1.1. Discovery of the Phospholipase A2 Superfamily
Phospholipases represent one of the earliest enzyme activities to be identified and studied and the phospholipase A2 (PLA2) superfamily (see defining specificity1 in Figure 1) traces its roots to the identification of lytic actions of snake venom at the end of the 19th century. The enzyme was first purified and characterized from cobra venom and later from rattlesnake venom. As protein sequencing methodologies advanced in the 1970’s, it became apparent that these enzymes had an unusually large number of cysteines (over 10% of the amino acids) and as secreted enzymes, that they were all in the form of disulfide bonds. It was further recognized that in the case of PLA2, cobras and rattlesnakes had six disulfides in common, but one disulfide bond is located in distinctly different locations. This led to the designation of Type 1 and Type 2 for cobras (old world snakes) and rattlesnakes (new world snakes), respectively.2 During that same period, studies on the porcine pancreatic digestive enzyme that hydrolyzes phospholipids led to the determination that this mammalian enzyme (and also the human pancreatic enzyme) had the same disulfide bonding pattern as cobras and hence the designation as IB with the cobra enzyme as IA.






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Figure 1


The specific reaction catalyzed by phospholipase A2 at the sn-2 position of the glycerol backbone is shown. X, any of a number of polar headgroups; R1, fatty acids, or alkyl, or alkenyl groups and R2, fatty acids or acyl moieties.

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Phospholipase A2 enzymes: physical structure, biological function, disease implication, chemical inhibition, and therapeutic intervention.

A b s t r ac t Background Obstructive sleep apnea is associated with an increased prevalence of the metabolic syndrome and its components. It is unclear whether treatment of obstructive sleep apnea syndrome with continuous positive airway pressure (CPAP) would modify these outcomes. Methods In our double-blind, placebo-controlled trial, we randomly assigned patients with obstructive sleep apnea syndrome to undergo 3 months of therapeutic CPAP followed by 3 months of sham CPAP, or vice versa, with a washout period of 1 month in between. Before and after each intervention, we obtained measurements of anthropometric variables, blood pressure, fasting blood glucose levels, insulin resistance (with the use of homeostasis model assessment), fasting blood lipid profile, glycated hemoglobin levels, carotid intima–media thickness, and visceral fat. The metabolic syndrome was defined according to National Cholesterol Education Program Adult Treatment Panel III criteria, with Asian cutoff values for abdominal obesity. Results A total of 86 patients completed the study, 75 (87%) of whom had the metabolic syndrome. CPAP treatment (vs. sham CPAP) was associated with significant mean decreases in systolic blood pressure (3.9 mm Hg; 95% confidence interval [CI], 1.4 to 6.4; P = 0.001), diastolic blood pressure (2.5 mm Hg; 95% CI, 0.9 to 4.1; P < 0.001), serum total cholesterol (13.3 mg per deciliter; 95% CI, 5.3 to 21.3; P = 0.005), non–highdensity lipoprotein cholesterol (13.3 mg per deciliter; 95% CI, 4.8 to 21.8; P = 0.009), low-density lipoprotein cholesterol (9.6 mg per deciliter; 95% CI, 2.5 to 16.7; P = 0.008), triglycerides (18.7 mg per deciliter; 95% CI, 4.3 to 41.6; P = 0.02), and glycated hemoglobin (0.2%; 95% CI, 0.1 to 0.4; P = 0.003). The frequency of the metabolic syndrome was reduced after CPAP therapy (reversal found in 11 of 86 patients [13%] undergoing CPAP therapy vs. 1 of 86 [1%] undergoing sham CPAP). Accelerated hypertension developed 1 patient receiving CPAP therapy first, intolerance to CPAP developed in 2 others, and another patient declined to continue sham CPAP. Conclusions In patients with moderate-to-severe obstructive sleep apnea syndrome, 3 months of CPAP therapy lowers blood pressure and partially reverses metabolic abnormalities. (Funded by Pfizer; ClinicalTrials.gov number, NCT00694616.)

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CPAP for the Metabolic Syndrome in Patients with Obstructive Sleep Apnea

Inflammation, bioactive lipids and atherosclerosis: potential roles of a lipoprotein-associated phospholipase A2, platelet activating factor-acetylhydrolase

Background: Evidence suggests that exercise training improves CVD risk factors. However, it is unclear whether health benefits are limited to aerobic training or if other exercise modalities such as resistance training or a combination are as effective or more effective in the overweight and obese. The aim of this study is to investigate whether 12 weeks of moderate-intensity aerobic, resistance, or combined exercise training would induce and sustain improvements in cardiovascular risk profile, weight and fat loss in overweight and obese adults compared to no exercise. Methods: Twelve-week randomized parallel design examining the effects of different exercise regimes on fasting measures of lipids, glucose and insulin and changes in body weight, fat mass and dietary intake. Participants were randomized to either: Group 1 (Control, n=16); Group 2 (Aerobic, n=15); Group 3 (Resistance, n=16); Group 4 (Combination, n=17). Data was analysed using General Linear Model to assess the effects of the groups after adjusting for baseline values. Within-group data was analyzed with the paired t-test and between-group effects using post hoc comparisons. Results: Significant improvements in body weight (�1.6%, p=0.044) for the Combination group compared to Control and Resistance groups and total body fat compared to Control (�4.4%, p=0.003) and Resistance (�3%, p=0.041). Significant improvements in body fat percentage (�2.6%, p=0.008), abdominal fat percentage (�2.8%, p=0.034) and cardio-respiratory fitness (13.3%, p=0.006) were seen in the Combination group compared to Control. Levels of ApoB48 were 32% lower in the Resistance group compared to Control (p=0.04). Conclusion: A 12-week training program comprising of resistance or combination exercise, at moderate-intensity for 30 min, five days/week resulted in improvements in the cardiovascular risk profile in overweight and obese participants compared to no exercise. From our observations, combination exercise gave greater benefits for weight loss, fat loss and cardio-respiratory fitness than aerobic and resistance training modalities. Therefore, combination exercise training should be recommended for overweight and obese adults in National Physical Activity Guidelines. This clinical trial was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR), registration number: ACTRN12609000684224.

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The effect of 12 weeks of aerobic, resistance or combination exercise training on cardiovascular risk factors in the overweight and obese in a randomized trial

The health benefits currently associated with increased dairy intake may be attributable to the whey component of dairy proteins. The present study evaluated the effects of whey protein supplementation on body composition, lipids, insulin and glucose in comparison to casein and glucose (control) supplementation in overweight/obese individuals for 12 weeks. The subjects were randomised to whey protein, casein or glucose supplementation for 12 weeks according to a parallel design. Fasting blood samples and dual-energy X-ray absorptiometry measurements were taken. Seventy men and women with a mean age of 48·4 (SEM 0·86) years and a mean BMI of 31·3 (SEM 0·8) kg/m 2 completed the study. Subjects supplemented with whey protein had no significant change in body composition or serum glucose at 12 weeks compared with the control or casein group. Fasting TAG levels were significantly lowered in the whey group compared with the control group at 6 weeks (P¼ 0·025) and 12 weeks (P¼ 0·035). There was a significant decrease in total cholesterol and LDL cholesterol at week 12 in the whey group compared with the casein (P¼ 0·026 and 0·045, respectively) and control groups (P,0·001 and 0·003, respectively). Fasting insulin levels and homeostasis model assessment of insulin resistance scores were also significantly decreased in the whey group compared with the control group (P¼ 0·049 and P¼ 0·034, respectively). The present study demonstrated that supplementation with whey proteins improves fasting lipids and insulin levels in overweight and obese individuals. Metabolic syndrome: Whey protein: Lipid: Obesity: Cholesterol: Insulin: Glucose

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Effects of whey protein isolate on body composition, lipids, insulin and glucose in overweight and obese individuals

Estimation of LDL cholesterol based on the Friedewald formula and on apo B levels.

Objective— Platelet-activating factor acetylhydrolase (PAF-AH) expresses a Ca 2+ -independent phospholipase A 2 activity and hydrolyzes platelet-activating factor as well as oxidized phospholipids. Two major types of PAF-AH have been described: the plasma type, which is associated with lipoproteins, and the intracellular type II PAF-AH. Methods and Results— We investigated the type(s) of PAF-AH expressed in human platelets as well as the mechanism and the enzyme type secreted from platelets during activation. The majority of the enzyme activity (75.1±14.3% of total) is found in the cytosol, whereas 24.9±7.3% is associated with the membranes. Immunofluorescence microscopy studies and Western blotting analysis showed that platelets contain the plasma type as well as the intracellular type II PAF-AH. Furthermore, platelets contain high levels of the mRNA of plasma PAF-AH, whereas only a small quantity of the type II PAF-AH mRNA was detected. On activation, platelets secrete the plasma type of PAF-AH mainly associated with platelet-derived microparticles (PMPs). The enzyme activity was also detected on circulating PMPs in plasma from normolipidemic healthy subjects. Conclusion— This is the first indication that in addition to lipoproteins, PAF-AH in human plasma is carried by PMPs, suggesting that the PMP-associated PAF-AH may play a role in the dissemination of biological activities mediated by these particles.

Human Platelets Secrete the Plasma Type of Platelet-Activating Factor Acetylhydrolase Primarily Associated With Microparticles

Background Platelet-activating factor (PAF), the lipid mediator of inflammation and potent platelet agonist, can be hydrolysed and inactivated by PAF-acetylhydrolase (PAFAH). We investigated the PAF-AH activity in relation to PAF formation in platelets from patients with stable angina undergoing elective percutaneous transluminal coronary angioplasty (PTCA). Design Twenty-seven patients with stable angina, undergoing PTCA, and 30 age- and sexmatched controls were studied. The platelet-associated and secreted PAF-AH activity was measured, before PTCA, as well as at 4 h, 48 h and 6 months afterwards. PAF formation by thrombin-stimulated platelets and the platelet aggregation responses to PAF and ADP were also determined. Results The PAF-AH activity secreted by thrombin-stimulated platelets before PTCA (in pmol/10 9 cells/h) was significantly higher compared to controls (892 ^ 222 vs. 624 ^ 144, P , 0·001). The enzyme activity was not altered at 4 h after PTCA, but was significantly increased at 48 h (1284 ^ 312, P , 0·005) to return to the levels observed in the control group 6 months afterwards. Detectable levels of PAF in thrombin-stimulated platelets were found only at 6 months after PTCA. Furthermore, the cell-associated enzyme activity in resting platelets before PTCA was significantly lower compared with controls. Unlike in controls, the platelet-associated enzyme activity in the patient group was not increased after stimulation with thrombin and it was associated by a platelet hyperaggregability to PAF. Both the intact cell-associated activity and the platelet hyper-reactivity to PAF were restored at 6 months after PTCA. Conclusions Alterations in the platelet PAF-AH activity, which affect the PAF formation in thrombin-stimulated platelets and are associated by an increased aggregatory response to PAF, are observed in patients with stable angina and are completely restored after PTCA.

Platelet-associated and secreted PAF-acetylhydrolase activity in patients with stable angina: sequential changes of the enzyme activity after angioplasty.

M.P. Vini

Papers

Estimation of LDL cholesterol based on the Friedewald formula and on apo B levels.

Human Platelets Secrete the Plasma Type of Platelet-Activating Factor Acetylhydrolase Primarily Associated With Microparticles

Platelet-associated and secreted PAF-acetylhydrolase activity in patients with stable angina: sequential changes of the enzyme activity after angioplasty.