Ascorbate on cell growth and differentiation

Influence of Ascorbic Acid as a Growth and Differentiation Factor on Dental Stem Cells Used in Regenerative Endodontic Therapies

BACKGROUND

Vitamin C is one of the major extracellular nonenzymatic antioxidants involved in the biosynthesis of collagen. It promotes the growth of fibroblasts, wound healing processes, and enhances the survival and differentiation of osteoblasts. The potential effects of ascorbic acid on human dental pulp cells (DPC) and the cells of the apical papilla (CAP) used in actual regenerative endodontic procedures remain largely unknown. In this study, we investigated the possible employment of ascorbic acid in the differentiation and regenerative therapies of DPC and CAP.

METHODS

Nine extracted human wisdom teeth were selected for this study. Subpopulations of stem cells within DPC and CAP were sorted with the mesenchymal stem cell marker STRO-1, followed by treatments with different concentrations (0 mM, 0.1 mM, 0.5 mM, and 1.0 mM) of ascorbic acid (AA), RT-PCR, and Western blot analysis.

RESULTS

FACS analysis revealed the presence of cell subpopulations characterized by a strong expression of mesenchymal stem cell marker STRO-1 and dental stem cell markers CD105, CD44, CD146, CD90, and CD29. Treatment of the cells with defined amounts of AA revealed a markedly increased expression of proliferation marker Ki-67, especially in the concentration range between 0.1 mM and 0.5 mM. Further investigations demonstrated that treatment with AA led to significantly increased expression of common stem cell markers OCT4, Nanog, and Sox2. The most potent proliferative and expressional effects of AA were observed in the concentration of 0.1 mM.

CONCLUSIONS

AA might be a novel and potent growth promoter of human dental cells. Increasing the properties of human dental pulp cells and the cells of the apical papilla using AA could be a useful factor for further clinical developments of regenerative endodontic procedures.

Essential Protective Role of Catalytically Active Antibodies (Abzymes) with Redox Antioxidant Functions in Animals and Humans

During the life of aerobic organisms, the oxygen resulting from numerous reactions is converted into reactive oxygen species (ROS). Many ROS are dangerous due to their high reactivity; they are strong oxidants, and react with various cell components, leading to their damage. To protect against ROS overproduction, enzymatic and non-enzymatic systems are evolved in aerobic cells. Several known non-enzymatic antioxidants have a relatively low specific antioxidant activity. Superoxide dismutases, catalase, glutathione peroxidase, glutathione S-transferase, thioredoxin, and the peroxiredoxin families are the most important enzyme antioxidants. Artificial antibodies catalyzing redox reactions using different approaches have been created. During the past several decades, it has been shown that the blood and various biological fluids of humans and animals contain natural antibodies that catalyze different redox reactions, such as classical enzymes. This review, for the first time, summarizes data on existing non-enzymatic antioxidants, canonical enzymes, and artificial or natural antibodies (abzymes) with redox functions. Comparing abzymes with superoxide dismutase, catalase, peroxide-dependent peroxidase, and H₂O₂-independent oxidoreductase activities with the same activities as classical enzymes was carried out. The features of abzymes with the redox activities are described, including their exceptional diversity in the optimal pH values, dependency and independence on various metal ions, and the reaction rate constants for healthy donors and patients with different autoimmune diseases. The entire body of evidence indicates that abzymes with redox antioxidant activities existing in the blood for a long time compared to enzymes are an essential part of the protection system of humans and animals from oxidative stress.

Vitamin C suppresses ovarian pathophysiology in experimental polycystic ovarian syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS), also known as the Stein-Leventhal syndrome is one of the most common causes of anovulation, infertility and hyperandrogenism in women, affecting between 5-10 % of women of reproductive age (12-35 years) worldwide. Despite substantial effort to define the cause of PCOS, its pathophysiology remains poorly understood. Consequently, determining the mechanisms of PCOS and the possible treatment is the major goal of medical research in endocrine and reproductive physiology.

AIM

To investigate the mechanism of ovarian metabolic changes in dehydroepiandrosterone (DHEA)-induced polycystic ovary in Wistar rats treated with vitamin C.

METHODS

Twenty-eight immature female Wistar rats weighing (16-21 g) were randomly divided into four groups (n = 7/group): group I served as control and was given water, group II were injected with DHEA (6 mg/100 g in 0.2 ml corn oil subcutaneously to induce PCOS condition), group III received 150 mg/kg BW of Vitamin C orally, group IV were co-administered with 6 mg/kg BW DHEA in 0.2 ml of corn oil subcutaneously and 150 mg/kg BW of Vitamin C orally. All treatments lasted for 15 days. Twenty-four hours after the last administration, the rats were sacrificed by cervical dislocation. Blood samples and ovaries were collected for reproductive hormonal analysis, biochemical and histopathological analysis. The expressions of mRNA androgen receptor gene in the ovary were determined by real-time reverse transcriptase polymerase chain reaction. All data were analysed using one-way ANOVA.

RESULTS

There was a significant decrease (p < 0.05) in the antioxidant and metabolic enzyme activity in the DHEA treated group compared with the control group. DHEA co-administration with Vitamin C showed a significant decrease in Malondialdehyde, cytokines and Estrogen and a significant increase (p < 0.05) in antioxidant and metabolic enzymes compared with DHEA treated group only. The histopathological evaluation demonstrates a reduction in cystic and atretic ovaries, increased expression of Bcl₂ and E-Cadherin with a reduction in Bax expression in the group co-administered with DHEA and Vitamin C. The DHEA group showed overexpression of mRNA Androgen Receptor gene in the ovaries compared to the control group.

CONCLUSION

This study shows that Vitamin C plays a protective role against DHEA-Induced Polycystic Ovary in Wistar rats via its antioxidant and anti-apoptotic mechanisms.

Nicotine and Cotinine Inhibit Catalase and Glutathione Reductase Activity Contributing to the Impaired Osteogenesis of SCP-1 Cells Exposed to Cigarette Smoke

Cigarette smoking has been identified as a major risk factor for osteoporosis decades ago. Several studies have shown a direct relationship between cigarette smoking, decreased bone mineral density, and impaired fracture healing. However, the mechanisms behind impaired fracture healing and cigarette smoking are yet to be elucidated. Migration and osteogenesis of mesenchymal stem/stromal cells (MSCs) into the fracture site play a vital role in the process of fracture healing. In human nicotine, the most pharmacologically active and major addictive component present in tobacco gets rapidly metabolized to the more stable cotinine. This study demonstrates that physiological concentrations of both nicotine and cotinine do not affect the osteogenic differentiation of MSCs. However, cigarette smoke exposure induces oxidative stress by increasing superoxide radicals and reducing intracellular glutathione in MSCs, negatively affecting osteogenic differentiation. Although, not actively producing reactive oxygen species (ROS) nicotine and cotinine inhibit catalase and glutathione reductase activity, contributing to an accumulation of ROS by cigarette smoke exposure. Coincubation with N-acetylcysteine or L-ascorbate improves impaired osteogenesis caused by cigarette smoke exposure by both activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling and scavenging of ROS, which thus might represent therapeutic targets to support fracture healing in smokers.

Ascorbic acid promotes 3T3-L1 cells adipogenesis by attenuating ERK signaling to upregulate the collagen VI

Background

Type VI collagen is supposed to be a regulation factor in adipogenesis. This study aimed to assess the promoting effect of vitamin C (VC) on adipogenic differentiation of preadipocytes as well as its mechanism.

Methods

Five sets of different combinations of chemicals were used to inhibit synthesis of type I to VI collagens, blocking ERK1/2 phosphorylation during adipogenesis of 3T3-L1 preadipocytes. Furthermore, to explore whether collagen VI plays a critical role during adipogenesis, specific knockdown of collagen VI was performed by using RNA interference. The morphology and expression patterns of several target factors involved in adipogenesis were assessed at various time points.

Results

A reduction in ERK1/2 phosphorylation and an increase in collagen VI and adipogenic-specific factors, such as C/EBPβ, PPARγ and C/EBPα, were observed after treating adipogenic 3T3-L1 cells with AA2P, a stable derivative of VC. Inhibition of collagen synthesis by ethyl-3, 4-dihydroxybenzoate (EDHB) or by specific knockdown of collagen VI by RNAi could promote ERK1/2 phosphorylation. The ERK1/2 phosphorylation in both cases could be attenuated by AA2P treatment. In addition, the inhibition of ERK1/2 phosphorylation by U0126, a highly selective inhibitor of both MEK1 and MEK2 and a type of MAPK/ERK kinase, up-regulated the expression of collagen VI, while it down-regulated the adipogenic-specific factors.

Conclusion

AA2P could up-regulate the expression of collagen VI by attenuating ERK1/2 phosphorylation, further up-regulating adipocyte-specific factors, thus finally promoting the adipogenesis of 3T3-L1 preadipocytes.

Electronic supplementary material

The online version of this article (10.1186/s12986-017-0234-y) contains supplementary material, which is available to authorized users.

Vitamin C in Stem Cell Biology: Impact on Extracellular Matrix Homeostasis and Epigenetics

Transcription factors and signaling molecules are well-known regulators of stem cell identity and behavior; however, increasing evidence indicates that environmental cues contribute to this complex network of stimuli, acting as crucial determinants of stem cell fate. l-Ascorbic acid (vitamin C (VitC)) has gained growing interest for its multiple functions and mechanisms of action, contributing to the homeostasis of normal tissues and organs as well as to tissue regeneration. Here, we review the main functions of VitC and its effects on stem cells, focusing on its activity as cofactor of Fe⁺²/αKG dioxygenases, which regulate the epigenetic signatures, the redox status, and the extracellular matrix (ECM) composition, depending on the enzymes' subcellular localization. Acting as cofactor of collagen prolyl hydroxylases in the endoplasmic reticulum, VitC regulates ECM/collagen homeostasis and plays a key role in the differentiation of mesenchymal stem cells towards osteoblasts, chondrocytes, and tendons. In the nucleus, VitC enhances the activity of DNA and histone demethylases, improving somatic cell reprogramming and pushing embryonic stem cell towards the naive pluripotent state. The broad spectrum of actions of VitC highlights its relevance for stem cell biology in both physiology and disease.

Orthomolecular Oncology Review: Ascorbic Acid and Cancer 25 Years Later

The effect of ascorbic acid on cancer has been a subject of great controversy. This is a follow-up review of the 1979 article by Cameron, Pauling, and Leibovitz published in Cancer Research. In this updated version, the authors address general aspects of ascorbic acid and cancer that have been presented before, while reviewing, analyzing, and updating new existing literature on the subject. In addition, they present and discuss their own mechanistic hypothesis on the effect of ascorbic acid on the cancer cell. The objective of this review is to provide an updated scientific basis for the use of ascorbic acid, especially intravenously as adjuvant treatment in pharmacological nutritional oncology.

Ascorbic acid enhances adipogenesis of 3T3-L1 murine preadipocyte through differential expression of collagens

Background

Adipogenesis from preadipocytes into mature adipocyte is precisely coordinated by transcription factors such as CCAAT-enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor γ (PPARγ), cytokines, and hormones, which is accompanied by extracellular matrix remodeling. Besides anti-oxidant activity, ascorbic acid (ASC) is participating in collagen biosynthesis and increase production and processing of collagens. Moreover, several studies demonstrated that ASC enhanced differentiation from preadipocytes into mature adipocytes.

Methods

The adipogenic effect of ascorbic acid was evaluated in chemical induced 3T3-L1 by Oil Red O staining. This effect was elucidated by immunoblotting which detected the expression level of collagens and transcription factors in adipogenesis. The immunocytochemical determination of type I collagen was performed in 3T3-L1 adipocyte to show the change of extracellular matrix during adipogenesis.

Results

In this study, Oil Red O staining in 3T3-L1 preadipocytes was increased dose-dependently by addition of ASC. These ASC-treated adipocytes increased collagen processing of α1(I) and α1(V) and expressed α1(VI) and α2(VI) collagens differentially. ASC also stimulated expression of C/EBPα and PPARγ, which is preceded by collagen enhancement. In addition, inhibition of ASC activity by ethyl-3,4-dihydroxybenzoate showed reduction of lipid accumulation by removal of large lipid droplets, not by inhibition of lipid production. This observation went with loss of α1(I) deposition on adipocyte surface, increase of α1(V) and α2(VI) collagens and decrease of C/EBPs.

Conclusion

Our findings imply that various actions of ASC on adipogenesis through differential collagen expression may provide diverse applications of ASC to adipose tissue technology.

Application of bone marrow and adipose-derived mesenchymal stem cells for testing the biocompatibility of metal-based biomaterials functionalized with ascorbic acid

In this study, metal-based biomaterials were functionalized with ascorbic acid (LAA). Two types of substrates were used: austenitic steel 316L and titanium Ti6Al4V. Coatings were prepared with the sol-gel method and applied on metal surfaces using the dip-coating technique. Ascorbic acid was delivered with SiO2-coating at concentrations of 0.1 and 0.4 M. The morphology of the surfaces and coatings was determined using scanning electron microscope (SEM), whereas their elemental composition by SEM-EDX. Immobilization of ascorbic acid in the coatings was confirmed with Raman spectroscopy. The biocompatibility of the materials obtained was tested in vitro using both bone marrow- and adipose-derived mesenchymal stem cells (BMMSC and ADMSC, respectively). Proliferation rate and morphology of cells cultured in the presence of designed biomaterials were monitored after 24, 48, 120 and 168 h of propagation. The results obtained indicated that silica coatings doped with 0.4 M LAA had a positive effect on the proliferation rate of investigated cells, and in some cases on the growth pattern of culture.

Additive manufacturing of star poly(ε-caprolactone) wet-spun scaffolds for bone tissue engineering applications

Three-dimensional fibrous scaffolds made of a three-arm star poly(ε-caprolactone) were developed by employing a novel computer-aided wet-spinning apparatus to precisely control the deposition pattern of an extruded polymeric solution as a filament into a coagulation bath. Star poly(ε-caprolactone)/hydroxyapatite composite scaffolds composed of fibres with a porous morphology both in the outer surface and in the cross section were successfully produced with a layer-by-layer approach achieving good reproducibility of the internal architecture and external shape. Changes in processing parameters were used to fabricate scaffolds with different architectural parameters in terms of average pore size in the xy-axes (from 190 to 297 µm) and in the z-axis (from 54 to 126 µm) and porosity (in the range of 20%–60%). Based on the mechanical characterization, processing variations and hydroxyapatite loading have an influence on scaffold compression properties. Cell cultures, using a murine pre-osteoblast cell line, had good cell responses in terms of proliferation and osteoblastic differentiation. Thus, this technique appears to be an effective method for producing customized polymeric scaffolds for bone tissue engineering applications.

Isolation and multilineage differentiation of bone marrow mesenchymal stem cells from abattoir-derived bovine fetuses

Background

Mesenchymal stem cells (MSC) are multipotent progenitor cells localized in the stromal compartment of the bone marrow (BM). The potential of MSC for mesenchymal differentiation has been well documented in different animal models predominantly on rodents. However, information regarding bovine MSC (bMSC) is limited, and the differentiation potential of bMSC derived from fetal BM remains unknown. In the present study we sought to isolate bMSC from abattoir-derived fetal BM and to characterize the multipotent and differentiation potential under osteogenic, chondrogenic and adipogenic conditions by quantitative and qualitative analyses.

Results

Plastic-adherent bMSC isolated from fetal BM maintained a fibroblast-like morphology under monolayer culture conditions. These cells expressed high levels of MSC surface markers (CD73, CD90, and CD105) and low levels of hematopoietic surface markers (CD34 and CD45). Culture of bMSC under osteogenic conditions during a 27-day period induced up-regulation of the osteocalcin (OC) gene expression and alkaline phosphatase (ALPL) activity, and promoted mineralization of the matrix. Increasing supplementation levels of ascorbic acid to culture media enhanced osteogenic differentiation of bMSC; whereas, reduction of FBS supplementation compromised osteogenesis. bMSC increased expression of cartilage-specific genes aggrecan (ACAN), collagen 2A1 (COL2A1) and SRY (sex-determining region Y) box 9 (SOX9) at Day 21 of chondrogenic differentiation. Treatment of bMSC with adipogenic factors increased levels of fatty acid-binding protein 2 (AP2) mRNA and accumulation of lipid vacuoles after 18 days of culture. NANOG mRNA levels in differentiating bMSC were not affected during adipogenic culture; however, osteogenic and chondrogenic conditions induced higher and lower levels, respectively.

Conclusions

Our analyses revealed the potential multilineage differentiation of bMSC isolated from abattoir-derived fetal BM. NANOG mRNA pattern in differentiating bMSC varied according to differentiation culture conditions. The osteogenic differentiation of bMSC was affected by ascorbic acid and FBS concentrations in culture media. The simplicity of isolation and the differentiation potential suggest that bMSC from abattoir-derived fetal BM are appropriate candidate for investigating MSC biology and for eventual applications for regenerative therapy.

Adaptive alterations in the fatty acids composition under induced oxidative stress in heavy metal-tolerant filamentous fungus Paecilomyces marquandii cultured in ascorbic acid presence

The ability of the heavy metal-tolerant fungus Paecilomyces marquandii to modulate whole cells fatty acid composition and saturation in response to IC50 of Cd, Pb, Zn, Ni, and Cu was studied. Cadmium and nickel caused the most significant growth reduction. In the mycelia cultured with all tested metals, with the exception of nickel, a rise in the fatty acid unsaturation was noted. The fungus exposure to Pb, Cu, and Ni led to significantly higher lipid peroxidation. P. marquandii incubated in the presence of the tested metals responded with an increase in the level of linoleic acid and escalation of electrolyte leakage. The highest efflux of electrolytes was caused by lead. In these conditions, the fungus was able to bind up to 100 mg g(-1) of lead, whereas the content of the other metals in the mycelium was significantly lower and reached from 3.18 mg g(-1) (Cu) to 15.21 mg g(-1) (Zn). Additionally, it was shown that ascorbic acid at the concentration of 1 mM protected fungal growth and prevented the changes in the fatty acid composition and saturation but did not alleviate lipid peroxidation or affect the increased permeability of membranes after lead exposure. Pro-oxidant properties of ascorbic acid in the copper-stressed cells manifested strong growth inhibition and enhanced metal accumulation as a result of membrane damage. Toxic metals action caused cellular modulations, which might contributed to P. marquandii tolerance to the studied metals. Moreover, these changes can enhance metal removal from contaminated environment.

Signal transduction mechanism for potentiation by α1- and β2-adrenoceptor agonists of L-ascorbic acid-induced DNA synthesis and proliferation in primary cultures of adult rat hepatocytes

We investigated the effects of α- and β-adrenoceptor agonists on L-ascorbic acid-induced hepatocyte DNA synthesis and proliferation in primary cultures of adult rat hepatocytes. The results showed that phenylephrine (10(-6) M) and metaproterenol (10(-6) M) alone did not induce hepatocyte DNA synthesis and proliferation. However, when combined with L-ascorbic acid (10(-6) M), these adrenoceptor agonists potentiated the hepatocyte DNA synthesis and proliferation induced by L-ascorbic acid. Then intracellular signal transduction mechanisms for the effects of phenylephrine and metaproterenol on L-ascorbic acid-induced hepatocyte mitogenesis were examined. Western blot analysis showed that phenylephrine and metaproterenol did not potentiate L-ascorbic acid-induced insulin-like growth factor I receptor tyrosine kinase phosphorylation. In contrast, they both significantly potentiated L-ascorbic acid-induced extracellular-signal regulated kinase-2 (ERK2) phosphorylation within 5 min. Moreover, cell-permeable second messenger analogs phorbol ester (10(-7) M) and 8-bromo cAMP (10(-7) M) mimicked the effects of phenylephrine and metaproterenol on L-ascorbic acid-induced ERK2 phosphorylation. The effects of these adrenoceptor agents were specifically antagonized by GF109203X and H-89, respectively. These results indicate that activation of ERK2 via protein kinas C and protein kinase A represents a mechanism for potentiation of L-ascorbic acid-induced hepatocyte DNA synthesis and proliferation in primary cultures of adult rat hepatocytes.

An in vitro study of osteoblast vitality influenced by the vitamins C and E

Vitamin C and vitamin E are known as important cellular antioxidants and are involved in several other non-antioxidant processes. Generally vitamin C and vitamin E are not synthesized by humans and therefore have to be applied by nutrition. The absence or deficiency of the vitamins can lead to several dysfunctions and even diseases (e.g. scurvy). The main interest in this study is that vitamin C and E are known to influence bone formation, e.g. vitamin C plays the key role in the synthesis of collagen, the major component of the extracellular bone matrix.

In the present study we evaluate the effect of ascorbic acid (vitamin C) and α-tocopherol (vitamin E) on the proliferation and differentiation of primary bovine osteoblasts in vitro. Starting from standard growth medium we minimized the foetal calf serum to reduce their stimulatory effect on proliferation.

An improved growth and an increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin was observed while increasing the ascorbic acid concentration up to 200 μg/ml. Furthermore the effects of α-tocopherol on cell growth and cell differentiation were examined, whereby neither improved growth nor increased synthesis of the extracellular matrix proteins collagen type I, osteonectin and osteocalcin were detected.

Further investigations are necessary to target at better supportive effect of vitamins on bone regeneration, and healing.

Effect of serum and insulin modulation on the organization and morphology of matrix synthesized by bovine corneal stromal cells

The in vitro production of highly organized collagen fibrils by corneal keratocytes in a three-dimensional scaffold-free culture system presents a unique opportunity for the direct observation of organized matrix formation. The objective of this investigation was to develop such a culture system in a glass substrate (for optical accessibility) and to directly examine the effect of reducing serum and/or increasing insulin on the stratification and secretion of aligned matrix by fourth- to fifth-passage bovine corneal stromal keratocytes. Medium concentrations of 0%, 1%, or 10% fetal bovine serum and 0% or 1% insulin-transferrin-selenium were investigated. High-resolution differential interference contrast microscopy, quick-freeze/deep-etch, and conventional transmission electron microscopy were used to monitor the evolution, morphology, and ultrastructure of the cell-matrix constructs. In a medium containing 1% each of serum and insulin-transferrin-selenium, stromal cells stratified and secreted abundant and locally aligned matrix, generating the thickest cell-matrix constructs (allowing handling with forceps). The results of this study have the potential to significantly advance the field of developmental functional engineering of load-bearing tissues by (i) elucidating cues that modulate in vitro cell secretion of organized matrix and (ii) establishing an optically accessible cell culture system for investigating the mechanism of cell secretion of aligned collagen fibrils.

ReviewPart of the Series: From Dietary Antioxidants to Regulators in Cellular Signalling and Gene ExpressionReview: When is an antioxidant not an antioxidant? A review of novel actions and reactions of vitamin C

Vitamin C (or ascorbic acid) is regarded as the most important water-soluble antioxidant in human plasma and mammalian cells which have mechanisms to recycle and accumulate it against a concentration gradient, suggesting that the vitamin might also have important intracellular functions. In this review we summarize evidence from human trials that have attempted an association between vitamin C supplementation and an effect on biomarkers of oxidative DNA damage. Most studies reviewed herein showed either a vitamin C-mediated reduction in oxidative DNA damage or a null effect, whereas only a few studies showed an increase in specific base lesions. We also address the possible beneficial effects of vitamin C supplementation for the prevention of cancer and cardiovascular disease. Finally, we discuss the contribution of cell culture studies to our understanding of the mode of action of vitamin C and we review recent evidence that vitamin C is able to modulate gene expression and cellular function, with a particular interest in cell differentiation.

Effect of ascorbic acid on bone marrow-derived mesenchymal stem cell proliferation and differentiation

Mesenchymal stem cells (MSCs) derived from bone marrow are an important tool in tissue engineering and cell-based therapies because of their multipotent capacity. Majority of studies on MSCs have investigated the roles of growth factors, cytokines, and hormones. Antioxidants such as ascorbic acid can be used to expand MSCs while preserving their differentiation ability. Moreover, ascorbic acid can also stimulate MSC proliferation without reciprocal loss of phenotype and differentiation potency. In this study, we evaluated the effects of ascorbic acid on the proliferation, differentiation, extracellular matrix (ECM) secretion of MSCs. The MSCs were cultured in media containing various concentrations (0-500 microM) of L-ascorbate-2-phosphate (Asc-2-P) for 2 weeks, following which they were differentiated into adipocytes and osteoblasts. Ascorbic acid stimulated ECM secretion (collagen and glycosaminoglycan) and cell proliferation. Moreover, the phenotypes of the experimental groups as well as the differentiation potential of MSCs remained unchanged. The apparent absence of decreased cell density or morphologic change is consistent with the toxicity observed with 5-250 microM concentrations of Asc-2-P. The results demonstrate that MSC proliferation or differentiation depends on ascorbic acid concentration.

Protective role of ascorbic acid isolated from Cissus quadrangularis on NSAID induced toxicity through immunomodulating response and growth factors expression

The present study investigate the effect of ascorbic acid, the major bioactive component isolated from Cissus quadrangularis extract (CAA) on inflammatory cytokines and growth factors in non-steroidal anti-inflammatory drug (NSAID) induced gastric ulcer. Analysis of serum cytokine profile using enzymelinked immunosorbent assay (ELISA) showed a drastic increase in interleukin (IL)-1beta, IL-6, tumour necrosis factor-alpha (TNF)-alpha, interferon-gamma (IFN-gamma) and decrease in IL-10, Il-4 and prostaglandin E2 (PGE2) levels in NSAID (aspirin) treated rats. The reduction of growth factors such as transforming growth factor-alpha (TGF)-alpha and vascular endothelial cell growth factor (VEGF) by aspirin was determined by immunohistochemistry method. Administration of CAA produced significant protection against aspirin induced gastric toxicity by showing significant increase in PGE2, TGF-alpha, VEGF expression and accompanied by a significant inhibition of nitric oxide and regulating the levels of cytokines in rats. These findings suggest that CAA prevents gastric ulcer formation due to its immunomodulatory effect, antioxidant activity along with the ability to modulate PG synthesis and up-regulation of the growth factors.

Regulatory role of vitamins E and C on extracellular matrix components of the vascular system

The protective effect of vitamins E (alpha-tocopherol) and C (L-ascorbic acid) in the prevention of cardiovascular disease (CVD) has been shown in a number of situations but a secure correlation is not universally accepted. Under certain conditions, both, L-ascorbic acid and alpha-tocopherol can exhibit antioxidant properties and thus may reduce the formation of oxidized small molecules, proteins and lipids, which are a possible cause of cellular de-regulation. However, non-antioxidant effects have also been suggested to play a role in the prevention of atherosclerosis. Vitamin E and C can modulate signal transduction and gene expression and thus affect many cellular reactions such as the proliferation of smooth muscle cells, the expression of cell adhesion and extracellular matrix molecules, the production of O(2)(-) by NADPH-oxidase, the aggregation of platelets and the inflammatory response. Vitamins E and C may modulate the extracellular matrix environment by affecting VSMC differentiation and the expression of connective tissue proteins involved in vascular remodeling as well as the maintenance of vascular wall integrity. This review summarizes individually the molecular activities of vitamins E and C on the cells within the connective tissue of the vasculature, which are centrally involved in the maintenance of an intact vascular wall as well as in the repair of atherosclerotic lesions during disease development.

Dexamethasone's enhancement of osteoblastic markers in human periodontal ligament cells is associated with inhibition of collagenase expression

Although dexamethasone (Dex) substantially enhances the osteoblastic phenotype in osteogenic cells, including human periodontal ligament (PDL) cells, the basis for this response remains poorly understood. Since the accretion of a collagenous matrix is important for an osteoblastic response and dexamethasone is known to decrease collagenase expression, we examined whether osteoblastic differentiation mediated by Dex is linked to a decrease in collagenase expression in PDL cells. Early passage human PDL cells were exposed to Dex, or ascorbic acid (AA) or beta-glycerophosphate (betaGP) alone, or in various combinations in serum-free media for 3 or 5 days. Cells exposed to Dex alone or any combinations of treatments that included Dex demonstrated increased core binding factor alpha 1 (Cbfa1), alkaline phosphatase (AP), osteonectin (ON), osteopontin (OP), bone sialoprotein (BSP) and collagen I (alpha1) expression when compared to control cells or those exposed to AA or betaGP. The induction of these osteoblastic markers was accompanied by a decrease in collagenase-1 expression. Collagenase activity showed a statistically significant strong negative relationship to Cbfa1 (Pearson's r=-0.97), AP (r=-0.87), OP (r=-0.95) and BSP (r=-0.82) in 5-day cultures, and moderately strong relationship to ON (r=-0.74) from 3 days culture. Dex also produced a dose-dependent increase in AP that was paralleled by a decrease in collagenase activity (r=-0.98). Addition of collagenase inhibitors increased AP expression while concomitantly suppressing collagenase activity. Conversely, addition of exogenous collagenase decreased the AP phenotype of the cells, which was more marked in the absence then in the presence of Dex. The findings indicate that Dex enhances specific markers of osteoblastic differentiation in PDL cells by decreasing collagenase expression, and suggest that endogenous collagenase may regulate osteoblastic differentiation of these cells.

Collagen, type V, alpha1 (COL5A1) is regulated by TGF-beta in osteoblasts

Bone matrix contains high concentrations of growth factors that are known to play important regulatory roles during osteogenesis, particularly transforming growth factor-beta (TGF-beta). Divergent effects of TGF-beta on bone formation have been reported both in vitro and in vivo depending upon experimental conditions, cells employed and their stage of maturation. In this study, we have used a clonal osteoblastic cell line MC3T3-E1, derived from newborn mouse calvaria, as an in vitro model of bone development. These cells undergo an ordered, time-dependent developmental sequence characterized by three stages (proliferation, differentiation and mineralization), over a 30-35-day period. In this study, cDNA microarray technology was used to study the expression profile of 8470 genes, in the presence of TGF-beta1 during osteoblast development. Microarray analysis revealed 120 cDNAs to be differentially expressed in MC3T3-E1 osteoblasts that had been treated with TGF-beta1. From the 120 differentially expressed genes, we selected Collagen, type V, alpha1 (COL5A1) {differential expression=+4.9} for further studies since it represents a previously uncharacterized component of the bone matrix. Using Northern blotting, we found that, when MC3T3-E1 cells were treated with TGF-beta1, COL5A1 was up-regulated during the proliferation and differentiation phases of osteogenesis. Furthermore, by a combination of RNA in situ hybridization and Northern blotting, we found COL5A1 mRNA to be expressed in the calvaria and developing bone of the E17.5 mouse embryos. Lastly, significant COL5A1 protein expression was observed by immunohistochemistry in the developing bone of the E17.5 mouse embryos. In conclusion, by the use of in vitro and in vivo approaches, we have discovered that the COL5A1 gene is a target of TGF-beta during osteogenesis.

Inhibition of COX activity by NSAIDs or ascorbate increases cAMP levels and enhances differentiation in 1alpha,25-dihydroxyvitamin D3-induced HL-60 cells

Arachidonic acid metabolism is modulated during differentiation induced by 1alpha,25(OH)(2)D(3) in HL-60 cells. Antioxidants that affect arachidonic acid metabolism enhance this differentiation program. Ascorbate also enhances differentiation in 1alpha,25(OH)(2)D(3)-induced cells depending on the induction of cAMP. The aim of this work was to study if this cAMP rise depends on modulation of arachidonic acid metabolism by ascorbate. Cyclooxygenase inhibitors, indomethacin and aspirin, increased cAMP levels and also enhanced 1alpha,25(OH)(2)D(3)-induced differentiation in HL-60 cells. Ascorbate did not affect the release of arachidonic acid-derived metabolites but decreased the levels of TXB(2) and PGE(2), suggesting the inhibition of cyclooxygenase. On the other hand, free arachidonic acid increased both cAMP levels and differentiation in the absence or presence of 1alpha,25(OH)(2)D(3). Neither cyclooxygenase inhibitors nor ascorbate modified AA effect. Then, inhibition of cyclooxygenase activity by ascorbate could accumulate free arachidonic acid or other metabolites that increase cAMP levels and enhance differentiation in 1alpha,25(OH)(2)D(3)-induced HL-60 cells.

Ascorbic acid induces collagenase-1 in human periodontal ligament cells but not in MC3T3-E1 osteoblast-like cells: potential association between collagenase expression and changes in alkaline phosphatase phenotype

Ascorbic acid (AA) enhances osteoblastic differentiation by increasing collagen accumulation, which in turn, results in increased alkaline phosphatase (AP) expression in some osteogenic cells. However, in other cells, including human periodontal ligament (PDL) cells, additional osteoinductive agents are required for this response. To understand the potential basis for the maintenance of the AP phenotype of PDL cells exposed to AA, we examined the modulation of the tissue-degrading matrix metalloproteinases (MMPs) and their inhibitors by AA in short-term cell cultures. Early passage PDL cells in serum-free medium were exposed to AA for 5 days. The samples were analyzed for MMPs and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), AP, collagen I(alpha1), and osteocalcin. We found that AA dose-dependently increased the expression of collagenase-1, and minimally TIMP-1, but not stromelysin-1 or TIMP-2. Additionally, AA caused substantial increases in levels of type I collagen. AA was unable to increase AP activity or osteocalcin messenger RNA in PDL cells. However, the cells retained the ability to show a significantly greater AP expression in high- versus low-density cultures, and increased osteocalcin as well as AP levels when cultured in the presence of dexamethasone. Moreover, in cells exposed to dexamethasone, increases in AP and osteocalcin were accompanied by a repression of collagenase-1 expression. In contrast to PDL cells, AA did not induce collagenase but produced a significant increase in AP expression in MC3T3-E1 cells. These findings provide the first evidence that AA, by modulating both collagen and collagenase-1 expression in PDL cells, most likely contributes to a net matrix remodeling response in these cells. Furthermore, the relationship between changes in collagenase expression and alterations in AP activity in PDL and MC3T3-E1 cells suggests a potential role for collagenase in modulating the AP phenotype of cells with osteoblastic potential.

The role of ascorbic acid role in the differentiation of sclerotia in Sclerotinia minor

Sclerotinia minor in culture produces ascorbic acid in levels dependent on oxidative growth conditions and stage of development. During differentiation reduced/oxidized ascorbate ratio decreased by 12 and 6 fold at high and low oxidative stress, respectively. Exogenous ascorbate caused a concentration-dependent decrease of oxidative stress (lipid peroxidation), inhibition of sclerotial differentiation (up to 100%) and delay of differentiatlon (up to 10 days). Ascorbic acid may be produced to help the fungus reduce oxidative stress during growth. The data of this study support our theory proposing that oxidative stress is the inducing factor of sclerotial differentiation in fungi.

L-Ascorbic acid is accumulated in source leaf phloem and transported to sink tissues in plants

L-Ascorbic acid (AsA) was found to be loaded into phloem of source leaves and transported to sink tissues. When L-[(14)C]AsA was applied to leaves of intact plants of three different species, autoradiographs and HPLC analysis demonstrated that AsA was accumulated into phloem and transported to root tips, shoots, and floral organs, but not to mature leaves. AsA was also directly detected in Arabidopsis sieve tube sap collected from an English green aphid (Sitobion avenae) stylet. Feeding a single leaf of intact Arabidopsis or Medicago sativa with 10 or 20 mM L-galactono-1,4-lactone (GAL-L), the immediate precursor of AsA, lead to a 7- to 8-fold increase in AsA in the treated leaf and a 2- to 3-fold increase of AsA in untreated sink tissues of the same plant. The amount of AsA produced in treated leaves and accumulated in sink tissues was proportional to the amount of GAL-L applied. Studies of the ability of organs to produce AsA from GAL-L showed mature leaves have a 3- to 10-fold higher biosynthetic capacity and much lower AsA turnover rate than sink tissues. The results indicate AsA transporters reside in the phloem, and that AsA translocation is likely required to meet AsA demands of rapidly growing non-photosynthetic tissues. This study also demonstrates that source leaf AsA biosynthesis is limited by substrate availability rather than biosynthetic capacity, and sink AsA levels may be limited to some extent by source production. Phloem translocation of AsA may be one factor regulating sink development because AsA is critical to cell division/growth.

Collagen IV promotes repair of renal cell physiological functions after toxicant injury

Collagen IV is found in the renal proximal tubular cell (RPTC) basement membrane and is a mediator of renal development and function. Pharmacological concentrations of L-ascorbic acid phosphate (AscP) promote the repair of physiological functions in RPTC sublethally injured by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). We hypothesized that AscP promotes RPTC repair by stimulating collagen IV synthesis and/or deposition. RPTC exhibited increased synthesis but decreased deposition of collagen IV after DCVC exposure. In contrast, RPTC cultured in pharmacological concentrations of AscP maintained collagen IV deposition. The activity of prolyl hydroxylase was decreased in RPTC after DCVC injury, an effect that was partially attenuated in injured RPTC cultured in pharmacological concentrations of AscP. The addition of exogenous collagen IV to the culture media of DCVC-injured RPTC promoted the repair of mitochondrial function and Na(+)-K(+)-ATPase activity. However, neither collagen I, laminin, nor fibronectin promoted cell repair. These data demonstrate an association between AscP-stimulated deposition of collagen IV and exogenous collagen IV and repair of physiological functions, suggesting that collagen IV plays a specific role in RPTC repair after sublethal injury.

Cellular redox state and activating protein-1 are involved in ascorbate effect on calcitriol-induced differentiation

Ascorbate has been related to the differentiation of several mesenchymal cells including haematopoietic cells. We have previously demonstrated that ascorbate enhances the activity of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) on monocytic differentiation of HL-60 cells. Here, we show that ascorbate-mediated modification of cellular redox state and AP-1 (activating protein-1) DNA binding during early phases are related to the enhancing effect of ascorbate on differentiation. Ascorbate, but not its fully oxidized form, dehydroascorbate, or an ascorbate analogue with a low rate of oxidation, ascorbate-2-phosphate, enhanced the differentiation induced by 1 alpha,25(OH)2D3, modified cytosolic reactive oxygen species levels and mitochondrial redox potential (delta psi m), and modulated AP-1 DNA binding in HL-60 cells. Ascorbate itself increased AP-1 binding to DNA in noninduced cells, whereas it inhibited AP-1 binding in 1 alpha,25(OH)2D3-induced cells. However, ascorbate increased the mRNA levels of c-jun, junB, and c-fos in 1 alpha,25(OH)2D3-induced cells. Taken together, these results suggest that the enhancing effect of ascorbate on HL-60 differentiation induced by 1 alpha, 25(OH)2D3 is related to its effect on the cellular redox state and the modulation of AP-1 activity.

Coordinate expression of novel genes during osteoblast differentiation

To achieve new insights into the coordinate regulation of gene expression during osteoblast differentiation we utilized an approach involving global analysis of gene expression to obtain the identities of messenger RNAs (mRNAs) expressed using an established in vitro model of bone development. MC3T3-E1 osteoblast-like cells were induced to differentiate by the addition of beta-glycerophosphate (beta-GP) and ascorbic acid. RNA samples derived from induced and uninduced control MC3T3-E1 cells were used to prepare complementary DNA (cDNA) for serial analysis of gene expression (SAGE). A preliminary SAGE database was produced and used to prepare a hybridization array to further facilitate the characterization of changes in the expression levels of 92 of the SAGE-mRNA assignments after induction of osteoblast differentiation, specifically after 6 days and 14 days of ascorbate treatment. SAGE-array hybridization analysis revealed coordinate induction of a number of mRNAs including Rab24, calponin, and calcyclin. Levels of MSY-1, SH3P2, fibronectin, alpha-collagen, procollagen, and LAMPI mRNAs, present at day 6 postinduction, were markedly reduced by day 14 postinduction. A number of unanticipated and potentially important developmental genes were identified including the transforming growth factor beta (TGF-beta) superfamily member Lefty-1. Lefty-1 transcript and translation product were found to be induced during the course of MC3T3-E1 cell differentiation. We present evidence, using transient transfection and antibody neutralization approaches, that Lefty-1 modulates the induction of alkaline phosphatase (ALP) after treatment of MC3T3-E1 cells with ascorbate and beta-GP. These data should provide useful new information for future analysis of transcriptional events in osteoblast differentiation and mineralization.

Plasma membrane redox system in the control of stress-induced apoptosis

The plasma membrane of animal cells contains an electron transport system based on coenzyme Q (CoQ) reductases. Cytochrome b5 reductase is NADH-specific and reduces CoQ through a one-electron reaction mechanism. DT-diaphorase also reduces CoQ, although through a two-electron reaction mechanism using both NADH and NADPH, which may be particularly important under oxidative stress conditions. Because reduced CoQ protects membranes against peroxidations, and also maintains the reduced forms of exogenous antioxidants such as alpha-tocopherol and ascorbate, this molecule can be considered a central component of the plasma membrane antioxidant system. Stress-induced apoptosis is mediated by the activation of plasma membrane-bound neutral sphingomyelinase, which releases ceramide to the cytosol. Ceramide-dependent caspase activation is part of the apoptosis pathway. The reduced components of the plasma membrane antioxidant system, mainly CoQ, prevent both lipid peroxidation and sphingomyelinase activation. This results in the prevention of ceramide accumulation and caspase 3 activation and, as consequence, apoptosis is inhibited. We propose the hypothesis that antioxidant protective function of the plasma membrane redox system can be enough to protect cells against the externally induced mild oxidative stress. If this system is overwhelmed, intracellular mechanisms of protection are required to avoid activation of the apoptosis pathway.

The redox state of the ascorbate-dehydroascorbate pair as a specific sensor of cell division in tobacco BY-2 cells

The effects of ascorbate (ASC) and dehydroascorbate (DHA) on cell proliferation were examined in the tobacco Bright Yellow 2 (TBY-2) cell line to test the hypothesis that the ASC-DHA pair is a specific regulator of cell division. The hypothesis was tested by measuring the levels of ASC and DHA or another general redox pair, glutathione (GSH) and glutathione disulfide (GSSG), during the exponential-growth phase of TBY-2 cells. A peak in ASC, but not GSH, levels coincided with a peak in the mitotic index. Moreover, when the cells were enriched with ascorbate, a stimulation of cell division occurred whereas, when the cells were enriched with DHA, the mitotic index was reduced. In contrast, glutathione did not affect the mitotic-index peak during this exponential-growth phase. The data are consistent in showing that the ASC-DHA pair acts as a specific redox sensor which is part of the mechanism that regulates cell cycle progression in this cell line.

17beta-estradiol inhibition of ascorbic acid accumulation in human intestinal Caco-2 cells

We investigated the effect of estrogen on the accumulation of ascorbic acid by human intestinal Caco-2 cells. 17beta-estradiol, synthetic estrogen diethylstilbestrol, and partial agonist tamoxifen were found to inhibit ascorbic acid accumulation in a dose-dependent fashion. The inhibitory effect of estrogens can be observed at as short as 5 min of incubation. An additive effect was observed when they were used in combination. Similar to dietary flavonoids, inhibition was also observed in two other intestinal cell lines, HT-29 and IEC-6. These chemicals affected both Na+ -dependent and Na+ -independent(K+ substituting Na+) accumulation of ascorbic acid and did not affect the efflux of accumulated ascorbic acid. Kinetic analysis of diethylstilbestrol showed a non-competitive inhibition with an apparent Ki of 23 microM. The hormone-ascorbic acid interaction in the intestinal cell could help to explain the known reduction in blood ascorbic acid level among oral contraceptive users and female guinea pigs given contraceptive hormones.

Determination of the ascorbate free radical concentration in mixtures of ascorbate and dehydroascorbate

Ascorbate free radical is considered to be a substrate for a plasma membrane redox system of eukaryotic cells, and might be involved in stimulation of cell proliferation. It can be generated by transition metal-dependent oxidation of ascorbate or by an equilibrium reaction of ascorbate with dehydroascorbic acid. Using ESR spectroscopic measurements at pH 7.4, we show that when ascorbate and dehydroascorbic acid are mixed at concentrations lower than 2.5 mM, the ascorbate free radical concentration was determined by metal-dependent reactions and not by the equilibrium reaction. We conclude that, for studies under physiological conditions, the ascorbate free radical concentration cannot simply be calculated from the equilibrium constant and the ascorbate and dehydroascorbic acid concentration, but has to be determined experimentally.

Differential expression of superoxide dismutase isoforms in neuronal and glial compartments in the course of excitotoxically mediated neurodegeneration: relation to oxidative and nitrergic stress

To examine the cellular distribution of radical scavenging enzymes in glia, in comparison to that in neurons and their behaviour during excitotoxically induced neurodegenerative processes, protein levels and the cellular localization of cytosolic and mitochondrial superoxide dismutase (Cu/Zn- and Mn-SOD) were investigated in the rat brain undergoing quinolinic acid (Quin)-induced neurodegeneration. Evidence for the specificity of the applied antibodies to detect immunocytochemically these SOD isoforms was obtained from electron microscopy and Western blotting. In control striatum Mn-SOD was clearly confined to neurons, whereas Cu/Zn-SOD was found, rather delicately, only in astrocytes. Microglia failed to stain with antibodies to both SOD isoforms. Quin application resulted in an initial formation of oxygen and nitrogen radicals as determined by the decline in the ratio of ascorbic to dehydroascorbic acid and by increased levels of nitrated proteins, an indicator for elevated peroxynitrite formation. Morphologically, massive neuronal damage was seen in parallel. Astroglia remained intact but showed initially decreased glutamine synthetase activities. The levels of Mn-SOD protein increased 2-fold 24 h after Quin injection (Western blotting) and declined only slowly over the time period considered (10 days). Cu/Zn-SOD levels increased only 1.3-fold. Immunocytochemical studies revealed that the increase in Mn-SOD is confined to neurons, whereas that of Cu/Zn-SOD was observed only in astroglial cells. Quiescent microglial cells were, as a rule, free of immunocytochemically detectable SOD, whereas in activated microglia a few Mn-SOD immunolabeled mitochondria occurred. Our results suggest a differential protective response in the Quin lesioned striatum in that Mn-SOD is upregulated in neurons and Cu/Zn-SOD in astroglia. Both SOD-isoforms are assumed to be induced to prevent oxidative and nitric oxide/peroxynitrite-mediated damage. In the border zone of the lesion core this strategy may contribute to resist the noxious stimulus.

Redox regulation of cAMP levels by ascorbate in 1,25-dihydroxy- vitamin D3-induced differentiation of HL-60 cells

1alpha,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] induces differentiation to monocyte-macrophage lineage of several leukaemic cell lines such as HL-60, U937, M1 and Mono Mac 6. Ascorbate also modulates growth and differentiation of different animal cells in culture. We have previously reported the stimulating effect of ascorbate on 1, 25-(OH)2D3-induced HL-60 cell differentiation. We show here that 1, 25-(OH)2D3 induces a transient increase in cAMP levels in these cells, and ascorbate significantly increases these cAMP levels. Ascorbate alone does not have any effect. Other cAMP-increasing agents such as isobutylmethylxanthine, forskolin and prostaglandin E2 maintain high levels of cAMP at 48 h of incubation and also enhance differentiation along the monocytic pathway induced by 1, 25-(OH)2D3, as revealed by specific differentiation markers, demonstrating the importance of cAMP in the differentiation process. It is also shown that the presence of ascorbate and its free radical (AFR) during 1,25-(OH)2D3-induced differentiation significantly decreases cytoplasmic NADH levels compared with those induced by 1,25-(OH)2D3 in HL-60 cells. The results indicate that NADH is an inhibitor of adenylate cyclase in these cells. AFR is an electron acceptor of the trans-plasma-membrane electron-transport system, and NADH is the electron donor. Through this system, ascorbate and AFR keep levels of NADH low, thereby decreasing its inhibitory effect on adenylate cyclase activity and so increasing cAMP synthesis. We also demonstrate that other ascorbate derivatives, such as ascorbate 2-phosphate and dehydroascorbate, both of which are unable to produce AFR, do not alter intracellular NADH levels during 1, 25-(OH)2D3-induced differentiation. Also, ascorbate and AFR increase specific differentiation markers (CD14 and NitroBlue Tetrazolium reduction) but neither ascorbate 2-phosphate nor dehydroascorbate show this enhancing activity. In summary, we propose that the effect of ascorbate on 1,25-(OH)2D3-induced differentiation of HL-60 cells can be explained by redox regulation of the cAMP pathway.

Modulation of chondrocyte proliferation by ascorbic acid and BMP-2

Chondrocytes show an unusual ability to thrive under serum-free conditions as long as insulin, thyroxine, and cysteine are present. Studies with sternal chondrocytes from chick embryos indicate that thymidine incorporation in chondrocytes cultured under serum-free conditions is 30-50% of that seen with fetal bovine serum (FBS). In contrast, skin fibroblast proliferation in serum-free culture is <5% of that seen with serum. Addition of 30-50 microM ascorbic acid to serum-free medium stimulates chondrocyte proliferation 4-5x, resulting in levels of thymidine incorporation higher than that seen with 10% serum. Three to five hours of ascorbate exposure is sufficient to stimulate proliferation, with maximal stimulation seen after 12-15 h. Bromo-deoxyuridine (BrdU) labelling indicated that approximately 25% of chondrocytes transit S phase during a 4-h period (16-20 h after ascorbate). Once maximal stimulation is reached, the proliferation rate remains fairly constant over at least 40 h. Ascorbate therefore increases the steady-state level of chondrocytes in the cycle. Because the stimulation of chondrocyte proliferation was greater than the net increase in cell numbers, we examined the level of apoptosis. Nuclear morphology, terminal uridine nucleotide end-labelling (TUNEL) assay, and 7-AAD/Hoechst dye FACS analyses all indicated that approximately 15% of the ascorbate-treated chondrocytes were undergoing apoptosis, while only 5% of the control chondrocytes were apoptotic. When prehypertrophic chondrocytes from the cephalic region of embryonic sternae were stimulated to undergo hypertrophy with rhBMP-2 + ascorbate, levels of apoptosis were similar to that seen with ascorbate alone. In contrast, treatment of caudal chondrocytes with BMP plus ascorbate does not induce hypertrophy, and the proportion of apoptotic cells was less than that seen with ascorbate alone. These results imply that in chondrocytes the transition to hypertrophy is associated with a decreased number of proliferating cells and a relatively high level of apoptosis.

The Fanconi anemia complementation group A protein contains a peroxidase domain

Computational analysis of the Fanconi anemia (FA) complementation group A protein suggests that it contains a peroxidase domain. FA proteins may be part of a general mechanism that protects cells from oxidative damage.

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.

Ascorbate and alpha-tocopherol prevent apoptosis induced by serum removal independent of Bcl-2

Cells require serum to maintain growth in vitro. Serum provides growth and survival factors and its removal causes an oxidative stress that induces peroxidations in membrane lipids and development of programmed cell death (apoptosis) in some cells. Cells containing Bcl-2 are partially protected against both lipid peroxidation and apoptosis and some cell lines, such as Daudi, which lack this protein, are very sensitive to serum removal. Thus, cells are grown for 48 h in the absence of fetal calf serum and apoptotic cells are scored. HL-60 cells containing a moderate amount of Bcl-2 show 30% apoptosis, while 55% cells are apoptotic of the Bcl-2-negative Daudi cell population. Apoptosis is reduced to 15% in the transiently transfected Daudi/Bcl-2 cells. Ascorbate (Asc) and alpha-tocopherol (alphaTOH) can prevent lipid peroxidation and apoptosis caused by serum withdrawal, when added to culture media, even in the absence of Bcl-2. Also, these two antioxidants increase survival of cells grown in the absence of serum independent of their Bcl-2 content. Immunostaining and quantification of Bcl-2 show that HL-60 cell line is a heterogeneous population relative to the expression of Bcl-2. When these cells are grown in the presence of serum, cells lacking Bcl-2 survive, but no Bcl-2-negative cells survive without serum. Part of this population of Bcl-2-negative cells is rescued by Asc and alphaTOH. Antioxidants effective at the plasma membrane such as Asc and alphaTOH can protect cells from oxidative damage and prevent apoptosis independent of Bcl-2 content.

Renal cell regeneration following oxidant exposure: inhibition by TGF-beta1 and stimulation by ascorbic acid

Renal proximal tubular cell (RPTC) monolayers exposed to the model oxidant tert-butylhydroperoxide (TBHP; 0.8 mM) for 1.5 hrs were 33 and 31% confluent after 1 and 4 days, respectively. Control monolayers remained 100% confluent throughout the experiment. Exogenous TGF-beta1 promoted monolayer deterioration by potentiating cellular death and suppressed EGF-stimulated regeneration of the RPTC monolayer. Net TGF-beta1 production in injured RPTC increased 1.7- and 3.2-fold on Days 1 and 2, respectively, and returned to control levels 4 days following TBHP treatment. An anti-TGF-beta antibody increased monolayer confluence to 50% and DNA content 1.3-fold 4 days after TBHP exposure. L-Ascorbic acid 2-phosphate (AscP) present only during the recovery period increased monolayer confluence to 67% but had no effect on RPTC proliferation, suggesting that AscP promoted monolayer regeneration by cellular migration/spreading. AscP present continuously had no effect on the extent of TBHP-induced injury but promoted regeneration of RPTC with increased monolayer confluence (1.8-fold) and DNA content (1.8-fold) and decreased cellular lysis by 52% 4 days following TBHP exposure. The results demonstrate that TBHP-induced injury increases net TGF-beta1 production in RPTC and that autocrine TGF-beta1 inhibits regeneration of the monolayer by potentiating cellular injury and monolayer deterioration. The data also show that AscP is not cytoprotective during TBHP exposure but promotes RPTC regeneration by stimulating proliferation and migration/spreading and decreasing cellular death during the recovery period.

Effect of antiproliferative flavonoids on ascorbic acid accumulation in human colon adenocarcinoma cells

Dietary flavonoids were found to be antiproliferative for human colon cancer cells, Caco-2 and HT-29, and rat nontransformed intestinal crypt cells, IEC-6. The antiproliferative potency was found to be structure-dependent. We report here a correlation between the antiproliferative potency of these flavonoids and their ability to inhibit cellular accumulation of ascorbic acid (vitamin C). Caco-2, HT-29 and IEC-6 cells were found to accumulate ascorbic acid in a sodium-dependent fashion although some ascorbic acid may also enter the cells through sodium-independent mechanisms. Flavonoids that have been found to be antiproliferative, quercetin and genistein, inhibited the accumulation of ascorbic acid. The inhibition was dose-dependent and could be observed after as short as 10-min of incubation. The degree of inhibition of accumulation was more during rapid cell division as compared to post-confluency Caco-2 cells. Flavonoids that were found to show little antiproliferative effect, naringenin and catechin, also had little effect on ascorbic acid accumulation. The antiproliferative property of flavonoids could be linked to their ascorbic acid deprivation property.