Eric E. Lloyd

The urate-lowering efficacy and safety of febuxostat in the treatment of the hyperuricemia of gout: the CONFIRMS trial.

IntroductionThe purpose of this study was to compare urate-lowering (UL) efficacy and safety of daily febuxostat and allopurinol in subjects with gout and serum urate (sUA) ≥ 8.0 mg/dL in a six-month trial.MethodsSubjects (n = 2,269) were randomized to febuxostat 40 mg or 80 mg, or allopurinol 300 mg (200 mg in moderate renal impairment). Endpoints included the proportion of all subjects with sUA <6.0 mg/dL and the proportion of subjects with mild/moderate renal impairment and sUA <6.0 mg/dL. Safety assessments included blinded adjudication of each cardiovascular (CV) adverse event (AE) and death.ResultsComorbidities included: renal impairment (65%); obesity (64%); hyperlipidemia (42%); and hypertension (53%). In febuxostat 40 mg, febuxostat 80 mg, and allopurinol groups, primary endpoint was achieved in 45%, 67%, and 42%, respectively. Febuxostat 40 mg UL was statistically non-inferior to allopurinol, but febuxostat 80 mg was superior to both (P < 0.001). Achievement of target sUA in subjects with renal impairment was also superior with febuxostat 80 mg (72%; P < 0.001) compared with febuxostat 40 mg (50%) or allopurinol (42%), but febuxostat 40 mg showed greater efficacy than allopurinol (P = 0.021). Rates of AEs did not differ across treatment groups. Adjudicated (APTC) CV event rates were 0.0% for febuxostat 40 mg and 0.4% for both febuxostat 80 mg and allopurinol. One death occurred in each febuxostat group and three in the allopurinol group.ConclusionsUrate-lowering efficacy of febuxostat 80 mg exceeded that of febuxostat 40 mg and allopurinol (300/200 mg), which were comparable. In subjects with mild/moderate renal impairment, both febuxostat doses were more efficacious than allopurinol and equally safe. At the doses tested, safety of febuxostat and allopurinol was comparable.Clinical Trial RegistrationNCT00430248

Clinical efficacy and safety of successful longterm urate lowering with febuxostat or allopurinol in subjects with gout.

Objective. To determine longterm urate-lowering efficacy and clinical benefits and safety of therapy with febuxostat or allopurinol in subjects with gout. Methods. Subjects (n = 1086) in this open-label extension study were assigned to fixed-dose daily urate-lowering treatment (ULT) with febuxostat (80 mg or 120 mg) or allopurinol (300 mg). ULT reassignment was permitted during months 1 to 6 to achieve serum urate (SUA) concentrations between 3.0 and < 6.0 mg/dl. Flares requiring treatment, tophus size, safety, and SUA levels were monitored during up to 40 months of ULT maintenance. Results. After 1 month initial treatment, > 80% of subjects receiving either febuxostat dose, but only 46% of subjects receiving allopurinol, achieved SUA < 6.0 mg/dl. After ULT reassignment, > 80% of all remaining subjects maintained the primary efficacy endpoint of SUA < 6.0 mg/dl at each visit. More subjects initially randomized to allopurinol required ULT reassignment to achieve SUA < 6.0 mg/dl compared with subjects receiving febuxostat. Maintenance of SUA < 6.0 mg/dl resulted in progressive reduction to nearly 0 in proportion of subjects requiring gout flare treatment. Baseline tophus resolution was achieved by 46%, 36%, and 29% of subjects maintained on febuxostat 80 mg, febuxostat 120 mg, and allopurinol, respectively. Overall adverse event rates (including cardiovascular adverse event rates), adjusted for 10-fold greater febuxostat than allopurinol exposure, did not differ significantly among treatment groups. Conclusion. Durable maintenance of goal range SUA level with either dose of febuxostat or in smaller numbers of subjects with allopurinol resulted in near elimination of gout flares and improved tophus status over time. Registered as NCT00175019.

Dynamics of dense electronegative low density lipoproteins and their preferential association with lipoprotein phospholipase A2

Small, dense, electronegative low density lipoprotein [LDL(−)] is increased in patients with familial hypercholesterolemia and diabetes, populations at increased risk for coronary artery disease. It is present to a lesser extent in normolipidemic subjects. The mechanistic link between small, dense LDL(−) and atherogenesis is not known. To begin to address this, we studied the composition and dynamics of small, dense LDL(−) from normolipidemic subjects. NEFA levels, which correlate with triglyceride content, are quantitatively linked to LDL electronegativity. Oxidized LDL is not specific to small, dense LDL(−) or lipoprotein [a] (i.e., abnormal lipoprotein). Apolipoprotein C-III is excluded from the most abundant LDL (i.e., that of intermediate density: 1.034 < d < 1.050 g/ml) but associated with both small and large LDL(−). In contrast, lipoprotein-associated phospholipase A2 (LpPLA2) is highly enriched only in small, dense LDL(−). The association of LpPLA2 with LDL may occur through amphipathic helical domains that are displaced from the LDL surface by contraction of the neutral lipid core.

Azilsartan Medoxomil Plus Chlorthalidone Reduces Blood Pressure More Effectively Than Olmesartan Plus Hydrochlorothiazide in Stage 2 Systolic Hypertension

Azilsartan medoxomil, an effective, long-acting angiotensin II receptor blocker, is a new treatment for hypertension that is also being developed in fixed-dose combinations with chlorthalidone, a potent, long-acting thiazide-like diuretic. We compared once-daily fixed-dose combinations of azilsartan medoxomil/chlorthalidone force titrated to a high dose of either 40/25 mg or 80/25 mg with a fixed-dose combination of the angiotensin II receptor blocker olmesartan medoxomil plus the thiazide diuretic hydrochlorothiazide force titrated to 40/25 mg. The design was a randomized, 3-arm, double-blind, 12-week study of 1071 participants with baseline clinic systolic blood pressure 160 to 190 mm Hg and diastolic blood pressure ⩽119 mm Hg. Patients had a mean age of 57 years; 59% were men, 73% were white, and 22% were black. At baseline, mean clinic blood pressure was 165/96 mm Hg and 24-hour mean blood pressure was 150/88 mm Hg. Changes in clinic (primary end point) and ambulatory systolic blood pressures at week 12 were significantly greater in both azilsartan medoxomil/chlorthalidone arms than in the olmesartan/hydrochlorothiazide arm (P<0.001). Changes in clinic systolic blood pressure (mean±SE) were −42.5±0.8, −44.0±0.8, and −37.1±0.8 mm Hg, respectively. Changes in 24-hour ambulatory systolic blood pressure were −33.9±0.8, −36.3±0.8, and −27.5±0.8 mm Hg, respectively. Adverse events leading to permanent drug discontinuation occurred in 7.9%, 14.5%, and 7.1% of the groups given azilsartan medoxomil/chlorthalidone 40/25 mg, azilsartan medoxomil/chlorthalidone 80/25 mg, and olmesartan/hydrochlorothiazide 40/25 mg, respectively. This large, forced-titration study has demonstrated superior antihypertensive efficacy of azilsartan medoxomil/chlorthalidone fixed-dose combinations compared with the maximum approved dose of olmesartan/hydrochlorothiazide.

Cerebrovascular responses in mice deficient in the potassium channel, TREK-1

We tested the hypothesis that TREK-1, a two-pore domain K channel, is involved with dilations in arteries. Because there are no selective activators or inhibitors of TREK-1, we generated a mouse line deficient in TREK-1. Endothelium-mediated dilations were not different in arteries from wild-type (WT) and TREK-1 knockout (KO) mice. This includes dilations of the middle cerebral artery to ATP, dilations of the basilar artery to ACh, and relaxations of the aorta to carbachol, a cholinergic agonist. The nitric oxide (NO) and endothelium-dependent hyperpolarizing factor components of ATP dilations were identical in the middle cerebral arteries of WT and TREK-1 KO mice. Furthermore, the NO and cyclooxygenase-dependent components were identical in the basilar arteries of the different genotypes. Dilations of the basilar artery to alpha-linolenic acid, an activator of TREK-1, were not affected by the absence of TREK-1. Whole cell currents recorded using patch-clamp techniques were similar in cerebrovascular smooth muscle cells (CVSMCs) from WT and TREK-1 KO mice. alpha-linolenic acid or arachidonic acid increased whole cell currents in CVSMCs from both WT and TREK-1 KO mice. The selective blockers of large-conductance Ca-activated K channels, penitrem A and iberiotoxin, blocked the increased currents elicited by either alpha-linolenic or arachidonic acid. In summary, dilations were similar in arteries from WT and TREK-1 KO mice. There was no sign of TREK-1-like currents in CVSMCs from WT mice, and there were no major differences in currents between the genotypes. We conclude that regulation of arterial diameter is not altered in mice lacking TREK-1.

A new rodent model for obstructive sleep apnea: effects on ATP-mediated dilations in cerebral arteries

Obstructive sleep apnea (OSA), a condition in which the upper airway collapses during sleep, is strongly associated with metabolic and cardiovascular diseases. Little is known how OSA affects the cerebral circulation. The goals of this study were 1) to develop a rat model of chronic OSA that involved apnea and 2) to test the hypothesis that 4 wk of apneas during the sleep cycle alters endothelium-mediated dilations in middle cerebral arteries (MCAs). An obstruction device, which was chronically implanted into the trachea of rats, inflated to obstruct the airway 30 times/h for 8 h during the sleep cycle. After 4 wk of apneas, MCAs were isolated, pressurized, and exposed to luminally applied ATP, an endothelial P2Y2 receptor agonist that dilates through endothelial-derived nitric oxide (NO) and endothelial-dependent hyperpolarization (EDH). Dilations to ATP were attenuated ~30% in MCAs from rats undergoing apneas compared with those from a sham control group (P < 0.04 group effect; n = 7 and 10, respectively). When the NO component of the dilation was blocked to isolate the EDH component, the response to ATP in MCAs from the sham and apnea groups was similar. This finding suggests that the attenuated dilation to ATP must occur through reduced NO. In summary, we have successfully developed a novel rat model for chronic OSA that incorporates apnea during the sleep cycle. Using this model, we demonstrate that endothelial dysfunction occurred by 4 wk of apnea, likely increasing the vulnerability of the brain to cerebrovascular related accidents.

Starring TREK-1 The Next Generation of Vascular K+ Channels

See related article, pages 176–184 “We are more alike than unlike, my dear Captain. I have pores, humans have pores.” Lieutenant Commander Data, Stardate 41209.2 Before 1996, all known mammalian K+ channels were classified into only two different structural families according to the number of transmembrane (TM) spanning and pore-forming (P) domains in their α subunit. One family is characterized by K+ channels composed of two TM domains and one P domain, and includes the inwardly rectifying and ATP-sensitive K+ channels. The second family represents K+ channels characterized by six or seven TM domains and one P domain, and includes the voltage-gated and Ca2+-activated K+ channels. To form one functional channel for either of these families, four α subunits assemble to establish one K+ permeable pore. In the mid 1990s, researchers took advantage of the fact that the P domain of each K+ channel’s pore-forming α subunit is highly conserved across species and represents a common structural motif.1 Genome searches for DNA sequences coding for the P domain revealed a unique K+ channel in yeast and Caenorhabditis elegans that contained two P domains within a single α subunit polypeptide having eight potential TM domains.2 The following year a human K+ channel was cloned that also showed the unique feature of two P domains, but displayed four TM domains in a single α subunit (Figure 1).3 The channel was given the name TWIK-1 ( T andem of P domains in a W eak I nward rectifying K + channel). Since the cloning of TWIK-1, a total of fifteen …

Genetic Deletion of TREK-1 or TWIK-1/TREK-1 Potassium Channels does not Alter the Basic Electrophysiological Properties of Mature Hippocampal Astrocytes In Situ

We have recently shown that a linear current-to-voltage (I-V) relationship of membrane conductance (passive conductance) reflects the intrinsic property of K+ channels in mature astrocytes. While passive conductance is known to underpin a highly negative and stable membrane potential (VM) essential for the basic homeostatic function of astrocytes, a complete repertoire of the involved K+ channels remains elusive. TREK-1 two-pore domain K+ channel (K2P) is highly expressed in astrocytes, and covalent association of TREK-1 with TWIK-1, another highly expressed astrocytic K2P, has been reported as a mechanism underlying the trafficking of heterodimer TWIK-1/TREK-1 channel to the membrane and contributing to astrocyte passive conductance. To decipher the individual contribution of TREK-1 and address whether the appearance of passive conductance is conditional to the co-expression of TWIK-1/TREK-1 in astrocytes, TREK-1 single and TWIK-1/TREK-1 double gene knockout mice were used in the present study. The relative quantity of mRNA encoding other astrocyte K+ channels, such as Kir4.1, Kir5.1, and TREK-2, was not altered in these gene knockout mice. Whole-cell recording from hippocampal astrocytes in situ revealed no detectable changes in astrocyte passive conductance, VM, or membrane input resistance (Rin) in either kind of gene knockout mouse. Additionally, TREK-1 proteins were mainly located in the intracellular compartments of the hippocampus. Altogether, genetic deletion of TREK-1 alone or together with TWIK-1 produced no obvious alteration in the basic electrophysiological properties of hippocampal astrocytes. Thus, future research focusing on other K+ channels may shed light on this long-standing and important question in astrocyte physiology.

Disruption of K2P6.1 Produces Vascular Dysfunction and Hypertension in Mice

K2P6.1, a member of the 2-pore domain K channel family, is highly expressed in the vascular system; however, its function is unknown. We tested the following hypotheses. K2P6.1 regulates the following: (1) systemic blood pressure; (2) the contractile state of arteries; (3) vascular smooth muscle cell migration; (4) proliferation; and/or (5) volume regulation. Mice lacking K2P6.1 (KO) were generated by deleting exon 1 of Kcnk6. Mean arterial blood pressure in both anesthetized and awake KO mice was increased by 17±2 and 26±3 mm Hg, respectively (P<0.05). The resting membrane potential in freshly dispersed vascular smooth muscle cells was depolarized by 17±2 mV in the KO compared with wild-type littermates (P<0.05). The contractile responses to KCl (P<0.05) and BAY K 8644 (P<0.01), an activator of L-type calcium channels, were enhanced in isolated segments of aorta from KO mice. However, there was no difference in the current density of L-type calcium channels. Responses to U46619, an agent that activates rho kinase, showed an enhanced contraction in aorta from KO mice (P<0.001). The BAY K 8644-mediated increase in contraction was decreased to wild-type levels when treated with Y27632, a rho kinase inhibitor, (P<0.05). K2P6.1 does not appear to be involved with migration, proliferation, or volume regulation in cultured vascular smooth muscle cells. We conclude that K2P6.1 deficiency induces vascular dysfunction and hypertension through a mechanism that may involve smooth muscle cell depolarization and enhanced rho kinase activity.

Alterations of N-3 Polyunsaturated Fatty Acid-Activated K2P Channels in Hypoxia-Induced Pulmonary Hypertension

Polyunsaturated fatty acid (PUFA)‐activated two‐pore domain potassium channels (K2P) have been proposed to be expressed in the pulmonary vasculature. However, their physiological or pathophysiological roles are poorly defined. Here, we tested the hypothesis that PUFA‐activated K2P are involved in pulmonary vasorelaxation and that alterations of channel expression are pathophysiologically linked to pulmonary hypertension. Expression of PUFA‐activated K2P in the murine lung was investigated by quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR), immunohistochemistry (IHC), by patch clamp (PC) and myography. K2P‐gene expression was examined in chronic hypoxic mice. qRT‐PCR showed that the K2P2.1 and K2P6.1 were the predominantly expressed K2P in the murine lung. IHC revealed protein expression of K2P2.1 and K2P6.1 in the endothelium of pulmonary arteries and of K2P6.1 in bronchial epithelium. PC showed pimozide‐sensitive K2P‐like K+‐current activated by docosahexaenoic acid (DHA) in freshly isolated endothelial cells as well as DHA‐induced membrane hyperpolarization. Myography on pulmonary arteries showed that DHA induced concentration‐dependent instantaneous relaxations that were resistant to endothelial removal and inhibition of NO and prostacyclin synthesis and to a cocktail of blockers of calcium‐activated K+ channels but were abolished by high extracellular (30 mM) K+‐concentration. Gene expression and protein of K2P2.1 were not altered in chronic hypoxic mice, while K2P6.1 was up‐regulated by fourfold. In conclusion, the PUFA‐activated K2P2.1 and K2P6.1 are expressed in murine lung and functional K2P‐like channels contribute to endothelium hyperpolarization and pulmonary artery relaxation. The increased K2P6.1‐gene expression may represent a novel counter‐regulatory mechanism in pulmonary hypertension and suggest that arterial K2P2.1 and K2P6.1 could be novel therapeutic targets.