Original Contributions |
From the Lipid Research Laboratory, Technion Faculty of Medicine, the Rappaport Family Institute for Research in the Medical Sciences and Rambam Medical Center, Haifa, Israel (M.A., M.R.); and the Department of Vascular and Cardiac Diseases, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, (C.B., R.N.), and the Departments of Pharmacology and Anesthesiology, The University of Michigan Medical School (S.B., R.S., J.E., C.H., C.D., B.L.D.), Ann Arbor, Mich.
Correspondence to Prof Michael Aviram, Lipid Research Laboratory, Rambam Medical Center, Bat-Galim, Haifa, Israel 31096. E-mail aviram{at}tx.technion.ac.il
| Abstract |
|---|
|
|
|---|
Key Words: paraoxonase arylesterase LDL lipid peroxidation sulfhydryl group
| Introduction |
|---|
|
|
|---|
Although the natural substrates for serum PON are unknown, recent studies suggest that PON prevents LDL oxidation by hydrolyzing lipid peroxides in the lipoprotein.6 7 8 9 10 11 12 The inverse relationship between serum PON activity and the risk for atherosclerotic diseases13 14 15 16 17 18 suggests that PON hydrolytic activity on oxidized LDL may be related to its antiatherogenicity.
The gene for human serum PON shows 2 common polymorphisms: Q or R at position 191 (glutamine or arginine, respectively) and M or L at position 54 (methionine or leucine, respectively).19 20 21 22 PON Q and PON R qualitatively differ in their abilities to hydrolyze various organophosphates.2 5 23 It has been suggested that the Q allele, which is more abundant than the R allele, is responsible for the protective effect of PON against atherosclerosis, whereas the R allele has been reported to be related to the risk for coronary heart disease.24 25 Recently, Mackness et al26 reported in a group of normolipidemic subjects that the protective effect of HDL from individuals with PON RR genotype against LDL oxidation was lower than that of HDL from subjects with the PON QQ genotype.
In the present study, we have compared the effects of purified human serum PON and recombinant PON Q and PON R on LDL oxidation and analyzed the active site requirements for PON arylesterase/paraoxonase activities and for PON's abilities to protect against LDL oxidation. Unexpectedly, we found that the protective role of PON against LDL oxidation is not identical to that for its hydrolytic activity with aromatic esters or organophosphates.
| Methods |
|---|
|
|
|---|
-D-mannopyranoside. Concanavalin A protein
fragments were removed by a Centricon 100 microconcentrator (Amicon).
The purity of the enzyme was verified by SDS-polyacrylamide gel
electrophoresis.27 28 PON Q and PON R hydrolytic
activities include both arylesterase (with phenyl acetate) and
paraoxonase(with paraoxon). PON arylesterase activity is substantially
higher than its paraoxonase activity (micromoles versus nanomoles
of substrate hydrolyzed per milliliter per minute, respectively).
Arylesterase Activity Measurements
Arylesterase activity was determined by using phenyl acetate as
the substrate. The initial rates of hydrolysis were determined
spectrophotometrically at 270 nm. The assay mixture included 1.0
mmol/L phenyl acetate and 0.9 mmol/L CaCl2
in 20 mmol/L Tris HCl, pH 8.0, at 25°C. Nonenzymatic
hydrolysis of phenyl acetate was subtracted from the total rate of
hydrolysis. The E270 for the reaction is 1310
mol · L-1 ·
cm-1, and 1 unit of arylesterase activity
is equal to 1 µmol of phenyl acetate hydrolyzed per milliliter
per minute.27
Paraoxonase Activity Measurements
Paraoxonase activity was assessed by measuring the initial rate
of paraoxon hydrolysis to yield p-nitrophenol at 412 nm at
25°C. The basal assay mixture included 1.0 mmol/L paraoxon and
1.0 mmol/L CaCl2 in 50 mmol/L
glycine/NaOH buffer, pH 10.5. Nonenzymatic hydrolysis of paraoxon was
subtracted from the total rate of hydrolysis. The
E412 for the reaction is 18 290 mol ·
L-1 · cm-1, and 1
unit of paraoxonase activity produced 1 nmol of
p-nitrophenol per milliliter per
minute.27
Inactivation of PON Arylesterase Activity
Removal of Calcium Ions by a Chelex 100 Column
One gram of Chelex 100 (200 mesh) was washed once with
double-distilled water and packed into a 3.0-mL polystyrene column. The
packed column was equilibrated with 50 mmol/L Tris/HCl buffer, pH
8.0. Subsequently, 1.0 mL of purified PON Q or PON R was passed through
the column at a rate of 0.3 mL/min. Sequential fractions were collected
and assayed for arylesterase activity.
Inhibition With EDTA
The purified human serum PON solution containing 1.0 mmol/L
Ca2+ in Tris/HCl buffer, pH 8.0, was diluted with
equal volume of 1 mmol/L Na2 EDTA.
Arylesterase activities were essentially zero after 18 hours of
incubation at room temperature.
Heat Inactivation
PON Q or PON R was incubated in PBS at 60°C for 15 minutes.
PON 1 was not precipitated by this treatment.
Blockage of Free Sulfhydryl Groups
p-Hydroxymercuribenzoate (PHMB) or iodoacetate (1 to
10 mmol/L) was incubated with PON Q or PON R for 1 hour at 37°C
in PBS. Excess sulfhydryl agent was removed before incubation, by
dialysis, using a Centricon 100 microconcentrator (Amicon).
Lipoproteins
Human serum LDL was obtained from PerImmune, Inc. Briefly, serum
LDL was isolated from fasted normolipidemic human volunteers.
Lipoproteins were prepared by discontinuous density gradient
ultracentrifugation.29 The LDL
was washed at d=1.063 g/mL and dialyzed overnight against
150 mmol/L NaCl (pH 7.4) at 4°C. The lipoproteins were then
sterilized by filtration (0.45 µm), stored at a concentration of
5 mg of protein per milliliter under nitrogen in the dark at 4°C, and
used within 2 weeks. The lipoproteins were found to be free of
lipopolysaccharide contamination, as analyzed by the
Limulus amebocyte lysate assay (Associated of Cape Cod Inc). Before LDL
oxidation, the lipoprotein was dialyzed against PBS, EDTA-free
solution, pH 7.4, under nitrogen at 4°C. Then the lipoproteins (100
µg of protein per milliliter) were incubated with 10 µmol/L
CuSO4 in the air, in the absence or presence of
the indicated concentrations of PON allozymes (Q or R) for up to 4
hours at 37°C. The kinetics of lipoprotein oxidation (conjugated
diene formation) was analyzed by monitoring the absorbance
change at 234 nm.30 The extent of LDL oxidation
was measured directly in the medium by the thiobarbituric
acidreactive substances (TBARS) assay at 532 nm, using
malondialdehyde (MDA) for the standard curve.31
Lipoprotein oxidation was also determined by the lipid peroxides test,
which analyzes lipid peroxides by their capacity to convert
iodide to iodine, as measured photometrically at 365
nm.32
Lipid Peroxidation
Palmitoyl arachidonyl phosphatidylcholine (PAPC) or
cholesteryl arachidonate (Sigma Co) were first completely
dried from their chloroform solvent using a heating block in
air. The lipids were then suspended in PBS to a concentration of 1
mg/mL and sonicated in an ultrasonic processor (3x30 seconds). Then,
CuSO4 (10 µmol/L) was added to the lipid
solution and incubation was carried out at 37°C for 3 hours. At the
various time points, lipid peroxides and associated TBARS were
assayed.31 32
Site-Directed Mutagenesis, Transfection, and Expression of
Recombinant Enzymes
The procedures for the production of recombinant PONs
(ie, production of wild types of PON Q and PON R, as well as
mutants with alanine or serine in place of cysteine-283 of PON Q) has
been described elsewhere in detail.33 As another
control, we also used cells transfected with the pGS expression vector
alone, without any PON cDNA insert. LDL oxidation assays using
recombinant PONs were carried in 1 mL Ultra Culture (BioWhittaker)
medium containing equal activities (0.2 arylesterase units per
milliliter) of the various PON preparations.
We have used 40 arylesterase units per milliliter of purified serum enzyme in order to have physiological serum levels. However, it is typical for the recombinant enzyme to have very low activity, which makes it not possible to get similar concentrations as for the serum enzyme. Nevertheless, the recombinant wild-type enzymes were still potent protectors against LDL oxidation.
| Results |
|---|
|
|
|---|
|
The PON Q allozyme's greater ability than the PON R allozyme's in
protecting LDL from oxidation was apparent at several enzyme
concentrations/activities (Figure 2
).
|
Similar patterns to those shown for serum purified PONs were obtained with recombinant PON Q or PON R (0.3 arylesterase units per milliliter). Copper ioninduced LDL (100 µg of protein per milliliter) oxidation produced 388±15 nmol of peroxides per milligram LDL protein (n=3) in the presence of control medium. Recombinant PON Q caused a 33% reduction (259±12, n=3), whereas recombinant PON R caused only 20% reduction (311±14, n=3) in LDL oxidation.
Next we analyzed the differences between PON Q and PON R in
regards to their inhibitory effects on LDL oxidation, under
various experimental conditions. Glutathione peroxidase (GPx, 0.1 U/mL)
was able to inhibit LDL oxidation by 20%, as measured by the formation
of peroxides after 4 hours of incubation with copper ions (10
µmol/L CuSO4) at 37°C (Figure 3A
). When LDL oxidation was carried out
in the presence of GPx and serum purified PON Q or PON R (40
arylesterase units per milliliter), the protective effect of PON R on
LDL oxidation was further increased by an additional 37% (Figure 3A
),
whereas PON Q did not show any additive effect with GPx (Figure 3A
).
Assessment of LDL oxidation by the TBARS assay (Figure 3B
) under these
conditions showed essentially identical results to those obtained by
measurement of peroxides (Figure 3A
).
|
To determine whether the PON allozymes showed divergence in their
mechanism of inhibiting LDL oxidation, experiments were carried out
under conditions in which the allozymic forms were added either at the
initiation of oxidation or later on, during the propagation phase of
LDL oxidation. When added at the initiation of LDL oxidation, both
allozymic forms of PON protected LDL from oxidation; however, PON Q was
markedly more protective than PON R, as determined by analysis
of lipid peroxides (Figure 4A
) and TBARS
(Figure 4B
) after 4 hours of oxidation. In contrast, when the allozymes
were added 1.5 hours after the initiation of copper ioninduced LDL
oxidation, PON R was more protective than PON Q (Figure 4A
versus 4B).
If added still later on (more than 3 hours), after extensive oxidation
of LDL had already taken place, both PON Q and PON R were ineffective
(data not shown).
|
Because the major sources of oxidized polyunsaturated fatty acids in
LDL are lipoprotein cholesteryl ester and phospholipid moieties, we
also studied PON's effect on the peroxidation of these components.
PAPC (1 mg/mL) was incubated with PON Q or with PON R for 3 hours at
37°C in the presence of copper ions (10 µmol/L
CuSO4). A dose-dependent reduction in the extent
of PAPC oxidation could be shown (Figure 5
), as determined by the peroxides
(Figure 5A
) and by the TBARS assays (Figure 5B
). Under these
conditions, PON Q was only a minimally better protector against PAPC
oxidation than PON R (Figure 5
).
|
Similar studies were performed with cholesteryl ester. Cholesteryl arachidonate (1 mg/mL) was incubated for 3 hours at 37°C alone, with PON Q, or with PON R (40 arylesterase units per milliliter), in the presence of 10 µmol/L CuSO4. Analysis of lipid peroxidation revealed a significant (P<0.01) reduction, from 375±35 nmol MDA equivalents per milligram cholesteryl ester in the absence of PONs to 300±19 (-20%) or 323±13 (-14%) in the presence of PON Q or PON R, respectively (n=3).
PON Arylesterase Activity During Its Protection Against LDL
Oxidation
Analysis of the enzyme's arylesterase activity as a
function of the duration of the LDL oxidation process revealed that PON
Q was more stable than PON R (Figure 6
).
Whereas arylesterase activity of PON Q was reduced by only 28%, PON R
lost about 55% of its activity during the 4 hours of incubation, and
most of this loss occurred gradually during the first hour of LDL
oxidation (Figure 6
). After 4 hours of LDL oxidation, PON R paraoxonase
activity, like its arylesterase activity, was also reduced to a greater
extent (by 51%, from 35±5 to 17±3 U/mL) than that of PON Q (by only
26%, from 15±3 to 11±3 U/mL, n=3).
|
Because the selective reduction in PON Q and PON R activities may be related to different sensitivity of these allozymes to peroxides produced during LDL oxidation, we compared the sensitivity of PON Q and PON R to H2O2. On incubation of the enzymes with 50 µg/mL H2O2 for 30 minutes at 37°C, PON Q arylesterase activity was not affected (values of 32±3 and 35±5 U · mL-1 · min-1 were obtained in the absence and presence of H2O2, respectively, n=3). Under similar conditions, PON R arylesterase activity was significantly reduced (P<0.01, n=3) by H2O2 treatment (from 36±5 to 24±5 U · mL-1 · min-1).
To assess whether the PON Q and PON R arylesterase activities were
directly related to their relative protective potency against LDL
oxidation, experiments were carried out with both PON preparations
previously inactivated for their arylesterase activities.
Because the arylesterase activity of PON is calcium dependent, each
allozymic form was treated by either preincubation with 1 mmol/L
Na2 EDTA for 30 minutes (resulting in a reduction
of PON activity from 40 to 4 arylesterase units per milliliter) or
removal of calcium ions with Chelex (activity was reduced to 1
arylesterase unit per milliliter). Under these conditions, paraoxonase
activity was also essentially abolished. Surprisingly, inactivation of
the arylesterase and paraoxonase activities did not reduce the PON's
inhibitory effect against LDL oxidation (Figure 7
). In contrast, complete inactivation of
the enzyme arylesterase/paraoxonase activities by heating (60°C, 15
minutes) resulted in a complete loss of protective activity of PON Q or
PON R against LDL oxidation (Figure 7
).
|
Possible Role of the PON's Free Sulfhydryl Group in the Protection
Against LDL Oxidation
PON contains 3 cysteines; 2 of them form an intramolecular
disulfide bond, while the third, at position 283, is
free.33 Cys283 was hypothesized to play a role in
PON esterase activity, but earlier site-directed mutagenesis from this
laboratory showed that substitution with either serine or alanine
resulted in retention of PON arylesterase
activity.33 In the current study, reaction of the
PON Cys283 with the sulfhydryl reagent PHMB caused a dose-dependent
reduction in PON arylesterase activity, by 21%, 42%, or 91% for PON
Q, and by 16%, 31%, or 97% for PON R, using PHMB concentrations of
0.1, 1.0, or 10.0 mmol/L, respectively. In parallel, a PHMB
dose-dependent reduction in the inhibitory effect of PON on
LDL oxidation was also observed (Figure 8
).
|
Preincubation of PON (40 arylesterase units of PON Q per milliliter) with 10 mmol/L PHMB for 1 hour at 37°C also reduced the ability of PON to protect against lipid peroxidation of PAPC (1 mg/mL). Values for lipid peroxidation obtained for control PAPC, PON-treated PAPC, and PHMB-inactivated PON-treated PAPC were 255±27, 128±18, and 237±31 nmol MDA equivalents per milligram PAPC, respectively (n=3). A similar pattern was obtained for the oxidation of cholesteryl arachidonate (1 mg/mL) with 10 mmol/L PHMB-treated PONs under similar conditions as described for PAPC (data not shown).
Iodoacetate, a smaller molecule than PHMB, was also used to block the
PON free sulfhydryl group. On incubation of PON Q with 0 mmol/L,
1 mmol/L, or 10 mmol/L iodoacetate, PON arylesterase
activities were 36+4, 32±3, or 28±3 U/mL, respectively (n=3). Even
though PON arylesterase activity was minimally affected by this
iodoacetate treatment, PON's ability to protect against LDL oxidation
was significantly reduced in an iodoacetate concentrationdependent
manner, as shown by analysis of LDL-associated peroxides
(Figure 9A
) and TBARS (Figure 9B
).
|
To address the possible role of the PON Cys283 residue in the
protection against LDL oxidation, we tested recombinant PON Q mutants,
in which the cysteine residue (Cys283) had been replaced with either
serine (Cys283Ser) or alanine (Cys283Ala).33 The
media obtained from the cells that were transfected with the wild-type
PON Q, the Cys283Ser, and the Cys283Ala contained 0.39±0.05,
0.20±0.05, and 0.28±0.04 arylesterase units per milliliter,
respectively (n=3). As a control we have used medium obtained from the
same number of cells, which were transfected with the same expression
vector (pGS) with the same selective genes, and the only difference
between this control and the PON recombinants was that the control
lacked the PON's cDNA. The medium (0.2 arylesterase units per
milliliter) from the PON wild type reduced copper ioninduced LDL
oxidation by 29%, whereas both PON mutants were unable to inhibit LDL
oxidation, as shown by determination of LDL-associated peroxides
(Figure 10A
) and TBARS (Figure 10B
).
|
| Discussion |
|---|
|
|
|---|
We would like to suggest that PON Q and PON R may act on different substrates generated during LDL oxidation and may possess different sensitivities to the action of peroxides formed during LDL oxidation. These differences may contribute to the divergence in the possible antiatherosclerotic roles of the PON allozymes.
Inactivation of PON arylesterase activity by the addition of EDTA or the removal of calcium ions did not reduce the abilities of the PON allozymic forms to protect LDL from oxidation. These results suggest that the active site requirements for protection against LDL oxidation and for its arylesterase activity differ to some degree.
We have no evidence to suggest that PON has 2 active sites, and it might be that there is an overlapping of the sites required for arylesterase/paraoxonase activities and the protection against LDL oxidation activity. Recently, a PON-independent inhibition of LDL oxidation by HDL was suggested.34 This suggestion was based on the observation that inactivation of PON arylesterase activity (by using EDTA-containing plasma) did not compromise the ability of HDL to inhibit LDL oxidation. The present study, however, clearly shows that arylesterase activity is not a quantitative measure of PON's ability to protect against LDL oxidation.
At one time, Cys-283 was believed to be the active center nucleophile, because organic mercurial compounds inactivated PON.33 35 We now know that this amino acid is not specifically required for PON arylesterase activity, because site-directed mutagenesis of this residue did not eliminate its arylesterase activity.33 The Cys-283 residue, however, may be located close to the active center of the enzyme and may be required for binding some substrates. The inhibitory effects of the sulfhydryl group agents PHMB and iodoacetate on the ability of PON to protect against LDL oxidation suggest that Cys-283 is essential for substrate orientation, or binding.35 36 The inability of Cys-283 PON mutants to protect LDL against oxidation further indicates the importance of this residue. PHMB inhibition of PON arylesterase activity is probably due to steric hindrance resulting from the introduction of a large substituent near a region of the molecule critical for substrate binding.33 Presumably, this is the reason that a smaller sulfhydryl binding agent, iodoacetate, has much lower inhibitory effect on PON arylesterase activity than PHMB. Interestingly, it has been recently shown37 that cigarette smoke extract can also inhibit PON paraoxonase activity by a modification of the enzyme's free thiol group, but as this research was performed in plasma, we cannot evaluate the preservation of PON activity in this study.
PON R has about 8-fold higher paraoxonase activity than PON Q,1 21 23 but the 2 allozymes are very similar in their ability to hydrolyze phenyl acetate (ie, arylesterase activity). In contrast, PON R has been shown to be far less efficient than PON Q in the hydrolysis of the organophosphates diazoxon, sarin, and soman, which is just the opposite of the findings for the activities of the PON allozymes with paraoxon.5 Thus, it is not unexpected that the relative activities of PON allozymes for protection against LDL oxidation are not the same for the 2 allozymes.
The polymorphic evolution of PON may have increased its enzymatic permissiveness and capacity to protect against LDL oxidation. Taken together, this hypothesis and the observed increased protection of PON Q versus PON R against LDL oxidation suggest that the 2 PON allozymes differ in their affinities for, and abilities to hydrolyze, various substrates. This evolutionary speculation is supported by our finding of the divergent protective characteristics of PON Q and PON R against LDL oxidation. The differences between PON Q and PON R in the protection against LDL oxidation were demonstrated when the PON's allozymes were added in the presence of GPx or during various time points of LDL oxidation. These differences may be related to increased sensitivity of PON R to short-lived lipid peroxides that are produced at the initiation of LDL oxidation and are also substrates to GPx.38 Indeed, in the present study, low H2O2 concentrations were shown to preferentially inactivate PON R but not PON Q arylesterase activity during a short incubation of H2O2 with the allozymes. Of interest along this line is the recent observation that human HDL from QQ/MM homozygotes was the most effective among all other PON allozyme-associated HDLs in protecting LDL from oxidation.39
Oxidative stress leads to a reduction in PON arylesterase activity, as shown in the present study for PON that was incubated with LDL and copper ions, as well as in serum from atherosclerotic apolipoprotein Edeficient mice40 or after enzyme incubation with oxidized LDL.41 Oxidized LDL inactivated PON arylesterase and paraoxonase activities, and this effect is shared by the oxidized polyunsaturated arachidonic fatty acids in phospholipids and in cholesteryl ester.41A Intervention to reduce oxidative stress, such as dietary polyphenolic flavonoids from red wine40 or licorice, or hypolipidemic therapy42 can preserve PON activities. Such intervention may enhance PON's hydrolytic action on specific oxidized lipids and hence lead to increased PON potency against oxidized LDL and oxidized HDL43 and against lipid-peroxidized arterial wall cells.44
We conclude that the structural requirements for PON's arylesterase and paraoxonase activities are not the same as those required for its protective effect against LDL oxidation. In addition, PON Q and PON R may show different affinities or preferences for the lipid peroxides that are produced in LDL during its oxidation and therefore may contribute in different ways, perhaps even synergistically, to reduce LDL oxidation and possibly impede atherogenesis.
Received January 28, 1998; accepted April 15, 1998.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
L. Gaidukov and D. S. Tawfik The development of human sera tests for HDL-bound serum PON1 and its lipolactonase activity J. Lipid Res., July 1, 2007; 48(7): 1637 - 1646. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Gaidukov, M. Rosenblat, M. Aviram, and D. S. Tawfik The 192R/Q polymorphs of serum paraoxonase PON1 differ in HDL binding, lipolactonase stimulation, and cholesterol efflux J. Lipid Res., November 1, 2006; 47(11): 2492 - 2502. [Abstract] [Full Text] [PDF] |
||||
![]() |
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] |
||||
![]() |
F. Marchegiani, M. Marra, L. Spazzafumo, R. W. James, M. Boemi, F. Olivieri, M. Cardelli, L. Cavallone, A. R. Bonfigli, and C. Franceschi Paraoxonase activity and genotype predispose to successful aging. J. Gerontol. A Biol. Sci. Med. Sci., June 1, 2006; 61(6): 541 - 546. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. S. Carlson, P. J. Heagerty, T. S. Hatsukami, R. J. Richter, J. Ranchalis, J. Lewis, T. J. Bacus, L. A. McKinstry, G. D. Schellenberg, M. Rieder, et al. TagSNP analyses of the PON gene cluster: effects on PON1 activity, LDL oxidative susceptibility, and vascular disease J. Lipid Res., May 1, 2006; 47(5): 1014 - 1024. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Rosenblat, L. Gaidukov, O. Khersonsky, J. Vaya, R. Oren, D. S. Tawfik, and M. Aviram The Catalytic Histidine Dyad of High Density Lipoprotein-associated Serum Paraoxonase-1 (PON1) Is Essential for PON1-mediated Inhibition of Low Density Lipoprotein Oxidation and Stimulation of Macrophage Cholesterol Efflux J. Biol. Chem., March 17, 2006; 281(11): 7657 - 7665. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Ranade, T. G. Kirchgessner, O. A. Iakoubova, J. J. Devlin, T. DelMonte, P. Vishnupad, L. Hui, Z. Tsuchihashi, F. M. Sacks, M. S. Sabatine, et al. Evaluation of the Paraoxonases as Candidate Genes for Stroke: Gln192Arg Polymorphism in the Paraoxonase 1 Gene Is Associated With Increased Risk of Stroke Stroke, November 1, 2005; 36(11): 2346 - 2350. [Abstract] [Full Text] [PDF] |
||||
![]() |
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] |
||||
![]() |
F. Rodriguez-Esparragon, J. C. Rodriguez-Perez, Y. Hernandez-Trujillo, A. Macias-Reyes, A. Medina, A. Caballero, and C. M. Ferrario Allelic Variants of the Human Scavenger Receptor Class B Type 1 and Paraoxonase 1 on Coronary Heart Disease: Genotype-Phenotype Correlations Arterioscler. Thromb. Vasc. Biol., April 1, 2005; 25(4): 854 - 860. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. F. Teiber, D. I. Draganov, and B. N. La Du Purified human serum PON1 does not protect LDL against oxidation in the in vitro assays initiated with copper or AAPH J. Lipid Res., December 1, 2004; 45(12): 2260 - 2268. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. D. Nguyen and D.-E. Sok Preferential inhibition of paraoxonase activity of human paraoxonase 1 by negatively charged lipids J. Lipid Res., December 1, 2004; 45(12): 2211 - 2220. [Abstract] [Full Text] [PDF] |
||||
![]() |
W. H. F. Sutherland, S. A. de Jong, and R. J. Walker Hypochlorous acid and low serum paraoxonase activity in haemodialysis patients: an in vitro study Nephrol. Dial. Transplant., January 1, 2004; 19(1): 75 - 82. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Kopprasch, J. Pietzsch, E. Kuhlisch, and J. Graessler Lack of Association between Serum Paraoxonase 1 Activ |