Antimicrobial properties of Lawsonia inermis : a review

Australian Journal of Medical Herbalism, Fall, 2007 by O.A. Habbal, A.A. Al-Jabri, A.G. El-Hag

Naphthoquinones are compounds present in various families of plants; their molecular structures endow them with redox properties which confer activity in various biological oxidative processes. In ethnomedicine, plants containing naphthoquinones have been employed for treatment of a number of diseases including cancer. Lawsonia inermis (henna) is widely cultivated and used in many oriental, Middle Eastern and northern African countries. It is best known for its colouring matter contained in the leaves. Henna extract contains lawsone (C10H6O3), the active ingredient and a naturally occurring naphthoquinone. The development of new antimicrobial agents is a research area of utmost importance. Antimicrobial resistance among key microbial pathogens continues to grow at an alarming rate worldwide. The challenge of synthesising derivatives of natural antimicrobial naphthoquinones to improve their pharmaceutical properties has been accepted by several laboratories. In this review we describe the antimicrobial activity of Lawsonia inermis Linn as a natural resource of naphthoquinones. Work in our laboratory in this area will also be elucidated.

Keywords: henna, Lawsonia inermis, naphthoquinones, antibacterial, antiviral, antiparasitic

Introduction

The small shrub of henna (Lawsonia inermis Linn.) is widely cultivated and used in many oriental, Middle Eastern and northern African countries. This dwarf shrub grows outdoors unsheltered at temperatures higher than 11[degrees]C (60[degrees]F). It needs around 5 years to mature and produce leaves with useful levels of tannins. It grows better in arid regions than moist or wet regions and achieves a height of 8 to 10 feet. It grows heavy sweet-smelling white and yellow flowers. The plant belongs to the family Lythraceae and is best known for its colouring matter contained in the leaves. Various cultures used the plant leaves as powdered, dissolved and then turned into paste mainly as a cosmetic. It has been used for dyeing wool, and in ancient times it was used in pigments and for dyeing hair and nails with the reddish-yellow tint.

Henna extract contains lawsone ([C.sub.10][H.sub.6][O.sub.3]), the active ingredient and a naturally occurring naphthoquinone (2-hydroxy-1,4-naphthoquinone 2) (Fig 1). When applied to wool and nylon it behaves as an acid levelling non metallised acid dye. Dye uptake increases with increased pH (Badri 1993) and it stains tissue preparations in histological paraffin sections of different organs (Veereshkumar 2005). The dye was used for colouring leather and skins. It was widely used in Europe from 1890 for tinting hair with many shades prepared by mixing the leaves with other plants such as indigo, catechu or lucerne. Henna brown colouring constituents are of a resinoid fracture having chemical properties similar to tannins, hence the name hennotannic acid.

Quinones (Fig 1) are aromatic rings (dienes = unsaturated hydrocarbon alkene containing two carbon-to-carbon double bonds) with two ketone substitutions. The word quinone refers to the entire class of cyclohexadienediones. They are ubiquitous in nature and are characteristically highly reactive. These compounds, being coloured, are responsible for the browning reaction in cut or injured fruits and vegetables and are an intermediate in the melanin synthesis pathway in human skin (Schmidt 1988).

[FIGURE 1 OMITTED]

Naphthoquinones are widely distributed in plants, fungi and some animals. Their biological activities have long been reported to include antibacterial effects on several species of both aerobic and anaerobic organisms (Didry 1968) and parasites (Wendel 1946).

Early discovery of henna's medicinal properties

Seeking healing by using plants is an ancient practice. Various cultures applied poultices and imbibed infusions of hundreds, if not thousands of indigenous plants dating back to prehistory.

Reports of Neanderthals living 60,000 years ago in present day Iraq used plants such as hollyhock (Alcea spp) (Stockwell 1988, Thompson 1978). Such plants are still used in ethnomedicine worldwide.

Ancient Egyptians are said to have prepared both oil and an ointment from the henna flowers for making the limbs supple. In early Islamic culture henna usage is very evident in the book of "Prophetic Medicine" where the medicinal practices of the Prophet Mohammed (PBUH), as mentioned by his followers and others that were close to him in his household, were recorded (Al-Arnaoutt 1987).

Henna was then used for the treatment of headaches, migraine, albinism, skin abrasions and ulcers, burns, smallpox, leprosy boils, wounds, some mycotic infections and cancers. It was also used for the treatment of scalp and hair infections and ailments.

Recent developments

The development of new antimicrobial agents is a research area of the utmost importance. Resistance to such antimicrobial agents by pathogens (Chopra 1992, Bhavani 2000) continues to be alarming worldwide. The increased prevalence of antibiotic resistant bacteria emerging from the extensive use of antibiotics may render the current antimicrobial agents insufficient to control at least some bacterial infections.