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Riboflavin (RF) is essential for the normal metabolic activities of pancreatic β-cells and provides protection against oxidative stress. Very little is known about the mechanism of RF uptake by these cells and how the process is regulated. We addressed these issues using mouse-derived pancreatic β-TC-6 cells and freshly isolated primary mouse and human pancreatic islets. Our results showed3H-RF uptake by β-TC-6 cells is Na+independent, cis inhibited by RF-related compounds, trans stimulated by unlabeled RF, and saturable as a function of concentration (apparent Kmof 0.17 ± 0.02 μM). The latter findings suggest involvement of a carrier-mediated process. Similarly, RF uptake by primary mouse and human pancreatic islets was via carrier-mediated process. RF transporters 1, 2, and 3 (RFVT-1, -3, and -2) were all expressed in mouse and human pancreatic β-cells/islets, with RFVT-1 being the predominant transporter expressed in the mouse and RFVT-3 in the human. Specific knockdown of RFVT-1 with gene-specific small interfering RNA leads to a significant inhibition in RF uptake by β-TC-6 cells. RF uptake by β-TC-6 cells was also found to be adaptively upregulated in RF deficiency via a transcriptional mechanism(s). Also, the process appears to be under the regulation of a Ca2+/calmodulin-mediated regulatory pathway. Results of these studies demonstrate, for the first time, the involvement of a carrier-mediated process for RF uptake by mouse and human pancreatic β-cells/islets. Furthermore, the process appears to be regulated by extracellular and intracellular factors.

The case of concomitant occurrence of schwannoma of the ethmoid sinus and meningothelial hyperplasia in female patient without neurofibromatosis-2 is presented. The components of Schwannoma tissue and meningothelial hyperplasia cells islets were confirmed by histopathological and immunohistochemical examinations. Transitional zones of these two different tissues macroscopically as well as microscopically were not observed. Histological and immunohistochemical findings and possible pathogenesis of this uncommon tumor combination is discussed.

Adult granulosa cell tumors were initially assessed by MR imaging in two women, age 31 and 34 years; radiologic–pathological correlation was performed thereafter. These sex-cord stromal tumors consist of a solid multinodular non-necrotic mass with fibrous septas and external wall surrounding granulosa cells islets, in which few small central and peripheral cysts are present. Some cysts are hemorrhagic, and parenchymal vasculature is poor. MR imaging is effective in our experience to assess this type of tumor prior to histological confirmation.