The role of ascorbic acid in the regulation of cholesterol metabolism and in the pathogenesis of artherosclerosis

Profile of key metabolites and identification of HMGCS1-DHEA pathway in porcine Sertoli cells treated by Vitamin C

Vitamin C (Ascorbic acid, AA), as vital micro-nutrient, plays an essential role for male animal reproduction. Previously, we showed that vitamin C reprogrammed the transcriptome and proteome to change phenotypes of porcine immature Sertoli cells (iSCs). Here, we used LC-MS-based non-targeted metabolomics to further investigate the metabolic effects of vitamin C on porcine iSCs. The results identified 43 significantly differential metabolites (DMs) (16 up and 27 down) as induced by vitamin C (L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate, AA2P) treatment of porcine iSCs, which were mainly enriched in steroid related and protein related metabolic pathways. ELISA (Enzyme-Linked ImmunoSorbent Assay) showed that significantly differential metabolites of Dehydroepiandrosterone (DHEA) (involved in steroid hormone biosynthesis) and Desmosterol (involved in steroid degradation) were significantly increased, which were partially consistent with metabolomic results. Further integrative analysis of metabolomics, transcriptomics and proteomics data identified the strong correlation between the key differential metabolite of Dehydroepiandrosterone and 6 differentially expressed genes (DEGs)/proteins (DEPs) (HMGCS1, P4HA1, STON2, LOXL2, EMILIN2 and CCN3). Further experiments validated that HMGCS1 could positively regulate Dehydroepiandrosterone level. These data indicate that vitamin C could modulate the metabolism profile, and HMGCS1-DHEA could be the pathway to mediate effects exerted by vitamin C on porcine iSCs.

Understanding Snail Mucus Biosynthesis and Shell Biomineralisation through Genomic Data Mining of the Reconstructed Carbohydrate and Glycan Metabolic Pathways of the Giant African Snail (Achatina fulica)

The giant African snail (Order Stylommatophora: Family Achatinidae), Achatina fulica (Bowdich, 1822), is the most significant and invasive land snail pest. The ecological adaptability of this snail involves high growth rate, reproductive capacity, and shell and mucus production, driven by several biochemical processes and metabolism. The available genomic information for A. fulica provides excellent opportunities to hinder the underlying processes of adaptation, mainly carbohydrate and glycan metabolic pathways toward the shell and mucus formation. The authors analysed the 1.78 Gb draft genomic contigs of A. fulica to identify enzyme-coding genes and reconstruct biochemical pathways related to the carbohydrate and glycan metabolism using a designed bioinformatic workflow. Three hundred and seventy-seven enzymes involved in the carbohydrate and glycan metabolic pathways were identified based on the KEGG pathway reference in combination with protein sequence comparison, structural analysis, and manual curation. Fourteen complete pathways of carbohydrate metabolism and seven complete pathways of glycan metabolism supported the nutrient acquisition and production of the mucus proteoglycans. Increased copy numbers of amylases, cellulases, and chitinases highlighted the snail advantage in food consumption and fast growth rate. The ascorbate biosynthesis pathway identified from the carbohydrate metabolic pathways of A. fulica was involved in the shell biomineralisation process in association with the collagen protein network, carbonic anhydrases, tyrosinases, and several ion transporters. Thus, our bioinformatic workflow was able to reconstruct carbohydrate metabolism, mucus biosynthesis, and shell biomineralisation pathways from the A. fulica genome and transcriptome data. These findings could reveal several evolutionary advantages of the A. fulica snail, and will benefit the discovery of valuable enzymes for industrial and medical applications.

The Effects of Surgery on Plasma/Serum Vitamin C Concentrations: A Systematic Review and Meta-Analysis

Vitamin C (ascorbic acid) is a water soluble vitamin with an array of biological functions. A number of proposed factors contribute to the vitamin’s plasma bioavailability and ability to exert optimal functionality. The aim of this review was to systematically assess plasma vitamin C levels post-surgery compared with pre-surgery/ the magnitude and timeframe of potential changes in concentration. We searched the PUBMED, SCOPUS, SciSearch and the Cochrane Library databases between 1970 to April 2020 for relevant research papers. Prospective studies, control groups and true placebo groups derived from controlled trials that reported means and standard deviations of plasma vitamin C concentrations pre and post operatively were included into the meta-analysis. Data were grouped into short-term (≤7 days) and long term (> 7 days) post-operative follow-up. 23 of 31 studies involving 642 patients included in the systematic review were suitable for meta-analysis. Pooled data from the meta-analysis revealed a mean depletion of plasma vitamin C concentration of -17.99 µmol/L (39% depletion) (CI = -22.81, -13.17) (trial arms = 25, n = 565, p < 0.001) during the first post-operative week and -18.80 µmol/L (21% depletion) (-25.04, -12.56) (trial arms = 6, n = 166, p < 0.001) 2-3 months post-operatively. Subgroup analyses revealed that these depletions occurred following different types of surgery, however, high heterogeneity was observed amongst trials assessing concentration change during the first post-operative week. Overall, our results warrant larger, long term investigations of changes in post-operative plasma vitamin C concentrations and their potential effects on clinical symptomology.

Liver Histological Improvement After Administration of High-Dose Vitamin C in Guinea Pig with Nonalcoholic Steatohepatitis

Background: Vitamin C is a strong antioxidant, and the health effects of vitamin C megadoses have not been validated despite the apparent health benefits. Therefore, the present study sought to confirm the effects of vitamin C megadoses. Materials and Methods : Four groups of six guinea pigs were used. Each group was fed one of the following diets for three weeks: normal diet, methionine choline-deficient diet, methionine choline-deficient diet + vitamin C megadose (MCD + vit C 2.5 g/kg/day), and methionine-choline deficient diet + ursodeoxycholic acid (MCD + UDCA 30 mg/kg/day). The MCD diet was given to induce nonalcoholic steatohepatitis, and UDCA was used to treat nonalcoholic steatohepatitis. Three weeks after initial diet administration, the results of biochemical tests and liver biopsy were compared between the groups. Results: The cytoplasm state was similar in the MCD + vit C and MCD + UDCA groups, exhibiting clearing of the cytoplasm and ballooning degeneration. However, macrovesicular steatosis was not observed in the MCD + vit C group. Aspartate transaminase and alanine transaminase were elevated significantly following vitamin C administration. Conclusions: The present study confirmed that alone vitamin C megadoses are potential remedies for nonalcoholic steatohepatitis, based on the liver biopsy results of guinea pigs that were unable to synthesize vitamin C.

Genome-wide expression profiling establishes novel modulatory roles of vitamin C in THP-1 human monocytic cell line

Background

Vitamin C (vit C) is an essential dietary nutrient, which is a potent antioxidant, a free radical scavenger and functions as a cofactor in many enzymatic reactions. Vit C is also considered to enhance the immune effector function of macrophages, which are regarded to be the first line of defence in response to any pathogen. The THP-1 cell line is widely used for studying macrophage functions and for analyzing host cell-pathogen interactions.

Results

We performed a genome-wide temporal gene expression and functional enrichment analysis of THP-1 cells treated with 100 μM of vit C, a physiologically relevant concentration of the vitamin. Modulatory effects of vitamin C on THP-1 cells were revealed by differential expression of genes starting from 8 h onwards. The number of differentially expressed genes peaked at the earliest time-point i.e. 8 h followed by temporal decline till 96 h. Further, functional enrichment analysis based on statistically stringent criteria revealed a gamut of functional responses, namely, ‘Regulation of gene expression’, ‘Signal transduction’, ‘Cell cycle’, ‘Immune system process’, ‘cAMP metabolic process’, ‘Cholesterol transport’ and ‘Ion homeostasis’. A comparative analysis of vit C-mediated modulation of gene expression data in THP-1cells and human skin fibroblasts disclosed an overlap in certain functional processes such as ‘Regulation of transcription’, ‘Cell cycle’ and ‘Extracellular matrix organization’, and THP-1 specific responses, namely, ‘Regulation of gene expression’ and ‘Ion homeostasis’. It was noteworthy that vit C modulated the ‘Immune system’ process throughout the time-course.

Conclusions

This study reveals the genome-wide effects of physiological levels of vit C on THP-1 gene expression. The multitude of effects impacted by vit C in macrophages highlights its role in maintaining homeostasis of several cellular functions. This study provides a rational basis for the use of the Vitamin C- THP-1 cell model, to study biochemical and cellular responses to stresses, including infection with M. tuberculosis and other intracellular pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3635-4) contains supplementary material, which is available to authorized users.

Vitamin C: update on physiology and pharmacology

Although ascorbic acid is an important water-soluble antioxidant and enzyme cofactor in plants and animals, humans and some other species do not synthesize ascorbate due to the lack of the enzyme catalyzing the final step of the biosynthetic pathway, and for them it has become a vitamin. This review focuses on the role of ascorbate in various hydroxylation reactions and in the redox homeostasis of subcellular compartments including mitochondria and endoplasmic reticulum. Recently discovered functions of ascorbate in nucleic acid and histone dealkylation and proteoglycan deglycanation are also summarized. These new findings might delineate a role for ascorbate in the modulation of both pro- and anti-carcinogenic mechanisms. Recent advances and perspectives in therapeutic applications are also reviewed. On the basis of new and earlier observations, the advantages of the lost ability to synthesize ascorbate are pondered. The increasing knowledge of the functions of ascorbate and of its molecular sites of action can mechanistically substantiate a place for ascorbate in the treatment of various diseases.

Guinea pigs as models for cholesterol and lipoprotein metabolism

Guinea pigs carry the majority of their plasma cholesterol in LDL, making them a unique animal model with which to study hepatic cholesterol and lipoprotein metabolism. In this review, the benefits and advantages of using this particular model are discussed. How dietary factors such as soluble fiber, cholesterol and fatty acids that vary in saturation and chain length affect hepatic cholesterol homeostasis and influence the synthesis, intravascular processing and catabolism of lipoproteins is reviewed. In addition, alterations in hepatic cholesterol metabolism and plasma lipoproteins as affected by treatment with cholestyramine or 3-hydroxyl-3-methylglutaryl coenzyme A reductase inhibitors, exercise, marginal intake of vitamin C, ovariectomy (a model for menopause) and similarities to the human situation are addressed. A review of guinea pigs as models for early atherosclerosis development is also presented.

The effect of iron overload on rat plasma and liver oxidant status in vivo

There is ample evidence implicating reactive oxygen species in a number of human degenerative diseases such as atherosclerosis and haemochromatosis. Although lipid peroxidation underlies many of the toxic effects of oxidative stress, there is a lack of a sensitive and reliable method for its assessment in vivo. To understand the implications of oxidative stress in vivo, we have used dietary iron overload (IO) in the rat. Oxidant status in these animals was determined by assessing depletion of endogenous antioxidants and formation of various lipid peroxidation products, including acylated F2-isoprostanes, a novel class of free-radical-derived prostaglandin-F2-like compounds. IO led to a significant decrease in the concentration of the antioxidants alpha-tocopherol and ascorbic acid in plasma, and alpha-tocopherol, beta-carotene and ubiquinol-10 in liver. Whereas there was no significant lipid peroxidation in plasma, hepatic F2-isoprostane levels were moderately but significantly increased in IO. In addition, IO caused a significant increase in plasma total and high-density lipoprotein cholesterol levels, an effect that was correlated with depletion of plasma ascorbic acid but not alpha-tocopherol. The data demonstrate that IO causes lipid metabolism disturbances and oxidative stress which is associated with substantial depletion of endogenous antioxidants and moderate lipid peroxidative damage.

Recovery of prostacyclin capacity of irradiated endothelial cells and the protective effect of vitamin C

Ionizing irradiation has been reported to affect prostacyclin (PGI2) production by intact blood vessels and cultured endothelial cells (EC) due to damage of enzymes of the arachidonate cascade. In the present study, we investigated whether EC can recover from radiation injury and regain their capacity to produce PGI2. Bovine aortic EC were exposed to radiation doses of 3 and 6 Gy and their capacity to produce PGI2 in response to stimulation with arachidonic acid was tested, at various times after irradiation. The results of these experiments showed clearly that EC exposed to single or fractionated irradiation could recover their capacity to produce PGI2 depending on the radiation dose and the time period following radiation. Radiation damage is associated with oxidant stress and the production of free radicals. We therefore tested the ability of an oxygen radical scavenger, vitamin C, to protect the capacity of irradiated EC to produce PGI2. Pretreatment of EC with low concentrations of vitamin C inhibited the radiation induced release of PGI2 to the culture medium. Vitamin C also enhanced the capacity of irradiated EC to produce PGI2 following short stimulation with arachidonic acid. Treatment with this scavenger however, did not protect the cells against the cytopathic effects of radiation.

Vitamin C intake and dietary sources by demographic characteristics

Evidence from several lines of research indicates a role for vitamin C in the prevention of some types of cancer in addition to a possible role in hypercholesterolemia and other conditions. It is not yet clear, however, whether observed relationships are due to ascorbic acid alone or in conjunction with other constituents present in the foods containing ascorbic acid. A knowledge of the particular food sources of vitamin C in different demographic groups thus becomes important to fully understand the etiology. This information will also aid in planning effective education or intervention programs. This paper identifies the dietary sources of vitamin C by age, sex, race, and poverty status, using data from the second National Health and Nutrition Examination Survey (NHANES II). Orange juice is the leading dietary source in all subgroups, but the importance of other sources varies markedly by subgroup. Fortified foods are major contributors among the young but not the old, and southern greens are very important sources among blacks but not among whites. The intake of vitamin C is substantially lower among the poor. Potential relationships with disease are also discussed.

Vitamin C increases the prostacyclin production and decreases the vascular lesions in experimental atherosclerosis in rabbits

Feeding a cholesterol-rich diet (0.3%) to rabbits resulted in an intimal thickening and lipid infiltration of the aorta. The prostacyclin production by the vascular endothelium was significantly decreased, after a transient increase after 2 weeks of diet. The arachidonic acid metabolism in platelets was hardly changed. Addition of a low dose vitamin C (150 mg/day) to the cholesterol rich diet resulted in decreased lipid infiltration and intimal thickening and the transient increase of the prostacyclin production was postponed to the 4th week. Although this dose of vitamin C could not restore the decreased prostacyclin production observed after 6 weeks diet, a higher dose of vitamin C (600 mg/day), besides its beneficial effect on the lipid infiltration and the intimal thickening in the thoracic aorta, kept the intimal prostacyclin production at normal levels for at least 8 weeks.

Vitamin C increases the formation of prostacyclin by aortic rings from various species and neutralizes the inhibitory effect of 15-hydroperoxy-arachidonic acid

Aortic rings from rats, rabbits and guinea-pigs produce different amounts of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), the stable breakdown product of prostacyclin, i.e. 2760 +/- 195, 160 +/- 10 and 87 +/- 17 pg 6-oxo-PGF1 alpha per mg wet weight in 30 min. Vitamin C enhances the production of 6-oxo-PGF1 alpha by the aortic tissue of these three species, independent of their basal release. This increase was only significant if vitamin C was present in the preincubation as well as in the incubation fluid. 15-Hydroperoxy-arachidonic acid inhibits the production of 6-oxo-PGF1 alpha (IC50:6 microM) and this inhibitory effect was completely neutralized by vitamin C. The increased production of 6-oxo-PGF1 alpha is not due to an increased release of the substrate arachidonic acid. It is suggested that vitamin C enhances the formation of 6-oxo-PGF1 alpha by protecting the cyclo-oxygenase and PGI-synthase.

Ascorbate increases the number of low density lipoprotein receptors in cultured arterial smooth muscle cells

Receptor-mediated catabolism of low density lipoprotein (LDL) was increased 2-3-fold in down-regulated smooth muscle cells when the culture medium was supplemented with physiological concentrations of sodium ascorbate for 24 h. The enhanced degradation of LDL was associated with increased LDL receptor activity and LDL uptake. The increase in receptor activity was rapid, transient and inhibited by cycloheximide. Kinetic analysis of saturable binding indicated that ascorbate increased the number of LDL receptors but had no effect on the affinity of the lipoprotein for its receptor. Our data indicate that ascorbic acid may play a role in the regulation of plasma cholesterol levels by influencing LDL receptor number.

Characterization of the aortic collagens in guinea pigs with chronic vitamin C deficiency

Marginal vitamin C deficiency lasting 19 weeks caused hypercholesterolemia and hypertriglyceridemia in guinea pigs. In the thoracic aorta of deficient animals a moderate decline of type I and an increase of type III collagen was observed. Both types of collagen isolated from deficient aortas proved to be slightly underhydroxylated.

Plasma ascorbic acid levels in sheep experimentally infected with Fasciola hepatica

Three groups of sheep, one control (A) and two infected with Fasciola hepatica metacercariae (B&C), were investigated. Each animal of group B was orally dosed with about 270 metacercariae and each sheep in group C received two such doses administered 14 days apart. In both infected groups, plasma ascorbic acid levels progressively decreased after exposure reaching a minimum by week 9, and then slightly increased during the subsequent five weeks. The decrease in ascorbic acid concentrations was mainly related to impaired synthesis as a result of the hepatic damage caused by the flukes.

Modulation by sodium ascorbate of the effect of chloroquine on low density lipoprotein retention and degradation in cultured human skin fibroblasts

Human skin fibroblasts in culture were incubated for 48 h with 125I-labelled low density lipoprotein and chloroquine in the presence and absence of sodium ascorbate. Pretreatment of the cells for 3 days with sodium ascorbate and addition of the vitamin during incubation resulted in a decrease in cellular retention and an increase in degradation of the labelled low density lipoprotein. Similar results were obtained when the cells were pretreated for 3 days but the vitamin was not added during the final 48 h of incubation. Pretreatment of the cells with dithiothreitol, butylated hydroxy-toluene, beta-mercaptoethanol and D-alpha-tocopherol had a similar effect to that of ascorbate, i.e. reduction in low density lipoprotein retention and increase in degradation. Neither ascorbate nor the other reducing agents affected low density lipoprotein catabolism in control cells not treated with chloroquine. Sodium ascorbate pretreatment resulted also in a slight but significant alleviation of the chloroquine-induced inhibition of hydrolysis of cholesterol linoleate. It is proposed that sodium ascorbate by virtue of its reducing properties provides some protection to the intralysosomal hydrolases against the inhibitory action of chloroquine. If cholesterol accumulation in human and experimental atheroma is caused by partial inhibition of lysosomal enzymes, sodium ascorbate could play a role in the alleviation of such an inhibition.

Fundamental studies on physiological and pharmacological actions of L-ascorbate 2-sulfate. VI. Effects of L-ascorbate 2-sulfate on lipid metabolism in guinea pigs

Effects of L-ascorbate 2-sulfate (AAS) on lipid metabolism were studied in guinea pigs maintained on diet I with sufficient L-ascorbic acid (AA) supplement or on diet II without AA supplement. AAS(300 mg/kg) inhibited an increase in serum and liver levels of lipids to a greater degree than AA (175 mg/kg), a reference compond, in hyperlipidemic guinea pigs induced by cholesterol feeding with diets I or II. AAS also induced a decrease in serum and liver levels of lipids in guinea pigs which had been previously maintained for 6 weeks on diet II containing 1.0% cholesterol. AA administration significantly increased AA level in various organs of animals maintained on both the diets containing cholesterol. It also rectified the AA level lowered by previous maintenance on diet II containing cholesterol. AAS showed a slight AA replacing effect on the AA level. Both AA and AAS exerted preventive and curative effects on several symptoms due to chronic AA deficiency.

Marathon running and immunity to atherosclerosis

This is an interim report of an on-going study of deaths in 42-km men. The absence of fatal ASCVD in these athletes can not be construed as evidence for the protective role of exercise alone. The ability to run 42 km depends on many factors. Exercise is only one. Avoiding tobacco is another. Dietary factors also play a role. It has not been feasible to remove one of these factors while maintaining the ability to cover the 42 km distance. Some 42-km men claim that megadoses of ascorbic acid protect them from collagen injury. This is supported by animal studies that show increased collagen synthesis proportional to ascorbic acid intake up to dosage levels that would equal 10 grams per day for humans. Their self-selected macrobiotic diet contains a high ratio of peanuts:steak resulting in a high P/S ratio (polyunsaturates/saturates). Dietary manipulation quickly effects their ability to train. Smoking is so rare among these runners that it must be related to specific effects, such as a catalytic agent in tobacco smoke converting linoleic acid into a toxic lipid oxide. Noakes and Opie recently confirmed again (May, 1976) that no cases of "death due to coronary atherosclerosis" have been recorded in marathon finishers. If this holds true for the second 10-year period of this study, then marathon runners will have joined the longshoremen by earning life-long protection against ASCVD. These longshoremen burned 1,876 kcals on the job, equivalent to a 30-km run. Roberts and Straus suggest that many factors can cause atherosclerosis. Only time will tell whether the marathoner is protected from all of them.

Siderophores: diverse roles in microbial and human physiology

Siderophores, defined as high affinity iron(III) ion transport agents, and their cognate membrane-bound receptor complexes, occur in the enteric bacteria Escherichia coli and Salmonella typhimurium. The total system is tightly regulated by iron repression. The transport properties of the specific siderophores enterobactin and ferrichrome (which is not made by these particular enteric bacteria) have been examined in detail. In E. coli the outer membrane receptor for ferrichrome is programmed by the tonA gene; the receptor also serves as the binding site for T1, T5, phi80, albomycin and colicin M. Similarly, in S. typhimurium phage ES18, ferrichrome and albomycin compete for the genetic equivalent of the tonA locus. The ability of ascorbic acid to protect against atherosclerosis as well as rhinovirus infection in humans may be related to the role of the vitamin in iron metabolism. Deferrisiderophores are clinically useful in the treatment of acute and chronic iron poisoning but, on the other hand, they could constitute a natural hazard by transporting actinides, such as 239Pu, through the food chain.