Paraoxonase activity and expression is modulated by therapeutics in experimental rat nonalcoholic Fatty liver disease

Hepatoprotective and Fat-Accumulation-Reductive Effects of Curcumin on Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Fat accumulation is the hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD). Given the intimidating nature of its treatment, curcumin (CUR) emerges as a potential therapeutic agent due to its proven effectiveness in managing MASLD. This review aimed to evaluate previous reports on the hepatoprotective and fat-accumulation-reductive effects of CUR administration in preventing or treating MASLD. CUR administration can modulate serum liver enzymes and lipid profiles. The fat accumulation of MASLD is the primary cause of oxidative stress and inflammation. By reducing fat accumulation, CUR may attenuate the inflammation and oxidative stress in MASLD. In addition, CUR has been proven to restore the dysfunctional cellular energy metabolism capacity and attenuate fibrogenesis (antifibrotic agent). Their hepatoprotective effects are associated with fat accumulation in MASLD. Lipid metabolism (lipogenesis, lipolysis, and lipophagy) is correlated with their hepatoprotective effects. CUR has prophylactic and therapeutic effects, particularly in early-stage MASLD, primarily when it is used as a fat reducer. It can be considered an excellent natural therapeutic drug for MASLD because it protects the liver and attenuates fat accumulation, especially in the early stage of MASLD development.

Paraoxonase-2 agonist vutiglabridin promotes autophagy activation and mitochondrial function to alleviate non-alcoholic steatohepatitis

BACKGROUND AND PURPOSE

Only limited therapeutic agents have been developed for non-alcoholic steatohepatitis (NASH). Glabridin, a promising anti-obesity candidate, has only limited druggability due to its low in vivo chemical stability and bioavailability. Therefore, we developed vutiglabridin (VUTI), which is based on a glabridin backbone, and investigated its mechanism of action in treating NASH in animal models.

EXPERIMENTAL APPROACH

Anti-NASH effects of VUTI were determined in in vitro fatty liver models, spheroids of primary human hepatocytes and L02 normal liver cell lines. To identify VUTI possible cellular target/s, biotin-labelled VUTI was synthesized and underwent chemical proteomic analysis. Further, the evaluation of VUTI therapeutic efficacy was carried out using an amylin-NASH and high-fat (HF) diet-induced obese (DIO) mouse models. This was carried out using transcriptomic, lipidomic and proteomic analyses of the livers from the amylin-NASH mouse model.

KEY RESULTS

VUTI treatment markedly reduces hepatic steatosis, fibrosis and inflammation by promoting lipid catabolism, activating autophagy and improving mitochondrial dysfunction, all of which are hallmarks of effective NASH treatment. The cellular target of VUTI was identified as paraoxonase 2 (PON2), a newly proposed protein target for the treatment of NASH, VUTI enhanced PON2 activity. The results using PON2 knockdown cells demonstrated that PON2 is important for VUTI- activation of autophagy, promoting mitochondrial function, decreasing oxidative stress and alleviating lipid accumulation under lipotoxic condition.

CONCLUSION AND IMPLICATIONS

Our data demonstrated that VUTI is a promising therapeutic for NASH. Targeting PON2 may be important for improving liver function in various immune-metabolic diseases including NASH.

Paraoxonase-2 contributes to promoting lipid metabolism and mitochondrial function via autophagy activation

Non-alcoholic fatty liver disease (NAFLD) is an increasingly prevalent immuno-metabolic disease that can progress to hepatic cirrhosis and cancer. NAFLD pathogenesis is extremely complex and is characterized by oxidative stress, impaired mitochondrial function and lipid metabolism, and cellular inflammation. Thus, in-depth research on its underlying mechanisms and subsequent investigation into a potential drug target that has overarching effects on these features will help in the discovery of effective treatments for NAFLD. Our study examines the role of endogenous paraoxonase-2 (PON2), a membrane protein with reported antioxidant activity, in an in vitro cell model of NAFLD. We found that the hepatic loss of PON2 activity aggravated steatosis and oxidative stress under lipotoxic conditions, and our transcriptome analysis revealed that the loss of PON2 disrupts the activation of numerous functional pathways closely related to NAFLD pathogenesis, including mitochondrial respiratory capacity, lipid metabolism, and hepatic fibrosis and inflammation. We found that PON2 promoted the activation of the autophagy pathway, specifically the mitophagy cargo sequestration, which could potentially aid PON2 in alleviating oxidative stress, mitochondrial dysfunction, lipid accumulation, and inflammation. These results provide a mechanistic foundation for the prospect of PON2 as a drug target, leading to the development of novel therapeutics for NAFLD.

Effects of Nigella sativa oil and thymoquinone on radiation-induced oxidative stress in kidney tissue of rats

Ionizing radiation leads to release of free radicals into the systemic circulation from irradiated tissues. These free radicals cause oxidative stress in distant organs. Oxidative status may be reversed by naturally occurring antioxidant agents. The aim of this study was to investigate protective and antioxidant effects of Nigella sativa oil (NSO) and thymoquinone (TQ) in kidney tissue of rats exposed to cranial irradiation. Forty-eight Sprague-Dawley rats were divided into six groups: IR group received irradiation (IR) to total cranium plus saline; IR plus NSO group received IR and NSO; IR plus TQ group received IR and TQ; sham group did not receive NSO, TQ or IR; control group of TQ received dimethyl sulfoxide; control group of NSO received saline. Total oxidant status (TOS), oxidative stress index (OSI) and lipid hydroperoxide (LOOH) levels were studied as oxidative parameters, and total antioxidant status (TAS), total sulfhydryl levels, paraoxonase (PON), ceruloplasmin (Cp) and arylesterase activities were determined as antioxidative parameters in the kidney tissue of rats. Kidney TOS, OSI and LOOH levels were significantly lower in IR plus TQ, IR plus NSO and sham groups compared to IR group (p < 0.001). TAS, PON and Cp activities in IR group were significantly lower compared to the control group (p < 0.001). PON and Cp activities were significantly higher in IR plus NSO and IR plus TQ groups compared to IR group (p < 0.001). In conclusion, free radicals generated by cranial ionizing radiation exposure cause oxidative stress in kidney. NSO and TQ exhibit protective and antioxidant effects against oxidative damage in rats.

Hydrogen influences HDL-associated enzymes and reduces oxidized phospholipids levels in rats fed with a high-fat diet

AIMS

Oxidized phospholipids (OxPLs) are formed as a result of oxidative stress, which potentially mediate multiple pathological effects. We aimed to evaluate the effects of hydrogen (H₂) on OxPLs in vivo and the underlying mechanism.

MAIN METHODS

Rats were randomly assigned to three groups: control group fed with a chow diet, model group fed with a high-fat diet, and H₂-treated group fed with a high-fat diet and treated by 4% H₂ inhalation for ten weeks. OxPLs in liver and plasma were analyzed by liquid chromatography-mass spectrometry. High-density lipoprotein (HDL) was separated by ultracentrifugation. A proteomic analysis was performed to reveal the alternation of HDL protein composition and he antioxidant capacity of HDL was tested by low-density lipoprotein oxidation experiment. Furthermore, the activity or expression of HDL-associated enzymes were evaluated.

KEY FINDINGS

Inhalation of 4% H₂ decreased the accumulation of OxPLs in rats. In vitro tests revealed that the different concentrations of H₂ did not inhibit the formation of OxPLs mediated by non-enzymatic oxidation. H₂ inhalation altered the components and enhanced the anti-oxidative capacity of HDL in rats fed with a high-fat diet. Further experiments showed that H₂ significantly regulated the activity of lipoprotein-associated phospholipase A₂, paraoxonase-1, and the expression of lecithin:cholesterol acyltransferase.

SIGNIFICANCE

Our findings revealed that H₂ may reduce the OxPLs levels through its influence on HDL-associated enzymes that can act on OxPLs, suggesting that H₂ can be used in alleviating diseases related to lipid peroxidation due to oxidative stress.

Importance of paraoxonase 1 (PON1) as an antioxidant and antiatherogenic enzyme in the cardiovascular complications of type 2 diabetes: Genotypic and phenotypic evaluation

Oxidant-antioxidant imbalance is involved in the etiology of different diseases, including cardiovascular diseases (CVDs), liver disorders, kidney diseases, cancers and diabetes mellitus. Antioxidant enzymes play a key role in striking an oxidant-antioxidant balance. Moreover, paraoxonase 1 (PON1) is an antioxidant enzyme that binds with high-density lipoprotein (HDL) in the circulation, and antioxidant and antiaterogenic properties of this lipoprotein are significantly associated with PON1. Research suggests PON1 contributes to the pathogenesis of certain human diseases such as type 2 diabetes (T2D). The association between PON1 and T2D appear to be reciprocal so that the disease significantly decreases PON1 levels and in turn, the genetics of PON1 may have a role the risk of susceptibility to T2D. Several factors that reduce the activity and concentration of PON1 in patients with T2D include increased glycation and loss-of-function polymorphisms. The genotypic and phenotypic evaluations of PON1 are therefore crucial for assessing the risk of cardiovascular complications in these patients, and strategies for increasing or restoring PON1 levels are useful for reducing or preventing their cardiovascular complications as their main cause of mortality. The present review aimed at discussing and emphasizing the key role of PON1 in T2D as a silent and dangerous disease.

Hyperglycemia induces key genetic and phenotypic changes in human liver epithelial HepG2 cells which parallel the Leprdb/J mouse model of non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is a growing global health concern. With a propensity to progress towards non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma, NAFLD is an important link amongst a multitude of comorbidities including obesity, diabetes, and cardiovascular and kidney disease. As several in vivo models of hyperglycemia and NAFLD are employed to investigate the pathophysiology of this disease process, we aimed to characterize an in vitro model of hyperglycemia that was amenable to address molecular mechanisms and therapeutic targets at the cellular level. Utilizing hyperglycemic cell culturing conditions, we induced steatosis within a human hepatocyte cell line (HepG2 cells), as confirmed by electron microscopy. The deposition and accumulation of lipids within hyperglycemic HepG2 cells is significantly greater than in normoglycemic cells, as visualized and quantified by Nile red staining. Alanine aminotransferase (ALT) and alkaline phosphatase (ALP), diagnostic biomarkers for liver damage and disease, were found to be upregulated in hyperglycemic HepG2 cells as compared with normoglycemic cells. Suppression of CEACAM1, GLUT2, and PON1, and elevation of CD36, PCK1, and G6PK were also found to be characteristic in hyperglycemic HepG2 cells compared with normoglycemic cells, suggesting insulin resistance and NAFLD. These in vitro findings mirror the characteristic genetic and phenotypic profile seen in Lepr^db/J mice, a well-established in vivo model of NAFLD. In conclusion, we characterize an in vitro model displaying several key genetic and phenotypic characteristics in common with NAFLD that may assist future studies in addressing the molecular mechanisms and therapeutic targets to combat this disease.

Betaine modulates oxidative stress, inflammation, apoptosis, autophagy, and Akt/mTOR signaling in methionine-choline deficiency-induced fatty liver disease

We examined the effects of betaine, an endogenous and dietary methyl donor essential for the methionine-homocysteine cycle, on oxidative stress, inflammation, apoptosis, and autophagy in methionine-choline deficient diet (MCD)-induced non-alcoholic fatty liver disease (NAFLD). Male C57BL/6 mice received standard chow (control), standard chow and betaine (1.5% w/v in drinking water), MCD, or MCD and betaine. After six weeks, serum and liver samples were collected for analysis. Betaine reduced MCD-induced increase in liver transaminases and inflammatory infiltration, as well as hepatosteatosis and serum levels of low-density lipoprotein, while it increased that of high-density lipoprotein. MCD-induced hepatic production of reactive oxygen and nitrogen species was significantly reduced by betaine, which also improved liver antioxidative defense by increasing glutathione content and superoxide-dismutase, catalase, glutathione peroxidase, and paraoxonase activity. Betaine reduced the liver expression of proinflammatory cytokines tumor necrosis factor and interleukin-6, as well as that of proapoptotic mediator Bax, while increasing the levels of anti-inflammatory cytokine interleukin-10 and antiapoptotic Bcl-2 in MCD-fed mice. In addition, betaine increased the expression of autophagy activators beclin 1, autophagy-related (Atg)4 and Atg5, as well as the presence of autophagic vesicles and degradation of autophagic target sequestosome 1/p62 in the liver of NAFLD mice. The observed effects of betaine coincided with the increase in the hepatic phosphorylation of mammalian target of rapamycin (mTOR) and its activator Akt. In conclusion, the beneficial effect of betaine in MCD-induced NAFLD is associated with the reduction of liver oxidative stress, inflammation, and apoptosis, and the increase in cytoprotective Akt/mTOR signaling and autophagy.

Decreases in Paraoxonase-1 Activities Promote a Pro-inflammatory Effect of Lipids Peroxidation Products in Non-smoking and Smoking Patients with Acute Pancreatitis

Aim: The study investigated the extent to which tobacco smoke exposure causes changes in lipids biochemistry through measurement blood concentrations of: paraoxonase-1 (PON-1) activities as lipid-bound enzyme into cell membrane, concentration of malonyldialdehyde (MDA), protein adducts of 4-hydroxynonenal (HNE-adducts), oxidized low density lipoproteins (oxLDL), total cholesterol (CH) and high-density lipoprotein cholesterol (HDL). Additionally, the activity of P isoform of glutathione S-transferase (GST-π) was measured. Methods: Investigations were performed in the blood of patients with acute pancreatitis (AP) on the 1st, 3rd and 7th day of hospitalization and in healthy volunteers. The activities of PON-1 forms, GST-π were determined spectrophotometrically. Concentrations of PON-1, MDA, HNE-adducts, oxLDL, HDL, CH were measured using commercial tests. Results: Near 2-fold higher concentrations of MDA, HNE-adducts, oxLDL, correlating with inflammatory markers in AP patients compared to healthy subjects were demonstrated, which were accompanied by gradually increasing CH/HDL ratio during hospitalization. During hospital treatment, decreased activities of all PON-1 subtypes were observed in AP patients compared to healthy subjects, more pronounced in tobacco smokers. A decreased PON-1 phosphotriesterase activity in non-AP control group smokers compared to non-smokers was noted. In non-smoking AP patients GST-π activity normalized during hospitalization in contrast to smokers. Conclusions: GST-π and PON-1 phosphotriesterase activities seem to be a sensitive marker of pro/antioxidative imbalance in smokers. Lipids peroxidation products generated during AP can intensify preexisting inflammation. Increasing stay in the hospital was associated with worsening of lipids peroxidation markers and the parameters of lipid profile, in both non-smoking and smoking AP patients, what can indicate that the oxidative-inflammatory process are not extinguished.

Paraoxonases: metabolic role and pharmacological projection

Atherosclerosis is one of the leading causes of death in Western countries, with high-density lipoproteins (HDL) playing an important protective role due to their ability to inhibit oxidation of low-density lipoproteins (LDL), thus relieving vascular subendothelial damage. One of the proteins constituting HDL particles is paraoxonase-1 (PON1), an enzyme able to hydrolyze aryl esters, lactones, and organophosphates. Other closely related paraoxonases are designated as PON2, which is a protein localized inside many different kinds of cells, and PON3, not only present in HDL but also in mitochondria and endoplasmic reticulum, as well. Given that the amount and the activity of PON1 in human serum are significantly lower in people suffering from cardiovascular diseases, enhancing both parameters might contribute to their treatment and prevention. One of the physiologically interesting substrates for the abovementioned hydrolytic cleavage is homocysteine thiolactone (HTL), an atherothrombotic active form of homocysteine. Although it was therefore postulated that PON1 would participate in preventing the HTL-mediated lipid peroxidation, some attention is recently paid to other enzymes, like biphenyl hydrolase-like protein, that seem to more selectively involved in lowering this risk factor. The aim of this paper is to elucidate the role of paraoxonases, especially PON1, by reviewing the latest studies in order to understand both its physiological role and modulation by drugs, nutrients, and plant extracts.

Metformin administration induces hepatotoxic effects in paraoxonase-1-deficient mice

Metformin is the first-line pharmacological treatment of diabetes. In these patients, metformin reduces body weight and decreases the risk of diabetes-related complications such as cardiovascular disease. However, whether metformin elicits beneficial effects on liver histology is a controversial issue and, as yet, there is no consensus. Paraoxonase-1 (PON1), an enzyme synthesized mainly by the liver, degrades lipid peroxides and reduces oxidative stress. PON1 activities are decreased in chronic liver diseases. We evaluated the effects of metformin in the liver of PON1-deficient mice which, untreated, present a mild degree of liver steatosis. Metformin administration aggravated inflammation in animals given a standard mouse chow and in those fed a high-fat diet. Also, it was associated with a higher degree of steatosis in animals fed a standard chow diet. This report is a cautionary note regarding the prescription of metformin for the treatment of diabetes in patients with concomitant liver impairment.

Anti-atherogenic properties of high-density lipoproteins in psychiatric patients before and after two months of atypical anti-psychotic therapy

Some of the medications used for the management of schizophrenia are associated with clinically significant increases in weight and adverse alterations in serum lipid levels. The aim of the study was to investigate the effect of short-term (two months) treatment with atypical anti-psychotics on coronary heart disease risk factors, including the functional properties of high-density lipoprotein (HDL), in psychiatric patients. Nineteen patients diagnosed with schizophrenia, schizoaffective, and bipolar disorder and ten healthy volunteers were enrolled in the study. In the present study blood was drawn at baseline and after two months of atypical anti-psychotic treatment. Wilcoxon non-parametric-test was used to examine differences in the psychotic group before and two months after treatment.Waist circumference and oxidative stress in psychiatric patients were higher compared with the control group. Serum-mediated cholesterol efflux capacity was lower in psychotic patients compared to controls. Two months of anti-psychotic therapy was associated with increased abdominal obesity, decreased paraoxonase lactonase activity, but with no further change in serum-mediated cholesterol efflux from macrophages. Psychotic patients have low serum-mediated cholesterol efflux from macrophages as a parameter of HDL functionality. Atypical anti-psychotic treatment for two months increased metabolic derangements in these patients but without further decrement in serum-mediated cholesterol efflux.

Fucoidan ameliorates steatohepatitis and insulin resistance by suppressing oxidative stress and inflammatory cytokines in experimental non-alcoholic fatty liver disease

Fucoidan, a sulfated polysaccharide derived from brown seaweeds, possesses a wide range of pharmacological properties. In the present study, we investigated the therapeutic effect of fucoidan on non-alcoholic fatty liver disease (NAFLD) in rats. Rats were fed a high-fat diet (HFD) for 12 weeks to induce NAFLD. Oral administrations of fucoidan (100mg/kg, orally), metformin (200mg/kg, orally) or the vehicle were started in the last four weeks. Results showed that administration of fucoidan for 4 weeks attenuated the development of NAFLD as evidenced by the significant decrease in liver index, serum liver enzymes activities, serum total cholesterol and triglycerides, fasting serum glucose, insulin, insulin resistance, and body composition index. Further, fucoidan decreased hepatic malondialdehyde as well as nitric oxide concentrations, and concomitantly increased hepatic reduced glutathione level. In addition, the effect of fucoidan was accompanied with significant decrease in hepatic mRNA expressions of tumor necrosis factor-α, interleukins-1β and matrix metalloproteinase-2. Furthermore, histopathological examination confirmed the effect of fucoidan. In conclusion, fucoidan ameliorated the development of HFD-induced NAFLD in rats that may be, at least partly, related to its hypolipidemic, insulin sensitizing, antioxidant and anti-inflammatory mechanisms.

Identification of master genes involved in liver key functions through transcriptomics and epigenomics of methyl donor deficiency in rat: relevance to nonalcoholic liver disease

SCOPE

Our study aims to investigate molecular events associated to methyl donor deficiency (MDD) by analyzing the transcriptome and the methylome of MDD rats in liver.

METHODS AND RESULTS

Twenty-one-day-old rats born to mothers fed either with a standard diet or a MDD diet during gestation and lactation were compared. From a total of 44 000 probes for 26 456 genes, we found two gene clusters in MDD rats whose expression levels had significant differences compared with controls: 3269 overexpressed (p < 0.0009) and 2841 underexpressed (p < 0.0004) genes. Modifications of DNA methylation were found in the promoter regions of 1032 genes out of 14 981 genes. Ontological analyses revealed that these genes are mainly involved in glucose and lipid metabolism, nervous system, coagulation, ER stress, and mitochondrial function.

CONCLUSION

Putative master genes exhibiting changes in both gene expression and DNA methylation are limited to 266 genes and are mainly involved in the renin-angiotensin system (n = 3), mitochondrion metabolism (n = 18), and phospholipid homeostasis (n = 3). Most of these master genes participate in nonalcoholic fatty liver disease. The adverse effects of MDD on the metabolic process indicate the beneficial impact of folate and vitamin B12, especially during the perinatal period.

Effects of rosiglitazone on serum paraoxonase activity and metabolic parameters in patients with type 2 diabetes mellitus

Human serum paraoxonase contributes to the anti-atherogenic effect of high-density lipoprotein cholesterol (HDL-C) and has been shown to protect both low-density lipoprotein cholesterol (LDL-C) and HDL-C against lipid peroxidation. We investigated the effects of rosiglitazone on paraoxonase activity and metabolic parameters in patients with type 2 diabetes mellitus [50 patients (30 males, 20 females); mean±SD age: 58.7±9.2 years, body mass index: 28.2±4.1'kg/m²], in whom glucose control could not be achieved despite treatment with metformin, sulphonylurea, and/or insulin. The patients were given 4'mg/day rosiglitazone for 3 months in addition to their usual treatment. Serum paraoxonase activity, malondialdehyde, homocysteine, and lipid profile were measured at the time of initiation and at the end of therapy with rosiglitazone. After rosiglitazone therapy, serum levels of HDL-C, apolipoprotein A-1, and paraoxonase activity increased significantly (P<0.05) and malondialdehyde, homocysteine, lipoprotein(a), and glucose levels decreased significantly (P<0.05), but no significant changes in levels of total cholesterol and apolipoprotein B were observed. Triglyceride levels also increased significantly (P<0.05). Rosiglitazone treatment led to an improvement in glycemic control and to an increase in paraoxonase activity and HDL-C levels. Although rosiglitazone showed favorable effects on oxidant/antioxidant balance and lipid profile, further studies are needed to determine the effect of rosiglitazone on cardiovascular risk factors and cardiovascular morbidity and mortality.

Paraoxonase-1 deficiency is associated with severe liver steatosis in mice fed a high-fat high-cholesterol diet: a metabolomic approach

Oxidative stress is a determinant of liver steatosis and the progression to more severe forms of disease. The present study investigated the effect of paraoxonase-1 (PON1) deficiency on histological alterations and hepatic metabolism in mice fed a high-fat high-cholesterol diet. We performed nontargeted metabolomics on liver tissues from 8 male PON1-deficient mice and 8 wild-type animals fed a high-fat, high-cholesterol diet for 22 weeks. We also measured 8-oxo-20-deoxyguanosine, reduced and oxidized glutathione, malondialdehyde, 8-isoprostanes and protein carbonyl concentrations. Results indicated lipid droplets in 14.5% of the hepatocytes of wild-type mice and in 83.3% of the PON1-deficient animals (P < 0.001). The metabolomic assay included 322 biochemical compounds, 169 of which were significantly decreased and 16 increased in PON1-deficient mice. There were significant increases in lipid peroxide concentrations and oxidative stress markers. We also found decreased glycolysis and the Krebs cycle. The urea cycle was decreased, and the pyrimidine cycle had a significant increase in orotate. The pathways of triglyceride and phospholipid synthesis were significantly increased. We conclude that PON1 deficiency is associated with oxidative stress and metabolic alterations leading to steatosis in the livers of mice receiving a high-fat high-cholesterol diet.