Antiproliferative eff ect of extracts of Sida rhombifolia L. (Malvaceae) on the Allium cepa cell cycle

Field collected roots of four populations of Sida rhombifolia were used for preparing aqueous decoctions at two concentrations: 4g/L; and 16g/L. Afterwards, we used three groups of six onion (Allium cepa) bulbs for testing each population. Slides were made with all bulbs through the smashing technique. Cells in all phases of the cell cycle of A. cepa were analyzed. The mitotic index (% of cells in mitosis) was calculated, and the statistical analysis through the χ2 test was carried out at 5% probability. The results showed that the aqueous extracts of S. rhombifolia have antiproliferative activity at high concentrations. Practically no chromosomal aberrations were induced by treatments. *Address correspondence to: Viviane Dal-Souto Frescura, vividfrescura@yahoo.com.br Received: April 21, 2014. Revised version received: October 23, 2014. Accepted: October 23, 2014

Medicinal plants are widely used in Brazilian folk medicine for treating human illnesses, mainly as infusions or decoctions (teas). However, their uncontrolled use may cause more damages than benefits to public health. According to Teixeira et al., (2003) the use of medicinal plants is a particularly common practice in developing countries, and Vicentini et al. (2001) reported that medicinal plants may contain toxic substances or cause mutagenic effects; on the other hand, the consumption of teas can suppress the effects of mutagenic agents which are acting upon humans (Vicentini et al., 2001).
Sida rhombifolia L. (known as guanxuma or broom) is native to the American continent and is found throughout Brazil (Lorenzi and Matos, 2008). It may be considered as a pest for agriculture, but its teas are popularly used in Brazilian folk medicine. Leaves are used for its mucilage and pleasant taste as a remedy for diarrhea. Australian aborigines also use a root decoction for similar purposes, and eat the raw roots to relieve 'indigestion' (Sens, 2002). In India, a root infusion is used for treating rheumatism. Also, several other uses are mentioned by Lorenzi and Matos (2008). However, neither the efficacy nor the safety of these uses have been tested in the laboratory.
This study was aimed at evaluating the antiproliferative effect of liquid extracts of S. rhombifolia on the A. cepa cell cycle.
Onion bulbs (3 groups of 6 onions) bulbs were allowed to root in water, and treatments were applied when rootlets were 5-10mm long for 24 h. Afterwards, the rootlet tips were collected and fixed in ethanol:acetic acid (3:1) for 24 hours, and then kept in 70% ethanol in the refrigerator until observations.
The number of cells in interphase and in each phase of mitosis was determined as previously described by Tedesco and Laughinghouse IV (2012), the percent of cells in mitosis (mitotic index) was calculated and differences in the mitotic index were evaluated with the χ 2 test (at P<0.05 level, Bioestat 3.0 program). The effect of S. rhombifolia extracts on the number of cells in interphase and in each phase of mitosis is shown in Table 1. With only some exceptions, extracts from the four studied populations decreased the number of cells in prophase, metaphase, anaphase and telophase, in a dose-dependent manner. Table 2 shows that extracts of S. rhombifolia from all the studied populations produced a statistically significant decrease (χ 2 test) in the mitotic index (MI), at the concentration popularly used for human use of these decoctions. With one exception (population 2), a 4-fold increase in concentration produced a further decrease.
It should be noted that only a very small number (2 or less among 6000 studied cells per treatment) showed chromosomal aberrations (not shown in Table 2). It is concluded that root decoctions of S. rhombifolia have a clear antiproliferative effect in the A. cepa test, but that they do not show genotoxic activity in terms of chromosomal aberrations, and that its use in folk medicine may be considered safe.
Antiproliferative activity in the A. cepa test has been shown for leaf and bark. extracts of Luehea divaricata Martius (Frescura et al., 2012), inflorescence extracts of Achyrocline satureioides (Lam.) DC (Fachinetto et al., 2007), and leaf extracts of Pterocaulon polystachyum DC (Knoll et al., 2006) and S. rhombifolia (Islam et al. 2003), but no studies on root extracts have been made before the current paper. Indexes followed by the same letter did not differ significantly (P<0.05, χ 2 test).