Low density lipoproteins inhibit the Na+/H+ antiport in human platelets via activation of p38MAP kinase

Strong relationship between cholesterol, low-density lipoprotein receptor, Na+/H+ exchanger, and SARS-COV-2: this association may be the cause of death in the patient with COVID-19

Lipids have a wide variety and vital functions. Lipids play roles in energy metabolism, intracellular and extracellular signal traffic, and transport of fat-soluble vitamins. Also, they form the structure of the cell membrane. SARS-CoV-2 interacts with lipids since its genetic material contains lipid-enveloped ribonucleic acid (RNA). Previous studies have shown that total cholesterol, high-density lipoprotein, and low-density lipoprotein (LDL) levels are lower in patients with severe novel coronavirus disease 2019 (COVID-19) compared to patients with non-severe COVID-19.Na⁺/H⁺ Exchanger (NHE) is an important antiport that keeps the intracellular pH value within physiological limits. When the intracellular pH falls, NHE is activated and pumps H⁺ ions outward. However, prolonged NHE activation causes cell damage and atherosclerosis. Prolonged NHE activation may increase susceptibility to SARS-CoV-2 infection and severity of COVID-19.In COVID-19, increased angiotensin II (Ang II) due to angiotensin-converting enzyme-2 (ACE2) dysfunction stimulates NHE. Lipids are in close association with the NHE pump. Prolonged NHE activity increases the influx of H⁺ ions and free fatty acid (FFA) inward. Ang II also causes increased low-density lipoprotein receptor (LDLR) levels by inhibiting proprotein convertase subtilisin/kexin type 9 (PCSK9). Thus, intracellular atheroma plaque formation is accelerated.Besides, SARS-CoV-2 may replicate more rapidly as intracellular cholesterol increases. SARS-CoV-2 swiftly infects the cell whose intracellular pH decreases with NHE activation and FFA movement. Novel treatment regimens based on NHE and lipids should be explored for the treatment of COVID-19.

Strong relationship between cholesterol, low-density lipoprotein receptor, Na+/H+ exchanger, and SARS-COV-2: this association may be the cause of death in the patient with COVID-19

Lipids have a wide variety and vital functions. Lipids play roles in energy metabolism, intracellular and extracellular signal traffic, and transport of fat-soluble vitamins. Also, they form the structure of the cell membrane. SARS-CoV-2 interacts with lipids since its genetic material contains lipid-enveloped ribonucleic acid (RNA). Previous studies have shown that total cholesterol, high-density lipoprotein, and low-density lipoprotein (LDL) levels are lower in patients with severe novel coronavirus disease 2019 (COVID-19) compared to patients with non-severe COVID-19.Na⁺/H⁺ Exchanger (NHE) is an important antiport that keeps the intracellular pH value within physiological limits. When the intracellular pH falls, NHE is activated and pumps H⁺ ions outward. However, prolonged NHE activation causes cell damage and atherosclerosis. Prolonged NHE activation may increase susceptibility to SARS-CoV-2 infection and severity of COVID-19.In COVID-19, increased angiotensin II (Ang II) due to angiotensin-converting enzyme-2 (ACE2) dysfunction stimulates NHE. Lipids are in close association with the NHE pump. Prolonged NHE activity increases the influx of H⁺ ions and free fatty acid (FFA) inward. Ang II also causes increased low-density lipoprotein receptor (LDLR) levels by inhibiting proprotein convertase subtilisin/kexin type 9 (PCSK9). Thus, intracellular atheroma plaque formation is accelerated.Besides, SARS-CoV-2 may replicate more rapidly as intracellular cholesterol increases. SARS-CoV-2 swiftly infects the cell whose intracellular pH decreases with NHE activation and FFA movement. Novel treatment regimens based on NHE and lipids should be explored for the treatment of COVID-19.

Delayed-onset of procoagulant signalling revealed by kinetic analysis of COAT platelet formation

The combined action of collagen and thrombin induces the formation of COAT platelets, which are characterised by a coat of procoagulant and adhesive molecules on their surface. Although recent work has started to highlight their clinical relevance, the exact mechanisms regulating the formation of procoagulant COAT platelets remain unclear. Therefore, we employed flow cytometry in order to visualise in real time surface and intracellular events following simultaneous platelet activation with convulxin and thrombin. After a rapid initial response pattern characterised by the homogenous activation of the fibrinogen receptor glycoprotein IIb/IIIa in all platelets, starting with a delay of about 2 minutes an increasing fraction transforms to procoagulant COAT platelets. Their surface is characterised by progressive loss of PAC-1 binding, expression of negative phospholipids and retention of α-granule von Willebrand factor. Intracellular events in procoagulant COAT platelets are a marked increase of free calcium into the low micromolar range, concomitantly with early depolarisation of the mitochondrial membrane and activation of caspase-3, while non-COAT platelets keep the intracellular free calcium in the nanomolar range and maintain an intact mitochondrial membrane. We show for the first time that the flow-cytometrically distinct fractions of COAT and non-COAT platelets differentially phosphorylate two signalling proteins, PKCα and p38MAPK, which may be involved in the regulation of the different calcium fluxes observed in COAT versus non-COAT platelets. This study demonstrates the utility of concomitant cellular and signalling evaluation using flow cytometry in order to further dissect the mechanisms underlying the dichotomous platelet response observed after collagen/thrombin stimulation.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Effects and mechanism of Xin Mai Jia in a rabbit model of atherosclerosis

The aim of this study was to investigate the protective effects of Xin Mai Jia (XMJ) on atherosclerosis (AS) in rabbits and to explore the underlying mechanisms in order to provide experimental evidence for the clinical application of XMJ. An intraperitoneal injection of vitamin D3, combined with a high-fat diet and sacculus injury, was utilized to establish the AS rabbit model. Following the oral administration of lovastatin, Zhibituo and different dosages of XMJ, respectively, blood was drawn from each rabbit for the detection of blood rheological indicators, such as serum lipids. The pathological changes in the right common carotid artery were observed. Vascular function experiments and the expression detection of common carotid artery-related proteins by immunohistochemistry were conducted. XMJ was observed to decrease the blood lipid levels of the AS rabbits; increase the concentration of high-density lipoprotein and apolipoprotein A; decrease blood viscosity, erythrocyte sedimentation rate and hematocrit; elevate the levels of endothelial nitric oxide synthase (eNOS) and Na⁺/H⁺ exchanger 1 in vascular tissues and decrease the levels of angiotensin II receptor, type 1 (AT-1) and endothelin-1 (ET-1). In conclusion, XMJ was shown to lower the blood lipid levels of the experimental AS rabbits, improve the abnormal changes in hemorheology, increase the eNOS content in the vascular tissue, decrease the AT-1 and ET-1 levels and increase the endothelium-dependent vasodilation reaction. XMJ therefore has an anti-AS effect.

Na(+)/H(+) exchanger in the regulation of platelet activation and paradoxical effects of cariporide

Platelets are anucleated cell fragments derived from mature megakaryocytes and function in hemostasis when the endothelium is injured. Hemostasis involving platelets can be divided into four phases: adhesion, activation, secretion, and aggregation. Platelet activation requires a rise in intracellular Ca(2+) concentrations and results in both a morphological change and the secretion of platelet granule contents. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates the intracellular pH (pHi) and the volume of platelets. In addition, NHE1 plays a large role in platelet activation. Thrombus generation involves NHE1 activation and an increase in [Ca(2+)]i, which results from NHE1-mediated Na(+) overload and the reversal of the Na(+)/Ca(2+) exchanger. Cariporide (HOE-642), a potent NHE1 inhibitor, has inhibitory effects on the degranulation of human platelets, the formation of platelet-leukocyte-aggregates, and the activation of the GPIIb/IIIa receptor (PAC-1). However, despite the demonstrated protection against myocardial infarction as mediated by cariporide in patients undergoing coronary artery bypass graft surgery, the EXPEDITION clinical trial revealed that cariporide treatment increased mortality due to thromboembolic stroke. These findings suggest that a better understanding of NHE1 and its effect on platelet function and procoagulant factor regulation is warranted in order to develop therapies using NHE inhibitors.

Photodynamic activity of aloe-emodin induces resensitization of lung cancer cells to anoikis

Aloe-emodin was found to be a photosensitizer and possess anti-tumor activity. However, the detailed mechanism underlying the biological effects of aloe-emodin remains unknown. In this study, we explored the mechanisms of photocytotoxicity induced by aloe-emodin in lung cancer H460 cells. According to the results of the photoactivated aloe-emodin-induced disruption of cytoskeleton, we verify that aloe-emodin with irradiation induces anoikis of H460 cells. Photosensitized aloe-emodin-induced anoikis is associated with the protein expression of α-actinin and mitogen-activated protein (MAP) kinase members. In this study, a rapid opening of the mitochondrial permeability transition pore and the change in apoptosis-related protein expression were involved in photoactivated aloe-emodin-induced cell death. We also demonstrated that anoikis induced by aloe-emodin with irradiation is mediated through the intrinsic and extrinsic death pathways in a caspase-dependent manner in H460 cells.

Proteomic analysis reveals ATP-dependent steps and chaperones involvement in luteolin-induced lung cancer CH27 cell apoptosis

The present study applied 2D electrophoresis to analyze the proteins involved in luteolin (50 microM)-induced CH27 cell apoptosis. We found 7 proteins to be markedly changed. According to the data of analysis of these protein spots, we hypothesized that ATP synthetic pathway and heat shock proteins were involved in luteolin-induced CH27 cell apoptosis. In this study, luteolin induced a significant change in intracellular ATP levels and mitochondrial activity of CH27 cells. Further experiments demonstrated that pretreatment with forskolin blocked the luteolin-induced cell death. P38 and heat shock protein 27 may be important participants in the luteolin-induced changes in organization of actin microfilaments in this study. In addition, endoplasmic reticulum stress is also important in the luteolin-induced CH27 cell apoptosis. Our findings suggested that the function of mitochondria and endoplasmic reticulum is the integral factor in luteolin-induced CH27 cell apoptosis.

Regulation of intracellular pH by p90Rsk-dependent activation of an Na(+)/H(+) exchanger in starfish oocytes

Starfish oocytes arrest at metaphase of the first meiotic division (MI arrest) in the ovary and resume meiosis after spawning into seawater. MI arrest is maintained by lower intracellular pH (pH(i)) and release from arrest by cellular alkalization. To elucidate pH(i) regulation in oocytes, we cloned the starfish (Asterina pectinifera) Na(+)/H(+) exchanger 3 (ApNHE3) expressed in the plasma membrane of oocytes. The cytoplasmic domain of ApNHE3 contains p90 ribosomal S6 kinase (p90Rsk) phosphorylation sites, and injection of a constitutively active p90Rsk and the upstream regulator Mos to immature oocytes, stimulated an increase in pH(i). This increase was blocked by 5-(N-ethyl-N-isopropyl)-amiloride, a NHE inhibitor, and SL0101, a specific Rsk inhibitor. The MAPK kinase (MEK) inhibitor U0126 blocked the Mos-induced, but not the p90Rsk-induced, pH(i) increase, suggesting that the Mos-MEK-MAPK-p90Rsk pathway promotes ApNHE3 activation. In a cell-free extract, the Mos-MEK-MAPK-p90Rsk pathway phosphorylates ApNHE3 at Ser-590, -606, and -673. When p90Rsk-dependent ApNHE3 phosphorylation was blocked by a dominant-negative C-terminal fragment, or neutralizing antibody, the p90Rsk-induced pH(i) increase was suppressed in immature oocytes. However, ApNHE3 is up-regulated via the upstream phosphatidylinositol 3-kinase pathway before MAPK activation and the active state is maintained until spawning, suggesting that the p90Rsk-dependent ApNHE3 phosphorylation is unlikely to be the primary regulatory mechanism involved in MI arrest exit. After meiosis is completed, unfertilized eggs maintain their elevated pH(i) ( approximately 7.4) until the onset of apoptosis. We suggest that the p90Rsk/ApNHE3-dependent elevation of pH(i) increases fertilization success by delaying apoptosis initiation.

Oxidized high-density lipoprotein inhibits platelet activation and aggregation via scavenger receptor BI

Numerous studies have reported the presence of oxidatively modified high-density lipoprotein (OxHDL) within the intima of atheromatous plaques as well as in plasma; however, its role in the pathogenesis of thrombotic disease is not established. We now report that OxHDL, but not native HDL, is a potent inhibitor of platelet activation and aggregation induced by physiologic agonists. This antithrombotic effect was concentration and time dependent and positively correlated with the degree of lipoprotein oxidation. Oxidized lipoproteins are known ligands for scavenger receptors type B, CD36 and scavenger receptor B type I (SR-BI), both of which are expressed on platelets. Studies using murine CD36(-/-) or SR-BI(-/-) platelets demonstrated that the antithrombotic activity of OxHDL depends on platelet SR-BI but not CD36. Binding to SR-BI was required since preincubation of human and murine platelets with anti-SR-BI blocking antibody abrogated the inhibitory effect of OxHDL. Agonist-induced aggregation of platelets from endothelial nitric oxide synthase (eNOS)(-/-), Akt-1(-/-), and Akt-2(-/-) mice was inhibited by OxHDL to the same degree as platelets from wild-type (WT) mice, indicating that the OxHDL effect is mediated by a pathway different from the eNOS/Akt pathway. These novel findings suggest that contrary to the prothrombotic activity of oxidized low-density lipoprotein (OxLDL), HDL upon oxidation acquires antithrombotic activity that depends on platelet SR-BI.

Primer: the practical use of biological markers of rheumatic and systemic inflammatory diseases

The assessment of systemic inflammation by means of laboratory tests often complements the results of medical examination. Traditionally, the erythrocyte sedimentation rate and leukocytosis with left shift are diagnostic markers for inflammatory and infectious diseases. The levels of acute-phase proteins--especially C-reactive protein--are used to assess both the presence of inflammation and any response to treatment. The determination of C-reactive protein levels may be advised in three types of pathological situation: infection, acute or chronic inflammation, and evaluation of metabolic risk. Procalcitonin is useful as a marker of sepsis and severe infection. The concentration of serum amyloid A predicts the chances of survival of patients with secondary (AA) amyloidosis. Ferritin and its glycosylated form are of interest in the study of specific diseases such as adult-onset Still's disease. Markers of cartilage and bone turnover are complementary to these markers of inflammation. Although cytokine serum levels are transiently crucial to the generation of inflammation, their usefulness in the clinic is still under investigation. Serum concentrations of cytokine inhibitors or soluble cytokine receptors, as well as the clinical response of patients to treatment with cytokine antagonists, might generate important information for monitoring autoinflammatory diseases.