Potentiation by febrifugine of host defense in mice against Plasmodium berghei NK65

Dichroa febrifuga Lour.: A review of its botany, traditional use, phytochemistry, pharmacological activities, toxicology, and progress in reducing toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Dichroa febrifuga Lour., a toxic but extensively used traditional Chinese medicine with a remarkable effect, is commonly called "Changshan" in China. It has been used to treat malaria and many other parasitic diseases.

AIM OF THE REVIEW

The study aims to provide a current overview of the progress in the research on traditional use, phytochemistry, pharmacological activities, toxicology, and methods of toxicity reduction of D. febrifuga. Additionally, further research directions and development prospects for the plant were put forward.

MATERIALS AND METHODS

The article uses "Dichroa febrifuga Lour." "D. febrifuga" as the keyword and all relevant information on D. febrifuga was collected from electronic searches (Elsevier, PubMed, ACS, CNKI, Google Scholar, and Baidu Scholar), doctoral and master's dissertations and classic books about Chinese herbs.

RESULTS

30 chemical compounds, including alkaloids, terpenoids, flavonoids and other kinds, were isolated and identified from D. febrifuga. Modern pharmacological studies have shown that these components have a variety of pharmacological activities, including anti-malarial activities, anti-inflammatory activities, anti-tumor activities, anti-parasitic activities and anti-oomycete activities. Meanwhile, alkaloids, as the material basis of its efficacy, are also the source of its toxicity. It can cause multiple organ damage, including liver, kidney and heart, and cause adverse reactions such as nausea and vomiting, abdominal pain and diarrhea. In the current study, the toxicity can be reduced by modifying the structure of the compound, processing and changing the dosage forms.

CONCLUSIONS

There are few studies on the chemical constituents of D. febrifuga, so the components and their structure characterization contained in it can become the focus of future research. In view of the toxicity of D. febrifuga, there are many methods to reduce it, but the safety and rationality of these methods need further study.

The anti-inflammatory activity of the compounds isolated from Dichroa febrifuga leaves

Dichroa febrifuga Lour. is a traditional medicinal herb that has been applied in the treatment of malaria and some other infectious diseases. Studies recently have focused on the anti-inflammation of the extracts of Dichroa febrifuga Lour. although there have not many reports about which compounds play the essential role. Therefore, in this study, we isolated hydrangenoside C (1), isoarborinol (2), and methyl 1,3,4,6-tetra-O-acetyl-fructofuranoside (3) from the leaves of Dichroa febrifuga. Subsequently, the anti-inflammatory property of 1-3 was assessed using an in vivo assay of edema mouse model which was induced by carrageenan. Out of the three, 2 inhibited the edema effectively and dose-dependently, similarly to diclofenac while there was no obvious activity observed in 1 and 3. The in silico results demonstrated that 2 enables binding to 5-LOX and PLA2 via generating h-bonds. This is the first study to mention the anti-inflammation of 2 in Dichroa febrifuga Lour., and would be a contribution to further studies to elucidate the promising bioactivities of this compound.

Toxicological evaluation of the ultrasonic extract from Dichroae radix in mice and wistar rats

This study was aimed at evaluating the acute and subchronic toxicity of ultrasonic extract of Dichroae radix (UEDR) in mice and rats. High performance liquid chromatography (HPLC) and thin layer chromatogrephy (TLC) were used to detect β-dichroine and α-dichroine in UEDR for quality control. The levels of β-dichroine and α-dichroine in UEDR were 1.46 and 1.53 mg/g, respectively. An oral LD₅₀ of 2.43 g/kg BW was observed in acute toxicity test. After 28-day repeated oral administration, compared with the control group, treatment-related changes in body weight (BW) and body weight gain (BWG), lymphocyte counts and ratios, as well as in the relative organ weights (ROWs) of liver, kidney, lung, and heart, were detected in the middle- and high-dose groups (P < 0.05, P < 0.01), no differences were noted in the serum biochemical parameters and necropsy examinations in both sexes at all doses. Histopathological examinations exhibited UEDR-associated signs of toxicity or abnormalities. After 14 days withdrawal, no statistically significant or toxicologically relevant differences were observed in any of the UEDR-treated groups, and the hispathological lesions in the high-dose group were alleviated. Findings showed that long-course and high-dose of UEDR administration was toxic, and showed dose-dependence, the toxic damage was reversible.

Antimalarial activity of vitamin D3 (VD3) does not result from VD3-induced antimicrobial agents including nitric oxide or cathelicidin

Recent evidence suggests that 1α,25-dihydroxyvitamin D3 (VD3), the active form of vitamin D, inhibits microbial proliferation. Previously, we used in vivo murine models to investigate the antimalarial activity of VD3 and confirmed potent antimalarial activity in the acute phase. This study aimed to clarify the mechanisms underlying the antimalarial activity of VD3 in vivo, particularly extensive inhibition of parasitemia in the acute phase, focusing on nitric oxide (NO), a potent antimalarial molecule. VD3 is a good NO inducer. When most Plasmodium chabaudi AS (PcAS)-infected mice treated with VD3 survived, NO was present in blood samples obtained from VD3-treated mice at a significantly higher rate at 2 and/or 3 days post-infection than that in vehicle-treated control mice. To verify the involvement of NO in the antimalarial activity of VD3, we used aminoguanidine (AG), an inducible NO synthase (iNOS) inhibitor, to abrogate the antimalarial activity of VD3. However, despite AG-induced reductions in NO levels, parasitemia remained inhibited during the acute phase, even in the presence of AG, and the antiplasmodial faculty of VD3 was not ablated. VD3-mediated antimalarial activity irrelevant of NO compelled us to consider another candidate. In a pilot experiment, we used cathelicidin (CAMP), an antimicrobial peptide, since it is known that VD3 induces CAMP synthesis. Serum CAMP levels increased on days 4 or 5 post-infection with or without VD3 administration, but experiments using exogenous CAMP did not display curative effects in PcAS-infected mice. The present study using VD3 to target the malarial parasite thus suggests a potential novel approach to treat malarial infections.

Chemical synthesis of febrifugine and analogues

The quinazolinone-containing 2,3-disubstituted piperidines febrifugine and isofebrifugine have been the subject of significant research efforts since their occurrence in Dichroa febrifuga and their anti-malarial actions were first described in the late 1940s. Subsequently they have also been shown to be present in other plants belonging to the hydrangea family and various analogues of febrifugine have been prepared in attempts to tune biological properties. The most notable analogue is termed halofuginone and a substantial body of work now demonstrates that this compound possesses potent human disease relevant activities. This review focuses on the literature associated with efforts dedicated towards uncovering the structures of febrifugine and isofebrifugine, the development of practical methods for their synthesis and the syntheses of structural analogues.

Dichroa febrifuga Lour. inhibits the production of IL-1beta and IL-6 through blocking NF-kappaB, MAPK and Akt activation in macrophages

AIM OF THE STUDY

The roots of Dichroa febrifuga Lour. have been used as a traditional antimalarial drug and also used in the treatment of productive cough and unstable fever caused by infection in China and Korea. In this study, we evaluated the anti-inflammatory effect and underlying molecular mechanism of aqueous extract of Dichroa febrifuga (AEDF) in C57BL/6 mouse peritoneal macrophages.

MATERIALS AND METHODS

The effect of AEDF on proinflammatory cytokine (IL-1beta and IL-6) production was analyzed by ELISA and real-time RT-PCR. The effects of AEDF on NF-kappaB/IkappaB-alpha/IKK were measured by reporter assay (in RAW 264.7 cells), EMSA, Western blotting and kinase assay. The effects of AEDF on Akt and MAPKs activity were assayed by Western blotting.

RESULTS

AEDF inhibited the production of IL-1beta and IL-6, NF-kappaB activation, IkappaB-alpha degradation, and IKK, Akt, ERK1/2 and JNK activities in LPS-stimulated mouse peritoneal macrophages.

CONCLUSIONS

These results suggest that AEDF inhibits proinflammatory cytokine (IL-1beta and IL-6) production in LPS-stimulated mouse peritoneal macrophages, and that these effects are mediated by the inhibition of the activity of IKK/IkappaB/NF-kappaB and the phosphorylation of Akt, ERK1/2, and JNK. Our results provide a molecular basis for understanding the inhibitory effects of Dichroa febrifuga roots on endotoxin-mediated inflammation.

Development of a pharmacodynamic model of murine malaria and antimalarial treatment with dihydroartemisinin

Antimalarial treatment strategies based on in vitro studies are limited by the paucity of pharmacodynamic information for dosage regimen design. We postulated that a murine model could be used for pre-clinical stages of drug development, especially in dose-response studies and evaluation of combination therapies. Swiss mice infected with Plasmodium berghei parasites (2-5% starting parasitaemia) were given dihydroartemisinin (0-100 mg/kg single dose). Parasite density was regularly determined from thin blood films. A parasite population growth model comprising parasite multiplication, decline in erythrocyte count with increasing parasitaemia and parasite clearance after drug administration was developed. This model described the rise in parasitaemia following inoculation, the nadir following dihydroartemisinin administration, and the subsequent resurgence of parasitaemia (analogous to 'recrudescence'). At doses of 10, 30 and 100 mg/kg dihydroartemisinin, there was a graded response with 2.5+/-1, 5+/-1 and 12+/-4-fold decreases in parasitaemia, respectively. The nadir parasitaemia (at 21-27 h) was also dose-dependent. This study demonstrates that a murine malaria pharmacodynamic model is a valuable tool for understanding how single drugs and their dosing schedules alter the time course and level of infection.

Nitric oxide metabolites induced in Anopheles stephensi control malaria parasite infection

Malaria parasite infection in anopheline mosquitoes is limited by inflammatory levels of nitric oxide metabolites. To assess the mechanisms of parasite stasis or toxicity, we investigated the biochemistry of these metabolites within the blood-filled mosquito midgut. Our data indicate that nitrates, but not nitrites, are elevated in the Plasmodium-infected midgut. Although levels of S-nitrosothiols do not change with infection, blood proteins are S-nitrosylated after ingestion by the mosquito. In addition, photolyzable nitric oxide, which can be attributed to metal nitrosyls, is elevated after infection and, based on the abundance of hemoglobin, likely includes heme iron nitrosyl. The persistence of oxyhemoglobin throughout blood digestion and changes in hemoglobin conformation in response to infection suggest that hemoglobin catalyzes the synthesis of nitric oxide metabolites in a reducing environment. Provision of urate, a potent reductant and scavenger of oxidants and nitrating agents, as a dietary supplement to mosquitoes increased parasite infection levels relative to allantoin-fed controls, suggesting that nitrosative and/or oxidative stresses negatively impact developing parasites. Collectively, our results reveal a unique role for nitric oxide in an oxyhemoglobin-rich environment. In contrast to facilitating oxygen delivery by hemoglobin in the mammalian vasculature, nitric oxide synthesis in the blood-filled mosquito midgut drives the formation of toxic metabolites that limit parasite development.

Antimalarial activities and therapeutic properties of febrifugine analogs

Febrifugine is the active principal isolated 50 years ago from the Chinese herb chang shan (Dichroa febrifuga Lour), which has been used as an antimalarial in Chinese traditional medicine for more than 2,000 years. However, intensive study of the properties of febrifugine has been hindered for decades due to its side effects. We report new findings on the effects of febrifugine analogs compared with those of febrifugine extracted from the dry roots of D. febrifuga. The properties of the extracted febrifugine were comparable to those obtained from the standard febrifugine provided by our collaborators. A febrifugine structure-based computer search of the Walter Reed Chemical Information System identified 10 analogs that inhibited parasite growth in vitro, with 50% inhibitory concentrations ranging from 0.141 to 290 ng/ml. The host macrophages (J744 cells) were 50 to 100 times less sensitive to the febrifugine analogs than the parasites. Neuronal (NG108) cells were even more insensitive to these drugs (selectivity indices, >1,000), indicating that a feasible therapeutic index for humans could be established. The analogs, particularly halofuginone, notably reduced parasitemias to undetectable levels and displayed curative effects in Plasmodium berghei-infected mice. Recrudescence of the parasites after treatment with the febrifugine analogs was the key factor that caused the death of most of the mice in groups receiving an effective dose. Subcutaneous treatments with the analogs did not cause irritation of the gastrointestinal tract when the animals were treated with doses within the antimalarial dose range. In summary, these analogs appear to be promising lead antimalarial compounds that require intensive study for optimization for further down-selection and development.

Mammalian transforming growth factor beta1 activated after ingestion by Anopheles stephensi modulates mosquito immunity

During the process of bloodfeeding by Anopheles stephensi, mammalian latent transforming growth factor beta1 (TGF-beta1) is ingested and activated rapidly in the mosquito midgut. Activation may involve heme and nitric oxide (NO), agents released in the midgut during blood digestion and catalysis of L-arginine oxidation by A. stephensi NO synthase (AsNOS). Active TGF-beta1 persists in the mosquito midgut to extended times postingestion and is recognized by mosquito cells as a cytokine. In a manner analogous to the regulation of vertebrate inducible NO synthase and malaria parasite (Plasmodium) infection in mammals by TGF-beta1, TGF-beta1 regulates AsNOS expression and Plasmodium development in A. stephensi. Together, these observations indicate that, through conserved immunological cross talk, mammalian and mosquito immune systems interface with each other to influence the cycle of Plasmodium development.

Effects of sodium artesunate, a new antimalarial drug, on renal function

BACKGROUND

Sodium artesunate is currently used in malaria treatment. Adverse effects of this drug have not been described, probably because they cannot be differentiated from malaria-related effects.

METHODS

The effects on renal function of an acute infusion of sodium artesunate (12 mg/kg body weight) were studied in the rat with clearance techniques. We also evaluate the effect of sodium artesunate on chloride lumen-bath flux (Cl Jlb) in the isolated thick ascending limb of the loop of Henle (TALH) microperfused in vitro.

RESULTS

Acute infusion of artesunate to the rat decreased inulin clearance, despite an increase in renal blood flow. These effects were associated with an increase in urinary excretion of sodium, chloride, potassium, and nitric oxide metabolites (NO(2)/NO(3)). In water-loaded animals, artesunate increased sodium and water distal delivery and decreased free water clearance (C(H(2)O)) factored for sodium and water delivery. Following hypertonic NaCl infusion, artesunate decreased free water excretion (Tc(H(2)O)) corrected by clearance of osmolarity (C(Osm)). In vitro, artesunate 10(-6) and 10(-3) mol/L added to bath solution decreased chloride lumen-bath flux in isolated rabbit TALH in a dose-dependent manner, with the threshold effect at 10(-4) mol/L. This effect was completely blocked by N(G)-nitroL-arginine-metilester (L-NAME) 5 mmol/L. Artesunate 10(-4) mol/L added to the perfusion solution did not change Cl Jlb.

CONCLUSION

These findings suggest that artesunate decreases glomerular filtration rate and increases renal blood flow and urinary excretion of Na, Cl, and K. These effects were due, at least in part, to the inhibition of Cl transport across cortical and medullary TALH, and were mediated by local production of nitric oxide, since it is associated with an increase in NO(2)/NO(3) urinary excretion and it is blocked by L-NAME in vitro.