Wortmannin-mediated inhibition of phosphatidylinositol 3-kinase activity triggers apoptosis in normal and neoplastic B lymphocytes which are in cell cycle

The B cell functional response following ligation of surface(s) lgM is dependent upon the differentiation stage of the populationstudied: cross-linking slgM promotes proliferation of restingtonsillar follicular mantle (FM) B lymphocytes but induces apoptosisin the susceptible Epstein- Barr virus genome-negative Burkittlymphoma (BL) cell line Ramos (Ramos-BL). This study investigateswhether phosphatidylinositol-3-kinase (Pl3-kinase), which hasbeen reported to be intimately involved in the regulation ofcellular growth, plays a role in the regulation of these sig-promoted B cell responses, and uses the selective and irreversibleinhibitor of Pl3-kinase activity, wortmannin (Wm). In Ramos-BLB cells, at 8 h post-treatment, Wm triggers a transient increasein apoptosis of 16 ± 6.9% with a concomitant cellularloss of 16 ± 6.1% from the G₁ phase of cell cycle; [³H]thymidineincorporation also decreases by 33 ± 5.0%, from 37,274c.p.m. ± 10% to 25,127 c.p.m. ± 4.0%. Moreover,at 72 h culture, Wm inhibits anti-lgM-induced FM B lymphocytelevels of [³H]thymidine incorporation typically by 47% and triggers80% apoptosis from the G₀G₁ phase of cell cycle. Ramos-BL Bcells exhibit high basal levels of Pl3-kinase activity, as determinedby immunoprecipitation with antibody to the p85 regulatory subunitof Pl3-kinase and ³²P incorporation into phosphatidylinositol,which is not significantly affected by anti-lgM stimulation;by contrast, anti-lgM stimulates significant Pl3-kinase activityover negligible basal levels in FM B lymphocytes. Pre-treatmentwith Wm inhibits Pl3-kinase activity in both cell types. Takentogether these data indicate that in Ramos-BL B cells slgM-triggeredgrowth arrest and apoptosis is Pl3- kinase independent, whereasPl3-kinase activity is critical for slgM-triggered mitogenesisof FM B lymphocytes. Thus Pl3-kinase plays a pivotal role inthe regulation of both normal and neoplastic B lymphocyte progressionthrough the cell cycle, such that if this Pl3-kinase-dependentpathway is inhibited these cells default to apoptosis.     

Estimating Potency for the E max-Model Without Attaining Maximal Effects

The most widely applied model relating drug concentrations to effects is the E_max model. In practice, concentration–effect relationships often deviate from a simple linear relationship but without reaching a clear maximum because a further increase in concentration might be associated with unacceptable or distorting side effects. The parameters for the E_max model can only be estimated with reasonable precision if the curve shows sign of reaching a maximum, otherwise both EC₅₀ and E_max estimates may be extremely imprecise. This paper provides a solution by introducing a new parameter (S₀ ) equal to E_max/EC₅₀ that can be used to characterize potency adequately even if there are no signs of a clear maximum. Simulations are presented to investigate the nature of the new parameter and published examples are used as illustration.     

Plasma leptin level and its relationship with body composition in hemodialysis patients

Leptin is a newly found hormone secreted by adipocytes that regulates food intake, thermogenesis, and body fat. We measured plasma leptin levels in 103 patients with chronic renal failure treated by hemodialysis and 167 age- and gender-matched healthy control subjects to examine the impact of renal failure on plasma leptin levels and the influence of leptin on body composition measured by dual-energy X-ray absorptiometry. Hemodialysis patients showed a significant decrease in both body fat mass and lean body mass compared with those of the control subjects. Plasma leptin was significantly elevated in the hemodialysis group over the controls. In both groups, leptin was higher in female than male subjects, and it correlated positively with percent body fat. The subjects were divided into six categories according to percent body fat, and plasma leptin levels were compared between the two groups in the same category. Leptin of hemodialysis patients was significantly higher than that of the control subjects in the percent body fat categories of 30 or greater, whereas there was no statistically significant difference in leptin concentrations in the lower percent body fat categories. This was also true in the comparison in each gender, and leptin levels in female subjects showed a more remarkable difference between the hemodialysis and control groups in obese categories. Multiple regression analysis in all subjects indicated that plasma leptin levels were independently affected by percent body fat, plasma insulin concentration, gender, and renal failure. The positive impact of renal failure on leptin remained significant in the subjects with percent body fat of 30 or greater in the multiple regression model, whereas it was no longer significant in the remaining lean subjects. In multiple regression analysis of factors affecting fat mass index and lean mass index, leptin level was selectively associated with fat mass index, but not with lean mass index, regardless of percent body fat ranges. These results indicate that renal failure is an important factor affecting plasma leptin levels, especially in obese female subjects, and that hyperleptinemia was closely related to fat mass but not to lean body mass in hemodialysis patients.     

SPARC, an extracellular matrix glycoprotein containing the follistatin module, is expressed by astrocytes in synaptic enriched regions of the adult brain

Although extracellular matrix (ECM) glycoproteins play important roles in neural development, their levels are generally believed to decrease in the adult brain. Immunohistochemical analysis indicates that the anti-adhesive ECM glycoprotein SPARC/osteonectin, which contains a follistatin ‘module’, is expressed in the adult rabbit nervous system. In the cerebellum, SPARC is present in Bergmann glia, with a strong signal along their radial fibres. SPARC, while enriched in membrane fractions, is not a transmembrane protein. In the hippocampus, colocalization of SPARC is observed in cells which express the astrocytic marker GFAP. The expression of SPARC by a subset of astrocytes, particularly in synaptic enriched areas, suggests a continuing role for the ECM in the adult brain.     

An analysis of astrocytic cell lines with different abilities to promote axon growth

The adult mammalian central nervous system (CNS) lacks the capacity to support axonal regeneration. There is increasing evidence to suggest that astrocytes, the major glial population in the CNS, may possess both axon-growth promoting and axon-growth inhibitory properties and the latter may contribute to the poor regenerative capacity of the CNS. In order to examine the molecular differences between axon-growth permissive and axon-growth inhibitory astrocytes, a panel of astrocyte cell lines exhibiting a range of axon-growth promoting properties was generated and analysed. No clear correlation was found between the axon-growth promoting properties of these astrocyte cell lines with: (i) the expression of known neurite-outgrowth promoting molecules such as laminin, fibronectin andN-cadherin; (ii) the expression of known inhibitory molecules such tenascin and chondroitin sulphate proteoglycan; (iii) plasminogen activator and plasminogen activator inhibitor activity; and (iv) growth cone collapsing activity. EM studies on aggregates formed from astrocyte cell lines, however, revealed the presence of an abundance of extracellular matrix material associated with the more inhibitory astrocyte cell lines. When matrix deposited by astrocyte cell lines was assessed for axon-growth promoting activity, matrix from permissive lines was found to be a good substrate, whereas matrix from the inhibitory astrocyte lines was a poor substrate for neuritic growth. Our findings, taken together, suggest that the functional differences between the permissive and the inhibitory astrocyte cell lines reside largely with the ECM.     

A mild form of captopril-induced pemphigus

We describe a mild form of drug-induced pemphigus in a woman with essential arterial hypertension treated with captopril. Complete recovery was observed three weeks after the therapy had been discontinued.     

The consequences of H2 receptor antagonist — piroxicam coadministration in patients with joint disorders

Summary A randomised crossover study was performed in subjects with rheumatoid arthritis (or other arthropathies) to investigate if any alteration in the steady pharmacokinetics of the NSAID piroxicam (a drug which is extensively metabolised via cytochrome P450) or its major metabolites occurred as a result of coadministering either cimetidine or nizatidine.Twelve females and 2 males with mean age, weight, and albumin concentrations of 58 years, 61 kg, and 40 g·L^–1 respectively, completed the study. Comparisons were made between the following parameters: plasma piroxicam AUCs [AUC_0-24(P)], plasma 5-hydroxypiroxicam AUCs [AUC_0-24(5-OHP)], the ratio of these i.e. AUC_0-24(5-OHP):AUC_0-24(p), the % piroxicam daily dose excreted in urine as 5-hydroxypiroxicam (before and after glucuronidase incubation); and the mean of the steady state trough piroxicam, and 5-hydroxypiroxicam concentrations (obtained during each study phase in addition to the wash-out period).A statistically significant difference as a result of initiating either cimetidine or nizatidine was obtained only for the ratio AUC_0-23(5-OHP):AUC_0-24(P). This was indicative of a weak potential to inhibit piroxicam hydroxylation.No clinically significant alteration in the steady state pharmacokinetics of piroxicam occurred in these subjects as a result of cimetidine or nizatidine coadministration. Consequently it is unlikely that any adverse events would arise from these combinations.