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  • Title: Accumulation of the recombinant factor VIIa in rat bone: importance of the Gla-domain and relevance to factor IX, another vitamin K-dependent clotting factor.
    Author: Thomsen MK, Wildgoose P, Nilsson P, Hedner U.
    Journal: Pharmacol Toxicol; 1993 Sep; 73(3):127-32. PubMed ID: 7903449.
    Abstract:
    The vitamin K-dependent clotting factors II, VII, IX, and X are proteins which undergo gamma-carboxylation of specific glutamic acid residues prior to secretion from the liver. These unique Ca2+ binding amino acids allow the interaction of the proteins with cell surface phospholipids, a function that is crucial for expression of full procoagulant activity of the proteins. The N-terminal region of the molecule contains the gamma-carboxylation sites and is termed the Gla-domain. A preliminary observation in rats suggested that mineralized bone accumulated activated recombinant FVII (rFVIIa: NovoSeven) as well as the non-activated, single chain rFVII. The present study investigated the role of the Gla-domain in the accumulation of rFVII in bone, as well as the influence of the activation state of FVII on this phenomenon. Rats were treated with 125I-labelled rFVII, rFVIIa, Gla-domainless rFVIIa, factor IX, iodide, or recombinant human growth hormone (rhGH). Following sacrifice, radioactivity was measured in mineralized bone, among other tissues. Following administration of 125I-radiolabelled rFVII, rFVIIa and factor IX, but not Gla-domainless rFVIIa, iodide or rhGH, extensive sequestration occurred in endochondrally as well as intramenbranously ossified bones. The results indicate that the proteins containing a Gla-domain, and only these, are sequestered in bone. Additionally, the normally occurring form of FVII in the circulation, the single-chain FVII, exhibited similar kinetics in rat bone and plasma, as the two-chain rFVIIa. The half-life of rFVII/rFVIIa in mineralized bone was between 3 and 4 days, implying that significant bone accumulation of the factor will take place at steady state.(ABSTRACT TRUNCATED AT 250 WORDS)
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