**13. Lipid metabolism**

in protein content of various tissues of fish exposed to different concentrations of insecticides are linked through a biochemical metabolic pathway. For example, Bose et al. (2011) reported the increase in the protein level in liver of freshwater fish (*Oreochromis niloticus*) was maybe due to check the influence of thiamethoxam and effort to recover from the stress of insecticide at lower doses. They found when the concentration of thiamethoxam was increased; there was decrease in liver protein level. Thus, reduce a significant portion of protein in different tissues, especially the liver, may have been due to their degradation and possible utilization for metabolic purposes. Increases in free amino acid levels were the result of breakdown of protein for energy and impaired incorporation of amino acids in protein synthesis. Since, free amino acids are used in gluconeogentic pathway to glucose production, reduced levels of protein

Transaminase play an important role in breakdown of protein to free amino acids which may be used an energy source for glyconegenic pathways or used to synthesis new proteins to repair damaged tissues. So, change in plasma free amino acid levels indicates either an increase

Aspartate transaminase (AST), or serum glutamic oxaloacetic transaminase (SGOT) is a pyridoxal phosphate (PLP)-dependent transaminase enzyme. AST catalyzes the reversible transfer of α-amino group between aspartate and glutamate and, as such, is an important enzyme in amino acid metabolism. Alanine transaminase or ALT is a transaminaseenzyme. It is also called serum glutamic pyruvic transaminase (SGPT). It catalyzes the transfer of an amino group from alanine to α-ketoglutarate, the products of this reversible transamination reaction being pyruvate and glutamate. Aspartate aminotransferase and alanine aminotransferase are found in the liver, heart, skeletal muscle, kidney, pancreas, spleen, erythrocyte, brain and gills (Banaee et al., 2011). Tyrosine aminotransferase (or tyrosine transaminase) is an enzyme present in the liver and catalyzes the conversion of tyrosine to 4-hydroxyphenylpyruvate. Alteration in deamination and transamination of amino acid are associated with changes in nitrogen metabolism, which can be detected in terms of plasma nitrogenous metabolite levels. Free amino acid is also contributed in the formation of excretory product by the process of

The increase in intracellular levels of ROS can lead to lipid peroxidation resulting in an increased permeability of liver cell membrane. As a result, liver enzymes including AST and ALT are released into plasma. In this sense, if the cellular injury is chronic AST and ALT levels will remain elevated (Srivastava et al., 2004; Rao, 2006). Increased activities of AST and ALT were observed in plasma of *Channa punctatus* (Agrahari et al., 2007) exposed to organophos‐ phorus pesticides. Banaee et al., (2008) have reported increased levels of AST and ALT followed by the exposure of common carp to diazinon. Similarly, ROS produced from the metabolism of organophosphate insecticide could be damaged other tissues such as gills, muscle, heart,

kidney and spleen causing the leakage of enzymes into plasma (Banaee et al., 2011).

Impact of different insecticides on the hormones involved in the process of protein synthesis can also affect the tissue protein levels. This was in conformity with the effects of dimethoate on *C. punctatus* (Tripathi et al., 2003). Similar changes in protein content was observed in *Labeo rohitha* (Ramani, 2001), *Etroplus maculatus* (Sulekha and Mercy, 2011), *Anabas testudineus*

synthesis in fish exposed to insecticides.

conjugation.

or a decrease in protein catabolism or biosynthesis.

118 Insecticides - Development of Safer and More Effective Technologies

Lipids play an important role as source of energy for fish. Since, most insecticides are lipophilic compounds, they can easy pass through biological barriers which content lipids and accumulate in fat tissue.Lipids molecules are highly susceptible to oxidative reactions. Due to cell membrane lipid peroxidation of unsaturated fatty acids, short chain fatty acids with R-COOH, R-OOH, R-CHO, and R-OH bases are created which seriously affect the cellular membrane functions such as the activity of hormone receptors and neural mediators, ion transport channels and the activity of membrane enzymes and the transportation of specific molecules. On the other hand, the formation of malondialdehyde (MAD) during peroxidation process of fatty acids having double bonds can create covalent bonds and polymerize cellular membrane components (Sureda et al., 2006; Tejada et al., 2007). In addition, accumulation of fatty acids in the cytosol increased peroxidation of fatty acids in peroxisomes and the endothelial reticulum, resulting in overproduction of ROS and further damage.

Increased levels of stress hormones such as cortisol in blood of fish exposed to various insecticides, stimulates lipid breakdown in adipose tissue. Both elevated and reduced free fatty acids levels in plasma have been observed in different fish species exposed to insecticides. Changes in cholesterol and triglycerides levels in the blood and other tissues such as muscles and liver of fish treated insecticides indicated that effect of these compounds on lipid metabolism.
