Defensin γ-thionin from Capsicum chinense has immunomodulatory effects on bovine mammary epithelial cells during Staphylococcus aureus internalization

Structural and Biochemical Characterization of Three Antimicrobial Peptides from Capsicum annuum L. var. annuum Leaves for Anti-Candida Use

The emergence of resistant microorganisms has reduced the effectiveness of currently available antimicrobials, necessitating the development of new strategies. Plant antimicrobial peptides (AMPs) are promising candidates for novel drug development. In this study, we aimed to isolate, characterize, and evaluate the antimicrobial activities of AMPs isolated from Capsicum annuum. The antifungal potential was tested against Candida species. Three AMPs from C. annuum leaves were isolated and characterized: a protease inhibitor, a defensin-like protein, and a lipid transporter protein, respectively named CaCPin-II, CaCDef-like, and CaCLTP2. All three peptides had a molecular mass between 3.5 and 6.5 kDa and caused morphological and physiological changes in four different species of the genus Candida, such as pseudohyphae formation, cell swelling and agglutination, growth inhibition, reduced cell viability, oxidative stress, membrane permeabilization, and metacaspase activation. Except for CaCPin-II, the peptides showed low or no hemolytic activity at the concentrations used in the yeast assays. CaCPin-II inhibited α-amylase activity. Together, these results suggest that these peptides have the potential as antimicrobial agents against species of the genus Candida and can serve as scaffolds for the development of synthetic peptides for this purpose.

Antifungal Plant Defensins as an Alternative Tool to Combat Candidiasis

Currently, the spread of fungal infections is becoming an urgent problem. Fungi of the Candida genus are opportunistic microorganisms that cause superficial and life-threatening systemic candidiasis in immunocompromised patients. The list of antifungal drugs for the treatment of candidiasis is very limited, while the prevalence of resistant strains is growing rapidly. Therefore, the search for new antimycotics, including those exhibiting immunomodulatory properties, is of great importance. Plenty of natural compounds with antifungal activities may be extremely useful in solving this problem. This review evaluates the features of natural antimicrobial peptides, namely plant defensins as possible prototypes of new anticandidal agents. Plant defensins are important components of the innate immune system, which provides the first line of defense against pathogens. The introduction presents a brief summary regarding pathogenic Candida species, the pathogenesis of candidiasis, and the mechanisms of antimycotic resistance. Then, the structural features of plant defensins, their anticandidal activities, their mechanisms of action on yeast-like fungi, their ability to prevent adhesion and biofilm formation, and their combined action with conventional antimycotics are described. The possible mechanisms of fungal resistance to plant defensins, their cytotoxic activity, and their effectiveness in in vivo experiments are also discussed. In addition, for the first time for plant defensins, knowledge about their immunomodulatory effects is also presented.

Expression, Regulation, and Function of β-Defensins in the Bovine Mammary Glands: Current Knowledge and Future Perspectives

β-Defensins are cationic antimicrobial peptides (AMPs) that play an important role in the innate immune defense of bovines. They are constitutively expressed in mammary glands and induced differently in response to pathogens. Their expression is influenced by various factors, including hormones, plant-derived compounds, and dietary energy imbalance. The toll-like receptors (TLRs)/nuclear factor-kappa B (NF-κB) pathway plays a crucial role in β-defensin induction, while alternative pathways such as mitogen-activated protein kinase (MAPK) and epigenetic regulation also make substantial contributions. β-Defensins exhibit bactericidal activity against a wide range of pathogens, including two major mastitis pathogens, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), primarily through membrane disruption. β-Defensins have low cytotoxicity to host cells and demonstrate immunomodulatory properties, and pathogens also display minimal resistance to these AMPs. Given the increasing concern in antimicrobial resistance, the potential of β-defensins as natural antimicrobials has garnered considerable attention. This article provides an overview of the characteristics of bovine β-defensins, their expression pathways, their mode of action, and factors influencing their expression in the mammary glands of cattle. Additionally, it identifies the current gaps in research within this field and suggests areas that require further investigation. Understanding the regulation and function of β-defensins offers valuable insights to develop effective strategies for strengthening the immune system of mammary glands, reducing the reliance on synthetic antimicrobials, and explore novel natural antimicrobial alternatives.

Immunomodulatory Effects of the Pea Defensin Psd1 in the Caco-2/Immune Cells Co-Culture upon Candida albicans Infection

Candidiasis is one of the most common fungal diseases that can pose a threat to life in immunodeficient individuals, particularly in its disseminated form. Not only fungal invasion but also fatal infection-related inflammation are common causes of systemic candidiasis. In this study, we investigated in vitro immunomodulatory properties of the antifungal pea defensin Psd1 upon Candida albicans infection. Using the real-time PCR, we showed that Psd1 inhibited the antimicrobial peptide HBD-2 and pro-inflammatory cytokines IL-1 and IL-8 downregulation at mRNA level in epithelium cells caused by C. albicans infection. By using the Caco-2/immune cells co-culture upon C. albicans infection and the multiplex xMAP assay, we demonstrated that this pathogenic fungus induced a pronounced host defense response; however, the cytokine responses were different in the presence of dendritic cells or monocytes. We revealed that Psd1 at a low concentration (2 µM) had a pronounced immunomodulatory effect on the Caco-2/immune cells co-culture upon fungal infection. Thus, we hypothesized that the pea defensin Psd1 might be an effective agent in the treatment of candidiasis not only due to its antifungal activity, but also owing to its ability to modulate a protective immune response upon infection.

The plant defensins PaDef and γ-thionin inhibit the endothelial cell response to VEGF

Angiogenesis is involved in wound repair and tissue maintenance but is associated with diverse diseases. Pro-angiogenic factors such as vascular endothelial growth factor (VEGF) regulate this process. Therefore, searching for treatments to inhibit or promote angiogenesis is attractive. Reports from our group showed that plant antimicrobial peptides (PAPs) PaDef from avocado and γ-thionin from habanero pepper are cytotoxic on cancer cells. However, their functions as angiogenic regulators are unknown. In this work, we evaluate the effect of PaDef and γ-thionin on the angiogenic processes of two different endothelial cell lines: bovine endothelial cells (BUVEC) and the human endothelial cell line EA.hy926. The results showed that VEGF (10ng/mL) stimulated the BUVEC (40 ± 7%) and EA.hy926 cell proliferation (30 ± 9%); however, peptides (5-500ng/mL) reverted this effect. Besides, VEGF increased the migration of BUVEC (20 ± 8%) and EA.hy926 cells (50 ± 6%), but both PAPs (5ng/mL) inhibited the VEGF stimulus (100%). Furthermore, DMOG 50μM (an inhibitor of HIF-hydroxylase) was used in BUVEC and EA.hy926 cells to determine the effect of hypoxia on VEGF and peptide activities. The DMOG reverted the inhibitory action of both peptides (100%), indicating that peptides act through a HIF-independent pathway. Also, the PAPs do not affect the tube formation but decrease it in EA.hy926 cells stimulated with VEGF (100%). Additionally, docking assays showed a possible interaction between PAPs and the VEGF receptor. These results suggest that plant defensins PaDef and γ-thionin are potential angiogenic modulators of the VEGF activity on endothelial cells.

Antifungal Activity of Avocado Seed Recombinant GASA/Snakin PaSn

The avocado fruit (Persea americana) has become a significant fruit in the human diet for its nutritional properties. However, the seed is a source of bioactive molecules and has been poorly utilized. Previously, we reported that the PaSn gene is expressed in the avocado seeds, a cysteine-rich antimicrobial peptide (GASA/Snakin), and demonstrated its antibacterial activity. In this work, we report the recombinant production of PaSn in the Escherichia coli system and evaluate its antifungal activity against plant and human pathogen fungi. The recombinant peptide showed antifungal activity at 200 μg/mL against phytopathogens Colletotrichum gloeosporioides and Fusarium oxysporum and human pathogens Candida albicans and C. glabrata. Our results demonstrate the usefulness of a prokaryotic expression system for avocado antimicrobial peptide production. In conclusion, the snakin PaSn could be helpful in the control of postharvest avocado and other fruits' fungal diseases and human fungal pathogens.

Antifungal Activity, Structural Stability, and Immunomodulatory Effects on Human Immune Cells of Defensin from the Lentil Lens culinaris

An increase in the frequency of mycoses and spreading of multidrug-resistant fungal pathogens necessitates the search for new antifungal agents. Earlier, we isolated the novel defensin from lentil Lensculinaris seeds, designated as Lc-def, which inhibited the growth of phytopathogenic fungi. Here, we studied an antifungal activity of Lc-def against human pathogenic Candida species, structural stability of the defensin, and its immunomodulatory effects that may help to prevent fungal infection. We showed that Lc-def caused 50% growth inhibition of clinical isolates of Candida albicans, C. krusei, and C. glabrata at concentrations of 25-50 μM, but was not toxic to different human cells. The lentil defensin was resistant to proteolysis by C. albicans and was not cleaved during simulated gastroduodenal digestion. By using the multiplex xMAP assay, we showed for the first time for plant defensins that Lc-def increased the production of such essential for immunity to candidiasis pro-inflammatory cytokines as IL-12 and IL-17 at the concentration of 2 μM. Thus, we hypothesized that the lentil Lc-def and plant defensins in general may be effective in suppressing of mucocutaneous candidiasis due to their antifungal activity, high structural stability, and ability to activate a protective immune response.

Bioactive peptides of plant origin: distribution, functionality, and evidence of benefits in food and health

The multiple functions of peptides released from proteins have immense potential in food and health. In the past few decades, research interest in bioactive peptides of plant origin has surged tremendously, and new plant-derived peptides are continually discovered with advances in extraction, purification, and characterization technology. Plant-derived peptides are mainly extracted from dicot plants possessing bioactive functions, including antioxidant, cholesterol-lowering, and antihypertensive activities. Although the distinct functions are said to depend on the composition and structure of amino acids, the practical or industrial application of plant-derived peptides with bioactive features is still a long way off. In summary, the present review mainly focuses on the state-of-the-art extraction, separation, and analytical techniques, functional properties, mechanism of action, and clinical study of plant-derived peptides. Special emphasis has been placed on the necessity of more pre-clinical and clinical trials to authenticate the health claims of plant-derived peptides.

Too Hot to Handle: Antibacterial Peptides Identified in Ghost Pepper

Capsicum spp. (hot peppers) demonstrate a range of interesting bioactive properties spanning anti-inflammatory, antioxidant, and antimicrobial activities. While several species within the genus are known to produce antimicrobial peptides (AMPs), AMP sequence mining of genomic data indicates this space remains largely unexplored. Herein, in silico AMP predictions were paired with peptidomics to identify novel AMPs from the interspecific hybrid ghost pepper (Capsicum chinense × frutescens). AMP prediction algorithms revealed 115 putative AMPs within the Capsicum chinense genome, of which 14 were identified in the aerial tissue peptidome. PepSAVI-MS, de novo sequencing, and complementary approaches were used to fully molecularly characterize two novel AMPs, CC-AMP1 and CC-AMP2, including elucidation of a pyroglutamic acid post-translational modification of CC-AMP1 and disulfide bond connectivity of both. Both CC-AMP1 and CC-AMP2 have little homology with known AMPs and exhibited low μM antimicrobial activity against Gram-negative bacteria, including Escherichia coli. These findings demonstrate the complementary nature of peptidomics, bioactivity-guided discovery, and bioinformatics-based investigations to characterize plant AMP profiles.

Plant Bioactive Peptides: Current Status and Prospects Towards Use on Human Health

Large numbers of bioactive peptides with potential applications in protecting against human diseases have been identified from plant sources. In this review, we summarized recent progress in the research of plant-derived bioactive peptides, encompassing their production, biological effects, and mechanisms. This review focuses on antioxidant, antimicrobial, antidiabetic, and anticancer peptides, giving special attention to evidence derived from cellular and animal models. Studies investigating peptides with known sequences and well-characterized peptidic fractions or protein hydrolysates will be discussed. The use of molecular docking tools to elucidate inter-molecular interactions between bioactive peptides and target proteins is highlighted. In conclusion, the accumulating evidence from in silico, in vitro and in vivo studies to date supports the envisioned applications of plant peptides as natural antioxidants as well as health-promoting agents. Notwithstanding, much work is still required before the envisioned applications of plant peptides can be realized. To this end, future researches for addressing current gaps were proposed.

Plant Defensin γ-Thionin Induces MAPKs and Activates Histone Deacetylases in Bovine Mammary Epithelial Cells Infected With Staphylococcus aureus

Defensins are an important group of host defense peptides. They have immunomodulatory properties, which have been mainly described for mammal defensins, but similar effects for plant defensins remain unknown. Previously, we showed that the defensin γ-thionin (Capsicum chinense) reduces Staphylococcus aureus internalization into bovine mammary epithelial cells (bMECs) while inducing Toll-like receptor 2 (TLR2), modulating the inflammatory response. Here, we analyze the effect of γ-thionin on the TLR2 pathway in bMECs infected with S. aureus and determine if it modulates epigenetic marks. Pre-treated bMECs with γ-thionin (100 ng/ml) reduced the basal activation of p38 and ERK1/2 (~3-fold), but JNK was increased (~1.5-fold). Also, infected bMECs induced p38, but this effect was reversed by γ-thionin, whereas ERK1/2 was reduced by infection but stimulated by γ-thionin. Likewise, γ-thionin reduced the activation of Akt kinase ~50%. Furthermore, γ-thionin induced the activation of transcriptional factors of inflammatory response, highlighting EGR, E2F-1, AP-1, and MEF, which were turned off by bacteria. Also, γ-thionin induced the activation of histone deacetylases (HDACs, ~4-fold) at 24 h in infected bMECs and reduced LSD1 demethylase (HDMs, ~30%) activity. Altogether, these results demonstrated the first time that a plant defensin interferes with inflammatory signaling pathways in mammalian cells.

Immunomodulatory Effects of 17β-Estradiol on Epithelial Cells during Bacterial Infections

The innate immune system can function under hormonal control. 17β-Estradiol (E2) is an important sexual hormone for the reproductive cycle of mammals, and it has immunomodulatory effects on epithelial cells, which are the first line of defense against incoming bacteria. E2 regulates various pathophysiological processes, including the response to infection in epithelial cells, and its effects involve the regulation of innate immune signaling pathways, which are mediated through estrogen receptors (ERs). E2 modulates the expression of inflammatory and antimicrobial elements such as cytokines and antimicrobial peptides. The E2 effects on epithelial cells during bacterial infections are characterized by an increase in the production of antimicrobial peptides and by the diminution of the inflammatory response to abrogate proinflammatory cytokine induction by bacteria. Here, we review several novel molecular mechanisms through which E2 regulates the innate immune response of epithelial cells against bacterial infections.

The protective effect of chlorogenic acid on bovine mammary epithelial cells and neutrophil function

Chlorogenic acid (CGA) is the ester of caffeic acid and quinic acid and plays an important role in antibacterial activity and anti-inflammatory properties. The objective of this study was to examine the effects of CGA on the growth of Staphylococcus aureus and the mRNA levels of the genes encoding the inflammatory response cytokines, κ-casein, and neutrophil function in bovine mammary epithelial cells (BMEC) exposed to S. aureus. Chlorogenic acid has important antibacterial, antioxidant, and anti-inflammatory functions; however, the effect of CGA on BMEC and neutrophils exposed to S. aureus has not been investigated previously. Our results demonstrated that 10, 20, and 30 μg/mL CGA had no cytotoxic effects on BMEC in culture, and that 20 μg/mL CGA enhanced the viability of BMEC exposed to S. aureus, whereas 30 μg/mL CGA reduced S. aureus growth after 9 h compared with controls. The rate of S. aureus invasion into BMEC was also attenuated by 30 μg/mL CGA compared with controls, whereas this treatment led to reduced abundance of IL6, IL8, and TLR2 mRNA in S. aureus-exposed BMEC. Migration of bovine polymorphonuclear leukocytes was significantly decreased in S. aureus-exposed BMEC with 10 and 20 μg/mL CGA treatment when compared with S. aureus treatment alone. In addition, incubation with 20 or 30 μg/mL CGA enhanced the phagocytic ability of polymorphonuclear leukocytes compared with the control group. Importantly, levels of κ-casein were enhanced by treatment of S. aureus-exposed BMEC with CGA. Our results suggest that the use of CGA may be a potent therapeutic tool against bovine mastitis caused by S. aureus.

Immunomodulatory effects of thionin Thi2.1 from Arabidopsis thaliana on bovine mammary epithelial cells

Antimicrobial peptides (AMPs) are key elements of plant defense mechanisms, resembling conserved protection strategies also present in mammals. Among the AMPs, plant thionins are particularly interesting due that display antibacterial and antifungal activities. In Arabidopsis thaliana have been described four thionins: Thi2.1, Thi2.2, Thi2.3 and Thi2.4. Work from our group shows that Thi2.1 expressed by bovine endothelial cells has direct antibacterial activity against Staphylococcus aureus mastitis isolates, bacteria able to persist inside bovine mammary epithelial cells (bMECs). Thus, the objective of this work was to analyze the immunomodulatory effects of the AMP thionin Thi2.1 from A. thaliana on bMECs during S. aureus infection. According to the results, S. aureus internalization into bMECs was reduced in cells pre-treated with Thi2.1 at 5 and 10 μg/mL during 24 h, effect related to the participation of TLR2. In addition, bMECs pre-treated with Thi2.1 (24 h) significantly increased TNF-α (~2-fold) and IL-6 (~7-fold), whereas decreased IL-10 gene expression (~0.5-fold). Interestingly, Thi2.1 inhibits the up-regulation induced by S. aureus of TNF-α and IL-10 gene expression, as well as NO production. In addition, Thi2.1 (10 μg/mL) up-regulates the expression of the chemokine IL-8 (~3-fold) in infected bMECs. Some of these effects are related to TLR2 activation. In this sense, Thi2.1 also reduces S. aureus-induced TLR2 gene expression and membrane abundance. In conclusion, Thi2.1 from A. thaliana modulates bMEC innate immune response by inducing the production of pro- and anti-inflammatory molecules while inhibits S. aureus internalization. Some of these effects are mediated by TLR2.

Preconditioning with Lipopolysaccharide or Lipoteichoic Acid Protects against Staphylococcus aureus Mammary Infection in Mice

Staphylococcus aureus is one of the most causative agents of mastitis and is associated with chronic udder infections. The persistency of the pathogen is believed to be the result of an insufficient triggering of local inflammatory signaling. In this study, the preclinical mastitis model was used, aiming to evaluate if lipopolysaccharide (LPS) or lipoteichoic acid (LTA) preconditioning could aid the host in more effectively clearing or at least limiting a subsequent S. aureus infection. A prototypic Gram-negative virulence factor, i.e., LPS and Gram-positive virulence factor, i.e., LTA were screened whether they were able to boost the local immune compartment. Compared to S. aureus-induced inflammation, both toxins had a remarkable high potency to efficiently induce two novel selected innate immunity biomarkers i.e., lipocalin 2 (LCN2) and chitinase 3-like 1 (CHI3L1). When combining mammary inoculation of LPS or LTA prior to a local S. aureus infection, we were able to modulate the innate immune response, reduce local bacterial loads, and induce either LCN2 or CHI3L1 at 24 h post-infection. Clodronate depletion of mammary macrophages also identified that macrophages contribute only to a limited extend to the LPS/LTA-induced immunomodulation upon S. aureus infection. Based on histological neutrophil influx evaluation, concomitant local cytokine profiles and LCN2/CHI3L1 patterns, the macrophage-independent signaling plays a major role in the LPS- or LTA-pretreated S. aureus-infected mouse mammary gland. Our results highlight the importance of a vigilant microenvironment during the innate immune response of the mammary gland and offer novel insights for new approaches concerning effective immunomodulation against a local bacterial infection.

Gomesin acts in the immune system and promotes myeloid differentiation and monocyte/macrophage activation in mouse

Due to the cytotoxic effect of antimicrobial peptides (AMP) against several microorganism and tumor cells has been proposed their association with the immune system. However, just a few reports have shown this relationship. In this study, mice were treated with gomesin, a β-hairpin AMP that exhibit high cytotoxicity against bacterial and tumor cells. Different effects in the immune system were observed, such as, decrease of CD3⁺ in T lymphocytes (Control: 17.7±1.4%; Gomesin: 7.67±1.2%) and in hematopoietic progenitors and increase of hematopoietic stem cell (Control: 0.046±0.004%; Gomesin: 0.067±0.003%), B220⁺ B lymphocytes (Control: 38.63±1.5%; Gomesin: 47.83±0.48%), and Mac-1⁺F4/80⁺ macrophages (Control: 11.76±3.4%; Gomesin: 27.13±4.0%). Additionally, macrophage increase was accompanied by an increase of macrophage phagocytosis (Control 20.85±1.53; Gomesin 31.32±1 Geometric mean), interleukin 6 (Control: 47.24±1.9ng/mL; Gomesin: 138.68±33.68ng/mL) and monocyte chemoattractant protein-1 (Control: 0.872±0.093ng/mL; Gomesin: 1.83±0.067ng/mL). Thus, this report showed immunomodulatory activity of gomesin in the immune system of mice.