Large-scale preparation and characterization of non-pegylated and pegylated superactive ovine leptin antagonist

The Postnatal Leptin Surge Supports Immune Cell Function in Rats

Background: Leptin plays an important role in the regulation of the immune response. There is a physiological surge of leptin in rodents during the neonatal period, which has mainly been studied in the context of brain development. However, little is known about the effects of this neonatal leptin surge on immunity. Therefore, we investigated whether blocking this leptin surge could affect several immune functions.Methods: Male and female rats were injected subcutaneously with 5 mg/Kg/day of rat pegylated super leptin antagonist during the neonatal period (PND5-9). On the peripubertal period, relevant functions as well as cytokine release by spleen leukocytes were studied in these animals.Results: The results showed that the animals significantly display an impaired anti-tumor NK activity and chemotactic and proliferation capacity of lymphocytes in response to mitogens. In addition, several cytokine concentrations, released under mitogen-stimulated conditions, were also altered.Conclusion: In conclusion, the neonatal leptin surge seems to be involved in the establishment of an adequate immune response and cytokine profile, which are crucial for the maintenance of a healthy life.

Technical note: Effects of pegylation and route of administration on leptin kinetics in newborn lambs1

Chronic energy insufficiency resulting from inadequate feed intake or increased nutrient demand reduces plasma leptin in ruminants. Treatment of energy-deficient ruminants with exogenous leptin has identified some physiological consequences of reduced plasma leptin, but their full complement remains unknown. Additional leptin-dependent responses could be identified by using strategies that interfere with leptin signaling such as administration of leptin mutants that act as competitive antagonists. The effectiveness of these antagonists depends on their fold excess over endogenous leptin, and this condition can be achieved under in vivo conditions by extending the half-life (t1/2) of the antagonist by addition of a polyethylene glycol (PEG) molecule (pegylation). Use of this approach in ruminants, however, is limited by the lack of information on the t1/2 of native and pegylated leptin and on the most effective route of administration. To answer these questions, newborn lambs (n = 3) were injected with an intravenous (i.v.) bolus of 150 µg of human leptin followed by blood sampling over the next 12 h. Analysis of the semilog plasma leptin concentration over time yielded a t1/2 of 43 ± 4.9 min; an i.v. bolus of 276 µg of bovine leptin yielded a comparable t1/2 (P > 0.05). Next, newborn lambs (n = 4) received a single dose of 229 μg/kg of metabolic body weight (BW0.75) of pegylated super human leptin antagonist (PEG-SHLA) via the i.v. or subcutaneous (s.c.) route. Plasma PEG-SHLA concentration reached a peak of 1,528 ± 78 ng/mL after 1 min and a nadir of 71 ± 9 ng/mL after 24 h with the i.v. route versus a peak of 423 ± 43 ng/mL after 300 min and a nadir of 146 ± 22 ng/mL after 24 h for the s.c. route; the t1/2 of PEG-SHLA was 394 ± 29 min for the i.v. route and 433 ± 58 min for the s.c. route. Finally, plasma concentration of PEG-SHLA was modeled when given either i.v. or s.c. at a dose of 229 μg/kg BW0.75 every 12 h. Once a steady state was reached, peak and lowest concentrations PEG-SHLA over the 12-h windows were 2,269 and 403 ng/mL for the i.v. route and 814 and 555 ng/mL for the s.c. route. Weighted PEG-SHLA concentrations over the 12-h period were 1,455 and 713 ng/mL for the i.v. and s.c. route, translating into 364- and 178-fold excess over endogenous plasma leptin. These data confirm the effectiveness of pegylation in extending the t1/2 of leptin antagonists in newborn lambs and in increasing their circulation in fold excess over endogenous leptin.

Pegylated Human Leptin D23L Mutant-Preparation and Biological Activity In Vitro and In Vivo in Male ob/ob Mice

Recombinant monomeric human leptin (hLEP) and its D23L mutant were prepared in Escherichia coli and pegylated at their N-terminus using 20-kDa methoxy pegylated (PEG)-propionylaldehyde. As determined by both SDS-PAGE and size-exclusion chromatography, the pegylated proteins consisted of >90% monopegylated and <10% double-pegylated species. Circular dichroism spectra showed that their secondary structure, characteristic of all four α-helix bundle cytokines, was not affected by either the D23L mutation or pegylation. Because of the D23L mutation, affinity for hLEP receptor increased 25- and 40-fold for the pegylated and nonpegylated mutant, respectively. However, whereas the proliferation-promoting activity in vitro of nonmutated and mutated nonpegylated hLEP was identical, that of the respective pegylated mutant was approximately sixfold higher compared with the pegylated nonmutated hLEP. This difference was also seen in vivo. Both pegylated hLEPs at all doses significantly decreased body weight and food consumption, as compared with the vehicle-treated control. Once-daily administration of pegylated hLEP D23L at doses of 0.1, 0.3, and 1 mg/kg for 14 consecutive days in ob/ob mice resulted in significantly decreased body weight and food consumption as compared with respective pegylated hLEP-treated animals, with the biggest difference observed at 0.1 mg/kg. Repeated administration of either pegylated hLEP D23L or pegylated hLEP significantly decreased blood glucose levels compared with the control before glucose challenge and after oral glucose tolerance test, but with no difference between the two treatments. The pegylated hLEP D23L mutant seems to be a more potent reagent suitable for in vivo studies than the pegylated nonmutated hLEP.

Leptin-induced signaling pathways in cancer cell migration and invasion

BACKGROUND

Increasing evidence indicates that obesity is associated with tumor development and progression. Leptin is an adipocyte-related hormone with a key role in energy metabolism and whose circulating levels are elevated in obesity. The effect of leptin on cancer progression and metastasis and its underlying mechanisms are still unclear. Leptin can impact various steps in tumor metastasis, including epithelial-mesenchymal transition, cell adhesion to the extracellular matrix (ECM), and proteolysis of ECM components. To do so, leptin binds to its receptor (OB-Rb) to activate signaling pathways and downstream effectors that participate in tumor cell invasion as well as distant metastasis.

CONCLUSIONS

In this review, we describe metastasis steps in detail and characterize metastasis-related molecules activated by leptin, which may help to develop a roadmap that guides future work. In addition, we conclude that a profound understanding of the fundamental molecular processes that contribute to leptin-induced metastasis may pave the way for the development of new prognostic molecules and appropriate approaches to the treatment of obesity-related cancers.

Sex- and bone-specific responses in bone structure to exogenous leptin and leptin receptor antagonism in the ovine fetus

Widespread expression of leptin and its receptor in developing cartilage and bone suggests that leptin may regulate bone growth and development in the fetus. Using microcomputed tomography, this study investigated the effects of exogenous leptin and leptin receptor antagonism on aspects of bone structure in the sheep fetus during late gestation. From 125 to 130 days of gestation (term ~145 days), chronically catheterized singleton sheep fetuses were infused intravenously for 5 days with either saline (0.9% saline, n = 13), recombinant ovine leptin at two doses (0.6 mg·kg^-1·day^-1 LEP1, n = 10 or 1.4 mg·kg^-1·day^-1 LEP2, n = 7), or recombinant superactive ovine leptin receptor antagonist (4.6 mg·kg^-1·day^-1 SOLA, n = 6). No significant differences in plasma insulin-like growth factor-I, osteocalcin, calcium, inorganic phosphate, or alkaline phosphatase were observed between treatment groups. Total femur midshaft diameter and metatarsal lumen diameter were narrower in male fetuses treated with exogenous leptin. In a fixed length of femur midshaft, total and bone volumes were reduced by the higher dose of leptin; nonbone space volume was lower in both groups of leptin-treated fetuses. Leptin infusion caused increments in femur porosity and connectivity density, and vertebral trabecular thickness. Leptin receptor antagonism decreased trabecular spacing and increased trabecular number, degree of anisotrophy, and connectivity density in the lumbar vertebrae. The increase in vertebral porosity observed following leptin receptor antagonism was greater in the malecompared with female, fetuses. Therefore, leptin may have a role in the growth and development of the fetal skeleton, dependent on the concentration of leptin, sex of the fetus, and bone type examined.

Leptin: From structural insights to the design of antagonists

After its discovery in 1994, it soon became clear that leptin acts as an adipocyte-derived hormone with a central role in the control of body weight and energy homeostasis. However, a growing body of evidence has revealed that leptin is a pleiotropic cytokine with activities on many peripheral cell types. Inappropriate leptin signaling can promote autoimmunity, certain cardiovascular diseases, elevated blood pressure and cancer, which makes leptin and the leptin receptor interesting targets for antagonism. Profound insights in the leptin receptor (LR) activation mechanisms are a prerequisite for the rational design of these antagonists. In this review, we focus on the molecular mechanisms underlying leptin receptor activation and signaling. We also discuss the current strategies to interfere with leptin signaling and their therapeutic potential.

The Multifaceted Mechanism of Leptin Signaling within Tumor Microenvironment in Driving Breast Cancer Growth and Progression

Adipokines represent likely candidates to mediate the increased breast cancer risk and the enhanced progression associated with obesity. Other contributors to obesity-related cancer progression are insulin/IGF-1 pathways and hormones. Among these, the adipokine leptin is the most intensively studied in both metabolism in general and in cancer due to the fact that leptin levels increase in proportion of fat mass. Leptin is primarily synthesized from adipocytes but it is also produced by other cells including fibroblasts. In this latter case, it has been well demonstrated how cancer-associated fibroblasts express leptin receptor and secrete leptin, which sustains a short autocrine loop and is able to target tumor epithelial cells enhancing breast cancer cell motility and invasiveness. In addition, it has been reported that leptin may induce breast cancer to undergo a transition from epithelial to spindle-like mesenchymal morphology, activating the signaling pathways devoted to the EMT. Thus, it emerges how leptin may play a crucial role in mediating malignant cell and tumor microenvironment interactions. Here, we present an overview of the role of leptin in breast cancer, covering the following topics: (1) leptin as an amplifier of estrogen signaling in tumor epithelial cells contributing to the promotion of carcinogenesis; (2) leptin as a crucial player in mediating tumor-stroma interaction and influencing EMT-linked mechanisms, that may sustain breast cancer growth and progression; (3) leptin and leptin receptor targeting as novel therapeutic strategies for breast cancer treatment.

PEGylation alleviates the non-specific toxicities of Alpha-Momorcharin and preserves its antitumor efficacy in vivo

Alpha-Momorcharin (α-MMC) is a ribosome inactivating protein from Momordica charantia with anti-tumor activity. Previously, we had observed that modification of α-MMC with polyethylene glycol (PEG) could reduce toxicity, but it also reduces its anti-tumor activity in vitro. This study aims to investigate whether the metabolism-extended properties of α-MMC resulting from PEGylation could preserve its anti-tumor efficacy in vivo through pharmacokinetics and antitumor experiments. The pharmacokinetics experiments were conducted in rats using the TCA (Trichloroacetic Acid) method. Antitumor activity in vivo was investigated in murine mammary carcinoma (EMT-6) and human mammary carcinoma (MDA-MB-231) transplanted tumor mouse models. The results showed that PEGylation increased the plasma half-life of α-MMC in rats from 6.2-7.5 h to 52-87 h. When administered at 1 mg/kg, α-MMC-PEG and α-MMC showed similar anti-tumor activities in vivo, with a T/C% of 38.56% for α-MMC versus 35.43% for α-MMC-PEG in the EMT-6 tumor model and 36.30% for α-MMC versus 39.88% for α-MMC-PEG in the MDA-MB-231 tumor model (p > 0.05). Importantly, at the dose of 3 mg/kg, all the animals treated with α-MMC died while the animals treated with α-MMC-PEG exhibited only moderate toxic reactions, and α-MMC-PEG exhibited improved anti-tumor efficacy with a T/C% (relative tumor growth rate) of 25.18% and 21.07% in the EMT-6 and MDA-MB-231 tumor models, respectively. The present study demonstrates that PEGylation extends the half-life of α-MMC and alleviates non-specific toxicity, thereby preserving its antitumor efficacy in vivo, and a higher lever of dosage can be used to achieve better therapeutic efficacy.

Leptin-induced endothelium-dependent vasorelaxation of peripheral arteries in lean and obese rats: role of nitric oxide and hydrogen sulfide

Adipose tissue hormone leptin induces endothelium-dependent vasorelaxation mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHF). Previously it has been demonstrated that in short-term obesity the NO-dependent and the EDHF-dependent components of vascular effect of leptin are impaired and up-regulated, respectively. Herein we examined the mechanism of the EDHF-dependent vasodilatory effect of leptin and tested the hypothesis that alterations of acute vascular effects of leptin in obesity are accounted for by chronic hyperleptinemia. The study was performed in 5 groups of rats: (1) control, (2) treated with exogenous leptin for 1 week to induce hyperleptinemia, (3) obese, fed highly-palatable diet for 4 weeks, (4) obese treated with pegylated superactive rat leptin receptor antagonist (PEG-SRLA) for 1 week, (5) fed standard chow and treated with PEG-SRLA. Acute effect of leptin on isometric tension of mesenteric artery segments was measured ex vivo. Leptin relaxed phenylephrine-preconstricted vascular segments in NO- and EDHF-dependent manner. The NO-dependent component was impaired and the EDHF-dependent component was increased in the leptin-treated and obese groups and in the latter group both these effects were abolished by PEG-SRLA. The EDHF-dependent vasodilatory effect of leptin was blocked by either the inhibitor of cystathionine γ-lyase, propargylglycine, or a hydrogen sulfide (H2S) scavenger, bismuth (III) subsalicylate. The results indicate that NO deficiency is compensated by the up-regulation of EDHF in obese rats and both effects are accounted for by chronic hyperleptinemia. The EDHF-dependent component of leptin-induced vasorelaxation is mediated, at least partially, by H2S.

Leptin-activity blockers: development and potential use in experimental biology and medicine

The first adipokine, leptin, discovered almost 20 years ago, is secreted into circulation mainly from adipose tissue and acts both centrally and peripherally. Leptin regulates energy metabolism, reproductive function, bone metabolism, and immune response. However in some physiological or pathological situations such as enhancement of undesired immune responses in autoimmune diseases, tumorigenesis, elevated blood pressure, and certain cardiovascular pathologies, leptin activity may be harmful. In this review we screen different approaches to blocking leptin action, in vitro and in vivo. The recent development of superactive leptin muteins exhibiting antagonistic properties, and other leptin-action-blocking peptides, proteins, monoclonal antibodies, and nanobodies, opens new perspectives for their use in research, and eventually, therapy for cachexia, autoimmune disease, cancer, and other pathologies.

Induction of receptor for advanced glycation end products by insufficient leptin action triggers pancreatic β-cell failure in type 2 diabetes

Glucolipotoxicity, which is exerted by free fatty acids (FFA) and prolonged hyperglycemia, is implicated in pancreatic β-cell failure in diabetes. Pattern recognition receptors such as receptor for advanced glycation end products (RAGE) and toll-like receptors 2 and 4 could mediate danger signals in β-cells. We examined whether RAGE contributes to β-cell failure in a type 2 diabetes mouse model. Pancreatic islets were isolated from ob/ob, db/db, diet-induced obesity (DIO), RAGE-null (RAGE(-/-) ), and RAGE(+/+) wild-type (WT) control mice and dispersed into single cells for flow cytometry. RAGE expression was detected in insulin-positive β-cells of ob/ob and db/db mice, but not of WT, DIO, or RAGE(-/-) mice: thus, inadequate leptin receptor signaling and RAGE expression may be linked. Compared with RAGE(+/+) db/db mice, RAGE(-/-) db/db mice showed higher β-cell number and mass with less apoptosis as well as glucose tolerance with higher insulin secretion without any differences in serum levels of FFA and adiponectin. Palmitate or oleate pretreatment combined with a leptin antagonist induced RAGE expression, AGE-elicited apoptosis, and impaired glucose-stimulated insulin secretion by advanced glycation end products (AGE) in MIN6 cells. FFA elevation with concomitant AGE formation during prolonged hyperglycemia could cause β-cell damage through insufficient leptin action and subsequent RAGE induction in type 2 diabetes.

Pegylated leptin antagonist with strong orexigenic activity in mice is not effective in chickens

A chicken gene orthologous to human leptin receptor (LEPR) has been characterized and found to be active in leptin signaling in vitro in response to a variety of recombinant leptins and leptin-containing blood samples. However, the endogenous ligand of chicken LEPR (cLEPR) - the putative chicken leptin - has been reported by us and others to be undetectable at the DNA, mRNA, protein and activity levels. These reports have raised questions as to cLEPR's role. Here we analyzed the effects of a pegylated superactive mouse leptin antagonist (PEG-SMLA) in chicken. We showed that the leptin antagonist efficiently and specifically blocks leptin signaling through the cLEPR in vitro. The effect of the leptin antagonist was then studied in vivo by daily administration of 10 mg/kg for 10 consecutive days to White Leghorn female chickens (G. gallus), at the age of two weeks. Despite the efficient attenuation of the cLEPR in vitro, no effect was observed on body weight, feed intake, feed efficiency or fat accumulation in the treated birds. Since similar treatment in rodents leads to a highly pronounced increase in appetite and body weight that are observed from the first day of treatment, it is concluded that the cLEPR is not implicated in the control of appetite or adipose homeostasis in chickens.