The effect of stannous and stannic (tin) chloride on DNA in Chinese hamster ovary cells

Evaluating tissue levels of the eight trace elements and heavy metals among esophagus and gastric cancer patients: A comparison between cancerous and non-cancerous tissues

BACKGROUND

Considering the affecting role of environmental factors including trace elements and heavy metals on the upper gastrointestinal (GI) cancers, there is paucity of empirical research in tissue evaluations.

OBJECTIVES

The present study aimed to measure the tissue content of some trace elements and heavy metals such as zinc (Zn), chromium (Cr), manganese (Mn), tin (Sn), copper (Cu), aluminum (Al), lead (Pb), and iron (Fe) in esophagus and gastric cancerous tissues compared to the adjacent healthy tissues.

METHODS

In a cross-sectional study, the aforementioned trace elements and heavy metals were evaluated among patients with esophagus and gastric cancers. During endoscopy, multiple samples were taken from cancerous lesions and the adjacent healthy tissues. The classic flame atomic absorption spectroscopy (FAAS) method was employed as the study framework.

RESULTS

Fifty patients with the mean age of 53.92 ± 8.73 were enrolled in the current study. Thirteen patients suffered from esophageal cancer and thirty-seven patients were afflicted with gastric cancer. The results revealed significant differences in the median concentrations of Zn, Cr, Sn and, Cu (P < 0.05) between the two groups. Although there were no significant changes in the tissue content in the esophageal samples, in the median concentrations of Zn, Cr and, Sn (P < 0.05) in gastric tissues, significant differences were observed. Further, the results indicated that gender enacted an affecting role in the level of some trace elements and heavy metals.

CONCLUSION

The tissue contents of some elements were altered in gastric and esophageal cancers; this difference may reflect the underlying mechanism of cellular changing during the tumorigenesis or direct exposure of these elements. It seems that under the shade of other coexisting risk factors, larger cohort studies are suggested to be conducted to investigate other probable aspects in this area of interest.

Factors influencing polyelectrolyte-aptamer multilayered films with target-controlled permeability for sensing applications

Portable, easy-to-use and cost-effective sensing devices are desirable in healthcare, environmental monitoring and food safety. Herein we employ polyelectrolyte-aptamer (PE-aptamer) multilayered films that exhibit target-responsive permeability for colorimetric and electrochemical sensing. We present the quantitative detection of an exemplary small molecule, quinine, and address the potential for detection in complex media by examining interference effects. We optimize the film composition and investigate the importance of the structural-switching ability of the aptamer. The results from both platforms are corroborated to provide an outlook on the applicability of the PE-aptamer film for sensing. The label-free detection combined with the readily adaptive assembly process could be invaluable for diverse analytical fields.

Re-evaluation of stannous chloride (E 512) as food additive

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re‐evaluating the safety of stannous chloride and stannous chloride dihydrate (E 512) as food additives. The Panel considered that adequate exposure and toxicity data were available. Stannous chloride is only permitted as food additives in one food category and no reply on the actual use level of stannous chloride (E 512) as a food additive and on its concentration in food was provided by any interested party. According to the Mintel's Global New Products Database (GNPD), stannous chloride was not labelled on any products in the EU nor in Norway. The regulatory maximum level exposure assessment scenario is based on the maximum permitted levels (MPLs) for stannous chloride (E 512), which is 25 mg Sn/kg. The mean exposure to stannous chloride (E 512) from its use as a food additive was below 1.3 μg Sn/kg body weight (bw) per day for all age groups. The 95th percentile of exposure to stannous chloride (E 512) ranged from 0.0 μg Sn/kg bw per day in all groups to 11.2 μg Sn/kg bw per day in adults. Absorption of stannous chloride from the gastrointestinal tract is low there is no concern with respect to carcinogenicity and genotoxicity. Gastrointestinal irritation was reported in humans after ingestion of a bolus dose of 40 mg Sn. The Panel concluded that stannous chloride (E 512) is of no safety concern in this current authorised use and use levels.

Evaluation of deoxyribonucleic acid toxicity induced by the radiopharmaceutical 99mTechnetium-Methylenediphosphonic acid and by stannous chloride in Wistar rats

Radiopharmaceuticals are employed in patient diagnostics and disease treatments. Concerning the diagnosis aspect, technetium-99m (^99mTc) is utilized to label radiopharmaceuticals for single photon computed emission tomography (SPECT) due to its physical and chemical characteristics. ^99mTc fixation on pharmaceuticals depends on a reducing agent, stannous chloride (SnCl₂) being the most widely-utilized. The genotoxic, clastogenic and anegenic properties of the ^99mTc-MDP(methylene diphosphonate used for bone SPECT) and SnCl₂ were evaluated in Wistar rat blood cells using the Comet assay and micronucleus test. The experimental approach was to endovenously administer NaCl 0.9% (negative control), cyclophosphamide 50 mg/kg b.w. (positive control), SnCl₂ 500 μg/mL or ^99mTc-MDP to animals and blood samples taken immediately before the injection, 3, and 24 h after (in the Comet assay) and 36 h after, for micronucleus test. The data showed that both SnCl₂ and ^99mTc-MDP-induced deoxyribonucleic acid (DNA) strand breaks in rat total blood cells, suggesting genotoxic potential. The ^99mTc-MDP was not able to induce a significant DNA strand breaks increase in in vivo assays. Taken together, the data presented here points to the formation of a complex between SnCl₂ in the radiopharmaceutical ^99mTc-MDP, responsible for the decrease in cell damage, compared to both isolated chemical agents. These findings are important for the practice of nuclear medicine.

A new look at biomedical Ti-based shape memory alloys

Shape memory alloys (SMAs) are materials that exhibit a distinct thermomechanical coupling, one that gives rise to a wide variety of applications across a broad range of fields. One of the most successful roles is in the construction of novel medical implants. Unfortunately, concerns have been raised about the biocompatibility of the most popular SMA, nitinol (NiTi), due to the known toxic, allergenic and carcinogenic properties of nickel. Given the unique capabilities of SMAs, it is apparent that there is a need for a new class of alloys - alloys that exhibit the full range of shape memory abilities yet are also free of any undesirable side effects. This article reviews the literature surrounding SMAs and identifies the metals Ti, Au, Sn, Ta, Nb, Ru and Zr as candidates for the production of thoroughly biocompatible SMAs. Hf and Re are also promising, though more research is necessary before a definitive statement can be made. Further, the Ti-(Ta,Nb)-(Zr,Hf) alloy system is particularly suited for orthopaedic implants due to a reduced Young's modulus. However, concerns over this system's shape memory properties exist, and should be taken into consideration. Alternate alloy systems that demonstrate higher bulk moduli may still be considered, however, if they are formed into a porous structure. Due to the nature of the alloying components, blended elemental powder metallurgy is recommended for the manufacture of these alloys, particularly due to the ease with which it may be adapted to the formation of porous alloys.

Early life stage and genetic toxicity of stannous chloride on zebrafish embryos and adults: toxic effects of tin on zebrafish

Humans are exposed to stannous chloride (SnCl(2)), known as tin chloride, present in packaged food, soft drinks, biocides, dentifrices, etc. Health effects in children exposed to tin and tin compounds have not been investigated yet. Therefore, we evaluated the possible teratogenic effects and genotoxic of SnCl(2) in zebrafish (Danio rerio) adults and their embryos. In the embryo-larval study, SnCl(2) showed embryo toxicity and developmental delay after exposure to the various concentrations of 10-250 μM for 120 h. Teratogenic effects including morphological malformations of the embryos and larvae were observed. The embryos exposed to 100 μM displayed tail deformation at 28 hpf and the larvae exposed to 50 μM showed reduced body growth, smaller head and eyes, bent trunk, mild pericardial edema, and smaller caudal fin at 96 hpf. The results of the teratological study show that SnCl(2) induced a significant decrease in the number of living embryos and larvae. Regarding the chromosome analysis, SnCl(2) induced a dose-dependent increase in the micronucleus (MN) frequency in peripheral erythrocytes of adult zebrafish. In blood cells, the 25 μM dose of SnCl(2) caused a nonsignificant increase in the total chromosomal aberrations, but the high doses significantly increased the total number of chromosomal aberrations compared with the control groups. Overall, the results clearly indicate that SnCl(2) is teratogenic and genotoxic to zebrafish.

Endonuclease IV is the main base excision repair enzyme involved in DNA damage induced by UVA radiation and stannous chloride

Stannous chloride (SnCl₂) and UVA induce DNA lesions through ROS. The aim of this work was to study the toxicity induced by UVA preillumination, followed by SnCl₂ treatment. E. coli BER mutants were used to identify genes which could play a role in DNA lesion repair generated by these agents. The survival assays showed (i) The nfo mutant was the most sensitive to SnCl₂; (ii) lethal synergistic effect was observed after UVA pre-illumination, plus SnCl₂ incubation, the nfo mutant being the most sensitive; (iii) wild type and nfo mutants, transformed with pBW21 plasmid (nfo⁺) had their survival increased following treatments. The alkaline agarose gel electrophoresis assays pointed that (i) UVA induced DNA breaks and fpg mutant was the most sensitive; (ii) SnCl₂-induced DNA strand breaks were higher than those from UVA and nfo mutant had the slowest repair kinetics; (iii) UVA + SnCl₂ promoted an increase in DNA breaks than SnCl₂ and, again, nfo mutant displayed the slowest repair kinetics. In summary, Nfo protects E. coli cells against damage induced by SnCl₂ and UVA + SnCl₂.

Interaction of tin(II) and arsenic(III) with DNA at the nanostructure film modified electrodes

Biosensors based on DNA and DNA-carbon nanotubes film immobilized at the surface of a screen-printed carbon electrode were used for simple in vitro tests of chemical toxicity. The damage to DNA caused by tin(II) and arsenic(III) compounds as components of specific reaction media was evaluated by means of an electrochemical DNA marker, [Co(phen)3](3+), as the portion of original dsDNA which survives an incubation of the biosensor in the cleavage medium. The results were confirmed by the electrically heated electrode and by the measurement of the DNA guanine moiety signal.

Cytotoxic and genotoxic effects induced by stannous chloride associated to nuclear medicine kits

At present, more than 75% of routine nuclear medicine diagnostic procedures use technetium-99m (99mTc). The binding between 99mTc and the drug to obtain the radiopharmaceutical needs a reducing agent, with stannous chloride (SnCl2) being one of the most used. There are controversies about the cytotoxic, genotoxic and mutagenic effects of SnCl2 in the literature. Thus, the approaches below were used to better understand the biological effects of this salt and its association in nuclear medicine kits [methylenediphosphonate (MDP) bone scintigraphy and diethylenetriaminepentaacetic acid (DTPA) kidney and brain scintigraphy]: (i) bacterial inactivation experiments; (ii) agarose gel electrophoresis of supercoiled and linear plasmid DNA and (iii) bacterial transformation assay. The Escherichia coli strains used here were AB1157 (wild type) and BW9091 (xthA mutant). Data obtained showed that both MDP and SnCl2 presented a high toxicity, but this was not observed when they were assayed together in the kit, thereby displaying a mutual protect effect. DTPA salt showed a moderate toxicity, and once more, the DTPA kit provided protection, compared to the SnCl2 effect alone. The results suggest a possible complex formation, either MDP-SnCl2 or DTPA-SnCl2, originating an atoxic compound. On the other hand, SnCl2-induced cell inactivation and the decrease in bacterial transformation generated by DTPA found in XthA mutant strain suggest that the lack of this enzyme could be responsible for the effects observed, being necessary to induce DNA damage repair.

Sensitivity to Sn2+ of the yeast Saccharomyces cerevisiae depends on general energy metabolism, metal transport, anti-oxidative defences, and DNA repair

Resistance to stannous chloride (SnCl(2)) of the yeast Saccharomyces cerevisiae is a product of several metabolic pathways of this unicellular eukaryote. Sensitivity testing of different null mutants of yeast to SnCl(2) revealed that DNA repair contributes to resistance, mainly via recombinational (Rad52p) and error-prone (Rev3p) steps. Independently, the membrane transporter Atr1p/Snq1p (facilitated transport) contributed significantly to Sn(2+)-resistance whereas absence of ABC export permease Snq2p did not enhance sensitivity. Sensitivity of the superoxide dismutase mutants sod1 and sod2 revealed the importance of these anti-oxidative defence enzymes against Sn(2+)-imposed DNA damage while a catalase-deficient mutant (ctt1) showed wild type (WT) resistance. Lack of transcription factor Yap1, responsible for the oxidative stress response in yeast, led to 3-fold increase in Sn(2+)-sensitivity. While loss of mitochondrial DNA did not change the Sn(2+)-resistance phenotype in any yeast strain, cells with defect cytochrome c oxidase (CcO mutants) showed gradually enhanced sensitivities to Sn(2+) and different spontaneous mutation rates. Highest sensitivity to Sn(2+) was observed when yeast was in exponential growth phase under glucose repression. During diauxic shift (release from glucose repression) Sn(2+)-resistance increased several hundred-fold and fully respiring and resting cells were sensitive only at more than 1000-fold exposure dose, i.e. they survived better at 25 mM than exponentially growing cells at 25 microM Sn(2+). This phenomenon was observed not only in WT but also in already Sn(2+)-sensitive rad52 as well as in sod1, sod2 and CcO mutant strains. The impact of metabolic steps in contribution to Sn(2+)-resistance had the following ranking: Resting WT cells > membrane transporter Snq1p > superoxide dismutases > transcription factor Yap1p >or= DNA repair >> exponentially growing WT cells.

Genotoxicity of stannous chloride in yeast and bacteria

Stannous chloride was found genotoxic in microbial test systems of the yeast Saccharomyces cerevisiae, in one strain of Salmonella typhimurium and in the Mutoxitest of Escherichia coli. Five isogenic haploid yeast strains differing only in a particular repair-deficiency had the following ranking in Sn2+ -sensitivity: rad52delta>rad6delta>rad2delta>rad4delta>RAD, indicating a higher relevance of recombinogenic repair mechanisms than nucleotide excision in repair of Sn2+ -induced DNA damage. Sn2+ -treated cells formed aggregates that lead to gross overestimation of toxicity when not undone before diluting and plating. Reliable inactivation assays at exposure doses of 25-75 mM SnCl2 were achieved by de-clumping with either EDTA- or phosphate buffer. Sn2+ -induced reversion of the yeast his1-798, his1-208 and lys1-1 mutant alleles, in diploid and haploid cells, respectively, and putative frameshift mutagenesis (reversion of the hom3-10 allele) was observed. In diploid yeast, SnCl2 induced intra-genic mitotic recombination while inter-genic (reciprocal) recombination was very weak and not significant. Yeast cells of exponentially growing cultures were killed to about the same extend at 0.1% of SnCl2 than respective cells in stationary phase, suggesting a major involvement of physiological parameters of post-diauxic shift oxidative stress resistance in enhanced Sn2+ -tolerance. Superoxide dismutases, but not catalase, protected against SnCl2-induced reactive oxygen species as sod1delta had a three-fold higher sensitivity than the WT while the sod2delta mutant was only slightly more sensitive but conferred significant sensitivity increase in a sod1delta sod2delta double mutant. In the Salmonella reversion assay, SnCl2 did not induce mutations in strains TA97, TA98 or TA100, while a positive response was seen in strain TA102. SnCl2 induced a two-fold increase in mutation in the Mutoxitest strain IC203 (uvrA oxyR), but was less mutagenic in strain IC188 (uvrA). We propose that the mutagenicity of SnCl2 in yeast and bacteria occurs via error-prone repair of DNA damage that is produced by reactive oxygen species.

Evaluation of the phytic acid effect on the labeling of blood elements with technetium-99m and on the survival of a strain of Escherichia coli treated with stannous fluoride

The labeling of red blood cells with technetium-99m (99mTc) depends on a reducing agent and stannous ions, as chloride or fluoride, are widely utilized. This labeling may also be altered by drugs. Moreover, some authors have reported that the survival of Escherichia coli (E. coli) cultures decreases in presence of stannous ions. Phytic acid is present in the daily diet and we evaluated its influence on: (i) the labeling of blood elements with 99mTc and (ii) on the survival of an E. coli strain treated with stannous fluoride. Heparinized whole blood was withdrawn from Wistar rats and it was incubated with stannous chloride and with 99mTc, as sodium pertechnetate, centrifuged and plasma (P) and blood cells (BC) were isolated. Samples of P and BC were also precipitated with trichloroacetic acid, centrifuged and soluble (SF) and insoluble fractions (IF) isolated. E. coli culture was treated with stannous fluoride in presence of phytic acid. As phytic acid altered the fixation of 99mTc on BC, on IF-P and on IF-BC and, moreover, it abolished the lethal effect of stannous fluoride on the E. coli culture, we can suggest that, probably, phytic acid would have chelating properties to the stannous ions.

Genotoxic effects of stannous chloride (SnCl2) in K562 cell line

The toxic effects of SnCl2 in K562 cells were analyzed in this study. This cell line is resistant to reactive oxygen species (ROS) making it suitable to evaluate the impact of SnCl2 in culture either through ROS or by direct toxicity using Trypan blue dye exclusion, comet and flow cytometry assays. An important loss of viability induced by SnCl2 in a dose-response manner was observed in cells treated in Tris-buffered saline (TBS). This necrotic cell death was further confirmed by flow cytometry. On the other hand, there was no loss of viability when cells were treated in rich medium (RPMI). DNA damage was visualized in SnCl2-treated K562 cells in both tested conditions. The data indicate that SnCl2 induces DNA damage and reduces K562 viability. Both actions seem to be correlated with ROS formation and direct linkage to DNA.

Effect of an extract of cauliflower (leaf) on the labeling of blood elements with technetium-99m and on the survival of Escherichia coli AB1157 submitted to the treatment with stannous chloride

The labeling of red blood cells (RBC) with technetium-99m (99mTc) depends on a reducing agent and stannous chloride (SnCl(2)) and is widely utilized. This labeling may also be altered by drugs, and SnCl(2) reduces the survival of Escherichia coli cultures. Cauliflower (Brassica oleracea L. var. botrytis) is used in folk medicine and we evaluated its influence on (i) the labeling of blood elements with 99mTc, and (ii) on the survival of an E. coli strain. Blood was withdrawn from rats that drank the extract of cauliflower (15 days). Blood was incubated with SnCl(2) and with 99mTc, as sodium pertechnetate, centrifuged and plasma (P) and RBC were isolated. Samples of P and RBC were also precipitated, centrifuged and soluble and insoluble fractions isolated. E. coli culture was treated with SnCl(2) in the presence of cauliflower. The extract of cauliflower did not alter the fixation of 99mTc on blood fractions; however, it abolished the lethal effect of SnCl(2) on the E. coli culture. We suggest that the substances present in the extract of cauliflower probably, would have redox property with different mechanisms of action. The oxidant action of the substances of the extract would not be strong enough to oxidise the stannous ions altering the 99mTc-labeling. However, the referred substances could oxidise these ions sufficiently to protect the E. coli culture against the lethal effect of the stannous ion.

Adaptive response to H(2)O(2) protects against SnCl(2) damage: the OxyR system involvement

The stannous ion, mainly the stannous chloride (SnCl(2)) salt form, is widely used as a reducing agent to label radiotracers with technetium-99m ((99m)Tc). These radiotracers can be employed as radiopharmaceuticals in nuclear medicine procedures. In this case, there is no doubt about absorption of this complex, because it is intravenously administered in humans, although biological effects of these agents have not been fully understood. In this work we used a bacterial system to study the cytotoxic potential of stannous chloride. It is known that SnCl(2) induces lesions that could be mediated by reactive oxygen species (ROS). We, thus, investigated the existence of cross-adaptive response between hydrogen peroxide (H(2)O(2)) and SnCl(2) and the role of the OxyR system known to promote cellular protection against oxidative damages. Here we describe the results obtained with prior treatment of different Escherichia coli strains with sub-lethal doses of H(2)O(2), followed by incubation with SnCl(2). Our data show that H(2)O(2) is capable of inducing cross-adaptive response against the lethality promoted by SnCl(2), suggesting the OxyR system participation through catalase, alkyl hydroperoxide reductase and superoxide dismutase enzymes

Preparation and biological evaluation of 188Re-ethylenediamine-N,N,N',N'-tetrakis(methylene phosphonic acid) as a potential agent for bone pain palliation

This study was undertaken in order to prepare 188Re labelled ethylenediamine-N,N,N',N'-tetrakis(methylene phosphonic acid) (EDTMP), and to determine its potential as a therapeutic radiopharmaceutical for the palliation of metastatic bone pain. The effects of pH, incubation methods, and concentrations of stannous chloride, EDTMP, and ammonium perrhenate as a carrier on radiochemical yield and stability were evaluated. Biodistribution studies were performed in male Wistar rats after intravenous injection of 188Re-EDTMP and compared with those of hydroxyethylidene diphosphonate (HEDP). Greater than 95% radiochemical yield of 188Re-EDTMP was obtained under the optimal conditions (0.1 mmol x ml(-1) of EDTMP, 0.5 mg x ml(-1) of stannous chloride, and pH 1.0). Heating the reaction mixture (boiling water for 15 min, and microwave heating for 15 s) and the addition of ammonium perrhenate increased the radiochemical stability (>90% at 3 h, and >80% at 48 h). The biodistribution of 188Re-EDTMP showed high bony uptake and rapid clearance from other organs, and high bone-to-soft tissue ratios, which are similar to 188Re-HEDP. In conclusion, 188Re-EDTMP was prepared with high radiochemical yield and stability, and showed favourable biological characteristics. Microwave heating was a convenient and rapid method for the preparation of 188Re-EDTMP. It is considered that 188Re-EDTMP is a potential therapeutic agent for bone metastasis.

Damage induced by stannous chloride in plasmid DNA

Stannous chloride (SnCl(2)) is widely used in daily human life, for example, to conserve soft drinks, in food manufacturing and biocidal preparations. In nuclear medicine, stannous chloride is used as a reducing agent of Technetium-99m, a radionuclide used to label different cells and molecules. In spite of this, stannous chloride is able to generate reactive oxygen species (ROS) which can damage DNA. In this work, plasmid DNA (pUC 9.1) was incubated with SnCl(2) under different conditions and the results analyzed through DNA migration in agarose gel electrophoresis. Our data reinforce the powerful damaging effect induced by stannous ion and suggest that this salt can play a direct role in inducing DNA lesions.

Stannous chloride mediates single strand breaks in plasmid DNA through reactive oxygen species formation

Stannous ion (Sn) has been employed in nuclear medicine and in food industry. We described that Stannous Chloride (SnCl2) inactivation effect in Escherichia coli is mediated by a Fenton-like reaction. The effect of SnCl2 was studied through: (i) the alteration of plasmid topology in neutral and acidic pH by gel electrophoresis; and (ii) the transformation efficiency of an wild type E. coli strain. Treatment of plasmid DNA pUC 9.1 with SnCl2, at pH 7.4, results in DNA single-strand breaks (SSB), in a dose-dependent manner. Addition of sodium benzoate partly inhibited the DNA damage, while EDTA completely abolishes DNA-SSB. Furthermore, the ability of the plasmid to transform E. coli was reduced. At pH 1.3, SnCl2 exerts a protective effect on plasmid against HCI depurination. Our results suggest the generation of ROS, such as *OH by a Fenton-like reaction, close to the site of the lesions due to a possible complexation of stannous ion to DNA.

Cellular inactivation induced by a radiopharmaceutical kit: role of stannous chloride

Stannous chloride (SnCl2) has been used in many sectors of human activities such as food manufacturing and in nuclear medicine to produce radiopharmaceuticals labeled with technetium-99m (99mTc). Due to its importance and genotoxic potentiality, we decided to evaluate the biological effect induced by a nuclear medicine kit, which includes SnCl2, in association with glucoheptonic acid (GHA) which is employed for brain and renal scintigraphies. These studies were carried out with the Escherichia coli AB1157 strain and the deoxyribonucleic acid (DNA) plasmid pUC 9.1. The experiments, with different concentrations of SnCl2 and GHA, show an inverse relationship between both agents. When the GHA concentration was increased, the cellular inactivation induced by SnCl2 was reduced, as measured by the number of viable cells. Moreover, GHA protects the DNA molecule against the damage induced by SnCl2.

Stannous chloride and the glucoheptonic acid effect: study of a kit used in nuclear medicine

Stannous dichloride is used as a reducing agent in the preparation of technetium-99m radiopharmaceuticals. We decided to evaluate the genotoxic potential of the tin (II)-glucoheptonate complex in the kit using a tester strain of Escherichia coli AB1157. Our results show that tin (II) chloride and the tin (II)-glucoheptonate complex exert a genotoxic effect in this system. While the genotoxic effect disappeared when the glucoheptonate concentration was increased, the glucoheptonate did not protect the cultures from the damaging effects of hydrogen peroxide. The ability of glucoheptonate to protect cultures from tin (II)-induced damage can be explained on the basis of its metal chelating properties.

Mutational potentiality of stannous chloride: an important reducing agent in the Tc-99m-radiopharmaceuticals

Stannous chloride (SnCl2) is frequently used in nuclear medicine as a reducing agent to label many radiopharmaceutical products with technetium-99m (99mTc). The aim of the present paper was to study the role of DNA repair genes in the repair of SnCl2-induced damage, using mutant strains of Escherichia coli lacking one or more DNA repair genes. Our results suggest that the product of the xthA gene, exonuclease III, is required for the repair of lesions induced by SnCl2. We further investigated the mutagenic properties of SnCl2 to a molecular level by using the supF tRNA gene as target in a forward mutational system. We have found that the survival of E. coli cells was strongly reduced with increasing concentrations of SnCl2. Moreover, when the shuttle vector pAC189 carrying the supF gene was treated with SnCl2, and then transfected to E. coli, we observed that its transformation efficiency dropped when compared to the non-treated control, with a parallel increase in mutation frequency after the damaged plasmids have replicated in bacterial cells. The mutation spectrum induced by SnCl2 reveals a high frequency of base substitutions, involving guanines. Sequence analysis of 41 independent supF mutant plasmids revealed that 39 mutants contained base substitutions, with 21 G:C to T:A and 17 G:C to C:G transversions. G to T transversions presumably resulted from 8-oxoG. However, the G to C one may be due to a yet unidentified lesion.

Lethality induced by stannous chloride on Escherichia coli AB1157: participation of reactive oxygen species

Stannous chloride (SnCl2) has been widely used in nuclear medicine as a reducing agent of pharmaceutical products radiolabelled with technetium-99m. To verify whether the lethality induced by this salt could be mediated by reactive oxygen species (ROS), Escherichia coli cultures were treated with SnCl2 in the presence of catalase, ROS scavengers or metal-ion chelators. The inactivation effect, as measured by survival determination, was abolished by thiourea, sodium benzoate, dipyridyl or catalase. The results suggest the participation of ROS, generated by a Fenton-like reaction, in the lethal effect induced by SnCl2.

Tri-n-butyltin chloride promotes morphological transformation and induces proliferin expression in C3H10T1/2 cells

Transcripts from the murine gene family proliferin, which are increased by a wide assortment of chemical promoters of C3H10T1/2 cell morphological transformation, were shown to be induced by tri-n-butyltin chloride at concentrations above 50 nM. Two-stage transformation assays, with 3-methylcholanthrene as inducer and tri-n-butyltin chloride as promoter, were performed to determine if promotion of morphological transformation and proliferin induction were properties shared by this compound. Tri-n-butyltin chloride synergistically enhanced focus formation at concentrations ranging from 20 to 75 nM. Di-n-butyltin dichloride, n-butyltin trichloride and tin (II) chloride, but not tin (IV) chloride, were also effective inducers of proliferin. Changes in patterns of TPA-inducible, secreted proteins, including those likely to be proliferin, were detected following organotin treatment of confluent monolayers. Tri-n-butyltin chloride resembles other agents active as promoters in C3H10T1/2 two-stage transformation assays by possessing an ability to induce proliferin expression.

Genetic toxicity of six carcinogens and six non-carcinogens in the Drosophila wing spot test

Six rodent carcinogens, 5 of which are also human carcinogens, and 6 compounds recognized as non-carcinogens were tested for their genotoxic activity in the Drosophila melanogaster wing spot test. 72-h-old larvae trans-heterozygous for the recessive wing cell markers 'multiple wing hairs' (mwh) and 'flare' (flr3) were fed various concentrations of the test compounds for a period of 48 h. With amitrole and 4-aminobiphenyl, larvae of the same age were also given an acute treatment of 6 h with higher concentrations, and, in addition, 48-h-old larvae were fed for a longer period of 72 h. Repeats of all experiments document the good reproducibility of the results in the wing spot test. Amitrole and 4-aminobiphenyl were genotoxic after both 48-h and 72-h treatments, but their activity could not be detected following acute exposure of only 6 h. Chlorambucil and melphalan were clearly genotoxic. The carcinogens sodium arsenite and sodium arsenate, however, which are highly toxic to Drosophila, could only be tested at low exposure levels and were negative under these treatment conditions. The 6 non-carcinogens (ascorbic acid, 2-aminobiphenyl, mannitol, piperonyl butoxide, stannous chloride and titanium dioxide) were all definitely non-genotoxic in the Drosophila wing spot test. The data for the non-carcinogens demonstrate that non-genotoxic compounds can be identified in the wing spot test with a reasonable experimental effort.

Anti-curare action of stannous ion in the frog neuromuscular junction

For the purpose of elucidating the mechanism of action of stannous ion (Sn2+), we investigated effects of stannous chloride (SnCl2) on the twitch and on the electrical phenomena in the muscle fiber. Sciatic nerve-sartorius muscle preparations from the bullfrog were used as the material. Effect of SnCl2 was examined on the twitch partially inhibited by pretreatment with d-tubocurarine. SnCl2 (1-100 microM) antagonized d-tubocurarine and enhanced the twitch dose-dependently. Tartaric acid, which is the solvent used for SnCl2 solution, had no augmentative effect on the twitch, even at a concentration as high as 250 microM. SnCl2 (1-50 microM) increased the amplitude of the endplate potential; that is, it exerted an anti-curare action. The resting potential and the membrane resistance of the muscle fiber were not altered by 30 microM SnCl2. These findings lead to the conclusion that Sn2+ enhances the twitch by increasing the endplate potential of the muscle fibers.

Effects of metals on chromosomes of higher organisms

An analysis of the available data on the clastogenic effects of metals and their compounds on higher organisms indicates some general trends. Following chronic exposure to subtoxic doses, a decrease in mitotic frequency and an increase in the number of chromosomal abnormalities are observed. These effects are usually directly proportional to the dose applied and the duration of treatment within the threshold limits. Recovery after acute treatment is inversely related to the dosage. The ultimate expression of the effects depends on certain factors, including the mode and vehicle of administration; the form administered; the test system used; the rate of detoxification, distribution, and retention in the different tissues; and interaction with foreign and endogenous substances as well as the mode of action with the biological macromolecules. In mammals, the clastogenic activity of the metals within each vertical group of the periodic table is directly proportional to the increase in atomic weight, electropositivity, and solubility of the metallic cations in water and lipids, except for Li and Ba. This pattern of inherent cytotoxicity increases with successive periods in the horizontal level. It is enhanced by the formation of covalent and coordinate covalent complexes by heavy metals with the biological macromolecules. In plants, the solubility of the metals in water is of much greater importance. The degree of dissociation of metallic salts and the rate of absorption affect significantly the frequency of chromosomal aberrations. In assessing the effects of environmental metal pollution, the presence of other metals and toxic chemicals and the level of nutrition should be taken into account, since in nature, metals occur in combination and these factors modify the cytotoxic effects to a significant extent.

Early nuclear events in lymphocyte proliferation. The role of DNA strand break repair and ADP ribosylation

The previously reported extensive DNA strand breakage in resting murine splenic lymphocytes is not an artifact of the extraction or assay procedure. The benzamide inhibitors of poly(ADP ribose) synthetase (pADPRS), such as 5-methoxybenzamide (MBA), had been shown to block the strand break repair occurring within 2 h of activation of splenic lymphocytes by the mitogen concanavalin A (conA); the inhibitors also blocked early events in proliferation, such as blast formation, as well as entry into S phase. Inhibitors of pADPRS blocked lymphocyte proliferation by inhibiting the activity of this enzyme, rather than by non-specific effects. Aphidicolin, an inhibitor of alpha-polymerase, also prevented DNA strand break repair in conA-stimulated cells but, unlike MBA, did not prevent blast formation. DNA strand breaks accumulated in the presence of MBA at the same linear rate (300-400/h) in both resting and conA-treated cells. We and others had hypothesized that this accumulation was due to a continuous production of strand breaks in lymphocytes, leading to their accumulation in presence of repair inhibitors. However, incubation of the cells with aphidicolin at concentrations that inhibited repair did not result in any increase in strand breaks. The hypothesis of continuous cycling of breaks is incorrect; accumulation of breaks was due to some indirect effect of MBA, such as a possible disinhibition of an ADP-ribosylation-sensitive endonuclease described in other cell types. All of the early stages of lymphocyte proliferation, including blast transformation (but not DNA synthesis) require ADP ribosylation. Repair of DNA strand breaks is not a precondition for blast formation, though experiments involving the combined effects of MBA and aphidicolin showed that repair of the breaks is essential in order for the cells to replicate their DNA. Our data are consistent with a model suggesting that DNA strand breaks introduced into differentiated cells act as an additional safety-catch mechanism that restrains them from replicating their genetic material but not from undergoing the early stages of proliferation.

Ca2+, Mg2+-dependent endonuclease activity in different subpopulations of spleen cells from normal and erythroleukemic mice

We have detected Ca2+, Mg2+-dependent endonuclease activity in spleen cells of normal, Friend erythroleukemic, and phenylhydrazine-treated mice. When nuclei were isolated and incubated in the presence of Ca2+ and Mg2+ ions, the activity resulted in the production of 3'-OH termini in the cellular DNA and the release of chromatin due to internucleosomal DNA fragmentation. This enzyme activity was chromatin-bound and could be extracted from chromatin in an active form in 0.35 M KCl. The majority of endonuclease activity from erythroleukemic spleens was present in nuclei of precursor erythroid cells of low buoyant density (1.025-1.05 g/ml). Uninfected normal splenic tissue contained an endonuclease activity which was almost entirely confined to a B-lymphocyte population of high buoyant density (greater than 1.07 g/ml). Erythroid cell-enriched spleens from phenylhydrazine-treated mice exhibited a distribution of endonuclease activity in cells at low and high densities reflecting a mixture of erythroid and lymphoid cells. Cloned erythroleukemic cell lines propagated in vitro lacked cells of low density and showed no detectable endonuclease activity. However, nuclei from these cell lines were susceptible to exogenously added endonuclease extracted from erythroleukemic spleen cells. These same cell lines propagated as subcutaneous tumors contained endonuclease activity and a morphologically-similar low-density cell population which accounted for the endonuclease activity in these tumors. Nuclei from cloned lymphoid cell lines, representing different B-lymphocyte phenotypes, showed differences in the presence of endonuclease activity. Among the cell lines tested, only those expressing late B-cell markers showed detectable endonuclease activity.

Significance of the genotoxic activities observed in vitro for 35 of 70 NTP noncarcinogens

A speculative analysis is presented of the in vitro genotoxicity data reported by Shelby and Stasiewicz for 70 chemicals defined as noncarcinogenic to rodents by the National Toxicology Program. It is concluded that the genotoxic activities observed are probably subject to logical explanation. It is suggested that short-term genotoxicity assays conducted in vivo on newly defined in vitro genotoxins may have a useful role to play in discriminating animal carcinogens from noncarcinogens. It is clear from the results reported that genotoxic activities observed in vitro for a new test chemical only provide evidence of its possible animal carcinogenicity; they are not definitive of carcinogenicity--the difference may be negligible in general but might prove unacceptable in the particular.

DNA strand breaks in murine lymphocytes: induction by purine and pyrimidine analogues

At the onset of culture of mouse splenic lymphocytes with concanavalin A (Con A), a 6 h pulse with 5-fluorouracil (5-FU) or 8-azaguanine (8-AG), under conditions previously shown to lead to an irreversible block of the stimulated cells in the G1 phase of the cell cycle (1,2), causes extensive DNA strand breakage. Breaks induced by the analogues early in culture were largely unrepaired even after 48 h culture. Analogues that did not block the proliferative response did not cause DNA strand breakage. Unrepaired DNA strand breaks, induced by the purine and pyrimidine analogues, provide a mechanism that can account for the block of the stimulated lymphocytes before S phase. Many strand breaks were found to exist in the DNA of normal, resting splenic lymphocytes; these were rapidly repaired within 2 h of stimulation with Con A, unlike those induced by the analogues.

The effect of tin chloride on the structure and function of DNA in human white blood cells

Tin compounds are being used increasingly in the home, in industry and in medicine. There have been relatively few studies on the long term biological effects of this metal, although acute effects have been documented. In this report we describe experiments which show that tin(II), as stannous chloride, is readily taken up by human white blood cells (WBC) and can cause damage to DNA. Damage was detected in WBC after exposure to 10-50 microM tin(II) for 30 min at either 0 degree or 37 degrees C. The amount of damage observed was more extensive than that produced by exposure of cells to equimolar amounts of chromium(VI), a known carcinogen and DNA damaging agent. Additional indication of cellular damage is that exposure of human lymphocytes or mouse splenocytes to tin(II) interfered with their ability to be stimulated by the polyvalent mitogen concanavalin A (Con A). By contrast, tin(IV) was not taken up by cells, did not cause DNA damage nor did it inhibit stimulation of DNA synthesis in cells that were exposed to Con A.