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Biomedical subjects

Philip J Lee

Publications and source records attributed to Philip J Lee.

At least 19 recordsLinked to original sources
PubMed2006

Effects of dietary management of phenylketonuria on long-term cognitive outcome.

BACKGROUND: Phenylketonuria (PKU) is associated with dopaminergic depletion in the dorsolateral prefrontal cortex and abnormalities of myelination. Both mechanisms may lead to deficits in cognitive functioning. Studies of cognitive outcome in children treated with PKU at an early stage have suggested that there are benefits in remaining on diet into adolescence. AIM: To assess the nature and extent of any cognitive deficits in adults treated at an early stage with PKU who had discontinued their diets in adolescence. METHOD: 25 patients (aged 18-38 years) who were diagnosed early and had discontinued their diets in adolescence were compared with 25 adults (aged 18-38 years) with PKU on continuous diet, and with a healthy control group (n = 45). RESULTS: The groups differed significantly on accuracy (p = 0.007) and speed (p = 0.001) of performance on an n-back working memory task and on speed of performance (p = 0.001) on a flanker inhibitory task, but not on flanker accuracy, object alternation learning or perceptual judgement tasks (all p>0.05). The off-diet group performed significantly below the on-diet group on n-back accuracy (p = 0.007) and flanker speed (p = 0.05), and significantly below the control group on n-back speed (p = 0.002) and flanker speed (p = 0.001). CONCLUSION: The findings suggest that although discontinuing diet in adolescence appears disadvantageous compared with remaining on continuous diet, any deficits are relatively subtle.

Adolescent↗
PubMed2006

Nanoliter scale microbioreactor array for quantitative cell biology.

A nanoliter scale microbioreactor array was designed for multiplexed quantitative cell biology. An addressable 8 x 8 array of three nanoliter chambers was demonstrated for observing the serum response of HeLa human cancer cells in 64 parallel cultures. The individual culture unit was designed with a "C" shaped ring that effectively decoupled the central cell growth regions from the outer fluid transport channels. The chamber layout mimics physiological tissue conditions by implementing an outer channel for convective "blood" flow that feeds cells through diffusion into the low shear "interstitial" space. The 2 microm opening at the base of the "C" ring established a differential fluidic resistance up to 3 orders of magnitude greater than the fluid transport channel within a single mold microfluidic device. Three-dimensional (3D) finite element simulation were used to predict fluid transport properties based on chamber dimensions and verified experimentally. The microbioreactor array provided a continuous flow culture environment with a Peclet number (0.02) and shear stress (0.01 Pa) that approximated in vivo tissue conditions without limiting mass transport (10 s nutrient turnover). This microfluidic design overcomes the major problems encountered in multiplexing nanoliter culture environments by enabling uniform cell loading, eliminating shear, and pressure stresses on cultured cells, providing stable control of fluidic addressing, and permitting continuous on-chip optical monitoring.

Bioreactors↗
PubMed2006

Evaluation of chemical enhancers in the transdermal delivery of lidocaine.

The effect of various classes of chemical enhancers was investigated for the transdermal delivery of the anesthetic lidocaine across pig and human skin in vitro. The lipid disrupting agents (LDA) oleic acid, oleyl alcohol, butenediol, and decanoic acid by themselves or in combination with isopropyl myristate (IPM) showed no significant flux enhancement. However, the binary system of IPM/n-methyl pyrrolidone (IPM/NMP) improved drug transport. At 2% lidocaine dose, this synergistic enhancement peaked at 25:75 (v/v) IPM:NMP with a steady state flux of 57.6 +/- 8.4 microg cm(-2) h(-1) through human skin. This observed flux corresponds to a four-fold enhancement over a 100% NMP solution and over 25-fold increase over 100% IPM at the same drug concentration (p < 0.001). NMP was also found to co-transport through human skin with lidocaine free base and improve enhancement due to LDA. These findings allow a more rational approach for designing oil-based formulations for the transdermal delivery of lidocaine free base and similar drugs.

Administration, Cutaneous↗
PubMed2006

Microfluidics-based systems biology.

Systems biology seeks to develop a complete understanding of cellular mechanisms by studying the functions of intra- and inter-cellular molecular interactions that trigger and coordinate cellular events. However, the complexity of biological systems causes accurate and precise systems biology experimentation to be a difficult task. Most biological experimentation focuses on highly detailed investigation of a single signaling mechanism, which lacks the throughput necessary to reconstruct the entirety of the biological system, while high-throughput testing often lacks the fidelity and detail necessary to fully comprehend the mechanisms of signal propagation. Systems biology experimentation, however, can benefit greatly from the progress in the development of microfluidic devices. Microfluidics provides the opportunity to study cells effectively on both a single- and multi-cellular level with high-resolution and localized application of experimental conditions with biomimetic physiological conditions. Additionally, the ability to massively array devices on a chip opens the door for high-throughput, high fidelity experimentation to aid in accurate and precise unraveling of the intertwined signaling systems that compose the inner workings of the cell.

Animals↗
PubMed2006

The longest-surviving patient with classical maple syrup urine disease.

The clinical problems, dietary management and biochemical monitoring over a 40-year period of the longest-surviving patient with maple syrup urine disease are described. Her case illustrates that a good outcome can be obtained with early diagnosis and institution of a diet restricted in branched-chain amino acids. Changes in dietary supplementation have benefited her in terms of nutrition and quality of life. Consistently high blood concentrations of branched-chain amino acids have not been associated with neuropsychometric decline.

Adult↗
PubMed2005

Continuous perfusion microfluidic cell culture array for high-throughput cell-based assays.

We present for the first time a microfluidic cell culture array for long-term cellular monitoring. The 10 x 10 array could potentially assay 100 different cell-based experiments in parallel. The device was designed to integrate the processes used in typical cell culture experiments on a single self-contained microfluidic system. Major functions include repeated cell growth/passage cycles, reagent introduction, and real-time optical analysis. The single unit of the array consists of a circular microfluidic chamber, multiple narrow perfusion channels surrounding the main chamber, and four ports for fluidic access. Human carcinoma (HeLa) cells were cultured inside the device with continuous perfusion of medium at 37 degrees C. The observed doubling time was 1.4 +/- 0.1 days with a peak cell density of approximately 2.5*10(5) cells/cm(2). Cell assay was demonstrated by monitoring the fluorescence localization of calcein AM from 1 min to 10 days after reagent introduction. Confluent cell cultures were passaged within the microfluidic chambers using trypsin and successfully regrown, suggesting a stable culture environment suitable for continuous operation. The cell culture array could offer a platform for a wide range of assays with applications in drug screening, bioinformatics, and quantitative cell biology.

Cell Culture Techniques↗
PubMed2005

Role of n-methyl pyrrolidone in the enhancement of aqueous phase transdermal transport.

The role of n-methyl pyrrolidone (NMP) as an enhancer for permeants delivered from an aqueous phase was investigated in the transdermal delivery of the local anesthetics lidocaine free base, lidocaine-hydrochloride (HCl), and prilocaine-HCl. Lidocaine free-base flux increased from H2O/NMP binary systems containing over 50% (v/v) NMP with significant flux enhancement observed above 80% NMP. In this range, drug flux was found to correlate with NMP flux. The addition of oleic acid (1% w/v) further enhanced lidocaine flux sixfold, in these formulations. The H2O/NMP (50% v/v) system enhanced the transport of water-soluble hydrochloride salt derivatives of lidocaine and prilocaine by factors of 4.3 and 2.6, respectively, indicating that NMP was capable of enhancing hydrophilic and hydrophobic drugs from an aqueous phase. These findings were consistent with the model that NMP flux across the stratum corneum improves the transport of formulation solutes.

Administration, Cutaneous↗
PubMed2005

Evidence for motor axon depolarization in Fabry disease.

To investigate the pathophysiology of neuropathy in Fabry disease, multiple nerve excitability properties of median motor axons in 20 patients with this disorder but without hyperkalemia were compared with 35 age-matched normal controls. In the patients, depolarizing threshold electrotonus was reduced (P < 0.0001) and superexcitability was reduced (P < 0.001), but late subexcitability was normal. These findings indicate that the axons were mildly depolarized, probably due to ischemia, and are consistent with the hypothesis that poor nerve perfusion in Fabry disease contributes to axonal damage.

Action Potentials↗
PubMed2004

A novel high aspect ratio microfluidic design to provide a stable and uniform microenvironment for cell growth in a high throughput mammalian cell culture array.

We present a high aspect ratio microfluidic device for culturing cells inside an array of microchambers with continuous perfusion of medium. The device was designed to provide a potential tool for cost-effective and automated cell culture. The single unit of the array consists of a circular microfluidic chamber 40 microm in height surrounded by multiple narrow perfusion channels 2 microm in height. The high aspect ratio (approximately 20) between the microchamber and the perfusion channels offers advantages such as localization of the cells inside the microchamber as well as creating a uniform microenvironment for cell growth. Finite element methods were used to simulate flow profile and mass transfer of the device. Human carcinoma (HeLa) cells were cultured inside the device with continuous perfusion of medium at 37 degrees C and was grown to confluency. The microfluidic cell culture array could potentially offer an affordable platform for a wide range of applications in high throughput cell-based screening, bioinformatics, synthetic biology, quantitative cell biology, and systems biology.

Cell Culture Techniques↗
PubMed2003

The regulation of growth in glycogen storage disease type 1.

OBJECTIVE: To study endocrine and metabolic variables that affect growth in patients with glycogen storage disease type 1 (GSD-1) receiving standard dietary therapy. DESIGN: Observational study. PATIENTS AND MEASUREMENTS: Thirty-eight patients with GSD-1, age range 0.6-32.9 years, were investigated on their usual dietary regimens. Data on height, height velocity in prepubertal children, endocrine and metabolic responses to oral glucose load, 24-h serum cortisol and GH concentration profiles and serum IGF-1 concentrations were collected. RESULTS: The population studied was shorter than average, with a median height standard deviation score (SDS) of -1.60, but significantly taller than a historical population studied at the same institution that had not received dietary therapy at the time of study. A wide range of height SDS was encountered (-5.28 to 1.21) and a subset still exhibit marked growth failure. Median body mass index (BMI) SDS was 0.72 (range -1.34 to 3.96). Those patients with the greatest BMI SDS had the lowest serum GH concentrations but serum IGF-1 concentrations were within the normal range. Patients with the poorest growth exhibit low serum insulin concentration responses to glucose load, GH insensitivity and higher mean 24-h plasma cortisol levels when compared to those patients who were better grown. CONCLUSION: This study shows that overall the growth of this group of patients with glycogen storage disease type 1 has improved compared to that of a historical control group. There remains a subset of this population with poor growth despite therapy. The measured endocrine responses in this subset are similar to those reported for untreated patients. To improve the growth further in these individuals it will be necessary to understand whether this is failure of prescribed therapy or failure to comply with therapy.

Adolescent↗
PubMed2003

Maternal phenylketonuria: experiences from the United Kingdom.

Charles Dent was one of the first physicians to recognize the teratogenic effects of maternal phenylalanine (Phe) on the fetus in 1956. This article describes the clinical experiences of women with phenylketonuria (PKU) within the unit that was established by Dent in the United Kingdom. Between 1977 and 2002, 79 infants were born to women with PKU. Of the 79, 18 (23%) were conceived while the women were on a normal diet with high blood Phe levels. The mean birth weight was 2.89 kg, and head circumference was 32.8 cm. At 1 year, the mean developmental quotient was 105.5 and at 4 years was 82.3. Four of these infants had congenital heart disease (2 of whom died as a result). In the remaining 61 infants, Phe-restricted diet started before conception. None of them had congenital heart disease. The mean birth weight was 3.23 kg, and head circumference was 34.0 cm. At 1 year, mean developmental quotient was 108.0 and at 4 years was 90.9. They continue to be followed up with additional neuropsychometric assessments at 8 and 14 years of age. This cohort is a proportion of infants who were born to mothers with PKU in the United Kingdom. Between 1978 and 1997, 255 live births were reported. Of these, 56% were conceived on unrestricted diet with subsequently poor outcome. This relatively high rate of conception off PKU diet is likely to reflect the scarcity of medical services for adults with metabolic disorders. We conclude that many features of the maternal PKU syndrome can be prevented but still occur because of the lack of appropriate resources to care for at-risk women. The precise targets for blood Phe and other nutrients during pregnancy are not entirely clear, neither are the reasons that some offspring are spared the harmful effects of Phe. The impact of the postnatal environment in which these infants find themselves requires additional assessment, too.

Birth Weight↗
PubMed2002

Glycogen storage disease type I: pathophysiology of liver adenomas.

UNLABELLED: Of the many complications associated with glycogen storage disease type I, hepatic tumours cause great concern because of their malignant potential and the current difficulties in monitoring them. Hepatic adenomas occur in 22%-75% of affected adults, according to the population studied, and from those reported in the literature are thought to have an approximately 10% risk of undergoing malignant transformation. Their aetiology is unclear, but they occur generally in post-pubertal patients, and can be either single or multiple. This article discusses theories of their aetiology, methods of detection and monitoring, and treatment options. CONCLUSION: the incidence of liver tumours in younger adults seems less than in older ones, suggesting that better dietary treatment, and thus improved metabolic control, may be protective. Surgery (partial hepatectomy or orthotopic liver transplantation) is the definitive therapy for these tumours, but the timing of this intervention is difficult to determine and it is not without its own hazards.

Adenoma↗
PubMed2002

Utilization of cornstarch in glycogen storage disease type Ia.

OBJECTIVE: Uncooked cornstarch (UCCS) is used widely for the treatment of patients with glycogen storage disease type I (GSD-I). Previous studies suggested that glucose absorption may be impaired in GSD-I. In order to measure utilization of UCCS in young adults with GSD-Ia and healthy controls, we used a C-breath test based on the natural enrichment of C in UCCS. DESIGN: Open, not randomized, prospective interventional study. METHODS: Following 1 g/kg UCCS, we studied eight subjects with GSD-Ia (7 males, 1 female; mean age 28.3 years, range 16-42 years) and 15 healthy controls (10 males, 5 females; mean age 23.5 years, range 19-36 years). Breath samples for analysis of CO enrichment were collected at baseline and at 30-min intervals for 6 h or until hypoglycaemia occurred. Indirect calorimetry was used to measure respiratory gas exchange. Intermediate metabolites, lipids and glucose were measured in plasma. Breath H concentrations were measured as an indicator of malabsorption. RESULTS: Cumulative utilization over 6 h was significantly higher in controls (18.35 +/- 6.2% of total carbohydrate intake) than in subjects with GSD-Ia (11.5 +/- 4.7%) (P < 0.02). However, utilization of UCCS was virtually identical up to 2.5 h. Two subjects with GSD-Ia fulfilled the criteria for malabsorption. CONCLUSIONS: Starch digestion and absorption are not impaired in GSD-Ia. However, overall utilization of UCCS appears to be lower in GSD-Ia, which is most likely secondary to perturbed intermediary metabolism. There are important implications for treatment of this disorder. Ways to improve the efficacy of UCCS in GSD-I are needed.

Adolescent↗
PubMed2002

Urinary megalin deficiency implicates abnormal tubular endocytic function in Fanconi syndrome.

Normal reabsorption of glomerular filtrate proteins probably requires recycling of the endocytic receptors megalin (gp330) and cubilin. Both receptors are located on the luminal surface of the renal proximal tubule epithelium. Whether abnormal amounts of receptor are present in the urine of patients with Dent's disease, Lowe's syndrome, or autosomal dominant idiopathic Fanconi syndrome was explored. They are all forms of the renal Fanconi syndrome and are associated with tubular proteinuria. Urine samples of equal creatinine contents were dialyzed, lyophilized, and subjected to electrophoresis on nonreducing sodium dodecyl sulfate-5% polyacrylamide gels. Proteins were blotted and probed with anti-megalin IgG, anti-cubilin IgG, or receptor-associated protein. Megalin and cubilin levels detected by immunochemiluminescence were measured as integrated pixels and expressed as percentages of the normal mean values. A striking deficiency of urinary megalin, compared with normal individuals (n = 42), was observed for eight of nine families with Dent's disease (n = 10) and for the two families with Lowe's syndrome (n = 3). The family with autosomal dominant idiopathic Fanconi syndrome (n = 2) exhibited megalin levels within the normal range. The measured levels of cubilin were normal for all patients. These results are consistent with defective recycling of megalin to the apical cell surface of the proximal tubules and thus decreased loss into urine in Dent's disease and Lowe's syndrome. This defect would interfere with the normal endocytic function of megalin, result in losses of potential ligands into the urine, and produce tubular proteinuria.

Endocytosis↗