Reduction of mercury bioaccessibility using dietary strategies

P. Oliveira MB, Prieto MA. Health benefits of bluefin tuna consumption: (Thunnus thynnus) as a case study

Consumers are increasingly interested in food products with high nutritional value and health benefits. For instance, fish consumption is linked with diverse positive health benefits and the prevention of certain widespread disorders, such as obesity, metabolic syndrome, or cardiovascular diseases. These benefits have been attributed to its excellent nutritional value (large amounts of high-quality fatty acids, proteins, vitamins, and minerals) and bioactive compounds, while being relatively low-caloric. Atlantic bluefin tuna (Thunnus tynnus) is one of the most consumed species worldwide, motivated by its good nutritional and organoleptic characteristics. Recently, some organizations have proposed limitations on its consumption due to the presence of contaminants, mainly heavy metals such as mercury. However, several studies have reported that most specimens hold lower levels of contaminants than the established limits and that their richness in selenium effectively limits the contaminants' bioaccessibility in the human body. Considering this situation, this study aims to provide baseline data about the nutritional composition and the latest evidence regarding the beneficial effects of Atlantic bluefin tuna consumption. A review of the risk-benefit ratio was also conducted to evaluate the safety of its consumption, considering the current suggested limitations to this species' consumption.

Effects of foods and food components on the in vitro bioaccessibility of total arsenic and arsenic species from Hizikia fusiforme seaweed

Seaweed is an important food source, especially in many Asian countries, because of its high nutritional value; however, increasing arsenic (As) accumulation may pose serious hazards to human health. The influence of food components on As bioaccessibility and transformation in the high As-containing seaweed Hizikia fusiforme was determined using an in vitro gastrointestinal digestion method. The results showed that co-digestion with several daily foods (such as celery, broccoli, onion, green chili, tomato) produced a higher As bioaccessibility (approximately 6-11 % increase) compared with that of seaweed alone. Vegetables such as fennel (Foeniculum valgare Mill.), celery (Apium grareolens L.), blanched garlic leaves (Allium sativum L.), scallions (Allium fistulosum L.), ginger (Zingiber officinale Rosc.), and green pepper (Capsicum frutescens L. vat. grussum Bailey) decreased bioaccessible inorganic As (18-35 %) in both the gastric and small intestinal phases. Meanwhile, the process of reducing As(V) to As(III) also occurred during co-digestion with some food matrices. Egg white and other animal proteins were the most effective reducing agents, transforming >70 % As(V) into As(III) in the solution system. These results may have important implications for health risk assessment via co-consumption. The present study provides the first evidence showing that the co-consumption of some vegetables and proteins leads to a higher toxicity of inorganic arsenic-containing food. In addition, the positive and negative effects of co-digestion on the bioaccessibility of essential metals (iron, manganese) compared to single digestion were evaluated in this study.

Effects of cooking methods and co-ingested foods on mercury bioaccessibility in pontic shad (Alosa immaculata)

Human mercury (Hg) exposure is mostly caused by eating fish. However, there are major differences between the measured and predicted mercury concentration on Hg bioavailability. This study investigated the effects of cooking (steaming, baking, frying, marinating, and smoking) and selected components' co-ingestion on Hg bioaccessibility. Baking and frying reduced Hg bioaccessibility compared to the raw sample. The bioaccessible Hg fraction in fish was assessed through in vitro digestion method. Hg bioaccessibility varied from 4.31 to nearly 24.95% and the Hg recovery rate varied from 63.44 to 78.74%. Co-ingested garlic and broccoli with pontic shad had a positive effect on decreasing fish Hg bioaccessibility. The antioxidant activity of co-ingested food items was also calculated and correlated with mercury bioaccessibility. These results highlighted a possible positive role of plant-based foods and other food processing techniques in the bioaccessibility reduction of other chemical contaminants found in food sources.

Challenges and strategies for preventing intestinal damage associated to mercury dietary exposure

Food represents the major risk factor for exposure to mercury in most human populations. Therefore, passage through the gastrointestinal tract plays a fundamental role in its entry into the organism. Despite the intense research carried out on the toxicity of Hg, the effects at the intestinal level have received increased attention only recently. In this review we first provide a critical appraisal of the recent advances on the toxic effects of Hg at the intestinal epithelium. Next, dietary strategies aimed to diminish Hg bioavailability or modulate the epithelial and microbiota responses will be revised. Food components and additives, including probiotics, will be considered. Finally, limitations of current approaches to tackle this problem and future lines of research will be discussed.

In Vitro Bioaccessibility and Health Risk Assessment of Arsenic and Zinc Contaminated Soil Stabilized by Ferrous Sulfate: Effect of Different Dietary Components

Iron-based materials have good stability in reducing the mobility and toxicity of heavy metals, but the behavior and human health risks of heavy metals could be affected by dietary components. This study investigated the effect of typical diets (lettuce, cooked rice and apples) on the bioaccessibility and morphological changes of arsenic (As) and zinc (Zn) in contaminated site after stabilization by ferrous sulfate (FeSO4). The results showed that the bioaccessibility of As and Zn were increased in a co-digestion system of food. The augmented effect on As bioaccessibility mainly occurred in the gastric phase: apple > lettuce > cooked rice (p < 0.05), while the augmented effect on Zn bioaccessibility mainly occurred in the intestinal phase: lettuce > apple > cooked rice (p < 0.05). FeSO4 weakened the dissolution effect of dietary components on As bioaccessibility, and reduced As bioaccessibility in the gastric and intestinal phases by 34.0% and 37.9% (p < 0.05), respectively. Dietary components and Fe fractions influenced the speciation and distribution of As and Zn. FeSO4 reduced the hazard quotient (HQ) and carcinogenic risk (CR) values of the contaminated soil by 33.97% and 33.59%, respectively. This study provides a reference for a better understanding of more realistic strategies to modulate exposure risks of heavy metal-contaminated sites.

Mitigating the impact of mercury contaminants in fish and other seafood-A review

Mercury (Hg) is a well-known toxicant which enters the marine environment by both natural and anthropogenic sources. Consumption of fish and other seafood that contain methylmercury (MeHg) is a leading source of Hg exposure in humans. Considerable efforts have been made to mitigate the Hg presence and reduce its risks to humans. In this review the acknowledged methods of mitigation are summarized such as regulation and maximum allowable limits, and culinary treatments. In addition, selected industrial level trials are reviewed, and studies on Hg intoxication and the protective effects of the essential trace element, selenium (Se), are discussed. In view of the available literature, Hg reduction in fish and other seafood on a large industrial scale still is largely unsuccessful. Hence, more research and further attempts are necessary in order to better mitigate the Hg problem in fish and other seafood products.

Assessment of In Vitro Bioaccessibility and In Vivo Oral Bioavailability as Complementary Tools to Better Understand the Effect of Cooking on Methylmercury, Arsenic, and Selenium in Tuna

Fish consumption is the main exposure pathway of the neurotoxicant methylmercury (MeHg) in humans. The risk associated with exposure to MeHg may be modified by its interactions with selenium (Se) and arsenic (As). In vitro bioaccessibility studies have demonstrated that cooking the fish muscle decreases MeHg solubility markedly and, as a consequence, its potential absorption by the consumer. However, this phenomenon has yet to be validated by in vivo models. Our study aimed to test whether MeHg bioaccessibility can be used as a surrogate to assess the effect of cooking on MeHg in vivo availability. We fed pigs raw and cooked tuna meals and collected blood samples from catheters in the portal vein and carotid artery at: 0, 30, 60, 90, 120, 180, 240, 300, 360, 420, 480 and 540 min post-meal. In contrast to in vitro models, pig oral bioavailability of MeHg was not affected by cooking, although the MeHg kinetics of absorption was faster for the cooked meal than for the raw meal. We conclude that bioaccessibility should not be readily used as a direct surrogate for in vivo studies and that, in contrast with the in vitro results, the cooking of fish muscle did not decrease the exposure of the consumer to MeHg.

Influence of nutrients on the bioaccessibility and transepithelial transport of polybrominated diphenyl ethers measured using an in vitro method and Caco-2 cell monolayers

Previous research has shown the absorption of polybrominated diphenyl ethers (PBDEs) in the human gastrointestinal tract, but limited attention has been given to the influence of nutrients on PBDE absorption from food matrices. We investigated the effects of nutrients (oil, starch, protein, and dietary fiber) on the absorption and transport of PBDEs in a Caco-2 cell model and bioaccessibility of PBDEs by an in vitro gastrointestinal digestion method. The results showed that the accumulation ratios of PBDE congeners in Caco-2 cells were higher in the nutrient addition groups (oil: 26.7-50.6%, starch: 27.0-58.7%, protein: 12.1-44.1%, and dietary fiber: 28.2-55.1%) than the control group (7.17-36.1%), whereas the transport ratios were lower (oil: 2.30-7.20%, starch: 1.55-9.15%, protein: 1.04-8.78%, and dietary fiber: 0.85-7.04%) than control group (3.78-11.1%). Additionally, the PBDE bioaccessibility could be increased by adding the nutrients, particularly oil and starch. This study clarified the differences in PBDE absorption in the presence of nutrients using the in vitro digestion and Caco-2 cell model. The findings showed that nutrients were an important factor that promoted PBDE absorption in the gastrointestinal tract. Therefore, it is important to focus on a novel dietary strategy of food consumption with contaminant compounds to protect human health.

Green tea infusion reduces mercury bioaccessibility and dietary exposure from raw and cooked fish

Human exposure to mercury (Hg) and methylmercury (MeHg) through the ingestion of seafood raises human health-related concerns. In contrast, green tea has health benefits and its consumption potentially reduces bioaccessibility of dietary Hg. The present study aimed to assess the effect of green tea in total mercury (THg) and MeHg bioaccessibility in raw and cooked marine fish species commonly having high Hg levels. Preliminary results demonstrated that significantly higher reductions of bioaccessible THg were attained after the co-ingestion of green tea infusion (1 cup or more) in the oral and intestinal phases. Overall, the present findings clearly show that the co-ingestion of green tea along with seafood grilling strongly reduces THg and MeHg bioaccessibility in all fish species and consequently diminishes the probability of exceeding MeHg provisional tolerable weekly intakes through the consumption of these species with high Hg levels. Such results point out the need to better understand the beneficial/preventive role of green tea infusions and other food processing techniques in bioaccessibility reduction of other chemical contaminants present in food products. Such information is certainly useful to help consumers to wisely select their food, and to enable food safety authorities to integrate such information in risk assessment.

Use of Dietary Components to Reduce the Bioaccessibility and Bioavailability of Cadmium in Rice

Reducing Cd bioavailability in the systemic circulation is an alternative strategy to reduce Cd exposure. The influence of 39 dietary components on Cd bioaccessibility in water or rice was determined using an in vitro gastrointestinal model, following which an in vivo bioassay was used to determine the most effective components on Cd bioavailability in rice. The results showed that several components significantly reduced the solubility of Cd (10-98%) in the intestinal phase. Tannic acid, TiO₂, zinc gluconate, CaCl₂, and proanthocyanidins were the most effective in decreasing Cd bioaccessibility in rice, with reductions of 93-97, 54-61, 32-49, 24-32, and 11-14%, respectively. Upon adding the dietary components, the reduction rates of the Cd-relative bioavailability (Cd-RBA) were 20-58 and 10-31% in the kidneys and the liver, respectively. The results may have important implications for reducing health risks associated with Cd exposure via consumption of rice.

Does the addition of ingredients affect mercury and cadmium bioaccessibility in seafood-based meals?

Despite the bioaccessibility of nutrients and contaminants present in individual seafood products has been thoroughly studied, information is extremely limited in what concerns complete seafood-based meals, where interactions between ingredients may occur. Hence, this study aimed to evaluate the effect of different ingredients and cooking processes in mercury (Hg) and cadmium (Cd) bioaccessibility in complete meals of tuna (Thunnus spp.) and edible crab (Cancer pagurus), respectively. The addition of ingredients/side dishes decreased Hg levels in cooked tuna meals, but increased Hg bioaccessibility (up to 31% of bioaccessible Hg in complete meals, against 13.5% in stewed tuna alone). Cd levels in edible crab meals were significantly decreased by the addition of ingredients (~36% and ~65% decrease in boiled crab and paté, respectively), but its' bioaccessibility was not significantly affected (>94% in all cases). Results showed that the weekly consumption of 2 complete tuna meals does not exceed MeHg tolerable weekly intake (TWI), whereas Cd's TWI is largely surpassed with the consumption of 50 g/week of edible crab meals. This highlights the importance of determining contaminant levels and bioaccessibility in a whole seafood-based meal context, as such approach enables a more realistic assessment of the risks that seafood can pose to consumers.

Toxic trace elements in dried mushrooms: Effects of cooking and gastrointestinal digestion on food safety

Mushrooms can accumulate toxic trace elements. The objectives of the present study are to evaluate levels of mercury, cadmium, lead, and arsenic in dried mushrooms, to determine the effect of cooking on the contents of these elements, and to evaluate their bioaccessibility in the mushrooms ready for consumption. The results showed that Hg levels in Amanita ponderosa, Boletus edulis, Marasmius oreades, and Tricholoma georgii, as well as Cd levels in some samples of Amanita caesarea and T. georgii, exceeded the legislated limits. Cooking significantly reduced the levels of As (26-72%), whereas the reduction in levels of Hg, Cd, and Pb was much lower. However, the bioaccessibility of As (63-81%) was higher than the values obtained for the metals (<40%). Taking the effects of cooking and gastrointestinal digestion into account gives a more realistic estimate of the risk associated with the consumption of mushrooms.

Change in mercury speciation in seafood after cooking and gastrointestinal digestion

Mercury (Hg) is readily bioaccumulated in seafood, a common ingredient in indigenous cuisines throughout the world. This study investigates Hg speciation in cooked seafood after gastric and intestinal digestion. The results showed that the removal of Hg by washing was negligible. Additionally, the results of our calculations regarding the mass balance of Hg concentration indicated that cooking reduced Hg mainly by means of volatilization and that Hg²⁺ was more readily reduced than MeHg. Moreover, cooking lowered the bioaccessibility of Hg in seafood: the reduced percent of bioaccessible Hg²⁺ after cooking ranged from 2 to 35% (on average, 16%). The corresponding numbers were slightly lower compared with those for MeHg (on average, 19%). Furthermore, there might be a chemical transformation of Hg during in vitro gastrointestinal digestion. The results of in vivo tests in laboratory mice suggested that methylation of Hg mainly took place in the gastric tract, whereas demethylation of Hg occurred primarily during intestinal digestion. These findings indicate that the bioaccessibility of Hg²⁺ and MeHg was not only related to their initial concentrations in the food samples, but also that further studies on the mechanisms of Hg demethylation and methylation during gastrointestinal digestion are essential for more realistic risk assessments.

Reducing methylmercury accumulation in fish using Escherichia coli with surface-displayed methylmercury-binding peptides

Seafood consumption is widely considered as the primary route for human exposure to the neurotoxin methylmercury (MeHg) that is produced by certain anaerobic microorganisms and can bioaccumulate to high concentration levels in natural aquatic food webs. In this study, a novel methylmercury-binding peptide with seven amino acids was displayed on the cell surfaces of Escherichia coli strain W-1, which was isolated from fish feces and fused with ice nucleation protein. These cells exhibited high affinity and selectivity toward methylmercury. They efficiently removed more than 96% of 12 μM methylmercury, and accumulation of methylmercury in the engineered strain was four times higher than that in the wild type. Transmission electron microscopy confirmed methylmercury accumulation on cell membranes. Carassius auratus was fed by engineered bacteria, which showed a decrease in methylmercury concentration in muscles of about 36.3 ± 0.7%; whereas an increase in methylmercury concentration was observed in the feces (36.7 ± 0.8%) in comparison to the control group. The engineered strain in the gut captured methylmercury and prevented it's absorption by muscles, while some bacteria with methylmercury were excreted in the feces. The surface-engineered E. coli effectively protected fish from methylmercury contamination.

Dietary strategies to reduce the oral bioaccessibility of cadmium and arsenic in rice

The study aims to seek the dietary strategies to reduce the bioaccessibility of Cd and As in contaminated rice. A total of 12 selected food matrices were assayed by using the in vitro gastrointestinal digestion models. The results showed that tomato, carrot, water spinach, and spinach reduced the solubility of Cd by 45-78%, 50-71%, 53-70%, and 45-71%, respectively. Meanwhile, tomato, carrot, potato, and sweet potato reduced the solubility of As by 53-79%, 50-80%, 40-71%, and 36-76% in aqueous solution, respectively. In both gastric and gastrointestinal phases, Cd and As bioaccessibility decreased as the amount (100, 200, or 400 mg) of food matrices increased (except for As in water spinach). These results suggested that the uses of some foodstuffs may be a good dietary strategy to reduce Cd and As bioaccessibility, although in vivo studies are required to confirm their suitability.

Cooking and co-ingested polyphenols reduce in vitro methylmercury bioaccessibility from fish and may alter exposure in humans

Fish consumption is a major pathway for mercury exposure in humans. Current guidelines and risk assessments assume that 100% of methylmercury (MeHg) in fish is absorbed by the human body after ingestion. However, a growing body of literature suggests that this absorption rate may be overestimated. We used an in vitro digestion method to measure MeHg bioaccessibility in commercially-purchased fish, and investigated the effects of dietary practices on MeHg bioaccessibility. Cooking had the greatest effect, decreasing bioaccessibility on average to 12.5±5.6%. Polyphenol-rich beverages also significantly reduced bioaccessibility to 22.7±3.8% and 28.6±13.9%, for green and black tea respectively. We confirmed the suspected role of polyphenols in tea as being a driver of MeHg's reduced bioaccessibility, and found that epicatechin, epigallocatechin gallate, rutin and cafeic acid could individually decrease MeHg bioaccessibility by up to 55%. When both cooking and polyphenol-rich beverage treatments were combined, only 1% of MeHg remained bioaccessible. These results call for in vivo validation, and suggest that dietary practices should be considered when setting consumer guidelines for MeHg. More realistic risk assessments could promote consumption of fish as a source of fatty acids, which can play a protective role against cardiovascular disease.

In vitro evaluation of dietary compounds to reduce mercury bioavailability

Mercury in foods, in inorganic form [Hg(II)] or as methylmercury (CH₃Hg), can have adverse effects. Its elimination from foods is not technologically viable. To reduce human exposure, possible alternatives might be based on reducing its intestinal absorption. This study evaluates the ability of 23 dietary components to reduce the amount of mercury that is absorbed and reaches the bloodstream (bioavailability). We determined their effect on uptake of mercury in Caco-2 cells, a model of intestinal epithelium, exposed to Hg(II) and CH₃Hg standards and to swordfish bioaccessible fractions. Cysteine, homocysteine, glutathione, quercetin, albumin and tannic reduce bioavailability of both mercury species. Fe(II), lipoic acid, pectin, epigallocatechin and thiamine are also effective for Hg(II). Some of these strategies also reduce Hg bioavailability in swordfish (glutathione, cysteine, homocysteine). Moreover, extracts and supplements rich in these compounds are also effective. This knowledge may help to define dietary strategies to reduce in vivo mercury bioavailability.

Risk estimation to human health caused by the mercury content of Sushi and Sashimi sold in Japanese restaurants in Brazil

Although fish is a healthy alternative for meat, it can be a vehicle for mercury (Hg), including in its most toxic organic form, methylmercury (MeHg). The objective of the present study was to estimate the risk to human health caused by the consumption of sushi and sashimi as commercialized by Japanese food restaurants in the city of Campinas (SP, Brazil). The total Hg content was determined by atomic absorption spectrometry with thermal decomposition and amalgamation, and the MeHg content calculated considering that 90% of the total Hg is in the organic form. The health risk was estimated from the values for the provisional tolerable weekly ingestion (PTWI) by both adults and children. The mean concentrations for total Hg were: 147.99, 6.13, and 3.42 µg kg^-1 in the tuna, kani, and salmon sushi samples, respectively, and 589.09, 85.09, and 11.38 µg kg^-1 in the tuna, octopus and salmon sashimi samples, respectively. The tuna samples showed the highest Hg concentrations. One portion of tuna sashimi exceeded the PTWI value for MeHg established for children and adults. The estimate of risk for human health indicated that the level of toxicity depended on the type of fish and size of the portion consumed.

Use of Saccharomyces cerevisiae To Reduce the Bioaccessibility of Mercury from Food

Food is the main pathway of exposure to inorganic mercury [Hg(II)] and methylmercury (CH₃Hg). Intestinal absorption of these mercury species is influenced by their chemical form, the luminal pH, and the composition of the diet. In this regard, strategies have been proposed for reducing mercury absorption using dietary components. This study evaluates the capacity of Saccharomyces cerevisiae to reduce the amount of mercury solubilized after gastrointestinal digestion that is available for intestinal absorption (bioaccessibility). The results show that S. cerevisiae strains reduce mercury bioaccessibility from aqueous solutions of Hg(II) (89 ± 6%) and CH₃Hg (83 ± 4%), and from mushrooms (19-77%), but not from seafood. The formation of mercury-cysteine or mercury-polypeptide complexes in the bioaccessible fraction may contribute to the reduced effect of yeasts on mercury bioaccessibility from seafood. Our study indicates that budding yeasts could be useful for reducing the extent of intestinal absorption of mercury present in water and some food matrices.