Effects of calcium and magnesium salts on nickel subsulfide carcinogenicity in Fischer rats

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Abstract
The effects of calcium or magnesium salts administered by one of three different routes on the formation of muscle tumors by nickel subsulfide (Ni 3 S 2 ) in Fischer F344 rats were determined. Eleven groups of 20 weanling male rats each received a single injection of 2.5 mg (31 μmol Ni) Ni 3 S 2 into the thigh muscles of both hind limbs (i.m.). Then the rats were fed 3% calcium acetate (CaAcet)- or 3% magnesium acetate (MgAcet)-supplemented diets for 3 and 6 months, or were injected s.c. three times weekly, with 0.16 mmol doses of CaAcet/kg/injection, or with 2 mmol doses of MgAcet/kg/ injection, for 1 or 4 months. Two other groups of 20 rats were injected i.m. with 2.5 mg (31 μmol Ni) of Ni 3 S 2 mixed with 6.2 mg (62 μmol Ca) of calcium carbonate (CaCarb), or with 6.3 mg (62 μmol Mg) of magnesium basic carbonate (MgCarb). The control groups of rats received single i.m. injections of the 0.15 M saline vehicle, 6.2 mg CaCarb, and 6.3 mg MgCarb, or s.c. injections of 0.15 M saline, or 4 mmol sodium acetate, NaAcet/kg/injection, three times weekly for 4 months. After 18 months, injection site tumors were found: (i) in 70–90% of the rats injected i.m. with Ni 3 S 2 and fed standard diet or the diets containing CaAcet or MgAcet, with no significant differences among the groups; (ii) in 95 –100% of the rats given i.m. Ni 3 S 2 and then treated with multiple s.c. injections of saline, NaAcet, CaAcet or MgAcet, with no significant differences among the groups; (iii) in 85% of rats injected i.m. with Ni 3 S 2 + CaCarb, and (iv) in 25% of the rats injected i.m. with Ni 3 S 2 + MgCarb. No tumors developed in the control rats. The admixtures of CaCarb or MgCarb to Ni 3 S 2 did not affect the mobilization of nickel from the injection site. They did, however, influence the cellular responses to Ni 3 S 2 in early stages, from 3 days to 22 weeks, after the injection. MgCarb, unlike CaCarb, strongly decreased the necrosis and increased macrophage proliferation at the Ni 3 S 2 injection site. It also delayed the occurrence and proliferation of histiocytic-stromal cells, and prevented the occurrence of altered myoblasts.