Towards an understanding of bacterial metabolites prodigiosin and violacein and their potential for use in commercial sunscreens.

OBJECTIVES: To exploit the microbial ecology of bacterial metabolite production and, specifically, to: (i) evaluate the potential use of the pigments prodigiosin and violacein as additives to commercial sunscreens for protection of human skin, and (ii) determine antioxidant and antimicrobial activities (against pathogenic bacteria) for these two pigments. METHODS: Prodigiosin and violacein were used to supplement extracts of Aloe vera leaf and Cucumis sativus (cucumber) fruit which are known to have photoprotective activity, as well as some commercial sunscreen preparations. For each, sunscreen protection factors (SPFs) were determined spectrophotometrically. Assays for antimicrobial activity were carried out using 96-well plates to quantify growth inhibition of Staphylococcus aureus and Escherichia coli. RESULTS: For the plant extracts, SPFs were increased by an order of magnitude (i.e. up to ~3.5) and those for the commercial sunscreens increased by 10-22% (for 4% w/w violacein) and 20-65% (for 4% w/w prodigiosin). The antioxidant activities of prodigiosin and violacein were approximately 30% and 20% those of ascorbic acid (a well-characterized, potent antioxidant). Violacein inhibited S. aureus (IC50 6.99 ± 0.146 µM) but not E. coli, whereas prodigiosin was effective against both of these bacteria (IC50 values were 0.68 ± 0.06 µM and 0.53 ± 0.03 µM, respectively). CONCLUSION: The bacterial pigments prodigiosin and violacein exhibited antioxidant and antimicrobial activities and were able to increase the SPF of commercial sunscreens as well as the extracts of the two plant species tested. These pigments have potential as ingredients for a new product range of and, indeed, represent a new paradigm for sunscreens that utilize substances of biological origin. We discussed the biotechnological potential of these bacterial metabolites for use in commercial sunscreens, and the need for studies of mammalian cells to determine safety.

Phytolatex synthesized gold nanoparticles as novel agent to enhance sun protection factor of commercial sunscreens.

OBJECTIVE: To study the potential of phytolatex (latex of Jatropha gossypifolia) fabricated gold nanoparticles as promising candidate in sunscreen formulations for enhancement in sun protection factor. METHODS: In this study, plant latex was used as reducing and capping agent to synthesize gold nanoparticles. Latex fabricated gold nanoparticles were characterized by different analytical techniques such as UV-Vis spectroscopy, Fourier transforms infrared spectroscopy, dynamic light scattering, zeta potential, transmission electron microscopy and X-ray diffraction. Potential of sunscreen preparations containing gold nanoparticles to protect skin from UV radiation was investigated by in vitro sun protection factor analysis. Transmission electron microscopy and UV-Vis spectroscopy techniques were used to get insight into mechanism by which AuNPs enhance sun protection factor of sunscreen. RESULTS: Monodisperse gold nanoparticles were synthesized using plant latex without need of hazardous chemical reducing and capping agents. Gold nanoparticles showed surface plasmon resonance peak at 550 nm in UV-Vis spectroscopic study. Gold nanoparticles were spherical and triangular in shape with size range of 30-50 nm. The zeta potential of gold nanoparticles was found to be -9.39 ± 0.19 mV. XRD analysis confirmed face-centred cubic (fcc) structure of gold nanoparticles. Incorporation of latex synthesized gold nanoparticles (2 and 4 [% w/w]) into commercial sunscreens increased the sun protection factor from 2.43 ± 0.74 to 24.11 ± 0.46% than sunscreen devoid of gold nanoparticles. From UV-Vis absorption spectroscopy and TEM analysis, it was observed that gold nanoparticles enhance the sun protection factor of commercial sunscreens due to reflection and scattering of UV radiation. CONCLUSION: Phytolatex synthesized gold nanoparticle is novel agent to enhance sun protection factor of commercial sunscreens. Gold nanoparticles aggregation in commercial sunscreen was the main factor behind SPF enhancement. This study showed that gold nanoparticles are potent alternative to traditionally used hazardous titanium dioxide and zinc oxide nanoparticles in sunscreen.