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Features: Original Investigation

TGF-β3 in the Treatment of Pressure Ulcers: A Preliminary Report

Hirshberg, James BS; Coleman, James MD; Marchant, Beverly RN; Rees, Riley S. MD, FACS

Author Information

Abstract

The management of pressure ulcers (PUs) is a sizeable clinical problem.1-4 Despite the heightened awareness of health care providers about the risks for PUs and the technologic advances in support systems, the prevalence of Stage III and Stage IV PUs has not declined in recent decades.5-9

Recently, there has been a great deal of interest in biologic agents as potential adjuvants in the treatment of chronic wounds. Clinical trials using platelet-derived growth factors (PDGF) have shown success in the treatment of diabetic foot ulcers and PUs.10,11 Encouraging results have been demonstrated in animal studies using transforming growth factor beta (TGF-β) for diabetic ulcers and poorly vascularized wounds.12-14

TGF-β is a polypeptide cytokine secreted by a variety of cells involved in wound repair.15,16 It has shown healing efficacy in venous wounds in animals and humans after topical application.17 TGF-β3 is a recombinant form of the TGF human molecule. To date, no studies have evaluated the efficacy of using TGF-β3 in the treatment of PUs in humans. The present study examined the effectiveness of topical applications of TGF-β3 on PUs in 3 groups of patients.

METHODS

Study design and population

This pilot study represents a subset analysis of the University of Michigan Wound Care Center's data from a larger (270 patients), randomized, blind, parallel, placebo-controlled trial of the safety, efficacy, and tolerability of the topical application of TGF-β3.

To be eligible for the trial, the patient's PU surface area had to be between 15 cm2 and 120 cm2 and the calcium alginate mold weight had to be 10 grams or more, following debridement at the baseline visit. If more than 1 full-thickness PU was present, the PU closest to a volume of 40 cm3 was designated as the target ulcer. The target ulcer had to have been present for at least 4 weeks. In addition, patients were required to have a serum albumin concentration of 2.5 grams/dL or more. Prior to randomization, debridement of the target ulcer was performed to remove any nonviable tissue. A biopsy confirmed that the target ulcer bed had bacterial counts of less than 105 per gram of tissue and no evidence of β-hemolytic streptococci or malignancy.

Patients were excluded from the trial if (1) the target ulcer had osteomyelitis, determined by clinical evaluation, χ-ray, and/or bone biopsy; (2) the target ulcer's calcium alginate mold weight was 10 grams or less after debridement; (3) topical antibiotics or disinfectants were applied to the target ulcer during cleansing; (4) autolytic or enzymatic debriding agents were used on the target ulcer; or (5) an experimental, nonapproved, or investigational drug was used within the past month or during the trial. Additional exclusion criteria were malignancy at any PU site, administration of systemic corticosteroids of more than 20 mg per day, or administration of other immunosuppressive therapy. Patients whose target ulcer failed to heal with previous cytokine therapy or who had received radiation therapy at the target ulcer site were also excluded from the trial. In addition, women who were pregnant, nursing, or of childbearing age and not using an accepted method of birth control were excluded.

The protocol was approved by the University of Michigan Institutional Review Board; all patients gave written informed consent prior to participating in the study.

Subset analysis was conducted on 14 patients (6 women and 8 men) age 18 years or older who met the inclusion criteria. The patients had between 1 and 3 chronic full-thickness PUs located on the trunk that were Stage III or Stage IV as defined by the National Pressure Ulcer Advisory Panel18,19; the PUs did not have bone exposure.

Patients with chronic PUs who met the defined inclusion criteria were randomly assigned to 1 of 3 treatment groups. Each group received once daily application of a topical agent. Group 1 (n = 4) received 1.0 μg/cm2 TGF-β3, Group 2 (n = 5) received 2.5 μg/cm2 TGF-β3, and Group 3 (n = 5) received a placebo gel.

The topical agent was evenly distributed over the target ulcer bed surface area with a disposable plastic syringe and was not disturbed for 15 minutes. The wound was then cleansed with saline and loosely packed with saline-moistened gauze.

The topical agent was applied to the target ulcer in conjunction with standardized wound care for 16 weeks or until the ulcer healed, whichever came first. Standardized wound care included adequate debridement of nonviable tissue, gentle cleansing of the wound bed with saline, maintenance of a moist wound environment, recognition and treatment of infection, off-loading of pressure from the affected area using low-air-loss surfaces, and nutritional support. The ulcers were carefully monitored for adverse experiences.

Efficacy evaluations

At each clinic visit, personnel involved in the study measured the target ulcer site by planimetry to determine the surface area of the ulcer. In addition, a calcium alginate mold was made to measure the ulcer's volume (the mold's weight was converted to a volume measurement).

The area of the PU bed was calculated using a dosage determination chart that converted area volume (cm3) to ulcer bed area (cm2). However, if the ulcer volume was less than 10 cm3, this calculation was not done. In these instances, the ulcer bed area was considered equal to the ulcer surface area as determined by planimetry.

Each week, PUs were visually inspected to determine if closure had occurred. Evaluations were based on functional assessment of the PU and scored as (1) complete closure with drainage, (2) complete closure with no drainage, or (3) complete closure. The primary end point was complete closure. The 2 secondary end points were the percentage reduction in ulcer volume and the percentage reduction in ulcer surface area.

Safety evaluations

Safety was evaluated by monitoring adverse experiences. The severity of an adverse experience was defined as a qualitative assessment determined by the investigator or reported by the patient. The assessment of severity was made regardless of the drug relationship or seriousness of the experience and was measured on a scale where 1 = mild, 2 = moderate, and 3 = severe.

A plasma anti-TGF-β3 antibody level was obtained on all patients before, during, and after the study. Trial personnel assessed the PU bed and the skin surrounding the PU at every visit; new physical findings or PU deterioration were recorded. In addition, the patient's subjective feelings of pain, itching, or burning at the PU site were recorded.

Statistical methods

The statistical analyses were based on the intent-to-treat population. If a patient was terminated from the study, his or her PU sizes were carried through to the end of the study. The Bonferroni adjustment (Dunn) t test, a 1-way analysis of variance, was performed on the data at visits 4, 10, and 16 at the .05 level of significance. The relative PU volume and relative PU bed surface area were defined as the size at a particular visit divided by the baseline size. Thus, the reduction in size of the PU was evaluated relative to the original ulcer size.

RESULTS

Demographic data

Fourteen patients were enrolled in the study and no clinically important differences were observed in their demographic or baseline characteristics (Table 1). Of the 14 patients, 6 discontinued treatment before completing the trial; none of these patients had a severe adverse experience related to the treatment. In Group 1, 1 subject discontinued treatment prematurely because of a ventricular fibrillation arrest resulting in death that was unrelated to the trial. In Group 2, 3 subjects discontinued prematurely. Two subjects discontinued because they developed osteomyelitis in the target PU, and the third subject was noncompliant with the pressure-relief protocol. In Group 3, 2 subjects discontinued prematurely. One subject discontinued because of an unsatisfactory therapeutic effect and another discontinued because of aspiration pneumonia. Despite these dropouts, all 14 patients were in the study at visit 4, and 11 patients were in the study at visit 10, leaving 8 patients who completed the study.

Table 1
Table 1:
PATIENT BASELINE CHARACTERISTICS

Efficacy data

Efficacy was determined by using target ulcer surface area and volume measurements relative to baseline values taken at the start of the trial. The mean relative surface areas and volumes were tested for significance during the study period (Figures 1 and 2). At visit 4, the mean relative surface areas included the following: Group 1 = 0.8 cm2, Group 2 = 0.5 cm2, and Group 3 = 0.9 cm2. When compared with Group 3, the results in Group 2 represented a significant reduction in the mean relative surface area (P <.05).

Figure 1
Figure 1:
PERCENTAGE OF PATIENTS WITH ULCER VOLUME >10 cm3
Figure 2
Figure 2:
MEAN RELATIVE ULCER SURFACE AREAS

A significant decrease in volume was also seen when comparing Group 1 with Group 3 (P <.05). The fact that there was no significant difference in closure in Groups 1 and 2 at visits 10 and 16 accounted for the increased closure rates in Group 3 at these points. The mean relative surface areas of the target PUs at the termination of the trial were as follows: Group 1 = 0.3 cm2, Group 2 = 0.4 cm2, and Group 3 = 0.7 cm2. The mean relative volumes at termination were as follows: Group 1 = 0.7 cm3, Group 2 = 0.2 cm3, and Group 3 = 0.3 cm3.

In Group 2, 1 subject achieved complete wound closure with no wound drainage. At visit 4, Group 2 showed a significant reduction in relative ulcer bed surface area and ulcer volume compared with Group 3. However, this reduction in relative size was not statistically significant over the 16 weeks of the trial.

DISCUSSION

The use of topical growth factors is a progressive adjuvant to the traditional treatment of PUs. The potential benefits of growth factors include faster closure rates, ease of application, and minimal adverse effects. The optimistic results from animal studies using TGF-β offer new opportunities for human clinical trials.20,21

TGF-β is one of the most biologically active cytokines.8 The secretion of TGF-β by various inflammatory cells, such as platelets, leukocytes, and fibroblasts, have prompted investigators to examine its role in wound healing.22 TGF-β has been implicated in angiogenesis, chemoattraction, and the development of extracellular matrix.23 Enhanced expression of this molecule is also thought to be a possible mechanism for fibrous disorders,24 and conversely, antagonists have shown to be potential therapeutic agents for hypertrophic scars.25-27 Wounds with characteristically poor healing behaviors, such as diabetic wounds, exhibit decreased expression of TGF-β. Because the topical application of TGF-β has been shown to enhance nascent expression by autoinduction, TGF-β, therefore, may facilitate healing.28,29

The findings of this pilot study are encouraging; however, they are also problematic. Multiple wound care variables, such as aggressive debridement techniques and the variability of pressure-relief surfaces used in this study, made it difficult to determine statistical significance.

There has been limited use of TGF-β3 in clinical trials because similar studies have shown clinical and statistical significance with topical application of fibroblast growth factors and PDGFs in PUs.11,30 The success with using these cytokines has intrigued and stimulated the search for other biologically active agents for the treatment of PUs.

This pilot study suggests that TGF-β3 may be effective in the treatment of PUs. The dosage of 1.0 μg/cm2 showed improved wound closure, but was not statistically significant. Group 2 showed statistically significant closure when compared with Group 3 and Group 1 at visit 4. One subject in Group 2 achieved complete closure. However, by the end of the trial, there was no significant difference in wound closure among the groups. Consistent with other reported trials of PUs, an enhanced healing response in the placebo-treated patients was noted.

The effectiveness of TGF-β3 in the healing of PUs was statistically significant only with the higher dosage and during the initial weeks of treatment. Thereafter, the rate of closure was not statistically significant.

This pilot study is hampered by a small sample size; 43% of the patients did not complete the trial. However, the enhanced wound closure observed in the early period of treatment could prove beneficial in the clinical setting. Marked decreases in wound size during the initial treatment period may translate to decreased costs from a reduction in hospitalization days, decreased morbidity, and a lower incidence of developing additional PUs. In addition, this type of treatment could make large wounds more amenable to surgical repair, as demonstrated with platelet-derived growth factor becaplermin (PDGF-BB) in the surgical treatment of PUs.31

A larger, multicenter, blinded study of TGF-β3 in the treatment of PUs is required to explore the potential benefits. Further investigation should provide data to more fully determine the efficacy of the topical application of TGF-β3 in the treatment of chronic wounds in humans.

References

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