**7.1. Tannins**

Tannins are natural polyphenols and in many cases the active constituents in plants in which they are found. Tannins have a wide range of pharmacological activities including antimicro‐ bial, wound healing, antioxidant and anti‐inflammatory activities. The physical and chemical properties of tannins suggest that they may act by virtue of their complexation, astringent, antioxidant and radical scavenging activities, and their ability to form complex with proteins [194].

### **7.2. Ellagitannins**

Ellagitannins, namely geraniin and furosin isolated from *Phyllanthus muellerianus*, were demonstrated to stimulate cellular activity, differentiation and collagen synthesis of human skin keratinocytes and dermal fibroblasts. Geraniin and furosin increased the cellular energy status of human skin cells (dermal fibroblasts NHDF, HaCaT keratinocytes) and triggered the cells towards higher proliferation rates. Furosin and geraniin stimulated the biosynthesis of collagen from normal human dermal fibroblasts. Geraniin also significantly stimulated the differentiation in normal human epidermal keratinocytes while furosin had a minor influence on the expression of involucrin and cytokeratins K1 and K10. The study proved that geraniin exhibit stimulating activity on dermal fibroblasts and keratinocytes, leading to increased cell proliferation, barrier formation and formation of extracellular matrix proteins [98].

### **7.3. Flavanols and proanthocyanidins**

Flavanols are a sub‐family of flavonoids which are present in plants as aglycones, as oligomers, or esterified with gallic acid and the most common oligomers of procyanidins present in edible plants are derived from epicatechin [189].

Flavanols and procyanidins are chemically able to prevent oxidation, and their administration has been associated with a decrease in oxidative stress markers in humans with improve blood supply to the wounded area to accelerate wound healing. They have been shown to exert a wide range of biological activities including wound healing property. The known biological activities of proanthocyanidins include antioxidant activity, anti‐inflammatory activity, antimicrobial activities and wound healing activities [92, 189, 195].

A redox‐active grape seed proanthocyanidin extract has been shown to up regulate oxidant and tumor necrosis factor‐α inducible VEGF expression in human keratinocytes. Furthermore this grape seed proanthocyanidin extract was shown to accelerate wound contraction and closure *in vivo*, to enhance deposition of connective tissue and to improve histological archi‐ tecture [186].

Wound healing property of *Camellia sinensis,* also known as green tea, has been linked to the presence of proanthocyanidins which are mainly made up of epicatechin, epigallocatechin, epicatechin‐3‐gallate and epigallocatechin‐3‐gallate and these induce differentiation of epidermal keratinocytes and also accelerate epithelial neoformation during wound healing [196].

scores, collagen deposition scores and the neovascularization scores on postoperative days 7 and 14 were found to be significantly higher in the resveratrol treatment group. The amount of granulation tissue and the fibroblast maturation scores were found to be significantly higher on postoperative day 14 in the treatment group when compared to the control group [193].

Tannins are natural polyphenols and in many cases the active constituents in plants in which they are found. Tannins have a wide range of pharmacological activities including antimicro‐ bial, wound healing, antioxidant and anti‐inflammatory activities. The physical and chemical properties of tannins suggest that they may act by virtue of their complexation, astringent, antioxidant and radical scavenging activities, and their ability to form complex with proteins

Ellagitannins, namely geraniin and furosin isolated from *Phyllanthus muellerianus*, were demonstrated to stimulate cellular activity, differentiation and collagen synthesis of human skin keratinocytes and dermal fibroblasts. Geraniin and furosin increased the cellular energy status of human skin cells (dermal fibroblasts NHDF, HaCaT keratinocytes) and triggered the cells towards higher proliferation rates. Furosin and geraniin stimulated the biosynthesis of collagen from normal human dermal fibroblasts. Geraniin also significantly stimulated the differentiation in normal human epidermal keratinocytes while furosin had a minor influence on the expression of involucrin and cytokeratins K1 and K10. The study proved that geraniin exhibit stimulating activity on dermal fibroblasts and keratinocytes, leading to increased cell

proliferation, barrier formation and formation of extracellular matrix proteins [98].

antimicrobial activities and wound healing activities [92, 189, 195].

Flavanols are a sub‐family of flavonoids which are present in plants as aglycones, as oligomers, or esterified with gallic acid and the most common oligomers of procyanidins present in edible

Flavanols and procyanidins are chemically able to prevent oxidation, and their administration has been associated with a decrease in oxidative stress markers in humans with improve blood supply to the wounded area to accelerate wound healing. They have been shown to exert a wide range of biological activities including wound healing property. The known biological activities of proanthocyanidins include antioxidant activity, anti‐inflammatory activity,

A redox‐active grape seed proanthocyanidin extract has been shown to up regulate oxidant and tumor necrosis factor‐α inducible VEGF expression in human keratinocytes. Furthermore this grape seed proanthocyanidin extract was shown to accelerate wound contraction and closure *in vivo*, to enhance deposition of connective tissue and to improve histological archi‐

**7.1. Tannins**

508 Wound Healing - New insights into Ancient Challenges

[194].

**7.2. Ellagitannins**

tecture [186].

**7.3. Flavanols and proanthocyanidins**

plants are derived from epicatechin [189].

Similarly, a fraction of the methanol extract of *Persea americana* Mill. seeds, containing high amounts of procyanidins B1 and B2 as well as an A‐type trimer, was shown to stimulate proliferation of normal primary keratinocytes and fibroblasts cells but on another hand inhibited the proliferation of HaCaT‐keratinocytes [197].

A study conducted on a proanthocyanidins rich fraction from *Hamamelis verginiana* showed that this fraction strongly increased the proliferation of skin cells. This effect was attributed to the tannin fraction, consisting of hydrolysable and condensed tannins, which account to 12% of Hamamelis bark [198].

A study of the wound healing activities of the hydrolyzable tannins from the hydro‐alcoholic stem bark extract of *Poincianella pluviosa* enhanced the proliferation of human keratinocytes and dermal fibroblasts, which suggests that epidermal barrier formation can be accelerated by the use of *P. pluviosa* [199]. Treatment of keratinocytes with apple procyanidins has been shown to inhibit apoptosis and promote cell proliferation, migration and survival, necessary for revascularization and re‐epithelialization of the wound. *In vivo* studies have shown that apple procyanidins (also known as procyanidins B1, B2 and C1) not only stimulate angiogenesis but also cause epithelial cells to grow mimicking keratinocyte re‐epithelialization [200].

Epicatechin also blocks radiation‐induced apoptosis via down‐regulation Jun N‐terminal kinase and p‐38 in the HaCaT cells [201]. Epicatechin and procyanidins dimers are known to inhibit NADPH‐oxidase and the subsequent superoxide production by directly binding to the enzyme or regulating calcium influx, or potentially inhibiting the binding of ligands that trigger NADPH‐oxidase activation to their receptors (e.g. TNF‐α). These functions are means by which epicatechin may provide cytoprotection to the cell. Both epicatechin and the respective procyanidin dimers can interact with the DNA‐binding site of the nuclear factor kappa B (NF‐κB) proteins, preventing the interaction of NF‐κB with κB sites in gene promoters, thus inhibiting gene transcription [189]. The reduced NF‐κB activation results in the suppres‐ sion of inflammatory cytokines [200].

Procyanidins are known to induce the differentiation of keratinocytes. It has been reported that epigallocatechin‐3‐gallate induces differentiation of human epidermal keratinocytes [202]. In comparison to epigallocatechin‐3‐gallate, procyanidin B2 is more inductive to differentia‐ tion at lower concentrations [92].

Procyanidin B2 is also known to have beneficial effects in pathologies with pro‐inflammatory components by inhibiting NF‐κB‐driven gene expression, including various cytokines and anti‐apoptotic prote [203, 204]. It has been reported that several selective protein kinase C inhibitors, including procyanidin B‐2, promote hair epithelial cell growth [205]. This presup‐ poses that procyanidin B2 could be useful for aesthetic purposes during wound healing by stimulating the regrowth of skin appendages in the wounded area.

Procyanidin C1 inhibits nitric oxide production and the release of pro-inflammatory cytokines (IL-6 and TNF-α). Additionally, the potent anti-inflammatory effect of procyanidin C1 occurs through inhibition of mitogen-activated protein kinase and NF-κB signaling pathways. These two factors play a major role in controlling inflammation in the wounds [206]. In wound healing, procyanidin C1 activity presents a novel and effective means of inflammation control. Procyanidin dimers and trimers extracted from grape seeds are also known to exhibit higher growth-promoting activity than the monomer on hair epithelial cells *in vivo* [207].
