Endocytosis and the Participation of Glycosaminoglycans Are Important to the Mechanism of Cell Death Induced by ß-Hairpin Antimicrobial Peptides.

The cytotoxic mode of action of four antimicrobial peptides (AMPs) (gomesin, tachyplesin, protegrin, and polyphemusin) against a HeLa cell tumor model is discussed. A study of cell death by AMP stimulation revealed some similarities, including annexin-V externalization, reduction of mitochondrial potential, insensitivity against inhibitors of cell death, and membrane permeabilization. Evaluation of signaling proteins and gene expression that control cell death revealed wide variation in the responses to AMPs. However, the ability to cross cell membranes emerged as an important characteristic of AMP-dependent cell death, where endocytosis mediated by dynamin is a common mechanism. Furthermore, the affinity between AMPs and glycosaminoglycans (GAGs) and GAG participation in the cytotoxicity of AMPs were verified. The results show that, despite their primary and secondary structure homology, these peptides present different modes of action, but endocytosis and GAG participation are an important and common mechanism of cytotoxicity for ß-hairpin peptides.

Involvement of P2 receptors in hematopoiesis and hematopoietic disorders, and as pharmacological targets.

Several reports have shown the presence of P2 receptors in hematopoietic stem cells (HSCs). These receptors are activated by extracellular nucleotides released from different sources. In the hematopoietic niche, the release of purines and pyrimidines in the milieu by lytic and nonlytic mechanisms has been described. The expression of P2 receptors from HSCs until maturity is still intriguing scientists. Several reports have shown the participation of P2 receptors in events associated with modulation of the immune system, but their participation in other physiological processes is under investigation. The presence of P2 receptors in HSCs and their ability to modulate this population have awakened interest in exploring the involvement of P2 receptors in hematopoiesis and their participation in hematopoietic disorders. Among the P2 receptors, the receptor P2X7 is of particular interest, because of its different roles in hematopoietic cells (e.g., infection, inflammation, cell death and survival, leukemias and lymphomas), making the P2X7 receptor a promising pharmacological target. Additionally, the role of P2Y12 receptor in platelet activation has been well-documented and is the main example of the importance of the pharmacological modulation of P2 receptor activity. In this review, we focus on the role of P2 receptors in the hematopoietic system, addressing these receptors as potential pharmacological targets.

Cytotoxic and Apoptotic Activity of Majoranolide from Mezilaurus crassiramea on HL-60 Leukemia Cells.

Majoranolide, a butanolide isolated from the nonpolar fraction of an ethanol extract of Mezilaurus crassiramea (Lauraceae) fruits, is being reported for the first time in this genus and the third time in plants. Structurally identified from 1D and 2D NMR and HRESIMS data, majoranolide proved cytotoxic against cancer cells-MCF-7 and MDA-MB-231 (breast), HT-29 (colon), PC-3 (prostate), 786-0 (renal), and HL-60 (leukemia)-inhibiting growth in HL-60 cells (GI50 = 0.21 µM) and exhibiting higher selectivity for this line than for nonneoplastic NIH/3T3 murine fibroblasts. Effects on the cell cycle, caspase-3 activation, and plasma membrane integrity were evaluated by flow cytometry. Expression of genes related to apoptotic pathways (BAX, BCL2, BIRC5, and CASP8) was investigated using RT-qPCR. At 50 µM, majoranolide induced cell cycle arrest at G1 in 24 h increased the sub-G1 population in 48 h and increased caspase-3 activation in a time-dependent manner. The compound upregulated BAX and CASP8 transcription (proapoptotic genes) and downregulated BIRC5 (antiapoptotic). Loss of plasma membrane integrity in 30% of cells occurred at 48 h, but not at 24 h, characterizing gradual, programmed death. The results suggest that majoranolide cytotoxicity involves apoptosis induction in HL-60 cells, although other mechanisms may contribute to this cell death.