Search

Pepper, a daily-used seasoning for promoting appetite, is widely used in folk medicine for treating gastrointestinal diseases. Piperine is the major alkaloid in pepper and possesses a wide range of pharmacological activities. However, the mechanism for linking metabolic and medicinal activities of piperine remains unknown. Here we report that piperine robustly boosts mTORC1 activity by recruiting more system L1 amino acid transporter (SLC7A5/SLC3A2) to the cell membrane, thus promoting amino acid metabolism. Piperine-induced increase of mTORC1 activity in resident peritoneal macrophages (pMΦs) is correlated with enhanced production of IL-6 and TNF-α upon LPS stimulation. Such an enhancement of cytokine production could be abrogated by inhibitors of the mTOR signaling pathway, indicating mTOR's action in this process. Moreover, piperine treatment protected resident pMΦs from bacterium-induced apoptosis and disappearance, and increased their bacterial phagocytic ability. Consequently, piperine administration conferred mice resistance against bacterial infection and even sepsis. Our data highlight that piperine has the capacity to metabolically reprogram peritoneal resident macrophages to fortify their innate functions against bacterial infection.

Apoptosis and autophagy are both highly regulated biological processes that have important roles in development, differentiation, homeostasis, and disease. These processes may take place independently, with autophagy being cytoprotective for preventing cells from apoptosis and apoptosis blocking autophagy. But in most circumstances, both may be induced sequentially with autophagy preceding apoptosis. The simultaneous activation of both processes has been observed not only in experimental settings but also in pathophysiological conditions. In fact, these two pathways are tightly connected with each other by substantial interplays between them, enabling the coordinated regulation of cell fates by these two pathways. They share some common upstream signaling components, and some components of one pathway may play important roles in the other, and vice versa. Such proteins represent the critical interconnections of the two pathways, which seem to determine the cell for survival or death. Here several critical molecular interconnections between apoptosis and autophagy pathways are reviewed, with their action mechanisms being highlighted.

Gossypol, a polyphenolic compound isolated from cottonseeds, has been reported to possess many pharmacological activities, but whether it can influence inflammasome activation remains unclear. In this study, we found that in mouse macrophages, gossypol induced cell death characterized by rapid membrane rupture and robust release of HMGB1 and pro-caspase-11 comparable to ATP treatment, suggesting an induction of pyroptotic cell death. Unlike ATP, gossypol induced much low levels of mature interleukin-1β (IL-1β) secretion from mouse peritoneal macrophages primed with LPS, although it caused pro-IL-1β release similar to that of ATP. Consistent with this, activated caspase-1 responsible for pro-IL-1β maturation was undetectable in gossypol-treated peritoneal macrophages. Besides, RAW 264.7 cells lacking ASC expression and caspase-1 activation also underwent pyroptotic cell death upon gossypol treatment. In further support of pyroptosis induction, both pan-caspase inhibitor and caspase-1 subfamily inhibitor, but not caspase-3 inhibitor, could sharply suppress gossypol-induced cell death. Other canonical pyroptotic inhibitors, including potassium chloride and N-acetyl-l-cysteine, could suppress ATP-induced pyroptosis but failed to inhibit or even enhanced gossypol-induced cell death, whereas nonspecific pore-formation inhibitor glycine could attenuate this process, suggesting involvement of a non-canonical pathway. Of note, gossypol treatment eliminated thioglycollate-induced macrophages in the peritoneal cavity with recruitment of other leukocytes. Moreover, gossypol administration markedly decreased the survival of mice in a bacterial sepsis model. Collectively, these results suggested that gossypol induced pyroptosis in mouse macrophages via a non-canonical inflammasome pathway, which raises a concern for its in vivo cytotoxicity to macrophages.

The anti-inflammatory property of chloroquine (CQ) has long been recognized. This study aimed to investigate the effect of CQ on proinflammatory cytokine expression in RAW 264.7 macrophages stimulated with heat-inactivated Staphylococcus aureus cells (SAC). The results showed that CQ treatment reduced the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and CC chemokine ligand 2 (CCL2) in culture medium but increased intracellular protein expression of TNF-α and CCL2 in SAC-activated cells. However, CQ showed differential effects on their messenger RNA (mRNA) levels: it reduced IL-6 mRNA expression, increased CCL2 mRNA levels, but had no effect on TNF-α mRNA. The SAC-activated inflammatory signaling pathways were slightly or minimally affected by CQ treatment. Additionally, CQ increased the accumulation of pro-TNF-α proteins within cells, suggesting an inhibition of pro-TNF-α processing and secretion. Collectively, CQ differentially modulated proinflammatory cytokine expression in Gram-positive bacterium-activated macrophages at multiple regulatory layers in the course of their biosynthesis.

Cucurbitacin IIb (CuIIb) is one of the major active compounds in Hemsleyadine tablets which have been used for clinical treatment of bacillary dysentery, enteritis and acute tonsilitis. However, its action mechanism has not been completely understood. This study aimed to explore the anti-inflammatory activity of CuIIb and its underlying mechanism in mitogen-activated lymphocytes isolated from mouse mesenteric lymph nodes. The results showed that CuIIb inhibited the proliferation of concanavalin A (Con A)-activated lymphocytes in a time- and dose-dependent manner. CuIIb treatment arrested their cell cycle in S and G2/M phases probably due to the disruption of the actin cytoskeleton and the modulation of p27(Kip1) and cyclin levels. Moreover, the surface expression of activation markers CD69 and CD25 on Con A-activated CD3(+) T lymphocytes was suppressed by CuIIb treatment. Both Con A- and phorbol ester plus ionomycin-induced expression of TNF-α, IFN-γ and IL-6 proteins was attenuated upon exposure to CuIIb. Mechanistically, CuIIb treatment suppressed the phosphorylation of JNK and Erk1/2 but not p38 in Con A-activated lymphocytes. Although CuIIb unexpectedly enhanced the phosphorylation of IκB and NF-κB (p65), it blocked the nuclear translocation of NF-κB (p65). In support of this, CuIIb significantly decreased the mRNA levels of IκBα and TNF-α, two target genes of NF-κB, in Con A-activated lymphocytes. In addition, CuIIb downregulated Con A-induced STAT3 phosphorylation and increased cell apoptosis. Collectively, these results suggest that CuIIb exhibits its anti-inflammatory activity through modulating multiple cellular behaviors and signaling pathways, leading to the suppression of the adaptive immune response.