Intracellular Phosphate Concentration Evolution During Hemodialysis by MR Spectroscopy (CIPHEMO)

Intracellular Phosphate and Adenosine Triphosphate (ATP) Concentration Evolution by Magnetic Resonance (MR) Spectroscopy in Patients During Hemodialysis

End-stage renal disease is associated with hyperphosphatemia due to a decrease of renal phosphate excretion. This hyperphosphatemia is associated with an increase of cardiovascular risk and mortality. Thus, three therapeutic options have been developed: dietary restriction, administration of phosphate binders and phosphorus clearance by hemodialysis (HD). During a standard HD session, around 600 to 700mg phosphate is removed from the plasma, whereas it contains only 90 mg inorganic phosphate (Pi); 85% of phosphate is stored in bones and teeth in hydroxyapatite form, 14% is stored in the intracellular space (90% organic phosphate and 10% Pi), and 1% remains in the extracellular space. Currently, the source of Pi cleared during HD remains to be determined. Phosphorus (31P) magnetic resonance spectroscopy allows reliable, dynamic and non-invasive measurements of phosphate intracellular concentration. The investigator's team recently published data obtained in anephric pigs, suggesting that phosphate intracellular concentration increases during a HD session. In parallel, we showed that ATP intracellular concentration decreased. These results suggest that the source of Pi cleared during HD could be located inside the cell. In this study, investigators will measure intracellular phosphate and ATP concentrations and intracellular potential of hydrogen (pH) evolution during hemodialysis in 12 patients suffering from end-stage renal disease by MR spectroscopy. If these results were confirmed in humans, it could explain, at least in part, HD intolerance in some patients and would lead to modify therapeutic approaches of hyperphosphatemia, for example, by modifying HD sessions time.

Patients aged from 18 to 80 years old, suffering from ESRD, treated by chronic hemodialysis since at least 6 months and whose phosphatemia at the beginning of HD sessions ranged from 1.5 to 3 mmol/L. Phosphorus (31P) magnetic resonance spectroscopy will be performed in these patients during hemodialysis in order to measure intracellular phosphate and ATP concentrations and intracellular pH evolution during hemodialysis.

Phosphorus MR spectroscopy realized using a 3-Tesla MR imaging system. A twenty-cm circular surface coil will be set to the 31P resonance frequency and placed over the leg muscle region to obtain spectroscopy acquisitions. 31P MR spectra will be acquired before, during (every 160 seconds), and 30 minutes after dialysis. 31P MR system data will be analyzed using jMRUI Software. Five different peaks will be analyzed: inorganic phosphate, phosphocreatine, α-, β-, and γ-ATP.

Hemodialysis realized using a 5008 generator, a portable plant, a FX80 Dialyzer, a dialyzing solution with a standard electrolytes composition. The dialysis generator will be placed outside of the MRI examination room. The dialysis lines will pass through a wave guide to connect patients positioned on the bed of the MRI. A suitably trained nurse will proceed to the cannulation of the fistula, the connection of the catheter, and the monitoring of the clinical tolerance of the session.

Measurement of phosphate intracellular concentration evolution during a 4 hours hemodialysis (HD) session using phosphorus magnetic resonance spectroscopy.

Measurement of ATP intracellular concentration evolution during a 4 hours HD session using phosphorus magnetic resonance spectroscopy.

Measurement of intracellular pH evolution during a 4 hours HD session using phosphorus magnetic resonance spectroscopy. Intracellular pH will be calculated using the Henderson-Hasselbach formula: Ph = 6.75 + log (δ-3.27)/(5.69-δ), with δ being the difference (in parts per million) between inorganic phosphate (Pi) and phosphocreatine (PCr) resonance frequencies.

Measurement of intracellular pH evolution during a 4 hours HD session using phosphorus magnetic resonance spectroscopy. Intracellular pH will be calculated using the Henderson-Hasselbach formula: Ph = 6.75 + log (δ-3.27)/(5.69-δ), with δ being the difference (in parts per million) between Pi (inorganic phosphate) and PCr (phosphocreatine) resonance frequencies.

At start of HD, every 15 minutes during first hour of HD, then every hour during HD, at the end of HD and 30 minutes after HD

Calcium balance will be measured using the formula: (Cae - Cab)(Ve - UF)+(Cae * UF), where Cae is the calcium in the effluent, Cab is the calcium in the dialysis solution, Ve is the volume of effluent, and UF is the ultrafiltration.

Inclusion Criteria: Patient suffering from end-stage renal disease, treated by chronic hemodialysis since at less 6 months Phosphatemia (at the start of the session) ≥ 1,5 mmol/L and ≤ 3 mmol/L written consent signed Exclusion Criteria: Major subject protected by law Prisoners or subjects who are involuntarily incarcerated Denutrition (weight loss ≥ 5 kg in one months/10 kg in 6 months, Body Mass Index (BMI) ≤ 21 kg/m2, albuminemia ≤ 35 g/L) Obesity (BMI ≥ 30 kg/m2) Phosphatemia at the start of the dialysis < 1,5 mmol/L or > 3 mmol/L Secondary hyperparathyroidism with parathormone (PTH) ≥ 1000 pg/mL Adynamic osteopathy (PTH ≤ 50 pg/mL) Hypoparathyroidism with a history of parathyroidectomy Hemoglobin ≤ 100 g/L Contraindication to heparin Temporary vascular access Contraindication to resonance magnetic spectroscopy (pacemaker or insulin pump, metallic valvular prosthesis, valvular prosthesis not compatible with resonance magnetic spectroscopy, dental appliance, intracerebral clip, claustrophobic subject). Simultaneous participation to another research protocol Patient not affiliated to a social security system

Chazot G, Lemoine S, Kocevar G, Kalbacher E, Sappey-Marinier D, Rouviere O, Juillard L. Intracellular Phosphate and ATP Depletion Measured by Magnetic Resonance Spectroscopy in Patients Receiving Maintenance Hemodialysis. J Am Soc Nephrol. 2021 Jan;32(1):229-237. doi: 10.1681/ASN.2020050716. Epub 2020 Oct 22.