Structural studies on an inhibitory antibody against Thermus aquaticus DNA polymerase suggest mode of inhibition

TP7, an antibody against Thermus aquaticus DNA polymerase I (TaqP), is used as a thermolabile switch in 'hot start' variations of PCR to minimize non-specific amplification events. Earlier studies have established that TP7 binds to the polymerase domain of TaqP, competes with primer template complex for binding and is a potent inhibitor of the polymerase activity of TaqP. We report crystallographic determination of the structure of an Fab fragment of TP7 and computational docking of the structure with the known three-dimensional structure of the enzyme. Our observations strongly suggest that the origin of inhibitory ability of TP7 is its binding to enzyme residues involved in DNA binding and polymerization mechanism. Although criteria unbiased by extant biochemical data have been used in identification of a putative solution, the resulting complex offers an eminently plausible structural explanation of biochemical observations. The results presented are of general significance for interpretation of docking experiments and in design of small molecular inhibitors of TaqP, that are not structurally similar to substrates, for use in PCR. Structural and functional similarities noted among DNA polymerases, and the fact that several DNA polymerases are pharmacological targets, make discovery of non-substrate based inhibitors of additional importance.      

Management of upper urinary tract calculi with ureteroscopic techniques

Frequent loss of heterozygosity on chromosome 8p in a variety of human malignancies, including head and neck cancers, has suggested the presence of a tumor suppressor gene (or genes) associated with the pathogenesis of these cancers. To test the role of genetic alterations at 8p23 in oral carcinogenesis, we studied 51 squamous cell carcinomas of the head and neck and 29 oral squamous cell carcinoma cell lines for allelic loss using 7 microsatellite markers spanning approximately 5 cM of chromosome band 8p23. Twenty-three of 51 tumors (45%) and 23 of 29 cell lines (79%) showed allelic loss at 1 or more loci. Three cell lines showed homozygous deletion of loci within a 3 cM region defined by the markers D8S1781 and D8S262. Our results suggest that a tumor suppressor gene (or genes) is located in 8p23 and is associated with the development and/or progression of oral carcinomas.     

Comparison of arterialized venous sampling from the hand and foot in the assessment of in vivo glucose metabolism

To determine whether arterialized venous blood obtained from a foot vein could be substituted for arterialized venous blood obtained from a hand vein during studies using the glucose clamp technique, we simultaneously measured glucose concentrations and PO2 in blood samples obtained from the heated hands and feet of five normal volunteers during the euglycemic and hyperglycemic steps of a hyperinsulinemic clamp. Plasma glucose concentrations were found to be virtually identical in arterialized venous blood drawn from the hand and the foot under both euglycemic and hyperglycemic conditions. The correlation between these values was significant (R2 = .99, P < .001). PO2 measurements in blood drawn from the heated hand or foot were not statistically different. We conclude that the glucose concentration measured in arterialized venous blood drawn from the foot is equivalent to the concentration in arterialized venous blood drawn from the hand. These observations will allow investigators to study in vivo glucose metabolism in individuals with poor venous access in the upper extremities and to use protocols that make the arms of the subject inaccessible for blood sampling during the study.     

Extreme leukoreduction of major histocompatibility complex class II positive B cells enhances allogeneic platelet immunity

In a murine model of platelet alloimmunization, we examined the definitive role that mononuclear cells (MC) have in modulating platelet immunity by using platelets from severe combined immunodeficient (SCID) mice. CB.17 (H-2(d)) SCID or BALB/c (H-2(d)) mouse platelets were transfused weekly into fully allogeneic CBA (H-2(k)) mice and antidonor antibodies measured by flow cytometry. MC levels in BALB/c platelets were 1.1 +/- 0.6/microL and SCID mouse platelets could be prepared to have significantly lower (<0. 05/microL) MC numbers. Transfusions with 10(8) BALB/c platelets (containing approximately 100 MC/transfusion) stimulated IgG antidonor antibodies in 100% of the recipients by the fifth transfusion, whereas 10(8) SCID mouse platelets (containing approximately 5 MC/transfusion) stimulated higher-titered IgG alloantibodies by the second transfusion. When titrations of BALB/c peripheral blood MC were added to the SCID mouse platelets, levels approaching 1 MC/microL reduced SCID platelet immunity to levels similar to BALB/c platelets. Characterization of the alloantibodies showed that the low levels of MC significantly influenced the isotype of the antidonor IgG; the presence of 1 MC/microL was associated with induction of noncomplement fixing IgG1 antidonor antibodies, whereas platelet transfusions, devoid of MC (<0. 05/microL), were responsible for complement-fixing IgG2a production. When magnetically sorted defined subpopulations of MC were added to the SCID platelets, major histocompatability complex (MHC) class II positive populations, particularly B cells, were found to be primarily responsible for the reduced SCID mouse platelet immunity. The presence of low numbers of MC within the platelets was also associated with an age-dependent reduction in platelet immunogenicity; this relationship however, was not observed with SCID mouse platelets devoid of MC. The results suggest that a residual number of MHC class II positive B cells within allogeneic platelets are required for maximally reducing alloimmunization.     

A randomized, controlled trial of a behavioral intervention to prevent sexually transmitted disease among minority women

Using annual bite-wing radiographs, the incidence and progression of approximal caries (4d-7m) were assessed longitudinally in teenagers and adolescents whose treatment had been based on remineralizing rather than restorative strategies. A closed cohort of 536 children initially was followed from 11 to 22 years of age. The scoring system was: 0 = no visible radiolucency; 1-2 = radiolucency in the enamel up to the enamel-dentin border; 3 = radiolucency with a broken enamel-dentin border but with no obvious progression in the dentin; 4 = radiolucency with obvious spread in the outer half of the dentin, and 5 = radiolucency in the inner half of the dentin. Caries rates were estimated as the number of new lesions/100 tooth surface-years, and the Kaplan-Meier estimate was used to calculate the cumulative survival time of each approximal surface. Three events were used: the transitions from states 0 to 2, 2 to 4 and 3 to 4. The results showed a considerable variation between the surfaces in both caries rates and survival time. For all surfaces combined, the median caries rate from state 0 to 2 was 3.9 new lesions/100 tooth surface-years; from state 2 to 4, the rate was 5.4, and from state 3 to 4 it was 20.3. Of the sound surfaces (state 0), 75% survived 6.3 years without reaching state 2. Given state 2, 75% survived 4.8 years without reaching the outer half of the dentin (state 4), while given a lesion at the enamel-dentin border (state 3), 75% survived 1.3 years without doing the same. The median survival time of lesions from state 3 to 4 was 3.1 years. The group with DMFSappr>1 at the age of 11-12 years had a risk of new approximal enamel lesions (state 0-2) that was 2.5 times greater than that of the group with DMFSappr = 0-1.