What effect do high levels of NADH have on the Citric Acid Cycle?

High levels of NADH inhibit the Citric Acid Cycle by indicating that the mitochondrial electron transport chain is saturated or that the energy state of the cell is already high. When NADH accumulates, it suggests that there are sufficient reducing equivalents available for cellular processes, and therefore, the cycle does not need to produce more energy. This feedback regulation occurs because NADH serves as a key electron carrier in the respiratory chain; its surplus signals that the energy needs of the cell are met, leading to a decrease in the activity of the enzymes that facilitate the cycle, such as isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Consequently, this results in a slowdown of oxidative reactions within the cycle, ultimately helping to maintain metabolic balance in the cell.