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Lysophospholipids have long been recognized as membrane phospholipid metabolites, but only recently lysophosphatidic acids (LPA) have been demonstrated to act on specific G protein-coupled receptors. The widespread expression of LPA receptors and coupling to several classes of G proteins allow LPA-dependent regulation of numerous processes, such as vascular development, neurogenesis, wound healing, immunity, and cancerogenesis. Lysophosphatidic acids have been found to induce many of the hallmarks of cancer including cellular processes such as proliferation, survival, migration, invasion, and neovascularization. Furthermore, autotaxin (ATX), the main enzyme converting lysophosphatidylcholine into LPA was identified as a tumor cell autocrine motility factor. On the other hand, cyclic phosphatidic acids (naturally occurring analogs of LPA generated by ATX) have anti-proliferative activity and inhibit tumor cell invasion and metastasis. Research achievements of the past decade suggest implementation of preclinical and clinical evaluation of LPA and its analogs, LPA receptors, as well as autotaxin as potential therapeutic targets.
Angiogenesis, the formation of new capillaries from pre-existing vascular network, plays an important role in physiological and pathological processes such as embryonic development, wound healing, and development of atherosclerosis. Extension of the circulatory network is also considered to be one the most important factors during cancerogenesis. Inhibition of angiogenesis may lead to inhibition of tumor growth whereas stimulation may improve wound healing. Research achievements suggest the use of plants and their extracts as potential therapeutic agents with pro- or antiangiogenic activity. Since the anticancer and antiangiogenic properties of many phytomedicines have been amply reviewed elsewhere this paper will focus on the treatment of vascular insufficiency in wound healing. Globally accepted herbal drugs are thought to be safe and effective, however, there is a need for more evidence-based confirmation in controlled and validated trials. Among the most frequently studied proangiogenic phytochemicals are ginsenosides from Panax ginseng, beta-sitosterol from Aloe vera, calycosin from Radix Astragali, and extracts from Hippophae rhamnoides L. and Angelica sinensis.
The use of nucleotides and their analogs in the pharmacological studies of nucleo­tide receptors (P2 class) should be preceded by detailed studies on their degradation connected with ecto-enzymes of a given cell type. In the present studies we have ana­lyzed stability of some phosphorothioate and phosphonate analogs of ATP and ADP in the HeLa epitheloid carcinoma and endothelial HUVEC cells cultures. Our studies have revealed that ecto-nucleotide pyrophosphatase (E-NPP) is one of the main en­zymes involved in the extracellular degradation of ATP and other nucleotides in the HeLa cells. On the other hand, the ecto-ATPDase is responsible for the hydrolysis of extracellular nucleotides in human endothelial cell cultures, while the E-NPP-like en­zymes of the HUVEC cells are not essential to this degradation. The concerted action of the aforementioned ecto-enzymes and nucleotide pyrophosphatase, 5 -nucleo- tidase and adenosine deaminase present in fetal bovine serum (FBS) supplied to the culture medium, results in partial or complete degradation of the phosphorothioate (ATPγS) and phosphonate analogs of adenosine nucleotides (α,β-methylene-ATP and β,γ-methylene-ATP) in the cell cultures. Only ADPβS appears to be resistant to these enzymes. The influence of some nucleotides and their analogs on the proliferation of the HeLa cells in presence or absence of FBS is also discussed.
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