Antithrombin III-beta associates more readily than antithrombin III-alpha with uninjured and de-endothelialized aortic wall in vitro and in vivo.

Abstract

The properties of two isoforms, or and fi, of rabbit antithrombin III (ATIII) were compared in the presence of undamaged or de-endothelialized rabbit aortic wall. Similar quantities of ATIII-tt and ATUI-fi bound to and rapidly saturated the endothelium in vitro, but the rate of transendothelial passage of ATIII-/3 exceeded that of ATIII-a by 22%. Furthermore, ATIII-0 was adsorbed approximately twice as rapidly as ATlII-a by the subendothelium of the de-endothelialized aorta. Binding of both isoforms was decreased (ATIII-/3 more than Al'lU-or) by pretreating the subendothelial surface with heparitinase. Also, subendothelium-bound ATIII-/J was desorbed more readily than bound ATlII-aby thrombin. In vivo, the rate of uptake of iodine-131-labeled ATI1I-/3 from the circulation by the aortic wall and the major organs was 30-50% faster than that of iodine-125-labeled ATIII-o: In contrast, the uptake of m I-ATIII-0 by the de-endothelialized aorta in vivo was three times faster than that of '"I-ATlII-a. By these criteria, ATIII-^ is the more active of the two isoforms. We surmise that plasma and, consequently, vessel wall levels of ATIII-/3 may be vital for controlling thrombogenic events caused by injury to the vascular wall. (Arteriosclerosis and Thrombosis 1991;ll:530-539) F rom recent reports, two forms of the glycoprotein antithrombin III (ATIII) have been isolated from rabbit 1 and human 2 plasma. Both the rabbit and human isoforms were separated by gradient elution from a heparin-Sepharose affinity column, the major human isoform, ATIII-a, eluting at 0.9-1.0 M NaCl, and the minor isoform, ATIII-ft at 1.4 M NaCl.2 Human ATIII-0 was shown to contain approximately 25-30% less carbohydrate than ATIII-a.2 More recently, Brennan et al 3 have reported that, unlike the human ATIII-a isoform, which has four biantennary /V-glycans (at asparagine [Asn] 96, 135, 155, and 172), the ATIII-0 isoform possesses only three 7V-glycans, lacking that at Asn 135. Can-ell et al 4 have suggested that the absence of the N-glycan at Asn 135 may extend the binding site for heparin and, consequently, increase the affinity of ATIII-/3 for heparin.

Protein adsorption on polyurethane catheters modified with a novel antithrombin‐heparin covalent complex

“…However, no AT was detected on the uncoated control catheter. Multiple bands were seen in the AT region for the heparinized catheter, possibly due to the well‐known heterogeneity in AT glycosylation 57. The ATH modified surfaces showed only a single AT band, suggesting that only one form of AT was adsorbed; the lower molecular weight of this band being suggestive of β‐AT isoform, which has a higher affinity for heparin binding sites 57…”

Intracellular retention of hepatic serpins caused by severe hyperlipidemia

“…Antithrombin plays an anti‐inflammatory role by promoting endothelial production of prostacyclins, inhibiting activation of leukocytes and endothelial cells directly and attenuating TNF‐α‐dependent responses (7). Additionally, heparin cofactor II (26) and the β‐form of antithrombin (27, 28) are relevant inhibitors of thrombin in the arterial wall, which is paramount to inhibit smooth muscle proliferation and macrophage migration in plaque formation. Thus, plasma deficiency of these serpins, caused by its intracellular accumulation, could also contribute to atherosclerosis.…”

Two distinct forms of human mast cell chymase

“…The presence of two distinct forms of chymase with different affinities for heparin is likely to have important consequences. It has been shown that the two isoforms of antithrombin III have different distributions, with the lower affinity form (AT III-A) being the dominant form in plasma, and the higher affinity form (AT III-β) preferentially binding heparan sulphate and being enriched in the sub-endothelial layers of blood vessels [58]. The differences in proteoglycan-binding ability of the two tryptases of the mouse have been shown to be associated with different rates of diffusion through tissues following their extrusion from mast cells, with the higher affinity form (MMCP-6) remaining bound to the granule remnant, and the lower affinity form (MMCP-7) diffusing away and, under some conditions, appearing in the circulation [59].…”