Hematometabolic profiles of breast cancer patients were presented at diagnosis and prior to treatment, and were obtained by combining target quantitative metabolomics and statistical and machine learning approaches. To our knowledge, this is the first metabolic study conducted in breast cancer patients in West African patients. To analyze the importance of this metabolic profile, we focused on bibliographic interpretations on the 13 most consensus-based discriminant variations identified by three approaches, and also looked at other less consensus-based discriminant metabolites.
A notable aspect of our findings is the involvement of two neurotransmitters, gamma aminobutyric acid (GABA) and serotonin (5-hydroxytryptamine, 5-HT). These were found to be present in the blood of breast cancer patients with reduced concentrations. These two metabolites were identified as most discriminant in each of the three analyses. These altered concentrations are further supported by other features identified within the signature. It was found that alpha aminobutyric acid (AABA), an isomer of GABA, is also reduced by two different analytical approaches. Tryptophan, a precursor to serotonin, was identified as one of the 13 most important metabolites and was found to be reduced in the blood of affected patients. Finally, 3-Indol solution acid (3-IAA), a serotonin degradation product identified through a machine learning approach alone, demonstrates increased concentrations in breast cancer patients and indicates potential metabolic blockade.
Serotonin is a biogenerating monoamine that is primarily known for its role as a neurotransmitter that regulates mood, sleep and appetite in the central nervous system. There is evidence that serotonin may have irritating effects on cancer cell proliferation, invasion, dissemination, and tumor angiogenesis in most cancerstwenty two. The breast glands express serotonin receptors that play a role in its development and maintenancetwenty two. Serotonin has been shown to cause tumorous breast cells growth through the 5-HT2A receptor cell signaling pathway, which promotes cancer cell survival and proliferation.twenty three. Human breast cancer and breast epithelial cells (MCF-10 A) have been shown to synthesize endemic serotonin. Furthermore, studies have shown that serotonin expression is higher in breast cancer tissues than in breast tissues.twenty four. Our study highlights this disruption of tumor serotonin metabolism. This may also be related to mood disorders and depression that may arise from a cancer diagnosis.twenty five.
GABA is a neurotransmitter that plays a role in inhibiting neural activity in the central nervous system. It is primarily recognized for its ability to promote relaxation, reduce anxiety and promote sleep. Further research is needed to determine whether GABA and its receptors are involved in cancer biology, including breast cancer. GABA receptors have been identified in breast cancer tissues and indicate the potential interaction between GABA signaling and cancer progression26. Reduced GABA levels within breast tumors have been demonstrated to have significant prognostic value27.
No clear data were found regarding variation in serotonin and GABA levels in blood in breast cancer patients. However, a case-control study of male breast cancer patients revealed a significant decrease in blood serotonin and GABA levels, and in line with the findings.28.
The second important feature of the most consistent part of the metabolic signature is the reduction in the concentration of six amino acids: tryptophan, lysine, threonine, leucine, methionine, and 3-methylhistidine. Additionally, seven other amino acids (valine, asparagine, tyrosine, histidine, aspartic acid, homonine and taurine) were also found to be reduced, but were less consistent across different analyses. Furthermore, our analysis revealed an increase in methionine sulfoxide concentration. This was identified through a machine learning approach. Coupled with a decrease in methionine, an increase in methionine sulfoxide leads to an increase in the Metso/MET ratio, a well-known biomarker of oxidative stress. This ratio is a particularly effective discriminant characteristic for both machine learning models and univariate analysis.
Reduction of blood amino acids was also identified in a metabolomics study comparing serum from 112 breast cancer patients with two groups: 95 and 112 healthy controls.29. This finding demonstrated that a decrease in certain amino acids may be related to breast cancer progression. was supported by several other studies, including the study of the study.30. It has been established that tumors can play a role in protein and nucleotide synthesis and increase the uptake of amino acids that function as energy substrates or cell signaling factors.29. This decrease in blood concentration of amino acids may also be due to changes in nutritional metabolism. This is a common problem among patients with advanced cancer.
Taurine and hypotaurine metabolism was identified as one of the most frequently altered metabolic pathways in breast cancer31. It has been demonstrated that taurine levels in the blood are reduced in plasma of breast cancer patients compared to healthy controls.32. Further research is needed to determine whether taurine can provide protective effects against breast cancer. For example, studies have demonstrated that taurine can inhibit the growth of human breast cancer cells and induce apoptosis by regulating mitochondrial apoptosis-related proteins.33.
The three phosphatidylcholines (PC AA C32:3, PC AE C40:1, and PC AE C34:3) are particularly important in terms of metabolic signatures, as shown in the Venn diagram. 12 additional phosphatidylcholines are located peripherally in the diagram. All of these phosphatidylcholines are present at low levels in the blood of breast cancer patients, along with one lysophosphatidylcholine. This applies to phosphatidylcholine and choline, an essential substrate for three sphingomyelins. The broader phospholipid signature was revealed primarily by OPLS-DA. Other studies have already demonstrated global decline in phosphatidylcholine, lysophosphatidylcholine, and sphingomyelin concentrations in the blood of breast cancer patients compared to healthy controls.34,35,36. This fatty agent remodeling can be attributed to altered lipoprotein metabolism and cell membrane remodeling of tumors.
One hexosylceramide (hexer (D18:1/16:0)) is crucial for metabolic signatures and ranks among the 13 most important discriminant metabolites, while the other three hexosylceramides are located close to the figure. All of these hexosylceramides show increased levels in the blood of breast cancer patients, while four ceramides show reduced levels. Ceramides are becoming increasingly important in the field of breast cancer research and treatment37,38. These sphingolipids are present in the cell membrane where they play an important role in cell signaling, particularly apoptosis. Hexosylceramides, which are associated with neutral sugar molecules, act as precursors within the cell membrane of complex glycolingolipids such as gangliosides. Furthermore, studies have shown that ceramide can be modified in breast tumors and blood.39,40,41. However, to our knowledge, an increase in the concentration of hexosylceramide in the patient's blood has not been previously demonstrated.
Finally, of the 13 most widely and continuously metabolites, xanthine is reduced in the blood of breast cancer patients, but hypoxanthine is also detected as reduced by Oprus DA alone. Xanthine and hypoxanthine are intermetabolites in the pathway of degradation of purines. They are produced by the degradation of purine nucleotides and can be converted to uric acid by the action of the enzyme xanthine oxidase. Xanthine oxidase has been demonstrated to play an important role in differentiation, and its reduced expression is associated with increased aggressiveness in breast cancer42.
In addition to the 13 most consistent metabolites, other metabolites of interest have been revealed by the overall signature.
Asymmetric dimethylarginine (ADMA) has been identified as increased concentrations in the blood of breast cancer patients through both machine learning and OPLS-DA analyses, whereas univariate analysis and machine learning show a decrease in homoalgin. ADMA is a metabolite derived from proteolysis. It functions as a competitive inhibitor of nitric oxide synthase (NOS), an enzyme that produces nitric oxide (NO) that plays a role in regulating a variety of physiological processes, including vasodilation and immune function. ADMA can affect tumor progression by disrupting NO production, which can promote cell proliferation, angiogenesis, and metastasis. This may create a favorable environment for tumor growth and disease progression. Our study revealed no studies showing elevated ADMA levels in individuals diagnosed with breast cancer. However, an increase in ADMA was observed in mice with metastatic breast cancer.43.
The concentrations of triglycerides in the blood of breast cancer patients increased, while the other three decreased. Recent research by Guma et al. (2021) shows a positive correlation between triglyceride-rich lipoproteins and breast cancer in patient blood samples44. Furthermore, elevated plasma triglycerides is associated with an increased risk of premenopausal breast cancer.45.
Two bile acids were found at higher concentrations in the blood of breast cancer patients. Glycococholic acid (GCA), has been identified in both univariate learning and machine learning analyses, while glycolsodeoxycholic acid (GUDCA) has been identified in machine learning. GCA shows a particularly strong increase, and it is noteworthy that concentrations are increased by 12 times. Three bile acids have already been demonstrated that exhibit significant elevations in the plasma of breast cancer patients, including glycolsodeoxycholic acid (FC 2.62), glycocenodeoxycholic acid (FC 4.46), and taursodeoxycholic acid (FC 6.04).46.
Bile acids also regulate gut bacteria growth, but gut microbiota is involved in the biotransformation of bile acids47. Two metabolites associated with microbiota metabolism have been found to have reduced concentrations in breast cancer patients: hippur acid (hydroacid) and indoxyl sulfate (IND-SO4). Hippur acid is a metabolite caused by the liver binding of benzoic acid and glycine, or the bacterial metabolism of phenylalanine in the intestine. Previous metabolic studies revealed a decrease in the concentration of this metabolite in the plasma of breast cancer patients compared to controls.32. Following the intake of plant foods rich in polyphenolic compounds, benzoic acids are usually produced by intestinal microbial metabolic pathways. Hippur acid has also been proposed as a biomarker of aging, as cellular and urinary levels can be affected by several age-related conditions, such as frailty, sarcopenia, and cognitive impairment.48. Furthermore, intestinal bacteria metabolize the amino acid tryptophan to indole. Subsequent oxidation and sulfonation of indole in the liver leads to the formation of 3-indoxyl sulfate (3-IS), which is subsequently excreted in the urine.
Finally, machine learning analysis confirmed a decrease in lactic acid concentration in the blood of breast cancer patients. Despite the Warburg effect observed in cancer (increased anaerobic glycolysis under aerobic conditions), blood levels of lactic acid have already been shown to have reduced breast cancer reduction (fold 0.69) despite the potential to suggest an increase in lactate tumor concentration.49.
Methodologically, this study allows for comparison of various machine learning approaches with more traditional univariate and multivariate (OPLS-DA) analyses, providing valuable insight into the relative benefits of each approach. All methodologies yielded comparable results in performance perspective, with Ridge logistic regression achieving the highest AUC. This combined approach identified the core signatures of the 13 metabolites that we consistently identify, but there was a discrepancy between the specific metabolites identified in each method. OPLS-DA provided the most comprehensive signature of the approach evaluated.
