DOI: 10.6084/m9.figshare.27075180.v1
title: Secondary metabolites in topical infectious diseases and nanomedicine applications

description: Topical infection affects nearly one-third of the world's population; it may result from poor sanitation, hygienic conditions and crowded living and working conditions that accelerate the spread of topical infectious diseases. The problems associated with the anti-infective agents are drug resistance and long-term therapy. Secondary metabolites are obtained from plants, microorganisms and animals, but they are metabolized inside the human body. The integration of nanotechnology into secondary metabolites is gaining attention due to their interaction at the subatomic and skin-tissue levels. Hydrogel, liposomes, lipidic nanoparticles, polymeric nanoparticles and metallic nanoparticles are the most suitable carriers for secondary metabolite delivery. Therefore, the present review article extensively discusses the topical applications of nanomedicines for the effective delivery of secondary metabolites. Plants possess several secondary metabolites demonstrating antimicrobial properties, including flavonoids, alkaloids, tannins and terpenoids. Only a handful of secondary metabolites that have antimicrobial properties have been identified from animal sources. To date, no nanoformulation has been developed from animal secondary metabolites to treat topical infections. This field requires more scientific investigation to gain a better understanding of animal secondary metabolites and their delivery for topical applications. Some researchers have reported that microbial pigments (e.g., melanin, carotenoids, violacein, quinones, flavonoids and manascins), which are the secondary metabolites of microorganisms, show good antimicrobial properties. The skin has a complex structure and diverse biophysical properties that modulate its barrier function. Specifically, the stratum corneum layer creates a barrier that facilitates the permeation of hydrophobic molecules more efficiently than hydrophilic molecules. However, the hydrophilic bilayer region hinders highly hydrophobic compounds. Drug delivery through the skin is heavily influenced by environmental factors (temperature, oxygen level, humidity and light) and individual factors (sex, age, skin anatomy, hormonal balance and humidity). Developing strategies to enter the skin and efficiently deliver therapeutics is a significant area of research. Drugs quickly and directly go through the skin through the intracellular route. This method is difficult, however, because the particle must get past the water- and fat-absorbing parts of skin cells. Moreover, the drug must be stable and compatible with the skin and the delivery system. Different kinds of nanocarriers, such as liposomes, microemulsions, hydrogels, solid lipids and polymeric nanoparticles, are used to deliver secondary metabolites such as curcumin, quercetin, berberine and eugenol into the skin. It has several advantages: controlled release, site-specific delivery, enhanced bioavailability, reduced toxicity, and increased solubility and stability. Several barriers impede the seamless integration of this technology into practical applications. Nanoparticle synthesis and formulation are difficult because one must design and optimize these carriers carefully to encapsulate and protect secondary metabolites while also ensuring controlled release. The toxicity of nanocarriers is influenced by composition, size, shape, surface charge, stability and biodegradability.