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Biomedical subjects

F Chan

Publications and source records attributed to F Chan.

At least 37 records · Page 2Linked to original sources
PubMed1997

Insulin-like growth factor-I in men with idiopathic osteoporosis.

The etiology of osteoporosis in most men without a history of alcohol abuse, hypogonadism, or glucocorticoid excess is unknown. Several histomorphometric reports have demonstrated a reduction in indices of bone formation. We tested the hypothesis that the putative reduction in bone formation in men with idiopathic osteoporosis may be related to deficiencies in skeletal mechanisms that are mediated by insulin-like growth factor I (IGF-I). Twenty-four middle-aged men (50.5 +/- 1.9 yr) with severe idiopathic osteoporosis (mean lumbar spine T-score -3.5 +/- 0.16) were studied. The following biochemical indices were all normal: serum calcium, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, testosterone, osteocalcin, carboxyterminal propeptide of type I collagen, bone specific alkaline phosphatase, urinary calcium, and collagen crosslinks. Parathyroid hormone level was in the lower range of normal, 25 +/- 2 pg/mL (nl: 10-65). Mean serum IGF-I level was also in the lower range of normal, 157.9 +/- 7.6 ng/mL (normal age-matched range, 140-260 ng/mL). Eight men had IGF-I levels that were below 140 ng/mL. The mean IGF-IZ score was -0.75, significantly different from the expected mean of zero (P = 0.0002). IGF-I was correlated negatively with age (r = -0.49, P < 0.02). With age held constant, serum IGF-I accounted for 15% of the variance in lumbar bone mineral density (BMD; P < 0.001). The osteocalcin concentration correlated well with bone density at the distal 1/3 radius (r = +0.44; P < 0.002). Histomorphometric analysis of bone biopsy specimens showed significant reductions in cancellous bone volume (31%; P < 0.001), cortical width (28%; P < 0.05), osteoid surface (33%; P < 0.01), and bone formation rate (54%; P < 0.01) when results were compared with age-matched control subjects. Percent eroded surface was normal and was correlated inversely with serum IGF-I levels (r = -0.5; P < 0.04). These results suggest that serum IGF-I levels are reduced in men with idiopathic osteoporosis and that IGF-I correlates with and may contribute to the reduction in lumbar spine bone mass density (BMD). The low IGF-I levels may reflect the reduction in bone formation demonstrated by histomorphometry. Insights into the etiology of idiopathic osteoporosis in men may be revealed by further studies of the IGF-I axis.

Adult↗
PubMed1996

Prevalence of Dientamoeba fragilis antibodies in children and recognition of a 39 kDa immunodominant protein antigen of the organism.

Dientamoeba fragilis, a common intestinal protozoan parasite in Canada, has been associated with diarrhoea and abdominal pain in some patients. Seroprevalence of this organism has not been reported previously. In the present study sera from three symptomatic patients, 12 age- and sex-matched controls, and 189 randomly selected healthy individuals (age 6 months to 19 years) were tested for antibodies against Dientamoeba fragilis by an indirect immunofluorescence (IIF) assay. All three symptomatic patients infected with Dientamoeba fragilis had positive IIF titres of 80, and all 12 matched controls had positive titres ranging 20 to 160 (geometric mean titre 48). Of the 189 healthy children, 172 (91%) were positive at a serum dilution of 1:10 or higher. The specificity of the IIF assay was reinforced by immunoblotting 20 representative serum samples against Dientamoeba fragilis. In all 17 IIF-positive serum samples, a 39 kDa protein band of Dientamoeba fragilis was identified, the same band recognized by a mouse monoclonal antibody raised in our laboratory. Findings over a five-year period indicate that Dientamoeba fra-gilis was the most common protozoan, followed closely by Giardia lamblia and more distantly by Cryptosporidium parvum. The high seropositivity of 91% for Dientamoeba fragilis compares reasonably well with serologic data obtained by IIF and reported previously for Giardia lamblia (85.6%) and Cryptosporidium parvum (86%).

Adolescent↗
PubMed1996

Total and functional antibody response to a quadrivalent meningococcal polysaccharide vaccine among children.

OBJECTIVE: To determine total and functional serogroup C antibody response after vaccination with a quadrivalent meningococcal polysaccharide vaccine. DESIGN: Prospective, before and after intervention study. SUBJECTS: Study subjects were between the ages of 0.5 and 19.9 years, and were eligible for a community-wide public health immunization campaign against Neisseria meningitidis serogroup C. METHODS: Total and functional antibody response was measured by enzyme-linked immunosorbent assay and bactericidal assay, respectively. RESULTS: One month after vaccination, total capsular polysaccharide antibody significantly increased in all age groups; a significant rise in bactericidal antibody, that correlated with total capsular polysaccharide antibody, was seen in children 18 months of age and older. At 1 year bactericidal antibody titers were maintained but capsular polysaccharide antibody declined substantially in children younger than 5 years. CONCLUSION: Total capsular polysaccharide antibody concentration appears to be a useful surrogate measure of bactericidal antibody in children 18 months and older. Children who originally received the vaccine at less than 18 months of age should be considered for revaccination if there is a new or continuing risk of disease. Because of the differences in the total and bactericidal antibodies formed, vaccine efficacy trials are required to define which serologic measures are associated with protection.

Adolescent↗
PubMed1996

An assessment of the validity of ICD Code 410 to identify hospital admissions for myocardial infarction: The Corpus Christi Heart Project.

BACKGROUND: The identification of myocardial infarction (MI) is typically based on finding events designated by a nosologist with the appropriate International Classification of Diseases (ICD) code, currently code 410. These codes are applied based on review of medical records or death certificates. However, other factors, including reimbursement considerations, may influence the coding process, especially for hospitalizations. Thus, the validity of using ICD code 410 to identify MI must be assessed. METHODS: The Corpus Christi Heart Project (CCHP) is a population-based surveillance programme for hospitalized MI. Patients were identified using concurrent ascertainment in coronary care units and retrospective review of medical records. Events were validated as definite or possible MI using data regarding chest pain, electrocardiographic changes and cardiac enzymes. The validity of using ICD code 410 to identify cases of MI was assessed by calculating the sensitivity, specificity, predictive values and efficiency of ICD code 410 versus the CCHP 'gold standard'. RESULTS: Use of ICD code 410 identified 80.9% (401/496) of definite MI, but only 19.0% (243/1280) of possible MI. Only 12.3% (90/734) of discharges with an ICD 410 code received a 'no MI' designation based on the 'gold standard'. The efficiency of ICD code 410 for identifying MI was 92.0% for definite MI and 77.1% for definite and possible MI. CONCLUSIONS: The use of ICD code 410 to identify hospitalized cases of MI results in a modestly biased overestimate of the number of definite MI hospitalizations; however, this approach warrants consideration due to the expense of validation procedures.

Adult↗
PubMed1995

Esters of 3-pyridylacetic acid that combine potent inhibition of 17 alpha-hydroxylase/C17,20-lyase (cytochrome P45017 alpha) with resistance to esterase hydrolysis.

Esters of 3- and 4-pyridylacetic acid have been prepared and tested for inhibitory activity toward the human testicular 17 alpha-hydroxylase/C17,20-lyase and human placental aromatase enzymes. The structural features required for optimal inhibition of the hydroxylase/lyase enzyme were a 3-pyridine ring, methyl substitution alpha to the carbonyl group, and a bulky alkoxycarbonyl substituent. The compounds with the greatest selectivity were isopinocampheyl 2-methyl-2-(3-pyridyl)propanoate, 9, 1-adamantyl 2-methyl-2-(3-pyridyl)propanoate, 12, and 2-methyl-2-adamantyl 2-methyl-2-(3-pyridyl)propanoate, 14, which, while inhibiting the aromatase activity with IC50 values of 30, 35, and 40 microM, respectively, exhibited IC50 values toward hydroxylase/lyase of between 13 and 90 nM. For comparison, ketoconazole gave an IC50 value of 15 microM against aromatase and values of 65 and 26 nM for inhibition of the hydroxylase and lyase activities, respectively. Some of the structural features required for enzyme inhibition also conferred resistance to esterase hydrolysis, in vitro using rat liver microsomes as a source of the esterase activity. Therefore these esters are lead compounds in the development of inhibitors of androgen biosynthesis for the treatment of hormone-dependent prostatic cancer.

Adamantane↗
PubMed1995

Structural deterioration in Carpentier-Edwards standard and supraannular porcine bioprostheses.

The Carpentier-Edwards standard (CE-S) porcine bioprosthesis was implanted in 1214 operations (1975 to 1985) and the Carpentier-Edwards supraannular (CE-SAV) bioprosthesis was implanted in 2,489 operations (1982 to 1992 inclusive). The early mortality was 7.6% and 7.4% for the CE-S and CE-SAV groups, respectively; the late mortality was 5.3% per patient-year and 4.9% per patient-year, respectively. The cumulative follow-up was 9,968 patient-years for the CE-S group and 12,784 patient-years for the CE-SAV group. Concomitant procedures were performed in 26.8% of the patients who received a CE-S and in 40.9% of those who received a CE-SAV (p < 0.05). The mean age of the patients receiving a CE-S was 57.3 years (range, 8 to 85 years) and was 64.1 years (range, 6 to 89 years) in those receiving a CE-SAV. The CE-S group consisted of 578 atrial valve replacements (AVRs), 512 mitral valve replacements (MVRs), and 115 multiple valve replacements (MRs). The CE-SAV group consisted of 1,335 AVRs, 938 MVRs, and 200 MRs. There was a total of 165 cases of structural valve deterioration (SDV) in the CE-SAV group (AVR, 35; MVR, 98; and MR, 32). The effect of trimming the aortic wall was also considered: 20 of the 931 trimmed prostheses used for MVRs and MRs and none of the 207 reduced-trimmed prostheses exhibited SVD. The cumulative follow-up was 5,422 years for the patients with trimmed prostheses and 470 for those with reduced-trimmed prostheses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Carpentier-Edwards supraannular porcine bioprosthesis: clinical performance to twelve years.

The Carpentier-Edwards supraannular porcine bioprosthesis, a second-generation biologic prosthesis, has had clinical performance assessment to 12 years. This bioprosthesis was used in 2,489 operations in 2,444 patients between 1982 and 1992, inclusive (mean age 64.1 years, age range 6 to 89 years). There were 1,335 aortic valve replacements (AVR), 938 mitral valve replacements (MVR), and 200 multiple valve replacements (MR). Concomitant procedures were performed in 1,017 cases (40.9%). The age group distribution was: 35 years or younger, 83 patients; 36 to 50 years, 245; 51 to 64 years, 728; 65 to 69 years, 458; and 70 years and older, 975. The total follow-up was 12,785 patient-years (mean, 5.1 years) and was 96% complete. The early mortality rate was 7.4% (185 patients), and the late mortality was 4.9%/patient year (623). Concomitant procedures influenced both early and late mortality (p < 0.05). The overall patient survival at 12 years was 44% +/- 3% (p < 0.05, AVR > MVR, MR). The freedom from thromboembolism was not different by valve position. The freedom from major thromboembolism at 12 years was 82% +/- 4% (p = not significant by valve position). The overall freedom from antithromboembolic hemorrhage was 96% +/- 1% at 12 years (p < 0.05, AVR > MVR > MR). The overall freedom from valve-related reoperation at 12 years was 58% +/- 5% (p < 0.05, AVR > MVR, MR), and from valve-related mortality 89% +/- 2% (p < 0.05, AVR > MVR > MR). The freedom from residual morbidity (permanent impairment) at 12 years was 87% +/- 4% (p = not significant by valve position).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Relationship between parental occupation and children's oropharyngeal colonization with Neisseria meningitidis.

We explored, during an outbreak of meningococcal disease, whether children of parents with workplace exposure to children were at increased risk of oropharyngeal colonization with Neisseria meningitidis. In comparison with children of parents without workplace exposure to children, the risk of colonization was not increased (odds ratio = 1.62; 95% confidence interval, 0.56 to 4.72). Therefore a parent's occupation does not appear to increase the risk of their children's colonization with N. meningitidis.

Adolescent↗
PubMed1994

Perceived prestige and health careers recruitment.

Perceived occupational prestige is an important factor in career choice. The purpose of this study was to obtain prestige ratings of 13 allied health occupations and 13 general occupations for high school students, community college students (nonhealth majors), and community college health occupations students. The obtained ratings were compared with ratings of a combined group of health care providers. There was little agreement among the groups as to level of prestige. The high school rankings were the most disparate. Career exploration and outreach programs as part of recruitment efforts by health care institutions are suggested.

Adolescent↗
PubMed1993

Rapid purification of monomer HIV-2 Tat protein expressed in Escherichia coli.

Human immunodeficiency viruses types 1 and 2 encode transactivator proteins, named Tat-1 and Tat-2, that stimulate transcription directed by the viral long terminal repeat sequences. The Tat-1 and Tat-2 proteins are related in protein sequence and mechanism of transactivation. We expressed Tat proteins by in vitro translation and found, as expected, that both Tat-1 and Tat-2 were monomers. Unexpectedly, we found that the Tat-1 and Tat-2 proteins displayed significantly different tertiary structures. As determined by velocity sedimentation and gel filtration, Tat-1 acted as a compact structure and Tat-2 acted as an extended, asymmetric structure. Additionally, we found that the in vitro-expressed Tat-2 protein was significantly less susceptible to aggregation than the Tat-1 protein. This observation led us to overexpress Tat-2 in Escherichia coli and develop a simple and rapid method to purify monomer Tat-2 to approximately 50% purity. These results suggest that large amounts of Tat-2 protein can be purified in suitable form for biochemical and biophysical studies of Tat protein structure.

Amino Acid Sequence↗
PubMed1993

Limited proteolytic digestions identify common structural features of HIV-1 Tat proteins expressed during infection from alternatively spliced mRNAs.

Although multiple forms of the HIV-1 Tat protein are synthesized during infection from alternatively spliced mRNAs, only 72 amino acid residues encoded in the first Tat exon are necessary for full transactivation activity. We used limited proteolytic digestions of proteins expressed in vitro to study the structures of three Tat proteins from isolate HXB2: 72R Tat (first Tat exon); 86R Tat (first and second Tat exons), Tev or TNV (first Tat exon plus Env and Rev exons). For the 86R and Tev proteins, either trypsin or chymotrypsin cleaved the majority of carboxyl residues from the first exon. Moreover, when released from carboxyl residues, the first exon of 86R and Tev was relatively resistant to subsequent proteolysis. The entire 72R Tat protein was relatively resistant to proteolysis. The protease-resistant first exon in all Tat proteins was abolished by EDTA treatment, suggesting that divalent cations are required for its conformation. Our results suggest that the first exon in the 86R, 72R, and Tev proteins is folded into a similar structure which, as defined by partial proteolysis, acts as a single biochemical domain.

Amino Acid Sequence↗
PubMed1992

Effects of RF amplifier distortion on selective excitation and their correction by prewarping.

In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective-excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted "skirt" in the out-of-slice region of a slice profile. We present an effective method of correction in which a selective-excitation pulse is prewarped to compensate for the distortion.

Algorithms↗
PubMed1991

Tat protein of human immunodeficiency virus type 1 is a monomer when expressed in mammalian cells.

Human immunodeficiency virus type 1 (HIV-1) encodes a transactivator protein, known as Tat, that stimulates transcription directed by the HIV-1 long terminal repeat sequences. Tat appears to bind directly to the TAR RNA element present at the 5' end of nascent HIV-1 transcripts and thereby stimulates the activity of transcription complexes. We have expressed Tat in simian COS cells by transfection of a mammalian expression vector. Using immunoblots to detect Tat, the results of gel filtration and velocity sedimentation analyses demonstrate that Tat is a monomer in COS cell extracts. These results agree with other studies which indicate that Tat is a monomeric protein.

Animals↗
PubMed1991

Cortical cytoarchitectural and immunohistochemical studies on Zellweger syndrome.

In two cases of Zellweger syndrome, Golgi studies revealed an irregular neuronal arrangement, the presence of immature neurons, poor dendritic arborization and poor spine development, all of which suggest abnormal morphogenesis and delayed maturation. In immunohistochemical studies with antisera against human catalase, negative staining of neurons suggested a decrease of catalase due to defects of microperoxisomes, and positive staining of myelination glia only in the internal capsule may have been related to delayed myelination. Abnormal peroxisomal membrane or its related metabolites may cause a migration disorder in intrauterine development and myelination disturbance in perinatal maturation.

Catalase↗
PubMed1991

The Carpentier-Edwards standard porcine bioprosthesis: clinical performance to 15 years.

The Carpentier-Edwards standard porcine bioprosthesis was implanted in 1,195 patients in 1,213 operative procedures between 1975 and 1987, with the majority of implants performed prior to 1982 at the University of British Columbia. The mean age of the patient population was 57.2 years (range 8 to 85 years). The mean follow-up was 7.4 years per patient. The freedom from the combination of thromboembolism and antithromboembolic therapy-related hemorrhage at 15 years was 79.5% for aortic valve replacement (AVR), 72% for mitral valve replacement (MVR), and 84% for multiple valve replacement (MR) (p less than 0.05, AVR greater than MR greater than MVR). The freedom from structural valve deterioration at 15 years was 71% for AVR, 41% for MVR, and 41% for MR (14 years) (p less than 0.05, AVR greater than MVR greater than MR). The freedom from nonstructural dysfunction and prosthetic valve endocarditis did not distinguish the valve positions (p = NS). The freedom from valve-related mortality from all causes including reoperation was 92% for AVR, 78% for MVR, and 77% for MR at 15 years (p less than 0.05, AVR greater than MVR greater than MR). The freedom from residual morbidity was not significantly different between valve positions (p = NS). The freedom from treatment failure (valve-related mortality and residual morbidity) at 15 years was 87% for AVR, 72% for MVR, and 75% for MR (p less than 0.05, AVR greater than MR greater than MVR). The freedom from all complications at 14 years was 50% for AVR, 25% for MVR, and 27% for MR (p less than 0.05, AVR greater than MR greater than MVR).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Impacting moral reasoning in allied health students.

This study was designed to assess the relative impact of a course in biomedical ethics on the moral reasoning skills of junior-level students in a school of allied health. A pretest-posttest nonequivalent control group design was used. The course was found to significantly impact principled moral reasoning scores as measured by Rest's Defining Issues Test (DIT). Male-female differences in DIT score changes were also suggested. The nature of the instruction appears paramount to possible changes in moral thinking, indicating that moral education programs need to emphasize dilemma discussion in their formats.

Allied Health Occupations↗
PubMed1989

Smoking policies among private employers and public agencies in Texas: a statewide analysis.

The present study examined the prevalence, correlates, and perceived impact of smoking policies among private employers and public agencies in Texas. An identical survey instrument was administered to two groups of Texas employers: a random sample of private industries and all state agencies (excluding universities). Response rates were 62% (n = 420) for private industries and 73% (n = 130) for public agencies. Fifty-two percent of state agencies and 53% of private employers reported having a smoking policy, with the majority of policies having been implemented since 1986. Concern about employees' health or comfort was the most important reason for implementing a policy for both state agencies and private employers. Both groups believed that implementation of a policy resulted in fewer complaints from employees and less smoking in the workplace but had less impact on productivity or morale. This study on the prevalence of smoking policies in the workplace is the first to document that the majority of surveyed employers have a restrictive smoking policy in place. In addition, this study found minimal differences in the prevalence, rationale, and perceived benefits of smoking policies between private employers and state agencies.

Humans↗