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99mTc-Hexamethylpropyleneamine oxime pH-sensitive liposomes.

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2008 Jul 02 [updated 2008 Aug 07].

Excerpt

Inflammatory and infectious diseases are a common cause of patient morbidity and mortality despite recent advances in antimicrobial therapy (1, 2). The detection and diagnosis of these lesions is essential for the development of appropriate and timely treatment of the ailment. Scintigraphy plays an important role in the assessment of patients suspected to have these illnesses because this technique is based on the in vivo detection of radiotracer distribution, which is usually based on the physiological characteristics of the tissues. Therefore, this method allows detection of the physiopathological processes during the initial stages and differs from the conventional methods that are based on visualization of anatomic alterations (3-5). Liposomes are nanocarriers that have been widely used for the in vivo delivery of a variety of drugs and molecules to detect or treat different pathological conditions such as cancer or microbial infections, or even used for the delivery of gene therapy (6-8). In addition, liposomes that are pH-sensitive have been developed and used for the preparation and delivery of radiolabeled drugs to detect and treat tissue lesions (9). An acidic environment in the inflamed or infected tissues collapses the liposomes into a non-bilayer structure, which leads to its disruption and the subsequent release of the trapped radioactive marker(s). Thus, these liposomes can be used to enhance the bioavailability of a radiotracer and improve the scintigraphic imaging quality. On the other hand, one limitation of the use of liposomes as diagnostic agents is the aspect of complement activation, which results in liposome clearance by the mononuclear phagocyte system (MPS) and may lead to the development of hypersensitivity in the treated individuals (10, 11). It has been reported that the inclusion of amphipathic poly(ethylene glycols) (PEGs) in the liposome composition can significantly reduce liposome uptake by the MPS, resulting in prolonged liposome circulation (9, 12). It is believed the liposomes accumulate around the tissue cells due to vasodilation and some macrophages may phagocytise the liposomes as a defense mechanism resulting in some inflammation (13). Carmo et al. developed a novel, meta-stable technetium (99mTc) containing hexamethylpropyleneamine oxime (HMPAO) and pH-sensitive liposomes (99mTc-SpHL) and investigated its tissue distribution, ability to detect inflammation, and complement activation in rats (14).

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