Effective selenium detoxification in the seed proteins of a hyperaccumulator plant: the analysis of selenium-containing proteins of monkeypot nut (Lecythis minor) seeds

Selenoproteins in Health

Selenium (Se) is a naturally occurring essential micronutrient that is required for human health. The existing form of Se includes inorganic and organic. In contrast to the inorganic Se, which has low bioavailability and high cytotoxicity, organic Se exhibits higher bioavailability, lower toxicity, and has a more diverse composition and structure. This review presents the nutritional benefits of Se by listing and linking selenoprotein (SeP) functions to evidence of health benefits. The research status of SeP from foods in recent years is introduced systematically, particularly the sources, biochemical transformation and speciation, and the bioactivities. These aspects are elaborated with references for further research and utilization of organic Se compounds in the field of health.

Selenium in Brazil nuts: An overview of agronomical aspects, recent trends in analytical chemistry, and health outcomes

Se is an essential element in mammals. We review how its bioavailability in soil and the ability of plants to accumulate Se in foods depends on the soil Se profile (including levels and formats), besides to describe how the various selenoproteins have important biochemical functions in the body and directly impact human health. Owing to its favorable characteristics, the scientific community has investigated selenomethionine in most nut matrices. Among nuts, Brazil nuts have been highlighted as one of the richest sources of bioavailable Se. We summarize the most commonly used analytical methods for Se species and total Se determination in nuts. We also discuss the chemical forms of Se metabolized by mammals, human biochemistry and health outcomes from daily dietary intake of Se from Brazil nuts. These findings may facilitate the understanding of the importance of adequate dietary Se intake and enable researchers to define methods to determine Se species.

Selenium in cereals: Insight into species of the element from total amount

Selenium (Se) is a trace mineral micronutrient essential for human health. The diet is the main source of Se intake. Se-deficiency is associated with many diseases, and up to 1 billion people suffer from Se-deficiency worldwide. Cereals are considered a good choice for Se intake due to their daily consumption as staple foods. Much attention has been paid to the contents of Se in cereals and other foods. Se-enriched cereals are produced by biofortification. Notably, the gap between the nutritional and toxic levels of Se is fairly narrow. The chemical structures of Se compounds, rather than their total contents, contribute to the bioavailability, bioactivity, and toxicity of Se. Organic Se species show better bioavailability, higher nutritional value, and less toxicity than inorganic species. In this paper, we reviewed the total content of Se in cereals, Se speciation methods, and the biological effects of Se species on human health. Selenomethionine (SeMet) is generally the most prevalent and important Se species in cereal grains. In conclusion, Se species should be considered in addition to the total Se content when evaluating the nutritional and toxic values of foods such as cereals.

Selenium-Containing Proteins/Peptides from Plants: A Review on the Structures and Functions

Selenium is an essential microelement required for biological processes. Traditional selenium supplements (selenite and selenomethionine mainly) remain concerns due to toxicity and bioavailability. In recent decades, biofortification strategies have been applied to produce selenium-enriched edible plants to address the challenges of superior nutritional quality requirements. Plant-derived selenium-containing proteins/peptides offer potential health benefits beyond the basic nutritional requirements of Se. Highly nucleophilic seleno-amino acids, special peptide sequences, and favorable bioavailability contribute to the biological activities of selenium-containing proteins/peptides, such as antioxidant, antihypertensive, anti-inflammatory, and immunomodulatory effects. However, their applications on a commercial scale are insufficient owing to the complexity of purification and identification techniques and the sparse information on bioavailability and metabolism. In this review, selenium status, structural features, bioactivities, structure-activity relationships, and bioavailability, as well as the mechanisms underlying the bioactivities and metabolism of plant-derived selenium-containing proteins/peptides, are summarized and discussed for their nutraceutical use.

Sapucaia nut: Morphophysiology, minerals content, methodological validation in image analysis, phenotypic and molecular diversity in Lecythis pisonis Cambess

Sapucaia or Lecythis pisonis Cambess. is an ornamental tree that produces edible, tasty, and nutritious nuts, and can be used for timber production. Sapucaia has potential as a functional food, owing to optimal nutritional and particularly Se levels. The present study sought to characterize the seeds of 21 sapucaia matrices from forest remnants of a neotropical hotspot (Atlantic Forest) and farms in two Brazilian states. Biometrics, germination, vigor, lignin content in the teguments, minerals content, and phenotypic and molecular diversity were analyzed. The seeds of matrices 16 and 21 were the most vigorous. Nuts from matrices 21 and 17 contained the highest amounts of Se. Matrices 5, 8, and 21 were the most phenotypically distant; whereas matrix 21 was the most genetically distant. Importantly, we validated a new non-destructive and efficient X-ray-based methodology for internal and densitometric analysis of sapucaia seeds, and demonstrated a high genetic divergence among matrices.

Dynamics of Selenium uptake, speciation, and antioxidant response in rice at different panicle initiation stages

Selenium (Se) is an essential element in animals and humans, and its deficiency may cause conditions such as cardiac disease. The production of Se-enriched rice is one of the most important ways to supply Se in the human body, and thus, understanding of the mechanisms of Se-enriched rice is of great significance. A pot experiment was conducted to study the effects of Se addition on the growth, antioxidation, Se uptake and distribution, and Se speciation in three different stages of panicle initiation stage (i.e., pistil and stamen formation stage, pollen mother cell formation stage, pollen mother cell meiosis stage) and the maturity stage. The results showed that soil Se application significantly increased Se uptake in rice. Low rates of Se (<5 mg kg^-1) application enhanced the plant growth and rice yield. Se speciation assays showed that SeCys and SeMet were the two main forms found in rice, of which SeMet accounted for 65.5%-100% in the ears and leaves, while SeCys accounted for 61.4%-75.6% in brown rice. SeMet was also the main Se-species found in different subcellular parts at the panicle initiation stage. However, inorganic Se was present in brown rice, mainly as Se(VI), when the soil Se addition exceeded 5 mg kg^-1. Lower rates of Se (<5 mg kg^-1) promoted the antioxidant capacity, while high levels of Se (≥5 mg kg^-1) reduced the antioxidant capacity of rice. The results indicate that Se effects are dose dependent, and the suitable amount of soil Se application for Se-enriched rice production would be <5 mg kg^-1.

Selenolanthionine is the major water-soluble selenium compound in the selenium tolerant plant Cardamine violifolia

BACKGROUND

Selenium hyperaccumulation in plants often involves the synthesis of non-proteinaceous methylated selenoamino acids serving for the elimination of excess selenium from plant metabolism to protect plant homeostasis.

METHODS

Our study aimed at the identification of the main selenium species of the selenium hyperaccumulator plant Cardamine violifolia (Brassicaceae) that grows in the wild in the seleniferous region of Enshi, China. A sample of this plant (3.7 g Se kg^-1 d.w.) was prepared with several extraction methods and the extracted selenium species were identified and quantified with liquid chromatography mass spectrometry set-ups.

RESULTS

The Cardamine violifolia sample did not contain in considerable amount any of the organic selenium species that are often formed in hyperaccumulator plants; the inorganic selenium content (mostly as elemental selenium) accounted only for <20% of total Se. The most abundant selenium compound, accounting for about 40% of total Se was proved to be selenolanthionine, a selenium species that has never been unambiguously identified before from any selenium containing sample. The identification process was completed with chemical synthesis too. The molar ratio of lanthionine:selenolanthionine in the water extract was ca. 1:8.

CONCLUSIONS

Finding selenolanthionine as the main organic selenium species in a plant possibly unearths a new way of selenium tolerance. This article is part of a Special Issue entitled Selenium research in biochemistry and biophysics - 200 year anniversary issue, edited by Dr. Elias Arnér and Dr. Regina Brigelius-Flohe.

Stuck between a ROS and a hard place: Analysis of the ubiquitin proteasome pathway in selenocysteine treated Brassica napus reveals different toxicities during selenium assimilation

During the selenium assimilation pathway, inorganic selenate and selenite are reduced to form selenocysteine (Sec). Tolerance to selenium in plants has long been attributable to minimizing the replacement of cysteine with selenocysteine, which can result in nonspecific selenoproteins that are potentially misfolded. Despite this widely accepted assumption, there is no evidence in higher plants demonstrating that selenocysteine induces toxicity by resulting in malformed proteins. In this study, we use Brassica napus to analyze the ubiquitin-proteasome pathway, which is capable of removing misfolded proteins. Sec rapidly increased proteasome activity and levels of ubiquitinated proteins, strongly indicating that selenocysteine induces protein misfolding. Proteasome inhibition increased the amount of selenium in protein in Sec-treated plants. Collectively, these data provide a mechanism that accounts for Sec toxicity. Additionally, Sec did not cause oxidative stress as judged by examining levels of superoxide using fluorescent microscopy. Therefore, the cellular response to Sec is different compared to selenite, which was recently shown to increase antioxidant metabolism in response to elevated mitochondrial superoxide that ultimately impaired proteasome activity. Therefore, plants must contend with two divergent modes of cytotoxicity during selenium assimilation. Selenite can result in oxidative stress, but increased flux of selenite reduction can yield Sec that in turn can cause protein misfolding.