Adenosine kinase deficiency disrupts the methionine cycle and causes hypermethioninemia, encephalopathy, and abnormal liver function

Novel homozygous ADK out-of-frame deletion causes adenosine kinase deficiency with rare phenotypes of sepsis, metabolites disruption and neutrophil dysfunction

Adenosine kinase deficiency (OMIM #614300) is a type of inborn errors of metabolism with multiorgan symptoms primarily neurological disorders, hepatic impairment, global developmental delay, and mild dysmorphism. The genetic causes of adenosine kinase deficiency are homozygous or compound heterozygous loss-of-function variants of ADK. To date, fewer than 25 cases of adenosine kinase deficiency have been reported worldwide and none have been reported in China. In this research, trio whole-exome sequencing (Trio-WES) identified a novel homozygous ADK (NM_001123.4) out-of-frame deletion, c.518_519delCA (p.Thr173Serfs*15), in a Chinese patient with rare phenotypes of sepsis, metabolites disruption and neutrophil dysfunction. This variant was dysfunctional, with marked reduction of ADK level in both the patient's peripheral blood and cells transfected with the corresponding variant. Additionally, metabolomics detected by high-throughput mass spectrometry showed disturbances in the methionine (Met) and energy pathway. RNA sequencing (RNA-seq) of the patient's peripheral blood suggested a defective anti-inflammatory response characterized by impaired neutrophil activation, migration, and degranulation, which might be the primary cause for the sepsis. To our knowledge, we identified the first Chinese patient of adenosine kinase deficiency with a novel homozygous out-of-frame deletion in ADK causing multiorgan disorders, metabolites disruption, rare phenotypes of sepsis, and neutrophil dysfunction. Our findings broaden the genetic spectrum and pathogenic mechanisms of adenosine kinase deficiency.

Adenosine kinase inhibits β-cell proliferation by upregulating DNA methyltransferase 3A expression

AIM

To investigate the effects of adenosine kinase (ADK), a key enzyme in determining intracellular adenosine levels, on β cells, and their underlying mechanism.

METHODS

Genetic animal models and transgenic immortalized cells were applied to study the effect of ADK on islet beta-cell proliferation and function. The beta-cell mass and response to glucose were measured in vivo using mice with beta-cell-specific ADK overexpression, and in vitro using ADK-overexpressed immortalized beta-cell.

RESULTS

The expression of ADK in human islets at high abundance, especially in β cells, was decreased during the process of β-cell proliferation. Additionally, a transgenic mouse model (ADKtg/tg /Mip-Cre) was generated wherein the mouse Insulin1 gene promoter specifically overexpressed ADK in pancreatic β cells. The ADKtg/tg /Mip-Cre model exhibited impaired glucose tolerance, decreased fasting plasma insulin, loss of β-cell mass, and inhibited β-cell proliferation. Proteomic analysis revealed that ADK overexpression inhibited the expression of several proteins that promote cell proliferation and insulin secretion. Upregulating ADK in the β-cell line inhibited the expression of β-cell related regulatory molecules, including FoxO1, Appl1, Pxn, Pdx-1, Creb and Slc16a3. Subsequent in vitro experiments indicated that the inhibition of β-cell proliferation and the decreased expression of Pdx-1, Creb and Slc16a3 were rescued by DNA methyltransferase 3A (DNMT3A) knockdown in β cells.

CONCLUSION

In this study, we found that the overexpression of ADK decreased the expression of several genes that regulate β cells, resulting in the inhibition of β-cell proliferation and dysfunction by upregulating the expression of DNMT3A.

Genetic screening and metabolomics identify glial adenosine metabolism as a therapeutic target in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder and lacks disease-modifying therapies. We developed a Drosophila model for identifying novel glial-based therapeutic targets for PD. Human alpha-synuclein is expressed in neurons and individual genes are independently knocked down in glia. We performed a forward genetic screen, knocking down the entire Drosophila kinome in glia in alpha-synuclein expressing flies. Among the top hits were five genes (Ak1, Ak6, Adk1, Adk2, and awd) involved in adenosine metabolism. Knockdown of each gene improved locomotor dysfunction, rescued neurodegeneration, and increased brain adenosine levels. We determined that the mechanism of neuroprotection involves adenosine itself, as opposed to a downstream metabolite. We dove deeper into the mechanism for one gene, Ak1, finding rescue of dopaminergic neuron loss, alpha-synuclein aggregation, and bioenergetic dysfunction after glial Ak1 knockdown. We performed metabolomics in Drosophila and in human PD patients, allowing us to comprehensively characterize changes in purine metabolism and identify potential biomarkers of dysfunctional adenosine metabolism in people. These experiments support glial adenosine as a novel therapeutic target in PD.

Diabetes and the fabkin complex: A dual-edged sword

The Fabkin complex, composed of FABP4, ADK, and NDPKs, emerges as a novel regulator of insulin-producing beta cells, offering promising prospects for diabetes treatment. Our approach, which combines literature review and database analysis, sets the stage for future research. These findings hold significant implications for both diabetes treatment and research, as they present potential therapeutic targets for personalized treatment, leading to enhanced patient outcomes and a deeper comprehension of the disease. The multifaceted role of the Fabkin complex in glucose metabolism, insulin resistance, anti-inflammation, beta cell proliferation, and vascular function underscores its therapeutic potential, reshaping diabetes management and propelling advancements in the field.

Roles of immune dysregulation in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide. Its occurrence and progression involve the process from simple hepatic steatosis to metabolic dysfunction associated steatohepatitis (MASH), which could develop into advanced liver fibrosis, cirrhosis, or hepatocellular carcinoma (HCC). Growing evidences support that the pathogenesis and progression of MASLD are closely related to immune system dysfunction. This review aims to summarize the association of MASLD with immune disorders and the prospect of using immunotherapy for MASLD.

Integrated Functions of Cardiac Energetics, Mechanics, and Purine Nucleotide Metabolism

Purine nucleotides play central roles in energy metabolism in the heart. Most fundamentally, the free energy of hydrolysis of the adenine nucleotide adenosine triphosphate (ATP) provides the thermodynamic driving force for numerous cellular processes including the actin-myosin crossbridge cycle. Perturbations to ATP supply and/or demand in the myocardium lead to changes in the homeostatic balance between purine nucleotide synthesis, degradation, and salvage, potentially affecting myocardial energetics and, consequently, myocardial mechanics. Indeed, both acute myocardial ischemia and decompensatory remodeling of the myocardium in heart failure are associated with depletion of myocardial adenine nucleotides and with impaired myocardial mechanical function. Yet there remain gaps in the understanding of mechanistic links between adenine nucleotide degradation and contractile dysfunction in heart disease. The scope of this article is to: (i) review current knowledge of the pathways of purine nucleotide depletion and salvage in acute ischemia and in chronic heart disease; (ii) review hypothesized mechanisms linking myocardial mechanics and energetics with myocardial adenine nucleotide regulation; and (iii) highlight potential targets for treating myocardial metabolic and mechanical dysfunction associated with these pathways. It is hypothesized that an imbalance in the degradation, salvage, and synthesis of adenine nucleotides leads to a net loss of adenine nucleotides in both acute ischemia and under chronic high-demand conditions associated with the development of heart failure. This reduction in adenine nucleotide levels results in reduced myocardial ATP and increased myocardial inorganic phosphate. Both of these changes have the potential to directly impact tension development and mechanical work at the cellular level. © 2024 American Physiological Society. Compr Physiol 14:5345-5369, 2024.

Developmental and foliation changes due to dysregulation of adenosine kinase in the cerebellum

Adenosine kinase (ADK), the major adenosine-metabolizing enzyme, plays a key role in brain development and disease. In humans, mutations in the Adk gene have been linked to developmental delay, stunted growth, and intellectual disability. To better understand the role of ADK in brain development, it is important to dissect the specific roles of the two isoforms of the enzyme expressed in the cytoplasm (ADK-S) and cell nucleus (ADK-L). We, therefore, studied brain development in Adk-tg transgenic mice, which only express ADK-S in the absence of ADK-L throughout development. In the mutant animals, we found a reduction in the overall brain, body size, and weight during fetal and postnatal development. As a major developmental abnormality, we found a profound change in the foliation pattern of the cerebellum. Strikingly, our results indicated aberrant Purkinje cells arborization at P9 and accelerated cell death at P6 and P9. We found defects in cerebellar cell proliferation and migration using a bromodeoxyuridine (BrdU)-based cell proliferation assay at postnatal day 7. Our data demonstrate that dysregulation of ADK expression during brain development profoundly affects brain growth and differentiation.

Accumulation of endogenous adenosine improves cardiomyocyte metabolism via epigenetic reprogramming in an ischemia-reperfusion model

Adenosine kinase (ADK) plays the major role in cardiac adenosine metabolism, so that inhibition of ADK increases myocardial adenosine levels. While the cardioprotective actions of extracellular adenosine against ischemia/reperfusion (I/R) are well-established, the role of cellular adenosine in protection against I/R remains unknown. Here we investigated the role of cellular adenosine in epigenetic regulation on cardiomyocyte gene expression, glucose metabolism and tolerance to I/R. Evans blue/TTC staining and echocardiography were used to assess the extent of I/R injury in mice. Glucose metabolism was evaluated by positron emission tomography and computed tomography (PET/CT). Methylated DNA immunoprecipitation (MeDIP) and bisulfite sequencing PCR (BSP) were used to evaluate DNA methylation. Lentiviral/adenovirus transduction was used to overexpress DNMT1, and the OSI-906 was administered to inhibit IGF-1. Cardiomyocyte-specific ADK/IGF-1-knockout mice were used for mechanistic experiments.Cardiomyocyte-specific ADK knockout enhanced glucose metabolism and ameliorated myocardial I/R injury in vivo. Mechanistically, ADK deletion caused cellular adenosine accumulation, decreased DNA methyltransferase 1 (DNMT1) expression and caused hypomethylation of multiple metabolic genes, including insulin growth factor 1 (IGF-1). DNMT1 overexpression abrogated these beneficial effects by enhancing apoptosis and decreasing IGF-1 expression. Inhibition of IGF-1 signaling with OSI-906 or genetic knocking down of IGF-1 also abrogated the cardioprotective effects of ADK knockout, revealing the therapeutic potential of increasing IGF-1 expression in attenuating myocardial I/R injury. In conclusion, the present study demonstrated that cardiomyocyte ADK deletion ameliorates myocardial I/R injury via epigenetic upregulation of IGF-1 expression via the cardiomyocyte adenosine/DNMT1/IGF-1 axis.

Improved diagnostics of purine and pyrimidine metabolism disorders using LC-MS/MS and its clinical application

OBJECTIVES

To develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify 41 different purine and pyrimidine (PuPy) metabolites in human urine to allow detection of most known disorders in this metabolic pathway and to determine reference intervals.

METHODS

Urine samples were diluted with an aqueous buffer to minimize ion suppression. For detection and quantification, liquid chromatography was combined with electrospray ionization, tandem mass spectrometry and multiple reaction monitoring. Transitions and instrument settings were established to quantify 41 analytes and nine stable-isotope-labeled internal standards (IS).

RESULTS

The established method is precise (intra-day CV: 1.4-6.3%; inter-day CV: 1.3-15.2%), accurate (95.2% external quality control results within ±2 SD and 99.0% within ±3 SD; analyte recoveries: 61-121%), sensitive and has a broad dynamic range to quantify normal and pathological metabolite concentrations within one run. All analytes except aminoimidazole ribonucleoside (AIr) are stable before, during and after sample preparation. Moreover, analytes are not affected by five cycles of freeze-thawing (variation: -5.6 to 7.4%), are stable in thymol (variation: -8.4 to 12.9%) and the lithogenic metabolites also in HCl conserved urine. Age-dependent reference intervals from 3,368 urine samples were determined and used to diagnose 11 new patients within 7 years (total performed tests: 4,206).

CONCLUSIONS

The presented method and reference intervals enable the quantification of 41 metabolites and the potential diagnosis of up to 25 disorders of PuPy metabolism.

Inborn Errors of Purine Salvage and Catabolism

Cellular purine nucleotides derive mainly from de novo synthesis or nucleic acid turnover and, only marginally, from dietary intake. They are subjected to catabolism, eventually forming uric acid in humans, while bases and nucleosides may be converted back to nucleotides through the salvage pathways. Inborn errors of the purine salvage pathway and catabolism have been described by several researchers and are usually referred to as rare diseases. Since purine compounds play a fundamental role, it is not surprising that their dysmetabolism is accompanied by devastating symptoms. Nevertheless, some of these manifestations are unexpected and, so far, have no explanation or therapy. Herein, we describe several known inborn errors of purine metabolism, highlighting their unexplained pathological aspects. Our intent is to offer new points of view on this topic and suggest diagnostic tools that may possibly indicate to clinicians that the inborn errors of purine metabolism may not be very rare diseases after all.

Hepatocyte Adenosine Kinase Promotes Excessive Fat Deposition and Liver Inflammation

BACKGROUND & AIMS

Nonalcoholic fatty liver disease is highly associated with obesity and progresses to nonalcoholic steatohepatitis when the liver develops overt inflammatory damage. While removing adenosine in the purine salvage pathway, adenosine kinase (ADK) regulates methylation reactions. We aimed to study whether hepatocyte ADK functions as an obesogenic gene/enzyme to promote excessive fat deposition and liver inflammation.

METHODS

Liver sections of human subjects were examined for ADK expression using immunohistochemistry. Mice with hepatocyte-specific ADK disruption or overexpression were examined for hepatic fat deposition and inflammation. Liver lipidomics, hepatocyte RNA sequencing (RNA-seq), and single-cell RNA-seq for liver nonparenchymal cells were performed to analyze ADK regulation of hepatocyte metabolic responses and hepatocyte-nonparenchymal cells crosstalk.

RESULTS

Whereas patients with nonalcoholic fatty liver disease had increased hepatic ADK levels, mice with hepatocyte-specific ADK disruption displayed decreased hepatic fat deposition on a chow diet and were protected from diet-induced excessive hepatic fat deposition and inflammation. In contrast, mice with hepatocyte-specific ADK overexpression displayed increased body weight and adiposity and elevated degrees of hepatic steatosis and inflammation compared with control mice. RNA-seq and epigenetic analyses indicated that ADK increased hepatic DNA methylation and decreased hepatic Ppara expression and fatty acid oxidation. Lipidomic and single-cell RNA-seq analyses indicated that ADK-driven hepatocyte factors, due to mitochondrial dysfunction, enhanced macrophage proinflammatory activation in manners involving increased expression of stimulator of interferon genes.

CONCLUSIONS

Hepatocyte ADK functions to promote excessive fat deposition and liver inflammation through suppressing hepatocyte fatty acid oxidation and producing hepatocyte-derived proinflammatory mediators. Therefore, hepatocyte ADK is a therapeutic target for managing obesity and nonalcoholic fatty liver disease.

Adenosine kinase (ADK) inhibition with ABT-702 induces ADK protein degradation and a distinct form of sustained cardioprotection

Pharmacological inhibition of adenosine kinase (ADK), the major route of myocardial adenosine metabolism, can elicit acute cardioprotection against ischemia-reperfusion (IR) by increasing adenosine signaling. Here, we identified a novel, extended effect of the ADK inhibitor, ABT-702, on cardiac ADK protein longevity and investigated its impact on sustained adenosinergic cardioprotection. We found that ABT-702 treatment significantly reduced cardiac ADK protein content in mice 24-72 h after administration (IP or oral). ABT-702 did not alter ADK mRNA levels, but strongly diminished (ADK-L) isoform protein content through a proteasome-dependent mechanism. Langendorff perfusion experiments revealed that hearts from ABT-702-treated mice maintain higher adenosine release long after ABT-702 tissue elimination, accompanied by increased basal coronary flow (CF) and robust tolerance to IR. Sustained cardioprotection by ABT-702 did not involve increased nitric oxide synthase expression, but was completely dependent upon increased adenosine release in the delayed phase (24 h), as indicated by the loss of cardioprotection and CF increase upon perfusion of adenosine deaminase or adenosine receptor antagonist, 8-phenyltheophylline. Importantly, blocking adenosine receptor activity with theophylline during ABT-702 administration prevented ADK degradation, preserved late cardiac ADK activity, diminished CF increase and abolished delayed cardioprotection, indicating that early adenosine receptor signaling induces late ADK degradation to elicit sustained adenosine release. Together, these results indicate that ABT-702 induces a distinct form of delayed cardioprotection mediated by adenosine receptor-dependent, proteasomal degradation of cardiac ADK and enhanced adenosine signaling in the late phase. These findings suggest ADK protein stability may be pharmacologically targeted to achieve sustained adenosinergic cardioprotection.

ATP and Adenosine Metabolism in Cancer: Exploitation for Therapeutic Gain

Adenosine is an evolutionary ancient metabolic regulator linking energy state to physiologic processes, including immunomodulation and cell proliferation. Tumors create an adenosine-rich immunosuppressive microenvironment through the increased release of ATP from dying and stressed cells and its ectoenzymatic conversion into adenosine. Therefore, the adenosine pathway becomes an important therapeutic target to improve the effectiveness of immune therapies. Prior research has focused largely on the two major ectonucleotidases, ectonucleoside triphosphate diphosphohydrolase 1/cluster of differentiation (CD)39 and ecto-5'-nucleotidase/CD73, which catalyze the breakdown of extracellular ATP into adenosine, and on the subsequent activation of different subtypes of adenosine receptors with mixed findings of antitumor and protumor effects. New findings, needed for more effective therapeutic approaches, require consideration of redundant pathways controlling intratumoral adenosine levels, including the alternative NAD-inactivating pathway through the CD38-ectonucleotide pyrophosphatase phosphodiesterase (ENPP)1-CD73 axis, the counteracting ATP-regenerating ectoenzymatic pathway, and cellular adenosine uptake and its phosphorylation by adenosine kinase. This review provides a holistic view of extracellular and intracellular adenosine metabolism as an integrated complex network and summarizes recent data on the underlying mechanisms through which adenosine and its precursors ATP and ADP control cancer immunosurveillance, tumor angiogenesis, lymphangiogenesis, cancer-associated thrombosis, blood flow, and tumor perfusion. Special attention is given to differences and commonalities in the purinome of different cancers, heterogeneity of the tumor microenvironment, subcellular compartmentalization of the adenosine system, and novel roles of purine-converting enzymes as targets for cancer therapy. SIGNIFICANCE STATEMENT: The discovery of the role of adenosine as immune checkpoint regulator in cancer has led to the development of novel therapeutic strategies targeting extracellular adenosine metabolism and signaling in multiple clinical trials and preclinical models. Here we identify major gaps in knowledge that need to be filled to improve the therapeutic gain from agents targeting key components of the adenosine metabolic network and, on this basis, provide a holistic view of the cancer purinome as a complex and integrated network.

The dynamic effect of genetic variation on the in vivo ER stress transcriptional response in different tissues

The genetic regulation of gene expression varies greatly across tissue-type and individuals and can be strongly influenced by the environment. Many variants, under healthy control conditions, may be silent or even have the opposite effect under diseased stress conditions. This study uses an in vivo mouse model to investigate how the effect of genetic variation changes with cellular stress across different tissues. Endoplasmic reticulum stress occurs when misfolded proteins accumulate in the endoplasmic reticulum. This triggers the unfolded protein response, a large transcriptional response which attempts to restore homeostasis. This transcriptional response, despite being a conserved, basic cellular process, is highly variable across different genetic backgrounds, making it an ideal system to study the dynamic effects of genetic variation. In this study, we sought to better understand how genetic variation alters expression across tissues, in the presence and absence of endoplasmic reticulum stress. The use of different mouse strains and their F1s allow us to also identify context-specific cis- and trans- regulatory variation underlying variable transcriptional responses. We found hundreds of genes that respond to endoplasmic reticulum stress in a tissue- and/or genotype-dependent manner. The majority of the regulatory effects we identified were acting in cis-, which in turn, contribute to the variable endoplasmic reticulum stress- and tissue-specific transcriptional response. This study demonstrates the need for incorporating environmental stressors across multiple different tissues in future studies to better elucidate the effect of any particular genetic factor in basic biological pathways, like the endoplasmic reticulum stress response.

Epigenetic Upregulation of H19 and AMPK Inhibition Concurrently Contribute to S-Adenosylhomocysteine Hydrolase Deficiency-Promoted Atherosclerotic Calcification

BACKGROUND

S-adenosylhomocysteine (SAH) is a risk factor of cardiovascular disease; inhibition of SAH hydrolase (SAHH) results in SAH accumulation and induces endothelial dysfunction and atherosclerosis. However, the effect and mechanism of SAHH in atherosclerotic calcification is still unclear. We aimed to explore the role and mechanism of SAHH in atherosclerotic calcification.

METHODS

The relationship between SAHH and atherosclerotic calcification was investigated in patients with coronary atherosclerotic calcification. Different in vivo genetic models were used to examine the effect of SAHH deficiency on atherosclerotic calcification. Human aortic and murine vascular smooth muscle cells (VSMCs) were cultured to explore the underlying mechanism of SAHH on osteoblastic differentiation of VSMCs.

RESULTS

The expression and activity of SAHH were decreased in calcified human coronary arteries and inversely associated with coronary atherosclerotic calcification severity, whereas plasma SAH and total homocysteine levels were positively associated with coronary atherosclerotic calcification severity. Heterozygote knockout of SAHH promoted atherosclerotic calcification. Specifically, VSMC-deficient but not endothelial cell-deficient or macrophage-deficient SAHH promoted atherosclerotic calcification. Mechanistically, SAHH deficiency accumulated SAH levels and induced H19-mediated Runx2 (runt-related transcription factor 2)-dependent osteoblastic differentiation of VSMCs by inhibiting DNMT3b (DNA methyltransferase 3 beta) and leading to hypomethylation of the H19 promoter. On the other hand, SAHH deficiency resulted in lower intracellular levels of adenosine and reduced AMPK (AMP-activated protein kinase) activation. Adenosine supplementation activated AMPK and abolished SAHH deficiency-induced expression of H19 and Runx2 and osteoblastic differentiation of VSMCs. Finally, AMPK activation by adenosine inhibited H19 expression by inducing Sirt1-mediated histone H3 hypoacetylation and DNMT3b-mediated hypermethylation of the H19 promoter in SAHH deficiency VSMCs.

CONCLUSIONS

We have confirmed a novel correlation between SAHH deficiency and atherosclerotic calcification and clarified a new mechanism that epigenetic upregulation of H19 and AMPK inhibition concurrently contribute to SAHH deficiency-promoted Runx2-dependent atherosclerotic calcification.

Methionine cycle in nonalcoholic fatty liver disease and its potential applications

As a chronic metabolic disease affecting epidemic proportions worldwide, the pathogenesis of Nonalcoholic Fatty Liver Disease (NAFLD) is not clear yet. There is also a lack of precise biomarkers and specific medicine for the diagnosis and treatment of NAFLD. Methionine metabolic cycle, which is critical for the maintaining of cellular methylation and redox state, is involved in the pathophysiology of NAFLD. However, the molecular basis and mechanism of methionine metabolism in NAFLD are not completely understood. Here, we mainly focus on specific enzymes that participates in methionine cycle, to reveal their interconnections with NAFLD, in order to recognize the pathogenesis of NAFLD from a new angle and at the same time, explore the clinical characteristics and therapeutic strategies.

Adenosine-Metabolizing Enzymes, Adenosine Kinase and Adenosine Deaminase, in Cancer

The immunosuppressive effect of adenosine in the microenvironment of a tumor is well established. Presently, researchers are developing approaches in immune therapy that target inhibition of adenosine or its signaling such as CD39 or CD73 inhibiting antibodies or adenosine A2A receptor antagonists. However, numerous enzymatic pathways that control ATP-adenosine balance, as well as understudied intracellular adenosine regulation, can prevent successful immunotherapy. This review contains the latest data on two adenosine-lowering enzymes: adenosine kinase (ADK) and adenosine deaminase (ADA). ADK deletes adenosine by its phosphorylation into 5′-adenosine monophosphate. Recent studies have revealed an association between a long nuclear ADK isoform and an increase in global DNA methylation, which explains epigenetic receptor-independent role of adenosine. ADA regulates the level of adenosine by converting it to inosine. The changes in the activity of ADA are detected in patients with various cancer types. The article focuses on the biological significance of these enzymes and their roles in the development of cancer. Perspectives of future studies on these enzymes in therapy for cancer are discussed.

Case Report: Adenosine kinase deficiency diagnosed 10 years after liver transplantation: Novel phenotypic insights

Adenosine kinase (ADK) deficiency is a rare inborn error of methionine and adenosine metabolism. So far, a total of 27 patients with ADK deficiency have been reported. Here, we describe the first Polish patient diagnosed with ADK deficiency, aiming to highlight the clinical presentation of disease, emphasize diagnostic difficulties, and report the long-term follow-up. Six-month-old patient presented with cholestatic liver disease, macrocytic anemia, developmental delay, generalized hypotonia, delayed brain myelination, and elevated levels of serum methionine. A decrease of mitochondrial respiratory chain complex II and III activity were found in the postnuclear supernatants obtained from skeletal muscle biopsy. The patient underwent living-donor liver transplantation (LTx) at 14 months of age. Ten-year follow-up after LTx revealed a preserved good liver function, persistent regenerative macrocytic anemia, progressive neurological disease but disappearance of brain MR changes, short stature, and cortisol deficiency. Whole exome sequencing revealed the patient to be affected with two novel ADK variants, which pathogenicity was confirmed biochemically by demonstration of elevated concentration of S-adenosylhomocysteine.

Adenosine kinase deficiency presenting with tortuous cervical arteries: A risk factor for recurrent stroke

Adenosine kinase (ADK) deficiency is a very rare inborn error of methionine and adenosine metabolism. It is characterized by developmental delay, hypotonia, epilepsy, facial dysmorphism, failure to thrive, transient liver dysfunction with cholestasis, recurrent hypoglycemia, and cardiac defects. Only 26 cases (16 families) of ADK deficiency have been published since its identification in 2011. Vascular abnormalities in cervical arteries and cerebral stroke have never been reported in this condition. Here, we describe two patients with ADK deficiency and vascular tortuosity leading to stroke in one of them. ADK deficiency is a rare inborn error of methionine metabolism with a complex phenotype that might be associated with cerebrovascular abnormalities and stroke.

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.

S-adenosylmethionine induces mitochondrial dysfunction, permeability transition pore opening and redox imbalance in subcellular preparations of rat liver

S-adenosylmethionine (AdoMet) predominantly accumulates in tissues and biological fluids of patients affected by liver dysmethylating diseases, particularly glycine N-methyltransferase, S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies, as well as in some hepatic mtDNA depletion syndromes, whose pathogenesis of liver dysfunction is still poorly established. Therefore, in the present work, we investigated the effects of S-adenosylmethionine (AdoMet) on mitochondrial functions and redox homeostasis in rat liver. AdoMet decreased mitochondrial membrane potential and Ca²⁺ retention capacity, and these effects were fully prevented by cyclosporin A and ADP, indicating mitochondrial permeability transition (mPT) induction. It was also verified that the thiol-alkylating agent NEM prevented AdoMet-induced ΔΨm dissipation, implying a role for thiol oxidation in the mPT pore opening. AdoMet also increased ROS production and provoked protein and lipid oxidation. Furthermore, AdoMet reduced GSH levels and the activities of aconitase and α-ketoglutarate dehydrogenase. Free radical scavengers attenuated AdoMet effects on lipid peroxidation and GSH levels, supporting a role of ROS in these effects. It is therefore presumed that disturbance of mitochondrial functions associated with mPT and redox unbalance may represent relevant pathomechanisms of liver damage provoked by AdoMet in disorders in which this metabolite accumulates.

Developmental Role of Adenosine Kinase in the Cerebellum

Adenosine acts as a neuromodulator and metabolic regulator of the brain through receptor dependent and independent mechanisms. In the brain, adenosine is tightly controlled through its metabolic enzyme adenosine kinase (ADK), which exists in a cytoplasmic (ADK-S) and nuclear (ADK-L) isoform. We recently discovered that ADK-L contributes to adult hippocampal neurogenesis regulation. Although the cerebellum (CB) is a highly plastic brain area with a delayed developmental trajectory, little is known about the role of ADK. Here, we investigated the developmental profile of ADK expression in C57BL/6 mice CB and assessed its role in developmental and proliferative processes. We found high levels of ADK-L during cerebellar development, which was maintained into adulthood. This pattern contrasts with that of the cerebrum, in which ADK-L expression is gradually downregulated postnatally and largely restricted to astrocytes in adulthood. Supporting a functional role in cell proliferation, we found that the ADK inhibitor 5-iodotubericine (5-ITU) reduced DNA synthesis of granular neuron precursors in a concentration-dependent manner in vitro. In the developing CB, immunohistochemical studies indicated ADK-L is expressed in immature Purkinje cells and granular neuron precursors, whereas in adulthood, ADK is absent from Purkinje cells, but widely expressed in mature granule neurons and their molecular layer (ML) processes. Furthermore, ADK-L is expressed in developing and mature Bergmann glia in the Purkinje cell layer, and in astrocytes in major cerebellar cortical layers. Together, our data demonstrate an association between neuronal ADK expression and developmental processes of the CB, which supports a functional role of ADK-L in the plasticity of the CB.

Metabolic Aspects of Adenosine Functions in the Brain

Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.

Adenosine kinase: An epigenetic modulator in development and disease

Adenosine kinase (ADK) is the key regulator of adenosine and catalyzes the metabolism of adenosine to 5'-adenosine monophosphate. The enzyme exists in two isoforms: a long isoform (ADK-long, ADK-L) and a short isoform (ADK-short, ADK-S). The two isoforms are developmentally regulated and are differentially expressed in distinct subcellular compartments with ADK-L localized in the nucleus and ADK-S localized in the cytoplasm. The nuclear localization of ADK-L and its biochemical link to the transmethylation pathway suggest a specific role for gene regulation via epigenetic mechanisms. Recent evidence reveals an adenosine receptor-independent role of ADK in determining the global methylation status of DNA and thereby contributing to epigenomic regulation. Here we summarize recent progress in understanding the biochemical interactions between adenosine metabolism by ADK-L and epigenetic modifications linked to transmethylation reactions. This review will provide a comprehensive overview of ADK-associated changes in DNA methylation in developmental, as well as in pathological conditions including brain injury, epilepsy, vascular diseases, cancer, and diabetes. Challenges in investigating the epigenetic role of ADK for therapeutic gains are briefly discussed.

Integration of whole genome sequencing into a healthcare setting: high diagnostic rates across multiple clinical entities in 3219 rare disease patients

BACKGROUND

We report the findings from 4437 individuals (3219 patients and 1218 relatives) who have been analyzed by whole genome sequencing (WGS) at the Genomic Medicine Center Karolinska-Rare Diseases (GMCK-RD) since mid-2015. GMCK-RD represents a long-term collaborative initiative between Karolinska University Hospital and Science for Life Laboratory to establish advanced, genomics-based diagnostics in the Stockholm healthcare setting.

METHODS

Our analysis covers detection and interpretation of SNVs, INDELs, uniparental disomy, CNVs, balanced structural variants, and short tandem repeat expansions. Visualization of results for clinical interpretation is carried out in Scout-a custom-developed decision support system. Results from both singleton (84%) and trio/family (16%) analyses are reported. Variant interpretation is done by 15 expert teams at the hospital involving staff from three clinics. For patients with complex phenotypes, data is shared between the teams.

RESULTS

Overall, 40% of the patients received a molecular diagnosis ranging from 19 to 54% for specific disease groups. There was heterogeneity regarding causative genes (n = 754) with some of the most common ones being COL2A1 (n = 12; skeletal dysplasia), SCN1A (n = 8; epilepsy), and TNFRSF13B (n = 4; inborn errors of immunity). Some causative variants were recurrent, including previously known founder mutations, some novel mutations, and recurrent de novo mutations. Overall, GMCK-RD has resulted in a large number of patients receiving specific molecular diagnoses. Furthermore, negative cases have been included in research studies that have resulted in the discovery of 17 published, novel disease-causing genes. To facilitate the discovery of new disease genes, GMCK-RD has joined international data sharing initiatives, including ClinVar, UDNI, Beacon, and MatchMaker Exchange.

CONCLUSIONS

Clinical WGS at GMCK-RD has provided molecular diagnoses to over 1200 individuals with a broad range of rare diseases. Consolidation and spread of this clinical-academic partnership will enable large-scale national collaboration.

Clinical Presentation, Genetic Etiology, and Coenzyme Q10 Levels in 55 Children with Combined Enzyme Deficiencies of the Mitochondrial Respiratory Chain

OBJECTIVES

To evaluate the clinical symptoms and biochemical findings and establish the genetic etiology in a cohort of pediatric patients with combined deficiencies of the mitochondrial respiratory chain complexes.

STUDY DESIGN

Clinical and biochemical data were collected from 55 children. All patients were subjected to sequence analysis of the entire mitochondrial genome, except when the causative mutations had been identified based on the clinical picture. Whole exome sequencing/whole genome sequencing (WES/WGS) was performed in 32 patients.

RESULTS

Onset of disease was generally early in life (median age, 6 weeks). The most common symptoms were muscle weakness, hypotonia, and developmental delay/intellectual disability. Nonneurologic symptoms were frequent. Disease causing mutations were found in 20 different nuclear genes, and 7 patients had mutations in mitochondrial DNA. Causative variants were found in 18 of the 32 patients subjected to WES/WGS. Interestingly, many patients had low levels of coenzyme Q10 in muscle, irrespective of genetic cause.

CONCLUSIONS

Children with combined enzyme defects display a diversity of clinical symptoms with varying age of presentation. We established the genetic diagnosis in 35 of the 55 patients (64%). The high diagnostic yield was achieved by the introduction of massive parallel sequencing, which also revealed novel genes and enabled elucidation of new disease mechanisms.

Adenosine kinase deficiency: Three new cases and diagnostic value of hypermethioninemia

Adenosine kinase (ADK) deficiency is characterized by liver disease, dysmorphic features, epilepsy and developmental delay. This defect disrupts the adenosine/AMP futile cycle and interferes with the upstream methionine cycle. We report the clinical, histological and biochemical courses of three ADK children carrying two new mutations and presenting with neonatal cholestasis and neurological disorders. One of them died of liver failure whereas the other two recovered from their liver damage. As the phenotype was consistent with a mitochondrial disorder, we studied liver mitochondrial respiratory chain activities in two patients and revealed a combined defect of several complexes. In addition, we retrospectively analyzed methionine plasma concentration, a hallmark of ADK deficiency, in a cohort of children and showed that methionine level in patients with ADK deficiency was strongly increased compared with patients with other liver diseases. ADK deficiency is a cause of neonatal or early infantile liver disease that may mimic primary mitochondrial disorders. In this context, an elevation of methionine plasma levels over twice the upper limit should not be considered as a nonspecific finding. ADK deficiency induced-liver dysfunction is most often transient, but could be life-threatening.

Adenosine kinase: A key regulator of purinergic physiology

Adenosine (ADO) is an essential biomolecule for life that provides critical regulation of energy utilization and homeostasis. Adenosine kinase (ADK) is an evolutionary ancient ribokinase derived from bacterial sugar kinases that is widely expressed in all forms of life, tissues and organ systems that tightly regulates intracellular and extracellular ADO concentrations. The facile ability of ADK to alter ADO availability provides a "site and event" specificity to the endogenous protective effects of ADO in situations of cellular stress. In addition to modulating the ability of ADO to activate its cognate receptors (P1 receptors), nuclear ADK isoform activity has been linked to epigenetic mechanisms based on transmethylation pathways. Previous drug discovery research has targeted ADK inhibition as a therapeutic approach to manage epilepsy, pain, and inflammation. These efforts generated multiple classes of highly potent and selective inhibitors. However, clinical development of early ADK inhibitors was stopped due to apparent mechanistic toxicity and the lack of suitable translational markers. New insights regarding the potential role of the nuclear ADK isoform (ADK-Long) in the epigenetic modulation of maladaptive DNA methylation offers the possibility of identifying novel ADK-isoform selective inhibitors and new interventional strategies that are independent of ADO receptor activation.

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.

Adenosine Kinase Expression in the Frontal Cortex in Schizophrenia

The adenosine hypothesis of schizophrenia posits that reduced availability of the neuromodulator adenosine contributes to dysregulation of dopamine and glutamate transmission and the symptoms associated with schizophrenia. It has been proposed that increased expression of the enzyme adenosine kinase (ADK) may drive hypofunction of the adenosine system. While animal models of ADK overexpression support such a role for altered ADK, the expression of ADK in schizophrenia has yet to be examined. In this study, we assayed ADK gene and protein expression in frontocortical tissue from schizophrenia subjects. In the dorsolateral prefrontal cortex (DLPFC), ADK-long and -short splice variant expression was not significantly altered in schizophrenia compared to controls. There was also no significant difference in ADK splice variant expression in the frontal cortex of rats treated chronically with haloperidol-decanoate, in a study to identify the effect of antipsychotics on ADK gene expression. ADK protein expression was not significantly altered in the DLPFC or anterior cingulate cortex (ACC). There was no significant effect of antipsychotic medication on ADK protein expression in the DLPFC or ACC. Overall, our results suggest that increased ADK expression does not contribute to hypofunction of the adenosine system in schizophrenia and that alternative mechanisms are involved in dysregulation of this system in schizophrenia.

Adenosine kinase inhibition promotes proliferation of neural stem cells after traumatic brain injury

Traumatic brain injury (TBI) is a major public health concern and remains a leading cause of disability and socio-economic burden. To date, there is no proven therapy that promotes brain repair following an injury to the brain. In this study, we explored the role of an isoform of adenosine kinase expressed in the cell nucleus (ADK-L) as a potential regulator of neural stem cell proliferation in the brain. The rationale for this hypothesis is based on coordinated expression changes of ADK-L during foetal and postnatal murine and human brain development indicating a role in the regulation of cell proliferation and plasticity in the brain. We first tested whether the genetic disruption of ADK-L would increase neural stem cell proliferation after TBI. Three days after TBI, modelled by a controlled cortical impact, transgenic mice, which lack ADK-L (ADK^Δneuron) in the dentate gyrus (DG) showed a significant increase in neural stem cell proliferation as evidenced by significant increases in doublecortin and Ki67-positive cells, whereas animals with transgenic overexpression of ADK-L in dorsal forebrain neurons (ADK-L^tg) showed an opposite effect of attenuated neural stem cell proliferation. Next, we translated those findings into a pharmacological approach to augment neural stem cell proliferation in the injured brain. Wild-type C57BL/6 mice were treated with the small molecule adenosine kinase inhibitor 5-iodotubercidin for 3 days after the induction of TBI. We demonstrate significantly enhanced neural stem cell proliferation in the DG of 5-iodotubercidin-treated mice compared to vehicle-treated injured animals. To rule out the possibility that blockade of ADK-L has any effects in non-injured animals, we quantified baseline neural stem cell proliferation in ADK^Δneuron mice, which was not altered, whereas baseline neural stem cell proliferation in ADK-L^tg mice was enhanced. Together these findings demonstrate a novel function of ADK-L involved in the regulation of neural stem cell proliferation after TBI.

Adenosine Metabolism: Emerging Concepts for Cancer Therapy

Adenosine is a key metabolic and immune-checkpoint regulator implicated in the tumor escape from the host immune system. Major gaps in knowledge that impede the development of effective adenosine-based therapeutics include: (1) lack of consideration of redundant pathways controlling ATP and adenosine levels; (2) lack of distinction between receptor-dependent and -independent effects of adenosine, and (3) focus on extracellular adenosine without consideration of intracellular metabolism and compartmentalization. In light of current clinical trials, we provide an overview of adenosine metabolism and point out the need for a more careful evaluation of the entire purinome in emerging cancer therapies.

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.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Adenosine Kinase Deficiency Increases Susceptibility to a Carcinogen

Background: Adenosine kinase (ADK) is a key regulator of hepatic metabolism. Its deficiency in the liver causes hepatic steatosis and methylation defects. In this study, we investigated whether reduced ADK expression affects the susceptibility of the liver to a carcinogen. Methods: We investigated ADK expression in samples from 11 liver cancer patients. We used transgenic Adk-tg mice with reduced hepatic ADK to study their susceptibility to a carcinogen. We exposed 45 Adk-tg and 21 wild-type (WT) mice to the carcinogen diethylnitrosamine (DEN) and the tumor promoter phenobarbital (PB) and examined the survival and body weight. Results: Seven of 11 patients with liver cancer had reduced ADK expression. A Kaplan-Meier survival curve showed a significantly increased mortality rate of DEN/PB-exposed Adk-tg mice compared with WT mice. Conclusions: Reduced hepatic ADK increases the susceptibility to the acute toxic effects of a carcinogen. Low hepatic ADK might be a risk factor and biomarker for cancer development.

Transient use of a systemic adenosine kinase inhibitor attenuates epilepsy development in mice

OBJECTIVE

Over one-third of all patients with epilepsy are refractory to treatment and there is an urgent need to develop new drugs that can prevent the development and progression of epilepsy. Epileptogenesis is characterized by distinct histopathologic and biochemical changes, which include astrogliosis and increased expression of the adenosine-metabolizing enzyme adenosine kinase (ADK; EC 2.7.1.20). Increased expression of ADK contributes to epileptogenesis and is therefore a target for therapeutic intervention. We tested the prediction that the transient use of an ADK inhibitor administered during the latent phase of epileptogenesis can mitigate the development of epilepsy.

METHODS

We used the intrahippocampal kainic acid (KA) mouse model of temporal lobe epilepsy, which is characterized by ipsilateral hippocampal sclerosis with granule cell dispersion and the development of recurrent hippocampal paroxysmal discharges (HPDs). KA-injected mice were treated with the ADK inhibitor 5-iodotubercidin (5-ITU, 1.6 mg/kg, b.i.d., i.p.) during the latent phase of epileptogenesis from day 3-8 after injury; the period when gradual increases in hippocampal ADK expression begin to manifest. HPDs were assessed at 6 and 9 weeks after KA administration followed by epilepsy histopathology including assessment of granule cell dispersion, astrogliosis, and ADK expression.

RESULTS

5-ITU significantly reduced the percent time in seizures by at least 80% in 56% of mice at 6 weeks post-KA. This reduction in seizure activity was maintained in 40% of 5-ITU-treated mice at 9 weeks. 5-ITU also suppressed granule cell dispersion and prevented maladaptive ADK increases in these protected mice.

SIGNIFICANCE

Our results show that the transient use of a small-molecule ADK inhibitor, given during the early stages of epileptogenesis, has antiepileptogenic disease-modifying properties, which provides the rationale for further investigation into the development of a novel class of antiepileptogenic ADK inhibitors with increased efficacy for epilepsy prevention.

Whole exome sequencing revealed mutations in FBXL4, UNC80, and ADK in Thai patients with severe intellectual disabilities

Intellectual disabilities (ID) are etiologically heterogeneous. Advanced molecular techniques could be helpful in identification of the underlying genetic defects. We aimed to characterize clinical and molecular features of three Thai patients with ID. Patient 1 had ID, hypotonia and lactic acidosis. Patient 2 had ID and growth failure. Patient 3 had ID, seizure, diarrhea and hypoglycemia. Whole exome sequencing found that Patient 1 was homozygous for a nonsense, c.1303C>T (p.Arg435Ter), mutation in FBXL4, a gene responsible for encephalomyopathic mitochondrial DNA depletion syndrome-13 (MTDPS13). Patient 2 was compound heterozygous for two novel mutations, c.3226C>T (p.Arg1076Ter) and c.3205C>T (p.Arg1069Ter), in UNC80, a known gene of infantile hypotonia with psychomotor retardation and characteristic facies-2 (IHPRF2). Patient 3 was homozygous for a novel missense, c.427T>C (p.Cys143Arg), mutation in ADK, a known gene of adenosine kinase deficiency leading to hypermethioninemia. This study expands the mutational spectra of ID genes.

Internal standard metabolites for obtaining absolute quantitative information on the components of bloodstains by standardization of samples

Analysis of the components of bloodstains found at crime scenes can provide important information for solving the crime. However, components of blood and bloodstains vary with volume and various other unpredictable factors. Therefore, it is necessary to specify the volume of the initial liquid blood droplet and standardize the analysis. In this study, internal standard metabolites that remained constant in a certain amount of bloodstain, long after deposition of the stain, were identified. Liquid chromatography-electrospray ionization-tandem mass spectrometry of the metabolites extracted from the bloodstain samples at various time points (0, 7, 14, 21, and 28 days) was performed. The coefficient of variation (CV) of the obtained molecular features was calculated for each criterion: time point, subject, and all data (time and subject, triplicate of each). Five molecular features with average CVs of less than or equal to 5% were selected as candidates. Partial least squares discriminant analysis and principal component analysis showed that the effect on the candidates was very low over time. The fold-change value of abundances was confirmed according to time. Stigmasterol exhibited the most stable pattern; l-methionine remained stable until day 14 and after day 21. This study was the first attempt to identify internal standard metabolites that were maintained at a constant level in a bloodstain for a sufficiently long time. Analysis of internal standard metabolites in bloodstains will facilitate determination of the initial blood volume from which the bloodstain was made. Moreover, this method will provide an approach for standardization of bloodstains to obtain absolute quantitative information of bloodstain components at crime scenes.

Emerging Role of Purine Metabolizing Enzymes in Brain Function and Tumors

The growing evidence of the involvement of purine compounds in signaling, of nucleotide imbalance in tumorigenesis, the discovery of purinosome and its regulation, cast new light on purine metabolism, indicating that well known biochemical pathways may still surprise. Adenosine deaminase is important not only to preserve functionality of immune system but also to ensure a correct development and function of central nervous system, probably because its activity regulates the extracellular concentration of adenosine and therefore its function in brain. A lot of work has been done on extracellular 5′-nucleotidase and its involvement in the purinergic signaling, but also intracellular nucleotidases, which regulate the purine nucleotide homeostasis, play unexpected roles, not only in tumorigenesis but also in brain function. Hypoxanthine guanine phosphoribosyl transferase (HPRT) appears to have a role in the purinosome formation and, therefore, in the regulation of purine synthesis rate during cell cycle with implications in brain development and tumors. The final product of purine catabolism, uric acid, also plays a recently highlighted novel role. In this review, we discuss the molecular mechanisms underlying the pathological manifestations of purine dysmetabolisms, focusing on the newly described/hypothesized roles of cytosolic 5′-nucleotidase II, adenosine kinase, adenosine deaminase, HPRT, and xanthine oxidase.

Developmental role of adenosine kinase for the expression of sex-dependent neuropsychiatric behavior

Deficits in social memory, cognition, and aberrant responses to stimulants are common among persons affected by schizophrenia and other conditions with a presumed developmental etiology. We previously found that expression changes in the adenosine metabolizing enzyme adenosine kinase (ADK) in the adult brain are associated with deficits in various cognitive domains. To distinguish between developmental and adult functions of ADK, we used two transgenic mouse lines with widespread disruption of ADK expression in the adult brain, but differences in the onset of ADK deletion. Specifically, we compared Nestin-Cre^+/-:ADK-flox^fl/fl (ADK^ΔBrain) mice with global loss of ADK in the whole brain, beginning in mid-gestation and persisting for life, with Gfa2-Cre^+/-:ADK-flox^fl/fl (ADK^ΔAstro) mice that have normal ADK expression throughout development, but lose astrocyte-specific ADK-expression in young adulthood. Because ADK-expression in adulthood is generally confined to astrocytes, adult ADK^ΔAstro mice show a similar expression profile of ADK in key areas of the brain related to neuropsychiatric behavior, compared to adult ADK^ΔBrain mice. We sought to determine a neurodevelopmental role of ADK on the expression of psychiatric behaviors in adult male and female mice. Adult ADK^ΔBrain mice showed significant deficits in social memory in males, significant contextual learning impairments in both sexes, and a hyper-responsiveness to amphetamine in males. In contrast, ADK^ΔAstro mice showed normal social memory and contextual learning but hypo-responsiveness to amphetamine in males. Our results demonstrate a key developmental role of ADK in mediating behaviors in adulthood related to neuropsychiatric disease and support the greater prevalence of these disorders among males.

Adenosine Kinase couples sensing of cellular potassium depletion to purine metabolism

Adenosine Kinase (ADK) regulates the cellular levels of adenosine (ADO) by fine-tuning its metabolic clearance. The transfer of γ-phosphate from ATP to ADO by ADK involves regulation by the substrates and products, as well as by Mg²⁺ and inorganic phosphate. Here we present new crystal structures of mouse ADK (mADK) binary (mADK:ADO; 1.2 Å) and ternary (mADK:ADO:ADP; 1.8 Å) complexes. In accordance with the structural demonstration of ADO occupancy of the ATP binding site, kinetic studies confirmed a competitive model of auto-inhibition of ADK by ADO. In the ternary complex, a K⁺ ion is hexacoordinated between loops adjacent to the ATP binding site, where Asp310 connects the K⁺ coordination sphere to the ATP binding site through an anion hole structure. Nuclear Magnetic Resonance 2D ¹⁵N-¹H HSQC experiments revealed that the binding of K⁺ perturbs Asp310 and residues of adjacent helices 14 and 15, engaging a transition to a catalytically productive structure. Consistent with the structural data, the mutants D310A and D310P are catalytically deficient and loose responsiveness to K⁺. Saturation Transfer Difference spectra of ATPγS provided evidence for an unfavorable interaction of the mADK D310P mutant for ATP. Reductions in K⁺ concentration diminish, whereas increases enhance the in vitro activity of mADK (maximum of 2.5-fold; apparent K_d = 10.4 mM). Mechanistically, K⁺ increases the catalytic turnover (K_cat) but does not affect the affinity of mADK for ADO or ATP. Depletion of intracellular K⁺ inhibited, while its restoration was accompanied by a full recovery of cellular ADK activity. Together, this novel dataset reveals the molecular basis of the allosteric activation of ADK by K⁺ and highlights the role of ADK in connecting depletion of intracellular K⁺ to the regulation of purine metabolism.

Targeted disruption of adenosine kinase in myeloid monocyte cells increases osteoclastogenesis and bone resorption in mice

Adenosine kinase (ADK) serves an important role in intracellular adenosine clearance via phosphorylating adenosine to AMP. The role of adenosine and its receptors in the maintenance of bone homeostasis is well studied, particularly in osteoclastogenesis and bone resorption; however, the function of ADK in bone metabolism is still unclear. In the present study, utilizing the cre/floxp recombination system, mice with conditional loss of ADK function in myeloid monocyte cells were used to assess the effect of ADK deficiency on bone metabolism. Mice were evaluated by means of gross observation and bone histomorphometric analysis. Ex vivo osteoclast differentiation and bone resorption were also examined using genetic deletion and pharmacologic inhibition of ADK in osteoclasts. Compared with control mice, the results of the present study demonstrate that adult mice lacking ADK in the myeloid monocyte cells had reduced body weight and nasoanal length. The results of bone histomorphometric analysis revealed that bone mass was significantly decreased and osteoclastic parameters were increased in the study mice. Furthermore, in vitro cell culture revealed that inhibition of ADK function promoted osteoclast differentiation and bone resorption. Osteoclast‑associated gene expression, including tartrate‑resistant acid phosphatase, nuclear factor of activated T‑cells, cytoplasmic 1, matrix metalloproteinase 9, Cathepsin K and calcitonin receptor, was also significantly increased. These results suggest that mice with ADK deficiency have reduced bone formation due to increased osteoclastogenesis and bone resorption. The present study provides further insight into the mechanism by which ADK serves a key role in bone metabolism.

Regulation of endothelial intracellular adenosine via adenosine kinase epigenetically modulates vascular inflammation

The molecular mechanisms underlying vascular inflammation and associated inflammatory vascular diseases are not well defined. Here we show that endothelial intracellular adenosine and its key regulator adenosine kinase (ADK) play important roles in vascular inflammation. Pro-inflammatory stimuli lead to endothelial inflammation by increasing endothelial ADK expression, reducing the level of intracellular adenosine in endothelial cells, and activating the transmethylation pathway through increasing the association of ADK with S-adenosylhomocysteine (SAH) hydrolase (SAHH). Increasing intracellular adenosine by genetic ADK knockdown or exogenous adenosine reduces activation of the transmethylation pathway and attenuates the endothelial inflammatory response. In addition, loss of endothelial ADK in mice leads to reduced atherosclerosis and affords protection against ischemia/reperfusion injury of the cerebral cortex. Taken together, these results demonstrate that intracellular adenosine, which is controlled by the key molecular regulator ADK, influences endothelial inflammation and vascular inflammatory diseases.

The molecular mechanisms underlying vascular inflammation are unclear. Here the authors show that pro-inflammatory stimuli lead to endothelial inflammation by increasing adenosine kinase expression, and that its knockdown in endothelial cells inhibits atherosclerosis and cerebral ischemic injury in mice.

Multi-omic network-based interrogation of rat liver metabolism following gastric bypass surgery featuring SWATH proteomics

Morbidly obese patients often elect for Roux-en-Y gastric bypass (RYGB), a form of bariatric surgery that triggers a remarkable 30% reduction in excess body weight and reversal of insulin resistance for those who are type II diabetic. A more complete understanding of the underlying molecular mechanisms that drive the complex metabolic reprogramming post-RYGB could lead to innovative non-invasive therapeutics that mimic the beneficial effects of the surgery, namely weight loss, achievement of glycemic control, or reversal of non-alcoholic steatohepatitis (NASH). To facilitate these discoveries, we hereby demonstrate the first multi-omic interrogation of a rodent RYGB model to reveal tissue-specific pathway modules implicated in the control of body weight regulation and energy homeostasis. In this study, we focus on and evaluate liver metabolism three months following RYGB in rats using both SWATH proteomics, a burgeoning label free approach using high resolution mass spectrometry to quantify protein levels in biological samples, as well as MRM metabolomics. The SWATH analysis enabled the quantification of 1378 proteins in liver tissue extracts, of which we report the significant down-regulation of Thrsp and Acot13 in RYGB as putative targets of lipid metabolism for weight loss. Furthermore, we develop a computational graph-based metabolic network module detection algorithm for the discovery of non-canonical pathways, or sub-networks, enriched with significantly elevated or depleted metabolites and proteins in RYGB-treated rat livers. The analysis revealed a network connection between the depleted protein Baat and the depleted metabolite taurine, corroborating the clinical observation that taurine-conjugated bile acid levels are perturbed post-RYGB.

Adenosine Kinase Deficiency in the Brain Results in Maladaptive Synaptic Plasticity

Adenosine kinase (ADK) deficiency in human patients (OMIM:614300) disrupts the methionine cycle and triggers hypermethioninemia, hepatic encephalopathy, cognitive impairment, and seizures. To identify whether this neurological phenotype is intrinsically based on ADK deficiency in the brain or if it is secondary to liver dysfunction, we generated a mouse model with a brain-wide deletion of ADK by introducing a Nestin-Cre transgene into a line of conditional ADK deficient Adk^fl/fl mice. These Adk^Δbrain mice developed a progressive stress-induced seizure phenotype associated with spontaneous convulsive seizures and profound deficits in hippocampus-dependent learning and memory. Pharmacological, biochemical, and electrophysiological studies suggest enhanced adenosine levels around synapses resulting in an enhanced adenosine A₁ receptor (A₁R)-dependent protective tone despite lower expression levels of the receptor. Theta-burst-induced LTP was enhanced in the mutants and this was dependent on adenosine A_2A receptor (A_2AR) and tropomyosin-related kinase B signaling, suggesting increased activation of these receptors in synaptic plasticity phenomena. Accordingly, reducing adenosine A_2A receptor activity in Adk^Δbrain mice restored normal associative learning and contextual memory and attenuated seizure risk. We conclude that ADK deficiency in the brain triggers neuronal adaptation processes that lead to dysregulated synaptic plasticity, cognitive deficits, and increased seizure risk. Therefore, ADK mutations have an intrinsic effect on brain physiology and may present a genetic risk factor for the development of seizures and learning impairments. Furthermore, our data show that blocking A_2AR activity therapeutically can attenuate neurological symptoms in ADK deficiency.

SIGNIFICANCE STATEMENT

A novel human genetic condition (OMIM #614300) that is based on mutations in the adenosine kinase (Adk) gene has been discovered recently. Affected patients develop hepatic encephalopathy, seizures, and severe cognitive impairment. To model and understand the neurological phenotype of the human mutation, we generated a new conditional knock-out mouse with a brain-specific deletion of Adk (Adk^Δbrain). Similar to ADK-deficient patients, Adk^Δbrain mice develop seizures and cognitive deficits. We identified increased basal synaptic transmission and enhanced adenosine A_2A receptor (A_2AR)-dependent synaptic plasticity as the underlying mechanisms that govern these phenotypes. Our data show that neurological phenotypes in ADK-deficient patients are intrinsic to ADK deficiency in the brain and that blocking A_2AR activity therapeutically can attenuate neurological symptoms in ADK deficiency.

Chromosomal contacts connect loci associated with autism, BMI and head circumference phenotypes

Copy number variants (CNVs) are major contributors to genomic imbalance disorders. Phenotyping of 137 unrelated deletion and reciprocal duplication carriers of the distal 16p11.2 220 kb BP2-BP3 interval showed that these rearrangements are associated with autism spectrum disorders and mirror phenotypes of obesity/underweight and macrocephaly/microcephaly. Such phenotypes were previously associated with rearrangements of the non-overlapping proximal 16p11.2 600 kb BP4-BP5 interval. These two CNV-prone regions at 16p11.2 are reciprocally engaged in complex chromatin looping, as successfully confirmed by 4C-seq, fluorescence in situ hybridization and Hi-C, as well as coordinated expression and regulation of encompassed genes. We observed that genes differentially expressed in 16p11.2 BP4-BP5 CNV carriers are concomitantly modified in their chromatin interactions, suggesting that disruption of chromatin interplays could participate in the observed phenotypes. We also identified cis- and trans-acting chromatin contacts to other genomic regions previously associated with analogous phenotypes. For example, we uncovered that individuals with reciprocal rearrangements of the trans-contacted 2p15 locus similarly display mirror phenotypes on head circumference and weight. Our results indicate that chromosomal contacts' maps could uncover functionally and clinically related genes.

Thermal Shock Induces Host Proteostasis Disruption and Endoplasmic Reticulum Stress in the Model Symbiotic Cnidarian Aiptasia

Coral bleaching has devastating effects on coral survival and reef ecosystem function, but many of the fundamental cellular effects of thermal stress on cnidarian physiology are unclear. We used label-free liquid chromatography-tandem mass spectrometry to compare the effects of rapidly (33.5 °C, 24 h) and gradually (30 and 33.5 °C, 12 days) elevated temperatures on the proteome of the model symbiotic anemone Aiptasia. We identified 2133 proteins in Aiptasia, 136 of which were differentially abundant between treatments. Thermal shock, but not acclimation, resulted in significant abundance changes in 104 proteins, including those involved in protein folding and synthesis, redox homeostasis, and central metabolism. Nineteen abundant structural proteins showed particularly reduced abundance, demonstrating proteostasis disruption and potential protein synthesis inhibition. Heat shock induced antioxidant mechanisms and proteins involved in stabilizing nascent proteins, preventing protein aggregation and degrading damaged proteins, which is indicative of endoplasmic reticulum stress. Host proteostasis disruption occurred before either bleaching or symbiont photoinhibition was detected, suggesting host-derived reactive oxygen species production as the proximate cause of thermal damage. The pronounced abundance changes in endoplasmic reticulum proteins associated with proteostasis and protein turnover indicate that these processes are essential in the cellular response of symbiotic cnidarians to severe thermal stress.

Metabolic Screening in Children with Neurodevelopmental Delay, Seizure and/or Regression

OBJECTIVE

Neurometabolic disorder is one of the important groups of diseases that prominently has presentation early infantile period. In this study, we evaluated the result of metabolic screening of the patient with seizure, developmental delay and/or regression in development, demographic disease clinical and radiological findings on admitted and outpatient visited children.

MATERIALS & METHODS

Two-year retrospective review of 187 children with seizure, developmental delay and/or regression in the Mofid Children Hospital, Tehran, Iran was performed. The diagnosis was based on observation, findings of EEG and history of the patient, besides evaluation of patient milestones. The result of metabolic screening with Tandem mass spectrometry was evaluated using SPSS (ver.18.0) Statistical software.

RESULTS

Totally, 187 children with seizure, regression and/or developmental delay were evaluated by metabolic screening with tandem mass spectrometry method. The results of laboratory examination had no relationship between positive results of metabolic screening and the mentioned disease. The relations between positive results of metabolic screening and seizure, regression and/or developmental delay were not statistically meaningful.

CONCLUSION

Positive results of metabolic screening and seizure, regression and/or developmental delay were not statistically meaningful.

Consensus recommendations for the diagnosis, treatment and follow-up of inherited methylation disorders

Inherited methylation disorders are a group of rarely reported, probably largely underdiagnosed disorders affecting transmethylation processes in the metabolic pathway between methionine and homocysteine. These are methionine adenosyltransferase I/III, glycine N-methyltransferase, S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. This paper provides the first consensus recommendations for the diagnosis and management of methylation disorders. Following search of the literature and evaluation according to the SIGN-methodology of all reported patients with methylation defects, graded recommendations are provided in a structured way comprising diagnosis (clinical presentation, biochemical abnormalities, differential diagnosis, newborn screening, prenatal diagnosis), therapy and follow-up. Methylation disorders predominantly affect the liver, central nervous system and muscles, but clinical presentation can vary considerably between and within disorders. Although isolated hypermethioninemia is the biochemical hallmark of this group of disorders, it is not always present, especially in early infancy. Plasma S-adenosylmethionine and S-adenosylhomocysteine are key metabolites for the biochemical clarification of isolated hypermethioninemia. Mild hyperhomocysteinemia can be present in all methylation disorders. Methylation disorders do not qualify as primary targets of newborn screening. A low-methionine diet can be beneficial in patients with methionine adenosyltransferase I/III deficiency if plasma methionine concentrations exceed 800 μmol/L. There is some evidence that this diet may also be beneficial in patients with S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. S-adenosylmethionine supplementation may be useful in patients with methionine adenosyltransferase I/III deficiency. Recommendations given in this article are based on general principles and in practice should be adjusted individually according to patient's age, severity of the disease, clinical and laboratory findings.