Abstract-Release of free fatty acid (FFA) from adipose tissue is implicated in insulin resistance and endothelial dysfunction in patients with visceral fat obesity. We demonstrated previously that increased FFA levels cause endothelial dysfunction that is prevented by inhibition of the renin-angiotensin system (RAS) in humans. However, the mechanisms for FFA-mediated activation of RAS and the resultant endothelial dysfunction were not elucidated. We investigated effects of elevated FFA on activity of circulating and vascular RAS, angiotensin II-forming activity of leukocytes, and leukocyte activation of normotensive subjects. We showed that increased FFA levels significantly enhanced angiotensin II-forming activity in human mononuclear (mean fold increase: 3.5 at 180 minutes; Pϭ0.0016) and polymorphonuclear (2.0; Pϭ0.0012) cells, whereas parameters of the circulating and vascular RAS were not affected. We also showed that FFA caused angiotensin II-dependent leukocyte activation, which impaired endothelial function partly via increased myeloperoxidase release and presumably enhanced adhesion of leukocytes. We propose that the enhanced production of angiotensin II by FFA in mononuclear and polymorphonuclear cells causes activation of leukocytes that consequently impairs endothelial function. RAS in leukocytes may regulate the leukocyte-vasculature interaction as the mobile RAS in humans. T he levels of circulating free fatty acid (FFA), mainly originating from lipolysis in adipose tissue, are increased in patients with metabolic syndrome and type 2 diabetes mellitus, 1-3 reflecting resistance to the antilipolytic action of insulin. Increased plasma FFA concentrations cause endothelial dysfunction, 4 insulin resistance, 5 and endothelial apoptosis. 6 These observations, together with results from epidemiological studies, 7,8 suggest that FFA is involved in atherosclerosis in subjects with insulin resistance. Recently, we have found that FFA-induced endothelial dysfunction is prevented by the inhibition of the renin-angiotensin (Ang) system (RAS) in humans, 9 suggesting that RAS activation by FFA may predominantly contribute to FFA-induced endothelial dysfunction. This hypothesis appears plausible because of the close relationship between obesity and RAS activity in humans. 10,11 In addition, RAS activation is also associated with enhanced oxidative stress, 12 which is an intermediary mechanism by which FFA adversely alters vascular function. 13 However, although the proatherogenic action of excessive Ang II has been well documented, there is little information regarding the mechanism of RAS activation in individuals with obesity. Indeed, only a few studies have investigated the effects of elevated FFA on RAS activity. 14 The aim of the present study was to investigate effects of elevated FFA on RAS and to elucidate mechanisms for FFA-induced endothelial dysfunction in humans. We also investigated the interaction between FFA and leukocytes, because FFA is involved in leukocyte activation through protein kinase C re...

ABSTRACT. We investigated whether de-differentiated fat (DFAT) cells, a mature adipocyte-derived preadipocyte cell line, can be induced to trans-differentiate into osteoblasts in vitro and in vivo. All-trans retinoic acid (RA) induced expression of osteoblast-specific mRNAs encoding Cbfa1/Runx2, osterix, alkaline phosphatase, osteopontin, parathyroid hormone receptor, and osteocalcin in the DFAT cells, but did not induce the expression of adipocytespecific mRNAs encoding PPARγ2, C/EBPα, and GLUT4. Moreover, alkaline phosphatase activity was expressed in DFAT cells and the cells underwent mineralization of the bone matrix in vitro. Furthermore, when DFAT cells were transplanted subcutaneously into C57BL/6N mice in diffusion chambers, these cells formed ectopic osteoid tissue without any host cell-invasion of the chambers. These results indicate that DFAT cells derived from mature adipocytes can be converted into fully differentiated osteoblasts in vitro and in vivo using RA. DFAT cells provide a unique model for studying the lineage commitment of the adipocytes and osteoblasts derived from mesenchymal stem cells. Identification of the pathways that regulate these processes could lead to the development of new therapeutic strategies for control of unwarranted growth of bone and adipose tissue.

Objective-An elevated free fatty acid (FFA) level impairs endothelium-dependent vasodilation in humans, which may be pathophysiologically relevant to the development of endothelial dysfunction in patients with insulin resistance. We investigated the effect of inhibition of the renin-angiotensin system (RAS) on FFA-induced endothelial dysfunction. Methods and Results-Changes in forearm blood flow during intra-arterial infusion of acetylcholine were measured by plethysmography before and after systemic infusion of lipid/heparin in 10 healthy subjects given a single dose of placebo, losartan (50 mg), or perindopril (8 mg). Endothelial function after lipid/heparin infusion was also investigated with the coinfusion of vitamin C or N G -monomethyl-L-arginine (L-NMMA). Elevated FFA significantly reduced the response to acetylcholine by 37.7% (Pϭ0.0096) without L-NMMA, but not the response with L-NMMA, whereas FFA did not affect the response to nitroprusside. The single dose of either losartan or perindopril completely prevented FFA-induced endothelial dysfunction. Vitamin C also prevented FFA-induced endothelial dysfunction. Conclusions-Elevated FFA levels by lipid/heparin infusion, which may partly mimic the abnormal lipid profile in patients with insulin resistance, caused endothelial dysfunction via RAS activation and the presumably resultant oxidative stress in humans. Our results suggest the therapeutic rationale for RAS inhibition in patients with high FFA levels. Key Words: fatty acids Ⅲ endothelium Ⅲ angiotensin II Ⅲ insulin resistance Ⅲ nitric oxide A n increased plasma level of free fatty acid (FFA) may play pivotal roles in the development and progression of endothelial dysfunction and insulin resistance in patients with type 2 diabetes as well as in the prediabetic state, including the metabolic syndrome and visceral adiposity. 1,2 In addition to a negative correlation between plasma FFA levels and endothelial function, 3 a direct vascular effect of FFA on endothelial function in humans has already been demonstrated. FFAs elevated by lipid/heparin infusion significantly attenuated the vasodilatory response to acetylcholine (ACh) in healthy subjects. 2,4 Although it has been suggested that reactive oxygen species 4 -6 and activation of a stress-sensitive pathway like the transcriptional factor nuclear factor-B 7,8 may be involved in FFA-induced endothelial dysfunction, no specific therapeutic intervention has yet been established.Several randomized, clinical trials have suggested that inhibition of the renin-angiotensin system (RAS) is particularly effective in patients with diabetic hypertension compared with nondiabetic hypertension. 9,10 Improvement in endothelial function by angiotensin-converting enzyme (ACE) inhibitors 11 and angiotensin II type 1 receptor (AT 1 ) antagonists (ARB) 12 in type 2 diabetic patients may partly explain the results of previous randomized, clinical trials. Moreover, there is much evidence in support of enhanced activity of the RAS in obese, hypertensive patients. 13 In the pr...