Limonene inhalation reduces allergic airway inflammation in Dermatophagoides farinae-treated mice

D-limonene inhibits peritoneal adhesion formation in rats via anti-inflammatory, anti-angiogenic, and antioxidative effects

The aim of this research was to investigate the effects of D-limonene on decreasing post-operative adhesion in rats and to understand the mechanisms involved. Peritoneal adhesions were induced by creating different incisions and excising a 1 × 1 cm section of the peritoneum. The experimental groups included a sham group, a control group in which peritoneal adhesions were induced without any treatment, and two treatment groups in which animals received D-limonene with dosages of 25 and 50 mg/kg after inducing peritoneal adhesions. Macroscopic examination of adhesions showed that both treatment groups had reduced adhesion bands in comparison to the control group. Immunohistochemical assessment of TGF-β1, TNF-α, and VEGF on day 14 revealed a significant increment in the level of immunopositive cells for the mentioned markers in the control group, whereas administration of limonene in both doses significantly reduced levels of TGF-β1, TNF-α, and VEGF (P < 0.05). Induction of peritoneal adhesions in the control group significantly increased TGF-β1, TNF-α, and VEGF on days 3 and 14 in western blot evaluation, while treatment with limonene significantly reduced TNF-α level on day 14 (P < 0.05). Moreover, VEGF levels in both treatment groups significantly reduced on days 3 and 14. In the control group, a significant increment in the levels of MDA and NO and a notable decline in the levels of GPX, CAT was observed (P < 0.05). Limonene 50 group significantly reduced MDA level and increased GPx and CAT levels on day 14 (P < 0.05). In summary, D-limonene reduced adhesion bands, inflammatory cytokines, angiogenesis, and oxidative stress.

Phytochemicals as treatment for allergic asthma: Therapeutic effects and mechanisms of action

BACKGROUND

Allergic asthma is an inflammatory disease caused by the immune system's reaction to allergens, inflammation and narrowing of the airways, and the production of more than normal mucus. One of the main reasons is an increased production of inflammatory cytokines in the lungs that leads to the appearance of symptoms of asthma, including inflammation and shortness of breath. On the other hand, it has been proven that phytochemicals with their antioxidant and anti-inflammatory properties can be useful in improving allergic asthma.

PURPOSE

Common chemical treatments for allergic asthma include corticosteroids, which have many side effects and temporarily relieve symptoms but are not a cure. Therefore, taking the help of natural compounds to improve the quality of life of asthmatic patients can be a valuable issue that has been evaluated in the present review.

STUDY DESIGN AND METHODS

In this study, three databases (Scopus, PubMed, and Cochrane) with the keywords: allergic asthma, phytochemical, plant, and herb were evaluated. The primary result was 5307 articles. Non-English, repetitive, and review articles were deleted from the study.

RESULTS AND DISCUSSION

Finally, after carefully reading the articles, 102 were included in the study (2006-2022). The results of this review state that phytochemicals suppress the inflammatory pathways via inhibition of inflammatory cytokines production/secretion, genes, and proteins involved in the inflammation process, reducing oxidative stress indicators and symptoms of allergic asthma, such as cough and mucus production in the lungs.

CONCLUSION

With their antioxidant effects, this study concluded that phytochemicals suppress cytokines and other inflammatory indicators and thus can be considered an adjunctive treatment for improving allergic asthma.

Proposed mechanisms of action of herbal drugs and their biologically active constituents in the treatment of coughs: an overview

Various medicinal plants find their use in cough treatment, based on traditions and long-term experience. Pharmacological principles of their action, however, are much less known. Herbal drugs usually contain a mixture of potentially active compounds, which can manifest diverse effects. Expectorant or antitussive effects, which can be accompanied by others, such as anti-inflammatory or antibacterial, are probably the most important in the treatment of coughs. The aim of this review is to summarize the current state of knowledge of the effects of medicinal plants or their constituents on cough, based on reliable pharmacological studies. First, a comprehensive description of each effect is provided in order to explain the possible mechanism of action in detail. Next, the results related to individual plants and substances are summarized and critically discussed based on pharmacological in vivo and in vitro investigation.

Pharmacologic effects approach of essential oils and their components on respiratory diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Essential oils (EOs) are concentrated hydrophobic liquids with volatility and a unique aroma. Formed by aromatic plants as secondary metabolites, EOs have been used as traditional medicines to treat various health problems worldwide. Historical records show that herbs rich in EOs have been widely used to treat respiratory diseases in China, Europe, and many other regions.

AIM OF THE REVIEW

This review summarizes the traditional applications and modern pharmacological mechanisms of EOs derived from aromatic herbs and their active ingredients in respiratory diseases in preclinical and clinical trials through multitarget synergy.

MATERIALS AND METHODS

Information about EOs and respiratory diseases was collected from electronic databases, such as ScienceDirect, Web of Science, PubMed, Google Scholar, Baidu Scholar, and the China National Knowledge Infrastructure (CNKI).

RESULTS

This review presents the preventive and therapeutic effects of EOs on respiratory diseases, including chronic obstructive pulmonary disease, bronchial asthma, acute lung injury, pulmonary infection, and pulmonary fibrosis. The molecular mechanisms of EOs in treating different lung diseases are summarized, including anti-inflammation, anti-oxidation, mucolytic, and immune regulatory mechanisms.

CONCLUSIONS

EOs show potential as supplements or substitutes for treating lung diseases.

Stressed out - The role of oxidative stress in airway smooth muscle dysfunction in asthma and COPD

The airway smooth muscle (ASM) surrounding the airways is dysfunctional in both asthma and chronic obstructive pulmonary disease (COPD), exhibiting; increased contraction, increased mass, increased inflammatory mediator release and decreased corticosteroid responsiveness. Due to this dysfunction, ASM is a key contributor to symptoms in patients that remain symptomatic despite optimal provision of currently available treatments. There is a significant body of research investigating the effects of oxidative stress/ROS on ASM behaviour, falling into the following categories; cigarette smoke and associated compounds, air pollutants, aero-allergens, asthma and COPD relevant mediators, and the anti-oxidant Nrf2/HO-1 signalling pathway. However, despite a number of recent reviews addressing the role of oxidative stress/ROS in asthma and COPD, the potential contribution of oxidative stress/ROS-related ASM dysfunction to asthma and COPD pathophysiology has not been comprehensively reviewed. We provide a thorough review of studies that have used primary airway, bronchial or tracheal smooth muscle cells to investigate the role of oxidative stress/ROS in ASM dysfunction and consider how they could contribute to the pathophysiology of asthma and COPD. We summarise the current state of play with regards to clinical trials/development of agents targeting oxidative stress and associated limitations, and the adverse effects of oxidative stress on the efficacy of current therapies, with reference to ASM related studies where appropriate. We also identify limitations in the current knowledge of the role of oxidative stress/ROS in ASM dysfunction and identify areas for future research.

Efficacy and mechanism of essential oil from Abies holophylla leaf on airway inflammation in asthma: Network pharmacology and in vivo study

BACKGROUND

Asthma is one of the most common chronic inflammatory diseases of the airways. Essential oil from Abies holophylla leaf (EOA) has been reported to have anti-inflammatory property. This study aimed to predict the inhibitory effect of EOA against asthma by network analysis and to confirm the underlying mechanism of EOA on airway inflammation.

PURPOSE AND STUDY DESIGN

The effects and underlying mechanisms of EOA on asthma were investigated by in silico network pharmacology and an experimental in vivo study.

METHODS

To define the effectiveness of EOA on asthma, the network pharmacology was constructed using major components of EOA. EOA (0.0003 and, 0.03 v/v%) was aerosolized by nebulizer 3 times a week for 5 min for 7 weeks. After 3 weeks of treating the mice with EOA, asthma was induced by sensitizing them with ovalbumin (OVA) and PM10. The effects of EOA on the IL-17 related signaling pathway was confirmed using an asthmatic model.

RESULTS

The network analysis showed that EOA is highly associated with the IL-17-related signaling pathway. EOA inhibited respiratory epithelium hyperplasia, collagen deposition and goblet cell activation in the lung and trachea tissues. In addition, EOA reduced the number of eosinophils, lymphocytes and macrophages in BALF. Furthermore, in the asthmatic model of mice, we showed that EOA inhibited IL-17-related cytokines, increased Treg-related cytokines and decreased the TRAF6 and MAPK and, suppressed the nuclear transcriptional activities of NF-kB.

CONCLUSIONS

The network pharmacology and in vivo study indicated that EOA may have an inhibitory effect on airway inflammation in asthma exposure through the IL-17-related signaling pathway.

Machine learning-informed and synthetic biology-enabled semi-continuous algal cultivation to unleash renewable fuel productivity

Algal biofuel is regarded as one of the ultimate solutions for renewable energy, but its commercialization is hindered by growth limitations caused by mutual shading and high harvest costs. We overcome these challenges by advancing machine learning to inform the design of a semi-continuous algal cultivation (SAC) to sustain optimal cell growth and minimize mutual shading. An aggregation-based sedimentation (ABS) strategy is then designed to achieve low-cost biomass harvesting and economical SAC. The ABS is achieved by engineering a fast-growing strain, Synechococcus elongatus UTEX 2973, to produce limonene, which increases cyanobacterial cell surface hydrophobicity and enables efficient cell aggregation and sedimentation. SAC unleashes cyanobacterial growth potential with 0.1 g/L/hour biomass productivity and 0.2 mg/L/hour limonene productivity over a sustained period in photobioreactors. Scaling-up the SAC with an outdoor pond system achieves a biomass yield of 43.3 g/m²/day, bringing the minimum biomass selling price down to approximately $281 per ton.

Growth limitation caused by mutual shading and the high harvest cost hamper algal biofuel production. Here, the authors overcome these two problems by designing a semi-continuous algal cultivation system and an aggregation-based sedimentation strategy to achieve high levels production of biomass and limonene.

Physiological and Psychological Assessments for the Establishment of Evidence-Based Forest Healing Programs

This study aimed to establish a health and medical foundation for forest healing programs and provide a basis for developing an evaluation system for such programs. While the number of visitors to forests and interest in forest healing effects are increasing, few studies have examined the various indicators of the persistent changes in forest healing effects. Therefore, this study conducted pre-, post-, and follow-up experiments on 87 health and clinical indicators in a sample of 88 adolescent participants. The relationships between pre-, post-, and follow-up experiment results for each indicator were analyzed. Of the 87 indicators, 46 showed significant changes, including systolic blood pressure, diastolic blood pressure, cholesterol, serotonin, vitamin D, CD16+CD56 count, interferon-γ, resilience, and self-esteem. The findings are significant for studying diverse participants and indicators and lay the foundation for developing forest healing programs by clarifying aspects such as the indicators suitable for short-term observation versus the indicators requiring long-term observation. Based on these analyses, the results of this study are expected to be useful when conducting research to establish an evidence-based forest healing program in the future.

Solidification of volatile D-Limonene by cyclodextrin metal-organic framework for pulmonary delivery via dry powder inhalers: In vitro and in vivo evaluation

D-Limonene (D-Lim), a volatile oil extracted from citrus fruits, has therapeutic effects on lung inflammation and cancer, whilst the deep delivery of D-Lim was challenging due to its physical instability for a long period of time. To prevent the volatilization of D-Lim and achieve efficient pulmonary delivery, herein, D-Lim was loaded into biodegradable γ-cyclodextrin metal-organic framework (γ-CD-MOF) with optimal loading efficiency achieving 13.79 ± 0.01% (molar ratio of D-Lim and γ-CD-MOF was 1.6:1), which possessed cubic shape with controllable particle size (1-5 μm). The experimental results indicated that γ-CD-MOF could improve the stability of D-Lim. A series of characterizations and molecular docking were used to reveal the interaction between D-Lim and γ-CD-MOF. The solidification of D-Lim by γ-CD-MOF played a crucial role in the exploitation of its inhalable dosage form, dry powder inhaler (DPI). Specifically, the aerosolization of D-Lim@γ-CD-MOF for inhalation was satisfactory with a fine particle fraction (FPF) of 33.12 ± 1.50% at 65 L/min of flow rate. Furthermore, in vivo study had shown a 2.23-fold increase in bioavailability of D-Lim solidified by γ-CD-MOF for inhalation compared to D-Lim for oral administration. Therefore, it is considered that γ-CD-MOF could be an excellent carrier for pulmonary drug delivery to realize solidification and lung therapeutic effects of volatile oils.

A Review of Hemp as Food and Nutritional Supplement

The term "hemp" refers to Cannabis sativa cultivars grown for industrial purposes that are characterized by lower levels of tetrahydrocannabinol (THC), the active principle responsible for Cannabis psychotropic effects. Hemp is an extraordinary crop, with enormous social and economic value, since it can be used to produce food, textiles, clothing, biodegradable plastics, paper, paint, biofuel, and animal feed, as well as lighting oil. Various parts of the hemp plant represent a valuable source of food and ingredients for nutritional supplements. While hemp inflorescence is rich in nonpsychoactive, yet biologically active cannabinoids, such as cannabidiol (CBD), which exerts potent anxiolytic, spasmolytic, as well as anticonvulsant effects, hempseed has a pleasant nutty taste and represents a valuable source of essential amino acids and fatty acids, minerals, vitamins, and fibers. In addition, hempseed oil is a source of healthy polyunsaturated fatty acids, and hemp sprouts are rich in antioxidants. This review article aims to provide a comprehensive outlook from a multidisciplinary perspective on the scientific evidence supporting hemp beneficial properties when consumed as food or supplement. Marketing of hemp-derived products is subjected to diversified and complex regulations worldwide for several reasons, including the fact that CBD is also the active principal of pharmaceutical agents and that regulatory bodies in some cases ban Cannabis inflorescence regardless of its THC content. Some key regulatory aspects of such a complex scenario are also analyzed and discussed in this review article.

Nature Exposure and Its Effects on Immune System Functioning: A Systematic Review

Given the drastic changes in our lifestyles and ecosystems worldwide, the potential health effects of natural environments have grown into a highly pervasive topic. Recent scientific findings suggest beneficial effects from nature exposure on human immune responses. This review aims at providing a comprehensive overview of literature published on immunomodulatory effects of nature exposure by inhalation of natural substances. A systematic database search was performed in SCOPUS and PubMed. The quality and potential bias of included studies (n = 33) were assessed by applying the EPHPP (Effective Public Health Practice Project) tool for human studies and the ARRIVE (Animal Research: Reporting of In Vivo Experiments) and SYRCLE (Systematic Review Centre for Laboratory Animal Experimentation) tools for animal studies. The synthesis of reviewed studies points to positive effects of nature exposure on immunological health parameters; such as anti-inflammatory, anti-allergic, anti-asthmatic effects or increased NK (natural killer) cell activity. Decreased expression of pro-inflammatory molecules, infiltration of leukocytes and release of cytotoxic mediators are outcomes that may serve as a baseline for further studies. However, partially weak study designs evoked uncertainties about outcome reproducibility and key questions remain open concerning effect sizes, duration of exposure and contributions of specific vegetation or ecosystem types.

Can limonene be a possible candidate for evaluation as an agent or adjuvant against infection, immunity, and inflammation in COVID-19?

Coronavirus disease (COVID-19) caused by novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing pandemic and presents a public health emergency. It has affected millions of people and continues to affect more, despite the tremendous social preventive measures. The therapeutic strategy relies on suppressing infectivity and inflammation, along with immune modulation. The identification of candidate drugs effective for COVID-19 is crucial, thus many natural products including phytochemicals are also being proposed for repurposing and evaluated for their potential in COVID-19. Among numerous phytochemicals, limonene (LMN), a dietary terpene of natural origin has been recently showed to target viral proteins in the in-silico studies. LMN is one of the main compounds identified in many citrus plants, available and accessible in diets and well-studied for its therapeutic benefits. Due to dietary nature, relative safety and efficacy along with favorable physicochemical properties, LMN has been suggested to be a fascinating candidate for further investigation in COVID-19. LMN showed to modulate numerous signaling pathways and inhibits inflammatory mediators, including cytokines, chemokines, adhesion molecules, prostanoids, and eicosanoids. We hypothesized that given the pathogenesis of COVID-19 involving infection, inflammation, and immunity, LMN may have potential to limit the severity and progression of the disease owing to its immunomodulatory, anti-inflammatory, and antiviral properties. The present article discusses the possibilities of LMN in SARS-CoV-2 infections based on its immunomodulatory, anti-inflammatory, and antiviral properties. Though, the suggestion on the possible use of LMN in COVID-19 remains inconclusive until the in-silico effects confirmed in the experimental studies and further proof of the concept studies. The candidature of LMN in COVID-19 treatment somewhat appear speculative but cannot be overlooked provided favorable physiochemical and druggable properties. The safety and efficacy of LMN are necessary to be established in preclinical and clinical studies before making suggestions for use in humans.

Anti-Inflammatory Activity of Limonene in the Prevention and Control of Injuries in the Respiratory System: A Systematic Review

INTRODUCTION

The pulmonary inflammatory response results from exposure to injurious factors and is associated with oxidative stress, which intensifies the pathological reaction. In this context, limonene, a monoterpene found in citrus fruits, can be a therapeutic alternative for the treatment of this pathology, as it presents known anti-inflammatory and antioxidant actions.

OBJECTIVE

The purpose of this article is to provide an overview of the anti-inflammatory activity of limonene and its capacity to prevent and control respiratory system injuries.

SEARCH STRATEGY

A comprehensive literature search of the Cochrane, Scopus, MEDLINE-PubMed, Web of Science, and Lilacs databases was performed using the keywords: "limonene", "lung", "pulmonary", "airway", "trachea", "lung injury", "respiratory system", "respiratory tract diseases".

SELECTION CRITERIA

Studies on the use of limonene in disorders of the respiratory system, published until August 2019, were included. Those that did not use limonene alone or treated lesions in different systems other than the respiratory system, without targeting its anti-inflammatory action were excluded. In addition, review articles, meta-analyses, abstracts, conference papers, editorials/letters and case reports were also excluded.

RESULTS

Of the 561 articles found, 64 were in the Cochrane database, 235 in Scopus, 99 in Web of science, 150 in PubMed and 13 in Lilacs. After completing the systematic steps, 25 articles were selected for full reading, after which 7 papers remained in the review. An article was added after a manual literature search, resulting in a total of 8 papers. There was a high level of agreement on inclusion/exclusion among the researchers who examined the papers (Kappa index > 88%).

CONCLUSION

Limonene has effective anti-inflammatory activity in both preventing and controlling respiratory system injuries.

Forest Volatile Organic Compounds and Their Effects on Human Health: A State-of-the-Art Review

The aim of this research work is to analyze the chemistry and diversity of forest VOCs (volatile organic compounds) and to outline their evidence-based effects on health. This research work was designed as a narrative overview of the scientific literature. Inhaling forest VOCs like limonene and pinene can result in useful antioxidant and anti-inflammatory effects on the airways, and the pharmacological activity of some terpenes absorbed through inhalation may be also beneficial to promote brain functions by decreasing mental fatigue, inducing relaxation, and improving cognitive performance and mood. The tree composition can markedly influence the concentration of specific VOCs in the forest air, which also exhibits cyclic diurnal variations. Moreover, beneficial psychological and physiological effects of visiting a forest cannot be solely attributed to VOC inhalation but are due to a global and integrated stimulation of the five senses, induced by all specific characteristics of the natural environment, with the visual component probably playing a fundamental role in the overall effect. Globally, these findings can have useful implications for individual wellbeing, public health, and landscape design. Further clinical and environmental studies are advised, since the majority of the existing evidence is derived from laboratory findings.

Limonene-induced activation of A2A adenosine receptors reduces airway inflammation and reactivity in a mouse model of asthma

Animal models of asthma have shown that limonene, a naturally occurring terpene in citrus fruits, can reduce inflammation and airway reactivity. However, the mechanism of these effects is unknown. We first performed computational and molecular docking analyses that showed limonene could bind to both A_2A and A_2B receptors. The pharmacological studies were carried out with A_2A adenosine receptor knock-out (A_2AKO) and wild-type (WT) mice using ovalbumin (OVA) to generate the asthma phenotype. We investigated the effects of limonene on lung inflammation and airway responsiveness to methacholine (MCh) and NECA (nonselective adenosine analog) by administering limonene as an inhalation prior to OVA aerosol challenges in one group of allergic mice for both WT and KO. In whole-body plethysmography studies, we observed that airway responsiveness to MCh in WT SEN group was significantly lowered upon limonene treatment but no effect was observed in A_2AKO. Limonene also attenuated NECA-induced airway responsiveness in WT allergic mice with no effect being observed in A_2AKO groups. Differential BAL analysis showed that limonene reduced levels of eosinophils in allergic WT mice but not in A_2AKO. However, limonene reduced neutrophils in sensitized A_2AKO mice, suggesting that it may activate A_2B receptors as well. These data indicate that limonene-induced reduction in airway inflammation and airway reactivity occurs mainly via activation of A_2AAR but A_2B receptors may also play a supporting role.

Essential oils and its bioactive compounds modulating cytokines: A systematic review on anti-asthmatic and immunomodulatory properties

BACKGROUND

Asthma, the main inflammatory chronic condition affecting the respiratory system, is characterized by hyperresponsiveness and reversible airway obstruction, recruitment of inflammatory cells and excessive production of mucus. Cytokines as biochemical messengers of immune cells, play an important role in the regulation of allergic inflammatory and infectious airway processes. Essential oils of plant origin are complex mixtures of volatile and semi volatile organic compounds that determine the specific aroma of plants and are categorized by their biological activities.

PURPOSE

We reviewed whether essential oils and their bioactive compounds of plant origin could modulate cytokines' immune responses and improve asthma therapy in experimental systems in vitro and in vivo.

METHODS

Electronic and manual search of articles in English available from inception up to November 2018 reporting the immunomodulatory activity of essential oils and their bioactive compounds for the management of asthma. We used PubMed, EMBASE, Scopus and Web of Science. Publications reporting preclinical experiments where cytokines were examined to evaluate the consequence of anti-asthmatic therapy were included.

RESULTS

914 publications were identified and 13 were included in the systematic review. Four articles described the role of essential oils and their bioactive compounds on bronchial asthma using cell lines; nine in vivo studies evaluated the anti-inflammatory efficacy and immunomodulating effects of essential oil and their secondary metabolites on cytokines production and inflammatory responses. The most important immunopharmacological mechanisms reported were the regulation of cytokine production, inhibition of reactive oxygen species accumulation, inactivation of eosinophil migration and remodeling of the airways and lung tissue, modulation of FOXP3 gene expression, regulation of inflammatory cells in the airways and decreasing inflammatory mediator expression levels.

CONCLUSION

Plant derived essential oils and related active compounds have potential therapeutic activity for the treatment of asthma by modulating the release of pro-inflammatory (TNF-α, IL-1β, IL-8), Th17 (IL-17), anti-inflammatory (IL-10), Th1 (IFN-γ, IL-2, IL-12) and Th2 (IL-4, IL-5, IL-6, IL-13) cytokines and the suppression of inflammatory cell accumulation.

Plants derived therapeutic strategies targeting chronic respiratory diseases: Chemical and immunological perspective

The apparent predicament of the representative chemotherapy for managing respiratory distress calls for an obligatory deliberation for identifying the pharmaceuticals that effectively counter the contemporary intricacies associated with target disease. Multiple, complex regulatory pathways manifest chronic pulmonary disorders, which require chemotherapeutics that produce composite inhibitory effect. The cost effective natural product based molecules hold a high fervor to meet the prospects posed by current respiratory-distress therapy by sparing the tedious drug design and development archetypes, present a robust standing for the possible replacement of the fading practice of poly-pharmacology, and ensure the subversion of a potential disease relapse. This study summarizes the experimental evidences on natural products moieties and their components that illustrates therapeutic efficacy on respiratory disorders.

•

Plant derived therapeutics for managing chronic respiratory disorders.

•

Activity of natural product based molecules on key regulatory pathways of COPD.

•

Preclinical evidence for the efficacy of natural product moieties.

•

Clinical significance of plant derived molecules in pulmonary distress.

Therapeutic Potential of Volatile Terpenes and Terpenoids from Forests for Inflammatory Diseases

Forest trees are a major source of biogenic volatile organic compounds (BVOCs). Terpenes and terpenoids are known as the main BVOCs of forest aerosols. These compounds have been shown to display a broad range of biological activities in various human disease models, thus implying that forest aerosols containing these compounds may be related to beneficial effects of forest bathing. In this review, we surveyed studies analyzing BVOCs and selected the most abundant 23 terpenes and terpenoids emitted in forested areas of the Northern Hemisphere, which were reported to display anti-inflammatory activities. We categorized anti-inflammatory processes related to the functions of these compounds into six groups and summarized their molecular mechanisms of action. Finally, among the major 23 compounds, we examined the therapeutic potentials of 12 compounds known to be effective against respiratory inflammation, atopic dermatitis, arthritis, and neuroinflammation among various inflammatory diseases. In conclusion, the updated studies support the beneficial effects of forest aerosols and propose their potential use as chemopreventive and therapeutic agents for treating various inflammatory diseases.

Indoor air chemistry: Terpene reaction products and airway effects

Reactive chemistry is ubiquitous indoors with a wealth of complex oxidation reactions; some of these are initiated by both homogeneous and heterogeneous reaction of ozone with unsaturated organic compounds and subsequent the hydroxyl radical, either in the gas-phase or on reactive surfaces. One major focus has been the reaction of common and abundant terpene-based fragrances in indoor air emitted from many wood-based materials, a variety of consumer products, and citrus fruits and flowers. Inhalation of the terpenes themselves are generally not considered a health concern (both acute and long-term) due to their low indoor air concentrations; however, their gas- and surface reactions with ozone and the hydroxyl radical produce a host of products, both gaseous, i. a. formaldehyde, and ultrafine particles formed by condensation/nucleation processes. These reaction products may be of health concern. Human cell bioassays with key reaction products from ozone-initiated terpene reactions have shown some inflammatory reactions, but results are difficult to interpret for human exposure and risk assessment. Acute effects like sensory irritation in eyes and airways are unlikely or present at very low intensity in real life conditions based on rodent and human exposure studies and known thresholds for sensory irritation in eyes and airways and derived human reference values for airflow limitation and pulmonary irritation. Some fragrances and their ozone-initiated reaction products may possess anti-inflammatory properties. However, long-term effects of the reaction products as ultrafine particles are poorly explored. Material and product surfaces with high ozone deposition velocities may significantly impact the perceived air quality by altered emissions from both homogeneous and heterogeneous surface reactions.

Major Bioactive Compounds in Essential Oils Extracted From the Rhizomes of Zingiber zerumbet (L) Smith: A Mini-Review on the Anti-allergic and Immunomodulatory Properties

Zingiber zerumbet (L) Smith is part of the Zingiberaceae family, one of the largest families of the plant kingdom. Z. zerumbet is a perennial, aromatic and tuberose plant that grows in humid locations where its center of distribution is located in the South-East Asia region. This plant has been traditionally used in foods and beverages and for ornamental purposes. Although many studies have reported on the biomedical applications of Z. zerumbet, the anti-allergic effects of Z. zerumbet and its major bioactive compounds have not yet been summarized in detail. Many major metabolites that have been reported to contain anti-allergic properties are terpene compounds which can be found in the essential oil extracted from the rhizomes of Z. zerumbet, such as zerumbone, limonene, and humulene. The rhizome is among the part of Z. zerumbet that has been widely used for many studies due to its exceptional biomedical applications. Most of these studies have shown that the essential oil, which can be obtained through hydro-distillation of the rhizomes from Z. zerumbet, is enriched with various active metabolites. Therefore, this mini-review provides an overview of the main aspects related to the anti-allergic and immunomodulatory properties of the major bioactive compounds found in the essential oils extracted from the rhizomes of Z. zerumbet, with the aim of demonstrating the importance of essential oil extracted from the rhizomes of Z. zerumbet and its bioactive compounds in the treatment of allergy and allergy-related diseases, in addition to other widely reported and extensively studied biomedical applications.

Limonene: Aroma of innovation in health and disease

Natural products obtained in dietary components may aid the prevention and treatment of a variety of diseases. Reports in the scientific literature have demonstrated that the consumption of terpenes is a successful alternative in the treatment of several diseases, triggering beneficial biological effects in clinical and preclinical studies. The monoterpene limonene is largely used in alimentary items, cleaning products, and it is one of the most frequent fragrances used in cosmetics formulation. The therapeutic effects of limonene have been extensively studied, proving anti-inflammatory, antioxidant, antinociceptive, anticancer, antidiabetic, antihyperalgesic, antiviral, and gastroprotective effects, among other beneficial effects in health. In this review, we collected, presented, and analyzed evidence from the scientific literature regarding the usage of limonene and its activities and underlying mechanisms involved in combating diseases. The highlighting of limonene applications could develop a useful targeting of innovative research in this field as well as the development of a limonene-based phytomedicine which could be used in a variety of conditions of health and disease.

Chronic diseases, inflammation, and spices: how are they linked?

Extensive research within the last several decades has revealed that the major risk factors for most chronic diseases are infections, obesity, alcohol, tobacco, radiation, environmental pollutants, and diet. It is now well established that these factors induce chronic diseases through induction of inflammation. However, inflammation could be either acute or chronic. Acute inflammation persists for a short duration and is the host defense against infections and allergens, whereas the chronic inflammation persists for a long time and leads to many chronic diseases including cancer, cardiovascular diseases, neurodegenerative diseases, respiratory diseases, etc. Numerous lines of evidence suggest that the aforementioned risk factors induced cancer through chronic inflammation. First, transcription factors NF-κB and STAT3 that regulate expression of inflammatory gene products, have been found to be constitutively active in most cancers; second, chronic inflammation such as pancreatitis, prostatitis, hepatitis etc. leads to cancers; third, activation of NF-κB and STAT3 leads to cancer cell proliferation, survival, invasion, angiogenesis and metastasis; fourth, activation of NF-κB and STAT3 leads to resistance to chemotherapy and radiation, and hypoxia and acidic conditions activate these transcription factors. Therefore, targeting these pathways may provide opportunities for both prevention and treatment of cancer and other chronic diseases. We will discuss in this review the potential of various dietary agents such as spices and its components in the suppression of inflammatory pathways and their roles in the prevention and therapy of cancer and other chronic diseases. In fact, epidemiological studies do indicate that cancer incidence in countries such as India where spices are consumed daily is much lower (94/100,000) than those where spices are not consumed such as United States (318/100,000), suggesting the potential role of spices in cancer prevention.

Reactive indoor air chemistry and health-A workshop summary

The chemical composition of indoor air changes due to the reactive nature of the indoor environment. Historically, only the stable parent compounds were investigated due to their ease of measurement by conventional methods. Today, however, scientists can better characterize oxidation products (gas and particulate-phase) formed by indoor chemistry. An understanding of occupant exposure can be developed through the investigation of indoor oxidants, the use of derivatization techniques, atmospheric pressure detection, the development of real-time technologies, and improved complex modeling techniques. Moreover, the connection between exposure and health effects is now receiving more attention from the research community. Nevertheless, a need still exists for improved understanding of the possible link between indoor air chemistry and observed acute or chronic health effects and long-term effects such as work-related asthma.

Effects by inhalation of abundant fragrances in indoor air - An overview

Odorous compounds (odors) like fragrances may cause adverse health effects. To assess their importance by inhalation, we have reviewed how the four major abundant and common airborne fragrances (α-pinene (APN), limonene (LIM), linalool (LIL), and eugenol (EUG)) impact the perceived indoor air quality as odor annoyance, sensory irritation and sensitization in the airways. Breathing and cardiovascular effects, and work performance, and the impact in the airways of ozone-initiated gas- and particle phase reactions products have also been assessed. Measured maximum indoor concentrations for APN, LIM and LIL are close to or above their odor thresholds, but far below their thresholds for sensory irritation in the eyes and upper airways; no information could be traced for EUG. Likewise, reported risk values for long-term effects are far above reported indoor concentrations. Human exposure studies with mixtures of APN and LIM and supported by animal inhalation models do not support sensitization of the airways at indoor levels by inhalation that include other selected fragrances. Human exposure studies, in general, indicate that reported lung function effects are likely due to the perception rather than toxic effects of the fragrances. In general, effects on the breathing rate and mood by exposure to the fragrances are inconclusive. The fragrances may increase the high-frequency heart rate variability, but aerosol exposure during cleaning activities may result in a reduction. Distractive effects influencing the work performance by fragrance/odor exposure are consistently reported, but their persistence over time is unknown. Mice inhalation studies indicate that LIM or its reaction mixture may possess anti-inflammatory properties. There is insufficient information that ozone-initiated reactions with APN or LIM at typical indoor levels cause airway effects in humans. Limited experimental information is available on long-term effects of ozone-initiated reaction products of APN and LIM at typical indoor levels.

D-limonene exhibits anti-inflammatory and antioxidant properties in an ulcerative colitis rat model via regulation of iNOS, COX-2, PGE2 and ERK signaling pathways

D-limonene has been demonstrated to have important immunomodulatory properties, including antitumor effects, and may alleviate asthma and allergies. In the present study, the anti‑inflammatory effects of D‑limonene were investigated in an ulcerative colitis (UC) rat model. Healthy male Sprague‑Dawley rats were randomly divided into control, untreated UC, and treatment with 50 or 100 mg/kg D‑limonene UC groups. In UC rats, disease activity and colonic mucosa damage were significantly reduced by the anti‑inflammatory effects of D‑limonene, via suppression of matrix metalloproteinase (MMP)‑2 and ‑9 gene expression. In addition, treatment with D‑limonene significantly increased antioxidant, inducible nitric oxide synthase (iNOS) and cyclooxygenase‑2 (COX‑2) protein expression levels in UC rats. A decrease in prostaglandin E2 (PGE2) production, transforming growth factor‑β (TGF‑β) gene expression and an increase phosphorylated‑extracellular signal regulated kinase (ERK) 1/2 expression levelswere observed in UC rats treated with D‑limonene. In conclusion, D‑limonene reduced MMP‑2 and ‑9 mRNA expression levels via regulation of the iNOS, COX‑2, PGE2, TGF‑β and ERK1/2 signaling pathways in a UC rat model, indicating its potential antioxidant and anti‑inflammatory properties.

Inhibition of airway epithelial-to-mesenchymal transition and fibrosis by kaempferol in endotoxin-induced epithelial cells and ovalbumin-sensitized mice

Chronic airway remodeling is characterized by structural changes within the airway wall, including smooth muscle hypertrophy, submucosal fibrosis and epithelial shedding. Epithelial-to-mesenchymal transition (EMT) is a fundamental mechanism of organ fibrosis, which can be induced by TGF-β. In the in vitro study, we investigated whether 1-20 μM kaempferol inhibited lipopolysaccharide (LPS)-induced bronchial EMT in BEAS-2B cells. The in vivo study explored demoting effects of 10-20 mg/kg kaempferol on airway fibrosis in BALB/c mice sensitized with ovalbumin (OVA). LPS induced airway epithelial TGF-β1 signaling that promoted EMT with concurrent loss of E-cadherin and induction of α-smooth muscle actin (α-SMA). Nontoxic kaempferol significantly inhibited TGF-β-induced EMT process through reversing E-cadherin expression and retarding the induction of N-cadherin and α-SMA. Consistently, OVA inhalation resulted in a striking loss of epithelial morphology by displaying myofibroblast appearance, which led to bronchial fibrosis with submucosal accumulation of collagen fibers. Oral administration of kaempferol suppressed collagen deposition, epithelial excrescency and goblet hyperplasia observed in the lung of OVA-challenged mice. The specific inhibition of TGF-β entailed epithelial protease-activated receptor-1 (PAR-1) as with 20 μM kaempferol. The epithelial PAR-1 inhibition by SCH-79797 restored E-cadherin induction and deterred α-SMA induction, indicating that epithelial PAR-1 localization was responsible for resulting in airway EMT. These results demonstrate that dietary kaempferol alleviated fibrotic airway remodeling via bronchial EMT by modulating PAR1 activation. Therefore, kaempferol may be a potential therapeutic agent targeting asthmatic airway constriction.

Flavonoids and asthma

Asthma is a chronic disease, characterized by airway inflammation, airflow limitation, hyper-reactivity and airway remodeling. It is believed that asthma is caused by the interaction between genetic and environmental factors. The prevalence of allergic diseases, including asthma, has increased worldwide during the past two decades. Although the precise reasons that have caused this increase remain unknown, dietary change is thought to be one of the environmental factors. Flavonoids, which are polyphenolic plant secondary metabolites ubiquitously present in vegetables, fruits and beverages, possess antioxidant and anti-allergic traits, as well as immune-modulating activities. Flavonoids are powerful antioxidants and anti-allergic nutrients that inhibit the release of chemical mediators, synthesis of Th2 type cytokines, such as interleukin (IL)-4 and IL-13, and CD40 ligand expression by high-affinity immunoglobulin E (IgE) receptor-expressing cells, such as mast cells and basophils. They also inhibit IL-4-induced signal transduction and affect the differentiation of naïve CD4+ T cells into effector T-cells through their inhibitory effect on the activation of the aryl hydrocarbon receptor. Various studies of flavonoids in asthmatic animal models have demonstrated their beneficial effects. The results of several epidemiological studies suggest that an increase in flavonoid intake is beneficial for asthma. Moreover, clinical trials of flavonoids have shown their ameliorative effects on symptoms related to asthma. However, these human studies are currently limited; further validation is required to clarify whether an appropriate intake of flavonoids may constitute dietary treatment and for part of a preventive strategy for asthma.

Adjuvant and inflammatory effects in mice after subchronic inhalation of allergen and ozone-initiated limonene reaction products

Inhalation of ozone (O3), a highly toxic environmental pollutant, produces airway inflammation and exacerbates asthma. However, in indoor air, O3 reacts with terpenes (cyclic alkenes), leading to formation of airway irritating pollutants. The aim of the study was to examine whether inhalation of the reaction products of O3 and the terpene, limonene, as well as limonene and low-level O3 by themselves, induced allergic sensitization (formation of specific immunoglobulin [Ig] E) and airway inflammation in a subchronic mouse inhalation model in combination with the model allergen ovalbumin (OVA). BALB/cJ mice were exposed exclusively by inhalation for 5 d/wk for 2 wk and thereafter once weekly for 12 wk. Exposures were low-dose OVA in combination with O3, limonene, or limonene/O3 reaction products. OVA alone and OVA + Al(OH)3 served as control groups. Subsequently, all groups were exposed to a high-dose OVA solution on three consecutive days. Serum and bronchoalveolar lavage fluid were collected 24 h later. Limonene by itself did not promote neither OVA-specific IgE nor leukocyte inflammation. Low-level O3 promoted eosinophilic airway inflammation, but not OVA-specific IgE formation. The reaction products of limonene/O3 promoted allergic (OVA-specific IgE) sensitization, but lung inflammation, which is a characteristic of allergic asthma, was not observed. In conclusion, the study does not support an allergic inflammatory effect attributed to O3-initiated limonene reaction products in the indoor environment.

Human reference values for acute airway effects of five common ozone-initiated terpene reaction products in indoor air

Ozone-initiated monoterpene reaction products have been hypothesized to cause eye and airway complaints in office environments and some have been proposed to cause skin irritation and sensitization. The respiratory effects of 60 min exposures to five common oxidation products from abundant terpenoids (e.g. limonene), used as solvent and fragrance in common household products or present in skin lipids (e.g. squalene), were studied in a head out mouse bioassay. This allowed determination of acute upper airway (sensory) irritation, airflow limitation in the conducting airways, and pulmonary irritation in the alveolar region. Derived human reference values (RFs) for sensory irritation were 1.3, 0.16 and 0.3 ppm, respectively, for 4-acetyl-1-methylcyclohexene ( 0.2 ppm) [corrected], 3-isopropenyl-6-oxo-heptanal (IPOH), and 6-methyl-5-heptene-2-one (6-MHO). Derived RFs for airflow limitation were 0.8, 0.45, 0.03, and 0.5 ppm, respectively, for dihydrocarvone (DHC), 0.2 ppm [corrected], 4-oxo-pentanal (0.3 ppm) [corrected], and 6-MHO. Pulmonary irritation was unobserved as a critical effect. The RFs indicate that the oxidation products would not contribute substantially to sensory irritation in eyes and upper airways in office environments. Reported concentrations in offices of 6-MHO and 0.3 ppm [corrected]would not result in airflow limitation. However, based upon the RFs for IPOH and 0.3 ppm [corrected], precautionary actions should be considered that disfavor their formation in excess.