Kinzo Matsumoto

Astaxanthin, a carotenoid with potential in human health and nutrition.

Astaxanthin (1), a red-orange carotenoid pigment, is a powerful biological antioxidant that occurs naturally in a wide variety of living organisms. The potent antioxidant property of 1 has been implicated in its various biological activities demonstrated in both experimental animals and clinical studies. Compound 1 has considerable potential and promising applications in human health and nutrition. In this review, the recent scientific literature (from 2002 to 2005) is covered on the most significant activities of 1, including its antioxidative and anti-inflammatory properties, its effects on cancer, diabetes, the immune system, and ocular health, and other related aspects. We also discuss the green microalga Haematococcus pluvialis, the richest source of natural 1, and its utilization in the promotion of human health, including the antihypertensive and neuroprotective potentials of 1, emphasizing our experimental data on the effects of dietary astaxanthin on blood pressure, stroke, and vascular dementia in animal models, is described.

Impairment of the spatial learning and memory induced by learned helplessness and chronic mild stress

Increasing evidences indicate the concurrence and interrelationship of depression and cognitive impairments. The present study was undertaken to investigate the effects of two depressive animal models, learned helplessness (LH) and chronic mild stress (CMS), on the cognitive functions of mice in the Morris water maze task. Our results demonstrated that both LH and CMS significantly decreased the cognitive performance of stressed mice in the water maze task. The escaping latency to the platform was prolonged and the probe test percentage in the platform quadrant was reduced. These two models also increased the plasma corticosterone concentration and decreased the brain derived neurotrophic factor (BDNF) and cAMP-response element-biding protein (CREB) messenger ribonucleic acid (mRNA) levels in hippocampus, which might cause the spatial cognition deficits. Repeated treatment with antidepressant drugs, imipramine (Imi) and fluoxetine (Flu), significantly reduced the plasma corticosterone concentration and enhanced the BDNF and CREB levels. Furthermore, antidepressant treated animals showed an ameliorated cognitive performance compared with the vehicle treated stressed animals. These data suggest that both LH and CMS impair the spatial cognitive function and repeated treatment with antidepressant drugs decreases the prevalence of cognitive impairments induced by these two animal models. Those might in part be attributed to the reduced plasma corticosterone and enhanced hippocampal BDNF and CREB expressions. This study provided a better understanding of molecular mechanisms underlying interactions of depression and cognitive impairments, although animal models used in this study can mimic only some aspects of depression or cognition of human.

Pteropodine and isopteropodine positively modulate the function of rat muscarinic M1 and 5-HT2 receptors expressed in Xenopus oocyte

Pteropodine and isopteropodine are heteroyohimbine-type oxindole alkaloid components of Uncaria tomentosa (Willd.) DC, a Peruvian medicinal plant known as cats claw. In this study, the effects of these alkaloids on the function of Ca(2+)-activated Cl(-) currents evoked by stimulation of G protein-coupled muscarinic M(1) acetylcholine and 5-HT(2) receptors were studied in Xenopus oocytes in which rat cortex total RNA was translated. Pteropodine and isopteropodine (1-30 microM) failed to induce membrane current by themselves. However, these alkaloids markedly enhanced the current responses evoked by both acetylcholine and 5-hydroxyhyptamine (5-HT) in a concentration-dependent and reversible manner with the maximal effects at 30 microM. Pteropodine and isopteropodine produced 2.7- and 3.3-fold increases in the acetylcholine response with EC(50) values of 9.52 and 9.92 microM, respectively, and 2.4- and 2.5-fold increases in the 5-HT response with EC(50) values of 13.5 and 14.5 microM, respectively. In contrast, in oocytes injected with total RNA from the rat cerebellum or spinal cord, neither alkaloid had an effect on the metabotropic current responses mediated by glutamate receptor(1 and 5) (mGlu(1/5)) receptors or ionotropic responses mediated by N-methyl-D-aspartate, kainic acid or glycine. Pteropodine and isopteropodine (10 microM) significantly reduced the EC(50) values of acetylcholine and 5-HT that elicited current responses, but had no effect on the maximal current responses elicited by acetylcholine and 5-HT. On the other hand, mitraphylline, a stereoisomer of pteropodine, failed to modulate acetylcholine- and 5-HT-induced responses. These results suggest that pteropodine and isopteropodine act as positive modulators of muscarinic M(1) and 5-HT(2) receptors.

Brain 5α-dihydroprogesterone and allopregnanolone synthesis in a mouse model of protracted social isolation

Allopregnanolone (ALLO), is a brain endogenous neurosteroid that binds with high affinity to γ-aminobutyric acid type A (GABAA) receptors and positively modulates the action of GABA at these receptors. Unlike ALLO, 5α-dihydroprogesterone (5α-DHP) binds with high affinity to intracellular progesterone receptors that regulate DNA transcription. To investigate the physiological roles of ALLO and 5α-DHP synthesized in brain, we have adopted a mouse model involving protracted social isolation. In the frontal cortex of mice, socially isolated for 6 weeks, both neurosteroids were decreased by approximately 50%. After administration of (17β)-17-(bis-1-methyl amino carbonyl) androstane-3,5-diene-3-carboxylic acid (SKF105,111), an inhibitor of the enzyme (5α-reductase Type I and II) that converts progesterone into 5α-DHP, the ALLO and 5α-DHP content of frontal cortex of both group-housed and socially isolated mice decreased exponentially to 10%–20% of control values in about 30 min. The fractional rate constants (k h−1) of ALLO and 5α-DHP decline multiplied by the ALLO and 5α-DHP concentrations at any given steady-state estimate the rate of synthesis required to maintain that steady state. After 6 weeks of social isolation, ALLO and 5α-DHP biosynthesis rates were decreased to 30% of the values calculated in group-housed mice. Moreover, in socially isolated mice, the expression of 5α-reductase Type I mRNA and protein was approximately 50% lower than in group-housed mice whereas 3α-hydroxysteroid oxidoreductase mRNA expression was equal in the two groups. Protracted social isolation in mice may provide a model to investigate whether 5α-DHP by a genomic action, and ALLO by a nongenomic mechanism down-regulate the action of drugs acting as agonists, partial agonists, or positive allosteric modulators of the benzodiazepine recognition sites expressed by GABAA receptors.

PROGRESSIVE COGNITIVE IMPAIRMENT FOLLOWING CHRONIC CEREBRAL HYPOPERFUSION INDUCED BY PERMANENT OCCLUSION OF BILATERAL CAROTID ARTERIES IN RATS

The effects of chronic cerebral hypoperfusion induced by permanent occlusion of bilateral common carotid arteries (2VO) on learning and memory performance were examined in rats using an eight-arm radial maze task. The learning of the task was severely impaired in the permanent 2VO rats that had not been pretrained, while the retention was slightly impaired and soon recovered in the permanent 2VO rats that had been fully pretrained when tested within 1 month after the 2VO operation. The performance, however, was impaired in the pretrained rats when a 3-min delay was interposed between the fourth and fifth choices. Moreover, when retrained in the radial maze 4 months after the permanent 2VO, these same rats showed a performance impairment. Some loss of the hippocampal pyramidal neurons was observed 1 month after the permanent 2VO, although the decrease was not significant. However, significant loss of the cells was observed in the hippocampus CA1 subfield 4 months after the operation. We concluded that: (1) In the early stage (1 month after permanent 2VO), a learning deficit was observed in the non-pretrained rats. In the pretrained rats, working memory was not impaired, whereas longer term memory was compromised; (2) in the late stage (4 months after permanent 2VO), working memory may have also been impaired in the pretrained rats; and (3) this progressive cognitive deficit seemed to parallel the progress of neuronal damage.

Antinociceptive effects of Nigella sativa oil and its major component, thymoquinone, in mice.

The antinociceptive effects of Nigella sativa oil and its major component, thymoquinone, were examined in mice. The p.o. administration of N. sativa oil (50-400 mg/kg) dose-dependently suppressed the nociceptive response in the hot-plate test, tail-pinch test, acetic acid-induced writhing test and in the early phase of the formalin test. The systemic administration (2.5-10 mg/kg, p.o. and 1-6 mg/kg, i.p.) and the i.c.v. injection (1-4 microgram/mouse) of thymoquinone attenuated the nociceptive response in not only the early phase but also the late phase of the formalin test. Naloxone injected s.c. (1 mg/kg) significantly blocked N. sativa oil- and thymoquinone-induced antinociception in the early phase of the formalin test. Moreover, the i.c.v. injection of naloxone (10 microgram/mouse), the mu(1)-opioid receptor antagonist, naloxonazine (1-5 microgram/mouse), or the kappa-opioid receptor antagonist, nor-binaltorphimine (1-5 microgram/mouse), significantly reversed thymoquinone-induced antinociception in the early phase but not the late phase of the formalin test, whereas the delta-opioid receptor antagonist, naltrindole (1-5 ng/mouse, i.c.v.), had no effect on either phase. The antinociceptive effect of morphine was significantly reduced in thymoquinone- and N. sativa oil-tolerant mice, but not vice versa. These results suggest that N. sativa oil and thymoquinone produce antinociceptive effects through indirect activation of the supraspinal mu(1)- and kappa-opioid receptor subtypes.

In socially isolated mice, the reversal of brain allopregnanolone down-regulation mediates the anti-aggressive action of fluoxetine

Social isolation (SI) of male mice lasting >4 weeks is associated with aggression toward intruders and a down-regulation of brain allopregnanolone (Allo) content. SI of female mice fails to down-regulate brain Allo content or to induce aggressiveness. Fluoxetine (Prozac in clinical use) is an S- and R-fluoxetine (FLX) mixture, which in mammals is metabolized into S- and R-norfluoxetine (NFLX). The S isomers of FLX and NFLX are more active than their respective R isomers in normalizing brain Allo down-regulation and in reducing the aggressiveness induced by SI. Thus, FLX stereospecifically reduces brain Allo down-regulation and the aggressiveness induced by SI, whereas serotonin (5-HT) uptake inhibition lacks stereospecificity. The doses of S-FLX and S-NFLX that reduce aggressiveness and Allo brain content down-regulation induced by SI are at least one order of magnitude lower than the doses that block 5-HT reuptake. Doses of imipramine that inhibit 5-HT uptake neither reduce aggressiveness nor normalize brain Allo down-regulation. We conclude that Allo brain content normalization is a better candidate than 5-HT reuptake inhibition to explain the reduction of aggressiveness elicited by S-FLX and S-NFLX.

Neuronal damage and decrease of central acetylcholine level following permanent occlusion of bilateral common carotid arteries in rat

The neuronal damages and the changes in central acetylcholine (ACh) and choline (Ch) contents following permanent occlusion of bilateral common carotid arteries (2VO) of rats were investigated 1 and 4 months after the operation. Two types of neuronal damages were observed in the rats with permanent 2VO. The first type was the infarctions observed in the cerebral cortex and striatum. The infarction in the cortex and striatum was observed in 28.6 and 42.9% of the animals examined 1 month after permanent 2VO, respectively. These ratios did not change even when examined 4 months after permanent 2VO, suggesting that this type of neuronal damage is due to acute ischemic attacks. The second type was progressive neuronal damages observed in the hippocampus and white matter: the neuronal loss in the CA1 subfield appeared 4 months but not 1 month after permanent 2VO and the rarefaction of white matter which was observed 1 months after permanent 2VO and markedly increased 4 months after the operation. Moreover, ACh level significantly decreased in the striatum but not in the cortex, hippocampus or hypothalamus 1 month after permanent 2VO, while the ACh levels in the cortex, striatum and hypothalamus, and Ch levels in all the regions tested significantly decreased when tested 4 months after the operation. These changes did not accompany necrosis. These results suggest that the progressive neuronal degeneration and cholinergic dysfunction following the permanent 2VO are in part involved in chronic cerebral hypoperfusion-induced long-lasting cognition deficits in rats.

Central antinociceptive effects of mitragynine in mice: contribution of descending noradrenergic and serotonergic systems.

Mitragynine is a major alkaloidal constituent of young leaves of Mitragyna speciosa Korth, that is known to exhibit narcotic-like activity. In this study, we investigated the roles of central monoaminergic systems in the antinociceptive action of mitragynine by means of the tail-pinch and hot-plate tests in mice. Mitragynine (1.0-10 micrograms) injected i.c.v. exerted a dose-dependent antinociceptive activity in both tests. The activity of mitragynine (10 micrograms, i.c.v.) in the tail-pinch test was antagonized by reserpine, 6-hydroxydopamine plus nomifensine, and p-chlorophenylalnine treatment, whereas the antinociceptive activity of morphine (3 micrograms) given i.c.v. in this test was attenuated by 6-hydroxydopamine plus nomifensine but not by p-chlorophenylalanine treatment. Moreover, the activity of i.c.v. mitragynine was also antagonized by the alpha 2-adrenoceptor antagonist, idazoxan (10 micrograms), and cyproheptadine (1 microgram) administered intrathecally (i.t.). On the other hand, the antinociceptive action of i.c.v. mitragynine (10 micrograms) in the hot-plate test was abolished by reserpine and 6-hydroxydopamine plus nomifensine, but not by p-chlorophenylalanine treatment. This action was also antagonized by i.t. injection of idazoxan (10 micrograms). These results suggest that both descending noradrenergic and serotonergic systems are involved in the antinociceptive activity of supraspinally administered mitragynine on the mechanical noxious stimulation, while the descending noradrenergic system predominantly contributes to the effect of supraspinal mitragynine on the thermal noxious stimulation. The mechanisms underlying the suppressive action of mitragynine on the nociceptive response may differ from those of morphine in mice.

Rhynchophylline and isorhynchophylline inhibit NMDA receptors expressed in Xenopus oocytes.

Rhynchophylline and isorhynchophylline are major tetracyclic oxindole alkaloid components of Uncaira species, which have been long used as medicinal plants. In this study, the effects of rhynchophylline and isorhynchophylline on the ionotropic and metabotropic glutamate receptor-mediated current responses were examined using Xenopus oocytes injected with total RNA prepared from rat cortices or cerebelli. Rhynchophylline and isorhynchophylline (1-100 microM) per se failed to induce membrane current, but these alkaloids reversibly reduced N-methyl-D-aspartate (NMDA)-induced current in a concentration-dependent but voltage-independent manner. The IC(50) values of rhynchophylline and isorhynchophylline were 43.2 and 48.3 microM, respectively. Substitution of Ba(2+) for Ca(2+) in the recording medium did not alter the extent of rhynchophylline- and isorhynchophylline-induced suppression of NMDA currents. In contrast, neither alkaloid had an effect on the currents mediated by ionotropic kainic acid-type and (+/-)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors or by the metabotropic glutamate receptor(1 and 5) (mGlu(1/5)). Rhynchophylline and isorhynchophylline (30 microM) significantly reduced the maximal current responses evoked by NMDA and glycine (a co-agonist of NMDA receptor), but had no effect on the EC(50) values and Hill coefficients of NMDA and glycine for inducing currents. These alkaloids showed no interaction with the polyamine binding site, the Zn(2+) site, proton site or redox modulatory site on the NMDA receptor. These results suggest that rhynchophylline and isorhynchophylline act as noncompetitive antagonists of the NMDA receptor and that this property may contribute to the neuroprotective and anticonvulsant activity of the Uncaira species plant extracts.