Visualizing Drug Efficacy In Vivo

Many enzymes are therapeutic targets for drug discovery, whereas other enzymes are important for understanding drug metabolism and pharmacokinetics during compound testing in animals. Testing of drug efficacy and metabolism in an animal model requires the measurement of disease endpoints as well as assays of enzyme activity in specific tissues at selected time points during treatment. This requires the removal of tissue and biochemical assays. Techniques to noninvasively assess drug effects on enzyme activity using imaging technology would facilitate understanding of drug efficacy, pharmacokinetics, and drug metabolism. Using a commercially available cytochrome P−450 3A substrate whose oxidized product is a luciferase substrate, we show for the first time that cytochrome P−450 enzyme activity can be measured in vivo in real time by bioluminescent imaging. This imaging approach could be applicable to study drug effects on therapeutic target enzymes, as well as drug metabolism enzymes.

Prevention and cure of complications from multiple-electrode radiofrequency treatment of liver tumors

BACKGROUND/AIMS

To determine the complication rate of multiple-electrode radiofrequency treatment of liver tumors, and their prevention and cure.

METHODS

114 patients with liver tumors were treated 170 times using multiple-electrode radiofrequency. The clinical complications and their prevention and cure were observed.

RESULTS

The complication rate was 9.6%. The complications included 1 case of colon perforation, 4 cases of skin burn, 5 cases of hydrothorax, and 1 case subcutaneous hemorrhage, but none of the patient died due to these complications.

CONCLUSION

The complication rate of multiple-electrode radiofrequency treatment of liver tumors is low and the complications could be prevented and cured.

Advanced glycation end products induce apoptosis and procoagulant activity in cultured human umbilical vein endothelial cells

Hyperglycemia and the late products of non-enzymatic glycosylation, called advanced glycation end products (AGEs), play an important role in the development of microvascular complications in diabetes mellitus. Previous studies have reported that a high glucose environment triggered apoptotic changes in human umbilical vein endothelial cells (HUVECs). Therefore, we investigated whether AGEs contribute to the development of apoptosis and prothrombotic activity in HUVECs. After incubation of HUVECs with 0.2, 2.2, 22, 220 and 2200 nM of AGE-bovine serum albumin (BSA) from 6 to 48 h, we assayed the degree of apoptosis and procoagulant activity (PCA). There were no significant differences between HUVECs cultured for 48 h with 0.2, 2.2 or 22 nM of AGE-BSA and in controls in the proportion of apoptotic cells (3.5 +/- 0.8%, 3.9 +/- 1.5% and 5.2 +/- 1.1% vs. 2.5 +/- 0.6%). However, the proportion of apoptotic cells increased significantly to 36.7 +/- 9.8% in 220 nM of AGE-BSA, and 72.3 +/- 10.2% in 2200 nM of AGE-BSA (P < 0.001). PCA levels were 142 +/- 10 s after 6 h of exposure to 22 nM (P < 0.01), 131 +/- 5 s after 6 h of exposure to 220 nM (P < 0.001), and 106 +/- 4 s after 6 h of exposure to 2200 nM of AGE-BSA (P < 0.001). These values show that PCA was shortened significantly from the basal value of 161 +/- 6 s, and remained below the basal level until the end of the study. The amount of tissue factor was also significantly increased in 22 and 220 nM of AGE-BSA compared to the controls. In conclusion, this study showed that AGEs could induce apoptosis and increase procoagulant activity in cultured HUVECs. We suggest that AGEs can contribute to the development of microvascular complications through cell death of HUVECs and functional changes of the blood vessels.

Immobilized metal affinity chromatography of DNA

Many of the most widely employed operations in molecular biology hinge upon the use of single-stranded DNA as a probe or template. Here we report a straightforward method by which to produce long single-stranded DNA molecules using the polymerase chain reaction (PCR) in combination with immobilized metal affinity chromatography (IMAC). We demonstrate that a tag consisting of six successive 6-histaminylpurine (H) residues (H6-tag) endows a DNA strand with selective retentivity onto a Ni2+-NTA-agarose chromatography matrix. The H6-tagged strand can then be eluted from the resin using 200 mM imidazole. Quantitative phosphorimaging analysis revealed that the PCR/IMAC procedure typically yields unmodified strands comprising >90% of the unbound DNA and H6-tagged strands comprising >95% of the bound fractions. DNA strands generated in this manner are shown to be excellent substrates for template-directed polymerization. The chemistry reported herein should facilitate a wide variety of operations in molecular biology, including automated DNA sequencing, hybridization screening of DNA libraries, assembly of gene cassettes, run-off transcription, site-directed mutagenesis and footprinting of protein-DNA complexes by template-directed interference footprinting.

Membrane-based, dry-reagent prothrombin time tests

The authors describe a prototype membrane-based, dry-reagent prothrombin time assay for whole blood. This system uses an asymmetric polysulfone membrane to separate plasma from red blood cells, and works with samples as small as 10 microliters. The membrane contains calcium and thromboplastin, and permits the reactions of the complete extrinsic pathway to occur with minimal distortion from membrane surface interactions. Thrombin generation is monitored optically using a rhodamine-110-based fluorescent thrombin substrate. Fluorescence kinetics are analyzed to produce a prothrombin-time--equivalent parameter that can be converted to an international normalized ratio (INR) value. The system provides results that correlate well with conventional liquid phase prothrombin time assays (R2 = 0.96).

Overexpression in Escherichia coli of 12 vitamin B12 biosynthetic enzymes

The first 12 enzymes involved in the biosynthesis of vitamin B12 from its five-carbon precursor, aminolevulinic acid, have been overexpressed in recombinant strains of Escherichia coli. The activity of each enzyme has been demonstrated by the biosynthesis of hydrogenobyrinic acid from aminolevulinic acid.

Genetically engineered synthesis of precorrin-6x and the complete corrinoid, hydrogenobyrinic acid, an advanced precursor of vitamin B12

BACKGROUND

Genetically engineered synthesis, in which the gene products, cofactors, and substrates of a complete pathway are combined in vitro in a single flask to give the target, can be a viable alternative to conventional chemical construction of molecules of complex structure and stereochemistry. We chose to attempt to synthesize the metal-free corrinoid hydrogenobyrinic acid, an advanced precursor of vitamin B12.

RESULTS

Cloning and overexpression of the genes necessary for the S-adenosyl methionine dependent conversion of 5-aminolevulinic acid (ALA) to precorrin-3 and those required for the synthesis of hydrogenobyrinic acid from precorrin-3 completed the repertoire of the 12 biosynthetic enzymes involved in corrin synthesis. Using these enzymes and the necessary cofactors, the multi-enzyme synthesis of hydrogenobyrinic acid from ALA can be achieved in 20% overall yield in a single reaction vessel, corresponding to an average of at least 90% conversion for each of the 17 steps involved.

CONCLUSIONS

By replacing the cell wall with glass, and by mixing the soluble biosynthetic enzymes and necessary cofactors, the major segment of the physiological synthesis of vitamin B12 has been accomplished. Since only those enzymes necessary for the synthesis of hydrogenobyrinic acid from ALA are supplied, none of the intermediates is deflected from the direct pathway. This results in an efficiency which in fact surpasses that of nature.

Conducting states of a mammalian serotonin transporter

We have studied permeation at a cloned rat 5-HT transporter expressed in Xenopus oocytes. [3H]5-HT uptake and [125I]RTI-55 binding yield a turnover rate of approximately 1/s that does not depend on membrane potential. However, in voltage-clamp experiments, three distinct currents results from 5-HT transporter expression. First, a steady-state, voltage-dependent transport-associated current is induced by 5-HT application. Second, a transient inward current is activated by voltage jumps to high negative potentials in the absence of 5-HT and is blocked by 5-HT itself. Third, a small leakage current is observed in the absence of 5-HT. All the observed currents are blocked by inhibitors of 5-HT uptake but are differentially affected by Na+, Li+, K+, Ba2+, Cs+, Cl-, and amiloride. The conducting states of the 5-HT transporter may reflect the existence of a permeation pathway similar to that of ionic channels.

Biodegradable microspheres as controlled-release tetanus toxoid delivery systems

Purified tetanus toxoid, a high-molecular-weight protein, was entrapped within poly(L-lactic acid) (PLA) and poly(D,L-lactic/glycolic acid) (PLGA) microspheres prepared by either a solvent extraction or a solvent evaporation method carried out in a multiple emulsion system (water-in-oil-in-water). The physical integrity and antigenicity of the protein treated under different processing conditions were investigated. A reduction of antigenicity that was related to the percentage of aggregated protein was noticed under some experimental conditions. This partial loss of antigenicity was associated with the lyophilization process and affected by the nature of the organic solvent. All types of microspheres prepared with different molecular weight PLA and PLGA displayed a high protein-loading efficiency (> 80%) but their size was strongly influenced by polymer molecular weight (3000 versus 100,000). Protein release pattern was influenced by both polymer molecular weight and composition (PLA versus PLGA). A constant release pattern after an induction period of 10 days was observed for microspheres composed of high-molecular-weight polymers (PLA and PLGA). The release rate was lower from PLA microspheres than from PLGA microspheres. In contrast, a continuously increasing release rate preceded by a burst was observed for low-molecular-weight (3000) PLGA microspheres. Microencapsulated tetanus toxoid was significantly more immunogenic in mice than fluid toxoid as determined by IgG anti-tetanus antibody levels and neutralizing antibodies. However, the magnitude and duration of the antibody response did not differ significantly from a similar dose of aluminium phosphate-adsorbed toxoid. We conclude that microencapsulated tetanus toxoid shows significant adjuvant activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of vitamin B12. Discovery of the enzymes for oxidative ring contraction and insertion of the fourth methyl group

In the vitamin B12 biosynthetic pathway the enzymes responsible for the conversion of precorrin-3 to precorrin-4 have been identified as the gene products of cobG and cobJ from Pseudomonas denitrificans. CobG catalyzes the oxidation of precorrin-3 to precorrin-3x (a hydroxy lactone) whereas CobJ is a SAM-dependent C-17 methyl transferase and is necessary for ring contraction. A mechanism for ring contraction is proposed.

Sequence of the Candida albicans erg7 gene

The nucleotide sequence of the Candida albicans erg7 gene, which complements erg7 mutants of Saccharomyces cerevisiae and restores oxidosqualene cyclase activity, was determined. The gene encodes a 728-aa protein that displays homology with squalene-hopene cyclase, providing further evidence that erg7 is the gene encoding 2,3-oxidosqualene cyclase.

Vitamin D metabolite-binding proteins in human tissue

Serum and post-microsomal supernatants of human lymphocyte, erythrocyte, skeletal muscle and parathyroid adenoma homogenates were examined for specific binding of 25-hydroxycholecalciferol (25-OHD3) and 1, 25-dihydroxycholecalciferol (1,25-(OH)2D3). Muscle, lymphocytes and parathyroid adenomata extracts contained a 6-S 25-OHD3-binding protein which was not found in erythrocyte extracts, and which was distinct from the smaller serum transport alpha-globulin. A cathodal, 1, 25-(OH)2D3-binding protein, which sedimented at 3-4 S was also detected in parathyroid tissue. These observations suggest the possibility of direct physiologic interaction between vitamin D metabolites and nucleated human tissues other than intestine and bone.

Competition by 24,25-dihydroxycholecalciferol in the competitive protein binding radioassay of 25-hydroxycalciferol

24,25-dihydroxycholecalciferol (24,25-(OH)2D3) is equipotent to 25-hydroxycholecalciferol in the displacement of 3H25-OHD3 from rat serum binding sites, and is extracted by the ethanol procedure recommended in non-chromatographic competitive protein binding radioassays for 25-OHD. Serum 24,25-(OH)2D content was measured following 24,25-(OH)2D3 isolation from lipid extracts by liquid-gel partition chromatography. Since normal serum 24,25-(OH)2D concentration is appreciable, non-chromatographic 25-OHD assays most probably overestimate serum 25-OHD levels as a result of their recognition of 24,25-(OH)2D3.