A Novel Immunosuppressant, Luteolin, Modulates Alloimmunity and Suppresses Murine Allograft Rejection

Research Progress on Immunomodulatory Effects of Poly (Lactic-co- Glycolic Acid) Nanoparticles Loaded with Traditional Chinese Medicine Monomers

Immunomodulatory mechanisms are indispensable and key factors in maintaining the balance of the environment in humans. When the immune function of the immune system is impaired, autoimmune diseases occur. Excessive body fatigue, natural aging of the human body, malnutrition, genetic factors and other reasons cause low immune function, due to which the body is prone to being infected by bacteria or cancer. Clinically, the existing therapeutic drugs still have problems such as high toxicity, long treatment cycle, drug resistance and high price, so we still need to explore and develop a high efficiency and low toxicity drug. Poly(lactic-co-glycolic acid) (PLGA) refers to a nontoxic polymer compound that exhibits excellent biocompatibility. Traditional Chinese medicine (TCM) monomers come from natural plants, and have the characteristics of high efficiency and low toxicity. Applying PLGA to TCM monomers can make up for the defects of traditional dosage forms, improve bioavailability, reduce the frequency and dosage of drug use, and reduce toxicity and side effects, thus having the characteristics of sustained release and targeting. Accordingly, PLGA nanoparticles loaded with TCM monomers have been the focus of development. The previous research on drug loading advantages, preparation methods, and immune regulation of TCM PLGA nanoparticles is summarized in the following sections.

Application of Luteolin in Neoplasms and Nonneoplastic Diseases

Researchers are amazed at the multitude of biological effects of 3',4',5,7-tetrahydroxyflavone, more commonly known as luteolin, as it simultaneously has antioxidant and pro-oxidant, as well as antimicrobial, anti-inflammatory, and cancer-preventive, properties. The anticancer properties of luteolin constitute a mosaic of pathways due to which this flavonoid influences cancer cells. Not only is it able to induce apoptosis and inhibit cancer cell proliferation, but it also suppresses angiogenesis and metastasis. Moreover, luteolin succeeds in cancer cell sensitization to therapeutically induced cytotoxicity. Nevertheless, apart from its promising role in chemoprevention, luteolin exhibits numerous potential utilizations in patients with conditions other than neoplasms, which include inflammatory skin diseases, diabetes mellitus, and COVID-19. This review aims to present the multidimensionality of the luteolin's impact on both neoplastic and nonneoplastic diseases. When it comes to neoplasms, we intend to describe the complexity of the molecular mechanisms that underlay luteolin's anticancer effectiveness, as well as to prove the usefulness of integrating this flavonoid in cancer therapy via the analysis of recent research on breast, colon, and lung cancer. Regarding nonneoplastic diseases, this review aims to emphasize the importance of researching the potential of luteolin in areas such as diabetology, virology, and dermatology as it summarizes the most important discoveries in those fields regarding its application.

Luteolin attenuates acute liver allograft rejection in rats by inhibiting T cell proliferation and regulating T cell subsets

Allograft rejection continues to be a significant cause of morbidity and graft failure for liver transplant recipients. Existing immunosuppressive regimens have many drawbacks, thus safe and effective long-term immunosuppressive regimens are still required. Luteolin (LUT), a natural component found in many plants, has a variety of biological and pharmacological effects and shows good anti-inflammatory activity in inflammatory and autoimmune diseases. Nevertheless, it remains unclear how it affects acute organ rejection after allogeneic transplantation. In this study, a rat liver transplantation model was constructed to investigate the effect of LUT on acute rejection of organ allografts. We found that LUT significantly protected the structure and function of liver grafts, prolonged recipient rat survival, ameliorated T cell infiltration, and downregulated proinflammatory cytokines. Moreover, LUT inhibited the proliferation of CD4+ T cells and Th cell differentiation but increased the proportion of Tregs, which is the key to its immunosuppressive effect. In vitro, LUT also significantly inhibited CD4+ T cell proliferation and Th1 differentiation. There may be important implications for improving immunosuppressive regimens for organ transplantation as a result of this discovery.

Forecasting of potential anti-inflammatory targets of some immunomodulatory plants and their constituents using in vitro, molecular docking and network pharmacology-based analysis

Most synthetic immunomodulatory medications are extremely expensive, have many disadvantages and suffer from a lot of side effects. So that, introducing immunomodulatory reagents from natural sources will have great impact on drug discovery. Therefore, this study aimed to comprehend the mechanism of the immunomodulatory activity of some natural plants via network pharmacology together with molecular docking and in vitro testing. Apigenin, luteolin, diallyl trisulfide, silibinin and allicin had the highest percentage of C-T interactions while, AKT1, CASP3, PTGS2, NOS3, TP53 and MMP9 were found to be the most enriched genes. Moreover, the most enriched pathways were pathways in cancer, fluid shear stress and atherosclerosis, relaxin signaling pathway, IL-17 signaling pathway and FoxO signaling pathway. Additionally, Curcuma longa, Allium sativum, Oleu europea, Salvia officinalis, Glycyrrhiza glabra and Silybum marianum had the highest number of P-C-T-P interactions. Furthermore, molecular docking analysis of the top hit compounds against the most enriched genes revealed that silibinin had the most stabilized interactions with AKT1, CASP3 and TP53, whereas luteolin and apigenin exhibited the most stabilized interactions with AKT1, PTGS2 and TP53. In vitro anti-inflammatory and cytotoxicity testing of the highest scoring plants exhibited equivalent outcomes to those of piroxicam.

Phytochemicals in the treatment of inflammation-associated diseases: the journey from preclinical trials to clinical practice

Advances in biomedical research have demonstrated that inflammation and its related diseases are the greatest threat to public health. Inflammatory action is the pathological response of the body towards the external stimuli such as infections, environmental factors, and autoimmune conditions to reduce tissue damage and improve patient comfort. However, when detrimental signal-transduction pathways are activated and inflammatory mediators are released over an extended period of time, the inflammatory process continues and a mild but persistent pro-inflammatory state may develop. Numerous degenerative disorders and chronic health issues including arthritis, diabetes, obesity, cancer, and cardiovascular diseases, among others, are associated with the emergence of a low-grade inflammatory state. Though, anti-inflammatory steroidal, as well as non-steroidal drugs, are extensively used against different inflammatory conditions, they show undesirable side effects upon long-term exposure, at times, leading to life-threatening consequences. Thus, drugs targeting chronic inflammation need to be developed to achieve better therapeutic management without or with a fewer side effects. Plants have been well known for their medicinal use for thousands of years due to their pharmacologically active phytochemicals belonging to diverse chemical classes with a number of these demonstrating potent anti-inflammatory activity. Some typical examples include colchicine (alkaloid), escin (triterpenoid saponin), capsaicin (methoxy phenol), bicyclol (lignan), borneol (monoterpene), and quercetin (flavonoid). These phytochemicals often act via regulating molecular mechanisms that synergize the anti-inflammatory pathways such as increased production of anti-inflammatory cytokines or interfere with the inflammatory pathways such as to reduce the production of pro-inflammatory cytokines and other modulators to improve the underlying pathological condition. This review describes the anti-inflammatory properties of a number of biologically active compounds derived from medicinal plants, and their mechanisms of pharmacological intervention to alleviate inflammation-associated diseases. The emphasis is given to information on anti-inflammatory phytochemicals that have been evaluated at the preclinical and clinical levels. Recent trends and gaps in the development of phytochemical-based anti-inflammatory drugs have also been included.

Targeting Neuroinflammation to Alleviate Chronic Olfactory Dysfunction in Long COVID: A Role for Investigating Disease-Modifying Therapy (DMT)?

Chronic olfactory dysfunction after SARS-CoV-2 infection occurs in approximately 10% of patients with COVID-19-induced anosmia, and it is a growing public health concern. A regimen of olfactory training and anti-neuroinflammatory therapy with co-ultramicronized palmitoylethanolamide with luteolin (um-PEA-LUT) has shown promising results in clinical trials; however, approximately 15% of treated patients do not achieve full recovery of a normal olfactory threshold, and almost 5% have no recovery. Disease-modifying therapies (DMTs), which are used to treat autoimmune neuroinflammation in multiple sclerosis (MS), have not been studied for treating persistent inflammation in refractory post-COVID-19 smell disorder. This study evaluated COVID-19-related smell loss and MS-related smell loss, comparing the responses to different therapies. Forty patients with MS and 45 reporting post-COVID-19 olfactory disorders were included in the study. All patients underwent nasal endoscopy and were evaluated by using validated Sniffin' Sticks testing. The patients with long COVID were treated for three months with um-PEA-LUT plus olfactory training. The patients with MS were treated with DMTs. Olfactory functions before and after treatment were analyzed in both groups. At the experimental endpoint, 13 patients in the COVID-19 group treated with um-PEA-LUT had residual olfactory impairment versus 10 patients in the MS group treated with DMTs. The severity of the persistent olfactory loss was lower in the MS group, and the patients with MS treated with IFN-beta and glatiramer acetate had the preservation of olfactory function. These data provide a rationale for considering prospective trials investigating the efficacy of DMTs for post-COVID-19 olfactory disorders that are refractory to um-PEA-LUT with olfactory training. This study is the first to consider the role of DMT in treating refractory post-viral olfactory loss in patients with long COVID.

Intermittent Exposure of Hypercapnia Suppresses Allograft Rejection via Induction of Treg Differentiation and Inhibition of Neutrophil Accumulation

Background: In the management of major burn wounds, allogeneic skin transplantation is a critical procedure to improve wound repair. Our previous works found that intermittent exposure to carbon dioxide leads to permissive hypercapnia (HCA) and prolongs skin allograft survival. However, the modulatory effects of HCA exposure on the immune system are not well understood. Objectives: Our purpose was to investigate how intermittent exposure to HCA can effectively reduce the immune reaction to allogeneic skin graft rejection. Methods: A fully major histocompatibility complex-incompatible skin transplant from BALB/c to C57BL/6 mice model was utilized. Immune cells from splenic and draining lymph nodes were analyzed by flow cytometry. Serum proinflammatory cytokines were analyzed by ELISA. Results: Serum levels of IFN-γ, IL-2, IL-6, and TNF-α were significantly decreased in the HCA group. Additionally, the percentage of CD8+ cells in draining lymph nodes was significantly lower in HCA than in the control group. Moreover, the generation rate of FoxP3+ regulatory T cells (Tregs) from spleen naïve CD4+ T cells was increased by intermittent exposure to carbon dioxide. The infiltrated neutrophils were also eliminated by HCA. Taken together, we concluded that intermittent hypercapnia exposure could effectively suppress skin rejection by stimulating Treg cell generation and suppressing immune reactions.

The Chinese Herbal Prescription JieZe-1 Inhibits Membrane Fusion and the Toll-like Receptor Signaling Pathway in a Genital Herpes Mouse Model

Chinese herbal prescription JieZe-1 is effective for genital herpes with no visible adverse effects clinically. It showed an excellent anti-HSV-2 effect in vitro. However, its mechanism of anti-HSV-2 effect in vivo remains unclear. This study was designed to evaluate the anti-HSV-2 effect of JieZe-1 and berberine in a genital herpes mouse model and explore the underlying mechanism. The fingerprint of JieZe-1 was determined by high-performance liquid chromatography. First, we optimized a mouse model of genital herpes. Next, the weight, symptom score, morphological changes, viral load, membrane fusion proteins, critical proteins of the Toll-like receptor signaling pathway, cytokines, and immune cells of vaginal tissue in mice at different time points were measured. Finally, we treated the genital herpes mouse model with JieZe-1 gel (2.5, 1.5, and 0.5 g/ml) and tested the above experimental indexes at 12 h and on the 9th day after modeling. JieZe-1 improved the symptoms, weight, and histopathological damage of genital herpes mice, promoted the keratin repair of tissues, and protected organelles to maintain the typical morphology of cells. It downregulated the expression of membrane fusion proteins, critical proteins of the Toll-like receptor signaling pathway, cytokines, and immune cells. The vaginal, vulvar, and spinal cord viral load and vaginal virus shedding were also significantly reduced. In summary, JieZe-1 shows significant anti-HSV-2 efficacy in vivo. The mechanism is related to the inhibition of membrane fusion, the Toll-like receptor signaling pathway, inflammatory cytokines, and cellular immunity. However, berberine, the main component of JieZe-1 monarch medicine, showed no efficacy at a concentration of 891.8 μM (0.3 mg/ml).

Luteolin activates Tregs to promote IL-10 expression and alleviating caspase-11-dependent pyroptosis in sepsis-induced lung injury

OBJECTIVES

Acute respiratory distress syndrome (ARDS) is characterized by an excessive pulmonary inflammatory response. Pyroptosis is a newly form of programmed inflammatory cell death that is triggered by inflammatory caspases. Studies have shown that Luteolin has powerful anti-inflammation effects through activating the function of regulatory T cells (Tregs). The study aimed at investigating the effects of Luteolin on CLP-induced ALI.

METHODS

In our study, we employed the mouse cecal ligation and puncture (CLP) model to explore whether Luteolin contributed to alleviated lung injury in vivo. H&E staining and wet/dry (W/D) weight ratios were used to evaluate the severity of lung injury. The serum and BALF of cytokines were assessed by ELISA. The number of neutrophils in the BALF was counted. Immunohistochemistry of IL-10 and MPO in lung tissue was detected. The ROS level in lung was tested by ROS Assay Kit and expression of Gpx4 in lung tissue was detected by qRT-PCR and Western blotting. The regulatory T cells (Treg) population was analyzed in spleen and Peripheral blood mononuclear cells (PBMCs). The levels of caspase-11 protein, caspase-1 protein, GSDMD protein, IL-1α and IL-1β protein in the lung tissue was evaluated by Western blotting.

RESULTS

We found Luteolin significantly inhibits inflammation and attenuated CLP-induced lung injury in vivo, and the levels of, caspase-11, caspase-1, GSDMD, IL-1α and IL-1β protein in the lungs of CLP mice decreased significantly after pretreatment with Luteolin. Furthermore, the results showed that Luteolin could increase Treg frequencies and IL-10 levels in serum and BALF of CLP mice. It is noteworthy that depleting Tregs reverse Luteolin ameliorated lung injury, and IL-10 neutralizing antibodies treatment aggravated lung pyroptosis.

CONCLUSIONS

Our study illustrated that Luteolin contributed to alleviated lung injury, and attenuated caspase-11-dependent pyroptosis in the lung tissue of the CLP-induced ALI mouse model. The mechanisms could be related to regulating the frequency of Tregs and the levels of Treg derived IL-10. Treg cells were show to produce IL-10 and could alleviating caspase-11-dependent lung pyroptosis.

Quercitrin Rapidly Alleviated Depression-like Behaviors in Lipopolysaccharide-Treated Mice: The Involvement of PI3K/AKT/NF-κB Signaling Suppression and CREB/BDNF Signaling Restoration in the Hippocampus

Quercitrin (Qc) is a well-known flavonoid compound that exerts anti-inflammation effects on various diseases. The present study aimed to investigate the antidepressant-like response of Qc and its underlying mechanisms concerning neuroinflammation and neuroplasticity in mice with lipopolysaccharide (LPS)-induced depression-like behaviors. The results showed a single dose of Qc (10 mg/kg) produced an antidepressant-like effect at 2 h postadministration and lasted for at least 3 days. The expressions of neuroplasticity signaling molecules of pCREB/BDNF/PSD95/Synapsin1 were upregulated at 2 h, and ERK signaling was upregulated for 3 days in the hippocampus after a single administration of Oc or ketamine. A 5-day treatment of LPS led to depression-like behaviors, including reduced sucrose preference and increased immobility in the tail suspension test or forced swim test, which were all reversed by a single dose of Qc. In LPS-treated mice, Qc reduced the levels of inflammation-related factors including IL-10, IL-1β, and TNF-α in serum, as well as the activations of PI3K/AKT/NF-κB and MEK/ERK pathways in the hippocampus. Moreover, Qc restored the expressions of pCREB/BDNF/PSD95/Synapsin1 signaling in the hippocampus that were impaired by LPS. LY294002, a PI3K inhibitor, but not PD98059, a MEK inhibitor, produced effects similar to Qc. LY294002 also restored the expressions of pCREB/BDNF/PSD95/Synapsin1 signaling in the hippocampus impaired by LPS. Additionally, subeffective doses of Qc and LY294002 induced behavioral and molecular synergism. Together, the depression-like behaviors in LPS-treated mice were alleviated by a single dose of Qc likely via inhibition of the activations PI3K/AKT/NF-κB inflammation signaling and subsequent improvement of neuroplasticity.

Luteolin as a modulator of skin aging and inflammation

Luteolin belongs to the group of flavonoids and can be found in flowers, herbs, vegetables and spices. It plays an important role in defending plants, for example against UV radiation by partially absorbing UVA and UVB radiation. Thus, luteolin can also decrease adverse photobiological effects in the skin by acting as a first line of defense. Furthermore, anti-oxidative and anti-inflammatory activities of luteolin were described on keratinocytes and fibroblasts as well as on several immune cells (e.g., macrophages, mast cell, neutrophils, dendritic cells and T cells). Luteolin can suppress proinflammatory mediators (e.g., IL-1β, IL-6, IL-8, IL-17, IL-22, TNF-α and COX-2) and regulate various signaling pathway (e.g., the NF-κB, JAK-STAT as well as TLR signaling pathway). In this way, luteolin modulates many inflammatory processes of the skin. The present review summarizes the recent in vitro and in vivo research on luteolin in the field of skin aging and skin cancer, wound healing as well as inflammatory skin diseases, including psoriasis, contact dermatitis and atopic dermatitis. In conclusion, luteolin might be a promising molecule for the development of topic formulations and systemic agents against inflammatory skin diseases.

Luteolin Regulates the Differentiation of Regulatory T Cells and Activates IL-10-Dependent Macrophage Polarization against Acute Lung Injury

Objectives

Inflammatory disease characterized by clinical destructive respiratory disorder is called acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Studies have shown that luteolin exerts anti-inflammatory effects by increasing regulatory T cells (Tregs). In this study, we aimed to determine the effects of luteolin on ALI/ARDS and Treg differentiation.

Methods

In this paper, we used cecal ligation puncture (CLP) to generate an ALI mouse model to determine the effects of luteolin on ALI/ARDS. Lung tissues were stained for interleukin- (IL-) 17A and myeloperoxidase (MPO) by immunohistochemical analysis. The levels of Treg-related cytokines in serum and bronchoalveolar lavage fluid (BALF) of mice were detected. The protein levels of NF-κB p65 in lung tissues were measured. Macrophage phenotypes in lung tissues were measured using immunofluorescence. The proportion of Tregs in splenic mononuclear cells and peripheral blood mononuclear cells (PBMCs) was quantified. Furthermore, in vitro, we evaluated the effects of luteolin on Treg differentiation, and the effects of IL-10 immune regulation on macrophage polarization were examined.

Results

Luteolin alleviated lung injury and suppressed uncontrolled inflammation and downregulated IL-17A, MPO, and NF-κB in the lungs of CLP-induced mouse models. At this time, luteolin upregulated the level of IL-10 in serum and BALF and the frequency of CD4⁺CD25⁺FOXP3⁺ Tregs in PBMCs and splenic mononuclear cells of CLP mice. Luteolin treatment decreased the proportion of M1 macrophages and increased the proportion of M2 macrophages in lungs of CLP-induced mouse models. In vitro, administration of luteolin significantly induced Treg differentiation, and IL-10 promoted the polarization of M2 macrophages but reduced the polarization of M1 macrophages.

Conclusions

Luteolin alleviated lung injury and suppressed uncontrolled inflammation by inducing the differentiation of CD4⁺CD25⁺FOXP3⁺ Tregs and upregulating the expression of IL-10. Furthermore, the anti-inflammatory cytokine IL-10 promoted polarization of M2 macrophages in vitro. Luteolin-induced Treg differentiation from naïve CD4⁺ T cells may be a potential mechanism for regulating IL-10 production.

Luteolin delays photoreceptor degeneration in a mouse model of retinitis pigmentosa

Luteolin is neuroprotective for retinal ganglion cells and retinal pigment epithelial cells after oxidative injury, whereby it can inhibit microglial neurotoxicity. Therefore, luteolin holds the potential to be useful for treatment of retinal diseases. The purpose of this study was to investigate whether luteolin exhibits neuroprotective effects on rod cells in rd10 mice, a slow photoreceptor-degenerative model of retinitis pigmentosa. Luteolin (100 mg/kg) intraperitoneally injected daily from postnatal day 14 (P14) to P25 significantly enhanced the visual performance and retinal light responses of rd10 mice at P25. Moreover, it increased the survival of photoreceptors and improved retinal structure. Mechanistically, luteolin treatment attenuated increases in reactive oxygen species, photoreceptor apoptosis, and reactive gliosis; increased mRNA levels of anti-inflammatory cytokines while lowering that of pro-inflammatory and chemoattractant cytokines; and lowered the ratio of phospho-JNK/JNK. Application of the JNK inhibitor SP600125 exerted a similar protective effect to luteolin, suggesting that luteolin delays photoreceptor degeneration and functional deterioration in rd10 mice through regulation of retinal oxidation and inflammation by inhibiting the JNK pathway. Therefore, luteolin may be useful as a supplementary treatment for retinitis pigmentosa. This study was approved by the Qualified Ethics Committee of Jinan University, China (approval No. IACUC-20181217-02) on December 17, 2018.

Allergy Modulation by N-3 Long Chain Polyunsaturated Fatty Acids and Fat Soluble Nutrients of the Mediterranean Diet

The Mediterranean diet, containing valuable nutrients such as n-3 long chain poly-unsaturated fatty acids (LCPUFAs) and other fat-soluble micronutrients, is known for its health promoting and anti-inflammatory effects. Its valuable elements might help in the battle against the rising prevalence of non-communicable diseases (NCD), including the development of allergic diseases and other (chronic) inflammatory diseases. The fat fraction of the Mediterranean diet contains bioactive fatty acids but can also serve as a matrix to dissolve and increase the uptake of fat-soluble vitamins and phytochemicals, such as luteolin, quercetin, resveratrol and lycopene with known immunomodulatory and anti-inflammatory capacities. Especially n-3 LCPUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived from marine oils can target specific receptors or signaling cascades, act as eicosanoid precursors and/or alter membrane fluidity and lipid raft formation, hereby exhibiting anti-inflammatory properties. Beyond n-3 LCPUFAs, fat-soluble vitamins A, D, E, and K1/2 have the potential to affect pro-inflammatory signaling cascades by interacting with receptors or activating/inhibiting signaling proteins or phosphorylation in immune cells (DCs, T-cells, mast cells) involved in allergic sensitization or the elicitation/effector phase of allergic reactions. Moreover, fat-soluble plant-derived phytochemicals can manipulate signaling cascades, mostly by interacting with other receptors or signaling proteins compared to those modified by fat-soluble vitamins, suggesting potential additive or synergistic actions by applying a combination of these nutrients which are all part of the regular Mediterranean diet. Research concerning the effects of phytochemicals such as polyphenols has been hampered due to their poor bio-availability. However, their solubility and uptake are improved by applying them within the dietary fat matrix. Alternatively, they can be prepared for targeted delivery by means of pharmaceutical approaches such as encapsulation within liposomes or even unique nanoparticles. This review illuminates the molecular mechanisms of action and possible immunomodulatory effects of n-3 LCPUFAs and fat-soluble micronutrients from the Mediterranean diet in allergic disease development and allergic inflammation. This will enable us to further appreciate how to make use of the beneficial effects of n-3 LCPUFAs, fat-soluble vitamins and a selection of phytochemicals as active biological components in allergy prevention and/or symptom reduction.