**Background:** Glutaredoxin 1 (Grx1) is a key enzyme that reverses S-glutathionylation, a reversible oxidative modification of protein cysteine residues, thereby regulating redox signaling and protecting against oxidative stress. Colorectal cancer (CRC) is the third most common cancer worldwide, and early diagnosis is critical as 5-year survival for stage I is ~92% but drops to <10% for stage IV. The role of Grx1 in gastrointestinal carcinogenesis is poorly understood. This study aimed to evaluate Grx1 protein expression in colon adenocarcinoma tissues and serum, correlate it with clinicopathological features and survival, and confirm findings in vitro using colorectal cancer cell lines.
**Methods:** The study included 135 patients (65 men, 70 women; mean age 64 years, range 55–77) with primary colon adenocarcinoma stages I–III, who underwent colon resection at Jaworzno Municipal Hospital (2014–2017). Exclusion criteria included preoperative radiotherapy/chemotherapy, severe comorbidities, distant metastases, inflammatory bowel disease, or recurrence. Grx1 expression was assessed by immunohistochemistry (IHC) on formalin-fixed paraffin-embedded tissue sections using anti-Grx1 antibody (GeneTex, dilution 1:700) and scored using an immunoreactive score (0–12) categorized as low (scores I–II) or high (scores III–IV). Immunofluorescence and immunogold electron microscopy were performed on selected samples. Serum Grx1 levels were measured by ELISA in 73 patients and 20 healthy controls. In vitro, GRX1 mRNA expression was analyzed by qRT-PCR in colorectal cancer cell lines SW 1116 (Duke A/stage I), LS 174T (Duke B/stage II), and HCA-2 (Duke C/stage III), with CCD 841 CoN as normal control; protein expression was confirmed by Western blot. Statistical analyses included chi-squared tests, Kaplan-Meier survival curves, log-rank tests, and multivariate analysis.
**Key Results:** High Grx1 IHC expression was found in 34/135 (25.19%) of colon adenocarcinoma samples, while 101/135 (74.81%) had low expression. Grx1 expression was significantly correlated with histological grade (p<0.001): high expression in 61.90% of G1, 22.22% of G2, and 11.90% of G3 tumors. For depth of invasion, 62.86% of T1/T2 patients had high Grx1 vs. 12% of T3/T4 patients. Angioinvasion-positive patients had 19.81% high Grx1 vs. 44.83% in angioinvasion-negative. Lymph node involvement: N1/N2 group had 3.85% high Grx1 vs. 57.39% in N0. By stage, 87.50% of stage I patients had high Grx1, while only 1.33% of stage III patients had high expression (p<0.001). PCNA expression inversely correlated: 86.02% of high PCNA cases had low Grx1. Kaplan-Meier analysis showed significantly better 5-year survival for patients with high Grx1 expression (log-rank, p<0.001). Subgroup analysis revealed significant survival benefit in G1 (p=0.046), G2 (p=0.001), T1/T2 (p<0.001), and high PCNA (p=0.007) groups, but not in G3, T3/T4, or by stage. Multivariate analysis indicated Grx1 was not an independent prognostic factor; staging, depth of invasion, and PCNA were independent. Serum Grx1 levels were significantly lower in patients (mean 17.76 ng/mL, median 11.61 ng/mL) vs. healthy controls (mean 45.43 ng/mL, median 47 ng/mL; p<0.001). Stage I patients had highest serum Grx1 (mean 40.69 ng/mL, median 45.66 ng/mL) vs. stage III (mean 6.21 ng/mL, median 3.55 ng/mL; p<0.001). Higher serum Grx1 was associated with better survival: median OS 51 months for high vs. 24 months for low (p=0.020). In vitro, GRX1 mRNA was highest in LS 174T (stage I) and lowest in HCA-2 (stage III); Western blot showed highest Grx1 protein in SW 1116 and control CCD 841 CoN.
**Clinical Implications:** Grx1 expression is high in normal colon mucosa and early-stage colon cancer but decreases with tumor progression, suggesting a protective role against oxidative stress. Low Grx1 expression in tissue and serum may serve as a biomarker for aggressive disease and poor prognosis. Serum Grx1 measurement could enable non-invasive monitoring of cancer progression. However, Grx1 is not an independent prognostic factor; its value is enhanced when combined with established parameters like depth of invasion and PCNA expression. Limitations include a relatively small cohort and exclusion of stage IV patients. Future studies with larger samples and molecular investigations are needed to clarify Grx1's mechanistic role.