Circadian rhythm connections to oxidative stress: implications for human health

Relationships of salivary cortisol and melatonin rhythms to sleep quality, emotion, and fatigue levels in patients with newly diagnosed lung cancer

PURPOSE

After being diagnosed with lung cancer, patients often experience sleep disturbance, anxiety, depression, and fatigue. These symptoms may occur because of changes in neurotransmitter secretion caused by tumors. This study investigated the correlation of cortisol and melatonin rhythms with sleep quality, anxiety, depression, and fatigue levels in patients with newly diagnosed lung cancer.

METHOD

We conducted a case-control study and recruited 40 patients with newly diagnosed lung cancer and 40 healthy adults.

RESULTS

The patient group had a lower salivary melatonin level and flatter slope (p < 0.001 and p < 0.001), higher salivary cortisol level and steeper slope (p < 0.001 and p < 0.001), higher sleep disturbance level (p = 0.004), and higher depression level (p < 0.001). The multivariate linear regression analysis indicated that the cortisol slope (p = 0.005) and fatigue score (p = 0.032) predicted the sleep quality score (p = 0.011).

CONCLUSION

Overall, the patients with newly diagnosed lung cancer had poorer sleep quality, higher depression levels, lower salivary melatonin levels, higher cortisol levels, and flatter melatonin and cortisol slopes than did the controls. The fatigue level and cortisol slope significantly predicted sleep quality. Therefore, the assessment of cortisol and melatonin rhythms and levels could provide crucial information that may be beneficial for managing symptoms in patients with newly diagnosed lung cancer.

Differential menopause- versus aging-induced changes in oxidative stress and circadian rhythm gene markers

Menopause is characterized by the depletion of estrogen that has been proposed to cause oxidative stress. Circadian rhythm is an internal biological clock that controls physiological processes. It was analyzed the gene expression in peripheral blood mononuclear cells and the lipids and glucose levels in plasma of a subgroup of 17 pre-menopausal women, 19 men age-matched as control group for the pre-menopausal women, 20 post-menopausal women and 20 men age-matched as control group for the post-menopausal women; all groups were matched by body mass index. Our study showed a decrease in the expression of the oxidative stress-related gene GPX1, and an increase in the expression of SOD1 as consequence of menopause. In addition, we found that the circadian rhythm-related gene PER2 decreased as consequence of menopause. On the other hand, we observed a decrease in the expression of the oxidative stress-related gene GPX4 and an increase in the expression of CAT as a consequence of aging, independently of menopause. Our results suggest that the menopause-induced oxidative stress parallels a disruption in the circadian clock in women, and part of the differences in oxidative stress observed between pre- and post-menopausal women was due to aging, independent of menopause. Clinical Trials.gov.Identifier: NCT00924937.

Neurodegeneration and the Circadian Clock

Despite varied etiologies and symptoms, several neurodegenerative diseases—specifically, Alzheimer’s (AD), Parkinson’s (PD), and Huntington’s diseases (HDs)—share the common feature of abnormal circadian rhythms, such as those in behavior (e.g., disrupted sleep/wake cycles), physiological processes (e.g., diminished hormone release) and biochemical activities (e.g., antioxidant production). Circadian disturbances are among the earliest symptoms of these diseases, and the molecular mechanisms of the circadian system are suspected to play a pivotal, and possibly causal, role in their natural histories. Here, we review the common circadian abnormalities observed in ADs, PDs and HDs, and summarize the evidence that the molecular circadian clockwork directly influences the course of these disease states. On the basis of this research, we explore several circadian-oriented interventions proposed as treatments for these neurological disorders.

Cellular detection of 50 Hz magnetic fields and weak blue light: effects on superoxide levels and genotoxicity

PURPOSE

We tested the hypothesis that the effects of 50 Hz magnetic fields (MFs) on superoxide levels and genotoxicity depend on the presence of blue light.

MATERIALS AND METHODS

Human SH-SY5Y neuroblastoma cells were exposed to a 50 Hz, 100 μT MF with or without non-phototoxic level of blue light for 24 h. We also studied whether these treatments alter responses to menadione, an agent that induces mitochondrial superoxide (O₂^{• -}) production and DNA damage. Micronuclei, proliferation, viability, cytosolic and mitochondrial O₂^{• -} levels were assessed.

RESULTS

MF (without blue light) increased cytosolic O₂^{• -} production and blue light suppressed this effect. Mitochondrial O₂^{• -} production was reduced by both MF and blue light, but these effects were not additive. Micronucleus frequency was not affected by blue light or MF alone, but blue light (significantly when combined with MF) enhanced menadione-induced micronuclei.

CONCLUSIONS

The original simple hypothesis (blue light is needed for MF effects) was not supported, but interaction of MF and blue light was nevertheless observed. The results are consistent with MF effects on light-independent radical reactions.

Effect of Circadian Rhythm Disruption and Alcohol on the Oxidative Stress Level in Rat Brain

Alcohol abuse is often associated with disrupted circadian rhythms and sleep, and the link seems to be bidirectional. In addition, it has been shown that exposure to constant illumination may increase lipid peroxidation in tissues. In this study, we investigated the effects of circadian rhythm disruption (CRD) and chronic alcohol intake (A) alone and in combination (CRD+A), on the oxidative stress in total rat brain homogenate. Our results demonstrated that lipid peroxidation was increased in the brain samples of all experimental animals compared with the control ones. The oxidative stress levels increased in the order: C<CRD<A<(CRD+A). Furthermore, xanthine oxidase activity changed in the order: C<CRD<A=CRD+A. It was proposed that chronic alcohol intake, if accompanied with CRD, might lead to significantly higher lipid peroxidation in the brain, than if present alone. Our data suggest that ethanol metabolites may be involved in the increase of the brain xanthine oxidase activity in rats with chronic alcohol intake.

Prevalence of sleep bruxism and awake bruxism in different chronotype profiles: Hypothesis of an association

Sleep (SB) and awake bruxism (AB) recognize a multifactorial etiology and have a relationship with several psychological factors. Psychological disorders have recently been associated also with the chronotype, which is the propensity for an individual to be especially active at a particular time during a 24-h period. Based on the chronotype, the two extreme profiles are morningness and eveningness individuals. Due to the relationship that both the chronotype and bruxism have with psychological factors and the fact that performing tasks not compatible with chronotype can trigger stress, this review presents the hypothesis that the prevalence of SB and AB can differ with the various chronotype profiles. New perspectives for the study of bruxism etiology may emerge from investigations on the topic.

Influence of Quercetin in the Temporal Regulation of Redox Homeostasis in Drosophila melanogaster

Numerous biological processes are governed by the biological clock. Studies using Drosophila melanogaster (L.) are valuable that could be of importance for their effective applications on rodent studies. In this study, the beneficial role of quercetin (a flavonoid) on H2O2 induced stress in D. melanogaster was investigated. D. melanogaster flies were divided into four groups (group I - control, group II - H2O2 (acute exposure), group III - quercetin, and group IV - quercetin + H2O2 treated). Negative geotaxis assay, oxidative stress indicators (protein carbonyls, thiobarbituric reactive substances [TBARS]), and antioxidants (superoxide dismutase [SOD], catalase [CAT], glutathione-S-transferase [GST], glutathione peroxidase, and reduced glutathione [GSH]) were measured at 4 h intervals over 24 h and temporal expression of heat shock protein-70 (Hsp70), Upd1 (homolog of IL-6 in Drosophila), and nitric oxide synthase (Nos) was analyzed by Western blotting. Groups II and IV showed altered biochemical rhythms (compared with controls). Decreased mesor values of negative geotaxis, SOD, CAT, GST, and GSH were noticed in H2O2, increased mesor of oxidative stress indicators (TBARS and protein carbonyl content) and a reversibility of the rhythmic characteristics were conspicuous after quercetin treatment. The expression levels of Hsp70, Upd1, and Nos were noticeably maximum at 04:00. Significant elevation of expression by H2O2 was nearly normalized by quercetin treatment. The possible mechanism by which quercetin modulates oxidant-antioxidant imbalance under oxidative stress could be ascribed to the modulation of the rhythmic properties. Our results will be helpful to understand the molecular interlink between circadian rhythm and oxidative stress mechanism.

Impact of the Circadian Clock on UV-Induced DNA Damage Response and Photocarcinogenesis

The skin is in constant exposure to various external environmental stressors, including solar ultraviolet (UV) radiation. Various wavelengths of UV light are absorbed by the DNA and other molecules in the skin to cause DNA damage and induce oxidative stress. The exposure to excessive ultraviolet (UV) radiation and/or accumulation of damage over time can lead to photocarcinogenesis and photoaging. The nucleotide excision repair (NER) system is the sole mechanism for removing UV photoproduct damage from DNA, and genetic disruption of this repair pathway leads to the photosensitive disorder xeroderma pigmentosum (XP). Interestingly, recent work has shown that NER is controlled by the circadian clock, the body's natural time-keeping mechanism, through regulation of the rate-limiting repair factor xeroderma pigmentosum group A (XPA). Studies have shown reduced UV-induced skin cancer after UV exposure in the evening compared to the morning, which corresponds with times of high and low repair capacities, respectively. However, most studies of the circadian clock-NER connection have utilized murine models, and it is therefore important to translate these findings to humans to improve skin cancer prevention and chronotherapy.

Evening and morning peroxiredoxin-2 redox/oligomeric state changes in obstructive sleep apnea red blood cells: Correlation with polysomnographic and metabolic parameters

We have examined the effects of Obstructive Sleep Apnea (OSA) on red blood cell (RBC) proteome variation at evening/morning day time to uncover new insights into OSA-induced RBC dysfunction that may lead to OSA manifestations. Dysregulated proteins mainly fall in the group of catalytic enzymes, stress response and redox regulators such as peroxiredoxin 2 (PRDX2). Validation assays confirmed that at morning the monomeric/dimeric forms of PRDX2 were more overoxidized in OSA RBC compared to evening samples. Six month of positive airway pressure (PAP) treatment decreased this overoxidation and generated multimeric overoxidized forms associated with chaperone/transduction signaling activity of PRDX2. Morning levels of overoxidized PRDX2 correlated with polysomnographic (PSG)-arousal index and metabolic parameters whereas the evening level of disulfide-linked dimer (associated with peroxidase activity of PRDX2) correlated with PSG parameters. After treatment, morning overoxidized multimer of PRDX2 negatively correlated with fasting glucose and dopamine levels. Overall, these data point toward severe oxidative stress and altered antioxidant homeostasis in OSA RBC occurring mainly at morning time but with consequences till evening. The beneficial effect of PAP involves modulation of the redox/oligomeric state of PRDX2, whose mechanism and associated chaperone/transduction signaling functions deserves further investigation. RBC PRDX2 is a promising candidate biomarker for OSA severity and treatment monitoring, warranting further investigation and validation.

Assessment of lipid peroxidation by measuring malondialdehyde (MDA) and relatives in biological samples: Analytical and biological challenges

Malondialdehyde (MDA), 4-hydroxy-nonenal (HNE) and the F₂-isoprostane 15(S)-8-iso-prostaglandin F_2α (15(S)-8-iso-PGF_2α) are the best investigated products of lipid peroxidation. MDA, HNE and 15(S)-8-iso-PGF_2α are produced from polyunsaturated fatty acids (PUFAs) both by chemical reactions and by reactions catalyzed by enzymes. 15(S)-8-iso-PGF_2α and other F₂-isoprostanes are derived exclusively from arachidonic acid (AA). The number of PUFAs that may contribute to MDA and HNE is much higher. MDA is the prototype of the so called thiobarbituric acid reactive substances (TBARS). MDA, HNE and 15(S)-8-iso-PGF_2α are the most frequently measured biomarkers of oxidative stress, namely of lipid peroxidation. In many diseases, higher concentrations of MDA, HNE and 15(S)-8-iso-PGF_2α are measured in biological samples as compared to health. Therefore, elevated oxidative stress is generally regarded as a pathological condition. Decreasing the concentration of biomarkers of oxidative stress by changing life style, by nutritional intake of antioxidants or by means of drugs is generally believed to be beneficial to health. Reliable assessment of oxidative stress by measuring MDA, HNE and 15(S)-8-iso-PGF_2α in biological fluids is highly challenging for two important reasons: Because of the duality of oxidative stress, i.e., its origin from chemical and enzymatic reactions, and because of pre-analytical and analytical issues. This article focuses on these key issues. It reviews reported analytical methods and their principles for the quantitative measurement of MDA, HNE and 15(S)-8-iso-PGF_2α in biological samples including plasma and urine, and critically discusses their biological and biomedical outcome which is rarely crystal clear and free of artefacts.

4-Hydroxyisophthalic acid from Decalepis hamiltonii rescues the neurobehavioral deficit in transgenic Drosophila model of taupathies

Oxidative stress is one of the major etiological factors implicated in pathogenesis of neurodegenerative diseases. Since neurons are more sensitive to oxidative damage there is an increasing interest in developing novel antioxidant therapies, especially herbal preparations due to their safety profile and high efficiency. In this regard, the neuroprotective potential of a novel antioxidant compound, 4-hydroxyisophthalic acid (4-HIPA) isolated from aqueous extract of Decalepis hamiltonii roots was examined using transgenic Drosophila model of taupathy expressing wild-type and mutant forms of 2N4R isoform of human microtubule associated protein tau (MAPT). Taupathy model flies showed cognitive deficits in olfactory memory and deteriorated circadian rhythm of locomotory activities. Administration of 0.1 mg/ml 4-HIPA, markedly enhanced their olfactory memory performance and restored circadian rhythmicity of the transgenic flies locomotory behavior to the normal range. The mechanism of action that underlies 4-HIPA neuroprotection involves enhancement in efficiency of cellular antioxidant defense system by means of elevation in antioxidant enzyme activities and attenuation of oxidative stress. The molecule could positively affect the activity of neurotransmitter enzymes, which in turn enhances neuronal function and ameliorates the Tau-induced neurobehavioral deficits. Our findings showed that 4-HIPA can be considered as a suitable therapeutic candidate for drug development towards treatment of neurodegenerative disorders.

Effect of LED photobiomodulation on fluorescent light induced changes in cellular ATPases and Cytochrome c oxidase activity in Wistar rat

BACKGROUND

Fluorescent light exposure at night alters cellular enzyme activities resulting in health defects. Studies have demonstrated that light emitting diode photobiomodulation enhances cellular enzyme activities.

OBJECTIVE

The objectives of this study are to evaluate the effects of fluorescent light induced changes in cellular enzymes and to assess the protective role of pre exposure to 670 nm LED in rat model.

METHODS

Male Wistar albino rats were divided into 10 groups of 6 animals each based on duration of exposure (1, 15, and 30 days) and exposure regimen (cage control, exposure to fluorescent light [1800 lx], LED preexposure followed by fluorescent light exposure and only LED exposure). Na⁺-K⁺ ATPase, Ca²⁺ ATPase, and cytochrome c oxidase of the brain, heart, kidney, liver, and skeletal muscle were assayed.

RESULTS

Animals of the fluorescent light exposure group showed a significant reduction in Na⁺-K⁺ ATPase and Ca²⁺ ATPase activities in 1 and 15 days and their increase in animals of 30-day group in most of the regions studied. Cytochrome c oxidase showed increase in their level at all the time points assessed in most of the tissues. LED light preexposure showed a significant enhancement in the degree of increase in the enzyme activities in almost all the tissues and at all the time points assessed.

CONCLUSIONS

This study demonstrates the protective effect of 670 nm LED pre exposure on cellular enzymes against fluorescent light induced change.

Circadian Rhythms of Oxidative Stress Markers and Melatonin Metabolite in Patients with Xeroderma Pigmentosum Group A

Xeroderma pigmentosum group A (XPA) is a genetic disorder in DNA nucleotide excision repair (NER) with severe neurological disorders, in which oxidative stress and disturbed melatonin metabolism may be involved. Herein we confirmed the diurnal variation of melatonin metabolites, oxidative stress markers, and antioxidant power in urine of patients with XPA and age-matched controls, using enzyme-linked immunosorbent assay (ELISA). The peak of 6-sulfatoxymelatonin, a metabolite of melatonin, was seen at 6:00 in both the XPA patients and controls, though the peak value is lower, specifically in the younger age group of XPA patients. The older XPA patients demonstrated an increase in the urinary levels of 8-hydroxy-2'-deoxyguanosine and hexanoyl-lysine, a marker of oxidative DNA damage and lipid peroxidation, having a robust peak at 6:00 and 18:00, respectively. In addition, the urinary level of total antioxidant power was decreased in the older XPA patients. Recently, it is speculated that oxidative stress and antioxidant properties may have a diurnal variation, and the circadian rhythm is likely to influence the NER itself. We believe that the administration of melatonin has the possibility of ameliorating the augmented oxidative stress in neurodegeneration, especially in the older XPA patients, modulating the melatonin metabolism and the circadian rhythm.

Potential Utility of Melatonin in Preeclampsia, Intrauterine Fetal Growth Retardation, and Perinatal Asphyxia

AIM

Reactive oxygen species play an important role in the pathogenesis of several diseases during gestation and the perinatal period. During pregnancy, increased oxygen demand augments the rate of production of free radicals. Oxidative stress is involved in pregnancy disorders including preeclampsia and intrauterine fetal growth retardation (IUGR). Moreover, increased levels of oxidative stress and reduced antioxidative capacities may contribute to the pathogenesis of perinatal asphyxia. Melatonin, an efficient antioxidant agent, diffuses through biological membranes easily and exerts pleiotropic actions on every cell and appears to be essential for successful gestation. This narrative review summarizes current knowledge concerning the role of melatonin in reducing complications during human pregnancy and in the perinatal period.

RESULTS

Melatonin levels are altered in women with abnormally functioning placentae during preeclampsia and IUGR. Short-term melatonin therapy is highly effective and safe in reducing complications during pregnancy and in the perinatal period. Because melatonin has been shown to be safe for both mother and fetus, it could be an attractive therapy in pregnancy and is considered a promising neuroprotective agent in perinatal asphyxia.

CONCLUSION

We believe that the use of melatonin treatment during the late fetal and early neonatal period might result in a wide range of health benefits, improved quality of life, and may help limit complications during the critical periods prior to, and shortly after, delivery.

Association of ARNTL and PER1 genes with Parkinson's disease: a case-control study of Han Chinese

Circadian disruptions may result in sleep problems, oxidative stress and an altered inflammatory response. These symptoms may contribute to PD pathogenesis, despite a lack of direct experimental evidence supporting this relationship. Clock genes are essential to drive and maintain circadian rhythm. To elucidate the possible role of circadian disruptions in PD, we investigated 132 tag variants in eight clock genes. We genotyped these tags within 1,394 Chinese cases and 1,342 controls using Illumina GoldenGate chips. We discovered that SNPs in ARNTL (rs900147, P = 3.33 × 10(-5), OR = 0.80) and PER1 (rs2253820, P = 5.30 × 10(-6), OR = 1.31) genes are significantly associated with PD risk. Moreover, the positive association of the ARNTL rs900147 variant was more robust in tremor dominant (TD) (P = 3.44 × 10(-4)) than postural instability and gait difficulty (PIGD) cases (P = 6.06 × 10(-2)). The association of the PER1 rs2253820 variant was more robust in PIGD (P = 5.42 × 10(-5)) than TD cases (P = 4.2 × 10(-2)). Haplotype analysis also showed that ARNTL and PER1 were associated with PD. Imputation analysis identified more SNPs within ARNTL and PER1 associated with PD, some of which may affect gene expression through altering the transcription factor binding site. In summary, our findings suggest that genetic polymorphisms in ARNTL and PER1 genes, as well as circadian disruptions, may contribute to PD pathogenesis.

Non-alcoholic fatty liver disease as a consequence of autonomic imbalance and circadian desynchronization

The circadian system, headed by the suprachiasmatic nucleus, synchronizes behaviour and metabolism according to the external light-dark cycle through neuroendocrine and autonomic signals. Metabolic diseases, such as steatosis, obesity and glucose intolerance, have been associated with conditions of circadian misalignment wherein the feeding schedule has been moved to the resting phase. Here we describe the physiological processes involved in liver lipid accumulation and show how they follow a circadian pattern importantly regulated by both the autonomic nervous system and the feeding-fasting cycle. We propose that an unbalanced activity of the sympathetic-parasympathetic branches between organs induced by circadian misalignment provides the conditions for the development and progression of non-alcoholic fatty liver disease.

The Redox Code

SIGNIFICANCE

The redox code is a set of principles that defines the positioning of the nicotinamide adenine dinucleotide (NAD, NADP) and thiol/disulfide and other redox systems as well as the thiol redox proteome in space and time in biological systems. The code is richly elaborated in an oxygen-dependent life, where activation/deactivation cycles involving O₂ and H₂O₂ contribute to spatiotemporal organization for differentiation, development, and adaptation to the environment. Disruption of this organizational structure during oxidative stress represents a fundamental mechanism in system failure and disease.

RECENT ADVANCES

Methodology in assessing components of the redox code under physiological conditions has progressed, permitting insight into spatiotemporal organization and allowing for identification of redox partners in redox proteomics and redox metabolomics.

CRITICAL ISSUES

Complexity of redox networks and redox regulation is being revealed step by step, yet much still needs to be learned.

FUTURE DIRECTIONS

Detailed knowledge of the molecular patterns generated from the principles of the redox code under defined physiological or pathological conditions in cells and organs will contribute to understanding the redox component in health and disease. Ultimately, there will be a scientific basis to a modern redox medicine.

Nuclear redox imbalance affects circadian oscillation in HaCaT keratinocytes

Circadian clock is regulated by a transcriptional/translational feedback loop (TTFL) lasting ∼24 h. Circadian oscillation of peroxiredoxins (PRDX1-6) redox status has been shown in mature erythrocytes. We have recently reported that nuclear levels of PRDX2 are circadian regulated in the HaCaT keratinocytes. In this study, we addressed whether PRDX2 translocation could influence the TTFL. A reporter HaCaT cell line stably expressing the luciferase gene under control of Bmal1 promoter was lentivirally transduced either with an empty vector (EV), a vector carrying a myc-tagged wild type PRDX2 (PRDX2-Myc) or the same gene with a nuclear localization sequence (PRDX2-MycNuc). PRDX2 overexpressing cells were protected from H2O2-induced oxidative stress. The amplitude of the Bmal1 promoter activity was significantly dampened in PRDX2-MycNuc versus EV cells when synchronized either by dexamethasone treatment or temperature cycles. Clock synchronization was not affected in PRDX2 silenced cells. N-acetyl cysteine or melatonin treatments, significantly dampened the Bmal1 promoter activity suggesting that sustained scavenging of ROS impairs clock synchronization. Noteworthy, H2O2 treatment rescued proper oscillation of the clock in synchronized PRDX2-MycNuc HaCaT cells. Since the histone deacetylase Sirtuin 1 (Sirt1) modulates clock gene expression amplitude, the effect of Sirt1 activator resveratrol or Sirt1 inhibitor nicotinamide were also investigated. Interestingly, NAM enhanced the molecular clock synchronization in PRDX2-MycNuc cells. Our findings demonstrate that PRDX2 regulates the TTFL oscillation by finely tuning the cellular redox status of the nucleus likely influencing the deacetilase activity of SIRT1 enzyme.

Circadian redox oscillations and metabolism

Circadian rhythms are 24h oscillations in physiology and behavior which allow organisms to anticipate and adapt to daily demands associated with the day/night cycle. The currently accepted model of the molecular clockwork is described as a transcriptional process composed of negative regulatory feedback loops. However, ample evidence underlines the important contribution of non-transcriptional and metabolic oscillations to cellular timekeeping. We summarize recent evidence pointing to the relationship between the transcriptional oscillator and metabolic redox state, with particular emphasis on the potential nodes of interaction. We highlight the intrinsic difficulty in segregating these two tightly coupled and interdependent processes, in living systems, and how disruption of their synchronicity impacts upon (patho)physiological processes as diverse as cardiovascular and metabolic disorders, aging, and cancer.

Circadian rhythms, alcohol and gut interactions

The circadian clock establishes rhythms throughout the body with an approximately 24 hour period that affect expression of hundreds of genes. Epidemiological data reveal chronic circadian misalignment, common in our society, significantly increases the risk for a myriad of diseases, including cardiovascular disease, diabetes, cancer, infertility and gastrointestinal disease. Disruption of intestinal barrier function, also known as gut leakiness, is especially important in alcoholic liver disease (ALD). Several studies have shown that alcohol causes ALD in only a 20-30% subset of alcoholics. Thus, a better understanding is needed of why only a subset of alcoholics develops ALD. Compelling evidence shows that increased gut leakiness to microbial products and especially LPS play a critical role in the pathogenesis of ALD. Clock and other circadian clock genes have been shown to regulate lipid transport, motility and other gut functions. We hypothesized that one possible mechanism for alcohol-induced intestinal hyperpermeability is through disruption of central or peripheral (intestinal) circadian regulation. In support of this hypothesis, our recent data shows that disruption of circadian rhythms makes the gut more susceptible to injury. Our in vitro data show that alcohol stimulates increased Clock and Per2 circadian clock proteins and that siRNA knockdown of these proteins prevents alcohol-induced permeability. We also show that intestinal Cyp2e1-mediated oxidative stress is required for alcohol-induced upregulation of Clock and Per2 and intestinal hyperpermeability. Our mouse model of chronic alcohol feeding shows that circadian disruption through genetics (in Clock(▵19) mice) or environmental disruption by weekly 12h phase shifting results in gut leakiness alone and exacerbates alcohol-induced gut leakiness and liver pathology. Our data in human alcoholics show they exhibit abnormal melatonin profiles characteristic of circadian disruption. Taken together our data support circadian mechanisms for alcohol-induced gut leakiness that could provide new therapeutic targets for ALD.

Redox regulation and pro-oxidant reactions in the physiology of circadian systems

Rhythms of approximately 24 h are pervasive in most organisms and are known as circadian. There is a molecular circadian clock in each cell sustained by a feedback system of interconnected "clock" genes and transcription factors. In mammals, the timing system is formed by a central pacemaker, the suprachiasmatic nucleus, in coordination with a collection of peripheral oscillators. Recently, an extensive interconnection has been recognized between the molecular circadian clock and the set of biochemical pathways that underlie the bioenergetics of the cell. A principle regulator of metabolic networks is the flow of electrons between electron donors and acceptors. The concomitant reduction and oxidation (redox) reactions directly influence the balance between anabolic and catabolic processes. This review summarizes and discusses recent findings concerning the mutual and dynamic interactions between the molecular circadian clock, redox reactions, and redox signaling. The scope includes the regulatory role played by redox coenzymes (NAD(P)+/NAD(P)H, GSH/GSSG), reactive oxygen species (superoxide anion, hydrogen peroxide), antioxidants (melatonin), and physiological events that modulate the redox state (feeding condition, circadian rhythms) in determining the timing capacity of the molecular circadian clock. In addition, we discuss a purely metabolic circadian clock, which is based on the redox enzymes known as peroxiredoxins and is present in mammalian red blood cells and in other biological systems. Both the timing system and the metabolic network are key to a better understanding of widespread pathological conditions such as the metabolic syndrome, obesity, and diabetes.

Drosophila melanogaster show a threshold effect in response to radiation

We investigate the biological effects of radiation using adult Drosophila melanogaster as a model organism, focusing on gene expression and lifespan analysis to determine the effect of different radiation doses. Our results support a threshold effect in response to radiation: no effect on lifespan and no permanent effect on gene expression is seen at incident radiation levels below 100 J/kg. We also find that it is more appropriate to compare radiation effects in flies using the absorbed energy rather than incident radiation levels.

Intestinal CYP2E1: A mediator of alcohol-induced gut leakiness

Chronic alcohol use can result in many pathological effects including alcoholic liver disease (ALD). While alcohol is necessary for the development of ALD, only 20-30% of alcoholics develop alcoholic steatohepatitis (ASH) with progressive liver disease leading to cirrhosis and liver failure (ALD). This suggests that while chronic alcohol consumption is necessary it is not sufficient to induce clinically relevant liver damage in the absence of a secondary risk factor. Studies in rodent models and alcoholic patients show that increased intestinal permeability to microbial products like endotoxin play a critical role in promoting liver inflammation in ALD pathogenesis. Therefore identifying mechanisms of alcohol-induced intestinal permeability is important in identifying mechanisms of ALD and for designing new avenues for therapy. Cyp2e1 is a cytochrome P450 enzyme that metabolizes alcohol has been shown to be upregulated by chronic alcohol use and to be a major source of oxidative stress and liver injury in alcoholics and in animal and in vitro models of chronic alcohol use. Because Cyp2e1 is also expressed in the intestine and is upregulated by chronic alcohol use, we hypothesized it could play a role in alcohol-induced intestinal hyperpermeability. Our in vitro studies with intestinal Caco-2 cells and in mice fed alcohol showed that circadian clock proteins CLOCK and PER2 are required for alcohol-induced permeability. We also showed that alcohol increases Cyp2e1 protein and activity but not mRNA in Caco-2 cells and that an inhibitor of oxidative stress or siRNA knockdown of Cyp2e1 prevents the increase in CLOCK or PER2 proteins and prevents alcohol-induced hyperpermeability. With our collaborators we have also shown that Cyp2e1 knockout mice are resistant to alcohol-induced gut leakiness and liver inflammation. Taken together our data support a novel Cyp2e1-circadian clock protein mechanism for alcohol-induced gut leakiness that could provide new avenues for therapy of ALD.

Local melatoninergic system as the protector of skin integrity

The human skin is not only a target for the protective actions of melatonin, but also a site of melatonin synthesis and metabolism, suggesting an important role for a local melatoninergic system in protection against ultraviolet radiation (UVR) induced damages. While melatonin exerts many effects on cell physiology and tissue homeostasis via membrane bound melatonin receptors, the strong protective effects of melatonin against the UVR-induced skin damage including DNA repair/protection seen at its high (pharmocological) concentrations indicate that these are mainly mediated through receptor-independent mechanisms or perhaps through activation of putative melatonin nuclear receptors. The destructive effects of the UVR are significantly counteracted or modulated by melatonin in the context of a complex intracutaneous melatoninergic anti-oxidative system with UVR-enhanced or UVR-independent melatonin metabolites. Therefore, endogenous intracutaneous melatonin production, together with topically-applied exogenous melatonin or metabolites would be expected to represent one of the most potent anti-oxidative defense systems against the UV-induced damage to the skin. In summary, we propose that melatonin can be exploited therapeutically as a protective agent or as a survival factor with anti-genotoxic properties or as a “guardian” of the genome and cellular integrity with clinical applications in UVR-induced pathology that includes carcinogenesis and skin aging.

A hypomagnetic field aggravates bone loss induced by hindlimb unloading in rat femurs

A hypomagnetic field is an extremely weak magnetic field--it is considerably weaker than the geomagnetic field. In deep-space exploration missions, such as those involving extended stays on the moon and interplanetary travel, astronauts will experience abnormal space environments involving hypomagnetic fields and microgravity. It is known that microgravity in space causes bone loss, which results in decreased bone mineral density. However, it is unclear whether hypomagnetic fields affect the skeletal system. In the present study, we aimed to investigate the complex effects of a hypomagnetic field and microgravity on bone loss. To study the effects of hypomagnetic fields on the femoral characteristics of rats in simulated weightlessness, we established a rat model of hindlimb unloading that was exposed to a hypomagnetic field. We used a geomagnetic field-shielding chamber to generate a hypomagnetic field of <300 nT. The results show that hypomagnetic fields can exacerbate bone mineral density loss and alter femoral biomechanical characteristics in hindlimb-unloaded rats. The underlying mechanism might involve changes in biological rhythms and the concentrations of trace elements due to the hypomagnetic field, which would result in the generation of oxidative stress responses in the rat. Excessive levels of reactive oxygen species would stimulate osteoblasts to secrete receptor activator of nuclear factor-κB ligand and promote the maturation and activation of osteoclasts and thus eventually cause bone resorption.

Alpha-lipoic acid as a pleiotropic compound with potential therapeutic use in diabetes and other chronic diseases

Alpha-lipoic acid is a naturally occurring substance, essential for the function of different enzymes that take part in mitochondria's oxidative metabolism. It is believed that alpha-lipoic acid or its reduced form, dihydrolipoic acid have many biochemical functions acting as biological antioxidants, as metal chelators, reducers of the oxidized forms of other antioxidant agents such as vitamin C and E, and modulator of the signaling transduction of several pathways. These above-mentioned actions have been shown in experimental studies emphasizing the use of alpha-lipoic acid as a potential therapeutic agent for many chronic diseases with great epidemiological as well economic and social impact such as brain diseases and cognitive dysfunctions like Alzheimer disease, obesity, nonalcoholic fatty liver disease, burning mouth syndrome, cardiovascular disease, hypertension, some types of cancer, glaucoma and osteoporosis. Many conflicting data have been found concerning the clinical use of alpha-lipoic acid in the treatment of diabetes and of diabetes-related chronic complications such as retinopathy, nephropathy, neuropathy, wound healing and diabetic cardiovascular autonomic neuropathy. The most frequent clinical condition in which alpha-lipoic acid has been studied was in the management of diabetic peripheral neuropathy in patients with type 1 as well type 2 diabetes. Considering that oxidative stress, a imbalance between pro and antioxidants with excessive production of reactive oxygen species, is a factor in the development of many diseases and that alpha-lipoic acid, a natural thiol antioxidant, has been shown to have beneficial effects on oxidative stress parameters in various tissues we wrote this article in order to make an up-to-date review of current thinking regarding alpha-lipoic acid and its use as an antioxidant drug therapy for a myriad of diseases that could have potential benefits from its use.

Skin, reactive oxygen species, and circadian clocks

SIGNIFICANCE

Skin, a complex organ and the body's first line of defense against environmental insults, plays a critical role in maintaining homeostasis in an organism. This balance is maintained through a complex network of cellular machinery and signaling events, including those regulating oxidative stress and circadian rhythms. These regulatory mechanisms have developed integral systems to protect skin cells and to signal to the rest of the body in the event of internal and environmental stresses.

RECENT ADVANCES

Interestingly, several signaling pathways and many bioactive molecules have been found to be involved and even important in the regulation of oxidative stress and circadian rhythms, especially in the skin. It is becoming increasingly evident that these two regulatory systems may, in fact, be interconnected in the regulation of homeostasis. Important examples of molecules that connect the two systems include serotonin, melatonin, vitamin D, and vitamin A.

CRITICAL ISSUES

Excessive reactive oxygen species and/or dysregulation of antioxidant system and circadian rhythms can cause critical errors in maintaining proper barrier function and skin health, as well as overall homeostasis. Unfortunately, the modern lifestyle seems to contribute to increasing alterations in redox balance and circadian rhythms, thereby posing a critical problem for normal functioning of the living system.

FUTURE DIRECTIONS

Since the oxidative stress and circadian rhythm systems seem to have areas of overlap, future research needs to be focused on defining the interactions between these two important systems. This may be especially important in the skin where both systems play critical roles in protecting the whole body.

Does disruption of circadian rhythms contribute to beta-cell failure in type 2 diabetes?

Type 2 diabetes mellitus (T2DM) is a complex metabolic disease characterized by the loss of beta-cell secretory function and mass. The pathophysiology of beta-cell failure in T2DM involves a complex interaction between genetic susceptibilities and environmental risk factors. One environmental condition that is gaining greater appreciation as a risk factor for T2DM is the disruption of circadian rhythms (eg, shift-work and sleep loss). In recent years, circadian disruption has become increasingly prevalent in modern societies and consistently shown to augment T2DM susceptibility (partly mediated through its effects on pancreatic beta-cells). Since beta-cell failure is essential for development of T2DM, we will review current work from epidemiologic, clinical, and animal studies designed to gain insights into the molecular and physiological mechanisms underlying the predisposition to beta-cell failure associated with circadian disruption. Elucidating the role of circadian clocks in regulating beta-cell health will add to our understanding of T2DM pathophysiology and may contribute to the development of novel therapeutic and preventative approaches.

The hallmarks of fibroblast ageing

Ageing is influenced by the intrinsic disposition delineating what is maximally possible and extrinsic factors determining how that frame is individually exploited. Intrinsic and extrinsic ageing processes act on the dermis, a post-mitotic skin compartment mainly consisting of extracellular matrix and fibroblasts. Dermal fibroblasts are long-lived cells constantly undergoing damage accumulation and (mal-)adaptation, thus constituting a powerful indicator system for human ageing. Here, we use the systematic of ubiquitous hallmarks of ageing (Lopez-Otin et al., 2013, Cell 153) to categorise the available knowledge regarding dermal fibroblast ageing. We discriminate processes inducible in culture from phenomena apparent in skin biopsies or primary cells from old donors, coming to the following conclusions: (i) Fibroblasts aged in culture exhibit most of the established, ubiquitous hallmarks of ageing. (ii) Not all of these hallmarks have been detected or investigated in fibroblasts aged in situ (in the skin). (iii) Dermal fibroblasts aged in vitro and in vivo exhibit additional features currently not considered ubiquitous hallmarks of ageing. (iv) The ageing process of dermal fibroblasts in their physiological tissue environment has only been partially elucidated, although these cells have been a preferred model of cell ageing in vitro for decades.

Role for intestinal CYP2E1 in alcohol-induced circadian gene-mediated intestinal hyperpermeability

We have shown that alcohol increases Caco-2 intestinal epithelial cell monolayer permeability in vitro by inducing the expression of redox-sensitive circadian clock proteins CLOCK and PER2 and that these proteins are necessary for alcohol-induced hyperpermeability. We hypothesized that alcohol metabolism by intestinal Cytochrome P450 isoform 2E1 (CYP2E1) could alter circadian gene expression (Clock and Per2), resulting in alcohol-induced hyperpermeability. In vitro Caco-2 intestinal epithelial cells were exposed to alcohol, and CYP2E1 protein, activity, and mRNA were measured. CYP2E1 expression was knocked down via siRNA and alcohol-induced hyperpermeability, and CLOCK and PER2 protein expression were measured. Caco-2 cells were also treated with alcohol or H₂O₂ with or without N-acetylcysteine (NAC) anti-oxidant, and CLOCK and PER2 proteins were measured at 4 or 2 h. In vivo Cyp2e1 protein and mRNA were also measured in colon tissue from alcohol-fed mice. Alcohol increased CYP2E1 protein by 93% and enzyme activity by 69% in intestinal cells in vitro. Alcohol feeding also increased mouse colonic Cyp2e1 protein by 73%. mRNA levels of Cyp2e1 were not changed by alcohol in vitro or in mouse intestine. siRNA knockdown of CYP2E1 in Caco-2 cells prevented alcohol-induced hyperpermeability and induction of CLOCK and PER2 proteins. Alcohol-induced and H₂O₂-induced increases in intestinal cell CLOCK and PER2 were significantly inhibited by treatment with NAC. We concluded that our data support a novel role for intestinal CYP2E1 in alcohol-induced intestinal hyperpermeability via a mechanism involving CYP2E1-dependent induction of oxidative stress and upregulation of circadian clock proteins CLOCK and PER2.

Antioxidants meet molecular targets for cancer prevention and therapeutics

A fine balance between oxidants and antioxidants is required for the normal functioning of living systems. A deregulation of this balance has been implicated in many adverse effects and diseases, including cancer. Extensive research has been done in the area of cancer prevention and therapeutics by a wide range of antioxidants, especially naturally occurring and diet-based agents. However, additional efforts are still needed toward clinical development of the most promising antioxidant agents. For this purpose, it is important to focus our efforts toward (i) defining/validating new targets; (ii) identifying novel agents followed by assessments of their efficacy, safety/toxicity, metabolism, and bioavailability in appropriate model systems; and (iii) conducting clinical trials in an appropriate population. Although research with specific antioxidants is important, an emerging critical issue that is up for a debate is whether the "whole foods" concept is better for cancer prevention than a single agent. Recent work has suggested that the dietary phytochemicals can enhance the bioavailability of different nutrients and can target multiple molecular pathways to yield a better response. Another critical issue that is often ignored during target-based agent development is a lack of focus on the appropriate population for a specific target. It is possible that a specific target may not be appropriate for certain people. Further, we need to design quick "phase 0" clinical trials to eliminate the agents with little clinical potential. Thus, multidisciplinary efforts of researchers from diverse scientific disciplines are needed in order to take the most promising antioxidant agents from the bench to the bedside.