Derek J. Maitland

Antiulcerogenic Activity of Alhagi maurorum

Abstract Six main flavonoid glycosides were isolated, for the first time, from the ethanol extract of Alhagi maurorum Boiss (Leguminosae).. They were identified as kaempferol, chrysoeriol, isorhamnetin, chrysoeriol-7-O.-xylosoid, kaempferol-3-galactorhamnoside, and isorhamnetin 3-O.-β-D-apio-furanosyl (1-2) β-D-galactopyranoside. Their identities were established by m.p., UV, EI-mass, Fab-mass, 600 MHz 1H and 13C NMR. The total extract (300 and 400 mg/kg) and two of the isolated compounds (chrysoeriol 7-O.-xylosoid and kaempferol-3-galactorhamnoside, 100 mg/kg each) showed a very promising antiulcerogenic activity with curative ratios 66.31%, 69.57%, 75.49%, and 77.93%, respectively.

Presence of epidermal allantoin further supports oxidative stress in vitiligo

Abstract:  Xanthine dehydrogenase/xanthine oxidase (XDH/XO) catalyses the hydroxylation of hypoxanthine to xanthine and finally to uric acid in purine degradation. These reactions generate H2O2 yielding allantoin from uric acid when reactive oxygen species accumulates. The presence of XO in the human epidermis has not been shown so far. As patients with vitiligo accumulate H2O2 up to mm levels in their epidermis, it was tempting to examine whether this enzyme and consequently allantoin contribute to the oxidative stress theory in this disease. To address this question, reverse transcription‐polymerase chain reaction, immunoreactivity, western blot, enzyme kinetics, computer modelling and high performance liquid chromatography/mass spectrometry analysis were carried out. Our results identified the presence of XDH/XO in epidermal keratinocytes and melanocytes. The enzyme is regulated by H2O2 in a concentration‐dependent manner, where concentrations of 10−6 m upregulates the activity. Moreover, we demonstrate the presence of epidermal allantoin in acute vitiligo, while this metabolite is absent in healthy controls. H2O2‐mediated oxidation of Trp and Met in XO yields only subtle alterations in the enzyme active site, which is in agreement with the enzyme kinetics in the presence of 10−3 m H2O2. Systemic XO activities are not affected. Taken together, our results provide evidence that epidermal XO contributes to H2O2‐mediated oxidative stress in vitiligo via H2O2‐production and allantoin formation in the epidermal compartment.

Specific interaction of the diastereomers 7(R)- and 7(S)-tetrahydrobiopterin with phenylalanine hydroxylase: implications for understanding primapterinuria and vitiligo

Pterin‐4a‐carbinolamine dehydratase (PCD) is an essential component of the phenylalanine hydroxylase (PAH) system, catalyzing the regeneration of the essential cofactor 6(R)‐L‐erythro‐5,6,7,8‐tetrahydrobiopterin [6(R)BH4]. Mutations in PCD or its deactivation by hydrogen peroxide result in the generation of 7(R,S)BH4, which is a potent inhibitor of PAH that has been implicated in primapterinuria, a variant form of phenylketonuria, and in the skin depigmentation disorder vitiligo. We have synthesized and separated the 7(R) and 7(S) diastereomers confirming their structure by NMR. Both 7(R)‐ and 7(S)BH4 function as poor cofactors for PAH, whereas only 7(S)BH4 acts as a potent competitive inhibitor vs. 6(R)BH4 (Ki2.3–4.9 µM). Kinetic and binding studies, as well as characterization of the pterin‐enzyme complexes by fluorescence spectroscopy, revealed that the inhibitory effects of 7(R,S)BH4 on PAH are in fact specifically based on 7(S)BH4 binding. The molecular dynamics simulated structures of the pterin‐PAH complexes indicate that 7(S)BH4 inhibition is due to its interaction with the polar region at the pterin binding site close to Ser‐251, whereas its low efficiency as cofactor is related to a suboptimal positioning toward the catalytic iron. 7(S)BH4 is not an inhibitor for tyrosine hydroxylase (TH) in the physiological range, presumably due to the replacement of Ser‐251 by the corresponding Ala297. Taken together, our results identified structural determinants for the specific regulation of PAH and TH by 7(S)BH4, which in turn aid in the understanding of primapterinuria and acute vitiligo. —Pey, A. L., Martinez, A., Charubala, R., Maitland, D. J., Teigen, K., Calvo, A., Pfleiderer, W., Wood, J. M., Schallreuter, K. U. Specific interaction of the diastereomers 7(R)‐ and 7(S)‐tetrahydrobiopterin with phenylalanine hydroxylase: implications for understanding primapterinuria and vitiligo FASEB J. 20, E1451–E1464 (2006)

Blunted epidermal l-tryptophan metabolism in vitiligo affects immune response and ROS scavenging by Fenton chemistry, part 2: epidermal H2O2/ONOO−-mediated stress in vitiligo hampers indoleamine 2,3-dioxygenase and aryl hydrocarbon receptor-mediated immune response signaling

Vitiligo is characterized by a mostly progressive loss of the inherited skin color. The cause of the disease is still unknown, despite accumulating in vivo and in vitro evidence of massive oxidative stress via hydrogen peroxide (H2O2) and peroxynitrite (ONOO–) in the skin of affected individuals. The most favored hypothesis is based on autoimmune mechanisms. Since depletion of the essential amino acid L‐tryptophan (Trp) severely affects various immune responses, we here looked at Trp metabolism and signaling in these patients. Our in vivo and in vitro data revealed total absence of epidermal Trp hydroxylase activities and the presence of H2O2/ONOO– deactivated indoleamine 2,3‐dioxygenase. Aryl hydrocarbon receptor signaling is severely impaired despite the ligand (Trp dimer) being formed, as shown by mass spectrometry. Loss of this signal is supported by the absence of downstream signals (COX‐2 and CYP1A1) as well as regulatory T‐lymphocytes and by computer modeling. In vivo Fourier transform Raman spectroscopy confirmed the presence of Trp metabolites together with H2O2 supporting deprivation of the epidermal Trp pool by Fenton chemistry. Taken together, our data support a long‐expressed role for in loco redox balance and a distinct immune response. These insights could open novel treatment strategies for this disease.—Schallreuter, K. U., Salem, M. A. E. L., Gibbons, N. C. J., Maitland, D. J., Marsch, E., Elwary, S., Healey, A. R. Blunted epidermal L‐tryptophan metabolism in vitiligo affects immune response and ROS scavenging by Fenton chemistry, part 2: epidermal H2O2/ONOO–‐mediated stress in vitiligo hampers indoleamine 2,3‐dioxygenase and aryl hydrocarbon receptor‐mediated immune response signaling. FASEB J. 26, 2471‐2485 (2012). www.fasebj.org

Tautomerism in 2-ketomethyl quinolines

Abstract The i.r.solution spectra of a series of 2-ketomethylquinolines have been studied. Tautomeric ratios have been determined by n.m.r. spectroscopy. With one exception the compounds were substantially or exclusively in the enaminone forms. The only compound carrying an α-methyl group (18) proved to be solely in the ketone form.

Metabolites of the higher fungi. Part 29. Maldoxin, maldoxone, dihydromaldoxin, isodihydromaldoxin and dechlorodihydromaldoxin. A spirocyclohexadienone, a depsidone and three diphenyl ethers: keys in the depsidone biosynthetic pathway from a member of the fungus genus Xylaria

2-(3′-Chloro-2′-hydroxy-4′-methoxy-6′-methoxycarbonylphenoxy)-6-hydroxy-4-methylbenzoic acid (dihydromaldoxin 1), 2-(3′-Chloro-4′-hydroxy-2′-methoxy-6′-methoxycarbonylphenoxy)-6-hydroxy-4-methylbenzoic acid (isodihydromaldoxin 2), dechlorodihydromaldoxin 3, a new chlorinated depsidone (maldoxone 4) and a new spirocyclohexadienone (maldoxin 5) have been isolated from the culture medium of an as yet unidentified Xylaria species. The structures have been determined by physical and chemical methods and the positions of the substituents in dihydromaldoxin 1 have been confirmed by a single crystal X-ray structure determination. Their role in the grisan–depsidone biosynthetic pathway is discussed.

Metabolites of the higher fungi. Part 24. Cytochalasin N, O, P, Q, and R. New cytochalasins from the fungus Hypoxylon terricola Mill

Punctaporonin B, cytochalasin C and D, and five new cytochalasins have been isolated from the culture medium and mycelium of the fungus Hypoxylon terricola. Cytochalasin C is the major metabolite. Cytochalasin N is the 5,6-epoxide of cytochalasin C, and cytochalasins O and P are two epimeric 6-hydroxy analogues. Cytochalasin Q is a 6,7-epoxide and R is a 6,7,13,14-diepoxide. The epoxides formed by cytochalasin C and D are described and the acid- and BF3-induced rearrangement products of cytochalasin N are identified.

Novel flavonoids with antioxidant activity from a Chenopodiaceous plant

Objective: Atriplex lentiformis (Torr.) S.Wats (Chenopodiaceae) is a wild plant which is in use by Bedouin in treatment of general fatigue, therefore, there is a need to explore the potential antioxidant activity of the extracts and isolated compounds of this plant. Methods: Column chromatography and spectroscopic analysis were used for isolation and identification of the compounds. The antioxidant activity was evaluated in vitro using the ABTS•+ (2,2′-azino-bis-3-ethyl-bezthiazoine-6-sulphuric acid) radical scavenging model. Liver and kidney functions were investigated after oral administration of total alcohol, successive extracts, and isolated compounds. Results: Two new flavonoids, quercetin-6,4′-dimethoxy-3-fructo-rhamnoside 1 and quercetin-4′-methoxy-3-fructo-rhamnoside 2 in addition to five known compounds (kaempferol-4′-methoxy-3-rutinoside 3, kaempferol-7-O-rhamnoside 4, kaempferol-3,7-O,O-dirhamnoside 5, quercetin 6, and kaempferol 7) were isolated. Oral administration of total ethanol, diethyl ether, chloroform, ethyl acetate and n-butanol extracts showed no signs of toxicity up to (5 g/kg. b.wt.). All extracts and isolated compounds showed varied antioxidant activity ranged from 129 to 952 µmol Trolox equivalent/gram dry weight with maximum level for the two new isolated flavonoids (985 and 895 µmol Trolox equivalent/gram dry weight). Animals received both total ethanol and n-butanol extracts showed a significant increase in ALT, AST, blood urea, and serum creatinine levels.

Metabolites of the higher fungi. Part 26. Cubensic acid, 3,7,11,15-tetra hydroxy-18-(hydroxymethyl)-2,4,6,10,14,16,20-heptamethyldocosa-4E,8E,12E,16E-tetraenoic acid, a novel polysubstituted C22 fatty acid from the fungus Xylaria cubensis(Mont.) Fr. with substituents and substitution pattern similar to the macrolide antibiotics

Cubensic acid, 3,7,11,15-tetrahydroxy-18-(hydroxymethyl)-2,4,6,10,14,16,20-heptamethyldocosa-4E,8E,12E,16E-tetraenoic acid, has been isolated from the mycelium and culture medium of Xylaria cubensis. Cytochalasin D is an additional metabolite isolated from the culture medium. The structure of cubensic acid has been determined by a combination of spectroscopic and chemical methods. A possible biosynthetic link between cubensic acid and certain macrolide antibiotics is suggested.

Anti-ulcer xanthones from the roots of Hypericum oblongifolium Wall

Three new xanthones, hypericorin C (1), hypericorin D (2) and 3,4-dihydroxy-5-methoxyxanthone (3), along with eight known compounds; 2,3-dimethoxyxanthone (4), 3,4-dihydroxy-2-methoxyxanthone (5), 3,5-dihydroxy-1-methoxyxanthone (6), 3-acetylbetulinic acid (7), 10H-1,3-dioxolo[4,5-b]xanthen-10-one (8), 3-hydroxy-2-methoxyxanthone (9), 3,4,5-trihydroxyxanthone (10) and betulinic acid (11) were isolated from the roots of Hypericum oblongifolium. The structures of the new compounds 1, 2 and 3 were deduced by spectroscopic techniques [ESI MS, (1)H NMR, (13)C NMR, and 2D NMR (HMQC, HMBC, COSY and NOESY)]. The entire series of compounds were evaluated for anti-ulcer activity.