Protective properties of melatonin-loaded nanoparticles against lipid peroxidation

Preparation and characterization of antioxidant nanospheres from multiple alpha-lipoic acid-containing compounds

The purpose of this study was to prepare and characterize antioxidant nanospheres composed of multiple alpha-lipoic acid-containing compounds (mALAs). It was found that the nanospheres were remarkably stable under physiologic conditions, maintained the antioxidant property of alpha-lipoic acid, and could be destabilized oxidatively and enzymatically. The preparations were simple and highly reproducible providing a new strategy for the development of nanometer-sized antioxidant biomaterials. The nanospheres may find applications as antioxidant therapeutics and oxidation-responsive antioxidant nanocontainers in drug delivery for pathological conditions characterized by oxidative stress including cancer and neurodegenerative diseases.

Analysis of the mechanism by which melatonin inhibits human eosinophil peroxidase

BACKGROUND AND PURPOSE

Eosinophil peroxidase (EPO) catalyses the formation of oxidants implicated in the pathogenesis of various respiratory diseases including allergy and asthma. Mechanisms for inhibiting EPO, once released, are poorly understood. The aim of this work is to determine the mechanisms by which melatonin, a hormone produced in the brain by the pineal gland, inhibits the catalytic activity of EPO.

EXPERIMENTAL APPROACH

We utilized H2O2-selective electrode and direct rapid kinetic measurements to determine the pathways by which melatonin inhibits human EPO.

KEY RESULTS

In the presence of plasma levels of bromide (Br-), melatonin inactivates EPO at two different points in the classic peroxidase cycle. First, it binds to EPO and forms an inactive complex, melatonin-EPO-Br, which restricts access of H2O2 to the catalytic site of the oxidation enzyme. Second, melatonin competes with Br- and switches the reaction from a two electron (2e-) to a one electron (1e-) pathway allowing the enzyme to function with catalase-like activity. Melatonin is a bulky molecule and binds to the entrance of the EPO haem pocket (regulatory sites). Furthermore, Br- seems to enhance the affinity of this binding. In the absence of Br-, melatonin accelerated formation of EPO Compound II and its decay by serving as a 1e- substrate for EPO Compounds I and II.

CONCLUSIONS AND IMPLICATIONS

The interplay between EPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new mechanism for melatonin to control EPO and its downstream inflammatory pathways.

Melatonin is a potent inhibitor for myeloperoxidase

Myeloperoxidase (MPO) catalyzes the formation of potent oxidants that have been implicated in the pathogenesis of various diseases including atherosclerosis, asthma, arthritis, and cancer. Melatonin plays an important part in the regulation of various body functions including circadian sleep rhythms, blood pressure, oncogenesis, retinal function, seasonal reproduction, and immunity. Here, we demonstrate that melatonin serves as a potent inhibitor of MPO under physiological-like conditions. In the presence of chloride (Cl-), melatonin inactivated MPO at two points in the classic peroxidase cycle through binding to MPO to form an inactive complex, melatonin-MPO-Cl, and accelerating MPO compound II formation, an inactive form of MPO. Inactivation of MPO was mirrored by the direct conversion of MPO-Fe(III) to MPO compound II without any sign of compound I accumulation. This behavior indicates that melatonin binding modulates the formation of MPO intermediates and their decay rates. The Cl- presence enhanced the affinity of MPO toward melatonin, which switches the enzyme activity from peroxidation to catalase-like activity. In the absence of Cl-, melatonin served as a 1e- substrate for MPO compound I, but at higher concentration it limited the reaction by its dissociation from the corresponding complex. Importantly, melatonin-dependent inhibition of MPO occurred with a wide range of concentrations that span various physiological and supplemental ranges. Thus, the interplay between MPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new means through which melatonin can control MPO and its downstream inflammatory pathways.

Incorporation in polymeric nanocapsules improves the antioxidant effect of melatonin against lipid peroxidation in mice brain and liver

It has been recently shown that the association of melatonin with polymeric nanoparticles causes a significant increase of the in vitro effect against lipid peroxidation. Hence, the aim of the present study was to compare the in vivo acute antioxidant effect of intraperitoneal administration of melatonin-loaded polysorbate 80-coated nanocapsules with that of melatonin aqueous solution in mice brain (frontal cortex and hippocampus) and liver. The lipid peroxidation through thiobarbituric acid reactive substance levels, the total antioxidant reactivity (luminol-enhanced chemiluminescence) and the free radical levels (formed dichlorofluorescein) has been carried out. Our results show that a single melatonin aqueous solution injection exerted no antioxidant activity in the evaluated range, while the administration of the melatonin-loaded polysorbate 80-coated nanocapsules caused a marked reduction on lipid peroxidation levels in all studied tissues. No differences on free radical content were found in the tissues. The melatonin-loaded nanocapsules also increased the total antioxidant reactivity in the hippocampus. These in vivo results are in accordance with our previous in vitro findings and confirm the hypothesis that polymeric nanocapsules improve the antioxidant effect of melatonin against lipid peroxidation.

Scavenging properties of metronidazole on free oxygen radicals in a skin lipid model system

Reactive oxygen species (ROS) play a vital role in the pathophysiology of the skin disease rosacea, a chronic, genetically-determined and UV-triggered disease, leading to facial redness and blemishes and exhibiting a deep impact on a patient's self-esteem and quality of life. ROS can cause oxidative damage to nucleic acids, sugars, proteins and lipids, thereby contributing to adverse effects on the skin. Metronidazole has been the first-line topical agent therapy for many years; nevertheless the mechanism of action is still not well understood. The therapeutic efficacy of metronidazole has been attributed to its antioxidant effects, which can involve two pathways: decreased generation of ROS within tissues or scavenging and inactivation of existing ROS. Previous investigations have shown that metronidazole reduces ROS by decreasing ROS production in cellular in-vitro systems. The aim of the following study was to demonstrate that metronidazole additionally exhibits antioxidative properties in a cell-free system, by acting as an antioxidant scavenger. A simple skin lipid model (oxidative) system and a complex skin adapted lipid system in conjunction with thiobarbituric acid (TBA) test, a quantitative assay for the detection of malondialdehyde (MDA) and therefore lipid peroxidation, were used to determine the antioxidative properties of metronidazole after UV irradiation. Results clearly show that metronidazole has antioxidative properties in a cell-free environment, acting as a free radical scavenger. Simple skin lipid model: in the presence of 10, 100 and 500 microg mL(-1)metronidazole the MDA concentration was reduced by 25, 36 and 49%, respectively. Complex skin lipid system: in the presence of 100 and 500 microg mL(-1)metronidazole the MDA concentration was reduced by 19 and 34%, respectively. The results obtained in this study and from previous publications strongly suggest that metronidazole exhibits antioxidative effects via two mechanisms: decrease in ROS production through modulation of neutrophil activity and decrease in ROS concentration by exhibiting ROS scavenging properties. The remarkable clinical efficacy of metronidazole in the treatment of rosacea is probably due to its ability to decrease ROS via different mechanisms, thereby protecting skin components from induced damage.

Human skin penetration and distribution of nimesulide from hydrophilic gels containing nanocarriers

The objective of this work was to study the in vitro skin penetration of a drug model (nimesulide) from semi-solid topical formulations containing nanospheres, nanocapsules or nanoemulsion. Nanoprecipitation, interfacial deposition and spontaneous emulsification methods were used to prepare the nanostructured suspension. The hydrodynamic diameters were 252nm for the nanoemulsion, 277nm for the nanocapsules and 202nm for the nanospheres containing nimesulide. The different nanocarrier systems were incorporated in the hydrophilic gels and their ability of delivering the drug into the human skin were investigated using stripping technique and Franz-type diffusion cells. The amount of nimesulide released into the stratum corneum (SC) from the gel containing nanocapsules (GNM-NC) and the gel containing nanospheres (GNM-NS) was similar. On the other hand, for the gel containing nanoemulsion (GNM-NE), the nimesulide was not quantified in SC, but it has been directly permeated for the dermis. The penetration of the nimesulide using the gel containing nanocapsules (GNM-NC) was larger in the deeper skin than using the gel containing nanospheres (GNM-NS) or the one containing nanoemulsion (GNM-NE). The gels containing nanocarriers (GNM-NC, GNM-NS and GNM-NE) were able to release the drug in the viable layer of the skin, comparing to a non-particulated nimesulide-loaded formulation at the same concentration.

Physico-chemical characterization of nanocapsule polymeric wall using fluorescent benzazole probes

Fluorescent polymers were used to prepare innovative formulations with the objective of verifying the chemical composition of the particle/water interface of nanocapsules at a molecular level. The benzazole dyes distinguish between apolar and polar/protic environments. Comparing the fluorescent behavior of benzoxazole-loaded nanocapsules (entrapped dye) with that of fluorescent-polymeric nanocapsules (chemically bound dye), the results indicated that the latter was exposed to a different environment than that to which the entrapped dye was exposed. The polymer in the nanocapsule suspensions is actually at the oil/water interface, interacting with both inner and outer pseudo-phases at the same time. The polymer is restricted at the particle/water interface forming a wall in nanocapsules. The physico-chemical stability of nanocapsules was studied by fluorescence, light scattering, zeta-potential and potentiometry. After 15, 30, 45 and 60 days of preparation different fluorescent behaviors were observed for the benzimidazole physically entrapped in nanocapsules compared to the benzimidazole chemically bound to the polymer wall. This spectrum presented an isoemissive point indicating that only two species were in equilibrium in the medium. The study showed that the water is increasingly interacting with the polymer in the nanocapsule suspensions.

The examination of polysaccharides as potential antioxidative compounds for topical administration using a lipid model system

Aim of this study was the detection of polysaccharides with antioxidative properties as potential lipid protectors for topical administration. The effects of eight different polysaccharides on UV irradiation induced lipid peroxidation were investigated in a concentration dependent manner. An aqueous linolenic acid dispersion was used as an in vitro test system to examine the influences of acacia gum, agar agar, alginic acid, guar gum, novelose 330 and xanthan gum on the lipid peroxidation level after UV exposure. Four different samples of pectin and locust bean gum resulting from a swing mill grinding series were tested as well. Iron ions were added as transition metal catalysts. A UV irradiation device was used to create high level radiation. The amount of lipid peroxidation secondary products was quantified by the thiobarbituric acid assay detecting malondialdehyde. All of the tested polysaccharides showed antioxidative effects at least at one concentration. For acacia and xanthan gum, a concentration dependency of the protective effects was measured. The samples of agar agar, guar gum and novelose 330 acted antioxidatively without showing any concentration dependency. For alginic acid, prooxidative effects were determined. A correlation between grinding time and the effects of pectin and locust bean gum on the model lipid was not observed. The administration of lipid protective polysaccharides in cosmetic formulations or sunscreens could be helpful for the protection of the human skin against UV induced damage. In vivo experiments with the lipid protective polysaccharides found in this study should follow.