Inhibitory effects of cyclosporin A on rat insulinoma cell proliferation, polyamine content and insulin secretion

Leptin receptor gene polymorphisms in kidney transplant patients with post-transplant diabetes mellitus treated with tacrolimus

Post-transplant diabetes mellitus (PTDM) is a metabolic complication that often occurs after kidney transplantation. Factors that increase the risk of this complication are currently being researched, including polymorphisms in genes affecting carbohydrate-lipid metabolism. Leptin is a hormone that affects appetite and adipose tissue and plays an important role in regulating insulin secretion as well as glucose and lipid metabolism. The aim of this study was to examine the association between leptin receptor gene polymorphisms and the development of post-transplant diabetes mellitus in patients treated with tacrolimus. The study was carried out in a group of 201 patients who underwent kidney transplantation. The follow-up period was 12 months. PTDM was diagnosed in 35 patients. Analysing the LEPR gene rs1137101 polymorphism, we observed in patients with PTDM an increased frequency of GG genotype carriers (GG vs AA, OR 3.36; 95 % CI 0.99-11.46; p = 0.04). There were no statistically significant differences in the distribution of the LEPR rs1137100 and LEPR rs1805094 polymorphisms between patients with and without PTDM. Multivariate regression analysis confirmed that female sex, advanced age, increased BMI and a higher number of LEPR rs1137101 G alleles were independent risk factors for PTDM development. The risk of PTDM development was almost 3.5 times greater in LEPR rs1137101 G allele carriers than in AA homozygotes (GG + AG vs AA; OR 3.48; 95 %CI (1.09-11.18), p = 0.035). The results suggest that patients after kidney transplantation with the LEPR gene rs1137101 G allele may have an increased risk of post-transplant diabetes development.

New-onset diabetes mellitus after pediatric liver transplantation

In the first five yr after liver transplant, approximately one in 10 pediatric recipients will develop NODAT. Factors associated with higher risk for NODAT have been difficult to identify due to lack of uniformity in reporting and data collection. Limited studies have reported higher risk in those who are at an older age at transplant, those with high-risk ethnic backgrounds, and in those with particular underlying conditions, such as CF and primary sclerosing cholangitis. Immunosuppressive medications, including tacrolimus, cyclosporine A, GC, and sirolimus, have been implicated as contributing to NODAT, to varying degrees. Identifying those at highest risk, appropriately screening, and diagnosing NODAT is critical to initiating timely treatment and avoiding potential complications. In the pediatric population, treatment is limited primarily to insulin, with some consideration for metformin. Children with NODAT should be monitored carefully for complications of DM, including microalbuminuria, hypertension, hyperlipidemia, and retinopathy.

Adiponectin and leptin gene polymorphisms in patients with post-transplant diabetes mellitus

Background: Post-transplant diabetes mellitus (PTDM) is a common metabolic complication after organ transplantation and may be associated with the use of calcineurin inhibitors (tacrolimus and cyclosporine). Leptin and adiponectin are adipokines and play an important role in the regulation of insulin secretion as well as glucose and lipid metabolism. Aim: The aim of this study was to examine the association between adiponectin and leptin gene polymorphisms and development of PTDM. Materials & methods: The study included 323 patients who received kidney transplants and were treated with calcineurin inhibitors (tacrolimus or cyclosporine). Results: The association between adiponectin and leptin gene polymorphisms and PTDM was studied in three models of Cox regression analysis – additive, dominant and recessive. In these three models, the LEP rs2167270 gene polymorphism was statistically significantly associated with increased risk of PTDM. The association between the LEP rs2167270 polymorphism and PTDM was confirmed by multivariate regression analysis. Conclusion: The results of our study suggest an association between the leptin rs2167270 gene A allele and PTDM.

Original submitted 27 February 2015; Revision submitted 22 May 2015

Protein phosphatases in pancreatic islets

The prevalence of diabetes is increasing rapidly worldwide. A cardinal feature of most forms of diabetes is the lack of insulin-producing capability, due to the loss of insulin-producing β-cells, impaired glucose-sensitive insulin secretion from the β-cell, or a combination thereof, the reasons for which largely remain elusive. Reversible phosphorylation is an important and versatile mechanism for regulating the biological activity of many intracellular proteins, which, in turn, controls a variety of cellular functions. For instance, significant changes in protein kinase activities and in protein phosphorylation patterns occur subsequent to the stimulation of insulin release by glucose. Therefore, the molecular mechanisms regulating the phosphorylation of proteins involved in the insulin secretory process by the β-cell have been extensively investigated. However, far less is known about the role and regulation of protein dephosphorylation by various protein phosphatases. Herein, we review extant data implicating serine/threonine and tyrosine phosphatases in various aspects of healthy and diabetic islet biology, ranging from control of hormonal stimulus-secretion coupling to mitogenesis and apoptosis.

The importance of different immunosuppressive regimens in the development of posttransplant diabetes mellitus

Solid-organ transplantation is the optimal long-term treatment for most patients with end-stage organ failure. After solid-organ transplantation, short-term graft survival significantly improved (1). However, due to chronic allograft nephropathy and death with functioning graft, long-term survival has not prolonged remarkably (2). Posttransplant immunosuppressive medications consist of one of the calcineurin inhibitors in combination with mycophenolate mofetil (MMF) or azathioprine (Aza) and steroids. All of them have different adverse effects, among which posttransplant diabetes mellitus (PTDM) is an independent risk factor for cardiovascular (CV) events and infections causing the death of many transplant patients and it may directly contribute to graft failure (3). According to the criteria of the American Diabetes Association (4), diabetes mellitus (DM) is defined by symptoms of diabetes (polyuria and polydipsia and weight loss) plus casual plasma glucose concentration ≥ 11.1 mmol/L or fasting plasma glucose (FPG) ≥ 7.0 mmol/L or 2-h plasma glucose level ≥ 11.1 mmol/L following oral glucose tolerance test (OGTT). This metabolic disorder occurring as a complication of organ transplantation has been recognized for many years. PTDM, which is a combination of decreased insulin secretion and increased insulin resistance, develops in 4.9/15.9% of liver transplant patients, in 4.7/11.5% of kidney recipients, and in 15/17.5% of heart and lung transplants [cyclosporine A (CyA)/tacrolimus (Tac)-based regimen, respectively] (5). Risk factors of PTDM can be divided into non-modifiable and modifiable ones (6), among which the most prominent is the immunosuppressive therapy being responsible for 74% of PTDM development (7). Emphasizing the importance of the PTDM, numerous studies have determined the long-term outcome. On the basis of these studies, graft and patient survival is tendentiously (8) or significantly (9, 10) decreased for those developing PTDM.

Targeted protein kinase A and PP-2B regulate insulin secretion through reversible phosphorylation

Protein kinases and phosphatases play key roles in integrating signals from various insulin secretagogues. In this study, we show that the activities of the cAMP-dependent protein kinase (PKA) and the calcium/calmodulin-dependent phosphatase, PP-2B are coordinated resulting in the regulation of insulin secretion. Transient inhibition of PP-2B, using the immunosuppressant FK506, increased forskolin stimulated insulin secretion by 2.5-fold +/- 0.3 (n = 6) in rat islets and RINm5F cells. Surprisingly, forskolin treatment resulted in the dephosphorylation of the vesicle-associated protein synapsin 1 and increased PP-2B activity by 2.98 +/- 0.97-fold (n = 4). One potential explanation for the observed coordination of PKA and PP-2B activity is their colocalization through a mutual anchoring protein, AKAP79/150. Accordingly, RINm5F cells expressing AKAP79 exhibited decreased insulin secretion, reduced PP-2B activity and were insensitive to FK506. This suggests that AKAP targeting of PKA and PP-2B maintains a signal transduction complex that may regulate reversible phosphorylation events involved in insulin secretion.

Cyclosporin A, but not FK506, increases arachidonic acid release and inhibits proliferation of pituitary corticotrope tumor cells

The selective immunosuppressants cyclosporin A (CsA) and tacrolimus (FK506) are used in the prevention of allogenic transplant rejection and in the therapy of chronic autoimmune inflammatory pathologies. Chronic treatment with CsA leads to secondary functional and trophic alterations of multiple organs and cell systems among which endocrine ones, through insofar uncharacterized mechanisms. With the recent use of FK506 there have been reports of an improved therapeutic efficacy and a reduction of side-effects, as compared to CsA. An intriguing hypothesis is that toxic damage could be due to a systemic CsA activation of arachidonic acid (AA) metabolism, through pathways as yet only partially characterized. The side-effects of both drugs have been poorly studied on cells from tissues other than blood or kidney. We have thus proceeded to study their action on AA release in corticotropic AtT-20/D16-16 cells. The results obtained are as follows: 1) during incubation times > or =12 h, basal AA release is increased by CsA, but not FK506; the acute effect (10 min) of melittin, a PLA2 activator, is significantly potentiated starting from a 30 min pretreatment with CsA but not FK506; manoalide, a PLA2 inhibitor, antagonizes the melittin potentiation of AA release by CsA whereas the inhibition of the melittin stimulus by glucocorticoids is antagonized both by CsA and FK506. 2) during longer (>2 d) incubation times, cell growth is inhibited by CsA but not FK506. These results indicate a role for CsA, not apparent for FK506, in the activation of PLA2 and in the inhibition of cell growth. They also suggest that CsA does not have a direct (i.e. not mediated by the immune system) therapeutic effect in inflammatory processes.