Effect of selenium-rich Bacillus subtilis against mercury-induced intestinal damage repair and oxidative stress in common carp

Multiple effects of dietary supplementation with Lactobacillus reuteri and Bacillus subtilis on the growth, immunity, and metabolism of largemouth bass (Micropterus salmoides)

Probiotics play an essential role in the largemouth bass (Micropterus salmoides) aquaculture sector. They aid the fish in sickness prevention, intestinal structure improvement, food absorption, and immune system strengthening. In this experiment, Bacillus subtilis (BS, 107 CFU/g) and Lactobacillus reuteri (LR, 107 CFU/g) were added to the feed and then fed to M. salmoides for 35 days. The effects of two probiotics on the growth, immunity, and metabolism of M. salmoides organisms were studied. The results revealed that the BS group significantly increased the growth rate and specific growth rate of M. salmoides, while both the BS and LR groups significantly increase the length of villi M. salmoides intestines. The BS group significantly increased the levels of AKP, T-AOC, and CAT in the blood of M. salmoides, as well as AKP levels in the intestine. Furthermore, the BS group significantly increased the expression of intestinal genes Nrf2, SOD1, GPX, and CAT, while significantly decreasing the expression of the keap1 gene. M. salmoides gut microbial analysis showed that the abundance of Planctomycetota was significantly different in both control and experimental groups. Analyzed at the genus level, the abundance of Citrobacter, Paracoccus, Luedemannella， Sphingomonas, Streptomyces and Xanthomonas in the both control and experimental groups were significantly different. The BS group's differentially expressed genes were predominantly enriched in oxidative phosphorylation pathways in the intestine, indicating that they had a good influence on intestinal metabolism and inflammation suppression. In contrast, differentially expressed genes in the LR group were primarily enriched in the insulin signaling and linoleic acid metabolism pathways, indicating improved intestine metabolic performance. In conclusion, B. subtilis and L. reuteri improve the growth and health of M. salmoides, indicating tremendous potential for enhancing intestinal metabolism and providing significant application value.

Probiotics in addressing heavy metal toxicities in fish farming: Current progress and perspective

Heavy metal contamination of aquatic environments adversely affects the health of aquatic organisms and consumption of fish contaminated with heavy metals poses serious health risks to humans. Among various strategies, probiotics (living microorganisms known to have beneficial effects on the host), which have been extensively applied in the aquaculture industry, could be helpful for heavy metal detoxification and remediation. Several probiotics, including Lactobacillus strains, exhibit heavy metal binding, high heavy metal tolerance, and other beneficial characteristics for the host. Notably, numerous probiotics have been reported to bind heavy metals and excrete them from the host. Various probiotic strains (Lactobacillus, Bacillus, Lactococcus, etc.) show beneficial effects in alleviating heavy metal toxicity in cultured fish species. Certain probiotic bacteria reduce the absorption and bioavailability of heavy metals by enhancing heavy metal detoxification and sequestration while preserving gut barrier function. This review summarises the toxic effects of selected heavy metals on the health of farmed fish and discusses the role of probiotic strains in remediating the consequential exposure-induced immune toxicity and oxidative stress. Moreover, we discussed the protective strategies of probiotics against heavy metal accumulation in various tissues and gut dysbiosis in fish to alleviate heavy metal toxicity in fish farming, thereby promoting a sustainable blue economy worldwide.

Selenium maintains intestinal epithelial cells to activate M2 macrophages against deoxynivalenol injury

Selenium (Se) is indispensable in alleviating various types of intestinal injuries. Here, we thoroughly investigated the protective effect of Se on the regulation of the epithelial cell-M2 macrophages pathway in deoxynivalenol (DON)-induced intestinal damage. In the present study, Se has positive impacts on gut health by improving gut barrier function and reducing the levels of serum DON in vivo. Furthermore, our study revealed that Se supplementation increased the abundances of GPX4, p-PI3K, and AKT, decreased the levels of 4-HNE and inhibited ferroptosis. Moreover, when mice were treated with DON and Fer-1(ferroptosis inhibitor), ferroptosis was suppressed and PI3K/AKT pathway was activated. These results indicated that GPX4-PI3K/AKT-ferroptosis was a predominant pathway in DON-induced intestinal inflammation. Interestingly, we discovered that both the number of M2 anti-inflammatory macrophages and the levels of CSF-1 decreased while the pro-inflammatory cytokine IL-6 increased in the intestine and MODE-K cells supernatant. Therefore, Se supplementation activated the CSF-1-M2 macrophages axis, resulting in a decrease in IL-6 expression and an enhancement of the intestinal anti-inflammatory capacity. This study provides novel insights into how intestinal epithelial cells regulate the CSF-1-M2 macrophage pathway, which is essential in maintaining intestinal homeostasis confer to environmental hazardous stimuli.

L-theanine attenuates H2O2-induced inflammation and apoptosis in IPEC-J2 cells via inhibiting p38 MAPK signaling pathway

This study investigated the protective effects of L-theanine on hydrogen peroxide (H2O2)-induced intestinal barrier dysfunction in IPEC-J2 cells. Results showed that L-theanine reduced H2O2-induced IPEC-J2 cells inflammation and apoptosis, and decreased protein phosphorylation levels of p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor kappa-B (NF-κB). The p38 MAPK inhibitor (SB203580) decreased oxidative stress, the protein expression of phosphorylation of p38 MAPK and NF-κB, the H2O2-induced increase in mRNA expression of pro-apoptotic and pro-inflammatory related genes expression and secretion, and tight junction protein related genes expression, which was similar to the effect of L-theanine. In conclusion, L-theanine inhibited H2O2-induced oxidative damage and inflammatory reaction, eliminated apoptosis, and protected intestinal epithelial barrier damage by inhibiting the activation of p38 MAPK signaling pathway.

Advances in the Study of Selenium-Enriched Probiotics: From the Inorganic Se into Se Nanoparticles

Selenium (Se) is a momentous metallic element that plays an irreplaceable role in biochemical activities. Se deficiency remains a nutritional challenge across the world. Organic Se supplementation is the most effective treatment means for Se deficiency. Organic Se transformed from Se-enriched probiotics show outstanding excellent properties in antibacteria, anti-oxidation, anti-inflammation, and immunoregulation. Studying the influencing factors for Se enrichment capacity and enrichment mechanisms of Se-enriched probiotics is conducive to the exploit of more potent Se-enriched probiotics. Se-enriched probiotics transform inorganic Se into Se nanoparticles (SeNPs), which have been widely used in animal husbandry and biomedical field. In this paper, the novel development of Se-enriched probiotics is reviewed, and the bioactivities of SeNPs are assessed, so as to display their potential application prospects. The excellent role of SeNPs in anti-oxidation is summarized, and the mechanism by which SeNPs improve Se deficiency and boost animal health is explained.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

The effects of mercury exposure on Amazonian fishes: An investigation of potential biomarkers

Exposure to mercury can interfere with the expression of proteins and enzymes, compromise important pathways, such as apoptosis and glucose metabolism, and even induce the expression of metallothioneins. In this study, analytical techniques were used to determine the concentration of total mercury (THg) in muscle and liver tissue, protein pellets, and spots [using graphite furnace atomic absorption spectrometry (GFAAS)], and molecular techniques were used to identify metalloproteins present in mercury-associated protein spots. Thirty individuals from three different fish species, Cichla sp. (n = 10), Brachyplatystoma filamentosum (n = 10), and Semaprochilodus sp. (n = 10) from the Brazilian Amazon were used. Oxidative stress indicators [such as glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD), a marker of lipid peroxidation (LPO)] and the possible expression of metallothioneins in muscle and liver tissues were investigated. The two piscivorous species, Cichla sp. and B. filamentosum, presented the highest concentrations of mercury in their hepatic tissue, 1219 ± 15.00 and 1044 ± 13.6 μg kg^-1, respectively, and in their muscle tissue, 101 ± 1.30 μg kg^-1 and 87.4 ± 0.900 μg kg^-1, respectively. The non-carnivorous species Semaprochilodus sp. had comparatively low concentrations of mercury in both its hepatic (852 ± 11.1 μg kg^-1) and muscle (71.4 ± 0.930 μg kg^-1) tissues. The presence of mercury was identified in 24 protein spots using GFAAS; concentrations ranged from 11.5 to 787 μg kg^-1, and mass spectrometry identified 21 metal-binding proteins. The activities of GSH-Px, CAT, and SOD, related to oxidative stress, decreased proportionally as tissue Hg concentrations increased, while the levels of LPO markers increased, indicating the presence of stress. Our study results demonstrate possible mercury interference in oxidative stress markers (GSH-Px, CAT, SOD, and LPO), in addition to the identification of 21 metal-binding proteins as possible biomarkers of mercury exposure in fish.

Selenium-Enriched Black Soybean Protein Prevents Benzo(a)pyrene-Induced Pyroptotic Colon Damage and Gut Dysbacteriosis

Selenium-enriched black soybean protein (SeBSP) is a kind of high-quality selenium resource with many physiological functions. Benzo(a)pyrene (BaP) is a well-known injurant that widely exists in high-temperature processed food and has been previously found to cause colon injury. In this study, the effects of SeBSP on colonic damage induced by BaP in BALB/C mice were investigated by comparing it with normal black soybean protein (BSP). SeBSP inhibited the BaP-induced reductions on body weight, food intake, and water intake. Moreover, metabolic enzymes, including AhR, CYP1A1, CYP1B1, and GST-P1, that were promoted by BaP were downregulated by SeBSP, reducing oxidative damage caused by BaP in the metabolic process. The classical pyroptosis indexes (i.e., NLRP3, ASC, Caspase-1, GSDMD) and inflammatory factors (i.e., TNF-α, IL-1β, IL-18, iNOS, COX-2) were downregulated by SeBSP in BaP-treated mice, suggesting the benefits of SeBSP in reducing colonic toxicity. Notably, SeBSP enhanced microbial diversity of gut microbiota and increased relative abundances of prebiotic bacteria, for example, Lactobacillus reuteri, Bacteroides thetaiotaomicron, and genera Bifidobacterium, and Blautia, along with the promotion of short-chain fatty acids. Integrative analysis showed strong links between the antioxidant and anti-inflammatory effects of SeBSP and its altered gut microbiota. Collectively, our study demonstrates the pronounced benefits of Se-enriched black soybean in preventing the colonic toxicity of BaP, and such effects could be mediated by gut microbiota.

Mercury Induced Tissue Damage, Redox Metabolism, Ion Transport, Apoptosis, and Intestinal Microbiota Change in Red Swamp Crayfish (Procambarus clarkii): Application of Multi-Omics Analysis in Risk Assessment of Hg

As one of the most toxic elements, mercury (Hg) is a widespread toxicant in aquatic environments. Crayfish are considered suitable for indicating the impact of heavy metals on aquatic crustaceans. Nevertheless, Hg toxicity on Procambarus clarkii is largely unknown. In this research, the acute Hg-induced alterations of biochemical responses, histopathology, hepatopancreatic transcriptome, and intestinal microbiome of Procambarus clarkii were studied. Firstly, Hg induced significant changes in reactive oxygen species (ROS) and malonaldehyde (MDA) content as well as antioxidant enzyme activity. Secondly, Hg exposure caused structural damage to the hepatopancreas (e.g., vacuolization of the epithelium and dilatation of the lumen) as well as to the intestines (e.g., dysregulation of lamina epithelialises and extension of lamina proprias). Thirdly, after treatment with three different concentrations of Hg, RNA-seq assays of the hepatopancreas revealed a large number of differentially expressed genes (DEGs) linked to a specific function. Among the DEGs, a lot of redox metabolism- (e.g., ACOX3, SMOX, GPX3, GLO1, and P4HA1), ion transport- (e.g., MICU3, MCTP, PYX, STEAP3, and SLC30A2), drug metabolism- (e.g., HSP70, HSP90A, CYP2L1, and CYP9E2), immune response- (e.g., SMAD4, HDAC1, and DUOX), and apoptosis-related genes (e.g., CTSL, CASP7, and BIRC2) were identified, which suggests that Hg exposure may perturb the redox equilibrium, disrupt the ion homeostasis, weaken immune response and ability, and cause apoptosis. Fourthly, bacterial 16S rRNA gene sequencing showed that Hg exposure decreased bacterial diversity and dysregulated intestinal microbiome composition. At the phylum level, there was a marked decrease in Proteobacteria and an increase in Firmicutes after exposure to high levels of Hg. With regards to genus, abundances of Bacteroides, Dysgonomonas, and Arcobacter were markedly dysregulated after Hg exposures. Our findings elucidate the mechanisms involved in Hg-mediated toxicity in aquatic crustaceans at the tissue, cellular, molecular as well as microbial levels.

Transcriptomics reveals the mechanism of selenium-enriched Lactobacillus plantarum alleviating brain oxidative stress under cadmium stress in Luciobarbus capito

Cadmium (Cd) is one of toxic metal in environment and is thought to affect nervous system. There were an increasing number of studies on selenium (Se)-enriched probiotics which were believed to produce bioactive nanoselenium. The antagonism of Se on heavy metals can significantly affect biological toxicity of heavy metals. This study aimed to elucidate possible mechanism of brain injury in Luciobarbus capito after Cd exposure and the mitigation of Se-enriched probiotics through transcriptome analysis. The results revealed 465 differentially expressed genes in the Cd and the control brains (Cd vs C), including 320 genes with upregulated expression and 145 genes with downregulated expression. In addition, we found that there were 4117 differentially expressed genes in the Se-enriched L. plantarum plus Cd and the control brains (S1L1-Cd vs C), including 2552 genes with upregulated expression and 1565 genes with downregulated expression. There were 147 differentially expressed genes in the Se-enriched L. plantarum plus Cd and the control brains (S1L1-Cd vs Cd), including 40 genes with upregulated expression and 107 genes with downregulated expression. Moreover, GO enrichment analysis indicated that the differentially expressed genes were involved in biological processes cellular component, and molecular function. KEGG enrichment analysis indicated that MAPK signaling pathway, calcium signaling pathway, and PI3K-Akt signaling pathway were significantly enriched. Subsequently, qRT-PCR was performed, and we selected 15 related differentially expressed genes for verification. The qRT-PCR results revealed the same trend as the RNA-Seq results. In conclusion, this study elucidated relieving effect of Se-enriched probiotics on Cd exposure-induced brain oxidative stress. This study provided a theoretical basis for further research on genes related to Cd poisoning and the amelioration of Se-enriched probiotics on Cd poisoning.

Probiotic Intervention in the Treatment of Diabetes Mellitus: A Review

Diabetes is a noncommunicable lifestyle condition that impacts millions of individuals worldwide. Diabetes is a physiological illness that affects several different organs in the human body. Several studies have found a direct relationship between gut microbiota and diabetes control. Probiotic intervention in the treatment of diabetes mellitus has been the center of focus in the current scenario. Alteration in composition and metabolic activity of gut microbiota significantly contributes to human health. However, the key mechanism of gut microbiota in the inhibition of diabetes is not fully understood. This review discusses the effect of probiotics on diabetes and the role of gut microbiota. It emphasizes on the pharmacological effects of probiotics on diabetic symptoms like glycemic response, hypercholesterolemia, hypertension, as well as gestational diabetes.

Selenium-enriched Bacillus subtilis reduces the effects of mercury-induced on inflammation and intestinal microbes in carp (Cyprinus carpio var. specularis)

Mercury (Hg) is a global pollutant that affects the health of humans and ecosystems. Selenium (Se) is an essential trace element for many organisms including humans. Bacillus subtilis is one of the main probiotics used in aquaculture, and has a certain adsorption effect on heavy metals. The interaction between Hg and Se was rigorously studied, especially due to the observation of the protective effect of Se on Hg toxicity. The objective of this study was to research the effects of Hg, Se, and B. subtilis on inflammation and intestinal microbes in common carp. The common carp was exposed to Hg (0.03 mg/L), and 10⁵ cfu/g Se-rich B. subtilis was added to the feed. After 30 days of feeding, samples were taken to evaluate the growth performance, serological response, inflammatory response, and intestinal microbial changes. In this study, when fish were exposed to Hg, the growth performance of the Se-rich B. subtilis plus 0.03 mg/L Hg fish group was lower than that of the control group and higher than 0.03 mg/L Hg; The levels of serum immunoglobulin M (IgM) and lysozyme (LZM) decreased, but after supplementation with Se-rich B. subtilis, the levels of LZM and IgM increased; Hg treatment significantly upregulated the mRNA expression of interleukin-1β (IL-1β), interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), and nuclear factor-kB (NF-κB P65), but downregulated the mRNA expression of interleukin-10 (IL-10), transforming growth factor-β (TGF-β) and NF-kappa-B inhibitor alpha (IkBα). However, compared with the Hg group, the Se-rich B. subtilis plus Hg group can significantly increase the mRNA expression levels of IL-1β, IL-8, TNF-α, and NF-κB P65, but reduce the regulation of IL-10, TGF-β, and IkBα expression. Through the analysis of the microbiological, we found that the Hg group was mainly composed of Aeromonas sobria and Aeromonas hydrophila. However, in the Se-rich B. subtilis treatment group, we found that Aeromonas sobria was significantly less than the Hg group. Se-rich B. subtilis improves Hg-induced intestinal microbial changes, alleviates the abundance of Aeromonas, and alleviates the inflammation of the fish. The results of this study show that Se-rich B. subtilis dietary supplements can effectively protect common carp against Hg toxicity.

Transcriptome analysis reveals the mechanism of alkalinity exposure on spleen oxidative stress, inflammation and immune function of Luciobarbus capito

Saline-alkali land is distributed all over the world, and it affects the economic development of fisheries. The alkalinity in water is related to the accumulation of carbonate, so the is generally higher. To understand how alkalinity impacts the immune response in Luciobarbus capito, we performed transcriptomic profiles for spleen, the immune organ of Luciobarbus capito which were underwent alkalinity exposure. Totally there are 47,727,954, 53,987,820 and 51,398,546 high quality clean reads obtained from the control groups, and 46,996,982, 49,650,460 and 45,964,986 clean reads from the alkalinity exposure groups. Among them, 611 genes were differently expressed, including 534 upregulated and 77 down-regulated genes. The identified genes were enriched using databases of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). It was found that differentially expressed genes in Luciobarbus capito spleen tissue were enriched into 14 GO pathways, and differentially expressed genes in Luciobarbus capito spleen were enriched into 25 corresponding KEGG pathways under alkalinity stress. Inflammation and immune function genes and pathways were identified and validated by quantitative real-time RT-PCR. Our results showed that alkalinity exposure leads to inflammation and immunoregulation in spleen of Luciobarbus capito. These results provide new insights for unveiling the biological effects of alkalinity in Luciobarbus capito.

Surfactin reduces particulate matter-induced VCAM-1-dependent monocyte adhesion in human gingival fibroblasts by increasing Nrf2-dependent HO-1 expression

BACKGROUND AND OBJECTIVES

The mechanisms of particulate matter (PM) toxicity involve the generation of ROS and upregulation of proinflammatory molecules. Nrf2 is a multifunctional cytoprotective transcription factor that regulates the expression of various antioxidant, anti-inflammatory, and detoxifying molecules, such as HO-1. As surfactin has potential to induce Nrf2 activation and HO-1 expression, this study aimed to investigate the anti-inflammatory effects of surfactin on PM-exposed human gingival fibroblasts (HGFs) and signaling pathways engaged by surfactin.

MATERIALS AND METHODS

Human gingival fibroblasts were challenged by PM with or without surfactin pretreatment. The expression of Nrf2, HO-1, VCAM-1, and other molecules was determined by western blot, real-time PCR, or ELISA. Human monocytic THP-1 cells labeled with fluorescent reagent were added to HGFs, and the cell adhesion was assessed. ROS generation and NADPH oxidase activity were also measured. The involvement of Nrf2/HO-1 and ROS signaling pathways was investigated by treating HGFs with specific pathway interventions, genetically or pharmacologically. One dose of surfactin was given to mice before PM treatment to explore its in vivo effect on VCAM-1 expression in gingival tissues.

RESULTS

Particulate matter led to VCAM-1-dependent monocyte adhesion in HGFs, which was regulated by PKCα/NADPH oxidase/ROS/STAT1/IL-6 pathway. Surfactin could attenuate monocyte adhesion by disrupting this VCAM-1-dependent pathway. Additionally, surfactin promoted Nrf2-dependent HO-1 expression in HGFs, mitigating VCAM-1 expression. PM-treated mice exhibited the lower expression of IL-6 and VCAM-1 in gingival tissues if they previously received surfactin.

CONCLUSION

Surfactin exerts anti-inflammatory effects against PM-induced inflammatory responses in HGFs by inhibiting VCAM-1-dependent pathway and inducing Nrf2/HO-1 axis.

Bacillus amyloliquefaciens SC06 Induced AKT-FOXO Signaling Pathway-Mediated Autophagy to Alleviate Oxidative Stress in IPEC-J2 Cells

Autophagy is a conserved proteolytic mechanism, which degrades and recycles damaged organs and proteins in cells to resist external stress. Probiotics could induce autophagy; however, its underlying molecular mechanisms remain elusive. Our previous study has found that BaSC06 could alleviate oxidative stress by inducing autophagy in rats. This research aimed to verify whether Bacillus amyloliquefaciens SC06 can induce autophagy to alleviate oxidative stress in IPEC-J2 cells, as well as explore its mechanisms. IPEC-J2 cells were first pretreated with 10⁸ CFU/mL BaSC06, and then were induced to oxidative stress by the optimal dose of diquat. The results showed that BaSC06 significantly triggered autophagy, indicated by the up-regulation of LC3 and Beclin1 along with downregulation of p62 in IPEC-J2 cells. Further analysis revealed that BaSC06 inhibited the AKT-FOXO signaling pathway by inhibiting the expression of p-AKT and p-FOXO and inducing the expression of SIRT1, resulting in increasing the transcriptional activity of FOXO3 and gene expression of the ATG5-ATG12 complex to induce autophagy, which alleviated oxidative stress and apoptosis. Taken together, BaSC06 can induce AKT-FOXO-mediated autophagy to alleviate oxidative stress-induced apoptosis and cell damage, thus providing novel theoretical support for probiotics in the prevention and treatment of oxidative damage.

Alleviation of the Adverse Effect of Dietary Carbohydrate by Supplementation of Myo-Inositol to the Diet of Nile Tilapia (Oreochromis niloticus)

This study investigated the effect of dietary myo-inositol (MI) on alleviating the adverse effect of the high carbohydrate diet in Nile tilapia (Oreochromis niloticus). Six diets contained either low carbohydrate (LC 30%) or high carbohydrate (HC 45%) with three levels of MI supplementation (0, 400 and 1200 mg/kg diet) to each level of the carbohydrate diet. After an 8-week trial, the fish fed 400 mg/kg MI under HC levels had the highest weight gain and fatness, but the fish fed 1200 mg/kg MI had the lowest hepatosomatic index, visceral index and crude lipid in the HC group. The diet of 1200 mg/kg MI significantly decreased triglyceride content in the serum and liver compared with those fed the MI supplemented diets regardless of carbohydrate levels. Dietary MI decreased triglyceride accumulation in the liver irrespective of carbohydrate levels. The content of malondialdehyde decreased with increasing dietary MI at both carbohydrate levels. Fish fed 1200 mg/kg MI had the highest glutathione peroxidase, superoxide dismutase, aspartate aminotransferase and glutamic-pyruvic transaminase activities. The HC diet increased the mRNA expression of key genes involved in lipid synthesis (DGAT, SREBP, FAS) in the fish fed the diet without MI supplementation. Dietary MI significantly under expressed fatty acid synthetase in fish fed the HC diets. Moreover, the mRNA expression of genes related to lipid catabolism (CPT, ATGL, PPAR-α) was significantly up-regulated with the increase of dietary MI levels despite dietary carbohydrate levels. The gene expressions of gluconeogenesis, glycolysis and MI biosynthesis were significantly down-regulated, while the expression of the pentose phosphate pathway was up-regulated with the increase of MI levels. This study indicates that HC diets can interrupt normal lipid metabolism and tend to form a fatty liver in fish. Dietary MI supplement can alleviate lipid accumulation in the liver by diverging some glucose metabolism into the pentose phosphate pathway and enhance the antioxidant capacity in O. niloticus.