Biomedical subjects
Publications and source records attributed to D T Chiu.
The reconstructive problems associated with providing durable coverage for full-thickness loss of the scalp are detailed and the options reviewed. Free tissue transfer offers a break-through in these difficult problems. A case of a successful parascapular flap transfer is described, offering an alternative to previously described methods.
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Activated neutrophils (ANs) are known to release reactive oxygen species that may cause oxidative damage to surrounding tissues. We determined if ANs could induce lipid peroxidation (LP) in human red cells and investigated the mechanism involved in this interaction. We studied neonatal glucose-6-phosphate dehydrogenase (G6PD) deficient, and sickle red cells, since each of these are known to be susceptible to oxidant injury. Neutrophils were isolated from whole blood and activated by incubation with opsonized zymosan. Mixtures of such neutrophils and red cells at a ratio of 1:100 were incubated for two hours at 37 degrees C, after which the malonyldialdehyde content in red cells was measured as an index of LP. All red cells underwent LP after AN treatment, and the degree of LP was proportional to the amount of AN in the mixture. Superoxide dismutase and catalase partially inhibited LP. When compared to normal red cells, only sickle cells demonstrated a significant increase in AN-mediated LP. Conversion of hemoglobin to carboxy-hemoglobin increased AN-mediated LP, whereas conversion to met-hemoglobin decreased AN-mediated LP. The protective effect of met-hemoglobin on LP was less in sickle cells than in normal cells. We conclude that AN can induce LP in red cells in vitro and that sickle cells are more susceptible to this process than normal cells. Hemoglobin can serve as an electron trap and protect the cell against peroxidative damage, but this mechanism is impaired in sickle cells. We speculate that the pathogenesis of hemolysis associated with infectious disease may include AN-induced red cell LP.
The transbilayer mobility of phosphatidylcholine (PC) molecules in the membrane of homozygous reversible sickle cells (RSCs) was studied using a PC-specific exchange protein from beef liver. In deoxygenated RSCs, all of the PC present in the membrane of the intact cell is rapidly available for exchange, mediated by this protein. Since a substantial amount of the PC is present in the inner membrane leaflet of these cells, this observation implies that the PC molecules in their membranes do experience rapid transbilayer movements. To determine the actual rate of transbilayer movement of the PC, radioactive PC was introduced into the outer monolayer of oxygenated RSCs using the PC-specific exchange protein. Subsequently, the cells were incubated at 37 degrees C under oxy- and deoxygenating conditions to enable the PC to equilibrate within the bilayer. At various time intervals, samples were taken and treated with phospholipase A2, which selectively degrades the PC in the outer monolayer. Analysis of the specific radioactivities of the lyso-PC thus produced, as well as of the residual PC, enabled us to follow the fate of the radioactive PC previously introduced into the outer membrane layer. The half-time value for transbilayer equilibration of the PC in deoxygenated RSCs was determined to be 3.5 h, which is about four times lower than that for oxygenated RSCs. This increased transbilayer mobility of PC, observed in deoxygenated RSCs, is immediately restored to the normal low rate upon reoxygenation of the cells, indicating a complete reversibility of this phenomenon.
The sickle erythrocyte (RBC) is a pathologic RBC that contains multiple membrane abnormalities. Some of these abnormalities have been implicated in the pathophysiology of vasoocclusive crises characteristic of sickle cell disease; others have yet to be defined in terms of their clinical significance. Recent information has shown that sickle RBC adhere abnormally to cultured endothelial cells yet little is known about the ways in which sickle cells interact with model membranes of defined size and lipid composition. We investigated this phenomenon by interacting sickle RBC with artificial lipid vesicles (liposomes) containing acidic phospholipids. Our results demonstrate that sickle disease (hemoglobin SS) RBC bind more of these liposomes than do normal or sickle trait (hemoglobin AS) RBC and that these differences are accentuated by hypoxia-induced sickling. Binding of liposome phospholipid to sickled RBC was not attributable to phospholipid exchange between liposomes and RBC and was consistent with a mechanism involving both membrane fusion and a stable reversible adhesion of liposomes to the RBC membrane.Investigations into the mechanism(s) underlying increased liposome binding to sickled RBC suggested that the known reversible translocation of aminophospholipids, phosphatidylserine (PS) and phosphatidyl-ethanolamine (PE), from the inner to the outer leaflet of the reversibly sickled RBC (RSC) plasma membrane during sickling may be a component of increased liposome binding to RSC. This idea was supported from results of experiments in which normal RBC were treated with diamide resulting in the expression of outer leaflet PE and PS and a stimulation of liposome binding to these cells. However, sickle RBC separated according to cell density on stractan gradients showed that irreversibly sickled RBC (ISC) were less capable of liposome binding than were discoid RSC. Since ISC are known to contain elevated levels of outer leaflet aminophospholipids, such a result suggests that other changes in the plasma membrane of sickle cells, in addition to phospholipid reorganization, are probably involved in enhanced liposome binding to these cells. In other experiments, we showed that liposomes containing l-phenylalanine were capable of delivering this antisickling agent into intact sickle RBC as demonstrated by the partial inhibition of hypoxia-induced sickling in vitro. Our results suggest that liposomes can be used as sensitive probes for investigating changes in RBC membrane properties, especially those that affect intermembrane interactions, and that liposomal transport systems may have significant implications in the therapy of sickle cell disease.
Our plan was to evaluate the potentially important role of phospholipids in erythrocyte shape alterations by determining if their orientation was altered during endocytosis. Stomatocytosis and endocytosis were induced in normal intact human erythrocytes by incubation with three agents: primaquine, vinblastine, and chlorpromazine, each of which has its own requirements and time course for producing endocytosis. The organization of the phospholipid bilayer was assessed by measuring the extent of degradation of phophatidylcholine (PC), phophatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM) produced by exposure of erythrocytes to a nonpenetrating protease-free phospholipase A2 alone or in combination with a purified sphingomyelinase as well. The induction of stomatocytosis did not change this orientation. However, correlating with the onset of endocytosis but not its extent, there was an increase in PE degradation, which could be detected regularly only by use of phospholipase A2 alone. Use of the combination of phospholipase A2 and sphingomyelinase showed that the extent and course of endocytosis was paralleled by an apparent movement of PC and SM from the outer to the inner half of the lipid bilayer. Since no further PE was hydrolyzed and because no PS was ever degraded, this inward movement of PC and SM did not represent the establishment of complete symmetry in the membrane. By adjusting the experimental design it was possible to implicate the endocytic process, and not insertion of drug in the membrane, as the cause of the alterations in phospholipid organization seen. Our findings indicate that the phospholipid orientation is very closely involved in the endocytosis process and that specific states of phospholipid asymmetry may be related to identifiable membrane events.
In experiments on rabbits the use of a vein graft for bridging defects of peripheral nerves was examined. A 10-20 mm long segment of sciatic nerve was removed bilaterally. On one side the gap was bridged with an autologous nerve graft, on the other one an autologous vein graft was used. With relatively small gaps (10 mm) both methods revealed comparable results. When bridging larger defects, the results with nerve grafts were superior to those obtained with vein grafts.
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This study was performed to determine whether vein grafts might serve as a conduit for nerve regeneration. A 1 cm segment of sciatic nerve was removed bilaterally in 12 Sprague-Dawley rats. On one side the gap was not repaired, and on the other side a segment of femoral vein was used to bridge the nerve gap. Nerve conduction studies and necropsies were performed at intervals. Reconstitution of nerve trunk continuity and healing of plantar ulcers occurred only in the vein-grafted side. Histologic examination revealed orderly growth of nerve fibers within the lumen of the vein grafts as early as 1 month after repair. Most regenerating nerve fibers passed through the proximal junction in an orderly pattern and reached the distal stumps within 2 months after repair. Results of nerve conduction study at 4 months after operation demonstrated restoration of conduction through the vein-grafted sciatic nerves with muscle reinnervation. Nearly normal muscle fibers in the gastrocnemius on the repaired side were confirmed at necropsy. This study demonstrated that autogenous vein grafts can serve as a conduit for nerve regeneration in rodents.
A supernumerary extensor tendon to the left thumb was observed in a black female cadaver. It came from a bipinnate extensor indicis proprius and passed through the fourth synovial compartment, where it fused with the extensor pollicis longus at the midshaft level of the first metacarpal. This appears to be a rare anatomic variation. Since the review of LeDouble in 1897, only two cases have been reported. A reminder of this oddity at this time seems appropriate because of its perceivable clinical significance.
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We hypothesized that epigenetic (non-genomic) factors, related to muscular function, significantly regulate the shape and position of the auricular cartilage. We tested this experimentally by doing unilateral partial and total facial neurectomies, auricular myectomies, and ear rotations with skin excisions in rats. The neurectomies produced muscle atrophy, abolished the horizontal scaphoid ridging, and produced characteristic changes in the auricular shape. The myectomies of extrinsic auricular musculature alone were followed routinely by complete muscle regeneration and no changes in shape. The auricular rotations, with skin excision, produced an antihelix-like complex analogous to the human ear--a configuration that was permanent and was accompanied by muscle relocation. The findings are believed to support our hypothesis.
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Gluthathione peroxidase (gluthatione:hydrogen-peroxide oxidoreductase, EC 1.11.1.9) has been purified approximately 2700-fold from rat lung soluble fraction. The purified enzyme was shown to be homogeneous by sodium dodecyl sulfate/urea polyacrylamide gel electrphoresis. Selenium-75 tracer cochromatographed with the enzyme activity, indicating that rat lung soluble gluthathione peroxidase is a selenium enzyme. The enzyme had an approximate molecular weight of 80000 and contained four identical subunits. The optimal activity of the enzyme was at between pH 8.8 and 9.1. The enzyme had general specificity toward hydroperoxides, and high specificity for reduced glutathione. The kinetic behavior or the purified lung soluble glutathione peroxidase followed a ping-pong-like mechanism; the enzyme first reduced the lipid hydroperoxide substrate to the corresponding hydroxy fatty acid, then was regenerated to the native form by reduced glutathione.
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1. The cardiovascular changes of conscious cold-acclimated (CA) and warm-acclimated (WA) rats during exposure to 5 degrees C or 28 degrees C were studied. 2. The cardiac output, heart rate and stroke volume of Ca rats exposed to 5 degrees C and of WA rats during cold stress were significantly greater, and their calculated total peripheral resistance significantly less than those of WA rats ats exposed to 28 degrees C. These results show that circulatory changes participate in cold acclimation and cold stress. The circulatory changes in the two conditions were compared and the mechanism of the observed differences were discussed. 3. CA rats exposed to 28 degrees C showed a striking decrease of oxygen consumption and arterio-venous O2 difference, but significant circulatory changes were decreased heart rate and cardiac index only, indicating that the response was mainly metabolic.