A Core Metabolome Response of Maize Leaves Subjected to Long-Duration Abiotic Stresses

Abiotic stresses reduce crop growth and yield in part by disrupting metabolic homeostasis and triggering responses that change the metabolome. Experiments designed to understand the mechanisms underlying these metabolomic responses have usually not used agriculturally relevant stress regimes. We therefore subjected maize plants to drought, salt, or heat stresses that mimic field conditions and analyzed leaf responses at metabolome and transcriptome levels. Shared features of stress metabolomes included synthesis of raffinose, a compatible solute implicated in tolerance to dehydration. In addition, a marked accumulation of amino acids including proline, arginine, and γ-aminobutyrate combined with depletion of key glycolysis and tricarboxylic acid cycle intermediates indicated a shift in balance of carbon and nitrogen metabolism in stressed leaves. Involvement of the γ-aminobutyrate shunt in this process is consistent with its previously proposed role as a workaround for stress-induced thiamin-deficiency. Although convergent metabolome shifts were correlated with gene expression changes in affected pathways, patterns of differential gene regulation induced by the three stresses indicated distinct signaling mechanisms highlighting the plasticity of plant metabolic responses to abiotic stress.

Thiamin Determination in Food: A Chromatographic Challenge (P13-038-19)

Objectives Thiamin plays an essential role during several metabolic reactions. Thiamin deficiency is a problem in developing countries, where a varied diet is lacking and people mainly rely on rice, which contains insufficient levels of thiamin, for their energy supply. A cost-effective strategy to fight this deficiency is the improvement of the nutritional quality of staple crops via biofortification. Although several methods for the determination of thiamin have been published, no method exists which allows a combined determination of thiamin, its phosphate derivatives and precursors. Methods LC-MS/MS was used to determine the low-level and labile thiamin vitamers. Volatile buffers are required for MS/MS detection, excluding commonly used phosphate buffers. Furthermore, determination of thiamin mono (TMP)- and diphosphate (TPP) is highly challenging due to their strong polar and ionogenic character, whereby regular C18 columns lack retention. HILIC columns are recommended for these types of compounds, however, the solubility of the phosphate derivatives is incompatible with the required organic injection solvent. Therefore, we tested numerous columns and mobile phases, in order to determine all five compounds in one chromatographic run from a single biological sample. Results With the Gemini® C18 column (Phenomenex) we were able to separate all compounds of interest. However, TMP and TPP could only be detected under basic conditions (≥pH 8.8), which resulted in secondary interactions between the charged silanol groups and the quaternary thiamin. We therefore transferred our method to a Gemini® NX C18 column, which offers a higher robustness at high pH and minimizes peak tailing since silanol groups are shielded. Finally, in an 8 minute run, we could achieve acceptable separation of all thiamin vitamers and precursors, with sufficient sensitivity for their determination in ≤200 mg of wild-type unpolished rice and Arabidopsis samples. Conclusions An LC-MS/MS method was successfully developed for the combined determination of all thiamin vitamers and precursors. Application of this method will allow to guide the effectiveness of biofortification strategies in order to fight thiamine deficiency in developing countries. Funding Sources The research was supported by the Research Foundation – Flanders. Supporting Tables, Images and/or Graphs

Thiamin deficiency in low- and middle-income countries: Disorders, prevalences, previous interventions and current recommendations

Background: Thiamin deficiency is a major public health concern in several low- and middle-income countries (LMICs)—current attention to the problem is lacking. Aim: This review discusses prevalence of thiamin insufficiency and thiamin-deficiency disorders (TDDs) in LMICs, outlines programmatic experience with thiamin interventions, and offers recommendations to improve public-health and research attention to thiamin in LMICs. Discussion: Thiamin insufficiency, i.e. low-blood-thiamin status, is endemic among several Southeast Asian countries: Cambodia (70–100% of infants and 27–100% of reproductive-age women); Laos (13% of hospitalized infants); Thailand (16–25% of children and 30% of elderly adults). Thiamin deficiency accounts for up to 45% of under-5 deaths in Cambodia, 34% of infant deaths in Laos, and 17% of infant deaths in Myanmar. Deficiency also exists in Africa, Asia, and the Americas, but these instances have typically been isolated. Exclusively breastfed infants of thiamin-deficient mothers are at highest risk for TDD and related death. Intervention strategies that have been employed to combat thiamin deficiency include food processing, fortification, supplementation, dietary diversification, and dietary behaviors, all of which have shown varying levels of effectiveness. Conclusions: We recommend universal thiamin-fortification of context-specific staple-foods in LMICs as a promising solution, as well as thiamin supplementation, particularly for pregnant and lactating women. Food processing regulations, dietary diversification, and modification of dietary behaviors to increase consumption of thiamin-rich foods may provide benefits in some circumstances, especially in countries without universal fortification programs or in populations dependent on food aid.

Thiamin deficiency on fetal brain development with and without prenatal alcohol exposure

Adequate thiamin levels are crucial for optimal health through maintenance of homeostasis and viability of metabolic enzymes, which require thiamine as a co-factor. Thiamin deficiency occurs during pregnancy when the dietary intake is inadequate or excessive alcohol is consumed. Thiamin deficiency leads to brain dysfunction because thiamin is involved in the synthesis of myelin and neurotransmitters (e.g., acetylcholine, γ-aminobutyric acid, glutamate), and its deficiency increases oxidative stress by decreasing the production of reducing agents. Thiamin deficiency also leads to neural membrane dysfunction, because thiamin is a structural component of mitochondrial and synaptosomal membranes. Similarly, in-utero exposure to alcohol leads to fetal brain dysfunction, resulting in negative effects such as fetal alcohol spectrum disorder (FASD). Thiamin deficiency and prenatal exposure to alcohol could act synergistically to produce negative effects on fetal development; however, this area of research is currently under-studied. This minireview summarizes the evidence for the potential role of thiamin deficiency in fetal brain development, with or without prenatal exposure to alcohol. Such evidence may influence the development of new nutritional strategies for preventing or mitigating the symptoms of FASD.