Significance of plasma nitric oxide/endothelial-1 ratio for prediction of coronary artery disease

Exploring nitric oxide as a crucial prognostic biomarker of coronary artery disease

PURPOSE

The study aimed to examine if the polymorphism of the endothelial nitric oxide synthase (eNOS) gene variable number of tandem repeats (VNTR) and the serum NO levels are associated with CAD.

MATERIALS/METHODS

Case-control study, 70 CAD and 30 control subjects were enrolled. The eNOS gene polymorphism was measured by polymerase chain reaction-agarose gel electrophoresis and the serum NO was assessed by using an ELISA plate and reader covering 540 nm.

RESULTS

Uncovering the area under curve (AUC) for serum NO, which was (0.6821), indicating that NO seemed to be a critical prognostic biomarker of CAD; also, glucose, serum creatinine and total bilirubin proved to be significant predictors of CAD with AUC (0.6793, 0.6717 and 0.6662) respectively. Furthermore, higher serum NO levels were associated with the eNOS (ab) genotype. Revealing the intron (a) allele was protective against CAD. Moreover, diminished levels of serum NO in CAD groups compared to controls (P < 0.05). Additionally, Multiple logistic regression analysis shows a significantly high Odds ratio associated with CAD in the Duhok population.

CONCLUSIONS

The eNOS (ab) variant seems to be a protective CAD factor for patients. Low serum NO levels are another risk factor for the advancement of CAD, suggesting their involvement in atherosclerosis. The (a) allele's protective effect is mediated through changes in eNOS promoter activity and higher NO levels.

Endothelial Reprogramming in Sports Traumatology: Role of the Widespread Neuro-Immuno-Endocrine-Endothelial System

This paper deals with the role of the widespread neuro-immuno-endocrine-endothelial system in sport traumatology. The aim of this work is to see if sport or regular physical activity is able to reprogram the endothelium, to advance the new concept of neuro-immuno-endocrine-endothelial diffused system, and to introduce in the practice of sport medicine a new test in the fields of “Athlete functional evaluation” and “Sports fitness”. The first object of this paper is to see whether sport or regular physical activity can change the functional structure of the endothelium. The second goal is to frame under a general view the knowledge and individual lines of research on endothelium, to highlight what we believe is, in the organization of homeostasis, the location of this ‘organ’, namely in the neuro-immune-endocrine system spread.

Endothelin-1 and nitrogen oxide metabolites in risk diagnostics of arterial hypertension in persons of young and middle ages occupied in harmful working conditions

Hypertension is a global public health problem. One of the reasons contributing to the development of arterial hypertension is endothelial dysfunction, which is expressed in the imbalance of vasoactive indicators of vascular tone - nitrogen oxide and endothelin-1. Monitoring the indicators of endothelial dysfunction in workers exposed to harmful occupational factors will help to identify a risk group for the development of occupationally caused diseases of the cardiovascular system and, in particular, arterial hypertension, for early implementation of preventive measures. This study aims to identify the relationship between endothelin-1, nitrogen oxide metabolites and blood pressure in young and middle-aged people occupied in harmful working conditions, to evaluate the studied parameters as possible markers for diagnosing the risk of hypertension. Two hundred thirty-six (236) employees of young and middle age were examined of one of the metallurgical plants of the Nizhny Novgorod region. In order to characterize the state of vascular tone, a coefficient was used that represents the ratio of the concentration of nitrogen oxide (μmol/L) to endothelin-1 (pg/ml) (NOx/ET-1). It was revealed that in one-third of people with normal and high normal blood pressure, the NOx/ET-1 value was 2-3 times less than in people with optimal blood pressure, which indicates the occurrence of endothelial dysfunction and the possible development of persistent arterial hypertension. Harmful occupational factors negatively affect vascular tone - the value of NOx/ET-1 in individuals exposed to harmful factors was 3-4 times less than in individuals not subjected to such exposure. The NOx/ET-1 coefficient can be used as an informative indicator when monitoring health conditions with an in-depth examination of working people; it can be a criterion for the risk of developing hypertension.

Associations of endothelial biomarkers, nitric oxide metabolites and endothelin, with blood pressure and coronary lesions depend on cardiovascular risk and sex to mark endothelial dysfunction on the SCORE scale

OBJECTIVES

Endothelial dysfunction contributes to the onset and progression of cardiovascular diseases. However, direct associations of vasoactive mediators with cardiovascular risk are poorly understood.

METHODS

We have determined associations of circulating levels of stable metabolites of nitric oxide, nitrate and nitrite (NOx), endothelin-1, and the endothelin-1/NOx ratio with blood pressure in 177 asymptomatic subjects without signs of coronary atherosclerosis; associations with blood pressure and with presence of coronary lesions were also evaluated in 457 patients suspected to have coronary heart disease with or without coronary lesions confirmed by coronary angiography. All participants were on a low nitrate diet 24 h prior to blood sampling.

RESULTS

In men, NOx levels were inversely correlated with blood pressure similar to women with low (0-4%) European Systematic Coronary Risk Estimation (SCORE). However, the correlation was not significant in women with high SCORE (5-8%). High systolic blood pressure over 140 mm Hg was negatively associated with NOx levels in asymptomatic men (p=0.05) but not in women. This association is disrupted in male and female patients with coronary atherosclerosis. In male patients, NOx (p=0.05), endothelin (p=0.01), and the endothelin/NOx ratio (p=0.04) were associated with presence of coronary lesions.

CONCLUSIONS

Thus, elevated cardiovascular risk according to SCORE over 4% in asymptomatic women, but not in men, is associated with a shift in markers of endothelial dysfunction. Presence of coronary lesions in patients is associated with significant changes in circulating levels of markers of endothelial dysfunction in men but not in women.

Added value of total serum nitrate/nitrite for prediction of cardiovascular disease in middle east caucasian residents in Tehran

Data on the association between serum nitrate/nitrite and cardiovascular disease (CVD) is controversial; the aim of this study was to examine the potential utility of serum nitrate/nitrite in prediction of CVD. A total of 2443 adult participants, free from CVD at baseline were included. The probability of developing CVD was estimated by incorporating traditional CVD risk factors into a logistic regression model in the presence of serum nitrate/nitrite. The probability of CVD was calculated using Ln-transformed CVD risk factors as a covariate in the presence of Ln-transformed nitrate/nitrite in the final model. The added value of nitrate/nitrite was estimated using receiver operating characteristic curves and the net reclassification index (NRI). During follow-up, 169 events occurred. The multivariate odds ratio (95% confidence interval) for each 1 unit of increase in the Ln-transformed traditional risk factors and Ln-transformed nitrate/nitrite, were 3.20 (2.67-3.84) and 1.35 (1.01-1.80) for incident CVD, respectively. The areas under the curves of discrimination for models with and without nitrate/nitrite were not significantly different; however, incorporating nitrate/nitrite to the traditional CVD risk model can help appropriately reclassify over 6% of individuals at risk. In conclusion, serum nitrate/nitrite levels were independently associated with incident CVD. Measurement of serum nitrate/nitrite provided information beyond individual data on risk factors and improved prediction of CVD.

Short-term aerobic exercise and vascular function in CKD stage 3: a randomized controlled trial

BACKGROUND

The present study was designed to determine the effect of short-term moderate-intensity exercise training on arterial stiffness in patients with chronic kidney disease (CKD) stage 3.

STUDY DESIGN

Randomized controlled trial with a parallel-group design.

SETTING & PARTICIPANTS

Testing and training sessions were performed at Springfield College. 46 (treatment group, n=25; control group, n=21) patients with CKD with diabetes and/or hypertension completed the study.

INTERVENTION

The aerobic training program consisted of 16 weeks of supervised exercise training at 50%-60% peak oxygen uptake (Vo2peak) 3 times per week, while the control group remained sedentary. Identical testing procedures were performed following the 16-week intervention.

OUTCOMES

The primary outcome was arterial stiffness. Secondary outcomes were aerobic capacity, various blood parameters (endothelin 1, nitrate/nitrite, and high-sensitivity C-reactive protein), and health-related quality of life.

MEASUREMENTS

Arterial stiffness was assessed with aortic pulse wave velocity (PWV), aerobic capacity by Vo2peak, blood parameters by enzyme-linked immunosorbent assays, and health-related quality of life by the 36-Item Short Form Health Survey (SF-36). Participants attended 4 sessions before being randomly assigned to either the treatment or control group. Participants gave consent during the first session, whereas a graded exercise test with measurement of Vo2peak was completed during the second session. During sessions 3 and 4, aortic PWV was measured at rest prior to 40 minutes of either moderate-intensity exercise training or seated rest. A venous blood sample was obtained prior to exercise or rest and participants completed the SF-36 questionnaire.

RESULTS

16 weeks of training led to an 8.2% increase in Vo2peak for the treatment group (P=0.05), but no changes in aortic PWV .

LIMITATIONS

Randomization was not concealed and was violated on one occasion; also, use of an indirect measurement of endothelial function and the short duration of the intervention.

CONCLUSIONS

Short-term moderate-intensity exercise training does not alter arterial stiffness in patients with CKD, but seems to reduce endothelin 1 levels.

Exercise training improves endothelial function in young prehypertensives

Prehypertensives exhibit marked endothelial dysfunction, a risk factor for future cardiovascular morbidity and mortality. However, the ability of exercise to ameliorate endothelial dysfunction in prehypertensives is grossly underinvestigated. This prospective randomized and controlled study examined the separate effects of resistance and endurance training on conduit artery endothelial function in young prehypertensives. Forty-three unmedicated prehypertensive (systolic blood pressure [SBP]=120-139 mmHg; diastolic blood pressure [DBP]=80-89 mmHg) but otherwise healthy men and women and 15 normotensive matched time-controls (NMTC); n = 15) between 18 and 35 y of age met screening requirements and participated in the study. Prehypertensive subjects were randomly assigned to either a resistance exercise training (PHRT; n = 15), endurance exercise training (PHET; n = 13) or time-control group (PHTC; n = 15). The treatment groups performed exercise training three days per week for eight weeks. The control groups did not initiate exercise programs throughout the study. Flow mediated dilation (FMD) of the brachial artery, biomarkers of enodothelial function and peripheral blood pressure were evaluated before and after exercise intervention or time-matched control. PHRT and PHET reduced resting SBP (9.6 ± 3.6 and 11.9 ± 3.4 mmHg, respectively; P < 0.05) and DBP (8.0 ± 5.1 and 7.2 ± 3.4 mmHg, respectively; P < 0.05). Exercise training improved brachial artery FMD absolute diameter, percent dilation and normalized percent dilation by 30%, 34% and 19% for PHRT, P < 0.05; and by 54%, 63% and 75% for PHET, P < 0.05; respectively. PHRT and PHET increased plasma concentrations of 6-keto prostaglandin F1α (19% and 22%, respectively; P < 0.05), NO x (19% and 23%, respectively; P < 0.05), and reduced endothelin-1 by (16% and 24%, respectively; P < 0.01). This study provides novel evidence that resistance and endurance exercise separately have beneficial effects on resting peripheral blood pressure, brachial artery FMD and endothelial-derived vasoactive agents in young prehypertensives.

Endothelial factors after selective retrograde coronary venous bypass under different pressures

BACKGROUND

Selective retrograde coronary venous bypass (SRCVB) may be a promising treatment for patients with advanced coronary artery disease (CAD). The aim of this study is to investigate the effect of SRCVB on plasma endothelial factor levels in dog myocardial ischemic model, and explore the possible mechanisms.

METHODS

24 crossbreed dogs were randomly divided into three groups: (1) control group; (2) SRCVB group with 60 mmHg perfusion pressure; (3) SRCVB group with 90 mmHg perfusion pressure. The posterior descending coronary artery (PDA) was ligated in all groups, and SRCVB was performed in the last two groups. The levels of plasma nitric oxide (NO) and endothelin (ET) at different time points were determined in each group. In SRCVB groups, ink and imaging agent were injected to the heart through SVG graft for assessment of vein perfusion.

RESULTS

At the acute period, there were significant increase in the plasma levels of NO and decrease in ET in SRCVB 90 mmHg group compared with the control (P < 0. 01), and a further improvement were found in SRCVB 60 mmHg group (P < 0. 01). The ink or imaging agent was found in the myocardial tissue and flowed back to right atrium through contralateral coronary vein.

CONCLUSIONS

SRCVB with low level of perfusion pressure could provide effective perfusion for ischemic myocardium and alleviate the myocardial endothelial cell injury. It may be a new therapeutic strategy for severe CAD.

Ginkgo biloba extract improves coronary artery circulation in patients with coronary artery disease: contribution of plasma nitric oxide and endothelin-1

In patients with coronary artery disease (CAD), coronary blood flow is usually impaired due to imbalanced vasoactive substances such as nitric oxide (NO) and endothelin-1 (ET-1). The study was designed to test the effects of Ginkgo biloba extract (GBE) on the distal left anterior descending coronary artery (LAD) blood flow and plasma NO and ET-1 levels. Eighty CAD patients were randomly assigned to GBE (n = 42) and control (n = 38) groups. The LAD blood flow was assessed non-invasively using Doppler echocardiography at baseline and after 2 weeks. GBE treatment demonstrated a significant improvement in maximal diastolic peak velocity (MDPV), maximal systolic peak velocity (MSPV) and diastolic time velocity integral (DTVI) compared with controls (14.61 +/- 4.51% vs 0.67 +/- 2.66%, 9.03 +/- 4.81% vs 0.34 +/- 2.67% and 14.69 +/- 5.08% vs 0.68 +/- 3.00%, respectively, p < 0.01). NO was increased by 12.42% (p < 0.01), whereas ET-1 was decreased by 5.82% (p < 0.01). The NO/ET-1 ratio was increased by 19.47% (p < 0.01). A linear correlation was confirmed between the percentage change in LAD blood flow and in NO, ET-1 or NO/ET-1 ratio following GBE treatment. The results suggest that GBE treatment in CAD patients led to an increase of LAD blood flow, which might at least be related partly to the restoration of the delicate equilibrium between NO and ET-1.

Markers for endothelial dysfunction, but not markers for oxidative stress correlate with classical risk factors and the severity of coronary artery disease. (A subgroup analysis from the Ludwigshafen Risk and Cardiovascular Health Study)

OBJECTIVE

Endothelial dysfunction and oxidative stress are involved in atherogenesis. In the search for predictors of vascular disease markers for endothelial dysfunction and oxidative stress were analyzed.

METHODS

Of 208 consecutive patients 22% were controls (CO) without coronary artery disease (CAD), 52% presented with stable angina (SAP) and 26% had acute coronary syndromes (ACS). Nitric oxide (NO), thrombomodulin (TM), von Willebrand factor (vW), sVCAM-1, sICAM-1, sP-selectin, sE-selectin, sL-selectin and C-reactive protein (CRP) were determined as markers for endothelial dysfunction, glutathione (GSH), glutathione peroxidase (Gpx), myeloperoxidase (Mpx), lipid peroxides (Lpx), 8-isoprostane (Iso), superoxide dismutase (SOD), total antioxidant capacity (TAC) and homocysteine (Hc) as markers for oxidative stress.

RESULTS

The increases of TM, vW, sVCAM-1, CRP, SOD and Mpx correlated with the CAD status in the order CO < SAP < ACS, whereas NO and sL-selectin were inversely correlated (p < 0.05, resp.). The other markers remained unchanged. For several markers a significant relationship to risk factors was detected.

CONCLUSIONS

Markers for endothelial dysfunction rather than those for oxidative stress may serve as indicators for the presence and severity of CAD.

Evaluation of hormone replacement therapy which may have an adrenomedullin-mediated protective effect on cardiovascular disorders

BACKGROUND AND AIMS

This study aimed to determine whether there is an adrenomedullin (AM)-mediated protective effect of postmenopausal estrogen/progestin therapy (HRT) against cardiovascular disorders.

METHODS

A total of 22 post-menopausal women without hysterectomy undergoing postmenopausal symptoms (aged 43-52) were treated with conjugated equine estrogen (0.625 mg/die) plus medroxyprogesterone acetate (2.5 mg/die) for six months. The flow velocity of the right middle cerebral artery [measured as resistance index (RI) and pulsatility index (PI)], plasma levels of adrenomedullin and endothelin- 1 (ET-1), mean baseline ratio of AM to ET-1, and lipid profiles were assessed before and after HRT.

RESULTS

A statistically significant difference was found for triglycerides, total cholesterol, AM/ET-1 ratio and right middle cerebral artery PI (p<0.05), without any significant differences in HDL, LDL, AM, ET-1, systolic blood pressure, diastolic blood pressure, a right middle cerebral artery RI (p>0.05) between pre- and post- HRT.

CONCLUSIONS

Adrenomedullin may be added to other vasoactive peptides as a new potential candidate for HRT-mediated vascular protection. The ratio of AM/ET-1 vs AM or ET-1 alone may be a useful biological marker of this protection.

Intra-arterial infusion of nitric oxide (NO) - first animal trial

OBJECTIVE

Nitric oxide (NO) is an important signaling molecule that acts in many tissues to regulate a diverse range of physiological processes. NO has been implicated in a number of cardiovascular diseases. Reduced basal NO synthesis or function may lead to: vasoconstriction, elevated blood pressure and thrombus formation. By contrast, overproduction of NO results in vasodilatation, hypotension, vascular leakage, and disruption of cell metabolism. The purpose of this study was to determine the effects of NO gas directly infused into the arteries.

METHODS

The study was performed on 28 rabbits and 10 pigs. We developed a device that enables quantitatively controlled infusion of NO gas, directly into the arteries.

RESULTS

We found that administration of NO gas via arteries caused widening of the blood vessels as well as increasing blood flow in the extremity. It emerges that. These effects persist up to 2-3 h after the NO infusion ceased. Although the NO breaks down when diffused in blood, its influence commences rapidly and continues for a relatively long time.

CONCLUSIONS

Our findings indicate that, administration of NO into blood vessels causes a long lasting vasodilatation and enhanced blood flow. Despite the fact that NO is broken down rapidly.

Increased oxidative stress impairs endothelial modulation of contractions in arteries from spontaneously hypertensive rats

OBJECTIVES

The endothelium modulates vascular contractions. We investigated the effects of oxidative stress on endothelial modulation of contractions in hypertension.

METHODS

Changes in isometric tension of femoral arterial rings from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were recorded.

RESULTS

The contractile response to norepinephrine of arteries with endothelium was greater in SHR than in WKY rats (P < 0.0001). Endothelium removal augmented the norepinephrine-induced contraction (P < 0.05). The augmentation was more pronounced in WKY than in SHR, which resulted in comparable contraction of arteries without endothelium in both strains. Nomega-nitro-L-arginine methyl ester (100 micromol/l) mimicked the effect of endothelium removal. Production of nitric oxide (NO, assessed by measuring nitrite/nitrate concentrations) during the contraction was not different between SHR and WKY. Vitamin C suppressed the contraction of arteries with endothelium from SHR but not from WKY (P < 0.05). Diphenyleneiodonium and apocynin, inhibitors of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase, attenuated the contraction of arteries with endothelium from SHR (P < 0.001) but not WKY, but did not affect contractions induced by serotonin. Superoxide generated by xanthine oxidase/hypoxanthine enhanced the norepinephrine-induced contraction of arteries with endothelium from WKY (P < 0.0001), and this effect was reversed by vitamin C.

CONCLUSIONS

In rat femoral arteries, NO released from the endothelium modulates vascular contraction. In SHR, production of superoxide by NADH/NADPH oxidase, which may be activated by norepinephrine, is enhanced, resulting in the inactivation of NO and impairment of endothelial modulation of vascular contractions. Vascular oxidative stress may contribute to the altered circulation in hypertension by impairing endothelial modulation of vascular contractions.

Inverse correlation between coronary blood flow velocity and sICAM-1 level observed in ischemic heart disease patients

Systemic factors and blood flow velocity related to atherosclerosis have been examined mainly separately or by in vitro studies. The aim of our study was to investigate the association between local coronary blood flow (corrected TIMI frame count, CTFC) and systemic atherosclerosis-related inflammatory parameters such as soluble intercellular adhesion molecule-1 (sICAM-1), interleukin-6 (Il-6), high sensitivity C-reactive protein (hsCRP) and von Willebrand factor (vWF) in humans. We enrolled the following groups of ischemic heart disease (IHD) patients: patients with coronary stenosis and stable (CAD, n = 96) or unstable angina (ACS, n = 27), patients with documented myocardial ischemia and normal coronary angiogram (NEG, n = 68). Patient groups showed only marginal differences in CTFC or sICAM-1 levels. In contrast, when IHD patients were studied individually, general positive correlation was found between CTFC and sICAM-1 level (r = 0.33; in NEG r = 0.25; in CAD r = 0.37; in ACS r = 0.61), being the strongest in ACS. The relation was independent from age, gender, BMI, smoking, hypertension, diabetes, previous myocardial infarction, family history of IHD, medication, hsCRP, IL-6 and vWF levels. (odds ratio, OR = 6.4; CI 95%: 2.43-16.84; p < 0.05). Nevertheless, correlation between CTFC and IL-6, hsCRP, vWF levels was not found. These results indicate inverse correlation between coronary blood flow and adhesion molecule production independently from conventional cardiovascular risk factors and inflammatory markers.

GATA2 is associated with familial early-onset coronary artery disease

The transcription factor GATA2 plays an essential role in the establishment and maintenance of adult hematopoiesis. It is expressed in hematopoietic stem cells, as well as the cells that make up the aortic vasculature, namely aortic endothelial cells and smooth muscle cells. We have shown that GATA2 expression is predictive of location within the thoracic aorta; location is suggested to be a surrogate for disease susceptibility. The GATA2 gene maps beneath the Chromosome 3q linkage peak from our family-based sample set (GENECARD) study of early-onset coronary artery disease. Given these observations, we investigated the relationship of several known and novel polymorphisms within GATA2 to coronary artery disease. We identified five single nucleotide polymorphisms that were significantly associated with early-onset coronary artery disease in GENECARD. These results were validated by identifying significant association of two of these single nucleotide polymorphisms in an independent case-control sample set that was phenotypically similar to the GENECARD families. These observations identify GATA2 as a novel susceptibility gene for coronary artery disease and suggest that the study of this transcription factor and its downstream targets may uncover a regulatory network important for coronary artery disease inheritance.

Coronary artery disease (CAD) is the most common form of heart disease in the Western world and is one of the leading causes of death in the United States. CAD is inherited and is a complex genetic disease because it results from changes to multiple genes acting in concert with one another and the environment. The authors locate CAD susceptibility genes by convergence of techniques and identify variation within a gene of interest in an early-onset CAD population. If a specific variant is found more often in affected individuals or families than in controls, this can suggest that this gene variant is associated with disease. The authors have identified a gene, GATA2, which is located in a genomic region suspected to contain genes for CAD and displays expression patterns predictive of location of disease within human donor aortas. They have identified several GATA2 variants that segregate with CAD in a family-based early-onset CAD population and have further validated two of these associations in a separate young case-control sample affected with CAD. These data imply that the transcription factor GATA2 may play a role in CAD susceptibility and suggest that the study of GATA2 targets may uncover a set of GATA2-regulated genes important to CAD inheritance.

Endothelin-1 inhibits adiponectin secretion through a phosphatidylinositol 4,5-bisphosphate/actin-dependent mechanism

Adiponectin is an adipokine with profound insulin-sensitizing, anti-inflammatory, and anti-atherogenic properties. Plasma levels of adiponectin are reduced in insulin resistant states such as obesity, type 2 diabetes and cardiovascular disease. However, the mechanism(s) by which adiponectin concentrations are decreased during disease development is unclear. Studies have shown that endothelin-1 (ET-1), a vasoconstrictor peptide, affects adipocyte glucose metabolism and secretion of adipokines such as leptin, resistin, and adiponectin. The goal of our study was to determine the mechanism by which ET-1 decreases adiponectin secretion. 3T3-L1 adipocytes were treated for 24h with ET-1 (10nM) and then stimulated with vehicle or insulin (100 nM) for a period of 1-2h. Chronic ET-1 (24h) treatment significantly decreased basal and insulin-stimulated adiponectin secretion by 66% and 47%, respectively. Inhibition of phosphatidylinositol 4,5-bisphosphate (PIP(2)) hydrolysis by the PLCbeta inhibitor, U73122, or exogenous addition of PIP(2):histone carrier complex (1.25:0.625 microM) ameliorated the decrease in basal and insulin-stimulated adiponectin secretion observed with ET-1. However, treatment with exogenous PIP(2):histone carrier complex and the actin depolymerizing agent latrunculin B (20 microM) did not reverse the ET-1-mediated decrease in adiponectin secretion. In conclusion, we demonstrate that ET-1 inhibits basal and insulin-stimulated adiponectin secretion through PIP(2) modulation of the actin cytoskeleton.