Pioglitazone prevents cholesterol gallstone formation through the regulation of cholesterol homeostasis in guinea pigs with a lithogenic diet.

BACKGROUND: The cholesterol gallstones diseases (CGD) is highly correlated with metabolic syndrome and type 2 diabetes. The present study aimed to investigate preventive effects of pioglitazone (PIO), an antidiabetic drug, on the CGD in guinea pigs fed with a lithogenic diet (LD). METHODS: The guinea pigs were fed with the LD for 8 weeks. All guinea pigs were grouped as follows: low fat diet; LD; LD plus PIO (4 mg/kg); LD plus PIO (8 mg/kg); LD plus ezetimibe (EZE) (2 mg/kg). Gallbladder stones were observed using microscopy. The profile of biliary composition, and blood glucose, insulin and lipid were analyzed. The liver or ileum was harvested for determinations of hydroxyl-methyl-glutaryl-CoA reductase (HMGCR), sterol regulatory element-binding proteins 2 (SREBP2), 7α-hydroxylase (CYP7A1), adenosine triphosphate-binding cassette (ABC) sterol transporters G5 and G8 (ABCG5, ABCG8), bile salt export pump (BSEP), Niemann-Pick C1-Like 1 (NPC1L1) and acetyl-coenzyme A cholesterol acyltransferase (ACAT2) by Western blot. The gallbladders were used for histological examination. RESULTS: The LD successfully induced gallstone. Both pioglitazone and ezetimibe prevented gallstone formation, as well as hepatic and cholecystic damages. Pioglitazone significantly decreased HMGCR and SREBP2, but increased CYP7A1, ABCG5, ABCG8, and BSEP in the liver. Pioglitazone also remarkably decreased NPC1L1 and ACAT2, while increased ABCG5/8 in the intestine. The beneficial alterations of cholesterol and bile acids in the bile, as well as profile of glucose, insulin and lipid in the blood were found in the guinea pigs treated with pioglitazone. CONCLUSION: Pioglitazone has a noticeable benefit towards the CGD, which is involved in changes of synthesis, transformation, absorption, and transportation of cholesterol.

Protective Effects of 1-Methylnicotinamide on Aß1-42-Induced Cognitive Deficits, Neuroinflammation and Apoptosis in Mice.

The neurotoxicity of Aß peptides has been well documented, but effective neuroprotective approaches against Aß neurotoxicity are unavailable. In the present study, we investigated effects of 1-Methylnicotinamide (MNA), known as a main metabolite of nicotinamide (NA), on the impairment of learning and memory induced by Aß and the underlying mechanisms. We found that intragastric administration of MNA at 100 or 200 mg/kg for 3 weeks significantly reversed bilateral intrahippocampal injection of Aß1-42-induced cognitive impairments in the Morris water maze (MWM), Y-maze and Novel object recognition tests. Furthermore, MNA suppressed Aß1-42-induced neuroinflammation, characterized by suppressed activation of microglia, decreased the expression of IL-6, TNF-α and nuclear translocation of NF-κB p65, as well as attenuated neuronal apoptosis as indicated by decreased TUNEL-positive cells and ratio of caspase-3 fragment to procaspase-3, and increased ratio of Bcl-2/Bax in the hippocampus. Our results show that MNA may ameliorate Aß1-42-induced cognition deficits, which is involved in inhibition of neuroinflammation and apoptosis mediated by NF-κB signaling, suggesting that MNA could have potential therapeutic value for AD. Graphical Abstract Neuroprotective affect of MNA on Aß1-42-induced cognitive deficits.

Inhibitory effect of INT-777 on lipopolysaccharide-induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction in mice.

Neuroinflammation plays an important role in the pathophysiology of Alzheimer's disease (AD) and memory impairment. Herein, we evaluated the neuroprotective effects of 6-ethyl-23(S)-methyl-cholic acid (INT-777), a specific G-protein coupled bile acid receptor 1 (TGR5) agonist, in the LPS-treated mouse model of acute neurotoxicity. Single intracerebroventricular (i.c.v.) injection of LPS remarkably induced mouse behavioral impairments in Morris water maze, novel object recognition, and Y-maze avoidance tests, which were ameliorated by INT-777 (1.5 or 3.0 µg/mouse, i.c.v.) treatment. Importantly, INT-777 treatment reversed LPS-induced TGR5 down-regulation, suppressed the increase of nuclear NF-κB p65, and mitigated neuroinflammation, evidenced by lower proinflammatory cytokines, less activation of microglia, and increased the ratio of p-CREB/CREB or mBDNF/proBDNF in the hippocampus and frontal cortex. In addition, INT-777 treatment also suppressed neuronal apoptosis, as indicated by the reduction of TUNEL-positive cells, decreased activation of caspase-3, increased the ratio of Bcl-2/Bax, and ameliorated synaptic dysfunction as evidenced by the upregulation of PSD95 and synaptophysin in the hippocampus and frontal cortex. Taken together, this study showed the potential neuroprotective effects of INT-777 against LPS-induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction in mice.

PPARγ overexpression regulates cholesterol metabolism in human L02 hepatocytes.

Peroxisome proliferator-activator receptor (PPAR) γ is a nuclear hormone receptor that regulates glucose homeostasis, lipid metabolism, and adipocyte function. It has been shown that activation of PPARγ can reduce the incidence of gallstone. Herein we aimed to clarify the role of PPARγ in the reduction of gallstones. The plasmid containing the coding sequence of PPARγ was constructed and transfected in the human liver cell line (L02 cells). Western blot and RT-PCR were used to detect hydroxyl-methyl-glutaryl-CoA reductase (HMGCR), sterol regulatory element-binding proteins 2 (SREBP2), 7α-hydroxylase (CYP7A1), adenosine triphosphate-binding cassette (ABC) sterol transporters G5 and G8 (ABCG5, ABCG8) and liver X receptor α (LXRα). The Amplex Red cholesterol assay kit was used to detect the intracellular or extracellular cholesterol level. Our data showed that PPARγ overexpression caused significant decreases in both extracellular and intracellular cholesterol in the L02 cells. The further studies indicated PPARγ overexpression substantially decreased expression of HMGCR and SREBP-2, increased expression of CYP7A1, ABCG5, ABCG8 and LXRα. These results indicated that upregulation of PPARγ may reduce cholesterol levels through multiple-pathways including HMGCR/SREBP2-mediated biosynthesis, CYP7A1-mediated transformation, and ABCG5/ABCG8-mediated efflux. We thus suggest that PPARγ might have beneficial effects for cholesterol gallstones diseases.

Neuroprotective effects of INT-777 against Aß1-42-induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction in mice.

Increasing evidence demonstrates that the neurotoxicity of amyloid-beta (Aß) deposition plays a causative role in Alzheimer's disease (AD). Herein, we evaluated the neuroprotective effects of 6α-ethyl-23(S)-methylcholic acid (S-EMCA, INT-777), a specific G-protein coupled bile acid receptor 1 (TGR5) agonist, in the Aß1-42-treated mouse model of acute neurotoxicity. Single intracerebroventricular (i.c.v.) injection of aggregated Aß1-42 (410 pmol/mouse; 5 µl) into the mouse brain induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction. In contrast, INT-777 (1.5 or 3.0 µg/mouse, i.c.v.) significantly improved Aß1-42-induced cognitive impairment, as reflected by better performance in memory tests. Importantly, INT-777 treatment reversed Aß1-42-induced TGR5 down-regulation, suppressed the increase of nuclear NF-κB p65, and mitigated neuroinflammation, as evidenced by lower proinflammatory cytokines and less Iba1-positive cells in the hippocampus and frontal cortex. INT-777 treatment also pronouncedly suppressed apoptosis through the reduction of TUNEL-positive cells, decreased caspase-3 activation, increased the ratio of Bcl-2/Bax, and ameliorated synaptic dysfunction by promoting dendritic spine generation with the upregulation of postsynaptic and presynaptic proteins (PSD95 and synaptophysin) in Aß1-42-treated mice. Our results indicate that INT-777 has potent neuroprotective effects against Aß1-42-induced neurotoxicity. Taken together, these findings suggest that the activation of TGR5 could be a novel and promising strategy for the treatment of AD.