Chemical diversity of the herbal decoction of Plectranthus ornatus and its anti-nociceptive and anti-inflammatory activities in zebrafish models

Ethnopharmacological relevance: Plectranthus ornatus is a medicinal plant originally from Africa but adapted to Brazil's climate conditions. It is recognized for its therapeutic properties, particularly for treating liver and stomach diseases, gastritis control, heartburn, and hangover. Therefore, studies on its chemical composition and pharmacological evaluation are important for the safe use of the plant.

Aim of the study: To investigate the chemical composition and pharmacological activity of leaf decoction of P. ornatus.

Materials and methods: The lyophilized herbal decoction from P. ornatus leaves was extracted with MeOH (methodology A), and CHCl₃ and n-BuOH (methodology B). The compounds were isolated using chromatographic techniques. Their structures were determined using spectroscopic methods (¹H and ¹³C NMR, IR, and HRESIMS) and comparison with published data. The lyophilized herbal decoctions DPO A (decoction from methodology A) and DPO B (methodology B), and compounds 8, 9, 15, and 16 (4, 20, and 40 mg/kg) were evaluated for their toxicity, anti-nociceptive, and anti-inflammatory effects in experimental adult zebrafish (Danio rerio) models.

Results: The present study focused on the CHCl₃ and MeOH soluble fractions from the lyophilized leaf decoction leading to the isolation of five new diterpenes (1, 4-7) and two new glucuronide flavonoid derivatives (2 and 3). In addition, four diterpenes (14-17), two glucuronide flavonoid derivatives (10 and 11), three phenolics (8, 12, and 13), and one disaccharide (9) previously reported were also isolated. In zebrafish essays, all samples showed no toxicity and exhibited an anti-nociceptive effect in at least one of the tested doses: 9, 15, 16, and DPO B (4 mg/kg), 8 (20 mg/kg), and DPO A (40 mg/kg). Moreover, the compounds 15 (4, 20, and 40 mg/kg) and 16 (4, 20, and 40 mg/kg) exhibited anti-inflammatory effects.

Conclusion: The lyophilized decoctions (DPO A and DPO B) including the compounds 8, 9, 15, and 16 exhibited significant anti-nociceptive effects in adult zebrafish and showed no toxicity. Since pain can be a symptom of liver, stomach, and gastrointestinal disorders, and all the samples proved to be non-toxic, the herbal decoction of P. ornatus leaf could be considered a potential therapeutic option in pain management, supporting the ethnopharmacological use of the plant.