Evolution of plant defense mechanisms. Relationships of phenylcoumaran benzylic ether reductases to pinoresinol-lariciresinol and isoflavone reductases.
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Pinoresinol-lariciresinol and isoflavone reductase classes are phylogenetically related, as is a third, the so-called "isoflavone reductase homologs." This study establishes the first known catalytic function for the latter, as being able to engender the NADPH-dependent reduction of phenylcoumaran benzylic ethers. Accordingly, all three reductase classes are involved in the biosynthesis of important and related phenylpropanoid-derived plant defense compounds. In this investigation, the phenylcoumaran benzylic ether reductase from the gymnosperm, Pinus taeda, was cloned, with the recombinant protein heterologously expressed in Escherichia coli. The purified enzyme reduces the benzylic ether functionalities of both dehydrodiconiferyl alcohol and dihydrodehydrodiconiferyl alcohol, with a higher affinity for the former, as measured by apparent Km and Vmax values and observed kinetic 3H-isotope effects. It abstracts the 4R-hydride of the required NADPH cofactor in a manner analogous to that of the pinoresinol-lariciresinol reductases and isoflavone reductases. A similar catalytic function was observed for the corresponding recombinant reductase whose gene was cloned from the angiosperm, Populus trichocarpa. Interestingly, both pinoresinol-lariciresinol reductases and isoflavone reductases catalyze enantiospecific conversions, whereas the phenylcoumaran benzylic ether reductase only shows regiospecific discrimination. A possible evolutionary relationship among the three reductase classes is proposed, based on the supposition that phenylcoumaran benzylic ether reductases represent the progenitors of pinoresinol-lariciresinol and isoflavone reductases. (+info)
Regiochemical control of monolignol radical coupling: a new paradigm for lignin and lignan biosynthesis.
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BACKGROUND: Although the lignins and lignans, both monolignol-derived coupling products, account for nearly 30% of the organic carbon circulating in the biosphere, the biosynthetic mechanism of their formation has been poorly understood. The prevailing view has been that lignins and lignans are produced by random free-radical polymerization and coupling, respectively. This view is challenged, mechanistically, by the recent discovery of dirigent proteins that precisely determine both the regiochemical and stereoselective outcome of monolignol radical coupling. RESULTS: To understand further the regulation and control of monolignol coupling, leading to both lignan and lignin formation, we sought to clone the first genes encoding dirigent proteins from several species. The encoding genes, described here, have no sequence homology with any other protein of known function. When expressed in a heterologous system, the recombinant protein was able to confer strict regiochemical and stereochemical control on monolignol free-radical coupling. The expression in plants of dirigent proteins and proposed dirigent protein arrays in developing xylem and in other lignified tissues indicates roles for these proteins in both lignan formation and lignification. CONCLUSIONS: The first understanding of regiochemical and stereochemical control of monolignol coupling in lignan biosynthesis has been established via the participation of a new class of dirigent proteins. Immunological studies have also implicated the involvement of potential corresponding arrays of dirigent protein sites in controlling lignin biopolymer assembly. (+info)
Human metabolism of mammalian lignan precursors in raw and processed flaxseed.
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BACKGROUND: The mammalian lignans enterolactone and enterodiol are produced in the colon by the action of bacteria on the plant precursor secoisolariciresinol diglycoside, which is found in high concentrations in flaxseed. OBJECTIVE: Two experiments were conducted to determine 1) whether there is a dose response in urinary lignan excretion with increasing flaxseed intake, 2) whether flaxseed processing affects lignan excretion, 3) peak plasma lignan concentrations, and 4) plasma lignan concentrations after chronic supplementation. DESIGN: Nine healthy young women supplemented their diets with 5, 15, or 25 g raw or 25 g processed (muffin or bread) flaxseed for 7 d during the follicular phase of their menstrual cycles. Twenty-four-hour urine samples were collected at baseline and on the final day of supplementation. As an adjunct to the 25-g-flaxseed arm, subjects consumed the supplement for an additional day and blood and urine samples were collected at specific intervals. All blood and urine samples were analyzed for enterolactone and enterodiol by gas chromatography-mass spectroscopy. RESULTS: A dose-dependent urinary lignan response to raw flaxseed was observed (r = 0.72, P < 0.001). The processing of flaxseed as a muffin or bread did not affect the quantity of lignan excretion. Plasma lignan concentrations were greater (P < or = 0.05) than baseline by 9 h after flaxseed ingestion (29.35+/-3.69 and 51.75+/-7.49 nmol/L, respectively). The total plasma area under the curve was higher on the eighth than on the first day (1840.15+/-343.02 and 1027.15+/-95.71 nmol x h/L, respectively). CONCLUSION: Mammalian lignan production from flaxseed precursors is dependent on time and dose but not on processing. (+info)
Structure-activity relationship of schisandrins in enhancing liver mitochondrial glutathione status in CCl4-poisoned mice.
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AIM: To explore whether the methylenedioxy group and cyclooctadiene ring of the dibenzocyclooctadiene skeleton of schisandrins (Sch) play a role in the liver mitochondrial glutathione status enhancing activity. METHOD: The effects of three dibenzocyclooctadiene derivatives, Sch A, Sch B, Sch C, and a synthetic intermediate of Sch C, (dimethyl biphenyl dicarboxylate, DBD) on carbon tetrachloride (CCl4)-hepatotoxicity and liver mitochondrial glutathione status were examined in mice. RESULTS: Pretreating mice with intragastric Sch B, Sch C, or DBD 1.mmol.kg-1.d-1 for 3 d protected against CCl4-hepatotoxicity. The hepatoprotection afforded by Sch B or Sch C pretreatment was associated with increases in liver mitochondrial reduced glutathione (mtGSH) level and glutathione reductase (mtGRD) activity, an indication of enhanced mitochondrial glutathione status. In contrast, the hepatoprotective action of DBD was not accompanied by any detectable changes in mtGSH level and mtGRD activity. CONCLUSION: Both the methylenedioxy group and the cyclooctadiene ring of the dibenzocyclooctadiene molecule are important structural determinants in the enhancement of liver mitochondrial glutathione status. (+info)
Stimulation of central cholinergic neurons by (-)clausenamide in vitro.
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AIM: To study the neurotrophic effects of (-) and (+)clausenamide on frontal cortex neurons in culture. METHODS: The activity of the choline acetyltransferase (ChAT) was determined by spectrophotometric method; protein content was assayed by Folin phenol method. RESULTS: (-)Clausenamide increased the activity of ChAT and protein content in cultured neurons, as well as stimulated proliferation of neuronal cells, support survival and neurite outgrowth of neurons. The neurotrophic action of (-)clausenamide (0.001-10 mumol.L-1) was similar to that of nerve growth factor. The (+)clausenamide had no neurotrophic action, even at high concentrations (0.1-10 mumol.L-1), but neurons were damaged. CONCLUSION: (-)Clausenamide stimulated central cholinergic neuron development. (+info)
Effects of naloxone on l-clausenamide-induced long-term potentiation in dentate gyrus of anesthetized rats.
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AIM: To investigate the mechanisms of l-clausenamide-induced long-term potentiation (LTP) in the dentate gyrus of anesthetized rats. METHODS: Extracellular recording technique was used to record the population spike (PS) in the dentate gyrus of anesthetized rats. RESULTS: I.c.v. injection of naloxone 1 nmol, affecting neither the basal PS amplitude nor the LTP induced by tetanus, reduced the l-clausenamide-potentiated LTP only when it was administrated prior to clausenamide. Naloxone 1 nmol (i.c.v.), administrated 10 min before l-clausenamide, reduced the PS amplitude at 20 min, 55 min, and 90 min after i.c.v. injection of l-clausenamide 4 nmol from 138% +/- 10%, 170% +/- 10%, and 169% +/- 12% to 111% +/- 7%, 124% +/- 14%, and 123% +/- 11%, respectively. All P < 0.01 (n = 8). The same dose of naloxone (i.c.v.), delivered 10 min after l-clausenamide, did not affect the l-clausenamide-induced potentiation. CONCLUSION: The activation of opioid receptors contributes to the induction of l-clausenamide-induced LTP of synaptic transmission in dentate gyrus of anesthetized rats. (+info)
Effects of 7-nitroindazole on long-term potentiation induced by l-clausenamide and high-frequency stimulation in rat hippocampus in vivo.
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AIM: To study the antagonistic effect of selective neuronal nitric-oxide synthase (nNOS) inhibitor 7-nitroindazole on the long-term potentiation (LTP) induced by l-clausenamide (Cla) in rat hippocampus in vivo. METHODS: Population spike (PS) of evoked potentials was determined by extracellular recording technique in the hippocampal dentate gyrus (DG) of anesthetized rats. RESULTS: 7-Nitroindazole 2 nmol icv blocked the induction of LTP elicited by high-frequency (100 Hz) stimulation or Cla 5 nmol icv (P < 0.01), and L-arginine 225 mg.kg-1 i.p. prevented the action of 7-nitroindazole (P < 0.01). CONCLUSION: Nitric oxide produced by nNOS plays a role in the induction of Cla-induced LTP in hippocampus. (+info)
Exposure to flaxseed or its lignan component during different developmental stages influences rat mammary gland structures.
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Reduction of the highly proliferative terminal end bud (TEB) structures in the developing mammary gland by differentiation to alveolar buds (ABs) and lobules has been suggested to be protective against mammary cancer. Flaxseed is high in alpha-linolenic acid (ALA) and secoisolariciresinol diglycoside (SDG). SDG is the precursor of mammalian lignans, which can affect mammary gland structures. Thus, the objective of this study was to determine the effect of lifetime, gestation and lactation or after-weaning exposure to 5 or 10% flaxseed or SDG and flaxseed oil components on the mammary gland structures of virgin female rat offspring at post-natal day 50. Lifetime or gestation and lactation exposure to flaxseed altered mammary gland structure development, whereas exposure to flaxseed after weaning had no effect. Lifetime or gestation and lactation exposure to 5% flaxseed caused endocrine changes, as suggested by delayed puberty onset and reduced number of estrous cycles. These changes reduced exposure to endogenous estrogens, leading to atrophy of mammary TEB structures. SDG, but not flaxseed oil, at the level found in 5% flaxseed produced similar effects as 5% flaxseed. This suggested that the lignans were the component in flaxseed responsible for the observed effects. Lifetime or gestation and lactation exposure to 10% flaxseed also caused endocrine changes, as suggested by early puberty onset and lengthened cycles due to prolonged estrus. This increased exposure to endogenous estrogens and stimulated mammary gland differentiation, as indicated by fewer TEBs and more ABs. Thus, lifetime or gestation and lactation exposure to 5 or 10% flaxseed induced structural changes in the mammary gland that may potentially reduce mammary cancer risk. (+info)