Hepatic retinaldehyde deficiency is involved in diabetes deterioration by enhancing PCK1- and G6PC-mediated gluconeogenesis

Structural characteristics of a polysaccharide isolated from Lactaruis volemus Fr. and its anti-diabetic effects regulated by the modulation of gut microbiota and metabolites

As natural bioactive compounds, polysaccharides have promising effects in the treatment of type 2 diabetes mellitus (T2DM) owing to their changes to the intestinal microenvironment; however, the mechanisms underlying their effects have not been elucidated. In the present study, a polysaccharide LV-P4-1 isolated from Lactaruis volemus Fr was purified and characterized. The hyperglycemic function and the regulatory effect of LV-P4-1 on the gut microbiota and its metabolites were investigated in a T2DM mouse model. LV-P4-1 was mainly consisted of Fuc, Gal, Glc, Man, and GlcA, with a molecular weight of 5.89 kDa. The functional groups and glycosyl linkage types of LV-P4-1 were investigated using Fourier transform infrared spectroscopy, methylation and nuclear magnetic resonance analyses. Oral administration of 400 mg/kg LV-P4-1 increased glucose metabolism and alleviated tissue damage in mice with T2DM. Moreover, LV-P4-1 significantly regulated the abundances of gut microbiota, changed metabolite levels, and altered some metabolic pathways involved in T2DM development. Spearman analysis showed that the alterations in the gut microbiota were closely related to the differential metabolites. These results suggest that LV-P4-1 may alleviate hyperglycemia by influencing the structure of the intestinal microbiota and regulating the metabolic profile by altering the activity of certain metabolic pathways.

Unveiling the Antiobesity Mechanism of Sweet Potato Extract by Microbiome, Transcriptome, and Metabolome Analyses in Mice

This study aimed to elucidate the antiobesity mechanisms of sweet potato extract (SPE) through biochemical, gut microbiome, liver transcriptome, and metabolome analyses. Administration of SPE to high-fat-diet-fed mice significantly reduced body weight gain, serum low-density lipoprotein cholesterol, hepatic lipid accumulation, and adipocyte hypertrophy, which were closely linked to gut microbiome composition. SPE notably increased the abundance of Eubacterium_coprostanoligenes_group_unclassified and decreased that of Kineothrix, both of which were strongly associated with short-chain fatty acid (SCFA) production. LC-QTOF-MS analysis identified resin glycoside compounds from SPE with reduced levels in mouse feces, suggesting their utilization in vivo. SPE also promoted dietary fat excretion. Liver transcriptomic and metabolomic profiling revealed that SPE may exert antiobesity effects by modulating the bile-sphingolipid metabolism, which was closely correlated with the reshaped gut microbiomes and SCFAs. These findings provide new insights into the antiobesity effects and mechanisms of SPE.

Clozapine impaired glucose-stimulated insulin secretion partly by increasing plasma 5-HT levels due to the inhibition of OCT1-mediated hepatic 5-HT uptake in mice

Patients taking atypical antipsychotics (AAPs), especially clozapine, are often associated with hyperglycaemia. Here, clozapine served as a representative agent for investigating how AAPs induce hyperglycaemia. In normal mice and mice fed a high fat diet (HFD), clozapine impaired glucose tolerance and glucose-stimulated insulin secretion (GSIS) following intraperitoneal glucose administration and increased plasma 5-HT levels. Intraperitoneal 5-HT administration also impaired glucose tolerance and GSIS in mice. In INS-1 cells, high 5-HT levels impaired GSIS, which was attenuated by the 5-HTR3 antagonist tropisetron or by silencing 5-HTR3a. The 5-HTR2a agonist TCB2 attenuated clozapine-induced GSIS impairment. Silencing 5-HTR2a or the 5-HTR2a antagonist ketanserin impaired GSIS. In mice, 5-HT administration impaired GSIS, which was attenuated by tropisetron but aggravated by clozapine. Clozapine increased plasma [2H]5-HT exposure following intravenous administration to mice. In HEK293-OCT1 cells, clozapine inhibited [2H]5-HT and MPP+ uptake. Clozapine or OCT1 silencing impaired 5-HT metabolism in mouse primary hepatocytes, demonstrating that clozapine increased plasma 5-HT levels via the inhibition of OCT1-mediated hepatic 5-HT uptake. Liver-specific silencing of OCT1 increased plasma [2H]5-HT exposure and 5-HT levels and impaired GSIS and glucose tolerance in mice. In conclusion, clozapine impaired GSIS and glucose tolerance by increasing plasma 5-HT levels via the inhibition of OCT1-mediated hepatic 5-HT uptake. Increased 5-HT impaired GSIS by activating islet 5-HTR3a. The antagonistic effect of clozapine on islet 5-HTR2a also contributed to GSIS impairment. The finding that clozapine-induced GSIS impairment was attributed to increased 5-HT levels via the inhibition of OCT1-mediated hepatic 5-HT uptake may partly explain hyperglycaemia caused by other AAPs.

Camel milk exosomes regulate glucose metabolism by inhibiting mitochondrial complex I in hepatocytes

BACKGROUND

Camel milk is known to have hypoglycemic properties. Previous studies found that camel milk exosomes (CM-exo) may regulate cellular glucose metabolism through the inhibition of mitochondrial complex I, but this hypothesis has not been verified by other experiments. The objective of this study was to verify the hypothesis that CM-exo regulated glucose metabolism in hepatocytes by inhibiting mitochondrial complex I pathway. AML12 cells were treated with extracted exosomes from camel milk and the effect of the CM-exo on cell viability was examined by cell counting kit (CCK)-8 assays. The glucose content of the cell culture medium was measured to determine the glucose consumption of the cells. Lactate release from the cells was determined by measuring the lactate content in the cell culture medium. The glycogen content of AML12 cells was detected. The activity of complex I and the contents of ATP, NAD+ and NADH were measured. The protein expression levels of adenosine monophosphate-activated protein kinase (AMPK) and phosphorylated AMPK (p-AMPK) were detected by western blotting. The AML12 cells were treated with medium containing CM-exo and gluconeogenic substrates and the glucose content in the cells was determined. The protein expression levels of ten-eleven translocation methylcytosine dioxygenases (TET3), hepatocyte nuclear factor 4α-Promoter 2 (HNF4α-P2), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6PC), glycogen synthase kinase 3β (GSK3β) and phosphorylation of GSK3β (p-GSK3β) were detected by western blotting.

RESULTS

The results of this study showed that a high dose of CM-exo inhibited the viability of AML12 cells. It promoted glucose consumption, glycogen content and lactate release in AML12 cells, inhibited complex I activity, ATP content, NAD+ content, and NAD+/NADH ratio, and increased NADH content. The CM-exo increased the protein levels of p-AMPK, p-GSK3β, the protein expression ratio of p-AMPK/AMPK, p-GSK3β/GSK3β and decreased the glucose content and the protein expression levels of intracellular TET3, HNF4α-P2, PEPCK and G6PC.

CONCLUSIONS

By inhibiting the activity of mitochondrial complex I in hepatocytes, CM-exo inhibited oxidative phosphorylation, oxidation of NADH to NAD+ and synthesis of ATP, enhanced glycolysis, activated AMPK and resulted in decreased gluconeogenesis and increased glycogen synthesis.

Identification of Novel Organo-Se BTSA-Based Derivatives as Potent, Reversible, and Selective PPARγ Covalent Modulators for Antidiabetic Drug Discovery

Recent studies have identified selective peroxisome proliferator-activated receptor γ (PPARγ) modulators, which synergistically engage in the inhibition mechanism of PPARγ-Ser273 phosphorylation, as a promising approach for developing safer and more effective antidiabetic drugs. Herein, we present the design, synthesis, and evaluation of a new class of organo-Se compounds, namely, benzothiaselenazole-1-oxides (BTSAs), acting as potent, reversible, and selective PPARγ covalent modulators. Notably, 2n, especially (R)-2n, displayed a high binding affinity and superior antidiabetic effects with diminished side effects. This is mainly because it can reversibly form a unique covalent bond with the Cys285 residue in PPARγ-LBD. Further mechanistic investigations revealed that it manifested such desired pharmacological profiles primarily by effectively suppressing PPARγ-Ser273 phosphorylation, enhancing glucose metabolism, and selectively upregulating the expression of insulin-sensitive genes. Collectively, our results suggest that (R)-2n holds promise as a lead compound for treating T2DM and also provides an innovative reversible covalent warhead reference for future covalent drug design.

ZBED3 exacerbates hyperglycemia by promoting hepatic gluconeogenesis through CREB signaling

BACKGROUND

Elevated hepatic glucose production (HGP) is a prominent manifestation of impaired hepatic glucose metabolism in individuals with diabetes. Increased hepatic gluconeogenesis plays a pivotal role in the dysregulation of hepatic glucose metabolism and contributes significantly to fasting hyperglycemia in diabetes. Previous studies have identified zinc-finger BED domain-containing 3 (ZBED3) as a risk gene for type 2 diabetes (T2DM), and its single nucleotide polymorphism (SNPs) is closely associated with the fasting blood glucose level, suggesting a potential correlation between ZBED3 and the onset of diabetes. This study primarily explores the effect of ZBED3 on hepatic gluconeogenesis and analyzes the relevant signaling pathways that regulate hepatic gluconeogenesis.

METHODS

The expression level of ZBED3 was assessed in the liver of insulin-resistant (IR)-related disease. RNA-seq and bioinformatics analyses were employed to examine the ZBED3-related pathway that modulated HGP. To investigate the role of ZBED3 in hepatic gluconeogenesis, the expression of ZBED3 was manipulated by upregulation or silencing using adeno-associated virus (AAV) in mouse primary hepatocytes (MPHs) and HHL-5 cells. In vivo, hepatocyte-specific ZBED3 knockout mice were generated. Moreover, AAV8 was employed to achieve hepatocyte-specific overexpression and knockdown of ZBED3 in C57BL/6 and db/db mice. Immunoprecipitation and mass spectrometry (IP-MS) analyses were employed to identify proteins that interacted with ZBED3. Co-immunoprecipitation (co-IP), glutathione S-transferase (GST) - pulldown, and dual-luciferase reporter assays were conducted to further elucidate the underlying mechanism of ZBED3 in regulating hepatic gluconeogenesis.

RESULTS

The expression of ZBED3 in the liver of IR-related disease models was found to be increased. Under the stimulation of glucagon, ZBED3 promoted the expression of hepatic gluconeogenesis-related genes PGC1A, PCK1, G6PC, thereby increasing HGP. Consistently, the rate of hepatic gluconeogenesis was found to be elevated in mice with hepatocyte-specific overexpression of ZBED3 and decreased in those with ZBED3 knockout. Additionally, the knockdown of ZBED3 in the liver of db/db mice resulted in a reduction in hepatic gluconeogenesis. Moreover, the study revealed that ZBED3 facilitated the nuclear translocation of protein arginine methyltransferases 5 (PRMT5) to influence the regulation of PRMT5-mediated symmetrical dimethylation of arginine (s-DMA) of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), which in turn affects the phosphorylation of CREB and ultimately promotes HGP.

CONCLUSIONS

This study indicates that ZBED3 promotes hepatic gluconeogenesis and serves as a critical regulator of the progression of diabetes.

Neurons enhance blood-brain barrier function via upregulating claudin-5 and VE-cadherin expression due to glial cell line-derived neurotrophic factor secretion

Blood-brain barrier (BBB) prevents neurotoxins from entering central nervous system. We aimed to establish and characterize an in vitro triple co-culture BBB model consisting of brain endothelial cells hCMEC/D3, astrocytoma U251 cells, and neuroblastoma SH-SY5Y cells. Co-culture of SH-SY5Y and U251 cells markedly enhanced claudin-5 and VE-cadherin expression in hCMEC/D3 cells, accompanied by increased transendothelial electrical resistance and decreased permeability. Conditioned medium (CM) from SH-SY5Y cells (S-CM), U251 cells (U-CM), and co-culture of SH-SY5Y and U251 cells (US-CM) also promoted claudin-5 and VE-cadherin expression. Glial cell line-derived neurotrophic factor (GDNF) levels in S-CM and US-CM were significantly higher than CMs from hCMEC/D3 and U-CM. Both GDNF and US-CM upregulated claudin-5 and VE-cadherin expression, which were attenuated by anti-GDNF antibody and GDNF signaling inhibitors. GDNF increased claudin-5 expression via the PI3K/AKT/FOXO1 and MAPK/ERK pathways. Meanwhile, GDNF promoted VE-cadherin expression by activating PI3K/AKT/ETS1 and MAPK/ERK/ETS1 signaling. The roles of GDNF in BBB integrity were validated using brain-specific Gdnf silencing mice. The developed triple co-culture BBB model was successfully applied to predict BBB permeability. In conclusion, neurons enhance BBB integrity by upregulating claudin-5 and VE-cadherin expression through GDNF secretion and established triple co-culture BBB model may be used to predict drugs' BBB permeability.

Plantaginis Semen Ameliorates Hyperuricemia Induced by Potassium Oxonate

Plantaginis semen is the dried ripe seed of Plantago asiatica L. or Plantago depressa Willd., which has a long history in alleviating hyperuricemia (HUA) and chronic kidney diseases. While the major chemical ingredients and mechanism remained to be illustrated. Therefore, this work aimed to elucidate the chemicals and working mechanisms of PS for HUA. UPLC-QE-Orbitrap-MS was applied to identify the main components of PS in vitro and in vivo. RNA sequencing (RNA-seq) was conducted to explore the gene expression profile, and the genes involved were further confirmed by real-time quantitative PCR (RT-qPCR). A total of 39 components were identified from PS, and 13 of them were detected in the rat serum after treating the rat with PS. The kidney tissue injury and serum uric acid (UA), xanthine oxidase (XOD), and cytokine levels were reversed by PS. Meanwhile, renal urate anion transporter 1 (Urat1) and glucose transporter 9 (Glut9) levels were reversed with PS treatment. RNA-seq analysis showed that the PPAR signaling pathway; glycine, serine, and threonine metabolism signaling pathway; and fatty acid metabolism signaling pathway were significantly modified by PS treatment. Further, the gene expression of Slc7a8, Pck1, Mgll, and Bhmt were significantly elevated, and Fkbp5 was downregulated, consistent with RNA-seq results. The PPAR signaling pathway involved Pparα, Pparγ, Lpl, Plin5, Atgl, and Hsl were elevated by PS treatment. URAT1 and PPARα proteins levels were confirmed by Western blotting. In conclusion, this study elucidates the chemical profile and working mechanisms of PS for prevention and therapy of HUA and provides a promising traditional Chinese medicine agency for HUA prophylaxis.

The effect of EGCG/tyrosol-loaded chitosan/lecithin nanoparticles on hyperglycemia and hepatic function in streptozotocin-induced diabetic mice

We aimed to study the potential of epigallocatechin-3-gallate/tyrosol-loaded chitosan/lecithin nanoparticles (EGCG/tyrosol-loaded C/L NPs) in streptozotocin-induced type 2 diabetes mellitus (T2DM) mice. The EGCG/tyrosol-loaded C/L NPs were created using the self-assembly method. Dynamic light scattering, Field Emission Scanning Electron Microscopy, and Fourier transform infrared spectroscopy were utilized to characterize the nanoparticle. Furthermore, in streptozotocin-induced T2DM mice, treatment with EGCG/tyrosol-loaded C/L NPs on fasting blood sugar levels, the expression of PCK1 and G6Pase, and IL-1β in the liver, liver glutathione content, nanoparticle toxicity on liver cells, and liver reactive oxygen species were measured. Our findings showed that EGCG/tyrosol-loaded C/L NPs had a uniform size distribution, and encapsulation efficiencies of 84 % and 89.1 % for tyrosol and EGCG, respectively. The nanoparticles inhibited PANC-1 cells without affecting normal HFF cells. Furthermore, EGCG/tyrosol-loaded C/L NP treatment reduced fasting blood sugar levels, elevated hepatic glutathione levels, enhanced liver cell viability, and decreased reactive oxygen species levels in diabetic mice. The expression of gluconeogenesis-related genes (PCK1 and G6 Pase) and the inflammatory gene IL-1β was downregulated by EGCG/tyrosol-loaded C/L NPs. In conclusion, the EGCG/tyrosol-loaded C/L NPs reduced hyperglycemia, oxidative stress, and inflammation in diabetic mice. These findings suggest that EGCG/tyrosol-loaded C/L NPs could be a promising therapeutic option for type 2 diabetes management.

Bile duct ligation elevates 5-HT levels in cerebral cortex of rats partly due to impairment of brain UGT1A6 expression and activity via ammonia accumulation

Hepatic encephalopathy (HE) is often associated with endogenous serotonin (5-HT) disorders. However, the reason for elevated brain 5-HT levels due to liver failure remains unclear. This study aimed to investigate the mechanism by which liver failure increases brain 5-HT levels and the role in behavioral abnormalities in HE. Using bile duct ligation (BDL) rats as a HE model, we verified the elevated 5-HT levels in the cortex but not in the hippocampus and striatum, and found that this cortical 5-HT overload may be caused by BDL-mediated inhibition of UDP-glucuronosyltransferase 1A6 (UGT1A6) expression and activity in the cortex. The intraventricular injection of the UGT1A6 inhibitor diclofenac into rats demonstrated that the inhibition of brain UGT1A6 activity significantly increased cerebral 5-HT levels and induced HE-like behaviors. Co-immunofluorescence experiments demonstrated that UGT1A6 is primarily expressed in astrocytes. In vitro studies confirmed that NH4Cl activates the ROS-ERK pathway to downregulate UGT1A6 activity and expression in U251 cells, which can be reversed by the oxidative stress antagonist N-acetyl-l-cysteine and the ERK inhibitor U0126. Silencing Hepatocyte Nuclear Factor 4α (HNF4α) suppressed UGT1A6 expression whilst overexpressing HNF4α increased Ugt1a6 promotor activity. Meanwhile, both NH4Cl and the ERK activator TBHQ downregulated HNF4α and UGT1A6 expression. In the cortex of hyperammonemic rats, we also found activation of the ROS-ERK pathway, decreases in HNF4α and UGT1A6 expression, and increases in brain 5-HT content. These results prove that the ammonia-mediated ROS-ERK pathway activation inhibits HNF4α expression to downregulate UGT1A6 expression and activity, thereby increasing cerebral 5-HT content and inducing manic-like HE symptoms. This is the first study to reveal the mechanism of elevated cortical 5-HT concentration in a state of liver failure and elucidate its association with manic-like behaviors in HE.

Thioacetamide-Induced Acute Liver Injury Increases Metformin Plasma Exposure by Downregulating Renal OCT2 and MATE1 Expression and Function

Metformin plasma exposure is increased in rats with thioacetamide (TAA)-induced liver failure. The absorption, distribution, and excretion process of metformin is mainly mediated by organic cation transporters (OCTs) and multidrug and toxin extrusion transporters (MATEs). To investigate the mechanisms of the increase in TAA-induced metformin plasma exposure, we employed intestinal perfusion and urinary excretion assays to evaluate the changes in the absorption and excretion of metformin and used Western blotting to investigate the metformin-related transport proteins' expression changes and mechanisms. The results showed that neither intestinal OCT2 expression nor metformin intestinal absorption were significantly altered by TAA-induced liver failure, while significantly decreased expression and function of renal OCT2 and MATE1 as well as impaired metformin excretion were observed in TAA rats. HK-2 cells were used as an in vitro model to explore the mechanism of liver-failure-mediated downregulation in renal OCT2 and MATE1. The results demonstrated that among numerous abnormal substances that changed in acute liver failure, elevated estrogen levels and tumor necrosis factor-α were the main factors mediating the downregulation of OCT2 and MATE1. In conclusion, this study highlights the downregulation of renal OCT2 and MATE1 in liver injury and its regulatory mechanism and reveals its roles in the increase in TAA-mediated metformin plasma exposure.