Optimal population designs for PK models with serial sampling

In various pharmaceutical applications, repeated measurements are taken from each subject, and model parameters are estimated from the collected data. Examples include dose response modeling and PK/PD studies with serial blood sampling, among others. The quality of the information in an experiment is reflected in the precision of estimates of model parameters, which is traditionally measured by their variance-covariance matrix. In this article, we concentrate on the example of a clinical PK study where multiple blood samples are taken for each enrolled patient, which leads to nonlinear mixed effects regression models with multiple responses. The sampling scheme for each patient is considered a multidimensional point in the space of admissible sampling sequences. We demonstrate how to optimize the precision of parameter estimates by finding the best number and allocation of sampling times. It is shown that a reduced number of samples may be taken without significant loss of precision of parameter estimates. Moreover, our approach allows for taking experimental costs into account, which leads to a more meaningful comparison of sampling schemes and to potential cost savings.     

Pyridoxamine lowers oxalate excretion and kidney crystals in experimental hyperoxaluria: a potential therapy for primary hyperoxaluria

In order to prevent kidney stones and nephrolithiasis in hyperoxaluria, a new treatment that specifically reduces oxalate production and therefore urinary oxalate excretion would be extremely valuable. Pyridoxamine(PM) could react with the carbonyl intermediates of oxalate biosynthesis, glycolaldehyde and glyoxylate, and prevent their metabolism to oxalate. In PM treated rats, endogenous urinary oxalate levels were consistently lower and became statistically different from controls after 12 days of experiment. In ethylene glycol-induced hyperoxaluria, PM treatment resulted in significantly lower (by ~50%) levels of urinary glycolate and oxalate excretion compared to untreated hyperoxaluric animals, as well as in a significant reduction in calcium oxalate crystal formation in papillary and medullary areas of the kidney. These results, coupled with favorable toxicity profiles of PM in humans, show promise for the therapeutic use of PM in primary hyperoxaluria and other kidney stone diseases.     

Human metapneumovirus RNA in encephalitis patient

We describe a fatal case of encephalitis that might be correlated with primary human metapneumovirus (HMPV) encephalitis. Postmortem HMPV RNA was detected in brain and lung tissue samples from the patient. Furthermore, HMPV RNA was found in culture fluids from cells coincubated with lung tissue.     

Pyridoxamine lowers kidney crystals in experimental hyperoxaluria: a potential therapy for primary hyperoxaluria

BACKGROUND: Primary hyperoxaluria is a rare genetic disorder of glyoxylate metabolism that results in overproduction of oxalate. The disease is characterized by severe calcium oxalate nephrolithiasis and nephrocalcinosis, resulting in end-stage renal disease (ESRD) early in life. Most patients eventually require dialysis and kidney transplantation, usually in combination with the replacement of the liver. Reduction of urinary oxalate levels can efficiently decrease calcium oxalate depositions; yet, no treatment is available that targets oxalate biosynthesis. In previous in vitro studies, we demonstrated that pyridoxamine can trap reactive carbonyl compounds, including intermediates of oxalate biosynthesis. METHODS: The effect of PM on urinary oxalate excretion and kidney crystal formation was determined using the ethylene glycol rat model of hyperoxaluria. Animals were given 0.75% to 0.8% ethylene glycol in drinking water to establish and maintain hyperoxaluria. After 2 weeks, pyridoxamine treatment (180 mg/day/kg body weight) started and continued for an additional 2 weeks. Urinary creatinine, glycolate, oxalate, and calcium were measured along with the microscopic analysis of kidney tissues for the presence of calcium oxalate crystals. RESULTS: Pyridoxamine treatment resulted in significantly lower (by approximately 50%) levels of urinary glycolate and oxalate excretion compared to untreated hyperoxaluric animals. This was accompanied by a significant reduction in calcium oxalate crystal formation in papillary and medullary areas of the kidney. CONCLUSION: These results, coupled with favorable toxicity profiles of pyridoxamine in humans, show promise for therapeutic use of pyridoxamine in primary hyperoxaluria and other kidney stone diseases.     

Diagnostic value of fine motor deficits in patients with low-grade hepatic encephalopathy

AIM: The role of motor dysfunction in early diagnosis of low-grade hepatic encephalopathy remains uncertain. We performed a pilot study to comparatively investigate the kinematic characteristics of small and large rapid alternating movements in patients with liver cirrhosis and low-grade hepatic encephalopathy. METHODS: A kinematic analysis of alternating handwriting (7.5mm) and large drawing movements (DM, 175 mm) was performed in 30 patients with liver cirrhosis (no hepatic encephalopathy: n=10; minimal hepatic encephalopathy: n=9; grade I hepatic encephalopathy: n=11; healthy controls: n=12). The correlation between kinematic parameters, clinical neuro-psychiatric symptoms of cerebral dysfunction and the grade of encephalopathy was investigated. RESULTS: Both movement types, handwriting and drawing, were significantly slower in cirrhotic patients. In contrast to large DM, the deterioration of handwriting movements significantly correlated with the increase of symptoms of motor dysfunction and differentiated significantly within the group of cirrhosis patients corresponding to the degree of hepatic encephalopathy. CONCLUSION: The deterioration of fine motor control is an important symptom of low-grade hepatic encephalopathy. The kinematic analysis of handwriting allows the quantitative analysis of alterations of motor function and is a possible tool for diagnostics and monitoring of motor dysfunction in patients with low-grade hepatic encephalopathy.     

Distinct properties of functional KCC2 expression in immature mouse hippocampal neurons in culture and in acute slices

A hallmark in the development of GABAergic neurotransmission is the switch in GABA(A)-mediated responses from depolarizing to hyperpolarizing. This occurs due to a gradual decrease in the intracellular concentration of chloride caused by the functional expression of the neuron-specific K-Cl cotransporter KCC2. Whether a mere increase in the amount of KCC2 protein is the rate-limiting step in vivo, or a further activation of the otherwise nonfunctional cotransporter is required, is not clear. Imposing a fixed Cl(-) load via patch pipette we measured the resultant somato-dendritic gradients in reversal potential of GABAergic currents to determine the time course of functional maturation of KCC2-mediated Cl(-) extrusion in two preparations: cultured mouse hippocampal neurons plated at embryonic day 17 and CA1 pyramidal cells in acute slices. We found that in immature neurons in both preparations the gradient is initially small or not detectable. It undergoes an abrupt increase at around days 13-14 in culture, while a more gradual increase occurs between postnatal days 5-14 in slices. Consistent with the presence of a nonfunctional form of KCC2 in immature hippocampal neurons grown in culture, application of the broad-spectrum kinase inhibitor staurosporine produces a rapid and potent up-regulation of KCC2 function in these cultured neurons, but not in neonatal slices. Taken together with our previously published data, these results indicate that the functional activity of KCC2 in vivo parallels the developmental expression of the protein, whereas cultured neurons require an additional activation step (mimicked by staurosporine) for KCC2 to become functional.     

A comparison of the ability of a 4:1 ketogenic diet and a 6.3:1 ketogenic diet to elevate seizure thresholds in adult and young rats

PURPOSE: The pentylenetetrazol (PTZ) infusion test was used to compare seizure thresholds in adult and young rats fed either a 4:1 ketogenic diet (KD) or a 6.3:1 KD. We hypothesized that both KDs would significantly elevate seizure thresholds and that the 4:1 KD would serve as a better model of the KD used clinically. METHODS: Ninety adult rats and 75 young rats were placed on one of five experimental diets: (a) a 4:1 KD, (b) a control diet balanced to the 4:1 KD, (c) a 6.3:1 KD, (d) a standard control diet, or (e) an ad libitum standard control diet. All subjects were seizure tested by using the PTZ infusion test. Blood glucose and beta-hydroxybutyrate (beta-OHB) levels were measured. RESULTS: Neither KD elevated absolute "latencies to seizure" in young or adult rats. Similarly, neither KD elevated "threshold doses" in adult rats. In young rats, the 6.3:1 KD, but not the 4:1 KD, significantly elevated threshold doses. The 6.3:1 KD group showed poorer weight gain than the 4:1 KD group when compared with respective controls. The most dramatic discrepancies were seen in young rats. CONCLUSIONS: "Threshold doses" and "latency to seizure" data provided conflicting measures of seizure threshold. This was likely due to the inflation of threshold doses calculated by using the much smaller body weights found in the 6.3:1 KD group. Ultimately, the PTZ infusion test in rats may not be a good preparation to model the anticonvulsant effects of the KD seen clinically, especially when dietary treatments lead to significantly mismatched body weights between the groups.     

Trimmed estimators for robust averaging of event-related potentials

Averaging (in statistical terms, estimation of the location of data) is one of the most commonly used procedures in neuroscience and the basic procedure for obtaining event-related potentials (ERP). Only the arithmetic mean is routinely used in the current practice of ERP research, though its sensitivity to outliers is well-known. Weighted averaging is sometimes used as a more robust procedure, however, it can be not sufficiently appropriate when the signal is nonstationary within a trial. Trimmed estimators provide an alternative way to average data. In this paper, a number of such location estimators (trimmed mean, Winsorized mean and recently introduced trimmed L-mean) are reviewed, as well as arithmetic mean and median. A new robust location estimator tanh, which allows the data-dependent optimization, is proposed for averaging of small number of trials. The possibilities to improve signal-to-noise ratio (SNR) of averaged waveforms using trimmed location estimators are demonstrated for epochs randomly drawn from a set of real auditory evoked potential data.     

Non-enhancing de novo glioblastoma: report of two cases

Malignant gliomas arise from two distinct pathways, as de novo lesions or from secondary transformation from low-grade lesions. Herein, we describe the cases of two patients to illustrate the proposition that de novo malignant gliomas can originate as non-enhancing tumors and rapidly progress to a pattern of ring enhancement characteristic of a glioblastoma. Both patients presented with new-onset seizures (simple partial and generalized). Their neurological examinations were unremarkable. Initial MRI evaluations revealed a right precentral gyrus and right medial temporal lobe lesions in each case, respectively. These lesions demonstrated increased T2 signal changes without contrast enhancement. The biopsy of the right frontal lesion in the first patient was consistent with an anaplastic astrocytoma; the second patient was followed expectantly. Repeat MRI for both patients within 17 weeks disclosed ring-enhancing lesions, consistent with an unusually rapid evolution to glioblastoma multiforme (GBM). Subsequent resection of the right medial temporal lesion in the second patient revealed a GBM. Neither tumor displayed abnormal overexpression of P53 by immunohistochemistry. Early MRI of de novo glioblastomas may demonstrate a non-enhancing tumor suggestive of a low-grade lesion. These tumors can rapidly evolve into ring-enhancing lesions more consistent with the traditional imaging findings.