PPAR Medicines and Human Disease: The ABCs of It All

Sequentially degradable hydrogel-microsphere loaded with doxorubicin and pioglitazone synergistically inhibits cancer stemness of osteosarcoma

Drug resistance represents one of the greatest challenges in cancer treatment. Cancer stem cells (CSCs) are thought to be the major cause of failure in cancer therapy due to their considerable resistance to most chemotherapeutic agents, resulting in tumor recurrence and eventually metastasis. Here, we report a treatment strategy for osteosarcoma using hydrogel-microspheres (Gel-Mps) complex mainly composed of collagenase (Col) and PLGA microspheres (Mps) carrying Pioglitazone (Pio) and Doxorubicin (Dox). Col was encapsulated in the thermosensitive gel to preferentially degrade tumor extracellular matrix (ECM), ensuring subsequent drug penetration, while Mps with Pio and Dox were co-delivered to synergistically inhibit tumor growth and metastasis. Our results showed that the Gel-Mps dyad functions as a highly biodegradable, extremely efficient, and low-toxic reservoir for sustained drug release, displaying potent inhibition of tumor proliferation and subsequent lung metastasis. Selective PPARγ agonist Pio reversed drug resistance to Dox by significantly down-regulating the expression of stemness markers and P-glycoprotein (P-gp) in osteosarcoma cells. The Gel@Col-Mps@Dox/Pio exhibited advanced therapeutic efficacy in vivo, demonstrating its great potential to serve a novel osteosarcoma therapy, which not only inhibits the growth of, but also attenuates the stemness of osteosarcoma. The dual effects reinforce the sensitivity and efficacy of chemotherapy.

Evaluating the effect of acute diesel exhaust particle exposure on P-glycoprotein efflux transporter in the blood-brain barrier co-cultured with microglia

A growing public health concern, chronic Diesel Exhaust Particle (DEP) exposure is a heavy risk factor for the development of neurodegenerative diseases like Alzheimer's (AD). Considered the brain's first line of defense, the Blood-Brain Barrier (BBB) and perivascular microglia work in tandem to protect the brain from circulating neurotoxic molecules like DEP. Importantly, there is a strong association between AD and BBB dysfunction, particularly in the Aβ transporter and multidrug resistant pump, P-glycoprotein (P-gp). However, the response of this efflux transporter is not well understood in the context of environmental exposures, such as to DEP. Moreover, microglia are seldom included in in vitro BBB models, despite their significance in neurovascular health and disease. Therefore, the goal of this study was to evaluate the effect of acute (24 hr.) DEP exposure (2000 μg/ml) on P-gp expression and function, paracellular permeability, and inflammation profiles of the human in vitro BBB model (hCMEC/D3) with and without microglia (hMC3). Our results suggested that DEP exposure can decrease both the expression and function of P-gp in the BBB, and corroborated that DEP exposure impairs BBB integrity (i.e. increased permeability), a response that was significantly worsened by the influence of microglia in co-culture. Interestingly, DEP exposure seemed to produce atypical inflammation profiles and an unexpected general downregulation in inflammatory markers in both the monoculture and co-culture, which differentially expressed IL-1β and GM-CSF. Interestingly, the microglia in co-culture did not appear to influence the response of the BBB, save in the permeability assay, where it worsened the BBB's response. Overall, our study is important because it is the first (to our knowledge) to investigate the effect of acute DEP exposure on P-gp in the in vitro human BBB, while also investigating the influence of microglia on the BBB's responses to this environmental chemical.

Millet Bran Protein Hydrolysate Displays the Anti-non-alcoholic Fatty Liver Disease Effect via Activating Peroxisome Proliferator-Activated Receptor γ to Restrain Fatty Acid Uptake

Non-alcoholic fatty liver disease (NAFLD) is a serious health problem worldwide. Impeding fatty acid uptake may be an attractive therapeutic strategy for NAFLD. In the current study, we found that millet bran protein hydrolysate (MBPH) prepared by in vitro gastrointestinal bionic digestion exhibits the potential of anti-NAFLD in vitro and in vivo, characterized by the alleviation of hepatic steatosis and the reduction of lipid accumulation. Further, MBPH significantly decreased the expression levels of fatty acid uptake related genes (FABP1, FABP2, FABP4, CD36, and CPT-1α) of liver tissue in a NAFLD mice model through activating peroxisome proliferator-activated receptor γ (PPARγ) and efficiently restrained the fatty acid uptake of liver tissue, thus exerting anti-NAFLD activity. As expected, the anti-NAFLD effect induced by MBPH, characterized by the alleviation of hepatic vacuolar degeneration, hepatic steatosis, and fibrosis, was effectively abrogated with PPARγ inhibitor (GW9662) treatment. These results indicate that the retardant of fatty acid uptake induced by PPARγ activation may be the critical factor for the anti-NAFLD effect of MBPH. Collectively, MBPH has the potential as a next-generation dietary supplementation for the prevention and treatment of NAFLD.

Cigarette smoke extract combined with LPS reduces ABCA3 expression in chronic pulmonary inflammation may be related to PPARγ/ P38 MAPK signaling pathway

ABCA3 (ATP-binding cassette class A3) is a transmembrane transporter that plays a positive role in chronic pulmonary inflammation by regulating lipid metabolism. However, it is not completely clear whether ABCA3 and its signaling factors are involved in chronic pulmonary inflammation induced by the combination of CSE (cigarette smoke extract) and LPS (lipopolysaccharide). In this study, we used the method of combining CSE and LPS which was widely used to study lung inflammation-related diseases and has been proven effective in our group's studies to create in vivo and in vitro pulmonary inflammation models. The result showed that, after CSE in combination with LPS treatment, ABCA3 expression was downregulated in rat lung in vivo and in a human alveolar cell line in vitro. ABCA3 expression was upregulated, and related inflammatory factors were downregulated in the state of overexpression of PPARγ or inhibition of the p38 MAPK pathway, while PPARγ deletion or MAPK14 overexpression showed the opposite results. The level of PPARγ remained unchanged, and the expression of ABCA3 was upregulated in the state of the p38 MAPK pathway was inhibited under overexpression of PPARγ. These results indicate that CSE combined with LPS can result in downregulation of ABCA3 under conditions of inflammation, and that the p38 MAPK signaling pathway mediated by PPARγ can regulate the expression changes of ABCA3, thus providing new targets for treating chronic pulmonary inflammation.

Glomerular Biomechanical Stress and Lipid Mediators during Cellular Changes Leading to Chronic Kidney Disease

Hyperfiltration is an important underlying cause of glomerular dysfunction associated with several systemic and intrinsic glomerular conditions leading to chronic kidney disease (CKD). These include obesity, diabetes, hypertension, focal segmental glomerulosclerosis (FSGS), congenital abnormalities and reduced renal mass (low nephron number). Hyperfiltration-associated biomechanical forces directly impact the cell membrane, generating tensile and fluid flow shear stresses in multiple segments of the nephron. Ongoing research suggests these biomechanical forces as the initial mediators of hyperfiltration-induced deterioration of podocyte structure and function leading to their detachment and irreplaceable loss from the glomerular filtration barrier. Membrane lipid-derived polyunsaturated fatty acids (PUFA) and their metabolites are potent transducers of biomechanical stress from the cell surface to intracellular compartments. Omega-6 and ω-3 long-chain PUFA from membrane phospholipids generate many versatile and autacoid oxylipins that modulate pro-inflammatory as well as anti-inflammatory autocrine and paracrine signaling. We advance the idea that lipid signaling molecules, related enzymes, metabolites and receptors are not just mediators of cellular stress but also potential targets for developing novel interventions. With the growing emphasis on lifestyle changes for wellness, dietary fatty acids are potential adjunct-therapeutics to minimize/treat hyperfiltration-induced progressive glomerular damage and CKD.

Brain endothelial LRP1 maintains blood-brain barrier integrity

The entry of blood-borne molecules into the brain is restricted by the blood–brain barrier (BBB). Various physical, transport and immune properties tightly regulate molecule movement between the blood and the brain to maintain brain homeostasis. A recent study utilizing a pan-endothelial, constitutive Tie2-Cre showed that paracellular passage of blood proteins into the brain is governed by endocytic and cell signaling protein low-density lipoprotein receptor–related protein 1 (LRP1). Taking advantage of conditional Slco1c1-CreER^T2 specific to CNS endothelial cells and choroid plexus epithelial cells we now supplement previous results and show that brain endothelial Lrp1 ablation results in protease-mediated tight junction degradation, P-glycoprotein (P-gp) reduction and a loss of BBB integrity.

Phenolic Compounds of Propolis Alleviate Lipid Metabolism Disorder

Lipid metabolism disorder is one of the significant risk factors for a multitude of human diseases and has become a serious threat to human health. The present study aimed to evaluate the effects of phenolics from poplar-type propolis on regulating lipid metabolism by using cell models of steatosis induced by palmitic acid (PA). Our study shows that phenolic esters have higher lipid-lowering activities than phenolic acids, especially for three caffeic acid esters, including caffeic acid phenethyl ester (CAPE), caffeic acid cinnamyl ester (CACE), and caffeic acid benzyl ester (CABE). Most notably, CACE presents prominent properties to prevent intracellular lipid accumulation and to amend extracellular adipokine secretion abnormalities. In addition, our results firstly reveal that CACE can alleviate lipid metabolism disorder through mediating protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6) signaling pathway-associated protein expression, suppressing endoplasmic reticulum (ER) stress, and activating peroxisome proliferator-activated receptors (PPARs) by distinct upregulation of PPARα and downregulation of PPARγ.

Pioglitazone modulates doxorubicin resistance in a in vivo model of drug resistant osteosarcoma xenograft

Osteosarcoma has been reported with treatment failure in up to 40% of cases. Our laboratory had identified genes involved in the PPARγ pathway to be associated with doxorubicin (DOX) resistance. We hence used PPARγ agonist pioglitazone (PIO) to modulate DOX resistance. DOX-resistant cell line (143B-DOX) was developed by gradient exposure to DOX. The cytotoxicity to PIO and in combination with DOX was assayed in vitro, followed by HPLC to estimate the metabolites of PIO in the presence of microsomes (HLMs). Gene expression studies revealed the mechanism behind the cytotoxicity of PIO. Further, the effects were evaluated in mice bearing 143B-DOX tumors treated either with PIO (20 mg/kg/p.o or 40 mg/kg/p.o Q1D) alone or in combination with DOX (0.5 mg/kg/i.p Q2W). 143B-DOX was 50-fold resistant over parental cells. While PIO did not show any activity on its own, the addition of HLMs to the cells in culture showed over 80% cell kill within 24 h, possibly due to the metabolites of PIO as determined by HPLC. In combination with DOX, PIO had shown synergistic activity. Additionally, cytotoxicity assay in the presence of HLMs revealed that PIO on its own showed promising activity compared to its metabolites-hydroxy pioglitazone and keto pioglitazone. In vivo studies demonstrated that treatment with 40 mg/kg/p.o PIO alone showed significant activity, followed by a combination with DOX. Gene expression studies revealed that PIO could modulate drug resistance by downregulating MDR1 and IL8. Our study suggests that PIO can modulate DOX resistance in osteosarcoma cells.

Pioglitazone, an agonist of PPARγ, reverses doxorubicin-resistance in an osteosarcoma patient-derived orthotopic xenograft model by downregulating P-glycoprotein expression

Multidrug resistance (MDR) which results in chemoresistance is a major problem in osteosarcoma. P-glycoprotein (P-gp) plays a critical role in MDR by pumping out chemotherapy agents. Peroxisome proliferator activated receptor gamma (PPARγ) is a nuclear receptor involved in cellular differentiation and proliferation. Recently, a correlation between the expression and activity of PPARγ and the expression of P-gp-associated with MDR, has been reported in several human cancers. The present study determined if pioglitazone (PIO), a PPARγ agonist, could modulate P-gp and overcome doxorubicin (DOX)-resistance in a patient-derived orthotopic xenograft (PDOX) model of osteosarcoma. P-gp mRNA expression was quantified in 143B human osteosarcoma cells treated with DOX with/without PIO. The osteosarcoma PDOX models were randomized into four treatment groups of six mice: Control; PIO alone; DOX alone; DOX and PIO combination. Tumor size and body weight were measured during the 14 days of treatment. DOX significantly induced P-gp mRNA in a dose-dependent manner in 143B cells. PIO inhibited the increase of P-gp mRNA induced by DOX treatment when co-administrated with DOX. Tumor growth was inhibited the most by the DOX-PIO combination. Tumors treated with the DOX-PIO combination also had the most tumor necrosis. This study suggests that the DOX-PIO combination could be used in the clinic for osteosarcoma patients who develop DOX-resistance.

The roles of PPARs in human diseases

Peroxisome proliferator-activated receptors (PPARs), as members of nuclear hormone receptor superfamily, can be activated by binding natural or synthetic ligands. The use of related ligands has revealed many potential roles for PPARs in the pathogenesis of some human metabolic disorders and inflammatory-related disease. Based on the previous studies, this review primarily concluded the current progress of knowledge regarding the specific biological activity of PPARs in cancers, atherosclerosis, and type 2 diabetes mellitus, providing a foundation for the potential therapeutic use of PPAR ligands in human diseases.

Peroxisome proliferator-activated receptors in cardiac energy metabolism and cardiovascular disease

Cardiomyocytes mainly depend on energy produced from the oxidation of fatty acids and mitochondrial oxidative phosphorylation. Shortage of energy or excessive fat accumulation can lead to cardiac disorders. High saturated fat intake and a sedentary life style have a major influence in the development of cardiovascular disease (CVD). Peroxisome proliferator-activated receptors (PPARs), one of the nuclear receptor super family members, play critical role in the metabolism of lipids by regulating their oxidation and storage. Furthermore, they are involved in glucose homeostasis as well. PPARs, mainly alpha (α) and beta/delta (β/δ), have a significant effect on the lipid metabolism and anti-inflammation in endothelial cells (ECs), vascular smooth muscle cells, and also in cardiomyocytes. Pro-inflammatory cytokines, mainly tumour necrosis factor-α, released at the site of inflammation in the sub-ECs of coronary arteries can inactivate the PPARs which can eventually lead to decreased energy production in the myocardium. Various synthetic ligands of PPAR-α and β/δ have many favourable effects in modulating the vascular diseases and heart failure. Despite the adverse effects from therapy using PPAR- gamma ligands, several laboratories are now focused on synthesizing partial activators which may combine their beneficial effects with lowering of undesirable side effects. This review discusses the role of isoforms of PPAR in the cardiomyocytes energy balance and CVD. The knowledge will help in the synthesis of ligands for their partial activation in order to render energy balance and protection from CVD.

Conformational Dynamics and Protein-Substrate Interaction of ABC Transporter BtuCD at the Occluded State Revealed by Molecular Dynamics Simulations

ATP-binding cassette (ABC) transporters are ubiquitous in all three kingdoms of life and are implicated in many clinically relevant physiological processes. They couple the energy released by ATP hydrolysis to facilitate substrate translocation across cell membranes. The crystal structures of type II ABC importers have revealed their unique transmembrane domain architecture consisting of 10 transmembrane helices and their structurally conserved nucleotide-binding domains among all ABC transporters. However, molecular details of the interactions between the importers and their substrate remain largely elusive. Taking vitamin B₁₂ importer BtuCD as an exemplar of type II importers, we investigated the dynamics of its occluded state and the detailed protein-substrate interactions using molecular dynamics simulation. Our trajectories show that the importer accommodates the substrate through a nonspecific binding mode as the substrate undergoes evident vertical and tilt motions inside the translocation cavity. Extensive hydrogen bond and hydrophobic interactions were observed between the substrate and the importer; however, most of these interactions are weak, with <38% occurrence. The presence of substrate leads to enlargement of the translocation cavity, especially at its cytoplasmic end, which may activate cytoplasmic regions and probably facilitate the transportation. The perturbations caused by periplasmic binding protein and nucleotides were also investigated. The study provides deeper insight into the translocation mechanism of BtuCD.

Characterization of Visceral and Subcutaneous Adipose Tissue Transcriptome and Biological Pathways in Pregnant and Non-Pregnant Women: Evidence for Pregnancy-Related Regional-Specific Differences in Adipose Tissue

Objective

The purpose of this study was to compare the transcriptome of visceral and subcutaneous adipose tissues between pregnant and non-pregnant women.

Study Design

The transcriptome of paired visceral and abdominal subcutaneous adipose tissues from pregnant women at term and matched non-pregnant women (n = 11) was profiled with the Affymetrix Human Exon 1.0 ST array. Differential expression of selected genes was validated with the use of quantitative reverse transcription–polymerase chain reaction.

Results

Six hundred forty-four transcripts from 633 known genes were differentially expressed (false discovery rate (FDR) <0.1; fold-change >1.5), while 42 exons from 36 genes showed differential usage (difference in FIRMA scores >2 and FDR<0.1) between the visceral and subcutaneous fat of pregnant women. Fifty-six known genes were differentially expressed between pregnant and non-pregnant subcutaneous fat and three genes in the visceral fat. Enriched biological processes in the subcutaneous adipose tissue of pregnant women were mostly related to inflammation.

Conclusion

The transcriptome of visceral and subcutaneous fat depots reveals pregnancy-related gene expression and splicing differences in both visceral and subcutaneous adipose tissue. Furthermore, for the first time, alternative splicing in adipose tissue has been associated with regional differences and human parturition.

PPAR gamma gene--a review

Peroxisome proliferator-activated receptor gamma (PPARγ) has been the focus of intense research because ligands for this receptor have emerged as potent insulin sensitizers used in the treatment of type 2 diabetes. There have been described three PPAR isotypes α, δ and γ which have an integrated role in controlling the expression of genes playing key roles in the storage and mobilization of lipids, in glucose metabolism, in morphogenesis and inflammatory response. Recent advances include the discovery of novel genes that are regulated by PPARγ, which helps to explain how activation of this adipocyte predominant transcription factor regulates glucose and lipid homeostasis. Increased levels of circulating free fatty acids and lipid accumulation in non-adipose tissue have been implicated in the development of insulin resistance. This situation is improved by PPARγ ligands, which promotes fatty acid storage in fat deposits and regulates the expression of adipocyte-secreted hormones that impacts on glucose homeostasis. So the net result of the pleiotropic effects of PPARγ ligands is improvement of insulin sensitivity. This review highlights the roles that PPAR gamma play in the regulation of gene expression of multiple diseases including obesity, diabetes and cancer and highlights the gene isolation transformation role. Further studies are needed for the transformation of PPAR gamma gene in plants and evaluate in animals for the treatment of type 2 diabetes.

Effects of maternal dietary olive oil on pathways involved in diabetic embryopathy

Maternal diabetes induces a pro-oxidant/pro-inflammatory intrauterine environment related to the induction of congenital anomalies. Peroxisome proliferator activated receptors (PPARs) are transcription factors that regulate antioxidant and anti-inflammatory pathways. We investigated whether maternal diets supplemented with olive oil, enriched in oleic acid, a PPAR agonist, can regulate the expression of PPAR system genes, levels of lipoperoxidation and activity of matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) in embryos and decidua from diabetic rats. The embryos and decidua from diabetic rats showed reduced expression of PPARs and increased concentration of lipoperoxidation, MMPs and TIMPs, whereas the maternal treatments enriched in olive oil increased PPARδ in embryos and PPARγ and PPARγ-coactivator-1α expression in decidua, and increased TIMPs concentrations and decreased lipoperoxidation and MMPs activity in both tissues. Thus, maternal diets enriched in olive oil can regulate embryonic and decidual PPAR system genes expression and reduce the pro-oxidant/pro-inflammatory environment during rat early organogenesis.

An in-silico model of lipoprotein metabolism and kinetics for the evaluation of targets and biomarkers in the reverse cholesterol transport pathway

High-density lipoprotein (HDL) is believed to play an important role in lowering cardiovascular disease (CVD) risk by mediating the process of reverse cholesterol transport (RCT). Via RCT, excess cholesterol from peripheral tissues is carried back to the liver and hence should lead to the reduction of atherosclerotic plaques. The recent failures of HDL-cholesterol (HDL-C) raising therapies have initiated a re-examination of the link between CVD risk and the rate of RCT, and have brought into question whether all target modulations that raise HDL-C would be atheroprotective. To help address these issues, a novel in-silico model has been built to incorporate modern concepts of HDL biology, including: the geometric structure of HDL linking the core radius with the number of ApoA-I molecules on it, and the regeneration of lipid-poor ApoA-I from spherical HDL due to remodeling processes. The ODE model has been calibrated using data from the literature and validated by simulating additional experiments not used in the calibration. Using a virtual population, we show that the model provides possible explanations for a number of well-known relationships in cholesterol metabolism, including the epidemiological relationship between HDL-C and CVD risk and the correlations between some HDL-related lipoprotein markers. In particular, the model has been used to explore two HDL-C raising target modulations, Cholesteryl Ester Transfer Protein (CETP) inhibition and ATP-binding cassette transporter member 1 (ABCA1) up-regulation. It predicts that while CETP inhibition would not result in an increased RCT rate, ABCA1 up-regulation should increase both HDL-C and RCT rate. Furthermore, the model predicts the two target modulations result in distinct changes in the lipoprotein measures. Finally, the model also allows for an evaluation of two candidate biomarkers for in-vivo whole-body ABCA1 activity: the absolute concentration and the % lipid-poor ApoA-I. These findings illustrate the potential utility of the model in drug development.

Effects of germinated brown rice and its bioactive compounds on the expression of the peroxisome proliferator-activated receptor gamma gene

Dysregulated metabolism is implicated in obesity and other disease conditions like type 2 diabetes mellitus and cardiovascular diseases, which are linked to abnormalities of peroxisome proliferator-activated receptor gamma (PPARγ). PPARγ has been the focus of much research aimed at managing these diseases. Also, germinated brown rice (GBR) is known to possess antidiabetic, antiobesity and hypocholesterolemic effects. We hypothesized that GBR bioactive compounds may mediate some of the improvements in metabolic indices through PPARγ modulation. Cultured HEP-G2 cells were treated with 50 ppm and 100 ppm of extracts from GBR (GABA, ASG and oryzanol) after determination of cell viabilities using MTT assays. Results showed that all extracts upregulated the expression of the PPARγ. However, combination of all three extracts showed downregulation of the gene, suggesting that, in combination, the effects of these bioactives differ from their individual effects likely mediated through competitive inhibition of the gene. Upregulation of the gene may have therapeutic potential in diabetes mellitus and cardiovascular diseases, while its downregulation likely contributes to GBR's antiobesity effects. These potentials are worth studying further.