The induction of stress-related proteins by lead

Infrared and 2-Dimensional Correlation Spectroscopy Study of the Effect of CH3NH3PbI3 and CH3NH3SnI3 Photovoltaic Perovskites on Eukaryotic Cells

We studied the effect of the exposure of human A549 and SH-SY5Y cell lines to aqueous solutions of organic/inorganic halide perovskites CH₃NH₃PbI₃ (MAPbI₃) and CH₃NH₃SnI₃ (MASnI₃) at the molecular level by using Fourier transform infrared microspectroscopy. We monitored the infrared spectra of some cells over a few days following exposure to the metals and observed the spectroscopic changes dominated by the appearance of a strong band at 1627 cm⁻¹. We used Infrared (IR) mapping to show that this change was associated with the cell itself or the cellular membrane. It is unclear whether the appearance of the 1627 cm⁻¹ band and heavy metal exposure are related by a direct causal relationship. The spectroscopic response of exposure to MAPbI₃ and MASnI₃ was similar, indicating that it may arise from a general cellular response to stressful environmental conditions. We used 2D correlation spectroscopy (2DCOS) analysis to interpret spectroscopic changes. In a novel application of the method, we demonstrated the viability of 2DCOS for band assignment in spatially resolved spectra. We assigned the 1627 cm⁻¹ band to the accumulation of an abundant amide or amine containing compound, while ruling out other hypotheses. We propose a few tentative assignments to specific biomolecules or classes of biomolecules, although additional biochemical characterization will be necessary to confirm such assignments.

Toxicogenomic approaches for understanding molecular mechanisms of heavy metal mutagenicity and carcinogenicity

Heavy metals that are harmful to humans include arsenic, cadmium, chromium, lead, mercury, and nickel. Some metals or their related compounds may even cause cancer. However, the mechanism underlying heavy metal-induced cancer remains unclear. Increasing data show a link between heavy metal exposure and aberrant changes in both genetic and epigenetic factors via non-targeted multiple toxicogenomic technologies of the transcriptome, proteome, metabolome, and epigenome. These modifications due to heavy metal exposure might provide a better understanding of environmental disorders. Such informative changes following heavy metal exposure might also be useful for screening of biomarker-monitored exposure to environmental pollutants and/or predicting the risk of disease. We summarize advances in high-throughput toxicogenomic-based technologies and studies related to exposure to individual heavy metal and/or mixtures and propose the underlying mechanism of action and toxicant signatures. Integrative multi-level expression analysis of the toxicity of heavy metals via system toxicology-based methodologies combined with statistical and computational tools might clarify the biological pathways involved in carcinogenic processes. Although standard in vitro and in vivo endpoint testing of mutagenicity and carcinogenicity are considered a complementary approach linked to disease, we also suggest that further evaluation of prominent biomarkers reflecting effects, responses, and disease susceptibility might be diagnostic. Furthermore, we discuss challenges in toxicogenomic applications for toxicological studies of metal mixtures and epidemiological research. Taken together, this review presents toxicogenomic data that will be useful for improvement of the knowledge of carcinogenesis and the development of better strategies for health risk assessment.

Roles of biomarkers in evaluating interactions among mixtures of lead, cadmium and arsenic

Human exposure to environmental chemicals is most correctly characterized as exposure to mixtures of these agents. The metals/metalloids, lead (Pb), cadmium (Cd), and arsenic (As), are among the leading toxic agents detected in the environment. Exposure to these elements, particularly at chronic low dose levels, is still a major public health concern. Concurrent exposure to Pb, Cd, or As may produce additive or synergistic interactions or even new effects that are not seen in single component exposures. Evaluating these interactions on a mechanistic basis is essential for risk assessment and management of metal/metalloid mixtures. This paper will review a number of individual studies that addressed interactions of these metals/metalloids in both experimental and human exposure studies with particular emphasis on biomarkers. In general, co-exposure to metal/metalloid mixtures produced more severe effects at both relatively high dose and low dose levels in a biomarker-specific manner. These effects were found to be mediated by dose, duration of exposure and genetic factors. While traditional endpoints, such as morphological changes and biochemical parameters for target organ toxicity, were effective measures for evaluating the toxicity of high dose metal/metalloid mixtures, biomarkers for oxidative stress, altered heme biosynthesis parameters, and stress proteins showed clear responses in evaluating toxicity of low dose metal/metalloid mixtures. Metallothionein, heat shock proteins, and glutathione are involved in regulating interactive effects of metal/metalloid mixtures at low dose levels. These findings suggest that further studies on interactions of these metal/metalloid mixtures utilizing biomarker endpoints are highly warranted.

Effects of N-acetylcysteine on lead-exposed PC-12 cells

The neurotoxicity of lead has been well established through numerous studies. However, the cellular processes of lead neurotoxicity, as well as techniques to prevent or reverse cellular damage after lead exposure, remain unknown. If oxidative stress plays a primary role in lead-induced neurotoxicity, antioxidants should assist in reviving lead-exposed cells. The present study explores N-acetylcysteine (NAC) as an antioxidant agent in PC-12 cells after lead exposure. Selective oxidative stress parameters, including glutathione (GSH), glutathione disulfide (GSSG), and malondialdehyde (MDA), were measured in PC-12 cells exposed to various concentrations of lead acetate. Administering NAC after lead exposure improved cell survival as measured by Trypan Blue exclusion. NAC treatment also increased the GSH/GSSG ratio compared to the lead-only group, and reduced MDA to near control levels. These results imply that NAC protects cells from lead-induced oxidative damage by boosting the PC-12 cells' antioxidant defense mechanisms.

Stress-70 proteins in marine mussel Mytilus galloprovincialis as biomarkers of environmental pollution: a field study

In the present work we have investigated levels of stress-70 proteins in the gills of mussel Mytilus galloprovincialis collected seasonally from subtidal rocky shores at 6 different sites of the Rovinj coastal area (Northern Adriatic, Croatia). 1-D analysis (SDS-PAGE) using monoclonal mouse antibodies anti-HSP70 detected two bands of stress-70 proteins, 70 and 72 kDa constitutively present during the year. 2-D analysis (IEF+SDS-PAGE) proved that the antibodies used detected HSP70 (pI 5.7-5.9) and HSP72 (pI 5.5-5.6). The quantification of stress-70 proteins was possible using 200 ng of external HSP70 protein standard included on every blot. Maximal levels of HSP72 and HSP70 were observed in mussels in summer (September), and minimal levels in winter (December), and only HSP70 showed significant correlation with the sea temperature (r=+0.822, p<0.05). Acclimatization of mussels to a different lower salinity under experimental conditions proved that small changes in sea salinity (Delta=2 psu) could not cause significant stress-70 proteins induction. Results indicated that there are significant differences in HSP70 and HSP72 content in mussels from the control site (S-1) and mussels from other sampling sites with urban and industrial pollution. The usefulness of stress-70 proteins as biomarkers of environmental pollution is discussed.

Effect of chronic exposure to lead on estrogen action in the prepubertal rat uterus

Lead is a widely spread environmental pollutant known to affect both male and female reproductive systems in humans and in experimental animals. The present study investigated the effect of a chronic exposure to lead on different parameters of estrogen stimulation in the uteri of prepubertal rats. Chronic exposure to lead enhanced some parameters of estrogen stimulation, inhibited other estrogenic responses, while the remainder were unaltered. Estrogen-induced uterine eosinophilia (24 h), the proportion of uterine eosinophils in the mesometrium (6 h), and luminal epithelial hypertrophy and RNA content (24 h) appeared to be enhanced by lead exposure, compared to lead-unexposed control animals. Eosinophilia in the endometrium (6 h), the proportion of uterine eosinophils in the endometrium (6 and 24 h), edema in superficial and deep endometria (6 h), luminal epithelial hypertrophy (6 h), and mitotic response (cell proliferation) in all uterine cell types were inhibited by lead exposure, whereas circular myometrial hypertrophy was not significantly modified. The effects of lead exposure on responses to estrogen found in this study showed some differences with those previously reported for acute or subacute exposure to lead. The results revealed an interaction with the different mechanisms of estrogen action in the uterus at various levels, suggesting that some uterine cell types are more sensitive to lead than others. The relevance of the results for lead-induced infertility is discussed in this article, and possible mechanisms of action are proposed.

Effects of arsenic, cadmium, chromium, and lead on gene expression regulated by a battery of 13 different promoters in recombinant HepG2 cells

Toxic metals occur naturally at low concentrations throughout the environment, but are found in higher concentrations at many of the hazardous waste sites on the EPA Superfund list. As part of the Agency for Toxic Substances and Disease Registry (ATSDR) mandate to evaluate the toxicity of metals and mixtures, we chose four of the high-priority metal pollutants from ATSDR's HAZDAT list, including arsenic, cadmium, chromium, and lead, to test in a commercially developed assay system, CAT-Tox(L) (Xenometrix). This assay employs a battery of recombinant HepG2 cell lines to test the transcriptional activation capacity of xenobiotics in any of 13 different signal transduction pathways. Our specific aims were to identify metal-responsive promoters and determine whether the pattern of gene expression changed with a mixture of metals. Humic acid was used in all assays as a carrier to help solubilize the metals and, in all cases, the cells were exposed to the humic acid-metal mixture for 48 h. Humic acid alone, at 50-100 microM, showed moderate activation of the XRE promoter, but little other notable activity. As(V), at doses of 50-250 microM, produced a complex profile of activity showing significant dose-dependent induction of the hMTIIA, GST Ya, HSP70, FOS, XRE, NFkappaBRE, GADD153, p53RE, and CRE promoters. Pb(II) showed dose-related induction of the GST Ya, XRE, hMTIIA, GRP78, and CYP IA1 promoters at doses in the range of 12-100 microM. Cd(II), at 1.25-15 microM, yielded significant dose-dependent induction of hMTIIA, XRE, CYP IA1, GST Ya, HSP70, NFkappaBRE, and FOS. Whereas Cr(III) yielded small, though significant inductions of the CRE, FOS, GADD153, and XRE promoters only at the highest dose (750 microM), Cr(VI) produced significant dose-related inductions of the p53RE, FOS, NFkappaBRE, XRE, GADD45, HSP70, and CRE promoters at much lower doses, in the range of 5-10 microM. Assays testing serial dilutions of a mixture comprising 7.5 microM Cd(II), 750 microM Cr(III), and 100 microM Pb(II) (the combination of metals most frequently found at National Priority List sites) showed significant dose-dependent induction of the hMTIIA promoter, but failed to show dose-related induction of any other promoter and showed no evidence of synergistic activation of gene expression by the metals in this mixture. Our results thus show metal activation of gene expression through several previously unreported signal transduction pathways, including As(V) induction of GST Ya, FOS, XRE, NFkBRE, GADD153, p53RE, and CRE; Pb(II) induction of GST Ya, XRE, Cyp IA1, and GADD153; Cd(II) induction of NFkBRE, Cyp IA1, XRE, and GST Ya; and Cr(VI) induction of p53RE, XRE, GADD45, HSP70, and CRE promoters, and thus suggest new insights into the biochemical mechanisms of toxicity and carcinogenicity of metals. It is also an important finding that no evidence of synergistic activity was detected with the mixture of Cd(II), Cr(III), and Pb(II) tested in these assays.

Lead: male-mediated effects on reproduction and development in the rat

The present study was designed to determine the effect of relatively low levels of lead acetate (25 and 250 ppm) exposure on fertility and offspring viability in male Sprague-Dawley rats. Protein synthesis in 2-cell embryos was monitored by [35S] methionine labeling and two-dimensional SDS gel electrophoresis. Fertility was reduced in males with blood lead levels in the range 27-60 microg/dL. Lead was found to affect initial genomic expression in embryos fathered by male rats with blood lead levels as low as 15-23 microg/dL. Dose-dependent increases were seen in an unidentified set of proteins with a relative molecular weight of approximately 70 kDa (Mr). These results indicate that male-mediated effects of lead may be observed in the 2-cell embryo. The alteration observed in embryonic gene expression with paternal lead exposure may be useful for studying the role of the paternal contribution to the activation of the embryonic genome and protein synthesis in the early embryo.

Roles of lead-binding proteins in mediating lead bioavailability

The intracellular bioavailability of lead (Pb) at low dosage levels in major target organs such as the kidney and brain appears to be largely determined by complexation with a group of low molecular weight proteins. These proteins are rich in aspartic and glutamic dicarboxyl amino acids. The proteins are chemically similar but not identical across all species examined to date and the brain protein appears to be different from that found in the kidney. These proteins possess dissociation constant values for Pb on the order of 10(-8) M and appear to normally bind zinc. In rats, these proteins attenuate the Pb inhibition of the heme pathway enzyme delta-aminolevulinic acid dehydratase by a mechanism involving both Pb chelation and zinc donation to this highly Pb-sensitive zinc-dependent enzyme. Other studies in rats have shown that the kidney protein facilitates the intranuclear movement of Pb in vitro followed by chromatin binding, suggesting that this protein may be involved in alterations of the pathognomonic Pb intranuclear inclusion bodies in renal gene expression associated with the mitogenic effects of Pb in the kidney.

Correlation between plasma 5-aminolevulinic acid concentrations and indicators of oxidative stress in lead-exposed workers

5-Aminolevulinic acid (ALA), a heme precursor accumulated in acute intermittent porphyria and lead poisoning, undergoes metal-catalyzed aerobic oxidation at physiological pH to yield reactive free radical species (O2−·&gt;, HO·, and ALA·). We analyzed the relationships between plasma ALA concentrations, blood concentrations of lead, protoporphyrin IX (PP-IX), superoxide dismutase (SOD), and methemoglobin (metHb), and urine chemiluminescence (CL) in samples collected from lead-exposed workers. All variables measured were substantially (P &lt;0.01) higher (2–8-fold) in the lead-exposed workers (n = 60). Plasma ALA concentrations were, on average, 6-fold higher in lead-exposed workers. We observed positive linear relationships between ALA and lead (r = 0.992), ALA and PP-IX (r = 0.891), ALA and metHb (r = 0.984), lead and SOD (r = 0.948), ALA and urine CL (r = 0.987), and lead and PP-IX (r = 0.993). These data are consistent with our free radical hypothesis for lead poisoning, where ALA distribution to and accumulation in several organs may trigger oxidative stress responses.

Approaches to define pathways of redox regulation of a eukaryotic gene: the heme oxygenase 1 example

Heme oxygenase 1 is a heme catabolic enzyme that is strongly induced in most eukaryotic cell types as a result of transcriptional activation by oxidants including UVA (320-380 nm) radiation. Three factors are clearly diagnostic for the characterization of this gene as redox regulated: (i) lowering the levels of cellular reduced glutathione using the drug buthionine (S, R)-sulfoximine enhances gene expression; (ii) iron depletion by various iron chelators suppresses activation; (iii) antioxidants suppress activation. Using chemical modulators to alter the levels of specific oxidizing intermediates, the nature of the effector species can be tentatively identified. A multiple approach is usually necessary because of the lack of specificity of most modulators. The involvement of a given species can be further implicated by generating the intermediate by an established protocol and confirming that it will activate the gene. As an example of such an approach, singlet oxygen has been implicated in the UVA radiation activation of HO-1 because the activation is enhanced by deuterium oxide (which enhances singlet oxygen lifetime) and suppressed by histidine (which scavenges the species). Singlet oxygen generated in a pure form using a photodynamic agent also strongly activates the gene. We describe a general approach designed to identify a role for singlet oxygen, superoxide anion, hydrogen peroxide, and/or hydroxyl radical in the activation of genes by oxidants.

Relationship of lead-induced proteins to stress response proteins in astroglial cells

Astroglial cells are resistant to cell death and morphologic damage following lead (Pb) exposure at concentrations which elicit detrimental effects in neurons. A possible explanation may be that astroglial cells respond to Pb by increasing the expression of specific proteins, such as heat-shock proteins (HSPs), which confer resistance to low levels of Pb. However, there has been relatively limited information regarding the ability of Pb to evoke the synthesis of HSPs. In the current study, pulse-labeling of cultured astroglial proteins with [3H]-leucine was used to evaluate the nature of Pb-induced changes in protein expression. The effect of Pb on newly synthesized proteins was compared to the response elicited by heat-shock and oxidative injury. Immunoblot analysis was utilized to examine alterations in levels of various stress proteins including HSP27, HSP70, HSP90, and heme oxygenase-1 (HO-1). Even though Pb induced the synthesis of proteins with estimated molecular weights of 23 kDa, 32 kDa, 70 kDa, and 90 kDa, the accumulation of HSPs other than HO-1 was not observed. Hyperthermia and treatment with Na arsenite both resulted in enhanced expression of HSP70 and HO-1. In addition, exposure to hydrogen peroxide (H2O2), cadmium (Cd), and lipopolysaccharide (LPS) stimulated a rise in HO-1 levels. Although cellular insult failed to elicit an increase in either HSP27 or HSP90, cultured astroglia expressed readily detectable levels of both these proteins. Furthermore, Pb exposure resulted in the development of crosstolerance to subsequent injury by treatment with either Cd or H2O2. The results of this study indicate that Pb triggers a less conventional stress response in astroglial cells, which may provide enhanced resistance to the toxic effects of Pb.

Chronic caloric restriction induces stress proteins in the hypothalamus of rats

The induction of stress proteins (sps) in the hypothalamus of female Fischer 344 rats in response to caloric restriction (CR) and to heat stress was investigated. Caloric restriction was found to elicit sps 27, 34, 70, and 90 in the hypothalamus of both young and old rats while none was found in the hypothalamus of ad libitum (AL) fed controls. Heat stress initiated heat shock proteins (hsps/sps) 27, 70, and 90 in the hypothalamus of the young (AL) fed animals, the same proteins evoked by feeding stress. The same sps were induced in the old (AL) rats although the expression showed substantial decline with age. This reduction was less marked, however, with the old CR rats. Stress protein 34, an infrequently reported protein, was related to feeding and was not induced by heat shock. Recent reports point to the important role sps play in the cellular reaction to stress, as well as their involvement in the higher functions. The findings reported here suggest that sps are involved in the regulatory mechanisms allowing CR animals to tolerate stress related to metabolic substrate deprivation.

Environment-immune interactions

The need for effective immune function for the maintenance of health has been clearly established in both agriculturally significant animal species and humans. Intensive agricultural practices present production species with numerous disease challenges during the rearing period. Environmental factors represent a ubiquitous, yet frequently manageable, category of immunomodulators that can influence immune performance and ultimately disease susceptibility or resistance. However, strategies for assessing overall immune potential have not been widely implemented for agricultural species. This is in contrast to the use of immune evaluation for human health considerations. Immune assessment relative to environmental-immune interactions can produce benefits in two areas. First, the efficiency of the production operation can be enhanced. Second, the welfare of the animals during the production cycle can be optimized. This paper presents an overview of environmental factors known to influence the immune function of poultry and the opportunities to manage environmental factors to benefit the health of the animals. In addition, the paper discusses the status of immunological assessment for humans and laboratory animals and proposes potential immune assessment panels that could serve as a tool to optimize the environmental management of poultry populations.

The homology of a novel polypeptide with stress protein characteristics in embryonic mice brain and in the hypothalamus of caloric restricted rats as determined by ultramicro western blotting

A novel protein (p34) was observed in polyacrylamide gel fluorographs of gestation day 13 embryonic mouse brain following retinoic acid dosing of dams. Another p34 polypeptide with identical gel migratory characteristics was seen in the hypothalamus of old caloric restricted rats after "food deprivation stress". Western blotting, employing an ultramicro trans-blot cell developed in our laboratory, detected identical immunochemical determinants between these proteins, verifying their homology. Peptide mapping and Western blotting further validated the uniqueness of p34 compared with other stress proteins including heme oxygenase.

Stress protein synthesis induced by cadmium-cysteine in rat kidney

Biomarkers are important tools which enable toxicologists to reliably predict and detect exposures to xenobiotics and resultant cell injury, ultimately improving risk assessments. Since the de novo synthesis of stress proteins can be detected early after exposure to some agents, analysis of toxicant-induced changes in gene expression, i.e. alterations in patterns of protein synthesis, may be useful to develop as biomarkers of exposure and toxicity. We are utilizing various xenobiotics as tools to study stress protein synthesis in target organs in order to evaluate the target tissue-specificity of this response. Previous data from this laboratory have demonstrated that induction of stress proteins in rat liver, but not kidney, after acute exposure to CdCl2 precedes hepatoxicity. Since kidney is a target tissue after chronic Cd exposure, it was of interest to examine stress protein synthesis in this tissue. However, dose-limiting hepatotoxicity precluded this evaluation. Cd complexed with molecules such as cysteine (cys) or metallothionein has been used in acute dosing regimens as a tool in order to study the nephrotoxicity of Cd. Therefore, this study was undertaken in order to evaluate Cd-induced stress protein synthesis in an important tissue known to be injured after chronic exposure, i.e. kidney. Specific objectives included comparing stress protein synthesis in rat kidney and liver after acute exposure to Cd-cys and CdCl2, determining the Cd threshold concentration for renal stress protein synthesis and assessing the relationship between stress protein synthesis and nephropathy. Male rats were exposed to equivalent doses of Cd as CdCl2 or Cd-cysteine (molar ratio Cd:cys = 1:15). Kidney Cd concentrations increased 5-fold after i.v. injection of Cd-cys compared to CdCl2, mimicking Cd distribution following chronic exposure. After exposure to Cd, tissue slices were incubated with 35S-methionine. Slices were subsequently homogenized and centrifuged, and the 16,000 g supernatants were subjected to SDS-polyacrylamide gel electrophoresis. Proteins which had incorporated 35S-methionine were detected by autoradiography. De novo synthesis of 70, 90 and 110 kDa proteins was enhanced in liver, but not in kidney, 4 h after injection of 2 mg Cd/kg as CdCl2. In contrast, dose-related increases in synthesis of these proteins were observed in kidney 4 h after injection of 1 and 2mg Cd/kg as Cd-cys, but not at lower dosages. In addition, synthesis of a 68 kDa kidney protein was inhibited at 2 mg Cd/kg as Cd-cys. The threshold for Cd-induced stress protein synthesis was shown to be between 4 and 8 micrograms Cd/g tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification and characterization of a heavy-metal-modulated nuclear protein from SV40-transformed cells

Sodium arsenite was found to stimulate an SV40-transformed BALB/c cell line (SVT2) to synthesize a 31-kDa protein within 2.5 h. This SVT2 protein was purified to homogeneity. It is a nuclear protein which appears to be associated with membranes because it is not extractable from nuclear membrane preparations by 2 M salt. It is highly hydrophobic, eluting from a reverse-phase HPLC column at a similar acetonitrile concentration as a previously described 31-kDa BALB/c-3T3 cell nuclear protein. However, digestion of highly purified BALB/c-3T3 and SVT2 cell proteins with V8 protease revealed nonidentical fragmentation patterns. Moreover, amino acid analysis of the two proteins was also dissimilar, indicating different primary structures. Thus, these two nuclear membrane associated proteins appear to be distinct species.

Induction of the human growth hormone gene placed under human hsp70 promoter control in mouse cells: a quantitative indicator of metal toxicity

An in vitro test method for general metal toxicity screening was designed, based on the cellular response to stress. The expression of a transfected human growth hormone gene sequence driven by the human heat-shock protein 70 promoter in NIH/3T3 cells was used as marker of noxious contact with metal compounds. Out of a series of 31 metals, 17 were competent for inducing this stress response system. According to the effective concentration and to the intensity of the response, three different clusters of positive compounds emerged and were ranked as strong, intermediate strength and weak inducers. These results correlated well with data from other in vivo and in vitro metal toxicity studies, including LD50 in mice. Apparently the positive/negative compounds also fitted well with data from genotoxicity and carcinogenesis studies on metal salts.

Lead inhibits secretion of osteonectin/SPARC without significantly altering collagen or Hsp47 production in osteoblast-like ROS 17/2.8 cells

In an effort to better understand the consequences of lead (Pb2+) on skeletal growth, the effects of Pb2+ were investigated using ROS 17/2.8 bone-like cells in vitro. These studies revealed that Pb2+ (4.5 x 10(-6) M -4.5 x 10(-7) M) has little or no effect on cell shape except when added immediately following seeding of the cells. However, proliferation of ROS cells was inhibited, in the absence of serum, at concentrations of 4.5 x 10(-6) M Pb2+. Protein production was generally increased, however, the major structural protein of bone, type I collagen, production was only slightly altered. Following treatment of ROS cells with Pb2+, intracellular levels of the calcium-binding protein osteonectin/SPARC were increased. Osteonectin/SPARC secretion into the media was delayed or inhibited. Coincident with retention of osteonectin/SPARC there was a decrease in the levels of osteonectin/SPARC mRNA as determined by Northern analysis. These studies suggest that processes associated with osteonectin/SPARC translation and secretion are sensitive to Pb2+.

Heat-shock protein synthesis in chicken macrophages: influence of in vivo and in vitro heat shock, lead acetate, and lipopolysaccharide

Synthesis of heat-shock proteins (HSP) in chicken macrophages, in response to thermal and nonthermal stressors, was determined. Cornell K-strain 6-wk-old White Leghorn females were injected with Sephadex and approximately 42 h later subjected to elevated temperatures in order to achieve a core body temperature (CBT) of 44 C. Peritoneal macrophages were isolated at 30 and 60 min after heat treatment. A parallel group of chickens, maintained at the normal CBT of 41 C, was used as controls and peritoneal macrophages were isolated after 60 min of treatment. For in vitro study of HSP response, cells of a chicken macrophage cell line (MQ-NCSU) were subjected to 45 C ambient temperature to produce heat shock (HS, thermal stress), lipopolysaccharide (LPS, 15 micrograms), and lead acetate (nonthermal stress) exposure for varying time periods. The HSP profiles of macrophages following various treatments were determined by one- and two-dimensional gel electrophoresis. The results showed that macrophages isolated from the 44 C CBT group synthesized HSP90, HSP70, HSP23, and a heat-inducible P32 protein. This HSP synthesis profile was similar to the HSP expression by MQ-NCSU cells exposed in vitro to 45 C conditions. Exposure to MQ-NCSU cells to lead acetate induced the same four proteins previously expressed by macrophages after in vivo or in vitro heat treatment. Two-dimensional analysis of lysates from cells treated with LPS, HS, or LPS plus HS treatments revealed a doublet protein molecule (70a and 70b) with identical molecular mass of 70 kDa. However, the pI value (isoelectric point) of 70b was higher (5.1) than that of 70a, which, along with HSP90 and HSP23, focused more toward the acidic side with a pI value of less than 4.6. The present study is the first to report pI profiles of chicken macrophage HSP. The in vitro and in vivo studies suggest that chicken macrophages respond to thermal and nonthermal stressors by producing similar kinds of "stress proteins".

Relationship between stress protein induction in rat kidney by mercuric chloride and nephrotoxicity

Adverse environmental stimuli increase the synthesis of a class of proteins referred to as stress proteins. The effect of mercuric chloride, a model nephrotoxin, on protein synthesis in male rat kidney has been evaluated. Renal slices from exposed rats were incubated with [35S]methionine for 1 hr and subjected to SDS-PAGE, after which 35S-labeled proteins were detected by autoradiography. Enhanced de novo synthesis of 70- and 90-kDa relative molecular mass (M(r)) proteins were detected 2 hr after exposure to 1 mg Hg/kg, with maximum activity occurring at 4-8 hr. By 16 hr postinjection, synthesis of these two proteins had decreased. Dose-related increases in synthesis of these proteins, and of a 110-kDa protein, were observed 4 hr after i.v. injection of 0.25, 0.5, and 1.0 mg Hg/kg, with concomitant inhibition of synthesis of proteins of M(r) 38 and 68 kDa. At a dose of 1 mg/kg, kidney proximal tubules exhibited progressive degenerative changes from 4 to 24 hr. A functional deficit, decreased uptake of [para-3H]aminohippurate into renal slices, was not observed until 16 hr after i.v. injection of 1 mg/kg. No significant histopathologic changes were observed in kidneys 4 hr after treatment with 0.25 or 0.5 mg Hg/kg, iv. No changes in liver protein synthesis were apparent until 16-24 hr, where an increase in the 70- and 90-kDa proteins was observed. A concomitant increase in plasma sorbitol dehydrogenase activity occurred at 16-24 hr; however, there was no histopathological evidence of liver injury. The 72-kDa inducible member of the 70-kDa stress protein family and the 88-kDa member of the 90-kDa protein family were detected by immunoblotting techniques using monoclonal antibodies. The data demonstrate that Hg induces alterations in the expression of renal gene products in vivo as evidenced by enhanced stress protein synthesis and inhibition of synthesis of constitutive proteins. These changes in renal protein synthesis preceded overt renal injury, occurring in the early stages of nephropathy. Altered patterns of stress protein synthesis appeared to be target organ specific. The data suggest that altered protein synthesis patterns may serve as biomarkers of renal injury.

A membrane-bound metallo-endopeptidase from rat kidney hydrolyzing parathyroid hormone. Purification and characterization

A metallo-endopeptidase, which appears to be an integral membrane protein of rat kidney, was purified to homogeneity by a series of standard chromatographic procedures. This enzyme significantly hydrolyzed human parathyroid hormone [hPTH(1-84)] and a synthetic substrate Suc-Leu-Leu-Val-Tyr-Mec (Suc = succinyl, Mec = 4-methyl-coumarinyl-7-amide). The purified enzyme had apparent molecular masses of 250 kDa on gel filtration, and 88 kDa and 245 kDa on sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing and non-reducing conditions, respectively. Its pH optimum for activity was 8.0-8.5 and its isoelectric point was pH 4.9. Its activity was inhibited by EDTA, EGTA and o-phenanthroline, but not by phosphoramidon. The metal-depleted enzyme was reactivated by the addition of metal ions. The enzyme was also inhibited by chymostatin and eglin C, and by thiol compounds. Of the synthetic substrates examined, the enzyme hydrolyzed only Suc-Leu-Leu-Val-Tyr-Mec, one of the synthetic substrates for alpha-chymotrypsin. It did not hydrolyze synthetic substrates with less than four amino acid residues with tyrosine in the P1 position. The enzyme hydrolyzed hPTH and reduced hen egg lysozyme but did not hydrolyze azocasein or [3H]methyl-casein. NH2-terminal amino acid sequence analyses of the degradation products of hPTH(1-84) and reduced hen egg lysozyme by the purified enzyme revealed that the enzyme preferentially cleaved these peptides at peptide bonds flanked by hydrophilic amino acid residues. Amino acid analyses showed that the main degradation products of PTH were hPTH(17-29), hPTH(30-38) and hPTH(74-84). The ability of the enzyme to hydrolyze peptide bonds flanked by hydrophilic amino acid residues and its inability to degrade azocasein distinguish it from several other kidney endopeptidases reported, such as endopeptidase 24.11 and meprin.

Are free radicals involved in lead poisoning?

1. The enolamine form of 5-aminolaevulinic acid (ALA), a haem precursor that accumulates in lead poisoning and in acute intermittent porphyria (AIP), undergoes fast autoxidation at slightly alkaline pH with concomitant generation of reactive oxygen species. 2. The transmembrane potential, Ca2+ ion fluxes and state-4 respiratory rate, of isolated rat liver mitochondria are severely affected by mM addition of ALA; the toxic role of ALA-produced oxygen radicals was demonstrated by use of appropriate scavengers. 3. Induction of superoxide dismutase biosynthesis in lead-exposed workers, in AIP carriers and in ALA-treated rats, is viewed as a protective response against oxygen radical toxicity. 4. 5-Aminolaevulinic acid-generated oxygen radicals, together with Pb-stimulated Fe-dependent lipid peroxidation, might be involved in the aetiology of the neuropsychiatric manifestations of both plumbism and acute intermittent porphyria.

Induction of a 31,000-dalton stress protein by prostaglandins D2 and J2 in porcine aortic endothelial cells

Prostaglandin (PG) D2 and PGJ2 stimulated porcine aortic endothelial cells to synthesize a 31,000-dalton protein (termed p31) in a time- and concentration-dependent manner. The induction of p31 synthesis was specific for PGD2, PGJ2 and PGA1 among the various PGs tested. p31 was also synthesized in response to the thiol-reactive agent diethylmaleate and heavy metal sodium arsenite but not to high temperature treatment, platelet-derived growth factor, and 12-O-tetradecanoylphorbol 13-acetate. Using two-dimensional polyacrylamide gel electrophoresis, p31 induced by PGJ2 had an isoelectric point of 5.4, which overlapped exactly with that induced by by arsenite. These results taken together indicate that p31 represents one of the stress proteins whose expression is regulated primarily by thio-active compounds but not by hyperthermia. Furthermore, it was induced by PGD2 and PGJ2 in rat capillary endothelial cells, rat skin fibroblasts, and rat hepatocytes. The data obtained from this study suggest that p31 induced by PGD2 and PGJ2 may play a role in the metabolic regulation of many mammalian cells.

A procedure for purifying low-abundance protein components from the brain cytoskeleton-nuclear matrix fraction

We describe a preparative procedure for low-abundance proteins of the cytoskeleton-nuclear matrix fraction from frozen bovine brain. Strigent centrifugation and washing conditions in the preparation of the cytoskeleton-nuclear matrix fraction are avoided to minimize loss of nuclear material. A recently described horizontal isoelectric focusing column, which tolerates appreciable precipitation, is used. In concert with selection of urea concentration and temperature, this isoelectric focusing apparatus provides a new approach to the fractionation of this complex, relatively insoluble mixture of proteins and other components. In addition, a heated, sodium dodecyl sulfate-sizing column has been utilized in order to eliminate interactions between the desired low abundance proteins and more abundant contaminating proteins. Together these procedures purify a specific low-abundance protein sufficiently to be detected by Coomassie blue staining in two-dimensional gels. The methods are robust and can be applied to multiple, relatively large brain samples (150 g of crude grey matter per batch); thus they should facilitate partial peptide sequencing for brain proteins of this operational class.

Localization of 90-kDa heat shock protein in the kidney

Antibody against 90-kDa heat shock protein (HSP 90) was produced in rabbits. The obtained antibody was highly specific to the antigen. Using the antibody, the intrarenal distribution of HSP 90 was studied in frozen sections of normal rat kidneys by fluorescent and enzymic immunohistochemistry. HSP 90 was predominantly present in the region from the distal convoluted tubule to the medullary collecting duct at a high intensity, and in glomerular podocytes and Bowman epithelial cells at a much lower intensity. Other segments of the nephron were stained little, even at a lower dilution of the antibody. Blood vessels and interstitial tissues were not stained. HSP 90 was localized in the cytoplasm and not in the nucleus. Moreover, immunohistochemical staining of HSP 90 showed greater intensity at the luminal side of the cells. These observations suggest that HSP 90 might play important roles in the kidney.

Differential expression of heat shock proteins in Drosophila embryonic cells following metal ion exposure

Drosophila embryonic cells were exposed to a number of metal ions that have been previously reported to act as teratogens in mammalian systems, including some known to induce heat shock (stress) proteins in a variety of model systems. This study examined the effects of these ions both on differentiation of muscles and neurons and on the induction of heat shock proteins. Metals such as arsenate, cadmium, and mercury all inhibited neuron and/or muscle differentiation in Drosophila embryonic cultures, while they also induced the entire set of heat shock proteins. Two metal ions, nickel and zinc, were shown to induce only the 22- and 23-K proteins, a pattern similar to that seen in "classical" teratogens reported previously. None of the metals tested induced only the 26- and 27-K proteins. These results suggest that there exist different regulatory mechanisms responsible for the heat shock response.

Parathyroid hormone degradation by chymotrypsin-like endopeptidase in the clonal osteogenic UMR-106 cell

Parathyroid hormone (PTH) -degrading activity was studied using osteoblast-like UMR-106 cells. PTH-degrading activity was assessed by the amount of PTH fragments produced in the medium after exposure of intact human PTH-(1-84) to UMR-106 cells. PTH immunoreactivity recovered in trichloroacetic acid-soluble products of the medium and in fractions eluted from reverse-phase high-performance liquid chromatography (HPLC) was measured by radioimmunoassay using an antibody specific for the mid-region and C-terminus of PTH. In this study, intact UMR-106 cells but not extracellular enzymes cleaved human PTH(1-84) into fragments which were released into the medium (in a time- and temperature-dependent fashion). HPLC analysis of the PTH fragments depicted three immunoreactive peaks (peaks 1, 2 and 3) besides intact PTH, indicating a limited PTH-hydrolyzing activity of the cells. Furthermore, a 1000-fold molar excess of either hPTH-(3-34) or [Nle8,Nle18,Tyr34]hPTH-(3-34)amide inhibited PTH-degrading activity by 63% and 80% of control, respectively, whereas neither calcitonin, vasopressin nor growth hormone suppressed it. Additionally, HPLC analysis of the samples treated with [Nle8,Nle18,Tyr34]hPTH-(3-34)amide showed a reduction of the three peaks, suggesting an involvement of PTH receptor in the production of PTH fragments. This PTH-degrading activity was strongly inhibited by phenylmethylsulfonyl fluoride and chymostatin, but not by soybean trypsin inhibitor, elastatinal or inhibitors of cysteine, aspartic or metalloproteinases, indicating that it is due to a seryl chymotrypsin-like endopeptidase. Chymotrypsin-like activity seems to be solely responsible for PTH-degrading activity in intact UMR-106 cells, since all three PTH fragments were predominantly suppressed in the presence of chymostatin. Further analysis of chymotrypsin-digested products of hPTH-(1-84) eluted from HPLC exhibited five fragments detected by ultraviolet absorbance at 210 nm, three of which were measurable by PTH radioimmunoassay, each corresponding to the three PTH fragments produced by UMR-106 cells. To explore the cleavage sites of PTH further, amino acid analysis of chymotrypsin-cleaved products was performed. The results strongly support the view that the chymotrypsin-like enzyme in UMR-106 cells cleaved the hormone between residues 23-24 and 34-35, to produce, at least, hPTH-(24-84) and -(35-84). Our present study indicates that a chymotrypsin-like endopeptidase is solely responsible for limited hydrolysis of PTH by intact UMR-106 cells.

Glutathione conjugation and induction of a 32,000 dalton stress protein

Chinese hamster ovary cells were exposed to various concentrations of diethylmaleate in order to produce various levels of intracellular glutathione (GSH) depletion. Exposure to a 20 microM concentration or more of diethylmaleate depleted the intracellular glutathione concentration by 80% or more and resulted in enhanced synthesis of two 32 kDa proteins which exhibited a pI of about 6.5. Exposure of cells to 50 microM buthionine sulfoximine for 24 hr reduced GSH levels by 95% but did not enhance the synthesis of this protein. Addition of diethylmaleate to buthionine sulfoximine-treated cells resulted in enhanced synthesis of the 32 kDa protein however. Exposure to 0.4 mM diamide triggered the synthesis of several heat shock proteins but did not induce the synthesis of the 32 kDa protein. These results indicated that enhanced synthesis of the 32 kDa protein occurred only after glutathione depletion exceeded 80% and required formation of a glutathione conjugate.

Induction of mammalian stress proteins by a triethylphosphine gold compound used in the therapy of rheumatoid arthritis

In vitro exposure of cultured human, murine and rat cells to pharmacologic concentrations (10(-8) to 10(-6) M) of auranofin, 2,3,4,6,-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S- triethylphosphine gold(I) (Ridaura), a gold containing compound approved for the treatment of rheumatoid arthritis, results in the induction of several stress proteins. The enhanced synthesis of two polypeptides, p32 and p34, was particularly prominent. A similar response was observed in freshly collected human monocytes challenged with auranofin. In addition, oral administration of auranofin to rats induced enhanced synthesis of a 32-kDa protein in peritoneal exudate cells analyzed ex vivo at various times following drug treatment. These data suggest that increased synthesis of p32 and p34 might participate in mediating certain aspects of auranofin pharmacology.