Formaldehyde as a pre-treatment for dermal collagen heterografts

The preparation, stability both in vitro and in vivo and resistance to bacterial collagenase of trypsin-purified pig dermal collagen cross-linked with a range of concentrations of formaldehyde in phosphate-buffered saline, was studied using 14C-labelled formaldehyde as a tracer. Washing in phosphate-buffered saline at 37 degrees C produced rapid loss of formaldehyde over 6 weeks before stability was reached. After 19 weeks washing, 12-20% of the initial radioactivity remained, representing 6, 18 and 35 mumol formaldehyde/g of collagen after 21 days reaction with 0.1, 1 and 5% formaldehyde, respectively. Collagen, incorporating stable-bound formaldehyde arising from reaction with formaldehyde in concentrations of 0.5% or over, was totally resistant to bacterial collagenase. The stabilizing effect of formaldehyde cross-linking was also demonstrated by implants of fibrous pig dermal collagen in rats. After 8 weeks a significant constant amount of formaldehyde was retained in all implants. There was no net loss of mass over a 24 week period when pre-treated with 1% formaldehyde but some loss when pre-treated with 0.1% formaldehyde.

Killing of juvenile Fasciola hepatica by purified bovine eosinophil proteins

Eosinophils were isolated from the mammary gland of Fasciola hepatica-infected cattle by intramammary infusion with a crude extract from adult F. hepatica. Up to 5 x 10(9) eosinophils with a purity of over 90% could be obtained from a single quarter of the gland. The major contaminating cells were monocytes which reached their peak several days following the eosinophil peak. Two major proteins were isolated from bovine eosinophil granules, a high molecular weight peroxidase-active protein and a smaller molecular weight predominantly basic protein. This smaller protein was thought to be the bovine equivalent of guinea-pig and human major basic protein (MBP), although it possessed an unusually high concentration of cysteine. The bovine MBP had a profound effect on juvenile F. hepatica in vitro causing damage and death at concentrations down to 1 x 10(-6) M. The damage was detected by a 51Cr release assay and/or a viability assay involving microscopical examination of the flukes. Other cations, especially protamine sulphate, were also shown to kill flukes, although both lysozyme, found in neutrophils, and the peroxidase-positive peak from bovine eosinophils were unable to mediate any detectable damage.

Culture conditions affect photoreactivating enzyme levels in human fibroblasts

Photoreactivation of pyrimidine dimers in mammalian cells occurs under our experimental conditions but has not been observed under conditions used by others. We have tested three possible differences in experimental procedures including dimer separation and analysis methods, illumination conditions and cell culture techniques. We show that out methods of dimer separation and analysis indeed measure cis-syn pyrimidine dimers and give results in quantitative agreement with the methods of others. We find that while light pre-illumination of fibroblasts from the xeroderma pigmentosum line XP12BE or of normal cells does not affect the cellular capacity for dimer photoreactivation. However, we show that cell culture conditions can affect photoreactivating enzyme levels and thus, cellular dimer photoreactivation capacity. Cells grown in Eagle's minimal essential medium (supplemented with 15% fetal bovine serum) contain very low levels of photoreactivating enzyme and cannot photoreactivate dimers in their DNA; however, companion cultures maintained in Dulbecco's modified Eagle's minimal medium do contain photoreactivating enzyme and can photoreactivate cellular dimers.

Photoreactivation of pyrimidine dimers in the DNA of normal and xeroderma pigmentosum cells

Photoproducts formed in the DNA of human cells irradiated with ultraviolet light (uv) were identified as cyclobuytl pyrimidine dimers by their chromatographic mobility, reversibility to monomers upon short wavelength uv irradiation, and comparison of the kinetics of this monomerization with that of authentic cis-syn thymine-thymine dimers prepared by irradiation of thymine in ice. The level of cellular photoreactivation of these dimers reflects the level of photoreactivating enzyme measured in cell extracts. Action spectra for cellular dimer photoreactivation in the xeroderma pigmentosum line XP12BE agree in range (300 nm to at least 577 nm) and maximum (near 400 nm) with that for photoreactivation by purified human photoreactivating enzyme. Normal human cells can also photoreactivate dimers in their DNA. The action spectrum for the cellular monomerization of dimers is similar to that for photoreactivation by the photoreactivating enzyme in extracts of normal human fibroblasts.

An investigation of chromosome damage in Vicia faba root tips after exposure to 1-5 MHz ultrasonic radiation

Roots of seedlings of Vicia faba were exposed to 1-5 MHz continuous-wave ultrasound at approximately 5 W cm-2 intensity, averaged over the dividing region of the meristem, thus producing considerable non-thermal cell damage and severe inhibition of root growth. No significant increase in the number of coventional chromosome aberrations was observed during the 26 hours after exposure, although a significant number of cells did show bridged, agglomerated or clumped chromosomes. It is concluded that after exposure to ultrasound, genetic damage in surviving cells is unlikely.