Title : Cell therapy for chronic ischemia
Abstract:
Background: In the presence of arterial occlusive disease, neovascularization (NV) is a natural process that strives to preserve tissue perfusion through growth of collateral arteries (arteriogenesis) and growth of capillaries, arterioles, and venules (angiogenesis). Endothelial shear stress initiates arteriogenesis, while hypoxia stimulates angiogenesis. NV becomes impaired as vascular disease progresses, leading to chronic limb-threatening ischemia (CLTI). Symptoms include forefoot ischemic rest pain, ulceration, and/or gangrene. Standard of care includes invasive revascularization by surgery or catheter-based interventions. Significant procedural risks, variable durability, and high cost have spurred efforts to develop an effective, durable, low-risk, home-based, inexpensive revascularization option. Phase II clinical trials attempting to orchestrate cellular or molecular aspects of NV have not yielded a solution to promoting this complex process.
A novel approach has since been tested clinically that sought to restore innate NV by overcoming obstacles that arise due to the multilevel arterial occlusive disease and progenitor cell deficits. These obstacles include attenuated endothelial shear stress precluding endothelial activation, an unhealthy biosynthetic environment in the ischemic tissue, and the diminished number and function of salutary progenitor cells. The outpatient cell therapy uses a programmed pneumatic compression pump (PCP) and Filgrastim (FDA approved for stem cell mobilization). In the first patients so treated, there was abatement of ischemic rest pain and healing of forefoot ischemic wounds. Hemodynamics improved (increase in ankle brachial index, development of photoplethysmographic pulsatility in the forefoot and toes). Angiography showed corkscrew collateral growth and improved contrast transit. Surprisingly, segmental recanalization of previously occluded infrageniculate arteries was also observed. Lysis of chronic thrombus was suspected. Molecular evidence for fibrinolysis and neovascularization was sought.
Methods: CLTI patients were treated with PCP alone (N = 19), or with Filgrastim (10mcg/kg every 72 hours SQ) and PCP (N = 8 and N = 6, at two institutions). ELISA was used to measure the plasma concentration of plasmin and of fibrin degradation products (FDP), and the serum concentration of proteins associated with neovascularization (VEGF, HGF, MMP-9, Angipoietin, PDGF et al) . In the PCP-alone group, blood was sampled on Day 1 (baseline) and after 30 days of daily PCP. In the Filgrastim and PCP group, blood was drawn on Day 1, and 1 day after the 5th and the 10th Filgrastim doses. Each blood draw occurred before and after 2 h of supervised PCP.
Results: In patients who received Filgrastim the expected significant increase in the circulating progenitor cell count was accompanied by a mean 6 fold increase in the absolute neutrophil count. Significant (p < 0.01) PCP independent increases in the plasma concentration of plasmin (>10-fold) and FDP (>5-fold) were observed 1 day after both the 5th and the 10th Filgrastim doses, compared to Day 1. Significant (p < 0.05) increases in the concentration of pro-angiogenic proteins were also observed. Filgrastim at this novel dosimetry induced fibrinolysis without causing acute hemorrhage, in addition to inducing a pro-angiogenic milieu conducive to NV.
Conclusion: These results substantiate recent reports that the fibrinolytic and angiogenic capacity of endothelial cells can be promoted by G-CSF, and that the significant G-CSF induced neutrophilia may also significantly enhance these effects in the context of ischemia. Further research is needed to clarify mechanism. Additionally, further clinical testing is warranted at this novel dosimetry in CLTI, as well as in other chronically ischemic tissue beds.
