Colorectal cancer (colorectal carcinoma, CRC) is a commonly occurring malignant intestinal tumor that poses a serious threat to public health owing to its high incidence (ranking third among reported cancers worldwide) and mortality (ranking fourth) [1]. Over recent decades, 10% of all annually diagnosed tumor cases were attributed to CRC [2]. About 1.9 million CRC cases were newly diagnosed and 880,000 CRC-related deaths occurred in 2018 [3]. The incidence of CRC has declined over the past decade in some developed regions; however, it remains high in some developing countries, and new cases are expected to rise to 2.5 million in 2035 worldwide [2, 4]. Risk factors including aging, lifestyle, and genetic and environmental influences play important roles in the malignant transformation processes of CRC [4, 5]. About 10–20% of CRC patients have family history of the disease [6]. Both genetic factors (various oncogenes such as carcinoembryonic antigen [CEA], carbohydrate antigen 19-9 and carbohydrate antigen 724, cytokines, and chemokines) and epigenetic factors (such as non-coding RNAs) have vital roles in the biological activities of CRC [7, 8]. Although various treatments (including surgical resection, radiotherapy, chemotherapy, and, most recently, immune-targeted therapy) are available for CRC patients, the 5-year survival rate (around 50–65%) has shown no substantial change in recent years, owing to local tissue relapse and distant metastasis [9]. Therefore, it is extremely important to understand the mechanisms involved in the occurrence and development of CRC so as to improve prevention, early diagnosis, and treatment.

Chemokines are a group of small soluble proteins released in pathological circumstances that play an essential role in immune reactions (for example, recruitment of Th1 lymphocytes, wound healing, cell differentiation, metabolism, and prostaglandin synthesis) by binding to their specific chemokine receptors [10]. One chemokine can have several receptors, and a receptor normally has several ligands [10]. Chemokines can be expressed in many cell types, including fibroblasts, neutrophils, macrophages, and endothelial cells [10, 11, 12]. Chemokines such as chemokine (C-X-C) ligand 17 (CXCL17) and chemokine (C-X-C) ligand 16 (CXCL16) were found to be produced by tumor cells in colon cancer, and shown to be associated with bad prognosis [13, 14, 15, 16]. Chemokines originating from the tumor microenvironment promote the signal transduction of tumor cells by activating related signal pathways [17, 18, 19]. The chemokine ligand 7 (CXCL7), also named NAP-2, is released mostly by platelets, and exerts effects in diverse cancers by activating its specific CXCR1 and CXCR2 receptors [20].

Metabolic reprogramming, a common feature of malignant tumors, can accelerate cancer progression and metastasis [21]. To sustain the growth of tumor tissue, cells must take in more nutrients to support rapid and sustained metabolism. Carbohydrates are an important energy source, so glucose metabolism has biological roles in various cellular physiological and pathological processes [22]. Glycolysis is a series of enzymatic reactions that can generate lactic acid and produce energy (adenosine triphosphate) in the cytoplasm [23]. Many studies have shown that even under aerobic conditions, tumor cells preferentially rely on glycolysis to meet the needs of cells; this phenomenon is known as the Warburg effect or aerobic glycolysis [23]. The acidic tumor microenvironment, which depends on lactic acid, can promote tumor tissue invasion and distant metastasis [24]. Lactate dehydrogenase (LDH), a key enzyme in glycolysis, is related to the occurrence, development, and prognosis of various tumors and is highly expressed in multiple cancers [21, 23, 25]. Depending on differences in its coding genes, LDH has six isozymes. Lactate dehydrogenase A (LDH-A), one of the most important subunits of LDH, is mainly expressed in skeletal muscle and preferentially converts pyruvate to lactate [26]. Moreover, LDH-A has been found to be highly expressed in a variety of tumors, and its expression level is closely related to clinical stage and prognosis [27].

Many studies have shown that chemokines play vital roles, via aerobic glycolysis, in tumor glucose metabolism and function in various aspects of proliferation, metastasis, and other physiological activities [13, 14, 15, 16, 17, 18, 19, 28, 29]. Our previous work also found that overexpression of CXCL7 led to worse survival in CRC patients [20]. However, the relationship between CXCL7 and glycolysis has remained unclear. In the present study, we used immunohistochemistry (IHC) to measure the expression of CXCL7 and LDH-A in 158 CRC patients, and comprehensively explored the relationship of the two proteins. We also investigated the prognostic value of CXCL7 and LDH-A in CRC patients by constructing Cox regression models and a nomogram.

CRC is one of the most common lethal tumors of the digestive system and represents a serious threat to human health and a heavy burden on families and society. The morbidity and mortality of CRC are increasing year by year, and in recent years, its incidence has been increasing in developing countries, especially in China [30]. Early accurate diagnosis is extremely important for CRC patients. Clinically, a diagnosis is based on the patient’s symptoms and signs and the results of auxiliary examinations [31]; however, early symptoms are often not obvious or representative, which may easily lead to missed diagnosis [32]. Laboratory examinations, such as conventional CEA, can facilitate patient screening to some extent [33]. Computed tomography, ultrasonography, and magnetic resonance imaging are all helpful for early diagnosis [34, 35, 36]. However, these methods and the diagnostic gold standard, tissue biopsy, have certain limitations. Appropriate treatments should be selected according to the clinical diagnosis of CRC patients. These treatments, which include surgery, neoadjuvant therapy, adjuvant therapy, targeted therapy, and comprehensive treatment [37], can extend patients’ survival time and improve postoperative quality of life. Recurrence and metastasis are the most important causes of cancer-related deaths. Numerous oncogenes, tumor suppressor genes, cytokines, and chemokines have been shown to play important roles in the processes of recurrence and metastasis [8, 13, 20, 23]. Previous studies have shown that glycolysis plays critical parts in tumor progression, especially in recurrence and metastasis [24, 38]. Although many molecules and pathways are involved in the regulation of glycolysis in CRC [39, 40], the association between CXCL7 and glycolysis has not yet been well explored. Therefore, the present study evaluated the relationship between CXCL7 and glycolysis, and the prognostic value of CXCL7 level in CRC.

Chemokines are gradually being recognized as important agents in tumor progression, with regulatory roles in tumor activity in addition to the traditional chemotaxis [14, 15, 16]. They function in both anti-cancer and cancer-promoting processes and can regulate proliferation, metastasis, communication between cells, and other activities of cancer cells [14, 41, 42]. In the present study, the results, which were similar to those of our previous study [20], showed that CXCL7 levels are higher in CRC tissue than in non-CRC tissue, and overexpression of CXCL7 was positively linked to N stage and TNM stage, as well as to worse outcomes for CRC patients. What is more important is that CXCL7 level was shown to be an independent risk factor in CRC prognosis by Cox regression analysis. Comprehensively, analysis of the results of this study, and of our previous study [20], demonstrate that increased levels of CXCL7 may be a good prognostic marker in CRC.

Cells require glycolysis for survival under hypoxic conditions and in certain physiological or pathological circumstances [43]. In the 1920s, Otto Warburg found significantly higher levels of glycolysis in tumor cells than in normal cells. Even under aerobic conditions, tumor cells tend to maintain high levels of glycolysis, whereas the glycolytic pathway is often inhibited in normal cells [44]. Several studies have identified glycolysis as a mediator of tumorigenesis in different types of tumors, and high levels of glycolysis are associated with a poor prognosis for patients [43, 45]. Various molecules, substances, and metabolic pathways are involved in the process of glycolysis. Notably, LDH-A is a catalytic enzyme that is highly expressed in a variety of tumor cell types and is associated with prognosis [21, 25, 26, 27, 46]. In the present study, we found that LDH-A was significantly more highly expressed in CRC tumor cells than in normal cells, and that this high level of expression was associated with poor survival time of CRC patients. These results were consistent with those of previous studies [46, 47].

Numerous chemokine receptors and ligand networks play crucial roles in the occurrence and development of tumors, especially in CRC [42, 48]. Our previous studies showed that CXCL7 was highly expressed in the serum of CRC patients [49, 50]. In addition, several noteworthy studies have revealed a relationship between chemokines and glycolysis [51, 52]. Therefore, the function of CXCL7 in glycolysis was explored in the present study using CRC tissue. First, LDH-A was selected as a biomarker of aerobic glycolysis owing to its vital roles in the catalytic process of glycolysis [52]. Then, the expression of CXCL7 and LDH-A was investigated by IHC staining, and a positive correlation was found between CXCL7 and LDH-A expression. Next, Cox regression analysis revealed that CXCL7 and LDH-A levels were correlated with OS according to univariate analysis. However, in the multivariate analysis, although CXCL7 level was still correlated with OS, LDH-A level was not found to be an independent risk factor. In view of the fact that receptors of CXCL7, CXCR1, and CXCR2 are important for tumor progression [53, 54], we speculate that there may exist a receptor-dependent process related to the prognostic value in the relationship between CXCL7 and LDH-A. Last, a nomogram was constructed and evaluated; the results showed that CXCL7 is an independent risk factor in CRC. In addition, in view of the high ROC curve of CXCL7 and LDH-A, multiple-biomarker dependent logistic regression model may have high value in clinical applications. In view of these results, we assume that CXCL7 may act on glycolysis by altering levels of LDH-A in CRC; this is consistent with the findings of several studies that the process of glycolysis in cancers may be promoted by chemokines [53, 54, 55].

Surgical methods, postoperative treatments, nursing methods, patient’s mental state, and other factors can all affect prognosis [56, 57, 58, 59], therefore these general factors will be included in our future study. The reason that the combination of high levels of LDH-A and CXCL7 did not increase the median OS, compared to CXCL7 alone, should be also explored. The numbers of CRC patients enrolled in future studies should be increased to better identify the connection between CXCL7 and LHD-A, and the correlation of CXCL7 score and LDH-A score may involve certain confounding factors, which should be thoroughly studied in future. In addition, future studies might include different methods of measuring the expression of CXCL7 and LHD-A (e.g., Western blot) to ensure the stability of results, and the decimal scale of scoring could be narrowed to 0.1. It is important that the mechanism by which CXCL7 affects glycolysis should be further explored by constructing cell and animal models. Further clarification is needed on the specific forms of regulation between CXCL7 and LDH-A. In future, series studies will be designed to determine whether targeting CXCL7 and LDHA expression proves to be beneficial in treating CRC patients.

In summary, this study offers firm evidence that CXCL7 expression is positively correlated with LDH-A expression, and that CXCL7 level is an independent risk factor in CRC prognosis.

CRC, colorectal cancer; LDH, lactate dehydrogenase; LDH-A, lactate dehydrogenase A; IHC, immunohistochemistry; TNM, tumor-node-metastasis; ROC, receiver operating characteristic; OS, overall survival time; HR: high risk factor; 95% CI, 95% confident intervals; T, depth of tumor invasion; N, nodal involvement; M, distant metastasis; r, correlation coefficient; AUC, area under the ROC curve.

All data are available from the authors for reasonable purposes.

HL, Conceptualization, Funding acquisition and Writing-review & editing; LL, Conceptualization, Formal analysis, Methodology, Supervision and Writing-review & editing; BH, Funding acquisition, Data curation, Investigation and Project administration; RJ, Software, Supervision and Writing-original draft; GC, Resources and Visualization; JA, Formal analysis and Validation; SH, Conceptualization, Formal analysis and Funding acquisition. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

The CRC samples were obtained with informed consent from patients and approved by the Institutional Research Ethics Committee of Bozhou Hospital of Anhui Medical University (No.202298).

We sincerely thank all the staff of the Central Laboratory of Bozhou Hospital of Anhui Medical University for their support.

This research was supported by the Bozhou science and technology major special projects (No. bzzd2020012), the Bozhou Key R&D projects (No. bzzc2021020), Key R&D and Development Projects in Anhui Province (No. 2022e07020066).

The authors declare no conflict of interest.