Resurrected Pigs
Pigs were restored organ functions an hour after death
Oleg Lischuk, N+1
American researchers have developed a system with which they were able to restore and maintain blood supply to organs in pigs for six hours an hour after death. At the same time, the biochemical parameters were almost normal and stable, and the organs were protected from degradation at the tissue, cellular and molecular level. The report on the work was published in the journal Nature (Andrijevic et al., Cellular recovery after prolonged warm ischaemia of the whole body).
Soon after the cessation of respiration and blood circulation, the cells in the tissues become acidified and swell, which leads to a violation of the integrity of their membranes and death. Hormones and cytokines are released in large quantities in the body, the nervous, immune and coagulation systems are activated. All this leads to organ damage, systemic acidosis and hyperkalemia. Nevertheless, researchers have repeatedly managed to obtain samples of viable cells and tissues, as well as to record electrophysiological activity long after death.
Maintaining the viability of organs and tissues is a key task of transplantology. Usually it is provided by washing the organ with a special solution and cooling it, but this approach only works for a few hours. In experiments, it is possible to significantly extend the lifetime of the kidneys, liver, heart and lungs extracted from the body by creating certain conditions and artificially providing their perfusion (fluid flow through the blood vessel system).
In 2019, the staff of Yale University under the leadership of Nenad Sestan (Nenad Sestan) They presented the BrainEx system, with which they managed to restore blood flow and individual functions in an isolated pig brain four hours after the death of the animal. Now they have perfected it and tested it on the scale of an entire organism. The new system is called OrganEx.
It consists of a tank with perfusion solution, an oxygenator (for oxygen saturation and removal of carbon dioxide), a dialyzer (for removal of metabolic products and tissue breakdown), heparin supply systems (to prevent blood clotting) and a mixture of drugs (including antioxidants and experimental suppressors of cell death mechanisms) connected by a pump system, as well as a temperature controller, a set of sensors and a control system. The prepared solution is fed from the outlet of the system through an arterial catheter into the aorta below the departure of the renal arteries from it and, having passed through the entire body and mixed with blood, is taken to the entrance via a venous catheter from the right atrium. The solution is supplied with pulsation, which simulates natural blood flow, under the control of blood pressure.
To obtain perfusate, the researchers modified the Hemopure they had previously developed, which is purified polymerized veal hemoglobin in a balanced solution of lactate and mineral salts. In accordance with the data from the metabolic sensors, the system adds electrolytes (or removes their surpluses), buffer solutions, glucose, amino acids, vitamins and other necessary substances to it during circulation.
The OrganEx device
Pigs (Sus scrofa domesticus) weighing 30-35 kilograms were used for OrganEx tests. After the introduction of heparin and drugs for anesthesia, they were caused to stop their heart. Tissues were taken from some of the animals for analysis immediately after that. The rest were left, maintaining body temperature at a physiological level of 36-37 degrees Celsius. After that, an autopsy was performed on some of the animals with sampling an hour and seven hours later.
The rest, an hour after cardiac arrest, either began standard extracorporeal membrane oxygenation (ECMO) of the animals' own blood, or connected them to OrganEx and observed for six hours, followed by sampling.
Fluoroscopic angiography, Dopplerography, oximetry and blood tests showed that the experimental system provided adequate perfusion and stable oxygen saturation of the internal organs and brain with normalization of acidity and electrolyte composition of the blood, while ECMO did not cope with this task.
Functional indicators, including glucose uptake by different tissues, contractile activity of the heart, protein synthesis in the liver, and others, confirmed the high preservation of organs in animals from the main group.
Immunohistochemical examination of samples of the prefrontal cortex, hippocampus, heart, liver and kidneys showed that six hours after connecting to OrganEx, these organs retain their tissue and cellular integrity at a level comparable to samples obtained immediately after death. In addition, in brain, heart, liver and kidney cells, suppression of the production of markers of various signaling pathways of cell death, such as activated caspase 3 (actCASP3), TUNEL results, interleukin-1ß, serine/threonine kinase 3 (RIPK3) and glutathione peroxidase 4 (GPX4), was observed. In ECMO, on the contrary, there was pronounced necrotic damage to cells and tissues.
The results of sequencing of single nuclei RNA in samples of the hippocampus, heart, liver and kidneys confirmed the suppression of cell damage and indicated the launch of some recovery processes in them when using OrganEx.
According to the authors of the work, the results obtained not only indicate the functional suitability of the developed technique, but also indicate an underestimated potential for cellular recovery after a prolonged absence of blood supply while maintaining body temperature in large mammals.
If further trials are successful, OrganEx can significantly increase the number of high-quality organs for transplantation. In the long term, modifications of this system may find application in the rescue of patients in critical condition.
As an expert on bioethics and legislation in the field of transplantation Brendan Parent from New York University noted in an accompanying comment in Nature, when introducing such systems into clinical practice, it will be necessary to seriously reconsider the approach to ending life support for hopeless patients, since here we are talking about preserving organs that have not been extracted from the donor's body.
The possibilities of organ transplantation are growing every year. In January, American doctors for the first time used a genetically modified pig heart for these purposes. It worked, but two months later the recipient died due to a porcine cytomegalovirus introduced with the transplant. This did not stop the researchers, and in July they transplanted two more similar organs to patients with diagnosed brain death. Meanwhile, their Swiss colleagues managed to successfully use the liver for transplantation, which was preserved by perfusion for three days.
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