Novel de novo synthesized phosphate carrier compound ABA-PEG20k-Pi20 suppresses collagenase production in Enterococcus faecalis and prevents colonic anastomotic leak in an experimental model.

BACKGROUND: Previous work has demonstrated that anastomotic leak can be caused by collagenolytic bacteria such as Enterococcus faecalis via an effect on wound collagen. In humans, E. faecalis is the organism cultured most commonly from a leaking anastomosis, and is not routinely eliminated by standard oral or intravenous antibiotics. Novel strategies are needed to contain the virulence of this pathogen when present on anastomotic tissues. METHODS: Polyphosphorylated polymer ABA-PEG20k-Pi20 was tested in mice for its ability to prevent anastomotic leak caused by collagenolytic E. faecalis. The study design included a distal colonic resection and anastomosis followed by introduction of E. faecalis to anastomotic tissues via enema. Mice were assigned randomly to receive either ABA-PEG20-Pi20 or its unphosphorylated precursor ABA-PEG20k in their drinking water. The development of anastomotic leak was determined after the animals had been killed. RESULTS: Overnight incubation of two different E. faecalis collagenolytic strains with 2 mmol/l of ABA-PEG20k-Pi20 led to near complete inhibition of collagenase production (from 21 000 to 1000 and from 68 000 to 5000 units; P < 0·001; 6 samples per group) without suppressing bacterial growth. In mice drinking 1 per cent ABA-PEG20k-Pi20, the phosphate concentration in the distal colonic mucosa increased twofold and leak rates decreased from eight of 15 to three of 15 animals (P < 0·001). In mice drinking ABA-PEG20k-Pi20, the percentage of collagenolytic colonies among E. faecalis populations present at anastomotic tissue sites was decreased by 6-4800-fold (P = 0·008; 5 animals). CONCLUSION: These data indicate that oral intake of ABA-PEG20k-Pi20 may be an effective agent to contain the virulence of E. faecalis and may prevent anastomotic leak caused by this organism. Clinical relevance Progress in understanding the pathogenesis of anastomotic leak continues to point to intestinal bacteria as key causative agents. The presence of pathogens such as Enterococcus faecalis that predominate on anastomotic tissues despite antibiotic use, coupled with their ability to produce collagenase, appears to alter the process of healing that leads to leakage. Further antibiotic administration may seem logical, but carries the unwanted risk of eliminating the normal microbiome, which functions competitively to exclude and suppress the virulence of pathogens such as E. faecalis. Therefore, non-antibiotic strategies that can suppress the production of collagenase by E. faecalis without affecting its growth, or potentially normal beneficial microbiota, may have unique advantages. The findings of this study demonstrate that drinking a phosphate-based polymer can achieve the goal of preventing anastomotic leak by suppressing collagenase production in E. faecalis without affecting its growth.

Spatial distribution and temporal change in cytosolic pH and [Ca2+] in resting and activated single human platelets.

In human platelets, a rapid rise in cytoplasmic Ca2+ and slower rise in cytoplasmic pH follow stimulation by thrombin. With the Ca2+ probe Fura-2 and the pH probe SNARF-1 for digitized fluorescence microscopy, we studied simultaneously the distribution and changes with time of [pH]i and [Ca2+]i in individual human platelets. In platelets coloaded with both probes, the probes had no detectable fluorescence at each other's excitation wavelength. The monovalent cation ionophore, nigericin (2 microM), produced a homogeneous rise in pH but no change in [Ca2+]. Platelets, in contact with glass, spread and developed an irregular, apparently mutually independent rise in both [Ca2+] and pH. Stimulation of platelets by thrombin 1.0 U/ml elevated [Ca2+]i and produced slow alkalinization without initial acidification. Replacement of extracellular Na+ by choline abolished thrombin-induced alkalinization, but had no effect on thrombin-induced [Ca2+]i elevation. ADP 10 microM caused a rapid rise of [Ca2+]i and transient alkalinization. Most stimulated platelets developed a gradient in pH, that was highest in the center. ADP and thrombin caused oscillation of [Ca2+]i but not of [pH]i. We conclude that alkalinization in stimulated platelets, presumably involving Na+/H+ antiport, is not essential for the rise of [Ca2+]i that may accompany it.

c-myb affects intracellular calcium handling in vascular smooth muscle cells.

The protooncogene c-myb is responsible for elevating intracellular calcium concentration ([Ca2+]i) at the G1/S interface in vascular smooth muscle cells (VSMC). However, the molecular components of this pathway are undefined, and the biological effects of increased levels of divalent cation are unknown. We have demonstrated that growth-arrested c-myb-transfected VSMC, compared with wild type VSMC, exhibit a fourfold increased number of insulin-like growth factor I (IGF-I) receptors, increased amount of secreted IGF-I activity, and a twofold increased level of [Ca2+]. The c-myb transfected cells, compared with wild type cells, also possess a twofold increased rate of calcium influx and a twofold decreased rate of calcium efflux. The elevated calcium influx rate of transfected cells is decreased to that of wild type cells with IGF-I neutralizing antibody, whereas the decreased calcium efflux rate of transfected cells is increased to that of wild type cells with antisense c-myb oligonucleotides. Proliferating wild type VSMC exhibit an increased calcium influx rate in late G1, which is dependent on production of augmented amounts of IGF-I activity but not increased levels of IGF-I receptors. The wild type VSMC also show a decreased calcium efflux rate at the same point in the cell cycle, which is dependent on expression of c-myb. The treatment of wild type cells with antisense c-myb or IGF-I receptor oligonucleotides induces a late G1 block in cell proliferation, which can be overcome by exposure to the calcium ionophore, 4-bromo-A-27318, in amounts sufficient to raise [Ca2+]i to levels observed at the G1/S interface. We conclude that IGF-I/IGF-I receptors and c-myb are involved in control of [Ca2+]i at the G1/S interface by separately regulating the rates of calcium influx and efflux and that elevated levels of divalent cation are necessary for progression of VSMC into the S phase of the cell cycle.

pp60src is an endogenous substrate for calpain in human blood platelets.

Calpain is distributed ubiquitously in virtually every tissue (Croall, D. E., and DeMartino, G. N. (1991) Physiol. Rev. 71, 813-846), but its physiological role remains to be determined. The identification of its natural endogenous substrates would be of great interest. Since pp60src, a major tyrosine kinase in platelets, is known to be easily cleaved during purification from cells (Feder, D., and Bishop, J. M. (1990) J. Biol. Chem. 265, 8205-8211), we examined the possibility that it is an endogenous substrate of calpain. In the whole cell lysate from resting platelets, which was analyzed by Western blotting with monoclonal antibody 327, we found pp60src almost exclusively in a 60-kDa form, with a trace of 52-kDa form. Addition of A23187 (a calcium ionophore) or dibucaine, which are known to be activators of platelet calpain (Croall and DeMartino, 1991; Fox, J. E., Reynolds, C., Morrow, J. S., and Phillips, D. R. (1987) Blood 76, 2510-2519; Fox, J. E., Austin, C. D., Boyles, J. K., and Steffen, P. K. (1990b) J. Cell Biol. 111, 483-493), caused dose- and time-dependent cleavage of actin-binding protein and p235 protein (talin). At the same time, loss of the 60-kDa species of pp60src and generation of the 52-kDa (occasionally seen as doublets) and 47-kDa species were detected by the Western blotting. In platelets aggregated by 1 unit/ml thrombin, apparently identical cleavage products were found. The cleavage of pp60src was inhibited by calpeptin (20 microM), an inhibitor of calpain (Tsujinaka, T., Kajiwara, Y., Kambayashi, J., Sakon, M., Higuchi, N., Tanaka, T., and Mori, T. (1988) Biochem. Biophys. Res. Commun. 153, 1201-1208; Tsujinaka, T., Ariyoshi, H., Uemura, Y., Sakon, M., Kambayashi, J., and Mori, T. (1990) Life Sci. 46, 1059-1066; Fox, J. E., Clifford, C. C., and Austin, C. D. (1990) Blood 76, 2510-2519; Fox, J. E., Austin, C. D., Boyles, J. K., and Steffen, P. K. (1990) J. Cell. Biol. 111, 483-493; Fox, J. E., Austin, C. D., Clifford, C. C., and Steffen, P. K. (1991) J. Biol. Chem. 266, 13289-13295). Addition of EGTA (3 mM) to the extracellular media completely inhibited the cleavage of actin-binding protein, talin, and pp60src in response to A23187 (1 microM). Intact pp60src was distributed in both cytosolic and particulate (membrane) fractions. Cleaved species were found exclusively in the cytosolic fraction. pp60src-associated enolase kinase activity was reduced. Thus, pp60src is an endogenous substrate for calpain, the cleavage of which may have regulatory effects on the kinase.

Adventures in hemostasis. Desmopressin in cardiac surgery.

Desmopressin acetate (1-deamino-8-D-arginine vasopressin [DDAVP]) improves hemostasis in hemophilia A and von Willebrand's disease and in some platelet disorders. In complex cardiac operations, excluding simple coronary artery bypass graft procedures, we found that desmopressin reduced blood loss by 40% and the need for transfusion by 34%. Conflicting reports followed. Future trials should emphasize patients with excessive bleeding. A possible post-desmopressin prothrombotic state was studied after hip replacement surgery. The incidence of deep vein thrombosis associated with warfarin sodium therapy was the same as that associated with desmopressin plus warfarin therapy. No desmopressin-induced thrombotic tendency was detected. A trend toward reduced blood loss with desmopressin was not significant. During cardiac catheterization, the plasma von Willebrand factor level was correlated with hemodynamic variables, including pulmonary vascular resistance, pulmonary arterial pressure, and (inversely) with cardiac index. von Willebrand factor concentration was highest in mitral stenosis. The relationship of these factors to the response to desmopressin remains to be defined.

Association of pp60src with Triton X-100-insoluble residue in human blood platelets requires platelet aggregation and actin polymerization.

Protein-tyrosine phosphorylation during platelet activation is inhibited under conditions that inhibit platelet binding of fibrinogen and aggregation. We suggested that pp60src, a major platelet tyrosine kinase, or its protein substrates might become associated with the cytoskeleton upon platelet stimulation, and that this might be related to aggregation. By Western blotting with an anti-Src monoclonal antibody, we found time-dependent association of pp60src with the cytoskeleton (10,000 x g Triton X-100-insoluble matrix) but not the "membrane" cytoskeleton (100,000 x g Triton X-100-insoluble matrix) in platelets activated by U46619 (PGH2 analog). Cytoskeletal association and platelet aggregation were inhibited by the peptide Arg-Gly-Asp-Ser (RGDS) (but not by Arg-Gly-Glu-Ser (RGES)), by 10E5 antibody against glycoprotein (Gp) IIb/IIIa, and by EGTA. U46619-induced association of pp60src with cytoskeleton but not secretion or aggregation was inhibited by cytochalasin D (2 microM). Both cytochalasin D and RGDS inhibited "slow" tyrosine phosphorylation of platelet proteins. Association of pp60src with cytoskeleton induced by U46619 or ADP was not blocked by aspirin. Aspirin blocked epinephrine-induced association of pp60src with the cytoskeleton during a second phase of aggregation when an initial phase had occurred without shape change or secretion. Association of GpIIb/IIIa with the cytoskeleton also accompanied platelet aggregation, shape change, and actin polymerization; this was shown with anti-GpIIb and anti-GpIIIa antibodies. Association of pp60src and GpIIb/IIIa with the cytoskeleton and slow tyrosine phosphorylation are related phenomena.

Inhibition by sodium nitroprusside or PGE1 of tyrosine phosphorylation induced in platelets by thrombin or ADP.

Upon platelet activation, numerous proteins are known to be tyrosine phosphorylated. To investigate the mechanisms of the regulation of tyrosine phosphorylation and its physiological significance, the effects on tyrosine phosphorylation of agents that elevate the platelet level of the cyclic nucleotides cAMP and cGMP were examined in aspirin-treated gel-filtered platelets by Western blotting with a specific antiphosphotyrosine antibody. The effects of these agents on other aspects of platelet activation, i.e., aggregation, secretion, and elevation of the concentration of cytosolic ionized calcium ([Ca2+]i), were also examined in parallel experiments. Tyrosine phosphorylation in platelets activated by alpha-thrombin (1 nM) was inhibited by prostaglandin (PG) E1 (2 microM) or by sodium nitroprusside (100 microM). Elevation of [Ca2+]i, aggregation, and serotonin secretion was also strongly inhibited. On the other hand, a higher concentration of alpha-thrombin (10 nM) induced tyrosine phosphorylation of the same proteins, elevation of [Ca2+]i, platelet aggregation, and serotonin secretion, irrespective of pretreatment of platelets by either PGE1 or sodium nitroprusside. Inhibition by sodium nitroprusside of tyrosine phosphorylation induced by alpha-thrombin (1 nM) was accompanied by an increased concentration of cGMP. 8-BrcGMP (2 mM) also inhibited tyrosine phosphorylation and aggregation, although less than sodium nitroprusside. ADP (20 microM) induced platelet shape change and tyrosine phosphorylation of only a few proteins; these effects were also inhibited by either PGE1 or sodium nitroprusside. Thus tyrosine phosphorylation in platelets can be inhibited by elevation of either cAMP or cGMP, an effect that is overcome by a high concentration of thrombin, resulting in granule secretion and aggregation. Some of the proteins that are tyrosine phosphorylated may be important in the regulation of platelet functions.

Heterogeneity in filamentous actin content among individual human blood platelets.

The content of filamentous actin in individual platelets was measured by flow cytometry, using a fluorescent probe specific for filamentous actin (F-actin), 7-nitrobenz-2-oxa-1,3-phallacidin (NBD-phallacidin). NBD-phallacidin binding to fixed platelets was specific in that either pretreatment of platelets with unlabeled phallacidin or absorption of NBD-phallacidin by rabbit skeletal F-actin, but not globular actin (G-actin), resulted in a significant loss in the bound fluorescent probe. Mean NBD-phallacidin binding to fixed platelets varied with the agonist and paralleled the changes in F-actin reported with the DNAse I inhibition assay. (1) NBD-phallacidin binding increased with stimulation by ADP, U46619 (a prostaglandin H2 analogue), or collagen and paralleled shape change. (2) Epinephrine did not increase NBD-phallacidin binding. (3) Platelets treated at 4 degrees C contained more F-actin than did platelets kept at 37 degrees C. (4) Cytochalasin D (10 mumol/L) inhibited the increase of phallacidin binding to individual platelets stimulated by either ADP or U46619. In measurements of cytosolic free calcium concentration ([Ca2+]i) by flow cytometry in Indo-1-loaded platelets, ADP's dose-response for actin polymerization was similar to that for calcium mobilization. As shown by flow cytometry, a tail population that had a minimal increase in F-actin upon stimulation with ADP or U46619 also contained the platelets with the least forward and right angle light scattering, which are functions of platelet size and shape. When platelets treated with NBD-phallacidin were incubated with S12-murine monoclonal antibody (a marker of alpha-granule secretion detected by phycoerythrin-conjugated antimouse IgG second antibody), phallacidin fluorescence paralleled S12 binding. Thus, human blood platelets are heterogeneous in regard to actin polymerization at rest and in association with platelet activation; different degrees of phallacidin binding may identify functionally different platelet populations.

Low-molecular-weight heparinoid compared with warfarin for prophylaxis of deep-vein thrombosis in patients who are operated on for fracture of the hip. A prospective, randomized trial.

In a randomized, prospective trial, a low-molecular-weight heparinoid (Org 10172 [Lomoparan]) was compared with warfarin for efficacy and safety in preventing deep-vein thrombosis in 263 patients who had an operatively treated fracture of the hip. One group of patients received Org 10172 in a dose of 750 units subcutaneously every twelve hours until the ninth postoperative day; on the seventh postoperative day, warfarin was added to the regimen. The other group received only warfarin. Both drugs were begun preoperatively, immediately after the admission evaluation. In the patients who received warfarin, the desired prothrombin time was one and one-half times the control level. Deep-vein thrombosis was detected by 125I-fibrinogen scanning and impedance plethysmography and was confirmed by phlebography and compression ultrasonography. Deep-vein thrombosis was found in nine (7 per cent) of the 132 patients who received Org 10172 and in twenty-eight (21 per cent) of the 131 patients who received warfarin (p less than 0.001). Adverse reactions were not significantly different in the two groups. Major bleeding complications occurred in eight patients in the Org-10172 group, only four of whom were receiving the drug at the time of bleeding, and in five patients who were receiving warfarin (not significant). There was no difference in intraoperative loss of blood or in requirements for transfusion. We concluded that the low-molecular-weight heparinoid Org 10172 is a safe, convenient, effective antithrombotic agent for the prevention of venous thrombosis after an operation for fracture of the hip.

Quasi-simultaneous measurement of ionized calcium and alpha-granule release in individual platelets.

The effect of alpha-thrombin and ADP on calcium mobilization and alpha-granule release in individual platelets was investigated by flow cytometry. alpha-Thrombin (4.5 nM) caused a uniform rise of free cytosolic calcium ([Ca2+]i) among indo-1-loaded human platelets. Despite the uniformity of this effect, approximately 20% of the cells failed to secrete alpha-granule content, as shown by binding of fluorescein isothiocyanate (FITC)-conjugated S12 monoclonal antibody. ADP (10 microM) caused a similar brisk and uniform rise of calcium but did not increase S12 binding to any platelets. On the other hand, with alpha-thrombin (0.5 nM), calcium mobilization was heterogeneous and paralleled granule release. [Ca2+]i increased rapidly in some platelets, while only slowly in others. When an electronic gate was set according to FITC-S12 fluorescence, cells with a greater secretory response proved to be those with a higher calcium level. With both alpha-thrombin and ADP, chelation of external calcium by EGTA (2 mM) reduced calcium response of individual cells. NiCl2 (1 mM) also inhibited calcium rise of individual platelets to the same extent as EGTA (2 mM) in spite of the presence of 1 mM CaCl2 in the extracellular media. The effects of EGTA and NiCl2 were not limited to a particular subpopulation of cells. These data suggest that the putative Ni2(+)-inhibitable divalent cation channel(s) may be responsible for the increased influx of calcium that occurs during platelet activation by alpha-thrombin and ADP. It appears that these calcium channels contribute to the elevation of [Ca2+]i among virtually all the platelets.

Activation of protein kinase C in platelets by epinephrine and A23187: correlation with fibrinogen binding.

Activation of protein kinase C (PKC), as revealed by phosphorylation of a 47 kd protein (p47), occurs in platelets stimulated by some agonists (eg, thrombin or phorbol esters). It is not known if activation of PKC occurs with pairs of agonists, such as epinephrine and A23187, that do not individually phosphorylate p47, nor is it known what role the concentration of cytoplasmic Ca++ ([Ca++]i) plays in these events. We stimulated aequorin-loaded platelets with subaggregating concentrations of epinephrine and A23187, neither of which by itself phosphorylated p47. The combination of agonists resulted in p47 phosphorylation, an increase in platelet-bound fibrinogen, and aggregation, but only if the concentration of each agonist was sufficient to increase [Ca++]i if it was added separately. Subaggregating concentrations of A23187 alone released platelet fibrinogen and increased platelet membrane binding of [3H]-phorbol dibutyrate, but these were not enhanced by epinephrine. Epinephrine and A23187 did not increase production of diacylglycerol. Thus, epinephrine and A23187 together activate PKC by a mechanism that does not require phospholipase C or enhanced binding of PKC to the plasma membrane; PKC activation in turn is correlated with enhanced platelet fibrinogen binding and aggregation. These events require an initial elevation of [Ca++]i above a threshold.

Abnormalities of cytoplasmic Ca2+ in platelets from patients with uremia.

Uremic patients have a hemorrhagic tendency, often associated with prolonged bleeding times and decreased platelet function in vitro. Whether these defects result from abnormalities in plasma factors affecting platelet activity, platelet surface receptors, intracellular platelet mediators, or other aspects of platelet behavior is unknown. To examine the possibility that the abnormality in platelet function may result from aberrations in Ca2+ homeostasis, blood was obtained from 29 patients with severe uremia. The platelets were washed, loaded with the Ca2+ -sensitive probes indo-1 and aequorin, gel-filtered, and resuspended in either plasma or buffer. Of the 29 patients, seven had template bleeding times prolonged to 11 minutes or more, but platelet aggregation in plasma was not consistently impaired in these patients. However, in aequorin-loaded platelets from the patients with long bleeding times, the highest elevation of cytoplasmic calcium [( Ca2+]i) in response to the Ca2+ ionophore A23187, arachidonate, adenosine diphosphate (ADP), or epinephrine was lower than that seen in platelets from both uremic patients with less prolonged bleeding times and normal volunteers. The reduced [Ca2+]i response was associated with decreased aggregation of gel-filtered platelets suspended in buffer. Suspending washed aequorin-loaded uremic platelets in normal plasma for 20 minutes did not reverse the decreased agonist-induced rise in [Ca2+]i; platelets from a normal donor resuspended in uremic plasma aggregated and produced a normal increase in [Ca2+]i in response to agonists. We conclude that the platelet defect seen in some patients with uremia is associated with a decreased rise in platelet [Ca2+]i after stimulation and that this is a manifestation of an intrinsic platelet defect.

Changes in von Willebrand factor during cardiac surgery: effect of desmopressin acetate.

Patients who receive desmopressin acetate (dDAVP) after cardiopulmonary bypass bleed less during operation and in the first 24 hours after operation than do patients who receive a placebo. To study the mechanism of improved hemostasis in bypass patients, we examined the relationship between von Willebrand factor (vWF) and blood loss in 70 cardiopulmonary bypass patients, one-half of whom received desmopressin intraoperatively. vWF concentration and multimeric composition were analyzed before and after bypass, after drug treatment, and 24 hours after operation. Before operation, patients with valvular disease had lower percentages of vWF high-mol-wt multimers (HMWMs) than did healthy subjects or patients with coronary artery disease, but subsequent blood loss, vWF activity, and bleeding times were not related to this finding. Irrespective of drug treatment, patients who had low preoperative vWF and who had a net loss of the protein during bypass bled more after bypass than did similar patients who had a net increase of vWF during bypass. HMWMs rose to above normal levels after bypass regardless of desmopressin infusion. Differences in the concentration of vWF between desmopressin and placebo patients after receipt of the drug, although small, were better correlated with reduced blood loss than were differences in HMWM distribution. We conclude that the beneficial effect of desmopressin on hemostasis following cardiopulmonary bypass cannot be attributed to a drug-induced change in HMWM distribution but may be related to an increase in overall vWF concentration.

Effect of optimization of hemodynamics on fibrinolytic activity and antithrombotic efficacy of external pneumatic calf compression.

External pneumatic calf compression is effective but imperfect for antithrombotic prophylaxis in surgical patients. In preliminary studies, sequential filling of multisegmented leggings with graded pressure decreasing from ankle to knee increased venous flow velocity and wall shear stress, decreased residual venous volume, and enhanced postoperative fibrinolysis more than uniform compression. To determine if improved hemodynamics also increased antithrombotic activity, we performed a prospective randomized trial in neurosurgical patients comparing sequential application of graded pressure with uniform pressure applied to either a segmented bladder or to a single bladder. Deep vein thrombosis was diagnosed by leg scanning and impedance plethysmography and confirmed by phlebography. Venous thrombosis developed in 3 of 45 patients with graded-sequential filling, 6 of 50 with uniform compression-multiple compartments, and 3 of 41 with uniform pressure single bladder (differences not significant). These results suggest either that uniform compression offers all that can be expected of external pneumatic calf compression in prevention of venous thrombosis, or that even if a study with greater statistical power showed graded-sequential filling to be superior, the benefit/cost ratio of the more complex latter system is not likely to be large.

Synergism of platelet-aggregating agents. Role of elevation of cytoplasmic calcium.

When a pair of platelet agonists, each in subthreshold concentration, is added together or in sequence to a platelet suspension, the platelet response is enhanced. Addition of two agonists to platelets loaded with aequorin also enhanced the observed rise in cytoplasmic ionized calcium ([Ca2+]i) in response to the second agonist if the agonists were added within 20 s of each other. Enhancement of aggregation and secretion required that an increase in [Ca2+]i (as indicated by aequorin but not necessarily indo-1) followed the first agonist, but not that the [Ca2+]i remain elevated until addition of the second agonist. Enhancement was not prevented by aspirin, ADP scavengers, or chelators of extracellular Ca2+. We conclude that a rise in [Ca2+]i induced by a first agonist "primes" platelets for an augmented functional response to a second agonist, which is not, however, determined by the [Ca2+]i at the time of addition of the second agonist.

Crosslinked polyether/polysiloxane networks for blood-interfacing applications.

The interaction of blood with new artificial surfaces is an area of continual medical interest. In this study, a series of polyether/polysiloxane networks were synthesized, characterized in terms of both bulk and surface compositions, and evaluated for blood compatibility. The crosslinked networks were produced by reacting the epoxy groups of polyglycidoxy propyl methyl siloxane (PGPMS) with the hydroxyl end groups of polypropylene glycol (PPG). Blood compatibility was evaluated using an in vitro platelet retention test and fibrinogen adsorption experiments from human plasma and buffered saline. The PPG/PGPMS networks exhibit low fibrinogen adsorption and low platelet activation. Such properties make the networks potentially attractive as materials for blood-interfacing applications.

Fibrinogen adsorption and platelet adhesion at the surface of modified polypropylene glycol/polysiloxane networks.

The protein film adsorbed at an artificial surface ultimately affects platelet adhesion and activation. This study examines the role of fibrinogen in platelet adhesion at the surface of crosslinked polypropylene glycol (PPG)/polyglycidoxy propyl methyl siloxane (PGPMS) networks which contain polyethylene glycol monomethyl ether (PEGME) chains. These crosslinked networks were produced by reacting the epoxy groups of PGPMS with the hydroxyl groups of the polyethers. PEGME chains were attached covalently to the network at only one end while PPG chains were attached at both ends. The incorporation of PEGME resulted in a substantial reduction in fibrinogen adsorption as compared to the model network (PPG + PGPMS only), but the expected concomitant decrease in platelet adhesion was not observed.