Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022672 (acute tubular necrosis)
 2,175 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heme proteins transport oxygen and facilitate redox reactions. Heme, however, may be dangerous, especially when free in biologic systems. For example, iron released from hemoglobin-derived heme can catalyze oxidative injury to neuronal cell membranes and may be a factor in post-traumatic damage to the central nervous system. We have shown that heme catalyzes the oxidation of low density lipoproteins which can damage vascular endothelial cells. The endothelium is susceptible to damage by oxidants generated by activated phagocytes, and this has been invoked as an important mechanism in a number of pathologies including the Adulte Respiratory Distress Syndrome (ARDS), acute tubular necrosis, reperfusion injury and atherosclerosis. Because of its highly hydrophobic nature, heme readily intercalates into endothelial membranes and potentiates oxidant-mediated damage. This injury is dependent on the iron content of heme and is completely blocked when concomitant hemopexin is added. Ferrohemoglobin, when added to cultured endothelial cells, is without deleterious effects, but if oxidized to ferrihemoglobin (methemoglobin), it greatly amplifies oxidant damage. Methemoglobin, but not ferrohemoglobin, releases its hemes which can then be incorporated into endothelial cells. Cultured endothelial cells, when exposed to methemoglobin but not ferrohemoglobin, cytochrome c or metmyoglobin, potentiate this oxidant injury. Stabilization of the methemoglobin by cyanide, haptoglobin or capture of the heme by hemopexin abrogates this effect. Paradoxically, more prolonged exposure of endothelium to heme or methemoglobin renders them remarkably resistant to oxidant challenge. Endothelium defends itself from heme by induction of the heme degrading enzyme heme oxygenase and the concomitant production of large amounts of the iron binding protein ferritin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Heme and the vasculature: an oxidative hazard that induces antioxidant defenses in the endothelium. 808 43

Rasburicase is a recombinant urate-oxidase enzyme and is a very important medication for tumor lysis syndrome. Methemoglobinemia and hemolysis are known side effects of rasburicase that result from oxidative stress caused by hydrogen peroxide, a byproduct generated during the breakdown of uric acid to allantoin. Patients with G6PD deficiency have a decreased tolerance to oxidative stress and are therefore at a greater risk of hemolysis and methemoglobinemia with rasburicase. Our patient is a 56-year-old Caucasian male with a recent diagnosis of grade 2-3a non-Hodgkin's lymphoma who presented to our emergency department with shortness of breath and dark discoloration of urine. Patient was discharged 36 hours ago from our hospital after he was given a first course of R-CHOP regimen and a dose of rasburicase. On further evaluation, patient was found to have severe anemia with hemolytic picture, hyperkalemia and acute kidney injury. He also had a discrepancy of the transcutaneous saturation (75%) and the saturation in an arterial blood gas value (99%). His methemoglobin level was found to be 11.9%. We were aware that methylene blue is a contraindication in patients with G6PD deficiency but considering patient being Caucasian and low risk for it and his deteriorating respiratory condition, it was decided to offer the treatment and patient received 1 dose of methylene blue which failed to improve his methemoglobinemia. He was also given vitamin C and 8 units of packed red blood cell throughout his stay in the hospital. Patient's hospital course was complicated by ARDS needed to be on mechanical ventilation support for 4 days and acute renal failure secondary to pigment nephropathy and acute tubular necrosis which required a hemodialysis support. Even if rasburicase induced methemoglobinemia and hemolysis are not very common complications, clinicians who prescribe and follow patients should detect this serious complication early and manage it accordingly. Our case can be used as a reminder that patients should be followed closely and given the right instructions on discharge to treat these complications which are associated with severe consequences. It is also vital to assume a diagnosis of G6PD deficiency until proven otherwise in a patient who presents with rasburicase induced hemolysis and avoid administration of methylene blue even if the patient is from a low risk ethnicity for G6PD as in our patient.
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PMID:Rasburicase induced severe hemolysis and methemoglobinemia in a Caucasian patient complicated by acute renal failure and ARDS. 3060 5

Self-aggregated vesicles have been considered to be promising candidates for hemoglobin-based oxygen carriers. Here, amphiphilic hetero-triblock copolymers are designed and synthesized with the capacity to self-assemble into polymer vesicles (polymersomes). Conceivably, vesicles are formed with asymmetric membranes, which achieve enhanced encapsulation efficiency of hemoglobin (Hb) beyond the diblock counterpart. Furthermore, hemoglobin-loaded vesicles (HbV) are fabricated with high Hb content and submicron particle sizes. The gas-binding capability, oxygen affinity and methemoglobin (metHb) level of the HbV dispersions are all comparable to the natural erythrocytes. In vitro HbV stability studies further reveal that the encapsulation of Hb within vesicles can greatly avoid the existence of free Hb and shows no interference with cells, especially for blood components. To evaluate the efficacy on ischemia reperfusion, HbV suspended in a plasma expander is transfused as a resuscitation fluid into an acute anemia rat model. Results demonstrate that the combined infusion of the plasma expander with HbV effectively ameliorates the lethal shock symptom and reduces short-term mortality. Concurrently, rats transfused with HbV are void of the acute tubular necrosis caused by the filtration of dissociated Hb dimers from glomeruli. We envision that the oxygen carriers derived from polymer self-assembly technology will become an alternative strategy for future development of blood substitutes.
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PMID:Asymmetric copolymer vesicles to serve as a hemoglobin vector for ischemia therapy. 3248 96