FK506 and rapamycin: novel pharmacological probes of the immune response

Ndufs4 knockout mouse models of Leigh syndrome: pathophysiology and intervention

Mitochondria are small cellular constituents that generate cellular energy (ATP) by oxidative phosphorylation (OXPHOS). Dysfunction of these organelles is linked to a heterogeneous group of multisystemic disorders, including diabetes, cancer, ageing-related pathologies and rare mitochondrial diseases. With respect to the latter, mutations in subunit-encoding genes and assembly factors of the first OXPHOS complex (complex I) induce isolated complex I deficiency and Leigh syndrome. This syndrome is an early-onset, often fatal, encephalopathy with a variable clinical presentation and poor prognosis due to the lack of effective intervention strategies. Mutations in the nuclear DNA-encoded NDUFS4 gene, encoding the NADH:ubiquinone oxidoreductase subunit S4 (NDUFS4) of complex I, induce ‘mitochondrial complex I deficiency, nuclear type 1’ (MC1DN1) and Leigh syndrome in paediatric patients. A variety of (tissue-specific) Ndufs4 knockout mouse models were developed to study the Leigh syndrome pathomechanism and intervention testing.

Here, we review and discuss the role of complex I and NDUFS4 mutations in human mitochondrial disease, and review how the analysis of Ndufs4 knockout mouse models has generated new insights into the MC1ND1/Leigh syndrome pathomechanism and its therapeutic targeting.

The road ahead for health and lifespan interventions

Aging is a modifiable risk factor for most chronic diseases and an inevitable process in humans. The development of pharmacological interventions aimed at delaying or preventing the onset of chronic conditions and other age-related diseases has been at the forefront of the aging field. Preclinical findings have demonstrated that species, sex and strain confer significant heterogeneity on reaching the desired health- and lifespan-promoting pharmacological responses in model organisms. Translating the safety and efficacy of these interventions to humans and the lack of reliable biomarkers that serve as predictors of health outcomes remain a challenge. Here, we will survey current pharmacological interventions that promote lifespan extension and/or increased healthspan in animals and humans, and review the various anti-aging interventions selected for inclusion in the NIA's Interventions Testing Program as well as the ClinicalTrials.gov database that target aging or age-related diseases in humans.

Potential therapeutic effects of the MTOR inhibitors for preventing ageing and progeria-related disorders

The mammalian target of rapamycin (mTOR) pathway is an highly conserved signal transduction axis involved in many cellular processes, such as cell growth, survival, transcription, translation, apoptosis, metabolism, motility and autophagy. Recently, this signalling pathway has come to the attention of the scientific community owing to the unexpected finding that inhibition of mTOR by rapamycin, an antibiotic with immunosuppressant and chemotherapeutic properties, extends lifespan in diverse animal models. Moreover, rapamycin has been reported to rescue the cellular phenotype in a progeroid syndrome [Hutchinson–Gilford Progeria syndrome (HGPS)] that recapitulates most of the traits of physiological ageing. The promising perspectives raised by these results warrant a better understanding of mTOR signalling and the potential applications of mTOR inhibitors to counteract ageing‐associated diseases and increase longevity. This review is focused on these issues.

Comparison of reendothelialization and neointimal formation with stents coated with antibodies against endoglin and CD34 in a porcine model

Anti-CD34 coated stents are the only commercialized antibody-coated stents currently used for coronary artery diseases with various limitations. Endoglin plays important roles in the proliferation of endothelial cells and vascular remodeling and could be an ideal target surface molecule. The objective of this study was to investigate the efficacy of stents coated with anti-endoglin antibodies (ENDs) in terms of endothelial recovery and the reduction of neointimal formation. The performance of ENDs was evaluated by comparing with stents coated with anti-CD34 antibodies (CD34s), sirolimus-eluting stents (SESs), and bare metal stents (BMSs). Stents were randomly assigned and placed in the coronary arteries of juvenile pigs. Histomorphometric analysis and scanning electron microscopy were performed after stent implantation. Our results showed at 14 days after stent implantation, the neointima area and percent area stenosis in ENDs and CD34s were remarkably decreased compared with those in BMSs and SESs (P<0.05). Moreover, the percentage of reendothelialization was significantly higher in ENDs and CD34s than that in SESs or BMSs at both 7 and 14 days (P<0.05). There was no difference in the neointima area, percent area stenosis, and percentage of reendothelialization in ENDs compared with CD34s. The artery injury and the inflammation scores were similar in all groups at both 7 and 14 days. Our results demonstrate that the performance of ENDs is similar to the commercial CD34s, without the disadvantages of CD34s, and both are better than SESs and BMSs. ENDs potentially offer an alternative approach to reduce restenotic process and enhance reendothelialization after stent implantation.

The role of small molecules in musculoskeletal regeneration

The uses of bone morphogenetic proteins and parathyroid hormone therapeutics are fraught with several fundamental problems, such as cost, protein stability, immunogenicity, contamination and supraphysiological dosage. These downsides may effectively limit their more universal use. Therefore, there is a clear need for alternative forms of biofactors to obviate the drawbacks of protein-based inductive factors for bone repair and regeneration. Our group has studied small molecules with the capacity to regulate osteoblast differentiation and mineralization because their inherent physical properties minimize limitations observed in protein growth factors. For instance, in general, small molecule inducers are usually more stable, highly soluble, nonimmunogenic, more affordable and require lower dosages. Small molecules with the ability to induce osteoblastic differentiation may represent the next generation of bone regenerative medicine. This review describes efforts to develop small molecule-based biofactors for induction, paying specific attention to their novel roles in bone regeneration.

Frontier of epilepsy research - mTOR signaling pathway

Studies of epilepsy have mainly focused on the membrane proteins that control neuronal excitability. Recently, attention has been shifting to intracellular proteins and their interactions, signaling cascades and feedback regulation as they relate to epilepsy. The mTOR (mammalian target of rapamycin) signal transduction pathway, especially, has been suggested to play an important role in this regard. These pathways are involved in major physiological processes as well as in numerous pathological conditions. Here, involvement of the mTOR pathway in epilepsy will be reviewed by presenting; an overview of the pathway, a brief description of key signaling molecules, a summary of independent reports and possible implications of abnormalities of those molecules in epilepsy, a discussion of the lack of experimental data, and questions raised for the understanding its epileptogenic mechanism.

CCR3 and choroidal neovascularization

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly in industrialized countries. The "wet" AMD, characterized by the development of choroidal neovacularization (CNV), could result in rapid and severe loss of central vision. The critical role of vascular endothelial growth factor A (VEGF-A) in CNV development has been established and VEGF-A neutralization has become the standard care for wet AMD. Recently, CCR3 was reported to play an important role in CNV development and that CCR3 targeting was reported to be superior to VEGF-A targeting in CNV suppression. We investigated the role of CCR3 in CNV development using the Matrigel induced CNV and found that in both rats and mice, CNV was well-developed in the control eyes as well as in eyes treated with CCR3 antagonist SB328437 or CCR3 neutralizing antibodies. No statistically significant difference in CNV areas was found between the control and SB328437 or CCR3-ab treated eyes. Immunostaining showed no specific expression of CCR3 in or near CNV. In contrast, both VEGF-A neutralizing antibodies and rapamycin significantly suppressed CNV. These results indicate that CCR3 plays no significant role in CNV development and question the therapeutic approach of CCR3 targeting to suppress CNV. On the other hand, our data support the therapeutic strategies of VEGF-A and mTOR (mammalian target of rapamycin) targeting for CNV.

SERCA2b activity is regulated by cyclophilins in human platelets

OBJECTIVE

The role of cyclophilins (chaperones that are widely expressed in different cell types, including human platelets) was explored in sarcoendoplasmic calcium (Ca(2+)) adenosine triphosphatase (SERCA) activity.

METHODS AND RESULTS

Cyclophilin inhibition by cyclosporin A (CsA) evoked a time- and concentration-dependent reduction of Ca(2+) uptake by SERCA2b. However, other Ca(2+)-adenosine triphosphatases expressed in platelets, such as SERCA3 and plasma membrane Ca(2+) adenosine triphophatase, remained unaltered after CsA treatment. Cypermethrin, a non-CsA-related calcineurin inhibitor, did not alter SERCA2b activity. Furthermore, SERCA2b was affected by other CsA analogues, which do not interfere with calcineurin, such as PKF-211-811-NX5 (NIM811) and sanglifehrin A. Inhibition of the immunophilin family members using FK506 (tacrolimus) did not alter SERCA2b ability to sequester Ca(2+) into the dense tubular system. Coimmunoprecipitation experiments confirmed that cyclophilin A associates with SERCA2b and stromal interaction molecule-1 in resting platelets. This interaction is attenuated by the physiological agonist thrombin but enhanced by treatment with CsA or sanglifehrin A.

CONCLUSIONS

Cyclophilin A is a regulator of SERCA2b in human platelets.

Functional drift of sequence attributes in the FK506-binding proteins (FKBPs)

Diverse members of the FK506-binding proteins (FKBPs) group and their complexes with different macrocyclic ligands of fungal origins such as FK506, rapamycin, ascomycin, and their immunosuppressive and nonimmunosuppressive derivatives display a variety of cellular and biological activities. The functional relatedness of the FKBPs was estimated from the following attributes of their aligned sequences: 1 degrees conservation of the consensus sequence; 2 degrees sequence similarity; 3 degrees pI; 4 degrees hydrophobicity; 5 degrees amino acid hydrophobicity and bulkiness profiles. Analyses of the multiple sequence alignments and intramolecular interaction networks calculated from a series of structures of the FKBPs revealed some variations in the interaction clusters formed by the AA residues that are crucial for sustaining peptidylprolyl cis/trans isomerases (PPIases) activity and binding capacity of the FKBPs. Fine diversification of the sequences of the multiple paralogues and orthologues of the FKBPs encoded in different genomes alter the intramolecular interaction patterns of their structures and allowed them to gain some selectivity in binding to diverse targets (functional drift).

Sirolimus-eluting coronary stents: a review

The sirolimus-eluting coronary stent received CE Mark approval in Europe in April 2002. In the US, FDA approval followed in April 2003. Since the preliminary results from the First-in-Man feasibility study were presented, several randomized, controlled trials have documented the profound antiproliferative effects of sirolimus, a macrolide antibiotic and potent cytostatic inhibitor of smooth muscle cell proliferation. Subsequently, the body of clinical evidence was increased by the second wave of evidence from trials in more complex lesions (such as in-stent restenosis, small vessels, chronic total occlusions) and "high-risk" patients such as those with diabetes. More recently we have had the opportunity to compare the two commercially available drug-eluting stents following the presentation of data from six head-to-head trials. As a result of numerous single and multi-center, national and international studies in which the safety and efficacy of sirolimus-eluting coronary stents have been subjected to close scrutiny, the global interventional cardiology community now has a wealth of evidence in support of the use of this technology resulting in dramatically improved patient outcomes after percutaneous intervention.

ISIS 2302, an antisense inhibitor of intercellular adhesion molecule 1

ISIS 2302 is a 20 base phosphorothioate oligodeoxynucleotide (ODN) that inhibits intercellular adhesion molecule 1 (ICAM-1) expression through an antisense mechanism. Murine and rat analogues have been effective at doses of 0.06 - 10 mg/kg in a spectrum of models of human inflammatory diseases and allograft transplantation, and ISIS 2302 inhibits the upregulation of ICAM-1 expression in a variety of human cells in vitro. In animals, including primates, plasma distribution half-life ranges from 30 - 60 min, but tissue elimination half-lives range from 1 - 5 days, and the compound is metabolised as other nucleic acids. In a Phase I iv. study, the pharmacokinetic behaviour of ISIS 2302 was similar to that in other primates, and single and multiple every other day doses from 0.06 - 2 mg/kg infused over 2 h were well-tolerated. Phase IIa studies have been completed in Crohn's disease, rheumatoid arthritis, and psoriasis, and a combined Phase I/II renal allograft acute rejection prophylaxis study has just completed enrolment. In these studies, ISIS 2302, 0.5 - 2 mg/kg, or placebo was administered iv. every 2 - 3 days over 14 - 26 days (7 - 13 infusions) to 17 - 52 patients, with follow up for 6 months. In the Crohn's study, evidence of highly durable (5+ month) remission-inducing and steroid-sparing properties were demonstrated, without clinically important adverse events. A 300-patient, pivotal quality trial investigating the steroid-sparing and remission-inducing qualities of ISIS 2302 in patients with steroid-dependent Crohn's disease is completely enrolled, with results expected in the first half of 2000. Modest efficacy and excellent tolerability were demonstrated in the psoriasis and rheumatoid arthritis trials. A Phase IIa trial of a topical formulation in patients with psoriasis is expected to commence in late 1999, as is a trial of an enema formulation in distal ulcerative colitis. Administration by nebulisation for asthma is undergoing preclinical evaluation. Execution of future plans in organ transplantation will await the results of the ongoing Phase I/II trial.

A note on clustering the functionally-related paralogues and orthologues of proteins: a case of the FK506-binding proteins (FKBPs)

The expression patterns of 18 FK506-binding proteins (FKBPs) encoded in the human genome have been established whereas the functional significance of the numerous ORFs coding for FKBP-like sequences remains unknown. Nominal masses of the human FKBPs vary from 12 to 135 kDa. Some large FKBPs consist up to four repeats of the 12 kDa FK506-like binding domain (FKBD) whereas other large FKBPs contain one FKBD linked to different functional domains such as TPRs, leucine-zipper, calmodulin-binding domain etc. The genomes of other eukaryotic organisms, namely D. melanogaster, C. elegans, A. thaliana, S. pombe and S. cerevisiae encode different numbers of the FKBPs' paralogues some of which are orthologues to the human FKBPs. A library of novel algorithms was developed and used for computation of the level of conservation of the hydrophobicity and bulkiness profiles, and the amino acid compositions (AACs) of 247 aligned sequences of FKBPs. The pairwisely-compared hydrophobicity and bulkiness profiles for some combinations of the aligned sequences of the FKBDs yielded high values of the correlation coefficients (CCF). The AACs of some combinations of the aligned sequences of the FKBDs also differed to a low degree. The functionally-related orthologues and paralogues of the FKBPs were clustered by using the following criteria: 1 degrees apparent conservation of the crucial amino acid (AA) residues for peptidylprolyl cis/trans isomerase (PPIase) acitity and binding of some immunosuppressive drugs; 2 degrees convergence of the three mentioned above properties of the polypeptide chain; 3 degrees similarity in the sequence attributes pI and total hydrophobicity index (HI). The clustering method was used for setting up several hypotheses on the emergence of certain classes of the FKBPs in the eukaryotic kingdom.

The suppressive effect of triptolide on experimental autoimmune uveoretinitis by down-regulating Th1-type response

We investigated the suppressive effect of triptolide (TRD), a purified component from a traditional Chinese herb, Tripterygium wilfordii Hook F. (TWHf), on uveitogenic peptide (K2)-induced experimental autoimmune uveoretinitis (EAU). K2-peptide immunized B10.A mice were divided into four groups. One group was EAU control which was treated with PBS. The other two groups were treated with TRD with different time courses (from day 0 to day 28 and from day 14 to day 28). The last group was treated with Cyclosporin A (CsA) as a positive control of the treatment. TRD was administered at dose of 0.1 mg/kg/day (i.p.). CsA was administered at dose of 20 mg/kg/day (i.p.) from day 0 to day 28 during whole period of EAU induction. The data showed that the EAU was suppressed in the whole period of TRD-treated mice, but was not in TRD-treated mice from day 14 to day 28 following immunization. The inhibition of EAU induced by TRD treatment was comparable to CsA-treated mice. The K2-specific lymphocyte proliferation and mRNA expressions of Th1-type cytokines (IL-12p40, IFN-gamma and TNF-alpha) in draining lymph node and inflamed eyes were reduced in TRD-treated mice. The K2-specific IFN-gamma production in the draining lymph node cells (LNC) of TRD-treated mice (whole period) was significantly inhibited. This effect was not related to an apoptotic effect of TRD on CD4+ T cells. Our results suggested that TRD suppressed the induction of EAU by down-regulating Th1-type response in B10.A mice. This preventive effect on EAU induction may be related to the inhibition of TRD on T cell priming and activation.

Mycophenolate mofetil treatment accelerates recovery from experimental allergic encephalomyelitis

Mycophenolate mofetil (MM) acts through its metabolite mycophenolic acid to inhibit inosine monophosphate dehydrogenase (IMPDH), an enzyme essential for purine synthesis in lymphocytes. Oral treatment with MM from the day of immunization for 2 weeks significantly delayed both the development of active experimental allergic encephalomyelitis (EAE) in Lewis rats and reduced the antibody response to myelin basic protein (MBP). MM did not deplete T and B cells, nor did it prevent induction of Th1 or Th2 cytokine in the regional nodes. Treatment of EAE with MM at the onset of clinical symptoms resulted in more rapid recovery from EAE than in control or cyclosporin A (CsA)-treated. MM-treated rats had less infiltration of T cells, B cells, macrophages and dendritic cells into brainstems than either the control or CsA-treated. MM-treated brainstems also had lower level of mRNA for Thl (IL-2, IL-12Rbeta2, IFN-gamma), Th2 (IL-4, IL-10) cytokines and TNF-alpha and TGF-beta compared to that in CsA and controls groups. This study shows MM was superior to CsA in the treatment of EAE and acted by reducing the inflammatory infiltrate, not by suppression of Ig response or by promotion of regulatory cells such as Th2 or Th3.

Current and future modalities for functional renal replacement

Approximately 310,000 Americans suffer from end-stage renal disease, with more than 70,000 new cases reported each year. Advances in immunosuppressive therapy for transplanted patients, in addition to the refined care of patients who are dependent on dialysis, have led to an improved survival for patients with renal failure. Structural, molecular, and pharmacologic developments continue to enhance the efficacy and safety of dialysis in the future. In addition, progressive improvements in the past 2 decades in organ transplantation, a greater insight into the immunobiology of graft rejection, and better surgical and medical management have resulted in improved outcomes. Although renal xenotransplantation is still in its early stages of development, additional research is leading this technology forward. Recent successes in harvesting and expanding renal cells in vitro and the development of biologically active synthetic materials allow for the creation of three-dimensional functioning renal units, which, in the future, may be applied ex vivo or in vivo for partial or full replacement of kidney function.

Expression and function of calcineurin in the mammalian nephron: physiological roles, receptor signaling, and ion transport

Protein phosphorylation is central to the regulation of sodium transport and other cellular processes in the nephron. Complex interactions between protein kinases and phosphatases catalyze the reversible phosphorylation of ion transporting proteins on the apical and basolateral surfaces of renal epithelia. Although the role of protein kinases in regulating sodium transport has been extensively studied, the function of phosphatases in the nephron is less well understood. Calcineurin is a serine-threonine phosphatase that was shown to be the target of cyclosporin A (CsA) and FK-506 in lymphocytes. Calcineurin exists in the cytosol as a heterotrimeric protein composed of an alpha-catalytic subunit, beta-regulatory subunit, and calmodulin; its activity depends on calcium and calmodulin. Three isoforms of the alpha-subunit (alpha-1, alpha-2, alpha-3) and two isoforms of the beta-subunit (beta-1 and beta-2) of calcineurin have been identified. In proximal tubules, alpha-1 isoforms are predominant and exceed alpha-2 expression by fourfold. In the CCD, alpha-1 and alpha-2 expression are approximately equal, whereas alpha-2 subunit expression is greatest in medullary thick ascending limbs (mTAL). Alpha-3 was not detected in any nephron segment. Calcineurin phosphatase activity in the proximal tubule is approximately 10-fold higher than in the connecting tubules (CNT), cortical collecting ducts (CCD), or the mTAL. Protein phosphatases 1 and 2a are also expressed in CCD, and only protein phosphatase 1 can be detected in the proximal tubule. Calcineurin influences basal and stimulated Na/ K-ATPase activity in the proximal and distal nephron. In the CCD, CsA or FK-506 decrease Na/K-ATPase activity by 35% and 85%, respectively; Na/K-ATPase activity in mTAL is decreased by 53% and 56%. Activation of membrane receptors, including adrenergic, dopamanergic, and angiotensin I receptors, also regulates Na/K-ATPAse activity through processes that involve calcineurin. Lastly, steroid hormones including glucocorticoids and mineralocorticoids appear to activate calcineurin phosphatase activity. The mechanism is independent of transcription and appears to involve mechanisms involving heat shock proteins associated with the steroid receptor complex.

Rapamycin inhibits alpha 1-adrenergic receptor-stimulated cardiac myocyte hypertrophy but not activation of hypertrophy-associated genes. Evidence for involvement of p70 S6 kinase

The 70-kD S6 kinase (p70S6K) has been implicated in the regulation of protein synthesis in many cell types and in the angiotensin II-stimulated hypertrophy of cardiac myocytes. Our purpose was to determine whether p70S6K plays a role in cardiomyocyte hypertrophy induced by the alpha 1-adrenergic receptor (alpha 1-AR) agonist phenylephrine (PE). PE stimulated the activity of p70S6K > 3-fold, and this increase was blocked by rapamycin, an immunosuppressant macrolide that selectively inhibits p70S6K. When administered for 3 days, PE stimulated a 30% increase in total protein content, a 2-fold increase in the incorporation of [14C]phenylalanine (14C-Phe) into protein, and a 50% increase in two-dimensional myocyte area. Rapamycin pretreatment (> or = 500 pg/mL) significantly inhibited each of these PE-stimulated changes. Two days of PE treatment resulted in a 1.6-fold increase in total RNA yield per dish, a 2-fold increase in incorporation of [14C]uridine into myocyte RNA, and increases in relative mRNA levels of the hypertrophy-associated atrial natriuretic factor (ANF, 2.1-fold) and skeletal alpha-actin (SK, 2.2-fold) genes. Although rapamycin abolished the PE-stimulated increases in total RNA and incorporation of [14C]uridine, it had no effect on the induction of the ANF and SK genes. LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited PE-stimulated increases in p70S6K activity and the incorporation of labeled precursors into myocyte protein and RNA. These results demonstrate that p70S6K is activated by the hypertrophic agent PE and that a PI3-K or PI3-K-like activity is required for p70S6K activation and myocyte hypertrophy. The data suggest that p70S6K activation may be required for PE-stimulated hypertrophy of cardiac myocytes. Our results demonstrate that intracellular signaling pathways responsible for transcriptional and translational responses diverge early after alpha 1-AR stimulation in cardiac myocytes.

Aldosterone and dexamethasone stimulate calcineurin activity through a transcription-independent mechanism involving steroid receptor-associated heat shock proteins

Heat shock proteins (HSP) are components of the steroid receptor complex and are released into the cell cytosol after hormone binding. We tested whether HSPs released from steroid receptors mediate an increase in calcineurin phosphatase activity by steroid hormones. Aldosterone increased calcineurin activity in microdissected rat cortical collecting ducts (CCD) and connecting tubules, but not in proximal tubules, medullary thick ascending limb, or outer medullary collecting ducts. In contrast, 5 microM dexamethasone increased calcineurin activity in both CCD and proximal tubules. Aldosterone increased CCD calcineurin activity after 30 min and this response was blocked by spironolactone, but not by actinomycin D. An antibody recognizing HSP-56 did not change basal calcineurin activity, but completely blocked the stimulation of calcineurin by aldosterone. Rapamycin, an immunosuppressive drug that stabilizes the HSP-steroid receptor complex, also blocked the aldosterone response, whereas HSP-90 or HSP-70 increased calcineurin activity in permeabilized CCD. In summary, (a) aldosterone increases calcineurin activity in CCD through a transcription-independent process; (b) maneuvers inactivating HSP-56 or slowing HSP disassociation from the receptor complex blocks stimulation of calcineurin by steroid hormones; (c) HSP-90 and HSP-70 increase CCD calcineurin activity in the absence of steroid hormone. We conclude that HSPs released from transformed steroid receptors can stimulate calcineurin activity through a transcription-independent pathway.

Progress in renal transplantation for children

Renal transplantation continues to be the goal of therapy for children with end-stage renal disease. Patient age, primary renal disease, psychosocial status, living versus cadaver donor allograft, optimal immunosuppressive therapy, urologic status, and maximization of growth and development must be considered in determining the optimal time for transplantation. Immunizations should be up to date, and the immune status of both the donor and the recipient with regard to Epstein-Barr virus, cytomegalovirus, human immunodeficiency virus, and hepatitis A, B, and C must be known. Prednisone, imuran, cyclosporine, and T cell antibodies remain the mainstay of immunosuppression. However, new therapies, such as FK-506, rapamycin, mofetil, brequinar, leflunomide, and human leukocyte antigen-derived peptides, are under investigation for use in transplantation. Complications, including infection, rejection, and malignancy, continue to be problematic in pediatric renal transplantation. Although patient and graft survival has improved over time, outcomes in pediatric renal transplantation continue to lag behind those in young adults.

Recent advances in the pharmacological control of experimental allergic encephalomyelitis (EAE) and the implications for multiple sclerosis treatment

The autoimmune, cell-mediated condition experimental allergic encephalomyelitis (EAE) is the representative model for the inflammatory central nervous system disease MS. EAE has been extensively employed to determine the efficacy of pharmacological agents that may be of ultimate use in the treatment of MS. A wide variety of drugs has been examined for activity in EAE but, over the last decade, three groups of compounds have emerged with clear and reproducible ability to modify significantly the onset and progression of the disease. The immunosuppressants, the modulators of catecholamine activity and the antineoplastic agents have convincingly altered the course of EAE and, as a consequence, provided understanding of the mechanisms of disease expression and offered further insight into the pathogenesis of MS. The article stresses the usefulness of EAE as a model to identify prospective pharmacological treatments for MS and, in particular, considers those compounds subsequently assessed for their ability to interfere with the progression of the human disease.

Horizons in pharmacologic intervention in allergic contact dermatitis

The treatment of allergic contact dermatitis remains a major challenge. Current management strategies consist of elimination of the allergen when possible and therapy for symptoms with topical or systemic corticosteroids. With increasing exposure of the human skin to environmental antigens and haptens, more selective treatment options are needed. Advances in the elucidation of the skin immune system and of the cellular and molecular events in immunologic processes may allow targeted methods of controlling delayed hypersensitivity reactions. This review focuses on mechanisms of established therapeutic agents and new developments, such as FK 506 (tacrolimus), pentoxifylline, and vitamin D3 derivative, for suppression of any phase of allergic contact dermatitis.

Cyclosporin A does not affect the absolute rate of cortical bone resorption at the organ level in the growing rat

The weanling rat, an animal model of rapid bone turnover, was used to evaluate the effects of various doses of cyclosporin A (CsA) on various bones during different time periods. Sprague-Dawley male rats were extensively prelabeled with 3H-tetracycline during 1-3 weeks of age. At 4 weeks of age, four groups of rats were given daily subcutaneous injections: vehicle or CsA--low dose (10 mg/kg), intermediary dose (20 mg/kg), or high dose (30 mg/kg) for 7, 14, or 28 days. Three different whole bones--the femur (low turnover), scapula (moderate turnover), and lumbar-6 vertebra (high turnover) were harvested intact at 4, 5, 6, and 8 weeks of age. The whole bones were assayed weekly for total dry defatted weight, calcium mass (formation), and loss of 3H-tetracycline (bone resorption) following treatment with CsA. Serum CsA levels, calcium creatinine, and alkaline phosphatase were measured weekly. Significant decreases in serum calcium and alkaline phosphatase were observed at 1 and 2 weeks, and were normalized by 4 weeks of treatment. No significant changes in serum creatinine were noted. For all three doses of CsA, no effect was observed on the absolute rate of cortical bone resorption of three different, whole bones over three time periods. Body weight and bone formation in treated animals was significantly smaller in a dose- and time-related fashion compared with control animals at sacrifice. However, compared with the initial control animals, body weights and bone masses of the final treated animals were much larger, suggesting that the smaller bone masses were due to insufficient growth and slow gain in bone mass.(ABSTRACT TRUNCATED AT 250 WORDS)

Transplantation immunology

A major function of the immune response is the discrimination of self from nonself. It is this response that must be overcome in transplant rejection. Progress in understanding these basic immune mechanisms has helped to improve clinical outcome and lays the foundation for a new generation of therapies.

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Renal effects of rapamycin in the spontaneously hypertensive rat

The effects of rapamycin (RAPA), administered at therapeutic doses, were investigated in the spontaneously hypertensive rat (SHR). Additionally, the reversibility of RAPA's renal effects was investigated at a supratherapeutic dose. At doses that were active in preventing heart and kidney allograft rejection in the rat (0.01-0.08 mg/kg i.v.), RAPA had no effect on kidney function or rat body weight gain. At higher doses (0.8 mg/kg), RAPA produced significant changes in kidney function parameters and caused a loss in body weight. Histopathologic changes, including necrotizing vasculopathy and tubular atrophy, were noted at therapeutic doses. The effects of RAPA on kidney function were completely reversible after a 2-week washout period, though the histopathologic changes were still evident. These studies demonstrate that RAPA does not impair kidney function at therapeutic doses when administered for 2 weeks but does appear to accelerate the naturally occurring renal lesions of the SHR.

Dose-dependent pharmacokinetics of rapamycin-28-N,N-dimethylglycinate in the mouse

Rapamycin-28-N,N-dimethylglycinate methanesulfonate salt (RG), synthesized as a potential water-soluble prodrug to facilitate parenteral administration of the antineoplastic macrolide rapamycin (RA), is active against intracranially implanted human glioma in mice. Preclinical pharmacokinetic studies to evaluate the prodrug were conducted in male CD2F1 mice treated with 10, 25, 50 and 100 mg/kg doses of RG by rapid i.v. injection. The plasma concentration of RG decayed in a distinctly triphasic manner following treatment with the 100 mg/kg dose; however, prodrug disposition was apparent biexponential at each of the lower doses. RG exhibited dose-dependent pharmacokinetics, characterized by an increase in the total plasma clearance from 12.5 to 39.3 ml.min-1.kg-1 for dosage escalations in the range 10-50 mg/kg, while clearance values at doses of 50 and 100 mg/kg were similar. The terminal rate constants decreased linearly as the dose was increased from 10 to 100 mg/kg, eliciting an apparent prolongation of the biological half-life from 2.1 to 4.8 h. There was also a sequential increase in the steady state apparent volume of distribution from 1.73 to 8.75 l/kg. These observations are consistent with saturable binding of RG to plasma proteins while binding to tissue remains linear. Nevertheless, conversion to RA appeared to represent a prominent route of RG elimination. The molar plasma concentration of RA exceeded that of the prodrug within 30-90 min after i.v. treatment and declined very slowly thereafter, with plasma levels sustained between 0.1 and 10 microM for 48 h at each of the doses evaluated. Thus, RG effectively served as a slow release delivery system for RA, implying the possibility of maintaining therapeutic plasma levels of the drug from a more convenient dosing regimen than a continuous infusion schedule. The present findings, coupled with the demonstrated in vivo activity of RG against human brain tumor models, warrant its continued development as a much needed chemotherapeutic agent for the treatment of brain neoplasms.

Small bowel transplantation: an overview

Small bowel transplantation (SBT) would, in theory, be the treatment of choice for patients suffering from the short bowel syndrome. Although SBT has been done with a considerable degree of success in some centers [36, 145], it is by no means an established or widely applicable therapy for those with short bowel syndrome. The small bowel is unique among vascularized organ grafts because it not only elicits a vigorous rejection reaction but is also capable of inducing graft-versus-host disease (GVHD). Rejection of the graft does not only lead to loss of function but also to bacterial translocation. The risk of fatal sepsis is aggravated by the immunosuppression given to prevent rejection. Here, the history of SBT is described, and recent developments in experimental and clinical SBT, as well as future prospects for this theoretically optimal treatment modality for patients dependent on total parenteral nutrition (TPN) for life, are outlined.

Inhibition by rapamycin of leukocyte migration and bronchial hyperreactivity induced by injection of Sephadex beads to guinea-pigs

1. The effect of rapamycin (0.001 to 5 mg kg-1) on the increased leukocyte counts in bronchoalveolar lavage (BAL) fluid and hyperreactivity of isolated bronchial strips to histamine and acetylcholine (ACh) was studied following the intravenous injection of Sephadex beads to guinea-pigs. 2. The intramuscular (i.m.) injection of rapamycin (0.012 to 5 mg kg-1) dose-dependently inhibited the increase in leukocyte counts in BAL fluid. Rapamycin (5 mg kg-1) reduced the numbers of eosinophils neutrophils, macrophages and lymphocytes in BAL fluid by 64, 55, 19 and 50% respectively. In addition, rapamycin (0.012 to 5 mg kg-1) significantly inhibited the Sephadex-induced hyperreactivity of bronchial tissue to both histamine and ACh. 3. At a dose of 0.001 mg kg-1, rapamycin did not significantly reduce leukocyte infiltration or bronchial hyperreactivity. 4. Cyclosporin (5 mg kg-1) significantly reduced both lymphocyte and eosinophil numbers in BAL fluid of Sephadex-injected guinea-pigs whereas dexamethasone (1 mg kg-1) significantly reduced lymphocyte numbers. Neither drug affected the bronchial hyperreactivity to histamine and ACh. 5. It is concluded that the new immunosuppressive drug, rapamycin, is a potent inhibitor of leukocyte migration and bronchial hyperreactivity observed following the intravenous injection of Sephadex beads to guinea-pigs. Rapamycin also appears to be more effective than cyclosporin or dexamethasone in reducing leukocyte counts and bronchial hyperreactivity in this model. 6. Our results suggest that inflammatory mechanisms which are inhibited by rapamycin may be important in the induction of Sephadex-induced hyperreactivity.

Immunosuppressant FK506 enhances phosphorylation of nitric oxide synthase and protects against glutamate neurotoxicity

Immunosuppressants FK506 and cyclosporin A inhibit neurotoxicity of N-methyl-D-aspartate in primary cortical cultures, while having no effect on quisqualate- and kainate-mediated neurotoxicity. Rapamycin completely reverses the neuroprotective effect of FK506. Both FK506 and cyclosporin A inhibit NMDA-elicited/nitric oxide-mediated increases in cGMP levels in cortical cultures. FK506 has no effect on sodium nitroprusside-induced increases in cGMP. In a stably transfected human kidney 293 cell line overexpressing the gene encoding nitric oxide synthase [L-arginine, NADPH:oxygen oxidoreductase (nitric oxide-forming), EC 1.14.13.39], FK506 inhibits the calcium ionophore A23187, stimulated increases in nitrite (a breakdown product of nitric oxide), and potentiates phorbol ester-mediated inhibition of nitrite formation. FK506-mediated inhibition of nitric oxide formation is completely reversed by rapamycin. Calcineurin dephosphorylates protein kinase C-mediated phosphorylation of nitric oxide synthase. FK506 prevents the calcineurin-mediated dephosphorylation of nitric oxide synthase and thereby diminishes the enzyme's catalytic activity. These data establish nitric oxide synthase as a calcineurin substrate. Nitric oxide synthase catalytic activity is regulated by the phosphorylation state of the enzyme. Enhanced phosphorylation of nitric oxide synthase diminishes catalytic activity, and dephosphorylation (through activation of calcineurin) enhances catalytic activity. The neuroprotective effect of FK506 and cyclosporin A presumably involves the inhibition of calcineurin, preventing the dephosphorylation of nitric oxide synthase and its subsequent activation.

Tacrolimus. A review of its pharmacology, and therapeutic potential in hepatic and renal transplantation

Tacrolimus (FK 506) is a macrolide immunosuppressant which possesses similar but more potent immunosuppressant properties compared with cyclosporin, inhibiting cell-mediated and humoral immune responses. Like cyclosporin, tacrolimus demonstrates considerable interindividual variation in its pharmacokinetic profile. This has caused difficulty in defining the optimum dosage regimen and has highlighted the usefulness of therapeutic drug monitoring. Most clinical studies with tacrolimus have neither been published in their entirety nor subjected to extensive peer review; there is also a paucity of published randomised investigations of tacrolimus versus cyclosporin, particularly in renal transplantation. Despite these drawbacks, tacrolimus has shown notable efficacy as a rescue or primary immunosuppressant therapy when combined with corticosteroids in adult and paediatric recipients following liver or kidney transplantation. Indeed, graft salvage rates in patients experiencing rejection or drug-related toxicity were > or = 50%, although data in renal transplantation are limited. Compared with cyclosporin as a primary immunosuppressant, tacrolimus showed comparable or greater patient/graft survival rates in liver allograft recipients (where cost savings associated with reduced hospitalisation costs were evident in one study), and comparable patient/graft survival in patients following kidney transplantation. Worthy of note was the efficacy of tacrolimus as a primary immunosuppressant in patients who received en bloc kidney allografts. The incidence of rejection was largely reduced following rescue therapy with tacrolimus and was generally lower (notably for refractory rejection) than that observed for cyclosporin, at least in liver allograft recipients. This was reflected in less need for adjunct immunotherapy including antilymphocyte preparations for the treatment of rejection episodes. The potential for reduction or withdrawal of corticosteroid therapy with tacrolimus appears to be a distinct advantage compared with cyclosporin, and this may be enhanced by the reduced incidence of infectious complications and of hypertension and hypercholesterolaemia reported by some investigators. In other respects, however, the tolerability profile of tacrolimus appears to be broadly similar to that of cyclosporin. Against this background, preliminary data indicate that tacrolimus provides a valuable therapeutic alternative to retransplantation in patients experiencing liver or kidney graft rejection or drug-related toxicity. Pending confirmation of initial randomised studies and preliminary results from large randomised investigations, tacrolimus may well be considered as an alternative primary immunosuppressant to cyclosporin in hepatic (particularly) and renal transplantation. Furthermore, the steroid-sparing effects of tacrolimus, although of benefit to all patient groups, may prove to be of particular worth in children and in en bloc kidney recipients. In these patients tacrolimus may well emerge as the drug of choice.(ABSTRACT TRUNCATED AT 400 WORDS)

Partial inhibition of human neutrophil activation by FK-506 at supratherapeutic concentrations

The macrolide, FK-506, is a potent and effective inhibitor of lymphocyte activation. We studied the effects of FK-506 on human neutrophil activation induced by chemoattractants and by various substances which circumvent receptor stimulation. After preincubation for 5 min at 37 degrees C, FK-506 (1 microM) inhibited N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe)- or platelet-activating factor-induced superoxide production in neutrophils by about 30%. At therapeutic concentrations (0.1-1 nM) FK-506 was ineffective. FK-506 did not inhibit exocytosis and rises in cytosolic Ca2+ concentration [Ca2+]i mediated by these stimuli, and it did not at all inhibit neutrophil activation induced by C5a, leukotriene B4 and 4 beta-phorbol 12-myristate 13-acetate. FK-506 (1 microM) inhibited A23187-induced exocytosis by about 35%, but A23187-induced superoxide production was unaffected. After preincubation for 5 min at 37 degrees C, FK-506 inhibited fMet-Leu-Phe-induced superoxide production in dibutyryl cAMP-differentiated HL-60 cells by about 20%; preincubation with the drug for 24 h did not result in inhibition of superoxide production. FK-506 did not inhibit agonist-binding to formyl peptide receptors and fMet-Leu-Phe-stimulated GTP hydrolysis of heterotrimeric regulatory guanine nucleotide-binding proteins (G-proteins) in membranes from dibutyryl cAMP-differentiated HL-60 cells. FK-506 did not change steady-state and differential polarized phase fluorescence in HL-60 membranes using 1,6-diphenylhexa-1,3,5-triene and 12-(9-anthroyloxy)-stearate as probes. Our results show that FK-506 at supratherapeutic concentrations partially inhibits neutrophil activation. Inhibition by FK-506 of fMet-Leu-Phe-induced superoxide production is rapid in onset and is not due to inhibition of agonist-binding to receptors, interference with G-proteins or protein kinase C, reduction of rises in [Ca2+]i or alteration in physical membrane state.