The implementation of ex vivo organ machine perfusion (MP) into clinical routine undoubtedly helped to increase the donor pool. It enables not just organ assessment, but potentially regeneration and treatment of marginal organs in the future. During organ procurement, redox-stress triggered ischemia-reperfusion injury (IRI) is inevitable, which in addition to pre-existing damage negatively affects such organs. Ex vivo MP enables to study IRI-associated tissue damage and its underlying mechanisms in a near to physiological setting. However, research using whole organs is limited and associated with high costs. Here, in vitro models well suited for early stage research or for studying particular disease mechanisms come into play. While cell lines convince with simplicity, they do not exert all organ-specific functions. Tissue slice cultures retain the three-dimensional anatomical architecture and cells remain within their naïve tissue-matrix configuration. Organoids may provide an even closer modelling of physiologic organ function and spatial orientation. In this review, we discuss the role of oxidative stress during ex vivo MP and the suitability of currently available in vitro models to further study the underlying mechanisms and to pretest potential treatment strategies.

Introduction: Normothermic machine perfusion (NMP) has emerged as a promising tool for assessing kidney quality prior to transplantation; however, reliable biomarkers remain to be established. Methods: In this study, thirteen porcine kidneys were perfused for 24 h using an autologous leukocyte‐filtered whole blood‐based perfusate applying urine recirculation. Functional, biochemical, and morphological parameters were assessed to comprehensively evaluate kidney quality. Results: Stable hemodynamics, sustained urine output, and oxygen consumption rates indicated preserved kidney viability. Within two hours of perfusion, microperfusion in renal cortex and ureter improved significantly, as confirmed by near‐infrared, tissue hemoglobin, and oxygen saturation metrics. Morphological assessment revealed progressive injury localized in proximal tubular cells, marked by increased vacuolization, reduced microvilli density, and swollen mitochondria with protruding membranes. In contrast, the architecture of distal tubules and glomeruli remained intact. Biomarker analysis corroborated these findings, with KIM‐1 and IGFBP‐7 levels, two biomarkers predominantly expressed in proximal tubular cells, rising. Notably, overall OXPHOS capacity declined with perfusion duration, while ATP production efficiency remained stable. Histological grading, in concordance with real‐time confocal assessment, showed no significant alteration over time. Conclusion: This study provides a detailed phenotypical and bioenergetic profiling of kidney grafts over 24 h of NMP, demonstrating preserved kidney viability and function. The observed subcellular and molecular alterations, especially affecting the proximal tubules, were not reflected in frequently gathered metrics like hemodynamic flow, urine output, oxygen consumption, or lactate levels. Further studies are needed to confirm these findings and evaluate their clinical impact after transplantation.