Therapeutic potential of Janus kinase 3 (JAK3) inhibitors.

Here we discuss the therapeutic potential of Janus kinase 3 (JAK3) inhibitors as a new class of immunomodulatory agents with immunosuppressive, anti-inflammatory, anti-allergic, anti-thrombotic and anti-leukemic properties. JAKs are abundantly expressed in primary leukemic cells from children with ALL (acute lymphoblastic leukemia) and are crucial for signals regulating apoptosis. Additional roles for JAK3 in mast cell-mediated immediate hypersensitivity reactions, autoimmune disorders and platelet function have recently been described. The preclinical studies on JAK3 inhibitors revealed their clinical potential as anti-leukemic agents with anti-thrombotic, anti-allergic and immunosuppressive properties. Results from multiple preclinical experimental model systems of autoimmune diabetes, pancreatic islet transplantation, solid organ transplantation, allergy, thrombosis and bone marrow transplantation are discussed in the context of the clinical need for new immunomodulatory agents with such properties.

Structure, chromosomal localization, and expression of the gene for mouse ecto-mono(ADP-ribosyl)transferase ART5.

Mono(ADP-ribosyl)transferases regulate the function of target proteins by attaching ADP-ribose to specific amino acid residues in their target proteins. The purpose of this study was to determine the structure, chromosomal localization, and expression profile of the gene for mouse ecto-ADP-ribosyltransferase ART5. Southern blot analyses indicate that Art5 is a single copy gene which maps to mouse chromosome 7 at offset 49.6 cM in close proximity to the Art1, Art2a and Art2b genes. Northern blot and RT-PCR analyses demonstrate prominent expression of Art5 in testis, and lower levels in cardiac and skeletal muscle. Sequence analyses reveal that the Art5 gene encompasses six exons spanning 8 kb of genomic DNA. The 5' end of the Art5 gene overlaps with that of the Art1 gene. A single long exon encodes the predicted ART5 catalytic domain. Separate exons encode the N-terminal leader peptide and a hydrophilic C-terminal extension. Sequencing of RT-PCR products and ESTs identified six splice variants. The deduced amino acid sequence of ART5 shows 87% sequence identity to its orthologue from the human, and 37 and 32% identity to its murine paralogues ART1 and ART2. Unlike ART1 and ART2, ART5 lacks a glycosylphosphatidylinositol-anchor signal sequence and is predicted to be a secretory enzyme. This prediction was confirmed by transfecting an Art5 cDNA expression construct into Sf9 insect cells. The secreted epitope-tagged ART5 protein resembled rat ART2 in exhibiting potent NAD-glycohydrolase activity. This study provides important experimental tools to further elucidate the function of ART5.

Targeting Janus kinase 3 to attenuate the severity of acute graft-versus-host disease across the major histocompatibility barrier in mice.

To prevent the development of acute graft-versus-host disease (GVHD) in lethally irradiated C57BL/6 (H-2b) recipient mice transplanted with bone marrow-splenocyte grafts from major histocompatibility complex (MHC) disparate BALB/c mice (H-2d), recipient mice were treated with the rationally designed JAK3 inhibitor WHI-P131 [4-(4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline] (20 mg/kg, 3 times a day [tid]) daily from the day of bone marrow transplantation (BMT) until the end of the 85-day observation period. Total body irradiation (TBI)-conditioned, vehicle-treated control C57BL/6 mice (n = 38) receiving bone marrow-splenocyte grafts from BALB/c mice survived acute TBI toxicity, but they all developed histologically confirmed severe multi-organ GVHD and died after a median survival time of 37 days. WHI-P131 treatment (20 mg/kg intraperitoneally, tid) prolonged the median survival time of the BMT recipients to 56 days. The probability of survival at 2 months after BMT was 11% +/- 5% for vehicle-treated control mice (n = 38) and 41% +/- 9% for mice treated with WHI-P131 (n = 32) (P <.0001). Notably, the combination regimen WHI-P131 plus the standard anti-GVHD drug methotrexate (MTX) (10 mg/m2 per day) was more effective than WHI-P131 or MTX alone. More than half the C57BL/6 recipients receiving this most effective GVHD prophylaxis remained alive and healthy throughout the 85-day observation period, with a cumulative survival probability of 70% +/- 10%. Taken together, these results indicate that targeting JAK3 in alloreactive donor lymphocytes with a chemical inhibitor such as WHI-P131 may attenuate the severity of GVHD after BMT.

Neonatal pancreas transplantation and liver enzyme activities in diabetic mice.

The aim of this study was to estimate the influence of transplantation of neonatal pancreas from singenic donors on glucose production and utilisation in alloxan diabetic mice. The alloxan diabetic mice, 20 days after alloxan, received neonatal pancreas from singenic donors under the kidney capsule. Enzymes involved in glycolytic, gluconeogenic, lipogenic and pentose phosphate pathway were examined in liver of experimental mice. The fructose-1, 6-diphosphatase (FDPase) activity in the liver of diabetics increased for about 60%, while the pyruvate inase (PK) and ATP-citrate lyase (CEE) activity decreased for about 40% of the values in the healthy mice. The values of glucose-6-phosphate dehydrogenase (G6P-DH) and 6-phosphogluconate dehydrogenase (6-PGDH) were not statistically different in diabetic liver compared with the liver off healthy animals. After pancreas transplantation some of diabetic animals become normoglycaemic, while the others remained hyperglycaemic. The FDPase activity in hyperglycaemic diabetic recipients was similar to those in diabetic mice that did not received transplant, while in normoglycaemic recipients the FDPase activity returned to the normal values. However, the activities of PK and CCE in hyperglycaemic recipients were similar to those in healthy animals, while in normogglycaemic recipients the enzyme activities were much higher. Results obtained showed that glycolytic, gluconeogenic and lipogenic enzyme activities in the liver of normoglycaemic mice that received pancreas transplant reached approximate the physiological values within 30 days after transplantation.

Differential protection in two transgenic lines of NOD/Lt mice hyperexpressing the autoantigen GAD65 in pancreatic beta-cells.

Although expressed at very low levels in islets of NOD mice, GAD65 is a candidate islet autoantigen. Two transgenic lines of NOD/Lt mice expressing high levels of human GAD65 from a rat insulin promoter were generated. Transgenes were integrated on proximal chromosome 15 of the A line and on the Y chromosome of the Y line. Transgenic A-line mice were obligate hemizygotes, since homozygous expression resulted in developmental lethality. A twofold higher level of hGAD65 transcripts in A-line islets from young donors was associated with higher GAD protein and enzyme activity levels. Y-line males developed diabetes at a similar rate and incidence as standard NOD/Lt males. In contrast, A-line mice of both sexes exhibited a markedly lowered incidence of diabetes. Insulitis, present in both transgenic lines, developed more slowly in A-line mice and correlated with a reduction in the ratio of gamma-interferon to interleukin-10 transcripts. Splenic leukocytes from young A-line donors transferred diabetes into NOD-scid recipients at a retarded rate compared with those from nontransgenic donors. Further, nontransgenic NOD T-cells transferred diabetes more slowly in NOD-scid recipients that were congenic for A-line transgenes as compared with standard NOD-scid recipients. Primed T-cell responses and spontaneous humoral reactivity to GAD65 failed to distinguish transgenic from nontransgenic mice. Quantitative differences in expression level or insertional mutagenesis are possible mechanisms of protection in the A line.

Retardation or acceleration of diabetes in NOD/Lt mice mediated by intrathymic administration of candidate beta-cell antigens.

A single injection of syngeneic islet cells into the thymus of 4-week-old NOD/Lt female mice strongly retards diabetogenesis. The present study used the intrathymic route of antigen administration to compare the relative efficacy of peptides/proteins derived from two major candidate pancreatic beta-cell autoantigens, insulin and GAD65, to modulate diabetogenesis. Intrathymic administration of insulin B chain or recombinant human GAD65 significantly suppressed diabetogenesis during a 20-week follow-up period, whereas no protection was mediated by either insulin A chain or a synthetic peptide (A2) derived from it. Quite unexpectedly, two GAD65-derived peptides near the COOH-terminus (p34 and p35) accelerated diabetes onset. Semiquantitative reverse transcription-polymerase chain reaction analysis was performed on cDNAs from isolated islets or whole pancreases of NOD/Lt females 4 weeks after intrathymic injections. Protection mediated by intrathymic administration with either intact islet cells or GAD65 were correlated with an upregulation of mRNA for T-helper 2 (Th2)-associated cytokines (interleukin [IL]-4, IL-10), concomitant with downregulation of Th1-associated interferon (IFN) transcripts (all normalized to T-cell receptor Cbeta transcripts) in islet-infiltrating lymphocytes. Protection mediated by the intrathymic administration of insulin B chain, however, correlated only with a modest upregulation of IL-4 and IL-10 transcript levels, and no diminution in IFN-gamma transcripts. In contrast, the diabetes-accelerating GAD65 p34 and p35 peptides were not associated with an immune deviation, expressing levels of IFN-gamma characteristic of islet-infiltrating lymphocytes in vehicle-injected NOD controls. Hence, Th1-to-Th2 immune deviation provides only a partial explanation for peptide immunotherapy of diabetes in NOD mice. The finding that certain peptides can accelerate rather than retard diabetogenesis as a function of route and age of administration adds a cautionary note to this type of therapy.

Mono(ADP-ribosyl)transferase genes and diabetes in NOD mice. Is there a relationship?

The answer to the question posed by the title (is there a relationship between aberrant Art gene expression and IDDM pathogenesis in NOD mice?) remains elusive. Conclusions are currently based almost entirely upon analysis of mRNA transcript levels rather than on T-cell-specific mono-ADP ribosylation activities. Our unpublished data, as well as data published in abstract form by Dr. L. Chatenoud and colleagues (48) indicate that gene transcription is not impaired in splenic leukocytes of older NOD mice, including those with spontaneous IDDM development. Based upon the limited data showing that there may be reduced expression of Art gene products in the earliest T cell immigrants from the NOD thymus, one would have to surmise that If there is a regulatory defect, it may be in allowing single positive thymic T cells to emigrate before they are fully mature. Therefore, development of anti-Art monoclonal antibody together with further studies regarding functions of mono(ADP-ribosyl)transferase in immunoregulation of different subpopulation of T-cells, may finally resolve the role that altered mono(ADP-ribosyl)transferase activities play in the pathogenesis of IDDM in NOD mice.

Quantitative thresholds of MHC class II I-E expressed on hemopoietically derived antigen-presenting cells in transgenic NOD/Lt mice determine level of diabetes resistance and indicate mechanism of protection.

Two homozygous lines of transgenic NOD/Lt mice expressing MHC class II I-E molecules at quantitatively different levels were utilized to study mechanisms of I-E-mediated diabetes prevention. In line 12, I-E expression on APC at levels comparable with that in BALB/cByJ controls conferred only partial diabetes resistance. In line 5, greater than normal I-E levels on APC correlated with nearly complete resistance. Levels of endogenously encoded I-Ag7 correlated inversely with transgene-induced I-E expression. T cell transfer experiments into NOD/severe combined immunodeficient mice demonstrated the presence of pathogenic T cells in I-E+ donors, and that continuous expression of I-E on hemopoietically derived APC was required to block their pathogenic function. T cells from transgenic and nontransgenic NOD/Lt mice primed in vivo against the beta cell autoantigen 65-kDa isoform of glutamic acid decarboxylase (GAD65) and two peptides derived from this protein proliferated when restimulated in vitro. However, reverse-transcription PCR and ELISA measurements of cytokine mRNA and protein levels showed that the GAD65-reactive T cells from both line 5 and line 12 mice produced higher levels of IL-4 and lower levels of IFN-gamma than similar T cells from standard NOD/Lt mice. Thus, the inverse relationship between I-E and I-Ag7 expression was associated with qualitative differences in T cell responses to putative beta cell autoantigens. Collectively, these data indicate quantitative increases in I-E expression on APC may block insulin-dependent diabetes mellitus by altering the balance of cytokines produced by beta cell autoreactive T cells.

TNF-alpha and IFN-gamma potentiate the deleterious effects of IL-1 beta on mouse pancreatic islets mainly via generation of nitric oxide.

Cytokines may be important mediators of beta-cell damage in early insulin-dependent diabetes mellitus. In order to further characterize the mechanism(s) of action of cytokines on insulin-producing cells, mouse pancreatic islets were exposed for 48 h to IL-1 beta, IFN-gamma or TNF-alpha, alone or in combinations. The three cytokines induced islet nitric oxide (NO) production, an effect most marked when islets were exposed to the three cytokines together. In parallel with NO production, IL-1 beta+IFN-gamma+TNF-alpha impaired islet function, as judged by decreased islet DNA and insulin content, decreased glucose metabolism and decreased glucose-induced insulin release. Aminoguanidine, an inhibitor of NO production, prevented all the above described suppressive effects of the cytokines, with exception of depletion in islet insulin content. In parallel experiments, insulin-producing RIN cells were exposed for 6 h to the same cytokines. Both IL-1 beta and TNF-alpha, but not IFN-gamma, induced NO production and expression of the mRNA encoding for the inducible form of the enzyme NO synthase (iNOS). These effects were most pronounced when combinations of IL-1 beta+IFN-gamma or IL-1 beta+IFN-gamma+TNF-alpha were used. As a whole, the data suggest that combinations of cytokines induce higher amounts of NO generation by mouse pancreatic islets than each of the cytokines isolated. An important source of islet NO production are probably the beta-cells, as pointed by data obtained with an insulinoma cell line. Most of the deleterious effects of the cytokines of mouse islets are prevented by blocking NO production, suggesting that NO is the main mediator of cytokine-induced beta-cell damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines suppress human islet function irrespective of their effects on nitric oxide generation.

Cytokines have been proposed as inducers of beta-cell damage in human insulin-dependent diabetes mellitus via the generation of nitric oxide (NO). This concept is mostly based on data obtained in rodent pancreatic islets using heterologous cytokine preparations. The present study examined whether exposure of human pancreatic islets to different cytokines induces NO and impairs beta-cell function. Islets from 30 human pancreata were exposed for 6-144 h to the following human recombinant cytokines, alone or in combination: IFN-gamma (1,000 U/ml), TNF-alpha (1,000 U/ml), IL-6 (25 U/ml), and IL-1 beta (50 U/ml). After 48 h, none of the cytokines alone increased islet nitrite production, but IFN-gamma induced a 20% decrease in glucose-induced insulin release. Combinations of cytokines, notably IL-1 beta plus IFN-gamma plus TNF-alpha, induced increased expression of inducible NO synthase mRNA after 6 h and resulted in a fivefold increase in medium nitrite accumulation after 48 h. These cytokines did not impair glucose metabolism or insulin release in response to 16.7 mM glucose, but there was an 80% decrease in islet insulin content. An exposure of 144 h to IL-1 beta plus IFN-gamma plus TNF-alpha increased NO production and decreased both glucose-induced insulin release and insulin content. Inhibitors of NO generation, aminoguanidine or NG-nitro-L-arginine, blocked this cytokine-induced NO generation, but did not prevent the suppressive effect of IL-1 beta plus IFN-gamma plus TNF-alpha on insulin release and content. In conclusion, isolated human islets are more resistant to the suppressive effects of cytokines and NO than isolated rodent islets. Moreover, the present study suggests that NO is not the major mediator of cytokine effects on human islets.

Irreversible loss of normal beta-cell regulation by glucose in neonatally streptozotocin diabetic rats.

Animals with NIDDM display abnormal glucose regulation of insulin secretion and biosynthesis. We tested reversibility of abnormal regulation by normoglycaemia using an islet transplantation technique. Inbred non-diabetic and neonatally STZ diabetic rats (n-STZ) were used. Transplantations insufficient to normalize the blood glucose levels (200 islets under kidney capsule) were performed from diabetic to normal (D-N) and from diabetic to diabetic (D-D), as well as from normal to normal (N-N) and from normal to diabetic (N-D) rats. Four weeks after transplantation, graft bearing kidneys were isolated and perfused with Krebs-Henseleit bicarbonate buffer to measure insulin secretion in response to 27.8 mmol/l glucose and 10 mmol/l arginine. Four weeks of normoglycaemia failed to restore glucose-induced insulin secretion from n-STZ islets (glucose induced increment: -1.7 +/- 2.5 fmol/min in D-N, 1.2 +/- 7.1 fmol/min in D-D). In contrast to normal islets, normoglycaemia reduced insulin mRNA contents (60 +/- 24 in D-N, 496 +/- 119 in D-D; O.D.-arbitrary units). However, arginine-induced secretion was markedly enhanced by diabetic environment in both normal and n-STZ islet grafts. These results indicate that selected aspects of glucose recognition are irreversibly damaged by a long-term diabetic state or, alternatively, by a lasting effect of STZ administration.

Nicotinamide and dexamethasone inhibit interleukin-1-induced nitric oxide production by RINm5F cells without decreasing messenger ribonucleic acid expression for nitric oxide synthase.

Nitric oxide (NO) generation may be a final common pathway for beta-cell damage in early insulin-dependent diabetes mellitus. Insulin-producing cells express an inducible form of NO synthase (iNOS), which is similar to that observed in activated macrophages. Induction of iNOS mRNA in these cells depends on protein synthesis. To further characterize the regulation of iNOS induction in insulin-producing cells, RINm5F cells (RIN cells) were exposed for 6 h to human recombinant interleukin-1 beta (rIL-1 beta; 1 ng/ml) alone or in combination with either nicotinamide (10, 20, or 50 mM) or dexamethasone (1 or 5 microM). These agents have been previously shown to prevent activation of iNOS in macrophages, fibroblasts, and hepatocytes. rIL-1 beta induced the expression of iNOS mRNA in RIN cells and a 12- to 13-fold increase in medium nitrite accumulation, the latter indicating NO production. Nicotinamide decreased nitrite production in a dose-dependent way. Thus, 10 mM nicotinamide decreased rIL-1 beta-induced nitrite formation by 30%, 20 mM by 60%, and 50 mM by 90%. The highest concentration of nicotinamide also prevented rIL-1 beta-induced iNOS mRNA, an effect associated with inhibition of total protein biosynthesis. However, 10 or 20 mM nicotinamide did not modify rIL-1 beta-induced iNOS mRNA expression or inhibit protein biosynthesis. Dexamethasone also decreased rIL-1 beta-induced nitrite production without affecting iNOS mRNA expression. As a whole, these data suggest that both nicotinamide and dexamethasone may prevent NO accumulation in insulin-producing cells by posttranscriptional mechanisms. It is also possible that these drugs induce direct inhibition of iNOS enzymatic activity and/or scavenge NO. Higher concentrations of nicotinamide might also inhibit iNOS mRNA expression, possibly by blocking protein biosynthesis.