Bernhard Michalke and colleagues at the Institute of Ecological Chemistry in Germany discuss our need for better methods to detect age-related diseases

Humans are living longer, particularly in industrialised countries. But with this extended lifespan comes an increased chance of suffering from age-related dementia and nervous system disorders such as Alzheimer's and Parkinson's diseases. These diseases severely reduce an individual's quality of life and are a heavy financial burden on national health systems. Any possible therapeutic cures have so far been limited.

The changes in the body's nervous system that can cause these diseases are the focus of neurotoxicology studies. Research has shown a link between exposure to metals such as aluminium, lead, manganese and mercury and nervous system degeneration. Elevated metal levels were found in the blood and brain samples of neurological disorder sufferers that had industrial manufacturing backgrounds. Exposure can happen in several ways, for example, aluminium is used as an additive in processed food and is present in cookware, contaminated water, medication and antiperspirants. Lead can be found in paints and water pipes in old houses, and glassware, some jewellery and tobacco. Occupational exposure occurs in lead smelters, lead refining and battery manufacturing. Exposure to elevated manganese levels occurs by mining and processing the element. Welding manganese alloys produces toxic fumes and dry-cell batteries and fireworks could contain manganese too. High mercury level sources include fish and dental amalgams. Occupational sources are combustion of fossil fuels or waste, the chloralkali industry, battery production, mercury alloys and polymer synthesis. 

Trace element speciation analysis shows how metals cross the neural barrier to cause disease in the brain

There have been many investigations into the metals' neurological and toxicological effects, but the characterisation of their chemical forms (or trace element speciation) has not always been considered. Knowledge of trace element speciation can lead to a better understanding of how metals cross neural barriers and their potential role in causing disease in the human brain.  
    

During the past few years, speciation analysis has become a valuable tool in highlighting neurotoxic chemical species and their pathways. Powerful techniques have been applied to human samples, mostly blood serum. More research is needed on other components that either transport species to the brain or are present in neuronal tissue or fluids. Some studies on cerebrospinal fluid and brain tissue have shown promise, but obtaining samples can be difficult. Results can also be hampered when the elements being studied are in low concentrations or their chemical forms are not stable. For example, in studies on the role of species such as aluminium-citrate, manganese-transferrin and manganese-citrate, forms in which the metals are able to cross the blood-brain barrier, in neurodegenerative diseases, even sample preparation, separation and storage time can change their identity or alter their concentration, making analytical quality control a challenge.

These challenges and limitations illustrate that element speciation analysis in human body fluids is not an easy task. Until these problems are resolved, there will continue to be a lack of speciation data - data that could be the key to helping us live longer. 

Read more in 'JEM Spotlight: Metal speciation related to neurotoxicity in humans' in issue 5, 2009 of the Journal of Environmental Monitoring.

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