βA 425–35 modulates substance P effect on rat skin microvasculature in aged rats: pharmacological manipulation using SEC-receptor ligands

Abstract

The primary constituent of the senile plaque core in Alzheimer's disease (AD) is the β-amyloid protein (βA 4). A discrete 11 amino acid fragment of the βA 4, βA 425–35, has been implicated in mediating in vitro neurotoxicity and an inflammatory response surrounding senile plaques in AD via interaction with the Serpin Enzyme Complex (SEC) receptor. Substance P (SP), a neuropeptide of the tachykinin family and a major mediator of neurogenic inflammation, shows sequence homology to βA 425–35 and has been shown to protect against the neurotoxicity of β-amyloid. SP also competes with βA 425–35 for binding to the SEC-receptor. SP neurons have also been found to be depleted in AD. Using a blister model of inflammation in the rat hind footpad, we have examined the effect of βA 425–35 and its interaction with SP in rat skin microvasculature and determined age-related changes to these phenomena. In addition, pharmacological manipulation of these responses using SEC-receptor ligands (peptide 105Y and 105C) was also undertaken. Because of the evidence for co-existence and co-release of SP and calcitonin gene-related peptide (CGRP) from the peripheral terminals of sensory nerves, it was of interest to examine the interaction of CGRP with βA 425–35 on rat skin microvasculature. βA 425–35 (10 μM) was perfused over the base of a blister raised on the hind footpad of anaesthetised young and old rats. This was followed by perfusion of SP (1 μM) or CGRP (1 μM) after Ringer's solution. Relative blood flow was monitored using a Laser-Doppler Flowmeter. Peptide 105Y or Peptide 105C (100 μM) was perfused over the blister base prior to perfusion of βA 425–35 and SP. The results showed that βA 425–35 induced a vasoconstrictor effect on rat skin microvasculature that was significantly greater in old than in young rats. Furthermore, βA 425–35 prevented a subsequent SP-, but not CGRP-induced vasodilator response in old rats. Perfusion of SEC receptor ligands (peptide 105Y and 105C) or brief perfusion of SP prior to βA 425–35 resulted in a reduction in the vasoconstrictor effect of βA 425–35 and allowed a subsequent SP perfusion to induce a small vasodilator response. This pharmacological manipulation was most evident using peptide 105C. This study demonstrates that skin can provide an index of the effect of βA 425–35 on the microvasculature in vivo and suggests that βA 425–35 prevents SP from inducing a vasodilator effect in old rats through an interaction with the SEC receptor. These modulatory effects can be pharmacologically manipulated using the SEC receptor ligands peptide 105Y, 105C and SP. This blister model of inflammation should be useful for examining further the nature of these interactions and their significance in AD.