hypertrophic gene expression in vitro, indicating that cardiac iFgf23 is biologically active. Likewise, AAV-Fgf23 mice revealed an activation of renal FGFR1/Klotho/MAPK signalling and subsequent down-regulation of renal sodium phosphate transporters NaPi-2a and NaPi-2c, causing reduced tubular phosphate reabsorption. Nevertheless, in unchallenged AAV-Fgf23 mice, impaired cardiac function, LVH and LV fibrosis were lacking. In contrast, HPD stimulated the bone expression of Fgf23 in both AAV-Fgf23 and Ctrl mice, while intra-cardiac Fgf23 mRNA levels were only increased in both AAV-Fgf23 groups irrespective of NPD or HPD. However, HPD in AAV-Fgf23 mice promoted O-glycosylation of cardiac iFgf23, suggesting stabilization of biologically active Fgf23 protein. Echocardiography showed impaired cardiac function in AAV-Fgf23 on HPD compared to its NPD group, demonstrated by enhanced end-systolic and end-diastolic volumes, increased systolic and diastolic LV diameters as well as enlarged LV inner diameters, respectively. Pressure-volume analysis using Millar catheter showed higher end-systolic and end-diastolic blood pressure (ESP, EDP) in AAV-Fgf23 mice on HPD compared to NPD. HPD in Ctrl only enhanced EDP, although this did not reach the level of statistical significance. Conclusion Chronic exposure to biologically active cardiac iFgf23 per se does not tackle the heart, while high intra-cardiac Fgf23 synthesis in the presence of high dietary phosphate promotes cardiotoxicity of Fgf23, which could pose a significant health risk to the general population.

A chronic high phosphate intake in mice is detrimental for bone health without major renal alterations

Background Phosphate intake has increased in the last decades due to a higher consumption of processed foods. This higher intake is detrimental for patients with chronic kidney disease, increasing mortality and cardiovascular disease risk and accelerating kidney dysfunction. Whether a chronic high phosphate diet is also detrimental for the healthy population is still under debate. Methods We fed healthy mature adult mice over a period of one year with either a high (1.2% w/w) or a standard (0.6% w/w) phosphate diet, and investigated the impact of a high phosphate diet on mineral homeostasis, kidney function and bone health. Results The high phosphate diet increased plasma phosphate, parathyroid hormone (PTH) and calcitriol levels, with no change in fibroblast growth factor 23 levels. Urinary phosphate, calcium and ammonium excretion were increased. Measured glomerular filtration rate was apparently unaffected, while blood urea was lower and urea clearance was higher in animals fed the high phosphate diet. No change was observed in plasma creatinine levels. Blood and urinary pH were more acidic paralleled by higher bone resorption observed in animals fed a high phosphate diet. Total and cortical bone mineral density was lower in animals fed a high phosphate diet and this effect is independent of the higher PTH levels observed. Conclusions A chronic high phosphate intake did not cause major renal alterations, but affected negatively bone health, increasing bone resorption and decreasing bone mineral density.

Murine Fetal Serum Phosphorus is Set Independent of FGF23 and PTH, Except in the Presence of Maternal Phosphate Loading

Fibroblast growth factor 23 (FGF23) appears to play no role until after birth, given unaltered phosphate and bone metabolism in Fgf23- and Klotho-null fetuses. However, in those studies maternal serum phosphorus was normal. We studied whether maternal phosphate loading alters fetal serum phosphorus and invokes a fetal FGF23 or parathyroid hormone (PTH) response. C57BL/6 wild-type (WT) female mice received low (0.3%), normal (0.7%), or high (1.65%) phosphate diets beginning 1 week prior to mating to WT males. Fgf23+/- female mice received the normal or high-phosphate diets 1 week before mating to Fgf23+/- males. One day before expected birth, we harvested maternal and fetal blood, intact fetuses, placentas, and fetal kidneys. Increasing phosphate intake in WT resulted in progressively higher maternal serum phosphorus and FGF23 during pregnancy, while PTH remained undetectable. Fetal serum phosphorus was independent of the maternal phosphorus and PTH remained low, but FGF23 showed a small nonsignificant increase with high maternal serum phosphorus. There were no differences in fetal ash weight and mineral content, or placental gene expression. High phosphate intake in Fgf23+/- mice also increased maternal serum phosphorus and FGF23, but there was no change in PTH. WT fetuses remained unaffected by maternal high-phosphate intake, while Fgf23-null fetuses became hyperphosphatemic but had no change in PTH, skeletal ash weight or mineral content. In conclusion, fetal phosphate metabolism is generally regulated independently of maternal serum phosphorus and fetal FGF23 or PTH. However, maternal phosphate loading reveals that fetal FGF23 can defend against the development of fetal hyperphosphatemia.

Nutritional Guideline for the Management of Mexican Patients with CKD and Hyperphosphatemia

Chronic kidney disease (CKD) represents a serious concern for the Mexican population since the main predisposing diseases (diabetes, hypertension, etc.) have a high prevalence in the country. The development of frequent comorbidities during CKD such as anemia, metabolic disorders, and hyperphosphatemia increases the costs, symptoms, and death risks of the patients. Hyperphosphatemia is likely the only CKD comorbidity in which pharmaceutical options are restricted to phosphate binders and where nutritional management seems to play an important role for the improvement of biochemical and clinical parameters. Nutritional interventions aiming to control serum phosphate levels need to be based on food tables, which should be specifically elaborated for the cultural context of each population. Until now, there are no available food charts compiling a high amount of Mexican foods and describing phosphorus content as well as the phosphate to protein ratio for nutritional management of hyperphosphatemia in CKD. In this work, we elaborate a highly complete food chart as a reference for Mexican clinicians and include charts of additives and drug phosphate contents to consider extra sources of inorganic phosphate intake. We aim to provide an easy guideline to contribute to the implementation of more nutritional interventions focusing on this population in the country.