1. Field of the Invention
This invention pertains to the field of diagnosis and treatment of atherosclerosis and blood clotting disorders such as von Willebrand disease.
2. Background
Heart disease is the leading cause of death in the United States, and the third leading cause of death is stroke. Both conditions often result from atherosclerosis, which is often referred to as hardening of the arteries. Atherosclerosis involves a buildup of plaque, fatty deposits made up of LDL-cholesterol, lipids and cellular debris, on the inner walls of arteries. The plaque buildups cause a progressive obstruction of the arteries, which can lead to an deficiency of oxygen in the tissues that are supplied by the affected arteries. Obstruction of the coronary arteries by plaque can cause ischemia due to a deficiency in the amount of oxygen that reaches the heart muscle; this can lead to a heart attack. Obstruction of arteries that lead to the brain can cause stroke. Peripheral arteries are also subject to atherosclerosis; this can result in formation of a blood clot that can block the blood supply to an organ. Aneurysms can also result from atherosclerosis, due to the weakening of the arteries at the point of plaque buildups.
Several risk factors for atherosclerosis are such that one can reduce the risk of atherosclerosis by lifestyle changes, such as a healthy diet and exercise, cessation of smoking, and control of blood pressure. Drugs are available for reducing cholesterol levels, another significant risk factor. Other risk factors not subject to modification by an individual. These risk factors include increasing age, diabetes, and family history of atherosclerosis are significant risk factors. Factor VIII (FVIII) has been found to be a risk factor for coronary artery disease and blood group O individuals who have low serum cholesterol. Individuals with low vWF/FVIII have a low frequency of peripheral arterial disease compared with the general population (Hall et al. (1971) Atherosclerosis 14: 241–246; Meade et al. (1980) Lancet 1: 1050–1054. However, any potential treatment or prophylactic method that attempted to reduce vWF and/or FVIII would be expected to cause a bleeding disorder such as hemophilia or Von Willebrand disease (VWD).
VWD, which is characterized by a marked deficiency in von Willebrand factor (vWF) activity, is the most common inherited bleeding disorder in humans, with a prevalence of up to 1.3% of the population (reviewed in Nichols and Ginsburg (1997) Medicine 76: 1–20). In the United States, up to two million people suffer from VWD. vWF is a multimeric plasma glycoprotein that stabilizes coagulation factor VIII (FVIII). vWF plays an essential role in hemostasis by mediating platelet adhesion and aggregation to subendothelium at sites of vascular injury (Savage et al. (1996) Cell 84, 289–97). At least six major subtypes of VWD are known. Multimer analysis shows qualitative and quantitative defects in vWF from the VWD variants (Nichols and Ginsburg, supra.).
VWD is inherited in an autosomal dominant manner, as are the majority of bleeding disorders, although the mechanisms underlying this observation are not well understood. Systemic mutagenesis in diploid organisms indicates that most mutations are recessive to wild type with a ratio of approximately 20–10:1 (reviewed in Wilkie (1994) J. Med. Genet. 31: 89–98). Defects in the von Willebrand factor (vWF) gene itself have been identified in a subset of VWD individuals. However, the genetic basis for the majority of clinical cases is unknown. The variability observed may be the result of contributions from other genetic loci (Ginsburg and Bowie (1992) Blood 79: 2507–19; Nichols and Ginsburg, supra.).
Some studies have examined the role of glycosylation in vWF structure and function. Normal polymerization of vWF involves initial N-linked glycosylation and acidic pH in the Golgi apparatus of endothelial cells (Wagner et al. (1986) J. Cell Biol. 102: 1320–4). It is known that approximately 30% of the variance in normal plasma vWF levels is related to the ABH blood group oligosaccharide determinants (Orstavik et al. (1989) Blood 73: 990–3). There is an increased number of group O individuals in patients with type I VWD, suggesting that upregulation of α2 fucosyltransferases results in a loss of vWF from the circulation (Gill et al. (1987) Blood 69: 1691–5). A role for glycosyltransferases has also been identified in the RIIIs/J mouse strain which has low plasma vWF. An N-acetylgalactosaminyltransferase, Galgt2 has switched gene expression from epithelial cells to endothelial cells resulting in misglycosylation of vWF and enhanced clearance in this strain (Mohlke et al. (1999) Cell 96: 111–20). This gain-of-function mutation results in Galgt2 expression in both heterozygous and homozygous null mice and thus has an autosomal dominant inheritance pattern.
Desialylation of vWF does not affect procoagulant activity, but does result in more rapid clearance in vivo, possibly due to the exposure of terminal galactose residues which can be recognized by hepatic asialoglycoprotein receptors (Sodetz et al. (1977) J. Biol. Chem. 252: 5538–46). The galactose residues are present in a terminal Galβ1,4GlcNAc and comprise over 60% of the total galactose on native vWF/FVIII. Sialic acid can be incorporated into desialylated vWF/FVIII by purified α2,6 sialyltransferase which has specificity for the Galβ1,4GlcNAc structure (Sodetz et al. (1978) J. Biol. Chem. 253: 7202–6). These studies have not, however, identified the specific sialyltransferase enzymes that are responsible for sialylating vWF/FVIII in vivo. Nor have these studies revealed how vWF levels might be involved in atherosclerosis.
The lack of knowledge that exists as to how certain risk factors are involved atherosclerosis has hampered development of diagnostic and treatment methods for atherosclerosis. The present invention fulfills this need, and provides novel methods for treating and preventing atherosclerosis.