Effects of vitamin A-deprivation on hamster tracheal epithelium. A quantitative morphologic study

Nutritional approach for increasing public health during pandemic of COVID-19: A comprehensive review of antiviral nutrients and nutraceuticals

Background: The novel coronavirus (COVID-19) is considered as the most life-threatening pandemic disease during the last decade. The individual nutritional status, though usually ignored in the management of COVID-19, plays a critical role in the immune function and pathogenesis of infection. Accordingly, the present review article aimed to report the effects of nutrients and nutraceuticals on respiratory viral infections including COVID-19, with a focus on their mechanisms of action. Methods: Studies were identified via systematic searches of the databases including PubMed/ MEDLINE, ScienceDirect, Scopus, and Google Scholar from 2000 until April 2020, using keywords. All relevant clinical and experimental studies published in English were included. Results: Protein-energy malnutrition (PEM) is common in severe respiratory infections and should be considered in the management of COVID-19 patients. On the other hand, obesity can be accompanied by decreasing the host immunity. Therefore, increasing physical activity at home and a slight caloric restriction with adequate intake of micronutrients and nutraceuticals are simple aids to boost host immunity and decrease the clinical manifestations of COVID-19. Conclusion: The most important nutrients which can be considered for COVID-19 management are vitamin D, vitamin C, vitamin A, folate, zinc, and probiotics. Their adequacy should be provided through dietary intake or appropriate supplementation. Moreover, adequate intake of some other dietary agents including vitamin E, magnesium, selenium, alpha linolenic acid and phytochemicals are required to maintain the host immunity.

Optimizations of In Vitro Mucus and Cell Culture Models to Better Predict In Vivo Gene Transfer in Pathological Lung Respiratory Airways: Cystic Fibrosis as an Example

The respiratory epithelium can be affected by many diseases that could be treated using aerosol gene therapy. Among these, cystic fibrosis (CF) is a lethal inherited disease characterized by airways complications, which determine the life expectancy and the effectiveness of aerosolized treatments. Beside evaluations performed under in vivo settings, cell culture models mimicking in vivo pathophysiological conditions can provide complementary insights into the potential of gene transfer strategies. Such models must consider multiple parameters, following the rationale that proper gene transfer evaluations depend on whether they are performed under experimental conditions close to pathophysiological settings. In addition, the mucus layer, which covers the epithelial cells, constitutes a physical barrier for gene delivery, especially in diseases such as CF. Artificial mucus models featuring physical and biological properties similar to CF mucus allow determining the ability of gene transfer systems to effectively reach the underlying epithelium. In this review, we describe mucus and cellular models relevant for CF aerosol gene therapy, with a particular emphasis on mucus rheology. We strongly believe that combining multiple pathophysiological features in single complex cell culture models could help bridge the gaps between in vitro and in vivo settings, as well as viral and non-viral gene delivery strategies.

Impact of Micronutrients on the Immune Response of Animals

Vitamins and minerals (micronutrients) play an important role in regulating and shaping an immune response. Deficiencies generally result in inadequate or dysregulated cellular activity and cytokine expression, thereby affecting the immune response. Decreased levels of natural killer, granulocyte, and phagocytic cell activity and T and B cell proliferation and trafficking are associated with inadequate levels of micronutrients, as well as increased susceptibility to various adverse health conditions, including inflammatory disorders, infection, and altered vaccine efficacy. In addition, most studies of micronutrient modulation of immune responses have been done in rodents and humans, thus limiting application to the health and well-being of livestock and companion animals. This exploratory review elucidates the role of vitamins and minerals on immune function and inflammatory responses in animals (pigs, dogs, cats, horses, goats, sheep, and cattle), with reference to rodents and humans.

Dietary Vitamin-a Deficiency: Effects on Growth, Infection, and Mortality

Vitamin A (VA) has been experimentally linked in animals to growth in weight, host resistance to infection, and survival for nearly eight decades. These consistent findings appear to have their human correlate. VA-deficient children are more likely to have comorbidity and to be stunted in growth, and they have a higher risk of mortality. In several large field trials VA supplementation has reduced mortality by >= 30%. Presumably a similar or greater public health impact can be achieved by improving dietary VA intake. The relation between dietary imbalance and VA deficiency starts at a young age. Early cessation of breast-feeding, poor quality of the weaning diet, and infrequent consumption of VA-rich foods appear to underlie mild xerophthalmia. These dietary imbalances often coexist with food access. We must know how to alter detrimental food habits before dietary interventions can be formulated. Improving dietary quality to enhance VA nutriture will likely carry numerous other nutritional benefits to children.

Effects of Vitamin-A Status on Hamster Tracheal Epithellum in Viva in Vitro

In this paper we have suggested the new concept of exotrophic cells, i.e. cells that have conditionally escaped the need for an essential nutrient, such as vitamin A. These exotrophs might become fixed by a mutation and eventually contribute to the tumorigenic phenotype.

The discovery of the retinoic acid receptor (RAR) has opened up new horizons in the search for the mechanism of action of retinoic acid [17; 18]. It is intriguing that a second retinoic acid receptor, RARE, is abundantly expressed in hepatoma tissue and not in normal liver; Benbrook et al. [191 suggest that the erroneous expression of the RARE might contribute to tumour development in liver. How and whether these findings relate to the vitamin-A-deficient status of hepatoma cells remains to be understood.

Low plasma vitamin A concentration is associated with tuberculosis in Moroccan population: a preliminary case control study

BACKGROUND

Vitamin A plays numerous roles in immune system. Its deficiency alters both the innate and adaptive immunity. Previous results reported that the micronutrients deficiency, particularly vitamin A, is observed in patients with tuberculosis. Thus, we aimed in this study to assess vitamin A concentrations in Moroccan patients with tuberculosis to set up a large efficacy study of vitamin A supplementation for TB infected patients. Plasma retinol concentration was measured by HPLC in 44 recently diagnosed TB patients and 40 healthy controls.

RESULTS

We showed that plasma vitamin A is significantly lower in tuberculosis patients as compared to healthy controls (p < 0.0001). Moreover, no significant association was found between vitamin A deficiency and, TB severity and patients' ages.

CONCLUSION

Our study confirms the association between low vitamin A levels and tuberculosis disease.

Reduction of adhesions and antrostomy stenosis with topical vitamin A after endoscopic sinus surgery

BACKGROUND

Prevention of adhesion formation and restoration of mucociliary mucosa are major determinants of the success of endoscopic sinus surgery (ESS). Vitamin A (VA) can promote mucociliary differentiation of respiratory epithelium. However, whether topical VA can promote sinonasal wound healing or reduce adhesion formation after ESS in humans remains unexplored.

OBJECTIVE

To investigate the effect of topical VA on sinonasal wound healing and adhesion formation after ESS.

METHODS

This is a within-subject control study. Patients with chronic rhinosinusitis were included. Each patient underwent ESS, and topical VA was applied over the sinonasal wound. Postoperative outcomes were assessed by using the Lund-Kennedy score, and the antrostomy size was measured. In vitro wound healing assay of fibroblasts with or without VA was evaluated. Restoration of ciliated epithelium was examined by using scanning electron microscopy.

RESULTS

Thirty patients were enrolled. The mean (standard deviation {SD}) scores for scarring/adhesion in the VA-treated side at 3 and 12 months after surgery (0.20 ± 0.40 and 0.23 ± 0.42, respectively) were significantly lower than those in the controls (0.47 ± 0.50 and 0.53 ± 0.62, respectively). The mean (SD) antrostomy size in the VA treated side at 1, 3, and 12 months after surgery (0.85 ± 0.30 cm(2), 0.7 ± 0.30 cm(2), and 0.70 ± 0.27 cm(2), respectively) were significantly larger than those in the controls (0.79 ± 0.26 cm(2), 0.60 ± 0.25 cm(2), and 0.57 ± 0.24 cm(2), respectively). Wound healing assay revealed that VA significantly inhibited the proliferation and migration of fibroblasts. Scanning electron microscopy showed mature ciliated cells in the VA-treated side.

CONCLUSION

Topical VA is a promising agent for sinonasal wound healing after ESS because it can promote mucociliary reepithelization, reduce adhesion, and prevent antrostomy stenosis.

Effect of bunching of cilia and their interplay on muco-ciliary transport

Cilia are hair-like organelles projecting from a eukaryotic cell, used either for locomotion or as sensors. Cilia commonly occur in patches. To take this into consideration, we represent cilia in multiple patches, instead of the conventional ‘dense mat’ representation. We focus on the combined action and interplay of these patches. The effects of varying the frequency, spacing and phase lag of the beating of one cilia bunch with respect to the beating of adjacent patches are studied. We model the Airway Surface Liquid (ASL) as a three-layer structure. The possibility of an optimum frequency of beating is noted and the change of mucous flow under different spacing and phase differences are observed.

Increased mucociliary differentiation and aquaporins formation of respiratory epithelial cells on retinoic acid-loaded hyaluronan-derivative membranes

While playing a major role in maintaining the mucociliary phenotype of respiratory epithelial cells (RECs), retinoids are critical determinants of their normal function. However, despite being a powerful biological agent, retinoic acid (RA) is generally not used in regenerative medicine due to its scarce bioavailability via conventional administration. Therefore, the ability to incorporate RA into biomaterials allows for a combination of the biological effects of RA and biomaterials in influencing cellular behavior. This study attempts to develop RA-loaded hyaluronan-derivative membrane (RA-HAm) and investigates how this membrane affects the mucociliary differentiation and aquaporins (AQP) formation of RECs. In a simulated in vitro culture condition, the RA release from membranes is maintained for 7days. On the seventh day, the cumulative release rate of RA from supportive biomaterials is ~87% under detect limitation. RECs cultured on RA-HAm reveal numerous mature ciliated cells and microvilli compared to aggregated cilia-like structures on hyaluronan-derivative membrane (HAm). Moreover, the expression levels of MUC5AC and AQP on RA-HAm are higher than those on HAm. The proposed model elucidates the release of hydrophobic RA from hyaluronan-derivative biomaterials. We believe that RA-loaded hyaluronan biomaterials are highly promising biomaterials for use in sinonasal surgery and tissue engineering of the respiratory system.

Tissue remodeling induced by hypersecreted epidermal growth factor and amphiregulin in the airway after an acute asthma attack

BACKGROUND

Epidermal growth factor receptor ligands, such as epidermal growth factor (EGF) and amphiregulin, may play key roles in tissue remodeling in asthma. However, the kinetics of EGF and amphiregulin secretion in the airway after an acute asthma attack and the effect of prolonged airway exposure to these ligands on airway remodeling are unknown.

OBJECTIVE

To measure the EGF and amphiregulin concentrations in sputa obtained from patients with asthma under various conditions, and to examine the effects of EGF and amphiregulin on the proliferation or differentiation of airway structural cells.

METHODS

Epidermal growth factor and amphiregulin levels were measured by ELISA in sputum specimens collected from 14 hospitalized children with asthma during an acute asthma attack, 13 stable outpatients with asthma, 8 healthy control children, and 7 children with respiratory tract infections. The effects of EGF and amphiregulin on the proliferation and/or differentiation of normal human bronchial epithelial cells (NHBE), bronchial smooth muscle cells (BSMC), and normal human lung fibroblasts (NHLF) were examined.

RESULTS

The sputum levels of EGF were significantly higher for about a week after an acute asthma attack compared with the levels in stable subjects with asthma and control subjects. In contrast, upregulation of amphiregulin in the sputa of patients with asthma was observed only during the acute attack. EGF caused proliferation of NHBE, BSMC, and NHLF, whereas amphiregulin induced proliferation of only NHBE. Prolonged exposure of NHBE to EGF and amphiregulin induced mucous cell metaplasia in an IL-13-independent manner.

CONCLUSION

Acute asthma attacks are associated with hypersecretion of EGF and amphiregulin in the airway. Recurrent acute attacks may aggravate airway remodeling.

Regulation of differentiation of tracheal epithelial cells by retinoids

An in vitro culture system of rabbit tracheal epithelial cells has been developed to study the regulation of differentiation of the respiratory epithelium on the molecular level. At high density in the absence of retinoids these cells become squamous, stratify, and ultimately form cross-linked envelopes. Several factors influence this terminal differentiation: high Ca2+ concentrations and serum factors promote, whereas retinoids and medium conditioned by fibroblasts inhibit this process. Terminal squamous cell differentiation is accompanied by several biochemical changes: the synthesis of proteoglycans is dramatically reduced and the expression of keratin intermediate filaments is altered. Besides the eight major keratins expressed in undifferentiated cells, terminally differentiated cells also express a 48 kDa keratin. The expression of this keratin correlates well with squamous cell differentiation and appears to be under the control of retinoic acid. The level at which these biochemical changes are regulated has yet to be established. Specific retinol- and retinoic acid-binding proteins have been identified in these cells; the correlation between binding and biological activity of retinoids in this system is in agreement with a role for these binding proteins in mediating the action of these agents.

Sp1 up-regulates cAMP-response-element-binding protein expression during retinoic acid-induced mucous differentiation of normal human bronchial epithelial cells

CREB [CRE (cAMP-response element)-binding protein] is an important transcription factor that is differentially regulated in cells of various types. We recently reported that RA (retinoic acid) rapidly activates CREB without using RARs (RA receptors) or RXRs (retinoid X receptors) in NHTBE cells (normal human tracheobronchial epithelial cells). However, little is known about the role of RA in the physiological regulation of CREB expression in the early mucous differentiation of NHTBE cells. In the present study, we report that RA up-regulates CREB gene expression and that, using 5'-serial deletion promoter analysis and mutagenesis analyses, two Sp1 (specificity protein 1)-binding sites located at nt -217 and -150, which flank the transcription initiation site, are essential for RA induction of CREB gene transcription. Furthermore, we found that CREs located at nt -119 and -98 contributed to basal promoter activity. Interestingly, RA also up-regulated Sp1 in a time- and dose-dependent manner. Knockdown of endogenous Sp1 using siRNA (small interfering RNA) decreased RA-induced CREB gene expression. However, the converse was not true: knockdown of CREB using CREB siRNA did not affect RA-induced Sp1 gene expression. We conclude that RA up-regulates CREB gene expression during the early stage of NHTBE cell differentiation and that RA-inducible Sp1 plays a major role in up-regulating human CREB gene expression. This result implies that co-operation of these two transcription factors plays a crucial role in mediating early events of normal mucous cell differentiation of bronchial epithelial cells.

Vitamin A and emphysema

Within the last several years, research scientists and clinicians have been intrigued with the potential use of an active form of vitamin A, retinoic acid (RA), for the treatment and prevention of emphysema. The interest in this area can be largely attributed to the work of Massaro and Massaro (1996, 1997, 2000) in which they presented evidence that RA partially protects against and to some degree restores elastase-induced emphysema in rats. The mechanism for this protective effect of RA is in part related to elastin metabolism. RA also inhibits inflammation, an upstream event that may lead to the development of emphysema. Although there is evidence of this protective effect in young rats and a mechanistic explanation, more studies are needed in humans in order to establish a role for vitamin A in protecting against emphysema. Too many unanswered questions remain to definitively state that vitamin A protects against this disease in humans. Nevertheless, the potential for this novel approach in prevention and treatment of emphysema is an exciting area of research.

Retinoic acid improves ciliogenesis after surgery of the maxillary sinus in rabbits

OBJECTIVES/HYPOTHESIS

Retinoids have been shown to be important cofactors in regulating the differentiation and proliferation of ciliated epithelial cells of the respiratory tract. In particular, retinoic acid has been shown to enhance the regeneration of paranasal sinus mucosa. The objective of this study is to use scanning electron microscopy techniques to evaluate the effect of topical retinoic acid on mucosal wound healing in a rabbit model of maxillary sinus surgery. It is hypothesized that the application of topical retinoic acid will enhance ciliogenesis and improve the morphology of regenerated cilia compared with controls.

STUDY DESIGN

Prospective multi-arm controlled animal trial.

METHODS

Eighteen New Zealand white rabbits underwent surgical opening of the maxillary sinuses through a midline incision. The rabbits were divided among four experimental groups: 1) mucosal stripping alone (stripped control), 2) stripping followed by topical application of an inert aqueous gel, 3) stripping followed by application of 0.01% retinoic acid in aqueous gel, and 4) no mucosal stripping and no topical treatment (nonstripped control). After 14 days, the medial wall of the maxillary sinus was harvested and examined by scanning electron microscopy at x2,000 and x5,000 magnification. The micrographs were then rated by a blinded review panel for ciliary density, orientation, and morphology.

RESULTS

Mean scores for ciliary density, orientation, and morphology were all significantly higher for the retinoic acid treatment group compared with both the inert aqueous gel treatment group and the stripped control group (P=.004-.03 for all comparisons, Student's t test). Mean scores for the retinoic acid treatment group were numerically lower than the nonstripped control group but did not approach statistical significance for any parameter (P=.23-.31).

CONCLUSIONS

In a rabbit model of maxillary sinus surgery, topically delivered retinoic acid enhances ciliogenesis. Qualitative assessment of ciliary density, orientation, and morphology shows improved healing in retinoic acid treated sinuses compared with both untreated control sinuses and aqueous gel treated sinuses.

Nonclassical action of retinoic acid on the activation of the cAMP response element-binding protein in normal human bronchial epithelial cells

Vitamin A (retinol) is essential for normal regulation of cell growth and differentiation. We have shown that the retinol metabolite retinoic acid (RA) induces mucous cell differentiation of normal human tracheobronchial epithelial (NHTBE) cells. However, early biological effects of RA in the differentiation of bronchial epithelia are largely unknown. Here, we showed that RA rapidly activated cAMP response element-binding protein (CREB). However, RA did not use the conventional retinoic acid receptor (RAR)/retinoid X receptor (RXR) to activate CREB. RA activated CREB in NHTBE and H1734 cells in which RARs/RXR were silenced with small interfering RNA (siRNA) targeting RAR/RXR expression or deactivated by antagonist. Inhibition of protein kinase C (PKC) or extracellular regulated kinase (ERK1/2) blocked the RA-mediated activation of CREB. In addition, depletion of p90 ribosomal S6 kinase (RSK) via siRSK1/2 completely abolished the activation, suggesting that PKC, ERK, and RSK are required for the activation. Altogether, this study provides the first evidence that RA rapidly activates CREB transcription factor via PKC, ERK, and RSK in a retinoid receptor-independent manner in normal bronchial epithelial cells. This noncanonical RA signaling pathway may play an important role in mediating early biological effects in the mucociliary differentiation of bronchial epithelia.

Effects of vitamin a supplementation on immune responses and correlation with clinical outcomes

Vitamin A supplementation to preschool children is known to decrease the risks of mortality and morbidity from some forms of diarrhea, measles, human immunodeficiency virus (HIV) infection, and malaria. These effects are likely to be the result of the actions of vitamin A on immunity. Some of the immunomodulatory mechanisms of vitamin A have been described in clinical trials and can be correlated with clinical outcomes of supplementation. The effects on morbidity from measles are related to enhanced antibody production and lymphocyte proliferation. Benefits for severe diarrhea could be attributable to the functions of vitamin A in sustaining the integrity of mucosal epithelia in the gut, whereas positive effects among HIV-infected children could also be related to increased T-cell lymphopoiesis. There is no conclusive evidence for a direct effect of vitamin A supplementation on cytokine production or lymphocyte activation. Under certain circumstances, vitamin A supplementation to infants has the potential to improve the antibody response to some vaccines, including tetanus and diphtheria toxoids and measles. There is limited research on the effects of vitamin A supplementation to adults and the elderly on their immune function; currently available data provide no consistent evidence for beneficial effects. Additional studies with these age groups are needed.

Meat as a component of a healthy diet - are there any risks or benefits if meat is avoided in the diet?

Meat is frequently associated with a "negative" health image due to its "high" fat content and in the case of red meat is seen as a cancer-promoting food. Therefore, a low meat intake, especially red meat is recommended to avoid the risk of cancer, obesity and metabolic syndrome. However, this discussion overlooks the fact, that meat is an important source for some of micronutrients such as iron, selenium, vitamins A, B12 and folic acid. These micronutrients are either not present in plant derived food or have poor bioavailability. In addition, meat as a protein rich and carbohydrate "low" product contributes to a low glycemic index which is assumed to be "beneficial" with respect to overweight, the development of diabetes and cancer (insulin resistance hypothesis). Taken together meat is an important nutrient for human health and development. As an essential part of a mixed diet, meat ensures adequate delivery of essential micronutrients and amino acids and is involved in regulatory processes of energy metabolism.

Mucin biosynthesis: upregulation of core 2 beta 1,6 N-acetylglucosaminyltransferase by retinoic acid and Th2 cytokines in a human airway epithelial cell line

Vitamin A and the T helper 2 cytokines IL-4 and IL-13 play important roles in the induction of mucin gene expression and mucus hypersecretion. However, the effects of these agents on enzymes responsible for mucin glycosylation have received little attention. Here, we report the upregulation of core 2 beta1,6 N-acetylglucosaminyltransferase (C2GnT) activity both by all-trans retinoic acid (RA) and by IL-4 and IL-13 in the H292 airway epithelial cell line. Northern blotting analysis showed that the M isoform of C2GnT, which is expressed in mucus-secreting tissues and can form all mucin glycan beta1,6-branched structures, including core 2, core 4, and blood group I antigen, was upregulated by both RA and IL-4/13. The L isoform, which forms only the core 2 structure, was moderately upregulated by IL-4/13 but not by RA. Enhancement of the M isoform of C2GnT by RA was abolished by an inhibitor of RA receptor alpha, implicating RA receptor alpha in the effect of RA. Likewise, an inhibitor of the Janus kinase 3 pathway blocked the enhancing effects of IL-4/13 on the L and M isoforms of C2GnT, suggesting a role of this pathway in the upregulation of these two C2GnTs by these cytokines. Taken together, the results suggest that IL-4/13 T helper 2 cytokines and RA can alter the activity of enzymes that synthesize branching mucin carbohydrate structure in airway epithelial cells, potentially leading to altered mucin carbohydrate structure and properties.

Cilia-related diseases

There are at least eight categories of cilia in the human body and malfunctioning of any one or several of them will have different consequences for the patient. A genetic error of the respiratory cilia (9 + 2) is the cause of the airways disease named immotile-cilia syndrome (or PCD), whereas defective ependymal cilia (9 + 2) carries an increased risk of hydrocephalus. When the so-called nodal cilia (9 + 0) of the early embryo are malfunctioning, there is a random determination of asymmetry of the heart and visceral organs ('a 50% risk of situs inversus'). Some genes are responsible for the synthesis, transport, and assembly of the cilia, and mutations in these genes may lead to progressive degeneration of ciliary structures, such as the connecting cilium (9 + 0) of the photoreceptor cells-this is the cause of retinitis pigmentosa. Ciliary malfunctions due to genetic errors tend to be systemic and life-long, whereas acquired diseases are local and may be temporary only.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Retinoic acid depletion induces keratinizing squamous differentiation in human middle ear epithelial cell cultures

OBJECTIVE

The pathogenesis of cholesteatoma behind an intact tympanic membrane remains controversial. Squamous metaplasia of the middle ear mucosa is thought to be a possible mechanism in such cases. However, to date, no definitive experimental results have proved this association. This study was undertaken to investigate whether normal human middle ear epithelial (NHMEE) cells undergo keratinizing squamous differentiation in a retinoic acid (RA)-deficient culture.

MATERIAL AND METHODS

We examined the morphological differences between RA-deficient and -sufficient cultures, and determined the expressions of the mucin gene and cornifin-alpha mRNAs as indicators of mucous and squamous differentiation, respectively.

RESULTS

Histomorphologically, the NHMEE cells differentiated into a keratinizing squamous epithelium in RA-deficient cultures. In addition, the expressions of mucin gene 5AC (MUCSAC) and MUC8 mRNAs were suppressed, and the expression of cornifin-alpha mRNA increased progressively as a function of differentiation in RA-deficient cultures.

CONCLUSIONS

This study shows that RA depletion induces keratinizing squamous differentiation in NHMEE cell cultures. This finding supports the hypothesis that middle ear cholesteatoma originates from metaplastic middle ear mucosa.

Retinoic acid receptors and retinoids are up-regulated in the developing and adult rat prostate by neonatal estrogen exposure

Exposure to estrogens during the neonatal period interrupts rat prostatic development by reducing branching morphogenesis and by blocking epithelial cells from entering a normal differentiation pathway. Upon aging, ventral prostates exhibit extensive hyperplasia, dysplasia, and massive lymphocytic infiltrate, suggesting that neonatal estrogens may predispose the prostate gland to precancerous lesions. Vitamin A (retinol) and their derivatives (retinoic acids) are known key developmental regulators that bind and activate retinoic acid receptors (RARs). To evaluate whether neonatal estrogenization alters the sensitivity of the developing rat prostate to retinoids, RARalpha, -beta, and -gamma cellular localization and protein levels were analyzed over the course of development and into adulthood by immunocytochemistry and Western analysis, whereas mRNA levels were measured using RT-PCR. In addition, intraprostatic retinol and retinoic acid levels were quantitated on d 10 and 90 using HPLC-mass spectroscopy. Male rats were given 25 micro g estradiol benzoate or oil on d 1, 3, and 5 of life, and prostatic complexes were removed on d 6, 10, 15, 30, and 90. The RARs localized to distinct cell populations: RARbeta was expressed within basal epithelial cells, RARalpha was localized to differentiated luminal epithelial cells and smooth muscle cells, and RARgamma was expressed within periductal stromal cells. Over the normal course of development, total protein and mRNA levels for the RARs declined, so that the adult prostate possessed the lowest amounts of RAR. Exposure to estrogens during the neonatal period resulted in an immediate and sustained increase in RARalpha levels and in the number of cells that expressed RARbeta, whereas RARgamma levels were unaffected. Western analysis confirmed that total prostatic RAR protein levels were significantly increased, whereas RT-PCR demonstrated that RARalpha and RARbeta mRNA levels were markedly elevated in response to estrogenic exposure. The total prostatic retinol content was tripled by estrogenic exposure on d 10 and 90, indicating that the ability to retain retinoids within the prostate was permanently increased. Intraprostatic levels of 9-cis- and all-trans-retinoic acid levels were reduced on d 10, whereas 13-cis-retinoic acid levels were increased in response to estrogens. In the adult prostates of rats exposed neonatally to estrogen, total retinoic acid levels were doubled due to significant increases in both 9-cis- and 13-cis-retinoic acids compared with those in control prostates. In summary, levels of specific RARs and their activating ligands are increased in the prostate gland after neonatal estrogenic exposure, and this effect is permanent throughout the life of the animal. Thus, we hypothesize that alterations in morphogenesis as well as dysplasia in the adult prostate may be mediated in part through augmentation of transcriptional signals in the retinoid pathway.

Effects of retinoic acid receptor-selective agonists on human nasal epithelial cell differentiation

Retinoids play a critical role in the maintenance of the mucociliary phenotype of epithelial cells in the upper respiratory tract. To determine the role of retinoic acid receptors (RARs) in the regulation of epithelial differentiation, we tested the effect of the synthetic retinoids CD336, CD2019, and CD666, selective agonists for RARalpha, RARbeta, and RARgamma, respectively, during differentiation of human nasal epithelial (HNE) cells in vitro. Using glutamylated tubulin and transglutaminase I (Tg I) as markers of ciliated cell and squamous cell differentiation, respectively, we showed that retinoic acid (RA) stimulated mucociliary differentiation and, in parallel, inhibited squamous cell differentiation. The agonists of the three RARs independently induced ciliogenesis and inhibited squamous cell differentiation by downregulating Tg I expression in a dose- and time-dependent manner. Antagonists specific for the three RARs abolished the effects of the corresponding agonists, demonstrating an RAR-specific mediated effect. Moreover, treatment of retinoid-deficient cultures with RAR agonists induced conversion of the squamous-like phenotype into a ciliated phenotype. In conclusion, all three RARs are potentially involved in the differentiating effects of RA in respiratory epithelial cells.

Vitamin A deficiency injures lung and liver parenchyma and impairs function of rat type II pneumocytes

The purpose of this research was to determine the effects of vitamin A deficiency on liver and lung morphology and type II pneumocyte function. Weanling rats were fed a retinol-adequate (control) or -deficient diet for 6 wk. Average food intakes and body weights were not different between the vitamin A-deficient and -adequate rats. Histologic examination revealed that the lungs of vitamin A-deficient rats had less collagen in the adventitia of small caliber arteries and arterioles and in the alveolar septa, which appeared thinner than that of controls. Many areas of the lungs of the same rats were also emphysematous (increased size of air spaces distal to the terminal bronchiole, with thinning and partial or total destruction of septal wall). Content of elastin also was lower in the lung parenchyma, as well as in the small arteries and arterioles, but not in the larger ones. Peribronchial collagen was not affected by the deficient diet. Scattered inflammation was observed in most of the vitamin A-deficient rats; a mild inflammatory reaction also was seen in one of the controls. Vitamin A-deficient rats also exhibited hepatocyte vacuolization and mild inflammation in the liver, specifically in the periportal tracts. Surfactant synthesis and ornithine decarboxylase activity were significantly lower in type II pneumocytes isolated from vitamin A-deficient rats. In conclusion, our data provide evidence that vitamin A deficiency produces profound morphologic alterations in liver and lung parenchyma and impairs pneumocyte function.

Mild vitamin A deficiency delays fetal lung maturation in the rat

During late pregnancy, the fetal lung stores surfactant in preparation for extrauterine life. Surfactant deficiency, most often due to prematurity, precipitates respiratory distress syndrome (RDS) of the neonate. Although vitamin A (retinol) and retinoic acid have been shown to enhance the synthesis of phospholipid surfactant components, their effect on surfactant-specific proteins is unclear. No attempt has been made to evaluate the consequences of vitamin A restriction on surfactant phospholipid storage or on the expression of the life-essential surfactant protein-B (SP-B). We induced in rats a partial vitamin A deficiency leading to a 30-60% reduction in blood retinol, a status compatible with maintenance of gestation and absence of gross abnormalities in offspring. At term, lung surfactant phospholipids were reduced by 21%, and the major surfactant phospholipid, disaturated phosphatidylcholine (DSPC), was reduced by 27% in vitamin A-deficient (VAD) fetuses. The decrease in surfactant phospholipids and DSPC correlated linearly with plasma retinol, and reached about 50% in fetuses with the lowest retinol concentrations; it was accompanied by reduced expression of the gene for fatty acid synthase, a key enzyme in the synthetic pathway for surfactant-phospholipid lipid precursors. The amounts of SP-A, SP-B, and SP-C messenger RNAs were decreased by 46%, 32%, and 28%, respectively, in VAD fetuses. Consistently, amounts of SP-A and SP-B proteins were diminished as assessed by Western blotting. The proportion of type II cells determined after SP-B labeling was unchanged in VAD as compared with control lungs. Vitamin A deficiency is therefore a cause of lung maturational delay. In view of its rather large incidence in human populations, it may represent an increased risk for RDS and an aggravating factor for prematurity.

Restoration of the mucous phenotype by retinoic acid in retinoid-deficient human bronchial cell cultures: changes in mucin gene expression

Retinoid-deficient cultures of airway epithelial cells undergo squamous differentiation. Treatment of such cultures with retinoic acid (RA) leads to restoration of the mucous phenotype. The purpose of our study was to characterize the cellular and molecular changes following RA treatment of retinoid-deficient human tracheobronchial epithelial cell cultures. Of particular interest was to determine when during the conversion of the squamous to the mucous phenotype the mucin genes MUC2, MUC5AC, and MUC5B were expressed. We used cornifin alpha and secreted mucin as markers to monitor the squamous and mucous phenotypes, respectively. Our studies showed that the RA responsiveness of the cultures progressively decreased with protracted retinoid deficiency, requiring higher RA concentrations to restore the mucous phenotype. Within 12 h after the start of RA treatment, cornifin alpha expression decreased, signaling the beginning of a change in cellular phenotype. At 24 h after addition of RA to the cultures, a significant number of mucous cells appeared, and at 72 h mucin was secreted in measurable amounts. Induction of mucin gene expression occurred sequentially: MUC2, MUC5AC, and MUC5B mRNAs were upregulated at 24, 48, and 72 h, respectively. When cultures maintained in 10(-8) M RA were treated with 10(-6) M RA, MUC2 but not MUC5AC and MUC5B mRNA levels were upregulated within 6 h. Our study indicates that MUC2 mRNA is an early marker of mucous differentiation, whereas MUC5AC and MUC5B mRNAs are expressed during more advanced stages of mucous differentiation. Our studies further suggest that each of the mucin genes is regulated by distinct mechanisms.

Integration of growth factor, extracellular matrix, and retinoid signals during bronchial epithelial cell differentiation

Epithelial cell differentiation is regulated by specific combinations of growth factors, hormones, and extracellular matrix (ECM). How these divergent signals are integrated is largely unknown. We used primary cultures of normal human bronchial epithelial cells (NHBEs) to investigate mechanisms of signal integration. In defined, serum-free media, NHBEs undergo mucosecretory differentiation only when grown in the presence of retinoids and on the appropriate substratum (collagen gels). We identified the retinoic acid receptor beta (RARbeta) gene as an early marker of NHBE differentiation. In contrast to immortalized cell lines, in NHBEs strong retinoid-induced RARbeta transcription occurs only when cells are grown on collagen gels, and it requires new protein synthesis and a cis-acting element that maps outside the known RARbeta promoter elements. NHBEs grown on collagen gels exhibit reduced epidermal growth factor (EGF)-induced Raf, MEK, and mitogen-activated protein kinase (MAPK) activity. This correlates with a specific inability to achieve high levels of p66(SHC) tyrosyl phosphorylation and association of p66(SHC) with GRB2, despite high levels of EGF receptor (EGFR) autophosphorylation. Notably, inhibition of EGFR or MEK/MAPK activation replaces the ECM requirement for RARbeta induction. Our results strongly suggest that a key mechanism by which specific ECMs facilitate retinoid-induced mucosecretory differentiation of NHBEs is by restricting the level of EGFR-dependent MEK/MAPK activation evoked by autocrine and/or paracrine EGFR ligands.

An Eastern Cooperative Oncology Group phase I trial of all-trans-retinoic acid and interferon-alpha: E2Y92

The Eastern Cooperative Oncology Group conducted a Phase I trial to determine the maximally tolerated doses of combination therapy with alpha interferon (IFN-alpha) and all-trans-retinoic acid (tRA). Fifty patients with incurable malignancies received IFN-alpha administered subcutaneously three times weekly, and tRA administered by mouth at bedtime. Doses were escalated between patient groups, starting at tRA dose level of 45 mg/m2 and 3 million units of IFN-alpha. Major, dose-limiting toxicities were attributable to either the tRA (rash, chelitis) or IFN (constitutional symptoms), and were observed only at tRA dose levels of 224 mg/m2 and 291 mg/m2, or 6 million units of IFN-alpha. The maximally tolerated dose level of 172.5 mg/m2 of tRA and 3 million units of IFN-alpha was well-tolerated, with no grade 3 or 4 toxicities attributable to therapy. One patient at the third dose level (75 mg/m2 of tRA and 3 million units of IFN-alpha) developed acute hepatic and renal failure and a metabolic encephalopathy of unclear etiology. We conclude that tRA and IFN-alpha may be safely administered together at the maximally tolerated dose of tRA as a single agent without unexpected side effects. The recommended doses of IFN-alpha and tRA for Phase II trials are 3 million units of IFN-alpha and 172.5 mg/m2 of tRA.

An ex vivo model of the rat trachea to study the effect of inhalable toxic compounds

Different cell culture and organ systems are used to evaluate the physiological responses of the airways to the effects of carcinogenic [e.g., benzo(a)pyrene] and anticarcinogenic (e.g., retinoids) compounds on cellular growth and differentiation. However, in contrast to in vivo conditions dissociated epithelial cells or tracheal ring cultures are covered with medium. Therefore, we developed an ex vivo perfusion model enabling evaluation of morphology and metabolism of different compounds under near-physiological conditions. The trachea was surrounded with culture medium and perfused with air by means of a small animal respirator. To test the viability of the system under various experimental conditions tracheal probes were incubated with either retinoids (retinol 10(-5) mol/l; retinyl palmitate 10(-5) mol/l) or benzo(a)pyrene (10(-7) mol/l) for up to 7 days. At the end of the incubation period metabolites in the trachea and in the medium were measured by means of high-performance liquid chromatography. Samples were examined by light microscopy, and by scanning and transmission electron microscopy for cell morphology. Glycoconjugate expression was assessed by lectin histochemistry. Specimens incubated in a retinoid-supplemented medium revealed no alterations in the distribution of cell types and characteristics of the epithelial layer compared with tracheal biopsies assessed immediately after removal from the animals. Glycoconjugate patterns especially remained intact. Histological changes after incubation with benzo(a)pyrene resembled in vivo morphology of vitamin A-deficient rats. An important advantage of this in vitro model compared with common cell or organ cultures is the preservation of the original phenotype and environment of the tracheobronchial surface. In addition, carcinogenic substances, such as benzo(a)pyrene, can easily be applied by airway or through the medium.

Response of rat salivary glands to mastication of pelleted vitamin A-deficient diet

Interpretation of previous studies of the effects of hypovitaminosis. A on salivary glands is confounded by the atrophic effects of liquid or powdered diets. The purpose of this study was to reevaluate the effects of vitamin. A deficiency on the morphology and function of rat salivary glands using a pelleted diet that promotes physiological levels of masticatory stimulation. Profound vitamin A deficiency resulted in a marked decrease in stimulated parotid secretion. Histological evaluation demonstrated the development of squamous metaplasia in the ducts of parotid, submandibular and sublingual salivary glands; however, atrophy was observed only in serious salivary glands. In the parotid gland the degree of atrophy corresponded to the decrease in stimulated secretion. Mild hypovitaminosis A (before the development of squamous metaplasia in ducts) was associated with distinctly different effects. The parotid gland was moderately enlarged. There was also a significant increase in stimulated secretion, which was not explained by changes in gland size, muscarinic receptor number or affinity, or receptor-mediated calcium signalling.

Cytokeratin expression in preneoplastic lesions and early squamous cell carcinoma of the bronchi

Cytokeratins are expressed in varying combination in the course of differentiation of epithelial cells and tumor cells. This is the first report of systematic immunohistochemical (ABC-method) investigations concerning the expression of different cytokeratin types (KL 1, CK 4, 10 and 17) within the transformation of the bronchial mucosal epithelium with epithelial hyperplasia to potential preneoplasia and early squamous cell carcinoma of the lung. In bioptical obtained specimens from 35 patients, 63 areas with diagnosis of regular bronchial mucosa (n = 10), basal cell hyperplasia (n = 9), goblet cell hyperplasia (n = 10), squamous cell metaplasia (n = 11), dysplasia I-III (n = 13), carcinoma in situ in the border zone of squamous cell carcinoma (n = 10) and in 5 surgically obtained specimens with findings of an early squamous cell carcinoma of the bronchus (n = 5), the expression of different cytokeratin types was investigated. The specimens were fixed in formalin and embedded in paraffin for lightmicroscopical and immunohistochemical investigations (ABC-method). KL 1 was detected in all regular and pathological mucosal epithelia, CK 4 in basal cells, squamous cell metaplasia, potentially preneoplastic changes and early squamous cell carcinoma of the bronchus. CK 10 was expressed only in early squamous cell carcinoma of the bronchus, and CK 17 in varying quantity in hyperplastic, preneoplastic and cancerous lesions of the bronchial mucosa. Our results reveal an increasing expression of squamous epithelial type-cytokeratins (CK 4, CK 17) in hyperplastic and metaplastic lesions of the bronchial mucosa. In dysplastic lesions and carcinomata in situ, a quantitative, as well as qualitative decrease of the CK 4- and CK 17-expression with a heterogeneous expression pattern for CK 17 was found. The heterogeneous neo-expression of CK 10 in early squamous cell carcinoma of the bronchus has to be emphasized.

Evidence for impaired retinoic acid receptor-thyroid hormone receptor AF-2 cofactor activity in human lung cancer

Retinoic acid (RA) is required for normal airway epithelial cell growth and differentiation both in vivo and in vitro. One of the earliest events following the exposure of bronchial epithelial cells to RA is the strong induction of RA receptor beta (RAR beta) mRNA. Previous work established that many lung cancer cell lines and primary tumors display abnormal RAR beta mRNA expression, most often absence or weak expression of the RAR beta 2 isoform, even after RA treatment. Restoration of RAR beta 2 into RAR beta-negative lung cancer cell lines has been reported to inhibit tumorigenicity. Since RAR beta 2 inactivation may contribute to lung cancer, we have investigated the molecular mechanism of defective RAR beta 2 expression. Nuclear run-on assays and transient transfections with RAR beta 2 promoter constructs indicate the presence of trans-acting transcriptional defects in most lung cancer cell lines, which map to the RA response element (RARE). These defects cannot be complemented by RAR-retinoid X receptor cotransfection and can be separated into two types: (i) one affecting transcription from direct repeat RAREs, but not palindromic RAREs, and (ii) another affecting transcription from both types of RARE. Studies using chimeras between RAR alpha, TR alpha, and other transcription factors suggest the existence of novel RAR-thyroid hormone receptor AF-2-specific cofactors, which are necessary for high levels of transcription. Furthermore, these factors may be frequently inactivated in human lung cancer.

A critical appraisal of intratracheal instillation of benzo[a]pyrene to Syrian golden hamsters as a model in respiratory tract carcinogenesis

Several experimental models have been developed to study respiratory tract carcinogenesis. The most widely applied in vivo model uses Syrian golden hamsters which receive intratracheal instillations of a suspension of benzo[a]pyrene (B[a]P) particles attached to ferric-oxide (Fe2O3) particles in saline; it was first described by Saffiotti et al. [1]. This model has several benefits compared with other experimental models; however, the large number of variables affecting the tumour response is a clear disadvantage because the tumour response is difficult to control. In this review, we describe a systematic analysis of various variables that may influence the tumour response of the respiratory tract with the aim to further standardize the method and increase, through that, its suitability and predictability. The most important variables influencing the tumour response, as shown by statistical analysis of 29 representative studies, turned out to be the administered dose and the particle size. Both these variables influence the actual dose and the contact-time of the B[a]P particles with the target cells. The present study does not support the widespread opinion that ferric-oxide particles enhance the tumour response of the respiratory tract. In conclusion to the present analysis, some recommendations are made which probably increase the predictability of the model.

Effects of vitamin A on proliferation of human distal airway epithelial cells in culture

Using a serum-free culture method, we investigated the effects of vitamin A on the proliferation of human distal airway epithelial cells. Outgrowth of epithelial cells from lung tissue explants was enhanced by treatment with all-trans retinol at concentrations of 10(-8) to 10(-7) M. The colony-forming activity of cells harvested from the primary culture and replated onto Swiss 3T3 fibroblastic feeders was, in contrast, significantly reduced by 10(-7) M to 10(-5) M retinol. When the primary cells were harvested and subcultured on Primaria plates, population expansion was also inhibited by retinol at 10(-10) to 10(-6) M. We further investigated the cells to determine whether there was any difference in sensitivity to the growth-inhibitory effects of vitamin A between cells from the primary culture incubated with and without retinol. The population increase in cells harvested from the primary culture was inhibited equally in retinol-treated and non-treated cells by subsequent treatment with retinol or retinoic acid, this inhibition being dose-dependent. DNA synthetic activity was also inhibited. Interestingly, both the growth rate and the colony-forming efficiency on feeders were greater in the subculture of cells from the retinol-treated primary culture than in those non-treated. When the cells in the secondary subculture were treated with retinoic acid and replated again, they showed a greater population increase rate than those non-treated. Our results showed that human distal airway epithelial cells isolated from lung tissue were sensitive to the growth-inhibitory effect of vitamin A, but the proliferative potential in some fraction of the epithelial cell population was possibly enhanced by vitamin A treatment.

Protein-energy malnutrition in cystic fibrosis patients

Protein-energy malnutrition with associated specific nutrient deficiencies is an important feature of cystic fibrosis and has been recognized as a poor prognostic factor. Therefore, the nutritional status of cystic fibrosis patients has to be evaluated regularly by diet diaries, clinical evaluation, anthropometry and more sophisticated methods, such as bioelectrical impedance analysis. Nutritional management, including nutritional rehabilitation programmes, of cystic fibrosis patients is well established today. Consequently, protein-energy malnutrition is no longer acceptable in cystic fibrosis patients, except perhaps in end-stage disease when lung transplantation is not considered.

Squamous cell metaplasia in the human lung: molecular characteristics of epithelial stratification

Squamous cell metaplasia (SCM) is a frequent epithelial alteration of the human tracheobronchial mucosa. This review pays particular attention to the fact that SCM can mimic esophageal, and in some instances even skin-type differentiation, showing striking similarities not only in morphology but also in terms of gene expression. Therefore, characterization of this dynamic process lends insight into the process of stratification, squamous cell formation, and "keratinization" in a pathologically relevant in vivo situation in man. First, the concept of metaplasia is presented with certain historical viewpoints on histogenesis. Then, the morphological characteristics of normal bronchial epithelium are compared with the altered phenotype of cells in SCM. These changes are described as a disturbance of the finely tuned balance of differentiation and proliferation through the action of a variety of extrinsic and intrinsic factors. Molecular aspects of altered cell/cell and cell/extracellular matrix interactions in stratified compared with single-layered epithelia are discussed with reference to SCM in the lung. Intracellular organizational and compositional changes are then summarized with special emphasis on the differential distribution of the cytokeratin (CK) polypeptides. Finally, the still unresolved problems of the histogenetic relationships between normal bronchial mucosa, SCM, and pulmonary neoplasms are addressed. As these questions remain open, examples for detection of well defined "markers" are provided that may be employed as objective criteria for determining clinically important cellular differentiation features.