Open flow microperfusion: pharmacokinetics of human insulin and insulin detemir in the interstitial fluid of subcutaneous adipose tissue.

AIMS: To compare the time profile of insulin detemir and human insulin concentrations in the interstitial fluid (ISF) of subcutaneous adipose tissue during constant i.v. infusion and to investigate the relationship between the pharmacokinetics of both insulin molecules in plasma and the ISF of subcutaneous adipose tissue. METHODS: During a 6-h hyperinsulinaemic-euglycaemic clamp (plasma glucose level 8 mmol/l) human insulin (21 and 42 pmol/min/kg) or insulin detemir (209 and 417 pmol/min/kg) were infused i.v. in eight rats per dose level. Open flow microperfusion (OFM) was used to continuously assess interstitial insulin concentrations in subcutaneous adipose tissue. RESULTS: At the lower infusion rate, insulin detemir appeared significantly later in the ISF than in the plasma (p < 0.05) and also appeared later in the ISF relative to human insulin (p < 0.005). CONCLUSIONS: By using OFM we were able to monitor albumin-bound insulin detemir directly in the ISF of subcutaneous tissue and confirm its delayed transendothelial passage to a peripheral site of action.

Structure-based design of a low molecular weight, nonphosphorus, nonpeptide, and highly selective inhibitor of protein-tyrosine phosphatase 1B.

Several protein-tyrosine phosphatases (PTPs) have been proposed to act as negative regulators of insulin signaling. Recent studies have shown increased insulin sensitivity and resistance to obesity in PTP1B knockout mice, thus pointing to this enzyme as a potential drug target in diabetes. Structure-based design, guided by PTP mutants and x-ray protein crystallography, was used to optimize a relatively weak, nonphosphorus, nonpeptide general PTP inhibitor (2-(oxalyl-amino)-benzoic acid) into a highly selective PTP1B inhibitor. This was achieved by addressing residue 48 as a selectivity determining residue. By introducing a basic nitrogen in the core structure of the inhibitor, a salt bridge was formed to Asp-48 in PTP1B. In contrast, the basic nitrogen causes repulsion in other PTPs containing an asparagine in the equivalent position resulting in a remarkable selectivity for PTP1B. Importantly, this was accomplished while retaining the molecular weight of the inhibitor below 300 g/mol.

2-(oxalylamino)-benzoic acid is a general, competitive inhibitor of protein-tyrosine phosphatases.

Protein-tyrosine phosphatases (PTPs) are critically involved in regulation of signal transduction processes. Members of this class of enzymes are considered attractive therapeutic targets in several disease states, e.g. diabetes, cancer, and inflammation. However, most reported PTP inhibitors have been phosphorus-containing compounds, tight binding inhibitors, and/or inhibitors that covalently modify the enzymes. We therefore embarked on identifying a general, reversible, competitive PTP inhibitor that could be used as a common scaffold for lead optimization for specific PTPs. We here report the identification of 2-(oxalylamino)-benzoic acid (OBA) as a classical competitive inhibitor of several PTPs. X-ray crystallography of PTP1B complexed with OBA and related non-phosphate low molecular weight derivatives reveals that the binding mode of these molecules to a large extent mimics that of the natural substrate including hydrogen bonding to the PTP signature motif. In addition, binding of OBA to the active site of PTP1B creates a unique arrangement involving Asp(181), Lys(120), and Tyr(46). PTP inhibitors are essential tools in elucidating the biological function of specific PTPs and they may eventually be developed into selective drug candidates. The unique enzyme kinetic features and the low molecular weight of OBA makes it an ideal starting point for further optimization.