2.3. Glucose Metabolism
Cirrhotic patients also suffer from impaired glucose metabolism and many of them develop diabetes mellitus. Synthesis of glycogen takes place in liver and SK muscles; they are the main reservoir of glycogen too. This glycogen store is very important in controlling blood glucose level. Cirrhotic patients have low level of glycogen store in their liver and SK muscle compared to healthy individuals [31]. BCAAs facilitate glucose uptake by liver and SK muscle as well as enhancing glycogen synthesis. Nishitani et al. [32] collected soleus muscles from healthy rats and incubated them with leucine in insulin-free conditions to test the effect of leucine on glucose uptake. They found that leucine promotes glucose uptake; moreover, α-ketoisocaproic acid, a metabolic product of leucine, showed similar stimulatory effect. They observed that inhibition of phosphatidylinositol 3-kinase (PI3-kinase) or protein kinase C (PKC) by selective inhibitors leads to complete loss of stimulatory effect of leucine. However, rapamycin treatment showed no effect. These observations indicate that leucine stimulates glucose transport in SK muscle by insulin-independent manner through PKC and PI3-kinase pathways rather than mTOR pathway. In another study Peyrollier et al. [33] deprived myoblast L6 cells ~1 h for AAs and after that incubated them with leucine. They observed a significant increase of PI3-kinase and p70 S6 kinase activity. They also found that glycogen synthase kinase-3 (GSK-3) is inactivated by leucine. GSK-3 is an enzyme that inactivates glycogen synthase (GS) activity and stops glycogen synthesis. These results suggest that BCAA supplementation may enhance glycogen synthesis by activating GS.