Ascorbate deficiency and oxidative stress in the alveolar type II cell

The objective of this study was to determine the impact of limited ascorbate (Asc) availability on type II cell sensitivity to oxidant stress. Guinea pigs were fed diets with or without Asc for 18 days, and type II cells were isolated. Although lung Asc was decreased by 90% in deficient animals (scorbutic), type II cell Asc was decreased by 50%. Upon treatment with 250 microM H2O2, the necrotic injury was twofold greater in scorbutic cells compared with control cells. With 100 microM H2O2 treatment, apoptotic injury was twofold greater in scorbutic cells compared with control cells. Although there was less necrotic injury in cells exposed to 95% O2, the scorbutic cells were more sensitive than control cells. Asc pretreatment protected against necrosis and apoptosis. The Asc analog isoascorbate provided partial protection and suggested that part of the protection was not chemical detoxification but was Asc specific. We conclude that limited Asc availability resulted in a functional type II cell but a cell more sensitive to oxidant-induced injury.

Mitochondria-mediated cell injury. Symposium overview

Mitochondria have long been known to participate in the process of cell injury associated with metabolic failure. Only recently, however, have we come to appreciate the role of mitochondria as primary intracellular targets in the initiation of cell dysfunction. In addition to ATP synthesis, mitochondria are also critical to modulation of cell redox status, osmotic regulation, pH control, and cytosolic calcium homeostasis and cell signaling. Mitochondria are susceptible to damage by oxidants, electrophiles, and lipophilic cations and weak acids. Chemical-induced mitochondrial dysfunction may be manifested as diverse bioenergetic disorders and considerable effort is required to distinguish between mechanisms involving critical mitochondrial targets and those in which mitochondrial dysfunction is secondary and plays only a modulatory role in cell injury. The following paragraphs review a few important examples of chemical-induced cytotoxic responses that are manifested as interference with mitochondrial metabolism and bioenergetics, gene regulation, or signal transduction in the form of apoptosis and altered cell cycle control. Greater understanding of the molecular mechanisms of mitochondrial bioenergetics, ion regulation, and genetics will lead to numerous additional examples of mitochondria-mediated cell injury, revealing important new insight regarding the prediction, prevention, diagnosis, and treatment of chemical-induced toxic tissue injury.

Prevention of apoptosis by Bcl-2: release of cytochrome c from mitochondria blocked

Bcl-2 is an integral membrane protein located mainly on the outer membrane of mitochondria. Overexpression of Bcl-2 prevents cells from undergoing apoptosis in response to a variety of stimuli. Cytosolic cytochrome c is necessary for the initiation of the apoptotic program, suggesting a possible connection between Bcl-2 and cytochrome c, which is normally located in the mitochondrial intermembrane space. Cells undergoing apoptosis were found to have an elevation of cytochrome c in the cytosol and a corresponding decrease in the mitochondria. Overexpression of Bcl-2 prevented the efflux of cytochrome c from the mitochondria and the initiation of apoptosis. Thus, one possible role of Bcl-2 in prevention of apoptosis is to block cytochrome c release from mitochondria.

A model for light toxicity of cultured human retinal pigment epithelium

BACKGROUND

The effect of visible light on human retinal pigment epithelial (HRPE) cells has not been characterized under conditions that provide strict thermal control.

METHODS

HRPE cells were isolated and grown to confluence. Cells were exposed to light in an incubator in which the cell temperature was controlled in response to a temperature sensor maintained in the tissue culture medium. Cells were exposed: (A) for 24, 36, and 48 h; and using a 24-h exposure followed by 24 h darkness; (B) at varying intensities of light using neutral density filters; (C) under a yellow filter; and (D) with a 12-h on-off cyclic light.

RESULTS

(A) Light exposure of 36 and 48 h resulted in significant cytotoxicity, while the initial 24-h exposure did not induce subsequent cytotoxicity. (B) Light irradiance levels from 43 to 54 mW/cm2 were required to demonstrate cytotoxicity. (C) Use of a yellow filter did not eliminate the observed cytotoxicity. (D) Cyclic exposure did not result in significant cytotoxicity.

CONCLUSION

This study establishes a model and basic parameters of light toxicity to HRPE cells in vitro using strict temperature control that may be used to evaluate photochemical injury to HRPE cells.

Epitope mapping using histidine-tagged protein fragments: application to Escherichia coli RNA polymerase sigma 70

We present a simple, rapid, and inexpensive method for mapping epitopes of monoclonal antibodies using His-tagged protein fragments. In essence, four steps are involved: (i) purify overproduced His-tagged protein from inclusion body; (ii) fragment the protein by partial chemical or enzymatic hydrolysis and isolate the His-tagged peptides with a Ni(2+)-chelate column to generate a "ladder" containing a distribution of peptide fragment sizes; (iii) fractionate the isolated peptides by SDS-polyacrylamide gel electrophoresis and probe the ladder by immunoblot analysis; (iv) determine the size of the fragments that do and do not bind the monoclonal antibody using size markers specific to the His-tagged protein being studied. We have applied this method successfully to map the epitope positions of known and new monoclonal antibodies to Escherichia coli sigma 70. We believe this method will find broad application.

GSH transport and GSH-dependent detoxication in small intestine of rats exposed in vivo to hypoxia

The effects of hypoxia on glutathione (GSH) concentration and GSH-related enzyme and transport systems were studied in the small intestine of rats exposed to 8-10 days of 10.5% O2. Exposure to hypoxia resulted in a 40% lower GSH concentration in enterocytes and a 50% lower concentration in blood plasma. Activities of GSH-related detoxication enzymes in the intestinal epithelium were largely unaffected by hypoxic exposure. GSH degradation and synthesis rates in enterocytes isolated from hypoxic rats were comparable with rates in normoxic controls, but GSH uptake rate was decreased by 30%. Stimulation of absorption of GSH by phenylephrine, such as occurs in control rats, was not detectable in isolated, vascularly perfused intestines of hypoxic rats. Decreased GSH uptake was associated with enhanced transepithelial appearance of thiobarbituric acid-reactive substances in everted intestinal sacs incubated with peroxidized methyl linoleate. These results suggest that chronic hypoxia results in impaired uptake of GSH in the small intestine, and this may result in impaired GSH-related defense mechanisms in the small intestine.

Accidental self inoculation with oil based veterinary vaccines

AIMS

To report the adverse local effects of inadvertent self inoculation with oil-based veterinary vaccines.

METHODS

Three case reports and a literature review.

RESULTS

One patient developed extensive chronic granulomatous inflammation in the thigh following intramuscular injection of Footvax vaccine requiring major surgical debridements. The other two cases developed chronic inflammation and sterile abscess formation following subcutaneous injections in the hand, requiring surgical drainage and corticosteroids to eventually heal.

CONCLUSIONS

The mineral oil used as an adjuvant in veterinary vaccines can cause a prolonged chronic granulomatous reaction with sterile abscess formation. Surgical debridement may be required to remove the oil to prevent chronic sequelae. Oral corticosteroids should be considered once infection has been excluded.

The nursing management of women experiencing preterm labor: clinical guidelines and why they are needed

Nursing care is a critical component of therapy for women experiencing preterm labor. Diversity exists, however, in the level of comprehensiveness and consistency in guidelines for clinical practice. Nonstandardized care interferes with the ability to achieve consistent, positive patient care outcomes. This article is intended for nurses who seek to organize and standardize their care for women experiencing preterm labor. This article presents a review of the applicable practice and research literature. Clinical guidelines for the nursing management of women experiencing preterm labor are presented in the appendix.

Compartmentation of glutathione: implications for the study of toxicity and disease

The fact that glutathione (GSH) plays many roles in biological protective mechanisms and critical physiological functions has been recognized for decades. Conjugates, disulfides, and other glutathione-derived products also have been studied as biomarkers of the chemical natures or specific identities of key metabolites of toxic agents and such studies have been crucial in the delineation of the nature of the interactions of proximal toxicants with target biomolecules. Despite the extensive evidence implicating the depletion and/or oxidation of glutathione in a wide variety of human and experimental toxicities, critical examination of such studies frequently reveals that injury is not simply related to glutathione status. GSH is compartmentalized at several levels and this compartmentation appears to exert considerable influence on the relationships between glutathione depletion or oxidation and the onset of injury. Although compartmentation is usually viewed from the perspective of different intracellular pools, the significance of extracellular glutathione in functionally important pools is gaining recognition. As the factors affecting the interactions of intracellular pools with extracellular pools are delineated, studies in humans can be designed and interpreted with greater precision and utility.

Effect of hypoxia on hepatic DNA methylation and tRNA methyltransferase in rat: similarities to effects of methyl-deficient diets

Young rats were maintained in a 10% oxygen atmosphere for 2, 6, and 10 days and administered normal rat chow and water ad libitum. Thereafter, their hepatic S-adenosyl-L-methionine (AdoMet) and activity and mRNA levels of AdoMet synthetase were assayed. AdoMet levels decreased by 45% after 10 days; hepatic AdoMet synthetase also declined by approximately 40%. In rats with low hepatic AdoMet, the mRNA level of AdoMet synthetase also declined by up to 80%. No significant change in AdoMet or AdoMet synthetase was noted in pair-fed normoxic rats. DNA hypomethylation was determined in terms of incorporation of [3H]methyl of AdoMet incorporated at unmethylated sites in DNA in reactions mediated by methylases HpaII and SssI. As compared to the normal hepatic DNA, [3H]methyl group incorporation in the 10-day hypoxic DNA was almost double in the HpaII-mediated reaction and approximately 10-fold in the SssI-mediated reaction. Hepatic tRNA methyltransferase activity doubled after 10 days of hypoxia. However, hypoxic rats showed no detectable mRNA transcripts for c-myc and c-fos oncogenes on Northern blot analysis. These observations show that because of subnormal activity of AdoMet synthetase, hypoxic liver is depleted of AdoMet, even when the animals are administered a complete diet. However, unlike rats on chronic lipotrope-deficient diets, hypoxic rats on a complete diet show no aberrant expression of oncogenes.

An assessment approach to abuse allegations made through facilitated communication

Over the last few years a number of cases have been reported in which accusations of sexual abuse have been made through the medium of facilitated communication. Although experimental evaluations of facilitated communication indicate that responses are almost always under the control of the facilitator, not the client, such allegations cannot be ignored. The following case study describes the procedures followed when a young girl with autism began to make accusations of abuse against family members. The paper suggests a number of guidelines that might be followed when professionals are faced with dilemmas of a similar kind.

Regulation of expression of taurine transport in two continuous renal epithelial cell lines and inhibition of taurine transporter by a site-directed antibody

The renal tubular epithelium adapts to changes in the sulfur amino acid composition of the diet, particularly in terms of reabsorption of taurine. The adaptive response is expressed by enhanced or decreased NaCl-dependent taurine transport by rat renal brush border membrane vesicles (BBMV). Taurine transport activity in two cultured renal epithelial cell lines (MDCK and LLC-PK1) is up- or down-regulated by extracellular taurine concentration as the result of reciprocal changes in the Vmax of the transporter. In MDCK cells, abundance of taurine transporter mRNA (pNCT mRNA) was up- or down-regulated after incubation in media containing 0, 50, or 500 microM taurine. Decreased mRNA was observed in both cell lines after 12 h, and it was appreciably reduced after 72 h exposure to 500 microM taurine. Northern blot analysis of mRNA from LLC-PK1 cells using pNCT cDNA as a riboprobe showed that two transcripts, 9.6 kb and 7.2 kb, were expressed; the abundance of mRNA was increased or decreased after incubation in taurine-free or high taurine medium, respectively. Down-regulation was observed primarily in the 7.2 kb transcript after 24 h incubation. Rapid up-regulation occurred in the 9.6 kb transcript within 12 h of transfer from high to low taurine. Nuclear run-off assays showed that the gene for pNCT is induced at the transcriptional level by taurine. Regulation of expression of the taurine transporter was also studied by injection of pNCT cRNA into Xenopus laevis oocytes. Expression of transport activity was significantly reduced (64%) when oocytes were incubated in 50 microM taurine as compared to 0 microM taurine. Transport activity was totally blocked when pNCT cRNA-injected oocytes were exposed to an active phorbol ester, PMA (10(-6) M). Inhibition of uptake was reversed by staurosporine, an inhibitor of protein kinase C activity. An inactive phorbol ester, 4 alpha-phorbol, had no effect on taurine transport. A polyclonal antibody directed a highly conserved intracellular segment between homologous transmembrane domains VI and VII inhibited taurine transport activity in both pNCT cRNA-injected oocytes and BBMV. Incubation of oocytes with 10 micrograms/ml antibody (Ab) reduced taurine uptake to 46% of control, and 20-80 micrograms/ml Ab reduced uptake to 20% of control. In BBMV, active taurine uptake (10 microM) was inhibited approximately 30% by 10 pg Ab/mg protein, whereas none specific IgG had no significant effect. Proline uptake (20 microM) by BBMV was not inhibited by the Ab, nor was GABA uptake (50 microM). Two pNCT proteins, approximately 70 kD and approximately 30 kD, were detected by Western blot, and the abundance of both was regulated by medium taurine.

IN CONCLUSION

(i) regulation of taurine transport activity in LLC-PK1 cells by medium taurine occurs at a level of mRNA transcription; (ii) regulation of pNCT occurs at both transcriptional and translational levels; (iii) pNCT expression is regulated by protein kinase C-dependent phosphorylation; and (iv) the intracellular segment between domains VI and VII may be required for activation of the taurine transporter; this segment may function as a gate in taurine transport.

Variability in glutathione-dependent detoxication in vivo and its relevance to detoxication of chemical mixtures

Glutathione (GSH) has multiple functions in detoxication and its depletion has been associated with an increased risk of chemical toxicity. Because GSH can be depleted by different agents, combinations of compounds in chemical mixtures are likely to enhance risk over that seen with individual chemicals. Our studies have focussed on factors affecting the status of GSH in humans. In addition, we have utilized animals models and cell culture systems to understand the role of GSH in protection against chemical injury. Results of these studies show that, while large variations in sulfur amino acid content occur in the human diet, these variations are not correlated simply with GSH levels in vivo as reflected in the blood plasma pool. However, plasma levels of GSH do vary with gender, age, race and dietary habits, and these factors could affect the risk of toxicity in individuals exposed to chemical mixtures. In animal studies, we found that extracellular pools of GSH, including the blood plasma, lung-lining fluid and small intestinal lumen can be very important in protection against chemically induced injury. These pools can function to detoxify chemicals extracellularly, supply GSH and its precursors to cells and protect the extracellular surface of the plasma membrane from damage. Finally, endogenous gene-activated mechanisms of cell death which produce the characteristic morphology of apoptosis are susceptible to thiol-disulfide redox regulation. Perturbations in GSH status induced by chemical mixtures could alter this regulation and lower the threshold for chemically induced cell death by apoptosis. Thus, in vivo GSH status could be an important determinant of toxicity from chemical mixtures and may be useful as a biomarker for such risk.