Effect of slow growth on metabolism of Escherichia coli, as revealed by global metabolite pool ("metabolome") analysis

Escherichia coli growing on glucose in minimal medium controls its metabolite pools in response to environmental conditions. The extent of pool changes was followed through two-dimensional thin-layer chromatography of all 14C-glucose labelled compounds extracted from bacteria. The patterns of metabolites and spot intensities detected by phosphorimaging were found to reproducibly differ depending on culture conditions. Clear trends were apparent in the pool sizes of several of the 70 most abundant metabolites extracted from bacteria growing in glucose-limited chemostats at different growth rates. The pools of glutamate, aspartate, trehalose, and adenosine as well as UDP-sugars and putrescine changed markedly. The data on pools observed by two-dimensional thin-layer chromatography were confirmed for amino acids by independent analysis. Other unidentified metabolites also displayed different spot intensities under various conditions, with four trend patterns depending on growth rate. As RpoS controls a number of metabolic genes in response to nutrient limitation, an rpoS mutant was also analyzed for metabolite pools. The mutant had altered metabolite profiles, but only some of the changes at slow growth rates were ascribable to the known control of metabolic genes by RpoS. These results indicate that total metabolite pool ("metabolome") analysis offers a means of revealing novel aspects of cellular metabolism and global regulation.

Screening of biogenic amine production by lactic acid bacteria isolated from grape must and wine

The potential to produce the biogenic amines tyramine, histamine and putrescine, was investigated for lactic acid bacteria (LAB) of various origin, including commercial malolactic starter cultures, type strains and 78 strains isolated from Spanish grape must and wine. The presence of biogenic amines in a decarboxylase synthetic broth was determined by reverse-phase high performance liquid chromatography (RP-HPLC). Tyramine was the main amine formed by the LAB strains investigated. Leuconostoc strains were the most intensive tyramine formers. No potential to form biogenic amines was observed in Oenococcus oeni strains. Two strains of Latobacillus buchneri were associated with putrescine formation. None of the lactic acid bacteria produced histamine. According to these in vitro results, the commercial starter bacteria analyzed did not produce histamine, tyramine and putrescine.

Amine content of vaginal fluid from untreated and treated patients with nonspecific vaginitis

We examined the vaginal washings from patients with nonspecific vaginitis (NSV) to seek biochemical markers and possible explanations for the signs and symptoms of this syndrome. Seven amines were identified including methylamine, isobutylamine, putrescine, cadaverine, histamine, tyramine, and phenethylamine. These amines may contribute to the symptoms of NSV and may contribute to the elevated pH of the vaginal discharge. They may also be partly responsible for the "fishy" odor that is characteristic of vaginal discharges from these patients. Among the seven amines, putrescine and cadaverine were the most abundant and were present in all vaginal discharges from each of ten patients before treatment. These amines are produced in vitro during growth of mixed vaginal bacteria in chemically defined medium, presumably by decarboxylation of the corresponding amino acids. We hypothesize the anaerobic vaginal organisms, previously shown to be quantitatively increased in NSV, are responsible for the amine production, because metronidazole inhibited the production of amines by vaginal bacteria in vitro, and Haemophilus vaginalis did not produce amines. H. vaginalis did release high concentrations of pyruvic acid and of amino acids during growth in peptone-starch-dextrose medium, whereas, other vaginal flora consumed both pyruvic acid and amino acids in the same medium during growth. These findings suggest that a symbiotic relationship may exist between H. vaginalis and other vaginal flora in patients with NSV.

Distribution of polyamines in methanogenic bacteria

Members of all four families of methanogenic bacteria were analyzed for polyamine concentrations. High-performance liquid chromatography analysis of dansylated cell extracts revealed typical polyamine patterns for each family. Members of Methanobacteriaceae (family I) were characterized by very low polyamine concentrations; members of Methanococcaceae (family II) were characterized by putrescine and high spermidine concentrations; members of Methanomicrobiaceae (family III) were characterized by the presence of putrescine, spermidine, and sym-homospermidine; and members of Methanosarcinaceae (family IV) contained only high concentrations of sym-homospermidine in addition to putrescine. The highest polyamine concentration was found in Methanosarcina barkeri Jülich, with 0.35% putrescine in the dry cell material. The polyamine distribution found coincides with the dendrogram based on comparative cataloguing of 16S rRNA and offers a new, rapid chemotaxonomic method for characterizing methanogenic bacteria. Variation of the growth substrates (H2-CO2, methanol, acetate, and trimethylamine) for M. barkeri resulted in quantitative but not qualitative differences in polyamine composition.

Cadaverine as a putative component of oral malodor

Whereas previous studies have shown correlations between volatile sulphur compounds (VSC) and bad breath levels, it is probable that other compounds found in the oral cavity may contribute to oral malodor. In the present investigation, the possibility that diamines (cadaverine and putrescine) are associated with oral malodor parameters was assessed. Saliva samples from 52 subjects were analyzed for cadaverine and putrescine by HPLC. Oral malodor of whole mouth, tongue, and saliva of the subjects was recorded by an experienced judge on a continuous 10-cm scale; peak and steady-state VSC intraoral levels were measured by the Interscan 1170 sulphide monitor. Log-transformed VSC and diamine levels were compared with odor judge measurements by Pearson analysis and stepwise forward multiple regression. Putrescine scores were not significantly associated with odor judge parameters or with VSC levels (p > 0.1). However, highly significant correlations (p < or = 0.003) were found between cadaverine levels and all three odor judge assessments. In contrast, associations between cadaverine and VSC measurements were non-significant. In an attempt to correlate odor judge results in terms of both VSC and diamines, we carried out stepwise forward multiple regression. Results showed that VSC and cadaverine both factor significantly in explaining each of the odor judge measurements, with multiple r values ranging from 0.545 (p = 0.0002) to 0.604 (p < 0.0001). The results suggest that cadaverine levels are associated with oral malodor, and that this association may be independent of VSC.

Changes in biogenic amines and microbiological analysis in albacore (Thunnus alalunga) muscle during frozen storage

Albacore specimens of extra quality were analyzed for their biogenic amine contents after 1, 3, 6, and 9 months of frozen storage at -18 degrees C or -25 degrees C. A high-performance liquid chromatography method involving a linear elution gradient was optimized for the identification and determination of putrescine, cadaverine, histamine, spermidine, and spermine in albacore tuna. Putrescine was the biogenic amine that showed the highest increase, reaching concentrations of 59.04 ppm (815% of the initial level) and 68.26 ppm (942% of the initial level) in the white muscle of albacore after 9 months of frozen storage at -18 and -25 degrees C, respectively. Cadaverine, histamine, and spermidine concentrations were below 3, 5, and 11 ppm, respectively, after 9 months of frozen storage, while spermidine underwent a significant decrease at both storage temperatures. Microbiological analysis confirmed the absence of species of Enterobacteriaceae in 75% of the albacore specimens after 9 months of frozen storage; coliforms were always below 3 CFU/g. The survival rate of the psychrotrophic microorganisms after 9 months of frozen storage at -25 degrees C was 4.6%, while 38.9 and 92.1% of the aerobic mesophiles present in the white muscle of albacore before freezing survived 9 months of storage at -18 and -25 degrees C, respectively.

Biogenic amines in wines from three Spanish regions

One hundred and sixty-three wines from La Rioja, Utiel-Requena, and Tarragona were analyzed to determine if there were any differences in the concentrations of six biogenic amines that are found in these three regions. The influence of grape variety, type of vinification, wine pH, malolactic fermentation, and storage in bottle on biogenic amine concentrations was studied. Results show important differences in putrescine and histamine concentrations among regions, varieties of grape, and type of wine; differences were less appreciable for the remaining biogenic amines studied. Low pH prevented biogenic amine formation. Malolactic fermentation and short storage periods in bottle (3-6 months) showed increases in histamine concentration, whereas longer periods of storage led to a general decrease in histamine. Several strains of lactic acid bacteria were isolated in this work, and their ability to form biogenic amines was assayed in synthetic media, grape must, and wine. Grape varieties, different types of winemaking, pH, and lactic acid bacteria may be responsible for the differences observed in the biogenic amine concentrations of the wines analyzed.

Enzyme sensor array for the determination of biogenic amines in food samples

An enzyme sensor array for the simultaneous determination of the three biogenic amines (histamine, tyramine and putrescine) by pattern recognition using an artificial neural network and its application to different food samples is described. A combination of a monoamine oxidase, a tyramine oxidase and a diamine oxidase (with specific activities sufficient for rapid detection) are immobilised each on a separate screen-printed thick-film electrode via transglutaminase and glutaraldehyde to compare these cross-linking reagents with regard to their suitability. To calculate the amount of a specific biogenic amine, the raw data from multichannel software were transferred to a neural network. The sensor array takes 20 min to complete (excluding statistical data analysis) with only one extraction and subsequent neutralisation step required prior to sensor measurement. The lower detection limits with the enzyme sensor were 10 mg/kg for histamine and tyramine, and 5 mg/kg for putrescine with a linear range up to 200 mg/kg for histamine and tyramine and 100 mg/kg for putrescine. The application area of the enzyme sensor array was tested from fish to meat products, sauerkraut, beer, dairy products, wine and further fermented foods and compared with the data of conventional LC analyses (mean correlation coefficient: 0.854).

Study on the Organoleptic Intensity Scale for Measuring Oral Malodor

The 0–5 organoleptic scale is used widely in breath research and in trials to measure the efficacy of anti-odor agents. However, the precise relationship between odor scores and gas concentrations of target odorants is unknown. The purpose of this study was to relate mean organoleptic scores from odor judges (n = 7) for pure odorants (n = 8) representative of those found in oral malodor. Judges used a common 0–5 scale to report the odor intensity of sample sets in random order of concentration. Regression analysis of data showed that odor score was proportional to the log concentration of odorant, and comparison of slopes showed H2S to be the most significant in terms of odor power. Detection thresholds (mol.dm−3) were: Skatole (7.2 × 10−13) < methylmercaptan (1.0 × 10−11) < trimethylamine (1.8 × 10−11) < isovalerate (1.8 × 10−11) < butyrate (2.3 × 10−10) < hydrogen sulphide (6.4 × 10−10) < putrescine (9.1 × 10−10) < dimethyl disulphide (5.9 × 10−8). The study demonstrates the exponential nature of the olfactory response and shows that any single compound’s contribution to malodor depends on odor power and threshold in addition to concentration.

Polyamines and ornithine decarboxylase during repair of duodenal mucosa after stress in rats

This investigation shows whether polyamines and ornithine decarboxylase have a role in duodenal mucosal repair following stress-induced microscopic damage. Rats were fasted for 22 hours, placed in restraint cages, and immersed in water to the xiphoid process for 6 hours. Animals were killed either immediately after the period of stress or at 2-hour intervals up to 24 hours thereafter. Duodenal mucosa was examined histologically, and ornithine decarboxylase and polyamine levels were measured. Ornithine decarboxylase activity was increased significantly up to 6 hours following stress, peaking at 4 hours at a level 10 times the prestress control. By 8 hours, enzyme activity had returned to near normal. Increases in mucosal putrescine, spermidine, and spermine content paralleled the changes in ornithine decarboxylase activity and peaked 4 hours after stress. Stress resulted in microscopic damage evidenced by a nearly complete absence of villi. Significant macroscopic lesions were not present following stress. Mucosal repair was evident 12 hours after stress and almost complete by 24 hours, although the restituted villi were short and blunted. The decreases in mucosal DNA, RNA, and protein content caused by stress were restored and reached near-normal levels 12 hours after the period of stress. In animals given the specific inhibitor of ornithine decarboxylase, alpha-difluoromethylornithine, increases in duodenal mucosal ornithine decarboxylase activity and polyamine levels were inhibited and mucosal repair was almost completely prevented following stress. alpha-Difluoromethylornithine also prevented the recovery of DNA, RNA, and protein content of the duodenal mucosa. These results indicate that duodenal mucosal damage following stress is repaired rapidly; the repair process is accompanied by significant increases in ornithine decarboxylase activity and polyamine levels; and the increases in ornithine decarboxylase and polyamines are absolutely required for the normal repair of the mucosa.

PCR detection of foodborne bacteria producing the biogenic amines histamine, tyramine, putrescine, and cadaverine

This study describes an easy PCR method for the detection of foodborne bacteria that potentially produce histamine, tyramine, putrescine, and cadaverine. Synthetic oligonucleotide pairs for the specific detection of the gene coding for each group of bacterial histidine, tyrosine, ornithine, or lysine decarboxylases were designed. Under the conditions used in this study, the assay yielded fragments of 372 and 531 bp from histidine decarboxylase-encoding genes, a 825-bp fragment from tyrosine decarboxylases, fragments of 624 and 1,440 bp from ornithine decarboxylases, and 1,098- and 1,185-bp fragments from lysine decarboxylases. This is the first PCR method for detection of cadaverine-producing bacteria. The method was successfully applied to several biogenic amine-producing bacterial strains.

Polyamine concentration in rat milk and food, human milk, and infant formulas

The polyamine concentration in rat milk and food, human milk, and infant formulas was estimated by HPLC. In rat milk, the concentration of putrescine and spermine was low (generally under 2.5 nmol.mL-1 for putrescine and under 1 nmol.mL-1 for spermine). The spermidine concentration was higher and seemed to increase during lactation. The rat food was richer in polyamines than the rat milk (about 150 times for putrescine and spermine, about 30 times for spermidine). We already proved that ingestion of spermine or spermidine can induce precocious maturation of the rat intestine. The present observations suggest that polyamines contained in rat food could play an important role in postnatal maturation of the rat intestine. The polyamine concentration of human milk was measured from 60 different mothers during a period extending from the 1st wk to the 6th mo of lactation. Great variation was observed. During the 1st mo of lactation, the general pattern was as follows: putrescine concentration generally varied little (from 1 to 3 nmol.mL-1), spermine and spermidine concentrations showed a similar pattern (the highest values appeared at the end of the 1st wk of suckling). After the 4th mo of lactation, putrescine concentration increased slightly, whereas spermine and spermidine concentration stayed almost stable. The concentrations of polyamines in 18 powdered milks for babies were estimated. Spermine and spermidine contents were lower than those in human milk. A protective effect of spermine or spermidine against alimentary allergies is suggested.

Polyamine changes in reversible cerebral ischemia

Putrescine, spermidine, and spermine levels were measured in the cortex, caudoputamen, and hippocampus of rats during 30 min of severe forebrain ischemia (induced by occlusion of both carotid and vertebral arteries) and subsequent recirculation. During ischemia, polyamine levels did not change significantly. During postischemic recirculation, however, putrescine levels dramatically increased whereas those of spermine and spermidine did not change, with the exception of the severely damaged caudoputamen, where the concentration declined after 24 h. The increase of putrescine is explained by postischemic activation of ornithine decarboxylase and inhibition of S-adenosylmethionine decarboxylase. It is suggested that the accumulation of putrescine during postischemic recirculation may be responsible for the delayed neuronal death occurring after ischemia.

Biochemical diagnosis of vaginitis: determination of diamines in vaginal fluid

To assess correlations between the content of the diamines putrescine and cadaverine in vaginal fluid and the clinical manifestations of vaginitis, a rapid procedure for the determination of diamines has been developed. The procedure involves thin-layer chromatography of the dansylated vaginal washings; then the fluorescence of dansyl diamines is compared with that of dansyl alanine. For 520 college women, the result of the test for diamines was positive in 173 (88%) of 197 women with nonspecific vaginitis or vaginitis due to Trichomonas vaginalis and was negative in 291 (90%) of 323 women without nonspecific vaginitis or vaginitis due to T. vaginalis. The diamine content of vaginal fluid specimens after therapy with metronidazole was correlated with the clinical response to treatment.

The biogenic amines putrescine and cadaverine show in vitro cytotoxicity at concentrations that can be found in foods

Putrescine and cadaverine are among the most common biogenic amines (BA) in foods, but it is advisable that their accumulation be avoided. Present knowledge about their toxicity is, however, limited; further research is needed if qualitative and quantitative risk assessments for foods are to be conducted. The present work describes a real-time analysis of the cytotoxicity of putrescine and cadaverine on intestinal cell cultures. Both BA were cytotoxic at concentrations found in BA-rich foods, although the cytotoxicity threshold for cadaverine was twice that of putrescine. Their mode of cytotoxic action was similar, with both BA causing cell necrosis; they did not induce apoptosis. The present results may help in establishing legal limits for both putrescine and cadaverine in food.

Polyamine biogenesis in the rat mammary gland during pregnancy and lactation

Polyamines and RNA accumulate in the rat mammary gland during pregnancy, but the major increases occur after parturition. Therefore the major increases occur after the gland has obtained its maximal complement of epithelial cells. During lactation, the spermidine concentration rises above 5mm and RNA content in the lactating mammary gland reaches a value 16 times that of the unstimulated mammary gland. The ratio of spermidine/spermine, an increase of which initially signals an elevation in biosynthetic activity, is near 1 in the normal mammary gland and is greater than 10 in the lactating mammary gland. Putrescine concentration is very low during the entire course of mammary-gland development, with the exception of early pregnancy. The low putrescine concentration probably reflects the very rapid conversion of putrescine into spermidine. Both ornithine decarboxylase, the enzyme that synthesizes putrescine, and putrescine-stimulated S-adenosyl-l-methionine decarboxylase, the enzyme that synthesizes spermidine, increase in activity during middle and late pregnancy; during lactation, both enzyme activities are elevated until the 21st day of lactation, and then decline. These declines are concomitant with involution. Also, it was found that the amount of ribonuclease activity in the mammary gland was very high during lactation, almost double that in the gland during pregnancy.

Polyamines in colorectal cancer

Polyamine levels (putrescine, spermidine and spermine) in colorectal cancers (n = 25) were measured in order to assess their importance as markers of cellular proliferation. Colonic mucosa from healthy resection margins of patients with diverticular disease (n = 5) was used as control material. Polyamine levels (expressed as nanomoles per 100 mg tumour) in cancers ranged from 0.8 to 7.9 for putrescine (mean: 2.3 +/- 0.7), from 6.5 to 22.8 for spermidine (mean: 13.9 +/- 0.9) and from 13.0 to 37.5 for spermine (mean: 22.1 +/- 1.3). Mean spermidine and spermine content of cancers was more than three times mean spermidine (3.92 +/- 0.8), and more than four times mean spermine (5.0 +/- 1.2), content of normal colonic mucosa (P less than 0.01). Polyamine content of colorectal cancers was independent of tumour site, Dukes' stage, histological grade and the presence of palpable liver metastases at laparotomy. Because colorectal cancers contain such high levels of spermidine and spermine, polyamines may play an essential role in the regulation of their growth.

Polyamines in human and rat milk and in infant formulas

Polyamines are ubiquitous compounds known to be involved in cell proliferation and differentiation in many tissues. Enteral administration of these compounds has been shown to produce effects in suckling and adult animals. Using HPLC techniques, we verified the presence of putrescine, spermidine, and spermine in human milk and quantitated their concentration in samples collected from the first week up to 4 mo of lactation. Mean values of these compounds ranged (per liter) from 0 to 615 nmol putrescine, from 73 to 3512 nmol spermidine, and from 722 to 4458 nmol spermine. Polyamine concentrations in infant formulas were dependent on the protein source, the particular polyamine, and the protein concentration of the formula. Concentrations of these three compounds in rat milk over the first 3 wk of lactation were higher than in human milk, with spermidine being the polyamine most elevated compared with human milk (almost 20-fold higher). An artificial formula used for the rearing of suckling rats contained trace to immeasurable amounts of polyamines. Our study identifies milk as one vehicle for polyamine delivery to the intestinal mucosa of suckling animals.

Polyamines in colorectal cancer. Evaluation of polyamine concentrations in the colon tissue, serum, and urine of 50 patients with colorectal cancer

Total, free, and acetylated polyamine concentrations were measured simultaneously in colon tissue, serum, and urine of 50 patients with histologically proven colorectal cancer, 40 patients with nonmalignant gastrointestinal diseases, and 30 healthy volunteers. Compared with histologically unaffected colon tissue, concentrations were significantly (P less than 0.001) higher for putrescine, elevated for cadaverine, and nearly identical for spermidine and spermine in colon carcinoma, whereas N1-acetylated and N8-acetylated spermidine were detectable in cancer tissue only. Serum and urine concentrations of all polyamines except total cadaverine and spermine in serum and free spermine in urine were significantly elevated compared with healthy controls and highest sensitivity for colon cancer was found for total spermidine (89.15%) in serum and acetylputrescine (84.5%), total putrescine (84.0%), N1-acetylspermidine (79.3%), and total spermidine (92.1%) in urine. However, nonmalignant gastrointestinal diseases partly showed similar elevations which resulted in a low specificity for polyamines in colorectal cancer. Therefore, polyamines are of little value only as diagnostic markers in colorectal carcinoma. Since polyamine concentrations in serum and urine normalized in patients after curative operation while they were further elevated in patients with proven tumor relapse or metastases, these substances might play a clinical role in predicting therapeutic success or indicating relapse of the tumor. Although a significant dependency of polyamine concentrations in serum or urine to Dukes' classification, tumor localization, CEA, CA 19-9, or CA 125 did not exist, a significant linear correlation was found for tumor size.

Selective release of spermine and spermidine from the rat striatum by N-methyl-D-aspartate receptor activation in vivo

The intrastriatal infusion of N-methyl-D-aspartate (NMDA; 250-1,000 microM) via a dialysis cannula in anesthetized rats resulted in a marked and rapid increase in the concentrations of spermine and spermidine recovered in the dialysate. Extracellular concentrations of NMDA-released spermine and spermidine were calculated to be in the low micromolar range. Putrescine levels were not significantly affected by NMDA. The effects of NMDA (500 microM) were blocked by the previous systemic injection of MK-801 (3 mg/kg, i.p.) but were insensitive to the intrastriatal infusion of tetrodotoxin (1 microM). Intrastriatally infused kainate or quisqualate (1,000 microM) did not increase polyamine levels in the dialysate. Spermine and spermidine dialysate levels were also significantly increased by the infusion of high concentrations of K+ (greater than 100 mM), although the effects of K+ were considerably less marked than those of NMDA. Striatal polyamines are released into the extracellular space specifically by NMDA receptor activation. Because of their multiple effects on receptor- and voltage-operated cation channels, polyamines that are released by NMDA receptor activation may play an important role in phenomena already attributed to NMDA receptor stimulation, such as long-term potentiation, synaptic plasticity, and neurotoxicity.

Effects of DL-alpha-difluoromethylornithine on Leishmania donovani promastigotes

Alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, has been demonstrated to be an effective agent against a variety of parasitic protozoa but not against Leishmania spp. In this report, we show that Leishmania donovani promastigotes in continuous culture are sensitive to the growth inhibitory and cytotoxic effects of DFMO. Incubation of the promastigotes with DFMO obliterates intracellular putrescine pools and depletes spermidine concentrations, which correlates with the onset of growth inhibition. The effects of DFMO on the growth and the intracellular polyamine pools can be reversed completely by the addition of 10 microM putrescine to the culture medium. These results suggest that the treatment of leishmaniasis may be amenable to chemotherapeutic manipulation by DFMO.

Polyamine modification increases the permeability of proteins at the blood-nerve and blood-brain barriers

The permeability of the blood-nerve barrier (BNB) and the blood-brain barrier (BBB) to superoxide dismutase (SOD), insulin, albumin, and IgG in normal adult rats was quantified by measuring the permeability coefficient-surface area product (PS) with the intravenous bolus injection technique before and after covalent protein modification with naturally occurring polyamines-putrescine (PUT), spermidine (SPD), and spermine (SPM). The PS value of the BNB for PUT-SOD was 21.1-fold greater than the native SOD, and the PS values of the BBB for PUT-SOD ranged from 17.6-fold greater for the thalamus to 23.6-fold greater for the caudate-putamen compared with native SOD. In a similar manner, polyamine-modified insulin showed a 1.7-2.0-fold increase in PS of the BNB and BBB compared with the high values of native insulin. Polyamine-modified albumin showed a remarkable 54-165-fold increase in PS of the BNB and BBB compared with native albumin, whereas PUT-IgG resulted in an even higher increase in the PS that ranged from 111- to 349-fold for nerve and different brain regions compared with native IgG. Polyamine modification of proteins, therefore, can dramatically increase the permeability at the BNB and BBB of a variety of proteins with widely differing M(r) and function. It is surprising that the PS values of the BNB and BBB decreased with the increasing number of positive charges of the protonated amino groups on the polyamines (PUT>SPD>SPM). Although cationic proteins are known to interact with fixed anionic charges on the lumen of the microvascular endothelium, this observation of decreased permeability with increased positive charge distribution along the aliphatic carbon chain of the polyamines implies mechanisms other than simple electrostatic interaction involving charge density. It is suggested that the polyamine transporter may be responsible for the transport of these polyamine-modified proteins. Systemic administration of polyamine-modified peptides and proteins might prove to be an efficient approach to deliver therapeutic agents into the CNS and PNS for the treatment of a variety of neurological diseases.