metallothionein as potential biomarker

1. Zn>Cd &Hg>Cu
Pathiratne et al(2009) and Ghedtra et al (2010)
Richard (1994) -MT induction -liver : Hg > Ag> Cu > Zn.
Metallothionein - a potential biomarker to assess the metal contamination in
marine fishes-A review
Metal
Transcription -of MT genes
MT synthesis
•Cd can induce MT expression in Fishes. (Chen et al. 2005, Rovira et
al. 2005, Choi et al. 2007)
•MT transcript proteins -bivalent metal - Zn, Cu, Pb, Fe, Co and Hg.
( Ikebuchi et al. 1986; Carginale et al. 1998; Riggio et al. 2003 )
• Thiele in 1992- MT gene expression ὰ Metal concentration.
•4 MT genes-common promoter-several MREs- which binds to
metal transcription factors-synthesis of MT.(Kling and Olsson in
1993).
Factors Affecting the Metallothionein Estimations
age
Sexual maturity- max variation-female
Olsson et al ( 1987) - Rainbow Trout –hepatic MT levels
Sex
Liver
Muscle
Kidney
brainSkin
Gills
Tissue type
Route of exposure and experimental conditions
MT
Levels
fish
species
tissue
physiology
experimental
conditions
• Chowdhury et al (2005) -Rainbow trout -sub lethal
concentration -waterborne Cd (0 or 3 μg/L) or dietary Cd
(0 or 500 mg/kg dry wt) -30 days
• Waterborne exposure group- highest MT- kidney - Gills
– liver.
• Dietary exposure group-kidney >> cecae and posterior
intestine > liver and stomach > midintestine > gills.
Exogenous and endogenous substances
Experimental problems with MTs
Olsson 1996
Metal Type
Seasonal variations
Future prospects
1. Inorganic Hg Invitro studies Cell culture
Invivo influence
Not clear
Organic-mercury complex
2. Standardization of methods
3.Different methodology used by researchers
•Thiele D J (1992).Metal Regulated Transscription in Eukaryotes. Nucleic Acid
Research.210;1183-1188.
•Kling, P. & Olsson. P. E. (1993). Metal regulation of the rainbow trout metallothionein-A gene.
In: proceedings of the Seventh International Symposium on Responses of Marine Organisms to
Pollutants.
•Geroge S.G.,Hadgson P.A.,Tybler .P.,Tedd.K.,(1996).Inducability of Metallothionein mRNA
expression and Cadmium tolerance in larva of teleosts the turbot (Scophthalmus
maximus).Fundamental Application of Toxicology 33:91-99.
•Singh M R. (2007). Impurities-heavy metals: IR prespective.(George et al.,1996)
Reference
Vijaya * and R. Jayakumar**
*Research Scholar, **Assistant Professor, Department of Environmental Science, GITAM University, Bengaluru Campus, Nagadenahalli-562 163.
KARNATAKA. E-mail:vijayhemmadi@gmail.com
MT as Biomarker
•Ubiquitous , stable & inducible proteins, Mw 6-8kDa, pI-8.3
•High cysteine content (20-30%) - 61 amino acids - no
aromatic amino acids.
• Binds to metals - metal thiolate bonds.
•Metal homeostasis –Zn ,Cu & detoxification – Cd, Hg, Pt, Ag
Introduction
Metallothionein (MTs)
Cd
Higher affinity to MTs tan Zn
Displace Zn from MT binding site
(Hollis L.C and C.M.Wood, 2001)
Maximum
induction
MTs in Tilapia 2mg/kg of Cd No further change
(Y.F.Ueng et al. 1996)