Effect of Quercetin loaded Silver nanoparticles on Gram negative and Gram positive bacteria

132-140Microorganisms are increasingly becoming resistant to multiple antibiotics and search for effective antibacterial agents continue to challenge researchers in the respective domain. Silver nanoparticles (AgNPs) with physicochemical properties different from their bulk counterparts and show better cellular penetration resulting in higher antimicrobial activity. Here, we studied the antimicrobial activity of AgNPs in pure state as well as when coated with quercetin, and also the mechanism of action. Quercetin is known for its antimicrobial activity, hence applied here for coating it on AgNPs. Spherical AgNPs of size ranging between 10 and 28 nm were synthesised using chemical reduction method. The AgNPs show promising antimicrobial activity in Gram negative bacteria Escherchia coli; however, AgNPs loaded with quercetin did not enhance the antimicrobial activity of AgNPs. The mechanism of antimicrobial activity of AgNPs unravelled in this study was inhibition of bacterial catalase and decrease in membrane potential (MMP) of the bacterial cell with increase in concentration of AgNPs. Another mechanistic aspect was production of reactive oxygen species (ROS) by AgNPs resulting in apoptosis. However, there was no degradation of cellular DNA which suggests that it does not contribute to antibacterial activity of AgNPs

Electrochemical oxidation and reduction of nitroxides : A cyclic voltammetric and simulation study

2231-2237The oxidation and reduction of the nitroxides namely, TEMPO (2,2,6,6-tetramethyl piperidine-N-oxyl). TEMPOL (4-hydroxy 2,2,6,6-tetramethyl piperidine-N-oxyl). TEMPO-NH2 or Tempamine (4-amino 2,2,6,6-tetramethyl piperidine-N-oxyl) 3 -carbamoyl proxyl and 4- methyl sulphonyloxy-TEMPO have been followed by cyclic voltammetry in aqueous medium at pH 6.8. The E1/2 values for the oxidation of these nitroxides to oxoammonium cation and then back to parent compound were found to be in the range of 0.85 to 1.0 V vs N HE. The diffusion coefficients (Dox) are of the order of 105 cm2/s and are dependent on the size of the molecule. The process is reversible, with a small amount undergoing chemical reaction after charge transfer. The rate constants for the forward chemical reaction after oxidation (kf) are of the order or 103 S-1. It has been observed that kf is the highest for NH2-TEMPO where the reversibility of the reaction is the lowest. In the negative potentials, where the reduction of nitroxides to hydroxylamines takes place irreversible waves have been observed. The reduction process or the above nitroxides when studied in methanol and acetonitrile also shows irreversibility. Since the reduction process of these nitroxides shows poor reversibility, methods like Condecon (a computer software) has been used to calculate E1/2 values and other parameters like (Do) and (αna) ' This method has been found very effective for obtaining reduction potentials of nitroxides in aqueous solutions

Inhibition of catalase by tea catechins in free and cellular state: a biophysical approach.

Tea flavonoids bind to variety of enzymes and inhibit their activities. In the present study, binding and inhibition of catalase activity by catechins with respect to their structure-affinity relationship has been elucidated. Fluorimetrically determined binding constants for (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) with catalase were observed to be 2.27×106 M(-1) and 1.66×106 M(-1), respectively. Thermodynamic parameters evidence exothermic and spontaneous interaction between catechins and catalase. Major forces of interaction are suggested to be through hydrogen bonding along with electrostatic contributions and conformational changes. Distinct loss of α-helical structure of catalase by interaction with EGCG was captured in circular dichroism (CD) spectra. Gallated catechins demonstrated higher binding constants and inhibition efficacy than non-gallated catechins. EGCG exhibited maximum inhibition of pure catalase. It also inhibited cellular catalase in K562 cancer cells with significant increase in cellular ROS and suppression of cell viability (IC50 54.5 µM). These results decipher the molecular mechanism by which tea catechins interact with catalase and highlight the potential of gallated catechin like EGCG as an anticancer drug. EGCG may have other non-specific targets in the cell, but its anticancer property is mainly defined by ROS accumulation due to catalase inhibition

Effect of Quercetin loaded Silver nanoparticles on Gram negative and Gram positive bacteria

Microorganisms are increasingly becoming resistant to multiple antibiotics and search for effective antibacterial agents continue to challenge researchers in the respective domain. Silver nanoparticles (AgNPs) with physicochemical properties different from their bulk counterparts and show better cellular penetration resulting in higher antimicrobial activity. Here, we studied the antimicrobial activity of AgNPs in pure state as well as when coated with quercetin, and also the mechanism of action. Quercetin is known for its antimicrobial activity, hence applied here for coating it on AgNPs. Spherical AgNPs of size ranging between 10 and 28 nm were synthesised using chemical reduction method. The AgNPs show promising antimicrobial activity in Gram negative bacteria Escherchia coli; however, AgNPs loaded with quercetin did not enhance the antimicrobial activity of AgNPs. The mechanism of antimicrobial activity of AgNPs unravelled in this study was inhibition of bacterial catalase and decrease in membrane potential (MMP) of the bacterial cell with increase in concentration of AgNPs. Another mechanistic aspect was production of reactive oxygen species (ROS) by AgNPs resulting in apoptosis. However, there was no degradation of cellular DNA which suggests that it does not contribute to antibacterial activity of AgNPs

ITC profiles for catalase (1 µM) when titrated with catechins (10 µM each) at 25°C: (A) EC-catalase, (B) EGC-catalase, (C) ECG-catalase, and (D) EGCG-catalase systems.

<p>ITC profiles for catalase (1 µM) when titrated with catechins (10 µM each) at 25°C: (A) EC-catalase, (B) EGC-catalase, (C) ECG-catalase, and (D) EGCG-catalase systems.</p

Data from: Anthracycline drugs on modified surface of quercetin-loaded polymer nanoparticles: a dual drug delivery model for cancer treatment

Polymer nanoparticles are vehicles used for delivery of hydrophobic anti-cancer drugs, like doxorubicin, paclitaxel or chemopreventors like quercetin (Q). The present study deals with the synthesis and characterisation of nano formulations (NFs) from Q loaded PLGA (poly lactic-co-glycolic acid) nano particles (NPs) by surface modification. The surface of Q-loaded (NPs) is modified by coating with biopolymers like bovine serum albumin (BSA) or histones (His). Conventional chemotherapeutic drugs adriamycin (ADR) and mitoxantrone (MTX) are bound to BSA and His respectively before being coated on Q-loaded NPs to nano formulate NF1 and NF2 respectively. The sizes of these NFs are in the range 400-500 nm as ascertained by SEM and DLS measurements. Encapsulation of Q in polymer NPs is confirmed from shifts in FT-IR, TGA and DSC traces of Q-loaded NPs compared to native PLGA and Q. Surface modification in NFs is evidenced by three distinct regions in their TEM images; the core, polymer capsule and the coated surface. Negative zeta potential of Q-loaded NPs shifted to positive potential on surface modification in NF1 and NF2. In vitro release of Q from the NFs lasted up to twenty days with an early burst release. NF2 is better formulation than NF1 as loading of MTX is 85% compared to 23% loading of ADR. Such NFs are expected to overcome multi-drug resistance (MDR) by reaching and treating the target cancerous cells by virtue of size, charge and retention

Schematic representation of drug DNA interaction.

<p>Possible events taking place during interaction of (a) N-DNA and (b) M-DNA with ADR/DNM.</p