Biomedical subjects

Hui Quan

Publications and source records attributed to Hui Quan.

15 recordsLinked to original sources

PubMed2006

Aminoaciduria and altered renal expression of luminal amino acid transporters in mice lacking novel gene collectrin.

Defects in renal proximal tubule transport manifest in a number of human diseases. Although variable in clinical presentation, disorders such as Hartnup disease, Dent's disease, and Fanconi syndrome are characterized by wasting of solutes commonly recovered by the proximal tubule. One common feature of these disorders is aminoaciduria. There are distinct classes of amino acid transporters located in the apical and basal membranes of the proximal tubules that reabsorb >95% of filtered amino acids, yet few details are known about their regulation. We present our physiological characterization of a mouse line with targeted deletion of the gene collectrin that is highly expressed in the kidney. Collectrin-deficient mice display a reduced urinary concentrating capacity due to enhanced solute clearance resulting from profound aminoaciduria. The aminoaciduria is generalized, characterized by loss of nearly every amino acid, and results in marked crystalluria. Furthermore, in the kidney, collectrin-deficient mice have decreased plasma membrane populations of amino acid transporter subtypes B(0)AT1, rBAT, and b(0,+)AT, as well as altered cellular distribution of EAAC1. Our data suggest that collectrin is a novel mediator of renal amino acid transport and may provide further insight into the pathogenesis of a number of human disease correlates.

Amino Acid Transport Systems↗

PubMed2006

Mice deficient for the vesicular acetylcholine transporter are myasthenic and have deficits in object and social recognition.

An important step for cholinergic transmission involves the vesicular storage of acetylcholine (ACh), a process mediated by the vesicular acetylcholine transporter (VAChT). In order to understand the physiological roles of the VAChT, we developed a genetically altered strain of mice with reduced expression of this transporter. Heterozygous and homozygous VAChT knockdown mice have a 45% and 65% decrease in VAChT protein expression, respectively. VAChT deficiency alters synaptic vesicle filling and affects ACh release. Whereas VAChT homozygous mutant mice demonstrate major neuromuscular deficits, VAChT heterozygous mice appear normal in that respect and could be used for analysis of central cholinergic function. Behavioral analyses revealed that aversive learning and memory are not altered in mutant mice; however, performance in cognitive tasks involving object and social recognition is severely impaired. These observations suggest a critical role of VAChT in the regulation of ACh release and physiological functions in the peripheral and central nervous system.

Acetylcholine↗

PubMed2006

A randomized trial of rofecoxib for the chemoprevention of colorectal adenomas.

BACKGROUND & AIMS: In human and animal studies, nonsteroidal anti-inflammatory drugs have been associated with a reduced risk of colorectal neoplasia. Although the underlying mechanisms are unknown, inhibition of cyclooxygenase (COX), particularly COX-2, is thought to play a role. We conducted a randomized, placebo-controlled, double-blind trial to assess whether use of the selective COX-2 inhibitor rofecoxib would reduce the risk of colorectal adenomas. METHODS: We randomized 2587 subjects with a recent history of histologically confirmed adenomas to receive daily placebo or 25 mg rofecoxib. Randomization was stratified by baseline use of cardioprotective aspirin. Colonoscopic follow-up evaluation was planned for 1 and 3 years after randomization. The primary end point was all adenomas diagnosed during 3 years' treatment. In a modified intent-to-treat analysis, we computed the relative risk of any adenoma after randomization, using Mantel-Haenszel statistics stratified by low-dose aspirin use at baseline. RESULTS: Adenoma recurrence was less frequent for rofecoxib subjects than for those randomized to placebo (41% vs 55%; P < .0001; relative risk [RR], 0.76; 95% confidence interval [CI], 0.69-0.83). Rofecoxib also conferred a reduction in risk of advanced adenomas (P < .01). The chemopreventive effect was more pronounced in the first year (RR, 0.65; 95% CI, 0.57-0.73) than in the subsequent 2 years (RR, 0.81; 95% CI, 0.71-0.93). As reported previously, rofecoxib was associated with increased risks of significant upper gastrointestinal events and serious thrombotic cardiovascular events. CONCLUSIONS: In this randomized trial, rofecoxib significantly reduced the risk of colorectal adenomas, but also had serious toxicity.

Adenoma↗

PubMed2006

A model-based approach in the estimation of the maximum tolerated dose in phase I cancer clinical trials.

The primary aim of a phase I cancer clinical trial is to determine the maximum tolerated dose (MTD) of a new agent. The MTD is determined as the highest dose level of a potential therapeutic agent at which the patients have experienced an acceptable level of dose limiting toxicity. Although many other types of designs have been proposed in recent years, the traditional algorithm-based designs, especially the 3+3 designs, are still widely used due to their practical simplicity. Simulation studies have shown that the traditional algorithm-based designs cannot provide reasonable estimates of the MTD due to their intrinsic design limitations. In this paper, we propose a model-based approach in the estimation of the MTD following a traditional 3+3 design. Simulation results indicate that our model-based approach produces much less biased estimates of the MTD compared to the estimates obtained from the traditional 3+3 designs. Furthermore, our model-based approach can be easily extended to any traditional A+B design.

Algorithms↗

PubMed2005

Multiplicity adjustment for multiple endpoints in clinical trials with multiple doses of an active treatment.

Frequently, multiple doses of an active treatment and multiple endpoints are simultaneously considered in the designs of clinical trials. For these trials, traditional multiplicity adjustment procedures such as Bonferroni, Hochberg and Hommel procedures can be applied when treating the comparisons of different doses to the control on all endpoints at the same level. However, these approaches will not take into account the possible dose-response relationship on each endpoint, and therefore are less specific and may have lower power. To gain power, in this paper, we consider the problem as a two-dimensional multiplicity problem: one dimension concerns the multiple doses and the other dimension concerns the multiple endpoints. We propose procedures which consider the dose order to form the closure of the procedures and control the family-wise type I error rate in a strong sense. For this two-dimensional problem, numerical examples show that procedures proposed in this paper in general have higher power than the commonly used procedures (e.g. the regular Hochberg procedure) especially for comparing the higher dose to the control.

Analgesics↗

PubMed2005

Cardiovascular events associated with rofecoxib in a colorectal adenoma chemoprevention trial.

BACKGROUND: Selective inhibition of cyclooxygenase-2 (COX-2) may be associated with an increased risk of thrombotic events, but only limited long-term data have been available for analysis. We report on the cardiovascular outcomes associated with the use of the selective COX-2 inhibitor rofecoxib in a long-term, multicenter, randomized, placebo-controlled, double-blind trial designed to determine the effect of three years of treatment with rofecoxib on the risk of recurrent neoplastic polyps of the large bowel in patients with a history of colorectal adenomas. METHODS: A total of 2586 patients with a history of colorectal adenomas underwent randomization: 1287 were assigned to receive 25 mg of rofecoxib daily, and 1299 to receive placebo. All investigator-reported serious adverse events that represented potential thrombotic cardiovascular events were adjudicated in a blinded fashion by an external committee. RESULTS: A total of 46 patients in the rofecoxib group had a confirmed thrombotic event during 3059 patient-years of follow-up (1.50 events per 100 patient-years), as compared with 26 patients in the placebo group during 3327 patient-years of follow-up (0.78 event per 100 patient-years); the corresponding relative risk was 1.92 (95 percent confidence interval, 1.19 to 3.11; P=0.008). The increased relative risk became apparent after 18 months of treatment; during the first 18 months, the event rates were similar in the two groups. The results primarily reflect a greater number of myocardial infarctions and ischemic cerebrovascular events in the rofecoxib group. There was earlier separation (at approximately five months) between groups in the incidence of nonadjudicated investigator-reported congestive heart failure, pulmonary edema, or cardiac failure (hazard ratio for the comparison of the rofecoxib group with the placebo group, 4.61; 95 percent confidence interval, 1.50 to 18.83). Overall and cardiovascular mortality was similar in the two groups. CONCLUSIONS: Among patients with a history of colorectal adenomas, the use of rofecoxib was associated with an increased cardiovascular risk.

Adenomatous Polyps↗

PubMed2005

Selective activation of mitogen-activated protein (MAP) kinase kinase 3 and p38alpha MAP kinase is essential for cyclic AMP-dependent UCP1 expression in adipocytes.

The sympathetic nervous system regulates the activity and expression of uncoupling protein 1 (UCP1) through the three beta-adrenergic receptor subtypes and their ability to raise intracellular cyclic AMP (cAMP) levels. Unexpectedly, we recently discovered that the cAMP-dependent regulation of multiple genes in brown adipocytes, including Ucp1, occurred through the p38 mitogen-activated protein kinases (MAPK) (W. Cao, K. W. Daniel, J. Robidoux, P. Puigserver, A. V. Medvedev, X. Bai, L. M. Floering, B. M. Spiegelman, and S. Collins, Mol. Cell. Biol. 24:3057-3067, 2004). However, no well-defined pathway linking cAMP accumulation or cAMP-dependent protein kinase (PKA) to p38 MAPK has been described. Therefore, in the present study using both in vivo and in vitro models, we have initiated a retrograde approach to define the required components, beginning with the p38 MAPK isoforms themselves and the MAP kinase kinase(s) that regulates them. Our strategy included ectopic expression of wild-type and mutant kinases as well as targeted inhibition of gene expression using small interfering RNA. The results indicate that the beta-adrenergic receptors and PKA lead to a highly selective activation of the p38alpha isoform of MAPK, which in turn promotes Ucp1 gene transcription. In addition, this specific activation of p38alpha relies solely on the presence of MAP kinase kinase 3, despite the expression in brown fat of MKK3, -4, and -6. Finally, of the three scaffold proteins of the JIP family expressed in brown adipocytes, only JIP2 co-immunoprecipitates p38alpha MAPK and MKK3. Therefore, in the brown adipocyte the recently described scaffold protein JIP2 assembles the required factors MKK3 and p38alpha MAPK linking PKA to the control of thermogenic gene expression.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Decision rule based multiplicity adjustment strategy.

To minimize potential controversies in determining the need for multiplicity adjustment for multiple hypotheses, we propose a decision rule based multiplicity adjustment strategy in this paper. Resorting to a predefined decision rule of a clinical trial, one may link the different hypotheses by their logical relationships and divide them into different families. A proper multiplicity adjustment procedure can then be developed by maintaining strong control of Type I error rate within each family. The paper applies the proposed multiplicity adjustment strategy to a published raloxifene clinical trial.

Bone Density Conservation Agents↗

PubMed2004

Two-stage adaptive strategy for superiority and non-inferiority hypotheses in active controlled clinical trials.

In active controlled trials without a placebo arm, there are usually two study objectives: to test a superiority hypothesis that the experimental treatment is more effective than the active control therapy, and to test a non-inferiority hypothesis that the experimental treatment is therapeutically no worse than the active control within a defined margin. For a two-stage adaptive design, it is not necessary to give a fixed sample size calculation at the planning stage of the study when treatment effect information is often insufficient. Instead, decision and estimation of the design specifications can be made more reliably after the first stage when interim results are available. We propose the use of conditional power approach to determine the sample size and critical values for testing the superiority and non-inferiority hypotheses for the second stage based on the observed result of the first stage. The proposed adaptive procedure preserves the overall type I error rate for both superiority and non-inferiority, and has the flexibility of early termination of the study (for futility or efficacy) or extending the study by appropriate sample size.

Controlled Clinical Trials as Topic↗

PubMed2004

Ulcer formation with low-dose enteric-coated aspirin and the effect of COX-2 selective inhibition: a double-blind trial.

BACKGROUND & AIMS: We assessed the risk of ulcers with low-dose aspirin and the interaction of low-dose aspirin with a COX-2 selective inhibitor in a double-blind trial that compared placebo, low-dose aspirin, rofecoxib + low-dose aspirin, and ibuprofen. METHODS: Osteoarthritis patients > or =50 years of age without ulcers or erosive esophagitis at baseline endoscopy were assigned randomly to placebo, enteric-coated aspirin 81 mg/day, rofecoxib 25 mg combined with aspirin 81 mg/day, or ibuprofen 800 mg 3 times a day. Repeat endoscopies were performed at 6 and 12 weeks. RESULTS: The 12-week cumulative incidence of ulcers was placebo (N = 381) 5.8%, aspirin (N = 387) 7.3%, rofecoxib combined with aspirin (N = 377) 16.1%, and ibuprofen (N = 374) 17.1% (P < 0.001 for rofecoxib combined with aspirin and for ibuprofen vs. each of placebo and aspirin). Over 12 weeks, mean increases in the number of erosions were placebo 0.17, aspirin 0.85 (P = 0.002 vs. placebo), rofecoxib combined with aspirin 1.67, and ibuprofen 1.91 (both P < 0.001 vs. aspirin and placebo). CONCLUSIONS: Low-dose aspirin alone did not significantly increase ulcer incidence. Addition of a cyclooxygenase-2 (COX-2) selective inhibitor to low-dose aspirin increased ulcer incidence, to a rate not significantly less than a nonselective nonsteroidal anti-inflammatory drug (NSAID) alone. Determining the relative impact of COX-2 selective inhibitors and nonselective NSAIDs on gastrointestinal mucosal injury in low-dose aspirin users will require further study.

Aged↗

PubMed2004

Hypertension and impaired glycine handling in mice lacking the orphan transporter XT2.

A family of orphan transporters has been discovered that are structurally related to the Na(+)-Cl(-)-dependent neurotransmitter transporters, including the dopamine transporter. One member of this family, the mouse XT2 gene, is predominantly expressed in the kidney and has 95% homology to rat ROSIT (renal osmotic stress-induced Na(+)-Cl(-) organic solute cotransporter). To study the physiological functions of this transporter, we generated XT2-knockout mice by gene targeting. XT2(-/-) mice develop and survive normally with no apparent abnormalities. To attempt to identify potential substrates for XT2, we screened urine from XT2-knockout mice by high-pressure liquid chromatography and mass spectrometry and found significantly elevated concentrations of glycine. To study glycine handling, XT2(+/+) and XT2(-/-) mice were injected with radiolabeled glycine, and urine samples were collected to monitor glycine excretion. After 2 h, XT2(-/-) mice were found to excrete almost twice as much glycine as the XT2(+/+) controls (P = 0.03). To determine whether the absence of the XT2 transporter affected sodium and fluid homeostasis, we measured systolic blood pressure by computerized tail-cuff manometry. Systolic blood pressure was significantly higher in XT2(-/-) mice (127 +/- 3 mmHg) than in wild-type controls (114 +/- 2 mmHg; P < 0.001). This difference in systolic blood pressure was maintained on high and low salt feeding. To examine whether the alteration in blood pressure and the defect in glycine handling were related, we measured systolic blood pressure in the XT2(-/-) mice during dietary glycine supplementation. Glycine loading caused systolic blood pressure to fall in the XT2(-/-) mice from 127 +/- 3 to 115 +/- 3 mmHg (P < 0.001), a level virtually identical to that of the wild-type controls. These data suggest that the XT2 orphan transporter is involved in glycine reabsorption and that the absence of this transporter is sufficient to cause hypertension.

Amino Acids↗

PubMed2003

Estimate of standard deviation for a log-transformed variable using arithmetic means and standard deviations.

Analyses of study variables are frequently based on log transformations. To calculate the power for detecting the between-treatment difference in the log scale, we need an estimate of the standard deviation of the log-transformed variable. However, in many situations a literature search only provides the arithmetic means and the corresponding standard deviations. Without individual log-transformed data to directly calculate the sample standard deviation, we need alternative methods to estimate it. This paper presents methods for estimating and constructing confidence intervals for the standard deviation of a log-transformed variable given the mean and standard deviation of the untransformed variable. It also presents methods for estimating the standard deviation of change from baseline in the log scale given the means and standard deviations of the untransformed baseline value, on-treatment value and change from baseline. Simulations and examples are provided to assess the performance of these estimates.

Confidence Intervals↗

PubMed2003

Controlling type I error rate for fast track drug development programmes.

The U.S. Food and Drug Administration (FDA) Modernization Act of 1997 has a Section (No. 112) entitled 'Expediting Study and Approval of Fast Track Drugs' (the Act). In 1998, the FDA issued a 'Guidance for Industry: the Fast Track Drug Development Programs' (the FTDD programmes) to meet the requirement of the Act. The purpose of FTDD programmes is to 'facilitate the development and expedite the review of new drugs that are intended to treat serious or life-threatening conditions and that demonstrate the potential to address unmet medical needs'. Since then many health products have reached patients who suffered from AIDS, cancer, osteoporosis, and many other diseases, sooner by utilizing the Fast Track Act and the FTDD programmes. In the meantime several scientific issues have also surfaced when following the FTDD programmes. In this paper we will discuss the concept of two kinds of type I errors, namely, the 'conditional approval' and the 'final approval' type I errors, and propose statistical methods for controlling them in a new drug submission process.

Clinical Trials, Phase III as Topic↗

PubMed2003

The gastrointestinal safety of the COX-2 selective inhibitor etoricoxib assessed by both endoscopy and analysis of upper gastrointestinal events.

OBJECTIVES: Etoricoxib is a selective cyclooxygenase inhibitor that in clinical studies has improved the signs and symptoms of osteoarthritis and rheumatoid arthritis and reduced the potential for GI injury. The incidence of endoscopically detected ulcers and of clinically important upper GI events (perforations, ulcers, and bleeding episodes) was compared in patients taking etoricoxib or nonselective nonsteroidal anti-inflammatory drugs (NSAIDs). METHODS: Upper GI endoscopy was performed at intervals over 12 wk in 680 patients taking etoricoxib 120 mg once daily, ibuprofen 800 mg three times daily, or placebo in a randomized, parallel-group, double-blind study. Survival analysis was used to analyze time-to-event data for the incidence of gastric or duodenal ulcers (> or =3 mm and > or =5 mm), and the log rank test was used to compare the cumulative incidence between treatment groups. A combined analysis of upper GI events in all 10 Phase II/III clinical trials of etoricoxib (60, 90, or 120 mg) versus nonselective NSAIDs (naproxen, ibuprofen, or diclofenac) for osteoarthritis, rheumatoid arthritis, and chronic low back pain was conducted. Investigators reported potential events for adjudication by an external, blinded committee, using prespecified criteria to confirm events. All events that occurred during active treatment periods (maximum 792 days) or within 14 days of stopping treatment were included in the analysis. Time to first event was evaluated using survival analysis; the Kaplan-Meier method was used to determine the cumulative incidence, and relative risk was estimated with the Cox proportional hazards model. RESULTS: In the endoscopy study, the cumulative incidence of ulcers >/=3 mm at 12 wk in the ibuprofen group (17%) was significantly higher than in the etoricoxib group (8.1%, p < 0.001); similar results were seen for ulcers >/=5 mm. In the placebo group, the rate of ulcers >/=3 mm was 1.86%. Of 3142 patients treated with once-daily etoricoxib and 1828 patients treated with a nonselective NSAID (ibuprofen, naproxen, or diclofenac), 82 patients with investigator-reported upper GI events (71 confirmed) were eligible for the combined analysis. For etoricoxib versus NSAIDs, the rate per 100 patient-yr for confirmed events was 1.16 versus 3.05 (relative risk = 0.44, 95% CI = 0.27-0.72, p < 0.001), whereas that for investigator-reported events was 1.35 versus 3.42 (relative risk = 0.47, 95% CI = 0.30-0.74, p = 0.001). Results were driven primarily by studies with naproxen as the comparator. CONCLUSIONS: The incidence of endoscopically detected ulcers was significantly lower with etoricoxib 120 mg than with ibuprofen 2400 mg. Treatment with etoricoxib reduced the incidence of investigator-reported and confirmed adverse upper GI events by approximately 50% compared with treatment with nonselective NSAIDs.

Aged↗

PubMed2002

The upper GI safety and tolerability of oral alendronate at a dose of 70 milligrams once weekly: a placebo-controlled endoscopy study.

OBJECTIVE: Alendronate (10 mg daily) has been shown in long term clinical trials to be an effective treatment for postmenopausal osteoporosis. A weekly dosing regimen of alendronate is preferred by both patients and physicians, as it has the potential to provide greater convenience and enhance compliance. In a 1-yr clinical trial, alendronate (70 mg once weekly) was equally efficacious and at least as well tolerated as the 10-mg daily dose in the treatment of postmenopausal osteoporosis, despite the higher unit dosage required. We conducted a randomized, double blind, placebo- and active-controlled endoscopy study to confirm the results of this clinical trial. We hypothesized that mean endoscopic gastric erosion scores would be similar in subjects receiving alendronate (70 mg once weekly) and those receiving a placebo. METHODS: Two hundred seventy-seven subjects (90 men and 187 women) were randomized to one of three treatment groups: 1) alendronate (70 mg once weekly) for 10 wk (N = 126), 2) placebo (once weekly) for 10 wk (N = 126), or 3) placebo (once weekly) for 10 wk followed by aspirin (650 mg q.i.d.) for the last week as the positive control (N = 25). Esophagogastroduodenoscopy was performed 5 to 7 days after the last dose of alendronate or matching placebo. RESULTS: The mean gastric erosion scores (Lanza scale) were similar in subjects given alendronate (70 mg once weekly) and those given a placebo (0.32 vs 0.35, respectively; 95% CI for difference = -0.22-0.16, p = 0.75), whereas scores in both groups were significantly lower than in those given aspirin (3.09; p < 0.001). Endoscopic gastroduodenal ulcers occurred in no alendronate (0%), two placebo (1.7%), and five aspirin (23.8%) subjects. The mean erosion scores in the esophagus and duodenum of alendronate and placebo subjects were also similar. The incidences of upper GI symptoms were similar in the alendronate and placebo subjects and did not suggest a relationship with endoscopic lesions. CONCLUSIONS: Alendronate (70 mg once weekly) was not associated with any increase in endoscopic lesions in the upper GI tract relative to a placebo.

Administration, Oral↗