Matrix metalloproteinase activity and immunohistochemical profile of matrix metalloproteinase-2 and -9 and tissue inhibitor of metalloproteinase-1 during human dermal wound healing

Characterization of lymphangiogenesis in a model of adult skin regeneration

To date, adult lymphangiogenesis is not well understood. In this study we describe the evolution of lymphatic capillaries in regenerating skin and correlate lymphatic migration and organization with the expression of matrix metalloproteinases (MMPs), immune cells, the growth factors VEGF-A and VEGF-C, and the heparan sulfate proteogylcan perlecan, a key component of basement membrane. We show that while lymphatic endothelial cells (LECs) migrate and organize unidirectionally, in the direction of interstitial fluid flow, they do not sprout into the region but rather migrate as single cells that later join together into vessels. Furthermore, in a modified "shunted flow" version of the model, infiltrated LECs fail to organize into functional vessels, indicating that interstitial fluid flow is necessary for lymphatic organization. Perlecan expression on new lymphatic vessels was only observed after vessel organization was complete and also appeared first in the distal region, consistent with the directionality of lymphatic migration and organization. VEGF-C expression peaked at the initiation of lymphangiogenesis but was reduced to lower levels throughout organization and maturation. In mice lacking MMP-9, lymphatics regenerated normally, suggesting that MMP-9 is not required for lymphangiogenesis, at least in mouse skin. This study thus characterizes the process of adult lymphangiogenesis and differentiates it from sprouting blood angiogenesis, verifies its dependence on interstitial fluid flow for vessel organization, and correlates its temporal evolution with those of relevant environmental factors.

Platelet gels and releasates

PURPOSE OF REVIEW

This review addresses potential roles for platelets and their derivatives (gels, releasates, and lysates) as therapeutic agents for regenerative medicine. Recognizing that activated platelets release chemotactic and growth factors, investigators have attempted to enhance tissue regeneration by applying platelets and various derivatives directly into sites of surgical interventions or injuries. This review analyzes the physiologic basis for this approach to tissue healing and examines the knowledge that has been derived from recent and relevant reports of in-vitro and in-vivo studies.

RECENT FINDINGS

In-vitro studies have established that platelets and their derivatives accelerate proliferation of an array of cells involved in soft and bony tissue regeneration. These effects have been evaluated, also, in vivo in humans and in animals. The outcomes of in-vivo studies are considerable less homogeneous than the outcomes of in-vitro investigations. The resultant discrepancies reflect not only differences of technical protocols, but also the greater complexity of healing vital tissues compared with circumscribed in-vitro studies.

SUMMARY

The preponderance of evidence indicates that platelets and their derivatives have the potential for a substantial therapeutic role in tissue regeneration. The results of recent research indicate that platelet-derived growth factors act in synergy with plasma-derived factors to activate a complex network of autocrine functions that modulate healing. Platelet-derivative products are promising therapeutics that offer new opportunities for research and applications of tissue engineering.

Remodeling of vaginal connective tissue in patients with prolapse

OBJECTIVE

As pelvic organ prolapse progresses, the morphology of the vagina dramatically changes. The objective of this study was to determine whether these changes observed clinically correlate with histologic and biochemical evidence of tissue remodeling

METHODS

After informed consent, full-thickness biopsies of the vaginal apex were obtained at the time of surgery from 77 women. The tissue of 15 premenopausal women with less than stage II prolapse (controls) was compared with that of 62 women with prolapse divided according to their menopausal status. All specimens were examined histologically. Scanning confocal microscopic analysis of fluorescent micrographs was used to quantitate collagen subtypes I, III, and V. Collagen fiber orientation was analyzed by scanning electron microscopy. Gelatin zymography was used to quantitate the expression of the proenzyme and active forms of matrix metalloproteinases (MMP) -2 and -9. Median values were compared using Mann-Whitney U or Kruskal-Wallis tests, where appropriate

RESULTS

Vaginal collagen fibers are arranged in a whorled pattern, with collagen III as the predominant fibrillar collagen. The amount of total collagen in the vagina was increased in women with prolapse relative to women without prolapse (P = .054) primarily due to increased expression of collagen III (P = .031). There was no difference in the expression of proMMP-2, active MMP-2, or proMMP-9; however, active MMP-9 was increased in patients with prolapse (P = .030) CONCLUSION: The increase in collagen III and active MMP-9 expression in the vaginal tissues of patients with prolapse suggests that this tissue is actively remodeling under the biomechanical stresses associated with prolapse.

LEVEL OF EVIDENCE

II-2.

Tissue regeneration and in loco administration of platelet derivatives: clinical outcome, heterogeneous products, and heterogeneity of the effector mechanisms

BACKGROUND

In loco administration of platelet (PLT) derivatives is a relatively new auxiliary treatment for tissue regeneration to be hastened. Enthusiastic reports are faced by more critical ones. The more obvious rationale for the in vivo administration of PLT derivatives resides in their growth factor content.

STUDY DESIGN AND METHODS

The relevant literature was systematically reviewed. Close scrutiny of the technical details was carried out to find out the procedural differences accounting for conflicting results.

RESULTS

An impressively vast heterogeneity of conduct was found in both in vitro and in vivo studies. Major outcome-affecting variables were recognized such as those associated with PLT preparation; growth factor measurement; proliferation test; dose, timing, and administration of the PLT derivatives; study design; and primary endpoints.

CONCLUSIONS

So many variables were found making standardization or confrontation of the in vitro and the in vivo studies barely conceivable or manageable. The mechanisms of action are very complex. The attribution of tissue regeneration capacity of PLT derivatives solely to the PLT-derived growth factors is simplistic. The results obtained through in vitro experiments are indicative for general mechanisms. Their simplistic hold to the complex in vivo environment may be misleading.