Sravendra Rana

Cycloaddition Reactions: A Controlled Approach for Carbon Nanotube Functionalization

Controlled functionalization of carbon nanotubes (CNTs) through the use of cycloaddition reactions is described. By employing various cycloaddition reactions, a wide range of molecules could be coupled onto CNTs without disruption of the structural integrity as well as with a statistical distribution of functional groups onto the surface of the CNTs. The cycloaddition reactions represent an effective and tailored approach for preparing CNT-based advanced hybrid materials that would be useful for a wide range of applications from nanobiotechnology to nanoelectronics.

Induction of DNA-protein cross-links by Hippophae rhamnoides: Implications in radioprotection and cytotoxicity

Recently Hippophae rhamnoides has been reported to render chromatin compaction and significantly inhibit radiation induced DNA strand breaks. To investigate the mechanism of action of RH-3, a preparation of Hippophae rhamnoides, in this connection, present study was undertaken. Chromatin compaction induced by RH-3 (100 μg/ml or more) was maximum at alkaline pH but was completely negated by acidic pH (< 6) or presence of free radical scavengers like glycerol, DMSO etc. In a concentration dependent manner, RH-3 inhibited the intercalation of ethidium ions from Et Br into calf thymus DNA and also increased the precipitation of DNA-protein cross-links (DPC) in thymocytes. Chromatin compaction caused by RH-3 treatment did not permit the separation of proteins from DNA even after treatment with 2 M NaCl solution. SDS-PAGE profiles also revealed that RH-3 in a dose dependent manner compacted the chromatin organization, induced DPC and inhibited the extraction of both histone and non-histone matrix proteins from chromatin maximally at 80 μg/ml. More than 80 μg/ml of RH-3, though extracted low molecular weight histones but did not separate non-histone proteins. The RH-3 mediated DPCs were resistant even to 1% SDS, 4 M NaCl and 3.8 M hydroxyl amine hydrochloride but were prone to both urea (8 M) and guanidine hydrochloride (6 M) indicating covalent bonding between DNA and proteins (serine/threonine). RH-3 in a concentration dependent manner induced superoxide anions and the phenomenon was dependent upon nature of medium, presence of metal ions and pH. RH-3 at concentrations up to 100 μg/ml in presence of 50 μM copper sulfate inflicted significant damage to extraneously added 2-deoxyribose molecules and maximum TBARS were formed at a concentration of 100 μg/ml. Higher concentrations of RH-3 more than 100 μg/ml quenched free radicals and inhibited 2-deoxyribose degradation. RH-3 also induced strand breaks in plasmid DNA at concentrations lower than 100 μg/ml but completely inhibited at concentrations higher than 250 μg/ml, indicating bimodal function. Strand breaks induced by lower concentrations of RH-3 (up to 100 μg/ml) were inhibited by antioxidants like GSH, DFR etc. RH-3, in a concentration dependent mode also inhibited the relaxation of supercoiled plasmid DNA (PBR322) by topoisomerase I.Present study indicated that RH-3 caused compaction of reversible (< 100 μg/ml) and irreversible (> 100 μg/ml) nature which was related to the magnitude of DNA-protein cross-links formed. Maintenance of chromatin organization, induction of hypoxia, hydrogen atom donation, free radical scavenging and blocking of cell cycle at G2-M phase by interfering with topoisomerase I activity seem to contribute towards the radioprotective efficacy of RH-3.

Enhancement of radiation-induced apoptosis by Podophyllum hexandrum

The aqueous extract of Podophyllum hexandrum (RP‐1), which has been recently reported to manifest radioprotective and anti‐tumour properties, has been investigated for its mode of action. RP‐1, under in‐vitro conditions dose‐dependently chelated metal ions, inhibited radiation or metal ion‐induced hydroxyl radicals and lipid peroxidation and scavenged superoxide anions. Intraperitoneal administration of RP‐1 to mice pre‐irradiation (10 Gy) induced more DNA fragmentation and lipid peroxidation in thymocytes maximally at 4 and 8 h, respectively, in comparison with RP‐1 treatment or irradiation. Flow‐cytometric quantification of sub‐diploid peak, oligonucleosomal cleavage assay (ladder) and depletion of total thiols also corroborated the ability of RP‐1 to enhance radiation‐induced apoptosis. RP‐1 in presence of 100 μM CuSO4 induced strand breaks in plasmid DNA and addition of metal chelators (EDTA and deferoxamine) inhibited the strand scission. Treatment with a major constituent of RP‐1, podophyllin, did not cause strand breaks, but isolated constituents of RP‐1, quercetin or podophyllotoxin, induced strand breaks. Depending on its concentration in the milieu, RP‐1 acted as a pro‐ or antioxidant modifying the radiation‐induced apoptosis and therefore could be exploited for cancer management.