Evaluation of the Current Evidence on Hyperhomocysteinaemia in Neurological Diseases
Evaluation of the Current Evidence on Hyperhomocysteinaemia in Neurological Diseases
US Neurology - Volume 4 Issue 2
Homocysteine – A Marker for Vitamin Deficiency and a Risk Factor for Neurological Diseases
Homocysteine (Hcy) is the demethylated product of methionine. This toxic amino acid can be removed by remethylation to methionine via methionine synthase, which utilises 5-methyl tetrahydrofolate as a methyl donor and methyl cobalamin as a co-factor. An alternative remethylation pathway for Hcy depends on betaine-Hcy-methyltransferase, which utilises betaine as a methyl donor. Another method of Hcy catabolism is via two vitamin-B6-dependent enzymes, cystathionine beta synthase and cystathioninase, to cysteine. The catabolism of Hcy in the brain depends mainly on its remethylation to methionine, utilising folate and methyl cobalamin. Because B vitamins (folate, vitamin B12, vitamin B6) are important co-factors for Hcy catabolism, an elevated concentration of Hcy can indicate B-vitamin deficiency.1 An important role of Hcy-methionine metabolism is to provide S-adenosylmethionine (SAM), the methyl donor for numerous biological reactions. SAM donates its methyl group to a methyl acceptor and is transformed to S-adenosylhomocysteine (SAH). SAH is hydrolysed to Hcy by SAH-hydrolase. The SAH-hydrolase reaction is reversible, but favours SAH formation in the presence of increased Hcy. Hcy metabolism in the brain is an important source of SAM.2 This methyl donor plays important roles in the formation and catabolism of neurotransmitters and phospholipids (phosphatidylcholine is the methylated product of phosphatidylethanolamine), DNA methylation and activation of several enzymes that have essential roles in the brain (e.g. protein phosphatase 2A [PP2A]). Elevated levels of Hcy can therefore cause damage to several key pathways in the central nervous system, either directly or by changing the methylation potential (SAM/SAH).
Changes in brain volume and intensity or the presence of small infarcts are early signs of dementia. These conditions can be detected by magnetic resonance imaging (MRI) of the brain. Changes in these MRI parameters indicate increased risk of stroke, dementia and Alzheimer’s disease (AD). Numerous studies have found an association between plasma concentrations of Hcy and qualitative or quantitative MRI analyses.3,4 Additionally, several longitudinal studies have documented an association between baseline Hcy, folate, vitamin B12 or vitamin B6 concentrations and decline in cognitive function with age.
Evidence has suggested that increasing intake of the B vitamins may have a protective effect on the central nervous system. This effect can be related either to lowering Hcy or to a direct effect of the vitamins. An improvement in cognitive impairment or delaying its progression by Hcylowering vitamins may support a causal role for hyperhomocysteinemia (HHcy) in neurodegenerative diseases. In this article we discuss recent findings from longitudinal, observational and treatment studies on the role of Hcy in neurodegeneration.
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Specialities:
- Neurology
- ADHD
- Advanced Parkinson's Disease
- Anxiety Disorder
- Brain Cancer
- Cerebrovascular Disease
- Dementia
- Epilepsy
- Mood Disorders
- Motor/Movement Disorder
- Multiple Sclerosis
- Neuroimaging
- Neurosurgery
- Obsessive-Compulsive Disorder
- Pain/Headache
- Parkinson's Disease
- Psychiatry
- Schizophrenia
- Sleep Disorder
- Stroke
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