Wound Healing and the Use of Medicinal Plants

Abstract

Cutaneous wound healing is the process by which skin repairs itself. It is generally accepted that cutaneous wound healing can be divided into 4 phases: haemostasis, inflammation, proliferation, and remodelling. In humans, keratinocytes re-form a functional epidermis (reepithelialization) as rapidly as possible, closing the wound and reestablishing tissue homeostasis. Dermal fibroblasts migrate into the wound bed and proliferate, creating "granulation tissue" rich in extracellular matrix proteins and supporting the growth of new blood vessels. Ultimately, this is remodelled over an extended period, returning the injured tissue to a state similar to that before injury. Dysregulation in any phase of the wound healing cascade delays healing and may result in various skin pathologies, including nonhealing, or chronic ulceration. Indigenous and traditional medicines make extensive use of natural products and derivatives of natural products and provide more than half of all medicines consumed today throughout the world. Recognising the important role traditional medicine continues to play, we have undertaken an extensive survey of literature reporting the use of medical plants and plant-based products for cutaneous wounds. We describe the active ingredients, bioactivities, clinical uses, formulations, methods of preparation, and clinical value of 36 medical plant species. Several species stand out, including Centella asiatica, Curcuma longa, and Paeonia suffruticosa, which are popular wound healing products used by several cultures and ethnic groups. The popularity and evidence of continued use clearly indicates that there are still lessons to be learned from traditional practices. Hidden in the myriad of natural products and derivatives from natural products are undescribed reagents, unexplored combinations, and adjunct compounds that could have a place in the contemporary therapeutic inventory.

Figure 1

Wound healing cascade—humans. The wound healing process is an orderly sequence of overlapping, interacting processes commonly categorised into four distinct phases: coagulation, inflammation, proliferation/migration/reepithelialization/granulation, and remodelling/maturation. (1) Coagulation: a clot is formed, providing a temporary barrier to fluid loss and pathogen entry, restores haemostasis; acts as a reservoir of bioactive factors and antimicrobials; provides provisional ECM which supports immune cell infiltration and migration; and initiates tissue repair pathways. (2) Inflammation: damage-associated molecular patterns, free radicals, and reactive molecular species are signals to recruit immune cells; increased blood vessel leakiness; release of antimicrobial species; infiltrating immune cells secretes amplifying alarmin (also known as DAMPs) signals; and activation of keratinocytes and fibroblasts. (3) Proliferation/migration/reepithelialization/granulation: migration and proliferation of keratinocytes, fibroblasts, endothelia; resolution of inflammation; collagen/ECM synthesis; decreased vessel permeability; new capillary and lymphatic vessel angiogenesis; reepithelialization; and de novo formation of granulation tissue. (4) Remodelling/maturation: collagen/ECM turnover (synthesis and degradation); ECM reorganisation and realignment; ECM contraction; endothelia and fibroblast apoptosis; repigmentation.

Figure 2

Nonhealing/chronic wounds—humans. The orderly sequence of overlapping, interacting wound healing processes fails to progress in chronic wounds, frequently due to failure to resolve inflammation. (1) Coagulation: usually unaffected. (2) Inflammation: damage-associated molecular patterns, free radicals, and reactive molecular species; high pH; functional activation of proteases, senescence of keratinocytes, and fibroblasts (vessel permeability sustained-aetiology specific). (3) Proliferation/migration: initiation of de novo granulation tissue formation; failure to sustain proliferation; failure to initiate angiogenesis; failure of keratinocytes to migrate and reepithelialise (failure of wound closure); failure to resolve inflammation; and failure to accumulate ECM. (4) Remodelling/maturation: fails to initiate reorganisation and maturation of ECM.