OBJECTIVEIncreased oxidative stress (OS) and impaired anti-OS defenses are important in the development and persistence of insulin resistance (IR). Several anti-inflammatory and cell-protective mechanisms, including advanced glycation end product (AGE) receptor-1 (AGER1) and sirtuin (silent mating-type information regulation 2 homolog) 1 (SIRT1) are suppressed in diabetes. Because basal OS in type 2 diabetic patients is influenced by the consumption of AGEs, we examined whether AGE consumption also affects IR and whether AGER1 and SIRT1 are involved.RESEARCH DESIGN AND METHODSThe study randomly assigned 36 subjects, 18 type 2 diabetic patients (age 61 ± 4 years) and 18 healthy subjects (age 67 ± 1.4 years), to a standard diet (>20 AGE equivalents [Eq]/day) or an isocaloric AGE-restricted diet (<10 AGE Eq/day) for 4 months. Circulating metabolic and inflammatory markers were assessed. Expression and activities of AGER1 and SIRT1 were examined in patients’ peripheral blood mononuclear cells (PMNC) and in AGE-stimulated, AGER1-transduced (AGER1+), or AGER1-silenced human monocyte-like THP-1 cells.RESULTSInsulin and homeostasis model assessment, leptin, tumor necrosis factor-α and nuclear factor-κB p65 acetylation, serum AGEs, and 8-isoprostanes decreased in AGE-restricted type 2 diabetic patients, whereas PMNC AGER1 and SIRT1 mRNA, and protein levels normalized and adiponectin markedly increased. AGEs suppressed AGER1, SIRT-1, and NAD+ levels in THP-1 cells. These effects were inhibited in AGER1+ but were enhanced in AGER1-silenced cells.CONCLUSIONSFood-derived pro-oxidant AGEs may contribute to IR in clinical type 2 diabetes and suppress protective mechanisms, AGER1 and SIRT1. AGE restriction may preserve native defenses and insulin sensitivity by maintaining lower basal OS.

The epidemics of insulin resistance (IR) and type 2 diabetes (T2D) affect the first world as well as less-developed countries, and now affect children as well. Persistently elevated oxidative stress and inflammation (OS/Infl) precede these polygenic conditions. A hallmark of contemporary lifestyle is a preference for thermally processed nutrients, replete with pro-OS/Infl advanced glycation endproducts (AGEs), which enhance appetite and cause overnutrition. We propose that chronic ingestion of oral AGEs promotes IR and T2D. The mechanism(s) involved in these findings were assessed in four generations of C57BL6 mice fed isocaloric diets with or without AGEs [synthetic methyl-glyoxal-derivatives (MG + )]. F3/MG + mice manifested increased adiposity and premature IR, marked by severe deficiency of anti-AGE advanced glycation receptor 1 (AGER1) and of survival factor sirtuin 1 (SIRT1) in white adipose tissue (WAT), skeletal muscle, and liver. Impaired 2-deoxy-glucose uptake was associated with marked changes in insulin receptor (InsR), IRS-1, IRS-2, Akt activation, and a macrophage and adipocyte shift to a pro-OS/inflammatory (M1) phenotype. These features were absent in F3/MG − mice. MG stimulation of 3T3-L1 adipocytes led to suppressed AGER1 and SIRT1, and altered InsR, IRS-1, IRS-2 phosphorylation, and nuclear factor kappa-light chain enhancer of activated B cells (Nf-κB) p65 acetylation. Gene modulation revealed these effects to be coregulated by AGER1 and SIRT1. Thus, prolonged oral exposure to MG-AGEs can deplete host-defenses AGER1 and SIRT1, raise basal OS/Infl, and increase susceptibility to dysmetabolic IR. Because exposure to AGEs can be decreased, these insights provide an important framework for alleviating a major lifestyle-linked disease epidemic.

SIRT1 and PPARγ, host defenses regulating inflammation and metabolic functions, are suppressed under chronic high oxidant stress and inflammation (OS/ Infl) conditions. In diabetes, dietary advanced glycation end products (dAGEs) cause OS/Infl and suppress SIRT1. Herein, we ask whether dAGEs also suppress host defense in adults without diabetes. The relationships between dAGEs and basal SIRT1 mRNA, PPARγ protein levels in mononuclear cells (MNC) and circulating inflammatory/metabolic markers were examined in 67 healthy adults aged >60 years and in 18 subjects, before and after random assignment to either a standard diet (regular>15 AGE Eq/ day) or an isocaloric AGE-restricted diet (<10 AGE Eq/ day) for 4 months. Also, the interactions of AGEs and anti-AGE receptor-1 (AGER1) with SIRT1 and PPARγ were assessed in wild type (WT) and AGER1-transduced (AGER1+) MNC-like THP-1 cells. We found that dAGE, but not caloric intake, correlated negatively with MNC SIRT1 mRNA levels and positively with circulating AGEs (sAGEs), OS/infl, MNC TNFα and RAGE. Basal MNC PPARγ protein was also lower in consumers of regular vs. AGE-restricted diet. AGE restriction restored MNC SIRT1 and PPARγ, and significantly decreased sAGEs, 8-iso-prostanes, VCAM-1, MNC TNFα and RAGE. Model AGEs suppressed SIRT1 protein and activity, and PPARγ protein in WT, but not in AGER1+ cells in vitro. In conclusion, chronic consumption of high-AGE diets depletes defenses such as SIRT1 and PPARγ, independent of calories, predisposing to OS/Infl and chronic metabolic disease. Restricted entry of oral AGEs may offer a disease-prevention alternative for healthy adults.

AHNAK is a 700 KD phosphoprotein primarily involved in calcium signaling in various cell types and regulating cytoskeletal organization and cell membrane architecture. AHNAK expression has also been associated with obesity. To investigate the role of AHNAK in regulating metabolic homeostasis, we studied whole body AHNAK knockout mice (KO) on either regular chow or high-fat diet (HFD). KO mice had a leaner phenotype and were resistant to high-fat diet-induced obesity (DIO), as reflected by a reduction in adipose tissue mass in conjunction with higher lean mass compared to wild-type controls (WT). However, KO mice exhibited higher fasting glucose levels, impaired glucose tolerance, and diminished serum insulin levels on either diet. Concomitantly, KO mice on HFD displayed defects in insulin signaling, as evident from reduced Akt phosphorylation and decreased cellular glucose transporter (Glut4) levels. Glucose intolerance and insulin resistance were also associated with changes in expression of genes regulating fat, glucose, and energy metabolism in adipose tissue and liver. Taken together, these data demonstrate that (a) AHNAK is involved in glucose homeostasis and weight balance (b) under normal feeding KO mice are insulin sensitive yet insulin deficient; and (c) AHNAK deletion protects against HFD-induced obesity, but not against HFD-induced insulin resistance and glucose intolerance in vivo.

Since the classic experiments by Tigerstedt and Bergman that established the role of renin in hypertension a century ago, aggressive efforts have been launched to effectively block the renin-angiotensin system (RAS). Blockade of RAS is advocated at multiple levels by direct renin inhibitor, angiotensin-converting enzyme inhibitor and/or angiotensin II type 1 receptor blocker, or aldosterone inhibitor (spironolactone), and has now become part of the standard of care to control hypertension and related metabolic diseases including diabetes. However, recent lessons learned from randomized clinical trials question the wisdom of blocking RAS at multiple levels. In this context, it is highly pertinent that components of RAS are evolutionarily conserved, and novel physiological/adaptive/protective roles for renin and angiotensin-converting enzyme are currently emerging. Angiotensin II, the classical RAS effector peptide responsible for hypertension, hypertrophy, fluid retention and fibrosis, manifests its cardiovascular protective effect when it activates the angiotensin II type 2 receptor. Additionally, angiotensin-converting enzyme 2 and the angiotensin II metabolite Ang-(1–7) that acts through the Mas proto-oncogene constitute the cardiovascular and renal protective branch of RAS. It is conceivable that modulating this vasodilative/anti-inflammatory branch of RAS by activation of the RAS components that constitute this branch may offer a safer long-term treatment strategy to balance RAS activity and achieve homeostasis compared to chronic multilevel RAS inhibition.