Autonomic neuropeptides in the interface membrane of aseptic loose hip prostheses

We analyzed the presence of autonomic nerve fibers in the interface membranes (n = 9) surrounding aseptic loosened hip prostheses by immunohistochemistry. The study focused on the autonomic messengers neuropeptide Y (NPY), tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of noradrenaline (NA), and vasoactive intestinal polypeptide (VIP). Protein gene product (PGP) 9.5, a general marker of peripheral nerve fibers, was also analyzed to establish the neuronal character of the immunoreactive structures. PGP 9.5-positive and NPY-positive nerve fibers were identified in all 9 samples, and VIP-immunoreactive and TH-immunoreactive fibers were found in 7. There was a difference in the distribution of nerve fibers both between and within the samples. Among the neuropeptides analyzed, NPY was most abundant. NPY-positive and TH-positive fibers were predominantly found around the blood vessel walls forming varicose nerve terminals. VIP-positive fibers were mainly observed as thin varicose nerve terminals with no relationship to blood vessels. Autonomic neuropeptides exert not only vasoactive and immunoregulatory effects, but also have been found to have direct effects on bone tissue. Moreover, the autonomic nervous system has been strongly implicated in nociception and inflammation. Neuronal NPY, TH, and VIP in the interface membrane may prove to contribute to the pathologic mechanisms leading to aseptic loosening of hip prostheses.