The significance of taurine for patients with Crimean-Congo hemorrhagic fever and COVID-19 diseases: a cross-sectional study

Introduction

Crimean-Congo hemorrhagic fever (CCHF) is caused by Crimean-Congo hemorrhagic fever virus (CCHFV; order Bunyavirales; family Nairoviridae) [1]. CCHF takes the form of a critical hemorrhagic fever, which may potentially conclude fatally. A fatality rate of 5–30 % is generally reported [2].

The new coronavirus disease (COVID-19), which was initially identified as an unknown factor of pneumonia in December 2019 within the Hubei state of China, was declared a pandemic in March 2020 by the World Health Organization and resulted in the global formation of issues within healthcare systems. COVID-19 has had a catastrophic effect on the world, resulting in more than six million deaths worldwide [3].

Many similarities as well as differences between these two viruses that have a significant impact on public health can be found. Common symptoms of COVID-19 are fever, dry cough, weakness, loss of taste/smell, and shortness of breath [4]. Common clinical findings of CCHF include fever, malaise, nausea, vomiting, stomach pain, myalgia, petechiae, and ecchymosis [2]. CCHFV is transmitted to humans through infected tick bites, viremic animals, or direct contact with humans [1]. The primary mode of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is via exposure to respiratory droplets carrying the infectious virus from close contact or direct transmission from presymptomatic, asymptomatic, or symptomatic individuals harboring the virus [3]. CCHF has many acute effects on various organs. These effects can cause widespread ecchymosis, internal bleeding, and impaired liver function. The main laboratory findings of it are compatible with leucopenia, thrombocytopenia, increases in liver enzymes, and extended bleeding profiles [4]. On the other hand, elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT) enzymes, lymphopenia, and thrombocytopenia in COVID-19 patients may be an indicator of poor prognosis [5].

Some studies have shown that increases or decreases in amino acids may be an important prognostic factor [6], 7]. Taurine is classified as a non-essential amino acid, not involved in protein synthesis because it lacks a carboxyl group [8]. Taurine, alongside its repressive effects on infections, oxidative stress, and inflammations, has also been reported to demonstrate antimicrobial, antidiabetic, and antitumor activities. On the one hand, the high concentration of taurine and its carrier in lymphocytes has provided significant pieces of evidence regarding the fact that taurine plays a significant role in defending against oxidative stress [8]. On the other hand, it has been correlated with many oxidative stress-mediated pathologies, including low serum taurine levels, hepatic disorders, epilepsy, cardiomyopathy, cystic fibrosis, alcoholism, Alzheimer’s disease, growth deficiencies, and retina degeneration [9]. Some studies in the literature have reported increased oxidative stress in patients with CCHF [10] and COVID-19 [11]. Therefore, it is probable that taurine levels were affected by CCHF and COVID-19 diseases.

The carnosine amino acid is formed through the combination of beta-alanine and l-histidine by the carnosine synthase enzyme [12]. Many biological effects of carnosine and its precursor, beta-alanine, have been identified. On a cellular level, carnosine enters reactions with the damage products of reactive oxygen species, reactive nitrogen species, and biomolecules. Thus, it protects other biomolecules from modifications and damage [13]. l-arginine is a substrate utilized by nitric oxide synthases for nitric oxide (NO) production. It is currently known that NO, which focuses on the effects of viral infections, has antiviral activity. The direct effect of NO may cause the inhibition of viruses, and NO is accepted to be among the most early antiviral responses [14].

In the CCHF and COVID-19 diseases caused by viruses, the behaviors of amino acids and the response of the amino acid metabolism are not definitively known. There are few studies on this subject. The authors did not find any other study in the literature comparing amino acid levels in COVID-19 and CCHF patients. Our purpose in this study was to compare taurine levels in these two significant diseases (CCHF and COVID-19), which have significant effects on public health and frequently cause mortality and morbidity.

Materials and methods

This study was conducted using data from two studies that were previously obtained from the ethics committee of a university hospital, with the ethics committee decisions numbered 2019-04/02 and 2020-04/02. In these studies, amino acid levels of COVID-19 and CCHF patients were determined. Approval was obtained from the University Medical Faculty Ethics Committee with decision number 2023-09/16.

G*Power (Version 3.1.9.6) program was used to calculate the power of the sample. In the study, the reliability was taken as 95 % and the effect level as 0.50, and the power was found to be 90 % with a sample of 35 people for each group (105 people in total). This study was carried out in a tertiary-level university hospital and included three groups. The CCHF group consisted of patients with a history of contact with ticks who presented to the emergency department after the onset of clinical symptoms and had acute complaints. The COVID-19 group consists of patients who presented to the emergency department after the onset of clinical symptoms, had acute complaints, and were found to have lung involvement with radiological imaging. CCHF and COVID-19 patients were hospitalized and followed up in the infectious diseases and clinical microbiology service. The control group consisted of 35 healthy volunteers who were similar to the patient groups in terms of age and gender and had no COVID-19 exposure.

All CCHF patients had some of the prehemorrhagic phase symptoms, such as fever, diarrhea, dizziness, headache, myalgia, nausea, vomiting, and malaise. All patients had contact with ticks. COVID-19 patients were mild/moderate hospitalized patients with some of the following symptoms: fever, cough, shortness of breath, sore throat, nasal congestion or runny nose, loss of taste and smell, headache, diarrhea, feeling weak, and muscle and body aches. In addition, thoracic tomography findings were detected in all COVID-19 patients. COVID-19 diagnoses were definitively confirmed with polymerase chain reaction (PCR) from nasopharyngeal swabs, while CCHF diagnoses were definitively confirmed with enzyme-linked immunosorbent assay (ELISA) and reverse transcription PCR.

Individuals with alcohol and substance use, acute or chronic diseases (such as diabetes mellitus, hypertension, chronic renal failure, heart failure, or liver damage), autoimmune diseases, and focal/systemic infections that may cause changes in plasma amino acid levels were excluded. In both patient groups, patients requiring intensive care and/or died were excluded from the study. Individuals over the age of 18 were included in the study.

Using BD Vacutainer^® PST-II™ (BD Diagnostics, Franklin Lakes, NJ, USA) tubes with lithium heparin, ∼5 cc venous blood samples were collected from volunteers with a prediagnosis of COVID-19 and CCHF who presented to the emergency department of a university hospital medical faculty. Venous blood samples obtained from patients and healthy individuals were allowed to cool at room temperature for ∼5 min and then centrifuged at 4 °C and 3,000 g for 10 min in a centrifuge. The supernatant (plasma) was stored in at least two seconder tubes ∼300 μL at −80 °C. After the desired number of patients was reached, the samples were removed from −80 °C and brought to room temperature. Experiments were performed on an Agilent high-performance liquid chromatography (HPLC) system (Agilent Technologies Santa Clara, CA, USA) consisting of an Agilent 6470 triple quadrupole liquid chromatography-mass spectrometry (LC/MS) (6470A, Agilent Technologies) coupled with a 1290 high-speed pump (G7120A), 1290 more multi-sample (G7129A) and 1260 multi-column thermostat (G7116A) and an electrospray ionization source. CE-IVD certified and validated Jasem quantitative amino acids LC-MS/MS analysis kit (Altium International Lab. Cih. AŞ, İstanbul, Türkiye) was used to measure free amino acid concentrations.

Results

The study consisted of 35 healthy individuals, as well as 35 patients with COVID-19 and 35 patients with CCHF diagnoses. Demographic characteristics and laboratory values were compared between the groups and are presented in Table 1. There was no significant difference between the groups in terms of their age (p=0.699) and gender (p=0.995). In CCHF patients, white blood cells (WBC), neutrophils, lymphocytes, and platelets count decreased significantly, whereas AST and ALT levels increased significantly (p<0.001).

Plasma levels of taurine and β-alanine were higher, and arginine was lower in CCHF and COVID-19 patients compared to the control group. Carnosine and lysine plasma levels were lower in COVID-19 patients and higher in CCHF patients compared to the control group. When the plasma levels of taurine, β-alanine, arginine, carnosine, cystine, histidine, and lysine were compared, it was found that the difference between the groups was statistically significant (p<0.001), while methionine plasma levels were not significant (p=0.113) (Table 1). The increase in plasma taurine and β-alanine levels was statistically significant in both CCHF and COVID-19 patients compared to the control group; however, the difference between the two disease groups was not significant. Changes in arginine, carnosine, and lysine plasma levels were statistically significant in all pairwise comparisons.

In multinomial logistic regression analysis in CCHF patients, taurine (OR: 1.03, 95 % CI: 1.01–1.04, p<0.001), β-alanine (OR: 3.56, 95 % CI: 1.69–7.48, p<0.001), arginine (OR: 0.95, 95 % CI: 0.93–0.97, p<0.001), carnosine (OR: 1.18, 95 % CI: 1.07–1.31, p=0.001), lysine (OR: 1.01, 95 % CI: 1.00–1.02, p=0.002) results were statistically significant. Similarly, in multinomial logistic regression analysis for COVID-19 patients, taurine (OR: 1.02, 95 % CI: 1.00–1.03, p=0.002), β-alanine (OR: 4.03, 95 % CI: 1.90–08.51, p<0.001), arginine (OR: 0.98, 95 % CI: 0.96–0.99, p=0.010), carnosine (OR: 3.97, 95 % CI: 1.82–8.68, p=0.047), cystine (OR: 1.40, 95 % CI: 1.20–1.62, p<0.001), histidine (OR: 0.91, 95 % CI: 0.87–0.94, p<0.001), lysine (OR: 0.97, 95 % CI: 0.95–0.98, p<0.001) were identified as significant predictors (Table 2). Linearity assumption was made for all amino acids. The results were taurine (p=0.756), β-alanine (p=0.012), arginine (p=0.502), carnosine (p=<0.001), cystine (p=<0.001), histidine (p=<0.001), lysine (p=<0.001), methionine (p=0.260). A goodness-of-fit test was performed for the final multinomial logistic regression model (p=0.114).

In CCHF patients, the area under the ROC curve was 0.82 (95 % CI: 0.71–0.92) for taurine, 0.69 (95 % CI: 0.56–0.81) for β-alanine, 0.87 (95 % CI: 0.78–0.96) for arginine, 0.79 (95 % CI: 0.68–0.90) for carnosine, 0.68 (95 % CI: 0.55–0.82) for cystine, 0.57 (95 % CI: 0.44–0.71) for histidine, 0.74 (95 % CI: 0.63–0.86) for lysine and 0.58 (95 % CI: 0.43–0.72) for methionine.

In addition, ROC curve analyses assessing the ability of amino acids to discriminate COVID-19 patients from healthy controls revealed the following area under the curve (AUC) results: 0.78 (95 % CI: 0.66–0.90) for taurine, 0.80 (95 % CI: 0.70–0.91) for β-alanine, 0.71 (95 % CI: 0.60–0.83) for arginine, 1.0 (95 % CI: 0.99–1.0) for carnosine, 0.95 (95 % CI: 0.90–1.0) for cystine, 0.92 (95 % CI: 0.85–0.98) for histidine, 0.85 (95 % CI: 0.76–0.95) for lysine and 0.66 (95 % CI: 0.54–0.79) for methionine.

Discussion

The primary reason for comparing these two diseases (CCHF and COVID-19), which are an important public health problem and where mortality and morbidity are frequently seen, is that we wanted to compare the metabolic effects in diseases caused by two different viruses. Another reason is that determination of amino acid levels in patients with CCHF and COVID-19, which are frequently seen in our region, may be necessary to understand the pathogenesis, diagnosis, follow-up, and treatment of the diseases.

Plasma taurine levels of CCHF and COVID-19 patients increased significantly compared to the control group. In addition, when the plasma taurine levels of these two diseases were compared, it was concluded that taurine levels were higher in CCHF patients than in COVID-19 patients, but this was not statistically significant (p=0.303). Some studies have demonstrated that various inflammatory cells are activated by many contagious diseases and that this results in the production of reactive oxygen and/or nitrogen types for the purpose of eliminating microorganisms [15], 16]. Previous studies have shown increased oxidative stress in both CCHF and COVID-19 patients [10], 17]. It has been suggested that excessive oxidative stress is important in the pathogenesis of respiratory infections such as SARS-CoV infections [11]. In almost all cases of viral pneumonia caused by COVID-19, where lung cells are affected, oxidative stress accompanies this pathological process [17]. The antioxidant activity of taurine has long been recognized. Due to the high concentration of taurine in lymphocytes, it is thought to play an important role in body defense against oxidative stress [8]. Oxidative stress drastically increases in respiratory tract infections [17]. We believe that the oxidative stress of COVID-19 patients is higher than CCHF patients. Because the most important area where COVID-19 causes infection is the respiratory system. While we expected higher taurine levels in COVID-19 patients with respiratory tract infections than in CCHF patients due to higher oxidative stress, we measured it to be low. Oxidative stress and the antioxidant system are in a balance which production and usage vary depending on. Oxidative stress is correlated to distortions in the prooxidant and antioxidant balance. Such an imbalance may be related to the excessive production of free oxygen radicals or insufficient antioxidant mechanisms [18]. Distorted oxidative balance is a factor that contributes to the continuance of inflammation as a result of increased oxidative stress and/or decreased antioxidant activities [8]. Taurine’s cytoprotective role has been proven in oxidative stress conditions through various toxins [8]. For instance, it has been demonstrated that taurine prevents oxidative stress-related lung injuries [8]. Another study, on the other hand, reported that added taurine increased the activity of antioxidant enzymes in the lung [19]. The lower plasma taurine levels in COVID-19 patients compared to those with CCHF have been attributed to the increased utilization of taurine in the COVID-19 group.

CCHF causes injuries to the endothelin, the activation of the coagulation cascade, and thrombocytopenia, which increases bleeding [2]. Nose bleeds, hematemesis, melena in rarer cases, hemoptysis, hematuria, and subcutaneous bleeding (ecchymosis/purpura) are observed frequently [5]. In some previously conducted studies, excluding taurine (single increasing) decreases in total plasma amino acid levels in the cold adaptation process of snakes have been demonstrated [20]. When the blood humoral coagulation of these animals was evaluated, the lengthening of their blood coagulation durations was recorded [20]. In addition, a recent study found that plasma taurine levels increased during the hemorrhagic phase of CCHF and reported that taurine was statistically significantly correlated with certain laboratory parameters related to coagulation and inflammation [21]. These findings have led to the formation of an interesting hypothesis regarding the role of taurine in preventing blood coagulation. Despite the existence of some uncertainties, potential mechanisms lying at the core of the effects taurine and its derivatives have on thrombocyte activity are decreased thrombocyte, thromboxane-A2 and thromboxane-B2 production, and the inhibition of thrombocyte cyclooxygenase activity [20]. According to our findings, taurine levels in CCHF patients increased. We believe that the cause of the bleeding disorders in CCHF patients may be due to high taurine levels and that studies with wide scopes must be conducted on the matter.

N-chlorotaurine (taurine chloramine, Tau-Cl), a form of taurine, forms when intercellular taurine concentration increases excessively (upon reaching 50–100 mM). Tau-Cl acts as an anti-inflammatory agent by killing a broad spectrum of pathogenic microbes (viruses, fungi, and bacteria) and has a suppressive effect on inflammatory cytokines [22]. Hoang et al. reported new findings regarding the effects of Tau-Cl treatments on pulmonary and systemic inflammation [23]. According to these findings, Tau-Cl treatments alleviated pulmonary edema and decreased the release of interleukin-6 and tumor necrosis factor-alpha, which are proinflammatory cytokines. Furthermore, lipopolysaccharide induced pneumonia was attenuated by Tau-Cl treatment [23]. Kimhofer et al.’s study, similar to our data, determined that COVID-19 patients demonstrated high taurine levels [24]. Holmes et al. found that plasma taurine levels in COVID-19 patients were higher than in the control group during the active period of the disease and in the follow-up three months later [25]. In our study, the increase in plasma levels for both CCHF and COVID-19 patients was thought to be due to the host’s immune response to viral infections.

In CCHF patients, Kupffer cells, hepatic endothelin cells, and hepatocytes are the main targets, and the necrosis of hepatocytes leads to increases in liver enzymes. High taurine levels have previously been correlated with liver damage and hepatotoxicity [25]. Increased taurine levels in plasma and urine have been reported to be signifiers of acute liver failure [26]. High plasma taurine levels relative to their controls may potentially reflect long-term multiorgan injuries, including heart and skeletal muscle components [25]. Similarly to the literature data, taurine levels increase in the liver pathology, which is the most frequent target of CCHF patients. This also serves to explain why plasma taurine levels are higher in CCHF patients.

In our study, while carnosine plasma levels of CCHF patients increased compared to the control group, they decreased significantly in COVID-19 patients compared to the control group. Gradually increasing pieces of evidence demonstrate that carnosine plays an extremely important role in protecting mammals against oxidative stress and injuries [12], 27]. Carnosine is a natural and strong antioxidant; it interacts with reactive oxygen types and cleans them [12], 13]. In some studies, it has been demonstrated that carnosine has antiviral properties [28], 29]. In the literature, no studies regarding the carnosine amino acid in CCHF patients could be found. Compatible with conducted studies, due to its antiviral, antioxidant, and anti-inflammatory [29] properties, an increase in carnosine levels was observed amongst CCHF patients.

The ability of carnosine to decrease nitric oxide and neutrophil influx into the upper respiratory tract has been noted to be important in controlling the initial stages of influenza A infection [29]. In rats, carnosine reduces mortality and pathologic lung alterations after viruses such as the H9N2 swine virus [30]. Due to all of these benefits, carnosine could also play a role in protecting patients against COVID-19. It has been demonstrated that carnosine, in lipopolysaccharide-related liver injuries [31] and H9N2 swine flu [30] animal models, provides protection against ARDS-related lung injuries by reducing the mediative toxicity of reactive oxygen types regarding lung cells. The combined anti-inflammatory and antioxidative effects of carnosine make it particularly suited to be considered as supportive treatment in patients with COVID-19 [29]. Carnosine has strong anti-inflammatory, antioxidant, and antiglycation effects [29]. These effects have put the importance of carnosine for COVID-19 forward. In addition to the literature, our studies found that carnosine was used excessively by COVID-19 patients and that plasma levels were low.

The arginine plasma levels were statistically lower in CCHF patients and COVID-19 patients compared to the control groups. When comparing CCHF and COVID-19 patients, it was found that the decrease in CCHF patients was statistically higher. Rees et al.’s study on adult patients reported low arginine levels in COVID-19 patients [32]. In the same year, a study conducted in France on 26 adult patients found that arginine levels were low [33]. Our data is consistent with other studies.

Nutrients, such as arginine, peptides, and bioactive molecules, have attracted more and more attention due to their ability to reduce oxidative stress, inhibit apoptosis, and regulate immune responses, thereby improving epithelial barriers [34]. Nitric oxide (NO) is the most important endothelin-sourced vasodilator and is synthesized from l-arginine with the NO synthase [35]. NO is a component of the body’s defense mechanism. In fatal CCHF cases, NO levels were reported to be lower than in non-fatal cases [35]. NO has an inhibitory effect on antiviral activity and the release of TNF-alpha from monocytes. High NO levels may play a protective role in CCHF [36]. Low NO levels are believed to be correlated to endothelin damage mortality [35], 36]. Our study, compatibly with other studies, found arginine plasma levels, which are the predecessors of NO, to be low in CCHF patients. We believe that arginine was utilized to keep NO levels high.

Conclusions

This is the first study in the literature comparing plasma taurine β-alanine, arginine, carnosine, cystine, histidine, lysine, and methionine levels in patients with CCHF and COVID-19. It is important in this respect. Taurine plasma levels, compared to control groups, demonstrated significant increases in both viral illnesses. The antioxidant activity of taurine plays an active role in defending the body against oxidative stress. Oxidative stress is known to play a role in the pathogenesis of viral infections. In our study, the increase in taurine levels in both patient groups supports this information. We believe that the determination of taurine levels throughout the treatment and observation processes of these two diseases, which severely impact public health, may be important. Studies with wider scopes are required on this matter. This study will contribute to a better understanding of the CCHF and COVID-19 disease pathogenesis. Moreover, it may shed light on studies that will be conducted on similar subjects.