A comprehensive review of Siraitia grosvenorii (Swingle) C. Jeffrey: chemical composition, pharmacology, toxicology, status of resources development, and applications

Siraitia grosvenorii (Swingle) C. Jeffrey (S. grosvenorii), a perennial indigenous liana from the Cucurbitaceae family, has historically played a significant role in southern China's traditional remedies for various ailments. Its dual classification by the Chinese Ministry of Health for both medicinal and food utility underscores its has the potential of versatile applications. Recent research has shed light on the chemical composition, pharmacological effects, and toxicity of S. grosvenorii. Its active ingredients include triterpenoids, flavonoids, amino acids, volatile oils, polysaccharides, minerals, vitamins, and other microconstituents. Apart from being a natural sweetener, S. grosvenorii has been found to have numerous pharmacological effects, including alleviating cough and phlegm, preventing dental caries, exerting anti-inflammatory and anti-allergic effects, anti-aging and anti-oxidative, hypoglycemic, lipid-lowering, anti-depression, anti-fatigue, anti-schizophrenic, anti-Parkinson, anti-fibrotic, and anti-tumor activities. Despite its versatile potential, there is still a lack of systematic research on S. grosvenorii to date. This paper aims to address this gap by providing an overview of the main active components, pharmacological efficacy, toxicity, current status of development and application, development dilemmas, and strategies for intensive exploitation and utilization of S. grosvenorii. This paper aims to serve as a guide for researchers and practitioners committed to exploiting the biological resources of S. grosvenorii and further exploring its interdisciplinary potential.

Post-Ripening and Key Glycosyltransferase Catalysis to Promote Sweet Mogrosides Accumulation of Siraitia grosvenorii Fruits

Sweet mogrosides are not only the primary bioactive ingredient in Siraitia grosvenorii fruits that exhibit anti-tussive properties and expectorate phlegm, but they are also responsible for the fruit's sweetness. Increasing the content or proportion of sweet mogrosides in Siraitia grosvenorii fruits is significant for improving their quality and industrial production. Post-ripening is an essential step in the post-harvest processing of Siraitia grosvenorii fruits, but the underlying mechanism and condition of post-ripening on Siraitia grosvenorii quality improvement need to be studied systematically. Therefore, this study analyzed the mogroside metabolism in Siraitia grosvenorii fruits under different post-ripening conditions. We further examined the catalytic activity of glycosyltransferase UGT94-289-3 in vitro. The results showed that the post-ripening process of fruits could catalyze the glycosylation of bitter-tasting mogroside IIE and III to form sweet mogrosides containing four to six glucose units. After ripening at 35 °C for two weeks, the content of mogroside V changed significantly, with a maximum increase of 80%, while the increase in mogroside VI was over twice its initial amount. Furthermore, under the suitable catalytic condition, UGT94-289-3 could efficiently convert the mogrosides with less than three glucose units into structurally diverse sweet mogrosides, i.e., with mogroside III as the substrate, 95% of it can converted into sweet mogrosides. These findings suggest that controlling the temperature and related catalytic conditions may activate UGT94-289-3 and promote the accumulation of sweet mogrosides. This study provides an effective method for improving the quality of Siraitia grosvenorii fruits and the accumulation of sweet mogrosides, as well as a new economical, green, and efficient method for producing sweet mogrosides.

Potential Anti-Alzheimer Properties of Mogrosides in Vitamin B12-Deficient Caenorhabditis elegans

Vitamin B12 deficiency can lead to oxidative stress, which is known to be involved in neurodegenerative diseases such as Alzheimer's disease (AD). Mogrosides are plant-derived triterpene glycosides that exhibit anti-inflammatory and antioxidant activity in animal cell lines and mouse models. Since amyloid-β toxicity is known to cause oxidative stress and damage to brain cells, we hypothesized that mogrosides may have a protective effect against AD. In this study, we investigated the potential anti-AD effect of mogrosides in vitamin B12-deficient wild-type N2 and in transgenic CL2355 Caenorhabditis elegans expressing amyloid-β peptide. Our data indicated that mogrosides have a beneficial effect on the lifespan and egg-laying rate of N2 and vitamin B12-deficient N2 worms. Additionally, the results revealed that mogrosides can effectively delay the paralysis of CL2355 worms as determined by serotonin sensitivity assay. Our analysis showed that mogrosides increase the expression of oxidative protective genes in N2 worms fed with vitamin B12-deficient OP50 bacterium. We conclude that mogrosides may exert preventative rather than curative effects that counteract the detrimental vitamin B12-deficient environment in N2 and CL2355 C. elegans by modulating oxidation-related gene expression.

A Review of the Phytochemistry and Pharmacology of the Fruit of Siraitia grosvenorii (Swingle): A Traditional Chinese Medicinal Food

Siraitia grosvenorii (Swingle) C. Jeffrey ex Lu et Z. Y. Zhang is a unique economic and medicinal plant of Cucurbitaceae in Southern China. For hundreds of years, Chinese people have used the fruit of S. grosvenorii as an excellent natural sweetener and traditional medicine for lung congestion, sore throat, and constipation. It is one of the first species in China to be classified as a medicinal food homology, which has received considerable attention as a natural product with high development potential. Various natural products, such as triterpenoids, flavonoids, amino acids, and lignans, have been released from this plant by previous phytochemical studies. Phar- macological research of the fruits of S. grosvenorii has attracted extensive attention, and an increasing number of extracts and compounds have been demonstrated to have antitussive, expectorant, antiasthmatic, antioxidant, hypoglycemic, immunologic, hepatoprotective, antibacte- rial, and other activities. In this review, based on a large number of previous studies, we summarized the related research progress of the chemical components and pharmacological effects of S. grosvenorii, which provides theoretical support for further investigation of its biological functions and potential clinical applications.

Structure-Dependent Activity of Plant-Derived Sweeteners

Human sensation for sweet tastes and the thus resulting over-consumption of sugar in recent decades has led to an increasing number of people suffering from caries, diabetes, and obesity. Therefore, a demand for sugar substitutes has arisen, which increasingly has turned towards natural sweeteners over the last 20 years. In the same period, thanks to advances in bioinformatics and structural biology, understanding of the sweet taste receptor and its different binding sites has made significant progress, thus explaining the various chemical structures found for sweet tasting molecules. The present review summarizes the data on natural sweeteners and their most important (semi-synthetic) derivatives until the end of 2019 and discusses their structure–activity relationships, with an emphasis on small-molecule high-intensity sweeteners.

Identification of a Novel Specific Cucurbitadienol Synthase Allele in Siraitia grosvenorii Correlates with High Catalytic Efficiency

Mogrosides, the main bioactive compounds isolated from the fruits of Siraitia grosvenorii, are a group of cucurbitane-type triterpenoid glycosides that exhibit a wide range of notable biological activities and are commercially available worldwide as natural sweeteners. However, the extraction cost is high due to their relatively low contents in plants. Therefore, molecular breeding needs to be achieved when conventional plant breeding can hardly improve the quality so far. In this study, the levels of 21 active mogrosides and two precursors in 15 S. grosvenorii varieties were determined by HPLC-MS/MS and GC-MS, respectively. The results showed that the variations in mogroside V content may be caused by the accumulation of cucurbitadienol. Furthermore, a total of four wild-type cucurbitadienol synthase protein variants (50R573L, 50C573L, 50R573Q, and 50C573Q) based on two missense mutation single nucleotide polymorphism (SNP) sites were discovered. An in vitro enzyme reaction analysis indicated that 50R573L had the highest activity, with a specific activity of 10.24 nmol min-1 mg-1. In addition, a site-directed mutant, namely, 50K573L, showed a 33% enhancement of catalytic efficiency compared to wild-type 50R573L. Our findings identify a novel cucurbitadienol synthase allele correlates with high catalytic efficiency. These results are valuable for the molecular breeding of luohanguo.

Effects of Mogrosides on High-Fat-Diet-Induced Obesity and Nonalcoholic Fatty Liver Disease in Mice

Obesity and nonalcoholic fatty liver disease (NAFLD) are highly prevalent and cause numerous metabolic diseases. However, drugs for the prevention and treatment of obesity and NAFLD remain unavailable. In this study, we investigated the effects of mogrosides (luo han guo, LH) in Siraitia grosvenorii saponins on high-fat-diet-induced obesity and NAFLD in mice. We found that compared with the negative control, LH reduced body and liver weight. LH also decreased fat accumulation and increased AMP-activated protein kinase (AMPK) phosphorylation (pAMPK) levels in mouse livers. We also found that high-purity mogroside V upregulated pAMPK expression in HepG2 cells. In addition, high-purity mogroside V inhibited reactive oxygen species production and upregulated sequestosome-1 (SQSTM1, p62) expression in THP-1 cells. These results suggest that LH may affect obesity and NAFLD by enhancing fat metabolism and antioxidative defenses. Mogroside V may be a main component of LH. However, the exact molecular mechanisms and active components responsible for the inhibitory effects of LH on obesity and NAFLD require further investigation.

Biotransformation of Total Saponins in Siraitia Fructus by Human Intestinal Microbiota of Normal and Type 2 Diabetic Patients: Comprehensive Metabolite Identification and Metabolic Profile Elucidation Using LC-Q-TOF/MS

Siraitia fructus, known as Luo-Han-Guo (LHG) in Chinese, shows good antidiabetic activity. Gut microbiota have emerged as parameter of the pathophysiology of type 2 diabetes (t2D) mellitus. In this study, in vitro biotransformation of LHG extract by t2D and normal human intestinal microbiota was analyzed using ultraperformance liquid chromatography with time-of-flight mass spectrometry. A total of 19 and 12 metabolites were characterized in t2D and normal human intestinal microbiota, respectively. These metabolites were formed by a series of metabolic reactions including deglycosylation, oxidation, isomerization, and/or deoxidation. The metabolite classes of LHG extract in normal and t2D human intestinal microbiota were nearly the same, but oxidation and isomerization reactions were usually present in t2D human intestinal bacteria. This might be due to metabolic activation by pathological human intestinal bacteria. Our study indicates that there are differences in the biotransformation of LHG extract in normal and t2D human intestinal bacteria.

The biosynthetic pathway of the nonsugar, high-intensity sweetener mogroside V from Siraitia grosvenorii

The consumption of sweeteners, natural as well as synthetic sugars, is implicated in an array of modern-day health problems. Therefore, natural nonsugar sweeteners are of increasing interest. We identify here the biosynthetic pathway of the sweet triterpenoid glycoside mogroside V, which has a sweetening strength of 250 times that of sucrose and is derived from mature fruit of luo-han-guo (Siraitia grosvenorii, monk fruit). A whole-genome sequencing of Siraitia, leading to a preliminary draft of the genome, was combined with an extensive transcriptomic analysis of developing fruit. A functional expression survey of nearly 200 candidate genes identified the members of the five enzyme families responsible for the synthesis of mogroside V: squalene epoxidases, triterpenoid synthases, epoxide hydrolases, cytochrome P450s, and UDP-glucosyltransferases. Protein modeling and docking studies corroborated the experimentally proven functional enzyme activities and indicated the order of the metabolic steps in the pathway. A comparison of the genomic organization and expression patterns of these Siraitia genes with the orthologs of other Cucurbitaceae implicates a strikingly coordinated expression of the pathway in the evolution of this species-specific and valuable metabolic pathway. The genomic organization of the pathway genes, syntenously preserved among the Cucurbitaceae, indicates, on the other hand, that gene clustering cannot account for this novel secondary metabolic pathway.

Metabolites of Siamenoside I and Their Distributions in Rats

Siamenoside I is the sweetest mogroside that has several kinds of bioactivities, and it is also a constituent of Siraitiae Fructus, a fruit and herb in China. Hitherto the metabolism of siamenoside I in human or animals remains unclear. To reveal its metabolic pathways, a high-performance liquid chromatography-electrospray ionization-ion trap-time of flight-multistage mass spectrometry (HPLC-ESI-IT-TOF-MSⁿ) method was used to profile and identify its metabolites in rats. Altogether, 86 new metabolites were identified or tentatively identified, and 23 of them were also new metabolites of mogrosides. In rats, siamenoside I was found to undergo deglycosylation, hydroxylation, dehydrogenation, deoxygenation, isomerization, and glycosylation reactions. Among them, deoxygenation, pentahydroxylation, and didehydrogenation were novel metabolic reactions of mogrosides. The distributions of siamenoside I and its 86 metabolites in rat organs were firstly reported, and they were mainly distributed to intestine, stomach, kidney, and brain. The most widely distributed metabolite was mogroside IIIE. In addition, eight metabolites were bioactive according to literature. These findings would help to understand the metabolism and effective forms of siamenoside I and other mogrosides in vivo.

Hyperproduction of β-Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition

Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and excessive leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.