Increasing metformin concentrations and its excretion in both rat and porcine ex vivo normothermic kidney perfusion model

Abstract

IntroductionMetformin can accumulate and cause lactic acidosis in patients with renal insufficiency. Metformin is known to inhibit mitochondria, while renal secretion of the drug by proximal tubules indirectly requires energy. We investigated whether addition of metformin before or during ex vivo isolated normothermic machine perfusion (NMP) of porcine and rat kidneys affects its elimination.Research design and methodsFirst, Lewis rats were pretreated with metformin or saline the day before nephrectomy. Subsequently, NMP of the kidney was performed for 90 min. Metformin was added to the perfusion fluid in one of three different concentrations (none, 30 mg/L or 300 mg/L). Second, metformin was added in increasing doses to the perfusion fluid during 4 hours of NMP of porcine kidneys. Metformin concentration was determined in the perfusion fluid and urine by liquid chromatography-tandem mass spectrometry.ResultsMetformin clearance was approximately 4–5 times higher than creatinine clearance in both models, underscoring secretion of the drug. Metformin clearance at the end of NMP in rat kidneys perfused with 30 mg/L was lower than in metformin pretreated rats without the addition of metformin during perfusion (both p≤0.05), but kidneys perfused with 300 mg/L trended toward lower metformin clearance (p=0.06). Creatinine clearance was not different between treatment groups. During NMP of porcine kidneys, metformin clearance peaked at 90 min of NMP (18.2±13.7 mL/min/100 g). Thereafter, metformin clearance declined, while creatinine clearance remained stable. This observation can be explained by saturation of metformin transporters with a Michaelis-Menten constant (95% CI) of 23.0 (10.0 to 52.3) mg/L.ConclusionsMetformin was secreted during NMP of both rat and porcine kidneys. Excretion of metformin decreased under increasing concentrations of metformin, which might be explained by saturation of metformin transporters rather than a self-inhibitory effect. It remains unknown whether a self-inhibitory effect contributes to metformin accumulation in humans with longer exposure times.

Inulin Clearance During Ex vivo Normothermic Machine Perfusion as a Marker of Renal Function

“…[20][21][22] Several therapeutic strategies have also been tested during NMP, mostly addressing the biochemical mechanism of ischemia/reperfusion injury. [23][24][25][26] In addition, research is focused on determining the ideal NMP setup. 27,28 To correctly assess the efficacy of, e.g., the suitability of an organ for transplantation, comprehensive quality assessment tools for kidneys during NMP are needed.…”

Development of a Porcine Slaughterhouse Kidney Perfusion Model

“…This resulted in a fruitful collaboration that has already lasted for 6 years. This collaboration has involved experiments with kidneys, livers and lungs and has resulted in several scientific papers in high ranked (transplantation) journals [27][28][29][30][31][32][33][34]. Publishing data from slaughterhouse models is hampered by the dogmatic view of many reviewers and editors that transplantation research needs to be conducted in laboratory animal models.…”

“…We first focused on basal renal function and injury to finalize protocols that we subsequently used for different research questions that we wanted to address. We have published several papers with the model [28][29][30][31][32][33].…”

Renal Normothermic Machine Perfusion: The Road Toward Clinical Implementation of a Promising Pretransplant Organ Assessment Tool

“…Over the past years, more complex formulas to express oxygen consumption have been derived based on insights into various aspects of ex vivo renal physiology. 27,33,[54][55][56][57][58] Most of these formulas also take the oxygen bound to an oxygen carrier into account, which more adequately reflects the total oxygen content when an oxygen carrier is added to the perfusate.…”