Improved myocardial preservation during cold storage using substrate enhancement

Biological role of granulocyte macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) on cells of the myeloid lineage

M-CSF and GM-CSF are 2 important cytokines that regulate macrophage numbers and function. Here, we review their known effects on cells of the macrophage-monocyte lineage. Important clues to their function come from their expression patterns. M-CSF exhibits a mostly homeostatic expression pattern, whereas GM-CSF is a product of cells activated during inflammatory or pathologic conditions. Accordingly, M-CSF regulates the numbers of various tissue macrophage and monocyte populations without altering their "activation" status. Conversely, GM-CSF induces activation of monocytes/macrophages and also mediates differentiation to other states that participate in immune responses [i.e., dendritic cells (DCs)]. Further insights into their function have come from analyses of mice deficient in either cytokine. M-CSF signals through its receptor (CSF-1R). Interestingly, mice deficient in CSF-1R expression exhibit a more significant phenotype than mice deficient in M-CSF. This observation was explained by the discovery of a novel cytokine (IL-34) that represents a second ligand of CSF-1R. Information about the function of these ligands/receptor system is still developing, but its complexity is intriguing and strongly suggests that more interesting biology remains to be elucidated. Based on our current knowledge, several therapeutic molecules targeting either the M-CSF or the GM-CSF pathways have been developed and are currently being tested in clinical trials targeting either autoimmune diseases or cancer. It is intriguing to consider how evolution has directed these pathways to develop; their complexity likely mirrors the multiple functions in which cells of the monocyte/macrophage system are involved.

The Challenge of Improving Donor Heart Preservation

Heart transplantation has in recent years become the treatment of choice for end stage heart failure. However while the waiting list for transplantation is growing steadily, the donor pool is not increasing. Therefore, in order to meet demand, transplant programs are using older, "marginal donors" and accepting longer ischaemic times for their donor hearts. As donor organs are injured as a consequence of brain death, during the period of donor management, at organ harvest, preservation, implantation and reperfusion, expansion of acceptance criteria places a great burden on achieving optimal long-term outcomes. However, at each step in the process of transplantation strategies can be employed to reduce the injury suffered by the donor organs. In this review, we set out what steps can be taken to improve the quality of donor organs.

Aspartate/glutamate-enriched blood does not improve myocardial energy metabolism during ischemia-reperfusion: a 31P magnetic resonance spectroscopic study in isolated pig hearts

OBJECTIVE

Our objective was to test the effects of exogenous L-aspartate and L-glutamate on myocardial energy metabolism during ischemia-reperfusion.

METHODS

Phosphorus 31-magnetic resonance spectroscopy was used to observe cellular energetics and intracellular pH in isolated pig hearts perfused with blood (group A, n = 8) or blood enriched with 13 mmol/L each of L-aspartate and L-glutamate (group B, n = 6). The hearts were subjected to 30 minutes of total normothermic ischemia and then reperfused for 40 minutes. Two hearts from each group were inotropically stimulated by titration with calcium after normokalemic reperfusion. Left ventricular function was measured with the use of a compliant balloon and oxygen consumption was calculated.

RESULTS

Magnetic resonance spectroscopy showed no decrease in the rate of energy decline during ischemia for group B versus group A. No significant differences were observed between the two groups in terms of myocardial function, oxygen consumption, or the rate or extent of high-energy phosphate recovery after normokalemic reperfusion or inotropic stimulation. Inotropic stimulation of postischemic hearts, however, led to dramatic improvement in myocardial function in both groups (p < 0.05 for all parameters) and significant improvement in oxygen consumption (p = 0.01).

CONCLUSIONS

In a normal, isolated, blood-perfused pig heart subjected to 30 minutes of total normothermic ischemia, (1) enrichment of the perfusate with aspartate/glutamate before and after ischemia affects neither myocardial energy metabolism during ischemia-reperfusion nor postischemic recovery of myocardial function or oxygen consumption and (2) inotropic stimulation can recruit significant postischemic function and sufficient aerobic respiration to support it, irrespective of aspartate/glutamate enrichment.

Effects of glutamate and aspartate on myocardial substrate oxidation during potassium arrest

OBJECTIVES

A recent report (J Clin Invest 1993;92:831-9) found no effect of glutamate plus aspartate on metabolic pathways in the heart, but the experimental conditions did not model clinical cardioplegia. The purpose of this study was to determine the effects of glutamate and aspartate on metabolic pathways feeding the citric acid cycle during cardioplegic arrest in the presence of physiologic substrates.

METHODS

Isolated rat hearts were supplied with fatty acids, lactate, pyruvate, glucose, and acetoacetate in physiologic concentrations. These substrates were enriched with 13C, which allowed a complete analysis of substrate oxidation by 13C-nuclear magnetic resonance spectroscopy in one experiment. Three groups of hearts were studied: arrest with potassium cardioplegic solution, arrest with cardioplegic solution supplemented with glutamate and aspartate (both in concentrations of 13 mmol/L), and a control group without cardioplegic arrest.

RESULTS

In potassium-arrested hearts, the contributions of fatty acids and lactate to acetyl coenzyme A were reduced, and acetoacetate was the preferred substrate for oxidation in the citric acid cycle. The addition of aspartate and glutamate in the presence of cardioplegic arrest did not further alter patterns of substrate utilization substantially, although acetoacetate use was somewhat lower than with simple cardioplegic arrest. When [U-13C]glutamate (13 mmol/L) and [U-13C]aspartate (13 mmol/L) were supplied as the only compounds labeled with 13C, little enrichment in citric acid cycle intermediates could be detected.

CONCLUSIONS

Glutamate and aspartate when added to potassium cardioplegic solutions have relatively minor effects on citric acid cycle metabolism.

Viability and primary culture of rat hepatocytes after hypothermic preservation: the superiority of the Leibovitz medium over the University of Wisconsin solution for cold storage

Hepatocytes isolated from adult rat livers were hypothermically preserved for 24 or 48 hr before being plated under conventional culture conditions. They were stored either in the Leibovitz medium, a cell culture medium with and without polyethylene glycol (PEG), a compound known to suppress ischemia-induced cell swelling, or in the University of Wisconsin solution, the most effective solution for cold organ preservation. After 24 or 48 hr of storage at 4.5 degrees C in Leibovitz medium, cell viability and adherence efficiency to plastic dish, were only slightly reduced, whereas University of Wisconsin hepatocytes had a decreased viability and (especially after 48-hr storage) lost their adhesion ability; they did not survive in vitro. The metabolic competence of hepatocytes maintained in Leibovitz medium was retained over the 3 days of culture, as shown by low extracellular levels of the membrane-bound and cytosolic hepatic enzymes, as well as by intracellular glutathione content, albumin secretion rate and several phase I and phase II drug metabolic reactions very close to those found with fresh hepatocytes maintained under similar culture conditions. Addition of polyethylene glycol to the Leibovitz medium resulted in slightly higher viability and function of hepatocytes after cold storage. These results clearly demonstrate that viability of a transplanted liver does not correlate with long-term in vitro viability of isolated hepatocytes after hypothermic preservation in University of Wisconsin solution. They also suggest that nutritional and energy substrates as found in the Leibovitz medium are probably required to define a suitable solution for cold preservation of isolated parenchymal cells. The findings with Leibovitz medium favor the conclusion that hypothermically preserved hepatocytes could be used for various metabolic studies and for the treatment of liver insufficiency.