ACTH and indomethacin-induced antidiuresis in low salt Brattleboro strain rats: induction and escape.
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Adrenocorticotropic Hormone↗
Biomedical subjects
S Khosla
Publications and source records attributed to S Khosla.
beta-Lactamase proceeds via an acyl-enzyme intermediate. Interaction of the Escherichia coli RTEM enzyme with cefoxitin.
The use of cefoxitin, a poor substrate of the RTEM beta-lactamase, has allowed the kinetic and spectroscopic characterization of a covalent acyl-enzyme intermediate in the enzyme-catalyzed reaction. The rate of reappearance of catalytic activity in an enzyme sample diluted from an incubation with cefoxitin is nearly identical with the observed Kcat. Burst kinetics are observed with this substrate, consistent with the rate-limiting deacylation of the cefoxitinoyl-enzyme. That the reaction intermediate involves a covalent link between enzyme and substrate was shown by gel filtration after rapid denaturation of an enzyme-[14C]cefoxitin reaction at the steady state. Fourier transform infrared measurements indicate that the intermediate is an acyl-enzyme involving a hydroxyl group of the beta-lactamase. The evident relationship between the acylation-deacylation sequence of the beta-lactamases and the acylation reaction suffered by the D-Ala-D-Ala-carboxypeptidases is discussed.
Binding Sites↗
Beta-lactamase inactivation by mechanism-based reagents.
The mechanistic pathway followed by the E. coli RTEM beta-lactamase has been studied with a view to clarifying the mode of action of a number of recently discovered inactivators of the enzyme. There is clear evidence that the beta-lactamase-catalysed hydrolysis of the 7-alpha-methoxycephem, cefoxitin, proceeds via an acyl-enzyme intermediate. An analysis of the inactivation reactions of all the known beta-lactam derivatives that result in irreversible loss of enzyme activity permits the identification of three structural features required for a beta-lactamase inactivator. The application of these principles suggests a new group of mechanism-based inactivators of the enzyme: the sulphones of N-acyl derivatives of 6-beta-aminopenicillanic acid that are themselves poor substrates for the enzyme. These sulphones are powerful inactivators of the beta-lactamase.
Anti-Bacterial Agents↗
An ultrastructural study of multifidus muscle in progressive idiopathic scoliosis. Changes resulting from a sarcolemmal defect at the myotendinous junction.
Biopsies of multifidus muscles were procured from patients with idiopathic scoliosis prior to Harrington rod instrumentation. Specimens from both convex and concave sides at the apex of the curve were examined by light and electron microscopy and compared with normal muscle samples. Abnormalities were detected on the concave aspect of the curve and the most dramatic morphological changes were noted at the myotendinous junction. Here a structural defect in the form of discontinuities in the sarcolemmal membranes of some muscle fibres was accompanied by large numbers of intimately-adhering connective tissue cells. Structural disorganization of the associated tendon occurred in conjunction with increased vascularization and with fatty cell and leukocyte infiltration. Further from the myotendon junction, structural lesions appeared more chronic and non-specific subsequent to the incipient sarcolemmal break in the affected muscle fibres. Hypertrophy, atrophy, centralization of nuclei, and disruption of sarcotubular and myofibrillar elements were noted in some muscle cells. While the aetiology of this disorder is unknown, a supposition is made that the primary change is an inherent weakness and subsequent break in the sarcolemma at the myotendon junction. This site is an important clue to the pathogenesis of this disease since it reflects morphological change in rapidly growing tissue occurring at the time of the rapid adolescent growth spurt leading to progression of the scoliotic curve.
Adolescent↗
Optimization of carrier frequency and duty cycle for pulse modulation of biological signals.
Digital modulation techniques are commonly used for the recording and transmission of biological signals. Hitherto, the choice of subcarrier frequency for recording or transmission of biological signals has been arbitary and this usually results in poor signal to noise ratio (SNR) due to the limited frequency characteristics of the system. In the present study the frequency characteristics of the system (first order approximation) has been taken to be that of a Butterworth filter. Computations based on this assumption show that for a given input signal there exists an optimum subcarrier frequency and a corresponding optimum duty cycle which would give maximum SNR of the system. For convenience, a nomogram has been prepared and it has been shown that for a given frequency response of the system, the nomogram could be used for selecting an optimum subcarrier frequency and a corresponding duty cycle. The theoretical formulations have been verified with experimental work.
Biomedical Engineering↗
UCS intensity and instructional set in classical eyelid conditioning: discrimination conditioning and signal-detection analysis.
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Conditioning, Eyelid↗
Regulation of osteoclastogenesis and RANK expression by TGF-beta1.
Transforming growth factor-beta (TGF-beta) has been shown to both inhibit and to stimulate bone resorption and osteoclastogenesis. This may be due, in part, to differential effects on bone marrow stromal cells that support osteoclastogenesis vs. direct effects on osteoclastic precursor cells. In the present study, we used the murine monocytic cell line, RAW 264.7, to define direct effects of TGF-beta on pre-osteoclastic cells. In the presence of macrophage-colony stimulating factor (M-CSF) (20 ng/ml) and receptor activator of NF-kappaB ligand (RANK-L) (50 ng/ml), TGF-beta1 (0.01-5 ng/ml) dose-dependently stimulated (by up to 120-fold) osteoclast formation (assessed by the presence of tartrate-resistant acid phosphatase (TRAP) positive multinucleated cells and expression of calcitonin and vitronectin receptors). In addition, TGF-beta1 also increased steady state RANK mRNA levels in a time- (by up to 3.5-fold at 48 h) and dose-dependent manner (by up to 2.2-fold at 10 ng/ml). TGF-beta1 induction of RANK mRNA levels was present both in undifferentiated RAW cells as well as in cells that had been induced to differentiate into osteoclasts by a 7-day treatment with M-CSF and RANK-L. Using a fluorescence-labeled RANK-L probe, we also demonstrated by flow cytometry that TGF-beta1 resulted in a significant increase in the percentage of RANK+ RAW cells (P < 0.05), as well as an increase in the fluorescence intensity per cell (P < 0.05), the latter consistent with an increase in RANK protein expression per cell. These data thus indicate that TGF-beta directly stimulates osteoclastic differentiation, and this is accompanied by increased RANK mRNA and protein expression.
Acid Phosphatase↗
Estrogen regulation of human osteoblast function is determined by the stage of differentiation and the estrogen receptor isoform.
Although osteoblasts have been shown to respond to estrogens and express both isoforms of the estrogen receptor (ER alpha and ER beta), the role each isoform plays in osteoblast cell function and differentiation is unknown. The two ER isoforms are known to differentially regulate estrogen-inducible promoter-reporter gene constructs, but their individual effects on endogenous gene expression in osteoblasts have not been reported. We compared the effects of 17 beta-estradiol (E) and tamoxifen (TAM) on gene expression and matrix formation during the differentiation of human osteoblast cell lines stably expressing either ER alpha (hFOB/ER alpha 9) or ER beta (hFOB/ER beta 6). Expression of the appropriate ER isoform in these cells was confirmed by northern and western blotting and the responses to E in the hFOB/ER beta 6 line were abolished by an ER beta-specific inhibitor. The data demonstrate that (1) in both the hFOB/ER cell lines, certain responses to E or TAM (including alkaline phosphatase, IL-6 and IL-11 production) are more pronounced at the late mineralization stage of differentiation compared to earlier stages, (2) E exerted a greater regulation of bone nodule formation and matrix protein/cytokine production in the ER alpha cells than in ER beta cells, and (3) the regulated expression of select genes differed between the ER alpha and ER beta cells. TAM had no effect on nodule formation in either cell line and was a less potent regulator of gene/protein expression than E. Thus, both the ER isoform and the stage of differentiation appear to influence the response of osteoblast cells to E and TAM.
Alkaline Phosphatase↗
Expression of a potential metastasis suppressor gene (nm23) in thyroid neoplasms.
Identification of multiple clinical and pathologic prognostic factors in differentiated thyroid cancer has permitted some degree of risk stratification. However, these clinical indices fail to distinguish potential intrinsic differences in tumor virulence. The nm23 gene has been identified as a potential metastasis suppressor gene that is homologous to nucleoside diphosphate kinases. Studies in human breast cancer have shown a significant inverse correlation between nm23 levels and nodal involvement/tumor recurrence. Given the possible clinical utility of a marker of metastatic potential in the management of thyroid carcinoma, we examined 34 thyroid neoplasms and a human medullary thyroid cancer (MTC) cell line (TT) for nm23 expression. Normalized nm23 expression was assessed by Northern analysis of tumor RNA. nm23 Expression (tumor expression/TT cell expression, mean +/- SE) was 1.14 +/- 0.15* in MTCs (n = 5), 0.70 +/- 0.10* in follicular cancers (n = 6), 0.51 +/- 0.11 in papillary cancers (n = 19), and 0.31 +/- 0.03 in follicular adenomas (n = 4) (*p < 0.05 when compared to adenomas). Within histologic groups, we found no correlation between nm23 expression and nodal involvement of distant metastases. Our results indicate that thyroid neoplasms of different histologies express varying levels of the nm23 transcript. Although nm23 expression seems diminished in metastatic breast cancer, it appears not to be the case in metastatic thyroid cancer. The nm23 gene may therefore have different roles in the evolution and metastases of different neoplasms.
Adenocarcinoma, Follicular↗
Epidemiology and clinical features of osteoporosis in young individuals.
Due to the lack of epidemiologic data on osteoporosis in the young, we identified all 22 Olmsted County, MN, residents aged 20-44 years when first diagnosed with established osteoporosis in 1976-1990. The overall age- and sex-adjusted incidence rate was 4.1 per 100,000 person-years (95% CI 2.4-5.9) with a female to male ratio of age-adjusted rates of 1.2:1. The majority represented secondary osteoporosis (12 steroid-induced, 3 postmenopausal, 2 delayed puberty, 2 anticonvulsant-induced, 2 gastrointestinal disease, 2 alcoholism, 1 anorexia nervosa, and 7 other etiologies; some individuals had more than one factor present) but two had idiopathic osteoporosis (incidence 0.4 per 100,000 person-years, 95% CI 0-0.9). To further characterize the patients with idiopathic osteoporosis, we also reviewed the entire Mayo Clinic experience with such patients from 1976 to 1990, regardless of residency. A total of 56 patients (30 female/26 male) were identified with a median age at diagnosis of 34 years. Only 8% were hypercalciuric at presentation. There was a preponderance of cancellous bone fractures (vertebral 81%, rib 37%, wrist 13%), although 13% did have hip fractures. Transiliac bone biopsies were available in 18 patients. As compared to age- and sex-matched controls, the osteoporotic subjects had a significant reduction in trabecular bone volume, cortical thickness, and mean wall thickness, the latter suggesting an abnormality in osteoblast function in these individuals.(ABSTRACT TRUNCATED AT 250 WORDS)
Absorptiometry, Photon↗
Culture of preimplantation embryos and its long-term effects on gene expression and phenotype.
A growing number of medical, scientific and biotechnological procedures rely on culture of mammalian preimplantation embryos. This review presents currently available data on aberrant offspring development that sometimes arises from commonly applied in-vitro procedures in humans, ruminant species and mice. Comparison between mammalian species reveals similarities in the phenotypic abnormalities that are observed at fetal and perinatal stages of development. In particular, aberrant effects on fetal growth have been observed in multiple studies in which serum complemented the preimplantation culture medium. Although it remains to be determined whether there is a common causal mechanism(s) involved, several hypotheses have been put forward to account for the variety of the observed developmental abnormalities. One of these postulates that culture can result in the epigenetic deregulation of developmentally important genes, and that such epigenetic alterations would affect in particular the expression of genes that are subject to genomic imprinting. Imprinted genes play key roles in the control of fetal growth, and altered imprinting can cause growth defects. Some recent in-vitro culture studies on mice and ruminant species now lend support to this hypothesis.
Animals↗