Gerard A. Rongen

Pharmacogenetics: from bench to byte--an update of guidelines.

Currently, there are very few guidelines linking the results of pharmacogenetic tests to specific therapeutic recommendations. Therefore, the Royal Dutch Association for the Advancement of Pharmacy established the Pharmacogenetics Working Group with the objective of developing pharmacogenetics‐based therapeutic (dose) recommendations. After systematic review of the literature, recommendations were developed for 53 drugs associated with genes coding for CYP2D6, CYP2C19, CYP2C9, thiopurine‐S‐methyltransferase (TPMT), dihydropyrimidine dehydrogenase (DPD), vitamin K epoxide reductase (VKORC1), uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), HLA‐B44, HLA‐B*5701, CYP3A5, and factor V Leiden (FVL).

Flow-mediated dilatation in the superficial femoral artery is nitric oxide mediated in humans

Flow‐mediated dilatation (FMD) of the brachial and radial arteries is an important research tool for assessment of endothelial function in vivo, and is nitric oxide (NO) dependent. The leg skeletal muscle vascular bed is an important territory for studies in exercise physiology. However, the role of endothelial NO in the FMD response of lower limb arteries has never been investigated. The purpose of this study was to examine the contribution of NO to FMD in the superficial femoral artery in healthy subjects. Since physical inactivity may affect endothelial function, and therefore NO availability, spinal cord‐injured (SCI) individuals were included as a model of extreme deconditioning. In eight healthy men (34 ± 13 years) and six SCI individuals (37 ± 10 years), the 5 min FMD response in the superficial femoral artery was assessed by echo‐Doppler, both during infusion of saline and during infusion of the NO synthase blocker NG‐monomethyl‐l‐arginine (l‐NMMA). In a subset of the controls (n= 6), the 10 min FMD response was also examined using the same procedure. The 5 min FMD response in controls (4.2 ± 0.3%) was significantly diminished during l‐NMMA infusion (1.0 ± 0.2%, P < 0.001). In SCI, l‐NMMA also significantly decreased the FMD response (from 8.2 ± 0.4% during saline to 2.4 ± 0.5% during l‐NMMA infusion). The hyperaemic flow response during the first 45 s after cuff deflation was lower in both groups during infusion of l‐NMMA, but the effect of l‐NMMA on FMD persisted in both groups after correction for the shear stress stimulus. The 10 min FMD was not affected by l‐NMMA (saline: 5.4 ± 1.6%, l‐NMMA: 5.6 ± 1.5%). Superficial femoral artery FMD in response to distal arterial occlusion for a period of 5 min is predominantly mediated by NO in healthy men and in the extremely deconditioned legs of SCI individuals.

Acute and long-term cardiovascular effects of coffee: implications for coronary heart disease.

Despite decades of research, the question as to whether coffee intake increases the risk of coronary heart disease (CHD) remains controversial. In the current paper, we discuss the acute and long-term cardiovascular effects of coffee, and its major constituents, which could underlie such an association. Experimental studies have shown that administration of coffee or caffeine acutely raises blood pressure, circulating concentrations of (nor)epinephrine, increases arterial stiffness, impairs endothelium dependent vasodilation and inhibits ischemic preconditioning. The adverse effects of chronic coffee consumption on traditional risk factors for CHD are less consistent: although coffee intake slightly increases blood pressure, and plasma concentrations of homocysteine and cholesterol, there is no association with the incidence of hypertension, and a strong negative association with the incidence of type 2 diabetes mellitus. Moreover, common polymorphisms in genes involved in the metabolism of caffeine, catecholamines, homocysteine, and cholesterol can modulate the effect of coffee intake on cardiovascular parameters. Many epidemiological studies have explored the association between coffee drinking and CHD. Most prospective studies have not shown a positive association, whereas case-control studies in general have reported such an association. This discrepancy could be explained by an acute adverse effect of coffee, rather than a long-term adverse effect. We postulate that coffee drinking may have an acute detrimental effect in triggering coronary events and increasing infarct size in selected patient groups, rather than promoting the development of atherosclerosis in the general population, and we propose an alternative approach to explore such an effect in epidemiological studies.

Ischemic preconditioning in the animal kidney, a systematic review and meta-analysis.

Ischemic preconditioning (IPC) is a potent renoprotective strategy which has not yet been translated successfully into clinical practice, in spite of promising results in animal studies. We performed a unique systematic review and meta-analysis of animal studies to identify factors modifying IPC efficacy in renal ischemia/reperfusion injury (IRI), in order to enhance the design of future (clinical) studies. An electronic literature search for animal studies on IPC in renal IRI yielded fifty-eight studies which met our inclusion criteria. We extracted data for serum creatinine, blood urea nitrogen and histological renal damage, as well as study quality indicators. Meta-analysis showed that IPC reduces serum creatinine (SMD 1.54 [95%CI 1.16, 1.93]), blood urea nitrogen (SMD 1.42 [95% CI 0.97, 1.87]) and histological renal damage (SMD 1.12 [95% CI 0.89, 1.35]) after IRI as compared to controls. Factors influencing IPC efficacy were the window of protection (<24 h = early vs. ≥24 h = late) and animal species (rat vs. mouse). No difference in efficacy between local and remote IPC was observed. In conclusion, our findings show that IPC effectively reduces renal damage after IRI, with higher efficacy in the late window of protection. However, there is a large gap in study data concerning the optimal window of protection, and IPC efficacy may differ per animal species. Moreover, current clinical trials on RIPC may not be optimally designed, and our findings identify a need for further standardization of animal experiments.

The cardioprotective effects of metformin

Purpose of review In patients with type 2 diabetes mellitus, treatment with metformin is associated with a lower cardiovascular morbidity and mortality, compared with alternative glucose-lowering drugs. It has been suggested that metformin might exert direct protective effects on the heart. Recent findings This review appraises recent experimental animal studies on the effect of metformin on myocardial ischaemia-reperfusion injury and remodeling. In murine models of myocardial infarction, the administration of metformin potently limits infarct size. Activation of adenosine monophosphate-activated protein kinase, increased formation of adenosine, and the prevention of opening of the mitochondrial permeability transition pore at reperfusion all contribute to this cardioprotective effect. In addition, metformin therapy attenuates postinfarction cardiac remodeling. There is evidence that activation of adenosine monophosphate-activated protein kinase and endothelial nitric oxide synthase, and a reduced collagen expression are crucial for this effect. Summary The finding that metformin limits myocardial infarct size and remodeling in animal models of myocardial infarction suggests that patients suffering from myocardial ischaemia could benefit from treatment with metformin, even when these patients do not have diabetes. Currently, several clinical trials are being performed to test this hypothesis.

Methotrexate modulates the kinetics of adenosine in humans in vivo

Background: Animal studies suggest that the anti-inflammatory effect of methotrexate (MTX) is mediated by increased adenosine concentrations. Objective: To assess the effect of MTX on the vasodilator effects of adenosine and the nucleoside uptake inhibitor, dipyridamole, in humans in vivo as a marker for changes in adenosine kinetics. Methods: Ten patients with active arthritis were treated with MTX (15 mg/week). Measurements were performed before and after 12 weeks of treatment. At these time points, the activity of adenosine deaminase was measured in isolated lymphocytes, and forearm blood flow (FBF) was determined by venous occlusion plethysmography during administration of adenosine and dipyridamole into the brachial artery. Results: The Vmax of adenosine deaminase in lymphocytes was reduced by MTX treatment (p<0.05). MTX significantly enhanced vasodilator response to adenosine (0.5 and 1.5 μg/min/dl of forearm tissue; mean (SE) FBF ratio increased from 1.2 (0.2) to 1.4 (0.2) and 2.2 (0.2) ml/dl/min, respectively, before and from 1.3 (0.1) to 1.8 (0.2) and 3.2 (0.5) ml/dl/min during MTX treatment; p<0.05). Also, dipyridamole-induced vasodilatation (30 and 100 μg/min/dl) was enhanced by MTX (FBF ratio increased from 1.2 (0.2) to 1.5 (0.3) and 1.8 (0.2), respectively, before and from 1.3 (0.1) to 1.8 (0.2) and 2.4 (0.4) during MTX treatment; p<0.05). Conclusions: MTX treatment inhibits deamination of adenosine and potentiates adenosine-induced vasodilatation. Also dipyridamole-induced vasodilatation is enhanced by MTX treatment, suggesting an increased extracellular formation of adenosine. These effects on the adenosine kinetics in humans may contribute to the therapeutic efficacy of MTX.

Comparison of intrabrachial and finger blood pressure in healthy elderly volunteers

This study was performed to compare continuous Finapres (FIN) and intrabrachial (IAP) blood pressure in healthy elderly volunteers. Fifteen elderly subjects (age 71 to 83) without cardiovascular disease and an intraarterial mean (range) systolic and diastolic blood pressure of 162 (122 to 195) and 73 (62 to 88) mm Hg, respectively, participated in the study. A 10-min head-up tilt, 10 min active standing, a 15-sec Valsalva, and a 5-min mental arithmetic were performed in random order. Beat-to-beat values of systolic, diastolic, and mean arterial pressure were analyzed. At rest, FIN underestimated IAP by 16.8 +/- 2.6 (SE), 10.8 +/- 1.5, and 17.5 +/- 1.6 mm Hg for systolic, diastolic, and mean arterial blood pressure, respectively (P < .05). During head-up tilt, FIN overestimated the intraarterial systolic blood pressure response by 7.2 +/- 1.6 (SE) mm Hg (P < .05). Group-averaged changes in diastolic and mean arterial IAP were followed closely by FIN. During standing, Finapres closely followed intraarterial diastolic and mean arterial pressure but the increase in systolic blood pressure was higher at the finger as compared to intrabrachial recordings, resembling the results of head-up tilt. During the Valsalva maneuver, maximal responses in systolic, diastolic, and mean arterial pressure were underestimated by FIN by 12.1 +/- 3.3 (SE), 6.8 +/- 2.7, and 7.1 +/- 1.7 mm Hg, respectively (P < .05 for all parameters). During mental arithmetic, FIN underestimated the intraarterial systolic blood pressure response by 6.1 +/- 2.7 (SE) mm Hg (P < .05), while diastolic and mean arterial pressure responses were followed correctly by FIN. It is concluded that apart from systolic blood pressure, FIN closely follows intraarterial blood pressure responses for the orthostatic maneuvers and mental arithmetic. During Valsalva, the rapid changes in blood pressure were followed in direction but not in magnitude.

High incidence of adverse events in healthy volunteers receiving rifampicin and adjusted doses of lopinavir/ritonavir tablets

Objective:Previous research in healthy volunteers has demonstrated that rifampicin and adjusted doses of lopinavir/ritonavir soft-gel capsules resulted in adequate exposure to lopinavir. Our objective was to study the combined use of rifampicin and the newly introduced lopinavir/ritonavir tablets. Methods:A total of 40 healthy volunteers were planned to start with 600 mg rifampicin once daily from days 1–5. From days 6–15, volunteers were randomized to receive lopinavir/ritonavir tablets dosed as either 600/150 or 800/200 mg twice daily, both in addition to 600 mg rifampicin once daily. A 12 h pharmacokinetic curve was planned on day 15. Safety assessments were conducted regularly throughout the study period. Results:Eleven volunteers started as the first group in this study. No major complaints occurred during day 1–5 (rifampicin only). After addition of lopinavir/ritonavir, eight volunteers suffered from both nausea and vomiting, one from nausea only, and one from vomiting only. On day 7, increases in aspartate aminotransferase/alanine aminotransferase (AST/ALT) levels were reported in all volunteers and on day 8, the study was prematurely terminated. The AST/ALT levels continued to rise and peaked (grade 2, n = 2; grade 3, n = 1; grade 4, n = 8) on days 9–10. All values returned to normal within 6 weeks. Conclusions:The study showed a high incidence of adverse events when a higher than standard dose of the new lopinavir/ritonavir tablets was combined with rifampicin. In the future, this drug combination should not be given to healthy volunteers. Liver function should be carefully monitored when rifampicin and lopinavir/ritonavir are combined in patients.

Characterization of ATP-induced vasodilation in the human forearm vascular bed.

BACKGROUND Animal data indicate that ATP derived from aggregating thrombocytes or endothelium induces an endothelium-dependent vasodilator response that is mediated by P2y-purinergic receptors and is reduced when high dosages are administered. This reduced vasodilator response to high ATP doses has been associated with the concomitant release of endothelium-derived contracting factors. In contrast to the endothelium-dependent vasodilator response, ATP as released from sympathetic nerve endings induces a P2x-purinergic receptor-mediated vasoconstrictor response that may contribute to the attenuated vasodilator response to high dosages of luminally applied ATP. The dual action of ATP might be important in the pathophysiology of disease states characterized by an impaired endothelial function and increased thrombocyte aggregation. This study was performed to characterize the vascular response to ATP in humans. METHODS AND RESULTS The brachial artery was cannulated in 50 healthy male volunteers (age, 18 to 44 years) for drug infusion and measurement of mean arterial pressure. Forearm blood flow was recorded by venous occlusion strain-gauge plethysmography. ATP induced a dose-dependent vasodilator response that was significantly higher than the effect of equimolar adenosine infusion and that was not reduced by concomitant infusion of the P1-purinergic receptor antagonist theophylline. The infusion of the NO synthase antagonist NG-monomethyl-L-arginine (L-NMMA) reduced the average fall in forearm vascular resistance (FVR) to acetylcholine (-59 +/- 6% [mean +/- SEM] versus -42 +/- 8%; P < .05; N = 10) but did not affect the vasodilator response to ATP (-68 +/- 3% versus -64 +/- 6%; P > .1; N = 10) or sodium nitroprusside (SNP; -53 +/- 3% versus -49 +/- 4%; P > .01; N = 6). The L-NMMA-induced increase in FVR appeared to be related to the type of vasodilator pretreatment, being 94.7 +/- 16.7%, 44.9 +/- 8.7%, and 40.8 +/- 7.3% for acetylcholine, ATP, and SNP pretreatment, respectively (P < .01 for acetylcholine versus ATP and SNP; P > .1 for ATP versus SNP). In contrast to animal data, high dosages of intra-arterially infused ATP (up to 1000 micrograms.100 mL forearm-1.min-1) did not reveal a reduction in the forearm vasodilator response but appeared to be similar to the maximal forearm vasodilation as observed during postocclusive reactive hyperemia. CONCLUSIONS These observations indicate that ATP induces a potent dose-dependent vasodilator response that is not mediated by P1-purinergic receptor stimulation or by the release of nitric oxide. Moreover, in healthy volunteers, the vasodilator response to high intra-arterial dosages of ATP is not reduced by the release of endothelium-derived contracting factors or by the stimulation of P2x-purinergic receptors on the smooth muscle cells.

The cardiovascular effects of methylxanthines.

In the concentration range that is normally achieved in humans, e.g., after the drinking of coffee or in patients treated with theophylline, the cardiovascular effects of methylxanthines are primarily due to antagonism of adenosine A(1) and A(2) receptors. Inhibition of phosphodiesterases or mobilization of intracellular calcium requires much higher concentrations. In conscious humans, acute exposure to caffeine results in an increase in blood pressure by an increased total peripheral resistance, and a slight decrease in heart rate. This overall hemodynamic response is composed of direct effects of caffeine on vascular tone, on myocardial contractility and conduction, and on the sympathetic nervous system. Caffeine is the most widely consumed methylxanthine, mainly derived from coffee intake. Regular coffee consumption can affect various traditional cardiovascular risk factors, including a slight increase in blood pressure, an increase in plasma cholesterol and homocysteine levels, and a reduced incidence of type 2 diabetes mellitus. Although most prospective studies have not reported an association between coffee consumption and coronary heart disease, these findings do not exclude that the acute hemodynamic and neurohumoral effects of coffee consumption could have an adverse effect in selected patient groups who are more vulnerable for these effects, based on their genetic profile or medication use.