Oxidized lipoprotein induces the macrophage ascorbate transporter (SVCT2): protection by intracellular ascorbate against oxidant stress and apoptosis

ATRX-dependent SVCT2 mediates macrophage infiltration in the glioblastoma xenograft model

Alpha thalassemia/mental retardation syndrome X-linked (ATRX) mutation impairs DNA damage repair in glioblastoma (GBM), making these cells more susceptible to treatment, which may contribute to the survival advantage in GBM patients containing ATRX mutations. To better understand the role of ATRX in GBM, genes correlated with ATRX expression were screened in the Cancer Genome Atlas (702 cases) and Chinese Glioma Genome Atlas (325 cases) databases. Sodium-vitamin C cotransporter 2 (SVCT2) was the most positively correlated gene with ATRX expression. ATRX (about 1.99-fold) and SVCT2 (about 2.25-fold) were upregulated in GBM tissues from 40 patients compared to normal brain tissues from 23 subjects. ShSVCT2 transfection did not alter the in vitro viability of GL261 cells. At the same time, it could inhibit the proliferation of GL261 cells in the orthotopic transplantation model with diminished infiltrating macrophages (CD45^highCD11b⁺), down-regulated chemokine (C-C motif) ligand 2 (Ccl2), Ccl4, C-X-C motif chemokine ligand 1 (Cxcl1), and Cxcl15 expression, and decreased p-IκBα and p-c-Jun expression. Effect of ShSVCT2 transfection could be reversed by overexpression of SVCT2. siRNA interference of ATRX-dependent SVCT2 signal with shSVCT2 could inhibit tumor cell proliferation in Glu261-LuNeo xenograft tumor model with more survival advantage, probably by the inhibited macrophage chemotaxis. These results indicate that ATRX-dependent SVCT2-mediated chemokine-induced macrophage infiltration is regulated by the NF-κB pathway, which could be considered as treatment targets.

Distinctive Neurochemistry in Alzheimer's Disease via 7 T In Vivo Magnetic Resonance Spectroscopy

This study's objective was to increase understanding of biological mechanisms underlying clinical Alzheimer's disease (AD) by noninvasively measuring an expanded neurochemical profile and exploring how well this advanced technology distinguishes AD from cognitively normal controls. We measured concentrations of 14 neurochemicals using ultra-high field (7 T) ultra-short echo time (8 ms) magnetic resonance spectroscopy (MRS) in 16 participants with mild to moderate clinical AD and 33 age- and gender-matched control participants. MRS was localized to the posterior cingulate cortex (PCC), a region known to be impacted by AD, and the occipital cortex (OCC), a control region. Participants with AD were recruited from dementia specialty clinics. Concentration of the antioxidant ascorbate was higher (p < 0.0007) in both brain regions. Concentrations of the glial marker myo-inositol and the choline-containing compounds involved in membrane turnover were higher (p≤0.0004) in PCC of participants with AD. Ascorbate and myo-inositol concentrations were strongly associated, especially in the PCC. Random forests, using the 14 neurochemicals in the two regions, distinguished participants with AD from controls: same-sample sensitivity and specificity were 88% and 97%, respectively, though out-of-sample-values would be lower. Ultra-high field ultra-short echo time MRS identified the co-occurrence of elevated ascorbate and myo-inositol in the PCC as markers that distinguish participants with mild to moderate AD from controls. While elevated myo-inositol may be a surrogate marker of neuroinflammation, the unexpected elevation of the antioxidant ascorbate may reflect infiltration of ascorbate-rich leukocytes.

Inhibition of intestinal ascorbic acid uptake by lipopolysaccharide is mediated via transcriptional mechanisms

Ascorbic acid (AA) accumulation in intestinal epithelial cells is an active transport process mainly mediated by two sodium-dependent vitamin C transporters (SVCT-1 and SVCT-2). To date, little is known about the effect of gut microbiota generated lipopolysaccharide (LPS) on intestinal absorption of water-soluble vitamins. Therefore, the objective of this study was to investigate the effects of bacterially-derived LPS on AA homeostasis in enterocytes using Caco-2 cells, mouse intestine and intestinal enteroids models. Pre-treating Caco-2 cells and mice with LPS led to a significant decrease in carrier-mediated AA uptake. This inhibition was associated with a significant reduction in SVCT-1 and SVCT-2 protein, mRNA, and hnRNA expression. Furthermore, pre-treating enteroids with LPS also led to a marked decrease in SVCT-1 and SVCT-2 protein and mRNA expression. Inhibition of SVCT-1 and SVCT-2 occurred at least in part at the transcriptional level as promoter activity of SLC23A1 and SLC23A2 was attenuated following LPS treatment. Subsequently, we examined the protein and mRNA expression levels of HNF1α and Sp1 transcription factors, which are needed for basal SLC23A1 and SLC23A2 promoter activity, and found that they were significantly decreased in the LPS treated Caco-2 cells and mouse jejunum; this was reflected on level of the observed reduction in the interaction of these transcription factors with their respective promoters in Caco-2 cells treated with LPS. Our findings indicate that LPS inhibits intestinal carrier- mediated AA uptake by down regulating the expression of both vitamin C transporters and transcriptional regulation of SLC23A1 and SLC23A2 genes.

Vitamin C may have similar beneficial effects to Gemfibrozil on serum high-density lipoprotein-cholesterol in type 2 diabetic patients

Objective:

Type 2 diabetes mellitus (DM-T2) is commonly associated with increased triglycerides (TG), low-density lipoprotein cholesterol (LDL-C) and low high-density lipoprotein cholesterol (HDL-C) levels. Fibrates like gemfibrozil are frequently used in diabetic patients to decrease TG and increase HDL-C levels. We compared the efficacy of Vitamin C, an antioxidant vitamin, with gemfibrozil on serum HDL-C in diabetic patients.

Methods:

Type 2 diabetic patients, referred to our out-patient clinic were randomly divided into three groups. After 1 month of lifestyle and diet modifications, groups A, B, and C were prescribed 1000 mg Vitamin C, 600 mg gemfibrozil and combination of both, respectively. Before the study initiation and after 6^th week of drug prescription, the blood samples were taken and analyzed for total cholesterol (Total-C), HDL-C, TG, fasting blood sugar (FBS), and hemoglobin A1c (HbA1c) levels.

Findings:

Sixty-seven patients entered, and 50 patients (18 male, 32 female) finished the study. Overall, serum HDL-C increased significantly from 39.8 to 45.2 mg/dL in the participants (P = 0.001). HDL-C increased 6.3, 4.4 and 5.0 mg/dL in groups A, B and C, respectively (related significances were 0.017, 0.022 and 0.033, respectively). Significant decrease of serum TG and Total-C occurred in gemfibrozil and combination groups, but not in Vitamin C group. Changes in serum HDL-C between three groups were not significant (P = 0.963). We found a significant decrease in TG and Total-C in the groups B and C (P < 0.05), but no significant changes of TG, Total-C, LDL-C, FBS and HbA1c in group A (P > 0.05).

Conclusion:

The results demonstrated that Vitamin C may have beneficial effects on HDL-C in diabetic patients without significant effects on plasma glucose or other lipid parameters; however, its role for the treatment of low HDL-C patients should be evaluated in larger studies.

Chronic vitamin C deficiency promotes redox imbalance in the brain but does not alter sodium-dependent vitamin C transporter 2 expression

Vitamin C (VitC) has several roles in the brain acting both as a specific and non-specific antioxidant. The brain upholds a very high VitC concentration and is able to preferentially retain VitC even during deficiency. The accumulation of brain VitC levels much higher than in blood is primarily achieved by the sodium dependent VitC transporter (SVCT2). This study investigated the effects of chronic pre-and postnatal VitC deficiency as well as the effects of postnatal VitC repletion, on brain SVCT2 expression and markers of oxidative stress in young guinea pigs. Biochemical analyses demonstrated significantly decreased total VitC and an increased percentage of dehydroascorbic acid, as well as increased lipid oxidation (malondialdehyde), in the brains of VitC deficient animals (p < 0.0001) compared to controls. VitC repleted animals were not significantly different from controls. No significant changes were detected in either gene or protein expression of SVCT2 between groups or brain regions. In conclusion, chronic pre-and postnatal VitC deficiency increased brain redox imbalance but did not increase SVCT2 expression. Our findings show potential implications for VitC deficiency induced negative effects of redox imbalance in the brain and provide novel insight to the regulation of VitC in the brain during deficiency.

Antioxidant micronutrients improve intrinsic and UV-induced apoptosis of human lymphocytes particularly in elderly people

OBJECTIVE

Aging and oxidative stress may lead to enhanced cellular damage and programmed cell death. To study the association of intrinsic apoptosis with age and the effect of antioxidant supplementation on intrinsic and UV-induced apoptosis in children, young and elderly people.

METHODS

The study was a 2 months, double-blind, randomized trial. Three age groups were studied: children, young adults and elderly people. A total of 274 healthy subjects were allocated to a group supplemented with moderate amounts of retinol, β-carotene, α-tocopherol, ascorbic acid and selenium or placebo. Plasma oxidative stress parameters were detected and apoptosis of lymphocytes was evaluated with TUNEL staining.

RESULTS

At baseline, percentages of intrinsic apoptosis were 13.8% and 11.1% in elderly and young people, respectively, both significantly higher than children (6.3%). A decrease of 1.7% and 2.3% in intrinsic apoptosis of lymphocytes was found in the supplemented groups of young and elderly people compared with their control groups (all p values <0.001), but no significant decrease in children. Moreover, percentages UV-induced apoptosis significantly decreased by 1.4%, 1.9% and 3.1% in children, young and elderly people, respectively, compared with control groups after the trial. There were considerable increments in concentrations of plasma β-carotene, retinol, tocopherol, ascorbic acid and selenium in all three treated groups after the supplementation.

CONCLUSIONS

Young and elderly people have a higher intrinsic apoptosis than children, which was improved by antioxidant supplementation. UV-induced damage was attenuated by the supplementation in all three age groups.

Vitamin C modulates the interaction between adipocytes and macrophages

SCOPE

Increased adiposity is related with monocyte infiltration into the adipose tissue that accentuates inflammation. Antioxidant treatments emerge as approaches to counteract this phenomenon.

METHODS AND RESULTS

Cocultures of differentiated 3T3-L1 adipocytes and RAW264.7 macrophages were incubated for 24-72 h with/without 100 nM insulin and/or 200 μM vitamin C (VC). Nitric oxide (NO) secretion (24 h) was measured. Also, expression (24 h) and secretion (72 h) of MCP-1, leptin and apelin were analyzed. NO secretion was significantly inhibited by insulin and VC only in cocultures. MCP-1 expression/secretion was enhanced in cocultures. Insulin incubation reduced MCP-1 expression in both cultures and VC only in controls. Both treatments inhibited MCP-1 secretion in cocultures. Apelin gene expression was induced in cocultures. Insulin induced apelin mRNA expression, but VC inhibited its expression in cocultures under insulin treatment. Apelin secretion was notably induced by insulin and inhibited by VC in cocultures. Leptin expression was decreased in coculture, while presented no effects by VC.

CONCLUSION

VC importantly modulates the established pro-inflammatory state in the interaction between adipocytes and macrophages.

Ascorbic acid prevents increased endothelial permeability caused by oxidized low density lipoprotein

Abstract Mildly oxidized low density lipoprotein (mLDL) acutely increases the permeability of the vascular endothelium to molecules that would not otherwise cross the barrier. This study has shown that ascorbic acid tightens the permeability barrier in the endothelial barrier in cells, so this work tested whether it might prevent the increase in endothelial permeability due to mLDL. Treatment of EA.hy926 endothelial cells with mLDL decreased intracellular GSH and activated the cells to further oxidize the mLDL. mLDL also increased endothelial permeability over 2 h to both inulin and ascorbate in cells cultured on semi-permeable filters. This effect was blocked by microtubule and microfilament inhibitors, but not by chelation of intracellular calcium. Intracellular ascorbate both prevented and reversed the mLDL-induced increase in endothelial permeability, an effect mimicked by other cell-penetrant antioxidants. These results suggest a role for endothelial cell ascorbate in ameliorating an important facet of endothelial dysfunction caused by mLDL.

Selective macrophage ascorbate deficiency suppresses early atherosclerosis

To test whether severe ascorbic acid deficiency in macrophages affects progression of early atherosclerosis, we used fetal liver cell transplantation to generate atherosclerosis-prone apolipoprotein E-deficient (apoE(-/-)) mice that selectively lacked the ascorbate transporter (SVCT2) in hematopoietic cells, including macrophages. After 13 weeks of chow diet, apoE(-/-) mice lacking the SVCT2 in macrophages had surprisingly less aortic atherosclerosis, decreased lesion macrophage numbers, and increased macrophage apoptosis compared to control-transplanted mice. Serum lipid levels were similar in both groups. Peritoneal macrophages lacking the SVCT2 had undetectable ascorbate; increased susceptibility to H(2)O(2)-induced mitochondrial dysfunction and apoptosis; decreased expression of genes for COX-2, IL1β, and IL6; and decreased lipopolysaccharide-stimulated NF-κB and antiapoptotic gene expression. These changes were associated with decreased expression of both the receptor for advanced glycation end products and HIF-1α, either or both of which could have been the proximal cause of decreased macrophage activation and apoptosis in ascorbate-deficient macrophages.

Oxidized LDL up-regulates the ascorbic acid transporter SVCT2 in endothelial cells

Endothelial dysfunction is an early manifestation of atherosclerosis caused in part by oxidized LDL (oxLDL). Since vitamin C, or ascorbic acid, prevents several aspects of endothelial dysfunction, the effects of oxLDL on oxidative stress and regulation of the ascorbate transporter, SVCT2, were studied in cultured EA.hy926 endothelial cells. Cells cultured for 18 h with 0.2 mg/ml oxLDL showed increased lipid peroxidation that was prevented by a single addition of 0.25 mM ascorbate at the beginning of the incubation. This protection caused a decrease in intracellular ascorbate, but no change in the cell content of GSH. In the absence of ascorbate, oxLDL increased SVCT2 protein and function during 18 h in culture. Although culture of the cells with ascorbate did not affect SVCT2 protein expression, the oxLDL-induced increase in SVCT2 protein expression was prevented by ascorbate. These results suggest that up-regulation of endothelial cell SVCT2 expression and function may help to maintain intracellular ascorbate during oxLDL-induced oxidative stress, and that ascorbate in turn can prevent this effect.

Cellular pathways for transport and efflux of ascorbate and dehydroascorbate

The mechanisms allowing the cellular transport of ascorbic acid represent a primary aspect for the understanding of the roles played by this vitamin in pathophysiology. Considerable research effort has been spent in the field, on several animal models and different cell types. Several mechanisms have been described to date, mediating the movements of different redox forms of ascorbic acid across cell membranes. Vitamin C can enter cells both in its reduced and oxidized form, ascorbic acid (AA) and dehydroascorbate (DHA), utilizing respectively sodium-dependent transporters (SVCT) or glucose transporters (GLUT). Modulation of SVCT expression and function has been described by cytokines, steroids and post-translational protein modification. Cellular uptake of DHA is followed by its intracellular reduction to AA by several enzymatic and non-enzymatic systems. Efflux of vitamin C has been also described in a number of cell types and different pathophysiological functions were proposed for this phenomenon, in dependence of the cell model studied. Cellular efflux of AA is mediated through volume-sensitive (VSOAC) and Ca(2+)-dependent anion channels, gap-junction hemichannels, exocytosis of secretory vesicles and possibly through homo- and hetero-exchange systems at the plasma membrane level. Altogether, available data suggest that cellular efflux of ascorbic acid - besides its uptake - should be taken into account when evaluating the cellular homeostasis and functions of this important vitamin.