Weighing in on heavy metals in biology and human health

It’s hard to miss the latest addition to the New York City skyline. The Freedom Tower, which opened earlier this year, stands almost 1,800 feet tall and weighs over 40,000 metric tons. The construction of this magnificent edifice would be impossible if not for the unique properties of the heavy metal alloys which account for most of its mass. Fascinatingly, and somewhat coincidentally, these elements and their unique properties have also been exploited by Mother Nature. In fact, many of the same metals used to build One World Trade Center play extremely vital roles in our biology and overall health.

Many people are aware of the presence of heavy metals in their jewelry, electronic devices, and household appliances. However, few realize that their cells also contain trace amounts of these lustrous entities.  In fact, every living thing requires certain quantities of heavy metals in order to survive. The most biologically relevant of these include: Iron, Copper, Zinc, and Manganese. These elements are often found acting as structural supports, catalytic workhorses, and chemical transporters. [share_this_post]

In most biological settings, metals exist as strong cations. A ‘cat-ion’ simply means that the atom has more protons than electrons (endowing it with a positive change). Because of their intrinsic charge, metal ions are highly reactive and even a potential danger to other molecules within the cell’s cytoplasm. To curb this threat, living cells have evolved mechanisms to keep the total amount of ‘free’ metal to almost zero percent.  So once a metal ion enters the cell, it is either quickly directed to storage or immediately used.

As mentioned, metal ions can be versatile structural supports. This is because, unlike the majority of atoms found within the cell, they can adopt extremely intricate geometries. This enables them to ‘glue’ together molecular interactions that would otherwise be impossible to satisfy. Nowhere is this better exemplified than in a family of proteins called Zinc Fingers. Zinc fingers use one or two charged zinc ions to contort the protein into a structure that can seamlessly fit into the grooves of a DNA molecule. Once bound to the DNA, this protein can regulate the transcription of whatever coding region it is associated with. Because of their unparalleled specificity, researchers are trying to customize Zinc fingers to bind and block access to specific stretches of abnormal DNA that may occur in individuals with certain diseases. – A therapy based on this principle is currently in trial for Huntington’s disease.

The power of metal ions is not limited to structural support. Metals have a hearty ability to facilitate the flow of charged particles –this is what makes them so useful for electronics. Amazingly, the machinery within the cell figured out how to utilize this attribute some 3 billion years before the first transistors were even conceived. Both Photosynthesis and Biological Respiration (the conversion of food into energy) require the facilitated movement of charged electrons in order to harvest useful energy that can be used by the cell. The proteins that perpetuate this electron movement rely on the conductive properties of manganese, copper and iron ions. This aptitude to transfer electrons, called redox (reduction and oxidation), accounts for some of the most intricate chemistry observed in living things.

Interestingly, Aβpeptides, which are related to the Alzheimer’s disease, have the ability to rip these metal ions from their proper places, destroying the cells ability to produce energy and likely perpetuating the ailment’s devastating symptoms. Some researchers are devising ways to attenuate Aβ peptide’s ability to bind metals in hopes that it may slow the progression of the disease.

Electrons are not the only molecules that metal ions can shuttle around. Red blood cells are composed mainly of one iron-binding molecule, called hemoglobin. Iron ions contain extremely strong positive charges. Because of this, they are prone to mingling with molecules that have negative charges, such as oxygen. Intriguingly, the oxidation of iron allows the body to hold onto and distribute oxygen to every cell in the body. The red color of blood is actually caused by a change in the way the iron is geometrically positioned when it interacts with oxygen; this is why veins carrying oxygenated blood appear red, while veins carrying deoxygenated blood appear blue. This exact phenomenon is why the steel bodies of old car eventually turn a rusted red color, as well as why the planet Mars has a rosy hue.

Misregulation of iron absorption may have severe consequence to a person’s health. Too little iron can be associated with anemia and lead to chronic fatigue and heart problems. Too much iron in the blood can be just as bad. Hemochromatosis occurs when the body absorbs too much iron from food, putting a storage and detoxification burden on the kidneys and liver. Dietary alterations in conjunction with iron supplementation (for anemia) or blood donations (for hemochromatosis) can significantly reduce any long term risks associated with these sicknesses (of course these means should only be pursued after one consults with a physician)

It may be hard to believe, but the same metals that shape our city’s skyscrapers, runs through our veins. Nature and evolution -like us- has used what has been available to it, to build. As scientists begin to better map out the complicated biology of the cell, they are opening up new routes for approaching sickness and disease as well as revising old perceptions about general biology. No doubt these investigations will identify even further examples of how trace entities can have towering impacts on our health.



Image Credit: NYC skyline take by Kenric Hoegler blended into Scanning electron micrograph of human erythrocytes (red blood cells) by David McCarthy- used with permission of photographer David McCarthy

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