Bioactivity-guided isolation and structural characterization of the antifungal compound,plumbagin, from Nepenthes gracilis

Context: Despite several phytochemical studies of Nepenthes gracilis Korth (Nepenthaceae), the biological activities of this pitcher plant remain to be explored.

Objective: This study evaluates the antifungal activity of N. gracilis extracts, isolates, and characterizes its bioactive compound and evaluates the cytotoxicity of the isolated compound.

Materials and methods: Fresh leaves of N. gracilis were sequentially extracted. The fungistatic and fungicidal activities of the extracts were evaluated against six species of fungi of medical importance using a colorimetric broth microdilution method. The most active extract was fractionated by liquid–liquid partitioning and further purified by a preparative thin layer chromatography. Structural elucidation was carried out using FT-IR, GC-MS, and NMR. Cytotoxicity testing against rhesus monkey kidney epithelial cells (LLC-MK2) was assessed by a neutral red uptake (NRU) assay.

Results: The hexane extract, which showed the lowest minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC), both at 20?μg/mL against Candida albicans, Issatchenkia orientalis, and Trichophyton mentagrophytes, was subjected to bioactivity-guided fractionation. The isolated compound exhibited potent activity with the MIC values ranging from 2 to 31?μg/mL against all the fungi. The active compound was identified as plumbagin (5-hydroxy-2-methyl-naphthalene-1,4-dione). The 50% cytotoxicity concentration (CC₅₀) of plumbagin was 0.60?μg/mL.

Discussion and conclusion: The selectivity indices of plumbagin against all the fungi were less than 1.0, indicating that plumbagin is more toxic to mammalian than fungal cells. This study provides information on the antifungal properties of N. gracilis leaf extracts, as well as the antifungal and cytotoxicity properties of plumbagin.     

Tricuspid regurgitant jet velocity and myocardial tissue Doppler parameters predict mortality in a cohort of patients with sickle cell disease spanning from pediatric to adult age groups ‐ revisiting this controversial concept after 16 years of additional evidence

Sickle cell disease (SCD) is a monogenic hemoglobinopathy associated with significant morbidity and mortality. Cardiopulmonary, vascular and sudden death are the reasons for the majority of young adult mortality in SCD. To better understand the clinical importance of multi‐level vascular dysfunction, in 2009 we assessed cardiac function including tricuspid regurgitant jet velocity (TRV), tissue velocity in systole(S′) and diastole (E′), inflammatory, rheologic and hemolytic biomarkers as predictors of mortality in patients with SCD. With up to 9 years of follow up, we determined survival in 95 children, adolescents and adults with SCD. Thirty‐eight patients (40%) were less than 21 years old at initial evaluation. Survival and Cox proportional‐hazards analysis were performed. There was 19% mortality in our cohort, with median age at death of 35 years. In the pediatric subset, there was 11% mortality during the follow up period. The causes of death included cardiovascular and pulmonary complications in addition to other end‐organ failure. On Cox proportional‐hazards analysis, our model predicts that a 0.1 m/s increase in TRV increases risk of mortality 3%, 1 cm/s increase in S′ results in a 91% increase, and 1 cm/s decrease in E′ results in a 43% increase in mortality. While excluding cardiac parameters, higher plasma free hemoglobin was significantly associated with risk of mortality (p=.049). In conclusion, elevated TRV and altered markers of cardiac systolic and diastolic function predict mortality in a cohort of adolescents and young adult patients with SCD. These predictors should be considered when counseling cardiovascular risk and therapeutic optimization at transition to adult providers.     

P-Glycoprotein and transporter MRP1 reduce HIV protease inhibitor uptake in CD4 cells: potential for accelerated viral drug resistance?

BACKGROUND: The multidrug transporters P-glycoprotein (P-gp) and MRP1 are functionally expressed in several subclasses of lymphocytes. HIV-1 protease inhibitors interact with both; consequently the transporters could reduce the local concentration of HIV-1 protease inhibitors and, thus, influence the selection of viral mutants. OBJECTIVES: To study the effect of the expression of P-gp and MRP1 on the transport and accumulation of HIV-1 protease inhibitors in human lymphocytes and to study the effects of specific P-gp and MRP1 inhibitors. METHODS: The initial rate and the steady-state intracellular accumulation of radiolabelled ritonavir, indinavir, saquinavir and nelfinavir was measured in three human lymphocyte cell lines: control CEM cells, CEM-MDR cells, which express 30-fold more P-gp than CEM cells, and CEM-MRP cells, which express fivefold more MRP1 protein than CEM cells. The effect of specific inhibitors of P-gp (GF 120918) and MRP1 (MK 571) was also examined. RESULTS: Compared with CEM cells, the initial rates of uptake and the steady-state intracellular concentrations of all protease inhibitors are significantly reduced in CEM-MDR cells. The intracellular concentrations of the protease inhibitors are increased upon co-administration with GF 120918, in some cases to levels approaching those in CEM cells. The intracellular concentrations of the protease inhibitors are also significantly reduced in CEM-MRP cells. Co-administration with MK -571 can partially overcome these effects. CONCLUSIONS: The overexpression of multidrug transporters significantly reduces the accumulation of protease inhibitors at this major site of virus replication, which, potentially, could accelerate the acquisition of viral resistance. Targeted inhibition of P-gp may represent an important strategy by which this problem can be overcome.     

Ligand-induced phosphorylation of the murine interleukin 3 receptor signals its cleavage.

The murine interleukin 3 receptor (mIL-3R) is a heterodimer consisting of a 70-kDa alpha subunit and one of two alternative 120-kDa beta subunits termed beta IL-3 and beta c. beta IL-3 (originally called Aic2A) is capable of binding mIL-3 by itself, whereas beta c (Aic2B) does not bind any ligand on its own but increases the affinity of mIL-3, murine granulocyte/macrophage-colony-stimulating factor, and mIL-5 for their respective alpha subunits. Interestingly, although the mIL-3R does not possess tyrosine kinase activity, its beta IL-3 subunit does become tyrosine phosphorylated upon binding mIL-3. To further investigate the properties of this subunit, we have purified it from the cell line B6SUtA1, which expresses a high level of mIL-3R. Intriguingly, studies comparing the stability of the 140-kDa, tyrosine-phosphorylated form of this subunit with its 120-kDa, non-tyrosine-phosphorylated form reveal that the former is far less stable and is rapidly degraded to a 70-kDa fragment. Mixing experiments demonstrate that the differential stability of the two forms is due to an intrinsic difference in protease susceptibility. Phosphatase studies indicate that the higher protease susceptibility of the tyrosine-phosphorylated beta IL-3 is due to the presence of both phosphotyrosine and phosphoserine residues. Western analyses using an anti-N-terminal mIL-3R beta IL-3 chain antibody reveal that this proteolytic cleavage also occurs rapidly in intact cells following stimulation with mIL-3 and occurs at the cell surface, since it takes place within minutes at 37 degrees C, is observed with purified plasma membranes, and is not inhibited by chloroquine. This degradative step may play an important role in the mechanism of action of mIL-3.