High-Density Lipoprotein Prevents Endoplasmic Reticulum Stress-Induced Downregulation of Liver LOX-1 Expression

Involvement of endoplasmic reticulum stress in rifampicin-induced liver injury

Rifampicin is a first-line antituberculosis drug. Hepatocyte toxicity caused by rifampicin is a significant clinical problem. However, the specific mechanism by which rifampicin causes liver injury is still poorly understood. Endoplasmic reticulum (ER) stress can have both protective and proapoptotic effects on an organism, depending on the environmental state of the organism. While causing cholestasis and oxidative stress in the liver, rifampicin also activates ER stress in different ways, including bile acid accumulation and cytochrome p450 (CYP) enzyme-induced toxic drug metabolites via pregnane X receptor (PXR). The short-term stress response helps the organism resist toxicity, but when persisting, the response aggravates liver damage. Therefore, ER stress may be closely related to the “adaptive” mechanism and the apoptotic toxicity of rifampicin. This article reviews the functional characteristics of ER stress and its potentially pathogenic role in liver injury caused by rifampicin.

Pathological Crosstalk Between Oxidized LDL and ER Stress in Human Diseases: A Comprehensive Review

The oxidative modification of the major cholesterol carrying lipoprotein, oxLDL, is a biomarker as well as a pathological factor in cardiovascular diseases (CVD), type 2 diabetes mellitus (T2DM), obesity and other metabolic diseases. Perturbed cellular homeostasis due to physiological, pathological and pharmacological factors hinder the proper functioning of the endoplasmic reticulum (ER), which is the major hub for protein folding and processing, lipid biosynthesis and calcium storage, thereby leading to ER stress. The cellular response to ER stress is marked by a defensive mechanism called unfolded protein response (UPR), wherein the cell adapts strategies that favor survival. Under conditions of excessive ER stress, when the survival mechanisms fail to restore balance, UPR switches to apoptosis and eliminates the defective cells. ER stress is a major hallmark in metabolic syndromes such as diabetes, non-alcoholic fatty liver disease (NAFLD), neurological and cardiovascular diseases. Though the pathological link between oxLDL and ER stress in cardiovascular diseases is well-documented, its involvement in other diseases is still largely unexplored. This review provides a deep insight into the common mechanisms in the pathogenicity of diseases involving oxLDL and ER stress as key players. In addition, the potential therapeutic intervention of the targets implicated in the pathogenic processes are also explored.

Machine Learning Algorithms Identify Pathogen-Specific Biomarkers of Clinical and Metabolomic Characteristics in Septic Patients with Bacterial Infections

Sepsis is a high-mortality disease that is infected by bacteria, but pathogens in individual patients are difficult to diagnosis. Metabolomic changes triggered by microbial activity provide us with the possibility of accurately identifying infection. We adopted machine learning methods for training different classifiers with a clinical-metabolomic database from sepsis cases to identify the pathogen of sepsis. Records of clinical indicators and concentration of metabolites were obtained for each patient upon their arrival at the hospital. Machine learning algorithms were used in 100 patients with clear infection and corresponding 29 controls to select specific biosignatures to discriminate microorganism in septic patients. The sensitivity, specificity, and AUC value of clinical and metabolomic characteristics in predicting diagnostic outcomes were determined at admission. Our analyses demonstrate that the biosignatures selected by machine learning algorithms could have diagnostic value on the identification of infected patients and Gram-positive from Gram-negative; related AUC values were 0.94 ± 0.054 and 0.80 ± 0.085, respectively. Pathway and blood disease enrichment analyses of clinical and metabolomic biomarkers among infected patients showed that sepsis disease was accompanied by abnormal nitrogen metabolism, cell respiratory disorder, and renal or intestinal failure. The panel of selected clinical and metabolomic characteristics might be powerful biomarkers to discriminate patients with sepsis.

Inhibition of Triggering Receptor Expressed on Myeloid Cells 1 Ameliorates Inflammation and Macrophage and Neutrophil Activation in Alcoholic Liver Disease in Mice

Alcoholic liver disease (ALD) is characterized by macrophage and neutrophil leukocyte recruitment and activation in the liver. Damage‐ and pathogen‐associated molecular patterns contribute to a self‐perpetuating proinflammatory state in ALD. Triggering receptor expressed on myeloid cells 1 (TREM‐1) is a surface receptor that amplifies inflammation induced by toll‐like receptors (TLRs) and is expressed on neutrophils and monocytes/macrophages. We hypothesized that TREM‐1 signaling contributes to proinflammatory pathway activation in ALD. Using an in vivo ALD model in mice, we tested the effects of ligand‐independent TREM‐1 inhibitory peptides that were formulated into human high‐density lipoprotein (HDL)‐mimicking complexes GF9‐HDL and GA/E31‐HDL. As revealed in vitro, macrophages endocytosed these rationally designed complexes through scavenger receptors. A 5‐week alcohol feeding with the Lieber‐DeCarli diet in mice resulted in increased serum alanine aminotransferase (ALT), liver steatosis, and increased proinflammatory cytokines in the liver. TREM‐1 messenger RNA (mRNA) expression was significantly increased in alcohol‐fed mice, and TREM‐1 inhibitors significantly reduced this increase. TREM‐1 inhibition significantly attenuated alcohol‐induced spleen tyrosine kinase (SYK) activation, an early event in both TLR4 and TREM‐1 signaling. The TREM‐1 inhibitors significantly inhibited macrophage (epidermal growth factor‐like module‐containing mucin‐like hormone receptor‐like 1 [F4/80], clusters of differentiation [CD]68) and neutrophil (lymphocyte antigen 6 complex, locus G [Ly6G] and myeloperoxidase [MPO]) markers and proinflammatory cytokines (monocyte chemoattractant protein 1 [MCP‐1], tumor necrosis factor α [TNF‐α], interleukin‐1β [IL‐1β], macrophage inflammatory protein 1α [MIP‐1α]) at the mRNA level compared to the HDL vehicle. Administration of TREM‐1 inhibitors ameliorated liver steatosis and early fibrosis markers (α‐smooth muscle actin [αSMA] and procollagen1α [Pro‐Col1α]) at the mRNA level in alcohol‐fed mice. However, the HDL vehicle also reduced serum ALT and some cytokine protein levels in alcohol‐fed mice, indicating HDL‐related effects. Conclusion: HDL‐delivered novel TREM‐1 peptide inhibitors ameliorate early phases of inflammation and neutrophil and macrophage recruitment and activation in the liver and attenuate hepatocyte damage and liver steatosis. TREM‐1 inhibition represents a promising therapeutic approach for further investigations in ALD.

Adaptive unfolded protein response promotes cell survival in rifampicin-treated L02 cells

An important concept in drug-induced liver injury (DILI) is adaptation, which means the injury reverses with the continuation of the drug. The mechanism of adaption of drugs remains enigmatic, adaptive unfolded protein response (UPR) is possibly involved. We once observed adaptation phenomenon of rifampicin (RFP) in animal models, in this study, we investigate the effects of RFP on adaptive UPR in L02 cells, and after inhibiting UPR by using 4-phenylbutyrate (4-PBA), the change of cell viability and cell apoptosis in RFP-treated cells. We found that with the concentration of RFP increased and the treatment time was prolonged, the glucose-regulated protein 78 (GRP78), a hallmark of the UPR, was upregulated, and was dose- and time-dependent. RFP also activates the p-eukaryotic initiation factor 2α (eIF2α) protein expression. 4-PBA decreased GRP78 and p-eIF2α protein expression levels. Moreover, FCA showed that cell apoptosis rate obviously increased, and MTT assay showed that cell survival rate obviously decreased, this indicates that after inhibiting the UPR, the cell damage increased, which shows that the UPR is an adaptation mechanism to protect cells against injury induced by RFP. This also proves that when the degree of UPR induced by RFP is relatively mild, adaptive UPR is helpful for cell survival.

A novel potential biomarker for metabolic syndrome in Chinese adults: Circulating protein disulfide isomerase family A, member 4

BACKGROUND/OBJECTIVES

Protein disulfide isomerase (PDI) family members are specific endoplasmic reticulum proteins that are involved in the pathogenesis of numerous diseases including neurodegenerative diseases, cancer and obesity. However, the metabolic effects of PDIA4 remain unclear in humans. The aims of this study were to investigate the associations of serum PDIA4 with the metabolic syndrome (MetS) and its components in Chinese adults.

SUBJECTS/METHODS

A total of 669 adults (399 men and 270 women) were recruited. Serum PDIA4 concentrations and biochemical variables were recorded. Insulin sensitivity and β-cell function were examined by homeostasis model assessment. MetS was defined based on the modified National Cholesterol Education Program Adult Treatment Panel III criteria for Asia Pacific.

RESULTS

The participants with MetS had significantly higher serum PDIA4 levels than those without MetS (P<0.001). After adjustments, the individuals with the highest PDIA4 tertile were associated with a higher risk of MetS than those with the lowest tertile (OR = 4.83, 95% CI: 2.71-8.60). The concentration of PDIA4 showed a stepwise increase with the components of MetS (P<0.001 for trend). The individuals with the highest PDIA4 tertile were significantly associated with waist circumference (OR = 2.41, 95% CI 1.34-4.32), blood pressure (OR = 2.71, 95% CI 1.57-4.67), fasting glucose concentration (OR = 3.17, 95% CI 1.80-5.57), and serum triglycerides (OR = 4.12, 95% CI 2.30-7.37) than those with the lowest tertile. At cutoff point of 15.24 ng/ml, the diagnostic sensitivity and specificity of PDIA4 for the metabolic syndrome were 67 and 72%, respectively, in male patients and 60 and 78%, respectively, in female patients. Finally, the result showed that PDIA4 had a significantly higher area under the curve compared with blood pressure to detect MetS using receiver operating characteristic analysis.

CONCLUSIONS

Serum PDIA4 concentrations are closely associated to MetS and its components in Chinese adults.

Lectin-type oxidized LDL receptor-1 distinguishes population of human polymorphonuclear myeloid-derived suppressor cells in cancer patients

Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) are important regulators of immune responses in cancer and have been directly implicated in promotion of tumor progression. However, the heterogeneity of these cells and lack of distinct markers hampers the progress in understanding of the biology and clinical importance of these cells. Using partial enrichment of PMN-MDSC with gradient centrifugation we determined that low density PMN-MDSC and high density neutrophils from the same cancer patients had a distinct gene profile. Most prominent changes were observed in the expression of genes associated with endoplasmic reticulum (ER) stress. Surprisingly, low-density lipoprotein (LDL) was one of the most increased regulators and its receptor oxidized LDL receptor 1 OLR1 was one of the most overexpressed genes in PMN-MDSC. Lectin-type oxidized LDL receptor 1 (LOX-1) encoded by OLR1 was practically undetectable in neutrophils in peripheral blood of healthy donors, whereas 5-15% of total neutrophils in cancer patients and 15-50% of neutrophils in tumor tissues were LOX-1⁺. In contrast to their LOX-1^- counterparts, LOX-1⁺ neutrophils had gene signature, potent immune suppressive activity, up-regulation of ER stress, and other biochemical characteristics of PMN-MDSC. Moreover, induction of ER stress in neutrophils from healthy donors up-regulated LOX-1 expression and converted these cells to suppressive PMN-MDSC. Thus, we identified a specific marker of human PMN-MDSC associated with ER stress and lipid metabolism, which provides new insight to the biology and potential therapeutic targeting of these cells.

The role of ER stress in lipid metabolism and lipotoxicity

The endoplasmic reticulum (ER) is a cellular organelle important for regulating calcium homeostasis, lipid metabolism, protein synthesis, and posttranslational modification and trafficking. Numerous environmental, physiological, and pathological insults disturb ER homeostasis, referred to as ER stress, in which a collection of conserved intracellular signaling pathways, termed the unfolded protein response (UPR), are activated to maintain ER function for cell survival. However, excessive and/or prolonged UPR activation leads to initiation of self-destruction through apoptosis. Excessive accumulation of lipids and their intermediate products causes metabolic abnormalities and cell death, called lipotoxicity, in peripheral organs, including the pancreatic islets, liver, muscle, and heart. Because accumulating evidence links chronic ER stress and defects in UPR signaling to lipotoxicity in peripheral tissues, understanding the role of ER stress in cell physiology is a topic under intense investigation. In this review, we highlight recent findings that link ER stress and UPR signaling to the pathogenesis of peripheral organs due to lipotoxicity.