Improvement of the hemocompatibility of PET surfaces using different sulphated polysaccharides as coating materials.

In this study, sulphated polysaccharides were investigated in respect to their blood compatibility properties (hemocompatibility). Pure chitosan was treated with sulphating agents such as SO(3)/pyridine complex and chlorosulfonic acid (HClSO(3)) to obtain 3,6-O-sulfochitosan with low and high concentration of sulfur. These synthetically derived materials and the commercially available sulphated polysaccharides heparin and dextran sulfate, both with high concentrations of sulfur, were coated onto PET foils to act as surfaces with strong antithrombotic activity. This treatment should lead to better blood compatibility properties of PET materials for medical applications. To examine this, the optimized free hemoglobin method was applied to determine the antithrombotic activity of these surfaces. Glass as the standard thrombotic surface and a heparin-coated PET surface as a surface well-known for its strong antithrombotic activity were used as internal references. The experiments showed that dextran sulfate and sulphated chitosan with high concentrations of sulfur demonstrated the same antithrombotic activity as heparin over the whole period of measurement time. In addition, a relationship between the sulfur concentration in these sulphated polysaccharides and their blood compatibility properties can be demonstrated in this article.

Mild and selective oxidation of cellulose fibers in the presence of N-hydroxyphthalimide.

The oxidation reaction of regenerated cellulose fibers mediated by N-hydroxyphthalimide (NHPI) and various cocatalysts at room temperature for different time intervals and various amounts of low concentration sodium hypochlorite solution has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed that the nonpersistent phthalimide-N-oxyl (PINO) radical generated in situ from NHPI in both, metallic or metal-free systems, is a powerful agent in this kind of transformation. Moreover, the reaction converts highly selectively C(6) primary hydroxyl groups to carboxylic groups under mild reaction conditions and shorter reaction times than previously reported. The amounts of negatively charged groups in OC were determined by means of potentiometric titration. Further characterization of the products were accomplished by using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR), environmental scanning electron microscopy (ESEM), and X-ray and energy-dispersive X-ray (EDX) spectroscopy. Notably, water retention values of the oxidized fibers increased by 30% in comparison with the original nonoxidized sample, as a result of the introduction of hydrophilic carboxylate groups.

Evaluation of functional response of cerebral arteries by a new morphometric technique.

The contractile response of the rabbit basilar artery under four conditions was determined: (1) response in a resting condition without exclusion of the sympathetic nervous system (control group I); (2) response in a resting condition with alpha-adrenoceptor blockade (group II); (3) response to subarachnoid haemorrhage (SAH) (group III); and (4) response to SAH with alpha-adrenoceptor blockade (group IV). It was also ascertained whether it was possible to measure contractile response using a new morphometric method. Vessels were prepared by intracardial perfusion fixation, stained by haematoxylin and eosin, and the length of the intimal corrugations were measured by computer image analysis. Two procedures were followed in order to express the intensity of intimal corrugation, indicating the contractibility of the basilar arteries: (1) the corrugation coefficient (CC) of the basilar artery intima was estimated by dividing the precisely measured length of the intimal corrugations by the length of the measured vessel wall section of the vessel cross-sections (obtained histologically); (2) the lumen reduction coefficient (LRC) of the basilar artery was determined by dividing the "ideal" luminal area (calculated from the total length of the intimal circumference) by the real luminal cross-section area. The results of CC measurements revealed the smoothest intima (mean CC = 1.146, P = 0.00) and the least reduction of lumen (mean LRC = 0.26, P = 0.000) in group II (rabbits without SAH but with alpha-blocker phenoxybenzamine), and in group IV (SAH group of rabbits with alpha-blocker phenoxybenzamine) where the mean CC was 1.141 (P = 0.001) and the mean LRC was 0.33 (P = 0.002) in comparison with the SAH-only group III, pointing out the effectiveness of alpha-blockade even against SAH vasospastic stimuli. Control group I (without SAH and without treatment) showed a greater degree of corrugation in the intima and an increased reduction in the lumina than in groups II and IV, but still significantly less than in group III (mean CC = 1.197, P = 0.001, and mean LRC = 0.40, P = 0.028), thus demonstrating a certain resting tone of the basilar arteries (in an ideal situation, without any tone at all, the CC and LRC would be equal one). The highest degree of intimal corrugation and the greatest lumina reduction were discovered in the SAH-only group III (mean CC = 1.374 and mean LRC = 0.60). The differences among groups I, II and IV were insignificant. The results of this study suggest four conclusions: (i) the possibility of evaluating the functional response of rabbit cerebral arteries using this new morphometric technique; (ii) the adrenergic influence on resting tone of these arteries; (iii) the likely preventive role of an alpha-blockade on post-SAH vasospasm of basilar arteries in rabbits; and (iv) good comparability of the results of CC and LRC measurements with the angiographically estimated vessel diameters of other similar studies.

Sympathetic nervous system exclusion following experimental subarachnoid haemorrhage prevents vasospasm in rabbits.

BACKGROUND: The objective of this study was to establish whether the exclusion of the effect of the sympathetic nervous system prevents vasospasm of cerebral arteries after experimental subarachnoid haemorrhage in rabbits. METHODS: The effect of sympathetic exclusion on vasospasm was studied in 29 New Zealand rabbits under conditions similar to human subarachnoid haemorrhage: 1. The activity of the sympathetic nervous system was excluded only after subarachnoid haemorrhage. 2. The effect of this exclusion was evaluated on the eighth day after subarachnoid haemorrhage. 3. The single haemorrhage model of experimental subarachnoid haemorrhage was chosen. Four groups of rabbits were investigated. The control group A comprised rabbits without subarachnoid haemorrhage; group B consisted of those with subarachnoid haemorrhage (1 ml autologous blood/kg BW suboccipitally into the cisterna magna); group C included those with subarachnoid haemorrhage and pharmacological sympathetic exclusion by the alpha blocker phenoxybenzamine, and group D was composed of those with subarachnoid haemorrhage and operative sympathetic exclusion by cervical gangliectomy. Changes in the basilar arteries of rabbits were evaluated by computer image analysis, using histologic specimens of vessel walls. A new measuring procedure was developed to assess the intensity of vasospasm; the method has a corrugation coefficient that expresses changes in intimal corrugation. RESULTS: Comparison of control group A and group B in regard of vessel intima corrugation showed significantly less corrugated intima in group A (P = 0.0042). In comparison with group B, corrugation of the vessel intima in group C was less intense after sympathetic exclusion by phenoxybenzamine following subarachnoid haemorrhage (P = 0.00012). In comparison with group B, a reduced corrugation was also found in group D after sympathetic exclusion by upper cervical gangliectomy following subarachnoid haemorrhage (P = 0.0026). CONCLUSIONS: The results of the study suggest that exclusion of sympathetic nervous system activity in rabbits prevents vasospasm in circumstances similar to subarachnoid haemorrhage in man. Thus, the sympathetic nervous system could play a critical role in the development of vasospasm in subarachnoid haemorrhage.

Specificity of Bacillus thuringiensis for lepidopteran larvae: factors involved in vivo and in the structure of a purified protoxin.

The relative LD50 values in two test Lepidoptera of Bacillus thuringiensis subspecies kurstaki HD1, which contains three crylA protoxin genes, was the same as a plasmid-cured derivative or a Bacillus cereus transcipient containing only one of the three genes. Differential rates of transcription of these genes in the original strain could account, at least partly, for this result. Strains containing only the single protoxin gene (crylA(b] produced inclusions when grown at 25 degrees C but not 32 degrees C, despite transcription of this gene at both temperatures. The instability of the crylA(b) protoxin was not found in the parental B. thuringiensis subsp. kurstaki HD1 strain grown at either temperature, however, so kurstaki HD1 strains with multiple protoxin genes must produce some stabilizing factor, perhaps another protoxin. The cryl protoxins contain a highly conserved carboxyl half which is proteolytically removed upon conversion to toxin. All of the protoxin cysteines are present in protease-sensitive regions and they are oxidized in inclusions. Most of the disulphides appear to be essential for specificity since their reduction in the crylA(b) protoxin resulted in loss of selectivity for one of the test insects. This lack of specificity was also found for this protoxin produced by an Escherichia coli clone, probably because of the reducing conditions in these cells. Specificity was restored by reoxidation of the pure protoxin, by removal of the carboxyl half of oxidized protoxin with trypsin, or by subcloning of the toxin portion. The oxidized form of protoxins must be important for specificity, for the formation of crystalline inclusions, and probably for interactions required for the stabilization of some protoxins.

Some biological characteristics of Escherichia coli strains isolated from acute diarrhoeal diseases of infants.

The aim of this study was to evaluate the methods of biological characterization of Escherichia coli strains, in order to use them as screening tests in clinical microbiological laboratories. In two thirds of the 45 E. coli, isolated from acute intestinal infection of infants, different factors of virulence were found. The strains showed prevalently an enterotoxigenic character (66,6%), which was in correlation with the increased permeability (62,2%). Adhesive properties were present in 20% of E. coli independent of their enterotoxigenicity; only 11,1% of the strains had penetrating abilities. The rabbit skin model seems to be accurate and quick for ETEC screening purposes, as is the guinea-pig eye for the EIEC. The mouse intestinal loop has been found sensitive but time-consuming. The infant mouse model is simple and quick, but in this study it has not given optimal results. The Vero cell culture system is simple and easy to perform, but at least for some strains the preparations should be concentrated. The investigation of adhesiveness by haemagglutination is possible to conduct in every small clinical laboratory. Our opinion is, however, that after the isolation of E. coli from different pathological materials, the determination of the antigenic structure of the strains is necessary and later on the additional biological characterization should be performed.