Most marine sessile organisms have a planktonic larval phase in their life cycles, and then larvae settle and metamorphose into their adult forms. The selection of settlement sites is a critical event for these organisms because settlement on unsuitable places affects their survivorship severely. Ascidians live gregariously, and conspecific chemical cues are thought to play an important role in gregarious settlement of larvae. The extracts of conspecific adults or larvae have been claimed to contain"natural metamorphosis inducers." Little is known, however, about their chemical properties. To discover natural signal substances for larval metamorphosis in ascidians, we surveyed the metamorphosis-inducing activity of the medium conditioned by ascidian larvae, and succeeded in isolating a metamorphosis-inducing substance from the conditioned medium of Halocycthia roretzi larvae and found that it was identical to lumichrome. We have also isolated more than 40 active metabolites, which may mimic lumichrome, from marine sponges. On the contrary, marine sessile organisms cause serious problems by settling on fishing nets, hulls of ships, and cooling systems of power plants. Organotin compounds have been widely used for the control of these organisms, but they are known to be toxic to marine biota. Therefore, nontoxic antifouling substances are urgently needed. Marine sessile organisms possess chemical defense systems using their secondary metabolites, which might be potential by nontoxic antifouling agents. We have attempted to obtain antibarnacle substances from marine sponges and isolated 26 antifoulants.
Bacterial phospholipases C are known to act on biomembranes, since they can cleave the phosphodiester linkage between the polar head and the hydrophobic moiety of each phospholipid in these membranes. These enzymes have been classified into three groups; phosphatidylcholine(PC)-, sphingomyelin(SM)- and phosphatidylinositol (PI)-degrading phospholipases C. Enzymatic properties and toxicities of these phospholipases C are reviewed, in relation to author's research. Studies on the hemolytic phospholipases of Clostridium sp., Bacillus cereus etc., revealed that hydrolysis of choline-containing phospholipids such as PC and SM was responsible for the hemolysis of mammalian erythrocytes by these enzymes in the presence of Ca2+ and/or Mg2+. Also, the studies on a structure-activity correlation of SM-hydrolyzing phospholipase C from B. cereus disclosed the similarity of active sites between this enzyme and bovine pancreatic DNase I. By action of PI-degrading phospholipases C, several membrane proteins such as alkaline phosphatase, 5'-nucleotidase, VSG(protozoal surface glycoprotein)etc., were shown to be released from the plasma membranes of eucaryotic cells. From structural analysis, these proteins have been revealed to be glycosylphosphatidylinositol(GPI)-anchored proteins bound to the plasma membranes with carboxyl terminal-attached glycolipid. Biochemistry and molecular biology of GPI-anchored proteins, including the structures and biosynthetic routes of GPI glycolipids as well as the process of GPI attachment to proteins, requirements of C-terminal signal peptide for the protein modification by GPI, and distribution of GPI-anchored proteins in living world, are described in relation to our studies.
Beta-adrenoceptor blocking agents (β-blockers)have been widely used for the treatment of angina pectoris. The average/standard therapeutic doses vary widely among β-blockers with the maximum of about a 120-fold difference. In order to clarify the mechanism of this difference, we analyzed retrospectively the pharmacological effects of β-blockers in consideration of the β1-receptor binding affinity and the vasodilative activity on the basis of pharmacokinetics and the receptor occupancy theory. The analysis was performed on eight β-blockers without a vasodilative effect and on four β-blockers with a vasodilative effect. The β1-receptor occupancies at the steady-state condition after oral administration of standard doses were calculated by the use of the data on the concentration of unbound agents in plasma and on the dissociation constant of receptors. The estimated receptor occupancies were 87±6% or 88±10% for the β-blockers with or without a vasodilative effect, respectively, and a significant difference was not observed between these groups. These results suggest that the β1-receptor occupancies may be a principal indicator for the therapeutic effects for angina pectoris regardless of their vasodilative effects.
Dipotassium β-glycyrrhizinate(GK2)is a saponin originated from "Kanzo" plant. We studied such two functions of GK2 as a drug carrier and a penetration enhancer on the eye mucosa. The interactions of GK2 with various drugs were investigated using the 1-octanol/water partition method. GK2 increased the partition of cationic drugs, i.e., antihistamines(chlorpheniramine maleate (CM), diphenhydramine hydrochloride (DH)), as well as decongestants(naphazoline hydrochloride (NA), tetrahydrozoline hydrochloride (TH)). The carrier effect of GK2 is remarkable at its concentration above critical miceller concentration (CMC) and, especially at its pH value of between 4 to 5, resulting that transfers of drugs increased 2 to 10 times as compared to drugs without GK2. In vivo experiments were carried out using rats and rabbits. The effect of GK2 on the inhibition efficiency by CM was evaluated using experimental conjunctivitis formed by injection of histamin on rat upper eyelid. The Inhibition efficiency of edema by CM with GK2 was 4 times stronger than that without GK2. Cornea permeability of TH increased 1.8 times by the addition of GK2. These results indicated that GK2 is applicable as a carrier of cationic drugs on the eye mucosa and cornea.
Convulsive seizures caused by many different stimuli have been shown to induce activator protein-1(AP-1)transcription factors in the brain, particularly in the hippocampus. Previous results from our laboratory demonstrated that thalamic and cerebral cortical AP-1 DNA-and cyclic AMP responsive element (CRE)-binding activities in the absence seizure model mice were significantly higher than those in nonepileptic control mice. In order to characterize further a correlation between convulsive seizures and inducible transcription factors, we investigated convulsive seizure-dependent increases in AP-1 DNA- and CRE- binding activities in various brain regions of the mice. Administration of pentylentetrazole and kainic acid provoked clonic and limbic type seizures, respectively, and increased AP-1 DNA- and CRE- binding activities in the cerebral cortex and hippocampus but not in other regions. Maximal electric shock(MES)induced tonic convulsions and increased hippocampal and cerebral cortical AP-1 DNA- and CRE- binding activities. Sodium phenobarbital (50mg/Kg, i.p.), an anticonvulsant, suppressed both convulsions and increases in these DNA-binding activities induced by MES. In contrast, ethosuximide, an antiabsence drug, did not affect MES-induced convulsions or increases in these DNA-binding activities. These data suggest that convulsive seizures increase not only AP-1 DNA-binding but also CRE-binding activities in the cerebral cortex and hippocampus. These data combined with our previous results also suggest that regional differences in increases in CRE- and AP-1 DNA-binding activities between convulsive seizures and absence seizures are attributable to differences in the regions and pathways which are responsible for the genesis and spreading seizure activities in the central nervous system.
The Baeyer-Villiger (B.V.) reaction using SeO2-H2O2 was examined for various benzaldehydes possessing methoxy groups and/or a furan ring. When benzaldehydes have an electron-donating group(methoxy group)at the ortho or para position to a formyl group, the B.V. reaction proceeded rapidly and in a good yield. Since the reaction using SeO2-H2O2 is carried out under a neutral condition, this reaction are applicable to aldehyde derivatives with a furan ring which is unstable against acid.