Effect of Stem Cells on the Lower Limb

Considerable research has explored the effects of autologous stem cells (ASCs) on lower extremity peripheral arterial disease (PAD) and related ischemic ulcers. Up to 50% of patients with critical limb ischemia (CLI; chronic ischemic rest pain with ulcers or gangrene) are not candidates for surgical revascularization.¹ Of these patients, 30% face likely amputation and 25% will likely die within 1 year following diagnosis,² resulting in a CLI prognosis grimmer than that of many forms of cancer.³ Studies exploring ASC efficacy for improving outcomes of patients with PAD are heterogeneous and results are inconsistent.¹ The 2 meta-analyses reviewed here — the first exploring the effects of ASC on several PAD-related outcomes, primarily amputation incidence,¹ and the other summarizing ASC effects on lower extremity ulcer healing⁴ — clarify these inconsistencies and ways to optimize ASC interventions and highlight delivery parameters offering patients with CLI a brighter future.

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Reference: Rigato M, Monami M, Fadini GP. Autologous cell therapy for peripheral arterial disease: systematic review and meta-analysis of randomized, nonrandomized, and noncontrolled studies [published online January 17, 2017]. Circ Res. 2017;120(8):1326–1340.

Rationale: Surgical revascularization of the limbs of patients with PAD/CLI can improve circulation, but 30% to 50% of patients with CLI are not good candidates for this surgery. Autologous stem cells may offer options to improve outcomes for those with PAD-related CLI, but placebo-controlled randomized clinical trials (RCTs) have reported inconsistent efficacy.

Objective: Present an updated critical review and meta-analysis of the effects of ASC intervention on PAD/CLI outcomes.

Methods: PubMed, ISI Web of Science, Scopus, ClinicalTrials.gov, and the Cochrane Central Register of Controlled Trials were searched for clinical trials involving PAD, CLI, and synonyms combined with ASC and synonyms and “lower extremity” up to July 2016. Data on the primary outcome major amputation or secondary outcomes (ie, amputation-free survival or all-cause mortality, complete wound healing, pain score, pain-free walking, ankle-to-brachial index [ABI], and transcutaneous tissue partial pressure of oxygen [TcPO₂]) were extracted from abstracts and/or full-text articles then independently assessed by 2 authors for methodological quality of the evidence. The primary analysis was reported during a mean follow-up interval of 6 months on 837 patients receiving some form of ASCs in 11 placebo-controlled RCTs and 8 RCTs with standard of care controls. A secondary analysis of all 26 randomized and nonrandomized controlled clinical trials also was performed and is not reviewed here. Trial-sequential analysis was conducted for the primary outcome estimating relative risk of reduced major amputation from placebo-controlled trials with 80% power and a 2-sided type 1 error value of 5%. This corrected for repeated data in different studies. Meta-regression explored multiple study endpoints and effects of covariates on outcomes.

Results: In the primary analysis of all 19 RCTs, ASC patients experienced a 37% reduction in annualized amputation rate (P = .0004), 18% higher probability of amputation-free survival (P = .01), and a 59% increase in complete wound healing (P = .002) with similar mortality compared with control patients. Surrogate endpoints (ABI, TcPO₂, and rest pain) all improved in ASC patients (P < .003), but the ASC-associated 100-m increase in pain-free walking distance was not statistically significant (P = .14). Most (80%–90%) ASC-treated patients experienced more non-severe adverse events than control patients, mainly injection site inflammation or musculoskeletal disorders (P < .05). A subanalysis of only the 11 placebo-controlled RCTs found significant improvements in ABI, TcPO₂, and rest pain (P < .003), but improvements in amputation or healing outcomes were no longer statistically significant.

The RCTs were heterogeneous, varying in setting, underlying disease, dose and type of ASCs, route of administration, and duration of follow-up. Failure to state randomization allocation technique resulted in most RCTs having unknown risk of bias. Funnel plot asymmetry to assess publication bias suggested that small studies with negative results were not being published.

Subset analyses revealed that only intramuscularly administered ASCs improved amputation rate, amputation-free survival, complete wound healing, ABI, and TcPO₂. Rest pain improved in response to either intramuscularly or intra-arterially administered ASCs. Only peripheral blood mononuclear cells (PB-MNC) significantly improved amputation rates and amputation-free survival, and only bone marrow-derived mononuclear cells (BM-MNC) significantly improved complete wound healing, though both types of cells improved ABI and TcPO₂. Bone marrow-derived mesenchymal stem cells (BM-MSC) improved pain-free walking distance, ABI, and TcPO₂.

Authors’ Conclusions: This primary analysis of RCTs seems to provide conclusive evidence on ASC efficacy in improving important objective outcomes and surrogate endpoints for those with PAD and intractable CLI.

Reference: Jiang X, Zhang H, Teng M. Effectiveness of autologous stem cell therapy for the treatment of lower extremity ulcers: a systematic review and meta-analysis. Medicine (Baltimore). 2016;95(11):e2716.

Rationale: Research has suggested ASC therapy may improve healing of lower extremity ulcers, but RCT results have been inconsistent.

Objective: Perform a systematic review and meta-analysis of RCT results to determine efficacy and safety of ASCs in healing patients with lower extremity ulcers.

Methods: After ethics board approval, the authors followed PRISMA and Cochrane methods to search PubMed, EMBASE, and the Cochrane Library databases through February 23, 2015, for clinical RCTs comparing ASC to a control group and measuring foot or leg ulcer healing outcomes and safety as adverse events. The first 2 authors independently searched the literature, assessed study quality, and extracted data from abstracts or full text articles. Random effects models were used to estimate pooled study results to minimize the effects of heterogeneity, with P = .05 for statistical significance. Publication bias was tested and sensitivity analyses were performed, removing single studies to evaluate if the pooled results were robust.

Results: Ten studies on 311 patients with lower extremity ulcers qualified for inclusion in the meta-analysis of studies performed in China, the United States, Germany, India, and Egypt. Mean patient age ranged from 40 to 71 years. The cause of lower extremity ulcers was CLI related to PAD for most studies, with some studies including patients with Buerger’s disease, diabetic foot ulcers, or traumatic ulcers. Four studies used granulocyte-colony stimulating factor (G-CSF)-mobilized PB-MNCs, 3 used BM-MSCs, 4 used BM-MNCs, 2 used bone marrow-enriched tissue repair cells, and 1 used bone marrow-derived stem cells (BM-SCs). Overall study quality was low, as the method of random allocation was rarely reported. The ASC-treated patients (N = 155) experienced better healing than the control patients (n = 135; P < .001). Similar results were obtained for both partial healing (3 comparisons involving 60 patients; P = .03) and complete healing (9 comparisons involving 230 patients; P < .001). Subset analyses revealed that G-CSF-mobilized PB-MNCs and BM-SC therapies were associated with better complete healing rates of lower extremity ulcers (P < .002). The effect was independent of baseline ulcer area and remained strong for lower extremity ulcers caused only by CLI (P < .001). During a 4-year follow-up, ASC therapy was not associated with increased risk of procedure-related adverse events.

Authors’ Conclusions: This meta-analysis indicates ASC therapy is safe and effective for improving the healing of lower extremity ulcers caused by ischemia or diabetes.

These 2 meta-analyses of RCTs^1,4 confirm limb salvage, hemodynamic, functional, and healing benefits of ASC therapy and clarify parameters optimizing efficacy. The broader of the 2 studies, analyzing larger sample sizes, reported increased adverse events associated with injection site reactions.¹ This suggests improvements are needed in ASC delivery procedures. Ischemic ulcers caused by PAD and CLI dominate the findings. One has to wonder if important opportunities to manage PAD before CLI and ulceration occur are missing. The observation that the effects of ASC on limb salvage and healing become less discernible when only placebo-controlled RCTs are analyzed¹ suggests the placebo effects of ASC therapy cannot be ruled out. Indeed, this type of subset analysis may offer a way to quantify the power of the placebo effect in any body of literature.

Rigato et al¹ note that PAD is not optimally managed in a vast number of patients. By the time ischemic ulcers occur, patients’ PAD is more challenging to repair. It may be more effective to diagnose and manage PAD earlier as one does with diabetes or hypertension, improving arterial circulation before the grim probabilities of amputation, morbidity, and mortality increase. For those who can walk, supervised exercise training has strong, good quality evidence of safety and efficacy in managing CLI alone⁵ or as an adjunct to endovascular revascularization.⁶ Intermittent pneumatic compression^7,8 or transcutaneous electrical stimulation of calf muscle nerves sufficient to generate comfortable calf muscle twitching^9,10 also have RCT evidence supporting increased pain-free walking distance and lower leg circulation. The research above alerts us that PAD challenges patients with pain, CLI, and delayed healing, but affected patients can respond to early, effective interventions to address it before they must face the grim prognosis of amputation with ensuing morbidity and mortality.

This article was not subject to the WOUNDS peer-review process.