K Babu, M Deepa, S Shankar, S Rai
clastogenic, genotoxicity, mitodepresseive, nano-silver, root meristem
K Babu, M Deepa, S Shankar, S Rai. Effect of Nano-Silver on Cell Division and Mitotic Chromosomes: A Prefatory Siren. The Internet Journal of Nanotechnology. 2007 Volume 2 Number 2.
Silver is relatively rare metal that occurs naturally in the earth. Silver has been in medical use for decades and was used in systemic drugs before the advent of antibiotics. Today, silver is used routinely in antibacterial salves. Some of the more common silver compounds used in medical devices and industries are nitrate, chloride, bromide, acetate, oxide, sulfate and cyanide (Stokinger 1981, Quinn 2002). Silver is also used in the form of colloidal state (Colloid silver or silver mineral water) and nano particles (Nano-silver). The microbicidal effects involve both altering the function of the cell membrane and linking to the cell's DNA, disrupting cell reproduction. The bactericidal action of silver ions is effective against a broad spectrum of bacteria, including the common strains, which cause infection, and the more virulent antibiotic-resistant strains (Russell 1994). Silver is known to kill more than 650 kinds of bacteria and suppress the viral activity (
A number of plant bioassay techniques had been developed for the detection of environmental mutagens because plant chromosomes are relatively large and respond to treatment with mutagens in a similar way to mammals and other eukaryotes (Grant 1978, 1994, WHO 1985). Among these assays, the
Materials and Methods
Commercially available onions,
Experimental results on the effects of nano-silver on cell division and mitotic chromosomes of
Effect on mitotic index
Nano-silver treated cells showed significant reduction in the frequency of mitotic index during all doses and durations when compared to control sets (P<0.05, P<0.001). This divisional frequency was found to reduce even at 1h exposure during all treatments indicating that the nano-silver has an immediate effect on dividing cells. The frequency further got reduced when dose and duration increased (Table 1).
Effect on chromosomal aberration
Nano-silver induced structural aberrations of chromosomes such as
C-metaphase (Fig – 1), disturbed metaphase (Fig – 2), fragments (Fig - 3&8), sticky metaphase (Fig – 4), laggards (Fig – 5), anaphasic bridge (Fig – 6), disturbed anaphase (Fig – 7) and micronuclei (Fig – 9). The chromosomal aberrations observed in the treated cells were found to be of higher frequency during longer exposure. A distinct dose dependent increase in chromosomal anomalies was observed in all treatments (Table 1). This data is found to be statistically highly significant when compared to control (P<0.001). Fragments, C-metaphase, disturbed metaphase and disturbed anaphase were found to be in higher frequency in all treatments (Table 2). The frequency of anaphasic bridge was found to be higher during 0.5 and 1h exposures where as in 2 & 4 h exposures, this was reduced (Table 2). Rare instances of micronuclei were also observed in the treated cells.
Nano-silver is a new product of the emerging nanotechnology and is a new age preservative.. Nano silver is used in personal care and consumer products owing to its high anti-microbial activity. Commercial Nano-silver is usually available as a suspension in pure de-ionized water with nanosized silver (Ag). Approximately 80% of the silver is in the form of metallic silver nano-particles. The remaining silver is in ionic form. Nano silver particles are much more smaller (2 nm in diameter) and exists in a stable form than colloidal silver (10 nm to 1 micron in diameter).
Nano-silver, though an effective antibacterial (She and Zhang 2003, Lok
In humans, less than 1% of topically applied silver compounds are absorbed through the skin (Snyder
Earlier reports showed that high concentrations of nano-silver based inorganic antibacterial agents have cytotoxic effects on rat's fibroblasts L-929 (Zhand
In proteomic studies nano-silver was shown to destabilize the outer membrane, collapse the plasma membranes' potential and deplete the levels of intracellular ATP of the bacterial cells (Lok
In the present preliminary toxicity assay, treatments with 10, 20, 40 and 50 ppm of
nano-silver produced a dose and duration-dependent MI and CA in
The present study provides an evidence for the possible genotoxic effect of nano-silver on plant system. Though the results in the plant system cannot be extrapolated directly to animal systems, the findings of the present study raise the need for elaborate evaluations to ensure the safety of nano-silver.
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