Effect of Plasma Exchange in Thyroid Storm With Consideration of Its Distribution Into the Extravascular Space

Plasma exchange (PE), which directly removes some plasma thyroid hormones, is a treatment option for thyroid storm. However, the effect of PE has not been accurately assessed yet. Here we assessed the effect of PE in a patient with thyroid storm while taking into consideration the distribution of thyroid hormones in the extravascular space. A 51-year-old woman with thyroid storm underwent 2 PE procedures at our hospital. By measuring changes in thyroid hormone levels in plasma, fresh frozen plasma (FFP) used, and waste fluid during each 2.5-hour PE procedure, we calculated the efficiency of thyroid hormone removal based on the hypothesis that total thyroid hormone content before and after PE is the same. During the patient’s first PE procedure, the estimated thyroxine (T4) balance in the extravascular space (ΔX) was −70 μg, which corresponds to approximately 19% of T4 in the waste fluid. During the second PE procedure, ΔX was −131 μg, which corresponds to approximately 52% of T4 in the waste fluid. These data indicated that the source of removed T4 during PE varies. The amount of T4 removed from the extravascular space should be taken into account during assessment of the effect of PE in thyroid storm.

A CCR2 macrophage endocytic pathway mediates extravascular fibrin clearance in vivo

Key PointsFibrin is cleared from extravascular space via endocytosis and lysosomal degradation by a CCR2-positive subset of inflammatory macrophages. This novel endocytic fibrin degradation pathway is mechanistically coupled to extracellular fibrin degradation pathways.

At Equal Doses FIXFc (Alprolix) Is Not Significanly Better in a Saphenous Vein Bleeding Model Than Recombinant FIX (BeneFix) Seven Days Post-Infusion

The use of extended half-life coagulation factors is predicated on the use of less frequent infusions to maintain a therapeutic plasma level. Factor IX presents a problem to this approach because much of the FIX is sequestered in the extravascular space in significantly greater quantities than that found within the circulation. Extravascular FIX may be important for either extended clotting activity, enhanced catalytic activity, or both. We previously demonstrated that: 1) FIX binds tightly to Collagen IV; 2) variant FIX with increased Collagen IV affinity (FIXK5R) protects mice from bleeding better than wild-type (wt) FIX; 3) knock-in mice expressing a variant FIX with decreased Collagen IV affinity (FIXK5A) have a bleeding diathesis. This is despite the fact that plasma activity of FIXK5A expressed as a knock-in the Hem B mouse, is not only normal and functional, it is present in the plasma of these animals at slightly greater levels than FIX in normal mice. Here, we report a direct comparison of the hemostatic efficacies of FIXFc (Alprolix) and recombinant FIXwt (BeneFix) in a murine saphenous vein bleeding model in which hemostasis was tested at 7 days post-infusion. Although the terminal half-life of FIXFc is significantly longer than BeneFix, Alprolix at equivalent doses is not significantly better at correcting bleeding (Fig. 1a). This unexpected result could be explained if the larger size, and/or cycling through the Fc receptor, renders FIXFc less accessible to the extravascular space. If binding to Collagen IV is physiologically relevant, we posited that more BeneFix would be required to achieve hemostasis in mice expressing a Collagen IV-binding FIX that is catalytically defective, compared to mice with complete FIX deficiency. This is because the infused, catalytically active FIX must compete with the endogenous, catalytically defective FIX for binding to Collagen IV. We confirmed this hypothesis using the saphenous vein bleeding model in a knockout mouse expressing only human FIXR333Q, which binds Collagen IV normally but is catalytically defective (Figure 1b). Clearly more FIX is required to achieve an equivalent clotting effect in mice expressing defective FIX that binds collagen IV normally. The extravascular space contains approximately 4 to 5 times more FIX than is present in the circulation. Thus, it would be expected that at least 4-5 times more infused FIX than current dosing regimens (40-60 IU/kg) would be required to obtain the maximum hemostatic effect and duration. To this end, we compared the hemostatic effect of 50, 100, 150, 200, and 250 IU/kg of BeneFix, 7 days post-infusion. The median value for the number of times that the saphenous vein can re-clot increases as the dose increases from 50 to 150 IU/kg with noticeable leveling off after this (Figure 2); at least 16 mice were used for each dose. Little or no consideration is given to the amount of extravascular FIX and the role of FIX's binding to Collagen IV in current dosing regimens. Based upon the results presented here, we predict that considerably greater doses of FIX will contribute to a longer protective effect. Furthermore, given the apparent importance of FIX's binding to Collagen IV, it is likely that still higher doses will be required for patients whose defective FIX binds normally to type IV Collagen. Finally, at equivalent doses, in mice, Benefix is not statistically different from Alprolix in bleeding protection 7 days post-injection. This observation may be explained by a different physical location of the two molecules. Disclosures Monahan: Chatham LLC: Consultancy; Pfizer: Honoraria; Asklepios BioPharmaceutical: Consultancy, Patents & Royalties: Author I.P. licensed by UNC to AskBio, Research Funding; Bayer: Consultancy; CSL Behring: Consultancy, Honoraria; Novo Nordisk: Consultancy, Honoraria, Research Funding; Baxter/Baxalta: Consultancy, Honoraria, Research Funding; Prolor: Research Funding. Stafford:Pfizer: Consultancy, Research Funding. Off Label Use: I am not sure what off-label really means. I doubt that I have a problem.But, I do believe that higher doses of FIX are required for most efficient treatment..

Validation of Microcirculatory Parameters Derived from the Standard Two-Compartment Model with Murine Xenografts Model

The purpose of this study was to validate DCE-MRI parameters such as blood flow (F), permeability surface area product (PS), fractional intravascular space (v1), and fractional extracellular extravascular space (v2), obtained using a standard two-compartment model against other established analysis methods and histological indices. DCE-MRI datasets of 28 mice implanted with various human cancer xenografts were acquired and analyzed. Statistically significant correlations were found between the parameters derived from the standard two-compartment model (v1, v2, F, and PS) with the histological markers of intravascular and interstitial space and with the corresponding flow and permeability estimates obtained by the initial slope method and Patlak plot, respectively.

Hemolysis and free hemoglobin revisited: exploring hemoglobin and hemin scavengers as a novel class of therapeutic proteins

Hemolysis occurs in many hematologic and nonhematologic diseases. Extracellular hemoglobin (Hb) has been found to trigger specific pathophysiologies that are associated with adverse clinical outcomes in patients with hemolysis, such as acute and chronic vascular disease, inflammation, thrombosis, and renal impairment. Among the molecular characteristics of extracellular Hb, translocation of the molecule into the extravascular space, oxidative and nitric oxide reactions, hemin release, and molecular signaling effects of hemin appear to be the most critical. Limited clinical experience with a plasma-derived haptoglobin (Hp) product in Japan and more recent preclinical animal studies suggest that the natural Hb and the hemin-scavenger proteins Hp and hemopexin have a strong potential to neutralize the adverse physiologic effects of Hb and hemin. This includes conditions that are as diverse as RBC transfusion, sickle cell disease, sepsis, and extracorporeal circulation. This perspective reviews the principal mechanisms of Hb and hemin toxicity in different disease states, updates how the natural scavengers efficiently control these toxic moieties, and explores critical issues in the development of human plasma–derived Hp and hemopexin as therapeutics for patients with excessive intravascular hemolysis.

Distinct roles for LFA-1 affinity regulation during T-cell adhesion, diapedesis, and interstitial migration in lymph nodes

During the course of homing to lymph nodes (LNs), T cells undergo a multistep adhesion cascade that culminates in a lymphocyte function-associated antigen 1 (LFA-1)–dependent firm adhesion to the luminal surface of high endothelial venules (HEVs). The importance of LFA-1 affinity regulation in supporting T-cell arrest on HEVs has been well established, however, its importance in the postadhesion phase, which involves intraluminal crawling and diapedesis to the extravascular space, remains elusive. Here we have shown that LFA-1 affinity needs to be appropriately regulated to support these essential steps in the homing cascade. Genetically engineered T cells that were unable to properly down-regulate LFA-1 affinity underwent enhanced, chemokine-independent arrest in HEVsbut showed perturbed intravascular crawling to transmigration sites and compromised diapedesis across HEVs. By contrast, the extravascular migration of T cells was insensitive to the affinity-enhancing LFA-1 mutation. These results highlight the requirement for balanced LFA-1 affinity regulation in intravascular and transvascular, but not extravascular, T-cell migration in LNs.