Clinical and experimental studies on adenine, various nucleosides and their analogs in hematology

The involvement of cation leaks in the storage lesion of red blood cells

Stored blood components are a critical life-saving tool provided to patients by health services worldwide. Red cells may be stored for up to 42 days, allowing for efficient blood bank inventory management, but with prolonged storage comes an unwanted side-effect known as the "storage lesion", which has been implicated in poorer patient outcomes. This lesion is comprised of a number of processes that are inter-dependent. Metabolic changes include a reduction in glycolysis and ATP production after the first week of storage. This leads to an accumulation of lactate and drop in pH. Longer term damage may be done by the consequent reduction in anti-oxidant enzymes, which contributes to protein and lipid oxidation via reactive oxygen species. The oxidative damage to the cytoskeleton and membrane is involved in increased vesiculation and loss of cation gradients across the membrane. The irreversible damage caused by extensive membrane loss via vesiculation alongside dehydration is likely to result in immediate splenic sequestration of these dense, spherocytic cells. Although often overlooked in the literature, the loss of the cation gradient in stored cells will be considered in more depth in this review as well as the possible effects it may have on other elements of the storage lesion. It has now become clear that blood donors can exhibit quite large variations in the properties of their red cells, including microvesicle production and the rate of cation leak. The implications for the quality of stored red cells from such donors is discussed.

Adenine in blood preservation

The recent Food and Drug Administration (U.S.) approval of a new blood preservative (CPDA-1) which contains adenine not only introduces a new blood product into the American blood banking system, but also heralds the advent of novel approaches to blood product preservation. The use of adenine to effect maintenance of red cell adenosine triphosphate (ATP), and hence to prolong storability, has a well-founded biochemical rationale. Effects of adenine on red cell metabolism are generally well understood, but effects on other blood components have not been fully delineated. The efficacy of adenine preservatives in enhancing the duration of red cell storage appears to outweigh the small risk of toxicity from free adenine. Clinical use of millions of units of adenine-preserved blood in Europe during more than a decade has resulted in only one report of possible adenine toxicity. Marginal acceptability of 24-hr 51Cr red cell recovery of packed red cells stored for 35 days in CPDA-1 has stimulated development and evaluation of an improved preservative (CPDA-2) which may extend blood storability beyond 35 days. A heightened awareness of the hematological consequences of prolonged storage has come with the extension of blood storage beyond 21 days. The concepts of component-specific preservation systems and optimal preservation systems have emerged as a result of experimentation on adenine preservatives. While the influence of adenine preservatives on American blood banking is yet to become manifest, the ultimte impact of adenine on blood preservation may be the development of novel systems which optimally preserve specific blood components at the option of the user.