Ascorbic acid deficiency changes hepatic gene expression of acute phase proteins in scurvy-prone ODS rats

Vitamin C deficiency alters the transcriptome of the rat brain in a glucocorticoid-dependent manner, leading to microglial activation and reduced neurogenesis

Vitamin C (VitC) is maintained at high concentrations in the brain and is an essential micronutrient for brain function. VitC deficiency leads to neuropsychiatric scurvy, which is characterized by depression and cognitive impairment. However, the molecular mechanism by which mild VitC deficiency impairs brain function is currently unknown. In the present study, we conducted RNA sequencing analysis and found that a short-term VitC deficiency altered the brain transcriptome in ODS rats, which cannot synthesize VitC. Bioinformatic analysis indicated that VitC deficiency affected the expression of genes controlled by the glucocorticoid receptor in the brain. We confirmed an increased secretion of glucocorticoids from the adrenal gland during VitC deficiency. We found that non-neuronal cells, including microglia, which are resident immune cells in the brain, changed their transcriptional patterns in response to VitC deficiency. Immunohistochemical analysis revealed that the quiescent ramified microglia transform into the activated amoeboid microglia during three weeks of VitC deficiency. The morphological activation of microglia was accompanied by increased expression of proinflammatory cytokines such as interleukin-6 in the hippocampus. Furthermore, VitC deficiency decreased the number of newly born neurons in the dentate gyrus of the hippocampus, suggesting that VitC was required for adult neurogenesis that plays a crucial role in learning and memory. Our findings may provide insights into the molecular mechanisms underlying the maintenance of normal brain function by adequate levels of VitC.

The evidence to date: implications of l-ascorbic acid in the pathophysiology of aging

L-Ascorbic acid, commonly known as vitamin C, has been used not only for disease prevention and in complementary and alternative medicine, but also for anti-aging purposes. However, the scientific evidence is not yet sufficient. Here, we review the physiological functions of vitamin C and its relationship with various pathological conditions, including our previous findings, and discuss the prospects of its application in healthy longevity. In summary, vitamin C levels are associated with lifespan in several animal models. Furthermore, clinical studies have shown that the blood vitamin C levels are lower in middle-aged and older adults than in younger adults. Lower blood vitamin C levels have also been observed in various pathological conditions such as chronic kidney disease and chronic obstructive pulmonary disease in the elderly. These observations suggest the implications of vitamin C in age-related pathological mechanisms owing to its physiological functions.

Release of SMP30 in Extracellular Vesicles under Conditions of Ascorbic Acid Deficiency Is Involved with Acute Phase Response in ODS Rat

Senescence marker protein-30 (SMP30) is a senescence marker molecule that exhibits lactonase activity in the ascorbic acid (AsA) biosynthesis pathway, except in primate mammals, including humans. Although numerous studies have shown that hepatic AsA deficiency causes acute-phase responses, details of the relationship between SMP30 expression and acute-phase responses in AsA-deficient conditions remain to be elucidated. Here, we investigated the effects of AsA deficiency on the relationship between SMP30 and acute liver injury in osteogenic disorder Shionogi (ODS) rats, which have a hereditary defect in AsA biosynthesis. Male-ODS rats (4 wk old) were pair-fed an AsA-free diet with distilled or 0.1% AsA-dissolved water for 14 d. Under AsA-deficient conditions, hepatic SMP30 protein level was decreased and liver injury markers, the serum aspartate aminotransferase/alanine transaminase ratio and cytokine-induced neutrophil chemoattractant-1 (CINC-1) concentration, were elevated. In contrast, SMP30 protein level in extracellular vesicles (EVs) was significantly increased in addition to the positive acute proteins haptoglobin and asialoglycoprotein receptor 1 (ASGPR1), hepatic-derived specific markers expression under AsA-deficient conditions. AsA deficiency also activated signal transducer and activator of transcription 3 (STAT3) which is linked to EVs release in the liver. These results suggest that the release of SMP30 in EVs by AsA deficiency is involved with acute-phase responses.

Low Ascorbic Acid Intake Induces Inflammatory Changes in Intestine and Liver of ODS Rats

We previously demonstrated that ascorbic acid (AsA) deficiency, caused by an AsA-free diet, induces inflammatory changes in the liver and intestine of osteogenic disorder Shionogi (ODS) rats that cannot synthesize AsA. However, whether low AsA intake induces inflammatory changes remains unknown. Here, we assessed the inflammatory changes in ODS rats caused by low AsA intake and compared them to ODS rats that were fed a diet supplemented with sufficient amounts of AsA (300 mg/kg). Male ODS rats (12-wk-old) were fed an AsA-free diet (0 ppm group), AsA 20 mg/kg diet (20 ppm group), AsA 40 mg/kg diet (40 ppm group) or AsA 300 mg/kg diet (300 ppm group) for 22 d. The hepatic mRNA levels of acute phase proteins, including C-reactive protein (CRP) and haptoglobin, were higher in the 0 and 20 ppm groups, than in the 300 and 40 ppm groups, but were not significantly higher in the 20 ppm group. Serum CRP concentrations were significantly higher in the 0 and 20 ppm groups than in the 300 and 40 ppm groups. Jejunal and ileal interleukin-1β (IL-1β) mRNA levels were higher in the 0 and 20 ppm groups than in the 300 ppm group. Jejunal and ileal IL-6 mRNA levels tended to be higher in the 0 and 20 ppm groups than in the 300 ppm group. Furthermore, the portal IL-6 concentration gradually increased with decrease in the AsA intake. Thus, inflammatory changes could occur in both AsA-deficient ODS rats and ODS rats with low AsA intake.

Determination of tissue-specific interaction between vitamin C and vitamin E in vivo using senescence marker protein-30 knockout mice as a vitamin C synthesis deficiency model

Vitamin E (α-tocopherol; VE) is known to be regenerated from VE radicals by vitamin C (L-ascorbic acid; VC) in vitro. However, their in vivo interaction in various tissues is still unclear. Therefore, we alternatively examined the in vivo interaction of VC and VE by measurement of their concentrations in various tissues of senescence marker protein-30 (SMP30) knockout (KO) mice as a VC synthesis deficiency model. Male SMP30-KO mice were divided into four groups (VC+/VE+, VC+/VE-, VC-/VE+ and VC-/VE-), fed diets with or without 500 mg/kg VE and given water with or without 1·5 g/l VC ad libitum. Then, VC and VE concentrations in the plasma and various tissues were determined. Further, gene expression levels of transporters associated with VC and VE, such as α-tocopherol transfer protein (α-TTP) and sodium-dependent vitamin C transporters (SVCTs), were examined. These results showed that the VE levels in the VC-depleted (VC-/VE+) group were significantly lower than those in the VC+/VE+ group in the liver and heart; the VC levels in the VE-depleted (VC+/VE-) group were significantly lower than those in the VC+/VE+ group in the kidneys. The α-TTP gene expression in the liver and kidneys was decreased by VC and/or VE depletion. Moreover, SVCT1 gene expression in the liver was decreased by both VC and VE depletion. In conclusion, these results indicate that VC spares VE mainly in the liver and heart and that VE spares VC in the kidneys of SMP30-KO mice. Thus, interaction between VC and VE is likely to be tissue specific.

Gut Microbiota Is Not Involved in the Induction of Acute Phase Protein Expression Caused by Vitamin C Deficiency

Using rats, we previously found that vitamin C deficiency increases serum levels of interleukin-6 (IL-6) and glucocorticoid, and changes the gene expression of acute phase proteins (APP) in the liver. However, it remains unclear how vitamin C deficiency causes these inflammation-like responses. In this study, we investigated the possibility that changes in gut microbiota are involved in the induction of APP gene expression by vitamin C deficiency. ODS rats that cannot genetically synthesize vitamin C were divided into 4 groups based on the presence or absence of vitamin C or antibiotics and were raised for 15 d. Neomycin, vancomycin, and ampicillin were used as antibiotics, and 300 mg L-ascorbic acid/kg was added to the AIN93G diet. Vitamin C deficiency affected neither the wet tissue weights nor relative abundance of bacteria in the cecal contents. Antibiotic administration increased wet weights of the cecum, cecal contents, and colon, changed the relative abundance of some bacteria in the cecal contents, and decreased serum IL-6 level. However, antibiotic administration had no effect on serum concentrations of corticosterone and α1-acid glycoprotein (AGP), vitamin C concentration in the liver, and mRNA levels of haptoglobin and AGP in the liver. Therefore, disturbance of gut microbiota did not attenuate the increase in glucocorticoid level and induction of APP gene expression due to vitamin C deficiency. This suggests that gut microbiota is not involved in the inflammation-like responses caused by vitamin C deficiency.

Ascorbic acid deficiency induces hepatic and intestinal expression of inflammation-related genes irrespective of the presence or absence of gut microbiota in ODS rats

We have previously demonstrated that ascorbic acid (AsA) deficiency causes inflammatory changes in the liver and intestine in Osteogenic Disorder Shionogi (ODS) rats, which are unable to synthesize AsA. We have suggested that AsA deficiency increased intestinal interleukine (IL)-6 production, stimulating hepatic acute phase proteins (APPs) expression via the portal vein. In this study, we determined whether these hepatic and intestinal inflammatory changes by AsA deficiency are induced in germ-free (GF) ODS rats. For 18 days, male specific pathogen-free (SPF) ODS rats were fed the basal diet containing 600 mg AsA/kg (control group) or the AsA-free diet (AsA-deficient group) in SPF conditions, while male GF ODS rats were fed the basal diet (control group) or the AsA-free diet (AsA-deficient group) in GF conditions. Firstly, AsA deficiency significantly elevated the hepatic expression of APPs in both SPF and GF rats. In hepatic mRNA levels of some APPs, significant interaction between GF and AsA-deficiency effects was observed. Secondly, AsA deficiency elevated intestinal IL-6 and IL-1β mRNA levels in both SPF and GF rats, and significant interaction between GF and AsA-deficiency effects was observed in these mRNA levels of jejunum and cecum. In SPF and GF rats, AsA deficiency elevated portal IL-6 concentration. These results show that AsA deficiency caused hepatic and intestinal inflammatory changes in both the GF and SPF ODS rats and indicate that AsA deficiency could directly induce intestinal inflammatory changes without the involvement of gut microbiota.

Increases in Acute Phase Reactants in a Patient with Scurvy Despite No Inflammation: Review of Literature

So far, little attention has been paid to the increase in acute phase reactants (APRs) in patients with scurvy. We report that elevated levels of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and serum amyloid A were shown in a pediatric patient with scurvy despite the absence of inflammation. These peculiar findings are important to discriminate scurvy from other rheumatic diseases.

Ascorbic acid deficiency increases hepatic expression of acute phase proteins through the intestine-derived IL-6 and hepatic STAT3 pathway in ODS rats

We have previously shown that ascorbic acid (AsA) deficiency elevates hepatic expression of acute phase proteins (APPs), inflammatory markers, in Osteogenic Disorder Shionogi (ODS) rats, which are unable to synthesize AsA. However, the precise mechanisms of this elevation are unknown. Signal transducer and activator of transcription 3 (STAT3) is one of the transcription factors inducing the expression of APPs and is activated by several cytokines including interleukin-6 (IL-6). The aim of this study was to determine whether AsA deficiency stimulates hepatic STAT3 activation and increases intestinal production of proinflammatory cytokines such as IL-6. Male ODS rats (6 weeks old) were fed either a basal diet containing 300 mg AsA/kg (control group) or an AsA-free diet (AsA-deficient group) for 18 days. AsA deficiency gradually and simultaneously elevated both mRNA levels of APPs (haptoglobin, α1-acid glycoprotein, C-reactive protein and α2-macroglobulin) and nuclear level of phosphorylated STAT3 (activated STAT3) in the liver. These results showed that the AsA-deficiency-induced expression of hepatic APPs is stimulated by proinflammatory cytokines activating STAT3. On day 14, AsA deficiency significantly elevated IL-6 mRNA level in the ileum and the concentration of IL-6 in portal blood. Furthermore, the portal concentration of IL-6 positively correlated with hepatic mRNA levels of STAT3-regulated genes. These findings suggest that IL-6, produced in the intestine as a result of AsA deficiency, is recruited to the liver via the portal vein and contributes to hepatic STAT3 activation and the elevated expression of APPs.

Dietary Intake of Ascorbic Acid Attenuates Lipopolysaccharide-Induced Sepsis and Septic Inflammation in ODS Rats

The aim of this study was to verify the protective effects of ascorbic acid (AsA) against lipopolysaccharide (LPS)-induced sepsis. The study was conducted using osteogenic disorder Shionogi (ODS) rats, which are unable to synthesize AsA. Male ODS rats (6 wk old) were fed either an AsA-free diet (AsA-deficient group), a diet supplemented with 300 mg/kg AsA (control group), or a diet supplemented with 3,000 mg/kg AsA (high-AsA group) for 8 d. On day 8, all the rats were intraperitoneally injected with LPS (15 mg/kg body weight). Forty-eight hours after the injection, the survival rates of the rats in the control (39%) and the high-AsA (61%) groups were significantly higher than that in the AsA-deficient group (5.5%). Next, we measured several inflammatory parameters during 10 h after administering LPS. At 6 h, elevated serum levels of markers for hepatic and systemic injuries were suppressed in rats fed AsA. Similarly, 10 h after LPS injection, the elevation in the serum levels of markers for renal injury were also suppressed proportionally to the amount of AsA in the diet. The elevated serum concentrations of TNFα and IL-1β by LPS in the AsA-deficient group decreased in groups fed AsA. Hematic TNFα mRNA levels at 6 h after the LPS injection were also lowered by feeding AsA. These results demonstrated that the dietary intake of AsA improved the survival rates and suppressed the inflammatory damage, in a dose-dependent manner, caused during sepsis induced by LPS in ODS rats.

The relationship between vitamin C status, the gut-liver axis, and metabolic syndrome

Metabolic syndrome (MetS) is a constellation of cardiometabolic risk factors, which together predict increased risk of more serious chronic diseases. We propose that one consequence of dietary overnutrition is increased abundance of Gram-negative bacteria in the gut that cause increased inflammation, impaired gut function, and endotoxemia that further dysregulate the already compromised antioxidant vitamin status in MetS. This discussion is timely because "healthy" individuals are no longer the societal norm and specialized dietary requirements are needed for the growing prevalence of MetS. Further, these lines of evidence provide the foundational basis for investigation that poor vitamin C status promotes endotoxemia, leading to metabolic dysfunction that impairs vitamin E trafficking through a mechanism involving the gut-liver axis. This report will establish a critical need for translational research aimed at validating therapeutic approaches to manage endotoxemia-an early, but inflammation-inducing phenomenon, which not only occurs in MetS, but is also prognostic of more advanced metabolic disorders including type 2 diabetes mellitus, as well as the increasing severity of nonalcoholic fatty liver diseases.

Ascorbic acid deficiency increases endotoxin influx to portal blood and liver inflammatory gene expressions in ODS rats

OBJECTIVE

The aim of this study was to determine whether ascorbic acid (AsA) deficiency-induced endotoxin influx into portal blood from the gastrointestinal tract contributes to the inflammatory changes in the liver.

METHOD

The mechanisms by which AsA deficiency provokes inflammatory changes in the liver were investigated in Osteogenic Disorder Shionogi (ODS) rats (which are unable to synthesize AsA). Male ODS rats (6-wk-old) were fed a diet containing sufficient (300 mg/kg) AsA (control group) or a diet without AsA (AsA-deficient group) for 14 or 18 d.

RESULTS

On day 14, the hepatic mRNA levels of acute-phase proteins and inflammation-related genes were significantly higher in the AsA-deficient group than the control group, and these elevations by AsA deficiency were exacerbated on day 18. The serum concentrations of interleukin (IL)-1β and IL-6, which induce acute-phase proteins in the liver, were also significantly elevated on day 14 in the AsA-deficient group compared with the respective values in the control group. IL-1β mRNA levels in the liver, spleen, and lung were increased by AsA deficiency. Moreover, on both days 14 and 18, the portal blood endotoxin concentration was significantly higher in the AsA-deficient group than in the control group, and a significant correlation between serum IL-1β concentrations and portal endotoxin concentrations was found in AsA-deficient rats. In the histologic analysis of the ileum tissues, the number of goblet cells per villi was increased by AsA deficiency.

CONCLUSION

These results suggest that AsA deficiency-induced endotoxin influx into portal blood from the gastrointestinal tract contributes to the inflammatory changes in the liver.

Exploring early micronutrient deficiencies in rainbow Trout (Oncorhynchus mykiss) by next-generation sequencing technology--from black box to functional genomics

This work studies final nutritional status and transcriptional responses of rainbow trout (Oncorhynchus mykiss Walbaum 1792) (28 g) after a 10 week feeding experiment designed to elucidate the effect of adding a vitamin and mineral premix on growth, health, and nutritional endpoints. Juvenile fish were fed a either a diet supplemented with a vitamin and mineral premix (Diet S) or the same diet without premix supplementation (Diet U). The analyzed micronutrient composition of diets differed accordingly. Pooled livers from 15 fish from each dietary group were used to create suppression subtractive hybridization (SSH) cDNA libraries that were sequenced with 454 FLX GS Titanium Technology. In total 552 812 reads were sequenced from the two cDNA libraries. Ingenuity pathway analysis (IPA) was then used to characterize the hepatic transcriptome of the two dietary groups of rainbow trout. In the present communication we discuss how selected micronutrients may affect the transcriptome at suboptimal status by directly impacting the cellular metabolism, functions, and structures, and by introducing respective compensatory mechanisms. Processes related to lipid metabolism, peptide hydrolysis, oxygen transportation, and growth development were mostly affected. Considering the transcriptomics data relative to changes in nutritional status from the feeding study and the background phenotypic outcome of growth performance and gill histopathology, the outcome of the transcriptional profiling are suggested to be mainly related to suboptimal pantothenic acid and vitamin C nutrition.

In vivo role of aldehyde reductase

BACKGROUND

Aldehyde reductase (AKR1A; EC 1.1.1.2) catalyzes the reduction of various types of aldehydes. To ascertain the physiological role of AKR1A, we examined AKR1A knockout mice.

METHODS

Ascorbic acid concentrations in AKR1A knockout mice tissues were examined, and the effects of human AKR1A transgene were analyzed. We purified AKR1A and studied the activities of glucuronate reductase and glucuronolactone reductase, which are involved in ascorbic acid biosynthesis. Metabolomic analysis and DNA microarray analysis were performed for a comprehensive study of AKR1A knockout mice.

RESULTS

The levels of ascorbic acid in tissues of AKR1A knockout mice were significantly decreased which were completely restored by human AKR1A transgene. The activities of glucuronate reductase and glucuronolactone reductase, which are involved in ascorbic acid biosynthesis, were suppressed in AKR1A knockout mice. The accumulation of d-glucuronic acid and saccharate in knockout mice tissue and the expression of acute-phase proteins such as serum amyloid A2 are significantly increased in knockout mice liver.

CONCLUSIONS

AKR1A plays a predominant role in the reduction of both d-glucuronic acid and d-glucurono-γ-lactone in vivo. The knockout of AKR1A in mice results in accumulation of d-glucuronic acid and saccharate as well as a deficiency of ascorbic acid, and also leads to upregulation of acute phase proteins.

GENERAL SIGNIFICANCE

AKR1A is a major enzyme that catalyzes the reduction of d-glucuronic acid and d-glucurono-γ-lactone in vivo, besides acting as an aldehyde-detoxification enzyme. Suppression of AKR1A by inhibitors, which are used to prevent diabetic complications, may lead to the accumulation of d-glucuronic acid and saccharate.

Dietary vitamin E deficiency increases anxiety-like behavior in juvenile and adult rats

Vitamin E deficiency from birth or infancy has recently been found to increase anxiety-like behavior in rodents. The present study was undertaken to elucidate the effect of dietary vitamin E deficiency on anxiety in adult rats in comparison with juvenile rats. Male Wistar rats, 3 or 10 weeks old, were divided into two groups and fed a control or vitamin E-deficient diet for 4 weeks. The results of behavioral analysis revealed that vitamin E-deficiency increased anxiety in both juvenile and adult rats. Plasma, liver, and brain α-tocopherol concentrations decreased significantly due to vitamin E deficiency in both age groups. Plasma corticosterone concentrations were higher in the vitamin E-deficient rats in response to the stress of a behavioral test. Based on these results, we conclude that dietary vitamin-E deficiency induces anxiety in adult rats as well as juvenile rats. This might be due to an elevated plasma corticosterone concentration.

Evaluation of gene expression profiling in a mouse model of L-gulonolactone oxidase gene deficiency

Humans and guinea pigs are species which are unable to synthesize ascorbic acid (vitamin C) because, unlike rodents, they lack the enzyme L-gulonolactone oxidase (Gulo). Although the phenotype of lacking vitamin C in humans, named scurvy, has long been well known, information on the impact of lacking Gulo on the gene expression profiles of different tissues is still missing. This knowledge could improve our understanding of molecular pathways in which Gulo may be involved. Recently, we discovered a deletion that includes all 12 exons in the gene for Gulo in the sfx mouse, characterized by spontaneous bone fractures. We report here the initial analysis of the impact of the Gulo gene deletion on the murine gene expression profiles in the liver, femur and kidney.

Ascorbic acid and alpha-tocopherol down-regulate apolipoprotein A-I gene expression in HepG2 and Caco-2 cell lines

HepG2 cells and Caco-2 cells were treated with various concentrations of select antioxidants to study some of the molecular pathways underlying antioxidant-related changes in apolipoprotein A-I (apoA-I) expression. Both alpha-tocopherol and ascorbate treatment over a time course of 72 hours caused a significant reduction in apoA-I messenger RNA and protein levels in a dose-dependent fashion. Albumin levels did not change with any treatment, suggesting that the effect is protein-specific. Similar changes were seen in Caco-2 cells. In contrast, apoA-I messenger RNA and protein levels significantly increased after 28 and 280 micromol/L dimethyl sulfoxide (DMSO) treatment. Cells were transfected with chloramphenicol acetyltransferase (CAT) reporter gene plasmid containing the full-length apoA-I promoter to determine if these changes occur at a transcriptional level, and after 24 hours, the HepG2 or Caco-2 cells were treated with varying concentrations of ascorbate or alpha-tocopherol. At the highest concentration of ascorbate and alpha-tocopherol used (5 mmol/L), there was a significant reduction in apoA-I promoter activity. DMSO treatment up-regulated apoA-I promoter activity, whereas increasing oxidative load with 50, 100, and 200 micromol/L hydrogen peroxide treatment did not significantly alter apoA-I promoter activity. Studies with deletional constructs of the promoter containing or lacking the antioxidant response element (ARE) indicated that the effect of ascorbate and alpha-tocopherol, unlike that of DMSO, was independent of this ARE. Using a series of apoA-I deletion constructs, it was shown that site A-containing segment of the promoter has a critical regulatory element. However, electromobility shift assays indicated that there was no significant change in nuclear factor binding activity to site A as a result of treatment with ascorbate or alpha-tocopherol. As expected, treatment with DMSO increased factor binding to the previously described ARE. It is concluded that the apoA-I promoter-stimulating effect of DMSO may be independent of its antioxidant activity and that some antioxidants at very high concentrations may have suppressive effect on the apoA-I gene expression. It appears that the inhibitory effect of ascorbate or alpha-tocopherol on the apoA-I promoter is either indirect or is the result of posttranslational modifications of the nuclear binding factors. The previously described ARE is not a response element for the ascorbate or alpha-tocopherol.

Ascorbic Acid Deficiency Stimulates Hepatic Expression of Inflammatory Chemokine, Cytokine-Induced Neutrophil Chemoattractant-1, in Scurvy-Prone ODS Rats

ODS rat has a hereditary defect in ascorbic acid biosynthesis and is a useful animal model for elucidating the physiological role of ascorbic acid. We previously demonstrated by using ODS rats that ascorbic acid deficiency changes the hepatic gene expression of acute phase proteins, as seen in acute inflammation. In this study, we investigated the effects of ascorbic acid deficiency on the production of inflammatory chemokine, cytokine-induced neutrophil chemoattractant-1 (CINC-1), in ODS rats. Male ODS rats (6 wk of age) were fed a basal diet containing ascorbic acid (300 mg/kg diet) or a diet without ascorbic acid for 14 d. Obvious symptoms of scurvy were not observed in the ascorbic acid-deficient rats. Ascorbic acid deficiency significantly elevated the serum concentration of CINC-1 on d 14. The liver and spleen CINC-1 concentrations in the ascorbic acid-deficient rats were significantly elevated to 600% and 180% of the respective values in the control rats. However, the lung concentration of CINC-1 was not affected by ascorbic acid deficiency. Ascorbic acid deficiency significantly elevated the hepatic mRNA level of CINC-1 (to 480% of the value in the control rats), but not the lung mRNA level. These results demonstrate that ascorbic acid deficiency elevates the serum, liver and spleen concentrations of CINC-1 as seen in acute inflammation, and suggest that ascorbic acid deficiency stimulate the hepatic CINC-1 gene expression.

Tissue carnitine fluxes in vitamin C depleted-repleted guinea pigs

The biosynthesis of carnitine requires vitamin C as a cofactor for two separate hydroxylation steps. The majority of body carnitine (approximately 98%) is located in muscle and less than 0.5% is present in plasma. We examined the physiologic dynamics of plasma free carnitine and muscle total acid-soluble carnitine in vitamin C-depleted guinea pigs repleted with increasing amounts of vitamin C. Animals were fed a vitamin C-deficient diet for 3 weeks at which time symptoms of scurvy were evident. Animals were repleted with increasing doses of vitamin C, from 0.5 to 10.0 mg vitamin C/100 g body weight daily. Muscle total acid-soluble carnitine concentrations tended to correlate directly with plasma vitamin C (r = 0.41, P = 0.087) during the repletion phase of the study. Conversely, plasma free carnitine was inversely related to liver vitamin C (r = -0.54, P = 0.020) and to muscle total acid-soluble carnitine (r = -0.56, P = 0.015). Mean plasma free carnitine values fell 30% over the course of vitamin C repletion (P > 0.05) and mean muscle total acid-soluble carnitine rose by 30% (P > 0.05). These data suggest that elevated plasma free carnitine may indicate a low to marginal vitamin C status.

Up-regulation and polarized expression of the sodium-ascorbic acid transporter SVCT1 in post-confluent differentiated CaCo-2 cells

Human cells acquire vitamin C using two different transporter systems, the sodium-ascorbic acid co-transporters with specificity for ascorbic acid, and the facilitative glucose transporters with specificity for dehydroascorbic acid. There is no information on the mechanism of vitamin C transport across the intestinal barrier, a step that determines the bioavailability of vitamin C in humans. We used the colon carcinoma cell line CaCo-2 as an in vitro model for vitamin C transport in enterocyte-like cells. The results of transport kinetics, sodium dependence, inhibition studies, and reverse transcriptase-PCR analysis indicated that CaCo-2 cells express the sodium-ascorbate co-transporters SVCT1 and SVCT2, the dehydroascorbic acid transporters GLUT1 and GLUT3, and a third dehydroascorbic acid transporter with properties expected for GLUT2. Analysis by real time quantitative PCR revealed that the post-confluent differentiation of CaCo-2 cells was accompanied by a marked increase (4-fold) in the steady-state level of SVCT1 mRNA, without changes in SVCT2 mRNA levels. Functional studies revealed that the differentiated cells expressed only one functional ascorbic acid transporter having properties expected for SVCT1, and transported ascorbic acid with a V(max) that was increased at least 2-fold compared with pre-confluent cells. Moreover, post-confluent Caco-2 cells growing as monolayers in permeable filter inserts showed selective sorting of SVCT1 to the apical membrane compartment, without functional evidence for the expression of SVCT2. The identification of SVCT1 as the transporter that allows vectorial uptake of ascorbic acid in differentiated CaCo-2 cells has a direct impact on our understanding of the mechanism for vitamin C transport across the intestinal barrier.

Hyperglycemia-induced ascorbic acid deficiency promotes endothelial dysfunction and the development of atherosclerosis

Dehydroascorbic acid, the oxidized form of vitamin C, is transported into mammalian cells via facilitative glucose transporters and hyperglycemia inhibits this process by competitive inhibition. This inhibited transport may promote oxidative stress and contribute to the increase in atherosclerotic cardiovascular disease observed in patients with diabetes mellitus. This review explores the importance of this proposed mechanism in light of current research. For example, recent reports suggest that administration of antioxidants, such as vitamin C, may slow atherogenesis by improving endothelium-dependent vasodilation in individuals with abnormal glucose and lipid metabolism, perhaps by preventing the oxidation of nitric oxide, an important regulator of vasomotor tone. Endothelial dysfunction plays a key role in the development of atherosclerosis and endothelial cells may be particularly affected by hyperglycemia-induced ascorbic acid deficiency as they line the interior of blood vessels. In addition, we discuss evidence of several other mechanisms by which vitamin C status may affect the development of atherosclerotic cardiovascular disease, particularly its inverse relationship to multiple cardiovascular disease risk factors and indicators. Given these factors, vitamin C administration is recommended during periods of both acute and chronic hyperglycemia to help preserve endothelial function.

Vitamin C and genomic stability

Vitamin C, a water-soluble glucose derivative, has considerable antioxidant activity in vitro, in part because of its ease of oxidation and because the semidehydroascorbate radical derived from it is of low reactivity. Vitamin C in vivo is an essential cofactor for a range of enzymes involved in diverse metabolic pathways, but much recent literature has focused on its antioxidant effects. Consumption of foods rich in Vitamin C (fruits and vegetables) is associated with decreased risk of cardiovascular disease, of many types of cancer and possibly of neurodegenerative disease, but the extent to which Vitamin C contributes to these effects is uncertain. Data using biomarkers of oxidative damage to DNA bases have given no compelling evidence to date that ascorbate supplements can decrease the levels of oxidative DNA damage in vivo, except perhaps in subjects with very low Vitamin C intakes. Similarly, there is no conclusive evidence from studies of strand breaks, micronuclei, or chromosomal aberrations for a protective effect of Vitamin C. There is limited evidence that supplements of Vitamin C might have beneficial effects in disorders of vascular function, and that diet-derived Vitamin C may decrease gastric cancer incidence in certain populations, but it is not clear whether it is the antioxidant or other properties of ascorbate that are responsible for these two actions.

Ascorbate deficiency impairs the muscarinic-cholinergic and ss-adrenergic receptor signaling systems in the guinea pig submandibular salivary gland

Ascorbic acid is preferentially concentrated in the hypothalamus, pituitary and adrenal glands. Its level in the acini of salivary glands is relatively high. We therefore hypothesized that ascorbate may have a role in salivary gland function. Ascorbate-deficient guinea pigs had lower stimulated whole salivary flow rates than well-fed, age-matched controls (P: < 0.005). Total salivary protein concentration was also markedly (P: < 0.005) reduced in the deficient guinea pigs. SDS-PAGE and densitometric quantification of protein bands confirmed significant reduction in specific salivary proteins (e.g., amylase, proline-rich proteins) in the saliva samples of malnourished guinea pigs. Some protein bands not seen in control saliva were detected in the saliva of malnourished guinea pigs. Ascorbate deficiency also produced a significant (P: < 0.005) reduction in the ss-adrenergic receptor density (subtype 1; 95 +/- 19 fmol/mg protein compared with 179 +/- 27 fmol/mg protein for the controls). No significant difference was observed between the two groups with respect to the ss-adrenergic receptor subtype 2. Additionally, ascorbate-deficient guinea pigs had significantly lower muscarinic-cholinergic receptor densities (50 +/- 5 vs. 74 +/- 8 fmol/mg protein for controls). Our data support the conclusion that diminished membrane receptors might impair the capacity of the transmembrane signaling system, resulting in salivary gland hypofunction in ascorbate-deficient guinea pigs. Without implying extrapolation of our findings in experimental animals to humans, it is perhaps relevant that many conditions often associated with salivary gland hypofunction in humans (e.g., smoking or drug ingestion) deplete cellular ascorbate.