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M J Willins

Publications and source records attributed to M J Willins.

5 recordsLinked to original sources
PubMed1992

Effect of chemical modifications on the susceptibility of collagen to proteolysis. II. Dehydrothermal crosslinking.

Collagen was dehydrothermally treated (heat cured) by heating dry under vacuum at 60, 80, 100 and 120 degrees C. The change in stability was determined by subjecting to measurement of gross crosslinking, content of lysino-alanine and naturally occurring collagen crosslinks, shrinkage temperature (TM), susceptibility to digestion by lysosomal thiol proteases, and susceptibility to pepsin and trypsin. Morphological changes were examined by electron microscopy. The in vivo biodegradation of dehydrothermally treated collagen sponges was investigated using a rat lumbar muscle implantation model for up to 28 days. For all heat-cured collagens, the data strongly indicated that both crosslinking and denaturation/degradation was present in increasing quantities with increasing temperature of treatment, its level was too low (maximum 179 pmol mg-1) to account for the decreased solubility and increased molecular weight gross changes observed. Increasing resistance of treated collagen to both lysosomal cathepsins and pepsin correlated well with increased crosslinking and increasing temperature of the heat-curing process. However, increased denaturation/degradation of the collagen at higher temperatures was revealed by electrophoretic analysis, trypsin hydrolysis data and by electron microscopy. Differential scanning calorimetry (d.s.c.) correlated well with these results showing an increased level of denaturation in heated samples. The in vivo study showed little difference between control and heat-cured samples except for the material treated at 120 degrees C which was biodegraded in vivo at a significantly faster rate. The data shows, therefore, that crosslinking induced by the dehydrothermal treatment of collagen decreases its rate of proteolysis at acid pH in vitro. However, the simultaneous denaturation/degradation of the protein during the heat-cure process appears to be a more important factor in determining the fate of the material implanted into rat muscle.

Animals↗
PubMed1990

Cellular invasion and breakdown of three different collagen films in the lumbar muscle of the rat.

Collagen films were prepared by three different methods involving acid homogenization at pH 3.0 of a collagen suspension for 1.5 min (film A) and 15 min (film B) and alkaline homogenization at pH 10 for 15 min (film C), after which the resulting slurries were degassed and dried over sterile air. Subsequent examination by scanning electron microscope (SEM) revealed that all samples showed a distinctly layered structure which was much finer in the acid films. Implantation into the lumbar muscle of rats followed by histology and SEM studies revealed that film B was completely resorbed at 14 d whereas remnants of film A could still be seen at this period. The slowest rate of resorption was observed with film C, traces of which could still be found at 70 d. Invading inflammatory cells moved into the collagen films between the layers from the edges only causing the whole structure to 'ribbon out'. The surfaces of all three films appeared to be impenetrable to cells. Incubation of the three films with bacterial collagenase revealed similar relative rates of degradation to those observed in vivo.

Absorption↗
PubMed1983

Genetic effects of 2-methoxyethanol and bis(2-methoxyethyl)ether.

2-Methoxyethanol and bis(2-methoxyethyl)ether were subjected to the following assays for genetic toxicity: Ames' test, unscheduled DNA synthesis (UDS) assay in human embryo fibroblasts, sex-linked recessive lethal (SLRL) test in Drosophila, dominant lethal test in male rats, bone marrow metaphase analysis in male and female rats, and the sperm abnormality test in mice. In vivo test animals were exposed to atmospheric concentrations of 25 or 500 ppm 2-methoxyethanol and 250 or 1000 ppm bis(2-methoxyethyl)ether. Point mutations in Ames' test and UDS in fibroblasts were not increased by either compound, while the SLRL test gave ambiguous results which deserve further investigation. Chromosomal aberration frequencies were not increased in rat bone marrow, but there was evidence from the dominant lethal tests that both compounds have profound effects upon male rat fertility during the meiotic phase. Pregnancy frequency was greatly reduced and preimplantation losses were large. In addition, there was evidence of postimplantation losses. Sperm abnormalities were increased in mice exposed to both compounds, but particularly bis(2-methoxyethyl)ether. These effects on male reproductive cells were confined to the higher concentrations of both compounds. It was concluded that the weak mutagenic and particularly the strong antifertility effects described here are important for the safety evaluation of these ethylene glycol ethers.

Animals↗
PubMed1983

In vitro and in vivo studies on the potential mutagenicity of alclofenac, dihydroxyalclofenac and alclofenac epoxide.

Alclofenac (A) and two of its metabolites, dihydroxyalclofenac (DHA) and alclofenac epoxide (AE), were tested for their mutagenic potential. Alclofenac and DHA showed no mutagenic, transforming or clastogenic potential in any in vitro experiment. The addition of a supplementary metabolic activation system did not change the response of those two compounds in any test procedures in vitro. AE, an intermediary metabolite between A and DHA, was mutagenic by itself in the Ames test, but in the presence of a liver post-mitochondrial fraction its activity of Salmonella typhimurium was greatly decreased. Dominant lethal mutations were not induced in male rats given alclofenac, and AE had no effect in the micronucleus test. In human volunteers given alclofenac at therapeutic dose levels, no mutagenic activity was found in the urine and no significant increase in the incidence of structural chromosome aberrations was observed in peripheral blood lymphocytes.

Animals↗