Prediction of subcutaneous drug absorption - Characterization of subcutaneous interstitial fluids as a basis for developing biorelevant in vitro models.

Unlike orally administered drugs, the absorption profile of subcutaneously injectable drugs in humans is difficult to predict from preclinical studies. Since the subcutaneous interstitial fluid (ISF) is the first fluid interacting with the administered formulation before the respective drug is absorbed, it could critically affect bioavailability. The aim of the present study was to gain a better understanding of the similarities and differences of ISF of different species.

Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency.

Protein catabolism ultimately yields toxic ammonia, which must be converted to urea by the liver for renal excretion. In extrahepatic tissues, ammonia is temporarily converted primarily to glutamine for subsequent hepatic extraction. Urea cycle disorders (UCDs) are inborn errors of metabolism causing impaired ureagenesis, leading to neurotoxic accumulation of ammonia and brain glutamine.

Comparison of Microflow and Analytical Flow Liquid Chromatography Coupled to Mass Spectrometry Global Metabolomics Methods Using a Urea Cycle Disorder Mouse Model.

Microscale-based separations are increasingly being applied in the field of metabolomics for the analysis of small-molecule metabolites. These methods have the potential to provide improved sensitivity, less solvent waste, and reduced sample-size requirements. Ion-pair free microflow-based global metabolomics methods, which we recently reported, were further compared to analytical flow ion-pairing reagent containing methods using a sample set from a urea cycle disorder (UCD) mouse model.

A systematic approach to development of analytical scale and microflow-based liquid chromatography coupled to mass spectrometry metabolomics methods to support drug discovery and development.

As the reliance on metabolic biomarkers within drug discovery and development increases, there is also an increased demand for global metabolomics methods to provide broad metabolome coverage and sensitivity towards differences in metabolite expression and reproducibility. A systematic approach is necessary for the development, and evaluation, of metabolomics methods using either conventional techniques or when establishing new methods that allow for additional gains in sensitivity and a reduction in requirements for amounts of a biological sample, such as those seen with methods based on microseparations. We developed a novel standard mixture and used a systematic approach for the development and optimization of optimal, ion-pair free, liquid chromatography-mass spectrometry (LC-MS) global profiling methods.

Inhibiting neutral amino acid transport for the treatment of phenylketonuria.

The neuropathological effects of phenylketonuria (PKU) stem from the inability of the body to metabolize excess phenylalanine (Phe), resulting in accumulation of Phe in the blood and brain. Since the kidney normally reabsorbs circulating amino acids with high efficiency, we hypothesized that preventing the renal uptake of Phe might provide a disposal pathway that could lower systemic Phe levels. SLC6A19 is a neutral amino acid transporter responsible for absorption of the majority of free Phe in the small intestine and reuptake of Phe by renal proximal tubule cells.

Erythrocytes encapsulated with phenylalanine hydroxylase exhibit improved pharmacokinetics and lowered plasma phenylalanine levels in normal mice.

Enzyme replacement therapy is often hampered by the rapid clearance and degradation of the administered enzyme, limiting its efficacy and requiring frequent dosing. Encapsulation of therapeutic molecules into red blood cells (RBCs) is a clinically proven approach to improve the pharmacokinetics and efficacy of biologics and small molecule drugs. Here we evaluated the ability of RBCs encapsulated with phenylalanine hydroxylase (PAH) to metabolize phenylalanine (Phe) from the blood and confer sustained enzymatic activity in the circulation.

Analysis of creatinine in mouse and rat serum by ion exchange high performance liquid chromatography for in vivo studies of renal function.

An ion exchange high performance liquid chromatography method was developed for determining creatinine levels in both mouse and rat serum samples. Separation of creatinine from other serum components was achieved in 10 min using a 100 x 4.1-mm, 10 microm strong cation exchange column following acetonitrile precipitation of serum proteins.

Separation of quaternary ammonium diastereomeric oligomers by capillary electrophoresis.

The separation of novel diastereomeric trimers (3M) and pentamers (5M), derived from quaternary ammonium salts, was studied in conventional, uncoated and coated capillaries using capillary zone electrophoresis (CZE) with a variety of buffers and additives. Resolution of 5M diastereomers was best achieved using gamma-cyclodextrin (gamma-CD) as a chiral selector, while no diastereomeric resolution was realized for the 3M material.