Meeting the oxygen requirements of an isolated perfused rat liver

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Cataloged from PDF version of thesis.Includes bibliographical references (p. 47-49).Liver perfusion systems can be used as organ culture platforms for metabolic, genetic and systems engineering, tissue regeneration, pharmacokinetics, organ storage and marginal donor reconditioning for transplantation. The primary requirement of such a system is that it maintain ex vivo organ function in a stable manner for indefinite periods of time. The more physiologically relevant the perfusion system is, the lower the likelihood of incurring functional instability, and the greater the clinical relevance of the data obtained. Currently, a major limiting factor in achieving such a design is the absence of organ-specific in vivo data to standardize, evaluate and optimize the state of perfused livers. Oxygen uptake rate, the primary indicator of organ metabolism and therefore a likely important marker of organ viability, was chosen as one such parameter to be investigated. A systematic review and reproduction of numerous oxygenation conditions cited in the literature in addition to in vivo data sampling across the rat liver shows a significant paucity of oxygen uptake in perfusion compared to in vivo. The reasons stem largely from the biological and mechanical flow properties of the perfusate, but also from the altered metabolic state of the organ in perfusion. In the absence of an oxygen carrier, the liver became oxygen starved and lost functionality. The addition of erythrocytes significantly improved oxygen delivery rates while reducing the flow rate and damaging shear stress.(cont.) However, as hematocrit approached physiological values perfusate viscosity became detrimentally high, causing severe structural and ultimately functional damage. Large strains of erythrocytes similarly impacted the liver. The addition of sodium heparin reduced erythrocyte-erythrocyte and erythrocyte-parenchyma interaction, thereby reducing sheer stress on the liver. The optimal oxygen carriers were small heparinized erythrocytes, such as goat or rat erythrocytes, at a hematocrit of 12%-20%. These conditions continued to provide adequate in vivo oxygen delivery rates and sustained organ structure and function.by Maria-Louisa Izamis.S.M

Ex vivo perfusion optimization of donor liver grafts for transplantation and cell isolation

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2010.Cataloged from PDF version of thesis.Includes bibliographical references.There is a constant demand for enormous numbers of high quality hepatocytes in the fields of cell transplantation, pharmacotoxicology, tissue engineering, and bioartificial assist devices. The scarcity of viable hepatocytes necessitates the use of suboptimal sources including damaged donor organs that are not transplantable. Many of these organs have potentially reversible pathologies however, that could be treated via ex vivo perfusion thereby increasing their cell yield. With the intent to translate organ recovery by perfusion into the clinic, we engineered a very simple room temperature-operated ex vivo organ perfusion system to test a rat liver model of uncontrolled non-heart beating donors. Seventeen times as many hepatocytes were recovered from livers exposed to an hour of warm ischemia (WI, 34*C) compared to untreated WI livers in only 3 hours of perfusion. Further, fresh liver hepatocyte yields were also increased by 32% postperfusion, demonstrating that both damaged and healthy donor livers could benefit from this methodology. A linear correlation between cell yield and tissue ATP content was established. This enables an accurate prediction of cell recovery during preservation and can be used as a direct measure of organ viability and the trajectory of organ recovery during perfusion resuscitation. Further, a strong correlation between perfusion flow rate and cell yield was also established supporting the use of flow rates as low as possible without causing hypoperfusion or oxygen deprivation. Morphologically and functionally, perfusion-isolated hepatocytes generally performed comparably or better than fresh hepatocytes in cell suspension and plate culture. Cumulatively, these findings strongly support the ubiquitous use of organ perfusion systems in the clinic for optimal enhancement of donor grafts.by Maria-Louisa Izamis.Ph.D