Vitamin C-deficient Guinea Pigs Research Articles

Vitamin C deficient reduces proliferation in a human periventricular tumor stem cell-derived glioblastoma model.

Glioblastoma multiforme (GBM) is the most common and aggressive brain tumor with a median survival of 14.6 months. GBM is highly resistant to radio- and chemotherapy, and remains without a cure; hence, new treatment strategies are constantly sought. Vitamin C, an essential micronutrient and antioxidant, was initially described as an antitumor molecule; however, several studies have shown that it can promote tumor progression and angiogenesis. Thus, considering the high concentrations of vitamin C present in the brain, our aim was to study the effect of vitamin C deficiency on the progression of GBM using a GBM model generated by the stereotactic injection of human GBM cells (U87-MG or HSVT-C3 cells) in the subventricular zone of guinea pig brain. Initial characterization of U87-MG and HSVT-C3 cells showed that HSVT-C3 are highly proliferative, overexpress p53, and are resistant to ferroptosis. To induce intraperiventricular tumors, animals received control or a vitamin C-deficient diet for 3 weeks, after which histopathological and confocal microscopy analyses were performed. We demonstrated that the vitamin C-deficient condition reduced the glomeruloid vasculature and microglia/macrophage infiltration in U87-MG tumors. Furthermore, tumor size, proliferation, glomeruloid vasculature, microglia/macrophage infiltration, and invasion were reduced in C3 tumors carried by vitamin C-deficient guinea pigs. In conclusion, the effect of the vitamin C deficiency was dependent on the tumor cell used for GBM induction. HSVT-C3 cells, a cell line with stem cell features isolated from a human subventricular GBM, showed higher sensitivity to the deficient condition; however, vitamin C deficiency displayed an antitumor effect in both GBM models analyzed.

Antioxidant effects of cultured wild ginseng root extracts on the male reproductive function of boars and guinea pigs

The main objective of this study was to investigate the effects of cultured wild ginseng root extracts (cWGRE) on the sperm of boars and the reproductive system of guinea pigs. Firstly, semen collected from boars (n=10) were incubated in 38°C for 1h with xanthine and xanthine oxidase to generate ROS. The cWGRE was added to the sperm culture system to test its antioxidant effect on the boar sperm. The amount of Reactive Oxygen Species (ROS) was measured by a chemiluminescence assay using luminol. The results indicated that the addition of cWGRE to boar sperm culture inhibited xanthine and xanthine oxidase-induced ROS concentrations. Treatment with cWGRE also had a positive effect on maintaining sperm motility. Effects of cWGRE administration on vitamin C-deficient guinea pigs were further investigated. Hartley guinea pigs (n=25) at 8 weeks of age were randomly divided into five groups. With the exception of the positive control group, each group was fed vitamin C-deficient feed for 21days (d). Respective groups were also orally administered cWGRE, ginseng extract, or mixed ginsenosides for 21 days. In comparison to the control group, oral administration of cWGRE reduced (P<0.05) amount of lipid peroxidation and increased (P<0.05) both glutathione peroxidase concentrations and the trolox equivalent antioxidant capacity. In addition, administration of cWGRE induced increases (P<0.05) in body weight, testosterone concentrations, and spermatid populations. The results of the present study support our hypothesis that cWGRE has positive effects on male reproductive functions via suppression of ROS production.

Molecular and cellular mechanisms of cigarette smoke-induced myocardial injury: prevention by vitamin C.

BackgroundCardiovascular disease (CVD) remains one of the major killers in modern society. One strong risk factor of CVD is cigarette smoking that causes myocardial injury and leads to the genesis of pathological cardiovascular events. However, the exact toxic component(s) of cigarette smoke (CS) and its molecular and cellular mechanisms for causing myocardial injury leading to heart damage and its prevention are largely unknown.Methodology/Principal FindingsUsing a guinea pig model, here we show that chronic exposure to CS produces myocardial injury that is prevented by vitamin C. Male guinea pigs were fed either vitamin C-deficient (0.5 mg/day) or vitamin C-sufficient (15 mg/day) diet and subjected to CS exposure from 5 Kentucky Research cigarettes (3R4F)/day (6 days/week) in a smoke chamber up to 8 weeks. Pair-fed sham controls were subjected to air exposure instead of CS exposure under similar conditions. Myocardial injury was produced in CS-exposed marginal vitamin C-deficient guinea pigs as evidenced by release of cardiac Troponin-T and I in the serum, oxidative stress, inflammation, apoptosis, thrombosis and collagen deposition in the myocardium. Treatment of rat cardiomyocyte cells (H9c2) in vitro and guinea pigs in vivo with p-benzoquinone (p-BQ) in amounts derived from CS revealed that p-BQ was a major factor responsible for CS-induced myocardial damage. A moderately large dose of vitamin C (15 mg/day) prevented CS/p-BQ-induced myocardial injury. Population based studies indicated that plasma vitamin C levels of smokers without disease were significantly lower (p = 0,0000) than that of non-smokers. Vitamin C levels of CS-related cardiovascular patients were further lower (p = 0.0000) than that of smokers without disease.Conclusions/SignificanceThe results indicate that dietary supplementation of vitamin C may be a novel and simple therapy for the prevention of pathological cardiovascular events in habitual smokers.

NAD(P)H: Quinone Oxidoreductase 1 Deficiency Conjoint with Marginal Vitamin C Deficiency Causes Cigarette Smoke Induced Myelodysplastic Syndromes

BackgroundThe etiology of myelodysplastic syndromes (MDS) is largely unknown. Exposure to cigarette smoke (CS) is reported to be associated with MDS risk. There is inconsistent evidence that deficiency of NAD(P)H-quinone: oxidoreductase 1 (NQO1) increases the risk of MDS. Earlier we had shown that CS induces toxicity only in marginal vitamin C-deficient guinea pigs but not in vitamin C-sufficient ones. We therefore considered that NQO1 deficiency along with marginal vitamin C deficiency might produce MDS in CS-exposed guinea pigs.Methodology and Principal FindingsHere we show that CS exposure for 21 days produces MDS in guinea pigs having deficiency of NQO1 (fed 3 mg dicoumarol/day) conjoint with marginal vitamin C deficiency (fed 0.5 mg vitamin C/day). As evidenced by morphology, histology and cytogenetics, MDS produced in the guinea pigs falls in the category of refractory cytopenia with unilineage dysplasia (RCUD): refractory anemia; refractory thrombocytopenia that is associated with ring sideroblasts, micromegakaryocytes, myeloid hyperplasia and aneuploidy. MDS is accompanied by increased CD34(+) cells and oxidative stress as shown by the formation of protein carbonyls and 8-oxodeoxyguanosine. Apoptosis precedes MDS but disappears later with marked decrease in the p53 protein. MDS produced in the guinea pigs are irreversible. MDS and all the aforesaid pathophysiological events do not occur in vitamin C-sufficient guinea pigs. However, after the onset of MDS vitamin C becomes ineffective.Conclusions and SignificanceCS exposure causes MDS in guinea pigs having deficiency of NQO1 conjoint with marginal vitamin C deficiency. The syndromes are not produced in singular deficiency of NQO1 or marginal vitamin C deficiency. Our results suggest that human smokers having NQO1 deficiency combined with marginal vitamin C deficiency are likely to be at high risk for developing MDS and that intake of a moderately large dose of vitamin C would prevent MDS.

Cerebral monoamine metabolism in guinea-pigs with ascorbic acid deficiency.

Guinea-pigs kept on a diet deficient in vitamin C showed, after 3 weeks, a marked decrease of ascorbic acid in brain and blood leucocytes as well as of the activity of alkaline phosphatase in blood plasma. Pair-fed animals did not exhibit these changes. The alpha-methyl-p-tyrosine (alpha MpT)-induced diminution of noradrenaline in the hypothalamus and the rest of the brain was attenuated in pair-fed animals, but restored in guinea-pigs deficient in ascorbic acid. The cerebral noradrenaline content (without administration of alpha MpT) showed a decrease in both pair-fed and ascorbic acid deficient animals. The noradrenaline of the heart exhibited a similar tendency. The alpha MpT-induced dopamine decrease in the striatum of ascorbic acid deficient animals was attenuated and the dopamine content (without alpha MpT administration) decreased. Pair-fed animals showed a similar tendency. The striatal concentration of homovanillic acid (HVA) was diminished in both pair-fed and ascorbic acid deficient guinea-pigs. The cerebral content of 5-hydroxyindoleacetic acid showed a decrease in pair-fed as well as in ascorbic acid deficient animals. It is concluded that ascorbic acid deficiency enhances the turnover of brain noradrenaline, whereas under-nutrition without ascorbic acid deficiency (pair-feeding) diminishes the turnover of cerebral noradrenaline, 5-hydroxytryptamine and striatal dopamine.

Reduction of dehydroerythorbic acid in vitamin C-deficient guinea pigs.

A reduction of dehydroerythorbic acid (DERA) to erythorbic acid (ERA) in vitamin C-deficient guinea pigs was evaluated and compared with that of dehydroascorbic acid (DASA). Thirty-six guinea pigs were fed with vitamin C-deficient diets for 18 days. On day 19, the guinea pigs were divided into four groups for the administration of 100 mg of DERA, ERA, ascorbic acid (ASA), or DASA every day. After 12 days of oral administration, the concentration of DERA, ERA, ASA, and DASA in the liver, adrenal, spleen, kidney, and plasma of guinea pigs was determined by HPLC. A recovery from scurvy was measured in terms of weight gain and serum alkaline phosphatase activity. All four groups showed similar recovery, indicating that the oral administration of relatively high concentrations of DERA reversed the effects of scurvy in vitamin C-deficient guinea pigs. In spite of DERA or DASA administration, ERA or ASA was mainly detected in the tissues. The reduction ratios of DEAR and DASA were similar (approximately 80%) in all tissues except spleen. These results suggest that both DASA and DERA are taken up and reduced to ASA or ERA in vivo.

Serum ascorbic acid and gallbladder disease prevalence among US adults: the Third National Health and Nutrition Examination Survey (NHANES III).

Ascorbic acid-deficient guinea pigs frequently develop gallstones, and ascorbic acid status may also affect the risk of gallbladder disease in humans. To examine the relationship of ascorbic acid, an antioxidant nutrient involved in cholesterol catabolism, to gallbladder disease, we analyzed data collected from a probability sample of US adults. Analyses of data from 7042 women and 6088 men enrolled in the Third National Health and Nutrition Examination Survey, 1988-1994, were performed. Multiple logistic regression models stratified by sex were examined, controlling for the effects of age, race, diet, body mass index, and other potential confounders. A total of 761 women (11%) and 235 men (4%) reported a history of clinical gallbladder disease (symptomatic gallstones or cholecystectomy). Of the 9650 participants without a history of clinical gallbladder disease or abdominal pain consistent with gallbladder disease, and with valid abdominal ultrasonography, 408 (8%) of 4863 women and 274 (6%) of 4787 men had asymptomatic gallstones. Serum ascorbic acid level was inversely related to prevalence of clinical and asymptomatic gallbladder disease among women, but not among men. Among women, each SD (27 micromol/L) increase in serum ascorbic acid level was independently associated with a 13% lower prevalence of clinical gallbladder disease (P = .006) and asymptomatic gallstones (P = .048). Ascorbic acid, which affects the catabolism of cholesterol to bile acids and, in turn, the development of gallbladder disease in experimental animals, may affect the risk of gallbladder disease among women.

Impaired inositol trisphosphate generation in carbachol-stimulated submandibular gland acinar cells from ascorbate deficient guinea pigs

Ascorbic acid (AA) is a ubiquitous component of animal tissues which is sequestered by cells achieving very high concentrations not only in the neurohormonal secreting cells of the hypothalamus and in endocrine cells of the pituitary and adrenal glands but also in the acinar cells of salivary glands. The ascorbate-dependent processes occurring in salivary glands are not clear. We hypothesized that AA might have some physiological role in the secretory processes of neurotransmitters in salivary glands. Using a guinea pig model of marginal ascorbate deficiency not complicated by anorexia with its attendant problems of reduced intakes of energy, protein, and other essential nutrients, we examined the specific role of vitamin C in stimulated salivary gland exocytosis in vitro. Ascorbate deficiency elicited prominent reductions in stimulated whole saliva flow rate (35.0 ± 6.0 compared with 80.0 ± 8.1 μL/min in control; P < 0.025). The ascorbate concentration in the deficient gland was only 4.4% of the control level ( P < 0.002). Muscarinic-cholinergic receptor stimulation of dispersed submandibular gland acinar cells with carbachol (20 μM) yielded a mean IP 3 generation (percent of unstimulated sample) of 236 ± 32 in the control animals, which was significantly ( P < 0.025) higher than the mean of 120 ± 11 for the deficient guinea pigs. In ascorbate-deficient guinea pigs refed an adequate vitamin C diet for 2 to 7 days (mean of 5 days), mean stimulated IP 3 generation (188%) showed marked recovery. An equally prominent impairment in [Ca 2+]i elevation was associated with reduced IP 3 production in ascorbate deficiency (292 ± 31 nM in deficient animals versus 578 ± 36 for the control group). The resting level of [Ca 2+]i was nonsignificantly higher in the control than in the malnourished group. Our data supported the conclusion that impairment in the muscarinic-cholinergic transmembrane signaling cascade system, particularly the metabolism of phosphatidylinositol phosphates, could explain the hyposalivation in vitamin C-deficient guinea pigs. The difficulty of extrapolating findings from experimental animals to humans notwithstanding, it should be noted that most of the seemingly unrelated factors/conditions implicated in the genesis of xerostomia (dry mouth) in the human promote increased requirement for and/or tissue depletion of vitamin C.

Ozone-Induced Pulmonary Functional, Pathological, and Biochemical Changes in Normal and Vitamin C-Deficient Guinea Pigs

Ozone-Induced Pulmonary Functional, Pathological, and Biochemical Changes in Normal and Vitamin C-Deficient Guinea Pigs. Kodavanti, U. P., Hatch, G. E., Starcher, B., Giri, S. N., Winsett, D., and Costa, D. L. (1995). Fundam. Appl. Toxicol. 24, 154-164.Since Vitamin C (ascorbate, AH2) is an important airway antioxidant and is an essential component of tissue repair, and since acute (4 hr) O3 toxicity is enhanced by AH2 deficiency, we hypothesized that longer-term O3 effects might also be increased. Female Hartley guinea pigs (260-330 g) were fed either and AH2-sufficient or an AH2-deficient diet 1 week prior to exposure, and were maintained on their respective diets during 1 week of continuous exposure to O3 (0, 0.2, 0.4, and 0.8 ppm, 23 hr/day), and during 1 week postexposure recovery in clean air. The AH2-deficient diet caused lung AH2 to drop to about 30% of control in 1 week, and to below 10% by the end of exposure and recovery. Body weight gains during exposure were decreased in the 0.8 ppm O3 group, while the AH2 deficiency began to affect body weights only during recovery. O3 caused a concentration-dependent decrease in total lung capacity, vital capacity, carbon monoxide diffusing capacity, nitrogen washout, and static compliance, while increasing forced expiratory flow rates and residual or end-expiratory volume (suggestive of pulmonary gas-trapping). The lung/body weight ratio and fixed lung displacement volume were also increased in O3-exposed animals. Lung pathology consisted of mononuclear cell and neutrophil infiltration, airway as well as alveolar epithelial cell hyperplasia, and general decrease in epithelial cell cytoplasm. Thickening of the interstitium and an apparent increase in collagen staining were seen at the terminal bronchiolar regions. Some of these effects were marginally exacerbated in AH2-deficient guinea pigs. One week postexposure to air reversed all O3-induced abnormalities, irrespective of AH3 deficiency. Whole lung hydroxyproline and desmosine were not changed at any time by either O3 or AH2 deficiency. Measurement of lung prolyl hydroxylase activity suggested that AH2 deficiency as well as O3 exposure may have increased the tissue levels of this enzyme. The lack of a significant increase in toxicity with the longer-term exposure scenario suggests that AH2 has minimal influence on other compensatory mechanisms developed over time.

Ozone-Induced Pulmonary Functional, Pathological, and Biochemical Changes in Normal and Vitamin C-Deficient Guinea Pigs

Ozone-Induced Pulmonary Functional, Pathological, and Biochemical Changes in Normal and Vitamin C-Deficient Guinea Pigs

Circulating insulin-like growth factor binding proteins (IGFBPs) 1 and 2 induced in vitamin C-deficient or fasted guinea pigs inhibit IGF-I action in cultured cells.

Collagen gene expression and proteoglycan synthesis are decreased in vitamin C-deficient guinea pigs losing weight and in fasted guinea pigs receiving ascorbate. Sera from such guinea pigs contain an insulin-like growth factor (IGF)-I-reversible inhibitor of collagen, proteoglycan and DNA synthesis and elevated levels of 29 and 35-kDa IGF binding proteins (IGFBPs). We now have identified the induced proteins as IGFBPs 1 and 2 and investigated their role as inhibitors. Guinea pig sera were treated with antibodies to IGFBPs 1 and 2 and antibody-IGFBP complexes were removed by passage through a Protein A-Sepharose column. Inhibitor content of fasted and scorbutic sera, and Protein A pass-through fractions derived from them, was assessed by their level of stimulation of DNA and collagen synthesis in 3T3 cells, compared to analogously treated normal guinea pig serum. Removal of IGFBP-1 from scorbutic serum reversed inhibition of collagen and DNA synthesis by more than half but removal of IGFBP-2 was less effective. Removal of both IGFBPs reversed inhibition almost completely. Similar results were obtained with fasted guinea pig serum. Conversely, purified rat IGFBPs 1 and 2 inhibited DNA and collagen synthesis in cells cultured in normal guinea pig serum or IGF-I-stimulated DNA synthesis, with IGFBP-1 being more potent. Thus, IGFBP-1 and, to a lesser extent IGFBP-2, cause inhibition of IGF-I action by sera from fasted and scorbutic guinea pigs and may inhibit collagen gene expression in vivo.

Ascorbic acid and cholesterol gallstones

Decreased activity of cholesterol 7 α-hydroxylase, the rate-limiting enzyme in the catabolism of cholesterol to bile acids, is known to result in increased biliary cholesterol concentration and supersaturation of bile. Supersaturation of bile by cholesterol is a necessary condition for cholesterol gallstone formation. In guinea pigs, the hepatic concentration of ascorbic acid affects the catabolism of cholesterol: hypovitaminosis C reduces cholesterol 7 α-hydroxylase activity. Cholesterol gallstones are frequently found in ascorbic acid-deficient guinea pigs. Risk factors for cholesterol gallstones in humans include obesity, aging, estrogen treatment, pregnancy and diabetes. Plasma ascorbic acid levels are reduced in these groups. Vegetarian diets, which typically have high ascorbic acid contents, protect against gallstones. Since ascorbic acid effects the rate-limiting step in the catabolism of cholesterol in the guinea pig and many human risk groups for cholesterol gallstones are associated with reduced ascorbic acid levels, ascorbic acid may play a contributory role in human gallbladder disease.

Effect of vitamin C on sorbitol in the lens of guinea-pigs made diabetic with streptozotocin.

Marginally vitamin C-deficient guinea-pigs treated with the diabetogenic agent streptozotocin were compared with those liberally supplied with vitamin C, for functional indices of vitamin C status, particularly in the eye lens. Weanling male Dunkin-Hartley guinea-pigs were fed on diets with 0.1 g vitamin C/kg (marginally deficient), or 5 g/kg (liberally supplied), and some received intraperitoneal streptozotocin (two doses of 150 mg/kg body-weight). About half the streptozotocin-treated animals had high urinary glucose following an oral glucose dose; these animals also grew more slowly than the others. At 4 months after streptozotocin the animals were killed for measurement of tissue vitamin C, glucose and sorbitol. Streptozotocin moderately increased the concentration of glucose in plasma, lens and aqueous humour. Lens sorbitol levels increased only in the group exposed to streptozotocin plus marginal vitamin C. There was a significant (P less than 0.02) positive correlation between urinary glucose and lens sorbitol levels overall. Liberal vitamin C intake may thus counteract the effect of streptozotocin diabetes on lens sorbitol, suggesting a new function of vitamin C, possibly related to cataractogenesis and to the biochemical lesions associated with diabetes.

Ascorbic acid deficiency affects the metabolism of cytosolic ferritin but not lipid-associated ferritin in livers of guinea pigs

Two physicochemically and metabolically separate pools of ferritin, namely cytosolic ferritin and lipid-associated ferritin, are present in the livers of guinea pigs. In this paper we establish that the iron content of cytosolic ferritin is dependent on and linearly related to ascorbic acid concentration, whereas changes in concentration of this vitamin do not affect the iron content of lipid-associated ferritin. In livers of ascorbic acid-deficient guinea pigs both synthesis and degradation of cytosolic ferritin are diminished equally. Consequently cytosolic ferritin is metabolized more slowly without changes in its pool size. In contrast with cytosolic ferritin, the metabolism of lipid-associated ferritin is unaffected by ascorbic acid deficiency. The differential effects of ascorbic acid deficiency on the physicochemical characteristics as well as on the metabolism of cytosolic ferritin and lipid-associated ferritin suggest that the two forms of ferritin have different functional roles.

Similar hormonal changes in sera from scorbutic and fasted (vitamin C-supplemented) guinea pigs, including decreased IGF-I and appearance of an IGF-I reversible mitogenic inhibitor.

We previously proposed that the decreased rates of synthesis of collagen and proteoglycans in vitamin C-deficient guinea pigs were unrelated to the role of ascorbate in proline hydroxylation but might result from modulation of hormones known to change during fasting. In the present studies, we found that sera from guinea pigs on an ascorbate-free diet for 24-28 days or from those fasted for 4 days, with vitamin C supplementation, showed similar changes in the concentrations of several hormones. EGF and IGF-II concentrations were unchanged, but cortisol was increased 3-5 times and growth hormone was increased to approximately twice normal levels. Thyroxine and IGF-I concentrations were decreased to 40% and 25-33% of normal levels, respectively. The decrease in serum IGF-I must occur by a growth hormone-independent pathway. The extent of changes in hormone concentrations in sera from ascorbate-deficient guinea pigs was correlated with the extent of weight loss. Sera from scorbutic and fasted guinea pigs failed to stimulate DNA synthesis in quiescent BALB 3T3 cells in the presence of saturating concentrations of EGF and PDGF. Addition of experimental sera to normal serum showed that lack of mitogenic activity was due to the presence of an inhibitor. Inhibition was not related to IGF-I concentrations in the sera, although it was reversed by the addition of IGF-I to sera from scorbutic or fasted animals. These results support our proposed model and suggest that IGF-I, as well as an inhibitor of its activity, plays a role in the regulation of growth by vitamin C and other nutrients.

Effects of methamphetamine on central monoaminergic systems in normal and ascorbic acid-deficient guinea pigs

Repeated injections (s.c.) of methamphetamine (METH) were administered to normal and ascorbic acid-deficient (scorbutic) guinea pigs to assess a potential role for ascorbic acid in the METH-induced effects in central monoaminergic systems. The ascorbic acid-deficient condition differentially influenced the METH-induced responses of dopaminergic and serotonergic variables in the striatum: drug-induced changes in dopaminergic variables were identical in normal and scorbutic animals; METH-induced decreases in serotonergic variables [tryptophan hydroxylase activity, serotonin (5-HT) and 5-hydroxyindoleacetic acid concentrations], however, were prevented in scorbutic animals. The scorbutic condition did not alter significantly the distribution of METH in the brain, nor were striatal concentrations of dopamine (DA) or 5-HT affected. In vitro, ascorbic acid increased significantly DA-mediated [ 3H]5-HT release from striatal slices, thus suggesting a potential role for ascorbate in DA-mediated actions of METH on serotonergic systems. Although supplemental ascorbate failed to restore the METH-induced serotonergic effects in scorbutic guinea pigs, these data suggest that, in a normal animal, the effects of multiple injections of METH, on serotonergic systems, involve ascorbic acid.

The pathological study of enterosiderosis in guinea pigs

Enterosiderosis in both SPF Hartley guinea pigs and vitamin C-deficient animals of the same strain were studied by light and electron microscopy. Enterosiderosis was detected in all animals in the present study. Macrophages, inclosing yellowish-brown pigments and erythrocytes, appeared in the lamina propria of the intestinal mucosa, mainly in the cecum. These pigments in the macrophages were positive for Prussian blue, PAS and the Nile blue reaction. Residual bodies containing highly electron-dense ferritin-like particles, lipofuscin granules and debris of phagocytized erythrocytes were found by electron microscopy in the macrophages. In vitamin C-deficient guinea pigs, the number of macrophages, including the same above pigments, appeared in the lamina propria of the intestinal mucosa, and there was severe enterosiderosis. In the absorptive cells of the intestinal mucous membrane, granules positive for the Prussian blue reaction appeared only in the duodenum. These findings strongly suggest that the pigments in the macrophages in enterosiderosis of the guinea pigs were mixtures of iron and lipofuscin granules and that the iron is derived from erythrocytes phagocytized by macrophages in the lamina propria, but not from iron absorbed by epithelial cells.

Modulation of the Flavin-Containing Monooxygenase in Guinea Pigs by Ascorbic Acid and Food Restriction

Modulation of the flavin-containing monooxygenase (FMO) by varying the ascorbic acid and food intake was investigated. Hepatic activity of the FMO in ascorbic acid-deficient guinea pigs fed a restricted amount of diet, which resulted in a 10–15% body weight loss, was 17% of that in animals fed restricted amounts of the adequate diet. FMO hepatic activity in ascorbic acid-supplemented guinea pigs on a food-restricted regimen was 176% of that found in animals fed the adequate diet ad libitum. This increase in activity was not related to stress. Alteration in the activity of this important drug-metabolizing enzyme system by a combination of ascorbic acid deficiency and reduced food intake could potentially alter the rate of metabolism of a great variety of pharmaceutical drugs and environmental chemicals.

Ascorbic acid-deficient condition alters central effects of methamphetamine

Effects of multiple doses of methamphetamine (METH) were examined in normal and ascorbic acid-deficient (scorbutic) guinea pigs. METH-induced decreases of striatal serotonin concentrations were completely antagonized in scorbutic animals. Elevations of nigral substance P-like immunoreactivity also differed significantly in METH-treated scorbutic compared to METH-treated normal animals. Various lines of evidence indicate that dopamine is an essential mediator of METH-induced effects in both serotonergic and substance P systems in the brain areas examined; however, results from the present study indicate that, along with dopamine, ascorbic acid also plays a role in mediating the effects of METH in the central nervous system.

Ascorbic acid deficiency and the flavin-containing monooxygenase

Activity of the flavin-containing monooxygenase (FMO) was reduced significantly in ascorbic acid deficient guinea pigs. Reduction in oxidation of dimethylaniline (DMA) and of thiobenzamide was associated with a decrease in the activity of the FMO. In both ascorbate supplemented and deficient guinea pig hepatic 12,000 g supernatant fractions, SKF-525A and n-octylamine did not inhibit DMA N-oxidation. Phenobarbital pretreatment did not increase the rate of N-oxidation of DMA. In addition, hepatic supernatant fractions thermally treated at 50° were unable to N-oxidize DMA, but 80% of the cytochrome P-450 activity was retained. Also, N-oxidation of DMA was reduced by 53% at pH 7.0, while oxidation of cytochrome P-450 specific substrates was inhibited by only 19%. Kinetic studies of DMA N-oxidation indicate no significant change in the apparent K m in ascorbate supplemented or deficient animals. The in vitro addition of ascorbic acid had no effect on the activity of the FMO. The toxicological implications of the reduction in FMO activity in ascorbic acid deficiency are discussed.