Nizam U. Khan

PRO-OXIDANT, ANTI-OXIDANT AND CLEAVAGE ACTIVITIES ON DNA OF CURCUMIN AND ITS DERIVATIVES DEMETHOXYCURCUMIN AND BISDEMETHOXYCURCUMIN

Curcumin, a naturally occurring phytochemical responsible for the colour of turmeric shows a wide range of pharmacological properties including antioxidant, anti-inflammatory and anti-cancer effects. We have earlier shown that curcumin in the presence of Cu(II) causes strand cleavage in DNA through generation of reactive oxygen species, particularly the hydroxyl radical. Thus, curcumin shows both antioxidant as well as pro-oxidant effects. In order to understand the chemical basis of various biological properties of curcumin, we have studied the structure-activity relationship between curcumin and its two naturally occurring derivatives namely demethoxycurcumin (dmC) and bisdemethoxycurcumin (bdmC). Curcumin was found to be the most effective in the DNA cleavage reaction and a reducer of Cu(II) followed by dmC and bdmC. The rate of formation of hydroxyl radicals by the three curcuminoids also showed a similar pattern. The relative antioxidant activity was examined by studying the effect of these curcuminoids on cleavage of plasmid DNA by Fe(II)-EDTA system (hydroxyl radicals) and the generation of singlet oxygen by riboflavin. The results indicate that curcumin is considerably more active both as an antioxidant as well as an oxidative DNA cleaving agent. The DNA cleavage activity is the consequence of binding of Cu(II) to various sites on the curcumin molecule. Based on the present results, we propose three binding sites for Cu(II). Two of the sites are provided by the phenolic and methoxy groups on the two benzene rings and the third site is due to the presence of 1,3-diketone system between the rings. Furthermore, both the antioxidant as well as pro-oxidant effects of curcuminoids are determined by the same structural moieties.

Prooxidant and antioxidant activities of bilirubin and its metabolic precursor biliverdin: a structure–activity study

Bilirubin, which is derived from its metabolic precursor biliverdin, is the end product of heme catabolism. It has been proposed as a physiological antioxidant present in human extracellular fluids. We have earlier shown that bilirubin in the presence of the transition metal ion Cu(II) causes strand cleavage in DNA through generation of reactive oxygen species, particularly the hydroxyl radical. Thus bilirubin possesses both antioxidant and prooxidant properties. In order to understand the chemical basis of various biological properties of bilirubin, we have studied the structure-activity relationship between bilirubin and its precursor biliverdin. The latter has also been reported to possess both antioxidant and toxic properties. In the present studies bilirubin was found to be more effective in the DNA cleavage reaction and a more efficient reducer of Cu(II). The rate of formation of hydrogen peroxide and hydroxyl radicals by the compounds also showed a similar pattern. The relative antioxidant activity was also examined by studying the effect of these compounds on DNA cleavage by a hydroxyl radical generating system and their quenching effect on hydroxyl radicals. The results indicate that bilirubin is more active both as an antioxidant as well as an oxidative DNA cleaving agent. A model for binding of copper to bilirubin has been proposed where two copper ions are bound to two molecules of bilirubin through their terminal pyrrole nitrogens. In order to account for the enhanced copper reducing capacity of bilirubin we have further proposed that an additional copper binding site is provided for in the case of bilirubin due to the absence of a double bond between pyrrole rings II and III. Further it would appear that the structural features of the bilirubin molecule which are important for its prooxidant action are also the ones that render it a more effective antioxidant.

Operculina turpethum attenuates N-nitrosodimethylamine induced toxic liver injury and clastogenicity in rats.

The root extract of Operculina turpethum (OTE) has been used as an anti-inflammatory, purgative, and hepato-protective agent. N-Nitrosodimethylamine (NDMA) is a potent hepatotoxin that induces fibrosis of the liver. In the present study, we examined the therapeutic effects of OTE root extract against NDMA-induced hepatotoxicity and clastogenicity in rats. Hepatic fibrosis was induced in adult male albino rats through serial intraperitoneal administrations of NDMA at a concentration of 10mg/kg body weight on three consecutive days of each week over a period of three weeks. A group of rats received OTE orally in doses of 75, 150 and 200mg/kg body weight at 5h after the administration of NDMA. The controls and treated animals were sacrificed on days-7, 14 and 21 after the start of the administration of NDMA. The progression of hepatic fibrosis as well as the amelioration effect of OTE was evaluated through histopathologically as well as by immunohistochemical staining for the activation of hepatic stellate cells. Alterations in serum and liver biochemical parameters and LDH isoenzymes were also studied. Serial administration of NDMA resulted in well formed fibrosis in the liver and induction of micronuclei in the bone marrow cells. Staining of alpha-SMA demonstrated activated stellate cells from day-7 onwards which was dramatically increased on day-21. An elevation of micronuclei count, liver function enzymes, serum hydroxyproline levels and LDH isoenzymes 4 and 5 were also observed. All these changes were remarkably reduced in OTE administered animals and fibrogenesis was completely absent. Our results suggest that OTE has hepatoprotective and anti-clastogenic effects against NDMA-induced hepatic fibrosis. Therefore OTE may be used as a hepatoprotective agent against various liver diseases including toxic liver injury.

Reactivities of flavonoids with different hydroxyl substituents for the cleavage of DNA in the presence of Cu(II).

DNA strand scission reactions of flavonoids in the presence of Cu(II) have been extended by using flavonoids with a variety of patterns of hydroxyl substitution. In particular we have examined for the first time a flavonoid (7,8‐dihydroxyflavone) that lacks the possibility of forming a complex involving the oxygen at position 4. By comparing the reactivities of several flavonoids, including data from the literature, we draw generalizations for the correlation of structure and activity and present evidence for at least three different modes of action of flavonoids as genotoxic agents. Copyright

Biflavones from the leaves of Araucaria bidwillii Hooker and Agathis alba foxworthy (araucariaceae)

Abstract Six biflavones have been isolated from the leaf extracts of Araucaria bidwillii Hooker and Agathis alba Foxworthy; 7-O-methylcupressuflavone (2a) and 7,7″-di-O-methylagathisflavone (1c) are new compounds. The others are 7-O-methylagathisflavone (1a), 4‴,7-di-O-methylagathisflavone (1b), 7,7″-di-O-methylcupressuflavone (2b) and bilobetin (3). In addition, the presence of several other biflavones has been indicated by TLC examination (Table 3).

Two xanthones from Garcinia mangostana

Two new xanthones, 1,5,8-trihydroxy-3-methoxy-2[3-methyl-2-butenyl] xanthone and 1,6-dihydroxy-3-methoxy-2[3-methyl-2-butenyl] xanthone were isolated alongwith the known xanthone gartanin from the leaves of Garcinia mangostana and their structures elucidated by 1H NMR, IR and mass spectral studies.

Serotonin–Cu(II)-mediated DNA cleavage: mechanism of copper binding by serotonin

It has been proposed that considerable DNA damage may be caused by endogenous metabolites produced during the bodys normal metabolic processes. 5-hydroxytryptamine (serotonin) is an important neurotransmitter in brain and spinal cord. We have previously shown that serotonin induces oxidative cleavage of DNA strands in the presence of copper ions. In the present paper we have examined the mechanism of copper binding by serotonin using absorption spectroscopy, Cu(II)-mediated lipid peroxidation and by determining the oxidation of the serotonin molecule. Addition of increasing concentrations of Cu(II) to serotonin leads to a progressive enhancement in the absorption band and is accompanied by a shift towards a lower wavelength indicative of the formation of an oxidised species of serotonin. Studies with the structurally related molecules tryptophan and melatonin showed that only serotonin is able to reduce Cu(II) to Cu(I). Similarly, only serotonin was found to be able to abolish the copper-mediated peroxidation of mitochondria. These results suggested the involvement of the phenolic group in copper binding. Further, it was also shown that the binding of copper to serotonin leads to the formation of a quinone in the absence of molecular oxygen. Based on these results, a model has been proposed in which serotonin reduces two molar equivalents of Cu(II) to Cu(I) through a reaction involving two electron oxidation of the phenolic ring to a quinone methide.

Potential antifilarial activity of the leaves and seeds extracts of Psoralea corylifolia on cattle filarial parasite Setaria cervi

The effect of aqueous and alcohol extracts of the leaves and seeds of Psoralea corylifolia, on the spontaneous movements of both the whole worm and the nerve muscle preparation of Setaria cervi and on the survival of microfilariae in vitro was studied. Alcohol extracts of both leaves and seeds caused the inhibition of spontaneous movements of the whole worm and the nerve muscle preparation of S. cervi, characterised by initial, short lasting small increase in tone of contractions followed by paralysis. The initial stimulatory effect was not observed by alcohol extract of leaves on nerve muscle preparation. The concentrations required to inhibit the movements of whole worm and nerve muscle preparations for alcohol extracts of leaves and seeds were 160, 30, and 150, 20 microg/ml, respectively suggesting a cuticular permeability barrier. Alcohol extracts of both leaves and seeds caused death of microfilariae in vitro, LC(50) and LC(90) being 15 and 25 ng/ml for alcohol extract of leaves and 12 and 18 ng/ml for alcohol extract of seeds, respectively.

A triterpene from Garcinia mangostana

Abstract A new triterpene, 3β-hydroxy-26-nor-9,19-cyclolanost-23-en-25-one was isolated from the leaves of Garcinia mangostana and its structure elucidated by 1H NMR and mass spectral studies.

Wampetin, a furocoumarin from Clausena wampi

Abstract A new furocoumarin wampetin has been isolated from Clausena wampi (syn. Clausena lansium ). The structure was established from 1 H NMR, 13 C NMR, MS and chemical data.