Physiological and mutagenic effects of N-methyl-N′-nitro-N-nitrosoguanidine in populations of chlorococcal algae

The suitability was evaluated of MNNG as a mutagen inducing increased frequencies of mutations in the cell populations of three strains of chlorococcal algae for the purposes of selection. MNNG has proved to be highly toxic to those algae as it produces severe physiological responses of the affected cells. The mutagenic effect of MNNG was relatively small in comparison with the recorded toxic effect. From these results it has been concluded that in reverse to NEU, MNNG can hardly be applied with such good an effect in the mutation breeding of chlorococcal algae that are suitable for mass cultivation.     

Streptomycin and N-Methyl-N’-nitro-N-nitroso-guanidine inhibit incorporation of14C-precursors of macromolecule synthesis inEuglena gracillis

Streptomycin and N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) cause a 100% hereditary bleaching ofEuglena gracilis. In spite of the outcomes being the same, the corresponding mechanisms differ. By investigating the incorporation of the¹⁴C-labelled precursors of macromolecule synthesis we showed streptomycin to inhibit the synthesis of nucleic acids and proteins to the same extent (56%), whereas in the case of MNNG a 66% inhibition of nucleic acid synthesis and a 24% one of protein synthesis were observed.     

Molecular and cellular mechanisms of transformation of C3H/10T1/2 Cl 8 and diploid human fibroblasts by unique carcinogenic,nonmutagenic metal compounds

Work from our laboratory showed that carcinogenic metal salts of arsenic, nickel, and chromium induced morphological transformation of cultured C3H/10T^1/2 Cl 8 (10T^1/2) mouse embryo cells, and that many of the transformants grow in soft agarose and form tumors in nude mice. Concentrations of arsenic, nickel, and chromium compounds that induced morphological transformation did not induce mutation to ouabain resistance in 10T^1/2 cells. This indicated that the mechanism of metal induced morphological transformation was likely not caused by induction of base substitution mutations, and in the case of lead chromate, likely not caused by frameshift or deletion mutations. In addition, we showed that carcinogenic arsenic, nickel, and chromium compounds, and MNNG, induced anchorage independence in diploid human fibroblasts. Anchorage-independent cell strains derived from anchorage-independent colonies were stable but did not form foci and eventually senesced, therefore, arsenic and nickel compounds and lead chromate induced stable anchorage independence as an isolated phenotype. Nickel compounds and lead chromate induced anchorage independence but not mutation to ouabain resistance or to 6-thioguanine resistance. Hence, the mechanism of induction of anchorage independence by these metal salts in human fibroblasts was likely not via induction of base substitution, frameshift, or deletion mutations that would be measured in these mutation assays. MNNG, on the other hand, induced mutation to 6-thioguanine resistance and to ouabain resistance over the same concentration ranges that induced anchorage independence was induced, indicating that MNNG might induce anchorage independence by inducing base substitution, frameshift, or deletion mutations. It is likely, therefore that the mechanisms of metal salt induced morphological and anchorage independent transformation in murine and human base substitution mutations. We hypothesize that rearrangements or amplification of proto-oncogenes, or, possibly, inactivation of suppressoro oncogenes, might play a role in the mechanism of metal salt induced morphological or anchorage independent transformation of 10T^1/2 and diploid human fibroblasts, respectively. *** DIRECT SUPPORT *** A03GS019 00027     

Trace element inhibition of carcinogenesis and angiogenesis

In separate experimental models the effects of selenium, zinc, potassium, and copper on angiogenesis and carcinogenesis are compared. Inhibitory effects of Se as Na₂SeO₃ and of chloride salts of K and Zn, but not of Cu, on vascularization induced by amelanotic tumor implants (A Mel-4B32) in the Syrian hamster cheek pouch membrane are reported. In an earlier study the induction of new vasculature, angiogenesis, in control chambers implanted with A Mel-4B32 was initially observed on day 4 after implant. Addition of 5, 10, and 50 μg Se at the time of tumor implant delayed the initial capillary proliferation to days 7, 9, 10, respectively (Cancer Lett. 9, 353, 1980). Similarly, in this report addition of 50 μg Zn or 50 μg K delayed angiogenesis to days 7.and 6, respectively. By contrast, addition of 50 μg Cu caused severe inflammation and necrosis of the membrane before capillary proliferation could be observed and the animals had to be sacrificed. In an earlier study we reported the colon tumor incidence in 1,2-dimethylhydrazine (20 mg DMG/kg body weight for 20 weeks) -treated Sprague Dawley rats was reduced from 87 to 40% by a 4 ppm Se (as Na₂SeO₃) supplement in the drinking water (Cancer Lett. 2, 133, 1977). In this study rats were treated with the same dose of carcinogen, but were sacrificed 14 weeks following the last DMH injection. Drinking water supplements with 0.02% Zn (as ZnCl₂), 0.5% K (as KCl), or 0.01% Cu (as CuCl₂) were provided concurrently with the carcinogen and were continued until death or sacrifice. The colon tumor incidence was 18/20 in the DMH control and was reduced to 16/20 by supplemental Zn, reduced to 12/20 by supplemental K, and was unchanged (18/20) by Cu. The tumor incidences in the small intestine and Zymbal gland were all reduced by Zn, K, and Cu supplements compared with the DMH control. The hamster cheek pouch technique may provide a prescreen for potential inhibitors of chemical carcinogenesis in other experimental models.     

Mechanisms of Na+ uptake,ammonia excretion,and their potential linkage in native Rio Negro tetras (Paracheirodon axelrodi,Hemigrammus rhodostomus,and Moenkhausia diktyota)

Mechanisms of Na⁺ uptake, ammonia excretion, and their potential linkage were investigated in three characids (cardinal, hemigrammus, moenkhausia tetras), using radiotracer flux techniques to study the unidirectional influx (J _in), efflux (J _out), and net flux rates (J _net) of Na⁺ and Cl^?, and the net excretion rate of ammonia (J _Amm). The fish were collected directly from the Rio Negro, and studied in their native “blackwater” which is acidic (pH 4.5), ion-poor (Na⁺, Cl^? ~20 µM), and rich in dissolved organic matter (DOM 11.5 mg C l^?1). J _in ^Na , J _in ^Cl , and J _Amm were higher than in previous reports on tetras obtained from the North America aquarium trade and/or studied in low DOM water. In all three species, J _in ^Na was unaffected by amiloride (10^?4 M, NHE and Na⁺ channel blocker), but both J _in ^Na and J _in ^Cl were virtually eliminated (85–99 % blockade) by AgNO₃ (10^?7 M). A time course study on cardinal tetras demonstrated that J _in ^Na blockade by AgNO₃ was very rapid (<5 min), suggesting inhibition of branchial carbonic anhydrase (CA), and exposure to the CA-blocker acetazolamide (10^?4 M) caused a 50 % reduction in J _in ^Na _.. Additionally, J _in ^Na was unaffected by phenamil (10^?5 M, Na⁺ channel blocker), bumetanide (10^?4 M, NKCC blocker), hydrochlorothiazide (5 × 10^?3 M, NCC blocker), and exposure to an acute 3 unit increase in water pH. None of these treatments, including partial or complete elimination of J _in ^Na (by acetazolamide and AgNO₃ respectively), had any inhibitory effect on J _Amm. Therefore, Na⁺ uptake in Rio Negro tetras depends on an internal supply of H⁺ from CA, but does not fit any of the currently accepted H⁺-dependent models (NHE, Na⁺ channel/V-type H⁺-ATPase), or co-transport schemes (NCC, NKCC), and ammonia excretion does not fit the current “Na⁺/NH₄ ⁺ exchange metabolon” paradigm. Na⁺, K⁺-ATPase and V-type H⁺-ATPase activities were present at similar levels in gill homogenates, Acute exposure to high environmental ammonia (NH₄Cl, 10^?3 M) significantly increased J _in ^Na , and NH₄ ⁺ was equally or more effective than K⁺ in activating branchial Na⁺,(K⁺) ATPase activity in vitro. We propose that ammonia excretion does not depend on Na⁺ uptake, but that Na⁺ uptake (by an as yet unknown H⁺-dependent apical mechanism) depends on ammonia excretion, driven by active NH₄ ⁺ entry via basolateral Na⁺,(K⁺)-ATPase.     

Different effects of selenium on cyclic AMP metabolism in hepatoma cells and normal liver cells

Sodium selenite administered to normal and hepatoma (HA)-bearing mice sc (2 mg/kg) or ip (1 mg/kg) led to a significant increase in cyclic AMP (cAMP) level and a decrease in cAMP phosphodiesterase (PDE) activity in HA cells. In contrast, in tumor host liver and normal liver the cAMP level was reduced, and the PDE activity was slightly elevated, whereas the cAMP adenylate cyclase (AC) was little affected by Na₂SeO₃, if at all. These results imply that selenite-induced changes in PDE activity play a decisive role in regulating intracellular cAMP level. Kinetic studies revealed that there were different forms of PDE. TheK _m value of PDE isozymes in normal liver and host liver were identical, but differed from those of HA. It seems likely that the selective responsiveness of PDE to selenite may be related to the difference in PDE isozyme patterns. Addition of DBcAMP to the culture medium resulted in an inhibition of³H-thymidine incorporation into hepatoma cells, indicating that the inhibition of HA cell proliferation was cAMP-mediated. Thus, selenium has been shown to exert a selective effect on cAMP metabolism of hepatoma cells, which may account for its inhibitory effects on cancer cells.     

Cadmium-Induced Injury and the Ameliorative Effects of Selenium on Chicken Splenic Lymphocytes: Mechanisms of Oxidative Stress and Apoptosis

Cadmium (Cd) is an important environmental pollutant present in soil, water, air, and food. Selenium (Se) can antagonize some metal element toxicity including Cd. To investigate the cytotoxicity of Cd and the protective effects of Se on bird immunocytes in vitro, chicken splenic lymphocytes with CdCl₂ (10^?6 mol/L), Na₂SeO₃ (10^?7 mol/L), and the mixture (10^?7 mol/L Na₂SeO₃ and 10^?6 mol/L CdCI₂) were incubated for 12, 24, 36, and 48 h, respectively. A high level of malondialdehyde (MDA) and reactive oxygen species (ROS) productions were observed in Cd treatment group; the activities of catalase (CAT), glutathione peroxidise (GSH-Px), superoxide dismutase (SOD), and the mitochondrial inner transmembrane potential (ΔΨm) were significantly lower in Cd treatment group than those in controls (P?P?mRNA level of Bak, p53, caspase-3, caspase-9, and cytochrome c (Cyt c) and decreased Bcl-2, Bcl-xl, and CaM were observed in Cd treatment group. Se ameliorated ΔΨm and [Ca²⁺]i for mitochondria function restoring, and Se was able to modulate the expression of relative genes. In conclusion, concurrent treatment with Se reduced the Cd-induced morphological changes and oxidative stress, ion disorder, and apoptosis, suggesting that the toxic effects of Cd on the chicken splenic lymphocytes were partly meliorated by Se.     

Effects of Selenium Source and Level on Growth Performance, Tissue Selenium Concentrations, Antioxidation, and Immune Functions of Heat-Stressed Broilers

An experiment is conducted to investigate the effects of selenium (Se) source and level on growth performance, tissue Se concentrations, antioxidation, and immune functions of heat-stressed broilers from 22 to 42?days of age. A total of 210 22-day-old Arbor Acres commercial male chicks were assigned by body weight to one of seven treatments with six replicates of five birds each in a completely randomized design involving a 3?×?2 factorial arrangement plus one Se-unsupplemented basal diet control (containing 0.027?mg of Se/kg). The three Se sources were sodium selenite (Na₂SeO₃), Se yeast, and AMMS Se (Se protein), and the two supplemental Se levels were 0.15 or 0.30?mg Se/kg. All birds were reared under heat-stressed condition (33?±?1?°C during 0900?C1700?hours and 27?±?1?°C during 1900?C0700?hours with a relative humidity of 60?C80?%). The results showed that heat-stressed chicks fed Se-supplemented diets had higher (P?<?0.10) average daily feed intake, Se concentrations in liver and breast muscle, liver glutathione peroxidase (GSH-Px) activity, serum antibody titers against H5N1(Re-4 strain), H5N1(Re-5 strain) and lower (P?<?0.01) mortality compared with the control. Chicks fed the diets supplemented with 0.30?mg/kg of Se had higher (P?<?0.05) Se concentrations in liver and breast muscle, liver GSH-Px activity, and serum antibody titer against H5N1 (Re-4 strain) than those fed the diets supplemented with 0.15?mg/kg of Se. Broilers fed the diets supplemented with Se yeast had higher (P?<?0.001) Se concentrations in liver and breast muscle than those fed the diets supplemented with Na₂SeO₃ or AMMS Se. However, broilers fed the diets supplemented with AMMS Se had higher (P?<?0.05) serum antibody titers against H5N1 (Re-4 strain) and H5N1 (Re-5 strain) than those fed the diets supplemented with Na₂SeO₃. These results indicated that Se yeast was more effective than Na₂SeO₃ or AMMS Se in increasing tissue Se retention; however, AMMS Se was more effective than Na₂SeO₃ or Se yeast in improving immune functions of heat-stressed broilers.     

Elements of margin of safety,toxicity and action of sodium selenite in a lipopolysaccharide rat model

ProjectBoth septic shock and sodium selenite (Na₂SeO₃) lead to multiple organ failure through oxidation. Na₂SeO₃ has direct oxidant effects above the nutritional level and indirect anti-oxidant properties.In a lipopolysaccharide (LPS) rat model we assessed margin of safety, toxicity and beneficial effect of pentahydrate Na₂SeO₃ (5H₂O·Na₂SeO₃) at oxidant doses.ProcedureIn a three-step study on 204 rats we: (i) observed toxic effects of Na₂SeO₃ injected intraperitoneously (IP) and determined its Minimum Dose Without Toxic effect (MDWT) 0.25–0.35 mg/kg selenium (Se) content; (ii) injected IP LPS at 70% lethal dose (LD) followed, or not, one hour later by IP Na₂SeO₃ at MDWT and (iii) by doses > MDWT. At 48 h, in survivors, we measured plasma creatinine, lactate, aspartate and alanine aminotransferase (AST, ALT), nitric oxide (NO) and Se concentrations.Results(i) Na₂SeO₃ alone did not increase NO and lactate. Encephalopathy appeared at 1 mg Se/kg. Creatinine increased at 1–1.75 mg Se/kg, AST, ALT at 3–4.5 mg Se/kg, and the minimum LD was 3 mg Se/kg. (ii) Mortality after LPS was 37/50 (74%, [62–86%]) vs. 20/30 (67%, [50–84%]) when followed by Na₂SeO₃ at MDWT (p = 0.483) with a decreased in NO (−31%, p = 0.038) a trend for lactate decrease (−19%, p = 0.068) and an increased Se in plasma of survivals. (iii) All rats died at doses ≥0.6 mg/kg (p < 0.001).ConclusionMechanisms of LPS and Na₂SeO₃ toxicity differ (i.e. NO, lactate). In septic shock 5H₂O·Na₂SeO₃ toxicity increased, margin of safety decrease, but IP administration of dose considered as oxidant of 5H₂O·Na₂SeO₃ showed beneficial effects.     

Cytotoxicity of sodium selenite in HaCaT cells induces cell death and alters the mRNA expression of PUMA,ATR, and mTOR genes

BackgroundBy identifying the molecular mechanisms underlying sodium selenite (Na₂SeO₃) cytotoxicity during exposure in non-tumor cells (HaCaT cells), we will improve the current understanding of its antiproliferative effects and modulation of gene expression in the main pathways related to the cell cycle, cell death, oxidative stress, and DNA damage and repair.MethodsNon-tumor HaCaT cells were treated with Na₂SeO₃ to induce cytotoxicity, and the effects were investigated using an MTT assay (cell viability), real-time cell analysis (profiling the cell index), flow cytometry (membrane integrity, cell cycle disruption, and apoptosis), a comet assay (genotoxicity, i.e., DNA damage), and RT-qPCR (mRNA expression of genes).ResultsTreatment with Na₂SeO₃ was cytotoxic at 10 μM, producing morphological changes in cells (cytoplasmic granulations); however, it did not have a genotoxic effect. Na₂SeO₃ induced cell membrane damage, cell death, and cell cycle arrest in HaCaT cells. It also altered the mRNA expression levels of PUMA, ATR, and mTOR genes. However, it had no effect on the mRNA expression of caspases or PARP1, BIRC5, BECN1, and c-MYC genes, suggesting that Na₂SeO₃ causes PUMA-dependent apoptosis in HaCaT cells. The mRNA expression of specific genes related to oxidative stress, DNA damage and repair, and cell cycle control were unchanged by Na₂SeO₃.ConclusionsWe demonstrated the cytotoxic effect of Na₂SeO₃ in HaCaT cells by analyzing mRNA expression patterns, changes in cell morphology, and proliferation kinetics.     

Induction and complementation of lysine auxotrophs in Saccharomyces

Four chemical agents, EMS EMS: Ethyl methanesulfonate; MNNG: N-methyl-N\t'-nitro-N\t'-nitrosoguanidine; NA: Nitrous acid; ICR-170: 2-methoxy-6-chloro-9-[3-(ethyl-2-chloroethyl) aminopropylamino] acridine 2 HCl; UV: Ultra violet radiation. , MNNG, NA, ICR-170, as well as UV were used to induce mutations in the wild-type haploid strain X2180-1B (α) of Saccharomyces. A total of 2053 (EMS, 427; MNNG, 444; NA, 469; ICR-170, 456; UV, 257) lysine-requiring mutant clones were isolated from many independent treatments and by nystatin enrichment technique. Mutants were classified into various functional groups on the basis of complementation analysis with 14 tester strains (lys 1 to lys 15 except lys 3). Of the clones analyzed, the number of isolates unable to complement with a given tester strain ranged from 2 for lys 5 to 918 for lys 4. Three of the mutually complementing lysine loci (lys 1, lys 2, and lys 4) accounted together for over 85% of the mutant clones whereas lys 6, lys 7, lys 8, and lys 14 had less than 10 noncomplementing isolates each. Mutants for lys 4 were most frequent with all of the mutagens tested except with NA in which case the mutants for lys 2 were most frequent. A total of 56 isolates failed to complement with lys 10, lys 11, and lys 12. Similarly, 47 isolates failed to complement with lys 9 and lys 13 simultaneously. Only 44 isolates complemented with all of the tester strains used.     

Additive coclastogenicity of sodium selenite and caffeine in CHO cells treated withN-methyl-N′-Nitro-N-Nitrosoguanidine

The clastogenic effect ofN-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster ovary (CHO) cells and its modulation by Na₂SeO₃ and caffeine were studied by metaphase analysis of chromosome aberrations (CA) as well as by measuring the formation and repair of single-strand (ss) DNA breaks employing hydroxylapatite chromatography. Treatment of CHO cells with MNNG (1.25 or 2.5 × 10-5M) for 3 h caused CA in 11 and 19% of metaphases scored, respectively. Pretreatment of cells with Na₂SeO₃ (1–5 μg/mL) or caffeine (0.2–2.0 mg/mL) for 2 h resulted in a 2–3.5-fold increase of CA frequency. Addition of both modulators during the mutagen exposure tended to cause a slight inhibition of clastogenic activity of MNNG (1.25 × 10⁻⁵ M) or had no effect on CA number when MNNG was used at a concentration of 2.5 × 10−5M. Posttreatment of CHO cells with Na₂SeO₃ for 20 h after MNNG was ineffective in influencing the number of metaphases with CA, whereas, at these conditions, caffeine enhanced up to 6-7-fold the clastogenic activity of MNNG. Addition of both modulators during the whole experiment, 2 h pretreatment included, resulted in a further significant increase of CA frequency up to the total pulverization of chromosomes in all metaphases scored. The coclastogenic effect of caffeine was greater in this case. The enhancement of chromosome-damaging activity of MNNG by selenite and caffeine was better expressed when this carcinogen was applied at the higher concentration used. An additive coclastogenic effect was observed in CHO cells treated simultaneously with Na₂SeO₃ and caffeine plus MNNG. In addition, the treatment of CHO cells with MNNG (5 × 10⁻⁶ M) caused a rapid increase of ssDNA breaks number reaching maximal values after 30–45 min. However, up to 50–60% of MNNG-induced ssDNA breaks were repaired during the first 60–150 min after the mutagen exposure. The 2 h pretreatment of CHO cells with Na₂SeO₃ (2 μg/mL) or the addition of this trace element after MNNG had no effect on formation and repair of MNNG-induced ssDNA breaks. The coclastogenic effect of Na₂SeO₃ in CHO cells treated with MNNG was not directly linked to the induction and disappearance of ssDNA breaks measured by hydroxylapatite chromatography.     

Aphidicolin allows a rapid and simple evaluation of DNA-repair synthesis in damaged human cells

The decrease in microbial mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitrosourea (MNU) was compared in an animal mediation with rats and in direct incubation with human as well as rat blood and blood components. The mutagenic activity was assayed by reverse mutation from streptomycin (SM) dependence to non-dependence in Escherichia coli, strain Sd-B (TC). The mutagenic response curves of both MNNG and MNU were approximately linear and parallel at non-cytotoxic concentrations. However, the mutagenic capabilities of MNNG were estimated to be 10-fold more potent than those of MNU. The mutagenic activity in blood and liver preparations from rats killed immediately after intravenous injection of MNNG, 50 mg/kg, was negative. Results with MNU, 100 mg/kg, were positive in both cases.For the detection of mutagenicity, blood was diluted 50 times for the final testing mixture (1 ml) to avoid bactericidal effects of the blood itself. When a larger amount of liver preparation was used in the tests, and diluted 8 times, mutagenic activity was still detected 15 min after injection of MNU, 80 mg/kg. Comparisons of the diminished rate of mutagenicity between MNNG and MNU during certain periods of incubation with blood indicated that MNNG was inactivated much more rapidly than MNU with both human and rat blood. Plasma showed a moderate inactivating effect on both MNNG and MNU. Red blood cells inactivated MNNG at a remarkably rapid rate similar to that of whole blood, but was less effective on MNU. In further experiments with red- cell components, the cell contents inactivated both MNNG and MNU at rates similar to those with red cells, but cell membrane had absolutely no effect in decreasing the mutagenicity in either MNNG or MNU.     

Selenium-enriched Candida utilis: Efficient preparation with l-methionine and antioxidant capacity in rats

Selenium-enriched Candida utilis has attracted much attention due to its expanding application in food and feed additives. The objective of this study was to efficiently prepare selenium-enriched C. utilis and to investigate the effects of the prepared yeast on antioxidant capacity in rats. A batch culture of selenium-enriched C. utilis was first carried out, and the addition of sodium selenite (Na₂SeO₃) after all glucose had been consumed was found to favor higher intracellular glutathione and organic selenium content. Moreover, l-methionine boosted yeast cell growth and glutathione biosynthesis, and prevented glutathione from leaking to the extracellular space that can be caused by Na₂SeO₃. We therefore developed a two-stage culture strategy involving supplementation with l-methionine and Na₂SeO₃ at separate culture phases to improve the performance of selenized C. utilis. Using this two-stage culture strategy, intracellular glutathione content reached 18.6 mg/g and 15.5 mg/g, respectively, in batch and fed-batch systems, and organic selenium content reached 905.2 μg/g and 984.7 μg/g, respectively. The effects of selenium-enriched C. utilis on the activities of antioxidant related enzymes in rats were investigated, and the prepared selenium-enriched C. utilis was shown to be an optimal dietary supplement for enhancing antioxidant capacity in rats.     

In vitro differential effects of sodium selenite on the growth of human hepatoma cells and human embryonic liver cells

The effects of various concentrations of Na₂SeO₃ on human hepatoma cells and human embryonic liver cells was investigated in vitro. For human hepatoma cells, mitotic index and cell count decreased with increasing selenium concentrations. At 1 μg/mL Na₂SeO₃, mitotic activity of human hepatoma cells were partially arrested. In human embryonic liver cells continuously treated with Na₂SeO₃, (1 μg/mL) cell count of the treated group decreased only by d 7; mitotic index, labeled index, and mean silver grain number per 50 labeled nuclei were the same as in the control group on exposure to 1, 3, and 5 μg/mL for up to 72 h. In mixed cultures of human hepatoma and embryonic liver cells treated with 3 and 5 μg/mL of Na₂SeO₃ for 24 h, hepatoma cells showed vacuolated cytoplasms, distorted nuclei, condensed chromatin, and even pyknosis, whereas the embryonic liver cells retained a normal morphology under the same treatment.     

Effects of Na2SeO3 on growth,metabolism, antioxidase and enzymes involved in polysaccharide synthesis of Cordyceps militaris

The main objective of our study was to illuminate effects of sodium selenite (Na₂SeO₃) on growth, metabolism and enzyme activities of Cordyceps militaris. By adding Na₂SeO₃ in fermentation medium (7 mg/L), it was found that mycelium of C. militaris was stronger with more plump spores and its biomass was higher accompanied by the maximum (13.19 g/L) at 6 d of culture. Besides, Na₂SeO₃ also caused the enhancement of total thiol (T-SH), non-protein thiol (NP-SH) contents and the biosynthesis of Se-polysaccharide (Se-CMP) with discriminatory molecular weight, optical rotation, UV–vis and FT-IR spectra. Activities of antioxidase including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and enzymes involved in polysaccharide synthesis including phosphoglucomutase (PGM), phosphoglucose isomerase (PGI), UDPG-pyrophosphorylase (UGP) enhanced to different extent. Their corresponding genes were also up-regulated but cat gene (encoding CAT). Se-enrichment of C. militaris provided a good way for desirable biomass and polysaccharide biosynthesis in further research.     

Mutagenic activation and carcinogenicity of aminoazo dyes ortho-aminoazotoluene and 3′-methyl-4-dimethylaminoazobenzene in experiments on suckling mice

It is found that after administration of 3′-methyl-4-dimethylaminoazobenzene (3′-Me-DAB,) which was hepatocarcinogenic to rats, in suckling mice, the number of neoplastic lesions in the liver of mice was 3 times higher than after analogous administration of equimolar dose of ortho-aminoazotoluene (OAT)). However, in the Ames test (TA-98 strain of Salmonella typhimurium) with activation by hepatic enzymes (S-9 fraction) of both intact and Aroclor-1254-induced mice and rats OAT contributed by an order of magnitude to revertant colonies compared to 3′-Me-DAB. In vivo inhibition of sulfotransferase activity, the enzyme which catalyzes the final stage of the mutagenic activation of aminoazo dyes, had no effect on carcinogenicity of 3′-Me-DAB but more than 4 times elevated that of OAT. It was concluded that the mechanism of carcinogenic action of aminoazo dyes studied is not genotoxic and that the carcinogenic potential of OAT is lost in the process of mutagenic activation.     

Modulation of diethylnitrosamine carcinogenesis in rat liver and oesophagus

A series of 16 experiments, using a total of 2,000 BD₆ rats, was designed in order to assess the ability of 8 individual agents or their combinations to modulate the liver and oesophageal carcinogenesis induced by multiple doses of diethylnitrosamine (DEN). Of the antioxidants tested, sodium selenite, ascorbic acid, and butylated hydroxytoluence generally exhibited protective effects on both types of tumors. In contrast, retinoic acid behaved as a promoter of DEN hepatocarcinogenesis, but this effect could be eliminated by its combination with either selenite or butylated hydroxytoluene. Caffeine and theophyline, when individually assayed, were devoid of significant protective effects, and the later methylxanthine stimulated oesophageal tumorigenesis when administered afer exposure to the carcinogen. Caffeine tended to decrease tje multiplicityof tumors and potentiated the inhibitory effect of selenite in the liver. Irrespective of combination with caffeine, treatment with phwnobarbital before each DEN injection tended to reduce the multiplicity of both liver and oesophageal tumors. On the other hand, the metabolic inhibitoe diethyldithiocarbamate, given after each DEN injection, dramatically enhancedd the incidence and multiplicity of oesophageal tumors. Thus, on the whole, modulation of DEN carcinogenesis varied depending on test agents, their conbinations, dosages, treatment schedules, and target organ.     

Effects of NaCl and Na2CO3 stresses on photosynthetic ability of Chlamydomonas reinhardtii

Chloride and carbonate salts are the main salts causing salinization and widely exist in aquatic environment, so algae may suffer from salinization stress for high water evaporation. In this study, in order to investigate and compare the toxic effects of the two salts on algal photosynthesis, we used NaCl and Na₂CO₃ to stress Chlamydomonas reinhardtii. Under the two salt stresses, the content of O ₂ ^?· and H₂O₂ in the cells was increased significantly, and it was much higher in Na₂CO₃ treatment than in NaCl treatment at the same Na⁺ concentration. The absorbance spectra and 4^th derivative spectra of photosynthetic pigments were declined under 300 mM NaCl and 25 mM Na₂CO₃ stresses, and remarkably changed under 50 mM and 100 mM Na₂CO₃ stresses. When the cells stressed by the two salts, the maximum quantum yield (Fv/Fm), electron transport rate (ETR) and photochemical quenching (qP) were reduced markedly, but the nonphotochemical dissipation (NPQ) was increased markedly. At the same Na⁺ concentration, Na₂CO₃ stress had stronger toxic effects on photosynthetic ability than NaCl stress.     

Microcalorimetric study of the toxic effect of sodium selenite on the mitochondria metabolism of Carassius auratus liver

The fundamental thermogenesis curves of the metabolic process of liver mitochondria from Carassius auratus and the toxic effect of Na₂SeO₃ on it were studied by using an LKB-2277 bioactivity monitor, ampoule method, at 28°C. From the thermogenesis curves, the thermokinetic equations were established under different conditions. The kinetics show that a low concentration of Na₂SeO₃ (1–4 mg/L) had promoting action on the metabolism process of Carassius auratus liver mitochondria, but that a high concentration of Na₂SeO₃ (8–16 mg/L) inhibited the mitochondria metabolism.