The aim of the present study was to compare the effect of oral consumption of propolis alone and in combination with SNPs to control on wound healing in male Wistar rats.
Wound healing occurs in a series of sequential, overlapping phases after injury. Immediately after tissue damage, hemostatic platelet plugs form as framework for inflammatory cell infiltration. The next phase involves inflammatory reaction and includes many cellular elements and chemokine. In the third phase, epithelial, endothelial, and fibroblast cells proliferate. Ultimately, remodeling or healing occurs. The authors used day 12 post-surgery to examine tissue for healing, seeking to assess the active wound healing phase.28
On day 12 post-surgery, the lowest mean tissue neutrophil count was observed in the propolis + 30 ppm SNPs group, the lowest amounts of eosinophil and mast cells were noted in the propolis + 60 ppm SNPs, and the highest levels of both eosinophil and mast cells were seen in the control group. Furthermore, the control group exhibited the lowest mean level scores for rate and amount of reepithelialization, granulation tissue formation, tissue collagen density, and tissue fibroblast count, while the highest levels of these measures occurred in the propolis + 30 ppm SNPs group. These differences were statistically significant in cases of collagen density, mast cell, fibroblast, eosinophil, and neutrophil counts. The combined treatment with propolis + 30 ppm SNPs induced significant differences in terms of collagen density and fibroblast, neutrophil, and eosinophil counts compared to the propolis alone treatment. Moreover, significant differences were detected in mast cell, fibroblast, and eosinophilic variables in the propolis + 60 ppm SNPs group compared to the propolis alone group. The granulation and reepithelialization scores were the highest in the propolis + 30 ppm SNPs group.
To the authors’ knowledge, no comprehensive study has yet been conducted to compare the efficacy of oral administration of propolis and SNPs with topical administration of propolis and SNPs in wound healing process. Generally, topical application of active substances such as silver sulfadiazine cream is recommended to obtain adequate effect and with minimal side effects; inactive materials such as propolis that may play a role appear to be activated during many complex processes after oral consumption. In addition, the results of Pina et al,13 Boateng et al,14 Jia et al,17 and Kim et al18 demonstrated oral provision at a nontoxic dose of these materials had beneficial effects on healing and therefore were safe to use in normal weight mice. Therefore, topical application of these materials is discussed as follows.
In an experimental study, Jafari et al29 tested the effect of topical yellow plant aloe vera and alcoholic extract of propolis on improving diabetic rat ulcers over 21 days in 50 rats and found the average wound healing rate in the treated group was lower than those of the other experimental groups (P ≤.01). These findings were similar to the results of the current study.
The meta-analysis results of the beneficial effects of topical propolis on wound healing conducted by Oryan et al30 also are consistent with the findings of the present study. Additionally, the authors30 recommended more research on dosing, effectiveness, and side eﬀects of propolis in wound healing.
The beneficial effects of SNPs also have been reported. Fatemi et al31 conducted an experimental study and found the use of topical modified chitosan gel (containing SNPs) accelerated burn wound healing and increased the number of fibroblasts compared to the treatment group with the conventional chitosan gel (without SNPs), findings consistent with the current study results. In an experimental study, Jameii et al32 demonstrated that treating Leishmaniasis ulcers in mice with half-wave rectified sine electricity plus SNPs significantly reduced the diameter of the lesion compared to the untreated group.
Results of the experimental study by Rahnema et al33 that investigated the macroscopic and microscopic effects of topical application of SNPs supported accelerated wound healing using topical SNPs, but use was associated with some toxic effects. The results of the Rahnema et al study33 were similar to the current study in terms of healing.
An experimental study by Heidarnejad et al34 that explored the effects of topical SNPs on hematological parameters during wound healing in mice noted treatment of the wound with SNPs significantly reduced the mean surface area of the wound with immune system stimulation 14 days post-wounding compared to a control group without side effects on certain blood-related parameters. The results of this study were consistent with the findings of the present study regarding healing process.
he experimental study by Seyyedmir et al35 evaluated the effects of nanosilver dressing (ie, a cloth filled with SNPs) on wounds created in rats. Results showed the dressing can reduce wound surface area and wound healing duration in rats and with fewer complications compared with a nonsilver dressing, findings similar to the current study.
Although the research is limited, it is consistent with the current study findings in terms of beneficial effects of medical application of SNPs confirmed by experimental study.36 SNPs can be applied as medication in the treatment of certain diseases and conditions, such as acne, various types of injuries, and burns, as well as bacterial and fungal infections. However, SNPs can produce reactive oxygen species; therefore, they can induce dose-dependent toxic effects. For instance, an animal study36 has shown long-term oral consumption of high doses of SNPs not only damages liver tissue, but it also decreases the number of white blood cells and may downregulate the immune system of the treated animal. This negative characteristic of SNPs may result in their limited therapeutic applications. However, not all experimental research has demonstrated the toxic effects of SNPs.37
Overall, SNPs appear to accelerate the wound healing process due to their antimicrobial effects and their ability to prevent the spread of infection. In an experimental study, Adomavičiūtė et al38 investigated a wound dressing comprised of an electrospun, fast-dissolving nano/microfiber mat formulation containing propolis and SNPs. The authors demonstrated the antimicrobial effects of combining propolis and SNPs in electrospun mats on many gram-positive, gram-negative bacteria, and Candida albicans strains, finding that this combination induced inhibitory effects on microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Bacillus subtilis, B cereus, and C albicans.
Just as the antimicrobial effects of SNPs have been proven by several experimental studies,39 the antimicrobial properties of propolis also have been widely reported. Caffeic acid phenethyl ester, a lipophilic compound, acts as a major propolis activator. In agreement with the findings of the present study, a review of the literature40 supported that the positive effects of propolis on wound healing are boosted when used in combination with SNPs.
Silver ions can replace the phosphate groups in the nucleotides of the DNA strands; therefore, they can reduce DNA replication. It initially was assumed that SNPs release silver ions in order to induce their antimicrobial effects. However, later experimental studies41 have indicated that SNPs exert their antimicrobial effects without releasing silver ions. SNPs can penetrate the cell membrane. This study utilized SNPs, not silver ions.
A review42 suggested that SNPs induce a pleiotropic effect on bacterial cells. SNPs bind to the surface of the membrane and disrupt its permeability by altering membrane potential and inhibiting cellular respiration. SNPs cations bind to the thiol groups of the bacterial proteins and disrupt their activity, which leads to cell death. Hence, the combination of SNPs with the lipophilic molecules of propolis is a desirable complex, and an experimental study43 suggested that this combination accelerates the burn wound healing.
Because the effects of SNPs are not cell-specific and all cell types are affected by them, it might be possible to reduce their side effects and enhance their beneficial effects by changing their formulation, combining them with other substances such as plant extracts and designing plant nanocomposites. Additional research with propolis and other compatible substances is warranted.