Cobalamin Deficiency Results in Increased Production of Formate Secondary to Decreased Mitochondrial Oxidation of One-Carbon Units in Rats

Enzymes encapsulated in organic-inorganic hybrid nanoflower with spatial localization for sensitive and colorimetric detection of formate

Formate is an important environmental pollutant, and meanwhile its concentration change is associated with a variety of diseases. Thus, rapid and sensitive detection of formate is critical for the biochemical analysis of complex samples and clinical diagnosis of multiple diseases. Herein, a colorimetric biosensor was constructed based on the cascade catalysis of formate oxidase (FOx) and horseradish peroxidase (HRP). These two enzymes were co-immobilized in Cu3(PO4)2-based hybrid nanoflower with spatial localization, in which FOx and HRP were located in the shell and core of nanoflower, respectively (FOx@HRP). In this system, FOx could catalyze the oxidation of formate to generate H2O2, which was then utilized by HRP to oxidize 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid to yield blue product. Ideal linear correlation could be obtained between the absorbance at 420 nm and formate concentration. Meanwhile, FOx@HRP exhibited excellent detection performance with low limit of detection (6 μM), wide linear detection range (10-900 μM), and favorable specificity, stability and reusability. Moreover, it could be applied in the detection of formate in environmental, food and biological samples with high accuracy. Collectively, FOx@HRP provides a useful strategy for the simple and sensitive detection of formate and is potentially to be used in biochemical analysis and clinical diagnosis.

Mutation in Smek2 regulating hepatic glucose metabolism causes hypersarcosinemia and hyperhomocysteinemia in rats

Suppressor of mek1 (Dictyostelium) homolog 2 (Smek2), was identified as one of the responsible genes for diet-induced hypercholesterolemia (DIHC) of exogenously hypercholesterolemic (ExHC) rats. A deletion mutation in Smek2 leads to DIHC via impaired glycolysis in the livers of ExHC rats. The intracellular role of Smek2 remains obscure. We used microarrays to investigate Smek2 functions with ExHC and ExHC.BN-Dihc2^BN congenic rats that harbor a non-pathological Smek2 allele from Brown-Norway rats on an ExHC background. Microarray analysis revealed that Smek2 dysfunction leads to extremely low sarcosine dehydrogenase (Sardh) expression in the liver of ExHC rats. Sarcosine dehydrogenase demethylates sarcosine, a byproduct of homocysteine metabolism. The ExHC rats with dysfunctional Sardh developed hypersarcosinemia and homocysteinemia, a risk factor for atherosclerosis, with or without dietary cholesterol. The mRNA expression of Bhmt, a homocysteine metabolic enzyme and the hepatic content of betaine (trimethylglycine), a methyl donor for homocysteine methylation were low in ExHC rats. Results suggest that homocysteine metabolism rendered fragile by a shortage of betaine results in homocysteinemia, and that Smek2 dysfunction causes abnormalities in sarcosine and homocysteine metabolism.

Reduced B12 uptake and increased gastrointestinal formate are associated with archaeome-mediated breath methane emission in humans

BACKGROUND

Methane is an end product of microbial fermentation in the human gastrointestinal tract. This gas is solely produced by an archaeal subpopulation of the human microbiome. Increased methane production has been associated with abdominal pain, bloating, constipation, IBD, CRC or other conditions. Twenty percent of the (healthy) Western populations innately exhale substantially higher amounts (>5 ppm) of this gas. The underlying principle for differential methane emission and its effect on human health is not sufficiently understood.

RESULTS

We assessed the breath methane content, the gastrointestinal microbiome, its function and metabolome, and dietary intake of one-hundred healthy young adults (female: n = 52, male: n = 48; mean age =24.1). On the basis of the amount of methane emitted, participants were grouped into high methane emitters (CH4 breath content 5-75 ppm) and low emitters (CH4 < 5 ppm). The microbiomes of high methane emitters were characterized by a 1000-fold increase in Methanobrevibacter smithii. This archaeon co-occurred with a bacterial community specialized on dietary fibre degradation, which included members of Ruminococcaceae and Christensenellaceae. As confirmed by metagenomics and metabolomics, the biology of high methane producers was further characterized by increased formate and acetate levels in the gut. These metabolites were strongly correlated with dietary habits, such as vitamin, fat and fibre intake, and microbiome function, altogether driving archaeal methanogenesis.

CONCLUSIONS

This study enlightens the complex, multi-level interplay of host diet, genetics and microbiome composition/function leading to two fundamentally different gastrointestinal phenotypes and identifies novel points of therapeutic action in methane-associated disorders. Video Abstract.

Micronutrients early in critical illness, selective or generous, enteral or intravenous?

PURPOSE OF REVIEW

Micronutrients have essential antioxidant and immune functions, while low blood concentrations are frequently observed in critically ill patients. This has led to the concepts of complementation, repletion, or even pharmacological supplementation. Over the last three decades, many clinical studies have tested the latter strategy, with controversial or negative results. Therefore, this review aims at evaluating micronutrient-related interventions that are mandatory or need to be assessed in future trials or clinical registries in all or specific critically ill patients.

RECENT FINDINGS

In the critically ill, low plasma/serum micronutrient levels not always reflect a true deficiency in the absence of demonstrable losses. Current practices of micronutrient provision and monitoring in critical care, vary substantially across the world. Also, recent clinical trials testing high dose as monotherapy (selenium, thiamine, vitamin C, vitamin D) or in combination have failed to demonstrate clinical benefits in sepsis. However, these studies have not applied a physiological integrative approach of micronutrient action.

SUMMARY

Micronutrients are essential in nutrition but their administration and monitoring are difficult. So far, different well designed RCTs on intravenous and oral high dose micronutrient supplementation have been conducted. Nevertheless, very high-dose single micronutrients cannot be advocated at this stage in sepsis, or any other critical condition. By contrast, studies using combination of moderate doses of micronutrients in specific diseases, such as burns and trauma have been associated with improved outcomes. Intravenous administration seems to be the most efficient route. Future clinical trials need to integrate the physiology underlying the interconnected micronutrient activity, and choose more specific primary and secondary endpoints.

Tracing Metabolic Fate of Mitochondrial Glycine Cleavage System Derived Formate In Vitro and In Vivo

Folate-mediated one-carbon (1C) metabolism is a major target of many therapies in human diseases. Studies have focused on the metabolism of serine 3-carbon as it serves as a major source for 1C units. The serine 3-carbon enters the mitochondria transferred by folate cofactors and eventually converted to formate and serves as a major building block for cytosolic 1C metabolism. Abnormal glycine metabolism has been reported in many human pathological conditions. The mitochondrial glycine cleavage system (GCS) catalyzes glycine degradation to CO₂ and ammonium, while tetrahydrofolate (THF) is converted into 5,10-methylene-THF. GCS accounts for a substantial proportion of whole-body glycine flux in humans, yet the particular metabolic route of glycine 2-carbon recycled from GCS during mitochondria glycine decarboxylation in hepatic or bone marrow 1C metabolism is not fully investigated, due to the limited accessibility of human tissues. Labeled glycine at 2-carbon was given to humans and primary cells in previous studies for investigating its incorporations into purines, its interconversion with serine, or the CO₂ production in the mitochondria. Less is known on the metabolic fate of the glycine 2-carbon recycled from the GCS; hence, a model system tracing its metabolic fate would help in this regard. We took the direct approach of isotopic labeling to further explore the in vitro and in vivo metabolic fate of the 2-carbon from [2-¹³C]glycine and [2-¹³C]serine. As the 2-carbon of glycine and serine is decarboxylated and catabolized via the GCS, the original 13C-labeled 2-carbon is transferred to THF and yield methyleneTHF in the mitochondria. In human hepatoma cell-lines, 2-carbon from glycine was found to be incorporated into deoxythymidine (dTMP, dT + 1), M + 3 species of purines (deoxyadenine, dA and deoxyguanine, dG), and methionine (Met + 1). In healthy mice, incorporation of GCS-derived formate from glycine 2-carbon was found in serine (Ser + 2 via cytosolic serine hydroxy methyl transferase), methionine, dTMP, and methylcytosine (mC + 1) in bone marrow DNA. In these experiments, labeled glycine 2-carbon directly incorporates into Ser + 1, A + 2, and G + 2 (at C2 and C8 of purine) in the cytosol. It is noteworthy that since the serine 3-carbon is unlabeled in these experiments, the isotopic enrichments in dT + 1, Ser + 2, dA + 3, dG + 3, and Met + 1 solely come from the 2-carbon of glycine/serine recycled from GCS, re-enters the cytosolic 1C metabolism as formate, and then being used for cytosolic syntheses of serine, dTMP, purine (M + 3) and methionine. Taken together, we established model systems and successfully traced the metabolic fate of mitochondrial GCS-derived formate from glycine 2-carbon in vitro and in vivo. Nutritional supply significantly alters formate generation from GCS. More GCS-derived formate was used in hepatic serine and methionine syntheses, whereas more GCS-derived formate was used in dTMP synthesis in the bone marrow, indicating that the utilization and partitioning of GCS-derived 1C unit are tissue-specific. These approaches enable better understanding concerning the utilization of 1C moiety generated from mitochondrial GCS that can help to further elucidate the role of GCS in human disease development and progression in future applications. More studies on GCS using these approaches are underway.

One-carbon metabolism, folate, zinc and translation

The translation process, central to life, is tightly connected to the one-carbon (1-C) metabolism via a plethora of macromolecule modifications and specific effectors. Using manual genome annotations and putting together a variety of experimental studies, we explore here the possible reasons of this critical interaction, likely to have originated during the earliest steps of the birth of the first cells. Methionine, S-adenosylmethionine and tetrahydrofolate dominate this interaction. Yet, 1-C metabolism is unlikely to be a simple frozen accident of primaeval conditions. Reactive 1-C species (ROCS) are buffered by the translation machinery in a way tightly associated with the metabolism of iron-sulfur clusters, zinc and potassium availability, possibly coupling carbon metabolism to nitrogen metabolism. In this process, the highly modified position 34 of tRNA molecules plays a critical role. Overall, this metabolic integration may serve both as a protection against the deleterious formation of excess carbon under various growth transitions or environmental unbalanced conditions and as a regulator of zinc homeostasis, while regulating input of prosthetic groups into nascent proteins. This knowledge should be taken into account in metabolic engineering.

Serum Metabolomic Profiles Associated With Untreated Metabolic Syndrome Patients in the Chinese Population

Metabolomics is a promising technology for elucidating the mechanisms of metabolic syndrome (MetS). However, measurements in patients with MetS under different conditions vary. Metabolomics experiments in different populations and pathophysiological conditions are, therefore, indispensable. We performed a serum metabolomics investigation in untreated patients with MetS in the Chinese population. Untreated patients with MetS were recruited to this study. Metabolites were measured using a traditional ¹H nuclear magnetic resonance (NMR) experiment followed by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS‐DA). Key metabolic pathways were identified by searching the Kyoto Encyclopedia of Genes and Genomes Pathway Database. A total of 28 patients with MetS and 30 healthy subjects were enrolled. All patients were untreated because they were unaware of or neglected to treat their MetS. By ¹H NMR, we identified 49 known substances. Following PCA and OPLS‐DA, 36 metabolites were confirmed to be closely associated with MetS compared with the control group; 33 metabolites were increased, whereas 3 metabolites were reduced. Importantly, 14 metabolites that changed in the serum of these untreated patients with MetS were previously unreported. Pathway analysis revealed the top 15 metabolic pathways associated with untreated MetS, which included 3 amino acid metabolic pathways. Our data suggest that untreated patients exhibit a worse pathophysiologic manifestation, which may result in more rapid progression of MetS. Thus, we propose that health education be reinforced to improve the public’s knowledge, attitude, and practice regarding MetS. The rates of “untreated” patients due to unawareness and neglect must be reduced immediately.

Do micronutrient deficiencies contribute to mitochondrial failure in critical illness?

PURPOSE OF REVIEW

Mitochondrial dysfunction seems to be the common denominator of several critical care conditions and particularly of sepsis. Faced with relative failure, and limited progress of sepsis therapies aiming at blocking some oxidative and/or inflammatory pathways, the question of antioxidants micronutrient therapy, particularly of selenium, ascorbic acid and thiamine remains open.

RECENT FINDINGS

The rationale for the essentiality of numerous micronutrients within the mitochondria is well established. Many studies have tested single micronutrients in animal and in-vitro models and provide positive evidences in favor of reduction of organ failure (cardiac and renal mainly). In clinical settings, high-dose selenium administration in sepsis has been disappointing. The most recent high dose, short-term ascorbic acid trial in sepsis is promising though, with an associated reduction of mortality, but analysis of the impact of this intervention on the various organs remains to be conducted.

SUMMARY

Results from animal and human studies indicate that there are indeed intervention options at the level of the mitochondria, but neither the optimal dose nor the optimal combination of micronutrients is yet identified.

Formate metabolism in health and disease

BACKGROUND

Formate is a one-carbon molecule at the crossroad between cellular and whole body metabolism, between host and microbiome metabolism, and between nutrition and toxicology. This centrality confers formate with a key role in human physiology and disease that is currently unappreciated.

SCOPE OF REVIEW

Here we review the scientific literature on formate metabolism, highlighting cellular pathways, whole body metabolism, and interactions with the diet and the gut microbiome. We will discuss the relevance of formate metabolism in the context of embryonic development, cancer, obesity, immunometabolism, and neurodegeneration.

MAJOR CONCLUSIONS

We will conclude with an outlook of some open questions bringing formate metabolism into the spotlight.

Size-dependent tissue-specific biological effects of core-shell structured Fe3O4@SiO2-NH2 nanoparticles

Background

Understanding the in vivo size-dependent pharmacokinetics and toxicity of nanoparticles is crucial to determine their successful development. Systematic studies on the size-dependent biological effects of nanoparticles not only help to unravel unknown toxicological mechanism but also contribute to the possible biological applications of nanomaterial.

Methods

In this study, the biodistribution and the size-dependent biological effects of Fe₃O₄@SiO₂–NH₂ nanoparticles (Fe@Si-NPs) in three diameters (10, 20 and 40 nm) were investigated by ICP-AES, serum biochemistry analysis and NMR-based metabolomic analysis after intravenous administration in a rat model.

Results

Our findings indicated that biodistribution and biological activities of Fe@Si-NPs demonstrated the obvious size-dependent and tissue-specific effects. Spleen and liver are the target tissues of Fe@Si-NPs, and 20 nm of Fe@Si-NPs showed a possible longer blood circulation time. Quantitative biochemical analysis showed that the alterations of lactate dehydrogenase (LDH) and uric acid (UA) were correlated to some extent with the sizes of Fe@Si-NPs. The untargeted metabolomic analyses of tissue metabolomes (kidney, liver, lung, and spleen) indicated that different sizes of Fe@Si-NPs were involved in the different biochemical mechanisms. LDH, formate, uric acid, and GSH related metabolites were suggested as sensitive indicators for the size-dependent toxic effects of Fe@Si-NPs. The findings from serum biochemical analysis and metabolomic analysis corroborate each other. Thus we proposed a toxicity hypothesis that size-dependent NAD depletion may occur in vivo in response to nanoparticle exposure. To our knowledge, this is the first report that links size-dependent biological effects of nanoparticles with in vivo NAD depletion in rats.

Conclusion

The integrated metabolomic approach is an effective tool to understand physiological responses to the size-specific properties of nanoparticles. Our results can provide a direction for the future biological applications of Fe@Si-NPs.

The Role of Single-Nucleotide Polymorphisms in the Function of Candidate Tumor Suppressor ALDH1L1

Folate (vitamin B9) is a common name for a group of coenzymes that function as carriers of chemical moieties called one-carbon groups in numerous biochemical reactions. The combination of these folate-dependent reactions constitutes one-carbon metabolism, the name synonymous to folate metabolism. Folate coenzymes and associated metabolic pathways are vital for cellular homeostasis due to their key roles in nucleic acid biosynthesis, DNA repair, methylation processes, amino acid biogenesis, and energy balance. Folate is an essential nutrient because humans are unable to synthesize this coenzyme and must obtain it from the diet. Insufficient folate intake can ultimately increase risk of certain diseases, most notably neural tube defects. More than 20 enzymes are known to participate in folate metabolism. Single-nucleotide polymorphisms (SNPs) in genes encoding for folate enzymes are associated with altered metabolism, changes in DNA methylation and modified risk for the development of human pathologies including cardiovascular diseases, birth defects, and cancer. ALDH1L1, one of the folate-metabolizing enzymes, serves a regulatory function in folate metabolism restricting the flux of one-carbon groups through biosynthetic processes. Numerous studies have established that ALDH1L1 is often silenced or strongly down-regulated in cancers. The loss of ALDH1L1 protein positively correlates with the occurrence of malignant tumors and tumor aggressiveness, hence the enzyme is viewed as a candidate tumor suppressor. ALDH1L1 has much higher frequency of non-synonymous exonic SNPs than most other genes for folate enzymes. Common SNPs at the polymorphic loci rs3796191, rs2886059, rs9282691, rs2276724, rs1127717, and rs4646750 in ALDH1L1 exons characterize more than 97% of Europeans while additional common variants are found in other ethnic populations. The effects of these SNPs on the enzyme is not clear but studies indicate that some coding and non-coding ALDH1L1 SNPs are associated with altered risk of certain cancer types and it is also likely that specific haplotypes define the metabolic response to dietary folate. This review discusses the role of ALDH1L1 in folate metabolism and etiology of diseases with the focus on non-synonymous coding ALDH1L1 SNPs and their effects on the enzyme structure/function, metabolic role and association with cancer.

Loss of ALDH1L1 folate enzyme confers a selective metabolic advantage for tumor progression

ALDH1L1 (cytosolic 10-formyltetrahydrofolate dehydrogenase) is the enzyme in folate metabolism commonly downregulated in human cancers. One of the mechanisms of the enzyme downregulation is methylation of the promoter of the ALDH1L1 gene. Recent studies underscored ALDH1L1 as a candidate tumor suppressor and potential marker of aggressive cancers. In agreement with the ALDH1L1 loss in cancer, its re-expression leads to inhibition of proliferation and to apoptosis, but also affects migration and invasion of cancer cells through a specific folate-dependent mechanism involved in invasive phenotype. A growing body of literature evaluated the prognostic value of ALDH1L1 expression for cancer disease, the regulatory role of the enzyme in cellular proliferation, and associated metabolic and signaling cellular responses. Overall, there is a strong indication that the ALDH1L1 silencing provides metabolic advantage for tumor progression at a later stage when unlimited proliferation and enhanced motility become critical processes for the tumor expansion. Whether the ALDH1L1 loss is involved in tumor initiation is still an open question.