Validation of a de-immunization strategy for monoclonal antibodies using cynomolgus macaque as a surrogate for human.

The immunogenicity of biotherapeutics presents a major challenge during the clinical development of new protein drugs including monoclonal antibodies. To address this, multiple humanization and de-immunization techniques that employ in silico algorithms and in vitro test systems have been proposed and implemented. However, the success of these approaches has been variable and to date, the ability of these techniques to predict immunogenicity has not been systematically tested in humans or other primates. This study tested whether antibody humanization and de-immunization strategies reduce the risk of anti-drug antibody (ADA) development using cynomolgus macaque as a surrogate for human. First human-cyno chimeric antibodies were constructed by grafting the variable domains of the adalimumab and golimumab monoclonal antibodies onto cynomolgus macaque IgG1 and Igκ constant domains followed by framework germlining to cyno to reduce the xenogenic content. Next, B and T cell epitopes and aggregation-prone regions were identified using common in silico methods to select domains with an ADA risk for additional modification. The resultant engineered antibodies had a comparable affinity for TNFα, demonstrated similar biophysical properties, and exhibited significantly reduced ADA levels in cynomolgus macaque compared with the parental antibodies, with a corresponding improvement in the pharmacokinetic profile. Notably, plasma concentrations of the engineered antibodies were quantifiable through 504 hours (chimeric) and 840 hours (germlined/de-immunized), compared with only 336 hours (adalimumab) or 336-672 hours (golimumab). The results point to the significant value in the investment in these engineering strategies as an important guide for monoclonal antibody optimization that can contribute to improved clinical outcomes.

Correlation between antidrug antibodies, pre-existing antidrug reactivity, and immunogenetics (MHC class II alleles) in cynomolgus macaque.

Immunogenicity of biomolecules is one of the largest concerns in biological therapeutic drug development. Adverse immune responses as a result of immunogenicity to biotherapeutics range from mild hypersensitivity reactions to potentially life-threatening anaphylactic reactions and can negatively impact human health and drug efficacy. Numerous confounding patient-, product- or treatment-related factors can influence the development of an immune reaction against therapeutic proteins. The goal of this study was to investigate the relationship between pre-existing drug reactivity (PE-ADA), individual immunogenetics (MHC class II haplotypes), and development of treatment-induced antidrug antibodies (TE-ADA) in cynomolgus macaque. PE-ADA refers to the presence of antibodies immunoreactive against the biotherapeutic in treatment-naïve individuals. We observed that PE-ADA frequency against four different bispecific antibodies in naïve cynomolgus macaque is similar to that reported in humans. Additionally, we report a trend towards an increased incidence of TE-ADA development in macaques with high PE-ADA levels. In order to explore the relationship between MHC class II alleles and risk of ADA development, we obtained full-length MHC class II sequences from 60 cynomolgus macaques in our colony. We identified a total of 248 DR, DP, and DQ alleles and 236 unique haplotypes in our cohort indicating a genetically complex set of animals potentially reflective of the human population. Based on our observations, we propose the evaluation of the magnitude/frequency of pre-existing reactivity and consideration of MHC class II genetics as additional useful tools to understand the immunogenic potential of biotherapeutics.

Peripheral and central nervous system distribution of the CGRP neutralizing antibody [125I] galcanezumab in male rats.

OBJECTIVE: The objective of this investigation was to examine the distribution of galcanezumab and a control immunoglobulin 4 antibody containing the same constant regions as galcanezumab, into peripheral and central tissues. METHODS: Galcanezumab and a control immunoglobulin 4 antibody were radioiodinated with Iodine-125 to specific activities of 0.11 mCi/mg and 0.16 mCi/mg, respectively. At 24, 72, and 168 hours following subcutaneous injection of either antibody (4 mg/kg), cerebrospinal fluid and plasma were obtained followed by saline perfusion to remove residual blood and collection of selected tissues for determination of Iodine-125 content by gamma counting. RESULTS: The peak plasma levels of Iodine-125 galcanezumab and Iodine-125 control immunoglobulin 4 were observed at 72 hours and remained high at 168 hours post-dose. The rank order of tissue levels was dura mater = spleen > trigeminal ganglia ≫hypothalamus = spinal cord = prefrontal cortex = cerebellum. Iodine-125 galcanezumab levels in peripheral tissue (dura mater, spleen, and trigeminal ganglia) averaged 5% to 11% of plasma, whereas all of the central nervous system (CNS) tissue levels and the cerebrospinal fluid levels were < 0.4% of plasma. Distribution of the antibodies into the dura mater and the trigeminal ganglia was similar to that observed in the spleen and significantly greater than exposure in the brain or spinal cord. CONCLUSIONS: The central levels of galcanezumab were relatively low, which would favor the dura mater and trigeminal ganglia as sites of action for its observed clinical efficacy. However, a central site of action cannot be excluded.

A Modeling and Experimental Investigation of the Effects of Antigen Density, Binding Affinity, and Antigen Expression Ratio on Bispecific Antibody Binding to Cell Surface Targets.

Despite the increasing number of multivalent antibodies, bispecific antibodies, fusion proteins, and targeted nanoparticles that have been generated and studied, the mechanism of multivalent binding to cell surface targets is not well understood. Here, we describe a conceptual and mathematical model of multivalent antibody binding to cell surface antigens. Our model predicts that properties beyond 1:1 antibody:antigen affinity to target antigens have a strong influence on multivalent binding. Predicted crucial properties include the structure and flexibility of the antibody construct, the target antigen(s) and binding epitope(s), and the density of antigens on the cell surface. For bispecific antibodies, the ratio of the expression levels of the two target antigens is predicted to be critical to target binding, particularly for the lower expressed of the antigens. Using bispecific antibodies of different valencies to cell surface antigens including MET and EGF receptor, we have experimentally validated our modeling approach and its predictions and observed several nonintuitive effects of avidity related to antigen density, target ratio, and antibody affinity. In some biological circumstances, the effect we have predicted and measured varied from the monovalent binding interaction by several orders of magnitude. Moreover, our mathematical framework affords us a mechanistic interpretation of our observations and suggests strategies to achieve the desired antibody-antigen binding goals. These mechanistic insights have implications in antibody engineering and structure/activity relationship determination in a variety of biological contexts.

Proteolytic cleavage of antigen extends the durability of an anti-PCSK9 monoclonal antibody.

Lilly PCSK9 antibody LY3015014 (LY) is a monoclonal antibody (mAb) that neutralizes proprotein convertase subtilisin-kexin type 9 (PCSK9). LY decreases LDL cholesterol in monkeys and, unlike other PCSK9 mAbs, does not cause an accumulation of intact PCSK9 in serum. Comparing the epitope of LY with other clinically tested PCSK9 mAbs, it was noted that the LY epitope excludes the furin cleavage site in PCSK9, whereas other mAbs span this site. In vitro exposure of PCSK9 to furin resulted in degradation of PCSK9 bound to LY, whereas cleavage was blocked by other mAbs. These other mAbs caused a significant accumulation of serum PCSK9 and displayed a shorter duration of LDL-cholesterol lowering than LY when administered to mice expressing the WT human PCSK9. In mice expressing a noncleavable variant of human PCSK9, LY behaved like a cleavage-blocking mAb, in that it caused significant PCSK9 accumulation, its duration of LDL lowering was reduced, and its clearance (CL) from serum was accelerated. Thus, LY neutralizes PCSK9 and allows its proteolytic degradation to proceed, which limits PCSK9 accumulation, reduces the CL rate of LY, and extends its duration of action. PCSK9 mAbs with this property are likely to achieve longer durability and require lower doses than mAbs that cause antigen to accumulate.

Translational Pharmacodynamics of Calcitonin Gene-Related Peptide Monoclonal Antibody LY2951742 in a Capsaicin-Induced Dermal Blood Flow Model.

LY2951742, a monoclonal antibody targeting calcitonin gene-related peptide (CGRP), is being developed for migraine prevention and osteoarthritis pain. To support the clinical development of LY2951742, capsaicin-induced dermal blood flow (DBF) was used as a target engagement biomarker to assess CGRP activity in nonhuman primates and healthy volunteers. Inhibition of capsaicin-induced DBF in nonhuman primates, measured with laser Doppler imaging, was dose dependent and sustained for at least 29 days after a single intravenous injection of the CGRP antibody. This information was used to generate a pharmacokinetic/pharmacodynamic model, which correctly predicted inhibition of capsaicin-induced DBF in humans starting at a single subcutaneous 5-mg dose. As expected, the degree of inhibition in capsaicin-induced DBF increased with higher LY2951742 plasma concentrations. Utilization of this pharmacodynamic biomarker with pharmacokinetic data collected in phase I studies provided the dose-response relationship that assisted in dose selection for the phase II clinical development of LY2951742.

Disposition of Basal Insulin Peglispro Compared with 20-kDa Polyethylene Glycol in Rats Following a Single Intravenous or Subcutaneous Dose.

Basal insulin peglispro (BIL) comprises insulin lispro covalently bound to a 20-kDa polyethylene glycol (PEG) at lysine B28. The biologic fate of BIL and unconjugated PEG were examined in rats given a single 0.5-mg/kg i.v. or 2-mg/kg s.c. dose of BIL with (14)C label in 20-kDa PEG or (125)I label in lispro. Unconjugated (14)C-labeled 20-kDa PEG was dosed at 10 mg/kg i.v. or s.c. Blood, urine, and feces were collected up to 336 hours after dosing. Radioactivity was measured by scintillation spectrometry, and BIL was quantitated by enzyme-linked immunosorbent assay. Area under the curve and half-life for immunoreactive BIL were lower than those for both (14)C and (125)I after subcutaneous and intravenous administration. The half-lives of (14)C after BIL and PEG dosing were similar. The clearance of immunoreactive BIL was 2.4-fold faster than that of (14)C and 1.6-fold faster than (125)I. After a subcutaneous dose of BIL, immunoreactive BIL accounted for 31% of the circulating (125)I and 16% of the circulating (14)C, indicating extensive catabolism of BIL. Subcutaneous bioavailability of BIL was 23%-29%; bioavailability for unconjugated PEG was 78%. For unconjugated PEG, most of the (14)C dose was recovered in urine. For BIL, ≥86% of (125)I was eliminated in urine and (14)C was eliminated about equally in urine and feces. The major (14)C-labeled catabolism product of BIL in urine was 20-kDa PEG with lysine attached. The attachment of 20-kDa PEG to lispro in BIL led to a different elimination pathway for PEG compared with unconjugated 20-kDa PEG.

Hypoxia induced downregulation of hepcidin is mediated by platelet derived growth factor BB.

OBJECTIVE: Hypoxia affects body iron homeostasis; however, the underlying mechanisms are incompletely understood. DESIGN: Using a standardised hypoxia chamber, 23 healthy volunteers were subjected to hypoxic conditions, equivalent to an altitude of 5600 m, for 6 h. Subsequent experiments were performed in C57BL/6 mice, CREB-H knockout mice, primary hepatocytes and HepG2 cells. RESULTS: Exposure of subjects to hypoxia resulted in a significant decrease of serum levels of the master regulator of iron homeostasis hepcidin and elevated concentrations of platelet derived growth factor (PDGF)-BB. Using correlation analysis, we identified PDGF-BB to be associated with hypoxia mediated hepcidin repression in humans. We then exposed mice to hypoxia using a standardised chamber and observed downregulation of hepatic hepcidin mRNA expression that was paralleled by elevated serum PDGF-BB protein concentrations and higher serum iron levels as compared with mice housed under normoxic conditions. PDGF-BB treatment in vitro and in vivo resulted in suppression of both steady state and BMP6 inducible hepcidin expression. Mechanistically, PDGF-BB inhibits hepcidin transcription by downregulating the protein expression of the transcription factors CREB and CREB-H, and pharmacological blockade or genetic ablation of these pathways abrogated the effects of PDGF-BB toward hepcidin expression. CONCLUSIONS: Hypoxia decreases hepatic hepcidin expression by a novel regulatory pathway exerted via PDGF-BB, leading to increased availability of circulating iron that can be used for erythropoiesis.

Application of FcRn binding assays to guide mAb development.

Monoclonal antibodies (mAbs) represent an important class of therapeutic modalities. To optimize their pharmaceutical properties, studies have focused on improving mAb pharmacokinetic/pharmacodynamic profiles by modulating their interactions with the neonatal Fc receptor (FcRn). The influence of both the chemical and physical properties of IgGs has been examined in the context of FcRn interactions. In this regard, a variety of FcRn binding assays and tools have been developed and used to characterize the interaction with IgGs. However, a predictive relationship between the FcRn binding interaction of IgGs in vitro and their pharmacokinetics in vivo broadly across mAbs remains elusive. Many studies have increasingly suggested that the interplay between the characteristics of the mAb and the nature of its target can influence disposition and elimination. Thus, it is becoming increasingly evident that along with FcRn interactions, consideration of the non-FcRn-based biologic processes active in mAb disposition should be integrated into mAb development and optimization. Herein, we describe how the pharmacokinetics of mAbs can be modulated through FcRn interactions and provide perspectives on interpreting the receptor binding parameters in relation to other mechanisms involved in antibody disposition to aid in guiding mAb development.

Identification of a common variant in the TFR2 gene implicated in the physiological regulation of serum iron levels.

The genetic determinants of variation in iron status are actively sought, but remain incompletely understood. Meta-analysis of two genome-wide association (GWA) studies and replication in three independent cohorts was performed to identify genetic loci associated in the general population with serum levels of iron and markers of iron status, including transferrin, ferritin, soluble transferrin receptor (sTfR) and sTfR-ferritin index. We identified and replicated a novel association of a common variant in the type-2 transferrin receptor (TFR2) gene with iron levels, with effect sizes highly consistent across samples. In addition, we identified and replicated an association between the HFE locus and ferritin and confirmed previously reported associations with the TF, TMPRSS6 and HFE genes. The five replicated variants were tested for association with expression levels of the corresponding genes in a publicly available data set of human liver samples, and nominally statistically significant expression differences by genotype were observed for all genes, although only rs3811647 in the TF gene survived the Bonferroni correction for multiple testing. In addition, we measured for the first time the effects of the common variant in TMPRSS6, rs4820268, on hepcidin mRNA in peripheral blood (n = 83 individuals) and on hepcidin levels in urine (n = 529) and observed an association in the same direction, though only borderline significant. These functional findings require confirmation in further studies with larger sample sizes, but they suggest that common variants in TMPRSS6 could modify the hepcidin-iron feedback loop in clinically unaffected individuals, thus making them more susceptible to imbalances of iron homeostasis.

A decoy receptor 3 analogue reduces localised defects in phagocyte function in pneumococcal pneumonia.

BACKGROUND: Therapeutic strategies to modulate the host response to bacterial pneumonia are needed to improve outcomes during community-acquired pneumonia. This study used mice with impaired Fas signalling to examine susceptibility to pneumococcal pneumonia and decoy receptor 3 analogue (DcR3-a) to correct factors associated with increased susceptibility. METHODS: Wild-type mice and those with varying degrees of impairment of Fas (lpr) or Fas ligand signalling (gld) were challenged with Streptococcus pneumoniae and microbiological and immunological outcomes measured in the presence or absence of DcR3-a. RESULTS: During established pneumonia, neutrophils became the predominant cell in the airway and gld mice were less able to clear bacteria from the lungs, demonstrating localised impairment of pulmonary neutrophil function in comparison to lpr or wild-type mice. T-cells from gld mice had enhanced activation and reduced apoptosis in comparison to wild-type and lpr mice during established pneumonia. Treatment with DcR3-a reduced T-cell activation and corrected the defect in pulmonary bacterial clearance in gld mice. CONCLUSIONS: The results suggest that imbalance in tumour necrosis factor superfamily signalling and excessive T-cell activation can impair bacterial clearance in the lung but that DcR3-a treatment can reduce T-cell activation, restore optimal pulmonary neutrophil function and enhance bacterial clearance during S pneumoniae infection.

FcRn affinity-pharmacokinetic relationship of five human IgG4 antibodies engineered for improved in vitro FcRn binding properties in cynomolgus monkeys.

The pH-dependent binding of IgGs to the neonatal Fc receptor (FcRn) plays a critical role in regulating IgG homeostasis in vivo. Enhancing interactions between Fc and FcRn via protein engineering has been successfully used as an approach for improving the pharmacokinetics of monoclonal antibodies (mAbs). Although the quantitative translatability of the in vitro FcRn affinity enhancement to an in vivo pharmacokinetic benefit has been supported by several studies, there are also published reports indicating a disconnect in this relation. The body of literature suggests there are likely additional biochemical and biophysical properties of the mAbs along with their FcRn affinity that influence the in vivo pharmacokinetics. Herein, we more broadly evaluate the in vitro Fc-FcRn interactions and biochemical properties of five humanized IgG4 antibodies each with two Fc variant sequences (T250Q/M428L and V308P) and their corresponding pharmacokinetics in cynomolgus monkeys. Our findings indicate that the FcRn affinity-pharmacokinetic relationship does not show a direct correlation either across different IgGs or between the two variant sequences within a platform. Other parameters that have been suggested to contribute to mAb pharmacokinetic properties, such as the pH-dependent dissociation of the FcRn-IgG complexes, mAb biophysical properties, and nonspecific/charge binding characteristics of the mAbs, also did not independently explain the differing pharmacokinetic behaviors. Our results suggest that there is likely not a single in vitro parameter that readily predicts in vivo pharmacokinetics, but that the relative contribution and interplay of several factors along with the FcRn binding affinity are important determinants of mAb pharmacokinetic properties.

Regulation of iron homeostasis in anemia of chronic disease and iron deficiency anemia: diagnostic and therapeutic implications.

The anemia of chronic disease (ACD) is characterized by macrophage iron retention induced by cytokines and the master regulator hepcidin. Hepcidin controls cellular iron efflux on binding to the iron export protein ferroportin. Many patients, however, present with both ACD and iron deficiency anemia (ACD/IDA), the latter resulting from chronic blood loss. We used a rat model of ACD resulting from chronic arthritis and mimicked ACD/IDA by additional phlebotomy to define differing iron-regulatory pathways. Iron retention during inflammation occurs in macrophages and the spleen, but not in the liver. In rats and humans with ACD, serum hepcidin concentrations are elevated, which is paralleled by reduced duodenal and macrophage expression of ferroportin. Individuals with ACD/IDA have significantly lower hepcidin levels than ACD subjects, and ACD/IDA persons, in contrast to ACD subjects, were able to absorb dietary iron from the gut and to mobilize iron from macrophages. Circulating hepcidin levels affect iron traffic in ACD and ACD/IDA and are more responsive to the erythropoietic demands for iron than to inflammation. Hepcidin determination may aid to differentiate between ACD and ACD/IDA and in selecting appropriate therapy for these patients.

Growth differentiation factor 15 in anaemia of chronic disease, iron deficiency anaemia and mixed type anaemia.

Recently, the iron and erythropoiesis-controlled growth differentiation factor 15 (GDF15) has been shown to inhibit the expression of hepcidin in beta-thalassaemia patients, thereby increasing iron absorption despite iron overload. To access the diagnostic and pathogenic impact of GDF15 in inflammatory anaemia the association of GDF15 expression with serum iron parameters and hepcidin was studied in patients suffering from iron deficiency anaemia (IDA), anaemia of chronic disease (ACD) and ACD subjects with true iron deficiency (ACD/IDA). GDF15 was significantly increased in both ACD and ACD/IDA, but not in IDA subjects as compared to controls. In contrast, hepcidin levels were significantly lower in IDA and ACD/IDA subjects than in ACD patients. IDA and ACD/IDA, but not ACD, showed an association between GDF15 and soluble transferrin receptor, an indicator of iron requirement for erythropoiesis. However, GDF15 did not correlate to hepcidin in either patient group. While GDF15 levels were linked to the needs for erythropoiesis and iron homeostasis in IDA, the immunity-driven increase of GDF15 may not primarily affect iron homeostasis and hepcidin expression. This indicates that other ACD-related factors may overcome the regulatory effects of GDF15 on hepcidin expression during inflammation.

A dual-monoclonal sandwich ELISA specific for hepcidin-25.

BACKGROUND: Hepcidin, a key regulator of iron metabolism, binds to the iron transporter ferroportin to cause its degradation. In humans, hepcidin deficiency has been linked to hemochromatosis and iron overload, whereas increased concentrations have been reported in anemia of cancer and chronic disease. There is currently an unmet clinical need for a specific immunoassay with a low limit of quantification to measure serum concentrations of hepcidin-25, the active form of the protein. METHODS: We generated 2 antihepcidin-25 monoclonal antibodies and used them to build a sandwich ELISA. We correlated ELISA results to hepcidin-25 measurements by LC-MS and used ELISA to measure serum hepcidin-25 concentrations in normal individuals, cancer patients, and patients with rheumatoid arthritis. RESULTS: The sandwich ELISA was highly specific for hepcidin-25, having a limit of quantification of 0.01 µg/L (10 pg/mL). Serum concentrations of hepcidin-25 measured by ELISA correlated with hepcidin-25 concentrations measured by using an independent LC-MS assay (r = 0.98, P < 0.001). Hepcidin-25 concentrations were increased in patients with cancer (median 54.8 µg/L, 25%-75% range 23.2-93.5 µg/L, n = 34) and rheumatoid arthritis (median 10.6 µg/L, 25%-75% range 5.9-18.4 µg/L, n = 76) compared with healthy individuals (median 1.20 µg/L, 25%-75% range 0.42-3.07 µg/L, n = 100). CONCLUSIONS: The use of 2 monoclonal antibodies in a sandwich ELISA format provides a robust and convenient method for measuring concentrations of the active form of hepcidin. This ELISA should help to improve our understanding of the role of hepcidin in regulating iron metabolism.

Regulation of iron metabolism through GDF15 and hepcidin in pyruvate kinase deficiency.

Iron absorption is inadequately increased in patients with chronic haemolytic anaemia, which is commonly complicated by iron overload. Growth differentiation factor 15 (GDF15) has been identified as a bone marrow-derived factor that abrogates hepcidin-mediated protection from iron overload under conditions of increased erythropoiesis. Increased concentrations of GDF15 have been reported in beta-thalassaemia patients and GDF15 has been found to suppress hepcidin expression in vitro. To further study the interdependencies of iron metabolism and erythropoiesis in vivo, the concentrations of hepcidin and GDF15 were determined in sera from 22 patients with pyruvate kinase deficiency (PKD) and 21 healthy control subjects. In PKD patients, serum hepcidin levels were 13-fold lower than in controls (2.0 ng/ml vs. 26.2 ng/ml) and GDF15 was significantly higher (859 pg/ml vs. 528 pg/ml). Serum hepcidin concentrations correlated positively with haemoglobin and negatively with serum GDF15. These results suggest that GDF15 contributes to low hepcidin expression and iron loading in PKD.

Development of tibulizumab, a tetravalent bispecific antibody targeting BAFF and IL-17A for the treatment of autoimmune disease.

We describe a bispecific dual-antagonist antibody against human B cell activating factor (BAFF) and interleukin 17A (IL-17). An anti-IL-17 single-chain variable fragment (scFv) derived from ixekizumab (Taltz®) was fused via a glycine-rich linker to anti-BAFF tabalumab. The IgG-scFv bound both BAFF and IL-17 simultaneously with identical stoichiometry as the parental mAbs. Stability studies of the initial IgG-scFv revealed chemical degradation and aggregation not observed in either parental antibody. The anti-IL-17 scFv showed a high melting temperature (Tm) by differential scanning calorimetry (73.1°C), but also concentration-dependent, initially reversible, protein self-association. To engineer scFv stability, three parallel approaches were taken: labile complementary-determining region (CDR) residues were replaced by stable, affinity-neutral amino acids, CDR charge distribution was balanced, and a H44-L100 interface disulfide bond was introduced. The Tm of the disulfide-stabilized scFv was largely unperturbed, yet it remained monodispersed at high protein concentration. Fluorescent dye binding titrations indicated reduced solvent exposure of hydrophobic residues and decreased proteolytic susceptibility was observed, both indicative of enhanced conformational stability. Superimposition of the H44-L100 scFv (PDB id: 6NOU) and ixekizumab antigen-binding fragment (PDB id: 6NOV) crystal structures revealed nearly identical orientation of the frameworks and CDR loops. The stabilized bispecific molecule LY3090106 (tibulizumab) potently antagonized both BAFF and IL-17 in cell-based and in vivo mouse models. In cynomolgus monkey, it suppressed B cell development and survival and remained functionally intact in circulation, with a prolonged half-life. In summary, we engineered a potent bispecific antibody targeting two key cytokines involved in human autoimmunity amenable to clinical development.

FGF-21 as a novel metabolic regulator.

Diabetes mellitus is a major health concern, affecting more than 5% of the population. Here we describe a potential novel therapeutic agent for this disease, FGF-21, which was discovered to be a potent regulator of glucose uptake in mouse 3T3-L1 and primary human adipocytes. FGF-21-transgenic mice were viable and resistant to diet-induced obesity. Therapeutic administration of FGF-21 reduced plasma glucose and triglycerides to near normal levels in both ob/ob and db/db mice. These effects persisted for at least 24 hours following the cessation of FGF-21 administration. Importantly, FGF-21 did not induce mitogenicity, hypoglycemia, or weight gain at any dose tested in diabetic or healthy animals or when overexpressed in transgenic mice. Thus, we conclude that FGF-21, which we have identified as a novel metabolic factor, exhibits the therapeutic characteristics necessary for an effective treatment of diabetes.

Behavioral, biochemical, and genetic analysis of iron metabolism in high-intensity blood donors.

BACKGROUND: Individuals donating whole blood 13 times in a 2-year period without development of iron deficiency anemia (superdonors) are a self-selected population that is deferred for low hematocrit (Hct) level less frequently than other donors. STUDY DESIGN AND METHODS: Iron metabolism was assessed in 138 superdonors through a questionnaire and measurement of Hct, serum ferritin, serum hepcidin, and serum growth differentiation factor 15 (GDF15). Genetic testing for HFE and JAK-2 mutations was also performed. RESULTS AND CONCLUSIONS: Iron deficiency (ferritin level, <30 microg/L) is present in more than 60 percent of superdonors. Behaviors altering iron status included casual use of iron supplements in males, but not in females, and cigarette smoking that produced increased Hct associated with decreased ferritin. The striking biochemical characteristic of superdonors is greatly decreased serum hepcidin, consistent with their need to absorb maximal amounts of dietary iron to replace that lost from blood donation. GDF15 is normal in most superdonors, indicating that GDF15 overexpression arising from the expanded erythroid pool necessary to replace donated red cells is not the biochemical mechanism for the decreased serum hepcidin. Mutations in JAK-2 were not found, indicating that undiagnosed polycythemia vera is not a common cause for successful repeated blood donation by superdonors. Mutations in HFE associated with hemochromatosis were present in superdonors at the same frequency as the normal population. However, superdonors heterozygous for the H63D mutation in HFE had significantly decreased hepcidin : ferritin ratios demonstrating for the first time that the heterozygous state for HFE mutations is associated with alterations in hepcidin expression.

The metabolic state of diabetic monkeys is regulated by fibroblast growth factor-21.

Fibroblast growth factor (FGF)-21 has been recently characterized as a potent metabolic regulator. Systemic administration of FGF-21 reduced plasma glucose and triglycerides to near normal levels in genetically compromised diabetic rodents. Importantly, these effects were durable and did not come at the expense of weight gain, hypoglycemia, or mitogenicity. To explore the therapeutic properties of FGF-21 in a nongenetically modified primate species, and thus demonstrate the potential for efficacy in humans, we evaluated its bioactivity in diabetic nonhuman primates. When administered daily for 6 wk to diabetic rhesus monkeys, FGF-21 caused a dramatic decline in fasting plasma glucose, fructosamine, triglycerides, insulin, and glucagon. Of significant importance in regard to safety, hypoglycemia was not observed at any point during the study. FGF-21 administration also led to significant improvements in lipoprotein profiles, including lowering of low-density lipoprotein cholesterol and raising of high-density lipoprotein cholesterol, beneficial changes in the circulating levels of several cardiovascular risk markers/factors, and the induction of a small but significant weight loss. These data support the development of FGF-21 for the treatment of diabetes and other metabolic diseases.