Far-infrared radiation prevents decline in ß-cell mass and function in diabetic mice via the mitochondria-mediated Sirtuin1 pathway.

Insulin deficiency in type 2 diabetes mellitus (DM) involves a decline in both pancreatic ß-cell mass and function. Enhancing ß-cell preservation represents an important therapeutic strategy to treat type 2 DM. Far-infrared (FIR) radiation has been found to induce promyelocytic leukemia zinc finger protein (PLZF) activation to protect the vascular endothelium in diabetic mice. The influence of FIR on ß-cell preservation is unknown. Our previous study reveals that the biologically effective wavelength of FIR is 8-10 µm. In the present study, we investigated the biological effects of FIR (8-10 µm) on both survival and insulin secretion function of ß-cells. FIR reduced pancreatic islets loss and increased insulin secretion in nicotinamide-streptozotocin-induced DM mice, but only promoted insulin secretion in DM PLZF-/- mice. FIR-upregulated PLZF to induce an anti-apoptotic effect in a ß cell line RIN-m5f. FIR also upregulated mitochondrial function and the ratio of NAD+/NADH, and then induced Sirtuin1 (Sirt1) expression. The mitochondria Complex I inhibitor rotenone blocked FIR-induced PLZF and Sirt1. The Sirt1 inhibitor EX527 and Sirt1 siRNA inhibited FIR-induced PLZF and insulin respectively. Sirt1 upregulation also increased CaV1.2 expression and calcium influx that promotes insulin secretion in ß-cells. In summary, FIR-enhanced mitochondrial function prevents ß-cell apoptosis and enhances insulin secretion in DM mice through the Sirt1 pathway.

Phenylephrine Alleviates 131I Radiation Damage in Submandibular Gland Through Maintaining Mitochondrial Homeostasis.

PURPOSE: The impairment of the salivary glands is a permanent side effect of 131I ablation therapy for patients with differentiated thyroid cancer. Effective and safe treatments for protecting the salivary glands against 131I are currently not available. Mitochondria are susceptible to ionizing radiation, but alterations after 131I exposure are unknown. Here, we investigated the mechanisms of 131I damage in submandibular glands (SMGs) and evaluated the cytoprotective effect of phenylephrine (PE) against mitochondrial radiation damage. METHODS AND MATERIALS: Rats were randomly divided into 4 groups: control, PE alone, 131I alone, and 131I with PE pretreatment. The mitochondrial structure of SMGs was observed under transmission electron microscopy. Apoptosis was detected using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Cytochrome c, cleaved-caspase 3, SIRT1, NAMPT, and PGC-1α protein levels were determined with Western blot and immunohistochemistry. Levels of mitochondrial membrane potential, nicotinamide adenine dinucleotide (NAD), and adenosine triphosphate (ATP) were measured with relevant kits. RESULTS: After exposing rat SMGs to 131I, the mitochondrial membrane structures were destroyed, the mitochondrial membrane potential decreased, the release of cytochrome c increased, and cleaved-caspase 3 and cell apoptosis were activated. Moreover, the expression of SIRT1, NAMPT, and PGC-1α was downregulated, and the levels of NAD and ATP decreased. In contrast, PE alleviated the 131I-induced mitochondrial damages and upregulated the expression of SIRT1/NAMPT/PGC-1α and the levels of NAD and ATP. CONCLUSIONS: These findings demonstrate that 131I impairs the salivary glands via the downregulation of SIRT1/NAMPT/PGC-1α signal pathways, which disturbs mitochondrial homeostasis. PE alleviated the 131I damage in SMGs at the mitochondrial level, suggesting that PE could be used as a potential radioprotector for patients with differentiated thyroid cancer with radiation sialadenitis.