The effect of thymosin treatment of venous ulcers

Progress on the Function and Application of Thymosin β4

Thymosin β4 (Tβ4) is a multifunctional and widely distributed peptide that plays a pivotal role in several physiological and pathological processes in the body, namely, increasing angiogenesis and proliferation and inhibiting apoptosis and inflammation. Moreover, Tβ4 is effectively utilized for several indications in animal experiments or clinical trials, such as myocardial infarction and myocardial ischemia-reperfusion injury, xerophthalmia, liver and renal fibrosis, ulcerative colitis and colon cancer, and skin trauma. Recent studies have reported the potential application of Tβ4 and its underlying mechanisms. The present study reveals the progress regarding functions and applications of Tβ4.

Thymosin β4-mediated protective effects in the heart

INTRODUCTION

Despite recent advances in the treatment of coronary heart disease, a significant number of patients progressively develop heart failure. Reduction of infarct size after acute myocardial infarction and normalization of microvasculature in chronic myocardial ischemia could enhance cardiac survival.

AREAS COVERED

Induction of neovascularization using vascular growth factors has emerged as a promising novel approach for cardiac regeneration. Thymosin β4 (Tβ4) might be a promising candidate for the treatment of ischemic heart disease. It has been characterized as a major G-actin-sequestering factor regulating cell motility, migration, and differentiation. During cardiac development, Thymosin β4 seems essential for vascularization of the myocardium. In the adult organism, Thymosin β4 has anti-inflammatory properties, increases myocyte and endothelial cell survival accompanied by differentiation of epicardial progenitor cells. In chronic myocardial ischemia, Tβ4 overexpression enhances micro- and macrovasculature in the ischemic area and thereby improves myocardial function. A comparable effect is seen in diabetic and dyslipidemic pig ischemic hearts, suggesting an attractive therapeutic potential of adeno-associated virus encoding for Tβ4 for patients with ischemic heart disease.

EXPERT OPINION

Induction of mature micro-vessels is a prerequisite for chronic myocardial ischemia and might be achieved via a long-term overexpression of Thymosin β4.

Dressings and topical agents for treating venous leg ulcers

BACKGROUND

Venous leg ulcers are open skin wounds on the lower leg which can be slow to heal, and are both painful and costly. The point prevalence of open venous leg ulcers in the UK is about 3 cases per 10,000 people, and many people experience recurrent episodes of prolonged ulceration. First-line treatment for venous leg ulcers is compression therapy, but a wide range of dressings and topical treatments are also used. This diversity of treatments makes evidence-based decision-making challenging, and a clear and current overview of all the evidence is required. This review is a network meta-analysis (NMA) which assesses the probability of complete ulcer healing associated with alternative dressings and topical agents.

OBJECTIVES

To assess the effects of (1) dressings and (2) topical agents for healing venous leg ulcers in any care setting and to rank treatments in order of effectiveness, with assessment of uncertainty and evidence quality.

SEARCH METHODS

In March 2017 we searched the Cochrane Wounds Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid MEDLINE (In-Process & Other Non-Indexed Citations); Ovid Embase and EBSCO CINAHL Plus. We also scanned reference lists of relevant included studies as well as reviews, meta-analyses, guidelines and health technology reports to identify additional studies. There were no restrictions with respect to language, date of publication or study setting. We updated this search in March 2018; as a result several studies are awaiting classification.

SELECTION CRITERIA

We included published or unpublished randomised controlled trials (RCTs) that enrolled adults with venous leg ulcers and compared the effects of at least one of the following interventions with any other intervention in the treatment of venous leg ulcers: any dressing, or any topical agent applied directly to an open venous leg ulcer and left in situ. We excluded from this review dressings attached to external devices such as negative pressure wound therapies, skin grafts, growth factors and other biological agents, larval therapy and treatments such as laser, heat or ultrasound. Studies were required to report complete wound healing to be eligible.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed study selection, 'Risk of bias' assessment and data extraction. We conducted this NMA using frequentist meta-regression methods for the efficacy outcome; the probability of complete healing. We assumed that treatment effects were similar within dressings classes (e.g. hydrocolloid, foam). We present estimates of effect with their 95% confidence intervals (CIs) for individual treatments focusing on comparisons with widely used dressing classes, and we report ranking probabilities for each intervention (probability of being the best, second best, etc treatment). We assessed the certainty (quality) of the body of evidence using GRADE for each network comparison and for the network as whole.

MAIN RESULTS

We included 78 RCTs (7014 participants) in this review. Of these, 59 studies (5156 participants, 25 different interventions) were included in the NMA; resulting in 40 direct contrasts which informed 300 mixed-treatment contrasts.The evidence for the network as a whole was of low certainty. This judgement was based on the sparsity of the network leading to imprecision and the general high risk of bias in the included studies. Sensitivity analyses also demonstrated instability in key aspects of the network and results are reported for the extended sensitivity analysis. Evidence for individual contrasts was mainly judged to be low or very low certainty.The uncertainty was perpetuated when the results were considered by ranking the treatments in terms of the probability that they were the most effective for ulcer healing, with many treatments having similar, low, probabilities of being the best treatment. The two most highly-ranked treatments both had more than 50% probability of being the best (sucralfate and silver dressings). However, the data for sucralfate was from one small study, which means that this finding should be interpreted with caution. When exploring the data for silver and sucralfate compared with widely-used dressing classes, there was some evidence that silver dressings may increase the probability of venous leg ulcer healing, compared with nonadherent dressings: RR 2.43, 95% CI 1.58 to 3.74 (moderate-certainty evidence in the context of a low-certainty network). For all other combinations of these five interventions it was unclear whether the intervention increased the probability of healing; in each case this was low- or very low-certainty evidence as a consequence of one or more of imprecision, risk of bias and inconsistency.

AUTHORS' CONCLUSIONS

More research is needed to determine whether particular dressings or topical agents improve the probability of healing of venous leg ulcers. However, the NMA is uninformative regarding which interventions might best be included in a large trial, largely because of the low certainty of the whole network and of individual comparisons.The results of this NMA focus exclusively on complete healing; whilst this is of key importance to people living with venous leg ulcers, clinicians may wish to take into account other patient-important outcomes and factors such as patient preference and cost.

Beneficial effects of thymosin β4 on spinal cord injury in the rat

Thymosin β4 (Tβ4) has many physiological functions that are highly relevant to spinal cord injury (SCI), including neuronal survival, anti-inflammation, wound repair promotion, and angiogenesis. The present study investigated the therapeutic value of Tβ4 in SCI, with a focus on its neuroprotective, anti-inflammatory, and vasculoprotective properties. Tβ4 or a saline control was administered by intraperitoneal injection 30 min, 3 days, or 5 days after SCI with mild compression in rat. Locomotor recovery was tested with the Basso-Beattie-Bresnahan scale and a footprint analysis. All behavioral assessments were markedly improved with Tβ4 treatment. Histological examination at 7 days post injury showed that the numbers of surviving neurons and oligodendrocytes were significantly increased in Tβ4-treated animals compared to saline-treated controls. Levels of myelin basic protein, a marker of mature oligodendrocytes, in Tβ4-treated rats were 57.8% greater than those in saline-treated controls. The expression of ED1, a marker of activated microglia/macrophages, was reduced by 36.9% in the Tβ4-treated group compared to that of the saline-treated group. Tβ4 treatment after SCI was also associated with a significant decrease in pro-inflammatory cytokine gene expression and a significant increase in the mRNA levels of IL-10 compared to the control. Moreover, the size of lesion cavity delineated by astrocyte scar in the injured spinal cord was markedly reduced in Tβ4-treated animals compared to saline-treated controls. Given the known safety of Tβ4 in clinical trials and its beneficial effects on SCI recovery, the results of this study suggested that Tβ4 is a good candidate for SCI treatment in humans.

A novel dimeric thymosin beta 4 with enhanced activities accelerates the rate of wound healing

OBJECTIVE

Thymosin beta 4 (Tβ4) is a peptide with 43 amino acids that is critical for repair and remodeling tissues on the skin, eye, heart, and neural system following injury. To fully realize its utility as a treatment for disease caused by injury, the authors constructed a cost-effective novel Tβ4 dimer and demonstrated that it was better able to accelerate tissue repair than native Tβ4.

METHODS

A prokaryotic vector harboring two complete Tβ4 genes with a short linker was constructed and expressed in Escherichia coli. A pilot-scale fermentation (10 L) was performed to produce engineered bacteria and the Tβ4 dimer was purified by one-step hydrophobic interaction chromatography. The activities of the Tβ4 dimer to promote endothelial cell proliferation, migration, and sprouting were assessed by tetramethylbenzidine (methylthiazol tetrazolium), trans-well, scratch, and tube formation assays. The ability to accelerate dermal healing was assessed on rats.

RESULTS

After fermentation, the Tβ4 dimer accounted for about 30% of all the bacteria proteins. The purity of the Tβ4 dimer reached 98% after hydrophobic interaction chromatography purification. An average of 562.4 mg/L Tβ4 dimer was acquired using a 10 L fermenter. In each assay, the dimeric Tβ4 exhibited enhanced activities compared with native Tβ4. Notably, the ability of the dimeric Tβ4 to promote cell migration was almost two times higher than that of Tβ4. The rate of dermal healing in the dimeric Tβ4-treated rats was approximately 1 day faster than with native Tβ4-treated rats.

CONCLUSION

The dimeric Tβ4 exhibited enhanced activity on wound healing than native Tβ4, and the purification process was simple and cost-effective. This data could be of significant benefit for the high pain and morbidity associated with chronic wounds disease. A better strategy to develop Tβ4 as a treatment for other diseases caused by injuries such as heart attack, neurotrophic keratitis, and multiple sclerosis was also described.

Bacterial expression, purification and angiogenesis-promoting activity of human thymosin β4

Thymosin β4 (Tβ4) is an actin-binding peptide involved in tissue regeneration and angiogenesis. This 43-amino acid peptide is chemically synthesized for research or clinical trials. To overcome the high costs of solid phase synthesis, we developed a genetic engineering procedure of Tβ4 expression in a protease-deficient host strain, Escherichia coli BL21(DE3), transformed with different expression vectors (pRSETA, pET-15b and pEcoli-Cterm6 × HN). The recombinant, non-glycosylated peptide was overexpressed in soluble form and purified by two-step immobilized metal ion affinity chromatography. Use of the pET vector expression system allowed for easy removal of the polyhistidine tag by thrombin. Functional studies revealed that recombinant Tβ4 stimulated angiogenesis via activation of the endothelial proteolytic systems, inhibition of endothelial cell adhesion, promotion of migration and capillary tube formation in Matrigel, and that its activity was similar to that observed for the synthetic peptide. The presented study comprises the first evidence that recombinant Tβ4 promotes angiogenesis in an in vitro endothelial cell model.

Epidemiology and aetiology of C4-6 disease

Although our understanding of chronic venous insufficiency (CVI) has improved, many important questions remain unanswered. Ensuring that patients are appropriately referred for specialist assessment and then receive evidence-based, cost-effective treatment continues to be challenging. The lifetime of risk of chronic venous ulceration (CVU) is around 1% with approximately 10% ulcers being open at any one time. The incidence skin changes disease is about 10 times greater (10%). However, many of the studies upon which these estimates are based are old and/or methodologically flawed. There is reason to believe that the incidence, prevalence and characteristics of CVI/CVU may have changed considerably over the last 10-20 years and that future change is likely. Further cross-sectional and longitudinal epidemiological studies are required to establish the size and nature of the health-care need going forward in developed and increasingly developing countries. CVI culminating CVU is primarily the result of sustained ambulatory venous hypertension, which in turn arises from superficial and/or deep venous reflux with or without deep vein obstruction. However, there are many other elements to this complex condition, for example, microvascular dysfunction; calf muscle pump efficiency; dermal inflammation; disordered fibroblast function and matrix production; failure of epithelialization; congenital and acquired thrombophilia; malnutrition, obesity and diet; and bacterial colonization. None of the currently available treatment modalities is entirely satisfactory and novel therapies based upon a clearer understanding of the disease at the psychological, genetic, mechanical, microvascular and microscopic level are required.