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Biomedical subjects

L Ho

Publications and source records attributed to L Ho.

At least 109 records · Page 6Linked to original sources
PubMed1993

Sequence variants of human papillomavirus type 16 from couples suggest sexual transmission with low infectivity and polyclonality in genital neoplasia.

Human papillomavirus type 16 (HPV-16) is causally involved in the pathogenesis of genital neoplasia, but important details of the natural history of infection and disease are not yet understood. Many individual HPV-16 DNA isolates differ by characteristic point mutations. In a study of the HPV-16 variants from genital lesions of 32 married couples, HPV-16 was detected in both the husband and the wife in 8 couples. Of these, 4 demonstrated identical HPV-16 variants between husband and wife, and 4 had mismatching HPV-16 variants. Five of 31 biopsies showed simultaneous presence of two different HPV-16 variants. The data suggest that sexual transmission of HPV-16 does occur, but with low infectivity, and that HPV-16-related premalignant lesions are frequently polyclonal.

Adult↗
PubMed1993

The genetic drift of human papillomavirus type 16 is a means of reconstructing prehistoric viral spread and the movement of ancient human populations.

We have investigated the diversity of a hypervariable segment of the human papillomavirus type 16 (HPV-16) genome among 301 virus isolates that were collected from 25 different ethnic groups and geographic locations. Altogether, we distinguished 48 different variants that had diversified from one another along five phylogenetic branches. Variants from two of these branches were nearly completely confined to Africa. Variants from a third branch were the only variants identified in Europeans but occurred at lower frequency in all other ethnic groups. A fourth branch was specific for Japanese and Chinese isolates. A small fraction of all isolates from Asia and from indigenous as well as immigrant populations in the Americas formed a fifth branch. Important patterns of HPV-16 phylogeny suggested coevolution of the virus with people of the three major human races, namely, Africans, Caucasians, and East Asians. But several minor patterns are indicative of smaller bottlenecks of viral evolution and spread, which may correlate with the migration of ethnic groups in prehistoric times. The colonization of the Americas by Europeans and Africans is reflected in the composition of their HPV-16 variants. We discuss arguments that today's HPV-16 genomes represent a degree of diversity that evolved over a large time span, probably exceeding 200,000 years, from a precursor genome that may have originated in Africa. The identification of molecular variants is a powerful epidemiological and phylogenetic tool for revealing the ancient spread of papillomaviruses, whose trace through the world has not yet been completely lost.

Africa↗
PubMed1992

Genomic heterogeneity of DNA repair. Role in aging?

The introduction and repair of DNA lesions are generally heterogeneous with respect to different genomic domains. In particular, the repair of helix-distorting damage, such as the cyclobutane pyrimidine dimers (CPD) induced by ultraviolet light occurs selectively in expressed genes. This is due in large part to the preferential repair of transcribed DNA strands, which is then reflected in a bias toward mutagenesis from persisting lesions in nontranscribed strands. Consequently, determination of overall genomic repair efficiencies may not be a good indicator of cellular sensitivity to agents that damage DNA. Although some studies suggest an age-related accumulation of altered nucleotides in DNA, we do not know the intragenomic distribution of those changes and whether they are relevant to the physiological aspects of aging. Subtle changes in the pattern of preferential repair during maturation could have profound effects on cell and tissue function. DNA repair has been analyzed in differentiating cell systems as possible models for aging. We have observed attenuated overall repair of CPD in differentiated rat myoblasts or PC12 neuron-like cells. In both model systems, several expressed genes have been shown to be repaired relatively efficiently but without strand specificity. In another model system of human HT1080 fibroblasts differentiating in the presence of dexamethasone, we demonstrated enhanced repair in the gene for plasminogen activator inhibitor I whose transcription is induced and, correspondingly, a reduced repair rate in the urokinase plasminogen activator gene whose transcription is suppressed. We conclude that any attempted correlation of the phenomena of aging with DNA repair should focus on the relevant genes in the tissue of interest.

Aging↗
PubMed1992

Human papillomavirus type 16 in cervical smears as predictor of high-grade cervical intraepithelial neoplasia [corrected].

The management of women with mild to moderately dyskaryotic cervical smears would benefit from a non-invasive test that predicts which women have high-grade cervical intraepithelial neoplasia. Detection of human papillomavirus type 16 (HPV16) DNA in cervical smears may be such a test. With the polymerase chain reaction (PCR), we estimated the amount of HPV16 DNA in cervical smears from 85 women referred for colposcopy because of abnormal cytology. An intermediate or high amount of HPV16 DNA predicted the presence of high-grade cervical intraepithelial neoplasia in a subsequent biopsy in almost 90% of patients irrespective of the cytological grade of the referral smear. This technique may allow early identification of those women with low-grade cytological abnormalities who have high-grade underlying cervical disease.

DNA, Viral↗
PubMed1992

Molecular variants of human papillomavirus type 16 from four continents suggest ancient pandemic spread of the virus and its coevolution with humankind.

We have amplified by the polymerase chain reaction, cloned, and sequenced genomic segments of 118 human papillomavirus type 16 (HPV-16) isolates from 76 cervical biopsy, 14 cervical smear, 3 vulval biopsy, 2 penile biopsy, 2 anal biopsy, and 1 vaginal biopsy sample and two cell lines. The specimens were taken from patients in four countries--Singapore, Brazil, Tanzania, and Germany. The sequence of a 364-bp fragment of the long control region of the virus revealed 38 variants, most of which differed by one or several point mutations. Phylogenetic trees were constructed by distance matrix methods and a transformation series approach. The trees based on the long control region were supported by another set based on the complete E5 protein-coding region. Both sets had two main branches. Nearly all of the variants from Tanzania were assigned to one (African) branch, and all of the German and most of the Singaporean variants were assigned to the other (Eurasian) branch. While some German and Singaporean variants were identical, each group also contained variants that formed unique branches. In contrast to the group-internal homogeneity of the Singaporean, German, and Tanzanian variants, the Brazilian variants were clearly divided between the two branches. Exceptions to this were the seven Singaporean isolates with mutational patterns typical of the Tanzanian isolates. The data suggest that HPV-16 evolved separately for a long period in Africa and Eurasia. Representatives of both branches may have been transferred to Brazil via past colonial immigration. The comparable efficiencies of transfer of the African and the Eurasian variants to the New World suggest pandemic spread of HPV-16 in past centuries. Representatives of the African branch were possibly transferred to the Far East along old Arab and Indonesian sailing routes. Our data also support the view that HPV-16 is a well-defined virus type, since the variants show only a maximal genomic divergence of about 5%. The small amount of divergence in any one geographic location and the lack of marked divergence between the Tanzanian and Brazilian African genome variants two centuries after their likely introduction into the New World suggest a very slow rate of viral evolution. The phylogenetic tree therefore probably represents a minimum of several centuries of evolution, if not an age equal to that of the respective human races.

Base Sequence↗
PubMed1992

Characterization of errors detected during central order review.

Characterization of prescribing errors detected by dispensary pharmacists in a tertiary-care teaching hospital is described. During the 25 week study period, 1330 prescribing errors were identified from a total of 237,798 medication orders processed by the pharmacy, representing a rate of 5.6 errors per 1000 orders. Resident physicians wrote more errant medication orders than any other physician class. Errors most often occurred on the general medicine teaching wards. The most common drug classes implicated were non-formulary medications and antibiotics. Approximately 11% of errors were defined as potentially fatal or severe (Type A) errors, 7% were potentially serious (Type B), 21% were potentially significant (Type C) and 61% were problem orders (Type D) based on a classification system of severity. The most common error types were inappropriate dosing of antibiotics and the prescribing of medications for patients who had a potential conflicting allergy history. The acceptance of pharmacists' suggestions was 67%. The study identified three major areas where future educational and corrective measures could be aimed: adherence to the formulary, antibiotic prescribing and allergy validation.

Canada↗
PubMed1992

Efficacy of Zaditen (ketotifen) in wheezy infants and young children.

This was a double-blind, randomised evaluation of the efficacy and safety of Zaditen in comparison with placebo in infants and young children (aged 6-36 months). These children either had (i) at least 2 episodes of wheezing over 8 weeks, or (ii) persistent wheeze over 4 weeks, prior to entering into the study. In the doctor's opinion, the group treated with Zaditen had more improvement in symptomatology (p < 0.05). They were more likely to have reduced or discontinued bronchodilators. They showed trends of improvement of symptom scores in night cough, wheeze and sputum production. These differences, however, did not reach statistical significance. There were no major adverse reaction of note.

Child, Preschool↗
PubMed1991

In vitro radiation resistance among cell lines established from patients with squamous cell carcinoma of the head and neck.

Twenty-five squamous cell carcinoma (SCC) cell lines from 20 patients with head and neck cancer were assessed for radiosensitivity in vitro using a 96-well plate assay. Four non-SCC lines were also tested. Radiation sensitivity of individual cell lines was compared using the area under the survival curve (AUC) as a measure of the mean inactivation dose. Tumor lines were tested with either a cobalt-60 (60Co) gamma-irradiator having a dose rate of 100 cGy/minute or with a 4-meV photon beam having a dose rate of 200 cGy/minute. The mean AUC of the 25 SCC cell lines was 188 +/- 7 (SEM) cGy (range, 100 to 250 cGy) whereas the four non-SCC lines had a mean AUC of 225 +/- 9 cGy. The SCC cell lines with mean inactivation dose values greater than 188 cGy were classified as relatively radioresistant whereas those with values less than 188 cGy were considered relatively radiosensitive. In seven cases SCC cell lines were derived from patients who had already received radiation therapy. In four of these cases the tumor cell lines were radioresistant (AUC, 210 to 250) but in the other three cases the tumor lines were radiosensitive (AUC, 160 to 180). Thus, failure of a tumor to respond to radiation did not always select for radioresistant cells. The mean of the AUC for cell lines from previously irradiated patients (197 +/- 11 cGy) did not differ significantly from that of the cell lines from patients who received no prior radiation therapy (182 +/- 9 cGy). However, among radiation-resistant lines those from the four previously irradiated patients were significantly more resistant (mean AUC = 235 +/- 9) than seven other radioresistant lines from nonirradiated patients (mean AUC, 208 +/- 4) (P = 0.0194). In four cases more than one cell line was derived from different tumor specimens in the same patient. In each of these cases the lines from the same patients were similar to one another in their degree of radioresistance. Based on these observations the authors conclude that the degree of in vitro radiation resistance is an inherent property of some squamous cell tumors.

Adult↗
PubMed1991

Gene-specific DNA repair in terminally differentiating rat myoblasts.

Preferential DNA repair in expressed genes has been well documented in proliferating mammalian cells following ultraviolet irradiation. It was of interest to learn whether excision repair is similarly selective in terminally differentiating cells. We have measured the removal of ultraviolet-induced cyclobutane pyrimidine dimers (detected as T4 endonuclease V-sensitive sites) from various genes in cultured L8 rat skeletal myoblasts. In these cells, the transcription of muscle-specific genes such as the embryonic myosin heavy chain (MHCemb) gene can be regulated by inducing cells to differentiate. L8 myoblasts are somewhat more sensitive than Chinese hamster ovary cells to ultraviolet radiation, and they exhibit relatively poor overall DNA-repair rates throughout differentiation. Irradiation severely reduces the rates of transcription and steady-state RNA levels for the genes studied. Although differences in kinetics are seen between the repair of active and inactive genes, repair rates are low relative to those previously measured in proliferating rodent cell lines. Repair efficiency in the MHCemb gene increases as it is activated during differentiation and, in fact, approaches 100% within 5 days, while that in the silent GAP43 gene is much lower. While repair efficiencies generally correlate with expression in the genes studied, the overall time course of repair appears to be prolonged in these cells compared to that in proliferating cells. These terminally differentiating cells seem to maintain a DNA damage surveillance and repair capacity for selected genes and/or genomic domains.

Animals↗
PubMed1991

Sequence variants of human papillomavirus type 16 in clinical samples permit verification and extension of epidemiological studies and construction of a phylogenetic tree.

Genomic variability between different viral isolates provides a powerful epidemiological tool for verifying ultrasensitive diagnostic procedures, understanding infectious pathways in individuals and human populations, and studying viral evolution. The potential of this approach has not yet been exploited for the diagnosis of human papillomaviruses (HPVs) like HPV type 16 (HPV-16), which are involved in genital cancer. Toward this end, we amplified by polymerase chain reaction, cloned, and sequenced a 364-bp noncoding segment of the HPV-16 genome from cell lines, cervical biopsy specimens, and cervical smears. The HPV-16 genomes in the cell lines SiHa and CaSki showed an identical point mutation, and in the SiHa cell line it had an additional 38-bp deletion. Only 4 of 22 cervical lesions biopsied from patients at several hospitals in Singapore contained HPV-16 DNA with the prototype sequence, while the DNAs of the other 18 cervical lesions differed by 1 to 10 mutations. This excludes contaminations with cloned HPV-16 DNA as the source of this DNA. To test whether this diversity was a geographic idiosyncrasy, we analyzed 25 cervical biopsy specimens from Brazil. Eight of these contained the prototype sequence, while 17 were mutated. Altogether, 11 genomic variants were found in the Singaporean samples and 12 genomic variants were found in the Brazilian samples, and only 5 of these occurred identically in both cohorts. All variants could be connected to form a phylogenetic tree, with some branches being specific for each cohort. This suggests that the variants did not originate over a short period in the individual patient but, rather, evolved consecutively while spreading throughout humankind.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1991

Effect of salbutamol on oxygen saturation in bronchiolitis.

Inhaled sympathomimetic agents are often used in bronchiolitis with little objective evidence of benefit. The arterial oxygen saturation (SaO2) reflects the adequacy of ventilation-perfusion balance. The aim of the current study was to determine the effect of inhaled salbutamol on SaO2. In a randomised, double blind study, 21 infants, admitted with bronchiolitis positive for respiratory syncytial virus, had continuous SaO2 measurements made before and after nebulised salbutamol or placebo. SaO2 was recorded over 30 minutes for a baseline, then during the 10 minutes of first nebulisation with either salbutamol or saline, then over 30 minutes after nebulisation, the 10 minutes of second nebulisation with the alternate regime, and another 30 minutes after this second nebulisation. Desaturation occurred after salbutamol and saline nebulisation. The fall in SaO2 with salbutamol was seen whether infants received it as the first or second nebulisation. The fall in SaO2 after saline was seen when given first, but not when given after salbutamol. The decrease in SaO2 was greater and more prolonged with salbutamol than with saline. Routine nebulised aerosol sympathomimetic treatment during acute bronchiolitis cannot be recommended.

Albuterol↗
PubMed1991

[Nemaline myopathy--a case report].

An 8-year-old Chinese girl who was noted to have feeding difficulty and poor weight gain since her infancy. Her motor development was delayed with sitting at 1-year-old and walking independently at 2-year-old. She visited our OPD when she was 8. Physically, she was thin and slender. Her height and weight were below the 10th and 3rd percentile. Her face was elongated with high arched palate. Neurologically, she had waddling gate with marked proximal muscle weakness. Her cranial nerves and sensation remained intact. Laboratory tests including blood routine, liver function, renal function, electrolytes, NCV and cardiac echo all were within normal limits. The EMG showed myopathic pattern. A fresh-frozen muscle biopsy stained with the modified Gomori trichrome, processed by histochemistry and electronmicroscopic examination showed typical nemaline rods with predominance of type 1 muscle fibers. She was then diagnosed to have nemaline myopathy.

Child↗
PubMed1990

Cloning and cDNA sequence of the beta-subunit component of human pyruvate dehydrogenase complex.

Two cDNA clones (lambda E1 beta 1, 1469 bp; lambda E1 beta 12, 1437 bp) encoding the beta-subunit of the pyruvate dehydrogenase (E1) component of the human pyruvate dehydrogenase complex were isolated from a human liver lambda gt11 cDNA library. The composite human liver E1 beta cDNA encoded the entire mature E1 beta [329 amino acids (aa)] as well as a portion (26 aa) of the E1 beta leader peptide. Significant discrepancies were identified between the nucleotide and deduced aa sequences of human liver E1 beta cDNAs and the corresponding sequences of a previously reported cultured human foreskin fibroblast E1 beta cDNA [Koike et al., Proc. Natl. Acad. Sci. USA 85 (1988) 41-45]. The composite human liver E1 beta cDNA generated in this study provides a reference sequence for investigating the structure-function relationship of human E1 beta and for characterizing genetic mutations in patients with E1 deficiency.

Amino Acid Sequence↗
PubMed1989

Characterization of cDNAs encoding human pyruvate dehydrogenase alpha subunit.

A cDNA clone (1423 base pairs) comprising the entire coding region of the precursor form of the alpha subunit of pyruvate dehydrogenase (E1 alpha) has been isolated from a human liver cDNA library in phage lambda gt11. The first 29 amino acids deduced from the open reading frame correspond to a typical mitochondrial targeting leader sequence. The remaining 361 amino acids, starting at the N terminus with phenylalanine, represent the mature mitochondrial E1 alpha peptide. The cDNA has 43 base pairs in the 5' untranslated region and 210 base pairs in the 3' untranslated region, including a polyadenylylation signal and a short poly(A) tract. The nucleotide sequence of human liver E1 alpha cDNA was confirmed by the nucleotide sequences of three overlapping fragments generated from human liver and fibroblast RNA by reverse transcription and DNA amplification by the polymerase chain reaction. This consensus nucleotide sequence of human liver E1 alpha cDNA resolves existing discrepancies among three previously reported human E1 alpha cDNAs and provides the unambiguous reference sequence needed for the characterization of genetic mutations in pyruvate dehydrogenase-deficient patients.

Amino Acid Sequence↗
PubMed1989

Genetic defects in human pyruvate dehydrogenase.

The nature of PDC deficiency has been characterized at the levels of total and component catalytic activities as well as at the levels of component proteins and specific mRNAs. Defects in 14 cases were shown to involve the E1 component, and there was one case each of an apparent E2 and E3 deficiency. Defects involving the E1 component exhibit heterogeneous expression of E1 proteins and mRNAs, indicating that different types of mutations cause E1 deficiency. E1 deficiencies can occur either in the presence or absence of E1 proteins, representing catalytic mutations or mutations affecting the expression of E1 proteins, respectively. In every case where the content of E1 proteins is reduced, both the E1 alpha and the E1 beta peptides are simultaneously affected. This is likely to be due to rapid degradation of any E1 peptide that is not complexed into the alpha 2 beta 2 conformation. Among subjects with reduced levels of both E1 peptides, some had normal amounts of specific E1 alpha and E1 beta mRNAs. In these subjects, the primary mutations affect either translational or post-translational processes leading to the formation of mature E1 proteins in the mitochondria. In contrast, two cases of simultaneous reduction of both E1 alpha and E1 beta proteins had decreases in the amounts of E1 alpha mRNA only. Mutations in these cases may impair the transcription, nuclear processing, or stability of E1 alpha mRNA. E1 deficiency may manifest in a variable manner. Further characterization of this phenomenon might provide insight into the discrepancy between the clinical severity of the defect and the residual level of PDC catalytic activity. Available information indicates that the E1 alpha gene is located on the X chromosome, but sex distribution of E1 alpha defects suggests that the mode of inheritance may not follow a simple X-linked pattern. The availability of specific PDC antibodies and cDNA clones, as well as the application of molecular biological techniques, should facilitate the characterization of the molecular basis of various PDC deficiencies. This information should provide better understanding of the function of PDC, pathophysiology of PDC deficiency, and mechanisms of inheritance and expression of these genes.

Amino Acid Metabolism, Inborn Errors↗
PubMed1989

Demethylation enhances removal of pyrimidine dimers from the overall genome and from specific DNA sequences in Chinese hamster ovary cells.

We have examined the effects of changes in cytosine methylation on DNA repair in UV-irradiated Chinese hamster ovary (CHO) cells. A hypomethylated derivative of the CHO K1B11 line, B11aza, was established by passaging B11 cells over several months in increasing concentrations of 5-azacytidine; greater than 60% demethylation was consistently demonstrated in these conditioned cells. Following a UV dose of 10 J/m2, the amount of repair replication performed within 24 h was approximately twofold higher in B11aza cells than in control B11 cells. Removal of T4 endonuclease V-sensitive sites (ESS) from specific restriction fragments within and around the dihydrofolate reductase (DHFR) gene was then examined in B11aza cells and compared with that in B11 cells. Although demethylation had little or no effect on repair in the 5' half of the DHFR gene, within a nontranscribed sequence immediately downstream from the gene, or within an extragenic region further downstream from the DHFR gene, significant increases in repair were observed at the 3' end of the DHFR gene and within an extragenic region upstream of the DHFR gene. However, the increases in DNA repair were not accompanied by any changes in overall cellular resistance to UV when colony-forming ability was assayed. We suggest that the level of DNA methylation may play an indirect role in the regulation of DNA repair, perhaps through an effect on chromatin structure or transcriptional activity.

Animals↗