Silver nitrate: antimicrobial activity related to cytotoxicity in cultured human fibroblasts

How safe is silver in wound care?

Use of silver in burns, chronic ulcers and diabetic ulcers can lead to circulatory absorption and deposits in wound sites, liver, kidney and other organs. Despite this, the risks of lasting tissue damage or functional disorders are low.

The use of silver nitrate for chemical de-epithelialization and urothelialization of intestine in a rabbit model of augmentation cystoplasty

Urinary tract reconstruction using bowel segments can result in complications such as electrolyte abnormalities, infections, stones and cancer. Intestinal mucosa is the primary site responsible for these complications. De-epithelialization of the mucosa and subsequent urothelialization might alleviate these problems. We recently reported our success in de-epithelialization and subsequent uroepithelialization of intestinal segments using 10 g/100 ml AgNO(3) solution in a rat model of augmentation. In this study, chemical de-epithelialization of a colonic segment was attempted using 10 g/100 ml AgNO(3) solution in a rabbit model of augmentation. Sigmoid cystoplasty was performed in 20 male New Zealand rabbits using a 6 cm patch of sigmoid colon. There were two groups, including one group of five rabbits (control, group 1) that underwent augmentation alone, while another group (15 rabbits, treatment group or group 2) was treated with 10 g/100 ml AgNO(3 )solution before augmentation. Control rabbits were killed at the week 8 of experimentation. Treatment rabbits were killed at 2-, 4-, 6- and 8-week intervals. Immediately before augmentation and at the end of the 8 week experimental period each rabbit underwent cystometry. De-epithelialization of the bowel epithelium without urothelialization was apparent in the treatment rabbits killed at 2 and 4 weeks. Histological analysis revealed almost complete urothelialization of the augmented sections treated with 10 g/100 ml AgNO(3 )solution at the end of the 6 and 8 week of experimental periods. The preoperative and postoperative bladder capacities increased substantially in all groups. There was no obvious histologic difference in the amount of collagen present in the augmented tissues in any of the experimental groups. The present study confirmed that the treatment of intestinal segments with 10 g/100 ml AgNO(3 )solution led to chemical de-epithelialization and urothelialization of the augmented segments. This procedure could, theoretically, have applications to human surgery.

Cytotoxicity mechanisms of sodium hypochlorite in cultured human dermal fibroblasts and its bactericidal effectiveness

We investigated the therapeutic efficacy of the topical antiseptic sodium hypochlorite (NaOCl) for antibacterial activity and in parallel the cytotoxicity mechanisms by which hypochlorite and the chloramines generated therefrom induce oxidative tissue damage, which further influences the wound-healing process. Human dermal fibroblasts were exposed to increasing concentrations of reagent NaOCl (0.00005-0.1%) at exposure times varying between 2 and 24 h and the protective effects of fetal calf serum (FCS) determined. Antibacterial power was studied by testing a wide range of hypochlorite concentrations (0.00025-0.5%) against four isolated bacterial species. Total bactericidal effects were observed only for 0.5%; concentration range 0.25-0.025% produced partial antimicrobial activity. The early NaOCl-produced cytotoxic action on cultured fibroblasts was cell ATP depletion which occurred at 0.00005% (with FCS 2%) followed by dose- and time-dependent decreases, reaching levels below 5% of control values. Using the 3'-[1-(phenylamino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid metabolic assay to evaluate cell death, we observed that NaOCl concentrations greater than 0.05% provoked null fibroblast survival at all exposure times assayed. Hypochlorous acid proved to exert a rapid inhibitory effect on DNA synthesis, consistent with its primary role in bacterial killing by phagocytes. Cytotoxicity produced by increasing NaOCl concentrations and assessed by measuring both mitochondrial function and cell DNA synthesis was reduced with the greatest presence of FCS (10%) in culture media.

Mechanisms underlying chlorhexidine-induced cytotoxicity

Chlorhexidine (CLX) is the most widely used antiseptic for wound and skin disinfection. Despite its potent bactericidal action, skin irritation is observed when it is used topically. This study aimed to evaluate the mechanisms underlying CLX-induced toxicity on human dermal fibroblasts with special emphasis on factors that may mediate or counteract its undesirable effects. Cells were exposed to CLX concentrations of 0.00005-0.025% for 3, 6, 8 or 24 h in the absence or presence of different concentrations of foetal calf serum (FCS) (2, 5 and 10%). Depletion of cell ATP occurred, in a time- and concentration-dependent manner, in all experimental conditions at [CLX] >0.001%. At 24 h of CLX exposure time, the decrease in intracellular ATP was produced from a 10-times lower CLX concentration (0.0001%). Concentrations > or =0.02% produced total loss of ATP. However, cell survival was maintained after CLX treatment for 3 and 8 h and CLX concentrations > or =0.005% were required to produce total cell death. CLX exerted an inhibitory concentration-dependent effect on DNA synthesis from concentrations as low as 0.0001%. Only FCS at 10% appeared to have a cytoprotective action against CLX-induced cytotoxicity.