The association between apolipoprotein A-I and prostacyclin binding in human serum

Lipoprotein lipase releases esterified oxylipins from very low-density lipoproteins

We previously demonstrated that defects in lipoprotein metabolism alter the distribution of oxygenated polyunsaturated fatty acids (PUFAs) in lipoprotein particles. If these oxidation products are released by lipoprotein lipase (LpL), then their delivery to peripheral tissues with bulk lipids could influence cellular function. Using 26-week-old normolipidemic and hyperlipidemic Zucker rats, we measured PUFA alcohols, epoxides, diols, ketones, and triols (i.e. oxylipins) in esterified and non-esterified fractions of whole plasma, VLDL, and LpL-generated VLDL-lipolysates. Whole plasma, VLDL, and lipolysate oxylipin profiles were distinct and altered by hyperlipidemia. While >90% of the whole plasma oxylipins were esterified, the fraction of each oxylipin class in the VLDL varied: 46% of alcohols, 30% of epoxides, 19% of diols, <10% of ketones, and <1% triols. Whole plasma was dominated by arachidonate alcohols, while the linoleate alcohols, epoxides, and ketones showed an increased prevalence in VLDL. LpL-mediated VLDL lipolysis of PUFA alcohols, diols and ketones was detected and the relative abundance of oxygenated linoleates was enhanced in the lipolysates, relative to their corresponding VLDL. In summary esterified oxylipins were seen to be LpL substrates with heterogeneous distributions among lipoprotein classes. Moreover, oxylipin distributions are changes within the context of obesity-associated dyslipidemia. These results support the notion that the VLDL-LpL axis may facilitate the delivery of plasma oxylipins to the periphery. The physiological implications of these findings are yet to be elucidated; however, these molecules are plausible indicators of systemic oxidative stress, and could report this status to the peripheral tissues.

Optimization of epoxyeicosatrienoic acid syntheses to test their effects on cerebral blood flow in vivo

Epoxyeicosatrienoic acids (EETs), normally present in brain and blood, appear to be released from atherosclerotic vessels in large amounts. Once intravascular, EETs can constrict renal arteries in vivo and dilate cerebral and coronary arteries in vitro. Whether EETs in blood will alter cerebral blood flow (CBF) in vivo is unknown. In the present study, the chemical synthesis of four EET regioisomers was optimized, and their identity and structural integrity established by chromatographic and mass spectral methods. The chemically labile EETs were converted to a sodium salt, complexed with albumin, and infused into anesthetized rats via the common carotid. The objective was to test whether sustained, high levels of intravascular EETs alter CBF. The CBF (cortical H2 clearance) was measured before and 30 min after the continuous infusion of 14,15- (n = 5), 11,12- (n = 5), 8,9- (n = 7) and 5,6-EET (unesterified or as the methyl ester, n = 5 for each). Neither the CBF nor the systemic blood pressure was affected by EETs. Because the infusions elevated the plasma concentrations of EETs about 700-fold above normal levels (1.0 nM), it is unlikely that EETs released from atherosclerotic vessels will alter CBF.

Determination of protein binding of a highly lipophilic drug, isocarbacyclin methyl ester (TEI-9090), using a polydimethylsiloxane-coated glass beads assay

An adsorption technique with polydimethylsiloxane-coated glass beads (PDMS-GB) was developed to determine the protein binding of a highly lipophilic and hydrophobic drug. The present assay method is based on the quantitative adsorption of unbound drug to the PDMS-GB. This method of batch separation in a glass assay tube has an advantage of simplicity and rapidity. To evaluate the reliability of PDMS-GB assay, we compared the protein binding of diazepam in serum in-vitro measured by ultrafiltration and PDMS-GB assay. There was no significant difference between the extent of binding measured by each method. Using PDMS-GB assay, we determined the protein binding of the prostaglandin I2 (PGI2) analogue isocarbacyclin methyl ester (TEI-9090), whose binding cannot be measured by commonly employed techniques (equilibrium dialysis, ultrafiltration, gel filtration or ultracentrifugation) because of a high degree of adsorption to membranes, resins or tubes. The percentage of TEI-9090 bound in human serum, 4% human serum albumin (HSA, fatty acid-free) and dog serum were approximately 98, approximately 87 and approximately 95%, respectively, and these values were independent of TEI-9090 concentration up to 10 ng mL-1. The binding of isocarbacyclin (TEI-7165) to serum protein in man, dogs, rabbits and rats, determined by ultrafiltration, was also high (> 90%). While the displacement of TEI-9090 and TEI-7165 binding to HSA by aspirin, salicylic acid and indomethacin was not observed, clofibric acid and free fatty acids significantly inhibited the protein binding of both compounds.(ABSTRACT TRUNCATED AT 250 WORDS)