U. Murali Krishna

14,15-Epoxyeicosa-5(Z)-Enoic Acid. A Selective Epoxyeicosatrienoic Acid Antagonist That Inhibits Endothelium-Dependent Hyperpolarization and Relaxation in Coronary Arteries

Endothelium-dependent hyperpolarization and relaxation of vascular smooth muscle are mediated by endothelium-derived hyperpolarizing factors (EDHFs). EDHF candidates include cytochrome P-450 metabolites of arachidonic acid, K+, hydrogen peroxide, or electrical coupling through gap junctions. In bovine coronary arteries, epoxyeicosatrienoic acids (EETs) appear to function as EDHFs. A 14,15-EET analogue, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) was synthesized and identified as an EET-specific antagonist. In bovine coronary arterial rings preconstricted with U46619, 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET induced concentration-related relaxations. Preincubation of the arterial rings with 14,15-EEZE (10 &mgr;mol/L) inhibited the relaxations to 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET but was most effective in inhibiting 14,15-EET–induced relaxations. 14,15-EEZE also inhibited indomethacin-resistant relaxations to methacholine and arachidonic acid and indomethacin-resistant and l-nitroarginine-resistant relaxations to bradykinin. It did not alter relaxation responses to sodium nitroprusside, iloprost, or the K+ channel activators (NS1619 and bimakalim). Additionally, in small bovine coronary arteries pretreated with indomethacin and l-nitroarginine and preconstricted with U46619, 14,15-EEZE (3 &mgr;mol/L) inhibited bradykinin (10 nmol/L)–induced smooth muscle hyperpolarizations and relaxations. In rat renal microsomes, 14,15-EEZE (10 &mgr;mol/L) did not decrease EET synthesis and did not alter 20-hydroxyeicosatetraenoic acid synthesis. This analogue acts as an EET antagonist by inhibiting the following: (1) EET-induced relaxations, (2) the EDHF component of methacholine-induced, bradykinin-induced, and arachidonic acid–induced relaxations, and (3) the smooth muscle hyperpolarization response to bradykinin. Thus, a distinct molecular structure is required for EET activity, and alteration of this structure modifies agonist and antagonist activity. These findings support a role of EETs as EDHFs.

Functional Coupling of Phosphatidylinositol 4,5-Bisphosphate to Inositol 1,4,5-Trisphosphate Receptor

The inositol 1,4,5-trisphosphate receptor (InsP3R) plays a key role in intracellular Ca2+ signaling. InsP3R is activated by InsP3 produced from phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C cleavage. Using planar lipid bilayer reconstitution technique, we demonstrate here that rat cerebellar InsP3R forms a stable inhibitory complex with endogenous PIP2. Disruption of InsP3R-PIP2 interaction by specific anti-PIP2 monoclonal antibody resulted in 3–4-fold increase in InsP3R activity and 10-fold shift in apparent affinity for InsP3. Exogenously added PIP2blocks InsP3 binding to InsP3R and inhibits InsP3R activity. Similar results were obtained with a newly synthesized water soluble analog of PIP2, dioctanoyl-(4,5)PIP2, indicating that insertion of PIP2 into membrane is not required to exert its inhibitory effects on the InsP3R. We hypothesize that the functional link between InsP3R and PIP2 described in the present report provides a basis for a local, rapid, and efficient coupling between phospholipase C activation, PIP2hydrolysis, and intracellular Ca2+ wave initiation in neuronal and non-neuronal cells.

Altered Mechanisms Underlying Hypoxic Dilation of Skeletal Muscle Resistance Arteries of Hypertensive versus Normotensive Dahl Rats

Objective: To determine mechanisms underlying hypoxic dilation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt‐sensitive (SS) rats.

20-HETE contributes to myogenic activation of skeletal muscle resistance arteries in Brown Norway and Sprague-Dawley rats.

Objective: To evaluate the role of 20‐hydroxyeicosatetraenoic acid (20‐HETE), a product of arachidonic acid ω‐hydroxylation via cytochrome P450 (CP450) 4A enzymes, in regulating myogenic activation of skeletal muscle resistance arteries from normotensive Brown Norway (BN) and Sprague‐Dawley (SD) rats.

Practical, enantiospecific syntheses of 14,15-EET and leukotoxin B (vernolic acid)

Abstract Cytochrome P450BM3 and its F87V mutant were exploited for a convenient, laboratory scale (1 mmol) preparation of 14( S ),15( R )-epoxyeicosatrienoic acid [14( S ),15( R )-EET] from arachidonic acid and (+)-leukotoxin B [(+)-12( S ),13( R )-vernolic acid] from linoleic acid, respectively. Their enantiomers were accessed via a four-step chemical inversion.

Relative Contributions of Cyclooxygenase- and Cytochrome P450 ω-Hydroxylase-Dependent Pathways to Hypoxic Dilation of Skeletal Muscle Resistance Arteries

This study determined the contribution of prostanoids, cytochrome P450 (CP450) 4A enzyme metabolites of arachidonic acid, and other potential mediators of hypoxic dilation of isolated rat skeletal muscle resistance arteries. Gracilis arteries (GA) were viewed via television microscopy and dilator responses to hypoxia (reduction in superfusate and perfusate PO2 from ∼145 to ∼40 mm Hg) were measured with a video micrometer. Hypoxic dilation of gracilis arteries was severely impaired by either endothelium removal or cyclooxygenase inhibition with indomethacin, but not by nitric oxide synthase inhibition with L-NAME. Treatment of GA with 17-octadecynoic acid (17-ODYA) alone to inhibit CP450 4A enzymes significantly reduced hypoxic dilation from control levels. Treatment of vessels with N-methylsulfonyl-6-(2-proparglyoxyphenyl)hexanoic acid (MS-PPOH) to inhibit the production of epoxyeicosatrienoic acids (EETs) did not alter hypoxic dilation, although treatment with dibromo-dodecenyl-methylsulfimide (DDMS) to inhibit 20-hydroxyeicosatetraenoic acid (20-HETE) production had similar effects as 17-ODYA. Treatment of GA with 6(Z),15(Z)-20-HEDE, a competitive antagonist of the actions of 20-HETE, mimicked the effects of 17-ODYA and DDMS treatment on hypoxic dilation. These results suggest that hypoxic dilation of skeletal muscle resistance arteries primarily represents the effects of enhanced prostanoid release from vascular endothelium, although a contribution of reduced 20-HETE production via CP450 ω-hydroxylase enzymes also regulates hypoxic dilation of these vessels.

A convenient synthesis of (Z)-1-chloro-1-alkenes and (Z)-1-chloro-2-alkoxy-1-alkenes

Abstract Mild, room temperature CrCl 2 reduction of 1,1,1-trichloroalkanes stereoselectively generates ( Z )-1-chloro-2-substituted-1-alkenes in excellent yields.

Stereospecific synthesis of trans-arachidonic acids.

An effective synthesis is described for the preparation of all four mono trans isomers of arachidonic acid via deoxidation of epoxide precursors with lithium diphenylphosphide and quaternization with methyl iodide.

Concise syntheses of l-α-phosphatidyl-d-myo-inositol 3-phosphate (3-PIP), 5-phosphate (5-PIP), and 3,5-bisphosphate (3,5-PIP2)

Abstract Highly efficient, asymmetric total syntheses of the title phospholipids as well as short chain and cross-linkable aminoether analogs were achieved in five to seven steps from a readily available myo -inositol derivative.

Preparation of l-α-phosphatidyl-d-myo-inositol 3-phosphate (3-PIP) and 3,5-bisphosphate (3,5-PIP2)

Practical, asymmetric total syntheses of the title phospholipids from a readily available myo-inositol derivative as well as short chain and cross-linkable aminoether analogues are described.