Analysis of DCD porcine kidney graft viability during sub-normothermic perfusion using magnetic resonance imaging and spectroscopy

Objective

Better preservation strategies for the storage of donation after circulatory death grafts could increase the number of kidneys available and improve patient survival. Warm (22°C and 37°C) ex-vivo perfusion has emerged as an alternative to hypothermia and a feasible strategy to recover/repair organs, but the underlying mechanism remains elusive. Here, using magnetic resonance imaging spectroscopy (MRIs), we evaluated kidney viability, and adenosine triphosphate (ATP) production during sub-normothermic ex-vivo kidney perfusion (22°C + O2) versus hypothermic machine perfusion (4°C and 4°C + O2) in a porcine kidney autotransplantation model.

Methods

To mimic donation after circulatory death (DCD), kidneys from 8-month-old pigs underwent 60 minutes of warm ischemia, prior to procurement. Kidneys were then perfused ex-vivo at 4°C with (4°C + O2), and without oxygen (4°C) or at 22°C (22°C + O2) before autotransplantation. During the ex-vivo perfusion, and after transplantation we assessed energy metabolites using MRIs. In addition, we performed Gadolinum (Gd) perfusion sequences. Each sample underwent histopathological analyzing and scoring. mRNA expression was analyzed on renal biopsies at various time points.

Results

Using MRI, we found that in pig kidney, total ATP content was 4 times higher during ex-vivo perfusion at sub-normothermic temperature compared to cold perfusion, with or without oxygen. At 22°C, ATP levels gradually increased up to 10 hrs of perfusion, then progressively declined. Similarly, AMP content was increased in SNOP perfused organs, then slowly consumed. over time. In addition, 22°C + O2 improved cortical and medullary perfusion (Gd elimination). Finally, sub-normothermic ex-vivo perfused graft had lower grade of histological damages 1 hour after transplantation compared to cold perfused organs (injury score 22°C + O2 : 8.8–12.2, 4°C : 13.5–18.8, 4°C + O2 : 17.5–18.5).

Conclusion

In kidneys, sub-normothermic perfusion improved graft viability when compared with hypothermic perfusions. These results suggest that sub-normothermic ex-vivo kidney perfusion might dampen the negative effect of warm ischemia and promote kidney metabolism such as ATP production. Future clinical studies will define the benefits of sub-normothermic ex-vivo kidney perfusion in improving kidney graft function, and patient's survival.

Ex vivo analysis of graft viability using 31P magnetic resonance imaging spectroscopy

Objective

Expansion in organ supply has been proposed through the use of organs after circulatory death (donation after circulatory death [DCD]) in order to face the chronic shortage of kidneys for transplantation. However, many DCD grafts are discarded because of long warm ischemia times, and the absence of reliable non-invasive means to determine kidney viability. P magnetic resonance imaging (pMRI) spectroscopy is a noninvasive method to detect high-energy phosphate metabolites, such as ATP. However, the reliability of pMRI to predict kidney energy state, and its viability before transplantation remain also unknown.

Methods

To mimic DCD, pig kidneys underwent 0, 30 min or 60 min of warm ischemia, before oxygenated hypothermic machine perfusion (HMP). During the ex vivo perfusion, we assessed energy metabolites and Gadolinium elimination using pMRI. Each sample underwent histopathological scoring.

Results

Using pMRI, we found that in pig kidney, ATP was rapidly generated in presence of oxygen (100 kPa), which remained stable up to 22 h. Warm ischemia (60 min) induced significant histological damages, delayed cortical and medullary Gadolinium elimination (perfusion), and reduced ATP levels, but not its precursors (AMP). Finally, ATP levels and kidney perfusion both inversely correlated with the severity of kidney histological injury.

Conclusion

ATP levels, and kidney perfusion measurements using pMRI, are biomarkers of kidney injury after warm ischemia. Future work will define the role of pMRI in predicting kidney graft viability and patient's survival.

Hydrogen sulfide (H2S) reduces oxygen and ATP consumption in the isolated perfused pig kidney

Objective

Organ donation after circulatory death [DCD] has the potential to reduce the shortage of kidneys available for transplantation. However, many DCD grafts are discarded because of long warm ischemia times. Strategies reducing oxygen demand may minimize damages caused by ischemia/reperfusion injury. Ex-vivo, Hydrogen sulfide (H2S) reduces oxygen and ATP consumption of the isolated perfused kidney, reduces inflammation and improves renal function following ischemia reperfusion injury in rodents. However, the benefits and applicability of H2S in clinically relevant model remain unknown.

Methods

To mimic DCD, pig kidneys underwent 0 or 60 min of warm ischemia, before oxygenated hypothermic machine perfusion (HMP). NaHS (100µM), an H2S donor, was added to the perfusion media or injected as an intra-arterial bolus before warm ischemia. After 2 hours of HMP, kidneys were transplanted and reperfused for 1 hour before harvest. Kidney function was assesses before, after and during ex vivo perfusion by measuring energy metabolites, Gadolinium elimination by pMRI and histopathological scoring.

Results

Warm ischemia (60 min) induced significant histological damages, delayed cortical and medullary Gadolinium elimination (perfusion), and reduced ATP levels, but not its precursors (AMP). As expected, ATP levels and kidney perfusion both inversely correlated with the severity of kidney histological injury. NaHS reduced metabolism during warm ischemia, and seemed to increase kidney ATP levels and viability after reperfusion.

Conclusion

Our preliminary data suggest that the H2S donor NaHS reduces kidney metabolism and protects from warm ischemia. Further experiments will identify the best administration protocol and the clinical relevance of H2S supplementation in the context of organ preservation.

Hepatitis A in Latin America: a changing epidemiologic pattern

In a multicenter study, hepatitis A virus (HAV) seroprevalence was surveyed in six countries in Latin America in which in 12,000 subjects were stratified for age. The highest rates of seroprevalence were recorded in the Dominican Republic (89.0%) and Mexico (81.0%), with lower rates in Brazil (64.7%), Chile (58.1%), Venezuela (55.7%), and Argentina (55.0%). The seroprevalence of HAV in children between 1 and 5 years of age was less than 50%, except in the Dominican Republic. In the 5-10-year-old age group, seroprevalence rates have also decreased compared with previous reports. This suggests that the epidemiology is shifting from high to intermediate endemicity, with the population susceptible to HAV infection shifting from children to adolescents and adults. Furthermore, data from Brazil, Argentina, and Mexico show that HAV seroprevalence is significantly lower in people living in medium and high socioeconomic conditions. This study suggests the need for appropriate vaccination programs to be implemented targeting children, adolescents, and adults, particularly in higher socioeconomic groups.