Long-Term Excessive Dietary Phosphate Intake Increases Arterial Blood Pressure, Activates the Renin–Angiotensin–Aldosterone System, and Stimulates Sympathetic Tone in Mice

Abstract

Increased dietary phosphate intake has been associated with severity of coronary artery disease, increased carotid intima–media thickness, left ventricular hypertrophy (LVH), and increased cardiovascular mortality and morbidity in individuals with normal renal function as well as in patients suffering from chronic kidney disease. However, the underlying mechanisms are still unclear. To further elucidate the cardiovascular sequelae of long-term elevated phosphate intake, we maintained male C57BL/6 mice on a calcium, phosphate, and lactose-enriched diet (CPD, 2% Ca, 1.25% P, 20% lactose) after weaning them for 14 months and compared them with age-matched male mice fed a normal mouse diet (ND, 1.0% Ca, 0.7% P). Notably, the CPD has a balanced calcium/phosphate ratio, allowing the effects of elevated dietary phosphate intake largely independent of changes in parathyroid hormone (PTH) to be investigated. In agreement with the rationale of this experiment, mice maintained on CPD for 14 months were characterized by unchanged serum PTH but showed elevated concentrations of circulating intact fibroblast growth factor-23 (FGF23) compared with mice on ND. Cardiovascular phenotyping did not provide evidence for LVH, as evidenced by unchanged LV chamber size, normal cardiomyocyte area, lack of fibrosis, and unchanged molecular markers of hypertrophy (Bnp) between the two groups. However, intra-arterial catheterization revealed increases in systolic pressure, mean arterial pressure, and pulse pressure in mice fed the CPD. Interestingly, chronically elevated dietary phosphate intake stimulated the renin–angiotensin–aldosterone system (RAAS) as evidenced by increased urinary aldosterone in animals fed the CPD, relative to the ND controls. Furthermore, the catecholamines epinephrine, norepinephrine, and dopamine as well as the catecholamine metabolites metanephrine. normetanephrine and methoxytyramine as measured by mass spectrometry were elevated in the urine of mice on CPD, relative to mice on the ND. These changes were partially reversed by switching 14-month-old mice on CPD back to ND for 2 weeks. In conclusion, our data suggest that excess dietary phosphate induces a rise in blood pressure independent of secondary hyperparathyroidism, and that this effect may be mediated through activation of the RAAS and stimulation of the sympathetic tone.

Ablation of Vitamin D Signaling in Cardiomyocytes Leads to Functional Impairment and Stimulation of Pro-Inflammatory and Pro-Fibrotic Gene Regulatory Networks in a Left Ventricular Hypertrophy Model in Mice

“…All phenotyping data are expressed as mean ± standard error of the mean (SEM). Sample sizes were determined by analysis based on data collected by our laboratory in published studies [ 22 , 51 , 52 ]. Statistical analysis of the data was carried out using GraphPad Prism software (GraphPad Software 8.3.0, San Diego, CA, USA).…”

“…RNA Isolation and Quantitative Real-Time PCR Hearts were harvested from mice and snap-frozen in liquid nitrogen. Total RNA was extracted from heart tissue using a TRI Reagent solution (Applied Biosystems, Thermo Fischer Scientific, Waltham, MA, USA) as described previously [51,52]. The purity and integrity of the extracted RNA were assessed using electrophoresis (Agilent Tapestation, Santa Clara, CA, USA).…”

The basics of phosphate metabolism

“…On the other hand, a few studies tested the effect of high Pi on endocrine or cardiovascular endpoints under controlled experimental conditions in healthy participants and animals. In these studies, high phosphate intake caused a higher sympathetic nerve outflow, higher systolic blood pressure or bone loss [ 91 , 98–100 ]. Moreover, animal studies suggest that high Pi intake can cause left ventricular hypertrophy as well as kidney damage [ 45 , 101 ].…”