Comparison of ascorbic acid and ascorbic acid 2-O-alpha-glucoside on the cytotoxicity and bioavailability to low density cultures of fibroblasts

Promoter engineering for efficient production of sucrose phosphorylase in Bacillus subtilis and its application in enzymatic synthesis of 2-O-α-D-glucopyranosyl-L-ascorbic acid

2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G), a stable glucoside derivative of L-ascorbic acid (L-AA), can be one-step synthesized by sucrose phosphorylase (SPase). In this study, we attempted to produce extracellular SPase in Bacillus subtilis WB800 for the food-grade production of AA-2G. The results showed that the secretion of SPases did not require signal peptide. Promoter and its compatibility to target SPase gene were proved to be the key factors for high-level secretion. The strong promoter P₄₃ and synthetic SPase gene derived from Bifidobacterium longum (BloSPase) were selected due to generate a relatively high extracellular activity (0.94 U/mL) for L-AA glycosylation. A highly active dual-promoter system P_sigH-100-P₄₃ was further constructed, which produced the highest extracellular and intracellular activity were 5.53 U/mL and 6.85 U/mL in fed-batch fermentation, respectively. Up to 113.58 g/L of AA-2G could be achieved by the supernatant of fermentation broth and a higher yield of 146.42 g/L was obtained by whole-cells biotransformation. Therefore, the optimal dual-promoter system in B. subtilis is suitable for the food-grade scale-up production of AA-2G.

Ascorbic Acid Enhances the Metabolic Activity, Growth and Collagen Production of Human Dermal Fibroblasts Growing in Three-dimensional (3D) Culture

Tissue engineering (TE) enables developing functional synthetic substitutes to be replaced with damaged tissues and organs instead of the use of auto or allografts. A wide range of biomaterials is currently in use as TE scaffolds. Among these materials, naturally-sourced ones are favourable due to being highly biocompatible and supporting cell growth and function whereas synthetic ones are advantageous because of the high tunability on mechanical and physical properties as well as being easy to process. Alongside the advantages of synthetic polymers, they mostly show hydrophobic behaviour that limits biomaterial-cell interaction and consequently the functioning of the developed TE constructs. In this study, we assessed the impact of L-Ascorbic acid 2-phosphate (AA2P) on improving the culture of human dermal fibroblasts (HDFs) growing on a three-dimensional (3D) scaffold made of polycaprolactone by emulsion templating technique. Our results demonstrated that AA2P enhances the metabolic activity, growth, and collagen production of HDFs when supplemented to their growth medium at 50 µg/mL concentration. It showed a great potential to be used as a growth medium supplement to circumvent the disadvantages of culturing human cells on a synthetic biomaterial that is not favoured in default. AA2P's potential to improve cell growth and collagen deposition may prove an effective way to culture human cells on 3D PCL PolyHIPE scaffolds for various TE applications.

Ascorbic acid 2-glucoside: An ascorbic acid pro-drug with longer-term antioxidant efficacy in skin

OBJECTIVE

Deleterious effects of pollutants and ultraviolet radiation on the skin can be attenuated using formulations containing antioxidants. However, these have disadvantages, including chemical instability, photodegradation, poor bioavailability or biological activity. Here, two commercial formulations were evaluated: one optimized to stabilize and deliver ascorbic acid (AA) at 15% and the other containing a glucoside form of AA, namely ascorbic acid 2-glucoside (AA2G), at 1.8% and at a physiological pH. We compared the skin delivery, antioxidative effects and chemical stability of AA2G with AA in their respective formulations.

METHODS

Skin delivery was measured using fresh viable human skin explants, and oxidative stress was measured using a human reconstructed epidermal (RHE) model according to levels of malondialdehyde (MDA), superoxide dismutase (SOD) and catalase.

RESULTS

Ascorbic acid 2-glucoside was completely metabolized to AA by the skin before entering the receptor compartment. The skin contained parent and AA, indicating a reserve of AA2G was present for further metabolism. For AA2G and AA, maximum flux of AA-equivalents was at 12 h, with continued absorption over 24 h. The absolute amount in µg was higher in the skin after application of AA than after application of AA2G. This may suggest a greater antioxidative effect; however, according to all three measurements of oxidative stress, the protective effect of AA and AA2G was similar. Unlike AA, AA2G was chemically stable under storage conditions.

CONCLUSION

A lower concentration of AA2G is as effective as the active metabolite, AA, in terms of antioxidant effects. AA2G was chemically stable and can be applied at a lower concentration than AA, thus avoiding the need for an acidic formulation with a pH below 3.5.

Ascorbic Acid 2-Glucoside Pretreatment Protects Cells from Ionizing Radiation, UVC, and Short Wavelength of UVB

Ascorbic acid 2-glucoside (AA2G), glucosylated ascorbic acid (AA), has superior properties for bioavailability and stability compared to AA. Although AA2G has shown radioprotective properties similar to AA, effects for UV light, especially UVC and UVB, are not studied. AA2G was tested for cytotoxicity and protective effects against ionizing radiation, UVC, and broadband and narrowband UVB in Chinese hamster ovary (CHO) cells and compared to AA and dimethyl sulfoxide (DMSO). Pretreatment with DMSO, AA, and AA2G showed comparative protective effects in CHO wild type and radiosensitive xrs5 cells for cell death against ionizing radiation with reducing the number of radiation-induced DNA damages. Pretreatment with AA and AA2G protected CHO wild type and UV sensitive UV135 cells from UVC and broadband UV, but not from narrowband UVB. DMSO showed no protective effects against tested UV. The UV filtration effects of AA and AA2G were analyzed with a spectrometer and spectroradiometer. AA and AA2G blocked UVC and reduced short wavelengths of UVB, but had no effect on wavelengths above 300nm. These results suggest that AA2G protects cells from radiation by acting as a radical scavenger to reduce initial DNA damage, as well as protecting cells from certain UVB wavelengths by filtration.

The Influence of Cell Culture Density on the Cytotoxicity of Adipose-Derived Stem Cells Induced by L-Ascorbic Acid-2-Phosphate

Ascorbic acid-2-phosphate (A2-P) is an oxidation-resistant derivative of ascorbic acid that has been widely employed in culturing adipose-derived stem cells (ASCs) for faster expansion and cell sheet formation. While high dose ascorbic acid is known to induce cellular apoptosis via metabolic stress and genotoxic effects, potential cytotoxic effects of A2-P at high concentrations has not been explored. In this study, the relationship between ASC seeding density and A2-P-induced cytotoxicity was investigated. Spheroid-derived ASCs with smaller cellular dimensions were generated to investigate the effect of cell-cell contact on the resistance to A2-P-induced cytotoxicity. Decreased viability of ASC, fibroblast, and spheroid-derived ASC was noted at higher A2-P concentration, and it could be reverted with high seeding density. Compared to control ASCs, spheroid-derived ASCs seeded at the same density exhibited decreased viability in the A2-P-supplemented medium. The expression of antioxidant enzymes (catalase, SOD1, and SOD2) was enhanced in ASCs at higher seeding densities. However, their enhanced expression in spheroid-derived ASCs was less evident. Furthermore, we found that co-administration of catalase or N-acetylcysteine nullified the observed cytotoxicity. Collectively, A2-P can induce ASC cytotoxicity at higher concentrations, which can be prevented by seeding ASCs at high density or co-administration of another antioxidant.

Enhanced 2- O-α-d-Glucopyranosyl-l-ascorbic Acid Synthesis through Iterative Saturation Mutagenesis of Acceptor Subsite Residues in Bacillus stearothermophilus NO2 Cyclodextrin Glycosyltransferase

Low synthesis yields of the l-ascorbic acid (l-AA) derivative 2- O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G) limit its application in the food industry. In this work, the AA-2G synthesis yield of Bacillus stearothermophilus NO2 cyclodextrin glycosyltransferase (CGTase) was improved. Nine residues within 10 Å of the catalytic residue Glu²⁵³ displaying ≤30% conservation and located in the acceptor subsite were selected for iterative saturation mutagenesis. The best mutant, K228R/M230L, produced a higher AA-2G yield with maltodextrin as the glucosyl donor than that produced by its parent wild-type. The l-AA K_m values of the mutant K228R/M230L decreased by 35%, whereas the k_cat/ K_m increased by 2.69-fold. Kinetic analysis indicated that K228R/M230L displayed enhanced l-AA specificity. These results demonstrate that acceptor subsite residues play an important role in acceptor substrate specificity. Mutant K228R/M230L afforded the highest AA-2G concentration (211 g L^-1, 624 mM) reported to date after optimization of the reaction conditions.

Production of ascorbic acid releasing biomaterials for pelvic floor repair

OBJECTIVE

An underlying abnormality in collagen turnover is implied in the occurrence of complications and recurrences after mesh augmented pelvic floor repair surgeries. Ascorbic acid is a potent stimulant of collagen synthesis. The aim of this study is to produce ascorbic acid releasing poly-lactic acid (PLA) scaffolds and evaluate them for their effects on extracellular matrix production and the strength of the materials.

MATERIALS AND METHODS

Scaffolds which contained either l-ascorbic acid (AA) and Ascorbate-2-Phosphate (A2P) were produced with emulsion electrospinning. The release of both drugs was measured by UV spectrophotometry. Human dermal fibroblasts were seeded on scaffolds and cultured for 2weeks. Cell attachment, viability and total collagen production were evaluated as well as mechanical properties.

RESULTS

No significant differences were observed between AA, A2P, Vehicle and PLA scaffolds in terms of fibre diameter and pore size. The encapsulation efficiency and successful release of both AA and A2P were demonstrated. Both AA and A2P containing scaffolds were significantly more hydrophilic and stronger in both dry and wet states compared to PLA scaffolds. Fibroblasts produced more collagen on scaffolds containing either AA or A2P compared to cells grown on control scaffolds.

CONCLUSION

This study is the first to directly compare the two ascorbic acid derivatives in a tissue engineered scaffold and shows that both AA and A2P releasing electrospun PLA scaffolds increased collagen production of fibroblasts to similar extents but AA scaffolds seemed to be more hydrophilic and stronger compared to A2P scaffolds.

STATEMENT OF SIGNIFICANCE

Mesh augmented surgical repair of the pelvic floor currently relies on non-degradable materials which results in severe complications in some patients. There is an unmet and urgent need for better pelvic floor repair materials. Our current understanding suggests that the ideal material should be able to better integrate into sites of implantation both biologically and mechanically. The impact of vitamin C on extracellular matrix production is well established but we in this study have undertaken a critical comparison of two derivatives of vitamin C as they are released from a biodegradable scaffold. This strategy proved to be equally useful with both derivatives in terms of new tissue production yet we observed significant differences in mechanical properties of these biomaterials.

Biosynthesis of 2-O-D-glucopyranosyl-l-ascorbic acid from maltose by an engineered cyclodextrin glycosyltransferase from Paenibacillus macerans

In this work, the specificity of cyclodextrin glycosyltransferase (CGTase) of Paenibacillus macerans towards maltose was improved by the site-saturation engineering of lysine 47, and the enzymatic synthesis of 2-O-d-glucopyranosyl-l-ascorbic acid (AA-2G) with l-ascorbic acid and maltose as substrates was optimized. Compared to the AA-2G yield of the wild-type CGTase, that of the mutants K47F (lysine→phenylalanine), K47P (lysine→proline), and K47Y (lysine→tyrosine) was increased by 17.1%, 32.9%, and 21.1%, respectively. Under the optimal transformation conditions (pH 6.5, temperature 36°C, the mass ratio of l-ascorbic acid to maltose 1:1), the highest AA-2G titer by the K47P reached 1.12g/L, which was 1.32-fold of that (0.85g/L) obtained by the wild-type CGTase. The reaction kinetics analysis confirmed the enhanced maltose specificity of the mutants K47F, K47P, and K47Y. It was also found that compared to the wild-type CGTase, the three mutants had relatively lower cyclization activities and higher disproportionation activities, which was favorable for AA-2G synthesis. As revealed by the interaction structure model of CGTase with substrate, the enhancement of maltose specificity may be due to the removal of hydrogen bonding interactions between the side chain of residue 47 and the sugar at -3 subsite. The obtained mutant CGTases, especially the K47P, has a great potential in the large-scale production of AA-2G with maltose as a cheap and soluble substrate.

Site-saturation engineering of lysine 47 in cyclodextrin glycosyltransferase from Paenibacillus macerans to enhance substrate specificity towards maltodextrin for enzymatic synthesis of 2-O-D-glucopyranosyl-L-ascorbic acid (AA-2G)

In this work, the site-saturation engineering of lysine 47 in cyclodextrin glycosyltransferase (CGTase) from Paenibacillus macerans was conducted to improve the specificity of CGTase towards maltodextrin, which can be used as a cheap and easily soluble glycosyl donor for the enzymatic synthesis of 2-O-D-glucopyranosyl-L-ascorbic acid (AA-2G) by CGTase. When using maltodextrin as glycosyl donor, four mutants K47F (lysine→ phenylalanine), K47L (lysine→ leucine), K47V (lysine→ valine) and K47W (lysine→ tryptophan) showed higher AA-2G yield as compared with that produced by the wild-type CGTase. The transformation conditions (temperature, pH and the mass ratio of L-ascorbic acid to maltodextrin) were optimized and the highest titer of AA-2G produced by the mutant K47L could reach 1.97 g/l, which was 64.2% higher than that (1.20 g/l) produced by the wild-type CGTase. The reaction kinetics analysis confirmed the enhanced maltodextrin specificity, and it was also found that compared with the wild-type CGTase, the four mutants had relatively lower cyclization activities and higher disproportionation activities, which was favorable for AA-2G synthesis. The mechanism responsible for the enhanced substrate specificity was further explored by structure modeling and it was indicated that the enhancement of maltodextrin specificity may be due to the short residue chain and the removal of hydrogen bonding interactions between the side chain of residue 47 and the sugar at -3 subsite. Here the obtained mutant CGTases, especially the K47L, has a great potential in the production of AA-2G with maltodextrin as a cheap and easily soluble substrate.

Vitamin C in human health and disease is still a mystery? An overview

Ascorbic acid is one of the important water soluble vitamins. It is essential for collagen, carnitine and neurotransmitters biosynthesis. Most plants and animals synthesize ascorbic acid for their own requirement. However, apes and humans can not synthesize ascorbic acid due to lack of an enzyme gulonolactone oxidase. Hence, ascorbic acid has to be supplemented mainly through fruits, vegetables and tablets. The current US recommended daily allowance (RDA) for ascorbic acid ranges between 100-120 mg/per day for adults. Many health benefits have been attributed to ascorbic acid such as antioxidant, anti-atherogenic, anti-carcinogenic, immunomodulator and prevents cold etc. However, lately the health benefits of ascorbic acid has been the subject of debate and controversies viz., Danger of mega doses of ascorbic acid? Does ascorbic acid act as a antioxidant or pro-oxidant? Does ascorbic acid cause cancer or may interfere with cancer therapy? However, the Panel on dietary antioxidants and related compounds stated that the in vivo data do not clearly show a relationship between excess ascorbic acid intake and kidney stone formation, pro-oxidant effects, excess iron absorption. A number of clinical and epidemiological studies on anti-carcinogenic effects of ascorbic acid in humans did not show any conclusive beneficial effects on various types of cancer except gastric cancer. Recently, a few derivatives of ascorbic acid were tested on cancer cells, among them ascorbic acid esters showed promising anticancer activity compared to ascorbic acid. Ascorbyl stearate was found to inhibit proliferation of human cancer cells by interfering with cell cycle progression, induced apoptosis by modulation of signal transduction pathways. However, more mechanistic and human in vivo studies are needed to understand and elucidate the molecular mechanism underlying the anti-carcinogenic property of ascorbic acid. Thus, though ascorbic acid was discovered in 17th century, the exact role of this vitamin/nutraceutical in human biology and health is still a mystery in view of many beneficial claims and controversies.

Inhibition of cell proliferation and fibronectin biosynthesis by Na ascorbate

BACKGROUND

The importance of ascorbate on the production of extracellular matrix proteins (as elastin and collagens) is now well documented, but no studies have been published concerning its effects on fibronectin biosynthesis. Fibronectin is important for cell attachment and for proliferation.

MATERIALS AND METHODS

The effects of Na ascorbate were investigated on cell attachment, proliferation, viability and fibronectin biosynthesis by human skin fibroblasts in vitro. Proliferation was followed by the monitoring of [(3)H]-thymidine incorporation; viability by the MTT-test, cell adherence by counting adherent and nonadherent cells and fibronectin biosynthesis by immunoprecipitation of biosynthetically labelled fibronectin.

RESULTS

In the presence of ascorbate, the fibroblasts showed a biphasic growth pattern. At 500 microM ascorbate, [(3)H]-thymidine incorporation was stimulated by 15% as compared to the controls. Higher concentrations gradually decreased proliferation up to 36% of the control value at 5 mM. These effects of ascorbate on DNA synthesis were followed to > 1.25 mM by a strong inhibition, cytotoxic effect and cell death. The non-adherent cell count increased to 10% of the total population at 2.5 mM and to 31% at 5.0 mM ascorbate.Increasing concentrations of ascorbate resulted in a dose-dependent decrease of fibronectin biosynthesis, both in the culture supernates and cell extracts. This inhibition mainly concerned cell membrane-associated fibronectin.Superoxide-dismutase or catalase could inhibit Na ascorbate-induced cytotoxicity and partially re-establish fibronectin biosynthesis. Desferrioxamine, ergothionein and vitamin E were inefficient.

CONCLUSIONS

Our results indicate that ascorbate decreases fibronectin biosynthesis of cultured human skin fibroblasts, thereby producing cell detachment and decreased proliferation. This effect is mainly mediated by the reactive oxygen species and can be inhibited by superoxide-dismutase and catalase.

Enhancement of developmental competence after in vitro fertilization of porcine oocytes by treatment with ascorbic acid 2-O-alpha-glucoside during in vitro maturation

The present study was conducted to examine the effect of ascorbic acid 2-O-alpha-glucoside (AA-2G), a stable ascorbate derivative, on the sustenance of cytoplasmic maturation responsible for subsequent developmental competence after in vitro fertilization of porcine oocytes. Cumulus-oocyte complexes were cultured for 44 h in North Carolina State University 37 medium supplemented with cysteine, gonadotropins, 10% (v:v) porcine follicular fluid, and 0-750 microM AA-2G. When oocytes were matured in the presence of 250 microM AA-2G, their ability to promote transformation of the sperm nucleus into the male pronucleus (MPN) was strongly enhanced after in vitro fertilization. Similarly, the presence of 25 microM beta-mercaptoethanol (ME) enhanced the degree of progression to MPN of penetrated sperm by associating with the increase in intracellular glutathione (GSH) content. Although the AA-2G treatment during oocyte maturation showed no influence on the GSH concentration, significantly higher levels of ascorbic acid (AsA) were detected in these oocytes than in those oocytes cultured without AA-2G (P < 0.05). The length of DNA migration encompassed by reactive oxygen species (ROS), generated by the hypoxanthine-xanthine oxidase system, was not increased in the oocytes treated with AA-2G, whereas ME treatment could not block the DNA damage by ROS. These findings indicate that AA-2G in maturation medium can potentiate the cellular protection of oocytes against oxidative stress by continuously supplying AsA. The proportion of development to the blastocyst stage after in vitro insemination was significantly increased in oocytes matured with AA-2G (P < 0.05), and this proportion showed no difference in comparison with that of oocytes treated with ME. These findings suggest that a critical concentration of intracellular AsA, supplied by AA-2G during in vitro maturation, plays an important role in supporting the cytoplasmic maturation responsible for developmental competence after fertilization by prevention of oxidative stress against porcine oocytes.

The effects of combined conventional treatment, oral antioxidants and essential fatty acids on sperm biology in subfertile men

We evaluated the effects of combined conventional treatment, oral antioxidants (N-acetyl-cysteine or vitamins A plus E) and essential fatty acids (FA) on sperm biology in an open prospective study including 27 infertile men. The evaluation included sperm characteristics, seminal reactive oxygen species (ROS), FA of sperm membrane phospholipids, sperm oxidized DNA (8-OH-dG), and induced acrosome reaction (AR). Treatment did not improve sperm motility and morphology, nor decrease the concentration of round cells and white blood cells in semen. Sperm concentration increased in oligozoospermic men (7.4+/-1.3 to 12.5+/-1.9 million/ml). Treatment significantly reduced ROS (mean+/-SEM) (775.3+/-372.2 to 150.3+/-105.2 x 10(3)counts/10 second) and 8-OH-dG (45.3+/-10.4 to 16. 8+/-3.3 fmol/microg DNA). Treatment increased the AR (55.1+/-2.2 to 71.6+/-2.2%), the proportion of polyunsaturated FA of the phospholipids, and sperm membrane fluidity. The overall pregnancy rate was 4.5% in 134 months. The per month pregnancy rate tended to be higher in partners of (ex)-smokers (7.15%, n=14,70 months) than in never-smokers (1.6%, n=13,64 months) (OR:4.57, 95% Cl:0.55-38.1).

Growth suppression of malignant leukemia cell line in vitro by ascorbic acid (vitamin C) and its derivatives

In recent years there has been a growing interest in the therapeutic application of L-ascorbic acid (AA) and its derivatives as anticancer agents. AA is a gamma-crotonolactone derivative with reactive hydroxyl groups at the 2- and 3-positions and an ethylene glycol substitution at the 4-position. Despite the various reports on AA toxicity, no work has been reported underlying the critical chemical structural features for its activity. The present study addresses this question. We tested in vivo, using malignant leukemia cell line P388D1, (i) L-AA and its isomers, (ii) substitution at the 2-position: -PO4, -SO4, O-Me, O-octadecyl, (iii) substitution at the 6-position: -PO4, -SO4, -palmitate, -stearate, (iv) substitution at the 2,6-position: dipalmitate, (v) 6-deoxy derivative: -Cl, -Br, -NH2 and (vi) dihydroxy gamma-crotonolactone with substitutions at the 4-position: -H, -CH3, -CH2-CH3 and -CH=CH2. L-AA and its isomers were very cytotoxic even at very low concentration. All 6-substituted and 6-deoxy derivatives were as toxic as AA. However, 2-substituted and 2,6-disubstituted AA derivatives were non-toxic. Interestingly, dihydroxy gamma-crotonolactone with or without substitution at the 5-position also exhibited toxicity. These results suggest that the underlying criterion for AA toxicity resides in dihydroxy gamma-crotonolactone moiety. Either substitution in the hydroxy groups or saturating the double bond render the molecule inactive.

Moderately controlled transport of ascorbate into aortic endothelial cells against slowdown of the cell cycle, decreasing of the concentration or increasing of coexistent glucose as compared with dehydroascorbate

Uptake of L-[1-(14)C]ascorbic acid (Asc) of 12.5-200 microM for 1 h into bovine aortic endothelial BAE-2 cells grown to confluence was as low as 43-64% (per cell) of uptake into the cells grown to nearly one-fourth confluence. [14C]Asc undergoing transmembrane uptake was concentrated and accumulated in the cell less efficiently ([Asc]in/ex = 8-13) at confluence than at subconfluence ([Asc]in/ex = 15-24). The declined Asc uptake at confluence is attributable to slowdown of the cell cycle, because a similar decrease in [Asc]in/ex was shown by subconfluent cells precultured in serum-insufficient medium, resulting in an increase in G1 phase and concurrent decreases in S and G2 + M phase distributions as determined by flow cytometry. [1-(14)C]Dehydroascorbic acid (DehAsc) was taken up and accumulated as Asc, after metabolic reduction, without detectable DehAsc. The [Asc]in/ex values for DehAsc at confluence were as low as 15-69% of those at subconfluence in contrast to the values as retentive as 62-75% for Asc, suggesting the moderate control of Asc uptake against slowdown of the cell cycle. At either confluence or subconfluence, dose-dependence for DehAsc uptake was more marked than for Asc uptake as shown by an uphill slope in a curve of doses versus [Asc]in/ex for DehAsc in contrast to a downhill slope for Asc, suggesting the moderate control for Asc uptake against fluctuation of the dose. Increasing of coexistent glucose of 5 mM to 20-40 mM, plasma concentrations in diabetic patients, declined DehAsc uptake to 46-48%, which was less moderately controlled than Asc uptake retained to 59-73%. Asc uptake did not compete with DehAsc uptake, suggesting different transporter proteins for Asc and DehAsc. Thus, Asc uptake into the aortic endothelial cells is more moderately controlled against slowdown of the cell cycle, decreasing of the extracellular concentrations or increasing of coexistent glucose than DehAsc uptake, suggesting a homeostatic advantage of Asc over DehAsc in terms of retention of intracellular Asc contents within a definite range.

Ascorbate availability and neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease in which upper and lower motoneurons progressively deteriorate and die. Neuronal damage is most evident in the lower central nervous system, and death generally occurs following central respiratory failure. Proposed and demonstrated mechanisms for amyotrophic lateral sclerosis are diverse, and include altered superoxide dismutase and neurofilament proteins, autoimmune attack, and hyperglutamatergic activity. However, they do not account for the late onset of the disease, its earlier onset in males, and the differential vulnerability of neurons located in the brainstem and spinal cord. It is proposed here that, within the context of a specific defect such as altered superoxide dismutase, age-dependent decline in ascorbate availability triggers the disease. A role for ascorbate, which is found in millimolar levels in neurons, is suggested by a number of consistencies: 1) superoxide radicals being a common substrate for superoxide dismutase and ascorbate; 2) a close association between central nervous system ascorbate levels and injury tolerance; 3) a steady decline in ascorbate plasma levels and cellular availability with age; 4) plasma ascorbate levels being lower in males; 5) an association of ascorbate release with motor activity in central nervous system regions, in vivo; 6) the coupling of brain-cell ascorbate release with glutamate uptake; 7) possible roles for ascorbate modulation of N-methyl-D-aspartate receptor activity; 9) the ability of ascorbate to prevent peroxynitrite anion formation; and 10) evidence supporting the scorbutic guinea pig as a model for amyotrophic lateral sclerosis. Emphasis is placed on the probable competition between superoxide dismutase and ascorbate within the context of a primary defect of metal-binding or metal access in high-concentration proteins such as superoxide dismutase and human heavy neurofilaments. Finally, distinct features of alpha-motoneuronal physiology suggest that cell physiological characteristics such as high metabolic activity and extensive calcium dynamics may render neurons differentially vulnerable in amyotrophic lateral sclerosis.

Evidence for the involvement of a muscarinic receptor in ascorbic acid secretion in the rat stomach

It has been demonstrated that ascorbic acid is present in human gastric juice at a very high level even in the fasting state. In this study, we confirmed such a physiological event in pylorus-ligated rats and investigated the mechanism for gastric ascorbic acid secretion using the rat in vivo perfusion method. Gastric juice from fasting rats after a 4-hr ligation contained a 6-fold higher level of ascorbic acid than that in sera, indicating the presence of its active transport system across the gastric wall. To identify an endogenous mediator, four kinds of gastric stimulants were compared for their secretory abilities. Although all four secretagogues used stimulated acid secretion to comparable levels, ascorbic acid secretion was stimulated only by carbamylcholine chloride (carbachol). Carbachol-stimulated ascorbic acid secretion was abolished by atropine pretreatment, showing that it is mediated via a muscarinic cholinergic receptor. This cholinergic stimulation was also demonstrated in a rat mutant that genetically lacks the ability to synthesize ascorbic acid in the liver, similar to humans. In addition, a potent inhibitor of the gastric proton pump, which is a final regulatory component in the mechanism of acid secretion, caused no inhibition of ascorbic acid secretion in Osteogenic Disorder Shionogi (ODS) rats. These results are the first evidence indicating that ascorbic acid, the reduced form of vitamin C, is actively and independently secreted into the gastric juice under regulation of a cholinergic receptor system.

Effect of ascorbic acid and cooling during egg incubation on hatchability, culling, mortality, and the body weights of broiler chickens

Five experiments involving 3,100 settable eggs with living embryos of commercial broiler parent stock were conducted to determine the effect of ascorbic acid (AA) and cooling during egg incubation on embryonic weight, hatchability, percentage of cull chicks, embryonic mortality, and body weights of the hatched chicks. The treatments were carried out at 15, 15, 17, 11 and 19 d of incubation for Experiments 1, 2, 3, 4, and 5, respectively. The treatments for the experiments were as follows: 1) eggs injected with 0.1 mL of sterile saline solution; 2) eggs injected with saline containing 0.5, 1, 3, and 12 mg of AA per egg; and 3) control for Experiment 1; 1) eggs injected with 3 mg of AA per egg; 2) eggs cooled at 22 C for 24 h; and 3) control for Experiments 2 and 3; 1) eggs injected with 3 mg AA per egg; and 2) control for Experiments 4 and 5. Ascorbic acid at a dose of 3 mg during egg incubation improved hatchability and body weight, and decreased number of cull chicks, whereas a dose of 12 mg decreased embryo weight and hatchability and increased the number of cull chicks and embryonic mortality. Injection of AA hatchability improved when injected on Days 11 and 15 of incubation; effects diminished if AA was injected on Day 19 of incubation. Cooling eggs at 22 C for 24 h had no significant effect on any of the variables studied when compared with controls. Comparison of AA injection at a dose of 3 mg per egg and egg cooling to 22 C for 24 h at 15 to 17 d of incubation led to the conclusion that AA had two advantages over cooling. These advantages were 1) low embryonic death and 2) greater chick weight at hatch and on Days 15 and 17 of incubation.

Ascorbate concentration in osteoblastic cells is elevated by transforming growth factor-beta

Transforming growth factor-beta modulates the proliferation, differentiation, and synthetic activity of osteoblasts, but its mechanisms of action are not fully understood. Because ascorbate also influences osteoblast differentiation and is a cofactor for collagen synthesis, the present study examined the effect of transforming growth factor-beta on the initial rate of transport and steady-state concentration of ascorbate in an osteoblastic cell line. UMR-106 rat osteosarcoma cells accumulated reduced vitamin C from culture medium. Virtually all accumulation of ascorbate was accomplished by a saturable Na(+)-dependent transport mechanism. Transforming growth factor-beta increased the initial rate of ascorbate transport, measured in either attached or suspended cells. Within 24 h, the growth factor also increased the steady-state intracellular concentration of ascorbate, without significantly changing cell volume or the DNA or protein content of cultures. These data provide evidence that Na(+)-ascorbate cotransport activity controls ascorbate concentration in osteoblasts. Furthermore, the results indicate that both the transport rate and steady-state concentration of ascorbate in these cells are regulated by transforming growth factor-beta.

6-Amino-6-deoxyascorbic acid induces apoptosis in human tumor cells

6-Amino-6-deoxyascorbic acid was found to inhibit human tumor cell growth. The antitumor effect depends on the tumor type and concentration of the acid. After cell treatment with 6-amino-6-deoxyascorbic acid, drastic morphological changes were found. Although image analysis did not show a difference in p53 and c-myc gene expression, the appearance of chromatin aggregation and DNA fragmentation points to apoptosis or programmed cell death.

Cell stage-dependent effects of ascorbic acid on cultured porcine bone cells

Pig bone cells were isolated from fetuses or young animals. In culture, they proliferated for 6 days, became confluent and began differentiating. The effects of ascorbic acid (AsA) on cell proliferation, alkaline phosphatase (ALP) activity, non-collagenous protein (NCP) and collagen synthesis, were studied by adding AsA to the medium at different times during culture. AsA affected fetal and post-natal cells similarly: ALP activity, NCP and collagen synthesis were markedly reduced in cells treated before confluence, but were strongly and dose-dependently stimulated in cells treated after confluence. AsA also stimulated cell proliferation. The cell stage-dependent action of AsA suggests that it may interfere with differentiation. The effects of AsA on ALP activity and DNA content were not coupled to its effect on collagen synthesis, raising the question of whether AsA action is matrix-mediated.