There is a growing evidence that the consumption of probiotics may have therapeutic and protective effects on CRC (
16-
19,
21,
35). Therefore, the present work was conducted to explore the preventive effect of
L. paracasei X12 opposing the progress of CRC in the rats. It was signified that the use of
L. paracasei X12 can prevent severe weight loss in DMH-induced rats. The obtained results also elucidated that the administration of L.
paracasei X12 can prevent the onset or the growth (cell proliferation) of the tumors. It was also observed that probiotic intake could decrease the size, multiplicity, and volume of the tumors.
L. paracasei X12 use resulted in the increased apoptotic markers in the colon.
The administration of
L. paracasei X12 can prevent severe weight loss induced by DMH. In the DM group, the increase in BW was not similar to the other groups. Li
et al. (
38) have also reported that BW of the rats with DMH injection was considerably reduced, compared to the healthy rats. One of the most critical reasons for weight loss after induction of cancer is the loss of muscle mass (
39). In several studies on CRC, it was found that inadequate muscle mass is a strong determinant of mortality (
40). On the other hand, low muscle mass could lead to mitochondrial dysfunction (
41), which may accelerate cancer progression (
42). BW loss could be the result of degeneration of lipids and proteins and changes in the metabolism of the body to provide energy for hyperplastic cells (
43). As denoted previously (
43,
44), it is also believed that the administration of probiotics could improve weight loss induced by cancer.
To the best of knowledge, it was illustrated that
L. paracasei X12 use could prevent the onset of the tumors caused by DMH injection in most of the rats. In some cases, it was observed that
L. paracasei X12 use has suppressive effects on the incidence, size, multiplicity, and volume of the tumors. Furthermore, tumors were adenocarcinomatous in the majority of the DMH-induced rats, while in the treated rats (DP) just four rats had adenoma. Other data also illustrated that the probiotic intake resulted in reduced mAgNORs and pAgNORs levels of the colon cell proliferation in comparison with DMH-induced rats. In this regard, Grimoud
et al. (
45) specified that the reason for the decrease in cell proliferation after probiotics (B.breve R0070 and L.lactis R1058) administration
in-vitro is the increase in cellular differentiation and reduction of the inflammation. In another study, Chen
et al. (
15) reported that administration of L. acidophilus NCFM (10
8 CFU/mice) in female BALB/cByJ mice for 28 days led to 35.5% decrease in mean tumor volume as well as the increase in the number of apoptotic cells in treated vs. untreated mice. Zhang
et al. (
35) also implied that L. salivarius (5 × 10
10 CFU/kg for 40 weeks) substantially reduced the size, multiplicity, and volume of the tumor. Meanwhile, L. salivarius could modulate the gut microbiota of the DMH-induced rats. The proposed mechanism in that study was the increase in the activity of the immune system via improving the gut microbial composition. In another study, Konishi
et al. (
17) revealed that probiotic-derived ferrichrome administration prevented the cell growth of colon cancer cells, while it did not have any effect on cell growth of non-cancerous cells of the small intestine in the rats. Notably, the tumor-suppressive effect of ferrichrome was stronger than anticancer drugs. In contrast to this study, Arthur
et al. (
22) suggested that VSL#3 probiotic intake (10
9 CFU/animal/day) for 17 weeks could not decrees inflammation and tumorigenesis in a mouse model of colitis-associated CRC (induced by azoxymethane injection). In addition, there was no notable difference in the tumor penetrance and dysplasia score among the experimental groups. However, tumor multiplicity was meaningfully decreased in VSL#3-treated animals. According to the evidence, among the proposed mechanisms for CRC, various probiotics may reduce inflammation and strengthen immune responses (
46-
48) by improving the gut microbial composition and maintaining the integrity of the intestine (
49-
51) which is probably the main reason for inhibition of the cell proliferation and prevention or suppression of colon tumors (
52,
53).
The present study marked that
L. paracasei X12 use can ameliorate the expression of apoptosis index in the colon cells. The apoptosis mechanism is one of the most noteworthy pathways against the growth of tumors. This pathway is disrupted in cancerous cells (
54). This paper’s finding well demonstrated that
L. paracasei X12 therapy led to notable improvement in M30 CytoDEATH cells (positive cells). Although recent evidence in different
in-vitro,
in-vivo and human clinical trials have implied that the consumption of probiotics can alleviate disease symptoms, especially gastrointestinal disorders and relieve negative symptoms of CRC; however, the exact mechanisms for anticancer and cancer preventive activity of probiotics remain yet unknown (
55). One of the possible mechanisms that researchers have proposed for the anticancer effect of probiotics is the induction of apoptosis in cancerous cells via down/up-regulation of key genes in apoptosis and proliferation pathways (
56-
58) The intrinsic apoptosis pathway was regulated by two main groups of the Bcl-2 proteins, 1) the pro-apoptotic proteins (
e.g. Bax, Bak, Bad, Bcl-Xs, Bid, Bik, Bim, and Hrk) that promote release of cytochrome c and 2) the anti-apoptotic proteins (
e.g. Bcl-2, Bcl-XL, Bcl-W, Bfl-1, and Mcl-1) that block the mitochondrial release of cytochrome-c (
59). Different studies reflected that some probiotic strains, such as L. bulgaricus, L. rhamnosus GG and B. latis Bb12 can modulate some anti-apoptotic and pro-apoptotic gene expression like Bax and Bcl-2 can stimulate apoptotic protein like caspase-3 can suppress some survival signaling and can produce some metabolites, such as surfactin and short-chain fatty acids which induce apoptosis in colorectal carcinoma cells (
60). On the other hand, some investigations detailed that Jak/signal transducer and activator of transcription (STAT) signaling pathway play an outstanding role in the progression of CRC. This pathway possesses such a notable role in several physiological pathways, including cell growth/differentiation, hematopoiesis, immunity, cell survival, invasion, angiogenesis and migration by regulation of some gene expressions, such as Bcl-2, p16ink4a, p21waf1/cip1, and p27kip1, E-cadherin, VEGF, and MMPs (
61). Some studies revealed that Akt1, Jak2, and STAT3 signaling pathway can be good potential therapeutic targets in the human CRC treatment due to their activity in numerous parts of tumorigenesis and progression. As well, Ma
et al. cited that there are particular correlations between STAT3, survivin and Bcl-xl expression levels and also the level of activated phospho-STAT3 (pSTAT3) has been increased in CRC patients (
62). However, the growth of cancer cells can suppress through inhibition of Jak/STAT signaling pathway and corresponding apoptosis induction (
63).
In this study, treatment with L. paracasei X12 remarkably downregulated anti-apoptotic and proliferation inducer genes like Bcl-2, Jak-1, and Akt-1 and upregulated pro-apoptotic genes like Bax, Cas-3, -9 in DP group in comparison with DC group. Also, administration of L.paracasei prevented from induction and progression of CRC tumors in rats through suppress tumor cell proliferation and induction of apoptosis by triggering both intrinsic and extrinsic apoptosis pathways.
However, the histopathological evaluation of the colon cells illustrated that
L. paracasei X12 increase apoptotic index and also there is a crucial deference in the percentage of early and late cell apoptosis in the colon tissue, compared with the DMH-alone-exposed rats. There were notable effects in either preventing the onset of tumor cells or suppressing their growth that was probably due to the beneficial effects of the probiotic on various apoptosis pathways and decrease of the cell proliferation. In a similar study, Konishi
et al. (
17) implied that L. casei ATCC334 induces apoptosis (
i.e. caspase-3) in colon cancer cells
in-vitro through the activation of c-jun N-terminal kinase (JNK). In addition, TUNEL staining indicated that the number of apoptotic cells in the probiotic-treated cells was higher than the control cells. However, it was mentioned that their results were not investigated
in-vivo. Another study reported that the administration of L. casei ATCC393 (10
9 CFU/day) for 13 days significantly inhibited the growth of colon carcinoma cells and diminution in the tumor volume of treated mice (
64). They also signaled that L. casei ATCC393 did not substantiate perceptible differences either in CT26 or HT29 cells
in-vitro using flow cytometry, compared to the control group. Apoptosis of colon cancer cells by Annexin V and PI was reported in another study (
64). According to the evidence mentioned above, it can be concluded that apoptotic effects (evaluate different pathways) of probiotics still need to be investigated. However, the final results have been manifested to be desirable in increasing tumor cell death via apoptosis. In another study by Sharma
et al. (
30), intake of L. acidophilus (10
8 CFU/day) could inhibit the expression of the pro-apoptotic protein (Bax) and increase the anti-apoptotic protein (Bcl-2) levels via reduced oxidative stress (
17). Inhibition of the cell proliferation could be due to the increased apoptosis or not as well; since a study reported that reduction of cell proliferation was not through modulating apoptosis. It was demonstrated that the anti-proliferative effect of probiotic was through the decrement of ErbB2 and ErbB3 receptors which resulted in downstream signaling molecules E2F and cyclin D1 (
65).
Generally, the used data examplified that L. paracasei X12 administration prevented severe weight loss in DMH-induced rats. It was also well demonstrated that L. paracasei X12 use resulted in preventing the incidence of the neoplastic cell and suppression of the development of the tumor. Distinguishable changes were observed in the apoptosis markers, flow cytometry index, and cell proliferation in L.paracasei-treated rats, as well. Despite the favorable results obtained in the present study, there were some limitations, including the lack of examination of gut microbial changes that contribute to the clarity of the mechanisms of the tumor-suppressive actions of probiotics administration.
| Target genes | Sequence (5′ ➔ 3′) | Amplicon size (bp) | Annealing temperature (°C) |
|---|
| GAPDH | F: 5'- CGTGTTCCTACCCCCAATGTATC-3'R: 5'- TAGCCCAGGATGCCCTTTAG-3' | 128 | 57.9 |
| Bcl-2 | F: 5'- TGGCGATGAACTGGACAACA-3'R: 5'- CCAGTTGAAGTTGCCGTCTG-3' | 124 | 58.6 |
| Bax | F: 5'- AGCTGCAGAGGATGATTGCT-3'R: 5'- AGCAAAGTAGAAAAGGGCAACC-3' | 128 | 58.4 |
| JAK-1 | F: 5'- CTAATCGGACAACCTTTCAGAACC-3'R: 5'- AAATGGCTTGGGAGAGAAGGA-3' | 110 | 58.3 |
| Akt-1 | F: 5'- AGGCATCCCTTCCTTACAGC-3'R: 5'- CCTCTGAAAACACGCGCTC-3' | 127 | 58.5 |
| Caspase-3 | F: 5'- TGGAACTGACGATGATATGGCA-3'R: 5'- CTGGATGAACCATGACCCGT-3' | 124 | 58.7 |
| Caspase-8 | F: 5'- TTTCCGGGTCAACAGGAGCTTG-3'R: 5'- TTGATGGTCACCTCATCCAAAAC-3' | 126 | 60.1 |
| Caspase-9 | F: 5'- ACATCGAGACCTTGGATGGTG-3'R: 5'- AGTTAAAACAGCCAGGAATCTGC-3' | 129 | 58.6 |
| Groups | HC n (12) | DC n (8) | DP n (12) |
|---|
| Tumor incidence | * 0/12 | 8/8 | * 4/12 |
| Adenoma (%) (mean) | * 0 | 6.8% | 100% |
| Adenocarcinoma (%) (mean) | * 0 | 93.1% | 0 |
| Carcinoma (%) (mean) | 0 | 0 | 0 |
| Tumor volume (mm2) (mean) | * 0 | 66.6 | * 3.4 |
| Tumor multiplicity (mean) | * 0 | 10.0 | * 0.8 |
| Groups | HC n (12) | DC n (8) | DP n (12) |
|---|
| M30-positive cells (mean ± SD) | * 91.41± 9.99 | 118.3 ± 14.43 | * 174.1 ± 76.01 |
| Apoptotic index (mean ± SD) | * 0.09 ± 0.01 | 0.11 ± 0.01 | * 0.17 ± 0.01 |
| mAgNOR (mean ± SD) | * 1.21 ± 0.07 | 4.4 ± 0.09 | * 1.6 ± 0.68 |
| PAgNOR (%) | * 2% | 67% | *7% |
Effects of L. paracasei X12 on macroscopic appearance of tumor incidence, multiplicity and volume in colon of rats (A). Representative photomicrographs of histological (hematoxylin and eosin) cross-sections of colons tissue with magnification 40X from the treated and untreated rats (B). Normal colorectal tissues (HC group), colorectal adenoma (DP group) and colorectal adenocarcinoma (DC group). HC: healthy control group; DC: DMH alone group; DP: DMH induced rats treated by the L.paracasei X12
Effects of the L. paracasei X12 treatment on apoptosis markers expression. HC: healthy control group; DC: DMH alone group; DP: DMH rats treated by the L.paracasei X12