Role of sialylation in determining the pharmacokinetics of neutrophil inhibitory factor (NIF) in the Fischer 344 rat

Effect of glycosylation on biodistribution of radiolabeled glucagon-like peptide 1

OBJECTIVE

Glycosylation is generally applicable as a strategy for increasing the activity of bioactive proteins. In this study, we examined the effect of glycosylation on biodistribution of radiolabeled glucagon-like peptide 1 (GLP-1) as a bioactive peptide for type 2 diabetes.

METHODS

Noninvasive imaging studies were performed using a gamma camera after the intravenous administration of (123)I-GLP-1 or (123)I-α2, 6-sialyl N-acetyllactosamine (glycosylated) GLP-1 in rats. In ex vivo biodistribution studies using (125)I-GLP-1 or (125)I-glycosylated GLP-1, organ samples were measured for radioactivity. Plasma samples were added to 15% trichloroacetic acid (TCA) to obtain TCA-insoluble and TCA-soluble fractions. The radioactivity in the TCA-insoluble and TCA-soluble fractions was measured.

RESULTS

In the noninvasive imaging studies, a relatively high accumulation level of (123)I-GLP-1 was found in the liver, which is the major organ to eliminate exogenous GLP-1. The area under the time-activity curve (AUC) of (123)I-glycosylated GLP-1 in the liver was significantly lower (89%) than that of (123)I-GLP-1. These results were consistent with those of ex vivo biodistribution studies using (125)I-labeled peptides. The AUC of (125)I-glycosylated GLP-1 in the TCA-insoluble fraction was significantly higher (1.7-fold) than that of GLP-1.

CONCLUSIONS

This study demonstrated that glycosylation significantly decreased the distribution of radiolabeled GLP-1 into the liver and increased the concentration of radiolabeled GLP-1 in plasma. These results suggested that glycosylation is a useful strategy for decreasing the distribution into the liver of bioactive peptides as desirable pharmaceuticals.

Evaluation of the role of the asialoglycoprotein receptor in the clearance of UK-279,276 (recombinant neutrophil inhibitory factor)

1. UK-279,276 or recombinant neutrophil inhibitory factor (rNIF) is a glycoprotein that has been investigated as an intravenous treatment for stroke. Previous data indicate that the asialoglycoprotein receptor (ASGPR) in the liver might have a role in the uptake and clearance of UK-279,276 from plasma in rats and dogs. 2. Biliary elimination of sialo UK-279,276 can be inhibited by the co-administration of asialo fetuin, a known substrate for ASGPR. These data are in keeping with sialo UK-279,276 being cleared by ASGPR. 3. In vitro experiments have demonstrated that asialo UK-279,276 (Sialo UK-279,276 treated to remove the sialic acid residues present on the glycans) shows a significantly greater uptake in rat, dog and human precision-cut liver slices than the sialylated protein. The addition of asialo fetuin to precision-cut liver slice incubations (rat, dog and man) containing asialo UK-279,276 reduced the uptake to levels similar to those seen for the sialylated protein. These data support the potential role of the ASGPR in the clearance of UK-279,276 in rat, dog and man.

Evidence for an asialoglycoprotein receptor on nonparenchymal cells for O-linked glycoproteins

B cell-activating factor receptor 3 (BR3)-Fc is an IgG1-receptor dimeric fusion protein that has multiple O-linked glycosylation sites and sialylation levels that can vary in the manufacturing process. Increased sialic acid levels resulted from increased site occupancy with the O-linked N-acetylgalactosamine (GalNAc-Gal), but because the ratio of sialic acid per mole of oligosaccharide remained approximately 1, this led to increased asialo terminal GalNAc. Previous studies have demonstrated an effect of terminal asialo Gal or GalNAc on the clearance of glycoproteins due to uptake and degradation by lectin receptors in the liver. However, the previous studies examined N-linked oligosaccharides, and there are less data regarding O-linked oligosaccharides. The objective of these studies was to determine the effects on the pharmacokinetics and distribution of the asialo terminal GalNAc and varying amounts of sialic acid residues on BR3-Fc. The results of the data presented here suggest that exposed Gal on the desialylated BR3-Fc led to rapid clearance due to uptake and degradation in the liver that was associated with nonparenchymal cells. It is interesting to note that the data indicated a decreased clearance and increased exposure of BR3-Fc as the sialic acid levels increased, even though increased sialic acid was associated with increased asialo GalNAc. Therefore, the exposed GalNAc did not seem to play a role in the clearance of BR3-Fc; although the Gal linked to the hydroxyl group at position 3 may have prevented an interaction. Because we did not see uptake of desialylated BR3-Fc in hepatocytes where the asialoglycoprotein receptor is localized, this nonparenchymal cell lectin may have preference for O-linked glycoproteins.

Pharmacokinetics and clearance processes of UK-279,276 (rNIF) in rat and dog: comparison with human data

UK-279,276, or recombinant neutrophil inhibitory factor (rNIF), is a glycoprotein that binds to the human CD11b receptor (IC(50) = <0.5 nM) and inhibits neutrophil binding to vascular endothelial cells. In dogs, the pharmacokinetics of UK-279,276 are non-linear with clearance slowing as dose increases (apparent clearance 0.06 ml min(-1) kg(-1) at 0.l mg kg(-1) decreasing to 0.02 ml min(-1) kg(-1) at 2 mg kg(-1)). The observations are in keeping with human pharmacokinetic data. In rats, clearance is linear (0.07-0.13 ml min(-1) kg(-1)) across a similar dose range (0.006-2.25 mg kg(-1)) compared with dogs and humans. These data indicate that two clearance processes act on UK-279,276 in dogs and humans, but only one clearance process occurs in rats. A non-saturable, low-affinity/high-capacity clearance process is present in all animal species studied as well as in human, and it is believed to be hepatic uptake mediated by the asialoglycoprotein receptor. A second, saturable, clearance process is present in dogs and humans that is not apparent in the rat. This high-affinity/low-capacity process is thought to be mediated by interaction with the CD11b receptor, which is the pharmacological target for this molecule. This hypothesis is supported by the marked species differences seen for the affinity of CD11b for UK-279,276, with dogs and humans having high-affinity (IC(50) = <0.5 nM), whilst the rat affinity is low (IC(50) = 134 nM).

Recombinant human antithrombin expressed in Chinese hamster ovary cells shows in vivo efficacy on rat DIC model similarly to plasma-derived antithrombin regardless of different N-glycosylation

Plasma-derived human antithrombin (pAT) is used for the treatments of disseminated intravascular coagulation (DIC) and hereditary antithrombin deficiencies. We expressed recombinant human antithrombin (rAT) in Chinese hamster ovary (CHO) cells. The purified rAT is composed of 55% alpha-isoform and 45% beta-isoform. The structure of the N-linked oligosaccharides of rAT is the same biantennary complex type as previously found in pAT with less sialylated on the non-reducing ends. Most of the oligosaccharides of rAT are fucosylated at the reducing ends of N-acetylglucosamine, while those of pAT are not fucosylated. Despite of the difference in sialylation and fucosylation of the oligosaccharide units, rAT and pAT showed indistinguishable heparin cofactor and progressive activities, and they bound to thrombin in a one-to-one stoichiometric manner. In lipopolysaccharide (LPS)-induced and thromboplastin-induced DIC rat models, rAT reduced fibrinogen and platelet consumption to a similar extent with pAT. In LPS-induced DIC model, both ATs similarly restrained the increase of alanine aminotransferase and aspartate aminotransferase activities. Finally, pharmacokinetic analysis showed that both ATs had similar half-lives in the circulation of normal rats. Together, the present study demonstrated that rAT prepared in CHO cells has potential for a substitute of pAT in therapeutic use.