Rosmarinic acid (RA), one of the main bioactive compounds of Rosmarinus officinalis L., exhibits diverse pharmacological effects. However, its oral absolute bioavailability and dose proportionality in vivo have not been comprehensively studied. In the present study, a validated LC-MS/MS method was developed for the determination of RA in rat plasma. Pharmacokinetic parameters were obtained following oral and intravenous dosing using DAS 3.0 software. Absolute bioavailability in rats was determined by comparing pharmacokinetic data after administration of single oral (12.5, 25 and 50 mg kg⁻¹) and intravenous (0.625 mg kg⁻¹) doses of RA. The dose proportionality of AUC and C_max were analyzed using a power model. After single-dose oral administration of RA, C_max values for groups with 12.5, 25 and 50 mg kg⁻¹ doses ranged from 215.29 to 790.96 ng mL⁻¹, with AUC_0–t values from 41 789.84 to 96 070.00 min ng mL⁻¹, while T_max and t_1/2 values ranged from 8.33 to 18.33 and from 332.34 to 295.32 min, respectively. The power model showed RA lacked dose proportionality over the dose range from 12.5–50 mg kg⁻¹. Oral absolute bioavailability was calculated to range from 0.91% to 1.69%. All the results demonstrated that the pharmacokinetic properties of RA in rats after oral administration were characterized as rapid absorption, middle-speed elimination and poor absolute bioavailability. Systemic exposure exhibited lack of dose proportionality over the dose range from 12.5 to 50 mg kg⁻¹. These presented data could provide useful information for the rational clinical application and optimal dosage form design of RA.

Background: The management of metastatic cancer remains a major challenge in cancer therapy worldwide. The targeted delivery of chemotherapeutic drugs through rationally designed formulations is one potential therapeutic option. Notably, excipient-free nanodispersions that are entirely composed of pharmaceutically active molecules have been evaluated as promising candidates for the next generation of drug formulations. Formulated from the self-assembly of drug molecules, these nanodispersions enable the safe and effective delivery of therapeutic drugs to local disease lesions. Here, we developed a novel and green approach for preparing nanoparticles via the self-assembly of rhein (RHE) and doxorubicin (DOX) molecules, named RHE/DOX nanoparticles (RD NPs); this assembly was associated with the interaction force and did not involve any organic solvents. Results: According to molecular dynamics (MD) simulations, DOX molecules tend to assemble around RHE molecules through intermolecular forces. This intermolecular retention of DOX was further improved by the nanosizing effect of RD NPs. Compared to free DOX, RD NPs exerted a slightly stronger inhibitory effect on 4T1 cells in the scratch healing assay. As a dual drug-loaded nanoformulation, the efficacy of RD NPs against tumor cells in vitro was synergistically enhanced. Compared to free DOX, the combination of DOX and RHE in nanoparticles exerted a synergistic effect with a combination index (CI) value of 0.51 and showed a stronger ability to induce cell apoptosis. Furthermore, the RD NP treatment not only effectively suppressed primary tumor growth but also significantly inhibited tumor metastasis both in vitro and in vivo, with a better safety profile. Conclusions: The generation of pure nanodrugs via a self-assembly approach might hold promise for the development of more efficient and novel excipient-free nanodispersions, particularly for two small molecular antitumor drugs that potentially exert synergistic antiproliferative effects on metastatic breast cancer.