Nature of chromosome gaps induced by alkylating agents and γ-rays as revealed by caffeine treatment

In the cells of primary roots of Crepis capillaris, post-treatment with caffeine increased the frequency of gaps and chromosomal aberrations induced by the alkylating agents ethyleneimine and N-nitroso-N-methylurethane and γ-rays. The increase in the frequency of gaps was considerably lower than that observed in chromosomal aberrations, this being more strongly expressed in the case of the alkylating agents. The potentiating effect of caffeine on the γ-ray-induced chromosomal gaps was a little higher in S as compared with G₂. These results lead to the conclusion that the alkylating agents and the γ-rays might induce 2 types of chromosomal gap.     

Specificity of mutations induced by carbon ions in budding yeast Saccharomyces cerevisiae

To investigate the nature of mutations induced by accelerated ions in eukaryotic cells, the effects of carbon-ion irradiation were compared with those of γ-ray irradiation in the budding yeast Saccharomyces cerevisiae.

The mutational effect and specificity of carbon-ion beams were studied in the URA3 gene of the yeast. Our experiments showed that the carbon ions generated more than 10 times the number of mutations induced by γ-rays, and that the types of base changes induced by carbon ions include transversions (68.7%), transitions (13.7%) and deletions/insertions (17.6%). The transversions were mainly G:C → T:A, and all the transitions were G:C → A:T. In comparison with the surrounding sequence context of mutational base sites, the C residues in the 5′-AC(A/T)-3′ sequence were found to be easily changed. Large deletions and duplications were not observed, whereas ion-induced mutations in Arabidopsis thaliana were mainly short deletions and rearrangements. The remarkable feature of yeast mutations induced by carbon ions was that the mutation sites were localized near the linker regions of nucleosomes, whereas mutations induced by γ-ray irradiation were located uniformly throughout the gene.     

Chromosomal responses to ionizing radiation reminiscent of and adaptive response in cultured Chinese hamster cells

When Chinese hamster V79 cells were internally exposed to low level chronic β-rays from incorporated tritiated thymidine (³H-dThd), the showed an “adaptive” response to the induction of chromosomal damage by subsequent higher acute doses of γ-rays.

The yield of sister-chromatid exchanges (SCEs) in the ³H-dThd pretreated cells was less than the yield induced by γ-rays alone (protective effects), and the micronucleus frequency was less than the sum of the induced frequencies by ³H-dThd and γ-rays separately (below-additivity effects). No adaptation to the micronucleus induction by γ-rays was observed after the ³H-adapted cells had divided once and when 3-aminobenzamide (3AB) was given before the challenge doses. The cross-resistance study revealed that the ³H-adapted cells were resistant to SCE induction but not to the micronucleus inductions by the challenge doses of reactor radiations. The results suggest that the SCE adaptation and the micronucleus adaptation or clastogenic adaptation are probably caused by different, inducible adaptive repair pathways.     

Synergism between caffeine and γ-radiation in the induction of dominant lethal mutations in oocytes and spermatozoa of Musca domestica

Caffeine was studied with regard to its synergism with γ-radiation in the induction of dominant lethal mutations in S14 oocytes and mature spermatozoa of M. domestica. In S14 oocytes an increase in the frequency of such a type of mutation was observed only when the exposure to γ-radiation followed a pretreatment with a diet containing 0.2% of caffeine. Negative results were obtained with (a) post-treatment with the same kind of diet, (b) pretreatment with diets containing 0.1 and 0.02% of caffeine and (c) exposure to the radiation 6 h after interruption of the feeding treatment with the diet containing 0.2% of caffeine. Such influence of the conditions under which the treatment is performed and the synergistic effects is probably related to the food intake pattern and the rapid metabolism of the caffeine. When the 0.2% caffeine pretreatment was combined with an exposure of the oocytes to variable doses of γ-radiation, the increments in the mutations observed seemed to be negatively correlated to the radiation doses used. Also, under such conditions, the dose/survival relationship fits well an exponential curve expressed by ln y = −0.866x. With mature spermatozoa, synergism by caffeine was found only when the females, after having been mated with the irradiated males, were fed for 24 h on a diet supplemented with 0.2% of caffeine.     

Effect of tumor promoter TPA on spontaneous and mitomycin C induced mitotic recombination in Drosophila melanogaster

It has been proposed that mitotic recombination is involved in tumor promotion. To test this idea, we investigated the effect of a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), on spontaneous and mitomycin C (MMC)-induced mitotic recombination in Drosophila melanogaster. The test system used was the wing-spot assay. Third instar larvae (mwh+/+flr) were treated with MMC (0-0.3 mM) for 6 h and fed media containing TPA (0-10 micrograms/ml), and the wings of surviving adults were analyzed for the presence of mutant spots. The results are: (1) MMC induced twin spots as well as single spots dose dependently (0.03-0.3 mM). (2) TPA itself did not induce twin spots or single spots in the range of doses examined (0.1-10 micrograms/ml). (3) TPA did not enhance the frequencies of twin or single spots induced by MMC. These results indicate that TPA induced neither mitotic recombination nor mutations under these experimental conditions. Thus the results would not support the mitotic recombination theory in tumor promotion. Rather, in this study, TPA posttreatment resulted in reduced frequencies of mutant single spots induced by MMC.     

昼夜不对称性与对称性升温对大豆产量和水分利用的影响

全球气候变暖并不是白天和夜间的平均变暖, 而是呈现一定的不对称性。大豆(Glycine max)是世界范围内种植较广泛的豆科作物, 也是中国重要的粮食作物。研究大豆的生长与水分利用对不对称性气候变暖的响应, 可为预测未来气候变暖情景下大豆的适应提供科学的参考依据。该实验在人工气候箱中采用盆栽方式进行, 设立对照(CON, 昼26 ℃夜16 ℃)、对称性升温(ETs, 昼夜均升高3 ℃)和不对称性升温(ETa, 昼升高2 ℃, 夜升高4 ℃)三个温度情景, 研究了大豆产量和水分利用对昼夜不对称性与对称性升温的差异性响应。结果表明: 在昼/夜26 ℃/16 ℃的背景下, 1) ETs对大豆产量影响不显著, 主要是因为生物量的增加缓解了收获指数下降对大豆的不利影响; ETa使大豆产量减少38.9%, 是由于大豆的收获指数和产量构成要素(荚数、粒数、百粒重)均显著降低。2) ETs对大豆全生育期蒸散量(ET)的影响不显著, ETa使大豆整个生育期ET减少14.8%。3)两种升温模式对大豆耗水量中蒸发量的影响都不显著, 耗水量的差异主要来自蒸腾量的差异, 其中ETs和ETa分别使大豆全生育期蒸腾量降低10.7%和26.1%。综上所述, 只针对ETs进行研究, 而没有对ETa进行研究的实验会低估真正的气候变暖情景(ETa)对大豆生长和产量的不利影响, 高估其对大豆耗水量的影响。     

Phorbol ester (12-O-tetradecanoylphorbol 13-acetate) prevents ornithine decarboxylase inhibition and apoptosis in L1210 leukemic cells exposed to TGF-β1

Previous studies have shown that growth suppression and apoptosis of leukemic cells exposed to TGF-β₁ is associated with the inhibition of ornithine decarboxylase (ODC) — the key enzyme of polyamine pathway. The aim of the present study was to evaluate the influence of 12-O-tetradecanoylphorbol 13-acetate (TPA) — a potent ODC inducer on antiproliferative and apoptotic effects of TGF-β₁ in L1210 leukemic cells. Cells were incubated in 2%FCS/RPMI1640 medium, supplemented with TGF-β₁ (2 ng/ml), TPA (100 ng/ml) or -difluoromethyl-ornithine (DFMO) (5 mM). Cell proliferation, apoptosis and necrosis were evaluated using [methyl-³H] thymidine, electron microscopy, electrophoresis of DNA and trypan blue exclusion. Expression and activity of ODC were determinated by RT-PCR and measurement of ¹⁴CO₂ release from L-1-¹⁴C ornithine, respectively. TGF-β₁ inhibited proliferation and induced apoptotic and necrotic cell death in L1210 leukemic cells. The above effects were associated with the inhibition of ODC expression and activity, measured 2 and 4 hr after TGF-β₁ administration, respectively. The presence of DFMO, an irreversible inhibitor of ODC, led to apoptotic fragmentation of DNA, similar to that observed in TGF-β₁-treated cultures. Administration of TPA simultaneously with TGF-β₁ significantly reduced antiproliferative, apoptotic and necrotic effects of TGF-β₁, and prevented its inhibitory action on ODC expression and activity. It is concluded that: down-regulation of ODC expression may be one of the early events associated with TGF-β₁-evoked suppression of growth and apoptosis; ODC is involved in the mechanism of protective action of TPA on TGF-β₁-related growth inhibition of L1210 leukemic cells.     

Differential effects of diurnal asymmetric and symmetric warming on yield and water utilization of soybean

Aims Global warming does not mean similar warmer temperatures between daytime and nighttime. Soybean (Glycine max) is a widely planted legume crop around the world and an important food crop in China. The aim of this study was to understand the responses of soybean growth and water utilization to future asymmetric warming, which would provide scientific reference for evaluating the adaptation of soybean to the future climate scenarios.Methods This experiment was carried out in artificial climate chambers, using the method of potted plants, under three temperature conditions; contrast (CON, 26 °C during the day and 16 °C during night), symmetric warming (ETs, elevated temperature of 3 °C both during the day and night), asymmetric warming (ETa, elevated temperature of 2 °C during the day and elevated temperature of 4 °C during night). We investigated the differential effects of diurnal asymmetric and symmetric warming on the yield and water consumption of soybean. Important findings The results revealed that, under the background of 26 °C during the day and 16 °C during night: 1) the effect of ETs on soybean yields showed no significant function that mainly benefit from the increase in the amount of biomass to ease negative influence of decrease in the harvest index. ETa reduced yields of soybean by 38.9% (p < 0.05) due to both significant decrease in harvest index and yield components (pod number per plant, grain number per pod and 100-grain weight). 2) ETs showed no obvious effect on the whole growing stage evapotranspiration (ET) of soybean, while ETa reduced the whole growing stage ET by 14.8% (p < 0.05). 3) The effect of the two warming pattern on water consumption of soybean were not significant. The difference in water consumption was mainly derived from the difference in transpiration (T). ETs and ETa reduced total transpiration by 10.7% (p < 0.05) and 26.1% (p < 0.05), respectively. In conclusion, our results suggest that ETs will underestimate the detrimental effects of real climate warming (ETa) on the growth and yield of soybean, and overestimate the effects on water consumption of soybean.     

The number of chlorophyll-less spots and the primary leaf area as criteria of radiation damage in soybean (Glycine max merill)

The number of chlorophyll-less spots occurring on the primary leaves as well as the primary leaf size were investigated in two soybean cultivars, differing genetically in radiosensitivity, after irradiation of seed with ⁶⁰Co γ-rays. A high correlation was found between increasing number of spots, decreasing leaf size and seedling growth inhibition.The number of spots can be used to monitor radiation effects over the small dose range where the growth inhibition is not pronounced. Primary leaf size can be used as a convenient criterion of seedling growth inhibition. Possible causes of leaf spotting are discussed.     

Role of radioadaptation on radiation-induced thymic lymphoma in mice

Thymic lymphoma (TL) was observed in different stages of development in 46% of male mice (23/50) following exposure to an acute challenge dose of 2 Gy ⁶⁰Co γ-rays. With an adapting dose of 1 cGy 24 h prior to the challenge dose of 2 Gy, similar growth of TL was seen in 42.5% of mice (17/40). TL was not found in unirradiated control mice (0/50) or in the group treated with 1 cGy (0/50). Multiple adapting doses for 5 or 10 consecutive days induced TL in 8/50 and 9/50 mice, respectively (17% in average). When multiple adapting doses were followed by the challenge dose, the yield of TL was much lower, 16% (8/50) and 30% (15/30), respectively. By 15, 30, 60, 90, and 120 days after exposure with 3 Gy of ⁶⁰Co γ-rays, TL developed in 30, 70, 70, 80 and 85% of the female mice, respectively. When mice were conditioned with an adapting dose of 1 cGy 24 h prior to the challenge dose, TL was not found 15 days post-irradiation, while about a 25% reduction in the occurrence of TL was noticed at all other intervals. The results suggested that an adapting dose could play a role in bringing about a change in terms of delay and inhibition of the acute effects of radiation, i.e., the onset of TL in mice.     

Somatic Crossing over in GLYCINE MAX (L.) Merrill: Mutagenicity of Sodium Azide and Lack of Synergistic Effect with Caffeine and Mitomycin C

Glycine max (soybean) is one angiosperm which lends itself to the study of somatic crossing over. This is made possible because some varieties have gene combinations Y(11)Y(11), Y(11)y(11) and y(11)y(11) in the segregating populations from Y(11)y(11) plants. The gene in question is responsible for chlorophyll synthesis. The Y(11)Y(11) plants have dark green leaves, Y(11)y(11) are light green and y(11)y(11) plants are golden yellow. The heterozygous plants have dark green, yellow and dark green-yellow (double) spots on the leaves of the untreated control material, whereas the two homozygotes are almost always devoid of somatic sectoring. Application of caffeine, or mitomycin C, to the seeds increased the frequency of double, dark green and yellow spots on the Y(11)y(11) background. Possibly, some dark green or yellow spots originate by failure of one of the two components of what might start as a double spot due to somatic crossing over. The application of NaN(3) increases the frequency of dark green or yellow spots, almost exclusively. The two spots increase in equal frequency. The y(11)y(11) plants so treated do not have any light green sectors, but dark green, Y(11)Y(11), plants do develop a few light green or very dark green spots. The data indicate that NaN(3) is capable of inducing nondisjunction, but does not cause mutations (at this locus), chromosome fragmentations (segmental losses) or somatic crossing over to an appreciable degree. It has previously been shown that caffeine-induced chromosome rejoining in Vicia faba can be inhibited by treating the roots with NaN(3). In the present experiments NaN(3) did not affect the processes of somatic crossing over as induced by caffeine or mitomycin C. The effect was additive. This system offers advantages for studying chemical mutagens in that somatic crossing over, point mutations, segmental losses through chromosome breakage and nondisjunction can all be studied in a single treatment to the seeds.     

The action of the tumour promoter, TPA, on mutagenesis induced by different agents (UV light, chemical and viral mutagens)

The present paper deals with effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the frequency of induced mutations to 6-mercaptopurine (6MP) and ouabain resistance in Chinese hamster and mouse cells. UV light, bovine adenovirus 3(BAV-3) and 5-bromodeoxyuridine (BrdU) were used as mutagens. TPA was shown to raise the frequency of gene mutations induced by UV light and BAV-3 but it did not enhance the mutagenic effect of BrdU. We also examined the ability of BAV-3 and BrdU to induce tumours in mice. BrdU was shown to have no carcinogenic effect. The results suggest that TPA enhances the mutagenic effect only for carcinogenic mutagens.     

Induction of chromosome aberrations by Sr β-particles in cultured human lymphocytes

Human blood was irradiated with β-particles from an external source of ⁹⁰Sr. The source was a rolled piece of silver foil, active dimensions: 100 × 12.5 mm, incorporating 3.7 × 10⁸ Bq (10 mCi) of ⁹⁰Sr/⁹⁰Y. After culturing for 48 h, the dicentric yield in the lymphocytes at the first metaphase was measured as a function of the dose in the blood. The aberration yield fitted the linear-quadratic function well, which is consistent with the single-track and two-track model for aberration formation at low LET radiation. The curve for ⁹⁰Sr β-rays was compared with a curve for ⁶⁰Co γ-rays. The main difference between the coefficients was in the values. With respect to ⁶⁰Co γ-rays, the RBE calculated from the dose-effect relationships for dicentric production was 2.8 at the dose of 0.14 Gy; it decreased with increasing doses. The distribution of dicentrics was consistent with the Poisson distribution but showed a tendency to over-dispersion in the region of higher doses. A reason for these discrepancies is discussed.     

Frequency of gamma-Ray Induced Specific Locus and Recessive Lethal Mutations in Mature Germ Cells of the Zebrafish, BRACHYDANIO RERIO

Specific locus and recessive lethal mutations are induced by γ-rays with approximately first order kinetics in the zebrafish (Brachydanio rerio) with frequencies of 4 x 10^-5 r^-1 and 4 x 10^-3 r^-1, respectively. The surprisingly low ratio (100:1) of recessive lethals to specific locus mutations may be due to the induction of large deficiencies by γ-rays.     

Caffeine decreases vitamin D receptor protein expression and 1,25(OH)2D3 stimulated alkaline phosphatase activity in human osteoblast cells

Of the various risk factors contributing to osteoporosis, dietary/lifestyle factors are important. In a clinical study we reported that women with caffeine intakes >300 mg/day had higher bone loss and women with vitamin D receptor (VDR) variant, tt were at a greater risk for this deleterious effect of caffeine. However, the mechanism of how caffeine effects bone metabolism is not clear. 1,25-Dihydroxy vitamin D₃ (1,25(OH)₂D₃) plays a critical role in regulating bone metabolism. The receptor for 1,25(OH)₂D₃, VDR has been demonstrated in osteoblast cells and it belongs to the superfamily of nuclear hormone receptors. To understand the molecular mechanism of the role of caffeine in relation to bone, we tested the effect of caffeine on VDR expression and 1,25(OH)₂D₃ mediated actions in bone. We therefore examined the effect of different doses of caffeine (0.2, 0.5, 1.0 and 10 mM) on 1,25(OH)₂D₃ induced VDR protein expression in human osteoblast cells. We also tested the effect of different doses of caffeine on 1,25(OH)₂D₃ induced alkaline phosphatase (ALP) activity, a widely used marker of osteoblastic activity. Caffeine dose dependently decreased the 1,25(OH)₂D₃ induced VDR expression and at concentrations of 1 and 10 mM, VDR expression was decreased by about 50–70%, respectively. In addition, the 1,25(OH)₂D₃ induced alkaline phosphatase activity was also reduced at similar doses thus affecting the osteoblastic function. The basal ALP activity was not affected with increasing doses of caffeine. Overall, our results suggest that caffeine affects 1,25(OH)₂D₃ stimulated VDR protein expression and 1,25(OH)₂D₃ mediated actions in human osteoblast cells.     

Oxysterol activation of arachidonic acid release and prostaglandin E2 biosynthesis in NRK 49F cells is partially dependent on protein kinase C activity [corrected]

We previously demonstrated that the oxysterol potentiation of arachidonic acid release and prostaglandin biosynthesis induced by foetal calf serum activation of normal rat kidney (NRK) cells (fibroblastic clone 49F) was not related to a direct effect of oxysterols on cell free Ca²⁺ level. Since both Ca²⁺ variations and protein C are involved in arachidonic acid release in some models, we looked for a possible modulation by protein C in the oxysterol effect on arachidonic acid release. We show that when the phorbol ester 12-O-tetradecanoyl-phorbol-13acetate (TPA), a protein kinase C activator, was added to the culture medium, the oxyterol effect on arachidonic acid release and prostaglandin synthesis clearly increased. Moreover, the effect of TPA was dose-dependent and TPA EC₅₀ (4 × 10⁻⁹ M) was unchanged in the presence of the oxysterol. Preincubation of cells with TPA for 24 h prevented the arachidonic acid release induced by TPA alone, whereas the oxysterol effect was decreased but not abolished. In the absence of serum, TPA and ionomycin added together induced the same noticeable (arachidonic acid) release and PGE₂ synthesis as serum alone. Nevertheless, the potentiating effect of cholest-5-ene-3β,25-diol was much higher when serum itself was used to activate NRK cells than it was in the present serum-mimicking experimental conditions. Thus, the presence of growth factors is probably required to obtain a full oxysterol effect. We conclude that the oxysterol effect was synergistic with, but not fully dependent on, protein kinase C and Ca²⁺ ion fluxes, therefore oxysterols could affed earlier events triggered by serum growth factor binding to their cell membrane receptors.     

Somatic Crossing over in GLYCINE MAX (L.) Merrill: Effect of Some Inhibitors of DNA Synthesis on the Induction of Somatic Crossing over and Point Mutations

Glycine max (soybean) is the only known higher plant with a definitely established occurrence of somatic crossing over. This material lends itself to the analysis of somatic crossing over, gross chromosomal aberrations and mutations, all of which may be induced by the same treatment of the mutagen given to seeds. This is made possible because gene Y₁₁ for chlorophyll development in the variety L65-1237 is incompletely dominant over its allele y₁₁, so that twin or double spots composed of a dark green (Y₁₁Y₁₁) and a yellow (y₁₁y₁₁) component can be observed adjacent to and as mirror images of each other on the light green Y₁₁y₁₁ leaves in the areas of complementary exchange for these genes. Lack of growth of either component of this double spot as well as several types of chromosomal disturbances give rise to single spots resembling phenotypes of y₁₁y₁₁ or Y₁₁Y₁₁ leaves. Point mutations can be studied by looking for green sectors originating from Y₁₁y₁₁ genotype on the y₁₁y₁₁ plants. Seeds obtained from heterozygous plants were treated with caffeine, cytosine arabinoside, actinomycin D and 5-fluoro-deoxyuridine, all known inhibitors of DNA synthesis, and puromycin, an inhibitor of synthesis of proteins. The treatments with caffeine and actinomycin D increased the frequency of somatic crossing over as measured by the frequency of double spots on Y₁₁y₁₁ leaves, but cytosine arabinoside, 5-fluorodeoxyuridine and puromycin did not. Thus somatic crossing over was induced only by those chemicals which are known to allow rejoining of chromosomes, thereby suggesting a correlation between the two phenomena. These observations indicate that it is not the mere inhibition of DNA synthesis, but some rather more specific event in DNA repair which is responsible for complementary exchanges. Some of these results differ from studies carried out with fungi. The main effect of all chemicals tested, except caffeine and actinomycin D, was inferred to be the production of deletions in Y₁₁y₁₁ plants which raised the frequency of single (dark green or yellow) spots relative to the doubles. Caffeine was the only chemical which constantly increased the frequency of specific point mutations. In the control material, the great majority of spots are found on the upper surface of the leaf. This picture could not be changed in any of the treated materials, thus indicating uniform resistance of spongy mesophyll tissue to the mutagens applied.     

优化子叶节转化法培育大豆MtDREB2A转基因植株

将正交因素试验与GUS基因组织化学染色等技术相结合, 优化大豆(Glycine max)品种东农50遗传转化体系, 导入抗旱关键基因MtDREB2A。结果表明, 大豆种子表面消毒, NaClO溶液法与Cl₂气熏蒸法的去污染率分别达到98.67%和93.33%。子叶节法转GUS基因组织化学染色率(68.33%)显著高于下胚轴法(14.00%)和胚尖法(0.67%) (P<0.05)。种子萌发5天, 农杆菌(Agrobacterium tumefaciens)培养温度25°C, OD₆₀₀=0.9, 共培养5天的转GUS基因子叶节最高达72.00%; 恢复培养5天, 草丁膦(3 mg·L^-1)、头孢噻肟钠(200 mg·L^-1)和羧苄青霉素(300 mg·L^-1)筛选诱导分化的转GUS基因不定芽最多为3.33%; 优化的大豆遗传转化体系转化效率为1.11%。转MtDREB2A基因大豆东农50植株根系更加密集, 主根长度和侧根数量均显著高于对照(P<0.05), 证实MtDREB2A基因具有促进大豆根系生长的作用, 为利用该基因进行大豆抗旱育种奠定了坚实的基础并提供了理论依据。     

Pro-oxidative effect of beta-carotene and the interaction with flavonoids on UVA-induced DNA strand breaks in mouse fibroblast C3H10T1/2 cells

It has been suggested that β-carotene itself is unstable under certain conditions and that a combination of antioxidants may prevent the pro-oxidative effects of β-carotene. Thus, the present study aimed to investigate the interaction of β-carotene with three flavonoids—naringin, rutin and quercetin—on DNA damage induced by ultraviolet A (UVA) in C3H10T1/2 cells, a mouse embryo fibroblast. The cells were preincubated with β-carotene and/or flavonoid for 1 h followed by UVA irradiation, and DNA damage was measured using comet assay. We showed that β-carotene at 20 μM enhanced DNA damage (by 35%; P<.05) induced by UVA (7.6 kJ/m²), whereas naringin, rutin and quercetin significantly decreased UVA-induced DNA damage. When each flavonoid was combined with β-carotene during preincubation, UVA-induced cellular DNA damage was significantly suppressed and the effects were in the order of naringin≥rutin>quercetin. The flavonoids decreased UVA-induced oxidation of preincorporated β-carotene in the same order. Using electron spin resonance spectroscopy, we showed that the ability of these flavonoids to quench singlet oxygen was consistent with protection against DNA damage and β-carotene oxidation. All three flavonoids had some absorption at the UVA range (320–380 nm), but the effects were opposite to those on DNA damage and β-carotene oxidation. Taken together, this cell culture study demonstrates an interaction between flavonoids and β-carotene in UVA-induced DNA damage, and the results suggest that a combination of β-carotene with naringin, rutin or quercetin may increase the safety of β-carotene.