Probing the biochemistry of toxic metals in the bloodstream

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Human activities, such as fossil fuel consumption and mining, emit quantities of toxic metals (arsenic, cadmium, mercury and manganese) that rival or exceed natural global emissions. These emissions are expected in increase. Coal consumption, for example, is expected to increase by 20% over the next 25 years. In addition, millions of people are exposed to toxic metals at their workplace through the inhalation/ingestion of toxic metal-containing dusts (e.g. sheet metal flame cutting, welding, etc.). Since toxic metals are absorbed from the gastrointestinal tract and/or the lungs, they will eventually enter the bloodstream. Although we accurately know the concentrations of the aforementioned toxic metals in the human bloodstream of the average population (these data are determined in regular intervals by the Centers of Disease Control and Prevention of the United States), we don't know at present what these concentrations mean. This undesirable situation must be largely attributed to our lack of understanding the fundamental chemical processes that unfold once these toxic metals enter the bloodstream, which in turn is associated with the difficulty of analyzing blood. Blood plasma, for example, contains up to 10,000 individual proteins. To gain much needed insight into the interactions of toxic metals in the bloodstream, my group has developed a unique visualization method for the analysis of plasma. Instead of analyzing the latter for the thousands of proteins, our method specifically analyzes plasma for those proteins which contain a bound metal and are therefore referred to as metalloproteins. The latter deliver sufficient amounts of dietary iron, copper and zinc to our organs where they are important building blocks for the assembly of proteins which maintain vital biochemical processes. From a toxicological point of view, the binding of dietary iron, copper and zinc to plasma proteins in the bloodstream is a critical step in their metabolism which can be adversely affected by toxic metals. In addition, a toxic metal may be inadvertently transported to an organ (where it causes toxicity) by binding to certain metalloproteins. Furthermore, the influx of a toxic metal into the bloodstream may change the concentration of certain metalloproteins over time. In order to probe all of these toxicologically highly relevant processes, we will use rabbits as a model organism. We will first conduct experiments with rabbit plasma to which a toxic metal is added. Simultaneous analysis of the plasma for metalloproteins and the added toxic metal will provide insight into the transport of the latter in the bloodstream and will contribute to establish the mechanisms which define the target organ of any given toxic metal. Next we will carry out similar experiments with rabbit whole blood. These investigations are expected to allow us to isolate novel toxic metal containing metabolites, which will be structurally characterized at the Canadian Light Source. This is important to identify metabolites which play a critical role in their toxicity. Since the methodology that we will employ can analyze plasma in 25 minutes, we will complement the aforementioned "test tube" experiments with studies using anesthesized rabbits. After the injection with a toxic metal, the analysis of plasma for the contained metalloproteins over an 8 h period will reveal changes of certain metalloprotein concentrations over time. It is expected that these studies will provide unique insight into the systemic toxicity of toxic metals. Overall, my research program will allow us to obtain fundamentally new insight into the toxicology of metals in the mammalian bloodstream, which will ultimately contribute to better inform Canadian public policy on the regulation of toxic metals.