Dietary selenium (Se) and vitamin E (V(E)) supplementation modulated methylmercury-mediated changes in markers of cardiovascular diseases in rats.

Epidemiological studies demonstrated that human exposure to methylmercury (MeHg) may contribute to the development and progression of metabolic and cardiovascular disorders. However, the mechanisms involved and the role of selenium (Se) and vitamin E (V(E)) supplementation in modulating MeHg cardiovascular toxicities remain unclear. This study examined the effects of Se and V(E) supplementation on MeHg-mediated systemic oxidative stress, antioxidant defense, inflammation, and endothelial dysfunction in an animal model. Male Sprague-Dawley rats were fed a starch-based casein diet or the same diet supplemented with 1 or 3 mg Se/kg diet and with or without 250 or 750 mg V(E)/kg diet. After 28 days of dietary treatment, rats were gavaged with 0 or 3 mg MeHg/kg BW for 14 consecutive days. Results suggested that exposure to MeHg may increase the risk of cardiovascular disease by decreasing circulating paraoxonase-1 activities, increasing serum oxidized low density lipoprotein levels, and associated systemic inflammation and endothelial dysfunction as reflected by increased leukocyte counts and serum levels of intercellular adhesion molecule-1 and monocyte chemotactic protein-1. Se and V(E) supplementation may either alleviate or augment the effects of MeHg, depending on their doses and combinations.

Soy isoflavones modulate azoxymethane-induced rat colon carcinogenesis exposed pre- and postnatally and inhibit growth of DLD-1 human colon adenocarcinoma cells by increasing the expression of estrogen receptor-beta.

We studied the effects of lifetime exposure to dietary soy isoflavones in an azoxymethane (AOM)-induced rat colon cancer model. Male pups born to Sprague-Dawley rats exposed (including during pregnancy and lactation) to soy isoflavones at either no (0 mg = control), low (40 mg), or high (1000 mg) doses/kg diet were weaned and continued receiving their respective parental diets until the end of the study. Weaned rats received 2 subcutaneous injections (15 mg/kg body weight) of AOM 1 wk apart. After 26 wk, rats were killed and the coordinates of colon aberrant crypt foci (ACF) and tumors were determined. Expression of estrogen receptor (ER)-beta was assessed in rat colon tumors and in DLD-1 human colon adenocarcinoma cells exposed to soy isoflavones. Compared with the control, soy isoflavones did not affect incidences or multiplicities of colon ACF or tumors. Low-dose soy isoflavones decreased tumor burden and size compared with the control (P < 0.05). Expression of ERbeta increased in colon tumors of soy isoflavone-treated groups compared with the control. Soy isoflavones dose-dependently arrested the growth of DLD-1 cells and at subcytotoxic levels increased the expression of ERbeta. Our results suggest that pre- and postnatal exposure to dietary soy isoflavones suppresses the growth of colon tumors in male rats. The overexpression of ERbeta in both rat colon tumors and DLD-1 cells caused by soy isoflavones suggests that ERbeta is a critical mediator in mitigating its cancer-preventive effects.

Dietary fats altered nephrotoxicity profile of methylmercury in rats.

Weanling male Sprague-Dawley rats were administered semi-purified isocaloric diet containing soy oil (SO), seal oil (SE), docosahexaenoic acid (DHA), fish oil (FO) or lard (LA) for 28 days, and then gavaged with 0, 1 or 3 mg MeHg kg(-1) body weight per day and fed the same diet for 14 days. Serum and 24 h urine samples were collected on the day of necropsy, and analyzed for markers of kidney function and diseases. Kidney slices were analyzed for para-amino-hippurate (PAH) and tetraethylammonium (TEA) uptake, total mercury and MeHg content, and examined for pathological lesions. Total mercury and MeHg contents increased significantly and dose-dependently in all dietary groups. MeHg significantly increased relative kidney weight in all groups, serum creatinine in all except SO group, serum uric acid in the DHA and LA groups, serum Mg in all except the LA group, and urinary protein in the SO group. MeHg significantly decreased serum urea nitrogen in SE, FO and LA groups, urinary creatinine in the DHA group, PAH uptake in all except the SE group, and TEA uptake in all groups. MeHg caused nephrosis in all dietary groups. MeHg also significantly increased neutrophil counts in all except the SE group, decreased serum albumin and triglyceride in all except the DHA group, and increased serum total cholesterol in all groups, suggesting a nephrotic syndrome-like outcome. These results confirmed that kidney tubules are major targets of MeHg nephrotoxicity. Treatment with dietary fats did not prevent, but rather altered the profile of, nephrotoxicity of MeHg in rats.

Dietary fats modulate methylmercury-mediated systemic oxidative stress and oxidative DNA damage in rats.

We examined the effects of dietary fats on methylmercury (MeHg)-induced systemic oxidative stress and oxidative DNA damage in liver and kidney of male Sprague-Dawley rats. Rats were treated with a casein-based purified isocaloric diet containing 15% by weight soy oil, docosahexaenoic acid (DHA), seal oil, fish oil, or lard for 28 days, and then gavaged with 0, 1, or 3 mg MeHg/kg BW/day for 14 days. Urine was analyzed for 8-hydroxydeoxyguanosine (8-OHdG) and isoprostane, and serum for total antioxidant capacity (TAC). Liver and kidney were analyzed immunohistochemically for 8-OHdG. Both diet and MeHg showed significant main effects on some of these markers. As compared with the vehicle control, 3 mg MeHg/kg BW significantly increased urinary 8-OHdG in the lard group, urinary isoprostane in the DHA, seal oil, and fish oil groups, while significantly decreasing serum TAC in the lard and fish oil groups. In all dietary groups, 8-OHdG positive staining was located mainly in the nuclei of various cell types in liver and kidney. MeHg expressed a significant main increasing effect on 8-OHdG-positive cells in kidney. These results suggest that both dietary fats and MeHg are important mediators of systemic oxidative stress and oxidative DNA damage.

Effects of dietary fats and proteins on rat testicular steroidogenic enzymes and serum testosterone levels.

It is known that certain dietary fats can modulate rat testosterone metabolism. In the current study we have investigated testicular steroidogenic enzyme activities and serum testosterone levels in rats fed diets containing either different protein sources (casein, fishmeal, whey) or different lipid sources (soybean oil, docosahexaenoic acid (DHA), seal oil, fish oil, lard). The diets examined reflect different marine oils and proteins which are significant components of Northern Canadian diets. Male rats (42-45 days old, 6 per group), were assigned to specific diets for 42 days. On the 43rd day of the study, rats were sacrificed and blood plasma and testes frozen (-80 degrees C) until analysis. Microsomal steroidogenic enzyme activities (3beta-HSD, 17-OHase, C-17,20-lyase, 17beta-HSD) were measured radiometrically. There were no differences in enzyme activities between the three dietary protein sources. In contrast, compared with the standard casein diet, all lipid sources caused reductions in C-17,20-lyase activity (>50%); seal oil and fish oil reduced 17-OHase activity (approximately 30%) and soybean oil, DHA fish oil and lard reduced 17beta-HSD activity (approximately 30%). No effect on 3beta-HSD activity was evident. Serum testosterone levels were determined using ELISA kits and were not affected by any diet with the exception of the soybean oil diet which was significantly elevated compared with the casein protein diet. Body and testis weights were not affected by diet. In conclusion, these data demonstrate that some dietary lipid sources caused reductions in testicular 17-OHase and C-17,20-lyase activities but not to the extent that serum T levels were affected, while soybean oil caused elevated serum testosterone in the absence of elevated steroidogenic enzyme activities.

An investigation of the effects of methylmercury in rats fed different dietary fats and proteins: testicular steroidogenic enzymes and serum testosterone levels.

Methylmercury (MeHg) is a testicular toxicant causing reduced steroidogenic enzyme activity, reduced serum testosterone (T) and abnormal spermatogenesis in mammals and fowl. It is also known that certain diets can alter androgen metabolism in rats. Previously we have shown that diets used in the current study impact circulating androgen levels and testicular steroidogenic enzyme activities in Sprague Dawley rats in the absence of MeHg. In the present study, we have investigated the impact of imposing an environmental contaminant (MeHg) commonly found in marine mammals and fish onto the rats' dietary intake of different proteins and lipids in order to determine if the different diets could modify MeHg toxicity in rats. Therefore, we examined the effects of MeHg on testicular steroidogenic enzymes and serum testosterone in rats fed diets containing either different protein sources (casein, fishmeal, whey) or different lipid sources (soybean oil, docosahexaenoic acid (DHA), seal oil, fish oil, lard). Male rats 42-45 days of age (18 per group) were assigned to different experimental diets for 28 days after which 6 rats in each group were gavaged daily with 0, 1 or 3 mg/kg body weight (BW)/day MeHg chloride in 5 mM Na(2)CO(3) solution for 14 days while being maintained on their diets. On the 43rd day of dosing, rats were sacrificed and blood plasma and testes frozen (-80 degrees C) until analysis. Microsomal steroidogenic enzyme activities (3beta-HSD, 17-OHase, C-17, 20-lyase, 17beta-HSD) were measured radiometrically. Serum testosterone was determined using ELISA kits. Testis weights were not affected by MeHg. MeHg at 3 mg/kg BW/day caused a reduction (>50%) in the activity of C-17, 20-lyase in all three protein diets and similar reductions in 17-OHase activity were seen in the casein and whey protein fed rats. At 3 mg/kg BW/day, MeHg reduced 17-OHase activity in the DHA diet but had no effect on 3beta-HSD activity and no inhibitory effects on 17beta-HSD activity. MeHg (3 mg/kg BW/day) caused significant reductions in serum T in the whey, soybean oil and fish oil groups. Interestingly, fishmeal protein but not fish oil offered some protection with respect to maintaining steroidogenic enzyme activities and serum T levels in rats dosed with MeHg. In conclusion, these studies show that different lipid diets can alter the toxic effects of MeHg on male rat steroidogenesis in terms of serum testosterone and steroidogenic enzyme activities.

Modulating effects of dietary fats on methylmercury toxicity and distribution in rats.

Fish consumption is the most important source of human exposure to methylmercury (MeHg). Since fish is also a rich source of n-3 polyunsaturated fatty acids, this study was conducted to examine the effects of dietary fats on MeHg-induced acute toxicity in rats. Weanling male Sprague Dawley rats were administered semi-purified casein-based isocaloric diet containing soy oil, seal oil, docosahexaenoic acid (DHA), fish oil, or lard for 28 days. Rats were then gavaged with 0, 1, or 3 mg MeHg/kg body weight (BW) per day and fed the same diet for 14 consecutive days. On 43rd day of the experiment, rats were sacrificed and blood samples were collected and analyzed for hematology. Liver and spleen were removed, fixed, and examined for pathological changes. Blood, feces, liver, and brain were analyzed for total mercury and/or MeHg contents. Serum samples were analyzed for clinical markers of hepatic injury and immunoglobulin. Total mercury contents in all tissues measured increased with dose. Mercury excretion in feces increased with dose and duration of MeHg treatment. Both diets and MeHg showed significant effects and interacted significantly on many of the toxicological endpoints measured. Many of the effects of MeHg were diet-dependent. For example, in the rats fed the lard diet, 3mg MeHg/kg BW significantly increased relative liver and spleen weight as compared with vehicle control; whereas in rats fed the fish oil, soy oil, seal oil, or DHA, this effect of MeHg was less obvious or absent, suggesting a protective effect of these diets. MeHg at 3mg/kg BW significantly decreased serum albumin level in all except DHA dietary groups, implying a protection by the DHA diet on this parameter. Only in the lard dietary group, did 3mg MeHg/kg BW significantly increase serum bilirubin level, indicating an enhancing effect of this diet on MeHg toxicity. MeHg suppressed the adaptive immune system and stimulated the innate immune system in rats in a diet-dependent fashion. The seal oil diet provided more resistance, while the fish oil diet rendered greater sensitivity to these effects of MeHg on the immune system. These results imply significant modulating effects of dietary fats on MeHg toxicity which may translate into more severe or protective clinical outcomes. Therefore, dietary fats are important factors to be considered in the risk assessment of MeHg exposure.

Mammary gland tumor promotion in F1 generation offspring from male and female rats exposed to soy isoflavones for a lifetime.

The effect of dietary isoflavones in the form of NOVASOY (NS) was investigated on methylnitrosourea-initiated mammary gland cancer in F1 generation female Sprague Dawley rats from parents who had undergone lifetime exposure to variable levels of dietary NS. In comparison to NS-free dietary groups, lifetime exposure of F1 rats to 40 and 1000 mg/kg diets of NS reduced tumor latency, but did not significantly affect tumor incidence, tumor size, or tumor multiplicity. A significantly lower tumor multiplicity was, however, observed in rats fed the soy-based, NS-free diet compared to the casein-based, NS-free diet. An evaluation of a dose-response relationship pointed towards a biphasic effect, with a trend showing lower tumor incidence, lower tumor multiplicity, and lower tumor size in rats fed 1000 mg/kg diet NS compared to 40 mg/kg diet NS; however, the data failed to achieve statistical significance. Histologically, tumor type significantly differed according to the administered basal diet variety and NS dose. Our data and that of others provide conflicting evidence for chemopreventive effects of soy isoflavones on mammary gland tumor induction. We suggest standardization of interlaboratory experimental approaches for establishing low dose-response relationships for soy and its isoflavones to aid in risk assessment.