Polyamine transport by the polyspecific organic cation transporters OCT1, OCT2, and OCT3

Interaction and Transport of Benzalkonium Chlorides by the Organic Cation and Multidrug and Toxin Extrusion Transporters

Humans are chronically exposed to benzalkonium chlorides (BACs) from environmental sources. The U.S. Food and Drug Administration (FDA) has recently called for additional BAC safety data, as these compounds are cytotoxic and have great potential for biochemical interactions. Biodistribution studies revealed that BACs extensively distribute to many tissues and accumulate at high levels, especially in the kidneys, but the underlying mechanisms are unclear. In this study, we characterized the interactions of BACs of varying alkyl chain length (C8 to C14) with the human organic cation transporters (hOCT1-3) and multidrug and toxin extrusion proteins (hMATE1/2K) with the goal to identify transporters that could be involved in BAC disposition. Using transporter-expressing cell lines, we showed that all BACs are inhibitors of hOCT1-3 and hMATE1/2K (IC50 ranging 0.83-25.8 μM). Further, the short-chain BACs (C8 and C10) were identified as substrates of these transporters. Interestingly, although BAC C8 displayed typical Michaelis-Menten kinetics, C10 demonstrated a more complex substrate-inhibition profile. Transwell studies with transfected Madin-Darby canine kidney cells revealed that intracellular accumulation of basally applied BAC C8 and C10 was substantially higher (8.2- and 3.7-fold, respectively) in hOCT2/hMATE1 double-transfected cells in comparison with vector-transfected cells, supporting a role of these transporters in mediating renal accumulation of these compounds in vivo. Together, our results suggest that BACs interact with hOCT1-3 and hMATE1/2K as both inhibitors and substrates and that these transporters may play important roles in tissue-specific accumulation and potential toxicity of short-chain BACs. Our findings have important implications for understanding human exposure and susceptibility to BACs due to environmental exposure. SIGNIFICANCE STATEMENT: Humans are systemically exposed to benzalkonium chlorides (BACs). These compounds broadly distribute through tissues, and their safety has been questioned by the FDA. Our results demonstrate that hOCT2 and hMATE1 contribute to the renal accumulation of BAC C8 and C10 and that hOCT1 and hOCT3 may be involved in the tissue distribution of these compounds. These findings can improve our understanding of BAC disposition and toxicology in humans, as their accumulation could lead to biochemical interactions and deleterious effects.

The efflux pumps Rv1877 and Rv0191 play differential roles in the protection of Mycobacterium tuberculosis against chemical stress

Background

It was previously shown that GlnA3sc enabled Streptomyces coelicolor to survive in excess polyamines. However, subsequent studies revealed that Rv1878, the corresponding Mycobacterium tuberculosis (M.tb) ortholog, was not essential for the detoxification of spermine (Spm), in M.tb. On the other hand, the multi-drug efflux pump Rv1877 was previously shown to enable export of a wide range of compounds, while Rv0191 was shown to be more specific to chloramphenicol.

Rationale

Therefore, we first wanted to determine if detoxification of Spm by efflux can be achieved by any efflux pump, or if that was dependent upon the function of the pump. Next, since Rv1878 was found not to be essential for the detoxification of Spm, we sought to follow-up on the investigation of the physiological role of Rv1878 along with Rv1877 and Rv0191.

Approach

To evaluate the specificity of efflux pumps in the mycobacterial tolerance to Spm, we generated unmarked ∆rv1877 and ∆rv0191 M.tb mutants and evaluated their susceptibility to Spm. To follow up on the investigation of any other physiological roles they may have, we characterized them along with the ∆rv1878 M.tb mutant.

Results

The ∆rv1877 mutant was sensitive to Spm stress, while the ∆rv0191 mutant was not. On the other hand, the ∆rv1878 mutant grew better than the wild-type during iron starvation yet was sensitive to cell wall stress. The proteins Rv1877 and Rv1878 seemed to play physiological roles during hypoxia and acidic stress. Lastly, the ∆rv0191 mutant was the only mutant that was sensitive to oxidative stress.

Conclusion

The multidrug MFS-type efflux pump Rv1877 is required for Spm detoxification, as opposed to Rv0191 which seems to play a more specific role. Moreover, Rv1878 seems to play a role in the regulation of iron homeostasis and the reconstitution of the cell wall of M.tb. On the other hand, the sensitivity of the ∆rv0191 mutant to oxidative stress, suggests that Rv0191 may be responsible for the transport of low molecular weight thiols.

Inhibition of nicotinic acetylcholine receptors by oligoarginine peptides and polyamine-related compounds

Oligoarginine peptides, known mostly for their cell-penetrating properties, are also inhibitors of the nicotinic acetylcholine receptors (nAChRs). Since octa-arginine (R8) inhibits α9α10 nAChR and suppresses neuropathic pain, we checked if other polycationic compounds containing amino and/or guanidino groups could be effective and tested the activity of the disulfide-fixed "cyclo"R8, a series of biogenic polyamines (putrescine, spermidine, and spermine), C-methylated spermine analogs, agmatine and its analogs, as well as acylpolyamine argiotoxin-636 from spider venom. Their inhibitory potency on muscle-type, α7 and α9α10 nAChRs was determined using radioligand analysis, electrophysiology, and calcium imaging. "Cyclo"R8 showed similar activity to that of R8 against α9α10 nAChR (IC50 ≈ 60 nM). Biogenic polyamines as well as agmatine and its analogs displayed low activity on muscle-type Torpedo californica, as well as α7 and α9α10 nAChRs, which increased with chain length, the most active being spermine and its C-methylated derivatives having IC50 of about 30 μM against muscle-type T. californica nAChR. Argiotoxin-636, which contains a polyamine backbone and terminal guanidino group, also weakly inhibited T. californica nAChR (IC50 ≈ 15 μM), but it revealed high potency against rat α9α10 nAChR (IC50 ≈ 200 nM). We conclude that oligoarginines and similar polycationic compounds effectively inhibiting α9α10 nAChR may serve as a basis for the development of analgesics to reduce neuropathic pain.

The Molecular Role of Polyamines in Age-Related Diseases: An Update

Polyamines (Pas) are short molecules that exhibit two or three amine groups that are positively charged at a physiological pH. These small molecules are present in high concentrations in a wide variety of organisms and tissues, suggesting that they play an important role in cellular physiology. Polyamines include spermine, spermidine, and putrescine, which play important roles in age-related diseases that have not been completely elucidated. Aging is a natural process, defined as the time-related deterioration of the physiological functions; it is considered a risk factor for degenerative diseases such as cardiovascular, neurodegenerative, and musculoskeletal diseases; arthritis; and even cancer. In this review, we provide a new perspective on the participation of Pas in the cellular and molecular processes related to age-related diseases, focusing our attention on important degenerative diseases such as Alzheimerߣs disease, Parkinsonߣs disease, osteoarthritis, sarcopenia, and osteoporosis. This new perspective leads us to propose that Pas function as novel biomarkers for age-related diseases, with the main purpose of achieving new molecular alternatives for healthier aging.

Identification of Novel Intronic SNPs in Transporter Genes Associated with Metformin Side Effects

Metformin is a widely used and effective medication in type 2 diabetes (T2DM) as well as in polycystic ovary syndrome (PCOS). Single nucleotide polymorphisms (SNPs) contribute to the occurrence of metformin side effects. The aim of the present study was to identify intronic genetic variants modifying the occurrence of metformin side effects and to replicate them in individuals with T2DM and in women with PCOS. We performed Next Generation Sequencing (Illumina Next Seq) of 115 SNPs in a discovery cohort of 120 metformin users and conducted a systematic literature review. Selected SNPs were analysed in two independent cohorts of individuals with either T2DM or PCOS, using 5'-3'exonucleaseassay. A total of 14 SNPs in the organic cation transporters (OCTs) showed associations with side effects in an unadjusted binary logistic regression model, with eight SNPs remaining significantly associated after appropriate adjustment in the discovery cohort. Five SNPs were confirmed in a combined analysis of both replication cohorts but showed different association patterns in subgroup analyses. In an unweighted polygenic risk score (PRS), the risk for metformin side effects increased with the number of risk alleles. Intronic SNPs in the OCT cluster contribute to the development of metformin side effects in individuals with T2DM and in women with PCOS and are therefore of interest for personalized therapy options.

The Polyamine Spermine Potentiates the Propagation of Negatively Charged Molecules through the Astrocytic Syncytium

The interest in astrocytes, the silent brain cells that accumulate polyamines (PAs), is growing. PAs exert anti-inflammatory, antioxidant, antidepressant, neuroprotective, and other beneficial effects, including increasing longevity in vivo. Unlike neurons, astrocytes are extensively coupled to others via connexin (Cx) gap junctions (GJs). Although there are striking modulatory effects of PAs on neuronal receptors and channels, PA regulation of the astrocytic GJs is not well understood. We studied GJ-propagation using molecules of different (i) electrical charge, (ii) structure, and (iii) molecular weight. Loading single astrocytes with patch pipettes containing membrane-impermeable dyes, we observed that (i) even small molecules do not easily permeate astrocytic GJs, (ii) the ratio of the charge to weight of these molecules is the key determinant of GJ permeation, (iii) the PA spermine (SPM) induced the propagation of negatively charged molecules via GJs, (iv) while no effects were observed on propagation of macromolecules with net-zero charge. The GJ uncoupler carbenoxolone (CBX) blocked such propagation. Taken together, these findings indicate that SPM is essential for astrocytic GJ communication and selectively facilitates intracellular propagation via GJs for negatively charged molecules through glial syncytium.

P5B-ATPases in the mammalian polyamine transport system and their role in disease

Polyamines (PAs) are physiologically relevant molecules that are ubiquitous in all organisms. The vitality of PAs to the healthy functioning of a cell is due to their polycationic nature causing them to interact with a vast plethora of cellular players and partake in numerous cellular pathways. Naturally, the homeostasis of such essential molecules is tightly regulated in a strictly controlled interplay between intracellular synthesis and degradation, uptake from and secretion to the extracellular compartment, as well as intracellular trafficking. Not surprisingly, dysregulated PA homeostasis and signaling are implicated in multiple disorders, ranging from cancer to neurodegeneration; leading many to propose rectifying the PA balance as a potential therapeutic strategy. Despite being well characterized in bacteria, fungi and plants, the molecular identity and properties of the PA transporters in animals are poorly understood. This review brings together the current knowledge of the cellular function of the mammalian PA transport system (PTS). We will focus on the role of P5B-ATPases ATP13A2-5 which are PA transporters in the endosomal system that have emerged as key players in cellular PA uptake and organelle homeostasis. We will discuss recent breakthroughs on their biochemical and structural properties as well as their implications for disease and therapy.

Multigenerational Exposure to Uranium Changes Sperm Metabolome in Rats

Male infertility is a major public health issue that can be induced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. Regarding the human population exposed to uranium, it is necessary to explore these effects on male reproduction in multigenerational studies. The sensitivity of mass spectrometry (MS)-based methods has already proved to be extremely useful in metabolite identification in rats exposed to low doses of uranium, but also in human sperm. We applied this method to rat sperm over three generations (F0, F1 and F2) with multigenerational uranium exposure. Our results show a significant content of uranium in generation F0, and a reduction in the pregnancy rate only in generation F1. Based on principal component analysis (PCA), we observed discriminant profiles between generations. The partial least squares discriminant analysis (PLS-DA) of the 48 annotated variables confirmed that parental exposure of generation F0 (during both the preconceptional and prenatal periods) can have metabolic effects on spermatozoa for the next two generations. Metabolomics applied to epididymal spermatozoa is a novel approach to detecting the multigenerational effects of uranium in an experimental model, but could be also recommended to identify potential biomarkers evaluating the impact of uranium on sperm in exposed infertile men.

Interrogation of T Cell-Enriched Tumors Reveals Prognostic and Immunotherapeutic Implications of Polyamine Metabolism

Metabolic features of the tumor microenvironment (TME) antagonize anti-tumor immunity. We hypothesized that T cell infiltrated tumors with a known antigen should exhibit superior clinical outcomes, though some fare worse given unfavorable metabolic features leveraging T cell-infiltrated (Thi), human papillomavirus-related (HPV+) head and neck squamous cell carcinomas (HNSC) to test this hypothesis. Expression of 2,520 metabolic genes were analyzed among Thi HPV+ HNSCs stratified by high-risk molecular subtype. RNAseq data from The Cancer Genome Atlas (TCGA; 10 cancer types), single cell RNAseq data, and an immunotherapy-treated melanoma cohort were used to test the association between metabolic gene expression and clinical outcomes and contribution of tumor versus stromal cells to metabolic gene expression. Polyamine (PA) metabolism genes were overexpressed in high-risk, Thi HPV+ HNSCs. Genes involved in PA biosynthesis and transport were associated with T cell infiltration, recurrent or persistent cancer, overall survival status, primary site, molecular subtype, and MYC genomic alterations. PA biogenesis gene sets were associated with tumor intrinsic features while myeloid cells in HPV+ HNSCs were enriched in PA catabolism, regulatory, transport, putrescine, and spermidine gene set expression. PA gene set expression also correlated with IFNγ or cytotoxic T cell ssGSEA scores across TCGA tumor types. PA transport ssGSEA scores were associated with poor survival whereas putrescine ssGSEA scores portended better survival for several tumor types. Thi melanomas enriched in PA synthesis or combined gene set expression exhibited worse anti-PD-1 responses. These data address hurdles to anti-tumor immunity warranting further investigation of divergent polyamine metabolism in the TME.

High Affinity Decynium-22 Binding to Brain Membrane Homogenates and Reduced Dorsal Camouflaging after Acute Exposure to it in Zebrafish

Organic cation transporters (OCTs) are expressed in the mammalian brain, kidney, liver, placenta, and intestines, where they facilitate the transport of cations and other substrates between extracellular fluids and cells. Despite increasing reliance on ectothermic vertebrates as alternative toxicology models, properties of their OCT homologs transporting many drugs and toxins remain poorly characterized. Recently, in zebrafish (Danio rerio), two proteins with functional similarities to human OCTs were shown to be highly expressed in the liver, kidney, eye, and brain. This study is the first to characterize in vivo uptake to the brain and the high-affinity brain membrane binding of the mammalian OCT blocker 1-1'-diethyl-2,2'cyanine iodide (decynium-22 or D-22) in zebrafish. Membrane saturation binding of [³H] D-22 in pooled zebrafish whole brain versus mouse hippocampal homogenates revealed a high-affinity binding site with a K_D of 5 ± 2.5 nM and Bmax of 1974 ± 410 fmol/mg protein in the zebrafish brain, and a K_D of 3.3 ± 2.3 and Bmax of 704 ± 182 fmol/mg protein in mouse hippocampus. The binding of [³H] D-22 to brain membrane homogenates was partially blocked by the neurotoxic cation 1-methyl-4-phenylpyridinium (MPP+), a known OCT substrate. To determine if D-22 bath exposures reach the brain, zebrafish were exposed to 25 nM [³H] D-22 for 10 min, and 736 ± 68 ng/g wet weight [³H] D-22 was bound. Acute behavioral effects of D-22 in zebrafish were characterized in two anxiety-relevant tests. In the first cohort of zebrafish, 12.5, 25, or 50 mg/L D-22 had no effect on their height in the dive tank or entries and time spent in white arms of a light/dark plus maze. By contrast, 25 mg/L buspirone increased zebrafish dive tank top-dwelling (p < 0.05), an anticipated anxiolytic effect. However, a second cohort of zebrafish treated with 50 mg/L D-22 made more white arm entries, and females spent more time in white than controls. Based on these findings, it appears that D-22 bath treatments reach the zebrafish brain and have partial anxiolytic properties, reducing anti-predator dorsal camouflaging, without increasing vertical exploration. High-affinity binding of [³H] D-22 in zebrafish brain and mouse brain was similar, with nanomolar affinity, possibly at conserved OCT site(s).

Unique Chemistry, Intake, and Metabolism of Polyamines in the Central Nervous System (CNS) and Its Body

Polyamines (PAs) are small, versatile molecules with two or more nitrogen-containing positively charged groups and provide widespread biological functions. Most of these aspects are well known and covered by quite a number of excellent surveys. Here, the present review includes novel aspects and questions: (1) It summarizes the role of most natural and some important synthetic PAs. (2) It depicts PA uptake from nutrition and bacterial production in the intestinal system following loss of PAs via defecation. (3) It highlights the discrepancy between the high concentrations of PAs in the gut lumen and their low concentration in the blood plasma and cerebrospinal fluid, while concentrations in cellular cytoplasm are much higher. (4) The present review provides a novel and complete scheme for the biosynthesis of Pas, including glycine, glutamate, proline and others as PA precursors, and provides a hypothesis that the agmatine pathway may rescue putrescine production when ODC knockout seems to be lethal (solving the apparent contradiction in the literature). (5) It summarizes novel data on PA transport in brain glial cells explaining why these cells but not neurons preferentially accumulate PAs. (6) Finally, it provides a novel and complete scheme for PA interconversion, including hypusine, putreanine, and GABA (unique gliotransmitter) as end-products. Altogether, this review can serve as an updated contribution to understanding the PA mystery.

Polyamine Immunometabolism: Central Regulators of Inflammation, Cancer and Autoimmunity

Polyamines are ubiquitous, amine-rich molecules with diverse processes in biology. Recent work has highlighted that polyamines exert profound roles on the mammalian immune system, particularly inflammation and cancer. The mechanisms by which they control immunity are still being described. In the context of inflammation and autoimmunity, polyamine levels inversely correlate to autoimmune phenotypes, with lower polyamine levels associated with higher inflammatory responses. Conversely, in the context of cancer, polyamines and polyamine biosynthetic genes positively correlate with the severity of malignancy. Blockade of polyamine metabolism in cancer results in reduced tumor growth, and the effects appear to be mediated by an increase in T-cell infiltration and a pro-inflammatory phenotype of macrophages. These studies suggest that polyamine depletion leads to inflammation and that polyamine enrichment potentiates myeloid cell immune suppression. Indeed, combinatorial treatment with polyamine blockade and immunotherapy has shown efficacy in pre-clinical models of cancer. Considering the efficacy of immunotherapies is linked to autoimmune sequelae in humans, termed immune-adverse related events (iAREs), this suggests that polyamine levels may govern the inflammatory response to immunotherapies. This review proposes that polyamine metabolism acts to balance autoimmune inflammation and anti-tumor immunity and that polyamine levels can be used to monitor immune responses and responsiveness to immunotherapy.

Polyamines protect boar sperm from oxidative stress in vitro

Sperm are susceptible to excessive reactive oxygen species (ROS). Spermine and spermidine are secreted in large amounts by the prostate and potent natural free radical scavengers and protect cells against redox disorder. Thus, we used boar sperm as a model to study the polyamines uptake and elucidate whether polyamines protected sperm from ROS stress. Seven mature and fertile Duroc boars (aged 15 to 30 mo) were used in this study. In experiment 1, spermine and spermidine (3.6 ± 0.3 and 3.3 ± 0.2 mmol/L, respectively) were abundant in seminal plasma, and the content of polyamine decreased (P < 0.05) after preservation at 17 °C for 7 d or incubation at 37 °C for 6 h. In experiment 2, using labeling of spermine or spermidine by conjugation with fluorescein isothiocyanate and ultra-high-performance liquid chromatography, we found that the accumulation of spermine or spermidine in sperm was inhibited by quinidine and dl-tetrahydropalmatine (THP, organic cation transporters [OCT] inhibitors, P < 0.05), but not mildronate and l-carnitine (organic cation/carnitine transporter [OCTN] inhibitors, P > 0.05). In experiment 3, the addition of spermine or spermidine (0.5 mmol/L) in the extender resulted in higher motility, plasma membrane and acrosome integrity, and lower ROS level after preservation in vitro at 17 °C for 7 d (P < 0.05). In experiment 4, in the condition of oxidative stress (treatment with H2O2 at 37 °C for 2 h), the addition of spermine (1 mmol/L) or spermidine (0.5 mmol/L) in extender increased activities of glutathione peroxidase, glutathione reductase, and glutathione S-transferase; reduced glutathione and oxidized glutathione ratio (P < 0.05); and alleviate oxidative stress-induced lipid peroxidation, DNA damage, mitochondrial membrane potential (ΔΨm) decline, adenosine triphosphate depletion, and intracellular calcium concentration ([Ca2+]i) overload (P < 0.05), thereby improving boar sperm motility, the integrity of plasma membrane and acrosome (P < 0.05) in vitro. These data suggest that spermine and spermidine alleviate oxidative stress via the antioxidant capacity, thereby improving the efficacy of boar semen preservation.

MPP+-Induced Changes in Cellular Impedance as a Measure for Organic Cation Transporter (SLC22A1-3) Activity and Inhibition

The organic cation transporters OCT1-3 (SLC22A1-3) facilitate the transport of cationic endo- and xenobiotics and are important mediators of drug distribution and elimination. Their polyspecific nature makes OCTs highly susceptible to drug-drug interactions (DDIs). Currently, screening of OCT inhibitors depends on uptake assays that require labeled substrates to detect transport activity. However, these uptake assays have several limitations. Hence, there is a need to develop novel assays to study OCT activity in a physiological relevant environment without the need to label the substrate. Here, a label-free impedance-based transport assay is established that detects OCT-mediated transport activity and inhibition utilizing the neurotoxin MPP⁺. Uptake of MPP⁺ by OCTs induced concentration-dependent changes in cellular impedance that were inhibited by decynium-22, corticosterone, and Tyrosine Kinase inhibitors. OCT-mediated MPP⁺ transport activity and inhibition were quantified on both OCT1-3 overexpressing cells and HeLa cells endogenously expressing OCT3. Moreover, the method presented here is a valuable tool to identify novel inhibitors and potential DDI partners for MPP⁺ transporting solute carrier proteins (SLCs) in general.

Polyamines and polyamine-metabolizing enzymes in schizophrenia: Current knowledge and concepts of therapy

Polyamines play preeminent roles in a variety of cellular functions in the central nervous system and other organs. A large body of evidence suggests that the polyamine pathway is prominently involved in the etiology and pathology of schizophrenia. Alterations in the expression and activity of polyamine metabolizing enzymes, as well as changes in the levels of the individual polyamines, their precursors and derivatives, have been measured in schizophrenia and animal models of the disease. Additionally, neuroleptic treatment has been shown to influence polyamine concentrations in brain and blood of individuals with schizophrenia. Thus, the polyamine system may appear to be a promising target for neuropharmacological treatment of schizophrenia. However, for a number of practical reasons there is currently only limited hope for a polyamine-based schizophrenia therapy.

Acute hypoxia elevates arginase 2 and induces polyamine stress response in zebrafish via evolutionarily conserved mechanism

Living organisms repeatedly encounter stressful events and apply various strategies to survive. Polyamines are omnipresent bioactive molecules with multiple functions. Their transient synthesis, inducible by numerous stressful stimuli, is termed the polyamine stress response. Animals developed evolutionarily conserved strategies to cope with stresses. The urea cycle is an ancient attribute that deals with ammonia excess in terrestrial species. Remarkably, most fish retain the urea cycle genes fully expressed during the early stages of development and silenced in adult animals. Environmental challenges instigate urea synthesis in fish despite substantial energetic costs, which poses the question of the urea cycle's evolutionary significance. Arginase plays a critical role in oxidative stress-dependent reactions being the final urea cycle enzyme. Its unique subcellular localization, high inducibility, and several regulation levels provide a supreme ability to control the polyamine synthesis rate. Notably, oxidative stress instigates the arginase-1 activity in mammals. Arginase is also dysregulated in aging organisms' brain and muscle tissues, indicating its role in the pathogenesis of age-associated diseases. We designed a study to investigate the levels of the urea cycle and polyamine synthesis-related enzymes in a fish model of acute hypoxia. We evidence synchronized elevation of arginase-2 and ornithine decarboxylase following oxidative stress in adult fish and aging animals signifying the specific function of arginase-2 in fish. Moreover, we demonstrate oxidative stress-associated polyamine synthesis' induction and urea cycle' arrest in adult fish. The subcellular arginase localization found in the fish seems to correspond to its possible evolutionary roles.

Interaction Profiles of Central Nervous System Active Drugs at Human Organic Cation Transporters 1-3 and Human Plasma Membrane Monoamine Transporter

Many psychoactive compounds have been shown to primarily interact with high-affinity and low-capacity solute carrier 6 (SLC6) monoamine transporters for norepinephrine (NET; norepinephrine transporter), dopamine (DAT; dopamine transporter) and serotonin (SERT; serotonin transporter). Previous studies indicate an overlap between the inhibitory capacities of substances at SLC6 and SLC22 human organic cation transporters (SLC22A1-3; hOCT1-3) and the human plasma membrane monoamine transporter (SLC29A4; hPMAT), which can be classified as high-capacity, low-affinity monoamine transporters. However, interactions between central nervous system active substances, the OCTs, and the functionally-related PMAT have largely been understudied. Herein, we report data from 17 psychoactive substances interacting with the SLC6 monoamine transporters, concerning their potential to interact with the human OCT isoforms and hPMAT by utilizing radiotracer-based in vitro uptake inhibition assays at stably expressing human embryonic kidney 293 cells (HEK293) cells. Many compounds inhibit substrate uptake by hOCT1 and hOCT2 in the low micromolar range, whereas only a few substances interact with hOCT3 and hPMAT. Interestingly, methylphenidate and ketamine selectively interact with hOCT1 or hOCT2, respectively. Additionally, 3,4-methylenedioxymethamphetamine (MDMA) is a potent inhibitor of hOCT1 and 2 and hPMAT. Enantiospecific differences of R- and S-α-pyrrolidinovalerophenone (R- and S-α-PVP) and R- and S-citalopram and the effects of aromatic substituents are explored. Our results highlight the significance of investigating drug interactions with hOCTs and hPMAT, due to their role in regulating monoamine concentrations and xenobiotic clearance.

Properties of Transport Mediated by the Human Organic Cation Transporter 2 Studied in a Polarized Three-Dimensional Epithelial Cell Culture Model

The renal secretory clearance for organic cations (neurotransmitters, metabolism products and drugs) is mediated by transporters specifically expressed in the basolateral and apical plasma membrane domains of proximal tubule cells. Here, human organic cation transporter 2 (hOCT2) is the main transporter for organic cations in the basolateral membrane domain. In this study, we stably expressed hOCT2 in Madin-Darby Canine Kidney (MDCK) cells and cultivated these cells in the presence of an extracellular matrix to obtain three-dimensional (3D) structures (cysts). The transport properties of hOCT2 expressed in MDCK cysts were compared with those measured using human embryonic kidney cells (HEK293) stably transfected with hOCT2 (hOCT2-HEK cells). In the MDCK cysts, hOCT2 was expressed in the basolateral membrane domain and showed a significant uptake of the fluorescent organic cation 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP⁺) with an affinity (K_m) of 3.6 ± 1.2 µM, similar to what was measured in the hOCT2-HEK cells (K_m = 3.1 ± 0.2 µM). ASP⁺ uptake was inhibited by tetraethylammonium (TEA⁺), tetrapentylammonium (TPA⁺), metformin and baricitinib both in the hOCT2-HEK cells and the hOCT2- MDCK cysts, even though the apparent affinities of TEA⁺ and baricitinib were dependent on the expression system. Then, hOCT2 was subjected to the same rapid regulation by inhibition of p56^lck tyrosine kinase or calmodulin in the hOCT2-HEK cells and hOCT2- MDCK cysts. However, inhibition of casein kinase II regulated only activity of hOCT2 expressed in MDCK cysts and not in HEK cells. Taken together, these results suggest that the 3D cell culture model is a suitable tool for the functional analysis of hOCT2 transport properties, depending on cell polarization.

Investigating how amine structure influences drug-amine ion-pair formation and uptake via the polyamine transporter in A549 lung cells

Transiently associating amines with therapeutic agents through the formation of ion-pairs has been established both in vitro and in vivo as an effective means to systemically direct drug delivery to the lung via the polyamine transport system (PTS). However, there remains a need to better understand the structural traits required for effective PTS uptake of drug ion-pairs. This study aimed to use a structurally related series of amine counterions to investigate how they influenced the stability of theophylline ion-pairs and their active uptake in A549 cells. Using ethylamine (mono-amine), ethylenediamine (di-amine), spermidine (tri-amine) and spermine (tetra-amine) as counterions the ion-pair affinity was shown to increase as the number of protonated amine groups in the counterion structure increased. The mono and diamines generated a single hydrogen bond and the weakest ion-pair affinities (pK_FTIR: 1.32 ± 0.04 and 1.43 ± 0.02) whereas the polyamines produced two hydrogen bonds and thus the strongest ion-pair affinities (pK_FTIR: 1.93 ± 0.05 and 1.96 ± 0.04). In A549 cells depleted of endogenous polyamines using α-difluoromethylornithine (DFMO), the spermine-theophylline uptake was significantly increased (p < 0.05) compared to non-amine depleted cells and this evidenced the active PTS sequestering of the ion-pair. The mono-amine and di-amine failed to enhance theophylline uptake in these A549 cells, but the tri-amine and tetra-amine both almost doubled the theophylline uptake into the cells when compared to the uptake of free drug. As the data indicated that polyamines with at least 3 amines were required to form ion-pairs that could enhance A549 cell uptake, it suggested that at least two amines were required to physically stabilise the ion-pair and one to interact with the PTS.

Uptake of Biotinylated Spermine in Astrocytes: Effect of Cx43 siRNA, HIV-Tat Protein and Polyamine Transport Inhibitor on Polyamine Uptake

Polyamines (PAs) are polycationic biomolecules containing multiple amino groups. Patients with HIV-associated neurocognitive disorder (HAND) have high concentrations of the polyamine N-acetylated spermine in their brain and cerebral spinal fluid (CSF) and have increased PA release from astrocytes. These effects are due to the exposure to HIV-Tat. In healthy adult brain, PAs are accumulated but not synthesized in astrocytes, suggesting that PAs must enter astrocytes to be N-acetylated and released. Therefore, we tested if Cx43 hemichannels (Cx43-HCs) are pathways for PA flux in control and HIV-Tat-treated astrocytes. We used biotinylated spermine (b-SPM) to examine polyamine uptake. We found that control astrocytes and those treated with siRNA-Cx43 took up b-SPM, similarly suggesting that PA uptake is via a transporter/channel other than Cx43-HCs. Surprisingly, astrocytes pretreated with both HIV-Tat and siRNA-Cx43 showed increased accumulation of b-SPM. Using a novel polyamine transport inhibitor (PTI), trimer 44NMe, we blocked b-SPM uptake, showing that PA uptake is via a PTI-sensitive transport mechanism such as organic cation transporter. Our data suggest that Cx43 HCs are not a major pathway for b-SPM uptake in the condition of normal extracellular calcium concentration but may be involved in the release of PAs to the extracellular space during viral infection.

Polyamines: Functions, Metabolism, and Role in Human Disease Management

Putrescine, spermine, and spermidine are the important polyamines (PAs), found in all living organisms. PAs are formed by the decarboxylation of amino acids, and they facilitate cell growth and development via different cellular responses. PAs are the integrated part of the cellular and genetic metabolism and help in transcription, translation, signaling, and post-translational modifications. At the cellular level, PA concentration may influence the condition of various diseases in the body. For instance, a high PA level is detrimental to patients suffering from aging, cognitive impairment, and cancer. The levels of PAs decline with age in humans, which is associated with different health disorders. On the other hand, PAs reduce the risk of many cardiovascular diseases and increase longevity, when taken in an optimum quantity. Therefore, a controlled diet is an easy way to maintain the level of PAs in the body. Based on the nutritional intake of PAs, healthy cell functioning can be maintained. Moreover, several diseases can also be controlled to a higher extend via maintaining the metabolism of PAs. The present review discusses the types, important functions, and metabolism of PAs in humans. It also highlights the nutritional role of PAs in the prevention of various diseases.

α-PPP and its derivatives are selective partial releasers at the human norepinephrine transporter: A pharmacological characterization of interactions between pyrrolidinopropiophenones and high and low affinity monoamine transporters

While classical cathinones, such as methcathinone, have been shown to be monoamine releasing agents at human monoamine transporters, the subgroup of α-pyrrolidinophenones has thus far solely been characterized as monoamine transporter reuptake inhibitors. Herein, we report data from previously undescribed α-pyrrolidinopropiophenone (α-PPP) derivatives and compare them with the pharmacologically well-researched α-PVP (α-pyrrolidinovalerophenone). Radiotracer-based in vitro uptake inhibition assays in HEK293 cells show that the investigated α-PPP derivatives inhibit the human high-affinity transporters of dopamine (hDAT) and norepinephrine (hNET) in the low micromolar range, with α-PVP being ten times more potent. Similar to α-PVP, no relevant pharmacological activity was found at the human serotonin transporter (hSERT). Unexpectedly, radiotracer-based in vitro release assays reveal α-PPP, MDPPP and 3Br-PPP, but not α-PVP, to be partial releasing agents at hNET (EC50 values in the low micromolar range). Furthermore, uptake inhibition assays at low-affinity monoamine transporters, i.e., the human organic cation transporters (hOCT) 1-3 and human plasma membrane monoamine transporter (hPMAT), bring to light that all compounds inhibit hOCT1 and 2 (IC50 values in the low micromolar range) while less potently interacting with hPMAT and hOCT3. In conclusion, this study describes (i) three new hybrid compounds that efficaciously block hDAT while being partial releasers at hNET, and (ii) highlights the interactions of α-PPP-derivatives with low-affinity monoamine transporters, giving impetus to further studies investigating the interaction of drugs of abuse with OCT1-3 and PMAT.

The Interaction of Organic Cation Transporters 1-3 and PMAT with Psychoactive Substances

Organic cation transporters 1-3 (OCT1-3, SLC22A1-3) and the plasma membrane monoamine transporter (PMAT, SLC29A4) play a major role in maintaining monoaminergic equilibrium in the central nervous system. With many psychoactive substances interacting with OCT1-3 and PMAT, a growing literature focuses on characterizing their properties via in vitro and in vivo studies. In vitro studies mainly aim at characterizing compounds as inhibitors or substrates of murine, rat, and human isoforms. The preponderance of studies has put emphasis on phenylalkylamine derivatives, but ketamine and opioids have also been investigated. Studies employing in vivo (knockout) models mostly concentrate on the interaction of psychoactive substances and OCT3, with an emphasis on stress and addiction, pharmacokinetics, and sensitization to psychoactive drugs. The results highlight the importance of OCT3 in the mechanism of action of psychoactive compounds. Concerning in vivo studies, a veritable research gap concerning OCT1, 2, and PMAT exists. This review provides an overview and summary of research conducted in this field of research.

Substrates and Inhibitors of Organic Cation Transporters (OCTs) and Plasma Membrane Monoamine Transporter (PMAT) and Therapeutic Implications

The gene products of the SLC22A gene family (hOCT1, hOCT2, and hOCT3) and of the SLC29A4 gene (hPMAT or hENT4) are all polyspecific organic cation transporters. Human OCTs (including hPMAT) are expressed in peripheral tissues such as small intestine, liver, and kidney involved in the pharmacokinetics of drugs. In the human brain, all four transporters are expressed at the blood-brain barrier (BBB), hOCT2 is additionally expressed in neurons, and hOCT3 and hPMAT in glia. More than 40% of the presently used drugs are organic cations. This chapter lists and discusses all known drugs acting as substrates or inhibitors of these four organic cation transporters, independently of whether the transporter is expressed in the central nervous system (CNS) or in peripheral tissues. Of interest is their involvement in drug absorption, distribution, and excretion as well as potential OCT-associated drug-drug interactions (DDIs), with a focus on drugs that act in the CNS.

Insight into the Anticancer Activity of Copper(II) 5-Methylenetrimethylammonium-Thiosemicarbazonates and Their Interaction with Organic Cation Transporters

A series of four water-soluble salicylaldehyde thiosemicarbazones with a positively charged trimethylammonium moiety ([H2LR]Cl, R = H, Me, Et, Ph) and four copper(II) complexes [Cu(HLR)Cl]Cl (1-4) were synthesised with the aim to study (i) their antiproliferative activity in cancer cells and, (ii) for the first time for thiosemicarbazones, the interaction with membrane transport proteins, specifically organic cation transporters OCT1-3. The compounds were comprehensively characterised by analytical, spectroscopic and X-ray diffraction methods. The highest cytotoxic effect was observed in the neuroblastoma cell line SH-5YSY after 24 h exposure and follows the rank order: 3 > 2 > 4 > cisplatin > 1 >>[H2LR]Cl. The copper(II) complexes showed marked interaction with OCT1-3, comparable to that of well-known OCT inhibitors (decynium 22, prazosin and corticosterone) in the cell-based radiotracer uptake assays. The work paves the way for the development of more potent and selective anticancer drugs and/or OCT inhibitors.

The involvement of polyamine uptake and synthesis pathways in the proliferation of neonatal astrocytes

Polyamines (PAs), such as spermidine (SPD) and spermine (SPM), are essential to promote cell growth, survival, proliferation, and longevity. In the adult central nervous system (CNS), SPD and SPM are accumulated predominantly in healthy adult glial cells where PA synthesis is not present. To date, the accumulation and biosynthesis of PAs in developing astrocytes are not well understood. The purpose of the present study was to determine the contribution of uptake and/or synthesis of PAs using proliferation of neonatal astrocytes as an endpoint. We inhibited synthesis of PAs using α-difluoromethylornithine (DFMO; an inhibitor of the PA biosynthetic enzyme ornithine decarboxylase (ODC)) and inhibited uptake of PAs using trimer44NMe (PTI; a novel polyamine transport inhibitor). DFMO, but not PTI alone, blocked proliferation, suggesting that PA biosynthesis was present. Furthermore, exogenous administration of SPD rescued cell proliferation when PA synthesis was blocked by DFMO. When both synthesis and uptake of PAs were inhibited (DFMO + PTI), exogenous SPD no longer supported proliferation. These data indicate that neonatal astrocytes synthesize sufficient quantities of PAs de novo to support cell proliferation, but are also able to import exogenous PAs. This suggests that the PA uptake mechanism is present in both neonates as well as in adults and can support cell proliferation in neonatal astrocytes when ODC is blocked.

Potassium channels and their role in glioma: A mini review

K⁺ channels regulate a multitude of biological processes and play important roles in a variety of diseases by controlling potassium flow across cell membranes. They are widely expressed in the central and peripheral nervous system. As a malignant tumor derived from nerve epithelium, glioma has the characteristics of high incidence, high recurrence rate, high mortality rate, and low cure rate. Since glioma cells show invasive growth, current surgical methods cannot completely remove tumors. Adjuvant chemotherapy is still needed after surgery. Because the blood-brain barrier and other factors lead to a lower effective concentration of chemotherapeutic drugs in the tumor, the recurrence rate of residual lesions is extremely high. Therefore, new therapeutic methods are needed. Numerous studies have shown that different K⁺ channel subtypes are differentially expressed in glioma cells and are involved in the regulation of the cell cycle of glioma cells to arrest them at different stages of the cell cycle. Increasing evidence suggests that K⁺ channels express in glioma cells and regulate glioma cell behaviors such as cell cycle, proliferation and apoptosis. This review article aims to summarize the current knowledge on the function of K⁺ channels in glioma, suggests K⁺ channels participating in the development of glioma.

Intronic Variants in OCT1 are Associated with All-Cause and Cardiovascular Mortality in Metformin Users with Type 2 Diabetes

PURPOSE

Organic cation transporters (Octs) use cations like endogenous compounds, toxins, and drugs, such as metformin, as substrates. Therefore, these proteins determine the pharmacokinetics and -dynamics of metformin and thus its efficacy. Of note, metformin is today the most commonly used pharmaceutical in the treatment of type 2 diabetes (T2DM) with nevertheless a great variability in clinical response, which attributes to genetic variances. The aim of this study was to determine the influence of intronic OCT1 SNPs on prevalence of all-cause and cardiovascular death.

PATIENTS AND METHODS

Genotypes of 27 intronic SNPs in OCT1 were investigated in the LURIC study, a prospective cohort of 3316 participants scheduled for coronary angiography. We investigated whether these variants were associated with all-cause and cardiovascular death in 73 individuals with T2DM under metformin therapy, in individuals without diabetes, individuals with T2DM and individuals with T2DM without metformin therapy.

RESULTS

In a multivariate Cox regression analysis adjusted for classical cardiovascular risk factors, 4 intronic OCT1 SNPs were significantly associated with all-cause and cardiovascular mortality in individuals with T2DM on metformin therapy.

CONCLUSION

According to their OCT1 genotype, some individuals with T2DM on metformin therapy might be prone to an increased risk of cardiovascular death.

Polyamine stimulation perturbs intracellular Ca2+ homeostasis and decreases viability of breast cancer BT474 cells

Intracellular polyamines such as spermine and spermidine are essential to cell growth in normal and especially in cancer cells. However, whether extracellular polyamines affect cancer cell survival is unknown. We therefore examined the actions of extracellular polyamines on breast cancer BT474 cells. Our data showed that spermine, spermidine, and putrescine decreased cell viability by apoptosis. These polyamines also elicited Ca2+ signals, but the latter were unlikely triggered via Ca2+-sensing receptor (CaSR) as BT474 cells have been demonstrated previously to lack CaSR expression. Spermine-elicited Ca2+ response composed of both Ca2+ release and Ca2+ influx. Spermine caused a complete discharge of the cyclopiazonic acid (CPA)-sensitive Ca2+ pool and, expectedly, endoplasmic reticulum (ER) stress. The Ca2+ influx pore opened by spermine was Mn2+-impermeable, distinct from the CPA-triggered store-operated Ca2+ channel, which was Mn2+-permeable. Spermine cytotoxic effects were not due to oxidative stress, as spermine did not trigger reactive oxygen species formation. Our results therefore suggest that spermine acted on a putative polyamine receptor in BT474 cells, causing cytotoxicity by Ca2+ overload, Ca2+ store depletion, and ER stress.

Inhibition of polyamine synthesis and uptake reduces tumor progression and prolongs survival in mouse models of neuroblastoma

Amplification of the MYCN oncogene is associated with an aggressive phenotype and poor outcome in childhood neuroblastoma. Polyamines are highly regulated essential cations that are frequently elevated in cancer cells, and the rate-limiting enzyme in polyamine synthesis, ornithine decarboxylase 1 (ODC1), is a direct transcriptional target of MYCN. Treatment of neuroblastoma cells with the ODC1 inhibitor difluoromethylornithine (DFMO), although a promising therapeutic strategy, is only partially effective at impeding neuroblastoma cell growth due to activation of compensatory mechanisms resulting in increased polyamine uptake from the surrounding microenvironment. In this study, we identified solute carrier family 3 member 2 (SLC3A2) as the key transporter involved in polyamine uptake in neuroblastoma. Knockdown of SLC3A2 in neuroblastoma cells reduced the uptake of the radiolabeled polyamine spermidine, and DFMO treatment increased SLC3A2 protein. In addition, MYCN directly increased polyamine synthesis and promoted neuroblastoma cell proliferation by regulating SLC3A2 and other regulatory components of the polyamine pathway. Inhibiting polyamine uptake with the small-molecule drug AMXT 1501, in combination with DFMO, prevented or delayed tumor development in neuroblastoma-prone mice and extended survival in rodent models of established tumors. Our findings suggest that combining AMXT 1501 and DFMO with standard chemotherapy might be an effective strategy for treating neuroblastoma.

Transporters in the Mammary Gland-Contribution to Presence of Nutrients and Drugs into Milk

A large number of nutrients and bioactive ingredients found in milk play an important role in the nourishment of breast-fed infants and dairy consumers. Some of these ingredients include physiologically relevant compounds such as vitamins, peptides, neuroactive compounds and hormones. Conversely, milk may contain substances-drugs, pesticides, carcinogens, environmental pollutants-which have undesirable effects on health. The transfer of these compounds into milk is unavoidably linked to the function of transport proteins. Expression of transporters belonging to the ATP-binding cassette (ABC-) and Solute Carrier (SLC-) superfamilies varies with the lactation stages of the mammary gland. In particular, Organic Anion Transporting Polypeptides 1A2 (OATP1A2) and 2B1 (OATP2B1), Organic Cation Transporter 1 (OCT1), Novel Organic Cation Transporter 1 (OCTN1), Concentrative Nucleoside Transporters 1, 2 and 3 (CNT1, CNT2 and CNT3), Peptide Transporter 2 (PEPT2), Sodium-dependent Vitamin C Transporter 2 (SVCT2), Multidrug Resistance-associated Protein 5 (ABCC5) and Breast Cancer Resistance Protein (ABCG2) are highly induced during lactation. This review will focus on these transporters overexpressed during lactation and their role in the transfer of products into the milk, including both beneficial and harmful compounds. Furthermore, additional factors, such as regulation, polymorphisms or drug-drug interactions will be described.

Synthesis and antiproliferative evaluation of some iron chelators as polyamine transporter targeting agents

A series of kojic acid derivatives based on monoamines, diamines, and triamines have been synthesized in good yield and purity. A spermidine (spd) rescue experiment was applied against MCF-7 cells to evaluate the polyamine transporter selectivity, and in vitro antiproliferative effects were determined against Hela and DU-145 cell lines. Overall, 5b showed the best selectivity for the polyamine transporter and antiproliferative effects. Therefore, the in-silico metabolism profile and ADMET properties of the title compounds were calculated by the PreADMET server. Additionally, physicochemical properties of ligands were predicted by using the Molinspiration online property calculation server.

Dietary and Gut Microbiota Polyamines in Obesity- and Age-Related Diseases

The polyamines putrescine, spermidine, and spermine are widely distributed polycationic compounds essential for cellular functions. Intracellular polyamine pools are tightly regulated by a complex regulatory mechanism involving de novo biosynthesis, catabolism, and transport across the plasma membrane. In mammals, both the production of polyamines and their uptake from the extracellular space are controlled by a set of proteins named antizymes and antizyme inhibitors. Dysregulation of polyamine levels has been implicated in a variety of human pathologies, especially cancer. Additionally, decreases in the intracellular and circulating polyamine levels during aging have been reported. The differences in the polyamine content existing among tissues are mainly due to the endogenous polyamine metabolism. In addition, a part of the tissue polyamines has its origin in the diet or their production by the intestinal microbiome. Emerging evidence has suggested that exogenous polyamines (either orally administrated or synthetized by the gut microbiota) are able to induce longevity in mice, and that spermidine supplementation exerts cardioprotective effects in animal models. Furthermore, the administration of either spermidine or spermine has been shown to be effective for improving glucose homeostasis and insulin sensitivity and reducing adiposity and hepatic fat accumulation in diet-induced obesity mouse models. The exogenous addition of agmatine, a cationic molecule produced through arginine decarboxylation by bacteria and plants, also exerts significant effects on glucose metabolism in obese models, as well as cardioprotective effects. In this review, we will discuss some aspects of polyamine metabolism and transport, how diet can affect circulating and local polyamine levels, and how the modulation of either polyamine intake or polyamine production by gut microbiota can be used for potential therapeutic purposes.

The Biology of Glial Cells and Their Complex Roles in Alzheimer's Disease: New Opportunities in Therapy

Even though Alzheimer's disease (AD) is of significant interest to the scientific community, its pathogenesis is very complicated and not well-understood. A great deal of progress has been made in AD research recently and with the advent of these new insights more therapeutic benefits may be identified that could help patients around the world. Much of the research in AD thus far has been very neuron-oriented; however, recent studies suggest that glial cells, i.e., microglia, astrocytes, oligodendrocytes, and oligodendrocyte progenitor cells (NG2 glia), are linked to the pathogenesis of AD and may offer several potential therapeutic targets against AD. In addition to a number of other functions, glial cells are responsible for maintaining homeostasis (i.e., concentration of ions, neurotransmitters, etc.) within the central nervous system (CNS) and are crucial to the structural integrity of neurons. This review explores the: (i) role of glial cells in AD pathogenesis; (ii) complex functionalities of the components involved; and (iii) potential therapeutic targets that could eventually lead to a better quality of life for AD patients.

Paraquat initially damages cochlear support cells leading to anoikis-like hair cell death

Paraquat (PQ), one of the most widely used herbicides, is extremely dangerous because it generates the highly toxic superoxide radical. When paraquat was applied to cochlear organotypic cultures, it not only damaged the outer hair cells (OHCs) and inner hair cells (IHCs), but also caused dislocation of the hair cell rows. We hypothesized that the dislocation arose from damage to the support cells (SCs) that anchors hair cells within the epithelium. To test this hypothesis, rat postnatal cochlear cultures were treated with PQ. Shortly after PQ treatment, the rows of OHCs separated from one another and migrated radially away from IHCs suggesting loss of cell-cell adhesion that hold the hair cells in proper alignment. Hair cells dislocation was associated with extensive loss of SCs in the organ of Corti, loss of tympanic border cells (TBCs) beneath the basilar membrane, the early appearance of superoxide staining and caspase-8 labeling in SCs below the OHCs and disintegration of E-cadherin and β-catenin in the organ of Corti. Damage to the TBCs and SCs occurred prior to loss of OHC or IHC loss suggesting a form of detachment-induced apoptosis referred to as anoikis.

Genetic Heterogeneity of SLC22 Family of Transporters in Drug Disposition

An important aspect of modern medicine is its orientation to achieve more personalized pharmacological treatments. In this context, transporters involved in drug disposition have gained well-justified attention. Owing to its broad spectrum of substrate specificity, including endogenous compounds and xenobiotics, and its strategical expression in organs accounting for drug disposition, such as intestine, liver and kidney, the SLC22 family of transporters plays an important role in physiology, pharmacology and toxicology. Among these carriers are plasma membrane transporters for organic cations (OCTs) and anions (OATs) with a marked overlap in substrate specificity. These two major clades of SLC22 proteins share a similar membrane topology but differ in their degree of genetic variability. Members of the OCT subfamily are highly polymorphic, whereas OATs have a lower number of genetic variants. Regarding drug disposition, changes in the activity of these variants affect intestinal absorption and target tissue uptake, but more frequently they modify plasma levels due to enhanced or reduced clearance by the liver and secretion by the kidney. The consequences of these changes in transport-associated function markedly affect the effectiveness and toxicity of the treatment in patients carrying the mutation. In solid tumors, changes in the expression of these transporters and the existence of genetic variants substantially determine the response to anticancer drugs. Moreover, chemoresistance usually evolves in response to pharmacological and radiological treatment. Future personalized medicine will require monitoring these changes in a dynamic way to adapt the treatment to the weaknesses shown by each tumor at each stage in each patient.

Stargazin and cornichon-3 relieve polyamine block of AMPA receptors by enhancing blocker permeation

Polyamine block of AMPA-type ionotropic glutamate receptors is attenuated by auxiliary proteins stargazin and cornichon-3. Brown et al. show that relief from block is due to enhanced blocker permeation and present a modified model of permeant channel block to account for their experimental findings.

Most ligand- and voltage-gated ion channels assemble as signaling complexes consisting of pore-forming and auxiliary subunits. In the mammalian brain, AMPA-type ionotropic glutamate receptors (AMPARs) coassemble with several families of auxiliary subunits that regulate channel gating as well as ion channel block and permeation. Previous work has shown that auxiliary proteins stargazin (or γ2) and cornichon-3 (CNIH-3) attenuate the cytoplasmic polyamine channel block of AMPARs, although the underlying mechanism has yet to be established. Here, we show that γ2 and CNIH-3 relieve channel block by enhancing the rate of blocker permeation. Surprisingly, the relative permeability of the polyamine spermine (Spm) through the pore of the AMPAR-γ2 or -CNIH-3 complexes is considerably more than AMPARs expressed alone. Spm permeability is comparable to that of Na⁺ for the GluA2-γ2 complex and four times greater than Na⁺ with GluA2 + CNIH-3. A modified model of permeant channel block fully accounts for both the voltage- and time-dependent nature of Spm block. Estimates of block rate constants reveal that auxiliary subunits do not attenuate block by shifting the location of the block site within the membrane electric field, and they do not affect the blocker’s ability to reach it. Instead, γ2 and CNIH-3 relieve channel block by facilitating the blocker’s exit rates from the open channel. From a physiological perspective, the relief of channel block exerted by γ2 and CNIH-3 ensures that there is unfettered signaling by AMPARs at glutamatergic synapses. Moreover, the pronounced ability of AMPARs to transport polyamines may have an unexpected role in regulating cellular polyamine levels.

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.

Reduction of Immunoreactivity Against the C-Terminal Region of the Intracellular α-Synuclein by Exogenous α-Synuclein Aggregates: Possibility of Conformational Changes

BACKGROUND

The formation of intracellular aggregates containing α-synuclein (α-syn) is a main pathological feature of Parkinson disease. The propagation of α-syn aggregation via cell-to-cell transmission has been implicated in the progression of Parkinson disease.

OBJECTIVE

Our aim is to clarify the molecular mechanisms underlying the formation of intracellular aggregation by extracellular α-syn.

METHODS

We investigated the effects of exogenous α-syn aggregates on intracellular α-syn immunoreactivity in α-syn-overexpressing SH-SY5Y cells using two antibodies to distinct epitopes of α-syn. To obtain α-syn aggregates, α-syn solution was aged with continuous agitation.

RESULTS

Immunoreactivity against the acidic C-terminal domain of the intracellular α-syn was reduced by exposure to agedα-syn, whereas that against the hydrophobic non-amyloid component region was not changed. The reduction in immunoreactivity was not suppressed by protease inhibitors but was mimicked by neutralization of the negative charges on the C-terminal of the intracellular α-syn induced by spermine or extracellular acidification.

CONCLUSIONS

These results suggest that the reduction in immunoreactivity is attributed not to proteolytic cleavage but to a conformational change at the C-terminus of the intracellular α-syn. The conformational change at the C-terminus of the intracellular α-syn might be involved in an initial step of fibril formation by exogenous α-syn aggregates.

Agmatine: multifunctional arginine metabolite and magic bullet in clinical neuroscience?

Agmatine, the decarboxylation product of arginine, was largely neglected as an important player in mammalian metabolism until the mid-1990s, when it was re-discovered as an endogenous ligand of imidazoline and α2-adrenergic receptors. Since then, a wide variety of agmatine-mediated effects have been observed, and consequently agmatine has moved from a wallflower existence into the limelight of clinical neuroscience research. Despite this quantum jump in scientific interest, the understanding of the anabolism and catabolism of this amine is still vague. The purification and biochemical characterization of natural mammalian arginine decarboxylase and agmatinase still are open issues. Nevertheless, the agmatinergic system is currently one of the most promising candidates in order to pharmacologically interfere with some major diseases of the central nervous system, which are summarized in the present review. Particularly with respect to major depression, agmatine, its derivatives, and metabolizing enzymes show great promise for the development of an improved treatment of this common disease.

Polyspecific organic cation transporters and their impact on drug intracellular levels and pharmacodynamics

Most drugs are intended to act on molecular targets residing within a specific tissue or cell type. Therefore, the drug concentration within the target tissue or cells is most relevant to its pharmacological effect. Increasing evidences suggest that drug transporters not only play a significant role in governing systemic drug levels, but are also an important gate keeper for intra-tissue and intracellular drug concentrations. This review focuses on polyspecific organic cation transporters, which include the organic cation transporters 1-3 (OCT1-3), the multidrug and toxin extrusion proteins 1-2 (MATE1-2) and the plasma membrane monoamine transporter (PMAT). Following an overview of the tissue distribution, transport mechanisms, and functional characteristics of these transporters, we highlight the studies demonstrating the ability of locally expressed OCTs to impact intracellular drug concentrations and directly influence their pharmacological and toxicological activities. Specifically, OCT1-mediated metformin access to its site of action in the liver is impacted by genetic polymorphisms and chemical inhibition of OCT1. The impact of renal OCT2 and MATE1/2-K in cisplatin intrarenal accumulation and nephrotoxicity is reviewed. New data demonstrating the role of OCT3 in salivary drug accumulation and secretion is discussed. Whenever possible, the pharmacodynamic response and toxicological effects is presented and discussed in light of intra-tissue and intracellular drug exposure. Current challenges, knowledge gaps, and future research directions are discussed. Understanding the impact of transporters on intra-tissue and intracellular drug concentrations has important implications for rational-based optimization of drug efficacy and safety.

Spermine modulates the expression of two probable polyamine transporter genes and determines growth responses to cadaverine in Arabidopsis

Two genes, LAT1 and OCT1 , are likely to be involved in polyamine transport in Arabidopsis. Endogenous spermine levels modulate their expression and determine the sensitivity to cadaverine. Arabidopsis spermine (Spm) synthase (SPMS) gene-deficient mutant was previously shown to be rather resistant to the diamine cadaverine (Cad). Furthermore, a mutant deficient in polyamine oxidase 4 gene, accumulating about twofold more of Spm than wild type plants, showed increased sensitivity to Cad. It suggests that endogenous Spm content determines growth responses to Cad in Arabidopsis thaliana. Here, we showed that Arabidopsis seedlings pretreated with Spm absorbs more Cad and has shorter root growth, and that the transgenic Arabidopsis plants overexpressing the SPMS gene are hypersensitive to Cad, further supporting the above idea. The transgenic Arabidopsis overexpressing L-Amino acid Transporter 1 (LAT1) absorbed more Cad and showed increased Cad sensitivity, suggesting that LAT1 functions as a Cad importer. Recently, other research group reported that Organic Cation Transporter 1 (OCT1) is a causal gene which determines the Cad sensitivity of various Arabidopsis accessions. Furthermore, their results suggested that OCT1 is involved in Cad efflux. Thus we monitored the expression of OCT1 and LAT1 during the above experiments. Based on the results, we proposed a model in which the level of Spm content modulates the expression of OCT1 and LAT1, and determines Cad sensitivity of Arabidopsis.

The human organic cation transporter OCT1 mediates high affinity uptake of the anticancer drug daunorubicin

Anthracyclines such as daunorubicin are anticancer agents that are transported into cells, and exert cytotoxicity by blocking DNA metabolism. Although there is evidence for active uptake of anthracyclines into cells, the specific transporter involved in this process has not been identified. Using the high-grade serous ovarian cancer cell line TOV2223G, we show that OCT1 mediated the high affinity (K_m ~ 5 μM) uptake of daunorubicin into the cells, and that micromolar amounts of choline completely abolished the drug entry. OCT1 downregulation by shRNA impaired daunorubicin uptake into the TOV2223G cells, and these cells were significantly more resistant to the drug in comparison to the control shRNA. Transfection of HEK293T cells, which accommodated the ectopic expression of OCT1, with a plasmid expressing OCT1-EYFP showed that the transporter was predominantly localized to the plasma membrane. These transfected cells exhibited an increase in the uptake of daunorubicin in comparison to control cells transfected with an empty EYFP vector. Furthermore, a variant of OCT1, OCT1-D474C-EYFP, failed to enhance daunorubicin uptake. This is the first report demonstrating that human OCT1 is involved in the high affinity transport of anthracyclines. We postulate that OCT1 defects may contribute to the resistance of cancer cells treated with anthracyclines.

Intracellular spermine prevents acid-induced uncoupling of Cx43 gap junction channels

Polyamines (PAs), such as spermine and spermidine, modulate the activity of numerous receptors and channels in the central nervous system (CNS) and are stored in glial cells; however, little attention has been paid to their role in the regulation of connexin (Cx)-based gap junction channels. We have previously shown that PAs facilitate diffusion of Lucifer Yellow through astrocytic gap junctions in acute brain slices; therefore, we hypothesized that spermine can regulate Cx43-mediated (as the most abundant Cx in astrocytes) gap junctional communication. We used electrophysiological patch-clamp recording from paired Novikoff cells endogenously expressing Cx43 and HeLaCx43-EGFP transfectants to study pH-dependent modulation of cell–cell coupling in the presence or absence of PAs. Our results showed (i) a higher increase in gap junctional communication at higher concentrations of cytoplasmic spermine, and (ii) that spermine prevented uncoupling of gap junctions at low intracellular pH. Taken together, we conclude that spermine enhances Cx43-mediated gap junctional communication and may preserve neuronal excitability during ischemia and trauma when pH in the brain acidifies. We, therefore, suggest a new role of spermine in the regulation of a Cx43-based network under (patho)physiological conditions.