Inhibition of platelet-neutrophil interactions by Fucoidan reduces adhesion and vasoconstriction after acute arterial injury by angioplasty in pigs

Fucoidan for cardiovascular application and the factors mediating its activities

Fucoidan is a sulfated polysaccharide with various bioactivities. The application of fucoidan in cancer treatment, wound healing, and food industry has been extensively studied. However, the therapeutic value of fucoidan in cardiovascular diseases has been less explored. Increasing number of investigations in the past years have demonstrated the effects of fucoidan on cardiovascular system. In this review, we will focus on the bioactivities related to cardiovascular applications, for example, the modulation functions of fucoidan on coagulation system, inflammation, and vascular cells. Factors mediating those activities will be discussed in detail. Current therapeutic strategies and future opportunities and challenges will be provided to inspire and guide further research.

Low-molecular-weight fucoidan protects endothelial function and ameliorates basal hypertension in diabetic Goto-Kakizaki rats

Endothelial dysfunction, characterized by impairment of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability, has been implicated in diabetic cardiovascular pathogenesis. In this study, low-molecular-weight fucoidan (LMWF), which has multiple biological activities including anti-inflammatory and anti-oxidative properties, was investigated for its protective effect against endothelial dysfunction in Goto-Kakizaki type 2 diabetic rats. LMWF (50, 100, or 200 mg/kg/day) or probucol (100 mg/kg/day) were given to diabetic rats for 12 weeks. Basal blood pressure, acetylcholine- or flow-mediated relaxation of mesenteric and paw arteries, endothelium-dependent dilation of aorta, eNOS phosphorylation, and NO production were measured using laser Doppler flowmetry, force myograph, hematoxylin and eosin staining, western blot analysis, and an NO assay. We found that LMWF robustly ameliorated the basal hypertension and impairment of endothelium-dependent relaxation in the aorta, as well as mesenteric and paw arteries in diabetic rats. In addition, the reduction in eNOS phosphorylation at Ser1177, eNOS expression, and NO production because of diabetes were partially reversed by LMWF treatment. However, probucol, a lipid-modifying drug with antioxidant properties, displayed only mild effects. Moreover, LMWF induced, in a dose-dependent manner, endothelium-dependent vasodilation and eNOS phosphorylation at Ser1177 in normal aorta, and also promoted Ser1177 phosphorylation and NO synthesis in primary cultured vasoendothelial cells. Thus, these data demonstrate for the first time that fucoidan protects vasoendothelial function and reduces basal blood pressure in type 2 diabetes rats via, at least in part, preservation of eNOS function. Fucoidan is therefore a potential candidate drug for protection of endothelium in diabetic cardiovascular complications.

Neutrophil and platelet complexes and their relevance to neutrophil recruitment and activation

The manifestation of platelet 'satallitism' around neutrophils in whole blood is a long acknowledged phenomenon [1]. Circulating platelet-neutrophil complexes (PNC) occur in a diverse range of inflammatory disorders and infections that affect numerous organs of the body. Animal models have revealed that the formation of PNC is required for the recruitment of neutrophils to inflamed tissue, since platelets 'prime' neutrophils for efficient adhesion to vascular endothelium via the up-regulation of integrins and enhanced responsiveness to chemokines (Fig. 1). Perhaps surprisingly, the surface contact between platelets and neutrophils additionally enhances other neutrophil functions, such as chemotaxis that is required for migration into tissues, trans-cellular production of eicosanoids, phagocytosis and trapping of pathogens, increased respiratory burst leading to the production of reactive oxygen species (ROS), and modulation of neutrophil apoptosis (Fig. 1). Platelet P-selectin appears to have a particular role in enhancing the majority of these activities, and the influence of platelet P-selectin is not therefore confined to the initial rolling events in the process of neutrophil extravasation.

Heparin-like entities from marine organisms

Polysaccharides are ubiquitous in animals and plant cells where they play a significant role in a number of physiological situations e.g. hydration, mechanical properties of cell walls and ionic regulation. This review concentrates on heparin-like entities from marine procaryotes and eukaryotes. Carbohydrates from marine prokaryotes offer a significant structural chemodiversity with novel material and biological properties. Cyanobacteria are Gram-negative photosynthetic prokaryotes considered as a rich source of novel molecules, and marine bacteria are a rich source of polysaccharides with novel structures, which may be a good starting point from which to synthesise heparinoid molecules. For example, some sulphated polysaccharides have been isolated from gamma-proteobacteria such as Alteromonas and Pseudoalteromonas sp. In contrast to marine bacteria, all marine algae contain sulphated wall polysaccharides, whereas such polymers are not found in terrestrial plants. In their native form, or after chemical modifications, a range of polysaccharides isolated from marine organisms have been described that have anticoagulant, anti-thrombotic, anti-tumour, anti-proliferative, anti-viral or anti-inflammatory activities.In spite of the enormous potential of sulphated oligosaccharides from marine sources, their technical and pharmaceutical usage is still limited because of the high complexity of these molecules. Thus, the production of tailor-made oligo- and polysaccharidic structures by biocatalysis is also a growing field of interest in biotechnology.

Progenitor cell mobilizing treatments prevent experimental transplant arteriosclerosis

OBJECTIVE

Vascular rejection after organ transplantation is characterized by an arterial occlusive lesion, resulting from intimal proliferation occurring in response to arterial wall immune aggression. Our hypothesis is that an early endothelial repair may prevent vascular graft rejection. The aim of the current study was to compare different pharmacologic progenitor cell mobilizing treatments for their protective effects against vascular rejection.

METHODS AND RESULTS

Aortic transplants were made from balb/c donor to C57Bl/6 recipient mice. Three different mobilizing pharmacologic agents were used: low molecular weight fucoidan (LMWF), simvastatin, and AMD3100. The circulating levels of progenitor cells were found to be increased by all three treatments, as determined by flow cytometry. For each treatment, the design was: treated allografts, nontreated allografts, treated isografts, and nontreated isografts. After 21 d, morphometric and immunohistochemical analyses were performed. We found that the three treatments significantly reduced intimal proliferation, compared with nontreated allografts. This was associated with intimal re-endothelialization of the grafts. Further, in chimeric mice that had previously received GFP-transgenic bone marrow transplantation, GFP-positive cells were found in the vascular allograft intima, indicating that re-endothelialization was, at least partly, due to the recruitment of bone marrow-derived, presumably endothelial progenitor circulating cells.

CONCLUSIONS

In this aortic allograft model, three different mobilizing treatments were found to partially prevent vascular transplant rejection. Bone marrow-derived progenitor cells mobilized by the three treatments may play a direct role in the endothelial repair process and in the suppression of intimal proliferation.

Structure, biology, evolution, and medical importance of sulfated fucans and galactans

Sulfated fucans and galactans are strongly anionic polysaccharides found in marine organisms. Their structures vary among species, but their major features are conserved among phyla. Sulfated fucans are found in marine brown algae and echinoderms, whereas sulfated galactans occur in red and green algae, marine angiosperms, tunicates (ascidians), and sea urchins. Polysaccharides with 3-linked, beta-galactose units are highly conserved in some taxonomic groups of marine organisms and show a strong tendency toward 4-sulfation in algae and marine angiosperms, and 2-sulfation in invertebrates. Marine algae mainly express sulfated polysaccharides with complex, heterogeneous structures, whereas marine invertebrates synthesize sulfated fucans and sulfated galactans with regular repetitive structures. These polysaccharides are structural components of the extracellular matrix. Sulfated fucans and galactans are involved in sea urchin fertilization acting as species-specific inducers of the sperm acrosome reaction. Because of this function the structural evolution of sulfated fucans could be a component in the speciation process. The algal and invertebrate polysaccharides are also potent anticoagulant agents of mammalian blood and represent a potential source of compounds for antithrombotic therapies.

Acute-phase protein alpha-1-acid glycoprotein mediates neutrophil migration failure in sepsis by a nitric oxide-dependent mechanism

The reduction of circulating neutrophil migration to infection sites is associated with a poor outcome of severe sepsis. alpha-1-Acid glycoprotein (AGP) was isolated from the sera of severely septic patients by HPLC and acrylamide gel electrophoresis and identified by mass spectrometry. Both the isolated protein and commercial AGP inhibited carrageenin-induced neutrophil migration into the rat peritoneal cavity when administered i.v. at a dose of 4.0 microg per rat (95 pmol per rat). Analysis by intravital microscopy demonstrated that both proteins inhibited the rolling and adhesion of leukocytes in the mesenteric microcirculation. The inhibitory activity was blocked by 50 mg/kg aminoguanidine, s.c., and was not demonstrable in inducible nitric oxide synthase (iNOS) knockout mice. Incubation of AGP with neutrophils from healthy subjects induced the production of NO and inhibited the neutrophil chemotaxis by an iNOS/NO/cyclic guanosine 3,5-monophosphate-dependent pathway. In addition, AGP induced the l-selectin shedding by neutrophils. The administration of AGP to rats with mild cecal ligation puncture sepsis inhibited neutrophil migration and reduced 7-day survival from approximately 80% to 20%. These data demonstrate that AGP, an acute-phase protein, inhibits neutrophil migration by an NO-dependent process and suggest that AGP also participates in human sepsis.

Low Molecular Weight Fucoidan Prevents Neointimal Hyperplasia After Aortic Allografting

BACKGROUND

Fucoidan, a new low molecular weight sulfated polysaccharide (LMWF), has previously been shown to mobilize bone marrow-derived progenitors cells via stimulation of stromal derived factor (SDF)-1 release. Mobilized progenitor cells have been suggested to repair intimal lesions after immune-mediated endothelial injury and thus prevent intimal proliferation. The aim of this study was to evaluate the effect of LMWF treatment in a rat aortic allograft model of transplant arteriosclerosis (TA).

METHODS

Aortic grafts were performed in Brown Norway (BN, donor) and Lewis (Lew, recipient) rats. The recipient rats were treated with LMWF (5 mg/kg/day) and sacrificed at 30 days. To determine the role of SDF-1 in mediating the effects of LMWF, a specific inhibitor of the SDF-1 receptor CXCR4, AMD 3100 (20 microg/kg/day), was used. The grafted segments were evaluated by morphometric (histochemical) analyses.

RESULTS

Untreated aortic allografts exhibited severe intimal proliferation, indicative of TA. In contrast, LMWF treatment significantly prevented allograft intimal proliferation as compared with controls (5.7+/-3 vs. 66.2+/-6 microm, P<0.01) and permitted a normalization of the intima/media ratio (0.1+/-0.1 vs. 1.7+/-0.3, P<0.01). Further, LMWF treatment stimulated allograft reendothelialization, as evidenced by strong intimal endothelial nitric oxide synthase antibody and CD31 signals. Unexpectedly, AMD treatment failed to prevent the protective effect of LMWF on intimal thickening and AMD treatment alone was found to reduced intimal proliferation in allografts.

CONCLUSIONS

We found that LMWF treatment reduced intimal thickness and induced the presence of an endothelial cell lining in the vascular graft at 30 days. Our findings may suggest a novel therapeutic strategy in the prevention of TA.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Low molecular weight fucan prevents transplant coronaropathy in rat cardiac allograft model

INTRODUCTION

Transplant arteriosclerosis is the main cause of long-term failure after cardiac transplantation. Vascular rejection is thought to be due to intimal proliferation occurring in response to arterial wall immune-mediated injury. A low molecular weight fucan (LMWF) compound, a sulfated polysaccharide, has been demonstrated to increase plasma levels of stromal cell-derived factor 1 (SDF-1) and consequently to mobilize bone marrow-derived vascular progenitor cells (BMVPC). The aim of this study was to evaluate the capacity of LMWF to prevent coronary intimal proliferation in a rat cardiac allograft model.

METHODS

Heterotopic abdominal cardiac graftings were performed in Brown Norway (BN) and Lewis (LEW) rats. Animals were divided into 4 groups of 10 rats. Two groups were treated intramuscularly with LMWF (5 mg/kg/day) (one BN to BN isograft group, and one BN to LEW allograft group); and two control groups were LMWF-untreated (one BN to BN isograft group and one BN to LEW allograft group). All animals were treated by cyclosporin (15 mg/kg/day) sub-cutaneously and sacrificed at day 30. The cardiac grafts were assessed by morphometry of structural parameters and by histological and immunohistochemical analyses.

RESULTS

All cardiac isografts were devoid of any coronary and parenchymal lesions. In contrast, the majority of untreated allografts developed coronary intimal proliferation in close association with intimal and adventitial inflammatory CD68(+) cell infiltration. Further, the parenchyma exhibited large areas of actin(+) cells (myofibroblasts) of recipient origin colocalized with the CD68(+) infiltrating cells. Interestingly, all LMWF-treated allografts were well protected against coronary and parenchymal lesions and the coronary arteries exhibited an intimal monolayer of flat cells, which however were CD34 negative.

CONCLUSION

treatment with LMWF appeared very effective in this rat cardiac allograft model to prevent arterial and parenchymal lesions occurring in response to alloimmune injury. However this protective effect does not appear to depend on mobilization of bone marrow-derived cells.

Sulfatides, L- and P-selectin ligands, exacerbate the intimal hyperplasia occurring after endothelial injury

Leukocytes may be important in the development of intimal hyperplasia, but little is known about the participation of sulfatides (3-sulfated galactosyl ceramides) which are native ligands of L- and P-selectin. This study was designed to determine whether sulfatides affect the development of intimal hyperplasia. ICR mice were randomized to receive vehicle or sulfatides intravenously either at 1, 3, or 10 mg/kg/day for 7 days, or at 10 mg/kg/day for 1, 3, or 7 days. Endothelial damage was inflicted on the femoral artery via the photochemical reaction between rose bengal and green light. Scanning electron and light microscopic observations 3 days after the injury indicated that sulfatides-treated animals had more neutrophils adhering to the injury site than vehicle-treated controls. At 21 days, sulfatides-treated animals had a greater neointimal area than controls. In in vitro studies, sulfatides (i) increased cytosolic free calcium in mouse neutrophils, (ii) caused increases in expression of Mac-1 (CD 11 b/CD 18) on the neutrophil membrane surface in mouse whole blood. These findings suggest that neutrophil accumulation on the subendothelial matrix or adherence of platelets mediated by adhesive interactions between L- or P-selectin and sulfatides may contribute to the development of intimal hyperplasia. The neutrophil accumulation may be mediated by an increase in Mac-1 caused by the agonistic effects of sulfatides on the neutrophil membrane surface, or by an increase in L- and P-selectin ligands resulting from the binding of sulfatides onto the exposed subendothelial matrix.

Antagonism of selectin function attenuates microvascular platelet deposition and platelet-mediated myocardial injury after transient ischemia

OBJECTIVES

The goal of this study was to assess whether selectin blockade reduces myocardial platelet deposition and platelet-mediated injury after transient ischemia.

BACKGROUND

Selectins participate in platelet adhesion to reperfused endothelium.

METHODS

Thiopental-anesthetized, open-chest pigs were subjected to mechanical injury of the left anterior descending coronary artery followed by a 48-min occlusion and 2 (n = 20) or 4 (n = 16) h of reperfusion. Fifteen minutes before occlusion, animals were blindly allocated to receive a continuous intravenous infusion of the selectin blocker fucoidan (30 microg/kg/min, plus a 1-mg/kg bolus in the latter group) or saline. In isolated rat hearts infused with thrombin-activated platelets, the effects of fucoidan (30 microg/ml) administered during reperfusion after 40 min of global ischemia were also analyzed.

RESULTS

Fucoidan did not prevent the development of cyclic reductions in coronary flow, but reduced the content of (99m)Tc-labeled platelets in reperfused myocardium after 2 h of reperfusion (23.4 +/- 3.3 vs. 42.1 +/- 8.3 x 10(6) platelets/g in treated and untreated animals, p = 0.03) and attenuated the impairment in the coronary flow reserve and reduced infarct size after 4 h (53 +/- 2% vs. 73 +/- 5% of the ischemic region, respectively, p = 0.003). Treated animals showed a trend toward less neutrophil infiltration early after reperfusion, but not after 4 h. In isolated hearts, fucoidan improved functional recovery and reduced coronary resistance and lactate dehydrogenase release, lacking any beneficial effects if given in the absence of platelets.

CONCLUSIONS

The results suggest that selectin-dependent adhesion is a prominent mechanism of platelet deposition in reperfused cardiac microvessels and highlight its potential as a therapeutic target in patients with acute myocardial infarction.

Mechanism of the stimulatory effect of native fucoidan, highly sulfated fucoidan and heparin on plasminogen activation by tissue plasminogen activator: The role of chloride

Native Fucoidan and unfractionated heparin enhanced by 6-fold the in vitro activation of human glutamic plasminogen (Glu-Plg) by tissue plasminogen activator (t-PA) using 0.05M Tris buffer pH 7.4, while sulfated fucoidan inhibited the activation under these conditions. Double reciprocal plots of these interactions showed that sulfated fucoidan inhibited the activation in a noncompetitive manner while the enhancements by heparin or native fucoidan were due to an increase of Vmax without affecting Km. To determine whether the stimulatory effect of the individual cofactor was due to its interaction with Glu-Plg or with t-PA, experiments were performed at a fixed level of the cofactor and either varying in a serial fashion the concentration of Glu-Plg or of t-PA. The ratios of the initial rate of plasmin generation in the presence or absence of the cofactors were plotted against the inverse of the volume fraction of Glu-Plg or of t-PA. The results showed that heparin interacted with Glu-Plg while native fucoidan and sulfated fucoidan interacted with t-PA. Studies were also conducted on the effect of the two fucoidans and heparin on the activation of Glu-Plg by t-PA using 0.05M Tris buffer pH 7.4 containing 0.1 M NaCl. Under these conditions, sulfated fucoidan was most effective in enhancing the activation followed by native fucoidan and heparin respectively. The results of this study showed that in presence of the buffer containing 0.1 M NaCl, heparin was interacting with t-PA while the two fucoidans were interacting with both t-PA and Glu-Plg. A comparison of the double reciprocal plots of the rate of enhancement by the cofactors using 0.05M Tris buffer pH 7.4 containing 0.1M NaCl or in presence of buffer alone showed that the cofactors were more effective using 0.05M Tris buffer pH 7.4 alone and that addition of NaCl to the buffer slowed down the reactions by decreasing Vmax without affecting Km. Circular Dichroism (CD) studies of Glu-Plg in the far ultraviolet (UV) range showed that addition of NaCl destabilized the beta sheet structure which was reversed by addition of 6-aminohexanoic acid (6-AH) or one of the cofactors, while the near UV CD spectra of Glu-Plg in presence of 0.1 M NaCl was enhanced by the cofactors by increasing its ellipticity as reported earlier for 6-AH.

Effects of pulmonary ischemia-reperfusion on platelet adhesion in subpleural arterioles in rabbits

Reperfusion of the ischemic lung is associated with increased pulmonary vascular resistance and reduced alveolar perfusion in conjunction with an inflammatory response. To determine the contribution of platelet-endothelial interactions, we examined effects of pulmonary ischemia-reperfusion (IR) on platelet adhesion and diameter of arterioles and investigated the hypothesis that this process is P-selectin mediated. In anesthetized rabbits with open-chest and ventilated lungs, we examined subpleural arterioles by fluorescence microscopy. Ischemia was caused by reversibly occluding the right pulmonary artery for 2 h. Fluorescently labeled platelets were injected into the right atrium and the right lung was observed after 0.5, 1.0, and 2.0 h of reperfusion. Platelets rolling and adherence along arterioles occurred with a decrease in diameter that was significant during IR, but not after 3- to 5-min occlusion (control). Systemic pretreatment with Fucoidan (a ligand to P- and L-selectin) inhibited platelet rolling, adherence, and the decrease in diameter. Pretreatment of only exogenously labeled platelets with monoclonal antibody (MoAb) to P-selectin prevented platelet rolling and adherence, but not the decrease in diameter. These results indicate that in the intact lung, pulmonary IR causes platelet rolling and adhesion along arteriolar walls, and suggest that this process, which is mediated by P-selectin, contributes to vasoconstriction and hypoperfusion. Thus, it appears that platelet-endothelial interactions may contribute to the development of pulmonary IR injury.

The effect of fucoidan, heparin and cyanogen bromide-fibrinogen on the activation of human glutamic-plasminogen by tissue plasminogen activator

Earlier studies on the stimulatory effect of fucoidan, heparin, and cyanogen bromide (CNBr)-fibrinogen digest on the in-vitro activation of glutamic type plasminogen by tissue plasminogen activator, which were performed using subphysiologic ionic strengths of buffers, gave inconsistent results because of the variation in the ionic strengths of the buffers used. Studies were therefore conducted on the effect of these cofactors using 0.05 mol/l Tris buffer containing a physiologic concentration of sodium chloride. The double reciprocal plots of the activation of glutamic type plasminogen by tissue plasminogen activator in the presence of fucoidan and 6-aminohexanoic acid (6-AH) or heparin and 6-AH showed a four- to six-fold increase in K(cat), while the K(m) remained unchanged. On the other hand, there was greater than six-fold lowering of K(m) from 0.213 to 0.035 micromol/l in the presence of CNBr-fibrinogen, while K(cat) was only slightly increased. The ratios of the initial rate of plasmin generation in the presence or absence of the cofactors were plotted against the inverse of the volume fraction of glutamic type plasminogen or of tissue plasminogen activator after serial dilution. The results suggested that the enhancements by fucoidan and 6-AH or CNBr-fibrinogen were due to their interactions directed towards glutamic type plasminogen, while for heparin and 6-AH, the interaction was directed towards tissue plasminogen activator. Circular dichroism studies in the near ultraviolet range (250-308 nm) showed that 6-AH enhanced the circular dichroism spectra of glutamic type plasminogen around certain chromophores, while fucoidan and heparin had no effect, suggesting that the enhancement by the cofactors may be related to the favorable conformational changes of glutamic type plasminogen by 6-AH.

Low molecular weight fucoidan prevents neointimal hyperplasia in rabbit iliac artery in-stent restenosis model

OBJECTIVE

Smooth muscle cell (SMC) proliferation within the intima is regulated by heparan sulfates. We studied a low molecular weight (LMW) fucoidan (sulfated polysaccharide from brown seaweed) on SMC proliferation in vitro and intimal hyperplasia in vivo.

METHODS AND RESULTS

In vitro study revealed that LMW fucoidan reduces rabbit SMC proliferation and is internalized in SMC perinuclear vesicles. On rabbit iliac arteries perfused in vivo with fluorolabeled LMW fucoidan after angioplasty, the labeling was mainly located on sites of injury. Pharmacokinetic studies showed that LMW fucoidan exhibited in rats an elimination half-life of 56+/-25 minutes (n=8) after intravenous administration and a constant plasma rate for > or =6 hours after intramuscular administration. After stent implantation in their iliac arteries, rabbits were also treated with LMW fucoidan (5 mg/kg IM twice a day). Histomorphometric analysis at day 14 indicated that LMW fucoidan reduced intimal hyperplasia by 59% (1.79+/-0.4 versus 0.73+/-0.2 mm2, P<0.0001) and luminal cross-sectional area narrowing by 58% (0.38+/-0.08 versus 0.16+/-0.04, P<0.0001). Blood samples showed no anticoagulant activity due to LMW fucoidan.

CONCLUSIONS

This natural polysaccharide with high affinity for SMCs and sustained plasma concentration markedly reduced intimal hyperplasia, suggesting its use for the prevention of human in-stent restenosis.

Intravascular granulocyte aggregates caused by the selectin-binding carbohydrate fucoidin in pig kidneys

1. Renal postischaemic reperfusion injury constitutes a significant problem after kidney transplantation. The polysaccharide fucoidin improves postischaemic function in lamb hearts, presumably by blocking selectin-mediated leucocyte adhesion. 2. In the present study, eight pairs of ischaemic pig kidneys were reperfused in an ex vivo model with autologous blood with or without fucoidin (100 mg/L). 3. Fucoidin resulted in a significant decrease in renal blood flow (45 +/- 5 vs 178 +/- 22 mL/min per 100 g; P < 0.001) and increased vascular resistance (3.80 +/- 0.07 vs 0.60 +/- 0.12 mmHg/mL per min per 100 g; P < 0.001). 4. Histological examination revealed granulocyte emboli in afferent glomerular arteries in five of six fucoidin-treated kidneys and in one of six controls (Fisher's exact test; P < 0.001). 5. In vitro experiments with human granulocytes showed that large granulocyte aggregates were induced by fucoidin at concentrations similar to those used in reperfused kidneys, whereas slightly lower doses of fucoidin prevented l-selectin-dependent homotypic granulocyte adhesion. 6. The formation of embolizing granulocyte aggregates defines a narrow therapeutic range for fucoidin and calls into question its experimental use as an inhibitor of selectin-mediated leucocyte adhesion.