PubMed Health⌕ Search

Biomedical subjects

J Koontz

Publications and source records attributed to J Koontz.

9 recordsLinked to original sources
PubMed2000

In vivo diffuse damage in human vertebral trabecular bone.

Accumulation of microdamage in vivo may lead to loss of bone quality. Until recently, linear microcracks were the only known form of in vivo microdamage, but through the use of confocal microscopy an additional level of damage (diffuse damage) has been identified. In this study, in vivo diffuse damage was characterized and quantified in human vertebral trabecular bone as a function of tissue morphology, age, race, gender, and previously quantified in vivo linear microcracks. Presence of diffuse damage in human vertebral tissue was confirmed and validated by simultaneous use of polarized, ultraviolet, and laser confocal microscopy. Diffuse damage was found to occur preferentially within trabecular packets rather than in interstitial bone (p < 0.05). It was consistently higher in men compared with women (p < 0.05), but was not different by race or age group. Diffuse damage did not correlate with linear microcracks, but both exhibited the same probability distribution in which the percentage of individuals having a particular amount of damage decreased exponentially as damage content increased. These findings suggest that diffuse damage accumulation and repair are governed by the same biological phenomena as microcracks, but diffuse damage contributes independently to the microdamage content of bone.

Adult↗
PubMed2000

Diazoxide down-regulates leptin and lipid metabolizing enzymes in adipose tissue of Zucker rats.

We have previously reported that attenuation of hyperinsulinemia by diazoxide (DZ), an inhibitor of glucose-mediated insulin secretion, increased insulin sensitivity and reduced body weight in obese Zucker rats. These findings prompted us to investigate the effects of DZ on key insulin-sensitive enzymes regulating adipose tissue metabolism, fatty acid synthase (FAS), and lipoprotein lipase (LPL), as well as on circulating levels of leptin. We also determined the direct effects of diazoxide on FAS in 3T3-L1 adipocytes. Seven-week-old female obese and lean Zucker rats were treated with DZ (150 mg/kg/d) or vehicle (C, control) for a period of 6 wk. Changes in plasma parameters by DZ include significant decreases in triglycerides, free fatty acids, glucose, and insulin, consistent with our previous reports. DZ obese rats exhibited lower plasma leptin levels (P<0.03) compared to their C animals. DZ significantly reduced adipose tissue FAS activity in both lean (P<0.0001) and obese (P<0.01) animals. LPL mRNA content was also decreased significantly in DZ-treated obese animals (P<0.009) as compared to their respective controls without a significant effect on lean animals. The possibility that DZ exerted a direct effect on adipocytes was further tested in cultured 3T3-L1 adipocytes. Although diazoxide (5 microM) alone did not change FAS activity in cultured 3T3-L1 adipocytes, it significantly attenuated insulin's effect on FAS activity (P<0.001). We demonstrate that DZ regulates key insulin-sensitive enzymes involved in regulation of adipose tissue metabolism. These findings suggest that modification of insulin-sensitive pathways can be therapeutically beneficial in obesity management.

3T3 Cells↗
PubMed1995

A fluorometric assay for pyridoxal kinase applicable to crude cell extracts.

We have developed an assay for pyridoxal kinase which takes advantage of the intense fluorescence yield of the oxime of pyridoxal or pyridoxal-5'-phosphate and the substantial difference in the rates of formation of these two oximes. Evidence is presented which demonstrates that the assay is linear with respect to time and amount of protein and is applicable to the activity in crude cell extracts as well as purified enzyme.

Animals↗
PubMed1995

Insulin enhances glucocorticoid receptor-mediated induction of gene expression independent of a specific insulin response element.

We have established a system in which we observe a synergistic interaction between insulin and glucocorticoids. This includes chimeric genes constructed to contain synthetic glucocorticoid-responsive elements, 5' of the HSV thymidine kinase promoter and the chloramphenicol acetyltransferase reporter gene. The magnitude of induction of gene expression by glucocorticoid was dependent on the number of GREs. Insulin alone had virtually no effect on the expression of any of these genes but together with dexamethasone acted in a synergistic manner. This synergy diminished as the number of GREs in the promoter increased. The synergy is independent of promoter sequences other than the GREs and a functional TATAA box. Three different approaches demonstrate that the effect of insulin is not directly on the glucocorticoid signal transduction pathway. Insulin does not change the dose-response relationship for dexamethasone. The effect of insulin is independent of the intracellular concentration of glucocorticoid receptor. The effect is independent of any specific domain of the glucocorticoid receptor. The target of insulin action is likely to be part of the normal host cell transcriptional initiation complex or a putative adaptor molecule.

Animals↗
PubMed1995

Detection of mutations by cleavage of DNA heteroduplexes with bacteriophage resolvases.

We have explored the application of the bacteriophage resolvases T4 endonuclease VII and T7 endonuclease I for detecting mutations in genomic DNA. Heteroduplex DNA fragments prepared by amplification from DNA containing known mutations were cleaved by one or both enzymes at nucleotide mismatches created by 3 of 3 short deletions and 13 of 14 point mutations in fragments as large as 940 basepairs. Heteroduplexes representing all four classes of possible single nucleotide mismatches were cleaved, and the sizes of the cleavage products generated correlated with the location of the mutation. We conclude that bacteriophage resolvases may be useful reagents for the rapid screening of DNA for mutations.

Bacteriophages↗
PubMed1992

Insulin-responsive tyrosine aminotransferase transcription requires multiple promoter regions.

This study used transient transfection analysis to determine the DNA regions which mediate basal and insulin-sensitive transcription from the gene encoding tyrosine aminotransferase (TAT; EC 2.6.1.5). Basal expression requires at least parts of two regions: a region at -3600 and a region from -208 to + 62. Insulin sensitivity requires at least one region of the promoter not required for basal expression. Thus, insulin cannot act solely by direct modification of any of the components required for basal transcription. Previous results from this laboratory suggest that the insulin effects on basal and glucocorticoid-induced TAT transcription require different regions of the proximal promoter.

Animals↗
PubMed1987

Insulin as a growth factor in rat hepatoma cells. Stimulation of proto-oncogene expression.

In a subline of Reuber H35 rat hepatoma cells that becomes quiescent under serum-deprived conditions, insulin acts as a growth factor. When added to serum-deprived H35 cells, physiologic concentrations of insulin stimulate DNA synthesis, demonstrating that insulin alone is capable of inducing a transition from G0/G1 into S phase. This response, which is induced by nanomolar concentrations of insulin, is mediated directly through the insulin receptor. Here we show that coincident with this growth response, insulin or serum induces dramatic increases in the steady-state levels of c-fos and c-myc mRNAs in serum-deprived H35 cells in a time course similar to that observed in the regenerating liver. Other growth factors, including epidermal growth factor, appear not to affect these cells either in terms of DNA synthesis or c-myc mRNA induction. The phorbol ester phorbol 12-myristate 13-acetate (PMA) also induces c-myc and c-fos mRNAs without inducing DNA synthesis. However, the mechanism of this induction appears to be different from the insulin-induced induction since pretreatment of cells with PMA blocks only the PMA-mediated, not the insulin-mediated, induction of c-myc and c-fos.

Actins↗