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Background Lippia javanica (lemon bush) is commonly used in the treatment of respiratory ailments, including asthma in southern African countries but there is no scientific evidence to support this claim. This study investigated the anti-inflammatory, antioxidant and anti-asthmatic effects of L. javanica using a rat model of asthma. Methods A 5% w/v L. javanica tea infusion was prepared and characterised by liquid chromatography–mass spectrometer (LC-MS). Animals were intraperitoneally sensitized with ovalbumin (OVA) and subsequently challenged intranasal with OVA on day 15 except the control group. Animals were grouped (n = 5/group) for treatment: unsensitised control, sensitised control, sensitised + prednisolone and sensitised + L. javanica at 50 mg/kg/day and 100 mg/kg/day – equivalent to 1 and 2 cups of tea per day, respectively. After 2 weeks of treatment, bronchoalveolar lavage fluid (BALF) was collected for total and differential white blood cell (WBC) count. Nitric oxide (NO), lipid peroxidation and antioxidants were also assessed in BALF. Ovalbumin specific IgE antibody and inflammatory cytokines: IL-4, IL-5, IL-13 and TNF-alpha were measured in serum. Lung and muscle tissues were histological examined. Results L. javanica was rich in phenolic compounds. OVA sensitisation resulted in development of allergic asthma in rats. L. javanica treatment resulted in a reduction in total WBC count as well as eosinophils, lymphocytes and neutrophils in BALF. L. javanica inhibited Th2-mediated immune response, which was evident by a decrease in serum IgE and inflammatory cytokines: IL-4, IL-5, IL-13 and TNF-α. L. javanica treatment also reduced malondialdehyde (MDA) and NO, and increased superoxide dismutase, glutathione and total antioxidant capacity. Histology showed significant attenuation of lung infiltration of inflammatory cells, alveolar thickening, and bronchiole smooth muscle thickening. Conclusion L. javanica suppressed allergic airway inflammation by reducing Th2-mediated immune response and oxidative stress in OVA-sensitized rats which may be attributed to the presence of phenolic compound in the plant. This finding validates the traditional use of L. javanica in the treatment of respiratory disorders.

The effects of nitrogen, potassium, water stress, and phytohormones were studied using a Salvia stenophylla (Burch. ex Benth.) microplant system. In vitro regeneration was monitored and then followed with volatile secondary metabolite profiling through headspace solid-phase microextraction gas chromatography. Plantlet growth was most prolific on half-strength Murashige and Skoog medium without phytohormones. An increase in macronutrients supplied to the microplants enhanced accumulation of the commercially important (−)-α-bisabolol, while no significant changes to the relative abundance of β-bisabolene, α-muurolene, α-patchoulene, and D-limonene (among others) became apparent. Water-stressed plants, treated with sorbitol and polyethylene glycol, had a lowered rooting capacity in vitro. Overall, as a plant production system, micropropagation did not have deleterious effects on the biochemistry of S. stenophylla as no significant differences in metabolic profiles existed between conventional garden plants and in vitro propagules, regardless of phytohormone treatment. We also show that nutrient manipulation can be used efficiently as a strategy for positively altering secondary metabolism. This will ultimately benefit the domestication of this commercially important medicinal herb.

The aromatic medicinal plant Salvia stenophylla contains α-bisabolol, making this plant an important contributor to the aromatherapy and cosmetic industries in South Africa. Due to its commercial importance, the cultivation of this plant using an in vitro system was considered. Firstly, seedlings were raised in vitro after breaking dormancy with light, smoke-water or chemical scarification treatments. Germination improved when seeds were smoke-treated or soaked in 70% (v/v) H2SO4. Vigorous plantlet regeneration was achieved when seedling explants were cultured on Murashige and Skoog (1962) medium with 5.7 μM IAA and 8.9 μM BA. The potential regeneration capacity for this protocol was estimated and over 1,000 plantlets can be produced from a single shoot (6.67 cm with 4–6 nodes) over a period of 3 months. Plants rooted easily regardless of their growth medium. This was followed by their successful rapid establishment and normal growth out of culture (75%). Finally, the volatile compounds in in vitro plants were compared to ex vitro plants via headspace solid phase microextraction linked to gas chromatography–mass spectrometry. The chemical complexity of microplants was similar to wild plants with in vitro plants continuing to produce α-bisabolol (21%) at high levels.