Increased SERCA2a sub-cellular heterogeneity in right-ventricular heart failure inhibits excitation-contraction coupling and modulates arrhythmogenic dynamics

The intracellular calcium handling system of cardiomyocytes is responsible for controlling excitation-contraction coupling (ECC) and has been linked to pro-arrhythmogenic cellular phenomena in conditions such as heart failure (HF). SERCA2a, responsible for intracellular uptake, is a primary regulator of calcium homeostasis, and remodelling of its function has been proposed as a causal factor underlying cellular and tissue dysfunction in disease. Whereas adaptations to the global (i.e. whole-cell) expression of SERCA2a have been previously investigated in the context of multiple diseases, the role of its spatial profile in the sub-cellular volume has yet to be elucidated. We present an approach to characterize the sub-cellular heterogeneity of SERCA2a and apply this approach to quantify adaptations to the length-scale of heterogeneity (the distance over which expression is correlated) associated with right-ventricular (RV)-HF. These characterizations informed simulations to predict the functional implications of this heterogeneity, and its remodelling in disease, on ECC, the dynamics of calcium-transient alternans and the emergence of spontaneous triggered activity. Image analysis reveals that RV-HF is associated with an increase in length-scale and its inter-cellular variability; simulations predict that this increase in length-scale can reduce ECC and critically modulate the vulnerability to both alternans and triggered activity. This article is part of the theme issue 'The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease'.

Pharmacokinetics of coadministration of levothyroxine sodium and alendronate sodium new effervescent formulation

No clinically important pharmacokinetic interference of alendronate occurred between a new effervescent formulation of alendronate and levothyroxine when coadministered. The combination does not materially affect levothyroxine absorption.

INTRODUCTION

Concurrent treatment of osteoporosis with alendronate (Aln) and hypothyroidism with levothyroxine (LT4) may be problematic because both drugs are to be taken separately after fasting overnight. The primary objective was to assess pharmacokinetic interactions between a new effervescent formulation of Aln (Aln-NEF) and LT4.

METHODS

A randomized, open-label, 3-way crossover study was conducted in 30 healthy adults (15 women). Subjects were dosed 3 times, separated by 35 days, after overnight fasts, with Aln-NEF alone (70 mg), LT4 alone (600 μg), or Aln-NEF and LT4 concurrently. Samples were analyzed for plasma Aln and serum LT4. Pharmacokinetic drug-drug interaction was assessed using 90% confidence intervals (CIs) for the test/reference ratio of the geometric means for area under the concentration-time curve from time zero to last measureable time point (AUC_0-t ) and maximum concentration (C _max). Results were compared to the default no-effect boundaries of 80 to 125% for the ratio Aln-NEF and LT4 concurrently/Aln-NEF alone and the ratio Aln-NEF and LT4 concurrently/LT4 alone.

RESULTS

Geometric mean ratios (Aln-NEF with LT4/Aln-NEF alone) were 0.927 (90% CI 0.795-1.081) for AUC_0-8 and 0.912 (90% CI 0.773-1.077) for C _max, demonstrating LT4 does not appreciably affect the pharmacokinetics of Aln. Geometric mean ratios (LT4 with Aln-NEF/LT4 alone) were 1.049 (90% CI 0.983-1.119) for AUC_0-48 and 1.075 (90% CI 1.006-1.148) for C _max, demonstrating LT4 is bioequivalent between the 2 treatments. Coadministration of Aln-NEF and LT4 was well tolerated.

CONCLUSIONS

There was no clinically important pharmacokinetic interference between the Aln-NEF formulation and LT4. Aln-NEF does not materially affect LT4 absorption.

External fixation in patients with panvertebral osteomyelitis and paraplegia

Vertebral osteomyelitis is a difficult problem in the spinal cord injured patient. We present three such cases treated with extensive debridement followed by grafting and stabilization with external fixation. In all three patients the infection resolved. We feel this is a viable option for treating this condition.

Single-incision combination biopsy (muscle and nerve) in the diagnosis of neuromuscular disease in children

The diagnosis of specific neuromuscular diseases in infants and children is often suspected clinically and confirmed histologically by muscle biopsy. In relatively few cases, the differential diagnosis includes hereditary or acquired peripheral neuropathies, and nerve biopsy is required for diagnosis. Historically, children who needed both muscle and nerve biopsies have had two separate incisions at the thigh (muscle) and ankle (nerve) to obtain the specimens. A procedure has been developed that employs a single incision on the posterior aspect of the calf, which allows for simultaneous muscle (soleus or peroneals) and nerve (sural) biopsies. A retrospective study of 22 patients who underwent single-incision combination biopsy was performed. Age at time of biopsy ranged from 2 months to 14 years. Adequate specimens for histologic analysis were obtained in all but one case. Histologic diagnoses were made in 32% of the muscle biopsies and 29% of the nerve biopsies. Mean follow-up after biopsy was 3 years 6 months. Potentially significant complications of nerve biopsy were not seen in this cohort. Single-incision combination biopsy is the preferred technique when simultaneous muscle and nerve biopsies are required. Knowledge of the location of the sural nerve in the calf is essential. This technique is relatively less invasive than separate muscle and nerve biopsies, allows for the harvest of adequate muscle and nerve specimens, is minimally morbid, and can be performed on very young infants.

Incidence of alcohol abuse in the parents of medical students

An anonymous self-report survey of the medical students at the University of Colorado Health Sciences Center assessed how many of the students' parents were alcohol abusers. The results indicated that 27% of the student body were children of alcohol abusers, a rate twice that of the general population. This finding has implications for teaching strategies, student substance abuse, prevention efforts during the medical-school years, and provision of appropriate programs through student health services.

Axes: focus of taxonomy II

A number of persistent issues in the nursing diagnosis community have challenged the ability of one nursing diagnosis taxonomy to account for nursing's practice. The North American Nursing Diagnosis Association (NANDA) Taxonomy Committee, charged with the preparation of one taxonomy for all, has struggled with some of these issues and has initiated development of axes. The issues, figuratively speaking, become the axes. The axes are intended to describe the dimensions of the human condition. This article, third in a series of four, describes the process and development of the proposed axes.

Development of definitions for taxonomy II

In the process of placing diagnoses into Taxonomy I, certain inconsistencies became apparent. Inadequate definition of both diagnoses and human response patterns, lack of defining characteristics, and inconsistency in the levels of abstraction within the taxonomic hierarchy made the task of assigning a diagnosis to a taxonomic pattern difficult. Ambiguity in the definitions of the nine patterns resulted in ambiguity in the basic foundation, which affected the entire structure. The Taxonomy Committee, before evaluating the current structure, had to make the following decisions regarding the current human response patterns: (1) Should the nine human response patterns be retained for further taxonomic work? and (2) If they are retained, what should be the first step in examining Taxonomy I-Revised? This second article in a series of four will familiarize the readers with the process and decisions by which Taxonomy II of the North American Nursing Diagnosis Association (NANDA) is evolving through the work of the Taxonomy Committee. This article also will identify the specific problems encountered in the development of Taxonomy I and Taxonomy I-Revised, and describe the steps establishing the validity of the process of formation of the nine human response patterns.

Effect of renal impairment on disposition of pentopril and its active metabolite

Disposition of pentopril was studied in 15 male volunteers with varying renal functions. Mild to moderate compromise in renal function did not demonstrate any appreciable changes in plasma concentration of pentopril, the prodrug ester of the active angiotensin-converting enzyme (ACE) inhibitor CGS 13934. This is consistent with the known elimination pattern for pentopril, which is eliminated primarily by hydrolysis to the active inhibitor. In contrast, the plasma concentration of the active ACE inhibitor was sensitive to moderate changes in renal function. Because of the reciprocal relationship of AUC and clearance, AUC did not change to any appreciable extent until creatinine clearance (CLCR) dropped to about 50 ml/min. Below 50 ml/min of CLCR, AUC and half-life increased sharply with reduced kidney function. Because of the significant contribution of the renal secretion process to total renal elimination of both pentopril and the active metabolite, prediction of renal clearance from CLCR was poor at relatively normal kidney function (CLCR greater than 80 ml/min). However, renal secretory clearances for both pentopril and metabolite were well correlated to p-aminohippuric acid clearance. In patients with moderately compromised renal function (glomerular filtration rate less than 40 ml/min), tubular secretion rate of creatinine approaches its glomerular filtration rate and hence CLCR could be used as a predictor of renal clearance and other disposition parameters. Plasma ACE activity also demonstrated prolonged inhibition with decreased renal function. Based on the prolonged blockade of plasma ACE activity, some correction in dose or dosing interval is anticipated in patients with moderately compromised renal function (CLCR less than 50 ml/min).

Pentopril-cimetidine interaction caused by a reduction in hepatic blood flow

The interactive effects of the coadministration of steady-state cimetidine and single-dose pentopril, an angiotensin converting enzyme inhibitor, on the pharmacokinetic disposition of each other were studied in humans. Cimetidine reduced the clearance of pentopril by 11 to 14%. This reduction in clearance was shown to be caused by a reduction in liver blood flow probably mediated through H2 receptor blockade. Meanwhile pentopril induced the oral clearance of cimetidine by 21%, presumably by a reduction in the bioavailable fraction of cimetidine. The mechanism of this interaction is unknown.

Pharmacokinetics of pentopril in the elderly

1 The pharmacokinetics of pentopril in elderly subjects aged 70 to 75 years were compared with those of healthy young subjects aged 22 to 26 years. 2 There were no appreciable differences between the two groups in any of the pharmacokinetic parameters for pentopril derived from its plasma data (Cmax, tmax, AUC and t1/2). 3 In contrast, the active metabolite CGS 13934 exhibited an increase in mean values of AUC by 56% in elderly compared to young. However, the difference was not statistically significant (0.1 greater than P greater than 0.05). The variability was, however, significantly higher (P less than 0.05) in the elderly group compared with young. The peak time for metabolite was also significantly delayed in elderly (3.9 vs 2.5 h). The mean half-life for metabolite however, was comparable for the two groups (3.6 vs 3.9 h). 4 Urinary analysis showed a significant decrease in renal clearance (CLR) with age for both pentopril (107 vs 203 ml min-1) and its active metabolite (116 vs 205 ml min-1). 5 Pharmacodynamic measurements of the renin-angiotensin system, in general, demonstrated a drug effect at 2 h with recovery almost to the basal value at 24 h except for plasma ACE activity at 24 h in the elderly. 6 Because of large variability and an increase in the mean AUC of active metabolite in elderly, greater caution may be necessary for dose selection in this group. However, no substantial difference in extent of drug accumulation is anticipated in elderly compared with young people based on the similarity in t1/2 values.

Gastroscopic localization of a microencapsulated KCl preparation in the human stomach

A slow release polymer-coated preparation of potassium chloride granules (Micro-K Extencaps) was initially thought not to be associated with gastric mucosal damage. Recent studies have shown that acute gastric ulcers occur with approximately the same frequency as in patients taking wax matrix KCl formulations. The development of acute gastric ulcers was not consistent with the proposed dispersion characteristics of the microencapsulated KCl preparation. The authors therefore endoscopically evaluated the dispersion characteristics of microencapsulated KCl in a double-blind, placebo-controlled study. Subjects received four capsules of Micro-K or matching placebo and endoscopy was performed 30, 60, or 120 min after each drug ingestion. The material was identified with the Olympus HM (high magnification) endoscope and then quantitatively aspirated using the 3.5-mm biopsy channel of the Pentax 34JA endoscope. Microencapsulated KCl particles dispersed poorly and were found adhering to the mucosa and to one another, as a semisolid mass, most frequently in the gastric antrum. In contrast, the placebo (ethyl cellulose) was widely dispersed throughout the stomach. The authors concluded that gastric emptying must be considered in three phases: liquids, solids, and solids which adhere to the mucosa. No unique dispersion characteristics of Micro-K Extencaps were identified, and adherence of the KCl to the gastric mucosa may explain its ability to cause occasional acute gastric ulceration.

Inhibition of renal clearance of furosemide by pentopril, an angiotensin-converting enzyme inhibitor

The pharmacokinetic interaction between pentopril (250 mg) and furosemide (40 mg) was studied in 12 normal healthy volunteers after oral administration of each drug alone and in combination. No significant changes in any pharmacokinetic parameters of pentopril or its active metabolite (CGS 13934) were observed on coadministration of furosemide. In contrast, pentopril induced significant changes in disposition of furosemide. Pentopril decreased renal clearance (CLR) of furosemide by 54% and the fraction excreted unchanged in urine also decreased by 55%. However, such decrease in CLR of furosemide was compensated by a simultaneous increase in glucuronidation (by 200%), resulting in a slight increase in systemic clearance (decreased AUC). Systemic bioavailability of furosemide appears to be unchanged in the presence of pentopril (0.46 vs. 0.41). No effect of pentopril on plasma protein binding of furosemide was detected. In spite of the decreased CLR and urinary excretion rate of furosemide, the urinary output (1749 vs. 1774 ml/6 hr) and Na+ excretion (757 vs. 816 mEq/6 hr) remained almost unchanged. These findings suggest that total furosemide (unchanged and glucuronide) might contribute to diuresis and natriuresis rather than the unchanged furosemide alone. Because of unchanged pharmacodynamic effect, such pharmacokinetic interaction may not require any dosage adjustment for furosemide on pentopril coadministration.

Pharmacokinetics and pharmacodynamics of pentopril, a new angiotensin-converting-enzyme inhibitor in humans

In a single, ascending-dose tolerance study, nine healthy volunteers were given oral pentopril 50 to 750 mg (CGS 13945) in groups of three each. Disposition characteristics of pentopril and its active metabolite (CGS 13934) were determined using plasma concentration and urinary excretion data. The drug was absorbed rapidly following zero-order kinetics. The drug has an apparent volume of distribution of 0.83 L/kg and an oral clearance of about 0.79 L/hr/kg. Urinary excretions, calculated after 125- and 250-mg doses, showed a dose proportional urinary recovery of 21% (+/- 5%) for pentopril and 40% (+/- 5%) for CGS 13934. In the multiple-dose study of 125 mg orally q12h in six healthy subjects, the plasma concentrations for both drug and metabolite showed no appreciable accumulation of either compound, which was expected from their short pharmacokinetic half-lives (pentopril, less than 1 hr; CGS 13934, approximately 2 hr). In a separate pharmacodynamic study, drug and metabolite concentrations were evaluated against angiotensin-I (AI)-induced changes in blood pressure and plasma angiotensin-converting-enzyme (ACE) activity in healthy volunteers after single oral doses (range, 10-500 mg). The pharmacodynamic half-life for plasma ACE inhibition increased with the dose (10 mg, 1.5 hr; 500 mg, 9.8 hr). There was a close relationship between the plasma level of the metabolite and the inhibition of plasma ACE activity and AI-induced pressor response. A hyperbolic function adequately described the dependence of plasma ACE activity on plasma metabolite concentration with a concentration at half-maximal inhibition of 53 ng/mL.

Effect of food on the bioavailability of pentopril, an angiotensin-converting-enzyme inhibitor, in healthy subjects

Pentopril (CGS 13945) was administered in 125-mg capsules to eight healthy men on two occasions according to a randomized schedule; on one occasion in the fasting state and on the other occasion immediately following the ingestion of a standardized meal. Unlike captopril, a prototype angiotensin-converting-enzyme inhibitor, there was no significant difference in the peak plasma concentration for either the drug or its active metabolite (CGS 13934) between the fasting and the fed states. There was also no appreciable change in the area under the plasma curve for the drug and its metabolite after administration of drug in the presence of food compared with a fasting state. There was, however, a lag time in drug absorption after ingestion of food, which resulted in a significant increase in peak time for the active metabolite in plasma. Food delays the body's absorption of the drug and hence the appearance of its active metabolite in plasma without any significant effect on the relative bioavailability. Because relative bioavailability is not affected in the presence of food, such a delay may not have any therapeutic importance on chronic administration.