Differential Macrophage Subsets in Muscle Damage Induced by a K49-PLA2 from Bothrops jararacussu Venom Modulate the Time Course of the Regeneration Process

Photobiomodulation mitigates Bothrops jararacussu venom-induced damage in myoblast cells by enhancing myogenic factors and reducing cytokine production

BACKGROUND

Photobiomodulation has exhibited promise in mitigating the local effects induced by Bothrops snakebite envenoming; however, the mechanisms underlying this protection are not yet fully understood. Herein, the effectiveness of photobiomodulation effects on regenerative response of C2C12 myoblast cells following exposure to Bothrops jararacussu venom (BjsuV), as well as the mechanisms involved was investigated.

METHODOLOGY/PRINCIPAL FINDINGS

C2C12 myoblast cells were exposed to BjsuV (12.5 μg/mL) and irradiated once for 10 seconds with laser light of 660 nm (14.08 mW; 0.04 cm2; 352 mW/cm2) or 780 nm (17.6 mW; 0.04 cm2; 440 mW/ cm2) to provide energy densities of 3.52 and 4.4 J/cm2, and total energies of 0.1408 and 0.176 J, respectively. Cell migration was assessed through a wound-healing assay. The expression of MAPK p38-α, NF-Кβ, Myf5, Pax-7, MyoD, and myogenin proteins were assessed by western blotting analysis. In addition, interleukin IL1-β, IL-6, TNF-alfa and IL-10 levels were measured in the supernatant by ELISA. The PBM applied to C2C12 cells exposed to BjsuV promoted cell migration, increase the expression of myogenic factors (Pax7, MyF5, MyoD and myogenin), reduced the levels of proinflammatory cytokines, IL1-β, IL-6, TNF-alfa, and increased the levels of anti-inflammatory cytokine IL-10. In addition, PBM downregulates the expression of NF-kB, and had no effect on p38 MAKP.

CONCLUSION/SIGNIFICANCE

These data demonstrated that protection of the muscle cell by PBM seems to be related to the increase of myogenic factors as well as the modulation of inflammatory mediators. PBM therapy may offer a new therapeutic strategy to address the local effects of snakebite envenoming by promoting muscle regeneration and reducing the inflammatory process.

Intramuscular Bleeding and Formation of Microthrombi during Skeletal Muscle Damage Caused by a Snake Venom Metalloprotease and a Cardiotoxin

The interactions between specific snake venom toxins and muscle constituents are the major cause of severe muscle damage that often result in amputations and subsequent socioeconomic ramifications for snakebite victims and/or their families. Therefore, improving our understanding of venom-induced muscle damage and determining the underlying mechanisms of muscle degeneration/regeneration following snakebites is critical to developing better strategies to tackle this issue. Here, we analysed intramuscular bleeding and thrombosis in muscle injuries induced by two different snake venom toxins (CAMP-Crotalus atrox metalloprotease (a PIII metalloprotease from the venom of this snake) and a three-finger toxin (CTX, a cardiotoxin from the venom of Naja pallida)). Classically, these toxins represent diverse scenarios characterised by persistent muscle damage (CAMP) and successful regeneration (CTX) following acute damage, as normally observed in envenomation by most vipers and some elapid snakes of Asian, Australasian, and African origin, respectively. Our immunohistochemical analysis confirmed that both CAMP and CTX induced extensive muscle destruction on day 5, although the effects of CTX were reversed over time. We identified the presence of fibrinogen and P-selectin exposure inside the damaged muscle sections, suggesting signs of bleeding and the formation of platelet aggregates/microthrombi in tissues, respectively. Intriguingly, CAMP causes integrin shedding but does not affect any blood clotting parameters, whereas CTX significantly extends the clotting time and has no impact on integrin shedding. The rates of fibrinogen clearance and reduction in microthrombi were greater in CTX-treated muscle compared to CAMP-treated muscle. Together, these findings reveal novel aspects of venom-induced muscle damage and highlight the relevance of haemostatic events such as bleeding and thrombosis for muscle regeneration and provide useful mechanistic insights for developing better therapeutic interventions.

Alarmins and inflammatory aspects related to snakebite envenomation

Snakebite envenoming is characterized by the injection of a mixture of proteins/toxins present in venom following the bite of a venomous snake. The toxins have potent bioactivity capability to impact different aspects of envenomation evolution. The cascade of immune responses initiated by the participation of venom and/or toxins isolated from snake venom can contribute to the systemic and local inflammatory effects observed in victims of envenomation. To understand envenomation, a deeper comprehension of the numerous cells, mediators, and components that comprise the immune system reaction to the venom components is required. Thus, activities related to the immune response are highlighted in this study, including the initial line of defense of the innate immune response as signals for the complicated reaction led by specialized cells.

Mapping the Immune Cell Microenvironment with Spatial Profiling in Muscle Tissue Injected with the Venom of Daboia russelii

Pathological and inflammatory events in muscle after the injection of snake venoms vary in different regions of the affected tissue and at different time intervals. In order to study such heterogeneity in the immune cell microenvironment, a murine model of muscle necrosis based on the injection of the venom of Daboia russelii was used. Histological and immunohistochemical methods were utilized to identify areas in muscle tissue with a different extent of muscle cell damage, based on the presence of hypercontracted muscle cells, a landmark of necrosis, and on the immunostaining for desmin. A gradient of inflammatory cells (neutrophils and macrophages) was observed from heavily necrotic areas to less damaged and non-necrotic areas. GeoMx® Digital Spatial Profiler (NanoString, Seattle, WA, USA) was used for assessing the presence of markers of various immune cells by comparing high-desmin (nondamaged) and low-desmin (damaged) regions of muscle. Markers of monocytes, macrophages, M2 macrophages, dendritic cells, neutrophils, leukocyte adhesion and migration markers, and hematopoietic precursor cells showed higher levels in low-desmin regions, especially in samples collected 24 hr after venom injection, whereas several markers of lymphocytes did not. Moreover, apoptosis (BAD) and extracellular matrix (fibronectin) markers were also increased in low-desmin regions. Our findings reveal a hitherto-unknown picture of immune cell microheterogeneity in venom-injected muscle which greatly depends on the extent of muscle cell damage and the time lapse after venom injection.

Phenotypic, functional and plasticity features of human PBMCs induced by venom secreted PLA2s

Bothrops venom contains a high amount of secreted phospholipase A₂ (sPLA₂s) enzymes responsible for the inflammatory reaction and activation of leukocytes in cases of envenoming. PLA₂s are proteins that have enzymatic activity and can hydrolyze phospholipids at the sn-2 position, thereby releasing fatty acids and lysophospholipids precursors of eicosanoids, which are significant mediators of inflammatory conditions. Whether these enzymes have a role in the activation and function of peripheral blood mononuclear cells (PBMCs) is not known. Here we show for the first time how two secreted PLA₂s (BthTX-I and BthTX-II) isolated from the venom of Bothrops jararacussu affect the function and polarization of PBMCs. Neither BthTX-I nor BthTX-II exhibited significant cytotoxicity to isolated PBMCs compared with the control at any of the time points studied. RT-qPCR and enzyme-linked immunosorbent assays were used to determine changes in gene expression and the release of pro-inflammatory (TNF-α, IL-6, and IL-12) and anti-inflammatory (TGF-β and IL-10) cytokines, respectively, during the cell differentiation process. Lipid droplets formation and phagocytosis were also investigated. Monocytes/macrophages were labeled with anti-CD14, -CD163, and -CD206 antibodies to assay cell polarization. Both toxins caused a heterogeneous morphology (M1 and M2) on days 1 and 7 based on immunofluorescence analysis, revealing the considerable flexibility of these cells even in the presence of typical polarization stimuli. Thus, these findings indicate that the two sPLA₂s trigger both immune response profiles in PBMCs indicating a significant degree of cell plasticity, which may be crucial for understanding the consequences of snake envenoming.

The early inhibition of the COX-2 pathway in viperid phospholipase A2-induced skeletal muscle myotoxicity accelerates the tissue regeneration

The administration of non-steroidal anti-inflammatory drugs in the treatment of injury and muscle regeneration is still contradictory in effectiveness, especially regarding the timing of their administration. This can interfere with the production of prostaglandins originating from inflammatory isoform cyclooxygenase-2 (COX-2), which is essential to modulate tissue regeneration. The phospholipases A₂ (PLA₂) from viperid venoms cause myotoxicity, therefore constituting a tool for the study of supportive therapies to improve skeletal muscle regeneration. This study investigated the effect of early administration of lumiracoxib (selective inhibitor of COX-2) on the degeneration and regeneration stages of skeletal muscle after injury induced by a myotoxic PLA₂. After 30 min and 48 h of intramuscular injection of PLA₂, mice received lumiracoxib orally and histological, functional, and transcriptional parameters of muscle were evaluated from 6 h to 21 days. Inhibition of COX-2 in the early periods of PLA₂-induced muscle degeneration reduced leukocyte influx, edema, and tissue damage. After the second administration of lumiracoxib, in regenerative stage, muscle showed increase in number of basophilic fibers, reduction in fibrosis content and advanced recovery of functionality characterized by the presence of fast type II fibers. The expression of Pax7 and myogenin were increased, indicating a great capacity for storing satellite cells and advanced mature state of tissue. Our data reveals a distinct role of COX-2-derived products during muscle degeneration and regeneration, in which early administration of lumiracoxib was a therapeutic strategy to modulate the effects of prostaglandins, providing a breakthrough in muscle tissue regeneration induced by a myotoxic PLA_2.

Regulatory T cells-centered regulatory networks of skeletal muscle inflammation and regeneration

As the understanding of skeletal muscle inflammation is increasingly clarified, the role of Treg cells in the treatment of skeletal muscle diseases has attracted more attention in recent years. A consensus has been reached that the regulation of Treg cells is the key to completing the switch of inflammation and repair of skeletal muscle, whose presence directly determine the repairing quality of the injured skeletal muscle. However, the functioning process of Treg cells remains unreported, thereby making it necessary to summarize the current role of Treg cells in skeletal muscle. In this review, the characteristics, origins, and cellular kinetics of these Treg cells are firstly described; Then, the relationship between Treg cells and muscle satellite cells (MuSCs), conventional T cells (Tconv) is discussed (the former is involved in the entire repair and regeneration process, while the latter matters considerably in causing most skeletal muscle autoimmune diseases); Next, focus is placed on the control of Treg cells on the phenotypic switch of macrophages, which is the key to the switch of inflammation; Finally, factors regulating the functional process of Treg cells are analyzed, and a regulatory network centered on Treg cells is summarized. The present study summarizes the cell-mediated interactions in skeletal muscle repair over the past decade, and elucidates the central role of regulatory T cells in this process, so that other researchers can more quickly and comprehensively understand the development and direction of this very field. It is believed that the hereby proposed viewpoints and problems can provide fresh visions for the latecomers.

Effects of venoms on neutrophil respiratory burst: a major inflammatory function

Neutrophils play a pivotal role in innate immunity and in the inflammatory response. Neutrophils are very motile cells that are rapidly recruited to the inflammatory site as the body first line of defense. Their bactericidal activity is due to the release into the phagocytic vacuole, called phagosome, of several toxic molecules directed against microbes. Neutrophil stimulation induces release of this arsenal into the phagosome and induces the assembly at the membrane of subunits of the NAPDH oxidase, the enzyme responsible for the production of superoxide anion that gives rise to other reactive oxygen species (ROS), a process called respiratory burst. Altogether, they are responsible for the bactericidal activity of the neutrophils. Excessive activation of neutrophils can lead to extensive release of these toxic agents, inducing tissue injury and the inflammatory reaction. Envenomation, caused by different animal species (bees, wasps, scorpions, snakes etc.), is well known to induce a local and acute inflammatory reaction, characterized by recruitment and activation of leukocytes and the release of several inflammatory mediators, including prostaglandins and cytokines. Venoms contain several molecules such as enzymes (phospholipase A2, L-amino acid oxidase and proteases, among others) and peptides (disintegrins, mastoporan, parabutoporin etc.). These molecules are able to stimulate or inhibit ROS production by neutrophils. The present review article gives a general overview of the main neutrophil functions focusing on ROS production and summarizes how venoms and venom molecules can affect this function.

Inflammatory effect of Bothropstoxin-I from Bothrops jararacussu venom mediated by NLRP3 inflammasome involves ATP and P2X7 receptor

Muscle tissue damage is one of the local effects described in bothropic envenomations. Bothropstoxin-I (BthTX-I), from Bothrops jararacussu venom, is a K49-phospholipase A2 (PLA2) that induces a massive muscle tissue injury, and, consequently, local inflammatory reaction. The NLRP3 inflammasome is a sensor that triggers inflammation by activating caspase 1 and releasing interleukin (IL)-1β and/or inducing pyroptotic cell death in response to tissue damage. We, therefore, aimed to address activation of NLRP3 inflammasome by BthTX-I-associated injury and the mechanism involved in this process. Intramuscular injection of BthTX-I results in infiltration of neutrophils and macrophages in gastrocnemius muscle, which is reduced in NLRP3- and Caspase-1-deficient mice. The in vitro IL-1β production induced by BthTX-I in peritoneal macrophages (PMs) requires caspase 1/11, ASC and NLRP3 and is dependent on adenosine 5'-triphosphate (ATP)-induced K+ efflux and P2X7 receptor (P2X7R). BthTX-I induces a dramatic release of ATP from C2C12 myotubes, therefore representing the major mechanism for P2X7R-dependent inflammasome activation in macrophages. A similar result was obtained when human monocyte-derived macrophages (HMDMs) were treated with BthTX-I. These findings demonstrated the inflammatory effect of BthTX-I on muscle tissue, pointing out a role for the ATP released by damaged cells for the NLRP3 activation on macrophages, contributing to the understanding of the microenvironment of the tissue damage of the Bothrops envenomation.

Edema, hyperalgesia and myonecrosis induced by Brazilian bothropic venoms: overview of the last decade

Snakebite accidents are considered serious public health problems. They are often neglected, and individuals who have received insufficient treatment are subjected to various disabling alterations. Snake venoms are secretions composed of biologically active molecules capable of triggering local and systemic effects in envenomation victims. Bothropic snakes are responsible for most of the ophidian accidents in Brazil; their venoms are mainly related to local manifestations, due to a composition that is especially rich in proteases and phospholipases A₂. The most common local damages are inflammation, with consequent cellular activation and release of inflammatory mediators, hemorrhage, edema, pain and (myo)necrosis, which may lead to amputation of the affected areas. Antivenom therapy is the main treatment for snakebites. However, the efficiency is mainly due to the neutralization of the toxins responsible for the systemic alterations. Thus, the local damages can evolve to markedly compromise the tissue. The complexity of these local effects associated with the toxicity of the snake venom components of the genus Bothrops, arouse interest in the study of the biochemical and pathophysiological mechanisms involved with the actions caused by toxins of the venom. Therefore, this review aims to analyze the edematogenic, hyperalgesic and myotoxic effects caused by Brazilian bothropic venoms in order to contribute to the study and elucidation of the mechanisms of action of its components and, consequently, enable discoveries of more effective combined therapies in the treatment of local damages resulting from envenoming.