Binding of a cationic phenazinium dye in anionic liposomal membrane: a spectacular modification in the photophysics

Interaction of a cationic phenazinium dye, phenosafranin (PSF), with the anionic liposomal vesicle/bilayer of dimyristoyl-l-α-phosphatidylglycerol (DMPG) has been demonstrated using steady state and time resolved fluorescence and fluorescence anisotropy techniques. The charge transfer emission spectrum of PSF shows a dramatic modification in terms of fluorescence yield together with an appreciable hypsochromic shift in the lipid environment. The blue shift indicates a lowering in polarity inside the vesicle as compared to that in bulk water. The fluorescence and fluorescence quenching studies and micropolarity determination reveal that the cationic fluorophore has a profound binding interaction with the anionic DMPG membrane. Anisotropy study indicates the imposition of a motional restriction on the probe inside the bilayer. The electrostatic interaction between the cationic dye and the anionic lipid membrane has been argued to be the reason behind all these observations. The results could be useful in analyzing membrane organization and heterogeneity in natural membranes exploiting PSF or alike compounds as fluorescent probes.     

Protective effect of curcumin on γ-radiation induced DNA damage and lipid peroxidation in cultured human lymphocytes

The present work is aimed at evaluating the radioprotective effect of curcumin, a naturally occurring phenolic compound on γ-radiation induced toxicity. The cellular changes were estimated by using lipid peroxidative indices like thiobarbituric acid reactive substances (TBARS), the antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and reduced glutathione (GSH). The DNA damage was analysed by using cytokinesis blocked micronucleus assay and dicentric aberration (DC). The γ-radiation at different doses (1, 2 and 4 Gy) were found to significantly increase micronuclei (MN), DC frequencies and TBARS level whereas the levels of GSH and antioxidant enzymes were significantly decreased. The maximum damage to lymphocytes was observed at 4 Gy irradiation. Curcumin pretreatment (1, 5 and 10 μg/ml) significantly decreased the frequency of MN and DC. The levels of TBARS decreased and activities of SOD, CAT and GPx significantly increased along with GSH levels. At 1 Gy irradiation all the concentrations of curcumin (1, 5 and 10 μg/ml) significantly protected the lymphocytes from radiation damage. At 2 Gy irradiation, 5 and 10 μg/ml of curcumin showed significant radioprotection. Since the highest damage was observed at 4 Gy irradiation both 1 and 5 μg/ml of curcumin pretreatment were not sufficient to protect the lymphocytes from radiation damage but 10 μg/ml of curcumin significantly protected the cultured lymphocytes from radiation damage. Thus, pretreatment with curcumin gives protection to lymphocytes against γ-radiation induced cellular damage.     

Protective effect of curcumin on gamma-radiation induced DNA damage and lipid peroxidation in cultured human lymphocytes

The present work is aimed at evaluating the radioprotective effect of curcumin, a naturally occurring phenolic compound on gamma-radiation induced toxicity. The cellular changes were estimated by using lipid peroxidative indices like thiobarbituric acid reactive substances (TBARS), the antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and reduced glutathione (GSH). The DNA damage was analysed by using cytokinesis blocked micronucleus assay and dicentric aberration (DC). The gamma-radiation at different doses (1, 2 and 4Gy) were found to significantly increase micronuclei (MN), DC frequencies and TBARS level whereas the levels of GSH and antioxidant enzymes were significantly decreased. The maximum damage to lymphocytes was observed at 4Gy irradiation. Curcumin pretreatment (1, 5 and 10microg/ml) significantly decreased the frequency of MN and DC. The levels of TBARS decreased and activities of SOD, CAT and GPx significantly increased along with GSH levels. At 1Gy irradiation all the concentrations of curcumin (1, 5 and 10microg/ml) significantly protected the lymphocytes from radiation damage. At 2Gy irradiation, 5 and 10microg/ml of curcumin showed significant radioprotection. Since the highest damage was observed at 4Gy irradiation both 1 and 5microg/ml of curcumin pretreatment were not sufficient to protect the lymphocytes from radiation damage but 10microg/ml of curcumin significantly protected the cultured lymphocytes from radiation damage. Thus, pretreatment with curcumin gives protection to lymphocytes against gamma-radiation induced cellular damage.     

Curcumin enhances the polyglutamine-expanded truncated N-terminal huntingtin-induced cell death by promoting proteasomal malfunction

Formation of neuronal intranuclear inclusions of the disease proteins that are ubiquitinated and often associated with various proteasome components is the major hallmark of the polyglutamine diseases. Curcumin is a polyphenolic compound having anti-inflammatory, anti-tumor, and anti-oxidative properties. Recently, curcumin has been reported to suppress the amyloid-beta accumulation, oxidative damage, and inflammation in the transgenic mice model of Alzheimer's disease. Here, we found that the treatment of curcumin increases the polyglutamine-expanded truncated N-terminal huntingtin (mutant huntingtin) aggregation and mutant huntingtin-dependent cell death. Curcumin also causes rapid proteasomal malfunction in the mutant huntingtin expressing cells in comparison with normal glutamine repeat expressing cells. Finally, we show that N-acetyl cysteine (NAC), a potent antioxidant, reverted the curcumin-induced mutant huntingtin aggregation and proteasomal malfunction in the mutant huntingtin expressing cells. NAC also protects curcumin-induced cell death. Our result suggests that curcumin promotes mutant huntingtin-induced cell death by mimicking proteasomal dysfunction.     

Role of phenylalanine B10 in plant nonsymbiotic hemoglobins

All plants contain an unusual class of hemoglobins that display bis-histidyl coordination yet are able to bind exogenous ligands such as oxygen. Structurally homologous hexacoordinate hemoglobins (hxHbs) are also found in animals (neuroglobin and cytoglobin) and some cyanobacteria, where they are thought to play a role in free radical scavenging or ligand sensing. The plant hxHbs can be distinguished from the others because they are only weakly hexcacoordinate in the ferrous state, yet no structural mechanism for regulating hexacoordination has been articulated to account for this behavior. Plant hxHbs contain a conserved Phe at position B10 (Phe(B10)), which is near the reversibly coordinated distal His(E7). We have investigated the effects of Phe(B10) mutation on kinetic and equilibrium constants for hexacoordination and exogenous ligand binding in the ferrous and ferric oxidation states. Kinetic and equilibrium constants for hexacoordination and ligand binding along with CO-FTIR spectroscopy, midpoint reduction potentials, and the crystal structures of two key mutant proteins (F40W and F40L) reveal that Phe(B10) is an important regulatory element in hexacoordination. We show that Phe at this position is the only amino acid that facilitates stable oxygen binding to the ferrous Hb and the only one that promotes ligand binding in the ferric oxidation states. This work presents a structural mechanism for regulating reversible intramolecular coordination in plant hxHbs.