Anticarcinogenic activity of blue fluorescent hexagonal boron nitride quantum dots: as an effective enhancer for DNA cleavage activity of anticancer drug doxorubicin

Blue fluorescent hexagonal boron nitride quantum dots (h-BNQDs) of ∼10 nm size as an effective enhancer for DNA cleavage activity of anticancer drug doxorubicin (DOX) were synthesized using simple one-step hydrothermal disintegration of exfoliated hexagonal boron nitride at very low temperature ∼ 120 °C. Boron nitride quantum dots (BNQDs) at a concentration of 25 μg/ml enhanced DNA cleavage activity of DOX up to 70% as checked by converting supercoiled fragment into nicked circular PBR322 DNA. The interaction of BNQDs with DOX is proportional to the concentration of BNQDs, with binding constant K b ∼0.07338 μg/ml. In addition, ab initio theoretical results indicate that DOX is absorbed on BNQDs at the N-terminated edge with binding energy -1.075 eV and prevented the normal replication mechanisms in DNA. BNQDs have been shown to kill the breast cancer cell MCF-7 extensively as compared with the normal human keratinocyte cell HaCaT. The cytotoxicity of BNQDs may be correlated with reduced reactive oxygen species level and increased apoptosis in MCF-7 cells, which may be liable to enhance the anticancerous activity of DOX. The results provide a base to develop BNQD-DOX as a more effective anticancer drug.

Comparison of tRNA activity under homologous and heterologous conditions during the reproductive cycle of Heteropneustes fossilis

Rate of protein synthesis in ovary is analyzed throughout the annual reproductive cycle of H. fossilis. It is highest during previtellogenic phase and lowest during post spawning phase. The variation pattern matches with aminoacylation capacity of tRNA. The aminoacylation capacity of tRNA is compared in the two phases under homologous and heterologous conditions. Both tRNA and aRS are obtained from the same phase under homologous conditions and from different phases under heterologous conditions. Aminoacylation capacity is also compared in ovary and liver under homologous and heterologous conditions. Both tRNA and aRS show higher activity in previtellogenic phase. However, tRNA contributes more for higher aminoacylation activity. Transfer RNA fractionates into similar isoacceptors during the two phases. This indicates that the primary structure of tRNA may not change during the reproductive cycle. Therefore, it is suggested that the difference in aminoacylation activity may be due to post-transcriptional modifications of tRNA leading to conformational changes. Gm modification and 2-O' methylation of tRNA are reported earlier to vary during the reproductive cycle [2]. The results support the earlier suggestion of conformational changes in tRNA in 'active' and 'inactive' forms in previtellogenic and post spawning phases respectively. Aminoacylation capacity of tRNA shows organ specificity. It is high in ovary than in liver. Poor aminoacylation capacity is shown under heterologous conditions. This may be due to incompatible aRS related to specific amino acid pool in the tissue, or post transcriptional changes in tRNA, which may not allow cross acylation with full efficiency.

Comparison of tRNA conformation during different phases of reproduction

The present study is a comparison of tRNA conformation from ovary of Heteropneustes fossilis in its active phase of reproduction (when it is highly engaged in protein synthesis i.e. previtellogenic phase) with inactive phase (when tRNA is mainly stored in mature ovary i.e. spawning phase). Transfer RNA of active phase is shown to be compact, flexible and susceptible towards nuclease. Compact tRNA structure is evidenced by higher hyperchromicity and presence of relatively less Gm modifications thereby allowing adequate hydrogen bonding between D loop and T loop. Higher sensitivity of tRNA towards Mg++ reflects its higher flexibility towards internal environment. This structure of tRNA may be required for active protein synthesis. On the other hand tRNA of inactive phase is shown to be relaxed but resistant towards nuclease which may be favoured for storage in mature ova of a teleost as maternal carry over.

Analysis of transfer RNA during the early embryogenesis of the freshwater teleost, Heteropneustes fossilis

Total RNA as well as transfer RNA were quantified from mature ova apart from four different embryonic stages namely mid-cleavage, early gastrula, mid-gastrula and organogenesis of the freshwater teleost Heteropneustes fossilis. Total RNA as well as transfer RNA quantity follow a similar variation pattern, being maximum during mid-gastrulation. When analysed by total amino acid acceptance capacity, transfer RNA shows its maximum activity during mid-gastrulation. This coincides with the higher ratio of tRNA to total RNA at this stage. The relative aminoacylation capacity for Ser, Gly, Asn and Thr are found to be higher (9-34%) compared to that for other amino acids. Total tRNA, resolved into three peaks upon HPLC fractionation, shows a high cumulative peak area during mid-gastrulation and organogenesis. These results indicate a switch over of maternal to embryonic translation machinery during gastrulation.

Transfer RNA analysis during the reproductive cycle of a freshwater teleost, H. fossilis

Transfer RNA was analyzed qualitatively as well as quantitatively from ovaries of the fresh water teleost Heteropneustes fossilis for twelve months. The tRNA samples were found to be pure and devoid of any high molecular weight RNA or DNA contaminations. The quantity of tRNA as well as its biological activity, assayed by in vitro aminoacylation using homologous aminoacyl tRNA synthetases, were found to be higher during resting and preparatory (pre-vitellogenic) phases, i.e. from November to March, as compared to vitellogenic and spawning phases of the fish, i.e. from April to October. The highest tRNA pool and its activity was found in the month of February, which coincides with the early preparatory phase. The results indicate that the accumulation of active tRNA starts in the resting phase. Such an accumulation of tRNA may be a part of the enrichment of mature eggs with complete translational machinery before ovulation in order to cope with the high rate of protein synthesis after fertilization.

A comparison of tRNA populations of rat liver and skeletal muscle during aging

Total tRNA extracted from liver as well as from skeletal muscle of young, adult and old female albino rats showed quantitative variation with age. The amount of liver total tRNA was maximum in adult rats when compared to that in young and old ones, whose levels were almost the same. Transfer RNA from skeletal muscle showed a different pattern with age. It was maximum in young rats and showed a gradual decline with age. Transfer RNAs were aminoacylated using homologous synthetase preparations to study their qualitative variation during aging, which followed the trend of quantitative variation in both the tissues. Arginyl and glutamyl-tRNAs were fractionated from both the tissues at the three ages. Isoacceptor profile of glutamyl-tRNAs showed neither tissue specificity nor age-related change, whereas a definite change was found in the case of arginyl-tRNA isoacceptors in the two tissues during aging.

Aminoacylation of rat liver transfer RNA with homologous and heterologous enzyme systems during aging

Total tRNA extracted from livers of young (7 +/- 1 weeks), adult (40 +/- 1 weeks) and old (80 +/- 1 weeks) rats showed quantitative variation with age, being maximal in adults. Young and old animals yielded almost the same level of tRNAs. Quantitative changes in tRNAs were also observed from the study of amino acid acceptor activity using homologous enzyme i.e., aminoacyl-tRNA synthetase preparations from rat liver of the same age group. Quantitative variation followed the trend of qualitative variation. When tRNA was amino-acylated with a heterologous enzyme system, i.e., synthetase preparation from rat liver of another age group, age-related variation in aminoacyl-tRNA did not follow a pattern similar to that in the case of the homologous enzyme system. Young and adult synthetase enzymes showed maximum affinity for their homologous tRNAs but synthetases from old rat liver did not show any specific affinity for "old" tRNAs. This shows that apart from tRNAs, enzyme activity also changes with age.