No synergism between caffeine and saccharin in the induction of sister chromatid exchange in human lymphocytes

Mutagenic and cytotoxic effectiveness of zinc dimethyl and zinc diisononyldithiocarbamate in human lymphocyte cultures

The mutagenic and cytotoxic effectiveness of the vulcanisation accelerators zinc dimethyldithiocarbamate (ZDMC; ziram) and zinc diisononyldithiocarbamate (ZDINDC; arbestab Z) was tested in lymphocyte cultures of five healthy probands. ZDMC and ZDINDC (c=0.1, 1.0 and 10.0microg/ml) were studied in lymphocyte cultures without external metabolic activation. Additionally, incubation of the compounds (c=10.0microg/ml) was performed in the presence of liver microsomes from aroclor-induced rats (1 and 2h, 1 and 2mg microsomal protein). Genotoxicity testing was performed by analysis of chromosomal aberrations (CA), sister chromatid exchanges (SCEs) and micronuclei (MN). For evaluation of antiproliferative effects, mitotic index (MI) and cell cycle kinetics (CCK) were determined. In contrast to earlier investigations we found no significantly increased mutagenic or cytotoxic activity of ZDMC; ZDINDC also was inactive under these conditions.

Saccharin mechanistic data and risk assessment: urine composition, enhanced cell proliferation, and tumor promotion

Sodium saccharin (NaSac) produces bladder tumors consistently in male rats only after lifetime exposure that begins at birth. NaSac is not metabolized and is negative in most genotoxicity tests. NaSac-induced cell damage and proliferation have been proposed as important factors in tumor promotion, and dose-response information demonstrating a threshold for these parameters is available. One theory proposes that high levels of NaSac, combined with protein in a high Na+, high pH environment found only in the male rat, form toxic microscopic crystals; therefore, NaSac-induced tumors may not be relevant to human carcinogenesis.

Baseline and mitomycin C (MMC)-induced sister-chromatid exchanges in XX and XY cells of Callithrix jacchus chimeric twins

Lymphocytes from chimeric individuals of the species Callithrix jacchus (Primates) were examined to evaluate differences in the frequency of sister chromatid exchanges (SCE) between XX and XY cells. The aim was to discover whether SCE differ according to genetic sex and whether XX and XY cells show a different sensitivity to SCE inducing agents. This experimental model has enabled us to eliminate the possible differences caused by environmental factors. The results obtained do not reveal significant differences between male and female cells, in either the baseline SCE frequency or that induced by mitomycin C at concentrations of 0.01 and 0.03 microgram/ml. No significant differences were observed in the distribution of high SCE frequency cells (HFC), even if it is possible to observe a higher level of exchanges in XX cells in each trial. With regard to the phenotypic sex, there appears to be a trend towards slightly higher SCE rates in females, even if results are not statistically significant.

Lack of sister-chromatid exchange induction by polymethyl methacrylate bone cement in human lymphocytes cultured in vitro

Human lymphocytes cultured in vitro were used to assess the ability of polymethyl methacrylate (PMMA), currently used in orthopedic surgery as bone cement, to induce sister-chromatid exchanges (SCE). Under the conditions used in this study, PMMA bone cement did not produce any significant increase in SCEs in phytohemagglutinin-stimulated human lymphocytes. However, a significant decline (p less than 0.05) in the proliferation rate index was observed, which might be an indicator of the cytotoxic effect of PMMA.

Clastogenicity in vitro of the Na, K, Ca and Mg salts of saccharin; and of magnesium chloride; consideration of significance

The sodium, potassium, calcium and magnesium salts of saccharin, and magnesium chloride, have been shown to be clastogenic to Chinese hamster lung (CHL) fibroblasts in vitro, but only at elevated dose levels (8-16 mg/ml). Saccharin acid was inactive to the limits of its solubility (4 mg/ml). When the data are expressed in terms of ionic concentration, each salt showed a similar clastogenic potency. This suggests that ionic effects induced by these salts in the assay medium may be the critical determinant of the clastogenic effects seen, rather than that the saccharin moiety presents a genotoxic insult to the chromosomes of the cells. The metal-chelating agents EDTA and EGTA were non-clastogenic, but the disodium salt of EDTA showed weak activity prior to toxicity at 0.5 mg/ml. The absence of a clastogenic response for the salts of saccharin at dose levels lower than 4 mg/ml is discussed within the context of the threshold-dependent tumour-promoting activity of high dose levels of sodium saccharin to the bladder of male rats. The doubtful value of conducting in vitro clastogenicity studies at dose levels greater than 10(-2) M is discussed.

The genotoxicity of sodium saccharin and sodium chloride in relation to their cancer-promoting properties

The literature indicates that sodium saccharin is non-reactive to DNA and inactive as a gene mutagen in vitro. At elevated dose levels it is capable of producing structural disturbances in eukaryotic chromosomes in vitro, and it shows intermittent activity as a very weak germ-cell and somatic-cell mutagen in vivo. Its possible mode of action in these respects is speculated on and related to its ability to promote bladder tumours in rats at elevated dose levels. A review of the toxicology of sodium chloride reveals a profile of genotoxic activities almost identical to that of sodium saccharin. It is suggested that the recorded genotoxic and cancer-promoting activities of these chemicals will only become apparent at elevated dose levels that define them as significant contributors to the biological medium (solvent) rather than as trace xenobiotic toxins (solutes). The possible activity of acid saccharin, or of its potassium, calcium and ammonium salts, as ionic genotoxins requires urgent evaluation.

Effects on mouse embryos of in utero exposure to saccharin: teratogenic and chromosome effects

For teratogenesis studies, pregnant ICR albino mice were administered saccharin by three routes and at three different doses by each route as follows: Intraperitoneal injection of 500, 1,000, or 2,000 mg/kg saccharin on day 10 of gestation; intragastric tube delivery of 5, 10, or 25 mg/kg/day of saccharin on days 5-15 of gestation; and as drinking water containing a 5, 10, or 20% solution of saccharin from day 0 through day 17. Appropriate controls were used for each set. No increase in either resorptions or malformations was found in mouse embryos whose dams had received saccharin by any of the three routes. For chromosome studies, saccharin was administered IP to pregnant ICR albino mice on day 10 of gestation as either a 1,000 mg/kg or 2,000 mg/kg dose. To demonstrate sister chromatid exchanges (SCE), bromodeoxyuridine was administered as 16 consecutive half-hourly doses of 25 mg/kg during the 8 h prior to saccharin injection. In addition, one group received two doses of BrdU and 2,000 mg/kg saccharin 8 h apart to demonstrate SCE frequency following exposure to saccharin for two cell cycles. The mice were given colchicine (4 mg/kg) 6 h after the final injection and killed 2 h later. Embryonic cell suspensions and metaphase spreads were prepared by routine methods. Metaphase spreads were examined for breaks or gaps (after Giemsa staining), for G-banding (using the ASG technique), for C-banding (using Giemsa staining after exposure to 0.07 N NaOH and incubation in 2 X SSC at 60 degrees C), and for SCE by the Hoechst-Giemsa method. Fifty metaphase spreads were counted for each experimental condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Saccharin: a toxicological and historical perspective

Saccharin, first synthesized in 1879, eventually became popular as an inexpensive substitute for sugar, particularly as a non-caloric sweetner. The dispute concerning the safety of saccharin for human consumption is almost as old as saccharin itself. In this article, the history concerning the uses of saccharin and the accompanying controversy are reviewed. In addition, the spectrum of toxicological and epidemiological studies to which saccharin has been subjected are also examined. While the toxicological data indicate that saccharin is probably the agent solely responsible for the bladder tumors observed in second generation male rats, the epidemiological studies provide, at best, an equivocal relationship between the consumption of saccharin and bladder cancer. A benefit-risk evaluation for saccharin showed few, if any documentable benefits from the use of saccharin and much genuine uncertainty concerning the potential risks for ingestion by man. This element of genuine uncertainty as to the extent of human risk posed to man is the crux of saccharin's past and its foreseeable future.

Cell kinetics and sister-chromatid-exchange frequency in human lymphocytes

Repeated cultures from 5 healthy donors were set up in 3 tissue-culture media: TC109, TC199 and TC1640. For each donor, 3 blood samples were taken at 1-week intervals, making a total of 5 x 3 x 3 = 45 cultures. Our results show a large variability in the individual SCE base-line frequency. This variability can be partly attributed to the different tissue-culture media or to the donors themselves. Our results, however, stress the importance of the proliferating rate of the culture in determining the SCE frequency.

Induction of sister chromatic exchanges and inhibition of cellular proliferation in vitro. I. Caffeine

Cytogenetic assay systems based on the detection of sister chromatid exchanges (SCE) are widely advocated as a sensitive screening method for assessing genotoxic potential. While many agents have been examined for their ability to induce SCE's, complete dose-response information has often been lacking. We have reexamined the ability of one such compound-caffeine-to induce SCEs and also to inhibit cellular proliferation in human peripheral lymphocytes in vitro. An acute exposure to caffeine prior to the DNA synthetic period did not affect either SCE frequency or the rate of cellular proliferation. Chronic exposure to caffeine throughout the culture period lead to both a dose-dependent increase in SCEs (SCEd or doubling dose = 2.4 mM; SCE10 or the dose capable of inducing 10 SCE = 1.4 mM) and a dose-dependent inhibition of cellular proliferation (IC50 or the 50% inhibition concentration = 2.6 mM). The relative proportion of first generation metaphase cels, an assessment of proliferative inhibition, increased linearly with increasing caffeine concentrations. However, SCE frequency increased nonlinearly over the same range of caffeine concentrations. Examination of the ratio of nonsymmetrical to symmetrical SCEs in third generation metaphase cells indicated that caffeine induced SCEs in equal frequency in each of three successive generations. The dependency of SCE induction and cellular proliferative inhibition on caffeine's presence during the DNa synthetic period suggests that caffeine may act as an antimetabolite in normal human cells. The significance of these results in regard to both caffeine's genotoxic potential and to the reliability of the SCE assay system are discussed.

Saccharin may act as a tumour promoter by inhibiting metabolic cooperation between cells

The possible role of saccharin in the carcinogenic process is, at present, still unclear. Carcinogenesis is a complex process involving, in many test systems, initiation and promotion phases. Current evidence favours the hypothesis that initiation is due to a mutagenic event, while promotion (at least the early portion) is the result of epigenetic changes. Although saccharin has been reported to be a weak mutagen in various in vitro test systems and a weak initiator in mouse skin, there is increasing evidence from in vitro, as well as in vivo, studies that it might act as a tumour promoter, rather than as a mutagen. Recently L.P.Y. et al and J.E.T. et al. developed an in vitro assay to detect tumour promoters, which has been independently reported by Murray and Fitzgerald. The assay is based on the principle that phorbol ester-type tumour promoters block 'metabolic cooperation' or a type of cell-cell communication between cells. We report here a series of experiments demonstrating the elimination of metabolic cooperation in the hypoxanthine guanine phosphoribosyltransferase (HGPRT) system in Chinese hamster V79 cells, indicating that saccharin shares properties similar to those of other known promoters.