Cadmium is a contributing factor to cardiovascular diseases and highly toxic to vascular endothelial cells. It has a distinct mode of injury, causing the de-endothelialization of regions in the monolayer structure of endothelial cells in a concentration-dependent manner. However, the specific molecules involved in the cadmium toxicity of endothelial cells remain unclear. The purpose of this study was to identify the specific molecular mechanisms through which cadmium affects endothelial detachment. Cadmium inhibited the expression of claudin-5 and zonula occludens (ZO)-1, which are components of tight junctions (strongest contributors to intercellular adhesion), in a concentration- and time-dependent manner. Compared to arsenite, zinc, and manganese, only cadmium suppressed the expression of both claudin-5 and ZO-1 molecules. Moreover, the knockdown of claudin-5 and ZO-1 exacerbated cadmium-induced endothelial cell injury and expansion of the detachment area, whereas their overexpression reversed these effects. CRE-binding protein inhibition reduced cadmium toxicity, suggesting that CRE-binding protein activation is involved in the cadmium-induced inhibition of claudin-5 and ZO-1 expression and endothelial detachment. These findings provide new insights into the toxicological mechanisms of cadmium-induced endothelial injury and risk of cardiovascular disease.

Proteoglycans are macromolecules consisting of a core protein and one or more glycosaminoglycan side chains. Proteoglycans synthesized by vascular endothelial cells modulate various functions, such as anticoagulant activity and vascular permeability. We previously reported that some heavy metals interfere with proteoglycan expression and that organic–inorganic hybrid molecules, such as metal complexes and organometallic compounds, serve as useful tools to analyze proteoglycan synthesis mechanisms. However, the effects of metal compounds lacking electrophilicity on proteoglycan synthesis remain unclear. Au25(SG)18, a nanoscale gold cluster consisting of a metal core protected by gold–glutathione complexes, exhibits extremely low intramolecular polarity. In this study, we investigated the effect of Au25(SG)18 on proteoglycan synthesis in vascular endothelial cells. Au25(SG)18 accumulated significantly in vascular endothelial cells at low cell density and suppressed the expression of perlecan, a major heparan sulfate proteoglycan in cells, by inactivating ADP-ribosylation factor 6 (Arf6). Additionally, Au25(SG)18 reduced the expression of biglycan, a small dermatan sulfate proteoglycan, in vascular endothelial cells at low cell density; however, the underlying mechanisms remain unclear. Overall, our findings suggest that organic–inorganic hybrid molecules regulate the activity of Arf6-mediated protein transport to the extracellular space and that perlecan is regulated through this mechanism, highlighting the importance of Arf6-mediated extracellular transport for maintaining vascular homeostasis.

Proteoglycans are macromolecules consisting of a core protein and one or more glycosaminoglycan side chains. Proteoglycans synthesized by vascular endothelial cells modulate various functions such as anticoagulant activity and vascular permeability. We previously reported that some heavy metals interfere with proteoglycan expression, and that organic–inorganic hybrid molecules, such as metal complexes and organometallic compounds, serve as useful tools to analyze proteoglycan synthesis mechanisms. However, the effects of metal compounds lacking electrophilicity on proteoglycan synthesis remain unclear. Au₂₅(SG)₁₈, a nanoscale gold cluster consisting of a metal core protected by gold–glutathione complexes, exhibits extremely low intramolecular polarity. In this study, we investigated the effect of Au₂₅(SG)₁₈ on proteoglycan synthesis in vascular endothelial cells. Au₂₅(SG)₁₈ accumulated significantly in vascular endothelial cells at low cell density and suppressed the expression of perlecan, a major heparan sulfate proteoglycan in cells, by inactivating ADP-ribosylation factor 6 (Arf6). Additionally, Au₂₅(SG)₁₈ reduced the expression of biglycan, a small dermatan sulfate proteoglycan, in vascular endothelial cells at low cell density; however, the underlying mechanisms remain unclear. Overall, our findings suggest that organic–inorganic hybrid molecules regulate the activity of Arf6-mediated protein transport to the extracellular space and that perlecan is regulated through this mechanism, highlighting the importance of Arf6-mediated extracellular transport for maintaining vascular homeostasis.

Cadmium is a heavy metal risk factor for various cardiovascular diseases, such as atherosclerosis. In atherosclerotic lesions, hyaluronan, a glycosaminoglycan consisting of β4-glucuronic acid-β3-N-acetylglucosamine disaccharides repeats, is highly accumulated, regulating signal transduction, cell migration, and angiogenesis. Hyaluronan is synthesized by hyaluronan synthase (HAS)1-3 in the plasma membrane and secreted into the extracellular space. Hyaluronan derived from HAS3 promotes inflammatory responses. Recently, we found that cadmium elongates chondroitin/dermatan sulfate chains in vascular endothelial cells and that glycosaminoglycan sugar chains are potential targets for the vascular toxicity of cadmium. Therefore, hyaluronan, a glycosaminoglycan sugar chain, may also affected by cadmium; however, this has not yet been clarified. In this study, we aimed to analyze the effect of cadmium on hyaluronan synthesis using cultured aortic endothelial cells. Cadmium at a concentration of 2 µM upregulated hyaluronan synthesis in the medium and specifically induced HAS3 mRNA and protein expression. However, cadmium-mediated HAS3 induction was abolished by the inhibition of the c-Jun N-terminal kinase (JNK)-c-Jun pathway. Moreover, JNK inhibition prevented the increase in hyaluronan levels in the medium. These results revealed that the JNK-c-Jun pathway was involved in HAS3-mediated hyaluronan synthesis by cadmium in vascular endothelial cells, suggesting that endothelial HAS3 induction contributes to atherosclerotic lesion formation by promoting inflammatory responses.