Effect of peroxisome proliferator-activated receptor-gamma ligand on inflammation of human gallbladder epithelial cells

Targeting of gallbladder megalin receptors with DHA-conjugated limonene albumin nanoparticles

Gallbladder stones are a major pathogenic factor leading to cholecystitis, and it is increasingly important to explore innovative drug delivery methods for gallstones. In the present study, docosahexaenoic acid-coupled limonene bovine serum albumin nanoparticles (LIM-DHA-BSA-NPs) were constructed. The LIM-DHA-BSA-NPs are spherical structures, and the distribution was relatively uniform, and, more importantly, it has low cytotoxicity and good safety. The LIM-DHA-BSA-NPs solution shows higher uptake rates by RAW264.7 cells when compared with free limonene (LIM). The fluorescence intensity of FITC-modified BSA NPs was significantly higher than that of free FITC, which further indicated that the uptake of DHA-conjugated BSA NPs by RAW264.7 cells was stronger than that of the free drugs. Moreover, the in vivo distribution experiment showed that the enrichment of DiD-loaded BSA NPs in the gallbladder was significantly enhanced when compared with that of free DiD. The semi-quantitative fluorescence intensity results showed that the uptake of DiD-DHA-BSA-NPs was 4.5 times higher when compared with the free DiD. It is preliminarily shown that the DHA-conjugated BSA NPs that were constructed, have an ability to target the gallbladder. Furthermore, the Pearson colocalization coefficient R_coloc from in vivo colocalization results indicates that the DHA-BSA-NPs had a good colocalization effect on the gallbladder epithelial cells (GBECs). In addition, the LIM-DHA-BSA-NPs solution not only significantly reduced the concentration of nitric oxide (NO) secreted by inflammatory model cells and the number of peripheral blood leukocytes in guinea pigs with cholecystitis, but also significantly decreased the activities of the aspartate transaminase (AST), alkaline phosphatase (ALP), alanine aminotransferase (ALT), glutamyl endopeptidase (GGT), total bile acid (TBA), and total bilirubin (TBIL) enzymes. Collectively, the LIM-DHA-BSA-NPs could be used as an effective anti-inflammatory agent at the cellular and animal levels. This experiment, for the first time, showed that DHA-conjugated BSA NPs could be absorbed into GBECs by megalin receptor-mediated endocytosis and then they exert an anti-cholecystitis effect because of the LIM. The active uptake of DHA-conjugated BSA NPs by the megalin receptors of the GBECs is expected to become an effective therapeutic strategy for cholecystolithiasis.

Megalin/LRP2 expression is induced by peroxisome proliferator-activated receptor -alpha and -gamma: implications for PPARs' roles in renal function

Background

Megalin is a large endocytic receptor with relevant functions during development and adult life. It is expressed at the apical surface of several epithelial cell types, including proximal tubule cells (PTCs) in the kidney, where it internalizes apolipoproteins, vitamins and hormones with their corresponding carrier proteins and signaling molecules. Despite the important physiological roles of megalin little is known about the regulation of its expression. By analyzing the human megalin promoter, we found three response elements for the peroxisomal proliferator-activated receptor (PPAR). The objective of this study was to test whether megalin expression is regulated by the PPARs.

Methodology/Principal Findings

Treatment of epithelial cell lines with PPARα or PPARγ ligands increased megalin mRNA and protein expression. The stimulation of megalin mRNA expression was blocked by the addition of specific PPARα or PPARγ antagonists. Furthermore, PPAR bound to three PPAR response elements located in the megalin promoter, as shown by EMSA, and PPARα and its agonist activated a luciferase construct containing a portion of the megalin promoter and the first response element. Accordingly, the activation of PPARα and PPARγ enhanced megalin expression in mouse kidney. As previously observed, high concentrations of bovine serum albumin (BSA) decreased megalin in PTCs in vitro; however, PTCs pretreated with PPARα and PPARγ agonists avoided this BSA-mediated reduction of megalin expression. Finally, we found that megalin expression was significantly inhibited in the PTCs of rats that were injected with BSA to induce tubulointerstitial damage and proteinuria. Treatment of these rats with PPARγ agonists counteracted the reduction in megalin expression and the proteinuria induced by BSA.

Conclusions

PPARα/γ and their agonists positively control megalin expression. This regulation could have an important impact on several megalin-mediated physiological processes and on pathophysiologies such as chronic kidney disease associated with diabetes and hypertension, in which megalin expression is impaired.

The effect of PPARalpha and PPARgamma ligands on inflammation and ABCA1 expression in cultured gallbladder epithelial cells

The preservation of gallbladder function by control of inflammation and elimination of cholesterol accumulation in gallbladder epithelial cells (GBEC) could contribute to the prevention of gallstone formation and cholecystitis. Peroxisome proliferator-activated receptors (PPARs) modulate inflammation and lipid metabolism in various cells and GBEC efflux of excessive amounts of absorbed cholesterol through the ATP-binding cassette transporter A1 (ABCA1)-mediated pathway. The aim of this study was to determine whether ligands of PPARalpha and PPARgamma modulate inflammation and have an effect on ABCA1 expression in GBEC. Canine GBEC were cultured on dishes coated with collagen matrix. We performed Western blot analysis for the expression of specific protein and/or RT-PCR for the expression of specific mRNA. PPARalpha and PPARgamma expression was observed and increased in GBEC treated with WY-14643 (PPARalpha ligand), troglitazone (PPARgamma ligand), and lipopolysaccharide (LPS) compared to the no-treatment control and PPARalpha( antagonist (GW-9662) treatment group. WY-14643, troglitazone, and LPS also induced an increase in the expression of ABCA1 protein and mRNA in cultured GBEC. LPS-induced TNFalpha mRNA expression was suppressed by pretreatment with WY-14643 and troglitazone preceding LPS treatment in GBEC. PPAR ligands, especially PPARgamma, may preserve gallbladder function by suppression of inflammatory reaction and prevention of cholesterol accumulation in GBEC, contributing to the prevention of gallstone formation and progression to cholecystitis.

A clinical trial of combined use of rosiglitazone and 5-aminosalicylate for ulcerative colitis

AIM: To investigate the therapeutic effects of the combined use of rosiglitazone and aminosalicylate on mild or moderately active ulcerative colitis (UC).

METHODS: According to the national guideline for diagnosis and treatment of inflammatory bowel disease (IBD) in China, patients with mild or moderately active UC in our hospital were selected from July to November, 2004. Patients with infectious colitis, amoebiasis, or cardiac, renal or hepatic failure and those who had received corticosteroid or immunosuppressant treatment within the last month were excluded. Following a quasi-randomization principle, patients were allocated alternatively into the treatment group (TG) with rosiglitazone 4 mg/d plus 5-ASA 2 g/d daily or the control group (CG) with 5-ASA 2 g/d alone, respectively, for 4 wk. Clinical changes were evaluated by Mayo scoring system and histological changes by Truelove-Richards’ grading system at initial and final point of treatment.

RESULTS: Forty-two patients completed the trial, 21 each in TG and CG. The Mayo scores in TG at initial and final points were 5.87 (range: 4.29-7.43) and 1.86 (range: 1.03-2.69) and those in CG were 6.05 (range: 4.97-7.13) and 2.57 (range: 1.92-3.22) respectively. The decrements of Mayo scores were 4.01 in TG and 3.48 in CG, with a remission rate of 71.4% in TG and 57.1% in CG, respectively. Along with the improvement of disease activity index (DAI), the histological grade improvement was more significant in TG than in CG (P < 0.05).

CONCLUSION: Combined treatment with rosiglitazone and 5-ASA achieved better therapeutic effect than 5-ASA alone without any side effects. Rosiglitazone can alleviate colonic inflammation which hopefully becomes a novel agent for UC treatment.