HPLC Separation of Fluorescent Products of Lipid Peroxidation in Erythrocytes and Mitochondria

Lipophilic fluorescent products as a potential biomarker of oxidative stress: A link between central (brain) and peripheral (blood)

Oxidative stress plays a key role in brain damage because of the sensitivity of brain tissue to oxidative damage. Biomarkers with easy measurement can be a candidate for reflecting the oxidative stress issue in humans. For this reason, we need to focus on specific metabolic products of the brain. End products of free radical reactions such as malondialdehydes form fluorescent products known as lipophilic fluorescent products (LFPs). The distinctive feature of LFPs is their autofluorescent properties. LFPs are detectable in the brain and cerebrospinal fluid. Furthermore, because of the diffusion into the bloodstream, these lipophilic molecules can be detected in the blood. Accumulations of these compounds produce more reactive oxygen species and increase the sensitivity of cells to oxidative damage. Hence, LFPs can be considered a danger signal for neurons and can be introduced as a strong index of oxidative damage both in the central and in the peripheral.

Assessment of lipophilic fluorescence products in β-amyloid-induced cognitive decline: A parallel track in hippocampus, CSF, plasma and erythrocytes

BACKGROUND

Oxidative stress implicates in Alzheimer's disease (AD) pathophysiology, and associates with the creation of end products of free radical reactions, are known as lipophilic fluorescent products (LFPs). This study aimed to evaluate the probable parallel alterations in the spectral properties of the LFPs in the hippocampus tissues, cerebrospinal fluid (CSF), plasma, and erythrocytes during AD model induction by intra-cerebroventricular (ICV) amyloid β-protein fragment 25-35 (Aβ) injection.

METHODS

Male rats received an intra-ICV injection of Aβ. Hippocampus, CSF, plasma, and erythrocytes were harvested at 5, 14, and 21 days after Aβ injection. The fluorescent intensity of LFPs was assessed by spectrofluorimetry using synchronous fluorescence spectra 25 (SYN 25) and 50 (SYN 50) in the range of 250-500 nm. Hippocampal tissue malondialdehyde (MDA) and superoxide dismutase (SOD) were also measured. Cognitive alterations were evaluated using Morris water maze (MWM) test.

RESULTS

The parallel significant rise in the fluorescence intensity of LFPs was detected in the hippocampus, CSF, plasma, and erythrocytes, 14, and 21 days after ICV-Aβ injection. These alterations were found in both types of synchronous spectra 25, and 50, and were coincided with hippocampal cognitive decline, the MDA rise, and decrease of SOD activity. There was a positive correlation between hippocampus homogenate, and plasma or CSF rise in fluorescence intensity.

CONCLUSION

Data showed that the Aβ increased hippocampal MDA, and decreased SOD activity, led to a higher rate of oxidative products and subsequently resulted in an increase in LFPs fluorescence intensity during the development of cognitive decline. LFPs' alterations reflect a comprehensive view of tissue redox status. The fluorescence properties of LFPs indicate their composition, which may pave the way to trace the different pathological states.

LC-MS Quantification of Malondialdehyde-Dansylhydrazine Derivatives in Urine and Serum Samples

We developed a robust analytical method for quantification of malondialdehyde (MDA) in urine and serum samples using dansylhydrazine (DH) as a derivatizing reagent. The derivatization procedure was partially carried out using an autosampler injection program to minimize errors associated with the low-volume addition of reagents and was optimized to yield a stable hydrazone derivative of MDA and its labeled d2-MDA analogue. The target MDA-DH derivatives were separated on an Agilent Zorbax Eclipse Plus Phenyl-Hexyl (3.0 × 100 mm, 3.5 μm) column. The mass-to-charge ratios of the target derivatives [(M+H)+ of 302 and 304 for MDA-DH and d2-MDA-DH, respectively] were analyzed in single ion monitoring mode using a single quadrupole mass spectrometer operated under positive electrospray ionization. The method limits of quantification were 5.63 nM (or 0.405 ng/mL) for urine analysis and 5.68 nM (or 0.409 ng/mL) for serum analysis. The quantification range for urine analysis was 5.63-500 nM (0.405-36.0 ng/mL) while the quantification range for serum analysis was 5.68-341 nM (0.409-24.6 ng/mL). The method showed good relative recoveries (98-103%), good accuracies (92-98%), and acceptable precisions (relative standard deviations 1.8-7.3% for inter-day precision; 1.8-6.1% for intra-day precision) as observed from the repeat analysis of quality control samples prepared at different concentrations. The method was used to measure MDA in individual urine samples (n = 287) and de-identified archived serum samples (n = 22) to assess the overall performance of the method. The results demonstrated that our method is capable of measuring urinary and serum levels of MDA, allowing its future application in epidemiologic investigations.