HEAVY METAL POLLUTANT-INDUCED CYTOTOXICITY INVOLVES PERTURBATIONS OF MITOCHONDRIAL FUNCTION

Abstract

Abstract BACKGROUND Environmental pollutants like heavy metals pose a tremendous risk to both animal and human health though the mechanisms underlying their cytotoxic actions at the cellular level remain largely unknown. The freshwater mollusc Lymnaea stagnalis carries hemocynin as its oxygen carrier whereby iron is replaced with copper. As such, this species is highly sensitive to its environmental copper contents and has been used as an important indicator of water quality. Studies have shown that miniscule levels of heavy metals (Pb, Ni, Cu, Co) dissolved in aqueous environments lead to detrimental effects on many of the Lymanea’s vital functions – including respiration and cardiac functions. OBJECTIVES The objective was to determine how heavy metal pulliutants target the cell and its vital functions and if the detirioration of cell motility and viability is a result of the reduced functioning and potential of the cells mitochondria. DESIGN/METHODS We tested the effects of Cu (EC20 as low as 1.8 ug L-1) on isolated blood cells (hemocytes) and neurons from Lymnaea. We sought to determine whether Cu2+ affected cellular viability, motility and neuronal growth cone movements involving cytoskeletal proteins such as actin and tubulin. Cells from the brain were harvested and plated on sigma coated dishes and left to incubate for 3 days to adjust to the environement. They were then stained with mitortracker dyes for mitochondrial potential and movement. The results were captured through live cell imaging and were later analyzed using neurite tracer. We demonstrate the effects of Cu on single mitochondrial movements, structure and function. RESULTS This study provides the first direct evidence that heavy metals such as Cu are indeed cytotoxic and that its detrimental effects on animal health likely involve perturbations of mitochondrial structure and function. Mitochondrial accumulation within the cell started detirioraiting within the first hour of live cell imaging. The mitochondria within the tested cells also started chainging how they cluster within an expanding growth cone. Mitochondrial density decreased substantially and clustered mitohochondira became more fragmeneted which is a positive indication of mitochndrial malfunction. The mitochondrial potential dropped substantially too, indicating that the mitochondria were unable to produce energy like they are suppose to in normal conditions. Finally, this also allowed us to show why heavy metal use in the dentistry profession and other medical professions where heavy metals are used can be linked to cell apoptosis and mitochondrial degradation. CONCLUSION Heavy metals indeed cause malfunction within the cells mitochondria and the reduced functioning disables the cells from fulfilling their associated functions. This was observed through the reduction of breathing, mastication, movement, and neuronal firing of the Lymnaea, which shows a direct realtionship to degraded mitochondria within these cells. Similar results were seen within the hemocytes, which demonstrates that their function of circulating and delivering oxygen was also impaired due to faulty mitochondria.