Clinics in haematology最新文献

The main purpose of this review is to emphasize the critical role that chromosome analysis can play in the diagnosis, prognosis and management of blood malignancies. Table 3 shows that most patients with AML, MDS and ALL can be placed into one of three major prognostic categories. When chromosome analysis is combined with a cytological study in AML and MDS and with a cytological and immunophenotypic study in ALL, the clinical value of such analysis is further enhanced. Because of critical prognostic information that may be obtained primarily from refined chromosome analysis, we recommend that a major effort be undertaken to develop capability for such analysis in all large institutions so that the information derived can be used routinely in the assessment of haematological malignancies. In particular, it is now necessary to reassess the value of current treatments taking into consideration refined chromosome studies. We believe that patients within specific chromosomal categories should be treated with specific types of therapy in an attempt to improve overall survival.

The evaluation of agents inhibiting platelet function is difficult because, in addition to primary aggregation by thrombin, there are three amplification loops involving respectively arachidonate, ADP and PAF-acether (platelet activating factor). Each amplification loop seems eventually to act via a common pathway: the mobilization of calcium ions from the dense tubular system into the cytoplasm. Inhibition of this mobilization would prevent platelet aggregation by any agonist. This could be an ideal step with which to intervene pharmacologically. An intracellular increase in cAMP reduces cytoplasm calcium levels and therefore counteracts the effect of whatever agonist is used (Vermylen et al, 1982, 1983; Verstraete et al, 1985). Depending on the pro-aggregatory stimulus, the relative importance of a given pathway of platelet activation may shift. There is also uncertainty about which pathway of platelet activation predominates in a given clinical condition. The second problem relates to the pharmacology of the ideal drug for the inhibition of platelet function. It is very difficult to delineate the desired profile of such a drug considering the properties of the various compounds presently being studied (see Table 1). Prolongation of a shortened platelet survival in man was considered to be one of the key markers of an anti-aggregatory agent; this characteristic was found to be present after administration of sulphinpyrazone, clofibrate, ticlopidine, suloctidil, dipyridamole (in patients with artificial heart valves) and dipyridamole (in patients with venous thrombosis). The protective antithrombotic effect is most clearly demonstrated for aspirin; it is rather surprising that this drug does not prolong the shortened platelet survival in man, not even in those clinical conditions in which it effectively prevents thromboembolism.

Arachidonic acid (AA) is metabolized by the cyclo-oxygenase and the lipoxygenase pathways to give a number of products, some of which have potent and sometimes opposing biological activities. Different cell types produce different metabolites, so that the chief AA metabolite produced by the platelet is the pro-aggregatory thromboxane A2 (TXA2), whereas that produced by the vascular endothelium is the anti-aggregatory prostacyclin. White blood cells, on the other hand, are the chief source of the leukotrienes, which are implicated in the inflammatory process. Generation of these products may be modified in certain pathological conditions, such as atherosclerosis and diabetes, where prostacyclin synthesis is reduced and TXA2 synthesis increased, resulting in a pro-thrombotic state. Synthesis of AA metabolites may be inhibited, either totally or selectively, using drugs which inhibit different enzymes in the metabolic pathway. These drugs may be beneficial in the treatment of thrombotic disorders and inflammation. AA metabolism may also be modified by dietary substitution with eicosapentaenoic acid, a fatty acid present in fish oils.