Assessment of Effect of Intraperitoneal Tacrolimus on Liver Regeneration in Major (70%) Hepatectomy Model After Experimental Pringle Maneuver in Rats.

AIM: Small-for-size grafts have become more important, especially in living donor liver transplants. The Pringle maneuver, used to reduce blood loss, and the immunosuppressive medications used to prevent graft rejection in liver transplants have different side effects on liver regeneration. We researched the effect of situations where tacrolimus and the Pringle maneuver were applied or not on liver regeneration in rats with partial hepatectomy. MATERIAL AND METHODS: This study was completed with 35 Wistar Albino rats. The subjects were randomly divided into 5 groups: Group 1 had the abdomen opened and no other procedure was performed; Group 2 underwent a 70% hepatectomy; Group 3 underwent a 15-minute Pringle maneuver + 70% hepatectomy; Group 4 underwent a 70% hepatectomy + 5 days of 1 mg/kg/day intraperitoneal tacrolimus; and Group 5 underwent a 150 minute Pringle maneuver + 0% hepatectomy + 5 days of 1 mg/kg/day intraperitoneal tacrolimus. All rats were sacrificed on the seventh postoperative day, remaining liver tissue was weighed, and weight indices created. The remaining liver tissue was stained with phosphohistone H3 and the mitotic index calculated. RESULTS: The groups that underwent the Pringle maneuver, 70% hepatectomy, and tacrolimus administration were compared with the control group in terms of mitotic index and weight index, but no statistically significant differences were identified. CONCLUSION: Suppression of regeneration forms a risk after liver transplantation with small-volume grafts. As a result, research on the effect of tacrolimus combined with the Pringle maneuver is important, especially for transplantations using segmented liver grafts. In our study, we showed that the use of tacrolimus had no negative effect on liver regeneration.

In Vitro and In Vivo Assessment of FK506 Analogs as Novel Antifungal Drug Candidates.

FK506 (tacrolimus) is an FDA-approved immunosuppressant indicated for the prevention of allograft rejections in patients undergoing organ transplants. In mammals, FK506 inhibits the calcineurin-nuclear factor of activated T cells (NFAT) pathway to prevent T-cell proliferation by forming a ternary complex with its binding protein, FKBP12, and calcineurin. FK506 also exerts antifungal activity by inhibiting calcineurin, which is essential for the virulence of human-pathogenic fungi. Nevertheless, FK506 cannot be used directly as an antifungal drug due to its immunosuppressive action. In this study, we analyzed the cytotoxicity, immunosuppressive activity, and antifungal activity of four FK506 analogs, 31-O-demethyl-FK506, 9-deoxo-FK506, 9-deoxo-31-O-demethyl-FK506, and 9-deoxo-prolyl-FK506, in comparison with that of FK506. The four FK506 analogs generally possessed lower cytotoxicity and immunosuppressive activity than FK506. The FK506 analogs, except for 9-deoxo-prolyl-FK506, had strong antifungal activity against Cryptococcus neoformans and Candida albicans, which are two major invasive pathogenic yeasts, due to the inhibition of the calcineurin pathway. Furthermore, the FK506 analogs, except for 9-deoxo-prolyl-FK506, had strong antifungal activity against the invasive filamentous fungus Aspergillus fumigatus Notably, 9-deoxo-31-O-demethyl-FK506 and 31-O-demethyl-FK506 exhibited robust synergistic antifungal activity with fluconazole, similar to FK506. Considering the antifungal efficacy, cytotoxicity, immunosuppressive activity, and synergistic effect with commercial antifungal drugs, we selected 9-deoxo-31-O-demethyl-FK506 for further evaluation of its in vivo antifungal efficacy in a murine model of systemic cryptococcosis. Although 9-deoxo-31-O-demethyl-FK506 alone was not sufficient to treat the cryptococcal infection, when it was used in combination with fluconazole, it significantly extended the survival of C. neoformans-infected mice, confirming the synergistic in vivo antifungal efficacy between these two agents.

Assessment of the synergic effect of immunomodulation on nerve repair using multiparametric magnetic resonance imaging.

INTRODUCTION: The immune system plays a pivotal role in nerve injury. The aim of this study was to determine the role of multiparametric magnetic resonance imaging (MRI) in evaluation of the synergic effect of immunomodulation on nerve regeneration in neurotmesis. METHODS: Rats with sciatic nerve neurotmesis and surgical repair underwent serial multiparametric MR examinations over an 8-week period after subepineurial microinjection of lipopolysaccharide (LPS) and subsequent subcutaneous injection of FK506 or subepineurial microinjection of LPS or phosphate-buffered saline (PBS) alone. RESULTS: Nerves treated with immunomodulation showed more prominent regeneration than those treated with LPS or PBS alone and more rapid restoration toward normal T2, fractional anisotropy (FA), and radial diffusivity (RD) values than nerves injected with LPS or PBS. DISCUSSION: Nerves treated with immunomodulation exert synergic beneficial effects on nerve regeneration that can be predicted by T2 measurements and FA and RD values. Muscle Nerve 57: E38-E45, 2018.

Wuzhi Tablet (Schisandra sphenanthera Extract) is a Promising Tacrolimus-Sparing Agent for Renal Transplant Recipients Who are CYP3A5 Expressers: a Two-Phase Prospective Study.

Tacrolimus is a potent but expensive first-line immunosuppressant, thus solutions to reduce tacrolimus consumption while maintain therapeutic level are in urgent need. A two-phase prospective study was conducted to assess the efficacy of an ethanolic extraction preparation of Schisandra sphenanthera (Wuzhi tablet) as a tacrolimus-sparing agent in renal transplant recipients who were high-dose tacrolimus consumers (CYP3A5*1 allele carriers, CYP3A5 expressers). A total of 12 patients were included in the Part I study. After co-administration of Wuzhi tablet, the average individual increment (%) in dose-adjusted C0, Cmax and AUC0-12 hour of tacrolimus were 198.8% (95% CI 149.2, 248.3), 111.0% (95% CI 63.4, 158.6) and 126.1% (95% CI 89.4, 162.8), respectively (P < 0.01), while the average individual reduction (%) in tacrolimus daily dose was 40.9% (95% CI 25.2, 56.6) (P < 0.01). Subsequently, 32 patients were enrolled in a prospective, randomized, controlled study and randomly assigned to receive tacrolimus by CYP3A5 genotype plus Wuzhi tablet co-administration guided dosing (study group) or standard dosing (control group). Besides less tacrolimus dose requirement (P < 0.01), a more accurate tacrolimus initial dose characterized by lower incidence of out-of-range C0 after initial dose (P < 0.01) and fewer dose changes (P < 0.01) was found in the study group. Moreover, no significant differences in acute rejection rate and serum creatinine levels were observed between two groups. Our results show that CYP3A5 genotype plus Wuzhi tablet co-administration guided tacrolimus dosing is a promising therapy for CYP3A5 expressers in the early post-transplant stage, while further study with a larger sample size is required to prove these findings.

Assessment of global ischemic/reperfusion and Tacrolimus administration on CA1 region of hippocampus: gene expression profiles of BAX and BCL2 genes.

BACKGROUND: It is well known that hippocampus has a pivotal role in learning, formation and consolidation of memory. Global cerebral ischemia causes severe damage to pyramidal neurons of the CA1 region and usually results in residual neurological deficits following a recovery from ischemia. Scientists investigate to find the molecular mechanism of apoptosis and to use this cell death for clinical treatment. OBJECTIVE: In this investigation, we evaluated the molecular mechanism of FK-506 in apoptosis using gene expression quantification of BAX and BCL-2 genes in hippocampus following global ischemic/reperfusion. MATERIALS AND METHODS: In the present experimental study, adult male Wistar rats were obtained and housed under standard conditions. Each experimental group consisted of five rats and was equally distributed in the normal control, ischemia/reperfusion, ischemia/reperfusion followed by FK-506. Global ischemia was induced for animals in ischemia and drug groups. In the drug group, moreover, two doses of FK-506 were injected as IV injection and intra-peritoneal (IP) injection after 48 h. Then, hippocampus tissue was removed. Consequently, RNA isolated, cDNA was synthesized and Real-Time PCR was performed. Finally, the obtained data was analyzed statistically (p<0.05). RESULTS: The quantitative results showed the BAX expression ratio increased approximately 3-times in ischemia/reperfusion (3.11 ± 0.28) group compared to the untreated (NR) and the drug group (p<0.001). The statistical analysis showed a significant difference for BCL-2 expression between the experimental groups (p<0.001). The mRNA level of BCL-2 decreased in the ischemia/reperfusion group, while it was without alteration in the other groups. CONCLUSION: The results showed that global cerebral ischemia/reperfusion induced BAX as pro-apoptotic gene and tacrolimus a neuroprotective drug inhibited BAX gene expression and induced BCL-2 gene expression as anti-apoptotic gene (Tab. 2, Fig. 3, Ref. 21).

Risk Assessment of Drug-Drug Interactions of Calcineurin Inhibitors Affecting Sirolimus Pharmacokinetics in Renal Transplant Patients.

BACKGROUND: Sirolimus is a mammalian target of rapamycin inhibitor that is being used to prevent organ rejection in kidney transplant patients often in combination with calcineurin inhibitors (CNIs; cyclosporine and tacrolimus). All 3 drugs are metabolized primarily by CYP3As. Clinical drug-drug interaction (DDI) studies of cyclosporine on sirolimus pharmacokinetics have been reported; however, there are a few clinical DDI data related to tacrolimus. METHODS: In vitro inhibition assay with sirolimus were conducted using recombinant CYP3As and human microsomes in the presence and absence of CNIs. Sirolimus concentrations were determined by validated high-performance liquid chromatography-tandem mass spectrometry (LC/MS-MS) assay. The DDI risk in terms of increase in sirolimus area under the curve (AUC) was evaluated by a mechanistic model using in vitro inhibition data and published pharmacokinetic parameters of CNIs. RESULTS: Both CNIs showed similar inhibitory effects on sirolimus metabolism in human liver and intestinal microsomes. Cyclosporine predominantly inhibited CYP3A4 (half maximal inhibitory concentration = 0.71 µM) rather than CYP3A5 (>5 µM), whereas tacrolimus showed similar inhibition for CYP3A4 (0.29 µM) and CYP3A5 (0.41 µM). The predicted increase in AUC of sirolimus during the coadministration of cyclosporine was 3.9-fold, which was comparable to the observed clinical data (3.3-fold) in healthy volunteers. Sirolimus AUC was estimated to a 2.8- to 3.2-fold increase during the coadministration of tacrolimus, based on the reported Cmax values and doses of tacrolimus in kidney transplant patients. In addition, exploratory sensitivity analysis indicated that the predicted increase in sirolimus AUC was sensitive to the free fraction of cyclosporine but not to the free fraction of tacrolimus. CONCLUSIONS: This study suggests that tacrolimus has a lower clinical DDI risk potential affecting sirolimus pharmacokinetics compared with cyclosporine in kidney transplant patients.

Reutilization of Tacrolimus Extracted from Expired Prograf® Capsules: Physical, Chemical, and Pharmacological Assessment.

In this study, we investigated whether tacrolimus extracted and purified from the commercial capsules (Prograf® 5 mg) have retained its original quality and activity beyond the capsules expiration date in order to be reused for research purposes after extraction. High-performance liquid chromatography (HPLC) assay method was developed and validated for the quantification of tacrolimus, using cyclosporine A as an internal standard (IS). Moreover, a combination of analytical methods, including nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GC-MS), Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) were used to assess the quality of extracted/purified tacrolimus. Suppression of murine peripheral-blood mononuclear cells (PBMC) proliferation and the levels of interleukin-2 (IL-2) and interferon gamma (IFN-γ) were also assessed. The data obtained showed no detectable differences in the quality profile between the authentic sample and extracted drug. Also, the results showed that the extracted/purified tacrolimus was able to suppress T cell proliferation, induced by concanavalin A, indicating the retained pharmacological activity. We proved that tacrolimus extracted/purified from expired Prograf® capsuled retains its purity and immunosuppressive activity and can be reused for research and possibly in pharmaceutical manufacturing.

Immunophenotyping and efficacy of low dose ATG in non-sensitized kidney recipients undergoing early steroid withdrawal: a randomized pilot study.

UNLABELLED: Rabbit antithymocyte globulin (ATG) is commonly used as an induction therapy in renal transplant recipients, but the ideal dosage in tacrolimus-based early steroid withdrawal protocols has not been established. The purpose of this pilot study was to determine the immunophenotyping and efficacy of lower dose ATG in low immunological-risk kidney transplant recipients. In this prospective study, 45 patients were randomized (1∶1) to our standard dose ATG (total dose 3.75 mg/kg)(sATG) vs. lower dose 2.25 mg/kg (lowATG). All patients underwent early steroid withdrawal within 7 days. The primary end point was biopsy-proven acute rejection at 12 months. Prospective immunophenotyping of freshly isolated PBMCs was performed at baseline, 3, 6, 12 months post-transplant. The rate of acute rejection was 17% and 10% in the sATG and lowATG, respectively. Effector memory T cells, Tregs and recent thymic emigrants T cells had similar kinetics post-transplant in both groups. No statistically significant differences were found in graft survival, patient survival or infections between the two groups, though there was a non-significant increase in leukopenia (43%v s. 30%), CMV (8% vs. 0) and BK (4% vs. 0) infections in sATG group vs. lowATG. In sum, in low immunological risk kidney recipients undergoing steroid withdrawal, low dose ATG seems to be efficacious in preventing acute rejection and depleting T cells with potentially lower infectious complications. A larger study is warranted to confirm these findings. TRIAL REGISTRATION: ClinicalTrials.gov NCT00548405.

Biomarker assessment of the immunomodulator effect of atorvastatin in stable renal transplant recipients and hypercholesterolemic patients.

BACKGROUND: HMG-CoA reductase inhibitors (statins) have effects beyond lipid lowering, including immunomodulatory and anti-inflammatory properties. Statins are frequently combined with immunosuppressive agents in transplant recipients to modulate the hyperlipidemic side effects of the immunosuppressants. However, the role of statins in the immunosuppressive response that is achieved in individual patients remains to be assessed. OBJECTIVE: The aim of this study was to evaluate the immunomodulatory effect of atorvastatin given alone and in combined treatment with tacrolimus and mycophenolate mofetil. STUDY DESIGN: Two patient groups were studied: renal transplant recipients receiving tacrolimus and mycophenolate mofetil therapy, and hypercholesterolemic patients (the control group). Fasting blood samples were taken from participants before and 1 month after atorvastatin treatment was started to study a small battery of biomarkers that are able to reflect the range of the effects of immunosuppressive therapy and atorvastatin. SETTING: All patients in the study were enrolled at the Hospital Clinic of Barcelona. PATIENTS: All patients enrolled in the study were candidates for treatment with atorvastatin because of high cholesterol levels. One group consisted of 25 stable renal transplant recipients with low-density lipoprotein (LDL) cholesterol levels above 100 mg/dL after 3 months of therapeutic lifestyle changes, according to the guidelines of the National Kidney Foundation - Kidney Disease Outcomes Quality Initiative. The other group included 25 hypercholesterolemic patients with LDL cholesterol levels above target values for the patients' overall risk, as derived from the National Cholesterol Education Program Adult Treatment Panel III criteria. INTERVENTION: Atorvastatin (Lipitor®) treatment was started at a fixed dose of 20 mg daily. MAIN OUTCOME MEASURE: The studied biomarkers were lymphocyte proliferation, intracellular adenosine triphosphate (ATP) synthesis in CD4+ T cells, intralymphocytary cytokine expression (interleukin [IL]-2, interferon [IFN]-γ), soluble cytokine production (IL-2, IFN-γ, IL-10, IL-17, and transforming growth factor-ß) and regulatory T (T(reg)) cells. RESULTS: Atorvastatin proved to be an immunomodulatory agent, significantly decreasing lymphocyte proliferation by 15% (p = 0.001), increasing ATP levels by 16% (p = 0.0004), and showing a trend toward increasing T(reg) cells in hypercholesterolemic patients (p = 0.09). In the renal transplant recipients, atorvastatin therapy did not modify any of the biomarkers of immunosuppression that were studied. CONCLUSION: Atorvastatin showed immunoregulatory effects on T cells in hypercholesterolemic patients. These effects were absent in renal transplant recipients, suggesting that the beneficial effects of atorvastatin in this patient group do not relate to immunoregulation. Therefore, statin treatment cannot be considered as a means to reduce the dose of immunosuppressive agents.

[Therapeutic monitoring of immunosuppressive drugs: interest of calcineurin activity assessment in liver transplantation]. / Place du suivi biologique des traitements immunosuppresseurs : exemple de la mesure de l'activité calcineurine en transplantation hépatique.

Therapeutic monitoring of calcineurin inhibitors (ciclosporin and tacrolimus) consists in pharmacokinetic monitoring. Pharmacodynamics based on calcineurin activity may be particularly interesting in liver transplantation due to the large intra- and interindividual variability of pharmacokinetics of ciclosporin and tacrolimus. A recent investigation on the pharmacokinetic-pharmacodynamic relationship of tacrolimus showed that monitoring of calcineurin activity in PBMC may be particularly relevant within the first three post-transplantation months. Thereafter, the monitoring of trough blood concentrations of tacrolimus remains adequate. Moreover, two clinical investigations carried out within the early and late post-transplantation periods reported a promising result which is a positive correlation between calcineurin activity and incidence of graft rejection, whatever graft type and calcineurin inhibitors. In each study, transplanted recipients with a graft rejection exhibited a greater trough calcineurin activity compared to patients without graft rejection. However, prospective investigations are required because of the small cohorts of patients enrolled in both studies. The aim of these investigations will be to confirm the interest of calcineurin activity monitoring as a marker of cellular immunity and its positive link with pharmacokinetic monitoring.

Role of timing in assessment of nerve regeneration.

Small animal models are indispensable for research on nerve injury and reconstruction, but their superlative regenerative potential may confound experimental interpretation. This study investigated time-dependent neuroregenerative phenomena in rodents. Forty-six Lewis rats were randomized to three nerve allograft groups treated with 2 mg/(kg day) tacrolimus; 5 mg/(kg day) Cyclosporine A; or placebo injection. Nerves were subjected to histomorphometric and walking track analysis at serial time points. Tacrolimus increased fiber density, percent neural tissue, and nerve fiber count and accelerated functional recovery at 40 days, but these differences were undetectable by 70 days. Serial walking track analysis showed a similar pattern of recovery. A "blow-through" effect is observed in rodents whereby an advancing nerve front overcomes an experimental defect given sufficient time, rendering experimental groups indistinguishable at late time points. Selection of validated time points and corroboration in higher animal models are essential prerequisites for the clinical application of basic research on nerve regeneration.

Comparison of low versus high tacrolimus levels in kidney transplantation: assessment of efficacy by protocol biopsies.

BACKGROUND: The use of calcineurin inhibitors is generally guided by drug blood levels. However, those levels are chosen based on clinical experience, lacking adequate titration studies. METHODS: In these analyses, we compared clinical and histologic endpoints in two groups of kidney transplant recipients: in the first (HiTAC, January 2000 to June 2002, n=245) tacrolimus levels were significantly higher than in the second (LoTAC, July 2002 to September 2004, n=330). This change in drug levels (15% reduction) was made in an attempt to reduce the incidence of polyoma virus nephropathy (PVAN). Other immunosuppressive medications were unchanged during these two time periods. RESULTS: The recipient and donor demographics were not statistically different between the two groups. Compared to HiTAC, at one year posttransplant LoTAC had: 1) lower incidence of PVAN (10.5% vs. 2.5%, P<0.0001); 2) lower fasting glucose levels; 3) higher iothalamate glomerular filtration rate (52+/-19 vs. 59+/-17 ml/min/m, P<0.0001); and 4) on protocol one-year biopsies, lower incidence and severity of interstitial fibrosis (67% vs. 45%, P=0.003) and tubular atrophy (82% vs., 66%, P=0.01). The incidence and severity of acute rejection episodes was similar between both groups (7.8% versus 7.6%). CONCLUSIONS: Modest reductions in tacrolimus exposure early posttransplant are associated with significant beneficial effects for the patient and the allograft without an increased immunologic risk.

Assessment of immunosuppressive drug interactions: inhibition of lymphocyte function in peripheral human blood.

Cyclosporin (CsA) or tacrolimus (TRL) is routinely combined with either sirolimus (SRL) or mycophenolate mofetil (MMF) in immunosuppressive regimes in organ transplantation. The aim of our study was to establish a specific human blood assay of lymphocyte function in order to assess interactions of these drug combinations. Different concentrations (10(6)-10(9) nM) of CsA, TRL, SRL or mycophenolic acid (MPA, the active metabolite of MMF) was added to whole blood of five human volunteers. Drug combinations were studied by adding 250, 500 or 1000 nM of MPA to different concentrations of CsA, TRL, or SRL or by adding 1, 10 or 25 nM of SRL to different concentrations of CsA or TRL. After concanavalin-A stimulation, whole blood cultures were analyzed by flow cytometry detecting lymphocyte proliferation and activation by bivariate expression of proliferating cell nuclear antigen (PCNA)/DNA content and T cell-surface activation antigens (e.g. CD25, CD95, and CD154). We found an order of potency inhibiting lymphocyte function with SRL>TRL>CsA>MPA. In addition, we observed enhanced inhibition of PCNA, CD25, CD95 or CD154, if either CsA or TRL was combined with low concentrations of MPA, or SRL alone or if SRL was combined with low concentrations of MPA. Data analysis revealed an independent functional synergism or partial agonism in most combinations. This human blood assay is able to assess lymphocyte function and to monitor immunosuppressive therapy. The assay also permits pharmacological analysis of drug interactions, which will lead to improved safety and therapeutic efficacy in transplanted patients.

Incidence and cost of new onset diabetes mellitus among U.S. wait-listed and transplanted renal allograft recipients.

This study sought to determine 1) the incidence and costs of new onset diabetes mellitus (NODM) associated with maintenance immunosuppression regimens following renal transplantation and 2) whether the mode of dialysis pretransplant or the type of calcineurin inhibition used for maintenance immunosuppression affected either the incidence or cost of NODM. The study examined the United States Renal Data System's clinical and financial records from 1994 to 1998 of all adult, first, single-organ, renal transplantations in either 1996 or 1997 with adequate financial records. It used the second diagnosis of diabetes in previously nondiabetic patients to identify NODM. While NODM had an incidence of approximately 6% per year among wait-listed dialysis patients, NODM over the first 2 years post-transplant had an incidence of almost 18% and 30% among patients receiving cyclosporine and tacrolimus, respectively. By 2 years post-transplant, Medicare paid an extra $21 500 per newly diabetic patient. We estimated the cost of diabetes attributable to maintenance immunosuppression regimens to be $2025 and $3308 for each tacrolimus patient and $1137 and $1611 for each cyclosporine patient at 1 and 2 years post-transplant, respectively.

Tacrolimus Fujisawa.

Fujisawa has launched the immunosuppressant tacrolimus extensively for use in organ transplantation. The compound has also been developed for the treatment of atopic dermatitis, for which it has been launched in the US, Japan, Switzerland, Canada and Germany [425053], [426616], [435668], [447770]. Tacrolimus has also been developed for chronic rheumatoid arthritis (RA) and several other autoimmune diseases [351891], [352195], [360717]. By March 2002, tacrolimus had entered phase III trials for inflammatory bowel disease (IBD) in Japan [442503]. This evaluation will focus on the development of tacrolimus for this indication.

Termination of cardiac Ca(2+) sparks: an investigative mathematical model of calcium-induced calcium release.

A Ca(2+) spark arises when a cluster of sarcoplasmic reticulum (SR) channels (ryanodine receptors or RyRs) opens to release calcium in a locally regenerative manner. Normally triggered by Ca(2+) influx across the sarcolemmal or transverse tubule membrane neighboring the cluster, the Ca(2+) spark has been shown to be the elementary Ca(2+) signaling event of excitation-contraction coupling in heart muscle. However, the question of how the Ca(2+) spark terminates remains a central, unresolved issue. Here we present a new model, "sticky cluster," of SR Ca(2+) release that simulates Ca(2+) spark behavior and enables robust Ca(2+) spark termination. Two newly documented features of RyR behavior have been incorporated in this otherwise simple model: "coupled gating" and an opening rate that depends on SR lumenal [Ca(2+)]. Using a Monte Carlo method, local Ca(2+)-induced Ca(2+) release from clusters containing between 10 and 100 RyRs is modeled. After release is triggered, Ca(2+) flux from RyRs diffuses into the cytosol and binds to intracellular buffers and the fluorescent Ca(2+) indicator fluo-3 to produce the model Ca(2+) spark. Ca(2+) sparks generated by the sticky cluster model resemble those observed experimentally, and Ca(2+) spark duration and amplitude are largely insensitive to the number of RyRs in a cluster. As expected from heart cell investigation, the spontaneous Ca(2+) spark rate in the model increases with elevated cytosolic or SR lumenal [Ca(2+)]. Furthermore, reduction of RyR coupling leads to prolonged model Ca(2+) sparks just as treatment with FK506 lengthens Ca(2+) sparks in heart cells. This new model of Ca(2+) spark behavior provides a "proof of principle" test of a new hypothesis for Ca(2+) spark termination and reproduces critical features of Ca(2+) sparks observed experimentally.

Protective effect of FK506 in the reperfusion model after short-term occlusion of middle cerebral artery in the rat: assessment by autoradiography using [125I]PK-11195.

The protective effect of the immunosuppressant agent FK506 in the reperfusion after short-term occlusion of the middle cerebral artery in the rat model was evaluated using [125I]PK-11195 autoradiography. FK506 0.5 mg kg-1 day-1 was administered intramurally to Wistar rats weighing 260-300 g from one day prior to ischemia to seven days after ischemia. Reperfusion was performed after 30 or 60 min occlusion. Infarct area was evaluated by [125I]PK-11195 autoradiography on the seventh day following occlusion. FK506 significantly reduced the infarct area in the caudate nucleus following 30 and 60 min occlusion, but significantly reduced the infarct area in the cortex only following 60 min occlusion. These results suggest that FK506 has a protective effect against reperfusion after short-term occlusion of the middle cerebral artery.

Tacrolimus: a further update of its pharmacology and therapeutic use in the management of organ transplantation.

UNLABELLED: Tacrolimus (FK-506) is an immunosuppressant agent that acts by a variety of different mechanisms which include inhibition of calcineurin. It is used as a therapeutic alternative to cyclosporin, and therefore represents a cornerstone of immunosuppressive therapy in organ transplant recipients. Tacrolimus is now well established for primary immunosuppression in liver and kidney transplantation, and experience with its use in other types of solid organ transplantation, including heart, lung, pancreas and intestinal, as well as its use for the prevention of graft-versus-host disease in allogeneic bone marrow transplantation (BMT), is rapidly accumulating. Large randomised nonblind multicentre studies conducted in the US and Europe in both liver and kidney transplantation showed similar patient and graft survival rates between treatment groups (although rates were numerically higher with tacrolimus- versus cyclosporin-based immunosuppression in adults with liver transplants), and a consistent statistically significant advantage for tacrolimus with respect to acute rejection rate. Chronic rejection rates were also significantly lower with tacrolimus in a large randomised liver transplantation trial, and a trend towards a lower rate of chronic rejection was noted with tacrolimus in a large multicentre renal transplantation study. In general, a similar trend in overall efficacy has been demonstrated in a number of additional clinical trials comparing tacrolimus- with cyclosporin-based immunosuppression in various types of transplantation. One notable exception is in BMT, where a large randomised trial showed significantly better 2-year patient survival with cyclosporin over tacrolimus, which was primarily attributed to patients with advanced haematological malignancies at the time of (matched sibling donor) BMT. These survival results in BMT require further elucidation. Tacrolimus has also demonstrated efficacy in various types of transplantation as rescue therapy in patients who experience persistent acute rejection (or significant adverse effect's) with cyclosporin-based therapy, whereas cyclosporin has not demonstrated a similar capacity to reverse refractory acute rejection. A corticosteroid-sparing effect has been demonstrated in several studies with tacrolimus, which may be a particularly useful consideration in children receiving transplants. The differences in the tolerability profiles of tacrolimus and cyclosporin may well be an influential factor in selecting the optimal treatment for patients undergoing organ transplantation. Although both drugs have a similar degree of nephrotoxicity, cyclosporin has a higher incidence of significant hypertension, hypercholesterolaemia, hirsutism and gingival hyperplasia, while tacrolimus has a higher incidence of diabetes mellitus, some types of neurotoxicity (e.g. tremor, paraesthesia), diarrhoea and alopecia. CONCLUSION: Tacrolimus is an important therapeutic option for the optimal individualisation of immunosuppressive therapy in transplant recipients.