Effects of Chlorella vulgaris on tumor growth in mammary tumor-bearing Balb/c mice: discussing association of an immune-suppressed protumor microenvironment with serum IFNγ and IgG decrease and spleen IgG potentiation

Abstract

Purpose: Chlorella vulgaris (CV) has exhibited immune-enhancing and protective activities against cancer and infections. However, there is an increasing concern about the use of Chlorella species in human, regarding its various molecules with antigenic features found in infectious microorganisms. Our goal was to investigate the impact of higher concentrations of CV on tumor growth in spontaneous mouse mammary tumor (SMMT) models.

Methods: Balb/c mice were daily given CV powder at doses of 0, 200, or 300 mg/kg for 42 days (CONTROL, CV200, and CV300 groups, respectively; n = 6/group). On day 14, the SMMT was inoculated. Tumor volume (TV) and body weight (BW) were monitored on 5-day intervals following tumor challenge. On day 43, blood, spleen, lungs, and tumor tissues were collected. Histopathological examinations on lungs and tumor tissues were performed following hematoxylin-eosin staining. Intratumor expression of 27 genes was assessed by real-time PCR. Total IgG, IFNγ, and IL-4 levels in serum and spleen culture supernatant were measured by ELISA.

Results: The TV/BW index showed significant increase in the CV200 group compared to the CONTROL (p = 0.047). The CV200 tumors exhibited more malignant phenotype, higher angiogenesis rate, and lower peritumoral neutrophil and macrophage-to-lymphocyte infiltration ratio compared to the CONTROL. Serum concentrations of IFNγ, IL-4, and IgG were declined, and the spleen IFNγ and IgG production was higher in the CV200 compared to the CONTROL. The IL-1β, IL-10, TGFβ1, FOXP3, HO-1, Gr1, CD11b, PCNA, LCN2, iNOS2, VEGFR2, CD31, and CD105L expressions were markedly increased in the CV200 tumors compared to the CONTROL (p = 0.001, 0.002, 0.006, 0.021, 0.004, 0.030, 0.016, 0.031, 0.025, 0.008, 0.014, 0.022, and 0.037, respectively). The changes in cytokine, IgG and gene expression values considerably correlated with tumor size, as well as with each other.

Conclusions: Our data provided evidence that C. vulgaris at a specific dose (200 mg/kg) promoted tumor growth in a mammary tumor model. This consequence might reflect an immune derangement in favor of developing a protumor microenvironment. However, this hypothesis needs to be further investigated in future.

Keywords: Angiogenesis; Chlorella vulgaris; Immunosuppression; Spontaneous mouse mammary tumor; Tumor progression.