A survey of the haematological, nutritional and biochemical state of the rural elderly with particular reference to vitamin C

Ascorbate Suppresses VEGF Expression in Retinal Pigment Epithelial Cells

Purpose

To investigate the impact of ascorbate, via DNA hydroxymethylation, on VEGF expression in retinal pigment epithelial (RPE) cells.

Methods

Dot-blot and hydroxymethylated DNA immunoprecipitation sequencing were applied to evaluate the impact of ascorbate on DNA hydroxymethylation in ARPE-19 cells. RNA sequencing (RNA-seq) was carried out to analyze the transcriptome. Quantitative RT-PCR and ELISA were conducted to examine the transcription and secretion of VEGF from cultured cells. Primary human fetal RPE cells and RPE-J cells were used to verify the effect of ascorbate on VEGF expression. ELISA was used to measure VEGF in the vitreous humor of Gulo^−/− mice, which, like humans, cannot synthesize ascorbate de novo.

Results

Treatment with ascorbate (50 μM) promoted 5-hydroxymethycytosine (5hmC) generation and changed the genome-wide profiles of 5hmC in ARPE-19 cells. Ascorbate also caused a dramatic shift in the transcriptome—3186 differential transcripts, of which 69.3% are correlated with altered 5hmC in promoters or gene bodies. One of the most downregulated genes was VEGFA, which encodes the VEGF protein. The suppression of VEGF by ascorbate is independent of hypoxia-inducible factor 1-alpha (HIF-1α) but correlates with increased 5hmC in the gene body. The decreased transcription and secretion of VEGF by ascorbate were verified in primary human fetal RPE cells. Furthermore, adding ascorbate in the diet for Gulo^−/− mice resulted in decreased levels of VEGF in the RPE/choroid and vitreous humor.

Conclusions

Ascorbate inhibits VEGF expression in RPE cells likely via DNA hydroxymethylation. Thus, ascorbate could be implicated in the prevention or treatment of diseases such as age-related macular degeneration (AMD).

Antioxidant and Oxidative Stress: A Mutual Interplay in Age-Related Diseases

Aging is the progressive loss of organ and tissue function over time. Growing older is positively linked to cognitive and biological degeneration such as physical frailty, psychological impairment, and cognitive decline. Oxidative stress is considered as an imbalance between pro- and antioxidant species, which results in molecular and cellular damage. Oxidative stress plays a crucial role in the development of age-related diseases. Emerging research evidence has suggested that antioxidant can control the autoxidation by interrupting the propagation of free radicals or by inhibiting the formation of free radicals and subsequently reduce oxidative stress, improve immune function, and increase healthy longevity. Indeed, oxidation damage is highly dependent on the inherited or acquired defects in enzymes involved in the redox-mediated signaling pathways. Therefore, the role of molecules with antioxidant activity that promote healthy aging and counteract oxidative stress is worth to discuss further. Of particular interest in this article, we highlighted the molecular mechanisms of antioxidants involved in the prevention of age-related diseases. Taken together, a better understanding of the role of antioxidants involved in redox modulation of inflammation would provide a useful approach for potential interventions, and subsequently promoting healthy longevity.

The mechanism of neuroprotective action of natural compounds

Disturbance of cerebral redox homeostasis is the primary cause of human neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease. Well known experimental research demonstrates that oxidative stress is a main cause of cell death. A high concentration of reactive oxygen and nitrogen species leads to damage of a lot of proteins, lipids and also DNA. Synthetic compounds used for the treatment in the neurodegenerative diseases failed to meet the hopes they had raised and often exhibit a number of side effects. Therefore, in recent years interest in natural compounds derived from plants appears to be on the rise. This review describes a few natural compounds (1MeTIQ, resveratrol, curcumin, vitamin C and Gingko biloba) which revealed neuroprotective potential both in experimental studies and clinical trials. 1MeTIQ has a privileged position because, as opposed to the remaining compounds, it is an endogenous amine synthesized in human and animal brain. Based on evidence from research, it seems that a common protective mechanism for all the above-mentioned natural compounds relies on their ability to inhibit or even scavenge the excess of free radicals generated in oxidative and neurotoxin-induced processes in nerve cells of the brain. However, it was demonstrated that further different molecular processes connected with neurotoxicity (e.g. the inhibition of mitochondrial complex I, activation of caspase-3, apoptosis) follow later and are initiated by the reactive oxygen species. What is more, these natural compounds are able to inhibit further stages of apoptosis triggered by neurotoxins in the brain.

The epigenetic role of vitamin C in health and disease

Recent advances have uncovered a previously unknown function of vitamin C in epigenetic regulation. Vitamin C exists predominantly as an ascorbate anion under physiological pH conditions. Ascorbate was discovered as a cofactor for methylcytosine dioxygenases that are responsible for DNA demethylation, and also as a likely cofactor for some JmjC domain-containing histone demethylases that catalyze histone demethylation. Variation in ascorbate bioavailability thus can influence the demethylation of both DNA and histone, further leading to different phenotypic presentations. Ascorbate deficiency can be presented systematically, spatially and temporally in different tissues at the different stages of development and aging. Here, we review how ascorbate deficiency could potentially be involved in embryonic and postnatal development, and plays a role in various diseases such as neurodegeneration and cancer through epigenetic dysregulation.