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All- trans retinoic acid (ATRA) is a poorly water-soluble derivate of vitamin A that has been difficult to be parenterally administrated for cancer therapy purposes. Thus, lipid nanocarriers such as solid lipid nanoparticles (SLN) have emerged as an interesting alternative to overcome this drawback of ATRA. In this work, a novel electrochemical method based on differential pulse voltammetry (DPV) to quantify ATRA in SLN is proposed. The scan rate and pulse amplitude were initially optimized and the best values were found to be 30 mV s−1 and 75 mV, respectively. The influence of pH of the supporting electrolyte on the ATRA oxidation peak was also evaluated and the optimal analysis condition was observed to occur at pH 5.0. No interference of blank SLN or degradation products were observed in the voltammetric ATRA peak and the method was considered to be highly selective for the compound. The method presented adequate linearity in the concentration range of 9.71–45.5 × 10−6 mol L−1, with a limit of detection (LOD) and quantification (LOQ) of 1.56 × 10−6 mol L−1 and 4.74 × 10−6 mol L−1, respectively. The intra-day and inter-days precision showed relative standard deviation lower than 5%. In the accuracy test, the recovery was found in the range of 93.21 to 100.22%. The method was also robust in terms of changes of methanol supplier, but changes in the supporting electrolyte composition and pH of acetate buffer significantly influenced on the method response. Thus, the validated electrochemical DPV method was considered to be highly applicable to the quantification ATRA in SLN.

Psidium guajava L. has extensive use in folk medicine. The aim of this study was to quantify the levels of phenolic, flavonoids, antioxidant activity, leathality assay and antibacterial and antitumoral activities of the extract of P. guajava. In the dry guava extract there were high levels of phenolics (766.08 ± 14.52 mg/g), flavonoids (118.90 ± 5.47 mg/g) and antioxidant activity (87.65%). The LD50 was 185.15 μg/ml. The MIC value was 250 μg/ml for Streptococcus mutans, Streptococcus mitis and Streptococcus oralis. IC50 of the extract tested in the HeLa, RKO and Wi cell lines was 15.6 ± 0.8 μg/ml, 21.2 ± 1.1 μg/ml and 68.9 ± 1.5 μg/ml, respectively. The results of all analyses allow us to conclude that the dry extract of guava leaves has promising activity to be applied topically in the oral cavity or in the development of antitumor formulation or even be used as a functional food.