Plant-derived alkaloids acting on dengue virus and their vectors: from chemistry to pharmacology

Evaluating the insecticidal potential of alkaloids for the management of Thrips palmi: in vivo and in silico perspectives

Insecticidal potential of seven commonly available alkaloids against melon thrips (Thrips palmi Karny) was investigated through in vivo experiments and the bioactivity was explained via in silico approaches. In vivo screening showed highest mortality of T. plami larvae for reserpine (43%), closely followed by tropinone (41%) after 24 h of incubation. After 48 h, tropinone surpassed reserpine with 83% mortality, indicating its prolonged insecticidal activity. A detailed bioassay of tropinone revealed its LC50 values as 1187.9 and 686.9 µg mL-1 after 24 and 48 h, respectively. While studying the molecular interactions between the alkaloids and four physiologically important target proteins of T. palmi, tropinone demonstrated the highest ligand efficiency and lowest predicted inhibitory constant, particularly when forming complexes with CathB protein. However, binding energy calculations of the docked complexes showed most favorable binding of reserpine with CathB. To clear the ambiguity, considering both binding energy and ligand efficiency as the evaluation parameters, a molecular dynamics study was carried out, which predicted higher stability of CathB-tropinone complex than CathB-reserpine complex in terms of the total energy of the system. These in silico findings aligned well with the in vivo results, confirming tropinone as a promising candidate for effective thrips management programs.

Sub-chronic oral toxicity study of the alkaloid rich fraction from Luffa cylindrica fruit in Sprague-Dawley rats

The loofah/sponge gourd Luffa cylindrica (L.), a member of the Cucurbitaceae family, is one of the neglected medicinal plants. Traditionally, Luffa cylindrica is prescribed for inducing labor. It has a long history of use in China for the treatment of fever, diabetes, dyspnea, and dysentery. This study investigated the toxicity profile of the alkaloid-rich fraction of Luffa cylindrica (ARF-LC) for the first time in Sprague Dawley rats. A total of 80 rats (40 male and 40 female rats) aged 13 weeks old and weighing 200-220 g were selected for this study. In SD rats, sub-chronic oral toxicity was investigated at doses of 100, 200, and 400 mg/kg/d for a total of 90 days, followed by a 30-day recovery period. The results showed no variation in body weight among the three dose groups compared to the control group. Treatment-related adverse events, such as alterations in hematology and serum biochemistry parameters and the histology of the liver were sporadic in the high-dose rats but within the reference range. However, these changes disappeared after the doses were withdrawn during the recovery period. In conclusion, the "no observed adverse effect level" (NOAEL) of oral administration of ARF-LC in SD rats was considered 400 mg/kg/d and can be studied for its potential in further in vivo chronic investigations.

Indispensable Biomolecules for Plant Defense Against Pathogens: NBS-LRR and "nitrogen pool" Alkaloids

In a complex natural environment, plants have evolved intricate and subtle defense response regulatory mechanisms for survival. Plant specific defenses, including the disease resistance protein nucleotide-binding site leucine-rich repeat (NBS-LRR) protein and metabolite derived alkaloids, are key components of these complex mechanisms. The NBS-LRR protein can specifically recognize the invasion of pathogenic microorganisms to trigger the immune response mechanism. Alkaloids, synthesized from amino acids or their derivatives, can also inhibit pathogens. This study reviews NBS-LRR protein activation, recognition, and downstream signal transduction in plant protection, as well as the synthetic signaling pathways and regulatory defense mechanisms associated with alkaloids. In addition, we clarify the basic regulation mechanism and summarize their current applications and the development of future applications in biotechnology for these plant defense molecules. Studies on the NBS-LRR protein and alkaloid plant disease resistance molecules may provide a theoretical foundation for the cultivation of disease resistant crops and the development of botanical pesticides.