Chemico-Biological Interactions 157–158 (2005) 51–55
Host-regulated disposition of mammalian AChEs
Chanoch Kronman, Ofer Cohen, Baruch Velan, Avigdor Shafferman
∗
Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 74100, Israel
Available online 9 November 2005
Abstract
Primates are characterized by a paucity of soluble acetylcholinesterase (AChE) in the circulation at the adult stage, where
the predominant circulating cholinesterase is butyrylcholinesterase. In recent years, we subjected recombinant human and bovine
acetylcholinesterase to extensivepharmacokineticstudiesinmice,ananimalsystemwhichalsodisplaysverylowlevels of circulating
AChE. In this system, a post-translation-related hierarchical pattern governing circulatory residence through AChE sialylation,
subunit tetramerization and glycan loading was elucidated. Based on these studies, coordinated modulation of the sialic acid
contents, state of subunit assembly and number of glycans allowed us to generate human or bovine AChE forms which reside in
the circulation of mice for long periods of time, mimicking the pharmacokinetic behavior of native serum-derived cholinesterases.
However, extension of the pharmacokinetic studies to primates, revealed an additional element, which affects circulatory residence
of AChEs in this animal system. Unlike in the case of bovine AChE, optimization of subunit assembly and glycan loading of
the primate versions of AChE (human or rhesus) did not increase their circulatory lifetime in rhesus macaques. This differential
pharmacokinetic behavior of bovine and primate AChEs in macaques appears to be related to the 35 diverging bovine/primate AChE
amino acids which are clustered within three defined domains at the enzyme surface, and thereby may facilitate the specific removal
of “self” or “self-like” cholinesterases from the circulation of monkeys and thus provide an explanation for the absence of soluble
AChE in the circulation of primates.
© 2005 Elsevier Ireland Ltd. All rights reserved.
Keywords: Acetylcholinesterase; N-glycan; Pharmacokinetics; Protein oligomerization; Sialic acid
1. Results and discussion
1.1. Post-translation modifications determine the
circulatory behavior of bovine AChE in a similar
manner in mice and rhesus macaques
Extensive pharmacokinetic studies carried out in the
past, utilizing arrays of differently processed bovine or
humanAChEforms,allowedusto demonstrate that sialic
acid occupancy, enzyme assembly status and the num-
ber of appendedN-glycans determine the fate ofAChEin
the circulation of mice. Moreover, these post-translation-
related factors were shown to contribute to the retention
∗
Corresponding author. Tel.: +972 8 9381595; fax: +972 8 9401404.
E-mail address: avigdor@iibr.gov.il (A. Shafferman).
of the enzyme in the circulation of mice by operating
within a hierarchical set of rules. This was manifested
by the findings that: (a) desialylated enzymes varying in
their degree of subunit assembly were eliminated from
the circulation of mice in an equally rapid manner; (b)
conversion of enzyme forms into uniformly assembled
tetramers conferred only a limited increase in the cir-
culatory retention of suboptimally sialylated bovine or
human AChEs; (c) the full effect of tetramerization on
circulatory longevity could be appreciated only in fully
sialylated enzyme forms; and (d) The effect of N-glycan
addition on the pharmacokinetics of human AChE is
fully manifested only in the case of efficiently sialy-
lated tetrameric forms of the enzyme [1–5]. In fact, by
optimizing sialic acid occupancy, enzyme tetrameriza-
tion and glycan loading, the bovine and human recom-
0009-2797/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.cbi.2005.10.005