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Biomedical subjects

J R Falck

Publications and source records attributed to J R Falck.

At least 271 records · Page 15Linked to original sources
PubMed1984

Receptor-mediated delivery of photoprotective agents by low-density lipoprotein.

Low density lipoprotein (LDL) has been used to deliver toxic molecules to cells by receptor-mediated endocytosis. In these studies, the cholesteryl ester core of LDL was replaced with a lipophilic, toxic molecule. We now report that photoprotective azo dyes can be stably incorporated into LDL, and that this reconstituted LDL protects cells from the photosensitizing action of pyrene methanol (PM) in a receptor-dependent process. The photoprotective action of the azo dye is due to its ability to scavenge singlet oxygen that is produced by the photosensitive agent in response to UV light.

Animals↗
PubMed1984

Selective delivery of cytotoxic compounds to cells by the LDL pathway.

Cancer cells need cholesterol to make new membrane. They get it either by de novo synthesis or from low-density lipoprotein (LDL), or both. Some types of cancer have very high LDL requirements. LDL particles, which circulate in the blood, contain a cholesteryl ester core surrounded by a phospholipid coat containing apoproteins that are recognized by LDL receptors on cell surfaces. After attachment to cells, LDL is endocytosed into lysosomes, where the core is exposed and hydrolyzed. A technique is known whereby LDL can be isolated, its core removed and replaced by a compatible lipophilic substance, and then reconstituted into intact LDL particles that are recognized and internalized by cells in the normal manner. A series of cytotoxic compounds has been synthesized, designed to be compatible with reconstituted LDL, and directed against cancers that copiously internalize LDL. They were evaluated by measuring the toxicity of reconstituted LDL toward test cells bearing LDL receptors. Selectivity was determined by comparison, either with mutant cells with few LDL receptors or with reconstituted methylated LDL (which is not recognized by LDL receptors) on normal cells. Two compounds, 19 and 25, were found that reconstitute well, kill or arrest the test cells at reasonably low concentrations, and are completely selective, suggesting that they are delivered to cells exclusively via the LDL pathway.

Amines↗
PubMed1984

Visualization of acidic organelles in intact cells by electron microscopy.

We report the synthesis of a probe that permits the visualization by electron microscopy of acidic organelles in intact cells. This probe, 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine (DAMP), is a basic congener of dinitrophenol that readily diffuses into intact cells. Its primary and tertiary amino groups (apparent pKa, 10.6) allow it to be concentrated in acidic organelles and to be retained there after fixation with aldehydes. The dinitroarene moiety of DAMP can then be localized with mouse monoclonal antibodies directed against dinitrophenol. The antibodies, in turn, can be visualized by light or electron microscopy by reaction with rabbit anti-mouse antibodies coupled to rhodamine or horseradish peroxidase, respectively. We have used these methods to show that DAMP concentrates in a variety of membrane-bound structures in cultured fibroblasts, including classic multivesicular bodies (resembling lysosomes), intermediate-sized vesicles with multiple shapes (resembling endosomes), and an abundant population of very small spherical vesicles. A small fraction of coated vesicles is labeled with DAMP. Labeling with DAMP does not occur when the pH gradient of fibroblasts is disrupted by the ionophore monensin or the weak base chloroquine. DAMP should be a useful probe for exploring the assembly, distribution, and function of acidic organelles by electron microscopy.

Antibodies, Monoclonal↗
PubMed1983

Epoxyeicosatrienoic acids stimulate glucagon and insulin release from isolated rat pancreatic islets.

Metapyrone and eicosatetraynoic acid but not indomethacin are effective inhibitors of the secretory response of isolated rat pancreatic islets to arginine and glucose. Epoxyeicosatrienoic acids, products of the cytochrome P-450-NADPH dependent arachidonic acid epoxygenase activity, are potent and selective mediators for the in vitro release of either insulin or glucagon from preparations of isolated rat pancreatic islets.

Animals↗
PubMed1983

The reaction of arachidonic acid epoxides (epoxyeicosatrienoic acids) with a cytosolic epoxide hydrolase.

Epoxyeicosatrienoic acids, formed during the cytochrome P-450-catalyzed oxidation of arachidonic acid, react with a liver cytosolic epoxide hydrolase to form vicinal diols of eicosatrienoic acid. The role of this cytosolic enzyme, rather than a microsomal bound type, explains previous results illustrating the ability to accumulate epoxides during the in vitro aerobic steady state of oxidative metabolism of arachidonic acid by liver microsomes. The inability of the 5,6-epoxyeicosatrienoic acid to serve as a suitable substrate for this enzyme is discussed in light of recent studies concerning possible unique physiological functions for this metabolite.

Animals↗
PubMed1983

Effects of newly reported arachidonic acid metabolites on microsomal Ca++ binding, uptake and release.

The 5,6-; 8,9-; 11,12- and 14,15-epoxyeicosatrienoic acids and their respective hydration products, the vic-diols, recently reported as metabolites of arachidonic acid in rat liver microsomes, were examined for effect on release of 45Ca from canine aortic smooth muscle microsomes. At 10(-6) M, the diols had no effect, but the 5,6-; 11,12- and 14,15-epoxyacids increased the loss of 45Ca. Further studies with the 14,15-epoxyacid demonstrated a dose-dependent decrease of Ca++ uptake (ATP present) in canine aortic microsomes in 0.03 mM Ca++, whereas Ca++ binding (ATP absent) was not affected. Ca++ uptake, binding and release in rat liver microsomes was similarly affected by the 14,15-epoxyacid, the major epoxyeicosatrienoic acid derivative produced by rat liver microsomal incubations. It is suggested that alterations in Ca++ metabolism might be a possible mechanism of action for these derivatives of arachidonic acid.

Animals↗
PubMed1983

Action of luteinizing hormone-releasing hormone: involvement of novel arachidonic acid metabolites.

Anterior pituitary cells were incubated in the presence of luteinizing hormone-releasing hormone and one of three inhibitors of arachidonic acid metabolism:indomethacin, an inhibitor of the cyclooxygenase system; nordihydroguaiaretic acid, an antioxidant that inhibits lipoxygenase; and icosatetraynoic acid, an acetylenic analogue of arachidonic acid that blocks all known pathways of arachidonic acid metabolism. Indomethacin was ineffective in blocking luteinizing hormone-releasing hormone-stimulated luteinizing hormone secretion. Nordihydroguaiaretic acid was only marginally capable of inhibiting luteinizing hormone-releasing hormone-stimulated luteinizing hormone secretion. Icosatetraynoic acid at 10 microM completely inhibited stimulated luteinizing hormone secretion. Addition of several epoxygenated arachidonic acid metabolites to cells in vitro resulted in secretion of luteinizing hormone equal to or greater than that induced by 10 nM luteinizing hormone-releasing hormone. The half-maximal effective dose for these compounds was approximately 50 nM. The 5,6-epoxyicosatrienoic acid was the most potent of the compounds tested. These studies suggest that luteinizing hormone-releasing hormone-stimulated luteinizing hormone release is closely coupled with the production of oxidized arachidonic acid metabolites. Moreover, one or more of the epoxygenated arachidonic acid metabolites might be a component of the cascade of reactions initiated by luteinizing hormone-releasing hormone that ultimately results in secretion of luteinizing hormone.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1983

Novel hypothalamic arachidonate products stimulate somatostatin release from the median eminence.

Arachidonic acid (AA) stimulates the in vitro release of somatostatin (SRIF) from the hypothalamic median eminence (ME). This effect is inhibited by 5, 8, 11, 14-eicosatetraynoic acid (ETYA) but not by indomethacin (ID). Microsomal fractions from the rat hypothalamus catalyze an NADPH-dependent metabolism of AA to form several oxygenated products of which the major metabolites are 5, 6-epoxyeicosatrienoic acid (5, 6-EET) and its hydration product, 5, 6-dihydroxyeicosatrienoic acid (5, 6-DHET). Both novel arachidonate metabolites, particularly 5, 6-EET, are potent in vitro stimuli for the release of SRIF. To a lesser extent, 5, 6-EET is also capable of evoking luteinizing hormone-releasing hormone (LHRH) release. The results suggest that these "epoxygenase" metabolites of AA may be physiologically involved in the control of SRIF release.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1983

Reconstitution of LDL with lipophilic fluorescein derivatives: quantitative analysis of the receptor activity of human lymphocytes.

Low density lipoprotein (LDL), the major cholesterol transport protein in human plasma, consists of an apolar core of cholesteryl esters surrounded by a polar shell containing phospholipids, unesterified cholesterol and protein. In the current paper we report the absorption and fluorescence spectra of members of a new class of lipophilic fluorescein derivatives which were designed to be reconstituted into the core of LDL in place of the native cholesteryl esters. One of these derivates, cholesteryl 12-O-[methyl 3-O-methyl-5' (6')-carboxyfluorescein]ricinoleyl carbonate (MMC) was reconstituted into the core of LDL. The resultant fluorescent reconstituted LDL was used in conjunction with flow cytometry to quantify the LDL receptor activity of fresh blood lymphocytes derived from normal individuals and from patients with the heterozygous and homozygous forms of familial hypercholesterolemia (FH). The LDL receptor activities of the heterozygous and homozygous FH lymphocytes were approximately 37% and 1% of normal, respectively. LDL reconstituted with these lipophilic fluorescein derivatives will be valuable in studying LDL metabolism and may be useful for the diagnosis of FH.

Fluoresceins↗
PubMed1981

Targeted killing of cultured cells by receptor-dependent photosensitization.

This paper describes a method, designated "receptor-dependent photosensitization," by which the receptor-mediated endocytosis of low density lipoprotein (LDL) can be used to deliver a photosensitizing agent, pyrene, to cultured human and animal cells. The hydrophobic core of LDL is extracted and replaced with pyrene covalently coupled to cholesteryl oleate. This reconstituted LDL enters cells in significant amounts only when the cells express LDL receptors, resulting in the accumulation of pyrene cholesteryl oleate within lysosomes. Subsequent exposure of the cells to ultraviolet light leads to cell death. Cells killed by this technique include normal and simian virus 40-transformed human fibroblasts, human A-431 epidermal carcinoma cells, Chinese hamster ovary cells, and mouse L cells, all of which express LDL receptors. Mutant fibroblasts from a patient with homozygous familial hypercholesterolemia, which lack LDL receptors, do not take up significant amounts of the pyrene-containing LDL and are not killed by subsequent exposure to light. The current experiments establish the feasibility of receptor-dependent photosensitization as an efficient and selective method for killing cultured human and animal cells.

Cell Survival↗
PubMed1980

The scavenger cell pathway for lipoprotein degradation: specificity of the binding site that mediates the uptake of negatively-charged LDL by macrophages.

Macrophages isolated from a variety of organs in several animal species exhibit high affinity binding sites that recognize chemically modified proteins. One of these binding sites recognizes human plasma low density lipoprotein (LDL) in which the positive charges on the epsilon-amino groups of lysine have been removed or neutralized by chemical modification, thus giving the protein an enhanced negative charge. Effective treatments include reaction of LDL with organic acid anhydrides (acetylation or maleylation) and reaction with aldehydes, such as treatment with malondialdehyde. After the negatively-charged LDL binds to the surface receptor sites, it is rapidly internalized by the macrophages by endocytosis and hydrolyzed in lysosomes. The liberated cholesterol is reesterified in the cytoplasm, producing massive cholesteryl ester deposition. The binding sites for negatively-charged LDL has been demonstrated so far only on macrophages and other scavenger cells. It is not expressed in cultured fibroblasts, smooth muscle cells, lymphocytes, or adrenal cells. In addition to its affinity for acetylated LDL and malondialdehyde-treated LDL, the macrophage site binds a variety of polyanions. It exhibits a particularly high affinity for certain sulfated polysaccharides (dextran sulfate and fucoidin), certain polynucleotides (polyinosinic acid and polyguanylic acid), polyvinyl sulfate, and maleylated albumin. It is possible that the site that binds negatively-charged LDL may be responsible for the massive accumulation of cholesteryl esters that occurs in vivo in macrophages and other scavenger cells in patients with high levels of circulating plasma LDL.

Acetylation↗
PubMedDate not supplied

Epoxygenase metabolites contribute to nitric oxide-independent afferent arteriolar vasodilation in response to bradykinin.

In the kidney, epoxyeicosatrienoic acids (EETs) have been suggested to be endothelium-derived hyperpolarizing factors (EDHFs). The aim of the present study was to determine the contribution of EETs to the preglomerular vasodilation elicited by bradykinin. Sprague-Dawley rats were studied utilizing an in vitro perfused juxtamedullary nephron preparation. The afferent arteriolar diameter was determined and the diameter averaged 19 +/- 1 microm (n = 26) at a renal perfusion pressure of 100 mm Hg. Addition of 1, 10 and 100 nM bradykinin to the perfusate dose-dependently increased afferent arteriolar diameter by 5 +/- 1, 12 +/- 2 and 17 +/- 2%, respectively. The nitric oxide inhibitor N(omega)-nitro-L-arginine reduced bradykinin-induced afferent arteriolar vasodilation by 50%, and the diameter increased by 9 +/- 2% in response to 100 nM bradykinin. Epoxygenase inhibitors N-methylsulphonyl-6-(2-propargyloxyphenyl)hexanamide or miconazole greatly attenuated the nitric oxide-independent component of the vasodilation elicited by bradykinin. Cyclooxygenase (COX) inhibition attenuated the nitric oxide-independent vasodilation elicited by 1 nM bradykinin but did not significantly affect the vascular response to 100 nM bradykinin. Combined inhibition of nitric oxide, COX and epoxygenase pathways completely abolished bradykinin-mediated afferent arteriolar vasodilation. In additional studies, renal microvessels were isolated and incubated with bradykinin and samples were analyzed by NICI/GC/MS. Under control conditions, renal microvascular EET levels averaged 49 +/- 9 pg/mg/20 min (n = 7). In the presence of bradykinin, EET levels were significantly higher and averaged 81 +/- 11 pg/mg/20 min (n = 7). These data support the concept that EETs are EDHFs and contribute to the nitric oxide-independent afferent arteriolar vasodilation elicited by bradykinin.

8,11,14-Eicosatrienoic Acid↗
PubMedDate not supplied

Relative contributions of cyclooxygenase- and cytochrome P450 omega-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 approximately 145 to approximately 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 omega-hydroxylase enzymes also regulates hypoxic dilation of these vessels.

Animals↗
PubMedDate not supplied

The mechanistic plurality of cytochrome P-450 and its biological ramifications.

The mechanistic plurality of the microsomal cytochrome P-450 enzyme system is illustrated by studies of the oxidative metabolism of benzo[a]pyrene, 3-hydroxybenzo[a]pyrene and arachidonic acid. Rat liver microsomal metabolism of benzo[a]pyrene or 3-hydroxy-benzo[a]pyrene, supported by cumene hydroperoxide, generates benzo[a]pyrene quinones via molecular oxygen-dependent and -independent pathways. Arachidonic acid is metabolized by rat liver microsomal fractions to a variety of oxygenated products, including cis-trans diene conjugated monohydroxy-acids, epoxy-acids as well as omega- and omega-1-oxidation products. The chemistry of the different reaction products is discussed in terms of the possible mechanisms responsible for their formation and the role of the haemoprotein during catalysis. An integrated view for the reaction cycle of cytochrome P-450 is presented.

Animals↗