Oxidative stress biomarkers in Clarias gariepinus (Burchel, 1822) exposed to Microcystin-LR

Comparative Bioaccumulation of PAH and BTEX in Malapterurus electricus (Siluriformes: Malapteruridae) and its Enteric Parasite, Electrotaenia malopteruri Sampled from Lekki Lagoon, Lagos, Nigeria

Contamination of Lekki lagoon by petrogenic chemicals such as polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylene (BTEX) has been widely reported. The study was aimed at investigating the bioaccumulation of PAH and BTEX in Malapterurus electricus collected from Lekki lagoon in Lagos, Nigeria. BTEX was analyzed in the intestine, water, and sediment samples using 8260B Agilent 7890B gas chromatograph coupled to a mass spectrometer (GC-MS). While PAHs were tested in the same media using a gas chromatograph coupled to a flame ionization detector (GC-FID). Histopathological analysis of the fish intestine was conducted using haematoxylin and eosin (H&E) stains. Parasite intensity, antioxidant enzymes, and lipid peroxidation activities were investigated in the fish. The parasitic infection detected in Malapterurus electricus was Electrotaenia malopteruri. The parasite showed weak and no depurative capacities for BTEX and PAH respectively. The decrease in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) in conjunction with an increase in Malondialdehyde (MDA) characterized relatively higher susceptibility among the male fish. Varieties of tissue injuries increased with the standard length of the fish groups. Results suggest that lengthier and uninfected M. electricus were more susceptible to PAH in Lekki lagoon than the shorter and infected ones. The study demonstrated a promising tendency of the enteric parasite, E. malopteruri to depurate chlorobenzene, ethylbenzene, o-xylene, m+p-xylene, and 1,4-dichlorobenzene from the intestine of its host fish, M. electricus, while PAHs were poorly mediated by the parasite.

The presence of microcystins in the coastal waters of Nigeria, from the Bights of Bonny and Benin, Gulf of Guinea

Microcystins (MCs) are the most studied toxins of cyanobacteria in freshwater bodies worldwide. However, they are poorly documented in coastal waters in several parts of the world. In this study, we investigated the composition of cyanobacteria and the presence of microcystins (MCs) in several coastal aquatic ecosystems of Nigeria. Direct morphological analysis revealed that members of the genus Oscillatoria were dominant with five species, followed by Trichodesmium with two species in Nigerian coastal waters. Oso Ibanilo had the highest cyanobacterial biomass (998 × 10³ cells/L), followed by Rivers Ocean (156 × 10³ cells/L). Except for the Cross River Ocean, cyanobacteria were present in all the investigated aquatic ecosystems. Ten (10) out of twenty water bodies examined had detectable levels of MCs. Furthermore, genomic DNA analysis for the mcyE gene of microcystin synthetase (mcy) cluster showed identities higher than 86% (query coverage > 96%) with toxic strains of cyanobacteria in all the samples analyzed. Also, the sequences of samples matched those of uncultured cyanobacteria from recreational lakes in Southern Germany. Our findings indicate that the presence of toxic cyanobacteria in coastal waters of Nigeria is of public and environmental health concern.

Biotransformations, Antioxidant System Responses, and Histopathological Indexes in the Liver of Fish Exposed to Cyanobacterial Extract

Radiocystis fernandoi, a microcystin (MC) producer, has been common in cyanobacterial blooms in tropical regions. Microcystin is a hepatotoxin that causes tissue damage and even death in animals, including humans; its detoxification process may involve biotransformation and activation of the antioxidant defense system. We evaluated the detoxification pathway, examined the antioxidant defense system responses, and determined the alterations and the organ histopathological indexes in the liver of the tropical fish Hoplias malabaricus after acute and subchronic intraperitoneal exposure to microcystin. The crude microcystin extract of R. fernandoi had predominantly MC-RR and MC-YR. The detoxification process was activated by increasing ethoxyresorufin-O-deethylase activity, whereas glutathione S-transferase was inhibited. The activity of the antioxidant defense enzymes superoxide dismutase (SOD) and glutathione peroxidase decreased after acute exposure; the SOD-catalase system and the glutathione level increased after subchronic exposure. The carbonyl protein level, lipid peroxidation (LPO), and DNA damage were unchanged after acute exposure, whereas protein carbonyl was unchanged, LPO decreased, and DNA damage increased after subchronic exposure. Histopathological alteration indexes differed between acute and subchronic exposure, but the histopathological organ indexes indicate liver dysfunction in both exposure periods. We conclude that MC-RR and MC-YR induce different liver responses depending on the time of exposure, and the antioxidant defense responses after subchronic exposure may help to partially restore the liver function. Environ Toxicol Chem 2020;39:1041-1051. © 2020 SETAC.

In vivo assessment of the hepatotoxicity of a new Nostoc isolate from the Nile River: Nostoc sp. strain NRI

Nostoc sp. is one of the most widely distributed cyanobacterial genera that produce potentially protein phosphatase (PP) inhibitor; microcystins (MCs). MCs have posed a worldwide concern due to predominant hepatotoxicity to human health. We have previously isolated a Nostoc strain (NR1) from the Nile River (the main water supply in Egypt) and this strain exerted production of rare and highly toxic MC; demethylated microcystin-LR. There is no data concerning risk factors of liver diseases for human and animal exposure to NR1-contaminated drinking water yet. It is thus important to evaluate acute (LD₅₀ dose), subacute (0.01% and 10% of LD₅₀ dose) and subchronic (0.01% and 10% of LD₅₀ dose) hepatotoxicity's NR1 extract using experimental mice. Mice groups, who orally received 0.01% LD₅₀, represented a permissible concentration of the World Health Organization (WHO) for MC in drinking water. Several parameters were detected, including hepatotoxicity (i.e. PP activity, liver function, oxidative stress markers and DNA fragmentation), pro-inflammatory cytokine (TNF-α) and liver histopathology. Our results demonstrated LD₅₀ of NR1 extract was at 15,350 mg/kg body weight and caused hepatotoxicity that attributed to PP inhibition and a significant increase of hepatic damage biomarkers with lipid accumulation. Moreover, NR1 extract induced hepatic oxidative damage that may have led to DNA fragmentation and production of TNF-α. As demonstrated from the histopathological study, NR1 extract caused a severe collapse of cytoskeleton with subsequent focal degeneration of hepatocytes, necroinflammation and steatosis. The grade of hepatotoxicity in subacute (10% of LD₅₀) group was higher than that in the subchronic (10% of LD₅₀ and 0.01% of LD₅₀, WHOch, respectively) groups. No significant hepatotoxicity was detectable for subacute (0.01% of LD₅₀, WHOac) group. NR1 is therefore considered as one of the harmful and life-threatening cyanobacteria for Egyptian people being exposed to dose above WHO guideline. Thus, biological indicators and thresholds for water treatment are extremely needed.