Micro-titer plate assay for measurement of total phenolic and total flavonoid contents in medicinal plant extracts

Total flavonoid content revised: An overview of past, present, and future determinations in phytochemical analysis

Flavonoids represent an important research topic in the analytical chemistry of secondary plant metabolites. During habitual laboratory determinations, preliminary quantitative analysis is often associated with in vitro colorimetric assessment. Total flavonoid content (TFC) is used as screening method with high relevance in the chemical analysis of plants and derived products, being typically applied before HPLC-MS phytochemical profiling. Its importance stems from affordability, simplicity, rapidity, and low cost. The AlCl3 assay, with or without NaNO2 addition, is the most used method in the present, although less frequently used methods (using 2,4-dinitrophenylhydrazine, dimethylamino-cinnamaldehyde, or diethylene glycol) show potential for complementary and specific determinations. Given the prevalence of research papers focusing on a single method for "total flavonoid" determination, we identified the need for an objective and critical comparison of existing methodologies. Moreover, a special notice is dedicated to the past and the future of in vitro TFC determinations, in the context of recent advances in flavonoid research. The focal point of this review is to serve as a basis for laboratory protocol reorganization regarding TFC determination, as a powerful tool before mass spectrometry, as well as to present a potential complementary analysis protocol applicable to biological samples. Among the methods found in the literature, SBC was the only assay providing accurate determinations of TFC.

Exploration of Secondary Metabolites in Platostoma menthoides (L.) Using Ethyl Acetate Extract and Its Antibacterial, Antioxidant, and Larvicidal Activities

Recently, there has been a growing demand for plant-based products to treat a range of health conditions. Platostoma menthoides (L.), a member of the Lamiaceae family, is widely known for its versatile therapeutic properties. The primary aim of this study is to analyze and identify the secondary metabolites found in the extract of P. menthoides obtained using ethyl acetate and to assess its antioxidant, antimicrobial, and mosquito larvicidal properties for the first time. For the chemical profiling, a GC-MS analysis of the extract was conducted, and it showed the presence of various phytoconstituents, and the FT-IR spectrum revealed the functional groups associated with them. The quantitative phytochemical estimations revealed values of 34.87 ± 0.53 mg of GAE equivalents/g and 22.19 ± 1.11 mg of QUE equivalents/g, respectively, for total phenolic and flavonoid content. The biological studies of P. menthoides extract showed potent mosquito larvicidal activity against fourth instar larvae of Aedes aegypti at a 100 µg/mL concentration with LC50 and LC90 values of 81.328 and 161.471 µg/mL, respectively. Moreover, the DPPH and FRAP radical scavenging potentials were evaluated, and the results revealed their ability to scavenge the free radicals. The extract also showed higher antibacterial effects against gram-negative bacteria when compared to gram-positive bacteria. All these findings suggest that P. menthoides is a rich source of phytoconstituents with various medicinal applications and can be used as an antioxidant, antibacterial, and mosquito-larvicidal agent.

Antihyperglycemic activity of a novel polyherbal formula (HF344), a mixture of fifteen herb extracts, for the management of type 2 diabetes: Evidence from in vitro, ex vivo, and in vivo studies

Antihyperglycemic effects of a novel polyherbal formula (HF344), comprising fifteen Thai herbal extracts, were elucidated for pharmacological mechanisms and potential for managing type 2 diabetes mellitus, by employing in vitro, ex vivo, and in vivo approaches. LC/MS analysis of HF344 extract revealed several phytoconstituents, with piperine identified as the major active compound. HF344 extract significantly enhanced insulin secretion in RINm5F cells in vitro and inhibited glucose uptake into the everted sacs of the mouse small intestine ex vivo in a concentration-dependent manner compared to the control (p < 0.05). It exhibited potent α-glucosidase inhibition in vitro, with an IC50 of 96.74 μg/mL. Moreover, HF344 extract upregulated mRNA levels of GLUT1 in L6 skeletal myoblasts, suggesting increased glucose uptake into skeletal muscle. In addition, in vivo antihyperglycemic effects were assessed in streptozotocin (STZ)-nicotinamide (NA)-induced diabetic mice. Acute oral toxicity testing confirmed the HF344 extract's safety, with an LD50 exceeding 2000 mg/kg. Oral administration of HF344 extract (500 and 1000 mg/kg) in STZ-NA-induced diabetic mice significantly reduced the area under the fasting blood glucose (FBG)-time curve (AUC) in the oral glucose tolerance test (OGTT) model and treatment for 28-day reduced the FBG levels as compared with control (p < 0.05). This was accompanied by increased serum insulin levels and improved insulin resistance. HF344 extract also demonstrated a concentration-dependent inhibitory effect on malondialdehyde (MDA) production in vitro, with an IC50 of 7.24 μg/mL. Oral treatment with HF344 extract decreased MDA production in the homogenized muscle ex vivo collected from STZ-NA-induced mice. Furthermore, pretreatment with HF344 extract effectively restored the survival of RINm5F cells from STZ-induced damage. These findings suggest that HF344 is a promising polyherbal formula for managing blood glucose levels, enhancing insulin production, and providing antioxidant benefits in T2DM. Further research is required to evaluate the clinical efficacy and safety profiles of HF344.

Exploring Medicinal Plants for Antimicrobial Activity and Synergistic Effects With Doxycycline Against Bacterial Species

Medicinal plants are rich sources of bioactive compounds with diverse pharmacological properties, including antimicrobial activities. This study aimed to assess the antibiofilm potential of methanol and ethanol extracts from nine selected medicinal plants, as well as their synergistic effects with doxycycline against Bacillus strains. Standard procedures were employed to determine the phytochemical composition, total phenolic, and flavonoid contents of the extracts. The antibacterial activity was evaluated using the broth microdilution method, while biofilm formation was assessed via the microtiter plate method. Antibiofilm activity was determined using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium-bromide (MTT) assay. Combination studies were conducted using the checkerboard microdilution method. All extracts contained phenols, flavonoids, steroids, triterpenes, and anthraquinones. The methanolic extract of Psidium guajava exhibited the highest total phenolic and flavonoid contents (90.48 ± 0.55 mg GAE/g), while the ethanolic extract of Olax subscorpioidea showed the highest flavonoid content (6.48 ± 0.33 mg QE/g). Ethanol extracts of Eucalyptus globulus and Psidium guajava and methanolic extract of Syzygium jambos demonstrated significant antibacterial activity against Bacillus anthracis 34F2 Sterne strains, with a MIC value of 64 μg/mL. Biofilm formation in Bacillus strains was notably enhanced in the presence of glucose. The methanolic extract of O. subscorpioides exhibited the highest biofilm imbibition (85%), while Picralima nitida methanolic extract showed the most effective biofilm eradication (79%). The combination of Solanum torvum ethanol extract with doxycycline displayed synergistic effects against biofilm formation inhibition and eradication in all tested Bacillus strains. Taken together, Solanum torvum ethanol extract shows promise for developing new combination antibacterial therapies.

Research on the pharmacognostic characteristics, physicochemical properties and in vitro antioxidant potency of Rosa laxa Retz. flos

Rosa laxa Retz. is an unexplored Rosaceae plant in Xinjiang, China, and its flower is traditionally used in Kazak to treat the common cold, fever, and epileptic seizures and lessen the effects of aging. In the present study, the pharmacognostic profiles, physicochemical properties, phytochemical characteristics, and in vitro antioxidant potency of Rosa laxa Retz. flos (RLF) were presented. In the pharmacognostic evaluation of RLF, organoleptic characteristics, internal structures, and powder information were observed, and physicochemical parameters, including moisture content, ash, pH value, swelling degree, and extractives were examined. The quantitative analysis of the chemical composition of four different polar extracts of RLF showed that the aqueous part had the highest total triterpene acid, flavonoid, and polyphenol content (4.50 ± 0.04 mg/g, 50.56 ± 0.03 mg/g, and 60.20 ± 0.09 mg/g, respectively). A high-performance liquid chromatography (HPLC)-diode array detector (DAD) method was established and the contents of gallic acid, ellagic acid, astragalin, and tiliroside in RLF were determined simultaneously. In the set concentration range, the linear relationship among the four components was good (r > 0.999), the average recoveries were 97.36%-100.54%. The contents of gallic acid, ellagic acid, astragalin, and tiliroside in RLF samples were (9.46 ± 2.31) mg/g, (10.60 ±0.75) mg/g, (1.13 ± 2.50) mg/g, and (1.11 ± 2.65) mg/g, respectively. The types of its secondary metabolites were determined by fluorescence, color reaction by chemical solvent method, and ultraviolet-visible (UV-Vis) spectroscopy. The functional groups of its secondary metabolites were determined by Fourier transform infrared (FTIR) spectroscopy. Results showed that RLF contains a variety of secondary metabolic products, including flavonoids, phenolic acid, glycoside, and organic acid. TLC identification showed it contains ursolic acid, β-sitosterol, tiliroside, astragalin, isoquercitrin, kaempferol-3-O-rutinoside, gallic acid, and ellagic acid. The in vitro antioxidant activity of different polar parts of RLF was investigated by DPPH, ABTS, and reduction performance experiments. The aqueous extract had the strongest antioxidant capacity, consistent with the high content of triterpene acids, flavonoids, and polyphenolic compounds. These findings will provide critical information for the study of quality standards and medicinal value of RLF and its extracts, justify its usage in traditional medicinal systems, and encourage the use of this plant in disease prevention and treatment. Its phytochemical composition and pharmacological studies need to be explored in future. RESEARCH HIGHLIGHTS: Optical microscope and scanning electron microscope (SEM) were used to observe the morphology, and microstructure of Rosa laxa Retz. flos (RLF). The physicochemical properties, fluorescence and phytochemical composition of four different polar extracts of RLF were analyzed by UV-Vis and FTIR. Determination of total triterpenic acid, total flavonoids, and total polyphenols in four different polar extracts of RLF by UV spectrophotometry. A high-performance liquid chromatography (HPLC)-diode array detector (DAD) method was established and the contents of gallic acid, ellagic acid, astragalin, and tiliroside in RLF were determined simultaneously. TLC confirmed that RLF contains ursolic acid, β-sitosterol, tiliroside, astragalin, isoquercitrin, kaempferol 3-rutinoside, gallic acid, and ellagic acid. The in vitro antioxidant activity of RLF was studied by DPPH, ABTS, and reducing ability experiments.

Green synthesis of chitosan nanoparticles using Cassia fistula leaf extract: evaluation of antimicrobial, antioxidant, antibiofilm, and cytotoxic activities

The emerging field of green synthesis within nanobiotechnology presents significant environmental and economic advantages compared to conventional methodologies. This study investigates the synthesis and application of chitosan nanoparticles (ChNPs) using Cassia fistula (CF) leaf extract as a sustainable, and bio-based approach. Characterization of CF-ChNPs confirmed effective bioconversion and also demonstrated significant antimicrobial activity. Notably, CF-ChNPs demonstrated a remarkable antimicrobial effect against Pseudomonas aeruginosa, with a zone of inhibition of 17 ± 0.2 mm surpassing the impact on other organisms tested. The CF-ChNPs exhibited an initial burst release of 28 ± 0.28% after 2 h, gradually achieving a controlled release of 76.3 ± 0.43% within 24 h. In addition, CF-ChNPs exhibited an antioxidant activity of 43.1 ± 0.48% and showed excellent antibiofilm activity against Staphylococcus aureus in comparison to other organisms. The cell viability assay results have confirmed that CF-ChNPs do not have any negative impact on the viability of L929 fibroblasts, further highlighting their potential as versatile nanomaterials for treating microbial infections and other therapeutic applications.

Extraction, Characterization, and In Vitro Biological Activity of Polyphenols from Discarded Young Fig Fruits Based on Deep Eutectic Solvents

(1) Background: Discarded young fig fruits (DYFFs) result in a waste of resources, such as sparse fruits and residual fruits, and there has been no research on the relationship between phenolic compounds and biological activity in DYFFs (2) Methods: Different deep eutectic solvents (DESs) and 80% ethanol were used to prepare DYFF extracts, and polyphenol extraction efficiency and bioactivities in the DYFFs extracts were compared. (3) Results: More than 1700 phytochemicals were identified in DYFFs, and thirteen of these typical phenolic compounds were analyzed quantitatively; chlorogenic acid, rutin, luteolin 8-C-glucoside, and epicatechin are the main polyphenols in DYFFs, especially chlorogenic acid with 2720-7980 mg/kg. Ferulic acid, caffeic acid, epicatechin, (+)-catechin, luteolin 8-C-glucoside, rutin, hesperetin, and chlorogenic acid showed different degrees of correlation with in vitro antioxidant activity. Moreover, the highest total phenol content found in the extracts of ChCl-Ethylene glycol (Choline chloride:Ethylene glycol = 1:2) was 8.88 mg GAE/g DW, and all quantitatively analyzed phenolic compounds had high levels in various DESs and 80% ethanol. The 80% ethanol and Choline chloride (ChCl) solvent system showed the greatest antioxidant properties, and the Choline chloride-Urea (Choline chloride: Urea = 1:2) extract of DYFFs exhibited the highest inhibitory activity. (4) Conclusions: DESs have demonstrated potential as promising green solvents, especially the ChCl solvent system, which facilitates the extraction of polyphenols.

A comprehensive and critical review of the unstandardized Folin-Ciocalteu assay to determine the total content of polyphenols: The conundrum of the experimental factors and method validation

The Folin-Ciocalteu method can be considered to be the most widely used in laboratories around the world, to quantify the total polyphenols content. Many different variations found in this assay have been reported in the scientific literature. In this review, the full experimental conditions influencing the Folin-Ciocalteu assay have been comparatively assessed and discussed. Furthermore, few studies relating to the method validation have been evaluated according to the results of selectivity, linearity, precision, trueness, limit of determination, limit of quantification and robustness. In general, the results derived from the reviewed literature are widely variable according to both, the experimental factors selected and the performance parameters reported, making difficult the comparison of the overall results published.