Melatonin alleviates lipopolysaccharide-induced placental cellular stress response in mice

Abstract: Melatonin protects mice from lipopolysaccharide (LPS)‐induced fetal death and intra‐uterine growth retardation. Nevertheless, its molecular mechanism remains obscure. In the present study, we investigated the effects of melatonin on LPS‐induced cellular stress in placenta. Pregnant mice were given with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before and 150 min after LPS (300 μg/kg, i.p.) on gestational day 15. Oxidative stress, endoplasmic reticulum (ER) stress, hypoxic stress, and heat stress in placenta were analyzed at 4 hr after LPS. As expected, maternal LPS administration resulted in placental glutathione (GSH) depletion and up‐regulated the expression of placental antioxidative enzymes. In addition, LPS significantly increased the level of inducible nitric oxide synthase (iNOS) and enhanced the intensity of placental 3‐nitrotyrosine residues. An ER stress, as determined by a decreased GRP78 expression, an obvious eIF2α and JNK phosphorylation, and an increased CHOP expression, were observed in placenta of pregnant mice injected with LPS. In addition, LPS significantly increased mRNA level of placental HIF‐1α, VEGF, and ET‐1, the markers of hypoxic stress. Heme oxygenase (HO)‐1, a marker of heat stress, was also up‐regulated in placenta of LPS‐treated pregnant mice. Interestingly, LPS‐induced placental oxidative stress, hypoxic stress, and ER stress were significantly alleviated when pregnant mice were given with melatonin, whereas melatonin had little effect on LPS‐evoked placental HO‐1 expression. In conclusion, maternally administered melatonin alleviates LPS‐induced cellular stress in the placenta. Melatonin may be useful as pharmacological agents to protect the fetuses against LPS‐induced intra‐uterine fetal death and intra‐uterine growth restriction.     

Melatonin enhances the occurrence of autophagy induced by oxidative stress in Arabidopsis seedlings

The beneficial effect that melatonin has against mitochondrial dysfunctioning seems to be linked to mitophagy. Roles for melatonin have been demonstrated in promoting health and preventing disease, as well as activating the process of autophagy in general. However, no reports have been made about how the application of melatonin regulates that process when plants are exposed to oxidative stress. We investigated the influence of different concentrations of melatonin (0.0, 0.5, 5.0, 10.0, or 50.0 μm ) on autophagy under methyl viologen (MV)‐induced oxidative stress. Arabidopsis seedlings that were pretreated with 5 or 10 μm melatonin underwent relatively strong induction of autophagy, as evidenced by the number of monodansylcadaverine (MDC)‐stained autophagosomes in root samples. Pretreatment with 10 μm melatonin also alleviated MV‐induced photo‐oxidation damage and significantly reduced the accumulation of oxidized proteins. Those responses might have been due to the strong upregulation of genes that involved in AtATG8‐PE conjugation pathway, which enhanced the capacity for autophagy. Histochemical staining revealed that both and H₂O₂ were highly accumulated upon MV exposure, although the response did not differ significantly between control and melatonin‐pretreated seedlings. By contrast, exogenous melatonin upregulated the expression of two genes for H₂O₂‐scavenging enzymes, that is, AtAPX1 and AtCATs. The activation of autophagy by melatonin without an alteration in ROS production may be part of a survival mechanism that is enhanced by melatonin after cellular damage. Therefore, it represents a second level of defense to remove damaged proteins when antioxidant activities are compromised.     

Melatonin induction and its role in high light stress tolerance in Arabidopsis thaliana

In plants, melatonin is a potent bioactive molecule involved in the response against various biotic and abiotic stresses. However, little is known of its defensive role against high light (HL ) stress. In this study, we found that melatonin was transiently induced in response to HL stress in Arabidopsis thaliana with a simultaneous increase in the expression of melatonin biosynthetic genes, including serotonin N ‐acetyltransferase1 (SNAT 1 ). Transient induction of melatonin was also observed in the flu mutant, a singlet oxygen (¹O₂)‐producing mutant, upon light exposure, suggestive of melatonin induction by chloroplastidic ¹O₂ against HL stress. An Arabidopsis snat1 mutant was devoid of melatonin induction upon HL stress, resulting in high susceptibility to HL stress. Exogenous melatonin treatment mitigated damage caused by HL stress in the snat1 mutant by reducing O₂^? production and increasing the expression of various ROS ‐responsive genes. In analogy, an Arabidopsis SNAT 1 ‐overexpressing line showed increased tolerance of HL stress concomitant with a reduction in malondialdehyde and ion leakage. A complementation line expressing an Arabidopsis SNAT 1 genomic fragment in the snat1 mutant completely restored HL stress susceptibility in the snat1 mutant to levels comparable to that of wild‐type Col‐0 plants. The results of the analysis of several Arabidopsis genetic lines reveal for the first time at the genetic level that melatonin is involved in conferring HL stress tolerance in plants.     

Melatonin alleviates Echis carinatus venom‐induced toxicities by modulating inflammatory mediators and oxidative stress

Viper bites cause high morbidity and mortality worldwide and regarded as a neglected tropical disease affecting a large healthy population. Classical antivenom therapy has appreciably reduced the snakebite mortality rate; it apparently fails to tackle viper venom‐induced local manifestations that persist even after the administration of antivenom. Recently, viper venom‐induced oxidative stress and vital organ damage is deemed as yet another reason for concern; these are considered as postmedicated complications of viper bite. Thus, treating viper bite has become a challenge demanding new treatment strategies, auxiliary to antivenin therapy. In the last decade, several studies have reported the use of plant products and clinically approved drugs to neutralize venom‐induced pharmacology. However, very few attempts were undertaken to study oxidative stress and vital organ damage. Based on this background, the present study evaluated the protective efficacy of melatonin in Echis carinatus (EC) venom‐induced tissue necrosis, oxidative stress, and organ toxicity. The results demonstrated that melatonin efficiently alleviated EC venom‐induced hemorrhage and myonecrosis. It also mitigated the altered levels of inflammatory mediators and oxidative stress markers of blood components in liver and kidney homogenates, and documented renal and hepatoprotective action of melatonin. The histopathology of skin, muscle, liver, and kidney tissues further substantiated the overall protection offered by melatonin against viper bite toxicities. Besides the inability of antivenoms to block local effects and the fact that melatonin is already a widely used drug promulgating a multitude of therapeutic functionalities, its use in viper bite management is of high interest and should be seriously considered.     

Melatonin prevents obesity through modulation of gut microbiota in mice

Excess weight and obesity are severe public health threats worldwide. Recent evidence demonstrates that gut microbiota dysbiosis contributes to obesity and its comorbidities. The body weight‐reducing and energy balancing effects of melatonin have been reported in several studies, but to date, no investigations toward examining whether the beneficial effects of melatonin are associated with gut microbiota have been carried out. In this study, we show that melatonin reduces body weight, liver steatosis, and low‐grade inflammation as well as improving insulin resistance in high fat diet (HFD)‐fed mice. High‐throughput pyrosequencing of the 16S rRNA demonstrated that melatonin treatment significantly changed the composition of the gut microbiota in mice fed an HFD. The richness and diversity of gut microbiota were notably decreased by melatonin. HFD feeding altered 69 operational taxonomic units (OTUs) compare with a normal chow diet (NCD) group, and melatonin supplementation reversed 14 OTUs to the same configuration than those present in the NCD group, thereby impacting various functions, in particular through its ability to decrease the Firmicutes‐to‐Bacteroidetes ratio and increase the abundance of mucin‐degrading bacteria Akkermansia, which is associated with healthy mucosa. Taken together, our results suggest that melatonin may be used as a probiotic agent to reverse HFD‐induced gut microbiota dysbiosis and help us to gain a better understanding of the mechanisms governing the various melatonin beneficial effects.     

Melatonin alleviates cadmium-induced cellular stress and germ cell apoptosis in testes

Increasing evidence demonstrates that melatonin has an anti-apoptotic effect in somatic cells. However, whether melatonin can protect against germ cell apoptosis remains obscure. Cadmium (Cd) is a testicular toxicant and induces germ cell apoptosis. In this study, we investigated the effects of melatonin on Cd-evoked germ cell apoptosis in testes. Male ICR mice were intraperitoneally (i.p.) injected with melatonin (5 mg/kg) every 8 hr, beginning at 8 hr before CdCl(2) (2.0 mg/kg, i.p.). As expected, acute Cd exposure resulted in germ cell apoptosis in testes, as determined by terminal dUTP nick-end labeling (TUNEL) staining. Melatonin significantly alleviated Cd-induced testicular germ cell apoptosis. An additional experiment showed that spliced form of XBP-1, the target of the IRE-1 pathway, was significantly increased in testes of mice injected with CdCl(2). GRP78, an endoplasmic reticulum (ER) chaperone, and CHOP, a downstream target of the PERK pathway, were upregulated in testes of Cd-treated mice. In addition, acute Cd exposure significantly increased testicular eIF2α and JNK phosphorylation, indicating that the unfolded protein response (UPR) pathway was activated by CdCl(2). Interestingly, melatonin almost completely inhibited Cd-induced ER stress and the UPR in testes. In addition, melatonin obviously attenuated Cd-induced heme oxygenase (HO)-1 expression and protein nitration in testes. Taken together, these results suggest that melatonin alleviates Cd-induced cellular stress and germ cell apoptosis in testes. Melatonin may be useful as pharmacological agents to protect against Cd-induced testicular toxicity.     

Role of melatonin in sleep deprivation‐induced intestinal barrier dysfunction in mice

Intestinal diseases caused by sleep deprivation (SD) are severe public health threats worldwide. This study focuses on the effect of melatonin on intestinal mucosal injury and microbiota dysbiosis in sleep‐deprived mice. Mice subjected to SD had significantly elevated norepinephrine levels and decreased melatonin content in plasma. Consistent with the decrease in melatonin levels, we observed a decrease of antioxidant ability, down‐regulation of anti‐inflammatory cytokines and up‐regulation of pro‐inflammatory cytokines in sleep‐deprived mice, which resulted in colonic mucosal injury, including a reduced number of goblet cells, proliferating cell nuclear antigen‐positive cells, expression of MUC2 and tight junction proteins and elevated expression of ATG5, Beclin1, p‐P65 and p‐IκB. High‐throughput pyrosequencing of 16S rRNA demonstrated that the diversity and richness of the colonic microbiota were decreased in sleep‐deprived mice, especially in probiotics, including Akkermansia, Bacteroides and Faecalibacterium. However, the pathogen Aeromonas was markedly increased. By contrast, supplementation with 20 and 40 mg/kg melatonin reversed these SD‐induced changes and improved the mucosal injury and dysbiosis of the microbiota in the colon. Our results suggest that the effect of SD on intestinal barrier dysfunction might be an outcome of melatonin suppression rather than a loss of sleep per se. SD‐induced intestinal barrier dysfunction involved the suppression of melatonin production and activation of the NF‐κB pathway by oxidative stress.     

The differences between fecal microbiota and intestinal fluid microbiota in colon polyps: An observational study

Generally, intestinal microbiota can be classified into intestinal cavity microbiota and mucosal microbiota, among which, the former is the default type. This study aimed to identify the differences between fecal microbiota and intestinal fluid microbiota in colon polys.This study enrolled patients with colon polys who met the Rome-III criteria to carry out 16s rDNA gene sequencing. Then, both fresh feces as well as intestinal fluid was sampled. Thereafter, α/β diversities, together with the heterogeneities with regard to microbial function and structure were assessed among those intestinal fluid and fresh feces samples collected.According to bioinformatics analysis, difference in α-diversity was not statistically significant between intestinal fluid microbiota and fecal microbiota among patients with colorectal polyps (CPs). Non-metric multidimensional scaling analysis of β-diversity revealed that differences were of statistical significance between both groups. In addition, linear discriminant analysis effect size analysis displayed great heterogeneities in intestinal microbiota of both groups, including Firmicutes, Clostridia, and Phascolarctobacterium. At the phylum level, difference (P = .016) in Spirochaetes was statistically significant between the intestinal fluid group and fecal group. At the family level, differences in Bacteroidaceae, Micrococcaceae, F16, Spirocheatacae, Enterobacteriaceae, Cardiobacteriaceae, Turkish Spirobacteriaceae, Bifidobacteriaceae, and Dethiosulfovibrionaceae were statistically significant between the 2 groups. At the genus level, there were statistical differences between the 2 groups in terms of Bacteroidetes, Rothia, Actinobacillus, F16, Treponema, Oscillospira, Turicibacter, Sharpea, Heamophilus, Veillonella, and Cardiobacterium.There are statistical differences in the composition between intestinal microbiota and fecal microbiota in CP patients, both of which are equally important and indispensable for analyzing the intestinal microbiota in CP patients.     

Melatonin reduces oxidative stress in erythrocytes and plasma of senescence-accelerated mice

It has been suggested that oxidative stress is a feature of aging. The goal of the present study was to assess the oxidant effects related to aging and the protective role of exogenous melatonin in senescence-accelerated mice (SAMP8). Two groups of SAMP8 mice (males and females) were compared with their respective control groups of SAMR1 mice (senescence-resistant inbred strain) to determine their oxidative status without melatonin treatment. Four other groups of the same characteristics were treated with melatonin (10 mg/kg/day) in their drinking water. The melatonin concentration in the feeding bottles was titrated according to water consumption and body weight (i.e. 0.06 mg/mL for 30 g of body weight and 5 mL/day of water consumption). The treatment began when animals were 1-month old and continued for 9 months. When mice were 10-month old, they were anesthetized and blood was obtained. Plasma and erythrocytes were processed to examine oxidative stress markers: reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST), thiobarbituric acid reactive substances (TBARS), and hemolysis. The results showed greater oxidative stress in SAMP8 than in SAMR1, largely because of a decrease in GSH levels and to an increase in GSSG and TBARS with the subsequent induction of the antioxidant enzymes GPX and GR. Melatonin, as an antioxidant molecule, improved the glutathione-related parameters, prevented the induction of GPX in senescent groups, and promoted a decrease in SOD and TBARS in almost all the groups.     

Akkermansia muciniphila strain ATCC BAA-835 does not promote short-term intestinal inflammation in gnotobiotic interleukin-10-deficient mice

Akkermansia muciniphila is a common member of the intestinal microbiota of healthy human individuals. Its abundance is negatively associated with inflammatory bowel disease and metabolic disorders and the oral administration of A. muciniphila improves the symptoms of metabolic disease in mice. Therefore, A. muciniphila is a promising candidate for the treatment of type-2 diabetes and obesity. However, some studies using animal models of intestinal inflammation reported that A. muciniphila may exacerbate gut inflammation. Because of these contradictory reports the present study aimed to clarify the role of A. muciniphila in the development of intestinal inflammation and the conditions promoting it. For this purpose, the short-term colitogenic potential of A. muciniphila strain ATCC BAA-835 was investigated in colitis-prone, gnotobiotic IL-10-deficient (Il10^-/-) mice. Il10^-/- mice mono-associated with A. muciniphila showed no signs of intestinal inflammation based on body-weight change, histopathological scoring and inflammatory markers. Additional association of the mice with the colitogenic Escherichia coli strain NC101 led to cecal but not colonic inflammation. However, the severity of the inflammation did not exceed that observed in mice mono-associated with E. coli NC101. Il10^-/- mice colonized with a simplified human intestinal microbiota showed increased histopathology, but no increase in inflammatory markers. Furthermore, co-colonization with A. muciniphila did not modify histopathology. The turnover of intestinal mucus was similar in all groups despite the mucus-degrading property of A. muciniphila. Overall, the data do not support a short-term pro-inflammatory effect of A. muciniphila strain ATCC BAA-835 in the Il10^-/- mouse model for inflammatory bowel disease.     

Altered enteric microbiota ecology in interleukin 10-deficient mice during development and progression of intestinal inflammation

Inflammatory bowel diseases (IBD) result from dysregulated immune responses toward microbial and perhaps other luminal antigens in a genetically susceptible host, and are associated with altered composition and diversity of the intestinal microbiota. The interleukin 10-deficient (IL-10^−/−) mouse has been widely used to model human IBD; however the specific alterations that occur in the intestinal microbiota of this mouse model during the onset of colonic inflammation have not yet been defined. The aim of our study was to define the changes in diversity and composition that occur in the intestinal microbiota of IL-10^−/− mice during the onset and progression of colonic inflammation. We used high throughput sequencing of the 16S rRNA gene to characterize the diversity and composition of formerly germ-free, wild-type and IL-10^−/− mice associated with the same intestinal microbiota over time. Following two weeks of colonization with a specific pathogen-free (SPF) microbiota we observed a significant increase in the diversity and richness of the intestinal microbiota of wild-type mice. In contrast, a progressive decrease in diversity and richness was observed at three and four weeks in IL-10^−/− mice. This decrease in diversity and richness was mirrored by an increase in Proteobacteria and Escherichia coli in IL-10^−/− mice. An increase in E. coli was also observed in conventionally raised IL-10^−/− mice at the point of colonic inflammation. Our data reports the sequential changes in diversity and composition of the intestinal microbiota in an immune-mediated mouse model that may help provide insights into the primary vs. secondary role of dysbiosis in human IBD patients.     

Melatonin action in Plasmodium infection: Searching for molecules that modulate the asexual cycle as a strategy to impair the parasite cycle

Half of the world's population lives in countries at risk of malaria infection, which results in approximately 450,000 deaths annually. Malaria parasites infect erythrocytes in a coordinated manner, with cycle durations in multiples of 24 hours, which reflects a behavior consistent with the host's circadian cycle. Interference in cycle coordination can help the immune system to naturally fight infection. Consequently, there is a search for new drugs that interfere with the cycle duration for combined treatment with conventional antimalarials. Melatonin appears to be a key host hormone responsible for regulating circadian behavior in the parasite cycle. In addition to host factors, there are still unknown factors intrinsic to the parasite that control the cycle duration. In this review, we present a series of reports of indole compounds and melatonin derivatives with antimalarial activity that were tested on several species of Plasmodium to evaluate the cytotoxicity to parasites and human cells, in addition to the ability to interfere with the development of the erythrocytic cycle. Most of the reported compounds had an IC50 value in the low micromolar range, without any toxicity to human cells. Triptosil, an indole derivative of melatonin, was able to inhibit the effect of melatonin in vitro without causing changes to the parasitemia. The wide variety of tested compounds indicates that it is possible to develop a compound capable of safely eliminating parasites from the host and interfering with the life cycle, which is promising for the development of new combined therapies against malaria.     

Melatonin regulates carbohydrate metabolism and defenses against Pseudomonas syringae pv. tomato DC3000 infection in Arabidopsis thaliana

Melatonin has been reported to promote plant growth and development. Our experiments with Arabidopsis thaliana showed that exogenous applications of this molecule mediated invertase inhibitor (C/VIF)‐regulated invertase activity and enhanced sucrose metabolism. Hexoses were accumulated in response to elevated activities by cell wall invertase (CWI) and vacuolar invertase (VI). Analyses of sugar metabolism‐related genes revealed differential expression during plant development that was modulated by melatonin. In particular, C/VIF1 and C/VIF2 were strongly down‐regulated by exogenous feeding. We also found the elevated CWI activity in melatonin‐treated Arabidopsis improved the factors (cellulose, xylose, and galactose) for cell wall reinforcement and callose deposition during Pseudomonas syringae pv. tomato DC3000 infection, therefore, partially induced the pathogen resistance. However, CWI did not involve in salicylic acid (SA)‐regulated defense pathway. Taken together, this study reveals that melatonin plays an important role in invertase‐related carbohydrate metabolism, plant growth, and pathogen defense.     

Melatonin promotes seed germination under high salinity by regulating antioxidant systems,ABA and GA4 interaction in cucumber (Cucumis sativus L.)

Although previous studies have found that melatonin can promote seed germination, the mechanisms involved in perceiving and signaling melatonin remain poorly understood. In this study, it was found that melatonin was synthesized during cucumber seed germination with a peak in melatonin levels occurring 14 hr into germination. This is indicative of a correlation between melatonin synthesis and seed germination. Meanwhile, seeds pretreated with exogenous melatonin (1 μm ) showed enhanced germination rates under 150 mm NaCl stress compared to water‐pretreated seeds under salinity stress. There are two apparent mechanisms by which melatonin alleviated salinity‐induced inhibition of seed germination. Exogenous melatonin decreased oxidative damage induced by NaCl stress by enhancing gene expression of antioxidants. Under NaCl stress, compared to untreated control, the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly increased by approximately 1.3–5.0‐fold, with a concomitant 1.4–2.0‐fold increase of CsCu‐ZnSOD, CsFe‐ZnSOD, CsCAT, and CsPOD in melatonin‐pretreated seeds. Melatonin also alleviated salinity stress by affecting abscisic acid (ABA) and gibberellin acid (GA) biosynthesis and catabolism during seed germination. Compared to NaCl treatment, melatonin significantly up‐regulated ABA catabolism genes (e.g., CsCYP707A1 and CsCYP707A2, 3.5 and 105‐fold higher than NaCl treatment at 16 hr, respectively) and down‐regulated ABA biosynthesis genes (e.g., CsNECD2, 0.29‐fold of CK2 at 16 hr), resulting in a rapid decrease of ABA content during the early stage of germination. At the same time, melatonin positively up‐regulated GA biosynthesis genes (e.g., GA20ox and GA3ox, 2.3 and 3.9‐fold higher than NaCl treatment at 0 and 12 hr, respectively), contributing to a significant increase of GA (especially GA₄) content. In this study, we provide new evidence suggesting that melatonin alleviates the inhibitory effects of NaCl stress on germination mainly by regulating the biosynthesis and catabolism of ABA and GA₄.     

Melatonin ameliorates ischemic-like injury-evoked nitrosative stress: Involvement of HtrA2/PED pathways in endothelial cells

Peroxynitrite contributes to diverse cellular stresses in the pathogenesis of ischemic complications. Here, we investigate the downstream effector signaling elements of nitrosative stress which regulate ischemia-like cell death in endothelial cells and protective effect of melatonin. When the mitochondrial membrane potential (ΔΨm) of oxygen-glucose deprivation (OGD)-treated cells was assessed using the fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol -carbocyanine iodide, we observed spontaneous changes in peroxynitrite formation. Concomitantly, western blot and confocal microscopy analyses indicated that prolonged OGD exposure initiates the release of mitochondrial HtrA2 and dramatically decreases phosphoprotein enriched in astrocytes (PED or PEA-15) protein levels. Consistently, cultured endothelial cells treated with peroxynitrite (1-50 μm) exhibited a concentration-dependent release of mitochondrial HtrA2 and concomitant PED degradation in vitro. Notably, HtrA2 activation coincided with increased nitrotyrosine immunoreactivity in microvessels of rats following microsphere embolism. Additionally, the protective effect of PED overexpression in OGD-induced apoptosis was abolished by transfection with the PED(S104A/S116A) mutant. Furthermore, the effect of melatonin, an potential antioxidant, on endothelial apoptotic cascade was examined in OGD-evoked nitrosative stress. Our data showed that the application of melatonin provided significant protection against OGD-induced peroxynitrite formation and mitochondrial HtrA2 release, accompanied with a decrease in degradation PED and x-linked inhibitor of apoptosis protein, which is associated with activation of the caspase cascade. Taken together, the protective effect of melatonin is likely mediated, in part, by inhibition of peroxynitrate-mediated nitrosative stress, which in turn relieves imbalance of mitochondrial HtrA2-PED signaling and endothelial cell death.     

Plant mitochondria synthesize melatonin and enhance the tolerance of plants to drought stress

Synthesis of melatonin in mitochondria was reported in animals. However, there is no report on whether plant mitochondria also produce melatonin. Herein, we show that plant mitochondria are a major site for melatonin synthesis. In an in vitro study, isolated apple mitochondria had the capacity to generate melatonin. Subcellular localization analysis documented that an apple SNAT isoform, MzSNAT5, was localized in the mitochondria of both Arabidopsis protoplasts and apple callus cells. The kinetic analysis revealed that the recombinant MzSNAT5 protein exhibited high enzymatic activity to catalyze serotonin to N‐acetylserotonin with the K_m and V_max of 55 μmol/L and 0.909 pmol/min/mg protein at 35°C, respectively; this pathway functioned over a wide range of temperatures from 5 to 75°C. In an in vivo study, MzSNAT5 was drought inducible. The transgenic Arabidopsis ectopically expressing MzSNAT5 elevated the melatonin level and, hence, enhanced drought tolerance. The mechanistic study indicated that the ectopically expressing MzSNAT5 allows plant mitochondria to increase melatonin synthesis. As a potent free radical scavenger, melatonin reduces the oxidative stress caused by the elevated reactive oxygen species which are generated under drought stress in plants. Our findings provide evidence that engineered melatonin‐enriched plants exhibit enhanced oxidative tolerance.     

Effects of psychological stress on small intestinal motility and bacteria and mucosa in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and bacteria and mucosa in mice, and to explore the relationship between small intestinal dysfunction and small intestinal motility and bacteria and mucosa under psychological stress. METHODS: Sixty mice were randomly divided into psychological stress group and control group. Each group were subdivided into small intestinal motility group (n= 10), bacteria group (n = 10), and D-xylose administered to stomach group (n= 10). An animal model with psychological stress was established housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. The proximal small intestine was harvested under sterile condition and processed for quantitation for aerobes (Escherichia coli) and anaerobes (Lactobacilli). The quantitation of bacteria was expressed as Iog10(colony forming units/g). D-xylose levels in plasma were measured for estimating trie damage of small intestinal mucosa. RESULTS: Small intestinal transit was inhibited (39.80±9.50% vs 58.79±11.47%,P<0.01) in mice after psychological stress, compared with the controls. Psychological stress resulted in quantitative alterations in the aerobes (E.coli). There was an increase in the number of E coli in the proximal small intestinal flora (1.78±0.30 log10(CFU/g) vs 1.37±0.21 log10(CFU/g), P<0.01), and there was decrease in relative proportion of Lactobacilli and E.coli of stressed mice (0.53±0.63 vs 1.14±1.07,P<0.05), while there was no significant difference in the anaerobes (Lactobacilli) between the two groups (2.31±0.70 log10 (CFU/g) vs 2.44±0.37 log10(CFU/g), P>0.05). D-xylose concentrations in plasma in psychological stress mice were significantly higher than those in the control group (2.90±0.89 mmol/L vs 0.97±0.33 mmol/L, P<0.01). CONCLUSION: Small intestinal dysfunction under psychological stress may be related to the small intestinal motility disorder and dysbacteriosis and the damage of mucosa probably caused by psychological stress.