Toxicity of organotin compounds for polymorphonuclear leukocytes: the effect on phagocytosis and exocytosis

Accumulation of organotin compounds and mercury in harbour porpoises (Phocoena phocoena) from the Danish waters and West Greenland

The concentrations of butyltin (summation operatorBT=TBT+DBT+MBT) and mercury (Hg) were determined in the liver of 35 harbour porpoises (Phocoena phocoena), which were found dead along the coastlines or caught as by-catch in the Danish North Sea and the Inner Danish waters. In addition, three harbour porpoises hunted in West Greenland were analysed. High levels of butyltin and mercury, within the range of 68-4605 mg BT/kg ww and 0.22-92 mg Hg/kg ww, were found in the liver of the Danish harbour porpoises and both substances tend to accumulate with age. The levels in the harbour porpoise from West Greenland were 2.0-18 mg BT/kg ww and 6.3-6.9 mg Hg/kg ww, respectively. The concentrations of butyltin and mercury were both found to be higher in stranded than in by-caught harbour porpoises but only the butyltin concentration was significantly higher in stranded porpoises in the age group 1-5 years. These substances are suspected of inducing adverse effects on immune and endocrine systems in mammals and they may thereby pose a threat to the animals. This study suggests that organotin compounds are also important, when assessing the risks of contaminants on the health and viability of harbour porpoises in Danish waters.

Tributyltin-sulfhydryl interaction as a cause of immunotoxicity in phagocytes of tunicates

We reported elsewhere that tributyltin (TBT) has detrimental effects on the immune system of the colonial ascidian Botryllus schlosseri, through interaction with calmodulin and alteration of Ca2+ homeostasis. Here, we studied the capability of TBT to react with intracellular thiols. After exposure to 0.1 microM TBT, a significant decrease in B. schlosseri hemocytes stained for total thiols and reduced glutathione (GSH) was detected. Exogenous sulfhydryl and sulfide compounds can prevent TBT-induced cell morphology alterations and decrease the percentage of tin-containing hemocytes, indicating the scavenging ability of thiol peptides. No effects were observed with disulfides, N-acetylcysteine, or the GSH fragment Cys-Gly. No interactions were observed with TBT and carmustine, whereas TBT and N-ethylmaleimide (NEM) showed a combined antagonistic action, suggesting direct interaction of TBT with thiol-containing compounds. Regulation of Ca2+ efflux from internal stores seems to depend on stimulation of the inositol 1,4,5-trisphosphate (InsP3) receptor by oxidized glutathione (GSSG), which results from interactions of both TBT-GSH and TBT-GSH reductase.

Brief exposure to triphenyltin produces irreversible inhibition of the cytotoxic function of human natural killer cells

Phenyltin (PT) compounds (mono-, di-, and triphenyltins) are used in agricultural and consumer products. They contaminate the environment and have toxic effects on aquatic and terrestrial animals including humans. In an earlier study we demonstrated that PTs (1 micro M, for 1h in vitro exposure) could cause considerable inhibition of the tumor-killing function of human natural killer (NK) cells (as much as 85%). In this study we examined whether cytotoxic function can be recovered after a brief exposure (1h) to PTs. Freshly isolated lymphocytes were exposed to triphenyltin (TPT) or diphenyltin (DPT) for 1h. The compound was then removed and the cells were incubated in PT-free medium for as long as 6 days. The results indicated that exposure to 750nM TPT for 1h caused an approximately 63+/-10% decrease in NK-cytotoxic function. However, if the cells were exposed to 750nM TPT for 1h and then allowed to incubate in TPT-free medium for 24h, there was a 91+/-12% loss of cytotoxic function. NK-cytotoxic function remained inhibited for as long as 6 days after removal of the TPT. A 1-h exposure to as much as 5 micro M DPT caused no loss of NK-cytotoxic function when the cells were tested immediately after the exposure. However, if the cells were allowed to incubate in DPT-free medium for 24h after the 1-h exposure to 5 micro M DPT, cytotoxicity was inhibited by 68+/-29% and this inhibition persisted for at least 6 days. These results indicated that short-term exposure to PTs caused persistent negative effects on human NK-cell function. The persistent effects of PTs are compared to those of the butyltins (BTs).

Triphenyltin enhances the neutrophilic differentiation of promyelocytic HL-60 cells

Triphenyltin (TPT) is an environmental endocrine disruptor and toxic substance, but little information is available on its immunological effects. To assess the effect of TPT on leukocyte differentiation, we investigated its effect on the neutrophilic differentiation of HL-60 cells induced by dimethyl sulfoxide and granulocyte colony-stimulating factor (G-CSF) for 6 days. At a low concentration, 10(-7)M, TPT increased superoxide production by differentiated HL-60 cells stimulated with opsonized zymosan (OZ) by about 45% and increased expression of CD18, a component of the OZ-receptor, by about 90%. Real-time PCR analysis revealed that TPT augmented the expression not only of CD18 but also of components of superoxide-generating NADPH-oxidase, p47phox, 2.7-fold, and p67phox, 2.0-fold, and of granulocyte colony-stimulating factor receptor (G-CSFR), 3.0-fold, whereas various other endocrine disruptors, including parathion, vinclozolin, and bisphenol A, had no such enhancing effects. The results of a DNA macroarray analysis showed that TPT enhanced the expression of G-CSFR and certain other neutrophil functional proteins, including CD14 and myeloid leukemia cell differentiation protein (MCL-1), and that TPT induced a decrease in expression of LC-PTP, leukocyte protein-tyrosine phosphatase, to about half the control level. The TPT-dependent suppression of LC-PTP was confirmed by real-time PCR analysis, and the results of immunoblotting indicated that TPT enhances the expression of myeloid specific tyrosine kinase hck by about 30% at the protein level, and this together with the reduction of LC-PTP may enhance tyrosine phosphorylation, in turn resulting in enhancement of superoxide production. These findings suggest that TPT may have an enhancing effect on the neutrophilic maturation of leukocytes.

Tributyltin induces human neutrophil apoptosis and selective degradation of cytoskeletal proteins by caspases

Tributyltin (TBT) has frequently been used as a pesticide and in biocidal paints for marine vessels, leading to its presence in the environment. Although TBT was recently found to induce apoptosis in different immune cells, by a mechanism that is not fully established, its effect on neutrophils is not known. In this study, it was found that TBT induced apoptosis in human neutrophils as assessed by cytology, flow cytometry, and degradation of the microfilament-associated protein gelsolin. Furthermore, data showed that TBT induced neutrophil apoptosis by a caspase-dependent mechanism, since addition of z-Val-Ala-Asp(MOe)-CH(2)F (z-VAD-FMK) in the culture prevented the effect of TBT. It was also found that the cytoskeletal proteins gelsolin, paxillin, and vimentin, but not vinculin, were degraded by TBT via caspases, as assessed by immunoblotting. Data indicate that gelsolin, paxillin, and vimentin are three caspase substrates involved in both spontaneous and TBT-induced neutrophil apoptosis. Cells were not necrotic as assessed by trypan blue dye exclusion, and this is in agreement with the absence of vinculin degradation. Evidence indicates that TBT-induced fragmentation of cytoskeletal proteins via caspases is a process that is tightly regulated.

Evaluation of tributyltin subchronic effects in tropical freshwater fish (Astyanax bimaculatus, Linnaeus, 1758)

Tributyltin (TBT) is widely used as a biocide in antifouling paints. Astyanax bimaculatus adult fish were acclimatized in a laboratory and isolated in groups of eight individuals. Two groups were used as a control (similar handling and corn oil control) and one group was exposed to TBTCI dissolved in corn oil (0.0688 +/- 0.0031 microg TBT.g(-1)) every 6 days for 32 days. Light and transmission electron microscopy were used to investigate the morphological effects on liver. A muscle fragment was excised for the determination of the acetylcholinesterase activity and blood smears were obtained for differential white cell counts. The results indicated nuclear irregular shapes, chromatin condensation, presence of intranuclear lipid bodies, and degenerative nuclei. Acetylcholinesterase activity was not affected by TBT exposure. The increasing number of neutrophils may represent cytotoxic and stress conditions facilitating the invasion of opportunist organisms. According to the authors' data, TBT was confirmed as a powerful aquatic contaminant to fish in tropical ecosystem.

Toxoplasmosis in beluga whales (Delphinapterus leucas) from the St Lawrence estuary: two case reports and a serological survey

Toxoplasmosis was diagnosed in two free-ranging beluga whales from the St Lawrence estuary, Quebec, Canada, in 1988 and 1998. Histologically, tachyzoites and bradyzoites were present in the brain, spleen, lymph nodes, adrenals and lungs of both animals, and in the thymus of one. These organisms were readily labelled by an indirect immunohistochemical method for Toxoplasma gondii antigens. In the lymph nodes, spleen and lungs the organisms were associated with histiocytic infiltration. In the brain of one animal they were associated with mild multifocal gliosis and haemorrhages. There was no evidence of concomitant morbillivirus infection. Serum samples were collected from 22 beluga whales stranded between 1995 and 1998 on the shores of the St Lawrence Estuary and examined for antibodies to T. gondii by the modified agglutination test. Antibody titres of s25 were found in six (27%) of the animals. This is the first confirmed report of toxoplasmosis in beluga whales.

Butyltin residues in livers of humans and wild terrestrial mammals and in plastic products

Butyltin compounds (BTs) including mono-(MBT), di-(DBT) and tributyltin (TBT) were determined in livers of humans and wild terrestrial mammals, such as raccoon dogs (Nyctereutes procyonoids) and monkeys (Macaca fuscata) from Japan. In addition, 22 samples of plastic products were analyzed. BT residues were detected in all the liver samples of humans and raccoon dogs, with concentrations of <360 ng/g wet wt, whereas concentrations in the liver of monkeys were either less than the detection limit or were only in trace levels. Elevated concentrations of BTs, particularly DBT (<140,000 ng/g) and MBT (<130,000 ng/g), were found in some plastic products, such as baking parchments made from siliconized paper and gloves made up from polyurethane. The results of a cooking test using the above baking parchment indicated the transfer of BTs to foodstuffs. These observations suggest expansion of BT contamination among terrestrial mammals. BT pollution from industrial appliances, such as plastic stabilizers and catalysts other than those of marine origin as antifouling agents, are suggested as alternative sources of exposure.

Immunotoxic effects of organotin compounds in Tapes philippinarum

One of the most harmful groups of coastal pollutants is the organotin compounds (OTCs) which have severe effects on both aquatic organisms and mammals including humans. The immunotoxic effects of OTCs were studied in the cultivated clam Tapes philippinarum by determining the immunosuppressant role on in vitro yeast phagocytosis at low doses (0.01, 0.05, 0.1 microM). The phagocytic index was significantly reduced in an irreversible non-lethal manner depending on concentration and lipophilic affinity. The order of inhibition was TBT > or = DBT > MBT for butyltins and TPTC > TPTA > or = TPTH for triphenyltins.

Cytoskeleton alterations by tributyltin (TBT) in tunicate phagocytes

The effects of tributyltin chloride (TBT) on cytoskeletal components, as possible cell targets of toxicity, were examined on cultured hemocytes of the colonial ascidian Botryllus schlosseri by means of indirect immunofluorescence. The immunotoxic effect of 10 microM TBT (sublethal concentration) consists of (1) inhibition of yeast phagocytosis, Ca2+ ATPase activity, and respiratory burst; (2) increase in intracellular Ca2+ concentration; and (3) alterations in cell morphology. After 60 min, TBT-exposed amebocytes become spherical, withdrawing their long pseudopodia, and lose motility. Their microfilaments assemble in clusters around the peripheric cytoplasm, indicating massive disassembly, with the exception of unaltered adhesion plaques. Analogously, their microtubules reveal extensive disaggregation, being scattered in the cytoplasm and not recognizable as single filaments, whereas the microtubule organizing center (MTOC) is still visible. Treatment together with 20 micrograms/ml calmodulin (CaM) can partially restore the cytoskeleton architecture. These results suggest a relationship between TBT and Ca2+ homeostasis in ascidian hemocytes. By interfering with Ca2+ ATPase activity through CaM inhibition, either directly or indirectly, TBT induces an excess of intracellular Ca2+ accumulation, which first causes internal disorganization of cytoskeletal proteins and consequently inhibition of phagocytosis, beginning from chemotaxis and particle adhesion.

In vitro inhibition of hepatic cytochrome P450 and enzyme activity by butyltin compounds in marine mammals

The present study attempted to examine the in-vitro inhibition of hepatic microsomal P450 content and activity by butyltins in marine mammals and discussed on their possible effects in animals in the wild. Decreases in P450 content and the activities of ethoxyresorufin O-deethylase (EROD, catalyzed by CYPIA subfamily) and penthoxyresorufin O-depentylase (PROD, catalyzed by CYP2B subfamily) by tributyltin (TBT) were observed in in-vitro experiments using hepatic microsomes of a pinniped and a cetacean. Among P450 family, EROD activity is more sensitive to TBT than P450 content and PROD activity, indicating a specific mode of action of TBT on different P450 forms. On the other hand, dibutyltin and monobutyltin have no inhibitory effect on EROD activity at concentrations less than 0.5 mM, indicating that the inhibition of enzyme activity in hepatic microsome of marine mammal is mainly by TBT. TBT concentrations that affect P450 contents and activities are above 10 times higher than the values found in the liver of various marine mammals.

F-actin levels but not actin polymerization are affected by triphenyltin in HL-60 cells

The toxin triphenyl tin (TPT), Sn(C(6)H(5))(+)(3) caused a rapid decrease in the F-actin content of promyelocytic human leukemia cells (HL-60) chemically differentiated to neutrophils. Prior incubation (2 min) of the cells with 10 μM TPT did not modify the extent of actin polymerization inducible either by a receptor-mediated stimulus (chemotactic peptide fMLP) or by a direct activator of G proteins (AlF(-)(4)). The inorganic tin salts SnCl(2) and SnCl(4) did not affect F-actin content or production of HL-60 cells. Microfilament thiol groups were not reduced by exposure of cells to TPT, but even increased. When F-actin was exposed to 10 |GmM triphenyltin in a cell-free system, the depolymerizing effect was not detectable. Thus, TPT does not affect cytoskeletal protein directly but depends for its toxicity on some other induced change, probably ionic/osmotic in the intact cell.

Tributyltin affects phagocytic activity of Ciona intestinalis hemocytes

Organotin compounds have been used in marine anti-fouling paints as biocides. Because tunicates are vulnerable to these compounds in their natural habitats, we used Ciona intestinalis to establish an assay for phagocytosis in vitro of yeast by hemocytes after exposure to different concentrations (0.0015, 0.015, 0.15 and 1.5 microM) of four organotin compounds: tributyltin (TBT), triphenyltin (TPT), dibutyltin (DBT) and diphenyltin (DPT). To evaluate the phagocytic activity, we used a method based on fluorescence excitation of yeast pre-treated with eosin-Y. The percentage of phagocytosis decreased from 45.1 +/- 3.49 to 22.4 +/- 5.14 at 1.5 microM of TBT (P < 0.001); it was significantly reduced in presence of the ionophore A23187. TPT, DPT and DBT did not show significant effects on phagocytosis. Because the effect of TBT was irreversible, differences between the inhibitory mechanisms of ionophore and TBT are suggested. These results indicate that for future analyses, tunicates should become excellent models for dissecting events such as phagocytosis that are associated with immunosuppression after exposure to xenobiotics.

The effect of tributyltin chloride on vascular responses to atrial natriuretic peptide

The effects of tributylin chloride (TBT) on vascular smooth muscle responses to norepinephrine, nitroprusside (SNP) and atrial natriuretic peptide (ANP) were studied in isolated aortic rings of rats. TBT did not interfere with norepinephrine-induced contraction or SNP-induced vasorelaxation. However, TBT produced a dose-dependent inhibition of ANP-induced vasorelaxation. Inhibition was not observed with inorganic tin chloride, SnCl2. The inhibition of vasorelaxation was accompanied by a parallel inhibition of ANP-induced cGMP generation. SNP-induced generation of cGMP was not affected by TBT. TBT did not interfere with binding of ANP to its receptor in bovine adrenal glands suggesting that the effects of TBT were mediated by direct interaction with membrane-bound guanylate cyclase.

Cytochalasin B-induced superoxide production in polycation-treated neutrophils

Cytochalasin B alone induces little superoxide production in intact rabbit peritoneal neutrophils. The cytochalasin causes a strong production of superoxide in cells treated with membrane-permeabilizing polycations. Several polycations were able to express the activating effect of cytochalasin B. Especially the poly-L-arginine with a molecular weight of 24,000 proved to be effective. The effectiveness of some polycations is limited because they inactivate the superoxide-generating oxidase system of the neutrophil. Cytochalasin B-induced superoxide production starts at poly-L-arginine concentrations that cause a change of membrane permeability. At the concentrations of cytochalasin B used in our experiments, the binding of [3H]cytochalasin B is not enhanced in poly-L-arginine-treated cells as compared with control cells. Activation of superoxide production by cytochalasin B in polycation-treated neutrophils occurs both in the presence or absence of extracellular Ca2+. When the cells are pretreated with agents that known to interfere with intracellular Ca2+, the subsequent activation is strongly inhibited, suggesting a role for intracellular Ca2+ in cytochalasin B-induced activation. It is suggested that cytochalasin B alone is not able to activate all the steps that eventually result in complete activation of the superoxide-generating oxidase and that membrane perturbation by polycation provides activation of the remaining steps.

Glutathione-induced enhancement of neutrophil locomotion

Both reduced glutathione (GSH) and and its oxidized form, glutathione disulfide (GSSG), enhance neutrophil locomotion. The enhancement is mainly due to a chemokinetic effect, and partly due to a chemotactic effect. A number of other SH-group containing compounds were not effective in enhancing neutrophil migration. While random locomotion is not inhibited by the slowly-penetrating sulfhydryl agent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), the enhancement of migration due to GSH is completely inhibited. Pretreatment of neutrophils with pertussis toxin completely inhibited the GSH-induced stimulation of locomotion, suggesting that stimulation of migration by glutathione was mediated by a pertussis toxin sensitive G-protein. Chemotaxis towards GSH is inhibited by the same agents that inhibit fMet-Leu-Phe induced chemotaxis, except that colchicine was a more effective inhibitor of GSH-induced chemotaxis than of fMet-Leu-Phe directed chemotaxis. GSH enhances the intracellular concentration of cGMP, which might indicate that the effect on neutrophil locomotion is mediated by an effect on cGMP.

Stimulation of rabbit polymorphonuclear leukocyte locomotion by D-penicillamine

Treatment of polymorphonuclear leukocytes (PMNs) with penicillamine has little effect on chemotaxis of the cells towards fMet-Leu-Phe. In the absence of fMet-Leu-Phe however, penicillamine has a strong effect on PMN locomotion. Penicillamine-induced enhancement of PMN migration is for an important part due to a chemokinetic effect, but there is also a chemotactic effect. Pretreatment of PMNs with membrane-impermeable sulfhydryl reagents has little effect on random locomotion, but completely abolishes the activating effect of penicillamine. This suggests that for the activating effect of penicillamine intact sulfhydryl groups on the outer surface of the PMN are required. Extracellular calcium is no absolute requirement for PMN migration, neither for random locomotion nor for the activating effect of penicillamine. Removal of intracellular Ca2+ with membrane-penetrating Ca2+-complexing agents strongly inhibit penicillamine-induced enhancement of PMN migration, underlining a role for intracellular calcium. Penicillamine causes an increase of cGMP level in PMNs. Though a simple relationship seems unlikely it is possible that the enhancement of PMN migration, and the increase of cGMP level by penicillamine are related processes.

Inhibitory effects of phenyltin compounds on stimulus-induced changes in cytosolic free calcium and plasma membrane potential of human neutrophils

To clarify the inhibitory mechanisms by triphenyltin chloride (TPTCl) on superoxide anion formation in neutrophils, the effects of phenyltin compounds [TPTCl, diphenyltin dichloride (DPTCl2) and phenyltin trichloride (MPTCl3) on the increase of cytosolic free calcium and the changes in membrane potential in neutrophils stimulated by n-formyl-methionyl-leucyl-phenylalanine (FMLP) were examined. TPTCl and DPTCl2 concentration dependently inhibited the increase of fluorescence intensity of the dye 3,3'-dipropyl-thiodicarbocyanine iodide [diS-C3-(5)] (membrane potential probe) in neutrophils induced by 0.1 microM FMLP in the presence or absence of extracellular calcium (1.26 mM). TPTCl had a greater inhibitory effect on FMLP-mediated membrane potential change than that of DPTCl2. In the presence of extracellular calcium, TPTCl and DPTCl2 increased intracellular free calcium [( Ca2+]i) of unstimulated fura-2-loaded neutrophils at concentrations from 1.0 to 10 microM TPTCl and from 2.5 to 10 microM DPTCl2. TPTCl and DPTCl2 also increased slightly, in the absence of extracellular calcium, [Ca2+]i without stimulation of FMLP in neutrophils. However, TPTCl and DPTCl2 significantly inhibited the rise of [Ca2+]i in neutrophils stimulated by FMLP at concentrations from 2.5 microM to 10 microM TPTCl and at a concentration of 10 microM DPTCl2 in the absence of extracellular calcium. TPTCl and DPTCl2 significantly inhibited the superoxide anion production by FMLP at concentrations over 2.5 microM in the presence of extracellular calcium. In the absence of extracellular calcium, TPTCl and DPTCl2 also inhibited the superoxide anion production by FMLP at concentrations over 1.5 microM TPTCl and over 5.0 microM DPTCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

Occupational triphenyltin acetate poisoning: a case report

A case of triphenyltin acetate (TPTA) poisoning is described. The patient, who had been exposed mainly to cutaneous absorption, showed acute stages of an urticarial eruption, signs of hepatic injury, slight glucose intolerance, and electroencephalographic abnormalities. Concomitant with the highest concentrations of tin in plasma and the peak of tin excretion in urine, neutrophils did not show the normal increase in actin polymerisation after stimulation with a chemotactic peptide (100 nM fMLP). The peak of urinary excretion of tin occurred between the fifth and the sixth day after poisoning; subsequently, the rate of excretion became slow, suggesting biphasic kinetics with the possibility of a cumulative trend.

The effect of organotin compounds on chloride secretion by the in vitro perfused rectal gland of Squalus acanthias

The effects of various organotins on membrane function and electrolyte transport were studied in the marine elasmobranch, Squalus acanthias. The isolated perfused rectal gland was used as a model of electrolyte transport. This gland can be stimulated to secrete chloride by atrial natriuretic peptide, veratrine, and vasoactive intestinal polypeptide although the mechanism of action of each secretagogue is different. By analysis of the inhibitory effect of an organotin in the presence of each secretagogue, the mechanism of inhibition can be inferred. Tributyltin (TBT) produced a reversible inhibition of epithelial transport at 10(-8) to 10(-7) M which resulted from inhibition of stimulus-secretion coupling in VIP-containing neurons within the gland. The transporting epithelial cells were unaffected at these concentrations. Trimethytin (TMT) produced inhibition at 10(-7) M which was not reversible and which affected primarily the transporting epithelial cells. Triethyltin and triphenyltin were without effect. The inhibitory effect of TBT and TMT was not affected by simultaneous administration of dithiothreitol. TBT also produced inhibition of oxygen consumption, Na+,K-ATPase, and proton ATPase in dispersed rectal gland cells. These results indicate that organotins are toxic to cell membrane functions which are intimately involved in the movement of electrolytes. This is the first evidence of toxicity to membrane transport functions in a marine species which is at risk from environmental exposure.

Permeabilization and calcium-dependent activation of rabbit polymorphonuclear leukocytes by poly-L-arginine

In the absence of extracellular Ca2+, poly-L-arginine induces little lysozyme release from rabbit polymorphonuclear leukocytes (PMNs). The polycation causes plasma membrane damage, which is evident from the release of the cytoplasmic enzyme lactate dehydrogenase (LDH). In the presence of Ca2+ concentrations higher than 0.2 mM, poly-L-arginine induces a strong lysozyme release that is superimposed on the membrane-damaging effect. The results suggest that poly-L-arginine permeabilizes the plasma membrane, enabling Ca2+ to enter the cell, which results in the exocytotic release of granule constituents. The GTP analog GTP gamma S shifts the Ca2+ requirement of exocytosis to slightly higher concentrations, whereas it completely inhibits poly-L-arginine-induced LDH release. Pertussis toxin gives a moderate inhibition, and La3+ completely inhibits poly-L-arginine-induced enzyme release. Whereas poly-L-arginine alone induces little superoxide generation in rabbit PMNs, there is a synergistic enhancement of superoxide production when GTP gamma S and poly-L-arginine are present together. Guanine nucleotides apparently have a modulating effect on the actions of poly-L-arginine on the PMN, but the nature of this effect remains to be determined.

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.

Guanine nucleotides inhibit poly-L-arginine-induced membrane damage in polymorphonuclear leukocytes

Poly-L-arginine induces a strong release of the cytoplasmic enzyme lactate dehydrogenase from rabbit polymorphonuclear leukocytes, indicating that plasma membrane damage occurs. GTP gamma S, a stable guanine nucleotide, completely inhibits poly-L-arginine-induced LDH release whereas pretreatment of the cells with pertussis toxin gives a moderate inhibition. The results suggest that poly-L-arginine-induced plasma membrane damage is mediated by guanine nucleotide binding structures.

Felodipine-induced inhibition of polymorphonuclear leukocyte functions

Felodipine inhibits fMet-Leu-Phe or ionophore A23187-induced exocytosis in rabbit peritoneal polymorphonuclear leukocytes (PMNs), in the concentration range 1-50 microM. Activation of the metabolic burst, and migration of PMNs towards fMet-Leu-Phe are equally inhibited by felodipine in the same concentration range. The effect is not due to blocking of calcium channels in the plasma membrane, because the degree of inhibition remains the same when Ca2+ is omitted from the medium. Felodipine interferes with ionophore A23187-induced association of 45Ca with the PMN but this interference occurs at lower concentrations than the inhibition of exocytosis. Hypotonic hemolysis of erythrocytes is inhibited by felodipine; maximal protection against hemolysis occurs at a concentration of 50 microM felodipine. It is suggested that at least a part of the inhibiting effect on PMN functions might be due to an anesthetic-like membrane effect of felodipine.