Mario F. Muñoz

Lipid Peroxidation: Production, Metabolism, and Signaling Mechanisms of Malondialdehyde and 4-Hydroxy-2-Nonenal

Lipid peroxidation can be described generally as a process under which oxidants such as free radicals attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs). Over the last four decades, an extensive body of literature regarding lipid peroxidation has shown its important role in cell biology and human health. Since the early 1970s, the total published research articles on the topic of lipid peroxidation was 98 (1970–1974) and has been increasing at almost 135-fold, by up to 13165 in last 4 years (2010–2013). New discoveries about the involvement in cellular physiology and pathology, as well as the control of lipid peroxidation, continue to emerge every day. Given the enormity of this field, this review focuses on biochemical concepts of lipid peroxidation, production, metabolism, and signaling mechanisms of two main omega-6 fatty acids lipid peroxidation products: malondialdehyde (MDA) and, in particular, 4-hydroxy-2-nonenal (4-HNE), summarizing not only its physiological and protective function as signaling molecule stimulating gene expression and cell survival, but also its cytotoxic role inhibiting gene expression and promoting cell death. Finally, overviews of in vivo mammalian model systems used to study the lipid peroxidation process, and common pathological processes linked to MDA and 4-HNE are shown.

Chronic stress enhances microglia activation and exacerbates death of nigral dopaminergic neurons under conditions of inflammation

BackgroundParkinson’s disease is an irreversible neurodegenerative disease linked to progressive movement disorders and is accompanied by an inflammatory reaction that is believed to contribute to its pathogenesis. Since sensitivity to inflammation is not the same in all brain structures, the aim of this work was to test whether physiological conditions as stress could enhance susceptibility to inflammation in the substantia nigra, where death of dopaminergic neurons takes place in Parkinson’s disease.MethodsTo achieve our aim, we induced an inflammatory process in nonstressed and stressed rats (subject to a chronic variate stress) by a single intranigral injection of lipopolysaccharide, a potent proinflammogen. The effect of this treatment was evaluated on inflammatory markers as well as on neuronal and glial populations.ResultsData showed a synergistic effect between inflammation and stress, thus resulting in higher microglial activation and expression of proinflammatory markers. More important, the higher inflammatory response seen in stressed animals was associated with a higher rate of death of dopaminergic neurons in the substantia nigra, the most characteristic feature seen in Parkinson’s disease. This effect was dependent on glucocorticoids.ConclusionsOur data demonstrate that stress sensitises midbrain microglia to further inflammatory stimulus. This suggests that stress may be an important risk factor in the degenerative processes and symptoms of Parkinson’s disease.

In vitro and in vivo protection by melatonin against the decline of elongation factor-2 caused by lipid peroxidation: preservation of protein synthesis.

Abstract:  As organisms age, a considerable decrease in protein synthesis takes place in all tissues. Among the possible causes of the decline of translation in old animals are the modifications of elongation factor‐2 (eEF‐2). eEF‐2 occupies an essential role in protein synthesis where it catalyzes the ribosomal translocation reaction. eEF‐2 is particularly sensitive to increased oxidative stress. However, all oxidants do not affect eEF‐2, only compounds that increase lipid peroxidation. As peroxides are unstable compounds, they decompose and generate a series of highly reactive compounds, including aldehydes malondialdehyde (MDA) and 4‐hydroxynoenal (HNE). We have previously reported that hepatic eEF‐2 forms adducts with low‐molecular weight aldehydes, MDA and HNE. Therefore, the protection of eEF‐2 must be specifically carried out by a compound with lipoperoxyl radical‐scavenging features such as melatonin. In this article, we show the ability of melatonin to protect against the changes that occur in the eEF‐2 under conditions of lipid peroxidation induced by cumene hydroperoxide (CH), a compound used experimentally to induce lipid breakdown. As experimental models, we used cultured cells and rats treated with this oxidant compound. eEF‐2 levels, adduct formation of this protein with MDA and HNE, and lipid peroxides were determined. In the cultured cells, protein synthesis rate was also measured. Our results show that melatonin prevented the molecular changes in eEF‐2 and the decline in protein synthesis rate secondary to lipid peroxidation. The results also show that serum levels of several hormones were affected by CH‐induced oxidative stress, which was partially or totally prevented by melatonin.

Chronic stress alters the expression levels of longevity-related genes in the rat hippocampus.

The molecular mechanisms underlying the negative effects of psychological stress on cellular stress during aging and neurodegenerative diseases are poorly understood. The main objective of this study was to test the effect of chronic psychological stress, and the consequent increase of circulating glucocorticoids, on several hippocampal genes involved in longevity. Sirtuin-1, p53, thioredoxin-interacting protein, and heat shock protein 70 were studied at the mRNA and protein levels in stressed and non-stressed animals. Stress treatment for 10 days decreased sirtuin-1 and heat shock protein 70 levels, but increased levels of p53, thioredoxin-interacting protein and the NADPH oxidase enzyme. Examination of protein expression following two months of stress treatment indicated that sirtuin-1 remained depressed. In contrast, an increase was observed for thioredoxin-interacting protein, heat shock protein 70, p53 and the NADPH oxidase enzyme. The effect of stress was reversed by mifepristone, a glucocorticoid receptor antagonist. These data suggest that chronic stress could contribute to aging in the hippocampus.

Time and dose dependent effects of oxidative stress induced by cumene hydroperoxide in neuronal excitability of rat motor cortex neurons

It has been claimed that oxidative stress and the production of reactive oxygen radicals can contribute to neuron degeneration and might be one factor in the development of different neurological diseases. In our study, we have attempted to clarify how oxidative damage induces dose dependent changes in functional membrane properties of neurons by means of whole cell patch clamp techniques in brain slices from young adult rats. Our research demonstrates physiological changes in membrane properties of pyramidal motor cortex neurons exposed to 3 concentrations of cumene hydroperoxide (CH; 1, 10 and 100μM) during 30min. Results show that oxidative stress induced by CH evokes important changes, in a concentration and time dependent manner, in the neuronal excitability of motor cortex neurons of the rat: (i) Low concentration of the drug (1μM) already blocks inward rectifications (sag) and decreases action potential amplitude and gain, a drug concentration which has no effects on other neuronal populations, (ii) 10μM of CH depresses the excitability of pyramidal motor cortex neurons by decreasing input resistance, amplitude of the action potential, and gain and maximum frequency of the repetitive firing discharge, and (iii) 100μM completely blocks the capability to produce repetitive discharge of action potentials in all cells. Both larger drug concentrations and/or longer times of exposure to CH narrow the current working range. This happens because of the increase in the rheobase, and the reduction of the cancelation current. The effects caused by oxidative stress, including those produced by the level of lipid peroxidation, are practically irreversible and, this, therefore, indicates that neuroprotective agents should be administered at the first symptoms of alterations to membrane properties. In fact, the pre-treatment with melatonin, acting as an antioxidant, prevented the lipid peroxidation and the physiological changes induced by CH. Larger cells (as estimated by their cell capacitance) were also more susceptible to oxidative stress. Our results provide previously unavailable observations that large size and high sensitivity to oxidative stress (even at low concentrations) make pyramidal neurons of the motor cortex, in particular corticofugal neurons, more susceptible to cell death when compared with other neuronal populations. These results could also shed some light on explaining the causes behind diseases such as Amyotrophic Lateral Sclerosis.

IMMUNOLOCALIZATION OF SUBSTANCE P AND NK-1 RECEPTOR IN ADIPOSE STEM CELLS†

Substance P (SP) is a neuropeptide belonging to the thachykinin peptide family. SP, after binding to its receptor, the neurokinin 1 receptor (NK1R), controls several transcription factors such as NF‐κB, hypoxia inducible factor (HIF‐1α), c‐myc, c‐fos, c‐jun, and AP‐1. SP and NK1R have a widespread distribution in both the central and peripheral nervous systems. They are also present in cells not belonging to the nervous system (immune cells, placenta, etc.). SP is located in all body fluids, that is, blood, cerebrospinal fluid, etc., making it ubiquitous throughout the human body. SP and NK1R genes are expressed in the stem cell line TF‐1 and in primary stem cells derived from human placental cord blood. However, to our knowledge, the presence of SP and the NK1R receptor in adipose stem cells (ADSC) is unknown. We demonstrated by immunofluorescence the localization of SP and NK1R in human and rat ADSC. SP and NK1R are located in both the cytoplasm and the nucleus of these cells. The NK1R is higher in the nucleus than in the cytoplasm of ADSCs. By Western blot we demonstrated the presence of different isoforms of NK1R that have different subcellular locations in the ADSC. SP induces proliferation and mitogenesis through NK1R in ADSCs. These findings reported here for the first time suggest an important role for a SP/NK1R system, either as genetic and/or epigenetic factor, in both the cytoplasm and nucleus functions of the ADSCs. J. Cell. Biochem. 118: 4686–4696, 2017.

Aging and Oxidative Stress Decrease Pineal Elongation Factor 2: In Vivo Protective Effect of Melatonin in Young Rats Treated With Cumene Hydroperoxide

We studied the alterations of Elongation Factor 2 (eEF2) in the pineal gland of aged rats as well as the possible protective role of exogenous melatonin on these changes in young rats treated with cumene hydroperoxide (CH), a compound that promotes lipid peroxidation and inhibits protein synthesis. The study was performed using male Wistar rats of 3 (control), 12, and 24 months and 3‐month‐old rats treated with CH, melatonin, and CH plus melatonin. We found that pineal eEF‐2 is affected by aging and CH, these changes being prevented by exogenous melatonin in the case of CH‐treated rats. The proteomic studies show that many other proteins are affected by aging and oxidative stress in the pineal gland. The results suggest that one of the possible mechanisms underlying pineal gland dysfunction during aging is the effect of lipid peroxidation on eEF‐2, which is a key component of protein synthesis machinery. J. Cell. Biochem. 118: 182–190, 2017.

Cell tracking, survival, and differentiation capacity of adipose-derived stem cells after engraftment in rat tissue

Adipose tissue is an important source of adipose derived stem cells (ADSCs). These cells have the potential of being used for certain therapies, in which the main objective is to recover the function of a tissue/organ affected by a disease. In order to contribute to repair of the tissue, these cells should be able to survive and carry out their functions in unfavorable conditions after being transplanted. This process requires a better understanding of the biology involved: such as the time cells remain in the implant site, how long they stay there, and whether or not they differentiate into host tissue cells. This report focuses on these questions. ADSC were injected into three different tissues (substantia nigra, ventricle, liver) and they were tracked in vivo with a dual GFP‐Luc reporter system. The results show that ADSCs were able to survive up to 4 months after the engraftment and some of them started showing resident cell tissue phenotype. These results demonstrate their long‐term capacity of survival and differentiation when injected in vivo.