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Turner ME, Mazzetti T, Neville K, Ward EC, Munroe J, Adams MA, Holden RM. Inorganic phosphate additives in meals and adaptations to 5-days of dietary inorganic phosphate loading alter acute calcium homeostasis in two randomized cross-over studies in healthy adults. JBMR Plus 2024; 8:ziae075. [PMID: 39238566 PMCID: PMC11376221 DOI: 10.1093/jbmrpl/ziae075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2024] [Accepted: 05/01/2024] [Indexed: 09/07/2024] Open
Abstract
Diets containing inorganic phosphate additives are unbalanced with respect to calcium and these diets have been linked to the development of altered bone metabolism. Using 2 randomized cross-over studies in healthy humans, we (1) characterized the hormonal and urinary response to 2 meals with the same reported phosphorus amount (562-572 mg), where one was manufactured with inorganic phosphate additives and a comparatively lower Ca:P molar ratio (0.26 vs 0.48), and (2) assessed how acute homeostatic mechanisms adapt following 5-d exposure to recommended dietary phosphorus amount (~700 mg P/d) compared to a diet enriched with inorganic phosphate additives (~1100 mg P/d). Participants were then challenged with 500 mg of oral phosphorus in the form of inorganic phosphate after an overnight fast following each diet condition. Measurements included serum calcium, phosphate, PTH, and fibroblast growth factor 23 , vitamin D metabolites, and urine calcium and phosphate excretion. Following the meal containing inorganic phosphate additives with a low Ca:P ratio, serum phosphate was higher and more phosphate was excreted in the urine compared to the low additive meal. Although the Ca:P and calcium content was lower in the high additive meal, the same amount of calcium was excreted into the urine. Subsequently, increasing only dietary phosphate through additives resulted in lower 24-h excretion of calcium. The oral phosphate challenge promoted urinary calcium excretion, despite no consumption of calcium, which was attenuated when pre-acclimated to a high phosphate diet. These data suggest that ingestion of inorganic phosphate promotes calcium excretion, but homeostatic mechanisms may exist to reduce calcium excretion that are responsive to dietary intake of phosphate. Future studies are required to evaluate potential implication of diets enriched with inorganic phosphate additives on bone health.
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Affiliation(s)
- Mandy E Turner
- Department of Biomedical and Molecular Science, Queen's University, Kingston, ON K7L 2V7, Canada
| | - Tom Mazzetti
- Department of Medicine, Queen's University, Kingston, ON K7L 2V6, Canada
| | - Kathryn Neville
- Department of Biomedical and Molecular Science, Queen's University, Kingston, ON K7L 2V7, Canada
| | - Emilie C Ward
- Department of Biomedical and Molecular Science, Queen's University, Kingston, ON K7L 2V7, Canada
| | - Jenny Munroe
- Department of Dietetics, Kingston Health Sciences Center, Kingston, ON K7L 2V7, Canada
| | - Michael A Adams
- Department of Biomedical and Molecular Science, Queen's University, Kingston, ON K7L 2V7, Canada
| | - Rachel M Holden
- Department of Biomedical and Molecular Science, Queen's University, Kingston, ON K7L 2V7, Canada
- Department of Medicine, Queen's University, Kingston, ON K7L 2V6, Canada
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2
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Abstract
Inorganic phosphate (Pi) is an essential component of many biologically important molecules such as DNA, RNA, ATP, phospholipids, or apatite. It is required for intracellular phosphorylation signaling events and acts as pH buffer in intra- and extracellular compartments. Intestinal absorption, uptake into cells, and renal reabsorption depend on a set of different phosphate transporters from the SLC20 (PiT transporters) and SLC34 (NaPi transporters) gene families. The physiological relevance of these transporters is evident from rare monogenic disorders in humans affecting SLC20A2 (Fahr's disease, basal ganglia calcification), SLC34A1 (idiopathic infantile hypercalcemia), SLC34A2 (pulmonary alveolar microlithiasis), and SLC34A3 (hereditary hypophosphatemic rickets with hypercalciuria). SLC34 transporters are inhibited by millimolar concentrations of phosphonoformic acid or arsenate while SLC20 are relatively resistant to these compounds. More recently, a series of more specific and potent drugs have been developed to target SLC34A2 to reduce intestinal Pi absorption and to inhibit SLC34A1 and/or SLC34A3 to increase renal Pi excretion in patients with renal disease and incipient hyperphosphatemia. Also, SLC20 inhibitors have been developed with the same intention. Some of these substances are currently undergoing preclinical and clinical testing. Tenapanor, a non-absorbable Na+/H+-exchanger isoform 3 inhibitor, reduces intestinal Pi absorption likely by indirectly acting on the paracellular pathway for Pi and has been tested in several phase III trials for reducing Pi overload in patients with renal insufficiency and dialysis.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.
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3
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MacDonald T, Beggs MR, O'Neill D, Kozuka K, Dimke H, Alexander RT. Increased Slc34a2 expression and paracellular phosphate permeability contribute to high intestinal phosphate absorption in young mice. Acta Physiol (Oxf) 2023; 239:e14029. [PMID: 37563989 DOI: 10.1111/apha.14029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 07/26/2023] [Accepted: 07/27/2023] [Indexed: 08/12/2023]
Abstract
AIM Phosphorus is a critical constituent of bone as a component of hydroxyapatite. Bone mineral content accrues rapidly early in life necessitating a positive phosphorus balance, which could be established by a combination of increased renal reabsorption and intestinal absorption. Intestinal absorption can occur via a transcellular pathway mediated by the apical sodium-phosphate cotransporter, Slc34a2/NaPiIIb or via the paracellular pathway. We sought to determine how young mammals increase dietary phosphorus absorption from the small intestine to establish a positive phosphorus balance, a prerequisite for rapid bone growth. METHODS The developmental expression profile of genes mediating phosphate absorption from the small intestine was determined in mice by qPCR and immunohistochemistry. Additionally, Ussing chamber studies were performed on small bowel of young (p7-p14) and older (8- to 17-week-old) mice to examine developmental changes in paracellular Pi permeability and transcellular Pi transport. RESULTS Blood and urinary Pi levels were higher in young mice. Intestinal paracellular phosphate permeability of young mice was significantly increased relative to older mice across all intestinal segments. NaPiIIb expression was markedly increased in juvenile mice, in comparison to adult animals. Consistent with this, young mice had increased transcellular phosphate flux across the jejunum and ileum relative to older animals. Moreover, transcellular phosphate transport was attenuated by the NaPiIIb inhibitor NTX1942 in the jejunum and ileum of young mice. CONCLUSION Our results are consistent with young mice increasing phosphate absorption via increasing paracellular permeability and the NaPiIIb-mediated transcellular pathway.
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Affiliation(s)
- Tate MacDonald
- Department of Physiology, The University of Alberta, Edmonton, Alberta, Canada
- The Women and Children's Health Research Institute, Edmonton, Alberta, Canada
| | - Megan R Beggs
- Department of Physiology, The University of Alberta, Edmonton, Alberta, Canada
- The Women and Children's Health Research Institute, Edmonton, Alberta, Canada
| | - Debbie O'Neill
- Department of Physiology, The University of Alberta, Edmonton, Alberta, Canada
| | | | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
- Department of Nephrology, Odense University Hospital, Odense, Denmark
| | - R Todd Alexander
- Department of Physiology, The University of Alberta, Edmonton, Alberta, Canada
- The Women and Children's Health Research Institute, Edmonton, Alberta, Canada
- Department of Pediatrics, The University of Alberta, Edmonton, Alberta, Canada
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Burstad KM, Cladis DP, Vorland CJ, Wastney ME, Biruete A, Dominguez JM, O'Neill KD, Chen NX, Moe SM, Hill Gallant KM. Acute High Dietary Phosphorus Following Low-Phosphorus Diet Acclimation Does Not Enhance Intestinal Fractional Phosphorus Absorption in Nephrectomized Male Rats. JBMR Plus 2022; 6:e10698. [PMID: 36530183 PMCID: PMC9751657 DOI: 10.1002/jbm4.10698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 10/05/2022] [Accepted: 10/27/2022] [Indexed: 05/21/2024] Open
Abstract
Dietary phosphorus restriction and phosphorus binders are commonly prescribed for patients with chronic kidney disease (CKD). However, occurrences of non-adherence to these interventions are common. As low-phosphorus (LP) diets have been consistently experimentally shown in vitro to increase intestinal phosphorus absorption efficiency, a bout of non-adherence to diet or binders may cause an unintended consequence of enhanced intestinal phosphorus absorption. Thus, we aimed to determine the effect of a single bout of high-phosphorus (HP) intake after acclimation to a LP diet. Male Sprague Dawley rats with 5/6 nephrectomy (n = 36) or sham operation (n = 36) were block-randomized to 1 of 3 diets: LP (0.1% P w/w), HP (1.2%), or LP followed by acute HP (LPHP 0.1% then 1.2%). Phosphorus absorption tests were conducted using 33P radioisotope administrated by oral gavage or intravenously (iv). Although the overall two-way ANCOVA model for intestinal fractional phosphorus absorption was non-significant, exploratory comparisons showed intestinal fractional phosphorus absorption efficiency tended to be higher in rats in the LP compared with HP or LPHP groups. Rats in the HP or LPHP groups had higher plasma phosphorus compared with rats in the LP group, but the LPHP group was not different from the HP group. Gene expression of the major intestinal phosphate transporter, NaPi-2b, was lower in the jejunum of rats in the LPHP group compared with rats in the HP group but not different in the duodenum. These results demonstrate that an acute HP load after acclimation to a LP diet does not lead to enhanced intestinal fractional phosphorus absorption efficiency in 5/6 nephrectomized male rats. These data provide evidence against the notion that dietary phosphorus restriction or binder use adversely increases absorption efficiency after a single instance of dietary or binder non-adherence. However, other adverse consequences of fluctuating dietary phosphorus intake cannot be ruled out. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
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Affiliation(s)
- Kendal M Burstad
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Dennis P Cladis
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Colby J Vorland
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Applied Health ScienceIndiana University School of Public Health‐BloomingtonBloomingtonINUSA
| | - Meryl E Wastney
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Annabel Biruete
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
- Department of Nutrition and DieteticsIndiana University‐Purdue University IndianapolisIndianapolisINUSA
| | - James M Dominguez
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Kalisha D O'Neill
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Neal X Chen
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Sharon M Moe
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
- Department of Anatomy and Cell BiologyIndiana University School of MedicineIndianapolisINUSA
- Department of MedicineRoudebush Veterans Affairs Medicine CenterIndianapolisINUSA
| | - Kathleen M Hill Gallant
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
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Byrne F, Gillman B, Palmer B, Kiely M, Eustace J, Kearney P, Davidson F, Shiely F. The effect of dietary phosphorus load and food matrix on postprandial serum phosphate in hemodialysis patients: a pilot study. HRB Open Res 2021; 4:119. [PMID: 35187396 PMCID: PMC8822142 DOI: 10.12688/hrbopenres.13382.1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/22/2021] [Indexed: 12/26/2022] Open
Abstract
Background: Potential dietary strategies for controlling hyperphosphataemia include the use of protein sources with lower phosphorus bioavailability such as pulses and nuts, focus on phosphorus to protein ratios and the avoidance of all phosphate additives. Methods: We conducted a controlled crossover feeding study in 8 haemodialysis (HD) patients to investigate the acute postprandial effect of a modified versus standard low phosphorus diet for one day on serum phosphate, potassium and intact parathyroid levels in prevalent HD patients. Each participant consumed the modified diet on one day and the standard diet on a second day one week apart. The modified diet included beef and less dairy, with a lower phosphorus to protein ratio, as well as plant-based protein, whole grains, pulses and nuts containing phytates which reduces phosphorus bioavailability. Both diets were tailored for each participant to provide 1.1g protein/kg ideal body weight. Participants provided fasting bloods before breakfast, a pre-prandial sample before the lunch time main meal and samples at one-hour intervals for the four hours after the lunch time main meal, for analysis of phosphate, potassium and intact parathyroid hormone (iPTH). Results: At four hours post the lunch time main meal on each study day, individuals on the modified diet had serum phosphate readings 0.30 mmol/l lower than when on the standard diet (p-value = 0.015, 95% confidence interval [CI] -0.57, -0.04). The corresponding change in serum potassium at four hours was a decrease of 0.675 mmol/l (p-value = 0.011, CI -1.25, -0.10). Conclusions: Decreases in both serum phosphate and serum potassium readings on a modified low phosphorus diet encourage further larger studies to explore the possibility of greater food choice and healthier plant-based diets in HD patients. ClinicalTrials.gov registration: NCT04845724 (15/04/2021).
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Affiliation(s)
- Fiona Byrne
- Department of Nutrition & Dietetics, Cork, Cork University Hospital, Cork, T12 DC4A, Ireland
- Department of Renal Medicine, Cork University Hospital, Cork, T12 DC4A, Ireland
- Health Research Board, Clinical Research Facility Cork, University College Cork, Cork, T12 WE28, Ireland
| | - Barbara Gillman
- Department of Nutrition & Dietetics, Mater Misericordiae University Hospital, Dublin, D07 R2WY, Ireland
| | - Brendan Palmer
- Health Research Board, Clinical Research Facility Cork, University College Cork, Cork, T12 WE28, Ireland
- School of Public Health, University College Cork, Cork, T12 XF62, Ireland
| | - Mairead Kiely
- School of Food and Nutritional Sciences, University College Cork, Cork, T12 T656, Ireland
| | - Joseph Eustace
- Department of Renal Medicine, Cork University Hospital, Cork, T12 DC4A, Ireland
- Health Research Board, Clinical Research Facility Cork, University College Cork, Cork, T12 WE28, Ireland
| | - Patricia Kearney
- School of Public Health, University College Cork, Cork, T12 XF62, Ireland
| | - Fred Davidson
- Cork Public Analyst's Laboratory, St. Finbarr's Hospital, Cork, T12 XH60, Ireland
| | - Frances Shiely
- Health Research Board, Clinical Research Facility Cork, University College Cork, Cork, T12 WE28, Ireland
- School of Public Health, University College Cork, Cork, T12 XF62, Ireland
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Chen NX, O'Neill KD, Dominguez JM, Moe SM. Regulation of reactive oxygen species in the pathogenesis of matrix vesicles induced calcification of recipient vascular smooth muscle cells. Vasc Med 2021; 26:585-594. [PMID: 34338093 DOI: 10.1177/1358863x211024721] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
INTRODUCTION Increased oxidative stress is associated with vascular calcification in patients with chronic kidney disease (CKD). We have previously demonstrated that cellular-derived matrix vesicles (MV), but not media-derived MV, are endocytosed in the presence of phosphorus by recipient normal rat vascular smooth muscle cells (VSMC) and induce calcification through ERK1/2 and [Ca2+]i signaling. We hypothesized that these changes were mediated by increased reactive oxygen species (ROS) production. METHODS MV were co-cultured with recipient VSMC in the presence of high phosphorus and ROS production and cell signaling assessed. RESULTS The results demonstrated MV endocytosis led to increased ROS production in recipient VSMC with no increase in mitochondrial oxygen consumption or oxidative phosphorylation (OXPHOS), indicating the ROS was not from the mitochondria. The use of inhibitors demonstrated that endocytosis of these MV by VSMC led to a signaling cascade in the cytoplasm beginning with ERK1/2 signaling, then increased [Ca2+]i and stimulation of ROS production, mediated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)1/4. Media-derived MV did not induce this cascade, indicating endocytosis itself was not a factor. Furthermore, inhibition of either ERK1/2 activation or [Ca2+]i reduced vascular calcification. CONCLUSION We conclude that endocytosis of pro-mineralizing MV can induce a series of signaling events in normal VSMC that culminate in generation of ROS via activation of NOX1/4. Understanding these pathways will allow the development of future targeted therapeutics.
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Affiliation(s)
- Neal X Chen
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Kalisha D O'Neill
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - James M Dominguez
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Sharon M Moe
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.,Roduebush Veterans Affairs Medical Center, Indianapolis, IN, USA
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7
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Stremke ER, Wiese GN, Moe SM, Wastney ME, Moorthi RN, Hill Gallant KM. Intestinal Phosphorus Absorption in Moderate CKD and Healthy Adults Determined Using a Radioisotopic Tracer. J Am Soc Nephrol 2021; 32:2057-2069. [PMID: 34244325 PMCID: PMC8455256 DOI: 10.1681/asn.2020091340] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 03/15/2021] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Reducing intestinal phosphorus absorption is a cornerstone in CKD-MBD management. Yet, knowledge gaps include how CKD pathophysiology affects intestinal phosphorus absorption. In vivo rodent studies suggest that intestinal phosphorus absorption remains inappropriately normal in early-moderate CKD, despite declining 1,25-dihydroxyvitamin D (1,25D). We measured intestinal phosphorus absorption in patients with moderate CKD versus healthy adults using a direct radiotracer method. METHODS Patients with CKD and healthy adults matched for age, sex, and race were enrolled in this 8-day controlled diet study: the first 6 days outpatient and the final 2 days inpatient. Oral and intravenous doses of 33P and serial blood and urine sampling determined intestinal phosphorus absorption during the final 2 days. Secondary outcomes included fasting biochemistries and 24-hour urine phosphorus (uP). RESULTS In total, n=8 patients with CKD (eGFR=29-55 ml/min per 1.73 m2) and n=8 matched healthy controls completed the study. On a controlled diet, no difference in fractional intestinal phosphorus absorption was detected between patients with CKD and healthy adults (0.69 versus 0.62, respectively; P=0.52), and this was similar for 24-hour uP (884 versus 935 mg/d, respectively; P=0.70). Fractional intestinal phosphorus absorption was not significantly related to 24-hour uP. Patients with CKD had higher serum intact PTH and intact FGF23 and lower 1,25D. The relationship between 1,25D and fractional intestinal phosphorus absorption was not statistically significant. CONCLUSIONS Intestinal phosphorus absorption with typical dietary intake did not differ in patients with moderate CKD compared with controls, despite lower serum 1,25D levels. In this setting, a relationship between 24-hour uP and fractional or absolute intestinal absorption was not evident. Further investigation is needed to determine what factors influence intestinal phosphorus absorption in CKD and the apparent lack of compensation by the intestine to limit phosphorus absorption in the face of declining kidney function and reduced 1,25D. Whether this is evident across a range of dietary phosphorus intakes, as well as CKD severity, also needs to be determined. CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER Phosphorus Absorption in Healthy Adults and in Patients with Moderate Chronic Kidney Disease, NCT03108222.
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Affiliation(s)
- Elizabeth R. Stremke
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, Minnesota
| | - Gretchen N. Wiese
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
| | - Sharon M. Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
- Department of Medicine, Roudebush Veterans Administration Medical Center, Indianapolis, Indiana
| | - Meryl E. Wastney
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Metabolic Modeling Services, West Lafayette, Indiana
| | - Ranjani N. Moorthi
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Kathleen M. Hill Gallant
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota
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Gallant KMH, Vorland CJ. Intestinal phosphorus absorption: recent findings in translational and clinical research. Curr Opin Nephrol Hypertens 2021; 30:404-410. [PMID: 34027902 PMCID: PMC8153371 DOI: 10.1097/mnh.0000000000000719] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW The purpose of this review is to discuss recent findings in intestinal phosphorus absorption pathways, particularly the contributions of paracellular versus transcellular absorption, and the differential findings from studies using in vitro versus in vivo techniques of assessing phosphorus absorption in experimental animal studies. RECENT FINDINGS Experimental animal studies show that in vivo effects of low phosphorus diets, 1,25D, and chronic kidney disease on intestinal phosphorus absorption efficiency contradict effects previously established ex vivo/in vitro. Recent in vivo studies also suggest that the paracellular pathway accounts for the majority of phosphorus absorption in animals across very low to high luminal phosphate concentrations. The data from experimental animal studies correspond to recent human studies showing the effectiveness of targeted inhibition of paracellular phosphate absorption. Additionally, recent human studies have demonstrated that NaPi-2b inhibition alone does not appear to be effective in lowering serum phosphate levels in patients with chronic kidney disease. Pursuit of other transcellular phosphate transporter inhibitors may still hold promise. SUMMARY In vivo animal and human studies have added to our understanding of intestinal phosphorus absorption pathways, regulation, and mechanisms. This is beneficial for developing effective new strategies for phosphate management in patients with chronic kidney disease.
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Affiliation(s)
- Kathleen M. Hill Gallant
- Department of Food Science and Nutrition, University of Minnesota, Minneapolis-St. Paul, MN
- Department of Medicine/Division of Nephrology, Indiana University School of Medicine, Indianapolis, IN
| | - Colby J. Vorland
- Department of Applied Health Science, Indiana University School of Public Health-Bloomington, Bloomington, IN
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Vorland CJ, Biruete A, Lachcik PJ, Srinivasan S, Chen NX, Moe SM, Hill Gallant KM. Kidney Disease Progression Does Not Decrease Intestinal Phosphorus Absorption in a Rat Model of Chronic Kidney Disease-Mineral Bone Disorder. J Bone Miner Res 2020; 35:333-342. [PMID: 31618470 PMCID: PMC7012714 DOI: 10.1002/jbmr.3894] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/29/2019] [Accepted: 10/13/2019] [Indexed: 11/05/2022]
Abstract
The Cy/+ rat has been characterized as a progressive model of chronic kidney disease-mineral bone disorder (CKD-MBD). We aimed to determine the effect of kidney disease progression on intestinal phosphorus absorption and whole-body phosphorus balance in this model. A total of 48 Cy/+ (CKD) and 48 normal littermates (NL) rats were studied at two ages: 20 weeks and 30 weeks, to model progressive kidney function decline at approximately 50% and 20% of normal kidney function. Sodium-dependent and sodium-independent intestinal phosphorus absorption efficiency were measured by the in situ jejunal ligated loop method using 33 P radioisotope. Our results show that CKD rats had slightly higher sodium-dependent phosphorus absorption compared to NL rats, and absorption decreased from 20 to 30 weeks. These results are in contrast to plasma 1,25OH2 D, which was lower in CKD rats. Gene expression of the major intestinal phosphorus transporter, NaPi-2b, was not different between CKD and NL rats in the jejunum but was lower in CKD rats versus NL rats in the duodenum. Jejunal ligated loop phosphorus absorption results are consistent with percent net phosphorus absorption results obtained from metabolic balance: higher net percent phosphorus absorption values in CKD rats compared with NL, and lower values in 30-week-olds compared with 20-week-olds. Phosphorus balance was negative (below zero) in CKD rats, significantly lower in 30-week-old rats compared with 20-week-old rats, and lower in CKD rats compared with NL rats at both ages. These results demonstrate no reduction in intestinal phosphorus absorption with progression of CKD despite lower 1,25OH2 D status when assessed by an in situ ligated loop test, which is in contrast to the majority of in vitro studies, and if confirmed in further studies, could challenge the physiological relevance of in vitro findings. © 2019 American Society for Bone and Mineral Research.
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Affiliation(s)
- Colby J Vorland
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
| | - Annabel Biruete
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Pamela J Lachcik
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
| | - Shruthi Srinivasan
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Neal X Chen
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Sharon M Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Medicine, Roudebush Veterans Affairs Medical Center, Indianapolis, IN, USA
| | - Kathleen M Hill Gallant
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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10
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Developmental Changes in Phosphate Homeostasis. Rev Physiol Biochem Pharmacol 2020; 179:117-138. [PMID: 33398502 DOI: 10.1007/112_2020_52] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Phosphate is a multivalent ion critical for a variety of physiological functions including bone formation, which occurs rapidly in the developing infant. In order to ensure maximal bone mineralization, young animals must maintain a positive phosphate balance. To accomplish this, intestinal absorption and renal phosphate reabsorption are greater in suckling and young animals relative to adults. This review discusses the known intestinal and renal adaptations that occur in young animals in order to achieve a positive phosphate balance. Additionally, we discuss the ontogenic changes in phosphotropic endocrine signalling as it pertains to intestinal and renal phosphate handling, including several endocrine factors not always considered in the traditional dogma of phosphotropic endocrine signalling, such as growth hormone, triiodothyronine, and glucocorticoids. Finally, a proposed model of how these factors may contribute to achieving a positive phosphate balance during development is proposed.
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