Inhibition of the mTOR pathway: A new mechanism of β cell toxicity induced by tacrolimus

Gut microbiota and metabolomic profile changes play critical roles in tacrolimus-induced diabetes in rats

Aims

Hyperglycemia is one of the adverse effects of tacrolimus (TAC), but the underlying mechanism is not fully identified. We used multi-omics analysis to evaluate the changes in the gut microbiota and metabolic profile of rats with TAC-induced diabetes.

Methods

To establish a diabetic animal model, Sprague Dawley rats were divided randomly into two groups. Those in the TAC group received intraperitoneal injections of TAC (3 mg/kg) for 8 weeks, and those in the CON group served as the control. 16S rRNA sequencing was used to analyze fecal microbiota. The metabolites of the two groups were detected and analyzed by nontargeted and targeted metabolomics, including amino acids (AAs), bile acids (BAs), and short-chain fatty acids (SCFAs).

Results

The rats treated with TAC exhibited hyperglycemia as well as changes in the gut microbiota and metabolites. Specifically, their gut microbiota had significantly higher abundances of Escherichia-Shigella, Enterococcus, and Allobaculum, and significantly lower abundances of Ruminococcus, Akkermansia, and Roseburia. In addition, they had significantly reduced serum levels of AAs including asparagine, aspartic acid, glutamic acid, and methionine. With respect to BAs, they had significantly higher serum levels of taurocholic acid (TCA), and glycochenodeoxycholic acid (GCDCA), but significantly lower levels of taurodeoxycholic acid (TDCA) and tauroursodeoxycholic acid (TUDCA). There were no differences in the levels of SCFAs between the two groups. Correlations existed among glucose metabolism indexes (fasting blood glucose and fasting insulin), gut microbiota (Ruminococcus and Akkermansia), and metabolites (glutamic acid, hydroxyproline, GCDCA, TDCA, and TUDCA).

Conclusions

Both AAs and BAs may play crucial roles as signaling molecules in the regulation of TAC-induced diabetes.

An update review of post-transplant diabetes mellitus: Concept, risk factors, clinical implications and management

OBJECTIVE

Kidney transplantation is the gold standard therapeutic alternative for patients with end-stage renal disease; nevertheless, it is not without potential complications leading to considerable morbidity and mortality such as post-transplant diabetes mellitus (PTDM). This narrative review aims to comprehensively evaluate PTDM in terms of its diagnostic approach, underlying pathophysiological pathways, epidemiological data, and management strategies.

METHODS

Articles were retrieved from electronic databases using predefined search terms. Inclusion criteria encompassed studies investigating PTDM diagnosis, pathophysiology, epidemiology, and management strategies.

RESULTS

PTDM emerges as a significant complication following kidney transplantation, influenced by various pathophysiological factors including peripheral insulin resistance, immunosuppressive medications, infections, and proinflammatory pathways. Despite discrepancies in prevalence estimates, PTDM poses substantial challenges to transplant. Diagnostic approaches, including traditional criteria such as fasting plasma glucose (FPG) and HbA1c, are limited in their ability to capture early PTDM manifestations. Oral glucose tolerance test (OGTT) emerges as a valuable tool, particularly in the early post-transplant period. Management strategies for PTDM remain unclear, within sufficient evidence from large-scale randomized clinical trials to guide optimal interventions. Nevertheless, glucose-lowering agents and life style modifications constitute primary modalities for managing hyperglycemia in transplant recipients.

DISCUSSION

The complex interplay between PTDM and the transplant process necessitates individualized diagnostic and management approaches. While early recognition and intervention are paramount, modifications to maintenance immunosuppressive regimens based solely on PTDM risk are not warranted, given the potential adverse consequences such as increased rejection risk. Further research is essential to refine management strategies and enhance outcomes for transplant recipients.

Pharmacodynamic Effect of mTOR Inhibition-based Immunosuppressive Therapy on T- and B-cell Subsets After Renal Transplantation

Background

The mammalian target of rapamycin inhibitor (mTORi) therapy after kidney transplantation is solely monitored pharmacokinetically, not necessarily reflecting PI3K-Akt-mTOR pathway blockade efficacy leading to potential under-or overimmunosuppression.

Methods

In this cross-sectional study, phosphoflow cytometry was used to determine the efficacy of mTOR inhibition in peripheral T- and B-lymphocyte subsets by assessing p70S6 kinase (p70S6K) phosphorylation in renal transplant recipients upon treatment with a combination of either mTORi and calcineurin inhibitors (n = 18), or mTORi with mycophenolic acid (n = 9). Nine dialysis patients with end-stage renal disease and 17 healthy age-matched volunteers served as controls.

Results

mTORi treatment reduced p70S6K phosphorylation in CD4+, CD8+ T, and CD19+ B cells compared with healthy controls (HCs). Subpopulation analysis of CD4+ T cells and CD19+ B cells revealed a significant reduction of p70S6K phosphorylation in CD4+CD45RA-CD25- Th cells (P < 0.05), CD24hiCD38hi transitional B cells (P < 0.001), CD24+CD38- memory B cells (P < 0.001), and CD24intCD38int-naive B cells (P < 0.05) upon mTORi treatment, whereas CD4+CD45RA-CD25++CD127- regulatory T cells and CD24-CD38hi plasmablasts were not affected. Compared with mTORi + mycophenolic acid therapy, mTORi + calcineurin inhibitor treatment exhibited an even stronger inhibition of p70S6K phosphorylation in CD4+CD45RA-CD25- Th cells and CD8+ T cells. However, trough levels of mTORi did not correlate with p70S6K phosphorylation.

Conclusions

mTORi selectively inhibited p70S6K phosphorylation in select lymphocyte subtypes. Assessing p70S6K phosphorylation by phosphoflow cytometry may serve as an approach to understand cell subset specific effects of mTORi providing detailed pharmacodynamic information for individualizing immunosuppression.

Tumorigenic role of tacrolimus through mTORC1/C2 activation in post-transplant renal cell carcinomas

BACKGROUND

Kidney transplant recipients (KTRs) face an increased risk of renal cell carcinoma (RCC), in which the immunosuppressive regimen plays an important role. This study aimed to identify intracellular signalling alterations associated with post-transplant (post-tx) tumour formation.

METHODS

Expression of mTOR-related proteins were analysed in kidneys obtained from end-stage renal disease (ESRD) patients and RCCs developed in KTRs or non-transplant patients. The effects of tacrolimus (TAC) and rapamycin (RAPA) on mTOR activity, proliferation, and tumour growth were investigated through different in vitro and in vivo experiments.

RESULTS

Elevated mTORC1/C2 activity was observed in post-tx RCCs and in kidneys of TAC-treated ESRD patients. In vitro experiments demonstrated that TAC increases mTOR activity in a normal tubular epithelial cell line and in the investigated RCC cell lines, moreover, promotes the proliferation of some RCC cell line. In vivo, TAC elevated mTORC1/C2 activity in ischaemic kidneys of mice and enhanced tumour growth in xenograft model.

CONCLUSIONS

We observed significantly increased mTOR activity in ischaemic kidneys and post-tx RCCs, which highlights involvement of mTOR pathway both in the healing or fibrotic processes of kidney and in tumorigenesis. TAC-treatment further augmented the already elevated mTOR activity of injured kidney, potentially contributing to tumorigenesis during immunosuppression.

International consensus on post-transplantation diabetes mellitus

Post-transplantation diabetes mellitus (PTDM) remains a leading complication after solid organ transplantation. Previous international PTDM consensus meetings in 2003 and 2013 provided standardized frameworks to reduce heterogeneity in diagnosis, risk stratification and management. However, the last decade has seen significant advancements in our PTDM knowledge complemented by rapidly changing treatment algorithms for management of diabetes in the general population. In view of these developments, and to ensure reduced variation in clinical practice, a 3rd international PTDM Consensus Meeting was planned and held from 6-8 May 2022 in Vienna, Austria involving global delegates with PTDM expertise to update the previous reports. This update includes opinion statements concerning optimal diagnostic tools, recognition of prediabetes (impaired fasting glucose and/or impaired glucose tolerance), new mechanistic insights, immunosuppression modification, evidence-based strategies to prevent PTDM, treatment hierarchy for incorporating novel glucose-lowering agents and suggestions for the future direction of PTDM research to address unmet needs. Due to the paucity of good quality evidence, consensus meeting participants agreed that making GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) recommendations would be flawed. Although kidney-allograft centric, we suggest that these opinion statements can be appraised by the transplantation community for implementation across different solid organ transplant cohorts. Acknowledging the paucity of published literature, this report reflects consensus expert opinion. Attaining evidence is desirable to ensure establishment of optimized care for any solid organ transplant recipient at risk of, or who develops, PTDM as we strive to improve long-term outcomes.

Vancomycin relieves tacrolimus-induced hyperglycemia by eliminating gut bacterial beta-glucuronidase enzyme activity

Up to 40% of transplant recipients treated long-term with tacrolimus (TAC) develop post-transplant diabetes mellitus (PTDM). TAC is an important risk factor for PTDM, but is also essential for immunosuppression after transplantation. Long-term TAC treatment alters the gut microbiome, but the mechanisms of TAC-induced gut microbiota in the pathogenesis of PTDM are poorly characterized. Here, we showed that vancomycin, an inhibitor of bacterial beta-glucuronidase (GUS), prevents TAC-induced glucose disorder and insulin resistance in mice. Metagenomics shows that GUS-producing bacteria are predominant and flourish in the TAC-induced hyperglycemia mouse model, with upregulation of intestinal GUS activity. Targeted metabolomics analysis revealed that in the presence of high GUS activity, the hydrolysis of bile acid (BAs)-glucuronic conjugates is increased and most BAs are overproduced in the serum and liver, which, in turn, activates the ileal farnesoid X receptor (FXR) and suppresses GLP-1 secretion by L-cells. The GUS inhibitor vancomycin significantly eliminated GUS-producing bacteria and inhibited bacterial GUS activity and BAs levels, thereby enhancing L-cell GLP-1 secretion and preventing hyperglycemia. Our results propose a novel clinical strategy for inhibiting the bacterial GUS enzyme to prevent hyperglycemia without requiring withdrawal of TAC treatment. This strategy exerted its effect through the ileal bile acid-FXR-GLP-1 pathway.

Hypoxia within subcutaneously implanted macroencapsulation devices limits the viability and functionality of densely loaded islets

Introduction

Subcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted devices containing densely packed human islets.

Methods

Partial pressure of oxygen (PO2) within implanted empty devices was measured by noninvasive 19F-MRS. A mathematical model was constructed, predicting internal PO2, viability and functionality of densely packed islets as a function of external PO2. Finally, viability was measured by oxygen consumption rate (OCR) in day 7 explants loaded at various islet densities.

Results

In empty devices, PO2 was 12 mmHg or lower, despite successful external vascularization. Devices loaded with human islets implanted for 7 days, then explanted and assessed by OCR confirmed trends proffered by the model but viability was substantially lower than predicted. Co-localization of insulin and caspase-3 immunostaining suggested that apoptosis contributed to loss of beta cells.

Discussion

Measured PO2 within empty devices declined during the first few days post-transplant then modestly increased with neovascularization around the device. Viability of islets is inversely related to islet density within devices.

A Multi-Modal Approach to Islet and Pancreas Transplantation With Calcineurin-Sparing Immunosuppression Maintains Long-Term Insulin Independence in Patients With Type I Diabetes

Long-term success in beta-cell replacement remains limited by the toxic effects of calcineurin inhibitors (CNI) on beta-cells and renal function. We report a multi-modal approach including islet and pancreas-after-islet (PAI) transplant utilizing calcineurin-sparing immunosuppression. Ten consecutive non-uremic patients with Type 1 diabetes underwent islet transplant with immunosuppression based on belatacept (BELA; n = 5) or efalizumab (EFA; n = 5). Following islet failure, patients were considered for repeat islet infusion and/or PAI transplant. 70% of patients (four EFA, three BELA) maintained insulin independence at 10 years post-islet transplant, including four patients receiving a single islet infusion and three patients undergoing PAI transplant. 60% remain insulin independent at mean follow-up of 13.3 ± 1.1 years, including one patient 9 years after discontinuing all immunosuppression for adverse events, suggesting operational tolerance. All patients who underwent repeat islet transplant experienced graft failure. Overall, patients demonstrated preserved renal function, with a mild decrease in GFR from 76.5 ± 23.1 mL/min to 50.2 ± 27.1 mL/min (p = 0.192). Patients undergoing PAI showed the greatest degree of renal impairment following initiation of CNI (56% ± 18.7% decrease in GFR). In our series, repeat islet transplant is ineffective at maintaining long-term insulin independence. PAI results in durable insulin independence but is associated with impaired renal function secondary to CNI dependence.

Kidney transplant in the next decade: Strategies, challenges and vision of the future

Although the results of kidney transplantation (KT) have improved substantially in recent years, a chronic and inexorable loss of grafts mainly due to the death of the patient and chronic dysfunction of the KT, continues to be observed. The objectives, thus, to optimize this situation in the next decade are fundamentally focused on minimizing the rate of kidney graft loss, improving patient survival, increasing the rate of organ procurement and its distribution, promoting research and training in health professionals and the development of scientific registries providing clinical and reliable information that allow us to optimize our clinical practice in the field of KT. With this perspective, this review will deep into: (1) strategies to avoid chronic dysfunction and graft loss in the medium and long term; (2) to prolong patient survival; (3) strategies to increase the donation, maintenance and allocation of organs; (4) promote clinical and basic research and training activity in KT; and (5) the analysis of the results in KT by optimizing and merging scientific registries.

Rapamycin ameliorates brain damage and maintains mitochondrial dynamic balance in diabetic rats subjected to middle cerebral artery occlusion

To investigate the effect of rapamycin on mitochondrial dynamic balance in diabetic rats subjected to cerebral ischemia-reperfusion injury. Male Sprague Dawley (SD) rats (n = 78) were treated with high fat diet combined with streptozotocin injection to construct diabetic model in rats. Transient middle cerebral artery occlusion (MCAO) of 2 hours was induced and the brains were harvested after 1 and 3 days of reperfusion. Rapamycin was injected intraperitoneally for 3 days prior to and immediately after operation, once a day. The neurological function was assessed, infarct volumes were measured and HE staining as well as immunohistochemistry were performed. The protein of hippocampus was extracted and Western blotting were performed to detect the levels of mTOR, mitochondrial dynamin related proteins (DRP1, p-DRP1, OPA1), SIRT3, and Nix/BNIP3L. Diabetic hyperglycemia worsened the neurological function performance (p < 0.01), enlarged infarct size (p < 0.01) and increased ischemic neuronal cell death (p < 0.01). The increased damage was associated with elevations of p-mTOR, p-S6, and p-DRP1; and suppressions of SIRT3 and Nix/BNIP3L. Rapamycin ameliorated diabetes-enhanced ischemic brain damage and reversed the biomarker alterations caused by diabetes. High glucose activated mTOR pathway and caused mitochondrial dynamics toward fission. The protective effect of rapamycin against diabetes-enhanced ischemic brain damage was associated with inhibiting mTOR pathway, redressing mitochondrial dynamic imbalance, and elevating SIRT3 and Nix/BNIP3L expression.

Nutrition Disturbances and Metabolic Complications in Kidney Transplant Recipients: Etiology, Methods of Assessment and Prevention-A Review

Nutrition disturbances occur at all stages of chronic kidney disease and progress with the decrease of the kidney filtration rate. Kidney transplantation (KTx) as the best form of kidney replacement therapy poses various nutritional challenges. Prior to transplantation, recipients often present with mild to advanced nutrition disturbances. A functioning allograft not only relieves uremia, acidosis, and electrolyte disturbances, but also resumes other kidney functions such as erythropoietin production and vitamin D3 metabolism. KTx recipients represent a whole spectrum of undernutrition and obesity. Since following transplantation, patients are relieved of most dietary restrictions and appetite disturbances; they resume old nutrition habits that result in weight gain. The immunosuppressive regimen often predisposes them to dyslipidemia, glucose intolerance, and hypertension. Moreover, most recipients present with chronic kidney graft disease at long-term follow-ups, usually in stages G2-G3T. Therefore, the nutritional status of KTx patients requires careful monitoring. Appropriate dietary and lifestyle habits prevent nutrition disturbances and may improve kidney graft function. Despite many nutritional guidelines and recommendations targeted at chronic kidney disease, there are few targeted at KTx recipients. We aimed to provide a brief review of nutrition disturbances and known nutritional recommendations for kidney transplant recipients based on the current literature and dietary trends.

Prevalence and Risk Factors of Abnormal Glucose Metabolism and New-Onset Diabetes Mellitus after Kidney Transplantation: A Single-Center Retrospective Observational Cohort Study

Background and objectives: New-onset diabetes after transplantation (NODAT) represents a primary cause of morbidity and allograft loss. We assessed prevalence and risk factors for NODAT in a population of Italian kidney transplant (KT) recipients. Methods: Data from 522 KT performed between January 2004 and December 2014 were analyzed. Participants underwent clinical examination; blood and urine laboratory tests were obtained at baseline, one, six, and 12-month of follow-up to detect glucose homeostasis abnormalities and associated metabolic disorders. An oral glucose tolerance test (OGTT) was performed at six months in 303 subjects. Results: Most patients were Caucasian (82.4%) with a mean age of 48 ± 12 years. The prevalence of abnormal glucose metabolism (AGM) and NODAT was 12.6% and 10.7%, respectively. Comparing characteristics of patients with normal glucose metabolism (NGM) to those with NODAT, we found a significant difference in living donation (16.6% vs. 6.1%; p = 0.03) and age at transplant (46 ± 12 vs. 56 ± 9 years; p = 0.0001). Also, we observed that patients developing NODAT had received higher cumulative steroid doses (1-month: 1165 ± 593 mg vs. 904 ± 427 mg; p = 0.002; 6-month:2194 ± 1159 mg vs. 1940 ± 744 mg; p = 0.002). The NODAT group showed inferior allograft function compared to patients with NGM (1-year eGFR: 50.1 ± 16.5 vs. 57 ± 20 mL/min/1.73 m²; p = 0.02). NODAT patients were more likely to exhibit elevated systolic blood pressure and higher total cholesterol and triglyceride levels than controls. Conclusions: The prevalence of NODAT in our cohort was relatively high. Patient age and early post-transplant events such as steroid abuse are associated with NODAT development.

Fast Tacrolimus Metabolism Does Not Promote Post-Transplant Diabetes Mellitus after Kidney Transplantation

Post-transplant diabetes mellitus (PTDM) after kidney transplantation induced by tacrolimus is an important issue. Fast tacrolimus metabolism, which can be estimated by concentration-to-dose (C/D) ratio, is associated with increased nephrotoxicity and unfavorable outcomes after kidney transplantation. Herein, we elucidate whether fast tacrolimus metabolism also increases the risk for PTDM. Data from 596 non-diabetic patients treated with tacrolimus-based immunosuppression at the time of kidney transplantation between 2007 and 2015 were retrospectively analyzed. The median follow-up time after kidney transplantation was 4.7 years (IQR 4.2 years). Our analysis was complemented by experimental modeling of fast and slow tacrolimus metabolism kinetics in cultured insulin-producing pancreatic cells (INS-1 cells). During the follow-up period, 117 (19.6%) patients developed PTDM. Of all patients, 210 (35.2%) were classified as fast metabolizers (C/D ratio < 1.05 ng/mL × 1/mg). Fast tacrolimus metabolizers did not have a higher incidence of PTDM than slow tacrolimus metabolizers (p = 0.496). Consistent with this, insulin secretion and the viability of tacrolimus-treated INS-1 cells exposed to 12 h of tacrolimus concentrations analogous to the serum profiles of fast or slow tacrolimus metabolizers or to continuous exposure did not differ (p = 0.286). In conclusion, fast tacrolimus metabolism is not associated with increased incidence of PTDM after kidney transplantation, either in vitro or in vivo. A short period of incubation of INS-1 cells with tacrolimus using different concentration profiles led to comparable effects on cell viability and insulin secretion in vitro. Consistent with this, in our patient, collective fast Tac metabolizers did not show a higher PTDM incidence compared to slow metabolizers.

Non-Immunologic Causes of Late Death-Censored Kidney Graft Failure: A Personalized Approach

Despite continuous advances in surgical and immunosuppressive protocols, the long-term survival of transplanted kidneys is still far from being satisfactory. Antibody-mediated rejection, recurrent autoimmune diseases, and death with functioning graft are the most frequent causes of late-kidney allograft failure. However, in addition to these complications, a number of other non-immunologic events may impair the function of transplanted kidneys and directly or indirectly lead to their failure. In this narrative review, we will list and discuss the most important nonimmune causes of late death-censored kidney graft failure, including quality of the donated kidney, adherence to prescriptions, drug toxicities, arterial hypertension, dyslipidemia, new onset diabetes mellitus, hyperuricemia, and lifestyle of the renal transplant recipient. For each of these risk factors, we will report the etiopathogenesis and the potential consequences on graft function, keeping in mind that in many cases, two or more risk factors may negatively interact together.

Targeting calcineurin induces cardiomyocyte proliferation in adult mice

The mammalian neonatal heart can regenerate for 1 week after birth, after which, the majority of cardiomyocytes exit the cell cycle. Recent studies demonstrated that calcineurin mediates cell-cycle arrest of postnatal cardiomyocytes, partly through induction of nuclear translocation of the transcription factor Hoxb13 (a cofactor of Meis1). Here we show that inducible cardiomyocyte-specific deletion of calcineurin B1 in adult cardiomyocytes markedly decreases cardiomyocyte size and promotes mitotic entry, resulting in increased total cardiomyocyte number and improved left ventricular (LV) systolic function after myocardial infarction (MI). Similarly, pharmacological inhibition of calcineurin activity using FK506 promotes cardiomyocyte proliferation in vivo and increases cardiomyocyte number; however, FK506 administration after MI in mice failed to improve LV systolic function, possibly due to inhibition of vasculogenesis and blunting of the post-MI inflammatory response. Collectively, our results demonstrate that loss of calcineurin activity in adult cardiomyocytes promotes cell cycle entry; however, the effects of the calcineurin inhibitor FK506 on other cell types preclude a significant improvement of LV systolic function after MI.

Effect of dual inhibition of DPP4 and SGLT2 on tacrolimus-induced diabetes mellitus and nephrotoxicity in a rat model

Sodium/glucose co-transporter-2 inhibitor (SGLT2i) or dipeptidyl peptidase IV inhibitor (DPP4i) is a newer anti-diabetic drug in type II diabetes mellitus (DM), but their use in tacrolimus (TAC)-induced DM is still undetermined. We performed this study to evaluate the effect of these two drugs in TAC-induced DM and nephrotoxicity in ex vivo and in vivo. In the experimental Sprague Dawley rat model of TAC-induced DM and nephrotoxicity, dual inhibition of DPP4 and SGLT2 significantly decreased blood glucose level, HbA1C and increased plasma insulin levels and pancreatic islet size compared with each drug. In the kidney, dual inhibition improved renal function decreased interstitial fibrosis and profibrotic cytokines compared with DPP4i and SGLT2i alone. Increased oxidative stress by TAC was remarkably decreased with DPP4i or SGLT2i in serum, pancreatic and renal tissues and this decrease was much more significant in the combination group. In in vitro study, TAC decreased the cell viability of human kidney-2(HK-2) cells and insulin-secreting beta-cell-derived line(INS-1) cells. SGLT2i protected TAC-induced cell death in HK-2 cells, but not in INS-1 cells. The addition of DPP4i to SGLT2i compensated for a lack of protective effect of SGLT2i on INS-1 cells. This finding provides the rationale for the combined treatment of SGLG2i and DPP4i in TAC-induced DM and nephrotoxicity.

Regenerating islet-derived protein 3 gamma (Reg3g) ameliorates tacrolimus-induced pancreatic β-cell dysfunction in mice by restoring mitochondrial function

BACKGROUND AND PURPOSE

Tacrolimus a first-line medication used after transplantation can induce β-cell dysfunction, causing new-onset diabetes mellitus (NODM). Regenerating islet-derived protein 3 gamma (Reg3g), a member of the pancreatic regenerative gene family, has been reported to improve type 1 diabetes by promoting β-cell regeneration. We aim to investigate the role of Reg3g in reversing tacrolimus-induced β-cell dysfunction and NODM in mice.

EXPERIMENTAL APPROACH

Circulating REG3A (the human homologue of mouse Reg3g) in heart transplantation patients treated with tacrolimus was detected. The glucose-stimulated insulin secretion and mitochondrial functions, including mitochondria membrane potential (MMP), mitochondria calcium, ATP production, oxygen consumption rate and mitochondrial morphology were investigated in β-cells. Additionally, effects of Reg3g on tacrolimus-induced NODM in mice were analysed.

KEY RESULTS

Circulating REG3A level in heart transplantation patients with NODM significantly decreased compared with those without diabetes. Tacrolimus down-regulated Reg3g via inhibiting STAT3-mediated transcription activation. Moreover, Reg3g restored glucose-stimulated insulin secretion suppressed by tacrolimus in β-cells by improving mitochondrial functions, including increased MMP, mitochondria calcium uptake, ATP production, oxygen consumption rate and contributing to an intact mitochondrial morphology. Mechanistically, Reg3g increased accumulation of pSTAT3(Ser727) in mitochondria by activating ERK1/2-STAT3 signalling pathway, leading to restoration of tacrolimus-induced mitochondrial impairment. Reg3g overexpression also effectively mitigated tacrolimus-induced NODM in mice.

CONCLUSION AND IMPLICATIONS

Reg3g can significantly ameliorate tacrolimus-induced β-cell dysfunction by restoring mitochondrial function in a pSTAT3(Ser727)-dependent manner. Our observations identify a novel Reg3g-mediated mechanism that is involved in tacrolimus-induced NODM and establish the novel role of Reg3g in reversing tacrolimus-induced β-cell dysfunction.

Anti-Oxidative Therapy in Islet Cell Transplantation

Islet cell transplantation has become a favorable therapeutic approach in the treatment of Type 1 Diabetes due to the lower surgical risks and potential complications compared to conventional pancreas transplantation. Despite significant improvements in islet cell transplantation outcomes, several limitations hamper long-term graft survival due to tremendous damage and loss of islet cells during the islet cell transplantation process. Oxidative stress has been identified as an omnipresent stressor that negatively affects both the viability and function of isolated islets. Furthermore, it has been established that at baseline, pancreatic β cells exhibit reduced antioxidative capacity, rendering them even more susceptible to oxidative stress during metabolic stress. Thus, identifying antioxidants capable of conferring protection against oxidative stressors present throughout the islet transplantation process is a valuable approach to improving the overall outcomes of islet cell transplantation. In this review we discuss the potential application of antioxidative therapy during each step of islet cell transplantation.

Role of the Transcription Factor MAFA in the Maintenance of Pancreatic β-Cells

Pancreatic β-cells are specialized to properly regulate blood glucose. Maintenance of the mature β-cell phenotype is critical for glucose metabolism, and β-cell failure results in diabetes mellitus. Recent studies provide strong evidence that the mature phenotype of β-cells is maintained by several transcription factors. These factors are also required for β-cell differentiation from endocrine precursors or maturation from immature β-cells during pancreatic development. Because the reduction or loss of these factors leads to β-cell failure and diabetes, inducing the upregulation or inhibiting downregulation of these transcription factors would be beneficial for studies in both diabetes and stem cell biology. Here, we discuss one such factor, i.e., the transcription factor MAFA. MAFA is a basic leucine zipper family transcription factor that can activate the expression of insulin in β-cells with PDX1 and NEUROD1. MAFA is indeed indispensable for the maintenance of not only insulin expression but also function of adult β-cells. With loss of MAFA in type 2 diabetes, β-cells cannot maintain their mature phenotype and are dedifferentiated. In this review, we first briefly summarize the functional roles of MAFA in β-cells and then mainly focus on the molecular mechanism of cell fate conversion regulated by MAFA.

Beta-Cell Dysfunction Induced by Tacrolimus: A Way to Explain Type 2 Diabetes?

The combination of insulin resistance and β-cells dysfunction leads to the onset of type-2 diabetes mellitus (T2DM). This process can last for decades, as β-cells are able to compensate the demand for insulin and maintain normoglycemia. Understanding the adaptive capacity of β-cells during this process and the causes of its failure is essential to the limit onset of diabetes. Post-transplant diabetes mellitus (PTDM) is a common and serious disease that affects 30% of renal transplant recipients. With the exception of immunosuppressive therapy, the risk factors for T2D are the same as for PTDM: obesity, dyslipidaemia, insulin resistance and metabolic syndrome. Tacrolimus (TAC) is the immunosuppressant of choice after renal transplantation but it has the highest rates of PTDM. Our group has shown that insulin resistance and glucolipotoxicity, without favouring the appearance of apoptosis, modify key nuclear factors for the maintenance of identity and functionality of β-cells. In this context, TAC accelerates or enhances these changes. Our hypothesis is that the pathways that are affected in the progression from pre-diabetes to diabetes in the general population are the same pathways that are affected by TAC. So, TAC can be considered a tool to study the pathogenesis of T2DM. Here, we review the common pathways of β-cells dysfunction on T2DM and TAC-induced diabetes.

An Analysis of the Risk Factors for New-Onset Diabetes Mellitus After Liver Transplantation

Objective

To investigate the risk factors related to new-onset diabetes mellitus (NODM) and the significance of IL-6.

Methods

A retrospective analysis was conducted on clinical data from 64 patients who received either a living donor liver transplantation or a donation after circulatory death from September 2013 to October 2020 and attended regular follow-up visits for six or more months. During follow-up, patients were randomized into groups and followed up until the completion of the study or the death of the patient.

Results

The incidence of NODM was 31.25% (n = 20). The median age in the NODM group was 52.15 years (p < 0.01). Age (OR = 1.089; 95% CI: 0.0211-0.1495, p = 0.003) and elevated preoperative IL-6 (OR = 1.122; 95% CI: 0.0619-0.1677, p = 0.029) were found to be independent risk factors for NODM. HBV-induced liver cirrhosis, warm ischemia time (WIT), body mass index (BMI), and high preoperative fasting blood glucose (FBG) were also found to be risk factors for NODM. The recipient had a higher risk of NODM if the donor had a high BMI and poor hepatic function. The concentrations of IL-6, procalcitonin (PCT), FBG, and tacrolimus (TAC) in the first month postoperatively were significantly higher in the NODM group than in the NO-NODM group. The survival rate of the patients was not affected by NODM.

Conclusion

HBV-induced liver cirrhosis, WIT, BMI, and high preoperative FBG levels are risk factors for NODM, and age and preoperative IL-6 levels are independent risk factors. To a certain extent, higher BMI and poor hepatic function had reference significance for the incidence of NODM. Patients with a high concentration of FBG, IL-6, and TAC in the first month postoperatively had an increased risk of suffering from NODM.

Tacrolimus inhibits insulin release and promotes apoptosis of Min6 cells through the inhibition of the PI3K/Akt/mTOR pathway

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 pathway, which may ultimately lead to the occurrence of diabetes mellitus, and may be considered as one of the specific mechanisms of PTDM caused by tacrolimus.

Glucagon-like peptide-1 receptor agonists and sodium-glucose cotransporter 2 inhibitors for diabetes after solid organ transplantation

Post-transplant diabetes mellitus (PTDM) is a common complication of solid organ transplantation and a major cause of increased morbidity and mortality. Additionally, solid organ transplant patients may have pre-existent type 2 diabetes mellitus (T2DM). While insulin is the treatment of choice for hyperglycemia in the first weeks after transplantation, there is no preferred first line agent for long-term management of PTDM or pre-existent T2DM. Glucagon-like peptide-1 receptor agonists (GLP-1RA) and sodium-glucose cotransporter 2 (SGLT2) inhibitors improve glycemic control, lower body weight, and blood pressure, are recommended after lifestyle and metformin as initial therapy for diabetic patients with cardiovascular or kidney comorbidities regarding their cardiorenal benefits. Furthermore, the mechanisms of action of GLP-1RA may counteract some of the driving forces for PTDM, as calcineurin-induced β cell toxicity as per preclinical data, and improve obesity. However, their use in the treatment of PTDM is currently limited by a paucity of data. Retrospective observational and small exploratory studies suggest that GLP-1RA effectively improve glycemic control and induce weight loss in patients with PTDM without interacting with commonly used immunosuppressive agents, although randomized-controlled clinical trials are required to confirm their safety and efficacy. In this narrative review, we evaluate the risk factors and pathogenesis of PTDM and compare the potential roles of GLP-1RA and SGLT2 inhibitors in PTDM prevention and management as well as in pre-existent T2DM, and providing a roadmap for evidence generation on newer antidiabetic drugs for solid organ transplantation.

Glycol chitosan-based tacrolimus-loaded nanomicelle therapy ameliorates lupus nephritis

Background

Recently, we developed hydrophobically modified glycol chitosan (HGC) nanomicelles loaded with tacrolimus (TAC) (HGC-TAC) for the targeted renal delivery of TAC. Herein, we determined whether the administration of the HGC-TAC nanomicelles decreases kidney injury in a model of lupus nephritis. Lupus-prone female MRL/lpr mice were randomly assigned into three groups that received intravenous administration of either vehicle control, an equivalent dose of TAC, or HGC-TAC (0.5 mg/kg TAC) weekly for 8 weeks. Age-matched MRL/MpJ mice without Fas^lpr mutation were also treated with HGC vehicle and used as healthy controls.

Results

Weekly intravenous treatment with HGC-TAC significantly reduced genetically attributable lupus activity in lupus nephritis-positive mice. In addition, HGC-TAC treatment mitigated renal dysfunction, proteinuria, and histological injury, including glomerular proliferative lesions and tubulointerstitial infiltration. Furthermore, HGC-TAC treatment reduced renal inflammation and inflammatory gene expression and ameliorated increased apoptosis and glomerular fibrosis. Moreover, HGC-TAC administration regulated renal injury via the TGF-β1/MAPK/NF-κB signaling pathway. These renoprotective effects of HGC-TAC treatment were more potent in lupus mice compared to those of TAC treatment alone.

Conclusion

Our study indicates that weekly treatment with the HGC-TAC nanomicelles reduces kidney injury resulting from lupus nephritis by preventing inflammation, fibrosis, and apoptosis. This advantage of a new therapeutic modality using kidney-targeted HGC-TAC nanocarriers may improve drug adherence and provide treatment efficacy in lupus nephritis mice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00857-w.

New-Onset Diabetes after Kidney Transplantation

New-onset diabetes mellitus after transplantation (NODAT) is a frequent complication in kidney allograft recipients. It may be caused by modifiable and non-modifiable factors. The non-modifiable factors are the same that may lead to the development of type 2 diabetes in the general population, whilst the modifiable factors include peri-operative stress, hepatitis C or cytomegalovirus infection, vitamin D deficiency, hypomagnesemia, and immunosuppressive medications such as glucocorticoids, calcineurin inhibitors (tacrolimus more than cyclosporine), and mTOR inhibitors. The most worrying complication of NODAT are major adverse cardiovascular events which represent a leading cause of morbidity and mortality in transplanted patients. However, NODAT may also result in progressive diabetic kidney disease and is frequently associated with microvascular complications, eventually determining blindness or amputation. Preventive measures for NODAT include a careful assessment of glucose tolerance before transplantation, loss of over-weight, lifestyle modification, reduced caloric intake, and physical exercise. Concomitant measures include aggressive control of systemic blood pressure and lipids levels to reduce the risk of cardiovascular events. Hypomagnesemia and low levels of vitamin D should be corrected. Immunosuppressive strategies limiting the use of diabetogenic drugs are encouraged. Many hypoglycemic drugs are available and may be used in combination with metformin in difficult cases. In patients requiring insulin treatment, the dose and type of insulin should be decided on an individual basis as insulin requirements depend on the patient's diet, amount of exercise, and renal function.

Pancreatic islet transplantation: toward definitive treatment for diabetes mellitus

Since the late 20th century, advances in pancreatic islet transplantation have targeted improved glycemic control and fewer hypoglycemic events in patients with type 1 diabetes, and some important milestones have been reached. Following the Edmonton group's success in achieving insulin independence in all transplanted patients with type 1 diabetes, clinical islet transplantation is now performed worldwide. β cell replacement therapy for type 1 diabetes was established based on the favorable outcomes of a phase 3, prospective, open-label, single-arm, clinical study conducted at 8 centers in North America, in which 42 of 48 patients who underwent islet transplantation from 2008 to 2011 achieved HbA1c < 7.0% (53 mmol/mol) at day 365, which was maintained at 2 years in 34 patients. In Japan, a phase 2 multicenter clinical trial of islet transplantation for type 1 diabetes patients is currently ongoing and will end soon, but the interim results have already led to positive changes, with allogeneic islet transplantation being covered by the national health insurance system since April 2020. Current efforts are being made to solve the problem of donor shortage by studying alternative donor sources, such as porcine islets and pancreatic progenitor cells derived from pluripotent stem cells. The results of clinical trials in this area are eagerly awaited. It is hoped that they will contribute to establishing alternative sources for insulin-producing β cells in the near future.

The use of LCP-Tacrolimus (Envarsus XR) in simultaneous pancreas and kidney (SPK) transplant recipients

BACKGROUND

Extended release LCP-tacrolimus (LCPT) allows once-daily dosing in transplant recipients. The improved bioavailability may be beneficial for simultaneous pancreas-kidney recipients (SPK).

METHODS

This is a study of 39 SPK recipients on standard immediate-release tacrolimus (IR-TAC, n = 21) or LCPT (n = 18). Coefficient of variability (CV = 100∗standard deviation/mean) was calculated to assess drug levels. Hemoglobin A1c (HbA1c), tacrolimus and creatinine levels were measured postoperatively.

RESULTS

There was no difference in tacrolimus CV in the IR-TAC and LCPT groups at 1 month or 3 months postoperatively; however, a greater difference was observed at 1 year (41.0 vs. 33.1%; p = 0.19). There were six episodes of acute rejection in the IR-TAC group compared to zero episodes in the LCPT group (p = 0.01). HbA1c was significantly higher in the IR-TAC group compared to LCPT at 3 (5.5 vs. 4.9%, p = 0.01), 6 (5.6 vs. 4.9%, p = 0.01) and 12 months (5.8 vs. 5.1%, p = 0.07).

CONCLUSIONS

Significantly lower rates of rejection were observed in patients receiving LCPT. The once daily dosing may facilitate medication adherence and result in improved long-term outcomes.