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Biomedical subjects

F F Hsu

Publications and source records attributed to F F Hsu.

At least 37 records · Page 2Linked to original sources
PubMed2000

Hypochlorous acid-mediated activation of N-acetylbenzidine to form N'-(3'-monophospho-deoxyguanosin-8-yl)-N-acetylbenzidine.

Hypochlorous acid (HOCl), a chemically reactive oxidant, is an important component of the inflammatory response and may contribute to carcinogenesis. This study assessed the possible activation of N-acetylbenzidine (ABZ) by HOCI to form a specific DNA adduct, N'-(3'-monophospho-deoxyguanosin-8-yl)-N-acetylbenzidine. HOCl was incubated with 0.06 mM 3H-ABZ, and transformation assessed by HPLC. Similar results were observed at pH 5.5 or 7.4. A linear increase in transformation was observed from 0.025 to 0.1 mM HOCl with up to 80% of ABZ changed. Approximately, 2 nmoles of HOCI oxidized 1 nmole of ABZ. N-oxidation products of ABZ metabolism, such as N'-hydroxy-N-acetylbenzidine, were not detected. Oxidation of ABZ was prevented by taurine, DMPO, glutathione, and ascorbic acid, whereas mannitol was without effect. Results are consistent with a radical mechanism. In the presence of 2'-deoxyguanosine 3'-monophosphate (dGp), a new product (dGp-ABZ) was observed. The same adduct was observed with DNA. dGp-ABZ was found to be quite stable (>80% remaining) at 70 degrees C in pH 5.5 (60 min) and 7.4 (240 min). Electrospray mass spectrometry indicated that dGp-ABZ was N'-(3'-monophospho-deoxyguanosin-8-yl)-N-acetylbenzidine, and this was confirmed by NMR. 32P-postlabeling in combination with TLC and HPLC determined that the adduct made by either HOCl or prostaglandin H synthase oxidation of ABZ in the presence of dGp or DNA was dGp-ABZ. Thus, HOCI activates ABZ to form dGp-ABZ and may be responsible for the presence of this adduct in peripheral white blood cells from workers exposed to benzidine. Reaction of ABZ with HOCl provides an easy, convenient method for preparing dGp-ABZ.

Animals↗
PubMed2000

Anti-hypercholesterolaemia, antioxidant activity and free radical scavenger effects of traditional Chinese medicine prescriptions used for stroke.

The generation of oxygen radicals and lipid peroxidation may be factors in the cerebral damage secondary to ischaemia of the cerebrovascular disease, as in stroke. Five traditional Chinese medicinal prescriptions were investigated for their antioxidant activity: Shiee Fuu Jwu Iu Tang (TCMP1), Oh Yaw Shuen Chin Saan (TCMP2), Buu Yang Hwan Wuu Tang (TCMP3), Sheau Shiuh Ming Tang (TCMP4), and Chir Hwu Jia Long Guu Muu Lih Tang (TCMP5). Anti-lipid peroxidation, anti-superoxide formation and free radical scavenger activity were determined by the FeCl2--ascorbic acid-induced lipid peroxidation effects on lipids in-vitro, xanthine oxidase inhibition, cytochrome C system and an electron spin resonance spectrometer, respectively. The results showed that TCMP5 had greater anti-lipid peroxidation and anti-superoxide formation activity than the other prescriptions. TCMP4 had the greatest free radical scavenging effect, TCMP5 showed the greatest superoxide radical scavenger activity and TCMP3 showed the greatest hydroxyl radical scavenger activity. Tests were also performed to evaluate the effects of the five prescriptions on blood lipid in-vivo. The test showed that the prescriptions decreased the level of total cholesterol and LDL-cholesterol in serum in high cholesterol-fed rats. From these results, it seems probable that these prescriptions may be effective in the prevention and therapy of stroke and ischaemia.

Animals↗
PubMed2000

Electrospray ionization mass spectrometry analyses of nuclear membrane phospholipid loss after reperfusion of ischemic myocardium.

The role of nuclear membrane phospholipids as targets of phospholipases resulting in the generation of nuclear signaling messengers has received attention. In the present study, we have exploited the utility of electrospray ionization mass spectrometry to determine the phospholipid content of nuclei isolated from perfused hearts. Rat heart nuclei contained choline glycerophospholipids composed of palmitoyl and stearoyl residues at the sn-1 position with oleoyl, linoleoyl, and arachidonoyl residues at the sn-2 position. Diacyl molecular species were the predominant molecular subclass in the choline glycerophospholipids, with the balance of the molecular species being plasmalogens. In the ethanolamine glycerophospholipid pool from rat heart nuclei approximately 50% of the molecular species were plasmalogens, which were enriched with arachidonic acid at the sn-2 position. A 50% loss of myocytic nuclear choline and ethanolamine glycerophospholipids was observed in hearts rendered globally ischemic for 15 min followed by 90 min of reperfusion in comparisons with the content of these phospholipids in control perfused hearts. The loss of nuclear choline and ethanolamine glycerophospholipids during reperfusion of ischemic myocardium was partially reversed by the calcium-independent phospholipase A(2) (iPLA(2)) inhibitor bromoenol lactone (BEL), suggesting that the loss of nuclear phospholipids during ischemia/reperfusion is mediated, in part, by iPLA(2). Western blot analyses of isolated nuclei from ischemic hearts demonstrated that iPLA(2) is translocated to the nucleus after myocardial ischemia. Taken toghether, these studies have demonstrated that nuclear phospholipid mass decreases after myocardial ischemia by a mechanism that involves, at least in part, phospholipolysis mediated by iPLA2.

Active Transport, Cell Nucleus↗
PubMed1999

Peroxygenase metabolism of N-acetylbenzidine by prostaglandin H synthase. Formation of an N-hydroxylamine.

Synthesis of prostaglandin H2 by prostaglandin H synthase (PHS) results in a two-electron oxidation of the enzyme. An active reduced enzyme is regenerated by reducing cofactors, which become oxidized. This report examines the mechanism by which PHS from ram seminal vesicle microsomes catalyzes the oxidation of the reducing cofactor N-acetylbenzidine (ABZ). During the conversion of 0.06 mM ABZ to its final end product, 4'-nitro-4-acetylaminobiphenyl, a new metabolite was observed when 1 mM ascorbic acid was present. Similar results were observed whether 0.2 mM arachidonic acid or 0.5 mM H2O2 was used as the substrate. This metabolite co-eluted with synthetic N'-hydroxy-N-acetylbenzidine (N'HA), but not with N-hydroxy-N-acetylbenzidine. The new metabolite was identified as N'HA by electrospray ionization/MS/MS. N'HA represented as much as 10% of the total radioactivity recovered by high pressure liquid chromatography. When N'HA was substituted for ABZ, PHS metabolized N'HA to 4'-nitro-4-acetylaminobiphenyl. Inhibitor studies demonstrated that metabolism was due to PHS, not cytochrome P-450. The lack of effect of 5,5-dimethyl-1-pyrroline N-oxide, mannitol, and superoxide dismutase suggests the lack of involvement of one-electron transfer reactions and suggests that hydroxyl radicals and superoxide are not sources of oxygen or oxidants. Oxygen uptake studies did not demonstrate a requirement for molecular oxygen. When [18O]H2O2 was used as the substrate, 18O enrichment was observed for 4'-nitro-4-acetylaminobiphenyl, but not for N'HA. A 97% enrichment was observed for one atom of 18O, and a 17 +/- 7% enrichment was observed for two 18O atoms. The rapid exchange of 18O-N'HA with water was suggested to explain the lack of enrichment of N'HA and the low enrichment of two 18O atoms into 4'-nitro-4-acetylaminobiphenyl. Results demonstrate a peroxygenase oxidation of ABZ and N'HA by PHS and suggest a stepwise oxidation of ABZ to N'-hydroxy, 4'-nitroso, and 4'-nitro products.

Benzidines↗
PubMed1999

Studies of the role of group VI phospholipase A2 in fatty acid incorporation, phospholipid remodeling, lysophosphatidylcholine generation, and secretagogue-induced arachidonic acid release in pancreatic islets and insulinoma cells.

An 84-kDa group VI phospholipase A2 (iPLA2) that does not require Ca2+ for catalysis has been cloned from Chinese hamster ovary cells, murine P388D1 cells, and pancreatic islet beta-cells. A housekeeping role for iPLA2 in generating lysophosphatidylcholine (LPC) acceptors for arachidonic acid incorporation into phosphatidylcholine (PC) has been proposed because iPLA2 inhibition reduces LPC levels and suppresses arachidonate incorporation and phospholipid remodeling in P388D1 cells. Because islet beta-cell phospholipids are enriched in arachidonate, we have examined the role of iPLA2 in arachidonate incorporation into islets and INS-1 insulinoma cells. Inhibition of iPLA2 with a bromoenol lactone (BEL) suicide substrate did not suppress and generally enhanced [3H]arachidonate incorporation into these cells in the presence or absence of extracellular calcium at varied time points and BEL concentrations. Arachidonate incorporation into islet phospholipids involved deacylation-reacylation and not de novo synthesis, as indicated by experiments with varied extracellular glucose concentrations and by examining [14C]glucose incorporation into phospholipids. BEL also inhibited islet cytosolic phosphatidate phosphohydrolase (PAPH), but the PAPH inhibitor propranolol did not affect arachidonate incorporation into islet or INS-1 cell phospholipids. Inhibition of islet iPLA2 did not alter the phospholipid head-group classes into which [3H]arachidonate was initially incorporated or its subsequent transfer from PC to other lipids. Electrospray ionization mass spectrometric measurements indicated that inhibition of INS-1 cell iPLA2 accelerated arachidonate incorporation into PC and that inhibition of islet iPLA2 reduced LPC levels by 25%, suggesting that LPC mass does not limit arachidonate incorporation into islet PC. Gas chromatography/mass spectrometry measurements indicated that BEL but not propranolol suppressed insulin secretagogue-induced hydrolysis of arachidonate from islet phospholipids. In islets and INS-1 cells, iPLA2 is thus not required for arachidonate incorporation or phospholipid remodeling and may play other roles in these cells.

Animals↗
PubMed1999

Structural characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument.

We describe features of tandem mass spectra of lithiated adducts of triacylglycerol (TAG) species obtained by electrospray ionization mass spectrometry (ms) with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument. The spectra distinguish isomeric triacylglycerol species and permit assignment of the mass of each fatty acid substituent and positions on the glycerol backbone to which substituents are esterified. Source CAD-MS2 experiments permit assignment of double bond locations in polyunsaturated fatty acid substituents. The ESI/MS/MS spectra contain [M + Li - (RnCO2H)]+, [M + Li - (RnCO2Li)]+, and RnCO+ ions, among others, that permit assignment of the masses of fatty acid substituents. Relative abundances of these ions reflect positions on the glycerol backbone to which substituents are esterified. The tandem spectra also contain ions reflecting combined elimination of two adjacent fatty acid residues, one of which is eliminated as a free fatty acid and the other as an alpha, beta-unsaturated fatty acid. Such combined losses always involve the sn-2 substituent, and this feature provides a robust means to identify that substituent. Fragment ions reflecting combined losses of both sn-1 and sn-3 substituents without loss of the sn-2 substituent are not observed. Schemes are proposed to rationalize formation of major fragment ions in tandem mass spectra of lithiated TAG that are supported by studies with deuterium-labeled TAG and by source CAD-MS2 experiments. These schemes involve initial elimination of a free fatty acid in concert with a hydrogen atom abstracted from the alpha-methylene group of an adjacent fatty acid, followed by formation of a cyclic intermediate that decomposes to yield other characteristic fragment ions. Determination of double bond location in polyunsaturated fatty acid substituents of TAG is achieved by source CAD experiments in which dilithiated adducts of fatty acid substituents are produced in the ion source and subjected to CAD in the collision cell. Product ions are analyzed in the final quadrupole to yield information on double bond location.

Fatty Acids↗
PubMed1999

Distinction among isomeric unsaturated fatty acids as lithiated adducts by electrospray ionization mass spectrometry using low energy collisionally activated dissociation on a triple stage quadrupole instrument.

Features of tandem mass spectra of dilithiated adduct ions of unsaturated fatty acids obtained by electrospray ionization mass spectrometry with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument are described. These spectra distinguish among isomeric unsaturated fatty acids and permit assignment of double-bond location. Informative fragment ions reflect cleavage of bonds remote from the charge site on the dilithiated carboxylate moiety. The spectra contain radical cations reflecting cleavage of bonds between the first and second and between the second and third carbon atoms in the fatty acid chain. These ions are followed by a closed-shell ion series with members separated by 14 m/z units that reflect cleavage of bonds between the third and fourth and then between subsequent adjacent pairs of carbon atoms. This ion series terminates at the member reflecting cleavage of the carbon-carbon single bond vinylic to the first carbon-carbon double bond. Ions reflecting cleavages of bonds distal to the double bond are rarely observed for monounsaturated fatty acids and are not abundant when they occur. For polyunsaturated fatty acids that contain double bonds separated by a single methylene group, ions reflecting cleavage of carbon-carbon single bonds between double bonds are abundant, but ions reflecting cleavages distal to the final double bond are not. Cleavages between double bonds observed in these spectra can be rationalized by a scheme involving a six-membered transition state and subsequent rearrangement of a bis-allylic hydrogen atom to yield a terminally unsaturated charge-carrying fragment and elimination of a neutral alkene. The location of the beta-hydroxy-alkene moiety in ricinoleic acid can be demonstrated by similar methods. These observations offer the opportunity for laboratories that have tandem quadrupole instruments but do not have instruments with high energy CAD capabilities to assign double bond location in unsaturated free fatty acids by mass spectrometric methods without derivatization.

Fatty Acids, Unsaturated↗
PubMed1999

Synthesis, isolation, and characterization of the adduct formed in the reaction of p-hydroxyphenylacetaldehyde with the amino headgroup of phosphatidylethanolamine and phosphatidylserine.

The adducts that form when aldehydes modify proteins have been implicated in the pathogenesis of vascular disease and aging. Our previous studies indicated that p-hydroxyphenylacetaldehyde (pHA), the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes, covalently modifies the epsilon-amino group of lysine residues at sites of inflammation. Here, we report that pHA also reacts with the amino group of synthetic phospholipids and red blood cell model systems. Using fast atom bombardment mass spectrometric analysis of ethanolamine glycerophospholipid or serine glycerophospholipid incubated with pHA and NaBH3CN, we detected products that were consistent with reduced phospholipid Schiff base adducts. We confirmed the reaction of the aldehyde with the amino group through 1H NMR and mass spectrometric analysis of polar headgroups recovered from the modified and reduced parent lipid. When phospholipid model systems and cell membranes were exposed to physiological levels of L-tyrosine and the myeloperoxidase/hydrogen peroxide/chloride system followed by treatment with NaBH3CN, reduced Schiff base adducts of pHA with ethanolamine glycerophospholipid and serine glycerophospholipid (pHA-PE and pHA-PS, respectively) were produced. The reaction required myeloperoxidase, hydrogen peroxide, L-tyrosine, and chloride ion; it was inhibited by catalase or heme poisons, implicating hydrogen peroxide and peroxidase in the pathway. Collectively, these results demonstrate that an aldehyde generated by the myeloperoxidase system of phagocytes can covalently modify the amino groups of phosphatidylethanolamine and phosphatidylserine. Because amino glycerophospholipids are critical components of cell membranes and circulating lipoproteins such as LDL, similar reactions may play important roles in the initiation or progression of disease at sites of inflammation.

Acetaldehyde↗
PubMed1998

Electrospray ionization tandem mass spectrometric analysis of sulfatide. Determination of fragmentation patterns and characterization of molecular species expressed in brain and in pancreatic islets.

The sphingolipid sulfatide is a component of myelin and some non-neuronal cells. Antibodies to sulfatide occur in some patients with autoimmune neuropathies and in patients with insulin-dependent diabetes mellitus (IDDM) caused by immunologic destruction of insulin-secreting pancreatic islet beta-cells. Distinct sulfatide molecular species may differ in immunogenicity, and facile means to identify sulfatide species in islets and other tissues obtainable in only small amounts could be useful. Electrospray ionization mass spectrometry (ESI/MS) permits structural determination of small quantities of phospholipids and is applied here to sulfatide analysis. We find that sulfatide standards are readily analyzed by negative ion ESI/MS, and tandem mass spectra of individual species exhibit some ions common to all species and other ions that reflect distinct fatty acid substituents in different sulfatide molecules. A signature ion cluster resulting from cleavage directed by the alpha-hydroxy group of sulfatide species with a hydroxylated fatty acid substituent identifies such species. Sulfatide profiles in tissue lipid extracts can be obtained by ESI/MS/MS scanning for common sulfatide ions and for ions reflecting fatty acid substituents. Islets are demonstrated to contain sulfatide and to exhibit a profile of species different from that of brain.

Animals↗
PubMed1998

Human neutrophils employ myeloperoxidase to convert alpha-amino acids to a battery of reactive aldehydes: a pathway for aldehyde generation at sites of inflammation.

We have recently demonstrated that activated phagocytes employ the heme protein myeloperoxidase, H2O2, and Cl- to oxidize the aromatic amino acid l-tyrosine to the reactive aldehyde p-hydroxyphenylacetaldehyde. We now present evidence for the generality of this reaction by demonstrating that neutrophils employ the myeloperoxidase-H2O2-Cl- system to oxidize nearly all of the common alpha-amino acids to yield a family of reactive aldehydes. Chemical characterization suggested that reactive carbonyl moieties were generated during amino acid oxidation by myeloperoxidase. The structures of amino-acid-derived aldehydes were confirmed using a variety of mass spectrometric methods. Aldehyde production required myeloperoxidase, H2O2, Cl-, and an amino acid; it was inhibited by heme poisons and catalase. Hypochlorous acid was the apparent oxidizing intermediate because its addition to alpha-amino acids resulted in the formation of the anticipated aldehyde. Stimulated human neutrophils likewise generated aldehydes from all classes of alpha-amino acids by a pathway inhibited by heme poisons and catalase, implicating myeloperoxidase and H2O2 in the cell-mediated reaction. Aldehyde production accounted for a significant fraction of the H2O2 generated by stimulated neutrophils at physiological concentrations of amino acids. Collectively, these results suggest that amino-acid-derived aldehydes represent a product of reactive oxidant species generated by activated phagocytes.

Aldehydes↗
PubMed1998

Electrospray ionization mass spectrometric analyses of phospholipids from rat and human pancreatic islets and subcellular membranes: comparison to other tissues and implications for membrane fusion in insulin exocytosis.

Glucose-induced insulin secretion from pancreatic islets involves hydrolysis of arachidonic acid from phospholipids as an intermediary event. Accumulation of nonesterified arachidonate in islet membranes may influence both ion fluxes that trigger insulin secretion and fusion of secretory granule and plasma membranes. Recent findings indicate that plasmenylethanolamine species may also participate in fusion of such membranes, but high-performance liquid chromatographic (HPLC) and gas chromatographic/mass spectrometric (GC/MS) analyses of islet secretory granule phospholipids suggested that they contain little plasmenylethanolamine. Here, electrospray ionization mass spectrometry (ESI/MS) of intact phospholipid molecules is used to demonstrate that the most prominent components of all major glycerophospholipid headgroup classes in islets are arachidonate-containing species. Such species contribute the majority of the ESI/MS negative ion current from rat and human islet glycerophosphoethanolamine (GPE), and the fraction of GPE negative ion current contributed by plasmenylethanolamine species in rat islets is higher than that for rat liver or heart and similar to that for brain. The most prominent sn-2 substituent of plasmenylethanolamine species in brain is docosahexaenoate and in islets is arachidonate. Arachidonate-containing plasmenylethanolamine species are also prominent components of GPE from islet secretory granules and plasma membranes. Fusion of islet secretory granule and plasma membranes is demonstrated to be catalyzed by cytosolic components from insulinoma cells and rat brain with chromatographic similarities to a rabbit brain factor that specifically catalyzes fusion of plasmenylethanolamine-containing membranes.

Animals↗
PubMed1998

Human neutrophils employ the myeloperoxidase-hydrogen peroxide-chloride system to oxidize alpha-amino acids to a family of reactive aldehydes. Mechanistic studies identifying labile intermediates along the reaction pathway.

We have recently demonstrated that neutrophils oxidize nearly all of the amino acids commonly found in plasma to a corresponding family of aldehydes in high yield. The reaction is mediated by hypochlorous acid (HOCl), the major oxidant generated by the myeloperoxidase-H2O2-Cl- system of phagocytes. We now present evidence for the underlying mechanism of this reaction, including the structural requirements and reaction intermediates formed. Utilizing mass spectrometry and isotopically labeled amino acids, we rule out hydrogen atom abstraction from the alpha-carbon as the initial event in aldehyde formation during amino acid oxidation, a pathway known to occur with ionizing radiation. Aldehyde generation from amino acids required the presence of an alpha-amino moiety; beta- and epsilon-amino acids did not form aldehydes upon oxidation by either the myeloperoxidase system or HOCl, generating stable monochloramines instead. UV difference spectroscopy, high pressure liquid chromatography, and multinuclear (1H,15N) NMR spectroscopy established that the conversion of alpha-amino acids into aldehydes begins with generation of an unstable alpha-monochloramine, which subsequently decomposes to yield an aldehyde. Precursor product relationships between alpha-amino acid and alpha-monochloramine, and alpha-monochloramine and aldehyde were confirmed by high pressure liquid chromatography purification of the reaction intermediate and subsequent 1H and 15N NMR spectroscopy. Collectively, these results detail the chemical mechanism and reaction intermediates generated during conversion of amino acids into aldehydes by myeloperoxidase-generated HOCl.

Aldehydes↗
PubMed1998

The selective activation of the cardiac sarcolemmal sodium-calcium exchanger by plasmalogenic phosphatidic acid produced by phospholipase D.

Since plasmalogens are the predominant phospholipid of cardiac sarcolemma, the activation of the sodium-calcium exchanger by either plasmenylethanolamine or plasmalogenic phosphatidic acid generated by phospholipase D was explored. Sodium-calcium exchange activity was 7-fold greater in proteoliposomes comprised of plasmenylethanolamine compared to proteoliposomes comprised of only plasmenylcholine. Phospholipase D treatment of proteoliposomes resulted in 1 mol % conversion of plasmenylcholine or phosphatidylcholine to their respective phosphatidic acid molecular species with a concomitant 8-fold or 2-fold activation of sodium-calcium exchange activity, respectfully. Thus, phospholipase D-mediated hydrolysis of plasmalogens to phosphatidic acid may be an important mechanism for the regulation of the sodium-calcium exchanger.

Animals↗
PubMed1998

Formation of lithiated adducts of glycerophosphocholine lipids facilitates their identification by electrospray ionization tandem mass spectrometry.

Electrospray ionization (ESI) tandem mass spectrometry (MS) has simplified analysis of phospholipid mixtures, and, in negative ion mode, permits structural identification of picomole amounts of phospholipid species. Collisionally activated dissociation (CAD) of phospholipid anions yields negative ion tandem mass spectra that contain fragment ions representing the fatty acid substituents as carboxylate anions. Glycerophosphocholine (GPC) lipids contain a quaternary nitrogen moiety and more readily form cationic adducts than anionic species, and positive ion tandem mass spectra of protonated GPC species contain no abundant ions that identify fatty acid substituents. We report here that lithiated adducts of GPC species are readily formed by adding lithium hydroxide to the solution in which phospholipid mixtures are infused into the ESI source. CAD of [MLi+] ions of GPC species yields tandem mass spectra that contain prominent ions representing losses of the fatty acid substituents. These ions and their relative abundances can be used to assign the identities and positions of the fatty acid substituents of GPC species. Tandem mass spectrometric scans monitoring neutral losses of the head-group or of fatty acid substituents from lithiated adducts can be used to identify GPC species in tissue phospholipid mixtures. Similar scans monitoring parents of specific product ions can also be used to identify the fatty acid substituents of GPC species, and this facilitates identification of distinct isobaric contributors to ions observed in the ESI/MS total ion current.

Animals↗
PubMed1998

Ma-huang strikes again: ephedrine nephrolithiasis.

Ephedrine and its metabolites are naturally occurring alkaloids that can be derived from evergreens worldwide and have been used as medicinals for hundreds of years. Because they have "real" pharmacological alpha and beta catecholamine effects and are "natural" products, the alternative medicine industry has popularized them for multiple uses, including asthma, weight loss, energy and sexual enhancement, and euphoria. Several recent reviews have documented the dangerous nature of using these "drugs" unsupervised, including multiple deaths, and the FDA is currently reviewing ephedrine's use in the alternative medicine industry. We report a new toxicity, ephedrine nephrolithiasis, in a patient using an energy supplement, Ma-Huang extract, which contains ephedrine. Although previously not reported, the Louis C. Herring and Company kidney stone database show that this is an endemic complication of ephedrine with hundreds of previous episodes. Using gas chromatography (GC) mass spectrometry, we were able to positively identify the chemical structure of our patient's stone, as well as other similar stones from Louis Herring, as containing ephedrine, norephedrine, and pseudoephedrine.

Adult↗
PubMed1998

Mass spectrometric evidence that agents that cause loss of Ca2+ from intracellular compartments induce hydrolysis of arachidonic acid from pancreatic islet membrane phospholipids by a mechanism that does not require a rise in cytosolic Ca2+ concentration.

Stimulation of pancreatic islets with glucose induces phospholipid hydrolysis and accumulation of nonesterified arachidonic acid, which may amplify the glucose-induced Ca2+ entry into islet beta-cells that triggers insulin secretion. Ca2+ loss from beta-cell intracellular compartments has been proposed to induce both Ca2+ entry and events dependent on arachidonate metabolism. We examine here effects of inducing Ca2+ loss from intracellular sequestration sites with ionophore A23187 and thapsigargin on arachidonate hydrolysis from islet phospholipids. A23187 induces a decline in islet arachidonate-containing phospholipids and release of nonesterified arachidonate. A23187-induced arachidonate release is of similar magnitude when islets are stimulated in Ca2+-replete or in Ca2+-free media or when islets loaded with the intracellular Ca2+ chelator BAPTA are stimulated in Ca2+-free medium, a condition in which A23187 induces no rise in beta-cell cytosolic [Ca2+]. Thapsigargin also induces islet arachidonate release under these conditions. A23187- or thapsigargin-induced arachidonate release is prevented by a bromoenol lactone (BEL) inhibitor of a beta-cell phospholipase A2 (iPLA2), which does not require Ca2+ for catalytic activity and which is negatively modulated by and physically interacts with calmodulin by Ca2+-dependent mechanisms. Agents that cause Ca2+ loss from islet intracellular compartments thus induce arachidonate hydrolysis from phospholipids by a BEL-sensitive mechanism that does not require a rise in cytosolic [Ca2+], and a BEL-sensitive enzyme-like iPLA2 or a related membranous activity may participate in sensing Ca2+ compartment content.

Animals↗