ARTICLE 60 FEED & ADDITIVE MAGAZINE January 2023 basal diet without AKG supplementation. A study conducted by Pradhan et al. (2021), showed that when AKG and L-carnitine combination was fed in the diet increased activity of digestive enzymes in tilapia. Increased digestive enzyme activity will improve the digestion and absorption of nutrients, thus enhance growth performance. 3. As an antioxidant Antioxidant capacity is an important indicator to reflect the health status of organisms. The antioxidant system includes the enzyme system (Superoxide dismutase, Catalase, Glutathione) and the coenzyme system, which will be affected by the breeding environment and the feed composition. AKG may indirectly regulate an organism's redox status as it is a highly ammonia and phosphate-binding factor. The antioxidant capacity of alpha-ketoglutarate helps in scavenging reactive oxygen species (ROS) in organisms. AKG plays an important role in antioxidant mechanism as precursors of Glu, Gln, and proline. Gln plays a role in eliminating free radicals because it acts as a precursor for synthesis of the antioxidant glutathione. Specially, proline, as conditionally essential amino acids in fish, can be produced from AKG and plays a key role in protein synthesis, wound healing, and antioxidative reaction. These may be the reasons for effective functions of AKG in antioxidant mechanism. Studies report that dietary AKG supplementation in fishes resulted in inhibiting lipid peroxidation by enhancing the activities of antioxidant enzymes like SOD, CAT, Glutathione peroxidase (GSHPx). The process of non-enzymatic oxidative decarboxylation of AKG in hydrogen peroxide decomposition reduces the level of hydrogen peroxide in the cells, resulting in the conversion of AKG to succinate with release of carbon dioxide and water. Recent studies on AKG supplementation proved that the rise in contents of CAT and total antioxidant capacity (T-AOC) are paralleled by a decrease in the content of malondialdehyde (MDA) in the intestine of Songpu mirror carp, and significantly increased SOD, GSHPx, and CAT activities in grass carp. This is indicating that AKG supplementation could reduce oxidative damage and increase antioxidant capacity, as well as promote the radical scavenging ability when supplemented in aquafeed. 4. As an immunomodulatory agent AKG is also known as the immune nutrition factor and therefore crucial for the function of the immune system. The importance of AKG as a source of Gln and Glu is already well documented, i.e., AKG as a glutamine homologue has immuno-enhancing properties, can maintain a gut barrier, increase immune cells and the activity of neutrophils and phagocytosis, reduce bacterial translocation in vivo derivative. Glutamine is one of the crucial fuels for lymphocytes and macrophages. Macrophages and neutrophils are involved in the early, nonspecific host-defence responses and play an important role in the pathophysiology and/or protection against sepsis. Supplementation of dietary AKG may activate the NF-kB, thereby upregulating the expression of pro-inflammatory cytokines and downregulating the expression of anti-inflammatory cytokines. AKG is also capable of reducing the expression of tumour necrosis factor-α. AKG and herbs together may provide a novel, alluring way to improve gut immunity. For example, the administration of AKG along with Chinese herbal medicine can enhance the size of intestinal epithelial lymph nodes and the amount of intestinal Immunoglobulin A (IgA) secreted, indicating that AKG has a positive impact on the immunological function. Wei et al., (2021) reported that AKG supplementation increased the alkaline phosphate which could improve intestinal injury in song-
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