Plasma levels of C-reactive protein, interleukin-6, tumor necrosis factor-alpha, and lipid peroxides are high whereas those of endothelial nitric oxide are low in insulin resistance, obesity, type 2 diabetes mellitus, hypertension, hyperlipidemias, metabolic syndrome X, and Alzheimer's disease suggesting that these diseases are characterized by low-grade systemic inflammation. Recent studies showed that the plasma and tissue activities of enzymes butyrylcholinesterase and acetylcholinesterase are elevated in patients with Alzheimer's disease, and diabetes mellitus, hypertension, insulin resistance, and hyperlipidemia. As a result of this increase in the activities of enzymes acetylcholinesterase and butyrylcholinesterase, the plasma and tissue levels of acetylcholine (ACh) will be low. The "cholinergic anti-inflammatory pathway" mediated by acetylcholine acts by inhibiting the production of tumor necrosis factor, interleukin-1, macrophage migration inhibitory factor, and high mobility group box-1 and suppresses the activation of nuclear factor-kappa B expression. ACh is a neurotransmitter and regulates the levels and activities of serotonin, dopamine and other neuropeptides and thus, modulates both immune response and neurotransmission. Hence, both acetylcholinesterase and butyrylcholinesterase by inactivating acetylcholine may enhance inflammation. This suggests that increased plasma and tissue activities of acetylcholinesterase and butyrylcholinesterase seen in various clinical conditions could serve as a marker of low-grade systemic inflammation.

Keywords: Metabolic Syndrome X - metabolism, Inflammation - metabolism, Cytokines - secretion, Butyrylcholinesterase - metabolism, Alzheimer Disease - metabolism, Biological Markers - metabolism, Acetylcholinesterase - metabolism, Acetylcholine - metabolism