Identification of novel metabolites of butadiene monoepoxide in rats and mice

Differences in the metabolism of 1,3-butadiene (Bd) in rats and mice may account for the observed species difference in carcinogenicity. Previous studies of the metabolic fate of Bd have identified epoxide formation as a key metabolic transformation which gives 1, 2-epoxy-3-butene (BMO), although some evidence of aldehyde metabolites is reported. In this study, male Sprague-Dawley rats and male B6C3F1 mice received single doses of [4-14C]BMO at 1, 5, 20, and 50 mg/kg of body weight (0.014, 0.071, 0.286, and 0.714 mmol/kg of body weight). Analysis of urinary metabolites indicated that both species preferentially metabolize BMO by direct reaction with GSH when given by ip administration. The excretion of (R)-2-(N-acetyl-L-cystein-S-yl)-1-hydroxybut-3-ene (IIa), 1-(N-acetyl-L-cystein-S-yl)-2-(S)-hydroxybut-3-ene (IIb), 1-(N-acetyl-L-cystein-S-yl)-2-(R)-hydroxybut-3-ene (IIc), and (S)-2-(N-acetyl-L-cystein-S-yl)-1-hydroxybut-3-ene (IId) accounted for 48-64% of urinary radioactivity in rats and 46-54% in mice. The metabolites originating from the R-stereoisomer of BMO (IIc and IId) predominated over those arising from the S-stereoisomer (IIa and IIb) in both species. IIc was formed preferentially in mice and IId in rats. The corresponding mercaptoacetic acids, S-(1-hydroxybut-3-en-2-yl)mercaptoacetic acid (IIf) and S-(2-hydroxybut-3-en-1-yl)mercaptoacetic acid (IIg), were identified only in mouse urine (ca. 20% of the recovered radioactivity). 4-(N-Acetyl-L-cystein-S-yl)-1,2-dihydroxybutane (Ia), a metabolite derived from hydrolysis of BMO, accounted for 10-17% of the radioactivity in rat and 6-10% in mouse urine. 4-(N-Acetyl-L-cystein-S-yl)-2-hydroxybutanoic acid (Ib), 3-(N-acetyl-L-cystein-S-yl)propan-1-ol (Ic), and 3-(N-acetyl-L-cystein-S-yl)propanoic acid (Id), also derived from the hydrolysis of BMO, were only present in the rat. Metabolites of 1,2,3,4-diepoxybutane (DEB) were not detected after administration of BMO in rat or mouse urine. This study showed both quantitative and qualitative differences in the metabolism of BMO with varying doses and between species. The data aid in the safety evaluation of Bd and contribute to the interpretation of mathematical models developed for quantitative risk assessment and extrapolation of animals to humans.     

Assessment of the injuries sustained by pregnant sows housed in groups using electronic feeders

The incidence of injuries to pregnant sows kept in dynamic groups in a commercial herd was recorded over a period of 18 months. The sows were maintained in a solid-floored building with a straw-bedded lying area allowing 1.7 m2 per sow and fed by means of electronic feeders. Injuries on 12 possible areas of the body were assessed every week, and graded on the scale of 0 to 3 (maximum body score 36). The lesion scores sustained by the sows were very low, with a maximum of 19 and a median of 4. Lesions of the greatest severity constituted only 0.16 per cent of all the recorded injuries. The injuries were not distributed uniformly over the body, most being on the shoulders, flanks and hindquarters, with very few on the head or in the vulval region. The total injury score was related to parity, with sows in parities one, two and three sustaining more injuries than sows in later parities, and it was also related negatively to bodyweight. More agonistic interactions were observed between sows in the lying area and in the vicinity of the feeders than in the dunging area.     

Molecular and biochemical characterization of new X-ray-sensitive hamster cell mutants defective in Ku80

Ku, a heterodimer of approximately 70 and approximately 80 kDa subunits, is a nuclear protein that binds to double-stranded DNA ends and is a component of the DNA-dependent protein kinase (DNA-PK). Cell lines defective in Ku80 belong to group XRCC5 of ionizing radiation-sensitive mutants. Five new independent Chinese hamster cell mutants, XR-V10B, XR-V11B, XR-V12B, XR-V13B and XR-V16B, that belong to this group were isolated. To shed light on the nature of the defect in Ku80, the molecular and biochemical characteristics of these mutants were examined. All mutants, except XR-V12B, express Ku80 mRNA, but no Ku80 protein could clearly be detected by immunoblot analysis in any of them. DNA sequence analysis of the Ku80 cDNA from these mutants showed a deletion of 252 bp in XR-V10B; a 6 bp deletion that results in a new amino acid residue at position 107 and the loss of two amino acid residues at positions 108 and 109 in XR-V11B; a missense mutation resulting in a substitution of Cys for Tyr at position 114 in XR-V13B; and two missense mutations in XR-V16B, resulting in a substitution of Met for Val at position 331 and Arg for Gly at position 354. All these mutations cause a similar, 5-7-fold, increase in X-ray sensitivity in comparison to wild-type cells, and a complete lack of DNA-end binding and DNA-PK activities. This indicates that all these mutations lead to loss of the Ku80 function due to instability of the defective protein.     

"Big Smoke" has big risks: daily cigar use causes cancer, heart disease

BACKGROUND: To study the behaviour of recurrent benign parotid tumours, recurrence characteristics and problems faced with the removal of these lesions. METHODS: We reviewed the charts of the work of a single surgeon between 1971 and 1996. RESULTS: There were 24 patients (13 women, 11 men) with a mean age of 44 years at re-operation. Mean follow-up period was 10 years (range 1-22 years). There were 21 recurrent pleomorphic adenomas, two monomorphic adenomas and one patient with recurrent oncocytoma. Nine patients had solitary recurrence with a mean size of 14 mm, 15 patients had multiple recurrences with a mean size of 8 mm. There was malignant transformation of a previously benign lump in one patient. Three patients presented with a second or third recurrence. Overall facial nerve paralysis was 53% (38% temporary and 15% permanent). Frey's syndrome occurred in four patients (17%). CONCLUSIONS: Recurrent benign parotid tumours are uncommon if superficial parotidectomy (SP) is the performed initially; recurrence rates are between 0-4%. The recurrences are usually slow growing and require lengthy follow-up. Pre-operative diagnosis of a lump in the region of previous excision is useful in treatment planning. Malignant transformation in previous benign lump should be considered and fine needle aspiration biopsy may help in diagnosis. Facial nerve injury is more likely if the tumour is deep, in multiple sites or involves extensive scar tissue. Radiotherapy is controversial, it should be considered if there has been tumour spillage following re-operation.     

Affordable implant prosthetics using a screwless implant system

Many dentists have been reluctant to place dental implants because they have found that most implants are costly and time-consuming to place and have long-term maintenance problems. Most of these problems are caused by using screws to connect the abutment to the implant, the crown to the abutment or both. The use of a screwless implant system and conventional prosthetics, the author contends, can make implant dentistry affordable, versatile and easy to incorporate into all general dental practices.     

Periosteal augmentation of the acetabulum

The periosteum in children and especially infants has significant osteogenic potential. To determine the efficacy of periosteal flaps to assist in improving acetabular coverage in children with acetabular dysplasia, a series of experiments were designed using young rabbits. Three groups of five rabbits each had periosteal flaps fashioned and brought down from the anterolateral aspect of the innominate bone superior to the acetabulum and sutured to the capsule of the hip. The study was designed to examine the effects of the periosteal cambium layer in the formation of new bone to augment the acetabulum and to determine the effects of a periosteal flap plus cancellous bone graft. A control group of five rabbits underwent a sham operation of an open arthrotomy of the hip. Radiographic and histologic examination at 12 weeks revealed augmentation of the acetabulum with periosteal flaps that resulted in an average improvement of the acetabular index of 3.5 degrees and 6.6 degrees, without and with bone graft, respectively. New bone formation from the rim of the acetabulum averaged 3.9 mm with periosteal flaps alone and 4.6 mm with bone graft added. Periosteal augmentation of the acetabulum in conjunction with established procedures for augmenting acetabular coverage would appear to be a useful procedure for improving coverage of the femoral head in children with acetabular dysplasia.     

Biological characterization of Rev variation in equine infectious anemia virus

Sequence analysis identified significant variation in the second exon of equine infectious anemia virus (EIAV) rev. Functional analysis indicated that limited amino acid variation in Rev significantly altered the export activity of the protein but did not affect Rev-dependent alternative splicing. EIAV Rev can mediate export through two independent cis-acting Rev-responsive elements (RREs), and differences among Rev variants were more pronounced when both RREs were present. Variation in Rev may be an important mechanism for regulation of virus replication in vivo and may contribute to changes in clinical disease.     

Critical factors in the performance and cost of two-dimensional gene scanning: RB1 as a model

Two-dimensional (2-D) gene scanning (TDGS) is a method for mutation detection based on the electrophoretic separation of PCR-amplified DNA fragments according to size and base pair sequence. The use of denaturing gradient gel electrophoresis (DGGE) as the second separation step provides virtually 100% sensitivity, while the 2-D format allows the inspection of multiple gene fragments simultaneously. Analysis of many exons in parallel is greatly facilitated by extensive PCR multiplexing based on preamplification by long-distance PCR. Recently, TDGS has been applied to detect mutations in the retinoblastoma tumor suppressor gene RB1. Using RB1 as a model, we have now analyzed each step of the protocol, presenting overall improvements and a detailed cost analysis, where the total cost of the assay is found to be about $40 (US). An overall picture of TDGS cost-performance, as compared to direct sequencing, is provided as a function of the number of target fragments.