The kidneys play an important role in the clearance of rFVIIa in rats.

INTRODUCTION: Previous distribution and histological studies have indicated that the kidneys and renal proximal tubular cells play a role in clearance of rFVIIa. However, the relative importance of the kidneys in clearance of rFVIIa has not previously been addressed. The objective of the present study was to evaluate the importance of the kidneys in the clearance process of rFVIIa after iv administration to rats using a nephrectomy model. MATERIALS AND METHODS: A nephrectomized rat model was established and validated using inulin, a compound primarily cleared by the kidneys, as a test substance and several physiological parameters were monitored to ensure viability and robustness of the model. The model was then used for pharmacokinetic evaluation of renal clearance of rFVIIa. The pharmacokinetic parameters for rFVIIa were evaluated both by use of standard non-compartmental methods and by use of mixed effects methods, where a pharmacokinetic model was used to simultaneously model all data from healthy, sham operated, and nephrectomized rats. RESULTS: Nephrectomized animals showed stable rectal temperature, SpO2 and pulse and as expected, clearance of inulin was essentially abolished compared to control animals (p<0.001). For rFVIIa, nephrectomy resulted in a clearance and terminal half-life of 34mL/h/kg and 2.8h compared to 68mL/h/kg and1.9h in rats exposed to sham surgery (p<0.0001 for both parameters). CONCLUSION: The present data show that about 50% of the total clearance of rFVIIa from circulation in rats under isoflurane anaesthesia is due to renal clearance.

The unsialylated subpopulation of recombinant activated factor VII binds to the asialo-glycoprotein receptor (ASGPR) on primary rat hepatocytes.

Recombinant activated factor VII (rFVIIa; NovoSeven®) is a heterogeneously glycosylated serine protease used for treatment of haemophiliacs with inhibitors. The drug substance contains a subpopulation consisting of ~20% of rFVIIa molecules which are unsialylated and consists of carbohydrate moieties with terminally exposed galactose and N-acetyl-D-galactosamine (GalNAc). Recently, data from an in situ perfused liver model showed that a subpopulation of rFVIIa, appearing to be unsialylated rFVIIa, was cleared by the liver, thus suggesting a carbohydrate-moiety mediated mechanism. The parenchymal cells of the liver, hepatocytes, are known to abundantly express functional carbohydrate-specific receptors and in this study we therefore used primary rat hepatocytes to study binding and intracellular fate of rFVIIa at a cellular level. Immunofluorescence microscopy showed that rFVIIa was distributed into distinct intracellular vesicles and electron microscopic autoradiography revealed that radioiodinated rFVIIa distributed only into cytoplasmic free vesicles resembling endosomes and lysosomes. These findings suggest that endocytosis of rFVIIa in hepatocytes could be partly mediated via initial membrane binding to a receptor. Quantitative binding studies showed that the presence of excess unlabelled asialo-orosomucoid, asialo-rFVIIa and GalNAc significantly decreased binding of 125I-rFVIIa. An antibody which specifically binds to the carbohydrate recognition domain of the asialoglycoprotein receptor (ASGPR) significantly decreased binding of asialo-rFVIIa by ~36% and rFVIIa by ~19%. Together our data showed that a receptor-mediated mechanism involving the ASGPR is able to bind a subpopulation of unsialylated rFVIIa, while a hepatic mechanism for binding and clearing sialylated rFVIIa is still unknown.

Investigating clearance mechanisms for recombinant activated factor VII in a perfused liver model.

Clearance mechanisms for recombinant activated human FVII (rFVIIa; NovoSeven), a heterogeneously glycosylated protein, have yet to be fully elucidated, but may involve the liver. The effects of the gamma-carboxy glutamic acid (Gla) domain and the sialic acid content of the protein on rFVIIa clearance were investigated following intravenous administration of rFVIIa lacking the Gla domain, des(1-44) rFVIIa and asialo-rFVIIa in pharmacokinetic (PK) studies and perfused rat livers. PK parameters for both rFVIIa and des(1-44) rFVIIa had similar biphasic clearance profiles, as well as half-lives ([t(1/2)]=80 and 88 minutes, respectively), while asialo-rFVIIa was cleared quickly (t(1/2)=21 minutes) with a linear clearance profile. Perfused liver studies with all proteins (10 nM) mirrored the trends in profiles observed in the PK study. rFVIIa and des(1-44) rFVIIa were cleared to a similar extent, 41% and 35%, respectively, after 1 h, whereas plasma-derived FVII from humans (which has a higher sialylation content than rFVIIa) was cleared to a lesser extent (21%). Asialo-rFVIIa, on the other hand, was almost totally cleared and when an excess of asialo-orosomucoid was added to the perfusate, its clearance was significantly reduced (by 34%) and also for rFVIIa, albeit to a lesser extent (by 14%). Together these data suggest that carbohydrate receptor(s) (e.g. the asialoglycoprotein receptor, ASGPR) play a role in asialo-rFVIIa and rFVIIa clearance. In vivo and liver clearance data correlated well showing similar trends and indicated that rFVIIa clearance is not affected by the Gla domain, but rather by a subpopulation of N-glycosylated structures on rFVIIa.