Improved specific assay for serum arylesterase using a water-soluble substrate

Paraoxonase-1: How a xenobiotic detoxifying enzyme has become an actor in the pathophysiology of infectious diseases and cancer

Both infectious and non-infectious diseases can share common molecular mechanisms, including oxidative stress and inflammation. External factors, such as bacterial or viral infections, excessive calorie intake, inadequate nutrients, or environmental factors, can cause metabolic disorders, resulting in an imbalance between free radical production and natural antioxidant systems. These factors may lead to the production of free radicals that can oxidize lipids, proteins, and nucleic acids, causing metabolic alterations that influence the pathogenesis of the disease. The relationship between oxidation and inflammation is crucial, as they both contribute to the development of cellular pathology. Paraoxonase 1 (PON1) is a vital enzyme in regulating these processes. PON1 is an enzyme that is bound to high-density lipoproteins and protects the organism against oxidative stress and toxic substances. It breaks down lipid peroxides in lipoproteins and cells, enhances the protection of high-density lipoproteins against different infectious agents, and is a critical component of the innate immune system. Impaired PON1 function can affect cellular homeostasis pathways and cause metabolically driven chronic inflammatory states. Therefore, understanding these relationships can help to improve treatments and identify new therapeutic targets. This review also examines the advantages and disadvantages of measuring serum PON1 levels in clinical settings, providing insight into the potential clinical use of this enzyme.

Paraoxonases and chemokine (C-C motif) ligand-2 in noncommunicable diseases

Oxidative stress and inflammation underpin most diseases; their mechanisms are inextricably linked. Chronic inflammation is associated with oxidation, anti-inflammatory cascades are linked to decreased oxidation, increased oxidative stress triggers inflammation, and redox balance inhibits the inflammatory cellular response. Whether or not oxidative stress and inflammation represent the cause or consequence of cellular pathology, they contribute significantly to the pathogenesis of noncommunicable diseases (NCD). The incidence of obesity and other related metabolic disturbances are increasing, as are age-related diseases due to a progressively aging population. Relationships between oxidative stress, inflammatory signaling, and metabolism are, in the broad sense of energy transformation, being increasingly recognized as part of the problem in NCD. In this chapter, we summarize the pathologic consequences of an imbalance between circulating and cellular paraoxonases, the system for scavenging excessive reactive oxygen species and circulating chemokines. They act as inducers of migration and infiltration of immune cells in target tissues as well as in the pathogenesis of disease that perturbs normal metabolic function. This disruption involves pathways controlling lipid and glucose homeostasis as well as metabolically driven chronic inflammatory states that encompass several response pathways. Dysfunction in the endoplasmic reticulum and/or mitochondria represents an important feature of chronic disease linked to oxidation and inflammation seen as self-reinforcing in NCD. Therefore, correct management requires a thorough understanding of these relationships and precise interpretation of laboratory test results.

A study of antioxidant activity in patients with schizophrenia taking atypical antipsychotics

INTRODUCTION

Atypical antipsychotics have significantly improved the quality of life for schizophrenic patients. Despite their beneficial effects, these antipsychotics induce weight gain, diabetes, and dyslipidemia. The aims of this study were to investigate the antioxidative activity of paraoxonase and assess lipid profile as a cardiovascular risk factor in patients with schizophrenia under long-term clozapine or risperidone treatment.

METHODS

The study included 66 patients with schizophrenia under clozapine or risperidone treatment and 19 healthy control subjects. Serum paraoxonase activities against paraoxon (PON(PO)), phenylacetate (PON(PA)), dihydrocoumarin (PON(DHC)), serum Trolox equivalent antioxidant activity (TEAC), antioxidant gap (GAP), and lipid profile were determined.

RESULTS

PON(DHC) activity was reduced in both antipsychotic drug-treated groups (clozapine 43.46 ± 1.06 U/ml, p < 0.001; risperidone 50.57 ± 1.54 U/ml, p < 0.01; control 52.27 ± 1.34 U/ml). A similar pattern was observed for the PON(DHC)/HDL-cholesterol (HDLC) ratio. On the contrary, PON(PO) and PON(PA) were increased in the treated group, but the corresponding paraoxonase/HDLC ratios were not significantly different from controls, except for PON/HDLC in the clozapine group. TEAC and GAP were only decreased in the clozapine-treated group.

CONCLUSIONS

In patients with schizophrenia, clozapine or risperidone treatment had different effects on various paraoxonase activities. The results of the present study suggest that patients with schizophrenia might be at increased risk for metabolic and cardiovascular disease related to reduced PON(DHC), TEAC, and GAP.

Interrelationships between paraoxonase-1 and monocyte chemoattractant protein-1 in the regulation of hepatic inflammation

Oxidative stress and inflammation play a central role in the onset and development of liver diseases irrespective of the agent causing the hepatic impairment. The monocyte chemoattractant protein-1 is intimately involved in the inflammatory reaction and is directly correlated with the degree of hepatic inflammation in patients with chronic liver disease. Recent studies showed that hepatic paraoxonase-1 may counteract the production of the monocyte chemoattractant protein-1, thus playing an anti-inflammatory role. The current review summarises experiments suggesting how paraoxonase-1 activity and expression are altered in liver diseases, and their relationships with the monocyte chemoattractant protein-1 and inflammation.

Serum paraoxonase 1 activity status in patients with liver disorders

BACKGROUND/AIM

Paraoxonase 1 (PON1) is an esterase, exclusively synthesized by liver. The present study has two objectives: to determine the PON1 activity status in various disorders associated with hepatocellular damage and to correlate the changes of PON1 activity with the standard liver function and fasting lipid profile tests in these disorders.

PATIENTS AND METHODS

The study groups consisted of 95 patients with liver diseases including acute viral hepatitis (14), cirrhosis with portal hypertension (33), leptospirosis (14), sepsis and multi organ failure (15), left ventricular failure (9), and falciparum malaria (10); and 53 healthy controls. Serum PON1 activity was measured manually using spectrophotometer. Liver function test parameters and fasting lipid profile were performed in clinical chemistry auto analyzer (Hitachi 912).

RESULTS

The serum PON1 activity in patients with acute viral hepatitis and sepsis decreased significantly ( P < 0.001) and moderately in falciparum malaria ( P < 0.05). However, in patients with cirrhosis, leptospirosis and left ventricular patients, its activity did not change significantly. On applying Pearson correlation, serum PON1 activity correlated positively with high-density lipoprotein-cholesterol (HDL-C) in patients with sepsis (r=0.633, P < 0.05), left ventricular failure patients (r=0.814, P < 0.05) and negatively with acute viral hepatitis patients (r=-0.528, P <0.05).

CONCLUSION

PON1 activity has decreased significantly in acute viral hepatitis, sepsis with multi organ failure and falciparum malaria patients. Determination of PON1 activity may serve as a useful additional test in assessing these conditions.

The paraoxonases: role in human diseases and methodological difficulties in measurement

Research into the paraoxonase (PON) gene family has flourished over the past few years. In the 1970s and 1980s, only PON1 was known, and the investigations were conducted, essentially, by toxicologists focusing on protection against organophosphate poisoning. Since then, two new members of the family, PON2 and PON3, have been identified, both being shown to play antioxidant and anti-inflammatory roles. Evidence exists indicating that the PON family is central to a wide variety of human illnesses such as cardiovascular disease, diabetes mellitus, metabolic syndrome, obesity, non-alcoholic steatohepatitis, and several mental disorders. However, research is hampered considerably by the methods currently available to measure the activity of these enzymes. In this review, we summarize the state of knowledge on PON biochemistry and function, the influence of genetic variations, and the involvement of PON in several diseases. The problems associated with PON measurement, such as sample acquisition, lack of reference methods, and variety of substrates, will be presented. Also, we cover some of the present lines of research and propose some others for future progress in this field.

Serum Paraoxonase Activity: A New Additional Test for the Improved Evaluation of Chronic Liver Damage

Background: Paraoxonase 1 (PON1) is an ester hydrolase present in serum and in the liver. The aims of the present study were to investigate the following: (a) the relationship between serum PON1 activity alterations and the degree of liver damage in patients with chronic liver disease; (b) the influence of genetic variability on serum PON1 activity; and (c) the efficacy of serum PON1 activity measurement, alone and in combination with standard liver function tests, in the assessment of liver damage.

Methods: We studied 68 patients with liver cirrhosis, 107 patients with chronic hepatitis, and 368 apparently healthy volunteers. Baseline and salt-stimulated PON1 activities were measured by the hydrolysis of paraoxon. PON1 genotyping at positions 55 and 192 was analyzed by PCR and restriction isotyping.

Results: Baseline and stimulated PON1 activities were decreased (P &lt;0.001) in chronic hepatitis and in liver cirrhosis. PON1 activity was significantly correlated with serum total proteins, albumin, and bilirubin in patients but not in controls. There were no significant differences with respect to allele and genotype frequencies between patients and controls. The combination of baseline serum PON1 with five standard biochemical tests had a higher classification accuracy (94% of patients; 96% of controls) than the five standard tests alone (75% of patients; 96% of controls). ROC plots demonstrated a high diagnostic accuracy for baseline serum PON1 [area under the curve, 0.89 (95% confidence interval, 0.86–0.93) in chronic hepatitis and 0.96 (95% confidence interval, 0.94–0.99) in cirrhosis]. Baseline PON1 provided the highest ROC area for cirrhosis vs controls.

Conclusions: The significant decrease of PON1 activity in chronic liver diseases is related to the degree of hepatic dysfunction and not to allelic or genotypic differences. Addition of serum PON1 activity measurement to the current battery of tests may improve the evaluation of chronic liver diseases.

Continuous monitoring of arylesterase in human serum

Arylesterase (EC 3.1.1.2) activity in serum was specifically measured using thiophenyl acetate in a mechanized assay at 37 degrees C with 4-bromophenylboronic acid as inhibitor of cholinesterase and hexacyanoferrate-III as indicator. The systematic development of a routine method, apparent limitations of thiophenyl compounds as arylesterase substrates, some kinetic constants of the enzyme, analytical variables such as precision (within-run <2% and between-run <2.5% relative standard deviation) and a preliminary reference interval (19.5-52.4 kU/l) for adults are described.

Molecular weight and substrate characteristics of human serum arylesterase following purification by immuno-affinity chromatography

Human serum arylesterase (EC 3.1.1.2) was purified over 400-fold with a recovery of 61-78% by single-step immuno-affinity chromatography using a monoclonal antibody, 12-1H8, as the adsorbent. The resultant preparation behaved as one component on SDS-PAGE with an apparent M(r) of 46,000, indicating its high homogeneity. Molecular weight was determined as 380,000 Da by HPLC on TSK-gel G-3000SW. The arylesterase molecule would thus appear to be comprised of octameric subunits. The purified protein hydrolyzed paraoxon. The present study suggests that a separate classification of EC 3.1.8.1 for its paraoxon hydrolyzing activity may not be appropriate to differentiate from arylesterase activity. In addition, the substrate for arylesterase is discussed in terms of its chemical structure.

ELISA using monoclonal antibody to human serum arylesterase

ELISA for determining arylesterase content in human serum has been developed by the one-step sandwich method using 2 monoclonal antibodies. While the content of arylesterase in healthy adults was 81 +/- 25 mg/l, a decrease was observed in patients with liver cirrhosis, where the mean +/- SD was 37 +/- 7 mg/l. ELISA of human serum arylesterase correlated with the activity determined by a specific substrate assay we devised recently.