Cysteine Thioesters as Myelin Proteolipid Protein Analogues to Examine the Role of Butyrylcholinesterase in Myelin Decompaction

Abstract

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disorder involving demyelination, axonal transection, and neuronal loss in the brain. Recent studies have indicated that active MS lesions express elevated levels of butyrylcholinesterase (BuChE). BuChE can hydrolyze a wide variety of esters, including fatty acid esters of protein. Proteolipid protein (PLP), an important transmembrane protein component of myelin, has six cysteine residues acylated, via thioester linkages, with fatty acids, usually palmitic, that contribute to the stability of myelin. Experimental chemical deacylation of PLP has been shown to lead to decompaction of myelin. Because of elevated levels of BuChE in active MS lesions and its propensity to catalyze the hydrolysis of acylated protein, we hypothesized that this enzyme may contribute to deacylation of PLP in MS, leading to decompaction of myelin and contributing to demyelination. To test this hypothesis, a series of increasing chain length (C2-C16) acyl thioester derivatives of N-acetyl-l-cysteine methyl ester were synthesized and examined for hydrolysis by human cholinesterases. All N-acetyl-l-cysteine fatty acyl thioester derivatives were hydrolyzed by BuChE but not by the related enzyme acetylcholinesterase. In addition, it was observed that the affinity of BuChE for the compound increased the longer the fatty acid chain, with the highest affinity for cysteine bound to palmitic acid. This suggests that the elevated levels of BuChE observed in active MS lesions could be related to the decompaction of myelin characteristic of the disorder.

Thioesters for the in vitro evaluation of agents to image brain cholinesterases

“…This is supported by the observation that for AChE, like the analogous thiocholine esters, the acetyl ester of N-methyl-4-piperidinethiol (7, Table 1) had the greatest affinity, followed by the propionyl ester (8), while the butyryl derivative (9) was not hydrolyzed by AChE under these conditions. In addition, BuChE affinity increased with longer substrate side chains, consistent with the known preference of this enzyme for longer acyl chains 27,35 . The observation that the thioester analogue of MP4B is BuChE-specific is also in keeping with the earlier report 25 that the ester is only hydrolyzed by BuChE.…”

“…The Ellman spectrophotometric method 26 , or variations thereof 27 , remains the most rapid, reliable and sensitive means to measure AChE or BuChE activity. The principle on which this assay is based is that, thioesters, such as acetylthiocholine and butyrylthiocholine, should be kinetically analogous to their corresponding esters with respect to cholinesterase catalysis.…”

The Effects of Repetitive Transcranial Magnetic Stimulation on Cognitive Impairment and the Brain Lipidome in a Cuprizone-Induced Mouse Model of Demyelination

“…However, rTMS only normalized the levels of sphingolipids in the hippocampus and PFC. Furthermore, a growing body of evidence indicates that abnormalities in glycerolipid and fatty acyl compositions may also be involved in demyelination ( Sanchez et al, 1998 ; Pottie et al, 2011 ). The present study showed that CPZ treatment decreased glycerolipid levels in both the PFC (DG and MG) and striatum (MG).…”

Structure and therapeutic uses of butyrylcholinesterase: Application in detoxification, Alzheimer's disease, and fat metabolism

“…In fact, many BChE inhibitors showed capacities to attenuate neuroinflammation. Additionally, in multiple sclerosis, the activation of immune cells microglia would promote the elevation of BChE, 248 and the role of BChE in immune system deserves further studying. In all, the in vivo effects of BChE inhibitors on reversing impaired cognition might not only through elevating ACh, but also through immune response, which is still an understudied field so far.…”