Ascorbic acid in tissues

The titer of L-ascorbic acid in tissues was examined during development. During the fifth instar, L-ascorbate increased about eightyfold in the labial gland and ten-fold in the hemolymph, where millimolar levels were measured (Figure 3). Regression analysis of the tissue kinetics revealed that the labial gland accumulated L-ascorbic acid about twice... 

Many reports demonstrating the distribution of ascorbic acid in tissues of guinea pigs have appeared. Because this species is not able to... 

Table II. Mean sd of Organ Weight and Steady State Concentration (Cgg) of Ascorbic Acid (AA) in Tissues and Mean Content (XT) of Ascorbic Acid in Tissues...

Binding of Ascorbic Acid in Tissues. Following Equation 1, the apparent volume of distribution (Vi) of the rapidly accessible part of the body (central compartment) was derived to be 0.47 L. Furthermore, an apparent volume of distribution (V ) of 2.2 L has been estimated (15). Vs8 relates the amount of ascorbic acid in the body in the steady state to the concentration in plasma. The value of Vi and are calculated assuming 100% absorption of the administered labeled ascorbic... 

D5. Daglish, G., The spectrophotometric determination of ascorbic acid in tissue extracts, particularly those of the walnut (Juglans regia). Biochetn. J. 49, 635-642 (1951). 

IV. The Function or Ascorbic Acid in Tissue Metabolism 1, Teleological Concepts... 

MEASUREMENT/ASSAY. The concentration of ascorbic acid in tissues and foods is expressed in milligrams. One lU is the activity of 0.05 mg of ascorbic acid. 

Evidence exists that the relative solubility of amines and inhibitors in heterogeneous oil-water systems could be decisive in formation of nitrosamines and blocking these reactions, Nitrosopyrrolidine formation in bacon predominates in the adipose tissue despite the fact that its precursor, proline, predominates in the lean tissue (5,6,7). Mottram and Patterson (8) partly attribute this phenomenon to the fact that the adipose tissue furnishes a medium in which nitrosation is favored, Massey, et al, (9) found that the presence of decane in a model heterogeneous system caused a 20-fold increase in rate of nitrosamine formation from lipophilic dihexylamine, but had no effect on nitrosation of hydrophilic pyrrolidine. Ascorbic acid in the presence of decane enhanced the synthesis of nitrosamines from lipophilic amines, but had no effect on nitrosation of pyrrolidine. The oil-soluble inhibitor ascorbyl palmitate had little influence on the formation of nitrosamines in the presence or absence of decane. 

A more recent study, which measured three established markers of free-radical activity in addition to serum ascorbic acid in two groups of elderly diabetic patients (with and without retinopathy), found no significant differences in any of the markers between patients and age-matched controls despite significant depletion of ascorbic acid in patients with diabetes, especially those with retinopathy (Sinclair et al., 1992). These rather paradoxical findings suggest the existence of a complex interrelationship between the levels of individual antioxidant molecules in cells and tissues. 

Dr. Rebec also said that the brains on post mortem studies of schizophrenics tended to be mushy and to have very low levels of ascorbic acid in their constituent tissue. 

In its biochemical functions, ascorbic acid acts as a regulator in tissue respiration and tends to serve as an antioxidant in vitro by reducing oxidizing chemicals. The effectiveness of ascorbic acid as an antioxidant when added to various processed food products, such as meats, is described in entry on Antioxidants. In plant tissues, the related glutathione system of oxidation and reduction is fairly widely distributed and there is evidence that election transfer reactions involving ascorbic acid are characteristic of animal systems. Peroxidase systems also may involve reactions with ascorbic acid In plants, either of two copper-protein enzymes are commonly involved in the oxidation of ascorbic acid. 

Ascorbic acid is synthesized by plants and many ani- mals but not by primates or guinea pigs. In scurvy, the disease associated with a severe deficiency of ascorbic acid, connective tissues throughout the body deteriorate. Weakening of the capillary walls results in hemorrhages, wounds heal poorly, and lesions occur in the bones. 

Berberine inhibits oxidative decarboxylation of yeast pyruvic acid (310) the same dose has, however, no effect upon aerobic glycolysis, Warburg s respiratory enzymes, indophenol oxidase, etc. Berberine and tetrahydroberberine have an inhibitory effect on oxidation of (+ )-alanine in rat kidney homogenates (498). Berberine and palmatine show a specific inhibitory effect upon cholinesterase in rabbit spleen and on pseudocholinesterase in horse serum (499). Berberine inhibits cellular respiration in ascitic tumors and even in tissue cultures (500-502). The specific toxic effect of berberine on the respiration of cells of ascitic tumors in mice was described (310). The glycolysis was not found to be affected, but the uptake of oxygen was smaller. Fluorescence was used in order to demonstrate berberine in cellular granules. Hirsch (503) assumed that respiration is inhibited by the effect of berberine on the yellow respiratory enzymes. Since the tumorous tissue contains a smaller number of yellow respiratory enzymes than normal tissue it is more readily affected by berberine. Subcutaneous injections of berberine, palmatine, or tetrahydropalmatine significantly reduce the content of ascorbic acid in the suprarenals, which is not affected by hypophysectomy (504). 

Compounds known to behave in this way in vivo are listed in recent reviews in this Series.1 2 The structures of some of the /3-D-glucopyranosiduronic acids isolated from urine have been proved by chemical synthesis.3 A few similar derivatives of flavones and triterpenes have been isolated from plants. D-Glucuronic acid also occurs in mammalian tissues as a constituent of acid mucopolysaccharides (aminodeoxypolysaccharides, containing uronic acid), such as hyaluronic acid, chondroitinsulfate, and heparin,4 and it is a direct precursor of L-ascorbic acid in plants and mammals.6 It is present in many of the plant polysaccharides classified as hemicelluloses6 and gums,7 and it has also been found in certain bacterial polysaccharides.4... 

Several inherited disorders are associated with faulty operation of the electron transport pathway. ATP production is diminished in such cases. These disorders are known as mitochondrial myopathies, and they are associated with the absence of specific polypeptide chains found in complexes I, III, or IV. In many cases, the problem may be traced to specific lesions in mitochondrial DNA, which codes for at least 13 polypeptide chains found in these complexes. Myopathies are tissue specific some affect the heart, others the skeletal muscle. Many are accompanied by lactic acidosis, because the inability to reduce NADH normally results in its accumulation and the channeling of pyruvate toward lactic acid production. In complex I disorders, the oxidation of FADH2 is not impeded. In complex III lesions, neither NADH nor FADH2 can be oxidized. However, use has been made by B. Chance and colleagues of menadione (Chapter 6) and ascorbic acid in such cases. The former can oxidize UQH2, whereas ascorbate can oxidize menadione and reduce cytochrome c. Marked clinical improvement in affected patients follows such treatment. 

This vitamin occurs in all living tissues, where it influences oxidation-reduction reactions. The major source of L-ascorbic acid in foods is vegetables and fmits (Table 9-13). 

D-lso-ascorbic acid (erythorbic acid see Figure 13.1) also has vitamin activity. in vivo and in cell culmre, it has only about 5% of the biological activity of ascorbate, but this seems to be from poor intestinal absorption and tissue uptake. In vitro with purified enzymes, it has the same cofactor activity as ascorbate. Although it is not a namrally occurring compound, erythorbic acid is widely used interchangeably with ascorbic acid, in cured meats and as an antioxidant in a variety of foods. 

Disposition in the Body. Readily absorbed after oral administration the proportion of a dose absorbed tends to decrease with increasing dose it is widely distributed in the body tissues. The concentration of ascorbic acid is higher in leucocytes and platelets than in erythrocytes and plasma. Ascorbic acid is metabolised to dehydroascorbic acid, 2,3-diketogulonic acid, oxalate, and carbon dioxide some conjugation with sulphate occurs to form ascorbate-3-sulphate. Ascorbic acid in excess of the body s requirements is rapidly eliminated in the urine. About 85% of an intravenous dose, given to subjects previously saturated with the vitamin, is excreted in the urine in 24 hours, with about 70% of the dose excreted unchanged and 15% as dehydroascorbic acid and diketogulonic acid. The amount normally present in the body is in excess of 1.5 g. 

The DNA adducts, deoxyadenosine and deoxygua-nosine, which are induced by malondialdehyde, the end-product of lipid peroxidation, accumulate in human breast tissues. These adducts are present at relatively higher concentrations in breast cancer cells compared to normal breast cells. In a recent study, serum antioxidative vitamin levels and lipid peroxidation were compared in gastric cancer patients. The level of serum ascorbic acid, a-tocopherol, p-carotene, and retinol were assessed. The levels of ascorbic acid in patients with gastric carcinoma were less than one-fifth of that in the control group, and the production of p-carotene and a-tocopherol were decreased, as well. 

Optical Absorbance and Spectrophotometric Methods. Direct spec-trophotometric methods involving light absorption have some limited value for very high potency material. The absorbance spectrum of ascorbic acid in neutral aqueous solutions has a peak value at 265 nm with E between 7500 and 16,650 as reported in the literature. The differences are due to nonanaerobic conditions (16,17). The maximum is shifted towards 245 nm in acidic solutions. Dehydroascorbic acid is transparent in the region of 230 nm to 280 nm, but has a weak absorption, Emax = 720 at 300 nm (18). A basic drawback to the successful application of spectrophotometric methods to the estimation of ascorbic acid is that the well-defined absorption band in the UV region of the spectrum is subject to interference from many substances, which would present a problem when applied to food and tissue extracts. 

Several reports have described the use of HPLC in the analyses of ascorbic acid in foods and vitamin products (71, 72,73,74) and in tissue samples (75). Procedures vary in the type of column, mobile-phase, detection systems and means of stabilization of extracts. Reversed-phased,... 

Figure 2. Analysis of ascorbic acid in a mouse brain tissue extract employing HPLC and an electrochemical detector. (Reproduced, with permission, from Ref. 75. Copyright 1975, Pergamon Press, Inc.)...

Prompt stabilization of ascorbic acid is especially important in the case of plasma or serum samples. Metaphosphoric acid is often used for this purpose because it also serves as a protein precipitant. Such properties are desirable in the inactivation of oxidase and the catalytic eflFect of copper. Oxalic acid is an attractive stabilizer for ascorbic acid analysis because of its lower cost and greater stability however, it is not a protein precipitant, therefore, it has a limited use for the extraction of animal tissues. The use of ethylenediaminetetraacetic acid (EDTA) in addition to the metaphosphoric acid has been recommended (96). EDTA would chelate divalent cations, and a study has shown it will stabilize ascorbic acid in the presence of copper for several days (96). Perchloric acid has been used also but because of its inherent dangerous properties its use is generally avoided. Trichloroacetic acid and EDTA also seem appropriate extractants for ascorbate in plant materials (97). 

A Method for the Determination of Ascorbic Acid in Biological Tissues by HPLC... 

---