High mobility group proteins 1 and 2 recognize chromium-damaged DNA

Chromium (Cr) is a human carcinogen and a potent DNA damaging agent. Incubation of DNA with CrCl3 resulted in dose-dependent binding of Cr to DNA and, at concentrations >20 microM, altered the electrophoretic mobility of a 100 bp oligonucleotide. We also demonstrate that high mobility group (HMG) proteins 1 and 2 bind Cr-damaged DNA (Cr-DNA). Protein binding was lesion density-dependent, with maximal binding to DNA treated with 100 microM CrCl3. HMG2 binds to Cr-DNA with a calculated Kd of approximately 10(-9) M. These proteins also bound DNA obtained from chromate-treated cells. These results suggest that the covalent attachment of Cr to DNA induces alterations in DNA structure which are recognized by HMG1 and HMG2. Therefore, these proteins may function as Cr-damaged DNA recognition proteins in vivo and as a consequence of binding, may play a role in directing the cellular response to Cr-DNA adduct formation.      

Sputum tumour necrosis factor-alpha and leukotriene concentrations in cystic fibrosis

It is postulated that a vigorous host inflammatory response in the cystic fibrosis lung contributes to lung injury. Tumour necrosis factor-alpha (TNF-alpha) may play a part in that process and in the generation of leukotrienes. Therefore, the relationships between sputum TNF-alpha, leukotriene concentration, and lung function abnormalities in 16 children with cystic fibrosis were investigated. Each subject provided sputum samples and performed spirometry. TNF-alpha was measured by enzyme linked immunosorbent assay; individual leukotrienes were separated using high performance liquid chromatography and quantified by radioimmunoassay. The geometric mean concentration of TNF-alpha was 129.7 pg/ml and 95% confidence interval 48.2 to 348.3. Mean (SEM) leukotriene B4 (LTB4) was 97.8 (22.9) pmol/g and total cysteinyl leukotrienes were 60.9 (14.8) pmol/g. Mean (SD) forced expiratory volume in one second (FEV1) of the group was 53 (15)% of predicted and forced vital capacity (FVC) was 65 (14)% of predicted. There was a significant positive correlation between TNF-alpha and both LTB4 and the total cysteinyl leukotriene sputum content. An inverse relationship existed between TNF-alpha and FEV1 and FVC. Moreover, a negative correlation was observed between sputum LTB4 and FEV1 and FVC. These results suggest that TNF-alpha and the leukotrienes may participate in the airways inflammation and airflow obstruction observed in cystic fibrosis subjects and support the hypothesis that TNF-alpha upregulates the 5-lipoxygenase pathway in vivo.     

Interleukin-1 alpha, soluble interleukin-2 receptor, and IgG concentrations in cystic fibrosis treated with prednisolone

The cytokines interleukin-1 and interleukin-2 participate in the inflammatory response, and may contribute to hypergammaglobulinaemia G and the development of lung injury in cystic fibrosis. Anti-inflammatory treatment with corticosteroids may attenuate this response. The effect of a 12 week course of oral prednisolone on spirometry and serum concentrations of interleukin-1 alpha (IL-1 alpha), soluble interleukin-2 receptor (sIL-2R), and IgG was investigated in 24 children with cystic fibrosis. Prednisolone was administered, in a double blind and placebo controlled manner, at an initial dose of 2 mg/kg daily for 14 days and tapered to 1 mg/kg on alternate days for 10 weeks. The treated group (n = 12) experienced an increase in forced expiratory volume in one second and forced vital capacity at 14 days, however, these changes were smaller at 12 weeks. In the treated group, change in pulmonary function was associated with decreased serum IgG and cytokine concentrations. Prednisolone suppresses serum concentrations of these cytokines, which may participate in the inflammatory response, the excessive synthesis of IgG, and airflow obstruction observed in cystic fibrosis patients.     

Involvement of p53 and interleukin 3 in the up-regulation of CD95 (APO-1/Fas) by X-ray irradiation

Interleukin 3-dependent bone marrow and Ba/F3 cells present constitutive Fas expression. A dose dependent increase in Fas surface expression was induced in these cells by X-ray irradiation. Using primary cell cultures and established cell lines derived from p53-null mice (p53-/-), we demonstrated that the increase in Fas expression upon X-ray irradiation is dependent on the presence of at least one wild-type p53 allele. Fas induction by X-ray irradiation was negatively modulated by IL-3; an earlier Fas induction was observed in the absence of IL-3 or at low IL-3 concentrations. However, IL-3 withdrawal in non-irradiated cells did not induce an increase in Fas expression. X-ray irradiation of Ba/F3 cells induced the expression of functional Fas receptors. Therefore, in IL-3-dependent cells, IL-3 regulates the rate of Fas expression, which is correlated with the degree of apoptosis observed in X-irradiated cells. Finally, we demonstrate that IL-3 controls the degree of Fas expression induced by irradiation through a p53-mediated pathway.     

Peripheral α2-adrenoceptor-mediated sympathoinhibitory effects of mivazerol

Summary— Mivazerol is a new compound that could potentially reduce perioperative cardiovascular morbidity and mortality in patients with or at risk of coronary disease and submitted to surgery. This action of mivazerol depends on a well documented centrally mediated reduction in sympathetic nerve activity, but a direct peripheral decrease in sympathetic neurotransmitter release induced by activation of prejunctional α₂-adrenoceptors located on sympathetic nerve endings could also contribute. To investigate this issue, the effects of mivazerol on the pressor, systemic and regional hemodynamic (pulsed Doppler technique) as well as on the cardiac responses to electrical stimulation of the spinal cord (SCS) were measured in pithed rats in the absence and in the presence of mivazerol. Mivazerol exerted strong sympathoinhibitory effects: SCS-induced increases in blood pressure, total peripheral resistance and heart rate were dose-dependently reduced by mivazerol, but among the regional vascular beds investigated, only the hindlimb vasoconstrictor responses were significantly drug-affected. All these sympathoinhibitory effects of mivazerol were abolished by prior yohimbine administration. Simultaneously, mivazerol did not induce any postjunctional adrenoceptor blockade as it did not affect noradrenaline cardiac and hemodynamic effects. On the contrary, through postjunctional α₂-adrenoceptor stimulation, mivazerol, in this pithed preparation, dose-dependently increased blood pressure, total peripheral and hindlimb vascular resistances, but heart rate was not affected. We conclude that, in the pithed rat, mivazerol exerts strong peripheral sympathoinhibitory effects. The mechanism involved is prejunctional α₂-adrenoceptor activation as i) mivazerol does not display any postsynaptic α-adrenoceptor blocking effect — it even behaves as a postsynaptic α₂-adrenoceptor agonist — and ii) yohimbine abolishes mivazerol's sympathoinhibitory effects. Thus, direct peripheral together with central mechanisms contribute to mivazerol's sympathoinhibitory effects and ultimately to its cardioprotective action.     

Metabolic Requirement for Inorganic Phosphate by the Rabbit Proximal Tubule: EVIDENCE FOR A CRABTREE EFFECT

These studies examine the effects of acute changes in the availability of inorganic phosphate on the function of isolated proximal renal tubules from rabbit kidney. We removed phosphate from the extracellular fluids and measured fluid absorption rates in isolated perfused tubules and oxygen consumption rates in suspensions of cortical tubules. In proximal convoluted tubules, the selective removal of phosphate from the luminal fluid reduced fluid absorption rates from 1.11±0.12 to −0.01±0.08 nl/mm · min. This effect on fluid absorption was dependent on the presence of glucose transport and metabolism. The addition of phlorizin to the phosphate-free luminal fluid preserved fluid absorption rates (1.12±0.12 nl/mm · min) as did the substitution of nonmetabolized α-methyl d-glucopyranoside for glucose (1.05±0.21 nl/mm · min) or the addition of 2-deoxyglucose, an inhibitor of glycolysis, to the bathing medium (1.01±0.15 nl/mm · min). There was no effect on fluid absorption if phosphate was removed from the bath only. Additionally, removal of phosphate from the luminal fluid of proximal straight rather than convoluted tubules had no effect on fluid absorption rates. Oxygen consumption rates in suspensions of cortical tubules were reduced from 18.9±0.6 to 10.6±0.6 nmol O₂/mg tubular protein · min by the removal of phosphate from the medium. This inhibition was prevented by the substitution of α-methyl d-glucopyranoside for glucose in the phosphate-free medium. The data indicate that under certain conditions, proximal convoluted tubules require the presence of phosphate in the luminal fluid to preserve tubular function. In the absence of intraluminal phosphate, glucose metabolism causes a reduction in both oxidative metabolism and fluid absorption. This response is analogous to the Crabtree effect and suggests limitations on the intracellular availability of inorganic phosphate.