Macrophage peroxisome proliferator activated receptor γ as a therapeutic target to combat Type 2 diabetes

Pharmacotherapy of type 2 diabetes: An update and future directions

Type 2 diabetes (T2D) is a widely prevalent disease with substantial economic and social impact for which multiple conventional and novel pharmacotherapies are currently available; however, the landscape of T2D treatment is constantly changing as new therapies emerge and the understanding of currently available agents deepens. This review aims to provide an updated summary of the pharmacotherapeutic approach to T2D. Each class of agents is presented by mechanism of action, details of administration, side effect profile, cost, and use in certain populations including heart failure, non-alcoholic fatty liver disease, obesity, chronic kidney disease, and older individuals. We also review targets of novel therapeutic T2D agent development. Finally, we outline an up-to-date treatment approach that starts with identification of an individualized goal for glycemic control then selection, initiation, and further intensification of a personalized therapeutic plan for T2D.

Microglial phenotypes in Parkinson's disease and animal models of the disease

Over the last decade the important concept has emerged that microglia, similar to other tissue macrophages, assume different phenotypes and serve several effector functions, generating the theory that activated microglia can be organized by their pro-inflammatory or anti-inflammatory and repairing functions. Importantly, microglia exist in a heterogenous population and their phenotypes are not permanently polarized into two categories; they exist along a continuum where they acquire different profiles based on their local environment. In Parkinson's disease (PD), neuroinflammation and microglia activation are considered neuropathological hallmarks, however their precise role in relation to disease progression is not clear, yet represent a critical challenge in the search of disease-modifying strategies. This review will critically address current knowledge on the activation states of microglia as well as microglial phenotypes found in PD and in animal models of PD, focusing on the expression of surface molecules as well as pro-inflammatory and anti-inflammatory cytokine production during the disease process. While human studies have reported an elevation of both pro- or anti-inflammatory markers in the serum and CSF of PD patients, animal models have provided insights on dynamic changes of microglia phenotypes in relation to disease progression especially prior to the development of motor deficits. We also review recent evidence of malfunction at multiple steps of NFκB signaling that may have a causal interrelationship with pathological microglia activation in animal models of PD. Finally, we discuss the immune-modifying strategies that have been explored regarding mechanisms of chronic microglial activation.

Nuclear Mechanisms of Insulin Resistance

Insulin resistance is a sine qua non of type 2 diabetes and is associated with many other clinical conditions. Decades of research into mechanisms underlying insulin resistance have mostly focused on problems in insulin signal transduction and other mitochondrial and cytosolic pathways. By contrast, relatively little attention has been focused on transcriptional and epigenetic contributors to insulin resistance, despite strong evidence that such nuclear mechanisms play a major role in the etiopathogenesis of this condition. In this review, we summarize the evidence for nuclear mechanisms of insulin resistance, focusing on three transcription factors with a major impact on insulin action in liver, muscle, and fat.

Macrophage polarization: an opportunity for improved outcomes in biomaterials and regenerative medicine

The host response to biomaterials has been studied for decades. Largely, the interaction of host immune cells, macrophages in particular, with implanted materials has been considered to be a precursor to granulation tissue formation, the classic foreign body reaction, and eventual encapsulation with associated negative impacts upon device functionality. However, more recently, it has been shown that macrophages, depending upon context dependent polarization profiles, are capable of affecting both detrimental and beneficial outcomes in a number of disease processes and in tissue remodeling following injury. Herein, the diverse roles played by macrophages in these processes are discussed in addition to the potential manipulation of macrophage effector mechanisms as a strategy for promoting site-appropriate and constructive tissue remodeling as opposed to deleterious persistent inflammation and scar tissue formation.

Long-term effects of placental growth on overweight and body composition

Obesity is programmed in utero and small babies generally have small placentas. In some circumstances, an undernourished fetus can expand its placental surface to extract more nutrients. We hypothesize that this results in an imbalanced nutrient supply to the fetus leading to obesity. To determine whether placental size determines overweight and body composition, we studied 2003 subjects in adult life. Associations between placental surface area and indices of overweight were restricted to people who carried the Pro12Pro genotype of the PPARγ2 gene. For every 1 SD increase in placental surface area, the odds ratio for overweight was 1.37 (95% CI 1.10 to 1.71; P = 0.005). Expansion of the placental surface in compensation for fetal undernutrition increases the risk of overweight and a higher body fat percentage in people carrying the Pro12Pro genotype. We suggest that similar underlying multifactorial mechanisms affect the development of obesity in general.

Correlation of Peroxisome Proliferator-Activated Receptor-gamma (PPAR-gamma) and Retinoid X Receptor-alpha (RXR-alpha) expression with clinical risk factors in patients with advanced carotid atherosclerosis

Background

Peroxisome proliferator-activated Receptor-γ (PPAR-γ) and its nuclear partners, the Retinoid X Receptors (RXRs), have been recognized as crucial players in the pathogenesis of atherosclerosis. The present study aimed to assess the clinical significance of PPAR-γ and RXR-α expression in different cellular populations localized within advanced carotid atherosclerosis lesions.

Material/Methods

PPAR-γ and RXR-α expression was assessed by immunohistochemistry ïn 134 carotid atherosclerotic plaques obtained from an equal number of patients that underwent endarterectomy procedure for vascular repair, and was correlated with patients’ medical history, risk factors and medication intake.

Results

Increased incidence of low PPAR-γ expression in both macrophages and smooth muscle cells was noted in patients presenting coronary artery disease (p=0.032 and p=0.046, respectively). PPAR-γ expression in smooth muscle cells was borderline down-regulated in symptomatic compared to asymptomatic patients (p=0.061), reaching statistical significance when analyzing groups of patients with specific cerebrovascular events; amaurosis fugax (p=0.008), amaurosis fugax/stroke (p=0.020) or amaurosis fugax/transient ischemic attack patients (p=0.028) compared to asymptomatic patients. Low RXR-α expression in macrophages was more frequently observed in hypertensive (p=0.048) and hyperlipidemic patients (p=0.049). Increased incidence of low RXR-α expression in smooth muscle cells was also noted in patients presenting advanced carotid stenosis grade (p=0.015).

Conclusions

PPAR-γ and RXR-α expression down-regulation in macrophages and smooth muscle cells was associated with a more pronounced disease progression in patients with advanced carotid atherosclerotic lesions.

Inflammatory phenotyping identifies CD11d as a gene markedly induced in white adipose tissue in obese rodents and women

In severe obesity, white adipose tissue (WAT) inflammation and macrophage infiltration are thought to contribute to WAT and whole-body insulin resistance. Specific players involved in triggering and maintaining inflammation (i.e. those regulating adipokine release and WAT macrophage recruitment, retention, or function) remain to be fully elaborated, and the degree to which moderate obesity promotes WAT inflammation remains to be clarified further. Therefore, we characterized adiposity and metabolic phenotypes in adult male C57BL/6J mice fed differing levels of dietary fat (10, 45, and 60% of energy) for 12 wk, concurrent with determinations of WAT inflammation markers and mRNA expression of leukocyte-derived integrins (CD11b, CD11c, CD11d) involved in macrophage extravasation and tissue macrophage homing/retention. As expected, a lard-based, very high-fat diet (60% energy) significantly increased adiposity and glucose intolerance compared with 10% fat-fed controls, coincident with higher retroperitoneal (RP) WAT transcript levels for proinflammatory factors and macrophage markers, including TNFα and CD68 mRNA, which were ~3- and ~15-fold of control levels, respectively (P < 0.001). Mice fed the 45% fat diet had more moderate obesity, less glucose intolerance, and lower WAT macrophage/inflammatory marker mRNA abundances compared with 60% fat-fed mice; TNFα and CD68 mRNA levels were ~2- and ~5-fold of control levels (P < 0.01). Relative WAT expression of CD11d was massively induced by obesity to an extent greater than any other inflammatory marker (to >300-fold of controls in the 45 and 60% fat groups) (P < 0.0001) and this induction was WAT specific. Because we found that CD11d expression also increased in RP-WAT of Zucker obese rats and in the subcutaneous WAT of obese adult women, this appears to be a common feature of obesity. Observed correlations of WAT macrophage transcript marker abundances with body weight in lean to modestly obese mice raises an interesting possibility that the activities of at least some WAT macrophages are closely linked to the normal adipose remodeling that is a requisite for changes in WAT energy storage capacity.

Lipid-sensing nuclear receptors in the pathophysiology and treatment of the metabolic syndrome

Metabolic syndrome (MS) is a cluster of different diseases, namely central obesity, hypertension, hyperglycemia, and dyslipidemia, together with a pro-thrombotic and pro-inflammatory state. These metabolic abnormalities are often associated with an increased risk for cardiovascular disease (CVD) and cancer. Dietary and lifestyle modifications are currently believed more effective than pharmacological therapies in the management of MS patients. Nevertheless, the relatively low grade of compliance of patients to these recommendations, as well as the failure of current therapies, highlights the need for the discovery of new pharmacological and nutraceutic approaches. A deeper knowledge of the patho-physiological events that initiate and support the MS is mandatory. Lipid-sensing nuclear receptors (NRs) are the master transcriptional regulators of lipid and carbohydrate metabolism and inflammatory responses, thus standing as suitable targets. This review focuses on the physiological relevance of the NRs (peroxisome proliferator-activated receptors, liver X receptors, and farnesoid X receptor) in the control of whole-body homeostasis, with a special emphasis on lipid and glucose metabolism, and on the relationships between metabolic unbalances, systemic inflammation, and the onset of CVD. Future perspectives and possible clinical applications are also presented.

Xanthones from mangosteen inhibit inflammation in human macrophages and in human adipocytes exposed to macrophage-conditioned media

Obesity-associated inflammation is characterized by recruitment of macrophages (MPhi) into white adipose tissue (WAT) and production of inflammatory cytokines, leading to the development of insulin resistance. The xanthones, alpha- and gamma-mangostin (MG), are major bioactive compounds found in mangosteen that are reported to have antiinflammatory and antioxidant properties. Thus, we examined the efficacy of MG to prevent lipopolysaccharide (LPS)-mediated inflammation in human MPhi (differentiated U937 cells) and cross-talk with primary cultures of newly differentiated human adipocytes. We found that alpha- and gamma-MG attenuated LPS-induced expression of inflammatory genes, including tumor necrosis factor-alpha, interleukin-6, and interferon gamma-inducible protein-10 in a dose-dependent manner in MPhi. We also found that alpha- and gamma-MG attenuated LPS-activated mitogen-activated protein kinases (MAPK) and activator protein (AP)-1, but only gamma-MG reduced nuclear factor-kappaB (NF-kappaB). In addition, alpha- and gamma-MG attenuated LPS suppression of PPARgamma gene expression in a dose-dependent manner. Notably, the ability of MPhi-conditioned media to cause inflammation and insulin resistance in primary cultures of human adipocytes was attenuated by pretreating MPhi with gamma-MG. Taken together, these data demonstrate that MG attenuates LPS-mediated inflammation in MPhi and insulin resistance in adipocytes, possibly by preventing the activation of MAPK, NF-kappaB, and AP-1, which are central to inflammatory cytokine production in WAT.

Amelioration of glucose intolerance by the synthetic androstene HE3286: link to inflammatory pathways

Insulin resistance, the major metabolic abnormality underlying type 2 diabetes, is associated with chronic inflammation and heavy macrophage infiltration in white adipose tissue (WAT). The therapeutic properties of the synthetic adrenal steroid Delta(5)-androstene-17alpha-ethynyl-3beta,7beta,17beta-triol (HE3286) were characterized in metabolic disease models. Treatment of diabetic db/db mice with HE3286 suppressed progression to hyperglycemia and markedly improved glucose clearance. Similar effects were also observed in insulin-resistant, diet-induced obese C57BL/6J mice and genetically obese ob/ob mice. This effect appeared to be a consequence of reduced insulin resistance because HE3286 lowered blood insulin levels in db/db and ob/ob mice. Treatment with HE3286 was accompanied by suppressed expression of the prototype macrophage-attracting chemokine monocyte chemoattractant protein-1 in WAT, along with its cognate receptor C-C motif chemokine receptor-2. Exposure of mouse macrophages to HE3286 in vitro caused partial suppression of endotoxin (lipopolysaccharide)-induced nuclear factor kappa-B (NF-kappaB)-sensitive reporter gene expression, NF-kappaB nuclear translocation, and NF-kappaB/p65 serine phosphorylation. Proinflammatory kinases, including IkappaB kinase, c-Jun NH2-terminal kinase, and p38, were also inhibited by HE3286. In ligand competition experiments HE3286 did not bind to classical sex steroid or corticosteroid receptors, including androgen receptor (AR), progesterone receptor, estrogen receptor (ER) alpha or ERbeta, and glucocorticoid receptor (GR). Likewise, in cells expressing nuclear receptor-sensitive reporter genes HE3286 did not substantially stimulate transactivation of AR, ER, GR, or peroxisome proliferator-activated receptor (PPAR) alpha, PPARdelta, and PPARgamma. These findings indicate that HE3286 improves glucose homeostasis in diabetic and insulin-resistant mice and suggest that the observed therapeutic effects result from attenuation of proinflammatory pathways, independent of classic sex steroid receptors, corticosteroid receptors, or PPARs.