Paraoxonase Activity Is Reduced by a Pro-atherosclerotic Diet in Rabbits Michael Mackness,* ,1 Agnes Bouiller,† Nathalie Hennuyer,† Bharti Mackness,* Maxine Hall,* Anne Tailleux,† Patrick Duriez,† Bernard Delfly,† Paul Durrington,* Jean-Charles Fruchart,† Nicolas Duverger,‡ Jean-Michel Caillaud,‡ and Graciela Castro† *Department of Medicine, University of Manchester, Manchester, United Kingdom; †INSERM U325, Institut Pasteur de Lille, France; and ‡Rho ˆne-Poulenc Rorer-Gencell Division, Atherosclerosis Department, Vitry sur Seine, France Received February 1, 2000 Serum paraoxonase (PON1) is believed to protect against the development of atherosclerosis because of its ability to retard the oxidation of low-density li- poprotein (LDL) by hydrolysing LDL-associated phos- pholipid and cholesteryl-ester hydroperoxides. We have examined the relationship between PON1 and atherosclerosis development in transgenic rabbits overexpressing human apolipoprotein (apo) A-I and nontransgenic littermates fed a pro-atherogenic diet. PON1 activity was higher in transgenic (4006.1  716.7 nmol/min/ml) compared to control (3078.5  623.3 nmol/min/ml) rabbits (P < 0.01) while high-density li- poprotein (HDL) cholesterol was 1.84  0.54 mmol/L in transgenic rabbits and 0.57  0.21 mmol/L in control rabbits (P  0.0001). After feeding rabbits a high- cholesterol diet for 14 weeks HDL-cholesterol fell by 70% in both transgenic and control rabbits (P < 0.001 compared to week 0) PON1 activity fell by 50% in both groups of rabbits (P < 0.01 compared to week 0). The amount of thoracic aortic surface area covered by le- sions was 29  16% in the control group and 26  15% in the transgenic group (P  NS). A pro-athero- sclerotic diet reduces PON1 which may exaggerate the effects of the diet on the development of athero- sclerosis. © 2000 Academic Press Key Words: paraoxonase; atherosclerosis; diet; lipo- proteins. Prospective epidemiological studies have consis- tently indicated that high levels of HDL protect against the development and progression of atherosclerosis [1, 2]. HDL is thought to directly limit the development of atherosclerosis. Repeated infusions of HDL into choles- terol fed rabbits resulted in less atherosclerosis when compared to controls [3]. Transgenic mice overexpress- ing human apo A-I have higher HDL and less aortic atherosclerosis than controls when they are main- tained on an atherogenic diet [4]. The mechanism evoked to explain the protective effect of HDL in these studies is that it has a rate-limiting role in reverse- cholesterol transport [1– 4]. In recent years, however, evidence has grown for an alternate mechanism for the protective effect of HDL: that it retards the oxidation of LDL, which is central to current theories of the initial and progression of ath- erosclerosis [5, 6]. Several studies have shown that HDL retards LDL-oxidation in vitro [7–10]. Klimov and colleagues [11] infused human HDL into choles- terol fed rabbits and significantly reduced the concen- tration of plasma LDL lipid-peroxidation products, in- dicating this mechanism may also operate in vivo. We were the first to show that the anti-oxidative affects of HDL were due to a mechanism which was enzymatic [10]. Several enzymes associated with HDL have been postulated to be responsible for the anti-oxidative ac- tivity of HDL [12]. However, the current weight of evidence would suggest that paraoxonase (PON1) is the major HDL component retarding LDL-oxidation. PON1 is capable of inhibiting LDL-oxidation in vitro [13–17] and HDL lacking PON1 (either from avian species which naturally lack PON1 or from PON1 gene knock-out mice) cannot prevent LDL-oxidation and can be pro-oxidative [18, 19]. This and other evidence [20] indicates that PON1 plays a pivotal role in the anti- oxidative/anti-inflammatory/anti-atherosclerotic prop- erties of HDL. The effects of overexpressing human apo A-I on PON1 and therefore, antioxidative protection against atherosclerosis in an animal model in which lipopro- tein metabolism and atherosclerosis resemble those of humans have yet to be established. As has whether PON1 is altered by feeding an atherogenic diet in this 1 To whom correspondence should be addressed at Department of Medicine, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, United Kingdom. Fax: +44 161 274 4833. E-mail: mmack@central.cmht.nwest.nhs.uk. Biochemical and Biophysical Research Communications 269, 232–236 (2000) doi:10.1006/bbrc.2000.2265, available online at http://www.idealibrary.com on 232 0006-291X/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.