[Necessity of Serum Calcium Concentration Measurement for Investigating Hypocalcemia Induced by Denosumab].

Denosumab is widely used for treating bone metastases in patients with advanced cancer. However, hypocalcemia has been reported as a serious adverse effect during this treatment. Therefore, monitoring serum calcium concentration is essential. During long-term continuous administration ofdenosumab, the burden ofeach blood sampling occasion and medical economics should be clarified; however, the appropriate blood sampling frequency has not yet been confirmed. In the present study, we performed a retrospective investigation of serum calcium concentration after denosumab administration. The results indicated that serum calcium concentration tended to increase with repeated administration. A significant increase was observed at the time ofthe third and sixth administration. This suggested that it was possible to reduce the frequency ofblood sampling during long-term administration ofdenosumab with appropriate calcium supplementation.

Roles of inner blood-retinal barrier organic anion transporter 3 in the vitreous/retina-to-blood efflux transport of p-aminohippuric acid, benzylpenicillin, and 6-mercaptopurine.

The purpose of the present study was to characterize rat organic anion transporter (Oat) 3 (Oat3, Slc22a8) in the efflux transport at the inner blood-retinal barrier (BRB). Reverse transcription-polymerase chain reaction analysis showed that rat (r) Oat3 mRNA is expressed in retinal vascular endothelial cells (RVECs), but not rOat1 and rOat2 mRNA. The expression of Oat3 in the retina and human cultured retinal endothelial cells was further confirmed by Western blot analysis. Immunohistochemical staining in RVECs showed that rOat3 is colocalized with glucose transporter 1, but not P-glycoprotein, suggesting that rOat3 is possibly located at the abluminal membrane of the RVEC. The contribution of rOat3 to the efflux of [(3)H]p-aminohippuric acid ([(3)H]PAH), [(3)H]benzylpenicillin ([(3)H]PCG), and [(14)C]6-mercaptopurine ([(14)C]6-MP), substrates of rOat3, from the vitreous humor/retina to the circulating blood across the inner BRB was evaluated using the microdialysis method. [(3)H]PAH, [(3)H]PCG, [(14)C]6-MP, and [(14)C] or [(3)H]d-mannitol, a bulk flow marker, were biexponentially eliminated from the vitreous humor after vitreous bolus injection. The elimination rate constant of [(3)H]PAH, [(3)H]PCG, and [(14)C]6-MP during the terminal phase was approximately 2-fold greater than that of d-mannitol. This efflux transport was reduced in the retinal presence of probenecid, PAH, and PCG, whereas it was not inhibited by digoxin. In conclusion, rOat3 is expressed at the inner BRB and involved in the vitreous humor/retina-to-blood transport of PAH, PCG, and 6-MP. This transport system is one mechanism to limit the retinal distribution of PAH, PCG, and 6-MP.