Mechanisms of dialkyltin induced immunopathology

An organotin mixture found in polyvinyl chloride (PVC) pipe is not immunotoxic to adult Sprague-Dawley rats

Organotin compounds used in polyvinyl chloride (PVC) pipe production are of concern to the U.S. Environmental Protection Agency (EPA) because they leach from supply pipes into drinking water and are reported multisystem toxicants. Immune function was assessed in male Sprague-Dawley rats exposed to the mixture of organotins used in PVC pipe production. Although several of these organotins are reported immunotoxicants, their immunotoxicity as a mixture when given by drinking water has not been evaluated. Adult male rats were given drinking water for 28 d containing a mixture of dibutyltin dichloride (DBTC), dimethyltin dichloride (DMTC), monobutyltin trichloride (MBT), and monomethyltin trichloride (MMT) in a 2:2:1:1 ratio, respectively, at 3 different concentrations (5:5:2.5:2.5, 10:10:5:5, or 20:20:10:10 mg organotin/L), MMT alone (20 or 40 mg MMT/L), or plain water as a control. Delayed-type hypersensitivity, antibody synthesis, and natural killer cell cytotoxicity were evaluated in separate endpoint groups (n = 8/dose; 24/endpoint) immediately after exposure ended. The evaluated immune functions were not affected by the mixture or by MMT alone. Our data suggest that immunotoxicity is unlikely to result from the concentration of organotins present in drinking water delivered via PVC pipes, as the concentrations used were several orders of magnitude higher than those expected to leach from PVC pipes.

Immune function is not impaired in Sprague–Dawley rats exposed to dimethyltin dichloride (DMTC) during development or adulthood

Organotins are used commercially as pesticides, antifouling agents and stabilizers for polyvinyl chloride (PVC) pipe. Mono- and di-substituted butyltins, used in PVC pipe production, are of concern to the US EPA because they leach from supply pipes into drinking water and are reported multisystem toxicants. We assessed several immune functions in Sprague-Dawley rats after adult or developmental dimethyltin dichloride (DMTC) exposure because various organotins have been reported to be immunotoxic. Adult male and female rats were given drinking water containing 0, 20 or 40 mg DMTC/L (0, 1.7, or 3.4 mg DMTC/kg body weight [BW]) for 28 days. Pregnant females were given the same DMTC drinking water concentrations for a total of 37 days, from gestational day (GD) six through weaning of pups (0, 2.4, or 4.6 mg DMTC/kg BW during gestational exposure; 0, 3.6, or 6.9 mg DMTC/kg BW during postnatal exposure). On postnatal day (PND) two, litters were sexed, weighed, and culled to four males and four females per dam. Delayed-type hypersensitivity (DTH), antibody synthesis, and natural killer (NK) cell activity were evaluated in adults (N=8/sex/group) and in immunologically mature offspring (N=6/sex/group). Although water consumption was decreased in all of the DMTC dose groups, the immune functions evaluated were not affected. Our data suggest that these immune functions are not sensitive to the levels of DMTC anticipated to occur in drinking water delivered via PVC pipe as the concentrations we used were several orders of magnitude higher than those expected to leach from PVC pipes.

Interactions of two cytotoxic organotin(IV) compounds with calf thymus DNA

The reactions with DNA of two antitumor active organotin(IV) compounds, the dimer of bis[(di-n-butyl 3,6-dioxaheptanoato)tin] (C(52)H(108)Sn(4)O(1) x 2H(2)O), compound 1, and tri-n-butyltin 3,6,9-trioxodecanoate (C(19)H(40)SnO(5) x 1/2H(2)O), compound 2, were analysed by circular dichroism, DNA melting experiments and gel mobility shift assays. It is found that both complexes modify only slightly the B-type circular dichroism spectroscopy (CD) spectrum of calf thymus DNA. On the other hand, both complexes were found to affect significantly the parameters of the thermally induced helix-to-coil transition. Addition of 1 or 2 to calf thymus DNA samples does not favor DNA renaturation after melting ruling out formation of interstrand crosslinks. Moreover, the effects of both compounds on plasmid DNA gel mobility were investigated. From the analysis of the present results it is inferred that both organotin(IV) compounds do interact with DNA, probably at the level of the phosphate groups.

Toxicity of dibutyltin, tributyltin and other organotin compounds to humans and to experimental animals

Alkyltin compounds are used as stabilizers and antifouling agents. Food chain accumulation and bioconcentration have been demonstrated in crabs, oysters and salmon exposed to tributyltin oxide. In mammalian species, tributyltin compounds may be metabolized to dibutyltin derivatives and related metabolites. Di- and tributyltins appear to be less potent neurotoxicants than trimethyltins and triethyltins. Dibutyltins and tributyltins produced bile duct damage in rats, mice and hamsters. Tributyltin oxide and dibutyltin and dioctyltin compounds are potent thymolytic and immunotoxic agents in rats. Tributyltin oxide at 5 ppm in the rat diet produced immunotoxicity in a 2-year feeding study, and at 50 ppm increased the incidence of tumors of endocrine origin. In preliminary reports, 5 ppm tributyltin produced no detectable increase in tumor incidence, and 0.5 ppm produced no detectable immunotoxicity in long-term studies. Tributyltin oxide and dibutyltin acetate did not appear to be mutagenic in a large battery of mutagenicity assays but produced base-pair substitutions in one of the bacterial strains tested. Tributyltin oxide produced mutations in Chinese hamster ovary cells, increased the incidence of micronuclei in the erythrocytes of exposed male BALB/c mice, and was highly embryotoxic in vitro. Embryotoxic and teratogenic effects in mice exposed to tributyltin oxide in vivo may have been due either to direct tributyltin oxide action or responses secondary to maternal toxicity. More information is needed to determine the applicability to human risk assessments of the immunotoxicity data derived from rat studies and to establish a definitive tolerable daily intake for tributyltin oxide.