Genetic variation in the beta, beta-carotene-9', 10'-dioxygenase gene and association with fat colour in bovine adipose tissue and milk

Functional Analysis of β-Carotene Oxygenase 2 (BCO2) Gene in Yesso Scallop (Patinopecten yessoensis)

Carotenoids are essential nutrients for humans and animals, and carotenoid coloration represents an important meat quality parameter for many farmed animals. Increasingly, studies have demonstrated that vertebrate carotenoid cleavage oxygenases (CCOs) are essential enzymes in carotenoid metabolism and are therefore potential candidate genes for improving carotenoid deposition. However, our understanding of carotenoid bioavailability and CCOs functions in invertebrates, particularly marine species, is currently quite limited. We previously identified that a CCO homolog, PyBCO-like 1, was the causal gene for carotenoid coloration in the 'Haida golden scallop', a variety of Yesso scallop (Patinopecten yessoensis) characterized by carotenoid enrichment. Here, we found that another CCO-encoding gene named PyBCO2 (β-carotene oxygenase 2) was widely expressed in P. yessoensis organs/tissues, with the highest expression in striated muscle. Inhibiting BCO2 expression in P. yessoensis through RNA interference led to increased carotenoid (pectenolone and pectenoxanthin) deposition in the striated muscle, and the color of the striated muscle changed from white to light orange. Our results indicate that PyBCO2 might be a candidate gene used for improving carotenoid content in normal Yesso scallops, and also in 'Haida golden scallops'.

Genetic deletion of Bco2 and Isx establishes a golden mouse model for carotenoid research

OBJECTIVE

Low plasma levels of carotenoids are associated with mortality and chronic disease states. Genetic studies in animals revealed that the tissue accumulation of these dietary pigments is associated with the genes encoding β-carotene oxygenase 2 (BCO2) and the scavenger receptor class B type 1 (SR-B1). Here we examined in mice how BCO2 and SR-B1 affect the metabolism of the model carotenoid zeaxanthin that serves as a macular pigment in the human retina.

METHODS

We used mice with a lacZ reporter gene knock-in to determine Bco2 expression patterns in the small intestine. By genetic dissection, we studied the contribution of BCO2 and SR-B1 to zeaxanthin uptake homeostasis and tissue accumulation under different supply conditions (50 mg/kg and 250 mg/kg). We determined the metabolic profiles of zeaxanthin and its metabolites in different tissues by LC-MS using standard and chiral columns. An albino Isx-/-/Bco2-/- mouse homozygous for Tyrc-2J was generated to study the effect of light on ocular zeaxanthin metabolites.

RESULTS

We demonstrate that BCO2 is highly expressed in enterocytes of the small intestine. Genetic deletion of Bco2 led to enhanced accumulation of zeaxanthin, indicating that the enzyme serves as a gatekeeper of zeaxanthin bioavailability. Relaxing the regulation of SR-B1 expression in enterocytes by genetic deletion of the transcription factor ISX further enhanced zeaxanthin accumulation in tissues. We observed that the absorption of zeaxanthin was dose-dependent and identified the jejunum as the major zeaxanthin-absorbing intestinal region. We further showed that zeaxanthin underwent oxidation to ε,ε-3,3'-carotene-dione in mouse tissues. We detected all three enantiomers of the zeaxanthin oxidation product whereas the parent zeaxanthin only existed as (3R, 3'R)-enantiomer in the diet. The ratio of oxidized to parent zeaxanthin varied between tissues and was dependent on the supplementation dose. We further showed in an albino Isx-/-/Bco2-/- mouse that supra-physiological supplementation doses (250 mg/kg) with zeaxanthin rapidly induced hypercarotenemia with a golden skin phenotype and that light stress increased the concentration of oxidized zeaxanthin in the eyes.

CONCLUSIONS

We established the biochemical basis of zeaxanthin metabolism in mice and showed that tissue factors and abiotic stress affect the metabolism and homeostasis of this dietary lipid.

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.

Aster la vista: Unraveling the biochemical basis of carotenoid homeostasis in the human retina

Carotenoids play pivotal roles in vision as light filters and precursor of chromophore. Many vertebrates also display the colorful pigments as ornaments in bare skin parts and feathers. Proteins involved in the transport and metabolism of these lipids have been identified including class B scavenger receptors and carotenoid cleavage dioxygenases. Recent research implicates members of the Aster protein family, also known as GRAM domain-containing (GRAMD), in carotenoid metabolism. These multi-domain proteins facilitate the intracellular movement of carotenoids from their site of cellular uptake by scavenger receptors to the site of their metabolic processing by carotenoid cleavage dioxygenases. We provide a model how the coordinated interplay of these proteins and their differential expression establishes carotenoid distribution patterns and function in tissues, with particular emphasis on the human retina.

Frequency of genotypic markers for genetic disorders, colour, polledness, and major genes in Blanco Orejinegro cattle

The purpose of this work was to establish DNA marker frequencies for genetic disorders, colour, horned/polled trait, and major genes of importance for productive and reproductive traits in Blanco Orejinegro (BON) cattle. The Blanco Orejinegro breed is a Colombian creole breed characterized by a white hair coat on black skin with black ears, black hair on the middle part of the legs, and absence of horns. We genotyped 420 animals of Colombia, 70 with the GGP-Bovine 150 K chip and 350 with the GGP-Bovine 50 K chip. The markers were associated with 50 genetic diseases, 52 major gene variants related to productive traits, and 12 variants related to coat coloration, presence of horns, and adaptation, selected from the information contained in the chips. Genotype frequencies were estimated using the R statistical program. Genetic disorder annotations were derived using the Online Mendelian Inheritance in Animals tool (OMIA) and the average inbreeding coefficient (F) (n = 7799) using the MTDFNRM program. Carriers were found for 16 of the genetic disorders evaluated but with low frequencies (0.24 to 2.46%); no homozygous animals were found for the disorders. Carriers were associated with disorders such as bovine leukocyte adhesion deficiency (BLAD), deficiency of uridine monophosphate synthase (DUMPS), syndactyly, and epidermolysis bullosa (EB). The F was 4.41%. Concerning the genes associated with colour (TYR, MC1R, and PMEL), alleles related to black pigmentation, the absence of horns (polledness), and slick coat (an adaptive trait) were highly frequent (> 81.90%). Markers associated with milk production and quality, yellow fat, and fertility showed variable frequencies, indicating selection potential. Allele frequency of genetic disorders in BON cattle was low, suggesting few genetic disorder problems, with syndactyly being the most frequent condition. The markers associated with colour and polledness were almost fixed, with a frequency at or near 100%. Production and reproduction markers showed variability for selection.

Carotenoid coloration and coloration-linked gene expression in red tilapia (Oreochromis sp.) tissues

Background

Production, marketability and consumer preference of red tilapia often depends upon the intensity of coloration. Hence, new approaches to develop coloration are now geared to improve market acceptability and profit. This study evaluated the effects of carotenoid-rich diets on the phenotypic coloration, carotenoid level, weight gain and expression of coloration-linked genes in skin, fin and muscle tissues. Carotenoids were extracted from dried Daucus carota peel, Ipomoea aquatica leaves, and Moringa oleifera leaves. Eighty (80) size-14 fish were fed with carotenoid-rich treatments twice a day for 120 days. The phenotypic effect of the carotenoid extracts was measured through a color chart. Skin carotenoid level was measured through UV-vis spectrophotometer. csf1ra, Bcdo2 and StAR expression analysis was done using qRT-PCR.

Results

Treatments with carotenoid extracts yielded higher overall scores on phenotypic coloration and tissue carotenoid levels. Differential expression of carotenoid-linked genes such as the elevated expression in csf1ra and lower expression in Bcdo2b following supplementation of the enhanced diet supports the phenotypic redness and increased carotenoid values in red tilapia fed with D. carota peel and I. aquatica leaves.

Conclusions

Overall improvement in the redness of the tilapia was achieved through the supplementation of carotenoid-rich diet derived from readily available plants. Differential expression of coloration-linked genes supports the increase in the intensity of phenotypic coloration and level of carotenoids in the tissues. The study emphasizes the importance of carotenoids in the commercial tilapia industry and highlights the potential of the plant extracts for integration and development of feeds for color enhancement in red tilapia.

Overflow phenomenon in serum lutein after supplementation: a systematic review supported with SNPs analyses

Lutein, a type of carotenoids, is found to delay the onset and progression of age-related macular degeneration (AMD). Several lutein supplementation studies showed that after an initial increase, lutein serum levels demonstrated a subsequent decrease despite continuous supplementation. In this systematic literature review, this obscure phenomenon was tried to be explained. The subsequent drop in lutein levels was postulated due to down-regulation of lutein receptors scavenger receptor class B type I (SR-BI) in the gastrointestinal tract, upregulation of lutein degrading enzyme β-carotene dioxygenase (BCDO2), or perhaps a combination of both. Some single nucleotides polymorphisms (SNPs) that could have influence on the occurrence of this phenomenon. To date, an exact scientific explanation for this phenomenon has not been established. Further research is needed to investigate this phenomenon in depth to reach an irrefutable explanation, giving that lutein is proven to be effective in delaying the onset and progression of AMD and its metabolism in the human body becomes of equal importance.

Insertion of an endogenous Jaagsiekte sheep retrovirus element into the BCO2 - gene abolishes its function and leads to yellow discoloration of adipose tissue in Norwegian Spælsau (Ovis aries)

Background

The accumulation of carotenoids in adipose tissue leading to yellow fat is, in sheep, a heritable recessive trait that can be attributed to a nonsense mutation in the beta-carotene oxygenase 2 (BCO2) gene. However, not all sheep breeds suffering from yellow fat have this nonsense mutation, meaning that other functional mechanisms must exist. We investigated one such breed, the Norwegian spælsau.

Results

In spælsau we detected an aberration in BCO2 mRNA. Nanopore sequencing of genomic DNA revealed the insertion of a 7.9 kb endogenous Jaagsiekte Sheep Retrovirus (enJSRV) sequence in the first intron of the BCO2 gene. Close examination of its cDNA revealed that the BCO2 genes first exon was spliced together with enJSRV-sequence immediately downstream of a potential -AG splice acceptor site at enJSRV position 415. The hybrid protein product consists of 29 amino acids coded by the BCO2 exon 1, one amino acid coded by the junction sequence, followed by 28 amino acids arbitrary coded for by the enJSRV-sequence, before a translation stop codon is reached.

Conclusions

Considering that the functional BCO2 protein consists of 575 amino acids, it is unlikely that the 58 amino acid BCO2/enJSRV hybrid protein can display any enzymatic function. The existence of this novel BCO2 allele represents an alternative functional mechanism accounting for BCO2 inactivation and is a perfect example of the potential benefits for searching for structural variants using long-read sequencing data.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07826-5.

Genetic Basis of De Novo Appearance of Carotenoid Ornamentation in Bare Parts of Canaries

Unlike wild and domestic canaries (Serinus canaria), or any of the three dozen species of finches in genus Serinus, the domestic urucum breed of canaries exhibits bright red bills and legs. This novel trait offers a unique opportunity to understand the mechanisms of bare-part coloration in birds. To identify the mutation producing the colorful phenotype, we resequenced the genome of urucum canaries and performed a range of analyses to search for genotype-to-phenotype associations across the genome. We identified a nonsynonymous mutation in the gene BCO2 (beta-carotene oxygenase 2, also known as BCDO2), an enzyme involved in the cleavage and breakdown of full-length carotenoids into short apocarotenoids. Protein structural models and in vitro functional assays indicate that the urucum mutation abrogates the carotenoid-cleavage activity of BCO2. Consistent with the predicted loss of carotenoid-cleavage activity, urucum canaries tended to have increased levels of full-length carotenoid pigments in bill tissue and reduced levels of carotenoid-cleavage products (apocarotenoids) in retinal tissue compared with other breeds of canaries. We hypothesize that carotenoid-based bare-part coloration might be readily gained, modified, or lost through simple switches in the enzymatic activity or regulation of BCO2 and this gene may be an important mediator in the evolution of bare-part coloration among bird species.

Genome-wide association study of four composite reproductive traits in Iranian fat-tailed sheep

Composite reproductive traits are a combination of growth and reproductive traits. They have the advantage of being better attuned to the market drivers since producers are paid on a per kilogram basis and not on a per head basis. In this study, 124 Lori---Bakhtiari ewes were genotyped using the medium-density Illumina Ovine SNP50 array. A genome-wide association study was performed on estimated breeding values of four composite reproductive traits and genetic parameters were also estimated. The traits were litter mean weight at birth, litter mean weight at weaning, total litter weight at birth and total litter weight at weaning. Several suggestive and associated single nucleotide polymorphisms (SNPs) were identified. Neighbouring the top SNPs there were five genes, inhibin β E subunit (INHBE), inhibin β C subunit (INHBC), testis expressed 12 (TEX12), β-carotene oxygenase 2 (BCO2) and WD Repeat Domain 70 (WDR70) identified as possible candidate genes for composite reproductive traits of the Lori-Bakhtiari sheep. These genes are in pathways known to be relevant to fertility and growth characteristics. The results provide new information for the functional annotation of genes associated with fertility traits and add new evidence towards a consensus of quantitative trait loci associated with reproductive traits in sheep.

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.

Molecular components affecting ocular carotenoid and retinoid homeostasis

The photochemistry of vision employs opsins and geometric isomerization of their covalently bound retinylidine chromophores. In different animal classes, these light receptors associate with distinct G proteins that either hyperpolarize or depolarize photoreceptor membranes. Vertebrates also use the acidic form of chromophore, retinoic acid, as the ligand of nuclear hormone receptors that orchestrate eye development. To establish and sustain these processes, animals must acquire carotenoids from the diet, transport them, and metabolize them to chromophore and retinoic acid. The understanding of carotenoid metabolism, however, lagged behind our knowledge about the biology of their receptor molecules. In the past decades, much progress has been made in identifying the genes encoding proteins that mediate the transport and enzymatic transformations of carotenoids and their retinoid metabolites. Comparative analysis in different animal classes revealed how evolutionary tinkering with a limited number of genes evolved different biochemical strategies to supply photoreceptors with chromophore. Mutations in these genes impair carotenoid metabolism and induce various ocular pathologies. This review summarizes this advancement and introduces the involved proteins, including the homeostatic regulation of their activities.

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.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. 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.

Carotenoid pigmentation in salmon: variation in expression at BCO2-l locus controls a key fitness trait affecting red coloration

Carotenoids are primarily responsible for the characteristic red flesh coloration of salmon. Flesh coloration is an economically and evolutionarily significant trait that varies inter- and intra-specifically, yet the underlying genetic mechanism is unknown. Chinook salmon (Oncorhynchus tshawytscha) represents an ideal system to study carotenoid variation as, unlike other salmonids, they exhibit extreme differences in carotenoid utilization due to genetic polymorphisms. Here, we crossed populations of Chinook salmon with fixed differences in flesh coloration (red versus white) for a genome-wide association study to identify loci associated with pigmentation. Here, the beta-carotene oxygenase 2-like (BCO2-l) gene was significantly associated with flesh colour, with the most significant single nucleotide polymorphism explaining 66% of the variation in colour. BCO2 gene disruption is linked to carotenoid accumulation in other taxa, therefore we hypothesize that an ancestral mutation partially disrupting BCO2-l activity (i.e. hypomorphic mutation) allowed the deposition and accumulation of carotenoids within Salmonidae. Indeed, we found elevated transcript levels of BCO2-l in white Chinook salmon relative to red. The long-standing mystery of why salmon are red, while no other fishes are, is thus probably explained by a hypomorphic mutation in the proto-salmonid at the time of divergence of red-fleshed salmonid genera (approx. 30 Ma).

Genotypes and allele frequencies of buried SNPs in a bovine single-nucleotide polymorphism array in Japanese Black cattle

Single nucleotide polymorphism (SNP) arrays are widely used for genetic and genomic analyses in cattle breeding; thus, data derived from SNP arrays have accumulated on a large scale nationwide. Commercial SNP arrays contain a considerable number of unassigned SNPs on the chromosome/position on the genome; these SNPs are excluded in subsequent analyses. Notably, the position-unassigned SNPs, or "buried SNPs" include some of the markers associated with genetic disease. In this study, we identified the position of buried SNPs using the Basic Local Alignment Search Tool against the surrounding sequences and characterized the relationship between SNPs and genetic diseases in Online Mendelian Inheritance in Animals based on the genomic position. We determined the position of 285 buried SNPs on the genome and surveyed the genotype and allele frequencies of these SNPs in 5,955 individual Japanese Black cattle. Eleven SNPs associated with genetic disease, which contained five buried SNPs, were found in the population with the risk allele frequency ranging from 0.00008396 to 0.46. These results indicate that buried SNPs in the bovine SNP array can be utilized to identify associations with genetic disorders from large scale accumulated SNP genotype data in Japanese Black cattle.

Evaluation of feedlot performance, carcass characteristics, carcass retail cut distribution, Warner-Bratzler shear force, and fatty acid composition of purebred Jersey and crossbred Jersey steers

Feedlot performance, carcass yield, fatty acid composition, and tenderness of crossbred Jersey steers compared with purebred Jersey steers was investigated. Purebred Jersey (n = 21) and crossbred Jersey steers sired by Angus (n = 9), SimAngus (n = 10), and Red Wagyu (n = 15) bulls were assessed. Adjusted to a common initial body weight (BW), crossbred Jersey steers had a greater rate of BW gain (P ≤ 0.01) compared with purebred Jersey steers. Angus sired steers had a greater daily dry matter intake (P ≤ 0.01) compared with Wagyu and Jersey sired steers, whereas SimAngus sired steers had a greater daily dry matter intake compared with Jersey sired steers. Wagyu sired steers were more feed efficient (P ≤ 0.03) compared with Jersey sired steers. Even with a greater (P ≤ 0.01) number of days on feed, off-test BW of purebred Jersey steers was less (P ≤ 0.01) compared with crossbred Jersey steers. Adjusted to a common hot carcass weight, Angus sired steers had a greater backfat thickness (P ≤ 0.01) compared with steers from the other sire breeds. Kidney fat percentage (P ≤ 0.01) was greatest for Jersey sired steers, with SimAngus and Wagyu sired steers being intermediate, and the lowest for Angus sired steers. Carcasses from Angus and Wagyu sired steers had a greater marbling score (P ≤ 0.03) compared with carcasses from Jersey sired steers. Carcasses from Wagyu sired steers had a greater (P ≤ 0.01) total red meat yield compared with Angus and Jersey sired steers, whereas SimAngus sired steers had a greater total red meat yield compared with Jersey sired steers. Carcasses from Angus sired steers tended (P = 0.07) to have a greater percentage of fat trim compared with Wagyu sired steer carcasses. There were no sire breed differences (P = 0.38) for the percentage of total bone from the carcasses. Tenderness, measured by Warner-Bratzler shear force (WBSF), was improved (P ≤ 0.01) with 14 d of postmortem aging compared with 7 d. Wagyu and SimAngus sired steers produced steaks with a lesser (P ≤ 0.01) WBSF compared with steaks from Angus and Jersey sired steers. Steaks from Angus sired steers tended (P = 0.10) to have a greater percentage of total lipid and had a greater (P ≤ 0.05) percentage of 16:0 compared with steaks from Jersey sired steers. Overall, crossbred Jersey steers improved economically relevant production parameters of feedlot performance, carcass quality, carcass yield, and instrumental predictors of eating quality compared with purebred Jersey steers.

Effect of the β-carotene oxygenase 2 genotype on the content of carotenoids, retinol and α-tocopherol in the liver, fat and milk of rabbit does, reproduction parameters and kitten growth

Mutations in the β-carotene oxygenase 2 (BCO2) gene can impair the function of the enzyme that breaks down carotenoids. As a result, gradual accumulation of unoxidized carotenoids in animal tissues gives them a yellow colour. The aim of the study was to determine the content of carotenoids, retinol and α-tocopherol in the liver, fat and milk of rabbit does with three different genotypes determined by AAT-deletion mutation at codon 248 of the BCO2 gene and to find out whether differences in the concentrations of the above compounds in the tissues and milk of the does affect reproduction parameters and the rearing rate of kittens. The experimental materials comprised 36 does, 12 of each genotype of the BCO2 gene, with their litters. Females with their litters were placed in individual cages, on deep litter. Between days 7 and 13 of lactation, samples of milk were collected from the does. The kittens stayed with their mothers until 35 days of age. After weaning, the does were sacrificed. Tissue samples of liver and perirenal fat were collected for chemical analyses. Additionally, based on samples taken from one female, RNA expression levels were determined from the mammary gland and liver, adipose tissue and skin. It was found that homozygous does with deletion at codon 248 of the BCO2 gene were characterized by considerably higher concentrations of xanthophylls and beta-carotene in the liver, adipose tissue and milk than does with the remaining genotypes. However, the differences in the content of the above compounds in milk had no influence on litter weight or the number and rearing rate of kittens. Additionally, RNA expression of the BCO2 gene was found in the mammary tissue of lactating doe and its level was similar to those noted in the liver and adipose tissue.

Tomato lycopene prevention of alcoholic fatty liver disease and hepatocellular carcinoma development

Alcoholic liver disease (ALD) is a major cause of morbidity and mortality worldwide. The incidence of hepatocellular carcinoma (HCC) is increasing in the United States, and chronic, excessive alcohol consumption is responsible for 32%–45% of all the liver cancer cases in the United States. Avoidance of chronic or excessive alcohol intake is the best protection against alcohol-related liver injury; however, the social presence and addictive power of alcohol are strong. Induction of the cytochrome P450 2E1 (CYP2E1) enzyme by chronic and excessive alcohol intake is known to play a role in the pathogenesis of ALD. High intake of tomatoes, rich in the carotenoid lycopene, is associated with a decreased risk of chronic disease. The review will overview the prevention of ALD and HCC through dietary tomato rich in lycopene as an effective intervention strategy and the crucial role of CYP2E1 induction as a molecular target. The review also indicates a need for caution among individuals consuming both alcohol and high dose lycopene as a dietary supplement.

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.

Comparative genomics and transcriptomics of Chrysolophus provide insights into the evolution of complex plumage coloration

Background

As one of the most recognizable characteristics in birds, plumage color has a high impact on understanding the evolution and mechanisms of coloration. Feather and skin are ideal tissues to explore the genomics and complexity of color patterns in vertebrates. Two species of the genus Chrysolophus, golden pheasant (Chrysolophus pictus) and Lady Amherst's pheasant (Chrysolophus amherstiae), exhibit brilliant colors in their plumage, but with extreme phenotypic differences, making these two species great models to investigate plumage coloration mechanisms in birds.

Results

We sequenced and assembled a genome of golden pheasant with high coverage and annotated 15,552 protein-coding genes. The genome of Lady Amherst's pheasant is sequenced with low coverage. Based on the feather pigment identification, a series of genomic and transcriptomic comparisons were conducted to investigate the complex features of plumage coloration. By identifying the lineage-specific sequence variations in Chrysolophus and golden pheasant against different backgrounds, we found that four melanogenesis biosynthesis genes and some lipid-related genes might be candidate genomic factors for the evolution of melanin and carotenoid pigmentation, respectively. In addition, a study among 47 birds showed some candidate genes related to carotenoid coloration in a broad range of birds. The transcriptome data further reveal important regulators of the two colorations, particularly one splicing transcript of the microphthalmia-associated transcription factor gene for pheomelanin synthesis.

Conclusions

Analysis of the golden pheasant and its sister pheasant genomes, as well as comparison with other avian genomes, are helpful to reveal the underlying regulation of their plumage coloration. The present study provides important genomic information and insights for further studies of avian plumage evolution and diversity.

Phylogenetic analysis of the metazoan carotenoid oxygenase superfamily: a new ancestral gene assemblage of BCO-like (BCOL) proteins

Here we describe a new family of carotenoid cleavage oxygenases (CCOs) in metazoans, the BCO2-like (BCOL) clade, which contains lancelet, nematode, and molluscan carotenoid oxygenase sequences. Phylogenetic analysis of CCOs in all kingdoms of life confirmed that the BCOL enzymes are an independent clade of ancient origin. One of the predicted lancelet BCOL proteins, cloned and analyzed for carotenoid cleavage activity in a bacterial carotenoid expression system, had activity similar to lancelet BCO2 proteins, although with a preference for cis isomers. Our docking predictions correlated well with the cis-favored activity. The extensive expansions of the new animal BCOL family in some species (e.g., lancelet) suggests that the carotenoid cleavage oxygenase superfamily has evolved in the “extremely high turnover” fashion: numerous losses and duplications of this family are likely to reflect complex regulation processes during development, and interactions with the environment. These findings also serve to provide a rationale for the evolution of the BCO-related outlier RPE65 retinol isomerase, an enzyme that does not utilize carotenoids as substrate or perform double-bond cleavage.

Host-related factors explaining interindividual variability of carotenoid bioavailability and tissue concentrations in humans

Carotenoid dietary intake and their endogenous levels have been associated with a decreased risk of several chronic diseases. There are indications that carotenoid bioavailability depends, in addition to the food matrix, on host factors. These include diseases (e.g. colitis), life-style habits (e.g. smoking), gender and age, as well as genetic variations including single nucleotide polymorphisms that govern carotenoid metabolism. These are expected to explain interindividual differences that contribute to carotenoid uptake, distribution, metabolism and excretion, and therefore possibly also their association with disease risk. For instance, digestion enzymes fostering micellization (PNLIP, CES), expression of uptake/efflux transporters (SR-BI, CD36, NPC1L1), cleavage enzymes (BCO1/2), intracellular transporters (FABP2), secretion into chylomicrons (APOB, MTTP), carotenoid metabolism in the blood and liver (LPL, APO C/E, LDLR), and distribution to target tissues such as adipose tissue or macula (GSTP1, StARD3) depend on the activity of these proteins. In addition, human microbiota, e.g. via altering bile-acid concentrations, may play a role in carotenoid bioavailability. In order to comprehend individual, variable responses to these compounds, an improved knowledge on intra-/interindividual factors determining carotenoid bioavailability, including tissue distribution, is required. Here, we highlight the current knowledge on factors that may explain such intra-/interindividual differences.

Genetic dissection in a mouse model reveals interactions between carotenoids and lipid metabolism

Carotenoids affect a rich variety of physiological functions in nature and are beneficial for human health. However, knowledge about their biological action and the consequences of their dietary accumulation in mammals is limited. Progress in this research field is limited by the expeditious metabolism of carotenoids in rodents and the confounding production of apocarotenoid signaling molecules. Herein, we established a mouse model lacking the enzymes responsible for carotenoid catabolism and apocarotenoid production, fed on either a β-carotene- or a zeaxanthin-enriched diet. Applying a genome wide microarray analysis, we assessed the effects of the parent carotenoids on the liver transcriptome. Our analysis documented changes in pathways for liver lipid metabolism and mitochondrial respiration. We biochemically defined these effects, and observed that β-carotene accumulation resulted in an elevation of liver triglycerides and liver cholesterol, while zeaxanthin accumulation increased serum cholesterol levels. We further show that carotenoids were predominantly transported within HDL particles in the serum of mice. Finally, we provide evidence that carotenoid accumulation influenced whole-body respiration and energy expenditure. Thus, we observed that accumulation of parent carotenoids interacts with lipid metabolism and that structurally related carotenoids display distinct biological functions in mammals.

Absorption, metabolism, and functions of β-cryptoxanthin

β-Cryptoxanthin, a carotenoid found in fruits and vegetables such as tangerines, red peppers, and pumpkin, has several functions important for human health. Most evidence from observational, in vitro, animal model, and human studies suggests that β-cryptoxanthin has relatively high bioavailability from its common food sources, to the extent that some β-cryptoxanthin-rich foods might be equivalent to β-carotene-rich foods as sources of retinol. β-Cryptoxanthin is an antioxidant in vitro and appears to be associated with decreased risk of some cancers and degenerative diseases. In addition, many in vitro, animal model, and human studies suggest that β-cryptoxanthin-rich foods may have an anabolic effect on bone and, thus, may help delay osteoporosis.

Purification and characterization of a novel β-carotene-9',10'-oxygenase from Saccharomyces cerevisiae ULI3

OBJECTIVES

A novel β-carotene-9,10'-oxygenase (ScBCO2) has been characterized from Saccharomyces cerevisiae ULI3 to convert β-carotene to β-apo-10'-carotenal, which is a precursor of the plant hormone strigolactone.

RESULTS

The ScBCO2 enzyme was purified to homogeneity by ammonium sulfate precipitation, Q sepharose and Superdex-200 chromatography. The molecular mass of the enzyme was ~50 kDa by SDS-PAGE. The purified ScBCO2 enzyme displayed optimal activity at 45 °C and pH 8. Tween 20 (1%, w/v), Trition X-100 (1%, w/v), Mg(2+) (5 mM), Zn(2+) (5 mM), Cu(2+) (5 mM), Ca(2+) (5 mM) or DTT (5 mM) increased in the activity by 3, 7, 14, 17, 23, 26 and 27%, respectively. ScBCO2 only exhibited cleavage activity towards carotenoid substrates containing two β-ionone rings and its catalytic efficiency (kcat/Km) followed the order β-carotene > α-carotene > lutein.

CONCLUSION

ScBCO2 could be used as a potential candidate for the enzymatic biotransformation of β-carotene to β-apo-10'-carotenal in biotechnological applications.

A 3-hydroxy β-end group in xanthophylls is preferentially oxidized to a 3-oxo ε-end group in mammals

We previously found that mice fed lutein accumulated its oxidative metabolites (3'-hydroxy-ε,ε-caroten-3-one and ε,ε-carotene-3,3'-dione) as major carotenoids, suggesting that mammals can convert xanthophylls to keto-carotenoids by the oxidation of hydroxyl groups. Here we elucidated the metabolic activities of mouse liver for several xanthophylls. When lutein was incubated with liver postmitochondrial fraction in the presence of NAD(+), (3'R,6'R)-3'-hydroxy-β,ε-caroten-3-one and (6RS,3'R,6'R)-3'-hydroxy-ε,ε-caroten-3-one were produced as major oxidation products. The former accumulated only at the early stage and was assumed to be an intermediate, followed by isomerization to the latter. The configuration at the C3' and C6' of the ε-end group in lutein was retained in the two oxidation products. These results indicate that the 3-hydroxy β-end group in lutein was preferentially oxidized to a 3-oxo ε-end group via a 3-oxo β-end group. Other xanthophylls such as β-cryptoxanthin and zeaxanthin, which have a 3-hydroxy β-end group, were also oxidized in the same manner as lutein. These keto-carotenoids, derived from dietary xanthophylls, were confirmed to be present in plasma of normal human subjects, and β,ε-caroten-3'-one was significantly increased by the ingestion of β-cryptoxanthin. Thus, humans as well as mice have oxidative activity to convert the 3-hydroxy β-end group of xanthophylls to a 3-oxo ε-end group.

Evidence for compartmentalization of mammalian carotenoid metabolism

The critical role of retinoids (vitamin A and its derivatives) for vision, reproduction, and survival has been well established. Vitamin A is produced from dietary carotenoids such as β-carotene by centric cleavage via the enzyme BCO1. The biochemical and molecular identification of a second structurally related β-carotene metabolizing enzyme, BCO2, has led to a prolonged debate about its relevance in vitamin A biology. While BCO1 cleaves provitamin A carotenoids, BCO2 is more promiscuous and also metabolizes nonprovitamin A carotenoids such as zeaxanthin into long-chain apo-carotenoids. Herein we demonstrate, in cell lines, that human BCO2 is associated with the inner mitochondrial membrane. Different human BCO2 isoforms possess cleavable N-terminal leader sequences critical for mitochondrial import. Subfractionation of murine hepatic mitochondria confirmed the localization of BCO2 to the inner mitochondrial membrane. Studies in BCO2-knockout mice revealed that zeaxanthin accumulates in the inner mitochondrial membrane; in contrast, β-carotene is retained predominantly in the cytoplasm. Thus, we provide evidence for a compartmentalization of carotenoid metabolism that prevents competition between BCO1 and BCO2 for the provitamin and the production of noncanonical β-carotene metabolites.

Inactivity of human β,β-carotene-9',10'-dioxygenase (BCO2) underlies retinal accumulation of the human macular carotenoid pigment

The macula of the primate retina uniquely concentrates high amounts of the xanthophyll carotenoids lutein, zeaxanthin, and meso-zeaxanthin, but the underlying biochemical mechanisms for this spatial- and species-specific localization have not been fully elucidated. For example, despite abundant retinal levels in mice and primates of a binding protein for zeaxanthin and meso-zeaxanthin, the pi isoform of glutathione S-transferase (GSTP1), only human and monkey retinas naturally contain detectable levels of these carotenoids. We therefore investigated whether or not differences in expression, localization, and activity between mouse and primate carotenoid metabolic enzymes could account for this species-specific difference in retinal accumulation. We focused on β,β-carotene-9',10'-dioxygenase (BCO2, also known as BCDO2), the only known mammalian xanthophyll cleavage enzyme. RT-PCR, Western blot analysis, and immunohistochemistry (IHC) confirmed that BCO2 is expressed in both mouse and primate retinas. Cotransfection of expression plasmids of human or mouse BCO2 into Escherichia coli strains engineered to produce zeaxanthin demonstrated that only mouse BCO2 is an active zeaxanthin cleavage enzyme. Surface plasmon resonance (SPR) binding studies showed that the binding affinities between human BCO2 and lutein, zeaxanthin, and meso-zeaxanthin are 10- to 40-fold weaker than those for mouse BCO2, implying that ineffective capture of carotenoids by human BCO2 prevents cleavage of xanthophyll carotenoids. Moreover, BCO2 knockout mice, unlike WT mice, accumulate zeaxanthin in their retinas. Our results provide a novel explanation for how primates uniquely concentrate xanthophyll carotenoids at high levels in retinal tissue.

Nutrigenetics of carotenoid metabolism in the chicken: a polymorphism at the β,β-carotene 15,15'-mono-oxygenase 1 (BCMO1) locus affects the response to dietary β-carotene

The enzyme β,β-carotene-15,15'-mono-oxygenase 1 (BCMO1) is responsible for the symmetrical cleavage of β-carotene into retinal. We identified a polymorphism in the promoter of the BCMO1 gene, inducing differences in BCMO1 mRNA levels (high in adenines (AA) and low in guanines (GG)) and colour in chicken breast muscle. The present study was designed to test whether this polymorphism could affect the response to dietary β-carotene. Dietary β-carotene supplementation did not change the effects of the genotypes on breast muscle properties: BCMO1 mRNA levels were lower and xanthophyll contents higher in GG than in AA chickens. Lower vitamin E levels in the plasma and duodenum, plasma cholesterol levels and body weight were also observed in GG than in AA chickens. In both genotypes, dietary β-carotene increased vitamin A storage in the liver; however, it reduced numerous parameters such as SCARB1 (scavenger receptor class B type I) in the duodenum, BCMO1 in the liver, vitamin E levels in the plasma and tissues, xanthophyll contents in the pectoralis major muscle and carcass adiposity. However, several diet × genotype interactions were observed. In the GG genotype, dietary β-carotene increased ISX (intestine-specific homeobox) and decreased BCMO1 mRNA levels in the duodenum, decreased xanthophyll concentrations in the duodenum, liver and plasma, and decreased colour index and HDL-cholesterol concentration in the plasma. Retinol accumulation following dietary β-carotene supplementation was observed in the duodenum of AA chickens only. Therefore, the negative feedback control on β-carotene conversion through ISX appears as functional in the duodenum of GG but not of AA chickens. This could result in a higher availability of β-carotene in the duodenum of GG chickens, reducing the uptake of xanthophylls, liposoluble vitamins and cholesterol.

Genetic evidence for role of carotenoids in age-related macular degeneration in the Carotenoids in Age-Related Eye Disease Study (CAREDS)

PURPOSE

We tested variants in genes related to lutein and zeaxanthin status for association with age-related macular degeneration (AMD) in the Carotenoids in Age-Related Eye Disease Study (CAREDS).

METHODS

Of 2005 CAREDS participants, 1663 were graded for AMD from fundus photography and genotyped for 424 single nucleotide polymorphisms (SNPs) from 24 candidate genes for carotenoid status. Of 337 AMD cases 91% had early or intermediate AMD. The SNPs were tested individually for association with AMD using logistic regression. A carotenoid-related genetic risk model was built using backward selection and compared to existing AMD risk factors using the area under the receiver operating characteristic curve (AUC).

RESULTS

A total of 24 variants from five genes (BCMO1, BCO2, NPCL1L1, ABCG8, and FADS2) not previously related to AMD and four genes related to AMD in previous studies (SCARB1, ABCA1, APOE, and ALDH3A2) were associated independently with AMD, after adjusting for age and ancestry. Variants in all genes (not always the identical SNPs) were associated with lutein and zeaxanthin in serum and/or macula, in this or other samples, except for BCO2 and FADS2. A genetic risk score including nine variants significantly (P = 0.002) discriminated between AMD cases and controls beyond age, smoking, CFH Y402H, and ARMS2 A69S. The odds ratio (95% confidence interval) for AMD among women in the highest versus lowest quintile for the risk score was 3.1 (2.0-4.9).

CONCLUSIONS

Variants in genes related to lutein and zeaxanthin status were associated with AMD in CAREDS, adding to the body of evidence supporting a protective role of lutein and zeaxanthin in risk of AMD.

Non-alcoholic steatohepatitis and hepatocellular carcinoma: implications for lycopene intervention

Increased prevalence of non-alcoholic fatty liver disease (NAFLD) is one of the consequences of the current obesity epidemic. NAFLD is a major form of chronic liver disease that is highly prevalent in obese and overweight adults and children. Nonalcoholic steatohepatitis (NASH) is the severe form of NAFLD, and uncontrolled inflammation as displayed in NASH has been identified as one of the key events in enhancing hepatic carcinogenesis. Lycopene is a non-provitamin A carotenoid and the pigment principally responsible for the characteristic deep-red color of ripe tomato and tomato products, as well as some fruits and vegetables. Lycopene's innate antioxidant and anti-inflammatory properties have generated research interests on its capacity to protect against human diseases that are associated with oxidative stress and inflammation. In addition, differential mechanisms of lycopene metabolism including endogenous cleavage by carotenoid cleavage oxygenases (BCOs), generate lycopene metabolites that may also have significant impact on human disease development. However, it remains to be elucidated as to whether lycopene or its metabolites apolycopenoids have protective effects against obesity-related complications including inflammation and tumorigenesis. This article summarizes the in vivo experiments that elucidated molecular mechanisms associated with obesity-related hepatic inflammation and carcinogenesis. This review also provides an overview of lycopene metabolism, and the molecular pathways involved in the potential beneficial properties of lycopene and apolycopenoids. More research is clearly needed to fully unravel the importance of BCOs in tomato carotenoid metabolism and the consequence on human health and diseases.

Provitamin A metabolism and functions in mammalian biology

Vitamin A deficiency is a major public health problem in developing countries. Some studies also implicate a suboptimal vitamin A intake in certain parts of the population of the industrialized world. Provitamin A carotenoids such as β-carotene are the major source for retinoids (vitamin A and its derivatives) in the human diet. However, it is still controversial how much β-carotene intake is required and safe. An important contributor to this uncertainty is the lack of knowledge about the biochemical and molecular basis of β-carotene metabolism. Recently, key players of provitamin A metabolism have been molecularly identified and biochemically characterized. Studies in knockout mouse models showed that intestinal β-carotene absorption and conversion to retinoids is under negative feedback regulation that adapts this process to the actual requirement of vitamin A of the body. These studies also showed that in peripheral tissues a conversion of β-carotene occurs and affects retinoid-dependent physiologic processes. Moreover, these analyses provided a possible explanation for the adverse health effects of carotenoids by showing that a pathologic accumulation of these compounds can induce oxidative stress in mitochondria and cell signaling pathways related to disease. Genetic polymorphisms in identified genes exist in humans and also alter carotenoid homeostasis. Here, the advanced knowledge of β-carotene metabolism is reviewed, which provides a molecular framework for understanding the role of this important micronutrient in health and disease.

BCDO2 acts as a carotenoid scavenger and gatekeeper for the mitochondrial apoptotic pathway

Carotenoids and their metabolites are widespread and exert key biological functions in living organisms. In vertebrates, the carotenoid oxygenase BCMO1 converts carotenoids such as β,β-carotene to retinoids, which are required for embryonic pattern formation and cell differentiation. Vertebrate genomes encode a structurally related protein named BCDO2 but its physiological function remains undefined. Here, we show that BCDO2 is expressed as an oxidative stress-regulated protein during zebrafish development. Targeted knockdown of this mitochondrial enzyme resulted in anemia at larval stages. Marker gene analysis and staining for hemoglobin revealed that erythropoiesis was not impaired but that erythrocytes underwent apoptosis in BCDO2-deficient larvae. To define the mechanism of this defect, we have analyzed the role of BCDO2 in human cell lines. We found that carotenoids caused oxidative stress in mitochondria that eventually led to cytochrome c release, proteolytic activation of caspase 3 and PARP1, and execution of the apoptotic pathway. Moreover, BCDO2 prevented this induction of the apoptotic pathway by carotenoids. Thus, our study identifying BCDO2 as a crucial protective component against oxidative stress establishes this enzyme as mitochondrial carotenoid scavenger and a gatekeeper of the intrinsic apoptotic pathway.

Association between CSN3 and BCO2 gene polymorphisms and milk performance traits in the Czech Fleckvieh cattle breed

Daily milk, fat and protein yield and amount of somatic cells in cow milk are very important factors that influence milk performance traits. An association between polymorphisms in the kappa casein (CSN3) gene and milk production, composition and technical properties has been previously reported; however, this type of information is not available for the bovine β-carotene oxygenase 2 (BCO2) gene--the BCO2 gene has relationship with milk color and meat fat color, which is dependent on content of β-carotene. We analyzed these two genes and their relationship with milk performance traits (daily milk, fat and protein yield, somatic cell count, SCC) in one cattle population, Czech Fleckvieh (N = 152). All animals were milked twice a day and kept in the same environmental conditions. The Fleckvieh is a typical Czech cattle breed farming for milk and meat production. It is the most common breed in the Czech Republic. DNA was isolated from milk or from hairs. Genes were analyzed using PCR-RFLP, frequencies of alleles and genotypes were calculated and association analysis was performed using a GLM Procedure in SAS. Statistical analysis established that the CSN3 gene has no statistically significant influence on daily milk, fat and protein yield and SCC. Compared to other references this result can be explained by, e.g., small group of animals and different cattle breed. The BCO2 gene (genotypes AA and AG) shows a statistically significant relationship (P = 0.05) with daily milk, protein yield and SCC.

Importance of β,β-carotene 15,15'-monooxygenase 1 (BCMO1) and β,β-carotene 9',10'-dioxygenase 2 (BCDO2) in nutrition and health

In humans, varying amounts of absorbed β-carotene are oxidatively cleaved by the enzyme β,β-carotene 15,15'-monooxygenase 1 (BCMO1) into two molecules of all-trans-retinal. The other carotenoid cleavage enzyme β,β-carotene 9',10'-dioxygenase (BCDO2) cleaves β-carotene at the 9',10' double bond forming β-apo-10'-carotenal and β-ionone. Although the contribution of BCDO2 to vitamin A formation has long been debated, BCMO1 is currently considered the key enzyme for retinoid metabolism. Furthermore, BCMO1 has limited enzyme activity towards carotenoids other than provitamin A carotenoids, whereas BCDO2 exhibits a broader specificity. Both enzymes are located at different sites within the cell, with BCMO1 being a cytosolic protein and BCDO2 being located in the mitochondria. Expression of BCMO1 in tissues other than the intestine has recently revealed its function for tissue-specific retinoid metabolism with importance in embryogenesis and lipid metabolism. On the other hand, biological activity of BCDO2 metabolites has been shown to be important in protecting against carotenoid-induced mitochondrial dysfunction. Single-nucleotide polymorphisms (SNPs) such as R267S and A379V in BCMO1 can partly explain inter-individual variations observed in carotenoid metabolism. Advancing knowledge about the physiological role of these two enzymes will contribute to understanding the importance of carotenoids in health and disease.

Effects of forage level in feedlot finishing diets on carcass characteristics and palatability of Jersey beef

Jersey cattle are known for producing carcasses with a greater amount of marbling, but they require more days on feed to achieve acceptable market weights compared with other breeds. The objective of this study was to evaluate the effect of dietary forage (12 vs. 24% sudangrass:alfalfa hay, DM basis) in steam-flaked, corn-based finishing diets on carcass characteristics, beef palatability, and retail color stability of steaks from Jersey beef compared with conventionally fed commodity beef strip loins (COM) of identified quality (Choice(-) and Select(+)). Jersey steers (n = 77) were blocked by BW and randomly assigned to 1 of the following treatments for a 383-d trial period: Jersey low 12% (JL; n = 38) or Jersey high 24% (JH; n = 39) forage (DM basis). A comparison group was selected from conventionally fed cattle on the same day of slaughter as the Jersey treatments, and strip loins from USDA Select(+) (COM; n = 20) and Choice(-) (COM; n = 20) were removed for data analysis. Seventy-two hours postmortem, strip loins were removed, vacuum-packaged, and aged at 3°C for 18 d postmortem. After the aging period, steaks from the LM were sliced, vacuum-packaged, and frozen (-20°C) until analyzed. Jersey steaks had reduced (P < 0.05) Warner-Bratzler shear force values compared with COM steaks. Trained sensory panelists rated JL greater (P < 0.05) for initial and sustained tenderness and initial juiciness than COM, whereas JH was intermediate. As expected, marbling was greater (P < 0.05) for both JL and JH compared with COM, and trained sensory panel sustained juiciness, beef flavor intensity, and overall acceptability scores were greater (P < 0.05) for both JL and JH compared with COM; however, no differences (P = 0.14) were reported for consumer tenderness and flavor. Objective color (L*, a*, b*) measurements decreased (P < 0.05) over time across treatments. There were no differences among treatments for lightness (L*); however, overall during retail display JL were less (P < 0.05) red (a*) and yellow (b*) than JH and COM. Subjective color scores indicated both JL and JH were less red (P < 0.05) than COM. Steaks from Jersey were equal to and on some measurements more desirable than steaks from COM carcasses for both color stability and palatability. These results suggest that dietary forage level had minimal effects on carcass characteristics and beef palatability. However, feeding a low-forage diet decreases input cost and potentially results in a greater valued carcass. Finishing long-fed (383 d) Jersey steers can meet beef industry expectations with respect to quality grade.

Enzymatic formation of apo-carotenoids from the xanthophyll carotenoids lutein, zeaxanthin and β-cryptoxanthin by ferret carotene-9',10'-monooxygenase

Xanthophyll carotenoids, such as lutein, zeaxanthin and β-cryptoxanthin, may provide potential health benefits against chronic and degenerative diseases. Investigating pathways of xanthophyll metabolism are important to understanding their biological functions. Carotene-15,15'-monooxygenase (CMO1) has been shown to be involved in vitamin A formation, while recent studies suggest that carotene-9',10'-monooxygenase (CMO2) may have a broader substrate specificity than previously recognized. In this in vitro study, we investigated baculovirus-generated recombinant ferret CMO2 cleavage activity towards the carotenoid substrates zeaxanthin, lutein and β-cryptoxanthin. Utilizing HPLC, LC-MS and GC-MS, we identified both volatile and non-volatile apo-carotenoid products including 3-OH-β-ionone, 3-OH-α-ionone, β-ionone, 3-OH-α-apo-10'-carotenal, 3-OH-β-apo-10'-carotenal, and β-apo-10'-carotenal, indicating cleavage at both the 9,10 and 9',10' carbon-carbon double bond. Enzyme kinetic analysis indicated the xanthophylls zeaxanthin and lutein are preferentially cleaved over β-cryptoxanthin, indicating a key role of CMO2 in non-provitamin A carotenoid metabolism. Furthermore, incubation of 3-OH-β-apo-10'-carotenal with CMO2 lysate resulted in the formation of 3-OH-β-ionone. In the presence of NAD(+), in vitro incubation of 3-OH-β-apo-10'-carotenal with ferret hepatic homogenates formed 3-OH-β-apo-10'-carotenoic acid. Since apo-carotenoids serve as important signaling molecules in a variety of biological processes, enzymatic cleavage of xanthophylls by mammalian CMO2 represents a new avenue of research regarding vertebrate carotenoid metabolism and biological function.

A mitochondrial enzyme degrades carotenoids and protects against oxidative stress

Carotenoids are the precursors for vitamin A and are proposed to prevent oxidative damage to cells. Mammalian genomes encode a family of structurally related nonheme iron oxygenases that modify double bonds of these compounds by oxidative cleavage and cis-to-trans isomerization. The roles of the family members BCMO1 and RPE65 for vitamin A production and vision have been well established. Surprisingly, we found that the third family member, β,β-carotene-9',10'-oxygenase (BCDO2), is a mitochondrial carotenoid-oxygenase with broad substrate specificity. In BCDO2-deficient mice, carotenoid homeostasis was abrogated, and carotenoids accumulated in several tissues. In hepatic mitochondria, accumulated carotenoids induced key markers of mitochondrial dysfunction, such as manganese superoxide dismutase (9-fold), and reduced rates of ADP-dependent respiration by 30%. This impairment was associated with an 8- to 9-fold induction of phosphor-MAP kinase and phosphor-AKT, markers of cell signaling pathways related to oxidative stress and disease. Administration of carotenoids to human HepG2 cells depolarized mitochondrial membranes and resulted in the production of reactive oxygen species. Thus, our studies in BCDO2-deficient mice and human cell cultures indicate that carotenoids can impair respiration and induce oxidative stress. Mammalian cells thus express a mitochondrial carotenoid-oxygenase that degrades carotenoids to protect these vital organelles.