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Biomedical subjects

W M Lee

Publications and source records attributed to W M Lee.

At least 145 records · Page 8Linked to original sources
PubMed1993

Central pontine myelinolysis: report of two occurrences after cisplatin-containing chemotherapy for nasopharyngeal carcinoma.

We report two patients with the classical clinical syndrome of central pontine myelinolysis following cisplatin based chemotherapy for nasopharyngeal carcinoma. The diagnosis was supported by typical features on magnetic resonance imaging. Rapid correction of hyponatraemia was the most likely cause. A short course of corticosteroids was tried in both patients. Although one patient experienced almost complete recovery, the other still suffered from residual motor deficit. The importance of careful monitoring of the rate of electrolyte correction is emphasized.

Adult↗
PubMed1993

Antibodies to polymerized albumin in woodchuck hepatitis virus infection.

Polymerized human serum albumin may play a role in the entry of hepatitis B virus into hepatocytes, and antibodies to polyalbumin that frequently appear during acute hepatitis may aid the process of viral clearance. We developed an enzyme-linked immunosorbent assay for antibodies to polymerized woodchuck albumin to enable us to evaluate further the role of these antibodies in an animal model system. Sera from 17 uninfected adult woodchucks and 8 newborns showed no binding to control plates coated with woodchuck transferrin, woodchuck albumin, or polymerized human serum albumin. One of 8 newborn animals demonstrated a significant antibody titer to polymerized woodchuck albumin, and 16 of 17 adults without evidence of prior woodchuck hepatitis virus infection had measurable serum antibody titers. Antibodies to polymerized woodchuck albumin could be adsorbed by prior incubation with the antigen. In 2 animals subjected to experimental infection, significant rises in polyalbumin antibody were seen. When 4 adult woodchucks were immunized with woodchuck polyalbumin, significant increases in antibody titer were observed in 2 of the 4 animals. Of the 4 immunized and 4 controls subsequently challenged with woodchuck hepatitis virus, 7 became viremic and all 8 developed antibody to woodchuck hepatitis virus core antigen. We conclude that naturally occurring antibodies to polymerized woodchuck albumin are observed in most adult woodchucks in the absence of woodchuck hepatitis virus infection and do not seem to confer immunity against infection with this virus.

Age Factors↗
PubMed1993

Structure of human rhinovirus complexed with Fab fragments from a neutralizing antibody.

We have determined the structure of a human rhinovirus (HRV)-Fab complex by using cryoelectron microscopy and image reconstruction techniques. This is the first view of an intact human virus complexed with a monoclonal Fab (Fab17-IA) for which both atomic structures are known. The surface area on HRV type 14 (HRV14) in contact with Fab17-IA was approximately 500 A2 (5 nm2), which is much larger than the area that constitutes the NIm-IA epitope (on viral protein VP1) defined by natural escape mutants. From modeling studies and electrostatic potential calculations, charged residues outside the neutralizing immunogenic site IA (NIm-IA) were also predicted to be involved in antibody recognition. These predictions were confirmed by site-specific mutations and analysis of the Fab17-IA-HRV14 complex, along with knowledge of the crystallographic structures of HRV14 and Fab17-IA. The bound Fab17-IA reaches across a surface depression (the canyon) and meets a related Fab at the nearest icosahedral twofold axis. By adjusting the elbow angles of the bound Fab fragments from 162 degrees to 198 degrees, an intact antibody molecule can be easily modeled. This, along with aggregation and binding stoichiometry results, supports the earlier proposal that this antibody binds bivalently to the surface of HRV14 across icosahedral twofold axes. One prediction of this model, that the intact canyon-spanning immunoglobulin G molecule would block attachment of the virus to HeLa cells, was confirmed experimentally.

Antibodies, Monoclonal↗
PubMed1993

Role of maturation cleavage in infectivity of picornaviruses: activation of an infectosome.

Maturation of picornaviruses involves assembly of a "provirion," which undergoes an autocatalytic cleavage of VP0 to VP2 plus VP4. RNA transcripts from a cDNA clone of human rhinovirus 14 mutated at asparagine 68, one of the residues in the maturation cleavage site, generated normal yields of 150S particles which were noninfectious in the plaque assay because they were unable to initiate a second cycle of infection. These cleavage-defective provirions were otherwise indistinguishable from mature virions in sedimentation coefficient, binding affinity to monoclonal antibodies against neutralization sites IA, II, and III, attachment to HeLa cell receptors, and rate of cell-mediated conformational changes to form 125S A-particles and 80S empty capsids. These results suggest that maturation cleavage is required for the function of a previously undescribed intermediate which transfers packaged RNA across the membrane and into the cytosol. For this hypothetical intermediate, we propose the name infectosome. Since the native virus has a particle/PFU ratio of about 800, such an intermediate will be difficult to find. Mutations at serine 10 in VP2 reduced maturation cleavage to a rate sufficiently slow to show that the infectivity of virus particles increased with the degree of cleavage of VP0 to VP4 and VP2. This article describes the first characterization of a pure form of a picornaviral provirion, and hence the first direct evidence that provirions of picornaviruses lack infectivity.

Amino Acid Sequence↗
PubMed1993

Review article: drug-induced hepatotoxicity.

The liver is central to the metabolic disposition of virtually all drugs and xenobiotics (foreign substances). For the most part, this process is accomplished without injury to the liver itself or to other organs. A few compounds such as acetaminophen, CCl4 and the toxin responsible for mushroom poisoning are toxic themselves or produce metabolites which cause liver injury in a uniform, dose-dependent fashion. However, most agents form a sufficiently toxic byproduct and cause liver injury only quite rarely, under special circumstances. Generation of a toxic metabolite within the hepatocyte may produce direct cell injury with disruption of intracellular function, or may cause indirect injury by immune-mediated membrane damage. Factors promoting the accumulation of toxins include genetic enzyme variants which allow greater formation of the harmful metabolite, induction of an isozyme species which produces more than the usual quantity of the toxin, interference with regular (non-toxic) metabolic pathways by substrate competition for enzyme, or depletion of required detoxifying substrates. The following review will provide clinical examples of some of these well-known metabolic reactions, discuss some new issues in drug-induced hepatotoxicity, such as use of combination agents and complex multiple drug regimens, alternative health strategies (vitamins and herbal remedies) as well as the widespread use of cocaine. The overall message is that, as new compounds are issued, new opportunities for drug-induced hepatotoxicity arise. Until extensive experience with any new compound has evolved, it is best to maintain a healthy paranoia concerning the newer drugs--there are very few totally safe agents.

Biotransformation↗
PubMed1993

Functional domains of c-Myc involved in the commitment and differentiation of murine erythroleukemia cells.

In the early event of the induction of mouse erythroleukemia (MEL) cell differentiation, c-myc mRNA levels show a drastic change. The elevated expression of a transfected c-myc gene inhibits the commitment and differentiation of MEL cell transformants. In the present work, we have introduced human c-myc mutants into MEL cells under the inducible promoter to define the functional domains of c-Myc involved in erythroid differentiation. The c-Myc domains necessary for commitment and differentiation are not co-localized; almost entire regions are required for inhibition of commitment, whereas domains II and IV that are essential for co-transforming activity with ras are required for inhibition of differentiation. Interestingly, mutants that delete domains for c-Myc dimerization motifs enhanced differentiation. These results suggest that c-Myc may regulate commitment and differentiation by interacting with proteins through different domains.

Animals↗
PubMed1992

Heat shock protein hsp70 protects cells from thermal stress even after deletion of its ATP-binding domain.

Retroviral-mediated gene transfer experiments show that rodent cells become heat resistant when stably and constitutively expressing a cloned human gene encoding an intact human 70-kDa heat shock protein (hsp70). Cells expressing higher levels of the hsp70 protein generally tolerate thermal stress better, whereas cells expressing either of two mutated hsp70-encoding genes, one with a 4-base pair out-of-frame deletion and one with an in-frame deletion of codons 438-618, are heat sensitive. These results provide strong evidence that expression of hsp70 leads directly to thermal tolerance. Surprisingly, cells expressing a mutant hsp70 of a human gene missing codons 120-428 are, nevertheless, heat resistant. Because the deleted region of this mutant contains the ATP-binding domain of human hsp70, this domain appears dispensable in the hsp70-mediated protection of cells from thermal stress.

Adenosine Triphosphate↗
PubMed1992

Max: functional domains and interaction with c-Myc.

The product of the c-myc proto-oncogene is a DNA-binding protein, the deregulated expression of which is associated with a variety of malignant neoplasms. The cDNA for the max gene was recently cloned as a result of the ability of its protein product to interact with the c-Myc protein. We studied bacterially produced Max, c-Myc, and a series of truncated c-Myc proteins. Full-length c-Myc alone cannot bind DNA. However, a truncated c-Myc protein comprising the basic, helix-loop-helix, and leucine zipper regions can bind specifically to DNA bearing the sequence GGGCAC(G/A)TGCCC. Max protein, either alone or in a heteromeric complex with full-length c-Myc, binds to the same core sequence. Using a novel combination of chemical and photo-cross-linking analysis, we demonstrate that either Max or a c-Myc/Max heteromeric complex binds to DNA virtually exclusively in a dimeric structure. Using fusion proteins in cultured cells, we establish a number of functional characteristics of Max. First, we show that Max can interact with c-Myc intracellularly in a manner dependent on the integrity of the helix-loop-helix and leucine zipper motifs. Second, a nuclear localization domain that contains the sequence PQSRKKLR is mapped to the carboxy-terminal region of Max. Third, Max lacks a transcriptional activation domain that is functional in Chinese hamster ovary cells when fused to a heterologous DNA-binding domain. These data suggest that Max may serve as a cofactor for c-Myc in transcriptional activation or, by itself, as a transcriptional repressor.

Amino Acid Sequence↗
PubMed1992

Selective removal of glycosylation sites from sex hormone-binding globulin by site-directed mutagenesis.

Sex hormone-binding globulin (SHBG) is a homodimeric plasma glycoprotein with high affinity for sex steroid hormones. It contains two N-linked carbohydrate chains and one O-linked oligosaccharide per subunit, but their functional significance is not known. Site-directed mutagenesis of a human SHBG cDNA has enabled us to selectively disrupt the known glycosylation sites individually and in various combinations. The mutant cDNAs were expressed in Chinese hamster ovary (CHO) cells, and it was found that the presence of carbohydrates is not an absolute requirement for the secretion of SHBG from these cells, but the absence of both N-linked oligosaccharides reduced the amount of SHBG in the culture medium. In addition, the affinity and specificity of SHBG for steroid ligands was unaffected by the lack of one or more carbohydrate chains. Proportionally greater amounts (26-31%) of the mutants lacking a single N-linked carbohydrate chain failed to interact with Concanavalin-A. (Con-A) compared to normal SHBG produced by CHO cells (15%). Western analysis demonstrated that both consensus sites for N-glycosylation are used and that the typical heavy [mol wt (M(r)), approximately 51,000] and light (M(r), approximately 47,000) subunit size-heterogeneity was maintained regardless of the absence of an O-linked carbohydrate at residue 7. Furthermore, the SHBG mutants containing only one N-linked oligosaccharide comprise only a single subunit with a M(r) of approximately 47,000. This suggests that the heavy subunit contains two N-linked oligosaccharides, while only one of these sites is used on the light subunit. The M(r) of the various SHBG mutants were also examined by gel filtration, and this indicated that they are all produced as homodimers and that carbohydrates are not involved in subunit association.

Animals↗
PubMed1992

Pregnancy in patients with chronic liver disease.

The pregnant patient with established chronic liver disease presents a unique situation in medicine. Although neither the pregnancy nor the liver disease is likely to specifically worsen the other, the combination can result in fatal complications for mother and infant. Fertility is decreased in patients with advanced liver disease and may provide a degree of protection for many patients who would be at increased risk should they become pregnant; however, pregnancy may occur even with advanced liver disease, and it is necessary to anticipate and plan for possible complications of the specific hepatic disease encountered. Counseling prior to pregnancy is the best policy, with consideration to transplantation prior to childbearing or to sterilization if it is more appropriate. Most problems associated with advanced liver disease are managed as in the nonpregnant patient; however, variceal bleeding may be a particularly difficult problem, and management here may necessitate portacaval shunt surgery.

Budd-Chiari Syndrome↗
PubMed1991

Thermal response of rat fibroblasts stably transfected with the human 70-kDa heat shock protein-encoding gene.

The major heat shock protein hsp70 is synthesized by cells of a wide variety of organisms in response to heat shock or other environmental stresses and is assumed to play an important role in protecting cells from thermal stress. We have tested this hypothesis directly by transfecting a constitutively expressed recombinant human hsp70-encoding gene into rat fibroblasts and examining the relationship between the levels of human hsp70 expressed and thermal resistance of the stably transfected rat cells. Successful transfection and expression of the gene for human hsp70 were characterized by RNA hybridization analysis, two-dimensional gel electrophoresis, and immunoblot analysis. When individual cloned cell lines were exposed to 45 degrees C and their thermal survivals were determined by colony-formation assay, we found that the expression of human hsp70 conferred heat resistance to the rat cells. These results reinforce the hypothesis that hsp70 has a protective function against thermal stress.

Animals↗
PubMed1990

Rabbit hepatocytes in primary culture: preparation, viability and use in studies of propranolol metabolism.

Isolated hepatocyte cultures have become a frequently used model system for investigating drug metabolism. Although rat and hamster hepatocytes are frequently used for this purpose, metabolism in these species differs in many respects from human metabolism. A species with a metabolism more closely resembling that of humans might be more useful. Our in vivo experiments demonstrated that the metabolism of propranolol in the rabbit is more similar to that in humans than in rats or hamsters. We therefore examined the usefulness of rabbit parenchymal liver cells for studies of propranolol metabolism. A detailed method is presented for their preparation and culture, along with data on their viability, structure and protein synthesizing capability. One- or two-day-old hepatocyte cultures were exposed to 10 mumol/L 3H-propranolol from 30 min to 2 hr; metabolites were identified by gas chromatography-mass spectrometry and quantitated by high-performance liquid chromatography. Propranolol metabolism was linear over 1 hr, with 15% of the substrate metabolized during this time. The cytochrome P-450 pathways, which result in ring oxidation and side-chain oxidation, were expressed in a reproducible fashion similar to that found in vivo in humans. The arylhydrocarbon hydroxylase inhibitor alpha-naphthoflavone (100 mumol/L) inhibited side-chain oxidation of propranolol by 90% without affecting ring oxidation. In contrast, chlorpromazine (100 mumol/L) was shown to inhibit ring oxidation of propranolol by 85% without affecting side-chain oxidation. Cimetidine (250 mumol/L) inhibited both pathways by about 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Orthotopic liver transplantation for graft-versus-host disease following bone marrow transplantation.

Chronic graft-vs.-host disease occurs in 30%-50% of long-term survivors of allogeneic bone marrow grafts, and may eventuate in cirrhosis. In this study, a young woman, originally diagnosed as having acute myelogenous leukemia, underwent successful bone marrow transplantation but later developed graft-vs.-host disease-induced cirrhosis and recurrent variceal hemorrhage. She underwent successful orthotopic liver transplant. Her postoperative course was uncomplicated, with no evidence of rejection or recurrence of graft-vs.-host disease. As bone marrow transplantation is more widely used and survival improves, the number of patients with graft-vs.-host disease or venoocclusive disease resulting in cirrhosis is likely to increase. Hepatic transplantation should be considered for bone marrow transplant patients who develop end-stage liver disease.

Adult↗