Molecular basis for the antiproliferative effect of agmatine in tumor cells of colonic, hepatic, and neuronal origin

Insights into the action of the pharmaceutical metformin: Targeted inhibition of the gut microbial enzyme agmatinase

Metformin is the first-line treatment for type 2 diabetes, yet its mechanism of action is not fully understood. Recent studies suggest metformin's interactions with gut microbiota are responsible for exerting therapeutic effects. In this study, we report that metformin targets the gut microbial enzyme agmatinase, as a competitive inhibitor, which may impair gut agmatine catabolism. The metformin inhibition constant (Ki) of E. coli agmatinase is 1 mM and relevant in the gut where the drug concentration is 1-10 mM. Metformin analogs phenformin, buformin, and galegine are even more potent inhibitors of E. coli agmatinase (Ki = 0.6, 0.1, and 0.007 mM, respectively) suggesting a shared mechanism. Agmatine is a known effector of human host metabolism and has been reported to augment metformin's therapeutic effects for type 2 diabetes. This gut-derived inhibition mechanism gives new insights on metformin's action in the gut and may lead to significant discoveries in improving metformin therapy.

Arginine Is a Novel Drug Target for Arginine Decarboxylase in Human Colorectal Cancer Cells

Colorectal cancer (CRC) has been proven to be highly reliant on arginine availability. Limiting arginine-rich foods or treating patients with arginine-depleting enzymes arginine deiminase (ADI) or arginase can suppress colon cancer. However, arginase and ADI are not the best drug candidates for CRC. Ornithine, the product of arginase, can enhance the supply of polyamine, which favors CRC cell growth, while citrulline, the product of ADI, faces the problem of arginine recycling due to the overexpression of argininosuccinate synthetase (ASS). Biosynthetic arginine decarboxylase (ADC), an enzyme that catalyzes the conversion of arginine to agmatine and carbon dioxide, may be a better choice as it combines both arginine depletion and suppression of intracellular polyamine synthesis via its product agmatine. ADC has anti-tumor potential yet has received much less attention than the other two arginine-depleting enzymes. In order to gain a better understanding of ADC, the preparation and the anti-cancer properties of this enzyme were explored in this study. When tested in vitro, ADC inhibited the proliferation of three colorectal cancer cell lines regardless of their ASS cellular expression. In contrast, ADC had a lesser cytotoxic effect on the human foreskin fibroblasts and rat primary hepatocytes. Further in vitro studies revealed that ADC induced S and G2/M phase cell-cycle arrest and apoptosis in HCT116 and LoVo cells. ADC-induced apoptosis in HCT116 cells followed the mitochondrial apoptotic pathway and was caspase-3-dependent. With all results obtained, we suggest that arginine is a potential target for treating colorectal cancer with ADC, and the anti-cancer properties of ADC should be more deeply investigated in the future.

Unlocking the Potential of Arginine Deprivation Therapy: Recent Breakthroughs and Promising Future for Cancer Treatment

Arginine is a semi-essential amino acid that supports protein synthesis to maintain cellular functions. Recent studies suggest that arginine also promotes wound healing, cell division, ammonia metabolism, immune system regulation, and hormone biosynthesis-all of which are critical for tumor growth. These discoveries, coupled with the understanding of cancer cell metabolic reprogramming, have led to renewed interest in arginine deprivation as a new anticancer therapy. Several arginine deprivation strategies have been developed and entered clinical trials. The main principle behind these therapies is that arginine auxotrophic tumors rely on external arginine sources for growth because they carry reduced key arginine-synthesizing enzymes such as argininosuccinate synthase 1 (ASS1) in the intracellular arginine cycle. To obtain anticancer effects, modified arginine-degrading enzymes, such as PEGylated recombinant human arginase 1 (rhArg1-PEG) and arginine deiminase (ADI-PEG 20), have been developed and shown to be safe and effective in clinical trials. They have been tried as a monotherapy or in combination with other existing therapies. This review discusses recent advances in arginine deprivation therapy, including the molecular basis of extracellular arginine degradation leading to tumor cell death, and how this approach could be a valuable addition to the current anticancer arsenal.

Agmatine prevents the manifestation of impulsive burying and depression-like behaviour in progesterone withdrawn female rats

Premenstrual dysphoric disorder (PMDD) is characterized by various physical and affective symptoms, including anxiety, irritability, anhedonia, social withdrawal, and depression. The present study investigated the role of the agmatinergic system in animal model of progesterone withdrawal in female rats. Chronic progesterone exposure of female rats for 21 days and its abrupt withdrawal showed enhanced marble burying, increased immobility time, and reduced no. of entries in open arm as compared to control animals. The progesterone withdrawal-induced enhanced marble burying anxiety and immobility time was significantly attenuated by agmatine (5-20 mg/kg, i.p.), and its endogenous modulators like L-arginine (100 mg/kg, i.p.), amino-guanidine (25 mg/kg, i.p.) and arcaine (50 mg/kg, i.p.) by their once-daily administration from day 14-day 21 of the protocol. We have also analysed the levels of agmatine, progesterone, and inflammatory cytokines in the hippocampal region of progesterone withdrawn rats. There was a significant decline in agmatine and progesterone levels and an elevation in cytokine levels in the hippocampal region of progesterone withdrawn rats compared to the control animals. In conclusion, the present studies suggest the importance of the endogenous agmatinergic system in progesterone withdrawal-induced anxiety-like and depression-like behaviour. The data also projects agmatine as a potential therapeutic target for the premenstrual dysphoric disorder.

Predictive markers for efficiency of the amino-acid deprivation therapies in cancer

Amino acid deprivation therapy (AADT) is a promising strategy for developing novel anticancer treatments, based on variations in metabolism of healthy and malignant cells. L-asparaginase was the first amino acid-degrading enzyme that received FDA approval for the treatment of acute lymphoblastic leukemia (ALL). Arginase and arginine deiminase were effective in clinical trials for the treatment of metastatic melanomas and hepatocellular carcinomas. Essential dependence of certain cancer cells on methionine explains the anticancer efficacy of methionine-g-lyase. Along with significant progress in identification of metabolic vulnerabilities of cancer cells, new amino acid-cleaving enzymes appear as promising agents for cancer treatment: lysine oxidase, tyrosine phenol-lyase, cysteinase, and phenylalanine ammonia-lyase. However, sensitivity of specific cancer cell types to these enzymes differs. Hence, search for prognostic and predictive markers for AADT and introduction of the markers into clinical practice are of great importance for translational medicine. As specific metabolic pathways in cancer cells are determined by the enzyme expression, some of these enzymes may define the sensitivity to AADT. This review considers the known predictors for efficiency of AADT, emphasizing the importance of knowledge on cancer-specific amino acid significance for such predictions.

Agmatinase facilitates the tumorigenesis of pancreatic adenocarcinoma through the TGFβ/Smad pathway

Pancreatic adenocarcinoma (PAAD) is one of the most lethal malignancies. Due to the lack of typical symptoms and difficulties in early diagnosis, PAAD has a high mortality rate. Therefore, it is essential to identify novel specific biomarkers for the application of targeted therapies. A previous study suggested that agmatinase (AGMAT) may fulfill important roles in tumor progression; however, these roles and the underlying mechanisms of AGMAT involvement in PAAD have yet to be thoroughly investigated. To address this shortcoming, in the present study the expression and prognostic significance of AGMAT were analyzed via several bioinformatics databases. Gain- and loss-of-function experiments were subsequently performed to observe the impact of AGMAT on the proliferation and metastasis of PAAD cells via Cell Counting Kit 8 (CCK-8) assay, colony formation assay, and cell migration and invasion assays in vitro. In order to probe the mechanisms involved, western blot assays were performed. AGMAT was found to be overexpressed in PAAD, and it was positively associated with a poor prognosis. Stable overexpression of AGMAT was found to lead to a marked increase in cell proliferation and metastasis through activation of the transforming growth factor-β (TGFβ)/Smad pathway, and via enhancing epithelial-mesenchymal transition (EMT). In conclusion, the results of the present study suggest that AGMAT may be an oncogene, and a pivotal mechanism has been uncovered in which AGMAT facilitates the progression of PAAD tumorigenesis through the TGFβ/Smad pathway.

Serotonin and beyond-a tribute to Manfred Göthert (1939-2019)

Manfred Göthert, who had served Naunyn-Schmiedeberg's Arch Pharmacol as Managing Editor from 1998 to 2005, deceased in June 2019. His scientific oeuvre encompasses more than 20 types of presynaptic receptors, mostly on serotoninergic and noradrenergic neurones. He was the first to identify presynaptic receptors for somatostatin and ACTH and described many presynaptic receptors, known from animal preparations, also in human tissue. In particular, he elucidated the pharmacology of presynaptic 5-HT receptors. A second field of interest included ligand-gated and voltage-dependent channels. The negative allosteric effect of anesthetics at peripheral nACh receptors is relevant for the peripheral clinical effects of these drugs and modified the Meyer-Overton hypothesis. The negative allosteric effect of ethanol at NMDA receptors in human brain tissue occurred at concentrations found in the range of clinical ethanol intoxication. Moreover, the inhibitory effect of gabapentinoids on P/Q Ca2+ channels and the subsequent decrease in AMPA-induced noradrenaline release may contribute to their clinical effect. Another ligand-gated ion channel, the 5-HT3 receptor, attracted the interest of Manfred Göthert from the whole animal via isolated preparations down to the cellular level. He contributed to that molecular study in which 5-HT3 receptor subtypes were disclosed. Finally, he found altered pharmacological properties of 5-HT receptor variants like the Arg219Leu 5-HT1A receptor (which was also shown to be associated with major depression) and the Phe124Cys 5-HT1B receptor (which may be related to sumatriptan-induced vasospasm). Manfred Göthert was a brilliant scientist and his papers have a major impact on today's pharmacology.

Arginine depriving enzymes: applications as emerging therapeutics in cancer treatment

Cancer is the second leading cause of death globally. Chemotherapy and radiation therapy and other medications are employed to treat various types of cancer. However, each treatment has its own set of side effects, owing to its low specificity. As a result, there is an urgent need for newer therapeutics that do not disrupt healthy cells' normal functioning. Depriving nutrient or non/semi-essential amino acids to which cancerous cells are auxotrophic remains one such promising anticancer strategy. L-Arginine (Arg) is a semi-essential vital amino acid involved in versatile metabolic processes, signaling pathways, and cancer cell proliferation. Hence, the administration of Arg depriving enzymes (ADE) such as arginase, arginine decarboxylase (ADC), and arginine deiminase (ADI) could be effective in cancer therapy. The Arg auxotrophic cancerous cells like hepatocellular carcinoma, human colon cancer, leukemia, and breast cancer cells are sensitive to ADE treatment due to low expression of crucial enzymes argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and ornithine transcarbamylase (OCT). These therapeutic enzyme treatments induce cell death through inducing autophagy, apoptosis, generation of oxidative species, i.e., oxidative stress, and arresting the progression and expansion of cancerous cells at certain cell cycle checkpoints. The enzymes are undergoing clinical trials and could be successfully exploited as potential anticancer agents in the future.

The Effects of Quercetin on the Gene Expression of Arginine Metabolism Key Enzymes in Human Embryonic Kidney 293 Cells

Background: Arginine metabolism is an important factor involved in tumorigenesis, progression, and survival of tumor cells. Besides, other metabolites produced in the arginine metabolism process, such as polyamines, nitric oxide, argininosuccinate, and agmatine, play key roles in different stages of tumor development. On the other hand, herbal metabolites are widely used to treat cancer. One of these herbal flavonoids is quercetin. Methods: In this study, according to MTT assay data, two concentrations of quercetin flavonoid were selected (57.5 and 115 µM) to treat human embryonic kidney 293 (HEK293) cells. Then RNA was extracted from the cells and used as a template for cDNA synthesis. Using real-time PCR, the expression of key enzymes involved in arginine metabolism was evaluated, including arginase 2 (Arg2), ornithine carbamoyl transferase (OTC), agmatinase (AGMAT), arginase 1 (Arg1), nitric oxide synthase 1 (nNOS), arginine decarboxylase (ADC), ornithine decarboxylase 1 (ODC), ornithine carbamoyl transferase (OCT), spermidine synthase (SRM), spermine synthase (SMS), argininosuccinate synthase 1 (ASS1), and argininosuccinate lyase (ASL). The Student t-test was used to analyze the data considering a P value of < 0.05 as the significance level. Results: Our results indicated significant changes in the expression of arginine metabolism enzymes after quercetin exposure, confirming a role for quercetin plant flavonoid in regulating arginine metabolism in HEK293 cells. Conclusions: Quercetin could alter the gene expression of the key enzymes involved in arginine metabolism. This was the first study investigating the effects of quercetin on arginine metabolism in HEK293 cells.

Endogenous toxic metabolites and implications in cancer therapy

It is well recognized that many metabolic enzymes play essential roles in cancer cells in producing building blocks such as nucleotides, which are required in greater amounts due to their increased proliferation. On the other hand, the significance of enzymes in preventing the accumulation of their substrates is less recognized. Here, we outline the evidence and underlying mechanisms for how many metabolites normally produced in cells are highly toxic, such as metabolites containing reactive groups (e.g., methylglyoxal, 4-hydroxynonenal, and glutaconyl-CoA), or metabolites that act as competitive analogs against other metabolites (e.g., deoxyuridine triphosphate and l-2-hydroxyglutarate). Thus, if a metabolic pathway contains a toxic intermediate, then we may be able to induce accumulation and poison a cancer cell by targeting the downstream enzyme. Furthermore, this poisoning may be cancer cell selective if this pathway is overactive in a cancer cell relative to a nontransformed cell. We describe this concept as illustrated in selenocysteine metabolism and other pathways and discuss future directions in exploiting toxic metabolites to kill cancer cells.

Unraveling the Structural Landscape of Chitosan-Based Heparan Sulfate Mimics Binding to Growth Factors: Deciphering Structural Determinants for Optimal Activity

Chitosan sulfates have demonstrated the ability to mimic heparan sulfate (HS) function. In this context, it is crucial to understand how the specific structural properties of HS domains determine their functionalities and biological activities. In this study, several HS-mimicking chitosans have been prepared to mimic the structure of HS domains that have proved to be functionally significant in cell processes. The results presented herein are in concordance with the hypothesis that sulfated chitosan-growth factor (GF) interactions are controlled by a combination of two effects: the electrostatic interactions and the conformational adaptation of the polysaccharide. Thus, we found that highly charged O-sulfated S-CS and S-DCS polysaccharides with a low degree of contraction interacted more strongly with GFs than N-sulfated N-DCS, with a higher degree of contraction and a low charge. Finally, the evidence gathered suggests that N-DCS would be able to bind to an allosteric zone and is likely to enhance GF signaling activity. This is because the bound protein remains able to bind to its cognate receptor, promoting an effect on cell proliferation as has been shown for PC12 cells. However, S-CS and S-DCS would sequester the protein, decreasing the GF signaling activity by depleting the protein or locally blocking its active site.

Agmatinase promotes the lung adenocarcinoma tumorigenesis by activating the NO-MAPKs-PI3K/Akt pathway

Lung adenocarcinoma (LUAD) is one of the leading causes of cancer-related death worldwide. There is an urgent need to uncover the pathogenic mechanism to develop new treatments. Agmatinase (AGMAT) expression and its association with clinicopathological characteristics were analyzed via GEO, Oncomine, and TCGA databases, and IHC staining in human LUAD specimens. An EdU cell proliferation kit, propidiumiodide staining, colony formation, cell migration, and invasion assays, and a xenograft tumor model were used to detect the biological function of AGMAT in LUAD. Furthermore, the expression level of nitric oxide (NO) was detected using a DAF-FMDA fluorescent probe or nitrite assay kit, and further validated with Carboxy-PTIO (a NO scavenger). The roles of three isoforms of nitric oxide synthases (nNOS, eNOS, and iNOS) were validated using L-NAME (eNOS inhibitor), SMT (iNOS inhibitor), and spermidine (nNOS inhibitor). AGMAT expression was up-regulated in LUAD tissues. LUAD patients with high AGMAT levels were associated with poorer prognoses. AGMAT promoted LUAD tumorigenesis in NO released by iNOS both in vitro and in vivo. Importantly, NO signaling up-regulated the expression of cyclin D1 via activating the MAPK and PI3K/Akt-dependent c-myc activity, ultimately promoting the malignant proliferation of tumor cells. On the whole, AGMAT promoted NO release via up-regulating the expression of iNOS. High levels of NO drove LUAD tumorigenesis via activating MAPK and PI3K/Akt cascades. AGMAT might be a potential diagnostic and therapeutic target for LUAD patients.

Arginine metabolism and deprivation in cancer therapy

Certain cancer cells with nutrient auxotrophy and have a much higher nutrient demand compared with normal human cells. Arginine as a versatile amino acid, has multiple biological functions in metabolic and signaling pathways. Depletion of this amino acid by arginine depletor is generally well tolerated and has become a targeted therapy for arginine auxotrophic cancers. However, the modulatory eff ;ect of arginine on cancer cells is very complicated and still controversial. Therefore, this article focuses on arginine metabolism and depletion therapy in cancer treatment to provide systemical review on this issue.

Metabolic strategies for the degradation of the neuromodulator agmatine in mammals

Agmatine (1-amino-4-guanidinobutane), a precursor for polyamine biosynthesis, has been identified as an important neuromodulator with anticonvulsant, antineurotoxic and antidepressant actions in the brain. In this context it has emerged as an important mediator of addiction/satiety pathways associated with alcohol misuse. Consequently, the regulation of the activity of key enzymes in agmatine metabolism is an attractive strategy to combat alcoholism and related addiction disorders. Agmatine results from the decarboxylation of L-arginine in a reaction catalyzed by arginine decarboxylase (ADC), and can be converted to either guanidine butyraldehyde by diamine oxidase (DAO) or putrescine and urea by the enzyme agmatinase (AGM) or the more recently identified AGM-like protein (ALP). In rat brain, agmatine, AGM and ALP are predominantly localised in areas associated with roles in appetitive and craving (drug-reinstatement) behaviors. Thus, inhibitors of AGM or ALP are promising agents for the treatment of addictions. In this review, the properties of DAO, AGM and ALP are discussed with a view to their role in the agmatine metabolism in mammals.

Functional roles of agmatinase during the peri-implantation period of pregnancy in sheep

This study investigated the effect of agmatine (Agm) in proliferation of ovine trophecdoderm cells (oTr1) as well as the importance of the arginine decarboxylase (ADC) and agmatinase (AGMAT) alternative pathway for synthesis of polyamines in ovine conceptuses during the peri-implantation period of pregnancy. Morpholino antisense oligonucleotides (MAOs) were used to inhibit translation of mRNAs for ODC1 alone, AGMAT alone, and their combination. Rambouillet ewes (N = 50) were assigned randomly to the following treatments on Day 8 of pregnancy: MAO control (n = 10); MAO-ODC1 (n = 8); MAO-ADC (n = 6); MAO-ODC1:MAO-ADC (n = 9); or MAO-ODC1:MAO-AGMAT (n = 9). Ewes were ovario-hysterectomized on Day 16 of pregnancy to obtain uterine flushings, uterine endometrium, and conceptus tissues. Inhibition of translation of both ODC1 and AGMAT resulted in 22% of ewes having morphologically and functionally normal (elongated and healthy) conceptuses designated MAO-ODC1:MAO-AGMAT (A). But, 78% of the MAO-ODC1:MAO-AGMAT ewes had morphologically and functionally abnormal (not elongated and fragmented) conceptuses designated MAO-ODC1:MAO-AGMAT (B). The pregnancy rate was less (22%; P < 0.05) for MAO-ODC1:MAO-AGMAT ewes than for MAO-control (80%), MAO-ODC1 (75%), MAO-ADC (84%), and MAO-ODC1:MAO-ADC (44%) ewes. Moreover, inhibition of translational of both ODC1 and AGMAT mRNAs increased expression of ADC, SLC22A1, SLC22A2, and SLC22A3 mRNAs, as well as abundances of agmatine, putrescine, spermindine, and spermine in conceptus tissue. However, MAO-ODC1:AGMAT(B) ewes had greater abundances of agmatine, putrescine, and spermidine and reduced amounts of spermine in uterine flushes. Thus, in vivo knockdown of translation of ODC1 and AGMAT mRNAs increased expression of genes for the synthesis and transport of polyamines in ovine conceptuses during the peri-implantation period of pregnancy.

Modulation of L-Arginine-Arginase Metabolic Pathway Enzymes: Immunocytochemistry and mRNA Expression in Peripheral Blood and Tissue Levels in Head and Neck Squamous Cell Carcinomas in North East India

BACKGROUND

Arginine may play important roles in tumor progression by providing ornithine for polyamine biosynthesis, required for cell growth. The aim of this work was to determine the expression of arginine metabolic pathway enzymes in head and neck squamous cell carcinoma (HNSCC) in northeast India.

MATERIALS AND METHODS

The expressions of arginase isoforms (ARG1 and ARG2), ornithine aminotransferase (OAT) and ornithine decarboxylase (ODC) were examined in fifty paired HNSCC and adjacent non-tumor tissues by immunohistochemistry. Immunocytochemistry, semiquantitative reverse transcription sq-PCR and quantitative real-time qPCR were used to assess protein and mRNA expressions in peripheral blood of fifty HNSCC patients and hundred controls.

RESULTS

ARG1 and ODC protein and mRNA were strongly expressed in peripheral blood from HNSCC patients. No ARG2 expression was observed. In vivo, expression of ARG1, ARG2 and ODC was significantly higher in tumor than in non-tumor tissues. Most tumors expressed low levels of OAT, with no difference in tissues or blood, compared to controls. The absolute extent of maximal ARG1 upregulation with qPCR showed 6.23 fold increase in HNSCC.

CONCLUSIONS

These findings strongly suggest that in HNSCCs, the ARG1 pathway is stimulated leading to the formation of polyamines as indicated by higher ODC expression, which promote tumor growth.

Polyamine metabolism-based dual functional gene delivery system to synergistically inhibit the proliferation of cancer

Polyamine content, which is associated with tumor growth, can be regulated by ornithine decarboxylase (ODC) and S-adenosyl methionine decarboxylase (SAMDC), two key enzymes in polyamine biosynthesis. Here we aim to develop a pH-responsive cationic poly(agmatine) based on a polyamine analogue-agmatine that can dually function as a gene delivery vector as well as an anticancer agent by inhibiting ODC after intracellular degradation. The core-shell nanoparticles, formed by poly(agmatine)/SAMDC siRNA complex as a core, were coated with bovine serum albumin for better in vivo circulation stability and tumor targeting. When the nanoparticles were taken up by tumor cells via endocytosis and degraded in endosome, the released agmatine and SAMDC siRNA can synergistically inhibit polyamines biosynthesis, inducing inhibition of tumor proliferation. Our study offered a potential way in tumor therapy based on polyamine metabolism.

Aliphatic polyamines in physiology and diseases

Aliphatic polyamines are a family of polycationic molecules derived from decarboxylation of the amino acid ornithine that classically comprise three molecules: putrescine, spermidine and spermine. In-cell polyamine homeostasis is tightly controlled at key steps of cell metabolism. Polyamines are involved in an array of cellular functions from DNA stabilization, and regulation of gene expression to ion channel function and, particularly, cell proliferation. As such, aliphatic polyamines play an essential role in rapidly dividing cells such as in the immune system and digestive tract. Because of their role in cell proliferation, polyamines are also involved in carcinogenesis, prompting intensive research into polyamine metabolism as a target in cancer therapy. More recently, another aliphatic polyamine, agmatine, the decarboxylated derivative of arginine, has been identified as a neurotransmitter in mammals, and investigations have focused on its effects in the CNS, notably as a neuroprotector in brain injury.

Administering the Optimum Dose of l-Arginine in Regional Tumor Therapy

The purpose of this study is optimizing the l-arginine (l-Arg) doses on the basis of chemical structure in regional accessible tumor therapy to settle down a new protocol for the treatment of cancer. (3)H-thymidine-based cell proliferation assay was performed in vitro on tumor cell lines of fibrosarcoma (FS), lymphosarcoma-ascitic and on normal cell line of NIH 3T3 after treatment with different concentrations of l-Arg in phosphate buffered saline (PBS). The cultures were harvested after 22 h and the incorporated radioactivity was counted to identify their histologic grades as described in earlier studies. In vivo therapy of murine tumors was conducted where FS cells injected subcutaneously at ventro-lateral position of mice. Various drug delivery schedules were injected into the centre of tumor base, once a day for 4 days. Tumor diameter and survivals were monitored where the day of sacrifice was considered for monitoring the survival period. By identifying the histologic grades of the treated cultures in vitro and in vivo by different concentrations of l-Arg, the corresponding energy of such concentrations were determined. An efficient model with a good fit (R(2) = 0.98) was established to describe the energy yield by l-Arg dose. The equivalence between the tumor histologic grade and energy of the l-Arg dose delivered in saline (PBS) environment is the optimum condition for regional tumor therapy achieves higher survival rate. The selective cytotoxicity to tumor cells with minimal damage to normal cells by l-Arg due to its chemical structure suggests to be considered the most promising drug for regional therapy of the accessible tumors like breast cancers of early stage with no distant metastasis.

Overexpression of human arginine decarboxylase rescues human mesenchymal stem cells against H₂O₂ toxicity through cell survival protein activation

In this study, we explored the potentiality of human arginine decarboxylase (ADC) to enhance the survival of mesenchymal stem cells (MSCs) against unfavorable milieu of host tissues as the low survival of MSCs is the issue in cell transplantation therapy. To address this, human MSCs overexpressing human ADC were treated with H2O2 and the resultant intracellular events were examined. First, we examined whether human ADC is overexpressed in human MSCs. Then, we investigated cell survival or death related events. We found that the overexpression of human ADC increases formazan production and reduces caspase 3 activation and the numbers of FITC, hoechst, or propidium iodide positive cells in human MSCs exposed to H2O2. To elucidate the factors underlying these phenomena, AKT, CREB, and BDNF were examined. We found that the overexpression of human ADC phosphorylates AKT and CREB and increases BDNF level in human MSCs exposed to H2O2. The changes of these proteins are possibly relevant to the elevation of agmatine. Collectively, our data demonstrate that the overexpression of human ADC stimulates pro-survival factors to protect human MSCs against H2O2 toxicity. In conclusion, the present findings support that ADC can enhance the survival of MSCs against hostile environment of host tissues.

Ornithine decarboxylase and glutamate decarboxylase 65 as prognostic markers of gallbladder malignancy: a clinicopathological study in benign and malignant lesions of the gallbladder

Ornithine decarboxylase (ODC) plays a critical role in cell proliferation and is overexpressed in a variety of cancers. Furthermore, γ-aminobutyric acid (GABA) content and glutamate decarboxylase (GAD) activity are increased in neoplastic tissues in colon and breast cancer. However, few studies have examined these molecules in gallbladder cancer specimens. We observed the expression levels of ODC and GAD65 in benign and malignant lesions of the gallbladder and investigated their clinicopathological significance for the first time. The expression levels of ODC and GAD65 in specimens from gallbladder adenocarcinoma (n=108), peritumoral tissues (n=46), adenomatous polyps (n=15) and chronic cholecystitis (n=35) were detected using immunohistochemical methods. Kaplan-Meier survival and Cox regression analyses were carried out to explore the clinical and pathological correlations. The levels of positive staining of ODC and GAD65 were significantly higher in gallbladder adenocarcinoma than in peritumoral tissues, adenomatous polyps and chronic cholecystitis. The Kaplan‑Meier survival analysis and Cox regression analysis showed that the expression of ODC and GAD65 correlated significantly with the one-year survival rate and the mean survival time of the patients postoperatively. We conclude that the overexpression of ODC and GAD65 are significant in the carcinogenesis and progression of gallbladder adenocarcinoma. They may be important biological markers for the evaluation of biological behaviors and the prognosis of gallbladder adenocarcinoma.

OCT2 and MATE1 provide bidirectional agmatine transport

Agmatine is a biogenic amine (l-arginine metabolite) of potential relevance to several central nervous system (CNS) conditions. The identities of transporters underlying agmatine and polyamine disposition in mammalian systems are not well-defined. The SLC-family organic cation transporters (OCT) OCT1 and OCT2 and multidrug and toxin extrusion transporter-1 (MATE1) are transport systems that may be of importance for the cellular disposition of agmatine and putrescine. We investigated the transport of [(3)H]agmatine and [(3)H]putrescine in human embryonic kidney (HEK293) cells stably transfected with hOCT1, hOCT2, and hMATE1. Agmatine transport by hOCT1 and hOCT2 was concentration-dependent, whereas only hOCT2 demonstrated pH-dependent transport. hOCT2 exhibited a greater affinity for agmatine (K(m) = 1.84 ± 0.38 mM) than did hOCT1 (K(m) = 18.73 ± 4.86 mM). Putrescine accumulation was pH- and concentration-dependent in hOCT2-HEK cells (K(m) = 11.29 ± 4.26 mM) but not hOCT1-HEK cells. Agmatine accumulation, in contrast to putrescine, was significantly enhanced by hMATE1 overexpression, and was saturable (K(m) = 240 ± 31 μM; V(max) = 192 ± 10 pmol/min/mg of protein). Intracellular agmatine was also trans-stimulated (effluxed) from hMATE1-HEK cells in the presence of an inward proton-gradient. The hMATE1-mediated transport of agmatine was inhibited by polyamines, the prototypical substrates MPP+ and paraquat, as well as guanidine and arcaine, but not l-arginine. These results suggest that agmatine disposition may be influenced by hOCT2 and hMATE1, two transporters critical in the renal elimination of xenobiotic compounds.

Arginine deprivation and argininosuccinate synthetase expression in the treatment of cancer

Arginine, a semi-essential amino acid in humans, is critical for the growth of human cancers, particularly those marked by de novo chemoresistance and a poor clinical outcome. In addition to protein synthesis, arginine is involved in diverse aspects of tumour metabolism, including the synthesis of nitric oxide, polyamines, nucleotides, proline and glutamate. Tumoural downregulation of the enzyme argininosuccinate synthetase (ASS1), a recognised rate-limiting step in arginine synthesis, results in an intrinsic dependence on extracellular arginine due to an inability to synthesise arginine for growth. This dependence on extracellular arginine is known as arginine auxotrophy. Several tumours are arginine auxotrophic, due to variable loss of ASS1, including hepatocellular carcinoma, malignant melanoma, malignant pleural mesothelioma, prostate and renal cancer. Importantly, targeting extracellular arginine for degradation in the absence of ASS1 triggers apoptosis in arginine auxotrophs. Several phase I/II clinical trials of the arginine-lowering drug, pegylated arginine deiminase, have shown encouraging evidence of clinical benefit and low toxicity in patients with ASS1-negative tumours. In part, ASS1 loss is due to epigenetic silencing of the ASS1 promoter in various human cancer cell lines and tumours, and it is this silencing that confers arginine auxotrophy. In relapsed ovarian cancer, this is associated with platinum refractoriness. In contrast, several platinum sensitive tumours, including primary ovarian, stomach and colorectal cancer, are characterised by ASS1 overexpression, which is regulated by proinflammatory cytokines. This review examines the prospects for novel approaches in the prevention, diagnosis and treatment of malignant disease based on ASS1 pathophysiology and its rate-limiting product, arginine.

Characterization and inactivation of an agmatine deiminase from Helicobacter pylori

Helicobacter pylori encodes a potential virulence factor, agmatine deiminase (HpAgD), which catalyzes the conversion of agmatine to N-carbamoyl putrescine (NCP) and ammonia - agmatine is decarboxylated arginine. Agmatine is an endogenous human cell signaling molecule that triggers the innate immune response in humans. Unlike H. pylori, humans do not encode an AgD; it is hypothesized that inhibition of this enzyme would increase the levels of agmatine, and thereby enhance the innate immune response. Taken together, these facts suggest that HpAgD is a potential drug target. Herein we describe the optimized expression, isolation, and purification of HpAgD (10-30 mg/L media). The initial kinetic characterization of this enzyme has also been performed. Additionally, the crystal structure of wild-type HpAgD has been determined at 2.1A resolution. This structure provides a molecular basis for the preferential deimination of agmatine, and identifies Asp198 as a key residue responsible for agmatine recognition, which has been confirmed experimentally. Information gathered from these studies led to the development and characterization of a novel class of haloacetamidine-based HpAgD inactivators. These compounds are the most potent AgD inhibitors ever described.

The arginine metabolite agmatine protects mitochondrial function and confers resistance to cellular apoptosis

Agmatine, an endogenous metabolite of arginine, selectively suppresses growth in cells with high proliferative kinetics, such as transformed cells, through depletion of intracellular polyamine levels. In the present study, we depleted intracellular polyamine content with agmatine to determine if attrition by cell death contributes to the growth-suppressive effects. We did not observe an increase in necrosis, DNA fragmentation, or chromatin condensation in Ha-Ras-transformed NIH-3T3 cells administered agmatine. In response to Ca(2+)-induced oxidative stress in kidney mitochondrial preparations, agmatine demonstrated attributes of a free radical scavenger by protecting against the oxidation of sulfhydryl groups and decreasing hydrogen peroxide content. The functional outcome was a protective effect against Ca(2+)-induced mitochondrial swelling and mitochondrial membrane potential collapse. We also observed decreased expression of proapoptotic Bcl-2 family members and of execution caspase-3, implying antiapoptotic potential. Indeed, we found that apoptosis induced by camptothecin or 5-fluorourocil was attenuated in cells administered agmatine. Agmatine may offer an alternative to the ornithine decarboxylase inhibitor difluoromethyl ornithine for depletion of intracellular polyamine content while avoiding the complications of increasing polyamine import and reducing the intracellular free radical scavenger capacity of polyamines. Depletion of intracellular polyamine content with agmatine suppressed cell growth, yet its antioxidant capacity afforded protection from mitochondrial insult and resistance to cellular apoptosis. These results could explain the beneficial outcomes observed with agmatine in models of injury and disease.

Regulatory mechanisms underlying agmatine homeostasis in humans

Regulation of agmatine homeostasis has so far only been poorly defined. In the present study, three mechanisms regulating human agmatine homeostasis were investigated. 1) Enzymatic regulation: expression of arginine decarboxylase, diamine oxidase, and ornithine decarboxylase in human colon neoplastic tissue was, at the mRNA level, about 75% and 50% lower and 150% higher, respectively, than in the adjacent normal tissue; expression of agmatinase was unchanged. 2) Bacteria-derived agmatine: ten representative bacteria strains of the human intestinal microbiota considerably differed in agmatine production and its efflux into their surrounding fluid, suggesting that the composition of the intestinal microbiota influences the agmatine availability in the gut lumen for absorption. 3) Regulation of blood plasma agmatine concentration by the human liver: at low concentrations in portal venous blood plasma, agmatine either slightly increased or further decreased in blood plasma through liver passage. Above a threshold of 14 ng/ml agmatine in the portal venous blood plasma, substantial hepatic agmatine removal from blood occurred. Taken together, a perturbation of agmatine homeostasis has been proven to be involved in the regulation of malignant cell proliferation. The amount of agmatine available for absorption, which is an important physiological source of agmatine in the human organism, should differ considerably depending on the composition of the bacterial flora in the chyme since the various species of intestinal bacteria largely differ in their ability to form agmatine. Finally, evidence has been presented that the liver plays a crucial physiological role in the maintenance of agmatine homeostasis in the human organism.

Chronic treatment with glucocorticoids alters rat hippocampal and prefrontal cortical morphology in parallel with endogenous agmatine and arginine decarboxylase levels

In the present study, we examined the possible effect of chronic treatment with glucocorticoids on the morphology of the rat brain and levels of endogenous agmatine and arginine decarboxylase (ADC) protein, the enzyme essential for agmatine synthesis. Seven-day treatment with dexamethasone, at a dose (10 and 50 mug/kg/day) associated to stress effects contributed by glucocorticoids, did not result in obvious morphologic changes in the medial prefrontal cortex and hippocampus, as measured by immunocytochemical staining with beta-tubulin III. However, 21-day treatment (50 mug/kg/day) produced noticeable structural changes such as the diminution and disarrangement of dendrites and neurons in these areas. Simultaneous treatment with agmatine (50 mg/kg/day) prevented these morphological changes. Further measurement with HPLC showed that endogenous agmatine levels in the prefrontal cortex and hippocampus were significantly increased after 7-day treatments with dexamethasone in a dose-dependent manner. On the contrary, 21-day treatment with glucocorticoids robustly reduced agmatine levels in these regions. The treatment-caused biphasic alterations of endogenous agmatine levels were also seen in the striatum and hypothalamus. Interestingly, treatment with glucocorticoids resulted in a similar change of ADC protein levels in most brain areas to endogenous agmatine levels: an increase after 7-day treatment versus a reduction after 21-day treatment. These results demonstrated that agmatine has neuroprotective effects against structural alterations caused by glucocorticoids in vivo. The parallel alterations in the endogenous agmatine levels and ADC expression in the brain after treatment with glucocorticoids indicate the possible regulatory effect of these stress hormones on the synthesis and metabolism of agmatine in vivo.

Anti-hypernociceptive properties of agmatine in persistent inflammatory and neuropathic models of pain in mice

The present study examined the anti-hypernociceptive effects of agmatine (AGM) in acute and chronic models of behavioural pain in mice. Agmatine (30 mg/kg, i.p. 30 min early), produced time-dependent inhibition of mechanical hypernociception induced by Complete Freund's Adjuvant (CFA) injected in the mice paw (inhibition of 52+/-7%) after 4 h. Given chronically (twice a day) during 10 days, AGM significantly reversed the mechanical hypernociception caused by CFA (inhibition of 43+/-6% to 67+/-5%). Moreover, AGM also significantly reduced the mechanical hypernociception caused by partial sciatic nerve ligation (PSNL) during 6 h, with inhibition of 81+/-8%. In thermal hypernociception (cold stimuli) caused by PSNL the antinociceptive effect of AGM was prolonged by 4 h with inhibition of 97+/-3% observed 1 h after the treatment. Nevertheless, AGM failed to inhibit the paw oedema caused by CFA and the myeloperoxidase enzyme activity. Of note, AGM (10-100 mg/kg, i.p., 30 min before) also elicited a pronounced inhibition of the biting response induced by TNF-alpha and IL-1beta in mice, with mean ID(50) values of 61.3 mg/kg (47.7-78.6 mg/kg) and 30.4 mg/kg (18.6-49.8 mg/kg) and inhibitions of 75+/-5% and 66+/-6%, respectively. Together, present and previous findings show that AGM given systemically is effective in inhibiting mechanical and thermal hypernociception present in chronic inflammatory processes caused by CFA and also the neuropathic pain caused by PSNL.