Environmental mercury and its toxic effects.

Mercury exists naturally and as a man-made contaminant. The release of processed mercury can lead to a progressive increase in the amount of atmospheric mercury, which enters the atmospheric-soil-water distribution cycles where it can remain in circulation for years. Mercury poisoning is the result of exposure to mercury or mercury compounds resulting in various toxic effects depend on its chemical form and route of exposure. The major route of human exposure to methylmercury (MeHg) is largely through eating contaminated fish, seafood, and wildlife which have been exposed to mercury through ingestion of contaminated lower organisms. MeHg toxicity is associated with nervous system damage in adults and impaired neurological development in infants and children. Ingested mercury may undergo bioaccumulation leading to progressive increases in body burdens. This review addresses the systemic pathophysiology of individual organ systems associated with mercury poisoning. Mercury has profound cellular, cardiovascular, hematological, pulmonary, renal, immunological, neurological, endocrine, reproductive, and embryonic toxicological effects.

Long-term efficacy of deferasirox in preventing cardiovascular complications in the iron-overloaded gerbil.

Iron-induced cardiovascular disease is the leading cause of death in iron-overloaded patients. Deferasirox is a novel tridentate oral chelator that exhibits a half-life suitable for once-daily dosing; however, little is known regarding the effectiveness of this agent in preventing iron-induced cardiovascular disease. Adult male Mongolian gerbils were randomly divided into 3 groups: control, iron overload, and iron overload followed by deferasirox treatment. Iron-overloaded animals received iron dextran 100 mg/kg intraperitoneally (ip)/5 days for 10 weeks, while deferasirox was given 100 mg/kg per d orally (po) for 9 months post iron loading. Cardiac and aortic iron levels were determined by inductively coupled plasma atomic emission spectrometry. Gerbil electro- and echocardiograms were obtained in anesthetized animals at regular intervals. Compared to control animals, iron concentration was 3.3- and 2.4-fold higher in iron-overloaded heart and aorta, respectively (P < .05). Deferasirox treatment reduced cardiac and aortic iron levels by 32% and 35%, respectively (P < .05). These results were consistent with the decrease in cellular iron deposition observed with Prussian Blue iron staining. Iron-overloaded gerbils were found to exhibit frequent arrhythmias including premature ventricular contractions, supraventricular tachycardia, and recurrent ventricular tachycardia. In addition, echocardiographic assessment demonstrated iron overload-associated increase in left ventricular dimensions including left ventricular posterior wall dimension (LVPWd: 49%), left ventricular internal dimension (LVIDd: 26%), and left ventricular septum thickness (LVSd: 42%). These parameters were significantly reduced with deferasirox treatment (LVPWd: 23%, LVIDd: 24%, and LVSd: 27%). Iron overload was also associated with reduced ejection fraction (EF: by 30%) and fractional shortening (FS: by 23%) in comparison with controls (P < .05). With deferasirox treatment, these values were higher (EF: by 30%, FS: by 28%) compared to iron-overloaded group. These findings suggest that deferasirox may be useful for attenuating iron-induced changes in cardiac structure and function.

Deferasirox protects against iron-induced hepatic injury in Mongolian gerbil.

Iron overload is associated with an increased risk of liver complications including fibrosis, cirrhosis, and hepatocellular carcinoma. Deferasirox is a new oral chelator with high iron-binding potency and selectivity. Here we investigate the ability of deferasirox to remove excessive hepatic iron and prevent iron-induced hepatic injury. Adult male Mongolian gerbils were divided into 3 groups (n=5/group)-control, iron overload (100 mg iron-dextran/kg body weight/5 days; intraperitoneal for 10 weeks), and iron overload followed by deferasirox treatment (100 mg deferasirox/kg body weight/d; pulse oral for 1 or 3 months). Compared with the nontreated iron overload group, deferasirox reduced hepatic iron concentration by 44% after 3 months of treatment (P<0.05). Histological analysis of hepatic tissue from the iron overloaded group detected frequent iron deposition, evidence of hepatic damage, and an accumulation of lipid vacuoles. Iron deposition was significantly diminished with deferasirox treatment, and no evidence of lipid accumulation was observed. Immunoblotting demonstrated that iron overload caused approximately 2-fold increase in hepatic ferritin expression (P<0.05), which was 48% lower after 3 months of deferasirox treatment (P<0.05). Deferasirox treatment also was associated with reduced hepatic protein oxidation, superoxide abundance, and cell death. The percentage of terminal deoxynucleotidyl transferase dUTP nick end labeling positive cells in the deferasirox-treated livers was 41% lower than that of iron overloaded group (P<0.05). Similarly, an iron-related increase in the expression of Bax/Bcl2, Bad, and caspase-3 were significantly lower after deferasirox treatment. These findings suggest that deferasirox may confer protection against iron-induced hepatic toxicity.

Chronic acetaminophen attenuates age-associated increases in cardiac ROS and apoptosis in the Fischer Brown Norway rat.

There is a growing need for pharmacological agents to manage cardiovascular disease in the rapidly growing elderly population. Here, we determine if acetaminophen is efficacious in decreasing age-related increases in cardiac reactive oxygen species (ROS) and apoptosis in aging Fischer 344 X Brown Norway rats. Compared to 6-month control animals, indices of oxidative (superoxide anion [O2( *-)] and 4-hydroxy-2-nonenal [4-HNE]) and nitrosative (protein nitrotyrosylation) stress were markedly increased in 33-month-old rat hearts. 33-month animals that had been treated with acetaminophen (30 mg/kg/day p.o. for 6 months) exhibited diminished age-related increases in cardiac ROS levels and TUNEL positive nuclei and these changes were accompanied by improvements in the Bax/Bcl2 ratio, diminished evidence of caspase-3 activation and increased phosphorylation of protein kinase B, ERK1/2, p70S6K and GSK-3beta. Taken together these results suggests that acetaminophen may attenuate the age-associated increases in the cardiomyocyte apoptosis, possibly via diminishing age associated elevation in ROS production.

Deferasirox decreases age-associated iron accumulation in the aging F344XBN rat heart and liver.

It is thought that aging in rats and humans is associated with increases in iron accumulation and cell apoptosis. Here, we examine the relationship between cardiac iron levels and apoptosis in aged F344XBN rats that had been treated with an oral iron chelator (Deferasirox; 100 mg/kg body weight) on alternate days for 6 months. Compared to adult animals (6 month), cardiac iron (+72%), liver iron (+87%), ferritin light chain (+59%), divalent metal transporter-1 (+56%) and the number of TdT-mediated dUTP nick end labeling (TUNEL) positive cells (4.3 fold increase) were higher in 33-month-old animals (P < 0.05). Deferasirox treatment decreased cardiac iron levels by 37% (P < 0.05), and this was associated with decreases in the number of TUNEL-positive cells. Age-associated increases in cell death were coupled with increases in Bax to Bcl-2 ratio, and the amount of Bad, full-length caspase-3, and cleaved caspase-3. Deferasirox treatment decreased the Bax to Bcl-2 ratio by 17% (P < 0.05) and the amount of Bad, full-length caspase-3, cleaved caspase-3 (19 kDa), and cleaved caspase-3 (17 kDa) by 41, 16, 22, and 37%, respectively (P < 0.05). Taken together, these data suggest that deferasirox may be effective in diminishing age-associated iron accumulation and cardiac apoptosis in the F344XBN rat model.

Fluprostenol-induced MAPK signaling is independent of aging in Fischer 344/NNiaHSd x Brown Norway/BiNia rat aorta.

The factors that regulate vascular mechanotransduction and how this process may be altered with aging are poorly understood and have not been widely studied. Recent data suggest that increased tissue loading can result in the release of prostaglandin F2 alpha (PGF2alpha) and other reports indicate that aging diminishes the ability of the aged aorta to activate mitogen activated protein kinase (MAPK) signaling in response to increased loading. Using ex vivo incubations, here we investigate whether aging affects the ability of the aorta to induce phosphorylation of extracellular signal-regulated kinase 1/2 (ERK(1/2)-MAPK), p38-MAPK, and Jun N-terminal kinase (JNK-MAPK) activation following stimulation with a PGF2alpha analog, fluprostenol. Compared to aortas from 6-mo animals, the amounts of ERK(1/2)- and p38-MAPK remained unchanged with aging, while the level of JNK-MAPK protein increased by 135% and 100% at 30- and 36-mo, respectively. Aging increased the basal phosphorylation of ERK(1/2) (115% and 47%) and JNK (29% and 69%) (p <0.05) in 30- and 36-mo aortas, while p38 phosphorylation levels remained unaltered. Compared to age-matched controls, fluprostenol induced phosphorylation of ERK(1/2) (310%, 286%, and 554%), p38-MAPK (unchanged, 48%, and 148%), and JNK (78%, 88%, and 95%) in 6-, 30- and 36-mo aortas, respectively. These findings suggest that aging does not affect the ability of the rat aorta to activate ERK(1/2)-, p38-MAPK, and JNK-MAPK phosphorylation in response to PGF2alpha stimulation.

Acetaminophen combinations protect against iron-induced cardiac damage in gerbils.

This study tested if acetaminophen, N-methyl-D-glucamine dithiocarbamate (NMGDTC), deferoxamine, and combinations of these agents reduce excess iron content, prevent iron-induced pathology, reduce cardiac arrhythmias, and reduce mortality in iron-overloaded gerbils. Eight groups of 16 gerbils received iron dextran injections (ferric hydroxide dextran complex, 120 mg/kg, ip) or saline solution (controls) twice/wk for 8 wk. The 8 groups were treated every Monday, Wednesday, and Friday with one of the following: saline control, acetaminophen, 150 mg/kg, ip), acetaminophen (150 mg/kg, po), deferoxamine, 83 mg/kg, ip), NMGDTC (200 mg/kg, ip), or combinations of acetaminophen (75 mg/kg) with deferoxamine (42 mg/kg, each ip, separately) or acetaminophen (75 mg/kg) with NMGDTC (100 mg/kg, each ip, separately). The treatments were given 4 hr after each iron injection on days when both iron administration and treatment occurred during iron overloading (8 wk) and were continued 4 wk thereafter. Echocardiography (ECHO) was used to evaluate iron-induced cardiac changes and detect arrhythmias. Acetaminophen and NMGDTC, or combinations thereof, reduced cardiac and hepatic excess iron content as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). Acetaminophen was effective whether administered po or ip. Acetaminophen treatment had a positive inotropic effect on cardiac function. Acetaminophen-deferoxamine combination conferred equal cardioprotection as acetaminophen or deferoxamine alone, was equally able to remove hepatic iron, and was superior to either acetaminophen or deferoxamine in removing cardiac iron from iron-overloaded gerbils. Acetaminophen-NMGDTC combination was also effective in removing cardiac and hepatic iron and protecting against iron-induced cardiac damage. ECHO evaluation of iron-overloaded, untreated gerbils demonstrated a high incidence of cardiac arrhythmias, usually PVCs (10/16 = 63%), and mortality prior to completion of the experiment (4/16 = 25%). All treatments except deferoxamine, alone, reduced the incidence of cardiac arrhythmias and deaths. All treatments reduced iron-induced increases in hepatic and cardiac weights. This study demonstrates injection alternates that are equally or more effective than deferoxamine injections and shows oral acetaminophen to be effective in treatment of iron-overload and associated cardiac complications.

Deferasirox removes cardiac iron and attenuates oxidative stress in the iron-overloaded gerbil.

Iron-induced cardiovascular disease is the leading cause of death in iron-overloaded patients. Deferasirox is a novel, once daily oral iron chelator that was recently approved for the treatment of transfusional iron overload. Here, we investigate whether deferasirox is capable of removing cardiac iron and improving iron-induced pathogenesis of the heart using the iron overload gerbil model. Animals were randomly divided into three groups: control, iron overload, and iron overload + deferasirox treatment. Iron-dextran was given 100 mg/kg per 5 days i.p for 10 weeks. Deferasirox treatment was taken post iron loading and was given at 100 mg/kg/day p.o for 1 or 3 months. Cardiac iron concentration was determined by inductively coupled plasma atomic emission spectroscopy. Compared with the untreated group, deferasirox treatment for 1 and 3 months decreased cardiac iron concentration 17.1% (P = 0.159) and 23.5% (P < 0.05), respectively. These treatment-associated reductions in cardiac iron were paralleled by decreases in tissue ferritin expression of 20% and 38% at 1 and 3 months, respectively (P < 0.05). Using oxyblot analysis and hydroethidine fluorescence, we showed that deferasirox significantly reduces cardiac protein oxidation and superoxide abundance by 36 and 47.1%, respectively (P < 0.05). Iron-induced increase in oxidative stress was also associated with increased phosphorylation of ERK-, p38-, and JNK-mitogen-activated protein kinase (MAPK). Interestingly, deferasirox treatment significantly diminished the phosphorylation of all three MAPK subfamilies. These results suggest that deferasirox may confer a cardioprotective effect against iron induced injury.

Acetaminophen prevents aging-associated hyperglycemia in aged rats: effect of aging-associated hyperactivation of p38-MAPK and ERK1/2.

BACKGROUND: Aging-related hyperglycemia is associated with increased oxidative stress and diminished muscle glucose transporter-4 (Glut4) that may be regulated, at least in part, by the mitogen-activated protein kinases (MAPK). METHODS: To test the possibility that aging-related hyperglycemia can be prevented by pharmacological manipulation of MAPK hyperactivation, aged (27-month old) Fischer 344/NNiaHSD x Brown Norway/BiNia F1 (F344BN) rats were administered acetaminophen (30 mg/kg body weight/day) for 6 months in drinking water. RESULTS: Hepatic histopathology, serum aspartate aminotransferase and alanine aminotransferase analyses suggested that chronic acetaminophen did not cause hepatotoxicity. Compared with adult (6-month) and aged (27-month) rats, very aged rats (33-month) had higher levels of blood glucose, phosphorylation of soleus p38-MAPK and extracellular-regulated kinase 1/2 (ERK1/2), superoxide and oxidatively modified proteins (p<0.05), and these changes were associated with decreased soleus Glut4 protein abundance (p<0.05). Chronic acetaminophen treatment attenuated age-associated increase in blood glucose by 61.3% (p<0.05) and increased soleus Glut4 protein by 157.2% (p<0.05). These changes were accompanied by diminished superoxide levels, decrease in oxidatively modified proteins (-60.8%; p<0.05) and reduced p38-MAPK and ERK1/2 hyperactivation (-50.4% and -35.4%, respectively; p<0.05). CONCLUSIONS: These results suggest that acetaminophen may be useful for the treatment of age-associated hyperglycemia.

Adaptation of Haplobothrium globuliforme (Cestoda: Pseudophyllidea) to the intestinal architecture of the bowfin (Amia calva L).

Haplobothrium globuliforme maintains its position in the proximal mid-gut epithelium of Amia calva with the aid of tentacles, i.e., proboscides, everted from scolices of a primary strobila and craspedote proglottids of a secondary strobila. Weakly developed scolices of the secondary strobila appear to have little holdfast action, but the distinctly craspedote proglottids of these individuals project into the intestinal mucosa, altering the configuration of gut epithelial cells and pushing the tapeworm deeper into mucosal crypts. The basement membrane underlying the epithelium appears to act as a barrier that prevents tapeworms from penetrating into the deeper tissue layers of the lamina propria, muscularis mucosa, or submucosa. Scolex tegument modification occurs at the point of contact with host basement membrane. A mild background infiltrate of lymphocytes and granulocytes was evident adjacent to the scolex and proglottid tegument. There was no evidence of blood vessel proliferation, edema, mast cell degranulation, eosinophilia, or subsequent collagen formation associated with tapeworm activity.

Aging influences multiple indices of oxidative stress in the heart of the Fischer 344/NNia x Brown Norway/BiNia rat.

We report the influence of aging on multiple markers of oxidative-nitrosative stress in the heart of adult (6-month), aged (30-month) and very aged (36-month) Fischer 344/NNiaHSd x Brown Norway/BiNia (F344/NXBN) rats. Compared to adult (6-month) hearts, indices of oxidative (superoxide anion [O2*-], 4-hydroxy-2-nonenal [4-HNE]) and nitrosative (protein nitrotyrosylation) stress were 34.1 +/- 28.1%, 186 +/- 28.1% and 94 +/- 5.8% higher, respectively, in 36-month hearts and these findings were highly correlated with increases in left ventricular wall thickness (r > 0.669; r > 0.710 and P < 0.01, respectively). Regression analysis showed that increases in cardiac oxidative-nitrosative stress with aging were significantly correlated with changes in the expression and/or regulation of proteins involved in transcriptional (NF-kappaB) activities, signaling (mitogen-activated protein kinases along with Src), apoptotic (Bcl-2, Traf-2), and cellular stress (HSPs). These results suggest that the aging F344/NXBN heart may be highly suited for unraveling the molecular events that lead to age-associated alterations in cardiac oxidative stress.

Acetaminophen protects against iron-induced cardiac damage in gerbils.

There are few effective agents that safely remove excess iron from iron-overloaded individuals. Our goal was to evaluate the iron-removing effectiveness of acetaminophen given ip or orally in the gerbil iron-overload model. Male gerbils were divided into 5 groups: saline controls, iron-overloaded controls, iron-overloaded treated with ip acetaminophen, iron-overloaded treated with oral acetaminophen, and iron-overloaded treated with ipdeferoxamine. Iron dextran was injected iptwice/wk for 8 wk. Acetaminophen and deferoxamine treatments were given on Mondays, Wednesdays, and Fridays during the same 8 wk and continued for 4 wk after completion of iron-overloading. Echocardiograms were performed after completion of the iron-overloading and drug treatments. Liver and cardiac iron contents were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Iron-overloaded controls had 232-fold and 16-fold increases in liver and cardiac iron content, respectively, compared to saline controls. In iron-overloaded controls, echocardiography showed cardiac hypertrophy, right and left ventricular distension, significant reduction in left ventricular ejection fraction (-22%), and fractional shortening (-31%) during systole. Treatments with acetaminophen (ip or oral) or deferoxamine (ip) were equally effective in reducing cardiac iron content and in preventing cardiac structural and functional changes. Both agents also significantly reduced excess hepatic iron content, although acetaminophen was less effective than deferoxamine. The results suggest that acetaminophen may be useful for treatment of iron-induced pathology.

Age-associated changes in hearts of male Fischer 344/Brown Norway F1 rats.

Aging is associated with left ventricular hypertrophy, dilatation, and fibrosis of the heart. The Fischer 344/Brown Norway F1 (F344/BNF1) rat is recommended for age-related studies by the National Institutes on Aging because this hybrid rat lives longer and has a lower rate of pathological conditions than inbred rats. However, little is known about age-associated changes in cardiac and aortic function and structure in this model. This study evaluated age-related cardiac changes in male F344/BNF1 rats using ECHO, gross, and microscopic examinations. Rats aged 6-, 30-, and 36-mo were anesthetized and two-dimensional ECHO measurements, two-dimensional guided M-mode, Doppler M-mode, and other recordings from parasternal long- and short-axis views were obtained using a Phillips 5500 ECHO system with a 12 megahertz transducer. Hearts and aortas from sacrificed rats were evaluated grossly and microscopically. The ECHO studies revealed persistent cardiac arrhythmias (chiefly PVCs) in 72% (13/18) of 36-mo rats, 10% (1/10) of 30-mo rats, and none in 6-mo rats (0/16). Gross and microscopic studies showed left ventricular (LV) dilatation, borderline to mild hypertrophy, and areas of fibrosis that were common in 36-mo rats, less evident in 30-mo rats, and absent in 6-mo rats. Aging was associated with mild to moderate decreases of LV diastolic and systolic function. Thus, male F344/BN F1 rats demonstrated progressive age-related (a) decline in cardiac function (diastolic and systolic indices), (b) LV structural changes (chamber dimensions, volumes, and wall thicknesses), and (c) persistent arrhythmias. These changes are consistent with those in humans. The noninvasive ECHO technique offers a means to monitor serial age-related cardiac failure and therapeutic responses in the same rats over designated time intervals.

Increased sensitivity of the obese Zucker rat to deoxycorticosterone-salt-induced hypertension.

OBJECTIVE: The objective of this study was to test the hypothesis that obesity increases the sensitivity of rats to experimentally induced hypertension. DESIGN AND METHODS: To induce hypertension, unilaterally nephrectomized lean and obese Zucker rats were injected with 25 mg/kg of deoxycorticosterone acetate (DOCA) twice weekly for 5 weeks and given water containing 1% NaCl to drink. Unilaterally nephrectomized control rats were injected with vehicle and drank tap water. Systolic blood pressure (SBP) was measured by the tail cuff method. Renal histology and urinary albumin excretion were used to assess the effects of the experimental treatment on the kidney. RESULTS: Obese rats exhibited a significant rise in SBP at 4 days after the start of DOCA-salt treatment. In contrast, SBP of DOCA-treated lean rats was not significantly elevated from pretreatment measurements until day 22. Moreover, SBP was significantly higher during the plateau phase of blood pressure development in obese DOCA-salt treated rats (196 mmHg) than in correspondingly treated lean rats (150 mmHg). Both obesity and DOCA-salt treatment promoted glomerulosclerosis and mild tubulointerstitial damage in the kidney with DOCA-salt treatment exacerbating the effect of obesity. Urinary albumin excretion was significantly greater in obese control rats compared with lean controls and in DOCA-treated obese rats relative to vehicle-treated obese rats. CONCLUSION: Results of this study indicate that obese Zucker rats are more sensitive to mineralocorticoid-induced hypertension than lean rats. This study provides experimental evidence supporting the epidemiological findings that obesity is a risk factor for the development of hypertension.