Inhibition of oxidized LDL aggregation with the calcium channel blocker amlodipine: role of electrostatic interactions

Photochlorination-induced degradation of microplastics and interaction with Cr(VI) and amlodipine

Wastewater treatment plants (WWTPs) are the important source of microplastics (MPs) in the environment, and disinfection processes bear high potential to degrade MPs. This study investigated the physicochemical degradation, dissolved organic products and interaction with co-existed pollutants (heavy metal and pharmaceutical) on polyethylene (PE), polypropylene (PP) and polystyrene (PS) MPs during simulated disinfection processes. Compared to photo or chlorination, photochlorination significantly resulted in the physicochemical degradation, including morphology alteration, fragmentation, and chemical oxidation on PP and PS MPs, but showed relatively low effect on PE, indicating the different resistance among polymers to disinfected treatment. Photochlorination also caused the formation of chain-scission organic compounds and even chlorinated products from MPs (e.g. C₁₁H₁₉O₄Cl for PP and monochlorophenol, dichlorophenol, chloroacetophenone and chlorobenzoic acid for PS), which may form disinfection byproducts to induce healthy risk. The adsorption potentials of MPs for Cr(VI) or amlodipine were enhanced by photochlorination since the cracking and formed oxygen functional groups enhanced the pore filling and surface precipitation of Cr(VI), and the electrostatic attraction and hydrogen bonding with amlodipine. The findings indicated the physicochemical degradation of MPs and the combined pollution with co-existed pollutants, highlighting the health risks of MP-derived organic products during the disinfection treatments (even in normal dosage) in WWTPs.

Contribution of aged polystyrene microplastics to the bioaccumulation of pharmaceuticals in marine organisms using experimental and model analysis

Microplastics (MPs) in the environment would undergo extensive weathering, which can act as a vector affecting the accumulation of pollutants in organisms. However, the risk of organic pollutants adsorbed on aged MPs to marine organisms is poorly understood. This study revealed the contribution of aged polystyrene (PS) MPs to the total bioaccumulation of atorvastatin (ATV) and amlodipine (AML), and assessed the environmental risks via experimental and model analysis. The results showed that pharmaceuticals were more easily released in gastrointestinal fluids from aged MPs relative to that in simulated seawater. The hydrophobic pharmaceuticals were more bioaccessible than hydrophilic ones by organisms. Model analysis showed that ingestion of water and food were the most important uptake routes for pharmaceuticals in marine fish and seabirds, while aged PS MPs could decrease the bioaccumulation of pharmaceuticals (contributed for -2.9% and -1.2% for the total uptake of ATV, and -25.8% and -4.4% for AML), indicating the cleaning effect of aged MPs, and the potential higher exposure risks of pharmaceuticals in warm-blooded organisms than that in cold-blooded ones via ingested MPs. The study revealed the effect of aged MPs to the bioaccumulation of pharmaceuticals in marine organisms, and highlighted the combined risks of aged MPs and pharmaceuticals in the environment.

Desorption of pharmaceuticals from pristine and aged polystyrene microplastics under simulated gastrointestinal conditions

Microplastics (MPs) in the environment usually undergo extensive weathering and can transport pollutants to organisms once being ingested. However, the transportation mechanism and effect of aging process are poorly understood. This study systematically investigated the desorption mechanisms of pharmaceuticals from pristine and aged polystyrene (PS) MPs under simulated gastric and intestinal conditions of marine organisms. Results showed that the increased desorption in stomach mainly depended on the solubilization of pepsin to pharmaceuticals and the competition for sorption sites on MPs via π-π and hydrophobic interactions. However, high desorption in gut relied on the solubilization of intestinal components (i.e. bovine serum albumin (BSA) and bile salts (NaT)) and the competitive sorption of NaT since the enhanced solubility increased the partition of pharmaceuticals in aqueous phase. Aging process suppressed the desorption of pharmaceuticals because aging decreased hydrophobic and π-π interactions but increased electrostatic interaction between aged MPs and pharmaceuticals, which became less affected by gastrointestinal components. Risk assessment indicated that the MP-associated pharmaceuticals posed low risks to organisms, and warm-blooded organisms suffered relatively higher risks than cold-blooded ones. This study reveals important information to understand the ecological risks of co-existed MPs and pollutants in the environment.

Effect of aging on adsorption behavior of polystyrene microplastics for pharmaceuticals: Adsorption mechanism and role of aging intermediates

In the environment, aging obviously changes physicochemical properties of microplastics (MPs), but the effects of aging process on adsorption behavior of MPs are not fully understood. In this study, the aging of polystyrene (PS) was accelerated by photo-Fenton reaction. The adsorption mechanism of different aged PS toward atorvastatin (ATV) and amlodipine (AML) and the role of PS-derived intermediates in adsorption process were investigated. Results showed that the adsorption of pristine PS toward pharmaceuticals relied on hydrophobic and π-π interaction, while for aged PS, electrostatic interaction and hydrogen bonding controlled the adsorption. The study revealed that the intermediates released from aging process in high concentration (TOC of 10 mg/L) significantly decreased the adsorption of ATV (10 mg/L) on PS (5.0 g/L) but increased the adsorption of AML (10 mg/L). However, those intermediates at environmental concentration (0.1 mg/L) exhibited low effects on adsorption of pharmaceuticals (1.0 mg/L) on MPs (0.5 g/L of PS). The impact mainly depended on electrostatic interaction between MPs and aging intermediates. Besides, the adsorption of low-degree aged PS was more susceptible to the aging intermediates than that of high-degree aged ones. These findings highlight significant implication of MP-derived intermediates in aquatic environments.

Radiolabeled cholesteryl ethers: A need to analyze for biological stability before use

Radiolabeled cholesteryl ethers are widely used as non-metabolizable tracers for lipoproteins and lipid emulsions in a variety of in vitro and in vivo experiments. Since cholesteryl ethers do not leave cells after uptake and are not hydrolyzed by mammalian cellular enzymes, these compounds can act as markers for cumulative cell uptakes of labeled particles. We have employed [³H]cholesteryl oleoyl ether to study the uptake and distribution of triglyceride-rich emulsion particles on animal models. However, questionable unexpected results compelled us to analyze the stability of these ethers. We tested the stability of two commercially available radiolabeled cholesteryl ethers - [³H]cholesteryl oleoyl ether and [³H]cholesteryl hexadecyl ether from different suppliers, employing in vitro, in vivo and chemical model systems. Our results show that, among the two cholesteryl ethers tested, one ether was hydrolyzed to free cholesterol in vitro, in vivo and chemically under alkaline hydrolyzing agent. Free cholesterol, unlike cholesteryl ether, can then re-enter the circulation leading to confounding results. The other ether was not hydrolyzed to free cholesterol and remained as a stable ether. Hence, radiolabeled cholesteryl ethers should be analyzed for biological stability before utilizing them for in vitro or in vivo experiments.

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Tested stability of two commercially available radiolabeled cholesteryl ethers.

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One ether was hydrolyzed to free cholesterol (FC) in vitro and in vivo.

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FC, re-entered circulation giving questionable unexpected results in experiments.

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The other ether was unhydrolyzed in all model systems.

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Radiolabeled cholesteryl ethers should be analyzed for stability before use.

Resolution of overlapped spectra for the determination of ternary mixture using different and modified spectrophotometric methods

Four new spectrophotometric methods were developed, applied to resolve the overlapped spectra of a ternary mixture of [aliskiren hemifumarate (ALS)-amlodipine besylate (AM)-hydrochlorothiazide (HCT)] and to determine the three drugs in pure form and in combined dosage form. Method A depends on simultaneous determination of ALS, AM and HCT using principal component regression and partial least squares chemometric methods. In Method B, a modified isosbestic spectrophotometric method was applied for the determination of the total concentration of ALS and HCT by measuring the absorbance at 274.5nm (isosbestic point, Aiso). On the other hand, the concentration of HCT in ternary mixture with ALS and AM could be calculated without interference using first derivative spectrophotometric method by measuring the amplitude at 279nm (zero crossing of ALS and zero value of AM). Thus, the content of ALS was calculated by subtraction. Method C, double divisor first derivative ratio spectrophotometry (double divisor (1)DD method), was based on that for the determination of one drug, the ratio spectra were obtained by dividing the absorption spectra of its different concentrations by the sum of the absorption spectra of the other two drugs as a double divisor. The first derivative of the obtained ratio spectra were then recorded using the appropriate smoothing factor. The amplitudes at 291nm, 380nm and 274.5nm were selected for the determination of ALS, AM and HCT in their ternary mixture, respectively. Method D was based on mean centering of ratio spectra. The mean centered values at 287, 295.5 and 269nm were recorded and used for the determination of ALS, AM and HCT, respectively. The developed methods were validated according to ICH guidelines and proved to be accurate, precise and selective. Satisfactory results were obtained by applying the proposed methods to the analysis of pharmaceutical dosage form.

Optimizing combination therapy in the management of hypertension: the role of the aliskiren, amlodipine, and hydrochlorothiazide fixed combination

High blood pressure is the leading risk factor for death and disability worldwide, and the prevalence is increasing. Effective treatment decreases the risk of adverse events in proportion to blood pressure reduction. Combination antihypertensive therapy reduces blood pressure promptly and effectively. Single-pill combinations reduce the pill burden and improve adherence, efficacy, and tolerability of treatment compared with single drug pills. A significant portion of the hypertensive population will require three drugs for adequate control. The single-pill combination of aliskiren, amlodipine, and hydrochlorothiazide is based on complementary mechanisms of action. Clinical trials have shown it to be a safe and effective treatment for hypertension. This combination is a reasonable choice in clinical practice for patients with hypertension that requires three drugs for effective treatment.

Glucose-β-CD interaction assisted ACN field-amplified sample stacking in CZE for determination of trace amlodipine in beagle dog plasma

A simple, sensitive and low-cost method using CE coupled with glucose-β-CD interaction assisted ACN stacking technique has been developed for quantification of trace amlodipine in dog plasma. The plasma samples were extracted with methyl tert-butyl ether. The separation was performed at 25°C in a 31.2 cm × 75 μm fused-silica capillary with an applied voltage of 15 kV. The BGE was composed of 6.25 mM borate/25 mM phosphate (pH 2.5) and 5 mg/mL glucose-β-CD. The detection wavelength was 200 nm. Because CD could diminish the interaction between drugs and matrix, and derivation groups of CD play an important role in separation performance, the effects of β-CD, and its derivatives on the separation were studied at several concentrations (0, 2.5, 5.0, 10.0 mg/mL). In this study, organic solvent field-amplified sample stacking technique in combination with glucose-β-CD enhanced the sensitivity about 60-70 folds and glucose-β-CD could effectively improve the peak shape. All the validation data, such as accuracy, precision extraction recovery, and stability, were within the required limits. The calibration curve was linear for amlodipine from 1 to 200 ng/mL. The method developed was successfully applied to the pharmacokinetic studies of amlodipine besylate in beagle dogs.

Relaxation of rat thoracic aorta by fibrate drugs correlates with their potency to disturb intracellular calcium of VSMCs

Phenotypic modifications of vascular smooth muscle cells (VSMCs) contribute to pathological changes in atherosclerosis where modulation of intracellular calcium plays an important role. In this study, three fibrate drugs, namely gemfibrozil (Gem), fenofibric acid (Fa) and bezafibrate (Beza), were revealed to relax thoracic aorta associated with their potency to reduce intracellular calcium ([Ca²⁺]i) in cultured VSMCs. Relaxation effect of Gem, Fa and Beza was assayed on precontracted rat aortic rings. [Ca²⁺]i level in VSMCs following addition of these fibrates was measured by laser scanning confocal microscopy or flow cytometry. Resultantly, three fibrates showed activity for vasodilation with potency order of Gem>Fa>Beza. Sustained potent reduction of [Ca²⁺]i was observed with Gem 50mg/L and mild reduction with Fa 400-600mg/L, while no effect had been detected for Beza under our current system. Thus, the potency of these fibrates to relax aortic rings correlate well with their effect on [Ca²⁺]i reduction, strongly implicating an underlying causal relationship. Considering that Gem potently reduces [Ca²⁺]i in its clinical concentration range, this study suggests an insight to in situ pharmacological effects of anti-atherosclerosis and clinical toxicity risk.

Modern views on amlodipine and new S-amlodipine medications

The review presents the latest evidence on the calcium antagonist amlodipine, summarizing its mechanisms of action, its pleiotropic, endothelial function-related effects, and its anti-atherogenic activity. Amlodipine suppresses the proliferation of vascular smooth myocytes and extracellular matrix and improves endothelial vasodilatation, despite the absence of L-type calcium channels in these cells. This mechanism is related to an increase in endothelial nitric oxide (NO) release. The results of experimental studies on the role of S and R amlodipine isomers in its hemodynamic and pleiotropic activity are presented. While S-amlodipine is a pharmacologically active blocker of L-type calcium channels, R-amlodipine increases endothelial NO release. New medications have been developed, based on S-amlodipine. It has been shown that S-amlodipine 5 mg/d is bioequivalent to amlodipine 10 mg/d. The pharmacodynamics analysis demonstrated that S-amlodipine 5 mg/d and amlodipine 10 mg/d did not differ significantly in terms of mean levels of systolic and diastolic blood pressure, or mean heart rate. S-amlodipine was better tolerated and characterised by a lower incidence of peripheral edema than amlodipine. However, the effects of S-amlodipine on hard end-points should be investigated in the long-term prospective studies.

Improving vascular function in hypertension: potential benefits of combination therapy with amlodipine and renin-angiotensin-aldosterone system blockers

Hypertension is characterized by endothelial dysfunction and increased risk for adverse cardiovascular outcomes. In addition to lowering blood pressure, the calcium-channel blocker amlodipine and blockers of the renin-angiotensin-aldosterone system (angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers) may further reduce cardiovascular risk by improving endothelial function when used alone or in combination. In fact, the beneficial effects of the combination of amlodipine and a renin-angiotensin-aldosterone system blocker on endothelial function have been found to be greater than the effect of either drug alone, likely due to additive effects on nitric oxide activity. This review summarizes the observed effects of these agents on endothelial function and the complementary mechanisms by which they act, thus providing rationale (beyond blood pressure benefits) for their use in combination.

Enhancement of amlodipine cardioprotection by quercetin in ischaemia/reperfusion injury in rats

Objectives

To investigate the possible modification of the cardioprotective effect of amlodipine when co-administered with quercetin in myocardial ischaemia/reperfusion-induced functional, metabolic and cellular alterations in rats.

Methods

Oral doses of amlodipine (15 mg/kg) and quercetin (5 mg/kg), alone or in combination, were administered once daily for 1 week. Rats were then subjected to myocardial ischaemia/reperfusion (35min/10min). Heart rates and ventricular arrhythmias were recorded during ischaemia/reperfusion progress. At the end of reperfusion, activities of plasma creatine kinase (CK) and cardiac myeloperoxidase were determined. In addition, cardiac contents of lactate, ATP, thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and total nitrate/nitrite (NOx) were estimated. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments.

Key findings

Combined therapy provided significant improvement in the amlodipine effect toward preserving cardiac electrophysiologic functions, ATP and GSH contents as well as reducing the elevated plasma CK, cardiac TBARS and NOx contents.

Conclusion

Quercetin could add benefits to the cardioprotective effect of amlodipine against injury induced in the heart by ischaemia/reperfusion.

Effects of amlodipine and candesartan on oxidized LDL level in patients with mild to moderate essential hypertension

OBJECTIVE

To compare the effects of amlodipine and candesartan on oxidized low-density lipoprotein (OxLDL), conjugated dienes (CD) and baseline diene conjugation in circulating low-density lipoproteins (LDL-BDC) level during antihypertensive treatment.

METHODS

Forty-nine patients with untreated mild to moderate essential hypertension were recruited in a randomized double-blind study to receive a daily dose either of 8 mg candesartan or 5 mg amlodipine for 16 weeks. Blood pressure, OxLDL, CD, LDL-BDC, triglycerides (TG), total cholesterol and lipoprotein cholesterol were measured at baseline, at week 2 and at week 16.

RESULTS

During treatment, in addition to a significant decrease in systolic and diastolic blood pressure, high level of OxLDL decreased significantly reaching practically upper kit reference values. Both treatment groups were similar with regard to the studied parameters at all time points. At the same time serum TG, lipoprotein and total cholesterol levels as well as LDL-BDC did not change and CD levels did not exceed endemic normal. Decrease in both systolic and diastolic blood pressure was associated with decrease in LDL-BDC/LDL.

CONCLUSIONS

Besides their antihypertensive effects, both candesartan and amlodipine are efficient drugs for reducing OxLDL level, being neutral with regard to serum lipids.

Liquid chromatography–tandem mass spectrometry in chiral study of amlodipine biotransformation in rat hepatocytes

A high proportion of drugs are chiral compounds used as racemic mixtures in a clinical practice. Very often only one of two enantiomers exhibits a desired pharmacological effect. Amlodipine, 2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-1,4-dihydropyridine, is a chiral calcium channel blocker, currently used as a racemate in clinical practice. Racemic mixture is used even though it is known that R- and S-amlodipine do not have the same biological activity and only S-amlodipine possesses vasodilating properties. In this work a novel reversed phase liquid chromatography (RP-LC) separation method for amlodipine and its metabolites was developed. Based on this separation chiral aspects of amlodipine biotransformation were studied by incubation of amlodipine and its two individual enantiomers with primary culture of rat hepatocytes. Structure of the metabolites was elucidated using a liquid chromatography (LC) separation with ultraviolet (UV) and mass spectrometry (MS) detection. An LC-tandem MS (MS/MS) method was used to establish fragmentation pattern of amlodipine and its metabolites. Eight metabolites presented in the highest amount were identified and semiquantified by employing an LC separation. Basically two types of metabolites were detected, reduced type--dihydropyridine metabolites and oxidized type--pyridine metabolites. Other metabolic modification included changes of functional groups, e.g., methylester hydrolysis or acetylation of amino group. The results exhibited that R-amlodipine was stereoselectively metabolized by the respective biotransformation enzymes in rat liver hepatocytes and it is also demonstrated by greater extent of R-amlodipine conversion into metabolites where the values for R-amlodipine are for the most metabolites higher than those for metabolites of S-amlodipine.

A rationale for combination therapy in risk factor management: a mechanistic perspective

Endothelial dysfunction contributes to mechanisms of atherogenesis and its clinical manifestations, including coronary heart disease. Cardiovascular risk factors have been linked directly to a loss of endothelial function, such as endothelium-dependent nitric oxide (NO) release, resulting in abnormal vasodilation in response to various stimuli. There is evidence that multiple risk factors, including hypertension and hyperlipidemia, lead to a synergistic effect on endothelial dysfunction, likely through oxidative stress mechanisms. Damage to the endothelium leads to reduced NO bioavailability and facilitates vessel wall permeability to low-density lipoprotein. Certain agents, including the antihypertensive drug amlodipine and the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statin) atorvastatin, are known to influence endothelial function and NO bioavailability directly; these properties may contribute to clinical benefits. Recent experimental evidence at the cellular level indicates that these agents stimulate NO release from human endothelial cells in a highly synergistic fashion. The clinical implications of these observations are discussed in this article in the context of cardiovascular risk factor management strategies.

Amlodipine and atorvastatin in atherosclerosis: a review of the potential of combination therapy

Hypertension and hyperlipidaemia are major risk factors for the development of atherosclerosis. Calcium channel blockers (CCBs) have been used for decades and have established antihypertensive effects. Statins have been extensively used because of their potent lipid lowering properties. Amongst other factors, inflammation and oxidation are involved in enhanced progression of atherosclerosis and new lesion development. Therefore, research has been initiated focusing on the antioxidant and anti-inflammatory properties of CCBs and statins, beyond their primary effect, in order to evaluate the possible additive effects of combined treatment of CCBs with statins as antiatherosclerotic therapy. Clinical studies (e.g., the International Nifedipine Trial on Antiatherosclerotic Therapy [INTACT]) have demonstrated that the antiatherosclerotic action of CCBs is limited to the attenuation of the first stage of atherosclerogenesis (fatty streak formation or new lesion growth). The lesions that pre-existed at the start of CCB therapy did not demonstrate progression or regression on angiography. However, because the mechanisms of action of lipid-lowering drugs and CCBs, and their role in preventing the progression of atherosclerosis differ, it is conceivable to conclude that these two classes may have an additive or synergic effect, not only on new lesion formation but also on inhibiting the progression of established coronary atherosclerosis. Indeed, this combined effect of lipid-lowering therapy and CCBs on human coronary atherosclerosis has been reported in the Regression Growth Evaluation Statin Study (REGRESS) trial. This beneficial effect of combining CCBs with statins has now been replicated in transgenic atherosclerotic mice, where the combination of amlodipine and atorvastatin produced an additional 60% reduction of atherosclerosis compared with that observed with the statin alone. Serum markers of atherosclerosis and vascular integrity also improved most in the combination group. Synergistic effects of the combination of atorvastatin and amlodipine on acute nitric oxide release/endothelial function, and additive effects of the combination of amlodipine and atorvastatin in the improvement of arterial compliance in hypertensive hyperlipidaemic patients has been demonstrated. Collectively, these studies support the clinical antiatherosclerotic advantages of combination of CCBs and statins and in particular, of atorvastatin with amlodipine beyond their established antihyperlipidaemic and antihypertensive modes of action.

Novel Vascular Biology of Third-Generation L-Type Calcium Channel Antagonists

Calcium channel blockers (CCBs) were developed as vasodilators, and their use in cardiovascular disease treatment remains largely based on that mechanism of action. More recently, with the evolution of second- and third-generation CCBs, pleiotropic effects have been observed, and at least some of CCBs’ benefit is attributable to these mechanisms. Understanding these effects has contributed greatly to elucidating disease mechanisms and the rationale for CCB use. Furthermore, this knowledge might clarify why drugs are useful in some disease states, such as atherosclerosis, but not in others, such as heart failure. Although numerous drugs used in the treatment of vascular disease, including statins and angiotensin-converting–enzyme inhibitors, have well-described pleiotropic effects universally accepted to contribute to their benefit, little attention has been paid to CCBs’ potentially similar effects. Accumulating evidence that at least 1 CCB, amlodipine, has pharmacologic actions distinct from L-type calcium channel blockade prompted us to investigate the pleiotropic actions of amlodipine and CCBs in general. There are several areas of research; foci here are (1) the physicochemical properties of amlodipine and its interaction with cholesterol and oxidants; (2) the mechanism by which amlodipine regulates NO production and implications; and (3) amlodipine’s role in controlling smooth muscle cell proliferation and matrix formation.