Platelet ascorbic acid levels in normal subjects and in disease

The benefits of ascorbate to protect healthy cells in the prevention and treatment of oncological diseases

Health status is determined by the balance of oxidants and antioxidants which protects healthy cells against the threat of internal and external risk factors. Antioxidants such as ascorbate (vitamin C, ascorbic acid) are of fundamental importance in this respect. Ascorbate neutralizes potential damage caused by cellular oxidative stress which may be the greatest risk of damage to healthy tissue. Cellular oxidative stress is mediated by external factors (e.g. psychological stress, physical exertion, drugs, various diseases, environmental pollution, preservatives, smoking, and alcohol) and internal factors (products of cellular metabolism including reactive oxygen species). When the products of oxidative stress are not sufficiently neutralized, healthy cells are at risk for both mitochondrial and DNA damage. In the short term, cell function may deteriorate, while an increased production of proinflammatory cytokines over time may lead to the development of chronic inflammatory changes and diseases, including cancer. Although pharmaceutical research continues to bring effective chemotherapeutic agents to the market, a limiting factor is often the normal tissue and organ toxicity of these substances, which leads to oxidative stress on healthy tissue. There is increasing interest and imperative to protect healthy tissues from the negative effects of radio-chemotherapeutic treatment. The action of ascorbate against the development of oxidative stress may justify its use not only in the prevention of carcinogenesis, but as a part of supportive or complementary therapy during treatment. Ascorbate (particularly when administered parentally at high doses) may have antioxidant effects that work to protect healthy cells and improve patient tolerability to some toxic radio-chemotherapy regimens. Additionally, ascorbate has demonstrated an immunomodulatory effect by supporting mechanisms essential to anti-tumor immunity. Intravenous administration of gram doses of vitamin C produce high plasma levels immediately, but the levels drop rapidly. Following oral vitamin C administration, plasma levels increase slowly to relatively low values, and then gradually decay. With an oral liposomal formulation, significantly higher levels are attainable than with standard oral formulations. Therefore, oral administration of liposomal vitamin C appears to be an optimal adjunct to intravenous administration. In this review, the basic mechanisms and clinical benefits of ascorbate as an antioxidant that may be useful as complementary therapy to chemotherapeutic regimens will be discussed.

Treatment of Pancreatic Cancer with Pharmacological Ascorbate

The prognosis for patients diagnosed with pancreatic cancer remains dismal, with less than 3% survival at 5 years. Recent studies have demonstrated that high-dose, intravenous pharmacological ascorbate (ascorbic acid, vitamin C) induces cytotoxicity and oxidative stress selectively in pancreatic cancer cells vs. normal cells, suggesting a promising new role of ascorbate as a therapeutic agent. At physiologic concentrations, ascorbate functions as a reducing agent and antioxidant. However, when pharmacological ascorbate is given intravenously, it is possible to achieve millimolar plasma concentration. At these pharmacological levels, and in the presence of catalytic metal ions, ascorbate can induce oxidative stress through the generation of hydrogen peroxide (H2O2). Recent in vitro and in vivo studies have demonstrated ascorbate oxidation occurs extracellularly, generating H2O2 flux into cells resulting in oxidative stress. Pharmacologic ascorbate also inhibits the growth of pancreatic tumor xenografts and displays synergistic cytotoxic effects when combined with gemcitabine in pancreatic cancer. Phase I trials of pharmacological ascorbate in pancreatic cancer patients have demonstrated safety and potential efficacy. In this chapter, we will review the mechanism of ascorbate-induced cytotoxicity, examine the use of pharmacological ascorbate in treatment and assess the current data supporting its potential as an adjuvant in pancreatic cancer.

Antioxidants and human diseases

Oxidative stress plays a pivotal role in the development of human diseases. Reactive oxygen species (ROS) that includes hydrogen peroxide, hyphochlorus acid, superoxide anion, singlet oxygen, lipid peroxides, hypochlorite and hydroxyl radical are involved in growth, differentiation, progression and death of the cell. They can react with membrane lipids, nucleic acids, proteins, enzymes and other small molecules. Low concentrations of ROS has an indispensable role in intracellular signalling and defence against pathogens, while, higher amounts of ROS play a role in number of human diseases, including arthritis, cancer, diabetes, atherosclerosis, ischemia, failures in immunity and endocrine functions. Antioxidants presumably act as safeguard against the accumulation of ROS and their elimination from the system. The aim of this review is to highlight advances in understanding of the ROS and also to summarize the detailed impact and involvement of antioxidants in selected human diseases.

The molecular basis of memory. Part 2: chemistry of the tripartite mechanism

We propose a tripartite mechanism to describe the processing of cognitive information (cog-info), comprising the (1) neuron, (2) surrounding neural extracellular matrix (nECM), and (3) numerous "trace" metals distributed therein. The neuron is encased in a polyanionic nECM lattice doped with metals (>10), wherein it processes (computes) and stores cog-info. Each [nECM:metal] complex is the molecular correlate of a cognitive unit of information (cuinfo), similar to a computer "bit". These are induced/sensed by the neuron via surface iontophoretic and electroelastic (piezoelectric) sensors. The generic cuinfo are used by neurons to biochemically encode and store cog-info in a rapid, energy efficient, but computationally expansive manner. Here, we describe chemical reactions involved in various processes that underline the tripartite mechanism. In addition, we present novel iconographic representations of various types of cuinfo resulting from"tagging" and cross-linking reactions, essential for the indexing cuinfo for organized retrieval and storage of memory.

Ascorbic acid: chemistry, biology and the treatment of cancer

Since the discovery of vitamin C, the number of its known biological functions is continually expanding. Both the names ascorbic acid and vitamin C reflect its antiscorbutic properties due to its role in the synthesis of collagen in connective tissues. Ascorbate acts as an electron-donor keeping iron in the ferrous state thereby maintaining the full activity of collagen hydroxylases; parallel reactions with a variety of dioxygenases affect the expression of a wide array of genes, for example via the HIF system, as well as via the epigenetic landscape of cells and tissues. In fact, all known physiological and biochemical functions of ascorbate are due to its action as an electron donor. The ability to donate one or two electrons makes AscH(-) an excellent reducing agent and antioxidant. Ascorbate readily undergoes pH-dependent autoxidation producing hydrogen peroxide (H(2)O(2)). In the presence of catalytic metals this oxidation is accelerated. In this review, we show that the chemical and biochemical nature of ascorbate contribute to its antioxidant as well as its prooxidant properties. Recent pharmacokinetic data indicate that intravenous (i.v.) administration of ascorbate bypasses the tight control of the gut producing highly elevated plasma levels; ascorbate at very high levels can act as prodrug to deliver a significant flux of H(2)O(2) to tumors. This new knowledge has rekindled interest and spurred new research into the clinical potential of pharmacological ascorbate. Knowledge and understanding of the mechanisms of action of pharmacological ascorbate bring a rationale to its use to treat disease especially the use of i.v. delivery of pharmacological ascorbate as an adjuvant in the treatment of cancer.

Enhancement of quinone redox cycling by ascorbate induces a caspase-3 independent cell death in human leukaemia cells. An in vitro comparative study

Since the higher redox potential of quinone molecules has been correlated with enhanced cellular deleterious effects, we studied the ability of the association of ascorbate with several quinones derivatives (having different redox potentials) to cause cell death in K562 human leukaemia cell line. The rationale is that the reduction of quinone by ascorbate should be dependent of the quinone half-redox potential thus determining if reactive oxygen species (ROS) are formed or not, leading ultimately to cell death or cell survival. Among different ROS that may be formed during redox cycling between ascorbate and the quinone, the use of different antioxidant compounds (mannitol, desferal, N-acetylcysteine, catalase and superoxide dismutase) led to support H2O2 as the main oxidizing agent. We observed that standard redox potentials, oxygen uptake, free ascorbyl radical formation and cell survival were linked. The oxidative stress induced by the mixture of ascorbate and the different quinones decreases cellular contents of ATP and GSH while caspase-3-like activity remains unchanged. Again, we observed that quinones having higher values of half-redox potential provoke a severe depletion of ATP and GSH when they were associated with ascorbate. Such a drop in ATP content may explain the lack of activation of caspase-3. In conclusion, our results indicate that the cytotoxicity of the association quinone/ascorbate on K562 cancer cells may be predicted on the basis of half-redox potentials of quinones.

Antioxidants and cancer therapy: a systematic review

PURPOSE

Many patients with cancer take antioxidant nutritional supplements during cancer treatment to alleviate treatment toxicities and to improve long-term outcomes, but little is known about the efficacy and safety of antioxidant use during cancer treatment. We reviewed English-language manuscripts published in the biomedical literature, reporting the results of observational studies of antioxidant status and cancer outcomes and of intervention trials of antioxidants among patients receiving chemotherapy with or without radiation for various malignancies.

METHODS

We searched the Medline database and the bibliographies of the retrieved manuscripts, reviews, and books on antioxidants and cancer. The retrieved studies are grouped by study design, malignancy, and end points.

RESULTS

More than 100 citations were retrieved; 52 met our criteria, 31 were observational studies, and 21 were intervention trials. The studies varied in study design, timing of observation/intervention, intervention protocol, malignancy, and anticancer regimen.

CONCLUSION

These inconsistencies preclude a definitive conclusion as to the effect of chemotherapy on antioxidant status in patients undergoing anticancer therapy. However, our review suggests that total antioxidant status (measured by total radical antioxidant parameter) declines during cancer treatment. Adequately powered trials or observational studies among patients with a specific cancer diagnosis receiving a specific treatment regimen are needed to address patients' and physicians' concerns regarding these associations.

Effects of sodium ascorbate (vitamin C) and 2-methyl-1,4-naphthoquinone (vitamin K3) treatment on human tumor cell growth in vitro. I. Synergism of combined vitamin C and K3 action

The effects of sodium ascorbate (vitamin C) and 2-methyl-1,4-naphthoquinone (vitamin K3) administered separately or in combination on the in vitro cultured human neoplastic cell lines MCF-7 (breast carcinoma), KB (oral epidermoid carcinoma), and AN3-CA (endometrial adenocarcinoma) have been examined. When given separately, vitamin C or K3 had a growth inhibiting action only at high concentrations (5.10(3) mumol/1 and 10(5) nmol/l, respectively). Combined administration of both vitamins demonstrated a synergistic inhibition of cell growth at 10 to 50 times lower concentrations. At this level separately given vitamins are not toxic. The sensitivity to this treatment was somewhat different in the three cell lines, being slightly higher for KB line. This tumor cell growth inhibitory effect was completely suppressed by the addition of catalase to the culture medium containing vitamins C and K3, suggesting an excessive production of hydrogen peroxide as being implied in mechanisms responsible for the above-mentioned effects.

Non-toxic potentiation of cancer chemotherapy by combined C and K3 vitamin pre-treatment

The influence on the survival of ascitic liver tumor (TLT)-bearing mice of combined vitamins C and K3 administered before or after a single i.p. dose of 6 different cytotoxic drugs, all commonly used in human cancer therapy, was investigated. Combined i.p. administration of these vitamins produced a distinct chemotherapy-potentiating effect for all drugs examined, especially when injected before chemotherapy. This potentiating treatment did not increase the general and organ toxicity that accompanies cancer chemotherapy. The possible generation of peroxides followed by membrane lipid alteration, DNase activation and DNA destruction by combined vitamin C and K3 in catalase-deficient cancer cells might be involved in the mechanisms of this selective potentiation.

A simple method for evaluating platelet superoxide dismutase

A simple and rapid spectrophotometric method for evaluating platelet superoxide dismutase is reported. Platelets prepared avoiding erythrocyte and leucocyte contamination were lysated and tested in a Tris-cacodylic buffer containing pyrogallol. Platelet superoxide dismutase was calculated by evaluating the degree of the pyrogallol autoxidation inhibition induced by platelet lysate. Possible interferences of hydrogen peroxide, peroxidases and reducing substances were excluded. Platelet superoxide dismutase content was studied in 38 healthy subjects and was 19.1 +/- 4.1 U/10(8) platelets or 35 +/- 7.8 U/mg protein.

Fibrinogen coagulation without thrombin: reaction with vitamin C and copper(II)

We describe a novel method for inducing fibrinogen derived clots. The addition of vitamin C (0.1-1 mM) to a solution of fibrinogen (1 mg/ml) and Cu(II) (20-150 microM) results in protein coming out of solution. This phenomenon can be "read" by fibrometers as "clotting time". The reaction requires Cu(II) and can be prevented by a chelating agent, such as citrate, as well by a hydroxyl radical scavenger, such as mannitol. The insoluble protein, called "neofibe", is soluble in 4 M urea and 2% SDS. Isoelectric focusing and SDS-electrophoretic comparison of native fibrinogen with neofibe reveal molecular modifications of the starting protein. This reaction is an interesting example of a free radical mediated transformation of soluble protein into insoluble material. Some findings on the connection between hemostasis, vitamin C and Cu(II) are discussed.

The distribution of ascorbic acid between various cellular components of blood, in normal individuals, and its relation to the plasma concentration

1. A study was undertaken to investigate the distribution of ascorbic acid between various cellular components of blood, in normal individuals, and its relation to the plasma concentration. Forty-one unsupplemented individuals and sixteen supplemented (2 g/d for 5 d) individuals were studied. 2. Granulocytes, mononuclear leucocytes, platelets and erythrocytes were separated by differential sedimentation and centrifugation. Ascorbic acid contents were measured by the dinitrophenylhydrazine method. 3. Ascorbic acid content per cell was higher in mononuclear leucocytes and granulocytes than in platelets and erythrocytes. Intracellular ascorbic acid concentrations, calculated from published values for cell volumes, when compared with the plasma concentration showed a marked ability to concentrate ascorbic acid in mononuclear leucocytes (80 times), platelets (40 times) and granulocytes (25 times). 4. Erythrocytes showed little ability to concentrate ascorbic acid over the normal range of plasma concentration but because of their relative numbers they and the plasma fraction accounted for most of the blood-borne ascorbic acid (greater than 70%). 5. The ascorbic acid content of granulocytes, platelets and erythrocytes showed a significant positive correlation with the plasma concentration and supplementation with ascorbic acid significantly increased the content of these cell types. Mononuclear leucocytes in contrast did not show any such relationship. 6. The ability of the mononuclear leucocytes to maintain the highest levels of ascorbic acid in the cell types studied, despite variation in plasma availability, warrants further study, particularly in view of the importance of these cells in immunocompetence.