Subrat Kumar Dash1 and Gloria Tigga2
1Assistant Professor-cum-Junior Scientist, Department of Veterinary Biochemistry, College of Veterinary Science and Animal Husbandry, Birsa Agricultural University, Ranchi-834 006, Jharkhand, India.
2Assistant Professor-cum-Junior Scientist, Department of Veterinary Physiology, College of Veterinary Science and Animal Husbandry, Birsa Agricultural University, Ranchi-834 006, Jharkhand, India.
Heavy metals (Pb, Ni, Cr, Hg., Cd etc.) are highly toxic environmental contaminants. Contamination of our environment by heavy metals is mainly due to human and industrial activities. The toxic effluents from various industries release heavy metals to the environment because of poor waste management system. As a result human along with livestock and plants in the environment are now facing the dangerous effects of heavy metals.
Heavy metals get accumulated in various concentrations in soil and water. Crops, feed, fodder, different plants and livestock including dairy animals acquire the contamination from water, fodder, feed and soil. Livestock get contaminated by heavy metals through environmental sources either by direct and indirect exposure. Drinking water is also a major source of exposure to heavy metals in livestock. The overall effect of heavy metal exposure is damage to animal and environmental health. It is also a serious threat to the public health due to its residual effect and transmission via milk, meat and its products. Hence, it can be considered as one health issue (Fig. 1A).
Heavy metals cause different biochemical, immunological and reproductive disturbances in livestock. They can trigger hematological, circulatory, renal, hepatic, neurological, immunological and reproductive dysfunctions along with different types of cancers. Heavy metals also affect the ovarian function and hormone systems. The exact biochemical mechanisms of different adverse health effects due to heavy metal exposure are still unclear. Generation of reactive oxygen species (ROS) and oxidative stress may play a major role in the pathogenesis due to heavy metal exposure. ROS reacts with cellular biomolecules and induce lipid peroxidation, membrane protein and DNA damage along with many more damage to the cellular system. This might leads to the disruption in antioxidant system of body which serve as the main source of protection against the free radicals. Several functions of the immune cells of body such as clonal expansion, B- and T-cell activation, proliferation, antibody production and apoptosis are under the influence of intracellular oxidant-antioxidant status. However, overproduction of oxidants and disrupted antioxidants due to heavy metal exposure may alter the immune cell’s function causing immunodeficiency, adversely affecting the livestock health and production.
Chelation and antioxidant therapy is considered as an efficient primary therapy for heavy metal exposure. The chelators bind with the heavy metals and enhance their excretion or removal from the body mainly through renal or biliary route. Nutraceutical chelation therapy is a choice with almost no side effects and having low cost for the improvement of livestock health and production. Bark of Terminalia arjuna (Arjun Tree or Arjuna tree) (Fig. 2) is a potential chelating and antioxidant agent. Its therapeutic effect is well mentioned in ancient Indian literature and Vedas. The bark of Terminalia arjuna contains tannins, saponins (arjunic acid, arjunolic acid, arjungenin, arjunglycosides), ellagic acid, gallic acid, flavonoids, oligomeric proanthocyanidines, calcium, zinc, magnesium, copper and coenzyme-Q. The dried bark powder Terminalia arjuna possesses high degree of antioxidant activity. Arjunolic acid isolated from Arjun tree bark possesses metal chelating property. It has been observed that two equatorial hydroxyl groups of arjunolic acid form a five-membered chelate complex with different metals. The formation of the chelate probably helps in removal of heavy metals from body system. However, biochemical mechanisms of heavy metal mediated adverse health effects in livestock and mechanism of chelation by arjunolic acid against different heavy metals is still not investigated. Hence, exploration of the mechanisms of heavy metal mediated adverse health effects in livestock and identification of the constituents of Arjun tree bark possessing metal chelating characteristics should be the current focus to establish the Arjuna bark as a heavy metal chelation therapy in livestock (Fig. 1B).
