Erythropoietin (EPO), recognized for its central role in erythropoiesis, also mediates neuroprotection when the recombinant form (r-Hu-EPO) is directly injected into ischemic rodent brain. We observed abundant expression of the EPO receptor at brain capillaries, which could provide a route for circulating EPO to enter the brain. In confirmation of this hypothesis, systemic administration of r-Hu-EPO before or up to 6 h after focal brain ischemia reduced injury by Ϸ50 -75%. R-Hu-EPO also ameliorates the extent of concussive brain injury, the immune damage in experimental autoimmune encephalomyelitis, and the toxicity of kainate. Given r-Hu-EPO's excellent safety profile, clinical trials evaluating systemically administered r-Hu-EPO as a general neuroprotective treatment are warranted. E rythropoietin (EPO) and its receptor (EPO-R) function as primary mediators of the normal physiologic response to hypoxia. EPO, a glycoprotein that increases red cell mass to improve tissue oxygenation, is produced by the kidney in response to hypoxia. Recombinant human EPO (r-Hu-EPO) is effective and widely used for the treatment of anemia associated with renal failure, HIV infection, cancer, and surgery. However, like other members of the cytokine superfamily to which EPO and its receptor belong, both are expressed by other tissues, including the nervous system. Similar to its regulation in the periphery, EPO within the central nervous system is inducible by hypoxia (1-4). An in vivo neuroprotective function for EPO has been demonstrated by the observation that direct intracerebraventricular injection of r-Hu-EPO in advance of hypoxic͞ ischemic stress offers significant protection of neuronal tissue (5-7). A critical neuroprotective role for endogenous EPO in the central nervous system has been confirmed by the administration of soluble EPO-R, which neutralizes EPO, consequently exacerbating ischemic stress and increasing tissue injury (7).Hypoxia may not be the only relevant stimulus for brain EPO production, however, as metabolic disturbances, including hypoglycemia and strong neuronal depolarization, generate mitochondrial reactive oxygen species that may increase brain EPO expression through hypoxia inducible factor 1 (8). EPO may thus protect nervous tissue under any condition characterized by a relative deficiency of ATP in the face of increased metabolic demands. EPO has been shown to exhibit classic neurotrophic effects in vivo and in vitro (2, 9-11). The mechanism of action of EPO in erythropoiesis, neuroprotection, and neurotrophic effects ultimately may involve activation of the bcl-x family of antiapoptotic genes, promoting survival rather than apoptosis (12)(13)(14).Despite the demonstrated benefit of intrathecally administered r-Hu-EPO in preventing ischemic neuronal damage, direct delivery of r-Hu-EPO into the brain is not a practical approach in most clinical contexts. Systemic delivery of r-Hu-EPO has not been evaluated because of the perception that the brain EPO system is parallel and distinct from the control ...

Smokers have a significantly higher risk for developing coronary and cerebrovascular disease than nonsmokers. Advanced glycation end products (AGEs) are reactive, cross-linking moieties that form from the reaction of reducing sugars and the amino groups of proteins, lipids, and nucleic acids. AGEs circulate in high concentrations in the plasma of patients with diabetes or renal insufficiency and have been linked to the accelerated vasculopathy seen in patients with these diseases. Because the curing of tobacco takes place under conditions that could lead to the formation of glycation products, we examined whether tobacco and tobacco smoke could generate these reactive species that would increase AGE formation in vivo. Our findings show that reactive glycation products are present in aqueous extracts of tobacco and in tobacco smoke in a form that can rapidly react with proteins to form AGEs. This reaction can be inhibited by aminoguanidine, a known inhibitor of AGE formation. We have named these glycation products ''glycotoxins.'' Like other known reducing sugars and reactive glycation products, glycotoxins form smoke, react with protein, exhibit a specific f luorescence when cross-linked to proteins, and are mutagenic. Glycotoxins are transferred to the serum proteins of human smokers. AGE-apolipoprotein B and serum AGE levels in cigarette smokers were significantly higher than those in nonsmokers. These results suggest that increased glycotoxin exposure may contribute to the increased incidence of atherosclerosis and high prevalence of cancer in smokers.

Recent studies (1-3) have indicated that glucose can react nonenzymatically with amino groups of a wide range of proteins throughout the body, including intracellular proteins such as hemoglobin and lens crystallins, extracellular proteins such as collagen, and cell membrane proteins on red cells (1) and endothelial cells (2, 3). Initially a reversible adduct, the Amadori product is formed from the nonenzymatic reaction of glucose with proteins (4, 5). However, these Amadori products can slowly undergo a series of further reactions and rearrangements that give rise to complex irreversible protein adducts, advanced glycosylation endproducts (AGE) .' These AGE continue to accumulate in extracellular and membrane proteins as a function of time and glucose concentration (2, 6).Recently, a new membrane-associated macrophage receptor has been identified that recognizes proteins modified by this process of long-term nonenzymatic AGE formation (7,8). This receptor has been shown not to recognize low-density lipoprotein (LDL), acetyl-LDL, mannose/fucose, and formaldehyde-treated proteins (9). Because formation of AGE increases with protein age (9-11) and AGE receptor-mediated uptake and degradation of these proteins increases with amount of AGE formation (7), it has been postulated (7, 8) that the AGE receptor preferentially mediates the removal of senescent macromolecules . In disorders such as diabetes mellitus, in which accelerated AGE formation occurs (2), the efficiency of such a removal mechanism may influence the rate at which diabetic tissue damage develops .Reasoning that certain cells have a long enough lifespan to allow AGE formation on their surface proteins, we hypothesized that the AGE receptor might also mediate the removal of aging cells by selectively recognizing a cell-surface alteration that accumulates over time. This mechanism would also account for

Erythropoietin and its receptor function as primary mediators of the normal physiological response to hypoxia. Erythropoietin is recognized for its central role in erythropoiesis, but studies in which recombinant human erythropoietin (epoetin alfa) is injected directly into ischaemic rodent brain show that erythropoietin also mediates neuroprotection. Abundant expression of the erythropoietin receptor has been observed at brain capillaries, which could provide a route for circulating erythropoietin to enter the brain. In confirmation of this hypothesis, systemic administration of epoetin alfa before or up to 6 h after focal brain ischaemia reduced injury by 50-75%. Epoetin alfa also limited the extent of concussive brain injury, the immune damage in experimental autoimmune encephalomyelitis and excitotoxicity induced by kainate. Thus, systemically administered epoetin alfa in animal models has neuroprotective effects, demonstrating its potential use after brain injury, trauma and multiple sclerosis. It is evident that erythropoietin has biological activities in addition to increasing red cell mass. Given the excellent safety profile of epoetin alfa, clinical trials evaluating systemically administered epoetin alfa as a general neuroprotective treatment are warranted.