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T Hassell

Publications and source records attributed to T Hassell.

14 recordsLinked to original sources
PubMed1998

Cyclosporin A and hydroxycyclosporine (M-17) affect the secretory phenotype of human gingival fibroblasts.

The responsiveness of human gingival fibroblast populations to cyclosporin A (CsA) and its principal metabolite, hydroxycyclosporine (M17), was evaluated in cell culture. Gingival fibroblasts exhibited a dose-dependent accumulation and bell-shaped distribution of dansylated CsA. A 100-fold excess of non-labeled CsA prevented the accumulation of the fluorescent probe in the fibroblasts. Both CsA (400 ng/ml) and M17 (100 ng/ml) stimulated mean gingival fibroblast cell number to 23.2% and 36.7% above controls, and reduced mean collagen production by 37.7% and 37.4% below controls, respectively; however, neither CsA nor M17 affected mean protein production in comparison to control cultures. Analyses of responses to CsA and M17 by ligand-accumulating and non-accumulating fibroblasts sorted out from the parent cultures did not provide consistent interstrain responses either by cells representing the upper quartile of fluorescence or cells representing the bottom quartiles of fluorescence. These data demonstrate that CsA is accumulated by gingival fibroblasts and that CsA and M17 are potent modulators of gingival fibroblast phenotype.

Adolescent↗
PubMed1997

Clinical performance of resin-bonded fixed partial dentures and extracoronal attachments for removable prostheses.

STATEMENT OF PROBLEM: It is important to evaluate the long-term clinical performance of resin-bonded fixed partial dentures and extracoronal attachments for removable prostheses. PURPOSE: A prospective, long-term clinical study was conducted to evaluate the success of resin-bonded fixed partial dentures since 1985 and of resin-bonded extracoronal attachments from 1987. METHODS: Until 1993, a total of 130 resin-bonded fixed partial dentures had been seated in 101 patients, as well as 12 removable partial dentures (RPDs) with 24 extracoronal retainers in 10 patients. The clinical treatment protocol and the laboratory procedures were standardized. By the end of 1993, it was possible to reexamine 98 patients with a total of 127 resin-bonded fixed partial dentures and all 10 patients with removable partial dentures. The average time in function for the resin-bonded fixed partial dentures at the time of examination was 3.4 years and 2.3 years for the removable restorations. RESULTS: During the period of observation, one retainer failed on six of the resin-bonded fixed partial dentures, which represents a failure rate of 4.7%. Debonding of extracoronal attachments was recorded for 8.3% of the total number of retainers. CONCLUSION: The resin-bonded fixed partial denture technique can be considered to be a clinically reliable method of treatment, and permits the expansion of indications beyond a classical three-unit resin-bonded fixed partial denture. Long-term clinical success of removable partial dentures with resin-bonded extracoronal retainers warrants additional clinical studies.

Adolescent↗
PubMed1993

Identification of the predominant glycosaminoglycan-attachment site in soluble recombinant human thrombomodulin: potential regulation of functionality by glycosyltransferase competition for serine474.

Thrombomodulin (TM) is an endothelial cell thrombin receptor that converts thrombin from a procoagulant to an anticoagulant enzyme. It has previously been shown that TM is expressed in both a high-M(r) form containing chondroitin sulphate and a low-M(r) form lacking this modification. Site-directed mutagenesis of a soluble human TM derivative (TMD1) was employed to determine the attachment site(s) of this functionally important oligosaccharide on the core protein. Although there are four serine residues within the Ser/Thr-rich domain of TMD1 that might support glycosaminoglycan assembly, our analysis demonstrates that the primary site of attachment is at Ser474, and evidence is presented for low levels of attachment at Ser472. It was possible to improve the overall degree of attachment by mutating Ser472 to glutamic acid (so as to conform Ser474 to the xylosyltransferase acceptor consensus acidic-Gly-Ser-Gly-acidic); however, a significant proportion (approx. 35%) of the total TM still lacked a glycosaminoglycan moiety. Mutants that possess a substitution for Ser474 show an increased mobility of their low-M(r) form on SDS/PAGE compared with native TMD1. Isolation and sequencing of a C-terminal peptide demonstrated that this serine is modified in the low-M(r) form of native TMD1. An apparent 'acceptor consensus overlap' at Ser474 suggests that the mechanism behind the glycosaminoglycan split of TM may involve a competition for substrate between xylosyltransferase and N-acetylgalactosaminyltransferase.

Amino Acid Sequence↗
PubMed1993

The influence of age on collagen and non-collagen protein production by human gingival epithelial cells.

The effects of donor age on the proliferation and secretory phenotype of cultured human gingival epithelial cells were investigated. Pure cultures of epithelial cells were isolated from human gingiva of old (61-75 yr) and young (18-30 yr) adults and serially cultivated in a serum-free medium at 37 degrees C in humidified air containing 5% CO2. For each experiment, cells were seeded at 150/mm2 and the medium changed every other day. Cell number, collagen and non-collagen protein production and relative collagen synthesis (percentage collagen synthesized) were determined at days 2, 4, 6 and 8. Epithelial strains from old and young adults became confluent by day 8 and there were no differences in their rates of proliferation. Likewise there was no difference in collagen production between the two groups; however, cells from elderly individuals produced significantly less non-collagen protein. Over time the decrease in non-collagen protein production ranged from 56% below the non-collagen protein levels of epithelium from young adults at day 2 to 24% below at day 8. The reduction of non-collagen protein coupled with the unchanged secretion of collagen resulted in a statistically significant increase in relative collagen synthesis by epithelial cells from elderly individuals. These differences in non-collagen protein production and relative collagen synthesis by cultured gingival epithelium of old adults suggest a selective conversion in protein secretion.

Adolescent↗
PubMed1991

Disulfide pairing of the recombinant kringle-2 domain of tissue plasminogen activator produced in Escherichia coli.

The kringle-2 domain of tissue plasminogen activator, cloned and expressed in Escherichia coli (Wilhelm, O.G., Jaskunas, S.R., Vlahos, C.J., and Bang, N.U. (1990) J. Biol. Chem. 265, 14606-14611), was internally radiolabeled using [35S]methionine-cysteine. Following refolding and isolation, the labeled polypeptide was further purified by reverse-phase high performance liquid chromatography. The purified kringle-2 domain was digested with thermolysin, and the resulting peptides were purified by high performance liquid chromatography. Five major peptides containing 35S were obtained. Amino acid sequence analysis showed that these peptides represented various cleavage products containing one or more of the following disulfides: Cys180-Cys261, Cys201-Cys243, Cys232-Cys256 (sequence numbering based on Pennica et al. (Pennica, D., Holmes, W.E., Kohr, W.J., Hakins, R.N., Vehar, G. A., Ward, C.A., Bennett, W.F., Yelverton E., Seeburg, P.H., Heynecker, H.L., Goeddel, E.V., and Collen, D. (1983) Nature 301, 214-221)). These results confirm that the refolding methodology used produced kringle-2 with the predicted disulfide linkage and, thus, yielded material suitable for structural and functional studies.

Amino Acid Sequence↗
PubMed1991

Growth inhibition in animal cell culture. The effect of lactate and ammonia.

Eight independent cell lines accumulated ammonia in culture to concentrations between 1.3 and 2.9 mM. The growth inhibition of such concentrations of ammonium chloride when added to culture medium was variable. The cell lines tested could be divided into 3 groups depending on their growth response to 2 mM added NH4Cl. In the first group (293, HDF, Vero, and PQXB1/2) little (less than 14%) or no growth inhibition occurred. In the second group (McCoy and MDCK) a reduction in final cell yield of 50-60% was observed. The third group (HeLa and BHK) was most sensitive to the effects of NH4Cl with growth inhibition (greater than 75%) compared to controls. The growth inhibitory effect of added lactate up to 20 mM was negligible (less than 10%) for 3 cell lines, although one cell line (PQXB1/2) showed greater sensitivity. The interactive effects of ammonia and lactate were determined in a matrix experiment. At lactate (greater than 12 mM) and ammonia (1-4 mM), the growth inhibitory effects of the two components were synergistic. However, at low concentrations of lactate (less than 12 mM) the toxic effect of ammonia was reduced. A proposed mechanism for the sparing effect of lactate on ammonia toxicity is discussed. This may have importance in developing strategies for the optimal growth of ammonia-sensitive cell lines.

Ammonia↗
PubMed1990

Characterization of an internally initiated integrase protein of HIV-1 produced in E. coli.

In E. coli cells transformed by an expression vector for the production of the protease (PR) integrase (IN) of HIV-1, three vitally encoded proteins were produced: an 11-kDa protein and a 32-kDa protein identified by immunoassays as the mature PR and IN protein, respectively, and an additional protein 15-kDa in size that reacted strongly with an antiserum recognizing a region in the carboxyl half of the IN protein. The kinetics of its synthesis indicated that it was not a degradation product of p32-IN, rather it probably arose from internal initiation at an AUG codon in the middle of the IN gene. Amino terminal sequence analysis of the first 70 residues demonstrated a perfect match with those predicted from the nucleotide sequence, beginning with the methionine codon at position 154 of the integrase gene.

Amino Acid Sequence↗
PubMed1990

Adaptation to non-ammoniagenic medium and selective substrate feeding lead to enhanced yields in animal cell cultures.

Methods for the adaptation of three animal cell lines to media in which glutamine is replaced with either glutamate or 2-oxoglutarate are described. The cell lines differ in their rate of adaptation. The consequences of the adaptation of the McCoy cell line to a glutamate-based medium was measured in terms of: cell yield (increased by 17%), ammonia accumulation (reduced by 70%), glucose consumption (decreased by greater than 70%) and lactate accumulation (decreased by greater than 75%). The value of such adaptation and concomitant changes in energy metabolism lies in the potential for increased cell yields. Batch feeding of adapted cells in a microcarrier culture with a cocktail of glucose and amino acids resulted in increases in cell yields of 80% compared to unfed controls.

Adaptation, Physiological↗
PubMed1984

Phenytoin induced gingival overgrowth in institutionalized epileptics.

In a cross-sectional, epidemiological study of phenytoin induced gingival overgrowth in 77 institutionalized persons with epilepsy, the severity of the gum lesions was quantified by means of a precise new technique. Lesion severity was then compared statistically to other clinical and laboratory parameters. Positive correlations were detected between overgrowth severity and gingival inflammation, probing depths, calculus accumulation, plaque score and the measurement gingival margin to mucogingival junction (GM-MGJ). No correlation was observed between lesion severity and patients age, daily drug dosage, plasma or saliva phenytoin level, or salivary concentration of the major phenytoin metabolite.

Adolescent↗
PubMed1983

Salivary phenytoin levels in institutionalized epileptics.

Measurement of phenytoin (PHT) levels in saliva has been advocated as a monitor of plasma levels, and therefore of effective dosage. All studies to date have been performed on outpatients. We have now analyzed whole saliva from 62 mentally retarded, institutionalized, PHT-treated persons with epilepsy. Both PHT and its major human metabolite, 5-(para-hydroxyphenyl)-5-phenylhydantoin (pHPPH) were measured using gas-liquid chromatography. We detected large inter-individual variations in saliva PHT and pHPPH levels. Data were ranked and subjected to statistical analysis according to Spearman. Significant positive correlations were detected between daily PHT dose and plasma total PHT concentration, plasma PHT and salivary PHT, and daily dose and salivary PHT level. When data were categorized and analyzed according to the type of medication being administered in addition to PHT, different results were obtained. Polypharmacy can influence drug and metabolite levels and relationships in institutionalized persons with epilepsy.

Adolescent↗