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. 2025 May 19:12:1582967.
doi: 10.3389/fmolb.2025.1582967. eCollection 2025.

Low-Dose naltrexone restored TRPM3 ion channel function in natural killer cells from long COVID patients

Etianne Martini Sasso  1   2   3 , Natalie Eaton-Fitch  1   2 , Peter Smith  2   4 , Katsuhiko Muraki  2   5 , Sonya Marshall-Gradisnik  1   2
Affiliations

Low-Dose naltrexone restored TRPM3 ion channel function in natural killer cells from long COVID patients

Etianne Martini Sasso et al. Front Mol Biosci. .

Abstract

Introduction: Long COVID is a multisystemic condition that includes neurocognitive, immunological, gastrointestinal, and cardiovascular manifestations, independent of the severity or duration of the acute SARS-CoV-2 infection. Dysfunctional Transient Receptor Potential Melastatin 3 (TRPM3) ion channels are associated with the pathophysiology of long COVID due to reduced calcium (Ca2+) influx, negatively impacting cellular processes in diverse systems. Accumulating evidence suggests the potential therapeutic benefits of low-dose naltrexone (LDN) for people suffering from long COVID. Our study aimed to investigate the efficacy of LDN in restoring TRPM3 ion channel function in natural killer (NK) cells from long COVID patients.

Methods: NK cells were isolated from nine individuals with long COVID, nine healthy controls, and nine individuals with long COVID who were administered LDN (3-4.5 mg/day). Electrophysiological experiments were conducted to assess TRPM3 ion channel functions modulated by pregnenolone sulfate (PregS) and ononetin.

Results: The findings from this current research are the first to demonstrate that long COVID patients treated with LDN have restored TRPM3 ion channel function and validate previous reports of TRPM3 ion channel dysfunction in NK cells from individuals with long COVID not on treatment. There was no significant difference in TRPM3 currents between long COVID patients treated with LDN and healthy controls (HC), in either PregS-induced current amplitude (p > 0.9999) or resistance to ononetin (p > 0.9999).

Discussion: Overall, our findings support LDN as a potentially beneficial treatment for long COVID patients by restoring TRPM3 ion channel function and reestablishing adequate Ca2+ influx necessary for homeostatic cellular processes.

Keywords: TRP ion channels; TRPM3; Transient Receptor Potential Melastatin 3; calcium; long COVID; low-dose naltrexone.

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Conflict of interest statement

EMS, NE-F, and SM-G declare that an Australian provisional patent application 2022902253 entitled “Methods for detecting post COVID-19 condition” relates to the use of Transient Receptor Potential ion channels dysfunction in identifying, screening, diagnosing, or managing/treating people with post COVID-19 condition. PS and KM declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
TRPM3 ion channel function in NK cells modulated with PregS and ononetin. (A–C) Current obtained on an NK cell from an HC participant. (A) A representative time-series of current amplitude at +100 mV and −100 mV. (B) I–V curve before (baseline) and after TRPM3 stimulation through PregS application. (C) I–V curve on PregS stimulation and after TRPM3 inhibition with ononetin in the presence of PregS. (D–F) Current obtained on an NK cell from a long COVID participant. (D) A representative time-series of current amplitude at +100 mV and −100 mV. (E) I–V curve before (baseline) and after TRPM3 stimulation through PregS application. (F) I–V curve on PregS stimulation and after TRPM3 inhibition with ononetin in the presence of PregS. (G–I) - Current obtained on an NK cell from a long COVID participant on treatment with LDN. (G) A representative time-series of current amplitude at +100 mV and −100 mV. (H) I–V curve before (baseline) and after TRPM3 stimulation through PregS application. (I) I–V curve on PregS stimulation and after TRPM3 inhibition with ononetin in the presence of PregS. Dash lines in (A,D,G) illustrate each trend of the baseline and PregS effects. Abbreviations: HC, healthy control; LC, long COVID; LDN, low-dose naltrexone; NK, natural killer; PregS, pregnenolone sulfate.
FIGURE 2
FIGURE 2
TRPM3 ion channel function comparison among long COVID, HC and long COVID taking LDN groups. (A) Bar graph showing TRPM3 current amplitude at +100 mV after TRPM3 stimulation through PregS application in long COVID (N = 9; n = 61), HC (N = 9; n = 65) and long COVID taking LDN (N = 9; n = 63). (B) Bar graphs illustrating TRPM3 inhibition with ononetin in the presence of PregS in long COVID (N = 9; n = 52), HC (N = 9; n = 53) and long COVID taking LDN (N = 9; n = 53). (C) Bar graphs representing the percentage of NK cells sensitive and insensitive to ononetin inhibition in the presence of PregS. (D–F) Scatter plots showing change of each current recording in NK cells from long COVID, HC and long COVID taking LDN groups, respectively; first point was measured at the end of TRPM3 stimulation through PregS application, and the second point shows the effect in current amplitude after TRPM3 inhibition with ononetin in the presence of PregS. Each red line represented a cell sensitive to ononetin as a reduction in amplitude was recorded. N = participants and n = number of records. Data presented as mean ± SEM and determined by Kruskal–Wallis (Dunn’s multiple comparisons, (A,B) in amplitude analysis and Fisher’s exact test (Bonferroni method, C) regarding ononetin response. Abbreviations: HC, healthy control; LC, long COVID; LDN, low-dose naltrexone; N, number of participants; n, number of records analyzed; NK, natural killer; PregS, pregnenolone sulfate.
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