Naturally occurring conjugated octadecatrienoic acids are strong inhibitors of prostaglandin biosynthesis

Fatty acids from natural sources (mostly seed oils) were isolated and assayed for their effect on the bioconversio of arachidonic acid into prostaglandin E₂, using sheep vesicular gland microsomes. Homologues and isomers of the naturally occurring fatty acids, obtained by chemical modification and/or organic synthetic methods, were also tested. Two very active cyclooxygenase inhibitors were discovered, namely jacarandic acid (8 , 10 , 12 -octadecatrienoic acid), isolated from , the concentration which gives 50% inhibition ([I]₅₀) being 2.4 μM and the synthetic 8 , 10 , 12 -octadecarienoic acid, having an [I]₅₀ of 1.0 μM. Under the conditions of the assay (75 μM substrate), earlier described potent inhibitors showed the following [I]₅₀′s: indomethacin: 1.3 μM; 9,12-octadecadiynoic acid: 1.3 μM, 8 , 12 , 14 -eicosatrienoic acid: 2.7 μM; 5,8,11,14-eicosatetraynoic acid: 4.4 μM. At a concentration of about half that of the substrate, the following naturally occurring fatty acids revealed inhibition ([I]₅₀): columbinic acid (29 μM), calendulic acid (31 μM), liagoric acid (31 μM), ximenynic acid (39 μM), crepenynic acid (40 μM) and timnodonic acid (43 μM). Other fatty acids, and some of the above acids, were converted themselves more or less rapidly, mostly into conjugated monohydroxy fatty acids.     

Naturally occurring inhibitors of intracellular proteinases

The papain inhibitor isolated from chicken egg white inhibits the enzymatic activity of cathepsin B1 and cathepsin C. The inhibitor bears two nonoverlapping reactive sites: one binds cathepsin B1, papain, ficin, and bromelain, the other one cathepsin C. The inhibitor decreases the degree of an immunologic hypersensitive reaction, the so-called Arthus reaction. A statistically significant inhibition of this immunologically developed inflammation occurs only if the inhibitor is applied intradermally and simultaneously with the provoking dose of the antigen to rabbits sensitized to the same antigen. The pepsin inhibitor from the body walls of the roundworm Ascaris lumbricoides inhibits the proteolytic activity of cathepsin E. This inhibitor covalently bound to Sepharose 4B was used for affinity chromatography of cathepsin E. A cathepsin D inhibitor was isolated from potato tubers and its inhibitory and chemical characteristics were studied. The inhibitor does not inhibit either cathepsin E or pepsin yet inhibits trypsin in the alkaline pH-range. The molecular weight of the inhibitor is 21 790 and its molecule consists of 199 amino acid residues. The sequence of 17 amino acid residues was determined by Edman degradation of the inhibitor molecule.     

Naturally occurring polyphenolic inhibitors of amyloid beta aggregation

Alzheimer’s disease is the most common neurodegenerative disease and is one of the main causes of death in developed countries. Consumption of foods rich in polyphenolics is strongly correlated with reduced incidence of Alzheimer’s disease. Our study has investigated the biological activity of previously untested polyphenolic compounds in preventing amyloid β aggregation. The anti-aggregatory potential of these compounds was assessed using the Thioflavin-T assay, transmission electron microscopy, dynamic light scattering and size exclusion chromatography. Two structurally related compounds, luteolin and transilitin were identified as potent inhibitors of Aβ fibril formation. Computational docking studies with an X-ray derived oligomeric structure offer a rationale for the inhibitory activity observed and may facilitate development of improved inhibitors of Aβ aggregation and toxicity.     

Territrems: Naturally occurring specific irreversible inhibitors of acetylcholinesterase

Territrem B (TRB), a fungal metabolite isolated fromAspergillus terreus, potently and noncompetitively inhibited Electrophorus acetylcholinesterase (AChE EC 3.1.1.7), but had no inhibitory effect on horse serum butyrylcholinesterase (BtChE EC 3.1.1.8). The TRB-treated AChE did not recover its enzyme activity after either dialysis or dilution of the inhibited enzyme. The binding of [¹⁴C]TRB to AChE, but not to BtChE, was demonstrated. The concentrations of territrems required for 50% inhibition of AchE were: TRA 2.4 × 10^–8 M; TRB 1.9 × 10^–8 M; TRC 1.5 × 10^–8 M; TRA 9.8 × 10^–8 M; TRB 9.2 × 10^–8 M.     

Inhibition of prostaglandin biosynthesis by triynoic acids

Prostaglandin biosynthesis from eicosa-8,11,14-trienoic acid in microsomes from bovine seminal vesicles is inhibited by acetylenic acids. Octadeca-6,9,12-triynoic acid and eicosa-8,11,14-triynoic acid are the most potent inhibitors. These acids both contain an ω-8 methylene group. Within the 20-carbon acetylenic acid series, inhibition decreases in the sequence eicosa-8,11,14-triynoic acid > eicosa-7,10,13-triynoic acid > eicosa-5,8,11-triynoic acid. Furthermore, eicosa-8,11,14-triynoic acid is a more potent inhibitor of arachidonic acid induced platelet aggregation than either eicosa-7,10,13-triynoic acid or eicosa-5,8,11-triynoic acid. The ω-8 methylene group is not the only determinent of inhibitory potency since docosa-10,13,16-triynoic acid is less potent than its 18 and 20 carbon analogs and all of these acids have an ω-8 methylene group.     

Naturally occurring sites within the Shigella dysenteriae tryptophan operon severely limit tryptophan biosynthesis.

We investigated the structural, functional, and regulatory properties of the Shigella dysenteriae tryptophan (trp.) operon in transduction hybrids in which the cysB-trp-region of Escherichia coli is replaced by the corresponding region from S. dysenteriae. Tryptophan biosynthesis was largely blocked in the hybrids, although the order of the structural genes was identical with that of E. coli. Nutritional tests and enzyme assays revealed that the hybrids produced a defective anthranilate synthetase (ASase). Deletion mapping identified two distinct sites in trpE, each of which was partially responsible for the instability and low activity of ASase. We also discovered a pleiotropic site trpP (S) that maps outside the structural gene region and is closely linked to the S. dysenteriae trp operator. trpP (S) reduced the rate of trp messenger ribonucleic acid synthesis, and consequently trp enzyme levels, 10-fold relative to wild-type E. coli. In recombinants in which the structural genes of E coli were under the control of the S. dysenteriae promoter, enzyme levels were also reduced 10-fold. In some fast-growing revertants of the original hybrids, the rates of trp messenger ribonucleic acid synthesis and levels of tryptophan synthetase were restored to values characteristic of wild-type E.coli. Thus, the Trp auxotrophy associated with the S dysenteriae trp operon derives from the combination of a defective ASase and decreased expression of the entire operon imposed by trpP (S).     

Naturally occurring naphthalenes: chemistry,biosynthesis, structural elucidation,and biological activities

Phytochemistry Reviews - In the recent years, discovery, identification, and development of biologically active compounds have gained a lot of importance. Naphthalenes are a class of arenes,...     

反刍动物体内共轭亚油酸生物合成途径研究进展

共轭亚油酸是一组共轭双键具有不同位置和几何构象的亚油酸异构体,主要存在于反刍动物的肉及乳中。本文就其中2种具有重要生理功能的共轭亚油酸(c-9,t-11CLA和t-10,c-12CLA)的生物合成途径的研究进行综述,以期了解共轭亚油酸代谢途径及其调控路径,为今后利用合成生物学指导共轭亚油酸的合成奠定基础。     

Naturally occurring monoepoxides of eicosapentaenoic acid and docosahexaenoic acid are bioactive antihyperalgesic lipids

Beneficial physiological effects of long-chain n-3 polyunsaturated fatty acids are widely accepted but the mechanism(s) by which these fatty acids act remains unclear. Herein, we report the presence, distribution, and regulation of the levels of n-3 epoxy-fatty acids by soluble epoxide hydrolase (sEH) and a direct antinociceptive role of n-3 epoxy-fatty acids, specifically those originating from docosahexaenoic acid (DHA). The monoepoxides of the C18:1 to C22:6 fatty acids in both the n-6 and n-3 series were prepared and the individual regioisomers purified. The kinetic constants of the hydrolysis of the pure regioisomers by sEH were measured. Surprisingly, the best substrates are the mid-chain DHA epoxides. We also demonstrate that the DHA epoxides are present in considerable amounts in the rat central nervous system. Furthermore, using an animal model of pain associated with inflammation, we show that DHA epoxides, but neither the parent fatty acid nor the corresponding diols, selectively modulate nociceptive pathophysiology. Our findings support an important function of epoxy-fatty acids in the n-3 series in modulating nociceptive signaling. Consequently, the DHA and eicosapentaenoic acid epoxides may be responsible for some of the beneficial effects associated with dietary n-3 fatty acid intake.     

Peroxidative oxidation of leuco-dichlorofluorescein by prostaglandin H synthase in prostaglandin biosynthesis from polyunsaturated fatty acids

Prostaglandin H synthase can oxidize arachidonic acid with leuco-dichlorofluorescein as reducing cosubstrate. Addition of 0.5 mM phenol increases the oxidation of leuco-dichlorofluorescein 5-fold, probably by acting as a cyclic intermediate in the oxidation. Tetramethyl-p-phenylenediamine is also oxidized as cosubstrate. Its oxidation is not influenced by phenol. A stoichiometry of close to one mole of tetramethyl-p-phenylenediamine or leuco-dichlorofluorescein consumed per mole of arachidonic acid was found in the initial phase of the reaction. In the presence of phenol + leuco-dichlorofluorescein, the oxidation rate of arachidonic acid is about 40% lower than with phenol alone as cosubstrate. Since dichlorofluorescein has a molar extinction coefficient of 91 · 10³ at 502 nm, the oxidation of less than 1 μM leuco-dichlorofluorescein can be detected spectrophotometrically. The rate of extinction change with leuco-dichlorofluorescein (at 502 nm) is about 4-fold more rapid than with tetramethyl-p-phenylenediamine (at 611 nm). With this spectrophotometric assay we have confirmed that arachidonic acid, linolenic acid, adrenic acid, γ-linolenic acid, eicosapentaenoic acid, are substrates for prostaglandin H synthase with decreasing reaction rates in the mentioned order. The same order of reaction rates were found when oxygen consumption was measured. The assay also shows that docosahexaenoic acid is substrate for the enzyme. The reaction rate of the enzyme evidently is decreased both by a n − 3 double bond and by deviation from a 20 carbon chain length of the fatty acid substrate.     

Annonaceous acetogenins: Naturally occurring inhibitors of ATP synthesis and photosystem II in spinach chloroplasts

The effects of squamocin ( 1 ), bullatacin ( 2 ) and motrilin ( 3 ), 3 bis-tetrahydrofuran Annonaceous acetogenins, isolated from Annona purpurea (Annonaceae), were investigated on several photosynthetic activities in spinach thylakoids. The results indicated that compounds 1 – 3 significantly inhibited both ATP synthesis and uncoupled electron transport. In addition, they enhanced light-activated Mg2+-ATPase, and basal electron flow. Therefore, acetogenins 1 – 3 behave as uncouplers and Hill reaction inhibitors. Natural products 1 – 3 did not affect photosystem I (PSI) activity but they inhibited photosystem II (PSII) electron flow. The study of the partial PSII reactions from H2O to DCPIPox, H2O to SiMo and diphenylcarbazide to DCPIP established that the site of inhibition was at the oxygen-evolving complex (OEC). Chlorophyll a fluorescence measurements confirmed the behavior of the Annonaceous acetogenins as water-splitting enzyme inhibitors.     

Fatty acids bound to serum albumin potentiate platelet prostaglandin biosynthesis.

Utilization of arachidonic acid by human platelets is increased when the fatty acid content of serum albumin is increased as well. Platelet aggregation induced by arachidonic acid and by low concentrations of thrombin is thus potentiated, suggesting that platelet responsiveness to aggregating agents is influenced by the plasma content in free fatty acids.     

Effects of inhibitors of steroid biosynthesis on prostaglandin formation in rabbit ovarian follicles

Rabbit ovarian follicles were incubated without stimulation, with LH and with LH + an inhibitor or steroid biosynthesis. Formation of prostaglandins PGE and PGF and of progesterone and estradiol was measured in these incubates. It was found that aminoglutethimide phosphate (AGP) inhibited the LH stimulated biosynthesis of both prostaglandins and steroids. However U 30870 and Metyrapone, while completely inhibiting the LH stimulated biosynthesis of progesterone and estradiol respectively, had no effect on the formation of prostaglandins. Further, the inhibition of prostaglandin formation by AGP could not be reversed by exogenou steroids. It, therefore, appears that the effect of AGP on prostaglandin biosynthesis may not be related to its effect on steroid biosynthesis. However, the response of rabbit follicles to AGP is contrary to that reported for rat follicles and indicates different control mechanisms for prostaglandin formation in the follicles of the two species.     

Effects of inhibitors of steroid biosynthesis on prostaglandin formation in rabbit ovarian follicles

Rabbit ovarian follicles were incubated without stimulation, with LH and with LH + an inhibitor of steroid biosynthesis. Formation of prostaglandins PGE and PGF and of progesterone and estradiol was measured in these incubates. It was found that aminoglutethimide phosphate (AGP) inhibited the LH stimulated biosynthesis of both prostaglandins and steroids. However U 30870 and Metyrapone, while completely inhibiting the LH stimulated biosynthesis of progesterone and estradiol respectively, had no effect on the formation of prostaglandins. Further, the inhibition of prostaglandin formation by AGP could not be reversed by exogenous steroids. It, therefore, appears that the effect of AGP on prostaglandin biosynthesis may not be related to its effect on steroid biosynthesis. However, the response of rabbit follicles to AGP is contrary to that reported for rat follicles and indicates different control mechanisms for prostaglandin formation in the follicles of the two species.     

The effect of reported prostaglandin synthetase inhibitors on estradiol - stimulated uterine prostaglandin biosynthesis in the ovariectomized rat

Aspirin, indomethacin and naproxen have been shown to inhibit the release of prostaglandins E and F (PGE and PGF) from the estradiol-stimulated uterus of progesterone-pretreated ovariectomized rats. Under the present experimental conditions indomethacin (1 mg/rat) was found to be a potent inhibitor of PGF and E biosynthesis, but the duration of action was less than 24 hours, after which a rebound above control levels was observed. The compounds were without effect on estradiol-stimulated increases in uterine wet weight. Δ′THC did not inhibit estradiol-stimulated PG biosynthesis but produced a significant rise (P<0.01) in PGE levels in uterine venous blood. A hypothesis is suggested to explain some of the pharmacological effects of Δ′THC.