Kocuria rosea - an overview (2023)

Kocuria rosea and Micrococcus luteus (Table 4.1) are members of the family Micrococcaceae (Actinobacteria).

From: Advances in Applied Microbiology, 2011

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Systems Approaches to Unraveling Nitric Oxide Response Networks in Prokaryotes

Laura R. Jarboe, ... James C. Liao, in Nitric Oxide (Second Edition), 2010

RNS Production and Interaction with Prokaryotes

The inhibitory effect of NO on E. coli was first noted in 1965 (Russell, 1965). Subsequent studies nearly 20 years later expanded the list of NO-sensitive species to include Micrococcus luteus, Micrococcus roseus and Staphylococcus aureus, but opportunistic pathogen Serratia marcescens and several Bacillus species were found to be NO resistant (Mancinelli and McKay, 1983). The NO tolerance displayed by Bacillus is consistent with its denitrification activity (Mevel and Prieur, 2000). In addition to the RNS produced by denitrification, microbes encounter RNS that are produced by a host’s immune system or by nitrite acidification, with the latter two sources being the most relevant to human health.

The mammalian immune system generates micromolar levels of NO (Krieglstein et al., 2001), a concentration that is often sufficient to inhibit microbial growth. NO is enzymatically produced from L-arginine by a variety of nitric oxide synthases (NOS) in plants and mammals, with the mammalian inducible NOS (iNOS) being the most significant enzymatic source of NO for pathogens. While some plants employ an iNOS in their immune arsenal, NO appears to be used as a signal instead of a weapon (Delledonne et al., 1998). NO is produced as an intermediate species during the reduction of nitrate to nitrite (Remde and Conrad, 1991a). During nitrite respiration, microbes are exposed to nanomolar levels of NO generated by nitrite reductase (Goretski et al., 1990; Remde and Conrad, 1991b). Although this low level of NO does not appear to be bacteriostatic, the observed activation of NO detoxification systems by these low levels of NO (Corker and Poole, 2003) implies that the NO-mediated damage is sufficient to justify the cost of NO detoxification. Similarly, nitrite can be reduced to NO and NO+ in highly acidic environments, such as the gastric juices. Organisms attempting to persist/survive in this type of environment, such as Helicobacter pylori (Dykhuizen et al., 1998; Thiele et al., 2005), must be able to cope with the micromolar concentrations of NO produced (McKnight et al., 1997).

One of the hallmarks of NO chemistry is its reactivity with metal groups (Wink et al., 1999). For bacterial species attempting to grow in the presence of NO, this translates to damage of metal-containing proteins. These protein-associated metal groups include, but are not limited to, iron–sulfur [Fe-S] clusters and heme groups. As reviewed in Johnson et al. (2005), [Fe-S]-containing proteins play key roles in metabolic and regulatory processes ranging from amino acid (AA) biosynthesis to the superoxide stress response. Unfortunately, the very properties that underlie their catalytic properties also make them targets for damage by compounds such as RNS and reactive oxygen species (ROS). Still, the sensitivity of these clusters to RNS- and ROS-mediated damage is variable. While E. coli’s branched chain amino acid (BCAA) biosynthesis protein dihydroxyacid dehydratase is particularly sensitive to damage from NO (Hyduke et al., 2007) and superoxide (Flint et al., 1993), other Fe-S-containing enzymes, such as the spinach dihydroxyacid dehydratase, are robust to damage from superoxide (Flint et al., 1993). Eukaryotic soluble guanylate cyclase (sGC) is the most well characterized heme-containing NO target, and a prokaryotic counterpart with femtomolar sensitivity to NO was found in Clostridium botulinum, the causative organism of botulism (Nioche et al., 2004). Bacterial species often exploit the vulnerability of these metal groups and use them as sensors, such as the Fe-S cluster in NsrR (Yuki et al., 2008), the non-heme iron center of NorR (D’Autreaux et al., 2005), and the heme group in Paracoccus denitrificans NO reductase regulator NNR (Lee et al., 2006).

As opposed to the metal reactivity of NO, nitrosothiols are noted for their reactivity with thiol groups (Hogg, 2002). This reactivity can inhibit bacterial growth by damaging enzymatic cysteine residues (Wink et al., 1994) or by reacting with and depleting free cysteine or homocysteine (Jarboe et al., 2008).

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(Video) Kocuria rhizophilia


M. Nuñez, in Encyclopedia of Food Microbiology (Second Edition), 2014

Taxonomic Status of Micrococcus and Micrococcaceae

Bacteria belonging to the genus Micrococcus are Gram-positive, spherical, 0.5–2.0 μm in diameter, nonsporing, and seldom motile. They occur in pairs, tetrads, or irregular clusters, not in chains. They are strictly aerobic, chemoorganotrophs, with a respiratory metabolism, and generally produce little or no acid from carbohydrates. They are catalase positive and often oxidase positive, although weakly. They contain cytochromes and are resistant to lysostaphin. They form colonies usually pigmented in shades of yellow or red. They grow on simple media and are usually halotolerant, able to grow with 5% NaCl. Their optimum temperature generally ranges from 25 to 37 °C. Their G+C content of DNA ranges from 64 to 75 mol%.

Micrococcus traditionally has been included in the Micrococcaceae family, together with the genera Staphylococcus, Stomatococcus, and Planococcus of aerobic and facultative anaerobic Gram-positive, catalase-positive cocci. However, a higher 5S rRNA sequence similarity of Micrococcus luteus strains ATCC 9341 and ATCC 4698 with Streptomyces griseus 45-H than with Staphylococcus epidermidis strain ATCC 14990 and Staphylococcus aureus strain Smith was found. According to some authors, Streptomyces and Micrococcus, characterized by a high genomic G+C content, emerged from the Gram-positive bacterial stem at an early time during bacterial evolution, and their unique 5S rRNA secondary structure is closer to the Gram-negative type than to the Gram-positive type.

A new genus, Macrococcus, was proposed in 1998 within the Micrococcaceae family on the basis of a phylogenetic analysis comparing 16S rRNA sequences, DNA–DNA liquid hybridization, DNA base composition, normalized ribotype patterns, macrorestriction pattern analysis, and estimation of genome size using pulsed field gel electrophoresis (PFGE) cell wall composition, phenotypic characteristics, and plasmid profiles. Compared with members of the genus Staphylococcus, their closest relatives, Macrococcus showed lower 16S rRNA sequence similarities (93.4–95.3%), higher G+C content in the DNA (38–45 mol%), absence of cell wall teichoic acids, with the possible exception of Micrococcus caseolyticus, unique ribotype pattern types and macrorestriction patterns, smaller genome size, of approximately 1500–1800 kb, and generally larger Gram-stained cell size, of 1.1–2.5 μm in diameter. The new genus is integrated by the four species M. caseolyticus (formerly Staphylococcus caseolyticus), Micrococcus bovicus, Micrococcus equipercicus, and Micrococcus carouselicus.

Nine species of Micrococcus, Micrococcus agilis, Micrococcus halobius, Micrococcus kristinae, M. luteus, Micrococcus lylae, Micrococcus nishinomiyaensis, Micrococcus roseus, Micrococcus sedentarius, and Micrococcus varians were recognized until 1995. Data on the G+C content of the DNA, fatty and mycolic acid patterns, peptidoglycan type, and 16S rDNA sequences revealed large heterogeneity within this genus. Consequently, strains previously identified as belonging to seven species of Micrococcus were transferred to genera Arthrobacter, Dermacoccus gen. nov., Kocuria gen. nov., Kytococcus gen. nov., and Nesterenkonia gen. nov. Thus, M. agilis, which grows best at 22–25 °C, has been renamed as Arthrobacter agilis; M. nishinomiyaensis as Dermacoccus nishinomiyaensis; M. kristinae, M. roseus, and M. varians as Kocuria kristinae, Kocuria rosea, and Kocuria varians, respectively; M. sedentarius as Kytococcus sedentarius; and M. halobius, which requires 5% NaCl in the culture medium, as Nesterenkonia halobia. Currently, only two species, M. luteus and M. lylae, remain in the genus Micrococcus.

After these changes, a new description of the genus Micrococcus (Cohn, 1872; Stackebrandt et al., 1995) was given, as follows: Micrococcus cells are spherical and nonmotile; endospores are nonformed, Gram-positive, and aerobic; chemoorganotrophic; metabolism is strictly respiratory; catalase and oxidase positive; and mesophilic and nonhalophilic. The peptidoglycan contains l-lysine as the diagnostic amino acid. The peptidoglycan variation is either A2, with the interpeptide bridge consisting of a peptide subunit, or A4α. The predominant menaquinones are either MK-8 and MK-8(H2) or MK-8(H2); MK-7 or MK-7(H2) and MK-9(H2) occur in minor amounts. The cytochromes are cytochromes aa3, b557, b567, and d626; cytochromes c550, c551, b563, b564, and b567 may be present. Mycolic acids and teichoic acids are absent; teichuronic acids may be present. Mannosamine-uronic acid may be present as an amino sugar in the cell wall polysaccharide. Cellular fatty acids are iso- and anteiso-branched fatty acids, with anteiso-C15:0 and iso-C15:0 predominating. Polar lipids are phosphatidylglycerol, diphosphatidylglycerol, and unknown ninhydrin-negative phospholipids and glycolipids; phosphatidylinositol may be present. The major aliphatic hydrocarbons (br-Δ-C) are C27 to C29 hydrocarbons. The G+C content of the DNA is 69–76 mol% (as determined by the Tm method). The primary habitat is mammalian skin. The type species is M. luteus (Schroeter; Cohn, 1872).

Emended descriptions of the genus Micrococcus and the species M. luteus and M. lylae were given in 2002, on the basis of a polyphasic approach to the classification of nine yellow-pigmented, spherical bacterial strains isolated from various sources. In addition to the properties given in the 1995 genus description, members of the genus Micrococcus show several common characteristics. Growth occurs up to pH 10. The polar lipids are phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, an unknown glycolipid, and an unknown ninhydrin-negative phospholipid. l-arabinose, p-arbutin, d-cellobiose, d-galactose, d-melibiose, d-ribose, and salicin are not assimilated. Members of the genus share the Micrococcaceae-specific signature nucleotides at positions 293–304, 610, 598, 615–625, 1025–1036, 1026–1035, 1265–1270, and 1278 of the 16S rRNA gene sequence (Escherichia coli numbering) and lack the signature nucleotides at positions 640, 839–847, and 859. The description of M. luteus and M. lylae also was emended, and M. luteus was dissected into three biovars, distinguishable by chemotaxonomic and biochemical traits: biovar I, represented by M. luteus DSM 20030T; biovar II, represented by M. luteus DSM 14234, and biovar III, represented by M. luteus DSM 14235.

In spite of these taxonomic studies, however, the nine species M. agilis, M. halobius, M. kristinae, M. luteus, M. lylae, M. nishinomiyaensis, M. roseus, M. sedentarius, and M. varians were still recognized in 2006 in the handbook The Prokaryotes, which included a scheme for the differentiation of these species based on physiological and chemotaxonomic characteristics.

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Biological Warfare of the Spiny Plant

Malka Halpern, ... Simcha Lev-Yadun, in Advances in Applied Microbiology, 2011

A The microflora of spines versus photosynthetic leaf parts

To understand whether spines are a different habitat than green photosynthetic leaf surfaces when it comes to the microbial flora, we compared the microbial communities of the phyllosphere on spines to the photosynthetic leaf surfaces of the palm tree W. filifera (unpublished study). Cotton palm trees have a single straight stem that can reach more than 20m in height and are usually 40–70cm in diameter (Fig. 4.2A). The petioles, which may reach more than 1m in length, usually have two rows of sharp spines along their right and left margins (Fig. 4.2C). Every cotton palm tree carries thousands of colorful aposematic spines. The spines may be straight, curved, or recurved and are yellow, orange, or brown in color depending on leaf age and individual tree characteristics, and a panel of the same color connects them along the edge of the petioles, enhancing spine conspicuousness.

Spines and green photosynthetic leaf surfaces (Fig. 4.1B and C) were sampled from different trees in Northern Israel in December 2008, March 2009, May 2009, and June 2009 (unpublished). Using culturable methods, we isolated and identified a total of 97 bacterial isolates (accession numbers HM163472–HM163568), which were then classified as pathogens or nonpathogens according to the scientific literature records. Fifteen pathogenic species were identified from spines, and 18 pathogenic species were identified from the green photosynthetic leaf surfaces (Table 4.1, columns 5 and 6). The following pathogenic or opportunistic pathogenic bacteria—Pantoea brenneri, Pseudomonas stutzeri, Acinetobacter johnsonii, Acinetobacter lwoffii, Clostridium sordellii, Bacillus anthracis, Staphylococcus hominis subsp. hominis, and Kocuria rosea—were isolated only from W. filifera spines and were not identified on green photosynthetic leaf surfaces (Table 4.1). In sum (including the nonpathogenic species), 28 bacterial species were found on the spines and 36 species on the green photosynthetic leaf surfaces. Out of these, 11 species were found on both the spines and green photosynthetic leaf surfaces. This data was used to calculate Sorensen's relatedness index (values are between 0 and 1.0; Wolda, 1981). The similarity between the bacterial flora on green photosynthetic leaf surfaces and spines according to Sorensen's index was 0.343, indicating that the microflora of the spines in cotton palms is different from that of the green photosynthetic leaf surfaces. Thus, the microbe–spine combination seems to be an important factor in the common evolution of the aposematic coloration of spiny, thorny, and prickly plants. Hence, bacteria that inhabit spines or thorns in plants seem to have enhanced the common, convergent evolution of aposematism in these organisms.

When specific pathogenic bacterial species are more common or more diverse on spines, thorns, and prickles than on photosynthetic surfaces, this is a good indication for an evolutionary development in which specific plant surfaces change to host pathogenic bacteria on its sharp defensive appendages. Even if such differences in the composition of pathogenic bacterial species will be found, the coevolution of spiny plants and bacteria will not be proven yet: The selection of surface characteristics that enhance the ability of specific bacteria species to exist may have occurred only in the plant partner, thus not establishing coevolutionary relations. However, if variations that cause a better adaptation of the bacteria to the thorn habitat than to the photosynthetic leaf surfaces can be observed in specific pathogenic bacterial species, this will indicate an established coevolutionary relation (e.g., production of molecules that result in a better adhesion of the bacteria to the thorns than to leaf surfaces). Theoretically, sharp appendages provide better opportunities for bacterial insertion into live animal tissues. Thus, bacteria that are able to exploit live internal animal tissues are expected to have evolved adaptations toward inhabiting sharp appendages (in plants and animals). For instance, Pantoea agglomerans was isolated from thorns (Table 4.1) and at the same time has been proven to cause infections via thorns, spines, or prickles (Table 4.2). This bacterium may have coevolved with palm spines to deter herbivores. However, the whole issue of surface characteristics (chemical and physical) of defensive sharp appendages as a potential advantageous habitat for pathogenic bacteria, fungi, and viruses has never been addressed systematically.

Table 4.2. Evidence from the literature indicating microbial infections after thorn injury

Microorganism speciesExamples for thorn sourceReferences
Pantoea agglomeransPalm spine, Rose prickle, Lemon tree thorn, Hawthorn thornCruz et al. (2007), De Champs et al. (2000), Duerinckx (2008), Flatauer and Khan (1978), Harris (2010), Kratz et al., 2003, Vincent and Szabo (1988), Ulloa-Gutierrez et al. (2004)
Enterobacter cloacaeRose prickle, Hawthorn thornCengiz et al. (2005), Harris (2010)
Serratia fonticolaHawthorn thornGorret et al. (2009)
Pseudomonas aeroginosaVidyadhara and Rao (2006)
C. tetaniRose prickleErgonul et al. (2003), Hodes and Teferedegne (1990), Pascual et al. (2003)
Staphylococcus aureusPalm spineCahill and King (1984), Vidyadhara and Rao (2006)
Mycobacterium marinumCactus spineMcManigal and Henderson (1986)
Gordona terraeNABakker et al. (2004)
Fusarium solaniRose prickleKantarcioglu et al. (2010)
Fonsecaea pedrosoiMimosa pudica spineLópez-Martínez and Méndez-Tovar (2007), Salgado et al. (2004)
Cladophialophora carrioniiNALópez-Martínez and Méndez-Tovar (2007), Son et al. (2010)
Sporothrix schenckiiRose prickleEngle et al. (2007), Haldar et al. (2007), Ware et al. (1999)
Candida parapsilosisRose prickleTurkal and Baumgardner (1995)

NA, The source of the thorn injury is not available.

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Artocarpus: A review of its traditional uses, phytochemistry and pharmacology

U.B. Jagtap, V.A. Bapat, in Journal of Ethnopharmacology, 2010

The crude methanolic extracts of the stem and root barks, stem and root heart wood, leaves, fruits and seeds of Artocarpus heterophyllus and their subsequent partitioning with petrol, dichloromethane, ethyl acetate and butanol gave fractions that exhibited a broad spectrum antibacterial activity against Bacillus cereus, Bacillus coagulans, Bacillus megaterium, Bacillus subtilis, Lactobacillus casei, Micrococcus luteus, Micrococcus roseus, Staphylococcus albus, Staphylococcus aurens, Staphylococcus epidermidis, Streptococcus faecalis, Streptococcus pneumoniae, Agrobacterium tumaefaciens, Citrobacter freundii, Enterobacter aerogenes, Escherichia coli, Klebsiella pneumonia, Neisseria gonorrhoeae, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella typhi, Salmonella typhimurium, Serratia marcescens, Trichomonas vaginalis. The butanol fractions (concentration 4mg/disc) of root bark and fruits of Artocarpus heterophyllus were found to be more active and have been examined by disc diffusion methods (Khan et al., 2003). The methanolic plant extract consists of two active isoprenyl flavones artocarpin and artocarpesin were isolated from Artocarpus heterophyllus. These inhibited the growth of primary cariogenic bacteria at concentration of 3.13–12.5μg/ml and also exhibited the growth inhibitory effects on plaque-forming Streptococci. This finding showed that phytochemicals from Artocarpus heterophyllus would be potent compounds for the prevention of dental caries (Sato et al., 1996). The artonin E has been isolated from the bark of Artocarpus rigida Blume The artonin E (concentration 250μg/disc) showed antimicrobial activity against Escherichia coli and Bacillus subtilis produced clear zone with a diameter of 1.2 and 0.9cm, respectively, while the standard used the canamycin sulphate (concentration 240μg/disc) produced clear zone with a diameter of 2.2cm. Therefore this compound has possibility to be used as an antibiotic (Suhartati et al., 2008).

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An overview of the traditional use, phytochemistry, and biological activity of the genus Homalanthus

Dyke Gita Wirasisya, Judit Hohmann, in Fitoterapia, 2023

(Video) How To Say Rosea

6 Biological activities

Several biological assays have been carried out to support the ethnomedicinal claims of Homalanthus species. The biological assays conducted were in vitro, together with three in vivo assays focusing on H. acuminatus, H. nervosus, H. nutans, H. novoguineensis, and H. populneus. Among the Homalanthus species, H. nutans and H. nervosus are the most explored ones. Table 4 summarizes the biological activities of the genus.

6.1 Antibacterial and anti-protozoal activity

H. nutans and H. nervosus were tested for their in vitro antibacterial activity. The antibacterial effects of these species were mainly demonstrated in gram-positive bacteria. The ethanolic extract of the leaves of H. nutans was tested on bacterial pathogens associated with infected skin injuries, and this extract has been proven to inhibit the growth of Pseudomonas aeruginosa and clinical isolates of Staphylococcus aureus at a minimum inhibitory concentration (MIC) of 4μg/mL [70]. In another study, ethanol extracts and their petroleum ether, dichloromethane, and ethyl-acetate fractions prepared from leaves, stem, and root barks of H. nervosus were tested against 13 gram-positive and 12gram-negative bacteria and against the protozoa Trichomonas vaginalis by disk diffusion method [71]. The ethyl-acetate fraction of H. nervosus at 4mg/disk had better activity than the positive control chloramphenicol against Micrococcus roseus, Staphylococcus epidermidis, Streptococcus faecalis, Klebsiella pneumoniae, and Serratia marcescens. The ethyl-acetate fraction of H. nervosus was found to have anti-protozoal activity against Trichomonas vaginalis; the activities of the leaf and root bark extracts were comparable to that of chloramphenicol [71].

The antibacterial activity from H. nervosus might be due to the existence of sterol and flavonoids. It was reported that stigmasterol (6) isolated from the stem bark of Phyllanthus columnaris shows antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) through modulation of genes that lead the interference of bacterial growth [72]. Stigmasterol was found to downregulate several genes that are involved in the biosynthesis of aminoacyl-tRNA (lysA and thrS), protein translation (tsf and tuf), RNA polymerase translation (rpoA and rpoB), and 43 genes that encoded the translation of ribosomal protein [72]. Hyperoside (10) and kaempferol 3-O-β-glucoside (11) can also contribute to the antibacterial activity by directly damaging the bacterial membrane [73]. However, antimicrobial mechanism of action of other compounds has not yet been elucidated.

6.2 Antiviral and HIV anti-latency activities

The antiviral activity of prostratin (5) was discovered in an experiment performed on H. nutans, although this compound was first isolated from Pimelea prostrata (strathmore weed), a small endemic shrub from New Zealand [17,62]. The leaves of H. nutans in the form of water infusions have been used by the Samoan healers to treat back pain, abdominal swelling, and circumcision wounds, while the root infusion was used to suppress diarrhea and as an analgesic, and stem woods were prepared to treat yellow fever (Table 2). Starting from the traditional medicine knowledge, the extracts of H. nutans was investigated in vitro for antiviral activity by tetrazolium-based assay, and the inhibition of cytopathic effects of human immunodeficiency virus (HIV-1) was detected. Prostratin (5) was isolated from the active extract by using a bioassay to monitor the HIV-1 cytopathic effect. This compound was found to be capable of preventing the reproduction of HIV-1 in lymphocytic and monocytoid target cells at noncytotoxic concentrations (from 20.1 to >25μM) and completely protecting susceptible cells from the lytic effects of HIV-1. Its cytoprotective concentration was ≥11μM that essentially stopped virus reproduction in the studied cell lines [17].

Furthermore, it was interesting to test if prostratin (5) as a phorbol derivative is able to bind to protein kinase C (PKC) and either activate or inhibit it. In vitro experiments have showed that prostratin (5) binds to and activates protein kinase C in CEM-SS cells and causes additional biochemical reactions in C3H10T1/2 cells that are typical of phorbol esters [17]. Prostratin (5) is also capable of inhibiting de novo HIV infection most likely as it induces the downregulation of HIV receptors from the surface of target cells. This compound blocks HIV infection by downregulating the HIV cellular entry receptors CD4 and CXCR4 [74]. Prostratin (5) shares structural similarities with phorbol esters, which are known to promote tumor growth, but it was found to have no tumor-promoting properties [17].

Prostratin (5) was reported to be able to upregulate viral expression from latent provirus. Latently infected cells serve as a constant source of viral reactivation; hence, this discovery was significant. The persistence of latently infected cellular reservoirs constitutes the principal obstacle to virus eradication with highly active anti-retroviral therapy. It was demonstrated that prostratin (5) effectively activate HIV-1 gene expression in the latently infected cells and activate nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and c-Jun N-terminal kinase and extracellular signal-regulated kinase pathways [75,76].

It was found by Brown et al. in 2005 that prostratin (5) induces the immediate–early, early, and late gene expression of Kaposi's sarcoma-associated herpesvirus (KSHV) in two lymphoma cell lines in vitro [77].

The extract of the tropical rainforest tree H. acuminatus was found to be active in the NCI AIDS-antiviral screen. A diterpene isolated from the extract, ent-3S-hydroxy-atis-16(17)-en-1,4-dione (1) was effective in the anti-HIV screen made by XTT-tetrazolium assay. It showed a maximum of 50% protection to HIV-infected cells at a concentration of 6μg/mL, and it was noncytotoxic to uninfected control cells. However, in a higher concentration (12μg/mL), cytotoxic effects increased in both control and HIV-infected cells; therefore this compound was not selected for further development [44].

A study by Sintya et al. aimed to analyze the effect of the extract of H. populneus on the expression of CD4 and CD8, both of which are critical components of the body's HIV defense system. The expressions of Gp41 and Gp120 were analyzed by using talicytometry and an enzyme-linked immunosorbent assay, respectively, to examine the impact of the extract on HIV-1. It was revealed that the extract of H. populneus decreased the expression of CD4 receptor in both T-lymphoblast cell line and peripheral blood mononuclear cell (PBMC) (CEM). On the other hand, this extract increased the expression of PBMC CD8, and it was able to lower the proportion of the proteins gp41 and gp120 in CEM cultures [78].

6.3 Other biological activities

As part of a study, the wound-healing properties of plants used in traditional Samoan medicine, including H. nutans (mentioned as Omalanthus), was investigated in vitro by Frankova et al. on the proliferation and migration of human dermal fibroblasts. It was demonstrated that H. nutans extract significantly stimulates cell migration to the wound area [70]. The wound-healing mechanism is closely related to the activation of NF-κB. The activation of NF-κB will trigger the release of pro-inflammatory cytokines, including IL-10 and IL-13, that stimulate tissue repair [79]. Prostratin (5) has been reported to stimulate IKK-dependent phosphorylation leading to the activation of NF-κB [80]. A fascinating in vivo experiment investigating the regeneration of Xenopus laevis tadpole tail was done by Bishop et al. A significant percentage of amputated tadpoles were able to regenerate after 30min of incubation in 10μM of prostratin compared to vehicle control [81].

The only compound isolated from H. nutans was prostratin (5). However, its mechanism on cell migration has not yet been reported. Nevertheless, another tigliane diterpene (12-tigloyl-13-(2-methylbutanoyl)-6,7-epoxy-4,5,9,12,13,20-hexahydroxy-1-tigliane-3-one) was reported to possess the ability to enhance keratinocyte migration and wound repopulation via PKC activation [82].

Bourdy et al. studied five plant species that were used in the traditional medicine of Vanuatu (Melanesia) for the purposes relating to human reproduction. H. nutans was involved in this study because its fruits were applied traditionally as abortifacients. The infusions of the plant materials were assayed for estrogenic effects in vivo and oxytocic activities on isolated rat uterus in vitro. The extract of H. nutans prepared from fresh plant exhibited no estrogenic activity, but it was effective in the oxytocic test at a concentration of 2.5×10−3g/mL [83]. This study of oxytocic activity confirmed the ethnobotanical use of the plant as a powerful abortifacient. However, the compounds responsible for this activity were not identified yet.

In the study by Nick et al., medicinal plants used in the traditional medicine of Papua New Guinea were analyzed for bioactivities. Seventeen species were tested, including H. nervosus and H. novoguineensis, for PKC and tyrosine-specific protein kinase (PTK) of epidermal growth factor receptor activities in vitro. The methanolic extract of H. nervosus and H. novoguineensis were demonstrated to have high PKC inhibitory activities with IC50 values of 10 and 17μg/mL, respectively. The predominance of activity in the methanolic extracts could be due to the presence of ubiquitous, hydroxylated flavones, known as inhibitors of protein kinases. Accordingly, in this assay, the dichloromethane and petroleum ether extracts, which do not contain such compounds, were inactive. The methanolic extract of H. nervosus moderately inhibited PTK; 42% inhibition was shown at a concentration of 50μg/mL [84]. Molluscicidal activities of H. nervosus and H. novoguineensis extracts were also tested, but both were inactive in this assay [84].

6.4 Toxicity

Three species (H. nutans, H. nervosus, and H. novoguineensis) have been reported for their moderate to high toxic activities. The methanol extracts from the leaves and flower of H. novoguineensis have been reported to be highly toxic against Artemia salina (LC50 6μg/mL). Highly toxic properties of the methanolic and petroleum ether extracts of H. nervosus sap (LC50 44μg/mL for both) in the brine shrimp test were observed [84]. The methanolic extract from the leaves of H. nutans had demonstrated moderate cytotoxicity against human dermal adult fibroblast cells with an IC50 value of 69.94±2.08μg/mL [70].

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