Carrageenan as a Preventive Agent Against Human Papillomavirus Infection: A Narrative Review

Safety of carrageenan-based gels as preventive microbicides: a narrative review

BACKGROUND

Carrageenan-containing gels researched for the prevention of sexually transmitted infections (STIs) have shown promising results for human papillomavirus prevention in women, but not in men. We conducted a narrative review to assess the safety of these gels for genital use.

METHODS

We searched PubMed using MeSH terms and keywords on 5 November 2023. Title/abstract of articles were screened to identify relevant ones. Full-text screening determined eligibility: empirical study evaluating safety of carrageenan-containing gel(s) for genital use.

RESULTS

Of the 125 identified records, 15 were eligible, comprising 14 (10 randomised controlled trials and 4 cohorts) unique study populations. Studies included women only (n=11), men only (n=1) or both (n=3); number of participants ranged from 4 to 6202. Safety was assessed for vaginal (n=13), penile (n=3) and anal use (n=2). Most studies assessed safety of Carraguard (53%), followed by Divine9 (14%), and one each of iota-carrageenan gel, lambda-carrageenan gel, Carvir, PC-6500 (griffithsin and carrageenan) and PC-1005 (MIV-150/zinc acetate/carrageenan). Safety assessment relied on self-report (80.0%), testing for STIs (53.3%), investigator-identified genital findings (93.3%) and/or testing for changes in genital flora (60.0%). Adverse events (AEs) were described by investigators as mostly mild, (mostly) comparable between groups, not observed and/or not significant for vaginal and penile use. Only one study, assessing anal use of carrageenan, reported a significantly higher proportion of AEs in the carrageenan compared with placebo group.

CONCLUSIONS

Carrageenan-based gels are generally well tolerated for vaginal and penile, but not anal use. Studies on carrageenan gel's safety for anal use are scarce.

Impact of a carrageenan gel on viral load of genital human papillomavirus infections in sexually active women: Findings from the Carrageenan-gel Against Transmission of Cervical Human papillomavirus (CATCH) trial

Previous research has shown that women's use of a carrageenan gel reduces the risk of acquiring genital human papillomavirus (HPV) infections but does not help to clear existing ones. Although gel use may not result in complete clearance, it may decrease the viral load of HPV infections. We tested this hypothesis in the Carrageenan-gel Against Transmission of Cervical Human papillomavirus (CATCH) randomized controlled trial. Participants of the CATCH study were selected for viral load testing if they had completed the first four study visits and tested positive for HPV42 or HPV51 in at least one of these visits. HPV42 and HPV51 were chosen as they were among the most abundant low- and high-risk types, respectively, in the study sample. We measured viral load with a type-specific real-time polymerase chain reaction. Results were displayed using summary statistics. Of 461 enrolled participants, 39 were included in the HPV42 analysis set and 56 in the HPV51 analysis set. The median time between visits 1 and 4 was 3.7 months. The viral load (copies/cell) of HPV42 ranged from <0.001 to 13 434.1, and that of HPV51 from <0.001 to 967.1. The net median change in HPV42 viral load over all four visits was -1.04 copies/cell in the carrageenan and -147 copies/cell in the placebo arm (Wilcoxon rank sum test, p = 0.26). There was no net median change in HPV51 viral load over all four visits in either arm (p = 0.45). The use of a carrageenan-based gel is unlikely to reduce the viral load of HPVs 42 or 51.

Use of a carrageenan-based gel had no impact on anal HPVs 16 and 18 viral loads in gay, bisexual, and other men who have sex with men

The Lubricant Investigation in Men to Inhibit Transmission of human papillomavirus (HPV) Infection randomized control trial in gay, bisexual, and other men who have sex with men (gbMSM) found that carrageenan use neither reduced acquisition of anal HPV infections nor influenced infection clearance. To investigate carrageenan's lack of protective effect, we compared the change in anal HPV16 and HPV18 viral loads following carrageenan use against placebo. We restricted our analysis to participants who completed the first four study visits and had a valid baseline sample (n = 161, 54 HIV-positive). Samples were tested for HPV detection using the linear array PCR assay. HPV16- and/or HPV18-positive samples were tested for viral load using real-time PCR. For participants who tested HPV16- (n = 29) or HPV18-positive (n = 10) at least once across visits 1-4, we compared the change in type-specific viral load between study arms using the Mann-Whitney U test. Although the median net change in HPV16 and HPV18 viral loads across visits 1-4 was higher in the treatment than placebo arm (HPV16: 0.68 vs. 0.18 copies/cell, p = 0.60; HPV18: 18.32 vs. 10.12 copies/cell, p = 0.52), these differences were not statistically significant. Results were similar by HIV status. Carrageenan use did not impact anal HPV16 or HPV18 viral loads, which may further explain its lack of protective effect in gbMSM.

In Vitro Toxicity Evaluation of Carrageenan on Cells and Tissues of the Oral Cavity

Carrageenan is a highly potent anti-human papillomavirus (HPV) agent with the potential for formulation as a mouthwash against oral HPV infection. However, its toxic effect on tissues of the oral cavity is currently unknown. This study aims to evaluate the safety of carrageenan on human cells and tissues of the oral cavity. Human salivary gland cells and reconstructed human oral epithelium (RHOE) were used for this in vitro study. The cells were subjected to 0.005–100 µg/mL of carrageenan for 4, 12, and 24 h in quadruplicate. RHOE were exposed to 100 µg/mL of carrageenan for 24 h in triplicate and stained with hematoxylin/eosin for histological analyses. All experiments had saline and 1% sodium dodecyl sulphate (SDS) as negative and positive controls, respectively. Carrageenan tissue toxicity was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to quantify cell viability. Tissue toxicity was further evaluated histologically by an oral pathologist to assess morphological changes. Our data showed that carrageenan did not significantly decrease cell and tissue viability when compared to the positive control. The histological evaluation of the RHOE also showed no loss of viability of the carrageenan-treated sample compared to untreated tissue. In contrast, 1% SDS-treated RHOE showed extensive tissue destruction. Our experiments suggest that carrageenan is safe for use in the oral cavity.

Characteristics of Marine Biomaterials and Their Applications in Biomedicine

Oceans have vast potential to develop high-value bioactive substances and biomaterials. In the past decades, many biomaterials have come from marine organisms, but due to the wide variety of organisms living in the oceans, the great diversity of marine-derived materials remains explored. The marine biomaterials that have been found and studied have excellent biological activity, unique chemical structure, good biocompatibility, low toxicity, and suitable degradation, and can be used as attractive tissue material engineering and regenerative medicine applications. In this review, we give an overview of the extraction and processing methods and chemical and biological characteristics of common marine polysaccharides and proteins. This review also briefly explains their important applications in anticancer, antiviral, drug delivery, tissue engineering, and other fields.

Influence of the Structural Features of Carrageenans from Red Algae of the Far Eastern Seas on Their Antiviral Properties

The structural diversity and unique physicochemical properties of sulphated polysaccharides of red algae carrageenans (CRGs), to a great extent, determine the wide range of their antiviral properties. This work aimed to compare the antiviral activities of different structural types of CRGs: against herpes simplex virus type 1 (HSV-1) and enterovirus (ECHO-1). We found that CRGs significantly increased the resistance of Vero cells to virus infection (preventive effect), directly affected virus particles (virucidal effect), inhibited the attachment and penetration of virus to cells, and were more effective against HSV-1. CRG1 showed the highest virucidal effect on HSV-1 particles with a selective index (SI) of 100. CRG2 exhibited the highest antiviral activity by inhibiting HSV-1 and ECHO-1 plaque formation, with a SI of 110 and 59, respectively, when it was added before virus infection. CRG2 also significantly reduced the attachment of HSV-1 and ECHO-1 to cells compared to other CRGs. It was shown by molecular docking that tetrasaccharides—CRGs are able to bind with the HSV-1 surface glycoprotein, gD, to prevent virus–cell interactions. The revealed differences in the effect of CRGs on different stages of the lifecycle of the viruses are apparently related to the structural features of the investigated compounds.

Efficacy of a carrageenan gel in preventing anal human papillomavirus (HPV) infection: interim analysis of the Lubricant Investigation in Men to Inhibit Transmission of HPV Infection (LIMIT-HPV) randomised controlled trial

BACKGROUND

Carrageenan, a non-toxic gelling agent derived from red algae, has potent anti-human papillomavirus (HPV) activity in in vitro and animal studies. We assessed, in an interim analysis, the efficacy of a carrageenan-based gel in reducing the risk of new detections of anal HPV among gay, bisexual and other men who have sex with men (gbMSM).

METHODS

The LIMIT-HPV study (Lubricant Investigation in Men to Inhibit Transmission of HPV Infection) is a phase IIb, double-blind, placebo-controlled randomised controlled trial conducted in Montreal, Canada. gbMSM were randomly assigned (1:1) to receive a carrageenan-based or placebo gel. Participants were instructed to apply the gel to the anus, condom and/or partners' penis before and-as required-during receptive anal intercourse. Questionnaire data and anal samples were collected at 0, 1, 2, 3, 6, 9 and 12 months. We estimated new detections of anal HPV infection(s) detected via Linear Array using Cox proportional hazards models.

RESULTS

Participants recruited from February 2016 to December 2019 were randomly assigned to the carrageenan (n=127) or placebo (n=128) arm. The efficacy and safety analyses included 201 and 210 participants. The median follow-up time was 7.6 months (range: 0-28.5) in the carrageenan group and 9.3 months (range: 0-40.7) in the placebo group. The HR for new detections was 1.21 (95% CI 0.86 to 1.70): 69.4% and 65.1% new detections of HPV in the carrageenan and placebo arms, respectively. More adverse events were reported in the carrageenan (59.8%) compared with the placebo (39.8%) arm.

CONCLUSIONS

The interim analysis did not demonstrate a protective effect of carrageenan on the risk of new detections of anal HPV infection among gbMSM. Carrageenan gel use was associated with a higher proportion of adverse events. Given these findings and the (assumed) low probability that a beneficial effect would be found by the study's end, the trial was terminated as recommended by the Data Safety and Monitoring Board.

TRIAL REGISTRATION NUMBER

NCT02354144.

Assessment of the possible inhibitory effect of carrageenan in human papillomavirus DNA testing by polymerase chain reaction amplification

We assessed carrageenan's potential to inhibit human papillomavirus (HPV) DNA extraction and amplification in vaginal swab samples collected in a trial, assessing the efficacy of a carrageenan-based gel against HPV infections. Experiment #1 consisted of adding gel (carrageenan-containing or placebo) to swabs and comparing HPV DNA detection by polymerase chain reaction (PCR) to unmanipulated samples collected from the same participants. For Experiments #2 and #3, we tested vaginal samples for inhibition by addition of an internal control and amplification by real-time PCR. Experiment #4 investigated carrageenan's interference with the extraction process by assessing HPV45 detectability in undiluted and diluted HPV45 positive samples (n = 3) with carrageenan versus no gel. In Experiment #1, there was a loss of HPV positivity with the addition of carrageenan (n = 9), but none with placebo gel (n = 5). In Experiments #2 and #3, the absence of the amplified product was observed in samples from the carrageenan arm: 3.3% (1/30) and 0.5% (1/199) of samples. In Experiment #4, HPV45 was not detected in undiluted carrageenan-containing samples, but after 1/50 dilution, the same HPV45 copy number was detected. Carrageenan does not affect the DNA extraction process, and inhibition of HPV DNA amplification by carrageenan occurs infrequently.