Marilyn C. Plowman

Teratogenicity of Ni2+ inXenopus laevis, assayed by the FETAX procedure

The teratogenicity of Ni2+ was tested by the FETAX (Frog Embryo Teratogenesis Assay:Xenopus) procedure in the South African frog,Xenopus laevis. In seven assays, beginning at 5 h postfertilization, groups ofXenopus embryos were incubated for 96 h in media that contained Ni2+ (added as NiCl2) at concentrations ranging from 1 × 10−7 to 3 × 10−3 mol/L; control groups were incubated in the same medium without added NiCl2. At 101 h postfertilization, surviving embryos were counted, fixed in formalin, and examined by microscopy to determine their developmental stages, malformations, and head-to-tail lengths. In control embryos, survival was ≥95% and malformations were ≤7%. Malformations were found in >95% of embryos exposed to Ni2+ concentrations ≥5.6 μmol/L. The most frequent malformations in Ni2+-exposed embryos were ocular, skele|tal, and intestinal deformities; less common malformations included facial, cardiac, and integumentary deformities. Other abnormalities, not categorized as malformations, included stunted growth, dermal hypopigmentation, and coelomic effusions or hemorrhages. Themedian embryolethal concentration (LC50) of Ni2+ was 365 (SE±9) μmol/L; themedian teratogenic concentration (EC50) was 2.5 (SE±0.1) μmol/L; theTeratogenic Index (TI=LC50/EC50) was 147 (SE±5), indicating that Ni2+-exposures were limited to specific 24 h periods showed thatXenopus embryos were most susceptible to Ni2+-induced malformations on the second and third days of life, during the most active period of organogenesis.

Intraarticular carcinogenesis bioassays of CoCrMo and TiAlV alloys in rats

Wear-debris powders of cobalt-chromium-molybdenum (CoCrMo) and titanium-aluminum-vanadium (TiAlV) alloys, which are widely used for orthopedic implants (eg, hip and knee prostheses), were tested for carcinogenic activity following intraarticular administration (20 mg/rat) to groups of 44 male Fischer-344 rats (Charles River Breeding Laboratories, North Wilmington, MA). Control groups received similar intraarticular injections of either a noncarcinogen (manganese powder, negative control rats) or a potent carcinogen (nickel subsulfide powder, positive control rats). The experimental groups of 8-12 rats were observed for 24 months after injection. No local tumors developed at the injection site in the negative control rats or in rats that received the CoCrMo or TiAlV powders; poorly differentiated or pleomorphic sarcomas developed at the injection site in 10 of the 12 positive control rats that were treated with nickel subsulfide. Incidences of primary tumors distant from the injection site did not differ significantly among the experimental groups. This study shows that, under experimental conditions, any carcinogenic activity of CoCrMo or TiAlV wear-debris powders is weak in comparison to nickel subsulfide. Based on this study and observations in other laboratories, intraarticular administration of test materials to rats provides a practical, reliable, and biologically relevant method for carcinogenesis testing of biomaterials used for orthopedic implants.

Uptake and release of63Ni2+ byXenopus embryos during early cleavage stages

Uptake and release of 63Ni was studied in dejellied Xenopus laevis embryos exposed to 63Ni2+ (0.3-30 mumol/l) for 0.5-h intervals during the period 1-4.5 h post-fertilization (i.e. from first cleavage to early blastula stage). At first cleavage, the mean uptake of 63Ni by embryos was 12-17 times that by non-fertilized eggs, suggesting that conversion of the vitelline envelope to the fertilization envelope enhanced integumental permeability to 63Ni2+. 63Ni uptake by embryos at the 1-2-cell stage averaged 1.8-2.5 times that at the early blastula stage. An average of 5% of total 63Ni in washed embryos was recovered in isolated fertilization envelopes, indicating that 63Ni2+ passed through the envelope into internal compartments. Progressive increases of 63Ni uptake were seen with increasing exposure levels; after exposure during 1-1.5 h post-fertilization to the highest concentration of 63Ni2+ (30 mumol/l), 63Ni uptake averaged 11.4 (SD +/- 5.1) pmol/embryo. Rapid efflux of 63Ni was noted after 63Ni2(+)-exposed embryos were transferred to nickel-free medium; mean 63Ni contents at 0.25 h and 2 h post-exposure diminished to 50% and 15% of the initial values, regardless of the exposure level. The finding that Xenopus embryos are permeable to 63Ni2+ during early cleavage stages provides a convenient experimental system to investigate the embryotoxicity and teratogenicity of nickel.SummaryUptake and release of63Ni was studied in dejelliedXenopus laevis embryos exposed to63Ni2+ (0.3–30 μmol/1) for 0.5-h intervals during the period 1–4.5 h post-fertilization (i.e. from first cleavage to early blastula stage). At first cleavage, the mean uptake of63Ni by embryos was 12-17 times that by non-fertilized eggs, suggesting that conversion of the vitelline envelope to the fertilization envelope enhanced integumental permeability to63Ni2+. 63 Ni uptake by embryos at the 1-2-cell stage averaged 1.8–2.5 times that at the early blastula stage. An average of 5% of total63Ni in washed embryos was recovered in isolated fertilization envelopes, indicating that63Ni2+ passed through the envelope into internal compartments. Progressive increases of63Ni uptake were seen with increasing exposure levels; after exposure during 1–1.5 h post-fertilization to the highest concentration of63Ni2+ (30 μmol/1),63Ni uptake averaged 11.4 (SD±5.1) pmol/embryo. Rapid efflux of63Ni was noted after63Ni2+-exposed embryos were transferred to nickel-free medium; mean63Ni contents at 0.25 h and 2 h post-exposure diminished to 50% and 15% of the initial values, regardless of the exposure level. The finding thatXenopus embryos are permeable to63Ni2+ during early cleavage stages provides a convenient experimental system to investigate the embryotoxicity and teratogenicity of nickel.