Zinc as a Biomarker of Cardiovascular Health

The importance of zinc (Zn) for cardiovascular health continuously gains recognition. As shown earlier, compromised Zn homeostasis and prolonged inflammation are common features in various cardiovascular diseases (CVDs). Similarly, Zn biochemistry alters several vascular processes, and Zn status is an important feature of cardiovascular health. Zn deficiency contributes to the development of CVDs; thus, Zn manipulations, including Zn supplementation, are beneficial for preventing and treating numerous cardiovascular (CV) disorders. Finally, additional long-term, well-designed studies, performed in various population groups, should be pursued to further clarify significant relationships between Zn and CVDs.

Walnut Consumption Induces Tissue-Specific Omega-6/Omega-3 Decrease in High-Fructose-Fed Wistar Rats

Increased dietary, blood, and tissue n-6/n-3 fatty acid ratios are associated with obesity and metabolic syndrome. Due to Westernized dietary patterns, the increasing n-6/n-3 ratio is of growing concern worldwide, and dietary strategies aimed at its lowering are of public health importance. Walnuts are rich in dietary fats, and their consumption promotes cardiometabolic health. This study aimed to examine the effect of 6-week walnut consumption on tissue-specific n-6/n-3 ratio and fatty acid metabolic conversion in fructose-fed rats with a cluster of metabolic disorders. Male Wistar rats were fed a standard diet with or without 10% fructose in drinking water for 9 weeks. Diets of half of the animals were then supplemented with walnuts (2.4 g/day) for 6 weeks, upon which fatty acid profiles were determined in plasma, liver, adipose tissue, and kidney total lipids. Results showed that walnuts induced significant decreases in the n-6/n-3 content of total lipid pool in plasma and examined tissues, irrespective of metabolic burden. Walnut intervention decreased plasma and liver palmitoleic/palmitic, arachidonic/linoleic, and docosahexaenoic/α-linolenic acid ratios. It also modulated individual fatty acid levels by reducing arachidonic and palmitic acid and increasing α-linolenic, eicosapentaenoic, and docosapentaenoic acid in plasma and most tissues. Our study demonstrated that 6-week consumption of walnuts favorably modulated n-6/n-3 plasma and tissue ratio in male Wistar rats regardless of high-fructose feeding, underscoring the promising potential of walnuts in both prevention and treatment of the metabolic syndrome.

FADS2 polymorphisms are associated with plasma arachidonic acid and estimated desaturase-5 activity in a cross-sectional study

Polymorphisms in FADS genes are associated with plasma long-chain polyunsaturated fatty acids (LC-PUFA) and modulate omega-6/omega-3 balance. We hypothesized that the FADS2 gene variants will be associated with lower product-to-precursor ratio in the fatty acid metabolic pathways. Thus, we explored FADS2 rs174593, rs174616, and rs174576 effects on plasma phospholipid fatty acid profile, markers of desaturase activities, and risk factors in a sample of apparently healthy Serbian adults. Food and nutrient intake data were compiled through 24 h recalls. Plasma phospholipid fatty acid content was assessed by gas-chromatography. Estimated desaturase activities were calculated as conversion rates towards LC-PUFA in omega-6 pathway. During the selection of FADS2 polymorphisms, we accounted for their positional and functional aspect. Genotyping was performed by Real-Time PCR. Multivariable-adjusted general linear and hierarchical regression models were applied. Study subjects (mean age = 40 ± 7 years, 70% who were overweight) had a median dietary omega-6/omega-3 ratio of 16.29. Alternative allele frequencies were 33%, 36%, and 51% for rs174593, rs174576, and rs174616, respectively. Addition of FADS2 alternative alleles was associated with lower plasma arachidonic acid (AA, C20:4 n-6, P < .001) and estimated desaturase-5 activity (P < .001), irrespective of gender, age, daily polyunsaturated/saturated fatty acid intake, and obesity. The rs174576 association with AA withstood multiple testing and additional adjustments for other variants (multivariable-adjusted β = -1.14 [95% CI: -2.25, -0.43]). None of the variants was associated with dietary intake, serum lipids, or obesity. We observed inverse associations between FADS2 variants and plasma AA but not omega-3 fatty acids in Serbian subjects, with rs174576 exhibiting the strongest relation.

Identifying sources of measurement error in assessing dietary intakes - Results of a multi-country ring-trial

BACKGROUND AND AIMS

Epidemiological investigations include dietary intakes as primary exposures or potential confounders. To reduce bias, data collection protocols include the administration of questionnaires together with measurements of biomarkers. Some error, however, remains and needs to be considered in the analysis and interpretation of results. The European Food Safety Authority supported a ring-trial to compare the precision and reproducibility of dietary assessment methods applied in Europe.

METHODS AND RESULTS

Software applications used to collect 24-hour recalls and food records in six countries (Estonia, Italy, Latvia, Portugal, Spain, and Sweden) were assessed. The intake of 256 foods was identically reported to each method. Experienced interviewers participated and were instructed to repeat national protocols closely. The error in recording quantities, compared with reference values, was variable but in about 60% of recorded quantities was in the range of ±20%. Errors were however unsystematic and independent of the food type or quantification method used - although food pictures performed better. The reproducibility of some tools was limited. The methods generally captured additional ingredients (usually flavoring agents), but not sweetening agents or fortification and failed to record packaging information in about 60% of the cases.

CONCLUSION

In a design that eliminated respondent bias, this study indicates that softwares, supporting databases and interviewers generally introduce random error in dietary assessments. The inclusion of large sample sizes and food pictures to quantify portions, together with enhanced attention on interviewers' training, standardisation of procedures and regular tool upgrades are essential in assuring a study's quality and comparability.

Vitamin D Is Inversely Related to Obesity: Cross-Sectional Study in a Small Cohort of Serbian Adults

Objective: Vitamin D (vitD) mediates numerous health conditions other than bone health and mineralization. Its role in cardiometabolic condition is still inconclusive. Methods: We conducted a cross-sectional study in 87 apparently healthy Serbian adults. We assessed their dietary intake, anthropometric and biochemical parameters, blood pressure, and vitD status (as serum 25-hydroxyvitamin D, 25(OH)D). Unexpectedly, the status was significantly higher in January than in July. Therefore, we pooled the data from two time points, to enhance the statistical power for carrying out association analyses. We employed linear regression models to evaluate the associations between vitD status and the obesity biomarkers of serum lipids and blood pressure. Results: Mean vitD intake of 3.85 ± 4.71 μg in the cohort was below recommended. Of the subjects in the pooled cohort, 60.58% were vitD deficient (with serum 25(OH)D below 50 nmol/L), with the majority of them being women who were overweight. VitD status tended to be inversely related to percent body fat and waist/height ratio in the crude regression model. After age and gender adjustment, the status was significantly related to waist circumference, waist/height ratio, and waist/hip ratio (β = -0.116, 95% confidence interval [CI]: -0.206, -0.025, β = -0.001, 95% CI: -0.001, 0.000, and β = -0.001, 95% CI: -0.001, 0.000, respectively). These associations remained only within women. Fully adjusted models supported the notion of vitD being independently associated with central adiposity, regardless of age, gender, and total obesity. Conclusions: In apparently healthy adults with low vitD intake, vitD status was inversely associated with obesity parameters, pronouncedly in women. Our data support the need for development and implementation of public health policies on increasing vitD intake also as part of obesity management strategies.

Impact of Selenium Addition to Animal Feeds on Human Selenium Status in Serbia

Research conducted during the 1980s demonstrated Se deficiency in humans. Increased inclusion of selenium in animal feeds started from the year 2000 onwards. The aim of this study was to estimate the effects of selenium inclusion in animal feeds on human selenium status and dietary habits of the Serbian population related to food of animal origin. Plasma selenium concentration in healthy adult volunteers, including residents of one of the regions with the lowest (Eastern Serbia, n = 60) and of one of the regions with the highest Se serum levels reported in the past (Belgrade, n = 82), was determined by hydride generation atomic absorption spectrometry. Multivariate analysis was employed to determine the correlation between Se plasma levels and dietary intake data derived from food frequency questionnaires and laboratory tests. The mean plasma Se level of the participants was 84.3 ± 15.9 μg/L (range: 47.3–132.1 μg/L), while 46% of participants had plasma Se levels lower than 80 μg/L. Frequency of meat, egg, and fish consumption was significantly correlated with plasma selenium level (r = 0.437, p = 0.000). Selenium addition to animal feed in the quantity of 0.14 mg/kg contributed to the improvement of human plasma selenium levels by approximately 30 μg/L.

N-acetyl-L-cysteine protects dental tissue stem cells against oxidative stress in vitro

OBJECTIVES

The aim of our study was to investigate whether N-acetyl-L-cysteine (NAC) could protect stem cells from exfoliated deciduous teeth (SHED) against oxidative damage, during in vitro cultivation, to preserve regenerative potential of these cells. Accordingly, we examined the potential of cell culture supplementation with NAC in prevention of lipid peroxidation, unfavorable changes of total lipids fatty acid composition, and the effects on the activity of antioxidant enzymes.

MATERIAL AND METHODS

We analyzed the extent of oxidative damage in SHED after 48 h treatment with different NAC concentrations. Cellular lipid peroxidation was determined upon reaction with thiobarbituric acid. All enzyme activities were measured spectrophotometrically, based on published methods. Fatty acid methyl esters were analyzed by gas-liquid chromatography.

RESULTS

Concentration of 0.1 mM NAC showed the most profound effects on SHED, significantly decreasing levels of lipid peroxidation in comparison to control. This dose also diminished the activities of antioxidant enzymes. Furthermore, NAC treatment significantly changed fatty acid composition of cells, reducing levels of oleic acid and monounsaturated fatty acids and increasing linoleic acid, n-6, and total polyunsaturated fatty acid (PUFA) proportions.

CONCLUSION

Low dose of NAC significantly decreased lipid peroxidation and altered fatty acid composition towards increasing PUFA. The reduced oxidative damage of cellular lipids could be strongly related to improved SHED survival in vitro.

CLINICAL RELEVANCE

Low doses of antioxidants, applied during stem cells culturing and maintenance, could improve cellular characteristics in vitro. This is prerequisite for successful use of stem cells in various clinical applications.

The Linoleic Acid: Dihomo-γ-Linolenic Acid Ratio (LA:DGLA)-An Emerging Biomarker of Zn Status

Zinc (Zn) deficiency is a common aliment predicted to affect 17% of the world's population. Zinc is a vital micronutrient used for over 300 enzymatic reactions and multiple biochemical and structural processes in the body. Although whole blood, plasma, and urine zinc decrease in severe zinc deficiency, accurate assessment of zinc status, especially in mild to moderate deficiency, is difficult as studies with these biomarkers are often contradictory and inconsistent. Hence, as suggested by the World Health Organization, sensitive and specific biological markers of zinc status are still needed. In this review, we provide evidence to demonstrate that the LA:DGLA ratio (linoleic acid:dihomo-γ-linolenic acid ratio) may be a useful additional indicator for assessing Zn status more precisely. However, this biomarker needs to be tested further in order to determine its full potential.

An initial evaluation of newly proposed biomarker of zinc status in humans - linoleic acid: dihomo-γ-linolenic acid (LA:DGLA) ratio

BACKGROUND

Zinc is an essential micronutrient for humans with important physiological functions. A sensitive and specific biomarker for assessing Zn status is still needed.

OBJECTIVE

The major aim of this study was to examine if the changes in the content of plasma phospholipid LA, DGLA and LA: DGLA ratio can be used to efficiently predict the dietary Zn intake and plasma Zn status of humans.

METHODS

The study was performed on healthy human volunteers, 25-55 years of age. The dietary Zn intake was assessed using 24 h recall questionnaires. Plasma phospholipid fatty acid analysis was done by gas chromatography, and plasma analysis of minerals by atomic absorption spectrometry. Biochemical, anthropometrical and hematological parameters were assessed.

RESULTS

No significant relationship was found between the dietary and plasma zinc status (r = 0.07; p = 0.6). There was a statistically significant correlation between DGLA and plasma Zn (r = 0.39, p = 0.00). No relationship was observed between the linoleic acid and plasma Zn, while there was a significant negative correlation between LA: DGLA ratio and plasma Zn status (r = -0.35, p = 0.01). Similarly, there were statistically significant difference in DGLA status (p = 0.004) and LA: DGLA ratio (p = 0.042) between the Zn formed groups.

CONCLUSIONS

This study is an initial step in evaluating LA: DGLA ratio as a biomarker of Zn status in humans. The results are encouraging as they show that concentration of DGLA is decreased and LA: DGLA ratio increased in people with lower dietary Zn intake. However, additional studies are needed to fully examine the sensitivity of this biomarker.

Lack of effect of bioactive-rich extracts of pomegranate, persimmon, nettle, dill, kale and Sideritis and isolated bioactives on platelet function

BACKGROUND

The health benefits of fruit and vegetable-rich diets may be partly due to modulation of platelet activity by bioactive phytochemicals. The aim of this study was to investigate the effects of bioactive-rich plant extracts and isolated bioactive metabolites on platelet function. Blood samples (n =15 subjects) were treated with extracts of bioactive-rich plants consumed as traditional foods in the Black Sea region, or with human metabolites of the bioactives quercetin and sulforaphane. Platelet function was assessed using the PFA-100.

RESULTS

None of the extracts containing various flavonoids, glucosinolates and other bioactives, or isolated bioactive metabolites of quercetin or sulforaphane, caused significant changes in PFA-100 closure time (CT). In contrast, the positive controls (aspirin and Abciximab) consistently caused significant increases in CT for the platelet agonists epinephrine and ADP, respectively.

CONCLUSION

These data do not support the notion that these plant bioactives can improve human platelet function.

Bioactive-rich extracts of persimmon, but not nettle, Sideritis, dill or kale, increase eNOS activation and NO bioavailability and decrease endothelin-1 secretion by human vascular endothelial cells

BACKGROUND

There is increasing evidence that consumption of plant bioactives such as polyphenols and glucosinolates reduces cardiovascular disease risk and improves endothelial function. In the Black Sea area, a number of plants are consumed alone and as ingredients in traditional foods, and dill, nettle, kale, Sideritis and persimmon were identified as bioactive-rich traditional food plants. The present study investigated the effects of plant extracts on cellular markers of endothelial function (eNOS activation and expression and ET-1 secretion).

RESULTS

Treatment of human umbilical vein endothelial cells with persimmon extract significantly increased Akt and eNOS phosphorylation and nitric oxide metabolites and significantly decreased secretion of ET-1 to the media after 24 h compared with a vehicle control (all P < 0.01). None of the other plant extracts significantly altered any markers of endothelial function.

CONCLUSION

These findings suggest that persimmon fruit contains bioactives that can improve endothelial function via activation of eNOS and reduction in ET-1 secretion, but that dill, kale, Sideritis and nettle do not.

Lipid profile as a prognostic factor in cancer patients

PURPOSE

The relationship between plasma lipid levels and neoplastic diseases is still unclear. The aim of this study was to analyse the lipid profile of individuals with non-Hodgkin's lymphoma (NHL) or prostate carcinoma (CaP) and to follow serum lipid levels changes in NHL patients according to their response to chemotherapy.

PATIENTS AND METHODS

Forty-seven patients with NHL, 57 patients with CaP, two control groups composed of 29 and 43 age- and sex-matched healthy adults, related to NHL and CaP patients, respectively, were included in the study. Follow-up studies of NHL patients were carried out after the 3rd and 6th cycle of chemotherapy.

RESULTS

Initial plasma cholesterol (Chol), HDL-cholesterol (HDL-Chol) and phospholipids (PL) values were significantly lower in patients with NHL or CaP than in controls. Following chemotherapy, we noticed a progressive increase in lipid levels in NHL patients with complete remission (CR) and stable disease (SD), and further decrease in patients with the disease progression.

CONCLUSION

Decreased plasma Chol, HDL-Chol and PL levels of patients with NHL or CaP can be considered as non-specific prognostic parameters in patients with these malignancies.

Methods of assessment of iodine status in humans: a systematic review

BACKGROUND

Biomarkers of iodine status are required to study iodine deficiency disorders in different parts of the world and to evaluate the effects of fortification strategies.

OBJECTIVE

The objective was to assess the usefulness of biomarkers of iodine status in humans by systematically reviewing intervention studies that altered iodine status.

DESIGN

We performed a structured search for iodine intervention studies on Ovid MEDLINE, EMBASE (Ovid), and the Cochrane Library. Studies were assessed for inclusion and validity, with independent duplication. A random-effects meta-analysis was performed.

RESULTS

Twenty-one intervention studies (12 randomized controlled trials, 3 controlled clinical trials, and 6 before-after studies) were included in the review. Urinary iodine (in children and adolescents and in those with low and moderate baseline iodine status), thyroglobulin (in children and adolescents but not in pregnant and lactating women), serum thyroxine (in children and adolescents, adults, women, and those with moderate baseline thyroxine status but not in pregnant and lactating women), and serum thyroid-stimulating hormone (in pregnant and lactating women but not in children and adolescents or those at moderate baseline status), but not triiodothyronine, proved to be useful biomarkers of iodine status.

CONCLUSIONS

Despite the high risk of bias of many of the included studies, the results suggested that urinary iodine, thyroglobin, serum thyroxine, and thyroid-stimulating hormone are useful biomarkers of iodine status, at least in some groups. High-quality controlled studies measuring relevant long-term outcomes are needed to address which biomarker is the most appropriate for assessing iodine intake in some population groups and settings.

Chorioamnionitis and ontogeny of circulating prostaglandin and thromboxane in preterm infants

Our objective was to determine the effect of chorioamnionitis on plasma prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) during the first week in preterm infants. Plasma PGE2 and TxB2 were measured at 1, 3, and 7 days of age in preterm infants (birth weights 501 to 1500 g), with ( N = 26) and without ( N = 22) chorioamnionitis. Infants with maternal chorioamnionitis had significantly lower mean gestational age ( P = 0.0001) and birth weight ( P = 0.03) and a marginally higher rate of bronchopulmonary dysplasia (37% versus 12.5, P = 0.05), a result that may be related to the lower mean gestational age. Plasma PGE2 and TxB2 varied widely, more so on the first day but did not significantly differ between the two groups. TxB2 was lower among infants who died or developed morbidities. Circulating PGE2 and TxB2 concentrations in preterm infants in the first week vary considerably, are relatively unaltered by chorioamnionitis, and are lower in association with mortality and clinical morbidities. Further research on their role in the causation of adverse neonatal outcomes is necessary.

Autologous infusion of expanded mobilized adult bone marrow-derived CD34+ cells into patients with alcoholic liver cirrhosis

OBJECTIVES

Recent advances in regenerative medicine, including hematopoietic stem cell (HSC) transplantation, have brought hope for patients with severe alcoholic liver cirrhosis (ALC). The aim of this study was to assess the safety and efficacy of administering autologous expanded mobilized adult progenitor CD34+ cells into the hepatic artery of ALC patients and the potential improvement in the liver function.

METHODS

Nine patients with biopsy-proven ALC, who had abstained from alcohol for at least 6 months, were recruited into the study. Following granulocyte colony-stimulating factor (G-CSF) mobilization and leukapheresis, the autologous CD34+ cells were expanded in vitro and injected into the hepatic artery. All patients were monitored for side effects, toxicities, and changes in the clinical, hematological, and biochemical parameters.

RESULTS

On average, a five-fold expansion in cell number was achieved in vitro, with a mean total nucleated cell count (TNCC) of 2.3 x 10(8) pre infusion. All patients tolerated the procedure well, and there were no treatment-related side effects or toxicities observed. There were significant decreases in serum bilirubin (P < 0.05) 4, 8, and 12 wk post infusion. The levels of alanine transaminase (ALT) and aspartate transaminase (AST) showed improvement through the study period and were significant (P < 0.05) 1 wk post infusion. The Child-Pugh score improved in 7 out of 9 patients, while 5 patients had improvement in ascites on imaging.

CONCLUSION

It is safe to mobilize, expand, and reinfuse autologous CD34+ cells in patients with ALC. The clinical and biochemical improvement in the study group is encouraging and warrants further clinical trials.

PGE2/TXB2 imbalance in neonatal hypoxemic respiratory failure

BACKGROUND

An imbalance of vaso-constrictor and -dilator mediators has been implicated in the pathogenesis of the pulmonary hypertension accompanying neonatal hypoxemic respiratory failure (NHRF).

AIM

To characterize plasma PGE2, TXB2 and their ratio in normal newborns and in those with NHRF.

METHODS

Twenty newborns with NHRF received inhaled PGE1 (IPGE1) by jet nebulizer in doses of 25, 50, 150 and 300 ng/kg/min followed by weaning. Blood for PGE2 and TXB2 assay using EIA was available in 8 neonates with NHRF prior to IPGE1. Umbilical cord arterial samples were also obtained at delivery from 10 normal newborns to serve as controls.

RESULTS

Compared to normal newborns, those with NHRF had significantly lower PGE2/TXB2 ratios after controlling for preterm gestation (< 37 weeks) and postnatal age (p < 0.05). Notably, all subjects except one in the NHRF group had a value of < 1.0 (range 0.1-1.2) compared to a value of > 1.0 in all subjects in the Control group (range 1.1-5.2).

CONCLUSIONS

Lower PGE2/TXB2 ratio in subjects with NHRF compared with controls reflects a predominance of vaso-constrictor activity in these patients as the basis of pulmonary hypertension. Plasma PGE2/TXB2 ratio may have important implications for the diagnosis and treatment of NHRF.

Comparison of the systemic and pulmonary inflammatory response to endotoxin of neutropenic and non-neutropenic rats

Background

Neutrophil infiltration commonly occurs in acute lung injury and may be partly responsible for the inflammatory response. However, acute lung injury still occurs in the neutropenic host. The objectives of this study are to determine if inflammation and acute lung injury are worse in neutropenic versus the normal host after endotoxemia.

Methods

Rats were divided into four groups: 1) control, 2) neutropenic, 3) endotoxemic and 4) endotoxemic and neutropenic. Tumor necrosis factor (TNF)-α and macrophage inflammatory protein (MIP-2) were measured in the blood, lung lavage and for mRNA in the lung. Arterial blood gases were measured to determine the alveolar-arterial oxygen gradient which reflects on lung injury.

Results

In endotoxemia, the neutropenic rats had lower plasma TNF-α (116 ± 73 vs. 202 ± 31 pg/ml) and higher plasma MIP-2 (26.8 + 11.9 vs. 15.6 + 6.9 ng/ml) when compared to non-neutropenic rats. The endotoxemic, neutropenic rats had worse lung injury than the endotoxemic, non-neutropenic rats as shown by increase in the alveolar-arterial oxygen gradient (24 ± 5 vs. 12 ± 9 torr). However, lavage concentrations of TNF-α and MIP-2 were similar in both groups.

Conclusion

Neutrophils may regulate TNF-α and MIP-2 production in endotoxemia. The elevation in plasma MIP-2 in the endotoxemic, neutropenic rat may be secondary to the lack of a neutrophil response to inhibit production or release of MIP-2. In endotoxemia, the severe lung injury observed in neutropenic rats does not depend on TNF-α or MIP-2 produced in the lung.

Nitric oxide and prostaglandin response to group B streptococcal infection in the lung

Group B streptococcus (GBS) causes a complex inflammatory process that involves prostaglandins (PG) and nitric oxide (NO). The goal of this study was to examine the inflammatory response to GBS in the lung and the co-regulation of the PG and NO pathways, if any, both in vitro and in vivo. Sprague Dawley rats were treated with various combinations of GBS, aminoguanidine (AG), a selective inducible nitric oxide synthase (iNOS) inhibitor, and L-arginine (LA), a NO donor. The mRNA expression of the COX 2 gene was studied by reverse transcriptase polymerase chain reaction (RTPCR) in rat lung tissue. The studies were confirmed in vitro using human lung epithelial (A549) cells treated with GBS, AG, and LA (in combinations similar to the rats) for 3 and 24 hr, after which PG E2 levels in the media were measured by enzyme linked immunosorbent assay (ELISA). COX 2 mRNA in rat lung tissue was significantly induced by GBS (p = 0.04), an effect that was suppressed by AG (p = 0.02). In the A549 cell line, PG E2 levels increased with GBS treatment at 3 and 24 hr (p <0.001). When AG was added, PG E2 levels were suppressed (p = 0.03) after 24 hr; LA partly reversed the suppression of PG E2 levels (p = 0.039). These data indicate that GBS infection causes significant COX 2 induction and PG E2 synthesis in lung tissue, regulated at least partly by the NO pathway. The interaction between the 2 pathways may play a pathogenic role in GBS lung infections and could be a potential target for pharmacological manipulation.

Systemic levels following PGE1 inhalation in neonatal hypoxemic respiratory failure

AIM

To measure plasma prostaglandin E1 (PGE1) levels in newborns with hypoxemic respiratory failure (NHRF) following inhaled PGE1 (IPGE1), normal term newborns, and newborns with congenital heart disease (CHD) following intravenous PGE1.

METHODS

Twenty newborns with NHRF received IPGE1 by jet nebulizer in doses of 25, 50, 150, and 300 ng/kg/min followed by weaning. Blood for PGE1 assay using enzyme immunoassay was available in eight neonates with NHRF, 10 normal newborns, and three neonates with CHD.

RESULTS

There were no differences in PGE1 levels between cord arterial blood in normal newborns and baseline samples from newborns with NHRF. Oxygenation improved significantly following IPGE1 (p=0.024) in newborns with NHRF. No adverse events were identified. Although a reversible increase in PGE1 levels was detected following a dose of 50 ng/kg/min (p<0.05), there was no association between PGE1 levels and IPGE1 duration, PaO2, temperature, heart rate, and blood pressure.

CONCLUSION

A reversible increase in mean PGE1 levels was demonstrable at low doses of IPGE1 in babies with NHRF using a sensitive assay, suggesting effective drug delivery. Levels did not increase further with increasing dose or duration of administration, suggesting local action in the lungs and a lack of systemic spillover due to extensive pulmonary metabolism offering pulmonary selectivity.

Heat stress response results in increased macrophage inflammatory protein-2 concentration in a lipopolysaccharide-exposed macrophage cell line

Pretreatment with heat confers cardiopulmonary protection in endotoxemic animals. This mechanism may be through suppression of pro-inflammatory mediator production. The objectives of this study were to determine the effect of heat stress on tumor necrosis factor-alpha (TNF-alpha) and macrophage inflammatory protein-2 (MIP-2) in a lipopolysaccharide-exposed macrophage cell line and to study the relationship between TNF-alpha and MIP-2 production. Heat pretreatment resulted in decreased TNF-alpha transcription and translation by lipopolysaccharide-exposed macrophages; and increased MIP-2 concentration without additional effect in transcription. Administration of TNF-alpha antibody prior to exposure to lipopolysaccharide resulted in increased MIP-2 concentration suggesting that TNF-alpha acts to down-regulate MIP-2 production. The mechanism by which heat stress causes an increase in MIP-2 concentration may be secondary to its suppressing effect on TNF-alpha production.

Heat stress protects against lung injury in the neutropenic, endotoxemic rat

The objective of this study is to determine if heat stress prior to endotoxemia diminishes cardiopulmonary dysfunction by attenuating the cytokine inflammatory response. Rats were assigned to either: 1) neutropenia; 2) heat; 3) neutropenia, LPS; or 4) heat, neutropenia, LPS. Heart rate, blood gases, and blood, lung lavage, and lung mRNA for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and macrophage inflammatory protein (MIP)-2 were measured. Heat given before LPS resulted in a similar A-a O(2) gradient as the heat-alone and neutropenic groups (8 +/- 8 versus 8 +/- 7 versus 4 +/- 3 mm Hg) and a lower A-a O(2) gradient when compared to the neutropenic, LPS rats (8 +/- 8 versus 22 +/- 8 mm Hg, p < 0.003). Blood, lung lavage, and lung mRNA for TNF-alpha, IL-1beta, and MIP-2 were similar in the LPS rats regardless of heat. Heart rate was similar in both LPS groups but higher than non-LPS groups. Heat pretreatment attenuates lung injury in the neutropenic, endotoxemic rat but not by decreasing TNF-alpha, IL-1beta, or MIP-2 in the lung. Heat prior to LPS did not prevent cardiac dysfunction in neutropenic rats.

Interferon-gamma sensitizes osteosarcoma cells to Fas-induced apoptosis by up-regulating Fas receptors and caspase-8

BACKGROUND

Osteosarcoma is the third most frequent neoplasm in adolescents. Although chemotherapy, frequently used in pre- and post-operative settings, has resulted in significant improvement in disease-free survival, some patients show little sensitivity to chemotherapy and alternative therapeutic strategies are needed. Because the Fas ligand/Fas receptor (CD95, APO-1) apoptosis pathway is a potential therapeutic target in osteosarcomas, we examined the effect of IFN-gamma on Fas-induced apoptosis in four osteosarcoma cell lines.

PROCEDURE AND RESULTS

As measured by flow cytometry, all cell lines expressed cell surface IFN-gamma receptors, and when cultured for 2 days in the presence of IFN-gamma, all cell lines exhibited a significant increase in expression of Fas receptors. By flow cytometric detection of intracellular fragmented DNA as a marker of apoptosis, all cell lines cultured with either IFN-gamma or anti-Fas antibody (clone CH-11) alone showed only moderate apoptosis, whereas significantly high levels of apoptosis occurred in cells cultured with both IFN-gamma and CH-11. Western blotting analysis also revealed that IFN-gamma caused up-regulation of caspase-8 in all cell lines, but no change in Fas-associated death domain protein (FADD/MORT1) or caspase-3. Both caspase-8 and caspase-3 were activated when apoptosis was induced with both IFN-gamma and CH-11. Addition to cultures of z-IETD-fmk, an inhibitor of caspase-8, significantly blocked this apoptosis.

CONCLUSIONS

IFN-gamma sensitizes osteosarcoma cells to Fas-induced apoptosis through up-regulation of Fas receptor and caspase-8. Combined immunotherapy with IFN-gamma and either anti-Fas monoclonal antibody or cytotoxic T cells that bear Fas ligand might be a useful adjunctive therapy for patients with osteosarcoma.

Nitric oxide-dependent regulation of pro-inflammatory cytokines in group B streptococcal inflammation of rat lung

Group B Streptococcus (GBS) infection leading to sepsis and lung injury is a major cause of neonatal morbidity and mortality. Lung injury may result from overproduction of pro-inflammatory mediators (cytokines), caused by nitric oxide (NO). Our objective was to characterize the molecular signaling events involving the pro-inflammatory mediators interleukin-6 (IL-6) and macrophage inflammatory protein (MIP-2) in the presence of aminoguanidine (AG), an inducible nitric oxide synthase (iNOS) specific inhibitor, in lung tissue from GBS-treated young rats. Changes in iNOS mRNA, lactic acid, and rectal temperature were determined as markers of the inflammatory response. Expression and regulation of IL-6 and MIP-2 mRNA in lung tissue were studied by RT-PCR with densitometry analysis. GBS treatment of young rats induced the expression of pro-inflammatory mediators IL-6 (6-fold) and MIP-2 (3-fold) in lung tissue compared to controls. AG decreased IL-6 and MIP-2 expression. Addition of L-arginine (L-arg) reversed the AG effect on IL-6 and MIP-2 expression. These data suggest a role for the nitric oxide pathway in the overproduction of pro-inflammatory mediators IL-6 and MIP-2 during GBS-induced lung inflammation. This pathway may be responsible for the initiation of lung injury.

Ibuprofen attenuates early lung injury in endotoxemic, neutropenic rats

The objective of our study was to determine the role of ibuprofen in protecting neutropenic rats from cardiopulmonary injury due to endotoxemia. We hypothesized that ibuprofen would offer pulmonary protection by altering cytokine production. Neutropenic rats received E. coli lipopolysaccharide (LPS) alone or ibuprofen and LPS. After 4 h, arterial blood gases, heart rate and blood pressure were measured. Blood and bronchoalveolar lavage fluid (BALF) were collected for TNF- alpha and MIP-2 concentrations. Lung tissue for iNOS mRNA and myeloperoxidase were obtained. The ibuprofen group had decreased heart rate and better oxygenation. Ibuprofen suppressed TNF- alpha and MIP-2 production in blood and MIP-2 concentrations in BALF. Lung mRNA for iNOS was higher in the ibuprofen group. Neutrophil infiltration in the lung was similar in both groups. Ibuprofen attenuated cardiopulmonary dysfunction by decreasing the early cytokine response. The balance of vasodilator to vasoconstrictor production in the lung may favor vasodilation as shown by increased iNOS mRNA and suppression of thromboxane.

Group B Streptococci and inducible nitric oxide synthase: modulation by nuclear factor kappa B and ibuprofen

Group B Streptococci (GBS) neonatal infections cause a complex inflammatory process involving numerous biochemical mediators. Nitric Oxide (NO) is generated by many cell types in response to different inflammatory signals. Nuclear factor kappa B (NFkappaB) plays an important role in the inflammatory process and may induce a number of biochemical mediator genes, including the inducible nitric oxide synthase (iNOS). We tested the hypothesis that GBS induces iNOS gene expression through activation of NFkappaB. We also tested whether ibuprofen (IBU) will suppress iNOS expression by blocking NFkappaB activation. Cerebral microvascular endothelial cells isolated from newborn piglets were harvested for the determination of iNOS gene expression and activation of NFkappaB. GBS significantly induced iNOS mRNA expression (5- to 6-fold, P < .005) and iNOS protein (3- to 4-fold, P < .01) at 24 hours. DNA-NFkappaB binding activity was detected within 15 minutes of GBS treatment and reached a maximal effect at 3 hours. Treatment with IBU significantly suppressed GBS-induced iNOS mRNA expression at 24 hours, and NFkappaB activity at 3 hours, suggesting that suppression of GBS-induced iNOS mRNA expression by IBU occurs by blocking of NFkappaB activation. These data show that NFkappaB activation is an early step in the induction of iNOS gene expression by GBS and that this interaction may play a vital role in the pathogenesis of GBS neonatal infections.

Nitric oxide, prostaglandins, and impaired cerebral blood flow autoregulation in group B streptococcal neonatal meningitis

Impaired autoregulation of cerebral blood flow (CBF) contributes to CNS damage during neonatal meningitis. We tested (i) the hypothesis that cerebrovascular autoregulation is impaired during early onset group B streptococcal (GBS) meningitis, (ii) whether this impairment is regulated by vasoactive mediators such as prostaglandins and (or) nitric oxide (NO), and (iii) whether this impairment is preventable by specific and (or) nonspecific inhibitors: dexamethasone, ibuprofen, and Nomega-nitro-L-arginine, a NO inhibitor. Sterile saline or 10(9) colony-forming units (cfu) of heat-killed GBS was injected into the cerebral ventricle of newborn piglets. CBF autoregulation was determined by altering cerebral perfusion pressure (CPP) with balloon-tipped catheters placed in the aorta. GBS produced a narrow range of CBF autoregulation due to an impairment at the upper limit of CPP. We report that in vivo in the early stages (first 2 h) of induced GBS inflammation (i) GBS impairs the upper limit of cerebrovascular autoregulation; (ii) ibuprofen, dexamethasone, and Nomega-nitro-L-arginine not only prevent this GBS-induced autoregulatory impairment but improve the range of cerebrovascular autoregulation; (iii) these autoregulatory changes do not involve circulating cerebral prostanoids; and (iv) the observed changes correlate with the induction of NO synthase gene expression. Thus, acute early onset GBS-induced impairment of the upper limit of CBF autoregulation can be correlated with increases of NO synthase production, suggesting that NO is a vasoactive mediator of CBF.

Nitric oxide, prostaglandins, and impaired cerebral blood flow autoregulation in group B streptococcal neonatal meningitis

Impaired autoregulation of cerebral blood flow (CBF) contributes to CNS damage during neonatal meningitis. We tested (i) the hypothesis that cerebrovascular autoregulation is impaired during early onset group B streptococcal (GBS) meningitis, (ii) whether this impairment is regulated by vasoactive mediators such as prostaglandins and (or) nitric oxide (NO), and (iii) whether this impairment is preventable by specific and (or) nonspecific inhibitors: dexamethasone, ibuprofen, and Nω-nitro-L-arginine, a NO inhibitor. Sterile saline or 109colony-forming units (cfu) of heat-killed GBS was injected into the cerebral ventricle of newborn piglets. CBF autoregulation was determined by altering cerebral perfusion pressure (CPP) with balloon-tipped catheters placed in the aorta. GBS produced a narrow range of CBF autoregulation due to an impairment at the upper limit of CPP. We report that in vivo in the early stages (first 2 h) of induced GBS inflammation (i) GBS impairs the upper limit of cerebrovascular autoregulation; (ii) ibuprofen, dexamethasone, and Nω-nitro-L-arginine not only prevent this GBS-induced autoregulatory impairment but improve the range of cerebrovascular autoregulation; (iii) these autoregulatory changes do not involve circulating cerebral prostanoids; and (iv) the observed changes correlate with the induction of NO synthase gene expression. Thus, acute early onset GBS-induced impairment of the upper limit of CBF autoregulation can be correlated with increases of NO synthase production, suggesting that NO is a vasoactive mediator of CBF.Key words: cerebrovascular autoregulation, group B Streptococcus, neonatal meningitis, anti-inflammatory agents, prostanoids, nitric oxide synthase, gene expression, nitric oxide.

Deregulation of cyclooxygenase and nitric oxide synthase gene expression in the inflammatory cascade triggered by experimental group B streptococcal meningitis in the newborn brain and cerebral microvessels

Group B Streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis. Despite antibiotics, GBS in the newborn initiates a cascade of molecular and biological events leading to altered cerebral perfusion, blood-brain barrier disruption, cerebral edema, intracranial hypertension, neurological damage, and even death. Having previously shown that GBS infection impairs cerebral blood flow autoregulation and increases prostaglandin (PG) levels, we examined the regulation of some crucial inflammatory mediators (PGs, nitric oxide (NO), tumor necrosis factor-a) in the brain and cerebral microvessels (MVs) from newborn piglets. Cyclooxygenase (COX), the key enzyme in PG biosynthesis, exists in two isoforms, COX-1 and COX-2. Both may be directly induced by NO in a model of renal inflammation. Besides its neurotransmitter role, NO is a potent vasorelaxant whose production is catalyzed by at least three distinct nitric oxide synthases (NOS) (bNOS, ecNOS, iNOS). Western blot analyses showed that the newborn (4 day old) brain expressed lower levels of COX-1 (8-fold), COX-2 (20-fold), bNOS (12-fold), and ecNOS (5-fold) than in the 1 day old. MV showed approximately equal levels of COX-2, lower levels of COX-1 (4-fold), bNOS (5-fold), and higher levels of ecNOS (20-fold) in comparison to 4-day-old cerebral MV. A 4-day-old brain expressed lower levels of bNOS (5-fold), ecNOS (10-fold), and COX-1 (2-fold) than the 6-week-old pig. COX-2 protein was undetected in a 4-day-old pig brain, but present in great excess in MV. Purified MV showed lower ecNOS (14-fold), COX-1 (2-fold), and about equal levels of bNOS and COX-2 in comparison with MV from 6-week-old pigs. Reverse transcription polymerase chain reaction analyses confirmed these results. Treatment with noo-nitro-L-arginine (LNA), a NOS inhibitor, downregulated COX-1 expression in the newborn brain and both COX-1 and COX-2 cerebral MV expression. GBS infection (10(9) colony-forming units, 0.5 mL intracerebroventricular) of sedated newborn piglets induced the expression of tumor necrosis factor-alpha in the cerebrospinal fluid after 2 hours, upregulated bNOS expression in both brain and MVs, upregulated ecNOS in MVs, and downregulated COX-1, COX-2, and ecNOS in the brain. GBS did not trigger the expression of iNOS. Our data suggest that there is a net deficiency of NOS isoforms in the immature brain and microvasculature of the 4-day-old piglet and that the differences in expression lead to the immature control of NO and PG production, rendering newborns particularly susceptible to neurological damage because of the undeveloped nature of their response mechanisms. Moreover, the GBS-induced cascade deregulates the gene expression of interacting inflammatory mediators and may cause a net vasoconstrictor/vasodilator imbalance, leading to cerebral hypertension and edema in the early stages of infection. Pharmacological manipulations of the inflammatory cascade could lead to novel therapeutic approaches for the treatment of GBS meningitis.

Structure of recombinant rat UBF by electron image analysis and homology modelling

We have studied the structure of recombinant rat UBF (rrUBF), an RNA polymerase I transcription factor, by electron microscopy and image analysis of single particles contrasted with methylamine tungstate. Recombinant rat UBF appeared to be a flat, U-shaped protein with a central region of low density. In the dominant projections, 2-fold mirror symmetry was seen, consistent with the dimerization properties of this molecule, and of dimensions in agreement with the length of DNA that rat UBF protects in footprinting studies. Electron microscopy of various rrUBF-DNA complexes confirmed that our recombinant protein was fully able to bind the 45S rDNA promoter, and that it caused substantial bends in the DNA. Upon extended incubation in a droplet covered by a lipid monolayer at the liquid-air interface, rrUBF formed long filamentous arrays with a railway track appearance. This structure was interpreted to consist of overlapping rrUBF dimers 3.5 nm apart, which value would represent the thickness of the protein. Our results show rrUBF to interact with and bend the promoter DNA into a roughly 10 nm diameter superhelix. Based on all these electron microscopical results, an atomic structure was predicted by homology modelling of the HMG fingers, and connected by energy minimized intervening segments.

CD40 expression by human peripheral blood eosinophils

In this study, we have investigated CD40 expression in human peripheral blood eosinophils and in human chronically inflamed nasal tissues, i.e., nasal polyps. We show by both reverse transcriptase-PCR and Northern blot analysis that eosinophils from allergic subjects express human CD40 mRNA. We also show that constitutive CD40 mRNA expression in eosinophils could be upregulated by exposure to IgA immune complexes and downregulated by IL-10 and the synthetic steroid budesonide. In addition, we demonstrate that eosinophils express CD40 protein by flow cytometry. Such expression is biologically functional as cross-linking CD40 with CD40 mAbs enhances eosinophil survival in a dose-dependent fashion; in addition, CD40 ligation stimulates eosinophils to release GM-CSF. CD40-mediated eosinophil survival was largely inhibited by an anti-GM-CSF neutralizing antibody suggesting GM-CSF involvement in the survival enhancing mechanism. CD40 mRNA was also detected in total RNA extracted from nasal polyp tissues but not in RNA isolated from normal nasal mucosa (inferior turbinate); by immunohistochemistry, we were able to detect immunoreactive CD40 protein in a variety of cell types in the polyp stroma, but primarily in eosinophils. These observations suggest previously unforeseen interactions between eosinophils and cells expressing the CD40 ligand and, thus, novel pathways by which eosinophils may contribute to the regulation of airway inflammation.

Interleukin (IL)-10 inhibits long-term IL-6 production but not preformed mediator release from rat peritoneal mast cells

Mast cells have been implicated in a number of diseases involving chronic inflammation including asthma, rheumatoid arthritis, and inflammatory bowel diseases. They are a potent source of several cytokines, including IL-6 and TNF-alpha. Freshly isolated rat peritoneal mast cells will produce IL-6 in response to anti-IgE, LPS, PGE1, or PGE2; however, the mechanisms by which such cytokine production is regulated are poorly understood. IL-10 is recognized as an important immunoregulatory cytokine with effects on T cell development and the production of inflammatory cytokines. IL-10 has previously been described to enhance mast cell development in the context of IL-3 and IL-4. In the current study, we have examined the ability of IL-10 to modulate rat peritoneal mast cell IL-6 and TNF-alpha production in response to a variety of stimuli. We have observed that recombinant murine IL-10 can inhibit the production of both IL-6 and TNF-alpha by mast cells without altering the degree of histamine release in response to anti-IgE. Concentrations of IL-10 as low as 0.2 ng/ml were sufficient to inhibit IL-6 production by LPS- or anti-IgE-activated cells significantly. IL-10 also inhibited PGE1- and PGE2-induced IL-6 production. The relative potency of IL-10 as an inhibitor of mast cell IL-6 production was highly dependent upon the stimulus used, with a 10-fold difference in the IC50 for LPS- or anti-IgE-activated cells (0.21 ng/ml) and cells activated with a combination of LPS and PGE2 (2.29 ng/ml). This suggests that prostanoids may limit the ability of IL-10 to modulate mast cell IL-6 production in the context of inflammation. These data have important implications for the regulation of mast cell IL-6 in inflammatory diseases involving prostanoid production and the effects of treatment with cyclooxygenase inhibitors. Our results also demonstrate a dual role for IL-10 on mast cells as a growth factor and inhibitor of cytokine production.

Distinct immunohistochemical localization of IL-4 in human inflamed airway tissues. IL-4 is localized to eosinophils in vivo and is released by peripheral blood eosinophils

Nasal polyposis and asthma are inflammatory conditions of the airways characterized by infiltration of activated inflammatory cells, particularly eosinophils. IL-4 is a multifunctional cytokine considered to play an important role in eosinophilic inflammation. We examined the cellular distribution of immunoreactive IL-4 in nasal polyps, as well as in the bronchial mucosa of both nonasthmatic control subjects (n = 6) and patients with well-characterized mild asthma (n = 6) subjected to a diluent or an allergen challenge. To determine eosinophilic contribution, tissue sections were counterstained with FITC after IL-4 immunostaining. No eosinophils were observed in the bronchial mucosa of nonasthmatic subjects. Nasal polyp tissues contained approximately 15 times more eosinophils per mm2 compared with bronchial tissues from asthmatics after a diluent challenge. Allergen challenge resulted in a marked increase in eosinophil density in bronchial tissues. A negligible number of cells immunostaining IL-4 was observed in bronchial tissues from nonasthmatic control subjects. The density of IL-4-positive cells in nasal polyp tissues was almost three times greater compared with asthmatics bronchial tissues after a diluent challenge. Approximately 90% of the IL-4-positive cells in bronchial tissues did not exhibit fluorescence after FITC counterstaining; in contrast, about 80% of the IL-4-positive cells in nasal polyp tissues did. We also show that peripheral blood eosinophils from allergic subjects express IL-4 mRNA by Northern blot analysis, particularly on stimulation with secretory IgA immune complexes. Finally, the supernatant of stimulated eosinophils contained approximately 50 pg/10(6) cells of IL-4 as determined by ELISA. These data demonstrate that eosinophils express the message and release IL-4 in vitro, and that these cells are the primary source of immunoreactive IL-4 in tissues undergoing chronic severe mucosal inflammation.

Distinct immunohistochemical localization of IL-4 in human inflamed airway tissues. IL-4 is localized to eosinophils in vivo and is released by peripheral blood eosinophils

Nasal polyposis and asthma are inflammatory conditions of the airways characterized by infiltration of activated inflammatory cells, particularly eosinophils. IL-4 is a multifunctional cytokine considered to play an important role in eosinophilic inflammation. We examined the cellular distribution of immunoreactive IL-4 in nasal polyps, as well as in the bronchial mucosa of both nonasthmatic control subjects (n = 6) and patients with well-characterized mild asthma (n = 6) subjected to a diluent or an allergen challenge. To determine eosinophilic contribution, tissue sections were counterstained with FITC after IL-4 immunostaining. No eosinophils were observed in the bronchial mucosa of nonasthmatic subjects. Nasal polyp tissues contained approximately 15 times more eosinophils per mm2 compared with bronchial tissues from asthmatics after a diluent challenge. Allergen challenge resulted in a marked increase in eosinophil density in bronchial tissues. A negligible number of cells immunostaining IL-4 was observed in bronchial tissues from nonasthmatic control subjects. The density of IL-4-positive cells in nasal polyp tissues was almost three times greater compared with asthmatics bronchial tissues after a diluent challenge. Approximately 90% of the IL-4-positive cells in bronchial tissues did not exhibit fluorescence after FITC counterstaining; in contrast, about 80% of the IL-4-positive cells in nasal polyp tissues did. We also show that peripheral blood eosinophils from allergic subjects express IL-4 mRNA by Northern blot analysis, particularly on stimulation with secretory IgA immune complexes. Finally, the supernatant of stimulated eosinophils contained approximately 50 pg/10(6) cells of IL-4 as determined by ELISA. These data demonstrate that eosinophils express the message and release IL-4 in vitro, and that these cells are the primary source of immunoreactive IL-4 in tissues undergoing chronic severe mucosal inflammation.

The RNA polymerase I transcription factor UBF is the product of a primary response gene

Transcription of the ribosomal RNA genes by RNA polymerase I is tightly coordinated with the rate of cell growth. The RNA polymerase I transcription factor, UBF, activates transcription by binding to elements within the promoter and enhancer elements within the intergenic spacer but is not required for basal transcription. To assess the role of UBF in modulating ribosomal DNA transcription, we studied its expression in NIH3T6 fibroblasts when transcription was repressed in response to serum starvation and stimulated following refeeding. Our results demonstrate a correlation between the amounts of UBF protein and the rates of ribosomal DNA transcription in quiescent and serum-stimulated cells. Nuclear run-on assays and Northern blot analyses demonstrated that the UBF gene was a primary response gene, exhibiting characteristics similar to those of c-myc and SRF. These results suggest that the regulation of transcription of the UBF gene by polymerase II represents a pathway by which cells modulate transcription by RNA polymerase I.

Coordinated decreases in rRNA gene transcription factors and rRNA synthesis during muscle cell differentiation

rRNA synthesis decreases significantly during the differentiation of rat L6 myoblasts to myotubes. Nuclear run-on assays demonstrated that the decrease was attributable to decreased rates of rRNA gene transcription. Immunoblot analysis indicated a marked reduction in amounts of the RNA polymerase I transcription factors UBF1 and UBF2 (upstream binding factors 1 and 2, respectively). The levels of these factors dropped in parallel with the down-shift in rRNA gene transcription. The amount of UBF does not fall due to a general decrease in cellular protein, as myosin heavy-chain protein accumulates markedly during this same time. RNA blots of total RNA isolated from myoblasts and differentiating myotubes showed a decrease in the mRNA for UBF, at the same time the mRNA for myogenin was accumulating. The down-shift in UBF mRNA levels preceded the decrease in the protein levels for UBF. There have been reports that the acute response of the rRNA gene transcription system to physiological signals in many systems involves an RNA polymerase I-associated factor. However, our results imply that the regulation of rRNA gene DNA transcription in response to physiological processes, such as differentiation, may involve multiple regulatory pathways.

Dexamethasone stimulates rRNA gene transcription in rat myoblasts

The glucocorticoid analogue, dexamethasone, stimulated RNA synthesis more than two-fold in rat L6 myoblasts, without affecting the rate of cell proliferation. Treatment of myoblasts for 24 h with 10(-7) M dexamethasone resulted in a 30% increase in the cellular RNA level. More than a two-fold stimulation of pre-rRNA gene transcription by dexamethasone, as measured in isolated nuclei and by cell-free transcription, was accompanied by a corresponding increase in pre-rRNA levels. Co-incubation of myoblasts with cycloheximide and dexamethasone did not affect the enhanced pre-rRNA gene transcription demonstrating that de novo protein synthesis was unnecessary to manifest the dexamethasone effect on rDNA transcription. Support for this conclusion is provided by the finding that the levels of UBF1 and UBF2, rDNA upstream binding transcription factors, remain unchanged. The glucocorticoid antagonist RU38486 [11 beta-(4-dimethylaminophenyl)17 beta-hydroxy-17 alpha-(prop-1-ynyl)estra- 4,9-dien-3-one] inhibited the dexamethasone-stimulated rRNA gene transcription suggesting that the glucocorticoid receptor is involved in the response mechanism.

Regulation of U3 snRNA expression during myoblast differentiation

Differentiation of proliferating rat L6 myoblasts to syncytial multinucleated myotubes results in a significant downshift in the rate of U3 snRNA gene transcription, paralleling the decrease in rRNA synthesis previously documented. Coordinate production of U3 snRNA and rRNA during the differentiation process adds further support for a role of U3 snRNA in ribosome biogenesis. Despite the dramatic decrease in U3 snRNA transcription during differentiation, a corresponding drop in the cellular level of U3 snRNA does not occur. In myotubes, the amount of U3 snRNA is regulated at the post-transcriptional level in which there is a significant accumulation of U3 snRNA in the cytoplasm of myotubes. This intracellular redistribution of U3 snRNA may significantly affect the entire process of rRNA maturation or result from the decrease in ribosome production accompanying terminal differentiation of myoblasts.