Antiviral activity of serum from the American alligator (Alligator mississippiensis)

Reptilian Innate Immunology and Ecoimmunology: What Do We Know and Where Are We Going?

Reptiles, the only ectothermic amniotes, employ a wide variety of physiological adaptations to adjust to their environments but remain vastly understudied in the field of immunology and ecoimmunology in comparison to other vertebrate taxa. To address this knowledge gap, we assessed the current state of research on reptilian innate immunology by conducting an extensive literature search of peer-reviewed articles published across the four orders of Reptilia (Crocodilia, Testudines, Squamata, and Rhynchocephalia). Using our compiled dataset, we investigated common techniques, characterization of immune components, differences in findings and type of research among the four orders, and immune responses to ecological and life-history variables. We found that there are differences in the types of questions asked and approaches used for each of these reptilian orders. The different conceptual frameworks applied to each group has led to a lack of unified understanding of reptilian immunological strategies, which, in turn, have resulted in large conceptual gaps in the field of ecoimmunology as a whole. To apply ecoimmunological concepts and techniques most effectively to reptiles, we must combine traditional immunological studies with ecoimmunological studies to continue to identify, characterize, and describe the reptilian immune components and responses. This review highlights the advances and gaps that remain to help identify targeted and cohesive approaches for future research in reptilian ecoimmunological studies.

Proteomic profiling reveals antitumor effects of RT2 peptide on a human colon carcinoma xenograft mouse model

A comparative study of human colon HCT-116 xenograft in nude mice treated with and without peptide RT2 at high doses is performed along with a label-free proteomic analysis of the tissue in order to understand the potential mechanisms by which RT2 acts in vivo against colorectal tumors. RT2 displays no significant systematic toxicity, but reduces tumor growth after either intraperitoneal or intratumoral injection demonstrating it is a safe and efficacious antitumor agent in vivo. Of the 3196 proteins identified by label-free proteomics, 61 proteins appear only in response to RT2 and are involved in cellular processes largely localized in the cells and cell parts. Some of the proteins identified, including CFTR, Wnt7a, TIA1, PADI2, NRBP2, GADL1, LZIC, TLR6, and GPR37, have been reported to suppress tumor growth and are associated with cell proliferation, invasion, metastasis, angiogenesis, apoptosis, and immune evasion. Our work supports their role as tumor biomarkers and reveals RT2 has a complex mechanism of action in vivo.

Gut microbiome-immune system interaction in reptiles

Reptiles are ectothermic amniotes in a world dominated by endotherms. Reptiles originated more than 300 million years ago and they often dwell in polluted environments which may expose them to pathogenic micro-organisms, radiation and/or heavy metals. Reptiles also possess greater longevity and may live much longer than similar-sized land mammals, for example, turtles, tortoises, crocodiles and tuatara are long-lived reptiles living up to 100 years or more. Many recent studies have emphasized the pivotal role of the gut microbiome on its host; thus, we postulated that reptilian gut microbiome and/or its metabolites and the interplay with their robust immune system may contribute to their longevity and overall hardiness. Herein, we discuss the composition of the reptilian gut microbiome, immune system-gut microbiome cross-talk, antimicrobial peptides, reptilian resistance to infectious diseases and cancer, ageing, as well the current knowledge of the genome and epigenome of these remarkable species. Preliminary studies have demonstrated that microbial gut flora of reptiles such as crocodiles, tortoises, water monitor lizard and python exhibit remarkable anticancer and antibacterial properties, as well as comprise novel gut bacterial metabolites and antimicrobial peptides. The underlying mechanisms between the gut microbiome and the immune system may hold clues to developing new therapies overall for health, and possible extrapolation to exploit the ancient defence systems of reptiles for Homo sapiens benefit.

Longevity, cellular senescence and the gut microbiome: lessons to be learned from crocodiles

Crocodiles are flourishing large-bodied ectotherms in a world dominated by endotherms. They survived the Cretaceous extinction event, that eradicated the dinosaurs who are thought to be their ancestral hosts. Crocodiles reside in polluted environments; and often inhabit water which contains heavy metals; frequent exposure to radiation; feed on rotten meat and considered as one of the hardy species that has successfully survived on this planet for millions of years. Another capability that crocodiles possess is their longevity. Crocodiles live much longer than similar-sized land mammals, sometimes living up to 100 years. But how do they withstand such harsh conditions that are detrimental to Homo sapiens? Given the importance of gut microbiome on its' host physiology, we postulate that the crocodile gut microbiome and/or its' metabolites produce substances contributing to their "hardiness" and longevity. Thus, we accomplished literature search in PubMed, Web of Science and Google Scholar and herein, we discuss the composition of the crocodile gut microbiome, longevity and cellular senescence in crocodiles, their resistance to infectious diseases and cancer, and our current knowledge of the genome and epigenome of these remarkable species. Furthermore, preliminary studies that demonstrate the remarkable properties of crocodile gut microbial flora are discussed. Given the profound role of the gut microbiome in the health of its' host, it is likely that the crocodile gut microbiome and its' metabolites may be contributing to their extended life expectancy and elucidating the underlying mechanisms and properties of these metabolites may hold clues to developing new treatments for age-related diseases for the benefit of Homo sapiens.

Potential of crocodile blood as a medication and dietary supplement: A systemic review

Crocodile blood has long been used as a traditional medicine in many Asian countries to treat diseases such as asthma, allergies, and many others. Yet, only recently has the safety and effectiveness of using crocodile blood as a medicine been examined using modern scientific methods; with both conserved and novel active components identified from crocodile blood. Further in vitro and in vivo investigations found that crocodile blood can have a wide range of beneficial effects, including antimicrobial, antiviral, anti-oxidative, anti-inflammatory, antitumour effects, anti-anaemia, and enhancement of wound healing. A systematic research of literature published in English-language journals up to April 2020 was conducted in PubMed, Google Scholar, and Web of Science. Based on the biological and chemical knowledge of crocodile immunity and crocodile blood, this article aims to: provide a critical review on the proposed properties of crocodile blood, identify the knowledge gap and offer some insights for future investigations regarding the use of crocodile blood as a medication or dietary supplement.

Repair function of essential oil from Crocodylus Siamensis (Schneider, 1801) on the burn wound healing via up-regulated growth factor expression and anti-inflammatory effect

ETHNOPHARMACOLOGICAL RELEVANCE

Crocodile oil has been used by traditional physicians around the world to treat wound healing and inflammation. However, the scientific rationale and mechanism behind its use in vivo has not been fully researched.

AIMS OF THE STUDY

We mainly investigated the mechanism during crocodile oil treatment of up-regulated growth factor expression and anti-inflammatory on burn wound healing in rats.

MATERIALS AND METHODS

The moisture and nitric oxide (NO) levels in the skin of rats were analyzed in the first 14 days after burn and the changes of the structure of the skin tissues in the wound healing were studied by hematoxylin-eosin (H.E.) staining within 21 days after scald. The inflammatory factor on burn wound healing in rats was dected by ELISA kits and Q-PCR. the expression of a variety of growth factors (TGF-β1, VEGE-α, EGF) and PCNA in the skin tissue after burns was evaluated using immunohistochemistry. The down-regulated phosphorylation of p38 MAPK in the wound healing was confirmed by Western-blot analysis. In addition, TEM was used to observe the ultrastructure of scalded skin.

RESULTS

This study showed that crocodile oil could significantly reduce the protein and mRNA levels of TNF-α, IL-1β and IL-6. And it was found that the phosphorylation of p38 MAPK was down-regulated in the wound healing (p < 0.05). Meanwhile, crocodile oil can promote the expression of a variety of growth factors (TGF-β1, VEGE-α, EGF) and PCNA in the skin tissue after burns, and promote the repair of collagen fibers in the dermis, preventing the production of melanin and maintain the appearance of repaired skin.

Anatomical and histological analyses reveal that tail repair is coupled with regrowth in wild-caught, juvenile American alligators (Alligator mississippiensis)

Reptiles are the only amniotes that maintain the capacity to regenerate appendages. This study presents the first anatomical and histological evidence of tail repair with regrowth in an archosaur, the American alligator. The regrown alligator tails constituted approximately 6–18% of the total body length and were morphologically distinct from original tail segments. Gross dissection, radiographs, and magnetic resonance imaging revealed that caudal vertebrae were replaced by a ventrally-positioned, unsegmented endoskeleton. This contrasts with lepidosaurs, where the regenerated tail is radially organized around a central endoskeleton. Furthermore, the regrown alligator tail lacked skeletal muscle and instead consisted of fibrous connective tissue composed of type I and type III collagen fibers. The overproduction of connective tissue shares features with mammalian wound healing or fibrosis. The lack of skeletal muscle contrasts with lizards, but shares similarities with regenerated tails in the tuatara and regenerated limbs in Xenopus adult frogs, which have a cartilaginous endoskeleton surrounded by connective tissue, but lack skeletal muscle. Overall, this study of wild-caught, juvenile American alligator tails identifies a distinct pattern of wound repair in mammals while exhibiting features in common with regeneration in lepidosaurs and amphibia.

Deimination Protein Profiles in Alligator mississippiensis Reveal Plasma and Extracellular Vesicle-Specific Signatures Relating to Immunity, Metabolic Function, and Gene Regulation

Alligators are crocodilians and among few species that endured the Cretaceous-Paleogene extinction event. With long life spans, low metabolic rates, unusual immunological characteristics, including strong antibacterial and antiviral ability, and cancer resistance, crocodilians may hold information for molecular pathways underlying such physiological traits. Peptidylarginine deiminases (PADs) are a group of calcium-activated enzymes that cause posttranslational protein deimination/citrullination in a range of target proteins contributing to protein moonlighting functions in health and disease. PADs are phylogenetically conserved and are also a key regulator of extracellular vesicle (EV) release, a critical part of cellular communication. As little is known about PAD-mediated mechanisms in reptile immunology, this study was aimed at profiling EVs and protein deimination in Alligator mississippiensis. Alligator plasma EVs were found to be polydispersed in a 50-400-nm size range. Key immune, metabolic, and gene regulatory proteins were identified to be posttranslationally deiminated in plasma and plasma EVs, with some overlapping hits, while some were unique to either plasma or plasma EVs. In whole plasma, 112 target proteins were identified to be deiminated, while 77 proteins were found as deiminated protein hits in plasma EVs, whereof 31 were specific for EVs only, including proteins specific for gene regulatory functions (e.g., histones). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed KEGG pathways specific to deiminated proteins in whole plasma related to adipocytokine signaling, while KEGG pathways of deiminated proteins specific to EVs included ribosome, biosynthesis of amino acids, and glycolysis/gluconeogenesis pathways as well as core histones. This highlights roles for EV-mediated export of deiminated protein cargo with roles in metabolism and gene regulation, also related to cancer. The identification of posttranslational deimination and EV-mediated communication in alligator plasma revealed here contributes to current understanding of protein moonlighting functions and EV-mediated communication in these ancient reptiles, providing novel insight into their unusual immune systems and physiological traits. In addition, our findings may shed light on pathways underlying cancer resistance, antibacterial and antiviral resistance, with translatable value to human pathologies.

Detection and analysis of autophagy in the American alligator (Alligator mississippiensis)

In response to environmental temperature depression in the fall and winter, American alligators (Alligator mississippiensis) brumate. Brumation is characterized by lethargy, fasting, decreased metabolism, and decreased body temperature. During brumation, alligators will periodically emerge for basking or other encounters when environmental conditions permit. This sporadic activity and lack of nutrient intake may place strain on nutrient reserves. Nutrient scarcity, at the cellular and/or organismal level, promotes autophagy, a well-conserved subcellular catabolic process used to maintain energy homeostasis during periods of metabolic or hypoxic stress. An analysis of the putative alligator autophagy-related proteins has been conducted, and the results will be used to investigate the physiological role of autophagy during the brumation period. Using published genomic data, we have determined that autophagy is highly conserved, and alligator amino acid sequences exhibit a high percentage of identity with human homologs. Transcriptome analysis conducted using liver tissue derived from alligators confirmed the expression of one or more isoforms of each of the 34 autophagy initiation and elongation genes assayed. Five autophagy-related proteins (ATG5, ATG9A, BECN1, ATG16L1, and MAP1-LC3B), with functions spanning the major stages of autophagy, have been detected in alligator liver tissue by western blot analysis. In addition, ATG5 was detected in alligator liver tissue by immunohistochemistry. This is the first characterization of autophagy in crocodylians, and the first description of autophagy-related protein expression in whole blood.

The Komodo dragon (Varanus komodoensis) genome and identification of innate immunity genes and clusters

Background

We report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons. They appear to be unaffected, suggesting that dragons have robust defenses against infection. While little information is available regarding the molecular biology of reptile immunity, it is believed that innate immunity, which employs antimicrobial host-defense peptides including defensins and cathelicidins, plays a more prominent role in reptile immunity than it does in mammals. .

Results

High molecular weight genomic DNA was extracted from Komodo dragon blood cells. Subsequent sequencing and assembly of the genome from the collected DNA yielded a genome size of 1.6 Gb with 45x coverage, and the identification of 17,213 predicted genes. Through further analyses of the genome, we identified genes and gene-clusters corresponding to antimicrobial host-defense peptide genes. Multiple β-defensin-related gene clusters were identified, as well as a cluster of potential Komodo dragon ovodefensin genes located in close proximity to a cluster of Komodo dragon β-defensin genes. In addition to these defensins, multiple cathelicidin-like genes were also identified in the genome. Overall, 66 β-defensin genes, six ovodefensin genes and three cathelicidin genes were identified in the Komodo dragon genome.

Conclusions

Genes with important roles in host-defense and innate immunity were identified in this newly sequenced Komodo dragon genome, suggesting that these organisms have a robust innate immune system. Specifically, multiple Komodo antimicrobial peptide genes were identified. Importantly, many of the antimicrobial peptide genes were found in gene clusters. We found that these innate immunity genes are conserved among reptiles, and the organization is similar to that seen in other avian and reptilian species. Having the genome of this important squamate will allow researchers to learn more about reptilian gene families and will be a valuable resource for researchers studying the evolution and biology of the endangered Komodo dragon.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6029-y) contains supplementary material, which is available to authorized users.

Ranaviruses and reptiles

Ranaviruses can infect many vertebrate classes including fish, amphibians and reptiles, but for the most part, research has been focused on non-reptilian hosts, amphibians in particular. More recently, reports of ranaviral infections of reptiles are increasing with over 12 families of reptiles currently susceptible to ranaviral infection. Reptiles are infected by ranaviruses that are genetically similar to, or the same as, the viruses that infect amphibians and fish; however, physiological and ecological differences result in differences in study designs. Although ranaviral disease in reptiles is often influenced by host species, viral strain and environmental differences, general trends in pathogenesis are emerging. More experimental studies using a variety of reptile species, life stages and routes of transmission are required to unravel the complexity of wild ranavirus transmission. Further, our understanding of the reptilian immune response to ranaviral infection is still lacking, although the considerable amount of work conducted in amphibians will serve as a useful guide for future studies in reptiles.

Patterns of Circulating Corticosterone in a Population of Rattlesnakes Afflicted with Snake Fungal Disease: Stress Hormones as a Potential Mediator of Seasonal Cycles in Disease Severity and Outcomes

Snake fungal disease (SFD) is an emerging threat to snake populations in the United States. Fungal pathogens are often associated with a physiological stress response mediated by the hypothalamo-pituitary-adrenal axis (HPA), and afflicted individuals may incur steep coping costs. The severity of SFD can vary seasonally; however, little is known regarding (1) how SFD infection relates to HPA activity and (2) how seasonal shifts in environment, life history, or HPA activity may interact to drive seasonal patterns of infection severity and outcomes. To test the hypothesis that SFD is associated with increased HPA activity and to identify potential environmental or physiological drivers of seasonal infection, we monitored baseline corticosterone, SFD infection severity, foraging success, body condition, and reproductive status in a field-active population of pigmy rattlesnakes. Both plasma corticosterone and the severity of clinical signs of SFD peaked in the winter. Corticosterone levels were also elevated in the fall before the seasonal rise in SFD severity. Severely symptomatic snakes were in low body condition and had elevated corticosterone levels compared to moderately infected and uninfected snakes. The monthly mean severity of SFD in the population was negatively related to population-wide estimates of body condition and temperature measured in the precedent month and positively correlated with corticosterone levels measured in the precedent month. Symptomatic females were less likely to enter reproductive bouts compared to asymptomatic females. We propose the hypothesis that the seasonal interplay among environment, host energetics, and HPA activity initiates trade-offs in the fall that drive the increase in SFD prevalence, symptom severity, and decline in condition observed in the population through winter.

Mining the tree of life: Host defense peptides as antiviral therapeutics

Discovering new therapeutics for human viral diseases is important for combatting emerging infectious viruses and omnipresent circulating viruses as well as those that can become resistant to the drugs we currently have available. The innate host defense peptide (HDP) repertoire present in animals is a wealth of potential antimicrobial agents that could be mined to meet these needs. While much of the body of research regarding HDPs is in the context of bacteria, there is increasing evidence that they can be an effective source for antivirals. Peptides can be identified in a number of ways, including eco-conservation-minded approaches. Those shown to have antiviral properties can be modified to exhibit desired properties as the relationship between structure and function is elucidated and then developed into therapeutics for human use. This review looks at the discovery and therapeutic potential of HDPs for human viral infections.

Anticancer potential of bioactive peptides from animal sources (Review)

Cancer is the most common cause of human death worldwide. Conventional anticancer therapies, including chemotherapy and radiation, are associated with severe side effects and toxicities as well as low specificity. Peptides are rapidly being developed as potential anticancer agents that specifically target cancer cells and are less toxic to normal tissues, thus making them a better alternative for the prevention and management of cancer. Recent research has focused on anticancer peptides from natural animal sources, such as terrestrial mammals, marine animals, amphibians, and animal venoms. However, the mode of action by which bioactive peptides inhibit the proliferation of cancer cells remains unclear. In this review, we present the animal sources from which bioactive peptides with anticancer activity are derived and discuss multiple proposed mechanisms by which these peptides exert cytotoxic effects against cancer cells.

Baseline values of immunologic parameters in the lizard Salvator merianae (Teiidae, Squamata)

The genus Salvator is widely distributed throughout South America. In Argentina, the species most abundant widely distributed is Salvator merianae. Particularly in Santa Fe province, the area occupied by populations of these lizards overlaps with areas where agriculture was extended. With the aim of established baseline values for four immunologic biomarkers widely used, 36 tegu lizards were evaluated tacking into account different age classes and both sexes. Total leukocyte counts were not different between age classes. Of the leucocytes count, eosinophils levels were higher in neonates compared with juvenile and adults; nevertheless, the heterophils group was the most prevalent leukocyte in the peripheral blood in all age classes. Lymphocytes, monocytes, heterophils, azurophils and basophils levels did not differ with age. Natural antibodies titres were higher in the adults compared with neonates and juveniles lizards. Lastly, complement system activity was low in neonates compared with juveniles and adults. Statistical analysis within each age group showed that gender was not a factor in the outcomes. Based on the results, we concluded that S. merianae demonstrated age (but not gender) related differences in the immune parameters analyzed. Having established baseline values for these four widely-used immunologic biomarkers, ongoing studies will seek to optimize the use of the S. merianae model in future research.

Cathelicidin antimicrobial peptide from Alligator mississippiensis has antibacterial activity against multi-drug resistant Acinetobacter baumanii and Klebsiella pneumoniae

Alligator mississippiensis (American alligator), a member of order Crocodilia, lives in bacteria-laden environments but is not often known to succumb to bacterial infections. Their serum has been shown to have antibacterial activity beyond that of human serum, and it is believed that this activity is partially due to cationic antimicrobial peptides (CAMPs). CAMPs are produced by many organisms as part of the innate immune system. CAMPs are attractive possible therapies against multi-drug resistant bacteria, such as those found in biofilm-infected war wounds, because they seldom cause genetic resistance in bacteria and are effective against antibiotic resistant bacteria. In this work, we identified, synthesized, and characterized a cathelicidin and two shorter fragments from the American alligator. We discovered the cathelicidin using Basic Local Alignment Search Tool (BLAST) alignment and by comparing A. mississippiensis expressed sequence tags (ESTs) with propeptide cathelicidins of other reptiles. We analyzed the structure using bioinformatics tools and circular dichroism and predicted that the full-length cathelicidin peptide has a mixed structure, with an N-terminal α-helix and a center Pro hinge. In minimal inhibitory concentration (MIC) assays, it was determined that the cathelicidin and the two shorter fragments have strong activity against multiple Gram-negative bacteria, including clinical isolates of multi-drug resistant (MDR) Acinetobacter baumannii and carbapenem-resistant Klebsiella pneumoniae. Using the ethidium bromide uptake assay, it was found that these peptides permeabilize the bacterial membrane and are less sensitive to salt inhibition than many other known CAMPs. The alligator cathelicidin peptides were not hemolytic against sheep red blood cells at 300 μg/ml and were not significantly cytotoxic against A549 human lung epithelial cells after 24 h exposure in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. These alligator cathelicidin peptides have activity similar to other CAMPs from reptiles such as NA-CATH. It is possible that the alligator cathelicidins play an important role in the innate immune response of A. mississippiensis, similar to LL-37 in humans. In addition, due to their activities against MDR bacteria and lack of cytotoxicity, the AM-CATH peptides could be an attractive platform for further development as a potential therapeutic.

The effect of environmental temperature on reptilian peripheral blood B cell functions

Recent studies have identified phagocytic B cells in a variety of species, yet little is understood about their function and how it is influenced by natural environmental variation, such as temperature. Phagocytic B-cells are present in red-eared slider turtles, Trachemys scripta, and the wide range of temperatures experienced by these ectotherms may have an effect on immunity, including B cell antibody secretion and phagocytosis. We examined the impact of environmental temperature on B cell function in vitro using phagocytic and ELISpot assays conducted at biologically relevant temperatures. We found a significant effect of temperature on antibody secretion, with maximal antibody secretion occurring at intermediate temperatures (estimated maximum of 28.8°C). There was no effect of temperature on phagocytosis. We also noted a difference in the efficiency of phagocytosis in this assay between B cells and non-B cells. Interestingly, in our in vitro assay, phagocytic B cells engulfed more foreign fluorescent beads per cell than phagocytes lacking surface immunoglobulin. This work sheds light on our understanding of phagocytic B cells and the importance of environmental temperature on the behavior of reptilian immune cells, which may have relevance for organismal fitness.

Inhibition of HeLa cells metastasis by bioactive compounds in crocodile (Crocodylus siamensis) white blood cells extract

Matrix metalloproteinases (MMPs) play a key role in cancer progression, including cell invasion, metastasis, cell growth, apoptosis, angiogenesis, and cell adhesion. Thus, suppression of the MMPs activities is crucial for inhibiting cancer cells metastasis. Herein, bioactive agents from crocodile (Crocodylus siamensis) leukocyte extracts (WBCex) showed the anticancer activity with HeLa cells and inhibited the migration and invasion process by reducing gelatinases (MMP-2, MMP-9) activity and their protein levels. This mechanism is regulated via interfering Ras and p38 signal transduction. Moreover, disrupting VEGF and integrin-signaling cascade by bioactive agents are the predictable mechanisms that cause the decreasing of MMP-2 and MMP-9 activity. Hence, bioactive substances in WBCex may play the mode of action similar with MMPs inhibitor due to HeLa cell metastasis being suppressed in vitro. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1329-1336, 2016.

Extracellular histones identified in crocodile blood inhibit in-vitro HIV-1 infection

OBJECTIVE

It has been reported that crocodile blood contains potent antibacterial and antiviral properties. However, its effects on HIV-1 infection remain unknown.

DESIGN

We obtained blood from saltwater crocodiles to examine whether serum or plasma could inhibit HIV-1 infection. We purified plasma fractions then used liquid chromatography-mass spectrometry to identify the inhibitory protein factor(s). We then analyzed the ability of recombinant proteins to recapitulate HIV-1 inhibition and determine their mechanism of action.

METHODS

Crocodylus porosus plasma was tested for inhibition of Jurkat T-cell HIV-1 infection. Inhibitor(s) were purified by reverse-phase chromatography then identified by protein liquid chromatography-mass spectrometry. Anti-HIV-1 activity of purified plasma or recombinant proteins were measured by p24 enzyme-linked immunosorbent assay and luciferase readouts, and mechanism of action was determined by measuring HIV-1 RNA, cDNA and transcription (using 1G5 cells).

RESULTS

Crocodile plasma contains potent inhibitors of HIV-1IIIB infection, which were identified as histones. Recombinant human histones H1 and H2A significantly reduced HIV-1JR-FL infection (IC50 of 0.79 and 0.45 μmol/l, respectively), whereas H4 enhanced JR-FL luciferase activity. The inhibitory effects of crocodile plasma, recombinant H1 or recombinant H2A on HIV-1 infection were during or post-viral transcription.

CONCLUSION

Circulating histones in crocodile blood, possibly released by neutrophil extracellular traps, are significant inhibitors of HIV-1 infection in-vitro. Extracellular recombinant histones have different effects on HIV-1 transcription and protein expression and are downregulated in HIV-1 patients. Circulating histones may be a novel resistance factor during HIV-1 infection, and peptide versions should be explored as future HIV-1 therapeutics that modulate viral transcription.

Bioactive compounds from crocodile (Crocodylus siamensis) white blood cells induced apoptotic cell death in hela cells

Crocodile (Crocodylus siamensis) white blood cell extracts (WBCex) were examined for anticancer activity in HeLa cell lines using the MTT assay. The percentage viability of HeLa cells significantly deceased after treatment with WBCex in a dose- and time-dependent manner. The IC50 dose was suggested to be approximately 225 μg/mL protein. Apoptotic cell death occurred in a time-dependent manner based on investigation by flow cytometry using annexin V-FITC and PI staining. DAPI nucleic acid staining indicated increased chromatin condensation. Caspase-3, -8 and -9 activities also increased, suggesting the induction of the caspase-dependent apoptotic pathway. Furthermore, the mitochondrial membrane potential (ΔΨm ) of HeLa cells was lost as a result of increasing levels of Bax and reduced levels of Bcl-2, Bcl-XL, Bcl-Xs, and XIAP. The decreased ΔΨm led to the release of cytochrome c and the activation of caspase-9 and -3. Apoptosis-inducing factor translocated into the nuclei, and endonuclease G (Endo G) was released from the mitochondria. These results suggest that anticancer agents in WBCex can induce apoptosis in HeLa cells via both caspase-dependent and -independent pathways. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 986-997, 2016.

Innate immunity in vertebrates: an overview

Innate immunity is a semi-specific and widely distributed form of immunity, which represents the first line of defence against pathogens. This type of immunity is critical to maintain homeostasis and prevent microbe invasion, eliminating a great variety of pathogens and contributing with the activation of the adaptive immune response. The components of innate immunity include physical and chemical barriers, humoral and cell-mediated components, which are present in all jawed vertebrates. The understanding of innate defence mechanisms in non-mammalian vertebrates is the key to comprehend the general picture of vertebrate innate immunity and its evolutionary history. This is also essential for the identification of new molecules with applications in immunopharmacology and immunotherapy. In this review, we describe and discuss the main elements of vertebrate innate immunity, presenting core findings in this field and identifying areas that need further investigation.

Black cobra (Naja naja karachiensis) lysates exhibit broad-spectrum antimicrobial activities

It is hypothesized that animals living in polluted environments possess antimicrobials to counter pathogenic microbes. The fact that snakes feed on germ-infested rodents suggests that they encounter pathogenic microbes and likely possess antimicrobials. The venom is used only to paralyze the rodent, but the ability of snakes to counter potential infections in the gut due to disease-ridden rodents requires robust action of the immune system against a broad range of pathogens. To test this hypothesis, crude lysates of different organs of Naja naja karachiensis (black cobra) were tested for antimicrobial properties. The antimicrobial activities of extracts were tested against selected bacterial pathogens (neuropathogenic Escherichia coli K1, methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Streptococcus pneumonia), protist (Acanthamoeba castellanii), and filamentous fungus (Fusarium solani). The findings revealed that plasma and various organ extracts of N. n. karachiensis exhibited antimicrobial activity against E. coli K1, MRSA, P. aeruginosa, S. pneumoniae, A. castellanii, and F. solani in a concentration-dependent manner. The results of this study are promising for the development of new antimicrobials.

Endocrine-disrupting chemical exposure and the American alligator: a review of the potential role of environmental estrogens on the immune system of a top trophic carnivore

Endocrine-disrupting chemicals (EDCs) alter cellular and organ system homeostasis by interfering with the body's normal physiologic processes. Numerous studies have identified environmental estrogens as modulators of EDC-related processes in crocodilians, notably in sex determination. Other broader studies have shown that environmental estrogens dysregulate normal immune function in mammals, birds, turtles, lizards, fish, and invertebrates; however, the effects of such estrogenic exposures on alligator immune function have not been elucidated. Alligators occupy a top trophic status, which may give them untapped utility as indicators of environmental quality. Environmental estrogens are also prevalent in the waters they occupy. Understanding the effects of these EDCs on alligator immunity is critical for managing and assessing changes in their health and is thus the focus of this review.

Molecular cloning and expression of α-globin and β-globin genes from crocodile (Crocodylus siamensis)

The first report of complete nucleotide sequences for α- and β-globin chains from the Siamese hemoglobin (Crocodylus siamensis) is given in this study. The cDNAs encoding α- and β-globins were cloned by RT-PCR using the degenerate primers and by the rapid amplification of cDNA ends method. The full-length α-globin cDNA contains an open reading frame of 423 nucleotides encoding 141 amino acid residues, whereas the β-globin cDNA contains an open reading frame of 438 nucleotides encoding 146 amino acid residues. The authenticity of both α- and β-globin cDNA clones were also confirmed by the heterologous expression in Escherichia coli (E. coli). This is the first time that the recombinant C. siamensis globins were produced in prokaryotic system. Additionally, the heme group was inserted into the recombinant proteins and purified heme-bound proteins were performed by affinity chromatography using Co(2+)-charged Talon resins. The heme-bound proteins appeared to have a maximum absorbance at 415 nm, indicated that the recombinant proteins bound to oxygen and formed active oxyhemoglobin (HbO2). The results indicated that recombinant C. siamensis globins were successfully expressed in prokaryotic system and possessed an activity as ligand binding protein.

An investigation of the antimicrobial and anti-inflammatory activities of crocodile oil

ETHNOPHARMACOLOGICAL RELEVANCE

Crocodile oil has been used by traditional practitioners world-wide to treat microbial infections and inflammatory conditions. However, the scientific rationale behind its use is not completely understood. This study provides an updated fatty acid profile and novel scientific evidence of the antimicrobial and anti-inflammatory properties of crocodile oil, obtained from the Nile crocodile (Crocodylus niloticus), justifying its use by traditional healers.

MATERIALS AND METHODS

The fatty acid content of the oil was determined by gas chromatography and the major fatty acids were identified. A microplate method was used to assess activity of the oil against Staphylococcus aureus, Klebsiella pneumoniae and Candida albicans. The anti-inflammatory activity of the oil was assessed by oral administration and topical application, utilising a mouse model of acute croton oil-induced contact dermatitis.

RESULTS

Sixteen fatty acids were identified with oleic, palmitic and linoleic acid being the major components of the oil. The optimal activity of the oil against the bacteria and fungus was obtained with 15% and 6% (w/v) oil respectively. No significant selectivity was observed against the bacterial species, but Candida albicans was more susceptible. The anti-inflammatory assays showed optimal activity at 3h after the oral administration of oil (60.8±5.5%) and at 12h after topical application (57.5±5.9%). This suggested a short duration of action when the oil was orally administered, and a longer duration of action when it was topically applied.

CONCLUSIONS

Subsequent studies may be directed towards the investigation of the mechanisms of action of the antimicrobial and anti-inflammatory activities of crocodile oil and its fatty acids.

Antibacterial activity of plasma from crocodile (Crocodylus siamensis) against pathogenic bacteria

Background

The Siamese crocodile (Crocodylus siamensis) is a critically endangered species of freshwater crocodiles. Crocodilians live with opportunistic bacterial infection but normally suffer no adverse effects. They are not totally immune to microbial infection, but their resistance thereto is remarkably effective. In this study, crude and purified plasma extracted from the Siamese crocodile were examined for antibacterial activity against clinically isolated, human pathogenic bacterial strains and the related reference strains.

Methods

Crude plasma was prepared from whole blood of the Siamese crocodile by differential sedimentation. The crude plasma was examined for antibacterial activity by the liquid growth inhibition assay. The scanning electron microscopy was performed to confirm the effect of crude crocodile plasma on the cells of Salmonella typhi ATCC 11778. Effect of crude crocodile plasma on cell viability was tested by MTT assay. In addition, the plasma was purified by anion exchange column chromatography with DEAE-Toyopearl 650 M and the purified plasma was tested for antibacterial activity.

Results

Crude plasma was prepared from whole blood of the Siamese crocodile and exhibited substantial antibacterial activities of more than 40% growth inhibition against the six reference strains of Staphylococcus aureus, Salmonella typhi, Escherichia coli, Vibrio cholerae, Pseudomonas aeruginosa, and Staphylococcus epidermidis, and the four clinical isolates of Staphylococcus epidermidis, Pseudomonas aeruginosa, Salmonella typhi, and Vibrio cholerae. Especially, more than 80% growth inhibition was found in the reference strains of Salmonella typhi, Vibrio cholerae, and Staphylococcus epidermidis and in the clinical isolates of Salmonella typhi and Vibrio cholerae. The effect of the crude plasma on bacterial cells of Salmonella typhi, a certain antibacterial material probably penetrates progressively into the cytoplasmic space, perturbing and damaging bacterial membranes. The effect of the crude plasma was not toxic by the yellow tetrazolium bromide (MTT) assay using a macrophage-like cell, RAW 264.7. The pooled four fractions, designated as fractions D1-D4, were obtained by column chromatography, and only fraction D1 showed growth inhibition in the reference strains and the clinical, human pathogenic isolates.

Conclusions

The crude and purified plasma from the Siamese crocodile significantly showed antibacterial activity against pathogenic bacteria and reference strains by damage cell membrane of target bacterial cells. From the MTT assay, the Siamese crocodile plasma was not cytotoxic to the cells.

Sequencing three crocodilian genomes to illuminate the evolution of archosaurs and amniotes

The International Crocodilian Genomes Working Group (ICGWG) will sequence and assemble the American alligator (Alligator mississippiensis), saltwater crocodile (Crocodylus porosus) and Indian gharial (Gavialis gangeticus) genomes. The status of these projects and our planned analyses are described.

Characterization of the novel antibacterial peptide Leucrocin from crocodile (Crocodylus siamensis) white blood cell extracts

Four novel antibacterial peptides, Leucrocin I-IV from Siamese crocodile white blood cell extracts were purified by reverse phase high performance liquid chromatography (RP-HPLC). Leucrocins exhibit strong antibacterial activity towards Staphylococcus epidermidis, Salmonella typhi and Vibrio cholerae. The peptides were 7-10 residues in length with different primary structure. The amino acid sequence of Leucrocin I is NGVQPKY with molecular mass around 806.99 Da and Leucrocin II is NAGSLLSGWG with molecular mass around 956.3 Da. Further, the interaction between peptides and bacterial membranes as part of their killing mechanism was studied by fluorescence and electron microscopy. The outer membrane and cytoplasmic membrane was the target of action of Leucrocins as assayed in model membrane by release of β-galactosidase due to the membrane permeabilization. Finally, the hemolytic effect was tested against human red blood cell. Leucrocin I, III and IV showed less toxicity against human red blood cells than Leucrocin II.

Proteome analysis of the leukocytes from the American alligator (Alligator mississippiensis) using mass spectrometry

Mass spectrometry was used in conjunction with gel electrophoresis and liquid chromatography, to determine peptide sequences from American alligator (Alligator mississippiensis) leukocytes and to identify similar proteins based on homology. The goal of the study was to generate an initial database of proteins related to the alligator immune system. We have adopted a typical proteomics approach for this study. Proteins from leukocyte extracts were separated using two-dimensional gel electrophoresis and the major bands were excised, digested and analyzed by on-line nano-LC MS/MS to generate peptide sequences. The sequences generated were used to identify proteins and characterize their functions. The protein identity and characterization of the protein function were based on matching two or more peptides to the same protein by searching against the NCBI database using MASCOT and Basic Local Alignment Search Tool (BLAST). For those proteins with only one peptide matching, the phylum of the matched protein was considered. Forty-three proteins were identified that exhibit sequence similarities to proteins from other vertebrates. Proteins related to the cytoskeletal system were the most abundant proteins identified. These proteins are known to regulate cell mobility and phagocytosis. Several other peptides were matched to proteins that potentially have immune-related function.

Understanding the vertebrate immune system: insights from the reptilian perspective

Reptiles are ectothermic amniotes, providing the key link between ectothermic anamniotic fishes and amphibians, and endothermic amniotic birds and mammals. A greater understanding of reptilian immunity will provide important insights into the evolutionary history of vertebrate immunity as well as the growing field of eco-immunology. Like mammals, reptile immunity is complex and involves innate, cell-mediated and humoral compartments but, overall, there is considerably less known about immune function in reptiles. We review the current literature on each branch of the reptilian immune system, placing this information in context to other vertebrates. Further, we identify key areas that are prime for research as well as areas that are lagging because of lack of reagents in non-model systems.

Effects of bacterial lipopolysachharide on peripheral leukocytes in the American alligator (Alligator mississippiensis)

Alligators were injected intraperitoneally with four different doses (10, 1.0, 0.1, and 0.01 mg/kg body weight) of a mixture of bacterial lipopolysaccharides (LPS) derived from three different types of bacteria (Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). Injection of the alligators with the LPS mixture resulted in a dose- and time-dependent increase in total peripheral leukocytes Lymphocytes increased at days 3 and 4 post-injection, and decreased back to baseline levels at day 7 for all doses. Alligators that were not treated, and those injected with pyrogen-free saline, did not exhibit statistically significant changes in total leukocytes during the course of the study. Injection of alligators with 0.5 mg LPS/kg body weight derived from one of three bacterial species revealed that the leukocyte increases observed were not statistically different for all three types of LPS. The animals displayed the same increases in total counts and the levels of all circulating leukocyte types were not different between animals treated with a combination of LPS from all three bacterial species.

Characterization of serum complement activity of saltwater (Crocodylus porosus) and freshwater (Crocodylus johnstoni) crocodiles

We employed a spectroscopic assay, based on the hemolysis of sheep red blood cells (SRBCs), to assess the innate immune function of saltwater and freshwater crocodiles in vitro. Incubation of serum from freshwater and saltwater crocodiles with SRBCs resulted in concentration-dependent increases in SRBC hemolysis. The hemolytic activity occurred rapidly, with detectable activity within 2 min and maximum activity at 20 min. These activities, in both crocodilian species, were heat sensitive, unaffected by 20 mM methylamine, and completely inhibited by low concentrations of EDTA, suggesting that the alternative serum complement cascade is responsible for the observed effects. The hemolytic activities of the sera were inhibited by other chelators of divalent metal ions, such as phosphate and citrate. The inhibition of SRBC hemolysis by EDTA could be completely restored by the addition of 10 mM Ca2+ or Mg2+, but not Ba2+, Cu2+ or Fe2+, indicating specificity for these metal ions. The serum complement activities of both crocodilians were temperature-dependent, with peak activities occurring at 25-30 degrees C and reduced activities below 25 degrees C and above 35 degrees C.

Comparisons of innate immune activity of all known living crocodylian species

Serum samples from all twenty-three known living members of the Crocodylia were tested for antibacterial activity against eight bacterial species. These data were used to generate an immune profile for each crocodylian species. Statistical analyses revealed that the three living lineages of crocodylians, Alligatoroidea, Crocodyloidea, and Gavialoidea, were distinguishable by their immunological activities. For instance, species within the Alligatoroidea and Crocodyloidea exhibited remarkable immune activity similarities to others in their own lineages. Comparisons of the members of the different lineages, however, revealed substantial differences in immune profiles. Furthermore, species that are in the same genus were shown to exhibit more immune similarities to each other than to members of other genera within the same family. Finally, our immunological analyses reveal that Tomistoma schlegelii aligns more closely with the Gavialoidea than the Crocodyloidea.

Broad spectrum antimicrobial activity of leukocyte extracts from the American alligator (Alligator mississippiensis)

Leukocytes were isolated from whole blood of wild alligators by differential sedimentation. The leukocytes were disrupted in 5% AcOH and the crude extracts processed by ultrafiltration. The extracts were subjected to solvent exchange (0.1% AcOH) and the fraction that contained macromolecules between 1 and 10 kDa were subjected to further analyses. The acid extracts of the alligator leukocytes exhibited substantial antimycotic activities against six of eight species of Candida yeast tested. In addition, the alligator leukocyte extracts were effective as antimicrobial agents against 10 of 12 bacterial species, and displayed moderate activity against two enveloped viruses (human immunodeficiency virus-1 and herpes simplex virus-1(HF)). Kinetic analyses revealed that the antimycotic effects of the leukocyte extract occurred rapidly, with 64% fungal growth inhibition within 3 min of exposure. The molecule(s) responsible for the antimicrobial activities were sensitive to proteases, heat-stable, acid soluble, and in the 1-10 kDa range. These data suggest that alligator leukocytes express cationic peptides that are responsible for their antimicrobial properties.

Identification of alternative pathway serum complement activity in the blood of the American alligator (Alligator mississippiensis)

Incubation of different dilutions of alligator serum with sheep red blood cells (SRBCs) that had not been sensitized with antibodies resulted in concentration-dependent hemolytic activity. This hemolytic activity was not affected by the presence of ammonium hydroxide and methylamine, known inactivators of the classical complement cascade. However, the hemolytic activities were inhibited by EDTA and salicylaldoxime, indicating that the alternate pathway is primarily responsible for these activities. Immunofixation of electrophoretically-resolved alligator serum proteins with antihuman C3 polyclonal antibodies resulted in detection of a protein antigenically similar to human C3 in alligator serum. SDS-PAGE, followed by Western blot analysis, revealed the presence of two alligator serum proteins with nearly identical molecular weights as human C3alpha and C3beta. SRBC hemolysis and antibacterial activity by alligator serum was significantly reduced in the presence of antihuman C3 antibodies. The hemolytic effect of alligator serum was shown to occur rapidly, with significant activity within 5 min and maximal activity occurring at 15 min. SRBC hemolysis was also temperature-dependent, with reduced activity below 15 degrees C and above 30 degrees C. These data suggest that the antibiotic properties of alligator serum are partially due to the presence of a complement-facilitated humoral immune response analogous to that described in mammalian systems.

Role of divalent metal ions in serum complement activity of the American alligator (Alligator mississippiensis)

Treatment of alligator serum with different concentrations of EDTA resulted in a concentration-dependent inhibition of serum-mediated sheep red blood cell (SRBC) hemolysis. This inhibition of serum-dependent hemolysis was observed for other chelators of divalent metal ions, such as phosphate and citrate. Treatment of alligator serum with 5 mM EDTA completely inhibited SRBC hemolysis, which could be totally restored by the addition of 5 mM Ca(2+) or Mg(2+), but not Cu(2+) or Ba(2+). These data indicate a specific need for Ca(2+) and/or Mg(2+) in the serum-mediated hemolysis of SRBCs. Kinetic analyses revealed that the addition of 30 mM EDTA 1 min after incubation of SRBCs with serum resulted in only 30% inhibition of hemolytic activity. However, addition of EDTA as early as 3 min post-incubation resulted in complete SRBC hemolysis. Pretreatment of serum with EDTA inhibited the hemolytic activity, but the activity could be restored in a time-dependent manner by the addition of Ca(2+)or Mg(2+). These data indicate that, as in human serum, the need for divalent metal ions occurs early in the alligator serum complement cascade.