GB2490265A - The Sub-critical water extraction of Senna leaves - Google Patents

Abstract

A method of preparing an extract from Senna leaves (Cassia Angustifolia) comprises reduction of the particle size of the Senna leaves, extraction with subcritical water and then removing the water to produce a pharmaceutically acceptable extract. The extraction may be conducted at 150-230°C and/or 15-100 bar. The water may be removed by evaporation, freeze drying or spray drying. The extract may be formulated in a self emulsifying drug delivery system (e.g. using lauroyl macrogolglycerides and a surfactant) to improve the oral bioavailability of the active constituents; it may be formulated in a topical vehicle (e.g. using cetostearyl alcohol, macrogol cetostearyl ether, liquid paraffin, parabens, water and propylene glycol). The extract may be similar to the corresponding methanolic extract. Extraction of Valerian, Rosemary, German Chamomile and Ginger root is also disclosed.

Description

The Sub-critical Water Extraction of Senna Leaves.

FIELD OF THE INVENTiON

This invention relates to a method of producing an extract of the leaves of senna (Cassia angustfolia), used traditionally in Europe for their medicinal value, without the use of an organic solvent.

BACKGROUND TO THE INVENTION.

Higher plants are unsurpassed in their ability to produce biologically active molecules often of great complexity. These plant "secondary metabolites" have proven a fruitful source of new pharmaceuticals. Often the first use of these compounds has been in the form of traditional herbal medicines. However the structure of the active compounds is frequently so complex that synthetic chemistry can provide no economically viable route to the molecule and this has to be isolated from the plant material.

Simple aqueous extraction of the biomass almost invariably results in a complex extract in which the target compound is diluted by a range of other unwanted phytochemicals derived from the plant, including proteins, sugars and other carbohydrates.

Extraction with a lower alcohol, typically ethanol or methanol, is traditionally a very popular means of obtaining a pharmacologically active preparation from a medicinal herb, The use of an alcohol has the advantage over an aqueous extraction that the highly polar compounds such as carbohydrates, sugars and proteins (which generally are inactive and serve only to add bulk and dilute the concentration of the active compounds) are not extracted.

However the obvious disadvantages of the use of an alcohol in extraction are that it is flammable, necessitating expensive precautions during processing, and also the recovery of the organic solvent for disposal or for further purification and re-use is required. Methanol in addition is highly toxic, and residual levels must be rigorously limited in a pharmaceutical preparation. Indeed due to this high toxicity of methanol, it is frequently substituted by a mixture of the more polar water and the less polar ethanol to produce an extraction solvent of comparable polarity.

A more recent approach that has also been successfully applied is the production of a high potency extract, standardised on the content of the active substance, using extraction with a sub-critical fluid or liquefied gas, most commonly carbon dioxide.

One drawback of liquid carbon dioxide(LCO2) extraction is that the technique is limited to less polarcompounds. It will not extract the compounds most readily soluble in methanol or aqueous alcohol mixtures, including the important class of flavonoids and other polyphenolic compounds such as lignans. The importance of polyphenolic compounds as potential new drugs is increasingly being recognised; with anti-inflammatory activity, anti-bacterial activity and a wide range of activities related to suppression of tumour growth (including inhibition of angiogenesis and reversal of multidrug resistance) being well established.

A more recent example of a high pressure liquefied gas which is being evaluated as an extraction agent and which promises capabilities not exhibited by LCO2 is high pressure superheated water at >150°C. Importantly, it is capable of solubilising more polar compounds than LCO2 extraction Sub-critical water has the unique property that the polarity changes in a well established and predicable manner as temperature is increased; thus at 150°C sub-critical water has a polarity equivalent to a 50:50 mixture of water and alcohol under normal conditions, and the polarity further decreases to a value equivalent to methanol alone at 230°C. It is this property that is the basis of this invention: by employing sub-critical water it is found that extracts equivalent in composition to those produced by methanol can be obtained without the disadvantages resulting from the use of a toxic and flammable solvent.

The traditionally used medicinal herbs described below all produce an extract with methanol that has been widely reported in the literature to contain flavonoid or other phenolic compounds which produce important pharmacological activities: The methanolic extract of Valerian ojjIcinalis root contains valerenic acid that is now established as the principal active substance responsible for the sedative and anxiolytic action of the traditionally used extracts.

The methanolic extract of Rosmarinus offlcinahs (rosemary) leaves contains high levels of rosmarinic acid and related compounds which are known to be largely responsible for the strong anti-inflammatory and anti-bacterial activity of the herb The methanolic extract of Matricaria recta Eta (German chamomile) flowers contains significant levels of apigenin and related flavonoids that are known to exhibit a range of anti-inflammatory actions.

The methanolic extract of Zingiber officinale (ginger) root contains significant levels of the gingerol and shogaol components known to be responsible for the anti-emetic and anti-inflammatory actions.

The metbanolic extract of Cassia angustfo1ia (senna) leaves contains the anthraquinone glycosides sennosides A-D, that are known to be responsible for the laxative action of the herb. The high polyphenolic content, particularly of the anthraquinone species, of such extracts is increasingly attracting attention in relation to non-laxative pharmaceutical applications.

Thus as the subcritical water extracts of the herbs as described in this invention are demonstrated to exhibit a composition essentially similar to that of the corresponding methanolic extract then it can be expected that these extracts will exhibit comparable pharmacological properties to these and to the compound contained therein.

A problem limiting the use of flavonoids and related polyphenolic compounds in therapeutic situations in which systemic treatment rather than local application is required is poor water solubility. This is largely responsible for the low circulating plasma levels after a single oral dose and results in the majority of the dose being excreted without absorption.

Hence this invention also describes self emulsifying formulations which increase the water solubility of these compounds, thus increasing their oral bioavailability and therapeutic efficacy.

STATEMENT OF INVENTION

A method of preparing an extract containing pharmacologically active constituents from the leaves of the traditionally used medicinal plant senna (Cassia angusqfiuia), and comprising reduction of the particle size of the raw material as appropriate, extracting the botanical raw material with sub-critical water, and then removing the water from the resulting solution to produce a pharmaceutically acceptable extract.

SUMMARY OF THE INVENTION.

Example 1 [REFERENCE EXAMPLE]: The extraction apparatus consists of: Two suitable stainless steel vessels capable of resisting high temperature and pressure connected by stainless steel tubing, the first to act as a reservoir in which sub-critical water is produced prior to introduction to the second extraction vessel. These are contained in a thermostatted oven.

* The first reservoir is connected via an inlet valve to a high pressure pump outside the thermostatted oven.

* The extraction vessel is connected via an outlet valve to a stainless steel receiver vessel outside the thennostatted oven but maintained at approximately 90°C.

* A valve from the receiver vessel allows the solution that accumulates to be transferred to a suitable storage vessel.

A schematic representation of a suitable arrangement of the extraction apparatus is provided as Figure 1.

Coarsely ground valerian root botanical raw material is packed into the stainless steel extraction vessel. The extraction vessel is then filled with deionised water (equivalent to approximately four times the mass of botanical raw material employed) and the temperature and pressure of the extraction vessel gradually raised to respectively 230°C and 85 bar. The extraction vessel is then held at these conditions for up to 15 minutes before the resulting solution is forced from the vessel by passing a second quantity of sub-critical water into the system to continue the extraction. In all four portions of sub-critical water are used to extract* the botanical raw material in the manner described above.

Alternatively the same extraction may be achieved in a dynamic mode by passing the same quantity of sub-critical water maintained at 230°C and 85 bar through the botanical raw material packed in the extraction vessel over the course of approximately 1 hour.

The extract is isolated from the solution resulting from the extraction by removing the water by evaporation, the final stages of which are preferably carried out under reduced pressure.

Alternatively the extract may be isolated from the solution resulting from the extraction by removing the water by the process of either freeze drying or spray drying.

A TLC fingerprint representative of the extract (also termed a botanical drug substance) produced in this example is given in Figure 2.

Example 2 [REFERENCE EXAMPLE).

A method as described in example I wherein the botanical raw material is ground rosemary leaves.

A TLC fingerprint representative of the extract produced in this example is given in Figure 3.

Example 3(REFERENCE EXAMPLE].

A method as described in example 1 wherein the botanical raw material is ground flowers of German chamomile.

A TLC fingerprint representative of the extract produced in this example is given in Figure 4.

Example 4 [REFERENCE EXAMPLE].

A method as described in example 1 wherein the botanical raw material is ground ginger root.

A TLC fingerprint representative of the extract produced in this example is given in Figure 5. *

Example 5.

A method as described in example 1 wherein the botanical raw material is ground senna leaves.

A TLC fingerprint representative of the extract produced in this example is given in Figure 6.

Example 6.

A Self Emulsifying Drug Delivery System (SEDDS) formulation for oral administration of the extract of senna leaves as described in Example 5 containing the poorly water soluble polyphenols can be prepared as follows: Extract (produced as described in ExampleS) 15% w/w Lauroyl macrogolglycerides EP (e.g Gelucire 44/14) (RTM) 65-85% w/w Surfactant (e.g. Cremophor 111-14001 Labrafac) 0-20% wlw. (RIM)

The extract is dispersed with stirring in the molten lauroyl macrogoiglycerides at 70-80°C. The surfactant is then added and stirring continued for a further 5 minutes. Using suitable automatic or manual equipment the molten mixture is then dispensed into two piece hard shell gel capsules which are then sealed.

Example 7a.

A cream formulation for topical application of the extract of senna leaves as described in Example 3 can be prepared as follows: Extract (produced as described in ExampleS) 2% wlw Cetostearyl alcohol EP 7% w/w Macrogol cetostearyl ether (e.g. Cremophor A6 or A25) 3% w/w LiquidparaftlnEP (RIM) 12%wlw Parabens (e.g. Nipastat) (RTM) 0.2% w/w Deionised water 67.8% w/w Propylene glycol EP 8% w/w The extract is dispersed in the propylene glycol at 70-80°C wIth stirring. All other ingredients except the water are mixed at 80°C and then added with stirring to the water that was heated separately to 80°C. The dispersion of extract in propylene glycol is then added to this mixture maintained at 70-80°C with stirring. The formulation is then filled into tubes.

Example Th.

A hydroalcoholic gel formulation for topical application of the extract of senna leaves as described in ExampleS can be prepared as follows: Extract (produced as described in ExampleS) 2% w/w Ethanol EP 44% w/w Carbomer (e.g. carbopol 980 NF) (RTM) 3%w/w De-ionised water 51% w/w Sodium hydroxide (aq) qs to neutralise The extract is dissolved in the ethanol at 50-60°C with stirring. The carbomer is then added slowly to the water with rapid stirring. The extract solution is then added to the aqueous carbomer whilst stirring. The resulting mixture is then neutralised by slowly adding aqueous sodium hydroxide to produce a smooth semi-solid.

The formulation is then filled into tubes.

While the preferred embodiments of the invention have been described above, it will be recognised and understood that various modifications may be made therein