Poor bioavailability of vitamin D2 from ultraviolet-irradiated D2-rich yeast in rats.

Ultraviolet-irradiated yeast (Saccharomyces cerevisiae) can be used to biofortify bakery products with vitamin D, but in bread, it was not effective in increasing serum 25-hydroxyvitamin D [25(OH)D] in humans, possibly because of the low digestibility of the yeast matrix. We investigated the effects of vitamin D2-rich intact yeast cells and their separated fraction, yeast cell walls, which we hypothesized to provide vitamin D2 in a more bioavailable form, on serum 25(OH)D and its metabolites in growing female Sprague-Dawley rats (n = 54) compared to vitamin D2 and D3 supplements (8 treatment groups: 300 or 600 IU vitamin D/d, and a control group, 8-week intervention). The D3 supplement groups had the highest 25(OH)D concentrations, and the vitamin D2 supplement at the 600-IU dose increased 25(OH)D better than any yeast form (P < .001 for all, analysis of covariance, adjusted for body weight). There were no significant differences between the yeast forms at the same dose (P > .05). Serum 24,25-dihydroxyvitamin D (a vitamin D catabolite) concentrations and the trend in the differences between the groups were in line with 25(OH)D (P < .001 for all). The 24,25-dihydroxyvitamin D to 25(OH)D ratio between the D2 supplement and the yeast groups did not differ (P > .05). These findings do not support the hypothesis: the ability of the different ultraviolet-treated vitamin D2-containing yeast forms to increase 25(OH)D did not differ, and the poor bioavailability of vitamin D2 in the yeasts compared D3 or D2 supplements could not be explained by the increased vitamin D catabolism in the yeast-treated groups.

An adult zebrafish model for preclinical tuberculosis vaccine development.

Tuberculosis remains a major global health challenge despite extensive vaccination schemes with the current live vaccine, Bacillus Calmette-Guérin. Tuberculosis vaccine research has been hampered by a scarcity of animal models which replicate human disease and are suitable for large-scale studies. We have shown recently that Mycobacterium marinum, a close relative of Mycobacterium tuberculosis, causes an infection resembling human tuberculosis in adult zebrafish (Danio rerio). In the present study we use this model to show that BCG vaccination as well as DNA vaccination with selected mycobacterial antigens (Ag85B, CFP-10 and ESAT-6) protects adult zebrafish from mycobacterial infection. Using a low-dose (∼20-30 bacteria) intraperitoneal M. marinum infection, both the number of granulomas and the amount of infected organs were reduced in the DNA vaccinated fish. Likewise, when infecting with a lethal infection dose (∼20,000-27,000 bacteria), vaccination significantly reduced both mortality and bacterial counts in a manner dependent on the adaptive immune response. Protective effects of vaccination were associated with enhanced expression of interferon gamma. Our results indicate that the zebrafish is a promising new model for preclinical tuberculosis vaccine research.

Mycobacterium marinum causes a latent infection that can be reactivated by gamma irradiation in adult zebrafish.

The mechanisms leading to latency and reactivation of human tuberculosis are still unclear, mainly due to the lack of standardized animal models for latent mycobacterial infection. In this longitudinal study of the progression of a mycobacterial disease in adult zebrafish, we show that an experimental intraperitoneal infection with a low dose (≈ 35 bacteria) of Mycobacterium marinum, results in the development of a latent disease in most individuals. The infection is characterized by limited mortality (25%), stable bacterial loads 4 weeks following infection and constant numbers of highly organized granulomas in few target organs. The majority of bacteria are dormant during a latent mycobacterial infection in zebrafish, and can be activated by resuscitation promoting factor ex vivo. In 5-10% of tuberculosis cases in humans, the disease is reactivated usually as a consequence of immune suppression. In our model, we are able to show that reactivation can be efficiently induced in infected zebrafish by γ-irradiation that transiently depletes granulo/monocyte and lymphocyte pools, as determined by flow cytometry. This immunosuppression causes reactivation of the dormant mycobacterial population and a rapid outgrowth of bacteria, leading to 88% mortality in four weeks. In this study, the adult zebrafish presents itself as a unique non-mammalian vertebrate model for studying the development of latency, regulation of mycobacterial dormancy, as well as reactivation of latent or subclinical tuberculosis. The possibilities for screening for host and pathogen factors affecting the disease progression, and identifying novel therapeutic agents and vaccine targets make this established model especially attractive.