and then fall with successful healing (Hardman M.J. and Ashcroft G.S., unpublished).
In ad- dition, MIF regulates a plethora of wound-healing-associated genes, indicating a fundamental regulatory role for this cytokine (Hardman M.J. and Ashcroft G.S., unpublished).
There is now considerable evidence that oestrogen treatment, either topical or systemic, will accelerate healing.
Moreover, Margolis et al. in a recent case, cohort study identified reduced risk of developing a venous leg or pressure ulcers in elderly females undergoing HRT.4 Neverthe- less, the possible detrimental effect of oestrogen treatment on other systems is problematic, highlighted by oestrogen’s addition to the federal list of cancer-causing agents in the United States.
For this reason, the authors are actively pursuing downstream genes/factors that mediate oestrogen’s effects, such as MIF.
Clinical manipulation of these factors should aid healing of ulcers without the detrimental effects of systemic oestrogen treatment on other physiological processes (Table 18.2).
In contrast to oestrogen, androgens inhibit healing.
Castrated mice, with reduced systemic testosterone, display accelerated healing.5 Unlike oestrogen, androgens appear to modulate healing by a direct action on wound cell populations, and cytokine profiles, thereby enhancing the inflammatory response.
The role of androgens in human healing is highlighted by neural network studies indicating that elderly males are more likely to develop non-healing ulcers than are elderly females.6
ROLE OF GROWTH FACTORS Growth factors play a critical role, regulating all aspects of wound healing7 (Table 18.1).
In clinical trials, both epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF-2) were found to accelerate healing of acute wounds by several days.8−9 Chronic wounds provide a more complex challenge, characterised by fluxes in the local non-healing wound environment in which growth factors can quickly become trapped within, or degraded by, the proteolytic extracellular milieu.10 Protein levels of platelet-derived growth factor (PDGF), EGF, FGF-2 and transforming growth factor β (TGF-β) are all reportedly reduced in chronic wounds.11 Furthermore, certain growth factors are selectively inhibited in the ulcer environment; for example, specific heparin-like factors expressed by non-healing wounds inhibit FGF activity.12 Numerous growth factors have been employed for the treatment of chronic wounds.
Nearly 20 years ago, Knighton et al. reported successful treatment of chronic ulcers with platelet wound-healing formula (PDWHF, an autologous platelet-derived product containing among other factors PDGF, EGF, FGF and TGF-β).13 This was soon followed by successful studies
JWBK089-18 JWBK089-Boulton April 22, 2006 18:10 Char Count= 0
218 TREATMENTS FOR DIABETIC FOOT ULCERS
Table 18.3 Current and potential exogenous agents for treatment of delayed healing
Factor Animal studies Human studies Therapeutic use
PDGF Reduced expression in Reduced in non-healing Current treatment for delayed-healing wounds ulcers.
Topically diabetic foot ulcers of diabetic mice accelerates ulcer healing FGF-2 Delayed healing in null Mixed results from clinical mice trials Effective in several ulcer Good clinical trials. studies Approved for use in ulcers EGF Topical treatment Topical treatment accelerates Limited clinical trials accelerates wound healing.
Limited effect on Approved for use in strength and venous ulcers ulcers re-epithelialisation KGF Normal healing in null Liposomal KGF cDNA gene No clinical trials mice.
Topically transfer accelerates accelerates healing of healing porcine wounds TGF-α Topical application Topical application No clinical trials accelerates healing of accelerates healing of acute wounds acute wounds TGF-β Multiple with complex Topical TGF-β3 accelerates Promising TGF-β3 trials findings healing of pressure ulcers VEGF Delayed wound VEGF neutralisation Stimulates blood vessel healing/angiogenesis in strongly impairs formation in arterial null/inhibitor treated. angiogenic activity of disease wound fluid GM-CSF Transgenic over-expression Promising acceleration of Initial studies with infected directly accelerates ulcer healing in several diabetic ulcers healing of acute wounds studies IGF-I Accelerates cutaneous Markedly reduced at the No clinical trials healing in a diabetic edge of diabetic foot mouse model ulcers HGF/SF Over-expression results in Decreased biologically No clinical trials increased angiogenesis active HGF in chronic and granulation ulcers deposition NGF Accelerated healing in Promotes healing of pressure No clinical trials healing-impaired ulcers diabetic mice MCP-1 Significantly delayed Upregulated in human No clinical trials wound healing in null excisional wounds mice IL-6 Up to threefold delayed Elevated in non-healing No clinical trials healing in null mice, ulcers with greatly delayed re-epithelialisation
(Continued )
JWBK089-18 JWBK089-Boulton April 22, 2006 18:10 Char Count= 0
TREATMENT METHODS 219
Table 18.3 (Continued)
Factor Animal studies Human studies Therapeutic use
MIF MIF neutralisation MIF levels are elevated in No clinical trials accelerates wound repair. chronic non-healing wounds Oestrogen In ovariectomised mice Topical or systemic Initial studies with acute acute wound healing is oestrogen accelerate wounds only delayed. Topical or age-associated delayed systemic oestrogen healing accelerates delayed healing Testosterone Accelerated acute wound None No clinical trials healing in castrated mice or following AR blockade
using PDWHF to specifically treat diabetic ulcers.14 Several subsequent studies have shown recombinant human PDGF alone to be effective in treating a range of non-healing wounds; of particular relevance is the combined analysis of multiple studies involving diabetic ulcer patients.15 In clinical trials, FGF-2 has been shown to be effective in accelerating healing of a range of chronic cutaneous wounds, such as pressure sores16 and diabetic ulcers.17 The outcome in patients with pressure sores was particularly impressive where 91% of FGF-treated wounds healed after 4 weeks, compared to 0% of untreated wounds.
EGF also accelerates healing of diabetic ulcers, in one study increasing 12-week healing rates from 42% in control patients to 95% in those topically treated with EGF.18 Increasing evidence points to an essential role for exogenous growth factors in non-healing wounds (see Table 18.3 for current factors and novel candidates).
Whether these exogenous factors exert their effects by binding their respective surface receptors directly or also act indirectly by inducing further endogenous growth factors is at present largely unknown.
Encouragingly for future treatment prospects, fibroblasts from wounds of patients with diabetes, with characteristically reduced proliferation, are particularly responsive to exogenous growth factors.19
TREATMENT METHODS In early trials, growth factors were applied in a liquid vehicle or via multiple injections around the ulcer margin.
The most common current methods of growth factor treatment are still via direct topical application generally in the form of a cream.
To overcome the possibility of degradation in the wound environment, several researchers have employed time release tech- nology with varying success.20 Gene therapy provides an interesting proposition.
Adenovirus- mediated transfection provides the prospect of continuous production of large quantities of growth factors within the wound environment.21 However, gene transfer technology is only in early-stage clinical trials and may be very difficult to introduce into the clinical practice.
A recent transgenic model, in which the secretory leucocyte protease inhibitor (SLPI) gene is deleted, suggests an alternative approach.
It appears that SLPI is a potent anti-proteolytic and
JWBK089-18 JWBK089-Boulton April 22, 2006 18:10 Char Count= 0
220 TREATMENTS FOR DIABETIC FOOT ULCERS
antibacterial agent, which could be applied alone or in combination with other growth factors to prevent destruction of the latter and to accelerate healing.