An investigation into the neuroprotective effects of dehydroepiandrosterone
- Authors: Palvie, Stefanie Michelle
- Date: 2006
- Subjects: Aging -- Physiological aspects , Nervous system -- Degeneration -- Treatment , Steroid hormones , Dehydroepiandrosterone , Dehydroepiandrosterone -- Therapeutic use , Neurosciences , Neuroanatomy , Apoptosis , Pineal gland -- Physiology , Neurotoxic agents , Free radicals (Chemistry) -- Physiological effect
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3782 , http://hdl.handle.net/10962/d1003260 , Aging -- Physiological aspects , Nervous system -- Degeneration -- Treatment , Steroid hormones , Dehydroepiandrosterone , Dehydroepiandrosterone -- Therapeutic use , Neurosciences , Neuroanatomy , Apoptosis , Pineal gland -- Physiology , Neurotoxic agents , Free radicals (Chemistry) -- Physiological effect
- Description: Dehydroepiandrosterone, a C-19 steroid, is found endogenously with the highest circulating serum levels. It is converted to important steroids such as the sex hormones oestrogen and testosterone. DHEA has come under the spotlight as a purported “fountain of youth” due to its well-characterised age-related decline. The supplementation of DHEA in both the elderly and those with a pathophysiological deficiency has been shown to be of benefit, particularly with regard to wellbeing and depression. The role of DHEA in the periphery has not been elucidated beyond its role as a precursor hormone in sex steroid biosynthesis, though it has been established as a neuroactive neurosteroid, capable of exerting neuroprotective effects in the brain. Since the importance of free radicals in aging and neurodegeneration is well established, investigations were conducted on the ability of DHEA to inhibit free radical generation or scavenge existing free radicals. DHEA was able to significantly inhibit quinolinic acid-induced lipid peroxidation, a measure of membrane damage, over a range of concentrations, although the reduction did not appear to be dose-dependent. This was observed in both in vitro and in vivo studies. Thus, the ability of a compound to reduce the degree of lipid peroxidation may indicate its value as a neuroprotectant. However, DHEA did not significantly reduce cyanide induced generation of the superoxide free radical, suggesting that DHEA is not an effective free radical scavenger of the superoxide anion and that the reduction in lipid peroxidation does not occur through a scavenging mechanism. Apoptosis is a physiological process which is necessary for development and homeostasis. However, this form of programmed cell death can be initiated through various mechanisms and too much apoptotic cell death results in deleterious effects in the body. DHEA was shown not to induce apoptosis. Even the lowest concentration of DHEA investigated in this thesis shows a remarkable decrease in the degree of apoptosis caused by intrahippocampal chemical insult by the neurotoxin quinolinic acid. Cresyl violet was used to visualise tissue for histological examination which revealed that DHEA is able to preserve the normal healthy morphology of hippocampal cells which have been exposed to quinolinic acid. Cells maintained their integrity and showed little evidence of swelling associated with necrosis. Organ culture studies were performed by assessing the impact of DHEA on several pineal metabolites. The study revealed that DHEA exerted an effect on the metabolism of indoleamines in the pineal gland. Melatonin, the chief pineal hormone, did not appear to be affected while the concentrations of N-acetylserotonin, serotonin and methoxytryptamine showed significant alterations. Thus, the neuroprotective mechanism of DHEA does not appear to be mediated by an increase in the presence of melatonin. The biological importance of metal ions in neurodegeneration is also well established and thus the potential interaction between DHEA and metal ions was considered as a mechanism of action. Spectroscopic and electrochemical analyses were performed to determine whether DHEA is able to interact with metal ions as a ligand. These reveal that DHEA does not form a strong bond with the metals investigated, namely copper (II) and iron (III), but that a weak interaction is evident. These investigations were conducted in a rodent model, which has neither large amounts of endogenous DHEA, nor the enzymatic infrastructure present in humans. Thus, the theory that DHEA exerts its effects through downstream metabolic products is unlikely. However, these investigations reveal that there is merit in the statement that DHEA itself is a neuroprotective molecule, and confirm that the further investigation of DHEA is an advisable strategy in the war against neurodegeneration and aging.
- Full Text:
- Date Issued: 2006
- Authors: Palvie, Stefanie Michelle
- Date: 2006
- Subjects: Aging -- Physiological aspects , Nervous system -- Degeneration -- Treatment , Steroid hormones , Dehydroepiandrosterone , Dehydroepiandrosterone -- Therapeutic use , Neurosciences , Neuroanatomy , Apoptosis , Pineal gland -- Physiology , Neurotoxic agents , Free radicals (Chemistry) -- Physiological effect
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3782 , http://hdl.handle.net/10962/d1003260 , Aging -- Physiological aspects , Nervous system -- Degeneration -- Treatment , Steroid hormones , Dehydroepiandrosterone , Dehydroepiandrosterone -- Therapeutic use , Neurosciences , Neuroanatomy , Apoptosis , Pineal gland -- Physiology , Neurotoxic agents , Free radicals (Chemistry) -- Physiological effect
- Description: Dehydroepiandrosterone, a C-19 steroid, is found endogenously with the highest circulating serum levels. It is converted to important steroids such as the sex hormones oestrogen and testosterone. DHEA has come under the spotlight as a purported “fountain of youth” due to its well-characterised age-related decline. The supplementation of DHEA in both the elderly and those with a pathophysiological deficiency has been shown to be of benefit, particularly with regard to wellbeing and depression. The role of DHEA in the periphery has not been elucidated beyond its role as a precursor hormone in sex steroid biosynthesis, though it has been established as a neuroactive neurosteroid, capable of exerting neuroprotective effects in the brain. Since the importance of free radicals in aging and neurodegeneration is well established, investigations were conducted on the ability of DHEA to inhibit free radical generation or scavenge existing free radicals. DHEA was able to significantly inhibit quinolinic acid-induced lipid peroxidation, a measure of membrane damage, over a range of concentrations, although the reduction did not appear to be dose-dependent. This was observed in both in vitro and in vivo studies. Thus, the ability of a compound to reduce the degree of lipid peroxidation may indicate its value as a neuroprotectant. However, DHEA did not significantly reduce cyanide induced generation of the superoxide free radical, suggesting that DHEA is not an effective free radical scavenger of the superoxide anion and that the reduction in lipid peroxidation does not occur through a scavenging mechanism. Apoptosis is a physiological process which is necessary for development and homeostasis. However, this form of programmed cell death can be initiated through various mechanisms and too much apoptotic cell death results in deleterious effects in the body. DHEA was shown not to induce apoptosis. Even the lowest concentration of DHEA investigated in this thesis shows a remarkable decrease in the degree of apoptosis caused by intrahippocampal chemical insult by the neurotoxin quinolinic acid. Cresyl violet was used to visualise tissue for histological examination which revealed that DHEA is able to preserve the normal healthy morphology of hippocampal cells which have been exposed to quinolinic acid. Cells maintained their integrity and showed little evidence of swelling associated with necrosis. Organ culture studies were performed by assessing the impact of DHEA on several pineal metabolites. The study revealed that DHEA exerted an effect on the metabolism of indoleamines in the pineal gland. Melatonin, the chief pineal hormone, did not appear to be affected while the concentrations of N-acetylserotonin, serotonin and methoxytryptamine showed significant alterations. Thus, the neuroprotective mechanism of DHEA does not appear to be mediated by an increase in the presence of melatonin. The biological importance of metal ions in neurodegeneration is also well established and thus the potential interaction between DHEA and metal ions was considered as a mechanism of action. Spectroscopic and electrochemical analyses were performed to determine whether DHEA is able to interact with metal ions as a ligand. These reveal that DHEA does not form a strong bond with the metals investigated, namely copper (II) and iron (III), but that a weak interaction is evident. These investigations were conducted in a rodent model, which has neither large amounts of endogenous DHEA, nor the enzymatic infrastructure present in humans. Thus, the theory that DHEA exerts its effects through downstream metabolic products is unlikely. However, these investigations reveal that there is merit in the statement that DHEA itself is a neuroprotective molecule, and confirm that the further investigation of DHEA is an advisable strategy in the war against neurodegeneration and aging.
- Full Text:
- Date Issued: 2006
An investigation into the neuroprotective properties of acyclovir
- Authors: Müller, Adrienne Carmel
- Date: 2006
- Subjects: Acyclovir -- Therapeutic use , Acyclovir -- Physiological effect , Nervous system -- Degeneration -- Treatment , Memory disorders -- Treatment , Quinolinic acid
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3776 , http://hdl.handle.net/10962/d1003254 , Acyclovir -- Therapeutic use , Acyclovir -- Physiological effect , Nervous system -- Degeneration -- Treatment , Memory disorders -- Treatment , Quinolinic acid
- Description: Accumulating evidence suggests that quinolinic acid has a role to play in disorders involving impairment of learning and memory. In the present study, the effect of the guanosine analogue antiherpetic, acyclovir, on quinolinic acid-induced spatial memory deficits was investigated, as well as some of the mechanisms which underlie this effect. Behavioural studies using a Morris water maze show that post-treatment of rats with acyclovir significantly improves spatial memory deficits induced by intrahippocampal injections of quinolinic acid. Histological analysis of the hippocampi show that the effect of acyclovir is related to its ability to alleviate quinolinic acid-induced necrotic cell death, through interference with some of the mechanisms of neurodegeneration. However, acyclovir is unable to alter a quinolinic acid-induced increase in glutamate release in the rat hippocampus, even though it alleviates quinolinic acid induced oxidative stress by scavenging the superoxide anion in vitro and in vivo in whole rat brain and hippocampus respectively. Due to the inverse relationship which exists between superoxide anion and glutathione levels, acyclovir also curtails the quinolinic acid-induced decrease in hippocampal glutathione levels. Acyclovir suppresses quinolinic acid-induced lipid peroxidation in vitro and in vivo, in whole rat brain and hippocampus respectively, through its alleviation of oxidative stress and possibly through the binding of iron (II) and / or iron (III), preventing the participation and redox recycling of iron (II) in the Fenton reaction, which quinolinic acid is thought to enhance by weak binding of ferrous ions. This argument is further strengthened by the ability of the drug to suppress iron (II)-induced lipid peroxidation in vitro directly. Inorganic studies including ultraviolet and visible spectroscopy, electrochemistry and the ferrozine assay show that acyclovir binds to iron (II) and iron (III) and that quinolinic acid forms an easily oxidisable association with iron (II). Acyclovir inhibits the endogenous biosynthesis of quinolinic acid by inhibiting the activity of liver tryptophan-2,3-dioxygenase, intestinal indoleamine-2,3-dioxygenase and rat liver 3-hydroxyanthranillic acid oxygenase in vitro and in vivo, possibly through competitive inhibition of haeme, scavenging of superoxide anion and binding of iron (II) respectively. An inverse relationship exists between tryptophan-2,3-dioxygenase activity and brain serotonin levels. Acyclovir administration in rats induces a rise in forebrain serotonin and 5-hydroxyindole acetic acid and reduces the turnover of forebrain serotonin to 5-hydroxyindole acetic acid. Furthermore, it shows that acyclovir does not alter forebrain norepinephrine levels. The results of the pineal indole metabolism study show that acyclovir increases 5-hydroxytryptophol, N-acetylserotonin and the neurohormone melatonin, but decreases 5-hydroxyindole acetic acid. The results of this study show that acyclovir has some neuroprotective properties which may make it useful in the alleviation of the anomalous neurobiology in neurodegenerative disorders.
- Full Text:
- Date Issued: 2006
- Authors: Müller, Adrienne Carmel
- Date: 2006
- Subjects: Acyclovir -- Therapeutic use , Acyclovir -- Physiological effect , Nervous system -- Degeneration -- Treatment , Memory disorders -- Treatment , Quinolinic acid
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3776 , http://hdl.handle.net/10962/d1003254 , Acyclovir -- Therapeutic use , Acyclovir -- Physiological effect , Nervous system -- Degeneration -- Treatment , Memory disorders -- Treatment , Quinolinic acid
- Description: Accumulating evidence suggests that quinolinic acid has a role to play in disorders involving impairment of learning and memory. In the present study, the effect of the guanosine analogue antiherpetic, acyclovir, on quinolinic acid-induced spatial memory deficits was investigated, as well as some of the mechanisms which underlie this effect. Behavioural studies using a Morris water maze show that post-treatment of rats with acyclovir significantly improves spatial memory deficits induced by intrahippocampal injections of quinolinic acid. Histological analysis of the hippocampi show that the effect of acyclovir is related to its ability to alleviate quinolinic acid-induced necrotic cell death, through interference with some of the mechanisms of neurodegeneration. However, acyclovir is unable to alter a quinolinic acid-induced increase in glutamate release in the rat hippocampus, even though it alleviates quinolinic acid induced oxidative stress by scavenging the superoxide anion in vitro and in vivo in whole rat brain and hippocampus respectively. Due to the inverse relationship which exists between superoxide anion and glutathione levels, acyclovir also curtails the quinolinic acid-induced decrease in hippocampal glutathione levels. Acyclovir suppresses quinolinic acid-induced lipid peroxidation in vitro and in vivo, in whole rat brain and hippocampus respectively, through its alleviation of oxidative stress and possibly through the binding of iron (II) and / or iron (III), preventing the participation and redox recycling of iron (II) in the Fenton reaction, which quinolinic acid is thought to enhance by weak binding of ferrous ions. This argument is further strengthened by the ability of the drug to suppress iron (II)-induced lipid peroxidation in vitro directly. Inorganic studies including ultraviolet and visible spectroscopy, electrochemistry and the ferrozine assay show that acyclovir binds to iron (II) and iron (III) and that quinolinic acid forms an easily oxidisable association with iron (II). Acyclovir inhibits the endogenous biosynthesis of quinolinic acid by inhibiting the activity of liver tryptophan-2,3-dioxygenase, intestinal indoleamine-2,3-dioxygenase and rat liver 3-hydroxyanthranillic acid oxygenase in vitro and in vivo, possibly through competitive inhibition of haeme, scavenging of superoxide anion and binding of iron (II) respectively. An inverse relationship exists between tryptophan-2,3-dioxygenase activity and brain serotonin levels. Acyclovir administration in rats induces a rise in forebrain serotonin and 5-hydroxyindole acetic acid and reduces the turnover of forebrain serotonin to 5-hydroxyindole acetic acid. Furthermore, it shows that acyclovir does not alter forebrain norepinephrine levels. The results of the pineal indole metabolism study show that acyclovir increases 5-hydroxytryptophol, N-acetylserotonin and the neurohormone melatonin, but decreases 5-hydroxyindole acetic acid. The results of this study show that acyclovir has some neuroprotective properties which may make it useful in the alleviation of the anomalous neurobiology in neurodegenerative disorders.
- Full Text:
- Date Issued: 2006
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