tacrolimus and Insulinoma

As a calcineurin inhibitor, tacrolimus is commonly used as a first‑line immunosuppressant in organ transplant recipients. Post‑transplantation diabetes mellitus (PTDM) is a common complication following kidney transplantation and is associated with immunosuppressant drugs, such as tacrolimus. PTDM caused by tacrolimus may be related to its influence on insulin secretion and insulin resistance. However, the specific mechanism has not been fully elucidated. The aim of the present study was to investigate whether the PI3K/Akt/mTOR signaling pathway served an important role in the pathogenesis of PTDM induced by tacrolimus. In the present study, the Cell Counting Kit‑8 assay was used to measure the effect of tacrolimus on the viability of Min6 mouse insulinoma cells. The effects of tacrolimus on the insulin secretion and the activity of caspase‑3 of Min6 cells stimulated by glucose exposure were measured by ELISA. Superoxide dismutase (SOD) and malondialdehyde (MDA) levels were measured using WST‑8 and thiobarbituric acid assays, respectively. The effects of tacrolimus on the mRNA expression levels of PI3K, Akt and mTOR were detected by reverse transcription‑quantitative PCR (RT‑qPCR), whereas the protein expression levels of PI3K, Akt, mTOR, phosphorylated (p)‑AKT and p‑mTOR in Min6 cells were assessed using western blotting. The present data indicated that, compared with the control group, 5, 25 and 50 ng/ml tacrolimus treatment could inhibit the insulin secretion of Min6 cells stimulated by glucose solution, and 50 ng/ml tacrolimus could notably decrease the stimulation index (P<0.05). Moreover, 50 ng/ml tacrolimus markedly increased the activity of caspase‑3 by 175.1% (P<0.05), it also decreased the SOD activity (P<0.01) and increased MDA levels (P<0.05). The RT‑qPCR results demonstrated that the mRNA expression levels of PI3K, Akt and mTOR were downregulated by 25 and 50 ng/ml tacrolimus (P<0.01). Furthermore, the western blotting results suggested that tacrolimus had no significant effects on the expression levels of total PI3K, Akt and mTOR proteins (P>0.05), but 25 and 50 ng/ml tacrolimus could significantly inhibit the expression levels of p‑Akt and p‑mTOR (P<0.01). In conclusion, tacrolimus decreased the activity and insulin secretion of pancreatic β cells and induced the apoptosis of islet β cells by inhibiting the mRNA expression levels of PI3K, Akt and mTOR and reducing the phosphorylation of Akt and mTOR proteins in the PI3K/Akt/mTOR signaling p

Topics: Animals; Apoptosis; Caspase 3; Cell Line, Tumor; Diabetes Mellitus; Insulin; Insulin Secretion; Insulinoma; Mice; Oxidative Stress; Phosphatidylinositol 3-Kinases; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Tacrolimus; TOR Serine-Threonine Kinases

Although transforming growth factor-beta (TGF-beta) stimulates pancreatic islet cells to synthesize and secret insulin, the mechanism underlying this effect is not known. To investigate this question, we examined the insulin promoter activity focusing on a transcription factor, pancreatic and duodenal homeobox gene-1 (PDX-1) that binds to the A3 element of the rat insulin promoter. Studies performed using the rat insulinoma cell line, INS-1 showed that TGF-beta stimulation of endogenous insulin mRNA expression correlated with increased activity of a reporter construct containing the insulin promoter. A potential mechanism for this increase arose from, electrophoretic mobility shift assay showing that the nuclear extract from TGF-beta treated cells contained higher levels of A3 binding activity. Western blot analysis confirmed that PDX-1 was increased in the nuclear extract from INS-1 cells treated with TGF-beta. As expected, a mutant insulin promoter that lacked the PDX-1 binding site was not stimulated by TGF-beta. In summary, the results of these studies show that TGF-beta stimulates the transcription of insulin gene and this action is mediated by the transcription factor, PDX-1.

Topics: Animals; DNA; Glucose; Homeodomain Proteins; Immunophilins; Insulin; Insulinoma; Islets of Langerhans; Mutation; Nuclear Proteins; Promoter Regions, Genetic; Protein Binding; Rats; Receptors, Transforming Growth Factor beta; Response Elements; RNA, Messenger; Tacrolimus; Tacrolimus Binding Proteins; Trans-Activators; Transcriptional Activation; Transfection; Transforming Growth Factor beta; Tumor Cells, Cultured

Immunosuppression is currently used for allotransplantation, and is being evaluated for the treatment of insulin-dependent diabetes mellitus and other autoimmune diseases. However, most available agents have a number of side effects that limit their use in clinical situations. It has been shown previously, for example, that cyclosporine may inhibit insulin release from islet tumor cells and rat islets. We have studied the effects of an analog of a newer agent (FK506) termed L-683,590 on insulin secretion by an islet tumor line, beta TC3, and rat islets, and compared the effects of this drug to those of cyclosporine, since both cause similar immunosuppression. L-683,590 and cyclosporine inhibited insulin release by beta TC3 cells by about 50% and 80%, respectively, at doses that inhibit lymphokine production by T cells. The inhibition by L-683,590 and cyclosporine was more pronounced at higher glucose levels, and was not simply attributable to a general toxic effect of the drugs on the cells. Insulin release during long-term (> 48 hr) cultures of isolated rat islets was also inhibited by the drugs. However, there was no effect of either agent on insulin release by islets during the first 4 hr following a glucose stimulus. Both drugs caused reduced levels of insulin mRNA (by 56 +/- 8.1% and 66 +/- 16% in the presence of L-683,590 and cyclosporine, respectively), accounting for reduced rates of insulin biosynthesis that were also seen. Our studies indicate that: (1) both cyclosporine and L-683,590 inhibit insulin release by beta TC3 cells and cultured rat islets after 48 hr (cyclosporine is a more potent inhibitor); (2) neither drug inhibits the release of insulin during the first 4 hr following a glucose stimulus; and (3) their mechanisms of action appear to be similar--both drugs cause reduced levels of insulin mRNA. Although the toxicity of FK506 on human islets in vivo is still unknown, it may be of particular importance in individuals with impaired beta cell function, such as patients with new-onset insulin-dependent diabetes or patients with non-insulin-dependent diabetes mellitus.

Topics: Actins; Animals; Cells, Cultured; Cyclosporine; Dose-Response Relationship, Drug; Glucose; Insulin; Insulin Secretion; Insulinoma; Islets of Langerhans; Mice; Rats; RNA, Messenger; Tacrolimus; Time Factors; Tumor Cells, Cultured