Biphasic Dose-response Relationship Research Articles

Antidepressant-like effect of Valeriana glechomifolia Meyer (Valerianaceae) in mice

The antidepressant-like effect of a supercritical CO2 (SCCO2) Valeriana glechomifolia extract enriched in valepotriates was investigated in a mice tail suspension test (TST) and forced swimming test (FST). The SCCO2 extract decreased mice immobility in the FST (0.5-20 mg/kg p.o.) and elicited a biphasic dose-response relationship in the TST (1-20 mg/kg p.o.) with no alterations in locomotor activity and motor coordination (assessed in the open-field and rota-rod tests, respectively). The anti-immobility effect of the SCCO2 extract (5 mg/kg, p.o.) was prevented by mice pre-treatment with yohimbine (1 mg/kg, i.p., an α2 adrenoceptor antagonist), SCH 23390 (15 μg/kg, s.c., D1 dopamine receptor antagonist) and sulpiride (50 mg/kg, i.p., D2 dopamine receptor antagonist). However, mice pre-treatments with prazosin (1 mg/kg, i.p., α1 adrenoceptor antagonist) and p-chlorophenilalanine methyl ester (4×100 mg/kg/day, i.p., a serotonin synthesis inhibitor) were not able to block the anti-immobility effect of the SCCO2 extract. Administration (p.o.) of the SCCO2 extract (0.25 mg/kg) and imipramine (10 mg/kg), desipramine (5 mg/kg) and bupropion (3 mg/kg) at sub-effective doses significantly reduced mice immobility time in the FST. These data provide the first evidence of the antidepressant-like activity of V. glechomifolia valepotriates, which is due to an interaction with dopaminergic and noradrenergic neurotransmission.

Redefining Low Lead Levels

Vol. 119, No. 5 PerspectivesOpen AccessRedefining Low Lead Levels Ivo Iavicoli Edward J. Calabrese Ivo Iavicoli Search for more papers by this author and Edward J. Calabrese Search for more papers by this author Published:1 May 2011https://doi.org/10.1289/ehp.1103489Cited by:1AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit In the January 2011 issue of EHP, Giddabasappa et al. (2011) reported that gestational lead exposure (GLE) of C57BL/6 mice produced selective nonmonotonic increases in the numbers of rods and cone bipolar cells (BCs) in the adult retina. Interestingly, this increase was characterized by an inverted U-shaped dose–response curve. Moreover, findings of this study showed that GLE increases and prolongs proliferation of retinal progenitor cells (RPCs) without decreasing apoptosis. Consequently, this phenomenon produced an adult retina with normal lamination and a selectively increased number of rods and BCs. These results should be considered to define a more adequate risk assessment at low levels of lead exposure. In fact, other published articles have indicated that lead induced a biphasic dose–response relationship (Calabrese and Baldwin 2003).In experiments in Swiss mice using low-level lead exposures similar to and lower than those used by Giddabasappa et al. (2011), we observed an increase in the number of red blood cells, in female gestational parameters, and in Th1 cytokine levels (Iavicoli et al. 2003, 2004, 2006a, 2006b). For this reason, it would be interesting if Giddabasappa et al. could verify this increase in the number of neurons in the rod-signaling pathway at even lower blood lead levels (< 10 μg/dL). The findings of our studies were also implicated over several generations.In any case, we agree with Giddabasappa et al. (2011) that their findings, as ours, raise complex issue for toxicologists, pediatricians, public health regulators, and risk assessors who need to incorporate the occurrence of such U-shaped dose responses in the hazard and risk assessment process. In this context, these findings could be explained by the hormesis phenomenon, which is a dose–response relationship characterized by low-dose stimulation and high-dose inhibition (Calabrese 2008, 2009).ReferencesCalabrese EJ. 2008. Hormesis: why it is important to toxicology and toxicologists. Environ Toxicol Chem 27:1451-147418275256. Crossref, Medline, Google ScholarCalabrese EJ. 2009. Getting the dose-response wrong: why hormesis became marginalized and the threshold model accepted. Arch Toxicol 83:227-24719234688. Crossref, Medline, Google ScholarCalabrese EJ, Baldwin LA. 2003. Inorganics and hormesis. Crit Rev Toxicol 33:215-30412809427. Crossref, Medline, Google ScholarGiddabasappa A, Hamilton WR, Chaney S, Xiao W, Johnson JE, Mukherjee Set al.. 2011. Low-level gestational lead exposure increases retinal progenitor cell proliferation and rod photoreceptor and bipolar cell neurogenesis in mice. Environ Health Perspect 119:71-7720840909. Link, Google ScholarIavicoli I, Carelli G, Stanek EJ, Castellino N, Calabrese EJ. 2003. Effects of low doses of dietary lead on red blood cell production in male and female mice. Toxicol Lett 137:193-19912523962. Crossref, Medline, Google ScholarIavicoli I, Carelli G, Stanek EJ, Castellino N, Calabrese EJ. 2006a. Below background levels of blood lead impact cytokine levels in male and female mice. Toxicol Appl Pharmacol 210:94-9916289177. Crossref, Medline, Google ScholarIavicoli I, Carelli G, Stanek EJ, Castellino N, Calabrese EJ. 2004. Effects of low doses of dietary lead on puberty onset in female mice. Reprod Toxicol 19:35-4115336710. Crossref, Medline, Google ScholarIavicoli I, Carelli G, Stanek EJ, Castellino N, Li Z, Calabrese EJ. 2006b. Low doses of dietary lead are associated with a profound reduction in the time to the onset of puberty in female mice. Reprod Toxicol 22:586-59016713174. Crossref, Medline, Google ScholarFiguresReferencesRelatedDetailsCited By Corsetti G, Romano C, Stacchiotti A, Pasini E and Dioguardi F (2016) Endoplasmic Reticulum Stress and Apoptosis Triggered by Sub-Chronic Lead Exposure in Mice Spleen: a Histopathological Study, Biological Trace Element Research, 10.1007/s12011-016-0912-z, 178:1, (86-97), Online publication date: 1-Jul-2017. Vol. 119, No. 5 May 2011Metrics About Article Metrics Publication History Originally published1 May 2011Published in print1 May 2011 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. 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Early postnatal blood manganese levels and children's neurodevelopment.

Recent evidence suggests that low-level environmental exposure to manganese adversely affects child growth and neurodevelopment. Previous studies have addressed the effects of prenatal exposure, but little is known about developmental effects of early postnatal exposure. We studied 448 children born in Mexico City from 1997 through 2000, using a longitudinal study to investigate neurotoxic effects of early-life manganese exposure. Archived blood samples, collected from children at 12 and 24 months of age, were analyzed for manganese levels using inductively coupled plasma mass spectrometry. Mental and psychomotor development were scored using Bayley Scales of Infant Development at 6-month intervals between 12 and 36 months of age. At 12 months of age, the mean (SD) blood manganese level was 24.3 (4.5)microg/L and the median was 23.7 microg/L; at 24 months, these values were 21.1 (6.2) microg/L and 20.3 microg/L, respectively. Twelve- and 24-month manganese concentrations were correlated (Spearman correlation = 0.55) and levels declined over time ([beta] = -5.7 [95% CI = -6.2 to -5.1]). We observed an inverted U-shaped association between 12-month blood manganese and concurrent mental development scores (compared with the middle 3 manganese quintiles, for the lowest manganese quintile, [beta] = -3.3 [-6.0 to -0.7] and for the highest manganese quintile, [beta] = -2.8 [-5.5 to -0.2]). This 12-month manganese effect was apparent but diminished with mental development scores at later ages. The 24-month manganese levels were not associated with neurodevelopment. These results suggest a possible biphasic dose-response relationship between early-life manganese exposure at lower exposure levels and infant neurodevelopment. The data are consistent with manganese as both an essential nutrient and a toxicant.

The Hormetic Role of Dietary Antioxidants in Free Radical-Related Diseases

Regular consumption of cruciferous vegetables or spices is associated with a reduced incidence of cancer and reduction of markers for neurodegenerative damage. Furthermore, greater health benefit may be obtained from raw as opposed to cooked vegetables. Nutritional interventions, by increasing dietary intake of fruits and vegetables, can retard and even reverse age-related declines in brain function and cognitive performance. The mechanisms through which dietary supplementation with antioxidants may be useful to prevent free radical-related diseases is related to their ability to counteract toxic production of both reactive oxygen and nitrogen species, along with the up-regulation of vitagenes, such as members of the heat shock protein (Hsp) family heme oxygenase-1 and Hsp70. The most prominent dietary factor that affects the risk of many different chronic diseases is energy intake - excessive calorie intake increases the risk. Reducing energy intake by controlled caloric restriction or intermittent fasting increases lifespan and protects various tissues against diseases, in part, by hormetic mechanisms that increase cellular stress resistance. This biphasic dose-response relationship, referred to here as hormesis, display low-dose stimulation and a high-dose inhibition. Despite the current interest in hormesis by the toxicology community, quantitatively similar U-shaped dose responses have long been recognized by researchers to be involved with factors affecting memory, learning, and performance, as well as nutritional antioxidants and oxidative stress-mediated degenerative reactions. Dietary polyphenols present strong cytoprotective effects, however under uncontrolled nutritional supplementation gene induction effects and the interaction with detoxification responses can have negative consequences through the generation of more reactive and harmful intermediates.

Insecticide‐induced hormesis in an insecticide‐resistant strain of the maize weevil, Sitophilus zeamais

AbstractSublethal responses to insecticides are frequently neglected in studies of insecticide resistance, although stimulatory effects associated with low doses of compounds toxic at higher doses, such as insecticides, have been recognized as a general toxicological phenomenon. Evidence for this biphasic dose–response relationship, or hormesis, was recognized as one of the potential causes underlying pest resurgence and secondary pest outbreaks. Hormesis has also potentially important implications for managing insecticide‐resistant populations of insect‐pest species, but evidence of its occurrence in such context is lacking and fitness parameters are seldom considered in these studies. Here, we reported the stimulatory effect of sublethal doses of the pyrethroid insecticide deltamethrin sprayed on maize grains infested with a pyrethroid‐resistant strain of the maize weevil (Sitophilus zeamais) (Coleoptera: Curculionidae). The parameters estimated from the fertility tables of resistant insects exposed to deltamethrin indicated a peak in the net reproductive rate at 0.05 ppm consequently leading to a peak in the intrinsic rate of population growth at this dose. The phenomenon is consistent with insecticide‐induced hormesis and its potential management implications are discussed.

Structure−Activity Relationship of Cyanine Tau Aggregation Inhibitors

A structure-activity relationship for symmetrical cyanine inhibitors of human tau aggregation was elaborated using a filter trap assay. Antagonist activity depended on cyanine heterocycle, polymethine bridge length, and the nature of meso- and N-substituents. One potent member of the series, 3,3'-diethyl-9-methylthiacarbocyanine iodide (compound 11), retained submicromolar potency and had calculated physical properties consistent with blood-brain barrier and cell membrane penetration. Exposure of organotypic slices prepared from JNPL3 transgenic mice (which express human tau harboring the aggregation prone P301L tauopathy mutation) to compound 11 for one week revealed a biphasic dose response relationship. Low nanomolar concentrations decreased insoluble tau aggregates to half those observed in slices treated with vehicle alone. In contrast, high concentrations (> or =300 nM) augmented tau aggregation and produced abnormalities in tissue tubulin levels. These data suggest that certain symmetrical carbocyanine dyes can modulate tau aggregation in the slice biological model at concentrations well below those associated with toxicity.

The role of MAPK in the biphasic dose-response phenomenon induced by cadmium and mercury in HEK293 cells

Some studies show that Cd 2+ and Hg 2+ may induce cell proliferation and apoptosis via biphasic dose-response relationship in human cells. However, mechanisms underlying this phenomenon are still in puzzle. In this study, we aim at detecting the biphasic effects of Cd 2+ and Hg 2+ on proliferation and apoptosis of human embryonic kidney 293 (HEK293) cells, analyzing the change of the mitogen-activated protein kinase (MAPK) pathways, and discussing the relationship between them. The results demonstrate that Cd 2+ and Hg 2+ can stimulate cell proliferation at lower concentrations (0.05 and 0.5 μM) but inhibit it at higher concentrations (50 and 500 μM). Apoptosis increases at higher concentrations (50 and 500 μM) of Cd 2+ and Hg 2+. While 0.5 μM Cd 2+ and Hg 2+ decrease the JNK phosphorylation, 50 μM Cd 2+ and Hg 2+ increase the JNK and P38 phosphorylation. When HEK293 cells are treated with 20 μM JNK inhibitor or 100 μM ERK1/2 inhibitor, the cell proliferation do not increase significantly at low concentrations (0.05 and 0.5 μM), but still decrease at high concentrations (50 and 500 μM). When HEK293 cells are treated with 20 μM P38 inhibitor, the tendency of cell proliferation is not affected. Data in our study suggests that activation of MAPK pathway may be involved in the biphasic effect induced by Cd 2+ and Hg 2+.

Requirement for protein kinase R in interleukin-1α-stimulated effects in cartilage

Interleukin-1 (IL-1) has pleiotropic effects in cartilage. The interferon-induced, double stranded RNA-activated protein kinase PKR that phosphorylates eukaryotic initiation factor 2 (eIF2) α has been implicated in cytokine effects in chondrocytes. A compound was recently identified that potently suppresses PKR autophosphorylation (IC50 approximately 200 ηM) and partially restores PKR-inhibited translation in a cell-free system with significant effect in the nanomolar range. The objectives of this study were to exploit this potent PKR inhibitor to assess whether PKR kinase activity is required for catabolic and proinflammatory effects of IL-1α in cartilage and to determine whether IL-1α causes an increase in eIF2α phosphorylation that is antagonized by the PKR inhibitor. Cartilage explants were incubated with the PKR inhibitor and IL-1α. Culture media were assessed for sulfated glycosaminoglycan as an indicator of proteoglycan degradation and for prostaglandin E 2. Cartilage extracts were analyzed by Western blot for cyclooxygenase-2 and phosphorylated signaling molecules. Nanomolar concentrations of the PKR inhibitor suppressed proteoglycan degradation and cyclooxygenase-2 accumulation in IL-1α-activated cartilage. The PKR inhibitor stimulated or inhibited PGE 2 production with a biphasic dose response relationship. IL-1α increased the phosphorylation of both PKR and eIF2α, and nanomolar concentrations of PKR inhibitor suppressed the IL-1α-induced changes in phosphorylation. The results strongly support PKR involvement in pathways activated by IL-1α in chondrocytes.

Converging concepts: Adaptive response, preconditioning, and the Yerkes–Dodson Law are manifestations of hormesis

The adaptive response in toxicology and environmental mutagenesis, preconditioning in biomedicine and the Yerkes–Dodson Law in psychology have dominating research themes with widespread and significant scientific and societal implications. This paper suggests that these apparently independent biological dose–response phenomena are manifestations of the common and more general biphasic dose–response relationship concept called hormesis. These three types of dose–response, as well as the hormesis concept, may represent the same general type of adaptation, which were discovered independently in different biological disciplines, amongst which there has been little communication. This intellectual isolation, due principally to progressively greater disciplinary specialization, resulted in the evolution of different terminologies for dose–response phenomena with strikingly similar quantitative features. This lack of recognition of converging dose–response concepts across disciplines has important implications since it limits the recognition of a common and basic biological concept while minimizing collaborations by investigators in related areas. The paper concludes that the broadly recognized biological adaptive responses, as described by the concepts of adaptive response, preconditioning and the Yerkes–Dodson Law, are special cases of the more general hormesis dose–response concept.

Biphasic effect of arsenite on cell proliferation and apoptosis is associated with the activation of JNK and ERK1/2 in human embryo lung fibroblast cells

Biphasic dose-response relationship induced by environmental agents is often characterized with the effect of low-dose stimulation and high-dose inhibition. Some studies showed that arsenite may induce cell proliferation and apoptosis via biphasic dose-response relationship in human cells; however, mechanisms underlying this phenomenon are not well understood. In the present study, we aimed at investigating the relationship between biphasic effect of arsenite on cell proliferation and apoptosis and activation of JNK and ERK1/2 in human embryo lung fibroblast (HELF) cells. Our results demonstrated that cell proliferation may be stimulated at lower concentrations (0.1 and 0.5 microM) arsenite but inhibited at higher concentrations (5 and 10 microM). When cell apoptosis was used as the endpoint, the concentration-response curves were changed to U-shapes. During stimulation phospho-JNK levels were significantly increased at 3, 6, and 12 h after 0.1 or 0.5 microM arsenite exposure. Phospho-ERK1/2 levels were increased with different concentrations (0.1-10 microM) of arsenite at 6, 12, and 24 h. Blocking of JNK pathway with 20 microM SP600125 or ERK1/2 by 100 microM PD98059 significantly inhibited biphasic effect of arsenite in cells. Data in the present study suggest that activation of JNK and ERK1/2 may be involved in biphasic effect of arsenite when measuring cell proliferation and apoptosis in HELF cells. JNK activation seems to play a more critical role than ERK1/2 activation in the biphasic process.

Biphasic effect of apomorphine on rat nociception and effect of dopamine D 2 receptor antagonists

Studies on the effect of dopaminergic agonists in behavioral measures of nociception have gathered numerous but rather conflicting data. We studied the effects of the D 1/D 2 receptor agonist apomorphine, as well as the modulatory effects of ( S)-(−)-sulpiride (selective D 2 receptor antagonist) and domperidone (peripheral D 2 receptor antagonist), on thermal, mechanical and chemical nociception on rats. Apomorphine induced a biphasic dose–response relationship, low doses producing hyperalgesia and high doses inducing antinociception. Tonic (chemical) pain was more sensitive to apomorphine than phasic (thermal and mechanical thresholds) pain. ( S)-(−)-sulpiride, but not domperidone, fully antagonized the antinociceptive effect of apomorphine in all three measures of nociception, pointing to a participation of D 2 dopaminergic receptors for the antinociceptive action of apomorphine. Although spinal sites for dopaminergic ligands mechanistically may account for the effects observed, involvement of dopaminergic receptors of the forebrain could probably explain better the antinociceptive effects of apomorphine, especially in chemical tonic pain.

Dose-response relationships in human experimental exposure to solvents.

Previous studies carried out in the field of experimental toxicology have shown evidence of biphasic dose-response relationships for different experimental models, endpoints and chemicals tested. As these studies excluded humans as the experimental model, we have examined the literature of the last three decades in order to verify data concerning human experimental exposure with the aim of highlighting possible biphasic dose-response relationships. The substances used for experimental exposures included hydrocarbons, esters, alcohols, ketones, ethers, glycoethers, halogenated hydrocarbons, and carbon sulphide; the absorption route was inhalation. We did not detect any biphasic dose-response relationship and, in the studies reviewed, our examination revealed major methodological limitations that prevented us making a more detailed examination of experimental data. We concluded that the experimental data available did not allow us to support evidence of biphasic dose-response relationships in human experimental exposure to the above-mentioned chemical substances.

Hormesis in Carcinogenicity of Non-genotoxic Carcinogens

Recently the idea of hormesis, a biphasic dose-response relationship in which a chemical exerts opposite effects dependent on the dose, has attracted interest in the field of carcinogenesis. With non-genotoxic agents there is considerable experimental evidence in support of hormesis and the present review highlights current knowledge of dose- response effects. In particular, several in vivo studies have provided support for the idea that non-genotoxic carcinogens may inhibit hepatocarcinogenesis at low doses. Here, we survey the examples and discuss possible mechanisms of hormesis with cytochrome P450 inducers, such as phenobarbital, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), α-benzene hexachloride (α-BHC), and other non-genotoxins. Epigenetic processes differentially can be affected by agents that impinge on oxidative stress, DNA repair, cell proliferation, apoptosis, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors, cause aberrant DNA methylation at the genomic level and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. Via multiple epigenetic lesions, non- genotoxic carcinogens can elicit a variety of changes contributing to cellular carcinogenesis. (J Toxicol Pathol 2006; 19: 111-122)

Hormesis and dose–response-mediated mechanisms in carcinogenesis: evidence for a threshold in carcinogenicity of non-genotoxic carcinogens

Recently the idea of hormesis, a biphasic dose-response relationship in which a chemical exerts opposite effects dependent on the dose, has attracted interest in the field of carcinogenesis. With non-genotoxic agents there is considerable experimental evidence in support of hormesis and the present review highlights current knowledge of dose-response effects. In particular, several in vivo studies have provided support for the idea that non-genotoxic carcinogens may inhibit hepatocarcinogenesis at low doses. Here, we survey the examples and discuss possible mechanisms of hormesis using phenobarbital, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), alpha-benzene hexachloride (alpha-BHC) and other non-genotoxins. Furthermore, the effects of low and high doses of non-genotoxic and genotoxic compounds on carcinogenesis are compared, with especial attention to differences in mechanisms of action in animals and possible application of the dose-response concept to cancer risk assessment in humans. Epigenetic processes differentially can be affected by agents that impinge on oxidative stress, DNA repair, cell proliferation, apoptosis, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors, cause aberrant DNA methylation at the genomic level and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. Genotoxic agents, in contrast, cause genetic change by directly attacking DNA and inducing mutations, in addition to temporarily modulating the gene activity. Carcinogens can elicit a variety of changes via multiple genetic and epigenetic lesions, contributing to cellular carcinogenesis.

Functional Central Nicotinic Acetylcholine Receptor Antagonism by Systemic Administration of Tinuvin 770 (BTMPS)

Tinuvin 770 (BTMPS) is a non-competitive, use-dependent antagonist of nicotinic acetylcholine receptors (nAChRs). The drug is highly lipid soluble and as such it has the potential to act within the brain. Presently the ganglionic blocking drug mecamylamine is used almost exclusively to block central nAChRs upon peripheral administration. These experiments were designed to confirm the nAChR antagonism effectiveness of BTMPS in both peripheral (ganglionic stimulation) and central (locomotor activity and thermal nociceptive sensitivity) nicotinic system in vivo. BTMPS inhibited the expression of the pressor response produced by i.v. injection of the ganglionic stimulant DMPP in anesthetized rats. The inhibition dose-response profile appeared to be biphasic with the maximal inhibition occurring after administration of the 0.48 mg/kg dose of BTMPS. In rats acclimated to the test apparatus, nicotine increased different measures of locomotor activity, particularly at the 0.75 mg/kg dose. BTMPS pretreatment significantly inhibited the nicotine-induced increase in motor behaviors, again with a biphasic dose-response relationship. Lastly, nicotine elicited an antinociceptive response in rats (hot plate test). BTMPS almost completely blocked the antinociceptive responses to 1 and 1.5 mg/kg nicotine. On its own, BTMPS failed to decrease blood pressure and to decrease the nociceptive threshold. The drug also generally failed to alter locomotor activity. The use-dependent aspect of BTMPS-induced inhibition of nAChRs was evident in the drug's greater effectiveness in the presence of the highest doses of nicotine. Therefore, BTMPS can be considered as an alternative to or as a confirmatory drug for mecamylamine when inhibition of central nicotinic receptors is required.

P, p′-DDE depresses the immune competence of chinook salmon ( Oncorhynchus tshawytscha) leukocytes

p, p′-DDE, the main metabolite of DDT, is still detected in aquatic environments throughout the world. Here, the effects and mechanisms by which p, p′-DDE exposure might affect the immune system of chinook salmon ( Oncorhynchus tshawytscha) was studied. Isolated salmon splenic and pronephric leukocytes were incubated with different concentrations of p, p′-DDE, and cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry and Alamar Blue assay. p, p′-DDE significantly reduced cell viability and proliferation and increased apoptosis. The effect of p, p′-DDE on pronephric leukocytes was more severe than on splenic leukocytes, likely because pronephric leukocytes had a higher proportion of granulocytes, cells that appear more sensitive to p, p′-DDE. The effect of p, p′-DDE on leukocytes appeared to vary between developmental stages or seasonal differences. The mitogenic response of leukocytes of chinook salmon exposed to p, p′-DDE in vivo exhibited a biphasic dose–response relationship. Only leukocytes isolated from salmon treated with 59 ppm p, p′-DDE had a significantly lower percentage of Ig+ blasting cells than controls, although the response was biphasic. These results support the theory that exposure to chemical contaminants could lead to an increase in disease susceptibility and mortality of fish due to immune suppression.

Fluorinated 2-(4-amino-3-methylphenyl)benzothiazoles induce CYP1A1 expression, become metabolized, and bind to macromolecules in sensitive human cancer cells.

Fluorinated 2-(4-amino-3-methylphenyl)benzothiazoles possess potent antiproliferative activity against certain cancer cells, similar to the unfluorinated 2-(4-amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495). In "sensitive" cancer cells, DF 203 is metabolized by, can induce expression of, and binds covalently to CYP1A1. Metabolism appears to be essential for its antiproliferative activity through DNA adduct formation. However, a biphasic dose-response relationship compromises its straightforward development as a chemotherapeutic agent. We investigated whether fluorinated benzothiazoles inhibit cancer cell growth without the biphasic dose-response, and whether the fluorinated benzothiazoles are also metabolized into reactive species, with binding to macromolecules in sensitive cancer cells. One fluorinated benzothiazole, 2-(4-amino-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) did exhibit potent, antiproliferative activity without a biphasic dose-response. The fluorinated benzothiazoles were also metabolized only in cells, which subsequently showed evidence of cell death. We used microsomes from genetically engineered human B-lymphoblastoid cells expressing cytochromes P450 (CYP1A1, CYP1A2, or CYP1B1) to clarify the basis for fluorinated benzothiazole metabolism. 5F 203 induced CYP1A1 and CYP1B1 mRNA expression in sensitive breast and renal cancer cells, whereas 5F 203 induced CYP1A1 mRNA but not CYP1B1 mRNA expression in sensitive ovarian cancer cells. 5F 203 did not induce CYP1A1 or CYP1B1 mRNA expression in any "resistant" cancer cells. The fluorinated benzothiazoles induced CYP1A1 protein expression exclusively in sensitive cells. [14C]5F 203 bound substantially to subcellular fractions in sensitive cells but only minimally in resistant cells. These data are concordant with the antiproliferative activity of fluorinated benzothiazoles deriving from their ability to become metabolized and bind to macromolecules within sensitive cells.

Effect of in vivo administered hexachlorobenzene on epidermal growth factor receptor levels, protein tyrosine kinase activity, and phosphotyrosine content in rat liver

In the present study, the effects of hexachlorobenzene (HCB) on epidermal growth factor receptor (EGFR) content of liver microsomes and plasma membrane, and on EGFR-tyrosine kinase activity in the microsomal fraction were investigated. In addition, we studied the parameters of the tyrosine kinase signalling pathway such as protein tyrosine kinase (PTK) activity and phosphotyrosine content in microsomal and cytosolic protein. To determine whether the observed alterations were correlated with a manifestation of overt toxicity, a single very low dose of HCB (1 mg/kg body wt) and two much higher doses (100 and 1000 mg/kg body wt), the highest being toxicologically significant in that it reduced serum thyroxine (T 4) and inhibited uroporphyrinogen decarboxylase (URO-D) (EC 4.1.1.37) activity, were tested. Our results demonstrated that liver microsomes of rats treated with HCB had higher levels of EGFR than untreated rats; treated rats also had less EGFR present in hepatocyte plasma membrane fractions than did untreated rats. HCB altered the phosphotyrosine content and protein phosphorylation of some microsomal and cytosolic proteins in a biphasic dose–response relationship. At the low dose, phosphorylation and phosphotyrosine content of several microsomal proteins were increased; however, these effects were diminished or reversed at the higher doses. Our results suggest that chronic HCB treatment produces a down-regulation of the EGFR and a dose-dependent increase in EGFR-tyrosine kinase activity in the microsomal fraction. This effect may contribute to the alteration of membrane and cytosolic protein tyrosine phosphorylation. The level of sensitivity encountered in our studies is extraordinary, occurring at 1/10 to 1/1000 the doses of HCB known to cause other toxicological lesions.

Mammary gland differentiation in female rats after prenatal exposure to 3,3′,4,4′,5-pentachlorobiphenyl

Recently we reported finding that prenatal exposure to a relatively low dose of 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) increases the rate of 7,12-dimethylbenz( a)anthracene (DMBA)-induced rat mammary carcinoma, while a high dose decreases it. One of the most important factors determining sensitivity of the mammary gland to neoplastic stimuli is its stage of differentiation at the time of exposure to the carcinogenic agent. Hence, to verify a biphasic dose-response relationship (enhancement of carcinogenesis at low dose, and inhibition at high dose), we investigated the effects of prenatal exposure to PCB126 on mammary gland differentiation. Female SD rats were injected (i.g.) with 25 pg, 2.5 ng, 250 ng, 7.5 μg of PCB126/kg, or the vehicle, on days 13–19 postconception. In 50-day-old offspring, regardless of the day of exposure to DMBA, only the 7.5 μg group showed statistically significant high levels of PCB126 in the fatty tissue of their mammary glands. Fifty-day-old female offspring of the 250 ng group showed apparent inhibition of the normal differentiation of terminal end buds (TEB) to alveolar buds and lobules (ABL), while those of the 7.5 μg group showed mammary gland hypoplasia. Expression levels of the estrogen receptor-α (ER) in TEBs and the ER mRNA in mammary glands were higher in the 7.5 μg, 250 ng, 2.5 ng groups. Proliferating cell nuclear antigen (PCNA) expression in TEBs of 50-day-old rats was statistically significantly higher in the 250 ng group and lower in the 7.5 μg group. In the developing mammary gland, TEBs are considered the most susceptible to mammary carcinogenesis, while ABLs are relatively protected from mammary carcinogenesis. Thus, prenatal exposure to a relatively low dose of PCB126 induced an alteration of mammary gland differentiation that might potentially increase the risk of DMBA-induced mammary carcinoma.

Regulation of rat carboxylesterase expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): a dose-dependent decrease in mRNA levels but a biphasic change in protein levels and activity.

Carboxylesterases play an important role in the metabolism of endogenous lipids and foreign compounds; therefore, xenobiotic regulation of carboxylesterase gene expression has both physiological and pharmacological significance. We previously reported that beta-naphthoflavone and 3-methylcholanthrene, two potent inducers for cytochrome P4501A enzymes, had opposing effects on the expression of hydrolase S, a secretory carboxylesterase. Beta-naphthoflavone caused suppression, whereas 3-methylcholanthrene caused induction of the expression of this enzyme. The aim of the present study was to determine the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), another prototypical cytochrome P4501A inducer, on the expression of this and several other rat carboxylesterases (hydrolases A, B, and C) in liver and extrahepatic tissues. Rats received TCDD treatment at nonlethal (<or=10 microg/kg), sublethal (30 microg/kg), or lethal doses (90 microg/kg). The overall hydrolytic activity in the liver microsomes toward both 1-naphthyl- and para-nitrophenylacetate was markedly increased in the nonlethal dosage groups, but markedly decreased in the lethal dosage group. Consistent with such a biphasic dose-response relationship, the levels of enzyme proteins exhibited an initial increase, followed by a decrease in response to nonlethal and lethal doses, respectively. In contrast, treatment with TCDD caused a dose-dependent decrease on the levels of mRNA encoding these enzymes. All liver carboxylesterases showed a similar pattern of change on activity, protein, and mRNA levels, suggesting that TCDD coregulates the expression of these genes. In the extrahepatic tissues, a similar biphasic change was observed in activity and in protein and mRNA levels. In both liver and kidney, the expression of cytochrome P4501A1 (CYP1A1) was significantly induced in a dose-dependent manner. TCDD is known to upregulate the expression of CYP1A1 gene through the aryl hydrocarbon receptor (AhR). The differential effects on the expression of liver carboxylesterases and CYP1A1 suggest that TCDD regulates the expression of hydrolytic enzymes via a mechanism(s) other than the AhR-mediated transcription activation, as observed in the CYP1A1 regulation. The different patterns of change on protein and mRNA levels in the nonlethal dosage groups suggest that TCDD regulates the expression of hepatic carboxylesterases by acting on both transcription and translation.