Antiprotozoal and Antidiabetic Activities of Secondary Metabolites Isolated From Vepris Glandulosa

Abstract

Protozoal infections, particularly malaria and neglected tropical diseases like kinetoplastid diseases affect impoverished populations in tropical regions. Similarly, diabetes mellitus is among the leading cause of global death and disability, with a significant ramification on the global economy. Amidst the diminishing effectiveness of existing treatments, the search for novel antiprotozoal and antidiabetic drugs is imperative. Plants have long been recognized as promising sources of bioactive compounds with therapeutic potential. Thus, researchers prioritize medicinal plants as critical targets for discovering novel therapeutic agents. This necessity prompted the search for the potent antiprotozoal and antidiabetic drugs from unexploited plant sources, such as Vepris glandulosa. V. glandulosa is endangered plant species, endemic in central Kenya. It has been utilized in folklore medicine to cure various conditions. In this study, the dried leaves of V. glandulosa were pulverized into a fine powder and extracted with methanol at room temperature by cold solvent percolation. Separation techniques involved liquid-liquid partitioning followed by column chromatography on silica gel as a stationary matrix, employing gradients of n-hexane and ethyl acetate for elution. The resulting fractions were further purified using finer silica gel through recurrent column chromatography, leading to the isolation of two known alkaloids: Choisyine acetate 29 and Choisyine 30. Their structure elucidation involved a detailed analysis using Nuclear Magnetic Resonance, Mass Spectrometry and a comparison with related compounds in the existing literature. Both in vitro and in silico assays were utilized to assess the activity and toxicity of the isolated compounds. The α-amylase inhibition assay revealed noncompetitive inhibition for both compounds with IC50 and Ki values of 4.74±0.17 and 4.75 mM for compound 29, and 11.29±0.44 and 12.37 mM for compound 30, respectively. In comparison, the standard drug acarbose displayed a competitive mode of inhibition, with IC50 and Ki values of 11.985±0.02 and 2.24 mM. Docking scores (kcal/mol) demonstrated significant interactions with the target proteins. Compound 29 revealed a binding score of -6.42 and -6.17 while compound 30 had -6.07 and -5.38 whereas acarbose, the standard drug showed -8.03 and -8.49 for α-amylase and glucosidase, respectively. For P. falciparum lactate dehydrogenase (P. falciparum), compound 29 showed a score of -7.10, and compound 30 scored -7.20, while the standard drug chloroquine scored -6.88. In the case of dihydroorotate dehydrogenase (L. donovani), compound 29 had a score of -7.19, compound 30 scored -7.09, and standard drug miltefosine scored -8.01. Trypanothione reductase (T. cruzi), compound 29 showed a score of -8.19, compound 30 scored -7.81, and the standard drug melarsoprol, scored -6.24. For L-threonine-3-dehydrogenase (T. brucei), compound 29 had a score of -6.31, compound 30 scored -6.97, and the standard drug benznidazole scored -7.33. These compounds demonstrated remarkable inhibition potential comparable to, and even greater than some currently available drugs, highlighting their potential as viable alternatives in the fight against these diseases. Their physicochemical properties, pharmacokinetics and lead-likeness further justify their potential as lead candidates in drug research. Synthetic accessibility, Pan Assay Interference Structures, Brenk alerts and toxicity evaluation revealed their ease of synthesis, lack of undesirable features and low toxicity profile. The findings from this study also revealed that V. glandulosa contains alkaloids with the potential to inhibit diabetes and protozoa-associated biomarkers, thereby providing a scientific rationale for using the plant in Kenyan folk medicine as treatment for various health issues. Compound 29 Compound 30