Effect of ascorbic acid on pituitary prolactin secretion in the non-ascorbate synthesizing Osteogenic Disorder Shionogi (ODS) rat

Neurobiology of vitamin C: Expanding the focus from antioxidant to endogenous neuromodulator

Ascorbic acid (AA) is a water-soluble vitamin (C) found in all bodily organs. Most mammals synthesize it, humans are required to eat it, but all mammals need it for healthy functioning. AA reaches its highest concentration in the brain where both neurons and glia rely on tightly regulated uptake from blood via the glucose transport system and sodium-coupled active transport to accumulate and maintain AA at millimolar levels. As a prototype antioxidant, AA is not only neuroprotective, but also functions as a cofactor in redox-coupled reactions essential for the synthesis of neurotransmitters (e.g., dopamine and norepinephrine) and paracrine lipid mediators (e.g., epoxiecoisatrienoic acids) as well as the epigenetic regulation of DNA. Although redox capacity led to the promotion of AA in high doses as potential treatment for various neuropathological and psychiatric conditions, ample evidence has not supported this therapeutic strategy. Here, we focus on some long-neglected aspects of AA neurobiology, including its modulatory role in synaptic transmission as demonstrated by the long-established link between release of endogenous AA in brain extracellular fluid and the clearance of glutamate, an excitatory amino acid. Evidence that this link can be disrupted in animal models of Huntington´s disease is revealing opportunities for new research pathways and therapeutic applications (e.g., epilepsy and pain management). In fact, we suggest that improved understanding of the regulation of endogenous AA and its interaction with key brain neurotransmitter systems, rather than administration of AA in excess, should be the target of future brain-based therapies.

Pharmacokinetic properties of phytochemicals in Hypericum perforatum influence efficacy of regulating oxidative stress

BACKGROUND

Hypericum perforatum is used in ethnopharmacology and has recently become popular in conventional medicine for treatment of mild to moderate depression. The abundance of potentially functional phytochemicals and their broader utilizations in traditional medicine suggests that ingestion of H. perforatum may impart additional secondary health benefits.

HYPOTHESIS/PURPOSE

Considering that many phytochemicals are known to display antioxidant activity, it was hypothesized that H. perforatum ingestion may inhibit oxidative stress and inflammation (OSI) which occurs in transient cycles following exercise and consumption of meals. The aim of this study was to explore the pharmacokinetics of H. perforatum phytochemicals after ingestion to predict the absorption timing of putative medicinal phytochemicals.

STUDY DESIGN/METHODS

In silico analyses of previously published plant extract phytochemical profiles were performed, wherein the Phytochemical Absorption Prediction (PCAP) model was used to predict the pharmacokinetics of phytochemicals. The predicted times for phytochemicals to reach maximum plasma concentration (T_max), and associated antioxidant activities, were compared to prior clinical in vivo studies to assess the accuracy and applicability of predictions.

RESULTS

The PCAP model identified that phytochemicals with antioxidant activity concurrently accumulate in plasma with T_max in the range of 1.6-2.3 h after ingestion. Comparison with previously published results identified that attenuation of OSI following H. perforatum ingestion aligns with the predicted T_max of antioxidant phytochemicals.

CONCLUSION

Based on these results it is therefore recommended that H. perforatum administration occurs 2 h before meals to provide optimal secondary health benefits associated with inhibition of postprandial stress. Additionally, these results highlight the use of in silico analyses to inform ingestion time and optimize the health benefits from ingestion of plant-based foods and medicines.

Possible interplay between vitamin C deficiency and prolactin in pregnant women with premature rupture of membranes: facts and hypothesis

The precise etiologic mechanisms involved in the premature rupture of membranes (PROM) during pregnancy, the main cause of preterm delivery worldwide, are unknown. Previous studies have shown that: (a) the rupture of chorioamniotic membranes is related to an imbalance between synthesis and degradation of collagen induced by the overexpression/activity of various matrix metalloproteinases (MMP); (b) during human labor and delivery the expression of prolactin receptors (PRL-R) increases in chorioamniotic membranes, decidua and placenta; (c) prolactin (PRL) can influence the synthesis of prostaglandins, the expression of some MMP (MMP-2, MMP-9 and decysin) and tissue inhibitors of MMP in general; (d) vitamin C deficiency induces the expression/activity of extracellular MMP and is considered a risk factor for PROM; and (e) vitamin C potentiates the dopamine-mediated inhibition of PRL in rats. The present hypothesis proposes that a decreased hypothalamic dopaminergic tone-and thus an increased synthesis/release of pituitary PRL - is induced by vitamin C deficiency below a critical threshold (<18 microg/10(8) leukocytes) and that both factors, in turn, would cause upregulation of the expression/activity of several MMP. The increased PRL concentrations (acting like a Th1-type cytokine) along with the overexpression of other proinflammatory cytokines would induce a premature switch from a favorable Th2-type immune response to a noxious Th1-type immune response in the intrauterine environment. This change, in conjunction with the upregulation of MMP-2 and MMP-9, would cause a premature imbalance between synthesis/degradation of collagen in chorioamniotic membranes (an "anticipation" of the normal parturition cascade?), which favors extracellular matrix degradation, proposed as the most relevant event in the genesis of PROM. This hypothesis represents a new dimension in the study of the etiology of PROM.

Vitamin C and genomic stability

Vitamin C, a water-soluble glucose derivative, has considerable antioxidant activity in vitro, in part because of its ease of oxidation and because the semidehydroascorbate radical derived from it is of low reactivity. Vitamin C in vivo is an essential cofactor for a range of enzymes involved in diverse metabolic pathways, but much recent literature has focused on its antioxidant effects. Consumption of foods rich in Vitamin C (fruits and vegetables) is associated with decreased risk of cardiovascular disease, of many types of cancer and possibly of neurodegenerative disease, but the extent to which Vitamin C contributes to these effects is uncertain. Data using biomarkers of oxidative damage to DNA bases have given no compelling evidence to date that ascorbate supplements can decrease the levels of oxidative DNA damage in vivo, except perhaps in subjects with very low Vitamin C intakes. Similarly, there is no conclusive evidence from studies of strand breaks, micronuclei, or chromosomal aberrations for a protective effect of Vitamin C. There is limited evidence that supplements of Vitamin C might have beneficial effects in disorders of vascular function, and that diet-derived Vitamin C may decrease gastric cancer incidence in certain populations, but it is not clear whether it is the antioxidant or other properties of ascorbate that are responsible for these two actions.