Exploring Methamphetamine Nonenantioselectively Targeting Toll-like Receptor 4/Myeloid Differentiation Protein 2 by in Silico Simulations and Wet-Lab Techniques

Methamphetamine (METH)
is one of the highly addictive nonopioid
psychostimulants, acting as a xenobiotic-associated molecular pattern
(XAMP) to target TLR4 and activate microglia. However, the molecule
recognition of METH by innate immune receptor TLR4/MD-2 is not well-understood.
METH exists in two enantiomeric forms, and it is unclear whether the
TLR4 innate immune recognition with METH is stereoselective. Herein,
molecular dynamics (MDs) simulations were performed to dissect the
recognition of (+)-METH and (−)-METH by TLR4/MD-2 at the atomic
level. Amphetamine (AMPH), which is an analogue of METH, was also
investigated for comparison. Computational simulations indicate that
METH binds into the interaction interface between MD-2 as well as
TLR4* that is from the adjacent copy of TLR4-MD-2, therefore stabilizing
the active heterotetramer (TLR4/MD-2)2 complex. The calculated
binding free energies and potential of mean force (PMF) values show
that (−)-METH and (+)-METH have similar TLR4/MD-2 binding affinity.
Further dynamics analyses of bindings with TLR4/MD-2 indicate that
(−)-METH and (+)-METH behave similarly. Unlike the stereoselective
neuron-stimulating activities of METH, no enantioselectivity was observed
for METH interacting with TLR4/MD-2 complex as well as activating
TLR4 signaling. Compared to METH, AMPH showed much weaker interactions
with TLR4/MD-2, indicating that the substituted methyl group is critical
in the molecular recognition of METH by TLR4/MD-2. In all, this study
provides molecular insight into the innate immune recognition of METH,
which demonstrates that METH could be nonenantioselectively sensed
by TLR4/MD-2.