Ascorbate regeneration in bovine ocular tissues by NADH-dependent semidehydroascorbate reductase

Cancer; an induced disease of twentieth century! Induction of tolerance, increased entropy and 'Dark Energy': loss of biorhythms (Anabolism v. Catabolism)

Maintenance of health involves a synchronized network of catabolic and anabolic signals among organs/tissues/cells that requires differential bioenergetics from mitochondria and glycolysis (biological laws or biorhythms). We defined biological circadian rhythms as Yin (tumoricidal) and Yang (tumorigenic) arms of acute inflammation (effective immunity) involving immune and non-immune systems. Role of pathogens in altering immunity and inducing diseases and cancer has been documented for over a century. However, in 1955s decision makers in cancer/medical establishment allowed public (current baby boomers) to consume million doses of virus-contaminated polio vaccines. The risk of cancer incidence and mortality sharply rose from 5% (rate of hereditary/genetic or innate disease) in 1900s, to its current scary status of 33% or 50% among women and men, respectively. Despite better hygiene, modern detection technologies and discovery of antibiotics, baby boomers and subsequent 2–3 generations are sicker than previous generations at same age. American health status ranks last among other developed nations while America invests highest amount of resources for healthcare. In this perspective we present evidence that cancer is an induced disease of twentieth century, facilitated by a great deception of cancer/medical establishment for huge corporate profits. Unlike popularized opinions that cancer is 100, 200 or 1000 diseases, we demonstrate that cancer is only one disease; the severe disturbances in biorhythms (differential bioenergetics) or loss of balance in Yin and Yang of effective immunity. Cancer projects that are promoted and funded by decision makers are reductionist approaches, wrong and unethical and resulted in loss of millions of precious lives and financial toxicity to society. Public vaccination with pathogen-specific vaccines (e.g., flu, hepatitis, HPV, meningitis, measles) weakens, not promotes, immunity. Results of irresponsible projects on cancer sciences or vaccines are increased population of drug-dependent sick society. Outcome failure rates of claimed ‘targeted’ drugs, ‘precision’ or ‘personalized’ medicine are 90% (± 5) for solid tumors. We demonstrate that aging, frequent exposures to environmental hazards, infections and pathogen-specific vaccines and ingredients are ‘antigen overload’ for immune system, skewing the Yin and Yang response profiles and leading to induction of ‘mild’, ‘moderate’ or ‘severe’ immune disorders. Induction of decoy or pattern recognition receptors (e.g., PRRs), such as IRAK-M or IL-1dRs (‘designer’ molecules) and associated genomic instability and over-expression of growth promoting factors (e.g., pyruvate kinases, mTOR and PI3Ks, histamine, PGE2, VEGF) could lead to immune tolerance, facilitating cancer cells to hijack anabolic machinery of immunity (Yang) for their increased growth requirements. Expression of constituent embryonic factors would negatively regulate differentiation of tumor cells through epithelial–mesenchymal-transition and create “dual negative feedback loop” that influence tissue metabolism under hypoxic conditions. It is further hypothesized that induction of tolerance creates ‘dark energy’ and increased entropy and temperature in cancer microenvironment allowing disorderly cancer proliferation and mitosis along with increased glucose metabolism via Crabtree and Pasteur Effects, under mitophagy and ribophagy, conditions that are toxic to host survival. Effective translational medicine into treatment requires systematic and logical studies of complex interactions of tumor cells with host environment that dictate clinical outcomes. Promoting effective immunity (biological circadian rhythms) are fundamental steps in correcting host differential bioenergetics and controlling cancer growth, preventing or delaying onset of diseases and maintaining public health. The author urges independent professionals and policy makers to take a closer look at cancer dilemma and stop the ‘scientific/medical ponzi schemes’ of a powerful group that control a drug-dependent sick society before all hopes for promoting public health evaporate.

Expression Profiling of Ascorbic Acid-Related Transporters in Human and Mouse Eyes

Purpose

Ascorbic acid (AsA) is an important antioxidant in the eye. Ascorbic acid is usually transported by sodium-dependent AsA transporters (SVCTs), and dehydroascorbic acid (DHA) by glucose transporters (GLUTs). This study investigates these AsA-related transporters in human compared with mouse eyes.

Methods

Five pairs of human donor eyes and 15 pairs of mouse eyes were collected. Immunofluorescence and in situ hybridization were performed to detect SVCTs and GLUTs expression in the ciliary epithelium, retina, and lens epithelial cells (LECs). These tissues were isolated with laser microdissection followed by extraction of total RNA. Quantitative PCR (qPCR) was performed to examine the mRNA level of SVCTs and GLUTs in human and mouse ocular tissues.

Results

Immunofluorescence and in situ hybridization showed SVCT2 and GLUT1 expression in human ciliary epithelium with varied distributions. Sodium-dependent AsA transporter 2 is expressed only in the pigmented epithelium (PE), and GLUT1 is predominately expressed in the nonpigmented epithelium (NPE). However, SVCT2 was not identified in mouse ciliary epithelium, whereas GLUT1 expressed in both PE and NPE. Laser microdissection and qPCR revealed high levels of SVCT2 mRNA in human RPE cells and murine neural retina. Sodium-dependent AsA transporter 1 mRNA could be detected only in human and murine LECs. Glucose transporter 3 and GLUT4 mRNA could not be detected in either the human or mouse ciliary processes or in the lens epithelium.

Conclusions

These fundamental findings indicate AsA transporter expression in eyes of humans is significantly different compared with mice. This may explain why human aqueous and vitreous humors contain higher AsA levels compared with other animals.

Antioxidant activity of retinol, glutathione, and taurine in bovine photoreceptor cell membranes

The antioxidant activities of compounds endogenous to mammalian rod outer segments (ROS) were investigated in vitro by measuring the oxidative loss of polyunsaturated fatty acids (PUFA's) from the membranes of intact ROS and from liposomes made from ROS phospholipids (PL) to which lipid soluble compounds had been added. The membranes were exposed to the water-soluble oxidant 2, 2'-azobis(2-amidinopropane) dihydrochloride (AAPH). Retinol protected PUFA's in ROS liposome PL's, whereas retinaldehyde promoted lipid peroxidation. When isolated ROS were stimulated to produce endogenous retinol, PUFA loss was inhibited by up to 17%. These findings suggest an antioxidant function for the enzymatic reduction of retinaldehyde to retinol during the visual cycle. Water-soluble antioxidants, taurine and reduced glutathione (GSH), were investigated individually and in combination with retinol in ROS PL liposomes. GSH protected PUFA's in ROS PL liposomes. Taurine alone showed little antioxidant activity, but in combination with retinol it protected lipids twice as much as retinol alone. These results support previous findings that taurine protects ROS lipids during exposure to cyclic light.

Purification and molecular properties of ascorbate peroxidase from bovine eye

Ascorbate peroxidase (APX) is a hydrogen peroxide-scavenging peroxidase which uses ascorbate (AsA) as the specific electron donor. APX has not been isolated in mammals. Ocular tissue contains AsA at high concentrations, and we detected APX activity in bovine retinal pigment epithelium (RPE) and choroid. We purified APX from bovine RPE and choroid by four chromatographic steps. The purified APX was a monomeric hemoprotein with a molecular mass of 43 kDa. The amino acid sequence of the amino-terminal region of the purified APX showed a high degree of homology to that of plants. The primary product of the APX reaction was identified as the monodehydroascorbate radical. The APX showed high specificity for AsA as an electron donor. This is the first isolation and characterization of APX from mammals, and its role in the protection against active species of oxygen in ocular tissue is discussed.

The redox couple between glutathione and ascorbic acid: a chemical and physiological perspective

This article provides a comprehensive analysis of the redox reaction between glutathione/glutathione disulfide and ascorbic acid/dehydroascorbic acid. It includes an historical perspective of the progression of the experiments, first begun more than 60 years ago and continuing today with heightened importance. Indeed, the antioxidant capacity of glutathione and ascorbic acid, whether singly or in combination, linked via the redox couple, is a subject of intense interest for studies by bench scientists and clinicians, particularly because a growing body of evidence suggests that free radicals may be involved in a variety of diseases. The authors begin with a detailed summary of "test tube" experiments (the chemical perspective) that have revealed the conditions that regulate the rate of the redox coupling between glutathione and dehydroascorbic acid and that promote or inhibit the decomposition of dehydroascorbic acid in ordinary, buffered aqueous media; results obtained in the authors' laboratory are used for illustration purposes and uniformity of presentation. The authors then proceed to a critical examination of the extent to which the redox couple between glutathione and ascorbic acid operates in a cell, using the often published antioxidant cascade (See Fig. 1) as the model for the analysis (the physiological perspective). The evidence for and the evidence against the presence of the enzyme dehydroascorbate reductase in animal cells is outlined in a balanced way in an attempt to make sense of this continuing controversy. Next, the authors carefully document the many studies showing that exogenous dehydroascorbic acid is transported into cells where it is reduced to ascorbic acid by glutathione. Finally, they probe the functional significance and efficiency of the redox couple in monolayer cultures of human retinal pigment epithelial (RPE) cells, as a prototypical cellular model. The authors include the results of new experiments showing that incubation of RPE cells with a nitroxide, TEMPOL, leads to the selective oxidation of intracellular ascorbic acid. This approach is desirable because it dissects the cascade at a specific site and permits measurements of the levels of ascorbic acid and glutathione in the cells before, during, and after oxidation. The results show that only partial regeneration of ascorbic acid is obtained when control conditions are restored. However, if either ascorbic acid or dehydroascorbic acid is added to the media during the recovery period following treatment of cells with TEMPOL, then full recovery of ascorbic acid is observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Monodehydroascorbate reductase activity in the surface membrane of leukemic cells. Characterization by a ferricyanide-driven redox cycle

A transmembrane monodehydroascorbate reductase activity with a high affinity in the subpicomolar concentration range of the free radical can be measured at the surface of erythroleukemic cells using a ferricyanide-driven redox cycle. The activity is dependent on the membrane potential and can therefore only be found in intact cells. It is independent of the glutathione content of the cells. Thenoyltrifluoroacetone is an efficient inhibitor of the activity, whereas ouabain, monensin and tetraethylammonium show no effect. Cells are able to generate ascorbate from dehydroascorbic acid. This explains why both forms of vitamin C show practically the same affinity for the redox cycle but why it does not drive the redox cycle by itself because it is much slower and is not inhibited by thenoyltrifluoroacetone. The reductase activity is independent of the degree of differentiation of the leukemic cells.

Ascorbic acid regeneration by bovine iris-ciliary body

Ocular tissues appear to require high levels of ascorbic acid and the elucidation of the mechanisms by which those tissues maintain the vitamin in its reduced state remains an important objective. The regeneration of ascorbate from its oxidative by-product, dehydroascorbic acid (DHAA), was studied in bovine iris-ciliary body. Iris-ciliary body was removed by scalpel, weighed, minced, and homogenized in 20 mM MOPS, 62 mM sucrose, and 0.1 mM EDTA at pH 7.0. The homogenate was centrifuged and precipitated with ammonium sulfate such that maximal DHAA reducing activity was enhanced in a 50-75% ammonium sulfate fraction. This fraction was employed for subsequent characterization of DHAA reduction by iris-ciliary body. Results indicate that the iris-ciliary body enzymatically reduces DHAA to ascorbate at a rate significantly greater than can be accounted for by a nonenzymatic glutathione-dependent mechanism. In addition, saturation kinetics are observed, and the enzymatic activity is dependent on protein concentration, DHAA concentration, and reduced glutathione (GSH) concentration. The activity is sensitive to pH, to high temperature, and to digestion by trypsin and is greatest in the presence of both GSH and NADPH. The reducing activity is therefore attributed to one or more proteins that are distinct from the known ascorbate regenerating enzyme, GSH-dependent DHAA reductase (EC 1.8.5.1).

Ascorbate is regenerated by HL-60 cells through the transplasmalemma redox system

Ascorbate was maintained in the media during a long-term culture by HL-60 cells. The chemical oxidation of ascorbate was reversed in vitro by living HL-60 cells and was related to the amount of cells added. The increase of NADH concentration by lactate addition to cells was accompanied by an increase of both ascorbate regeneration and ferricyanide reduction. Further, plasma membrane enriched fractions from HL-60 cells revealed enhancement of both ascorbate regeneration and ferricyanide reduction in the presence of NADH when previously treated with detergent. The blockage of cell surface carbohydrates by wheat germ agglutinin (WGA) and Concanavalina ensiformis (Con A) lectins significantly inhibited the regeneration of ascorbate caused by the cells. These results support the idea that ascorbate is externally regenerated by the NADH-ascorbate free radical reductase as a part of the transplasma membrane redox system.

Ocular ascorbate transport and metabolism

1. The concept is reviewed that the eye is subject to photo-oxidative damage through chemical free radical species that interact with sensitive tissue components. 2. The role of ascorbic acid may be to protect the eye by scavenging free radicals. 3. Ascorbic acid is present at a high concentration in various ocular compartments of diurnal animals, regardless of whether the animal synthesizes the compound or extracts it from the diet. 4. Ascorbic acid accumulates in the eye by active transport through the iris-ciliary body into aqueous humor, and subsequent transport into the lens and cornea. 5. Conservation of ascorbic acid occurs by reduction of dehydro-L-ascorbic acid and the ascorbate free radical through processes that appear to be enzymatic.

Reduced and total ascorbate in guinea pig eye tissues in response to dietary intake

Guinea pigs were fed 5 different levels of dietary ascorbate representing a 65-fold range (0.8-52 mg animal-1 day-1). After two months on the diets, levels of reduced and total ascorbate were determined in aqueous humor, vitreous humor, lens and plasma. At low-dietary levels, proportionally higher levels of ascorbate are found in the lens than in other eye tissues. Tissue ascorbate levels began to plateau at dietary intake of approximately 11 mg animal-1 day-1. This is the amount suggested for optimal health, but it is ten times the level needed to prevent scurvy. Over 75% of the eye tissue ascorbate is in the reduced form in animals fed diets which provided 11 mg ascorbate. However, there was less than 50% reduced ascorbate in the eye tissues of the animals fed about 1mg ascorbate per day.

Effects of age and dietary vitamin C on the contents of ascorbic acid and acid-soluble thiol in lens and aqueous humour of guinea-pigs

Variations in ascorbate and thiol concentration in lens and aqueous humour, with age and vitamin C nutrition, are of potential biological importance. To study these relationships, Dunkin-Hartley guinea-pigs were maintained for periods of up to 1.3 yr on diets containing either high or low (marginal) vitamin C. Ascorbate contents of liver, spleen, adrenals, lens and aqueous humour, and acid-soluble thiol of lens and aqueous humour were measured. High vitamin C intake maintained ascorbate levels in the internal organs between five and 30 times the level attained by the low vitamin C intake and aqueous humour vitamin C was 10-20 times higher at high vitamin C intake. Lens ascorbate, however, was only about twice as high at high vitamin C intake than at low intake, and at both intake levels it declined steadily to about half its initial value, after 1.3 yr. Thus an animal aged 1.3 yr on the low intake had about one-quarter to one-fifth of the lens ascorbate level of a young animal receiving a generous intake. Acid-soluble thiol in the lens, in contrast to ascorbic acid, increased significantly with age but was not significantly affected by dietary vitamin C intake. Acid-soluble thiol in the aqueous humour was only 0.5-2% of the concentration found in lens, and unlike the lens thiol level, it declined with age. No sex differences were observed for ascorbate or thiol levels either in lens or in aqueous humour.

Na+-linked active transport of ascorbate into cultured bovine retinal pigment epithelial cells: heterologous inhibition by glucose

The transport of ascorbate into cultured bovine retinal pigment epithelial (RPE) cells is reported. Primary or subcultured RPE cells were incubated in the presence of 10-500 microM L-[carboxyl-14C]-ascorbate for various periods of time. Accumulation of ascorbate into RPE cells followed a saturable active transport with a Km of 125 microM and a Vmax of 28 pmole/micrograms DNA/min. RPE intracellular water was calculated to be 0.8 pL/cell, and the transported cellular ascorbate concentration was 7.5 +/- 0.8 mM. Replacement of 150 mM NaCl in the incubation media with choline-Cl strongly inhibited (80 +/- 8%) ascorbate uptake into cultured RPE cells. Although the depletion of cellular ATP by 2,4-dinitrophenol and the inhibition of Na+-K+-ATPase by ouabain reduced ascorbate transport into RPE significantly, active transport of ascorbate was not entirely inhibited by these metabolic inhibitors. The ascorbate analogue, D-isoascorbate, competitively inhibited ascorbate transport into cultured RPE with a Ki of 12.5 mM. Cells grown in the presence of 5 to 50 mM alpha-D-glucose in the growth media did not differ in their ability to transport ascorbate. In contrast, the presence of alpha-D-glucose or its nonmetabolizable analogues, 3-0-methyl-glucose, alpha-methyl-glucose, and 2-deoxy-glucose, but not L-glucose or beta-D-fructose, in the incubation media inhibited ascorbate transport. myo-Inositol (10 or 20 mM) also inhibited ascorbate transport into RPE cells. The active uptake of ascorbate into cultured RPE cells was primarily coupled to the movement of sodium ion down its electrochemical gradient. A bifunctional, cotransport carrier possessing an ascorbate-binding site and a sodium-binding site may be involved in the ascorbate uptake system. The inhibition of ascorbate uptake by sugars appeared to be heterologous in nature, occurring between two distinct carrier systems, both of which were dependent on the sodium ions.

Ascorbate transport in cultured cat retinal pigment epithelial cells

Transport of ascorbate by primary cultures of cat retinal pigment epithelial cells (RPE) was studied. Confluent primary cultures were incubated with 10-500 microM L-[carboxyl-14C] ascorbic acid in balanced salt solution (BSS) at 37 degrees C for 1 to 40 min. The uptake of radioactive ascorbate followed saturation kinetics with a Km of 42 microM and Vmax of 117 pmol min-1 microgram-1 DNA. Cells incubated with 10 microM radioactive ascorbate for 40 min showed a ratio of intracellular to extracellular radioactive ascorbate of greater than 40. The transport of ascorbate was sodium- and energy-dependent. Replacement of 150 mM NaCl in BSS with 150 mM LiCl reduced ascorbate uptake significantly. Ouabain, 2,4-dinitrophenol, alpha-D-glucose, 3-O-methyl-D-glucose, and the ascorbate analogues, D-isoascorbate and dehydroascorbate, each inhibited ascorbate uptake into RPE cells. The efflux of radioactivity into the incubation media was slow when cells were preloaded with either 50- or 500 microM radioactive ascorbate, but increased when cells preloaded with 50 microM ascorbate were incubated in the presence of excess non-radioactive ascorbate. These studies demonstrated that a sodium-dependent carrier system is involved in transport of ascorbate in primary cultures of cat RPE.