Antimicrobial macrozones interact with biological macromolecules via two-site binding mode of action: Fluorimetric, NMR and docking studies.

Macrozones are novel conjugates of azithromycin and thiosemicarbazones, which exhibit very good in vitro antibacterial activities against susceptible and some resistant bacterial strains thus showing a potential for further development. A combination of spectrometric (fluorimetry, STD and WaterLOGSY NMR) and molecular docking studies provided insights into atomic details of interactions between selected macrozones and biological receptors such as E. coli ribosome and bovine serum albumin. Fluorimetric measurements revealed binding constants in the micro-molar range while NMR experiments provided data on binding epitopes. It has been demonstrated that both STD and WaterLOGSY gave comparable and consistent results unveiling atoms in intimate contacts with biological receptors. Docking studies pointed towards main interactions between macrozones and E. coli ribosome which included specific π - π stacking and hydrogen bonding interactions with thiosemicarbazone part extending down the ribosome exit tunnel. The results of the docking experiments were in fine correlation with those obtained by NMR and fluorimetry. Our investigation pointed towards a two-site binding mechanism of interactions between macrozones and E. coli ribosome which is the most probable reason for their activity against azithromycin-resistant strains. Much better activity of macrozone-nickel coordinated compound against E. coli ribosome compared to other macrozones has been attributed to the higher polarity which enabled better bacterial membrane penetration and binding of the two thiosemicarbazone units thus additionally contributing to the overall binding energy. The knowledge gained in this study should play an important role in anti-infective macrolide design in the future.

Azithromycin-loaded liposomes and niosomes for the treatment of skin infections: Influence of excipients and preparative methods on the functional properties.

The aim of this study was to develop azithromycin (AZT)-loaded liposomes (LP) and niosomes (NS) useful for the treatment of bacterial skin infections and acne. LP based on phosphatidylcholine from egg yolk (EPC) or from soybean lecithin (SPC), and NS composed of sorbitan monopalmitate (Span 40) or sorbitan monostearate (Span 60) were prepared through the thin film hydration (TFH) and the ethanol injection (EI) methods. The formulations were subsequently characterized for their physico-chemical and functional properties. Vesicles prepared through TFH showed higher average sizes than the corresponding formulations obtained by EI. All the vesicles presented adequate encapsulation efficiency and a negative ζ potential, which assured good stability during the storage period (except for LP-SPC). Formulations prepared with TFH showed a more prolonged AZT release than those prepared through EI, due to their lower surface area and multilamellar structure, as confirmed by atomic force microscopy nanomechanical characterization. Finally, among all the formulations, NS-Span 40-TFH and LP-EPC-TFH allowed the highest drug accumulation in the skin, retained the antimicrobial activity and did not alter fibroblast metabolism and viability. Overall, they could ensure to minimize the dosing and the administration frequency, thus representing promising candidates for the treatment of bacterial skin infections and acne.

Poly(sebacic acid) microparticles loaded with azithromycin as potential pulmonary drug delivery system: Physicochemical properties, antibacterial behavior, and cytocompatibility studies.

Recurrent bacterial infections are a common cause of death for patients with cystic fibrosis and chronic obstructive pulmonary disease. Herein, we present the development of the degradable poly(sebacic acid) (PSA) microparticles loaded with different concentrations of azithromycin (AZ) as a potential powder formulation to deliver AZ locally to the lungs. We characterized microparticle size, morphology, zeta potential, encapsulation efficiency, interaction PSA with AZ and degradation profile in phosphate buffered saline (PBS). The antibacterial properties were evaluated using the Kirby-Bauer method against Staphylococcus aureus. Potential cytotoxicity was evaluated in BEAS-2B and A549 lung epithelial cells by the resazurin reduction assay and live/dead staining. The results show that microparticles are spherical and their size, being in the range of 1-5 µm, should be optimal for pulmonary delivery. The AZ encapsulation efficiency is nearly 100 % for all types of microparticles. The microparticles degradation rate is relatively fast - after 24 h their mass decreased by around 50 %. The antibacterial test showed that released AZ was able to successfully inhibit bacteria growth. The cytotoxicity test showed that the safe concentration of both unloaded and AZ-loaded microparticles was equal to 50 µg/ml. Thus, appropriate physicochemical properties, controlled degradation and drug release, cytocompatibility, and antibacterial behavior showed that our microparticles may be promising for the local treatment of lung infections.

Azithromycin inhibits glioblastoma angiogenesis in mice via inducing mitochondrial dysfunction and oxidative stress.

The poor outcomes in glioblastoma (GBM) necessitate new treatments. As GBM is highly vascularized and its growth is largely dependent on angiogenesis, angiogenesis inhibitors have been hotly evaluated in clinical trials for GBM treatment for the last decade. In line with these efforts, our work reveals that azithromycin, a clinically available antibiotic, is a novel angiogenesis inhibitor. Azithromycin inhibits vessel structure formation on Matrigel of GBM-derived endothelial cell (ECs) and other types of ECs. Time course analysis shows that azithromycin interferes with the early stage of angiogenesis. Azithromycin also inhibits GBM-derived EC adhesion, growth and survival but not migration. The transgenic zebrafish Tg (fli1a: EGFP) model clearly shows that azithromycin inhibits angiogenesis in vivo. Of note, azithromycin at non-toxic dose inhibits GBM growth in mice and increases overall survival, and furthermore, this is associated with angiogenesis inhibition. Mechanism studies show that azithromycin decreases mitochondrial respiration by suppressing the activity of multiple complexes, leading to ATP reduction, oxidative stress and damage. In addition, oxidative stress induced by azithromycin is through thiol redox-mediated pathways. Our work demonstrates the anti-angiogenic activity of azithromycin via inducing mitochondrial dysfunction and oxidative stress. Our pre-clinical evidence provides a rationale for initiating clinical trials using azithromycin in combination with standard-of-care drugs for GBM patients.

Azithromycin Mechanisms of Action in CRS Include Epithelial Barrier Restoration and Type 1 Inflammation Reduction.

OBJECTIVE: Previous in vitro transcriptomic profiling suggests azithromycin exerts its effects in patients with chronic rhinosinusitis (CRS) via modulation of type 1 inflammation and restoration of epithelial barrier function. We wished to verify these postulated effects using in vitro models of epithelial repair and in vivo transcriptional profiling. STUDY DESIGN: Functional effects of azithromycin in CRS were verified using in vitro models of wounding. The mechanism of the effect of azithromycin was assessed in vivo using transcriptomic profiling. SETTING: Academic medical center. METHODS: Effects of azithromycin on the speed of epithelial repair were verified in a wounding model using primary nasal epithelial cells (pNEC) from CRS patients. Nasal brushings collected pre-and posttreatment during a placebo-controlled trial of azithromycin for CRS patients unresponsive to surgery underwent transcriptomic profiling to identify implicated pathways. RESULTS: Administration of azithromycin improved the wound healing rates in CRS pNECs and prevented the negative effect of Staphylococcus aureus on epithelial repair. In vivo, response to azithromycin was associated with downregulation in pathways of type 1 inflammation, and upregulation of pathways implicated in the restoration of the cell cycle. CONCLUSION: Restoration of healthy epithelial function may represent a major mode of action of azithromycin in CRS. In vitro models show enhanced epithelial repair, while in vivo transcriptomics shows downregulation of pathways type 1 inflammation accompanied by upregulation of DNA repair and cell-cycle pathways. The maximal effect in patients with high levels of type 1-enhanced inflammation suggests that azithromycin may represent a novel therapeutic option for surgery-unresponsive CRS patients.

Novel silk protein/hyaluronic acid hydrogel loaded with azithromycin as an immunomodulatory barrier to prevent postoperative adhesions.

Peritoneal adhesions, a common postoperative complication of laparotomy, are still treated with physical barriers, but their efficacy and ease of use are controversial. In this paper, we developed a wound microenvironment-responsive hydrogel composed of Antheraea pernyi silk protein (ASF) from wild cocoons and tyramine-modified hyaluronic acid (HA-Ph) loaded with azithromycin (AZI), glucose oxidase (GOX), and horseradish peroxidase (HRP). In addition, GOX-catalyzed oxygen production enhanced the antibacterial ability of the hydrogel. Moreover, the drug-loaded hydrogel increased macrophage CD206 expression while decreasing IL-6 and TNF-α expression. More importantly, the retarding effect of this novel hydrogel system on AZI almost eliminated the appearance of postoperative adhesions in rats. It was also found that the novel hydrogel enhanced the modulation of the TLR-4/Myd88/NF-κB pathway and TGF-ß/Smad2/3 pathway by azithromycin in the locally damaged peritoneum of rats, which accelerated the remodeling of damaged tissues and dramatically reduced the deposition of collagen. Therefore, spraying the novel drug-loaded hydrogel on postoperative abdominal wounds can effectively inhibit the formation of postoperative adhesions.

Azithromycin suppresses TGF-ß1-related epithelial-mesenchymal transition in airway epithelial cells via targeting RACK1.

Transforming growth factor-ß1 (TGF-ß1) associated epithelial-mesenchymal transition (EMT) contributes to multiple respiration diseases via Smad or MAPKs pathway. Our previous study has demonstrated that the typical macrolide antibiotic, azithromycin (AZM) played a notable anti-EMT role in ovalbumin (OVA)-challenged mice. However, the precise mechanism of AZM on TGF-ß1 mediated EMT in bronchial epithelial cells is still unclear. The purpose of this study was to elucidate whether azithromycin targeting RACK1 inhibits TGF-ß1 mediated EMT in vitro. The results showed that AZM significantly inhibited the expression of RACK1 and the activation of the downstream JNK, ERK, and Smad3 signaling pathways, thereby suppressing the migration of bronchial epithelial cells and reversing the TGF-ß1-induced EMT. The effect of AZM on TGF-ß1 mediated EMT in vitro is dependent on the dose of AZM. Although RACK1 has been shown to regulate IRE1α expression with siRACK1 transfection, there was no direct interaction between IRE1α and AZM. On the contrary, weak interaction between AZM and RACK1 was predicted with molecular docking. In summary, AZM targets RACK1 to trigger downstream JNK, ERK, and Smad3 signaling pathways and is an effective anti-EMT drug for bronchial epithelial cells in a dose-dependent manner.

Combination effect of azithromycin with TCM preparation Xiyanping injection against Klebsiella pneumoniae infection in rats.

BACKGROUND: Klebsiella pneumoniae is known as one of the most principal opportunistic human pathogens. Although antibiotics such as the first-line agent azithromycin (AZM) usually are efficient for the treatment of K. pneumonia-related infections, growing threat from antibiotic resistance has become a major challenge. Various preparations based on traditional Chinese medicine (TCM) clinical experience have been developed to help combat such a global public health threat, including Xiyanping injection (XYP) that is made from the natural product andrographolide with potent heat-clearing and toxin-resolving functions. PURPOSE: The present study aimed to demonstrate the therapeutic potential, as well as the action of mechanism of AZM in combination with XYP against K. pneumonia infection in rats. METHODS: Pneumonia model of K. pneumoniae infection in rats was established and subjected to various treatments. The lung histopathological lesions were evaluated. ELISA and Griess techniques were used to determine the level of crucial cytokines. The protein expressions of MAPKs and NF-κB pathways were analyzed by Western blotting. RESULTS: The combination in vivo could significantly inhibit the proliferation of K. pneumoniae in lung, improve the pathological changes of lung and reduce inflammatory factors in lung homogenate and bronchoalveolar lavage fluid, mainly by inactivating MAPKs and NF-κB signaling pathways. Combination therapy caused one-fold increase in apparent distribution volume of AZM in rats after multiple dosing, along with a significant increase of AZM level in lungs but obvious decrease in livers. CONCLUSION: The combination therapy of AZM and XYP showed increased antibacterial and anti-inflammatory properties, indicating that it might be used to treat K. pneumoniae infection.

Azithromycin Protects Oligodendrocyte Progenitor Cells against Lipopolysaccharide-Activated Microglia-Induced Damage.

Oligodendrocyte progenitor cells (OPC) are the primary cellular targets of brain white matter injury (WMI) in very low-birth weight (VLBW) infants. Microglia plays a significant role in inflammation-induced WMI. Our previous study showed that lipopolysaccharide (LPS)-induced OPC damage is mediated by activated microglia in vitro. We hypothesized that azithromycin (AZ) could protect OPCs against LPS-induced cytotoxicity by blocking microglial activation. Highly enriched primary rat microglia and OPCs were treated with LPS. There were 4 groups: control, LPS + Veh, AZ, and LPS + AZ. Microglia conditioned medium (MCM) was used to determine inflammatory cytokines by enzyme-linked immunosorbent assay or subsequent treatment of OPCs. We found that AZ significantly suppressed TNF-α, IL-1ß, and IL-6 in LPS+Veh-treated-microglial MCM and blocked microglial nuclear factor-κB p65 nuclear translocation. AZ prevented LPS-MCM-induced OPC death and improved OPC survival as measured by activated caspase-3 immunostaining and XTT assay, respectively. AZ ameliorated LPS-MCM-induced differentiation arrest and myelin basic protein deficit in oligodendrocytes. Our data suggest that AZ is a potent inhibitor for microglia activation and may hold the therapeutic potential for WMI in VLBW infants.

Azithromycin alleviates the severity of rheumatoid arthritis by targeting the unfolded protein response component of glucose-regulated protein 78 (GRP78).

BACKGROUND AND PURPOSE: Azithromycin is a macrolide antibiotic with anti-inflammatory properties. We aim to substantiate the treatment potential of azithromycin in rheumatoid arthritis. EXPERIMENTAL APPROACH: Gene expression profiles were collected by RNA sequencing and the effects of azithromycin were assessed by in vitro and in vivo assays on the effects of azithromycin-mediated blockade of glucose-regulated protein 78 (GRP78). Anti-inflammatory activity of azithromycin was measured in fibroblast-like synoviocytes from rheumatoid arthritis patients and in collagen-induced arthritis in DBA/1 mice. Characterization of the binding of azithromycin to GRP78 was performed using drug affinity responsive target stability, proteomics and cellular thermal shift assays. Azithromycin-mediated inhibition of GRP78 and its relationship to its anti-arthritic activity was assessed. KEY RESULTS: Azithromycin reduced proinflammatory factor production, cell migration, invasion and chemoattraction and enhanced apoptosis, reducing the deleterious inflammatory response of rheumatoid arthritis fibroblast-like synoviocytes in vitro. Azithromycin ameliorated the severity of collagen-induced arthritis lesions as efficiently as the TNFα inhibitor etanercept. Transcriptional analyses suggested that azithromycin treatment impairs signalling cascades associated with cholesterol and lipid biosynthesis. GRP78 was identified as a novel target of azithromycin. Azithromycin-mediated activation of the unfolded protein response via the inhibition of GRP78 activity is required not only for inducing the expression of C/EBP-homologous protein (ChOP) but also for the activating sterol-regulatory element binding protein (SREBP) and its targeted genes involved in cholesterol and lipid biosynthetic processes. Furthermore, deletion of GRP78 abolished the anti-arthritic activity of azithromycin. CONCLUSION AND IMPLICATIONS: These findings indicate that azithromycin can used to treat rheumatoid arthritis.

Therapeutic Effects of Azithromycin on Spinal Cord Injury in Male Wistar Rats: A Role for Inflammatory Pathways.

BACKGROUND: Inflammatory responses, including macrophages/microglia imbalance, are associated with spinal cord injury (SCI) complications. Accumulating evidence also suggests an anti-inflammatory property of azithromycin (AZM). MATERIAL AND METHODS: Male Wistar rats were subjected to T9 vertebra laminectomy. SCI was induced by spinal cord compression at this level with an aneurysmal clip for 60 seconds. They were divided into three groups: the sham-operated group and two SCI treatment (normal saline as a vehicle control vs. AZM at 180 mg/kg/d intraperitoneally for 3 days postsurgery; first dose: 30 minutes after surgery) groups. Locomotor scaling and behavioral tests for neuropathic pain were evaluated and compared through a 28-day period. At the end of the study, tissue samples were taken to assess neuroinflammatory changes and neural demyelination using ELISA and histopathologic examinations, respectively. In addition, the proportion of M1/M2 macrophage polarization was assessed by using flow cytometry. RESULTS: Post-SCI AZM treatment (180 mg/kg/d for 3 days) significantly improved locomotion (p < 0.01) and decreased sensitivity to mechanical (p < 0.01) and thermal allodynia (p < 0.001). Moreover, there was a significant tumor necrosis factor-α (TNF-α) decline (p < 0.01) and interleukin-10 (IL-10) elevation (p < 0.01) in the spinal cord tissue of the AZM-treated group compared with the control groups 28 days post-SCI. AZM significantly improved neuroinflammation as evidenced by reduction of the M1 expression, elevation of M2 macrophages, and reduction of the M1/M2 ratio in both the dorsal root ganglion and the spinal cord tissue after SCI compared with controls (p < 0.01). CONCLUSION: AZM treatment can be considered a therapeutic agent for SCI, as it could reduce neuroinflammation and SCI sensory/locomotor complications.

Transport Dynamics of MtrD: An RND Multidrug Efflux Pump from Neisseria gonorrhoeae.

The MtrCDE system confers multidrug resistance to Neisseria gonorrhoeae, the causative agent of gonorrhea. Using free and directed molecular dynamics (MD) simulations, we analyzed the interactions between MtrD and azithromycin, a transport substrate of MtrD, and a last-resort clinical treatment for multidrug-resistant gonorrhea. We then simulated the interactions between MtrD and streptomycin, an apparent nonsubstrate of MtrD. Using known conformations of MtrD homologues, we simulated a potential dynamic transport cycle of MtrD using targeted MD techniques (TMD), and we noted that forces were not applied to ligands of interest. In these TMD simulations, we observed the transport of azithromycin and the rejection of streptomycin. In an unbiased, long-time scale simulation of AZY-bound MtrD, we observed the spontaneous diffusion of azithromycin through the periplasmic cleft. Our simulations show how the peristaltic motions of the periplasmic cleft facilitate the transport of substrates by MtrD. Our data also suggest that multiple transport pathways for macrolides may exist within the periplasmic cleft of MtrD.

Design, synthesis and antibacterial evaluation of novel 3-O-substituted 15-membered azalides possessing 1,2,3-triazole side chains.

The acquired and intrinsic resistance of bacteria to macrolide antibiotics limits the clinical application of these agents, and thus it is particularly important to discover novel macrolide antibiotics that can be administered to counteract the prevalence of bacterial resistance. In this study, we introduced some active 1,2,3-triazole side chains into the azithromycin at position 3-O, thereby obtaining a number of 3-O-substituted 15-membered azalides. Determination of the minimum inhibitory concentration (MIC) of these target compounds revealed that the compound 9g possessed the strongest antibacterial activity (MIC = 8-16 µg/mL) against drug-resistant strains and was generally 16- to 32-fold more active than the azithromycin (MIC ≥ 256 µg/mL). Combined analysis of the results of antibacterial activity together with theoretically calculated lipid/water partition coefficients (ClogP) indicated the importance of the chemical nature of the alkyl groups attached to the 1,2,3-triazole side chain in conferring promising antibacterial activity. The findings of molecular docking analyses indicated that compound 9g may bind to the A752 base of 23S rRNA in bacterial ribosome via hydrophobic or electrostatic interactions, resulting in the excellent antibacterial activity of this compound. Furthermore, the data of minimum bactericidal concentration revealed that compounds 9e, 9f, 9g and 9h are excellent bacteriostatic agents. In addition, the study of bactericidal kinetics confirmed that compound 9g is a time- and concentration-dependent agent.

Mapping the effect of drugs on ACE2 as a novel target site for COVID-19 therapy.

Angiotensin converting enzyme 2 (ACE2) has potentially conflicting roles in health and disease. COVID-19 coronavirus binds to human cells via ACE2 receptor, which is expressed on almost all body organs. Boosting the ACE2 receptor levels on heart and lung cells may provide more cellular enter to virus thereby worsening the infection. Therefore, among the drug targets, ACE2 is suggested as a vital target of COVID-19 therapy. This hypothesis is based on the protective role of the drugs acting on ACE2. Therefore, this review discusses the impact and challenges of using ACE2 as a target in the current therapy of COVID-19.

SARS-CoV-2 Persistent Viral Shedding in the Context of Hydroxychloroquine-Azithromycin Treatment.

SARS-CoV-2 nasopharyngeal shedding contributes to the spread of the COVID-19 epidemic. Among 3271 COVID-19 patients treated at the Hospital University Institute Méditerranée Infection, Marseille, France from 3 March to 27 April 2020, tested at least twice by qRT-PCR, the median SARS-CoV-2 nasopharyngeal shedding duration was 6 days (range 2-54 days). Compared with short shedders (qRT-PCR positivity < 10 days), 34 (1.04%) persistent shedders (qRT-PCR positivity ≥ 17 days; mean ± SD: 23.3 ± 3.8 days) were significantly older, with associated comorbidities, exhibiting lymphopenia, eosinopenia, increased D-dimer and increased troponin (p < 0.05), and were hospitalized in intensive care unit in 17.7% vs. 1.1% of cases (p < 0.0001). Viral culture was positive in six persistent shedders after day 10, including in one patient after day 17, and no viral co-pathogen was detected in 33 tested patients. Persistent shedders received azithromycin plus hydroxychloroquine ≥ 3 days in 26/34 (76.5%) patients, a figure significantly lower than in short shedders (86.6%) (p = 0.042). Accordingly, mortality was 14.7% vs. 0.5% (p < 0.0001). Persistent shedding was significantly associated with persistent dyspnea and anosmia/ageusia (p < 0.05). In the context of COVID-19 treatment, including treatment with azithromycin plus hydroxychloroquine, the persistence of SARS-CoV-2 nasopharyngeal shedding was a rare event, most frequently encountered in elderly patients with comorbidities and lacking azithromycin plus hydroxychloroquine treatment.

Azithromycin inhibited oxidative stress and apoptosis of high glucose-induced podocytes by inhibiting STAT1 pathway.

Azithromycin (AZM) has a therapeutic effect on diabetes, but there is no report on whether AZM has a therapeutic effect on diabetic nephropathy (DN) and its specific mechanism. Cell survival was detected by CCK-8. The expression of the inflammatory factors TNF-α, IL-1ß, and IL-6 was determined by ELISA. The expression of inflammatory proteins MCP-1, NLPR3, and ASC was detected by western blot. The expression of MDA, LDH, and SOD was detected by the appropriate kit. Apoptosis was detected by flow cytometry and apoptosis-related proteins Bcl-2, Bax, Caspase-3, 6, 9, and Cleaved caspase-3, 6, 9 were detected by western blot. In addition, the expression of STAT1 was detected by western blot. AZM can increase the activity of high glucose-induced podocytes (p < .05). After high glucose induction, the expression of TNF-α, IL-1ß, and IL-6 was increased and the expression of MCP-1, NLPR3, and ASC proteins was also increased (p < .001). When AZM was added, the expression of all the above-mentioned proteins was decreased (p < .001). In addition, MDA, LDH, and SOD were increased after high glucose induction, while decreased after AZM treatment (p < .001). AZM can inhibit apoptosis and the expression of Bax and Cleaved caspase-3, 6, 9, and promote the expression of Bcl-2 (p < .001). Furthermore, the expression of STAT1 was increased after high glucose induction, while the expression of STAT1 was decreased after AZM action (p < .01). By adding a STAT1 agonist IFN-γ, the effects of AZM on inflammation, oxidative stress, and apoptosis of high glucose-induced podocytes were inhibited (p < .05). AZM inhibited inflammation, oxidative stress, and apoptosis of high glucose-induced podocytes by inhibiting STAT1 pathway.

Mechanism of azithromycin in airway diseases.

Azithromycin (AZM) has been used to treat chronic inflammatory airway diseases because it regulates cell-cell contact between airway epithelial cells. Airway mucus hypersecretion is an important component of chronic respiratory diseases. Mucin 5AC (MUC5AC) is the major mucin produced by airway epithelial cells, and hypersecretion of MUC5AC is a sign of various pulmonary inflammatory diseases. Recently, it was found that matrix metallopeptidase 9 is involved in mucus hypersecretion. Moreover, AZM can inhibit the ability of TNF-α-to induce interleukin (IL)-8 production. This review focuses on the effects on AZM that may be beneficial in inhibiting MUC5AC, matrix metalloprotease-9 and IL-8 production in airway epithelial cells. In addition, recent studies have begun to assess activation of mitogen-activated protein kinase (MAPK) signaling pathways in response to AZM. Understanding these new developments may be helpful for clinicians.

Effects of azithromycin on feeding behavior and nutrition accumulation of Daphnia magna under the different exposure pathways.

Antibiotics had been paid more and more attention to their toxicity to non-target aquatic organisms in the aquatic environment. As azithromycin (AZI) was an important antibiotic pollutant in water, its toxicity to aquatic organisms had been investigated. In this study, the potential aquatic ecological risk of AZI was identified by assessing the toxicity on the feeding behavior and physiological function of Daphnia magna (D. magna) under the different exposure pathways (aqueous phase exposure vs. food phase exposure). For the food Chlorella pyrenoidosa (C. pyrenoidosa), AZI could inhibit the growth and nutrition accumulation with concentration- and time-response relationship. For D. magna, the feeding behavior was inhibited by AZI under the aqueous phase exposure pathway. However, the feeding behavior was inhibited firstly and then reversed into promotion in the low and medium concentration groups and was continually promoted in the high concentration group under the food phase exposure pathway. The accumulation of polysaccharides and total protein were decreased in D. magna n the high concentration group under the aqueous phase exposure pathway, while the accumulation of polysaccharides and crude fat were decreased in the high concentration group under the food phase exposure pathway. The activity of amylase (AMS) and trypsin in D. magna were decreased after exposure to AZI under the aqueous phase exposure pathway. On the other hand, the activity of AMS in the medium and high concentration groups was decreased under the food phase exposure pathway, but the activity of trypsin was decreased in the medium concentration group and increased in the high concentration group. The levels of ROS in D. magna were also measured and increased in both exposure pathways except in the low concentration group under the food phase exposure pathway, indicating the oxidative stress injury of D. magna. Our results showed that AZI could affect the digestive enzyme activities and oxidative stress-antioxidative system, ultimately leading to the change of D. magna's feeding behavior and nutrition accumulation. These results also provided a comprehensive perspective to evaluate the toxic effects of non-lethal dose antibiotics to non-target aquatic organisms via different exposure pathways.

A mevalonate bypass system facilitates elucidation of plastid biology in malaria parasites.

Malaria parasites rely on a plastid organelle for survival during the blood stages of infection. However, the entire organelle is dispensable as long as the isoprenoid precursor, isopentenyl pyrophosphate (IPP), is supplemented in the culture medium. We engineered parasites to produce isoprenoid precursors from a mevalonate-dependent pathway, creating a parasite line that replicates normally after the loss of the apicoplast organelle. We show that carbon-labeled mevalonate is specifically incorporated into isoprenoid products, opening new avenues for researching this essential class of metabolites in malaria parasites. We also show that essential apicoplast proteins, such as the enzyme target of the drug fosmidomycin, can be deleted in this mevalonate bypass parasite line, providing a new method to determine the roles of other important apicoplast-resident proteins. Several antibacterial drugs kill malaria parasites by targeting basic processes, such as transcription, in the organelle. We used metabolomic and transcriptomic methods to characterize parasite metabolism after azithromycin treatment triggered loss of the apicoplast and found that parasite metabolism and the production of apicoplast proteins is largely unaltered. These results provide insight into the effects of apicoplast-disrupting drugs, several of which have been used to treat malaria infections in humans. Overall, the mevalonate bypass system provides a way to probe essential aspects of apicoplast biology and study the effects of drugs that target apicoplast processes.