The Vitamin E Analog Gamma-Tocotrienol (GT3) and Statins Synergistically Up-Regulate Endothelial Thrombomodulin (TM)

Abstract

Statins; a class of routinely prescribed cholesterol-lowering drugs; inhibit 3-hydroxy-3-methylglutaryl-coenzymeA reductase (HMGCR) and strongly induce endothelial thrombomodulin (TM); which is known to have anti-inflammatory; anti-coagulation; anti-oxidant; and radioprotective properties. However; high-dose toxicity limits the clinical use of statins. The vitamin E family member gamma-tocotrienol (GT3) also suppresses HMGCR activity and induces TM expression without causing significant adverse side effects; even at high concentrations. To investigate the synergistic effect of statins and GT3 on TM; a low dose of atorvastatin and GT3 was used to treat human primary endothelial cells. Protein-level TM expression was measured by flow cytometry. TM functional activity was determined by activated protein C (APC) generation assay. Expression of Kruppel-like factor 2 (KLF2), one of the key transcription factors of TM, was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR). TM expression increased in a dose-dependent manner after both atorvastatin and GT3 treatment. A combined treatment of a low-dose of atorvastatin and GT3 synergistically up-regulated TM expression and functional activity. Finally; atorvastatin and GT3 synergistically increased KLF2 expression. These findings suggest that combined treatment of statins with GT3 may provide significant health benefits in treating a number of pathophysiological conditions; including inflammatory and cardiovascular diseases.

Thrombomodulin and Endothelial Dysfunction: A Disease-Modifier Shared between Malignant Hypertension and Atypical Hemolytic Uremic Syndrome

“…The pleiotropic endothelium-modifying properties of TM are translated into beneficial effects of recombinant human TM in rodent models of endotoxininduced pulmonary vascular damage, ischemia-reperfusion kidney or liver injury, preeclampsia, STEC-HUS and acute ischemic stroke [30][31][32][33][34][35]. Of note, statins increase the endothelial expression of TM, possibly contributing to its beneficial cardiovascular properties [36], and acti- The thrombin (IIa)-binding region has been localized to the fifth and sixth EGF-like domains, while the fourth EGF-like domain is required for protein C binding to the thrombin-TM complex. The serine/threonine-rich spacer region is the site of glycosaminoglycan (GAG) and especially chondroitin sulphate attachment, enabling the interaction between TM and factor H, which is a cofactor for the factor I-mediated cleavage of C3b into inactive fragments (iC3b).…”

Fractionated radiation suppresses Kruppel-like factor 2 pathway to a greater extent than by single exposure to the same total dose

“…However, no study has investigated whether GT3, which can also inhibit HMG-CoA reductase by triggering posttranslational degradation of the enzyme, has efficacy similar to that of statins for ERK5 activation in endothelial cells. Notably, we demonstrated that GT3 and statins synergistically upregulate expression of KLF2 and TM and generation of APC in endothelial cells 38 , which are under positive control of ERK5 activation. In addition, GGTi upregulates KLF2 via ERK5 activation 37 .…”

“…We tested the efficacy of inhibitors of the mevalonate pathway, specifically, HMG-CoA reductase inhibitors (i.e., atorvastatin and GT3) and GGTi, in attenuating KLF2 suppression after fractionated radiation. We and others have shown HMG-CoA reductase inhibitors enhanced the expression of KLF2 and its downstream target molecules, such as TM and eNOS and provided radiation protection 28,30,38,39,41 . Treatment with atorvastatin, GT3, and GGTi significantly prevented fractionated radiation-induced suppression of not only KLF2 but also its downstream target molecules TM and eNOS (Fig.…”

Utilization of Vitamin E Analogs to Protect Normal Tissues While Enhancing Antitumor Effects

“…Ionizing radiation negatively affects TM expression (48,49), while activation of the APC pathway and administration of exogenous recombinant TM protect against radiation toxicity (50,51). γ-Tocotrienol induces the expression of TM in primary and immortalized human endothelial cells (45). Moreover, γ-tocotrienol-mediated protection against radiation lethality is dependent on TM, indicating the importance of TM in γ-tocotrienol’s mechanisms of action (52).…”

“…KLF2 has been associated with endothelial anti-inflammatory, anti-coagulant, antioxidant, anti-adhesive, and anti-permeability properties (58). γ-Tocotrienol and statins synergistically enhance endothelial KLF2 expression as well as the expression and functional activity of TM (45). TM’s transcription can also be positively regulated by the transcription factor, heat shock factor 1 (HSF1).…”