Diquat hepatotoxicity in the Fischer-344 rat: the role of covalent binding to tissue proteins and lipids

Diquat produces hepatic necrosis in the Fischer-344 rat, and although reactive oxygen species generated by redox cycling are thought to mediate the damage, the possibility that covalent binding of diquat or diquat metabolites to tissue macromolecules contributes to the observed hepatotoxicity of diquat needed to be examined experimentally. Intraperitoneal administration of [ethylene-14C]diquat (0.1 mmol/kg) results in distribution of radioactivity to all organs examined. Measurable radioactivity remains associated with hepatic and renal protein even after extensive solvent extraction, but the amount (12-16 pmol/mg protein) is 100-fold less than the extent of covalent binding observed with comparably hepatotoxic doses of other hepatotoxins such as acetaminophen and bromobenzene. Similarly, although small amounts of radioactivity remain in Folch lipid extracts of liver and kidney (56-179 pmol/mg lipid), this is virtually completely removed by transesterification of the lipid (less than 5 pmol/mg lipid), indicating that the radioactivity does not represent an alkylation of electroneutral alkyl residues of the lipid. The diquat-induced increase in biliary excretion of glutathione disulfide temporally parallels the biliary excretion of radioactivity. Although the present results do not prove the absence of a contribution by alkylation mechanisms to diquat hepatotoxicity, the extremely low upper limits placed on possible covalent interactions reinforce the confidence with which the diquat-treated Fischer-344 rat can be employed as an animal model for mechanisms of cell death mediated by reactive oxygen species.     

Retinal ganglion cell neurotrophin receptor levels and trophic requirements following target ablation in the neonatal rat

Superior colliculus (SC) ablation in neonatal rats results in a rapid increase in retinal ganglion cell (RGC) death. This injury-induced death is reduced by exogenous brain-derived neurotrophic factor or neurotrophin-4/5 (NT-4/5), but the protective effect of these molecules is transient, delaying but not preventing neuronal loss. We sought to discover why neurotrophins only temporarily reduce RGC death after target ablation, focusing on changes in neurotrophin receptor expression and possible changes in growth factor dependency. In unlesioned rats, receptor tyrosine kinase B (trkB) immunohistochemistry revealed no change in the number of trkB positive cells in the RGC layer 24 h after intraocular NT-4/5 injection. However, after SC lesions there were significantly less immunoreactive cells and, surprisingly, even fewer immunoreactive cells in NT-4/5 injected eyes. Semi-quantitative confocal analysis of immunofluorescence intensity revealed an increase in trkB staining in the RGC layer in unlesioned rats 24 h after NT-4/5 injection, whereas in SC-lesioned animals exposed to NT-4/5 there was a significant decrease in staining. To determine whether injured neonatal RGCs can switch their trophic requirements, different doses of ciliary neurotrophic factor were given intraocularly, either alone or combined with NT-4/5. We also tested an SC-derived chondroitin sulfate proteoglycan that has been reported to promote neonatal RGC survival. None of these interventions reduced lesion-induced RGC death 24 or 36 h after SC ablation. In summary, we show that developing RGCs do not shift their trophic dependence to other survival factors following injury; rather, the application of neurotrophins causes a down-regulation of the cognate trkB receptor, presumably altering the long-term responsiveness of neonatal RGCs to exogenous neurotrophins. These data highlight the difficulty in promoting long-term neuronal survival when using one-off administration of recombinant growth factors.     

The effect of methodology on the determination of nasal resistance

Confusion and controversy continue to characterize scientific understanding of the role that respiration plays in modifying growth. Identification of specific methods to provide valid measurement of nasorespiratory function can help clinicians to (1) make an informed judgment regarding postulated relationships between respiration and growth, (2) test the validity of a diagnosis of impaired nasal respiration or "mouth breathing," and (3) evaluate the efficacy of treatment for nasal obstruction. A method that has been frequently used to quantify nasorespiratory function is nasal resistance measurement or rhinomanometry. This investigation used a common form of this method, studying 25 adult subjects to examine the effect of a number of variables in methodology on nasal airway resistance values. Results indicate that resistance to nasally inspired air was not significantly different from resistance to nasally expired air. However, a significant difference in estimating resistance was found between airflow rates of 0.25 and 0.5 L/sec, with nasal resistance increasing at the higher flow rate. Determination of the method error indicated that the technique was reliable and accurate for the sample studied. It was found that both expansion of the anterior nares and use of a nasal decongestant spray produced a decrease in mean nasal resistance. The study emphasizes the need to standardize the method of determining nasal resistance in order to permit comparisons among studies, to obtain a more reliable estimate of resistance, and to identify the location of maximum constriction in the nasal airway.     

Effects of Mercury on Health and First-Year Survival of Free-Ranging Great Egrets (Ardea albus) from Southern Florida

The objectives of this study were to determine whether elevated mercury (Hg) concentrations have a negative impact on the health and survival of nestling and juvenile free-ranging great egrets (Ardea albus) from southern Florida. During 1994, when health and survival was monitored in a cohort of young birds with naturally variable concentrations of Hg, packed cell volume was positively correlated with blood Hg concentrations, and high Hg concentration in blood was not related to the probability of surviving during the first 10.5 months of life. During 1995, 70 first-hatched great egret chicks were included in a Hg field-dosing experiment to compare the effects of elevated Hg on health and survival. Birds were dosed while in the nest orally every 2.5 days for 15 days with 0.5 mg of methyl mercury chloride (MeHgCl) for an estimated intake of 1.54 mg MeHgCl/kg food intake. These birds were compared with controls, which received an estimated 0.41 mg MeHgCl/kg food. No differences were observed in health parameters or in the probability of surviving during the first 8 months of age between egrets that were dosed with Hg and those that were not. A likely explanation for the lack of any effects on health and survival between both groups could be that chicks at this age were eliminating most of the dietary Hg through the production of new feathers. Received: 10 November 1998/Accepted: 8 April 1999     

Growth of Pakistani children in relation to the 1990 growth standards

This study was designed to compare the growth of Pakistani schoolchildren in the UK with the 1990 UK growth standards. Measurements of height, weight, and sitting height were performed on 785 Pakistani schoolchildren aged 5-14 years with the mean values for each age and sex being plotted on the UK growth standards. The results were expressed as SD scores relative to the 1990 reference data. The mean height for the boys was only 0.2 SD scores below the mean for the new growth standards with the mean height for the girls being 0.4 SD scores below the mean. The mean values for weight and body mass index were 0.3 and 0.5 SD scores less than the mean for boys and girls respectively. This study demonstrates that the growth of Pakistani schoolchildren in the UK is comparable to the 1990 UK growth standards with only minor differences. It is not safe to assume that short stature or low body weight in a Pakistani child is due to his or her ethnic background.     

Hemorrhagic tumor necrosis during a pilot trial of tumor necrosis factor-alpha and anti-GD3 ganglioside monoclonal antibody in patients with metastatic melanoma

Hemorrhagic tumor necrosis is an inflammatory event that leads to selective destruction of malignant tissues, with both potentially toxic and beneficial consequences. A pilot clinical trial was undertaken combining tumor necrosis factor-alpha (TNF-alpha) with the monoclonal antibody R24 (MoAb R24) against GD3 ganglioside in patients with metastatic melanoma. Patients received MoAb R24 to recruit leukocytes to the tumor followed by low doses of recombinant TNF-alpha to activate leukocytes. Eight patients were treated and seven patients had mild toxicity. One patient with extensive metastatic melanoma developed tumor lysis syndrome within hours after treatment with almost complete necrosis of bulky tumors in multiple visceral sites. To our knowledge, this is the first documented case of hemorrhagic tumor necrosis in a patient with metastatic cancer in multiple visceral sites.     

Induction of immune tolerance in patients with hemophilia A and inhibitors treated with porcine VIIIC by home therapy

Home therapy with porcine factor VIIIC was safe and effective when administered to five hemophilic patients over periods of 8 1/2, 6, 4, 3 1/2, and 2 years. No significant transfusion reactions occurred. Before treatment with porcine factor VIIIC, all five had high-level, high- responding anti-human VIIIC inhibitors initially lacking anti-porcine factor VIIIC activity. Although specific anti-porcine VIIIC inhibitors arose in all patients, these were generally transient, and only one patient became refractory to treatment. We believe that porcine factor VIIIC is the treatment of choice in patients whose inhibitors do not cross-react. All five patients lost their original anti-human VIIIC inhibitors after starting treatment with porcine VIIIC, permitting the reintroduction of human VIIIC in three of them. There has been no recurrence of anti-human VIIIC inhibitor activity during 2 to 3 years of regular treatment with human VIIIC in these patients. This suggests that tolerance to human VIIIC has arisen as a result of treatment with porcine VIIIC. Porcine VIIIC may have a role in the desensitization of some factor VIIIC inhibitor patients.