Ascorbate-induced release of LHRH: noradrenergic and opioid modulation

Exploring the Pivotal Neurophysiologic and Therapeutic Potentials of Vitamin C in Glioma

Gliomas represent solely primary brain cancers of glial cell or neuroepithelial origin. Gliomas are still the most lethal human cancers despite modern innovations in both diagnostic techniques as well as therapeutic regimes. Gliomas have the lowest overall survival rate compared to other cancers 5 years after definitive diagnosis. The dietary intake of vitamin C has protective effect on glioma risk. Vitamin C is an essential compound that plays a vital role in the regulation of lysyl and prolyl hydroxylase activity. Neurons store high levels of vitamin C via sodium dependent-vitamin C transporters (SVCTs) to protect them from oxidative ischemia-reperfusion injury. Vitamin C is a water-soluble enzyme, typically seen as a powerful antioxidant in plants as well as animals. The key function of vitamin C is the inhibition of redox imbalance from reactive oxygen species produced via the stimulation of glutamate receptors. Gliomas absorb vitamin C primarily via its oxidized dehydroascorbate form by means of GLUT 1, 3, and 4 and its reduced form, ascorbate, by SVCT2. Vitamin C is able to preserve prosthetic metal ions like Fe2+ and Cu+ in their reduced forms in several enzymatic reactions as well as scavenge free radicals in order to safeguard tissues from oxidative damage. Therapeutic concentrations of vitamin C are able to trigger H2O2 generation in glioma. High-dose combination of vitamin C and radiation has a much more profound cytotoxic effect on primary glioblastoma multiforme cells compared to normal astrocytes. Control trials are needed to validate the use of vitamin C and standardization of the doses of vitamin C in the treatment of patients with glioma.

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.

Reproductive and Developmental Toxicity of Arsenic in Rodents: A Review

Arsenic is a recognized reproductive toxicant in humans and induces malformations, especially neural tube defects, in laboratory animals. Early studies showed that murine malformations occurred only when a high dose of inorganic arsenic was given by intravenous or intraperitoneal injection in early gestation. Oral gavage of inorganic arsenic at maternally toxic doses caused reduced fetal body weight and increased resorptions. Recently, arsenic reproductive and developmental toxicity has been studied in situations more similar to human exposures and using broader endpoints, such as behavioral changes and gene expression. For the general population, exposure to arsenic is mostly oral, particularly via drinking water, repeated and prolonged over time. In mice and rats, methylated or inorganic arsenic via drinking water or by repeated oral gavage induced male and female reproductive and developmental toxicities. Furthermore, at nonmaternally toxic levels, inorganic arsenic given to pregnant dams via drinking water affected fetal brain development and postnatal behaviors. However, arsenic given by repeated oral gavage to pregnant mice and rats was not morphologically teratogenic. In this review of arsenic reproductive and developmental toxicity in rats and mice, the authors summarize recent in vivo studies and discuss possible underlying mechanisms. The influences of folate, selenium, zinc, and arsenic methylation on arsenic reproductive and developmental toxicity are also discussed.

Protective effect of sodium selenite and zinc sulfate on intensive swimming-induced testicular gamatogenic and steroidogenic disorders in mature male rats

To investigate the ameliorative potential of sodium selenite and zinc sulfate on intensive-swimming-induced testicular disorders, 48 Wistar male rats (age, 4 months; mass, 146.2 ± 3.6 g) were randomly divided into 4 groups: the unexercised-control group (n = 12); the exercised group (n = 12); the control supplemented group (n = 12); and the exercised supplemented group (n = 12). For 10 weeks, the exercised rats underwent a protocol that consisted of 4 h·d–1swimming, for 6 d·week–1; the control rats did not exercise. For 10 weeks, both the supplemented groups received an oral daily dose of a combination of sodium selenite and zinc sulfate (6  and 3 mg·kg body mass–1, respectively). After 10 weeks, a significant reduction (p < 0.05) was seen in rats in the exercised group, compared with rats in both control groups, in paired testicular masses; in epididymal sperm count; in testicular Δ5, 3β-hydroxysteroid dehydrogenase (HSD) and 17β-HSD; in plasma levels of testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin; in the numbers of preleptotine spermatocytes, midpachytene spermatocytes, and stage 7 spermatids of the stage VII seminiferous epithelium cycle; and in fertility performance. As well, a significant increase (p < 0.05) was seen in the exercised group, compared with both control groups, in plasma corticosterone levels and in testicular content of malondialdehyde and catalase activity. At the same time, there was a significant reduction (p < 0.05) in the exercised group, compared with both control groups, in plasma concentrations of zinc and selenium; in the testicular content of glutathione (GSH), the glutathione and glutathione disulphide (GSSG) ratio, ascorbic acid, and α-tocopherol; and in testicular activities of superoxide dismutase, glutathione-peroxidase, and glutathione-S-transferase in the testes. No significant changes were seen in the number of spermatogonia-A from the stage VII seminiferous epithelium cycle or the testicular content of GSSG among the groups. Sodium selenite and zinc sulfate supplementation significantly protected against exercise-induced testicular gamatogenic and spermatogenic disorders, prevented testicular oxidative stress, and increased antioxidant status. It can be concluded that intensive-swimming-induced oxidative stress causes dysfunctions in the male reproductive system, which can be protected by the coadministration of sodium selenite and zinc sulfate.

Effect of L-ascorbic acid supplementation on testicular oxidative stress and endocrine disorders in mature male rats exposed to intensive swimming exercise

In order to investigate the ameliorative potential of L-ascorbic acid on intensive swimming exercise induced testicular oxidative stress, 18 Wistar male rats (age: 3 months, weight: 127.5 ± 5.3 g) were randomly divided into the following groups: (i) control group (CG, n = 6); (ii) experimental group (EG, n = 6); and (iii) supplemented group (SG, n = 6). An exercise protocol of 3 h swimming per day, five days per week was followed for 6 weeks in EG and SG with no exercise in CG. In SG, L-ascorbic acid was supplied orally at a dose of 25-mg/kg of bodyweight each day for 6 weeks. A significant decrease (P < 0.05) was noted in paired testicular weights, epididymal sperm count, testicular Δ⁵, 3β-hydroxyseroid dehydrogenase, 17β-hydroxyseroid dehydrogenase, plasma levels of testosterone luteinizing hormone, follicle stimulating hormone, prolactin, the numbers of preleptotine spermatocytes, midpachytene spermatocytes and stage 7 spermatids of stage VII seminiferous epithelium cycle in EG when compared with CG. A significant elevation (P < 0.05) in plasma corticosterone and testicular content of malondialdehyde along with a significant reduction (P < 0.05) in glutathione, ascorbic acid, α-tocopherol, superoxide dismutase, catalase and glutathione-peroxidase, and glutathione-S-transferase were noted in testes of EG compared with CG. No significant change was noted in final bodyweight or numbers of spermatogonia-A among the groups. Furthermore, L-ascorbic acid supplementation restored the above parameters to the control level. Conclusion:  It can be concluded that intensive swimming exercise induced oxidative stress causes dysfunctions in the male reproductive system, which can be protected by L-ascorbic acid. (Reprod Med Biol 2006; 5: 145-153).

Effect of L-ascorbic acid supplementation on testicular oxidative stress and endocrine disorders in mature male rats exposed to intensive swimming exercise

In order to investigate the ameliorative potential of L-ascorbic acid on intensive swimming exercise induced testicular oxidative stress, 18 Wistar male rats (age: 3 months, weight: 127.5 ± 5.3 g) were randomly divided into the following groups: (i) control group (CG, n = 6); (ii) experimental group (EG, n = 6); and (iii) supplemented group (SG, n = 6). An exercise protocol of 3 h swimming per day, five days per week was followed for 6 weeks in EG and SG with no exercise in CG. In SG, L-ascorbic acid was supplied orally at a dose of 25-mg/kg of bodyweight each day for 6 weeks. A significant decrease (P < 0.05) was noted in paired testicular weights, epididymal sperm count, testicular Δ⁵, 3β-hydroxyseroid dehydrogenase, 17β-hydroxyseroid dehydrogenase, plasma levels of testosterone luteinizing hormone, follicle stimulating hormone, prolactin, the numbers of preleptotine spermatocytes, midpachytene spermatocytes and stage 7 spermatids of stage VII seminiferous epithelium cycle in EG when compared with CG. A significant elevation (P < 0.05) in plasma corticosterone and testicular content of malondialdehyde along with a significant reduction (P < 0.05) in glutathione, ascorbic acid, α-tocopherol, superoxide dismutase, catalase and glutathione-peroxidase, and glutathione-S-transferase were noted in testes of EG compared with CG. No significant change was noted in final bodyweight or numbers of spermatogonia-A among the groups. Furthermore, L-ascorbic acid supplementation restored the above parameters to the control level. Conclusion:  It can be concluded that intensive swimming exercise induced oxidative stress causes dysfunctions in the male reproductive system, which can be protected by L-ascorbic acid. (Reprod Med Biol 2006; 5: 145-153).

Effect of intensive exercise-induced testicular gametogenic and steroidogenic disorders in mature male Wistar strain rats: a correlative approach to oxidative stress

AIMS

In order to investigate the effects of intensive exercise on reproductive dysfunctions in relation to oxidative stress, a total of 12 male rats (age: 3 months, weight: 127 +/- 2.86 g) were randomly divided into: (1) control group (CG, n = 6) and (2) experimental group (Exp. G, n = 6).

METHODS

An exercise protocol of 3 h swimming day(-1), 5 days week(-1) was followed for 4 weeks in Exp. G, with no exercise in CG. All the animals were killed; blood, testes and the accessory sex organs were collected for estimation of different parameters.

RESULTS

A significant diminution (P < 0.001) was noted in testicular Delta5, 3beta-hydroxy-steroid dehydrogenase (Delta5, 3beta-HSD), 17beta-hydroxy steroid dehydrogenase (17beta-HSD); plasma levels of testosterone, luteinizing hormone (LH); preleptotine spermatocytes (pLSc), midpachytene spermatocytes (mPSc) and stage 7 spermatids (7Sd); with no significant alteration in follicle stimulating hormone (FSH) and spermatogoia A (Asg) after intensive exercise. A significant elevation (P < 0.001) in malondialdehyde (MDA) and conjugated dienes (CD) along with significant reduction (P < 0.001) in glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferase (GST) and peroxidase were found in testes of Exp. G. Moreover, the somatic index of testes and accessory sex organs were also decreased significantly (P < 0.001) after exercise. High correlations have been found in 17 beta-HSD with CAT (r = 0.90, P < 0.05) and peroxidase (r = 0.83, P < 0.05), epididymal somatic index with CD (r = -0.91; P < 0.05) and GSH (r = 0.84, P < 0.05).

CONCLUSION

The present study focused an chronic intensive exercise-induced oxidative stress that may cause dysfunctions in male reproductive system including steroidogenesis and spermatogenesis.

In vitro regulation of rat derived microglia

The cell culture approach to the study of the nervous system attempts to reduce cellular complexity to various extents and to characterize the influences of extrinsic molecules on the cell population under study. To date, the main source of culture model systems to explore CNS function and dysfunction is fetal brain material from experimental animals, typically rodents. We have developed primary microglial cell cultures and focused on the concentration-dependent effects of different amino acids and growth promoting additives on microglial morphology and function. We used Basal Medium Eagle (BME) with 1g/L of glucose instead of Dulbecco's modified Eagle medium (DMEM) as serum-free condition, since BME does not contain L-Glycine (Gly) and L-Serine (Ser), and investigated the effects of these two amino acids on microglial morphology and functions by adding various concentrations of the amino acids to BME and different concentrations of ascorbic acid (10-75 micro g/ ml), hydrocortisone (1-7.5 nM) and DL-alpha-tocopherol (0.01-0.5 micro g/ml) as growth promoters. Under Gly/Ser-free, serum-free condition, and growth promoters-free conditions, the majority of rat microglial cells displayed round morphology, whereas in the presence of 5 micro M Gly and 25 micro M Ser, which correspond to the concentrations of Gly and Ser in the cerebrospinal fluid, they extended multiple branched processes and formed clusters of rough endoplasmic reticulum. Ascorbic acid (25 micro g/ml), 2.5 nM hydrocortisone and 0.05 micro g/ml of DL-alpha-tocopherol elicited the highest level of microglial activation as measured by an increased expression of MHC class-I and MHC class-II antigens. Neuron culture experiments using the conditioned medium obtained from the different microglial culture conditions indicate neurotoxic and neurotrophic effects depending on the concentrations of amino acids as well as on the concentration of the growth promoters. These findings suggest that resting ramified microglial cells with neurotrophic activity can be induced with the combination of BME medium and small amounts of extracellular matrix growth promoters.

Ascorbate regulation and its neuroprotective role in the brain

Ascorbic acid (vitamin C) occurs physiologically as the ascorbate anion: a water-soluble antioxidant that is found throughout the body. However, despite the high, homeostatically regulated levels of brain ascorbate, its specific functions in the CNS are only beginning to be elucidated. Certainly, it acts as part of the intracellular antioxidant network, and as such is normally neuroprotective. There is also evidence that it acts as a neuromodulator. A possibly unique role it might have is as an antioxidant in the brain extracellular microenvironment, where its concentration is modulated by glutamate-ascorbate heteroexchange at glutamate uptake sites. Ongoing studies of ascorbate and glutamate transporters should lead to rapid progress in understanding ascorbate regulation and function.

Ascorbate compartmentalization in the CNS

Ascorbic acid, found physiologically as the ascorbate anion, is an abundant water-soluble antioxidant. It is concentrated in the intracellular compartment of all tissues in the body. The CNS has particularly high levels of ascorbate. Recent data from this laboratory indicate that ascorbate is distinctly compartmentalized between neurons and glia, with an average intracellular concentration of 10 mM in neurons and 1 mM in glial cells. These data can be contrasted with those for another important low molecular weight antioxidant, glutathione, which is somewhat more concentrated in glia than in neurons. The present review summarizes evidence for ascorbate compartmentalization between neurons and glia and considers these data in light of evidence for the roles of ascorbate as a neuroprotective antioxidant and as a neuromodulator in the CNS.

Ascorbic acid concentration in the lateral hypothalamus is related to plasma osmolality

Microdialysis was used to measure extracellular ascorbic and uric acid concentrations in the lateral hypothalamus of water-restricted rats as they drank distilled water or 1.5% NaCl. Other water-restricted rats, not implanted with microdialysis probes, were decapitated 2 h after beginning to drink these fluids. Rats were inverted and their blood was collected for measurements of plasma osmolality and percent hematocrit. Results showed that drinking distilled water produced a significant increase in the ascorbic acid concentration but not in the uric acid concentration. Drinking 1.5% NaCl produced a significant decrease in the uric acid concentration but not in the ascorbic acid concentration. Drinking distilled water decreased mean osmolality from 306.0 to 291.5 mOsm/kg, whereas drinking 1.5% NaCl maintained mean osmolality at water-restricted levels. These results indicate that the extracellular fluid concentration of ascorbic acid in the lateral hypothalamus rises in response to a fall in plasma osmolality.