Factores de riesgo biomecánico lumbar por manejo manual de cargas en el reparto de productos cárnicos / Lumbar biomechanical risk factors due to manual handling of loads in the distribution of meat products

Introducción: Identificar los factores de riesgo de trastornos musculoesqueléticos (TME) lumbares asociados al manejo manual (MMC) de productos cárnicos en las actividades de carga y descarga de camiones. Método: Estudio observacional descriptivo transversal con enfoque mixto, basado en el análisis ergonómico de la actividad de trabajo. Participaron los 4 trabajadores de los puestos de cargador y cargador-conductor. Se realizaron análisis cinemáticos y dinamométricos para determinar las fuerzas de compresión y cizallamiento y el riesgo biomecánico musculoesquelético en la zona lumbar. Se realizaron entrevistas y observaciones para analizar tareas y determinar los tiempos involucrados en cada operación, tipo de exposición y los determinantes de la actividad de trabajo. Resultados: El contexto de trabajo es sumamente variable durante la carga y descarga del camión, considerando la variabilidad en cada punto de entrega las características de los estacionamientos, las condiciones climáticas, la presencia de animales y otros obstáculos durante el transporte manual de la carga. El MMC produce fuerzas sobre los 4000 N de compresión discal en los niveles L4-L5 y L5-S1, las fuerzas iniciales de empuje y arrastre fueron de 51.2 kg*f y 27.3 kg*f respectivamente, lo que evidencia el riesgo de TME. La actividad de trabajo está determinada por el tipo de jornada, la organización del reparto y la falta de medios mecánicos de apoyo para la carga y descarga de los camiones. Conclusiones: Las tareas de MMC en esta industria son físicamente muy exigentes y mejorar estas condiciones de trabajo representa un desafío importante para la prevención (AU)

Introduction: Identify risk factors for lumbar musculoskeletal disorders (MSD) associated with manual handling (MHL) of meat products in truck loading and unloading activities. Method: Cross-sectional descriptive observational study with a mixed approach, based on ergonomic analysis of work activity. The 4 workers from the loader and loader-driver positions participated. Kinematic and dynamometric analyzes were performed to determine compression and shear forces and musculoskeletal risk in the lumbar area. Interviews and observations were conducted to analyze tasks and determine the times involved in each operation, type of exposure and the determinants of work activity. Results: The work context is highly variable during the loading and unloading of the truck, considering the variability at each delivery point the characteristics of the parking lots, weather conditions, the presence of animals and other obstacles during manual transport of the load. The MHL produces forces over 4000 N of disc compression at levels L4-L5 and L5-S1, the initial push and pull forces were 51.2 kg*f and 27.3 kg*f respectively, which shows the risk of MSD. The work activity is determined by the type of working day, the organization of the distribution and the lack of mechanical means to support the loading and unloading of trucks. Conclusions: The manual handling tasks in this industry are physically very demanding and improving these working conditions represents a significant challenge for prevention (AU)

[Lumbar biomechanical risk factors due to manual handling of loads in the distribution of meat products]. / Factores de riesgo biomecánico lumbar por manejo manual de cargas en el reparto de productos cárnicos.

INTRODUCTION: Identify risk factors for lumbar musculoskeletal disorders (MSD) associated with manual handling (MHL) of meat products in truck loading and unloading activities. METHOD: Cross-sectional descriptive observational study with a mixed approach, based on ergonomic analysis of work activity. The 4 workers from the loader and loader-driver positions participated. Kinematic and dynamometric analyzes were performed to determine compression and shear forces and musculoskeletal risk in the lumbar area. Interviews and observations were conducted to analyze tasks and determine the times involved in each operation, type of exposure and the determinants of work activity. RESULTS: The work context is highly variable during the loading and unloading of the truck, considering the variability at each delivery point the characteristics of the parking lots, weather conditions, the presence of animals and other obstacles during manual transport of the load. The MHL produces forces over 4000 N of disc compression at levels L4-L5 and L5-S1, the initial push and pull forces were 51.2 kg*f and 27.3 kg*f respectively, which shows the risk of MSD. The work activity is determined by the type of working day, the organization of the distribution and the lack of mechanical means to support the loading and unloading of trucks. CONCLUSIONS: The manual handling tasks in this industry are physically very demanding and improving these working conditions represents a significant challenge for prevention.

Introducción: Identificar los factores de riesgo de trastornos musculoesqueléticos (TME) lumbares asociados al manejo manual (MMC) de productos cárnicos en las actividades de carga y descarga de camiones. Método: Estudio observacional descriptivo transversal con enfoque mixto, basado en el análisis ergonómico de la actividad de trabajo. Participaron los 4 trabajadores de los puestos de cargador y cargador-conductor. Se realizaron análisis cinemáticos y dinamométricos para determinar las fuerzas de compresión y cizallamiento y el riesgo biomecánico musculoesquelético en la zona lumbar. Se realizaron entrevistas y observaciones para analizar tareas y determinar los tiempos involucrados en cada operación, tipo de exposición y los determinantes de la actividad de trabajo. Resultados: El contexto de trabajo es sumamente variable durante la carga y descarga del camión, considerando la variabilidad en cada punto de entrega las características de los estacionamientos, las condiciones climáticas, la presencia de animales y otros obstáculos durante el transporte manual de la carga. El MMC produce fuerzas sobre los 4000 N de compresión discal en los niveles L4-L5 y L5-S1, las fuerzas iniciales de empuje y arrastre fueron de 51.2 kg*f y 27.3 kg*f respectivamente, lo que evidencia el riesgo de TME. La actividad de trabajo está determinada por el tipo de jornada, la organización del reparto y la falta de medios mecánicos de apoyo para la carga y descarga de los camiones. Conclusiones: Las tareas de MMC en esta industria son físicamente muy exigentes y mejorar estas condiciones de trabajo representa un desafío importante para la prevención.

Docosahexaenoic acid-thyroid hormone combined protocol as a novel approach to metabolic stress disorders: Relation to mitochondrial adaptation via liver PGC-1α and sirtuin1 activation.

Docosahexaenoic acid (DHA) and 3,3',5-triiodothyronine (T3 ) combined protocol affords protection against liver injury via AMPK signaling supporting energy requirements. The aim of this work was to test the hypothesis that a DHA + T3 accomplish mitochondrial adaptation through downstream upregulation of PPAR-γ coactivator 1α (PGC-1α). Male Sprague-Dawley rats were given daily oral doses of 300 mg DHA/kg or saline (controls) for three consecutive days, followed by 0.05 mg T3 /kg (or hormone vehicle) ip at the fourth day, or single dose of 0.1 mg T3 /kg alone. Liver mRNA levels were assayed by qPCR, NAD+ /NADH ratios, hepatic proteins, histone 3 acetylation and serum T3 and ß-hydroxybutyrate levels were determined by specific ELISA kits. Combined DHA + T3 protocol led to increased liver AMPK, PGC-1α, NRF-2, COX-IV, and ß-ATP synthase mRNAs, with concomitant higher protein levels of COX-IV and NRF-2, 369% enhancement in the NAD+ /NADH ratio, 47% decrease in histone 3 acetylation and 162% increase in serum levels of ß-hydroxybutyrate over control values. These changes were reproduced by the higher dose of T3 without major alterations by DHA or T3 alone. In conclusion, liver mitochondrial adaptation by DHA + T3 is associated with PGC-1α upregulation involving enhanced transcription of the coactivator, which may be contributed by PGC-1α deacetylation and phosphorylation by SIRT1 and AMPK activation, respectively. This contention is supported by NRF-2-dependent enhancement in COX-1 and ß-ATP synthase induction with higher fatty acid oxidation resulting in a significant ketogenic response, which may represent a suitable strategy for hepatic steatosis with future clinical applications. © 2018 BioFactors, 45(2):271-278, 2019.

Upregulation of rat liver PPARα-FGF21 signaling by a docosahexaenoic acid and thyroid hormone combined protocol.

Prevention of ischemia-reperfusion liver injury is achieved by a combined omega-3 and thyroid hormone (T3 ) protocol, which may involve peroxisome-proliferator activated receptor-α (PPAR-α)-fibroblast growth factor 21 (FGF21) signaling supporting energy requirements. Combined docosahexaenoic acid (DHA; daily doses of 300 mg/kg for 3 days) plus 0.05 mg T3 /kg given to fed rats elicited higher hepatic DHA contents and serum T3 levels, increased PPAR-α mRNA and its DNA binding, with higher mRNA expression of the PPAR-α target genes for carnitine-palmitoyl transferase 1α, acyl-CoA oxidase, and 3-hydroxyl-3-methylglutaryl-CoA synthase 2, effects that were mimicked by 0.1 mg T3 /kg given alone or by the PPAR-α agonist WY-14632. Under these conditions, the mRNA expression of retinoic X receptor-α (RXR-α) is also increased, with concomitant elevation of the hepatic mRNA and protein FGF21 levels and those of serum FGF21. It is concluded that PPAR-α-FGF21 induction by DHA combined with T3 may involve ligand activation of PPAR-α by DHA and enhanced expression of PPAR-α by T3 , with consequent upregulation of the FGF21 that is controlled by PPAR-α. Considering the beneficial effects of PPAR-α-FGF21 signaling on carbohydrate and lipid metabolism, further investigations are required to clarify its potential therapeutic applications in human metabolic disorders. © 2016 BioFactors, 42(6):638-646, 2016.

Causal role of oxidative stress in unfolded protein response development in the hyperthyroid state.

L-3,3',5-Triiodothyronine (T3)-induced liver oxidative stress underlies significant protein oxidation, which may trigger the unfolded protein response (UPR). Administration of daily doses of 0.1mg T3 for three consecutive days significantly increased the rectal temperature of rats and liver O2 consumption rate, with higher protein carbonyl and 8-isoprostane levels, glutathione depletion, and absence of morphological changes in liver parenchyma. Concomitantly, liver protein kinase RNA-like endoplasmic reticulum (ER) kinase and eukaryotic translation initiator factor 2α were phosphorylated in T3-treated rats compared to controls, with increased protein levels of binding immunoglobulin protein and activating transcription factor 4. In addition, higher mRNA levels of C/EBP homologous protein, growth arrest and DNA damage 34, protein disulfide isomerase, and ER oxidoreductin 1α were observed, changes that were suppressed by N-acetylcysteine (0.5 g/kg) given before each dose of T3. In conclusion, T3-induced liver oxidative stress involving higher protein oxidation status has a causal role in UPR development, a response that is aimed to alleviate ER stress and promote cell survival.

Thyroid hormone in the frontier of cell protection, survival and functional recovery.

Thyroid hormone (TH) exerts important actions on cellular energy metabolism, accelerating O2 consumption with consequent reactive oxygen species (ROS) generation and redox signalling affording cell protection, a response that is contributed by redox-independent mechanisms. These processes underlie genomic and non-genomic pathways, which are integrated and exhibit hierarchical organisation. ROS production led to the activation of the redox-sensitive transcription factors nuclear factor-κB, signal transducer and activator of transcription 3, activating protein 1 and nuclear factor erythroid 2-related factor 2, promoting cell protection and survival by TH. These features involve enhancement in the homeostatic potential including antioxidant, antiapoptotic, antiinflammatory and cell proliferation responses, besides higher detoxification capabilities and energy supply through AMP-activated protein kinase upregulation. The above aspects constitute the molecular basis for TH-induced preconditioning of the liver that exerts protection against ischemia-reperfusion injury, a strategy also observed in extrahepatic organs of experimental animals and with other types of injury, which awaits application in the clinical setting. Noteworthy, re-adjusting TH to normal levels results in several beneficial effects; for example, it lengthens the cold storage time of organs for transplantation from brain-dead donors; allows a superior neurological outcome in infants of <28 weeks of gestation; reduces the cognitive side-effects of lithium and improves electroconvulsive therapy in patients with bipolar disorders.

T3-induced liver AMP-activated protein kinase signaling: redox dependency and upregulation of downstream targets.

AIM: To investigate the redox dependency and promotion of downstream targets in thyroid hormone (T3)-induced AMP-activated protein kinase (AMPK) signaling as cellular energy sensor to limit metabolic stresses in the liver. METHODS: Fed male Sprague-Dawley rats were given a single ip dose of 0.1 mg T3/kg or T3 vehicle (NaOH 0.1 N; controls) and studied at 8 or 24 h after treatment. Separate groups of animals received 500 mg N-acetylcysteine (NAC)/kg or saline ip 30 min prior T3. Measurements included plasma and liver 8-isoprostane and serum ß-hydroxybutyrate levels (ELISA), hepatic levels of mRNAs (qPCR), proteins (Western blot), and phosphorylated AMPK (ELISA). RESULTS: T3 upregulates AMPK signaling, including the upstream kinases Ca(2+)-calmodulin-dependent protein kinase kinase-ß and transforming growth factor-ß-activated kinase-1, with T3-induced reactive oxygen species having a causal role due to its suppression by pretreatment with the antioxidant NAC. Accordingly, AMPK targets acetyl-CoA carboxylase and cyclic AMP response element binding protein are phosphorylated, with the concomitant carnitine palmitoyltransferase-1α (CPT-1α) activation and higher expression of peroxisome proliferator-activated receptor-γ co-activator-1α and that of the fatty acid oxidation (FAO)-related enzymes CPT-1α, acyl-CoA oxidase 1, and acyl-CoA thioesterase 2. Under these conditions, T3 induced a significant increase in the serum levels of ß-hydroxybutyrate, a surrogate marker for hepatic FAO. CONCLUSION: T3 administration activates liver AMPK signaling in a redox-dependent manner, leading to FAO enhancement as evidenced by the consequent ketogenic response, which may constitute a key molecular mechanism regulating energy dynamics to support T3 preconditioning against ischemia-reperfusion injury.

La perspectiva de género, desafíos para la ergonomía en Chile: una revisión sistemática de literatura / The gender perspective, challenges for ergonomics in Chile: a systematic literature review

Contexto: Aun cuando la división sexual del trabajo remunerado ha sido examinada en muchos estudios, a veces considerada como la extensión de los roles diferenciados en el ámbito doméstico, el resultado de la jerarquía vertical donde los hombres se encuentran en los puestos superiores, la asociación de los hombres a las máquinas (distintas a las de limpieza o la costura) o la división de otras condiciones de trabajo y empleo por género. El género y el sexo rara vez son considerados en la investigación en ergonomía. Metodología: A través de una revisión de los datos publicados en encuestas chilenas con representación nacional, en bases de datos gubernamentales y artículos de ergónomos chilenos publicados en Ergonomics, Ciencia y Trabajo, etc. Objetivo: Este artículo busca orientar sobre las principales diferencias de sexo y género en los hombres y las mujeres para comprender sus implicancias en actividad de trabajo en Chile y cuál ha sido la contribución de la ergonomía a este aspecto. Conclusiones: El tomar en cuenta el sexo de las trabajadoras/es enriquece el análisis del trabajo y el análisis ergonómico a su vez enriquece la comprensión sobre la división sexual del trabajo y cómo esta genera diferentes exposiciones a los riesgos profesionales para las mujeres y los hombres.

Context: Even though the sexual division of paid work has been examined in many studies, sometimes thought of as the extension of differentiated roles in the domestic sphere, the result of a vertical hierarchy where men are found in higher positions, the association of men with machines (other than those used in cleaning or sewing), or a division of other working and employment conditions by gender. Gender and sex have rarely been considered in ergonomics research. Methodology: Through a review of published data from Chilean surveys with national representation, from governmental databases and published articles in Ergonomics, Ciencia y Trabajo, etc. Objective: This article aims to guide about the principals differences of sex and gender in men and women to understand the implications of sex and gender for work activity in Chile and what has been the contribution of ergonomics to this issue. Conclusions: Taking into account the sex of women and men workers enriches the analysis of work and the ergonomic analysis in turn enriches the understanding of the sexual division of work and how this generates different exposures to occupational risks for women and men.

Nrf2-regulated phase-II detoxification enzymes and phase-III transporters are induced by thyroid hormone in rat liver.

Thyroid hormone (T3)-induced calorigenesis triggers the hepatic production of reactive oxygen species (ROS) and redox-sensitive nuclear transcription factor erythroid 2-related factor 2 (Nrf2) activation. The aim of this study was to test the hypothesis that in vivo T3 administration upregulates the expression of phase II and III detoxification proteins that is controlled by Nrf2. Male Sprague-Dawley rats were given a single intraperitoneal dose of 0.1 mg T3/kg or T3 vehicle (controls). After treatment, rectal temperature of the animals, liver Nrf2 DNA binding (EMSA), protein levels of epoxide hydrolase 1 (Eh1), NADPH-quinone oxidoreductase 1 (NQO1), glutathione-S-transferases Ya (GST Ya) and Yp (GST Yp), and multidrug resistance-associated proteins 2 (MRP-2) and 4 (MRP-4) (Western blot), and MRP-3 (RT-PCR) were determined at different times. T3 significantly rose the rectal temperature of the animals in the time period studied, concomitantly with increases (P < 0.05) of liver Nrf2 DNA binding at 1 and 2 h after treatment, which was normalized at 4-12 h. Within 1-2 h after T3 treatment, liver phase II enzymes Eh1, NQO1, GST Ya, and GST Yp were enhanced (P < 0.05) as did phase III transporters MRP-2 and MRP-3, whereas MRP-4 remained unchanged. In conclusion, enhancement of liver Nrf2 DNA binding elicited by in vivo T3 administration is associated with upregulation of the expression of detoxification and drug transport proteins. These changes, in addition to antioxidant protein induction previously observed, may represent cytoprotective mechanisms underlying T3 preconditioning against liver injury mediated by ROS and chemical toxicity.

Metabolic basis for thyroid hormone liver preconditioning: upregulation of AMP-activated protein kinase signaling.

The liver is a major organ responsible for most functions of cellular metabolism and a mediator between dietary and endogenous sources of energy for extrahepatic tissues. In this context, adenosine-monophosphate- (AMP-) activated protein kinase (AMPK) constitutes an intrahepatic energy sensor regulating physiological energy dynamics by limiting anabolism and stimulating catabolism, thus increasing ATP availability. This is achieved by mechanisms involving direct allosteric activation and reversible phosphorylation of AMPK, in response to signals such as energy status, serum insulin/glucagon ratio, nutritional stresses, pharmacological and natural compounds, and oxidative stress status. Reactive oxygen species (ROS) lead to cellular AMPK activation and downstream signaling under several experimental conditions. Thyroid hormone (L-3,3',5-triiodothyronine, T(3)) administration, a condition that enhances liver ROS generation, triggers the redox upregulation of cytoprotective proteins affording preconditioning against ischemia-reperfusion (IR) liver injury. Data discussed in this work suggest that T(3)-induced liver activation of AMPK may be of importance in the promotion of metabolic processes favouring energy supply for the induction and operation of preconditioning mechanisms. These include antioxidant, antiapoptotic, and anti-inflammatory mechanisms, repair or resynthesis of altered biomolecules, induction of the homeostatic acute-phase response, and stimulation of liver cell proliferation, which are required to cope with the damaging processes set in by IR.

Thyroid hormone-induced cytosol-to-nuclear translocation of rat liver Nrf2 is dependent on Kupffer cell functioning.

L-3,3',5-triiodothyronine (T(3)) administration upregulates nuclear factor-E2-related factor 2 (Nrf2) in rat liver, which is redox-sensitive transcription factor mediating cytoprotection. In this work, we studied the role of Kupffer cell respiratory burst activity, a process related to reactive oxygen species generation and liver homeostasis, in Nrf2 activation using the macrophage inactivator gadolinium chloride (GdCl(3); 10 mg/kg i.v. 72 h before T(3) [0.1 mg/kg i.p.]) or NADPH oxidase inhibitor apocynin (1.5 mmol/L added to the drinking water for 7 days before T(3)), and determinations were performed 2 h after T(3). T(3) increased nuclear/cytosolic Nrf2 content ratio and levels of heme oxygenase 1 (HO-1), catalytic subunit of glutamate cysteine ligase, and thioredoxin (Western blot) over control values, proteins whose gene transcription is induced by Nrf2. These changes were suppressed by GdCl(3) treatment prior to T(3), an agent-eliciting Kupffer-cell depletion, inhibition of colloidal carbon phagocytosis, and the associated respiratory burst activity, with enhancement in nuclear inhibitor of Nrf2 kelch-like ECH-associated protein 1 (Keap1)/Nrf2 content ratios suggesting Nrf2 degradation. Under these conditions, T(3)-induced tumor necrosis factor-α (TNF-α) response was eliminated by previous GdCl(3) administration. Similar to GdCl(3), apocynin given before T(3) significantly reduced liver Nrf2 activation and HO-1 expression, a NADPH oxidase inhibitor eliciting abolishment of colloidal carbon-induced respiratory burst activity without altering carbon phagocytosis. It is concluded that Kupffer cell functioning is essential for upregulation of liver Nrf2-signaling pathway by T(3). This contention is supported by suppression of the respiratory burst activity of Kupffer cells and the associated reactive oxygen species production by GdCl(3) or apocynin given prior to T(3), thus hindering Nrf2 activation.

Thyroid hormone administration induces rat liver Nrf2 activation: suppression by N-acetylcysteine pretreatment.

BACKGROUND: Oxidative stress associated with 3,3',5-triiodo-l-thyronine (T(3))-induced calorigenesis upregulates the hepatic expression of mediators of cytoprotective mechanisms. The aim of this study was to evaluate the hypothesis that in vivo T(3) administration triggers a redox-mediated translocation of the cytoprotective nuclear transcription factor erythroid 2-related factor 2 (Nrf2) from the cytosol to the nucleus in rat liver. Such translocation of transcription factors is considered to be an activating step. MATERIALS AND METHODS: The effect of T(3) administration in the presence and absence of N-acetylcysteine (NAC) on cytosol-to-nuclear translocation of Nrf2 was evaluated, with inhibition of this process by NAC taken as evidence that the process was redox mediated. Male Sprague-Dawley rats weighing 180-200 g were given a single intraperitoneal dose of 0.1 mg T(3)/kg. Another group of rats were given the same dose of T(3) and were also pretreated with NAC (0.5 g/kg) at 0.5 hour before T(3) administration. Two other groups of rats received vehicle treatment and NAC, respectively. Following these treatments, rectal temperature of the animals, liver O(2) consumption, serum and hepatic levels of 8-isoprostanes, and liver protein levels of Nrf2, Akt, p38, and thioredoxin (Western blot) were determined at different times up to 48 hours. RESULTS: T(3) administration induced a significant increase in the hepatic nuclear levels of Nrf2 at 1 and 2 hours after treatment and a concomitant decrease in cytosolic Nrf2. It also increased hepatic thioredoxin, a protein whose gene transcription is induced by nuclear Nrf2. Levels of nuclear Nrf2 were at a plateau from 4 to 6 hours after T(3). Rectal temperature of the animals rose from 36.6°C to 37.5°C as did liver O(2) consumption. Serum and liver 8-isoprostanes levels increased (p < 0.05) from 38.4 ± 4.0 pg/mL (n = 4) to 69.2 ± 2.0 pg/mL (n = 3) and from 0.75 ± 0.09 ng/g liver (n = 3) to 1.53 ± 0.10 ng/g liver (n = 5), respectively. In the group of rats pretreated with NAC, the increase in cytosol-to-nuclear translocation of Nrf2 was only 28% that induced by T(3). In addition, T(3) induced liver Akt and p38 activation during the period of 1-4 hours after T(3) administration. p38 activation at 2 hours after T(3) administration was abolished in NAC-pretreated animals. CONCLUSIONS: In vivo T(3) administration leads to a rapid and transient cytosol-to-nuclear translocation of liver Nrf2. This appears to be promoted by a redox-dependent mechanism as it is blocked by NAC. It may also be contributed by concomitant p38 activation, which in turn promoted Nrf2 phosphorylation. Nrf2 cytosol-to-nuclear translocation may represent a novel cytoprotective mechanism of T(3) to limit free radical or electrophile toxicity, as this would likely entail promoting thioredoxin production.

Upregulation of liver inducible nitric oxide synthase following thyroid hormone preconditioning: suppression by N-acetylcysteine.

3,3-5-L-Triiodothyronine (T(3)) exerts significant protection against ischemia-reperfusion (IR) liver injury in rats. Considering that the underlying mechanisms are unknown, the aim of this study was to assess the involvement of inducible nitric oxide synthase (iNOS) expression and oxidative stress in T(3) preconditioning (PC). Male Sprague-Dawley rats given a single dose of 0.1 mg of T(3)/kg were subjected to 1-hour ischemia followed by 20 hours reperfusion, in groups of animals pretreated with 0.5 g of N-acetylcysteine (NAC)/kg 0.5-hour prior to T3 or with the respective control vehicles. At the end of the reperfusion period, liver samples were taken for analysis of iNOS mRNA levels (RT-PCR), liver NOS activity, and hepatic histology. T(3) protected against hepatic IR injury, with 119% enhancement in liver iNOS mRNA/18S rRNA ratios (p<0.05) and 12.7-fold increase (p<0.05) in NOS activity in T(3)-treated animals subjected to IR over values in control-sham operated rats, with a net 7.7-fold enhancement (p<0.05) in the net effect of T(3) on liver iNOS expression and a net enhancement of 0.58 units in NOS activity, changes that were abolished by NAC treatment before T(3). It is concluded that T(3)-induced liver PC is associated with upregulation of iNOS expression as a protective mechanisms against IR injury, which is achieved through development of transient and reversible oxidative stress.

Upregulation of liver inducible nitric oxide synthase following thyroid hormone preconditioning: suppression by N-acetylcysteine

3,3-5-L-Triiodothyronine (T3) exerts significant protection against ischemia-reperfusion (IR) liver injury in rats. Considering that the underlying mechanisms are unknown, the aim of this study was to assess the involvement of inducible nitric oxide synthase (iNOS) expression and oxidative stress in T3 preconditioning (PC). Male Sprague-Dawley rats given a single dose of 0.1 mg of T3/kg were subjected to 1-hour ischemia followed by 20 hours reperfusion, in groups of animals pretreated with 0.5 g of N-acetylcysteine (NAC)/kg 0.5-hour prior to T3 or with the respective control vehicles. At the end of the reperfusion period, liver samples were taken for analysis of iNOS mRNA levels (RT-PCR), liver NOS activity, and hepatic histology. T3 protected against hepatic IR injury, with 119 percent enhancement in liver iNOS mRNA/18S rRNA ratios (p<0.05) and 12.7-fold increase (p<0.05) in NOS activity in T3-treated animals subjected to IR over values in control-sham operated rats, with a net 7.7-fold enhancement (p<0.05) in the net effect of T3 on liver iNOS expression and a net enhancement of 0.58 units in NOS activity, changes that were abolished by NAC treatment before T3. It is concluded that T3-induced liver PC is associated with upregulation of iNOS expression as a protective mechanisms against IR injury, which is achieved through development of transient and reversible oxidative stress.

Hepatoprotective role of nitric oxide in an experimental model of chronic iron overload.

Chronic iron overload (CIO) enhances nitric oxide (*NO) production in the liver, which may represent a hepatoprotective mechanism against CIO toxicity. In order to test this hypothesis, the influence of CIO (diet enriched with 3% (wt/wt) carbonyl-iron for 8 weeks) in the absence or presence of the (*)NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) on NOS activity, extracellular signal-regulated kinase (ERK1/2) and NF-kappaB activation was studied, in relation to ferritin expression and liver morphology. CIO increased liver NOS activity, ERK1/2 phosphorylation, NF-kappaB DNA binding, and ferritin expression, with normal liver histology. These changes were suppressed by combined CIO and L-NAME treatment, with the resulting inflammatory response of the liver. It is concluded that (*)NO response induced by CIO represents a molecular mechanism affording protection against iron toxicity, which is related to both the activation of the ERK/NF-kappaB pathway involving inducible NOS expression and ferritin upregulation, changes that may be interrelated.

Chronic iron overload enhances inducible nitric oxide synthase expression in rat liver.

Iron is an essential micronutrient promoting oxidative stress in the liver of overloaded animals and human, which may trigger the expression of redox-sensitive genes. We have tested the hypothesis that chronic iron overload (CIO) enhances inducible nitric oxide synthase (iNOS) expression in rat liver by extracellular signal-regulated kinase (ERK1/2) and NF-kappaB activation. CIO (diet enriched with 3%(wt/wt) carbonyl-iron for 12 weeks) increased liver protein carbonylation and decreased reduced glutathione (GSH) content and the GSH/GSSG ratio after 6 weeks, parameters that are normalized after 8-12 weeks of treatment. These changes are paralleled by higher phosphorylated-ERK1/2 to non-phosphorylated-ERK1/2 ratios at 6 and 8 weeks, increased NF-kappaB DNA binding to the iNOS gene promoter at 8-12 weeks, and higher iNOS mRNA expression and activity at 8 and 12 weeks. It is concluded that CIO triggers liver oxidative stress at early times, with upregulation of iNOS expression involving the ERK/NF-kappaB pathway at later times, a finding that may represent a hepatoprotective mechanism against CIO toxicity in addition to the recovery of GSH homeostasis.

Effects of acute lindane intoxication and thyroid hormone administration in relation to nuclear factor-kappaB activation, tumor necrosis factor-alpha expression, and Kupffer cell function in the rat.

Nuclear factor-kappaB (NF-kappaB) DNA binding, tumor necrosis factor-alpha (TNF-alpha) expression, and parameters related to liver oxidative stress and Kupffer cell function were assessed in control rats and in animals given 3,3',5-triiodothyronine (T3) (0.1 mg T3/kg) and/or lindane (50 mg/kg; 4 h after T3). Liver NF-kappaB DNA binding and serum TNF-alpha levels were enhanced by the combined T3-lindane administration after 16-22 h, effects that were lower than those elicited by the separate treatments and coincided with increased hepatic TNF-alpha mRNA levels. Thyroid calorigenesis occurred independently of lindane, whereas T3, lindane and T3-lindane groups showed liver glutathione (GSH) depletion, with higher protein carbonyl levels in lindane and T3-lindane groups. Carbon-induced O2 consumption/carbon uptake ratios were not altered by T3 or lindane compared to controls, whereas combined T3-lindane administration elicited a 92% diminution with enhancement in the sinusoidal efflux of lactate dehydrogenase (LDH). In conclusion, depression of T3- or lindane-induced liver NF-kappaB activation and TNF-alpha expression occurred after their combined treatment, effects that correlate with the impairment of the respiratory burst activity of Kupffer cells and exacerbation of liver injury.

Effects of acute gamma-hexachlorocyclohexane intoxication in relation to the redox regulation of nuclear factor-kappaB, cytokine gene expression, and liver injury in the rat.

gamma-Hexachlorocyclohexane-induced hepatotoxicity is associated with oxidative stress. We tested the hypothesis that gamma-hexachlorocyclohexane triggers the redox activation of nuclear factor-kappaB (NF-kappaB), leading to proinflammatory cytokine expression. Liver NF-kappaB activation (electrophoretic mobility shift assay), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1alpha (IL-1alpha) mRNA expression (reverse transcription-polymerase chain reaction), and their serum levels (enzyme-linked immunosorbent assay) were measured at different times after gamma-hexachlorocyclohexane treatment (50 mg/kg). The relationship between these and hepatic O(2) uptake, glutathione and protein carbonyl levels, and sinusoidal lactate dehydrogenase (LDH) efflux in liver perfusion studies was determined. gamma-Hexachlorocyclohexane increased liver NF-kappaB DNA binding at 14-22 h after treatment, concomitantly with significant glutathione depletion and an increase in the rate of O(2) consumption, the content of protein carbonyls, and the sinusoidal LDH efflux. In these conditions, the expression of TNF-alpha and IL-1alpha is enhanced, with maximal increases in their respective mRNA content and serum levels of the cytokines being elicited at 18 h after gamma-hexachlorocyclohexane treatment. All these changes are suppressed by the administration of alpha-tocopherol (100 mg/kg) or the Kupffer cell inactivator gadolinium chloride (10 mg/kg) prior to gamma-hexachlorocyclohexane. gamma-Hexachlorocyclohexane-induced TNF-alpha levels in serum are suppressed by pretreatment with an antisense oligonucleotide (ASO TJU-2755; daily doses of 10 mg/kg for 2 days) targeting the primary transcript for the cytokine, whereas those of IL-1alpha are not modified. It is concluded that gamma-hexachlorocyclohexane-induced liver oxidative stress triggers the DNA binding activity of NF-kappaB, with the consequent increase in the expression of NF-kappaB-dependent genes for TNF-alpha and for IL-1alpha, factors that may mediate the hepatotoxicity of the insecticide.

Thyroid hormone-induced oxidative stress triggers nuclear factor-kappaB activation and cytokine gene expression in rat liver.

Nuclear factor-kappaB (NF-kappaB) is a redox-sensitive factor responsible for the transcriptional activation of cytokine-encoding genes. In this study, we show that 3,3,5-triiodothyronine (T(3)) administration to rats activates hepatic NF-kappaB, as assessed by electrophoretic mobility shift assay. This response coincides with the onset of calorigenesis and enhancement in hepatic respiration, and is suppressed by the antioxidants alpha-tocopherol and N-acetylcysteine or by the Kupffer cell inactivator gadolinium chloride. Livers from hyperthyroid rats with enhanced NF-kappaB DNA-binding activity show induced mRNA expression of the NF-kappaB-responsive genes for tumor necrosis factor-alpha (TNF-alpha) and interleukin- (IL-) 10, as evidenced by reverse transcription-polymerase chain reaction assay, which is correlated with increases in the serum levels of the cytokines. T(3) also increased the hepatic levels of mRNA for IL-1alpha and those of IL-1alpha in serum, with a time profile closely related to that of TNF-alpha. It is concluded that T(3)-induced oxidative stress enhances the DNA-binding activity of NF-kappaB and the NF-kappaB-dependent expression of TNF-alpha and IL-10 genes.