Two Parameters for Biomarker Assessment - Essay Example

Biomarker Assays Biomarkers are Biochemical, physiological or histological indicators of either exposure to or effects of physical stressors or xenobiotic chemicals at the sub-organismal or organismal level (Huggett et al. 1992). In other words "biochemical, cellular, physiological or behavioral variations in the tissue or body fluids or at the level of whole organism that provide evidence of exposure to chemical pollutants, and may also indicate a toxic effect" (English Nature, 2004). The term biomarker encompasses all biological material ranging from bio-molecules such as nucleic acids and proteins (e.g. enzymes) to organelles, cells, tissues, organs and whole organisms which may effect survival of a living being. Biomarkers can be used for analyzing the responses of an organism to the various environmental factors and their effects in its development and reproduction. The development of biomarker assays is required to detect changes in immune responsiveness of an organism to the exposure of different chemicals and organic molecules. Following are the after effects of environmental stress: An increase or decrease of metabolism storage, excretion (MXR, MT, PAH-metabolites) inhibition (ALA-D, AChE) abnormal functioning of endocrine glands damage and repair of DNA, protein, lipid may be affected in case of DNA adducts, antioxidant enzymes, antioxidants biomarkers cellular morphology (lysosomal stability, peroxisomal proliferation) and tissue morphology (histopathology) physiological status such as physical development may be affected behavioral distortions may occur histological alterations In aquatic environment, biomarkers depend upon the physical environmental conditions such as temperature, pH or salinity, as well as toxic concentrations of chemical pollutants or any combination of these. Methods to be used for monitoring biomarker assays: should be contaminant-specific and should be able to separate between natural and anthropogenic factors should be sufficiently sensitive to detect contaminant-related effects under relevant exposure scenarios there should be sufficient information available concerning species, gender, size/age, season, temperature agreed protocols must be available and results must be comparable over years and between laboratories (QA) criteria with which to assess results should be available Biomarkers can be categorized as non-specific and specific according to their responses to a particular element or a group of environmental factors (Mayer et al., 1992). non-specific biomarkers, for example ribonucleic acid/deoxyribonucleic acid, radiolabelled amino acid or nucleotide incorporation, and adenylate energy charge, give direct information on the growth rate or potential of an organism but they can not be used to determine the particular toxicant. Specific biomarkers can be again categorized n to two sub-categories, organ, and toxicant specific according to method of their recognition. Organ specific biomarkers are analyzed by examining changes in concentration specific enzymes in organisms whether as Toxicant-specific biomarkers are analyzed according to the exposure and effects on an organism due to a chemical or group of chemicals. Lactate dehydrogenase (LDH), transaminases, creatine phosphokinase, lysosomal enzymes, alkaline phosphatases and mixed function oxidase are the examples of organ specific biomarkers while as inhibition of acetylcholinesterase (AChE) by organophosphates and inhibition of cytochrome P monooxygenase, methallothionein and metal binding proteins by metals are some of the toxicant specific biomarkers (Mayer et al., 1992; Gagn and Blaise, 1993). There are basically two parameters for biomarker assessment: global reference values and comparative values. global reference values can be developed for DNA adducts, ALA-D, AChE, scope for growth, CEA, PAH-metabolites, GST, lysosomal stability, micronucleus formation, vitellogenin, MT biomarkers and comparative values can be used for ethoxyresoroufin-o-deethylase (EROD), antioxidant enzymes, peroxisomal proliferation, MXR biomarkers. Following are major biomarker assays in aquatic life: Metallothionien (MT): Metallothioneins (MTs) are low-molecular-weight, cysteine-rich proteins that have a high affinity for divalent metallic ions that are assumed to be involved in detoxification and homeostasis of heavy metals. Metallothionien markers involves the measurement of induction of metallothinien by certain metals present in aquatic environment such as Zn, Cd, Cu, Hg etc. and their effects in its effects on the normal organic processes like metabolism and hormonal activities. Metallothionien biomarkers depends upon the availability of intracellular trace metals as Zn, Cu, Cd, Hg, their toxicity, their binding capacity and resistance of the organism. This biomarker shows the metals homeostasis capacity whether the metal is toxic or not. Various researches at Dartmouth points out that mercury and other metal toxication in an aquatic environment may seriously harmful to the development of planktons. Excessive exposure to metals can activate the genes responsible for metallothionein production and heat shock gene which is responsible for stress adoption. Metallothionein is major biomarker to monitor pollution levels of fish habitats. P450 (CYP) The cytochrome P450 (CYP) comprises of a large group of microsomal monooxygenases that catalyze various environmental contaminants such as dioxins, leading to either detoxification or excretion from the animal or generation of carcinogenic intermediates (Shyamal C MAHATA, Ryoichi MITSUO, Jun-Ya AOKI, Hironori KATO AND Takao ITAKURA, 2003) CYP1A1 mRNA Level The the cytochrome P450 (CYP) level in living organism is induces the productin of messenger RNA (mRNA). Therefore CYP1A1 mRNA level in blood circulation of living organisms can be used as a good biomarker. It can be used effectively to analyse the effects of dioxins and carcinogens presents in environments. Concentration of P4501A1 Protein Concentration of P4501A1 protein directly affects the DNA activities within cell nucleolus. This makes P4501A1 protein concentration a good biomarker as DNA activities are basis of physical and behavioral developments of organisms. For example experiment shows existence of two loci of CYP1A in Japanese and European eels this may be inferred as two forms of CYP1A exist widely among the eel species. The analysis of CYP1A concentration may explain genetic distance between European and Japanese eels and differences in there physics (Shyamal C MAHATA, Ryoichi MITSUO, Jun-Ya AOKI, Hironori KATO AND Takao ITAKURA, 2003). Ethoxyresoroufin-o-deethylase Activity (EROD) EROD activity is used to analyze induction of enzymes which metabolize planar organic contaminants such as polycyclic aromatic hydrocarbons (PAHs), planar PCBs, dioxins etc. PAH which are the main components of industrial especially oil industry wastes create potential hazards for aquatic life. Its concentration in aquatic environment is a direct indicator of aquatic life developments. Analysis of all of the above three biomarker together is necessary to correctly evaluate health of living environments. Each biomarker shows the presence of a specific or group of specific toxic elements in environment. A biological alteration in an organism is resultant of every component of its living environment so analyzing just a single biomarker will not give accurate inferences. DNA Adducts DNA adducts are group of chemicals and biological molecules that may entice any DNA activity. Presence and concentration of these DNA adduct such as polycyclic aromatic hydrocarbons (PAHs); other synthetic organics, e.g., nitro-organics, amino triazine pesticides (triazines) influence the development of biomarkers in organisms. It can be used to measure genotoxic effects of hazardous elements present in an environment. The analysis of DNA modifications in aquatic animals may serve as a sensitive marker of exposure to genotoxic contaminants. This is of importance in assessing water quality regarding pollution with genotoxic compounds, food safety analyzing edible aquatic animals and in terms of ecotoxicology. Covalent modification of DNA is considered a crucial event in chemical carcinogenesis and thus may be considered a biomarker of an early genotoxic effect. Measuring DNA adducts is unique in that these lesions may be considered a biomarker of both exposure and effect. Lysosomal Perturbations Lysosomal perturbations are not contaminant-specific biomarker but responds to a wide variety of xenobiotic contaminants and metals. These biomarkers can be used to measures cellular damage and is a good predictor of pathology of an environment. Reactive Oxygen Species Presence of Reactive oxygenated species (ROS), such as superoxide anion radical, singlet oxygen, and hydroxyl radical can cause various cellular injuries, including lipid peroxidation, DNA alteration, protein damage and enzyme deactivation thus effects the growth of living beings and alter their physical development as well as environmental responsiveness. Conclusions Biomarkers are definitive indicators of living conditions of a living being. Presence of various metallic toxicants, oxygenated species, DNA adducts and other elements can be analyzed to monitor their effects in living being. Reference: 1. Baumann JW, Liu J, Klaassen CD. 1993. Production of metallothionein and heat shock proteins in response to metals. Fund Appl Toxicol 21:15-22. 2. Bennett WA, Moyle PB. 1996. Where have all the fishes gone Interactive factors producing fish declines in the Sacramento-San Joaquin estuary. In: Hollibaugh JT (ed.). San Francisco Bay: The Ecosystem. San Francisco: Pacific Division, AAAS, California Academy of Sciences. p 519-42. 3. Brown CL, Luoma SN. 1995. Use of the euryhaline bivalve Potamocorbula amurensis as a biosentinel species to assess trace metal contamination in San Francisco Bay. Mar Ecol Progr Ser 124:129-42. 4. Kjellstrm T (1979) Exposure and accumulation of cadmium in populations from Japan, the United States, and Sweden. 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