Uptake of polyamines by human endothelial cells. Characterization and lack of effect of agonists of endothelial function

Upregulation of Polyamine Transport in Human Colorectal Cancer Cells

Polyamines are essential growth factors that have a positive role in cancer cell growth. Their metabolic pathway and the diverse enzymes involved have been studied in depth in multiple organisms and cells. Polyamine transport also contributes to the intracellular polyamine content but this is less well-studied in mammalian cells. As the polyamine transporters could provide a means of selective drug delivery to cancer cells, a greater understanding of polyamine transport and its regulation is needed. In this study, transport of polyamines and polyamine content was measured and the effect of modulating each was determined in human colorectal cancer cells. The results provide evidence that upregulation of polyamine transport depends on polyamine depletion and on the rate of cell growth. Polyamine transport occurred in all colorectal cancer cell lines tested but to varying extents. The cell lines with the lowest basal uptake showed the greatest increase in response to polyamine depletion. Kinetic parameters for putrescine and spermidine suggest the existence of two separate transporters. Transport was shown to be a saturable but non-polarised process that can be regulated both positively and negatively. Using the polyamine transporter to deliver anticancer drugs more selectively is now a reality, and the ability to manipulate the polyamine transport process increases the possibility of using these transporters therapeutically.

Microbial Metabolites Determine Host Health and the Status of Some Diseases

The gastrointestinal (GI) tract is a highly complex organ composed of the intestinal epithelium layer, intestinal microbiota, and local immune system. Intestinal microbiota residing in the GI tract engages in a mutualistic relationship with the host. Different sections of the GI tract contain distinct proportions of the intestinal microbiota, resulting in the presence of unique bacterial products in each GI section. The intestinal microbiota converts ingested nutrients into metabolites that target either the intestinal microbiota population or host cells. Metabolites act as messengers of information between the intestinal microbiota and host cells. The intestinal microbiota composition and resulting metabolites thus impact host development, health, and pathogenesis. Many recent studies have focused on modulation of the gut microbiota and their metabolites to improve host health and prevent or treat diseases. In this review, we focus on the production of microbial metabolites, their biological impact on the intestinal microbiota composition and host cells, and the effect of microbial metabolites that contribute to improvements in inflammatory bowel diseases and metabolic diseases. Understanding the role of microbial metabolites in protection against disease might offer an intriguing approach to regulate disease.

Does polyamine oxidase activity influence the oxidative metabolism of children who suffer of diabetes mellitus?

Diabetes mellitus is a metabolic disease characterized by inadequate secretion of insulin. Polyamine oxidase (PAO), a FAD-containing enzyme is involved in the biodegradation of Sp and Spd, catalyzing the oxidative deamination of Sp and Spd, resulting in production of ammonia (NH(3)), corresponding amino aldehydes and H(2)O(2). Malondialdehyde (MDA) and acrolein (CH2=CHCHO), potentially toxic agents, which induce oxidative stress in mammalian cells, are then spontaneously formed from aminoaldehydes. The main signs of oxidative stress in diabetic children were the values of HbA1c and MDA levels. Polyamines have an insulin-like action. Antiglycation property of spermine and spermidine has been recently confirmed. There are no data in the literature about plasma polyamine oxidase (PAO) activities in children with type 1 diabetes. The idea of this study was to evaluate the polyamine metabolism through the estimation of polyamine oxidase activity. We have study children with newly diagnosed type 1 diabetes mellitus (n = 35, age group of 5-16 years, as well as age-matched healthy control subjects (n = 25). The biochemical investigations were done on diabetic children who have the pathological values of glucose (9.11-17.33 mmol/l) and glycosylated Hb (7.57-14.49% HbA(1c)). The children in the control group have referent values of glucose and glycated hemoglobin (4.11-5.84 mmol/L and HbA(1c) 4.22-6.81% of the total Hb. Glucose levels in blood plasma and glycosylated hemoglobin in erythrocythes hemolysates (HbA1c) were measured by using standard laboratory methods. PAO activity in venous blood plasma and the amount of malondialdehyde (MDA) were measured by the spectrophotometric methods. PAO activity, glycemia, HbA1c and MDA were significantly increased in diabetic children compared to the control subjects. PAO activity in children with type 1 diabetes mellitus was very high. The findings of higher blood HbA(1C) and MDA levels confirm the presence of oxidant stress in children with type 1 diabetes mellitus and demonstrate that PAO activity may participate in these circumstances.

A perspective of polyamine metabolism

Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation. In addition, novel features such as the +1 frameshift required for antizyme production and the rapid turnover of several of the enzymes involved in the pathway make the regulation of polyamine metabolism a fascinating subject. The link between polyamine content and human disease is unequivocal, and significant success has been obtained in the treatment of a number of parasitic infections. Targeting the polyamine pathway as a means of treating cancer has met with limited success, although the development of drugs such as DFMO (alpha-difluoromethylornithine), a rationally designed anticancer agent, has revolutionized our understanding of polyamine function in cell growth and provided 'proof of concept' that influencing polyamine metabolism and content within tumour cells will prevent tumour growth. The more recent development of the polyamine analogues has been pivotal in advancing our understanding of the necessity to deplete all three polyamines to induce apoptosis in tumour cells. The current thinking is that the polyamine inhibitors/analogues may also be useful agents in the chemoprevention of cancer and, in this area, we may yet see a revival of DFMO. The future will be in adopting a functional genomics approach to identifying polyamine-regulated genes linked to either carcinogenesis or apoptosis.

Non-viral vectors in cancer gene therapy: principles and progress

This review focuses on the use of synthetic (non-viral) delivery systems for cancer gene therapy. Therapeutic strategies such as gene replacement/mutation correction, immune modulation and molecular therapy/'suicide' gene therapy type approaches potentially offer unique and novel ways of fighting cancer, some of which have already shown promise in early clinical trials. However, the specific and efficient delivery of the genetic material to remote tumors/metastases remains a challenge, which is being addressed using a variety of viral and non-viral systems. Each of these disparate systems has distinct advantages and disadvantages, which need to be taken into account when a specific therapeutic gene is being used. The review concentrates on particulate gene delivery systems, which are formed through non-covalent complexation of cationic carrier molecules (e.g. lipids or polymers) and the negatively charged plasmid DNA. Such systems tend to be comparatively less efficient than viral systems, but have the inherent advantage of flexibility and safety. The DNA-carrier complex acts as a protective package, and needs to be inert and stable while in circulation. Once the remote site has been reached the complex needs to efficiently transfect the targeted (tumor) cells. In order to improve overall transfection specificity and efficiency it is necessary to optimize intracellular trafficking of the DNA complex as well as the performance after systemic administration. Common principles and specific advantages or disadvantages of the individual synthetic gene delivery systems are discussed, and their interaction with tumor-specific and generic biological barriers are examined in order to identify potential strategies to overcome them.

Agmatine uptake by cultured hamster kidney cells

Agmatine, the product of arginine decarboxylation, has been recently found in a wide variety of animal tissues. In spite of the emergent interest on agmatine in animals, the mechanism of agmatine uptake in mammalian cells has been scarcely studied. An analysis of radiolabeled agmatine uptake was carried out by using a classical, kinetic approach with BHK-21 hamster kidney cells in culture. A high affinity, temperature- and energy-dependent agmatine transport system in BHK-21 kidney cells is here kinetically characterized which seems to be a "general" transporter shared by di- and triamines and different to a highly specific carrier for the tetraamine spermine.

Interactions between agmatine and polyamine uptake pathways in rat pulmonary artery endothelial cells

Agmatine, a product of arginine metabolism in vascular endothelial cells, is structurally similar to the natural polyamines, putrescine, spermidine and spermine. To test the hypothesis that agmatine and polyamines interacted at the level of the polyamine transporter, we determined if polyamines competed with agmatine for import and whether interventions modulating polyamine import exerted coordinate effects on agmatine uptake. Multiple lines of evidence were obtained to suggest that agmatine enters pulmonary artery endothelial cells (PAECs) via the polyamine transporter, though its intracellular disposition after uptake appears different from the natural polyamines.

Polyamines. An overview

The polyamines spermine, spermidine, and putrescine are small organic molecules one or more of which are present in all living organisms. Many natural products contain polyamine residues. Polyamines are synthesized by a highly regulated pathway from arginine or ornithine and also can be transported in and out of cells. Polyamines are degraded to a variety of compounds the functions of which are largely unknown. Polyamines influence the transcriptional and translational stages of protein synthesis, stabilize membranes, and, in mammalian systems, modulate neurophysiological functions and may act as intracellular messengers. However, at the molecular level the mode of action of the polyamines is largely unknown.

Selective sites for polyamine binding to rabbit intestinal brush-border membranes

The intestinal polyamine transporters have not yet been identified. Our aim was to characterize specific polyamine binding sites in rabbit intestinal brush-border membranes (IBBM) as a starting step for identification of polyamine transporters. This was investigated at 4 degrees and at low membrane concentration. Saturation isotherms for [3H]putrescine (PUT) binding indicated a single population of sites (puT) with a dissociation equilibrium constant Kd of 3.8 microM and a density of sites Bmax of 58 pmol/mg of protein. [3H]spermidine (SPD) binding also involved only one class of sites (spD), albeit with a lower affinity (Kd = 106 microM) and higher abundance (Bmax = 1240 pmol/mg of protein) than puT. On the contrary, [14C]spermine (SPM) bound two classes of sites (spM1 and spM2) differing in their affinity (Kd = 2.5 and 31.4 microM) and abundance (Bmax = 467 and 1617 pmol/mg of protein, respectively). Membrane association of SPM at 4 degrees was much faster than that of SPD and PUT, both of which proceeded at a similar rate. In contrast to PUT and SPD dissociation, SPM dissociation at 23 degrees did not follow a first-order reaction. Specifically bound [3H]PUT, unlike [3H]SPD and [14C]SPM, dissociated at 23 degrees independently of the addition of nonradioactive polyamine. Methylglyoxal-bis-(guanylhydrazone) was an extremely potent inhibitor of PUT binding (Ki = 3.2 +/- 1.5 nM), but as with PUT and cadaverine (CAD), it did not alter [3H]SPD and [14C]SPM binding substantially. The intestinal brush-border membrane may contain at least three sites specific for polyamine binding and exhibiting different ligand selectivity. Site puT might be associated with the transport system already described for intestinal uptake of PUT.

Putrescine export in Xenopus laevis oocytes occurs against a concentration gradient: evidence for a non-diffusional export process

Putrescine export was found to occur by a non-diffusional highly regulated process using Xenopus oocytes as a model system of polyamine transport. Untreated oocytes were observed to possess high endogenous intracellular putrescine and spermidine levels with no detectable polyamine interconversion or biosynthesis over the assay intervals. The putrescine uptake process demonstrated a rapid saturation within a 5 min interval. Spermidine demonstrated a relatively larger uptake capacity with only a minimal ability to export. A kinetic analysis of the concentration-dependence of the putrescine and spermidine uptake processes indicated that the putrescine uptake process may possess two concurrent uptake components while spermidine uptake may possess a two-component process with an allosteric regulation. Elevated intracellular putrescine levels were observed to decrease against a 10-fold higher extracellular concentration gradient in a rapid and specific manner. No noticeable changes in the intracellular levels of other polyamines were observed over the same time interval. The uptake and export rates of putrescine transport also showed a concurrent, rapid and cyclical regulation. These findings support a non-diffusional putrescine export process which is highly regulated.

A kinetic characterization of putrescine and spermidine uptake and export in human erythrocytes

Using human erythrocytes as a model system for the study of mammalian polyamine transport, detailed kinetic parameters regarding the uptake and export of putrescine and spermidine were determined. The putrescine uptake data indicated a multi-component uptake system comprised of a low-capacity saturable component and a non-saturable component. The saturable putrescine uptake component demonstrated a calculated Km of 21.0 microM and a V(max) of only 6.52 x 10(-13) M/s. The non-saturable linear putrescine uptake rate was defined by a significant pH dependence, a lack of uptake inhibition by related polyamines, and a permeability pi of 3.19 x 10(-8) s-1. These findings suggested that non-saturable putrescine uptake involved a process of simple diffusion. Spermidine uptake exhibited Michaelis-Menten kinetics with a Km and Vmax of 12.5 microM and 1.36 x 10(-12) M/s, respectively. Spermidine uptake did not demonstrate pH dependence and was not significantly inhibited by any of the tested polyamines. The Arrhenius plot of spermidine uptake was determined to be biphasic with calculated activation energies of spermidine uptake of 135.2 kJ/mol for 19-21 degrees C and 59.3 kJ/mol for 21-35 degrees C. These data suggest the possibility of multiple spermidine uptake processes which are not mediated by simple diffusion across the cell membrane. The putrescine export process demonstrated both saturable and non-saturable components. The calculated Km, V(max) and pi for putrescine export were 33.8 microM, 1.19 x 10(-11) M/s and 2.81 x 10(-7) s-1, respectively. The spermidine export process was non-saturable up to intracellular spermidine concentrations of 4 microM. At similar intracellular and extracellular concentrations of putrescine and spermidine, however, export processes displayed rates which were an order of magnitude greater than their respective uptake rates. This finding supports the possible presence of mediated putrescine and spermidine export processes different than simple diffusion.

Regulation of polyamine synthesis and transport by fibroblast growth factor in aortic smooth muscle cells

Basic-FGF (FGF2) is implicated as a regulator of smooth muscle cell proliferation that develops after arterial injury. Polyamines are essential for cell growth and differentiation and may mediate some of the FGF2-elicited responses. To examine this possibility, the effect of FGF2 on polyamine synthesis and uptake was tested on rat arterial smooth muscle cells. Exposure of cells to FGF2 for 24 and 48 h resulted in increased intracellular polyamine content. Ornithine decarboxylase (ODC) activity increased in FGF2-treated cells after 6 h of treatment, whereas no increases were detected in ODC mRNA steady-state levels. Basic-FGF increased maximal polyamine transport rate without changes in Km. Treatment with actinomycin D decreased polyamine transport. The effect of cyclohexamide on polyamine uptake was dose dependent. These studies indicate that treatment of vascular smooth muscle cells with FGF2 results in increases in intracellular polyamine content, polyamine synthetic activity, and polyamine transport.

Role of ATP and sodium in polyamine transport in bovine pulmonary artery smooth cells

Increased polyamine transport may be a key mechanism driving elevations in lung cell polyamine content necessary for the development of chronic hypoxic pulmonary hypertension. Bovine pulmonary artery smooth muscle cells (PASMCs) in culture exhibit two carriers for polyamines, a non-selective one shared by the three polyamines, putrescine (PUT), spermidine (SPD), and spermine (SPM), and another that is selective for SPD and SPM. Hypoxia appears to up-regulate both carriers. In this study, we examined the role of ATP and the Na+ gradient in regulating polyamine transport in control PASMCs and in PASMCs with polyamine transport augmented by culture under hypoxic conditions (Po2: 15-30 torr). Inhibition of ATP synthesis with dinitrophenol+iodoacetate profoundly reduced polyamine uptake in both control and hypoxic PASMCs. Putrescine uptake was somewhat more sensitive to iso-osmotic replacement of extracellular Na+ with choline chloride or sucrose than were SPD or SPM in both hypoxic and standard cells, but under no conditions did Na+ replacement substantially alter polyamine uptake. Treatment of PASMCs with ouabain, a Na(+)-K+ ATPase inhibitor, or with gramicidin, a Na+ ionophore, minimally attenuated polyamine transport, whereas the Na+/K+ ionophore monensin increased polyamine uptake in standard, but not in hypoxic, cells. In general, the reduction in the extracellular Na+ content or ionophore-induced increases in Na+ permeability had a greater suppressive effect on polyamine transport in hypoxic cells than in standard cells, suggestive of the induction of Na(+)-dependent polyamine carriers by hypoxia. These observations indicate that the activities of the two putative polyamine transport pathways in standard PASMCs, as well as their up-regulation by hypoxia, require ATP synthesis. In addition, it appears that polyamine transport in PASMCs is composed of two components: one a prominent sodium-independent transporter and the other a relatively minor component that is sodium dependent. The latter may be activated by hypoxic exposure in combination with the induction of new polyamine carriers.

Endothelial polyamine uptake: selective stimulation by L-arginine deprivation or polyamine depletion

Uptake of putrescine and spermidine by cultured porcine aortic endothelial cells was time dependent and linear for 60 min. Transport, against a 5- to 10-fold concentration gradient, demonstrated both saturable and non-saturable components. Apparent concentration giving one-half maximal transport (Kt) values for putrescine and spermidine were 9 and 0.6 microM, respectively. Transport was reduced at 0 degrees C, suggesting that the process is energy requiring; inhibition by N-ethylmaleimide or p-chloromercuribenzoate suggested a requirement for sulfydryl groups. Transport of putrescine, but not spermidine, was partially activated by Na+. Spermidine and spermine did not inhibit putrescine uptake, and putrescine and spermine did not inhibit spermidine uptake, suggesting the presence of a separate transporter for each polyamine. Pretreatment with DL-2-difluoromethy-lornithine increased the uptake of putrescine but not spermidine. The endothelial cell putrescine transporter is thus sensitive to polyamine depletion, suggesting that transport from the extracellular space may be an important source of polyamines. L-Ornithine or L-arginine were not inhibitory, indicating that polyamine and cationic amino acid transport is mediated by independent systems. The sensitivity of putrescine transport to L-arginine but not to L-ornithine deprivation suggests that intracellular levels of arginine rather than ornithine regulate polyamine metabolism and transport in these cells. Thus factors that affect arginine utilization may also influence polyamine metabolism.