Ebselen, a selenoorganic compound as glutathione peroxidase mimic

Free Radical Biology & Medicine, Vol. 14, lap. 313-323, 1993 Printed in the USA. All fights reserved.

0891-5849/93 $6.00 + .00 Copyright © 1993 Pergamon Press Ltd.

Review Article EBSELEN, A SELENOORGANIC COMPOUND AS GLUTATHIONE PEROXIDASE MIMIC

H E L M U T SIES Institut f'tir Physiologische Chemie I, Heinrich Heine Universitat Dtisseldorf, Moorenstrasse 5, D-4000-Dtisseldorf, Germany (Received 19 August 1992; Revised and Accepted 16 September 1992) Abstract--The selenoorganic compound ebselen, 2-phenyl-l,2-benzisoselenazol-3(2H)-one, exhibits activity as an enzyme mimic. The reaction catalyzed is that ofa glutathione (GSH) peroxidase (i.e., the reduction ofa hydroperoxide at the expense of thiol). The specificity for substrates ranges from hydrogen peroxide and smaller organic hydroperoxides to membrane-bound phospholipid and cholesterol hydroperoxides. In addition to glutathione, the thiol reductant cosubstrate can be dithioerythritol, N-acetylcysteine or dihydrolipoate, or other suitable thiol compounds. Ebselen also has properties such as free radical and singlet oxygen quenching. Model experiments in vitro with liposomes, microsomes, isolated cells, and organs show that the protection against oxidative challenge afforded by ebselen can be explained largely by the activity as GSH peroxidase mimic. Whether this also explains the known preliminary results in clinical settings is yet open. The metabolism and disposition of ebselen is presented in this review. The main point is that the selenium is not bioavailable, explaining the extremely low toxicity observed in animal studies. The occurrence of natural GPx mimics, ovothiol and related compounds, is briefly mentioned. Keywords--Enzyme mimic, Selenoorganic compounds, Ebselen, Oxidative stress, Antioxidant, Glutathione peroxidase, Phospholipid hydroperoxide cytoprotection, Free radicals

antioxidant defense in tissues, so that a potential pharmacological application becomes of interest. Early on, it became clear that many of the biological properties of ebselen were related to its property as an enzyme mimic, carrying out the function of the selenoenzyme, GSH peroxidase (GPx) and, as found by Maiorino et al., 3 of phospholipid hydroperoxide GSH peroxidase (PHGPx). This overview presents the properties of ebselen as a GSH peroxidase mimic and discusses some of the biochemical and pharmacological reactivities. It is obvious that biological functions ofebselen and its derivatives might extend to other reactions in addition to the reduction of hydroperoxides, with the role of selenium in biology and medicine not yet being fully known. Klayman 4 and Shamberger 5 and Parnham and Graf 6 reviewed a number of selenoorganic compounds as potential therapeutic agents.

INTRODUCTION

In 1984, the glutathione peroxidase-like activity of a novel biologically active selenoorganic compound, ebselen (then called PZ 51), was described. 1'2 Since then, extended research on this interesting molecule ranged from pulse-radiolytic studies on radical reactivity through its biological properties in cells and organs all the way to clinical settings. Basically, the compound is considered capable of contributing to the

Helmut Sies has been Professor and Chairman, Department of Physiological Chemistry l, at the Faculty of Medicine, University of Diisseldorf, since 1979. After studying medicine at T~bingen, Paris, and Munich (MD, 1967), he received his Habilitation for Physiological Chemistry and Physical Biochemistry at the University of Munich in 1972. He worked with Britton Chance, Johnson Research Foundation (Philadelphia, 1969-1970), and was at the University of California at Berkeley as Visiting Professor, Department of Biochemistry (1984-1985) and at the Department of Molecular and Cell Biology as Miller Visiting Professor, 1992. In 1990, he was Burroughs-Wellcome Visiting Professor of Pharmacology at the University of Texas at Austin. He served as President of the Society for Free Radical Research (SFRR), European Region, in 19891990. His research interests in biological oxidations include oxidative stress, oxidants, and antioxidants (glutathione, tocopherols, and carotenoids).

BACKGROUND

The biological importance of selenium was first recognized by Schwarz and Foltz 7 in their classical nutri313

314

H. SIES

tional studies, identifying selenium as an integral part of an essential protective micronutrient, then called factor 3, against dietary liver necrosis. The milestones in development of current knowledge on the enzymatic reduction of hydroperoxides by GSH peroxidases also go back 35 years (see review by Floh68): The "classical" GPx of bovine erythrocytes was discovered by Mills. 9 It was shown to be a selenoprotein l°'~l with a selenocysteine in each of the four active sites) 2'13 Its amino acid sequence was elucidated 14 and confirmed by sequencing the corresponding cDNA, 15 and the three-dimensional structure was determined, t6,17 Another GSH peroxidase was isolated by Ursini et al. 18,19that acts on peroxidized phospholipids in biological membranes. This enzyme is the phospholipid hydroperoxide GSH peroxidase, called PHGPx. It is monomeric and has recently been established as a selenoenzyme distinct from the classical GPx based on cDNA and amino acid sequencing. 2° GPx activity in plasma has been attributed to a protein immunologically distinct from, but homologous to, the classical GPx. 21'2z Thus, there are at least three different glutathione peroxidases, and a number of further selenopeptides and selenoproteins of unknown function have been discovered. 23 The catalytic mechanism at the selenocysteine moiety in the reaction center of these different enzyme proteins seems to be similar. 8 Further, the catalytic cycle is related to that deduced for ebselen (see later in this review). CHEMISTRY

Synthesis The compound ebselen, 2-phenyl-l,2-benzisoselenazol-3(2H)-one, also called PZ 51, was synthesized at Nattermann & Cie. GmbH, Cologne, Germany, under the following patents: European Patent 44,971; Germany 3,027,073; Japan K-8256,427; U.S. 4,352,799. The synthesis is based on those described by Lesser and Weiflz4 and Weber and Renson, 2s reacting 2-chlorocarbonylbenzeneselenenyl chloride with aniline in a Schotten-Baumann reaction as described by Fischer and Dereu. 26 Several analogs and derivatives were also synthesized.26-31

Reaction scheme for GPx-like activity The reaction cycle for the enzymatic catalysis is thought to proceed in three main steps, involving the enzyme-bound selenocysteine, E-Cys-SeH, present as the selenol or more likely as the selenolate (see Ref. 8 for a detailed discussion of this and of the interme-

© II

0

•

,.

H20

slow •

!

SG Scheme 1. GPx-like activity of ebselen as discussed by Fischer and Dereu. From Ref. 26.

diate complexes involved). In the first step (reaction 1), the organic hydroperoxide ROOH reacts to yield the selenenic acid, E-Cys-SeOH and the corresponding alcohol, ROH. The following two steps consist of the sequential reduction by thiol, GSH; reaction 2 gives the selenodisulfide and water, and reaction 3 regenerates the selenol and the disulfide, oxidized glutathione (GSSG). The overall reaction is that of GPx or PHGPx (reaction 4). E-Cys-SeH + ROOH --~ E-Cys-SeOH + ROH (1) E-Cys-SeOH + GSH --~ E-Cys-Se-SG + H20 (2) E-Cys-Se-SG + GSH --~ E-Cys-SeH + GSSG

(3)

ROOH + 2 GSH --~ ROH + H20 + GSSG (4) In their chemical analysis of the GPx-like reactivity of ebselen, Fischer and Dereu 26 proposed that the reduction and oxidation ofebselen can be summarized by two cycles, explaining the catalytic reduction of hydroperoxides in the presence of thiol (Scheme 1). This scheme differs from those proposed for the enzyme GPx (see Ref. 8) and for selenocysteine32'33 (see

Ebselen as GSH peroxidase mimic

315

0 H II I ~

GSSG

FA-yC-N-LV2 ~I..SeH

ROOH

GSH

0 H ,,

Se- SG Ebselen Seienodisulfide

H20

Ebselen Selenenic Acid

GSH

Scheme 2. GPx-like activity of ebselen in analogy to the enzymatic catalysis.

also Ref. 34) in that it is independent of a selenol intermediate. For ebselen, the stabilisation of the intermediate selenenic acid is thought by these authors to be achieved through reaction with the NH function of the benzamide to yield a cyclic benzoyl selenenamide, benzisoselenazole. Fischer and D e r e u 26 suggest that this way of stabilisation of a selenenic acid through cyclization might also occur in the enzyme, GPx, as peptidic NH-bonds from tryptophan (Trp 148; highly conserved in different peroxidases 2°) as well as the NH2 moiety ofglutamine (GIN 70), both in proximity of the selenocysteine (Se Cys 35), as shown by crystallography. 16,17 Cycle A in Scheme 1 is dependent on a low thiol concentration and a high hydroperoxide concentration, unlikely to resemble biological conditions. Cycle B in Scheme 1 will take place in the presence of excess thiol and low hydroperoxide, as occurs in biology. The formation of the diselenide is a key step for catalytic activity, being the slowest one. According to Ref. 26 and further work, 35 the diselenide would react with the hydroperoxide to yield the parent compound and water. It was also noted 26 that the selenenyl sulfide might constitute a storage form ofebselen and eventually be responsible for transport of the drug. However, in a kinetic study of the catalysis of the GPx reaction by ebselen, Maiorino et al. 36 concluded that the mechanism appeared kinetically identical to that of the enzyme reaction, a ter uni ping pong mechanism. Carboxymethylation ofebselen by iodoacetate to an inactive derivative suggested that a selenol moiety is involved. Recently, Cotgreave et al. 31 have

devised a method to detect ebselen selenol by its reaction with l-chloro-2,4,-dinitrobenzene. In applying this method, it w a s c o n c l u d e d 37 that the selenol is the predominant molecular species responsible for the GSH- or dithiothreitol-dependent peroxidase activity of ebselen. Thus, it appears that the reaction scheme of the catalysis of the GPx reaction by ebselen occurs as written in Scheme 2, in analogy to the mechanism of GPx enzyme catalysis8,38as initially deduced by Wendel et al. 2 The redox chemistry of selenocysteine model systems was studied by Reich and J a s p e r s e . 39 Unlike the enzyme-catalyzed reaction with binding sites conferring specificity for GSH (see Ref. 8), ebselen can utilize other thiols in addition to GSH (e.g., dithioerythritol, 4° N-acetylcysteine,41 or dihydrolipoate35).

Detection of GPx-like activity of ebselen The first demonstration of the ability of ebselen to carry out the reduction of hydroperoxides at the expense of thiol reducing equivalents (i.e., the reaction carried out by GSH peroxidase) was performed using a coupled enzymatic assay;* the compound, then called PZ51, was compared to the sulfur analog, PZ 25, which did not exhibit this activity. These data, together with further work on the antioxidant properties of ebselen, were published by MUller et al.t Wen* Sies et al., unpublished work, 1981.

316

H. SIES

10,000-

A

(~) 0

PZ 51

5~00-

lb 0JM)

2b PZ 51, Phorone pretreated

025

~

10/300-

i 5~00-

(.9 0

o

lo.ooo-

!

lb C

(~1

o

1s PZ 25

lb Time (rain)

Fig. 1. Time course of ADP/iron-induced generation of low-level chemiluminescence and the effects of different concentrations of ebselen(PZ S1) and its sulfur analog (PZ 25) isolated rat hepatocytes.A and C, hepatocytes from untreated rats; B, hepatocytes from phorone-pretreated rats. From Ref. 40.

del et al. 2 reported GPx-like activity by measuring the loss of GSH and extended the kinetic analysis. The activation energy for the ebselen-catalyzed reaction is 55 kJ/mol per °K, in comparison to 36.5 kJ/mol per °K for the enzyme-catalyzed reaction for GPx. 2 The following assay systems for the detection of GPx-like activity have been described:

1. Coupled enzymatic assay. As in usual coupled enzymatic assays, the test reaction (here GPx) is coupled to an indicator reaction operated such that the test reaction is rate limiting. The indicator reaction is that of glutathione disulfide (GSSG) reductase, and the loss of reduced nicotinamide adenine dinucleotide phosphate (NADPH) is monitored

Ebselen as GSH peroxidase mimic Table 1. Biological Model Studies Employing Ebselen Biological Model

Reference

Ethanol-induced liver cell damage Lipid peroxidation in liver microsomes Secretory activities of macrophages Oxidative damage to hepatocytes Anti-inflammatory effects Inhibition of neutrophil lipoxygenase Lipid peroxidation in liver microsomes Galactosamine/endotoxin-induced hepatitis Inhibition of cytochrome P450 reductase Leukotriene B4 formation in leukocytes Exudative diathesis in chicken Experimental allergic neuritis Periarticular inflammation Gingivitis Superoxide production in leukocytes Diquat toxicity in hepatocytes Alveolitis and bronchiolitis Granulocyte oxidative burst Cerebral ischemic edema Arachidonate metabolism in ocular tissue Interaction with cytochrome P450 Microsomal drug biotransformation Microsomal electron transport Antimalarial activity Inflammatory and gastric effects Gastric acid secretion Contractile responses in lung strips Acute gastric mucosal injury Endotoxin-induced fetal resorption Interferon and cytokine induction Platinum(ll) nephrotoxicity Oxidative damage to mitochondria Experimental diabetes Ischemic brain edema Superoxide production in leukocytes Acute pancreatitis Lymphocyte proliferation Mitogenic activity in blood Inhibition of mitomycin C toxicity Calcium homeostasis in platelets IP3 receptor binding Low-density lipoprotein oxidation Renal preservation in ischemia Reoxygenation injury in Kupffer cells Nitric oxide synthesis in Kupffer cells Endothelial cell injury

continuously etry. 1,36

by

Cadenas et al.7° Miiller et alJ Parnham & Kindt7t Miiller et al.4° Parnham et al.4s Safayhi et al. 72 Hayashi & Slater45 Wendel & Tiegs73 Wendel et al.74 Kuhl et al. 75'76 Mercurio & C o m b s 77 Hartung et al. TM Schalkwijk et al.79 Van Dyke et al.s° Ishikawa et al.st Cotgreave et al.4j Cotgreave et al.sz Cotgreave et al. s3 Tanaka & Yamadas4 Hurst et al.s5 Ktihn-Velten & Siess6 Laguna et at.s7 Nagi et aLas Htither et at.s9 Leyck and Parnham 9° Beil et al.9t Leurs et al. 92 Ueda et al. 93 Gower et al.94 lnglot et al.95 Baldew et at.96 Narayanaswami & Sies 97 Flechner et al.9s Johshita et al.99 Wakamura et a1.1°° Niederau et al.~°~ Hunt et alJ °2 Czyrski & Inglot ~°3 Gustafson & Pritsos ~°4 Brtine et alJ °5 Dimmeler et alJ °6 Thomas & Jackson '°7 Oower et al. l°s Wang et al. t°9 Wang et al. t°9 Ochi et al. t~°

absorbance

spectrophotom-

3.

G S H (e.g., b y t h e f o r m a t i o n o f t h i o n i t r o b e n z o a t e from Ellman's reagent 2 or of a monobromobim a n e adduct42). Assay of hydroperoxide removal: A s t a n d a r d m e t h o d u s i n g the i r o n - t h i o c y a n a t e c o m p l e x has b e e n e m p l o y e d , for e x a m p l e . 42

Radical scavenging T h e r e a c t i v i t y o f ebselen a n d r e l a t e d s e l e n o o r g a n i c c o m p o u n d s with 1 , 2 - d i c h l o r o e t h a n e r a d i c a l c a t i o n s a n d h a l o g e n a t e d p e r o x y l r a d i c a l s was s t u d i e d b y pulse radiolysis. 43 T h e rate c o n s t a n t for t h e r e a c t i o n o f e b s e len with t r i c h l o r o m e t h y l p e r o x y l r a d i c a l s was determ i n e d to be 2.9 × 108 M -~ s -I, while its sulfur a n a logue, 2 - p h e n y l - l , 2 - b e n z i s o t h i a z o l - 3 ( 2 H ) - o n e , was o x i d i z e d at m u c h l o w e r rates. T h e rate c o n s t a n t observed for ebselen is c o m p a r a b l e to t h a t o f a l p h a - t o c o pherol under similar conditions.

Singlet oxygen quenching R e a c t i v i t y o f ebselen with singlet m o l e c u l a r oxygen is o n l y sluggish, t h e rate c o n s t a n t b e i n g 2.5 × 106 M -~ s -~ (Ref. 44).* T h e sulfur a n a l o g exhibits a rate c o n s t a n t a n o r d e r o f m a g n i t u d e l o w e r t h a n this. ACTIVITY IN BIOLOGICAL MODEL SYSTEMS

Protection against lipid peroxidation T h e p r o t e c t i v e effect o f ebselen a g a i n s t i r o n - A D P i n d u c e d l i p i d p e r o x i d a t i o n in h e p a t i c m i c r o s o m a l f r a c t i o n s using a s c o r b a t e o r N A D P H as r e d u c t a n t has b e e n a m p l y d o c u m e n t e d . 1,45,46 In i n t a c t cells, it was s h o w n t h a t the p r o t e c t i v e effect d e p e n d s o n t h e presence o f G S H . H e p a t o c y t e s d e p l e t e d o f G S H c o u l d n o t be p r o t e c t e d b y ebselen, w h e r e a s n o r m a l cells were p r o t e c t e d , 4° suggesting t h a t t h e G P x - l i k e a c t i v i t y o f ebselen is i n v o l v e d in t h e p r o t e c t i o n o f i n t a c t cells a g a i n s t l i p i d p e r o x i d a t i o n (Fig. 1). In these experim e n t s , several p a r a m e t e r s o f l i p i d p e r o x i d a t i o n were followed, i n c l u d i n g t h e g e n e r a t i o n o f low-level c h e m i l u m i n e s c e n c e a n d t h e f o r m a t i o n o f a l k a n e s (ethane, n-pentane) and malondialdehyde. In t w o r e c e n t studies, 3'47 it was c o n c l u d e d t h a t t h e m a j o r role o f ebselen in p r o t e c t i n g against different t y p e s o f o x i d a t i v e a t t a c k is t o act in its c a p a c i t y as G P x m i m i c a n d , in p a r t i c u l a r , as P H G P x m i m i c . M a i o r i n o et al. 36 h a d o b s e r v e d t h a t ebselen a c t e d p a r t i c u l a r l y well w i t h t h e p h o s p h o l i p i d h y d r o p e r o x i d e s a n d with

2. Assay of GSH removal." T h i s c a n be d o n e b y stopp i n g t h e r e a c t i o n a n d t h e n assaying for r e m a i n i n g

317

* Sies et al., unpublished results, 1989.

318

H. SIES

(A)

0 I

2-Phenyl-l,2- benzisoselenazol-3(2Hlone Ebselen; PZ 51

J 0

H

in Ebselen-Protein - Selenodisulfide - -

- -

o H

Ebselen Selenol

f\

OH

COOH

[~x]~ C - N --Se--CH 3

2-(Glucuronylseleno}-benzoic acidN- phenylamide

OH II I

/7--~

~

2-(Methylseleno)-benzoic Qcid-N-phenylomide

~

_yO o COOH

4'-Glucuronyloxy-2- methylselenobenzanilide

OH II I

4'- Hydrox y-2-lmethylselenolbenzoic ocid- N- ohenvlomide

Fig. 2. Proposed biotransformation ofebselen in rats. Modified from Ref. 52. Fig. 2A gives the major pathway. Fig. 2B (see next page) presents some further metabolites observed in urine.

cholesterol hydroperoxide and cholesterol ester hydroperoxides? This conclusion came from experiments with photooxidized liposomes and peroxidized low-density lipoproteins. The radical scavenging activity of ebselen had little, if any, effect. This was shown by competition kinetics based on free-radical-dependent bleaching of crocin a or the lack of reaction with 2,2-diphenyl-l-picrylhydrazyl (DPPH) or the lack of suppression of oxidation of methyl linoleate induced by the radical generators 2,2'-azobis (amidinopropane) dihydrochloride (AAPH) or 2,2'-azobis (2,4-dimethylvaleronitrile) (AMVN). 47 Further, Noguchi et al. 47 concluded from

their results that a role ofebselen in the sequestration of iron is minimal.

Biological effects This topic is beyond the scope of the present article. However, some details should be mentioned in order to put the role of the enzyme mimic into perspective. Floh6, s in his comprehensive review, has collected the literature on the role of GPx in different tissues and organs and in their pathophysiology. As GPx and PHGPx are present in most organs, an additional expression of this activity would be of interest

Ebselen as GSH peroxidasemimic (B)

0 H

II I _ @ [~C-N

OH

Se--CH3 O-CH3 Z.'-Hydroxy- 5'- (methoxy)-2-(methylseleno)benzoic acid -N- phenylornide

0 H

~

Se_CH3 S-CH3 4'-Hydroxy-5'-(methylthio)-2- (methylseleno)benzoic acid-N- phenylernide

0 II [~C--OH

Se--CH3 2-(Methylseleno)-benzoic acid Fig. 2. Continued.

in conditions of enhanced oxidative challenge. Further, especially in those spaces and compartments where these enzymes are not present at high activity, the low molecular weight compound, ebselen, as an enzyme mimic might have pathophysiological interest. Table l gives an overview on studies in which ebselen was employed. In these studies, beneficial (protective) effects of ebselen were observed, and sometimes they were compared to the sulfur analog which was not protective. The anti-inflammatory effect was the initial property that attracted attention, 6,4s,49 but the wide range of experimental conditions covered by the studies cited in Table 1 indicates a broader range of potential clinical interest. One common basis for many of the diverse effects is that ebselen, by its property as GPx and PHGPx mimic, can lower the peroxide tone, 5° important in the control of lipoxygenases and cyclooxygenases, a topic not discussed here in depth.

Metabolism and disposition of ebselen Ebselen metabolism has been studied in isolated perfused liver51 and in intact rats, pigs, and human volunteers,52 as reviewed by Sies. 53 The detected metabolites share the characteristic that the isoselenazole ring is opened by cleavage of the Se-N bond. Apparently, the putative intermediate product, a selenodi-

319

sulfide with glutathione, S-(2-phenylcarbamoyl-phenylselenyl) glutathione, is labile. As shown in Fig. 2, the metabolism after ring opening involves methylation to form 2-methylselenobenzanilide, or glucuronidation to form 2-glucuronylselenobenzanilide. While the latter is released into bile, the former undergoes further metabolism. This includes hydroxylation at the phenyl ring in the paraposition, which, in turn, then can be glucuronidated (Fig. 2). The microsomal metabolism of 2-methylselenobenzanilide was further investigated)4 In pigs and in the human, the dominant metabolite in plasma and urine is the selenoglucuronide M 1. It is important to note that no unchanged ebselen was detectable in urine, plasma, or bile. 52 The facile ring opening of the isoselenazolone ring55"s6to form a selenosulfide is a probable basis for this. Whether ebselen is attacked by sulfhydryl compounds already in the stomach or intestine before absorption or while transported through the mucosa is not yet known. In model studies using bovine serum albumin, Nomura et al. 57 observed a rapid binding of ebselen to albumin. In preliminary work on human plasma, we detected radioactivity from labeled ebselen only on albumin and negligible amounts with the globulin fractions upon gel electrophoresis.* It is assumed that ebselen binds to the reactive thiol group at cysteine-34 in albumin, the location of bound cysteine and glutathione. 58 Thus, the current concept of transport ofebselen in the organism is that it is bound to proteins and that there is an interchange with low molecular weight thiols within cells and tissues. It is important to note that some of the experimental observations (Table l) obtained with ebselen in vitro should be controlled by employing ebselen in a protein-bound form (e.g., as the albumin complex). It is likely that some of the inhibitory effects of ebselen reported for isolated enzymes simply reflect the high reactivity of ebselen with protein thiols, and in vivo there was no detectable free ebselen2 ~'52Ziegler et al. 59 showed that ebselen in the selenol form can be a substrate for pig liver flavin-containing monooxygenase, as was 2-methylselenobenzanilide. An early observation by Wendel et al. 2 was that the selenium moiety in ebselen was not bioavailable; in selenium-deficient animals the selenoprotein GPx could not be augmented by ebselen but was by selenite. The property of not entering the body pool of selenium but rather being metabolized as explained earlier may explain the lack of toxicity observed in

*Wagneret al., unpublishedwork.

320

H. SIES

experimental studies. In a study with a volunteer, 500 m g o f 77Se-ebselen was given orally, a n d urinary metabolites followed by nuclear magnetic resonance ( N M R ) . 6° T h e metabolites m e n t i o n e d in Fig. 2 were observed, a n d the indicator o f metabolically bioavailable selenium, trimethylselenonium, was blank. Terlinden et al. 6~ also analyzed the metabolites in h u m a n plasma, the results being in a c c o r d a n c e with Fig. 2.

O t h e r selenoorganic c o m p o u n d s

There have been a n u m b e r o f a t t e m p t s to m o d i f y the basic structure o f ebselen. Structure-activity relationships o f a series o f a n t i - i n f l a m m a t o r y benzisoselenazolones have been reported by P a r n h a m et al. 62 a n d by Tarino. 63 Further, Wilson et al. 3° a n d Cotgreave et al. 42 reported on related c o m p o u n d s . T h e p h a r m a c o l o g y o f synthetic organic selenium c o m p o u n d s was m o s t recently reviewed by P a r n h a m a n d Graf. 6

Ovothiols." G P x m i m i c s as natural c o m p o u n d s

T h e principle o f G P x m i m i c s is realized in nature e m p l o y i n g a different strategy. T u r n e r et al. 64'6Sdiscovered that ovothiol, a thiohistidine c o m p o u n d , exhibited the ovoperoxidase activity in sea urchin eggs. T h e function o f this G P x m i m i c is the control o f the oxidative stress at fertilization. 66'67 Ovothiols can also act as free radical scavengers. 6s A function o f ovothiols as e n d o g e n o u s regulators in redox control in chloroplasts o f an alga has recently been described. 69 SUMMARY T h e redox properties ofebselen, a synthetic selenoorganic c o m p o u n d , a n d ofovothiols, naturally occurring methylhistidine derivatives, confer activity as glutathione peroxidases to these low molecular weight c o m p o u n d s . Thus, in the presence o f thiols, they act as e n z y m e mimics. T h e constraints o f substrate specificity are m u c h less, since the m i m i c s are m o r e readily accessible than active sites in proteins. This explains the relative unspecificity t o w a r d the thiol reductant: Whereas the e n z y m e G P x is highly specific for G S H , the m i m i c s also accept other thiol c o m p o u n d s , s o m e even at higher rates t h a n G S H . Similarly, the accessibility o f organic hydroperoxides as substrates is given with the relatively h y d r o p h o b i c ebselen molecule, so that its range o f substrates covers that o f P H G P x . There are m a n y interesting research p r o b l e m s generated by these e n z y m e mimics. F o r example, this pertains to the transport p a t h w a y o n proteins, with the albumin-ebselen c o m p l e x in the p l a s m a a n d its

subsequent transfer to other binding sites probably being the key to the surprisingly low toxicity observed. It will be o f interest to see in which area o f pathology the c o n c e p t o f G P x m i m i c s will c o m e to fruition in the future. Acknowledgements - - The work of the colleagues and co-workers from the author's laboratory as cited in the references is gratefully acknowledged. It is a particular pleasure to thank Dr. Erich Graf and his team at Nattermann & Cie., Cologne (now Rhone-Poulenc/ Nattermann) for their long-term fruitful collaboration. These groups, together with Professor Albrecht Wendel, Konstanz, were awarded the Claudius Galenus Prize, 1990, for their work on ebselen. Also, the collaboration with Dr. Hiroyuki Masayasu and his team at Daiichi Pharmaceutical Co., Tokyo, is gratefully acknowledged. Support by the Fonds der chemischen Industrie, Alexandervon-Humboldt-Stiftung, Jung-Stifiung f'dr Wissenschaft und Forschung, and the National Foundation for Cancer Research is gratefully acknowledged.

REFERENCES

1. Mtiller, A.; Cadenas, E.; Graf, P.; Sies, H. A novel biologically active seleno-organic compound. I. Glutathione peroxidaselike activity in-vitro and antioxidant capacity of PZ 51 (ebselen). Biochem. Pharmacol. 33:3235-3239; 1984. 2. Wendel, A.; Fausel, M.; Safayhi, H.; Tiegs, G.; Otter, R. A novel biologically active seleno-organic compound. II. Activity PZ 51 in relation to glutathione peroxidase. Biochem. Pharmacol. 33:3241-3245; 1984. 3. Maiorino, M.; Roveri, A.; Ursini, F. Antioxidant effect of ebselen (PZ51 ): Peroxidase mimetic activity on phospholipid and cholesterol hydroperoxides vs free radical scavenger activity. Arch. Biochem. Biophys. 295:404-409; 1992. 4. Klayman, D. L. Selenium compounds as potential chemotherapeutic agents. In: Klayman, D. L.; Giinther, W. H. eds. Organic" selenium compounds: Their chemistry and biology. New York: John Wiley & Sons; 1973:727-761. 5. Shamberger, R. J. Synthetic forms of selenium and their chemotherapeutic uses. In: Shamberger, R. J. ed. Biochemistry of selenium. New York: Plenum Press; 1983:273-310. 6. Parnham, M. J.; Graf, E. Pharmacology of synthetic organic selenium compounds. Prog. Drug Res. 36:9-47; 1991. 7. Schwarz, K.; Foltz, C. M. Selenium as an integral part of factor 3 against dietary necrotic liver degeneration. J. Am. Chem. Soc. 79:3292-3293; 1957. 8. Flohr, L. The selenoprotein glutathione peroxidase. In: Dolphin, D.; Poulson, R.; Avramovic, O., eds. Glutathione. New York: John Wiley & Sons; 1989:643-731. 9. Mills, G. C. Hemoglobin catabolism. I. Glutathione peroxidase, an erythrocyte enzyme which protects hemoglobin from oxidase breakdown. J. Biol. Chem. 229:189-197; 1957. 10. Flohr, L.; Giinzler, W. A.; Schock, H. H. Glutathione peroxidase: A selenoenzyme. FEBS Lett. 32:132-134; 1973. 11. Rotruck, J. T.; Pope, A. L.; Ganther, H. E.; Swanson, A. B.; Hafeman, D. G.; Hoekstra, W. G. Selenium: Biochemical role as a component of glutathione peroxidase. Science 179:588; 1973. 12. Forstrom, J. W.; Zakowski, J. J.; Tappel, A. L. Identification of the catalytic site of rat liver glutathione peroxidase as selenocysteine. Biochemistry 17:2639-2644; 1978. 13. Wendel, A.; Kerner, B.; Graupe, K. The selenium moiety of glutathione peroxidase. Hoppe-Seyler's Z. Physiol. Chem. 359:1035-1036; 1978. 14. Gianzler, W. A.; Steffens, G. J.; Grossmann, A.; Kim, S.-M. A.; Otting, F.; Wendel, A.; Flohr, L. The amino-acid

321

Ebselen as GSH peroxidase mimic sequence of bovine glutathione peroxidase. Hoppe-Seyler’s Z. Physiol. Chem. 365:195-2

12; 1984.

15. Mullenbach, G. T.; Tabrizi, A.; Irvine, B. D.; Bell, G. I.; Tainer, J. A.; Hallewell, R. A. Selenocysteine’s mechanism of incorporation and evolution revealed in cDNAs ofthree glutathione peroxidases. Protein Engineering 2~239-246; 1988. 16. Ladenstein, R.; Epp, 0.; Bartels, K.; Jones, A.; Huber, R.; Wendel, A. Structure analysis and molecular model of the selenoenzyme glutathione peroxidase at 2.8 A resolution. J. Molecular Biol. 134:199-218; 1979. 17. Epp, 0.; Ladenstein, R.; Wendel, A. The refined structure of the selenoenzyme glutathione peroxidase at 0.2-nm resolution. Eur. J. Biochem. 133:51-69; 1983. 18. Ursini, F.; Maiorino, M.; Valente, M.; Ferri, L.; Gregolin, C. Purification from pig liver of a protein which protects liposomes and biomembranes from peroxidative degradation and exhibits glutathione peroxidase activity on phosphatidylcholine hydroperoxides. Biochim. Biophys. Acta 710: 197-2 I I; 1982. 19. Ursini, F.; Maiorino, M.; Gregolin, C. The selenoenzyme phospholipid hydroperoxide ghrtathione peroxidase. Biochim. Biophys. Acta 839:62-70;

1985.

20. Schuckelt, R.; Brigelius-FlohC, R.; Maiorino, M.; Roveri, A.; Reumkens, J.; StraBburger, W.; Ursini, F.; Wolf, B.; Flohe, L. Phospholipid hydroperoxide glutathione peroxidase is a seleno-enzyme distinct from the classical glutathione peroxidase as evident from cDNA and amino acid sequencing. Free Radic. Res. Comm. 14:343-36

I; 1991.

21. Takahashi, K.; Cohen, H. J. Selenium-dependent glutathione peroxidase protein and activity: Immunological investigations on cellular and plasma enzymes. Blood 68:640-645; 1986.

22. Takahashi, K.; Akasaka, M.; Yamamoto, Y.; Kobayashi, C.; Mizoguchi, J.; Koyama, J. Primary structure of human plasma glutathione peroxidase deduced from cDNA sequences. J. Biochem. 108:145-148; 1990. 23. Behne, D.; Hilmert, H.: Scheid, S.; Gessner, H.; Elger, W. Evidence for specific selenium target tissues and new biologically important selenoproteins. Biochim. Biophys. Acta 966:12-21;

1988.

24. Lesser, R.; WeiB, R. Uber selenhaltige aromatische Verbindungen (VI). Chem. Berichte 57:1077-1082; 1924. 25. Weber, R.; Renson, M. Les chlorures de chloro-3 benzisoselenazolium- I ,2: Synthese, hydrolyse, thiolation, ammonolyse. Bull. Sot. Chim. France 2(S): 1 I24- I 126; 1976. 26. Fischer, H.; Dereu, N. Mechanism of the catalytic reduction of hydroperoxides by ebselen: A selenium-77 NMR study. Bull. Sot. Chim. Belg. 96~757-768;

1987.

27. Cantineau, R.; Thiange, G.; Plenevaux, A.; Christiaens, L.; Guillaume. M. Svnthesis of “Se-2-ohenvl. , I .2_benzisoselenazol-3(2H)-one (PZ 51; ebselen). A novel biologically active organo-selenium compound. J. Labell. Comp. Radiopharmaceut. 23:59-65;

1986.

28. Lambert, C.; Cantineau, R.; Christiaens, L.; Biedermann, J.; Dereu, N. Syntheses and spectral characterization of the metabolites of a new organo-selenium drug: Ebselen. Bull. Sot. Chim. Belg. 96:383-389;

1987.

29. Engmann, L.; Hallberg, A. Expedient synthesis of ebselen and related compounds. J. Org. Chem. 54:2964-2966; 1989. 30. Wilson, S. R.; Zucker, P. A.; Huang, R.-R. C.; Spector, A. Development of synthetic compounds with glutathione peroxidase activity. J. Am. Chem. Sot. 111:5936-5939; 1989. 31. Cotgreave, 1. A.; Morgenstem, R.; Engman, L.; Ahokas, J. Characterisation and quantitation ofa selenol intermediate in the reaction of ebselen with thiols. Chem.-Biol. Interact. 84:69-76;

1992.

32. Caldwell, K. A.; Tappel, A. L. Reactions of seleno- and sulfonamino acids with hydroperoxides. Biochemistry 3: 16431648; 1964.

33. Caldwell, K. A.; Tappel, A. L. Acceleration of sulthydryl oxi-

dations by selenocysteine. Arch. Biochem. Biophys. 112: 196202; 1965.

34. Yasuda, K.; Watanabe, H.; Yamazaki, S.; Toda, S. Glutathione peroxidase activity of D, L-selenocystine and selenocystamine. Biochem. Biophys. Res. Comm. %:243-249; 1980. 35. Haenen, G. R. M. M.; de Rooij, B. M.; Vermeulen, N. P. E.; Bast, A. Mechanism of the reaction of ebselen with endogenous thiols. Dihydrolipoate is a better cofactor than glutathione in the peroxidase activity of ebselen. Mol. Pharmacol. 37:4 12-422; 1990. 36. Maiorino, M.; Roveri, A.; Coassin, M.; Ursini, F. Kinetic mechanism and substrate specificity of glutathione peroxidase activity of ebselen (PZ5I). Biochem. Pharmacol. 37:2267-227

1; 1988.

37. Morgenstem, R.; Cotgreave, I. A.; Engman, L. Determination of the relative contributions of the diselenide and selenol forms of ebselen in the mechanism of its glutathione peroxidase-like activity. Chem.-Biol. Interact. 84:77-84;1992. 38. Wendel, A.; Pilz, W.; Ladenstein, R.; Sawatzki, G.; Weser, U. Substrate-induced redox change of selenium in glutathione peroxidase studied by X-ray photoelectron spectroscopy. Biochim. Biophys. Acta 377:211-215; 1975. 39. Reich, H. J.; Jasperse, C. P. Organoselenium chemistry. Redox chemistry of selenocysteine model systems. J. Am. Chem. Sot. 109:5549-5551;

1987.

40. Mtiller, A.; Gabriel, H.; Sies, H. A novel biologically active selenoorganic compound. IV. Protective glutathione-dependent effect of PZ 5 1 (ebselen) against ADP-Fe induced lipid peroxidation in isolated hepatocytes. Biochem. Pharmacol. 34:1185-l

189; 1985.

41. Cotgreave, I. A.; Sandy, M. S.; Berggren, M.; Mold&us, P. M.; Smith, M. T. N-acetylcysteine and glutathione dependent protective Effect of PZ 51 (ebselen) against diquat induced cytotoxicity in isolated hepatocytes. Biochem. Pharmacol. 36:2899-2904;

1987.

42. Cotgreave, I. A.; Mold&s, P.; Brattsand, R.; Hallberg, A.; Andersson, C. M.; Engman, L. Alpha-(phenylselenenyl)aceto-phenone derivates with glutathione peroxidase-like activity. Biochem. Pharmacol. 43:793-802; 1992. 43. Schoneich, C.; Narayanaswami, V.; Asmus, K.-D.; Sies, H. Reactivity of ebselen and related senoorganic compounds with 1,2-dichloroethane radical cations and halogenated peroxyl radicals. Arch. Biochem. Biophys. 282: 18-25; 1990. 44. Scurlock, R.; Rougee, M.; Bensasson, R. V.; Evers, M.; Dereu, N. Deactivation of singlet molecular oxygen by organselenium compounds exhibiting glutathione peroxidase. activity and by sulfur-containing homologs. Photochem. Photobiol. S&733-736;

199 I.

45. Hayashi, M.; Slater, T. F. Inhibitory effects ofebselen on lipid peroxidation in rat liver microsomes. Free Radic. Res. Comm. 2:179-185;

1986.

46. Narayanaswami, V.; Sies, H. Antioxidant activity of ebselen and related selenoorganic compounds in microsomal lipid peroxidation. Free Radic. Res. Comm. 10:237-244; 1990. 47. Noguchi, N.; Yoshida, Y.; Kaneda, H.; Yamamoto, Y.; Niki, E. Action of ebselen as an antioxidant against lipid peroxidation. Biochem. Pharmacol. 44:39-44: 1992. 48. Parnham, M. J.; Leyck, S.; Dereu, N.; Winkelmann, J.; Graf, E. Ebselen (PZ 5 1)-A GSH-peroxidase-like organoselenium compound with antiinflammatory activity. Adv. InJlam. Res. 10:397-400;

1985.

49. Parnham, M. J.; Graf, E. Seleno-organic compounds and the therapy of hydroperoxide-linked -pathological conditions. Biochem. Pharmacol. 3613095-3 102: 1987. 50. Hemler, M. E.; Cook, H. W.; Lands,‘W. E. M. Prostaglandin biosynthesis can be triggered by lipid peroxides. Arch. Biothem. Biophys. 193:340-345;

1979.

51. Mtiller, A.; Gabriel, H.; Sies, H.; Terlinden, R.; Fischer, H.; Rtimer, A. A novel biologically active selenoorganic compound. VII. Biotransformation of ebselen in perfused rat liver. Biochem. Pharmacol. 37:1103-l 109; 1988.

322

H. SIES

52. Fischer, H.; Terlinden, R.; L0hr, J. P.; RSmer, A. A novel biologically active selenoorganic compound. VIII. Biotransformation of ebselen. Xenobiotica 18:1347-1359; 1988. 53. Sies, H. Metabolism and disposition of ebselen. In: Wendel, A., ed. Selenium in biology and medicine. Heidelberg: Springer-Verlag; 1989:153-162. 54. John, N. J.; Terlinden, R.; Fischer, H.; Evers, M.; Sies, H. Microsomal metabolism of 2-methylselenobenzanilide. Chem. Res. Toxicol. 3:199-203; 1990. 55. van Caneghem, P, Influences comparatives de diffrrentes substances srirnires et soufrres sur la fragilit6 des lysosomes et des mitochondries in vitro. Biochem. Pharmacol. 23:34913500; 1974. 56. Kamigata, N.; Takata, M.; Matsuyama, H.; Kobayashi, M. Novel ring opening reaction of 2-aryl-l,2-benziselenazol3(2H)-one with thiols. Heterocycles 2,t:3027-3030; 1986. 57. Nomura, H.; Hakusui, H.; Takegoshi, T. Binding of ebselen to plasma protein. In: Wendel, A. ed. Selenium in biology and medicine. Heidelberg: Springer-Verlag; 1989:189-193. 58. Peters, T., Jr. Serum albumin. Adv. Prot. Chem. 37:161-245; 1985. 59. Ziegler, D. M.; Graf, P.; Poulsen, L. L.; Stahl, W.; Sies, H. NADPH-dependent oxidation of reduced ebselen, 2-selenylbenzanilide, and of 2-(methylseleno)benzanilide catalyzed by pig liver flavin-containing monooxygenase. Chem. Res. ToMcol. 5:163-166; 1992. 60. Dereu, N.; Fischer, H.; Hilboll, G.; Roemer, A.; Terlinden, R. The use of highly enriched 77Se in metabolic studies of ebselen in man. An NMR investigation. In: Wendel, A. ed. Selenium in biology and medicine. Heidelberg: Springer-Verlag; 1989:163-168. 6 I. Terlinden, R.; Feige, M.; R6mer, A. Determination of the two major metabolites of ebselen in human plasma by high-performance liquid chromatography. J. Chromatogr. 430:438442; 1988. 62. Parnham, M. J.; Biedermann, J.; Bittner, Ch.; Dereu, N.; Leyck, S.; Wetzig, H. Structure-activity relationships of a series of anti-inflammatory benzisoselenazolones (BISAs). Agents and Actions 27:306-308; 1989. 63. Tarino, J. Z. Evaluation of selected organic and inorganic selenium compounds for selenium-dependent glutathione peroxidase activity. Nutr. Reports Int. 33:299-306; 1986. 64. Turner, E.; Hager, L. J.; Shapiro, B. M. Ovothiol replaces glutathione peroxidase as a hydrogen peroxide scavenger in sea urchin eggs. Science 242:939-941; 1988. 65. Turner, E.; Klevit, R.; Hopkins, P. B.; Shapiro, B. M. Ovothiol: A novel thiohistidine compound from sea urchin eggs that confers NAD(P)H2 oxidoreductase activity on ovoperoxidase. Z Biol. Chem. 261:13056-13063; 1986. 66. Shapiro, B. M.; Hopkins, P. B. Ovothiols: Biological and chemical perspectives. Adv. Enzymol. Relat. Areas Mol. Biol. 64:291-316; 1991. 67. Shapiro, B. M. The control of oxidant stress at fertilization. Science 252:533-536; 1991. 68. Holler, T. P.; Hopkins, P. B. Ovothiols as free-radical scavengers and the mechanism of ovothiol-promoted NAD(P)H 2 oxidoreductase activity. Biochemistry 29:1953-1961; 1990. 69. Selman-Reimer, S.; Duhe, R. J.; Stockman, B. J.; Selman, B. R. L-1-N-methyl-4-mercaptohistidine disulfide, a potential endogenous regulator in the redox control of chloroplast coupling factor 1 in Dunaliella. J. Biol. Chem. 266:182-188; 1991. 70. Cadenas, E.; Wefers, H.; MOiler, A.; Brigelius, R.; Sies, H. Active oxygen metabolites and their action in the hepatocyte studies on chemiluminescence responses and alkane production. Agents and Actions 11:203-216; 1982. 71. Parnham, M. J.; Kindt, S. A novel biologically active selenoorganic compound-IlI. Effects ofPZ 51 (ebselen) on glutathione peroxidase and secretory activities of mouse macrophages. Biochem. Pharmacol. 33:3247-3250; 1984. 72. Safayhi, H.; Tiegs, G.; Wendel, A. A novel biologically active seleno-organic compound-V. Inhibition by ebselen (PZ 51 ) of rat peritoneal neutrophil lipoxygenase. Biochem. Pharmacol. 34:2691-2694; 1985.

73. Wendel, A.; Tiegs, G. A novel biologically active seleno-organic compound-Vl. Protection by ebselen (PZ 51) against galactosamine/endotoxin-induced hepatitis in mice. Biochem. Pharmacol. 35:2115-2118; 1986. 74. Wendel, A.; Otter, R.; Tiegs, G. Inhibition by ebselen of microsomal NADPH-cytochrome P 450-reductase in vitro but not in vivo. Bioehem. Pharmacol. 35:2995-2997; 1986. 75. Kuhl, P.; Borbe, H. O.; R0mer, A.; Fischer, H.; Parnham, M. J. Selective inhibition of leukotriene B4 formation by ebselen: A novel approach to antiinflammatory therapy. Agents andActions 17:366-367; 1985. 76. Kuhl, P.; Borbe, H. O.; Fischer, H.; Roemer, A.; Safayhi, H. Ebselen reduces the formation of LTB4 in human and porcine leukocytes by isomerisation to its 5S, 12R-6-transisomer. Prostaglandins 31:1029-1048; 1986. 77. Mercurio, S. D.; Combs, G. F., Jr. Synthetic seleno-organic compound with glutathione peroxidase-like activity in the chick. Biochem. Pharmacol. 35:4505-4509; 1986. 78. Hartung, H. P.; Schaefer, B.; Heininger, K.; Toyka, K. V. Interference with arachidonic acid metabolism suppresses experimental allergic neuritis. Ann. Neurol. 20:168; 1986. 79. Schalkwijk, J.; van den Berg, W. B.; van de Putte, L. B. A.; Joosten, L. A. B. An experimental model for hydrogen peroxide-induced tissue damage. Effects of a single inflammatory mediator on (peri)articular tissues. Arthritis Rheum. 29:532538; 1986. 80. van Dyke, T. E.; Braswell, L.; Offenbacher, S. Inhibition of gingivitis by topical application of ebselen and rosmarinic acid. Agents andActions 19:376-377; 1986. 81. Ishikawa, S.; Omura, K.; Katayama, T.; Okamura, N.; Ohtsuka, T.; Ishibashi, S.; Masayasu, H. Inhibition of superoxide anion production in guinea pig polymorphonuclear leukocytes by a seleno-organic compound, ebselen. J. Pharmacobio-Dyn. 10:595-597; 1987. 82. Cotgreave, I. A.; Johansson, U.; Westergren, G.; Moldrus, P. W.; Brattsand, R. The anti-inflammatory activity of ebselen but not thiols in experimental alveolitis and brochiolitis. Agents and Actions 24:313-319; 1988. 83. Cotgreave, I. A.; Duddy, S. K.; Kass, G. E. N.; Thompson, D.: Moldrus, P. Studies on the anti-inflammatory activity ofebselen. Ebselen interferes with granulocyte oxidative burst by dual inhibition of NADPH oxidase and protein kinase C? Biochem. Pharmacol. 38:649-656; 1989. 84. Tanaka, J.; Yamada, F. Ebselen (PZ51) inhibits the formation of ischemic brain edema. In: Wendel, A., ed. Selenium in biology and medicine. Heidelberg: Springer-Verlag; 1989: 173-176. 85. Hurst, J. S.; Paterson, C. A.; Bhattacherjee, P.; Pierce, W. M. Effects of ebselen on arachidonate metabolism by ocular and non-ocular tissues. Biochem. Pharmacol. 38:3357-3363; 1989. 86. KOhn-Velten, N.; Sies, H. Optical spectral studies of ebselen interaction with cytochrome P-450 of rat liver microsomes. Biochem. Pharmacol. 38:619-625:1989. 87. Laguna, J. C.; Nagi, M. N.; Cook, L.; Cinti, D. L. Action of ebselen on rat hepatic microsomal enzyme-catalyzed fatty acid chain elongation, desaturation, and drug biotransformation. Arch. Biochem. Biophys. 269:272-283; 1989. 88. Nagi, M. N.; Laguna, J. C.; Cook, L.; Cinti, D. L. Disruption of rat hepatic microsomal electron transport chains by the selenium-containing anti-inflammatory agent ebselen. Arch. Biochem. Biophys. 269:264-271 ; 1989. 89. Huether, A. M.; Zhang, Y.; Sauer, A.; Parnham, M. J. Antimalarial properties of ebselen. Parasitol Res. 75:353-360; 1989. 90. Leyck, S.; Parnham, M. J. Acute inflammatory and gastric effects of the seleno-organic compound ebselen. Agents and Actions 30:425-431; 1990. 91. Beil, W.; Staar, U.; Sewing, K. F. Interaction of the anti-inflammatory seleno-organic compound ebselen with acid secretion in isolated parietal cells and gastric H+/K+-ATPase. Biochem. PharmacoL 40:1997-2003; 1990. 92. Leurs, R.; Bast, A.; Timmermann, H. Ebselen inhibits con-

Ebselen as GSH peroxidase mimic

93.

94.

95.

96.

97. 98. 99.

100.

101.

tractile responses of guinea-pig parenchymal lung strips. Eur. J. Pharmacol. 179:193-199; 1990. Ueda, S.; Yoshikawa, T.; Takahashi, S.; Naito, T.; Oyamada, H.; Takemura, T.; Morita, Y.; Tanigawa, T.; Sugino, S.; Kondo, M. Protection by seleno-organic compound, ebselen, against acute gastric mucosal injury induced by ischemia-reperfusion in rats. Adv. Exp. Med. BioL 264:187-190; 1990. Gower, J. D.; Baldock, R. J.; Sullivan, A. M.; Dote, C. J.; Coid, C. R.; Green, C. J. Protection against endotoxin induced foetal resorption in mice by desferrioxamine and ebselen. Int. J. Exp. Pathol. 71:433-440; 1990. Inglot, A. D.; Zielinska-Jenczylik, J.; Piasecki, E.; Syper, L.; Mlochowski, J. Organoselenides as potential immunostimulants and inducers of interferon gamma and other cytokines in human peripheral blood leukocytes. Experientia 46:30831 l; 1990. Baldew, G. S.; McVie, J. G.; van der Valk, M. A., Los, G.; de Goeij, J. J.; Verrneulen, N. P. Selective reduction ofcis-diamminedichloroplatinum(II) nephrotoxicity by ebselen. Cancer Res. 50:7031-7036; 1990. Narayanaswami, V.; Sies, H. Oxidative damage to mitochondria and protection by ebselen and other antioxidants. Biochem. Pharmacol. 40:1623-1629; 1990. Flechner, I.; Maruta, K.; Burkart, V.; Kawai, K.; Kolb, H.; Kiesel, U. Effects of radical scavengers on the development of experimental diabetes. Diabetes Res. 13:67-73; 1990. Johshita, H.; Sasaki, T.; Matsui, T.; Hanamura, T.; Masayasu, H.; Asano, T. Effects of ebselen (PZSI) on ischemic brain edema after focal ischemia in cats. Acta Neurochir. Suppl. 51:239-241; 1990. Wakamura, K.; Ohtsuka, T.; Okamura, N.; Ishibashi, S.; Masayasu, H. Mechanism for the inhibitory effect ofa selenoorgamc compound, ebselen, and its analogues on superoxide anion production in guinea pig polymorphonuclear leukocytes. J. Pharmacobiodyn. 13:421-425; 1990. Niederau, C.; Ude, K.; Niederau, M.; Ltithen, R.; Strohmeyer, G.; Ferrell, L. D.; Grendell, J. H. Effects of the selenoorganic substance ebselen in two different models of acute pancreatitis. Pancreas 6:282-290; 199 I.

323

102. Hunt, N. H.; Cook, E. P.; Fragonas, J. C. Interference with oxidative processes inhibits proliferation of human peripheral blood iymphocytes and murine B-lymphocytes. Int. J. Immunopharmacol. 13:1019-1026; 1991. 103. Czyrski, J. A.; Inglot, A. D. Mitogenic activity of selenoorganic compounds in human peripheral blood. Experientia 47:95-97; 1991. 104. Gustafson, D. L.; Pritsos, C. A. Inhibition of mitomycin C's aerobic toxicity by the seleno-organic antioxidant PZ-51. Cancer Chemother. Pharmacol. 28:228-230; 1991. 105. Brfine, B.; Diewald, B.; Ullrich, V. Ebselen affects calcium homeostasis in human platelets. Biochem. Pharmacol. 41:1805-1811; 1991. 106. Dimmeler, S.; Brtine, B.; Ullrich, V. Ebselen prevents inositol ( 1,4,5)-trisphosphate binding to its receptor. Biochem. Pharmacol. 42:1151-1153; 1991. 107. Thomas, C. E.; Jackson, R. L. Lipid hydroperoxide involvement in copper-dependent and independent oxidation of low density lipoproteins. J. Pharmacol. Exp. Ther. 256:11821188; 1991. 108. Gower, J. D.; Lane, N. J.; Goddard, G.; Manek, S.; Ambrose, I. J.; Green, C. J. Ebselen. Antioxidant capacity in renal preservation. Biochem. Pharmacol. 43:2341-2348; 1992. 109. Wang, J.-F.; Komarov, P.; Sies, H.; de Groot, H. Inhibition of superoxide and nitric oxide release and protection from reoxygenation injury by ebselen in rat Kupffer cells. Hepatology 15:1112-1116; 1992. 110. Ochi, H.; Morita, I.; Murota, S. Roles ofglutathione and glutathione peroxidase in the protection against endothelial cell injury induced by 15-hydroperoxyeicosatetraenoic acid. Arch. Biochem Biophys. 294:407-411; 1992. ABBREVIATIONS

GPx--glutathione peroxidase PHGPx--phospholipid hydroperoxide glutathione peroxidase