Influence of CNTs decomposition during reactive friction-stir processing of an Al-Mg alloy on the correlation between microstructural characteristics and microtextural components.

Multipass friction-stir processing was employed to uniformly disperse multiwalled carbon nanotubes (MW-CNTs) within an Al-Mg alloy metal matrix. Decomposition of MW-CNTs occurs in situ as a result of solid-state chemical reactions, forming fullerene (C60) and aluminium carbide (Al4 C3 ) phases during reactive high temperature severe plastic processing. The effects of this decomposition on the microstructural features, dynamic restoration mechanisms and crystallographic microtextural developments are studied for the first time by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis. The formation of an equiaxed grain structure with an average size of ∼1.5 µm occurs within the stirred zone (SZ) under the influence of inclusions which hinder grain boundary migration via Zener-Smith pinning mechanisms during the discontinuous dynamic recrystallisation (DDRX). Formation of two strong Cubic and Brass microtextural components in the heat affected zone (HAZ) and thermomechanical affected zone (TMAZ) was noted as compared to the completely random and Cube components found in the base and SZ regions, respectively. The microstructural modification led to hardening and tensile strength improvement for the processed nanocomposite by ∼55% and 110%, respectively with respect to the annealed Al-Mg base alloy.

Electron backscattered diffraction analysis of friction stir processed nanocomposites produced via spark plasma sintering.

In the present study, Spark Plasma Sintered (SPSed) aluminium matrix composites were severely deformed through Friction stir processing (FSP). Pure aluminium powders and bimodal sized Al2 O3 particles (80 nm and 25 µm) were firstly mixed by ball milling and then consolidated by spark plasma sintering. The effect of the heat input as well the bimodal particle size of the alumina on the materials' microstructure and texture development was evaluated by electron back scattered diffraction (EBSD) analysis. The EBSD analysis clearly showed that the SPSed nanocomposites possessed bimodal aluminium matrix grain structure as well as a crystallography characterised by random texture. In addition, microstructural examination revealed that the partial recrystallisation occurred during SPS for all the nanocomposites. Also, it is revealed that the Zener pinning effect of Al2 O3 nanoparticles retarded recrystallised grain growth following recrystallisation during FSP and then leading to grain refinement of the aluminium. The results revealed that the heat generated during FSP has a remarkable effect on the grain distribution as well as on the crystallographic orientation. Also, a mixture of {112} <110> shear elements and an ideal strong B/B¯ component were observed. The microstructural changes, occurred during FSP in the stir zone region for Al-Al2 O3 nanocomposites, were attributed to both the discontinuous along with the continuous recrystallisation (DDRX/CDRX). It should be pointed out that with increasing the heat input, recrystallised grains portion increased.

Nimodipine and chronic vasospasm in monkeys: Part 2. Pharmacological studies of vessels in spasm.

The effect of nimodipine on the in vitro reactivity of cerebral vessels after subarachnoid hemorrhage (SAH) was studied. With the use of a primate model of chronic cerebral vasospasm, 12 female cynomolgous monkeys underwent the induction of a SAH by the direct placement of an average 6.4-ml autologous hematoma against the major anterior cerebral vessels in the right basal subarachnoid spaces (Day 0). The animals were then randomized to one of four groups and within 14 to 20 hours after clot placement were started on oral q8h therapy with nimodipine (3, 6, or 12 mg/kg) or placebo. On Day 7, the animals were killed and the right and left middle cerebral arteries (MCAs) were immediately resected and placed in oxygenated Krebs' solution. Ring preparations from the arteries were suspended in organ baths, and dose-effect curves to varying concentrations of norepinephrine, 5-hydroxytryptamine, and potassium chloride were obtained. There was a highly significant reduction in the response of the MCA on the clot side (right) relative to the nonclot side (left) to all three agonists. The clot side contractility was not influenced by nimodipine treatment at any of the four doses tested. The nonclot side arteries of the 12-mg/kg treatment group demonstrated significantly enhanced reactivity for all three agonists. Oral treatment with high dose nimodipine enhances the reactivity of normal cerebral vessels to the agonists tested, but it does not seem to affect the reactivity of arteries in chronic spasm at any of the four doses tested.

Effects of vasospasm on levels of prostacyclin and thromboxane A2 in cerebral arteries of the monkey.

To determine whether cerebral arteries in spasm have an altered capacity to synthesize the vasoactive substances prostacyclin and thromboxane A2, we measured levels of these arachidonic acid metabolites using a primate model of vasospasm. Twenty-four cynomolgus monkeys were assigned at random to one of three groups designated sham, clot, or clot-removal. All animals underwent base line cerebral angiography and bilateral dissection of the major cerebral arteries from the arachnoid. The clot and clot-removal groups had autologous hematomas placed around the vessels to simulate subarachnoid hemorrhages. The sham group had a similar volume of saline instilled into the subarachnoid space. Twenty-four hours later, the clot-removal group underwent a second craniotomy to remove the hematomas. Seven days after the initial operation, angiography was repeated on all animals. The animals were then killed, and the cerebral arteries were removed. Basal levels of prostacyclin and thromboxane in the cerebral vessels were measured after incubation in vitro by radioimmunoassay. No detectable leukotriene C4 release by these arteries was measurable using radioimmunoassay. Angiography revealed severe cerebral vasospasm in the clot group, but not in the clot-removal or sham groups. There were no statistical differences among the groups in thromboxane release, but prostacyclin levels were significantly lower in the clot group than in the clot-removal group (P less than 0.05). It thus seems that, if an imbalance in constrictor and dilator eicosanoids occurs in association with vasospasm, this is more likely to arise from a relative lack of the vasodilator component prostacyclin than from a surplus of the vasoconstrictor thromboxane.(ABSTRACT TRUNCATED AT 250 WORDS)

Nimodipine and chronic vasospasm in monkeys: Part 3. Cardiopulmonary effects.

A subarachnoid hemorrhage was induced in 30 cynomolgus monkeys by the placement of a 6- to 7-ml blood clot through a frontotemporal craniectomy (Day 0). The monkeys underwent a 1-week-long, randomized, blind trial comparing various doses of nimodipine to placebo, sham, and no treatment. The treatment groups were: nimodipine, 3 mg/kg every 8 hours (n = 6), 6 mg/kg every 8 hours (n = 6), and 12 mg/kg every 8 hours (n = 6); placebo (polyethylene glycol 400), 0.33 ml/kg every 8 hours (n = 6); and no treatment (n = 6). An additional sham group underwent craniectomy without clot placement (n = 6) so that 36 animals in total were operated upon. Differences in cardiopulmonary indices between Day 0 and Day 7 were compared within and between groups. No significant differences were obtained in the sham and no treatment groups. The nimodipine 6- and 12-mg/kg groups showed significant decreases in blood pressure (P less than 0.04 and P less than 0.015). Systemic vascular resistance was increased in the placebo and 3-mg/kg groups (P less than 0.02) and decreased in the 12-mg/kg group (P less than 0.015). Stroke index was increased in the 12-mg/kg group (P less than 0.05). Cardiac index and stroke index correlated positively with nimodipine dosage (r = 0.99, P less than 0.05). There were no pronounced changes in pulmonary artery wedge pressure, central venous pressure, alveolar-arterial oxygen pressure difference, arteriovenous oxygen content difference, and percentage of shunting.

Nimodipine and chronic vasospasm in monkeys: Part 1. Clinical and radiological findings.

The efficacy of the calcium channel blocker nimodipine in the prevention of chronic cerebral vasospasm (VSP) and delayed ischemia after subarachnoid hemorrhage (SAH) in monkeys was examined in a blind, randomized, placebo-controlled trial. The primate model developed in this laboratory reliably induces chronic cerebral vasospasm and can induce pathologically proven delayed ischemic neurological deficits (DINDs). With standard microsurgical procedures, an average 6.4-ml autologous hematoma was placed directly against the major anterior cerebral vessels in the right basal subarachnoid spaces of 24 monkeys. The monkeys were randomized to one of four groups and were treated orally q8h for 7 days with nimodipine (3, 6, or 12mg/kg)or placebo. An additional 2 monkeys underwent the surgical procedure without clot placement. Drug administration began between 14 and 20 hours after clot placement. Indices monitored before and after SAH included neurological status, angiographic cerebral vessel caliber, and cerebral blood flow. Significant VSP (25 to 100% reduction in vessel caliber) was present on Day 7 on the clot side in 83% of the animals (P less than or equal to 0.001). There was no significant difference (P greater than 0.05) in the incidence of VSP among the four groups. Similarly, there was no significant difference (P greater than 0.05) in the mean vessel caliber reduction after SAH among the four treatment groups. There was no VSP present on Day 7 in the sham-operated animals. One animal receiving high dose nimodipine (12 mg/kg p.o. q8h) developed a DIND on Day 5 after SAH. A second animal in the 12-mg/kg group developed a transient neurological deficit between Days 4 and 7.

Intrathecal nimodipine therapy in a primate model of chronic cerebral vasospasm.

The safety, prevention, and treatment of chronic vasospasm by repeated administration of intrathecally applied nimodipine was evaluated in a primate model of chronic cerebral vasospasm. Twenty-four female cynomolgous monkeys were randomized into three groups of 8: sham, clot, and clot + intrathecal nimodipine. All animals underwent a subarachnoid hemorrhage (SAH) induction operative procedure after base line angiography. Nimodipine was administered postoperatively by subcutaneous injection of 1 ml/0.2 mg tid for 6 days through an Ommaya reservoir with the catheter placed in the subarachnoid basal cisterns. Angiography was performed on Day 7 post-SAH induction. Intrathecally applied nimodipine was not effective in the prevention of angiographic vasospasm. It also did not seem to decrease the degree of pathological change when compared to controls. One animal in the nimodipine group died 2 hours after an intrathecal injection secondary to a respiratory arrest. Transient sedation and hypoventilation were common. No adverse pathological effects were noted. Intrathecal nimodipine did not produce a significant dilation of vessels in moderate or severe spasm when assessed by angiography 2 hours after intrathecal injection. Only 1 animal in 8 showed diffuse dilation of vasospastic cerebral vessels after an intrathecal nimodipine injection. Three other animals in this group developed dilation only of the basilar artery, which was in mild spasm.

Cerebral perivascular nerves in subarachnoid hemorrhage. A histochemical and immunohistochemical study.

The authors have studied the changes induced by subarachnoid hemorrhage (SAH) in the density and distribution of cerebral perivascular nerves in monkeys and rats. The SAH was induced in monkeys by placement of an autologous blood clot after opening the basal cisterns over the arteries of the circle of Willis on one side. In the rat study, SAH was induced by injection of autologous arterial blood into the cisterna magna. The nerves examined were adrenergic nerves, acetylcholinesterase (AChE)-containing nerves, vasoactive intestinal polypeptide (VIP)-like immunoreactive nerves, and substance P-like immunoreactive nerves. In the monkey study, all animals underwent baseline cerebral angiography, then had repeat angiography just before sacrifice on Day 2, 7, 28, or 70 after SAH. Two sham-operated monkeys underwent the surgical procedure without clot placement and were sacrificed on postoperative Day 7, after repeat angiography. Clot placement in monkeys reduced staining of all middle cerebral artery (MCA) perivascular nerves for between 2 and 28 days post-SAH. The number of stained nerve fibers of MCA's on the non-operated side was slightly reduced on Days 2 and 7 after SAH. Sham-operated monkeys showed a mild reduction of staining in all nerves, but only on the operated side. Cerebral vasospasm was observed on all angiograms taken on Days 2 and 7 following SAH. No vasospasm was found in normal or sham-operated monkeys. The disappearance of nerve staining without associated vasospasm was found on the operated side of the sham-operated monkeys and on the clot side of the animal sacrificed on Day 28 after SAH. Rats sacrificed on Days 2 and 7 post-SAH showed reduction in adrenergic and VIP-like immunoreactive staining around basilar arteries, while nerves containing AChE were not affected. Saline-injected rats exhibited no change in the appearance of perivascular innervation. These results suggest that SAH as well as surgical manipulation of the vessel wall caused a reduction of the studied substances in cerebral perivascular nerves. This reduction in immunoreactive staining of perivascular nerves did not correlate with the development of angiographic vasospasm after SAH.

Effects of nimodipine on in vitro contractility of cerebral arteries of dog, monkey, and man.

Cerebrovascular spasm in the cynomolgus monkey does not appear to be modified by nimodipine. It is possible that cerebral arteries from this species are unusually resistant to the action of calcium antagonists. To test this hypothesis, parallel studies on the in vitro response of cerebral arteries from monkey, dog, and man have been carried out. Rings of basilar or middle cerebral artery were tested with potassium chloride, noradrenaline, 5-hydroxytryptamine, prostaglandin F2 alpha, and hemoglobin. The responses were then reexamined in the presence of various concentrations of nimodipine. There is a significant variation among species in sensitivity to nimodipine, the vessels from the monkey being more resistant to nimodipine than those from other species. There is, as expected, a considerable difference in the ability of nimodipine to block the different agonists. Responses to potassium chloride are blocked by low concentrations of nimodipine in all species, whereas noradrenaline and 5-hydroxytryptamine are more resistant. It is noteworthy that, in all species tested, hemoglobin and prostaglandin F2 alpha were antagonized poorly even by higher concentrations of nimodipine. If these agonists play a major role in the development of vasospasm and subsequent delayed ischemia, it may be that the calcium antagonists exert a beneficial effect by some mechanism other than dilation of spastic arteries.

The effect of timing of clot removal on chronic vasospasm in a primate model.

The effect of complete clot removal at times from 48 to 96 hours after subarachnoid hemorrhage (SAH) on the development of chronic cerebral vasospasm was evaluated to determine whether there is a critical point after which clot removal is ineffective in preventing vasospasm. Thirty cynomolgus monkeys were randomized to one of five groups: sham-operated group, clot removal at 48 hours after SAH (48-hour group), clot removal at 72 hours after SAH (72-hour group), clot removal at 96 hours after SAH (96-hour group), and clot placement only (clot group). Standard microsurgical techniques were used to dissect bilaterally the major cerebral arteries free of arachnoid. An autologous blood clot averaging 4.2 gm was placed around the vessels in the subarachnoid space of the monkeys in the 48-hour, 72-hour, 96-hour, and clot groups. Physiological saline was instilled into the subarachnoid space of the sham-operated animals. Animals in the clot-removal groups underwent surgical clot removal at the determined times for each group. Two animals in each of the sham-operated and clot groups were subjected to reoperation at each of 48, 72, and 96 hours after SAH. The incisions were reopened and then simply reclosed. Neurological status, angiographic cerebral vessel caliber, and physiological status were evaluated before and 7 days after SAH induction. There were no significant neurological deficits in the sham-operated, 48-hour, or 72-hour groups. Two animals in each of the 96-hour and clot groups showed deterioration in level of consciousness developing on Day 4 or 5 after SAH induction. All the major cerebral arteries of the animals in the clot and 96-hour groups showed significant vasospasm (p less than 0.01) on Day 7. Animals in the 72-hour group had significant vasospasm (p less than 0.05) of the internal carotid and middle cerebral arteries but not the anterior cerebral arteries. There was no significant vasospasm (p greater than 0.05) in any of the cerebral arteries in the 48-hour group. Severity of vasospasm paralleled the duration of contact between the blood clot and the cerebral vessels. Evacuation of the subarachnoid hematoma later than 48 hours after SAH resulted in no significant reduction in the degree of chronic cerebral vasospasm. It is suggested that clot removal at early operation is likely to be useful only if it is performed within 48 hours of SAH.

Effect of clot removal at 24 hours on chronic vasospasm after SAH in the primate model.

The efficacy of complete clot removal 24 hours after subarachnoid hemorrhage (SAH) in the prevention of chronic cerebral vasospasm was evaluated in monkeys in a blind randomized controlled trial. Twenty-four monkeys were randomized to one of three groups to undergo sham-operation (sham-operated group), clot placement only (clot group), or clot placement and removal (clot-removal group). By means of standard microsurgical techniques, the major cerebral vessels bilaterally were dissected free of arachnoid. An autologous hematoma averaging 5 gm was placed around the vessels in the subarachnoid spaces in the clot and clot-removal groups. Saline solution was instilled in the subarachnoid spaces of the sham-operated group. All animals underwent reoperation 24 hours after the first procedure. In the clot-removal group, the hematoma was evacuated. In the sham-operated and clot groups, the incision was simply closed again after 3 hours of anesthesia. Indices monitored before and 7 days after SAH induction included neurological status, angiographic cerebral vessel caliber, and arterial blood pressure. All animals were evaluated with magnetic resonance imaging (MRI); representative animals were evaluated with computerized tomography (CT) brain scans. There were no neurological deficits in either the sham-operated or the clot-removal groups. One animal in the clot group developed a progressive delayed ischemic deficit on Day 5 after SAH. A second animal in this group died suddenly on Day 4 post-SAH. An autopsy revealed a recent infarct in the territory of the superior cerebellar artery. Clinical findings correlated with MRI and CT images. Significant vasospasm (25% to 100% reduction in vessel caliber) was present on Day 7 in 100% of the clot animals (p less than 0.01). There was no significant vasospasm (p greater than 0.05) on Day 7 in either the sham-operated or the clot-removal groups. A large volume of clot placed bilaterally resulted in a 25% incidence of delayed ischemic deficit. Evacuation of subarachnoid hematoma within 24 hours of SAH prevented the development of chronic vasospasm and delayed ischemic deficit in the primate model.

Evaluation of DNA damage by the Comet assay in shoe workers exposed to toluene and other organic solvents.

The alkaline single-cell gel electrophoresis (or Comet) assay was applied to evaluate DNA damage in cryopreserved peripheral blood mononuclear leukocytes from 34 female shoe workers exposed to organic solvents and a group of 19 non-exposed women. We also investigated whether the polymorphisms of glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) genes affect individual level of DNA damage possibly induced by the solvent exposure. Chemical measurements of workplace air in the two factories studied showed that the workers were exposed to acetone, gasoline, and toluene in both factories and to ethylacetate and diisocyanate in one factory. In the exposed workers, the average level of blood hemoglobin was lower and that of urinary hippuric acid higher than in the non-exposed individuals. However, the occupational exposure to organic solvents did not affect the Comet values. Neither did age, smoking, or the GSTM1 genotype have any effect on the outcome of this assay. The low prevalence of the GSTT1-null genotype precluded conclusions on the influence of GSTT1 polymorphism.

Genotoxicity and radioresistance in electroplating workers exposed to chromium.

A biomonitoring study was carried out to investigate the genetic risk associated to occupational exposure to chromium. The induction of genetic damage was measured by analysing the frequency of micronuclei (MN) in peripheral blood lymphocytes. In addition to the 40 electroplater exposed workers who participated in the study, a group constituted by 18 volunteer donors, without exposure to chromium, was analysed as a control group. Measures of chromium levels at working place and in erythrocytes and urine were obtained, as indicators of exposure. The results from this study indicate that the blood from exposed workers contained higher levels of chromium, when compared with those obtained in the control group, and that a significant increase in the frequency of both the total number of MN and the number of binucleated cells carrying MN (BNMN) was detected. Furthermore, a good direct relationship was obtained between the amount of chromium present in air, erythrocytes or urine and the frequency of MN. To determine the existence of radioresistance as consequence of chromium exposure, the response of lymphocytes to the in vitro gamma-radiation was studied. The results of this experiment show a lower induction in the increase of the frequency of MN after challenge irradiation in the lymphocytes of chromium exposed workers, which should be indicative of an adaptive response.

Immune mechanisms of the occupational sensitization with methylen-dyphenyl diisocyanate (MDI).

The aim of this study was to objectify and to clarity some mechanisms of the immune response of the professional sensitization with MDI. 26 workers were tested for sensitization of immediate type (ST with a broad set of indoor allergens and serum MDI-IgE) and of delayed type (ST with a standard battery of antigens for cellular immunity and with MDI), also the lymphocyte sub-populations and their functional state by flow cytometric analysis. The most frequent allergic complaints were: rhinits (70%), skin manifestations (53%), conjunctivitis (35%) and initial bronchial asthma in two cases (12%). We found indoor sensitization in 41% and normal cellular immune reactivity in all the workers tested. Specific MDI sensitization of immediate type was found in 28.5% of the workers and of delayed type--in 70% of the workers with allergic complaints. The laboratory immune indices suggest prevalence of cell--mediated mechanisms for the workers with allergic symptoms--production of INF gamma, responding to stimulation and deficient or insignificant production of IL-4, as well as linear correlation between the data for CMI, INF gamma, and IL-4. Our results suggest the participation of more than one mechanism of immune injury in the clinically manifested allergic reactions.

Alteration in lipid composition of plasma membranes of sensitive and resistant Guerin carcinoma cells due to the action of free and liposomal form of cisplatin.

AIM: To study in vivo changes of lipid composition of plasma membranes of sensitive and resistant to cisplatin Guerin carcinoma cells under influence of free and liposomal cisplatin forms. MATERIALS AND METHODS: The isolation of plasma membranes from parental (sensitive) and resistant to cisplatin Guerin carcinoma cells was by differential ultracentrifugation in sucrose density gradient. Lipids were detected by method of thin-layer chromatography. RESULTS: It was determined that more effective action of cisplatin liposomal form on resistant cells is associated with essential abnormalities of conformation of plasma membrane due to change of lipid components and architectonics of rafts. It results in the increase of membrane fluidity. CONCLUSION: Reconstructions in lipid composition of plasma membranes of cisplatin-resistant Guerin carcinoma cells provide more intensive delivery of drug into the cells, increase of its concentration and more effective interaction with cellular structural elements.

Biodistribution analysis of cisplatin in liposomal form in animals with cisplatin-resistant and cisplatin-sensitive carcinoma.

AIM: To analyze the relation between pharmacokinetics of cisplatin in liposomal form and antitumor efficacy toward cisplatin-resistant and cisplatin-sensitive variants of Guerin carcinoma. METHODS: Concentration of platinum was measured by atomic absorption spectrophotometry (C115M1 "Selmi", Ukraine). Elimination constant was calculated based on the dynamics of cisplatin concentration in time period between 1 h to 24 h using nonlinear regression analysis. Area under curve (AUC24) was calculated by the trapezium method. RESULTS: It was shown that for liposomal form of cisplatin (LCp) AUC24 in tumor practically didn't depend on the level of the tumor sensitivity, while in animals with the resistant variant (CpRGC), AUC24 for free cisplatin (FCp) decreased by 70% less (p < 0.001) as compared to the sensitive tumor strain (CpSGC). Significant decrease of elimination constant of LCp compared to FCp in blood serum of rats bearing either CpRGC or CpSGC tumors favors cisplatin accumulation in tumor tissues with low vascularization level. The dynamics of cisplatin concentration in CpRGC variant was characterized by 90% higher level in 24 h after administration of LCp as compared to FCp (p < 0.05). This fact may explain increased antitumor efficacy of LCp compared to FCp toward CpRGC variant. In the study of kidney function, AUC24 index for LCp was by 68.6% (p < 0.01) and 50.7% (p < 0.05) lower than AUC24 index for FCp in rats with CpRGC and CpSGC variants, respectively. No significant differences have been found in biodistribution of cisplatin in both pharmaceutical forms in liver and lung in CpRGC- or CpSGC-bearing rats. CONCLUSION: The results suggest that cisplatin in liposomal form possesses higher specificity of antitumor action than free cisplatin.

[Toxicological characteristics of glycol monoacetate]. / Toksikologichna kharakteristika na glikolmonoatsetata.

Experimental investigations were undertaken to establish the acute and subacute inhalatory, oral and dermal toxicity of glycolmonophosphate. Modern toxicologic, biochemical and pathomorphologic methods were used. It was found that glucomonoacetate has a mild acute and subacute inhalatory, oral and dermal toxicity. The changes in some enzyme activities (GOT, GPT, AP, HE) and the parenchymatous dystrophy of the liver are considered transient and of functional nature. The toxic effect of glucomonoacetate is studied for the first time. Its use in the production of cigarette filters has a definite economical effect.