Apocynin protects endothelial cells from endoplasmic reticulum stress-induced apoptosis via IRE1α engagement

Apocynin alleviates weight gain and obesity-induced adipose tissue inflammation in high-fat diet-fed C57BL/6 mice

Obesity involves chronic low-grade inflammation within adipose tissue. Apocynin (APO) is a therapeutic agent for the treatment of inflammatory diseases. Therefore, the present study aimed to investigate whether APO can reduce weight gain and obesity-induced adipose tissue inflammation. C57BL/6 mice were administered APO or orlistat (Orli) as a positive control with a high-fat diet (HFD) for 12 weeks. Lipopolysaccharide-stimulated 3T3-L1 adipocytes were used for the in vitro study. Our results showed a significantly lower white adipose tissue (WAT) mass index in 10 mg/kg APO-treated mice than in 20 mg/kg Orli-treated mice. Moreover, the protein expression of adipose triglyceride lipase, fatty acid synthase, sterol regulatory element-binding transcription factor 1, and peroxisome proliferator-activated receptor γ was reversed in the WAT of 10 mg/kg APO-treated mice. Furthermore, APO reduced the expression of the macrophage marker F4/80, decreased the mRNA levels of tumor necrosis factor-α and monocyte chemoattractant protein-1, and increased the mRNA levels of interleukin-10 in WAT. APO decreased the phosphorylation of c-Jun N-terminal kinase, extracellular signal-regulated kinase, and p65 in vivo and in vitro. Notably, APO had a stronger effect on the amelioration of adipose tissue inflammation than Orli did. Our findings lay the foundation for research on the use of APO as an agent to ameliorate weight gain and obesity-induced inflammatory diseases.

The Effects of Apocynin on Monosodium Glutamate Induced Liver Damage of Rats

Monosodium glutamate (MSG) is found in refined foods. Apocynin (APO) is a selective NADPH oxidase (NOX) inhibitor. The aim of this experimental study was to investigate possible effects of MSG and the curative effects of APO in rats. Twenty-eight male Sprague-Dawley rats were randomly divided into four groups (Normal control, APO, MSG and MSG + APO, n:7 for each group). The MSG and MSG + APO groups received 120 mg/kg MSG solution orally for 28 consecutive days. The APO and MSG + APO groups received 25 mg/kg APO solution orally for 5 days until the end of the experiment. At the end of the experiment, all rats were sacrificed and liver tissue and blood samples were taken for histological, ultrastructural, and biochemical analyses. In the MSG group, vacuolization and loss in glycogen content in the hepatocytes, leukocyte infiltration and fibrosis in the liver parenchyme and portal triads, were observed. Terminal deoxynucleotidyl transferase dUTP (TUNEL)-positivity and NADPH oxidase (NOX)-2-positivity were higher in the MSG group compared with the other experimental groups. The concentrations of alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total bilirubin, malondialdehyde (MDA), and myeloperoxidase (MPO) were higher, whereas albumin, glutathione (GSH), and superoxide (SOD) levels were lower in the MSG group. All these data has been reversed in MSG + APO group. The histological and biochemical criteria indicated the prominent ameliorating effect of APO on MSG -induced liver injury.

Apocynin attenuates patulin-induced cytotoxicity through reduction of oxidation stress and apoptosis in HEK293cells

Patulin (PAT) is a natural mycotoxin that commonly contaminates fruits and their derivative products and has been proven to induce cytotoxicity and oxidative damage in renal cells. In the present study, we aimed to evaluate the effect of apocynin, a potent phenolic antioxidant isolated from plants, on PAT-induced cell injury in human embryonic kidney (HEK293) cells. Compared with 7.5 μM PAT treatment alone, 10 μM apocynin co-treatment elevated cell viability, alleviated lactate dehydrogenase release and reduced caspase activities. Furthermore, apocynin inhibited reactive oxygen species overproduction, re-established mitochondria membrane potential and elevated intracellular ATP content. In addition, the results showed that apocynin aggrandized reduced glutathione (GSH) content, reduced oxidized glutathione (GSSG) content, raised the GSH/GSSG ratio and elevated superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase activities. Collectively, results of the study clearly show that apocynin supplement may serve as an alternative intervention to protect HEK293 cells against cytotoxicity induced by PAT through reduction of oxidation stress and apoptosis.

Therapeutic benefits of apocynin in mice with lipopolysaccharide/D-galactosamine-induced acute liver injury via suppression of the late stage pro-apoptotic AMPK/JNK pathway

The excessive generation of reactive oxygen species (ROS) plays crucial roles in the development of acute liver injury. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is responsible for the robust production of ROS under inflammatory circumstance, but the pathological roles of NOX and the pharmacological significance of NOX inhibitor in acute liver injury remains unclear. In the present study, the potential roles of NOX in acute liver injury were investigated in a mouse model with lipopolysaccharide (LPS)/D-galactosamine (D-Gal)-induced acute liver injury. The results indicated that LPS/D-Gal exposure time-dependently increased the level of ROS in liver tissue. Pretreatment with the NOX inhibitor apocynin suppressed LPS/D-Gal induced upregulation of ROS, 8-hydroxy-2-deoxyguanosine (8-OH-dG), protein carbonyl content and thiobarbituric acid reactive substances (TBARS). Pretreatment with apocynin also suppressed LPS/D-Gal-induced elevation of aminotransferase, alleviated histological abnormalities, inhibited the production of pro-inflammatory cytokine tumor necrosis factor α (TNF-α), blocked the activation of caspase cascade, reduced the count of TUNEL-positive cells and prevented LPS/D-Gal-induced mortality. Interestingly, post insult treatment with apocynin also suppressed LPS/D-Gal-induced oxidative stress, hepatocyte apoptosis, liver damage but improved the survival rate. Mechanistically, posttreatment with apocynin prohibited LPS/D-Gal-induced activation of the late stage pro-apoptotic AMP-activated protein kinase (AMPK)/c-Jun N-terminal kinase (JNK) pathway. Post-insult treatment with the antioxidant N-acetylcysteine also resulted in suppressed activation of AMPK/JNK, mitigated apoptosis and alleviated liver injury. These data suggest that NOX-derived ROS might be a crucial late stage detrimental factor in LPS/D-Gal-induced acute liver injury via promoting the activation of the pro-apoptotic AMPK/JNK pathway, and the NOX inhibitor might have important value in the pharmacological intervention of inflammation-base liver damage.

Natural antioxidants' effects on endoplasmic reticulum stress-related diseases

Endoplasmic reticulum (ER) stress is a normal molecular process induced by the over-accumulation of misfolded or unfolded proteins. ER stress induces the unfolded protein response (UPR), which reduces global protein synthesis, increases ER capacity and protein degradation, to restart ER homeostasis, allowing cell survival. However, the over-induction of UPR can also trigger inflammatory processes, tissue damage and cell death. ER stress is involved in several pathologies, like endothelial dysfunction, diabetes and heart, liver, kidney or neurological diseases. Although the progression of these diseases is the result of several pathological mechanisms, oxidative stress has been widely related to these pathologies. Moreover, ER stress can establish a progressive pathological cycle with oxidative stress. Therefore, the use of natural antioxidants, able to modulate both oxidative and ER stress, can be a new strategy to mitigate these diseases. This review is focused on the effects of natural antioxidant compounds on ER stress in endothelial dysfunction, diabetes and heart, liver, kidney or neurological diseases.