Comprehensive Phytochemical Profiling and Multi-Target Biological Evaluation of Hibiscus sabdariffa L. Calyx Extracts...

The global escalation of antimicrobial resistance necessitates the exploration of plant-based therapeutics with multi-target mechanisms. This study provides a comprehensive evaluation of the Libyan Hibiscus sabdariffa L. calyx extract, encompassing phytochemical characterization, in vitro bioactivity, and in silico validation. Aqueous and ethanolic extracts were prepared and screened for antibacterial activity against clinically relevant multidrug-resistant isolates (including determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)), antioxidant capacity via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay, anti-inflammatory effects by measuring their inhibition of albumin denaturation, and cytotoxicity using the brine shrimp lethality model. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of the ethanolic extract revealed that the predominant fatty acid esters were oleic acid methyl ester (41.01%) and palmitic acid methyl ester (28.76%). Both extracts exhibited broad-spectrum antibacterial activity, with MIC values ranging from 6.25 to 25 mg/mL and MBC/MIC ratios ≤ 2, confirming their bactericidal activity. The aqueous and ethanolic extracts showed superior efficacy against Pseudomonas aeruginosa (20.0 ± 1.73 mm inhibition zone; MIC: 6.25 mg/mL) and Staphylococcus aureus (20.0 ± 1.00 mm; MIC: 6.25 mg/mL), respectively. The antioxidant activities were comparable (IC₅₀: 283.6 vs. 292.1 μg/mL). Remarkably, the aqueous extract demonstrated potent anti-inflammatory activity (IC₅₀: 129.81 μg/mL) and showed low preliminary toxicity in the brine shrimp lethality assay (LD₅₀ > 1000 μg/mL), whereas the ethanolic extract exhibited moderate toxicity (LD₅₀: 345.5 μg/mL). Preliminary phytochemical screening of the aqueous extract revealed the presence of anthocyanins, flavonoids, tannins, phenolics, saponins, and reducing sugars, with a total phenolic content of 184.3 ± 5.2 mg GAE/g and a total flavonoid content of 92.7 ± 3.8 mg QE/g. Molecular docking showed that the identified compounds, such as linoleic acid methyl ester, exhibited strong binding affinities to bacterial DNA gyrase (up to -5.9 kcal/mol) and inflammatory targets, including COX-2, 5-LOX, and TNF-α. ADMET predictions indicated favorable pharmacokinetic profiles for these compounds. These findings scientifically validate the traditional use of H. sabdariffa and highlight the potential of its aqueous extract as a promising source of bioactive compounds warranting further preclinical investigation for functional food and complementary health applications.