Activation of PPARγ by a Natural Flavonoid Modulator, Apigenin Ameliorates Obesity-Related Inflammation Via Regulation of Macrophage Polarization

Molecular Mechanisms Modulating the Phenotype of Macrophages and Microglia

Macrophages and microglia play crucial roles during central nervous system development, homeostasis and acute events such as infection or injury. The diverse functions of tissue macrophages and microglia are mirrored by equally diverse phenotypes. A model of inflammatory/M1 versus a resolution phase/M2 macrophages has been widely used. However, the complexity of macrophage function can only be achieved by the existence of varied, plastic and tridimensional macrophage phenotypes. Understanding how tissue macrophages integrate environmental signals via molecular programs to define pathogen/injury inflammatory responses provides an opportunity to better understand the multilayered nature of macrophages, as well as target and modulate cellular programs to control excessive inflammation. This is particularly important in MS and other neuroinflammatory diseases, where chronic inflammatory macrophage and microglial responses may contribute to pathology. Here, we perform a comprehensive review of our current understanding of how molecular pathways modulate tissue macrophage phenotype, covering both classic pathways and the emerging role of microRNAs, receptor-tyrosine kinases and metabolism in macrophage phenotype. In addition, we discuss pathway parallels in microglia, novel markers helpful in the identification of peripheral macrophages versus microglia and markers linked to their phenotype.

Flavonoids as Putative Inducers of the Transcription Factors Nrf2, FoxO, and PPARγ

Dietary flavonoids have been shown to extend the lifespan of some model organisms and may delay the onset of chronic ageing-related diseases. Mechanistically, the effects could be explained by the compounds scavenging free radicals or modulating signalling pathways. Transcription factors Nrf2, FoxO, and PPARγ possibly affect ageing by regulating stress response, adipogenesis, and insulin sensitivity. Using Hek-293 cells transfected with luciferase reporter constructs, we tested the potency of flavonoids from different subclasses (flavonols, flavones, flavanols, and isoflavones) to activate these transcription factors. Under cell-free conditions (ABTS and FRAP assays), we tested their free radical scavenging activities and used α-tocopherol and ascorbic acid as positive controls. Most of the tested flavonoids, but not the antioxidant vitamins, stimulated Nrf2-, FoxO-, and PPARγ-dependent promoter activities. Flavonoids activating Nrf2 also tended to induce a FoxO and PPARγ response. Interestingly, activation patterns of cellular stress response by flavonoids were not mirrored by their activities in ABTS and FRAP assays, which depended mostly on hydroxylation in the flavonoid B ring and, in some cases, extended that of the vitamins. In conclusion, the free radical scavenging properties of flavonoids do not predict whether these molecules can stimulate a cellular response linked to activation of longevity-associated transcription factors.

Apigenin, a modulator of PPARγ, attenuates HFD-induced NAFLD by regulating hepatocyte lipid metabolism and oxidative stress via Nrf2 activation

Lipid metabolic disorders and oxidative stress in the liver are key steps in the progression of nonalcoholic fatty liver disease (NAFLD), which is a major risk factor for the development of metabolic syndrome. To date, no pharmacological treatment for this condition has been approved. Our previous study has found that the food-derived compound apigenin (Api) significantly attenuates obesity-induced metabolic syndrome by acting as a peroxisome proliferator-activated receptor gamma modulator (PPARM). Herein, a high fat diet (HFD) induced NAFLD model was used to dig out whether Api had the effect on NAFLD. The results showed that Api had obvious effect in restraining NAFLD progression, including attenuating HFD induced lipid accumulation and oxidative stress in vivo. As a PPARM, although Api did significantly inhibit the expression of PPARγ target genes encoding the protein associated with lipid metabolism, it had no obvious activating effect on PPARγ. Interestingly, we found that Api promoted Nrf2 into the nucleus, thereby markedly activating Nrf2 to inhibit the lipid metabolism related genes and increase the oxidative stress related genes. Further Nrf2 knockdown/knockout and overexpression experiments showed that Api regulating PPARγ target genes was dependent on Nrf2 activation and the activation of Nrf2 counteracted the activation effect of PPARγ by Api. Importantly, we also found that Api might bind with Nrf2 via auto dock and ITC assay. Therefore, our results indicate that Api ameliorates NAFLD by a novel regulating mode of Nrf2 and PPARγ in inhibiting lipid metabolism and oxidative stress abnormity.

Effect of modulation of PPAR-γ activity on Kupffer cells M1/M2 polarization in the development of non-alcoholic fatty liver disease

Abnormal lipid-mediated hepatic inflammatory-immune dysfunction and chronic low grade inflammation play an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Macrophage polarization is an important mechanism for the regulation of inflammatory response. Since PPAR-γ has emerged as a master regulator of macrophage polarization, we aimed to investigate the lipid-induced macrophage/Kupffer cell polarization in vivo and in vitro, and explore the association between PPAR-γ activity and macrophages M1/M2 polarization shifting. Here we showed that long-term high-fat diet increased Kupffer cells content with M1-predominant phenotype and increasing production of pro-inflammatory cytokines. Saturated fatty acids polarized Kupffer cells/macrophages to an M1-predominant phenotype while n-3 PUFA polarized Kupffer cells/macrophages to an M2 phenotype, which was associated with activation of NF-κB signal pathway and PPAR-γ respectively. Furthermore, up-regulation of PPAR-γ shifted lipid-induced macrophages polarization from M1-predominant phenotype to M2 phenotype. Macrophages polarization switch was associated with the interaction between PPAR-γ and NF-κBp65 signal pathway. Rosiglitazone restored high-fat diet-induced imblance of Kupffer cells M1/M2 polarization and alleviated hepatic steatosis as well as local pro-inflammatory response. These findings suggest that manipulation of PPAR-γ activity has the potential to balance lipid-induced M1/M2 macrophage/Kupffer cell polarization, and leading to prevent the development of NAFLD.

Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients

BACKGROUND AND OBJECTIVES

Multiple chemical sensitivity (MCS) is a chronic, multisystem syndrome of unknown etiology. The aim of the present study was to describe the nutritional status and quality of life of patients suffering from MCS, as well as to identify potential polymorphisms associated with this illness.

PATIENTS AND METHODS

A cross-sectional, descriptive study was performed on patients with a diagnosis of MCS. Data on anthropometric and body composition variables, hand muscle strength and quality of life were collected. The selection of single nucleotide polymorphisms (SNPs) was based on genes previously associated with MCS and genes involved in inflammatory and oxidative stress pathways.

RESULTS

A total of 52 patients (93.2% female), with a mean age of 50.9 (10.3) years were included in the study. Among them, based on their BMI, 48% had an inadequate nutritional status (17% were underweight and 32% were overweight or obese). Thirty percent of patients had a low muscle mass for their age, 84% had muscle strength below the tenth percentile, and 51.8% had a high fat mass percentage. Regarding quality of life, all median scores were lower than those of other illnesses assessed for every subscale assessed. Statistically significant differences between patient cases and controls were found with respect to rs1801133 (MTHFR), rs174546 (FADS1) and rs1801282 (PPARγ) polymorphisms.

CONCLUSION

A high percentage of patients had a poor nutritional status, low muscle strength and decreased muscle mass. These facts exacerbate the already-lower quality of life of these patients. Specific genetic polymorphisms associated with the syndrome or its pathogenesis were not identified.