Apolipoprotein A-I promotes the formation of phosphatidylcholine core aldehydes that are hydrolyzed by paraoxonase (PON-1) during high density lipoprotein oxidation with a peroxynitrite donor

High density lipoprotein (HDL) is rich in polyunsaturated phospholipids that are sensitive to oxidation. However, the effect of apolipoprotein A-I and paraoxonase-1 (PON-1) on phosphatidylcholine oxidation products has not been identified. We subjected native HDL, trypsinized HDL, and HDL lipid suspensions to oxidation by the peroxynitrite donor, 3-morpholinosydnonimine. HDL had a basal level of phosphatidylcholine mono- and di-hydroperoxides that increased to a greater extent in HDL, compared with either trypsinized HDL or HDL lipid alone. Phosphatidylcholine core aldehydes, which were present in small amounts, increased 10-fold during oxidation of native HDL, compared with trypsinized HDL (p = 0.004), and 4-fold compared with HDL lipid suspensions (p = 0.0021). In addition, the content of lysophosphatidylcholine increased 300% during oxidation of native HDL, but only 80 and 25%, respectively, during oxidation of trypsinized HDL and HDL lipid suspensions. Phosphatidylcholine isoprostanes accumulated in comparable amounts during the oxidation of all three preparations. Incubation of apolipoprotein A-I with 1-palmitoyl-2-linoleoyl glycerophosphocholine proteoliposomes in the presence of 3-morpholinosydnonimine or apoAI with phosphatidylcholine hydroperoxides resulted in a significant increase in phosphatidylcholine core aldehydes with no formation of lysophosphatidylcholine. We propose that apolipoprotein A-I catalyzes a one-electron oxidation of alkoxyl radicals. Purified PON-1 hydrolyzed phosphatidylcholine core aldehydes to lysophosphatidylcholine. We conclude that, upon HDL oxidation with peroxynitrite, apolipoprotein AI increases the formation of phosphatidylcholine core aldehydes that are subsequently hydrolyzed by PON1.

Human serum paraoxonase (PON1) isozymes Q and R hydrolyze lactones and cyclic carbonate esters

It is well established that human serum paraoxonase (PON1) catalyzes the hydrolysis of organophosphate insecticides and nerve agents, as well as that of a number of aromatic carboxylic acid esters. Our laboratory has recently found a new class of PON1 substrates that includes at least 30 lactones and cyclic carbonate esters. The lactone substrates vary in their ring size from 4 to 7 atoms. Substituents on the ring carbons may enhance or reduce the rate of lactone hydrolysis. An appreciable degree of stereospecificity exists with some activities differing up to 9-fold between enantiomers (i.e., S-alpha-hydroxy-gamma-butyrolactone is hydrolyzed 5 to 9 times faster than the R form). Thiolactones are hydrolyzed less efficiently, and some lactams are potent inhibitors. Four lactone-containing drugs-spironolactone, mevastatin, simvastatin, and lovastatin-have been identified as substrates for PON1. All lactone substrates are hydrolyzed by both the Q and R isozymes of human serum PON1. However, some lactone substrates are hydrolyzed faster by the Q than R isozyme, whereas others show a reverse preference. Moreover, these new substrates include homogentisic acid lactone, mevalonic acid lactone, homocysteine thiolactone, and gamma-hydroxybutyric acid lactone-all lactone forms of endogenous compounds. It is reasonable to expect that further investigations may uncover PON1 lactone substrates that are, themselves, endogenous compounds. In this article we characterize the basic enzymatic properties of PON1's newly identified hydrolytic activities with lactone and cyclic carbonate ester substrates and compare these properties with those of representative arylesters and organophosphates.

Human serum paraoxonases (PON1) Q and R selectively decrease lipid peroxides in human coronary and carotid atherosclerotic lesions: PON1 esterase and peroxidase-like activities

BACKGROUND

Human serum paraoxonase (PON1) exists in two polymorphic forms: one that differs in the amino acid at position 192 (glutamine and arginine, Q and R, respectively) and the second one that differs in the amino acid at position 55 (methionine and leucine, M and L, respectively). PON1 protects LDL from oxidation, and during LDL oxidation, PON1 is inactivated.

METHODS AND RESULTS

The present study compared PON1 isoforms Q and R for their effect on lipid peroxide content in human coronary and carotid lesions. After 24 hours of incubation with PON1Q or PON1R (10 arylesterase units/mL), lipid peroxides content in both coronary and carotid lesion homogenates (0.1 g/mL) was reduced up to 27% and 16%, respectively. The above incubation was associated with inactivation of PON1Q and PON1R by 15% and 45%, respectively. Lesion cholesteryl linoleate hydroperoxides and cholesteryl linoleate hydroxides were hydrolyzed by PON1 to yield linoleic acid hydroperoxides and linoleic acid hydroxides. Furthermore, lesion and pure linoleic acid hydroperoxides were reduced to yield linoleic acid hydroxides. These results thus indicate that PON1 demonstrates esterase-like and peroxidase-like activities. Recombinant PON1 mutants in which the PON1-free sulfhydryl group at cysteine-284 was replaced with either alanine or serine were no longer able to reduce lipid peroxide content in carotid lesions.

CONCLUSIONS

We conclude that PON1 may be antiatherogenic because it hydrolyzes lipid peroxides in human atherosclerotic lesions.

[Colostral immunoglobulin levels in dead calves as related to microbiological and pathoanatomic findings]

At the age from three days to one month, 76 deceased calves were subjected to examination. Their average weight was 36.2 kg. The patho-anatomic examination revealed gastro-enteritis in 76.3% of the dead calves, pneumonia in 46 percent. A reduced level of immunoglobulins was recorded in 78% of the deceased calves. A low average immunoglobulin level was found in the calves in which septicaemia (IgG 217.9 mg and IgM 9.1 mg per 100 ml) or pyaemia (IgG 236.6 mg and IgM 8.3 mg per 100 ml) had been demonstrated. In the calves which had died from pneumonia or dietetic and technological defects, the average immunoglobulin values were higher (IgG 813.1 mg and 856.3 mg, IgM 41.1 and 47.4 mg per 100 ml). The microbiological finding was positive in 66 calves.