Synthesis of a Novel Pyrazine⁻Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine–pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure–fluorescence relationship analysis of the substituent effects with/without Zn²⁺, compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm), a large fluorescence enhancement in response to Zn²⁺ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn²⁺ toward understanding its functions in living systems.

An experimental study of a splenic inhibitory factor influencing hepatic regeneration

The effect of splenectomy on hepatic regeneration after 70 per cent partial hepatectomy was studied in rats. Compared with nonsplenectomized rats, preliminarily splenectomized rats showed significantly increased weights of the liver in the early stage (up to four days) after hepatectomy and significantly promoted deoxyribonucleic acid synthesis in the regenerating liver in terms of high levels of 3H-thymidine uptake, thymidine kinase activity and mitotic index in the residual liver 24 hours after hepatectomy. The splenic factor inhibiting hepatic regeneration, as previously suggested, was investigated by using primary cultures of rat hepatocytes. At 48 hours when the 3H-thymidine uptake by cultured hepatocytes reached maximum, the group containing a splenic extract showed significantly lower levels (p less than 0.005) of uptake than did the group without the extract and the group containing splenic venous serum also showed lower levels. This splenic factor was labile against heat and lost activity by trypsinization. Furthermore, gel filtration by the use of Sephadex G-75 column suggested the factor to be a protein-like substance with a molecular weight of 50,000 to 60,000. It is likely that a protein-like substance inhibiting hepatic regeneration after hepatectomy is present in the spleen.

[Effect of splenectomy on hepatic regeneration in rats]

The effect of splenectomy on hepatic regeneration after partial hepatectomy was investigated in splenectomized and non-splenectomized rats. The results were as follows: The liver weight per body weight after partial hepatectomy increased significantly at 2 and 4 days in splenectomized group compared with non-splenectomized one. The rates of 3H-thymidine uptake in the regenerating liver cells at 24 hours after partial hepatectomy were more enhanced in splenectomized group than in non-splenectomized one. Thymidine kinase activity of the regenerating liver at 24 hours after partial hepatectomy in splenectomized rats was significantly higher than those in non-splenectomized rats. Both mitotic indices and labeling indices at 24 hours after partial hepatectomy in splenectomized rats were significantly higher than those in non-splenectomized group. The cells of mitotic stage were distributed mainly periportal area. From those results, it is suggested that the spleen has some inhibitory factors on hepatic regeneration after partial hepatectomy.