Antiplatelet activity of alpha-lipoic acid

Impact of Surface Ligand on the Biocompatibility of InP/ZnS Quantum Dots with Platelets

InP/ZnS quantum dots (QDs) have received a large focus in recent years as a safer alternative to heavy metal-based QDs. Given their intrinsic fluorescent imaging capabilities, these QDs can be potentially relevant for in vivo platelet imaging. The InP/ZnS QDs are synthesized and their biocompatibility investigated through the use of different phase transfer agents. Analysis of platelet function indicates that platelet-QD interaction can occur at all concentrations and for all QD permutations tested. However, as the QD concentration increases, platelet aggregation is induced by QDs alone independent of natural platelet agonists. This study helps to define a range of concentrations and coatings (thioglycolic acid and penicillamine) that are biocompatible with platelet function. With this information, the platelet-QD interaction can be identified using multiple methods. Fluorescent lifetime imaging microscopy (FLIM) and confocal studies have shown QDs localize on the surface of the platelet toward the center while showing evidence of energy transfer within the QD population. It is believed that these findings are an important stepping point for the development of fluorescent probes for platelet imaging.

α-Lipoic Acid Alleviates Hepatic Lipid Deposition by Inhibiting FASN Expression via miR-3548 in Rats

Excessive liver lipid deposition is a vital risk factor for the development of many diseases. Here, we fed Sprague-Dawley rats with a control or α-lipoic acid-supplemented diet (0.2%) for 5 weeks to elucidate the effects of α-lipoic acid on preventive ability, hepatic lipid metabolism-related gene expression, and the involved regulatory mechanisms. In the current study, α-lipoic acid supplementation lowered plasma triglyceride level and hepatic triglyceride content. Reduced hepatic lipid deposition was closely associated with inhibiting fatty acid-binding protein 1 and fatty acid synthase expression, as well as increasing phosphorylated hormone-sensitive lipase expression at the protein level in α-lipoic acid-exposed rats. Hepatic miRNA sequencing revealed increased expression of miR-3548 targeting the 3'untranslated region of Fasn mRNA, and the direct regulatory link between miRNA-3548 and FASN was verified by dual-luciferase reporter assay. Taken together, α-lipoic acid lowered hepatic lipid accumulation, which involved changes in miRNA-mediated lipogenic genes.

Transient Howell-Jolly-body-like cytoplasmic inclusions in neutrophils after severe intoxication with alpha-lipoic acid

After intravenous supplementation of an unintentionally high dose of the antioxidant alpha-lipoic acid (ALA), a 53-year-old female complained of myalgia, chills and nausea, and showed signs of haemorrhagic diathesis. The laboratory findings were excessive hyperferritinemia, leukoerythroblastosis, severe thrombocytopenia, elevated liver enzymes and impaired coagulation. The toxicological tests resulted in an ALA serum concentration of 10 280 µg/L. The peripheral blood film of the patient showed some neutrophil dysplasia with unusual small dark-blue stained round cytoplasmic inclusions resembling 'Howell-Jolly-body-like' (HJBL) cytoplasmic inclusions, aptly named due to the morphologic similarity to their erythrocytic counterparts. Such HJBL inclusions are occasionally associated with acquired immunodeficiency, or immunosuppressive or cytostatic treatment. An association with ALA intoxication has not been described before. There are only a few reports on unintentional, harmful and lethal intoxications with ALA. The underlying molecular background of its toxicity on liver function or haematopoiesis is not yet known in detail, but ALA seems to interact with enzyme functions, e.g. with mitochondrial enzyme-complexes, possibly due to its pro-oxidant potential at high doses.

Effects of α-Lipoic Acid, Carnosine, and Thiamine Supplementation in Obese Patients with Type 2 Diabetes Mellitus: A Randomized, Double-Blind Study

Type 2 diabetes mellitus (T2DM) is evolving to an epidemic of the modern world. T2DM is associated with a number of pathological complications, including cardiovascular disease that is mostly promoted by the increased oxidative stress in type 2 diabetic patients. We performed a randomized double-blind placebo-controlled trial to investigate the effectiveness of an individualized oral supplementation with α-lipoic acid (ALA), carnosine, and thiamine. For that purpose, 82 obese type 2 diabetic patients were randomly assigned to 2 groups, and were either supplemented daily with 7 mg ALA/kg body weight, 6 mg carnosine/kg body weight, and 1 mg thiamine/kg body weight or placebo for 8 weeks. An array of biochemical tests including the estimation of oxidative stress and platelet aggregation were performed at baseline and at follow-up. Moreover, the antiplatelet activity of each of the supplement's components was determined ex vivo at human and washed rabbit platelets. Glucose and HbA_1c levels were significantly reduced after supplementation (135.7 ± 19.5 mg/dL vs. 126.5 ± 16.8 mg/dL and 8.3% ± 0.3% vs. 6.03% ± 0.58%, respectively, P < .05); however, insulin was significantly increased (3.6 ± 0.7 μIU/mL vs. 6.8 ± 0.2 μIU/mL, P < .05). The patients treated with the supplement recorded higher follow-up values for HOMA-IR and HOMA-β, and a significant drop in serum hydroperoxide level. Only ALA inhibited platelets aggregation ex vivo through ADP, platelet activating factor, arachidonic acid, epinephrine, collagen, and thrombin pathways. Daily supplementation with an individualized ALA, carnosine, and thiamine supplement effectively reduced glucose concentration in type 2 diabetic patients, probably by increasing insulin production from the pancreas. In addition to that, the reduction of oxidative stress and inhibition of platelet aggregation could potentially provide greater cardiovascular protection. Further studies are needed to fine-tune the supplementation dose-response effects in T2DM patients.

The novel compound MP407 inhibits platelet aggregation through cyclic AMP-dependent processes

Platelet hyperactivity plays a critical role for initiating several vascular diseases such as atherothrombosis. Therefore, development of effective antiplatelet agents is necessary for ameliorating platelet-related diseases. In this study, we investigated the effects of the new synthesized compound, MP407 on platelet aggregation and further elucidated the underlying mechanisms. Our results demonstrated that MP407 dose-dependently inhibited collagen-induced platelet aggregation, thromboxane B₂ (TXB₂) production, intracellular Ca²⁺ mobilization, platelet membrane GPIIb/IIIa expression, and the phosphorylation of Akt, GSK3β, p38MAPK, and phospho (Ser) PKC substrate (p47). Moreover, MP407 is able to increase the cyclic AMP formation both in resting and activated platelets. However, blocking cyclic AMP formation with 2'5'-ddAdo, an inhibitor of adenylate cyclase, greatly reversed the antiplatelet activity of MP407 and related platelet-activating pathways. MP407 also enhanced VASP phosphorylation at Ser157 in collagen-stimulated platelets, which was attenuated by addition of 2'5'-ddAdo. Therefore, the antiplatelet activity of MP407 may be modulated by cyclic AMP-dependent regulation of Akt, GSK3β, p38MAPK and VASP phosphorylation. Notably, treatment with MP407 markedly reduced the pulmonary thrombosis and the numbers of paralysis and death in mice induced by ADP injection, but did not affect the bleeding time. Taken together, MP407 may be a potential candidate or lead compound for developing novel antiplatelet or antithrombotic agents for platelet hyperactivity-triggered disease therapy.

[Liposomal form of lipoic acid: preparation and determination of antiplatelet and antioxidant activity]

Optimal conditions for obtaining phosphatidylholine (PC) liposomes with lipoic acid (LA) are chosen that lead to the formation of nanoparticles with a size of 175¸284 nm with efficiency (extent) of inclusion of LA in liposomes equal 85% and characterized by a slow release of substance from the nanoparticles. The effect of "empty" liposomes and liposomal form of LA on platelet aggregation induced by arachidonic acid (AA) is established. It is found that liposomes with LА inhibit platelet aggregation, caused by AА, to 80%. In addition, it is shown that "empty" liposomes slightly (to 30%) suppress platelet aggregation, caused by AА. The amount of TBA-sensitive products in samples of platelet-rich plasma (PRP) incubated with liposomal LA is determined. It is shown that LA in the composition of liposomes retains its antioxidant properties, and the amount of products of lipid peroxidation in platelet-rich plasma decreases in a dose-dependent manner when arachidonic acid is used as an inductor of platelet aggregation. It is assumed that the antiplatelet action of the liposomal form of LА is induced by inhibition of the initiation of lipid peroxidation products caused by exogenous inducer AА. It is supposed that, after additional research, the liposomal form of LA can be considered as a new drug in complex treatment of cerebral ischemia.

Mechanisms of Nifedipine-Downregulated CD40L/sCD40L Signaling in Collagen Stimulated Human Platelets

The platelet-derived soluble CD40L (sCD40L) release plays a critical role in the development of atherosclerosis. Nifedipine, a dihydropyridine-based L-type calcium channel blocker (CCB), has been reported to have an anti-atherosclerotic effect beyond its blood pressure-lowering effect, but the molecular mechanisms remain unclear. The present study was designed to investigate whether nifedipine affects sCD40L release from collagen-stimulated human platelets and to determine the potential role of peroxisome proliferator-activated receptor-β/-γ (PPAR-β/-γ). We found that treatment with nifedipine significantly inhibited the platelet surface CD40L expression and sCD40L release in response to collagen, while the inhibition was markedly reversed by blocking PPAR-β/-γ activity with specific antagonist such as GSK0660 and GW9662. Meanwhile, nifedipine also enhanced nitric oxide (NO) and cyclic GMP formation in a PPAR-β/-γ-dependent manner. When the NO/cyclic GMP pathway was suppressed, nifedipine-mediated inhibition of sCD40L release was abolished significantly. Collagen-induced phosphorylation of p38MAPK, ERK1/2 and HSP27, matrix metalloproteinase-2 (MMP-2) expression/activity and reactive oxygen species (ROS) formation were significantly inhibited by nifedipine, whereas these alterations were all attenuated by co-treatment with PPAR-β/-γ antagonists. Collectively, these results demonstrate that PPAR-β/-γ-dependent pathways contribute to nifedipine-mediated downregulation of CD40L/sCD40L signaling in activated platelets through regulation of NO/ p38MAPK/ERK1/2/HSP27/MMP-2 signalings and provide a novel mechanism regarding the anti-atherosclerotic effect of nifedipine.

Inhibition of adenosine diphosphate-induced platelet aggregation by alpha-lipoic acid and dihydroquercetin in vitro

Objectives:

To investigate the antiplatelet activity of alpha-lipoic acid (α-LA) and dihydroquercetin (DHQ).

Materials and

Methods: Antiplatelet activity of the α-LA and DHQ was evaluated in rich platelet plasma of rat. The platelet aggregation was induced by adenosine diphosphate (ADP) in concentration of 4 × 10^-5 M.

Results:

α-LA and DHQ inhibited platelet aggregation in concentration-dependent manner. The antiplatelet activity of α-LA was more pronounced than DHQ. DHQ also increased the antiplatelet activity of α-LA by 1.4 times.

Conclusion:

Combined simultaneous use of α-LA and DHQ possessed the high antiplatelet activity, and DHQ potentiated the activity of α-LA.

New mechanisms of antiplatelet activity of nifedipine, an L-type calcium channel blocker

Platelet hyperactivity often occursd in hypertensive patients and is a key factor in the development of cardiovascular diseases including thrombosis and atherosclerosis. Nifedipine, an L-type calcium channel blocker, is widely used for hypertension and coronary heart disease therapy. In addition, nifedipine is known to exhibit an antiplatelet activity, but the underlying mechanisms involved remain unclear. Several transcription factors such as peroxisome proliferator-activated receptors (PPARs) and nuclear factor kappa B (NF-κB) exist in platelets and have an ability to regulate platelet aggregation through a non-genomic mechanism. The present article focuses on describing the mechanisms of the antiplatelet activity of nifedipine via PPAR activation. It has been demonstrated that nifedipine treatment increases the activity and intracellular amount of PPAR-β/-γ in activated platelets. Moreover, the antiplatelet activity of nifedipine is mediated by PPAR-β/-γ-dependent upon the up-regulation of the PI3K/AKT/NO/cyclic GMP/PKG pathway, and inhibition of protein kinase Cα (PKCα) activity via an interaction between PPAR-β/-γ and PKCα. Furthermore, suppressing NF-κB activation by nifedipine through enhanced association of PPAR-β/-γ with NF-κB has also been observed in collagen-stimulated platelets. Blocking PPAR-β/-γ activity or increasing NF-κB activation greatly reverses the antiplatelet activity and inhibition of intracellular Ca²⁺ mobilization, PKCα activity, and surface glycoprotein IIb/IIIa expression caused by nifedipine. Thus, PPAR-β/-γ- dependent suppression of NF-κB activation also contributes to the antiplatelet activity of nifedipine. Consistently, administration of nifedipine markedly reduces fluorescein sodium-induced vessel thrombus formation in mice, which is considerably inhibited when the PPAR-β/-γ antagonists are administrated simultaneously. Collectively, these results provide important information regarding the mechanism by which nifedipine inhibits platelet aggregation and thrombus formation through activation of PPAR-β/-γ- mediated signaling pathways. These findings highlight that PPARs are novel therapeutic targets for preventing and treating platelet-hyperactivity-related vascular diseases.

Relationship between Platelet PPARs, cAMP Levels, and P-Selectin Expression: Antiplatelet Activity of Natural Products

Platelets are no longer considered simply as cells participating in thrombosis. In atherosclerosis, platelets are regulators of multiple processes, with the recruitment of inflammatory cells towards the lesion sites, inflammatory mediators release, and regulation of endothelial function. The antiplatelet therapy has been used for a long time in an effort to prevent and treat cardiovascular diseases. However, limited efficacy in some patients, drug resistance, and side effects are limitations of current antiplatelet therapy. In this context, a large number of natural products (polyphenols, terpenoids, alkaloids, and fatty acids) have been reported with antiplatelet activity. In this sense, the present paper describes mechanisms of antiplatelet action of natural products on platelet P-selectin expression through cAMP levels and its role as peroxisome proliferator-activated receptors agonists.

Dihydroasparagusic acid: antioxidant and tyrosinase inhibitory activities and improved synthesis

Dihydroasparagusic acid (DHAA) is the reduced form of asparagusic acid, a sulfur-containing flavor component produced by Asparagus plants. In this work, DHAA was synthetically produced by modifying some published protocols, and the synthesized molecule was tested in several in vitro assays (DPPH, ABTS, FRAP-ferrozine, BCB, deoxyribose assays) to evaluate its radical scavenging activity. Results show that DHAA is endowed with a significant in vitro antioxidant activity, comparable to that of Trolox. DHAA was also evaluated for its inhibitory activity toward tyrosinase, an enzyme involved, among others, in melanogenesis and in browning processes of plant-derived foods. DHAA was shown to exert an inhibitory effect on tyrosinase activity, and the inhibitor kinetics, analyzed by a Lineweaver-Burk plot, exhibited a competitive mechanism. Taken together, these results suggest that DHAA may be considered as a potentially active molecule for use in various fields of application, such as pharmaceutical, cosmetics, agronomic and food.

Effect of α-lipoic acid on platelet reactivity in type 1 diabetic patients

OBJECTIVE

Type 1 diabetes is associated with increased platelet reactivity. We investigated whether α-lipoic acid (ALA) has any effect on platelet reactivity in these patients.

RESEARCH DESIGN AND METHODS

We randomly assigned 51 type 1 diabetic patients to ALA (600 mg once daily) or placebo for 5 weeks. Platelet reactivity was evaluated by the PFA-100 method and by measuring CD41 and CD62 platelet expression. C-reactive protein (CRP) and 8-iso-prostaglandin F2α serum levels also were measured.

RESULTS

Baseline variables were similar in the two groups. After treatment, closure time was longer (P = 0.006) and CD62P platelet expression was lower, both before (P = 0.002) and after (P = 0.009) ADP stimulation in the ALA group compared with the placebo group. CRP and 8-iso-prostaglandin F2α levels showed no differences between the two groups.

CONCLUSIONS

Our data show that ALA reduces measures of platelet reactivity ex vivo in type 1 diabetic patients, independently of antioxidant or anti-inflammatory effects.

Bioorganic synthesis, characterization and antioxidant activity of esters of natural phenolics and α-lipoic acid

Chemo-enzymatic synthesis of six esters of natural phenolics and α-lipoic acid was carried to produce novel compounds with potential bioactivity. The synthetic route was mild, simple, and efficient with satisfactory yields. The synthesized compounds were screened for antioxidant activities. The prepared derivatives exhibited very good antioxidant activities as determined by DPPH radical scavenging assay and inhibition of lipid oxidation in fish oil emulsion system. Among the prepared derivatives, three compounds exhibited radical scavenging activity similar to the reference antioxidants, BHT and alpha-tocopherol in the DPPH radical scavenging assay, where as in fish oil emulsion system, two derivatives showed activity, which was similar to the reference antioxidants.

Inhibitory effect of α-lipoic acid on platelet aggregation is mediated by PPARs

Peroxisome proliferator-activated receptors (PPARs) isoforms (α, β/δ, and γ are present in human platelets, and activation of PPARs inhibits platelet aggregation. α-Lipoic acid (ALA), occurring naturally in human food, has been reported to exhibit an antiplatelet activity. However, the mechanisms underlying ALA-mediated inhibition of platelet aggregation remain unknown. The aim of this study was to investigate whether the antiplatelet activity of ALA is mediated by PPARs. ALA itself significantly induced PPARα/γ activation in platelets and increased intracellular amounts of PPARα/γ by blocking PPARα/γ secretion from arachidonic acid (AA)-activated platelets. Moreover, ALA significantly inhibited AA-induced platelet aggregation, Ca(2+) mobilization, and cyclooxygenase-1 (COX-1) activity, but increased cyclic AMP production in rabbit washed platelets. Importantly, ALA also enhanced interaction of PPARα/γ with protein kinase Cα (PKCα) and COX-1 accompanied by an inhibition of PKCα activity in resting and AA-activated platelets. However, the above effects of ALA on platelets were markedly reversed by simultaneous addition of selective PPARα antagonist (GW6471) or PPARγ antagonist (GW9662). Taken together, the present study provides a novel mechanism by which ALA inhibition of platelet aggregation is mediated by PPARα/γ-dependent processes, which involve interaction with PKCα and COX-1, increase of cyclic AMP formation, and inhibition of intracellular Ca(2+) mobilization.