Biomedical subjects

D Chan

Publications and source records attributed to D Chan.

At least 145 records · Page 8Linked to original sources

PubMed1992

Lethal perinatal osteogenesis imperfecta due to a type I collagen alpha 2(I) Gly to Arg substitution detected by chemical cleavage of an mRNA:cDNA sequence mismatch.

A single base mismatch was detected by a chemical cleavage method in heteroduplexes formed between patient mRNA and a control collagen alpha 2(I) cDNA probe in a case of osteogenesis imperfecta type II. The region of the mRNA mismatch was amplified using the polymerase chain reaction, cloned and sequenced. A heterozygous point mutation of G to C at base pair 1,774 of the collagen alpha 2(I) mRNA resulted in the substitution of glycine with arginine at amino acid position 457 of the helix. Type I collagen of alpha 1(I)- and alpha 2(I)-chains from the patient migrated slowly on electrophoresis due to increased levels of posttranslational modification of lysine. The parents' fibroblast collagen did not contain the mRNA mismatch and the collagens showed normal electrophoretic behaviour. Two-dimensional electrophoresis of the CNBr peptides from the patient's collagen confirmed the excessive posttranslational modification of the alpha 1(I)- and alpha 2(I)-chains in the CNBr peptides N-terminal to the mutation due to disruption of the obligatory Gly-X-Y triplet repeat of the helix. The mutation led to reduced procollagen secretion and helix destabilization as evidenced by a decreased thermal stability. These data lend further support to the accumulating evidence that type I collagen alpha 2(I) glycine substitution mutations result in the same spectrum of clinical severity as those in the alpha 1(I)-chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1992

Epitope specificity of antibodies to type II collagen in rheumatoid arthritis and systemic lupus erythematosus.

Antibodies to human type II collagen were examined in the sera of 105 patients with rheumatoid arthritis (RA), 44 patients with systemic lupus erythematosus (SLE) and 11 patients who fulfilled the criteria of both diseases (RA-SLE overlap), using a solid-phase radioimmunoassay (RIA). The frequencies of antibodies to native and denatured human type II collagen were 20% and 27% in RA, 14% and 16% in SLE, and 45% and 36% in RA-SLE overlap. The specificity of the antibodies was further examined by inhibition with native and denatured type II collagen, by immunoblotting on native and denatured type II collagen, and by immunoblotting on cyanogen-bromide derived polypeptides of type II collagen. We could not identify any disease-specific patterns of reactivity. Thus, in the three disease groups the antibody response was polyclonal; there were antibody populations that reacted with native and/or denatured collagen, and epitopes could be assigned to at least three CB peptides, CB10.5, CB11 and CB8.

Antibodies↗

PubMed1992

Overuse injuries of the olecranon in young gymnasts.

We report overuse injuries in 14 elbows of ten élite young gymnasts. In 12 elbows of eight patients aged 11 to 15 years there was a spectrum of radiological abnormalities including widening of the olecranon physis and fragmentation of the epiphysis. The radiographs were compared with those of normal elbows matched for age and sex. The radiograph appearances were very similar to those of the Osgood-Schlatter lesion of the tibial tuberosity. Two older boys, aged 18 and 19, had stress fractures through the olecranon growth plate. Conservative management was successful in all except one case of stress fracture which required internal fixation.

Adolescent↗

PubMed1992

Endoprosthetic replacement for bony metastases.

A series of 38 patients with long bone metastases treated at the Birmingham Bone Tumour Treatment Service with resection of the metastatic lesion and replacement of the bone defect with an endoprosthesis was reviewed. The majority of cases had pathological fractures due to a massive destructive lesion. Two-thirds of the patients had a solitary metastasis. Metastases from hypernephroma and breast carcinoma accounted for the majority of cases. All the patients were independently mobile after the endoprosthetic replacement and were pain free. The average survival rate after the endoprosthetic replacement was 14.7 months and this varies with the primary tumour. The indications for endoprosthetic replacement for the treatment of long bone metastases are outlined and the results and complications are discussed. It is concluded that endoprosthetic replacement for bony metastases is an effective palliative procedure for a selected group of patients.

Adult↗

PubMed1992

Effects of neuropeptides on human lung and breast cancer cells.

We evaluated the effect of seven classes of neuropeptides [bradykinin, cholecystokinin 26-33 (CCK), neurotensin, arginine-8 vasopressin (AVP), tyr-4 bombesin (BN), somatostatin, and motilin] on 18 human lung cancer and four human breast cancer cell lines to determine the pattern of responses. Flow cytometric analysis of Indo-1 AM-loaded cells was used to quantitate the intracellular calcium response of individual cells produced by these peptides alone or in simultaneous or sequential combinations. All 18 lung cancer cell lines responded to one or more peptide classes with classic small cell lines displaying the greatest responsiveness, followed by variant small-cell lines and non-small-cell lung cancer cell lines. Breast cancer cell lines demonstrated little or no response to any peptide. There was great variability in the magnitude of response and pattern of response in individual cell lines and between cell lines. Bradykinin was the most potent peptide and produced responses in the largest number of lung cancer cell lines. Simultaneous administration of active peptides produced greater intracellular calcium release than single peptides, though in a less than additive manner. Response to each peptide was followed by a refractory period lasting several hours or more. The refractoriness was peptide-specific, implying that each peptide has a distinct pathway, at least at the receptor level. Bradykinin antagonists could abrogate the calcium response to bradykinin but not to other peptides. Similarly, specific peptide antagonists for CCK, BN, and AVP blocked the response for only their specific agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗

PubMed1991

Low basal transcription of genes for tissue-specific collagens by fibroblasts and lymphoblastoid cells. Application to the characterization of a glycine 997 to serine substitution in alpha 1(II) collagen chains of a patient with spondyloepiphyseal dysplasia.

Cultured dermal fibroblasts were shown, using amplification of cDNA by the polymerase chain reaction, to produce very low levels of spliced transcripts from the COL2A1 gene that encodes the cartilage-specific alpha 1(II) chains of type II collagen. Cultured lymphoblastoid cells were also shown to produce very low levels of spliced transcripts from the COL1A1 and COL1A2 genes that encode the alpha 1(I) and alpha 2(I) chains of type I collagen, the COL2A1 gene that encodes type II collagen, and the COL3A1 gene that encodes the alpha 1(III) chains of type III collagen. Amplified cDNAs prepared from lymphoblastoid cells were used to identify previously characterized heterozygous mutations in the COL1A1 and COL1A2 genes from two patients with osteogenesis imperfecta and in the COL3A1 gene from a patient with the Ehlers-Danlos syndrome type IV. Amplified alpha 1(II) cDNA from fibroblasts and lymphoblastoid cells of a child with spondyloepiphyseal dysplasia congenita was also used to localize sequence mismatches using chemical modification of cDNA:cDNA heteroduplexes by hydroxylamine and cleavage with piperidine. The amplification products containing the mismatched region were sequenced and the mutation was shown to change the codon GGC for glycine 997 to AGC for serine in the triple helical domain of the alpha 1(II) chains. The corresponding region of the genomic DNA was sequenced and the heterozygous point mutation was shown to be in exon 48 of the COL2A1 gene. Allelic restriction mapping showed that neither parent carried the mutation in their leucocytes. This mutation emphasizes the importance of COL2A1 mutations in producing the spondyloepiphyseal dysplasia phenotype. The low basal rate of transcription ("illegitimate transcription"), splicing, and polyadenylation of tissue-specific mRNAs by cultured dermal fibroblasts and lymphoblastoid cells provides the opportunity to localize and sequence mutations in amplified cDNA in patients from whom affected tissue is unavailable.

Base Sequence↗

PubMed1991

Characterization of a type I collagen alpha 2(I) glycine-586 to valine substitution in osteogenesis imperfecta type IV. Detection of the mutation and prenatal diagnosis by a chemical cleavage method.

A chemical cleavage method for detecting mismatched bases in heteroduplexes formed between patient mRNA and control cDNA probes was employed to identify a single base mutation in a heterozygous case of osteogenesis imperfecta type IV. The parents' fibroblast mRNA did not contain the mutation. The region of the mRNA mismatch was amplified by using the polymerase chain reaction, cloned and sequenced. A point mutation of G to U at base-pair 2162 of the collagen alpha 2(I) mRNA resulted in the substitution of glycine by valine at amino acid position 586 of the helix. This substitution disrupted the critical Gly-Xaa-Yaa repeating unit of the collagen triple helix and resulted in helix destabilization, as evidenced by a decreased thermal stability. This local disturbance to helix propagation from the C-terminus to the N-terminus led to the overmodification of the collagen helix downstream towards the N-terminus. However, collagen secretion in vitro was normal, and the clinical phenotype probably resulted from the secretion into the extracellular matrix of the mutant collagen combined with a decrease in collagen production to 65% of control values. The rapid detection of the osteogenesis imperfecta mutation by using the chemical cleavage method afforded the opportunity to apply the technique to prenatal diagnosis in the next pregnancy of the mother of the osteogenesis imperfecta patient. The absence of a mismatched base in chorionic villus mRNA and control cDNA heteroduplexes indicated that the foetus did not carry the mutation, which was confirmed by the subsequent delivery of a normal baby.

Amino Acid Sequence↗

PubMed1991

Cross-resistance of an amsacrine-resistant human leukemia line to topoisomerase II reactive DNA intercalating agents. Evidence for two topoisomerase II directed drug actions.

HL-60/AMSA is a human leukemia cell line that is 50-100-fold more resistant than its drug-sensitive HL-60 parent line to the cytotoxic actions of the DNA intercalator amsacrine (m-AMSA). HL-60/AMSA topoisomerase II is also resistant to the inhibitory actions of m-AMSA. HL-60/AMSA cells and topoisomerase II are cross-resistant to anthracycline and ellipticine intercalators but relatively sensitive to the nonintercalating topoisomerase II reactive epipodophyllotoxin etoposide. We now demonstrate that HL-60/AMSA and its topoisomerase II are cross-resistant to the DNA intercalators mitoxantrone and amonafide, thus strongly indicating that HL-60/AMSA and its topoisomerase II are resistant to topoisomerase II reactive intercalators but not to nonintercalators. At high concentrations, mitoxantrone and amonafide were also found to inhibit their own, m-AMSA's, and etoposide's abilities to stabilize topoisomerase II-DNA complexes. This appears to be due to the ability of these concentrations of mitoxantrone and amonafide to inhibit topoisomerase II mediated DNA strand passage at a point in the topoisomerization cycle prior to the acquisition of the enzyme-DNA configuration that yields DNA cleavage and topoisomerase II-DNA cross-links. In addition, amonafide can inhibit the cytotoxic actions of m-AMSA and etoposide. Taken together, these results suggest that the cytotoxicity of m-AMSA and etoposide is initiated primarily by the stabilization of the topoisomerase II-DNA complex. Other topoisomerase II reactive drugs may inhibit the enzyme at other steps in the topoisomerization cycle, particularly at elevated concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Amsacrine↗

PubMed1991

Inhibition of tumor invasion of smooth muscle cell layers by recombinant human metalloproteinase inhibitor.

Matrix metalloproteinases secreted by tumor cells play an important role in the proteolytic degradation of the extracellular matrix during invasion. In a previous study, we showed that the degradation of extra-cellular matrices by human HT 1080 fibrosarcoma cells is suppressed by endothelial cells. The identification of inhibitors of metalloproteinases secreted by endothelial cells led us to postulate that these inhibitors were responsible for the suppressive effect (Cancer Res., 46: 3580-3586, 1986). In the present study, we have investigated the inhibitory activity of one of these inhibitors designated metalloproteinase inhibitor (MI)/tissue inhibitor of metalloproteinases (TIMP)-2 on the degradation and invasion of rat smooth muscle cell matrices by two invasive tumor cell lines, the c-Ha-ras-1 transfected rat embryo cell line 4R and the HT 1080 human fibrosarcoma cell line. The inhibitor was obtained in recombinant form from the culture medium of Chinese hamster ovary cells transfected with a human MI complementary DNA. Recombinant MI/TIMP-2 inhibited several matrix metalloproteinases identified in the culture medium of the tumor cell lines including interstitial collagenase. Mr 72,000 gelatinase (type IV collagenase), and Mr 92,000 gelatinase. Approximately 70% inhibition of the degradation of smooth muscle cell matrices was observed when the recombinant inhibitor was present along with cultured cells at a concentration of 10 micrograms/ml. Similarly, inhibition of the penetration of a multilayer of growing smooth muscle cells and their surrounding matrix was demonstrated. The inhibitor had no effect on cell growth or attachment. Thus, recombinant MI/TIMP-2, like TIMP, is a potent inhibitor of tumor invasion. Since both inhibitors are secreted by endothelial cells (J. Biol. Chem., 264: 17445-17453, 1989), they may play an important role in protecting large blood vessels from invasion.

Cell Adhesion↗

PubMed1991

Effect of bryostatin 1 on drug-induced, topoisomerase II-mediated DNA cleavage and topoisomerase II gene expression in human leukemia cells.

Unlike PMA, bryostatin 1 has been found to have a minimal effect on drug-induced topoisomerase II-mediated DNA cleavage and no effect on topoisomerase II mRNA levels. Furthermore, bryostatin 1 overcame the down-regulatory effects of PMA treatment on (1) drug-induced, topoisomerase II-mediated DNA cleavage, (2) drug-induced cytotoxicity, and (3) topoisomerase II gene expression. Thus, it is unlikely that the effects of phorbol ester treatment on topoisomerase II-mediated events are a direct consequence of protein kinase C activation per se. Rather, the results with bryostatin 1 suggest that the phorbol ester effects are related to more distal effects of phorbol ester treatment that may be related to monocytoid differentiation.

Bryostatins↗

PubMed1991

The effect of staurosporine on drug-induced, topoisomerase II-mediated DNA cleavage in human leukemia cells.

Phorbol-12-myristate 13-acetate (PMA), a stimulator of protein kinase C, dramatically decreased topoisomerase II-reactive drug-induced DNA cleavage in HL-60 human leukemia cells. The effect of staurosporine, an inhibitor of protein kinase C, on drug-induced, topoisomerase II-mediated DNA cleavage was quantified in the same cells. Staurosporine decreased the magnitude of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA)- and etoposide-induced DNA cleavage in a dose- and time-dependent fashion. Measurement of several parameters of cell proliferation revealed no clear and uniform correlation between staurosporine's inhibition of these parameters and its effects on drug-induced DNA cleavage. A direct comparison with PMA's effects on drug-induced DNA cleavage showed that whereas PMA's inhibition of etoposide-induced cleavage was much greater than its inhibition of m-AMSA-induced cleavage, the magnitude of staurosporine's effect on the cleavage produced by the two topoisomerase II-reactive drugs was similar. Thus, although PMA stimulates protein kinase C and staurosporine inhibits this enzyme, it is unlikely that the actions of either on topoisomerase II-reactive, drug-induced DNA cleavage are mediated directly via protein kinase C. Furthermore, it is likely that the mechanisms by which PMA and staurosporine inhibit topoisomerase II-reactive drug-induced cleavage are different.

Alkaloids↗

PubMed1991

Pharmacokinetics of fosinopril in patients with various degrees of renal function.

Single-dose kinetics of fosinopril, a new phosphorus-containing angiotensin-converting enzyme inhibitor and its active diacid, fosinoprilat, were investigated in patients with mild, moderate, or severe renal impairment and in those with normal renal function. After an intravenous dose of 14C-fosinoprilat (7.5 mg), total body clearance of fosinoprilat was significantly greater (p less than 0.05) in patients with normal renal function than in renally impaired patients but was not related to the degree of renal impairment in patients with creatinine clearance values of 11 to 72 ml/min/1.73 m2. Decreases in renal clearance were compensated for by increases in hepatic clearance, so that total clearance was maintained. After oral 14C-fosinopril (10 mg), plasma kinetics and bioavailability of fosinoprilat were similar for the three groups of renally impaired patients. The dual elimination of fosinoprilat by the liver and the kidney distinguishes fosinopril from other angiotensin-converting enzyme inhibitors.

Administration, Oral↗

PubMed1991

Chronic stress injuries of the elbow in young gymnasts.

The radiological changes of chronic stress injuries of the elbow in 19 adolescent elite gymnasts are reported. The principal abnormalities were avascular necrosis of the capitellar epiphysis (Panner's disease) (one patient), post-traumatic subarticular necrosis (osteochondritis dissecans) of the capitellum (six patients) and the medial articular eminence of the distal humerus (one patient). Flattening and anterior depression of the radial head epiphysis with an underlying metaphyseal notch associated with an epiphyseal cleft (three patients), which, in one patient who continued training, developed into a chronic Salter Type IV stress fracture. A further patient, post-epiphyseal fusion, showed osteochondritis dissecans of the anterior aspect of the radial head. Seven patients exhibited a spectrum of olecranon changes from fragmentation of the epiphysis to chronic Salter Type I stress fractures of the growth plate. A follow-up survey found that, of those who responded to a questionnaire, nearly all the patients with articular surface damage failed to continue with competitive gymnastics whereas those with olecranon abnormalities were able to continue gymnastics at the same level. The mechanism of injury and the pathological changes are discussed.

Adolescent↗

PubMed1991

Prosthetic replacement of the distal femur for primary bone tumours.

Over a 16-year period, 135 custom-made distal femoral prostheses, based on a fully constrained Stanmore-type knee replacement, were used in the treatment of primary malignant or aggressive benign tumours. Survivorship analysis showed a cumulative success rate of 72% at five years and 64% at seven years. Intact prostheses in 91% of the surviving patients gave good or excellent functional results. Deep infection was the major complication, occurring in 6.8% of cases; clinical aseptic loosening occurred in 6.0%. Revision surgery was carried out for loosening and infection, and the early results are encouraging. We conclude that prosthetic replacement of the distal femur can meet the objectives of limb salvage surgery.

Adolescent↗

PubMed1991

Fracture of the humeral diaphysis with extreme rotation.

We report a spiral fracture of the humeral diaphysis with marked rotational deformity complicated by radial nerve neuropraxia in a young girl. Conservative management resulted in fracture healing and full recovery of the radial nerve palsy.

Child↗

PubMed1991

Relationship of serum copper and zinc levels to HIV-1 seropositivity and progression to AIDS.

Dietary, serum, and tissue levels of copper and zinc were determined at baseline in a cohort of homosexual men to investigate the relationship of these factors to human immunodeficiency virus type 1 (HIV-1) seropositivity and subsequent progression to AIDS. Using a nested case control design, 54 asymptomatic HIV-1 seropositives who later progressed to AIDS were compared with 54 HIV-1 seropositives who did not progress and 54 seronegatives (mean follow-up time 2.5 years). Serum levels of copper and zinc were estimated from frozen serum samples, tissue levels from stored toenail samples, and dietary intakes from a semiquantitative food frequency questionnaire administered at baseline. Neither dietary copper and zinc nor their levels in toenails were associated with HIV-1 seropositivity or progression to AIDS. However, serum copper levels were higher (p = 0.002) in HIV-1-seropositive progressors (mean = 115.6 micrograms/dl; SD = 17.1) than the seropositive nonprogressors (mean = 109.0 micrograms/dl; SD = 15.8) and the seronegatives (mean = 101.9 micrograms/dl; SD = 16.7). Conversely, serum zinc levels were lower (p = 0.016) in the seropositive progressors (mean = 85.2 micrograms/dl; SD = 11.5) than the seropositive nonprogressors (mean = 90.7 micrograms/dl; SD = 12.0) and the seronegatives (mean = 92.0 micrograms/dl; SD = 14.7). Furthermore, in a logistic regression, higher serum copper (odds ratio per 20-micrograms/dl increase = 2.23; 95% confidence interval = 1.02-4.87) and lower serum zinc (odds ratio per 20-micrograms/dl increase = 0.30; 95% confidence interval = 0.14-0.66) predicted progression to AIDS independently of baseline CD4+ lymphocyte level, age, and calorie-adjusted dietary intakes of both nutrients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗

PubMed1990

Phorbol ester effects on topoisomerase II activity and gene expression in HL-60 human leukemia cells with different proclivities toward monocytoid differentiation.

We examined the effects of phorbol ester treatment on topoisomerase II-mediated events in two human leukemia cell lines with different proclivities toward phorbol ester-induced monocytoid differentiation. HL-60 is the parent line that will terminally differentiate; 1E3 is a derived line that will not terminally differentiate. Within 24 h of phorbol ester treatment, etoposide-induced, topoisomerase II-mediated DNA cleavage declined 10-fold, whereas 4'-(9-acridinylamino)-methanesulfon-m-anisidide- induced DNA cleavage declined 3-fold in HL-60. In phorbol-treated 1E3, etoposide-induced DNA cleavage declined only 2-fold, whereas 4'-(9-acridinylamino)methanesulfon-m-anisidide-induced cleavage was barely affected. There was a 2- to 3-fold decline in topoisomerase II activity within the nuclear extracts from phorbol-treated HL-60 cells but not from phorbol-treated 1E3 cells. Immunoblotting experiments with anti-topoisomerase II antibodies indicated that phorbol treatment produced a structural change in the immunoreactive topiosomerase II in HL-60 nuclear extracts but produced no change in 1E3 topoisomerase II. Phorbol ester treatment also produced a decline in the level of topoisomerase II gene expression in HL-60 but not in 1E3 cells. By contrast, the cytotoxicity of etoposide in both lines was decreased following phorbol treatment. Thus, phorbols may uncouple the mechanisms linking drug-induced, topoisomerase II-DNA cleavable complex stabilization with drug-induced cytotoxicity, particularly in 1E3.

Amsacrine↗

PubMed1990

A base substitution at a splice site in the COL3A1 gene causes exon skipping and generates abnormal type III procollagen in a patient with Ehlers-Danlos syndrome type IV.

The dermis of a child with Ehlers-Danlos syndrome type IV (EDS-IV) contained about 11% of the normal amount of type III collagen and cultured dermal fibroblasts produced a reduced amount of type III procollagen which was secreted poorly. Type III collagen produced by these cells contained normal and abnormal alpha-chains and cyanogen bromide peptides. The site of the structural defect in the abnormal alpha 1 (III) chains was localized to the region of Met797, which is at the junction of the two carboxyl-terminal CB5 and CB9 cyanogen bromide peptides. Chemical cleavage of heteroduplexes formed between EDS-IV mRNA and a normal cDNA clone covering the CB5 and CB9 region showed that about 100 nucleotides were mismatched. Sequencing of amplified and cloned cDNA spanning the mutant region revealed a 108 nucleotide deletion corresponding to amino acid residues Gly775 to Lys810. The deleted nucleotide sequence corresponded to sequences that, by analogy to the organization of the type I collagen genes, should be precisely encoded by exon 41 of the COL3A1 gene. Sequencing of amplified genomic DNA, prepared using disimilar amounts of primers specific for exons 41 and 42, displayed a base substitution (G-to-A) in the highly conserved GT dinucleotide of the 5' splice site of intron 41. Normal sequences were also obtained from the normal allele. It is likely that the GT-to-AT transition at the splice donor site of intron 41 generated an abnormally spliced mRNA in which sequences of exon 40 and 42 were joined together with maintenance of the reading frame. The corresponding peptide deletion included the cyanogen bromide cleavage site Met797-Pro798 and the mammalian collagenase cleavage site at Gly781-Ile782. These losses account for the resistance of EDS-IV collagen to cyanogen bromide and mammalian collagenase digestion. Cultured fibroblasts produced normal homotrimer, mutant homotrimer, and mixed heterotrimer type III collagen molecules. The mutant homotrimer molecules were the major pepsin-resistant species and about 69% of the alpha 1(III) mRNA was in the mutant form.

Adenosine Triphosphatases↗