Ablation of calcineurin Aβ reveals hyperlipidemia and signaling cross-talks with phosphodiesterases

Prevention of complications from use of conventional immunosuppressants: a critical review

Synthetic immunosuppressive drugs are largely used in immune-related renal diseases and in kidney transplantation. Most of these drugs have a low therapeutic index (the ratio that compares the blood concentration at which a drug becomes toxic and the concentration at which the drug is effective), which means that the drug should be dosed carefully and the patient monitored frequently. In this review, we consider the categories of synthetic immunosuppressive agents more frequently and conventionally used in clinical nephrology: glucocorticoids, Aalkylating agents (cyclophosphamide, chlorambucil), purine synthesis inhibitors (azathioprine, mycophenolate salts) and calcineurin inhibitors (cyclosporine, tacrolimus). For each category the possible side effects will be reviewed, the general and specific measures to prevent or treat the adverse events will be suggested, and the more common mistakes that may increase the risk of toxicity will be described. However, the efficacy and safety of immunosuppressive agents depend not only on the pharmacologic characteristics of single drugs but can be influenced also by the clinical condition and genetic characteristics of the patient, by the typology and severity of the underlying disease and by the interaction with other concomitantly used drugs.

The Proposal of Molecular Mechanisms of Weak Organic Acids Intake-Induced Improvement of Insulin Resistance in Diabetes Mellitus via Elevation of Interstitial Fluid pH

Blood contains powerful pH-buffering molecules such as hemoglobin (Hb) and albumin, while interstitial fluids have little pH-buffering molecules. Thus, even under metabolic disorder conditions except severe cases, arterial blood pH is kept constant within the normal range (7.35~7.45), but the interstitial fluid pH under metabolic disorder conditions becomes lower than the normal level. Insulin resistance is one of the most important key factors in pathogenesis of diabetes mellitus, nevertheless the molecular mechanism of insulin resistance occurrence is still unclear. Our studies indicate that lowered interstitial fluid pH occurs in diabetes mellitus, causing insulin resistance via reduction of the binding affinity of insulin to its receptor. Therefore, the key point for improvement of insulin resistance occurring in diabetes mellitus is development of methods or techniques elevating the lowered interstitial fluid pH. Intake of weak organic acids is found to improve the insulin resistance by elevating the lowered interstitial fluid pH in diabetes mellitus. One of the molecular mechanisms of the pH elevation is that: (1) the carboxyl group (R-COO⁻) but not H⁺ composing weak organic acids in foods is absorbed into the body, and (2) the absorbed the carboxyl group (R-COO⁻) behaves as a pH buffer material, elevating the interstitial fluid pH. On the other hand, high salt intake has been suggested to cause diabetes mellitus; however, the molecular mechanism is unclear. A possible mechanism of high salt intake-caused diabetes mellitus is proposed from a viewpoint of regulation of the interstitial fluid pH: high salt intake lowers the interstitial fluid pH via high production of H⁺ associated with ATP synthesis required for the Na⁺,K⁺-ATPase to extrude the high leveled intracellular Na⁺ caused by high salt intake. This review article introduces the molecular mechanism causing the lowered interstitial fluid pH and insulin resistance in diabetes mellitus, the improvement of insulin resistance via intake of weak organic acid-containing foods, and a proposal mechanism of high salt intake-caused diabetes mellitus.

Calcineurin Antagonizes AMPK to Regulate Lipolysis in Caenorhabditis elegans

Calcineurin is a calcium- and calmodulin-dependent serine/threonine protein phosphatase, and the target of immunosuppressive agent tacrolimus (TAC). The dysfunction of calcineurin, or clinical applications of tacrolimus, have been reported to be associated with dyslipidemia. The underlying mechanisms of calcineurin and tacrolimus in lipid metabolism are largely unknown. Here, we showed that mutations of tax-6 and cnb-1, which respectively encode the catalytic subunit and the regulatory subunit of calcineurin, together with tacrolimus treatment, consistently led to decreased fat accumulation and delayed growth in the nematode Caenorhabditis elegans. In contrast, disruption of the AMP-activated protein kinase (AMPK) encoded by aak-1 and aak-2 reversed the above effects in worms. Moreover, calcineurin deficiency and tacrolimus treatment consistently activated the transcriptional expression of the lipolytic gene atgl-1, encoding triglyceride lipase. Furthermore, RNAi knockdown of atgl-1 recovered the decreased fat accumulation in both calcineurin deficient and tacrolimus treated worms. Collectively, our results reveal that immunosuppressive agent tacrolimus and their target calcineurin may antagonize AMPK to regulate ATGL and lipolysis, thereby providing potential therapy for the application of immunosuppressive agents.

Inhibition of calcineurin by FK506 stimulates germinal vesicle breakdown of mouse oocytes in hypoxanthine-supplemented medium

Calcineurin (CN) is a serine/threonine phosphatase which plays important roles in meiosis maturation in invertebrate oocytes; however, the role of CN in mouse oocytes is relatively unexplored. In this study, we examined the expression, localization and functional roles of CN in mouse oocytes and granulosa cells. The RT-PCR results showed that the β isoform of calcineurin A subunit (Cn A) expressed significantly higher than α and γ isoforms, and the expression of Cn Aβ mRNA obviously decreased in oocytes in which germinal vesicle breakdown (GVBD) occurred, while only B1 of calcineurin B subunit (Cn B) was detected in oocytes and stably expressed during oocytes maturation. The following fluorescence experiment showed that Cn A was mainly located in the nucleus of germinal vesicle (GV) stage oocytes and gruanlosa cells, and subsequently dispersed into the entire cytoplasm after GVBD. The decline of Cn A in oocytes suggested that it may play an important role in GVBD. To further clarify the role of calcineurin during meiotic maturation, FK506 (a calcineurin inhibitor) was used in the culture medium contained hypoxanthine (HX) which could keep mouse oocytes staying at GV stage. As expected, FK506 could induce a significant elevation of GVBD rate and increase the MPF level of denuded oocytes (DOs). Furthermore, FK506 could also play an induction role of GVBD of oocytes in COCs and follicles, and the process could be counteracted by MAPK kinase inhibitor (U0126). Above all, the results implied that calcineurin might play a crucial role in development of mouse oocytes and MPF and MAPK pathways are involved in this process.

Metabolic consequences of modern immunosuppressive agents in solid organ transplantation

Among other factors, sophistication of immunosuppressive (IS) regimen accounts for the remarkable success attained in the short- and medium-term solid organ transplant (SOT) survival. The use of steroids, mycophenolate mofetil and calcineurin inhibitors (CNI) have led to annual renal graft survival rates exceeding 90% in the last six decades. On the other hand, attrition rates of the allograft beyond the first year have remained unchanged. In addition, there is a persistent high cardiovascular (CV) mortality rate among transplant recipients with functioning grafts. These shortcomings are in part due to the metabolic effects of steroids, CNI and sirolimus (SRL), all of which are implicated in hypertension, new onset diabetes after transplant (NODAT), and dyslipidemia. In a bid to reduce the required amount of harmful maintenance agents, T-cell-depleting antibodies are increasingly used for induction therapy. The downsides to their use are greater incidence of opportunistic viral infections and malignancy. On the other hand, inadequate immunosuppression causes recurrent rejection episodes and therefore early-onset chronic allograft dysfunction. In addition to the adverse metabolic effects of the steroid rescue needed in these settings, the generated proinflammatory milieu may promote accelerated atherosclerotic disorders, thus setting up a vicious cycle. The recent availability of newer agent, belatacept holds a promise in reducing the incidence of metabolic disorders and hopefully its long-term CV consequences. Although therapeutic drug monitoring as applied to CNI may be helpful, pharmacodynamic tools are needed to promote a customized selection of IS agents that offer the most benefit to an individual without jeopardizing the allograft survival.

The effect of adropin on lipid and glucose metabolism in rats with hyperlipidemia

OBJECTIVES

The aim of this study was to evaluate, for the first time, whether the effects of low-dose adropin administration is effective in rats with hyperlipidemia.

MATERIALS AND METHODS

Twenty one Wistar albino female rats were randomly divided into 3 groups and fed with high-fat diet for 4 weeks to establish the hyperlipidemia model. Meanwhile, adropin was administrated intraperitonealy (2.1 μg/kg/day), once a day for continuous 10 days. Then, body weights and serum biochemical parameters, adropin, insulin and blood glucose levels were determined. Additionally, in liver tissue, inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) mRNA gene expressions were evaluated by RT-PCR.

RESULTS

The results showed that intraperitoneal administration of adropin to hyperlipidemic rats for 10 days were extremely effective in decreasing the levels of serum triglycerides (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), aspartate aminotransferase (AST), alkaline phosphatase (ALP), alanine aminotransferase (ALT), and gamma glutamil transferase (GGT) and increasing the levels of high density lipoprotein cholesterol (HDL-C). It could decrease mRNA expressions of pro-inflammatory cytokines TNF-α and IL-6 via regulating the expressions of iNOS. In addition, treatment with adropin showed a significant reduction in blood glucose, serum insulin levels, HbA1c (%), and HOMA-IR, and increase in serum adropin levels.

CONCLUSION

Adropin may ameliorate lipid metabolism, reduce insulin resistance, and inhibit hepatocytes inflammation. Thus, adropin had significant therapeutic benefits and could be suggested as a potential candidate agent against hyperlipidemia.

Calcineurin Links Mitochondrial Elongation with Energy Metabolism

Canonical protein phosphatase 3/calcineurin signaling is central to numerous physiological processes. Here we provide evidence that calcineurin plays a pivotal role in controlling systemic energy and body weight homeostasis. Knockdown of calcineurin in Drosophila melanogaster led to a decrease in body weight and energy stores, and increased energy expenditure. In mice, global deficiency of catalytic subunit Ppp3cb, and tissue-specific ablation of regulatory subunit Ppp3r1 from skeletal muscle, but not adipose tissue or liver, led to protection from high-fat-diet-induced obesity and comorbid sequelæ. Ser637 hyperphosphorylation of dynamin-related protein 1 (Drp1) in skeletal muscle of calcineurin-deficient mice was associated with mitochondrial elongation into power-cable-shaped filaments and increased mitochondrial respiration, but also with attenuated exercise performance. Our data suggest that calcineurin acts as highly conserved pivot for the adaptive metabolic responses to environmental changes such as high-fat, high-sugar diets or exercise.

Red yeast rice repairs kidney damage and reduces inflammatory transcription factors in rat models of hyperlipidemia

Xuezhikang (XZK), an extract of red yeast rice, has been widely used for the management of hyperlipidemia and coronary heart disease (CHD); however, the effects of XZK treatment on kidney injury have not yet been fully identified. The aim of the current study was to evaluate the effects of XZK on the kidneys and investigate the related mechanisms in a rat model of hyperlipidemia. Thus, the effect on inflammatory transcription factors and kidney damage was investigated with in vitro and in vivo experiments on hyperlipidemic rats following XZK treatment. The results revealed that the plasma levels of total cholesterol (TC), triglycerides (TG) and low-density lipoprotein-cholesterol (LDL-C) were significantly decreased, while the levels of high-density lipoprotein-cholesterol (HDL-C) were significantly upregulated in the XZK treatment group, as compared with those in the hyperlipidemia group (P<0.05). In addition, the results demonstrated that XZK was able to repair the kidney damage caused by hyperlipidemia. Furthermore, the expression levels of the inflammatory transcription factors, tumor necrosis factor-α and interleukin-6, were shown to be reduced in the XZK group when compared with the hyperlipidemia group. In summary, XZK reduces kidney injury, downregulates the levels of TG, TC and LDL-C, as well as the expression levels of inflammatory transcription factors, and upregulates HDL-C. These results further the understanding of the molecular pathogenic mechanisms underlying hyperlipidemia and aid the development of XZK as an effective therapeutic agent for hyperlipidemia.

Short and long term in vivo effects of Cyclosporine A and Sirolimus on genes and proteins involved in lipid metabolism in Wistar rats

OBJECTIVE

Cyclosporine A (CsA) and sirolimus (SRL) are immunosuppressive agents (IA) associated with new onset diabetes after transplantation and dyslipidemia. We aim to evaluate the molecular effects of CsA (5mg/kg/day) and SRL (1mg/kg/day) treatment for 3 and 9weeks on lipid metabolism, in Wistar rats.

MATERIALS/METHODS

Lipolysis was evaluated in isolated adipocytes, while triglycerides (TG) and non-esterified fatty acid (NEFA) were measured in serum. Gene and protein expression involved in lipid metabolism was assessed in adipose tissue and liver.

RESULTS

CsA and SRL treatments of rats for 3 and 9weeks increased isoproterenol-stimulated lipolysis by 5-9 fold and 4-6 fold in isolated adipocytes, respectively. While CsA increased adipocyte weight and diameter, as well as NEFA and TG levels in circulation after 9weeks, SRL treatment caused ectopic deposition of TG in the liver after 3weeks. Moreover, ACC1 and FAS protein expression was increased after 3weeks (>100%, p<0.01), while HSL was increased after 9weeks of CsA treatment. On the other hand, SRL decreased the expression of lipogenic genes, including ACC1 (50%, p<0.05), lipin1 (25%, p<0.05), PPAR-γ (42%, p<0.05) and SCD1 (80%, p<0.001) in adipose tissue, after 3weeks of treatment.

CONCLUSION

The effects of both IAs on expression of lipolytic and lipogenic genes suggest that these agents influence lipid metabolism, thus contributing to the dyslipidemia observed during immunosuppressive therapy.

Pathogenesis and management of FK506- and CsA-induced post-transplant diabetes mellitus: Similarities and differences

Tacrolimus (FK506) and cyclosporine (CsA) are clinically commonly used immunosuppressive agents, and both of them belong to calcineurin inhibitors. FK506 is more excellent in anti-rejection therapy. They are similar in pharmacological mechanism, but FK506 is more likely to induce post-transplant diabetes mellitus than CsA. This paper analyzes and compares the similarities and differences in the pathogenesis and management between FK506- and CsA-induced post-transplant diabetes mellitus.

Population PKPD of voclosporin in renal allograft patients

The aims of this population-pharmacokinetic/pharmacodynamic (POP-PKPD) analysis of voclosporin in renal allograft patients were to build a POP-PKPD model for voclosporin and calcineurin activity (CNa) and identify clinically relevant covariates that could assist dosing of the drug. POP-PKPD modeling was performed using a stochastic approximation of the standard expectation maximization (SAEM) algorithm for nonlinear mixed-effects as implemented in Monolix™ 3.2. Voclosporin whole blood concentrations were obtained from de novo renal allograft patients and assayed using a validated LC/MS/MS assay. CNa was measured using a (32)P-radiolabeled assay. A two-compartment model with simultaneous sigmoid inhibitory Emax model was used to describe the PKPD relationship between voclosporin concentration and CNa. The POP-PKPD model was then utilized to simulate an optimal initial dosing strategy. Eighty-seven patients were included in the POP-PKPD study. Population mean estimates (relative standard error, rse) for oral clearance (CL/F) and first compartment volume of distribution (V1), were 717 mL min(-1) (35%) and 2010 mL (17%), respectively. Maximum CNa Inhibition (Imax), effective concentration (C50), and baseline immunosuppression (S0) were 0.87 pmol/min/mg (8.0%), 123 ng/mL (10%), and 1.15 pmol/min/mg (4.0%), respectively. Covariate analyses demonstrated that age and body surface area significantly influenced CL/F: CLi=717(Agei/48.8)-0.57(BSAi/1.99)1.1, while serum triglycerides significantly altered S0: S0i=1.15(TRIGi/1.97)0.15.