POS1412 FIRSTS RESULTS OF THE PRAISE STUDY (PATIENT-REPORTED AUTOIMMUNITY SECONDARY TO CANCER IMMUNOTHERAPY): MULTICENTRIC PROSPECTIVE COHORT STUDY ON AUTOIMMUNE DISEASES SECONDARY TO CANCER IMMUNOTHÉRAPY

Background

In cancer immunotherapy, T-lymphocyte activation can lead to secondary autoimmune diseases named OASI for Opportunistic Autoimmunity Secondary to cancer Immunotherapy [1]. The epidemiology of OASI deserves to be further studied due to the unadapted reporting of clinical trials and the lack of prospective studies. Moreover, literature focuses on the most severe OASI and/or on specific OASI (myocarditis, colitis, arthritis).

Objectives

Our goal was to determine incidence, severity of all grade OASI using a multicentric prospective patient cohort starting treatment with cancer immunotherapy.

Methods

We present a multicentric, prospective, observational, longitudinal, real life, French e-cohort. 900 patients treated with ipilimumumab and/or nivolumab will be included. Data is collected from the patient and the oncologist at inclusion, then patients report directly any symptom that could be suggestive of OASI with the help of monthly digital questionaries. In case an OASI is suspected, further confirmation is made with the practician in charge and by a paired analysis with the Système National De Santé (SNDS), the French health insurance registry.

Results

On the 19/01/2022, 439 patients were included, 310 males (70.6%) and 129 females (29.4%). Mean age is 66 years old with a median follow up of 192 days. 354 patients (80.6%) are treated with Nivolumab alone, 7 (1.6%) with Ipilimumab alone and 76 (17.8 %) with combined Nivolumab + Ipilimumab. 136 patients (31.6%) are treated for a non-small cell lung carcinoma, 107 patients (24.9%) for a clear cell renal carcinoma, 91 patients (21.2%) for a skin melanoma, 49 patients (11.4%) for a head or neck epidermoid carcinoma, 24 patients (5.6%) for another lung cancer sub-type, and 32 patients (5.3%) for another histological cancer type. The mean follow-up is 294 days (+/- 192). 83 patients (18.9%) died since the beginning of the follow up.

47 patients (10.7%) developed 63 OASI. The mean delay between the beginning of cancer immunotherapy and the OASI is 134.7 days (+/- 103.4).

Approximately, one third of the OASI were musculoskeletal diseases. The OASI included polymyalgia rheumatica (3 patients), psoriatic arthritis (1 patient), polyarthritis (1 patient) systemic lupus (1 patient), arthralgias and myalgias (8 patients), colitis (11 patients), dysthyroïditis (6 patients), hepatitis (4 patients), nephritis (3 patients), pneumonitis (2 patients), hypophysitis (2 patients), adrenal insufficiency (4 patients), myocarditis (1 patient), hemophagocytic lympho-histiocytosis (1 patient), and other types of OASI (15 patients).

26 patients (55% of patients with OASI, 5,9% of all patients) had to stop cancer immunotherapy due to an OASI, one because of a rheumatic disease (systemic lupus). 52 patients were treated with corticosteroids, 1 patient with methotrexate (psoriatic arthritis), 3 patients with infliximab (colitis) and 1 patient with abatacept (myocarditis). 1 patient died after an OASI (colitis).

Conclusion

The first results of this prospective study, using an original patient-centered methodology, confirm the expected incidence of autoimmune events secondary to cancer immunotherapy and the role of rheumatologists in their therapeutic management.

References

[1]Kostine M, Chiche L, Lazaro E, et al. Opportunistic autoimmunity secondary to cancer immunotherapy (OASI): An emerging challenge. Rev Med Interne. 2017;38(8):513-525. doi:10.1016/j.revmed.2017.01.004

Acknowledgements

BMS funded the study (unrestricted grant) but had no role in study design, data collection, analysis or decision to publish.

Disclosure of Interests

Eden Sebbag: None declared, Nicolas Cloarec: None declared, Philippe Barthelemy: None declared, Nathanaël Sedmak: None declared, Naima Hamamouche Consultant of: Work for Sanoia Digital CRO, Hervé Servy Consultant of: Work for Sanoia Digital CRO, Guillaume Desjeux Consultant of: Work for Sanoia Digital CRO, Isabelle Monnet: None declared, Abeer Najem: None declared, Marc Porneuf: None declared, Laetitia-Shanna Rajpar: None declared, Jérôme Meunier: None declared, Tévy San: None declared, Laure Chauvenet: None declared, Ariane DARUT JOUVE: None declared, Sabrina FALKOWSKI: None declared, Claudia Rizzo: None declared, Noémie Litrowski: None declared, Anthony Canellas: None declared, Jean-François Paitel: None declared, Marc Pracht: None declared, Jacques Cadranel: None declared, Laurence Weiss: None declared, Christos Chouaid: None declared, Thomas Aparicio: None declared, Stephane Nancey: None declared, Cécile Arnold: None declared, Erik Sauleau: None declared, Jaqcues-Eric Gottenberg: None declared

First detection of the mcr-1 colistin resistance gene in Escherichia coli from a patient with urinary tract infection in Myanmar

Colistin-resistance gene mcr-1 was detected in an Escherichia coli sample among 442 clinical isolates collected in a tertiary-care hospital in Yangon, Myanmar, in 2018. This isolate was classified into phylogroup A–ST23 complex and harboured bla_CTX-M-15 and bla_TEM-1, associated with multiple mutations in quinolone-resistance–determining regions in gyrA and parC.

Nasal septal body and inferior turbinate sizes differ in subjects grouped by sex and age

OBJECTIVES

To compare the size of the nasal septal body (SB) and inferior turbinate (IT) of subjects grouped by sex and age.

METHOD

We measured SB and IT areas (in cm2) bilaterally in computed tomography (CT) sections of 150 para nasal sinuses from 72 males and 78 females.

RESULTS

The right and left SB areas were smaller in females than in males. In the s25-year-old group, the right IT (RIT) was significantly smaller in females than in males. In the 26-35 and 46-45 age groups, the right SB (RSB) was significantly smaller in females than in males.

CONCLUSION

The nasal SB may play a role in nasal physiology similar to a turbinate and help support optimal airflow. The vascular and glandular structures of the SB should be investigated in detail, and minimal invasive procedures should be performed in nasal surgery to avoid damaging essential structures.

Effect of aging on the distribution of basic fibroblast growth factor immunoreactive cells in the rat hippocampus

Hippocampal formation is extremely sensitive to the aging process and appears to be one of the first regions to show structural and physiological changes with advancing age. Basic fibroblast growth factor (bFGF) plays an important role in the stimulation of mitogenesis in glial cells, the support of neuronal survival and the promotion of neurite outgrowth in vitro. In the present study, the effect of aging on the distribution of bFGF immunoreactive (bFGF-ir) cells was investigated. The protein product of bFGF was visualized immunohistochemically in the dorsal hippocampus of Wistar albino rats. bFGF-ir astrocytes in different subfields of hippocampus and neurons in CA2 field were quantified to determine whether changes in immunoreactivity were correlated with advancing age. Aging was accompanied by a decrease in bFGF-ir cell density in subfields of hippocampus. We concluded that aging was associated with a reduction in bFGF-ir cell density that may reflect a decreased expression of bFGF in the rat hippocampus.

The effects of quantum energy surgical device and of bipolar coagulation: a comparative experimental study

OBJECTIVE

The quantum energy surgical device (QESD) employs an innovative, "no-touch" thermal coagulation, incision and evaporation technique in which thermal energy is delivered to tissue in the format of high-energy neutral argon gas atoms. The aim of this study is to compare QESD and bipolar coagulation (BC) through assessment of both haemostasis and histological damage to isolated femoral arteries of rats.

METHODS

Sixty rats were randomly divided into acute and short-term experimental groups. In the acute group (n=20) histopathological evaluation was performed immediately following coagulation, whereas in the short-term experimental group (n=20) the evaluation was performed 10 days later. Each sham group consisted of ten rats. Viewed under the surgical microscope, only normal-appearing, freshly sectioned, and bleeding femoral arteries were studied. Right femoral arteries subject to QESD coagulation, and left femoral arteries to BC. Haemorrhaging was controlled using the minimal coagulation time necessary to stop it. All vascular layers, including endothelium, internal elastic lamina, media and adventitia were examined histologically and ultrastructurally in a "blind" fashion to critically compare morphological damage due to QESD and BC.

RESULTS

Surgical haemostasis induced by QESD was found to be as safe as BC. Light microscopy revealed more marked histopathological changes in the BC than in the QESD group. These involved mainly the endothelial and medial compartments and, at the ultrastructural level, consisted of endothelial degeneration and exfoliation, irregularity of internal elastic lamina, degeneration, and loss of medial smooth muscle.

CONCLUSION

The results indicate that QESD coagulation induces significantly less histological damage than does BC. Thus QESD coagulation is a safe, less tissue destructive, and equally effective method of haemostasis.

The effect of alpha-melanocyte stimulating hormone on endotoxin-induced intestinal injury

We investigated the effect of alpha-melanocyte stimulating hormone (alpha-MSH) on endotoxin-induced intestinal inflammation and the role of nitric oxide and prostaglandins in this response. alpha-MSH treatment (25 microg/rat, intraperitoneally (i.p.); twice daily) reduced the severity of the lesions macroscopically and microscopically. This protective effect was found to be confined mainly to the distal ileum. These lesions were reversed by pretreatment with the non-selective COX inhibitor indomethacin (10 mg/kg, subcutaneously (s.c.)) but not by the selective COX-2 inhibitor nimesulide (3 mg/kg, s.c.), the NO donor sodium nitroprusside (4 mg/kg, i.v.) or the iNOS inhibitor dexamethasone (3 mg./kg, i.p.) at macroscopic level and reversed by Indo or Dex at microscopic level. Increased peroxidase activity -index of tissue neutrophil infiltration- in the distal ileum of LPS-treated rats was decreased by alpha-MSH and this effect was reversed by pretreatment with Indo. In conclusion, the neuropeptide alpha-MSH has a beneficial effect on endotoxin-induced distal intestinal lesions by a mechanism which probably involves nitric oxide and COX-1 derived prostaglandins.

Morphological examination of the effects of defibrotide on experimentally induced bladder injury and its relation to interstitial cystitis

This morphological study aims to investigate the effects of defibrotide, a deoxyribonucleic acid derivative drug with cytoprotective, immunosuppressive and vasorelaxant effects, on protamine sulfate induced bladder injury. Wistar albino female rats were catheterized and intravesically infused with phosphate buffered solution (control group) or, either protamine sulfate (bladder injury group) or protamine sulfate+defibrotide (bladder injury+defibrotide group) dissolved in phosphate buffered solution. The morphology of the urinary bladder was investigated using light and electron microscopy. The number of mast cells in the mucosa, mucosal alterations, intercellular junctions, surface topography and the glycosaminoglycan (GAG) layer as well as microvillus formation on the luminal surface were evaluated. In the bladder injury group, ulcerated areas, irregularity of the GAG layer, increased number of mast cells, vacuole formation, dilated perinuclear cistern, formation of pleomorphic and uniform microvilli and dilatations in the intercellular spaces in the urothelium were observed. In the bladder injury+defibrotide group a relatively normal urothelial topography, GAG layer and a few mast cells in the mucosa, some dilatations between the intercellular areas, less uniform microvilli, regular perinuclear cistern and tight junctions were observed. These results show that defibrotide can inhibit PS induced bladder damage.

Early histological changes of ileal mucosa after augmentation cystoplasty

Segments of bowel are used routinely for transplantation in various pathological conditions such as contracted bladders or poorly compliant neuropathic bladders. However, little is known how these intestinal segments adopt to a toxic environment caused by urine. Therefore, the present study was performed to determine early histological changes of ileal mucosa after augmentation cystoplasty. Seven patients with augmentation cystoplasty underwent random cold-cup biopsies of ileal segments after a mean period of 14.4 months after cystoplasty and morphological changes were evaluated using light microscopy and transmission and scanning electron microscopy. Most pronounced features were varying degrees of villous atrophy, increased numbers of Paneth and goblet cells. Severity of atrophic villous changes were not related to the length of the interval between surgery and endoscopic biopsy. These findings may be explained as adaptations of bowel tissue to counteract noxious effects of urine and to maintain its epithelial function in the bladder.

The effect of tizanidine on chronic vasospasm in rats

BACKGROUND

Cerebral vasospasm after subarachnoid hemorrhage (SAH) has remained a major cause of morbidity and mortality in patients with SAH. Excitatory neurotransmitters are gathered in the extracellular space during ischemia due to cerebral vasospasm and initiate or stimulate a series of pathophysiological biochemical processes which consequently lead to neuronal death. Tizanidine (Sandoz compound DS 103-282, 5-chloro-4,2 (2-imidazolin-2-yl-amino)-2,1,3-benzothiazol hydrochloride) is a centrally-acting muscle relaxant and a selective alpha 2 adrenoreceptor agonist which shows its effect by stimulating presynaptic alpha 2 adrenoreceptors in central ASPergic and GLUergic system by inhibiting aspartic acid and glutamic acid release. In this study, the effect of Tizanidine on vasospasm was evaluated.

METHODS

We used a femoral artery vasospasm model in rats which has been described by Okada et al. 60 rats were examined in three groups. The first group was used as control group (Control) (n = 20), in the second group subarachnoid hemorrhage was performed (SAH) (n = 20), in the third group Tizanidine was administered in addition to SAH (SAH + Tizanidine administration) (n = 20). Animals in SAH + Tizanidine administration group received 0.3 mg/kg/day intraperitoneally for 7 days. Seven days after the experiment, after perfusion-fixation, 10 mm segments of both femoral arteries were removed and the femoral artery was prepared for light microscope examination, scanning and transmission electron microscopy and for morphometric analysis.

RESULTS

There was a statistically significant difference between the electron, scanning and light microscopic observations and morphometric analysis of SAH + Tizanidine administration group and SAH group, and no statistically significant difference between SAH + Tizanidine administration group and control group.

CONCLUSION

This study has disclosed that Tizanidine administration before the vasospasm reduces ultrastructural and morphometric vasospastic insult significantly. However, the clinical application of Tizanidine as a protective and therapeutic agent in cerebral vasospasm needs further studies including the employment of clinically more relevant SAH models.

The afferent connections of the posterior hypothalamic nucleus in the rat using horseradish peroxidase

The posterior hypothalamic nucleus has been implicated as an area controlling autonomic activity. The afferent input to the nucleus will provide evidence as to its role in autonomic function. In the present study, we aimed to identify the detailed anatomical projections to the posterior hypothalamic nucleus from cortical, subcortical and brainstem structures, using the horseradish peroxidase (HRP) retrograde axonal transport technique in the rat. Subsequent to the injection of HRP into the posterior hypothalamic nucleus, extensive cell labelling was observed bilaterally in various areas of the cerebral cortex including the cingulate, frontal, parietal and insular cortices. At subcortical levels, labelled cells were observed in the medial and lateral septal nuclei, the bed nucleus of stria terminalis, and various thalamic and amygdaloid nuclei. Also axons of the vertical and horizontal limbs of the diagonal band were labelled and labelled cells were localised at the CA1 and CA3 fields of the hippocampus and the dentate gyrus. The brainstem projections were from the medial, lateral and parasolitary nuclei, the intercalated nucleus of the medulla, the sensory nuclei of the trigeminal nerve, and various reticular, vestibular, raphe and central grey nuclei. The posterior hypothalamic nucleus also received projections from the lateral and medial cerebellar nuclei and from upper cervical spinal levels. The results are discussed in relation to the involvement of the posterior hypothalamic nucleus in autonomic function and allows a better understanding of how the brain controls visceral function.

Eversion with four sutures: an easy, fast, and reliable technique for microvascular anastomosis

In this study, a microvascular anastomosing technique called "eversion with four sutures" is introduced. For microvascular anastomosis, this technique requires fishmouth incisions at both vessel ends and the completion of four sutures. In 120 Wistar-Albino rats, 120 eversion and 120 conventional anastomoses were done in 240 femoral arteries. Each rat received both treatments. Operating time, bleeding time, number of sutures used, patency rates, and pseudoaneurysm formation were analyzed statistically; healing was evaluated with both light and electron microscopy. When compared with the conventional technique using nine sutures, the eversion with four sutures technique was found to be a faster and easier method of anastomosis and as reliable as the conventional technique. Without compromising patency rates, bleeding time, or rates of pseudoaneurysm formation, anastomosis time and amount of suture material exposed to the lumen were significantly reduced when using this technique. In conclusion, the authors think that eversion with four sutures is a reliable alternative to the conventional suturing technique, especially for emergency cases that require multiple microvascular anastomoses.

Protective effect of defibrotide on perfusion induced endothelial damage

In the present study, in vitro effects of Defibrotide (D) on perfusion-induced changes in the morphology of endothelium were investigated by scanning (SEM) and transmission (TEM) electron microscope. Human umbilical cord veins were incubated or perfused with platelet-rich plasma alone (PRP) or platelet-rich plasma with Defibrotide (PRP+D) at 3ml/min or 14ml/min and the changes observed were compared. SEM examination of luminal surfaces demonstrated that perfusion with high flow rates may damage endothelial cells and lead to morphological changes which may be prevented by the presence of Defibrotide in the perfusate. Also, the marked reduction in the number of adhered platelets on luminal surface of veins incubated or perfused with Defibrotide compared to veins treated with platelet-rich plasma only revealed that Defibrotide has anti-thrombotic effects. TEM examination of ruthenium red (RR) stained thin sections of veins demonstrated that perfusion disrupts the glycosaminoglcan (GAG) coat on endothelial cells. But the presence of D in the perfusate preserves the integrity of GAG, indicating further cytoprotective effects of the drug on endothelium.

The effects of cold-restraint stress on urinary bladder wall compared with interstitial cystitis morphology

Stress is associated with many diseases of unknown aetiology. This study demonstrates the effects of cold-restraint stress on the morphology of the urinary bladder. Additionally, it compares the results obtained with the morphology of the interstitial cystitis. The animals were subjected to three hours of cold-restraint stress and then starved for 48 h. The morphology and histochemistry of the urinary bladder was investigated with light and electron microscopy. The proliferative activity was analysed via flow cytometry. Increased and degranulated mast cells in the mucosa, leucocyte infiltration in the lamina propria, vacuole formation in the urothelial cells, loose tight junction, dilated intercellular spaces and altered proliferative activity were observed in the stress group when compared with the control. The increase in the number of mast cells and especially degranulated mast cells and vacuole formation and the loose tight junction of the urothelium correlated with the histopathological findings of interstitial cystitis.

Effects of hematoma on the short-term fate of experimental microvenous autografts

The early effects of hematoma on the healing pattern of interpositional vein grafts were studied in 60 rats. In all animals, vein grafts approximately 10-mm in length were used to bridge defects created in the femoral artery and vein on the same side, with a 1:1 graft-to-host diameter match. Grafted vessels were completely covered with hematoma and separated from the surrounding tissue in 30 animals, while the other 30 rats served as controls. Both groups were divided into six subgroups of five animals each, according to the age of the grafts: 1, 3, 5, 7, 14, and 21 days. Graft patency and healing were assessed both clinically and histologically 20/30 (66.6 percent) of the interarterial and 27/30 (90 percent) of the intervenous vein grafts in Group 1 (hematoma group), and 28/30 (93.3 percent) of the interarterial and 29/30 196.6 percent) of the intervenous vein grafts in Group 2 (controls) were found patent. The patency rate of the interarterial vein grafts in the hematoma group was statistically significantly lower than in the control group and than in the intervenous vein grafts of the same group (p<0.005). The majority of interarterial vein-graft failures occurred after postoperative day 7 in Group 1. Patent specimens were examined under scanning electron and light microscopy. The authors concluded that perivascular hematoma caused spasm and flow disturbance, prolonged vessel-wall ischemia, and severe vessel-wall injury in the arterial circulation of the microvenous grafts. It also delayed the healing process and subjected the grafts to the development of occlusive mural thrombus. In contrast, the healing pattern of the intervenous vein grafts was not markedly influenced by perivascular hematoma, and equilibrium between thrombogenic and antithrombogenic factors on the graft surface was restored over a short period of time.

Effect of vitamin E and probucol on dietary cholesterol-induced atherosclerosis in rabbits

The preventive effect of vitamin E and Probucol against atherosclerosis in rabbits were compared. Atherosclerosis was induced by a 2% cholesterol-containing vitamin E-poor diet (5-10 ppm). Six groups of five rabbits each were studied. Group I (control) was fed on a vitamin E-poor diet. The other groups had the following supplements: group II, 50 mg/kg vitamin E i.m.; group III, 2% cholesterol; group IV, 2% cholesterol plus 50 mg/kg vitamin E i.m., group V, 2% cholesterol plus 1% Probucol; group VI, 2% cholesterol + 1% Probucol plus 50 mg/kg vitamin E i.m. After 4 weeks, aortas were removed and analyzed by light and scanning electron microscopy for atherosclerotic lesions. Samples of the media were analyzed for protein kinase C activity. The aortas of cholesterol-fed rabbits showed typical atherosclerotic lesions, detected by microscopic examination, their media smooth muscle cells exhibited an increase in protein kinase C activity. Vitamin E fully prevented cholesterol-induced atherosclerotic lesions and the induction of protein kinase C activity. Probucol was not effective in preventing either cholesterol-induced atherosclerotic lesions or the induction of protein kinase C activity. These results show that the protective effect of vitamin E against hypercholesterolemic atherosclerosis is not produced by an other antioxidant such as Probucol, and therefore, may not be linked to the antioxidant properties of this vitamin. The effects observed at the level of smooth muscle cells ex vivo suggest an involvement of signal transduction events in the protective effect of vitamin E against atherosclerosis.

Role of paraventricular and dorsomedial nuclei of the hypothalamus and central nucleus of the amygdala on muscimol-induced cardiovascular responses

Gamma-aminobutyric acid (GABA) plays an important role in the central control of cardiovascular functions. Previous evidence indicates that a tonically active GABAergic system exists in forebrain structures. The purpose of this study was to examine the role of the unilateral lesion of the central nucleus of amygdala, paraventricular or dorsomedial nuclei of the hypothalamus on muscimol-induced cardiovascular responses. Electrolytic ablation of nuclei was made by a monopolar isolated electrode under a stereotaxic instrument, 3-5 days before the experiments. Effects of intracerebroventricular injections of muscimol were investigated in intact, lesioned and sham-lesioned rats. On the day of the experiments, blood pressure and heart rate recordings were carried out in male Sprague-Dawley conscious rats. Muscimol produced decreases in arterial blood pressure and heart rate. The hypotensive effect of muscimol was completely inhibited in rats with dorsomedial nucleus lesions, whereas the bradycardic effect was partially prevented. The results indicate that the dorsomedial nucleus of the hypothalamus plays an important role on muscimol-induced blood pressure and heart rate responses.

Cyclosporin A reduces the severity of cold-restraint-induced gastric lesions: role of leukocytes

The objective of this study was to determine the role of cyclosporin A (CsA) on cold-restraint-induced gastric lesions. Animals were subjected to 3 h immobilization at 4 degrees C in plastic restraining devices following a starvation period of 48 h. Gastric samples were obtained for the measurement of myeloperoxidase (MPO) activity, an index of number of peroxidase positive cells and thiobarbituric acid-reactive substances (TBARS; lipid peroxidation). Animals were pretreated with CsA which is a potent immunosuppressant and inhibits ischemia/reperfusion-induced polymorphonuclear leukocyte (PMN) infiltration. Cold-restraint administration significantly elevated the tissue MPO activity and TBARS formation. CsA pretreatment significantly reduced the severity of cold-restraint-induced gastric lesions while attenuating the elevated MPO measurements observed during cold-restraint administration. Animals rendered neutropenic with antineutrophil serum (ANS) exhibited significantly less gastric mucosal injury normally observed after cold-restraint stress. Neither CsA nor ANS treatment effected the elevated TBAR levels, indicating that PMNs are not involved in the lipid peroxidation process observed after cold-restraint stress. In conclusion, the results of this study indicate that CsA is capable of inhibiting cold-restraint-induced gastric mucosal injury and can attenuate the cold-restraint-induced increases in gastric MPO measurements. Our results also indicate that PMNs may be the important mediators of cold-restraint-induced gastric lesions.

Morphological changes in carotid arteries of rabbits induced by defibrotide infusion

Defibrotide is an antithrombotic and profibrinolytic drug which modulates endothelial function. The drug increases prostacyclin and tissue plasminogen activator while it decreases plasminogen activator inhibitor synthesis by endothelial cells. In this study, in vivo effects of defibrotide on the morphology of endothelial cells and vessel wall of the healthy rabbits were investigated by light and electron microscopy. The examination of the carotid arteries of healthy rabbits after infusion of saline or defibrotide (10 mg/kg/hr) in saline solution for three hours revealed that the drug had induced dramatic morphological changes in all the test animals while no change was observed in control group. The changes observed after defibrotide administration, such as the decrease in hill and valley-like appearance of endothelial surface, and thinning of the intimal layer provides evidence for the vasorelaxant effect of the drug, while the decrease in the number of blood cells adhering to the endothelial surface confirms the antithrombotic effect of defibrotide. Finally the decrease in the number of crater-like structures may be due to the cytoprotective effect of the drug.