In vitro activity of zinc salts against human rhinoviruses

Abstract

The antiviral activity of zinc salts against rhinovirus types 1A and 39 was assayed by yield reduction and inhibition of cytopathic effect in cell culture. The findings indicate that the zinc salts tested have low in vitro therapeutic indices and suggest that the possible beneficial effects of zinc lozenges in reducing cold symptoms may not be related to selective antirhinovirus activity.Zinc ions inhibit the in vitro replication of diverse viruses, including rhinovirus (4, 5), herpes simplex virus (7), and vaccinia virus (3), and other pathogenic organisms, including Chlamydia trachomatis (2). Zinc chloride (0.1 mM) inhibited plaque formation by eight of nine human rhinoviruses in HeLa cells and reduced the yield of rhinovirus 1A when added as late as 6 to 8 h after infection (5). The antirhinovirus activity of this zinc salt appears to be mediated by inhibition of posttranslational cleavage of precursor polypeptides (4). Zinc gluconate lozenges were reported to be effective in reducing the duration of symptoms in natural colds of undefined viral etiology (1). In contrast, another study, using a somewhat lower dosage of zinc acetate lozenges, found no clinical benefit compared with a placebo in the treatment of natural colds (R. Douglas, personal communication). Unpalatable taste, mouth irritation, and nausea have been reported side effects of zinc lozenge administration (1; B. M. Farr and J. M. Gwaltney, Jr., J. Chronic Dis., in press).The present studies were undertaken to determine the in vitro antiviral activity of a variety of zinc salts against two human rhinoviruses representing serotypes previously shown to be inhibited by zinc chloride (5). Serotype 1A (passage history: MRC-5/5, WI-38/1, fetal tonsil/1) and serotype 39 (passage history: WI-38/2, MRC-5/4) were used. The following zinc salts (molecular weight) were provided by R. G. Achari, Bristol Meyers Products, Inc., Hillside, N.J.: acetate (243.5), carbonate (125.4), chloride (136.3), gluconate (455.7), lactate (183.5), sulfate (161.4), and oxide (81.4). The salts were dissolved in sterile distilled water or 0.1 N HCl to make stock solutions of 10 mM concentration. Serial logl0 or 0.5 log10 dilutions of the stock solutions were made in cell culture maintenance medium appropriate to the cell type. MRC-5 and WI-38 human embryonic lung fibroblast cells (M.A. Bioproducts, Inc., Walkersville, Md.) at passage levels 23 to 25 were maintained in Eagle minimal essential medium supplemented with glutamine, 2% fetal bovine serum (HyClone Laboratories, Logan, Utah), vancomycin (20 jig/ml), gentamicin (50 ,ug/ml), and amphotericin (1 jig/ml). For cytopathic effect (CPE) inhibition and infectious virus yield reduction assays, monolayers of a particular cell type were inoculated with 0.2 ml of Hanks balanced salt solution (HBSS) containing 30 to 1,000 50% tissue culture infective doses (TCID50) of virus. After incubation at 35°C for 1 h, the inoculum was decanted, and the monolayers were rinsed once or twice with Hanks balanced salt solution. The monolayers were o...

Inhibition of Polyprotein Processing and RNA Replication of Human Rhinovirus by Pyrrolidine Dithiocarbamate Involves Metal Ions

“…Comparison of the antiviral activities of various zinc salts showed that the therapeutic index is very low (12). There are conflicting results on the effectiveness of zinc gluconate or zinc acetate in the treatment of the common cold in clinical trials (42,46).…”

Two randomized controlled trials of zinc gluconate lozenge therapy of experimentally induced rhinovirus colds

“…Nasal mucus weights and the numbers of paper tissues used were slightly higher in zinc recipients. A statistically significant increase in levels of zinc in serum was documented in zinc recipients after 5 days of therapy. These data suggest that zinc gluconate lozenge therapy is not therapeutically useful in the treatment of rhinovirus colds.…”

“…There is still no effective therapy for the many viruses causing this condition. Zinc has been shown to inhibit viral polypeptide cleavage, thus inhibiting the replication of several viruses which cause common colds (1, 2, 9, 10), but the antirhinoviral activity in WI-38 or HeLa cell monolayers is only modest (5). A randomized controlled trial of zinc gluconate lozenge therapy in naturally acquired common colds has suggested remarkable efficacy, with symptom duration reduced by half (4).…”

“…In trial 1, lozenges containing either zinc gluconate (23 mg of elemental zinc) or placebo were given 36 h after nasal inoculation of rhinovirus type 39 and administered eight times per day for 5 days. All of the volunteers had early cold symptoms at the time that treatment was begun.…”

Antipicornavirus Drugs: Current Status

“…However, no reduction in the rate or amount ofvirus shedding occurred. The results of further studies suggested that no beneficial effect resulted from the use of either zinc acetate or zinc gluconate Douglas et al, 1987;Geist et al, 1987). In addition, the results of a study involving the ingestion ofzinc where subjects ingested 300 mg day-l for 6 weeks indicated that there was a significant reduction in lymphocyte proliferative responses, polymorphonuclear phagocytic function and high-density lipoprotein concentrations (Chandra, 1984).…”