Lerink 2022 Abstract Bioblast
|Lerink Lente JS, Lindeman JHN (2022) Renal respiratory conductance: a complex matter. Bioblast 2022: BEC Inaugural Conference.|
Event: Bioblast 2022
The kidney’s energy requirements equal that of the heart. In line with this, it has recently been shown that metabolic derailment during transplantation or major surgery underlies delayed graft function  or acute kidney injury , respectively. Hence, strategies to prevent or minimize the post-ischemic injury should focus on prevention of metabolic injury or optimal use of residual metabolic capacity.
Recently, normothermic machine perfusion (NMP) has been introduced as an ex-situ means to preserve, assess and remodel, and to test interventions on an organ under relatively physiological circumstances. Although this technique proved successful for shorter periods of perfusion, longer periods unveil profound (metabolic) challenges, such as excessive lactate production, indicative of failing renal metabolism. This implies that the basic physiologic metabolic requirements, let alone the conditions required to test metabolic interventions, are not fulfilled in the prevailing NMP protocols. Therefore, better tailored strategies, such as optimal substrate composition to drive ATP synthesis, are of major importance.
McLaughlin et al previously used the creatine kinase (CK) clamp to measure respiratory conductance, a measure for the tissue’s mitochondrial metabolic competence in the presence of the supplied substrates . The authors exposed murine mitochondria from different tissues to a physiologically relevant change in ATP/ADP ratio to monitor tissue-specific metabolic responses to an energy challenge. This technique could provide insight in optimal substrate compositions to drive ATP synthesis in renal cells. It was reported that renal mitochondria showed a peculiar phenotype, by uniquely responding to the clamp in the presence of succinate in combination with Complex I-inhibitor rotenone .
Since our previous work indicated profound interspecies differences in mitochondrial function and susceptibility , and because the use of isolated mitochondria ignores the critical cytoplasm-mitochondrial axis, we aimed to validate their findings in permeabilized porcine renal biopsies.
Kidneys from abattoir pigs were retrieved after a period of brief warm ischemia. Kidneys were subsequently transported on ice, and cortex biopsies were taken. Cellular plasma membranes were permeabilized before assessment. The biopsies were subsequently transferred to an O2k-respirometer and exposed to the CK clamp in the presence of different substrate combinations. Maximal respiration and respiratory conductance were calculated, and mitochondrial membrane integrity was assessed to monitor physical mitochondrial damage.
In line with the sparsely available preclinical data, renal cells did not respond to a change in energy availability in terms of respiratory activity when pyruvate, glutamate, malate or a combination of the three were provided. Only when Complex I-inhibitor rotenone was supplied before adding succinate, the biopsies showed a response to a change in ATP/ADP ratio. Moreover, maximal respiration is higher in the presence of succinate and rotenone compared to other substrate combinations.
In conclusion, the CK clamp provides in-detail information on metabolic responses to a change in ATP/ADP ratio in the presence of specific substrate combinations, which may help to define an optimal perfusate composition to stimulate renal metabolism during NMP. Previous findings regarding the need for Complex I inhibition to observe a response to changing ATP/ADP ratios have been validated, but are still poorly understood.
• Keywords: substrate preference, metabolic conductance, kidney, Complex I, respirometry
- Lerink LJS1,2, Lindeman JHN1
- Dept of Surgery, Leiden Univ Medical Centre - email@example.com
- Nuffield Dept of Surgical Sciences, Univ of Oxford
- Lerink LJS1,2, Lindeman JHN1
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