Multiple independent L-gulonolactone oxidase (GULO) gene losses and vitamin C synthesis reacquisition events in non-Deuterostomian animal species

Recombinant C-Terminal Catalytic Domain of Rat L-Gulono Lactone Oxidase Produced in Bacterial Cells Is Enzymatically Active

The L-gulonolactone oxidase enzyme (GULO) catalyzes the last step of L-ascorbic acid (vitamin C) biosynthesis. This enzymatic activity is lost in primates. The full-length rat GULO has been previously produced in plants and demonstrated to be active. In this study, we compared the activity of two variants of GULO produced in Escheriachia coli cells, full-length rat GULO (fGULO) and its C-terminal catalytic domain (cGULO). The expression and purification of the recombinant proteins were optimized, and their biological activity was confirmed by two methods, the GULO activity assay in the protein extracts and the 'in-gel' staining for GULO activity. Both variants of recombinant GULO were biologically active in both assays. However, cGULO is more promising than fGULO for ascorbic acid production because it is more efficiently produced by bacteria. Furthermore, the optimal activities of the fGULO and cGULO recombinant proteins were observed at pH 7 and 6.5, and at temperatures of 40 and 30 °C, respectively. Kinetic studies revealed that at low substrate concentrations, Km values for fGULO and cGULO were 53.5 ± 5 and 42 ± 6.3 µM, respectively.

Inferences on the evolution of the ascorbic acid synthesis pathway in insects using Phylogenetic Tree Collapser (PTC), a tool for the automated collapsing of phylogenetic trees using taxonomic information

When inferring the evolution of a gene/gene family, it is advisable to use all available coding sequences (CDS) from as many species genomes as possible in order to infer and date all gene duplications and losses. Nowadays, this means using hundreds or even thousands of CDSs, which makes the inferred phylogenetic trees difficult to visualize and interpret. Therefore, it is useful to have an automated way of collapsing large phylogenetic trees according to a taxonomic term decided by the user (family, class, or order, for instance), in order to highlight the minimal set of sequences that should be used to recapitulate the full history of the gene/gene family being studied at that taxonomic level, that can be refined using additional software. Here we present the Phylogenetic Tree Collapser (PTC) program (https://github.com/pegi3s/phylogenetic-tree-collapser), a flexible tool for automated tree collapsing using taxonomic information, that can be easily used by researchers without a background in informatics, since it only requires the installation of Docker, Podman or Singularity. The utility of PTC is demonstrated by addressing the evolution of the ascorbic acid synthesis pathway in insects. A Docker image is available at Docker Hub (https://hub.docker.com/r/pegi3s/phylogenetic-tree-collapser) with PTC installed and ready-to-run.

Structure, mechanism, and evolution of the last step in vitamin C biosynthesis

Photosynthetic organisms, fungi, and animals comprise distinct pathways for vitamin C biosynthesis. Besides this diversity, the final biosynthetic step consistently involves an oxidation reaction carried out by the aldonolactone oxidoreductases. Here, we study the origin and evolution of the diversified activities and substrate preferences featured by these flavoenzymes using molecular phylogeny, kinetics, mutagenesis, and crystallographic experiments. We find clear evidence that they share a common ancestor. A flavin-interacting amino acid modulates the reactivity with the electron acceptors, including oxygen, and determines whether an enzyme functions as an oxidase or a dehydrogenase. We show that a few side chains in the catalytic cavity impart the reaction stereoselectivity. Ancestral sequence reconstruction outlines how these critical positions were affixed to specific amino acids along the evolution of the major eukaryotic clades. During Eukarya evolution, the aldonolactone oxidoreductases adapted to the varying metabolic demands while retaining their overarching vitamin C-generating function.

Ascorbic acid biosynthesis in Pacific abalone Haliotis discus hannai Ino and L-gulonolactone oxidase gene loss as an independent event

Up to now, it has been believed that invertebrates are unable to synthesize ascorbic acid (AA) in vivo. However, in the present study, the full-length CDs (Coding sequence) of L-gulonolactone oxidase (GLO) from Pacific abalone (Haliotis discus hannai Ino) were obtained through molecular cloning. The Pacific abalone GLO contained a FAD-binding domain in the N-termination, and ALO domain and conserved HWAK motif in the C-termination. The GLO gene possesses 12 exons and 11 introns. The Pacific abalone GLO was expressed in various tissues, including the kidney, digestive gland, gill, intestine, muscle and mantle. The GLO activity assay revealed that GLO activity was only detected in the kidney of Pacific abalone. After a 100-day feeding trial, dietary AA levels did not significantly affect the survival, weight gain, daily increment in shell length, and feed conversion ratio of Pacific abalone. The expression of GLO in the kidney was downregulated by dietary AA. These results implied that the ability to synthesize AA in abalone had not been lost. From the evolutionary perspective, the loss of GLO occurred independently as an independent event by matching with the genomes of various species. The positive selection analysis revealed that the GLO gene underwent purifying selective pressure during its evolution. In conclusion, the present study provided direct evidence to prove that the GLO activity and the ability to synthesize AA exist in abalone. The AA synthesis ability in vertebrates might have originated from invertebrates dating back 930.31 million years.

Molecular modelling and biological evaluation of phyto-molecules as potential activators of gluconolactone oxidase (GULO)

Diabetes, the cause of colossal economic and disease burden, is a key area of research in drug discovery programs. Elevated blood glucose levels in diabetes lead to several adverse consequences due to the formation of advanced glycation end products and free radicals. Vitamin C, a potent antioxidant, protects the body's cells and tissues from oxidative damage and dysfunctions. Glucose is the precursor of Vitamin C synthesis in plants and some mammals. L-gulono lactone oxidase (GULO) is the rate-limiting enzyme in producing Vitamin C. However, it is not synthesized in bats, primates, humans, and guinea pigs because of the pseudogene. Several phytomolecules having antioxidant properties are hypothesized to be promising and selective activators of GULO. Therefore, the present study focused on screening agonists of GULO from phytomolecules as an effective augmentor for Vitamin C synthesis, thereby suppressing the sequela of diabetic events. The 3D structure of GULO was generated by the ab-initio method. Subsequently, molecular docking explored the possible binding patterns of GULO protein with different plant phenolic compounds, followed by supplementation of the potent phytomolecules to diabetic guinea pigs. It is noteworthy that Resveratrol and Hydroxytyrosol showed better binding affinity. The molecular simulation also confirmed that Resveratrol is an activator of the GULO enzyme. Interestingly, it was also established that Vitamin C levels were improved in diabetic guinea pigs supplemented with the phytomolecules and comparatively Resveratrol modulates the concentration of glucose and Vitamin C levels substantially, thereby alleviating hyperglycemia. However, further studies are warranted to study the mechanisms.Communicated by Ramaswamy H. Sarma.

Spontaneous Lymphoma in a SMP30 Knock-Out C57BL/6 Mouse

70-weeks-old female C57BL6 senescence marker protein 30 knock out mice exhibited anorexia, lethargy and enlarged abdomen because of an intraperitoneal mass. On necropsy, the mouse revealed a large brown-whitish mass located on the mesentery. The mass also exhibited systemic metastasis and spread over in various organs. On microscopic findings, the neoplastic masses were mainly composed of neoplastic round cells characterized by severe anisokaryosis, narrow cytoplasm, round nuclei, prominent nucleoli, and numerous mitotic figures (13-15 in a 400X field). Consequently, the present case was diagnosed as a metastatic lymphoma arising from a mesenteric lymph node, the tumor spread to other organs such as the intestine, kidney and thoracic cavity. According to previous studies, SMP30 plays an important role in inhibiting cancer in both human and mouse. Taken together, it seems that the present case can be used as a valuable asset for evaluating the potential risks of SMP30 depletion in developing lymphoma.

The evolution of vitamin C biosynthesis and transport in animals

Background

Vitamin C (VC) is an indispensable antioxidant and co-factor for optimal function and development of eukaryotic cells. In animals, VC can be synthesized by the organism, acquired through the diet, or both. In the single VC synthesis pathway described in animals, the penultimate step is catalysed by Regucalcin, and the last step by l-gulonolactone oxidase (GULO). The GULO gene has been implicated in VC synthesis only, while Regucalcin has been shown to have multiple functions in mammals.

Results

Both GULO and Regucalcin can be found in non-bilaterian, protostome and deuterostome species. Regucalcin, as here shown, is involved in multiple functions such as VC synthesis, calcium homeostasis, and the oxidative stress response in both Deuterostomes and Protostomes, and in insects in receptor-mediated uptake of hexamerin storage proteins from haemolymph. In Insecta and Nematoda, however, there is no GULO gene, and in the latter no Regucalcin gene, but species from these lineages are still able to synthesize VC, implying at least one novel synthesis pathway. In vertebrates, SVCT1, a gene that belongs to a family with up to five members, as here shown, is the only gene involved in the uptake of VC in the gut. This specificity is likely the result of a subfunctionalization event that happened at the base of the Craniata subphylum. SVCT-like genes present in non-Vertebrate animals are likely involved in both VC and nucleobase transport. It is also shown that in lineages where GULO has been lost, SVCT1 is now an essential gene, while in lineages where SVCT1 gene has been lost, GULO is now an essential gene.

Conclusions

The simultaneous study, for the first time, of GULO, Regucalcin and SVCTs evolution provides a clear picture of VC synthesis/acquisition and reveals very different selective pressures in different animal taxonomic groups.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02040-7.

Advances in Novel Animal Vitamin C Biosynthesis Pathways and the Role of Prokaryote-Based Inferences to Understand Their Origin

Vitamin C (VC) is an essential nutrient required for the optimal function and development of many organisms. VC has been studied for many decades, and still today, the characterization of its functions is a dynamic scientific field, mainly because of its commercial and therapeutic applications. In this review, we discuss, in a comparative way, the increasing evidence for alternative VC synthesis pathways in insects and nematodes, and the potential of myo-inositol as a possible substrate for this metabolic process in metazoans. Methodological approaches that may be useful for the future characterization of the VC synthesis pathways of Caenorhabditis elegans and Drosophila melanogaster are here discussed. We also summarize the current distribution of the eukaryote aldonolactone oxidoreductases gene lineages, while highlighting the added value of studies on prokaryote species that are likely able to synthesize VC for both the characterization of novel VC synthesis pathways and inferences on the complex evolutionary history of such pathways. Such work may help improve the industrial production of VC.

Dynamic changes in genomic 5-hydroxymethyluracil and N6-methyladenine levels in the Drosophila melanogaster life cycle and in response to different temperature conditions

In this study, the level of DNA modifications was investigated in three developmental stages of Drosophila melanogaster (larvae, pupae, imago) and in an in vitro model (Schneider 2 cells). Analysis was carried out using two-dimensional ultra-performance liquid chromatography with tandem mass spectrometry. Our method made it possible, for the first time, to analyze a broad spectrum of DNA modifications in the three stages of Drosophila. Each stage was characterized by a specific modification pattern, and the levels of these compounds fluctuated throughout the D. melanogaster life cycle. The level of DNA modification was also compared between insects bred at 25 °C (optimal temperature) and at 18 °C, and the groups differed significantly. The profound changes in N6-methyladenine and 5-hydroxymethyluracil levels during the Drosophila life cycle and as a result of breeding temperature changes indicate that these DNA modifications can play important regulatory roles in response to environmental changes and/or biological conditions. Moreover, the supplementation of Schneider 2 cells with 1 mM L-ascorbic acid caused a time-dependent increase in the level of 5-(hydroxymethyl)-2'-deoxyuridine. These data suggest that a certain pool of this compound may arise from the enzymatic activity of the dTET protein.

Ascorbate Is a Primary Antioxidant in Mammals

Ascorbate (vitamin C in primates) functions as a cofactor for a number of enzymatic reactions represented by prolyl hydroxylases and as an antioxidant due to its ability to donate electrons, which is mostly accomplished through non-enzymatic reaction in mammals. Ascorbate directly reacts with radical species and is converted to ascorbyl radical followed by dehydroascorbate. Ambiguities in physiological relevance of ascorbate observed during in vivo situations could be attributed in part to presence of other redox systems and the pro-oxidant properties of ascorbate. Most mammals are able to synthesize ascorbate from glucose, which is also considered to be an obstacle to verify its action. In addition to animals with natural deficiency in the ascorbate synthesis, such as guinea pigs and ODS rats, three strains of mice with genetic removal of the responsive genes (GULO, RGN, or AKR1A) for the ascorbate synthesis have been established and are being used to investigate the physiological roles of ascorbate. Studies using these mice, along with ascorbate transporter (SVCT)-deficient mice, largely support its ability in protection against oxidative insults. While combined actions of ascorbate in regulating epigenetics and antioxidation appear to effectively prevent cancer development, pharmacological doses of ascorbate and dehydroascorbate may exert tumoricidal activity through redox-dependent mechanisms.

Vitamin C Enema Advances Induction of Remission in the Dextran Sodium Sulfate-Induced Colitis Model in Rats

The current main treatment for ulcerative colitis (UC) is induction therapy by long-term administration of 5-aminosalicylic acid (5-ASA), but various side effects have been reported. Therefore, a radical cure for UC is desired. A vitamin C (VC) has anti-inflammatory effects. Therefore, this study investigated whether a VC solution enema shortens induction of remission in colitis model rats. Wistar rats (6 wk old/male) were allowed to freely ingest a 1% dextran sulfate sodium (DSS) solution for 10 d and then switched to tap water for normal breeding for 10 d (UC group). At the time of switching to tap water, an enema was performed with a 5-ASA solution (40 mg/kg/d) or VC solution (460 mg/kg/d) for 10 d. The neutrophil number, COX-2, which is an index of inflammation, and type III collagen, which is an early healing marker, were significantly increased in the UC group. However, the VC group showed decreases compared with UC groups. Furthermore, compared with UC and 5-ASA groups, the VC group showed increased expression of type I collagen, which is expressed late in healing, and significant epithelial regeneration was observed in colon tissue. The VC solution enema shortened the induction of remission by directly suppressing inflammation of damaged large intestinal tissues and promoting mucosal healing.

Bombyx mori can synthesize ascorbic acid through the l-gulose pathway to varying degrees depending on developmental stage

Vitamin C (VC) is an essential nutrient for many animals. However, whether insects, including Bombyx mori, can synthesize VC remains unclear. In this article, the optimized HPLC method was used to determine the content of l-ascorbic acid (AsA) in silkworm eggs, larvae and pupae, and the activity of l-gulono-1,4-lactone oxidase (GULO), a key enzyme in VC synthesis. The RNA interference method was used to determine the effect of the BmGulo-like gene on embryonic development and GULO activity in the pupal fat body. The AsA content increased significantly during E144 h-E168 h in the late embryonic stage and P48 h-P144 h in the middle-late pupal stage, in which exogenous VC was not ingested. Furthermore, the body AsA content in larvae fed VC-free feed also increased with larval stage. The GULO enzymatic activity was present in eggs and the fat bodies of larvae and pupae, even when the larvae were reared with fresh mulberry leaves. Moreover, the activity was higher in the later embryonic stages (E144 h-E168 h) and the early pupal stage (before P24 h). The GULO activity in the pupal fat body dramatically decreased when the screened BmGulo-like gene (BGIBMGA005735) was knocked down with small interfering RNA; in addition, the survival rate and hatching rate of eggs significantly decreased 21% and 44%, respectively, and embryonic development was delayed. Thus, Bombyx mori can synthesize AsA through the l-gulose pathway, albeit with low activity, and this synthesis ability varies with developmental stages.

Pretreatment serum vitamin level predicts severity of radiation-induced oral mucositis in patients with nasopharyngeal carcinoma

BACKGROUND

Radiation-induced mucositis (RIOM) is a common radiotherapy toxicity. We aimed to evaluate the relationship of serum vitamin status with RIOM among nasopharyngeal carcinoma (NPC) patients who underwent radiotherapy.

METHODS

NPC patients who underwent concurrent chemoradiotherapy with available pretreatment serum vitamin values were included. Serum vitamin levels and clinical characteristics were collected. Logistic regression analysis and receiver operating characteristic curves were conducted to explore the potential risk factors and corresponding cut-off values for severe RIOM.

RESULTS

Two hundred and forty NPC patients were enrolled. Multivariate regression analysis showed that mean oral cavity radiation dose (OR = 2.042; 95% CI = 1.585-2.630; P < .001), weekly concurrent chemotherapy (OR = 3.898; 95% CI = 1.085-14.004; P = .037), lower serum level of vitamin B2 (OR = 0.951; 95% CI = 0.924-0.978; P < .001), and vitamin C (OR = 0.455; 95% CI = 0.346-0.598; P < .001) were independent risk factors for developing severe RIOM.

CONCLUSIONS

The findings of this study revealed that serum vitamin status could predict the severity of RIOM, providing a theoretical basis for the prevention and treatment of RIOM.

The diet-microbiome tango: how nutrients lead the gut brain axis

Nutrients and the microbiome have a profound impact on the brain by influencing its development and function in health and disease. The mechanisms by which they shape brain function have only started to be uncovered. Here we propose that the interaction of diet with the microbiome is at the core of most mechanisms by which gut microbes affect host brain function. The microbiome acts on the host by altering the nutrients in the diet and by using them as precursors for synthetizing psychoactive metabolites. Diet is also a major modulator of gut microbiome composition making this another key mechanism by which they affect the host brain. Nutrient-microbiome-host interactions therefore provide an overarching framework to understand the function of the gut-brain axis.