Energy metabolism following reduction of renal mass.
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Adenosine Triphosphate↗
Biomedical subjects
L Chan
Publications and source records attributed to L Chan.
Recent advances in lipoprotein and atherosclerosis research at Baylor College of Medicine. Apolipoprotein B, lipoprotein[a], and transplantation arteriopathy.
A multidisciplinary team approach with focused objectives characterizes research at Baylor College of Medicine into the causes, prevention, and treatment of atherosclerotic disease. Current clinical activities range from programs to modify lifestyle for the primary prevention of coronary artery disease to a large, angiographically monitored lipid-lowering trial. In basic research, much attention has been focused on the plasma lipoproteins and their roles in atherogenesis. The current review highlights recent advances in ongoing basic research involving 1) apolipoprotein (apo) B, whose form apo B-100 serves as a ligand for the low-density lipoprotein receptor; 2) lipoprotein[a], elevated plasma levels of which are predictive of atherosclerotic disease; and 3) transplantation arteriopathy, which impedes long-term survival of cardiac transplant recipients.
Amino Acid Sequence↗
Blood cholinesterase levels in a group of Malaysian blood donors.
Data on blood cholinesterase levels in the Malaysian population is lacking. The spectrophotometric method of Ellman was used to determine the red cell, plasma and whole blood cholinesterase (ChE) levels in 407 Malaysian blood donors. The mean+1SD for plasma ChE in females (n = 48) was 2.37 + 0.70 umol/min/ml and 2.76 + 0.75 umol/min/ml in males (n = 359). The mean plasma ChE in males was higher than in females (p < 0.001). The mean+1SD for red cell ChE in females was 9.01 + 1.20 umol/min/ml whereas in males it was 7.69 +1.30 umol/min/ml (the mean red cell ChE in females was higher than in males, p < 0.0001). The mean+1SD for whole blood ChE for females was 4.31+ 0.58 umol/min/ml and for males it was 4.95 + 0.71 umol/min/ml. The mean whole blood ChE in males was higher than in females (p < 0.0001). Sex influenced the plasma, red cell and whole blood ChE. In males the plasma ChE was affected by the race factor. The mean+1SD plasma ChE for the Malay, Chinese and Indian were 2.92 + 0.80, 2.73 + 0.71 and 2.61+ 0.73 respectively (p < 0.002). The age factor in males affected the red cell ChE with 7.88 + 1.32 in the (30-69) age group and 7.47 + 1.23 in the (15-29) age group (p < 0.005). The whole blood ChE in females was affected by blood groups. The mean+1SD whole blood ChE for blood groups A,B and O were 4.19 + 0.42, 3.93 + 0.46 and 4.49 + 0.62 respectively (p < 0.03). The significant difference is between the ChE of group B and O, but the ChE of group A could not be determined to be different from group B or O. These results serve as guidelines for our local population in the evaluation of cholinesterase levels with regard to pesticide poisoning, liver biosynthetic capacity and unusual sensitivity to succinylcholine.
Adolescent↗
RNA editing: exploring one mode with apolipoprotein B mRNA.
RNA editing is a newly described genetic phenomenon. It encompasses widely different molecular mechanisms and events. According to the specific RNA modification, RNA editing can be broadly classified into six major types. Type II RNA editing occurs in plants and mammals; it consists predominantly in cytidine to uridine conversions resulting from deamination/transamination or transglycosylation, although in plants other mechanisms have not been excluded. Apolipoprotein B mRNA editing is the only well-documented editing phenomenon in mammals. It is an intranuclear event that occurs posttranscriptionally, coincident with splicing and polyadenylation. Recent observations indicate that the tissue- and sequence-specific process is mediated by an enzyme that has separate domains for editing and sequence recognition. The presence of apolipoprotein B mRNA editing activity in tissues that do not produce the protein suggests that other RNAs may be edited and RNA editing may be a genetic phenomenon of general biological importance to the cell.
APOBEC-1 Deaminase↗
Effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on the androgen-induced growth of the lateral prostate of the prepubertally castrated guinea pig.
The aim of this study was to examine the effects of beta-D-xyloside (XYL), a compound which interferes with stromal proteoglycan (PG) synthesis, on androgen induced growth of the lateral prostate (LP). Young male guinea pigs were castrated at 3 weeks of age and divided into three groups 6 weeks after castration. In group one, the animals were injected subcutaneously daily with 80 mg/kg of XYL, followed 3 days later by a daily dose of 10 mg/kg of dihydrotestosterone (DHT) for 2 more weeks. The second group served as control and received DHT only. In the third group, animals were treated first with XYL, like those in group one, and then followed by DHT alone for 2 weeks to check reversibility of the XYL effect. At the end of the experiment, the lateral prostate was removed and processed for morphological and cytochemical examination. The results showed that XYL inhibited the DHT stimulated growth of the lateral prostate. The fibroblasts showed a dilated granular endoplasmic reticulum filled with granular substances. In the interstitial spaces, there was a drastic increase in Cuprolinic Blue (CB) positive filaments and polygonal granules believed to be PGs or glycosaminoglycans (GAGs). Their number was much greater than the control. The distribution and density of the collagen fibers appeared similar to the control. The secretory alveoli were lined by epithelium with few secretory granules of low electron density and a larger number of clear vesicles. There was a slight reduction in glycoconjugate reactivities in the epithelial cells. The lectin binding patterns and the structural features were comparable between the control and recovery groups, indicating the XYL effects were reversible. The results suggest that stromal PG biosynthesis may play a role in epithelial function and an altered stromal matrix would hamper the effects of DHT on the target organ.
Animals↗
Isotypic and IgG subclass restriction of the humoral immune responses to human T-lymphotropic virus type-I.
We have investigated the isotypic and IgG subclass profile of the antibody response to HTLV-I structural proteins (gag and env) in patients with HTLV-I-associated myelopathy (HAM; n = 20), adult T-cell leukemia (ATL; n = 15), and HTLV-I-positive asymptomatic carriers (ASY; n = 21). IgG, IgM, and IgA were the predominant antibody responses in all HTLV-I-infected individuals; minimal IgE response was detectable in the HAM and ATL groups. Among the IgG subclasses, IgG1 was the most predominant antibody detected in responses to HTLV-I antigens, followed by IgG3 and IgG2; IgG4 could not be detected in any patient group. Levels of both IgG1 and IgG3 were significantly higher in patients with HAM, when compared to ATL and ASY (P < 0.01 for both comparisons). In addition, Ig isotypes and IgG subclass antibody in patient sera reactive with purified viral proteins and several immunodominant epitopes, represented by synthetic peptides, Gag-1a102-117, Env-1(191-214), Env-5(242-257), and recombinant proteins, MTA-1(162-209) and r21e303-440, were examined to delineate specific epitopes responsible for inducing the host immune responses of each isotype and subclass to the structural proteins of HTLV-I. IgG, IgM, and IgA responses were directed against both the gag and env gene products. Among IgG subclasses, the IgG1 and IgG3 responses were directed against both the gag (p53, p24, p19, and Gag-1a) and env (recombinant MTA-1, r21e, and synthetic Env-1, Env-5) proteins; IgG2 responses were mainly restricted to gag proteins. The frequency profile of HTLV-I-specific antigen recognition in all four IgG subclasses were similar in all of the clinical groups. These results further define the fine specificity of anti-HTLV-I immune reaction for understanding the mechanism of pathogenesis in these individuals and suggest that factors other than the humoral immune responses may be associated with the clinical manifestation of the disease.
Amino Acid Sequence↗
Reference accuracy in the emergency medicine literature.
STUDY OBJECTIVE: To determine the incidence and nature of errors in the citation and quotation of references contained in the emergency medicine literature. DESIGN: A retrospective analysis of a random sample of articles and references found in the three major emergency medicine journals. SETTING: A university/county hospital. METHODS: We examined single issues of three emergency medicine journals: Annals of Emergency Medicine, Journal of Emergency Medicine, and American Journal of Emergency Medicine. INTERVENTIONS: None. MEASUREMENTS: Four independent reviewers assessed 145 references from 46 referring authors for citational and quotational accuracy. MAIN RESULTS: Major and minor citation errors were found in 10.3% and 17.2% of reference listings, respectively. Qualitative quotational errors were found in 35.2% of references. Eighty-two percent of these errors were considered to be major. Quantitative quotational errors were found in 47% of references reviewed. Secondary rather than primary reference sources were used in 41.4% of references reviewed. CONCLUSION: This study demonstrates a substantial error rate in the citation and quotation of reference sources in the emergency medicine literature. In addition, verification of primary source material was not done by a large percentage of the authors reviewed. Recommendations for improving the accuracy of the emergency medicine literature are offered.
Bias↗
Epidemic meningococcemia and purpura fulminans with induced protein C deficiency.
Patients with epidemic infections caused by Neisseria meningitidis serogroup C were studied to assess the relationship of abnormal coagulation parameters to prognosis. Patients were categorized into stages within the first hour of observation according to severity of illness. During the epidemic years 1986 through 1991, 113 patients with bacteriologically proven N. meningitidis infection were observed, 15 of whom died. Purpura fulminans was seen in 28 patients, of whom 14 (50%) died. Among the 14 surviving patients who had purpura fulminans, 10 suffered gangrene with deforming autoamputation secondary to the dermal microvascular thrombosis and hemorrhagic necrosis. Evaluation of the induced diffuse intravascular coagulation in 59 patients included studies of the naturally occurring anticoagulants, focusing on protein C and protein S. The magnitude of the declining levels of protein C, the degree of thrombocytopenia, and the presence of fibrin split products are directly related to the clinical severity of the illness (P = .0053). Thus, in individuals with severe disease expression, the risk of purpura fulminans with death or deformity was significantly increased when the platelet count was < 50,000 cells/mm3 (P = .0001) and protein C levels were low (P = .0158). The immaturity of the protein C system in children who are < 4 years of age may contribute to the rapid and more frequent pathogenesis of purpura fulminans. Therapy directed at replacement of the naturally occurring anticoagulants, such as protein C, may ultimately improve the prognosis for individuals with purpura fulminans.
Adolescent↗
Evaluation of an immunoblot assay for serological confirmation and differentiation of human T-cell lymphotropic virus types I and II.
The confirmation of infection with human T-cell lymphotropic virus type I (HTLV-I) and type II (HTLV-II) currently involves multiple assays. These include Western blot (immunoblot) (WB) and/or radioimmunoprecipitation assay for detection of antibodies to HTLV-specific viral proteins and polymerase chain reaction and/or peptide-based enzyme immunoassays for differentiating between the two viruses. We undertook an evaluation of a modified WB assay that includes native HTLV-I viral proteins from MT-2 cells spiked with an HTLV-I transmembrane glycoprotein (recombinant p21e) and the HTLV-I- and HTLV-II-specific recombinant proteins MTA-1 and K55. The test panel consisted of well-characterized sera from U.S. blood donors, American Indians, intravenous drug users, and patients seen in sexually transmitted disease clinics. Of 158 HTLV-I/II-seropositive serum specimens tested, 156 (98.7%) were confirmed and typed as HTLV-I or HTLV-II. Of 82 HTLV-I/II-seroindeterminate or -seronegative serum specimens, only 1 was classified as HTLV-II positive: the sample had weak gag p19 and strong gag p24 and env p21e reactivity and was radioimmunoprecipitation assay negative for env gp61/68 but polymerase chain reaction positive for HTLV-II. The specificity of the modified WB for confirming and typing serum samples was therefore 100%. We conclude that this WB assay is useful for confirming and typing HTLV infection and can help simplify HTLV-I/II testing algorithms.
Blotting, Western↗
Functional role of N-linked glycosylation in human hepatic lipase: asparagine-56 is important for both enzyme activity and secretion.
Hepatic lipase (HL) and lipoprotein lipase (LPL) are evolutionarily related enzymes that are essential for normal lipoprotein metabolism. While much has been published on the structure-function relationship of LPL, little is known concerning the structural basis of HL action and secretion. Human HL is a glycoprotein and its predicted amino acid sequence contains four putative N-linked glycosylation sites at Asn residues 20, 56, 340, and 375. We studied the role of these residues in the secretion and catalytic activity of hHL by analysis of hHL expressed in stable CHO cell lines. Using site-specific mutagenesis, the wild-type human HL and substitution mutants of each of the four Asn residues were expressed in vitro. The relative sizes of these site-specific mutants indicate that all four putative sites are utilized for glycosylation in CHO cells. Abolition of N-linked glycosylation of three (residues 20, 340, and 375) of the four sites did not affect enzyme secretion or activity. Mutations of Asn-56 to either Gln or Ala resulted in the production of a totally inactive HL which accumulated intracellularly but was not secreted into the culture medium. Therefore, Asn-56 is required for both HL enzyme activity and secretion. The fact that the homologous N-linked glycosylation site (Asn-43) is required for both enzyme activity and secretion for human LPL (Semenkovich et al. 1990. J. Biol. Chem. 265: 5429-5433) indicates that carbohydrate chains at this site are essential for the active conformation and correct folding for secretion of these evolutionarily related lipases. Our observations provide insight into the structural basis of lipase action and secretion.
Animals↗
Regulation of hepatic triglyceride lipase by thyroid hormone in HepG2 cells.
Hypothyroidism has been reported to be associated with reduced hepatic triglyceride lipase (HTGL) activity. In order to understand the molecular mechanism by which thyroid hormone regulates HTGL activity, effects of triiodothyronine (T3) on HTGL activity, mRNA level, transcription run-on activity, and protein synthetic rate were studied in HepG2 cells. HepG2 cells treated with 1 nM T3 showed an increase in HTGL activity that was first detected at 24 h; HTGL activity continued to increase at 36 h and stayed at the elevated level at 48 and 60 h. At maximal stimulation (48 h), T3-treated cells had the following HTGL activities: 155% in spontaneously released (SR) and 224% in heparin-releasable (HR) HTGL activities (mean levels compared to control). Stimulation of HTGL activity by T3 was dose-dependent and saturable. There was, however, no change in HTGL mRNA level throughout the course of T3 treatment. The effects of T3 were reduced when transcription was blocked by actinomycin D (mean level compared to actinomycin D treatment in the absence of T3: 109% in SR and 127% in HR activities) or translation was blocked by cycloheximide (127% in SR and 122% in HR activities), but HTGL activities were still significantly higher than control. Nuclear run-on assays indicate that T3 did not change the rate of transcription of the HTGL gene. We further determined the rate of HTGL synthesis by measuring the amount of [35S]methionine incorporated into newly synthesized HTGL immunoprecipitated by a monospecific anti-human HTGL antibody. We found that the T3-stimulated increase in HTGL activity was not accompanied by any change in the rate of HTGL biosynthesis. Our experimental data indicate that the T3 stimulation of HTGL activity in HepG2 cells is mediated at posttranscriptional and posttranslational levels. The partial but significant inhibition of the T3 stimulation of HTGL activity by actinomycin D and cycloheximide suggests that the effects of T3 may be mediated by other cellular processes that are more directly regulated by the hormone. This study represents the initial report on the mechanism of HTGL activation by physiological concentrations of thyroid hormone.
Base Sequence↗
Endotoxin-induced hypertriglyceridemia is mediated by suppression of lipoprotein lipase at a post-transcriptional level.
Previous studies have demonstrated that endotoxin/lipopolysaccharide treatment causes a decrease in adipose tissue and heart lipoprotein lipase (LPL) activities in rats, producing hypertriglyceridemia in these animals. To examine the mechanisms for this effect of endotoxin, we studied the effects of endotoxin administration on LPL mRNA, and LPL synthetic rates and activity in rat adipose tissue and heart. Endotoxin treatment (i.p., 3 mg/100 g body weight or higher doses) produced a pronounced increase in serum triglycerides associated with a 65% decrease in adipose tissue and heart LPL activities within 7 h. Fast protein liquid chromatography (FPLC), used to separate lipoproteins in rat serum, showed that the increase in triglyceride was all in the very low density lipoprotein fraction which was accompanied by a concomitant decrease in high density lipoprotein. In contrast, there was no change in adipose tissue or heart LPL mRNA up to 24 h after treatment and no change in adipose tissue LPL synthetic rate, as measured by L-[35S]methionine incorporation and immunoprecipitation. Plasma insulin levels remained unchanged. The results indicate that endotoxin-induced hypertriglyceridemia in rats can be attributed to an impaired triglyceride clearance associated with a decrease of LPL activity mediated at a post-transcriptional level.
Adipose Tissue↗
Apolipoprotein B, the major protein component of triglyceride-rich and low density lipoproteins.
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Amino Acid Sequence↗
Transgenic mice expressing full-length human apolipoprotein B-100. Full-length human apolipoprotein B mRNA is essentially not edited in mouse intestine or liver.
Apolipoprotein (apo) B-100 mRNA is edited in the small intestine (in all mammals examined) and the liver (in mice and rats only) to produce apoB-48 mRNA. ApoB mRNA editing involves a C-->U conversion of the first base of the codon CAA for Gln-2153 in apoB-100, changing it to an in-frame stop codon (UAA). The edited mRNA encodes apoB-48, which is colinear with the N-terminal 48% of apoB-100. ApoB mRNA editing can be reproduced in vitro using cellular extracts from one species to edit synthetic apoB mRNA sequences from a different species. Editing of transcripts from transfected genes also appears not to be species-specific. We have produced transgenic mice that express full-length human apoB-100 mRNA at high levels in the liver and small intestine. Human apoB-100 (a 550-kDa protein) but not apoB-48 (a 260-kDa protein) is detected in total plasma (at approximately 22 mg/dl) and in very low density and low density lipoproteins. The endogenous mouse plasma apoB concentration is reduced by approximately 45% in the transgenic animals. Thus, the transgenic mice form an animal model for familial hyperapolipoprotein B, an inherited form of hyperlipidemia. To our surprise, we found that the full-length human apoB mRNA consists of > 99% apoB-100 mRNA in both the liver and small intestine; < 1% of edited (apoB-48) mRNA was detected. The proportions of endogenous mouse apoB-48 (edited) mRNA (60 and 90% in the liver and small intestine, respectively) were identical in transgenic mice and their nontransgenic littermates. Therefore, full-length human apoB mRNA is resistant to editing by the mouse editing enzyme in vivo; the unchanged proportion of endogenous mouse apoB-48 mRNA in the transgenic mice suggests that the human mRNA competes poorly with the mouse sequence for interacting with the editing enzyme. This observation has implications for the sequence specificity and mechanism of RNA editing. Furthermore, we should exercise caution in the interpretation of in vitro RNA-editing experiments.
Animals↗
Functional topology of a surface loop shielding the catalytic center in lipoprotein lipase.
Lipoprotein lipase (LPL), hepatic lipase, and pancreatic lipase show high sequence homology to one another. The crystal structure of pancreatic lipase suggests that it contains a trypsin-like Asp-His-Ser catalytic triad at the active center, which is shielded by a disulfide bridge-bounded surface loop that must be repositioned before the substrate can gain access to the catalytic residues. By sequence alignment, the homologous catalytic triad in LPL corresponds to Asp156-His241-Ser132, absolutely conserved residues, and the homologous surface loop to residues 217-238, a poorly conserved region. To verify these assignments, we expressed in vitro wild-type LPL and mutant LPLs having single amino acid mutations involving residue Asp156 (to His, Ser, Asn, Ala, Glu, or Gly), His241 (to Asn, Ala, Arg, Gln, or Trp), or Ser132 (to Gly, Ala, Thu, or Asp) individually. All 15 mutant LPLs were totally devoid of enzyme activity, while wild-type LPL and other mutant LPLs containing substitutions in other positions were fully active. We further replaced the 22-residue LPL loop which shields the catalytic center either partially (replacing 6 of 22 residues) or completely with the corresponding hepatic lipase loop. The partial loop-replacement chimeric LPL was found to be fully active, and the complete loop-replacement mutant had approximately 60% activity, although the primary sequence of the hepatic lipase loop is quite different. In contrast, replacement with the pancreatic lipase loop completely inactivated the enzyme. Our results are consistent with Asp156-His241-Ser132 being the catalytic triad in lipoprotein lipase.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Sequence↗
Polysaccharide encapsulated bacterial infection in sickle cell anemia: a thirty year epidemiologic experience.
Annual age-specific incidence rates of Streptococcus pneumoniae or Haemophilus influenzae bacterial septicemia in sickle cell anemia (SS) were determined for the years of 1957 through 1989. Forty-nine patients had 64 episodes of septicemia among a population of 786 SS patients observed for 8,138 person-years. Peak frequency of infection occurred between 1968-1971 and 1975-1981 with a conspicuous absence of episodes in 1972, 1973, 1982-1984, and 1986-1987, thus demonstrating cycles of high and low attack rates. The annual age-specific incidence rate of septicemia varied from 64.5 (1965) to 421.1 (1980) per 1,000 person-years for those under 2 years of age and never exceeded 10.2 per 1,000 in those over 4 years of age. Following the introduction of pneumococcal polyvalent vaccine in 1978, incidence of infection decreased in SS children greater than 2 years of age. No modification of the risk of infection was observed in immunized children less than 2 years of age. During these three decades, there has been a ten-fold increase in the number of SS adults over 20 years of age. The relative risk of chronic sickle complications comparing the survivors of septicemia to the non-infected patients was: subsequent death 1.76, retinopathy 4.06, avascular necrosis 1.95, symptomatic cholelithiasis 1.33, stroke 1.30, and priapism 1.26. These data suggest that prognosis for lifetime severe SS is initially manifested as an increased risk of septicemia during childhood.
Adolescent↗
Differential regulation of hepatic apolipoprotein A-I and A-II gene expression by thyroid hormone in rat liver.
Apolipoproteins A-I and A-II (apo A-I, apo A-II) are major protein components of high density lipoproteins. Thyroid hormone has a differential effect on the expression of the apo A-I and apo A-II genes in rat liver. Apo A-I gene expression is stimulated by thyroid hormone, whereas apo A-II mRNA abundance is decreased in chronic hyperthyroidism. To determine the regulatory steps involved in this differential effect of thyroid hormone on hepatic apo A-I and apo A-II gene expression, we studied the effect of short term and chronic hyperthyroidism on apo A-I and apo A-II gene transcription rates, nuclear RNA abundance and total cellular mRNA levels. After a single receptor saturating dose of L-triiodothyronine (T3) apo A-II gene transcription was transiently increased to 164% +/- 13% of basal values (P < 0.05) without affecting nuclear apo A-II RNA abundance. Apo A-I gene transcription, however, increased to 158% +/- 8% of baseline levels (P < 0.05) and remained elevated for at least 24 h. Nuclear and total cellular apo A-I mRNA increased more than expected from the increased transcription rate suggesting nuclear RNA stabilization and/or more efficient processing of the primary transcripts. In chronic hyperthyroidism, total cellular apo A-II mRNA abundance decreased to 62% +/- 18% (P < 0.05) and apo A-II gene transcription and apo A-II nuclear RNA were moderately reduced. By contrast, apo A-I nuclear and total cellular RNA were increased several fold by post-transcriptional mechanisms, whereas apo A-I gene transcription was drastically decreased. We conclude that the apo A-I and apo A-II genes in rat liver respond differently to both acute and chronic hyperthyroidism and that their expression is regulated at transcriptional and posttranscriptional levels.
Animals↗
Allele frequency distribution of the (TG)n(AG)m microsatellite in the apolipoprotein C-II gene.
The dinucleotide (TG)n interspersed repetitive sequences are the most abundant microsatellites in the human genome. Using the polymerase chain reaction to amplify a (TG)n(AG)m microsatellite in the first intron of the apo C-II gene, we have detected 15 different alleles in 242 unrelated individuals of French ancestry. The heterozygosity index was 0.85 and codominant Mendelian inheritance of the alleles was observed in individuals from 121 nuclear families. We report that polymorphism at this locus is attributable to length variation at both (TG)n and (AG)m motifs, although the (AG)m motif contains only two alleles differing by one repeat unit. A quadrimodal allele frequency distribution was observed at the (TG)n(AG)m locus. Each of the first three modes comprises one frequent allele and one very rare allele adjacent in size. No alleles of intermediate size were found between the three first modes. The fourth mode encompasses nine alleles that span from 27 to 35 repeat units. We suggest that this distribution reflects the molecular mechanisms by which alleles give rise to one another.
Alleles↗