Biomedical subjects
Publications and source records attributed to P Blomquist.
The temperature dependence of the interlayer exchange coupling in ferromagnetic films coupled across nonmagnetic spacers is determined via in situ ferromagnetic resonance experiments for various systems. Clear evidence for a T(3/2) law is found over a wide temperature regime.
Nuclear receptors CAR and PXR play a key role in cytochrome P450 gene induction by xenobiotics. Human cytochrome P450 3A7 (CYP3A7) is expressed from early in gestation until the perinatal period, when there is a switch in expression to CYP3A4. Here we demonstrate that a PXR and CAR responsive enhancer is located approximately 8 kb upstream of the proximal CYP3A7 promoter. This distal xenobiotic responsive enhancer module (XREM) is conserved with the XREM of CYP3A4. Interestingly, not only the XREM, but also the entire promoters exhibit 90% sequence identity up to -8.8 kb, indicating a close evolutionary distance. We propose that the promoters have coevolved to functionally conserve P450 gene induction in response to xenobiotics through CAR and PXR. Thus, nuclear receptors for xenobiotics may not only play a role to provide a survival advantage during adulthood, but also to protect the embryo against endogenous and exogenous toxins.
HYPOTHESIS: Placing stitches close to the cut wound edge does not produce low wound bursting strength in midline laparotomy incisions closed with a suture length:wound length ratio of 4. DESIGN: Experimental study in rats. METHODS: Midline incisions were closed with a running suture in 51 Sprague-Dawley rats. A suture length:wound length ratio of 4 was used and stitches were placed at a distance of 3, 6, or 10 mm from the wound edge. Wound bursting strength was studied immediately after and 4 days after wound closure. RESULTS: Immediately after wound closure, bursting pressure was higher with stitches placed 10 mm from the wound edge than those at a distance of 3 mm. After 4 days, bursting pressure and bursting volume were lower with stitches placed 10 mm from the wound edge than those at a distance of 3 or 6 mm. The abdominal wall ruptured outside the suture line in 14 of 17 wounds closed with 21 stitches, in 11 of 17 wounds closed with 16 stitches, and in 6 of 17 wounds closed with 11 stitches (P=.02). CONCLUSIONS: Four days after closure of midline laparotomy incisions using a suture length-wound length ratio of 4, wound bursting strength is higher with stitches placed 3 to 6 mm from the wound edge than those at a distance of 10 mm. Wound bursting strength increases with the number of stitches used.
The organization of DNA into chromatin is important in the regulation of transcription, by influencing the access of transcription factors to their DNA binding sites. Nuclear factor 1 (NF-1) is a transcription factor which binds to DNA constitutively and which interacts with its cognate DNA site with high affinity. However, this affinity is drastically reduced, approximately 100- to 300-fold, when the binding site is organized into a nucleosome. Here we demonstrate that the introduction of stretches of adenines of length 5 nt (A-tracts) on both sides of the NF-1 binding site has a distinct effect on NF-1 binding to a nucleosomal, but not to a free, NF-1 binding site. The position of the A-tracts, relative to the rotational phase of a synthetic DNA bending sequence, the TG-motif, decides whether the NF-1 affinity increases or decreases. The NF-1 binding affinity is seven times stronger when the flanking A-tracts are positioned out-of-phase with the TG-motif than it is when the A-tracts are positioned in-phase with the TG-motif. We demonstrate that this effect correlates with differences in DNA curvature and apparent histone octamer affinity. We conclude that DNA curvature influences the local histone-DNA contacts and hence the accessibility of the NF-1 site in a nucleosome context.
Nuclear receptors regulate metabolic pathways in response to changes in the environment by appropriate alterations in gene expression of key metabolic enzymes. Here, a computational search approach based on iteratively built hidden Markov models of nuclear receptors was used to identify a human nuclear receptor, termed hPAR, that is expressed in liver and intestines. hPAR was found to be efficiently activated by pregnanes and by clinically used drugs including rifampicin, an antibiotic known to selectively induce human but not murine CYP3A expression. The CYP3A drug-metabolizing enzymes are expressed in gut and liver in response to environmental chemicals and clinically used drugs. Interestingly, hPAR is not activated by pregnenolone 16alpha-carbonitrile, which is a potent inducer of murine CYP3A genes and an activator of the mouse receptor PXR.1. Furthermore, hPAR was found to bind to and trans-activate through a conserved regulatory sequence present in human but not murine CYP3A genes. These results provide evidence that hPAR and PXR.1 may represent orthologous genes from different species that have evolved to regulate overlapping target genes in response to pharmacologically distinct CYP3A activators, and have potential implications for the in vitro identification of drug interactions important to humans.
OBJECTIVE: To test the hypothesis that subcutaneous wound oxygen tension (PsqO2) has a predictive relation to the development of wound infection in surgical patients. DESIGN: A noninterventional, prospective study. SETTING: A university department of surgery. PATIENTS: One hundred thirty operative general surgical patients at notable risk of infection as predicted by an anticipated Study on the Effect of Nosocomial Infection Control (SENIC) score of 1 or greater. OUTCOME MEASURES: PsqO2 was measured perioperatively. Its relation to the subsequent incidence of surgical wound infection was then determined and compared with the SENIC score as a criterion standard. RESULTS: Although the SENIC score and PsqO2 are inversely correlated, PsqO2 is the stronger predictor of infection. Low PsqO2 identified patients at risk and concentrated them in a cohort that was about half the size of that identified by the SENIC score. CONCLUSIONS: Subcutaneous perfusion and oxygenation are important components of immunity to wound infections. The SENIC score identifies systemic physiological variables that are important to the development of wound infection. Nevertheless, PsqO2 is the more powerful predictor of wound infection. Moreover, PsqO2 can be manipulated by available clinical means, and thus may direct interventions to prevent infection.
The organization of DNA in chromatin is involved in repressing basal transcription of a number of inducible genes. Biochemically defined multiprotein complexes such as SWI/SNF (J. Côté, J. Quinn, J. L. Workman, and C. L. Peterson, Science 265:53-60, 1994) and nucleosome remodeling factor (T. Tsukiyama and C. Wu, Cell 83:1011-1020, 1995) disrupt nucleosomes in vitro and are thus candidates for complexes which cause chromatin decondensation during gene induction. In this study we show that the glucocorticoid receptor (GR), a hormone-inducible transcription factor, stimulates the nucleosome-disrupting activity of the SWI/SNF complex partially purified either from HeLa cells or from rat liver tissue. This GR-mediated stimulation of SWI/SNF nucleosome disruption depended on the presence of a glucocorticoid response element. The in vitro-reconstituted nucleosome probes used in these experiments harbored 95 bp of synthetic DNA-bending sequence in order to rotationally position the DNA. The GR-dependent stimulation of SWI/SNF-mediated nucleosome disruption, as evaluated by DNase I footprinting, was 2.7- to 3.8-fold for the human SWI/SNF complex and 2.5- to 3.2-fold for the rat SWI/SNF complex. When nuclear factor 1 (NF1) was used instead of GR, there was no stimulation of SWI/SNF activity in the presence of a mononucleosome containing an NF1 binding site. On the other hand, the SWI/SNF nucleosome disruption activity increased the access of NF1 for its nucleosomal binding site. No such effect was seen on binding of GR to its response element. Our results suggest that GR, but not NF1, is able to target the nucleosome-disrupting activity of the SWI/SNF complex.
A DNA-bending sequence has been used for in vitro reconstitution of nucleosomes in order to direct a nuclear factor 1 (NF-1) binding site into different nucleosome positions. By this strategy nucleosomes were obtained that had one of two rotational positions of the NF-1 binding site, one oriented toward the periphery and the other toward the histone octamer, translationally positioned 50 and 45 base pairs, respectively, from the nucleosome dyad. The affinity of partially purified NF-1 for these nucleosomal targets was compared with its affinity for free DNA by dimethylsulfate methylation protection and DNase I footprinting assays. The binding affinity of NF-1 to all nucleosomal targets was reduced 100-300-fold compared with its affinity for free DNA. The two rotational settings of the NF-1 site showed the same binding affinity for NF-1 as did other nucleosome constructs in which the NF-1 binding site was translationally positioned from 10 to 40 base pairs from the nucleosome dyad. We conclude that the nucleosomal inhibition of NF-1 binding is an inherent characteristic of NF-1 since another transcription factor, the glucocorticoid receptor, is able to bind to its DNA site in a nucleosome.
Oligonucleotides which form triple helical complexes on double-stranded DNA have been previously reported to selectively inhibit transcription both in vitro and in vivo by physically blocking RNA polymerase or transcription factor access to the DNA template. Here we show that a 16mer oligonucleotide, which forms triple helix DNA by binding to a 16 bp homopurine segment, alters the formation of histone-DNA contacts during in vitro nucleosome reconstitution. This effect was DNA sequence-specific and required the oligonucleotide to be present during in vitro nucleosome reconstitution. Binding of the triple helix oligonucleotide on a 199 bp mouse mammary tumour virus promoter DNA fragment with a centrally located triplex DNA resulted in interruption of histone-DNA contacts flanking the triplex DNA segment. When nucleosome reconstitution is carried out on a longer, 279 bp DNA fragment with an asymmetrically located triplex site, nucleosome formation occurred at the border of the triple helical DNA. In this case the triplex DNA functioned as a nucleosome barrier. We conclude that triplex DNA cannot be accommodated within a nucleosome context and thus may be used to site-specifically manipulate nucleosome organization.
A standardized stenosis of the left colon was created in the rat model. After four days the stenosis was resected and a primary anastomosis made. Half of the animals (n = 21) were randomized to a proximal diverting colostomy and the other half to a non-colostomy control group. On postoperative days two and seven anastomotic complications were recorded and anastomotic strength was determined. Collagen content in the anastomotic area was measured. In the colostomy group no anastomotic complications occurred, while 6/21 (29%) animals in the non-colostomy group had complications. On day two there was no difference between the groups as regards anastomotic strength and collagen content. After a week, however, the control group showed a significant increase in both anastomotic strength and collagen content which was not observed in the colostomy group. The absence of increase in anastomotic strength in the colostomy group had no adverse effect on anastomotic healing, as judged by complications. Thus, a diverting colostomy may be of value in reducing anastomotic complications after resection of a left colon obstruction.
Anastomotic breaking strength and collagen metabolism in the colonic wall were studied after resection of a standardized left-colon stenosis in the rat. An increased complication rate was found in the stenosis group compared with the control group (27 percent vs. 2 percent) and the complications arise soon after surgery. The collagen turnover in the anastomotic area, as well as the changes of breaking strength, were equal between the groups in the early healing course, implying that the stenosis group, as an entity, did not show impairment in the studied parameters predisposing for complications. Other factors such as mechanical strain by the increased fecal bulk and increased bacterial load may contribute to occurrence of the anastomotic complications.
The influence of bacteria on metabolism of collagen in the colonic wall under normal conditions and after obstruction was evaluated by using germ-free and conventionally bred rats. Under normal conditions, no differences in synthesis and content of collagen or tissue dry weight in the colonic wall were found between germ-free and conventionally bred rats. After obstruction, both groups reacted similarly with an equally increased collagen synthesis. The findings imply that bacteria do not play any major role in the regulation of collagen metabolism in the colonic wall, neither under normal conditions nor in the strained situation with colonic obstruction and fecal impaction.
The healing of an experimental left colon anastomosis protected by a proximal diverting colostomy was studied in the rat. Collagen synthesis in the anastomotic area was measured by incorporation of [3H]proline. With a defunctioning proximal colostomy, the synthesis and accumulation of collagen in the anastomosis was diminished, and the anastomotic strength development delayed and reduced. The development of anastomotic strength seems to proceed according to the level of strain from intraluminal bulk. As the healing of the anastomosis protected by a diverting colostomy was uncomplicated, these findings should not contra-indicate the use of diverting colostomy.
The healing of a standardized left colon anastomosis after early (7 days) closure of a concomitant proximal diverting colostomy was studied experimentally. Early closure of the diverting colostomy could be conducted safely by an intraperitoneal technique and the healing of the primary anastomosis was uncomplicated. Colostomy closure in the proliferative phase of wound healing resulted in development of anastomotic strength similar to colonic healing without faecal diversion. The anastomotic strength had doubled after three weeks. As compared to colostomy closure in the remodelling phase of anastomotic healing development of anastomotic strength was more rapid and without serious local complications.
The influence of long-term relative bowel rest, using a low residue diet, on healing of a left colon anastomosis was experimentally studied. Retarded and diminished gain of postoperative anastomotic collagen and strength was found. The healing of the anastomosis was uncomplicated, however, and it is concluded that anastomotic integrity after surgery in this condition is safe.
Collagen content, bursting wall tension, and suture-holding capacity in the proximal and distal colon of the rat were studied after long-term treatment with a low-residue or a standard laboratory chow diet. Collagen content decreased uniformly in both the proximal and distal colon of the low-residue diet group. In addition, the bursting wall tension of the nonoperated proximal colon was reduced, whereas the breaking strength of a newly constructed anastomosis at three different colonic sites was unaffected.
The impact of colostomy closure on the healing of a left colonic anastomosis performed 4 weeks earlier was studied in rats. Colostomy closure could be safely accomplished but in 3 of 25 rats was followed by faecal obstruction due to narrowing of the primary left colonic anastomosis. After colostomy closure the gain in anastomotic strength was slow and did not exceed the outset value until after 3 weeks. After colostomy closure, accumulation of collagen in the anastomotic region increased earlier than anastomotic strength, indicating delay in collagen maturation.
The influence of standard heparin or low molecular weight (LMW) heparin on healing of abdominal wounds and colonic anastomoses was studied in rats. Subcutaneous injection of 1 XaI U/g b.w. of standard or LMW-heparin or 0.5 ml physiologic saline was given 12 hours preoperatively and daily for 3 or 7 days postoperatively. Breaking strength of the abdominal wound and the anastomosis was measured, as were haemoglobin and albumin in serum. Hydroxyproline as a measure of collagen and tissue dry weight was determined in standardized segments of colonic wall adjacent to the anastomosis. Except for significant increase in breaking strength of the anastomosis after 7-day injection of LMW heparin, no differences in the parameters of wound healing were found after 3 or 7 days. In rats receiving standard heparin there was increased bleeding tendency (reduced haemoglobin) compared with the LMW-heparin group and the controls. The administered heparin thus did not negatively influence healing, and standard and LMW-heparin did not differ in this respect.