RESUMEN
In the present study, it is shown for the first time that an extract of Hintonia latiflora (HLE) which is used as an antidiabetic herbal medicine, is not only able to decrease blood glucose concentration but additionally exerts a vasodilating effect. Accordingly, this extract might have a positive influence on diabetes-associated dysfunction of blood vessels. The vasodilating effect was demonstrated in vitro in aortic rings of guinea pigs as well as in vivo in rabbits. Aortic rings pre-contracted with noradrenaline (NA) could completely be relaxed by HLE (EC50: 51.98 mg/l). In contrast, potassium-induced contractions were not diminished by HLE. Therefore, it can be suggested that the vasodilating effect of HLE is primarily the result of an inhibition of G protein-induced increase in intracellular calcium and not of a blockade of voltage-operated L-type calcium channels. The neoflavonoid coutareagenin (COU), a constituent of HLE which in part is responsible for the blood glucose-lowering effect of HLE, also relaxed NA-induced contractions of aortic rings (EC50: 32.55 mg/l) and only weakly inhibited potassium-induced contractions. Experiments in aortic rat cells revealed that calcium transients evoked by vasopressin were suppressed by 60 mg/l COU supporting the idea of an inhibition of G protein-induced intracellular calcium release by a constituent of HLE. To study the effect of HLE on vascular tone under in vivo conditions, ultrasound measurements were carried out in conscious rabbits which received a single oral dose of HLE. Under the influence of HLE, a vasodilation combined with a lowering of blood flow velocity could be observed in the abdominal aorta and the common carotid artery. Additionally, a decrease in blood glucose concentration in the HLE group occurred. The combination of a blood glucose-lowering with a vasodilating effect may be helpful for reducing angiopathies, typical long-term complications in patients with diabetes mellitus.
Asunto(s)
Flavonoides/farmacología , Hipoglucemiantes/farmacología , Extractos Vegetales/farmacología , Rubiaceae/química , Vasodilatadores/farmacología , Animales , Aorta/efectos de los fármacos , Cobayas , Técnicas In Vitro , Músculo Liso Vascular/citología , Miocitos del Músculo Liso/efectos de los fármacos , Norepinefrina/farmacología , Corteza de la Planta/química , Conejos , Ratas , Vasodilatación/efectos de los fármacosRESUMEN
Engineered nanoparticles (ENPs) are produced and used in increasing quantities for industrial products, food, and drugs. The fate of ENPs after usage and impact on health is less known. Especially as air pollution, suspended nanoparticles have raised some attention, causing diseases of the lung and cardiovascular system. Human health risks may arise from inhalation of ENPs with associated inflammation, dispersion in the body, and exposure of vulnerable organs (e.g., heart, brain) and tissues with associated toxicity. However, underlying mechanisms are largely unknown. Furthermore future use of ENPs in therapeutic applications is being researched. Therefore knowledge about potential cardiovascular risks due to exposure to ENPs is highly demanded, but there are no established biological testing models yet. Therefore, we established the isolated beating heart (Langendorff heart) as a model system to study cardiovascular effects of ENPs. This model enables observation and analysis of electrophysiological parameters over a minimal time period of 4 h without influence by systemic effects and allows the determination of stimulated release of substances under influence of ENPs. We found a significant dose and material dependent increase in heart rate accompanied by arrhythmia evoked by ENPs made of flame soot (Printex 90), spark discharge generated soot, anatas (TiO(2)), and silicon dioxide (SiO(2)). However, flame derived SiO(2) (Aerosil) and monodisperse polystyrene lattices exhibited no effects. The increase in heart rate is assigned to catecholamine release from adrenergic nerve endings within the heart. We propose the isolated Langendorff heart and its electrophysiological characterization as a suitable test model for studying cardiovascular ENP toxicity.
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Ingeniería , Corazón/efectos de los fármacos , Nanopartículas/efectos adversos , Animales , Calcio/metabolismo , Catecolaminas/metabolismo , Relación Dosis-Respuesta a Droga , Electrocardiografía/efectos de los fármacos , Cobayas , Corazón/metabolismo , Corazón/fisiología , Frecuencia Cardíaca/efectos de los fármacos , Humanos , Técnicas In Vitro , Espacio Intracelular/efectos de los fármacos , Espacio Intracelular/metabolismoRESUMEN
BACKGROUND: In nanotoxicology, the exact role of particle shape, in relation to the composition, on the capacity to induce toxicity is largely unknown. We investigated the toxic and immunotoxic effects of silver wires (length: 1.5 - 25 µm; diameter 100 - 160 nm), spherical silver nanoparticles (30 nm) and silver microparticles (<45 µm) on alveolar epithelial cells (A549). METHODS: Wires and nanoparticles were synthesized by wet-chemistry methods and extensively characterized. Cell viability and cytotoxicity were assessed and potential immunotoxic effects were investigated. To compare the effects on an activated and a resting immune system, cells were stimulated with rhTNF-α or left untreated. Changes in intracellular free calcium levels were determined using calcium imaging. Finally, ion release from the particles was assessed by ICP-MS and the effects of released ions on cell viability and cytotoxicity were tested. RESULTS: No effects were observed for the spherical particles, whereas the silver wires significantly reduced cell viability and increased LDH release from A549 cells. Cytokine promoter induction and NF-κB activation decreased in a concentration dependent manner similar to the decrease seen in cell viability. In addition, a strong increase of intracellular calcium levels within minutes after addition of wires was observed. This toxicity was not due to free silver ions, since the samples with the highest ion release did not induce toxicity and ion release control experiments with cells treated with pre-incubated medium did not show any effects either. CONCLUSIONS: These data showed that silver wires strongly affect the alveolar epithelial cells, whereas spherical silver particles had no effect. This supports the hypothesis that shape is one of the important factors that determine particle toxicity.
Asunto(s)
Células Epiteliales/efectos de los fármacos , Nanopartículas del Metal/toxicidad , Alveolos Pulmonares/efectos de los fármacos , Plata/toxicidad , Calcio/metabolismo , Línea Celular , Supervivencia Celular/efectos de los fármacos , Células Epiteliales/inmunología , Células Epiteliales/patología , Humanos , L-Lactato Deshidrogenasa/metabolismo , Tamaño de la Partícula , Alveolos Pulmonares/inmunología , Alveolos Pulmonares/patologíaRESUMEN
BACKGROUND: Exposure to particulate matter is a risk factor for cardiopulmonary disease but the underlying molecular mechanisms remain poorly understood. In the present study we sought to investigate the cardiopulmonary responses on spontaneously hypertensive rats (SHRs) following inhalation of UfCPs (24 h, 172 mug.m-3), to assess whether compromised animals (SHR) exhibit a different response pattern compared to the previously studied healthy rats (WKY). METHODS: Cardiophysiological response in SHRs was analyzed using radiotelemetry. Blood pressure (BP) and its biomarkers plasma renin-angiotensin system were also assessed. Lung and cardiac mRNA expressions for markers of oxidative stress (hemeoxygenase-1), blood coagulation (tissue factor, plasminogen activator inhibitor-1), and endothelial function (endothelin-1, and endothelin receptors A and B) were analyzed following UfCPs exposure in SHRs. UfCPs-mediated inflammatory responses were assessed from broncho-alveolar-lavage fluid (BALF). RESULTS: Increased BP and heart rate (HR) by about 5% with a lag of 1-3 days were detected in UfCPs exposed SHRs. Inflammatory markers of BALF, lung (pulmonary) and blood (systemic) were not affected. However, mRNA expression of hemeoxygenase-1, endothelin-1, endothelin receptors A and B, tissue factor, and plasminogen activator inhibitor showed a significant induction (~2.5-fold; p < 0.05) with endothelin 1 being the maximally induced factor (6-fold; p < 0.05) on the third recovery day in the lungs of UfCPs exposed SHRs; while all of these factors - except hemeoxygenase-1 - were not affected in cardiac tissues. Strikingly, the UfCPs-mediated altered BP is paralleled by the induction of renin-angiotensin system in plasma. CONCLUSION: Our finding shows that UfCPs exposure at levels which does not induce detectable pulmonary neutrophilic inflammation, triggers distinct effects in the lung and also at the systemic level in compromised SHRs. These effects are characterized by increased activity of plasma renin-angiotensin system and circulating white blood cells together with moderate increases in the BP, HR and decreases in heart rate variability. This systemic effect is associated with pulmonary, but not cardiac, mRNA induction of biomarkers reflective of oxidative stress; activation of vasoconstriction, stimulation of blood coagulation factors, and inhibition of fibrinolysis. Thus, UfCPs may cause cardiovascular and pulmonary impairment, in the absence of detectable pulmonary inflammation, in individuals suffering from preexisting cardiovascular diseases.
RESUMEN
Neurosteroids, such as progesterone, influence central nervous system development and function by regulating a broad spectrum of physiological processes. Here, we investigated membrane-initiated actions of progesterone in the retina and identified the membrane-associated progesterone receptor component 1 (PGRMC1). We found PGRMC1 expressed mainly in retinal Muller glia (RMG) and retinal pigment epithelium, and localized uniquely to microsomal and plasma membrane fractions. In RMG, membrane-impermeable progesterone conjugate induced calcium influx and subsequent phosphatidylinositol 3-kinase-mediated phosphorylation of PKC and ERK-1/2. Induction by progesterone also led to PKC-dependent activation of VEGF gene expression and protein synthesis, suggesting a contribution of membrane-initiated hormone effects to VEGF induced neovascularization within retina.
Asunto(s)
Señalización del Calcio/fisiología , Regulación de la Expresión Génica/fisiología , Neuroglía/metabolismo , Progesterona/fisiología , Retina/metabolismo , Factor A de Crecimiento Endotelial Vascular/genética , Animales , Señalización del Calcio/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Regulación de la Expresión Génica/efectos de los fármacos , Homeostasis/efectos de los fármacos , Homeostasis/fisiología , Proteínas de la Membrana/efectos de los fármacos , Proteínas de la Membrana/metabolismo , Proteína Quinasa 3 Activada por Mitógenos/efectos de los fármacos , Proteína Quinasa 3 Activada por Mitógenos/metabolismo , Neuroglía/citología , Neuroglía/efectos de los fármacos , Fosfatidilinositol 3-Quinasas/efectos de los fármacos , Fosfatidilinositol 3-Quinasas/metabolismo , Progesterona/farmacología , Proteína Quinasa C/efectos de los fármacos , Proteína Quinasa C/metabolismo , ARN Mensajero/efectos de los fármacos , ARN Mensajero/metabolismo , Receptores de Progesterona/efectos de los fármacos , Receptores de Progesterona/metabolismo , Retina/citología , Retina/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Transducción de Señal/fisiología , Sus scrofaRESUMEN
BACKGROUND AND AIM: Numerous herbicides and xenobiotic organic pollutants are detoxified in plants to glutathione conjugates. Following this enzyme catalyzed reaction, xenobiotic GS-conjugates are thought to be compartmentalized in the vacuole of plant cells. In the present study, evidence is presented from experiments with roots of barley (Hordeum vulgare cv. Cherie) that part of these conjugates will undergo long range transport in plants, rather than be stored in the vacuole. To our knowledge, this is the first report about the unidirectional long-range transport of xenobiotic conjugates in plants and the exsudation of a glutathione conjugate from the root tips. This could mean that plants possess an excretion system for unwanted compounds giving them similar advantages as animals. METHODS: Barley plants (Hordeum vulgare) were grown in Petri dishes soaked with tap water in the greenhouse. Fluorescence Microscopy. Roots of barley seedlings were cut under water, and the end at which the pesticides were applied was fixed in an aperture with a thin latex foil and transferred into a drop of water on a cover slide. The cover slide was fixed in a measuring chamber on the stage of an inverse fluorescence microscope (Zeiss Axiovert 100). Monobromo- and Monochlorobimane, two model xenobiotics that are conjugated rapidly in plant cells with glutathione, hereby forming fluorescent metabolites, were used as markers. Their transport in the root could be followed with high time resolution. Spectrometric enzyme assay. Glutathione S-transferase (GST) activity was determined in the protein extracts following established methods. Aliquots of the enzyme extract were incubated with 1-chloro-2,4-dinitrobenzene (CDNB), or monochlorobimane. Controls lacking enzyme or GSH were measured. Pitman chamber experiments. Ten days old barley plants or detached roots were inserted into special incubation chambers, either complete with tips or decapitated, as well as 10 days old barley plants without root tips. Compartment A was filled with a transport medium and GSH conjugate or L-cysteine conjugate. Compartments B and C contained sugar free media. Samples were taken from the root tip containing compartment C and the amount of conjugate transported was determined spectro-photometrically. Results. The transport in roots is unidirectional towards the root tips and leads to exsudation of the conjugates at rates between 20 and 200 nmol min(-1). The microscopic studies have been complemented by transport studies in small root chambers and spectroscopic quantification of dinitrobenzene-conjugates. The latter experiments confirm the microscopic studies. Furthermore it was shown that glutathione conjugates are transported at higher rates than cysteine conjugates, despite of their higher molecular weights. This observation points to the existence of glutathione specific carriers and a specific role of glutathione in the root. DISCUSSION: It can be assumed that long distance transport of glutathione conjugates within the plant proceeds like GSH or amino acid transport in both, phloem and xylem. The high velocity of this translocation of the GS-X is indicative of an active transport. For free glutathione, a rapid transport-system is essential because an accumulation of GSH in the root tip inhibits further uptake of sulfur. Taking into account that all described MRP transporters and also the GSH plasmalemma ATPases have side activities for glutathione derivatives and conjugates, co-transport of these xenobiotic metabolites seems credible. On the other hand, when GS-B was applied to the root tips from the outside, no significant uptake was observed. Thus it can be concluded that only those conjugates can be transported in the xylem which are formed inside the root apex. Having left the root once, there seems to be no return into the root vessels, probably because of a lack of inward directed transporters. CONCLUSIONS: Plants seem to possess the capability to store glutathione conjugates in the vacuole, but under certain conditions, these metabolites might also undergo long range transport, predominantly into the plant root. The transport seems dependent on specific carriers and is unidirectional, this means that xenobiotic conjugates from the rhizosphere are not taken up again. The exudation of xenobiotic metabolites offers an opportunity to avoid the accumulation of such compounds in the plant. RECOMMENDATIONS AND PERSPECTIVES: The role of glutathione and glutathione related metabolites in the rhizosphere has not been studied in any detail, and only scattered data are available on interactions between the plant root and rhizosphere bacteria that encounter such conjugates. The final fate of these compounds in the root zone has also not been addressed so far. It will be interesting to study effects of the exsuded metabolites on the biology of rhizosphere bacteria and fungi.
Asunto(s)
Glutatión/metabolismo , Hordeum/metabolismo , Raíces de Plantas/metabolismo , Xenobióticos/metabolismo , Transporte Biológico , Dinitroclorobenceno/metabolismo , Colorantes Fluorescentes , Glutatión Transferasa/metabolismo , Hordeum/enzimología , Microscopía Fluorescente , Raíces de Plantas/enzimología , PirazolesRESUMEN
Based on epidemiologic observations, the issue of adverse health effects of inhaled ultrafine particles (UFP) is currently under intensive discussion. We therefore examined cardiovascular effects of UFP in a controlled animal exposure on young, healthy WKY rats. Short-term exposure (24 h) to carbon UFPs (38 nm, 180 microg m (-3)), generated by spark discharging, induced a mild but consistent increase in heart rate (18 bpm, 4.8%), which was associated with a significant decrease in heart-rate variability during particle inhalation. The timing and the transient character of these responses point to a particle induced alteration of cardiac autonomic balance, mediated by a pulmonary receptor activation. After 24 h of inhalation exposure, bronchoalveolar lavage revealed significant but low-grade pulmonary inflammation (clean air 1.9% vs. UFPs 6.9% polymorphonuclear cells) and on histopathology sporadic accumulation of particle-laden macrophages was found in the alveolar region. There was no evidence of an inflammation-mediated increase in blood coagulability, as UFP inhalation did not induce any significant changes in plasma fibrinogen or factor VIIa levels and there were no prothrombotic changes in the lung or the heart at both the protein and mRNA level. Histological analysis revealed no signs of cardiac inflammation or cardiomyopathy. This study therefore provides toxicological evidence for UFP-associated pulmonary and cardiac effects in healthy rats. Our findings suggest that the observed changes are mediated by an altered sympatho-vagal balance in response to UFP inhalation, but do not support the concept of an inflammation-mediated prothrombotic state by UFP.
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Contaminantes Atmosféricos/toxicidad , Carbono/toxicidad , Enfermedades Cardiovasculares/etiología , Frecuencia Cardíaca/efectos de los fármacos , Exposición por Inhalación , Pulmón/inmunología , Animales , Líquido del Lavado Bronquioalveolar/inmunología , Enfermedades Cardiovasculares/veterinaria , Inflamación , Pulmón/patología , Macrófagos , Masculino , Tamaño de la Partícula , Ratas , Ratas WistarRESUMEN
Epidemiological studies of the past decades have provided a strong body of evidence that elevated levels of ambient particulate air pollution (PM) are associated with increased cardiovascular and respiratory morbidity and mortality. Exacerbations of ischemic and/or arrhythmic cardiac diseases have been linked to PM exposure. At a workshop held at the GSF- National Center for Environment and Health in November 2003, relevant epidemiological and toxicological data of the past 5 years were compiled and potential biological pathways discussed. Available clinical and experimental evidence lends support to the following mechanisms mediating cardiovascular effects of inhaled ambient particles: (i) pulmonary and/or systemic inflammatory responses inducing endothelial dysfunction, a pro-coagulatory state and promotion of atherosclerotic lesions, (ii) dysfunction of the autonomic nervous system in response to direct reflexes from receptors in the lungs and/or to local or systemic inflammatory stimuli, and (iii) cardiac malfunction due to ischemic responses in the myocardium and/or altered ion-channel functions in myocardial cells. While an increasing number of studies addressing these questions support the notion that PM exposure is associated with cardiovascular effects, these studies at present provide only a fragmentary and at times inconclusive picture of the complex biological pathways involved. The available data are consistent with the occurrence of a systemic inflammatory response and an alteration of autonomic cardiac control, but evidence on endothelial dysfunction, pro-coagulatory states, and PM-related myocardial malfunction is as yet scarce. Further studies are therefore needed to substantiate our current understanding of the pathophysiological links between PM exposure and adverse cardiovascular outcomes.
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Contaminación del Aire/efectos adversos , Enfermedades Cardiovasculares/etiología , Trastornos Respiratorios/etiología , Animales , Enfermedades del Sistema Nervioso Autónomo/epidemiología , Enfermedades del Sistema Nervioso Autónomo/etiología , Enfermedades Cardiovasculares/epidemiología , Endotelio Vascular/fisiopatología , Cardiopatías/epidemiología , Cardiopatías/etiología , Humanos , Pulmón/irrigación sanguínea , Tamaño de la Partícula , Trastornos Respiratorios/epidemiologíaRESUMEN
Cytochrome P450s and glutathione-S-transferases (GSTs) constitute two of the largest groups of enzyme families that are responsible for detoxification of exogenous molecules in plants. Their activities differ from plant to plant with respect to metabolism and substrate specificity which is one of the reasons for herbicide selectivity. In the tuber forming yam bean, the legume Pachyrhizus erosus, their activities at the microsomal level were investigated to determine the detoxification status of the plant. The breakdown of the herbicide isoproturon (IPU) to two distinct metabolites, 1-OH-IPU and monodesmethyl-IPU, was demonstrated. GST activity was determined with model substrates, but also by the catalysed formation of the fluorescent glutathione bimane conjugate. This study demonstrates for the first time microsomal detoxification activity in Pachyrhizus and the fluorescence image description of microsomal GST catalysed reaction in a legume.
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Glutatión Transferasa/metabolismo , Microsomas/enzimología , Pachyrhizus/enzimología , Herbicidas/farmacocinética , Inactivación Metabólica/fisiología , Cinética , Microscopía Fluorescente , Compuestos de Fenilurea/farmacocinética , Extractos Vegetales/aislamiento & purificación , Extractos Vegetales/metabolismo , Hojas de la Planta/enzimologíaRESUMEN
The molecular mechanism of how hepatocytes maintain cholesterol homeostasis has become much more transparent with the discovery of sterol regulatory element binding proteins (SREBPs) in recent years. These membrane proteins are members of the basic helix-loop-helix-leucine zipper (bHLH-Zip) family of transcription factors. They activate the expression of at least 30 genes involved in the synthesis of cholesterol and lipids. SREBPs are synthesized as precursor proteins in the endoplasmic reticulum (ER), where they form a complex with another protein, SREBP cleavage activating protein (SCAP). The SCAP molecule contains a sterol sensory domain. In the presence of high cellular sterol concentrations SCAP confines SREBP to the ER. With low cellular concentrations, SCAP escorts SREBP to activation in the Golgi. There, SREBP undergoes two proteolytic cleavage steps to release the mature, biologically active transcription factor, nuclear SREBP (nSREBP). nSREBP translocates to the nucleus and binds to sterol response elements (SRE) in the promoter/enhancer regions of target genes. Additional transcription factors are required to activate transcription of these genes. Three different SREBPs are known, SREBPs-1a, -1c and -2. SREBP-1a and -1c are isoforms produced from a single gene by alternate splicing. SREBP-2 is encoded by a different gene and does not display any isoforms. It appears that SREBPs alone, in the sequence described above, can exert complete control over cholesterol synthesis, whereas many additional factors (hormones, cytokines, etc.) are required for complete control of lipid metabolism. Medicinal manipulation of the SREBP/SCAP system is expected to prove highly beneficial in the management of cholesterol-related disease.
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Proteínas Potenciadoras de Unión a CCAAT/fisiología , Colesterol/metabolismo , Proteínas de Unión al ADN/fisiología , Homeostasis/fisiología , Factores de Transcripción/fisiología , Animales , Humanos , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Proteína 2 de Unión a Elementos Reguladores de EsterolesRESUMEN
BACKGROUND: Air pollution episodes are strongly associated with increased cardiovascular morbidity and mortality. The effect of ultrafine particles (UFPs), when translocated after inhalation, on the microcirculation of extrapulmonary organs remains unclear. METHODS AND RESULTS: In C57BL/6 mice, either carbon black UFPs (1x10(7) and 5x10(7)) or vehicle was infused intra-arterially. Two hours after infusion, platelet- and leukocyte-endothelial cell interactions, sinusoidal perfusion, endothelial fibrin(ogen) deposition, and phagocytic activity of Kupffer cells were analyzed by intravital video fluorescence microscopy in the liver microvasculature. Expression of fibrin(ogen), von Willebrand factor (vWF), and P-selectin on hepatic endothelium was determined by immunostaining. Apoptotic cells were quantified in TUNEL-stained tissue sections. Application of UFPs caused significantly enhanced platelet accumulation on endothelium of postsinusoidal venules and sinusoids in healthy mice. UFP-induced platelet adhesion was not preceded by platelet rolling but was strongly associated with fibrin deposition and an increase in vWF expression on the endothelial surface. In contrast, inflammatory parameters such as the number of rolling/adherent leukocytes, P-selectin expression/translocation, and the number of apoptotic cells were not elevated 2 hours after UFP exposure. In addition, UFPs did not affect sinusoidal perfusion and Kupffer cell function. CONCLUSIONS: UFPs induce platelet accumulation in the hepatic microvasculature of healthy mice that is associated with prothrombotic changes on the endothelial surface of hepatic microvessels. Accumulation of particles in the liver exerts a strong procoagulatory impact but does not trigger an inflammatory reaction and does not induce microvascular/hepatocellular tissue injury.
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Contaminantes Atmosféricos/toxicidad , Carbono/toxicidad , Circulación Hepática/efectos de los fármacos , Trombofilia/etiología , Administración por Inhalación , Animales , Apoptosis/efectos de los fármacos , Transporte Biológico , Plaquetas/fisiología , Células Endoteliales/fisiología , Fibrinógeno/metabolismo , Inflamación , Macrófagos del Hígado/fisiología , Leucocitos/fisiología , Ratones , Ratones Endogámicos C57BL , Microcirculación/efectos de los fármacos , Microscopía Fluorescente , Selectina-P/biosíntesis , Tamaño de la Partícula , Fagocitosis , Distribución Tisular , Factor de von Willebrand/biosíntesisRESUMEN
The use of many halogenated alkanes such as carbon tetrachloride (CCl4), chloroform (CHCl3) or iodoform (CHI3), has been banned or severely restricted because of their distinct toxicity. Yet CCl4 continues to provide an important service today as a model substance to elucidate the mechanisms of action of hepatotoxic effects such as fatty degeneration, fibrosis, hepatocellular death, and carcinogenicity. In a matter of dose,exposure time, presence of potentiating agents, or age of the affected organism, regeneration can take place and lead to full recovery from liver damage. CCl4 is activated by cytochrome (CYP)2E1, CYP2B1 or CYP2B2, and possibly CYP3A, to form the trichloromethyl radical, CCl3*. This radical can bind to cellular molecules (nucleic acid, protein, lipid), impairing crucial cellular processes such as lipid metabolism, with the potential outcome of fatty degeneration (steatosis). Adduct formation between CCl3* and DNA is thought to function as initiator of hepatic cancer. This radical can also react with oxygen to form the trichloromethylperoxy radical CCl3OO*, a highly reactive species. CCl3OO* initiates the chain reaction of lipid peroxidation, which attacks and destroys polyunsaturated fatty acids, in particular those associated with phospholipids. This affects the permeabilities of mitochondrial, endoplasmic reticulum, and plasma membranes, resulting in the loss of cellular calcium sequestration and homeostasis, which can contribute heavily to subsequent cell damage. Among the degradation products of fatty acids are reactive aldehydes, especially 4-hydroxynonenal, which bind easily to functional groups of proteins and inhibit important enzyme activities. CCl4 intoxication also leads to hypomethylation of cellular components; in the case of RNA the outcome is thought to be inhibition of protein synthesis, in the case of phospholipids it plays a role in the inhibition of lipoprotein secretion. None of these processes per se is considered the ultimate cause of CCl4-induced cell death; it is by cooperation that they achieve a fatal outcome, provided the toxicant acts in a high single dose, or over longer periods of time at low doses. At the molecular level CCl4 activates tumor necrosis factor (TNF)alpha, nitric oxide (NO), and transforming growth factors (TGF)-alpha and -beta in the cell, processes that appear to direct the cell primarily toward (self-)destruction or fibrosis. TNFalpha pushes toward apoptosis, whereas the TGFs appear to direct toward fibrosis. Interleukin (IL)-6, although induced by TNFalpha, has a clearly antiapoptotic effect, and IL-10 also counteracts TNFalpha action. Thus, both interleukins have the potential to initiate recovery of the CCl4-damaged hepatocyte. Several of the above-mentioned toxication processes can be specifically interrupted with the use of antioxidants and mitogens, respectively, by restoring cellular methylation, or by preserving calcium sequestration. Chemicals that induce cytochromes that metabolize CCl4, or delay tissue regeneration when co-administered with CCl4 will potentiate its toxicity thoroughly, while appropriate CYP450 inhibitors will alleviate much of the toxicity. Oxygen partial pressure can also direct the course of CCl4 hepatotoxicity. Pressures between 5 and 35 mmHg favor lipid peroxidation, whereas absence of oxygen, as well as a partial pressure above 100 mmHg, both prevent lipid peroxidation entirely. Consequently, the location of CCl4-induced damage mirrors the oxygen gradient across the liver lobule. Mixed halogenated methanes and ethanes, found as so-called disinfection byproducts at low concentration in drinking water, elicit symptoms of toxicity very similar to carbon tetrachloride, including carcinogenicity.