PON1 activity is inversely related to LDL apoB carbonyl content in patients with coronary artery disease

The objective of this study was to investigate apolipoprotein B (apoB) carbonyl content as a parameter for studying low-density lipoprotein (LDL) oxidation in coronary artery disease (CAD) risk assessment and to explore the relationship between apoB carbonyl content (an index of protein oxidation) and paraoxonase 1 (PON1) activity in CAD patients and controls. A total of 200 patients suffering from CAD and 150 normal individuals were included in the present study. CAD patients were classified into two groups on the basis of associated risk factors (diabetes mellitus, hypertension): group 1 (n = 120; CAD patients with associated risk factors) and group 2 (n = 80; CAD patients with no associated risk factors). All subjects were assayed for apoB carbonyl content, LDL-malondialdehyde (LDL-MDA), PON1 activity, and lipid and apolipoprotein levels. ApoB carbonyl content was significantly (p < 0.01) raised in CAD patients (with or without associated risk factors) as compared to controls. Patients also had relatively raised LDL-MDA levels. Serum PON1 activity was significantly low (p < 0.01) in CAD patients. A significantly (p < 0.01) negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. CAD patients with associated risk factors had highly raised (p < 0.01) apoB carbonyl content and considerably depressed PON1 activity compared to those with no associated risk factors. LDL-MDA levels did not differ significantly (p > 0.05) between the two groups. CAD patients in group 1 also had significantly raised apoB levels and low HDL-cholesterol and apoA1 levels as compared to patients in group 2, while the other lipid variables did not show any significant difference. A significantly negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. This is a new piece of information that needs to be further explored. Quantification of apoB carbonyl content may act as a suitable parameter for studying LDL oxidation in the evaluation of CAD risk, especially when confounding risk factors are present.     

The ratio of serum paraoxonase/arylesterase activity using an improved assay for arylesterase activity to discriminate PON1(R192) from PON1(Q192)

Human serum paraoxonase (PON1) exists in 2 major polymorphic forms: Q (glutamine) or R (arginine) at codon 192. The PON1(192) activity polymorphism is substrate dependent. The PON1(Q192) isoform has a higher rate of in vitro hydrolysis of diazoxon, sarin, and soman, whereas the PON1(R192) isoform has higher activity for the hydrolysis of paraoxon and chlorpyrifos oxon. Both isoforms hydrolyze phenyl acetate at approximately the same rate. The present study described and evaluated a kinetic method of arylesterase activity determination with a modified fixed incubation method that used the oxidative coupling of phenol with 4-aminoantipyrine of phenyl acetate as the substrate. Our improved method shows that arylesterase activity is lower with the PON1(R192) isoform than with the PON1(Q192) isoform. The average activities of serum of individuals of a specific PON1(Q192) genotype showed higher arylesterase and lower paraoxonase activity than the PON1(R192) genotype. The ratio of paraoxonase/arylesterase activity showed a clear separation of all three PON1(192) genotypes with no overlap between the groups (QQ: < 5.0, QR: 5.0-11.0, RR: > 11.0). PCR has suggested that the PON1(192) phenotypes correspond to the PON1(192) genotypes. Therefore, when conducting epidemiological or mechanistic studies that examine the role of PON1 in organophosphorus or lipid metabolism, this ratio is more useful and informative than a PCR-based genotype alone.     

Age-related decrease in the activity of collagenase in the femoral head in patients with hip osteoarthritis

The aim of the study was to evaluate the relation between the activity of collagenase in the subchondral bone of the femoral head and the age of patients with hip osteoarthritis. Thirty-two patients were enrolled into the study. The mean age was 66 (range from 37 to 80 years). Bone samples of the femoral head were harvested during total hip replacement. The activity of collagenase was measured through spectrofluorimetry. We found statistically a significant correlation between collagenase activity in the bone and age. The mean activity of collagenase in younger patients (37–68 years) was 64.17 IU/μg. In older patients (69–80 years), the mean collagenase activity was 52.26 IU/μg. In patients with hip osteoarthritis the activity of collagenase in the subchondral bone of the femoral head tended to decrease with an increase in age.     

Blunted coronary vasoreactivity to insulin is an early alteration in hypertension

Insulin resistance in the heart is not localized to the myocardium, but may also occur in blood vessels. We studied the effects of insulin on coronary vasodilation in hypertension. Coronary vascular resistance was quantitated in 11 nonsmoking men with untreated mild essential hypertension and 9 healthy normotensive men using positron emission tomography and (15)O-labeled water. The measurements were performed at baseline and during adenosine infusion (140 microg x kg(-1) x min(-1)) with or without simultaneous euglycemic physiological (serum insulin approximately 70 mU/l) and supraphysiological (serum insulin approximately 460 mU/l) hyperinsulinemia. Coronary resistance was significantly higher in hypertensive than normotensive subjects at baseline and during adenosine infusion. Physiological hyperinsulinemia decreased hyperemic coronary resistance significantly in both groups. Supraphysiological hyperinsulinemia further decreased the hyperemic coronary resistance in normotensive but not in hypertensive subjects, leading to higher hyperemic coronary resistance in hypertensive than normotensive subjects (27.2 +/- 8.7 vs. 19.2 +/- 4.9 mm Hg x min x g x ml(-1), p < 0.05). However, insulin-stimulated whole body glucose uptake values were similar between the groups during both insulin infusions. In conclusion, insulin-induced coronary vasodilation is blunted in young subjects with mild essential hypertension who are otherwise healthy. Coronary vascular resistance to insulin occurs although no change in peripheral glucose uptake can be detected. While we do not know whether the same results can be extrapolated to female or older subjects, these results indicate a novel defect in the regulation of coronary arteries in the early phase of hypertension.     

Fibrinogen is an antioxidant that protects beta-lipoproteins at physiological concentrations in a cell free system

Oxidation of beta-lipoproteins has been linked to the development of arteriosclerosis. Using a copper mediated cell free system to oxidize beta-lipoproteins, we found that beta -lipoproteins isolated from plasma were less susceptible to oxidation than lipoproteins from serum and that this was probably due to inhibition by fibrinogen, because removal of fibrinogen from plasma enhanced oxidation, while addition of fibrinogen restored inhibition. Fibrinogen inhibited conjugated diene formation and peroxide formation assayed by the xylenol orange assay (absorbance+/-confidence interval: 0.155+/-0.007 with fibrinogen vs 0.255+/-0.014 without) and retarded copper mediated oxidation of apolipoproteins in low density lipoproteins, reducing the distance of electrophoretic migration by 5 mm. The effect of fibrinogen was not due to chelation of copper, since it provided protection when hydrogen peroxide was substituted for copper as an oxidizing agent. At normal physiological concentration equivalents, fibrinogen showed superior antioxidant properties compared to albumin, melatonin, vitamin C and vitamin E and was superior to the vitamins when compared on an equimolar basis. Other studies have shown the fibrinogen to be more oxidizable than other major plasma proteins and to inhibit peroxide production. Because of its high mass concentration, we postulate fibrinogen is an important antioxidant protecting beta-lipoproteins in plasma and that it may be important in protecting lipoproteins in tissue spaces.     

The biphasic ventilatory response to hypoxia in preterm infants is not due to a decrease in metabolism

The mechanism underlying the biphasic ventilatory response to hypoxia in neonates is poorly understood. Because alveolar P_CO2 (P_ACO2) decreases and remains low during hypoxia, it has been argued that a decrease in metabolism may occur. We hypothesized that if the late decrease in ventilation during hypoxia is due to a decrease in CO₂ production, an increase in P_ACO2 should abolish it. We studied 27 preterm infants [birth weight, 1,700 ± 41 g (mean ± SEM); study weight, 1,760 ± 36 g; gestational age 32 ± 0.2 weeks; postnatal age, 17 ± 1 days]. A flow-through system and Beckman analyzers were used to measure ventilation and alveolar gases. Metabolism was expressed as changes in oxygen consumption. Infants were studied randomly during hypoxia alone (15% O₂ + N₂, n = 55) and during hypoxia plus CO₂, (0.5% CO₂, n = 30; 2% CO₂, n = 10). Each experiment consisted of 2 minutes of control measurements (21% O₂), 5 minutes of measurements during hypoxia alone or hypoxia plus CO₂, followed by 2 minutes of recovery (21% O₂). We found a biphasic response to hypoxia with or without CO₂ supplementation, the percent change in ventilation from initial peak hyperventilation to late hypoventilation at 5 minutes being -16 ± 2 on 15% O₂; -9 ± 3 on 15% O₂; + 0.5% CO₂ and -15 ± 9 on 15% O₂; + 2% CO₂; (P < 0.05).The decrease in ventilation was primarily due to a significant decrease in frequency; tidal volume increased. Oxygen consumption decreased similarly with the various inspired gas mixtures during hypoxia. These findings indicate that the decrease in ventilation during hypoxia is unlikely to be solely due to a decrease in metabolism since the late decrease in ventilation following initial hyperventilation still occurred despite the elimination of a fall in P_ACO2. We speculate that the mechanism underlying the late decrease in ventilation is likely of central origin, probably mediated through the release of inhibitory neurotransmitters. Pediatr Pulmonol. 1996; 22:287–294. © 1996 Wiley-Liss, Inc.     

Age-related decrease in serum angiotensin converting enzyme activity: the role of thyroidal status and food intake

The serum ACE activity was determined in male Fischer 344 rats at 2, 6, 13, and 25 months of age to determine whether serum angiotensin converting enzyme (ACE) activity is a potential biomarker of tissue hypothyroidism in aged rats. Since rodent serum contains an ACE activity inhibitor, the measurements were done in both undiluted and 1:8 diluted sera. The highest serum inhibitor activity was found in the 2-month-old animals. The serum ACE activity measured in the diluted serum of the aged rats (77.6 +/- 2.9 units/ml) was significantly reduced compared to 2-month-old (178.2 +/- 6.4 units/ml), 6-month-old (101.5 +/- 6.1 units/ml) and 13-month-old rats (84.9 +/- 8.6 units/ml); (p less than 0.001). Hyperthyroidism induced by injecting L-triiodothyronine (T3) 15 micrograms/100 gm body weight intraperitoneally for 10 days increased the serum ACE activity in the older rats, but reduced the levels in 2-month-old rats. There was no significant change in 6-month-old rats. The levels of serum ACE activity in hypothyroid 6-month-old rats (95.5 +/- 3.5 units/ml) and in 2-month-old-rats (94.2 +/- 4.0 units/ml) were similar to the level seen in hypothyroid old rats (88.9 +/- 5.8 units/ml). Pair feeding of young rats (8 months old) with old did not alter the baseline ACE level (117.4 +/- 3.7 units/ml) or the T3 stimulated (105.2 +/- 10.2 units/ml) serum ACE activity. It is concluded that the reduced serum ACE activity in aged rats cannot be accounted for by the reduced caloric intake or reduced serum thyroid hormone levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human serum albumin inhibits prostacyclin production by endothelial cells: the relation of the inhibitory activity to sulfhydryl groups in albumin

Human serum inhibited calcium ionophore-induced production of prostacyclin by cultured bovine aortic endothelial cells. The inhibitory fraction was purified from serum by anion-exchange and Blue-Sepharose affinity chromatography. The molecular weight of the purified substance was 67k dalton as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was identified as human serum albumin by N-terminal amino acid sequence analysis. Human serum albumin was separated to two forms by high-performance liquid chromatography: mercaptalbumin (SH type) and nonmercaptalbumin (SS type). Both types of albumin inhibited the conversion of arachidonic acid to prostaglandin H2 in a dose-dependent manner without affecting phospholipase A2 or prostacyclin synthetase. This inhibition was more potent in mercaptalbumin than in nonmercaptalbumin. These results suggest that the conversion between mercaptalbumin and nonmercaptalbumin may play an important role in the modulation of prostacyclin synthesis by endothelial cells.     

The story of PON1: how an organophosphate-hydrolysing enzyme is becoming a player in cardiovascular medicine

Since the discovery of human serum paraoxonase (PON1), the enzyme has been the subject of various fields of research. Initially, PON1 was identified as an enzyme capable of hydrolysing organophosphate compounds, but there is a growing body of evidence that PON1 plays a role in lipid metabolism and the onset of cardiovascular disease. Still, the precise mechanism by which PON1 functions in vivo remains to be clarified. Here we will briefly review developments in the field of PON1 research which merit further attention.     

Paraoxonase 1 (PON1) is a more potent antioxidant and stimulant of macrophage cholesterol efflux, when present in HDL than in lipoprotein-deficient serum: relevance to diabetes

The present study analyzed serum paraoxonase 1 (PON1) distribution among HDL and lipoprotein-deficient serum (LPDS) in atherosclerotic patients, and compared PON1 biological functions in these fractions. Serum HDL and LPDS fractions were isolated from control healthy subjects, diabetic and hypercholesterolemic patients. PON1 activities and protein in HDL/LPDS, as well as its ability to protect against lipid peroxidation and to stimulate HDL/LPDS-mediated macrophage cholesterol efflux were measured. In LPDS from controls, PON1 protein and a significant paraoxonase activity were found, whereas arylesterase and lactonase activities were substantially reduced compared to HDL, by 78% and 88%, respectively. In diabetic patients, PON1 protein and paraoxonase activity in HDL were significantly decreased by 2.8- and 1.7-fold, respectively, compared with controls' HDL. In parallel, in these patient's LPDS, PON1 protein and paraoxonase activity were markedly increased by 3.7- and 1.7-fold, respectively, compared with controls' LPDS. PON1 in HDL (but not PON1 in LPDS) significantly decreased AAPH-induced lipid peroxides formation by 33%, and increased macrophage cholesterol efflux by 31%. We conclude that PON1 is less antiatherogenic when present in LPDS than in HDL. The abnormal serum PON1 distribution in diabetic patients, could be responsible for the accelerated atherosclerosis development in these patients.     

Cooperative effect of hydrocortisone, adrenaline and high-density lipoproteins in regulating the glucose-6-phosphate dehydrogenase activity of the liver

The role of adaptive hormones and serum lipoproteins in the regulation of glucose-6-phosphate dehydrogenase (G-6-PDH) activity was investigated. The test was performed on experimental hepatic sections of Wistar rats. It was shown that timely regulation of G-6-PDH by epinephrine and hydrocortisone which inhibits the activity of enzyme is manifested through the cAMP-dependent mechanism. The cooperative effect of epinephrine, hydrocortisone and high-density lipoproteins that enables G-6-PDH activation was revealed. It was stated that only high-density lipoproteins of subpopulation III were capable of hormonal mediating. The effect was caused by the induction of enzyme synthesis and manifested through lysosome-dependent activation of chromatin.     

Protective effect of paraoxonase activity in high-density lipoproteins against erythrocyte membranes peroxidation: a comparison between healthy subjects and type 1 diabetic patients

High-density lipoproteins (HDL) plays a key role in the protection against oxidative damage of lipoprotein and biological membranes. The aim of the present study was to investigate the relationship between the antioxidant role of HDL and the HDL-paraoxonase (PON) activity in healthy subjects and in type 1 diabetic patients. Moreover, the ability of HDL of controls and diabetic patients to protect and/or repair biological membranes from oxidative damage was studied. HDL were isolated from 31 type 1 diabetic patients and 31 sex- and age-matched healthy subjects and immediately used to evaluate lipid hydroperoxides and HDL-PON activity. Erythrocyte membranes obtained from healthy subjects were oxidized with 2,2-azo-bis(2-aminidinopropane)dihydrochloride and then incubated in the presence of HDL isolated from healthy or type 1 diabetic subjects, with measurements of membrane lipid hydroperoxides before and after the incubation. HDL from type 1 diabetic patients showed higher levels of lipid hydroperoxides and a lower activity of HDL-PON than healthy subjects. Moreover, HDL of type 1 diabetic patients protected less efficiently erythrocyte membranes against oxidative damage compared with HDL from healthy subjects. A negative correlation was found between HDL-PON activity and the levels of hydroperoxides of HDL, confirming the relationship between PON and lipid peroxidation and suggesting that subjects with low PON activity are more exposed to oxidative damage than subjects with high PON activity. The ability of HDL to protect erythrocyte membranes was positively correlated with HDL-PON activity and negatively correlated with the levels of lipid hydroperoxides of HDL of healthy subjects. These results confirm a linkage between PON activity and lipid peroxidation of lipoproteins and suggest that the ability of HDL to protect erythrocyte membranes might be related to the PON activity. It might be hypothesized that the decrease of PON activity in diabetic patients and the lower HDL protective action against membrane peroxidation could contribute to acceleration of arteriosclerosis in type 1 diabetes mellitus.     

Higher level of plasma cholesteryl ester transfer activity from high-density lipoprotein to Apo B-containing lipoproteins in subjects with angiographically detectable coronary artery disease

Background and hypothesis: Plasma high-density lipoprotein cholesterol (HDL-C) levels correlate inversely with the incidence of coronary artery disease. In order to ascertain whether the transfer activity is related to coronary atherosclerosis, we studied plasma cholesteryl ester transfer activity (CETA) from HDL to apo B-containing lipoproteins in a consecutive series of 64 Japanese men aged <60 years who had undergone diagnostic coronary angiography. Methods: The subjects were divided into two groups: those who had ≥50% luminal stenosis in one or more coronary arteries (Group 1) and those who had <50% stenosis (Group 2). Results: CETA was 20.8±6.0%/2h in 38 subjects in Group 1. significantly higher than 17.4±6.9%/2h in 26 subjects in Group 2(p<0.05). Plasma HDL-C levels in Group 1 were significantly lower than those in Group 2(p<0.05). CETA correlated inversely with HDL-C levels (r = ?0.46, p<0.001). Plasma total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and Lp(a) levels did not differ significantly between the two groups. There was no significant correlation between CETA and either LDL-C or TG levels. Conclusion: Results suggest that high CETA is realted to low plasma HDL-C levels and may lead to the development of coronary atherosclerosis. Also, CETA was independent of plasma LDL-C or TG levels.     

The failure of the ACCLAIM trial is due to an irrational technology

The excessive blood oxidation devised with the Celacade System does not procure any advantage in chronic heart failure's patients. The irrationality of the procedure delays a therapeutic advantage and ought to be fully revised.     

Metabolomics reveals that aldose reductase activity due to AKR1B10 is upregulated in hepatitis C virus infection

To understand the changes in the metabolome of hepatitis C virus (HCV)‐infected persons, we conducted a metabolomic investigation in both plasma and urine of 30 HCV‐positive individuals using plasmas from 30 HCV‐negative blood donors and urines from 30 healthy volunteers. Samples were analysed by gas chromatography–mass spectrometry and data subjected to multivariate analysis. The plasma metabolomic phenotype of HCV‐positive persons was found to have elevated glucose, mannose and oleamide, together with depressed plasma lactate. The urinary metabolomic phenotype of HCV‐positive persons comprised reduced excretion of fructose and galactose combined with elevated urinary excretion of 6‐deoxygalactose (fucose) and the polyols sorbitol, galactitol and xylitol. HCV‐infected persons had elevated galactitol/galactose and sorbitol/glucose urinary ratios, which were highly correlated. These observations pointed to enhanced aldose reductase activity, and this was confirmed by real‐time quantitative polymerase chain reaction with AKR1B10 gene expression elevated sixfold in the liver. In contrast, AKR1B1 gene expression was reduced 40% in HCV‐positive livers. Interestingly, persons who were formerly HCV infected retained the metabolomic phenotype of HCV infection without reverting to the HCV‐negative metabolomic phenotype. This suggests that the effects of HCV on hepatic metabolism may be long lived. Hepatic AKR1B10 has been reported to be elevated in hepatocellular carcinoma and in several premalignant liver diseases. It would appear that HCV infection alone increases AKR1B10 expression, which manifests itself as enhanced urinary excretion of polyols with reduced urinary excretion of their corresponding hexoses. What role the polyols play in hepatic pathophysiology of HCV infection and its sequelae is currently unknown.