Deficiencies and improvement of methemoglobin assay

Effect of propolis on erythrocyte rheology in experimental mercury intoxication in rats

In the present study, changes in erythrocyte rheology in association with mercury toxicity and the role of propolis were analyzed in rats. Forty male Wistar Albino rats that were 4-5 months old were used in the study. The control group was administered normal saline intraperitoneal (ip) injections; the mercury chloride group was administered HgCl2 (4 mg/kg, ip); the propolis group was administered propolis (200 mg/kg, by gavage); and the HgCl2+ propolis group was administered HgCl2 (4 mg/kg, ip) + propolis (200 mg/kg, by gavage) for 3 days. The following parameters were analyzed: hematological parameters, plasma potassium (K) levels, methemoglobin, 2,3-DPG, erythrocyte deformability, and hemolysis as a percentage. The results revealed that leukocyte count significantly increased, and a significant decline occurred in the platelet count (p < 0.01). Serum K(+), MetHb, 2, 3-DPG, and hemolysis percentage significantly increased in the rats exposed to mercury (p < 0.01). However, the values of rats administered only with propolis were close to the values of the control group and the changes were avoided by the administration of propolis as protection in the rats exposed to mercury chloride.

Doxorubicin in vivo rapidly alters expression and translation of myocardial electron transport chain genes, leads to ATP loss and caspase 3 activation

Background

Doxorubicin is one of the most effective anti-cancer drugs but its use is limited by cumulative cardiotoxicity that restricts lifetime dose. Redox damage is one of the most accepted mechanisms of toxicity, but not fully substantiated. Moreover doxorubicin is not an efficient redox cycling compound due to its low redox potential. Here we used genomic and chemical systems approaches in vivo to investigate the mechanisms of doxorubicin cardiotoxicity, and specifically test the hypothesis of redox cycling mediated cardiotoxicity.

Methodology/Principal Findings

Mice were treated with an acute dose of either doxorubicin (DOX) (15 mg/kg) or 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) (25 mg/kg). DMNQ is a more efficient redox cycling agent than DOX but unlike DOX has limited ability to inhibit gene transcription and DNA replication. This allowed specific testing of the redox hypothesis for cardiotoxicity. An acute dose was used to avoid pathophysiological effects in the genomic analysis. However similar data were obtained with a chronic model, but are not specifically presented. All data are deposited in the Gene Expression Omnibus (GEO). Pathway and biochemical analysis of cardiac global gene transcription and mRNA translation data derived at time points from 5 min after an acute exposure in vivo showed a pronounced effect on electron transport chain activity. This led to loss of ATP, increased AMPK expression, mitochondrial genome amplification and activation of caspase 3. No data gathered with either compound indicated general redox damage, though site specific redox damage in mitochondria cannot be entirely discounted.

Conclusions/Significance

These data indicate the major mechanism of doxorubicin cardiotoxicity is via damage or inhibition of the electron transport chain and not general redox stress. There is a rapid response at transcriptional and translational level of many of the genes coding for proteins of the electron transport chain complexes. Still though ATP loss occurs with activation caspase 3 and these events probably account for the heart damage.

Concentration-dependence of aniline-induced methemoglobinemia in dogs: A derivation of an acute reference concentration

Four male Beagle dogs per group were head-only exposed to aniline vapor in concentrations ranging from 15.8 to 493.6 mg/m3. Each exposure session was for 4h. Additionally, one group of dogs was both head-only and whole-body exposed to approximately 241 mg/m3 to better appreciate the contribution of dermal uptake on methemoglobin (MetHb) induction. The exposure paradigm chosen was comparable to a dose-escalation type of study, however, providing adequate recovery periods between each exposure session to exclude 'carry-over' effects from one exposure session to another. This was verified by the determination of standard hematology endpoints before and after each exposure session. The time- and concentration-dependence of MetHb was analyzed as the key endpoint. The results of this study show that MetHb was maximal around the end of the 4 h exposure period. Significantly increased MetHb was observed at concentrations equal and above 30.3 mg/m3 at a duration of exposure of at least 60 min. The extent of MetHb formation observed in some hyperventilating dogs suggests that the dosing-rate is important for the outcome of test. Whole body exposed dogs displayed markedly higher MetHb values when compared to head-only exposed dogs. Taking into account the entire concentration-time-effect relationship 23.6 and 20.6 mg/m3 were estimated to be the threshold concentrations to cause 0.8% MetHb following a 4 and 8h exposure period, respectively. The C(n)xt analysis of MetHb formation is consistent with a concentration-dependent restoration kinetics of MetHb suggesting that results from high level exposures cannot readily be extrapolated to low-level exposures. In summary, this study demonstrates that for aniline, an agent known to be bioactivated by a hepatic first-pass metabolism, the rate of delivery and uptake appears to be decisive for the extent of MetHb formation. Carry-over effects related to erythrotoxicity or Heinz body formation were not observed at any exposure level.

Simultaneous modeling of the pharmacokinetics and methemoglobin pharmacodynamics of an 8-aminoquinoline candidate antimalarial (WR 238605)

Methemoglobin (MHb) formation can be a clinically significant and dose-limiting side effect of 8-aminoquinoline antimalarials. MHb may also protect against cyanide poisoning. A two-compartment pharmacokinetic model, linked to a sigmoid Emax pharmacodynamic model, was developed to predict the MHb levels after administration of 8-[(4-amino-1-methylbutyl)amino]-2,6-dimethoxy-4-methyl-5-[(3- trifluoromethyl)phenoxy] quinoline succinate (WR 238605 succinate), a primaquine analogue. Six healthy male beagle dogs received four daily doses of 6.0 mg/kg (base) orally. Forty plasma drug concentrations and 19 MHb levels (effect) were determined over 7 weeks on each dog. Compartmental and noncompartmental pharmacokinetic and parametric and nonparametric pharmacodynamic analyses were performed. Model parameters (mean +/- SD) included a Vss/f of 18.5 +/- 2.8 L/kg, CL/f of 83 +/- 24 ml/hr/kg, terminal elimination t1/2 of 169.7 +/- 52.0 hr, t1/2keo of 123.0 +/- 22.4 hr, an Emax of 31.3 +/- 15.9% MHb, an EC50 of 596 +/- 128 ng/ml, and a sigmoidicity coefficient (n) of 1.94 +/- 0.47. The model was then validated in three additional dogs given three different dosing regimens. It predicted the peak plasma concentrations and MHb levels and the times of their occurrence well. This model could be useful for dose and sampling time selection in further animal studies and initial human phase I clinical testing.