74
prepared from different sources, namely, steam explosion lignin (SE), Curan 100
lignin (CU), lignosulfonate (LS, is a lignin product with good dispersion, antioxidant and ultraviolet (UV) protective properties) and sugarcane bagasse lignin (BG),
in murine fibroblast 3 T3 and human keratinocyte (HaCaT) cells. The toxicity of the
four lignin samples increased with the exposure time, however, all these lignins
were hypotoxic and had cytotoxic influences only at very high concentrations (>
400 μg/mL). Among the lignins, CU was the most cytotoxic on HaCaT cells, BG
was the most cytotoxic on murine fibroblast 3 T3 cells, while LS was the least cytotoxic on both cell lines. The effective concentration of lignin as an antioxidant, i.e.
the concentration at which lignins compromise cancer cell growth, is less than the
concentrations that are harmful to normal cells. That means lignins are effective
antioxidants at non-cytotoxic concentrations. Barapatre et al. (2016) tested the cytotoxic activity of eleven lignin fractions isolated from Acacia nilotica on the breast
cancer cell line (MCF-7) and the human hepatic stellate cells (HHSteCs). The
MCF-7 cell survival rate decreased with the increase of lignin dose.
Differences in lignin components as a result of the use of different extraction
solvents could lead to variations in the effect of lignin on cell viability. Lignin fractions extracted with chloroform, diethyl ether, ethanol, ethyl acetate, n-hexane and
water, in the concentration range from 0.5 to 50 μg/mL were cytotoxic for the
MCF-7 cells, while lignin fractions extracted with acetone, butyl alcohol and methanol within the same concentration range were non-cytotoxic. In addition, the lignin
fractions extracted with chloroform, diethyl ether, ethyl acetate and water showed a
high cytotoxic effect and had an IC 50 < 15 μg/mL. Their IC 50 values were lower than
those of the standard drugs: phenethylisothiocyanate and tamoxifen. However, all
lignin fractions at similar concentrations had non-cytotoxic effects on HHSteCs.
Cytotoxicity was tested on HHSteCs only at concentrations greater than 100 μg/
mL. In summary, lignin fractions had specific cytotoxicity for cancer cells. Wang
et al. (2015) reported the cytotoxicity of two LCC fractions from Inonotus obliquus
on cancer cells. The LCC fractions appear to inhibit the NF-κB activation through
the suppression of nuclear translocation in cancer cells. LCC induced cell death
primarily in a cell cycle-independent manner. Athinarayanan et al. (2018) analyzed
the cytotoxic effects of lignin on the morphology of human mesenchymal stem cells
(hMSCs). The nuclei of low-dose lignin-treated cells did not undergo morphological changes, but DNA fragmentation and nuclear condensation were observed in
high-dose lignin-exposed cells.
It is an important part of the study of the toxicology of lignin to evaluate the possibility of irritation of the eyes and skin (Vinardell and Mitjans 2008). Vinardell
et al. (2008) carried out an eye and skin irritation test on male albino rabbits with
five types of lignins. 0.1 g lignin samples were applied to the eyes, and 0.5 g lignin
samples to the skin. None of the samples caused an irritation response in the eyes or
skin. This indicated that lignin can be used in cosmetic and topical formulations.
It should be noted that lignins are less cytotoxic than some other phenolic compounds: epicatechin and tannin (Ugartondo et al. 2008; Libralato et al. 2011). This
may be related to the relative high Mw of lignin, i.e. the cytotoxicity of lignin is
inversely proportional to Mw. The cytotoxicity of lignin was inversely proportional
Z. Qin et al.
prepared from different sources, namely, steam explosion lignin (SE), Curan 100
lignin (CU), lignosulfonate (LS, is a lignin product with good dispersion, antioxidant and ultraviolet (UV) protective properties) and sugarcane bagasse lignin (BG),
in murine fibroblast 3 T3 and human keratinocyte (HaCaT) cells. The toxicity of the
four lignin samples increased with the exposure time, however, all these lignins
were hypotoxic and had cytotoxic influences only at very high concentrations (>
400 μg/mL). Among the lignins, CU was the most cytotoxic on HaCaT cells, BG
was the most cytotoxic on murine fibroblast 3 T3 cells, while LS was the least cytotoxic on both cell lines. The effective concentration of lignin as an antioxidant, i.e.
the concentration at which lignins compromise cancer cell growth, is less than the
concentrations that are harmful to normal cells. That means lignins are effective
antioxidants at non-cytotoxic concentrations. Barapatre et al. (2016) tested the cytotoxic activity of eleven lignin fractions isolated from Acacia nilotica on the breast
cancer cell line (MCF-7) and the human hepatic stellate cells (HHSteCs). The
MCF-7 cell survival rate decreased with the increase of lignin dose.
Differences in lignin components as a result of the use of different extraction
solvents could lead to variations in the effect of lignin on cell viability. Lignin fractions extracted with chloroform, diethyl ether, ethanol, ethyl acetate, n-hexane and
water, in the concentration range from 0.5 to 50 μg/mL were cytotoxic for the
MCF-7 cells, while lignin fractions extracted with acetone, butyl alcohol and methanol within the same concentration range were non-cytotoxic. In addition, the lignin
fractions extracted with chloroform, diethyl ether, ethyl acetate and water showed a
high cytotoxic effect and had an IC 50 < 15 μg/mL. Their IC 50 values were lower than
those of the standard drugs: phenethylisothiocyanate and tamoxifen. However, all
lignin fractions at similar concentrations had non-cytotoxic effects on HHSteCs.
Cytotoxicity was tested on HHSteCs only at concentrations greater than 100 μg/
mL. In summary, lignin fractions had specific cytotoxicity for cancer cells. Wang
et al. (2015) reported the cytotoxicity of two LCC fractions from Inonotus obliquus
on cancer cells. The LCC fractions appear to inhibit the NF-κB activation through
the suppression of nuclear translocation in cancer cells. LCC induced cell death
primarily in a cell cycle-independent manner. Athinarayanan et al. (2018) analyzed
the cytotoxic effects of lignin on the morphology of human mesenchymal stem cells
(hMSCs). The nuclei of low-dose lignin-treated cells did not undergo morphological changes, but DNA fragmentation and nuclear condensation were observed in
high-dose lignin-exposed cells.
It is an important part of the study of the toxicology of lignin to evaluate the possibility of irritation of the eyes and skin (Vinardell and Mitjans 2008). Vinardell
et al. (2008) carried out an eye and skin irritation test on male albino rabbits with
five types of lignins. 0.1 g lignin samples were applied to the eyes, and 0.5 g lignin
samples to the skin. None of the samples caused an irritation response in the eyes or
skin. This indicated that lignin can be used in cosmetic and topical formulations.
It should be noted that lignins are less cytotoxic than some other phenolic compounds: epicatechin and tannin (Ugartondo et al. 2008; Libralato et al. 2011). This
may be related to the relative high Mw of lignin, i.e. the cytotoxicity of lignin is
inversely proportional to Mw. The cytotoxicity of lignin was inversely proportional
Z. Qin et al.