Flavonoids from Piper Species as Promising Antiprotozoal Agents against Giardia intestinalis. Structure-Activity Relationship and Drug-Likeness Studies

Diarrhea diseases caused by the intestinal protozoan parasite Giardia intestinalis are a major global health burden. Moreover, there is an ongoing need for novel anti-Giardia drugs due to drawbacks with currently available treatments. This paper reports on the isolation and structural elucidation of six new flavonoids (1-6), along with twenty-three known ones (7-29) from the Piper species. Their structures were established by spectroscopic and spectrometric techniques. Flavonoids were tested for in vitro antiprotozoal activity against Giardia intestinalis trophozoites. In addition, structure-activity relationship (SAR) and in silico ADME studies were performed to understand the pharmacophore and pharmacokinetic properties of these natural compounds. Eight flavonoids from this series exhibited remarkable activity in the micromolar range. Moreover, compound 4 was identified as having a 40-fold greater antiparasitic effect (IC50 61.0 nM) than the clinical reference drug, metronidazole (IC50 2.5 µM). This antiprotozoal potency was coupled with an excellent selectivity index (SI 233) on murine macrophages and in silico drug-likeness. SAR studies revealed that the substitution patterns, type of functional group, and flavonoid skeleton played an essential role in the activity. These findings highlight flavonoid 4 as a promising candidate to develop new drugs for the treatment of Giardia infections.

Efficient DNA barcode regions for classifying Piper species (Piperaceae)

Piper species are used for spices, in traditional and processed forms of medicines, in cosmetic compounds, in cultural activities and insecticides. Here barcode analysis was performed for identification of plant parts, young plants and modified forms of plants. Thirty-six Piper species were collected and the three barcode regions, matK, rbcL and psbA-trnH spacer, were amplified, sequenced and aligned to determine their genetic distances. For intraspecific genetic distances, the most effective values for the species identification ranged from no difference to very low distance values. However, Piper betle had the highest values at 0.386 for the matK region. This finding may be due to Piper betle being an economic and cultivated species, and thus is supported with growth factors, which may have affected its genetic distance. The interspecific genetic distances that were most effective for identification of different species were from the matK region and ranged from a low of 0.002 in 27 paired species to a high of 0.486. Eight species pairs, Piper kraense and Piper dominantinervium, Piper magnibaccum and Piper kraense, Piper phuwuaense and Piper dominantinervium, Piper phuwuaense and Piper kraense, Piper pilobracteatum and Piper dominantinervium, Piper pilobracteatum and Piper kraense, Piper pilobracteatum and Piper phuwuaense and Piper sylvestre and Piper polysyphonum, that presented a genetic distance of 0.000 and were identified by independently using each of the other two regions. Concisely, these three barcode regions are powerful for further efficient identification of the 36 Piper species.