Prostaglandin E2 modulation of human monocyte antibody-dependent cell-mediated cytotoxicity against human red blood cells

Quantitative evolutionary design of glucose 6-phosphate dehydrogenase expression in human erythrocytes

Why do the activities of some enzymes greatly exceed the flux capacity of the embedding pathways? This is a puzzling open problem in quantitative evolutionary design. In this work we investigate reasons for high expression of a thoroughly characterized enzyme: glucose 6-phosphate dehydrogenase (G6PD) in human erythrocytes. G6PD catalyses the first step of the pathway that supplies NADPH for antioxidant defense mechanisms. Normal G6PD activity far exceeds the capacity of human erythrocytes for a steady NADPH supply, which is limited upstream of G6PD. However, the distribution of erythrocyte G6PD activity in human populations reveals a selective pressure for maintaining high activity. To clarify the nature of this selective pressure, we studied how G6PD activity and other parameters in a model of the NADPH redox cycle affect metabolic performance. Our analysis indicates that normal G6PD activity is sufficient but not superfluous to avoid NADPH depletion and ensure timely adaptation of the NADPH supply during pulses of oxidative load such as those that occur during adherence of erythrocytes to phagocytes. These results suggest that large excess capacities found in some biochemical and physiological systems, rather than representing large safety factors, may reflect a close match of system design to unscrutinized performance requirements. Understanding quantitative evolutionary design thus calls for careful consideration of the various performance specifications that biological components/processes must meet in order for the organism to be fit. The biochemical systems framework used in this paper is generally applicable for such a detailed examination of the quantitative evolutionary design of gene expression levels in other systems.

Effect of ibuprofen on monocyte activation by liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (CGP 19835A): can ibuprofen reduce fever and chills without compromising immune stimulation?

The purpose of this study was to determine the effects of ibuprofen on the ability of liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE) to activate human blood monocytes in vitro. We undertook these experiments because the major toxic side-effects following L-MTP-PE infusion, fever and chills, could be prevented when ibuprofen was given orally immediately before L-MTP-PE infusion. It was therefore important to determine whether ibuprofen interfered with the macrophage-activation properties of L-MTP-PE. Peripheral blood monocytes were isolated from normal donors, then incubated with L-MTP-PE in the presence or absence of ibuprofen. The cytotoxic properties of the monocytes were assessed by a radioisotope-release assay against A375 cells. Ibuprofen at dose levels of 40 micrograms/ml suppressed the generation of the cytotoxic phenotype but did not interfere with the killing process once the cells were activated. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) production, as well as the mRNA expression of these cytokines, was suppressed by 40 micrograms/ml ibuprofen. Since IL-1 and TNF play a crucial role in the cytotoxic function of monocytes, these findings may explain the mechanism by which ibuprofen inhibited the generation of the cytotoxic phenotype by L-MTP-PE. By contrast, ibuprofen dose levels up to 10 micrograms/ml had no effect on the generation of monocyte-mediated cytotoxicity by L-MTP-PE and no effect on the production, secretion, or mRNA expression of TNF and IL-1. Therefore, we concluded that if ibuprofen is to be used to control the side-effects of L-MTP-PE, blood levels of up to 10 micrograms/ml are desirable. In two of three patients, we determined that an oral dose of 200 mg given immediately before L-MTP-PE infusion could achieve these desired blood levels.

Macrophages and cancer

The uncontrolled growth of metastases resistant to conventional therapeutic modalities is a major cause of death from cancer. Data from our laboratory and others indicate that metastases arise from the nonrandom spread of specialized malignant cells that preexist within a primary neoplasm. These metastases can be clonal in their origin, and different metastases can originate from different progenitor cells. In addition, metastatic cells can exhibit an increased rate of spontaneous mutation compared with benign nonmetastatic cells. These data provide an explanation for the clinical observation that multiple metastases can exhibit different sensitivities to the same therapeutic modalities. These findings suggest that the successful therapy of disseminated metastases will have to circumvent the problems of neoplastic heterogeneity and the development of resistance. Appropriately activated macrophages can fulfill these demanding criteria. Macrophages can be activated to become tumoricidal by interaction with phospholipid vesicles (liposomes) containing immunomodulators. Tumoricidal macrophages can recognize and destroy neoplastic cells in vitro and in vivo, leaving nonneoplastic cells uninjured. Although the exact mechanism(s) by which macrophages discriminate between tumorigenic and normal cells is unknown, it is independent of tumor cell characteristics such as immunogenicity, metastatic potential, and sensitivity to cytotoxic drugs. Moreover, macrophage destruction of tumor cells apparently is not associated with the development of tumor cell resistance. Macrophages are found in association with malignant tumors in a definable pattern, suggesting that the most direct way to achieve macrophage-mediated tumor regression is in situ macrophage activation. Intravenously administered liposomes are cleared from the circulation by phagocytic cells, including macrophages, so when liposomes containing immunomodulators are endocytosed, cytotoxic macrophages are generated in situ. The administration of such liposomes in certain protocols has been shown to bring about eradication of cancer metastases. Macrophage destruction of metastases in vivo is significant, provided that the total tumor burden at the start of treatment is minimal. For this reason, we have been investigating various methods to achieve maximal cytoreduction in metastases by modalities such as chemotherapy or radiotherapy prior to macrophage-directed therapy. It is important to note that even the destruction of 99.9% of cells in a metastasis measuring 1 cm2 would leave 10(6) cells to proliferate and kill the host. The ability of tumoricidal macrophages to distinguish neoplastic from bystander nonneoplastic cells presents an attractive possibility for treatment of the few tumor cells which escape destruction by conventional treatments. Macrophage-directed therapy has been studied in several human protocols, yielding important biological information about the use of liposome-encapsulated macrophage activators in cancer patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Muramyl dipeptide protects decomplemented mice from surgically-induced infection

Muramyl dipeptide (MDP) is a natural product of bacterial cell-wall breakdown, which can now be produced synthetically; it is the smallest component of the mycobacterial cell wall capable of reproducing the adjuvant activities of Freund's complete adjuvant. We tested the well-documented, protective effect of MDP to increase survival in a murine model simulating surgically-induced bacteremia. The protocol involved the bacterial innoculation of control and decomplemented mice in the presence and the absence of pretreatment with MDP. Bacteremia in both the control and decomplemented groups pretreated with MDP was decreased statistically at 24 h (P less than 0.01) as compared to controls. Likewise, survival was increased significantly at 24 h (P less than 0.05), 48 h (P less than 0.001), and 72 h (P less than 0.001) using the same group comparisons. We conclude, therefore, that MDP maintains its protective effect in the absence of complement, supporting the view that the mechanism of action of MDP is complement independent.