Use of the abdominal aorta for arterial input function determination in hepatic and renal PET studies.

A method using the activity in the abdominal aorta of human and animal subjects to noninvasively estimate blood-pool input function in dynamic, abdominal PET scans is proposed and validated in this paper. Partial volume effects due to the aorta's dimensions are corrected by a semi-automated algorithm based on the transaxial resolution in the reconstructed images. The technique was validated by comparing PET measurements of abdominal aortic activity to well counter measurements of arterial blood samples (eight canine renal studies) and to PET measurements of left ventricular cavity activity (eight human hepatic studies). In renal studies, correlation analysis of the areas subtended by the two input functions yielded an essentially unitary slope (1.03 +/- 0.09), with high correlation (R2 greater than 0.95, p less than 0.001). In hepatic studies, similar values (0.99 +/- 0.03 and R2 greater than 0.85, p less than 0.001) were found. Correlation of the blood flow estimates based on the two input functions and a two-compartment model produced slopes of 1.07 +/- 0.16 and 1.03 +/- 0.07, and correlations of (R2 greater than 0.98, p less than 0.001) and (R2 greater than 0.97, p less than 0.001) for the renal and hepatic studies, respectively. We conclude that noninvasive, accurate measurements of the arterial input function by dynamic PET imaging are possible and represent a clinically viable alternative to arterial blood sampling.     

Combination of ABO blood group incompatibility and glucose-6-phosphate dehydrogenase deficiency: effect on hemolysis and neonatal hyperbilirubinemia

The incidence (%) of hyperbilirubinemia (serum bilirubin ≥257 μmol/l) was similar in neonates with a combination of ABO incompatibility and glucose-6-phosphate dehydrogenase (G-6-PD) deficiency (45%), with ABO incompatibility (54%) or G-6-PD deficiency (37%), alone (ns). Carboxyhemoglobin values, corrected for inspired CO, were similarly elevated in all three groups (0.87 ± 0.32%, 0.82 ± 0.29%, 0.76 ± 0.18%, respectively, ns), but correlated with bilirubin only in those with ABO incompatibility alone. ABO-incompatible/G-6-PD-deficient neonates, compared with those with either condition alone, are not at increased risk for hemolysis or hyperbilirubinemia.     

Development of a novel class of cyclic hexapeptide oxytocin antagonists based on a natural product.

A new structural class of cyclic hexapeptide oxytocin antagonists derived from Streptomyces silvensis and typified by L-365,209 (cyclo-[L-prolyl1-D-phenylalanyl2-L- isoleucyl3-D-dehydropiperazyl4-L-dehydroperazyl5-D-(N- methyl)phenylalanyl6]) was recently reported. In this paper we further delineate the structure-activity profile for this new class by systematic study of L-365,209 analogs obtained by total synthesis. The optimal combination of cyclic amino acid ring sizes at positions 1, 4, and 5 and the role of the N-alkyl substituent at position 6 was elucidated. The lipophilic amino acids at positions 2 and 3 and the unusual amino acid D-dehydropiperazic acid at position 4 were found to be the most critical residues for obtaining good oxytocin receptor affinity. Analogs containing a basic side chain at the less critical 5- and 6-positions maintained good receptor affinity and also had useful levels of water solubility for intravenous formulation. By combining potency- and solubility-enhancing substitutions, several analogs were identified that have the desired combination of properties in vitro (22, cyclo-[L-prolyl-D-tryptophanyl-L-isoleucyl-D-pipecolyl-L-pipeco lyl-D- histidyl]; 25, cyclo-[L-prolyl-D-2-naphthylalanyl-L-isoleucyl-D-pipecolyl-L -pipecolyl-D- histidyl]; 26, cyclo-[L-prolyl-D-tryptophanyl-L-isoleucyl-D-dehydropiperazyl-L-++ pipecolyl-D-histidyl]; 33, cyclo-[L-prolyl-D-tryptophanyl-L-isoleucyl-D-pipecolyl-L- piperazinylcarboxy-D-(N-methyl)phenylalanyl]; 34, cyclo-[L-prolyl-D-phenylalanyl-L-isoleucyl-D-dehydropiperazyl-L-or nithyl- D-(N-methyl)phenylalanyl]). In general, this class exhibited good selectivity for binding to the oxytocin receptor versus the arginine vasopressin V1a and V2 receptor subtypes, although increased V2 receptor affinity was observed in one case (32, cyclo[L-prolyl-D-2-naphthylalanyl-L-isoleucyl-D-pipecolyl-L- lysyl-D-(N- methyl)phenylalanyl]). Unexpectedly, compound 33 was found to stimulate contractions of the isolated rat uterus via activation of the uterine bradykinin receptor. Compounds 22, 25, 26, 33, and 34 were found to be potent antagonists of oxytocin-stimulated contraction of the rat uterus in vitro and in vivo. Compounds 22 and 25 were additionally characterized as potent antagonists of oxytocin-stimulated uterine contractions in the near-term pregnant rhesus monkey. These studies thus demonstrate the selectivity and efficacy of certain members of this novel class of antagonists and suggest their use as pharmacological tools in further defining the role of oxytocin in both term and preterm labor.     

One-stage repair of the anterior abdominal wall using bilateral rectus femoris myocutaneous flaps

Total lower abdominal wall resection was required to remove a recurrent exophytic bladder carcinoma in a 36-year-old woman. The resulting 25 x 30-cm fascial defect was repaired with Marlex mesh. Bilateral rectus femoris myocutaneous flaps were rotated to close the 25 x 18-cm area of skin deficiency. These provided the advantages of robust cover of the lower abdominal wall in a single-stage procedure and primary closure of the donor sites.     

Operative strategy for recurrent laryngeal cleft: a case report and review of the literature

A case is reported of recurrent laryngotracheoesophageal cleft following two attempted repairs. The anterior approach to the larynx and trachea provided excellent exposure for defining the extent of the recurrent cleft, and allowed precise anatomic repair. Neurovascular structures were easily avoided by this operative method. Of 170 clefts reported in the literature, 19 recurred necessitating reoperation. The anterior approach to the larynx and trachea is appropriate in recurrent clefts and may be preferable at the initial repair.     

Topically active carbonic anhydrase inhibitors. 1. O-acyl derivatives of 6-hydroxybenzothiazole-2-sulfonamide

A series of O-acyl derivatives of 6-hydroxybenzothiazole-2-sulfonamide (4, L-643,799) was prepared and the potential utility of each series member as a topically active inhibitor of ocular carbonic anhydrase was determined. In vitro studies showed these esters to be substrates for ocular esterases which liberate 4 during corneal translocation. The most interesting series member, 2-sulfamoyl-6-benzothiazolyl 2,2-dimethylpropionate (22, L-645,151), acting as a prodrug form of 4, was found to enhance delivery through the isolated albino rabbit cornea by 40-fold when compared to the parent phenol 4. Studies in rabbits revealed that 22 is a potent topically active ocular hypotensive carbonic anhydrase inhibitor.     

Immobilization and characterization of beta-galactosidase in thermally reversible hydrogel beads

Beta-Galactosidase has been immobilized within thermally reversible hydrogel beads and has been studied in batch and packed bed reactor systems. The enzyme was entrapped in a copolymer hydrogel of N-isopropylacrylamide (NIPAAm) and acrylamide (AAm) as beads were formed in an inverse suspension polymerization. A reversible deswelling and reswelling of the hydrogel matrix was induced by first warming and then cooling through 37-40 degrees C, which is the lower critical solution temperature, LCST, of the backbone copolymer. The optimum temperature for maximum activity of the immobilized enzyme-gel bead system was found to be 30-35 degrees C in a batch mode and 40 degrees C in a packed bed reactor, which were both below the 50 degrees C optimum for the free enzyme. These differences are understandable, since the mass transfer rates of substrate and product within the pores of the gel matrix are controlled mainly by the temperature, so therefore it is the temperature which governs the overall activity of the immobilized enzyme system. It was also found that when the operational temperature in the packed bed reactor was cycled between temperatures below (35 degrees C) and above (45 degrees C) the copolymer gel LCST, the activity of the immobilized enzyme almost fully recovered after each cycle. In fact, the enzyme-gel system exhibited a complete "shut-off" in activity at 50 degrees C which was the temperature where the free enzyme showed its maximum activity. The thermal cycling operation of LCST enzyme-gel beads can be used to enhance overall activity and productivity of a packed bed reactor, when compared to isothermal operation of this reactor. This is due to the thermally induced "pumping" which enhances mass transfer rates of substrate in and product out of the gel beads.     

Present and emerging applications of polymeric biomaterials

An important trend in biomaterials research and development is the synthesis of polymers, which combine capabilities of biologic recognition ('biomimetic') with special physicochemical properties of the synthetic polymer system. For example, an antibody may be conjugated to the backbone of a polymer which precipitates upon small changes in pH, temperature, or ionic strength. Crosslinked gels may also be synthesized from such polymers, and a biomolecule such as an enzyme may be chemically or physically entrapped in these gels. Such gels will shrink and swell in response to small changes in environmental stimuli. Another approach is to 'engineer', perhaps via computer-aided molecular design, new artificial biomimetic systems by exact placement of functional groups on rigid polymer backbones, crosslinked structures, or macromolecular assemblies. In this way, biocatalytic functioning or biorecognition similar to enzymes and antibodies can be achieved without the inherent instability often encountered with the native biomolecules or assemblies. In addition to these synthetic approaches, new and exciting analytical tools, such as the scanning tunnelling microscope and the atomic force microscope, are permitting visualization of individual and small clusters of proteins and other biomolecules on surfaces. Cell attachments and spreading may also be visualized at various depths within the cell using the confocal laser microscope. Such analytical techniques can lead to important new knowledge about biologic interactions with biomaterials, and, therefore, to development of even more biocompatible implants and devices. This paper overviews the field of polymeric biomaterials and highlights the important emerging trends in synthesis and analysis of these materials.