Hiroshi Saitoh

High Heat Flux Cooling by Microbubble Emission Boiling

Abstract: In subcooled flow boiling of water in a horizontal rectangular channel, microbubble emission boiling occurred at higher subcooling of liquid in transition boiling, and the heat flux increased more than the critical heat flux. The maximum heat flux reached 10 MW/m2 for a channel with 12 mm × 14mm cross‐section at 40K liquid subcooling and 0.5 m/sec liquid velocity. For smaller rectangular channels with 14 mm × 5mm, 14mm × 3mm, and 14mm × 1mm cross‐sections, the maximum heat flux was 7 MW/m2—more than 20 times the cooling limit of a present day CPU. Microbubble emission boiling is expected to realize high heat flux cooling for electronic devices. In convection boiling with subcooled water jet, the same boiling regime and heat flux were obtained for a downward heating surface and an upward heating surface. In subcooled flow boiling with strong convection, the hydrodynamic force is predominant for vapor‐liquid exchange. Accordingly, microbubble emission boiling is expected for high heat flux cooling or high heat flux heat transfer in microgravity.

Synthesis of C-2 substituted vitamin D derivatives having ringed side chains and their biological evaluation, especially biological effect on bone by modification at the C-2 position

In order to obtain vitamin D derivatives, which have strong activity for enhancing bone growth, we designed vitamin D derivatives with various substitutions at the C-2 position. Novel 2 α-substituted vitamin D derivatives were synthesized starting from d-glucose as a chiral template of the A-ring with a CD-ring bromoolefin unit using the Trost coupling method. We evaluated these compounds by two in vitro assays, affinity to VDR and transactivation assays, using human osteosarcoma (Hos) cells, and demonstrated the SAR of the C-2 position of VD(3). Furthermore, by using the OVX model, we found that compound 5c, which has a hydroxypropoxy side chain at C-2 and 2,2-dimethyl cyclopentanone in the CD-ring side chain, has a strong activity for enhancing bone growth, same as the reported compound, 2α-(3-hydroxypropoxy)-1α,25-dihydroxyvitamin D(3)1d, and this derivative shows a possibility that calcemic activity is less than 1d in vivo.

Vitamin D derivatives inhibit hepatitis C virus production through the suppression of apolipoprotein

ABSTRACT Supplementation with vitamin D (VD) has been reported to improve the efficacy of interferon‐based therapy for chronic hepatitis C. We found that 25‐hydroxyvitamin D3 (25‐(OH)D3), one of the metabolites of VD, has antiviral effects by inhibiting the infectious virus production of the hepatitis C virus (HCV). In this study, to clarify the underlying mechanisms of the anti‐HCV effects, we searched VD derivatives that have anti‐HCV effects and identified the common target molecule in the HCV life cycle by using an HCV cell culture system. After infection of Huh‐7.5.1 cells with cell culture‐generated HCV, VD derivatives were added to culture media, and the propagation of HCV was assessed by measuring the HCV core antigen levels in culture media and cell lysates. To determine the step in the HCV life cycle affected by these compounds, the single‐cycle virus production assay was used with a CD81‐negative cell line. Of the 14 structural derivatives of VD, an anti‐HCV effect was detected in 9 compounds. Cell viability was not affected by these effective compounds. The 2 representative VD derivatives inhibited the infectious virus production in the single‐cycle virus production assay. Treatment with these compounds and 25‐(OH)D3 suppressed the expression of apolipoprotein A1 and C3, which are known to be involved in infectious virus production of HCV, and the knockdown of these apolipoproteins reduced infectious virus production. In conclusion, we identified several compounds with anti‐HCV activity by screening VD derivatives. These compounds reduce the infectious virus production of HCV by suppressing the expression of apolipoproteins in host cells. HighlightsWe identified VD derivatives with anti‐HCV activity by a screening of structural derivatives of 1&agr;,25‐dihydroxy VD3.The anti‐HCV effect of VD derivatives is not associated with the binding affinity to VDR and the signaling activation.The VD derivatives reduce the infectious virus production of HCV by suppressing the expression of apolipoproteins.