KLF10/CBS increases the sensitivity of gastric carcinoma cells to methionine restriction by promoting sulfur transfer pathway

Gastric cancer metastasis is a major cause of poor prognosis. Our previous research showed that methionine restriction (MR) lowers the invasiveness and motility of gastric carcinoma. In this study, we investigated the particular mechanisms of MR on gastric carcinoma metastasis. In vitro, gastric carcinoma cells (AGS, SNU-5, MKN7, KATO III, SNU-1, and MKN45) were grown in an MR medium for 24 h. In vivo, BALB/c mice were given a methionine-free (Met-) diet. Transwell assays were used to investigate cell invasion and migration. The amounts of Krüppel like factor 10 (KLF10) and cystathionine β-synthase (CBS) were determined using quantitative real-time PCR and Western blot. To determine the relationship between KLF10 and CBS, chromatin immunoprecipitation and a dual-luciferase reporter experiment were used. Hematoxylin-eosin staining was used to detect lung metastasis. Liquid chromatography-mass spectrometry was used to determine cystathionine content. MR therapy had varying effects on the invasion and migration of gastric carcinoma cells AGS, SNU-5, MKN7, KATO III, SNU-1, and MKN45. KLF10 was highly expressed in AGS cells but poorly expressed in KATO III cells. KLF10 improved MR's ability to prevent gastric carcinoma cell invasion and migration. In addition, KLF10 may interact with CBS, facilitating transcription. Further detection revealed that inhibiting the KLF10/CBS-mediated trans-sulfur pathway lowered Met-'s inhibitory effect on lung metastasis development. KLF10 transcription activated CBS, accelerated the trans-sulfur pathway, and increased gastric carcinoma cells' susceptibility to MR.

Methionine restriction of glioma does not induce MGMT and greatly improves temozolomide efficacy in an orthotopic nude-mouse model: A potential curable approach to a clinically-incurable disease

Glioma is a highly recalcitrant disease with a 5-year survival of 6.8 %. Temozolomide (TMZ), first-line therapy for glioma, is more effective in O6-methylguanine-DNA methyltransferase (MGMT)-negative gliomas than in MGMT-positive gliomas as MGMT confers resistance to TMZ. Methionine restriction is effective for many cancers in mouse models including glioma. The concern is that methionine restriction could induce MGMT by decreasing DNA methylation and confer resistance to TMZ. In the present study, we investigated the efficacy of combining methionine restriction with TMZ for the treatment of MGMT-negative glioma, and whether methionine restriction induced MGMT. Human MGMT-negative U87 glioma cells were used to determine the efficacy of TMZ combined with methionine restriction. Recombinant methioninase (rMETase) inhibited U87 glioma growth without induction of MGMT in vitro. The combination of rMETase and TMZ inhibited U87 cell proliferation more than either agent alone in vitro. In the orthotopic nude-mouse model, the combination of TMZ and a methionine-deficient diet was much more effective than TMZ alone: two mice out of five were cured of glioma by the combination. No mice died during the treatment period. Methionine restriction enhanced the efficacy of TMZ in MGMT-negative glioma without inducing MGMT, demonstrating potential clinical promise for improved outcome of a currently incurable disease.

Mitochondrial complex I inhibition triggers NAD+-independent glucose oxidation via successive NADPH formation, "futile" fatty acid cycling, and FADH2 oxidation

Inhibition of mitochondrial complex I (NADH dehydrogenase) is the primary mechanism of the antidiabetic drug metformin and various unrelated natural toxins. Complex I inhibition can also be induced by antidiabetic PPAR agonists, and it is elicited by methionine restriction, a nutritional intervention causing resistance to diabetes and obesity. Still, a comprehensible explanation to why complex I inhibition exerts antidiabetic properties and engenders metabolic inefficiency is missing. To evaluate this issue, we have systematically reanalyzed published transcriptomic datasets from MPP-treated neurons, metformin-treated hepatocytes, and methionine-restricted rats. We found that pathways leading to NADPH formation were widely induced, together with anabolic fatty acid biosynthesis, the latter appearing highly paradoxical in a state of mitochondrial impairment. However, concomitant induction of catabolic fatty acid oxidation indicated that complex I inhibition created a "futile" cycle of fatty acid synthesis and degradation, which was anatomically distributed between adipose tissue and liver in vivo. Cofactor balance analysis unveiled that such cycling would indeed be energetically futile (-3 ATP per acetyl-CoA), though it would not be redox-futile, as it would convert NADPH into respirable FADH2 without any net production of NADH. We conclude that inhibition of NADH dehydrogenase leads to a metabolic shift from glycolysis and the citric acid cycle (both generating NADH) towards the pentose phosphate pathway, whose product NADPH is translated 1:1 into FADH2 by fatty acid cycling. The diabetes-resistant phenotype following hepatic and intestinal complex I inhibition is attributed to FGF21- and GDF15-dependent fat hunger signaling, which remodels adipose tissue into a glucose-metabolizing organ.

Dietary sulfur amino acid restriction in humans with overweight and obesity: a translational randomized controlled trial

BACKGROUND

Dietary sulfur amino acid restriction (SAAR) improves metabolic health in animals. In this study, we investigated the effect of dietary SAAR on body weight, body composition, resting metabolic rate, gene expression profiles in white adipose tissue (WAT), and an extensive blood biomarker profile in humans with overweight or obesity.

METHODS

N = 59 participants with overweight or obesity (73% women) were randomized stratified by sex to an 8-week plant-based dietary intervention low (~ 2 g/day, SAAR) or high (~ 5.6 g/day, control group) in sulfur amino acids. The diets were provided in full to the participants, and both investigators and participants were blinded to the intervention. Outcome analyses were performed using linear mixed model regression adjusted for baseline values of the outcome and sex.

RESULTS

SAAR led to a ~ 20% greater weight loss compared to controls (β 95% CI - 1.14 (- 2.04, - 0.25) kg, p = 0.013). Despite greater weight loss, resting metabolic rate remained similar between groups. Furthermore, SAAR decreased serum leptin, and increased ketone bodies compared to controls. In WAT, 20 genes were upregulated whereas 24 genes were downregulated (FDR < 5%) in the SAAR group compared to controls. Generally applicable gene set enrichment analyses revealed that processes associated with ribosomes were upregulated, whereas processes related to structural components were downregulated.

CONCLUSION

Our study shows that SAAR leads to greater weight loss, decreased leptin and increased ketone bodies compared to controls. Further research on SAAR is needed to investigate the therapeutic potential for metabolic conditions in humans.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04701346, registered Jan 8th 2021, https://www.

CLINICALTRIALS

gov/study/NCT04701346.

Methionine-producing tumor micro(be) environment fuels growth of solid tumors

BACKGROUND

Recent studies have uncovered the near-ubiquitous presence of microbes in solid tumors of diverse origins. Previous literature has shown the impact of specific bacterial species on the progression of cancer. We propose that local microbial dysbiosis enables certain cancer phenotypes through provisioning of essential metabolites directly to tumor cells.

METHODS

16S rDNA sequencing of 75 patient lung samples revealed the lung tumor microbiome specifically enriched for bacteria capable of producing methionine. Wild-type (WT) and methionine auxotrophic (metA mutant) E. coli cells were used to condition cell culture media and the proliferation of lung adenocarcinoma (LUAD) cells were measured using SYTO60 staining. Further, colony forming assay, Annexin V Staining, BrdU, AlamarBlue, western blot, qPCR, LINE microarray and subcutaneous injection with methionine modulated feed were used to analyze cellular proliferation, cell-cycle, cell death, methylation potential, and xenograft formation under methionine restriction. Moreover, C14-labeled glucose was used to illustrate the interplay between tumor cells and bacteria.

RESULTS/DISCUSSION

Our results show bacteria found locally within the tumor microenvironment are enriched for methionine synthetic pathways, while having reduced S-adenosylmethionine metabolizing pathways. As methionine is one of nine essential amino acids that mammals are unable to synthesize de novo, we investigated a potentially novel function for the microbiome, supplying essential nutrients, such as methionine, to cancer cells. We demonstrate that LUAD cells can utilize methionine generated by bacteria to rescue phenotypes that would otherwise be inhibited due to nutrient restriction. In addition to this, with WT and metA mutant E. coli, we saw a selective advantage for bacteria with an intact methionine synthetic pathway to survive under the conditions induced by LUAD cells. These results would suggest that there is a potential bi-directional cross-talk between the local microbiome and adjacent tumor cells. In this study, we focused on methionine as one of the critical molecules, but we also hypothesize that additional bacterial metabolites may also be utilized by LUAD. Indeed, our radiolabeling data suggest that other biomolecules are shared between cancer cells and bacteria. Thus, modulating the local microbiome may have an indirect effect on tumor development, progression, and metastasis.

Methionine restriction and cancer treatment: a systems biology study of yeast to investigate the possible key players

Background/aim

Dietary restriction, mainly carbon and/or methionine restriction are among the upcoming supporting interventions along with chemotherapy in various cancers. Although dietary restriction has been proven to be beneficial, the main cellular machineries affected by its administration lacks deeper information considerably, a notable pitfall in its use as a personalized nutritional approach.

Materials and methods

In this study, cellular effects of methionine restriction on a yeast model are explored via systems biology approaches. The methionine biosynthesis network, constructed by integrating interaction data with gene ontology terms, was analysed topologically, and proved to be informative about the intertwined relationship of methionine biosynthesis and cancer. Experimentally, effects of methionine restriction on the yeast model were explored in vivo, with transcriptome analyses.

Results

The integrative analysis of the transcriptional data together with the reconstructed network gave insight into cellular machineries such as TOR, MAPK, and sphingolipid-mediated signaling cascades as the mostly responsive cellular pathways in the methionine-restricted cases with Sch9p (functional orthologue of mammalian S6 kinase) being placed at the intersection of these signaling routes.

Cystine rather than cysteine is the preferred substrate for β-elimination by cystathionine γ-lyase: implications for dietary methionine restriction

Dietary methionine restriction (MR) increases longevity by improving health. In experimental models, MR is accompanied by decreased cystathionine β-synthase activity and increased cystathionine γ-lyase activity. These enzymes are parts of the transsulfuration pathway which produces cysteine and 2-oxobutanoate. Thus, the decrease in cystathionine β-synthase activity is likely to account for the loss of tissue cysteine observed in MR animals. Despite this decrease in cysteine levels, these tissues exhibit increased H₂S production which is thought to be generated by β-elimination of the thiol moiety of cysteine, as catalyzed by cystathionine β-synthase or cystathionine γ-lyase. Another possibility for this H₂S production is the cystathionine γ-lyase-catalyzed β-elimination of cysteine persulfide from cystine, which upon reduction yields H₂S and cysteine. Here, we demonstrate that MR increases cystathionine γ-lyase production and activities in the liver and kidneys, and that cystine is a superior substrate for cystathionine γ-lyase catalyzed β-elimination as compared to cysteine. Moreover, cystine and cystathionine exhibit comparable K_cat/K_m values (6000 M^-1 s^-1) as substrates for cystathionine γ-lyase-catalyzed β-elimination. By contrast, cysteine inhibits cystathionine γ-lyase in a non-competitive manner (K_i ~ 0.5 mM), which limits its ability to function as a substrate for β-elimination by this enzyme. Cysteine inhibits the enzyme by reacting with its pyridoxal 5'-phosphate cofactor to form a thiazolidine and in so doing prevents further catalysis. These enzymological observations are consistent with the notion that during MR cystathionine γ-lyase is repurposed to catabolize cystine and thereby form cysteine persulfide, which upon reduction produces cysteine.

Synergy of Combining Methionine Restriction and Chemotherapy: The Disruptive Next Generation of Cancer Treatment

All cancer cell types are methionine-addicted, which is termed the Hoffman effect. Cancer cells, unlike normal cells, cannot survive without large amount of methionine. In general, when methionine is depleted, both normal cells and cancer cells synthesize methionine from homocysteine, but cancer cells consume large amounts of methionine and they cannot survive without exogenous methionine. For this reason, methionine restriction has been shown to be effective against many cancers in vitro and in vivo. Methionine restriction arrests cancer cells in the S/G₂-phase of the cell cycle. Cytotoxic agents that act in the S/G₂-phase are highly effective when used in combination with methionine restriction due to the cancer cells being trapped in S/G₂-phase, unlike normal cells which arrest in G₁/G₀-phase. Combining methionine restriction and chemotherapeutic drugs for cancer treatment is termed the Hoffman protocol. The efficacy of many cytotoxic agents and molecular-targeted drugs in combination with methionine restriction has been demonstrated. The most effective method of methionine restriction is the administration of recombinant methioninase (rMETase), which degrades methionine. The efficacy of rMETase has been reported in mice and human patients by oral administration. The present review describes studies on anticancer drugs that showed synergistic efficacy in combination with methionine restriction, including rMETase administration. It is proposed that the next disruptive generation of cancer chemotherapy should employ current therapy in combination with methionine restriction for all cancer types.

Effects of methionine intake on cognitive function in mild cognitive impairment patients and APP/PS1 Alzheimer's Disease model mice: Role of the cystathionine-β-synthase/H2S pathway

As a dietary intervention, methionine restriction (MR) has been reported to increase longevity and improve metabolism disorders. However, the effects of MR on alleviating neurodegenerative diseases such as Alzheimer's disease (AD) are largely unexplored. Here we sought to investigate the neuroprotective effects of low methionine intake in mild cognitive impairment (MCI) patients and APP/PS1 AD model mice, and to uncover the underlying mechanisms. In a cohort composed of 45 individuals diagnosed with MCI and 61 healthy controls without cognitive impairment, methionine intake was found to be positively associated with the increased risk of MCI, where no sex differences were observed. We further conducted a 16-week MR intervention (0.17% methionine, w/w) on APP/PS1 AD model mice. Although MR reduced Aβ accumulation in the brain of both male and female APP/PS1 mice, MR improved cognitive function only in male mice, as assessed by the Morris water maze test. Consistently, MR restored synapse ultrastructure and alleviated mitochondrial dysfunction by enhancing mitochondrial biogenesis in the brain of male APP/PS1 mice. Importantly, MR effectively balanced the redox status and activated cystathionine-β-synthase (CBS)/H₂S pathway in the brain of male APP/PS1 mice. Together, our study indicated that lower dietary methionine intake is associated with improved cognitive function, in which CBS/H₂S pathway plays an essential role. MR could be a promising nutritional intervention for preventing AD development.

Methionine restriction - Association with redox homeostasis and implications on aging and diseases

Methionine is an essential amino acid, involved in the promotion of growth, immunity, and regulation of energy metabolism. Over the decades, research has long focused on the beneficial effects of methionine supplementation, while data on positive effects of methionine restriction (MR) were first published in 1993. MR is a low-methionine dietary intervention that has been reported to ameliorate aging and aging-related health concomitants and diseases, such as obesity, type 2 diabetes, and cognitive disorders. In addition, MR seems to be an approach to prolong lifespan which has been validated extensively in various animal models, such as Caenorhabditis elegans, Drosophila, yeast, and murine models. MR appears to be associated with a reduction in oxidative stress via so far mainly undiscovered mechanisms, and these changes in redox status appear to be one of the underlying mechanisms for lifespan extension and beneficial health effects. In the present review, the association of methionine metabolism pathways with redox homeostasis is described. In addition, the effects of MR on lifespan, age-related implications, comorbidities, and diseases are discussed.

Impact of methionine restriction on muscle aerobic metabolism and hypertrophy in young and old mice on an obesogenic diet

Methionine restriction (MR) reduces inflammation and increases longevity. We studied the effects of MR (0.17% kCal methionine, 10% kCal fat) and MR + high-fat diet (HFD) (0.17% methionine, 45% kCal fat) and overload-induced hypertrophy on inflammation, angiogenesis and mitochondrial activity in the hind-limb muscle in 10- and 26-month-old male C57BL/6J mice. Plasma IL-6 concentrations were higher in old compared to young mice. M. plantaris hypertrophy was accompanied by increased p-Akt, without a significant change in Akt and VEGF levels. In young mice on a HFD or MR + HFD diet the SDH activity was higher than in those from mice on other diets, irrespective of overload. There were no significant differences in total NAD concentration in the m. gastrocnemius. MR enhanced the skeletal muscle hypertrophic response in old age that was accompanied with an increase in p-Akt without significant changes in muscle oxidative capacity, low-grade systemic inflammation, NAD, VEGF or Akt levels.

Methionine restriction enhances the chemotherapeutic sensitivity of colorectal cancer stem cells by miR-320d/c-Myc axis

Chemotherapy resistance of colorectal cancer stem cells (CRC-SCs) has become a major challenge in clinical treatment of cancer. Methionine restriction (MR) enhances the therapeutic effect of chemotherapeutic agents. The aim of this study was to explore the molecular pathways that MR affects the chemotherapeutic sensitivity of CRC-SCs. CD133⁺ and CD133^- SW480 or SW620 cells were isolated by magnetic-activated cell sorting (MACS). Mouse xenograft tumor model was established by subcutaneous inoculation of CD133⁺ SW480. MTT assay was used to detect cell viability. Phase distribution of cell cycle was detected by flow cytometry. Western blotting was used to detect drug-resistant related protein expression. miR-320d and transcription factor c-Myc expressions were detected by qRT-PCR. The interaction between miR-320d and c-Myc was verified by luciferase assay. CD133⁺ SW480 and SW620 cells were more resistant to 5-fluorouracil (5-FU) than CD133^- cells. In vitro and in vivo experiments showed that 5-FU and MR combined therapy further inhibited CD133⁺ cell activity and ATP binding cassette subfamily G member 2 (ABCG2) expression, and reduced tumor volume compared with drug administration alone. Interference with miR-320d or overexpression of c-Myc reversed the increased chemotherapeutic sensitivity of CRC-SCs induced by synergistic therapy with 5-FU and MR. miR-320d can target and regulate c-Myc. Interference with c-Myc could reverse the increase in cell viability and ABCG2 expression caused by down-regulation of miR-320d. In conclusion, the combined chemotherapy with MR can enhance the chemotherapeutic sensitivity of CRC-SCs by up-regulation of miR-320d to inhibit c-Myc expression, which lays a molecular basis for MR regulation of chemotherapeutic sensitivity of CRC-SCs.

Histone H3 lysine-trimethylation markers are decreased by recombinant methioninase and increased by methotrexate at concentrations which inhibit methionine-addicted osteosarcoma cell proliferation

Methionine addiction is a fundamental and general hallmark of cancer cells, which require exogenous methionine, despite their ability to synthesize normal amounts of methionine from homocysteine. In contrast, methionine-independent normal cells do not require exogenous methionine in the presence of a methionine precursor. The methionine addiction of cancer cells is due to excess transmethylation reactions. We have previously shown that histone H3 lysine marks are over-methylated in cancer cells and the over-methylation is unstable when the cancer cells are restricted of methionine. In the present study, we show that methionine-addicted osteosarcoma cells are sensitive to both methotrexate (MTX) and recombinant methioninase (rMETase), but they affect histone H3 lysine-methylation in the opposite direction. Concentrations of MTX and rMETase, which inhibit osteosarcoma cells viability to 20%, had opposing effects on the status of histone methylation of H3K9me3 and H3K27me3. rMETase significantly decreased the amount of H3K9me3 and H3K27me3. In contrast, MTX significantly increased the amount of H3K9me and H3K27me3. The results suggest that increase or decrease in these methylated histone lysine marks is associated with proliferation arrest of methionine-addicted osteosarcoma.

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Osteosarcoma cells are sensitive to both methotrexate and recombinant methioninase.

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MTX increased the amount of H3K9me and H3K27me3.

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RMETase decreased the amount of H3K9me3 and H3K27me3.

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Increase/decrease in H3K9me3 and H3K27me3 is associated with proliferation arrest.

Methionine as a double-edged sword in health and disease: Current perspective and future challenges

Methionine is one of the essential amino acids and plays a vital role in various cellular processes. Reports advocate that methionine restriction and supplementation provide promising outcomes, and its regulation is critical for maintaining a healthy life. Dietary methionine restriction in houseflies and rodents has been proven to extend lifespan. Contrary to these findings, long-term dietary restriction of methionine leads to adverse events such as bone-related disorders, stunted growth, and hyperhomocysteinemia. Conversely, dietary supplementation of methionine improves hepatic steatosis, insulin resistance, inflammation, fibrosis, and bone health. However, a high level of methionine intake shows adverse effects such as hyperhomocysteinemia, reduced body weight, and increased cholesterol levels. Therefore, dietary methionine in a safe dose could have medicinal values. Hence, this review is aimed to provide a snapshot of the dietary role and regulation of methionine in the modulation of health and age-related diseases.

Sulfur amino acid restriction, energy metabolism and obesity: a study protocol of an 8-week randomized controlled dietary intervention with whole foods and amino acid supplements

Background

Dietary sulfur amino acid (SAA) restriction is an established animal model for increasing lifespan and improving metabolic health. Data from human studies are limited. In the study outlined in this protocol, we will evaluate if dietary SAA restriction can reduce body weight and improve resting energy expenditure (REE) and parameters related to metabolic health.

Method/design

Men and women (calculated sample size = 60), aged 18–45 years, with body mass index of 27–35 kg/m² will be included in a double-blind 8-week dietary intervention study. The participants will be randomized in a 1:1 manner to a diet with either low or high SAA. Both groups will receive an equal base diet consisting of low-SAA plant-based whole foods and an amino acid supplement free of SAA. Contrasting SAA contents will be achieved using capsules with or without methionine and cysteine (SAA_high, total diet SAA ~ 50–60 mg/kg body weight/day; SAA_low, total diet SAA ~ 15–25 mg/kg body weight/day). The primary outcome is body weight change. Data and material collection will also include body composition (dual X-ray absorptiometry), resting energy expenditure (whole-room indirect calorimetry) and samples of blood, urine, feces and adipose tissue at baseline, at 4 weeks and at study completion. Measures will be taken to promote and monitor diet adherence. Data will be analyzed using linear mixed model regression to account for the repeated measures design and within-subject correlation.

Discussion

The strength of this study is the randomized double-blind design. A limitation is the restrictive nature of the diet which may lead to poor compliance. If this study reveals a beneficial effect of the SAA_low diet on body composition and metabolic health, it opens up for new strategies for prevention and treatment of overweight, obesity and its associated disorders.

Trial registration ClinicalTrials.gov: NCT04701346, Registration date: January 8th, 2021

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02824-3.

Methionine restriction alleviates age-associated cognitive decline via fibroblast growth factor 21

Methionine restriction (MR) extends lifespan and delays the onset of aging-associated pathologies. However, the effect of MR on age-related cognitive decline remains unclear. Here, we find that a 3-month MR ameliorates working memory, short-term memory, and spatial memory in 15-month-old and 18-month-old mice by preserving synaptic ultrastructure, increasing mitochondrial biogenesis, and reducing the brain MDA level in aged mice hippocampi. Transcriptome data suggest that the receptor of fibroblast growth factor 21 (FGF21)-related gene expressions were altered in the hippocampi of MR-treated aged mice. MR increased FGF21 expression in serum, liver, and brain. Integrative modelling reveals strong correlations among behavioral performance, MR altered nervous structure-related genes, and circulating FGF21 levels. Recombinant FGF21 treatment balanced the cellular redox status, prevented mitochondrial structure damages, and upregulated antioxidant enzymes HO-1 and NQO1 expression by transcriptional activation of Nrf2 in SH-SY5Y cells. Moreover, knockdown of Fgf21 by i.v. injection of adeno-associated virus abolished the neuroprotective effects of MR in aged mice. In conclusion, the MR exhibited the protective effects against age-related behavioral disorders, which could be partly explained by activating circulating FGF21 and promoting mitochondrial biogenesis, and consequently suppressing the neuroinflammation and oxidative damages. These results demonstrate that FGF21 can be used as a potential nutritional factor in dietary restriction-based strategies for improving cognition associated with neurodegeneration disorders.

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MR suppresses age-associated cognitive impairment.

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MR improves synapse ultrastructure and mitochondrial biogenesis in the hippocampus.

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FGF21 is required for the beneficial effects of MR.

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FGF21 activates Nrf2 signaling and alleviates neuroinflammation and oxidative stress.

Effects of short-term methionine and cysteine restriction and enrichment with polyunsaturated fatty acids on oral glucose tolerance, plasma amino acids, fatty acids, lactate and pyruvate: results from a pilot study

Objective

In this 7-day pilot study we randomized healthy, normal-weight men and women to either a dietary intervention with methionine and cysteine restriction enriched in PUFA (Met/Cys_low + PUFA, n = 7) or with high contents of methionine, cysteine and SFA (Met/Cys_high + SFA, n = 7). The objective was to describe the short-term responses in oral glucose tolerance, amino acid profile, total fatty acid profile, pyruvate and lactate following a Met/Cys_low + PUFA diet vs. Met/Cys_high + SFA.

Results

The diet groups consisted of five women and two men, aged 20–38 years. After the 7-d intervention median pre- and post-oral glucose tolerance test (OGTT) glucose concentrations were 5 mmol/L and 4 mmol/L respectively in the Met/Cys_low + PUFA group. In the Met/Cys_high + SFA group, median pre- and post-OGTT glucose concentrations were 4.8 mmol/L and 4.65 mmol/L after the 7-d intervention. The responses in the amino acid profiles were similar in both groups during the intervention with the exception of serine. Fatty acids decreased from baseline to day 7 in both groups. Plasma lactate and pyruvate were similar for both groups with an increase to day 3 before approaching baseline values at day 7.

Trial registration

ClinicalTrials.gov: NCT02647970, registration date: January 6^th 2016.

BDNF secretion from C2C12 cells is enhanced by methionine restriction

Brain derived neurotrophic factor (BDNF) is produced in skeletal muscle as a myokine that plays a role in muscle metabolism. However, how metabolic changes affect skeletal muscle BDNF expression and release remains to be fully understood. Amino acid restrictions such as methionine restriction (MR) are considered as an alternative fasting approach. Here we reported that in C2C12 myotubes, MR enhanced BDNF release, which was measured using ELISA, RT-qPCR, cell immunostaining, and Western blot. Inhibition of protein transport pathway blocked the MR enhanced BDNF release, confirming that MR-induced BDNF release involved classic protein secretory pathway. MR increased l-lactate product in media, suggesting that MR promoted glycolysis. Treatment with 2-deoxy glucose (2-DG) attenuated lactate production as well as BDNF release, suggesting that glycolysis is involved in the enhanced BDNF release induced by MR. Moreover, treatment with l-Lactate, the end-product of glycolysis, enhanced BDNF gene expression and release in control cells in a dose dependent manner, suggesting lactate produced by glycolysis may mediate the enhanced BDNF release by MR. Overall, the results of this study suggest that MR promotes BDNF secretion from C2C12 myotubes at least partially via enhancing glycolysis and lactate production.

Histone methylation status of H3K4me3 and H3K9me3 under methionine restriction is unstable in methionine-addicted cancer cells, but stable in normal cells

Methionine addiction is a fundamental and general hallmark of cancer. Methionine addiction prevents cancer cells, but not normal cells from proliferation under methionine restriction (MR). Previous studies reported that MR altered the histone methylation levels in methionine-addicted cancer cells. However, no study has yet compared the status of histone methylation status, under MR, between cancer cells and normal cells. In the present study, we compared the histone methylation status between cancer cells and normal fibroblasts of H3K4me3 and H3K9me3, using recombinant methioninase (rMETase) to effect MR. Human lung and colon cancer cell lines and human normal foreskin fibroblasts were cultured in control medium or medium with rMETase. The viability of foreskin fibroblasts was approximately 10 times more resistant to rMETase than the cancer cells in vitro. Proliferation only of the cancer cells ceased under MR. The histone methylation status of H3K4me3 and H3K9me3 under MR was evaluated by immunoblotting. The levels of the H3K4me3 and H3K9me3 were strongly decreased by MR in the cancer cells. In contrast, the levels of H3K4me3 and H3K9me3 were not altered by MR in normal fibroblasts. The present results suggest that histone methylation status of H3K4me3 and H3K9me3 under MR was unstable in cancer cells but stable in normal cells and the instability of histone methylation status under MR may determine the high methionine dependency of cancer cells to survive and proliferate.

Effects of dietary restriction on metabolic and cognitive health

Life expectancy in most developed countries has been rising over the past century. In the UK alone, there are about 12 million people over 65 years old and centenarians have increased by 85% in the past 15 years. As a result of the ageing population, which is due mainly to improvements in medical treatments, public health, improved housing and lifestyle choices, there is an associated increase in the prevalence of pathological conditions, such as metabolic disorders, type 2 diabetes, cardiovascular and neurodegenerative diseases, many types of cancer and others. Statistics suggest that nearly 54% of elderly people in the UK live with at least two chronic conditions, revealing the urgency for identifying interventions that can prevent and/or treat such disorders. Non-pharmacological, dietary interventions such as energetic restriction (ER) and methionine restriction (MR) have revealed promising outcomes in increasing longevity and preventing and/or reversing the development of ageing-associated disorders. In this review, we discuss the evidence and mechanisms that are involved in these processes. Fibroblast growth factor 1 and hydrogen sulphide are important molecules involved in the effects of ER and MR in the extension of life span. Their role is also associated with the prevention of metabolic and cognitive disorders, highlighting these interventions as promising modulators for improvement of health span.

The effect of short-term methionine restriction on hydrogen peroxide metabolism in Fischer-344 rat skeletal muscle mitochondria

Skeletal muscle, a significant contributor to resting energy expenditure and reactive oxygen species, may play a critical role in body-weight regulation and aging processes. Methionine restriction (MR) is a dietary intervention which extends lifespan, lowers body-weight and enhances energy expenditure in rodents, all of which have been linked to mitochondrial function in various tissues including liver, kidney, heart and brown adipose tissue; however, mitochondrial responses to MR in skeletal muscle is largely unknown. Given the importance of skeletal muscle on energy metabolism and aging-related processes, we investigated if there are changes in skeletal muscle mitochondrial energetics in response to MR. Although MR lowers body-weight in rats, neither respiration, proton leak nor hydrogen peroxide metabolism were altered in isolated skeletal muscle mitochondria. This suggests that mitochondrial function in skeletal muscle remains conserved while MR alters metabolism in other tissues.

Postprandial effects of a meal low in sulfur amino acids and high in polyunsaturated fatty acids compared to a meal high in sulfur amino acids and saturated fatty acids on stearoyl CoA-desaturase indices and plasma sulfur amino acids: a pilot study

Objective

The sulfur amino acid (SAA) cysteine is positively related, whereas polyunsaturated fatty acids (PUFAs) are inversely related to activity of the lipogenic enzyme stearoyl-CoA desaturase (SCD). High SCD activity promotes obesity in animals, and plasma activity indices positively associates with fat mass in humans. SCD may thus be a target for dietary intervention with SAA restriction and PUFA enrichment with unknown potential benefits for body composition. We randomized ten healthy individuals to a meal restricted in SAAs and enriched with PUFAs (Cys/Met_low + PUFA) (n = 5) or a meal enriched in SAA and saturated fatty acids (Cys/Met_high + SFA) (n = 5). We measured plasma SCD activity indices (SCD16 and SCD18) and SAAs response hourly from baseline and up to 4 h postprandial.

Results

SCD16 was unchanged whereas SCD18 tended to increase in the Cys/Met_low + PUFA compared to the Cys/Met_high + SFA group (p_{time*group interaction} = 0.08). Plasma concentrations of total cysteine fractions including free and reduced cysteine decreased in the Cys/Met_low + PUFA compared to the Cys/Met_high + SFA group (both p_{time*group interaction} < 0.001). In conclusion, a meal low in SAA but high in PUFAs reduced plasma cysteine fractions but not SCD activity indices. This pilot study can be useful for the design and diet composition of future dietary interventions that targets SCD and SAA.

Trial registration ClinicalTrials.gov: NCT02647970, registration date: 6 January 2016

Methionine restriction alleviates high-fat diet-induced obesity: Involvement of diurnal metabolism of lipids and bile acids

Circadian misalignment induced by a high-fat diet (HFD) increases the risk of metabolic diseases. Methionine restriction (MR) is known to have the potential of alleviating obesity by improving insulin sensitivity. However, the role of the circadian clock in mediating the effects of MR on obesity-related metabolic disorders remains unclear. Ten-week-old male C57BL/6 J mice were fed with a low-fat diet (LFD) or a HFD for 4 wk., followed with a full diet (0.86% methionine, w/w) or a methionine-restricted diet (0.17% methionine, w/w) for 8 wk. Our results showed that MR attenuated insulin resistance triggered by HFD, especially at ZT12. Moreover, MR led to a time-specific enhancement of the expression of FGF21 and activated the AMPK/PGC-1α signaling. Notably, MR upregulated the cyclical levels of cholic acid (CA) and chenodeoxycholic acid (CDCA), and downregulated the cyclical level of deoxycholic acid (DCA) in the dark phase. MR restored the HFD-disrupted cyclical fluctuations of lipidolysis genes and BAs synthetic genes and improved the circulating lipid profile. Also, MR improved the expressions of clock-controlled genes (CCGs) in the liver and the brown adipose tissue throughout one day. In conclusion, MR exhibited the lipid-lowering effects on HFD-induced obesity and restored the diurnal metabolism of lipids and BAs, which could be partly explained by improving the expression of CCGs. These findings suggested that MR could be a potential nutritional intervention for attenuating obesity-induced metabolic misalignment.

Oral recombinant methioninase increases TRAIL receptor-2 expression to regress pancreatic cancer in combination with agonist tigatuzumab in an orthotopic mouse model

Methionine addiction is a fundamental and general hallmark of cancer. Gene expression analysis showed that methionine restriction (MR) of methionine-addicted cancer cells increases TNF-related apoptosis-induced ligand receptor-2 (TRAIL-R2) expression. Here, we determined the effects of MR on TRAIL-R2 targeted therapy in pancreatic cancer by the TRAIL-R2 agonist tigatuzumab. Human pancreatic cancer cell lines were cultured in control or methionine-free medium. The effects of MR on TRAIL-R2 expression and sensitivity to tigatuzumab were evaluated in vitro. An orthotopic pancreatic cancer mouse model was established to evaluate the efficacy of MR using oral recombinant methioninase (o-rMETase), and the efficacy of tigatuzumab and their combination. MR enabled tigatuzumab-induced apoptosis, by increasing TRAIL-R2 expression in pancreatic cancer cells in vitro. The protein expression level of the melanoma-associated antigen MAGED2, which reduces TRAIL-R2 expression, was decreased by MR. In the orthotopic pancreatic cancer mouse model, o-rMETase increased TRAIL-R2 expression level in the tumors and enabled the antitumor efficacy of tigatuzumab. MR, effected by o-rMETase, enabled the efficacy of the TRAIL-R2 agonist tigatuzumab by increasing TRAIL-R2 expression in pancreatic cancer. Our results suggest that o-rMETase has clinical potential for treating pancreatic cancer.

Effects of dietary methionine and cysteine restriction on plasma biomarkers, serum fibroblast growth factor 21, and adipose tissue gene expression in women with overweight or obesity: a double-blind randomized controlled pilot study

Background

Dietary restriction of methionine and cysteine is a well-described model that improves metabolic health in rodents. To investigate the translational potential in humans, we evaluated the effects of dietary methionine and cysteine restriction on cardiometabolic risk factors, plasma and urinary amino acid profile, serum fibroblast growth factor 21 (FGF21), and subcutaneous adipose tissue gene expression in women with overweight and obesity in a double-blind randomized controlled pilot study.

Methods

Twenty women with overweight or obesity were allocated to a diet low (Met/Cys_-low, n = 7), medium (Met/Cys_-medium, n = 7) or high (Met/Cys_-high, n = 6) in methionine and cysteine for 7 days. The diets differed only by methionine and cysteine content. Blood and urine were collected at day 0, 1, 3 and 7 and subcutaneous adipose tissue biopsies were taken at day 0 and 7.

Results

Plasma methionine and cystathionine and urinary total cysteine decreased, whereas FGF21 increased in the Met/Cys_-low vs. Met/Cys_-high group. The Met/Cys_-low group had increased mRNA expression of lipogenic genes in adipose tissue including DGAT1. When we excluded one participant with high fasting insulin at baseline, the Met/Cys_-low group showed increased expression of ACAC, DGAT1, and tendencies for increased expression of FASN and SCD1 compared to the Met/Cys_-high group. The participants reported satisfactory compliance and that the diets were moderately easy to follow.

Conclusions

Our data suggest that dietary methionine and cysteine restriction may have beneficial effects on circulating biomarkers, including FGF21, and influence subcutaneous adipose tissue gene expression. These results will aid in the design and implementation of future large-scale dietary interventions with methionine and cysteine restriction.

Trial registration ClinicalTrials.gov Identifier: NCT03629392, registration date: 14/08/2018 https://clinicaltrials.gov/ct2/show/NCT03629392.

Methionine restriction delays aging-related urogenital diseases in male Fischer 344 rats

Dietary methionine restriction (MR) has been found to enhance longevity across many species. We hypothesized that MR might enhance longevity in part by delaying or inhibiting age-related disease processes. To this end, male Fischer 344 rats were fed control (CF, 0.86% methionine) or MR (0.17% methionine) diets throughout their life until sacrifice at approximately 30 months of age, and histopathology was performed to identify the incidence and progression of two important aging-related pathologies, namely, chronic progressive nephropathy (CPN) and testicular tumorigenesis. Although kidney pathology was observed in 87% CF rats and CPN in 62% of CF animals, no evidence of kidney disease was observed in MR rats. Consistent with the absence of renal pathology, urinary albumin levels were lower in the MR group compared to controls throughout the study, with over a six-fold difference between the groups at 30 months of age. Biomarkers associated with renal disease, namely, clusterin, cystatin C, and β-2 microglobulin, were reduced following 18 months of MR. A reduction in testicular tumor incidence from 88% in CF to 22% in MR rats was also observed. These results suggest that MR may lead to metabolic and cellular changes providing protection against age-related diseases.

Dietary sulfur amino acid restriction upregulates DICER to confer beneficial effects

Objective

Dietary restriction (DR) improves health and prolongs lifespan in part by upregulating type III endoribonuclease DICER in adipose tissue. In this study, we aimed to specifically test which missing dietary component was responsible for DICER upregulation.

Methods

We performed a nutrient screen in mouse preadipocytes and validated the results in vivo using different kinds of dietary interventions in wild type or genetically modified mice and worms, also testing the requirement of DICER on the effects of the diets.

Results

We found that sulfur amino acid restriction (i.e., methionine or cysteine) is sufficient to increase Dicer mRNA expression in preadipocytes. Consistently, while DR increases DICER expression in adipose tissue of mice, this effect is blunted by supplementation of the diet with methionine, cysteine, or casein, but not with a lipid or carbohydrate source. Accordingly, dietary methionine or protein restriction mirrors the effects of DR. These changes are associated with alterations in serum adiponectin. We also found that DICER controls and is controlled by adiponectin. In mice, DICER plays a role in methionine restriction-induced upregulation of Ucp1 in adipose tissue. In C. elegans, DR and a model of methionine restriction also promote DICER expression in the intestine (an analog of the adipose tissue) and prolong lifespan in a DICER-dependent manner.

Conclusions

We propose an evolutionary conserved mechanism in which dietary sulfur amino acid restriction upregulates DICER levels in adipose tissue leading to beneficial health effects.

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DICER is upregulated in adipose tissue by dietary sulfur amino acid restriction.

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Adiponectin and DICER co-regulate each other in adipocytes.

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Methionine restriction requires DICER to promote adipose tissue browning.

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DICER is upregulated in Caenorhabditis elegans intestine upon dietary restriction.

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Methionine restriction requires DICER to prolong lifespan in C. elegans.

The effect of short-term methionine restriction on glutathione synthetic capacity and antioxidant responses at the whole tissue and mitochondrial level in the rat liver

Dietary methionine restriction (MR) where methionine is the sole source of sulfur amino acid increases lifespan in diverse species. Methionine restricted rodents experience a decrease in glutathione (GSH), a major antioxidant, in several tissues, which is paradoxical to longevity interventions because tissues with low GSH might experience more oxidative damage. Liver plays a key role in GSH synthesis and here we examined how MR influences GSH metabolism in the liver. We also hypothesised that low GSH might be subsidized by compensatory pathway(s) in the liver. To investigate GSH synthesis and antioxidant responses, Fischer-344 rats were given either a MR diet or a control diet for 8 weeks. Based on γ-glutamylcysteine synthetase activity, GSH synthetic capacity did not respond to low dietary methionine availability. Tissue level protein and lipid oxidation markers do not support elevated oxidative damage, despite low GSH availability. Whole tissue and mitochondrial level responses to MR differed. Specifically, the activity of glutathione reductase and thioredoxin reductase increase in whole liver tissue which might offset the effects of declined GSH availability whereas mitochondrial GSH levels were unperturbed by MR. Moreover, enhanced proton leak in liver mitochondria by MR (4 week) presumably diminishes ROS production. Taken together, we suggest that the effect of low GSH in liver tissue is subsidized, at least in part, by increased antioxidant activity and possibly by enhanced mitochondrial proton leak.

Methionine restriction activates the integrated stress response in triple-negative breast cancer cells by a GCN2- and PERK-independent mechanism

Transformed cells are often selectively susceptible to depletion of the amino acid methionine, which induces growth arrest and/or apoptosis. In non-transformed cells, amino acid deficiency is sensed by two stress-activated kinases, general control nonderepressible 2 (GCN2) and protein kinase R-like endoplasmic reticulum kinase (PERK), which phosphorylate and inactivate elongation initiation factor 2 α (eIF2α), thereby suppressing global mRNA translation and inducing activated transcription factor (ATF4). ATF4 and its downstream transcriptional targets including Sestrin-2 constitute an adaptive integrated stress response. We postulated that methionine depletion activates the integrated stress response in breast cancer cells by a GCN2- and/or PERK-dependent mechanism and that selective disruption of one or both of these kinases would enhance the therapeutic activity of methionine restriction. Here we demonstrate that methionine restriction induces eIF2α phosphorylation and enhances ATF4 gene expression and protein levels of ATF4 and Sestrin-2 in triple (ER/PR/HER2)-negative breast cancer (TNBC) cells. However, knockdown of GCN2, PERK or both in TNBC cells did not prevent induction of ATF4 or Sestrin-2 by methionine restriction. In contrast, deletion of GCN2 in murine embryonic fibroblasts abrogated ATF4 and Sestrin-2 induction in response to methionine restriction. Moreover, knockdown of GCN2, PERK or both did not affect TNBC cell growth or apoptosis in response to methionine restriction. Overall, our findings point to a GCN2- and PERK-independent mechanism(s) by which methionine restriction activates the integrated stress response in TNBC cells. Elucidation of this pathway(s) could lead to strategies to enhance the therapeutic response of methionine restriction.

Development of Recombinant Methioninase for Cancer Treatment

The elevated requirement for methionine (MET) of cancer cells is termed MET dependence. To selectively target the MET dependence of tumors for treatment on a large-scale preclinical and clinical basis, the L-methionine α-deamino-γ-mercaptomethane-lyase (EC 4.4.1.11) (methioninase, [METase]) gene from Pseudomonas putida has been cloned in Escherichia coli using the polymerase chain reaction (PCR). Purification using two DEAE Sepharose FF ion-exchange column and one ActiClean Etox endotoxin-affinity chromatography column has been established. Plasmid pMGLTrc03, which has a trc promoter and a spacing of 12 nucleotides between the Shine-Dalgarno sequence and the ATG translation initiation codon, was selected as the most suitable plasmid. The recombinant bacteria produced rMETase at 43% of the total proteins in soluble fraction by simple batch fermentation using a 500 L fermentor. Crystals were directly obtained from crude enzyme with 87% yield by a crystallization in the presence of 9.0% polyethylene glycol 6000, 3.6% ammonium sulfate, and 0.18 M sodium chloride using a 100 L crystallizer. After recrystallization, the enzyme was purified by anion-exchange column chromatography to remove endotoxins and by gel filtration for polishing. Purified rMETase is stable to lyophilization. In order to prevent immunological reactions which might be produced by multiple dosing of rMETase and to prolong the serum half-life of rMETase, the N-hydroxysuccinimidyl ester of methoxypolyethylene glycol propionic acid (M-SPA-PEG 5000) has been coupled to rMETase. The PEGylated molecules (PEG-rMETase) were purified from unreacted PEG with Amicon 30 K centriprep concentrators or by Sephacryl S-300 HR gel-filtration chromatography. Unreacted rMETase was removed by DEAE Sepharose FF anion-exchange chromatography. The resulting PEG-rMETase subunit, produced from a PEG/rMETase ratio of 30/1 in the synthetic reaction, had a molecular mass of approximately 53 kda determined by matrix-assisted laser desorption/ionization mass spectrometry, indicating the conjugation of two PEG molecules per subunit of rMETase and eight per tetramer. PEG-rMETase molecules obtained from reacting ratios of PEG/rMETase of 30/1 had an enzyme activity of 70% of unmodified rMETase. PEGylation of rMETase increased the serum half-life of the enzyme in rats to approximately 160 min compared to 80 min for unmodified rMETase. PEG-rMETase could deplete serum MET levels to less than 0.1 μM for approximately 8 h compared to 2 h for rMETase in rats. A significant prolongation of in vivo activity and effective MET depletion by the PEG-rMETase were achieved by the simultaneous administration of pyridoxal 5'-phosphate. rMETase was also conjugated with methoxypolyethylene glycol succinimidyl glutarate 5000 (MEGC-PEG). Miniosmotic pumps containing various concentrations of PLP were implanted in BALB-C mice. PLP-infused mice were then injected with a single dose of 4000 or 8000 units/kg PEG-rMETase. Mice infused with 5, 50, 100, 200, and 500 mg/mL PLP-containing miniosmotic pumps increased plasma PLP to 7, 24, 34, 60, and 95 μM, respectively, from the PLP baseline of 0.3 μM. PLP increased the half-life of MEGC-PEG-rMETase holoenzyme in a dose-dependent manner. The extended time of MET depletion by MEGC-PEG-rMETase was due to the maintenance of active MEGC-PEG-rMETase holoenzyme by infused PLP.

Methionine Restriction and Life-Span Extension

It has been known for almost a century that caloric restriction can extend the life span of rodents and many other types of animals. Approximately 25 years ago, it was found that a methionine-restricted (MR) diet could replace a caloric-restricted diet with the result of extending the life span of animals. This chapter summarizes the effects of MR on the reversal of diabetes, obesity, and other aspects of the metabolic syndrome, as well as extending the normal life span. The most effective way to restrict methionine in the body, using orally-delivered methioninase, is also explored.

Dietary Methionine Restriction-Based Cancer Chemotherapy in Rodents

The elevated methionine (MET) requirement for the growth of tumors, first observed by Sugimura in 1959, termed MET dependence, is a potentially highly effective therapeutic target. Proof of this principle is that when MET restriction (MR) was initially established in co-cultures of cancer and normal cells, MET dependence could be exploited to selectively kill cancer cells without killing co-cultured normal cells. MET-dependent cells become reversibly blocked in the late S/G₂ phase of the cell cycle under MR enabling selective and effective S-phase chemotherapy against these blocked cancer cells. Subsequent MET repletion with an anti-mitotic drug was totally effective at selectively eliminating the MET-dependent cancer cells enabling the normal MET-dependent cells to take over the culture. We have also observed that the MET analog ethionine (ETH) is synergistic with MR in arresting the growth of the Yoshida sarcoma both in vitro and eliminating metastasis when transplanted to nude mice. MR increased the efficacy of cisplatinum (CDDP) against the MX-1 human breast carcinoma cell line when grown in nude mice. MR increased 5-fluorouracil (5-FU) efficacy on a human gastric cancer xenograft, SC-1-NU, in nude mice. MET-restricted total parenteral nutrition (MR TPN) was effective in Yoshida sarcoma-bearing rats. MR TPN with doxorubicin (DOX) and vincristine (VCR) resulted in significant tumor suppression and prolonged survival of Yoshida-sarcoma-bearing rats. These results were the basis of subsequent studies that used methioninase to effect MR for effective cancer therapy.

Isolation and Characterization of Methionine-Independent Clones from Methionine-Dependent Cancer Cells

Unlike normal cells, transformed cells are unable to grow when methionine in the growth media is restricted. Reversion to methionine independence is a rare event in transformed and malignant cells. Methionine-independent revertants provide an excellent system to identify metabolic signatures and molecular characteristics associated with methionine dependency of transformed cells. Revertants maintain the genetic background and general growth behavior of the parental cell line, except that they proliferate under methionine restriction such as in methionine-free media supplemented with homocysteine. Here we describe a general approach to generate methionine-independent revertants using the example of the triple-negative breast cancer cell line MDA-MB-468. To validate and characterize reversion we describe assays to evaluate cell proliferation and anchorage-independent growth in soft agar.

Altered Methionine Metabolism in Cancer Cells

Many different types of cancer cells have been shown to be methionine (MET) dependent. Cancer cells, unlike normal cells, grow poorly or not at all when MET is restricted. Cancer cells have an elevated requirement for exogenous MET for growth, despite high levels of endogenous synthesis. This requirement reflects increased utilization of MET by cancer cells, analogous to increased utilization glucose by cancer cells (Warburg effect). To answer the critical question of whether MET-dependent cancer cells synthesize normal amounts of MET, we determined the levels of MET, S-adenosylmethionine (AdoMET), and S-adenosylhomocysteine (AdoHCY) that were synthesized by MET-dependent cancer cells under conditions of MET restriction. We demonstrated that MET-dependent cells synthesize a normal amount of endogenously synthesized MET but are still deficient in AdoMET. In contrast, exogenously supplied MET results in normal AdoMET levels. The ratio of AdoMET to AdoHCY is low in MET-dependent cells growing in MET-restricted medium but is normal when MET is supplied. Under conditions of MET restriction, the low AdoMET/AdoHCY ratio probably limits proliferation of MET-dependent cancer cells. The amount of free MET is also low in MET-dependent cancer cells under MET restriction. The elevated MET requirement for cancer cells may be due to enhanced overall rates of transmethylation compared to normal human cells. Thus, MET-dependent cancer cells have low levels of free MET, low levels of AdoMET, and elevated levels of AdoHCY under conditions of MET restriction probably due to overuse of MET for transmethylation reactions ("Hoffman effect"), thereby blocking cellular proliferation.

Clinical Studies of Methionine-Restricted Diets for Cancer Patients

Methionine (MET) restriction (MR) has been shown to arrest cancer growth and sensitizes tumors to chemotherapy. MR total parenteral nutrition (MR TPN) with a chemotherapy-containing amino acid solution ("AO-90") (lacking both MET and L-cysteine[CYS]) showed synergistic effects with 5-fluorouracil (5-FU) in tumor-bearing rats and in a Phase I clinical trial with gastrointestinal tract cancers compared to 5-FU in a MET-containing TPN. All gastric cancer patients underwent gastrectomy. Resected tumors in the AO-90 group showed significant reduction of cancer histologically, while almost no effect was seen in the control group. A Phase II clinical trial of dietary MR combined with cystemustine treatment for melanoma or glioma was carried out. Twenty-two patients (20 with metastatic melanoma and 2 with recurrent gloma) received a median of four cycles of the combination of a 1-day MR diet with cystemustine (60 mg/m²) every 2 weeks. This combination was well tolerated (toxicity and nutritional status). The median disease-free survival was 1.8 months and the median survival was 4.6 months, with two long-duration stabilizations. MET depletion in plasma was 40%. In another study, eight patients with a variety of metastatic solid tumors were enrolled in a Phase I clinical trial of a commercially available MR medical food. Participants remained on the experimental diet for an average of 17.3 weeks. Plasma methionine levels fell from 21.6 to 9 μm within 2 weeks, a 58% decline. The only side effect was weight loss of approximately 0.5 kg per week. A feasibility study combining dietary MR with a FOLFOX regimen in patients with metastatic colorectal cancer was carried out. The plasma MET concentration was reduced by dietary MR by 58% on the first day of the MR diet. Among the four patients evaluable for response, three experienced a partial response and one patient had disease stabilization. The results of the above-described clinical trials indicate the clinical potential of MR.

Tumor-Specific S/G2-Phase Cell Cycle Arrest of Cancer Cells by Methionine Restriction

Cancer cells require elevated amounts of methionine (MET) and arrest their growth under conditions of MET restriction (MR). This phenomenon is termed MET dependence. Fluorescence-activated cell sorting (FACS) first indicated that the MET-dependent SV40-transformed cancer cells were arrested in the S and G₂ phases of the cell cycle when under MR. This is in contrast to a G₁-phase accumulation of cells, which occurs only in MET-supplemented medium at very high cell densities and which is similar to the G₁ cell-cycle block which occurs in cultures of normal fibroblasts at high density. When the human PC-3 prostate carcinoma cell line was cultured in MET-free, homocysteine-containing (MET^-HCY⁺) medium, there was an extreme increment in DNA content without cell division indicating that the cells were blocked in S phase. Recombinant methioninase (rMETase) treatment of cancer cells also selectively trapped cancer cells in S/G₂: The cell cycle phase of the cancer cells was visualized with the fluorescence ubiquitination cell cycle indicator (FUCCI). At the time of rMETase-induced S/G₂-phase trap, identified by the cancer cells' green fluorescence by FUCCI imaging, the cancer cells were administered S-phase-dependent chemotherapy drugs, which interact with DNA or block DNA synthesis such as doxorubicin, cisplatin, or 5-fluorouracil (5-FU) and which were highly effective in killing the cancer cells. In contrast, treatment of cancer cells with drugs in the presence of MET, only led to the majority of the cancer cell population being blocked in G₀/G₁ phase, identified by the cancer cells becoming red fluorescent in the FUCCI system. The G₀/G₁ blocked cells were resistant to the chemotherapy. MR has the potential for highly effective cell-cycle-based treatment strategy for cancer in the clinic.

Preoperative Protein or Methionine Restriction Preserves Wound Healing and Reduces Hyperglycemia

BACKGROUND

Dietary restriction (DR), defined as reduced nutrient intake without malnutrition, is associated with longevity extension, improved glucose metabolism, and increased stress resistance, but also poor wound healing. Short-term preoperative DR followed by a return to normal feeding after surgery results in improved surgical outcomes in preclinical models. However, the effect of preoperative DR on wound healing and perioperative glucose homeostasis is currently unknown. Here, we tested the effects of two different preoperative DR regimens-protein restriction (PR) and methionine restriction (MR)-on wound healing and perioperative glucose homeostasis using an established murine model of wound healing in both nondiabetic and diabetic mice.

MATERIALS AND METHODS

Surgical outcomes were tested using the McFarlane flap in nondiabetic and streptozotocin-induced diabetic mice. Short-term dietary preconditioning included 1 wk of PR or MR diet (1-2 wk) versus an isocaloric complete diet before surgery; all mice were returned to a complete diet postoperatively. Outcome measures of flap wound recovery included skin viability and laser Doppler imaging of flap perfusion and assessment of CD45+ cell infiltration. Glucose homeostasis was assessed by glucose tolerance testing and by perioperative glucose levels in the diabetic cohort.

RESULTS

No significant differences were observed in percentage of viable skin, perfusion, or immune cell infiltration at 7-10 d after surgery in PR or MR mice compared with controls in healthy or diabetic mice. Preoperative glucose tolerance and postoperative glucose levels were however significantly improved by both PR and MR in diabetic mice.

CONCLUSIONS

Short-term dietary preconditioning with PR or MR did not impair wound healing in nondiabetic or diabetic mice. However, both regimens reduced preoperative hyperglycemia in diabetic mice. Thus, brief preoperative dietary manipulations stand as strategies to potentially improve perioperative hyperglycemia with no deleterious effects on wound healing in mice.

Methionine restriction leads to hyperhomocysteinemia and alters hepatic H2S production capacity in Fischer-344 rats

Dietary methionine restriction (MR) increases lifespan in several animal models. Despite low dietary intake of sulphur amino acids, rodents on MR develop hyperhomocysteinemia. On the contrary, MR has been reported to increase H₂S production in mice. Enzymes involved in homocysteine metabolism also take part in H₂S production and hence, in this study, the impact of MR on hyperhomocysteinemia and H₂S production capacity were investigated using Fischer-344 rats assigned either a control or a MR diet for 8 weeks. The MR animals showed elevated plasma homocysteine accompanied with a reduction in liver cysteine content and methylation potential. It was further found that MR decreased cystathionine-β-synthase (CBS) activity in the liver, however, MR increased hepatic cystathionine-γ-lyase (CGL) activity which is the second enzyme in the transsulfuration pathway and also participates in regulating H₂S production. The relative contribution of CGL in H₂S production increased concomitantly with the increased CGL activity. Additionally, hepatic mercaptopyruvate-sulphur-transferase (MPST) activity also increased in response to MR. Taken together, our results suggest that reduced CBS activity and S-Adenosylmethionine availability contributes to hyperhomocysteinimia in MR animals. Elevated CGL and MPST activities may provide a compensatory mechanism for maintaining hepatic H₂S production capacity in response to the decreased CBS activity.

Dietary methionine restriction: Effects on glucose tolerance, lipid content and micro-RNA composition in the muscle of rainbow trout

Lean muscle mass plays an important role in overall health, as altered skeletal muscle metabolism can impact both the incidence and prevention of conditions related to metabolic health. Intriguingly, dietary methionine restriction (MR) has been shown to ameliorate this phenotype over time potentially through mechanisms related to changes in myogenic precursor cell (MPC) differentiation status. Recently the role of micro-RNAs (miRs) in regulating the expression of muscle specific transcription factors myoD and myogenin as well as signaling molecules involved in skeletal muscle differentiation has been reported in vitro. We performed an 8week feeding trial to determine if MR in vivo could alter miR abundance as well as change metabolic markers. Results show changes in muscle miR abundance for miR-133a at 4weeks with no significant difference seen in miR-210 or miR-206. After 8weeks of MR feeding fish demonstrated increased clearance of glucose, increased fat accumulation in the liver, and decreased fat accumulation in the muscle. These data demonstrate conservation of MR effects on fish metabolism, and suggest, for the first time, that miR-133a might play a role in tissue response to MR.

Exploiting methionine restriction for cancer treatment

Normal cells can synthesize sufficient methionine for growth requirements from homocysteine and 5-methyltetrahydrofolate and vitamin B12. However, many cancer-cell types require exogenous methionine for survival and therefore methionine restriction is a promising avenue for treatment. While the lack of the methionine salvage enzyme methylthioadenosine phosphorylase (MTAP) deficiency is associated with methionine dependence in cancer cells, there are other causes for tumors to require exogenous methionine. In this review we describe studies that show restricting methionine to certain cancers by diet or by enzyme depletion, alone or in combination with certain chemotherapeutics is a promising antitumor strategy. The basis for methionine dependence in tumor cells is also briefly reviewed.

A window into extreme longevity; the circulating metabolomic signature of the naked mole-rat, a mammal that shows negligible senescence

Mouse-sized naked mole-rats (Heterocephalus glaber), unlike other mammals, do not conform to Gompertzian laws of age-related mortality; adults show no age-related change in mortality risk. Moreover, we observe negligible hallmarks of aging with well-maintained physiological and molecular functions, commonly altered with age in other species. We questioned whether naked mole-rats, living an order of magnitude longer than laboratory mice, exhibit different plasma metabolite profiles, which could then highlight novel mechanisms or targets involved in disease and longevity. Using a comprehensive, unbiased metabolomics screen, we observe striking inter-species differences in amino acid, peptide, and lipid metabolites. Low circulating levels of specific amino acids, particularly those linked to the methionine pathway, resemble those observed during the fasting period at late torpor in hibernating ground squirrels and those seen in longer-lived methionine-restricted rats. These data also concur with metabolome reports on long-lived mutant mice, including the Ames dwarf mice and calorically restricted mice, as well as fruit flies, and even show similarities to circulating metabolite differences observed in young human adults when compared to older humans. During evolution, some of these beneficial nutrient/stress response pathways may have been positively selected in the naked mole-rat. These observations suggest that interventions that modify the aging metabolomic profile to a more youthful one may enable people to lead healthier and longer lives.

Methionine Dependency Determination of Human Patient Tumors in Gelfoam® Histoculture

The elevated requirement of methionine by cancer cells (methionine dependence) is a general metabolic abnormality in cancer. Methionine-dependent cancer cells are unable to proliferate and arrest in the late S/G₂ phase of the cell cycle when methionine is restricted in vitro or in vivo. Cell-cycle arrest in late S/G₂ was used as a biomarker of methionine dependence for patient tumors in Gelfoam^® histoculture. Human cancer patient tumors, including tumors of the colon, breast, ovary, prostate, and a melanoma, were observed to be methionine dependent in Gelfoam^® histoculture based on cell cycle analysis. This simple method can be used to screen patient tumors for methionine dependence and then subsequently apply appropriate chemotherapy for these patients to target this cancer-specific metabolic abnormality.

Targeting metabolism in cellular senescence, a role for intervention

Cellular senescence has gained much attention as a contributor to aging and susceptibility to disease. Senescent cells undergo a stable cell cycle arrest and produce pro-inflammatory cytokines. However, an additional feature of the senescence phenotype is an altered metabolic state. Despite maintaining a non-dividing state, senescent cells display a high metabolic rate. Metabolic changes characteristic of replicative senescence include altered mitochondrial function and perturbations in growth signaling pathways, such as the mTORC1-signaling pathway. Recent evidence has raised the possibility that these metabolic changes may be essential for the induction and maintenance of the senescent state. Interventions such as rapamycin treatment and methionine restriction impact key aspects of metabolism and delay cellular senescence to extend cellular lifespan. Here, we review the metabolic changes and potential metabolic regulators of the senescence program. In addition, we will discuss how lifespan-extending regimens prevent metabolic stress that accompanies and potentially regulates the senescence program.

Cutting back on the essentials: Can manipulating intake of specific amino acids modulate health and lifespan?

With few exceptions, nutritional and dietary interventions generally impact upon both old-age quality of life and longevity. The life prolonging effects, commonly observed with dietary restriction reportedly are linked to alterations in protein intake and specifically limiting the dietary intake of certain essential amino acids. There is however a paucity of data methodically evaluating the various essential amino acids on health- and lifespan and the mechanisms involved. Rodent diets containing either lower methionine content, or tryptophan, than that found in commercially available chow, appear to elicit beneficial effects. It is unclear whether all of these favorable effects associated with restricted intake of methionine and tryptophan are due to their specific unique properties or if restriction of other essential amino acids, or proteins in general, may produce similar results. Considerably more work remains to be done to elucidate the mechanisms by which limiting these vital molecules may delay the onset of age-associated diseases and improve quality of life at older ages.

Dietary protein, aging and nutritional geometry

Nearly a century of research has shown that nutritional interventions can delay aging and age- related diseases in many animal models and possibly humans. The most robust and widely studied intervention is caloric restriction, while protein restriction and restriction of various amino acids (methionine, tryptophan) have also been shown to delay aging. However, there is still debate over whether the major impact on aging is secondary to caloric intake, protein intake or specific amino acids. Nutritional geometry provides new perspectives on the relationship between nutrition and aging by focusing on calories, macronutrients and their interactions across a landscape of diets, and taking into account compensatory feeding in ad libitum-fed experiments. Nutritional geometry is a state-space modelling approach that explores how animals respond to and balance changes in nutrient availability. Such studies in insects and mice have shown that low protein, high carbohydrate diets are associated with longest lifespan in ad libitum fed animals suggesting that the interaction between macronutrients may be as important as their total intake.

Pleiotropic responses to methionine restriction

Methionine restriction (MR) extends lifespan across different species. The main responses of rodent models to MR are well-documented in adipose tissue (AT) and liver, which have reduced mass and improved insulin sensitivity, respectively. Recently, molecular mechanisms that improve healthspan have been identified in both organs during MR. In fat, MR induced a futile lipid cycle concomitant with beige AT accumulation, producing elevated energy expenditure. In liver, MR upregulated fibroblast growth factor 21 and improved glucose metabolism in aged mice and in response to a high-fat diet. Furthermore, MR also reduces mitochondrial oxidative stress in various organs such as liver, heart, kidneys, and brain. Other effects of MR have also been reported in such areas as cardiac function in response to hyperhomocysteinemia (HHcy), identification of molecular mechanisms in bone development, and enhanced epithelial tight junction. In addition, rodent models of cancer responded positively to MR, as has been reported in colon, prostate, and breast cancer studies. The beneficial effects of MR have also been documented in a number of invertebrate model organisms, including yeast, nematodes, and fruit flies. MR not only promotes extended longevity in these organisms, but in the case of yeast has also been shown to improve stress tolerance. In addition, expression analyses of yeast and Drosophila undergoing MR have identified multiple candidate mediators of the beneficial effects of MR in these models. In this review, we emphasize other in vivo effects of MR such as in cardiovascular function, bone development, epithelial tight junction, and cancer. We also discuss the effects of MR in invertebrates.

Methionine restriction alters bone morphology and affects osteoblast differentiation

Methionine restriction (MR) extends the lifespan of a wide variety of species, including rodents, drosophila, nematodes, and yeasts. MR has also been demonstrated to affect the overall growth of mice and rats. The objective of this study was to evaluate the effect of MR on bone structure in young and aged male and female C57BL/6J mice. This study indicated that MR affected the growth rates of males and young females, but not aged females. MR reduced volumetric bone mass density (vBMD) and bone mineral content (BMC), while bone microarchitecture parameters were decreased in males and young females, but not in aged females compared to control-fed (CF) mice. However, when adjusted for bodyweight, the effect of MR in reducing vBMD, BMC and microarchitecture measurements was either attenuated or reversed suggesting that the smaller bones in MR mice is appropriate for its body size. In addition, CF and MR mice had similar intrinsic strength properties as measured by nanoindentation. Plasma biomarkers suggested that the low bone mass in MR mice could be due to increased collagen degradation, which may be influenced by leptin, IGF-1, adiponectin and FGF21 hormone levels. Mouse preosteoblast cell line cultured under low sulfur amino acid growth media attenuated gene expression levels of Col1al, Runx2, Bglap, Alpl and Spp1 suggesting delayed collagen formation and bone differentiation. Collectively, our studies revealed that MR altered bone morphology which could be mediated by delays in osteoblast differentiation.

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MR affected the growth rates of males and young females, but not aged females.

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CF and MR mice had similar intrinsic strength properties.

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Low methionine media attenuated bone differentiation genes in MC3T3-E1 preosteoblast cells.

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The lower bone mass in MR mice is appropriate for its smaller body size.

The mitochondrial free radical theory of aging

The mitochondrial free radical theory of aging is reviewed. Only two parameters currently correlate with species longevity in the right sense: the mitochondrial rate of reactive oxygen species (mitROS) production and the degree of fatty acid unsaturation of tissue membranes. Both are low in long-lived animals. In addition, the best-known manipulation that extends longevity, dietary restriction, also decreases the rate of mitROS production and oxidative damage to mtDNA. The same occurs during protein restriction as well as during methionine restriction. These two manipulations also increase maximum longevity in rodents. The decrease in mitROS generation and oxidative stress that takes place in caloric restriction seems to be due to restriction of a single dietary substance: methionine. The information available supports a mitochondrial free radical theory of aging focused on low generation of endogenous damage and low sensitivity of membranes to oxidation in long-lived animals.

Dietary L-methionine restriction decreases oxidative stress in porcine liver mitochondria

Dietary methionine restriction (MetR) has been reported to improve hepatocyte function in mammals. However, the underlying mechanisms remain largely unknown. This study was conducted with a swine model to test the hypothesis that MetR decreases generation of reactive oxygen species (ROS) and attenuates oxidative damage in hepatic mitochondria. Twenty-four 35-day old pigs were fed a control diet or a Met-restricted diet for two weeks. Liver mitochondria were isolated to determine: 8-oxodG in mitochondrial DNA, oxidative-derived proteins markers, including glutamic semialdehyde (GSA), aminoadipic semialdehydes (AASA), carboxyethyl-lysine (CEL), carboxymethyl-lysine (CML), and malondialdehyde lysine (MDAL), mitochondrial H2O2 generation rate; rates of oxygen consumption; free radical leak (FRL); anti-oxidative capacity, electron transport complex activity; and protein abundances of respiratory chain complex subunits (NDUFA9, SDHA, Core 2, and Cox 1), manganese superoxide dismutase (MnSOD), and apoptosis-inducing factor (AIF). Compared with the control, MetR decreased mitochondrial 8-oxodG content, H2O2 generation, FRL (P<0.05), and increased rates of oxygen consumption. Abundances of markers for protein oxidative damage, including GSA, AASA, CEL, and CML, were decreased (P<0.05) by 40%, 30%, 32%, and 28%, respectively, compared with the control. Western blot analysis revealed that MetR decreased (P<0.05) the protein abundances of complex subunits, NDUFA9 and AIF without affecting expression of SDHA, Core 2, Cox 1 or MnSOD. The complex I activity (P<0.05) were lowered in MetR group as compared with that of control. Collectively, our findings indicate that dietary MetR decreases mitochondrial ROS generation primarily via inhibiting complex I activity and ROS generation rather than augmenting anti-oxidative capacity, thereby ameliorating oxidative damage to hepatic mitochondrial DNA and proteins.

Methionine concentration in the diet has a tissue-specific effect on chromosomal stability in female mice

Inadequate nutrient intake can influence the genome. Since methionine is an essential amino acid that may influence DNA integrity due to its role in the one-carbon metabolism pathway, we were interested in whether methionine imbalance can lead to genotoxic events. Adult female Swiss mice were fed a control (0.3% dl-methionine), methionine-supplemented (2.0% DL-methionine) or methionine-deficient (0% DL-methionine) diet over a 10-week period. Chromosomal damage was assessed in peripheral blood using a micronucleus test, and DNA damage was assessed in the liver, heart and peripheral blood tissues using a comet assay. The mRNA expression of the mismatch repair genes Mlh1 and Msh2 was analyzed in the liver. The frequency of micronucleus in peripheral blood was increased by 122% in the methionine-supplemented group (p<0.05). The methionine-supplemented diet did not induce DNA damage in the heart and liver tissues, but it increased DNA damage in the peripheral blood. The methionine-deficient diet reduced basal DNA damage in liver tissue. This reduction was correlated with decreased mRNA expression of Msh2. Our results demonstrate that methionine has a tissue-specific effect because methionine-supplemented diet induced both chromosomal and DNA damage in peripheral blood while the methionine-deficient diet reduced basal DNA damage in the liver.