Antiproliferative Effects of Crocin in HepG2 Cells by Telomerase Inhibition and hTERT Down-Regulation Crocin;telomerase;hTERT;hepatocarcinoma; Crocin, the main pigment of Crocus sativus L., has been shown to have antiproliferative effects on cancer cells, but the involved mechanisms are only poor understood. This study focused on probable effect of crocin on the immortality of hepatic cancer cells. Cytotoxicity of crocin ($IC_{50}$ 3 mg/ml) in hepatocarcinoma HepG2 cells was determined after 48 h by neutral red uptake assay and MTT test. Immortality was investigated through quantification of relative telomerase activity with a quantitative real-time PCR-based telomerase repeat amplification protocol (qTRAP). Telomerase activity in 0.5 ${\mu}g$ protein extract of HepG2 cells treated with 3 mg/ml crocin was reduced to about 51% as compared to untreated control cells. Two mechanisms of inhibition, i.e. interaction of crocin with telomeric quadruplex sequences and down regulation of hTERT expression, were examined using FRET analysis to measure melting temperature of a synthetic telomeric oligonucleotide in the presence of crocin and quantitative real-time RT-PCR, respectively. No significant changes were observed in the $T_m$ telomeric oligonucleotides, while the relative expression level of the catalytic subunit of telomerase (hTERT) gene showed a 60% decrease as compared to untreated control cells. In conclusion, telomerase activity of HepG2 cells decreases after treatment with crocin, which is probably caused by down-regulation of the expression of the catalytic subunit of the enzyme.

AIM: To investigate the potential effects of chelidonine, the main alkaloid of Chelidonium majus, on telomerase activity and its regulation in HepG2 cells.

This report focuses on the application of zinc oxide nanoparticles (ZnO NPs) carrying phycomolecule ligands as a novel plant growth promoter aimed at increasing the crop productivity of purslane (Portulaca oleracea L.). Experiments were performed under controlled greenhouse conditions using a completely randomized design with nine replications. Purslane seeds were treated with four concentrations of ZnO NPs (0, 10, 100, and 500 mg L−1) and four concentrations of bulk ZnO (0, 10, 100, and 500 mg L−1). The ultrastructural characteristics of the leaves of the plants treated with of 500 mg L−1 ZnO NPs were determined using transmission electron microscopy (TEM). The results indicated that the treatment with ZnO NPs increased the content of chlorophyll a and chlorophyll b, carotenoids, and total phenolic and flavonoid compounds significantly more than the treatment with bulk ZnO. Our findings also showed that the application of high concentrations of ZnO NPs is the most effective strategy to considerably induce the antioxidant capacity and enzymes of purslane plants. Furthermore, the seed germination percentage and sprout growth rates were significantly higher in the plants treated with 500 mg L−1 of ZnO NPs (100% ±0.00), compared to the control plants (93.33% ±1.66). The TEM images revealed the concentration of ZnO NPs and cell membrane rupture, as well as a deformation in the shape of chloroplasts and a decrease in their number in the plants treated with 500 mg L−1 ZnO NPs, compared to the control plants. Owing to their toxicity, high concentrations of ZnO NPs lead to oxidative stress in plants. Thus, our findings provide a new alternative strategy for increasing crop productivity, i.e., the application of ZnO NPs as a novel plant growth booster, in comparison with the bulk ZnO treatment.

Cancer cells are often immortal through up-regulation of the hTERT gene, which encodes the catalytic subunit of a special reverse transcriptase to overcome end-replication problem of chromosomes. This study demonstrates that papaverine, an isoquinoline alkaloid from the Papaveraceae, can overcome telomerase dependent immortality of HepG-2 cells that was used as a model of hepatocarcinoma. Although this alkaloid does not directly interact with telomeric sequences, papaverine inhibits telomerase through down-regulation of hTERT, which was analysed using thermal FRET and qRT-PCR, respectively. The IC₅₀ values for the reduction of both telomerase activity and hTERT expression was 60 µM, while IC₅₀ for cytotoxicity was 120 µM. Repeated treatments of the cells with very low non-toxic concentrations of papaverine resulted in growth arrest and strong reduction of population doublings after 40 days. This treatment induced senescent morphology in HepG-2 cells, which was evaluated by beta-galactosidase staining. Altogether, papaverine can be regarded as a promising model compound for drug design targeting cancer development.