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© 2005 The American Society for Nutritional Sciences J. Nutr. 135:2411-2416, October 2005

Nutrient Metabolism

Endotoxin Increases Ascorbate Recycling and Concentration in Mouse Liver1

Shiu-Ming Kuo, Chee-Ho Tan, Magdalena Dragan and John X. Wilson2

Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY

2To whom correspondence should be addressed. E-mail: jxwilson{at}buffalo.edu.


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Sublethal exposure to Escherichia coli endotoxin [lipopolysaccharide (LPS)] attenuates the lethal effects of subsequent insults associated with oxidative stress, such as higher LPS dose, septic peritonitis, and ischemia. Because administration of the antioxidant ascorbate protects against these same insults and injection of dehydroascorbic acid (DHAA) protects against ischemia, the hypothesis that sublethal LPS increases endogenous ascorbate concentration and recycling (i.e., synthesis from DHAA) was tested. Injection of LPS [5 x 106 endotoxin units/kg body weight, i.p.] in mice caused a temporary inhibition of food intake, which was significant by 20 h and recovered within 3 d. LPS increased ascorbate concentration in adrenal gland, heart, kidney, and liver. LPS had similar effects in wild-type and Slc23a2+/– mice despite the latter’s deficiency in the ascorbate transporter SVCT2. In liver, the ascorbate response to LPS was not accompanied by change in glutathione concentration. LPS decreased gulonolactone oxidase activity, which is rate-limiting for de novo synthesis of ascorbate from glucose, but increased the rate of DHAA reduction to ascorbate. In conclusion, sublethal endotoxin increases ascorbate recycling in liver and ascorbate concentration in liver, adrenal gland, heart, and kidney. The enhanced rate of ascorbate production from DHAA may protect these organs against the reactive oxygen species produced by subsequent, potentially lethal challenges.

KEY WORDS: • ascorbate • dehydroascorbic acid • lipopolysaccharide • gulonolactone oxidase • transport

Lipopolysaccharide (LPS)3 is a cell wall constituent of gram-negative bacteria that is detectable in the plasma of septic patients (1). High plasma levels of LPS are associated with excess risk of morbidity and mortality (2). Paradoxically, injection of LPS at sublethal doses attenuates the lethal effects of subsequent challenges by high-dose LPS, septic peritonitis, and ischemia, all of which are insults associated with oxidative stress (3–6). Multiple lines of evidence suggest that the delayed protection conferred by LPS is attributable in part to enhanced antioxidant defense. For instance, pretreatment with low-dose LPS decreases the hepatic production of reactive oxygen species (ROS) elicited by high-dose LPS (7). Injection (i.p.) of sublethal LPS increases ROS in liver within 1 h (8) but subsequently increases the activities of antioxidant enzymes (glutathione peroxidase, superoxide dismutase) and decreases lipid peroxidation in this organ (9). In heart, too, sublethal LPS triggers lipid peroxidation within 1 h, but the oxidative stress then declines and antioxidant enzyme activities (catalase, glutathione peroxidase, superoxide dismutase) rise above initial levels within 12–24 h (10). These results are consistent with the hypothesis that LPS injection triggers oxidative stress that is followed by augmentation of antioxidant defenses.

Ascorbate is a low-molecular-weight antioxidant that protects against the same insults as does LPS-induced tolerance (11–15). At the cellular level, ascorbate mitigates the ROS production triggered by LPS and thereby prevents the induction of nitric oxide synthase and excessive production of nitric oxide that worsens oxidative stress in hepatocytes, endothelial cells, and brain astrocytes (14,16–18). Additionally, ascorbate acts through redox-sensitive signaling pathways to induce tolerance in the dendritic cells of the immune system (19). Although most evidence is based on administering exogenous vitamin C, endogenous ascorbate was also shown to protect rodent hepatocytes from lethal oxidative stress (20).

The ascorbate concentrations in cells may be increased through several physiological mechanisms. Enterocytes absorb ascorbate and its oxidation product, dehydroascorbic acid (DHAA), from ingested food (21). The hepatocytes of most animal species (but not humans) synthesize ascorbate de novo from glucose, through a pathway in which gulonolactone oxidase is the rate-limiting enzyme (22). Ascorbate may be exported from these cells to the extracellular fluid (23) and then taken up by other cells that express the ascorbate transporters SVCT1 and SVCT2 (21). Reduction of DHAA to ascorbate (i.e., ascorbate recycling) also increases intracellular ascorbate concentration and protects against ischemia-reperfusion injury in vivo (24,25). Ascorbate recycling may be stimulated by insults that are associated with oxidative stress, such as smoking (26) and administration of the glutathione synthesis inhibitor buthionine sulfoximine (27). Therefore, the present experiments were designed to test the hypothesis that ascorbate recycling and concentration are increased by LPS.


   MATERIALS AND METHODS
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 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
    Mice. The study protocol was approved by the Institutional Animal Care and Use Committee of the University at Buffalo. Male mice were used from a colony of heterozygous SVCT2 knockout (Slc23a2+/–) mice (28) that was maintained in the specific pathogen-free facility of the University at Buffalo. Slc23a2+/–mice are a valuable model because they survive to adulthood, unlike the homozygous Slc23a2–/–mice that die shortly after birth. Genotyping was performed according to the procedure described previously (29). The mice were allowed free access to water and a commercial diet (PicoLab Mouse Chow 20). The proximate composition of this diet as stated by the manufacturer was 20.5% protein, 9.5% fat, and 2.7% crude fiber. It did not contain ascorbic acid; therefore, none was absorbed intestinally. The mice were used for experiments at 11–12 wk of age. Starting 1 wk before the experiments, the mice were housed individually.

    Experimental protocol. The first of the 3 studies with these mice determined whether i.p. injection of LPS [from Escherichia coli 0127:B8, catalog number L3880, 106 endotoxin units (EU)/mg, Sigma-Aldrich], at doses of 0.2 x 106 and 5 x 106 EU/kg body weight, altered food intake and survival. Wild-type mice were administered either dose 1 h before the 12-h dark period. Food intake and survival were monitored at 20- to 24-h intervals, from 24 h before to 68 h after injection.

The second study examined the effects of LPS and partial SVCT2 deficiency on ascorbate, glutathione, and gulonolactone oxidase at 20 h postinjection. Wild-type and SVCT2-deficient (Slc23a2+/–) mice were administered an i.p. injection of either LPS (5 x 106 EU/kg) or vehicle (sterile PBS, 5 mL/kg) 1 h before the dark period. The mice were killed by cervical dislocation 20 h postinjection. They were immediately decapitated and blood was drained from the body into heparinized vials for 20 s; the blood was centrifuged at 1400 x g for 10 min to separate the plasma. Liver, heart, spleen, brain, adrenal gland, kidney, and hind limb skeletal muscle were also collected, so that the study included organs that express predominantly SVCT1 or SVCT2 (28–31). The heart was blotted to remove blood from its chambers. Some liver samples were used immediately for determination of gulonolactone oxidase activity. Liver samples for RNA analysis were placed in RNAlater (Ambion). The plasma and remaining tissue samples were frozen in liquid nitrogen and then transferred to a –80°C freezer for storage until analysis for ascorbate and glutathione.

The third study determined the time course of changes in organ ascorbate concentration and the effect of LPS on the hepatic ascorbate recycling rate. Wild-type mice were randomly assigned to be injected with LPS (5 x 106 EU/kg) or vehicle (sterile PBS, 5 mL/kg) 1 h before the dark period. The mice were killed by cervical dislocation at 1, 3, 6, or 20 h postinjection and liver, kidney, and spleen were collected. From each liver collected at 20 h postinjection, a portion was used for determination of ascorbate recycling rate. The remaining samples were frozen in liquid nitrogen and then transferred to a –80°C freezer for storage until analysis.

    Biochemical analysis. Ascorbate was extracted from plasma and tissues and its concentration was measured by HPLC with electrochemical detection, according to a procedure we described previously (11). Hepatic ascorbate content was calculated as the product of the ascorbate concentration times the organ weight. The concentrations of total glutathione (i.e., reduced glutathione and glutathione disulfide combined) and glutathione disulfide were measured by enzyme-linked spectrophotometric assay (32,33) in livers that had been stored at –80°C for up to 2 wk. Preliminary studies showed that glutathione concentration and redox state were maintained under these storage conditions. The concentration of reduced glutathione was calculated as the difference between the levels of total glutathione and glutathione disulfide.

Gulonolactone oxidase mRNA expression was determined by real-time RT-PCR and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA expression, as described previously (29). Gulonolactone oxidase activity was measured by incubating liver homogenate in PBS containing L-gulonolactone (5 mmol/L) or vehicle for 30 min at 37°C (29). The reaction was terminated by rapid freezing and the ascorbate was extracted and assayed by HPLC with electrochemical detection. For each liver, the activity was calculated as the difference between the rates of ascorbate production by the incubate that received L-gulonolactone and the one that did not.

The ascorbate recycling rate was measured by incubating liver homogenate with DHAA (1 mmol/L) in PBS for 30 min at 37°C and then assaying the ascorbate concentration by HPLC. DHAA was dissolved immediately before incubation and its contamination by ascorbate was 0.1%. To calculate the recycling rate, the amounts of ascorbate measured in the DHAA solution and in homogenates incubated without DHAA were subtracted from the amount of ascorbate measured in homogenates incubated with DHAA. The rate for each liver was normalized to the concentration of total protein that was measured by a modified Lowry method.

    Statistical analysis. Data are presented as means ± SEM. The homogeneity of variance in the untransformed or cubic transformed data was evaluated by Levene’s test. If homogeneity was observed in the variance, then the differences between means were evaluated using 2-way ANOVA, 1-way ANOVA with repeated measures, and the Tukey-Kramer multiple comparison test, or the 2-tailed t test for pooled samples. If heterogeneity was observed in the variance, then the data were evaluated using the nonparametric Mann-Whitney U test. Differences with P < 0.05 were considered significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
LPS at a dose of 5 x 106 EU/kg led to a temporary inhibition of food intake, which was significant at 20 h and recovered at 68 h postinjection, whereas food intake remained constant after the lower dose of LPS (0.2 x 106 EU/kg) (Fig. 1). Neither dose of LPS affected survival, which was 100% at 68 h postinjection.



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  		FIGURE 1 Food intake in wild-type mice from 24 h before to 68 h after i.p. injection at time zero of LPS 0.2 x 106 EU/kg (Panel A) and 5 x 106 EU/kg (Panel B). Values are means ± SEM, n = 4–7. Data were evaluated using either 1-way ANOVA with repeated measures and the Tukey-Kramer multiple comparisons test (Panel A) or the Mann-Whitney U test (Panel B). Within each panel, means without a common letter differ, P < 0.5.

 
The ascorbate concentrations of plasma and organs that express predominantly the SVCT1 isoform of ascorbate transporter (kidney, liver) are presented in Table 1. Partial SVCT2 deficiency (Slc23a2+/– genotype) did not change the ascorbate concentration in plasma or kidney. Although partial SVCT2 deficiency increased hepatic ascorbate concentration (Table 1), the livers of SVCT2-deficient and wild-type mice did not differ in ascorbate content (2.20 ± 0.18 and 1.97 ± 0.14 µmol, respectively), organ weight (885 ± 23 and 900 ± 27 mg), the gulonolactone oxidase:GAPDH mRNA expression ratio (0.722 ± 0.206 and 0.716 ± 0.239), or gulonolactone oxidase activity (70.8 ± 8.8 nmol ascorbate/mg protein and 65.4 ± 3.5 nmol ascorbate/mg protein). The ascorbate concentrations in organs that express predominantly the SVCT2 isoform of ascorbate transporter (adrenal gland, brain, heart, skeletal muscle, and spleen) are presented in Table 2. SVCT2 deficiency was associated with decreased ascorbate concentrations in adrenal gland, brain, heart, and skeletal muscle.


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  		TABLE 1 Ascorbate concentrations in plasma and predominantly SVCT1-expressing organs of mice 20 h after i.p. injection of LPS (5 x 106 EU/kg body weight) or vehicle (5 mL PBS/kg)1

 

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  		TABLE 2 Ascorbate concentrations in predominantly SVCT2-expressing organs of mice 20 h after i.p. injection of LPS (5 x 106 EU/kg) or vehicle (5 mL PBS/kg)1

 
The effects of LPS (5 x 106 EU/kg) on ascorbate levels were examined at 20 h postinjection in Slc23a2+/– and wild-type mice. No significant interactions were found between genotype and LPS treatment. LPS did not change plasma or renal ascorbate concentration at this time point (Table 1), but it increased hepatic ascorbate concentration by 38% (Table 1) and hepatic ascorbate content by 45% (2.44 ± 0.15 µmol for LPS and 1.68 ± 0.06 µmol for vehicle, n = 12, P = 0.0001). LPS also increased ascorbate concentrations in adrenal gland and heart by 26 and 42%, respectively, but did not change the concentrations in brain, skeletal muscle, or spleen at 20 h (Table 2).

Glutathione was measured in liver and spleen of Slc23a2+/– and wild-type mice at 20 h postinjection, to compare this low-molecular-weight antioxidant to ascorbate. Neither partial SVCT2 deficiency nor LPS treatment altered the concentrations of total or reduced glutathione in these organs (Table 3). Thus the effects of SVCT2 deficiency and LPS were different for glutathione than for ascorbate.


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  		TABLE 3 Total glutathione and reduced glutathione concentrations in liver and spleen of mice 20 h after i.p. injection of LPS (5 x 106 EU/kg) or vehicle (5 mL PBS/kg)1

 
Time-course experiments with wild-type mice showed that LPS (5 x 106 EU/kg) elicited a transient rise in the ascorbate concentration in kidney that was significant at 3 and 6 h (increases of 20 and 25%, respectively) but dissipated by 20 h postinjection (Fig. 2). In these experiments, LPS also elevated the ascorbate concentration in liver at 3 h (40%, P = 0.0001) and 6 h (43%, P = 0.0001), and tended to increase it 17% at 20 h (P = 0.05, Fig. 2). In spleen, LPS decreased ascorbate concentration transiently at 3 h (22%, P = 0.0001) and 6 h (21%, P = 0.0002) postinjection (Fig. 2).



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  		FIGURE 2 Time course of ascorbate concentrations in liver (Panel A), kidney (Panel B), and spleen (Panel C) of wild-type mice after i.p. injection of LPS (5 x 106 EU/kg) or vehicle (5 mL PBS/kg). Values are means ± SEM, n = 6. In each panel, the effect of time was evaluated in the vehicle control group by 1-way ANOVA and the Tukey-Kramer multiple comparisons test. Means without a common letter differ, P < 0.05. To assess the effects of LPS, data at each time point were evaluated using the 2-tailed t test for pooled samples. Asterisks indicate different from vehicle at that time: *P < 0.05, **P < 0.001.

 
The effects of LPS on gulonolactone oxidase activity and ascorbate recycling in the livers of wild-type mice were determined at 20 h postinjection. LPS decreased gulonolactone oxidase activity to 51 ± 3 nmol ascorbate/(mg protein · 30 min), which was significantly lower than the vehicle-injected control value of 69 ± 5 nmol ascorbate/(mg protein · 30 min) (n = 6, P = 0.03). In contrast, LPS stimulated ascorbate recycling because the rates were 107 ± 4 nmol ascorbate/(mg protein · 30 min) in the LPS-injected group and 90 ± 5 nmol ascorbate/(mg protein · 30 min) in the vehicle-injected group (n = 6, P = 0.02).


   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
In the present model, the ascorbate concentrations in adrenal gland, heart, kidney, and liver were increased by LPS (5 x 106 EU/kg, i.p.). This dose was sublethal, as indicated by the reversibility of its initial inhibition of food intake and the 100% survival in mice at 68 h postinjection. It is unlikely that the drop in food intake caused the rise in ascorbate concentrations because previous studies showed that food restriction decreased ascorbate concentrations in adrenal gland and liver (34,35). We did not find evidence that the rise in ascorbate concentration above control was a rebound or overshoot phenomenon triggered by depletion of ascorbate because time-course experiments showed that ascorbate levels in liver and kidney were unchanged at 1 h and elevated at 3 h post-LPS compared with vehicle control. Although the ascorbate concentration in spleen did fall after sublethal LPS exposure, this change was short-lived and did not lead to an overshoot. Higher doses of LPS depleted ascorbate from the heart and lung of guinea pigs, but this may have been a consequence of lethal endotoxemia (36,37).

There was a stimulatory effect of partial SVCT2 deficiency on hepatic ascorbate concentration in the present experiments but not in an earlier study (28). However, the present and earlier results (28) both supported an important role for SVCT2 in organs that express predominantly this transporter isoform, by showing that ascorbate concentrations in adrenal gland, brain, heart, and skeletal muscle were lower for Slc23a2+/– than for wild-type mice. LPS may act independently of SVCT2 to raise ascorbate concentration in adrenal gland, heart, kidney, and liver because no interaction between LPS and SVCT2 deficiency was observed. Even in organs for which SVCT2 is the only known transporter mediating direct uptake of ascorbate, namely, the adrenal gland (30) and heart (31), SVCT2 deficiency did not alter the response to LPS.

Ascorbate recycling may be an important pathway for accumulating ascorbate in the adult brain, heart, and liver, because exogenous DHAA was more effective than exogenous ascorbic acid for rapidly conferring protection against ischemia-reperfusion injury in these organs (24,25,38). However, the brain differed from heart and liver in its endogenous ascorbate response to systemic LPS. The dose of LPS administered in the present experiments did not alter cerebral ascorbate concentration, possibly because of the blood-brain barrier. Indeed, when low doses of LPS are injected by the i.p. route into normal rodents, the endotoxin may not cross the blood-brain barrier (39).

The liver is an important organ for ascorbate synthesis and storage; it contains approximately one third of the body’s ascorbate content (40). Hepatocytes synthesize ascorbate de novo from glucose (22). However, it is unlikely that de novo synthesis accounted for the elevated ascorbate concentration and content in the livers of LPS-injected mice because we found that gulonolactone oxidase activity was diminished 20 h postinjection. Although the time course of this change in the hepatic enzyme was not determined, it may have resulted from the decreased food intake induced by LPS because a previous study found that food restriction lowered gulonolactone oxidase activity (34).

Ascorbate recycling is an alterative pathway by which the liver produces ascorbate for local use and export (23). LPS increased the activity of the facilitative glucose transporter isoform mediating DHAA uptake (55 kDa isoform of GLUT1) in hepatocytes (41). Once inside the cells, DHAA can be reduced to ascorbate by glutathione directly or by enzymes that transfer reducing equivalents from glutathione and NAD(P)H. It is not likely that LPS accelerated the reduction of DHAA through increases in the supply of glutathione because there was no change in the concentrations of total or reduced glutathione in liver 20 h postinjection. It is possible that LPS altered glutathione levels at earlier time points that were not examined. However, the inference that DHAA reduction rate can increase independently of glutathione is consistent with previous reports that accelerated rates of ascorbate recycling in erythrocytes and skeletal muscle cells were induced by stressors that did not raise intracellular glutathione levels (26,27). In contrast, thioredoxin, thioredoxin reductase, and protein disulfide isomerase are important catalysts of intracellular DHAA reduction (21,42,43), and their expression levels were elevated by sublethal doses of LPS (42–44). Taken together, the increases in glucose transporter 1 (41), DHAA-reducing enzymes (44–46), and the rate of DHAA reduction (present study) are consistent with the hypothesis that LPS stimulates ascorbate recycling.

In conclusion, sublethal endotoxin increases ascorbate recycling in liver and ascorbate concentration in liver, kidney, adrenal gland, and heart. The enhanced rate of ascorbate production from DHAA may protect these organs against the ROS produced by subsequent, potentially lethal challenges.


   ACKNOWLEDGMENTS
 
The excellent technical assistance of Ewa Jaworski, Marlene MacLean, James Boyer, and Lana Burl is gratefully acknowledged.


   FOOTNOTES
 
1 Supported by grants from the National Institutes of Health (R01KD54728 to S.M.K.) and the University at Buffalo Foundation (to J.X.W.). Back

3 Abbreviations used: DHAA, dehydroascorbic acid; EU, endotoxin units; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LPS, lipopolysaccharide. Back

Manuscript received 27 June 2005. Initial review completed 14 July 2005. Revision accepted 28 July 2005.


   LITERATURE CITED
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 LITERATURE CITED
 

1. Venet C, Zeni F, Viallon A, Ross A, Pain P, Gery P, Page D, Vermesch R, Bertrand M, et al. Endotoxaemia in patients with severe sepsis or septic shock. Intensive Care Med. 2000;26:538-544.[Medline]

2. Opal SM. The clinical relevance of endotoxin in human sepsis: a critical analysis. J Endotoxin Res. 2002;8:473-476.[Medline]

3. Barroso-Aranda J, Schmid-Schonbein GW, Zweifach BW, Mathison JC. Polymorphonuclear neutrophil contribution to induced tolerance to bacterial lipopolysaccharide. Circ Res. 1991;69:1196-1206.[Abstract]

4. Cavaillon JM, Adrie C, Fitting C, Adib-Conquy M. Endotoxin tolerance: is there a clinical relevance?. J Endotoxin Res. 2003;9:101-107.[Medline]

5. Ebisawa Y, Kono T, Yoneda M, Asama T, Chisato N, Sugawara M, Ishikawa K, Iwamoto J, Ayabe T, et al. Direct evidence that induced nitric oxide production in hepatocytes prevents liver damage during lipopolysaccharide tolerance in rats. J Surg Res. 2004;118:183-189.[Medline]

6. Echtenacher B, Mannel DN. Requirement of TNF and TNF receptor type 2 for LPS-induced protection from lethal septic peritonitis. J Endotoxin Res. 2002;8:365-369.[Medline]

7. Bautista AP, Spitzer JJ. Acute endotoxin tolerance downregulates superoxide anion release by the perfused liver and isolated hepatic nonparenchymal cells. Hepatology. 1995;21:855-862.[Medline]

8. Brackett DJ, Lai EK, Lerner MR, Wilson MF, McCay PB. Spin trapping of free radicals produced in vivo in heart and liver during endotoxemia. Free Radic Res Commun. 1989;7:315-324.[Medline]

9. Ben-Shaul V, Sofer Y, Bergman M, Zurovsky Y, Grossman S. Lipopolysaccharide-induced oxidative stress in the liver: comparison between rat and rabbit. Shock. 1999;12:288-293.[Medline]

10. Maulik N, Watanabe M, Engelman D, Engelman RM, Kagan VE, Kisin E, Tyurin V, Cordis GA, Das DK. Myocardial adaptation to ischemia by oxidative stress induced by endotoxin. Am J Physiol Cell Physiol. 1995;269:C907-C16.[Abstract/Free Full Text]

11. Armour J, Tyml K, Lidington D, Wilson JX. Ascorbate prevents microvascular dysfunction in the skeletal muscle of the septic rat. J Appl Physiol. 2001;90:795-803.[Abstract/Free Full Text]

12. Kanter M, Coskun O, Armutcu F, Uz YH, Kizilay G. Protective effects of vitamin C, alone or in combination with vitamin A, on endotoxin-induced oxidative renal tissue damage in rats. Tohoku J Exp Med. 2005;206:155-162.[Medline]

13. Nathens AB, Neff MJ, Jurkovich GJ, Klotz P, Farver K, Ruzinski JT, Radella F, Garcia I, Maier RV. Randomized, prospective trial of antioxidant supplementation in critically ill surgical patients. Ann Surg. 2002;236:814-822.[Medline]

14. Wu F, Tyml K, Wilson JX. Ascorbate inhibits iNOS expression in endotoxin- and IFN gamma-stimulated rat skeletal muscle endothelial cells. FEBS Lett. 2002;520:122-126.[Medline]

15. Wu F, Wilson JX, Tyml K. Ascorbate protects against impaired arteriolar constriction in sepsis by inhibiting inducible nitric oxide synthase expression. Free Radic Biol Med. 2004;37:1282-1289.[Medline]

16. De la Fuente M, Victor VM. Ascorbic acid and N-acetylcysteine improve in vitro the function of lymphocytes from mice with endotoxin-induced oxidative stress. Free Radic Res. 2001;35:73-84.[Medline]

17. Kim JY, Lee SM. Effect of ascorbic acid on hepatic vasoregulatory gene expression during polymicrobial sepsis. Life Sci. 2004;75:2015-2026.[Medline]

18. Korcok J, Wu F, Tyml K, Hammond RR, Wilson JX. Sepsis inhibits reduction of dehydroascorbic acid and accumulation of ascorbate in astroglial cultures: intracellular ascorbate depletion increases nitric oxide synthase induction and glutamate uptake inhibition. J Neurochem. 2002;81:185-193.[Medline]

19. Tan PH, Sagoo P, Chan C, Yates JB, Campbell J, Beutelspacher SC, Foxwell BM, Lombardi G, George AJ. Inhibition of NF-kappaB and oxidative pathways in human dendritic cells by antioxidative vitamins generates regulatory T cells. J Immunol. 2005;174:7633-7644.[Abstract/Free Full Text]

20. Chan TS, Shangari N, Wilson JX, Chan H, Butterworth RF, O’Brien PJ. The biosynthesis of ascorbate protects isolated rat hepatocytes from cumene hydroperoxide-mediated oxidative stress. Free Radic Biol Med. 2005;38:867-873.[Medline]

21. Wilson JX. Regulation of vitamin C transport. Annu Rev Nutr. 2005;25:105-125.[Medline]

22. Banhegyi G, Braun L, Csala M, Puskas F, Mandl J. Ascorbate metabolism and its regulation in animals. Free Radic Biol Med. 1997;23:793-803.[Medline]

23. Upston JM, Karjalainen A, Bygrave FL, Stocker R. Efflux of hepatic ascorbate: a potential contributor to the maintenance of plasma vitamin C. Biochem J. 1999;342:49-56.

24. De Tata V, Brizzi S, Saviozzi M, Lazzarotti A, Fierabracci V, Malvaldi G, Casini A. Protective role of dehydroascorbate in rat liver ischemia-reperfusion injury. J Surg Res. 2005;123:215-221.[Medline]

25. Guaiquil VH, Golde DW, Beckles DL, Mascareno EJ, Siddiqui MA. Vitamin C inhibits hypoxia-induced damage and apoptotic signaling pathways in cardiomyocytes and ischemic hearts. Free Radic Biol Med. 2004;37:1419-1429.[Medline]

26. Lykkesfeldt J, Viscovich M, Poulsen HE. Ascorbic acid recycling in human erythrocytes is induced by smoking in vivo. Free Radic Biol Med. 2003;35:1439-1447.[Medline]

27. Savini I, Catani MV, Duranti G, Ceci R, Sabatini S, Avigliano L. Vitamin C homeostasis in skeletal muscle cells. Free Radic Biol Med. 2005;38:898-907.[Medline]

28. Sotiriou S, Gispert S, Cheng J, Wang Y, Chen A, Hoogstraten-Miller S, Miller GF, Kwon O, Levine M, et al. Ascorbic-acid transporter Slc23a1 is essential for vitamin C transport into the brain and for perinatal survival. Nat Med. 2002;8:514-517.[Medline]

29. Kuo SM, MacLean ME, McCormick K, Wilson JX. Gender and sodium-ascorbate transporter isoforms determine ascorbate concentrations in mice. J Nutr. 2004;134:2216-2221.[Abstract/Free Full Text]

30. Takanaga H, Mackenzie B, Hediger MA. Sodium-dependent ascorbic acid transporter family SLC23. Pflugers Arch. 2004;447:677-682.[Medline]

31. Wilson JX, MacLean ME, Jaworski EJ, McCormick K, Kuo SM. The contributions of sodium-dependent vitamin C transporters SVCT1 and SVCT2 to tissue concentrations of ascorbate [abstract]. FASEB J. 2004;18:A694.

32. Griffith OW. Determination of glutathione and glutathione disulfide using glutathione reductase and 2-vinylpyridine. Anal Biochem. 1980;106:207-212.[Medline]

33. Paradkar PN, Blum PS, Berhow MA, Baumann H, Kuo SM. Dietary isoflavones suppress endotoxin-induced inflammatory reaction in liver and intestine. Cancer Lett. 2004;215:21-28.[Medline]

34. Stubbs DW, Griffin JF. Effects of fasting on gulonolactone hydrolase, gulonate NADP oxidoreductase, and hepatic ascorbate in male and female rats. Proc Soc Exp Biol Med. 1973;144:195-198.[Medline]

35. Davies JE, Hughes RE. A note on the effect of food restriction on tissue ascorbic acid in guinea-pigs. Br J Nutr. 1977;38:299-300.[Medline]

36. Benito E, Bosch MA. Impaired phosphatidylcholine biosynthesis and ascorbic acid depletion in lung during lipopolysaccharide-induced endotoxaemia in guinea pigs. Mol Cell Biochem. 1997;175:117-123.[Medline]

37. Rojas C, Cadenas S, Herrero A, Mendez J, Barja G. Endotoxin depletes ascorbate in the guinea pig heart. Protective effects of vitamins C and E against oxidative stress. Life Sci. 1996;59:649-657.[Medline]

38. Huang J, Agus DB, Winfree CJ, Kiss S, Mack WJ, McTaggart RA, Choudhri TF, Kim LJ, Mocco J, et al. Dehydroascorbic acid, a blood-brain barrier transportable form of vitamin C, mediates potent cerebroprotection in experimental stroke. Proc Natl Acad Sci U S A. 2001;98:11720-11724.[Abstract/Free Full Text]

39. Singh AK, Jiang Y. How does peripheral lipopolysaccharide induce gene expression in the brain of rats?. Toxicology. 2004;201:197-207.[Medline]

40. Toutain PL, Bechu D, Hidiroglou M. Ascorbic acid disposition kinetics in the plasma and tissues of calves. Am J Physiol Regul Integr Comp Physiol. 1997;273:R1585-R1597.[Abstract/Free Full Text]

41. Battelino T, Goto M, Krzisnik C, Zeller WP. Tissue glucose transport and glucose transporters in suckling rats with endotoxic shock. Shock. 1996;6:259-262.[Medline]

42. Li X, Qu ZC, May JM. GSH is required to recycle ascorbic acid in cultured liver cell lines. Antioxid Redox Signal. 2001;3:1089-1097.[Medline]

43. May JM, Mendiratta S, Hill KE, Burk RF. Reduction of dehydroascorbate to ascorbate by the selenoenzyme thioredoxin reductase. J Biol Chem. 1997;272:2607-2610.[Abstract/Free Full Text]

44. Jung HI, Lim HW, Kim BC, Park EH, Lim CJ. Differential thioredoxin reductase activity from human normal hepatic and hepatoma cell lines. Yonsei Med J. 2004;45:263-272.[Medline]

45. Paver JL, Freedman RB, Parkhouse RM. Induction of expression of protein disulphide-isomerase during lymphocyte maturation stimulated by bacterial lipopolysaccharide. FEBS Lett. 1989;242:357-362.[Medline]

46. Sano H, Sata T, Nanri H, Ikeda M, Shigematsu A. Thioredoxin is associated with endotoxin tolerance in mice. Crit Care Med. 2002;30:190-194.[Medline]





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