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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a process for treating hair; and to a
composition for use in such treatment. It is particularly applicable to
the styling of human hair, e.g. by `permanent waving`.
It has long been known that hair consists largely of protein (`keratin`)
and that its physical form is affected by the arrangement of disulphide
linkages between cysteine residues. Thus known hair treatment compositions
employ thiols which are believed to undergo redox reactions so that the
keratin disulphide linkages are unmade and remade, allowing the hair to be
given a new configuration during the process. However, the thiols are
disagreeable, even dangerous, compounds and the compositions generally
need to be strongly alkaline. They are unpleasant to use, and can harm the
skin and hair.
SUMMARY OF THE INVENTION
Broadly the present invention is based on the discovery that certain
enzymes and enzyme preparations can be used to treat hair safely, under
very mild conditions. They can thus be used to alter its configuration,
e.g. for curling, waving or straightening.
In one aspect the invention provides a process for treating hair in which
the hair is reconfigured while being contacted with a composition which
comprises an aqueous medium containing a protein disulphide isomerase,
under conditions such that the enzyme can catalyse rearrangement of
disulphide linkages in the hair. Generally the composition will contain a
cofactor for the enzyme.
An isomerase is preferably to (for example) a reductase since the latter
requires the presence of a hydrogen donor such as NADPH. However for some
purposes other types of enzyme may be useful.
Preferably the composition contains substantial amounts of only one enzyme.
In a second aspect the invention provides an enzyme-containing composition
for use in such a process. The composition may be usable directly or, more
usually, after one or more preliminary steps such as dilution, solution or
admixture. A composition may comprise a stable enzyme preparation
comprising an enzyme and a carrier (which may be water, generally
including a buffer; and/or may be a (preferably soluble) solid).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A suitable type of enzyme is the protein disulphide isomerase E.C.5.3.4.1,
hereafter referred to as PDI. This enzyme is well-characterised and is
commercially available from GENZYME (Genzyme Biochemicals Ltd., Maidstone,
England; Genzyme Corp., Boston, Mass., U.S.A.). It has been described by
N. Lambert and R. B. Freedman (1983 Biochem. J. 213 225-234). This type of
enzyme seems to occur in every eukaryotic tissue which synthesises a
secreted protein. The most easily obtainable tissue type is bovine liver
PDI. This may be isolated as follows.
500 g of diced bovine liver is washed with physiological saline and
extracted at neutral pH with phosphate buffer which contains 1% Triton.
This gives an enzyme extract which is then concentrated and purified by
procedures involving heat treatment, ammonium sulphate precipitation, ion
exchange chromatography, dialysis and finally lyophilization. (See the
paper by Lambert and Freedman for fuller details.)
A purer enzyme may be prepared by genetic engineering, i.e. using cloned
DNA in a suitable culture.
For use, it is generally necessary to add a very small amount of a low
molecular weight thiol as a cofactor. (The concentration need only be of
the order of micromolar.)
Suitable thiols which are readily available and are acceptable for in vivo
treatment of human hair include cysteine and reduced glutathione.
A suitable composition for use contains 0.03 to 1.5 g (and preferably 0.5
to 1.5 g) of PDI and 1 to 1000 (and preferably 10 to 1000) micromoles of a
cofactor per liter, buffered to a pH in the range 7-8, and preferably pH
7.5, suitably with a phosphate buffer. It may also contain other
components, e.g. selected from wetting agents, perfumes, and carriers.
Since the thiol is susceptible to aerial oxidation, the storage form of
the composition should provide protection from air. The enzyme and
cofactor are preferably stored separately as freeze dried powders. The
cofactor component thereof, may include the phosphate buffer and any other
components, and be stored in an air-free vessel, e.g. a foil sachet,
possible under nitrogen, and/or in an encapsulated form. The enzyme should
be protected from harmful materials, e.g. by being packaged analogously to
the cofactor. For use, a sachet of cofactor and phosphate buffer is opened
and the contents are dissolved in water, preferably at 28.degree. C. Then
the enzyme is added.
Hair is treated at a temperature slightly above room temperature, e.g.
25.degree. to 40.degree. C., preferably 25.degree. to 32.degree. C., for a
period of up to 1 hour.
The PDI may be modified to improve its stability or effectiveness. Thus it
may be dissociated into its subunits, which can show greater activity
(presumably since the active sites are then more accessible, particularly
to bulky substrates such as keratin, than in the whole enzyme). The enzyme
(which term includes a dissociated subunit of natural PDI) may be
immobilised on a carrier. A suitable carrier has a large surface area,
since an insoluble substrate such as keratin cannot penetrate into the
interior. Thus we may use polystyrene beads or other carriers of synthetic
polymers (such as polyvinyl resins, nylon, and isocyanate-capped
polyurethane foam). This can improve stability and aid storage and use. A
carrier may be given a convenient shape, e.g. forming at least part of a
hair roller.
The enzyme may be chemically modified to alter its binding properties and
Km value.
An example of the use of a composition according to the invention follows.
EXAMPLE
A subject's hair was washed with a conventional shampoo and rinsed. The wet
hair was wound tightly on curling rollers of diameter 0.5 cm, and a
solution of the following composition at a temperature of 28.degree. C.
was applied:
PDI (Genzyme . . . ) 1 g/l
Reduced glutathione (SIGMA) 1 mM
50 mM Phosphate buffer to pH 7.5
Distilled water.
The hair was kept warm (25.degree.-32.degree.) for 45 minutes, then the
rollers were removed and the hair was washed free of the composition.
After conventional drying, it was found to be well curled, comparable to
the result of treatment with a conventional waving lotion.
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