Sanjoy Dutta

Pdx1 restores β cell function in Irs2 knockout mice

The homeodomain transcription factor Pdx1 is required for pancreas development, including the differentiation and function of beta cells. Mutations in Pdx1 or upstream hepatocyte nuclear factors cause autosomal forms of early-onset diabetes (maturity-onset diabetes of the young [MODY]). In mice, the Irs2 branch of the insulin/Igf signaling system mediates peripheral insulin action and pancreatic beta cell growth and function. To investigate whether beta cell failure in Irs2(-/-) mice might be related to dysfunction of MODY-related transcription factors, we measured the expression of Pdx1 in islets from young Irs2(-/-) mice. Before the onset of diabetes, Pdx1 was reduced in islets from Irs2(-/-) mice, whereas it was expressed normally in islets from wild-type or Irs1(-/-) mice, which do not develop diabetes. Whereas male Irs2(-/-)Pdx1(+/+) mice developed diabetes between 8 and 10 weeks of age, haploinsufficiency for Pdx1 caused diabetes in newborn Irs2(-/-) mice. By contrast, transgenic expression of Pdx1 restored beta cell mass and function in Irs2(-/-) mice and promoted glucose tolerance throughout life, as these mice survived for at least 20 months without diabetes. Our results suggest that dysregulation of Pdx1 might represent a common link between ordinary type 2 diabetes and MODY.

Regulatory factor linked to late-onset diabetes?

Maintenance of glucose balance in mammals depends on the production of insulin by the β-cells of the pancreas, in response to raised concentrations of blood glucose. In humans suffering from non-insulindependent diabetes (NIDDM), β-cell failure follows chronic resistance to insulin-stimulated glucose uptake and causes the development of hyperglycaemia. NIDDM shows a polygenic inheritance pattern in most cases: defined genetic defects that have little effect on their own, in combination induce diabetes by epistatic interactions. Here we show that mice heterozygous for the gene pdx-1, which encodes a transcription factor for the insulin gene and regulates pancreatic development, have impaired glucose tolerance. This pancreatic nuclear regulatory factor is required for glucose homeostasis even when the pancreas is morphologically normal.

Prolonged Regional Nerve Blockade by Controlled Release of Local Anesthetic from a Biodegradable Polymer Matrix

Background:Prolonged nerve blockade is potentially useful in the management of many acute and chronic pain problems. Aside from infusions via an indwelling catheter, most currently available nondestructive techniques for prolonging local anesthetic action cannot provide more than 1–2 days of blockade. Bioerodible polymer matrixes have been used to deliver a variety of drugs in patients and animals for periods lasting weeks to years. Previously, dibucaine and bupivacaine were incorporated into copolymers of 1,3 bis(p-carboxyphenoxy) propane-sebacic acid anhydride (1:4), and demonstrated sustained release in vitro following incubation of the drug-polymer matrixes in phosphate-buffered solution (pH 7.4, 37° C). Methods:In the present study, cylindrical pellets made from polymer matrixes incorporated with buplvacaine-HCl were implanted surgically along the sciatic nerves of rats. Neural block was assessed by direct observation of motor skills and by leg-withdrawal latency to a hot surface. Biochemical and hlstologic examinations were performed 2 weeks after implantation. Results:Sensory and motor blockade was produced for periods ranging from 2 to 6 days. Contralateral control legs receiving polymer implants without drug showed no block. Blockade was reversible, and animals appeared to recover sensory and motor function normally. Biochemical indexes of nerve and muscle function were indistinguishable from contralateral controls. Conclusions:This biodegradable polymer system provides a promising new alternative for the delivery of local anesthetics to peripheral nerves to produce prolonged blockade for the management of acute and chronic pain.

Pbx-Hox Heterodimers Recruit Coactivator-Corepressor Complexes in an Isoform-Specific Manner

ABSTRACT Homeobox (hox) proteins have been shown to regulate cell fate and segment identity by promoting the expression of specific genetic programs. In contrast to their restricted biological action in vivo, however, most homeodomain factors exhibit promiscuous DNA binding properties in vitro, suggesting a requirement for additional cofactors that enhance target site selectivity. In this regard, thepbx family of homeobox genes has been found to heterodimerize with and thereby augment the DNA binding activity of certain hox proteins on a subset of potential target sites. Here we examine the transcriptional properties of a forcedhox-pbx heterodimer containing the pancreas-specific orphan homeobox factor pdx fused to pbx-1a. Compared to the pdx monomer, the forced pdx-pbx1a dimer, displayed 10- to 20-fold-higher affinity for a consensushox-pbx binding site but was completely unable to bind ahox monomer recognition site. The pdx-pbx dimer stimulated target gene expression via an N-terminaltrans-activation domain in pdx that interacts with the coactivator CREB binding protein. The pdx-pbxdimer was also found to repress transcription via a C-terminal domain in pbx-1a that associates with the corepressors SMRT and NCoR. The transcriptional properties of the pdx-pbx1complex appear to be regulated at the level of alternative splicing; apdx-pbx polypeptide containing the pbx1bisoform, which lacks the C-terminal extension in pbx1a, was unable to repress target gene expression via NCoR-SMRT. Sincepbx1a and pbx1b are differentially expressed in endocrine versus exocrine compartments of the adult pancreas, our results illustrate a novel mechanism by which pbx proteins may modulate the expression of specific genetic programs, either positively or negatively, during development.

Sustained local anesthetic release from bioerodible polymer matrices: a potential method for prolonged regional anesthesia.

Polyanhydride polymer matrices have been used successfully for sustained release of a number of drugs in vitro and in vivo. Dibucaine free base, dibucaine HC1, and bupivacaine HC1 were incorporated into polymer matrices with copolymer l,3-bis(p-carboxyphenoxy)propane-sebacic acid anhydride (1:4). Drug release was measured in vitro following incubation of the drug-polymer matrices in phosphate buffered solution, pH 7.4, at 37°C, to approximate in vivo conditions. Local anesthetics were released in a sustained manner yielding 90% cumulative drug release over periods ranging from 3 to 14 days. The kinetics of release varied with both the choice of local anesthetic and the method of drug incorporation into the matrix (hot melt versus compression molding). Polymer local anesthetic matrix devices (PLAM), loaded by hot melt incorporation with 20% bupivacaine, were implanted in vivo adjacent to the sciatic nerve in three rats. Reversible neural blockade was observed for 4 days in all animals. Polymer implants without local anesthetic showed no neural blockade. This technology could lead to methods of prolonged blockade of peripheral nerves or of sympathetic ganglia, which may be utilized for the management of postoperative pain, sympathetically maintained pain, or certain forms of chronic pain.

Glucose-responsive insulin by molecular and physical design

Glucose-responsive insulin is a therapeutic that modulates its potency, concentration or dosing relative to a patient’s dynamic glucose concentration. This Perspective summarizes some of the recent accomplishments in this field as well as discussing new computational algorithms that may aid in the development of such therapeutics. The concept of a glucose-responsive insulin (GRI) has been a recent objective of diabetes technology. The idea behind the GRI is to create a therapeutic that modulates its potency, concentration or dosing relative to a patients dynamic glucose concentration, thereby approximating aspects of a normally functioning pancreas. From the perspective of the medicinal chemist, the GRI is also important as a generalized model of a potentially new generation of therapeutics that adjust potency in response to a critical therapeutic marker. The aim of this Perspective is to highlight emerging concepts, including mathematical modelling and the molecular engineering of insulin itself and its potency, towards a viable GRI. We briefly outline some of the most important recent progress toward this goal and also provide a forward-looking viewpoint, which asks if there are new approaches that could spur innovation in this area as well as to encourage synthetic chemists and chemical engineers to address the challenges and promises offered by this therapeutic approach.

Erratum: Glucose-responsive insulin by molecular and physical design

This corrects the article DOI: 10.1038/nchem.2857.