A leading cause of severe disability and limb amputation in the developed world is critical limb ischemia (CLI) from severe peripheral artery disease (PAD). Current treatments for CLI, like surgical revascularization, endovascular intervention, and medical treatment, typically result in less than satisfying results. Moreover, despite early promise, phase II clinical trials of exogenous pro-angiogenic growth factors for CLI have not demonstrated efficacy, and the prospects for successful gene and cell therapies for CLI are far from certain1. In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, Nagahama, et al demonstrate an innovative nanoparticle-mediated delivery of pioglitazone for enhancing therapeutic neovascularization in a murine model of hindlimb ischemia2.
While the thiazolidine (TZD) class of peroxisome proliferator activated receptor-γ (PPAR-γ) agonists like pioglitazone has been in clinical use as treatment for type-2 diabetes mellitus, recent studies have demonstrated various pro-angiogenic effects of TZDs. For instance, TZDs have been shown to stimulate endothelial cell and progenitor migration, proliferation, and survival via the expression of angiogenic factors like vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)3–5. Moreover, pioglitazone have been shown to promote therapeutic angiogenesis in a murine hindlimb ischemia model although it was unclear whether this reflected a direct effect of pioglitazone on endothelial cells or the secondary effects of improved glycemic control6. Conversely, there have also been reports of anti-angiogenic effects of TZDs in in vitro and in vivo models7, 8. The prospects for TZDs as potential pro-angiogenic therapies were further diminished by the fact that systemic administration of TZDs sometimes resulted in undesirable cardiovascular side effects, like edema and heart failure.
To clarify the uncertainties of the direct pro-angiogenic effects of TZDs, Nagahama and colleagues utilized a nanoparticle-mediated drug delivery system (DDS) for the targeted delivery of pioglitazone to the ischemic vasculature. The authors had previously demonstrated that polylactic-glycolic acid (PLGA) nanoparticles (NP) accumulated in the capillary and arteriolar endothelium after intramuscular injection in animal models of hindlimb ischemia9. In the present paper, they demonstrate that a single injection of pioglitazone-incorporated NP (Pio-NP) into the ischemic muscles results in a significant augmentation of angiogenesis and arteriogenesis, as well as significant improvements in blood flow to the ischemic limb. Remarkably, the 1 μg/kg dose of Pio-NP used to achieve enhanced blood flow recovery was far lower than the oral pioglitazone dose (1000 μg/kg) necessary for similar improvement. Presumably, such a remarkable enhancement reflects the NP-dependent optimization of drug tissue distribution and release kinetics.
By a number of measures the therapeutic neovascularization by Pio-NP appears to be mediated by PPARγ activation. The Pio-NP injection resulted in PPARγ activity in the ipsilateral limb and the PPARγ antagonist GW9662 abrogated the blood flow recovery by Pio-NP. Pio-NP induced multiple pro-angiogenic genes necessary to form functional collateral vessels. Moreover, the therapeutic effects of Pio-NP required endothelial NO synthase (eNOS) activation, as these were not observed in eNOS−/− mice. Importantly, therapeutic neovascularization by Pio-NP injection was independent of systemic insulin sensitivity.
The nanoparticle-mediated delivery of pioglitazone offers an exciting new therapeutic modality with numerous opportunities for follow-up studies. An interesting finding was the persistence of therapeutic effects 21 days following a single intramuscular injection. One wonders whether such a sustained effect is due to the fact that pioglitazone acts upstream of vascular growth factors and eNOS, thereby stimulating a cascade of multiple pro-angiogenic programs. Thus, while pioglitazone itself might disappear from tissues after only several days, the downstream mediators remain activated for much longer. It also seems plausible that the Pio-NP delivery system may be useful for promoting therapeutic angiogenesis in other contexts, such as cerebral or myocardial ischemia. Finally, pioglitazone is already FDA-approved, which should facilitate the translation into clinical testing. Prior studies indicate that the synthetic PLGA nanoparticles gradually undergo hydrolysis over 21 days9 and are generally non-toxic10; however future studies will need to rigorously address their clearance and safety in preclinical models and eventually in humans. With luck, the neovascularization strategies involving the nanoparticle-mediated delivery of pioglitazone and other pro-angiogenic compounds may prove efficacious in patients with severe PAD and CLI.
This is a commentary on article Nagahama R, Matoba T, Nakano K, Kim-Mitsuyama S, Sunagawa K, Egashira K. Nanoparticle-mediated delivery of pioglitazone enhances therapeutic neovascularization in a murine model of hindlimb ischemia. Arterioscler Thromb Vasc Biol.. 2012;32(10):2427-34.
References
- 1.van Royen N, Piek JJ, Schaper W, Fulton WF. A critical review of clinical arteriogenesis research. Journal of the American College of Cardiology. 2009;55:17–25. doi: 10.1016/j.jacc.2009.06.058. [DOI] [PubMed] [Google Scholar]
- 2.Nagaham R, Matoba T, Nakano K, Kim-Mitsuyama S, Sunagawa K, Egashira K. Nanoparticle-mediated delivery of pioglitazone enhances therapeutic neovascularization in murin model of hindlimb ischemia. Arterioscler Thromb Vasc Biol. 2012 doi: 10.1161/ATVBAHA.112.253823. this issue. [DOI] [PubMed] [Google Scholar]
- 3.Fukunaga Y, Itoh H, Doi K, Tanaka T, Yamashita J, Chun TH, Inoue M, Masatsugu K, Sawada N, Saito T, Hosoda K, Kook H, Ueda M, Nakao K. Thiazolidinediones, peroxisome proliferator-activated receptor gamma agonists, regulate endothelial cell growth and secretion of vasoactive peptides. Atherosclerosis. 2001;158:113–119. doi: 10.1016/s0021-9150(01)00430-0. [DOI] [PubMed] [Google Scholar]
- 4.Gensch C, Clever YP, Werner C, Hanhoun M, Bohm M, Laufs U. The ppar-gamma agonist pioglitazone increases neoangiogenesis and prevents apoptosis of endothelial progenitor cells. Atherosclerosis. 2007;192:67–74. doi: 10.1016/j.atherosclerosis.2006.06.026. [DOI] [PubMed] [Google Scholar]
- 5.Biscetti F, Gaetani E, Flex A, Aprahamian T, Hopkins T, Straface G, Pecorini G, Stigliano E, Smith RC, Angelini F, Castellot JJ, Jr, Pola R. Selective activation of peroxisome proliferator-activated receptor (ppar)alpha and ppar gamma induces neoangiogenesis through a vascular endothelial growth factor-dependent mechanism. Diabetes. 2008;57:1394–1404. doi: 10.2337/db07-0765. [DOI] [PubMed] [Google Scholar]
- 6.Huang PH, Sata M, Nishimatsu H, Sumi M, Hirata Y, Nagai R. Pioglitazone ameliorates endothelial dysfunction and restores ischemia-induced angiogenesis in diabetic mice. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 2008;62:46–52. doi: 10.1016/j.biopha.2007.06.014. [DOI] [PubMed] [Google Scholar]
- 7.Murata T, He S, Hangai M, Ishibashi T, Xi XP, Kim S, Hsueh WA, Ryan SJ, Law RE, Hinton DR. Peroxisome proliferator-activated receptor-gamma ligands inhibit choroidal neovascularization. Investigative ophthalmology & visual science. 2000;41:2309–2317. [PubMed] [Google Scholar]
- 8.Panigrahy D, Singer S, Shen LQ, Butterfield CE, Freedman DA, Chen EJ, Moses MA, Kilroy S, Duensing S, Fletcher C, Fletcher JA, Hlatky L, Hahnfeldt P, Folkman J, Kaipainen A. Ppargamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis. J Clin Invest. 2002;110:923–932. doi: 10.1172/JCI15634. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Kubo M, Egashira K, Inoue T, Koga J, Oda S, Chen L, Nakano K, Matoba T, Kawashima Y, Hara K, Tsujimoto H, Sueishi K, Tominaga R, Sunagawa K. Therapeutic neovascularization by nanotechnology-mediated cell-selective delivery of pitavastatin into the vascular endothelium. Arterioscler Thromb Vasc Biol. 2009;29:796–801. doi: 10.1161/ATVBAHA.108.182584. [DOI] [PubMed] [Google Scholar]
- 10.Semete B, Booysen L, Lemmer Y, Kalombo L, Katata L, Verschoor J, Swai HS. In vivo evaluation of the biodistribution and safety of plga nanoparticles as drug delivery systems. Nanomedicine: nanotechnology, biology, and medicine. 2010;6:662–671. doi: 10.1016/j.nano.2010.02.002. [DOI] [PubMed] [Google Scholar]