Michiaki Yamashita

Stress response and apoptosis in zebrafish embryos

In order to characterize the heat shock response and apoptosis upon exposure to stress conditions, we isolated the genes encoding stress protein HSP70, heat shock transcription factor, HSF, and apoptosis-inducing protease, caspase-3, in zebrafish embryos. Since HSF mRNA expression was paralleled with the heat-inducible expression of the HSP70, the spatial and developmental expression partterns of the HSF gene in embryos may determine the heat-inducible expression of HSP genes during development.

Selenoneine in Marine Organisms

A novel selenium-containing compound, selenoneine, 2-selenyl- N α Open image in new window, N α Open image in new window, N α Open image in new window-trimethyl-l-histidine, has been identified as the predominant form of organic selenium in the blood and tissues of tuna. This selenium compound has a selenium atom in the imidazole ring, and is a selenium analog of a thiol compound, ergothioneine. Selenoneine has radical scavenging activity and exerts an antioxidant effect by binding to hemoglobin and myoglobin, protecting them from iron auto-oxidation. In addition, selenoneine has detoxifying activity against methylmercury (MeHg). Selenoneine has been found to be a specific substrate for the organic cation/carnitine transporter OCTN1 (solute carrier family 22 Open image in new window member 4 Open image in new window, SLC22A4), and mediated the excretion and demethylation of MeHg by exosomal small vesicle formation. The dietary intake of selenoneine through fish consumption is an important selenium source in the human diet. Since selenoneine and its related selenoproteins have strong antioxidant activities, disease protective functions, such as anticarcinogenesis and aging effects, may be expected.

Comparison of connective tissue structure and muscle toughness of spotted mackerel Scomber australasicus and Pacific mackerel S. japonicus during chilled and frozen storage

To characterize post-mortem changes in fish meat quality during chilled and frozen storage, muscle toughness and the connective tissue structure of muscle were compared between two mackerel species, spotted mackerel Scomber australasicus and Pacific mackerel S. japonicus. Measurement of the breaking strength of meat slices from both non-frozen fresh fish and frozen-thawed fish revealed that spotted mackerel meat was softer than Pacific mackerel meat. Under scanning electron microscopic observation, the connective tissue of non-frozen meat of spotted mackerel was thinner than that of Pacific mackerel. In addition, the collagen content in the spotted mackerel meat was lower than that of Pacific mackerel. These findings suggest that connective tissue structure might influence muscle toughness in mackerel.

Determination of Inorganic Arsenic in Seaweed and Seafood by LC-ICP-MS: Method Validation

Background: Seaweed and seafood often contain both inorganic and organic arsenic compounds showing distinct toxicities. Speciation must be taken into account when determining the concentrations of arsenic compounds and how they relate to overall toxicity. Objective: An analytical method for the quantitation of inorganic arsenic was validated in seaweed and seafood. Methods: Food samples were heated at 100°C in 0.3 mol/L nitric acid. Arsenic speciation was quantitatively determined by LC-inductively coupled plasma-MS (LC-ICP-MS) using an octadecilsilane (ODS) column with a mobile phase containing an ion-pair reagent. Results: Limits of detection (0.0023-0.012 mg/kg), LOQ (0.0077-0.042 mg/kg), repeatability (3.0-7.4%), intermediate precision (4.4-7.4%), and trueness (recoveries 94-107%) of the proposed method were satisfactory for inorganic arsenic in seaweed and seafood. Inorganic arsenic was detected in almost all the evaluated dried seaweed products, the Japanese oyster, nam pla, oyster sauce, and the intestinal organs of seafood. Conclusions: Among the dried seaweed products, significant inorganic arsenic was detected in the brown algae akamoku, hijiki, and mozuku. The small amounts of inorganic arsenic detected in nam pla and oyster sauce likely derive from the internal organs of the raw seafood used in their preparation. Highlights: Arsenic speciation in seaweed and seafood was measured by LC-ICP-MS using an ODS column with a mobile phase containing an ion-pair reagent. Among the dried seaweed products, brown algae akamoku, hijiki, and mozuku contained significantly high levels of inorganic arsenic. The intestinal organs of oyster, sardine, and scallop contained higher arsenic levels than the muscles.

Methylmercury and Selenium in Seafood

化学と生物 Vol. 50, No. 11, 2012 807 マグロ類やカジキ類,ハクジラ類などの海洋の高次捕食者に は,食物連鎖によって生物濃縮されたメチル水銀が,筋肉に 含まれることから,魚食からのメチル水銀の摂取による毒性 を明らかにする必要がある.水俣病のように,メチル水銀の 中毒事例から予想すると,低濃度のメチル水銀の長期曝露に よって,脳神経系や心臓・血管系の分化・発達異常が生じる 可能性がありうるが,実際には魚食によって微量なメチル水 銀を摂取し続けても,メチル水銀中毒は生じない.その理由 は,魚から高度不飽和脂肪酸やセレンなどを多量に摂取する ので,これらの成分がメチル水銀の蓄積や毒性発現の機序に 作用して,毒性を軽減することがわかってきた.魚食由来の メチル水銀の健康リスクは過大に評価されているのではない か.なぜ,魚食ではメチル水銀の毒性が打ち消されるのか. 水産物のメチル水銀とセレンによる解毒に関する最近の知見 を紹介する.