Jean Paul Kamdem

Involvement of oxidative stress in 4-vinylcyclohexene-induced toxicity in Drosophila melanogaster

4-Vinylcyclohexene (VCH) is a dimer of 1,3-butadiene produced as a by-product of pesticides, plastic, rubber, flame retardants, and tire production. Although, several studies have reported the ovotoxicity of VCH, information on a possible involvement of oxidative stress in the toxicity of this occupational chemical is scarce. Hence, this study was carried out to investigate further possible mechanisms of toxicity of VCH with a specific emphasis on oxidative stress using a Drosophila melanogaster model. D. melanogaster (both genders) of 1 to 3 days old were exposed to different concentrations of VCH (10 µM-1 mM) in the diet for 5 days. Subsequently, the survival and negative geotaxis assays and the quantification of reactive oxygen species (ROS) generation were determined. In addition, we evaluated RT-PCR expressions of selected oxidative stress and antioxidant mRNA genes (HSP27, 70, and 83, SOD, Nrf-2, MAPK2, and catalase). Furthermore, catalase, glutathione-S-transferase (GST), delta aminolevulinic acid dehydratase (δ-ALA-D), and acetylcholinesterase (AChE) activities were determined. VCH exposure impaired negative geotaxic behavior and induced the mRNA of SOD, Nrf-2, and MAPK2 genes expressions. There were increases in catalase and ROS production, as well as inhibitions of GST, δ-ALA-D, and AChE activities (P<0.05). Our results suggest that the VCH mechanism of toxicity is associated with oxidative damage, as evidenced by the alteration in the oxidative stress-antioxidant balance, and possible neurotoxic consequences due to decreased AChE activity, and impairments in negative geotaxic behavior. Thus, we conclude that D. melanogaster is a useful model for investigating the toxicity of VCH exposure, and here, we have provided further insights on the mechanism of VCH-induced toxicity.

Polyphenolic Composition and Evaluation of Antioxidant Activity, Osmotic Fragility and Cytotoxic Effects of Raphiodon echinus (Nees & Mart.) Schauer

Raphiodon echinus (R. echinus) is used in Brazilian folk medicine for the treatment of inflammation, coughs, and infectious diseases. However, no information is available on the potential antioxidant, cytotoxicity and genotoxicity of this plant. In this study, the polyphenolic constituents, antioxidant capacity and potential toxic effects of aqueous and ethanolic extracts of R. echinus on human erythrocytes and leukocytes were investigated for the first time. R. echinus extracts showed the presence of Gallic, chlorogenic, caffeic and ellagic acids, rutin, quercitrin and quercetin. Aqueous and ethanolic extracts of R. echinus exhibited antioxidant activity in DPPH radical scavenging with IC50 = 111.9 μg/mL (EtOH extract) and IC50 = 227.9 μg/mL (aqueous extract). The extracts inhibited Fe2+ (10 μM) induced thiobarbituric acid reactive substances (TBARS) formation in rat brain and liver homogenates. The extracts (30–480 μg/mL) did not induce genotoxicity, cytotoxicity or osmotic fragility in human blood cells. The findings of this present study therefore suggest that the therapeutic effect of R. echinus may be, in part, related to its antioxidant potential. Nevertheless, further in vitro and in vivo studies are required to ascertain the safety margin of its use in folk medicine.

Ovotoxicants 4-vinylcyclohexene 1,2-monoepoxide and 4-vinylcyclohexene diepoxide disrupt redox status and modify different electrophile sensitive target enzymes and genes in Drosophila melanogaster.

The compounds 4-vinylcyclohexene 1,2-monoepoxide (VCM) and 4-Vinylcyclohexene diepoxide (VCD) are the two downstream metabolites of 4-vinylcyclohexene (VCH), an ovotoxic agent in mammals. In addition, VCM and VCD may be found as by-products of VCH oxidation in the environment. Recently, we reported the involvement of oxidative stress in the toxicity of VCH in Drosophila melanogaster. However, it was not possible to determine the individual contributions of VCM and VCD in VCH toxicity. Hence, we investigated the toxicity of VCM and VCD (10–1000 µM) in flies after 5 days of exposure via the diet. Our results indicated impairments in climbing behaviour and disruptions in antioxidant balance and redox status evidenced by an increase in DCFH oxidation, decreases in total thiol content and glutathione-S-transferase (GST) activity in the flies exposed to VCM and VCD (p<0.05). These effects were accompanied by disruptions in the transcription of the genes encoding the proteins superoxide dismutase (SOD1), kelch-like erythroid-derived cap-n-collar (CNC) homology (ECH)-associated protein 1 (Keap-1), mitogen activated protein kinase 2 (MAPK-2), catalase, Cyp18a1, JAFRAC 1 (thioredoxin peroxidase 1) and thioredoxin reductase 1 (TrxR-1) (p<0.05). VCM and VCD inhibited acetylcholinesterase (AChE) and delta aminolevulinic acid dehydratase (δ-ALA D) activities in the flies (p<0.05). Indeed, here, we demonstrated that different target enzymes and genes were modified by the electrophiles VCM and VCD in the flies. Thus, D. melanogaster has provided further lessons on the toxicity of VCM and VCD which suggest that the reported toxicity of VCH may be mediated by its transformation to VCM and VCD.

In vitro evaluation of glutathione peroxidase (GPx)-like activity and antioxidant properties of an organoselenium compound

The amine based diselenide, (Z)-N-(4-methylbenzylidene)-1-(2-((2-(1-((E)-4-methyl benzylideneamino)ethyl)phenyl)diselanyl)phenyl)ethanamine ethyl)phenyl) diselanyl) phenyl) ethylimino) methyl)phenol (Compound A) an organoselenium compound that can mimic endogenous antioxidant enzymes, such as glutathione peroxidase (GPx), and diphenyl diselenide (PhSe)2 were tested against lipid peroxidation induced by sodium nitroprusside (SNP) and Fe(II) in rat brain, interaction with 1,1-diphenyl-2-picrylhydrazyl stable free radical (DPPH) and glutathione peroxidase (GPx) like antioxidant activities with H2O2 or tBuOOH as substrates and with PhSH as thiol co-substrates as well as their ability to oxidize thiols were evaluated. From this study, we concluded that Compound A catalyze the reduction of H2O2 with thiol was ∼2-fold more active than (PhSe)2) in both tBuOOH and H2O2 systems when PhSH was used as a substrate. (PhSe)2 exhibited an increased ability to oxidize thiols while Compound A was not a good substrate for the oxidation of thiol used namely DTT and Cystine and showed DPPH radical-scavenging activity, while (PhSe)2 did not present radical scavenging activity. Compound A (amine based diselenide) presented better antioxidant profiles than (PhSe)2 against lipid peroxidation. The results clear showed that nitrogen atom in the Compound A can have a profound effect on their pharmacological properties.

Biochemical and behavioral deficits in the lobster cockroach Nauphoeta cinerea model of methylmercury exposure

Methylmercury (MeHg) is well-known for its neurodevelopmental effects both in animals and in humans. As an alternative to utilizing conventional animal models, this study evaluated behavioral and biochemical parameters using the nymphs of the lobster cockroach Nauphoeta cinerea. Animals were exposed to MeHg at 0, 0.03125, 0.0625, 0.125, 0.25 and 0.5 mg per g feed for 35 consecutive days. Locomotor activity and exploratory profiles were analyzed using video-tracking software during a 10 minute trial. Subsequently, biochemical estimations were carried out using cockroach heads. MeHg exposure caused behavioral impairment as evidenced by a significant decrease in distance travelled, time spent walking, turn angle and body rotation. The marked decrease in the exploratory profiles of MeHg-exposed cockroaches was confirmed by track plots, whereas occupancy plot analyses revealed a gradual dispersal in home-base formation, starting from 0.0625 mg per g feed. Biochemically, MeHg exposure significantly decreased acetylcholinesterase activity (AChE), an enzyme which plays a pivotal role in neurotransmission. Moreover, MeHg caused increased oxidative stress as evidenced by decreased total thiol levels and glutathione S-transferase (GST) activity, along with increased 2′,7′-dichlorofluorescein (DFCH) oxidation and thiobarbituric acid reactive substance (TBARS) production. In conclusion, these data demonstrated that Nauphoeta cinerea mimics the behavioral and biochemical deficits observed in rodents exposed to MeHg, thus highlighting its validity as an alternative model for basic toxicological studies.

In vitro antioxidant activity of stem bark of Trichilia catigua Adr. Juss

Antioxidant activity of the ethanolic extract and fractions from the stem bark of T. catigua was investigated. IC50 (for DPPH scavenging) by T. catigua varied from 9.17 ± 0.63 to 76.42 ± 5.87 mg mL-1 and total phenolic content varied from 345.63 ± 41.08 to 601.27 ± 42.59 mg GAE g-1 of dry extract. Fe2+-induced lipid peroxidation was significantly reduced by the ethanolic extract and fractions. Mitochondrial Ca2+-induced dichlorofluorescein oxidation was significantly reduced by the ethanolic extract in a concentration-dependent manner. Ethanolic extract reduced mitochondrial Dym only at high concentrations (40-100 mg mL-1), which indicates that its toxicity does not overlap with its antioxidant effects. Results suggest involvement of antioxidant activities of T. catigua in its pharmacological properties. U radu je opisano ispitivanje antioksidativnog u~inka etanolnog ekstrakta i pojedinih frakcija kore stabljike T. catigua. IC50 (za DPPH test) varirao je izme|u 9,17 ± 0,63 i 76,42 ± 5,87 mg mL-1, a ukupni sadr`aj fenola od 345,63 ± 41,08 i 601,27 ± 42,59 mg GAE po gramu suhog ekstrakta. Etanolni ekstrakt i frakcije zna~ajno su reducirale Fe2+-induciranu lipidnu peroksidaciju. Nadalje, reducirana je oksidacija diklorfluoresceina inducirana ionima kalcija u mitohondrijima, a redukcija je ovisila o dozi etanolnog ekstrakta. Etanolni ekstrakt smanjio je mitohondrijsku Dym samo pri visokim koncentracijama (40 ± 100 mg mL-1), {to ukazuje da se toksi~nost ne preklapa s antioksidativnim u~inkom. Rezultati pokazuju da u farmakolo{ko djelovanje T. catigua treba uklju~iti i antioksidativni u~inak.

1-(2-(2-(2-(1-Aminoethyl)phenyl)diselanyl)phenyl)ethanamine: An amino organoselenium compound with interesting antioxidant profile

Free radical scavenging and antioxidant activities of 1-(2-(2-(2-(1-aminoethyl)phenyl)diselanyl)phenyl)ethanamine (compound A) and diphenyl diselenide (PhSe)2 were examined and compared for inhibition of Fe(II) and sodium nitroprusside (SNP) stimulated lipid peroxidation in rat brain, interaction with 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable free radical and their glutathione peroxidase (GPx) like antioxidant activities with H2O2 or tBuOOH as substrates and with PhSH as thiol co-substrates as well as their ability to oxidize mono- and di-thiols were also evaluated. This study revealed that an amino group in amino diselenide drastically enhances their catalytic activities in the aromatic thiol (PhSH) assay system. Compound A was ~2-fold more active than (PhSe)2 in both tBuOOH and H2O2 assay systems. In addition, the present results showed that (PhSe)2 exhibited an increased ability to oxidize di-thiols, compound A was not a good substrate for the oxidation of thiol used namely DTT, cystine and DMPS. The antioxidant potency against Fe(II) and SNP-induced brain TBARS were in this order [(compound A); IC50 2 μM and 4 μM]>[(PhSe)2; IC50 19 μM and 27.5 μM. Compound A showed DPPH radical-scavenging activity. This study provides in vitro evidence anti-oxidant action of the tested organoselenium compounds, that the nitrogen atom in the organochalcogens can have a profound effect on their antioxidant activity.

Euphorbia tirucalli aqueous extract induces cytotoxicity, genotoxicity and changes in antioxidant gene expression in human leukocytes

Euphorbia tirucalli, popularly known as “avelos”, is a toxic plant used as tea in Brazilian folk medicine as an antibacterial, antiviral and anticarcinogenic agent. However, there is no scientific report about its potential toxicity in human cells. Therefore, the objective of the present study was to evaluate the in vitro genotoxicity and cytotoxicity of aqueous extracts of E. tirucalli in human leukocytes using a comet assay and trypan blue exclusion assay, respectively. In addition, the effect of E. tirucalli on the osmotic fragility was investigated in human erythrocytes. The expressions of selected antioxidant mRNA genes (SOD2, CAT and GPx4) as well as tumor protein p53 (TP53) were evaluated by qRT-PCR. Exposure of human leukocytes to high concentrations of aqueous extracts of E. tirucalli (100–150 μg mL−1) caused a significant increase in DNA damage. Leukocyte viability was decreased in the presence of 50–150 μg mL−1E. tirucalli extract. E. tirucalli did not change the osmotic fragility of human erythrocytes. High concentrations of E. tirucalli (10–50 μg mL−1) significantly up-regulated the mRNA of SOD2 and CAT and decreased the mRNA of GPx4 expression in human leukocytes. In addition, the mRNA gene expression of SOD2 was down-regulated at the highest concentration tested (150 μg mL−1). In summary, based on the results of genotoxicity observed in our study, we recommend caution regarding the acute or chronic use of this homemade preparation. Taken together, our results suggest that the aqueous extract of E. tirucalli induces genotoxicity and cytotoxicity in human leukocytes, possibly by interacting with the antioxidant enzyme system, thereby, increasing the formation of ROS and decreasing the cellular tolerance level to chemical constituents of this plant.

Saponin as regulator of biofuel: implication for ethnobotanical management of diabetes

There has been a sharp rise in the global prevalence of diabetes, obesity, and their comorbid conditions within the last decade prompting significant research into possible causes and cure via therapeutic intervention and lifestyle adjustments. Here, the molecular bases of antidiabetic plants used in the prehistorical treatment of diabetes and obesity are reviewed with particular focus on saponin as the phytotherapeutic principle. Until recently, the phytotherapeutic potentials of saponins have been masked in the heterogeneity of phytochemicals co-extractable during traditional preparations. With improved technique of purification and cutting edge biological assay methods, saponins have emerged as a regulator of primary biofuel availability through direct interaction with energy metabolism, cell signaling, and gene expression. Specific cases of lipoprotein lipase/peroxisome proliferator-activated receptor (PPAR)-gamma/phosphatidylinositide 3-kinase (PI-3-K)/protein kinase B (Akt) activation, adiponectin gene upregulation, fatty acid binding protein 4 repression (FABP4), and glucose transporter type 4 (Glut4) membrane exocytosis have been documented which provide molecular basis for hypocholesterolemic, hypoglycemic, and anti-obesity manifestations observed in experimental animals following saponin treatment. Although intensified research is required to characterize the pharmacophoric features in saponins exhibiting these interactions, however, this preliminary lead is valuable if the world will be free of diabetes, obesity, hypertension, hyperlipidemia, and atherosclerosis in no distant future.

Antimicrobial Activity and Modulatory Effect of Essential Oil from the Leaf of Rhaphiodon echinus (Nees & Mart) Schauer on Some Antimicrobial Drugs

Background: Rhaphiodon echinus is a weed plant used in the Brazilian folk medicinal for the treatment of infectious diseases. In this study, the essential oil of R. echinus leaf was investigated for its antimicrobial properties. Methods: The chemical constituents of the essential oil were characterized by GC-MS. The antimicrobial properties were determined by studying by the microdilution method the effect of the oil alone, and in combination with antifungal or antibiotic drugs against the fungi Candida albicans, Candida krusei and Candida tropicalis and the microbes Escherichia coli, Staphylococcus aureus and Pseudomonas. In addition, the iron (II) chelation potential of the oil was determined. Results: The results showed the presence of β-caryophyllene and bicyclogermacrene in major compounds, and revealed a low antifungal and antibacterial activity of the essential oil, but a strong modulatory effect on antimicrobial drugs when associated with the oil. The essential oil showed iron (II) chelation activity. Conclusions: The GC-MS characterization revealed the presence of monoterpenes and sesquiterpenes in the essential oil and metal chelation potential, which may be responsible in part for the modulatory effect of the oil. These findings suggest that essential oil of R. echinus is a natural product capable of enhancing the antibacterial and antifungal activity of antimicrobial drugs.