PN3 sodium channel distribution in the dorsal root ganglia of normal and neuropathic rats.
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Animals↗
Biomedical subjects
K Wong
Publications and source records attributed to K Wong.
Thiazolidinediones repress ob gene expression in rodents via activation of peroxisome proliferator-activated receptor gamma.
The ob gene product, leptin, is a signaling factor regulating body weight and energy balance. ob gene expression in rodents is increased in obesity and is regulated by feeding patterns and hormones, such as insulin and glucocorticoids. In humans with gross obesity, ob mRNA levels are higher, but other modulators of human ob expression are unknown. In view of the importance of peroxisome proliferator-activated receptor gamma (PPARgamma) in adipocyte differentiation, we analyzed whether ob gene expression is subject to regulation by factors activating PPARs. Treatment of rats with the PPARalpha activator fenofibrate did not change adipose tissue and body weight and had no significant effect on ob mRNA levels. However, administration of the thiazolidinedione BRL49653, a PPARgamma ligand, increased food intake and adipose tissue weight while reducing ob mRNA levels in rats in a dose-dependent manner. The inhibitory action of the thiazolidinedione BRL49653 on ob mRNA levels was also observed in vitro. Thiazolidinediones reduced the expression of the human ob promoter in primary adipocytes, however, in undifferentiated 3T3-L1 preadipocytes lacking endogenous PPARgamma, cotransfection of PPARgamma was required to observe the decrease. In conclusion, these data suggest that PPARgamma activators reduce ob mRNA levels through an effect of PPARgamma on the ob promoter.
Adipocytes↗
The adipocyte specific transcription factor C/EBPalpha modulates human ob gene expression.
The ob gene product, leptin, apparently exclusively expressed in adipose tissue, is a signaling factor regulating body weight homeostasis and energy balance. ob gene expression is increased in obese rodents and regulated by feeding, insulin, and glucocorticoids, which supports the concept that ob gene expression is under hormonal control, which is expected for a key factor controlling body weight homeostasis and energy balance. In humans, ob mRNA expression is increased in gross obesity; however, the effects of the above factors on human ob expression are unknown. We describe the structure of the human ob gene and initial functional analysis of its promoter. The human ob gene's three exons cover approximately 15 kb of genomic DNA. The entire coding region is contained in exons 2 and 3, which are separated by a 2-kb intron. The first small 30-bp untranslated exon is located >10.5 kb upstream of the initiator ATG codon. Three kilobases of DNA upstream of the transcription start site has been cloned and characterized. Only 217 bp of 5' sequence are required for basal adipose tissue-specific expression of the ob gene as well as enhanced expression by C/EBPalpha. Mutation of the single C/EBPalpha site in this region abolished inducibility of the promoter by C/EBPalpha in cotransfection assays. The gene structure will facilitate our analysis of ob mutations in human obesity, whereas knowledge of sequence elements and factors regulating ob gene expression should be of major importance in the prevention and treatment of obesity.
Adipocytes↗
Maintaining low HIV seroprevalence among injecting drug users.
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HIV Infections↗
C6-ceramide maintains elevated cytosolic calcium levels in activated platelets.
The effects of cell-permeable C2 and C6-ceramides on human platelet responses were investigated. In thrombin-activated platelets, C6(5-30 microM) potentiated Ca2+ mobilization and Ca2+ influx, and decreased the rate of removal of Ca2+ from cytosol. The effect of C2 was not significant. Phorbol ester or calyculin A inhibition of thrombin-induced rises in platelet [Ca2+]i was attenuated by C6. Assays show that C6 either prolonged the generation, or retarded the metabolism of inositol trisphosphates. Previous studies indicate that protein kinase C (PKC) acts in a negative feedback manner by inhibiting phosphatidylinositol breakdown, accelerating inositol trisphosphate metabolism, and increasing Ca2+ pump activity. C6 may counter these PKC effects indirectly. The synthetic ceramides inhibited platelet aggregation weakly and had no effect on pleckstrin (p47) phosphorylation. Recently we reported that C2 but not C6 inhibits superoxide generation and store-regulated Ca2+ influx in neutrophils at similar concentrations. Cellular differences in ceramide metabolism or ceramide-sensitive enzymes and their substrates may account for the disparate results.
Blood Platelets↗
Large-conductance calcium-activated potassium channels of cultured rat melanotrophs.
A large conductance, Ca(2+)-activated K+ channel of the BK type was examined in cultured pituitary melanotrophs obtained from adult male rats. In cell-attached recordings the slope conductance for the BK channel was approximately 190 pS and the probability (Po) of finding the channel in the open state at the resting membrane potential was low (< < 0.1). Channels in inside-out patches and in symmetrical 150 mM K+ had a conductance of approximately 260 pS. The lower conductance in the cell-attached recordings is provisionally attributed to an intracellular K+ concentration of approximately 113 mM. The permeability sequence, relative to K+, was K+ > Rb+ (0.87) > NH4+ (0.17) > Cs+ > or = Na+ (< or = 0.02). The slope conductance for Rb+ was much less than for K+. Neither Na+ nor Cs+ carried measurable currents and 150 mM internal Cs+ caused a flickery block of the channel. Internal tetraethylammonium ions (TEA+) produced a fast block for which the dissociation constant at 0 mV (KD(0 mV)) was 50 mM. The KD(0 mV) for external TEA+ was much lower, 0.25 mM, and the blocking reaction was slower as evidenced by flickery open channel currents. With both internal and external TEA+ the blocking reaction was bimolecular and weakly voltage dependent. External charybdotoxin (40 nM) caused a large and reversible decrease of Po. The Po was increased by depolarization and/or by increasing the concentration of internal Ca2+. In 0.1 microM Ca2+ the half-maximal Po occurred at approximately 100 mV; increasing Ca2+ to 1 microM shifted the voltage for the half-maximal Po to -75 mV. The Ca2+ dependence of the gating was approximated by a fourth power relationship suggesting the presence of four Ca2+ binding sites on the BK channel.
Animals↗
Development of an objective method for assessing viscosity of formulated foods and beverages for the dysphagic diet.
OBJECTIVE: To develop and validate a practical, economical, and objective viscosity assessment tool, the line-spread test, for foods and beverages formulated for the dysphagic diet. The line-spread test is based on the measure of product dispersion over a flat surface. DESIGN: Viscosity-altering formulations for a selection of soups and beverages commonly served to patients with dysphagia at a local hospital were developed under controlled conditions. The samples were presented to a trained sensory panel for evaluation by quantitative descriptive analysis and were measured by the line-spread test. Numeric results of the two tests were compared. SETTING: The Food Research Laboratory with private sensory booths at Mount Saint Vincent University. MAIN OUTCOME MEASURES: Results of the sensory evaluation and the line-spread test would strongly correlate, indicating predictive validity, but the line-spread test would be more reliable and show variability in measurement. STATISTICAL ANALYSES PERFORMED: Correlation, analysis of variance (ANOVA), and standard deviations (calculated from the within-group mean square error of the ANOVAs). RESULTS: ANOVA showed that both the sensory panel results and the line-spread test values indicated significant differences among the samples. Standard deviations indicated less variability in line-spread values. There was a strong positive correlation (r = .90 to .97) between the two types of results, which indicated strong predictive validity for the line-spread test. APPLICATIONS: The line-spread test is a reliable and valid tool to assess viscosity of formulated foods and beverages for the dysphagic diet and can be readily and economically adapted to any dietary department for product development and quality control.
Analysis of Variance↗
Vulnerability of paediatric myocardium to cardiac surgery.
OBJECTIVE: Myocardial injury is an important cause of mortality and morbidity after paediatric cardiac surgery. Data obtained from studies in animals imply that juvenile myocardium is more resistant to the effects of ischaemia and reperfusion than adult myocardium but there is little confirmatory evidence in the clinical setting. DESIGN: Prospective observational study of biochemical markers of myocardial injury in a paediatric population undergoing cardiac surgery. SETTING: Tertiary referral centre for paediatric cardiac surgery. PATIENTS: Forty patients undergoing paediatric cardiac surgery of varying complexity including closure of atrial and ventricular septal defects and arterial switch for simple transposition. A control group included patients undergoing thoracotomy for closure of a patent ductus arteriosus or repair of a coarctation. INTERVENTIONS: Serial measurements of myoglobin, the MB isoenzyme of creatine kinase (CK-MB), and the highly specific markers of myocardial damage cardiac troponin T (cTnT) and I (cTnI) were made before and 1, 6, 24, and 48 to 72 hours after operation. RESULTS: There were significant increases in myoglobin and CK-MB, but not cTnT or cTnI, in the control group. There were significant increases in the four biochemical markers in all the cardiac operations but especially in the ventricular septal defect and transposition group. Increases in CK-MB and cTnT were about five times greater than those previously reported in adult patients. CONCLUSIONS: (i) Cardiac troponins are more specific markers of myocardial injury in paediatric cardiac surgery than myoglobin and CK-MB. (ii) Paediatric myocardium seems to be more vulnerable to injury during cardiac surgery than adult myocardium.
Adult↗
Glioblastoma multiforme: radiologic-pathologic correlation.
Astrocytic tumors are divided into two basic categories: circumscribed (grade I) or diffuse (grades II-IV). All diffuse astrocytomas tend to progress to grade IV astrocytoma, which is synonymous with glioblastoma multiforme (GBM). GBMs are characterized by marked neovascularity, increased mitosis, greater degree of cellularity and nuclear pleomorphism, and microscopic evidence of necrosis. Several genetic abnormalities have been associated with the development of GBM: In some cases, the abnormality is inherited (e.g., Li-Fraumeni syndrome); in others, genetic alteration appears to result from mutation into an oncogene or deterioration of the tumor-suppressor gene p53. A common, distinctive histopathologic feature of GBM is pseudopalisading. The most common imaging appearance of GBM is a large heterogeneous mass in the supratentorial white matter that exerts considerable mass effect. Less frequently, GBM can occur near the dura mater or in the corpus callosum, posterior fossa, and spinal cord. GBM typically contains central areas of necrosis, has thick irregular walls, and is surrounded by extensive, vasogenic edema, but the tumor may also have thin round walls, scant edema, or a cystic appearance with a mural nodule. GBMs most commonly metastasize from their original location by direct extension along white matter tracts; however, cerebrospinal fluid, subependymal, and hematogenous spread also can occur. Given the rapidly growing body of knowledge about GBM, the radiologist's role is more important than ever in accurate and timely diagnosis.
Aged↗
Decreased receptor-mediated calcium response in prion-infected cells correlates with decreased membrane fluidity and IP3 release.
The most characteristic neuropathologic features of prion diseases are accumulation of PrPSc in the brain and vacuolation of neurons. Neuronal vacuolation suggests plasma membrane dysfunction. In an earlier study, we found that bradykinin (Bk)-stimulated Ca2+ responses in scrapie-infected ScN2a cells were reduced by 30 to 50% compared with uninfected N2a cells. In this study, we investigated the cause. The IP3 second-messenger response to Bk stimulation was reduced 90%, indicating that a defect occurs in the plasma membrane. Receptor-binding assays showed a 3- to 4-fold increase in Bk receptor numbers on ScN2a cells; however, their binding affinity was reduced 5- to 13-fold, which may account for the decreased IP3 and Ca2+ responses. These results argue that scrapie causes a more fundamental change in the properties of the plasma membrane. We verified this by fluorescence recovery after photobleaching (FRAP) analysis with a lipid probe that measures lateral membrane fluidity. A 7-fold reduction of fluidity was found. These results support the hypothesis that the conversion of PrPc to PrPSc or the accumulation of PrPSc in scrapie-infected cells alters the composition of their plasma membranes that secondarily causes the abnormal receptor-mediated function.
Animals↗
Abnormal plasma membrane properties and functions in prion-infected cell lines.
A long trail of evidence indicates that the formation of PrPSc or its accumulation causes the neuronal dysfunction and clinical features of prion diseases. The results of our current line of studies argue that the main neuropathological and clinical features of prion diseases are explained by altered ion channel function secondary to decreased plasma membrane fluidity. This kind of mechanism has the potential to functionally disconnect neuronal networks and cause neuronal vacuolation. Our laboratory is currently focusing its investigations on pathogenic mechanisms that have the potential to link the formation of PrPSc with plasma membrane abnormalities in prion diseases. In summary, the first hypothesis suggests that the conversion of PrPC to PrPSc affects plasma membrane fluidity directly, which secondarily alters the properties and functions of its components. In contrast, the second hypothesis argues that PrPSc accumulation alters the ability of chaperones to correctly fold plasma-membrane proteins during their synthesis, which directly affects the properties of nascent proteins and secondarily affects membrane fluidity. Our current investigations are attempting to determine which of these mechanisms are plausible and, then, which is primary.
Animals↗
Intracellular tyrosine residues of the human growth hormone receptor are not required for the signaling of proliferation or Jak-STAT activation.
Ligand binding and dimerization of the growth hormone (GH) receptor leads to the rapid tyrosine phosphorylation of the intracellular kinase, Jak2, to the tyrosine phosphorylation and activation of STAT protein(s) and to the tyrosine phosphorylation of the receptor itself. Expression of the human GH receptor in the mouse promyeloid, interleukin-3-dependent cell line, FDC-P1, shows that this receptor can signal ligand-dependent proliferation in these cells as well as induce the tyrosine phosphorylation of Jak2 and the activation of transcription factors. We now examine the requirement for tyrosine phosphorylation of the GH receptor for these three events by expression of a receptor without tyrosine residues in the intracellular domain. Six of the seven intracellular tyrosine residues were removed by a carboxyl-terminal truncation, and the remaining tyrosine was changed to phenylalanine to yield the GH receptor D351Stop/Y314F. When expressed in FDC-P1 cells, this receptor retained its ability to induce the tyrosine phosphorylation of Jak2, to induce the activation of transcription factors, and to signal ligand-dependent cell proliferation. Thus, tyrosine phosphorylation of the GH receptor is not essential for the signaling of these three events at least in this system. This finding contrasts with that for the interferon-gamma receptor system where data indicate that the specific tyrosine phosphorylation of the interferon-gamma receptor leads to an association with the STAT protein, p91, that is the mechanism by which ligand couples the receptor to the signal transduction system.
Amino Acid Sequence↗
N-acetylsphingosine (C2-ceramide) inhibited neutrophil superoxide formation and calcium influx.
Ceramide, a product arising from sphingomyelinase activity, has been shown to act as an intracellular second messenger in effecting growth inhibition, cellular differentiation, and apoptosis. In the present study, the relative effects of cell-permeable ceramides, N-acetylsphingosine (C2-ceramide) and N-hexanoylsphingosine (C6-ceramide), on neutrophil responses were measured. When cells were activated with fMet-Leu-Phe, C2-ceramide both potentiated (< 1 microM) and inhibited (> 1 microM) superoxide generation. C2- and C6-ceramide inhibited phorbol ester-induced superoxide release from neutrophils at IC50 values of 5 and 120 microM, respectively. C2-ceramide had no effect on semipurified protein kinase C activity. Neither ceramide affected significantly the general level of phosphorylated proteins in phorbol ester-treated cells. C2-ceramide (1-20 microM) alone did not change cytosolic free Ca2+ levels but inhibited Ca2+ and Mn2+ influx in fMet-Leu-Phe-activated neutrophils. In contrast, sphingosine enhanced Ca2+ entry; thus, ceramide conversion to sphingosine was not significant. Unlike C2-ceramide, C2-dihydroceramide failed to block superoxide generation or Ca2+ influx. Preincubation of cells with 10 nM okadaic acid reversed slightly the effects of C2-ceramide. Calyculin A, tautomycin, and much higher concentrations of okadaic acid inhibited agonist-induced Ca2+ influx. We postulate that C2-ceramide may inhibit neutrophil superoxide release by activation of type 2A protein phosphatases. Results suggest that protein phosphatase type 1 up-regulates Ca2+ entry, whereas type 2A (or a ceramide-activated subtype) forestalls Ca2+ entry by inactivating a calcium influx factor.
Alkaloids↗
Reoperative aortic valve operation after homograft root replacement: surgical options and results.
The surgical options available and the associated operative risks for repeat aortic valve replacement after free-standing homograft root replacement with reimplantation of the coronary arteries are as yet undefined. We therefore reviewed our experience with repeat aortic valve replacement between January 1976 and July 1994 and identified 22 such procedures performed on 21 patients after homograft or autograft root replacement. Reoperation was indicated for structural deterioration in 16 and for bacterial endocarditis in 6 patients. Associated procedures were undertaken in 5 patients, and 4 procedures were performed emergently. Significant calcification of the homograft wall was noted in over half of all patients. There were no coronary ostial complications. In 13 patients new valves were inserted within the previous root: 9 mechanical valves and 4 subcoronary homografts. In 9 patients the root was re-replaced. The mean cross-clamp time was 85 (+/- 20) minutes and mean cardiopulmonary bypass time was 123 (+/- 32) minutes. There were no early deaths and 5 late deaths. Two patients required reoperation for bleeding and 2 experienced low cardiac output syndromes postoperatively. Univariate analysis failed to identify any variables predictive of outcome. We conclude that repeat aortic valve replacement after homograft root replacement, even in the presence of significant calcification, can be undertaken with an acceptable operative risk and should not be delayed until irreversible ventricular dysfunction has occurred. The same options available at initial valve replacement may be employed at reoperation, although extensive calcification mandates repeat root replacement.
Adolescent↗
Early experience with the Toronto stentless porcine valve.
Stentless porcine valves in the aortic position offer many theoretic advantages, but their clinical performance has not been adequately defined. We evaluated the clinical and echocardiographic results of 103 patients who had aortic valve replacement with the Toronto stentless porcine valve over a 2-year period. There were 67 men with a mean age of 68 years. The predominant native valve lesion was aortic stenosis (64%), and 4 patients had prosthetic valve dysfunction. Forty-two patients had concomitant procedures. The 30-day mortality rate was 3.3% (n = 2) for isolated valve replacement and 5.8% (n = 6) for the series. The sole determinant of early death was poor left ventricular function. There were three late deaths due to non-valve-related complications over a median follow-up of 11.87 months. In addition, prosthetic valve endocarditis developed in 1 patient, necessitating a homograft valve replacement at 6 weeks. Doppler echocardiography performed at 3 to 6 months showed low peak and mean transvalvular gradients, with no substantial change at 1 year. None of the patients showed signs of clinically significant aortic regurgitation, although echocardiography demonstrated trivial or mild regurgitation in 12 patients at discharge or early follow-up, which was less marked or absent at 1 year. We conclude that the Toronto stentless porcine valve appears to offer promising early results.
Adult↗
The incidence and spectrum of neurological injury after open fetal surgery.
A preterm infant's immature brain is susceptible to both anoxic and hemorrhagic injury during periods of physiological stress. The advent of in utero surgery has created a new population of premature patients at risk for central nervous system (CNS) injury. The aim of this study was to evaluate the frequency and nature of CNS injuries in fetal surgical patients. Of 33 fetuses with known neurological outcome after fetal surgery, CNS injuries were identified in seven (21%). Of the seven, four had significant episodes of fetal bradycardia (3) or neonatal hypotension (1), which suggests that asphyxia contributed to the neurological injury. The CNS injuries in the other three patients occurred unexpectedly and without associated signs of fetal distress. The authors speculate that these injuries may have been caused by sudden fluxes in cerebral blood flow, induced by maternal hypoxia (1) or by maternally administered tocolytic drugs (2) used to treat postoperative preterm labor.
Bradycardia↗
Role of covered esophageal stents in malignant esophagorespiratory fistula.
Malignant esophagorespiratory fistulas are distressing for patients who already have a limited prognosis. Palliative treatment by surgical bypass is often unjustified, and although the use of esophageal stents is more appropriate, their results are variable due to their inability to provide a tight seal. We have managed 2 patients with self-expanding covered esophageal stents, which appear to offer excellent prospects for palliation.
Aged↗
Infection with Chlamydia trachomatis lymphogranuloma venereum serovar L1 in homosexual men with proctitis: molecular analysis of an unusual case cluster.
Among 767 rectal isolates of Chlamydia trachomatis obtained from men over the period 1981-1991, 7 were found to be a rare lymphogranuloma venereum serovar, L1. These isolates were from rectal specimens taken from five male patients in 1982-1983. Six of the seven isolates were available for DNA sequencing studies. All six of these isolates shared the same DNA sequence in the major outer membrane protein (MOMP) gene variable domains and had different MOMP sequences than did the prototype L1, L2, and L3 strains, suggesting a point source outbreak. All five patients infected with serovar L-1 were homosexual men who had symptomatic proctitis characterized by rectal pain, discharge, tenesmus, abnormalities seen on anoscopy, and leukocytes seen on gram stains of rectal specimens. We conclude that an unrecognized point source outbreak of the rare chlamydial L1 serovar occurred among homosexual men in Seattle in 1982-1983, and that the clinical manifestations of L1 infection may be less severe than those of L2 infections.
Adult↗