Asperpyridone A: An Unusual Pyridone Alkaloid Exerts Hypoglycemic Activity through the Insulin Signaling Pathway

Natural products with potential hypoglycemic activity in T2DM: 2019-2023

As currently the most common metabolic disease, type 2 diabetes mellitus (T2DM) has shown a continuous increase in the number of patients in recent decades. Most anti-T2DM drugs tend to cause some side effects. Given the pathogenesis of T2DM, natural products have emerged as an important source of anti-T2DM drugs. This article reviews natural products with potential hypoglycemic activity from 2019 to 2023. A total of 200 previously natural products were discovered on SciFinder, PubMed and Web of Science. These products were categorized based on their structural frameworks and their biological activities were summarized. Although the mechanisms of action of most compounds are unclear, these compounds could still serve as candidates for the development of lead compounds. Therefore, further structure and activity research of natural products will significantly contribute to the development of potential anti-T2DM drugs.

HMG-CoA reductase inhibitor from the endophytic fungus Colletotrichum Capsici

Two new fungal polyketides with unusual skeleton, collecapsins A and B (1-2), along with two known macrolactins A and B (3-4), were isolated from the rice cultures of an endophytic fungus Colletotrichum capsici obtained from the fresh Siegesbeckia pubescens Makino. Their structures were established by a combination of NMR, HRESIMS, and IR analysis. The absolute configurations of 1 and 2 were determined on the detailed analysis of the modified Mosher's derivatives' spectra and its key NOEs correlations. In this case, the absolute configurations of all chiral centres of 1 were determined for the first time, showed that 1 is a C-6/C-8 epimer of colletruncoic acid methyl ester. Compounds 1-2 demonstrated promising lipid lowing activity via the inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase with IC50 values of 8.72 and 15.28 μM. Compounds 3-4 exhibited antibacterial activity with MIC values ranging from 0.25-25.8 μM.

Research progress on the hypoglycemic activity and mechanisms of natural polysaccharides

The incidence of diabetes, as a metabolic disease characterized by high blood sugar levels, is increasing every year. The predominantly western medicine treatment is associated with certain side effects, which has prompted people to turn their attention to natural active substances. Natural polysaccharide is a safe and low-toxic natural substance with various biological activities. Hypoglycemic activity is one of the important biological activities of natural polysaccharides, which has great potential for development. A systematic review of the latest research progress and possible molecular mechanisms of hypoglycemic activity of natural polysaccharides is of great significance for better understanding them. In this review, we systematically reviewed the relationship between the hypoglycemic activity of polysaccharides and their structure in terms of molecular weight, monosaccharide composition, and glycosidic bonds, and summarized underlying molecular mechanisms the hypoglycemic activity of natural polysaccharides. In addition, the potential mechanisms of natural polysaccharides improving the complications of diabetes were analyzed and discussed. This paper provides some valuable insights and important guidance for further research on the hypoglycemic mechanisms of natural polysaccharides.

Bioactive Alkaloids as Secondary Metabolites from Plant Endophytic Aspergillus Genus

Alkaloids represent a large family of natural products with diverse structures and bioactivities. These compounds and their derivatives have been widely used in clinics to treat various diseases. The endophytic Aspergillus is a filamentous fungus renowned for its extraordinary ability to produce active natural products of high therapeutic value and economic importance. This review is the first to focus on Aspergillus-derived alkaloids. Through an extensive literature review and data analysis, 263 alkaloids are categorized according to their structural features into those containing cytochalasans, diketopiperazine alkaloids, quinazoline alkaloids, quinoline alkaloids, indole alkaloids, pyrrolidine alkaloids, and others. These metabolites exhibited diverse biological activities, such as antibacterial activity, cytotoxicity, anti-inflammatory activity, and α-glucosidase, ACE, and DPPH inhibitory activities. The bioactivity, structural diversity, and occurrence of these alkaloids are reviewed in detail.

A Novel Zn2Cys6 Transcription Factor, TopC, Positively Regulates Trichodin A and Asperpyridone A Biosynthesis in Tolypocladium ophioglossoides

Asperpyridone A represents an unusual class of pyridone alkaloids with demonstrated potential for hypoglycemic activity, primarily by promoting glucose consumption in HepG2 cells. Trichodin A, initially isolated from the marine fungus Trichoderma sp. strain MF106, exhibits notable antibiotic activities against Staphylococcus epidermidis. Despite their pharmacological significance, the regulatory mechanisms governing their biosynthesis have remained elusive. In this investigation, we initiated the activation of a latent gene cluster, denoted as "top", through the overexpression of the Zn2Cys6 transcription factor TopC in Tolypocladium ophioglossoides. The activation of the top cluster led to the biosynthesis of asperpyridone A, pyridoxatin, and trichodin A. Our study also elucidated that the regulator TopC exerts precise control over the biosynthesis of asperpyridone A and trichodin A through the detection of protein-nucleic acid interactions. Moreover, by complementing these findings with gene deletions involving topA and topH, we proposed a comprehensive biosynthesis pathway for asperpyridone A and trichodin A in T. ophioglossoides.

Self-[3+2] annulation reaction of pyridinium salts: synthesis of N-indolizine-substituted pyridine-2(1H)-ones

A self-[3+2] annulation reaction of pyridinium salts has been developed for the synthesis of N-indolizine-substituted pyridine-2(1H)-ones.

Asperosin A, a [4 + 2] Diels–Alder cycloaddition polyketide dimer from Aspergillus rugulosa with immunosuppressive activity

A novel homologous polyketide dimer, asperosin A (1), constructed with a unique hetero-bicycle 6/5 core skeleton featuring four continuous quaternary carbons, was isolated from a solid culture of the fungus Aspergillus rugulosa.

Perfluorooctanesulfonic Acid (PFOS) Thwarts the Beneficial Effects of Calorie Restriction and Metformin

A combination of calorie restriction (CR), dietary modification, and exercise is the recommended therapy to reverse obesity and nonalcoholic fatty liver disease. In the liver, CR shifts hepatic metabolism from lipid storage to lipid utilization pathways, such as AMP-activated protein kinase (AMPK). Perfluorooctanesulfonic acid (PFOS), a fluorosurfactant previously used in stain repellents and anti-stick materials, can increase hepatic lipids in mice following relatively low-dose exposures. To test the hypothesis that PFOS administration interferes with CR, adult male C57BL/6N mice were fed ad libitum or a 25% reduced calorie diet concomitant with either vehicle (water) or 100 μg PFOS/kg/day via oral gavage for 6 weeks. CR alone improved hepatic lipids and glucose tolerance. PFOS did not significantly alter CR-induced weight loss, white adipose tissue mass, or liver weight over 6 weeks. However, PFOS increased hepatic triglyceride accumulation, in both mice fed ad libitum and subjected to CR. This was associated with decreased phosphorylated AMPK expression in liver. Glucagon (100 nM) treatment induced glucose production in hepatocytes, which was further upregulated with PFOS (2.5 μM) co-treatment. Next, to explore whether the observed changes were related to AMPK signaling, HepG2 cells were treated with metformin or AICAR alone or in combination with PFOS (25 μM). PFOS interfered with glucose-lowering effects of metformin, and AICAR treatment partially impaired PFOS-induced increase in glucose production. In 3T3-L1 adipocytes, metformin was less effective with PFOS co-treatment. Overall, PFOS administration disrupted hepatic lipid and glucose homeostasis and interfered with beneficial glucose-lowering effects of CR and metformin.

Z, Cubilla-Rios L. Structurally Uncommon Secondary Metabolites Derived from Endophytic Fungi

Among microorganisms, endophytic fungi are the least studied, but they have attracted attention due to their high biological diversity and ability to produce novel and bioactive secondary metabolites to protect their host plant against biotic and abiotic stress. These compounds belong to different structural classes, such as alkaloids, peptides, terpenoids, polyketides, and steroids, which could present significant biological activities that are useful for pharmacological or medical applications. Recent reviews on endophytic fungi have mainly focused on the production of novel bioactive compounds. Here, we focus on compounds produced by endophytic fungi, reported with uncommon bioactive structures, establishing the neighbor net and diversity of endophytic fungi. The review includes compounds published from January 2015 to December 2020 that were catalogued as unprecedented, rare, uncommon, or possessing novel structural skeletons from more than 39 different genera, with Aspergillus and Penicillium being the most mentioned. They were reported as displaying cytotoxic, antitumor, antimicrobial, antiviral, or anti-inflammatory activity. The solid culture, using rice as a carbon source, was the most common medium utilized in the fermentation process when this type of compound was isolated.

New Polyketides With Anti-Inflammatory Activity From the Fungus Aspergillus rugulosa

Two new polyketide compounds, asperulosins A and B (1–2), and one new prenylated small molecule, asperulosin C (3), along with nine known compounds (4–12), were isolated and identified from a fungus Aspergillus rugulosa. Their structures were extensively elucidated via HRESIMS, 1D, and 2D NMR analysis. The absolute configurations of the new compounds were determined by the comparison of their electronic circular dichroism (ECD), calculated ECD spectra, and the detailed discussion with those in previous reports. Structurally, compounds 1 and 2 belonged to the polyketide family and were from different origins. Compound 2 was constructed by five continuous quaternary carbon atoms, which occur rarely in natural products. All of the isolates were evaluated for anti-inflammatory activity against the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced RAW264.7 cells. Among those, compounds 1 and 5 showed a significant inhibitory effect on NO production with IC₅₀ values of 1.49 ± 0.31 and 3.41 ± 0.85 μM, respectively. Additionally, compounds 1 and 5 markedly increased the secretion of anti-inflammatory cytokine IL10 while suppressing the secretion of pro-inflammatory cytokines IL6, TNF-α, IFN-γ, MCP-1, and IL12. Besides, 1 and 5 inhibited the transcription level of pro-inflammatory macrophage markers IL6, IL1β, and TNF-α while remarkably elevating the anti-inflammatory factor IL10 and M2 macrophage markers ARG1 and CD206. Moreover, 1 and 5 restrained the expression and nuclear translocation of NF-κB, as well as its downstream signaling proteins COX-2 and iNOS. All these results suggest that 1 and 5 have potential as anti-inflammatory agents, with better or comparable activities than those of the positive control, dexamethasone.

The antidiabetic potential of endophytic fungi: Future prospects as therapeutic agents

Diabetes mellitus is one of the most common systemic diseases in the world, and it occurs when the body becomes resistant to insulin or does not make enough insulin. As described by the World Health Organization, diabetes mellitus of all types has exponentially grown in the past decades across the globe and it is estimated to be 629 million by 2045. Despite this alarming prevalence of diabetes mellitus, there is still the lack of harmless preventive medicines. Natural products and compounds obtained from plants, fungi, bacteria, and other living organisms have been used for many decades in folklore medicine to prepare a varied range of natural formulations to treat multiple diseases and illnesses. Endophytic fungi reside inside the plant while causing no harm to the host plant and are relatively less explored as the primary source for the bioactive metabolites such as anticancer, antioxidant, antimicrobial, antidiabetic, and industrial enzymes. This mini-review summarizes the potential of compounds and extracts from endophytic fungi against diabetes mellitus. Not much research has been dedicated in-depth understanding of the role of extracts of endophytic fungi and their effect on diabetes mellitus. Therefore, this article will focus on recent work and warrant further commentaries on the published articles.

Biologically Significant and Recently Isolated Alkaloids from Endophytic Fungi

A selection of the established and recently characterized alkaloids from the exploration of plant- and some marine-associated endophytic fungi is reviewed, with reference to alkaloids of biological significance.

An enzymatic Alder-ene reaction

An ongoing challenge in chemical research is to design catalysts that select the outcomes of the reactions of complex molecules. Chemists rely on organo- or transition metal catalysts to control stereo-, regio-, and periselectivity (selectivity among possible pericyclic reactions). Nature achieves these types of selectivity with a variety of enzymes such as the recently discovered pericyclases – a family of enzymes that catalyze pericyclic reactions.¹ To date, the majority of characterized enzymatic pericyclic reactions are cycloadditions and it has been difficult to rationalize how observed selectivities are achieved.^2-13 We report here the discovery of two homologous groups of pericyclases that catalyze distinct reactions: one group catalyzes an Alder-ene reaction, previously unknown in biology; the second catalyzes a stereoselective hetero-Diels–Alder reaction. Guided by computational studies, we rationalized the observed differences in reactivities and designed mutants that reverse periselectivities from Alder-ene to hetero-Diels–Alder and vice versa. A combination of in vitro biochemical characterizations, computational studies, enzyme co-crystal structures, and mutational studies provide a picture of how high regio- and periselectivities are achieved in nearly identical active sites.