Synthesis, pulse radiolysis, and in vitro radioprotection studies of melatoninolipoamide, a novel conjugate of melatonin and alpha-lipoic acid.

A novel conjugate of melatonin 2 and alpha-lipoic acid 4 has been prepared using DCC mediated coupling. The conjugate named melatoninolipoamide has been assigned its structure 1 on the basis of spectral analysis (UV, IR, NMR, and EI-MS). Pulse radiolysis studies of the conjugate were carried out in aqueous solutions with both oxidizing and reducing radicals. The results indicate that the melatonin moiety of the conjugate reacts preferably with oxidizing radicals and the lipoic acid moiety exhibits preferential reaction with reducing radicals. The in vitro radioprotection ability of 1 was examined by gamma-radiation induced lipid peroxidation in liposomes and hemolysis of erythrocytes, and compared the results with those of melatonin and alpha-lipoic acid. The studies suggest that the conjugate can be explored as a probable radioprotector.

Antioxidant properties of Asparagus racemosus against damage induced by gamma-radiation in rat liver mitochondria.

The possible antioxidant effects of crude extract and a purified aqueous fraction of Asparagus racemosus against membrane damage induced by the free radicals generated during gamma-radiation were examined in rat liver mitochondria. gamma-Radiation, in the dose range of 75-900 Gy, induced lipid peroxidation as assessed by the formation of thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxides (LOOH). Using an effective dose of 450 Gy, antioxidant effects of A. racemosus extract were studied against oxidative damage in terms of protection against lipid peroxidation, protein oxidation, depletion of protein thiols and the levels of the antioxidant enzyme, superoxide dismutase. An active fraction consisting of polysaccharides (termed as P3) was effective even at a low concentration of 10 microg/ml. Both the crude extract as well as the P3 fraction significantly inhibited lipid peroxidation and protein oxidation. The antioxidant effect of P3 fraction was more pronounced against lipid peroxidation, as assessed by TBARS formation, while that of the crude extract was more effective in inhibiting protein oxidation. Both the crude extract and P3 fraction also partly protects against radiation-induced loss of protein thiols and inactivation of superoxide dismutase. The inhibitory effects of these active principles, at the concentration of 10 microg/ml, are comparable to that of the established antioxidants glutathione and ascorbic acid. Hence our results indicate that extracts from A. racemosus have potent antioxidant properties in vitro in mitochondrial membranes of rat liver.

Inhibition of dihydrofolate reductase and cell growth activity by the phenanthroindolizidine alkaloids pergularinine and tylophorinidine: the in vitro cytotoxicity of these plant alkaloids and their potential as antimicrobial and anticancer agents.

The phenanthroindolizidine plant alkaloids pergularinine (PGL) and tylophorinidine (TPD) isolated from the Indian medicinal herb Pergularia pallida have been evaluated for their biological activity and assessed for the first time employing dihydrofolate reductase (DHFR) (5,6,7,8-THF: NADP(+) oxidoreductase, EC 1.5.1.3) as the probe in the present investigations. The enzyme is a key target in cancer chemotherapy and has been purified from Lactobacillus leichmannii. Cytotoxicity studies showed that both PGL and TPD are potently toxic and inhibited the growth of L. leichmannii cells (IC(50)=45 and 40 microM, respectively). Both the alkaloids significantly inhibited DHFR activity (IC(50)=40 and 32 microM for PGL and TPD, respectively). Alkaloid concentrations greater than 75-95 microM resulted in a complete loss of DHFR activity. Our results are suggestive of the alkaloids as potential antimicrobial and antitumour compounds. Alkaloid binding to DHFR is slow and reversible. Inhibition kinetics revealed K(i) values of 9x10(-6) M and 7x10(-6) M for PGL and TPD, respectively for the enzyme and inhibition in both the cases was a simple linear 'non-competitive' type.

Dihydrofolate reductase and cell growth activity inhibition by the beta-carboline-benzoquinolizidine plant alkaloid deoxytubulosine from Alangium lamarckii: its potential as an antimicrobial and anticancer agent.

Beta-carboline-benzoquinolizidine plant alkaloid deoxytubulosine (DTB) was evaluated and assessed for the first time for its biochemical and biological activity employing the biomarker dihydrofolate reductase (DHFR) (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) as the probe enzyme, a key target in cancer chemotherapy. DHFR, employed in the present investigations was purified from Lactobacillus leichmannii. DTB, isolated from the Indian medicinal plant Alangium lamarckii was demonstrated to exhibit potent cytotoxicity. The alkaloid potently inhibited the cell growth of L. leichmannii and the cellular enzyme activity of DHFR (IC50=40 and 30 microM for the cell growth and enzyme inhibitions, respectively). DTB concentrations >75 microM resulted in a total loss of the DHFR activity, thus suggesting that the beta-carboline-benzoquinolizidine plant alkaloid is a promising potential antitumor agent. Our results are also suggestive of its potential antimicrobial activity. DTB binding to DHFR appears to be slow and reversible. Inhibition kinetics revealed that DHFR has a Ki value of 5x10(-6) M for DTB and that the enzyme inhibition is a simple linear 'non-competitive' type.

beta-Carboline-benzoquinolizidine alkaloid deoxytubulosine inhibits thymidylate synthase activity in leukemic leukocytes from patients with chronic myeloblastic leukemia and acute lymphoblastic leukemia.

Precursor 2'-deoxythymidine 5'-monophosphate for DNA biosynthesis is supplied by thymidylate synthase (TS) (EC 2.1.1.45) through a de novo pathway and the enzyme levels are elevated in malignancy. TS is therefore a key target for cancer chemotherapy. Human leukocyte TS levels in patients with chronic myeloblastic leukemia (CML) and acute lymphoblastic leukemia (ALL) are highly elevated (66- and 33-fold, respectively) compared to the low baseline activity of normal healthy controls. Preliminary screening tests for the antitumor activity of the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine (DTB) (isolated from the Indian medicinal plant Alanguim lamarckii) were performed employing in vitro inhibition studies on the leukemic leukocyte TS as the probe enzyme. Enzyme activity of the leukemic leukocytes was potently inhibited by DTB (IC50 = 50 microM) in both CML and ALL. The emetine alkaloid DTB was assessed for its biochemical and biological evaluation for the first time as a potential antileukemic agent.

Thymidylate synthase activity in leukocytes from patients with chronic myelocytic leukemia and acute lymphocytic leukemia and its inhibition by phenanthroindolizidine alkaloids pergularinine and tylophorinidine.

Thymidylate synthase (TS) (EC 2.1.1.45) provides precursors for DNA biosynthesis through a de novo pathway and is a key target enzyme for cancer chemotherapy. TS levels of human leukemic leukocytes from patients with chronic myelocytic leukemia (CML) and acute lymphocytic leukemia (ALL) were observed to be highly elevated (66- and 33-fold for CML and ALL, respectively) compared to the usual low level of basal activity in normal healthy controls. In vitro inhibition studies on the human leukemic leukocyte TS with the phenanthroindolizidine alkaloids pergularinine (PGL) and tylophorinidine (TPD) (isolated from the Indian medicinal herb Pergularia pallida) were conducted for the preliminary screening tests for their antitumor activity. The leukemic leukocyte enzyme activity was potently inhibited by PGL and TPD (IC50 = 50 microM) in both types of leukemias. These alkaloids were assessed for biological evaluation for the first time as potential antileukemic agents.

Thymidylate synthase activity and the cell growth are inhibited by the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine.

Employing thymidylate synthase (TS) (5, 10-CH2-H4PteGlu: dUMP C-methyltransferase, EC 2.1.1.45), a key target enzyme in chemotherapy, the biological activity of the beta-carboline-benzoquinolizidine alkaloid deoxytubulosine (DTB) isolated from the Indian medicinal plant Alangium lamarckii has been evaluated and assessed for the first time. The TS employed in the present studies was purified from Lactobacillus leichmannii. The DTB was demonstrated to exhibit potent cytotoxicity and inhibited the cell growth of L. leichmannii, and DTB potently inhibited TS activity (IC50 = 40 microM). The DTB concentrations > 80 microM resulted in a total loss of the TS activity, thus suggesting that the beta-carboline-benzoquinolizidine alkaloid is a promising potential antitumor agent. The DTB binding to TS appears to be irreversible and tight through a possible covalent linkage. Although DTB strongly binds to DNA, it is not known whether DTB binds to RNA associated with TS. Inhibition kinetics showed that TS has a Ki value of 7 x 10(-6) M for DTB and that the inhibition is a simple linear "noncompetitive" type.

Inhibition of thymidylate synthase and cell growth by the phenanthroindolizidine alkaloids pergularinine and tylophorinidine.

Biological activity of the phenanthroindolizidine alkaloids pergularinine (PGL) and tylophorinidine (TPD) isolated from the Indian medicinal herb Pergularia pallida has been evaluated and assessed for the first time employing thymidylate synthase (TS) (5,10-CH2H4 PteGlu: dUMP-C-methyltransferase, EC 2.1.1.45), a key target enzyme in cancer chemotherapy. TS used in the present investigations was purified from Lactobacillus leichmannii. Toxicity studies showed that PGL and TPD were potently toxic and inhibited growth of L.leichmannii cells. Both PGL and TPD significantly inhibited TS activity (IC50 = 40 and 45 microM, respectively). PGL concentrations > 80 microM and TPD concentrations > 90 microM resulted in a complete loss of the TS activity, thus suggesting that both these phenanthroindolizidine alkaloids are promising potential antitumor agents. Our results show that the alkaloid-binding to TS is irreversibly tight through a probable covalent linkage. Inhibition kinetics reveal that the enzyme has Ki values of 10 x 10(-6) and 9 x 10(-6) M for PGL and TPD, respectively and that the inhibition in both the cases is a simple linear 'noncompetitive' type.