Topical vanadate optimizes collagen organization within granulation tissue

Abstract

Systemic ingestion of vanadate, a nonspecific inhibitor of tyrosine phosphatases, doubles wound breaking strength, enhances the packing of collagen fibers, and prevents the appearance of myofibroblasts in granulation tissue. Will the local application of vanadate mimic the systemic effects? Pairs of polyvinyl alcohol sponges, each with a central reservoir and attached injection port, were subcutaneously implanted in rats. Daily, one implant received 0.2 ml of saline and the other received 0.2 ml of 0.03 mM vanadate in saline. On day 7, harvested sponges had equivalent wet weights. The vanadate-treated sponges had fibroblasts separated by connective tissue, with a more intense birefringence of the collagen fibers. Transmission electron microscopy showed collagen more uniformly packed in the vanadate treated sponges where collagen fibers were equally spaced and had equal diameters. By immunohistology, myofibroblasts, defined by the expression of alpha-smooth muscle actin within stress fibers, were absent in vanadate-treated granulation tissue. The expression of alpha-smooth muscle actin was restricted to smooth muscle cells of blood vessels. Controls had densely packed alpha-smooth muscle actin staining myofibroblasts, weak birefringence, and randomly spaced collagen fibers with irregular diameters. We conclude that the local application of vanadate prevents the appearance of myofibroblasts and optimizes the organization of collagen fibers in developing granulation tissue.

Beta‐adrenoceptor blockade delays granulation tissue formation in polyurethane sponge implants

“…It has been reported that sponge implants are a good model for studying the formation of granulation tissue 8–11 . In that model, involvement of the clotting cascade is minimal and there is no influence of epithelial cells or wound contraction, thereby emphasizing the role of endothelial cells and fibroblasts in the development of granulation tissue 10 .…”

“…In animal wound models, the specific participation of myofibroblasts and endothelial cells in granulation tissue formation is difficult to study because these cells are directly influenced by epithelial cells and wound contraction. Subcutaneous implantation of polyurethane (PU) sponges is an alternative animal model with which to study granulation tissue development and angiogenesis 8–10 . Subcutaneous sponge implants stimulate a foreign body reaction that initiates infiltration by inflammatory cells.…”

Collagen Organization Critical Role in Wound Contraction

“…For instance, vanadate blocks protein tyrosine phosphatases and prevents the expression of aSMA within fibroblasts in full-thickness rat open wounds. 10,11 Vanadate stops the inhibition of MLCP activity, which, in turn, blocks sustained myosin ATPase activity, inhibiting the appearance of myofibroblasts; while leaving the rate and degree of wound contraction unaffected. Thus, the lack of sustained myosin ATPase activity and the absence of myofibroblasts are not essential to wound contraction.…”

A review of fibroblast‐populated collagen lattices

“…The relaxed‐FPCL, which contracts through fibroblast generated tractional forces contain cells that lack stress fibers with α‐SMA, will undergo contraction in the presence of vanadate. Rats topically or systemically treated with vanadate show normal wound contraction in the absence of myofibroblasts 44,45 . The granulation tissue fibroblasts from vanadate‐treated open wounds do not have stress fibers or express α ‐ SMA 44 …”