Biomedical subjects

S Klein

Publications and source records attributed to S Klein.

At least 163 records · Page 9Linked to original sources

PubMed1996

Integrin regulation by endogenous expression of 18-kDa fibroblast growth factor-2.

The three high molecular weight (HMW) forms of fibroblast growth factor-2 (FGF-2) have a distinct intracellular localization and differentially affect cell mobility and growth compared with the fourth 18-kDa form. To characterize further the effects of the 18-kDa and HMW forms of FGF-2, we have examined their ability to modulate integrin expression. Transfected NIH 3T3 cells expressing only 18-kDa FGF-2 exhibited increased cell surface levels of alpha5beta1, whereas cells expressing only HMW FGF-2 exhibited cell surface alpha5beta1 levels similar to parental cells. When cells synthesizing 18-kDa FGF-2 were transfected with a cDNA encoding a dominant negative FGF receptor, alpha5beta1 cell surface levels decreased. Immunoprecipitation of biosynthetically labeled cells indicated that expression of 18-kDa FGF-2 increased the biosynthesis and rate of maturation of alpha5. Northern blot analysis showed that 18-kDa FGF-2 increases the level of the alpha5 subunit mRNA but does not affect beta1 subunit transcript levels. Experiments utilizing luciferase reporter gene activity revealed increased alpha5 promoter activity in cells expressing 18-kDa FGF-2 indicating that the enhanced alpha5 transcript level is due to modulation of the transcription rate. Therefore, interaction of 18-kDa FGF-2 with FGF receptors results in changes in alpha5beta1 biosynthesis and processing. In contrast, endogenous expression of HMW FGF-2 does not mediate this effect.

3T3 Cells↗

PubMed1996

Colored diffraction catastrophes.

On fine scales, caustics produced with white light show vividly colored diffraction fringes. For caustics described by the elementary catastrophes of singularity theory, the colors are characteristic of the type of singularity. We study the diffraction colors of the fold and cusp catastrophes. The colors can be simulated computationally as the superposition of monochromatic patterns for different wavelengths. Far from the caustic, where the luminosity contrast is negligible, the fringe colors persist; an asymptotic theory explains why. Experiments with caustics produced by refraction through irregular bathroom-window glass show good agreement with theory. Colored fringes near the cusp reveal fine lines that are not present in any of the monochromatic components; these lines are explained in terms of partial decoherence between rays with widely differing path differences.

Journal Article↗

PubMed1996

Role of cdc25-C phosphatase in the immediate G2 delay induced by the exogenous factors epidermal growth factor and phorbolester.

Studies on the link between cellular signalling and cell cycle control at the G2 checkpoint have shown that, in HeLa cells, epidermal growth factor (EGF) and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) rapidly inhibit the G2-M transition by preventing the key component of mitosis-promoting factor (MPF), p34cdc2, from expressing protein kinase activity. The kinase activity of active MPF is not inhibited; rather, the conversion of pre-MPF to MPF, i.e., the activating dephosphorylation of p34cdc2, at tyrosine is rapidly blocked (Barth and Kinzel, 1994, Exp. Cell Res. 212:383-388; 1995, J. Cell. Physiol., 162:44-51). The phosphatase responsible, cdc25-C, is activated by phosphorylation in mitotic cells starting at the G2-M transition in an autocatalytic loop with MPF (Hoffmann et al., 1993, EMBO J. 12:53-63). We now show that, concomitant with the prevention of MPF activation, EGF and TPA induced a reduction of the activity of cdc25-C in synchronized cultures. Furthermore, treatment of mitotic HeLa cells with TPA did not influence the kinase activity of MPF but caused a rapid decrease of the specific enzyme activity of cdc25-C, probably due to dephosphorylation of the enzyme, as indicated by reduced binding of monoclonal MPM-2 antibody specific for phosphoepitopes in M phase. Because of its inability to induce signalling during division, EGF failed to influence the activity of cdc25-C in mitotic cells. The scenario in cells late in G2 that are committed to enter mitosis may be as follows: In those cells where the signalling pathways responding to EGF as well as those responding to TPA are still open, cdc25-C is prevented by dephosphorylation from exceeding the threshold level of activity required to initiate the activation of and the autocatalytic feedback loop with p34cdc2 and to enter mitosis. Therefore, cdc25-C appears to represent part of an interface between cellular signalling and cell cycle control in G2 phase.

CDC2 Protein Kinase↗

PubMed1996

Patterns of meiotic double-strand breakage on native and artificial yeast chromosomes.

The preferred positions for meiotic double-strand breakage were mapped on Saccharomyces cerevisiae chromosomes I and VI, and on a number of yeast artificial chromosomes carrying human DNA inserts. Each chromosome had strong and weak double-strand break (DSB) sites. On average one DSB-prone region was detected by pulsed-field gel electrophoresis per 25 kb of DNA, but each chromosome had a unique distribution of DSB sites. There were no preferred meiotic DSB sites near the telomeres. DSB-prone regions were associated with all of the known "hot spots" for meiotic recombination on chromosomes I, III and VI.

Chromosomes, Artificial, Yeast↗

PubMed1996

Relationship between neonatal nucleated red blood cell counts and hypoxic-ischemic injury.

OBJECTIVE: To determine if nucleated red blood cell counts(RBC) are different in infants who develop intraventricular hemorrhage and periventricular leukomalacia in the first week of life and in those who do not. METHODS: Nucleated RBCs were obtained from 441 infants weighing more than 499 g and less than 1751 g. Neonatal cranial fontanel sonography was performed on days 3 and 7 of life, and neonates were divided into those with normal and abnormal sonographic findings. The nucleated RBCs were compared between these groups and between normal and abnormal groups matched for birth weight and gestational age. RESULTS: Mean gestational age, birth weight, birth weight percentile, Apgar score, respiratory distress syndrome and mortality were different between the infants with normal and abnormal ultrasound findings. The nucleated RBCs (per 100 white blood cells) were not different (40.5 +/- 126.8 versus 41.8 +/- 71.7, t = 0.09, P = .9). When we controlled for gestational age and birth weight, there was no significant difference between nucleated RBCs in those with normal and abnormal sonography (54.3 +/- 206.5 versus 41.4 +/- 72.0,t = 0.56, P = .6). In growth-restricted neonates, there was a significant increase in nucleated RBCs regardless of whether growth restriction was defined as tenth percentile or less, 25th percentile or less, or 50th percentile or less, even when we controlled for gestational age. CONCLUSION: Nucleated RBCs are not different in preterm infants with or without intraventricular hemorrhage and periventricular leukomalacia, even when one controls for gestational age and birth weight. There are significant elevations in nucleated RBCs in growth-restricted fetuses. Birth weight percentile must be considered when using nucleated RBCs as a marker of intrauterine hypoxia.

Cerebral Hemorrhage↗

PubMed1996

Gastric adenocarcinoma in patients 40 years of age or younger.

BACKGROUND: Gastric adenocarcinoma is considered a disease of the middle aged and elderly and has been infrequently reported in patients under 40 years of age. The purpose of this study was to determine the proportion of young patients diagnosed with gastric adenocarcinoma and to compare the demographic, clinical and pathologic features of younger and older patients with gastric adenocarcinoma. METHODS: A retrospective cohort study using tumor registry records of all patients with gastric adenocarcinoma diagnosed from 1982 through 1996 at a public teaching hospital. Demographic, clinical, and pathologic comparisons were made between patients younger than 41 years of age and race- and sex-matched older patients with gastric adenocarcinoma. RESULTS: Thirty of 203 (15%) cases of gastric adenocarcinoma were diagnosed in patients less than 41 years (range 23 to 40). Male to female ratio was 1:1. Young patients were more likely to be black (33% versus 17%, P = 0.04) Both younger and older patients presented with advanced disease, with nearly half of each group having metastases. Twelve of 29 (41%) younger patients were operated on without a histologic diagnosis of gastric adenocarcinoma in contrast to only 1 older patient (P < 0.001). One of 30 (3%) young patients is alive 39 months following gastrectomy. Twenty patients died and the remaining 9 were lost to follow-up, all with known residual or recurrent disease. Six-month survival of young patients (23%) was less than older patients (42%) (P = 0.14). Young patients were more likely to have diffuse histology (80% versus 55%, P = 0.12). Overt infection with Helicobacter pylori was uncommon in both groups. CONCLUSIONS: Young patients accounted for an unusually high proportion of patients with gastric adenocarcinoma diagnosed at our public teaching hospital. Young patients were significantly more likely to be black and less likely to have an accurate preoperative histologic diagnosis. Both young and older patients presented with advanced disease and had poor survival. Young patients were more likely to have diffuse histology and had poorer 6-month survival, suggesting a more aggressive variety of the disease in this group.

Adenocarcinoma↗

PubMed1996

Metabolic response to radiation therapy in patients with cancer.

The effect of radiation therapy on substrate metabolism was evaluated in five patients with head and neck or lung cancer. Stable isotope tracer methodology was used to determine urea, amino acid, glucose, and lipid kinetics during postabsorptive conditions before initiation, near the midpoint (after receiving 2,672 +/- 36 rads), and at completion (after receiving 6,072 +/- 307 rad) of a 6- to 8-week course of radiation therapy. Nutritional status was maintained throughout the treatment period by providing supplemental enteral feedings as needed. Postabsorptive plasma insulin, catecholamine, and amino acid concentrations did not change during the course of treatment. Before radiation therapy was initiated, values for the plasma rate of appearance (Ra) of urea (3.35 +/- 0.33 micromol x kg(-1) x min(-1)), alpha-ketoisocaproate ([alpha-KIC] 2.16 +/- 0.19 micromol x kg(-1) x min(-1)), phenylalanine (0.59 +/- 0.052 micromol x kg(-1) x min(-1)), and glucose (10.56 +/- 1.31 micromol x kg(-1) x min(-1)) were in the normal range. However, glycerol and palmitate Ra values (3.11 +/- 0.30 and 2.01 +/- 0.33 micromol x kg(-1) x min(-1), respectively) were 25% higher than values observed previously in normal subjects. Substrate flux did not change during radiation therapy, and measurements obtained during the midpoint and at completion of treatment were similar to initial values. These results demonstrate that large doses of radiation therapy, administered over 6 to 8 weeks to the upper body, do not cause significant metabolic stress.

Amino Acids↗

PubMed1996

Effect of endurance training on glycerol kinetics during strenuous exercise in humans.

Glycerol kinetics were evaluated during high-intensity exercise in five untrained and five endurance-trained subjects. Glycerol rate of appearance (Ra) in plasma was determined by infusing [2H5]glycerol during rest and 60 minutes of cycle ergometer exercise performed at 70% V02 peak. Mean plasma glycerol concentration was greater in trained than untrained subjects throughout exercise (P<.05). The average glycerol Ra during exercise and the integrated lipolytic response to exercise, expressed as total glycerol Ra above baseline, were both greater in trained (7.85 +/- 0.72 micromol x kg(-1) x min(-1) and 289 +/- 50 micromol x kg(-1) x h(-1), respectively) than in untrained (5.68 +/- 0.90 micromol x kg(-1) x min(-1), and 198 +/- 31 micromol x kg(-1) x h(-1), respectively) subjects (P<.05). We conclude that whole-body lipolytic rates are greater in endurance-trained athletes than in sedentary controls during high-intensity exercise performed at the same relative intensity.

Adult↗

PubMed1996

Double-strand breaks on YACs during yeast meiosis may reflect meiotic recombination in the human genome.

Meiotic recombination in the yeast Saccharomyces cerevisiae is initiated at double-strand breaks (DSBs), which occur preferentially at specific locations. Genetically mapped regions of elevated meiotic recombination ('hotspots') coincide with meiotic DSB sites, which can be identified on chromosome blots of meiotic DNA (refs 4,5; S.K. et al., manuscript submitted). The morphology of yeast artificial chromosomes (YACs) containing human DNA during the pachytene stage of meiosis resembles that of native yeast chromosomes. Homologous YAC pairs segregate faithfully and recombine at the high rates characteristic of S. cerevisiae (vs. approximately 0.4 cM/kb in S. cerevisiae versus approximately 10-3 cM/kb in humans). We have examined a variety of YACs carrying human DNA inserts for double-strand breakage during yeast meiosis. Each YAC has a characteristic set of meiotic DSB sites, as do yeast chromosomes (S.K. et al., manuscript submitted). We show that the positions of the DSB sites in the YACs depend on the human-derived DNA in the clones. The degree of double-strand breakage in yeast meiosis of the YACs in our study appears to reflect the degree of meiotic recombination in humans.

Chromosome Mapping↗

PubMed1996

Angiogenesis and the fibrinolytic system.

Angiogenesis is defined as the formation of capillaries from preexisting blood vessels. This involves a balanced spatiotemporal modulation of endothelial cell adhesion, migration, and proliferation. An array of proteolytic enzymes expressed from endothelial cells including those of the plasminogen activator/plasmin system are required for angiogenesis to occur. In this review we focus on the growth factors that are involved in the angiogenic process and that modulate the expression and/or the activity of the plasminogen activator/plasmin system. The elucidation of the interactions between angiogenic growth factors, endothelial cell proteolytic enzymes, and the extracellular environment could ultimately lead to the therapeutic approaches to block angiogenesis and the pathophysiological conditions associated with it.

Animals↗

PubMed1996

Infusion of labeled KIC is more accurate than labeled leucine to determine human muscle protein synthesis.

The leucine constant infusion method is the most commonly used method for measuring fractional synthetic rates (FSR) of muscle protein. However, this method has been criticized because of the uncertainty involved in measuring precursor pool enrichment. We present an alternative method for measuring muscle FSR by giving a constant infusion of alpha-[1-13C]ketoisocaproate (alpha-[1-13C]KIC). We infused alpha-[1-13C]KIC and [5,5,5-2H3]leucine for 4 h in five volunteers and took plasma samples half-hourly and muscle biopsies at 1 and 4 h of isotope infusion. When KIC was infused, intramuscular free leucine enrichment was the same as arterial leucine enrichment. However, when labeled leucine was infused, intramuscular free leucine enrichment was only 76 +/- 3% of arterial KIC enrichment, which agrees with previous reports that plasma KIC enrichment does not accurately reflect intramuscular leucine enrichment. We obtained an FSR of 2.25 +/- 0.12%/day by use of this method, which agrees with a previous report using tRNA bound leucine as the precursor. In conclusion, the KIC infusion method overcomes the theoretical limitations of the leucine infusion.

Carbon Isotopes↗

PubMed1996

Effect of weight loss on whole body and cellular lipid metabolism in severely obese humans.

We evaluated the effect of diet-induced weight loss on whole body and cellular lipid metabolism in persons with severe upper body obesity in two study protocols. In protocol 1, palmitate and glycerol rates of appearance (Ra) in plasma were determined during basal conditions in seven subjects [initial body mass index (BMI) = 41.3 +/- 2.2 kg/m2] before and after 20.4 +/- 3.0 kg weight loss. Total glycerol and palmitate Ra decreased from 231.0 +/- 19.4 and 166.2 +/- 16.6 mumol/min, respectively, before weight loss to 162.7 +/- 9.5 and 105.0 +/- 9.7 mumol/min, respectively, after weight loss (P < 0.01). However, glycerol and palmitate Ra expressed per kilogram fat mass were similar both before and after weight loss. In protocol 2, subcutaneous abdominal adipose tissue was obtained before and after 14.4 +/- 2.1 kg weight loss in five subjects (initial BMI = 41.6 +/- 2.6 kg/m2). Weight loss caused a 38 +/- 8% decrease in adipocyte hormone-sensitive lipase concentration (P < 0.05) but was not associated with any consistent changes in the concentrations of GTP-dependent regulatory proteins, Gi1 alpha, Gi2 alpha, and G3 alpha. We conclude that diet-induced weight loss ameliorates the increase in basal lipolytic rates in persons with severe upper body obesity. These alterations are associated with changes in cellular hormone-sensitive lipase but not GTP-dependent regulatory protein concentrations.

Adult↗

PubMed1996

Fat and carbohydrate metabolism during exercise in elderly and young subjects.

We evaluated the effect of aging on fat and carbohydrate metabolism during moderate intensity exercise. Glycerol, free fatty acid (FFA), and glucose rate of appearance (Ra) in plasma and substrate oxidation were determined during 60 min of cycle ergometer exercise in six elderly (73 +/- 2 yr) and six young adults (26 +/- 2 yr) matched by gender and lean body mass. The elderly group was studied during exercise performed at 56 +/- 3% of maximum oxygen uptake, whereas the young adults were studied during exercise performed at the same absolute and at a similar relative intensity as the elderly subjects. Mean fat oxidation during exercise was 25-35% lower in the elderly subjects than in the young adults exercising at either the same absolute or similar relative intensities (P < 0.05). Mean carbohydrate oxidation in the elderly group was 35% higher than the young adults exercising at the same absolute intensity (P < 0.001) but 40% lower than the young adults exercising at the same relative intensity (P < 0.001). Average FFA Ra in the elderly subjects was 85% higher than in the young adults exercising at the same absolute intensity (P < 0.05) but 35% lower than the young adults exercising at a similar relative intensity (P < 0.05). We conclude that fat oxidation is decreased while carbohydrate oxidation is increased during moderate intensity exercise in elderly men and women. The shift in substrate oxidation was caused by age-related changes in skeletal muscle respiratory capacity because lipolytic rates and FFA availability were not rate limiting in the older subjects.

Adult↗

PubMed1996

Relation between plasma leptin concentration and body fat, gender, diet, age, and metabolic covariates.

We measured plasma leptin concentrations by RIA in 204 normal weight and obese subjects, aged 18-80 yr, using full-length recombinant human leptin as a standard. Fasting levels between 1.2-97.9 ng/mL were observed. The plasma leptin concentration was highly correlated with percent body fat (r = 0.710; P < 0.0001) and was 3 times as high in women as in men (17.1 vs. 5.8 ng/mL; P < 0.0001). Circulating leptin was inversely related to age and was reduced 53% in subjects over age 60 yr. A statistical model containing percent body fat, gender, and age accounted for 65% of the variance in plasma leptin levels. Leptin was not independently related to abdominal fat distribution, plasma lipids and lipoproteins, chronic energy intake, diet composition, plasma insulin, or maximum oxygen consumption. However, plasma leptin was reduced by 26% in 5 obese subjects who consumed a 1000-Cal diet for 10 days (P = 0.004). We conclude that circulating leptin rises continuously with increasing adiposity. Gender, age, and short term caloric restriction may be important secondary regulators of plasma leptin.

Adipose Tissue↗

PubMed1996

Adipose tissue leptin production and plasma leptin kinetics in humans.

Abdominal adipose tissue leptin production was determined in vivo by arteriovenous balance in 14 lean and obese men (mean BMI 27.0 +/- 1.9, range 21.4-45.2). Blood samples were taken simultaneously from an abdominal vein that drains subcutaneous adipose tissue and from a radial artery. Adipose tissue blood flow was measured by xenon washout. Abdominal vein leptin concentrations (mean 8.9 +/- 2.4 ng/ml, range 2.1-36.5 ng/ml) were consistently greater than arterial values (mean 6.6 +/- 1.9 ng/ml, range 1.7-28.2 ng/ml) (P < 0.001). The net rate of abdominal adipose tissue leptin production (mean 3.2 +/- 0.5 ng x 100 g(-1) x min(-1)) correlated directly with percentage body fat (rs = 0.59, P = 0.016). Estimated whole-body leptin production rate (797 +/- 283 ng x person(-1) x min(-1)) correlated directly with percent body fat (rs = 0.93, P < 0.0001) and with regional leptin production (rs = 0.81, P < 0.001). In contrast, the rate of leptin clearance from plasma (mean 1.50 +/- 0.23 ml x kg(-1) x min(-1)) and plasma leptin half-life (mean 24.9 +/- 4.4 min) was unrelated to adiposity (rs = 0.06, P = 0.30; rs = 0.16, P = 0.30, respectively). These results provide direct evidence that leptin is produced by adipose tissue in humans and that the rate of production is directly related to adiposity. A combination of greater leptin production per unit of body fat and increased production from expanded total body fat mass, rather than alterations in leptin clearance, account for the increase in plasma leptin concentrations observed in obese humans.

Abdomen↗

PubMed1996

Relationship between insulin sensitivity and plasma leptin concentration in lean and obese men.

Alterations in the production of or the sensitivity to leptin, the protein encoded by the ob gene, cause obesity and diabetes in rodents. We evaluated the isolated relationship between leptin and insulin sensitivity in lean and obese humans. Three groups of subjects who were carefully matched for either insulin sensitivity (determined by the modified intravenous glucose tolerance test and minimal model analysis) or adiposity (determined by hydrodensitometry) were studied: 1) lean insulin-sensitive men (percentage body fat, 15 +/- 1%); 2) lean insulin-resistant men (percentage body fat, 16 +/- 1%), matched on percentage body fat and fat mass with the lean insulin-sensitive group; and 3) obese insulin-resistant men (percentage body fat, 31 +/- 3), matched on insulin sensitivity with the lean insulin-resistant group. Basal plasma leptin concentrations were significantly lower in the lean insulin-sensitive than in the lean insulin-resistant men (1.90 +/- 0.4 vs. 4.35 +/- 1.21 ng/ml, P < 0.05) despite identical body composition. Plasma leptin in the obese men (9.27 +/- 1.4 ng/ml) was significantly higher than values in the two lean groups (P < 0.01). Marked alterations in plasma glucose and insulin concentrations induced by glucose and tolbutamide injection did not cause any change in plasma leptin levels. These results demonstrate that insulin resistance is associated with elevated plasma leptin levels independent of body fat mass. However, plasma insulin itself does not acutely regulate leptin production.

Adult↗

PubMed1996

Characterization of fibroblast growth factor-2 binding to ribosomes.

We have examined the binding of FGF-2 to ribosomes and have found that in NIH 3T3 cells that synthesize high amounts of all FGF-2 forms, both 18 kDa and HMW forms of FGF-2 bind to ribosomes. Ribosomes purified from these cells were treated with RNase or puromycin to identify the binding site of FGF-2 on the ribosome. Neither RNase nor puromycin treatment affected the in vivo binding of FGF-2 to ribosomes suggesting that FGF-2 binds ribosomal protein or rRNA, but not mRNA. The stoichiometry of binding in these cells was approximately 1 FGF-2 molecule bound per 1 ribosome. Binding was unaffected by high salt treatment indicating that FGF-2 tightly associates with polysomes. An in vitro binding experiment performed with purified ribosomes and recombinant FGF-2 suggested that the binding site is saturable. HBNF, a protein with similar charge and size to FGF-2, bound 15-fold less than FGF-2 to purified ribosomes. These results indicate that the binding of FGF-2 to ribosomes is specific.

3T3 Cells↗

PubMed1996

Extracorporeal methods of vascular control for difficult IVC procedures.

Surgical procedures in the juxtaheptic and intrapericardial inferior vena cava (IVC) are difficult because of the complexity of achieving vascular control in the area. We describe 10 patients with a variety of pathologies in this region who underwent venovenous bypass (VVB) or cardiopulmonary bypass with hypothermic circulatory arrest (CBCA). Renal cell carcinoma with IVC extension was present in three patients (with tumor extension into the right atrium in two), adrenal adenocarcinoma in one, septic IVC thrombus in one, and blunt IVC/hepatic trauma in five. Those patients without atrial involvement underwent VVB with a mean bypass time of 40 minutes (range 12-144). Those patients with tumor extension into the right atrium underwent CBCA with systemic hypothermia to 18(0)C, total body exsanguination for a bloodless field, and removal of the tumor by cavotomy and right atriotomy. The mean bypass, aortic cross-clamp, and circulatory arrest times were 152, 92, and 36 minutes, respectively. Eight of the 10 patients did well and went home within 4 weeks of surgery. Two patients died, one from metabolic sequelae of exsanguinating IVC injury (VVB) and one from sepsis 2 weeks postoperatively (CBCA).

Adult↗