Effects of the porphyrinogenic compounds hexachlorobenzene and 3,5-diethoxycarbonyl-1,4-dihydrocollidine on polyamine metabolism

Polyamines are traps for reactive intermediates in furan metabolism

Furan is toxic and carcinogenic in rodents. Because of the large potential for human exposure, furan is classified as a possible human carcinogen. The detailed mechanism by which furan causes toxicity and cancer is not yet known. Since furan toxicity requires cytochrome P450-catalyzed oxidation of furan, we have characterized the urinary and hepatocyte metabolites of furan to gain insight into the chemical nature of the reactive intermediate. Previous studies in hepatocytes indicated that furan is oxidized to the reactive α,β-unsaturated dialdehyde, cis-2-butene-1,4-dial (BDA), which reacts with glutathione (GSH) to form 2-(S-glutathionyl)succinaldehyde (GSH-BDA). This intermediate forms pyrrole cross-links with cellular amines such as lysine and glutamine. In this article, we demonstrate that GSH-BDA also forms cross-links with ornithine, putrescine, and spermidine when furan is incubated with rat hepatocytes. The relative levels of these metabolites are not completely explained by hepatocellular levels of the amines or by their reactivity with GSH-BDA. Mercapturic acid derivatives of the spermidine cross-links were detected in the urine of furan-treated rats, which indicates that this metabolic pathway occurs in vivo. Their detection in furan-treated hepatocytes and in urine from furan-treated rats indicates that polyamines may play an important role in the toxicity of furan.

Interactions of natural polyamines with mammalian proteins

The ubiquitously expressed natural polyamines putrescine, spermidine, and spermine are small, flexible cationic compounds that exert pleiotropic actions on various regulatory systems and, accordingly, are essentially involved in diverse life functions. These roles of polyamines result from their capability to interact with negatively charged regions of all major classes of biomolecules, which might act in response by changing their structures and functions. The present review deals with polyamine-protein interactions, thereby focusing on mammalian proteins. We discuss the various modes in which polyamines can interact with proteins, describe major types of affected functions illustrated by representative examples of involved proteins, and support information with respective structural evidence from elucidated three-dimensional structures. A specific focus is put on polyamine interactions at protein surfaces that can modulate the aggregation of proteins to organized structural networks as well as to toxic aggregates and, moreover, can play a role in important transient protein-protein interactions.

Early increases in transglutaminase activity and polyamine levels in a Mallory-Denk body mouse model

Rodents treated with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) are a model of two hepatic toxic manifestations: porphyria and the appearance of hepatic cytoplasmic protein aggregates (Mallory-Denk Bodies, MDBs). MDBs are induced after long-term DDC feeding, consist primarily of keratins 8 and 18, and contain glutamine-lysine cross-links generated by transglutaminases (TGs). TGs are Ca(2+)-dependent enzymes which catalyze the formation of covalent bonds between proteins and between proteins and polyamines. The aim of the current study was to investigate the time-course of TG hepatic activity in CF1 male mice either acutely or chronically treated with DDC and to correlate this activity with polyamine and porphyrin levels. On day 3 of the treatment, statistically significant increases in TG activity (75%), porphyrin content (6740%) and spermidine levels (73%) were observed. Although not statistically significant, at this time point putrescine levels showed an increase of 52%. The highest TG activity was observed on day 30 (522%), while porphyrin levels were still gradually increasing by day 45 (37,000%). From day 7 of the treatment and until the end of the experiment, putrescine levels remained increased (781%). Spermine levels were not affected by the treatment. The DDC-induced increases in putrescine and spermidine levels herein reported seem to be an early event contributing to the stimulation of liver TG activity, and thus to the promotion of cross-linking reactions between keratin proteins. This in turn would contribute to the formation of protein aggregates, which would lead to the appearance of MDBs. Due to the pro-oxidant and antioxidant properties of polyamines, it is possible to speculate that putrescine and spermidine may also participate at several levels in the oxidative stress processes associated with MDB formation.

Polyamines: naturally occurring small molecule modulators of electrostatic protein-protein interactions

Modulations of protein-protein interactions are a key step in regulating protein function, especially in networks. Modulators of these interactions are supposed to be candidates for the development of novel drugs. Here, we describe the role of the small, polycationic and highly abundant natural polyamines that could efficiently bind to charged spots at protein interfaces as modulators of such protein-protein interactions. Using the mitochondrial cytochrome P45011A1 (CYP11A1) electron transfer system as a model, we have analyzed the capability of putrescine, spermidine, and spermine at physiologically relevant concentrations to affect the protein-protein interactions between adrenodoxin reductase (AdR), adrenodoxin (Adx), and CYP11A1. The actions of polyamines on the individual components, on their association/dissociation, on electron transfer, and on substrate conversion were examined. These studies revealed modulating effects of polyamines on distinct interactions and on the entire system in a complex way. Modulation via changed protein-protein interactions appeared plausible from docking experiments that suggested favourable high-affinity binding sites of polyamines (spermine>spermidine>putrescine) at the AdR-Adx interface. Our findings imply for the first time that small endogenous compounds are capable of interfering with distinct components of transient protein complexes and might control protein functions by modulating electrostatic protein-protein interactions.

Differential effects of paraquat on oxidative stress parameters and polyamine levels in two freshwater invertebrates

Paraquat is still a widely used herbicide in several countries. Its toxic action on plants occurs through a one-electron reduction interfering with the photosynthesis process. By a similar reaction, the herbicide may induce peroxidation processes in non-target animal species. Furthermore, paraquat may interfere with the cellular transport of polyamines. The aim of this work was to investigate some aspects related to paraquat-induction of oxidative stress (lipoperoxidation, enzymatic activities of catalase and superoxide dismutase) and also the levels of polyamines (putrescine, spermidine and spermine) in two species of freshwater invertebrates, the oligochaete Lumbriculus variegatus and the gastropod Biomphalaria glabrata. The results showed that both organisms elicited differential responses. In addition, the data suggested that polyamines may play an important role against lipoperoxidation processes.

A CD133-expressing murine liver oval cell population with bilineage potential

Although oval cells are postulated to be adult liver stem cells, a well-defined phenotype of a bipotent liver stem cell remains elusive. The heterogeneity of cells within the oval cell fraction has hindered lineage potential studies. Our goal was to identify an enriched population of bipotent oval cells using a combination of flow cytometry and single cell gene expression in conjunction with lineage-specific liver injury models. Expression of cell surface markers on nonparenchymal, nonhematopoietic (CD45-) cells were characterized. Cell populations were isolated by flow cytometry for gene expression studies. 3,5-Diethoxycarbonyl-1,4-dihydrocollidine toxic injury induced cell cycling and expansion specifically in the subpopulation of oval cells in the periportal zone that express CD133. CD133+CD45- cells expressed hepatoblast and stem cell-associated genes, and single cells coexpressed both hepatocyte and cholangiocyte-associated genes, indicating bilineage potential. CD133+CD45- cells proliferated in response to liver injury. Following toxic hepatocyte damage, CD133+CD45- cells demonstrated upregulated expression of the hepatocyte gene Albumin. In contrast, toxic cholangiocyte injury resulted in upregulation of the cholangiocyte gene Ck19. After 21-28 days in culture, CD133+CD45- cells continued to generate cells of both hepatocyte and cholangiocyte lineages. Thus, CD133 expression identifies a population of oval cells in adult murine liver with the gene expression profile and function of primitive, bipotent liver stem cells. In response to lineage-specific injury, these cells demonstrate a lineage-appropriate genetic response. Disclosure of potential conflicts of interest is found at the end of this article.

Bone marrow fails to differentiate into liver epithelium during murine development and regeneration

Recent reports have provided conflicting conclusions regarding the role for bone marrow (BM)-derived cells in the regeneration of liver. Our aim was to investigate the potential of BM to contribute to liver epithelium using different BM transplant models designed to explore differentiation during normal liver development and regeneration after toxic injury. BM cells from transgenic green fluorescent protein (GFP) mice were injected into neonatal and adult immunodeficient and neonatal immune-competent mice. Three distinct models of liver injury were employed to test the contribution of marrow to the regeneration of hepatocytes, cholangiocytes, and oval cells in immune-deficient adult animals after neonatal transplant. Immunohistochemistry was combined with flow cytometry (FACS) and reverse transcription (RT)-PCR to increase the sensitivity and specificity of the analyses. Although GFP+ marrow-derived cells were observed in the livers of all transplanted animals, immunohistochemistry failed to demonstrate any marrow derived hepatocytes or cholangiocytes. FACS confirmed that GFP+ marrow-derived cells in the liver maintained expression of CD45, a leukocyte marker. Gene expression studies of GFP+ cells isolated by FACS failed to demonstrate expression of liver specific genes in these marrow-derived cells.

CONCLUSION

Through highly sensitive and specific analyses, we were unable to demonstrate any evidence of transdifferentiation of BM-derived cells into epithelial hepatic tissue during the period of rapid growth in the neonatal period. Furthermore, although increased migration of hematopoietic cells to the liver occurred after toxic injury, these cells did not contribute directly to the replacement of hepatocytes, cholangiocytes, or oval cells.

Tryptophan metabolism via serotonin in rats with hexachlorobenzene experimental porphyria

One of the three pathways for the metabolisation of dietary tryptophan is the formation of serotonin. Tryptophan hydroxylase catalyses the formation of 5-hydroxytryptophan, the first and regulatory step of this biosynthesis. The aim of the present work is to study alterations in this tryptophan metabolism in rats with experimental Porphyria Cutanea Tarda induced by hexachlorobenzene. With this purpose, the content of tryptophan and its metabolites related to the serotonin pathway are determined by HPLC techniques, in tissues (brain, liver and gut) and in fluids (blood, plasma and urine) of controls and hexachlorobenzene-porphyric rats. In these experimental-porphyric animals, we determine a significant increase in the excretion of 5-hydroxyindole acetic acid in urine and a decrease in the content of serotonin in small gut, respect to controls. Significant increases in contents of serotonin in 24-hr urine and tryptophan in liver are also found. No other significant variations for the different metabolites are detected in any of the tissues and fluids studied. Brain and liver activities of the rate-limiting enzyme tryptophan hydroxylase can only be measured in porphyric rats. Our results agree with an increased turnover of gastrointestinal serotonin derived from dietary tryptophan and its excretion as urinary 5-hydroxyindole acetic acid, which is formed in liver. An increased serotonin pathway in porphyric livers is confirmed by the measured increase in the activity of hepatic tryptophan hydroxylase. The absence of neurological symptoms in patients with Porphyria Cutanea Tarda could be related to the absence of a statistically significant variation in serotonin content shown in brain.