Polyamines (putrescine, spermidine and spermine) fulfil an array of roles in human cellular metabolism and in the synthesis of protein, RNA and DNA. Only a proportion of polyamines are synthesized in situ according to needs. However, as is the case for semi-essential amino acids, food is an important source of the polyamines required to support cell renewal and growth. Although the bioavailability and the mechanism of the uptake of polyamines in the gastrointestinal tract are not fully established, it is evident that at least some proportion of the polyamines in the diet can be absorbed and utilized by the body.

Polyamines in food and their consequences for food quality and human health

The polyamines putrescine, spermidine and spermine are essential for cell renewal and, therefore, are needed to keep the body healthy. It was previously believed that polyamines are synthesized by every cell in the body when required. However, in the present paper evidence is provided to show that, as in the case of the essential amino acids, the diet can supply sufficient amounts of polyamines to support cell renewal and growth. Systematic analysis of different foods was carried out and from the data obtained, the average daily polyamine consumption of British adults was calculated to be in the range 350-500 mumol/person per d. The major sources of putrescine were fruit, cheese and non-green vegetables. All foods contributed similar amounts of spermidine to the diet, although levels were generally higher in green vegetables. Meat was the richest source of spermine. However, only a part of the polyamines supplied by the diet is available for use by the body. Based on experiments with rats it was established that polyamines were readily taken up from the gut lumen, probably by passive diffusion, and were partly metabolized during the process of absorption. More than 80% of the putrescine was converted to other polyamines and non-polyamine metabolites, mostly to amino acids. The enzyme responsible for controlling the bioavailability of putrescine was diamine oxidase (EC 1.4.3.6). For spermidine and spermine, however, about 70-80% of the intragastrically intubated dose remained in the original form. Considering the limitations on bioavailability (metabolism and conversion), the amounts of polyamines supplied by the average daily diet in Britain should satisfy metabolic requirements.

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The importance of dietary polyamines in cell regeneration and growth

Owing to the establishment of cells and transgenic animals which either lack or over-express acetylCoA:spermidine N1-acetyltransferase a major progress was made in our understanding of the role of polyamine acetylation. Cloning of polyamine oxidases of mammalian cell origin revealed the existence of several enzymes with different substrate and molecular properties. One appears to be identical with the polyamine oxidase that was postulated to catalyse the conversion of spermidine to putrescine within the interconversion cycle. The other oxidases are presumably spermine oxidases, because they prefer free spermine to its acetyl derivatives as substrate. Transgenic mice and cells which lack spermine synthase revealed that spermine is not of vital importance for the mammalian organism, but its transformation into spermidine is a vitally important reaction, since in the absence of active polyamine oxidase, spermine accumulates in blood and causes lethal toxic effects.

Catabolism of polyamines

Increased polyamine concentrations in the blood and urine of cancer patients reflect the enhanced levels of polyamine synthesis in cancer tissues arising from increased activity of enzymes responsible for polyamine synthesis. In addition to their de novo polyamine synthesis, cells can take up polyamines from extracellular sources, such as cancer tissues, food, and intestinal microbiota. Because polyamines are indispensable for cell growth, increased polyamine availability enhances cell growth. However, the malignant potential of cancer is determined by its capability to invade to surrounding tissues and metastasize to distant organs. The mechanisms by which increased polyamine levels enhance the malignant potential of cancer cells and decrease anti-tumor immunity are reviewed. Cancer cells with a greater capability to synthesize polyamines are associated with increased production of proteinases, such as serine proteinase, matrix metalloproteinases, cathepsins, and plasminogen activator, which can degrade surrounding tissues. Although cancer tissues produce vascular growth factors, their deregulated growth induces hypoxia, which in turn enhances polyamine uptake by cancer cells to further augment cell migration and suppress CD44 expression. Increased polyamine uptake by immune cells also results in reduced cytokine production needed for anti-tumor activities and decreases expression of adhesion molecules involved in anti-tumor immunity, such as CD11a and CD56. Immune cells in an environment with increased polyamine levels lose anti-tumor immune functions, such as lymphokine activated killer activities. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues while diminishing immune cells' anti-tumor immune functions.

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The mechanisms by which polyamines accelerate tumor spread

This chapter provides an overview of the polyamine field and introduces the 32 other chapters that make up this volume. These chapters provide a wide range of methods, advice, and background relevant to studies of the function of polyamines, the regulation of their content, their role in disease, and the therapeutic potential of drugs targeting polyamine content and function. The methodology provided in this new volume will enable laboratories already working in this area to expand their experimental techniques and facilitate the entry of additional workers into this rapidly expanding field.

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Current Status of the Polyamine Research Field

We reported previously that polyamine deprivation by feeding a polyamine deficient diet combined with gastrointestinal tract decontamination and polyamine oxidase inhibition considerably enhanced the antitumoral effect of DFMO, a selective inhibitor of ornithine decarboxylase. The combination of polyamine deprivation and administration of well established cytotoxic drugs was expected to improve further the antitumoral effect of polyamine deprivation in Lewis lung carcinoma grafted in mice. Simultaneous treatment, i.e. administration of the cytotoxic drugs during the polyamine deprivation regimen, reduced tumor growth, but enhanced toxic effects. By alternating treatment and polyamine deprivation (1st day methotrexate (1.7 mg/kg), 2nd day cyclophosphamide (90 mg/kg), 3rd day vindesine (0.25 mg/kg), followed by five days of polyamine deprivation), tumor growth was reduced by 90% and an increase of 64% in the survival time of the animals was observed, demonstrating that a significant enhancement of the efficacy of chemotherapy was achieved without concomitant enhancement of toxic effects.

Polyamine deprivation enhances antitumoral efficacy of chemotherapy.

An almost complete prevention of tumor growth was achieved in U-251 human glioblastoma xenografted nude mice, by partial decontamination of the gastrointestinal tract and feeding of a polyamine-free diet containing inhibitors of ornithine decarboxylase (DFMO) and of polyamine oxidase (MDL 72527). After one week of polyamine deprivation, spermidine concentrations were lowered, and spermine levels were increased in all tissues. In contrast, putrescine concentrations were only reduced in tumor and in brain. Erythrocyte polyamine determinations revealed differences similar to those observed in tissues: spermidine concentration was lowered by 50% and spermine level was 3-fold increased. If this or related treatments should become of therapeutic importance in the future, then the determination of erythrocyte polyamine levels might be of diagnostic value.

Inhibition of the growth of U-251 human glioblastoma in nude mice by polyamine deprivation.

(Z)-1,4-diamino-2-butene as a vector of boron, fluorine, or iodine for cancer therapy and imaging: synthesis and biological evaluation.

Bis(7-amino-4-azaheptyl)dimethylsilane is a new type of aliphatic polycation with structural features resembling those of spermine. The elongation to a seven-membered carbon chain in which the central CH 2 -group was substituted by (CH3)2Si renders the molecule more lipophilic than spermine. Cells accumulate the compound via the polyamine transport system. Due to suppression of ornithine decarboxylase, de novo putrescine biosynthesis is impaired, and intracellular putrescine and spermidine concentrations are depleted. Depletion of intracellular spermidine together with binding to functionally important polyamine binding sites are considered the main features of the compound which cause cytostatic, and at high concentrations, cytotoxic effects.

Bis(7-amino-4-azaheptyl)dimethylsilane: a new tetramine with polyamine-like features. Effects on cell growth.

A sensitive assay for the determination of hydrogen peroxide formation and a method for the identification and characterization of amine oxidases in cells and other oxidase sources of limited accessibility are described. The enzymes are characterized by substrate and inhibitor patterns. The method was applied to the identification and characterization of polyamine oxidizing enzymes in macrophages from human peripheral blood. The major oxidase activity in these cells was found to be a tissue-type polyamine oxidase, but with distinct characteristics. Diamine oxidase and monoamine oxidase activities were also detected in homogenates of macrophages. Since the formation of toxic products by a releasable polyamine oxidase is supposed to be an integral part of a regulatory function of macrophages, we consider our work as a basis for the elucidation of this function.

Seiler N

Papers

Polyamine deprivation enhances antitumoral efficacy of chemotherapy.

Inhibition of the growth of U-251 human glioblastoma in nude mice by polyamine deprivation.

(Z)-1,4-diamino-2-butene as a vector of boron, fluorine, or iodine for cancer therapy and imaging: synthesis and biological evaluation.

Bis(7-amino-4-azaheptyl)dimethylsilane: a new tetramine with polyamine-like features. Effects on cell growth.

Characterization of amine oxidase activities in macrophages from human peripheral blood.