The Best Time to Take Your Blood Pressure Pills

Majority of blood pressure medicines are one daily and people take their blood pressure medicines often in the morning. There have been some data based on our understanding of the diurnal variations or circadian rhythms that taking medications at bedtime may work better. For example, peak activity of the renin–angiotensin–aldosterone system (RAAS) occurs during sleep. Further, data from some uncontrolled studies have suggested that taking blood pressure medications at evening (or bedtime) may be beneficial. However, a randomized controlled clinical trial (the gold standard for scientific evidence) has been lacking. That is until now!

A recent study published in the European Heart Journal, by Hermida et al, addressed this very same question. Investigators enrolled 19 084 hypertensive patients (10 614 men and 8470 women) and assigned patients to take the entire dose of their blood pressure pills at bedtime or in the morning. Of all the patients, 1752 experienced either a death due to heart attack, heart attack without death, had stent placed in their heart blood vessels, developed new heart failure, or a stroke. Patients who were taking their medications had 45% lower risk of all outcomes combined, 56% lower risk of heart attach death, 34% lower risk of heart attack, 40% lower risk of stents in their heart blood vessels, 42% lower risk of heart failure, and 49% lower risk of stroke.

Note, these are large differences – these patients were taking their blood pressure pills but just taking pills at a different time made a huge difference. The difference is larger than many other pills that are often prescribed by physicians. If you, or your loved one, takes blood pressure pills, consider talking to your doctor if you should take your pills at bed-time.

Anti-platelet Drugs after Coronary Intervention

The type and duration of anti-platelet therapy after cardiac catheterization and stent placement (also called percutaneous coronary intervention or PCI) is an ongoing debate.

There are two main groups of drugs. One is aspirin which is under use for over 100 years and we know a lot about it. The other group is P2Y12 blockers. P2Y12 is a receptor on the surface of platelets and these drugs block this receptor. The most well-known drug in this group is clopidogrel or Plavix.

A Japanese study examined the role of aspirin + clopidogrel for one month followed by 12-months of clopidogrel versus aspirin + clopidogrel for 12 months showed that the earlier strategy was superior. In contrast, a Korean study, also published in JAMA, found that there is no statistically significant difference between the two.

The results may appear different and the reason my be that the two studies were somewhat different. Below are some of the differences:

1. Korean study allowed the use of other P2Y12 inhibitors/blockers such as prasugrel or ticagrelor while Japanese study allowed on clopidogrel.

2. Korean study had lower adherence to drug therapy in the P2Y12 group as compared to combined group (79% vs. 95%).

3. P2Y12 inhibitors were given for 3-months in the first group in Korean study while Japanese study had for 1-month only.

Despite these somewhat difference results, the overall message is the same. Patients may have similar outcomes when given clopidogrel (or other P2Y12 inhibitors) alone after an initial period of combined therapy with aspirin. This may be a particularly good news for those patients who are at higher risk of bleeding.

Anti-platelet Therapy after Cardiac Stent Placement

The type and duration of anti-platelet therapy after cardiac catheterization and stent placement (also called percutaneous coronary intervention or PCI) is an ongoing debate. Aspirin is under use for over 100 years and we know a lot about it. Plus, it is a cheaper drug. Clopidogrel, better known by its market name Plavix, is now in marker for many years and its generic versions are available. Almost all studies have examined the use of additional anti-platelet drugs after PCI on top of aspirin use. What if we examine the use of anti-platelet drugs on top of clopidogrel use?

A study published in JAMA examined this question in a multi-center, open-label, randomized clinical trial conducted in Japan. They enrolled 3045 patients to either 1 month of aspirin + clopidogrel therapy followed by clopidogrel therapy alone versus 12 months of aspirin + clopidogrel therapy. The outcome they were looking at was a combined outcome of cardiovascular death, myocardial infarction, stroke (ischemic or hemorrhagic), stent thrombosis, or bleeding.

I am certain that authors were hoping for finding that the two treatments were similar. To their surprise, not only 1-month of aspirin + clopidogrel followed by clopidogrel alone was similar in efficacy but was superior to the 12-months of aspirin + clopidogrel (2.35% vs. 3.70%; P<0.001). In other words, a shorter duration of combined therapy followed by clopidogrel therapy is as effective, if not better, than 12-months of combined therapy. These findings are important especially for patients who are at high risk of bleeding.

Platelet Glycoprotein IIIa and Aspirin Resistance

Aspirin is the mainstay of treatment for the prevention of cardiovascular disease. It acts by irreversibly inhibiting COX1 enzymes and hence blocking arachidonic acid-thromboxane pathway. Due to lack of a nucleus, platelets cannot generate new COX1 and hence COX1 is inhibited for the lifetime of platelets (8 days). Aspirin treatment results in marked decrease in the excretion of urinary metabolites of thromboxane; the residual excretion is thought to be of endothelial origin where presence of nucleus results in formation of new COX1.

Despite adequate aspirin therapy, a significant number of individuals continue to have higher platelet reactivity and incomplete inhibition of platelet function. Such individuals are also at increased risk of future cardiovascular events. However, the underlying mechanisms that result in higher residual platelet reactivity after aspirin treatment are unclear and are being extensively explored by several researchers.

To identify mechanism of aspirin resistance, this study examined the differences in proteome of 2 aspirin resistant and 4 aspirin sensitive individuals and found that the levels of glycoprotein IIIa were higher in aspirin resistant individuals than in those without aspirin resistance.

Due to small sample size, it is difficult to rule-out the possibility of a type I error, however, considering the role of glycoprotein IIIa in platelet biology, it is conceivable that protein may play a role in aspirin resistant although exact mechanism remains unknown.

Platelet Diameters in Inherited Thrombocytopenia

An interesting article providing a systematic evidence for what is well-known but not reported in a systematic manner.

“To improve knowledge in this field, we evaluated platelet size on blood films obtained from 376 patients with all 19 forms of IT identified so far and found that these conditions differ not only in mean platelet diameter, but also in platelet diameter distribution width and the percentage of platelets with increased or reduced diameters………….. We also measured platelet diameters in 87 patients with immune thrombocytopenia and identified cutoff values for mean platelet diameter and the percentage of platelets with increased or reduced size….”

Greater Collagen-Induced Platelet Aggregation Following Cyclooxygenase 1 Inhibition Predicts Incident Acute Coronary Syndromes

Platelets have several pathways that initiate aggregation such as thrombin-, collagen-, thromboxane-, and ADP-mediated pathways. Individuals vary widely in their ability to have platelet aggregation through each of these pathways. Furthermore, this variability is not correlated. In other words, an individual may have low aggregation though one pathway but may have high aggregation through another pathway. This phenomenon may be more important when we try to measure platelet aggregation the laboratory to assess whether there is increased risk of in vivo platelet aggregation (and hence cardiovascular events).

Collagen is one of the first agonists that initiates platelet aggregation at the site of vessel wall injury. Therefore, examining an association of collagen-mediated platelet aggregation with subsequent cardiovascular events makes sense. Moreover, if we can decrease variability in platelet aggregation by blocking one or another pathway, we may be better able to assess activation through collagen pathway.

Aspirin is commonly used for prevention of cardiovascular disease and works by inhibiting thromboxane-pathway an dis very effective in completely inhibiting activity through this pathway. Thus aspirin can be used to inhibit variability through one pathway and effect of collagen can be studied with fewer interactions. We followed the same logic in this paper where we examined platelet aggregation after 2-week aspirin therapy in healthy individuals. Most of these individuals did not use aspirin after the 2-week study period. During follow-up increased collagen-mediated platelet aggregation was significantly associated with acute coronary syndrome.

“After COX1 pathway inhibition, collagen-induced aggregation was significantly greater in participants with ACS compared with those without (29.0 vs. 23.6 ohms, p < 0.001). In Cox proportional hazards models, this association remained significant after adjusting for traditional cardiovascular risk factors (HR = 1.10, 95%CI = 1.06-1.15; p < 0.001).”

Some interesting articles

Sticky Platelet Syndrome: History and Future Perspectives
in Seminars in thrombosis and hemostasis

The relationship between platelet to lymphocyte ratio and the clinical outcomes in ST elevation myocardial infarction
in Blood coagulation & fibrinolysis

Detection of platelet microRNA expression in patients with diabetes mellitus with or without ischemic stroke
in Journal of Diabetes Complications

Aspirin may modify tumor microenvironment via antiplatelet effect
in Medical Hypothesis

High-Platelet Reactivity and Stroke

Nevio Taglieri, and his colleagues from the University of Bologna (Bologna, Italy), conducted a meta-analysis of 14 studies (collectively enrolling 11,959 patients) to evaluate the risk of stroke in patients who had platelet testing while undergoing percutaneous coronary intervention (PCI). Among the studies included in the meta-analysis, prevalence of high platelet reactivity was 30% ±15% (range, 6% to 67%). As expected, prevalence of platelet hyperactivity was higher in studies using VerifyNow than in those using light-transmission aggregometery (LTA) (42% ±13% vs 22% ±10%; P = 0.006). Overall, the annual stroke rate was 0.9%. After pooled analysis, the risk of stroke was higher in patients with high platelet reactivity than in those without (1.2% vs 0.7%; RR 1.84; 95% CI 1.21-2.80).

The study provides interesting insights: first, it confirms the role of platelet aggregation in the athero-thrombo-embolic phenomena. Secondly, it suggests that there is a group of people who, despite having complete (near complete) blockage of P2Y12 receptors, may have higher activity through other platelet aggregation pathways and may benefit from a different drug. Of note, most patients in this meta-analysis were already on clopidogrel and aspirin, two of the several platelet aggregation pathways.

Triple Anti-platelet Therapy

Role of platelets in acute coronary syndromes (ACS) is well established. Anti-platelet agents are standard of care for the prevention of ACS. However, due to the high risk of bleeding, anti-platelet agents except aspirin are not indicated for the prevention of ACS in primary prevention population as the risk of an ACS event is low. However, individuals with established CAD are at an increased risk of subsequent events and aspirin is indicated for such patients. In addition, those who has had a stent placed, usually get dual anti-platelet therapy (aspirin + either clopidogrel, prasugrel, or ticagrelor). One would imagine that in a very high-risk population, inhibition of an additional pathway may provide additional benefit. However, the TRACER trial, found that addition of vorapaxar, an oral protease-activated-receptor 1 (PAR 1) antagonist that inhibits thrombin-induced platelet activation, had no additional benefit in patient with acute coronary syndrome. In stead, addition of vorapaxar to the standard dual anti-platelet regiment was associated with increase risk of major bleeding. This study, suggested that perhaps too much of platelet inhibition may not be beneficial for ACS prevention but increases risk of bleeding.

More recently, a meta-analysis found that adding cilostazol, another anti-platelet agent that acts by inhibiting phosphodiestrase, to standard dual anti-platelet therapy was associated with 36% reduction in major adverse cardiac events (MACE; odds ratio (OR) = 0.64; 95% confidence interval (CI) = 0.51-0.81, P < .01), a 40% reduction (OR = 0.60, 95% CI = 0.44-0.80; P < .01) in target vessel revascularization (TVR), a 44% reduction (OR = 0.56, 95% CI = 0.34-0.91; P = .02) in target lesion revascularization (TLR) and a 47%/44% reduction in in-segment/in-stent restenosis (P < .01) and lower in-segment/in-stent late loss (P < .01). The effect sizes are large showing that the addition of cilostazol is very effective in reducing events. Cilostazol also inhibits smooth muscle contraction resulting in peripheral arterial dilatation. It is possible that the beneficial effect may be due to a combination of these two effects.

Thrombocytopenia in vWD type 2B

Von Willebrand factor (vWF) is a chaperone protein for coagulation factor VIII and is essential for the recruitment of platelets to the growing thrombus under conditions of high shear stress usually present in the arterial system. Deficiency (quantitative or qualitative) of vWF is associated with bleeding tendency, clinically known as von Willebrand disease (vWD).   Type 2 vWD is due to functional defect in vWF and type 2B is associated with gain-of-function mutations in the exon 28 of vWF gene resulting in an increase in the affinity of VWF for platelets. The region encoded by exon 28 binds to the platelet vWF receptor, glycoprotein Iba (GpIba). Patient with type 2B vWD present with bleeding and moderate to severe thrombocytopenia as well as a decreased in the high molecular weight vWF multimers. Thrombocytopenia is associated with the presence of giant platelets and spontaneous platelet aggregates. The molecular mechanism underlying the thrombocytopenia are unclear.

GpIba is present on the surface of megakaryocytes as well on platelets. Thus it is possible that interaction of mutated vWF from patients with type 2B vWD with megakaryocytes results in decreased platelet formation and release of giant platelets. In fact, Nurden et al showed that this may be the case. They showed that culture of megakaryocytes from controls performed with or without purified vWF had a positive influence on platelet production with specific inhibition by an antibody blocking vWF binding to GpIba . Megakaryocytes cultured with vWF from patients with type 2B vWD showed disorganized demarcation membrane system and abnormal granule distribution when examined under electron microscopy. The platelets produced from such megakaryocytes had abnormalities similar to those found in patients with vWD type 2B. This impaired megakaryocytopoiesis could not only explain the occurrence of giant platelets, but also contribute to a lower platelet count in VWD type 2B patients.

In addition to defects in platelet production, there may also be defects in platelet utilization, that is increased uptake of platelets (with attached vWF) by the monocyte-macrophage system of the body. Casari et al showed that this is also the case in a series of experiments reported here. They found that vWD type 2B platelets have a shorter circulatory half-life than wild-type (wt) platelets, which could contribute to the lower platelet counts in vWD type 2B mice. Further analysis revealed that VWF type 2B is present at the surface of platelets of thrombocytopenic
vWD type 2B mice, and that these vWF/platelet complexes were taken up efficiently by macrophages in liver and spleen. Thus, they provide direct evidence that part of the thrombocytopenia in vWD type 2B can be explained by an increased clearance of VWF/platelet
complexes.

CARMIL or LRRC16A

CARMIL (protein CP ARp2/3 myosin I linker) was initially named Acan125 when it was discovered in amoeba where it was found to bind the SH3 domain of class I myosin molecules. Subsequently, this protein was found to bind capping protein (CP) and to Arp2/3 complex which to it being named as CARMIL. This is a large protein and has a long leucine-rich repeat (LRR) region. The function of this LRR region is unclear (PMID: 18544499).

CARMIL is important in actin-based cell motility. In addition to its role in many cellular process, actin is also involved in cell motility and shape change. Actin polymerization occurs mainly at the barbed ends of the actin filament. Addition of new actin molecules to the barbed ends of actin filaments are thought to be responsible for cell motility and change in shape. The assembly of actin filament by addition of actin monomers to the barbed ends is inhibited by Capping Proteins (CP). These capping proteins bind and thus hide the barbed ends of the actin filaments making them inaccessible to other actin molecules. CP is  a heterodimer of two subunits with a shape similar to a mushroom. CARMIL binds to the CP and this binding of CARMIL to CP results in decreased affinity of the CP to barbed ends of actin filament and dislodges itself from it. Thus barbed ends are exposed and actin polymerization starts resulting in cell-shape (PMID: 16434392).

Of note, the ability of CARMIL to expose barbed ends of actin filament is specific to CP and doesn’t include other proteins that inhibit actin polymerization. The CP binding region of CARMIL resides in the later part of the protein called CAH3 region (CARMIL homology domain 3; amino acid residues 940-1121). Within this region, a portion of 25 amino acids that is highly conserved from protozoa to flies, to worms to vertebrates. Point mutations in this region result in loss of CP-binding ability of CARMIL (PMID: 16434392).

A patch consisting of basic amino acids on CP is essential for its interaction with barbed ends of the actin. Using nuclear magnetic resonance (NMR), Zwolak et al  studied the interaction of the CAH3 domain and CP in a mouse model. They found that the highly basic mouse CAH3a subdomain binds with high affinity to a complementary “acidic groove” on CP.  This CAH3a-CP interaction orients the CAH3b subdomain directly adjacent to the basic patch of CP. The importance of specific residue interactions between CP and CAH3a/b was confirmed by site-directed mutagenesis of both proteins (PMID: 20630878).

In another study Hernandez-Valladares identified two similar regions  within the CAH3(965–1038) performing essentially the same two functions. The first region, Ile971–Cys1004, is CP interacting motif. The second region, Arg1021–Thr1035, binds to the underside of the CP mushroom cap on the opposite side of the CP mushroom stalk to which the CP interaction motif binds. Together, these two regions resemble a finger (CPI) and thumb (CSI) encircling the stalk on the underside of the mushroom cap (PMID: 20357771).

LRRC16A or CARMIL gene is located on chromosome 6p22.2, has 341,453 base-pairs, and 36 exons. As is also clear from the LD block of YRI (data from HapMap, software used Haploview) the later part of the gene is conserved and is present in a larger LD block.

Intra-individual Variability in Platelet Responsiveness to Clopidogrel

Clopidogrel, in combination with aspirin, is a commonly used anti-platelet agents after PCI (percutaneous coronary intervention) in CHD patients. In one study, about 70% of the inter-individual variability in platelet response to clopidogrel is due to hereditary factors. A polymorphism in the CYP2C19 has been shown to be significantly associated with poor platelet response to clopidogrel. Even more important, poor platelet responsiveness to clopidogrel in patients with PCI has been shown to be associated with increased MACE (major adverse cardiac events).

While focus has been generally on inter-individual variation, it is possible that there is a significant intra-individual variability. This difference can't be explained by stable factors such as genetics or gender but is likely to be due to factors that vary over a short period of time. These include inflammatory state.

In recently published study, Armero et al examined patients on two different occasions after they had clopidogrel 600 mg loading dose. Platelet reactivity was measured using VASP (vasodilator-stimulated phosphoprotein). Interestingly, they found that there was a poor intra-individual correlation between the two occasions (kappa 0.33). In 65% of patients, platelet inhibition increased on the second evaluation while in 35% of the patients, platelet inhibition decreased.

The implications of this finding are worthy of notice. This mean that there are some rapidly varying factors that can alter platelet responsiveness to clopidogrel. On potential candidate is inflammation, although this was not measured and tested as such in this study. Investigators did measure leukocyte count and fibrinogen (and there was no difference) but both are rather crude measures of low-grade inflammation. Other possibilities include poor glycemic control in diabetics; in fact, investigators did find a relationship between the presence of diabetes and poor clopidogrel responsiveness.