Being sessile organisms, plants are frequently exposed to various environmental stresses that cause several physiological disorders and even death. Oxidative stress is one of the common consequences of abiotic stress in plants, which is caused by excess generation of reactive oxygen species (ROS). Sometimes ROS production exceeds the capacity of antioxidant defense systems, which leads to oxidative stress. In line with ROS, plants also produce a high amount of methylglyoxal (MG), which is an α-oxoaldehyde compound, highly reactive, cytotoxic, and produced via different enzymatic and non-enzymatic reactions. This MG can impair cells or cell components and can even destroy DNA or cause mutation. Under stress conditions, MG concentration in plants can be increased 2- to 6-fold compared with normal conditions depending on the plant species. However, plants have a system developed to detoxify this MG consisting of two major enzymes: glyoxalase I (Gly I) and glyoxalase II (Gly II), and hence known as the glyoxalase system. Recently, a novel glyoxalase enzyme, named glyoxalase III (Gly III), has been detected in plants, providing a shorter pathway for MG detoxification, which is also a signpost in the research of abiotic stress tolerance. Glutathione (GSH) acts as a co-factor for this system. Therefore, this system not only detoxifies MG but also plays a role in maintaining GSH homeostasis and subsequent ROS detoxification. Upregulation of both Gly I and Gly II as well as their overexpression in plant species showed enhanced tolerance to various abiotic stresses including salinity, drought, metal toxicity, and extreme temperature. In the past few decades, a considerable amount of reports have indicated that both antioxidant defense and glyoxalase systems have strong interactions in conferring abiotic stress tolerance in plants through the detoxification of ROS and MG. In this review, we will focus on the mechanisms of these interactions and the coordinated action of these systems towards stress tolerance.

Facultative halophyte Kandelia obovata plants were exposed to mild (1.5% NaCl) and severe (3% NaCl) salt stress with or without sodium nitroprusside (SNP; 100 µM; a NO donor), hemoglobin (Hb, 100 µM; a NO scavenger), or Nω-nitro-L-arginine methyl ester (L-NAME, 100 µM; a NO synthase inhibitor). The plants were significantly affected by severe salt stress. They showed decreases in seedling growth, stomatal conductance, intercellular CO₂ concentration, SPAD value, photosynthetic rate, transpiration rate, water use efficiency, and disrupted antioxidant defense systems, overproduction of reactive oxygen species, and visible oxidative damage. Salt stress also induced ion toxicity and disrupted nutrient homeostasis, as indicated by elevated leaf and root Na⁺ contents, decreased K⁺ contents, lower K⁺/Na⁺ ratios, and decreased Ca contents while increasing osmolyte (proline) levels. Treatment of salt-stressed plants with SNP increased endogenous NO levels, reduced ion toxicity, and improved nutrient homeostasis while further increasing Pro levels to maintain osmotic balance. SNP treatment also improved gas exchange parameters and enhanced antioxidant enzymes’ activities (catalase, ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase). Treatment with Hb and l-NAME reversed these beneficial SNP effects and exacerbated salt damage, confirming that SNP promoted stress recovery and improved plant growth under salt stress.

Cirsium brevicaule A. GRAY is a wild perennial herb, and its roots (CbR) have traditionally been used as both food and medicine on the Japanese islands of Okinawa and Amami. The present study evaluated the antiadipogenic effect of CbR using mouse embryonic fibroblast cell line 3T3-L1 from JCRB cell bank. Dried CbR powder was serially extracted with solvents of various polarities, and these crude extracts were tested for antiadipogenic activity. Treatment with the methanol extract of CbR showed a significant suppression of lipid accumulation in 3T3-L1 cells. Methanol extract of CbR was then fractionated and subjected to further activity analyses. The phenylpropanoid glycosidic molecule syringin was identified as an active compound. Syringin dose dependently suppressed lipid accumulation of 3T3-L1 cells without cytotoxicity, and significantly reduced the expressions of peroxisome proliferator-activated receptor gamma, the master regulator of adipogenesis, and other differentiation markers. It was demonstrated that syringin effectively enhanced the phosphorylation of the AMP-activated protein kinase and acetyl-CoA carboxylase. These results indicate that syringin attenuates adipocyte differentiation, adipogenesis, and promotes lipid metabolism; thus, syringin may potentially serve as a therapeutic candidate for treatment of obesity.

Ivy gourd (Coccinia grandis L. Voigt) is a tropical plant widely distributed throughout Asia, Africa, and the Pacific Islands. The anti-obesity property of this plant has been claimed but still remains to be scientifically proven. We therefore investigated the effects of ivy gourd leaf, stem, and root on adipocyte differentiation by employing cell culture model. Dried roots, stems, and leaves of ivy gourd were separately extracted with ethanol. Each extract was then applied to 3T3-L1 pre-adipocytes upon induction with a mixture of insulin, 3-isobutyl-1-methylxanthine, and dexamethasone, for anti-adipogenesis assay. The active extract was further fractionated by a sequential solvent partitioning method, and the resulting fractions were examined for their abilities to inhibit adipogenesis in 3T3-L1 cells. Differences in the expression of adipogenesis-related genes between the treated and untreated cells were determined from their mRNA and protein levels. Of the three ivy gourd extracts, the root extract exhibited an anti-adipogenic effect. It significantly reduced intracellular fat accumulation during the early stages of adipocyte differentiation. Together with the suppression of differentiation, expression of the genes encoding PPARγ, C/EBPα, adiponectin, and GLUT4 were down-regulated. Hexane-soluble fraction of the root extract also inhibited adipocyte differentiation and decreased the mRNA levels of various adipogenic genes in the differentiating cells. This is the first study to demonstrate that ivy gourd root may prevent obesity based mainly on the ability of its active constituent(s) to suppress adipocyte differentiation in vitro. Such an inhibitory effect is mediated by at least down-regulating the expression of PPARγ-the key transcription factor of adipogenesis in pre-adipocytes during their early differentiation processes.

Background: Various flavonoids obtained from the genus Cirsium have been reported to exhibit beneficial effects on health. The present study evaluated the antiobesity effects of Cirsium brevicaule A. GRAY leaf (CL) by using 3T3-L1 cells and C57BL/6 mice that were fed a high-fat diet (HFD). Methods: Dried CL powder was serially extracted with solvents of various polarities, and these extracts were tested for antiadipogenic activity using 3T3-L1 adipocytes. Mice were fed experimental HFD supplemented with dried CL powder for 4 wk. Lipid levels and mRNA levels of genes related to lipid metabolism were determined in 3T3-L1 adipocytes and the white adipose tissue (WAT) and liver of mice fed on a HFD. Results: Treatment of 3T3-L1 adipocytes with a hexane extract of CL significantly reduced cellular lipid accumulation and expression of the fatty acid synthase (FASN) gene. Dietary CL reduced the serum levels of non-esterified fatty acids in HFD-fed mice. Significant decreases in subcutaneous WAT weight and associated FASN gene expression were observed in the mice fed the experimental CL diet. Dietary CL also reduced the hepatic lipid and serum levels of a hepatopathic indicator in the HFD-fed mice. A significant reduction in mRNA levels of FASN and HMG-CoA reductase were observed in the livers of the CL-diet group. Dietary CL, on the other hand, increased in the hepatic mRNA levels of genes related to β-oxidation, namely peroxisome proliferator-activated receptor α, calnitine palmitoyltrasferase 1A, and uncoupling protein 2. Expression of the insulin receptor gene was also significantly increased in the livers of mice-fed the CL diet. Conclusions: The present study therefore demonstrated that CL suppresses lipid accumulation in the WAT and liver partly through inhibiting mRNA levels of FASN gene and enhancing the lipolysis-related gene expression.

Background: Various mushrooms have been used in folk medicine for the treatment of lifestyle diseases in eastern countries, and several compounds that modulate the immune system, lower blood lipid levels, and inhibit tumor and viral action have been isolated. The fruiting body of Panellus serotinus (Mukitake) is recognized in Japan as one of the most delicious edible mushrooms, and previous studies have demonstrated that the dietary intake of powdered whole Mukitake or Mukitake extracts prevents the development of non-alcoholic fatty liver disease (NAFLD) in leptin-resistant db/db mice. In the present study, we evaluated the effect of the Mukitake diet on the pathogenesis of metabolic disorders in leptin-deficient ob/ob mice. Results: After 4 weeks of feeding, hepatomegaly, hepatic lipid accumulation, and elevated hepatic injury markers in the serum were markedly alleviated in Mukitake-fed ob/ob mice compared with control mice. Moreover, the mild hyperlipidemia in control ob/ob mice was attenuated and the elevated atherogenic index was reduced in Mukitake-fed ob/ob mice. These effects were partly attributable to the suppression of hepatic lipogenic enzyme activity due to the Mukitake diet. Conclusion: The current results showed that Mukitake supplementation is beneficial for the alleviation of NAFLD and dyslipidemia in obese, diabetic ob/ob mice.