Metabolic consequences of sepsis. Correlation with altered intracellular calcium homeostasis

The availability of adequate substrate for energy homeostasis is a minimal requirement for vital organ function that normally is provided through dietary intake. When dietary sources of nutrients are inadequate, the body relies on alternate sources of energy provided by gluconeogenesis, lipolysis, and ketogenesis. Sepsis is associated with disruption of virtually all these provisional sources of energy substrate (see Fig. 4). In addition, sepsis impairs the function of the glycolytic pathway, the integrity of which is necessary for glucose to be used effectively for energy production. These abnormalities, coupled with disruption of the intracellular energy-producing machinery (e.g., glycolytic and gluconeogenic enzymes, mitochondria) eventually lead to a reduction in intracellular ATP. Furthermore, a reduction in intracellular ATP can undermine virtually all the energy-consuming functions of the cell, including energy substrate formation (e.g., failed gluconeogenesis), antioxidant production, and calcium homeostasis. High levels of intracellular calcium, in turn, are known to activate many potentially destructive enzymatic pathways (e.g., proteases, phospholipases, endonucleases) that further diminish cell function and may result in cell death. In this context, iCa2+ accumulation may play an important role in the progression from early sepsis to MODS, the most common cause of mortality in the ICU.