Alpha2-antiplasmin: potential therapeutic roles in fibrin survival and removal

Alpha2-antiplasmin (alpha2AP) is the primary inhibitor of plasmin, a proteinase that digests fibrin, the main component of blood clots. Two forms of alpha2AP circulate in human plasma: a 464-residue protein with methionine as the amino-terminus (Met-alpha2AP) and an N-terminally-shortened 452-residue form with asparagine as the amino-terminus (Asn-alpha2AP). Human plasma alpha2AP concentration is 1 micro M and consists of approximately 30% Met-alpha2AP and approximately 70% Asn-alpha2AP. The major form (Asn-alpha2AP) is rapidly crosslinked to fibrin during blood clotting by activated coagulation factor XIII and as a consequence, fibrin becomes more resistant to fibrinolysis. It is apparent that alpha2AP is important in modulating the effectiveness and persistence of fibrin with respect to its susceptibility to digestion and removal by plasmin. Hence, the physiologic role of alpha2AP suggests that it may be a useful target for developing more effective treatment of thrombotic diseases. Research on alpha2AP appears to be moving in two main directions: (1) efforts to use variant forms of alpha2AP to reduce bleeding secondary to thrombolytic therapy while not slowing thrombolysis; and (2) efforts to use variant forms to diminish the activity of alpha2AP as a plasmin inhibitor so that fibrinolysis becomes enhanced. Methods to accomplish these two goals mostly involve manipulation of defined functional domains within the molecular structure of alpha2AP, or inhibition of a newly described novel plasma proteinase, termed antiplasmin-cleaving enzyme, that generates the more favorable form of alpha2AP, Asn-alpha2AP, for crosslinking to fibrin. The antiplasmin-cleaving enzyme has similarity in primary structure and catalytic properties to fibroblast activation protein/seprase. This review summarizes recent studies that may hold promise for modulating alpha2AP activity and its interactions with certain proteins as new therapeutic strategies for preventing and treating thrombotic disorders.     

Flt3-ligand induces adhesion of haematopoietic progenitor cells via a very late antigen (VLA)-4- and VLA-5-dependent mechanism

The adhesion of haematopoietic progenitor cells (HPC) to the bone marrow microenvironment is a process regulated by cytokines. In this study, we have shown that flt3-ligand (FL), a growth factor that controls early haematopoiesis, regulated the function and expression of the beta-1 integrins, very late antigen (VLA)-4 and VLA-5 on HPC. The modulation of the adhesiveness of HPC by FL was studied by adhesion assays on umbilical vein endothelial cells (HUVEC). Stimulation by FL induced two peaks of increased adhesiveness of HPC. The first peak was at around 30 min and was mechanistically related to an activation of the beta-1 integrins, mainly VLA-4 and VLA-5. The second peak was at around 12 h and was related to increased expression of VLA-4 and VLA-5. The control of HPC adhesiveness by FL is a previously unreported property of FL that may be important for the homing and the retention of flt3-expressing HPC within the bone marrow microenvironment.     

Severe refractory hypoxemia following a gunshot injury

We describe the case of a 57-year-old man with severe refractory hypoxemia, despite receiving ventilation therapy with 100% oxygen, following a gunshot wound to his left chest. A limited CT scan of the chest with contrast raised the suspicion of an arteriovenous (AV) fistula. Contrast-enhanced transthoracic echocardiography confirmed the presence of a pulmonary AV fistula. Traumatic pulmonary AV fistula is a rare, but serious and life-threatening condition that should be suspected in patients with thoracic injuries with persistent unexplained hypoxemia. Contrast echocardiography is a relatively simple, inexpensive, and readily available bedside test that can be used to confirm this diagnosis.     

Comparative quantitative angiographic analysis of directional coronary atherectomy and balloon coronary angioplasty

An attempt to assess the “utility” of directional atherectomy was made using a new quantitative angiographic index. This index can be subdivided into an initial gain component and a restenosis component. The initial gain index is the ratio between the gain in diameter during intervention and the theoretically achievable gain (i.e., reference diameter). The restenosis index is the ratio between the decrease at follow-up and the initial gain during the procedure. The net result at long-term follow-up is characterized by the utility index, which is the ratio between the final gain in diameter at follow-up and what theoretically could have been achieved. For this purpose, 30 coronary artery lesions were selected from a consecutive series of successfully dilated primary angioplasty lesions and were matched with the initial 30 successfully treated primary atherectomy lesions. Matching by location of stenosis and reference diameter resulted in 2 comparable groups with identical preprocedural stenosis characteristics. Atherectomy resulted in an increase in minimal luminal diameter 2 times larger than angioplasty (1.53 vs 0.77 mm; p < 0.0001). However, at follow-up there was a significant decrease in minimal luminal diameter and a significant increase in percent diameter stenosis in the groups with atherectomy and angioplasty (1.69 ± 0.58 vs 1.57 ± 0.58 mm, P = not significant [NS], and 37 ± 18 vs 47 ± 18%, P = NS, respectively). The decrease in minimal luminal gain was more pronounced in the group with atherectomy than in that with angioplasty (0.92 ± 0.69 vs 0.35 ± 0.51 mm; P = 0.0005). Consequently, directional atherectomy resulted in a significantly higher initial gain ratio than did balloon angioplasty (0.84 vs 0.41, p < 0.00001). At follow-up, restenosis and utility ratios were comparable in both groups (0.56 vs 0.62, P = NS, and 0.29 vs 0.23, P = NS, respectively). In matched groups, directional atherectomy is a very effective device with a substantially better initial result than that with balloon angioplasty. However, it appears to be a potent stimulator of the restenosis process, because at follow-up this initial favorable result is lost, and the minimal luminal diameter is comparable to that after balloon angioplasty. Thus, the final utility of directional coronary atherectomy is not significantly different from that of conventional balloon angioplasty.     

Ischemic colitis and immunosuppression

The incidence of ischemic colitis in renal transplant recipients approaches 1 percent. The mortality in these patients with ischemic colitis is nearly 70 percent. Immunosuppressive agents have been implicated in the development of ischemic colitis. To study the effect of immunosuppressive agents on ischemic colitis, a 4-cm segment of the colon was devascularized in 27 male Fischer rats. The animals were divided into one control and two treatment groups. One treatment group received methylprednisolone and the other, azathioprine, in doses similar to those of renal transplant recipients. Both experimental groups, either separately or combined, showed significantly greater areas of colonic ischemic changes than did the control group. This study demonstrates that systemic administration of immunosuppressive agents may augment the development of ischemic colitis. Poster presentation at the meeting of the American Society of Colon and Rectal Surgeons, San Diego, California, May 5 to 10, 1985. Supported by Biomedical Research Support Grant RR 05374 from the Division of Research Facilities and Resources, NIH.     

Effect of the alpha-adrenergic blocker, doxazosin, on endothelial function and insulin action

Essential hypertension is associated with impairment of both endothelial function and insulin action, and this has provided rationale for the use of antihypertensive agents that are at least neutral, if not beneficial, in these areas. This study examines the effect of the alpha-adrenergic blocker, doxazosin, on endothelial function and insulin action. Sixteen patients with essential hypertension were recruited with 13 (3 men/10 women; median age, 55 years; range, 38 to 65 years) completing the study. A double-blind, placebo-controlled crossover study design was used. After a 6-week placebo run-in, there were two 12-week treatment periods of either placebo or doxazosin, separated by a 6-week wash out period. Subjects were studied at the end of each treatment period with endothelial function assessed by forearm plethysmography and insulin action by the hyperinsulinemic clamp technique. Blood pressure was significantly lowered by doxazosin (doxazosin 144 +/-3/86 +/- 2 mm Hg; placebo 159 +/- 3/96 +/- 1 mm Hg, P <.005 for both systolic and diastolic pressure; mean +/- SEM). Baseline forearm blood flow (FBF) was unchanged (doxazosin 4.9 +/- 0.9; placebo 4.0 +/- 0.7 mL x 100 mL(-1) x min(-1), P >.05), however, FBF responses (area under dose response curve, percentage change in infused:control arm ratio) to acetylcholine (endothelium-dependent vasodilation) were improved by doxazosin (doxazosin 58.6 +/- 11.7 standard units [SU]; placebo 22.1 +/- 7.0 SU, P =.03) with responses to sodium nitroprusside (endothelium-independent vasodilation) unchanged (doxazosin 40.3 +/- 5.5 SU; placebo 46.3 +/- 8.1 SU, P >.05). Exogenous glucose infusion rates to maintain euglycemia during hyperinsulinemia were not significantly different (doxazosin 30.4 +/- 0.9; placebo 32.3 +/- 1.0 micromol x kg(-1) min(-1), P >.05). Suppression of postabsorptive endogenous glucose production by insulin was also unchanged by treatment (doxazosin 65.6% +/- 7.5% suppression; placebo 68.3% +/- 11.2% suppression, P >.05). Doxazosin has a neutral effect on both peripheral and hepatic insulin action, but improves endothelium-dependent vasodilation. These results indicate that doxazosin can be used safely in patients with insulin resistance, while its positive effect on endothelial function may lessen the subsequent incidence of atherosclerosis.     

Accuracy in precordial ECG lead placement: Improving performance through a peer-led educational intervention

Background and objectives

Inaccurate electrocardiography (ECG) lead placement may lead to erroneous diagnoses, such as poor R wave progression. We sought to assess the accuracy of precordial ECG lead placement amongst hospital staff members, and to re-evaluate performance after an educational intervention.

Effects of percutaneous transluminal septal myocardial ablation for obstructive hypertrophic cardiomyopathy on systolic and diastolic left ventricular function assessed by pressure-volume loops

The aim of the present study was to determine the long-term effects of percutaneous transluminal septal myocardial ablation (PTSMA) on systolic and diastolic left ventricular (LV) functions in patients with obstructive hypertrophic cardiomyopathy (HC). Ten consecutive patients with symptomatic HC despite optimal medical treatment were referred for PTSMA at our center. LV systolic and diastolic functions were assessed by online LV pressure-volume loops obtained by conductance catheter at baseline and at 6 months after the procedure. At follow-up, the mean gradients at rest and after extrasystole were significantly decreased compared with baseline (88 +/- 29 to 21 +/- 11 mm Hg and 130 +/- 50 to 35 +/- 22 mm Hg, respectively, p <0.01 for the 2 comparisons). End-systolic and end-diastolic pressures significantly decreased (p <0.01), whereas end-systolic and end-diastolic LV volumes significantly increased (p <0.01 for the 2 comparisons). Cardiac output and stroke volume were unchanged, as were ejection fraction (p = 0.25) and maximum dP/dt (p = 0.13). The slope of the end-systolic pressure-volume relation was not decreased, indicating a preserved contractility. The relaxation constant time, end-diastolic stiffness, projected volume of the end-diastolic pressure-volume relation at 30 mm Hg, and diastolic stiffness constant showed a significant improvement of active and passive myocardial diastolic properties. In conclusion, PTSMA is an effective method in the treatment of symptomatic patients with HC. At 6-month follow-up, the LV-aortic gradient was decreased and active and passive LV diastolic properties were increased. Myocardial contractility was not decreased and general hemodynamics was maintained.     

Central projections of photoreceptor axons originating from ectopic eyes in Drosophila

Ectopic expression of the retinal determination gene eyeless (ey) induces the formation of supernumerary eyes on antennae, legs, wings, and halteres. These ectopic eyes form ommatidia that contain photoreceptors and accessory cells and respond to light. Here, we demonstrate that ectopic eyes on antennae and legs extend axonal projections to the central nervous system. Furthermore, electroretinograms and morphological evidence indicate that the photoreceptor axons of at least the antennal ectopic eyes can form completely constituted ectopic synapses with foreign postsynaptic elements and suggest that transmission at these sites may be functional. However, the ectopic axons do not connect to their correct optic lobe targets and do not project deeply into the neuropile, but rather form synapses at superficial positions in the neuropils. By means of confocal and electron microscopy we show that these ectopic synapses resemble normal synapses, albeit with some distinct morphological differences. Our data strongly suggest that the developmental programs controlling photoreceptor synaptogenesis and visual map formation depend to a considerable extent on presynaptic and thus photoreceptor-autonomous steps. Our data also suggest that photoreceptor axon projections and the establishment of the highly stereotypical neural circuitry in the optic lobe, the normal target neuropil, may depend on target-specific cues that appear to be absent from the antennal lobe and thoracic ganglion.