Hatzi Vasiliki I, Karakosta Maria, Barszczewska Katarzyna, Karachristou Ioanna, Pantelias Gabriel, Terzoudi Georgia I
Laboratory of Health Physics, Radiobiology & Cytogenetics, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, NCSR "Demokritos", Athens, Greece.
Laboratory of Health Physics, Radiobiology & Cytogenetics, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, NCSR "Demokritos", Athens, Greece.
Mutat Res Genet Toxicol Environ Mutagen. 2015 Nov;793:71-8. doi: 10.1016/j.mrgentox.2015.08.002. Epub 2015 Aug 5.
The dual role of caffeine as a chromosomal damage inducer and G2/M-checkpoint abrogator is well known but it is observed mainly at relatively high concentrations. At low concentrations, caffeine enhances the cytogenetic effects of several carcinogens and its intake during pregnancy has been recently reported to cause adverse birth outcomes. Interestingly, a threshold below which this association is not apparent was not identified. Since chromosomal abnormalities and aneuploidy are the major genetic etiologies of spontaneous abortions and adverse birth outcomes, we re-evaluate here the effects of caffeine at the cytogenetic level and propose a model for the mechanisms involved. Our hypothesis is that low caffeine concentrations affect DNA replication and cause chromosomal aberrations and asymmetric cell divisions not easily detected at metaphase since damaged cells are delayed during their G2/M-phase transition and the low caffeine concentrations cannot abrogate the G2-checkpoint. To test this hypothesis, caffeine-induced chromatid breaks and micronuclei in peripheral blood lymphocytes (PBLs) were evaluated in vitro after low caffeine concentration exposures, followed by a short treatment with 4mM of caffeine to abrogate the G2-checkpoint. The results show a statistically significant increase in chromatid breaks at caffeine concentrations ≥1mM. When caffeine was applied for G2/M-checkpoint abrogation, a statistically significant increase in chromatid breaks, compared to an active checkpoint, was only observed at 4mM of caffeine. The potential of low concentrations to induce asymmetric cell divisions was tested by applying a methodology combining the cytochalasin-B mediated cytokinesis-block micronucleus assay (CBMN) with interphase FISH (iFISH), using selected centromeric probes. Interestingly, low caffeine concentrations induce a dose dependent aneuploidy through asymmetric cell divisions, which are caused by misalignment of chromosomes through a mechanism unrelated to the formation of chromatid breaks. The cytogenetic approach used, combining CBMN with iFISH, is proposed as a valuable tool to test chemically induced asymmetric cell divisions.
咖啡因作为染色体损伤诱导剂和G2/M检查点消除剂的双重作用是众所周知的，但主要是在相对较高的浓度下观察到的。在低浓度时，咖啡因会增强几种致癌物的细胞遗传学效应，最近有报道称孕期摄入咖啡因会导致不良出生结局。有趣的是，尚未确定这种关联不明显的阈值。由于染色体异常和非整倍体是自然流产和不良出生结局的主要遗传病因，我们在此重新评估咖啡因在细胞遗传学水平上的作用，并提出所涉及机制的模型。我们的假设是，低浓度咖啡因会影响DNA复制并导致染色体畸变和不对称细胞分裂，由于受损细胞在G2/M期转换过程中延迟，且低浓度咖啡因无法消除G2检查点，因此在中期不易检测到。为了验证这一假设，在低浓度咖啡因暴露后，体外评估外周血淋巴细胞（PBL）中咖啡因诱导的染色单体断裂和微核，随后用4mM咖啡因进行短期处理以消除G2检查点。结果显示，咖啡因浓度≥1mM时，染色单体断裂有统计学意义的增加。当应用咖啡因消除G2/M检查点时，与活跃检查点相比，仅在4mM咖啡因时观察到染色单体断裂有统计学意义的增加。通过应用一种将细胞松弛素B介导的胞质分裂阻滞微核试验（CBMN）与间期荧光原位杂交（iFISH）相结合的方法，使用选定的着丝粒探针，测试了低浓度咖啡因诱导不对称细胞分裂的可能性。有趣的是，低浓度咖啡因通过不对称细胞分裂诱导剂量依赖性非整倍体，这种不对称细胞分裂是由染色体错位引起的，其机制与染色单体断裂的形成无关。所采用的将CBMN与iFISH相结合的细胞遗传学方法被认为是测试化学诱导的不对称细胞分裂的有价值工具。
