To study mechanisms by which free fatty acids (FFAs) cause hepatic insulin resistance, we have used euglycemichyperinsulinemic clamping with and without infusion of lipid/heparin (to raise or to lower plasma FFAs) in alert male rats. FFA-induced hepatic insulin resistance was associated with increased hepatic diacylglycerol content (؉210%), increased activities of two serine/threonine kinases (protein kinase C-␦ and inhibitor of B [IB] kinase-␤), increased activation of the proinflammatory nuclear factor-B (NF-B) pathway (IB kinase-␤, ؉640%; IB-␣, ؊54%; and NF-B, ؉73%), and increased expression of inflammatory cytokines (tumor necrosis factor-␣, ؉1,700% and interleukin-1␤, ؉440%) and plasma levels of monocyte chemoattractant protein-1 (؉220%). We conclude that FFAs caused hepatic insulin resistance, which can produce overproduction of glucose and hyperglycemia, and initiated inflammatory processes in the liver that could potentially result in the development of steatohepatitis. Diabetes 54: 3458 -3465, 2005 O besity is closely associated with insulin resistance, type 2 diabetes, and the metabolic syndrome (also called the insulin resistance syndrome) (1). Obesity is also associated with increased presence in the circulation of several proinflammatory cytokines and chemokines and because of that has also been considered an inflammatory condition (rev. in 2). Whereas the reason for these associations is not entirely clear, it has been established that free fatty acids (FFAs) are a major link between obesity and insulin resistance/type 2 diabetes. This is based on the following evidence: most obese people have elevated plasma FFA levels, and FFAs cause insulin resistance dose dependently in skeletal muscle and liver (rev in 3). In skeletal muscle, FFAs inhibit insulin-stimulated glucose uptake at the level of glucose transport and/or phosphorylation (4,5) through mechanisms that involve intramyocellular accumulation of diacylglycerol (DAG) and long-chain acyl-CoA, activation of protein kinase C (PKC), and decreased tyrosine phosphorylation of insulin receptor substrate 1/2 (IRS-1/2) (6,7). The mechanisms by which FFAs cause hepatic insulin resistance have been directly addressed by only one study. In that study, Lam et al. (8) have shown that infusion of lipids (which increased plasma FFA levels) resulted in activation of PKC-␦ in rat liver.In the present study, we have used the lipid/heparin infusion to study effects of acutely elevated plasma FFA levels on insulin action in the rat liver. In this model, plasma FFA levels rise about equally in the systemic and the portal circulation. This is similar to the situation in postabsorptive, obese individuals who have ϳ80% of their fat in subcutaneous and intramuscular adipose tissue (releasing FFAs into the peripheral circulation) and ϳ20% of their fat in visceral adipose tissue (releasing FFAs at an increased rate into the portal circulation) (9,10). RESEARCH DESIGN AND METHODSAdult male Sprague-Dawley rats (250 -300 g) were purchased from Charles River Laboratorie...

OBJECTIVE-To examine fat biopsy samples from lean insulinsensitive and obese insulin-resistant nondiabetic individuals for evidence of endoplasmic reticulum (ER) stress.RESEARCH DESIGN AND METHODS-Subcutaneous fat biopsies were obtained from the upper thighs of six lean and six obese nondiabetic subjects. Fat homogenates were used for proteomic (two-dimensional gel and MALDI-TOF/TOF), Western blot, and RT-PCR analysis.RESULTS-Proteomic analysis revealed 19 differentially upregulated proteins in fat of obese subjects. Three of these proteins were the ER stress-related unfolded protein response (UPR) proteins calreticulin, protein disulfide-isomerase A3, and glutathione-S-transferase P. Western blotting revealed upregulation of several other UPR stress-related proteins, including calnexin, a membrane-bound chaperone, and phospho c-jun NH 2 -terminal kinase (JNK)-1, a downstream effector protein of ER stress. RT-PCR analysis revealed upregulation of the spliced form of X-box binding protein-1s, a potent transcription factor and part of the proximal ER stress sensor inositol-requiring enzyme-1 pathway.CONCLUSIONS-These findings represent the first demonstration of UPR activation in subcutaneous adipose tissue of obese human subjects. As JNK can inhibit insulin action and activate proinflammatory pathways, ER stress activation of JNK may be a link between obesity, insulin resistance, and inflammation. Diabetes 57: [2438][2439][2440][2441][2442][2443][2444] 2008 O besity is associated with insulin resistance and with a low-grade state of inflammation (1). Whereas the cause of neither is completely understood, there is good evidence to show that free fatty acids (FFAs) play an important role in the development of obesity-related insulin resistance and inflammation (2). Plasma FFA levels are increased in most obese people (3). Acutely raising plasma FFA levels increases insulin resistance (4), whereas lowering plasma FFA levels reduces insulin resistance (5). Mechanisms involved in FFAinduced insulin resistance include accumulation (in muscle and liver) of lipids and lipid intermediates, including diacylglycerol; activation of several protein kinase C isoforms; and reduction in tyrosine phosphorylation of insulin receptor substrate-1/2 (6 -8). FFAs also activate the proinflammatory nuclear factor B pathway (6,9), in part, via signaling through toll-like receptor-4 pathways (10). However, not all obese, insulin-resistant subjects have elevated plasma FFA levels. It is therefore likely that there are other causes for obesityrelated insulin resistance. One of these appears to be endoplasmic reticulum (ER) stress. Indeed, chronic excessive nutrient intake has been shown to cause ER stress in adipose tissue of ob/ob mice and mice fed high-fat diets (11-13).The ER is a major site for protein as well as for lipid and sterol synthesis (14,15). Ribosomes attached to the ER membranes release newly synthesized peptides into the ER lumen, where protein chaperones and foldases assist in the proper posttranslational modification a...

A high prevalence of comorbidities in SpA has been shown. Rigorous application of systematic evaluation of comorbidities may permit earlier detection, which may ultimately result in an improved outcome of patients with SpA.

Tumor necrosis factor (TNF) is a key regulator of inflammatory responses and has been implicated in many pathological conditions. We used structure-based design to engineer variant TNF proteins that rapidly form heterotrimers with native TNF to give complexes that neither bind to nor stimulate signaling through TNF receptors. Thus, TNF is inactivated by sequestration. Dominant-negative TNFs represent a possible approach to anti-inflammatory biotherapeutics, and experiments in animal models show that the strategy can attenuate TNF-mediated pathology. Similar rational design could be used to engineer inhibitors of additional TNF superfamily cytokines as well as other multimeric ligands.