PEGylation of cholecystokinin prolongs its anorectic effect in rats

PEGylated neuromedin U-8 shows long-lasting anorectic activity and anti-obesity effect in mice by peripheral administration

Neuromedin U (NMU) is a neuropeptide found in the brain and gastrointestinal tract. The NMU system has been shown to regulate energy homeostasis by both a central and a peripheral mechanism. Peripheral administration of human NMU-25 was recently shown to inhibit food intake in mice. We examined the possibility that other NMU-related peptides exert an anorectic activity by intraperitoneal (i.p.) administration. We found that rat NMU-23 and its structurally-related peptide rat neuromedin S (NMS) significantly reduced food intake in lean mice, whereas NMU-8, an active fragment of the octapeptide sequence conserved in porcine, human and mouse NMU, had no effect. When rat NMU-23, NMU-8, and rat NMS were covalently conjugated to polyethylene glycol (PEG) (PEGylation) at the N-terminus of these peptides, PEGylated NMU-8 showed the most long-lasting and robust anorectic activity. The exploration of the linker between NMU-8 and PEG using hetero-bifunctional chemical cross-linkers led to an identification of PEGylated NMU-8 analogs with higher affinity for NMU receptors and with more potent anorectic activity in lean mice. The PEGylated NMU-8 showed potent and robust anorectic activity and anti-obesity effect in diet-induced obesity (DIO) mice by once-daily subcutaneous (s.c.) administration. These results suggest that PEGylated NMU-8 has the therapeutic potential for treatment of obesity.

Long-lasting hypoglycemic effect of modified FGF-21 analog with polyethylene glycol in type 1 diabetic mice and its systematic toxicity

Fibroblast growth factor-21 (FGF-21) is a novel metabolic regulator and has the potential to become a powerful therapy to treat diabetes mellitus. However, we found that the clinical application of wild type FGF-21 was influenced by its low intrinsic bio-stability and poor hypoglycemic potency. In this study, The N-terminus of FGF-21 analog (mFGF-21) was PEGylated in a site-specific manner by 20kD methoxy poly-ethylene glycol-propionaldehyde (mPEG-ALD). PEGylated mFGF-21 was isolated by Capto Q anion exchange chromatography. The properties of PEGylated mFGF-21 including the in vitro bio-stability and biological activity were evaluated. As well as the anti-diabetic effect of PEGylated mFGF-21 were studied in streptozotocin (STZ)-induced type 1 diabetic mice. Results demonstrated that PEGylated mFGF-21 had a similar capacity of stimulating glucose uptake in HepG2 cells with mFGF-21 and PEGylation of mFGF-21 significantly enhanced the anti-protease ability and the long acting anti-diabetic effect in type 1 diabetic mice. Furthermore, the preliminary safety of PEGylated mFGF-21 following subcutaneously injection was assessed using healthy mice by measuring the body weight, histopathology and clinical biochemical parameters, and the results showed no subacute toxicity to major organs or tissues and no significant changes in physiological and biochemical parameters in healthy mice. Taken together, under the premise of remaining the in vitro biological activity of mFGF-21, PEGylation significantly improves the long lasting hypoglycemic effect of mFGF-21 in type 1 diabetic mice. Our valuation shows that PEGylated mFGF-21 is a potential drug for the effective treatment of type 1 diabetes.

(pGlu-Gln)-CCK-8[mPEG]: a novel, long-acting, mini-PEGylated cholecystokinin (CCK) agonist that improves metabolic status in dietary-induced diabetes

BACKGROUND

Cholecystokinin (CCK) is a gastrointestinal hormone that has been proposed as a potential therapeutic option for obesity-diabetes. As such, (pGlu-Gln)-CCK-8 is an N-terminally modified CCK-8 analogue with improved biological effectiveness over the native peptide.

METHODS

The current study has examined the in vitro stability, biological activity and in vivo therapeutic applicability of a novel second generation mini-PEGylated form of (pGlu-Gln)-CCK-8, (pGlu-Gln)-CCK-8[mPEG].

RESULTS

(pGlu-Gln)-CCK-8[mPEG] was completely resistant to enzymatic degradation and in addition displayed similar insulinotropic (p<0.05 to p<0.001) and satiating effects (p<0.01 to p<0.001) as (pGlu-Gln)-CCK-8. This confirmed the capability of (pGlu-Gln)-CCK-8[mPEG] to bind to and activate the CCK receptor. Sub-chronic twice daily injection of (pGlu-Gln)-CCK-8[mPEG] in high fat fed mice for 35days significantly decreased body weight gain (p<0.05), food intake (p<0.01 to p<0.001) and triacylglycerol deposition in liver (p<0.001) and muscle (p<0.001). Furthermore, (pGlu-Gln)-CCK-8[mPEG] markedly improved intraperitoneal glucose tolerance (p<0.05) and insulin sensitivity (p<0.001). Despite this therapeutic profile, once daily injection of (pGlu-Gln)-CCK-8[mPEG] in high fat fed mice for 33days, at the same dose, was not associated with alterations in food intake and body weight. In addition, metabolic responses to exogenous glucose and insulin injection were similar to saline treated controls.

CONCLUSION

These studies emphasise the therapeutic potential of (pGlu-Gln)-CCK-8[mPEG] and similar molecules.

GENERAL SIGNIFICANCE

A more detailed analysis of the dose and administration schedule employed for (pGlu-Gln)-CCK-8[mPEG] could provide a novel and effective compound to treat obesity-diabetes.

Scheduled feeding results in adipogenesis and increased acylated ghrelin

Ghrelin, known to stimulate adipogenesis, displays an endogenous secretory rhythmicity closely related to meal patterns. Therefore, a chronic imposed feeding schedule might induce modified ghrelin levels and consequently adiposity. Growing Wistar rats were schedule-fed by imposing a particular fixed feeding schedule of 3 meals/day without caloric restriction compared with total daily control intake. After 14 days, their body composition was measured by DEXA and compared with ad libitum-fed controls and to rats daily intraperitoneal injection with ghrelin. Feeding patterns, circadian activity, and pulsatile acylated ghrelin variations were monitored. After 14 days, rats on the imposed feeding schedule displayed, despite an equal daily calorie intake, a slower growth rate compared with ad libitum-fed controls. Moreover, schedule-fed rats exhibiting a feeding pattern with intermittent fasting periods had a higher fat/lean ratio compared with ad libitum-fed controls. Interestingly, ghrelin-treated rats also showed an increase in fat mass, but the fat/lean ratio was not significantly increased compared with controls. In the schedule-fed rats, spontaneous activity and acylated ghrelin levels were increased and associated with the scheduled meals, indicating anticipatory effects. Our results suggest that scheduled feeding, associated with intermittent fasting periods, even without nutrient/calorie restriction on a daily basis, results in adipogenesis. This repartitioning effect is associated with increased endogenous acylated ghrelin levels. This schedule-fed model points out the delicate role of meal frequency in adipogenesis and provides an investigative tool to clarify any effects of endogenous ghrelin without the need for ghrelin administration.

Uniform polymer-protein conjugate by aqueous AGET ATRP using protein as a macroinitiator

In situ aqueous activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) in air, using an enzyme as a macroinitiator, has been proposed to prepare uniform polymer-protein conjugates with improved stability under adverse conditions. In the first step, an initiator, 2-bromoisobutyryl bromide (BIB), was grafted onto the protein surface by reaction with the amino groups. The second step was in situ AGET ATRP polymerization in air using CuBr(2)/1,1,4,7,7-pentamethyldiethylenetriamine as a catalyst and ascorbic acid as a reducing agent. The effectiveness of this method has been demonstrated using horseradish peroxidase (HRP) as a model protein and acrylamide as the monomer, which yielded HRP-polyacrylamide conjugate with a mean particle size of about 20-30 nm. The grafting of BIB onto HRP and the subsequent polymerization yielding a polyacrylamide chain were confirmed by nuclear magnetic resonance and matrix-assisted laser desorption ionization time-of-flight spectrometry analysis. The size of the conjugate was shown to be a function of monomer loading and reaction time. The HRP conjugates yielded essentially retained the catalytic behavior of HRP in free form, as shown by K(m) and V(max) values, but exhibited significantly enhanced thermal stability against high temperature and trypsin digestion. The use of protein as the macroinitiator prevented the formation of copolymer and thus facilitated purification of the protein conjugate. The uniform size indicates a well-defined composition of protein and polymer, which is essential for applications that request a precise control of the dosage of enzyme activity.

Lack of tolerance development with long-term administration of PEGylated cholecystokinin

Cholecystokinin (CCK) is a short acting satiating peptide hormone produced in the proximal small intestine. Daily CCK injection in rats initially inhibits food intake, but after several days, food intake is no longer affected, suggesting development of tolerance. Previously, we covalently coupled CCK to a 10kDa polyethylene glycol (mPEG-OH) and showed that this conjugate, PEG-CCK(9), produced a significantly longer anorectic effect than unmodified CCK(9). The present study examined whether tolerance to the anorectic effect develops during long-term administration of PEG-CCK(9). For 14 consecutive days, male Wistar rats (n=12) received a daily i.p injection of 8microgkg(-1) of PEG-CCK(9) and a control group received a daily control injection of mPEG-OH. Body weight and food intake were monitored daily during the experiment. Effects on the pancreas were investigated. On each day, injection of PEG-CCK(9) induced an anorectic effect lasting 3-6h, but failed to significantly reduce daily total food intake compared to controls. The body weight gain of the PEG-CCK(9)-treated animals was not different from controls. The PEG-CCK(9)-treated group had a significantly higher pancreas weight, mainly due to hyperplasia. In conclusion, PEG-CCK(9) continued to have a daily suppressive effect on food intake when administered for 14 consecutive days, showing there was no development of tolerance.

PEGylated cholecystokinin is more potent in inducing anorexia than conditioned taste aversion in rats

BACKGROUND AND PURPOSE

The physiological involvement of endogenous cholecystokinin (CCK) in the termination of feeding has been challenged by evidence of aversive effects of exogenous CCK8. We previously prolonged the anorectic effect of CCK by conjugation to polyethylene glycol (PEGylation) to produce PEG-CCK9. In this study, we investigated the ability of different doses of PEG-CCK9 to induce conditioned taste aversion (CTA) and satiety and identified the receptors involved in CTA induction.

EXPERIMENTAL APPROACH

Induction of CTA, measured by the saccharin preference ratio determined in a two-bottle CTA procedure, and of satiety in adult male Wistar rats after intraperitoneal (i.p.) injection of different doses of PEG-CCK9 (1, 2, 4, 8, 16 or 32 microg kg(-1)) was compared. Devazepide (100 microg kg(-1)) and 2-NAP (3 mg kg(-1)), two selective CCK1-receptor antagonists, were co-administered i.p. with PEG-CCK9 (8 microg kg(-1)) and the CTA effects monitored.

KEY RESULTS

PEG-CCK9 dose-dependently induced CTA, with a minimal effective dose of 8 microg kg(-1), whereas the minimal effective dose to induce satiety was 1 microg kg(-1). The CTA effects of PEG-CCK9 were completely abolished by i.p. administration of devazepide prior to PEG-CCK9 treatment and only partially abolished by administration of 2-NAP.

CONCLUSIONS AND IMPLICATIONS

Although PEG-CCK9-induced satiety and PEG-CCK9-induced CTA both increased with dose, the conjugate was more potent in inducing satiety, suggesting that the anorexia could not be completely attributed to the aversiveness of the drug. As observed with induction of satiety, PEG-CCK9-induced CTA was mediated by CCK1-receptors.

PEGylated cholecystokinin prolongs satiation in rats: dose dependency and receptor involvement

BACKGROUND AND PURPOSE

Acute intraperitoneal (i.p.) administration of cholecystokinin (CCK) is known to induce a significant, but short-lasting, reduction in food intake, followed by recovery within hours. Therefore, we had covalently coupled CCK to a 10 kDa polyethylene glycol and showed that this conjugate, PEG-CCK(9), produced a significantly longer anorectic effect than unmodified CCK(9). The present study assessed the dose-dependency of this response and the effect of two selective CCK(1) receptor antagonists, with different abilities to cross the blood-brain barrier (BBB), on PEG-CCK(9)-induced anorexia.

EXPERIMENTAL APPROACH

Food intake was measured, for up to 23 h, after i.p. administration of different doses (2, 4, 8, 16 and 32 microg kg(-1)) of CCK(9) or PEG-CCK(9) in male Wistar rats. Devazepide (100 microg kg(-1)), which penetrates the BBB or 2-NAP (3 mg kg(-1)), which does not cross the BBB, were coadministered i.p. with PEG-CCK(9) (6 microg kg(-1)) and food intake was monitored.

KEY RESULTS

In PEG-CCK(9)-treated rats, a clear dose-dependency was seen for both the duration and initial intensity of the anorexia whereas, for CCK(9), only the initial intensity was dose-dependent. Intraperitoneal administration of devazepide or 2-NAP, injected immediately prior to PEG-CCK(9), completely abolished the anorectic effect of PEG-CCK(9).

CONCLUSIONS AND IMPLICATIONS

The duration of the anorexia for PEG-CCK(9) was dose-dependent, suggesting that PEGylation of CCK(9) increases its circulation time. Both devazepide and 2-NAP completely abolished the anorectic effect of i.p. PEG-CCK(9) indicating that its anorectic effect was solely due to stimulation of peripheral CCK(1) receptors.