Prospecção de atividade antifúngica e potencial modulador para fármacos de referência em extratos e frações de Tephrosia toxicaria (Sw.) Pers.

Abstract

Fungal infections represent a major contributor to the increasing global mortality rate associated with infectious diseases and the indiscriminate use of antibiotics and antifungal agents compromises the effectiveness of the drug through the development of resistance to pathogens. Furthermore, drugs for clinical use can cause adverse effects on non-target organisms. In this scenario, botanical extracts and their fractions have been highlighted as promising sources for the development of new antifungals and therapeutic adjuvants. In which, Tephrosia toxicaria (Sw.) Pers, a legume well adapted to the northeastern semi-arid region, has stood out for its biopotential. In this context, the present research aimed to investigate the antifungal potential of extracts and protein fractions obtained from T. toxicaria seeds against species of the Candida albicans, Candida parapsilosis, Cryptococcus gattii and Cryptococcus neoformans and their modulating activity for reference antimicrobials. The extracts and fractions obtained by the Scopes and Osborne methods were partially biochemically characterized and evaluated for their antifungal activity by determining the MICs (Minimum Inhibitory Concentration). Subsequently, the most active fraction and its combinations were also investigated for their modulating activity with drugs for clinical use, using the association method (checkerboard) using ICIF (Fractional Inhibitory Concentration Index) and mathematical models. Of the 2 extracts and 13 fractions produced, all showed antifungal activity against at least one of the yeasts tested, to different degrees. Highlighting, the T 50-75 fraction was the most active against C. gattii, C. neoformans and C. parapsilosis and presented the Minimum Inhibitory Concentration capable of inhibiting 100% of growth (MIC100), found with 32 µg/mL for the T 50-75 fraction against C. gattii (R-265), followed by the Seed extract in Tris-HCl Buffer (ST) with 128 µg/mL and the fractions T 50-75 and T 75-100 with 256 µg/mL, all against C. gattii (FC1). Therefore, the ST extract and the fractions T 50-75 and T 75-100 were the most promising as they presented the lowest MIC100 values, were selected to investigate their modulating potential in combination with Amphotericin B, Fluconazole and 5-Flucytosine on C. gattii. All tested combinations were able to reduce the MIC100 for C. gattii and after data harmonization, the combinations between the T 50-75 and T 75-100 fractions with Amphotericin B and Fluconazole were classified as synergistic, however the combinations with the fraction T 50-75 showed greater sensitivity (93%) and degree of synergistic intensity. The combination of the T 50-75 fraction with the drugs caused greater interference in the growth curve, melanization and a significant reduction in capsule size. However, exposure of C. gattii to treatment with only the T 50-75 fraction also caused morphological changes in the cell wall and capsule, indicating that the fraction contributed strongly to the result observed in combination with the drug. Therefore, the T 50-75 fraction presents itself as a promising candidate for the development of adjuvants and/or new drugs for antifungal chemotherapy. Analysis of the results suggests that the fungistatic action of the T 50-75 fraction can contribute to minimizing the emergence of resistance in the pathogen, acting in redundant pathways and reducing the effective concentrations of clinical reference drugs, thus improving treatment and minimizing toxicity generated.