Novel aspects of vitamin C: how important is glypican-1 recycling?

Acute and subacute hepatotoxicity of genipin in mice and its potential mechanism

Gardenia, as a medicinal and edible herb, has the pharmacological activity of protecting the liver and cholagogue, but the hepatotoxicity induced by the chemical component genipin (GP) limits its application. The aim of this study was to evaluate the acute and subacute hepatotoxicity of genipin in normal mice and mice with α-naphthalene isothiocyanate (ANIT)-induced liver injury. The results of the acute study showed that the LD50 of genipin was 510 mg/kg. Genipin exhibited hepatotoxicity in normal and jaundiced mice at doses of 125 mg/kg, 250 mg/kg, and 500 mg/kg, which increased with dose. In a 28-day subacute study, the 50 mg/kg and 100 mg/kg dose groups showed some pharmacodynamic effects at 7 days but exhibited hepatotoxicity that increased with time and improved after drug withdrawal. In addition, based on proteomics, the mechanism of liver injury induced by genipin may be related to the disruption of the UDP-glucuronosyltransferase system and cytochrome P450 enzyme activity. In conclusion, this study showed that genipin hepatotoxicity was time- and dose dependent, but it is worth mentioning that hepatotoxicity was reversible. It is hoped that this study will provide a scientific basis for circumventing the adverse effects of genipin.

The mechanisms underlying the enrichment and action of glypican-1-positive exosomes in colorectal cancer cells

BACKGROUND

Glypican-1 (GPC1) is overexpressed in several tumors, and GPC1⁺ exosomes have shown the potential to predict early colorectal cancer (CRC). However, the mechanisms underlying the enrichment and action of GPC1⁺ exosomes in CRC remain unknown.

METHODS

The expression of slit guidance ligand 2 (SLIT2), hypoxia-inducible factor (HIF)-1α/2α, and GPC1 in clinical CRC tissues was detected using immunohistochemistry and western blot. Exosomes were isolated from the supernatants of CRC cell cultures. The effects of SLIT2, hypoxia, heparin, and phospholipase C (PLC) on exosomal GPC1 expression and GPC1⁺ exosome enrichment in CRC cells were analyzed with western blot and flow cytometry. CRC cell proliferation was assessed with MTT and colony formation assays. Co-immunoprecipitation was used to detect the binding of GPC1 and SLIT2 in SW480 cells. Nude mice were subcutaneously inoculated with SW480 cells with different treatments. The Wnt signaling was detected.

RESULTS

SLIT2 was poorly expressed and GPC1, HIF-1α, and HIF-2α were highly expressed in human CRC tissues. SLIT2 in CRC cells inhibited GPC1⁺ exosome enrichment and exosomal GPC1 expression. PLC and heparin increased GPC1⁺ exosome enrichment in CRC cells in a concentration-dependent manner. Hypoxia increased the enrichment of GPC1⁺ exosomes in CRC cells depending on HIF-2α expression. GPC1⁺ exosomes stimulated CRC cell proliferation and xenograft tumor growth through activation of Wnt signaling.

CONCLUSIONS

GPC1⁺ exosome enrichment is related to PLC and heparin. Hypoxia increases the enrichment of GPC1⁺ exosomes in CRC cells by activating HIF-2α and downregulating SLIT2. GPC1⁺ exosomes further drive CRC progression by activating Wnt signaling.

Identification of key genes controlling L-ascorbic acid during Jujube (Ziziphus jujuba Mill.) fruit development by integrating transcriptome and metabolome analysis

Chinese jujube (Ziziphus jujuba) is a vital economic tree native to China. Jujube fruit with abundant L-Ascorbic Acid (AsA) is an ideal material for studying the mechanism of AsA biosynthesis and metabolism. However, the key transcription factors regulating AsA anabolism in jujube have not been reported. Here, we used jujube variety "Mazao" as the experimental material, conducted an integrative analysis of transcriptome and metabolome to investigate changes in differential genes and metabolites, and find the key genes regulating AsA during jujube fruit growth. The results showed that AsA was mostly synthesized in the young stage and enlargement stage, ZjMDHAR gene takes an important part in the AsA recycling. Three gene networks/modules were highly correlated with AsA, among them, three genes were identified as candidates controlling AsA, including ZjERF17 (LOC107404975), ZjbZIP9 (LOC107406320), and ZjGBF4 (LOC107421670). These results provide new directions and insights for further study on the regulation mechanism of AsA in jujube.

Ascorbate and Tumor Cell Iron Metabolism: The Evolving Story and Its Link to Pathology

Significance: Vitamin C or ascorbate (Asc) is a water-soluble vitamin and an antioxidant that is involved in many crucial biological functions. Asc's ability to reduce metals makes it an essential enzyme cofactor. Recent Advances: The ability of Asc to act as a reductant also plays an important part in its overall role in iron metabolism, where Asc induces both nontransferrin-bound iron and transferrin-bound iron uptake at physiological concentrations (∼50 μM). Moreover, Asc has emerged to play an important role in multiple diseases and its effects at pharmacological doses could be important for their treatment. Critical Issues: Asc's role as a regulator of cellular iron metabolism, along with its cytotoxic effects and different roles at pharmacological concentrations, makes it a candidate as an anticancer agent. Ever since the controversy regarding the studies from the Mayo Clinic was finally explained, there has been a renewed interest in using Asc as a therapeutic approach toward cancer due to its minimal side effects. Numerous studies have been able to demonstrate the anticancer activity of Asc through selective oxidative stress toward cancer cells via H₂O₂ generation at pharmacological concentrations. Studies have demonstrated that Asc's cytotoxic mechanism at concentrations (>1 mM) has been associated with decreased cellular iron uptake. Future Directions: Recent studies have also suggested other mechanisms, such as Asc's effects on autophagy, polyamine metabolism, and the cell cycle. Clearly, more has yet to be discovered about Asc's mechanism of action to facilitate safe and effective treatment options for cancer and other diseases.

Common traffic routes for imported spermine and endosomal glypican-1-derived heparan sulfate in fibroblasts

Import of the polyamine spermine from the extracellular environment depends on the presence of cell surface heparan sulfate proteoglycans, such as glypican-1. This proteoglycan is internalized by endocytosis, releases its heparan sulfate chains in endosomes by a nitric oxide-, copper- and amyloid precursor protein-dependent mechanism, then penetrates the membrane and is transported to the nucleus and then to autophagosomes. This process is spontaneous or induced by ascorbate depending on the growth-state of the cell. Here, we have explored possible connections between the heparan sulfate traffic route and spermine uptake and delivery in wild-type and Tg2576 mouse fibroblasts. Cells were examined by deconvolution immunofluorescence microscopy. The antibodies used were specific for spermine, glypican-1-derived heparan sulfate, Rab7, nucleolin and a marker for autophagosomes. Endogenous immunostainable spermine was primarily associated with autophagosomes. When spermine synthesis was inhibited, imported spermine appeared in Rab7-positive endosomes. When ascorbate was added, heparan sulfate and spermine were transported to the nucleus where they colocalized with nucleolin. Spermine also appeared in autophagosomes. In a pulse-chase experiment, heparan sulfate and spermine were first arrested in late endosomes by actinomycin D treatment. During the chase, when arrest was abolished, heparan sulfate and spermine were both transported to the nucleus and targeted nucleolin. In amyloid precursor protein^-/--fibroblasts, ascorbate failed to induce release of heparan sulfate and spermine remained in the endosomes. We propose that cell surface glypican-1 carries spermine to the endosomes and that the released heparan sulfate carries spermine across the membrane into the cytosol and then to the nucleus.

Nucleolin is a nuclear target of heparan sulfate derived from glypican-1

The recycling, S-nitrosylated heparan sulfate (HS) proteoglycan glypican-1 releases anhydromannose (anMan)-containing HS chains by a nitrosothiol-catalyzed cleavage in endosomes that can be constitutive or induced by ascorbate. The HS-anMan chains are then transported to the nucleus. A specific nuclear target for HS-anMan has not been identified. We have monitored endosome-to-nucleus trafficking of HS-anMan by deconvolution and confocal immunofluorescence microscopy using an anMan-specific monoclonal antibody in non-growing, ascorbate-treated, and growing, untreated, wild-type mouse embryonic fibroblasts and hypoxia-exposed Alzheimer mouse Tg2576 fibroblasts and human U87 glioblastoma cells. In all cells, nuclear HS-anMan targeted a limited number of sites of variable size where it colocalized with DNA and nucleolin, an established marker for nucleoli. HS-anMan also colocalized with ethynyl uridine-tagged nascent RNA and two acetylated forms of histone H3. Acute hypoxia increased the formation of HS-anMan in both Tg2576 and U87 cells. A portion of HS-anMan colocalized with nucleolin at small discrete sites, while most of the nucleolin and nascent RNA was dispersed. In U87 cells, HS-anMan, nucleolin and nascent RNA reassembled after prolonged hypoxia. Nucleolar HS may modulate synthesis and/or release of rRNA.

Valve interstitial cell culture: Production of mature type I collagen and precise detection

Collagen often acts as an extracellular and intracellular marker for in vitro experiments, and its quality defines tissue constructs. To validate collagen detection techniques, cardiac valve interstitial cells were isolated from pigs and cultured under two different conditions; with and without ascorbic acid. The culture with ascorbic acid reached higher cell growth and collagen deposition, although the expression levels of collagen gene stayed similar to the culture without ascorbic acid. The fluorescent microscopy was positive for collagen fibers in both the cultures. Visualization of only extracellular collagen returned a higher correlation coefficient when comparing the immunolabeling and second harmonic generation microscopy images in the culture with ascorbic acid. Lastly, it was proved that the hydroxyproline strongly contributes to the second-order susceptibility tensor of collagen molecules, and therefore the second harmonic generation signal is impaired in the culture without ascorbic acid.

Suppression of amyloid beta A11 antibody immunoreactivity by vitamin C: possible role of heparan sulfate oligosaccharides derived from glypican-1 by ascorbate-induced, nitric oxide (NO)-catalyzed degradation

Amyloid β (Aβ) is generated from the copper- and heparan sulfate (HS)-binding amyloid precursor protein (APP) by proteolytic processing. APP supports S-nitrosylation of the HS proteoglycan glypican-1 (Gpc-1). In the presence of ascorbate, there is NO-catalyzed release of anhydromannose (anMan)-containing oligosaccharides from Gpc-1-nitrosothiol. We investigated whether these oligosaccharides interact with Aβ during APP processing and plaque formation. anMan immunoreactivity was detected in amyloid plaques of Alzheimer (AD) and APP transgenic (Tg2576) mouse brains by immunofluorescence microscopy. APP/APP degradation products detected by antibodies to the C terminus of APP, but not Aβ oligomers detected by the anti-Aβ A11 antibody, colocalized with anMan immunoreactivity in Tg2576 fibroblasts. A 50-55-kDa anionic, sodium dodecyl sulfate-stable, anMan- and Aβ-immunoreactive species was obtained from Tg2576 fibroblasts using immunoprecipitation with anti-APP (C terminus). anMan-containing HS oligo- and disaccharide preparations modulated or suppressed A11 immunoreactivity and oligomerization of Aβ42 peptide in an in vitro assay. A11 immunoreactivity increased in Tg2576 fibroblasts when Gpc-1 autoprocessing was inhibited by 3-β[2(diethylamino)ethoxy]androst-5-en-17-one (U18666A) and decreased when Gpc-1 autoprocessing was stimulated by ascorbate. Neither overexpression of Gpc-1 in Tg2576 fibroblasts nor addition of copper ion and NO donor to hippocampal slices from 3xTg-AD mice affected A11 immunoreactivity levels. However, A11 immunoreactivity was greatly suppressed by the subsequent addition of ascorbate. We speculate that temporary interaction between the Aβ domain and small, anMan-containing oligosaccharides may preclude formation of toxic Aβ oligomers. A portion of the oligosaccharides are co-secreted with the Aβ peptides and deposited in plaques. These results support the notion that an inadequate supply of vitamin C could contribute to late onset AD in humans.

Nocturnal haemoglobin oxygen saturation variability is associated with vitamin C deficiency in Tanzanian children with sickle cell anaemia

Aim

To compare pulse oximetry in children with sickle cell anaemia (SCA) and controls and test the hypothesis that vitamin C deficiency (VCD; <11.4 μmol/L) is associated with nocturnal haemoglobin oxygen desaturation in SCA.

Methods

We undertook nocturnal and daytime pulse oximetry in 23 children with SCA (median age 8 years) with known steady-state plasma vitamin C concentrations and 18 siblings (median 7 years).

Results

Median nocturnal delta 12 s index (delta12 s), a measure of haemoglobin oxygen saturation (SpO₂) variability, was 0.38 (interquartile range 0.28–0.51) in SCA and 0.35 (0.23–0.48) in controls, with 9/23 and 6/18, respectively, having a delta12 s >0.4, compatible with obstructive sleep apnoea (OSA). Eleven of twenty-three with SCA had VCD; logged vitamin C concentrations showed a 66% decrease per 0.1 unit increase in delta12 s ([95% CI −86%, −15%]; p = 0.023) and delta12 s >0.4 was associated with VCD (odds ratio 8.75 [1.24–61.7], p = 0.029). Daytime and mean nocturnal SpO₂ were lower in SCA but there was no association with vitamin C.

Conclusion

Obstructive sleep apnoea (OSA), detected from nocturnal haemoglobin oxygen saturation variability, is common in Tanzanian children and associated with vitamin C Deficiency in SCA. The direction of causality could be determined by comparing OSA treatment with vitamin C supplementation.

6-Deoxy-6-[131I]iodo-L-ascorbic acid for the in vivo study of ascorbate: autoradiography, biodistribution in normal and hypolipidemic rats, and in tumor-bearing nude mice

Normal female rat distribution studies showed high and specific uptake of 6-deoxy-6-[(131)I]iodo-L-ascorbic acid (6-(131)IAsA) into the adrenal glands, known to highly express the ascorbate sodium-dependent vitamin C transporter-2 (SVCT-2), and the adrenal gland was clearly visualized by whole-body autoradiography. Preinjection of sulfinpyrazone, a known blocker of ascorbate transport, with 6-(131)IAsA resulted in decreased uptake of radioactivity in rat adrenal glands compared to the control group, seemingly illustrating the participation of the SVCT transporter (probably the SVCT-2 subtype) in the uptake process in vivo. 4-Aminopyrazolo[3,4-d]pyrimidine-induced hypolipidemic rats showed a 1.7-fold increase in adrenal uptake of radioactivity at 30 min postinjection of 6-(131)IAsA, compared to the control, with increased adrenal-to-liver and adrenal-to-kidney ratios. To further characterize 6-(131)IAsA for its tumor uptake properties, biodistribution studies were also performed using male nude mice implanted with either Y-1 adrenocortical tumor cells or adrenal medulla-derived PC12 cells. None of these tumors exhibited relevant uptake of 6-(131)IAsA while normal adrenal glands showed high uptake of radioactivity, suggesting that these tumors in this model have only a poor transport capacity for this agent. The present study demonstrates that the use of radioiodinated 6-IAsA may help to obtain information about functional alterations in diseased adrenal glands, but it does not exhibit desirable properties as a tumor-seeking agent for ascorbic acid bioactivity.

Role of the vitamin C in diethylnitrosamine-induced esophageal cancer in Wistar rats

PURPOSE: To evaluate the inhibitory effect of vitamin C on the experimental esophageal carcinogenesis induced by diethylnitrosamine (NDEA). METHODS: Sixty Wistar male rats aged three months, with mean weight of 210 g were employed in the study and were divided into four different groups according to the drinking drugs: group I - controls: only water, seven days a week; group II - only vitamin C, seven days a week; group III - NDEA, three days a week and water during the other four days; group IV - NDEA, three days a week and vitamin C during the other four days; group V - NDEA together with vitamin C three days a week, and only water during the other four days and group VI - NDEA together with vitamin C three days a week and vitamin C during the other four days. The dosages of NDEA were: - 10 mg. / Kg / day and vitamin C - 200 mg / animal / day, dissolved in drinking water. The animals were observed during 180 days and after that each one was sacrificed and its esophagus and the stomach were removed together and macro and microscopically analyzed to identify any tumors. RESULTS: The largest number of tumors was observed in the group III: 48 macroscopic lesions (4.8 lesions per animal) and 23 microscopic lesions (2.3 lesions per animal). The groups that received vitamin C (groups IV, V and VI) showed smaller number of tumors: group V - 0.5 macroscopic lesions and 0.3 microscopic lesions per animal and group VI - 0.1 macroscopic lesions and 0.1 microscopic lesions per animal. The incidence of tumors in the groups V and VI showed statistical significance (p<0.05), when compared to the other groups. CONCLUSION: The vitamin C administered together with diethylnitrosamine showed an inhibitory effect on the experimental esophageal carcinogenesis in Wistar rats.

The pro-oxidant effects of interactions of ascorbate with photoexcited melanin fade away with aging of the retina

Photoexcited melanin from retinal pigment epithelium (RPE) has been shown to induce photo-oxidation of ascorbate with concomitant generation of hydrogen peroxide. The aim of this study was to test whether the age-related changes in melanin content and distribution in the RPE affect the susceptibility of RPE cells to ascorbate-mediated photo-oxidation. Our results demonstrate that there is an age-dependent shift in the pathways with which ascorbate interacts in human RPE. In young RPE, melanin-ascorbate interactions may lead to pro-oxidant effects, but in the aged there is no net increase in photo-oxidation in the presence of ascorbate in comparison with samples without ascorbate. However, as ascorbate undergoes light-induced depletion and photogenerates ascorbyl free radical in the old RPE cells with initial yields similar to that observed for young RPE, an influence of ascorbate on oxidation pathways is revealed in the old RPE as well. Interestingly, the pro-oxidant effects of photoexcited melanolipofuscin-ascorbate interactions are greater than for photoexcited melanosomes when normalized to the same melanin content. The pro-oxidant effects of photoexcited melanin-ascorbate interactions are strongly dependent on the irradiation wavelength, this being the greatest for the shortest wavelength studied (340 nm) and steeply decreasing with increasing wavelength but still detectable even at 600 nm.

Ascorbate analogs for use in medical imaging: synthesis and radical scavenging activity of 5-O-(4'-iodobenzyl)-L-ascorbic acid

As part of our program to develop potential imaging agents for ascorbate bioactivity in the brain, 5-O-(4'-iodobenzyl)-L-ascorbic acid was prepared through a seven-step sequence which involved C5-O-alkylation with p-iodobenzyl bromide in the presence of Ag2O and CaSO4 as the key step, starting from L-ascorbic acid. The scavenging activity of the p-iodobenzylated analog against 2,2-diphenyl-1-picrylhyrazyl (DPPH) radical was almost the same as that of L-ascorbic acid itself.