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Plasma membranes of animal cells are generally impermeable to macromolecules. Protein transduction mediated by protein transduction domains (PTDs) covalently cross-linked to cargoes for cellular internalization has previously been demonstrated. Peptides with PTDs could be an effective way to deliver proteins into living cells or tissues in vitro. In this report, we demonstrate that arginine-rich intracellular delivery (AID) peptides are able to facilitate the delivery of proteins into animal cells and to penetrate skin tissues rapidly. This cellular internalization and transdermal delivery of proteins is mediated by non-toxic AID peptides in a non-fusion protein and non-conjugation dependent manner. The efficiency of intracellular transport is further increased in the presence of chemical enhancer oleic acid. The mechanism of the AID-mediated cellular entry may involve macropinocytosis and actin rearrangement. Thus, we confirm that direct delivery of bioactive proteins into living cells and tissues mediated by non-covalent actions of AID peptides represents a useful strategy in pharmaceutics, therapeutics and cosmetics.

The antinociceptive effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, were investigated on animal paw licking responses and thermal hyperalgesia induced by glutamate receptor agonists including glutamate, N-methyl-D-aspartate (NMDA), and metabotropic glutamate 5 receptor (mGluR5) activator (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), as well as inflammatory mediators such as substance P and prostaglandin E2 (PGE2) in mice. The actions of honokiol and magnolol on glutamate-induced c-Fos expression in the spinal cord dorsal horn were also examined. Our data showed that honokiol and magnolol blocked glutamate-, substance P- and PGE2-induced inflammatory pain with similar potency and efficacy. Consistently, honokiol and magnolol significantly decreased glutamate-induced c-Fos protein expression in superficial (I-II) laminae of the L4-L5 lumbar dorsal horn. However, honokiol was more selective than magnolol for inhibition of NMDA-induced licking behavioral and thermal hyperalgesia. In contrast, magnolol was more potent to block CHPG-mediated thermal hyperalgesia. These results demonstrate that honokiol and magnolol effectively decreased the inflammatory pain. Furthermore, their different potency on inhibition of nociception provoked by NMDA receptor and mGluR5 activation should be considered.