Evaluation of extracellular lipid peroxidation in brain cortex of anaesthetized rats by microdialysis perfusion and high-performance liquid chromatography with fluorimetric detection

Antioxidant potential and total phenolic content of methanolic bark extract of Madhuca indica (koenig) Gmelin

This study was carried out to investigate the antioxidant and free radical scavenging activity of methanolic extract of Madhuca indica bark in varios systems. DPPH radical, superoxide anion radical, nitric oxide radical, hydroxyl radical, lipid peroxidation, and total phenolic content assays were carried out to evaluate the antioxidant potential of the extract. The percentage inhibition of 40 μg/ml concentration of MMI in DPPH radical scavenging model was found as 74.1%. The scavenging of nitric oxide by the plant extract was concentration dependent and IC₅₀ value of rutin was found to be 161.7 μg/ml. MMI elicited significant and concentration-dependent superoxide radical scavenging effect with MMI as well as standard curcumin, which exhibited IC₅₀ values of 38.1 and 5.84 μg/ml, respectively. MMI demonstrated significant scavenging activity of OH^- radical generated from Fe²⁺-ascorbate-EDTA-H₂O₂ in a concentration-dependent manner. The extract showed a significant dose-dependent free radical scavenging activity in all the models. The extract showed the presence of high phenolic content corresponding to 98.48 μg equivalent of gallic acid and the antioxidant activity could be attributed to this.

Detection of malondialdehyde in vivo using microdialysis sampling with CE-fluorescence

Oxidative damage is a naturally occurring process where reactive oxygen species (ROS) attack and disrupt normal cellular function; however, these effects become elevated during a stress event, such as ischemia/reperfusion or seizure. One result of oxidative stress is lipid peroxidation, where ROS attack free unsaturated fatty acids forming lipid hydorperoxides, which then break down to form secondary products acrolein, 4-hydroxynonenal, and malondialdehyde (MDA) resulting in irreversible membrane damage and ultimately cell death. Described here is a CE-fluorescence method for the determination of MDA in conjunction with in vivo microdialysis sampling. MDA was derivatized with thiobarbituric acid under acidic conditions for 20 minutes and injected directly into the capillary without any pretreatment. This method provided a limit of detection of 25 nM (S/N=3) and a linear range of 25-2400 nM (1.8-174 ng/mL). This method was used to quantify MDA in rat heart, muscle, liver, and brain dialysate.

Assaying protein unbound drugs using microdialysis techniques

Compared with traditional sampling methods, microdialysis is a technique for protein unbound drug sampling without withdrawal of biological fluids and involving minimal disturbance of physiological function. Conventional total drug sample consists of unbound drugs and protein bound drugs, which are loosely bound to plasma proteins such as albumin and alpha-1 acid glycoprotein, forming an equilibrium ratio between bound and unbound drugs. However, only the unbound fraction of drug is available for absorption, distribution, metabolism and elimination, and delivery to the target sites for pharmacodynamic actions. Although several techniques have been used to determine protein unbound drugs from biological fluids, including ultrafiltration, equilibrium dialysis and microdialysis, only microdialysis allows simultaneous sampling of protein unbound chemicals from plasma, tissues and body fluids such as the bile juice and cerebral spinal fluid for pharmacokinetic and pharmacodynamic studies. This review article describes the technique of microdialysis and its application in pharmacokinetic studies. Furthermore, the advantages and limitations of microdialysis are discussed, including the detailed surgical techniques in animal experiments from rat blood, brain, liver, bile duct and in vitro cell culture for unbound drug analysis.

Reactive oxygen species and UV-B: effect on cyanobacteria

Reactive oxygen species (ROS) are involved in the damage and response of cyanobacteria to UV-B irradiation. In cyanobacteria, there are several targets for the potentially toxic ROS such as lipids, DNA and protein. The damage to photosynthetic apparatus induces the inhibition of photosynthesis that is mediated partially by ROS. UV-B-induced oxidative stress and oxidative damage increases with irradiation time and can be reversed after long-term irradiation. This raises the interesting question of whether cyanobacteria can acclimatize to the present UV-B stress. On one hand, ROS may also act as signal molecules and mediate the genetic regulation of photosynthetic genes and the induction of antioxidant enzymes. On the other hand, the efficient defense and repair system allows cyanobacteria to recover from the oxidative damage under moderate UV-B irradiation. In addition, the following methods are discussed: the fluorogenic probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), used to detect oxidative stress induced by UV-B; thiobarbituric acid reactive substances (TBARS), used to determine lipid peroxidation in cyanobacteria; fluorimetric analysis of DNA unwinding (FADU), used to quantify DNA strand breaks induced by ROS formation under UV-B stress.

Highly specific, simple and rapid method for the determination of malondialdehyde in blood using high-performance liquid chromatography

A novel, highly specific, simple and rapid method for the determination of malondialdehyde (MDA), the routinely used marker for free radical generation in body fluids has been developed and evaluated. Serum samples from 30 healthy volunteers in heparin and 1,4-dithiothreitol-containing tubes stored at -80 degrees C were analyzed. The MDA-thiobarbituric acid complex was separated from interfering substances using HPLC. For the separation, reverse phase column MAC (4 x 250 mm, Biospher SI 120 PSI C18, particle size 7 microm) was used. The mixture of methanol and 8.3 mmol/l phosphate buffer, pH= 7.2, (35:65, v/v) was used as mobile phase. The volume of serum samples injected on the column was 50 microl. The analyte was detected at 532 nm. Retention time of MDA-thiobarbituric acid complex was 4.9+/-0.1 min at the flow rate 0.7 ml/min. Excellent linearity was achieved. The intra- and interassay coefficient of variation was 7.3% and 8.8%, respectively. The recovery was 95.6% and the detection limit was 0.1 micromol/l. The validity of this method was proved by comparison with the spectrophotometric determination of MDA-thiobarbituric acid complex by the method of Yagi at three different wavelengths (485, 532 and 560 nm) with Allen's correction.

On-line, continuous and automatic monitoring of extracellular malondialdehyde concentration in anesthetized rat brain cortex

An assay for in vivo, continuous and automatic monitoring of extracellular malondialdehyde concentrations in anesthetized rat brain cortex was developed. This method involved the use of microdialysis perfusion, on-line derivatization and on-line high-performance liquid chromatographic analysis. Microdialysate from an implanted microdialysis probe was on-line reacted with thiobarbituric acid at 80 degrees C for 10 min prior to on-line collection and automatic injection into a HPLC system equipped with a fluorescence detector. This method gave a linear response between the concentrations of the malondialdehyde in the microdialysates and the TEP solution where the microdialysis probe was placed. This method was used to observe the increased extracellular malondialdehyde production following elevated extracellular glutamate levels, which were achieved by perfusion of L-trans-pyrrolidine-2,4-dicarboxylate, a competitive inhibitor of glutamate uptake transporter.

Indole-3-propionate: a potent hydroxyl radical scavenger in rat brain

The hydroxyl radical scavenging activity of indole-3-propionate was evaluated by kinetic competition studies with the hydroxyl radical trapping reagent 2,2'-azino-bis-(3-ethyl-benz-thiazoline-6-sulfonic acid) (ABTS) and by measuring hydroxyl radical-initiated lipid peroxidation in the rat striatum. Using ABTS, the indole was shown to act as a potent hydroxyl radical scavenger with a rate constant of 7.8x1010 mol l-1 s-1. Hydroxyl radical-initiated lipid peroxidation, determined by measuring tissue malondialdehyde formation, was inhibited dose-dependently both in vitro and in vivo. Indole-3-propionate reacts with hydroxyl radicals at a diffusion controlled rate and can thereby provide on-site protection against the oxidative damage of biomolecules induced by these highly reactive and toxic oxygen intermediates. While it remains to be established if endogenous brain tissue levels of indole-3-propionate are sufficiently high to have a significant impact on total antioxidative capacity, the compound itself or a structurally related agent may be useful as an antioxidant adjuvant to combat hydroxyl radical-mediated oxidative stress.

Improvement in the high-performance liquid chromatography malondialdehyde level determination in normal human plasma

We report a very rapid and simple isocratic reversed-phase HPLC separation of malondialdehyde (MDA) in normal human plasma without previous purification of the MDA-2-thiobarbituric acid (TBA) complex. The separation of MDA-TBA complex was performed using a 250x4.6 mm Nucleosil-5C18 column with a mobile phase composed of 35% methanol and 65% 50 mM sodium phosphate buffer, pH 7.0. Samples of 50 microl (composed of 100 microl plasma mixed with 1.0 ml of 0.2% 2-thiobarbituric acid in 2 M sodium acetate buffer containing 1 mM diethylenetriaminepentaacetic acid, pH 3.5, and 10 microl of 5% 2,6-di-tert.-butyl-4-methylphenol in 96% ethanol, incubated at 95 degrees C for 45 min [K. Fukunaga, K. Takama and T. Suzuki, Anal. Biochem., 230 (1995) 20] were injected into the column. The MDA-TBA complex was eluted at a flow-rate of 1 ml/min and monitored by fluorescence detection with excitation at 515 nm and emission at 553 nm. Analysis of groups of normal male and female volunteers gave plasma levels of MDA of 1.076 nmol/ml with a coefficient of variation of about 58%. No significant statistical differences were found between male and female groups, and no correlation was discovered on the age.

Elevated extracellular glutamate concentrations increased malondialdehyde production in anesthetized rat brain cortex

Oxidative stress is believed to be involved in the damaging mechanism of excitotoxic insult. Thus, we investigated the effect of elevated extracellular glutamate levels on malondialdehyde production, a common index of lipid peroxidation, in anesthetized rat brain cortex. Elevation of extracellular glutamate levels was achieved either by exogenously perfusing glutamate solutions, or by perfusing L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a competitive inhibitor of glutamate uptake transporter, through an implanted microdialysis probe. Malondialdehyde levels in the microdialysates, which were reacted with thiobarbituric acid, were analyzed by a high performance liquid chromatography system equipped with a fluorescence detector. Perfusion of glutamate (1.5 and 15 mM) resulted in dose-dependent increases in extracellular malondialdehyde production (as high as a 6-fold increase in malondialdehyde production following perfusion of 15 mM glutamate solution). PDC (3.14 and 31.4 mM), not only significantly increased the extracellular glutamate levels in a dose-dependent manner, but also dramatically increased malondialdehyde production (as high as 20-fold increase). These results suggest that excitotoxicity induces oxidative stress in anesthetized rat brain cortex, as evidenced by the glutamate-induced increase in malondialdehyde production.