Colors with functions: elucidating the biochemical and molecular basis of carotenoid metabolism

Effects of fermentation on the structures of yellow compounds in citrus pomace

To enhance the stability and light resistance of the yellow compounds in citrus pomace, our study successfully isolated and purified five compounds using ultrasonic-assisted extraction and column chromatography. The identified compounds include methyl linoleate, (2-ethyl)hexyl phthalate, 1,3-distearoyl-2-oleoylglycerol, 6,6-ditetradecyl-6,7-dihydroxazepin-2(3H)-one, and n-octadeca-17-enoic acid. The monomers extracted from fresh pomace, compounds 1 and 2, exhibit structural similarities to flavonoids and carotenoids. In contrast, the polymers isolated from fermented pomace, compounds 3, 4, and 5, share structural units with the fresh pomace compounds, indicating the transformation to stable polymeric forms. This suggests that the microbial fermentation process not only enhances the value of citrus pomace, but also provides a promising pathway for the synthesis of natural antioxidant yellow pigments with far-reaching theoretical and practical significance.

Advances in the metabolic engineering of Saccharomyces cerevisiae and Yarrowia lipolytica for the production of -carotene

β-Carotene is one kind of the most important carotenoids. The major functions of β-carotene include the antioxidant and anti-cardiovascular properties, which make it a growing market. Recently, the use of metabolic engineering to construct microbial cell factories to synthesize β-carotene has become the latest model for its industrial production. Among these cell factories, yeasts including Saccharomyces cerevisiae and Yarrowia lipolytica have attracted the most attention because of the: security, mature genetic manipulation tools, high flux toward carotenoids using the native mevalonate pathway and robustness for large-scale fermentation. In this review, the latest strategies for β-carotene biosynthesis, including protein engineering, promoters engineering and morphological engineering are summarized in detail. Finally, perspectives for future engineering approaches are proposed to improve β-carotene production.

Evolution and expression analysis of carotenoid cleavage oxygenase gene family in Chinese mitten crab Eriocheir sinensis

Carotenoid cleavage oxygenase (CCO) plays a pivotal role in various biological activities, including antioxidant and immune functions in animals. This paper investigates the evolution and expression of CCO genes based on three chordates and 27 arthropods. Aquatic animals exhibit a higher abundance of CCO genes. Despite this, research on CCO in crustaceans has been notably limited, with a complete absence of any previous studies on the CCO genes for the Chinese mitten crab (Eriocheir sinensis). In this study, six CCO genes were identified in the E. sinensis genome database. Results reveal that the evolution of the CCO gene family in Crustacea is primarily characterized by purifying selection, with a preference for employing similar codons. EsCCO1 and EsCCO3 were mainly expressed in the epidermal layer, and EsCCO4 was mainly expressed in the hindgut. Meanwhile, EsCCO5 and EsCCO6 were mainly expressed in the hepatopancreas and endometrium. A notable detail that different EsCCO genes demonstrate distinct expression patterns within various tissues of E. sinensis. The findings of this study offer fundamental insights that could serve as a basis for further exploration into the functions and regulatory mechanisms of CCO genes in crustacean species.

A Review of the Anti-Obesity Effects of Wild Edible Plants in the Mediterranean Diet and Their Active Compounds: From Traditional Uses to Action Mechanisms and Therapeutic Targets

Obesity is a long-term condition resulting from a continuous imbalance between the amount of energy consumed and expended. It is associated with premature mortality and contributes to a large portion of the global chronic disease burden, including diabesity, cardiovascular disease, hypertension, and some cancers. While lifestyle changes and dietary adjustments are the primary ways to manage obesity, they may not always be sufficient for long-term weight loss. In these cases, medication may be necessary. However, the options for drugs are limited due to their potential side effects. As a result, there is a need to identify safe and effective alternative treatments. Recently, dietary compounds, plants, and bioactive phytochemicals have been considered as promising sources for discovering new pharmacological agents to treat obesity and its related complications. These natural products can function independently or synergistically with other plants to augment their effects at various levels of the body. They can modulate appetite, lipase activity, thermogenesis and fat synthesis and degradation, satiation, adipogenesis, and adipocyte apoptosis. Additionally, targeting adipocyte growth and differentiation with diverse medicinal plants/diet is a significant strategy for devising new anti-obesity drugs that can intervene in preadipocytes, maturing preadipocytes, and mature adipocytes. Clinical trials have shown that the wild edible plants in the Mediterranean diet can reduce the risk of obesity and its related diseases. This review examines the effectiveness of the common components of the Mediterranean diet in managing obesity and its associated health issues. We conducted a comprehensive literature review using PubMed, Science Direct, Google Scholar, and Medline Plus to gather data on the therapeutic effects of the Mediterranean diet and phytochemicals in treating obesity and its associated diseases.

BCH1 expression pattern contributes to the fruit carotenoid diversity between peach and apricot

Peach (Prunus persica L. Batsch) and apricot (Prunus armeniaca L.) are two species of economic importance for fruit production in the genus Prunus. Peach and apricot fruits exhibit significant differences in carotenoid levels and profiles. HPLC-PAD analysis showed that a greater content of β-carotene in mature apricot fruits is primarily responsible for orange color, while peach fruits showed a prominent accumulation of xanthophylls (violaxanthin and cryptoxanthin) with yellow color. There are two β-carotene hydroxylase genes in both peach and apricot genomes. Transcriptional analysis revealed that BCH1 expresses highly in peach but lowly in apricot fruit, showing a correlation with peach and apricot fruit carotenoid profiles. By using a carotenoid engineered bacterial system, it was demonstrated that there was no difference in the BCH1 enzymatic activity between peach and apricot. Comparative analysis about the putative cis-acting regulatory elements between peach and apricot BCH1 promoters provided important information for our understanding of the differences in promoter activity of the BCH1 genes in peach and apricot. Therefore, we investigated the promoter activity of BCH1 gene through a GUS detection system, and confirmed that the difference in the transcription level of the BCH1 gene resulted from the difference of the promoter function. This study provides important perspective to understanding the diversity of carotenoid accumulation in Prunus fruits such as peach and apricot. In particular, BCH1 gene is proposed as a main predictor for β-carotene content in peach and apricot fruits during the ripening process.

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.

Biofortification to avoid malnutrition in humans in a changing climate: Enhancing micronutrient bioavailability in seed, tuber, and storage roots

Malnutrition results in enormous socio-economic costs to the individual, their community, and the nation's economy. The evidence suggests an overall negative impact of climate change on the agricultural productivity and nutritional quality of food crops. Producing more food with better nutritional quality, which is feasible, should be prioritized in crop improvement programs. Biofortification refers to developing micronutrient -dense cultivars through crossbreeding or genetic engineering. This review provides updates on nutrient acquisition, transport, and storage in plant organs; the cross-talk between macro- and micronutrients transport and signaling; nutrient profiling and spatial and temporal distribution; the putative and functionally characterized genes/single-nucleotide polymorphisms associated with Fe, Zn, and β-carotene; and global efforts to breed nutrient-dense crops and map adoption of such crops globally. This article also includes an overview on the bioavailability, bioaccessibility, and bioactivity of nutrients as well as the molecular basis of nutrient transport and absorption in human. Over 400 minerals (Fe, Zn) and provitamin A-rich cultivars have been released in the Global South. Approximately 4.6 million households currently cultivate Zn-rich rice and wheat, while ~3 million households in sub-Saharan Africa and Latin America benefit from Fe-rich beans, and 2.6 million people in sub-Saharan Africa and Brazil eat provitamin A-rich cassava. Furthermore, nutrient profiles can be improved through genetic engineering in an agronomically acceptable genetic background. The development of "Golden Rice" and provitamin A-rich dessert bananas and subsequent transfer of this trait into locally adapted cultivars are evident, with no significant change in nutritional profile, except for the trait incorporated. A greater understanding of nutrient transport and absorption may lead to the development of diet therapy for the betterment of human health.

Lycopene Improves Metabolic Disorders and Liver Injury Induced by a Hight-Fat Diet in Obese Rats

Epidemiological studies have shown that the consumption of a high-fat diet (HFD) is positively related to the development of obesity. Lycopene (LYC) can potentially combat HFD-induced obesity and metabolic disorders in rats. This study aimed to investigate the effect of LYC on metabolic syndrome and assess its anti-inflammatory and antioxidant effects on the liver and adipose tissue in rats fed an HFD. Thirty-six male Wistar albino rats were divided into three groups. Group Ι (the control group) was fed a normal diet, group ΙΙ (HFD) received an HFD for 16 weeks, and group ΙΙΙ (HFD + LYC) received an HFD for 12 weeks and then LYC (25 mg/kg b.wt) was administered for four weeks. Lipid peroxidation, antioxidants, lipid profile, liver function biomarkers, and inflammatory markers were determined. The results showed that long-term consumption of an HFD significantly increased weight gain, liver weight, and cholesterol and triglyceride levels. Rats on an HFD displayed higher levels of lipid peroxidation and inflammatory markers. Moreover, liver and white adipose tissue histopathological investigations showed that LYC treatment mended the damaged tissue. Overall, LYC supplementation successfully reversed HFD-induced changes and shifts through its antioxidant and anti-inflammatory activity. Therefore, LYC displayed a therapeutic potential to manage obesity and its associated pathologies.

NRF2 in dermatological disorders: Pharmacological activation for protection against cutaneous photodamage and photodermatosis

The skin barrier and its endogenous protective mechanisms cope daily with exogenous stressors, of which ultraviolet radiation (UVR) poses an imminent danger. Although the skin is able to reduce the potential damage, there is a need for comprehensive strategies for protection. This is particularly important when developing pharmacological approaches to protect against photocarcinogenesis. Activation of NRF2 has the potential to provide comprehensive and long-lasting protection due to the upregulation of numerous cytoprotective downstream effector proteins that can counteract the damaging effects of UVR. This is also applicable to photodermatosis conditions that exacerbate the damage caused by UVR. This review describes the alterations caused by UVR in normal skin and photosensitive disorders, and provides evidence to support the development of NRF2 activators as pharmacological treatments. Key natural and synthetic activators with photoprotective properties are summarized. Lastly, the gap in knowledge in research associated with photodermatosis conditions is highlighted.

Retinol-binding protein-4 and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming increasingly common as the global economy grows and living standards improve. Timely and effective preventions and treatments for NAFLD are urgently needed. Retinol-binding protein-4 (RBP4), the protein that transports retinol through the circulation, was found to be positively related to diabetes, obesity, cardiovascular disease, and other metabolic diseases. Observational studies on the association between serum RBP4 level and the prevalence of NAFLD found contradictory results. Some of the underlying mechanisms responsible for this association have been revealed, and the possible clinical implications of treating NAFLD by targeting RBP4 have been demonstrated. Future studies should focus on the predictive value of RBP4 on NAFLD development and its potential as a therapeutic target in NAFLD.

Chemical manipulation of mitochondrial function affects metabolism of red carotenoids in a marine copepod (Tigriopus californicus)

The shared-pathway hypothesis offers a cellular explanation for the connection between ketocarotenoid pigmentation and individual quality. Under this hypothesis, ketocarotenoid metabolism shares cellular pathways with mitochondrial oxidative phosphorylation such that red carotenoid-based coloration is inextricably linked mitochondrial function. To test this hypothesis, we exposed Tigriopus californicus copepods to a mitochondrially targeted protonophore, 2,4-dinitrophenol (DNP), to induce proton leak in the inner mitochondrial membranes. We then measured whole-animal metabolic rate and ketocarotenoid accumulation. As observed in prior studies of vertebrates, we observed that DNP treatment of copepods significantly increased respiration and that DNP-treated copepods accumulated more ketocarotenoid than control animals. Moreover, we observed a relationship between ketocarotenoid concentration and metabolic rate, and this association was strongest in DNP-treated copepods. These data support the hypothesis that ketocarotenoid and mitochondrial metabolism are biochemically intertwined. Moreover, these results corroborate observations in vertebrates, perhaps suggesting a fundamental connection between ketocarotenoid pigmentation and mitochondrial function that should be explored further.

Carotenoids and Vitamin A in Breastmilk of Hong Kong Lactating Mothers and Their Relationships with Maternal Diet

Carotenoids and vitamin A are nutrients crucial to infants’ development. To date, there is limited data on their availability in breastmilk and the associated dietary factors, especially in Hong Kong, where people follow a westernized Chinese diet. This study determined the selected breastmilk’s carotenoid and vitamin A (retinol) contents by ultraperformance liquid chromatography with photodiode detection (UPLC-PDA) and the dietary intakes by three-day food records in 87 Hong Kong lactating mothers, who were grouped into tertiles based on their daily carotenoid intake. Low vitamin A intake (530.2 ± 34.2 µg RAE/day) and breastmilk retinol level (1013.4 ± 36.8 nmol/L) were reported in our participants, suggesting a poor vitamin A status of the lactating participants having relatively higher socioeconomic status in Hong Kong. Mothers in the highest tertile (T3) had higher breastmilk carotenoid levels than those in the lowest (T1) (p < 0.05). There were significant associations between maternal carotenoid intakes and breastmilk lutein levels in the linear regression models (p < 0.05) regardless of dietary supplement intake. Furthermore, maternal dark green vegetable intakes were associated with breastmilk retinol, lutein, and β-carotene levels. These findings can serve as dietary references for lactating mothers to enhance breastmilk carotenoid and vitamin A contents for the benefits of child growth and development.

Transcriptome analysis based on dietary beta-carotene supplement reveals genes potentially involved in carotenoid metabolism in Crassostrea gigas

Carotenoids are essential micronutrients for animals, and they can only be obtained from the diet for mollusk as well as other animals. In the body, carotenoids undergo processes including absorption, transport, deposition, and metabolic conversion; however, knowledge of the involved genes is still limited. To elucidate the molecular mechanisms of carotenoid processing and identify the related genes in Pacific oyster (Crassostrea gigas), we performed a comparative transcriptome analysis using digestive gland tissues of oysters on a beta-carotene supplemented diet or a normal diet. A total of 718 differentially expressed genes were obtained, including 505 upregulated and 213 downregulated genes in the beta-carotene supplemented group. Function Annotation and enrichment analyses revealed enrichment in genes possibly involved in carotenoid transport and storage (e.g., LOC105342035), carotenoid cleavage (e.g., LOC105341121), retinoid homeostasis (e.g., LOC105339597) and PPAR signaling pathway (e.g., LOC105323212). Notably, down-regulation of mRNA expressions of two apolipoprotein genes (LOC105342035 and LOC105342186) by RNA interference significantly decreased the carotenoid level in the digestive gland, supporting their role in carotenoid transport and storage. Based on these differentially expressed genes, we propose that there may be a negative feedback mechanism regulated by nuclear receptor transcription factors controlling carotenoid oxygenases. Our findings provide useful hints for elucidating the molecular basis of carotenoid metabolism and functions of carotenoid-related genes in the oyster.

Aster proteins mediate carotenoid transport in mammalian cells

Carotenoid pigments accumulate in specific patterns in vertebrate tissues and play important roles as colorants, chromophores, and hormone precursors. However, proteins that facilitate transportation of these lipophilic pigments within cells have not been identified. We provide evidence that Aster proteins are key components for this process and show that they bind the pigments with high affinity. We observed in mice that carotenoids accumulate in tissues that express Aster-B and this accumulation can be prevented by enzymatic turnover by the BCO2 protein. Accordingly, we found opposing expression patterns of the Aster-B protein and BCO2 in the human retina that seemingly contribute to the unique carotenoid concentration in the macula lutea.

Some mammalian tissues uniquely concentrate carotenoids, but the underlying biochemical mechanism for this accumulation has not been fully elucidated. For instance, the central retina of the primate eyes displays high levels of the carotenoids, lutein, and zeaxanthin, whereas the pigments are largely absent in rodent retinas. We previously identified the scavenger receptor class B type 1 and the enzyme β-carotene-oxygenase-2 (BCO2) as key components that determine carotenoid concentration in tissues. We now provide evidence that Aster (GRAM-domain-containing) proteins, recently recognized for their role in nonvesicular cholesterol transport, engage in carotenoid metabolism. Our analyses revealed that the StART-like lipid binding domain of Aster proteins can accommodate the bulky pigments and bind them with high affinity. We further showed that carotenoids and cholesterol compete for the same binding site. We established a bacterial test system to demonstrate that the StART-like domains of mouse and human Aster proteins can extract carotenoids from biological membranes. Mice deficient for the carotenoid catabolizing enzyme BCO2 concentrated carotenoids in Aster-B protein-expressing tissues such as the adrenal glands. Remarkably, Aster-B was expressed in the human but not in the mouse retina. Within the retina, Aster-B and BCO2 showed opposite expression patterns in central versus peripheral parts. Together, our study unravels the biochemical basis for intracellular carotenoid transport and implicates Aster-B in the pathway for macula pigment concentration in the human retina.

Structural and Functional Analysis of Nonheme Iron Enzymes BCMO-1 and BCMO-2 from Caenorhabditis elegans

Carotenoid metabolism is critical for diverse physiological processes. The nematode Caenorhabditis elegans has two genes that are annotated as β-carotene 15,15′-monooxygenase (BCMO) and are 17 centimorgan apart on chromosome II, but the function of BCMO-1 and BCMO-2 remains uncharacterized. Sequence homology indicates that the two enzymes belong to the carotenoid cleavage dioxygenase family that share a seven-bladed β-propeller fold with a nonheme iron center. Here we determined crystal structures of BCMO-1 and BCMO-2 at resolutions of 1.8 and 1.9 Å, respectively. Structural analysis reveals that BCMO-1 and BCMO-2 are strikingly similar to each other. We also characterized their β-carotene cleavage activity, but the results suggest that they may not act as β-carotene 15,15′-oxygenases.

De novo assembly transcriptome analysis reveals the genes associated with body color formation in the freshwater ornamental shrimps Neocaridina denticulate sinensis

The body color of Neocaridina denticulate sinensis is a compelling phenotypic trait, in which a cascade of carotenoid metabolic processes plays an important role. The study was conducted to compare the transcriptome of cephalothoraxes among three pigmentation phenotypes (red, blue, and chocolate) of N. denticulate sinensis. The purpose of this study was to explore the candidate genes associated with different colors of N. denticulate sinensis. Nine cDNA libraries in three groups were constructed from the cephalothoraxes of shrimps. After assembly, 75022 unigenes were obtained in total with an average length of 1026 bp and N50 length of 1876 bp. There were 45977, 25284, 23605, 21913 unigenes annotated in the Nr, Swissprot, KOG, and KEGG databases, respectively. Differential expression analysis revealed that there were 829, 554, and 3194 differentially expressed genes (DEGs) in RD vs BL, RD vs CH, and BL vs CH, respectively. These DEGs may play roles in the absorption, transport, and metabolism of carotenoids. We also emphasized that electron transfer across the inner mitochondrial membrane (IMM) was a key process in pigment metabolism. In addition, a total of 6328 simple sequence repeats (SSRs) were also detected in N. denticulate sinensis. The results laid a solid foundation for further research on the molecular mechanism of integument pigmentation in the crustacean and contributed to developing more attractive aquatic animals.

Carotenoids and Carcinogenesis: Exploring the Antioxidant and Cell Signaling Roles of Carotenoids in the Prevention of Cancer

Carotenoids are lipid soluble pigments found in various fruits and vegetables and are naturally produced in photoautotrophic plants. Various studies have investigated the properties of carotenoids to determine how they are able to mitigate numerous diseases, including cancer. Carotenoids present in human serum, including β-carotene, α-carotene, lycopene, β-cryptoxanthin, zeaxanthin, and lutein have demonstrated the ability to act as anticarcinogenic agents. Prevention of disease is often described to be more effective than treatment; as cancer impacts millions of lives globally, the role of carotenoids in the prevention of oncogenesis for numerous types of cancers have been extensively researched. This review provides an in-depth analysis of the structure and properties of carotenoids, as well as the identified and potential mechanisms by which carotenoids can act as a chemopreventative agent.

Exploring the Diversity and Regulation of Apocarotenoid Metabolic Pathways in Plants

In plants, carotenoids are subjected to enzyme-catalyzed oxidative cleavage reactions as well as to non-enzymatic degradation processes, which produce various carbonyl products called apocarotenoids. These conversions control carotenoid content in different tissues and give rise to apocarotenoid hormones and signaling molecules, which play important roles in plant growth and development, response to environmental stimuli, and in interactions with surrounding organisms. In addition, carotenoid cleavage gives rise to apocarotenoid pigments and volatiles that contribute to the color and flavor of many flowers and several fruits. Some apocarotenoid pigments, such as crocins and bixin, are widely utilized as colorants and additives in food and cosmetic industry and also have health-promoting properties. Considering the importance of this class of metabolites, investigation of apocarotenoid diversity and regulation has increasingly attracted the attention of plant biologists. Here, we provide an update on the plant apocarotenoid biosynthetic pathway, especially highlighting the diversity of the enzyme carotenoid cleavage dioxygenase 4 (CCD4) from different plant species with respect to substrate specificity and regioselectivity, which contribute to the formation of diverse apocarotenoid volatiles and pigments. In addition, we summarize the regulation of apocarotenoid metabolic pathway at transcriptional, post-translational, and epigenetic levels. Finally, we describe inter- and intraspecies variation in apocarotenoid production observed in many important horticulture crops and depict recent progress in elucidating the genetic basis of the natural variation in the composition and amount of apocarotenoids. We propose that the illustration of biochemical, genetic, and evolutionary background of apocarotenoid diversity would not only accelerate the discovery of unknown biosynthetic and regulatory genes of bioactive apocarotenoids but also enable the identification of genetic variation of causal genes for marker-assisted improvement of aroma and color of fruits and vegetables and CRISPR-based next-generation metabolic engineering of high-value apocarotenoids.

Role of Peroxisome Proliferator-Activated Receptors (PPARs) in Energy Homeostasis of Dairy Animals: Exploiting Their Modulation through Nutrigenomic Interventions

Peroxisome proliferator-activated receptors (PPARs) are the nuclear receptors that could mediate the nutrient-dependent transcriptional activation and regulate metabolic networks through energy homeostasis. However, these receptors cannot work properly under metabolic stress. PPARs and their subtypes can be modulated by nutrigenomic interventions, particularly under stress conditions to restore cellular homeostasis. Many nutrients such as polyunsaturated fatty acids, vitamins, dietary amino acids and phytochemicals have shown their ability for potential activation or inhibition of PPARs. Thus, through different mechanisms, all these nutrients can modulate PPARs and are ultimately helpful to prevent various metabolic disorders, particularly in transition dairy cows. This review aims to provide insights into the crucial role of PPARs in energy metabolism and their potential modulation through nutrigenomic interventions to improve energy homeostasis in dairy animals.

Redox regulation by carotenoids: Evidence and conflicts for their application in cancer

Carotenoids have been constantly investigated since the early fifty for their chemical, biochemical and biological properties being presence in foods. Among the more than 1100 carotenoids synthesized by plants and microorganisms, approximately 50 are present in the human diet, and about 20 can be detected in human blood and tissues. Review articles that discuss the anticancer and cancer preventing activity of phytochemicals have often in common the difficulty to find a coherency between the results deriving from experimental studies and the controversial or weak clinical indications arising from epidemiological and interventional studies. In this scenario, the class of carotenoids does not represent an exception. In fact, according with World Cancer Research Fund, strong evidence exists that high-dose supplementation of β-carotene increases the risk of lung cancer, while for other types of cancer, the protective or harmful effects of food-containing carotenoids or carotenoid supplements have been considered limited, suggestive or unlikely. The analysis of the mechanistic evidence is complicated by the double nature of carotenoids being molecules acting either as antioxidant or pro-oxidant compounds. The present review analyzes the ambiguity and the unexpected results deriving from the epidemiological and interventional studies and discusses how the effects of carotenoids on cancer risk can be explained by understanding their capacity to modulate the cellular antioxidant response, depending on the concentration applied and the cellular metabolism. In the final part, a new global approach is proposed to study the contribution of carotenoids, but also of other phytochemicals, to disease prevention, including cancer.

Evidence for hybrid breakdown in production of red carotenoids in the marine invertebrate Tigriopus californicus

The marine copepod, Tigriopus californicus, produces the red carotenoid pigment astaxanthin from yellow dietary precursors. This ‘bioconversion’ of yellow carotenoids to red is hypothesized to be linked to individual condition, possibly through shared metabolic pathways with mitochondrial oxidative phosphorylation. Experimental inter-population crosses of lab-reared T. californicus typically produces low-fitness hybrids is due in large part to the disruption of coadapted sets nuclear and mitochondrial genes within the parental populations. These hybrid incompatibilities can increase variability in life history traits and energy production among hybrid lines. Here, we tested if production of astaxanthin was compromised in hybrid copepods and if it was linked to mitochondrial metabolism and offspring development. We observed no clear mitonuclear dysfunction in hybrids fed a limited, carotenoid-deficient diet of nutritional yeast. However, when yellow carotenoids were restored to their diet, hybrid lines produced less astaxanthin than parental lines. We observed that lines fed a yeast diet produced less ATP and had slower offspring development compared to lines fed a more complete diet of algae, suggesting the yeast-only diet may have obscured effects of mitonuclear dysfunction. Astaxanthin production was not significantly associated with development among lines fed a yeast diet but was negatively related to development in early generation hybrids fed an algal diet. In lines fed yeast, astaxanthin was negatively related to ATP synthesis, but in lines fed algae, the relationship was reversed. Although the effects of the yeast diet may have obscured evidence of hybrid dysfunction, these results suggest that astaxanthin bioconversion may still be related to mitochondrial performance and reproductive success.

Avian Coloration Genetics: Recent Advances and Emerging Questions

The colorful phenotypes of birds have long provided rich source material for evolutionary biologists. Avian plumage, beaks, skin, and eggs-which exhibit a stunning range of cryptic and conspicuous forms-inspired early work on adaptive coloration. More recently, avian color has fueled discoveries on the physiological, developmental, and-increasingly-genetic mechanisms responsible for phenotypic variation. The relative ease with which avian color traits can be quantified has made birds an attractive system for uncovering links between phenotype and genotype. Accordingly, the field of avian coloration genetics is burgeoning. In this review, we highlight recent advances and emerging questions associated with the genetic underpinnings of bird color. We start by describing breakthroughs related to 2 pigment classes: carotenoids that produce red, yellow, and orange in most birds and psittacofulvins that produce similar colors in parrots. We then discuss structural colors, which are produced by the interaction of light with nanoscale materials and greatly extend the plumage palette. Structural color genetics remain understudied-but this paradigm is changing. We next explore how colors that arise from interactions among pigmentary and structural mechanisms may be controlled by genes that are co-expressed or co-regulated. We also identify opportunities to investigate genes mediating within-feather micropatterning and the coloration of bare parts and eggs. We conclude by spotlighting 2 research areas-mechanistic links between color vision and color production, and speciation-that have been invigorated by genetic insights, a trend likely to continue as new genomic approaches are applied to non-model species.

Mechanisms of vitamin A metabolism and deficiency in the mammalian and fly visual system

Vitamin A deficiency can cause human pathologies that range from blindness to embryonic malformations. This diversity is due to the lack of two major vitamin A metabolites with very different functions: the chromophore 11-cis-retinal (vitamin A aldehyde) is a critical component of the visual pigment that mediates phototransduction, while the signaling molecule all-trans-retinoic acid regulates the development of various tissues and is required for the function of the immune system. Since animals cannot synthesize vitamin A de novo, they must obtain it either as preformed vitamin A from animal products or as carotenoid precursors from plant sources. Due to its essential role in the visual system, acute vitamin A deprivation impairs photoreceptor function and causes night blindness (poor vision under dim light conditions), while chronic deprivation results in retinal dystrophies and photoreceptor cell death. Chronic vitamin A deficiency is the leading cause of preventable childhood blindness according to the World Health Organization. Due to the requirement of vitamin A for retinoic acid signaling in development and in the immune system, vitamin A deficiency also causes increased mortality in children and pregnant women in developing countries. Drosophila melanogaster is an excellent model to study the effects of vitamin A deprivation on the eye because vitamin A is not essential for Drosophila development and chronic deficiency does not cause lethality. Moreover, genetic screens in Drosophila have identified evolutionarily conserved factors that mediate the production of vitamin A and its cellular uptake. Here, we review our current knowledge about the role of vitamin A in the visual system of mammals and Drosophila melanogaster. We compare the molecular mechanisms that mediate the uptake of dietary vitamin A precursors and the metabolism of vitamin A, as well as the consequences of vitamin A deficiency for the structure and function of the eye.

Associations between serum carotenoid levels and the risk of non-Hodgkin lymphoma: a case-control study

Limited studies have investigated the effects of serum carotenoids on the risk of non-Hodgkin lymphoma (NHL), and the findings have been inconclusive. This study aims to assess the association between serum total or specific carotenoid levels and NHL risk. This 1:1 matched, hospital-based case-control study enrolled 512 newly diagnosed (within 1 month) NHL patients and 512 healthy controls who were matched by age (±5 years) and sex in Urumqi, China. Serum carotenoid levels were measured by HPLC. Conditional logistic regression showed that higher serum total carotenoid levels and their subtypes (e.g. α-carotene, β-carotene, β-cryptoxanthin and lycopene) were dose-dependently associated with decreased NHL risk. The multivariable-adjusted OR and their 95 % CI for NHL risk for quartile 4 (v. quartile 1) were 0·31 (95 % CI 0·22, 0·48; Pfor trend < 0·001) for total carotenoids, 0·52 (95 % CI 0·33, 0·79; Pfor trend: 0·003) for α-carotene, 0·63 (95 % CI 0·42, 0·94; Pfor trend: 0·031) for β-carotene, 0·73 (95 % CI 0·49, 1·05; Pfor trend: 0·034) for β-cryptoxanthin and 0·51 (95 % CI 0·34, 0·75; Pfor trend: 0·001) for lycopene. A null association was observed between serum lutein + zeaxanthin and NHL risk (OR 0·89, 95 % CI 0·57, 1·38; Pfor trend: 0·556). Significant interactions were observed after stratifying according to smoking status, and inverse associations were more evident among current smokers than past or never smokers for total carotenoids, α-carotene and lycopene (Pfor heterogeneity: 0·047, 0·042 and 0·046). This study indicates that higher serum carotenoid levels might be inversely associated with NHL risk, especially among current smokers.

Modulation of Gut Microbiota and Oxidative Status by β-Carotene in Late Pregnant Sows

Recent evidences suggest that gut microbiota plays an important role in regulating physiological and metabolic activities of pregnant sows, and β-carotene has a potentially positive effect on reproduction, but the impact of β-carotene on gut microbiota in pregnant sows remains unknown. This study aimed to explore the effect and mechanisms of β-carotene on the reproductive performance of sows from the aspect of gut microbiota. A total of 48 hybrid pregnant sows (Landrace × Yorkshire) with similar parity were randomly allocated into three groups (n = 16) and fed with a basal diet or a diet containing 30 or 90 mg/kg of β-carotene from day 90 of gestation until parturition. Dietary supplementation of 30 or 90 mg/kg β-carotene increased the number of live birth to 11.82 ± 1.54 and 12.29 ± 2.09, respectively, while the control group was 11.00 ± 1.41 (P = 0.201). Moreover, β-carotene increased significantly the serum nitric oxide (NO) level and glutathione peroxidase (GSH-Px) activity (P < 0.05). Characterization of fecal microbiota revealed that 90 mg/kg β-carotene increased the diversity of the gut flora (P < 0.05). In particular, β-carotene decreased the relative abundance of Firmicutes including Lachnospiraceae AC2044 group, Lachnospiraceae NK4B4 group and Ruminococcaceae UCG-008, but enriched Proteobacteria including Bilophila and Sutterella, and Actinobacteria including Corynebacterium and Corynebacterium 1 which are related to NO synthesis. These data demonstrated that dietary supplementation of β-carotene may increase antioxidant enzyme activity and NO, an important vasodilator to promote the neonatal blood circulation, through regulating gut microbiota in sows.

Lutein supplementation combined with a low-calorie diet in middle-aged obese individuals: effects on anthropometric indices, body composition and metabolic parameters

Lutein is considered as a major biologically active carotenoid, with potential benefits for obesity and cardiometabolic health. This double-blind, randomised controlled trial aimed to assess whether the consumption of lutein along with a low-calorie diet (LCD) can influence anthropometric indices, body composition and metabolic parameters in obese middle-aged individuals. After a 2-week run-in period with an LCD, forty-eight participants aged 45–65 years were randomly assigned to consume 20 mg/d lutein or placebo along with the LCD for 10 weeks. Dietary intake, anthropometric indices, body composition, lipid profile, glucose homoeostasis parameters, NEFA and appetite sensations were assessed at the beginning and end of the study. After 10 weeks, body weight and waist circumference significantly decreased in both groups, although between-group differences were not significant. There was more of a decrease in the percentage of body fat in the lutein group v. the placebo group. Moreover, the placebo group experienced a significant reduction in fat-free mass (FFM), whereas the lutein group preserved FFM during calorie restriction, although the between-group difference did not reach statistical significance. Visceral fat and serum levels of total cholesterol (TC) and LDL-cholesterol were significantly decreased only in the lutein group, with a statistically significant difference between the two arms only for TC. No significant changes were observed in the TAG, HDL-cholesterol, glucose homoeostasis parameters, NEFA and appetite sensations. Lutein supplementation in combination with an LCD could improve body composition and lipid profile in obese middle-aged individuals.

β-Carotene: Preventive Role for Type 2 Diabetes Mellitus and Obesity: A Review

Carotenoids are vital antioxidants for plants and animals. They protect cells from oxidative events and act against the inflammatory process and carcinogenesis. Among the most abundant carotenoids in human and foods is β-carotene. This carotenoid has the highest level of provitamin A activity, as it splits into two molecules of retinol through the actions of the cytosolic enzymes: β-carotene-15,15′-monooxygenase (β-carotene-15,15′-oxygenase 1) and β-carotene-9′,10′-dioxygenase (β-carotene-9′,10′-oxygenase 2). The literature supports the idea that β-carotene acts against type 2 diabetes mellitus, cardiovascular diseases, obesity, and metabolic syndrome. Due to the many processes involved in β-carotene biosynthesis and metabolic function, little is known about such components, since many mechanisms have not yet been fully elucidated. Therefore, our study concisely described the relationships between the consumption of carotenoids, with emphasis on β-carotene, and obesity and type 2 diabetes mellitus and its associated parameters in order to understand the preventive role of carotenoids better and encourage their consumption.

Carotenoid metabolism at the intestinal barrier

Carotenoids exert a rich variety of physiological functions in mammals and are beneficial for human health. These lipids are acquired from the diet and metabolized to apocarotenoids, including retinoids (vitamin A and its metabolites). The small intestine is a major site for their absorption and bioconversion. From here, carotenoids and their metabolites are distributed within the body in triacylglycerol-rich lipoproteins to support retinoid signaling in peripheral tissues and photoreceptor function in the eyes. In recent years, much progress has been made in identifying carotenoid metabolizing enzymes, transporters, and binding proteins. A diet-responsive regulatory network controls the activity of these components and adapts carotenoid absorption and bioconversion to the bodily requirements of these lipids. Genetic variability in the genes encoding these components alters carotenoid homeostasis and is associated with pathologies. We here summarize the advanced state of knowledge about intestinal carotenoid metabolism and its impact on carotenoid and retinoid homeostasis of other organ systems, including the eyes, liver, and immune system. The implication of the findings for science-based intake recommendations for these essential dietary lipids is discussed. 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.

Characterization and Function Analysis of the Beta-Carotene Oxygenase-like Genes in Carotenoids Metabolism of the Ridgetail White Prawn Exopalaemon carinicauda

Carotenoids are almost universally distributed in living organisms. The oxidative metabolism by carotene oxygenase contributes to the metabolic processes of carotenoids. 15,15'-beta-carotene oxygenase (BCO1) and 9',10'-beta-carotene oxygenase (BCO2) are two important carotenoid oxygenases. In order to understand the function of carotenoid oxygenases in crustaceans, seven genes encoding carotenoid oxygenases (named EcBCO-like) were isolated from the transcriptome database of Exopalaemon carinicauda. After phylogenetic analysis with carotenoid oxygenases reported in other species, EcBCO-like1, EcBCO-like3, and EcBCO-like6 were chosen for further functional study. The prawns after EcBCO-like1 knockdown suffered continuous death, which suggested its important role for the survival of the animals. For the prawns after EcBCO-like3 knockdown, no phenotype change was observed. The prawns after EcBCO-like6 knockdown showed color changes in their hepatopancreas when they were fed with carotenoids-containing diet, and the content of carotenoid in their hepatopancreas was much higher than that in the control prawns. The present study will pave the way for further understanding the carotenoids metabolism in the prawns.

A ketocarotenoid-based colour polymorphism in the Sira poison frog Ranitomeya sirensis indicates novel gene interactions underlying aposematic signal variation

The accumulation of red ketocarotenoids is an important component of coloration in many organisms, but the underlying mechanisms are poorly understood. In some organisms, ketocarotenoids are sequestered from the diet and can accumulate when enzymes responsible for carotenoid breakdown are disrupted. In other organisms, ketocarotenoids are formed endogenously from dietary precursors via oxidation reactions carried out by carotenoid ketolase enzymes. Here, we study the genetic basis of carotenoid coloration in an amphibian. We demonstrate that a red/yellow polymorphism in the dendrobatid poison frog Ranitomeya sirensis is due to the presence/absence of ketocarotenoids. Using whole-transcriptome sequencing of skins and livers, we found that a transcript encoding a cytochrome P450 enzyme (CYP3A80) is expressed 3.4-fold higher in livers of red frogs versus yellow. As CYP3A enzymes are known carotenoid ketolases in other organisms, our results point to CYP3A80 as a strong candidate for a carotenoid ketolase in amphibians. Furthermore, in red frogs, the transcript encoding the carotenoid cleavage enzyme BCO2 is expressed at a low level or as a splice variant lacking key catalytic amino acids. This suggests that BCO2 function may be disrupted in red frogs, providing a mechanism whereby the accumulation of ketocarotenoids and their dietary precursors may be enhanced.

Diversity of carotenoid composition, sequestering structures and gene transcription in mature fruits of four Prunus species

The genus Prunus contains many fruits used in the human diet, which exhibit a variety of different flavors. However, publications on the diversity of carotenoid profiles and sequestering structures in Prunus fruits are limited. In this study, carotenoids and their associated sequestering structures in mature fruits of four Prunus species, including peach [Prunus persica (L.) Batschi], nectarine [Prunus persica (L.) Batschi var. nucipersica], plum (Prunus salicina L.), and apricot (Prunus armeniaca L.) were investigated. HPLC-PAD analysis revealed that mature fruits all accumulated carotenoid esters, while their profiles and levels differed significantly. Transcription analysis suggested a positive correlation between carotenogenic genes and carotenoid profiles. Transmission electron microscopy (TEM) analysis revealed a common globular chromoplast in Prunus. However, the number and size of plastids and plastoglobules varied between species. Noticeably, the white-flesh Ruiguang 19 nectarine contained plastids similar to chromoplasts, except with smaller plastoglobules. In addition, it seemed like a lipid-dissolved β-carotene form in apricot fruits, which is more effectively absorbed by humans than the solid-crystalline form. Moreover, the lowest transcriptions of plastid-related genes were found in Friar plum, and GLK2 and OR genes were presumed to be associated with the largest chromoplasts observed in apricot. We investigated the correlations among carotenoid accumulation, plastid characteristics and gene transcription and found that chromoplast development is likely more important in determining carotenoid accumulation than carotenogenic transcription in Prunus fruits. This study presents the first report on the diversity of carotenoid sequestering structures in Prunus fruits and suggests some crucial genes associated with diversity.

De novo assembly transcriptome analysis reveals the preliminary molecular mechanism of pigmentation in juveniles of the hard clam Mercenaria mercenaria

Color plays a vital function in camouflage, sexual selection, immunity, and evolution. Mollusca possess vivid shell colors and pigmentation starts at the juvenile stage. The hard clam Mercenaria mercenaria is a widely cultivated bivalve of high economic value. To explore the molecular mechanism of pigmentation in juvenile clams, here, we performed RNA-Seq analysis on non-pigmented, white, and red M. mercenaria specimens. Clean reads were assembled into 358,285 transcripts and 149,234 unigenes, whose N50 lengths were 2107 bp and 1567 bp, respectively. Differentially expressed genes were identified and analyzed for KEGG enrichment. "Melanoma/Melanogenesis", "ABC transporters", and "Porphyrin and chlorophyll metabolism" pathways appeared to be associated with pigmentation. Pathways related to carotenoid metabolism seemed to also play a vital role in pigmentation in juveniles. Our results provide new insights into the formation of shell color in juvenile hard clams.

In-vivo biotransformation of citrus functional components and their effects on health

Citrus, one of the most popular fruits worldwide, contains various functional components, including flavonoids, dietary fibers (DFs), essential oils (EOs), synephrines, limonoids, and carotenoids. The functional components of citrus attract special attention due to their health-promoting effects. Food components undergo complex biotransformation by host itself and the gut microbiota after oral intake, which alters their bioaccessibility, bioavailability, and bioactivity in the host body. To better understand the health effects of citrus fruits, it is important to understand the in-vivo biotransformation of citrus functional components. We reviewed the biotransformation of citrus functional components (flavonoids, DFs, EOs, synephrines, limonoids, and carotenoids) in the body from their intake to excretion. In addition, we described the importance of biotransformation in terms of health effects. This review would facilitate mechanistic understanding of the health-promoting effect of citrus and its functional components, and also provide guidance for the development of health-promoting foods based on citrus and its functional components.

Improving the In Vitro Bioaccessibility of β-Carotene Using Pectin Added Nanoemulsions

The intestinal absorption of lipophilic compounds such as β-carotene has been reported to increase when they are incorporated in emulsion-based delivery systems. Moreover, the reduction of emulsions particle size and the addition of biopolymers in the systems seems to play an important role in the emulsion properties but also in their behavior under gastrointestinal conditions and the absorption of the encapsulated compound in the intestine. Hence, the present study aimed to evaluate the effect of pectin addition (0%, 1%, and 2%) on the physicochemical stability of oil-in-water nanoemulsions containing β-carotene during 35 days at 4 °C, the oil digestibility and the compound bioaccessibility. The results showed that nanoemulsions presented greater stability and lower β-carotene degradation over time in comparison with coarse emulsion, which was further reduced with the addition of pectin. Moreover, nanoemulsions presented a faster digestibility irrespective of the pectin concentration used and a higher β-carotene bioaccessibility as the pectin concentration increased, being the maximum of ≈36% in nanoemulsion with 2% of pectin. These results highlight the potential of adding pectin to β-carotene nanoemulsions to enhance their functionality by efficiently preventing the compound degradation and increasing the in vitro bioaccessibility.

Molecular Breeding for Nutritionally Enriched Maize: Status and Prospects

Maize is a major source of food security and economic development in sub-Saharan Africa (SSA), Latin America, and the Caribbean, and is among the top three cereal crops in Asia. Yet, maize is deficient in certain essential amino acids, vitamins, and minerals. Biofortified maize cultivars enriched with essential minerals and vitamins could be particularly impactful in rural areas with limited access to diversified diet, dietary supplements, and fortified foods. Significant progress has been made in developing, testing, and deploying maize cultivars biofortified with quality protein maize (QPM), provitamin A, and kernel zinc. In this review, we outline the status and prospects of developing nutritionally enriched maize by successfully harnessing conventional and molecular marker-assisted breeding, highlighting the need for intensification of efforts to create greater impacts on malnutrition in maize-consuming populations, especially in the low- and middle-income countries. Molecular marker-assisted selection methods are particularly useful for improving nutritional traits since conventional breeding methods are relatively constrained by the cost and throughput of nutritional trait phenotyping.

Carotenoid biofortification in crop plants: citius, altius, fortius

Carotenoids are indispensable for human health, required as precursors of vitamin A and efficient antioxidants. However, these plant pigments that play a vital role in photosynthesis are represented at insufficient levels in edible parts of several crops, which creates a need for increasing their content or optimizing their composition through biofortification. In particular, vitamin A deficiency, a severe health problem affecting the lives of millions in developing countries, has triggered the development of a series of high-provitamin A crops, including Golden Rice as the best-known example. Further carotenoid-biofortified crops have been generated by using genetic engineering approaches or through classical breeding. In this review, we depict carotenoid metabolism in plants and provide an update on the development of carotenoid-biofortified plants and their potential to meet needs and expectations. Furthermore, we discuss the possibility of using natural variation for carotenoid biofortification and the potential of gene editing tools. 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.

Structural and mechanistic aspects of carotenoid cleavage dioxygenases (CCDs)

Carotenoid cleavage dioxygenases (CCDs) comprise a superfamily of mononuclear non-heme iron proteins that catalyze the oxygenolytic fission of alkene bonds in carotenoids to generate apocarotenoid products. Some of these enzymes exhibit additional activities such as carbon skeleton rearrangement and trans-cis isomerization. The group also includes a subfamily of enzymes that split the interphenyl alkene bond in molecules such as resveratrol and lignostilbene. CCDs are involved in numerous biological processes ranging from production of light-sensing chromophores to degradation of lignin derivatives in pulping waste sludge. These enzymes exhibit unique features that distinguish them from other families of non-heme iron enzymes. The distinctive properties and biological importance of CCDs have stimulated interest in their modes of catalysis. Recent structural, spectroscopic, and computational studies have helped clarify mechanistic aspects of CCD catalysis. Here, we review these findings emphasizing common and unique properties of CCDs that enable their variable substrate specificity and regioselectivity. 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 Role of Vitamin A in Wound Healing

Vitamin A is an essential micronutrient that comes in multiple forms, including retinols, retinals, and retinoic acids. Dietary vitamin A is absorbed as retinol from preformed retinoids or as pro-vitamin A carotenoids that are converted into retinol in the enterocyte. These are then delivered to the liver for storage via chylomicrons and later released into the circulation and to its biologically active tissues bound to retinol-binding protein. Vitamin A is a crucial component of many important and diverse biological functions, including reproduction, embryological development, cellular differentiation, growth, immunity, and vision. Vitamin A functions mostly through nuclear retinoic acid receptors, retinoid X receptors, and peroxisome proliferator-activated receptors. Retinoids regulate the growth and differentiation of many cell types within skin, and its deficiency leads to abnormal epithelial keratinization. In wounded tissue, vitamin A stimulates epidermal turnover, increases the rate of re-epithelialization, and restores epithelial structure. Retinoids have the unique ability to reverse the inhibitory effects of anti-inflammatory steroids on wound healing. In addition to its role in the inflammatory phase of wound healing, retinoic acid has been demonstrated to enhance production of extracellular matrix components such as collagen type I and fibronectin, increase proliferation of keratinocytes and fibroblasts, and decrease levels of degrading matrix metalloproteinases.

Red carotenoids and associated gene expression explain colour variation in frillneck lizards

A long-standing hypothesis in evolutionary ecology is that red-orange ornamental colours reliably signal individual quality owing to limited dietary availability of carotenoids and metabolic costs associated with their production, such as the bioconversion of dietary yellow carotenoids to red ketocarotenoids. However, in ectothermic vertebrates, these colours can also be produced by self-synthesized pteridine pigments. As a consequence, the relative ratio of pigment types and their biochemical and genetic basis have implications for the costs and information content of colour signals; yet they remain poorly known in most taxonomic groups. We tested whether red- and yellow-frilled populations of the frillneck lizard, Chlamydosaurus kingii, differ in the ratio of different biochemical classes of carotenoid and pteridine pigments, and examined associated differences in gene expression. We found that, unlike other squamate reptiles, red hues derive from a higher proportion of ketocarotenoids relative to both dietary yellow carotenoids and to pteridines. Whereas red frill skin showed higher expression of several genes associated with carotenoid metabolism, yellow frill skin showed higher expression of genes associated with steroid hormones. Based on the different mechanisms underlying red and yellow signals, we hypothesize that frill colour conveys different information in the two populations. More generally, the data expand our knowledge of the genetic and biochemical basis of colour signals in vertebrates.

Convergent evolution of cytochrome P450s underlies independent origins of keto-carotenoid pigmentation in animals

Keto-carotenoids contribute to many important traits in animals, including vision and coloration. In a great number of animal species, keto-carotenoids are endogenously produced from carotenoids by carotenoid ketolases. Despite the ubiquity and functional importance of keto-carotenoids in animals, the underlying genetic architectures of their production have remained enigmatic. The body and eye colorations of spider mites (Arthropoda: Chelicerata) are determined by β-carotene and keto-carotenoid derivatives. Here, we focus on a carotenoid pigment mutant of the spider mite Tetranychus kanzawai that, as shown by chromatography, lost the ability to produce keto-carotenoids. We employed bulked segregant analysis and linked the causal locus to a single narrow genomic interval. The causal mutation was fine-mapped to a minimal candidate region that held only one complete gene, the cytochrome P450 monooxygenase CYP384A1, of the CYP3 clan. Using a number of genomic approaches, we revealed that an inactivating deletion in the fourth exon of CYP384A1 caused the aberrant pigmentation. Phylogenetic analysis indicated that CYP384A1 is orthologous across mite species of the ancient Trombidiformes order where carotenoids typify eye and body coloration, suggesting a deeply conserved function of CYP384A1 as a carotenoid ketolase. Previously, CYP2J19, a cytochrome P450 of the CYP2 clan, has been identified as a carotenoid ketolase in birds and turtles. Our study shows that selection for endogenous production of keto-carotenoids led to convergent evolution, whereby cytochrome P450s were independently co-opted in vertebrate and invertebrate animal lineages.

Anti-Obesity Effect of Carotenoids: Direct Impact on Adipose Tissue and Adipose Tissue-Driven Indirect Effects

This review summarizes current knowledge on the biological relevance of carotenoids and some of their metabolites in obesity management. The relationship between carotenoids and obesity is considered in clinical studies and in preclinical studies. Adipose tissue is a key organ in obesity etiology and the main storage site for carotenoids. We thus first describe carotenoid metabolism in adipocyte and adipose tissue and the effects of carotenoids on biological processes in adipose tissue that may be linked to obesity management in in vitro and preclinical studies. It is also now well established that the brain is strongly involved in obesity processes. A section is accordingly devoted to the potential effect of carotenoids on obesity via their direct and/or adipose tissue-driven indirect biological effects on the brain.

Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles

Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna. The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna. Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.

Alternative retinoid X receptor (RXR) ligands

Retinoid X receptors (RXRs) control a wide variety of functions by virtue of their dimerization with other nuclear hormone receptors (NRs), contributing thereby to activities of different signaling pathways. We review known RXR ligands as transcriptional modulators of specific RXR-dimers and the associated biological processes. We also discuss the physiological relevance of such ligands, which remains frequently a matter of debate and which at present is best met by member(s) of a novel family of retinoids, postulated as Vitamin A5. Through comparison with other natural, but also with synthetic ligands, we discuss high diversity in the modes of ligand binding to RXRs resulting in agonistic or antagonistic profiles and selectivity towards specific subtypes of permissive heterodimers. Despite such diversity, direct ligand binding to the ligand binding pocket resulting in agonistic activity was preferentially preserved in the course of animal evolution pointing to its functional relevance, and potential for existence of other, species-specific endogenous RXR ligands sharing the same mode of function.

Characterization of the novel role of NinaB orthologs from Bombyx mori and Tribolium castaneum

Carotenoids can be enzymatically converted to apocarotenoids by carotenoid cleavage dioxygenases. Insect genomes encode only one member of this ancestral enzyme family. We cloned and characterized the ninaB genes from the silk worm (Bombyx mori) and the flour beetle (Tribolium castaneum). We expressed BmNinaB and TcNinaB in E. coli and analyzed their biochemical properties. Both enzymes catalyzed a conversion of carotenoids into cis-retinoids. The enzymes catalyzed a combined trans to cis isomerization at the C11, C12 double bond and oxidative cleavage reaction at the C15, C15' bond of the carotenoid carbon backbone. Analyses of the spatial and temporal expression patterns revealed that ninaB genes were differentially expressed during the beetle and moth life cycles with high expression in reproductive organs. In Bombyx mori, ninaB was almost exclusively expressed in female reproductive organs of the pupa and adult. In Tribolium castaneum, low expression was found in reproductive organs of females but high expressions in male reproductive organs of the pupa and imagoes. We performed RNAi experiments to characterize the role of NinaB in insect reproduction. We observed that RNAi treatment significantly decreased the expression levels of BmninaB and TcninaB and reduced the egg laying capacity of both insects. Together, our study revealed that NinaB's unique enzymatic properties are well conserved among insects and implicate NinaB function in insect reproduction.