Ablation of carotenoid cleavage enzymes (BCO1 and BCO2) induced hepatic steatosis by altering the farnesoid X receptor/miR-34a/sirtuin 1 pathway

Effects of carotenoids on mitochondrial dysfunction

Oxidative stress, an imbalance between pro-oxidant and antioxidant status, favouring the pro-oxidant state is a result of increased production of reactive oxygen species (ROS) or inadequate antioxidant protection. ROS are produced through several mechanisms in cells including during mitochondrial oxidative phosphorylation. Increased mitochondrial-derived ROS are associated with mitochondrial dysfunction, an early event in age-related diseases such as Alzheimer's diseases (ADs) and in metabolic disorders including diabetes. AD post-mortem investigations of affected brain regions have shown the accumulation of oxidative damage to macromolecules, and oxidative stress has been considered an important contributor to disease pathology. An increase in oxidative stress, which leads to increased levels of superoxide, hydrogen peroxide and other ROS in a potentially vicious cycle is both causative and a consequence of mitochondrial dysfunction. Mitochondrial dysfunction may be ameliorated by molecules with antioxidant capacities that accumulate in mitochondria such as carotenoids. However, the role of carotenoids in mitigating mitochondrial dysfunction is not fully understood. A better understanding of the role of antioxidants in mitochondrial function is a promising lead towards the development of novel and effective treatment strategies for age-related diseases. This review evaluates and summarises some of the latest developments and insights into the effects of carotenoids on mitochondrial dysfunction with a focus on the antioxidant properties of carotenoids. The mitochondria-protective role of carotenoids may be key in therapeutic strategies and targeting the mitochondria ROS is emerging in drug development for age-related diseases.

Adapting to stress: The effects of hibernation and hibernacula temperature on the hepatic transcriptome of Rhinolophus pusillus

Hibernation, a survival strategy in mammals for extreme climates, induces physiological phenomena such as ischemia-reperfusion and metabolic shifts that hold great potential for advancements in modern medicine. Despite this, the molecular mechanisms underpinning hibernation remain largely unclear. This study used RNA-seq and Iso-seq techniques to investigate the changes in liver transcriptome expression of Rhinolophus pusillus during hibernation and active periods, as well as under different microhabitat temperatures. We identified 11 457 differentially expressed genes during hibernation and active periods, of which 395 showed significant differential expression. Genes associated with fatty acid catabolism were significantly upregulated during hibernation, whereas genes related to carbohydrate metabolism and glycogen synthesis were downregulated. Conversely, immune-related genes displayed differential expression patterns: genes tied to innate immunity were significantly upregulated, while those linked to adaptive immunity and inflammatory response were downregulated. The analysis of transcriptomic data obtained from different microhabitat temperatures revealed that R. pusillus exhibited an upregulation of genes associated with lipid metabolism in lower microhabitat temperature. This upregulation facilitated an enhanced utilization rate of triglyceride, ultimately resulting in increased energy provision for the organism. Additionally, R. pusillus upregulated gluconeogenesis-related genes regardless of the microhabitat temperature, demonstrating the importance of maintaining blood glucose levels during hibernation. Our transcriptomic data reveal that these changes in liver gene expression optimize energy allocation during hibernation, suggesting that liver tissue adaptively responds to the inherent stress of its function during hibernation. This study sheds light on the role of differential gene expression in promoting more efficient energy allocation during hibernation. It contributes to our understanding of how liver tissue adapts to the stressors associated with this state.

Preventive Action of Beta-Carotene against the Indoxyl Sulfate-Induced Renal Dysfunction in Male Adult Zebrafish via Regulations of Mitochondrial Inflammatory and β-Carotene Oxygenase-2 Actions

Indoxyl sulfate (IS) is a metabolic byproduct of indole metabolism. IS readily interacts with the mitochondrial redox metabolism, leading to altered renal function. The β-carotene oxygenase-2 (BCO2) enzyme converts carotenoids to intermediate products. However, the role of β-carotene (BC) in IS-induced renal dysfunction in zebrafish and their modulatory action on BCO2 and mitochondrial inflammations have not been explored yet. Hence, the present study is designed to investigate the role of BC in the attenuation of IS-induced renal dysfunction via regulations of mitochondrial redox balance by BCO2 actions. Renal dysfunction was induced by exposure to IS (10 mg/L/hour/day) for 4 weeks. BC (50 and 100 mg/L/hour/day) and coenzyme Q10 (CoQ10; 20 mg/L/hour/day) were added before IS exposure. BC attenuated the IS-induced increase in blood urea nitrogen (BUN) and creatinine concentrations, adenosine triphosphate (ATP), and complex I activity levels, and the reduction of renal mitochondrial biomarkers, i.e., BCO2, superoxide dismutase-2 (SOD2), glutathione peroxidase-1 (GPX1), reduced and oxidized glutathione (GSH/GSSG) ratio, and carbonylated proteins. Moreover, renal histopathological changes were analyzed by the eosin and hematoxylin staining method. As a result, the administration of BC attenuated the IS-induced renal damage via the regulation of mitochondrial function.

Lycopene Accumulation in Transgenic Mice Lacking One or Both Carotenoid Cleaving Enzymes

BACKGROUND

β-carotene oxygenase 1 (BCO1) and β-carotene oxygenase 2 (BCO2) are responsible for the cleavage of carotenoids in mammals.

OBJECTIVE

The goals of this study were to (1) establish the relative contribution of each enzyme on lycopene accumulation in mice and (2) examine the role of lycopene on gene expression in the gut of wild type (WT) mice.

METHODS

We utilized male and female WT, Bco1-/-, Bco2-/-, and Bco1-/-Bco2-/- double knockout (DKO) mice. We gavaged the mice with either 1 mg of lycopene resuspended in cottonseed oil or vehicle as a control group daily for 2 wk. In a second study, we evaluated the effect of dietary vitamin A on lycopene absorption and intestinal gene expression by RT-PCR. We also quantified lycopene concentration isomer distribution by high performance liquid chromatography.

RESULTS

Of the 11 tissues measured, the liver accounted for 94 to 98% of the lycopene content across genotypes. We did not observe sex differences between genotypes, although hepatic lycopene levels in Bco1-/- mice were approximately half in comparison to the other genotypes; Bco1-/- verses Bco2-/- (P < 0.0001), DKO mice (P < 0.001), WT (ns). Analyses of mitochondrial lycopene content revealed a 3- to 5-fold enrichment compared with total hepatic content (P < 0.05) in all genotypes and sexes. In our second study, WT mice fed a vitamin A-deficient diet (VAD) accumulated greater amounts of lycopene in the liver than those fed a vitamin A-sufficient diet (VAS) (P < 0.01). These changes were accompanied by an upregulation of the vitamin A-responsive transcription factor intestine specific homeobox (ISX) in mice fed VAD + lycopene and VAS + lycopene diets compared with VAD control-fed mice (P < 0.05).

CONCLUSIONS

Our data suggest that BCO2 is the primary lycopene cleavage enzyme in mice. Lycopene concentration was enriched in the mitochondria of hepatocytes independently of genotype, and lycopene stimulated vitamin A signaling in WT mice.

β-Cryptoxanthin Attenuates Cigarette-Smoke-Induced Lung Lesions in the Absence of Carotenoid Cleavage Enzymes (BCO1/BCO2) in Mice

High dietary intake of β-cryptoxanthin (BCX, an oxygenated provitamin A carotenoid) is associated with a lower risk of lung disease in smokers. BCX can be cleaved by β-carotene-15,15'-oxygenase (BCO1) and β-carotene-9',10'-oxygenase (BCO2) to produce retinol and apo-10'-carotenoids. We investigated whether BCX has protective effects against cigarette smoke (CS)-induced lung injury, dependent or independent of BCO1/BCO2 and their metabolites. Both BCO1^-/-/BCO2^-/- double knockout mice (DKO) and wild type (WT) littermates were supplemented with BCX 14 days and then exposed to CS for an additional 14 days. CS exposure significantly induced macrophage and neutrophil infiltration in the lung tissues of mice, regardless of genotypes, compared to the non-exposed littermates. BCX treatment significantly inhibited CS-induced inflammatory cell infiltration, hyperplasia in the bronchial epithelium, and enlarged alveolar airspaces in both WT and DKO mice, regardless of sex. The protective effects of BCX were associated with lower expression of IL-6, TNF-α, and matrix metalloproteinases-2 and -9. BCX treatment led to a significant increase in hepatic BCX levels in DKO mice, but not in WT mice, which had significant increase in hepatic retinol concentration. No apo-10'-carotenoids were detected in any of the groups. In vitro BCX, at comparable doses of 3-OH-β-apo-10'-carotenal, was effective at inhibiting the lipopolysaccharide-induced inflammatory response in a human bronchial epithelial cell line. These data indicate that BCX can serve as an effective protective agent against CS-induced lung lesions in the absence of carotenoid cleavage enzymes.

MiR-34a-5p promotes hepatic gluconeogenesis by suppressing SIRT1 expression

Elevated hepatic gluconeogenesis is a major contributor of fasting hyperglycemia in diabetes. MicroRNAs (miRNAs) are tightly linked to glucose metabolism, but their role in hepatic gluconeogenesis remains largely unkown. In this current study, miR-34a-5p expression was significantly increased in liver tissues of db/db mice. Overexpression of miR-34a-5p promoted hepatic glucose production in mouse primary hepatocytes with increased expressions of gluconeogenic genes while miR-34a-5p inhibition displayed a contrary action. MiR-34a-5p overexpression in mouse primary hepatocytes repressed SIRT1 expression. SIRT1 inhibition by EX527 blocked phosphoenolpyruvate carboxykinase (PEPCK) protein degradation and enhanced hepatic gluconeogenesis. Treatment of A485 (a CBP/p300 inhibitor) decreased miR-34a-5p and PEPCK expressions in the livers of db/db mice, but elevated SIRT1 protein expression. In mouse primary hepatocytes, A485 exhibited a similar result. Overexpression of miR-34a-5p attenuated A485-inhibited gluconeogenic gene expressions and A485-induced SIRT1 protein expression. Finally, after miR-34a-5p was inhibited in the livers of db/db mice, hepatic glucose production and gluconeogenic gene expressions were markedly lowered. Our findings highlight a critical role of miR-34a-5p in the regulation of hepatic gluconeogenesis and miR-34a-5p may be a potential target in the treatment of type 2 diabetes.

Long Non-coding RNA Signatures Associated With Liver Aging in Senescence-Accelerated Mouse Prone 8 Model

The liver is sensitive to aging because the risk of hepatopathy, including fatty liver, hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma, increases dramatically with age. Long non-coding RNAs (lncRNAs) are >200 nucleotides long and affect many pathological and physiological processes. A potential link was recently discovered between lncRNAs and liver aging; however, comprehensive and systematic research on this topic is still limited. In this study, the mouse liver genome-wide lncRNA profiles of 8-month-old SAMP8 and SAMR1 models were explored through deep RNA sequencing. A total of 605,801,688 clean reads were generated. Among the 2,182 identified lncRNAs, 28 were differentially expressed between SAMP8 and SAMR1 mice. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) surveys showed that these substantially dysregulated lncRNAs participated in liver aging from different aspects, such as lipid catabolic (GO: 0016042) and metabolic pathways. Further assessment was conducted on lncRNAs that are most likely to be involved in liver aging and related diseases, such as LNC_000027, LNC_000204E, NSMUST00000144661.1, and ENSMUST00000181906.1 acted on Ces1g. This study provided the first comprehensive dissection of lncRNA landscape in SAMP8 mouse liver. These lncRNAs could be exploited as potential targets for the molecular-based diagnosis and therapy of age-related liver diseases.

The long and the small collide: LncRNAs and small heterodimer partner (SHP) in liver disease

Long non-coding RNAs (lncRNAs) are a large and diverse class of RNA molecules that are transcribed but not translated into proteins, with a length of more than 200 nucleotides. LncRNAs are involved in gene expression and regulation. The abnormal expression of lncRNAs is associated with disease pathogenesis. Small heterodimer partner (SHP, NR0B2) is a unique orphan nuclear receptor that plays a pivotal role in many biological processes by acting as a transcriptional repressor. In this review, we present the critical roles of SHP and summarize recent findings demonstrating the regulation between lncRNAs and SHP in liver disease.

MicroRNAs in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), or, more accurately, metabolic associated fatty liver disease, accounts for a large proportion of chronic liver disorders worldwide and is closely associated with other conditions such as cardiovascular disease, obesity, and type 2 diabetes mellitus. NAFLD ranges from simple steatosis to nonalcoholic steatohepatitis (NASH) and can progress to cirrhosis and, eventually, also hepatocellular carcinoma. The morbidity and mortality associated with NAFLD are increasing rapidly year on year. Consequently, there is an urgent need to understand the etiology and pathogenesis of NAFLD and identify effective therapeutic targets. MicroRNAs (miRNAs), important epigenetic factors, have recently been proposed to participate in NAFLD pathogenesis. Here, we review the roles of miRNAs in lipid metabolism, inflammation, apoptosis, fibrosis, hepatic stellate cell activation, insulin resistance, and oxidative stress, key factors that contribute to the occurrence and progression of NAFLD. Additionally, we summarize the role of miRNA-enriched extracellular vesicles in NAFLD. These miRNAs may comprise suitable therapeutic targets for the treatment of this condition.

Dietary lycopene attenuates cigarette smoke-promoted nonalcoholic steatohepatitis by preventing suppression of antioxidant enzymes in ferrets

Cigarette smoke (CS) is an independent risk factor in development of nonalcoholic steatohepatitis (NASH) and fibrosis. Lycopene, a carotenoid naturally occurring in tomatoes, has been shown to be a protective agent against tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced NASH. In the present study using a ferret model we investigated whether CS promotes NASH and whether dietary lycopene can inhibit CS-promoted NASH development, and if so, what potential mechanisms were involved. Ferrets were divided into 4 groups (n=12-16/group): control, NNK/CS exposed, NNK/CS plus low-dose lycopene (2.2 mg/kg BW/day), and NNK/CS plus high-dose lycopene (6.6 mg/kg BW/day) groups, for 26 weeks. Results showed that hepatic steatosis, infiltrates of inflammatory cells, and the number and size of inflammatory foci in liver, together with key genes involved in hepatic fibrogenesis were higher in the NNK/CS group compared to the control group; a lycopene diet reversed these changes to the levels of the control group. Interestingly, a major lycopene cleavage enzyme, beta-carotene 9',10'-oxygenase (BCO2), which recently has been recognized to play metabolic roles beyond cleavage function, was down-regulated by NNK/CS exposure, but this decrease was prevented by lycopene feeding. NNK/CS exposure also downregulated liver expression of antioxidant enzymes and upregulated oxidative stress marker, which were all prevented by lycopene. In conclusion, our results suggest that CS can promote development of NASH and liver fibrosis in ferrets, which is associated with downregulation of BCO2 and impairment of antioxidant system in liver; dietary lycopene may inhibit CS-promoted NASH by preventing suppression of BCO2 and decline in antioxidant network.

A Novel MicroRNA Signature for Cholestatic Drugs in Human Hepatocytes and Its Translation into Novel Circulating Biomarkers for Drug-Induced Liver Injury Patients

Drug-induced liver injury (DILI) diagnosis and classification (hepatocellular, cholestatic, and mixed) relies on traditional clinical biomarkers (eg ALT and ALP), despite limitations such as extrahepatic interferences, narrow dynamic ranges, and low mechanistic value. microRNAs may be very useful for complementing traditional DILI biomarkers but most studies in this direction have considered only paracetamol poisoning. Thus the value of microRNAs (miRNAs) as biomarkers for idiosyncratic DILI has not yet been demonstrated. In this study, we first examined the effect of model cholestatic drugs on the human hepatocyte miRNome by RNAseq and RT-qPCR. Results demonstrated that chlorpromazine, cyclosporin A, and ANIT induced (miR-21-3p, -21-5p, -22-3p, -27a-5p, -1260b, -34a-5p, and -98-5p) and repressed (-122-5p, -192-5p, -30c-5p, -424-5p, and -16-5p) specific miRNAs in sandwich-cultured upcyte hepatocytes. However, no common signature was found for cholestatic drugs. Next we investigated the levels of these miRNA in human serum and found that most were also significantly altered in cholestatic/mixed DILI patients upon hospital/ambulatory admission. However, miR-122-5p, -192-5p, -34a-5p, and -22-3p demonstrated a much more significant induction in patients with hepatocellular DILI, thus revealing better specificity for hepatocellular damage. Time-course analyses demonstrated that -1260b and -146 had a very similar profile to ALP, but with wider dynamic ranges, while -16-5p and -451a showed a negative correlation. Conversely, -122-5p and -192-5p correlated with ALT but with wider dynamic ranges and faster recoveries. Finally, the 122/451a and 122/16 ratios showed excellent prediction performances in both the study [area under the receiver operating characteristic curve (AUROC) >0.93] and the validation cohort (AUROC > 0.82), and can, therefore, be postulated for the first time as circulating miRNA biomarkers for idiosyncratic DILI.

Enzymology of vertebrate carotenoid oxygenases

Mammals and higher vertebrates including humans have only three members of the carotenoid cleavage dioxygenase family of enzymes. This review focuses on the two that function as carotenoid oxygenases. β-Carotene 15,15'-dioxygenase (BCO1) catalyzes the oxidative cleavage of the central 15,15' carbon-carbon double of β-carotene bond by addition of molecular oxygen. The product of the reaction is retinaldehyde (retinal or β-apo-15-carotenal). Thus, BCO1 is the enzyme responsible for the conversion of provitamin A carotenoids to vitamin A. It also cleaves the 15,15' bond of β-apocarotenals to yield retinal and of lycopene to yield apo-15-lycopenal. β-Carotene 9',10'-dioxygenase (BCO2) catalyzes the cleavage of the 9,10 and 9',10' double bonds of a wider variety of carotenoids, including both provitamin A and non-provitamin A carotenoids, as well as the xanthophylls, lutein and zeaxanthin. Indeed, the enzyme shows a marked preference for utilization of these xanthophylls and other substrates with hydroxylated terminal rings. Studies of the phenotypes of BCO1 null, BCO2 null, and BCO1/2 double knockout mice and of humans with polymorphisms in the enzymes, has clarified the role of these enzymes in whole body carotenoid and vitamin A homeostasis. These studies also demonstrate the relationship between enzyme expression and whole body lipid and energy metabolism and oxidative stress. In addition, relationships between BCO1 and BCO2 and the development or risk of metabolic diseases, eye diseases and cancer have been observed. While the precise roles of the enzymes in the pathophysiology of most of these diseases is not presently clear, these gaps in knowledge provide fertile ground for rigorous future investigations. This article is part of a Special Issue entitled Carotenoids: Recent Advances in Cell and Molecular Biology edited by Johannes von Lintig and Loredana Quadro.

The human mitochondrial enzyme BCO2 exhibits catalytic activity toward carotenoids and apocarotenoids

The enzyme β-carotene oxygenase 2 (BCO2) converts carotenoids into more polar metabolites. Studies in mammals, fish, and birds revealed that BCO2 controls carotenoid homeostasis and is involved in the pathway for vitamin A production. However, it is controversial whether BCO2 function is conserved in humans, because of a 4-amino acid long insertion caused by a splice acceptor site polymorphism. We here show that human BCO2 splice variants, BCO2a and BCO2b, are expressed as pre-proteins with mitochondrial targeting sequence (MTS). The MTS of BCO2a directed a green fluorescent reporter protein to the mitochondria when expressed in ARPE-19 cells. Removal of the MTS increased solubility of BCO2a when expressed in Escherichia coli and rendered the recombinant protein enzymatically active. The expression of the enzymatically active recombinant human BCO2a was further improved by codon optimization and its fusion with maltose-binding protein. Introduction of the 4-amino acid insertion into mouse Bco2 did not impede the chimeric enzyme's catalytic proficiency. We further showed that the chimeric BCO2 displayed broad substrate specificity and converted carotenoids into two ionones and a central C14-apocarotendial by oxidative cleavage reactions at C9,C10 and C9',C10'. Thus, our study demonstrates that human BCO2 is a catalytically competent enzyme. Consequently, information on BCO2 becomes broadly applicable in human biology with important implications for the physiology of the eyes and other tissues.

Role of lycopene in smoke-promoted chronic obstructive pulmonary disease and lung carcinogenesis

Chronic obstructive pulmonary disease (COPD) and lung cancer are a major cause of morbidity and mortality worldwide, with cigarette smoking being the single most important risk factor for both. Emerging evidence indicates alterations in reverse cholesterol transport-mediated removal of excess cholesterol from lung, and intracellular cholesterol overload to be involved in smoke-promoted COPD and lung cancer development. Since there are currently few effective treatments for COPD and lung cancer, it is important to identify food-derived, biologically active compounds, which can protect against COPD and lung cancer development. High intake of the carotenoid lycopene, as one of phytochemicals, is associated with a decreased risk of chronic lung lesions. This review article summarizes and discusses epidemiologic evidence, in vitro and in vivo studies regarding the prevention of smoke-promoted COPD and lung carcinogenesis through dietary lycopene as an effective intervention strategy. We focus on the recent research implying that lycopene preventive effect is through targeting the main genes involved in reverse cholesterol transport. This review also indicates gaps in knowledge about the function of lycopene against COPD and lung cancer, offering directions for further research.

Gan-Jiang-Ling-Zhu decoction alleviates hepatic steatosis in rats by the miR-138-5p/CPT1B axis

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a commonly-encountered chronic liver disease which lacks verified pharmacological interventions. Gan-Jiang-Ling-Zhu decoction (GJLZ) is a classic formula utilized in clinical practice. In this study, we aimed to evaluate the therapeutic effect of GJLZ in NAFLD and explore the possible underlying mechanisms.

METHODS

Twenty-four rats were randomly divided into three groups: normal group, fed with chow diet for 8 weeks; model group, fed with high fat diet for 8 weeks; and GJLZ group, initially fed HFD for 4 weeks, and then administered the GJLZ decoction for 4 weeks by oral gavage while continuously feeding HFD. Rats were sacrificed after the intervention, and liver tissues and blood samples were harvested. Liver steatosis was detected by HE and Oil Red O staining. Body weight and liver index were analyzed. Liver triglyceride (TG), total cholesterol (TC), and low-density lipoprotein (LDL), serum almandine aminotransferase (ALT), aspartate aminotransferase (AST), and nonesterified fatty acid (NEFA) were assayed using commercial kits. Differentially expressed genes were identified by RNA-sequencing and verified using real-time PCR (RT-PCR) and western blotting. Whole miRNAs were detected by RNA-sequence analysis, and mRNA-targeted miRNAs were verified by RT-PCR. The miRNA-mRNA regulation pattern was confirmed using the dual-luciferase reporter assay.

RESULTS

Treatment with GJLZ significantly improved hepatic steatosis and inflammation, reduced liver index and liver TG content, and also significantly reduced serum ALT and AST levels. Based on the results of RNA-sequence analysis, five differentially expressed genes (DEGs) in the peroxisome proliferator-activated receptor (PPAR) signaling pathway were recognized. RT-PCR confirmed that carnitine palmitoyltransferase 1b (CPT1B) expression was significantly regulated by GJLZ treatment. GJLZ decoction intervention also increased significantly hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha (HADHA) expression. Next, miRNA profiling and screening were performed based on CPT1B alteration. Rno-miR-138-5p likely responded to GJLZ intervention, and rno-miR-138-5p inhibitor increased CPT1B expression while rno-miR-138-5p mimic reduced CPT1B expression. When CPT1B mutated, miR-138-5p mimic and inhibitor could not regulate the luciferase activity of CPT1B.

CONCLUSIONS

GJLZ is an effective formula for NAFLD management, and its possible mechanism of action involves the regulation of CPT1B expression via rno-miR-138-5p.

Mechanistic understanding of β-cryptoxanthin and lycopene in cancer prevention in animal models

To better understand the potential function of carotenoids in the chemoprevention of cancers, mechanistic understanding of carotenoid action on genetic and epigenetic signaling pathways is critically needed for human studies. The use of appropriate animal models is the most justifiable approach to resolve mechanistic issues regarding protective effects of carotenoids at specific organs and tissue sites. While the initial impetus for studying the benefits of carotenoids in cancer prevention was their antioxidant capacity and pro-vitamin A activity, significant advances have been made in the understanding of the action of carotenoids with regards to other mechanisms. This review will focus on two common carotenoids, provitamin A carotenoid β-cryptoxanthin and non-provitamin A carotenoid lycopene, as promising chemopreventive agents or chemotherapeutic compounds against cancer development and progression. We reviewed animal studies demonstrating that β-cryptoxanthin and lycopene effectively prevent the development or progression of various cancers and the potential mechanisms involved. We highlight recent research that the biological functions of β-cryptoxanthin and lycopene are mediated, partially via their oxidative metabolites, through their effects on key molecular targeting events, such as NF-κB signaling pathway, RAR/PPARs signaling, SIRT1 signaling pathway, and p53 tumor suppressor pathways. The molecular targets by β-cryptoxanthin and lycopene, offer new opportunities to further our understanding of common and distinct mechanisms that involve carotenoids in cancer prevention. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Xanthophyll β-Cryptoxanthin Inhibits Highly Refined Carbohydrate Diet-Promoted Hepatocellular Carcinoma Progression in Mice

SCOPE

β-Cryptoxanthin (BCX) can be cleaved by both β-carotene 15,15'-oxygenase (BCO1) and β-carotene 9',10'-oxygenase (BCO2), generating biological active vitamin A and apocarotenoids. We examined whether BCX feeding could inhibit diethylnitrosamine (DEN)-initiated, highly refined carbohydrate diet (HRCD)-promoted hepatocellular carcinoma (HCC) development, dependent or independent of BCO1/BCO2 activity.

METHODS AND RESULTS

Two-week-old male wild-type (WT) and BCO1^-/- /BCO2^-/- double knockout (DKO) mice are given a single intraperitoneal injection of DEN (25 mg kg^-1 body weight) to initiate hepatic carcinogenesis. At 6 weeks of age, all animals are fed HRCD (66.5% of energy from carbohydrate) with or without BCX for 24 weeks. BCX feeding increases hepatic vitamin A levels in WT mice, but not in DKO mice that shows a significant accumulation of hepatic BCX. Compared to their respective HRCD littermates, both WT and DKO fed BCX have significantly lower HCC multiplicity, average tumor size, and total tumor volume, and the steatosis scores. The chemopreventive effects of BCX are associated with increased p53 protein acetylation and decreased protein levels of lactate dehydrogenase and hypoxia-inducible factor-1α in tumors.

CONCLUSION

This study suggests that BCX feeding may alleviate HRCD-promoted HCC progression by modulating the acetylation of p53, hypoxic tumor microenvironment, and glucose metabolism, independent of BCO1/BCO2.

Carotenoids and fatty liver disease: Current knowledge and research gaps

Carotenoids form an important part of the human diet, consumption of which has been associated with many health benefits. With the growing global burden of liver disease, increasing attention has been paid on the possible beneficial role that carotenoids may play in the liver. This review focuses on carotenoid actions in non-alcoholic fatty liver disease (NAFLD), and alcoholic liver disease (ALD). Indeed, many human studies have suggested an association between decreased circulating levels of carotenoids and increased incidence of NAFLD and ALD. The literature describing supplementation of individual carotenoids in rodent models of NAFLD and ALD is reviewed, with particular attention paid to β-carotene and lycopene, but also including β-cryptoxanthin, lutein, zeaxanthin, and astaxanthin. The effect of beta-carotene oxygenase 1 and 2 knock-out mice on hepatic lipid metabolism is also discussed. In general, there is evidence to suggest that carotenoids have beneficial effects in animal models of both NAFLD and ALD. Mechanistically, these benefits may occur via three possible modes of action: 1) improved hepatic antioxidative status broadly attributed to carotenoids in general, 2) the generation of vitamin A from β-carotene and β-cryptoxanthin, leading to improved hepatic retinoid signaling, and 3) the generation of apocarotenoid metabolites from β-carotene and lycopene, that may regulate hepatic signaling pathways. Gaps in our knowledge regarding carotenoid mechanisms of action in the liver are highlighted throughout, and the review ends by emphasizing the importance of dose effects, mode of delivery, and mechanism of action as important areas for further study. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Dietary β-Cryptoxanthin Inhibits High-Refined Carbohydrate Diet-Induced Fatty Liver via Differential Protective Mechanisms Depending on Carotenoid Cleavage Enzymes in Male Mice

BACKGROUND

β-Cryptoxanthin (BCX), a provitamin A carotenoid shown to protect against nonalcoholic fatty liver disease (NAFLD), can be cleaved by β-carotene-15,15'-oxygenase (BCO1) to generate vitamin A, and by β-carotene-9',10'-oxygenase (BCO2) to produce bioactive apo-carotenoids. BCO1/BCO2 polymorphisms have been associated with variations in plasma carotenoid amounts in both humans and animals.

OBJECTIVES

We investigated whether BCX feeding inhibits high refined-carbohydrate diet (HRCD)-induced NAFLD, dependent or independent of BCO1/BCO2.

METHODS

Six-week-old male wild-type (WT) and BCO1-/-/BCO2-/- double knockout (DKO) mice were randomly fed HRCD (66.5% of energy from carbohydrate) with or without BCX (10 mg/kg diet) for 24 wk. Pathological and biochemical variables were analyzed in the liver and mesenteric adipose tissues (MATs). Data were analyzed by 2-factor ANOVA.

RESULTS

Compared to their respective HRCD controls, BCX reduced hepatic steatosis severity by 33‒43% and hepatic total cholesterol by 43‒70% in both WT and DKO mice (P < 0.01). Hepatic concentrations of BCX, but not retinol and retinyl palmitate, were 33-fold higher in DKO mice than in WT mice (P < 0.001). BCX feeding increased the hepatic fatty acid oxidation protein peroxisome proliferator-activated receptor-α, and the cholesterol efflux gene ATP-binding cassette transporter5, and suppressed the lipogenesis gene acetyl-CoA carboxylase 1 (Acc1) in the MAT of WT mice but not DKO mice (P < 0.05). BCX feeding decreased the hepatic lipogenesis proteins ACC and stearoyl-CoA desaturase-1 (3-fold and 5-fold) and the cholesterol synthesis genes 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase and HMG-CoA synthase 1 (2.7-fold and 1.8-fold) and increased the cholesterol catabolism gene cholesterol 7α-hydroxylase (1.9-fold) in the DKO but not WT mice (P < 0.05). BCX feeding increased hepatic protein sirtuin1 (2.5-fold) and AMP-activated protein kinase (9-fold) and decreased hepatic farnesoid X receptor protein (80%) and the inflammatory cytokine gene Il6 (6-fold) in the MAT of DKO mice but not WT mice (P < 0.05).

CONCLUSION

BCX feeding mitigates HRCD-induced NAFLD in both WT and DKO mice through different mechanisms in the liver-MAT axis, depending on the presence or absence of BCO1/BCO2.

Associations for BCO2, PCSK9, and TR1B1 Polymorphism and Lifestyle Factors with Ischemic Stroke: A Nested Case-Control Study

PURPOSE

To investigate associations for polymorphisms in β-carotene 9',10'-oxygenase (BCO2, rs10431036 and rs11214109), proprotein convertase subtilisin kexin type 9 (PCSK9, rs11583680), and tribbles pseudokinase 1 (TRIB1, rs17321515 and rs2954029), as well as lifestyle factors, with ischemic stroke (IS).

MATERIALS AND METHODS

This nested case-control study included 161 patients with IS and 483 matched control individuals. We collected medical reports, lifestyle details, and blood samples from individuals and used the PCR-ligase detection reaction method to genotype single nucleotide polymorphisms (SNPs).

RESULTS

The GA+AA genotype of rs10431036 (p<0.001) and rs17321515 (p=0.003), the CT+TT genotype of rs11214109 (p=0.005), and the TA+AA genotype of rs2954029 (p=0.006) in dominant models increased the risk of IS. In additive models, the GG genotype of rs17321515 (p=0.005) and the TT genotype of rs2954029 (p=0.008) increased the risk of IS. Adequate intake of fruits/vegetables reduced the risk of IS (p=0.005). Although there was no interaction between genes and fruits/vegetables, people with inadequate intake of fruits/vegetables who carried a risk genotype had a higher risk of IS than those only having inadequate fruits/vegetables intake or those only carrying a risk genotype. Also, the haplotypes AC, AT, and GT (comprising rs10431036 and rs11214109) and GT (comprising rs2954029 and rs17321515) were found to be associated with an increased risk of IS (p<0.05).

CONCLUSION

Polymorphisms in BCO2 and TRIB1 and fruits/vegetables intake were associated with IS. These results provide the theoretical basis for gene screening to prevent chronic cerebrovascular diseases.

β-Carotene 15,15'-oxygenase inhibits cancer cell stemness and metastasis by regulating differentiation-related miRNAs in human neuroblastoma

Neuroblastoma (NB) is the most common pediatric malignancy and is considered to possess cancer stem cells (CSCs) properties which can drive tumor initiation and metastasis. β-carotene 15,15'-oxygenase (BCO1) is the main enzyme that catalyzes the first step in vitamin A biosynthesis from pro-vitamin A carotenoids. Retinoids (vitamin A) play a critical role in NB differentiation. However, the biological functions of BCO1 in NB remained to be elucidated. Here, we investigated the effects of BCO1 on NB CSCs with stably expressing BCO1 in NB cells. We show that BCO1 significantly suppressed self-renewal and markers of NB CSCs. Moreover, BCO1 inhibited the metastatic potential of NB cells and suppressed the enzymatic activity and expression of MMPs, as well as expression of HIF-1α and its downstream targets. In vivo, BCO1 reduced the metastatic incidence and volumes of metastatic tumors and downregulated the expression of CSCs markers, MMPs, and HIF-1α in tumor tissues of a mouse xenograft model. A possible mechanism underlying the anti-cancer activities of BCO1 is proposed based on miRNAs sequencing array data which suggests a role for BCO1 in regulating miRNAs associated with neuronal differentiation, cell-cell adhesion, and the Wnt signaling pathway. Thus, our results demonstrate new chemotherapeutic roles for BCO1 in malignant NB that mediate suppression of cancer stemness and metastasis.

Dietary Tomato Powder Inhibits High-Fat Diet-Promoted Hepatocellular Carcinoma with Alteration of Gut Microbiota in Mice Lacking Carotenoid Cleavage Enzymes

Both incidence and death rate due to liver cancer have increased in the United States. Higher consumption of lycopene-rich tomato and tomato products is associated with a decreased risk of cancers. β-Carotene-15, 15'-oxygenase (BCO1), and β-carotene-9', 10'-oxygenase (BCO2) cleave lycopene to produce bioactive apo-lycopenoids. Although BCO1/BCO2 polymorphisms affect human and animal lycopene levels, whether dietary tomato consumption can inhibit high-fat diet (HFD)-promoted hepatocellular carcinoma (HCC) development and affect gut microbiota in the absence of BCO1/BCO2 is unclear. BCO1/BCO2 double knockout mice were initiated with a hepatic carcinogen (diethylnitrosamine) at 2 weeks of age. At 6 weeks of age, the mice were randomly assigned to an HFD (60% of energy as fat) with or without tomato powder (TP) feeding for 24 weeks. Results showed that TP feeding significantly decreased HCC development (67%, 83%, and 95% reduction in incidence, multiplicity, and tumor volume, respectively, P < 0.05). Protective effects of TP feeding were associated with (1) decreased hepatic inflammatory foci development and mRNA expression of proinflammatory biomarkers (IL1β, IL6, IL12α, monocyte chemoattractant protein-1, and inducible NO synthase); (2) increased mRNA expression of deacetylase sirtuin 1 and nicotinamide phosphoribosyltransferase involving NAD⁺ production; and (3) increased hepatic circadian clock genes (circadian locomotor output cycles kaput, period 2, and cryptochrome-2, Wee1). Furthermore, TP feeding increased gut microbial richness and diversity, and significantly decreased the relative abundance of the genus Clostridium and Mucispirillum, respectively. The present study demonstrates that dietary tomato feeding independent of carotenoid cleavage enzymes prevents HFD-induced inflammation with potential modulating gut microbiota and inhibits HFD-promoted HCC development.

Effects of Ginsenoside Rg3 on fatigue resistance and SIRT1 in aged rats

BACKGROUND

Ginsenoside Rg3 (Rg3) is one of the key components of a frequently used herbal tonic panax ginseng for fatigue treatment. However, the molecular mechanisms of Rg3 on anti-fatigue effects have not been completely understood yet.

METHODS AND MATERIALS

We built a postoperative fatigue syndrome (POFS) model and tried to elucidate the molecular mechanisms responsible for anti-fatigue effects of Rg3. 160 aged male rats were randomly divided into four groups (n = 40/group): normal group, Rg3-treated normal group (Rg3 group), postoperative fatigue syndrome model group (POFS group) and Rg3-treated postoperative fatigue syndrome model group (POFS + Rg3 group). The open field test (OFT) was used to assess general activity and exploratory behavior of rats in different groups. We then analyzed total cholesterol (TC), serum triglyceride (TG) and lactate dehydrogenase (LDH) in the blood, as well as superoxide dismutase (SOD), malondialdehyde (MDA), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression in skeletal muscles of rats. We also detected the influence of Rg3 on silent information regulator of transcription 1 (sirtuin1, SIRT1) activity and protein 53 (p53) transcriptional activity in vitro.

RESULTS

Rg3 significantly increased the journey distance and rearing frequency, while slowed down the rest time. The serum concentrations of TC, TG and LDH were all up-regulated by Rg3. Meanwhile, Rg3 increased concentrations of SOD, but also decreased MDA release out of skeletal muscles. The mRNA expressions of PGC-1α and PEPCK were also enhanced by Rg3. Besides, Rg3 could activate SIRT1 and suppress p53 transcriptional activity in the biological process.

DISCUSSION AND CONCLUSION

Rg3 could improve exercise performance and resist fatigue possibly through elevating SIRT1 deacetylase activity.