Hypermethioninemias of genetic and non-genetic origin: A review

The History of Animal and Plant Sulfite Oxidase-A Personal View

Sulfite oxidase is one of five molybdenum-containing enzymes known in eukaryotes where it catalyzes the oxidation of sulfite to sulfate. This review covers the history of sulfite oxidase research starting out with the early years of its discovery as a hepatic mitochondrial enzyme in vertebrates, leading to basic biochemical and structural properties that have inspired research for decades. A personal view on sulfite oxidase in plants, that sulfates are assimilated for their de novo synthesis of cysteine, is presented by Ralf Mendel with numerous unexpected findings and unique properties of this single-cofactor sulfite oxidase localized to peroxisomes. Guenter Schwarz connects his research to sulfite oxidase via its deficiency in humans, demonstrating its unique role amongst all molybdenum enzymes in humans. In essence, in both the plant and animal kingdoms, sulfite oxidase represents an important player in redox regulation, signaling and metabolism, thereby connecting sulfur and nitrogen metabolism in multiple ways.

Pathological role of methionine in the initiation and progression of biliary atresia

Methionine (Met) is an essential amino acid, and its excessive dietary intake and/or its metabolism disturbance could lead to accumulation/depletion of hepatic Met and some of the key intermediates of these pathways, which would interfere normal liver function and would be associated with liver diseases. Biliary atresia (BA) is a life-threatening disease characterized by inflammatory fibrosclerosing changes of the intrahepatic and extrahepatic biliary systems and is the primary cause of obstructive neonatal cholestasis with a rapid course of liver failure. However, its pathogenesis remains unknown. Previous studies reported elevated Met level in patients with obstructive cholestasis, suggesting a potential link between Met and BA. This paper reviews the Met metabolism in normal conditions and its dysregulation under abnormal conditions, the possible causes of hypermethioninemia, and its connection to BA pathogenesis: Abnormal hepatic level of Met could lead to a perturbation of redox homeostasis and mitochondrial functions of hepatocytes, enhancement of viral infectivity, and dysregulation of innate and adaptative immune cells in response to infection/damage of the liver contributing to the initiation/progression of BA.

Paracetamol toxicity in classic homocystinuria: Effect of N-acetylcysteine on total homocysteine

Classical homocystinuria (HCU) is caused by cystathionine β-synthase deficiency leading to impaired homocysteine transsulfuration and accumulation of homocysteine and methionine. Patients present with a wide spectrum of manifestations including ocular, skeletal, neuropsychiatric, and vascular manifestations. We report a 48-year-old female with pyridoxine-unresponsive HCU treated with betaine, cyanocobalamin, and folate. Her diet was non-restricted due to intolerance of low-methionine diet. She was admitted to hospital following a fall, with multiple fractures and subsequently developed acute liver failure with encephalopathy. Shock, sepsis, and liver ischaemia/thrombosis were excluded. In the context of glutathione depletion expected in HCU, hepatic dysfunction was presumed to be due to iatrogenic paracetamol toxicity, despite paracetamol intake at conventional therapeutic dose, with role of hypermethioninemia as a contributing factor being uncertain. Betaine was discontinued on hospital admission. N-Acetylcysteine (NAC) infusion was initiated. Plasma total homocysteine (tHcy) was 3.4 μmol/L 9 days following initiation of NAC treatment with a markedly elevated plasma methionine of 1278 μmol/L. tHcy concentration returned to pre-admission baseline after NAC was discontinued. Recovery following this episode was slow with a prolonged cholestatic phase and gradual improvement in jaundice and coagulopathy. We recommend that paracetamol should be administered cautiously in HCU patients due to underlying glutathione depletion and risk of toxicity even at therapeutic doses. NAC is clearly effective in lowering tHcy in classical HCU in the short-term however further research is required to assess clinical efficacy and use as a potential therapy in classical HCU.

Cystathionine Beta-Synthase Deficiency: Three Consecutive Cases Detected in 40 Days by Newborn Screening in Emilia Romagna (Italy) and a Comprehensive Review of the Literature

Cysthiatonine beta-synthase (CBS) deficiency (CBSD) is an autosomal recessive rare disorder caused by variations on CBS that leads to impaired conversion of homocysteine (Hcy) to cystathionine. Marked hyperhomocysteinemia is the hallmark of the disease. The administration of pyridoxine, the natural cofactor of CBS, may reduce total plasma Hcy. Patient phenotype is classified on pyridoxine responsivity in two groups: pyridoxine-responsive and non-responsive patients. Ectopia lentis, bone deformities, developmental delay, and thromboembolism are the classic signs and symptoms of the disease. Early diagnosis and treatment impact patients' natural history. Therapy aims to lower promptly and maintain Hcy concentrations below 100 μmol/L. Depending on the patient's phenotype, the treatment goals could be obtained by the administration of pyridoxine and/or betaine associated with a methionine-restricted diet. CBSD could be diagnosed in the early days of life by expanded newborn screening (ENS), however, the risk of false negative results is not negligible. In Emilia-Romagna (Italy), during the first 10 years of screening experience, only three cases of CBSD identified have been diagnosed, all in the last two years (incidence 1:118,000 live births). We present the cases and a comprehensive review of the literature to emphasize the role of ENS for early diagnosis of CBSD and its potential pitfalls, reiterating the need for a more effective method to screen for CBSD.

The metabolic and lipidomic profiling of the effects of tracheal occlusion in a rabbit model of congenital diaphragmatic hernia

PURPOSE

Fetal tracheal occlusion (TO) reverses the pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH), but its mechanism of action remains poorly understood. 'Omic' readouts capture metabolic and lipid processing function, which aid in understanding CDH and TO metabolic mechanisms.

METHODS

CDH was created in fetal rabbits at 23 days, TO at 28 days and lung collection at 31 days (Term ∼32 days). Lung-body weight ratio (LBWR) and mean terminal bronchiole density (MTBD) were determined. In a cohort, left and right lungs were collected, weighed, and samples homogenized, and extracts collected for non-targeted metabolomic and lipidomic profiling via LC-MS and LC-MS/MS, respectively.

RESULTS

LBWR was significantly lower in CDH while CDH + TO was similar to controls (p = 0.003). MTBD was significantly higher in CDH fetuses and restored to control and sham levels in CDH + TO (p < 0.001). CDH and CDH + TO resulted in significant differences in metabolome and lipidome profiles compared to sham controls. A significant number of altered metabolites and lipids between the controls and CDH groups and the CDH and CDH + TO fetuses were identified. Significant changes in the ubiquinone and other terpenoid-quinone biosynthesis pathway and the tyrosine metabolism pathway were observed in CDH + TO.

CONCLUSION

CDH + TO reverses pulmonary hypoplasia in the CDH rabbit, in association with a specific metabolic and lipid signature. A synergistic untargeted 'omics' approach provides a global signature for CDH and CDH + TO, highlighting cellular mechanisms among lipids and other metabolites, enabling comprehensive network analysis to identify critical metabolic drivers in disease pathology and recovery.

TYPE OF STUDY

Basic Science, Prospective.

LEVEL OF EVIDENCE

II.

Long-term prognosis of 35 patients with methionine adenosyltransferase deficiency based on newborn screening in China

Methionine adenosyltransferase deficiency (MATD) is a rare metabolic disorder caused by mono- or biallelic MAT1A mutations that are not yet well understood. Of the 4,065,644 neonates screened between November 2010 and December 2021, 35 individuals have been diagnosed with an estimated incidence of 1: 116,161 by a cutoff value of methionine 82.7 μmol/L and follow-up over 11 years. MATD patients with autosomal recessive (AR) type had higher clinical and genetic heterogeneity than those with autosomal dominant (AD) type. Fifteen unrelated AD patients harbored one well-known dominant variant, c.791 G>A or c.776 C>T, and were clinically unaffected with a mean plasma methionine (Met) value <300 μmol/L. Twenty AR cases have unique genotypes and presented a wide range of clinical abnormalities from asymptomatic to white matter lesions. Of them, 10 AR patients displayed severe manifestations, such as verbal difficulty, motor delay, development delay, and white matter lesions, with mean Met >500 μmol/L and thereby were treated with a methionine-restricted diet alone or in combination with betaine, folate, or vitamin B6, and were healthy finally. Neurological abnormalities were evidenced in two patients (P16 and P27) with Met values >800 μmol/L by MRI scan. Neurological abnormalities were reversed here by liver transplantation or by the determination of S-adenosylmethionine supplementation. Additionally, 38 variants of MAT1A were distributed within patients and carriers, of which 24 were novel and mostly predicted to be damaged. Our findings with an extensive clinical and genetic dataset provided new insights into its diagnosis and treatment and will be helpful for its optimal management in the future.

Hippocampal vulnerability to hyperhomocysteinemia worsens pathological outcomes of mild traumatic brain injury in rats

Background

Mild traumatic brain injury (mTBI) generally resolves within weeks. However, 15-30% of patients present persistent pathological and neurobehavioral sequelae that negatively affect their quality of life. Hyperhomocysteinemia (HHCY) is a neurotoxic condition derived from homocysteine accumulation above 15 μM. HHCY can occur in diverse stressful situations, including those sustained by U.S. active-duty service members on the battlefield or during routine combat practice. Mild-TBI accounts for more than 80% of all TBI cases, and HHCY exists in 5-7% of the general population. We recently reported that moderate HHCY exacerbates mTBI-induced cortical injury pathophysiology, including increased oxidative stress. Several studies have demonstrated hippocampus vulnerability to oxidative stress and its downstream effects on inflammation and cell death.

Objective

This study aimed to assess the deleterious impact of HHCY on mTBI-associated hippocampal pathological changes. We tested the hypothesis that moderate HHCY aggravates mTBI-induced hippocampal pathological changes.

Methods

HHCY was induced in adult male Sprague-Dawley rats with a high methionine dose. Rats were then subjected to mTBI by controlled cortical impact under sustained HHCY. Blood plasma was assessed for homocysteine levels and brain tissue for markers of oxidative stress, blood-brain barrier integrity, and cell death. Endothelial cell ultrastructure was assessed by Electron Microscopy and working memory performance using the Y maze test.

Results

HHCY increased the hippocampal expression of nitrotyrosine in astroglial cells and decreased tight junction protein occludin levels associated with the enlargement of the endothelial cell nucleus. Furthermore, HHCY altered the expression of apoptosis-regulating proteins α-ii spectrin hydrolysis, ERK1/2, and AKT phosphorylation, mirrored by exacerbated mTBI-related hippocampal neuronal loss and working memory deficits.

Conclusion

Our findings indicate that HHCY is an epigenetic factor that modulates mTBI pathological progression in the hippocampus and represents a putative therapeutic target for mitigating such physiological stressors that increase severity.

Chemical hypermethioninemia in young mice: oxidative damage and reduction of antioxidant enzyme activity in brain, kidney, and liver

High levels of methionine (Met) and its metabolites, such as methionine sulfoxide (MetO), found in hypermethioninemia, can be detrimental to the body; however, the underlying mechanisms are still uncertain. Using a recently standardized protocol, the aim of this study was to investigate the effects of chronic administration of Met and/or MetO on parameters of oxidative damage in the total brain, liver, and kidney of young mice. Swiss male mice were subcutaneously injected with Met and MetO at concentrations of 0.35-1.2 g/kg body weight and 0.09-0.3 g/kg body weight, respectively, from the 10th-38th day post-birth, while the control group was treated with saline solution. Results showed that Met and/or MetO caused an increase in reactive oxygen species (ROS) and lipoperoxidation, along with a reduction of superoxide dismutase (SOD) and catalase (CAT) activities in the brain. In the liver, Met and/or MetO enhanced ROS and nitrite levels, and reduced SOD, CAT, and delta aminolevulinic dehydratase activities. The effects on the kidney were an increase in ROS production and SOD activity, and a reduction in thiol content and CAT activity. These data demonstrated the contribution of redox imbalance to the systemic changes found in patients with hypermethioninemia. In conclusion, our findings may help future studies to better understand the pathophysiological mechanisms of hypermethioninemia as well as contribute to the search for new therapeutic agents for this pathology.

Quantification of Plasma S-adenosylmethionine and S-adenosylhomocysteine Using Liquid Chromatography-Electrospray-Tandem Mass Spectrometry

We describe a simple stable isotope dilution method for accurate determination of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) in plasma as a clinical diagnostic test. Determination of SAM/SAH in plasma (20 μL) was performed by high-performance liquid chromatography coupled with electrospray positive ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Calibrators (SAM and SAH) and internal standards (²H₃-SAM and ²H₄-SAH) were included in each analytical run for calibration. Sample preparation involved combining 20 μL sample with 180 μL of internal standard solution consisting of heavy-isotope-labeled internal standards in mobile phase A and filtering by ultracentrifugation through a 10 kd MW cutoff membrane. Sample filtrate (3 μL) was injected by a Shimadzu Nexera LC System interfaced with a 5500 QTRAP® (Sciex). Chromatographic separation was achieved on a 250 mm × 2.0 mm EZ-faast column from Phenomenex. Samples were eluted at a flow rate of 0.20 mL/min with a binary gradient with a total run time of 10 min. The source operated in positive ion mode at an ion spray voltage of +5000 V. SAM and SAH resolved by a gradient to 100% methanol with retention times of 5.8 and 5.5 min, respectively. HPLC chromatographic conditions did not produce complete separation of SAM and SAH, but they were completely discerned by their different fragmentation pattern in the mass spectrometer working in the MS-MS mode. The observed m/z values of the fragment ions were m/z 399→250 for SAM, m/z 385→136 for SAH, m/z 402→250 for ²H₃-SAM, and m/z 203→46. The calibration curve was linear over the range of 12.5-5000 nmol/L for SAM and SAH.

Homocystinuria and ocular complications - A review

Homocystinuria is a rare metabolic inborn disorder caused due to dysfunctional cystathionine β-synthase (CBS) enzyme activity, thus resulting in elevated levels of methionine and homocysteine in the blood and urine. The timely recognition of this rare metabolic disorder and prompt methionine-restricted diet are crucial in lessening the systemic consequences. The recalcitrant cases have a higher risk for cardiovascular diseases, neurodegenerative diseases, neural tube defects, and other severe clinical complications. This review aims to present the ophthalmic spectrum of homocystinuria and its molecular basis, the disease management, as well as the current and potential treatment approaches with a greater emphasis on preventive strategies.

Methionine Adenosyltransferase I/III Deficiency Detected by Newborn Screening

Methionine adenosyltransferase I/III deficiency is an inborn error of metabolism due to mutations in the MAT1A gene. It is the most common cause of hypermethioninemia in newborn screening. Heterozygotes are often asymptomatic. In contrast, homozygous or compound heterozygous individuals can develop severe neurological symptoms. Less than 70 cases with biallelic variants have been reported worldwide. A methionine-restricted diet is recommended if methionine levels are above 500−600 µmol/L. In this study, we report on a female patient identified with elevated methionine concentrations in a pilot newborn screening program. The patient carries a previously described variant c.1132G>A (p.Gly378Ser) in homozygosity. It is located at the C-terminus of MAT1A. In silico analysis suggests impaired protein stability by β-turn disruption. On a methionine-restricted diet, her serum methionine concentration ranged between 49−605 µmol/L (median 358 µmol/L). Her clinical course was characterized by early-onset muscular hypotonia, mild developmental delay, delayed myelination and mild periventricular diffusion interference in MRI. At 21 months, the girl showed age-appropriate neurological development, but progressive diffusion disturbances in MRI. Little is known about the long-term outcome of this disorder and the necessity of treatment. Our case demonstrates that neurological symptoms can be transient and even patients with initial neurologic manifestations can show normal development under dietary management.

Analysis of S-Adenosylmethionine and S-Adenosylhomocysteine: Method Optimisation and Profiling in Healthy Adults upon Short-Term Dietary Intervention

S-adenosylmethionine (SAM) is essential for methyl transfer reactions. All SAM is produced de novo via the methionine cycle. The demethylation of SAM produces S-adenosylhomocysteine (SAH), an inhibitor of methyltransferases and the precursor of homocysteine (Hcy). The measurement of SAM and SAH in plasma has value in the diagnosis of inborn errors of metabolism (IEM) and in research to assess methyl group homeostasis. The determination of SAM and SAH is complicated by the instability of SAM under neutral and alkaline conditions and the naturally low concentration of both SAM and SAH in plasma (nM range). Herein, we describe an optimised LC-MS/MS method for the determination of SAM and SAH in plasma, urine, and cells. The method is based on isotopic dilution and employs 20 µL of plasma or urine, or 500,000 cells, and has an instrumental running time of 5 min. The reference ranges for plasma SAM and SAH in a cohort of 33 healthy individuals (age: 19-60 years old; mean ± 2 SD) were 120 ± 36 nM and 21.5 ± 6.5 nM, respectively, in accordance with independent studies and diagnostic determinations. The method detected abnormal concentrations of SAM and SAH in patients with inborn errors of methyl group metabolism. Plasma and urinary SAM and SAH concentrations were determined for the first time in a randomised controlled trial of 53 healthy adult omnivores (age: 18-60 years old), before and after a 4 week intervention with a vegan or meat-rich diet, and revealed preserved variations of both metabolites and the SAM/SAH index.

Long-term functional correction of cystathionine β-synthase deficiency in mice by adeno-associated viral gene therapy

Cystathionine β-synthase (CBS) deficiency is a recessive inborn error of sulfur metabolism characterized by elevated blood levels of total homocysteine (tHcy). Patients diagnosed with CBS deficiency are currently treated by a combination of vitamin supplementation and restriction of foods containing the homocysteine precursor methionine, but the effectiveness of this therapy is limited due to poor compliance. A mouse model for CBS deficiency (Tg-I278T Cbs^-/- ) was used to evaluate a potential gene therapy approach to treat CBS deficiency utilizing an AAVrh.10-based vector containing the human CBS cDNA downstream of the constitutive, strong CAG promoter (AAVrh.10hCBS). Mice were administered a single dose of virus and followed for up to 1 year. The data demonstrated a dose-dependent increase in liver CBS activity and a dose-dependent decrease in serum tHcy. Liver CBS enzyme activity at 1 year was similar to Cbs^+/- control mice. Mice given the highest dose (5.6 × 10¹¹ genomes/mouse) had mean serum tHcy decrease of 97% 1 week after injection and an 81% reduction 1 year after injection. Treated mice had either full- or substantial correction of alopecia, bone loss, and fat mass phenotypes associated with Cbs deficiency in mice. Our findings show that AAVrh.10-based gene therapy is highly effective in treating CBS deficiency in mice and supports additional pre-clinical testing for eventual use human trials.

A genetic model of methionine restriction extends Drosophila health- and lifespan

Loss of metabolic homeostasis is a hallmark of aging and is characterized by dramatic metabolic reprogramming. To analyze how the fate of labeled methionine is altered during aging, we applied ¹³C5-Methionine labeling to Drosophila and demonstrated significant changes in the activity of different branches of the methionine metabolism as flies age. We further tested whether targeted degradation of methionine metabolism components would "reset" methionine metabolism flux and extend the fly lifespan. Specifically, we created transgenic flies with inducible expression of Methioninase, a bacterial enzyme capable of degrading methionine and revealed methionine requirements for normal maintenance of lifespan. We also demonstrated that microbiota-derived methionine is an alternative and important source in addition to food-derived methionine. In this genetic model of methionine restriction (MetR), we also demonstrate that either whole-body or tissue-specific Methioninase expression can dramatically extend Drosophila health- and lifespan and exerts physiological effects associated with MetR. Interestingly, while previous dietary MetR extended lifespan in flies only in low amino acid conditions, MetR from Methioninase expression extends lifespan independently of amino acid levels in the food. Finally, because impairment of the methionine metabolism has been previously associated with the development of Alzheimer's disease, we compared methionine metabolism reprogramming between aging flies and a Drosophila model relevant to Alzheimer's disease, and found that overexpression of human Tau caused methionine metabolism flux reprogramming similar to the changes found in aged flies. Altogether, our study highlights Methioninase as a potential agent for health- and lifespan extension.

Methionine supplementation for multi-organ dysfunction in MetRS-related pulmonary alveolar proteinosis

INTRODUCTION

Pulmonary alveolar proteinosis related to mutations in the methionine tRNA synthetase (MARS1) gene is a severe, early-onset disease that results in death before the age of 2 years in one-third of patients. It is associated with a liver disease, growth failure and systemic inflammation. As methionine supplementation in yeast models restored normal enzymatic activity of the synthetase, we studied the tolerance, safety and efficacy of daily oral methionine supplementation in patients with severe and early disease.

METHODS

Four patients received methionine supplementation and were followed for respiratory, hepatic, growth, and inflammation-related outcomes. Their course was compared to those of historical controls. Reactive oxygen species (ROS) production by patient monocytes before and after methionine supplementation was also studied.

RESULTS

Methionine supplementation was associated with respiratory improvement, clearance of the extracellular lipoproteinaceous material, and discontinuation of whole-lung lavage in all patients. The three patients who required oxygen or non-invasive ventilation could be weaned off within 60 days. Liver dysfunction, inflammation, and growth delay also improved or resolved. At a cellular level, methionine supplementation normalised the production of reactive oxygen species by peripheral monocytes.

CONCLUSION

Methionine supplementation was associated with important improvements in children with pulmonary alveolar proteinosis related to mutations in the MARS1 gene. This study paves the way for similar strategies for other tRNA synthetase deficiencies.

Clinical utility of methionine restriction in adenosine kinase deficiency

Adenosine kinase (ADK) deficiency is a rare autosomal recessive inborn error of metabolism involving the methionine and purine metabolic pathways. Prior reports show that most patients present in infancy with jaundice, hypotonia, developmental delay, and mild dysmorphic features. Characteristic biochemical findings included hypoglycemic hyperinsulinism, cholestasis, elevated liver functions, methionine, S-adenosylhomocysteine, and S-adenosylmethionine, with normal or mildly elevated homocysteine level. Brain imaging demonstrated atrophy, hydrocephalus, and delayed myelination. There are 26 reported patients of ADK deficiency, of which 14 patients were placed on a methionine-restricted diet. Clinical improvement with methionine restriction was not well described.

CASE REPORT

We report an infant who presented at birth with persistently elevated ammonia (100-163 μmol/L), hypoglycemia, cholestasis, and liver dysfunction. The initial metabolic and genetic work-up was nondiagnostic, with only a mildly increased plasma methionine level (51 [<38 μmol/L]). Iron depositions in the liver and in lip mucosa led to suspicion of gestational alloimmune liver disease. Immunoglobulin therapy and exchange transfusion treatments demonstrated transient clinical and biochemical improvements. However, subsequent episodes of acute liver failure with development of neurological abnormalities led to further evaluation. Metabolic studies showed a 25-fold increase in plasma methionine level at 8 months of life (1022 [<38 μmol/L]) with white matter abnormalities on brain MRI. Expanded molecular testing identified the disease. Urinary purines profile showed elevations of adenosine and related metabolites. Introduction of a low-methionine diet resulted in rapid clinical amelioration, improvement of brain MRI findings, and normalization of liver functions and methionine levels.

Early Diagnosis of Classic Homocystinuria in Kuwait through Newborn Screening: A 6-Year Experience

Kuwait is a small Arabian Gulf country with a high rate of consanguinity and where a national newborn screening program was expanded in October 2014 to include a wide range of endocrine and metabolic disorders. A retrospective study conducted between January 2015 and December 2020 revealed a total of 304,086 newborns have been screened in Kuwait. Six newborns were diagnosed with classic homocystinuria with an incidence of 1:50,000, which is not as high as in Qatar but higher than the global incidence. Molecular testing for five of them has revealed three previously reported pathogenic variants in the CBS gene, c.969G>A, p.(Trp323Ter); c.982G>A, p.(Asp328Asn); and the Qatari founder variant c.1006C>T, p.(Arg336Cys). This is the first study to review the screening of newborns in Kuwait for classic homocystinuria, starting with the detection of elevated blood methionine and providing a follow-up strategy for positive results, including plasma total homocysteine and amino acid analyses. Further, we have demonstrated an increase in the specificity of the current newborn screening test for classic homocystinuria by including the methionine to phenylalanine ratio along with the elevated methionine blood levels in first-tier testing. Here, we provide evidence that the newborn screening in Kuwait has led to the early detection of classic homocystinuria cases and enabled the affected individuals to lead active and productive lives.

Four Weeks of Aerobic Training Affects Cardiac Tissue Matrix Metalloproteinase, Lactate Dehydrogenase and Malate Dehydrogenase Enzymes Activities, and Hepatorenal Biomarkers in Experimental Hyperhomocysteinemia in Rats

The aim of this study was to investigate the effect of the application of homocysteine as well as its effect under the condition of aerobic physical activity on the activities of matrix metalloproteinases (MMP), lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) in cardiac tissue and on hepato-renal biochemical parameters in sera of rats. Male Wistar albino rats were divided into four groups (n = 10, per group): C: 0.9% NaCl 0.2 mL/day subcutaneous injection (s.c.); H: homocysteine 0.45 µmol/g b.w./day s.c.; CPA saline (0.9% NaCl 0.2 mL/day s.c.) and a program of physical activity on a treadmill; and HPA homocysteine (0.45 µmol/g b.w./day s.c.) and a program of physical activity on a treadmill. Subcutaneous injection of substances was applied 2 times a day at intervals of 8 h during the first two weeks of experimental protocol. Hcy level in serum was significantly higher in the HPA group compared to the CPA group (p < 0.05). Levels of glucose, proteins, albumin, and hepatorenal biomarkers were higher in active groups compared with the sedentary group. It was demonstrated that the increased activities of LDH (mainly caused by higher activity of isoform LDH2) and mMDH were found under the condition of homocysteine-treated rats plus aerobic physical activity. Independent application of homocysteine did not lead to these changes. Physical activity leads to activation of MMP-2 isoform and to increased activity of MMP-9 isoform in both homocysteine-treated and control rats.

Paternal exposure to excessive methionine altered behavior and neurochemical activities in zebrafish offspring

An increase in plasma L-methionine (Met) levels, even if transitory, can cause important toxicological alterations in the affected individuals. Met is essential in the regulation of epigenetic mechanisms and its influence on the subsequent generation has been investigated. However, few studies have explored the influence of a temporary increase in Met levels in parents on their offspring. This study evaluated the behavioral and neurochemical effects of parental exposure to high Met concentration (3 mM) in zebrafish offspring. Adult zebrafish were exposed to Met for 7 days, maintained for additional 7 days in tanks that contained only water, and then used for breeding. The offspring obtained from these fish (F1) were tested in this study. During the early stages of offspring development, morphology, heart rate, survival, locomotion, and anxiety-like behavior were assessed. When these animals reached the adult stage, locomotion, anxiety, aggression, social interaction, memory, oxidative stress, and levels of amino acids and neurotransmitters were analyzed. F1 larvae Met group presented an increase in the distance and mean speed when compared to the control group. F1 adult Met group showed decreased anxiety-like behavior and locomotion. An increase in reactive oxygen species was also observed in the F1 adult Met group whereas lipid peroxidation and antioxidant enzymes did not change when compared to the control group. Dopamine, serotonin, glutamate, and glutathione levels were increased in the F1 adult Met group. Taken together, our data show that even a transient increase in Met in parents can cause behavioral and neurochemical changes in the offspring, promoting transgenerational effects.

Methionine Diet Evoked Hyperhomocysteinemia Causes Hippocampal Alterations, Metabolomics Plasma Changes and Behavioral Pattern in Wild Type Rats

L-methionine, an essential amino acid, plays a critical role in cell physiology. High intake and/or dysregulation in methionine (Met) metabolism results in accumulation of its intermediate(s) or breakdown products in plasma, including homocysteine (Hcy). High level of Hcy in plasma, hyperhomocysteinemia (hHcy), is considered to be an independent risk factor for cerebrovascular diseases, stroke and dementias. To evoke a mild hHcy in adult male Wistar rats we used an enriched Met diet at a dose of 2 g/kg of animal weight/day in duration of 4 weeks. The study contributes to the exploration of the impact of Met enriched diet inducing mild hHcy on nervous tissue by detecting the histo-morphological, metabolomic and behavioural alterations. We found an altered plasma metabolomic profile, modified spatial and learning memory acquisition as well as remarkable histo-morphological changes such as a decrease in neurons' vitality, alterations in the morphology of neurons in the selective vulnerable hippocampal CA 1 area of animals treated with Met enriched diet. Results of these approaches suggest that the mild hHcy alters plasma metabolome and behavioural and histo-morphological patterns in rats, likely due to the potential Met induced changes in "methylation index" of hippocampal brain area, which eventually aggravates the noxious effect of high methionine intake.

Neonatal hyperinsulinism in transient and classical forms of tyrosinemia

BACKGROUND

The spectrum of disorders associated with hyperinsulinemic hypoglycemia (HHI) has vastly increased over the past 20 years with identification of molecular, metabolic and cellular pathways involved in the regulation of insulin secretion and its actions. Hereditary tyrosinemia (HT1) is a rare metabolic disorder associated with accumulation of toxic metabolites of the tyrosine pathway due to a genetically mediated enzyme defect of fumarylacetoacetate hydrolase. Transient tyrosinemia of the newborn (TTN) is a benign condition with a maturational defect of the enzymes associated with tyrosine metabolism without any genetic abnormalities.

RESULTS

We describe two rare cases of HHI, one in a patient with HT1 and for the first time, in a patient with TTN. Each of our patients presented in the neonatal period with persistent hypoglycemia that on biochemical evaluation was consistent with HHI. Each patient received diazoxide therapy for 3.5 months and 17 months of life, respectively and HHI resolved thereafter.

CONCLUSION

Despite the fact that HHI has been described in HT1 for several decades, no specific mechanism has been delineated. Although we considered the common embryonal origin of the liver and pancreas with the hepatotoxic effect in HT1 also impacting the latter, this was not a possible explanation for TTN. The commonality between our two patients is the accumulation of certain amino acids which are known to be insulinotropic. We therefore hypothesize that the excess of amino acids such as leucine, lysine, valine and isoleucine in our patients resulted in HHI, which was transient. Both patients responded to diazoxide. This novel presentation in TTN and the reassuring response in both HT1 and TTN to diazoxide will be useful to inform physicians about managing HHI in these patients. Further studies are required to delineate the mechanism of HHI in these infants.

Holistic Approach in the Management of Skeletal Deformity in a Case of Homocystinuria

INTRODUCTION

Homocystinuria has a wide range of clinical presentations ranging from near normal intelligence and appearance with just lens dislocation and minimal skeletal deformities to severe mental retardation with gross skeletal deformities. In this background, we describe one such case with skeletal deformity managed comprehensively.

CASE REPORT

A 17-year-old boy presented with complaints of deformity of the left lower limb since childhood more evident for the past 5 years along with a history of blurring of vision. On examination the pubis-heal length > crown-pubis length along with genu valgum of left lower-limb with 16 cm intermalleolar distance. He also had a superolateral subluxation of the lens in both eyes. Valgus angle was 16° on the left leg compared to 6° on the right. The diagnosis of homocystinuria was confirmed by biochemical investigations. The left side genu valgum was addressed with medial closing wedge osteotomy and fixed with distal femur locking compression plating. Lens subluxation was treated with posterior chamber intra-ocular lens surgery. He was also given medical treatment and on regular monitoring of his homocysteine levels. The patient had good functional outcome at 2-year follow-up.

CONCLUSION

Homocystinuria is a rare disease that needs early identification and effective management to avoid complications. Skeletal complications are common and include genu valgum, pes cavus, chest wall deformities, and skeletal deformities such as kyphosis and scoliosis. Skeletal deformities can be avoided when identified early and associated osteoporosis which is managed effectively. A holistic approach is needed in the management of such patients with inter-departmental coordination to bring quality to the life of patients with homocystinuria.

Hyperhomocysteinemia-Induced Oxidative Stress Exacerbates Cortical Traumatic Brain Injury Outcomes in Rats

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality among military service members and civilians in the United States. Despite significant advances in the understanding of TBI pathophysiology, several clinical reports indicate that multiple genetic and epigenetic factors can influence outcome. Homocysteine (HCY) is a non-proteinogenic amino acid, the catabolism of which can be dysregulated by stress, lifestyle, aging, or genetic abnormalities leading to hyperhomocysteinemia (HHCY). HHCY is a neurotoxic condition and a risk factor for multiple neurological and cardiovascular disorders that occurs when HCY levels is clinically > 15 µM. Although the deleterious impact of HHCY has been studied in human and animal models of neurological disorders such as stroke, Alzheimer's disease and Parkinson's disease, it has not been addressed in TBI models. This study tested the hypothesis that HHCY has detrimental effects on TBI pathophysiology. Moderate HHCY was induced in adult male Sprague Dawley rats via daily administration of methionine followed by impact-induced traumatic brain injury. In this model, HHCY increased oxidative stress, upregulated expression of proteins that promote blood coagulation, exacerbated TBI-associated blood-brain barrier dysfunction and promoted the infiltration of inflammatory cells into the cortex. We also observed an increase of brain injury-induced lesion size and aggravated anxiety-like behavior. These findings show that moderate HHCY exacerbates TBI outcomes and suggest that HCY catabolic dysregulation may be a significant biological variable that could contribute to TBI pathophysiology heterogeneity.

Homocysteine and Gliotoxicity

Homocysteine is a sulfur amino acid that does not occur in the diet, but it is an essential intermediate in normal mammalian metabolism of methionine. Hyperhomocysteinemia results from dietary intakes of Met, folate, and vitamin B12 and lifestyle or from the deficiency of specific enzymes, leading to tissue accumulation of this amino acid and/or its metabolites. Severe hyperhomocysteinemic patients can present neurological symptoms and structural brain abnormalities, of which the pathogenesis is poorly understood. Moreover, a possible link between homocysteine (mild hyperhomocysteinemia) and neurodegenerative/neuropsychiatric disorders has been suggested. In recent years, increasing evidence has emerged suggesting that astrocyte dysfunction is involved in the neurotoxicity of homocysteine and possibly associated with the physiopathology of hyperhomocysteinemia. This review addresses some of the findings obtained from in vivo and in vitro experimental models, indicating high homocysteine levels as an important neurotoxin determinant of the neuropathophysiology of brain damage. Recent data show that this amino acid impairs glutamate uptake, redox/mitochondrial homeostasis, inflammatory response, and cell signaling pathways. Therefore, the discussion of this review focuses on homocysteine-induced gliotoxicity, and its impacts in the brain functions. Through understanding the Hcy-induced gliotoxicity, novel preventive/therapeutic strategies might emerge for these diseases.

Acute hypermethioninemia impairs redox homeostasis and acetylcholinesterase activity in the hippocampus, striatum, and cerebellum of young rats

Hypermethioninemia is characterized by high plasma concentrations of methionine (Met) and its metabolites, such as methionine sulfoxide (MetO), and neurological changes, such as cerebral edema and cognitive deficits. The aim of this study was to analyze the redox status and acetylcholinesterase (AChE) activity in the hippocampus, striatum, and cerebellum of young Wistar rats subjected to an acute hypermethioninemia protocol. The animals received, by subcutaneous injection, a single dose of Met (0.4 g/kg), MetO (0.1 g/kg), and Met + MetO, and 1 or 3 hr after administration, the animals were euthanatized for brain structure obtaining. In the hippocampus, an increase in lipid peroxidation and glutathione peroxidase (GPx) activity was observed at 1 hr in the MetO and Met + MetO groups, and a reduction in the superoxide dismutase activity was found in the Met + MetO group. Met and/or MetO induced a decrease in the thiol content and GPx activity and enhanced the lipid peroxidation at 3 hr. In the striatum, a reduction in the thiol content and GPx activity, an increase in lipid peroxidation, and AChE activity were induced by Met and/or MetO at 1 or 3 hr. Additionally, in the cerebellum, an increase in the AChE in the MetO and Met + MetO groups 1 hr after administration was observed. These data help to better understand the pathophysiological mechanisms that underlie the neurological changes found in hypermethioninemia patients.

Sensing of L-methionine in biological samples through fully 3D-printed electrodes

The variation in biomarkers levels, such as L-methionine, can be an indicator of health problems or diseases, such as metabolism, neuropsychiatric disorders, or some virus infections. Thus, the development of accurate sensors, with low-cost and rapid response has been gaining increasing importance and attractiveness for the early diagnosis of diseases. In this regard, we have proposed a method for L-methionine electrochemical detection using a low-cost and simple arrangement of 3D-printed electrodes (working, reference, and auxiliary electrodes) based on polylactic acid/graphene filament (PLA-G), in which all electrodes were printed. The working electrode was chemically and electrochemically treated, showing a high electroactive area, with graphene edge plans exposure and better electron transfer when compared to the untreated electrode. An excellent analytical performance was obtained with a sensitivity of 0.176 μAL μmol^-1, a linear dynamic range of 5.0 μmol L^-1- 3000 μmol L^-1 and limit of detection of 1.39 μmol L^-1. The proposed device was successfully applied for L-methionine detection in spiked serum samples, showing satisfactory recovery values. This indicates the potentiality of the proposed arrangement of electrodes for the L-methionine detection in biological samples at different concentration levels.

Ameliorative effect of tannic acid on hypermethioninemia-induced oxidative and nitrosative damage in rats: biochemical-based evidences in liver, kidney, brain, and serum

We investigated the ability of tannic acid (TA) to prevent oxidative and nitrosative damage in the brain, liver, kidney, and serum of a rat model of acute hypermethioninemia. Young Wistar rats were divided into four groups: I (control), II (TA 30 mg/kg), III (methionine (Met) 0.4 g/kg + methionine sulfoxide (MetO) 0.1 g/kg), and IV (TA/Met + MetO). Rats in groups II and IV received TA orally for seven days, and rats of groups I and III received an equal volume of water. After pretreatment with TA, rats from groups II and IV received a single subcutaneous injection of Met + MetO, and were euthanized 3 h afterwards. In specific brain structures and the kidneys, we observed that Met + MetO led to increased reactive oxygen species (ROS), nitrite, and lipid peroxidation levels, followed by a reduction in thiol content and antioxidant enzyme activity. On the other hand, pretreatment with TA prevented both oxidative and nitrosative damage. In the serum, Met + MetO caused a decrease in the activity of antioxidant enzymes, which was again prevented by TA pretreatment. In contrast, in the liver, there was a reduction in ROS levels and an increase in total thiol content, which was accompanied by a reduction in catalase and superoxide dismutase activities in the Met + MetO group, and pretreatment with TA was able to prevent only the reduction in catalase activity. Conclusively, pretreatment with TA has proven effective in preventing oxidative and nitrosative changes caused by the administration of Met + MetO, and may thus represent an adjunctive therapeutic approach for treatment of hypermethioninemia.

Hyperhomocysteinemia: Clinical Insights

Homocysteine (Hcy) is a sulfhydryl-containing amino acid, and intermediate metabolite formed in metabolising methionine (Met) to cysteine (Cys); defective Met metabolism can increase Hcy. The effect of hyperhomocysteinemia (HHcy) on human health, is well described and associated with multiple clinical conditions. HHcy is considered to be an independent risk factor for common cardiovascular and central nervous disorders, where its role in folate metabolism and choline catabolism is fundamental in many metabolic pathways. HHcy induces inflammatory responses via increasing the pro-inflammatory cytokines and downregulation of anti-inflammatory cytokines which lead to Hcy-induced cell apoptosis. Conflicting evidence indicates that the development of the homocysteine-associated cerebrovascular disease may be prevented by the maintenance of normal Hcy levels. In this review, we discuss common conditions associated with HHcy and biochemical diagnostic workup that may help in reaching diagnosis at early stages. Furthermore, future systematic studies need to prove the exact pathophysiological mechanism of HHcy at the cellular level and the effect of Hcy lowering agents on disease courses.

Alterations in Sulfur Amino Acids as Biomarkers of Disease

Homocysteine (Hcy) is methylated by methionine synthase to form methionine with methyl-cobalamin as a cofactor. The reaction demethylates 5-methyltetrahydrofolate to tetrahydrofolate, which is required for DNA and RNA synthesis. Deficiency of either of the cobalamin (Cbl) and/or folate cofactors results in elevated Hcy and megaloblastic anemia. Elevated Hcy is a sensitive biomarker of Cbl and/or folate status and more specific than serum vitamin assays. Elevated Hcy normalizes when the correct vitamin is given. Elevated Hcy is associated with alcohol use disorder and drugs that target folate or Cbl metabolism, and is a risk factor for thrombotic vascular disease. Elevated methionine and cystathionine are associated with liver disease. Elevated Hcy, cystathionine, and cysteine, but not methionine, are common in patients with chronic renal failure. Higher cysteine predicts obesity and future weight gain. Serum S-adenosylhomocysteine (AdoHcy) is elevated in Cbl deficiency and chronic renal failure. Drugs that require methylation for catabolism may deplete liver S-adenosylmethionine and raise AdoHcy and Hcy. Deficiency of Cbl or folate or perturbations of their metabolism cause major changes in sulfur amino acids.

Lessons Learned from Inherited Metabolic Disorders of Sulfur-Containing Amino Acids Metabolism

The metabolism of sulfur-containing amino acids (SAAs) requires an orchestrated interplay among several dozen enzymes and transporters, and an adequate dietary intake of methionine (Met), cysteine (Cys), and B vitamins. Known human genetic disorders are due to defects in Met demethylation, homocysteine (Hcy) remethylation, or cobalamin and folate metabolism, in Hcy transsulfuration, and Cys and hydrogen sulfide (H2S) catabolism. These disorders may manifest between the newborn period and late adulthood by a combination of neuropsychiatric abnormalities, thromboembolism, megaloblastic anemia, hepatopathy, myopathy, and bone and connective tissue abnormalities. Biochemical features include metabolite deficiencies (e.g. Met, S-adenosylmethionine (AdoMet), intermediates in 1-carbon metabolism, Cys, or glutathione) and/or their accumulation (e.g. S-adenosylhomocysteine, Hcy, H2S, or sulfite). Treatment should be started as early as possible and may include a low-protein/low-Met diet with Cys-enriched amino acid supplements, pharmacological doses of B vitamins, betaine to stimulate Hcy remethylation, the provision of N-acetylcysteine or AdoMet, or experimental approaches such as liver transplantation or enzyme replacement therapy. In several disorders, patients are exposed to long-term markedly elevated Met concentrations. Although these conditions may inform on Met toxicity, interpretation is difficult due to the presence of additional metabolic changes. Two disorders seem to exhibit Met-associated toxicity in the brain. An increased risk of demyelination in patients with Met adenosyltransferase I/III (MATI/III) deficiency due to biallelic mutations in the MATIA gene has been attributed to very high blood Met concentrations (typically >800 μmol/L) and possibly also to decreased liver AdoMet synthesis. An excessively high Met concentration in some patients with cystathionine β-synthase deficiency has been associated with encephalopathy and brain edema, and direct toxicity of Met has been postulated. In summary, studies in patients with various disorders of SAA metabolism showed complex metabolic changes with distant cellular consequences, most of which are not attributable to direct Met toxicity.

A cautionary tale of pyridoxine toxicity in cystathionine beta-synthase deficiency detected by two-tier newborn screening highlights the need for clear pyridoxine dosing guidelines

Classic homocystinuria is due to deficiency of cystathionine beta-synthase (CBS), a pyridoxine-dependent enzyme that, depending on the molecular variants, may be co-factor responsive. Elevated methionine is often used as the primary analyte to detect CBS deficiency (CBSD) on newborn screening (NBS), but is limited by increased detection of other biochemical disorders with less clear clinical significance such as methionine aminotransferase (MAT) I/III heterozygotes. Our state has implemented a two-tier NBS algorithm for CBSD that successfully reduced the number of MATI/III heterozygotes, yet effectively detected a mild, co-factor responsive form of CBSD. After initial diagnosis, newborns with CBSD often undergo a pyridoxine challenge with high-dose pyridoxine to determine responsiveness. Here we describe our NBS-identified patient with a mild form of pyridoxine responsive CBSD who developed respiratory failure and rhabdomyolysis consistent with pyridoxine toxicity during a pyridoxine challenge. This case highlights the need for weight-based dosing and duration recommendations for pyridoxine challenge in neonates.

Implication of Hyperhomocysteinemia in Blood Retinal Barrier (BRB) Dysfunction

Elevated plasma homocysteine (Hcy) level, known as hyperhomocysteinemia (HHcy) has been linked to different systemic and neurological diseases, well-known as a risk factor for systemic atherosclerosis and cardiovascular disease (CVD) and has been identified as a risk factor for several ocular disorders, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). Different mechanisms have been proposed to explain HHcy-induced visual dysfunction, including oxidative stress, upregulation of inflammatory mediators, retinal ganglion cell apoptosis, and extracellular matrix remodeling. Our previous studies using in vivo and in vitro models of HHcy have demonstrated that Hcy impairs the function of both inner and outer blood retinal barrier (BRB). Dysfunction of BRB is a hallmark of vision loss in DR and AMD. Our findings highlighted oxidative stress, ER stress, inflammation, and epigenetic modifications as possible mechanisms of HHcy-induced BRB dysfunction. In addition, we recently reported HHcy-induced brain inflammation as a mechanism of blood–brain barrier (BBB) dysfunction and pathogenesis of Alzheimer’s disease (AD). Moreover, we are currently investigating the activation of glutamate receptor N-methyl-d-aspartate receptor (NMDAR) as the molecular mechanism for HHcy-induced BRB dysfunction. This review focuses on the studied effects of HHcy on BRB and the controversial role of HHcy in the pathogenesis of aging neurological diseases such as DR, AMD, and AD. We also highlight the possible mechanisms for such deleterious effects of HHcy.

Withdrawal Effects Following Methionine Exposure in Adult Zebrafish

Methionine (Met) has important functions for homeostasis of various species, including zebrafish. However, the increased levels of this amino acid in plasma, a condition known as hypermethioninemia, can lead to cell alterations. Met is crucial for the methylation process and its excesses interfere with the cell cycle, an effect that persists even after the removal of this amino acid. Some conditions may lead to a transient increase of this amino acid with unexplored persistent effects of Met exposure. In the present study, we investigated the behavioral and neurochemical effects after the withdrawal of Met exposure. Zebrafish were divided into two groups: control and Met-treated group (3 mM) for 7 days and after maintained for 8 days in tanks containing only water. In the eighth day post-exposure, we evaluated locomotion, anxiety, aggression, social interaction, and memory, as well as oxidative stress parameters, amino acid, and neurotransmitter levels in the zebrafish brain. Our results showed that 8 days after Met exposure, the treated group showed decreased locomotion and aggressive responses, as well as impaired aversive memory. The Met withdrawal did not change thiobarbituric acid reactive substances, reactive oxygen species, and nitrite levels; however, we observed a decrease in antioxidant enzymes superoxide dismutase, catalase, and total thiols. Epinephrine and cysteine levels were decreased after the Met withdrawal whereas carnitine and creatine levels were elevated. Our findings indicate that a transient increase in Met causes persistent neurotoxicity, observed by behavioral and cognitive changes after Met withdrawal and that the mechanisms underlying these effects are related to changes in antioxidant system, amino acid, and neurotransmitter levels.

Structural basis of the dominant inheritance of hypermethioninemia associated with the Arg264His mutation in the MAT1A gene

Methionine adenosyltransferase (MAT) deficiency, characterized by isolated persistent hypermethioninemia (IPH), is caused by mutations in the MAT1A gene encoding MATαl, one of the major hepatic enzymes. Most of the associated hypermethioninemic conditions are inherited as autosomal recessive traits; however, dominant inheritance of hypermethioninemia is caused by an Arg264His (R264H) mutation. This mutation has been confirmed in a screening programme of newborns as the most common mutation in babies with IPH. Arg264 makes an inter-subunit salt bridge located at the dimer interface where the active site assembles. Here, it is demonstrated that the R264H mutation results in greatly reduced MAT activity, while retaining its ability to dimerize, indicating that the lower activity arises from alteration at the active site. The first crystallographic structure of the apo form of the wild-type MATαl enzyme is provided, which shows a tetrameric assembly in which two compact dimers combine to form a catalytic tetramer. In contrast, the crystal structure of the MATαl R264H mutant reveals a weaker dimeric assembly, suggesting that the mutation lowers the affinity for dimer-dimer interaction. The formation of a hetero-oligomer with the regulatory MATβV1 subunit or incubation with a quinolone-based compound (SCR0911) results in the near-full recovery of the enzymatic activity of the pathogenic mutation R264H, opening a clear avenue for a therapeutic solution based on chemical interventions that help to correct the defect of the enzyme in its ability to metabolize methionine.

The Combined Impact of CLIR Post-Analytical Tools and Second Tier Testing on the Performance of Newborn Screening for Disorders of Propionate, Methionine, and Cobalamin Metabolism

The expansion of the recommend uniform screening panel to include more than 50 primary and secondary target conditions has resulted in a substantial increase of false positive results. As an alternative to subjective manipulation of cutoff values and overutilization of molecular testing, here we describe the performance outcome of an algorithm for disorders of methionine, cobalamin, and propionate metabolism that includes: (1) first tier screening inclusive of the broadest available spectrum of markers measured by tandem mass spectrometry; (2) integration of all results into a score of likelihood of disease for each target condition calculated by post-analytical interpretive tools created byCollaborative Laboratory Integrated Reports (CLIR), a multivariate pattern recognition software; and (3) further evaluation of abnormal scores by a second tier test measuring homocysteine, methylmalonic acid, and methylcitric acid. This approach can consistently reduce false positive rates to a <0.01% level, which is the threshold of precision newborn screening. We postulate that broader adoption of this algorithm could lead to substantial savings in health care expenditures. More importantly, it could prevent the stress and anxiety experienced by many families when faced with an abnormal newborn screening result that is later resolved as a false positive outcome.

Nuclear Magnetic Resonance Metabolomics Reveals Qualitative and Quantitative Differences in the Composition of Human Breast Milk and Milk Formulas

Commercial formula milk (FM) constitutes the best alternative to fulfill the nutritional requirements of infants when breastfeeding is precluded. Here, we present the comparative study of polar metabolite composition of human breast milk (HBM) and seven different brands of FM by nuclear magnetic resonance spectroscopy. The results of the multivariate data analysis exposed qualitative and quantitative differences between HBM and FM composition as well as within FM of various brands and in HBM itself (between individual mothers and lactation period). Several metabolites were found exclusively in HBM and FM. Statistically significant higher levels of isoleucine and methionine in their free form were detected in FM samples based on caprine milk, while FM samples based on bovine milk showed a higher level of glucose and galactose in comparison to HBM. The results suggest that the amelioration of FM formulation is imperative to better mimic the composition of minor nutrients in HBM.

Cystathionine beta synthase deficiency and brain edema associated with methionine excess under betaine supplementation: Four new cases and a review of the evidence

CBS deficient individuals undergoing betaine supplementation without sufficient dietary methionine restriction can develop severe hypermethioninemia and brain edema. Brain edema has also been observed in individuals with severe hypermethioninemia without concomitant betaine supplementation. We systematically evaluated reports from 11 published and 4 unpublished patients with CBS deficiency and from additional four cases of encephalopathy in association with elevated methionine. We conclude that, while betaine supplementation does greatly exacerbate methionine accumulation, the primary agent causing brain edema is methionine rather than betaine. Clinical signs of increased intracranial pressure have not been seen in patients with plasma methionine levels below 559 μmol/L but occurred in one patient whose levels did not knowingly exceed 972 μmol/L at the time of manifestation. While levels below 500 μmol/L can be deemed safe it appears that brain edema can develop with plasma methionine levels close to 1000 μmol/L. Patients with CBS deficiency on betaine supplementation need to be regularly monitored for concordance with their dietary plan and for plasma methionine concentrations. Recurrent methionine levels above 500 μmol/L should alert clinicians to check for clinical signs and symptoms of brain edema and review dietary methionine intake. Levels approaching 1000 μmol/L do increase the risk of complications and levels exceeding 1000 μmol/L, despite best dietetic efforts, should be acutely addressed by reducing the prescribed betaine dose.

Hypermethioninemia induces memory deficits and morphological changes in hippocampus of young rats: implications on pathogenesis

The aim of this study was to investigate the effect of the chronic administration of methionine (Met) and/or its metabolite, methionine sulfoxide (MetO), on the behavior and neurochemical parameters of young rats. Rats were treated with saline (control), Met (0.2-0.4 g/kg), MetO (0.05-0.1 g/kg), and/or a combination of Met + MetO, subcutaneously twice a day from postnatal day 6 (P6) to P28. The results showed that Met, MetO, and Met + MetO impaired short-term and spatial memories (P < 0.05), reduced rearing and grooming (P < 0.05), but did not alter locomotor activity (P > 0.05). Acetylcholinesterase activity was increased in the cerebral cortex, hippocampus, and striatum following Met and/or MetO (P < 0.05) treatment, while Na⁺, K⁺-ATPase activity was reduced in the hippocampus (P < 0.05). There was an increase in the level of thiobarbituric acid reactive substances (TBARS) in the cerebral cortex in Met-, MetO-, and Met + MetO-treated rats (P < 0.05). Met and/or MetO treatment reduced superoxide dismutase, catalase, and glutathione peroxidase activity, total thiol content, and nitrite levels, and increased reactive oxygen species and TBARS levels in the hippocampus and striatum (P < 0.05). Hippocampal brain-derived neurotrophic factor was reduced by MetO and Met + MetO compared with the control group. The number of NeuN-positive cells was decreased in the CA3 in Met + MetO group and in the dentate gyrus in the Met, MetO, and Met + MetO groups compared to control group (P < 0.05). Taken together, these findings further increase our understanding of changes in the brain in hypermethioninemia by elucidating behavioral alterations, biological mechanisms, and the vulnerability of brain function to high concentrations of Met and MetO.

Methionine and methionine sulfoxide induces neurochemical and morphological changes in cultured astrocytes: Involvement of Na+, K+-ATPase activity, oxidative status, and cholinergic and purinergic signaling

Hypermethioninemia is an inherited metabolic disorder characterized by high concentration of methionine (Met) and its metabolites such as methionine sulfoxide (Met-SO), which may lead to development of neurological alterations. The aim of this study was to investigate the in vitro effects of Met or Met-SO on viability, proliferation, morphology, and neurochemical parameters in primary culture of cortical astrocytes, after treatment with 1 or 2 mM Met or 0.5 mM Met-SO, for 24, 48, and 72 h. Met or Met-SO did not affect cell viability and proliferation but induced astrocyte hypertrophy. Acetylcholinesterase activity was increased, while Na⁺, K⁺-ATPase activity was decreased by 2 mM Met, Met-SO, or Met (1 and 2 mM) + Met-SO (P < 0.05). ATP and AMP hydrolysis was decreased by Met (1 and 2 mM), Met-SO and Met (1 and 2 mM) + Met-SO treatment, while ADP hydrolysis was enhanced by Met-SO and Met (1 and 2 mM) + Met-SO (P < 0.05). Superoxide dismutase activity was increased by Met-SO and Met (1 and 2 mM) + Met-SO (P < 0.05). Catalase and glutathione S-transferase activities were reduced by Met or Met-SO treatment for 48 and 72 h (P < 0.05). Reactive oxygen species and total thiol content was reduced by Met or Met-SO treatment for 24, 48, and 72 h while nitrite and thiobarbituric acid reactive substance levels were increased under the same experimental conditions (P < 0.05). High concentrations of Met and Met-SO do not cause cell death but induced changes in astrocyte function. These alterations in astrocytic homeostasis may be associated with neurological symptoms found in hypermethioninemia.

Hypermethioninemia in Campania: Results from 10 years of newborn screening

In the last years tandem mass spectrometry (MS/MS) has become a leading technology used for neonatal screening purposes. Newborn screening by MS/MS on dried blood spot samples (DBS) has one of its items in methionine levels: the knowledge of this parameter allows the identification of infant affected by homocystinuria (cystathionine β-synthase, CBS, deficiency) but can also lead, as side effect, to identify cases of methionine adenosyltransferase (MAT) type I/III deficiency. We started an expanded newborn screening for inborn errors of metabolism in Campania region in 2007. Here we report our ten years experience on expanded newborn screening in identifying patients affected by hypermethioninemia. During this period we screened approximately 77,000 infants and identified two cases: one case of classical homocystinuria and one patient affected by defect of MAT I/III. In this paper we describe these patients and their biochemical follow-up and review the literature concerning worldwide newborn screening reports on incidence of CBS and MAT deficiency.

Methionine metabolism and methyltransferases in the regulation of aging and lifespan extension across species

Methionine restriction (MetR) extends lifespan across different species and exerts beneficial effects on metabolic health and inflammatory responses. In contrast, certain cancer cells exhibit methionine auxotrophy that can be exploited for therapeutic treatment, as decreasing dietary methionine selectively suppresses tumor growth. Thus, MetR represents an intervention that can extend lifespan with a complementary effect of delaying tumor growth. Beyond its function in protein synthesis, methionine feeds into complex metabolic pathways including the methionine cycle, the transsulfuration pathway, and polyamine biosynthesis. Manipulation of each of these branches extends lifespan; however, the interplay between MetR and these branches during regulation of lifespan is not well understood. In addition, a potential mechanism linking the activity of methionine metabolism and lifespan is regulation of production of the methyl donor S-adenosylmethionine, which, after transferring its methyl group, is converted to S-adenosylhomocysteine. Methylation regulates a wide range of processes, including those thought to be responsible for lifespan extension by MetR. Although the exact mechanisms of lifespan extension by MetR or methionine metabolism reprogramming are unknown, it may act via reducing the rate of translation, modifying gene expression, inducing a hormetic response, modulating autophagy, or inducing mitochondrial function, antioxidant defense, or other metabolic processes. Here, we review the mechanisms of lifespan extension by MetR and different branches of methionine metabolism in different species and the potential for exploiting the regulation of methyltransferases to delay aging.

Expanded Newborn Screening for Inborn Errors of Metabolism by Tandem Mass Spectrometry in Suzhou, China: Disease Spectrum, Prevalence, Genetic Characteristics in a Chinese Population

Expanded newborn screening for inborn errors of metabolism (IEMs) by tandem mass spectrometry (MS/MS) could simultaneously analyze more than 40 metabolites and identify about 50 kinds of IEMs. Next generation sequencing (NGS) targeting hundreds of IMEs-associated genes as a follow-up test in expanded newborn screening has been used for genetic analysis of patients. The spectrum, prevalence, and genetic characteristic of IEMs vary dramatically in different populations. To determine the spectrum, prevalence, and gene mutations of IEMs in newborns in Suzhou, China, 401,660 newborns were screened by MS/MS and 138 patients were referred to genetic analysis by NGS. The spectrum of 22 IEMs were observed in Suzhou population of newborns, and the overall incidence (excluding short chain acyl-CoA dehydrogenase deficiency (SCADD) and 3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)) was 1/3,163. The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166). Moreover, 89 reported mutations and 51 novel mutations in 25 IMEs-associated genes were detected in 138 patients with one of 22 IEMs. Some hotspot mutations were observed for ten IEMs, including PAH gene c.728G > A, c.611A > G, and c.721C > T for Phenylketonuria, PAH gene c.158G > A, c.1238G > C, c.728G > A, and c.1315+6T > A for M-HPA, SLC22A5 gene c.1400C > G, c.51C > G, and c.760C > T for PCUD, ACADS gene c.1031A > G, c.164C > T, and c.1130C > T for SCAD deficiency, MAT1A gene c.791G > A for H-MET, MCCC1 gene c.639+2T > A and c.863A > G for 3-MCCD, MMUT gene c.1663G > A for MMA, SLC25A13 gene c.IVS16ins3Kb and c.852_855delTATG for cittrullinemia II, PTS gene c.259C > T and c.166G > A for Tetrahydrobiopterin deficiency, and ACAD8 gene c.1000C > T and c.286C > A for Isobutyryl coa dehydrogenase deficiency. All these hotspot mutations were reported to be pathogenic or likely pathogenic, except a novel mutation of ACAD8 gene c.286C > A. These mutational hotspots could be potential candidates for gene screening and these novel mutations expanded the mutational spectrum of IEMs. Therefore, our findings could be of value for genetic counseling and genetic diagnosis of IEMs.

Analysis of the Qatari R336C cystathionine β-synthase protein in mice

Classical homocystinuria is a recessive inborn error of metabolism caused by mutations in the cystathionine beta-synthase (CBS) gene. The highest incidence of CBS deficiency in the world is found in the country of Qatar due to the combination of high rates of consanguinity and the presence of a founder mutation, c.1006C>T (p.R336C). This mutation does not respond to pyridoxine and is considered severe. Here we describe the creation of a mouse that is null for the mouse Cbs gene and expresses human p.R336C CBS from a zinc-inducible transgene (Tg-R336C Cbs ^-/- ). Zinc-treated Tg-R336C Cbs ^-/- mice have extreme elevation in both serum total homocysteine (tHcy) and liver tHcy compared with control transgenic mice. Both the steady-state protein levels and CBS enzyme activity levels in liver lysates from Tg-R336C Cbs ^-/- mice are significantly reduced compared to that found in Tg-hCBS Cbs ^-/- mice expressing wild-type human CBS. Treatment of Tg-R336C Cbs ^-/- mice with the proteasome inhibitor bortezomib results in stabilization of liver CBS protein and an increase in activity to levels found in corresponding Tg-hCBS Cbs ^-/- wild type mice. Surprisingly, serum tHcy did not fully correct even though liver enzyme activity was as high as control animals. This discrepancy is explained by in vitro enzymatic studies of mouse liver extracts showing that p.R336C causes reduced binding affinity for the substrate serine by almost 7-fold and significantly increased dependence on pyridoxal phosphate in the reaction buffer. These studies demonstrate that the p.R336C alteration effects both protein stability and substrate/cofactor binding.

Treatment of Cystathionine β-Synthase Deficiency in Mice Using a Minicircle-Based Naked DNA Vector

Cystathionine β-synthase (CBS) deficiency is a recessive inborn error of metabolism characterized by extremely elevated total homocysteine (tHcy) in the blood. Patients diagnosed with CBS deficiency have a variety of clinical problems, including dislocated lenses, osteoporosis, cognitive and behavioral issues, and a significantly increased risk of thrombosis. Current treatment strategies involve a combination of vitamin supplementation and restriction of foods containing the homocysteine precursor methionine. Here, a mouse model for CBS deficiency (Tg-I278T Cbs-/-) was used to evaluate the potential of minicircle-based naked DNA gene therapy to treat CBS deficiency. A 2.3 kb DNA-minicircle containing the liver-specific P3 promoter driving the human CBS cDNA (MC.P3-hCBS) was delivered into Tg-I278T Cbs-/- mice via a single hydrodynamic tail vein injection. Mean serum tHcy decreased from 351 μM before injection to 176 μM 7 days after injection (p = 0.0005), and remained decreased for at least 42 days. Western blot analysis reveals significant minicircle-directed CBS expression in the liver tissue. Liver CBS activity increased 34-fold (12.8 vs. 432 units; p = 0.0004) in MC.P3-hCBS-injected animals. Injection of MC.P3-hCBS in young mice, subsequently followed for 202 days, showed that the vector can ameliorate the mouse homocystinuria alopecia phenotype. The present findings show that minicircle-based gene therapy can lower tHcy in a mouse model of CBS deficiency.

The neuroprotective role of melatonin in a gestational hypermethioninemia model

Elevated levels of methionine in blood characterize the hypermethioninemia, which may have genetic or non-genetic origin, as for example from high protein diet. Born rats from hypermethioninemic mothers presented cerebral oxidative stress, inhibition of Na⁺,K⁺-ATPase, memory deficit and ultrastructure cerebral changes. Melatonin is a hormone involved in circadian rhythm and has antioxidant effects. The aim of this study was to verify the possible neuroprotective effects of melatonin administration in hypermethioninemic pregnant rats on damage to biomolecules (Na⁺,K⁺-ATPase, sulfhydryl content and DNA damage index) and behavior (open field, novel object recognition and water maze tasks), as well as its effect on cells morphology by electron microscopy in offspring. Wistar female rats received methionine (2.68 μmol/g body weight) and/or melatonin (10 mg/kg body weight) by subcutaneous injections during entire pregnancy. Control rats received saline. Biochemical analyzes were performed at 21 and 30 days of life of offspring and behavioral analyzes were performed only at 30 days of age in male pups. Results showed that gestational hypermethioninemia diminished Na⁺,K⁺-ATPase activity and sulfhydryl content and increased DNA damage at 21 and 30 days of life. Melatonin was able to totally prevent Na⁺,K⁺-ATPase activity alteration at 21 days and partially prevent its alteration at 30 days of rats life. Melatonin was unable in to prevent sulfhydryl and DNA damage at two ages. It also improved DNA damage, but not at level of saline animals (controls). Regarding to behavioral tests, data showed that pups exposed to gestational hypermethioninemia decreased reference memory in water maze, spent more time to the center of the open field and did not differentiate the objects in the recognition test. Melatonin was able to prevent the deficit in novel object recognition task. Electron microscopy revealed ultrastructure alterations in neurons of hypermethioninemic at both ages of offspring, whose were prevented by melatonin. These findings suggest that melatonin may be a good neuroprotective to minimize the harmful effects of gestational hypermethioninemia on offspring.

Chronic mild Hyperhomocysteinemia impairs energy metabolism, promotes DNA damage and induces a Nrf2 response to oxidative stress in rats brain

Homocysteine (HCY) has been linked to oxidative stress and varied metabolic changes that are dependent on its concentration and affected tissues. In the present study we evaluate parameters of energy metabolism [succinate dehydrogenase (SDH), complex II and IV (cytochrome c oxidase), and ATP levels] and oxidative stress [DCFH oxidation, nitrite levels, antioxidant enzymes and lipid, protein and DNA damages, as well as nuclear factor erythroid 2-related (Nrf2) protein abundance] in amygdala and prefrontal cortex of HCY-treated rats. Wistar male rats were treated with a subcutaneous injection of HCY (0.03 µmol/g of body weight) from the 30th to 60th post-natal day, twice a day, to induce mild hyperhomocysteinemia (HHCY). The rats were euthanatized without anesthesia at 12 h after the last injection, and amygdala and prefrontal cortex were dissected for biochemical analyses. In the amygdala, mild HHCY increased activities of SDH and complex II and decreased complex IV and ATP level, as well as increased antioxidant enzymes activities (glutathione peroxidase and superoxide dismutase), nitrite levels, DNA damage, and Nrf 2 protein abundance. In the prefrontal cortex, mild HHCY did not alter energy metabolism, but increased glutathione peroxidase, catalase and DNA damage. Other analyzed parameters were not altered by HCY-treatment. Our findings suggested that chronic mild HHCY changes each brain structure, particularly and specifically. These changes may be associated with the mechanisms by which chronic mild HHCY has been linked to the risk factor of fear, mood disorders and depression, as well as in neurodegenerative diseases.

High levels of methionine and methionine sulfoxide: Impact on adenine nucleotide hydrolysis and redox status in platelets and serum of young rats

We investigated acute and chronic effects administration of methionine (Met) and/or methionine sulfoxide (MetO) on ectonucleotidases and oxidative stress in platelets and serum of young rats. Wistar rats were divided into four groups: control, Met, MetO, and Met + MetO. In acute treatment, the animals received a single subcutaneous injection of amino acid(s) and were euthanized after 1 and 3 hours. In chronic protocol, Met and/or MetO were administered twice a day with an 8-hour interval from the 6th to the 28th day of life. Nucleoside triphosphate phosphohydrolase and 5'-nucleotidase activities were reduced in platelets and serum by Met, MetO, and Met + MetO after 3 hours and 21 days. Adenosine deaminase activity reduced in platelets at 3 hours after MetO and Met + MetO administration and increased after 21 days in animals treated with Met + MetO. Superoxide dismutase and catalase activities decreased in platelets in MetO and Met + MetO groups after 3 hours, while reactive oxygen species (ROS) levels increased in same groups. Catalase activity in platelets decreased in all experimental groups after chronic treatment. Met, MetO, and Met + MetO administration increased plasmatic ROS levels in acute and chronic protocols; glutathione S-transferase activity increased by MetO and Met + MetO administration at 3 hours, and ascorbic acid decreased in all experimental groups in acute and chronic protocols. Thiobarbituric acid reactive substances increased, superoxide dismutase and catalase activities reduced in the Met and/or MetO groups at 3 hours and in chronic treatment. Our data demonstrated that Met and/or MetO induced changes in adenine nucleotide hydrolysis and redox status of platelets and serum, which can be associated with platelet dysfunction in hypermethioninemia.

Mouse modeling and structural analysis of the p.G307S mutation in human cystathionine β-synthase (CBS) reveal effects on CBS activity but not stability

Mutations in the cystathionine β-synthase (CBS) gene are the cause of classical homocystinuria, the most common inborn error in sulfur metabolism. The p.G307S mutation is the most frequent cause of CBS deficiency in Ireland, which has the highest prevalence of CBS deficiency in Europe. Individuals homozygous for this mutation tend to be severely affected and are pyridoxine nonresponsive, but the molecular basis for the strong effects of this mutation is unclear. Here, we characterized a transgenic mouse model lacking endogenous Cbs and expressing human p.G307S CBS protein from a zinc-inducible metallothionein promoter (Tg-G307S Cbs^-/-). Unlike mice expressing other mutant CBS alleles, the Tg-G307S transgene could not efficiently rescue neonatal lethality of Cbs^-/- in a C57BL/6J background. In a C3H/HeJ background, zinc-induced Tg-G307S Cbs^-/- mice expressed high levels of p.G307S CBS in the liver, and this protein variant forms multimers, similarly to mice expressing WT human CBS. However, the p.G307S enzyme had no detectable residual activity. Moreover, treating mice with proteasome inhibitors failed to significantly increase CBS-specific activity. These findings indicated that the G307S substitution likely affects catalytic function as opposed to causing a folding defect. Using molecular dynamics simulation techniques, we found that the G307S substitution likely impairs catalytic function by limiting the ability of the tyrosine at position 308 to assume the proper conformational state(s) required for the formation of the pyridoxal-cystathionine intermediate. These results indicate that the p.G307S CBS is stable but enzymatically inert and therefore unlikely to respond to chaperone-based therapy.