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Biomedical subjects

L S Stein

Publications and source records attributed to L S Stein.

At least 19 recordsLinked to original sources
PubMed2001

Incidence of major venous and renal anomalies relevant to aortoiliac surgery as demonstrated by computed tomography.

Preoperative knowledge of the presence of major venous anomalies facilitates the safe performance of aortic surgery. The purpose of the study was to estimate the incidence, as detected by abdominal and pelvic computed tomography (CT), of major venous and renal anomalies related to the abdominal aorta in an adult population. A total of 1822 intravenous contrast-enhanced abdominal and pelvic CT scans done in 1822 patients at two university teaching hospitals were randomly selected and prospectively reviewed (between June 1999 and March 2000) to identify major venous and renal anomalies associated with the abdominal aorta and iliac arteries. An interpreting staff radiologist then indicated on adata sheet whether any of the following anomalies were present or absent: (1) retroaortic left renal vein, (2) circumaortic left renal vein, (3) left-sided inferior vena cava (IVC) without situs inversus, (4) left-sided IVC with situs inversus, (5) duplicate IVC, (6) preaortic confluence of the iliac veins, or (7) horseshoe kidney. The CT scans reviewed had been performed for a wide variety of indications. Thirty-four scans were excluded from the study because either the anomalies we were looking for could not be assessed for technical reasons or the patient had a previous left nephrectomy and therefore assessment of the left renal vein was impossible. From this analysis we found that in an adult population, the prevalence of major venous and renal anomalies related to the abdominal aortaand iliac arteries and detected by CT scan was 5.65%. Prior to aortic surgery, preoperative knowledge of the presence of such anomalies helps with operative planning and may reduce the risk of major venous hemorrhage associated with these anomalies.

Abnormalities, Multiple↗
PubMed1997

Glucocorticoids inhibit bone resorption by isolated rat osteoclasts by enhancing apoptosis.

We have studied the effects of glucocorticoids on the activity and viability of neonatal rat osteoclasts in vitro. In the bone slice assay, glucocorticoids caused a dose-dependent decrease in the amount of bone resorbed, which was accompanied by a parallel decrease in osteoclast number. Loss of osteoclasts was due to their death, which occurred by the process of apoptosis. Evidence for the latter was obtained by a range of techniques, including time-lapse video microscopy, acridine orange staining, DNA fragment detection and transmission electron microscopy. Immunocytochemistry revealed the presence of glucocorticoid receptors in osteoclasts, and glucocorticoid-induced cell death could be prevented by the glucocorticoid receptor antagonist, RU486. These observations suggest that glucocorticoids promote receptor-mediated apoptosis of rat osteoclasts in vitro. This finding may help to explain recent data indicating that, in sharp contrast with their effects on the human skeleton, glucocorticoids inhibit bone resorption and increase bone mass in rats in vivo.

Animals↗
PubMed1996

Effect of diacylglycerols on osteoclastic bone resorption.

We studied the effect of various synthetic diacylglycerols (DAGs) on bone resorption by rat and chick osteoclasts. 1-stearoyl-2-arachidonoyl-sn-glycerol (DAG IV), at a concentration of 100 microM, caused a significant reduction in resorption pit number in both species at 6 and 24 hours without any toxic effect. Over a 6-hour incubation period, a significant inhibition was seen at 10 and 100 microM in both species. 1,2-dioctanoyl-sn-glycerol (DAG I) and 1,2-dihexanoyl-sn-glycerol (DAG III) caused a marked inhibition of resorption by rat osteoclasts at 6 hours, but there was recovery of bone-resorptive ability over a 24-hour incubation period. DAGs with the -rac conformation failed to have any effect on bone resorption. In time-lapse video studies, osteoclast motility was not influenced by any of the DAGs at any of the concentrations used. Our results indicate that DAGs with the -sn conformation inhibit bone resorption, and DAGs with the -rac conformation do not. The finding that DAGs, the physiological activators of protein kinase C (PKC), inhibit bone resorption provides further evidence for an important role of the PKC pathway in the regulation of osteoclast activity.

Analysis of Variance↗
PubMed1995

Lack of significant effect of carboxyl-terminal parathyroid hormone-related peptide fragments on isolated rat and chick osteoclasts.

Parathyroid hormone-related protein (PTHrP) fragments 107-111, 107-138, and 107-139 were all found to be without consistent significant inhibitory effect on the resorptive activity of isolated rat and chick osteoclasts over the dose range 10(-13) M-10(-9) M. In the rat, these results contrasted with a strong and significant inhibition (100%) by calcitonin. Our results differ from that previously reported for C-terminal fragments of PTHrP by Fenton et al. [1-3], who noted up to a 70% inhibition of resorptive activity of isolated rat or chick osteoclasts at femtomolar doses and greater. It is possible that the lack of response observed in our osteoclast assays is due to unknown variables in the bone slice assay that influence the responsiveness of isolated osteoclasts to these fragments.

Animals↗
PubMed1993

Concurrent analysis of intracellular glutathione content and gap junctional intercellular communication.

The potential for performing dual analysis of intracellular glutathione levels and assessment of gap junctional intercellular communication with thiol-specific fluorescent probes in anchored cells was evaluated. Gap junction-mediated diffusion of monochlorobimane and 5-chloromethylfluorescein diacetate following intracellular loading and conjugation with glutathione was compared with 5-carboxyfluorescein diacetate (which is routinely used in laser cytometry to monitor intercellular communication) by means of fluorescence recovery after photobleaching using a variety of communication-competent and communication-incompetent cells. The rate of diffusion of fluorescence among communication-competent cells was inversely proportional to the size of the fluorescent probe employed. The thiol-specific probes were also employed to monitor depletion and synthesis of glutathione following treatments to inhibit glutathione synthesis or consume glutathione by adduct formation. Analysis of gap junctional intercellular communication following glutathione depletion revealed a direct correlation between glutathione levels and intercellular communication. These studies support the utility of the thiol-specific probes to monitor the respective role of cellular glutathione and intercellular communication in the mechanisms of cellular injury.

Animals↗
PubMed1993

Stimulation of bone resorption and osteoclast clear zone formation by low pH: a time-course study.

The significance of low pH-induced stimulation of osteoclastic bone resorption has recently been questioned following the finding that embryonic chick osteoclasts were only weakly stimulated by extremely low pH (6.5) and that the effect was transient, apparently due to cytotoxicity. Although low pH in the range 6.8-7.2 is known to stimulate rat osteoclasts over 24 h, the long-term effects of low pH on mammalian osteoclasts are not known. We have therefore conducted time-course studies over 72 h on the effect of pH in the range 6.3-7.3 on bone resorption and cytotoxicity in both rat and chick osteoclasts. In neonatal rat osteoclasts, lowering extracellular pH produced a powerful and significant stimulation of resorption over 24 h. Detailed analysis of the resorption focus revealed that this was due mainly to a higher proportion of active osteoclasts at lower pH. In addition, osteoclasts excavated slightly larger pits at low pH. Stimulation was no longer significant at 72 h, however, due to a pH-dependent slowing of resorption at acid pH associated 1) with cytotoxicity primarily of nonosteoclastic cells and 2) with an acceleration of bone resorption after 24 h at more alkaline pH. Resorption stimulated by low pH was associated with the formation of actin-rich "clear zones" within the osteoclast. Chick osteoclasts were less sensitive to low pH than rat osteoclasts but nonetheless showed a consistently higher level of resorption at low pH over 24-72 h. These results suggest that protons play an important regulatory role in neonatal rat osteoclasts, and stimulate the formation of clear zones. The lower sensitivity of the chick osteoclast to acid pH may be due to a species difference or the chick osteoclast's higher basal level of resorption.

Actins↗
PubMed1993

Concomitant alterations of desmosomes, adhesiveness, and diffusion through gap junction channels in a rat ovarian transformation model system.

Gap junctional intercellular communication (GJIC), desmosomes, and cell movement were evaluated in a rat ovarian epithelial cell model system which consisted of an immortalized clonal cell line (SIGC), a pSV3neotransfected clonal derivative (SV-SIGC), and a nude mouse SV-SIGC-tumor-derived cell line (T-SV-SIGC). Complementary ultrastructural, indirect immunofluorescence, and Western blot data identified a relatively small loss of desmosomes and associated cytokeratins in SV-SIGC compared to SIGC but a near total loss in T-SV-SIGC. SIGC and SV-SIGC migrated outward from monolayer-coated microcarrier beads as epithelial sheets, whereas in T-SV-SIGC there was dissociation and migration of individual fibroblastoid cells. GJIC was assessed by fluorescence recovery after photobleaching (gap FRAP) and equations based on Fick's first law of diffusion were derived to quantitatively compare GJIC of systems with different recovery equilibria after photobleaching. Taken together the data suggested that GJIC in SIGC was quantitatively reduced to similar levels by various conditions associated with reduced cell-cell adhesiveness including transformation to T-SV-SIGC, mitosis, and culture in low calcium medium. These results supported linkage between changes in desmosomal adhesiveness, cell movement, and GJIC.

Animals↗
PubMed1992

Effects of phorbol myristate acetate on rat and chick osteoclasts.

The role of protein kinase C in the regulation of osteoclast function is not known. We therefore compared the effect of phorbol myristate acetate (PMA), which activates protein kinase C, on the resorptive function, motility, and morphology of osteoclasts from rat and chick. PMA caused a significant reduction in resorption pit number in both species; rat osteoclasts were more sensitive, being significantly inhibited at doses of 10(-9)-10(-6) M compared with 10(-7)-10(-6) M for chick osteoclasts. The inactive analog PMA-alpha was without significant effect, and inhibition was not blocked by 10(-6) M indomethacin. In time course experiments, inhibition at 24 h was similar to or greater than inhibition at 6 h, indicating a persistent or progressive effect on bone resorption. Removal of PMA after 6 h prompted partial recovery of bone-resorptive ability in chick osteoclasts but not rat, at least over a 48 h incubation. In time-lapse video studies of rat osteoclasts, 10(-6) M PMA produced an immediate but transient cessation of motility and retraction of the cell margin into prominent filopodia. Motility resumed within 2.5 h after addition, but the osteoclasts remained partially contracted. Chick osteoclasts behaved similarly but showed no formation of filopodia at the cell periphery and a more rapid recovery of motility than rat osteoclasts; chick osteoclasts also underwent a transient vacuolation following PMA exposure, whereas rat osteoclasts did not. Despite differences in the sensitivity of rat and chick osteoclasts to PMA, these results suggest a fundamental role for protein kinase C in the inhibition of osteoclasts from both species.

Animals↗
PubMed1992

Cell-to-cell communication competence in simian virus 40-transfected rat ovarian cells is reduced following tumor selection.

A pSV3neo-transfected rat ovarian cell line (SV-GC) was developed from a primary granulosa culture (GC) to study gap junctional intercellular communication (GJIC) during Simian virus 40 (SV40) transformation. SV-GC expressed SV40 large T-antigen (T-ag), grew indefinitely in culture without luteinization, was anchorage independent, and formed tumors in nude mice. Ultrastructural analysis identified abundant gap junctional membrane and suggested that SV-GC was arrested at an early stage of differentiation. Functional GJIC, measured by a dye transfer technique (gap FRAP), was comparable to that observed in normal granulosa cells, suggesting that the expression of T-ag alone was insufficient to reduce GJIC. However, there was approximately a 50% loss in the rate of GJIC in the nude mouse SV-GC-tumor derived and G418 selected cell line (T-SV-GC). SV-GC----T-SV-GC also resulted in a transition from migration of cells as an epithelial sheet to the dissociation of individual fibroblastoid cells. Tumor cell detachment was also seen in migrating malignant human (A2780 and 547) and rat (DC3) ovarian cell lines. Co-culture combinations of normal (GC)----transformed (SV-GC)----tumor-derived (T-SV-GC) cells indicated that the rate of heterologous GJIC was characteristic of the least communicating partner. Taken together, these data suggested that SV-GC----T-SV-GC represented progression toward metastasis with concomitant reduction of GJIC and adhesiveness. These sequentially derived cell lines may be a useful in vitro model system for studies focusing on the mechanism involved in the detachment of cells during the progression of ovarian cancer.

Animals↗
PubMed1992

Reduced cell-cell communication between mitotic and nonmitotic coupled cells.

The effects of mitosis on gap junctional intercellular communication (GJIC) were quantified in a clonal cell line of spontaneously immortalized rat granulosa cells (SIGC) using a fluorescence recovery after photobleaching assay. Reduction of GJIC was associated with the process of mitosis and was first apparent at the onset of prophase. Resumption of GJIC between newly divided cells and surrounding cells occurred slowly, requiring several hours following cytokinesis before reestablishment of maximal rates. Mitotic rates of GJIC in SIGC were comparable to values obtained in interphase cells partially uncoupled by 0.5 mM octanol. Limited studies of other cell lines generalized the mitotic-associated reduction of GJIC observed in SIGC. The data suggest that mitosis is one process which alters GJIC. This could be of significance when there is a change in the rate of proliferation, such as in the acquisition of immortalization, an early stage of transformation.

1-Octanol↗
PubMed1991

Rat ovarian granulosa cell culture: a model system for the study of cell-cell communication during multistep transformation.

A spontaneously immortalized clonal granulosa cell line (SIGC) derived from primary rat ovarian granulosa cell cultures was developed as a model system to explore the process of transformation using an epithelial cell type. SIGC has an epithelial morphology and grows in culture without undergoing luteinization. The cell line is thought to represent an intermediate step in carcinogenesis because it seems to grow indefinitely in culture but does not form clones in soft agar or tumors in nude mice. Indirect immunofluorescence and Western blot analysis verified the constitutive expression of the recessive oncogene product p53 in the cell line, thereby suggesting a possible mechanism of immortalization. Ultrastructural studies indicated that SIGC cells are characterized by an undifferentiated phenotype with prominent intermediate filaments, desmosomes, and gap junctions. The identification of cytokeratin by indirect immunofluorescence and Western blot analysis suggests that SIGC functions as an epithelial cell type. Functional studies of cell-cell communication by a dye transfer technique (fluorescence recovery after photobleaching) showed reduced communication compared to normal primary granulosa cells in culture. SIGC cells were transfected with early region genes of SV40 virus in an attempt to generate fully transformed cell lines. The resulting cell line SV-SIGC expressed T-antigen, was anchorage independent, formed tumors in nude mice, and had reduced intercellular communication as compared to SIGC cells. Explants from the tumors in nude mice were used to generate another cell line (T-SV-SIGC), which exhibited further reduction in both the incidence and the rate of communication. These results clearly demonstrated a progressive loss of functional communication during multistep transformation of an ovarian cell type. These data demonstrate that this assay system based on an epithelioid cell type can be used to study the relationship between intercellular communication and the multistep process of carcinogenesis.

Animals↗
PubMed1990

The effects of parathyroid hormone (PTH) and PTH-related peptide on osteoclast resorption of bone slices in vitro: an analysis of pit size and the resorption focus.

The mechanism whereby PTH, a potent stimulator of bone resorption, may under certain circumstances exert anabolic effects on bone is not known, but it is possible that it involves reduction of the size of osteoclast resorption lacunae. We have therefore made a detailed in vitro study of the effects of PTH and PTH-related peptide (PTHrP) on resorption by neonatal rat osteoclasts paying particular attention to the plan area of resorption pits. In order to distinguish between increased resorption at a particular site and increased numbers of sites, we have used an eyepiece graticule to define a focus of resorption, namely an area occupying 1/116th of the bone slice, which may contain either one or several pits. In addition we have studied the relationship between the number of pits in a resorption focus and the total area of bone resorbed at the focus. We found that PTH and PTHrP, at doses between 2 x 10(-10) M and 2 x 10(-8) M, while exerting significant stimulatory effects on bone resorption, caused a reduction in the median plan area of pits. An increase in the number of resorption foci was the primary stimulatory effect of PTH and PTHrP, occurring within 6 h in the case of PTH. However, the plan area of bone resorbed at a focus showed no significant increase, despite an increase in the number of pits per focus, because as more pits were formed at a focus, the pits were smaller, thus partially dissipating the stimulatory effect of PTH on resorption. These results are consistent with the activation of new remodeling sites by PTH in vivo. Furthermore, the formation of smaller pits under the resorptive influence of PTH may, together with the maintenance of coupling between formation and resorption, play a role in the preservation of cancellous bone recorded in cases of primary hyperparathyroidism and the anabolic effect of exogenous PTH.

Animals↗
PubMed1981

The effectiveness of continuing medical education: eight research reports.

Continuing medical education has been widely criticized as ineffective; most such criticism is directed at the assumption that the mere transmission of information on new research findings is sufficient to change physician performance. Eight studies published during the 1970s report changes in physician behaviour (and, in one, improved patient outcomes) as a result of CME organized on sound educational principles, including systematic effort to evaluate program effectiveness and learner achievement. It is also suggested that additional information on CME effectiveness is likely to be obscured by the form in which much medical literature is presented.

Clinical Competence↗