An aqueous extract of the root of comfrey (Symphytum officinale L.) was
obtained by the Soxlet method using water as an extractant. Extraction with water
was carried out at predetermined optimal conditions of extraction (extraction
time 240min and hydromodule 1:10w/v). For modeling the kinetics of
extraction of total extractable compounds from comfrey root with water,
Ponomarev’s kinetic model was applied wherein extraction degree (SE) in the
period of rapid extraction and coefficients b and k in the equations of
extraction kinetics were determined. Chemical composition of an aqueous
extract of comfrey root obtained under optimal conditions was examined. The
content of total phenols (473.16mg GKE/g d.e.) and flavonoids (18.90 mg
RE/g d.e.) was determined. HPLC, UHPLC-DAD-HESI-MS and ICP-OES
methods for identification and quantification of bioactive compounds and
micro and macro elements present in the aqueous extract of comfrey root
were validated. The most abundant bioactive compounds... in the examined
aqueous extract of comfrey root were rosmarinic acid, allantoin and ellagic
acid (7.4g/100g d.e, 8.91g/100g d.e and 12.891g/100 g s.e), respectively. The
mineral composition of an aqueous extract of comfrey root showed that there
was a relatively high content of K (560,4mg/dm3) and Ca (129,3mg/dm3).
Other trace elements contained in an aqueous extract of comfrey root in
descending values were Na, Pb, Mg, Fe, Al, Zn, B, Ba, Cu.
Examination of the effects of aqueous comfrey root extract included the
examination of antioxidant activity by monitoring the ability of neutralization
of free radicals and antimicrobial activity in vitro in parallel with the
standards of bioactive compounds that are the most present in the extract.
Obtained EC50 values for tested samples showed that the highest antioxidant
activity have ellagic, then rosmarinic acid, and finally aqueous extract of
comfrey root, while allantoin did not show antioxidant activity. The aqueous
extract of comfrey root showed antimicrobial activity against gram-negative
bacteria Escherichia coli and Salmonella typhimirium, while its activity was
not observed on the examined gram-positive bacteria and fungi. The effect of
an aqueous extract of the comfrey root and allantoin on viability and
proliferation of epithelial (MDCK) and fibroblastic (L929) cell line was
examined in vitro. Allantoin did not act on the viability of examined cell
lines. The comfrey root extract, in all tested concentrations, showed a mild
stimulatory effect on the viability of L929 cells, while there was no change in
the viability of MDCK cells. Allantoin showed mild inhibitory effect on
proliferation of both cell lines at concentrations 0.04mg/cm3 and 0.1mg/cm3,
but more pronounced on MDCK cells. Effect of comfrey root extract on cell
proliferation in concentrations higher than 0.04mg/cm3 was significant
stimulatory for L929, but inhibitory for MDCK cells.
In the final phase of the study it was examined in vivo anti-irritant
potential of dry aqueous extract of comfrey root and allantoin incorporated
into prepared semisolid hydrophilic carriers of hydrogel-type and cream-type.
The most effective hydration was achieved when creams and gels containing
aqueous extract of comfrey root was used and a slightly less when they
contained allantoin. More effective influence of creams compared to the gels
on skin hydration was also maintained. All tested samples had an impact on
the reduction of the erythema index wherein the creams were more effective
than the gels. Cream with the comfrey root extract achieved more efficient
antieritematous effect in relation to the cream with allantoin. Changes in skin
barrier function were monitored by measuring transepidermal water loss
(TEWL) after irritation. More efficient reduction of TEWL was recorded after
application of the gel with comfrey root extract compared to the gel with
allantoin and compared to the appropriate creams. For all tested creams that
presented U/V type emulsions, the stability was examined by polarization
microscopy, based on the presence of dispersed droplets of oil phase as well
as turquoise and pink stripes of colored varying intensity, which occur due to
the formation of lamellar liquid-crystalline phase or α-crystalline gel phases
which form a mixed emulsifiers and stabilized prepared creams. Cream
containing a dispersion of dry extract of comfrey root showed the most
intense presence of structures that point to a stabilization of the system by
forming a liquid crystal and α-crystalline gel phase and presented a system
that has good stability and also good hydration potential.
On the basis of conducted study it can be concluded that an aqueous
extract of the comfrey root can be used as a pharmaco-logically active
supplement in pharmaceutical preparations for external application.
