High Phosphate Diet Research Articles

High Phosphate Diet Induces the Development of Tertiary Lymphoid Structures and Fibrosis in Murine Kidneys

High Phosphate Diet Induces the Development of Tertiary Lymphoid Structures and Fibrosis in Murine Kidneys

Correction of Vascular Calcification and Hyperphosphatemia in CKD Rats Treated with ASARM Peptide.

Abnormalities in calcium, phosphorus, PTH, vitamin D metabolism, bone, and vascular calcification occur in chronic kidney disease mineral bone disorder (CKD-MBD). Calciphylaxis, involving painful, ulcerative skin lesions, is also a major problem associated with CKD-MBD. There are no quality medical interventions to address these clinical issues. Bone ASARM peptides are strong inhibitors of mineralization and induce hypophosphatemia by inhibiting phosphate uptake from the gut. We hypothesize treatment of CKD-MBD rats with ASARM peptides will reverse hyperphosphatemia, reduce soft-tissue calcification, and prevent calciphylaxis. To test our hypothesis, we assessed the effects of synthetic ASARM peptide in rats that had undergone a subtotal 5/6th nephrectomy (56NEPHREX), a rodent model of CKD-MBD. All rats were fed a high phosphate diet (2% Pi) to worsen mineral metabolism defects. Changes in serum potassium, phosphate, BUN, creatinine, PTH, FGF23, and calcium were assessed in response to 28 days of ASARM peptide infusion. Also, changes in bone quality, soft-tissue calcification, and expression of gut Npt2b (Slc34a2) were studied following ASARM peptide treatment. Rats that had undergone 56NEPHREX treated with ASARM peptide showed major improvements in hyperphosphatemia, blood urea nitrogen (BUN), and bone quality compared with vehicle controls. Also, ASARM-infused 56NEPHREX rats displayed improved renal, brain, and cardiovascular calcification. Notably, ASARM peptide infusion prevented the genesis of subdermal medial blood vessel calcification and calciphylaxis-like lesions in 56NEPHREX rats compared with vehicle controls. ASARM peptide infusion corrects hyperphosphatemia and improves vascular calcification, renal calcification, brain calcification, bone quality, renal function, and skin mineralization abnormalities in 56NEPHREX rats. These findings confirm our hypothesis and support the utility of ASARM peptide treatment in patients with CKD-MBD.

Kidney Failure Alters Parathyroid Pin1 Phosphorylation and Parathyroid Hormone mRNA-Binding Proteins, Leading to Secondary Hyperparathyroidism.

Secondary hyperparathyroidism (SHP) is a common complication of CKD that increases morbidity and mortality. In experimental SHP, increased parathyroid hormone (PTH) expression is due to enhanced PTH mRNA stability, mediated by changes in its interaction with stabilizing AUF1 and destabilizing KSRP. The isomerase Pin1 leads to KSRP dephosphorylation, but in SHP parathyroid Pin1 activity is decreased and hence phosphorylated KSRP fails to bind PTH mRNA, resulting in high PTH mRNA stability and levels. The up- and downstream mechanisms by which CKD stimulates the parathyroid glands remain elusive. Adenine-rich high-phosphate diets induced CKD in rats and mice. Parathyroid organ cultures and transfected cells were incubated with Pin1 inhibitors for their effect on PTH expression. Mass spectrometry was performed on both parathyroid and PTH mRNA pulled-down proteins. CKD led to changes in rat parathyroid proteome and phosphoproteome profiles, including KSRP phosphorylation at Pin1 target sites. Furthermore, both acute and chronic kidney failure led to parathyroid-specific Pin1 Ser16 and Ser71 phosphorylation, which disrupts Pin1 activity. Pharmacologic Pin1 inhibition, which mimics the decreased Pin1 activity in SHP, increased PTH expression ex vivo in parathyroid glands in culture and in transfected cells through the PTH mRNA-protein interaction element and KSRP phosphorylation. Kidney failure leads to loss of parathyroid Pin1 activity by inducing Pin1 phosphorylation. This predisposes parathyroids to increase PTH production through impaired PTH mRNA decay that is dependent on KSRP phosphorylation at Pin1-target motifs. Pin1 and KSRP phosphorylation and the Pin1-KSRP-PTH mRNA axis thus drive SHP.

The crosstalk between endothelial cells and vascular smooth muscle cells aggravates high phosphorus-induced arterial calcification

Arterial calcification is highly prevalent, particularly in patients with end-stage renal disease (ESRD). The osteogenic differentiation of vascular smooth muscle cells (VSMCs) is the critical process for the development of arterial calcification. However, the detailed mechanism of VSMCs calcification remains to be elucidated. Here, we investigated the role of exosomes (Exos) derived from endothelial cells (ECs) in arterial calcification and its potential mechanisms in ESRD. Accelerated VSMCs calcification was observed when VSMCs were exposed to ECs culture media stimulated by uremic serum or high concentration of inorganic phosphate (3.5 mM Pi). and the pro-calcification effect of the ECs culture media was attenuated by exosome depletion. Exosomes derived from high concentrations of inorganic phosphate-induced ECs (ECsHPi-Exos) could be uptaken by VSMCs and promoted VSMCs calcification. Microarray analysis showed that miR-670-3p was dramatically increased in ECsHPi-Exos compared with exosomes derived from normal concentrations of inorganic phosphate (0.9 mM Pi) induced ECs (ECsNPi-Exos). Mechanistically, insulin-like growth factor 1 (IGF-1) was identified as the downstream target of miR-670-3p in regulating VSMCs calcification. Notably, ECs-specific knock-in of miR-670-3p of the 5/6 nephrectomy with a high-phosphate diet (miR-670-3pEC-KI + NTP) mice that upregulated the level of miR-670-3p in artery tissues and significantly increased artery calcification. Finally, we validated that the level of circulation of plasma exosomal miR-670-3p was much higher in patients with ESRD compared with healthy controls. Elevated levels of plasma exosomal miR-670-3p were associated with a decline in IGF-1 and more severe artery calcification in patients with ESRD. Collectively, these findings suggested that ECs-derived exosomal miR-670-3p could promote arterial calcification by targeting IGF-1, which may serve as a potential therapeutic target for arterial calcification in ESRD patients.

High phosphate-induced progressive proximal tubular injury is associated with the activation of Stat3/Kim-1 signaling pathway and macrophage recruitment.

Dietary phosphate intake in the Western population greatly exceeds the recommended dietary allowance and is linked to enhanced cardiovascular and all-cause mortality. It is unclear whether a chronic high phosphate diet (HPD) causes kidney injury in healthy individuals. Here, we show that feeding a 2% HPD in C57BL/6N mice for one up to six months resulted in hyperphosphatemia, hyperphosphaturia, increased plasma levels of fibroblast growth factor (FGF) 23, and parathyroid hormone (PTH) compared to mice on a 0.8% phosphate diet. Kidney injury was already noted after two months of HPD characterized by loss of proximal tubular (PT) cell polarity, flattened epithelia, disruption of brush border membranes, vacuolization, increased PT cell proliferation, marked interstitial mononuclear infiltration, and progressive accumulation of collagen fibers. HPD increased Stat3 activation and Kim-1 expression in PT epithelial cells and enhanced renal synthesis of chemokines recruiting monocytes and macrophages as well as macrophage related factors. Enhanced recruitment of F4/80+ macrophages around injured PT lesions was timely associated with increased Kim-1 synthesis, tubular MCP-1 expression, and degree of PT injury score. Likewise, tubulointerstitial fibrosis was associated with activation of Stat3/Kim-1 signaling pathway. The stimulation of human proximal tubular cells with high phosphate activated Stat3 signaling and induced HAVCR1 and CCL2 expression. We conclude that high phosphate results in progressive proximal tubular injury, indicating that high dietary phosphate intake may affect kidney health and therefore represents an underestimated health problem for the general population.

Inactivation of Osteoblast PKC Signaling Reduces Cortical Bone Mass and Density and Aggravates Renal Osteodystrophy in Mice with Chronic Kidney Disease on High Phosphate Diet.

Chronic kidney disease (CKD) frequently leads to hyperphosphatemia and hyperparathyroidism, mineral bone disorder (CKD-MBD), ectopic calcifications and cardiovascular mortality. PTH activates the osteoanabolic Gαs/PKA and the Gαq/11/PKC pathways in osteoblasts, the specific impact of the latter in CKD-MBD is unknown. We generated osteoblast specific Gαq/11 knockout (KO) mice and established CKD-MBD by subtotal nephrectomy and dietary phosphate load. Bone morphology was assessed by micro-CT, osteoblast function by bone planar scintigraphy at week 10 and 22 and by histomorphometry. Osteoblasts isolated from Gαq/11 KO mice increased cAMP but not IP3 in response to PTH 1-34, demonstrating the specific KO of the PKC signaling pathway. Osteoblast specific Gαq/11 KO mice exhibited increased serum calcium and reduced bone cortical thickness and mineral density at 24 weeks. CKD Gαq/11 KO mice had similar bone morphology compared to WT, while CKD Gαq/11-KO on high phosphate diet developed decreased metaphyseal and diaphyseal cortical thickness and area, as well as a reduction in trabecular number. Gαq/11-KO increased bone scintigraphic tracer uptake at week 10 and mitigated tracer uptake in CKD mice at week 22. Histological bone parameters indicated similar trends. Gαq/11-KO in osteoblast modulates calcium homeostasis, bone formation rate, bone morphometry, and bone mineral density. In CKD and high dietary phosphate intake, osteoblast Gαq/11/PKC KO further aggravates mineral bone disease.

S2 Heart Sound Detects Aortic Valve Calcification Independent of Hemodynamic Changes in Mice.

BackgroundCalcific aortic valve disease (CAVD) is often undiagnosed in asymptomatic patients, especially in underserved populations. Although artificial intelligence has improved murmur detection in auscultation exams, murmur manifestation depends on hemodynamic factors that can be independent of aortic valve (AoV) calcium load and function. The aim of this study was to determine if the presence of AoV calcification directly influences the S2 heart sound.MethodsAdult C57BL/6J mice were assigned to the following 12-week-long diets: (1) Control group (n = 11) fed a normal chow, (2) Adenine group (n = 4) fed an adenine-supplemented diet to induce chronic kidney disease (CKD), and (3) Adenine + HP (n = 9) group fed the CKD diet for 6 weeks, then supplemented with high phosphate (HP) for another 6 weeks to induce AoV calcification. Phonocardiograms, echocardiogram-based valvular function, and AoV calcification were assessed at endpoint.ResultsMice on the Adenine + HP diet had detectable AoV calcification (9.28 ± 0.74% by volume). After segmentation and dimensionality reduction, S2 sounds were labeled based on the presence of disease: Healthy, CKD, or CKD + CAVD. The dataset (2,516 S2 sounds) was split subject-wise, and an ensemble learning-based algorithm was developed to classify S2 sound features. For external validation, the areas under the receiver operating characteristic curve of the algorithm to classify mice were 0.9940 for Healthy, 0.9717 for CKD, and 0.9593 for CKD + CAVD. The algorithm had a low misclassification performance of testing set S2 sounds (1.27% false positive, 1.99% false negative).ConclusionOur ensemble learning-based algorithm demonstrated the feasibility of using the S2 sound to detect the presence of AoV calcification. The S2 sound can be used as a marker to identify AoV calcification independent of hemodynamic changes observed in echocardiography.

MO448: Progressive Tubular Injury Caused by High Phosphate Intake is Associated With Activation of STAT3/KIM-1 Signalling and Macrophage Recruitment in Mice

Abstract BACKGROUND AND AIMS Dietary phosphate intake greatly exceeds the recommended daily allowance in the Western population. Elevated phosphate levels are linked to increased cardiovascular and all-cause mortality, impaired bone health and premature ageing. The renal effects of chronic high dietary phosphate intake for healthy individuals are still not clear. METHOD Male C57BL/6 mice received a 2% high phosphate diet (HPD) or a 0.8% normal phosphate diet (NPD) for 1 to 6 months. We collected blood, urine and kidneys to investigate phosphate metabolism and progression of kidney injury. In vitro analysis for the toxic effects of phosphate or the phosphaturic hormones parathyroid hormone (PTH) and fibroblast growth factor (FGF) 23 was done in HK-2 humane proximal tubule (PT) cells. RESULTS HPD in mice caused hyperphosphataemia despite increased phosphaturia. Both intact FGF23 and PTH plasma levels were significantly increased in mice on HPD at 1 month onward. Mice on HPD showed significantly increased creatinine levels and albuminuria. Histopathological analysis of the kidneys revealed increased PT injury in mice receiving HPD compared to NPD controls from 2 months onward followed by a rapid progression of organ damage from month 5 to 6. Picrosirius red staining of kidney sections showed a progressively increased accumulation of collagen fibers in renal cortex of mice on HPD, which was significant from 4 months onward and accompanied by enhanced expression of transforming growth factor-β1, collagen 1 and fibronectin. The significant induction of the tubular injury marker Havcr1, encodes for Kim-1, started already after 1 month of feeding HPD, progressed over time and was strongest after 6 months. Immunofluorescence staining revealed Kim-1 localization to damaged PT, which was most prominent after 3 and 6 months of HPD. Renal Kim-1 protein levels were positively associated with tubular injury score and tubulointerstitial fibrosis. Histological staining and quantification revealed significantly increased number of pStat3+ cells in PTs of HPD-fed mice at months 1, 2, 5 and 6, indicating activated Stat3 signaling. The number of pStat3+ cells was positively associated with Kim-1 synthesis. Inflammation cytokine array with kidney tissue lysates showed, among others, enhanced expression of monocyte chemoattractant protein (MCP)-1 and macrophage colony-stimulating factor (MCSF) in HPD-fed mice. The mRNA expression of Csf1 (encodes for MCSF) was upregulated in HPD-fed mice and most pronounced after 6 months. Ccl2 mRNA expression (encodes for MCP-1) was significantly enhanced after 3, 5 and 6 months of HPD compared to NPD. Immunofluorescence staining showed a strong and specific induction of MCP-1 in PT epithelial cells due to HPD. The HPD-induced Ccl2 expression was positively associated with Kim-1 expression indicating an interaction between pStat3/Kim-1 signalling pathway and MCP-1. Immunohistochemical staining and flow cytometry analysis revealed a significantly increased recruitment of F4/80+ macrophages in renal tissue of HPD-fed mice after 3 and 6 months. The enhanced renal macrophage recruitment in the entire HPD cohort was associated with increased MCP-1 protein synthesis and increased tubular injury score. In vitro experiments using HK-2 cells showed that stimulation with FGF23 or high phosphate, but not PTH, induced the phosphorylation of STAT3. Interestingly, only treatment with high phosphate significantly upregulated HAVCR1 and CCL2 expression. CONCLUSION Chronic oral phosphate load in mice induced progressive inflammatory kidney injury dominated by macrophages. The direct toxic effects of phosphate are mediated by Stat3/Kim-1 signalling activation in PT cells. Our data support the hypothesis that kidney injury induced by widespread high dietary phosphate intake may cause a global health problem and underline the urgent need for clinical studies on this issue.

MO549: Chronic Kidney Disease and Vascular Calcification Result in Inflammation and Dysfunction of Colon Tissue in Rats

Abstract BACKGROUND AND AIMS Chronic Kidney Disease (CKD) results in modifications in the activity and/or structure of many organs. One of them is the intestine. Intestinal barrier dysfunction may result in turn, in gut leakage and aggravation of the course of CKD. The interaction between the colon and kidneys may be relevant for both, the kidneys as well as the colon. This study aimed to evaluate the impact of CKD and vascular calcification on colon tissue and function. METHOD Sprague–Dawley rats underwent 5/6 nephrectomy (SNx, n = 18) or sham surgery (Control, n = 6). A total of 8 weeks after surgery, SNx rats were divided into three groups: normal chow (SNx, n = 6); high phosphate (1.2%) with high vitamin D; 5 days/week at a dose of 0.1 µg/day (SNx-VC1, n = 6) or 0.4 µg/day (SNx-VC2, n = 6) to induce vascular calcification. Four weeks after dietary intervention, rats were sacrificed and colon tissue was sampled for analysis. The inflammation of colon tissue was scored on haematoxylin-eosin staining (score 1–4) and the presence of macrophages was quantified by immunostaining with CD68 antibody. The mucus production was also quantified by Alcian blue staining. RESULTS Haematoxylin-eosin staining showed increased inflammation in SNx-VC2 rats (2.47 ± 0.26) compared with the Control group (1.52 ± 0.14) (P < 0.05), Figure 1. The number of CD68 + cells did not differ between groups. Compared with the Control group (19.87 ± 2.20), mucus production was reduced significantly in SNx-VC2 rats (11.98 ± 2.61) (P < 0.05) and close to significance (P < 0.0505) in SNx-VC1 (13.21 ± 1.22). CONCLUSION CKD was associated with a decrease in mucus production and an increase in inflammation in colon tissue. These changes are more marked in the animals with associated vascular calcification (high vitamin D and high phosphate diet).

MO550: Vascular Cells Senescence and Modifications in NRF2 Pathway in a Model of URaEMIC Vascular Calcification

Abstract BACKGROUND AND AIMS Vascular dysfunction including vascular calcification (VC), is a consequence of ageing and chronic kidney disease (CKD) that increase the risk of cardiovascular events. Accumulation of senescent cells in arteries can lead to structural and functional alterations and contributes to increased arterial stiffness, reduced compliance and impaired contractility. We tested the hypothesis that senescent cells in the arterial wall are involved in the pathophysiology of vascular calcification in a rat model of CKD and VC induced by a high phosphate diet and vitamin D supplementation. METHOD Eight-week-old Sprague–Dawley rats underwent subtotal nephrectomy (SNx, n = 18), or no surgery (Control, n = 6). Eight weeks after, control animals (n = 6) and part of the SNx group (n = 6) were maintained on the standard diet while the remaining rats underwent a 4-week VC-diet, where a standard diet was supplemented with high phosphate and 1-hydroxy-vitamin D at a dose of 0.1 µg/day (SNx 0.1 group, n = 6) or 0.4 µg/day (SNx 0.4 group, n = 6). At the end of the protocol, renal function, blood pressure and VC (von Kossa) were studied. mRNA and protein expressions of cellular senescence markers (p16, p21, yH2AX), antioxidants (NRF2, Nqo-1), VC inducers/inhibitors and osteoblastic transition drivers were assessed by qPCR, immunohistochemistry (IHC), or immunofluorescence (IF). Correlations between mRNA or protein levels and VC were computed for the VC-diets animals (n = 12). RESULTS A decrease in creatinine clearance (P < 0.05), increase in urinary protein excretion (P < 0.05) and tubulointerstitial fibrosis were observed in the three SNx groups. VC-diets induced vascular calcification in thoracic aorta and aortic arch associated with an increase in pulse pressure (P < 0.01). NRF2 mRNA and protein expression increased in the calcified groups (P < 0.05) and were positively correlated with VC (Figure 1). In addition, mRNA expression of NRF2 target Nqo-1 was strongly correlated to VC (P < 0.01). p16 mRNA (P < 0.05) and protein (IHC, P < 0.01) levels were correlated to VC; a similar expression pattern was observed for p21 protein (P < 0.05) (Figure 1). The number of yH2AX positive cells increased in calcified groups (IF, P < 0.05) and some of the positive cells for p16 were co-labelled with yH2AX (Figure 1). CONCLUSION In our rat model of induced VC associated with CKD, NRF2 and downstream targets expression was increased in thoracic aorta, confirming the link between NRF2 and VC. This might be a response mechanism as observed with other ‘protective’ factors with increased mRNA expression in this model (data not presented here). Furthermore, we observed that cellular senescence was clearly associated with VC. The co-labelling for p16 and yH2AX in some vascular cells in the media layer, exclusively observed in calcified aortas, is another clue that highlights the link between VC and vascular cell senescence.

FC026: Chronic High Phosphate Level Impairs Cardiac Health

Abstract BACKGROUND AND AIMS Patients with chronic kidney disease (CKD) suffer from disturbed mineral metabolism in which the chronic phosphate load leads to the elevation of the phosphaturic hormones parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). Persistent hyperphosphatemia predisposes to cardiovascular events and increased morbidity and mortality rates. It is discussed that even in the general population, consumption of highly processed food increases phosphate level, which in turn may increase cardiovascular risk. Here, we aim to elucidate the pathological mechanisms of how chronic high phosphate intake mediates cardiac remodeling and dysfunction, respectively. METHOD Male C57BL/6 wild type mice received a high phosphate diet containing 2% inorganic phosphate (HPD) or a 0.8% normal phosphate diet (NPD) for 6 months. Echocardiographic analysis and ex-vivo measurements in cardiomyocytes using IonOptix system were assessed to evaluated cardiac function and contractility. Bulk RNA sequencing of whole heart tissue followed by pathway analysis was done to identify affected relevant signaling pathways, which were verified by in vitro studies using neonatal rat ventricular myocytes (NRVM). RESULTS Chronic phosphate overload resulted in increased level of serum and urinary phosphate and high plasma PTH and FGF23 concentrations. HPD caused impaired heart function as shown by reduced ejection fraction, increased end-systolic volumes and enlarged systolic left ventricular internal diameter accompanied by impaired left ventricular relaxation as seen in Doppler echocardiography. Histological analysis showed increased cardiomyocyte area and length in HPD-fed mice compared with NPD demonstrating cellular hypertrophy. RNA sequencing revealed differentially expressed genes of calcium signaling pathways in the HPD group. Besides, immunoblot analysis of whole heart tissue showed altered Phospholamban activity after 6 months of HPD compared with NPD, indicating altered calcium pump in cardiomyocytes. Preliminary analysis of sarcomere movements and changes of intracellular calcium levels in single cardiomyocytes isolated from NPD and HPD mice after 6 months suggested impaired contractility. Detailed results will be presented here. In vitro stimulation of isolated NRVM with high phosphate induced a hypertrophic growth response, verifying a direct effect of high phosphate on the heart. CONCLUSION HPD in mice causes a dilated cardiac phenotype including cellular hypertrophy, altered contractility and differentially expressed genes involved in calcium signaling pathways, indicating that a chronic high phosphate load is harmful for the heart also in the general population.

Phosphate restriction using a processed clay mineral reduces vascular pathologies and microalbuminuria in rats with chronic renal failure

BackgroundThe progression of chronic kidney disease (CKD) is associated with an increasing risk of cardiovascular morbidity and mortality due to elevated serum phosphate levels. Besides low phosphate diets and hemodialysis, oral phosphate binders are prescribed to treat hyperphosphatemia in CKD patients. This study reports on a processed clay mineral as a novel and efficient phosphate sorbent with comparable efficacy of a clinically approved phosphate binder.Methods5/6 nephrectomized rats, which develop chronic renal failure (CRF), received a high phosphate and calcium diet supplemented with either a processed Montmorillonite-Illite clay mineral (pClM) or lanthanum carbonate (LaC) for 12 weeks. Levels of plasma uremic toxins, glomerular filtration rates and microalbuminuria were determined and the histomorphology of blood vessels and smooth muscle cells was analyzed.Results5/6 nephrectomy induced an increase in plasma uremic toxins levels and progressive proteinuria. Treatment of CRF rats with pClM decreased observed vascular pathologies such as vascular fibrosis, especially in coronary vessels. The transition of vascular smooth muscle cells from a contractile to a secretory phenotype was delayed. Moreover, pClM administration resulted in decreased blood creatinine and urea levels, and increased glomerular filtration rates, reduced microalbuminuria and eventually the mortality rate in CRF rats.ConclusionOur study reveals pClM as a potent phosphate binding agent with beneficial impacts on pathophysiological processes in an animal model of CKD. pClM effectively attenuates the progression of vascular damage and loss of renal function which are the most severe consequences of chronic renal failure.

429 Elevated Phosphate Levels Induce Lung Inflammation and Exacerbate Pulmonary Fibrosis

OBJECTIVES/GOALS: Using a cell culture model, we will determine the effects of phosphate on primary lung cell cultures and use our results to delineate a pathway through which these changes are carried out. Using animal models, we will determine the effects of phosphate on inflammatory and fibrotic lung injury, both in the presence and absence of CKD. METHODS/STUDY POPULATION: For our in vitro experiments, human lung fibroblasts were treated with concentrations of 1 to 5 mM sodium phosphate and FGFR inhibitors. Expression levels of interleukin (IL)-1beta, IL-6, and IL-8 were analyzed by qPCR and secretion of these cytokines was measured by ELISA. Phosphorylation of PLCy and ERK was measured by western blot. Using an in vivo approach, we placed C57Bl/6 mice on a high phosphate (3%) diet to elevate serum phosphate levels in the absence of kidney injury and administered bleomycin via oropharyngeal aspiration to generate an acute inflammatory response. Serum FGF23 levels were measured by ELISA and serum analysis for phosphate and renal function were obtained. Furthermore, expression of FGF23 pathway and inflammatory markers were analyzed in murine lung tissue using qPCR and western blotting. RESULTS/ANTICIPATED RESULTS: Augmented phosphate concentrations led to increased cytokine expression and secretion from human lung fibroblasts as well as a concomitant increase in PLCy and ERK phosphorylation. Inhibition of FGFR1 reversed the effects of phosphate on the inflammatory cytokines and PLCy/ERK phosphorylation. Serum FGF23 levels were significantly upregulated in mice on a high phosphate diet and further increased in mice subjected to a high phosphate diet with exposure to bleomycin. Both serum phosphate and creatinine levels were significantly elevated as well. Additionally, high phosphate and bleomycin increased local FGF23 expression in murine lung tissue, when compared to controls or each stimulus alone. DISCUSSION/SIGNIFICANCE: Phosphate has a significant impact on inflammation and fibrosis in the lung, indicating that the existence of pulmo-renal crosstalk exaggerates pulmonary injury and that there are biological pathways that may be targeted therapeutically to mediate these effects. These results could have a substantial impact on the quality of life for CKD patients.

Excessive proliferation and apoptosis of parathyroid cells contribute to primary hyperparathyroidism in rabbit model

To explore the molecular pathogenesis of primary hyperparathyroidism (PHPT), we investigated the proliferation and apoptosis of parathyroid cells in a rabbit model of diet-induced PHPT. A total of 120 adult...

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.

Distinct Effects of High-Fat and High-Phosphate Diet on Glucose Metabolism and the Response to Voluntary Exercise in Male Mice.

The prevalence of metabolic diseases is rapidly increasing and a principal contributor to this is diet, including increased consumption of energy-rich foods and foods with added phosphates. Exercise is an effective therapeutic approach to combat metabolic disease. While exercise is effective to combat the detrimental effects of a high-fat diet on metabolic health, the effects of exercise on a high-phosphate diet have not been thoroughly investigated. Here, we investigated the effects of a high-fat or high-phosphate diet in the presence or absence of voluntary exercise on metabolic function in male mice. To do this, mice were fed a low-fat, normal-phosphate diet (LFPD), a high-phosphate diet (HPD) or a high-fat diet (HFD) for 6 weeks and then subdivided into either sedentary or exercised (housed with running wheels) for an additional 8 weeks. An HFD severely impaired metabolic function in mice, increasing total fat mass and worsening whole-body glucose tolerance, while HPD did not induce any notable effects on glucose metabolism. Exercise reverted most of the detrimental metabolic adaptations induced by HFD, decreasing total fat mass and restoring whole-body glucose tolerance and insulin sensitivity. Interestingly, voluntary exercise had a similar effect on LFPD and HPD mice. These data suggest that a high-phosphate diet does not significantly impair glucose metabolism in sedentary or voluntary exercised conditions.

Contribution of phosphate and FGF23 to CKD progression.

Progressive forms of chronic kidney disease (CKD) exhibit kidney inflammation and fibrosis that drive continued nephron loss; however, factors responsible for the development of these common pathologic features remain poorly defined. Recent investigations suggest pathways involved in maintaining urinary phosphate excretion in CKD may be contributing to kidney function decline. This review provides an update on recent evidence linking altered phosphate homeostasis to CKD progression. High dietary phosphate intake and increased serum concentrations of fibroblast growth factor 23 (FGF23) both increase urinary phosphate excretion and are associated with increased risk of kidney function decline. Recent investigations have discovered high concentrations of tubular phosphate promote phosphate-based nanocrystal formation that drives tubular injury, cyst formation, and fibrosis. Studies presented in this review highlight important scientific discoveries that have molded our current understanding of the contribution of altered phosphate homeostasis to CKD progression. The collective observations from these investigations implicate phosphaturia, and the resulting formation of phosphate-based crystals in tubular fluid, as unique risk factors for kidney function decline. Developing a better understanding of the relationship between tubular phosphate handling and kidney pathology could result in innovative strategies for improving kidney outcomes in patients with CKD.

Chronic High Phosphate Intake in Mice Affects Macronutrient Utilization and Body Composition.

In the last decades, dietary phosphate intake has increased due to a higher consumption of ultraprocessed food. This higher intake has an impact on body composition and health state. Recently, this study finds that a high chronic phosphate diet leads to no major renal alterations, but negatively affects parameters of bone health probably due to the chronic acid load. Here the effect of high phosphate consumption on parameters of energy metabolism is assessed. Healthy mature adult mice are fed for 1 year or 4 months with either a standard (0.6 % w/w) or a high phosphate (1.2 % w/w) diet. Males and females of two different genetic backgrounds are investigated. Mice feed the high phosphate diet show an attenuated body-weight gain, lower respiratory exchange ratio, decreased body fat mass, and increased lean-to-fat mass ratio. Moreover, the high phosphate diet leads to fasting hypoglycemia with no differences in the glucose response to an oral glucose tolerance test. Triglycerides and cholesterol in blood are similar independently of dietary phosphate content. However, 1-methylhistidine is lower in animals feed a chronic high phosphate intake. High phosphate diet attenuates body weight gain, but induces hypoglycemia and may alter muscle homeostasis.

Phosphate-Sensing.

The blood level of phosphate is tightly regulated in a narrow range. Hyperphosphatemia and hypophosphatemia both lead to the development of diseases, such as hyperphosphatemic tumoral calcinosis and rickets/osteomalacia, respectively. Although several humoral factors have been known to affect blood phosphate levels, fibroblast growth factor 23 (FGF23) is the principal hormone involved in the regulation of blood phosphate. This hormone is produced by bone, particularly by osteocytes and osteoblasts, and has the effect of lowering the blood level of phosphate in the renal proximal tubules. Therefore, some phosphate-sensing mechanism should exist, at least in the bone. However, the mechanisms through which bone senses changes in the blood level of phosphate, and through which the bone regulates FGF23 production remain to be fully elucidated. Our recent findings demonstrate that high extracellular phosphate phosphorylates FGF receptor 1c (FGFR1c). Its downstream extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK signaling pathway regulates the expression of several transcription factors and the GALNT3 gene, which encodes GalNAc-T3, which plays a role in the regulation of posttranslational modification of FGF23 protein, which in turn enhances FGF23 production. The FGFR1c-GALNT3 gene axis is considered to be the most important mechanism for regulating the production of FGF23 in bone in the response to a high phosphate diet. Thus-in the regulation of FGF23 production and blood phosphate levels-FGFR1c may be considered to function as a phosphate-sensing molecule. A feedback mechanism, in which FGFR1c and FGF23 are involved, is present in blood phosphate regulation. In addition, other reports indicate that PiT1 and PiT2 (type III sodium-phosphate cotransporters), and calcium-sensing receptor are also involved in the phosphate-sensing mechanism. In the present chapter, we summarize new insights on phosphate-sensing mechanisms.

Relationship Between Urinary Phosphate and All-Cause and Cardiovascular Mortality in a National Population-Based Longitudinal Cohort Study

High dietary phosphate intake may lead to adverse outcomes including cardiovascular disease (CVD). Urinary phosphate excretion, a marker of intestinal phosphate absorption, may be a more reliable marker of phosphate homeostasis in steady state than serum phosphate. Studies report good agreement between urine phosphate-to-creatinine ratio (uPiCr) and 24-hour urinary phosphate; however, whether uPiCr is associated with increased risk of CVD or mortality remains uncertain. This study aimed to assess the relationship between uPiCr and all-cause and CVD mortality. This is an observational longitudinal cohort study using data from the population-based national Australian Diabetes, Obesity and Lifestyle study (n=10,014 participants). Non-linear association between uPiCr and all-cause and CVD mortality was assessed using fractional polynomial transformations. Cox proportional hazards regression models were used to estimate adjusted hazard ratios for all-cause and CVD mortality. Median age [interquartile range] was 50 [41-62] years, and 46% were male. Median uPiCr was 1.38 [1.02-1.79] mmol/mmol. Median follow-up time was 16.9years with 1,735 deaths. uPiCr was associated with all-cause and CVD mortality in univariate models and when adjusted for age and gender. However, associations were not significant in multivariate models. Sensitivity analyses excluding participants with chronic kidney disease (CKD) revealed a significant J-shaped association between uPiCr and all-cause mortality. Urine phosphate alone showed an association with increased all-cause mortality in a similar J-shape relationship. Although no association between uPiCr and all-cause and CVD mortality was observed in multivariate analyses in the whole cohort, a significant relationship between uPiCr and mortality in those without CKD suggests that uPiCr may have predictive validity for future adverse outcomes in people with no CKD.