Defective Translocation of PKCε in EtOH‐Induced Inhibition of Mg2+ Accumulation in Rat Hepatocytes

Background: Rats chronically fed ethanol for 3 weeks presented a marked decreased in total hepatic Mg²⁺ content and required approximately 12 days to restore Mg²⁺ homeostasis upon ethanol withdrawal. This study was aimed at investigating the mechanisms responsible for the EtOH‐induced delay. Methods: Hepatocytes from rats fed ethanol for 3 weeks (Lieber‐De Carli diet—chronic model), rats re‐fed a control diet for varying periods of time following ethanol withdrawal, and age‐matched control rats fed a liquid or a pellet diet were used. As acute models, hepatocytes from control animals or HepG2 cells were exposed to varying doses of ethanol in vitro for 8 minutes. Results: Hepatocytes from ethanol‐fed rats presented a marked inhibition of Mg²⁺ accumulation and a defective translocation of PKCε to the cell membrane. Upon ethanol withdrawal, 12 days were necessary for PKCε translocation and Mg²⁺ accumulation to return to normal levels. Exposure of control hepatocytes or HepG2 cells to a dose of ethanol as low as 0.01% for 8 minutes was already sufficient to inhibit Mg²⁺ accumulation and PKCε translocation for more than 60 minutes. Also in this model, recovery of Mg²⁺ accumulation was associated with restoration of PKCε translocation. The use of specific antisense in HepG2 cells confirmed the involvement of PKCε in modulating Mg²⁺ accumulation. Conclusions: Translocation of PKCε isoform to the hepatocyte membrane is essential for Mg²⁺ accumulation to occur. Both acute and chronic ethanol administrations inhibit Mg²⁺ accumulation by specifically altering PKCε translocation to the cell membrane.     

Hereditary coproporphyria and epilepsy

A 9-year-old boy with mental deterioration and epilepsy suffered an acute attack of hereditary coproporphyria associated with worsening of seizure control. Leucocyte coproporphyrinogen oxidase activity was undetectable in the patient during this attack, and was reduced in his mother, a latent case. The complex relationship between porphyria, epilepsy, and anticonvulsant drugs is discussed.     

Health related quality of life after mitral valve repairs and replacements

Background: The decision to replace or repair mitral valves is often a difficult decision, and outcomes from the patients’ perspective should guide decision-making. We investigated whether the change in health related quality of life (HRQOL) after mitral valve surgery is different after valve repairs compared with replacements.Methods: We prospectively studied 25 patients with mitral valve replacement and 45 patients with valve repairs performed in 1998–99. We measured HRQOL at baseline and at 18 months using the Medical Outcomes Trust Short Form 36-item Health Survey (SF-36) questionnaire. We compared mean HRQOL scores of the groups with age-adjusted U.S. population scores. We used analysis of covariance to determine a change in HRQOL within groups (repair or replacement) and if the change in HRQOL was different between the groups.Results: We found few differences between the groups, with more men and simultaneous coronary artery bypass graft surgery in the valve repair group and more prior operation in the valve replacement group. HRQOL improved after surgery in most domains, and was comparable to age-adjusted U.S. norms in the valve repair group. In the multivariable analysis, mitral valve repair recipients reported higher social functioning compared with patients who received valve replacement (p = 0.04). We did not find other statistically significant differences. However, the adjusted improvements in the component scales of physical functioning (PCS) and mental functioning (MCS) were substantial in the valve repair group (mean changes: PCS = 6.8, p = 0.003; MCS = 8.1, p = 0.014) and less pronounced in the replacement group (mean changes: PCS = 3.6, p = 0.09; MCS = 4.3, fsp = 0.16).Conclusions: While many considerations influence the decision to repair or replace mitral valves, these findings suggest that repair may be better from the health status perspective. Further studies are necessary to validate this finding.     

Hemodynamic effects of a new inotropic compound,PST-2744, in dogs with chronic ischemic heart failure

Inotropic agents for acute decompensated heart failure are associated with a lack of efficacy or increased mortality. New compounds are needed to support patients with acute exacerbations of heart failure. This study examined the hemodynamic effects of a new inotropic agent (PST-2744) in dogs with chronic ischemic heart failure. Eight mongrel dogs at low risk for postmyocardial infarction (MI) sudden death entered the protocol. Dogs were studied after ischemic left ventricular dysfunction was induced by repeated injections of latex microspheres into the circumflex artery until the ejection fraction reached 35%. Hemodynamic parameters were measured at baseline and peak drug effect (PST-2744 5 microg.kg-1.min-1). In 5 animals, PST-2744 effects were compared with dobutamine. Heart rates, PR intervals and QT intervals were unchanged following PST-2744 administration. PST-2744 increased contractility (+dP/dt) by 56% from 1881 +/- 282 mm Hg/s to 2939 +/- 734 mm Hg/s (P < 0.01). The inotropic effect of PST-2744 was equal to that produced by 5-microg.kg-1.min-1 dobutamine (56% increase in +dP/dt), but peak heart rates were significantly higher with dobutamine (129 +/- 24 bpm PST-2744 versus 160 +/- 6 bpm 5-microg.kg-1.min-1 dobutamine, P < 0.002). No arrhythmias or conduction delays were seen with either compound. PST-2744 is an effective inotropic agent without positive chronotropic effect in subjects with stable moderate left ventricular dysfunction.     

Alteration in methyl-methanesulfonate-induced poly(ADP-ribosyl)ation by 2-butoxyethanol in Syrian hamster embryo cells

The effects of 2-butoxyethanol (2-BE) on poly(ADP-ribosyl)ation were studied in Syrian hamster embryo (SHE) cells by measuring the cellular concentrations of the polymer poly(ADP-ribose) (pADPr) and of NAD+, the substrate of poly(ADP-ribose) polymerase (PARP). As biotransformation pathways of ethylene glycol ethers involve NAD+-dehydrogenases, it was hypothesized that 2-BE could reduce poly(ADP-ribosyl)ation by consuming NAD+. As a result DNA repair could be altered, which would explain that 2-BE had been shown to potentiate the effects of clastogenic substances such as methyl-methanesulfonate (MMS). In this study, the effects of 2- BE on MMS-induced pADPr metabolism were analyzed. The results indicated that: (i) 2-BE (5 mM) by itself did not influence significantly pADPr or NAD+ levels. (ii) 2-BE inhibited pADPr synthesis in MMS (0.2 mM)- pretreated cells, without any change in NAD+ concentrations. (iii) MMS treatment, which rapidly increased pADPr levels, also affected the poly(ADP-ribosyl)ation system as a secondary effect by damaging cell structures. Membrane permeabilization, which occurred at concentrations >1 mM MMS, led to a dramatic leakage of cellular NAD+ resulting in a strong reduction in pADPr levels. (iv) A bleomycin pulse (100 microM) applied after MMS and/or 2-BE treatment confirmed that 2-BE reduced poly(ADP-ribosyl)ation capacities of MMS-treated cells, though the glycol ether had no effect alone. This study confirmed that the inhibition of pADPr synthesis could be responsible for the synergistic effects of 2-BE with genotoxic substances. The mechanism of this inhibition cannot be explained by a lack of NAD+ at the concentrations of 2-BE tested.      

Local metabolism in lung airways increases the uncertainty of pyrene as a biomarker of polycyclic aromatic hydrocarbon exposure

While inhaled polycyclic aromatic hydrocarbons have long been suspected to induce lung cancer in humans, their dosimetry has not been fully elucidated. A key question is whether the critical exposure occurs during absorption in the lungs, or if toxicants in the systemic circulation contribute significantly to lung cancer risk. In particular, data are needed to determine how the physical properties of inhalants affect local dosimetry in the respiratory tract. Pyrene, a tobacco smoke component, was selected for study because it has physical properties between those of highly lipophilic benzo[a]pyrene and water- soluble nitrosamines. Aliquots of 5 ng of pyrene dissolved in a phospholipid/ saline suspension were instilled as a single-spray bolus in the posterior trachea of the dog just anterior to the carina. For 3 h after instillation, blood was repeatedly sampled from the azygous vein, which drains the mucosa around the point of instillation, and from both sides of the systemic circulation. At 3 h post-instillation, tissue samples were taken. Autoradiography was used to determine the depth distribution of pyrene in the tracheal mucosa. The concentration of pyrene-equivalent radioactivity in the azygous vein peaked 9 min after the instillation. At approximately 30 min after instillation, a rapid early clearance phase shifted into a distinctly slower second clearance phase. Rates of rapid clearance were, however, sufficiently slow to indicate diffusion-limited absorption of pyrene in the trachea. This finding was corroborated by high concentrations of pyrene in the epithelium as determined by autoradiography. High epithelial concentration of pyrene combined with a slow penetration into the circulating blood allowed substantial first-pass metabolic conversion of pyrene in the tracheal mucosa. A total of 13% of the instilled pyrene was retained in the tracheal mucosa 3.2 h after instillation; of this, 29% was parent compound, 52% was organic-extractable metabolites, 14% was water-soluble metabolites and 6% (approximately 1% of the instilled amount) was covalently bound to tracheal tissues. Results support the inference that lipophilic protoxicants, because of slow, diffusion-limited absorption, are more likely than water-soluble protoxicants to be bioactivated in the lining epithelium and, in turn, induce first-pass toxicity at the site of entry. In addition, limitations were identified in the use of systemically distributed biomarkers of PAHs, such as urinary hydroxypyrene levels, as indicators of the biologically effective dose in airway target cells.