Activation of translation initiation factor eIF2B by insulin requires phosphatidyl inositol 3-kinase

Eukaryotic initiation factor eIF2B mediates a key regulatory step in peptide-chain initiation and is acutely activated by insulin, although it is not clear how. Inhibitors of phosphatidylinositide 3-kinase blocked activation of eIF2B, although rapamycin, which inhibits the p70 S6 kinase pathway, did not. Furthermore, a dominant negative mutant of PI 3-kinase also prevented activation of eIF2B, while a Sos-mutant, which blocks MAP kinase activation, did not. The data demonstrate that a pathway distinct from MAP and p70 S6 kinases regulates eIF2B. Glycogen synthase kinase-3 (GSK-3) phosphorylates and inactivates eIF2B. In all cases, eIF2B and GSK-3 were regulated reciprocally. Dominant negative PI 3-kinase abolished the insulin-induced inhibition of GSK-3. These data strongly support the hypothesis that insulin activates eIF2B through a signalling pathway involving PI 3-kinase and inhibition of GSK-3.     

Sensitive and selective method for the determination of chlormezanone in plasma by electron-capture gas chromatography

A sensitive and selective determination method of chlormezanone in plasma has been divised. Chlormezanone in plasma was extracted with toluene at pH 4.5, and converted into p-chlorobenzaldehyde in 0.1 N NaOH. Using p-bromobenzaldehyde as an internal standard, the hydrolysis product and the internal standard were extracted with n-hexane, and the extract was concentrated in vacuo in the presence of isoamyl alcohol to prepare the sample solution. The sample solution was submitted to electron-capture gas chromatography. Chlormezanone was determined by use of the peak height ratio of p-chlorobenzaldehyde against the internal standard. The method was utilized successfully for pharmacokinetic studies of chlormezanone in plasma.     

The Selective SGLT2 Inhibitor Ipragliflozin Has a Therapeutic Effect on Nonalcoholic Steatohepatitis in Mice

Background & Aims

In recent years, nonalcoholic steatohepatitis (NASH) has become a considerable healthcare burden worldwide. Pathogenesis of NASH is associated with type 2 diabetes mellitus (T2DM) and insulin resistance. However, a specific drug to treat NASH is lacking. We investigated the effect of the selective sodium glucose cotransporter 2 inhibitor (SGLT2I) ipragliflozin on NASH in mice.

Methods

We used the Amylin liver NASH model (AMLN), which is a diet-induced model of NASH that results in obesity and T2DM. AMLN mice were fed an AMLN diet for 20 weeks. SGLT2I mice were fed an AMLN diet for 12 weeks and an AMLN diet with 40 mg ipragliflozin/kg for 8 weeks.

Results

AMLN mice showed steatosis, inflammation, and fibrosis in the liver as well as obesity and insulin resistance, features that are recognized in human NASH. Ipragliflozin improved insulin resistance and liver injury. Ipragliflozin decreased serum levels of free fatty acids, hepatic lipid content, the number of apoptotic cells, and areas of fibrosis; it also increased lipid outflow from the liver.

Conclusions

Ipragliflozin improved the pathogenesis of NASH by reducing insulin resistance and lipotoxicity in NASH-model mice. Our results suggest that ipragliflozin has a therapeutic effect on NASH with T2DM.     

Evolutionary trajectory of phytoalexin biosynthetic gene clusters in rice

Plants frequently possess operon‐like gene clusters for specialized metabolism. Cultivated rice, Oryza sativa, produces antimicrobial diterpene phytoalexins represented by phytocassanes and momilactones, and the majority of their biosynthetic genes are clustered on chromosomes 2 and 4, respectively. These labdane‐related diterpene phytoalexins are biosynthesized from geranylgeranyl diphosphate via ent‐copalyl diphosphate or syn‐copalyl diphosphate. The two gene clusters consist of genes encoding diterpene synthases and chemical‐modification enzymes including P450s. In contrast, genes for the biosynthesis of gibberellins, which are labdane‐related phytohormones, are scattered throughout the rice genome similar to other plant genomes. The mechanism of operon‐like gene cluster formation remains undefined despite previous studies in other plant species. Here we show an evolutionary insight into the rice gene clusters by a comparison with wild Oryza species. Comparative genomics and biochemical studies using wild rice species from the AA genome lineage, including Oryza barthii, Oryza glumaepatula, Oryza meridionalis and the progenitor of Asian cultivated rice Oryza rufipogon indicate that gene clustering for biosynthesis of momilactones and phytocassanes had already been accomplished before the domestication of rice. Similar studies using the species Oryza punctata from the BB genome lineage, the distant FF genome lineage species Oryza brachyantha and an outgroup species Leersia perrieri suggest that the phytocassane biosynthetic gene cluster was present in the common ancestor of the Oryza species despite the different locations, directions and numbers of their member genes. However, the momilactone biosynthetic gene cluster evolved within Oryza before the divergence of the BB genome via assembly of ancestral genes.     

Production and sex‐pheromonal activity of alkaloid‐derived androconial compounds in the danaine butterfly,Parantica sita (Lepidoptera: Nymphalidae: Danainae)

Close associations of certain lepidopteran taxa with pyrrolizidine alkaloids (PAs), a typical class of plant secondary metabolites, have been well documented from the perspective of evolutionary ecology. Male danaine butterflies are thought to utilize PAs as precursors for the production of dihydropyrrolizines [e.g. danaidone (DO) and hydroxydanaidal (HD)] in their two distinct androconial organs, viz. alar scent organs (sex brands) and abdominal hairpencils. However, little is known about the quantitative profiles of these compounds in danaines, the mechanism for their formation in the androconial organs, or their biological functions, particularly in mating behaviour. The present study addressed these unanswered questions posed for males of the danaine butterfly, Parantica sita. Chemical analyses of androconial extracts revealed considerable seasonal/regional and individual variations of the amounts of DO (the major dihydropyrrolizine produced) and 7R‐HD (the 7R‐enantiomer of HD detected in this study) found in the two organs. These variations seemed to depend primarily on the age of the male and the phenological traits of PA‐containing plants available. Males were found to acquire an adequate capability to produce DO ~1 week after eclosion. DO was shown to be produced exclusively in the sex brand and subsequently physically transferred to the hairpencil through a contact behaviour between the two organs, here termed ‘perfuming behaviour’. The results of behavioural experiments with PA‐fed and PA‐unfed males that were allowed to compete for mates, combined with the positive electroantennographic (EAG) responses of the female, to both DO and 7R‐HD, led to the conclusion that either or both of these compounds can act as the sex pheromone. Oral administration of PAs to males indicated that DO can be biosynthesized from various PA precursors, while 7R‐HD, unlike in arctiid moths, is derived only from PAs with the 7R‐configuration. The putative biosynthetic pathways of DO and 7R‐HD, and the evolutionary provenance of the binate androconial system in the Danainae are also discussed.     

Microhabitat use by larvae of the endangered dragonfly <Emphasis Type="Italic">Sympetrum pedemontanum</Emphasis><Emphasis Type="Italic">elatum</Emphasis> (Selys) in Japan

Sympetrum pedemontanum (Müller in Allioni) (Odonata: Libellulidae), which is distributed widely in the Eurasian continent and its neighboring islands, is listed as a Least Concern species in the International Union for Conservation of Nature Red List (2015). In Japan, however, the population of its subspecies S. pedemontanum elatum (Selys) has been rapidly decreasing since the 1970s. In order to conserve this subspecies, it is important to understand the seasonal microhabitat use by its larvae. However, this has been a difficult task because larvae of S. pedemontanum elatum often coexist with those of a common congener, S. eroticum (Selys), and cannot be morphologically distinguished from the latter. Thus, in this study, we first established a molecular technique based on the polymerase chain reaction to accurately identify each species. In the subsequent field survey in 2015 with its application in the Sakasegawa River, Hyogo Prefecture, we found that S. pedemontanum elatum larvae hatch in stagnant water and subsequently advance into weakly flowing water. Our results indicated a change in the microhabitats during the larval developmental process, reflecting the need for a continuous spectrum of stagnant, transitional, and flowing water. Such aquatic environments with a spectrum of water conditions are disappearing in Satoyama, a rural farming area in Japan. This has endangered species such as S. pedemontanum elatum and Oryzias latipes (Beloniformes: Adrianichthyidae) by depriving them of their favorable habitats. For their conservation, it is necessary to develop methods to recover the traditional aquatic environments in Satoyama.