Xarelto Lawsuit
Xarelto Lawsuit News – 2/24/2012: If you were prescribed Xarelto and have suffered negative side effects, please contact us today so that we can put you in touch with an attorney to advise you of your legal rights.
Xarelto Lawsuit: Blood coagulation is regulated by the sequential activation of vitamin K-dependent coagulation proteases within the intrinsic and extrinsic pathways. This involves a complex series of reactions that occur as a cascade and culminates in the generation of thrombin to convert soluble fibrinogen into insoluble fibrin. Maintenance of hemostasis relies on the regulated interaction of the vitamin K-dependent proteases, protease cofactors, membrane surfaces and receptors, calcium ions, and protease inhibitors. Three central and fundamental enzyme complexes in the coagulation cascade are the factor Xa (FXa)-generating complex, consisting of factor IXa (FIXa) and the cofactor factor Villa (FVIIIa), the FXa-generating complex consisting of factor Vila (FVIIa) and tissue factor, and the thrombin-generating complex, consisting of FXa and the cofactor factor Va (FVa). The physiologic significance of these pathways is evident from genetic deficiencies that result in bleeding disorders. All the proteins involved in the coagulation cascade require post-translational modifications for appropriate secretion, plasma half life, and function. The two most common genetic bleeding diseases involving this cascade are hemophilia A and B, which are due to deficiency in coagulation factors VIII and IX respectively. Recombinant DNA technology has provided the ability to produce safe and efficacious preparations of both FVIII and FIX for hemophilia replacement therapy. Gene therapy approaches for these diseases are rapidly approaching and need to consider the requirement for proper post-translational modification in protein secretion and function.
The domain structures of the vitamin K-dependent coagulation factors FVII, FIX, FX, prothrombin, protein C, and protein S deduced from their cDNA sequences demonstrate they contain common structural features (Figure 2.1). All contain a signal peptide that is required for translocation into the lumen of the endoplasmic reticulum (ER). This is followed by a propeptide that directs vitamin-K dependent g-carboxylation of the mature polypeptide. Upon transit through the trans-Golgi apparatus, the propeptide is cleaved away. The amino terminus of the mature protein contains a g-carboxyglutamic acid-rich region (Gla) that includes a short a-helical stack of aromatic amino acids. Then there are two epidermal growth factor (EGF)-like domains. In FIX, protein C, and FX, the amino-terminal EGF domain contains b-hydroxyaspartic acid (Hya) at homologouslocations. The next region is the activation peptide (12-52 residues), which is glycosylated on asparagine residues and is released by specific proteolysis accompanying activation. The remainder of the vitamin K-dependent protease comprises the serine protease catalytic triad, which is absent in protein S.
Regardless of what kind of doctor a student decides to become, a well-grounded understanding of disorders of the blood and the hematopoietic tissues is essential. Primary hematologic disorders are commonly encountered in community and hospital-based clinical practices, and a wide variety of other diseases come to attention by producing secondary abnormalities of the blood. Beyond their everyday clinical importance, studies of hematologic diseases have yielded seminal insights into the molecular pathogenesis of cancer and basic aspects of stem cell biology. Lessons have had far-reaching influences on biomedical research and are beginning to shape the practice of molecular medicine. Plasma, the fluid phase of the blood, consists of water and solutes such as proteins, lipids, and electrolytes. The homeostatic mechanisms that regulate plasma volume, electrolytes, and lipids are beyond our scope. Here, our chief focus will be on the plasma proteins that are involved in the formation and dissolution of blood clots. The most important of these are the proteins of the coagulation cascade, certain coagulation cascade regulatory factors, von Willebrand factor, and proteins that promote the lysis of clots, such as plasmin. The laboratory tests that are used to assess these factors as well as the function of platelets, which have an essential role in hemostasis.
Under normal circumstances, the bone marrow is the only site of blood ccll production (hematopoiesis) following birth. Early in life, most bones contain hematopoietically active marrow, but by adulthood hematopoiesis is normally confincd to the axial skeleton, the proximal long bones, and the skull. The marrow is supplied by nutrient arteries, which divide and eventually give rise to venous sinusoids that are lined by endothelial cells and adventitial cells. The frond-like tissue between the sinusoids contains a mixture of fibroblasts, fat cells, mononuclear cells (including lymphocytes and macrophages), and hematopoietic cell.
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Xarelto Lawsuit: Indications for performing a bone marrow examination include an unexplained decrease or increase in blood cell counts beyond the normal range and the presence of abnormal cells in the blood (such as immature marrow precursors). Because myeloid elements (red cells, neutrophils, and platelets) have short life spans relative to lymphocytes, a decrease in marrow function, whatever the cause, affects these formed elements first. A decrease in all of the myeloid elements is called paticytopeuia and usually indicates the existence of a disorder that causes a decrease in marrow output. An increase in all of the myeloid elements is an unusual circumstance referred to as pancylosis.
Once released from the marrow, terminally differentiated myeloid elements (red cells, granulocytes, monocytes, and platelets) have defined fates and life spans. The story is quite different for T and B lymphocytes. After their release from the marrow or the thymus, these cells circulate through the blood and home to the secondary lymphoid tissues—the spleen, the lymph nodes, and the mucosa-associated lymphoid tissues (the most important of which are the Peyer patches of the small intestine and tonsillar tissues of the oropharynx). The anatomy of these tissues serves to optimize the probability that cells of the adaptive and innate immune systems will encounter pathogens and foreign antigens. If activated by antigen at these sites, T and B cells begin to proliferate and may undergo further differentiation to a variety of fates, which are dictated by factors produced locally at the site of the immune reaction. T cells can differentiate into effector T cells (helper and cytotoxic T cells), regulatory T cells, or memory T cells, whereas B cells can become memory B cells or plasma cells secreting one of a number of possible types of immunoglobulin.
The spleen has two chief functions: 1) it serves as a filter for particulate matter in the blood, and 2) it is a site of adaptive immune responses. Blood enters the splenic hilum through the splenic artery, which divides within the substance of the spleen to give rise to small arteries. During their course, these small arteries give rise to branches that are surrounded by lymphoid follicles, organized collections of T cells and B cells that are poised to respond to immunologic stimuli; these constitute the splenic white pulp. The arteries eventually give rise to small, arborizing arterioles, which empty into the splenic red pulp, an interstitial space separated from the venous sinuses of the spleen by a basement membrane with slit-like openings.
The developmental origins of hematopoietic cells are complex and incompletely understood. Cells with the properties of hematopoietic stem cells (HSCs; described in the following section) arise several times in different tissues during prenatal development, producing successive waves of hematopoiesis (Fig. 2-1). Hematopoiesis first appears around day 16 of gestation in the embryonic yolk sac; at this site, it is limited to the production of red cells, which are needed for oxygen transport in the newly developed circulatory system. Hematopoietic cells arise anew around 3 to 4 weeks of gestation in a portion of the ventral mesoderm referred to as the aorta-gonad-mesonephros region. HSCs derived from this region (and possibly the yolk sac as well) are believed to migrate through the blood and take up residence in the liver, which becomes a hematopoietic organ at around 6 week.
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Xarelto Lawsuit: Some HSC divisions may be symmetric, such that both daughter cells either become HSCs or begin to differentiate into progenitors. Symmetric divisions that give rise to two HSCs may occur in the fetal liver, a stage of development during which HSC numbers increase. Symmetric divisions in which both daughter cells begin to differentiate into an early hematopoietic progenitor, a process termed commitment, may occur following periods of hematopoietic stress. Other HSC divisions are asymmetric, such that one cell remains an HSC, and the second commits to differentiation. Asymmetric cell divisions are dominant in the bone marrow, in which the number of HSCs remains fairly constant. Details still remain to be worked out, but it appears that the potential of very early committed progenitors is first restricted to myeloid (red cell, granulocyte, and megakaryocyte) or lymphoid (B cell, T cell, and natural killer cell) differentiation. With subsequent divisions, the differentiation potential of progenitors is further refined, so that it is ultimately restricted to a single cell type.
Bone marrow HSCs normally spend most of the time in a resting state referred to as quiescence, only “awakening” to divide, at most, every few months. Quiescence may help to maintain the multipotent state and protect HSCs against the acquisition of mutations that could lead to transformation and cancer development. Under conditions of increased hematopoietic demand, however, HSCs in the marrow divide more frequently and are more likely to divide symmetrically, expanding their numbers. In extreme circumstances, substantial numbers of HSCs and early progenitors may leave the marrow and migrate to the liver, spleen, and lymph nodes, where they can produce extramedullary hematopoiesis.
HSC behavior in ways that are not yet completely understood. HSCs are resistant to stimulation by hematopoietic growth factors (described in the following section), possibly because niche factors actively promote quiescence. It may be that HSCs expand only when growth factors increase and quiescence factors decrease concomitantly. Another idea posits that HSC numbers are regulated by niche “vacancy,” such that HSCs expand their numbers only when open niches are available. Under conditions of severe hematopoietic stress, it is possible that secondary niches appear in sites of extramedullary hematopoiesis, such as the liver.
Because HSCs are rare cells that are morphologically indistinguishable from lymphocytes, special means must be used to identify them. HSCs express particular surface markers such as CD34 and actively pump out certain dyes, properties that can be used to identify populations of cells that are enriched for HSCs. However, proof that viable HSCs are present in a sample requires functional testing. If a cell preparation can completely reconstitute long-term hematopoiesis when transfused into a host that has had its own marrow cells destroyed (e.g., by high doses of radiation), then it must contain HSCs, which can be quantified by serial dilution of the sample. Although this procedure, termed stem cell transplantation, was originally developed (and is still widely used) for experimental purposes, it was rapidly adopted as a means to treat a variety of diseases (described later in this chapter). It remains the only form of stem cell therapy that is widely used in clinical practice.
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Xarelto Lawsuit: Myelopoiesis (the production of myeloid elements—red cells, granulocytes, and platelets) is regulated at the level of myeloid progenitors by hematopoietic growth factors. As differentiation proceeds, myeloid progenitors lose multipotency and the capacity for self-renewal, but in turn acquire two other key properties: 1) an increased capacity for cell division, and 2) surface expression of specific receptors for hematopoietic growth factors. By controlling the growth and survival of committed myeloid progenitors, growth factors regulate the production of red cells, granulocytes, and platelets from the marrow. Some growth factors, such as stem cell factor (also known as c-KIT ligand) and interleukin (IL)-3, have growth- and survival-promoting effects on multiple types of progenitors, whereas other factors, such as erythropoietin and thrombopoietin, have effects that are restricted to progenitors committed to a single line of differentiation.
Once an early progenitor commits to differentiate, what determines which kind of cell it becomes? Two models have been proposed. One supposes that factors produced in the microenvironment instruct progenitors to differentiate along certain lines. In some instances, this appears to be true. For example, lymphoid progenitors exposed to factors that activate the Notch pathway become T cells, whereas, in the absence of Notch signals, these progenitors mainly become B cells instead, The other model supposes that progenitors randomly (stochastically) become competent to adopt particular fates and that hematopoietic growth factors act on this pool of cells to control their growth and survival. This model appears to hold for myeloid progenitors, which (as described earlier) are regulated by hematopoietic growth factors.
One important group of disorders in which these regulatory mechanisms go awry is the various kinds of malignancies, cancers of hematopoietic cells. ‘Ihese cancers are commonly associated with acquired mutations that alter the function of the same transcription factors that control differentiation. In fact, mutations in particular transcription factors tend to be found in tumors composed of cells that correspond to the stage in development at which the affected transcription factor normally acts. For example, PAX5 mutations are found in tumors composed of early B-cell progenitors, whereas BCL6 mutations are confined to tumors derived from germinal center B cells. In general, cancer-specific mutations in transcription factors interfere with differentiation, holding cells in an immature state. In addition to transcription factor mutations, mutations in one or another component of the signaling pathways that arc normally activated by growth factors are often found in hematopoietic cancers. These mutations typically stimulate signaling even in the absence of growth factors, permitting tumors to proliferate in a growth factor-independent fashion. These themes are expanded upon in later chapters describing the hematopoietic neoplasms.
Both models require that progenitors turn on the expression of a set of genes that allows hematopoietic differentiation to proceed. Experimental work with “knockout” mice has shown that certain transcription factors, proteins that associate with DNA and control gene expression, are critically important in directing differentiation along particular lines. For example, the loss of the transcription factor PAX5 specifically blocks B-cell development, while leaving other lineages intact. Similarly, loss of Notch 1, a unique type of receptor that also acts directly as a transcription factor, selectively blocks T-cell development, while mutations in C/EBPa block granulocytopoiesis. Other factors are required in early hematopoietic progenitors, and, as a result, their loss causes a complete failure of hematopoiesis. MLL is an example of one such factor. On the other end of the developmental spectrum, some factors have no role in early progenitors or in lineage determination but arc instead required for the further differentiation of mature cells. For example, loss of the transcription factor BCL6 prevents antigen-stimulated B lymphocytes from maturing into germinal center B cells. Thus, hematopoiesis is orchestrated by a complex interplay between extrinsic factors (hematopoietic growth factors and local factors produced in the microenvironment) and factors intrinsic to hematopoietic progenitors (growth factor receptors and hematopoietic transcription factors).
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Xarelto Lawsuit: Except for identical twins, the recipients of allogeneic SCT are reconstituted with cells that are genetically distinct from the host. In this situation, the transplanted HSCs will be recognized as foreign and rejected by the patient’s immune system unless a “conditioning” regimen consisting of radiation and/or chemotherapy is given. Conditioning serves two purposes: 1) it suppresses the recipients immune system, helping to prevent rejection of the transplanted cells, and 2) it destroys or displaces the recipients HSCs, creating vacancies in the marrow niche for the transplanted HSCs. The successful reconstitution of allogeneic SCT recipients with HSCs from another individual has several important immunologic consequences. On the one hand, because lymphocytes derived from the transplanted HSCs recognize the recipients cells as foreign, recipients will develop potentially fatal graft-versus-host disease unless immunosuppressive drugs are given. On the other hand, when allogeneic SCT is performed in patients with cancer, donor lymphocytes derived from the transplanted HSCs also recognize host cancer cells as foreign, producing a beneficial graft-versus-tumor effect.
An attractive but as yet unfulfilled use of SCT is as a means to deliver “gene therapy” to individuals with inherited hematopoietic disorders. In principle, it should be possible to repair genetic defects (for example, a defective P-globin gene encoding sickle hemoglobin) in stem cells in the laboratory and then reconstitute the patient with “corrected” HSCs through autologous SCT. Recent advances in reprogramming of somatic cells into stem cells with the capacity for hematopoiesis provide a reason for optimism about the long-term prospects of this approach. Epo is the most widely used growth factor. It is most effective when given to treat anemias associated with inappropriately low levels of Epo. These include the anemia of renal failure, in which the production of Epo is diminished by damage to the kidney parenchyma, and the anemia of chronic inflammation, in which inflammatory cytokines suppress the production of Epo. Anemia of inflammation is common in patients with certain inflammatory disorders and various forms of cancer. Epo is also used with varied success in patients with hematopoietic neoplasms, such as myelodysplastic syndromes, that are associated with ineffective hematopoiesis.
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Xarelto Lawsuit