Relationship between mortality and rice cadmium concentration in inhabitants of the polluted Jinzu River basin, Toyama, Japan: A 26 year follow-up

Transcriptomics integrated with metabolomics unravels the interweaving of inflammatory response and 1-stearoyl-2-arachidonoyl-sn-glycerol metabolic disorder in chronic cadmium exposure-induced hepatotoxicity

Chronic Cd exposure induces an inflammatory response that contributes to liver damage. In the present study, C57BL/6J mice (8 weeks) were administered CdCl₂ (0.6mg/L) orally for 6 months, and the underlying mechanism of chronic Cd-induced hepatotoxicity was explored through the application of transcriptomics and metabolomics. Chronic Cd exposure induced focal necrosis and inflammatory cell infiltration in the livers of mice. Importantly, hepatic IL-1β, IL-6, IL-9, IL-10, IL-17 and GM-CSF levels were significantly increased following chronic Cd exposure. Ingenuity Pathway Analysis of the transcriptomics profiles combined with RTqPCR was used to identify and optimize a crucial inflammatory response network in chronic Cd hepatotoxicity. Furthermore, an integrative analysis combining inflammatory response genes with differential metabolites revealed that 1-stearoyl-2-arachidonoyl-sn-glycerol and 4-hydroxybutanoic acid lactone levels were significantly correlated with all inflammatory response genes. Overall, our findings in this study help decipher the underlying mechanisms and key molecular events of chronic Cd hepatotoxicity.

Nodes play a major role in cadmium (Cd) storage and redistribution in low-Cd-accumulating rice (Oryza sativa L.) cultivars

Rice cadmium (Cd) contamination is one of the critical agricultural issues. Breeding of low-Cd-accumulating cultivar is an effective approach to reduce Cd bioaccumulation in rice. To investigate the molecular mechanism underlying Cd transport in rice, the functions of nodes in Cd transport are explored. The results show that different nodes have different functions of Cd transport in the rice plant and the physiological structure of the first node under panicle (N1) determine the Cd accumulation in the brown rice. The upper nodes can redistribute the Cd transport in aboveground tissues. The expressions of Cd-efflux transporter genes (OsLCT1 and OsHMA2) located on the plasma-membrane are the main factors affecting the Cd transport form node to brown rice, which are more depended on the node functions but not the node Cd concentrations. Lower expressions of OsLCT1 and OsHMA2 in N1 result in lower Cd transport from node to brown rice. The size of vascular-bundle (VB) areas in the junctional node with the flag leaf can determine the expression of OsHMA2 and the expression of OsLCT1 positively correlated with the Cd transport ability of first node (N1). The expressions of OsVIT2 and OsABCC1 cannot allow Cd to be immobilized into the vacuoles in node. The VB structure and Cd transporter gene expression level of N1 proved that the Cd concentration of N1 can be used as an important indicator for screening low-Cd-accumulating cultivars. The major implication is that selecting or breeding cultivars with lower Cd accumulations in N1 could be an effective strategy to reduce Cd accumulation in rice grains.

Estimation of health risks associated with dietary cadmium exposure

In much of the world, currently employed upper limits of tolerable intake and acceptable excretion of cadmium (Cd) (ECd/Ecr) are 0.83 µg/kg body weight/day and 5.24 µg/g creatinine, respectively. These figures were derived from a risk assessment model that interpreted β2-microglobulin (β2MG) excretion > 300 μg/g creatinine as a "critical" endpoint. However, current evidence suggests that Cd accumulation reduces glomerular filtration rate at values of ECd/Ecr much lower than 5.24 µg/g creatinine. Low ECd/Ecr has also been associated with increased risks of kidney disease, type 2 diabetes, osteoporosis, cancer, and other disorders. These associations have cast considerable doubt on conventional guidelines. The goals of this paper are to evaluate whether these guidelines are low enough to minimize associated health risks reliably, and indeed whether permissible intake of a cumulative toxin like Cd is a valid concept. We highlight sources and levels of Cd in the human diet and review absorption, distribution, kidney accumulation, and excretion of the metal. We present evidence for the following propositions: excreted Cd emanates from injured tubular epithelial cells of the kidney; Cd excretion is a manifestation of current tissue injury; reduction of present and future exposure to environmental Cd cannot mitigate injury in progress; and Cd excretion is optimally expressed as a function of creatinine clearance rather than creatinine excretion. We comprehensively review the adverse health effects of Cd and urine and blood Cd levels at which adverse effects have been observed. The cumulative nature of Cd toxicity and the susceptibility of multiple organs to toxicity at low body burdens raise serious doubt that guidelines concerning permissible intake of Cd can be meaningful.

A 30-year follow-up study in a former cadmium-polluted area of Japan: the relationship between cadmium exposure and β2-microglobulin in the urine of Japanese people

Cadmium (Cd) is an environmental pollutant. Long-term exposure to Cd may lead to adverse health effects in humans. Our epidemiological studies showed that urinary Cd (U-Cd) concentrations increased from 2008 through 2014, although they decreased from 1986 through 2008. The aim of this study was to elucidate the long-term effects of the changing trend of cadmium exposure levels (U-Cd) on residents' renal function within 30 years after Cd exposure ceased. In 2016, urine samples were collected from each subject by visiting 20 elderly Japanese people (9 females and 11 males) living in the Kakehashi River basin, a previously Cd-polluted area in Ishikawa, Japan. The geometric means of the β₂-microglobulin (β₂-MG) and urinary Cd (U-Cd) continued to increase from 2014 until 2016. Furthermore, Cd concentration and β₂-MG in urine were still higher than those in the non-polluted areas in Japan. Multivariate linear regression was performed to associate β₂-MG (dependent variable) and U-Cd with sex and age (independent variables). Significant correlations were found among age, U-Cd, and β₂-MG, and these were clearer in females than in males. In summary, we propose that three decades after Cd exposure ceased, age is associated with β₂-MG more strongly than Cd for bodily impact. Moreover, renal tubular dysfunction is irreversible and worsens after exposure to Cd, with females being more sensitive to exposure.

Speciation, transportation, and pathways of cadmium in soil-rice systems: A review on the environmental implications and remediation approaches for food safety

Cadmium (Cd) contamination in paddy fields is a serious health concern because of its high toxicity and widespread pollution. Recently, much progress has been made in elucidating the mechanisms involved in Cd uptake, transport, and transformation from paddy soils to rice grains, aiming to mitigate the associated health risk; however, these topics have not been critically reviewed to date. Here, we summarized and reviewed the (1) geochemical distribution and speciation of Cd in soil-rice systems, (2) mobilization, uptake, and transport of Cd from soil to rice grains and the associated health risks, (3) pathways and transformation mechanisms of Cd from soil to rice grains, (4) transporters involved in reducing Cd uptake, transport, and accumulation in rice plants, (5) factors governing Cd bioavailability in paddy, and (6) comparison of remediation approaches for mitigating the environmental and health risks of Cd contamination in paddy fields. Briefly, this review presents the state of the art about the fate of Cd in paddy fields and its transport from soil to grains, contributing to a better understanding of the environmental hazards of Cd in rice ecosystems. Challenges and perspectives for controlling Cd risks in rice are thus raised. The summarized findings in this review may help to develop innovative and applicable methods for controlling Cd accumulation in rice grains and sustainably manage Cd-contaminated paddy fields.

Epigallocatechin Gallate for Management of Heavy Metal-Induced Oxidative Stress: Mechanisms of Action, Efficacy, and Concerns

In this review, we highlight the effects of epigallocatechin gallate (EGCG) against toxicities induced by heavy metals (HMs). This most active green tea polyphenol was demonstrated to reduce HM toxicity in such cells and tissues as testis, liver, kidney, and neural cells. Several protective mechanisms that seem to play a pivotal role in EGCG-induced effects, including reactive oxygen species scavenging, HM chelation, activation of nuclear factor erythroid 2-related factor 2 (Nrf2), anti-inflammatory effects, and protection of mitochondria, are described. However, some studies, especially in vitro experiments, reported potentiation of harmful HM actions in the presence of EGCG. The adverse impact of EGCG on HM toxicity may be explained by such events as autooxidation of EGCG, EGCG-mediated iron (Fe3+) reduction, depletion of intracellular glutathione (GSH) levels, and disruption of mitochondrial functions. Furthermore, challenges hampering the potential EGCG application related to its low bioavailability and proper dosing are also discussed. Overall, in this review, we point out insights into mechanisms that might account for both the beneficial and adverse effects of EGCG in HM poisoning, which may have a bearing on the design of new therapeutics for HM intoxication therapy.

Investigating the Bioaccessibility and Bioavailability of Cadmium in a Cooked Rice Food Matrix by Using an 11-Day Rapid Caco-2/HT-29 Co-culture Cell Model Combined with an In Vitro Digestion Model

Investigating the bioaccessibility and bioavailability of Cd based on real contaminated cooked rice matrixes helps establish an accurate risk assessment method and effectively reduce the digestion and absorption of Cd. An 11-day in vitro rapid Caco-2/HT-29 co-culture cell model was used to establish and evaluate the simulation of the absorption and transport of Cd in the small intestine with a 70:30 Caco-2/HT-29 co-culture ratio and 1.0 mmol L^-1 butyric acid as a differentiation inducer. The bioaccessibility and bioavailability of Cd in cooked rice were studied using the cell model combined with an in vitro digestion model. The bioaccessibility of Cd of each of the three cooked rice samples was significantly higher in the gastric phase (59.04-80.23%) than in the gastrointestinal phase (37.14-52.93%). Despite the extension of the digestion time of the gastrointestinal phase, no significant difference was found among the time points. Results demonstrated that the amount of undigested residue, not the level of Cd contamination, significantly contributed to the bioaccessibility of Cd, which was affected by pH or ion. The absorption rate of Cd (25.08% ± 3.05%) was greater than the values obtained using the pure Caco-2 cell models. The bioavailability of Cd (8.29% ± 1.95%) was almost similar to that of Zn²⁺ (6.66% ± 1.41%) in the cooked rice matrix, indicating that the intestinal epithelium expressed a strong absorptive capacity of Cd during the absorption of essential metallic elements. The 11-day rapid Caco-2/HT-29 co-culture cell model combined with the in vitro digestion model was an efficient tool for studying the bioaccessibility and bioavailability of Cd or other substances in a food matrix to further investigate mechanistic steps and screen a broad set of food matrix factors.