Caenorhabditis elegans as a model for obesity research.

Caenorhabditis elegans, a free-living nematode, is an animal model that has been extensively employed in a variety of research fields, including in the study of obesity. Its favorable features include its compact size, short life cycle, large brood size, easy handling, low cost, availability of complete genetic information, 65% conserved human diseases-associated genes, relatively easy genetic manipulation, and research using Caenorhabditis elegans does not require approvals by the Institutional Animal Care and Use Committee. These advantages make Caenorhabditis elegans a great in vivo model for life science research including obesity research. In this review, we provide graphic overviews of Caenorhabditis elegans' basic anatomy, growth conditions, routes of compound delivery, and fat metabolism, both synthesis and degradation pathways, including major signaling pathways involved. Our aim is to provide an overview for researchers interested in applying C. elegans as an in vivo model for the screening and identification of anti-obesity bioactive compounds prior to testing in vertebrate animal models.

Curcumin reduced fat accumulation in Caenorhabditis elegans.

Curcumin, the primary bioactive substance in turmeric, is known to be associated with weight loss. In this study, we employed Caenorhabditis elegans, a well-established in vivo nematode model to explore the role of curcumin in regulating lipid metabolism. C. elegans administrated with curcumin (10, 25 and 50 µM) exhibited significantly reduced fat accumulation, along with smaller body size (width) when compared to the control, without significantly affecting the feeding behavior. Locomotive activity (average moving speed) was significantly increased by curcumin treatment, suggesting a potential increase in energy expenditure. The reduced fat accumulation by curcumin was dependent on lipogenesis-associated genes, sbp-1 (encodes the homolog of sterol response element binding proteins) and fat-6 (encodes a homolog of stearoyl-CoA desaturase), as curcumin significantly down-regulated the expression levels of these two genes and its fat reduction effect was nulled by the mutation of sbp-1 and fat-6. Additionally, the increased locomotive activity by curcumin was dependent on sbp-1. Current results suggest that curcumin decreases fat accumulation by inhibiting sbp-1/fat-6-mediated signaling in Caenorhabditis elegans.

Natural Products in the Prevention of Metabolic Diseases: Lessons Learned from the 20th KAST Frontier Scientists Workshop.

The incidence of metabolic and chronic diseases including cancer, obesity, inflammation-related diseases sharply increased in the 21st century. Major underlying causes for these diseases are inflammation and oxidative stress. Accordingly, natural products and their bioactive components are obvious therapeutic agents for these diseases, given their antioxidant and anti-inflammatory properties. Research in this area has been significantly expanded to include chemical identification of these compounds using advanced analytical techniques, determining their mechanism of action, food fortification and supplement development, and enhancing their bioavailability and bioactivity using nanotechnology. These timely topics were discussed at the 20th Frontier Scientists Workshop sponsored by the Korean Academy of Science and Technology, held at the University of Hawaii at Manoa on 23 November 2019. Scientists from South Korea and the U.S. shared their recent research under the overarching theme of Bioactive Compounds, Nanoparticles, and Disease Prevention. This review summarizes presentations at the workshop to provide current knowledge of the role of natural products in the prevention and treatment of metabolic diseases.

Methylglyoxal influences development of Caenorhabditis elegans via lin-41-dependent pathway.

Methylglyoxal is a highly reactive dicarbonyl compound. It can be obtained either endogenously through biological enzymatic/non-enzymatic pathways or exogenously via the uptake of certain foods and beverages, such as Manuka honey. Studies about its biological properties are quite controversial, though the majority reported a positive association between methylglyoxal and certain pathologies. In this report, we tested if methylglyoxal can alter the development of animals using Caenorhabditis elegans as the in vivo model. Treatment of methylglyoxal at 0.1 and 1 mmol/L for 2 days significantly inhibited the development of Caenorhabditis elegans, particularly targeting the transition from L3 stage. Pharyngeal pumping rate, the food intake marker was also significantly reduced by methylglyoxal at both 0.1 and 1 mmol/L. Additionally, treatment of 0.1 mmol/L methylglyoxal increased, while 1 mmol/L methylglyoxal decreased the nematodes' average moving speed. The effect of methylglyoxal on development was in part due to the modulation of lin-41, which encodes a homolog of human TRIM71. The mutation of lin-41 could alleviate or abolish the effects of methylglyoxal on growth rate, body size, pumping rate and locomotive activity. In summary, these results suggested that methylglyoxal influenced the development of Caenorhabditis elegans, which is in part via the lin-41-dependent pathway.

Fat-lowering effects of isorhamnetin are via NHR-49-dependent pathway in Caenorhabditis elegans.

Isorhamnetin (3-O-methylquercetin), a flavonol found in dill weed, sea buckthorn berries, kale and onions, has been suggested to have anti-obesity effects, but there is limited evidence of its mechanisms of action on lipid metabolism. The goal of this study was to investigate the effects of isorhamnetin on lipid metabolism using Caenorhabditis elegans as an animal model. Isorhamnetin reduced fat accumulation without affecting food intake or energy expenditure in C. elegans. The isorhamnetin's fat-lowering effects were dependent on nhr-49, a homolog of the human peroxisome proliferator-activated receptor alpha (PPARα). Isorhamnetin upregulated an enoyl-CoA hydratase (ech-1.1, involved in fatty acid ß-oxidation) and adipose triglyceride lipase (atgl-1, involved in lipolysis) via NHR-49-dependent pathway at transcriptional levels. Isorhamnetin also upregulated the C. elegans AMP-activated protein kinase (AMPK) subunits homologs (aak-1 and aak-2), involved in energy homeostasis. These results suggest that isorhamnetin reduces body fat by increasing fat oxidation in part via NHR-49/PPARα-dependent pathway.

Perfluorooctanesulfonic acid (PFOS) and perfluorobutanesulfonic acid (PFBS) impaired reproduction and altered offspring physiological functions in Caenorhabditis elegans.

Perfluorobutanesulfonic acid (PFBS), a shorter chain Per- and polyfluoroalkyl substances (PFASs) cognate of perfluorooctanesulfonic acid (PFOS), has been used as replacement for the toxic surfactant PFOS. However, emerging evidences suggest safety concerns for PFBS and its effect on reproductive health is still understudied. Therefore, the current work aimed to investigate the effect of PFBS, in comparison to PFOS, on reproductive health using Caenorhabditis elegans as an in vivo animal model. PFOS (≥10 µM) and PFBS (≥1000 µM) significantly impaired the reproduction capacity of C. elegans, represented as reduced brood size (total egg number) and progeny number (hatched offspring number), without affecting the hatchability. Additionally, the preconception exposure of PFOS and PFBS significantly altered the embryonic nutrient loading and composition, which further led to abnormalities in growth rate, body size and locomotive activity in F1 offspring. Though the effective exposure concentration of PFBS was approximately 100 times higher than PFOS, the internal concentration of PFBS was lower than that of PFOS to produce the similar effects of PFOS. In conclusion, PFOS and PFBS significantly impaired the reproductive capacities in C. elegans and the preconception exposure of these two compounds can lead to offspring physiological dysfunctions.

trans-Trismethoxy resveratrol decreased fat accumulation dependent on fat-6 and fat-7 in Caenorhabditis elegans.

trans-Trismethoxy resveratrol (TMR) is a methyl analog of resveratrol. It is found to exhibit enhanced biological effects compared to resveratrol, such as inhibition of cancer cell growth and pro-apoptotic activities. However, the role of TMR in lipid metabolism is not fully understood. In this study, we used Caenorhabditis elegans, an in vivo nematode model which has been widely applied in disease research, including research on obesity, to investigate the effect of TMR on lipid metabolism. Treatment with TMR (100 and 200 µM) for 4 days significantly reduced triglyceride accumulation (14% and 20% reduction over the control, respectively) of C. elegans, without affecting nematode growth, food intake and reproduction. Treatment with TMR significantly downregulated stearoyl-CoA desaturase genes, fat-6 and fat-7, accompanied by a decrease in the desaturation index of fatty acids, the ratio of oleic acid to stearic acid. These results suggest that TMR inhibits fat accumulation by downregulating stearoyl-CoA desaturase in C. elegans.

p-Coumaric acid improves oxidative and osmosis stress responses in Caenorhabditis elegans.

BACKGROUND: Stress-response pathways in Caenorhabditis elegans (C. elegans) were found to be closely related to human diseases and aging. Research on stress responses in C. elegans can therefore significantly facilitate understanding of related human diseases. p-Coumaric acid is present in peanuts, carrots, and garlic, and exerts many biological effects, however, its responses to various environmental stressors remain unknown. Thus, in the current study, we employed C. elegans as the in vivo animal model to examine the function of p-coumaric acid under various stressed conditions. RESULTS: Treatment of C. elegans with p-coumaric acid resulted in a significant reduction in the intercellular reactive oxygen species levels, which suggests the in vivo antioxidant capacity of p-coumaric acid. Moreover, p-coumaric acid significantly increased the worms' survival under oxidative and osmosis stressed conditions but had no effect under normal or heat-stressed conditions. The increased oxidative resistance induced by p-coumaric acid was mediated by skn-1, an ortholog of the Nrf2 (nuclear factor erythroid 2-related factor 2) transcriptional factor. Downregulation of the osmosis regulatory gene, osr-1, might contribute to p-coumaric acids' effect on increased resistance to high osmolarity. CONCLUSION: Taken together, our results suggest that p-coumaric acid, an antioxidant agent, ameliorated oxidative and osmosis stresses in C. elegans. © 2018 Society of Chemical Industry.

Epigallocatechin-3-Gallate Reduces Fat Accumulation in Caenorhabditis elegans.

Epigallocatechin gallate (EGCG) is a polyphenol that is abundant in green tea. It has been reported that consumption of EGCG can contribute to weight loss, however, the underlying mechanism is not fully understood. To determine how EGCG reduces body fat, an organism model Caenorhabditis elegans was used, which is a useful animal model system in exploring crucial biological mechanisms that are readily applicable to humans. In this study, different strains were raised for two days on Escherichia coli OP 50 diet with or without 100 µM and 200 µM EGCG treatment. The current results showed that 100 µM and 200 µM EGCG significantly reduced the triglyceride content of wild type worms by 10% and 20% (P-value<0.01 and <0.001, respectively) compared to the control, respectively, without affecting its food intake and physiological behaviors. Additionally, EGCG could effectively reduce fat accumulation in C. elegans dependent on atgl-1 (encoding a homolog of adipose triglyceride lipase), which suggests that EGCG controls the body fat by inhibiting adipogenesis.

Effects of conjugated linoleic acid (CLA) on fat accumulation, activity, and proteomics analysis in Caenorhabditis elegans.

Conjugated linoleic acid (CLA) has been reported to reduce fat storage in cell culture and animal models. In the current study, the effects of CLA on the fat accumulation, activities, and proteomics were investigated using Caenorhabditis elegans. 100 µM CLA-TG nanoemulsion significantly reduced fat accumulation by 29% compared to linoleic acid (LA)-TG treatment via sir-2.1 (the ortholog of Sirtuin 1), without altering the worm size, growth rate, and pumping rate of C. elegans. CLA significantly increased moving speed and amplitude (the average centroid displacement over the entire track) of wild type worms compared to the LA group and these effects were dependent on aak-2 (AMPKα ortholog) and sir-2.1. Proteomics analysis showed CLA treatment influences various proteins associated in reproduction and development, translation, metabolic processes, and catabolism and proteolysis, in C. elegans. We have also confirmed the proteomics data that CLA reduced the fat accumulation via abs-1 (ATP Synthase B homolog). However, there were no significant effects of CLA on brood size, progeny numbers, and hatchability compared to LA treatment.

A living model for obesity and aging research: Caenorhabditis elegans.

Caenorhabditis elegans (C. elegans) is a free-living nematode that has been extensively utilized as an animal model for research involving aging and neurodegenerative diseases, like Alzheimer's and Parkinson's, etc. Compared with traditional animal models, this small nematode possesses many benefits, such as small body size, short lifespan, completely sequenced genome, and more than 65% of the genes associated with human disease. All these characteristics make this organism an ideal living system for obesity and aging studies. This review gives a brief introduction of C. elegans as an animal model, highlights some advantages of research using this model and describes methods to evaluate the effect of treatments on obesity and aging of this organism.

Caenorhabditis elegans: A Convenient In Vivo Model for Assessing the Impact of Food Bioactive Compounds on Obesity, Aging, and Alzheimer's Disease.

Caenorhabditis elegans is a small free-living nematode that lives in temperate soil environments. It has been widely employed as an animal model in research involving obesity, aging, and neurodegenerative diseases, including Alzheimer's disease, because of its various advantages, such as small size, large number of progeny, completely sequenced genome, and short life span, over traditional animal models of vertebrates. These benefits contribute to an ideal research model organism. In this review, we provide an introduction to C. elegans and its applications in obesity, aging, and Alzheimer's disease studies, with the aim of stimulating scientists to use C. elegans as an experimental model in various fields of research.

Comprehensive in vitro and in vivo risk assessments of chitosan microparticles using human epithelial cells and Caenorhabditis elegans.

The safety of using nano- and microparticles is a developing concern. In this study, we conducted risk assessments of chitosan microparticles (CMs) using in vitro human epithelial cell lines and in vivo animal model, Caenorhabditis elegans. After engineering of various CMs, we screened four CMs based on antimicrobial activity, which is a potential usage for disease treatment caused by multidrug resistant bacteria, and evaluated for risk assessments. CMs, with strong antimicrobial activity, and inorganic nanoparticles (SiO2, TiO2, and ZnO) did not cause toxicity in human cells measured by cell membrane integrity, mitochondria activity, and reactive oxygen species concentration. However, when applied to C. elegans, only CMs generated with low molecular weight chitosan and tripolyphosphate at 0.1% did not affect the lifespan, while the other CMs and inorganic nanoparticles shortened the lifespan, suggesting that they may cause subtle toxicity. These results suggest that C. elegans could be a sensitive animal model to measure low level of toxicity of nano- and microparticles. Taken together, although CMs do not cause toxicity at working concentrations of antimicrobial activity in human epithelial cells, they may cause toxicity at high concentration, suggesting that nano- and microparicles should be thoroughly investigated before they are applied.

Piceatannol Reduces Fat Accumulation in Caenorhabditis elegans.

Excess fat accumulation and abnormal metabolism are involved in numerous diseases and thus the research on identification of compounds that can regulate energy homeostasis could significantly facilitate the current effort to prevent and/or treat metabolic disorders. Piceatannol, one of the natural stilbenes, was previously found to decrease lipid accumulation of 3T3-L1 adipocytes. However, its role in fat metabolism in vivo is not known. Thus, Caenorhabditis elegans as an animal model was used in the current study to determine the effect of piceatannol on fat accumulation and its underlying mechanisms. The results showed that 50 and 100 µM piceatannol significantly reduced fat accumulation of wild-type worms grown in normal and high-glucose conditions without altering the growth rate, worm length, pumping rate, or moving speed. The current study further indicated that piceatannol decreased the expression of sbp-1 (encodes an ortholog of mammalian sterol regulatory element-binding protein) and its target gene fasn-1 (encodes an ortholog of fatty acid synthase) as well as increased the expression of hosl-1 (encodes an ortholog of hormone-sensitive lipase) in glucose-treated worms. These data suggested that piceatannol reduced fat accumulation in C. elegans by suppression of genes involved in lipid synthesis and possibly through stimulation of lipolysis. Given that piceatannol exerts similar effects in both C. elegans and 3T3-L1 cells, our finding could provide a mechanistic insight into the role of piceatannol in lipid metabolism in mammals.

3,3'-Diindolylmethane Suppresses Adipogenesis Using AMPKα-Dependent Mechanism in 3T3-L1 Adipocytes and Caenorhabditis elegans.

3,3'-diindolylmethane is a major in vivo metabolite of indole-3-carbinol, a bioactive compound found in cruciferous vegetables. Although 3,3'-diindolylmethane has been implicated to possess antitumorigenic and anti-inflammatory properties, the effect of 3,3'-diindolylmethane on adipogenesis has not been explored previously. Thus, the present study was conducted to determine if 3,3'-diindolylmethane affects adipogenesis using 3T3-L1 adipocytes and Caenorhabditis elegans. Treatment of 3,3'-diindolylmethane significantly reduced fat accumulation without affecting viability in 3T3-L1 adipocytes. 3,3'-diindolylmethane suppressed expression of peroxisome proliferator-activated receptor γ (PPARγ), CCAAT-enhancer-binding protein α (C/EBPα), fatty acid binding protein 4 (FABP4), and perilipin. In addition, 3,3'-diindolylmethane activated AMP-activated protein kinase α (AMPKα), which subsequently inactivated acetyl CoA carboxylase (ACC), resulting in reduced fat accumulation. These observations were further confirmed in C. elegans as treatment with 3,3'-diindolylmethane significantly reduced body fat accumulation, which was partly associated with aak-1, but not aak-2, orthologs of AMPKα catalytic subunits α1 and α2, respectively. The current results demonstrate that 3,3'-diindolylmethane, a biologically active metabolite of indole-3-carbinol, may prevent adipogenesis through the AMPKα-dependent pathway.

Deltamethrin increases the fat accumulation in 3T3-L1 adipocytes and Caenorhabditis elegans.

Research has shown that permethrin, a Type-I pyrethroid, increases triglyceride (fat) accumulation in adipocytes. Little is known, however, about any similar effect of deltamethrin, a Type-II pyrethroid, which produces a distinct syndrome of poisoning in mammals compared with permethrin. This study was therefore aimed to explore the role of deltamethrin on fat accumulation in 3T3-L1 adipocytes and Caenorhabditis elegans. Deltamethrin (10 µM) significantly increased the fat accumulation in 3T3-L1 adipocytes and wild type C. elegans compared to respective controls. Deltamethrin decreased the ratio of phosphorylated AMP-activated kinase (pAMPKα) over AMPKα and phosphorylated acetyl-CoA carboxylase (ACC) over ACC, while it increased expression of CCAAT/enhancer-binding protein (C/EBPα) and peroxisome proliferator-activated receptor-γ (PPARγ) in 3T3-L1 adipocytes. Similarly, deltamethrin potentiated fat accumulation in C. elegans without affecting growth or pharyngeal pumping rate. Moreover, deltamethrin significantly reduced the total progeny number and locomotive activities in C. elegans in a dose-dependent manner. Deltamethrin increased fat accumulation via aak-2 (an ortholog of AMPKα) and nhr-49 (a homolog of peroxisome proliferator-activated receptor-α and also downstream target of aak-2) mediated mechanisms. The current work is the first report of the effects of deltamethrin on increased fat storage by 3T3- L1 adipocytes and C. elegans via aak-2 (AMPKα ortholog)-mediated mechanism.

Piceatannol extends the lifespan of Caenorhabditis elegans via DAF-16.

Piceatannol is a natural stilbene with many beneficial effects, such as antioxidative, anti-inflammatory, antiatherogenic activities; however, its role on aging is not known. In this study, we used Caenorhabditis elegans as an animal model to study the effect of piceatannol on its lifespan and investigated the underlying mechanisms. The results showed that 50 and 100 µM piceatannol significantly extended the lifespan of C. elegans without altering the growth rate, worm size and progeny production. Piceatannol delayed the age-related decline of pumping rate and locomotive activity, and protected the worms from heat and oxidative stress. This study further indicated that lifespan extension and enhanced stress resistance induced by piceatannol requires DAF-16. Since DAF-16 is conserved from nematodes to mammals, our study may have important implications in utilizing piceatannol to promote healthy aging and combat age-related disease in humans. © 2016 BioFactors, 43(3):379-387, 2017.

4,4'-Dichlorodiphenyltrichloroethane (DDT) and 4,4'-dichlorodiphenyldichloroethylene (DDE) promote adipogenesis in 3T3-L1 adipocyte cell culture.

4,4'-Dichlorodiphenyltrichloroethane (DDT), a chlorinated hydrocarbon insecticide, was extensively used in the 1940s and 1950s. DDT is mainly metabolically converted into 4,4'-dichlorodiphenyldichloroethylene (DDE). Even though most countries banned DDT in the 1970s, due to the highly lipophilic nature and very stable characteristics, DDT and its metabolites are present ubiquitously in the environment, including food. Recently, there are publications on relationships between exposure to insecticides, including DDT and DDE, and weight gain and altered glucose homeostasis. However, there are limited reports regarding DDT or DDE and adipogenesis, thus we investigated effects of DDT and DDE on adipogenesis using 3T3-L1 adipocytes. Treatment of DDT or DDE resulted in increased lipid accumulation accompanied by increased expression of CCAAT/enhancer-binding protein α (C/EBPα), peroxisome-proliferator activated receptor-γ (PPARγ), fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), adipose triglyceride lipase, and leptin. Moreover, treatment of DDT or DDE increased protein levels of C/EBPα, PPARγ, AMP-activated protein kinase-α (AMPKα), and ACC, while significant decrease of phosphorylated forms of AMPKα and ACC were observed. These finding suggest that increased lipid accumulation caused by DDT and DDE may mediate AMPKα pathway in 3T3-L1 adipocytes.

Cranberry Product Decreases Fat Accumulation in Caenorhabditis elegans.

Cranberry phenolic compounds have been linked to many health benefits. A recent report suggested that cranberry bioactives inhibit adipogenesis in 3T3-L1 adipocytes. Thus, we investigated the effects and mechanisms of the cranberry product (CP) on lipid metabolism using the Caenorhabditis elegans (C. elegans) model. CP (0.016% and 0.08%) dose-dependently reduced overall fat accumulation in C. elegans (N2, wild type) by 43% and 74%, respectively, without affecting its pumping rates or locomotive activities. CP decreased fat accumulation in aak-2 (an ortholog of AMP-activated kinase α) and tub-1 (an ortholog of TUBBY) mutants significantly, but only minimal effects were observed in sbp-1 (an ortholog of sterol response element-binding protein-1) and nhr-49 (an ortholog of peroxisome proliferator-activated receptor-α) mutant strains. We further confirmed that CP downregulated sbp-1, cebp, and hosl-1 (an ortholog of hormone-sensitive lipase homolog) expression, while increasing the expression of nhr-49 in wild-type C. elegans. These results suggest that CP could effectively reduce fat accumulation in C. elegans dependent on sbp-1, cebp, and nhr-49, but not aak-2 and tub-1.

Delivery of dietary triglycerides to Caenorhabditis elegans using lipid nanoparticles: Nanoemulsion-based delivery systems.

The nematode Caenorhabditis elegans is a powerful tool for studying food bioactives on specific biochemical pathways. However, many food bioactives are highly hydrophobic with extremely low water-solubilities, thereby making them difficult to study using C. elegans. The purpose of this study was to develop nanoemulsion-based systems to deliver hydrophobic molecules in a form that could be ingested by C. elegans. Optical microscopy showed that oil-in-water nanoemulsions with a range of particle diameters (40-500nm) could be ingested by C. elegans. The amount of lipid ingested depended on the size and concentration of the nanoparticles. Fatty acid analysis showed incorporation of conjugated linoleic acid and there was a significant reduction in the fat levels of C. elegans when they were incubated with nanoemulsions containing conjugated linoleic acid, which suggested that this hydrophobic lipid was successfully delivered to the nematodes. The incorporation of hydrophobic molecules into nanoemulsion based-delivery systems may therefore enable their activities to be studied using C. elegans.