Marco Valussi's Report on Resurrection Bush Essential Oil

Introduction

Resurrection bush/plant is, as the vernacular names imply, a plant with a remarkable and unique characteristic, it can revive from apparent death (a feature noted by Weiss in 1906).  It normally grows in areas which are exposed to considerable day/night temperature extremes, and an erratic water supply, with conditions of dry winter months with summer rains. For this reason plants must be able to survive severe dehydration and exist in a desiccated quiescent state for extended periods of up to two years.

When desiccated, the leaves fold up and change colour from green to dull- brown and the plant appears completely dead. But stunningly, the plant "resurrects" on rehydration, usually 24–72 h after the first significant amount of rainfall.  This can happen because of some exceptional features of this species, the only resurrection plant with woody stems: apparently the xylem conduits are rich in lipids that prevent irreversible cavitation and facilitate re-hydration; moreover, the species keeps its chlorophyll and thylakoids intact during desiccation (its a homoiochlorophyllous desiccation-tolerant plant), allowing a more rapid recovery of photosynthesis and growth upon re-hydration (Tuba, Lichtenthaler 2011); also, the plant’s leaf fold in a fan-like manner against the stem to reduce the level of incident light reaching the photosystems (Moore, et al. 2007). It loses losing up to 95% of its protoplasmic water content, resulting in important anatomical and ultra-structural re-organization of the leaf tissue, and it shows stacking of the thylakoid membranes of the chloroplasts, to minimize photo-oxidative stress.  On rehydration the plant can revitalize metabolism, photosynthetic activity and growth (Moore, et al. 2007; Nantapo, Marume 2022; Viljoen et al. 2002; Erhabor et al. 2020).

The plant is native to Southern Africa, but it's distributed widely in Equatorial and Southern Africa (Kenya, Tanzania, Malawi, Mozambique, Zambia, Zimbabwe, Swaziland, Lesotho, Botswana, Namibia, Angola and Zaïre) (POWO 2023; Chagonda, Makanda, Chalchat 1999).  It normally grows in rocky areas, wedged into the shallow, well-drained crevices of large sandstone and granite outcrops or boulders, in mountainous regions between 900 and 1200 m a.s.l. (Keraudren-Aymonin 1975).

It is a small, woody, shrubby dioecious plant, xeromorphic and aromatic, about 0.3 to 0.9 m in height (although in literature it is stated that it can grow up to 2m). It can be either prostrate or erect, and it bears many tetragonous branches that soon become woody.  The leaves are small, opposite, sessile and aromatic, fan-shaped when fresh but plaited when dried out. The flowers (male and female) flower from November to May, and are green to deep pink, clustered in terminal spikes usually 2–3 cm. long.  The resins and volatile compounds that give the aroma to the aerial parts are contained in resin or oil ducts (Viljoen et al. 2002; Figueiredo, Smith 2008; Germishuizen, Meyer 2003; Retief Meyer 2017; WFO 2023).

Uses

This plant holds an important position in traditional African folklore and medicine.  Firstly, the special, resurrecting feature of this plant is used as a symbol of hope in traditional African psychological treatment against severe depression, and the tea is used to 'bring sufferers back to life' (Viljoen et al. 2002) and in the treatment of several ailments including epilepsy, mental disorder, cough, colds and respiratory ailments, asthma, pain, stroke, shingles, diabetes,  hypertension, wounds, kidneys and chest ailments, backache, haemorrhoids and menstrual pains, infections, inflammation. (Erhabor et al. 2020; Viljoen et al. 2002; Nantapo, Marume 2022; Lisowski, Malaisse Symoens 1970a; Lisowski, Malaisse, Symoens 1970b).

Externally the plant has been used to treat abrasions and the dried powdered leaves are used in dressings for burns and wounds.   There is also an intriguing (given the content in resins and volatile compounds) use of the plant, the inhalation of the smoke produced in burning the plant material.  This smoke is supposed to treat chest pains and asthma: the Pedi people smoke the leaves in pipes to obtain this effect, and the leaves can be mixed with tobacco and smoked as a cure for bronchial disease The smoke can also be redirected into the vagina to treat infections and pains in the uterus. (Viljoen et al. 2002; Nantapo, Marume 2022; Kokwaro 1993).

In terms of possible developments in the commercial exploitation of the plant, it must be pointed out that the plant has been classified as underutilised, and only harvested by herbalists or rural communities for medicinal purposes. One of the problems is that the plant does not produce large quantities of above-ground biomass (20–30 kg of twigs per day harvested by professional collectors), and it does so only in the summer season if the rain is sufficient to resurrect the dry plant. (Nantapo, Marume 2022).

The leaves and twigs are used to brew a medicinal herbal tea said to have a potential for commercialization due to its pleasant flavour (Chukwuma et al. 2019), as a functional tea, a source of cosmetic products, and other pharmacological products (Nantapo, Marume 2022).

Secondary metabolites as products.

It appears that the two large classes of secondary metabolites with promising applications are polyphenols and volatile (terpenic) compounds.

Polyphenols

The dominant polyphenols in the plant are galloylquinic acids and derivatives of galloyl glucose hexahydroxydiphenic acid: 3,4,5-tri-O-galloylquinic acid (44% (by weight) in hydrated leaves and 74% (by weight) in dehydrated leaves.) and higher molecular weight galloylquinic acids; gallic acid, caffeic acid, ferulic acid, methyl gallate, epicatechin, quercitrin, isoquercitrin, hyperoside, and in addition, kaempferol glycosides such as astragalin, Trifolin, Afzelin. The galloylquinic acids can be used as chemotaxonomic markers to distinguish between plants from different regions (Nantapo, Marume 20222; Chukwuma et al. 2019; Moore et al. 2005a; Moore et al. 2005b).  These polyphenols are with all likelihood linked to several of the pharmacological properties of the plant: antioxidant, antimicrobial, antiviral, antidiabetic, and anticancer (Nantapo, Marume 2022).

Volatile compounds

Since earlier papers were confused regarding the composition of the essential oil, reporting carvone and perillic acid as major components, alongside 1,8-cineole and diosphenol, Chagonda, Makanda and Chalchat (1999) went on to analyze the composition of Zimbabwe EOs, averaged over 3 years (1994-1996) with the following results: trans-pinocarveol (28.7–28.8%), pinocarvone (13.4–21.3%), α-pinene (tr-23.0 %) and β-selinene (5–9.9%) were the major constituents, followed by linalool (2.4-3.2%), borneol (0.4-3.5%), 1.8-cineole (0.6-2.5%), camphene (1.6-1.7%), alpha-campholenal (0.9-1.0%), beta-pinene (0.8-0.9%), myrtenal (0.7-0.8%), myrcene (0.5-0.6%), alpha-muurolene (0.4-0.5%), gamma-muurolene (0.2-0.7%), delta-cadinene (0.5%), and many others.  While this composition matches pert well that of the South African essential oils found in literature, it is fairly different from that of the EOs from Angola, reinforcing the idea that there is much chemical diversity in African oils.

Examples of essential oil composition

Angolan oil (internal analysis): cis-verbenol (17.4-18.9%), pinocarvone (8.8-13.3%), α-pinene (7.4-10.8%), limonene (7.0-10.9%), 1,8-cineole (4.4-11.8%), β-selinene (3.9%), cis-carveol (3.5-5.2%), p-cymene (1.8-2.5%), verbenone (1.4-2.2%), germacrene D (0.9-1.6%), carvone (0.9-1.5%), myrtenal (0.8-1.1%), α-humulene (0.7-2.3%), 2,5-dimethyl styrene (0.6-0.8%), α-copaene (0.5-1.1%), δ-cadinene (0.4-1.3%), β-caryophyllene (0.3-0.9%), β-pinene (0.3-0.7%), bornyl acetate (0.3-0.5%), camphene (0.2-0.6%), α-muurolene (0.2-0.5%), β- myrcene (0.2%), γ-terpinene (0.2%), α-terpenyl acetate (0.2%), γ-muurolene (0.1-0.4%), sabinene (0.1-0.3%), thuja-2,4(10)-diene (0.1-0.2%), β-bourbonene (0.1-0.2%), γ- cadinene (0.1-0.2%), α-cubebene (0.1%)
South African oil (Viljoen et al. 2002): trans-pinocarveol (19.57%), pinocarvone (11.13%), limonene (6.09%), trans-p-mentha-2,8-diene-1-ol (2.70%), cis-p-menth-2,8- dien-1-ol (2.3%), linalool (1.80%), bornyl acetate (1.78%), α-pinene (1.61%), myrtenal (0.94%), α-copaene (0.83%), camphene (0.12%), β-pinene (0.16%), sabinene (0.03%), myrcene (0.16%), 1,8-cineole (0.15%), β-phellandrene (0.02%), cis-anhydrolinalool oxide (0.01%), o-mentha-1(17)5,8-triene (0.18%), p-cymene (0.17%), α-pinene oxide (0.01%), 1,3,8-p-menthtriene (0.08%), γ-campholene aldehyde (0.04%), α-p-dimethylstyrene (0.18%), α-cubebene (0.03%), trans-1,2-limonene epoxide (0.03%), fenchyl acetate (0.05%), α-bourbonene (0.02%), β-bourbonene (0.20%), pinocamphone (0.10%), benzaldehyde (0.01%), β-cubebene (0.09%), isopinocamphone (0.15%), linalyl acetate (0.23%), trans-p-menth-2-en-1-ol (0.02%), β-elemene (0.47%), terpinen-4-ol (0.40%), hotrienol (0.33%), cis-dihydrocarvone (0.08%), sabinyl acetate (0.09%), alloaromadendrene (0.05%), trans-pinocarvyl acetate (0.02%), α-humulene (0.12%).

The product

The essential oils are produced mainly by steam distillation of the aerial parts for 2-4 hours, although at times it has been produced with the cheaper, but less efficient, method of hydro-distillation (Viljoen et al. 2002). The yield can vary accordingly, between 0.14% and 0.04% (hydro-distillation) (Viljoen et al. 2002; Nantapo, Marume 2022).  The EO obtained from Angolan plant material has a light greenish-yellow colour, with a citrus top note, fresh and slightly cineolic, with a turpentine aspect that reveals itself in a few seconds. There's an underlying spiciness that grows a little with time. The turpentine aspect becomes gradually more penetrating, becomes warmer and sweeter, with a frankincense-like character which becomes stronger with time. The dry note is long-lasting and more and more reminiscent of Frankincense, albeit with more of a fresh aspect and less luxurious.

Possible activities

Undoubtedly the most plausible biological activity for the EO is the antimicrobial one since it was active in vitro on several bacterial and fungi strains. It was particularly effective against Pseudomonas aeruginosa and Aspergillus niger, in both cases as effective as the standard treatment; it wasn't so effective with other strains (Proteus vulgaris, Serratia odorifera, Salmonella typhimurium, Alternaria alternata), but notable are the effects on Escherichia coli, Enterococcus faecalis, Cryptococcus neoformans, and Candida albicans (Viljoen et al. 2002). In another study, the EO was very effective in its tidal effects on Staphylococcus aureus, Klebsiella pneumoniae and Candida albicans (van Vuuren, Viljoen 2006).

The authors have suggested that the possible active compounds are pinocarvone, trans-pinocarveol, limonene, trans-p-menth-1-(7)-8-diene-2-ol, and cis-p-menth-1-(7)-8-diene-2-ol, but at the same time caution against drawing un-called for cause-effect relationships. (Nantapo, Marume 2022)

There are also suggestions for other activities. Trans-pinocarveol has been linked to stomachic, digestive and gastroprotective activities (Nantapo, Marume 2022), and there are preliminary suggestions of anticancer, anti-inflammatory, antiarthritic, and antioxidant properties, albeit based only on mechanistic data (Erhabor et al. 2020).

Toxicology

There hasn't been any specific toxicological investigation on the EO, but there are some theoretical hazards that can be inferred from the chemical composition.  α-Pinene and β-pinene (average 7.0-12.0%) are monoterpene hydrocarbons that are prone to oxidative damage and are classified as Category B, moderately allergenic molecules, but sensitization by peroxides is particularly high in old or oxidized EOs. Similarly, limonene (7.0-11.0%) when oxidized can be skin reactive.

The presence of 1,8-cineole (4.4-11.8%) calls for some caution in pediatric use near the nose, mouth and eyes, or by direct inhalation or by mouth, but the risk is minimal.

Carvone (0.9-1.5%) has a weak allergenic or toxic profile. (-)- Carvone might be moderately allergenic, but there is no information on the (+)- isomer, which is reproductively toxic at 500 mg/kg in male rats, but not at 375 mg/kg. Its NOAEL is 93 mg/kg (13 weeks), while that of the unspecified carvone is 125 mg/kg.  The Council of Europe has carvone's ADI at 2 mg/kg, and IFRA has a dermal limit of 1,2% for leave-on products for (-)-carvone.  The daily oral maximum is 12,5 mg/kg for both isomers, and the dermal limit is 23%.  This translates into a daily oral maximum of 875 mg carvone for an adult of 70 kg, which means roughly 8-13 mg of the EO (for an adult of 70 kg).

References

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• Chukwuma CI, Matsabisa MG, Rautenbach F, Rademan S, Oyedemi  SO, Chaudhary SK, Javu M (2019) “Evaluation of the nutritional composition of Myrothamnus flabellifolius (Welw.) herbal tea and its protective effect against oxidative hepatic cell injury”. J Food Biochem.;43(11):e13026
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