Propionic acid supplementation promotes the expansion of regulatory T cells in patients with end-stage renal disease but not in renal transplant patients

Abstract

In a previous study, we showed an anti-inflammatory effect of propionic acid supplementation in dialysis patients. The present study intends to analyze the effect of propionic acid on the chronic inflammatory state and T-cell composition in kidney transplant patients compared to dialysis patients. A total of 10 dialysis patients and 16 kidney transplant patients under immunosuppressive standard triple immunosuppressive therapy received 2 × 500 mg propionic acid per day for 30 days. The cellular immune system was analyzed before and after the propionic acid supplementation and 30-90 days thereafter as a follow-up. We measured the main immune cell types and performed an in-depth characterization of T cells including regulatory T cells (Tregs), B cells, and dendritic cells. In addition, we assessed the functional activity and antigenic responsiveness by analysis of third-party antigen-specific T cells after their stimulation by recall (tetanus diphtheria vaccine) antigen. In dialysis patients, we observed an expansion of CD25^highCD127^- Tregs after propionic acid intake. In contrast, the same supplementation did not result in any expansion of Tregs in transplant patients under immunosuppressive therapy. We also did not observe any changes in the frequencies of the main immune cell subsets except for CD4⁺/CD8⁺ distribution with an increase of CD4⁺ T cells and decrease of CD8⁺ T cells in the transplant population. Our data suggest that dietary supplements containing propionate might have a beneficial effect decreasing systemic inflammation in dialysis patients through Treg expansion. However, this effect was not observed in transplant patients, which could be explained by counteracting effect of immunosuppressive drugs preventing Treg expansion.

Keywords: immunity; immunosuppression; kidney transplantation; propionate; regulatory T cells.

Figure 1

Percentage of regulatory T cells (Tregs) in hemodialysis patients and kidney transplant recipients (KTR) after propionic acid treatment. Peripheral blood mononuclear cells from hemodialysis patients and KTR were isolated at the beginning (D0) and end (D30) of propionic acid supplementation and 60 days thereafter (D90), stained with the appropriate antibodies and analyzed in a flow cytometer. (A) Regulatory T cells were identified as CD3+CD4+CD25+FoxP3+. (B,C) In the Treg population, gut homing (GH) Tregs were identified as Beta7+CCR9+ and thymus generated natural Tregs (nTregs) as Helios+. (D–F) Central memory (CM), effector memory (EM), and naïve T cells were identified by CCR7 and CD45RA. Pairwise Mann–Whitney U test was performed. ns, not significant. *p-value < 0.05.

Figure 2

Percentage of monocyte and granulocyte populations in hemodialysis patients and kidney transplant recipients (KTR) before and after propionic acid treatment. Peripheral blood mononuclear cells from hemodialysis patients and KTR were isolated at the beginning (D0) and end (D30) of propionic acid supplementation stained with the appropriate antibodies and analyzed in a flow cytometer. (A–D) Monocytes were identified by sidescatter profile and CD45, CD14, and CD16 expression. (E–H) Granulocytes were identified by sidescatter profile, CD45, and CD16 expression. Pairwise Mann–Whitney U test was performed. ns, not significant. *p-value < 0.05.

Figure 3

Percentage of monocyte and granulocyte populations in hemodialysis patients and kidney transplant recipients (KTR) before and after propionic acid treatment. PBMCs from hemodialysis patients and KTR were isolated at the beginning (D0) and end (D30) of propionic acid supplementation stained with the appropriate antibodies and analyzed in a flow cytometer. (A–I) Lymphocytes were identified by sidescatter profile and CD45. B cells as CD19+CD3-, natural killer (NK) cells as CD3-CD56+, natural killer T (NKT) cells as CD3+CD56+, and T cells as CD3+ and CD4+ or CD8+. (J,K) Peripheral blood mononuclear cells were stimulate for 18h with tetanus-diphtheria (TD) vaccine and stained with the appropriate antibodies and analyzed in a flow cytometer. Activated T helper cells were identified as CD4+ CD154+CD137+ and activated cytotoxic T cells as CD8+CD137+. Pairwise Mann–Whitney U test was performed. ns, not significant. *p-value < 0.05.