Characteristics of lysophosphatidylcholine-induced Ca2+ response in human neuroblastoma SH-SY5Y cells

The Ryanodine Receptor Contributes to the Lysophosphatidylcholine-Induced Mineralization in Valvular Interstitial Cells

PURPOSE

Fibrocalcific aortic valve disease (CAVD) is caused by the deposition of calcific nodules in the aortic valve leaflets, resulting in progressive loss of function that ultimately requires surgical intervention. This process is actively mediated by the resident valvular interstitial cells (VICs), which, in response to oxidized lipids, transition from a quiescent to an osteoblast-like state. The purpose of this study was to examine if the ryanodine receptor, an intracellular calcium channel, could be therapeutically targeted to prevent this phenotypic conversion.

METHODS

The expression of the ryanodine receptor in porcine aortic VICs was characterized by qRT-PCR and immunofluorescence. Next, the VICs were exposed to lysophosphatidylcholine, an oxidized lipid commonly found in low-density lipoprotein, while the activity of the ryanodine receptor was modulated with ryanodine. The cultures were analyzed for markers of cellular mineralization, alkaline phosphatase activity, proliferation, and apoptosis.

RESULTS

Porcine aortic VICs predominantly express isoform 3 of the ryanodine receptors, and this protein mediates the cellular response to LPC. Exposure to LPC caused elevated intracellular calcium concentration in VICs, raised levels of alkaline phosphatase activity, and increased calcific nodule formation, but these changes were reversed when the activity of the ryanodine receptor was blocked.

CONCLUSIONS

Our findings suggest blocking the activity of the ryanodine receptor can attenuate the valvular mineralization caused by LPC. We conclude that oxidized lipids, such as LPC, play an important role in the development and progression of CAVD and that the ryanodine receptor is a promising target for pharmacological intervention.

4-Pyridinio-1,4-Dihydropyridines as Calcium Ion Transport Modulators: Antagonist, Agonist, and Dual Action

A set of six new 4-pyridinio-1,4-dihydropyridine (1,4-DHP) compounds has been synthesized. The calcium channel modulating activity of these compounds was evaluated in an aorta vascular smooth muscle cell line (A7R5), in an isolated rat aortic ring model, and in human neuroblastoma cell lines (SH-SY5Y). The antagonistic effect of these 1,4-DHP was tested by modulating the impact of carbachol-dependent mobilization of intracellular Ca²⁺ in SH-SY5Y cells. The intracellular free Ca²⁺ concentration was measured in confluent monolayers of SH-SY5Y cells and A7R5 cells with the Ca²⁺-sensitive fluorescent indicator Fluo-4 NW. Only four compounds showed calcium channel blocking activity in SH-SY5Y and A7R5 cells as well as in the aortic ring model. Among them, compound 3 was the most active calcium channel antagonist, which had 3 times higher activity on carbachol-activated SH-SY5Y cells than amlodipine. Two of the compounds were inactive. Compound 4 had 9 times higher calcium agonist activity than the classic DHP calcium agonist Bay K8644. The intracellular mechanism for the action of compound 4 using inhibitor analysis was elucidated. Nicotinic as well as muscarinic receptors were not involved. Sarcoplasmic reticulum (ER) Ca²⁺ (SERCA) stores were not affected. Ryanodine receptors (RyRs), another class of intracellular Ca²⁺ releasing channels, participated in the agonist response evoked by compound 4. The electrooxidation data suggest that the studied compounds could serve as antioxidants in OS.

Small molecule RL71 targets SERCA2 at a novel site in the treatment of human colorectal cancer

While targeted agents are an important part of the treatment arsenal for colorectal cancer, there is still a lack of efficient small-molecule targeted agents based on the understanding of pathogenic molecular mechanisms. In this study, curcumin analog RL71 displayed potent cytotoxicity towards human colon cancer cells with an IC₅₀ of 0.8 μM in SW480 cells and inhibited xenotransplanted tumor growth in a dose-dependent manner. Using affinity chromatography, we identified sarco/endoplasmic reticulum calcium-ATPase (SERCA) 2 as the binding target of RL71. Most notably, RL71 demonstrated special binding to SERCA2 at a novel site with the lowest estimated free energy −8.89 kcal mol⁻¹, and the SERCA2 residues critical for RL71 binding were identified. RL71 suppressed the Ca²⁺-ATPase activity of SERCA2 both in vitro and in vivo, accompanied by the induction of endoplasmic reticulum stress leading to apoptosis and G2/M cycle arrest in SW480 cells. In addition, RL71 showed synergistic cytotoxicity with the pan-SERCA inhibitor thapsigargin. These results suggest that RL71 could be a selective small-molecule inhibitor of SERCA2, and that it may serve as a lead compound for the study of targeted colorectal cancer therapy.

Native LDL-induced oxidative stress in human proximal tubular cells: multiple players involved

Dyslipidemia is a well-established condition proved to accelerate the progression of chronic kidney disease leading to tubulo-interstitial injury. However, the molecular aspects of the dyslipidemia-induced renal damage have not been fully clarified and in particular the role played by low-density lipoproteins (LDLs). This study aimed to examine the effects of native non-oxidized LDL on cellular oxidative metabolism in cultured human proximal tubular cells. By means of confocal microscopy imaging combined to respirometric and enzymatic assays it is shown that purified native LDL caused a marked increase of cellular reactive oxygen species (ROS) production, which was mediated by activation of NADPH oxidase(s) and by mitochondrial dysfunction by means of a ROS-induced ROS release mechanism. The LDL-dependent mitochondrial alterations comprised inhibition of the respiratory chain activity, enhanced ROS production, uncoupling of the oxidative phosphorylation efficiency, collapse of the mtΔΨ, increased Ca²⁺ uptake and loss of cytochrome c. All the above LDL-induced effects were completely abrogated by chelating extracellular Ca²⁺ as well as by inhibition of the Ca²⁺-activated cytoplas-mic phospholipase A2, NADPH oxidase and mitochondrial permeability transition. We propose a mechanicistic model whereby the LDL-induced intracellular redox unbalance is triggered by a Ca²⁺ inward flux-dependent commencement of cPLA2 followed by activation of a lipid- and ROS-based cross-talking signalling pathway. This involves first oxidants production via the plasmamembrane NADPH oxidase and then propagates downstream to mitochondria eliciting redox- and Ca²⁺-dependent dysfunctions leading to cell-harming conditions. These findings may help to clarify the mechanism of dyslipidemia-induced renal damage and suggest new potential targets for specific therapeutic strategies to prevent oxidative stress implicated in kidney diseases.

Magnesium lithospermate B extracted from Salvia miltiorrhiza elevates intracellular Ca(2+) level in SH-SY5Y cells

AIM

To examine if magnesium lithospermate B (MLB), a potent inhibitor of Na(+)/K(+)-ATPase, leads to the elevation of intracellular Ca(2+) level as observed in cells treated with cardiac glycosides.

METHODS

Viability of SH-SY5Y neuroblastoma cells treated with various concentrations of ouabain or MLB was measured. Intracellular Ca(2+) levels were visualized using Fluo4-AM (fluorescent dye) when cells were treated with ouabain or MLB in the presence or absence of KB-R7943 (Na(+)/Ca(2+) exchanger inhibitor) and 2-APB (IP(3) receptor antagonist). Molecular modeling was conducted for the docking of ouabain or MLB to Na(+)/K(+)-ATPase. Changes of cell body and dendrite morphology were monitored under a microscope.

RESULTS

severe toxicity was observed in cells treated with ouabain of concentration higher than 1 micromol/L for 24 h while no apparent toxicity was observed in those treated with MLB. Intracellular Ca(2+) levels were substantially elevated by MLB (1 micromol/L) and ouabain (1 micromol/L) in similar patterns, and significantly reduced in the presence of KB-R7943 (10 micromol/L) or 2-APB (100 micromol/L). Equivalent interaction with the binding cavity of Na(+)/K(+)-ATPase was simulated for ouabain and MLB by forming five hydrogen bonds, respectively. Treatment of ouabain (1 micromol/L), but not MLB (1 mumol/L), induced dendritic shrink of SH-SY5Y cells.

CONCLUSION

Comparable to ouabain, MLB leads to the elevation of intracellular Ca(2+) level presumably via the same mechanism by inhibiting Na(+)/K(+)-ATPase. The elevated Ca(2+) levels seem to be supplied by Ca(2+) influx through the reversed mode of the Na(+)/Ca(2+) exchanger and intracellular release from endoplasmic reticulum.

Modulation of nonselective cation current by oxidized LDL and lysophosphatidylcholine and its inhibitory contribution to endothelial damage

AIMS

This study examined the effects of oxidized low-density lipoprotein (LDL) and its major lipid constituent lysophosphatidylcholine (LPC) on nonselective cation (NSC) current and its inhibitory contribution to LPC-induced cytotoxicity in cultured human umbilical endothelial cells (HUVECs).

MAIN METHODS

Patch-clamp technique and the resazurin-based cell viability assay were used.

KEY FINDINGS

In voltage-clamped cells, oxidized LDL or LPC slowly activated NSC current. NSC current was also activated by loading cells with Ca(2+) solution buffered at various concentrations using a patch pipette or by applying the sarcoplasmic reticulum Ca(2+) pump blocker 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), the metabolic inhibitor CN(-) or the hydroperoxide donor tert-butyl hydroperoxide (TBHP). On the contrary, when intracellular Ca(2+) was strongly buffered with 12mM BAPTA or cells were loaded with superoxide dismutase using a patch pipette, LPC or BHQ did not activate NSC current. Furthermore, NSC current activated by LPC, TBHP or CN(-) was inhibited by the antioxidant tempol or extracellular Ca(2+) depletion and NSC current activated by intracellular Ca(2+) was further augmented by oxidized LDL or LPC. LPC or oxidized LDL released Ca(2+) from intracellular stores and further enhanced store-operated Ca(2+) entry. LPC-induced cytotoxicity was augmented by inhibiting Ca(2+) influx and NO synthesis.

SIGNIFICANCE

Oxidized LDL or its main component LPC activated Ca(2+)-permeable NSC current via releasing Ca(2+) from intracellular stores and producing ROS and thereby increased Ca(2+) influx. Ca(2+) influx through NSC channel might protect endothelial cells by producing NO.

Dual effects of sodium aescinate on vascular tension in rat thoracic aorta

OBJECTIVE

Sodium aescinate (SA) is used as a vasoactive drug in clinical treatment. This study was designed to investigate the effects of SA on rat isolated thoracic aorta and the possible mechanisms.

METHODS

Isometric tension was recorded in response to drugs in organ bath.

RESULTS

The effects of SA obeyed an all-or-nothing response. SA in relatively low dose (> or = 50 microg/ml) had an endothelium-independent contractile effect in rat aorta (P<0.01), which depended on extracellular Ca(2+) influx via L-type Ca(2+) channel (P<0.05). SA in relatively high dose (> or = 100 microg/ml) also induced vasoconstriction in Ca(2+)-free medium (P<0.01), which was independent of the activity of inositol-1,4,5-trisphosphate receptor (IP(3)R), ryanodine receptor (RYR), and protein kinase C (PKC). SA in relatively high dose (> or = 100 microg/ml) dilated both endothelium-intact and endothelium-denuded aortic rings precontracted by phenylephrine (PE) or KCl (each P<0.01). SA inhibited extracellular Ca(2+) influx induced by PE or KCl (each P<0.01) and had no activation effect on K(+) channels on vascular smooth muscle. The relaxant effect of SA partly depended on the activity of NO synthase but not on the activity of cyclooxygenase.

CONCLUSIONS

Taken together, this study indicated that SA had dual effects on vascular tension in rat isolated thoracic aorta.

Calcium Signaling in Neuronal Cells Exposed to the Munitions Compound Cyclotrimethylenetrinitramine (RDX)

Cyclotrimethylenetrinitramine (RDX) has been used extensively as an explosive in military munitions. Mechanisms for seizure production, seen in past animal studies, have not been described. Increased calcium levels contribute to excitotoxicity, so in this study neuroblastoma cells are loaded with calcium-indicating dye before application of 1.5 µM to 7.5 mM RDX, with fluorescence recorded for 30 cycles of 11 seconds each. The lowest concentration of RDX increases calcium fluorescence significantly above baseline for cycles 2 to 8; millimolar concentrations increase calcium fluorescence significantly above baseline for cycles 2 to 30. Increases in calcium, like those of 200 nM carbachol, are prevented with 10 mM of calcium chelator ethylene glycol-bis(β-aminoethyl ether)-N,N,N,N tetra-acetic acid (EGTA, tetrasodium salt). Calcium channel blocker verapamil (20 μM), Ca2+-ATPase inhibitor thapsigargin (5 μM), and general membrane stabilizer lidocaine (10 mM) partially attenuate carbachol- and RDX-induced increases in calcium, suggesting that RDX transiently increases intracellular calcium by multiple mechanisms.