Specific inhibition of viral neuraminidases by an inhibitor, neuraminin, produced by Streptomyces sp

In vivo anti-influenza virus activity of plant flavonoids possessing inhibitory activity for influenza virus sialidase

Isoscutellarein (5,7,8,4'-tetrahydroxyflavone) from the leaf of Scutellaria baicalensis non-competitively inhibited (IC50, 20 microM) the hydrolysis of sodium p-nitrophenyl-N-acetyl-alpha-D-neuraminate by influenza virus sialidase with an apparent Ki value of 41 microM. Negligible inhibitory activity was observed for mouse liver sialidase at a concentration of 79 microM. Isoscutellarein also inhibited the replication of influenza virus A/WSN/33 in Madin-Darby bovine kidney cells with 50% virus inhibitory dose at 16 nmol/well and influenza virus A/PR/8/34 in the allantoic sac of embryonated egg with little toxic effects. The flavone showed significant anti-influenza virus activity in vitro similar to isoscutellarein-8-methylether (F36) (Nagai, T., Miyaichi, Y., Tomimori, T., Suzuki, Y. and Yamada H., 1990, Chem. Pharm. Bull. 38, 1329-1332), and more potent virucidal activity in ovo than F36. However, F36 completely prevented proliferation of mouse-adapted influenza virus A/PR/8/34 in mouse lung by the intranasal (0.5 mg/kg) and intraperitoneal (4 mg/kg) administrations, and it was more potent than the known anti-influenza virus substance, amantadine. Intranasal administration of F36 (0.5 mg/kg) also protected mice against a lethal influenza virus A/PR/8/34 infection. Isoscutellarein significantly inhibited lung virus proliferation when administered intranasally or orally to mice. F36 and isoscutellarein showed negligible toxic effect against mice. These results suggested that flavones, which have potent influenza virus sialidase inhibitory activity, have anti-influenza virus activity in vivo.

New ganglioside analogs that inhibit influenza virus sialidase

Synthetic thioglycoside-analogs of gangliosides such as Neu5Ac alpha(2-S-6)Glc beta(1-1)Ceramide (1) and the GM3 analog Neu5Ac alpha(2-S-6)Gal beta(1-4)Glc beta(1-1)Ceramide (2), competitively inhibited GM3 hydrolysis by the sialidase of different subtypes of human and animal influenza viruses with an apparent Ki value of 2.8 x 10(-6) and 1.5 x 10(-5) M, respectively. The inhibitory activity of the ganglioside GM4 analog [Neu5Ac alpha(2-S-6)Gal beta(1-1)Ceramide (3)], in which the glucose of 1 was substituted by galactose, was lower than that of 1 (Ki = 1.0 x 10(-4) M). The thioglycoside-analogs (1, 2, 3) of the gangliosides were non-hydrolyzable substrates for influenza virus sialidase. The inhibitory activity of 1 to bacterial sialidases from Clostridium perfringens and Arthrobacter ureafaciens was considerably lower than that to influenza virus sialidase, indicating that the structure of the active site in bacterial and influenza virus sialidase may be different and the analogs may be useful to determine the orientation of the substrate to the active site of sialidases, especially of influenza viruses.

Enzymological heterogeneity of influenza B virus neuraminidase demonstrated by the fluorometric assay method

The neuraminidase activity of 26 strains of influenza B virus isolated from all over the world was investigated colorimetrically, using fetuin as a substrate, and fluorometrically, using 4-methylumbelliferyl(4-MU)-N-Ac-alpha-D-neuraminide as a substrate, with special reference to enzymological heterogeneity. The activity of influenza A viral neuraminidases and of a commercially available pure viral one was strongly inactivated by either ethylenediaminetetraacetic acid or glycoletherdiaminetetraacetic acid, when measured by the fluorometric assay method, whereas that of influenza B ones was not at all. However, the viral neuraminidases of both influenza A and B viruses were found to be calcium ion-dependent by the colorimetric assay method. A difference in the catalytic rate between the two assay methods was observed with influenza B viral neuraminidase to a much greater extent as compared with that of influenza A. A difference in substrate specificity of these enzymes was demonstrated to be due to a difference in the degree of competitive inhibition by N-acetylneuraminic acid. These findings strongly suggest that enzymological heterogeneity in influenza B viral neuraminidase may be attributed to delicate structural differences, between the enzymes of influenza A and B viruses demonstratable only by the fluorometric neuraminidase assay method using 4-MU-N-Ac-alpha-D-neuraminide as a substrate.