Improved biological properties of synthetic distearoyl phosphatidyl choline-based liposome in the conscious rat

We have previously produced and tested a liposome preparation based on hydrogenated soy lecithin (HSL-L) for the purpose of designing blood replacement in the form of liposome encapsulated hemoglobin (LEH). While these liposomes had acceptable physicochemical properties which addressed many of the desirable characteristics of "artificial blood," they produced hypotension, hemoconcentration, and thrombocytopenia when administered to rats. The following studies present improved synthetic distearoyl phosphatidylcholine-based liposomes (sDSPC-L) which were compared to the HSL-L for their biological effects in the conscious normovolemic rat (n = 6 - 11). HSL-L induced hypotension (-25 +/- 3 mmHg, P less than 0.01), tachycardia (+88 +/- 11 beats/min, P less than 0.01), decrease in cardiac index (-33 +/- 4%, P less than 0.01), and elevation of the total peripheral resistance index (+0.450 +/- 0.003 mmHg/ml/min/kg, P less than 0.01). The hematologic responses to HSL-L were: leukocytosis (+6,070 +/- 1,064/microliters, P less than 0.01), hemoconcentration (+4.0 +/- 0.1%, P less than 0.01), 0.01), and thrombocytopenia (-160 +/- 18 X 10(3)/microliters, P less than 0.01). Plasma thromboxane B2 (TXB2) was elevated to 30.4 +/- 5.6 pg/100 microliters (P less than 0.01). In contrast, the only effects induced by sDSPC-L were slight tachycardia (+37 +/- 9 beats/min, P less than 0.05) and a marginal increase in plasma TXB2 to 9.7 +/- 3.3 pg/100 microliters (P less than 0.05). All effects, except for those related to cardiac output and peripheral resistance, were transient. These data underscore the importance of pure synthetic DSPC in improving the biological effects of liposomes and suggest sDSPC-L as a promising vehicle for encapsulating hemoglobin.     

Calcium channel blockers in cerebral ischaemia

Ischaemic stroke usually results from the obstruction of a major cerebral vessel which leads to a decrease in cerebral blood flow, and a subsequent reduction in ATP. This energy loss leads to impaired cellular function due to reduced ATP-dependent processes and a disruption in ionic gradients across membranes. Under these conditions, there is a significant efflux of K+ from cells producing cellular depolarisation and the movement of extracellular calcium into cells through calcium channels. It is this increase in intracellular calcium that leads to the 'calcium toxicity' that has been associated with cerebral ischaemia. Increased intracellular calcium triggers the break-down of phospholipids, proteins and nucleic acids. This is activated by calcium-dependent phospholipases, proteases and endonucleases, and contributes to structural and functional damage of the cell membrane, which compromises cell function and facilitates cell death. Calcium channel blockers are used routinely to treat cardiovascular disease and hypertension. Although some experimental studies over the last decade suggest efficacy/benefit in the treatment of experimental ischaemic stroke, clinical data do not bear this out. This article discusses the role of voltage-operated calcium channel blockers in stroke, and reviews much of the available experimental and clinical data.     

An inhibitory anti-factor IX antibody effectively reduces thrombus formation in a rat model of venous thrombosis

An inhibitory anti-factor IX/IXa antibody (BC2) has been investigated as an anti-thrombotic agent in a rat venous thrombosis model. The treatment of rats post-injury with a single bolus dose of BC2 (3 mg/kg, i.v.) resulted in an approximately 4 fold reduction in venous thrombus mass (P = 0.043). This efficacy was matched by a minimal (<2.5 fold) prolongation of the aPTT and had no effect on the prothrombin time (PT). Heparin by comparison, given as a bolus followed by continuous infusion, at doses comparable in efficacy at reducing thrombus formation, prolonged the aPTT >50 fold. These results demonstrate that the anti-factor IX/IXa antibody (BC2), when compared to heparin, can effectively reduce venous thrombosis with less disruptive consequences on blood clotting.     

Estimation of the biophase concentration of noradrenaline at presynaptic α2-adrenoceptors in brain slices

Summary The aim of the present study was to determine the local concentrations of noradrenaline existing at presynaptic ₂-adrenoceptors during electrical pulse train stimulation of brain slices at different frequencies. The experiments are based on the assumption that the concentration of released noradrenaline at the ₂-adrenoceptors exerting a certain autoinhibition should be equal to the concentration of exogenous noradrenaline causing the same inhibition under conditions in which any influence of the released transmitter is excluded. In order to avoid autoinhibition, hippocampus and cortex slices of the rabbit and the rat, prelabelled with [³H]noradrenaline and superfused in presence of an uptake inhibitor, were electrically stimulated using 4 pulses delivered at 100 Hz (POP stimulation). Exogenous noradrenaline diminished the overflow of tritium elicited by POP stimulation in a concentration-dependent manner. In rabbit brain tissues the EC₅₀ value and maximum inhibition of noradrenaline release were found to be approximately 6 nmol/l and more than 95%, respectively, whereas in rat tissues the corresponding values were between 20 and 30 nmol/l and approximately 90%. When electrical stimulation was performed with trains of 36 pulses delivered at 0.1, 0.3 or 3 Hz in absence or presence of an uptake inhibitor, the ₂-adrenoceptor antagonist yohimbine (1 or 10 mol/l) enhanced the evoked tritium overflow in a manner which was dependent on the frequency of stimulation and on blockade of the re-uptake mechanism. The facilitatory effects of yohimbine reflected an extent of autoinhibition which was between 53% (36 pulses/0.1 Hz, no uptake inhibitor) and 85% (36 pulses/3 Hz, uptake inhibitor present) in rabbit and between 16% (36 pulses/0.3 Hz, no uptake inhibitor) and 71% (36 pulses/3 Hz, uptake inhibitor present) in rat brain slices. Accordingly, the corresponding estimated biophase concentrations of noradrenaline were generally higher in rat than in rabbit tissues (they were between 32.5 and 74.5 or 5.1 and 51.6 nmol/l in the presence or absence of an uptake inhibitor, respectively, in the rat, and between 15 and 23.1 or 6.1 and 18.6 nmol/l in the rabbit). The observed frequency dependence of the effect of re-uptake blockade on the calculated biophase concentrations of noradrenaline would be compatible with the idea of a dependence of the effectiveness of the re-uptake mechanism on the firing rate of the neurone in being more effective at lower frequencies. Moreover, the stikingly low biophase concentrations of noradrenaline suggest that also in brain tissue noradrenaline causes lateral inhibition of release as has recently been shown for guinea-pig vas deferens. Send offprint requests to C. Allgaier at the above address     

Hypoxia and cyanosis in alpha-1-antitrypsin deficiency. Cirrhosis as an unusual etiologic factor

A patient with type PiZZ alpha-1-antitrypsin deficiency was found to have severe hypoxia despite normal pulmonary function testing and a normal chest radiograph. A nuclear medicine ventilation-perfusion study revealed a right-to-left shunt. Computed tomography showed minimal bleb formation, no diffuse changes, and hepatic changes of cirrhosis with portal hypertension. No nodular pulmonary masses or enlarged peripheral pulmonary vessels were found. The diagnosis of diffuse intrapulmonic arteriovenous shunts ("pulmonary spiders of cirrhosis") was suggested and then confirmed with a dynamic radionuclide flow study.     

No modulatory effect of neurokinin-1 receptor antagonists on serotonin uptake in human and rat brain synaptosomes

Some studies have demonstrated antidepressant activity of neurokinin-1-receptor antagonists (NK-1-RA) in major depressive disorder. However, the underlying mechanisms of this antidepressant effect are largely unknown. Preclinical studies in rats and mice have suggested that NK-1-RA do increase the neuronal release of serotonin (5-HT). This, however, seems to be compensated by an increased 5-HT reuptake, indicating that NK-1-RA have no inhibitory effect on the 5-HT transporter in rodents. Given the possibility that modulation of neurotransmitter release and reuptake may differ between species, with major differences found between rodents and humans, we investigated for the first time the possible modulatory effect of NK-1-RA on 5-HT uptake in human brain synaptosomes and compared it with the situation in rat cortex. We found that the specific human NK-1-RA L-733060, in contrast to the SSRI fluvoxamine (IC₅₀ = 10^− 7.96 M) did not inhibit 5-HT uptake in human brain synaptosomes and did not modulate fluvoxamine-induced 5-HT uptake inhibition at 1 μM. Furthermore, substance P as well as Sar⁹Met(O₂)¹¹SP, as the major agonists at the NK-1-R, did not modulate 5-HT uptake in human brain synaptosomes. Similar results were found in rat cortex synaptosomes by using the rat-specific NK-1-RA WIN51708. These results show that in humans, as in rodents, inhibition of the 5-HT transporter is probably not the underlying mechanism of the assumed antidepressant activity of NK-1-RA.     

Occurrence of the t(2;5)(p23;q35) in non-Hodgkin's lymphoma

Primary CD30(Ki-1)-positive anaplastic large-cell lymphoma (ALCL) is considered by some to be a distinct clinicopathologic entity associated with the t(2;5) (p23;q35). However, the specificity of t(2;5) for ALCL has not been carefully studied. Therefore, we performed a detailed analysis of all cases of ALCL with abnormal cytogenetics results in the Nebraska Lymphoma Study Group registry, as well as all other cases of non-Hodgkin's lymphoma with t(2;5) in the registry. We found the t(2;5) in only five of 10 cases of ALCL, four of whom were young patients. However, we also found the t(2;5) in 11 other cases of nonanaplastic lymphoma, including eight children with typical peripheral T-cell lymphomas of various types. The t(2;5) was also found in three older adults with B-cell lymphomas of various types. Thus, the t(2;5) was not specific for CD30+ ALCL. However, t(2;5) may define a clinicopathologic entity in children and young adults characterized by variable morphologies with a T-cell or indeterminate phenotype, CD30-positivity, nodal disease with frequent extranodal involvement, advanced stage, and an excellent response to therapy, including bone marrow transplantation for relapsed disease. The clinical relevance of the t(2;5) in older patients requires further study.