Phytochemical Elucidation and Biological Activity Spectrum of Rosmarinus officinalis L.: Mechanistic Insights into the Antimicrobial, Antioxidant, and Apoptosis-Inducing Anticancer Effects of Carnosic Acid

Background: Rosmarinus officinalis L. is a medicinally important aromatic plant rich in bioactive secondary metabolites with diverse therapeutic properties. This study aimed to characterize the phytochemical profile of R. officinalis leaf extracts, isolate carnosic acid as a major bioactive diterpene, and evaluate its biological activities. Methods: Leaf extracts were prepared using solvents of increasing polarity and analyzed by phytochemical screening and UHPLC/QTOF-MS. Carnosic acid was isolated by thin-layer chromatography and assessed for antibacterial, antibiofilm, antioxidant, anti-inflammatory, antidiabetic, and antiproliferative activities using in vitro assays. Expression of apoptosis-related genes was also investigated. Results: Methanolic and ethanolic extracts exhibited the highest abundance of phenolic compounds and secondary metabolites, whereas the hexane extract showed lower phytochemical content. UHPLC/QTOF-MS identified seven major metabolites, including phenolic acids, flavonoids, and abietane-type diterpenes. Purified carnosic acid demonstrated potent antibacterial activity (MIC: 10–23 μg/mL) and inhibited biofilm formation by up to 90%. Strong antioxidant activity was observed, with DPPH and ABTS radical-scavenging IC50 values of 125 and 130 μg/mL, respectively. The compound also exhibited notable anti-inflammatory activity and markedly inhibited α-amylase and α-glucosidase activities. Furthermore, carnosic acid exhibited dose-dependent antiproliferative activity against MCF-7, HepG2, and MCF-10A cells, reducing cell viability to 10.8%, 16.9%, and 70.4 ± 1.8%, respectively, at 250 μg/mL, with corresponding IC50 values of 28.3, 37.8, and >250 μg/mL, respectively. Gene expression analysis revealed upregulation of BAX and downregulation of BCL2, indicating activation of mitochondrial-mediated apoptosis. Conclusions:R. officinalis leaves represent a valuable source of multifunctional phytochemicals, particularly carnosic acid. Its broad-spectrum biological activities and apoptosis-inducing potential support its promising application in pharmaceutical, nutraceutical, and biomedical fields.