The impact of the chromium supplementation on insulin signalling pathway in different tissues and milk yield in dairy cows
Chromium can modulate insulin metabolism in periparturient dairy cows (Hayirli et al., 2001). It is well known that dairy cows develop insulin resistance in peripartum period and redirect nutrients from insulin‐dependent to insulin‐independent tissues such as mammary gland in order to maintain high milk production (Sinclair, 2010). Insulin resistance, if pronounced, especially in the early lactation period when the cows are in the state of negative energy balance may be a risk factor for development of post‐partum metabolic and reproductive diseases in dairy cows (Ingvartsen, 2006). As shown by Bunting et al. (1994), the impact of chromium on insulin resistance can be properly evaluated by intravenous glucose tolerance test (IVGTT).
The molecular‐based interference of chromium with insulin signalling pathway was studied mostly in humans and laboratory animals (Chen et al., 2009; Hua et al., 2012). Obtained results indicated that chromium enhances insulin signalling in different tissues.
Stimulating the uptake of glucose into muscle and fat, insulin regulates the disposal and storage of dietary glucose as glycogen and fat (Taniguchi et al., 2006). Insulin regulates glucose uptake into these cells by recruiting membrane vesicles containing the glucose transporters 4 (GLUT4) from the interior of cells to the cell surface, where it allows glucose to enter cells. Insulin transmits its signals through a cell surface tyrosine kinase receptor which stimulates multiple intracellular signalling events. Tyrosine phosphorylated IRS‐1 recruits and activates phosphatidylinositol 3‐kinase (PI3K), which increases serine phosphorylation downstream, starting with protein kinase B (Akt). Therefore, maintaining proper responses of the IRS‐PI3K‐Akt pathway is crucial for normal metabolic signalling of insulin in skeletal muscle (Saltiel and Pessin, 2003). According to the research of Wang et al. (2005), chromium is capable of regulating signal transduction that is mediated via the insulin effector molecules downstream of the insulin receptor, as evidenced by enhanced levels of tyrosine phosphorylation of IRS‐1, elevated phosphorylation of Akt at serine 473 and increased PI3K activity in a variety of cellular models of insulin resistance. Contrary to phosphorylation at tyrosine phosphorylation at serine 307 within IRS‐1 has been shown to significantly attenuate insulin signalling (Hua et al., 2012).
To the best of our knowledge, there is no in vivo study that clarifies the impact of dietary chromium on insulin signalling pathways in tissues of dairy cows. We suppose that investigation of molecular mechanisms underlying the metabolic effects of chromium could contribute to proper establishment of nutrient requirements of dairy cows. National Research Council (2001) did not give a recommendation for chromium intake for ruminants as the Institute of Medicine (2001) did for human population. Additionally, chromium affects milk yield, although the literature data are contradictory if chromium supplementation increases or decreases milk yield (Al‐Saiadya et al., 2004; Bryan et al., 2004; Soltan, 2010), indicating that better understanding of mechanisms involved in chromium interrelationship with energy metabolism is needed.