The Role of Peroxisome Proliferator-Activated Receptor beta/delta on the Inflammatory Basis of Metabolic Disease

The Healing Capability of Clove Flower Extract (CFE) in Streptozotocin-Induced (STZ-Induced) Diabetic Rat Wounds Infected with Multidrug Resistant Bacteria

Treatment of diabetic foot ulcer (DFU) is of great challenge as it is shown to be infected by multidrug resistant bacteria (MDR bacteria). Sixty four bacterial isolates were isolated from DFU cases; antibiotic susceptibility tests were carried out for all of them. One bacterial isolate (number 11) was shown to resist the action of 8 out of 12 antibiotics used and was identified by both a Vitek-2 system and 16S rRNA fingerprints as belonging to Proteus mirabilis, and was designated Proteus mirabilis LC587231 (P. mirabilis). Clove flower extract (CFE) inhibited distinctively the P. mirabilis bacterium obtained. GC-MS spectroscopy showed that this CFE contained nine bioactive compounds. The effect of CFE on wound healing of Type 1 diabetic albino rats (Rattus norvegicus) was studied. The results indicated that topical application of CFE hydrogel improved wound size, wound index, mRNA expression of the wound healing markers (Coli1, MMP9, Fibronectin, PCNA, and TGFβ), growth factor signaling pathways (PPAR-α, PGC1-α, GLP-1, GLPr-1, EGF-β, EGF-βr, VEGF-β, and FGF-β), inflammatory cytokine expression (IL8, TNFα, NFKβ, IL1β, and MCP1), as well as anti-inflammatory cytokines (IL4 & IL10), pro-apoptotic markers (FAS, FAS-L, BAX, BAX/BCL-2, Caspase-3, P53, P38), as well as an antiapoptotic one (BCL2). Furthermore, it improved the wound oxidative state and reduced the wound microbial load, as the cefepime therapy improved the wound healing parameters. Based on the previous notions, it could be concluded that CFE represents a valid antibiotics alternative for DFU therapy since it improves diabetic wound healing and exerts antibacterial activity either in vitro or in vivo.

Obesity: A Chronic Low-Grade Inflammation and Its Markers

As the prevalence of obesity continues to rise, the world is facing a major public health concern. Obesity is a complex disease associated with an increase in several inflammatory markers, leading to chronic low-grade inflammation. Of multifactorial etiology, it is often used as a measurement of morbidity and mortality. There remains much unknown regarding the association between obesity and inflammation. This review seeks to compile scientific literature on obesity and its associated inflammatory markers in chronic disease and further discusses the role of adipose tissue, macrophages, B-cells, T-cells, fatty acids, amino acids, adipokines, and hormones in obesity. Data were obtained using PubMed and Google Scholar. Obesity, inflammation, immune cells, hormones, fatty acids, and others were search words used to acquire relevant articles. Studies suggest brown adipose tissue is negatively associated with body mass index (BMI) and body fat percentage. Researchers also found the adipose tissue of lean individuals predominantly secretes anti-inflammatory markers, while in obese individuals more pro-inflammatory markers are secreted. Many studies found that adipose tissue in obese individuals showed a shift in immune cells from anti-inflammatory M2 macrophages to pro-inflammatory M1 macrophages, which was also correlated with insulin resistance. Obese individuals generally present with higher levels of hormones such as leptin, visfatin, and resistin. With obesity on the rise globally, it is predicted that severe obesity will become most common amongst low-income adults, black individuals, and women by 2030, making the need for intervention urgent. Further investigation into the association between obesity and inflammation is required to understand the mechanism behind this disease.

PPARβ/δ Agonist Alleviates Diabetic Osteoporosis via Regulating M1/M2 Macrophage Polarization

Diabetic osteoporosis is a common complication in diabetic patients, leading to increased fracture risk and impaired bone healing. As a member of the peroxisome proliferator-activated receptor (PPAR) family, PPARβ/δ agonist is suggested as a therapeutic target for the treatment of metabolic syndrome, and has been reported to positively regulate bone turnover by improving osteogenesis. However, its regulatory role in diabetic osteoporosis has not been reported yet. Here, we explored the therapeutic effects and potential mechanisms of PPARβ/δ agonist to the osteoporotic phenotypes of diabetic mice. Our results indicated that the osteoporotic phenotypes could be significantly ameliorated in diabetic mice by the administration of PPARβ/δ agonists. In vitro experiments suggested that PPARβ/δ agonist treatment could alleviate the abnormal increase of osteoclast activity in diabetic mice by rectifying high glucose-mediated macrophage dysfunction instead of directly inhibiting osteoclast differentiation. Mechanistically, Angptl4 may act as a downstream target of PPARβ/δ to regulate macrophage polarization. In conclusion, our study demonstrates the potential of PPARβ/δ agonist as a therapeutic target for the treatment of osteoporosis and immune homeostasis disorder in diabetic patients.

ω3 fatty acid metabolite, 12-hydroxyeicosapentaenoic acid, alleviates contact hypersensitivity by downregulation of CXCL1 and CXCL2 gene expression in keratinocytes via retinoid X receptor α

ω3 fatty acids show potent bioactivities via conversion into lipid mediators; therefore, metabolism of dietary lipids is a critical determinant in the properties of ω3 fatty acids in the control of allergic inflammatory diseases. However, metabolic progression of ω3 fatty acids in the skin and their roles in the regulation of skin inflammation remains to be clarified. In this study, we found that 12-hydroxyeicosapentaenoic acid (12-HEPE), which is a 12-lipoxygenase metabolite of eicosapentaenoic acid, was the prominent metabolite accumulated in the skin of mice fed ω3 fatty acid-rich linseed oil. Consistently, the gene expression levels of Alox12 and Alox12b, which encode proteins involved in the generation of 12-HEPE, were much higher in the skin than in the other tissues (eg, gut). We also found that the topical application of 12-HEPE inhibited the inflammation associated with contact hypersensitivity by inhibiting neutrophil infiltration into the skin. In human keratinocytes in vitro, 12-HEPE inhibited the expression of two genes encoding neutrophil chemoattractants, CXCL1 and CXCL2, via retinoid X receptor α. Together, the present results demonstrate that the metabolic progression of dietary ω3 fatty acids differs in different organs, and identify 12-HEPE as the dominant ω3 fatty acid metabolite in the skin.

Peroxisome Proliferator-Activated Receptor Beta/Delta Agonist Suppresses Inflammation and Promotes Neovascularization

The effects of peroxisome proliferator-activated receptor (PPAR)β/δ ophthalmic solution were investigated in a rat corneal alkali burn model. After alkali injury, GW501516 (PPARβ/δ agonist) or vehicle ophthalmic solution was topically instilled onto the rat’s cornea twice a day until day 7. Pathological findings were evaluated, and real-time reverse transcription polymerase chain reaction was performed. GW501516 strongly suppressed infiltration of neutrophils and pan-macrophages, and reduced the mRNA expression of interleukin-6, interleukin-1β, tumor necrosis factor alpha, and nuclear factor-kappa B. On the other hand, GW501516 promoted infiltration of M2 macrophages, infiltration of vascular endothelial cells associated with neovascularization in the wounded area, and expression of vascular endothelial growth factor A mRNA. However, 7-day administration of GW501516 did not promote neovascularization in uninjured normal corneas. Thus, the PPARβ/δ ligand suppressed inflammation and promoted neovascularization in the corneal wound healing process. These results will help to elucidate the role of PPARβ/δ in the field of ophthalmology.

Effect of the antioxidant idebenone on maternal diabetes-induced embryo alterations during early organogenesis

RESEARCH QUESTION

Can maternal treatments with idebenone, a structural analogue of coenzyme Q10, prevent alterations on markers of proinflammatory-prooxidant processes, on the expression of genes involved in mitochondrial biogenesis and function, and on the apoptotic rate in embryos from mild diabetic rats?

DESIGN

A mild diabetic rat model was induced by neonatal-streptozotocin administration (90 mg/kg subcutaneously). Female diabetic rats and controls were mated with healthy males. From day 1 of pregnancy, control and diabetic rats were orally treated with idebenone (100 mg/kg daily). On day 10.5 of gestation, the embryos were explanted and prepared for immunohistochemical studies, for the evaluation of gene expression by reverse transcription polymerase chain reaction and for TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end-labelling assay analysis.

RESULTS

Embryos from mild diabetic rats showed increased levels of nitrated proteins, 4-hydroxynonenal and matrix metalloproteinase 9, which were prevented by idebenone administration. We also found a decreased embryonic expression of cytochrome c oxidase and reduced mRNA levels of peroxisome proliferator activated receptor-γ coactivator-1-α and nuclear respiratory factor-1, both of which were prevented by idebenone administration to the diabetic pregnant rats. Embryos from mild diabetic rats also showed an increased apoptotic rate, which was diminished by idebenone treatment.

CONCLUSION

Maternal idebenone treatment ameliorates altered parameters related to the prooxidant-proinflammatory environment found in embryos from mild diabetic rats, suggesting a putative treatment to prevent diabetes-induced embryo alterations.

Peroxisome proliferator-activated receptors as therapeutic targets for heart failure

Heart failure (HF) is a common clinical syndrome that affects more than 23 million individuals worldwide. Despite the marked advances in its management, the mortality rates in HF patients have remained unacceptably high. Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription regulators, involved in the regulation of fatty acid and glucose metabolism. PPAR agonists are currently used for the treatment of type II diabetes mellitus and hyperlipidemia; however, their role as therapeutic agents for HF remains under investigation. Preclinical studies have shown that pharmacological modulation of PPARs can upregulate the expression of fatty acid oxidation genes in cardiomyocytes. Moreover, PPAR agonists were proven able to improve ventricular contractility and reduce cardiac remodelling in animal models through their anti-inflammatory, anti-oxidant, anti-fibrotic, and anti-apoptotic activities. Whether these effects can be replicated in humans is yet to be proven. This article reviews the interactions of PPARs with the pathophysiological mechanisms of HF and how the pharmacological modulation of these receptors can be of benefit for HF patients.

Short-term administration of GW501516 improves inflammatory state in white adipose tissue and liver damage in high-fructose-fed mice through modulation of the renin-angiotensin system

High activation of the angiotensin-converting enzyme (ACE)/(angiotensin-II type 1 receptor) AT1r axis is closely linked to pro-inflammatory effects and liver damage. The aim of this study was to evaluate the effects of the short-term administration of GW501516 on pro-inflammatory markers in white adipose tissue (WAT) and hepatic stellate cells (HSCs), lipogenesis and insulin resistance in the liver upon high-fructose diet (HFru)-induced ACE/AT1r axis activation. Three-month-old male C57Bl/6 mice were fed a standard chow diet or a HFru for 8 weeks. Then, the animals were separated randomly into four groups and treated with GW501516 for 3 weeks. Morphological variables, systolic blood pressure, and plasma determinations were analyzed. In the WAT, the ACE/AT1r axis and pro-inflammatory cytokines were assessed, and in the liver, the ACE/AT1r axis, HSCs, fatty acid oxidation, insulin resistance, and AMPK activation were evaluated. The HFru group displayed a high activation of the ACE/AT1r axis in both the WAT and liver; consequently, we detected inflammation and liver damage. Although GW501516 abolished the increased activation of the ACE/AT1r axis in the WAT, no differences were found in the liver. GW501516 blunted the inflammatory state in the WAT and reduced HSC activation in the liver. In addition, GW501516 alleviates damage in the liver by increasing the expression of the genes that regulate beta-oxidation and decreasing the expression of the genes and proteins that are involved in lipogenesis and gluconeogenesis. We conclude that GW501516 may serve as a therapeutic option for the treatment of a highly activated ACE/AT1r axis in WAT and liver.

Hematopoietic knockdown of PPARδ reduces atherosclerosis in LDLR-/- mice

PPARδ (peroxisome proliferator-activated receptor δ) mediates inflammation in response to lipid accumulation. Systemic administration of a PPARδ agonist can ameliorate atherosclerosis. Paradoxically, genetic deletion of PPARδ in hematopoietic cells led to a reduction of atherosclerosis in murine models, suggesting that downregulation of PPARδ expression in these cells may mitigate atherogenesis. To advance this finding forward to potential clinical translation through hematopoietic stem cell transplantation-based gene therapy, we employed a microRNA (miRNA) approach to knock down PPARδ expression in bone marrow cells followed by transplantation of the cells into LDLR-/- mice. We found that knockdown of PPARδ expression in the hematopoietic system caused a dramatic reduction in aortic atherosclerotic lesions. In macrophages, a key component in atherogenesis, knockdown of PPARδ led to decreased expression of multiple pro-inflammatory factors, including monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-1β and IL-6. Expression of CCR2, a receptor for MCP-1, was also decreased. The downregulation of pro-inflammatory factors is consistent with significant reduction of macrophage presence in the lesions, which may also be attributable to elevation of ABCA1 (ATP-binding cassette, subfamily A, member 1) and depression of adipocyte differentiate-related protein. Furthermore, the abundance of both MCP-1 and matrix metalloproteinase-9 proteins was reduced in plaque areas. Our results demonstrate that miRNA-mediated PPARδ knockdown in hematopoietic cells is able to ameliorate atherosclerosis.

Inactivation of PPARβ/δ adversely affects satellite cells and reduces postnatal myogenesis

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a ubiquitously expressed gene with higher levels observed in skeletal muscle. Recently, our laboratory showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that PPARβ/δ modulates myostatin activity to induce myogenesis in skeletal muscle. In the present study, we show that PPARβ/δ-null mice display reduced body weight, skeletal muscle weight, and myofiber atrophy during postnatal development. In addition, a significant reduction in satellite cell number was observed in PPARβ/δ-null mice, suggesting a role for PPARβ/δ in muscle regeneration. To investigate this, tibialis anterior muscles were injured with notexin, and muscle regeneration was monitored on days 3, 5, 7, and 28 postinjury. Immunohistochemical analysis revealed an increased inflammatory response and reduced myoblast proliferation in regenerating muscle from PPARβ/δ-null mice. Histological analysis confirmed that the regenerated muscle fibers of PPARβ/δ-null mice maintained an atrophy phenotype with reduced numbers of centrally placed nuclei. Even though satellite cell numbers were reduced before injury, satellite cell self-renewal was found to be unaffected in PPARβ/δ-null mice after regeneration. Previously, our laboratory had showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that inactivation of PPARβ/δ increases myostatin signaling and inhibits myogenesis. Our results here indeed confirm that inactivation of myostatin signaling rescues the atrophy phenotype and improves muscle fiber cross-sectional area in both uninjured and regenerated tibialis anterior muscle from PPARβ/δ-null mice. Taken together, these data suggest that absence of PPARβ/δ leads to loss of satellite cells, impaired skeletal muscle regeneration, and postnatal myogenesis. Furthermore, our results also demonstrate that functional antagonism of myostatin has utility in rescuing these effects.

Targeting Peroxisome Proliferator-Activated Receptor-β/δ (PPARβ/δ) for Cancer Chemoprevention

The role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in cancer remains contentious due in large part to divergent publications indicating opposing effects in different rodent and human cell culture models. During the past 10 years, some facts regarding PPARβ/δ in cancer have become clearer, while others remain uncertain. For example, it is now well accepted that (1) expression of PPARβ/δ is relatively lower in most human tumors as compared to the corresponding non-transformed tissue, (2) PPARβ/δ promotes terminal differentiation, and (3) PPARβ/δ inhibits pro-inflammatory signaling in multiple in vivo models. However, whether PPARβ/δ is suitable to target with natural and/or synthetic agonists or antagonists for cancer chemoprevention is hindered because of the uncertainty in the mechanism of action and role in carcinogenesis. Recent findings that shed new insight into the possibility of targeting this nuclear receptor to improve human health will be discussed.

Myelin alters the inflammatory phenotype of macrophages by activating PPARs

Background

Foamy macrophages, containing myelin degradation products, are abundantly found in active multiple sclerosis (MS) lesions. Recent studies have described an altered phenotype of macrophages after myelin internalization. However, mechanisms by which myelin affects the phenotype of macrophages and how this phenotype influences lesion progression remain unclear.

Results

We demonstrate that myelin as well as phosphatidylserine (PS), a phospholipid found in myelin, reduce nitric oxide production by macrophages through activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ). Furthermore, uptake of PS by macrophages, after intravenous injection of PS-containing liposomes (PSLs), suppresses the production of inflammatory mediators and ameliorates experimental autoimmune encephalomyelitis (EAE), an animal model of MS. The protective effect of PSLs in EAE animals is associated with a reduced immune cell infiltration into the central nervous system and decreased splenic cognate antigen specific proliferation. Interestingly, PPARβ/δ is activated in foamy macrophages in active MS lesions, indicating that myelin also activates PPARβ/δ in macrophages in the human brain.

Conclusion

Our data show that myelin modulates the phenotype of macrophages by PPAR activation, which may subsequently dampen MS lesion progression. Moreover, our results suggest that myelin-derived PS mediates PPARβ/δ activation in macrophages after myelin uptake. The immunoregulatory impact of naturally-occurring myelin lipids may hold promise for future MS therapeutics.

A role for peroxisome proliferator-activated receptors in the immunopathology of schistosomiasis?

Peroxisome proliferator-activated receptors (PPARs) have been demonstrated to have a role in immune regulation. In general, they are anti-inflammatory and promote Th2 type responses, and they are associated with the alternative activation of macrophages. Interestingly, helminth infections, such as the schistosome blood flukes that cause schistosomiasis, are characterised by a Th2 response and the accumulation of alternative activated macrophages. This would suggest that at some level, PPARs could have a role in the modulation of the immune response in schistosomiasis. This paper discusses possible areas where PPARs could have a role in this disease.