Interaction of mithramycin with chromatin

Mithramycin (MTR) is an anti-cancer antibiotic that blocks the macromolecular biosynthesis via reversible interaction with DNA template in the presence of bivalent metal ion such as Mg2+. In absence of DNA, mithramycin forms two types of complexes with Mg2+, complex I (with 1:1 stoichiometry in terms of MTR: Mg2+) and complex II (with 1:2 stoichiometry in terms of MTR: Mg2+). In an eukaryotic system, the drug would interact with chromatin, a protein-DNA complex. We have employed the spectroscopic techniques such as absorption and fluorescence to study the interaction of MTR: Mg2+ complexes with rat liver chromatin. In this report, we have shown that the two types of ligands have different binding potentials with the same chromatin. This supports our proposition that complexes I and II, are different molecular species. We have also shown that the histone protein(s) reduce the binding potential and the number of available sites for both ligands.

Interaction of antitumor drug, mithramycin, with chromatin

Mithramycin (MTR) is an anticancer drug that blocks macromolecular biosynthesis via reversible interaction with DNA in the presence of bivalent cation such as Mg2+. Mithramycin forms two types of complexes with Mg2+: complex I (1:1 in terms of MTR:Mg2+) and complex II (2:1 in terms of MTR:Mg2+). In vivo antibiotic would interact with chromatin, a protein-DNA complex. For the first time we have demonstrated and characterized the association of both complexes of MTR with chromatin and nucleosome core. From an evaluation and comparison of the binding and thermodynamic parameters and CD spectra of bound complexes, we have shown the following. Histone(s) stand in the say of the access of the ligand(s) to chromosomal DNA. Chromatin and core particle interact differentially with the same ligand. Mode of interaction of the two complexes, I and II, with the same system is different. Significance of these results to understand the transcription inhibitory property of the drug in eukaryotic chromosome is discussed.

Infant sleep position and SIDS: a hospital-based interventional study

CONTEXT

Avoidance of the prone sleeping position is considered an important factor contributing to the decline in the incidence of sudden infant death syndrome (SIDS).

OBJECTIVES

To determine infant sleep positioning practices and SIDS awareness before and after a hospital-based Back to Sleep campaign.

DESIGN

A questionnaire-based, descriptive, and cross-sectional before-after trial.

SETTING

The pediatric outpatient department of an inner-city hospital in Brooklyn, New York.

SUBJECTS

Two consecutive samples of 250 mothers of healthy infants younger than 6 months old born in and attending the outpatient clinics of the hospital before and after the intervention.

INTERVENTION AND MAIN OUTCOME MEASURES

Specific policies promoting Back to Sleep were established in our newborn nursery and outpatient department. Reduction in prone infant sleep positioning was the primary outcome measure. Increased parental SIDS awareness was a secondary outcome.

RESULTS

The proportion of infants sleeping prone was reduced significantly (from 27% to 18%) after the intervention (P < .005). Among the mothers who chose the prone sleeping position for their infants, 49.6% worried about choking. Older mothers (> 22 years) responded to the intervention by a 45.6% reduction in prone placement (P < .005) as opposed to a 11.4% reduction among younger mothers (< 22 years) (P = ns). Other factors contributing to reduced prone positioning included marriage (adjusted odds ratio [OR] 0.57; 95% confidence interval [CI] 0.93, 0.34) and breast feeding (adjusted OR 0.66; 95% CI 1.1, 0.4). SIDS awareness was 79.6% and 82.4% in the preintervention and postintervention groups, respectively (P = ns).

CONCLUSIONS

The Back to Sleep campaign was effective in our hospital setting. Our data indicate the need for special targeting of young, unmarried, and non-breast-feeding mothers. Fear of choking remains an important deterrent to proper infant sleep positioning.

Iron deficiency in 1- to 3-year-old children. A pediatric failure?

OBJECTIVE

To determine the prevalence of iron deficiency and iron deficiency anemia in children aged 1 to 3 years in an urban population.

DESIGN

Venous blood was measured for levels of hemoglobin, ferritin, free erythrocyte protoporphyrin, and lead in children seen for well-child visits. Children with histories of chronic illness, prematurity, blood dyscrasias, and acute illness were excluded.

SETTING

The private practice offices of 4 pediatricians in the New York City area.

PATIENTS

A consecutive sample of 504 children aged 1 to 3 years was included.

RESULTS

More than one third (35%) of the children demonstrated evidence of iron insufficiency; 7% were iron deficient without anemia, and 10% had iron deficiency anemia.

CONCLUSION

Because the association of iron deficiency anemia with mental and psychomotor impairment during the first 2 years of life no longer seems to be in doubt, the high prevalence of iron deficiency anemia found in the 1- to 2-year-old children in this study is disturbing. This suggests the need for greater efforts at the prevention of iron deficiency during the second year of life.

A new breakfast cereal containing guar gum reduces postprandial plasma glucose and insulin concentrations in normal-weight human subjects

A new guar-containing wheatflake product was developed to assess its effect on carbohydrate tolerance in normal-weight, healthy subjects. The extruded wheatflake breakfast cereals containing 0 (control) or approximately 90 g guar gum/kg DM were fed to ten fasting, normal-weight, healthy subjects using a repeated measures design. The meals were similar in energy (approximately 1.8 MJ), available carbohydrate (78 g), protein (15 g) and fat (5.4 g) content. The guar gum content of the test meals was 6.3 g. Venous blood samples were taken fasting and at 15, 30, 45, 60, 90, 120, 150 and 240 min after commencing each breakfast and analysed for plasma glucose, insulin and C-peptide. The guar wheatflake meal produced a significant main effect for glucose and insulin at 0-60 min and 0-240 min time intervals respectively, but not for the C-peptide levels compared with the control meal. Significant reductions in postprandial glucose and insulin responses were seen following the guar wheatflake meal compared with the control meal at 15 and 60 min (glucose) and 15, 60, 90 and 120 min (insulin). The 60 and 120 min areas under the curve for glucose and insulin were significantly reduced by the guar gum meal, as was the 240 min area under the curve for insulin. Thus, it can be concluded that the use of a severe method of heat extrusion to produce guar wheatflakes does not diminish the physiological activity of the guar gum.

Comparison of lipid-lowering effects of low-dose fluvastatin and conventional-dose gemfibrozil in patients with primary hypercholesterolemia

A total of 123 patients with primary hypercholesterolemia were randomized on a 2:1 ratio to receive either fluvastatin at 20 mg once daily at night (n = 82) or gemfibrozil at 600 mg twice daily (n = 41) in a double-blind, double-dummy comparison of the effects on plasma lipid parameters and tolerability over 8 weeks. All patients had either low-density lipoprotein cholesterol (LDL-C) concentrations > or = 160 mg/dL (4.1 mmol/L) in association with definite coronary artery disease (CAD) or > or = 2 risk factors, or LDL-C > or = 190 mg/dL (4.9 mmol/L) with no CAD and < 2 risk factors. All had triglyceride (TG) levels < or = 350 mg/dL (4.0 mmol/L). After 8 weeks of treatment, fluvastatin produced significant reductions from baseline of 17.4% (p < 0.001) in LDL-C, 13.2% (p < 0.001) in total cholesterol (TC), 13.8% (p < 0.001) in very low-density lipoprotein cholesterol (VLDL-C), and 6.4% (NS) in TG. High-density lipoprotein cholesterol (HDL-C) was increased by 5.6% (p < 0.001), and the ratio of LDL-C:HDL-C (Friedewald) was decreased by 21.2% (p < 0.001). Gemfibrozil reduced LDL-C by 15.8%, TC by 13.4%, VLDL-C by 32.2%, LDL-C:HDL-C by 24.8%, and TG by 34.2%, and increased HDL-C by 13.9% (all changes were statistically significant, p < 0.001) compared with baseline. Gemfibrozil produced significantly greater changes in VLDL-C (p < 0.01), HDL-C (p < 0.001), and TG (p < 0.001), but not in LDL-C: HDL-C, compared with fluvastatin. Both drugs significantly reduced apolipoprotein (apo) B and lipoparticles (Lp) E:B, and increased apo A-I but had divergent effects on LpA-I (increased with fluvastatin and reduced with gemfibrozil; p < 0.05). At the end of the study, 43.8% of fluvastatin patients and 45% of gemfibrozil patients achieved a reduction of > 20% in LDL-C levels. Normalization of LDL-C levels was achieved (according to European Atherosclerosis Society guidelines) by 13.4% of fluvastatin- and 14.6% of gemfibrozil-treated patients. Both drugs were well tolerated; adverse events occurred in 36.6% of fluvastatin recipients compared with 58.5% of patients taking gemfibrozil. No clinically notable elevations of aspartate or alanine aminotransferases, alkaline phosphatase, or creatine phosphokinase occurred. No patient developed new or worsening lens opacities associated with a reduction in optically corrected visual acuity. The most commonly reported adverse events were headache and gastrointestinal upset. There were no serious drug-related adverse events.

Effect of British-made videotapes on clinical performance of medical students in Pakistan

The efficacy of videotapes, recorded in Cardiff, in improving the clinical performance of final-year medical students in Abbottabad (Pakistan) was tested, by carrying out a structured, stepwise, clinical assessment before and after video teaching in 32 students. All students examined eight systems/subsystems at eight stations and spent 5 min with each patient, during which their performance was checked against structured check-lists by eight examiners. These students had not received any clinical instruction from a specialist rheumatologist, neurologist or endocrinologist during their clinical apprenticeship. Before the video teaching they performed poorly when examining the knee joint, motor system, hands and thyroid status, but when tested again 2 days after video teaching, there was a transformation in their clinical behaviour and their mean (s.d.) score improved from 40 (6.6 per cent) to 57.6 (9.4 per cent; P = 0.001). In contrast to their pre-video performance, they interacted well with the patients and examiners providing a running commentary of their findings, as demonstrated in the videotapes. Among the residual problems were a poor technique of testing tendon reflexes and percussion. All the examiners and 21 of 32 students thought that the structured examination was fairer than the conventional examination. Of the 32 students, 20 thought that video teaching was less effective than personal bedside teaching, while 12 students thought that video was structured better than bedside instruction. All students would welcome video teaching to supplement their existing teaching and would like the structured examination introduced to their curriculum. This study suggests that videotaped demonstrations can be used effectively in transmitting clinical skills to students not exposed to clinical teaching by specialists in various subjects.

Interaction of inhibitin with the human erythrocyte Na+(Li+)i/Nao+ exchanger

The kinetic interactions of inhibitin, a peptide isolated from cultured leukaemic promyelocytes, with erythrocyte Na+/Na+ and Na+/Li+ exchanges have been investigated. Inhibitin (1 microM) reduced the ouabain- and bumetanide-resistant sodium efflux and influx by equivalent amounts indicating an inhibitin-sensitive exchange component of 0.52 mmol/l per h. This value was not significantly different from that measured as the difference in sodium-rich (140 mM) and sodium-free media (0.49 mmol/l per h). Similarly, the inhibitin-sensitive lithium efflux was equivalent to the sodium/lithium countertransport component (0.36 vs. 0.34 mmol/l per h), indicating that both exchanges were mediated by the same transport process, which is inhibitin-sensitive. The dose-response curve revealed the presence of a single inhibitin binding site per exchanger with a Ki of 2.10(-7) M. In kinetic inhibition studies, inhibitin (0.1 microM) decreased the Vmax of ouabain- and bumetanide-resistant sodium efflux with no effect on the Km for external sodium, i.e., inhibitin displayed a non-competitive mechanism of action. These findings indicate that inhibitin interacts with the Na+(Li+)i/Nao+ exchanger at a site distinct from the sodium binding site.

Characterization of Na+ transport in normal human fibroblasts and neoplastic H.Ep.2 cells and the role of inhibitin

Na+ transport was characterized in normal human fibroblasts and neoplastic H.Ep.2 cells in order to investigate the role of the endogenous peptidic factor 'inhibitin' that is secreted by a variety of neoplastic cells (including H.Ep.2) and inhibits Na+/Na+ exchange in human erythrocytes. Although active (Na+,K+-ATPase mediated) Na+ fluxes were similar in the two cell types, H.Ep.2 cells maintained higher intracellular Na+ concentration (26 mM) compared to fibroblasts (12 mM). An analysis of passive Na+ fluxes showed a difference in the handling of Na+ via ouabain and bumetanide-insensitive transport between the two cell types: H.Ep.2 cells achieved net Na+ influx via an amiloride-sensitive pathway that was only demonstrated in fibroblasts when 10% fetal calf serum (FCS) was present. Kinetic studies were undertaken to investigate the interaction between Na+ flux via Na+/H+ and Na+/Na+ exchanges. For this purpose, an outwardly directed Na+ gradient was created by loading the cells with Na+ (Nai greater than 100 mM) to activate the reverse functioning of Na+/H+ exchange (i.e., Na+out H+in). The rates of ouabain- and bumetanide-insensitive Na+ efflux were measured over a range of extracellular Na+ concentrations (Na+o 14-140 mM). In the presence of 10% FCS, the two cell types showed different responses: in fibroblasts the Na+ efflux rate showed an inverse correlation with extracellular Na+ concentration, while H.Ep.2 cells significantly increased their rate of Na+ efflux as extracellular Na+ concentration increased. So although the thermodynamic force would direct net Na+ efflux when Na+i greater than Na+o, H.Ep.2 cells were under kinetic control to perform Na+/Na+ exchange. When exogenous inhibitin was tested on fibroblasts, the steady-state intracellular Na+ concentration increased from 14 to 19 mM (p less than 0.01). In Na+-loaded fibroblasts, serum-stimulated Na+ efflux was partially inhibitin sensitive and the maximal inhibitory effect was seen when extracellular Na+ concentration was 14 mM and presumably the Na+/H+ exchanger operating in the reverse mode. This study demonstrated that, in contrast to fibroblasts, H.Ep.2 cells have a modified Na+/H+ exchange system whereby it acts in the Na+in H+out mode without exogenous growth factor activation and resists functioning in the reversed mode. It is proposed that inhibitin is the endogenous modifier of this transport system in H.Ep.2 cells with the result that H.Ep.2 cells maintain a higher concentration of intracellular Na+ compared to fibroblasts.

The relationship of dietary salt and blood pressure in three farming communities in Kashmir

The relationship between salt intake and blood pressure was explored in three different areas of Northern Kashmir, where people consume large quantities of salt in tea. Six villages were selected from each area and all the available family members of every second or third house were studied. Food and salt were weighed and the intake of each family member was obtained from the amount consumed out of the total cooked. Complete data were available from 361 subjects (191 males, 170 females). There was no significant difference between the three areas as regards age, height, weight, salt intake and blood pressure. Their age ranged from 15 to 88 yrs (mean 44) and the daily salt intake ranged from 70 to 420 mmol (mean 169 mmol). No correlation was found between age and salt intake or weight but there was a significant correlation between age and systolic blood pressure (r = 0.296; P less than 0.01). Both the systolic and diastolic blood pressure correlated significantly with the salt intake with correlation coefficients of 0.385 and 0.318 respectively (P less than 0.001). Multiple regression analyses showed that the significant relationship between salt and blood pressure was unaltered by adjustment for age. Of the 361 subjects, 46 (12.7%) had a blood pressure of 160/95 mmHg or more. This study suggests a similar relationship between habitual salt intake and blood pressure in each of three different areas of Northern Kashmir.

Calcium retention and increased vascular reactivity caused by a hypothalamic sodium transport inhibitor

1. Using a previously established method of isolating an active-sodium-transport inhibitor (ASTI) from hypothalamic cell culture medium, the inhibitor was isolated and partially purified from sequential passages through Sephadex G-25 and h.p.l.c., and its effects on de-endothelialized rabbit aortic strips were investigated. 2. ASTI caused a cumulative concentration-dependent increase in tension which reversed slowly after wash, and the wash showed an identical effect on fresh strips. 3. Ouabain, used as a control, also caused a concentration-dependent increase in tension which reached a plateau at a concentration of 10 mmol/l. Both ouabain and ASTI caused a significant potentiation of the vasoconstrictor effect of noradrenaline at concentrations of 1 nmol/l-0.1 mmol/l. 4. Both ASTI and ouabain caused a significantly greater (P less than 0.01) calcium retention than control medium in aortic strips. 5. Incubation of ASTI with prolidase, chymotrypsin and carboxypeptidase A destroyed the vasoconstrictor effects as well as its inhibitory effects on sodium, potassium-dependent adenosine triphosphatase and sodium efflux from erythrocytes, but leucine aminopeptidase was ineffective. 6. These studies suggest that hypothalamic cells in culture release a peptidic inhibitor of active sodium transport which increases vascular reactivity, potentiates vasoconstrictor effects of noradrenaline and causes calcium retention.

An active sodium transport inhibitor released from spontaneously hypertensive and normotensive rat fetal hypothalamic cells in culture

An inhibitor of active sodium transport (Na+ + K+-ATPase inhibitor), partially purified from the culture medium of fetal rat hypothalamic cells, has been shown to possess vasoactive properties. In order to explore whether fetal hypothalamic neurons from spontaneously hypertensive rats produce higher concentrations of the inhibitor than produced by those from normotensive rats, we cultured hypothalamic cells from both sources. An average of 10(6) cells per hypothalamus was obtained, and heat-treated (80 degrees C for 10 minutes) culture medium (120 ml) after lyophilization yielded 0.8 g of material. After Sephadex G-15 chromatography, 0.5 g of lyophilized medium from fetal hypothalamic neurons of spontaneously hypertensive rats yielded 254 +/- 47 arbitrarily defined units of Na+ + K+-ATPase inhibitory activity compared with 238 +/- 59 units from identical material of normotensive source. These studies show that the production of the hypothalamic Na+ + K+-ATPase inhibitor is not increased at the fetal stage in the spontaneously hypertensive rats.

Relationship between red cell sodium transport, blood pressure, and family history of hypertension

Numerous studies have demonstrated that Na+/Li+ countertransport is increased in erythrocytes from hypertensive patients. Since Na+/Li+ countertransport is conducted through the physiologically occurring Na+/Na+ exchange, we studied the latter pathway in 20 subjects with essential hypertension and 20 normotensive subjects matched for age and sex. Ten hypertensives and six normotensives had a positive family history of hypertension. Ouabain (0.1 mM) and furosemide (0.1 mM) were used to assess the active Na+ efflux and Na+-K+-Cl- pathway. There was no significant difference between hypertensive and normotensive subjects in any of the three pathways studied. Among the 16 subjects with a positive family history of hypertension, the mean value for external Na+-dependent Na+/Na+ exchange was significantly higher than in 24 subjects with no family history of hypertension (0.0457 +/- 0.0337 versus 0.0283 +/- 0.0202; P less than 0.05). This study suggests that an inherited membrane transport defect may exist for Na+/Na+ exchange in families of hypertensive subjects.

Problems and pitfalls in the isolation of an endogenous Na+, K+-ATPase inhibitor

Plasma from volume-expanded and salt-loaded hypertensive animals and from patients with essential hypertension has been reported to inhibit Na+, K+-adenosine triphosphatase (ATPase). Inhibition of the sodium pump in vascular smooth muscle caused by such a circulating factor could increase vascular tone and sensitivity to vasoactive agents, and thereby result in arterial hypertension. Numerous efforts in the past failed to isolate the putative factor from urine and plasma. Recent studies have suggested that the hypothalamus is an important source of an endogenous Na+, K+-ATPase inhibitor, but its isolation from the tissue extracts has been rendered difficult by the presence of other cellular constituents that cause artifactual interference with the assays and purification procedures. Using an alternative approach of isolating the inhibitor from culture medium, we found that dispersed fetal rat hypothalamic neurons in a capillary culture system release a heat-stable, peptidic, low-molecular-weight, active sodium transport inhibitor that causes a reversible increase in vascular tone, sensitizes vascular smooth muscle to the vasoactive effect of norepinephrine, and possesses several characteristics of the putative endogenous digitalislike factor. This inhibitor may be a chemical mediator linking kidney, brain, and cardiovascular system in the genesis of experimental volume-expanded and salt-loaded hypertension and human essential hypertension.

Beneficial effects of dietary carbohydrate restriction in chronic cor pulmonale

To explore the effects of moderate and severe reductions in carbohydrate intake on abnormal pulmonary physiology in chronic hypercapneic respiratory failure, spirometric, metabolic, arterial blood gas tension, and oximetric studies were carried out in eight patients who took, in random order daily for a week, either 50 g or 200 g of carbohydrate in an isocaloric diet. At the end of a week's daily intake of an isocaloric diet containing 200 g of carbohydrate, all patients experienced a subjective improvement; the mean body weight was 55.5 +/- 15.4 kg (1 SD) compared with 56.0 +/- 16.0 kg during the control dietary period, the arterial carbon dioxide tension decreased from a mean of 56.9 +/- 6.7 to 50.9 +/- 6.2 mm Hg (p less than 0.005), and the arterial oxygen tension increased from a mean of 50.6 +/- 7.3 to 62.0 +/- 14.5 mm Hg (p less than 0.02). After a week's intake of 50 g of carbohydrate in an isocaloric diet, the body weight and arterial oxygen tension did not change significantly, but the arterial carbon dioxide tension decreased still further to 48.0 +/- 7.8 mm Hg (p less than 0.05). Mouth pressure at 100 msec after the start of inspiration, as a measure of respiratory center output, was significantly higher during both the low carbohydrate intakes compared with the control dietary period. The spirometric data, ventilation-perfusion distribution measurements, oxygen consumption, and carbon dioxide production did not change significantly during various dietary periods. It is concluded that, under these short-term, hospital-controlled conditions, a reduction in the carbohydrate intake to 200 g a day improves the general well-being of patients with chronic hypercapneic respiratory failure, increases arterial oxygen tension, and decreases arterial carbon dioxide tension. A further reduction in the carbohydrate intake to 50 g a day provides further beneficial effects, and such a diet may be used in patients with intractable respiratory failure.

The relationship of salt intake and arterial blood pressure in salted-tea drinking Kashmiris

In this study we attempted to explore the relationship between salt and blood pressure in a salted-tea drinking population of Northern Kashmir which has not been exposed to a Western way of life. All the available family members of randomly selected houses in 14 villages were studied. Dietary intake was documented for the whole month of the study period to estimate the daily salt consumption in 281 subjects (193 males, 88 females), whose ages were reliably known. Their age ranged from 15 to 85 years (median 35) and their mean daily salt intake was 150 +/- 52 mmol (range 80-440). Both the systolic and diastolic blood pressures showed a significant increase with the salt intake and age; multiple regression analysis suggested an independent effect of salt intake on blood pressure after adjusting for age. Twenty-six subjects (9.3%) had hypertension (blood pressure greater than or equal to 160/95 mm Hg); their daily salt intake was significantly higher than that of normotensive subjects (mean 167 +/- SD 53 vs 142 +/- 46 mmol; P less than 0.001). These studies suggest a relationship between habitual high salt intake and blood pressure.