A 13-week subchronic intravaginal toxicity study of pokeweed antiviral protein in mice

[Acute and chronic toxicity of 0.5% podophyllotoxin-loaded nanostructured lipid carriers to vaginal mucosa in rabbits and rats]

OBJECTIVE

To test the acute and chronic toxicity of topical application of 0.5% podophyllotoxin-loaded nanostructured lipid carriers (POD-NLC) to the vaginal mucosa.

METHODS

Twelve New Zealand rabbits were randomized into 3 groups and subjected to daily topical applications of normal saline (control group), 0.5% podophyllotoxin tincture (POD-T) or 0.5% POD-NLC on the vaginal mucosa for 10 consecutive days, and the pathological changes in the mucosa were graded using the Eckstein scoring system.The acute toxicity of POD-NLC was tested in 20 SD female rats, which received intravaginal administration of POD-NLC or vehicle for 3 times within 24 h; After 14 days of continuous observation, the rats were dissected for calculating the viscera coefficient.For testing the chronic toxicity of POD-NLC, 80 SD female rats were randomized into 4 groups and subjected to daily intravaginal administration of the vehicle or POD-NLC at low, moderate or high doses for 13 consecutive weeks.The rats were weighed once a week and at the end of the experiment, 2/3 of the rats from each group were sacrificed to collect blood samples, calculate the viscera coefficient, and examine the pathological changes in the liver.The remaining 1/3 rats were observed for another 2 weeks without further drug treatment and the same examinations were performed.

RESULTS

In the rabbits, 0.5% POD-NLC elicited only mild irritation while POD-T caused moderate irritation of the vaginal mucosa.In the acute toxicity test, the organ coefficients were comparable between the rats treated with the vehicle and POD-NLC (P>0.05).Long-term intravaginal administration of POD-NLC did not produce significant changes in the behavior, activity, body weight, blood biochemical profiles or organ coefficient as compared with the vehicle control group (P>0.05).

CONCLUSIONS

Intravaginal administration of 0.5% POD-NLC causes very mild irritation without obvious acute or chronic toxicity to the vaginal mucosa in rabbits and rats.

Structural analysis of a type 1 ribosome inactivating protein reveals multiple L‑asparagine‑N‑acetyl‑D‑glucosamine monosaccharide modifications: Implications for cytotoxicity

Pokeweed antiviral protein (PAP) belongs to the family of type I ribosome-inactivating proteins (RIPs): Ribotoxins, which function by depurinating the sarcin-ricin loop of ribosomal RNA. In addition to its antibacterial and antifungal properties, PAP has shown promise in antiviral and targeted tumor therapy owing to its ability to depurinate viral RNA and eukaryotic rRNA. Several PAP genes are differentially expressed across pokeweed tissues, with natively isolated seed forms of PAP exhibiting the greatest cytotoxicity. To help elucidate the molecular basis of increased cytotoxicity of PAP isoenzymes from seeds, the present study used protein sequencing, mass spectroscopy and X-ray crystallography to determine the complete covalent structure and 1.7 Å X-ray crystal structure of PAP-S1_aci isolated from seeds of Asian pokeweed (Phytolacca acinosa). PAP-S1_aci shares ~95% sequence identity with PAP-S1 from P. americana and contains the signature catalytic residues of the RIP superfamily, corresponding to Tyr72, Tyr122, Glu175 and Arg178 in PAP-S1_aci. A rare proline substitution (Pro174) was identified in the active site of PAP-S1_aci, which has no effect on catalytic Glu175 positioning or overall active-site topology, yet appears to come at the expense of strained main-chain geometry at the pre-proline residue Val173. Notably, a rare type of N-glycosylation was detected consisting of N-acetyl-D-glucosamine monosaccharide residues linked to Asn10, Asn44 and Asn255 of PAP-S1_aci. Of note, our modeling studies suggested that the ribosome depurination activity of seed PAPs would be adversely affected by the N-glycosylation of Asn44 and Asn255 with larger and more typical oligosaccharide chains, as they would shield the rRNA-binding sites on the protein. These results, coupled with evidence gathered from the literature, suggest that this type of minimal N-glycosylation in seed PAPs and other type I seed RIPs may serve to enhance cytotoxicity by exploiting receptor-mediated uptake pathways of seed predators while preserving ribosome affinity and rRNA recognition.

Pokeweed antiviral protein alters splicing of HIV-1 RNAs, resulting in reduced virus production

Processing of HIV-1 transcripts results in three populations in the cytoplasm of infected cells: full-length RNA, singly spliced, and multiply spliced RNAs. Rev, regulator of virion expression, is an essential regulatory protein of HIV-1 required for transporting unspliced and singly spliced viral transcripts from the nucleus to the cytoplasm. Export allows these RNAs to be translated and the full-length RNA to be packaged into virus particles. In our study, we investigate the activity of pokeweed antiviral protein (PAP), a glycosidase isolated from the pokeweed plant Phytolacca americana, on the processing of viral RNAs. We show that coexpression of PAP with a proviral clone alters the splicing ratio of HIV-1 RNAs. Specifically, PAP causes the accumulation of multiply spliced 2-kb RNAs at the expense of full-length 9-kb and singly spliced 4-kb RNAs. The change in splicing ratio is due to a decrease in activity of Rev. We show that PAP depurinates the rev open reading frame and that this damage to the viral RNA inhibits its translation. By decreasing Rev expression, PAP indirectly reduces the availability of full-length 9-kb RNA for packaging and translation of the encoded structural proteins required for synthesis of viral particles. The decline we observe in virus protein expression is not due to cellular toxicity as PAP did not diminish translation rate. Our results describing the reduced activity of a regulatory protein of HIV-1, with resulting change in virus mRNA ratios, provides new insight into the antiviral mechanism of PAP.

Short communication: expression of transporters and metabolizing enzymes in the female lower genital tract: implications for microbicide research

Topical vaginal microbicides have been considered a promising option for preventing the male-to-female sexual transmission of HIV; however, clinical trials to date have not clearly demonstrated robust and reproducible effectiveness results. While multiple approaches may help enhance product effectiveness observed in clinical trials, increasing the drug exposure in lower genital tract tissues is a compelling option, given the difficulty in achieving sufficient drug exposure and positive correlation between tissue exposure and microbicide efficacy. Since many microbicide drug candidates are substrates of transporters and/or metabolizing enzymes, there is emerging interest in improving microbicide exposure and efficacy through local modulation of transporters and enzymes in the female lower genital tract. However, no systematic information on transporter/enzyme expression is available for ectocervical and vaginal tissues of premenopausal women, the genital sites most relevant to microbicide drug delivery. The current study utilized reverse transcriptase polymerase chain reaction (RT-PCR) to examine the mRNA expression profile of 22 transporters and 19 metabolizing enzymes in premenopausal normal human ectocervix and vagina. Efflux and uptake transporters important for antiretroviral drugs, such as P-gp, BCRP, OCT2, and ENT1, were found to be moderately or highly expressed in the lower genital tract as compared to liver. Among the metabolizing enzymes examined, most CYP isoforms were not detected while a number of UGTs such as UGT1A1 were highly expressed. Moderate to high expression of select transporters and enzymes was also observed in mouse cervix and vagina. The implications of this information on microbicide research is also discussed, including microbicide pharmacokinetics, the utilization of the mouse model in microbicide screening, as well as the in vivo functional studies of cervicovaginal transporters and enzymes.

Contraceptive efficacy and safety of HerbOshield™ vaginal gel in rats

BACKGROUND

Spermicides represent one of the methods of contraception. The synthetic agents available as spermicides produce severe side effects. Hence, there is a need to replace these agents with safe and effective agents such as plant-based contraceptive agents.

STUDY DESIGN

The objective of the present study was to develop and evaluate a stable, safe, effective and easily acceptable contraceptive delivery system containing herbal drug. Efforts were made to evaluate the contraceptive potential of the hydroalcoholic extract from the seeds of Annona squamosa Linn. and the vaginal gel HerbOshield™ containing the extract.

RESULTS

Spermicidal effect was evaluated in vitro using healthy human spermatozoa and in vivo in rats. The in vitro results demonstrated that HerbOshield™ vaginal gel is an effective spermicide. At a 100-mg/mL dose, complete immobilization of human spermatozoa was observed within 20 s. None of the treated animals conceived, indicating 100% contraceptive effect as compared to Gynol II, a nonoxynol-9-containing marketed formulation, which showed only 67% contraceptive effect in vivo. HerbOshield™ vaginal gel was found to be safe in animals during a 14-day toxicity study.

CONCLUSIONS

HerbOshield™ vaginal gel was found to be safe and effective in rats and could be developed as a potential vaginal contraceptive for future use in humans.

Inhibition of hepatitis B virus replication by pokeweed antiviral protein in vitro

AIM: To explore the inhibitory effects of pokeweed antiviral protein seed (PAP-S) and PAP encoded by a eukaryotic expression plasmid on hepatitis B virus (HBV) replication in vitro.

METHODS: HepG2 2.2.15 cells in cultured medium were treated with different concentrations of PAP-S. HBsAg, HBeAg and HBV DNA in supernatants were determined by ELISA and fluorescent quantitative PCR respectively. MTT method was used to assay for cytotoxicity. HepG2 were cotransfected with various amounts of PAP encoded by a eukaryotic expression plasmid and replication competent wild-type HBV 1.3 fold over-length plasmid. On d 3 after transfection, HBsAg and HBeAg were determined by using ELISA. Levels of HBV core-associated DNA and RNA were detected by using Southern and Northern blot, respectively.

RESULTS: The inhibitory effects of PAP-S on HBsAg, HBeAg and HBV DNA were gradually enhanced with the increase of PAP concentration. When the concentration of PAP-S was 10 &mgr;g/mL, the inhibition rates of HBsAg, HBeAg and HBV DNA were 20.9%, 30.2% and 50%, respectively. After transfection of 1.0 &mgr;g and 2.0 &mgr;g plasmid pXF3H-PAP, the levels of HBV nucleocapside-associated DNA were reduced by 38.0% and 74.0% respectively, the levels of HBsAg in the media by 76.8% and 99.7% respectively, and the levels of HBeAg by 72.7% and 99.3% respectively as compared with controls. Transfection with 2 &mgr;g plasmid pXF3H-PAP reduced the levels of HBV nucleocapside-associated RNA by 69.0%.

CONCLUSION: Both PAP-S and PAP encoded by a eukaryotic expression plasmid could effectively inhibit HBV replication and antigen expression in vitro, and the inhibitory effects were dose-dependent.

Naturally derived anti-HIV agents

The urgent need for new anti-HIV/AIDS drugs is a global concern. In addition to obvious economical and commercial hurdles, HIV/AIDS patients are faced with multifarious difficulties associated with the currently approved anti-HIV drugs. Adverse effects, the emergence of drug resistance and the narrow spectrum of activity have limited the therapeutic usefulness of the various reverse transcriptase and protease inhibitors that are currently available on the market. This has driven many scientists to look for new anti-retrovirals with better efficacy, safety and affordability. As has always been the case in the search for cures, natural sources offer great promise. Several natural products, mostly of plant origin have been shown to possess promising activities that could assist in the prevention and/or amelioration of the disease. Many of these anti-HIV agents have other medicinal values as well, which afford them further prospective as novel leads for the development of new drugs that can deal with both the virus and the various disorders that characterize HIV/AIDS. The aim of this review is to report new discoveries and updates pertaining to anti-HIV natural products. In the review anti-HIV agents have been classified according to their chemical classes rather than their target in the HIV replicative cycle, which is the most frequently encountered approach. Perusal of the literature revealed that most of these promising naturally derived anti-HIV compounds are flavonoids, coumarins, terpenoids, alkaloids, polyphenols, polysaccharides or proteins. It is our strong conviction that the results and experiences with many of the anti-HIV natural products will inspire and motivate even more researchers to look for new leads from plants and other natural sources.

CNS activity of Pokeweed anti-viral protein (PAP) in mice infected with lymphocytic choriomeningitis virus (LCMV)

Background

Others and we have previously described the potent in vivo and in vitro activity of the broad-spectrum antiviral agent PAP (Pokeweed antiviral protein) against a wide range of viruses. The purpose of the present study was to further elucidate the anti-viral spectrum of PAP by examining its effects on the survival of mice challenged with lymphocytic choriomeningitis virus (LCMV).

Methods

We examined the therapeutic effect of PAP in CBA mice inoculated with intracerebral injections of the WE54 strain of LCMV at a 1000 PFU dose level that is lethal to 100% of mice within 7–9 days. Mice were treated either with vehicle or PAP administered intraperitoneally 24 hours prior to, 1 hour prior to and 24 hours, 48 hours 72 hours and 96 hours after virus inoculation.

Results

PAP exhibits significant in vivo anti- LCMV activity in mice challenged intracerebrally with an otherwise invariably fatal dose of LCMV. At non-toxic dose levels, PAP significantly prolonged survival in the absence of the majority of disease-associated symptoms. The median survival time of PAP-treated mice was >21 days as opposed to 7 days median survival for the control (p = 0.0069).

Conclusion

Our results presented herein provide unprecedented experimental evidence that PAP exhibits antiviral activity in the CNS of LCMV-infected mice.