© 1995 American Heart Association, Inc.
Articles |
Serum Paraoxonase Activity, Concentration, and Phenotype Distribution in Diabetes Mellitus and Its Relationship to Serum Lipids and Lipoproteins
From the University Department of Medicine, Manchester Royal Infirmary (UK).
Correspondence to Michael I. Mackness, Department of Medicine, University of Manchester, Manchester Royal Infirmary, Oxford Rd, Manchester M13 9WL, UK.
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Abstract Human serum paraoxonase is physically associated with HDL and has been implicated in the detoxification of organophosphates and possibly in the prevention of LDL lipid peroxidation. We investigated the serum activity and concentration of paraoxonase in 78 patients with type 1 diabetes mellitus, 92 with type 2 diabetes, and 82 nondiabetic control subjects. Paraoxonase activity was generally lower in diabetics than in control subjects. This decrease was unrelated to differences in paraoxonase phenotype distribution or its serum concentration. Rather, the difference in paraoxonase activity was explained by its specific activity, which was lower in diabetics, indicating either the presence of a circulating inhibitor or disturbance of the interaction of paraoxonase with HDL affecting its activity. Paraoxonase specific activity was lowest in patients with peripheral neuropathy, suggesting an association of paraoxonase with neuropathy. In control subjects but not patients with diabetes, paraoxonase correlated with HDL cholesterol and apolipoprotein A-1. Our results indicate that the low paraoxonase activity in diabetes is due to decreased specific activity. In other studies low serum paraoxonase activity has been associated with increased susceptibility to atherosclerosis, and the present results also suggest an association with peripheral neuropathy, which could be due to reduced capacity to detoxify lipid peroxides in diabetes.
Key Words: paraoxonase • high-density lipoprotein • apolipoprotein A-1 • neuropathy • diabetes mellitus
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Introduction |
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Paraoxonase (aryldialkylphosphatase [EC 3.1.8.1]) is a serum esterase that is synthesized by the liver and hydrolyzes aromatic carboxylic acid esters and organophosphorus insecticides and nerve gases.1 Many studies have indicated the existence of a genetic polymorphism of paraoxonase in Europid populations that is a determinant of its activity (for review, see Reference 22 ). This polymorphism is due to an amino acid substitution in the active site of the enzyme, giving rise to low- and high-activity isoenzymes.3 4 The resulting polymorphic variation in serum paraoxonase activity may affect the metabolism of organophosphates in individuals at risk of exposure and therefore increase the risk of acute organophosphate intoxication or of organophosphorus-induced delayed polyneuropathy.5
In human serum, paraoxonase is in close physical association with HDL,6 7 which thus acts as its carrier and site of action. Several epidemiological studies have shown serum HDL concentration to be inversely related to the risk of developing atherosclerosis.8 9 Currently the oxidation of LDL in the artery wall is believed to have a central role in atherogenesis (for review, see Reference 1010 ). Recently HDL was shown to be effective in preventing the oxidative modification of LDL in vitro,11 12 probably due to a mechanism that is at least partly enzymatic.12 Paraoxonase isolated from human HDL in liposomes has also been shown to decrease the susceptibility of LDL to lipid peroxidation.13 This suggests a potential role for paraoxonase in the detoxification of lipid peroxides and suggests that individuals with a low paraoxonase activity phenotype may have a greater risk of developing a disease such as atherosclerosis, which may involve lipid peroxidation, than high-activity individuals.
Populations with insulin-dependent diabetes mellitus have been shown to have marked reductions in serum paraoxonase activity without having a significantly lower HDL cholesterol concentration.14 Furthermore, streptozotocin-induced diabetes results in a progressive decrease in serum paraoxonase activity.15 Therefore, the decrease in activity of serum paraoxonase associated with diabetes may play a role in the increased incidence of premature atherosclerosis associated with this disease. Furthermore, it may influence susceptibility to neuropathy, in which lipid peroxidation has also been implicated.16
In this report we show that low serum paraoxonase activity in type 1 and type 2 diabetes is caused by low paraoxonase specific activity and that this effect is even more marked in subjects with clinical peripheral neuropathy.
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Methods |
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Subjects
The control population consisted of 82 apparently healthy people not taking medication, who either attended a routine health check at a general practice or were staff of the Manchester Royal Infirmary. The patients studied were attending the Manchester Diabetes Centre and comprised 78 men and women with type 1 diabetes mellitus, 32 of whom had clinical neuropathy, and 92 patients with type 2 diabetes, including 41 with clinical neuropathy. Diabetes mellitus was diagnosed according to the 1980 World Health Organisation Expert Committee Report.17
Neuropathy was diagnosed clinically on the basis of a modified neuropathy disability score derived from the findings on examination. Pain, temperature, and vibration perception were scored as either 0 for present or 1 for absent for each leg. Ankle reflexes were scored as 0 for present, 1 for present with reinforcement, and 2 for absent for each side. Thus, summing the scores for both sides, the maximum possible score on this scale is 10, which would imply complete absence of sensory perception and absent ankle reflexes on both sides. A score of 6 or greater, representing moderate to severe neuropathy, was deemed to be diagnostic of peripheral neuropathy.18
All of the type 1 patients were receiving insulin therapy (dose,
48.5±17.0 U/d). Thirteen of the type 2 patients with
neuropathy were receiving insulin therapy (dose, 53.0±34.0
U/d), 10 were receiving treatment with oral hypoglycemic agents, and 4
were being treated by diet only. Of the type 2 patients without
neuropathy, 9 were receiving insulin therapy (dose,
34.3±28.8 U/d), 9 were receiving treatment with oral hypoglycemic
drugs, and 33 were being treated by diet only. One type 2 patient was
receiving treatment with an angiotensin-converting
enzyme inhibitor, and the diet of another was supplemented
with 
-linolenic acid. The demographic characteristics of
the control and diabetic populations are given in Table 1
.
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This study was approved by the Central Manchester Health Authority Research Ethics Committee.
Blood Sampling
Venous blood was obtained from the control and diabetic subjects
between 9 and 10 AM after a 12-hour fast. Serum and EDTA
plasma were obtained by low-speed centrifugation.
Plasma was used immediately to separate HDL. Serum and HDL were stored
at -20°C before further analysis.
Analytical Methods
Plasma HDL (d=1.063 to 1.21 g/mL) was isolated by
ultracentrifugation in an L7-55
ultracentrifuge fitted with a 50.4 Ti rotor (Beckman
Instruments).19 Serum triglycerides were
measured by the enzymatic GPO-PAP method (Biostat Ltd). Total serum
cholesterol and HDL cholesterol were determined
by the CHOD-PAP method (Biostat Ltd). We measured serum apolipoprotein
(apo) B and apoA-1 by rate immunonephelometric techniques using the
Beckman Array with antisera and standards supplied by the
manufacturer.
Analysis of Paraoxonase Activity
Before the analysis of paraoxonase activity, serum was
preincubated with 5x10-6 mol/L eserine
for 10 minutes at room temperature to inhibit serum
butyrylcholinesterase activity, which is markedly elevated in diabetes
and would otherwise interfere with the determination of paraoxonase
activity in serum from individuals with diabetes. Preliminary
experiments showed that these conditions completely inhibited
butyrylcholinesterase without affecting paraoxonase activity.
Paraoxonase activity was measured by adding serum to 1 mL Tris/HCl buffer (100 mmol/L, pH 8.0) containing 2 mmol/L CaCl2 and 5.5 mmol/L paraoxon (O,O-diethyl-O-p-nitrophenylphosphate; Sigma Chemical Co). The rate of generation of p-nitrophenol was determined at 405 nm, 25°C, with the use of a continuously recording spectrophotometer (Beckman DU-68).
Paraoxonase Phenotype Distribution
The phenotypic distribution of paraoxonase activity was
determined by the dual substrate method.20 Briefly, the
ratio of the hydrolysis of paraoxon in the presence of 1 mol/L NaCl
(salt-stimulated paraoxonase) to the hydrolysis of phenylacetate
was used to assign individuals to one of the three possible
phenotypes: AA (homozygous low activity), AB (heterozygous
activity), or BB (homozygous high activity), which are defined by
ratios of activity with the ranges 1.21±0.19 for AA, 4.68±0.85 for
AB, and 8.36±0.70 for BB. These ratios were used to assign
phenotype in all the populations studied.
Serum Paraoxonase Concentration
Serum paraoxonase concentration was determined by our
competitive enzyme-linked immunosorbent assay (ELISA), which has
been described in detail.21
Calibration of Paraoxonase Immunoassay
Fasting, normolipemic serum was pooled and stored in 250-µL
aliquots at -20°C. The paraoxonase concentration of this pool
was determined by SDS-PAGE followed by Western blotting.21
Dilutions of the pooled standard serum (0.2 to 1.2 µL) and purified
paraoxonase (10 to 120 ng) were subjected to SDS-PAGE on
one-dimensional slab gels. After electrophoresis, the protein
profiles were electrotransferred to nitrocellulose sheets and then
hybridized, first with rabbit anti-human paraoxonase polyclonal
antibody (1/5000 dilution) and then with sheep anti-rabbit IgG
peroxidase conjugate (1/5000 dilution, Sigma Chemical Co).
The stained nitrocellulose sheets were scanned with a densitometer (Molecular Dynamics), and the intensity of the band corresponding to paraoxonase was measured. A calibration curve was constructed from the optical density of the purified paraoxonase samples and used to quantify the concentration of paraoxonase in the standard serum pool, which was subsequently used to produce a calibration curve in the competitive ELISA described below.
Determination of Paraoxonase Concentration
Microtiter plate wells were coated with 100 µL human HDL
prepared by ultracentrifugation (d=1.063
to 1.225 g/mL) diluted to 20 µg/mL with 50 mmol/L carbonate buffer,
pH 9.6, overnight at room temperature. After they were washed with
0.1% BSA in PBS (pH 7.2) for 2 minutes, the remaining absorption sites
were blocked with 1% BSA in PBS for 1 hour at room temperature. The
standard serum pool was diluted with 1% BSA/PBS that contained 1.4
µg/mL of IgG, purified from the polyclonal antiserum,22
producing a 1/25 to 1/1600 diluted serum range, producing a calibration
curve from 0.073 to 4.7 µg/mL of paraoxonase. Sera to be assayed for
paraoxonase concentration were diluted 1/400 in 1% BSA in PBS
similarly prepared. All serum dilutions were incubated in a 37°C
water bath for 15 minutes. After the wells were washed twice, the
calibration curve and test sera dilutions were added to the wells (150
µL per well, in triplicate) and incubated for 2 hours at room
temperature. The wells were washed twice and incubated for 2 hours at
room temperature with anti-rabbit IgG peroxidase conjugate (Sigma
Chemical Co) (200 µL per well diluted 1/2500 in 1% BSA/PBS). After
they were washed a third time, 200 µL of hydrogen peroxide (5 µL
diluted in 10 mL citrate buffer, pH 5.0, containing 0.04%
o-phenylenediamine-HCl) was added. The plate
was incubated at room temperature with shaking for 20 minutes, and the
absorbance at 405 nm was measured with a multiwell plate reader
(Multiskan Multisoft, Labsystems Group).
The intra-assay and interassay coefficients of variation as determined by the use of an international reference serum were 6.0% (n=30) and 2.8% (n=40), respectively. The linear range of the assay was 0.15 to 1.18 µg paraoxonase per milliliter.
Statistical Analysis
Comparisons between the unmatched groups were made by Student's
unpaired t test. Statistical analysis was also
undertaken with the use of Student's paired t test after
the groups were matched for age and sex. Individuals in the groups were
arranged in a random order. Subjects with diabetes were matched to the
first control subject of the same sex of the same age ±4 years. Values
for triglycerides and paraoxonase activity were
logarithmically transformed to give a gaussian distribution before
analysis. Spearman's rank correlation was used to examine the
strength of the association between different variables.
Paraoxonase phenotype distribution and gene frequency were
analyzed by the 
2 test.
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Results |
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The serum lipid and lipoprotein levels of the populations are given in Table 2
. The groups with diabetes had
significantly elevated serum triglycerides compared with
the control subjects (P<.001). HDL cholesterol
and apoA-1 were significantly lower than in the control subjects in
those with type 2 diabetes (P<.01 and P<.05,
respectively) but not in those with type 1 diabetes. The serum
concentration of apoB was elevated in those with type 2 diabetes
(P<.05) but not in those with type 1 diabetes.
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The median (+1 SD; -1 SD) serum paraoxonase activity in the
control population was 142.9 (+283.1; -72.1) U/mL (Table 3). Serum paraoxonase activity was
significantly reduced in both groups with diabetes, at 124.1 (+226.9;
-67.8) U/mL (P<.05) in the group with type 1 diabetes
and 123.4 (+246.9; -61.6) U/mL (P<.05) in the group
with type 2 diabetes and was lower still in both groups with
neuropathy than in those without this complication, at
100.7 (+219.8; -46.1) and 108.8 (+218.3; -54.3) in those
with type 1 and type 2 diabetes, respectively (both P<.01
compared with groups without neuropathy).
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The groups with diabetes mellitus had a decreased percentage of women,
were on average older, and were more obese than the control subjects
(Table 1
). However, none of these parameters
was related to serum paraoxonase activity, concentration, or
phenotype in any of the populations. Some studies have found
serum paraoxonase activity to be correlated with various lipid and
lipoprotein parameters such as triglycerides,
apoB, and HDL.23 However, paraoxonase was only correlated
with HDL cholesterol and apoA-1 in the control population
in this study.
The distribution of activity in the different populations was further
investigated by determining the phenotypes of the populations.
Neither the phenotype nor genotype of paraoxonase
differed significantly between any of the populations (Table 3). However, the paraoxonase specific activity was
significantly lower overall in both type 1 (3.71±0.43 nmol/min per
milligram) and type 2 (3.27±0.3 nmol/min per milligram) diabetes than
in the control subjects (4.9±0.4 nmol/min per milligram) (both
P<.05). When the two diabetic populations were divided into
those with and without neuropathy, it was evident that
those with neuropathy had the most severe decrease in serum
paraoxonase activity and that in the diabetic populations there was a
greater prevalence of neuropathy in subjects with low
paraoxonase activity (Table 3). In patients with type 1
diabetes who did not have neuropathy, serum paraoxonase
activity was not significantly different from the nondiabetic control
subjects, whereas in type 2 diabetic patients without
neuropathy, paraoxonase activity was still depressed
compared with control subjects, albeit less so than in those in whom
neuropathy was present. After they were matched for age
and sex, the groups with diabetes had consistently higher serum
paraoxonase concentrations and lower paraoxonase specific activity than
the control subjects (Table 4). In the
subjects with diabetes and neuropathy, paraoxonase specific
activity was lower than in those without neuropathy.
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The paraoxonase concentration and specific activity in the three
phenotypes of the different populations are given in Table 5. The decrease in serum paraoxonase activity in type 1
or type 2 diabetes could not be explained on the basis of its
phenotypic distribution and also did not relate to the even lower
activities in patients with neuropathy. Furthermore,
variation in the paraoxonase concentration did not explain the
different enzymatic activities observed.
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In the control population the paraoxonase concentration correlated with
salt-stimulated paraoxonase activity, phenylacetate hydrolysis, and
apoA-1 (all P<.001) and with HDL cholesterol
(P<.05) (Table 5). However, in all the
populations with diabetes these correlations were either absent or much
weaker than in the control subjects and were replaced by correlations
with LDL-associated parameters such as apoB and LDL
cholesterol (Table 5), possibly indicating a
perturbation of the interaction between paraoxonase and HDL. In all the
populations studied, serum apoA-1 and serum HDL cholesterol
and serum apoB and LDL cholesterol were highly correlated
(both P<.001).
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Discussion |
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The results confirm our previous report that serum paraoxonase activity is low in insulin-dependent diabetics14 and extends this finding to non-insulin-dependent diabetics. Furthermore, the present study has shown that the low serum paraoxonase activity associated with diabetes was not caused by phenotypic differences in the diabetic population when compared with healthy control subjects, nor was it due to a lower paraoxonase concentration in diabetics. Interpopulation differences in serum paraoxonase specific activity have been shown previously in healthy populations.21 Thus, the serum paraoxonase concentration was lower and the specific activity higher in people living in Manchester compared with those in Geneva. In that study the variation in paraoxonase specific activity was not caused by differences in phenotype distribution and was independent of any differences in the serum lipid and lipoprotein concentrations in the two populations, which was also the case in the present study of diabetes. This conclusion is, however, qualified because if diabetes were to alter the reactivity of paraoxonase to either substrate in the double-substrate phenotyping method used in the present study, it could give misleading information about the phenotype distribution and the gene frequency estimated by this method. Further confirmation of our findings must therefore await DNA studies of the genotype distribution.
The present study has also confirmed our earlier findings that serum paraoxonase activity does not correlate with the serum concentrations of most lipids and lipoproteins in populations with diabetes. The findings of Saha et al,23 who found correlations with triglycerides and apoB as well as HDL, may be due to the intrinsic differences in serum paraoxonase distribution between the Europid populations studied in this investigation and the non-Europid populations studied by Saha et al. A recent report has indicated that paraoxonase genotype is a major determinant of serum lipid and lipoprotein concentrations, particularly HDL-associated parameters.24 In the control population described here, paraoxonase concentration was similarly correlated with the same parameters.
The paraoxonase specific activity in both type 1 and type 2 diabetic populations with clinical peripheral neuropathy was significantly lower than in either of the diabetic populations without neuropathy or in the nondiabetic control subjects. The reason for this is at present unclear but was not due to a difference in glycemic control between the populations. Whether other macrovascular complications are related to paraoxonase activity deficiency must be addressed in future studies because nephropathy was present in only three subjects in each diabetic population in the present study, and retinopathy was not recorded in this investigation.
Paraoxonase is known to be associated with a specific HDL subspecies containing only apoA-1 and clusterin.7 The cause of the lower paraoxonase specific activity in diabetes is at present unknown. However, several explanations are suggested by our findings that the low activity found in diabetes is associated with normal or higher than normal concentrations of the protein and the weakening or loss of correlation between the protein concentration and HDL cholesterol and apoA-1. A larger proportion of the paraoxonase protein could be inactive in diabetes either because of the presence of an endogenous circulating inhibitor or perhaps because of increased glycosylation of paraoxonase. The loss of the strong correlation between paraoxonase concentration and glycation of apoA-1 found in healthy subjects in this and other studies25 in all the diabetic populations might indicate a disruption in the interaction between paraoxonase and the HDL particle. The ratio of apoA-1 to paraoxonase protein was lower in all the diabetic populations studied, and this may be explained on a similar basis. It is currently not known whether paraoxonase is present in the same HDL subclass containing apoA-1 and clusterin in diabetes as it is in normal control subjects, nor is it known whether the serum concentration of clusterin is different in diabetic compared with nondiabetic populations. These are the subjects of continuing investigations in our laboratory. Paraoxonase is believed to be anchored to the HDL lipids by its hydrophobic N-terminal end26 and also to be bound to apoA-1.25 The conformation of the enzyme within the hydrophobic environment of HDL may be crucial to its activity. Diabetic HDL is known to be compositionally abnormal,8 and it is possible that this affects the binding of paraoxonase to HDL, leading to a conformational change in paraoxonase or to the availability of substrates within the hydrophobic region of HDL in which paraoxonase is active.
The consequences of the low activity in diabetes could be twofold. First, it could give rise to an increase in susceptibility to organophosphate poisoning.5 Mammalian serum paraoxonase is a primary defense against organophosphates, which are widely used, for example, as pesticides.27 Low serum paraoxonase activity would reduce the capacity of an individual to detoxify these compounds, which are common contaminants of food, via hydrolysis. Organophosphate pesticides are known to cause neuropathy (organophosphate-induced delayed polyneuropathy). Higher susceptibility to neural damage by substances such as these entering the body from the environment might occur as a consequence of low paraoxonase activity in diabetes and an increase in organophosphate-induced delayed polyneuropathy in diabetic populations. However, it is not known whether subjects with diabetes are more susceptible to the toxic effects of organophosphates.
Second, we have previously shown that paraoxonase is an important component of HDL responsible in part for the ability of HDL to prevent LDL lipid peroxidation.11 13 Platelet-activating factor acetylhydrolase (PAFAH) has also been shown to inhibit the formation of lipid peroxides on LDL,28 and it is possible that HDL-associated paraoxonase and PAFAH act in concert to inhibit LDL lipid peroxidation and that a number of other HDL-associated proteins, such as apoA-1 and lecithin-cholesterol acyltransferase, may also aid this process.29 Whether PAFAH exhibits similar reductions in activity in diabetes as paraoxonase remains to be established. LDL modification by lipid peroxides might thus be accelerated in diabetes because of low paraoxonase activity, and this has been implicated in the genesis of atherosclerosis, the risk of which is increased in diabetes. Previous studies have shown an increase in the concentration of lipid peroxides in the plasma of subjects with diabetes,30 31 indicating an increase in the peroxidation of lipoprotein and cell membrane lipids that may be related to the low paraoxonase activity in diabetes. Two studies have indicated a relationship between low serum paraoxonase activity and the presence of atherosclerosis, as indicated by myocardial infarction32 33 ; however, the statistical analysis performed in the latter study has been disputed. One study found no significant changes in serum paraoxonase activity after a myocardial infarction.34 The differences in the findings of the study of Secchiero et al34 compared with the others could be explained if paraoxonase activity was lower before the myocardial infarction and paraoxonase was a predisposing factor rather than an acute-phase reactant. All these studies were performed before anti-paraoxonase antibodies were available, and it is therefore not known whether the low activity was due to low specific activity.
The effects of lipid peroxidation are not confined to lipoproteins. For example, lipid peroxidation in cell membranes has been implicated in the etiology of neurodegenerative diseases.16 HDL is the most abundant lipoprotein in the tissue fluid, where it may serve a general function in protecting cell membranes against oxidative damage, particularly the HDL subspecies, which is composed of apoA-1, clusterin, and paraoxonase.7 The low paraoxonase specific activity found in diabetic patients with clinical neuropathy in this study may have predisposed these individuals to the development of neuropathy by a mechanism involving increased lipid peroxidation.
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Acknowledgments |
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This study was supported by grants from the Medical Research Council and the North-Western Regional Health Authority. The authors wish to thank Dr R.W. James for helpful advice in developing the ELISA for paraoxonase.
Received April 18, 1995; accepted September 8, 1995.
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 P. Jaichander, K. Selvarajan, M. Garelnabi, and S. Parthasarathy Induction of paraoxonase 1 and apolipoprotein A-I gene expression by aspirin J. Lipid Res., October 1, 2008; 49(10): 2142 - 2148. [Abstract] [Full Text] [PDF]
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 P. H. Gallego, M. E. Craig, A. C. Duffin, B. Bennetts, A. J. Jenkins, S. Hofer, A. Lam, and K. C. Donaghue Association Between p.Leu54Met Polymorphism at the Paraoxonase-1 Gene and Plantar Fascia Thickness in Young Subjects With Type 1 Diabetes Diabetes Care, August 1, 2008; 31(8): 1585 - 1589. [Abstract] [Full Text] [PDF]
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 M. V. Poulakou, K. I. Paraskevas, I. S. Vlachos, S.-A. P. Karabina, M. R. Wilson, D. C. Iliopoulos, S. I. Tsitsilonis, D. P. Mikhailidis, and D. N. Perrea Effect of Statins on Serum Apolipoprotein J and Paraoxonase-1 Levels in Patients With Ischemic Heart Disease Undergoing Coronary Angiography Angiology, May 1, 2008; 59(2): 137 - 144. [Abstract] [PDF]
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P. W. Connelly, G. F. Maguire, C. M. Picardo, J. F. Teiber, and D. Draganov Development of an immunoblot assay with infrared fluorescence to quantify paraoxonase 1 in serum and plasma J. Lipid Res., January 1, 2008; 49(1): 245 - 250. [Abstract] [Full Text] [PDF]
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 R. S. Rector, S. O. Warner, Y. Liu, P. S. Hinton, G. Y. Sun, R. H. Cox, C. S. Stump, M. H. Laughlin, K. C. Dellsperger, and T. R. Thomas Exercise and diet induced weight loss improves measures of oxidative stress and insulin sensitivity in adults with characteristics of the metabolic syndrome Am J Physiol Endocrinol Metab, August 1, 2007; 293(2): E500 - E506. [Abstract] [Full Text] [PDF]
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 S. Deakin, X. Moren, and R. W. James HDL Oxidation Compromises its Influence on Paraoxonase-1 Secretion and its Capacity to Modulate Enzyme Activity Arterioscler Thromb Vasc Biol, May 1, 2007; 27(5): 1146 - 1152. [Abstract] [Full Text] [PDF]
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 M. Graner, R. W. James, J. Kahri, M. S. Nieminen, M. Syvanne, and M.-R. Taskinen Association of Paraoxonase-1 Activity and Concentration With Angiographic Severity and Extent of Coronary Artery Disease J. Am. Coll. Cardiol., June 20, 2006; 47(12): 2429 - 2435. [Abstract] [Full Text] [PDF]
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 V. Charlton-Menys, Y. Liu, and P. N. Durrington Semiautomated Method for Determination of Serum Paraoxonase Activity Using Paraoxon as Substrate Clin. Chem., March 1, 2006; 52(3): 453 - 457. [Abstract] [Full Text] [PDF]
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 P. Dursun, E. Demirtas, A. Bayrak, and H. Yarali Decreased serum paraoxonase 1 (PON1) activity: an additional risk factor for atherosclerotic heart disease in patients with PCOS? Hum. Reprod., January 1, 2006; 21(1): 104 - 108. [Abstract] [Full Text] [PDF]
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 G Ferretti, T Bacchetti, F Principi, F Di Ludovico, B Viti, V A Angeleri, M Danni, and L Provinciali Increased levels of lipid hydroperoxides in plasma of patients with multiple sclerosis: a relationship with paraoxonase activity Multiple Sclerosis, December 1, 2005; 11(6): 677 - 682. [Abstract] [PDF]
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L. S. Rozek, T. S. Hatsukami, R. J. Richter, J. Ranchalis, K. Nakayama, L. A. McKinstry, D. A. Gortner, E. Boyko, G. D. Schellenberg, C. E. Furlong, et al. The correlation of paraoxonase (PON1) activity with lipid and lipoprotein levels differs with vascular disease status J. Lipid Res., September 1, 2005; 46(9): 1888 - 1895. [Abstract] [Full Text] [PDF]
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N. Ferre, J. Camps, J. Marsillach, B. Mackness, M. Mackness, B. Coll, M. Tous, and J. Joven Comparison of Paraoxonase 1 Measurements in Serum and in Lithium-Heparin-Anticoagulated Plasma Samples Clin. Chem., May 1, 2005; 51(5): 922 - 923. [Full Text] [PDF]
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M.-C. B. Garin, B. Kalix, A. Morabia, and R. W. James Small, Dense Lipoprotein Particles and Reduced Paraoxonase-1 in Patients with the Metabolic Syndrome J. Clin. Endocrinol. Metab., April 1, 2005; 90(4): 2264 - 2269. [Abstract] [Full Text] [PDF]
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B. Hansel, P. Giral, E. Nobecourt, S. Chantepie, E. Bruckert, M. J. Chapman, and A. Kontush Metabolic Syndrome Is Associated with Elevated Oxidative Stress and Dysfunctional Dense High-Density Lipoprotein Particles Displaying Impaired Antioxidative Activity J. Clin. Endocrinol. Metab., October 1, 2004; 89(10): 4963 - 4971. [Abstract] [Full Text] [PDF]
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G. Ferretti, T. Bacchetti, D. Busni, R. A. Rabini, and G. Curatola Protective Effect of Paraoxonase Activity in High-Density Lipoproteins against Erythrocyte Membranes Peroxidation: A Comparison between Healthy Subjects and Type 1 Diabetic Patients J. Clin. Endocrinol. Metab., June 1, 2004; 89(6): 2957 - 2962. [Abstract] [Full Text] [PDF]
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S. Kopprasch, J. Pietzsch, E. Kuhlisch, and J. Graessler Lack of Association between Serum Paraoxonase 1 Activities and Increased Oxidized Low-Density Lipoprotein Levels in Impaired Glucose Tolerance and Newly Diagnosed Diabetes Mellitus J. Clin. Endocrinol. Metab., April 1, 2003; 88(4): 1711 - 1716. [Abstract] [Full Text] [PDF]
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 S. Kopprasch, J. Pietzsch, E. Kuhlisch, K. Fuecker, T. Temelkova-Kurktschiev, M. Hanefeld, H. Kuhne, U. Julius, and J. Graessler In Vivo Evidence for Increased Oxidation of Circulating LDL in Impaired Glucose Tolerance Diabetes, October 1, 2002; 51(10): 3102 - 3106. [Abstract] [Full Text] [PDF]
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 E Y Sozmen, B Mackness, B Sozmen, P Durrington, F K Girgin, L Aslan, and M Mackness Effect of organophosphate intoxication on human serum paraoxonase Human and Experimental Toxicology, May 1, 2002; 21(5): 247 - 252. [Abstract] [PDF]
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S. Deakin, I. Leviev, V. Nicaud, M.-C. B. Meynet, L. Tiret, and R. W. James Paraoxonase-1 L55M Polymorphism Is Associated with an Abnormal Oral Glucose Tolerance Test and Differentiates High Risk Coronary Disease Families J. Clin. Endocrinol. Metab., March 1, 2002; 87(3): 1268 - 1273. [Abstract] [Full Text] [PDF]
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 S. Deakin, I. Leviev, M. Gomaraschi, L. Calabresi, G. Franceschini, and R. W. James Enzymatically Active Paraoxonase-1 Is Located at the External Membrane of Producing Cells and Released by a High Affinity, Saturable, Desorption Mechanism J. Biol. Chem., February 1, 2002; 277(6): 4301 - 4308. [Abstract] [Full Text] [PDF]
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 P. K. Shah, S. Kaul, J. Nilsson, and B. Cercek Exploiting the Vascular Protective Effects of High-Density Lipoprotein and its Apolipoproteins: An Idea Whose Time for Testing Is Coming, Part II Circulation, November 13, 2001; 104(20): 2498 - 2502. [Full Text] [PDF]
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P. K. Shah, S. Kaul, J. Nilsson, and B. Cercek Exploiting the Vascular Protective Effects of High-Density Lipoprotein and Its Apolipoproteins: An Idea Whose Time for Testing Is Coming, Part I Circulation, November 6, 2001; 104(19): 2376 - 2383. [Full Text] [PDF]
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B. Mackness, G. K. Davies, W. Turkie, E. Lee, D. H. Roberts, E. Hill, C. Roberts, P. N. Durrington, and M. I. Mackness Paraoxonase Status in Coronary Heart Disease: Are Activity and Concentration More Important Than Genotype? Arterioscler Thromb Vasc Biol, September 1, 2001; 21(9): 1451 - 1457. [Abstract] [Full Text] [PDF]
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P. N. Durrington, B. Mackness, and M. I. Mackness Paraoxonase and Atherosclerosis Arterioscler Thromb Vasc Biol, April 1, 2001; 21(4): 473 - 480. [Abstract] [Full Text] [PDF]
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 B. J. Kudchodkar, A. G. Lacko, L. Dory, and T. V. Fungwe Dietary Fat Modulates Serum Paraoxonase 1 Activity in Rats J. Nutr., October 1, 2000; 130(10): 2427 - 2433. [Abstract] [Full Text]
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R. Schmidt, H. Schmidt, F. Fazekas, P. Kapeller, G. Roob, A. Lechner, G. M. Kostner, and H.-P. Hartung MRI Cerebral White Matter Lesions and Paraoxonase PON1 Polymorphisms : Three-Year Follow-Up of the Austrian Stroke Prevention Study Arterioscler Thromb Vasc Biol, July 1, 2000; 20(7): 1811 - 1816. [Abstract] [Full Text] [PDF]
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R. W. James, I. Leviev, and A. Righetti Smoking Is Associated With Reduced Serum Paraoxonase Activity and Concentration in Patients With Coronary Artery Disease Circulation, May 16, 2000; 101(19): 2252 - 2257. [Abstract] [Full Text] [PDF]
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 C Aubo, M Senti, J Marrugat, M Tomas, J Vila, J Sala, and R Masia Risk of myocardial infarction associated with Gln/Arg 192 polymorphism in the human paraoxonase gene and diabetes mellitus Eur. Heart J., January 1, 2000; 21(1): 33 - 38. [Abstract] [PDF]
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M. S. Gowri, D. R. Van der Westhuyzen, S. R. Bridges, and J. W. Anderson Decreased Protection by HDL From Poorly Controlled Type 2 Diabetic Subjects Against LDL Oxidation May Be Due to the Abnormal Composition of HDL Arterioscler Thromb Vasc Biol, September 1, 1999; 19(9): 2226 - 2233. [Abstract] [Full Text] [PDF]
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T. M. Forte, M. N. Oda, L. Knoff, B. Frei, J. Suh, J. A. K. Harmony, W. D. Stuart, E. M. Rubin, and D. S. Ng Targeted disruption of the murine lecithin:cholesterol acyltransferase gene is associated with reductions in plasma paraoxonase and platelet-activating factor acetylhydrolase activities but not in apolipoprotein J concentration J. Lipid Res., July 1, 1999; 40(7): 1276 - 1283. [Abstract] [Full Text]
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W. H. F. Sutherland, R. J. Walker, S. A. de Jong, A. M. van Rij, V. Phillips, and H. L. Walker Reduced Postprandial Serum Paraoxonase Activity After a Meal Rich in Used Cooking Fat Arterioscler Thromb Vasc Biol, May 1, 1999; 19(5): 1340 - 1347. [Abstract] [Full Text] [PDF]
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A. Ayub, M. I. Mackness, S. Arrol, B. Mackness, J. Patel, and P. N. Durrington Serum Paraoxonase After Myocardial Infarction Arterioscler Thromb Vasc Biol, February 1, 1999; 19(2): 330 - 335. [Abstract] [Full Text] [PDF]
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M. Aviram, S. Billecke, R. Sorenson, C. Bisgaier, R. Newton, M. Rosenblat, J. Erogul, C. Hsu, C. Dunlop, and B. La Du Paraoxonase Active Site Required for Protection Against LDL Oxidation Involves Its Free Sulfhydryl Group and Is Different From That Required for Its Arylesterase/Paraoxonase Activities : Selective Action of Human Paraoxonase Allozymes Q and R Arterioscler Thromb Vasc Biol, October 1, 1998; 18(10): 1617 - 1624. [Abstract] [Full Text] [PDF]
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 H. Schmidt, R. Schmidt, K. Niederkorn, A. Gradert, M. Schumacher, N. Watzinger, H.-P. Hartung, and G. M. Kostner Paraoxonase PON1 Polymorphism Leu-Met54 Is Associated With Carotid Atherosclerosis : Results of the Austrian Stroke Prevention Study Stroke, October 1, 1998; 29(10): 2043 - 2048. [Abstract] [Full Text] [PDF]
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H. Yoshida, T. Ishikawa, and H. Nakamura Vitamin E/Lipid Peroxide Ratio and Susceptibility of LDL to Oxidative Modification in Non–Insulin-Dependent Diabetes Mellitus Arterioscler Thromb Vasc Biol, July 1, 1997; 17(7): 1438 - 1446. [Abstract] [Full Text]
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D. K. Sanghera, N. Saha, C. E. Aston, and M. I. Kamboh Genetic Polymorphism of Paraoxonase and the Risk of Coronary Heart Disease Arterioscler Thromb Vasc Biol, June 1, 1997; 17(6): 1067 - 1073. [Abstract] [Full Text]
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B. J. Van Lenten, A. C. Wagner, M. Navab, and A. M. Fogelman Oxidized Phospholipids Induce Changes in Hepatic Paraoxonase and ApoJ but Not Monocyte Chemoattractant Protein-1 via Interleukin-6 J. Biol. Chem., January 12, 2001; 276(3): 1923 - 1929. [Abstract] [Full Text] [PDF]
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