Environmental exposure, obesity, and Parkinson's disease: lessons from fat and old worms

Polychlorinated biphenyls and risk of metabolic syndrome and comparison with the risk of diabetes: A systematic review and meta-analysis

With the increasing incidence of metabolic syndrome (MetS) worldwide and no consistent results on PCBs and MetS. A meta-analysis to explore their relationship was conducted. Given the high correlation and overlap of MetS with diabetes, analysis of diabetes risk, was used as a supplement to compare with MetS. Seven studies included MetS, 15 studies for diabetes, and one study included both outcomes. It was found that PCBs may not be a risk factor for MetS, but their high heterogeneity indicates that they are under-represented. In addition, our results showed that total PCBs might be a protective factor against diabetes. In the whole blood subgroup, which can reflect the accumulation of more than one body load, heterogeneity was reduced, and its OR value suggested that PCBs increased the risk of MetS in the whole blood biomaterial. DL-PCBs were positively associated with MetS and diabetes, while NDL-PCBs were negatively associated with diabetes. In the subgroup analysis of PCBs homologs, DL-PCB-126 and DL-PCB-118 were risk factors for MetS and diabetes, respectively. In addition, PCB-153 and 180 showed a dose-response relationship between them and diabetes mellitus, respectively. The results of total analysis of MetS and diabetes mellitus and subgroup analysis of PCBs were mixed, and this reason might be attributed to the different mechanisms of action and effect sizes of different PCBs, so based on subgroup results and in vivo and in vitro experiments, we considered PCBs to be a risk factor for MetS and diabetes. Due to various reasons, there are still many shortcomings in the evaluation of PCBs impact on human health, and more high-quality research are needed to further explore the role of PCBs of different species and congeners in MetS and diabetes.

Evaluation of Carnosine Intervention in the Thy1-aSyn Mouse Model of Parkinson's Disease

Parkinson disease (PD) is a leading neurodegenerative disease, with multifaceted interacting mechanisms. The Thy1-aSyn mouse model of PD exhibits many features of PD patients, including sensorimotor and olfactory dysfunction and protein aggregation. Here, we tested the hypothesis that the dipeptide carnosine, which has anti-aggregating and metal-chelating properties, would provide beneficial effects on the motor and olfactory deficits observed in Thy1-aSyn mice. After 2 months of daily treatment with either intranasal (2 mg/day) or oral (10 mM in drinking water) carnosine, Thy1-aSyn mice and wild-type BDF1 mice were assessed for sensorimotor (challenging beam traversal test and spontaneous activity) and olfactory (buried pellet test) function. In addition, the olfactory epithelium was evaluated immunohistochemically for expression of alpha-synuclein (aSyn) and the carnosine transporter Pept2. Olfactory function was unaffected by carnosine treatment via either administration route. In contrast, intranasal carnosine prevented the normal decline in gait function seen in the challenging beam test in the Thy1-aSyn mice. Moreover, carnosine-treated Thy1-aSyn mice exhibited decreased aSyn immunostaining in the olfactory epithelium compared to vehicle-treated Thy1-aSyn mice, and the carnosine transporter Pept2 was immunolocalized to the apical surface of the olfactory epithelium. These findings demonstrate that intranasal carnosine shows promise in slowing the progression of motor deficits and aSyn deposition in PD.

Organotins in obesity and associated metabolic disturbances

The objective of the present study was to review the mechanisms of organotin-induced adipogenesis, obesity, and associated metabolic disturbances. Peroxisome proliferator-activated receptor γ (PPARγ) and retinoid X receptor α (RXRα) activation is considered as the key mechanism of organotin-induced adipogenesis. Particularly, organotin exposure results in increased adipogenesis both in cell and animal models. Moreover, transgenerational inheritance of organotin-induced obese phenotype was demonstrated in vivo. At the same time, the existing data demonstrate that organotin compounds (OTCs) induces aberrant expression of PPARγ-targeted genes, resulting in altered of adipokine, glucose transporter, proinflammatory cytokines levels, and lipid and carbohydrate metabolism. The latter is generally characterized by hyperglycemia and insulin resistance. Other mechanisms involved in organotin-induced obesity may include estrogen receptor and corticosteroid signaling, altered DNA methylation, and gut dysfunction. In addition to cellular effects, organotin exposure may also affect neural circuits of appetite regulation, being characterized by neuropeptide Y (NPY) up-regulation in parallel with of pro-opiomelanocortin (POMC), Agouti-related protein (AgRP), and cocaine and amphetamine regulated transcript (CART) down-regulation in the arcuate nucleus. These changes result in increased orexigenic and reduced anorexigenic signaling, leading to increased food intake. The existing data demonstrate that organotins are potent adipogenic agents, however, no epidemiologic studies have been performed to reveal the association between organotin exposure and obesity and the existing indirect human data are contradictory.

Adiposity Genetic Risk Score Modifies the Association Between Blood Lead Level and Body Mass Index

CONTEXT

Previous epidemiological studies had inconsistent results regarding the relationship between blood lead level (BLL) and adiposity.

OBJECTIVE

We aimed to investigate the associations of BLL with body mass index (BMI) particularly using Mendelian randomization analyses and examine the interaction between obesity-predisposing genes and BLL on the associations.

DESIGN AND SETTING

A total of 3922 participants were enrolled from 16 sites in East China in 2014 from the Survey on Prevalence in East China for Metabolic Diseases and Risk Factors (ChiCTR-ECS-14005052, www.chictr.org.cn). We calculated the weighted BMI genetic risk score (GRS) based on 29 variants that were identified and validated in East Asians. BLL was measured by atomic absorption spectrometry.

MAIN OUTCOME MEASURE

BMI was calculated, and BMI ≥25 kg/m2 was defined as overweight.

RESULTS

Multivariable logistic regression analysis demonstrated significant associations between BMI with each unit increase in lnBLL (β = 0.24; 95% CI, 0.08 to 0.40; P < 0.001) and each 1-point increase in BMI-GRS (β = 0.08; 95% CI, 0.05 to 0.11; P < 0.001). The causal regression coefficients of genetically determined BMI for lnBLL were -0.003 (95% CI, -0.075 to 0.070), which showed no significance. The GRS modified the association of BLL with BMI and overweight (BMI ≥25 kg/m2; P for interaction = 0.031 and 0.001, respectively). Each unit of lnBLL was associated with 63% higher odds of overweight (OR 1.63; 95% CI, 1.30 to 2.05) in the highest quartile of GRS, but no significant associations were found in the lower three quartiles.

CONCLUSIONS

The associations of BLL with BMI and overweight (BMI ≥25 kg/m2) were significantly modulated by BMI genetic susceptibility.

Assessment of Cognitive Impairment in a Mouse Model of High-Fat Diet-Induced Metabolic Stress with Touchscreen-Based Automated Battery System

Obesity-related metabolic disorders can affect not only systemic health but also brain function. Recent studies have elucidated that amyloid beta deposition cannot satisfactorily explain the development of Alzheimer's disease (AD) and that dysregulation of glucose metabolism is a critical factor for the sporadic onset of non-genetic AD. Identifying the pathophysiology of AD due to changes in brain metabolism is crucial; however, it is limited in measuring changes in brain cognitive function due to metabolic changes in animal models. The touchscreen-based automated battery system, which is more accurate and less invasive than conventional behavioral test tools, is used to assess the cognition of mice with dysregulated metabolism. This system was introduced in humans to evaluate cognitive function and was recently back-translated in monkeys and rodents. We used outbred ICR mice fed on high-fat diet (HFD) and performed the paired associates learning (PAL) test to detect their visual memory and new learning ability loss as well as to assess memory impairment. The behavioral performance of the HFD mice was weaker than that of normal mice in the training but was not significantly associated with motivation. In the PAL test, the average number of trials completed and proportion of correct touches was significantly lower in HFD mice than in normal diet-fed mice. Our results reveal that HFD-induced metabolic dysregulation has detrimental effects on operant learning according to the percentage of correct responses in PAL. These findings establish that HFD-induced metabolic stress may have an effect in accelerating AD-like pathogenesis.

Role of Caenorhabditis elegans AKT-1/2 and SGK-1 in Manganese Toxicity

Excessive levels of the essential metal manganese (Mn) may cause a syndrome similar to Parkinson's disease. The model organism Caenorhabditis elegans mimics some of Mn effects in mammals, including dopaminergic neurodegeneration, oxidative stress, and increased levels of AKT. The evolutionarily conserved insulin/insulin-like growth factor-1 signaling pathway (IIS) modulates worm longevity, metabolism, and antioxidant responses by antagonizing the transcription factors DAF-16/FOXO and SKN-1/Nrf-2. AKT-1, AKT-2, and SGK-1 act upstream of these transcription factors. To study the role of these proteins in C. elegans response to Mn intoxication, wild-type N2 and loss-of-function mutants were exposed to Mn (2.5 to 100 mM) for 1 h at the L1 larval stage. Strains with loss-of-function in akt-1, akt-2, and sgk-1 had higher resistance to Mn compared to N2 in the survival test. All strains tested accumulated Mn similarly, as shown by ICP-MS. DAF-16 nuclear translocation was observed by fluorescence microscopy in WT and loss-of-function strains exposed to Mn. qRT-PCR data indicate increased expression of γ-glutamyl cysteine synthetase (GCS-1) antioxidant enzyme in akt-1 mutants. The expression of sod-3 (superoxide dismutase homologue) was increased in the akt-1 mutant worms, independent of Mn treatment. However, dopaminergic neurons degenerated even in the more resistant strains. Dopaminergic function was evaluated with the basal slowing response behavioral test and dopaminergic neuron integrity was evaluated using worms expressing green fluorescent protein (GFP) under the dopamine transporter (DAT-1) promoter. These results suggest that AKT-1/2 and SGK-1 play a role in C. elegans response to Mn intoxication. However, tissue-specific responses may occur in dopaminergic neurons, contributing to degeneration.

Uptake of TiO2 Nanoparticles into C. elegans Neurons Negatively Affects Axonal Growth and Worm Locomotion Behavior

We employ model organism Caenorhabditis elegans to effectively study the toxicology of anatase and rutile phase titanium dioxide (TiO₂) nanoparticles (NPs). The experimental results show that nematode C. elegans can take up fluorescein isothiocyanate-labeled TiO₂ NPs and that both anatase and rutile TiO₂ NPs can be detected in the cytoplasm of cultured primary neurons imaged by transmission electron microscopy. After TiO₂ NP exposure, these neurons also grow shorter axons, which may be related to the detected impeded worm locomotion behavior. Furthermore, anatase TiO₂ NPs did not affect the worm's body length; however, we determined that a concentration of 500 μg/mL of anatase TiO₂ NPs reduced the worm population by 50% within 72 h. Notably, rutile TiO₂ NPs negatively affect both the body size and worm population. Worms unable to enter the L4 larval stage explain a severe reduction in the worm population at TiO₂ NPs LC₅₀/3d. To obtain a better understanding of the cellular mechanisms involved in TiO₂ NP intoxication, DNA microarray assays were employed to determine changes in gene expression in the presence or absence of TiO₂ NP exposure. Our data reveal that three genes (with significant changes in expression levels) were related to metal binding or metal detoxification (mtl-2, C45B2.2, and nhr-247), six genes were involved in fertility and reproduction (mtl-2, F26F2.3, ZK970.7, clec-70, K08C9.7, and C38C3.7), four genes were involved in worm growth and body morphogenesis (mtl-2, F26F2.3, C38C3.7, and nhr-247), and five genes were involved in neuronal function (C41G6.13, C45B2.2, srr-6, K08C9.7, and C38C3.7).

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells

The circadian rhythm is a fundamental physiological process present in all organisms that regulates biological processes ranging from gene expression to sleep behavior. In vertebrates, circadian rhythm is controlled by a molecular oscillator that functions in both the suprachiasmatic nucleus (SCN; central pacemaker) and individual cells comprising most peripheral tissues. More importantly, disruption of circadian rhythm by exposure to light-at-night, environmental stressors and/or toxicants is associated with increased risk of chronic diseases and aging. The ability to identify agents that can disrupt central and/or peripheral biological clocks, and agents that can prevent or mitigate the effects of circadian disruption, has significant implications for prevention of chronic diseases. Although rodent models can be used to identify exposures and agents that induce or prevent/mitigate circadian disruption, these experiments require large numbers of animals. In vivo studies also require significant resources and infrastructure, and require researchers to work all night. Thus, there is an urgent need for a cell-type appropriate in vitro system to screen for environmental circadian disruptors and enhancers in cell types from different organs and disease states. We constructed a vector that drives transcription of the destabilized luciferase in eukaryotic cells under the control of the human PERIOD 2 gene promoter. This circadian reporter construct was stably transfected into human mammary epithelial cells, and circadian responsive reporter cells were selected to develop the in vitro bioluminescence assay. Here, we present a detailed protocol to establish and validate the assay. We further provide details for proof of concept experiments demonstrating the ability of our in vitro assay to recapitulate the in vivo effects of various chemicals on the cellular biological clock. The results indicate that the assay can be adapted to a variety of cell types to screen for both environmental disruptors and chemopreventive enhancers of circadian clocks.

Epigenetics, obesity and early-life cadmium or lead exposure

Obesity is a complex and multifactorial disease, which likely comprises multiple subtypes. Emerging data have linked chemical exposures to obesity. As organismal response to environmental exposures includes altered gene expression, identifying the regulatory epigenetic changes involved would be key to understanding the path from exposure to phenotype and provide new tools for exposure detection and risk assessment. In this report, we summarize published data linking early-life exposure to the heavy metals, cadmium and lead, to obesity. We also discuss potential mechanisms, as well as the need for complete coverage in epigenetic screening to fully identify alterations. The keys to understanding how metal exposure contributes to obesity are improved assessment of exposure and comprehensive establishment of epigenetic profiles that may serve as markers for exposures.

Developmental Effects of the ToxCast™ Phase I and Phase II Chemicals in Caenorhabditis elegans and Corresponding Responses in Zebrafish, Rats, and Rabbits

BACKGROUND

Modern toxicology is shifting from an observational to a mechanistic science. As part of this shift, high-throughput toxicity assays are being developed using alternative, nonmammalian species to prioritize chemicals and develop prediction models of human toxicity.

METHODS

The nematode Caenorhabditis elegans (C. elegans) was used to screen the U.S. Environmental Protection Agency's (EPA's) ToxCast™ Phase I and Phase II libraries, which contain 292 and 676 chemicals, respectively, for chemicals leading to decreased larval development and growth. Chemical toxicity was evaluated using three parameters: a biologically defined effect size threshold, half-maximal activity concentration (AC50), and lowest effective concentration (LEC).

RESULTS

Across both the Phase I and Phase II libraries, 62% of the chemicals were classified as active ≤ 200 μM in the C. elegans assay. Chemical activities and potencies in C. elegans were compared with those from two zebrafish embryonic development toxicity studies and developmental toxicity data for rats and rabbits. Concordance of chemical activity was higher between C. elegans and one zebrafish assay across Phase I chemicals (79%) than with a second zebrafish assay (59%). Using C. elegans or zebrafish to predict rat or rabbit developmental toxicity resulted in balanced accuracies (the average value of the sensitivity and specificity for an assay) ranging from 45% to 53%, slightly lower than the concordance between rat and rabbit (58%).

CONCLUSIONS

Here, we present an assay that quantitatively and reliably describes the effects of chemical toxicants on C. elegans growth and development. We found significant overlap in the activity of chemicals in the ToxCast™ libraries between C. elegans and zebrafish developmental screens. Incorporating C. elegans toxicological assays as part of a battery of in vitro and in vivo assays provides additional information for the development of models to predict a chemical's potential toxicity to humans.

CITATION

Boyd WA, Smith MV, Co CA, Pirone JR, Rice JR, Shockley KR, Freedman JH. 2016. Developmental effects of the ToxCast™ Phase I and II chemicals in Caenorhabditis elegans and corresponding responses in zebrafish, rats, and rabbits. Environ Health Perspect 124:586-593; http://dx.doi.org/10.1289/ehp.1409645.

Age- and manganese-dependent modulation of dopaminergic phenotypes in a C. elegans DJ-1 genetic model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, yet its etiology and pathogenesis are poorly understood. PD is characterized by selective dopaminergic (DAergic) degeneration and progressive hypokinetic motor impairment. Mutations in dj-1 cause autosomal recessive early-onset PD. DJ-1 is thought to protect DAergic neurons via an antioxidant mechanism, but the precise basis of this protection has not yet been resolved. Aging and manganese (Mn) exposure are significant non-genetic risk factors for PD. Caenorhabditis elegans (C. elegans) is an optimal model for PD and aging studies because of its simple nervous system, conserved DAergic machinery, and short 20-day lifespan. Here we tested the hypothesis that C. elegans DJ-1 homologues were protective against Mn-induced DAergic toxicity in an age-dependent manner. We showed that the deletion of C. elegans DJ-1 related (djr) genes, djr-1.2, decreased survival after Mn exposure. djr-1.2, the DJ-1 homologue was expressed in DAergic neurons and its deletion decreased lifespan and dopamine (DA)-dependent dauer movement behavior after Mn exposure. We also tested the role of DAF-16 as a regulator of dj-1.2 interaction with Mn toxicity. Lifespan defects resulting from djr-1.2 deletion could be restored to normal by overexpression of either DJR-1.2 or DAF-16. Furthermore, dauer movement alterations after djr-1.2 deletion were abolished by constitutive activation of DAF-16 through mutation of its inhibitor, DAF-2 insulin receptor. Taken together, our results reveal PD-relevant interactions between aging, the PD environmental risk factor manganese, and homologues of the established PD genetic risk factor DJ-1. Our data demonstrate a novel role for the DJ-1 homologue, djr-1.2, in mitigating Mn-dependent lifespan reduction and DA signaling alterations, involving DAF-2/DAF-16 signaling.

Biochemical alterations during the obese-aging process in female and male monosodium glutamate (MSG)-treated mice

Obesity, from children to the elderly, has increased in the world at an alarming rate over the past three decades, implying long-term detrimental consequences for individual’s health. Obesity and aging are known to be risk factors for metabolic disorder development, insulin resistance and inflammation, but their relationship is not fully understood. Prevention and appropriate therapies for metabolic disorders and physical disabilities in older adults have become a major public health challenge. Hence, the aim of this study was to evaluate inflammation markers, biochemical parameters and glucose homeostasis during the obese-aging process, to understand the relationship between obesity and health span during the lifetime. In order to do this, the monosodium glutamate (MSG) obesity mice model was used, and data were evaluated at 4, 8, 12, 16 and 20 months in both female and male mice. Our results showed that obesity was a major factor contributing to premature alterations in MSG-treated mice metabolism; however, at older ages, obesity effects were attenuated and MSG-mice became more similar to normal mice. At a younger age (four months old), the Lee index, triglycerides, total cholesterol, TNF-α and transaminases levels increased; while adiponectin decreased and glucose tolerance and insulin sensitivity levels were remarkably altered. However, from 16 months old-on, the Lee index and TNF-α levels diminished significantly, while adiponectin increased, and glucose and insulin homeostasis was recovered. In summary, MSG-treated obese mice showed metabolic changes and differential susceptibility by gender throughout life and during the aging process. Understanding metabolic differences between genders during the lifespan will allow the discovery of specific preventive treatment strategies for chronic diseases and functional decline.

Behavioral and metabolic effects of the atypical antipsychotic ziprasidone on the nematode Caenorhabditis elegans

Atypical antipsychotics are associated with metabolic syndrome, primarily associated with weight gain. The effects of Ziprasidone, an atypical antipsychotic, on metabolic syndrome has yet to be evaluated. Here in, we evaluated lipid accumulation and behavioral changes in a new experimental model, the nematode Caenorhabditis elegans (C. elegans). Behavioral parameters in the worms were evaluated 24 h after Ziprasidone treatment. Subsequently, lipid accumulation was examined using Nile red, LipidTox green and BODIPY labeling. Ziprasidone at 40 µM for 24 h effectively decreased the fluorescence labeling of all markers in intestinal cells of C. elegans compared to control (0.16% dimethyl sulfoxide). Ziprasidone did not alter behaviors related to energetic balance, such as pharynx pumping, defecation cycles and movement. There was, however, a reduction in egg-production, egg-laying and body-length in nematodes exposed to Ziprasidone without any changes in the progression of larval stages. The serotoninergic pathway did not appear to modulate Ziprasidone’s effects on Nile red fluorescence. Additionally, Ziprasidone did not alter lipid accumulation in daf-16 or crh-1 deletion mutants (orthologous of the transcription factors DAF-16 and CREB, respectively). These results suggest that Ziprasidone alters reproductive behavior, morphology and lipid reserves in the intestinal cells of C. elegans. Our results highlight that the DAF-16 and CREB transcription factors are essential for Ziprasidone-induced fat store reduction.