Programmable site-selective labeling of oligonucleotides based on carbene catalysis

Site-selective modification of oligonucleotides serves as an indispensable tool in many fields of research including research of fundamental biological processes, biotechnology, and nanotechnology. Here we report chemo- and regioselective modification of oligonucleotides based on rhodium(I)-carbene catalysis in a programmable fashion. Extensive screening identifies a rhodium(I)-catalyst that displays robust chemoselectivity toward base-unpaired guanosines in single and double-strand oligonucleotides with structurally complex secondary structures. Moreover, high regioselectivity among multiple guanosines in a substrate is achieved by introducing guanosine-bulge loops in a duplex. This approach allows the introduction of multiple unique functional handles in an iterative fashion, the utility of which is exemplified in DNA-protein cross-linking in cell lysates.

Effect of thiram on rat kidney: inhibition of brush border membrane and antioxidant enzymes, diminution of antioxidant capacity, enhanced DNA damage and DNA-protein cross-linking

Thiram is a dithiocarbamate pesticide that is widely used as a fungicide to protect crops and seeds, especially in China and India. Although thiram is considered relatively safe for humans but due to its persistent nature it may become a health hazard for human beings and animal if long term exposure takes place. The aim of the present work was to study the effects of oral administration of thiram on kidney of male rats given different doses of thiram (100, 250, 500, 750 mg/kg body weight) for 4 consecutive days. This treatment significantly reduced cellular glutathione and total sulfhydryl content but enhanced protein carbonyl and hydrogen peroxide levels. The plasma creatinine and BUN levels were also elevated indicating nephrotoxicity. The activities of antioxidant enzymes catalase, superoxide dismutase, glutathione peroxidase, thioredoxin reductase and glutathione-S-transferase were significantly decreased. The antioxidant capacity was diminished resulting in less free radical quenching and metal reducing ability of kidney. Administration of thiram also led to inhibition of intestinal brush border membrane enzymes: alkaline phosphatase, leucine aminopeptidase, γ-glutamyl transferase and maltase. Activities of enzymes of glucose metabolism viz. glycolysis, citric acid cycle, pentose phosphate pathway and gluconeogenesis were also inhibited. Histopathology of kidney tissue revealed tubular dilation, tubular cast, breaking of apical cytoplasm and intestinal hemorrhage. A significant increase in DNA fragmentation, DNA strand breaks and DNA-protein cross-linking was also observed in thiram treated rats compare to control group. These changes in kidney could be due to marked perturbation in antioxidant defense system induced by free radicals generated upon exposure to thiram.