Iron stimulation of free radical-mediated porphyrinogen oxidation by hepatic and renal mitochondria

Oxoisoaporphines and Aporphines: Versatile Molecules with Anticancer Effects

Cancer is a disease that involves impaired genome stability with a high mortality index globally. Since its discovery, many have searched for effective treatment, assessing different molecules for their anticancer activity. One of the most studied sources for anticancer therapy is natural compounds and their derivates, like alkaloids, which are organic molecules containing nitrogen atoms in their structure. Among them, oxoisoaporphine and sampangine compounds are receiving increased attention due to their potential anticancer effects. Boldine has also been tested as an anticancer molecule. Boldine is the primary alkaloid extract from boldo, an endemic tree in Chile. These compounds and their derivatives have unique structural properties that potentially have an anticancer mechanism. Different studies showed that this molecule can target cancer cells through several mechanisms, including reactive oxygen species generation, DNA binding, and telomerase enzyme inhibition. In this review, we summarize the state-of-art research related to oxoisoaporphine, sampangine, and boldine, with emphasis on their structural characteristics and the relationship between structure, activity, methods of extraction or synthesis, and anticancer mechanism. With an effective cancer therapy still lacking, these three compounds are good candidates for new anticancer research.

Feather content of porphyrins in Eurasian eagle owl (Bubo bubo) fledglings depends on body condition and breeding site quality

Porphyrins are pigments produced in most animal cells during the synthesis of heme, but their importance for external coloration is unclear. Owls (Order Strigiformes) are among the few animals that accumulate porphyrins in the integument, where it could serve as a means of signaling. Here we hypothesized that the porphyrin content of feathers may depend on body condition and breeding site quality in Eurasian eagle owl (Bubo bubo) fledglings and, thus, constitute amplifiers of the quality of the area where they are born. Using high-performance liquid chromatography, we found 2 porphyrins (protoporphyrin IX and coproporphyrin III) in the body feathers of 19 eagle owl fledglings from 7 breeding territories. Coproporphyrin III, but not protoporphyrin IX feather concentration, was positively associated with the body mass of fledglings and with the quality of the breeding sites where they were reared with respect to food quality and availability. As coproporphyrin III is produced under oxidative stress, we suggest that good breeding sites may lead to fledglings in good condition. This, in turn, may make fledglings induce a certain level of free radical and coproporphyrin III production to signal to conspecifics their site-mediated capacity to cope with oxidative stress. This is the first time that porphyrin content in the integument has been found to be related to individual quality, opening a new scenario for studying evolution of animal coloration.

Systematic identification and analysis of frequent gene fusion events in metabolic pathways

Background

Gene fusions are the most powerful type of in silico-derived functional associations. However, many fusion compilations were made when <100 genomes were available, and algorithms for identifying fusions need updating to handle the current avalanche of sequenced genomes. The availability of a large fusion dataset would help probe functional associations and enable systematic analysis of where and why fusion events occur.

Results

Here we present a systematic analysis of fusions in prokaryotes. We manually generated two training sets: (i) 121 fusions in the model organism Escherichia coli; (ii) 131 fusions found in B vitamin metabolism. These sets were used to develop a fusion prediction algorithm that captured the training set fusions with only 7 % false negatives and 50 % false positives, a substantial improvement over existing approaches. This algorithm was then applied to identify 3.8 million potential fusions across 11,473 genomes. The results of the analysis are available in a searchable database at http://modelseed.org/projects/fusions/. A functional analysis identified 3,000 reactions associated with frequent fusion events and revealed areas of metabolism where fusions are particularly prevalent.

Conclusions

Customary definitions of fusions were shown to be ambiguous, and a stricter one was proposed. Exploring the genes participating in fusion events showed that they most commonly encode transporters, regulators, and metabolic enzymes. The major rationales for fusions between metabolic genes appear to be overcoming pathway bottlenecks, avoiding toxicity, controlling competing pathways, and facilitating expression and assembly of protein complexes. Finally, our fusion dataset provides powerful clues to decipher the biological activities of domains of unknown function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2782-3) contains supplementary material, which is available to authorized users.

Sampangine (a Copyrine Alkaloid) Exerts Biological Activities through Cellular Redox Cycling of Its Quinone and Semiquinone Intermediates

The cananga tree alkaloid sampangine (1) has been extensively investigated for its antimicrobial and antitumor potential. Mechanistic studies have linked its biological activities to the reduction of cellular oxygen, the induction of reactive oxygen species (ROS), and alterations in heme biosynthesis. Based on the yeast gene deletion library screening results that indicated mitochondrial gene deletions enhanced the sensitivity to 1, the effects of 1 on cellular respiration were examined. Sampangine increased oxygen consumption rates in both yeast and human tumor cells. Mechanistic investigation indicated that 1 may have a modest uncoupling effect, but predominately acts by increasing oxygen consumption independent of mitochondrial complex IV. Sampangine thus appears to undergo redox cycling that may involve respiratory chain-dependent reduction to a semi-iminoquinone followed by oxidation and consequent superoxide production. Relatively high concentrations of 1 showed significant neurotoxicity in studies conducted with rat cerebellar granule neurons, indicating that sampangine use may be associated with potential neurotoxicity.

Increased urinary coproporphyrin excretion observed in patients with differently staged Hodgkin's disease treated with chemotherapy

It has been reported that patients with Hodgkin's disease (HD) show altered porphyrin metabolism, and suggested that the cause is the neoplastic process itself. If this is true, disease progression should be associated with higher levels of porphyrin excretion. The aim of this study was to evaluate urinary coproporphyrin levels in patients with Hodgkin's disease at different stages. As many of the patients received chemotherapy, another aim was to verify experimentally whether chemotherapeutic agents might increase porphyrin levels in rabbits. All of the patients had above-normal urinary coproporphyrin levels. On the other hand, rabbits receiving the porphyrin precursor 5-aminolevulinic acid (5-ALA), and also treated with doxorubicin, showed very high plasma porphyrin levels. The increased levels of urinary coproporphyrins seem to be due to the disease itself, since the patients in stages III and IV had higher excretion values, presumably due to biochemical heme synthesis lesions that lead to the availability of the porphyrin precursor, as well as coproporphyrin accumulation and excretion. The altered porphyrin synthesis may be attributable to the cytotoxic oxygen species generated in the presence of NADH and iron. As the patients also received extensive chemotherapy regimes, the altered porphyrin metabolism may be affected by antineoplastic treatment generating oxygen reactive radicals. The alterations in porphyrin metabolism induced by chemotherapeutic agents appear to be demonstrated in rabbits in which doxorubicin increases porphyrin synthesis after porphyrin precursor treatment.

High-dose vitamin E lowers urine porphyrin levels in patients affected by porphyria cutanea tarda

Porphyria cutanea tarda (PCT) is a metabolic disorder of heme biosynthesis, characterized by reduced uroporphyrinogen decarboxylase (UROD) activity and increased urinary excretion of eight and seven carboxyl group porphyrins. Specific factors such as iron, alcohol and halogenated compounds further inhibit enzyme activity by generating reactive oxygen species. Antioxidant vitamin E has frequently been used to counteract oxidative stress in porphyria patients, but a number of studies have failed to detect any significant effect on porphyrin metabolism. Since the use of vitamin E in the treatment of porphyria is a debated question, it seemed of interest to administer high doses to five patients with PCT in order to evaluate the effects on urine porphyrin excretion. The patients had high urinary porphyrin excretion levels, but vitamin E significantly reduced the urinary excretion of eight carboxyl group porphyrins. This result is attributable to the increase in UROD activity caused by the vitamin, which is a known scavenger of the oxygen reactive species that interfere with the activity of the enzyme. In conclusion, this paper shows that vitamin E high doses significantly lowers the urine porphyrin excretion in studied patients affected by PCT.

Urinary excretion of biomarkers for radical-induced damage in rats treated with NDMA or diquat and the effects of calcium carbimide co-administration

The urinary excretion of seven aldehydes, acetone, coproporphyrin III and 8-hydroxy-2'-deoxyguanosine (8-OH-dG) as non-invasive biomarkers of oxidative damage was measured in rats treated with diquat or N-nitrosodimethylamine (NDMA), two compounds causing hepatic damage by different mechanisms. Furthermore, the effect of co-administration of the aldehyde dehydrogenase inhibitor, calcium carbimide (CC) on the urinary excretion of the aldehydes was determined. Slight hepatotoxicity was found at the end of the experiment after treatment with NDMA (0.5, 4 and 8 mg/kg at t = 0, 48 and 96 h, respectively) or diquat (6.8 and 13.6 mg/kg at t = 0 and 48 h, respectively). In diquat treated rats slight nephrotoxicity was also found. Urinary excretion of aldehydes, acetone and coproporphyrin III remained largely unchanged in rats treated with NDMA. In the rats treated with diquat, the urinary excretion of several aldehydes was several-fold increased. An increase was also found in the urinary excretion of 8-OH-dG after the second dose of diquat. Treatment of rats with CC did not significantly influence the urinary excretion of aldehydes in control and NDMA rats. However, in rats treated with diquat, CC caused a potentiating effect on the excretion of acetaldehyde, hexanal and malondialdehyde (MDA), indicating that oxidation of aldehydes to carbonylic acids by aldehyde dehydrogenases (ALDHs) might be an important route of metabolism of aldehydes. In conclusion, increased urinary excretion of various aldehydes, acetone, coproporphyrin III and 8-OH-dG was observed after administration of diquat, probably reflecting oxidative damage induced by this compound. No such increases were found after NDMA administration, which is consistent with a different toxicity mechanism for NDMA. Therefore, excretion of aldehydes, acetone, coproporphyrin III and 8-OH-dG might be used as easily accessible urinary biomarkers of free radical damage.

Evaluation of urinary biomarkers for radical-induced liver damage in rats treated with carbon tetrachloride

Carbon tetrachloride (CCl4) is a model compound for inducing free radical damage in liver. In this study 10 biomarkers in rats treated i.p. with three different single doses of CCl4 (0.25, 0.50, and 1.00 ml/kg body wt) were measured dose and time dependently and compared to evaluate these urinary products as noninvasive biomarkers for radical damage. Eight degradation products of lipid peroxides, namely, formaldehyde, acetaldehyde, acetone, propanal, butanal, pentanal, hexanal, and malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and coproporphyrin III were measured in this study. As general measures of toxicity, several clinical chemical parameters (n = 12) and histopathological damage were determined. A dose-dependent increase in both the clinical parameters and the lipid degradation products was found. Increases in lipid degradation products were statistically significant at doses of 0.5 and 1 ml/kg CCl4. An increase in these products was already found in the first 12 h after exposure. At the lowest dose, 0.25 ml/kg CCl4, acetaldehyde and propanal already showed a statistically significant increase as well. No change in the urinary levels of 8-OH-dG could be found in this study and a decrease in the urinary excretion of coproporphyrin III was found. It is concluded that 8-OH-dG and coproporphyrin III are not useful biomarkers for radical damage induced by CCl4. Lipid degradation products, however, are promising noninvasive biomarkers for in vivo radical damage, although the precise specificity of these biomarkers for damage induced by radicals needs to be further investigated.

Urinary porphyrins as biological indicators of oxidative stress in the kidney. Interaction of mercury and cephaloridine

Reduced porphyrins (hexahydroporphyrins, porphyrinogens) are readily oxidized in vitro by free radicals which are known to mediate oxidative stress in tissue cells. To determine if increased urinary porphyrin concentrations may reflect oxidative stress to the kidney in vivo, we measured the urinary porphyrin content of rats treated with mercury as methyl mercury hydroxide (MMH) or cephaloridine, both nephrotoxic, oxidative stress-inducing agents. Rats exposed to MMH at 5 ppm in the drinking water for 4 weeks showed a 4-fold increase in 24-hr total urinary porphyrin content and a 1.3-fold increase in urinary malondialdehyde (MDA), an established measure of oxidative stress in vivo. Treatment with cephaloridine alone (10-500 mg/kg, i.p.) produced a dose-related increase in urinary MDA and total porphyrin levels up to 1.6 and 7 times control values, respectively. Injection of MMH-treated rats with cephaloridine (500 mg/kg) caused a synergistic (20-fold) increase in urinary porphyrin levels, but an additive (1.9-fold) increase in the MDA concentration. Studies in vitro demonstrated that cephaloridine stimulated the iron-catalyzed H2O2-dependent oxidation of porphyrinogens to porphyrins in the absence of either microsomes or mitochondria. Additionally, porphyrinogens were oxidized to porphyrins in an iron-dependent microsomal lipid peroxidation system. Moreover, porphyrinogens served as an effective antioxidant (EC50 approximately 1-2 microM) to lipid peroxidation. These results demonstrate that MMH and cephaloridine synergistically, as well as individually, promote increased oxidation of reduced porphyrins in the kidney and that this action may be mechanistically linked to oxidative stress elicited by these chemicals. Increased urinary porphyrin levels may, therefore, represent a sensitive indicator of oxidative stress in the kidney in vivo.

Redox activities of mercury-thiol complexes: implications for mercury-induced porphyria and toxicity

Mercury exposure causes oxidative damage to the kidney, resulting in numerous biochemical changes, including the excretion of excess porphyrins in the urine (porphyrinuria). Hg(II)-induced porphyrinuria may occur, in part, by the previously reported oxidation of reduced porphyrins (porphyrinogens) by a GSH/Hg(II) complex and H2O2. To further elucidate the mechanism(s) of porphyrinogen oxidation by GSH, Hg(II), and H2O2, we compared the ability of several thiol compounds and peroxides to substitute for GSH or H2O2, respectively, in the oxidation of uroporphyrinogen (urogen). Every thiol compound tested resulted in enhanced urogen oxidation in the presence of Hg(II) and H2O2, albeit at different rates. Additionally, t-butyl or cumene hydroperoxide substituted for H2O2 in promoting urogen oxidation, although neither peroxide was as effective in this regard. Mercury-thiol complexes synthesized from Hg(I) and GSSG also promoted urogen oxidation in the presence of H2O2. Additionally, in the absence of urogen, both GSH/Hg(II) or GSSG/Hg(I) catalyzed the decomposition of H2O2. Finally, incubation of GSH/Hg(II) or GSSG/Hg(I) with H2O2 resulted in HPLC-detectable products distinct from GSH, GSSG, or GS2Hg(II). These findings suggest that mercury-thiol complexes possess redox activity in biological systems, which promotes the oxidation of porphyrinogens and possibly other biomolecules.