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Biomedical subjects

L Manzo

Publications and source records attributed to L Manzo.

At least 19 recordsLinked to original sources
PubMed1999

Effect of styrene on monoamine oxidase B activity in rat brain.

Previous studies have indicated that workers exposed to styrene present a decreased activity of platelet monoamine oxidase B (MAO B), suggesting that this biochemical assay may represent a biomarker for styrene-induced neurotoxicity. This study was undertaken to determine whether exposure to styrene would cause changes in MAO B activity in the target organ--the brain. Groups of rats were exposed to styrene by inhalation at concentrations of 300 ppm for 4 wk or 50 ppm for 13 wk. Both treatments caused significant decreases of MAO B activity in several brain areas, while MAO A activity was not affected. Decreases in MAO B activity were also found in brainstem of rats given styrene (400 mg/kg) or styrene oxide (100 mg/kg) by i.p. injection for 2 wk. Styrene, styrene oxide, and other styrene metabolites (mandelic acid, phenylglyoxylic acid, and styrene glycol) had no direct inhibitory effect on brain MAO B activity when tested in vitro. These results indicate that exposure to low concentrations of styrene alters MAO B activity in rat brain, suggesting that the observed changes in human platelets may reflect alterations in the nervous system.

Administration, Inhalation↗
PubMed1998

Ethanol selectively interferes with the trophic action of NMDA and carbachol on cultured cerebellar granule neurons undergoing apoptosis.

Exposure of mature rat cerebellar granule neurons to non-depolarizing conditions (5 mM K+) for 24 h resulted in the onset of apoptosis. NMDA, forskolin, carbachol and GABA attenuated low K+-induced toxicity, although to a different extent, with NMDA and GABA being the most effective agents. When cells were co-exposed for 24 h to ethanol, the survival promoting action of NMDA and carbachol, but not that of forskolin and GABA, was attenuated. By contrast, a 24 h cell pre-treatment with ethanol, followed by its removal prior to K+ deprivation, was ineffective towards the neurotrophic action of NMDA and carbachol. The concomitant presence of alcohol and neurotrophic factors was not required for the pro-apoptotic effect of ethanol to be manifest after a long-term alcohol exposure: inhibition of NMDA- and carbachol-mediated neurotrophism was still observed when cells were pre-exposed for 72 h to alcohol in depolarizing conditions, prior to the challenge with 5 mM K+-containing medium and the test compounds in the absence of ethanol. The present study shows that ethanol promotes apoptotic cell death of cultured cerebellar neurons by selectively inhibiting the neurotrophic effect of NMDA and carbachol, and suggests that alcohol may cause permanent changes in the control mechanisms of apoptosis: this finding may have significant implications for the in vivo toxicity of prenatal ethanol exposure on the developing cerebellum.

Animals↗
PubMed1998

Chronic exposure to aluminum impairs neuronal glutamate-nitric oxide-cyclic GMP pathway.

Humans are exposed to aluminum from environmental sources and therapeutic treatments. However, aluminum is neurotoxic and is considered a possible etiologic factor in Alzheimer's disease and other neurological disorders. The molecular mechanism of aluminum neurotoxicity is not understood. We tested the effects of aluminum on the glutamate-nitric oxide-cyclic GMP pathway in cultured neurons. Neurons were exposed to 50 microM aluminum in culture medium for short-term (4 h) or long-term (8-14 days) periods, or rats were prenatally exposed, i.e., 3.7% aluminum sulfate in the drinking water, during gestation. Chronic (but not short-term) exposure of neurons to aluminum decreased glutamate-induced activation of nitric oxide synthase by 38% and the formation of cyclic GMP by 77%. The formation of cyclic GMP induced by the nitric oxide-generating agent S-nitroso-N-acetylpenicillamine was reduced by 33%. In neurons from rats prenatally exposed to aluminum but not exposed to it during culture, glutamate-induced formation of cyclic GMP was inhibited by 81%, and activation of nitric oxide synthase was decreased by 85%. The formation of cyclic GMP induced by S-nitroso-N-acetylpenicillamine was not affected. These results indicate that chronic exposure to aluminum impairs glutamate-induced activation of nitric oxide synthase and nitric oxide-induced activation of guanylate cyclase. Impairment of the glutamate-nitric oxide-cyclic GMP pathway in neurons may contribute to aluminum neurotoxicity.

Aluminum↗
PubMed1997

Styrene-induced alterations in the respiratory tract of rats treated by inhalation or intraperitoneally.

Although exposure to styrene occurs primarily via inhalation, the action of this agent on the respiratory tract has scarcely been investigated. This article describes morphological and biochemical changes occurring in the respiratory tract of rats after either inhalation of styrene vapors (300 ppm, 6 h/d, 5 d/wk, for 2 wk) or systemic (ip) treatment with 40 or 400 mg/kg styrene for 3 consecutive days. Electron microscopy analysis showed diffuse cell damage involving the tracheal, bronchiolar, and alveolar epithelium. In the tracheal epithelium, several cell types were affected. Ciliated cells presented vacuolation, detachment of cilia, blebbing of the apical cytoplasm, and compound cilia. Most secretory cells showed scant secretory granules and blebbings. Dense bodies and fibrillary inclusions were seen in intermediate and basal cells. Styrene also caused alterations of cytoplasmic components in type II pneumocytes and bronchiolar cells as well as thickness of the alveolar wall. These abnormalities were accompanied by depletion of glutathione (GSH) in the lung tissue. Pneumotoxic effects of systemic administration of styrene were dose dependent and tended to be more severe than those seen in the animals exposed for longer periods to styrene by inhalation. Metabolic activation of styrene and subsequent cell damage induced by the reactive metabolite styrene oxide may be involved in the sequence of events culminating in the toxic insult to the respiratory tract.

Administration, Inhalation↗
PubMed1997

Effects of mercuric chloride and methyl mercury on cholinergic neuromuscular transmission in the guinea-pig ileum.

The effects of mercuric chloride (HgCl2) and methyl mercury (MeHg) were examined on basal mechanical activity and electrically-induced neurogenic cholinergic contractions (twitch contractions) in longitudinal muscle-myenteric plexus strips from guinea-pig distal ileum. Both compounds at 0.33 microM slightly enhanced the amplitude of twitch contractions in approximately 50% preparations. This effect was probably due to facilitation of acetylcholine (ACh) release since 0.1 and 1 microM mercurials increased electrically-evoked tritium outflow from [3H]choline preloaded muscle layer with attached myenteric plexus. Conversely, higher mercury concentrations inhibited twitch contractions (HgCl2 IC50 = 21.3 +/- 6.4 microM; MeHg IC50 = 45.1 +/- 5.5 microM), as well as contractions to exogenous ACh (0.1 microM) in resting preparations, and concomitantly increased the basal tone. The former effects possibly reflected an antimuscarinic activity of mercury, while the latter was related to alterations of calcium homeostasis in the effector cells. Indeed, the effect of HgCl2 on basal tone was antagonized by the Ca2+ entry blocker nifedipine (3, 10, 30 nM), indicating Hg-induced facilitation of Ca2+ influx through voltage-dependent channels. On the whole, our results suggest that cholinergic neuromuscular transmission and Ca(2+)-dependent mechanisms underlying smooth muscle contractility are targets for mercury toxicity in the intestine.

Acetylcholine↗
PubMed1996

Effects of ethanol administration on cerebral non-protein sulfhydryl content in rats exposed to styrene vapour.

Glutathione (GSH) and other non-protein sulfhydryls (NPS) are known to protect cells from oxidative stress and from potentially toxic electrophiles formed by biotransformation of xenobiotics. This study examined the effect of a simultaneous administration of styrene and ethanol on NPS content and lipid peroxidation in rat liver and brain. Hepatic cytochrome P450 and cytochrome b5 content, aniline hydroxylase and aminopyrine N-demethylase activities as well as the two major urinary metabolites of styrene, mandelic and phenylglyoxylic acids were also measured. Groups of rats given ethanol for 3 weeks in a liquid diet were exposed, starting from the second week, to 326 ppm of styrene (6 h daily, 5 days a week, for 2 weeks). In control pair-fed animals, styrene produced about 30% depletion of brain NPS and 50% depletion of hepatic NPS. Subchronic ethanol treatment did not affect hepatic NPS levels, but caused 23% depletion of brain NPS. Concomitant administration of ethanol and styrene caused a NPS depletion in brain tissue in the order of 60%. These results suggest that in the rat, simultaneous exposure to ethanol and styrene may lead to considerable depletion of brain NPS. This effect is seen when both compounds are given on a subchronic basis, a situation which better resembles possible human exposure.

Administration, Inhalation↗
PubMed1996

Urinary mercapturic acid diastereoisomers in rats subchronically exposed to styrene and ethanol.

Styrene is stereoselectively oxidized by cytochrome P450 to its reactive metabolite, styrene oxide. The (R)- and (S)-enantiomers of styrene oxide can be conjugated with glutathione (GSH) to both (R)- and (S)-diastereoisomers of the specific mercapturic acids, N-acetyl-S-(1-phenyl-2-hydroxyethyl)-L-cysteine (M1) and N-acetyl-S-(2-phenyl-2-hydroxyethyl)-L-cysteine (M2). Several investigations have indicated different toxic potential of the (R)- and (S)-configurations of styrene oxide and its GSH- and N-acetyl-conjugates. In this study the mercapturic acid diastereoisomers were measured in the urine of rats exposed to styrene in combination with ethanol, a good inducer of styrene metabolism. Male Sprague-Dawley rats were given an isocaloric liquid diet containing ethanol (5% w/v) for 3 weeks. Starting from the 2nd week, the animals were also exposed to styrene vapours (300 ppm, 6 h/day, 5 days/week) in a dynamic exposure chamber. Both the (R)- and (S)-diastereoisomers of the M1 and M2 as well as the conventional biomarkers, mandelic acid (MA) and phenylglyoxylic acid (PGA) were measured in urinary samples. Approximately 30 and 25% reduction of the levels of brain non-protein sulfhydryls (NPS) was observed in the animals given styrene and ethanol, respectively, while the combined ethanol and styrene treatment resulted in a 60% decrease. Ethanol consumption also resulted in higher urinary levels of the M1-R, M1-S and M2 metabolites associated with increased M1-R/S ratio and higher urinary MA excretion compared to animals treated with styrene. These results suggest that the urinary mercapturic acid diastereoisomers may be used as a noninvasive tool to examine stereoselective patterns of styrene metabolism in vivo, as well as their alterations caused by ethanol. These compound-specific mercapturic acids may also be valuable indicators of styrene-induced disorders of GSH homeostasis in nonaccessible organs.

Acetylcysteine↗
PubMed1996

Biochemical markers of neurotoxicity. A review of mechanistic studies and applications.

Neurotoxicology presents major challenges to the development of biological markers in accordance to conventional research strategies. Because of the inaccessibility of the nervous system, one of the proposed alternatives is the study of biochemical signals in peripheral tissues which can easily and ethically be obtained in humans, and which could represent surrogate indicators of equivalent parameters in the nervous tissue. Considerable scientific support to this approach is provided by the results of recent investigations in major areas of pharmacology and psychobiology. Studies examining parameters of neurotransmission and second messenger systems in peripheral blood cells, and variations in the peripheral body fluid content of endogenous substances reflecting nervous tissue dysfunction or damage are presented in this paper as examples of efforts toward rational development and validation of novel indicators of nervous system toxicity. Cholinergic muscarinic receptors and calcium signalling in peripheral blood lymphocytes, myelin basic protein in cerebrospinal fluid, and blood polyamines are discussed as potential surrogate indicators based on the results of in vitro or in vivo animal studies of neurotoxic metals (mercury, triethyltin), pesticides (disulfoton), drugs of abuse (d-fenfluramine) and model epileptogenic compounds (kainic acid). Data from investigations examining serum prolactin, type B monoamine oxidase (MAO-B) and dopamine beta-hydroxylase (DBH) in workers occupationally exposed to manganese, lead or styrene are also presented. Although research in this field is still at its very early stage, current evidence suggests that (i) certain neurochemical markers may be valuably used in animal studies as a complement to conventional laboratory tests to augment their sensitivity or predictivity; (ii) a mechanistic research approach is required to establish which markers offer the greatest promise for application in human biomonitoring.

Animals↗
PubMed1995

Heterogeneity of cholinergic muscarinic receptors coupled to phosphoinositide metabolism in immature rat brain.

The effects of muscarinic agonists and antagonists on phosphoinositide (PtdIns) metabolism were examined in the cerebral cortex and brainstem of 7-day-old rats, in order to evaluate the role of muscarinic receptor subtypes in this process. Additionally, comparative experiments were performed in cortices from adult animals. Accumulation of [3H]inositol phosphates ([3H]InsPs) in [3H]inositol pre-labeled brain slices was taken as an index of PtdIns hydrolysis. In neonatal cortex, maximal stimulation induced by the full agonists acetylcholine, carbachol and methacholine was 8-10 fold over basal [3H]InsPs accumulation. The effect of the partial agonists bethanechol, pilocarpine and oxotremorine varied from 3 to 4 fold over basal. Smaller responses to cholinergic stimulation were found in the brainstem and in the adult cortex. In neonatal cortex, muscarinic antagonists inhibited the stimulatory responses with the following order of potency: 4-DAMP > pirenzepine > AF-DX 116 approximately p-F-HHSiD. Pirenzepine inhibition of full agonist-induced [3H]InsPs accumulation showed biphasic curves, with two thirds of the response being inhibited with high affinity. When partial agonists were used, the resulting pirenzepine curves were better described by interaction at one high affinity site. No differences were found between immature and adult rats in the effect of pirenzepine on [3H]InsPs accumulation induced by carbachol, methacholine, or bethanechol. Inhibition by pirenzepine of PtdIns hydrolysis induced by carbachol or methacholine showed biphasic curves also in the brainstem. In this area, only one third of the response was inhibited with high affinity, and p-F-HHSiD was more potent as an antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Colchicine induces apoptosis in cerebellar granule cells.

Exposure to 1 microM colchicine, a microtubule disrupting agent, triggered apoptosis in rat cerebellar granule cells (CGC). Apoptotic nuclei began to appear after 12 h followed by oligonucleosomal DNA laddering, whereas inhibition of the mitochondrial 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide metabolism became significant between 18 and 24 h, when most cells already had apoptotic nuclei. These events were preceded by loss of tau protein and fragmentation of alpha and beta tubulins. Colchicine treatment also caused alterations in Ca2+ responses to chemical depolarization and a moderate, but progressive, increase in the resting intracellular Ca2+ concentration. Nearly all neurons expressed c-Fos after the treatment with colchicine. However, while in part of the cell population c-Fos levels subsequently declined, in the neurons undergoing apoptosis the protein was still expressed, but had an abnormal intracellular localization. An increased expression of the constitutive nitric oxide synthase (NOS-I) was also detected at 12 h and was followed by increased nitrite production. Treatment with 100 nM taxol to stabilize the microtubuli prevented DNA laddering and apoptotic body formation induced by colchicine. In contrast, pretreatment with the N-methyl-D-aspartate receptor-antagonist, MK-801, or L-type Ca2+ channel blockers did not prevent colchicine-induced CGC apoptosis. Inhibitors of NOS were also ineffective in preventing apoptotic body formation and DNA laddering, whereas they delayed the secondary cell lysis. These results support the idea that colchicine-induced cytoskeletal alterations directly initiate the genetic and structural modifications that result in CGC apoptosis.

Amino Acid Oxidoreductases↗
PubMed1995

Mechanisms of neurotoxicity: applications to human biomonitoring.

Interactions of chemicals with cerebral neurotransmitters, receptors, and second messenger systems are often accompanied by similar changes involving components in non-neural tissues. On this basis, indirect strategies have been developed to investigate neural cell function parameters by methods using accessible cells such as platelets or peripheral blood lymphocytes. The validity of certain surrogate markers of biochemical events occurring in the nervous system has been documented by recent studies in both laboratory animals and humans. Although experience with neurotoxicants is still limited, advantages and limitations of methods using peripheral blood cells as indicators of chemically-induced nervous system changes have been documented by a number of studies in psychopharmacology and biological psychiatry. Applicability of this approach in conventional population studies of environmental chemicals remains to be demonstrated. However, recent data regarding the action of low doses of mercury and organophosphates on receptors and signal transduction pathways in peripheral lymphocytes suggest useful applications of certain surrogate markers in mechanistic studies of neurotoxicity in vivo and, possibly, in assessing early biochemical effects of neurotoxicants in humans.

Biomarkers↗
PubMed1995

Biochemical markers of neurotoxicity: research strategies and epidemiological applications.

A great deal of attention has been given in the past few years to the development and validation of biomarkers for non-cancer endpoints, to be used in human epidemiological studies. In this research, as they apply to the field of neurotoxicology, will be discussed. As biomarkers are often divided into indicators of exposure, effect and susceptibility, one example for each of these classes is presented. Measurements of hemoglobin adducts were developed as a way to monitor exposure to acrylamide (a peripheral neurotoxicant) in animals as well as humans, and have been successfully applied in a field study in occupationally exposed workers. Activity of monoamine oxidase B (MAO-B) in platelets was found to be inversely correlated with the levels of exposure to styrene, suggesting that this biochemical measurement may be a useful effect-related biomarker, though additional studies are needed to understand the mechanistic implications of these findings. Serum paraoxonase activity has been shown in animals to modulate the toxicity of organophosphorus insecticides. Studies in humans have lead to the identification of a genetic polymorphism for this enzyme and to define its underlying molecular basis. Epidemiological studies are needed to determine the relevance of this polymorphism in determining susceptibility to organophosphate toxicity.

Biomarkers↗
PubMed1995

[Toxicity of chemical elements].

A survey is presented of the most important facets of toxicity due to chemical elements as well as of the mechanisms through which it may be triggered. In particular, a detailed discussion is made on the characteristics shown by arsenic, cadmium, chromium, lead, mercury, barium and beryllium, with specific reference to the influence exerted by physiological, environmental and life-style factors.

Adult↗
PubMed1994

Effects of styrene oxide on differentiation and viability of rodent embryo cultures.

Epidemiological investigations on the reproductive and developmental outcomes of rubber and plastic industry workers have focused on the potential developmental toxicity of styrene, an important occupational chemical, and its metabolite, styrene oxide using two in vitro culture systems: micromass cell cultures and whole embryo culture (WEC). Further, we have compared the effects of styrene oxide in both culture systems to the developmental toxicity of styrene in the micromass system. The ability of styrene oxide to affect the differentiation of rat embryo midbrain (CNS) and limb bud (LB) cells was compared to general cytotoxicity over 5 days in high-density micromass cultures. The IC50 for differentiation was 9.2 micrograms/ml (76 microM) for CNS and 6.7 micrograms/ml (56 microM) for LB. The LC50 for cytotoxicity was 9.6 micrograms/ml (80 microM) and 27.5 micrograms/ml (228 microM) for CNS and LB, respectively. The values for CNS sensitivities suggest that inhibition of differentiation is probably a consequence of high levels of cytotoxicity. In contrast, effects of styrene oxide on LB endpoints of differentiation were evident at concentration levels which had minimal effects on cell viability. Styrene alone or in the presence of an exogenous monooxygenase system had minimal effects when tested at concentrations 4-12 times the highest IC50 values seen with styrene oxide alone. In whole embryo culture experiments, styrene oxide produced growth retardation and embryo malformations (primarily neural) with an MC50 value of 20 micrograms/ml (167 microM). The LC50 value for styrene oxide was approximately 1.7-fold higher (33.2 micrograms/ml, 276 microM). Our in vitro studies suggest that further evaluations of the relationship of developmental toxicity and generalized cytotoxicity of styrene and its metabolite are needed, especially given the low concentrations at which effects were seen.

Animals↗
PubMed1994

Investigation into vanadate-induced potentiation of smooth muscle contractility in the rabbit isolated ileum.

The action of sodium orthovanadate (Na3VO4) on spontaneous mechanical activity of the longitudinal muscle was investigated in isolated segments of rabbit distal ileum. Vanadate (0.3-1000 microM) concentration-dependently enhanced the amplitude of phasic contractions (pendular movements) and caused the muscle tone to slightly increase at the highest concentrations. Both these effects were mimicked by the Ca2+ channel activator BAY K 8644 (10-1000 nM). Vanadate- and BAY K 8644-induced potentiation of mechanical activity was antagonized by the Ca2+ entry blocker nifedipine (3 nM). In Ca(2+)-free, K(+)-depolarized preparations, vanadate (100 microM) failed to contract the musculature, but potentiated the contractile response to applied calcium (CaCl2: 30-300 microM). The action of vanadate was similar to that of BAY K 8644 (3 nM) and was antagonized by nifedipine (0.1 nM). These results suggest that extracellular calcium is required for vanadate-induced smooth muscle excitation which, at least in part, appears to arise from facilitation of calcium influx through voltage-dependent Ca2+ channels.

Animals↗
PubMed1994

A new conductivity staining method for tissue analysis under scanning electron microscope.

A conductivity staining method for tissue samples were developed using a solution of 10 ml of 5% carbolic acid solution, 2 g of tannic acid, and 10 ml of saturated aluminium sulfate 12-hydrated after fixation with osmium. Specimens of kidney (mouse) with the above treatment can be analyzed under a scanning electron microscopy without the charging phenomenon.

Animals↗
PubMed1994

Nutrition and alcohol neurotoxicity.

Neurological complications of alcoholism such as Wernicke-Korsakoff syndrome and polyneuropathy often originate from interactive factors involving direct nervous system toxicity of ethanol and nutrient deficiencies associated to heavy drinking. Not all patients are equally susceptible to these disorders and a genetic predisposition to thiamine deficiency has been described in subjects with Wernicke's encephalopathy. At moderate alcohol dosages, nutrient abnormalities may be marginal, inducing no obvious manifestations until other neurotoxic agents are absorbed. Examples are presented illustrating the interaction of ethanol and styrene on brain glutathione metabolism in rats, and cases of methanol poisoning in alcoholics. In these patients, ethanol-induced folate deficiency can potentiate visual toxicity of methanol due to impairment of the folate-dependent pathway involved in formate detoxication. The notion that nutritional deficiencies and ethanol toxicity may act synergistically in the nervous system outlines the importance of adequate nutritional strategies in the treatment of alcoholism and also indicates that methodological flaws may result during experimental studies from failure to control for nutritional variables.

Animals↗