A nonsynonymous SNP in human cytosolic sialidase in a small Asian population results in reduced enzyme activity: potential link with severe adverse reactions to oseltamivir

The use of oseltamivir, widely stockpiled as one of the drugs for use in a possible avian influenza pandemic, has been reported to be associated with neuropsychiatric disorders and severe skin reactions, primarily in Japan. Here we identified a nonsynonymous SNP （single nucleotide polymorphism） in dbSNP database, R41Q, near the enzymatic active site of human cytosolic sialidase, a homologue of virus neuraminidase that is the target of oseltamivir. This SNP occurred in 9.29% of Asian population and none of European and African American population. Our structural analyses and Ki measurements using in vitro sialidase assays indicated that this SNP could increase the unintended binding affinity of human sialidase to oseltamivir carboxylate, the active form of oseltamivir, thus reducing sialidase activity. In addition, this SNP itself results in an enzyme with an intrinsically lower sialidase activity, as shown by its increased Km and decreased Vmax values. Theoretically administration of oseltamivir to people with this SNP might further reduce their sialidase activity. We note the similarity between the reported neuropsychiatric side effects ofoseltamivir and the known symptoms of human sialidase-related disorders. We propose that this Asian-enriched sialidase variation caused by the SNP, likely in homozygous form, may be associated with certain severe adverse reactions to oseltamivir.

An update on Gardneralla vaginalis associated bacterial vaginosis in Malaysia

Objective: To update the status of Gardnerella vaginalis(G. vaginalis) as a causative agent of bacterial vaginosis(BV) in Malaysia and to define its epidemiology, metronidazole resistance and virulence properties.Methods: It is a single-centre(Gynaecology clinic at the Hospital Kuala Lumpur,Malaysia) prospective study with laboratory-based microbiological follow up and analyses. Vaginal swabs collected from the patients suspected for BV were subjected to clinical BV diagnosis, isolation and identification of G. vaginalis, metronidazole susceptibility testing, vaginolysin and sialidase gene PCR, Piot's biotyping and amplified ribosomal DNA restriction analysis genotyping.Results: Among the 207 patients suspected for BV, G. vaginalis was isolated from 47 subjects. G. vaginalis coexisted with Trichomonas vaginalis and Candida albicans in 26 samples. Three G. vaginalis isolates were resistant to metronidazole. Biotyping revealed 1 and 7 as the common types. Amplified ribosomal DNA restriction analysis genotype II was found to be more common(n = 22; 46%) than I(n = 12; 25.53%) and III(n = 13;27.6%). All genotype I and III isolates carried the sialidase gene, while 91.6% and 84.6%contained the vaginolysin gene. Genotype I was significantly associated with postgynaecological surgical complications and abortions(P = 0.002).Conclusions: The existence of pathogenic G. vaginalis clones in Malaysia including drug resistant strains should not be taken lightly and needs to be monitored as these may bring more complications especially among women of child bearing age and pregnant women.

Mechanism of gangliosides GD3 increment in hepatocellular carcinoma tissue

Determination of sialidase activity in hepatocellular carcinoma (HCC) to complete the mechanism study of GD3 change in HCC. A sensitive assay for ganglioside sialidase activity was used based on the specific binding of ricinus communis agglutinin Ⅱ (RCAⅡ) to lactose reside. The substrate used for sialidase assay was ganglioside GM3 coated on a 96- well microtiterplate. After removing static acids from the terminal positions of the ganglioside glycans by sialidase, the glycans were subjected to biotin-labeled RCAⅡ. Then, the ABC assay was used to determine the activity of sialidase. The activities of sialidase with both soluble form and membrane-bound form in HCC decreased significantly as compared with those in peritumor tissue. Our results indicated that the increase in ganglioside GD3 in HCC is not only due to the enhancement of GD3 sythase activity but also due to the decrease in the sialidase