Abstract. – Objectives: Metals such as iron are needed for physiological functions of the body. However, their excess may cause serious damage including poisoning. The effects of Fe 2+ and Fe 3+ ions on human plasma cholinesterase activity were investigated. Material and Methods: Plasma were ob- tained (n=24) from healthy male volunteers, and treated with five various concentrations of Fe 2+ and Fe 3+ ions. Activity of butyryl cholinesterase (BChE) was assayed according to colorimetric Ellman procedure. The activity was calculated as micromole of hydrolyzed substrate, per minute in each ml. Results: Both ferric (Fe 3+ ) and ferrous (Fe 2+ ) ions significantly decreased the BChE activity in all tested concentrations. The effect of ferric (Fe 3+ ) ions on the reduction of plasma enzyme activity was more pronounced than ferrous (Fe 2+ ) ions (p<0.001, respect to control group). Conclusions: The present paper represents the effect of Fe 2+ and Fe 3+ ions on ButyrylChE activity in human plasma. It reveals that both ions suppress BChE activity. Key Words: Ellman procedure, Iron, Fe 2+ ions, Fe 3+ ions, Plasma cholinesterase, BChE activity. Introduction Heavy metals, pesticides, chemical sewage and waste water can effect environment. Since these compounds inhibit cholinesterase (ChE) activity, determination of activity of this enzyme is a reliable and widely used biological indicator for exposure to these agents 1-4 . There are two dif- ferent types of ChE in human body, which differ in their location in tissues, substrate affinity, physiological function and sensitivity toward var- ious inhibitors: acetyl cholinesterase (AChE; European Review for Medical and Pharmacological Sciences Effect of Fe 2+ and Fe 3+ ions on human plasma cholinesterase activity M. KARAMI 1 , M.A. EBRAHIMZADEH 1 , M.R. MAHDAVI 2 , A. KAZEMI 1 1 Pharmaceutical Sciences Research Center, School of Pharmacy and Traditional and Complementary Medicine Research Center; 2 Faculty of Paramedical, Mazandaran University of Medical Sciences, Sari (Iran) Corresponding Author: Mohamamd Ali Ebrahimzadeh, Ph.D; e-mail: zadeh20@yahoo.com 897 E.C. 3.1.1.7) which mainly found in the brain, muscles, erythrocytes and cholinergic neurons. ChE plays a major role in the regulation of sever- al physiological events by hydrolyzing the neuro- transmitter acetylcholine in cholinergic synapses. Butyryl cholinesterase (BChE; E.C. 3.1.1.8) is present in glial cells, plasma, originates mainly from the liver and is capable of splitting several choline esters, including acetylcholine 4-7 . This group of enzymes is present not only in liver but also in intestine, kidney, heart, lung, serum and cholinergic synapses, within CNS and plays a major role in the metabolism of ester containing compounds. BChE can also take the place of AChE in the acetylcholine degradation, when acetyl cholinesterase is inhibited or absent 3 . Therefore, the knowledge of the cholinesterase status is crucial for the early diagnosis of organophosphate pesticides (OPs) exposure or intoxication and for monitoring the therapeutic effects of reactivates 8 . The inhibiting power on AChE and BChE varies widely among the differ- ent OP compounds. Some OPs inhibit AChE more strongly and some others BChE. Some oth- ers are stronger inhibitors of BChE than AChE 4 . In exposure to these substances, plasma BChE determination is a more sensitive indicator of ex- posure than AChE. However, BChE inhibition is not associated with symptoms or signs of toxicity 4 . Among the bivalent metal ions, the effects of Hg 2+ , Cd 2+ , Cu 2+ , Mg 2+ and Ca 2+ on BChE from different sources have been investigated 5 . Al 3+ , also has been showed to inhibit sheep brain BChE 6 . Plasma cholinesterase can be depressed by inherited traits or by other causes, notably liv- er disease. Thus, estimation of AChE activity gives us more reliable information in these situa- tions 4 . Iron ions (Fe 2+ and Fe 3+ ) have many func- tions in body including oxygen transport and en- zyme activity 5 . The main function of iron is to 2010; 14: 897-901