Evaluation of cytokines, antibodies to neurotransmitter receptors, and their interrelations in individuals with hand-arm vibration syndrome

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BACKGROUND

In recent decades, one of the primary objectives of the healthcare system in the Russian Federation has been the preservation of the health of the working population. Despite the modernization and automation of industrial facilities, improvements in technological processes, and the implementation of robotics and artificial intelligence, a high incidence of diseases caused by harmful occupational exposures persists in several industrial sectors. Vibration disease (VD) and sensorineural hearing loss (SHL) continue to rank among the leading occupational disorders resulting from physical hazards.¹ These diseases tend to develop over a short period (5 to 7 years of work under hazardous conditions) and lead to reduced work capacity and disability, which determines the high medical and social significance of these professional disorders. The economic costs associated with treatment and social benefits for individuals with occupational diseases exceed 200 billion rubles [1].

The clinical presentation of VD is characterized primarily by angiodystonic syndrome, sensory polyneuropathy of the extremities, and functional disorders of the central nervous system, the severity of which increases with the duration and intensity of vibration exposure. Vibration is known to cause dysfunctions not only in the peripheral but also in the central nervous system, affecting the cerebellum, brainstem structures, hypothalamus, and reticular formation. In SHL, pathological changes occur in the auditory nerve, nerve fibers of the inner ear, as well as the brainstem and cerebral cortex [2]. In addition to nervous system involvement, patients with VD and SHL also present with immune, endocrine, and cardiovascular disorders [3, 4]. According to published data, specific autoantibodies targeting neuronal cell components and structures are detected in the serum of individuals with neurodegenerative diseases [5, 6]. Our earlier findings have revealed altered levels of cytokines and neuronal autoantibodies in patients with VD and SHL. Moreover, differences in cytokine profiles have been noted in individuals with SHL compared to those with VD, as well as depending on the etiology of VD [3, 7]. Despite numerous articles on cytokine profiles, lymphocyte subpopulations, specific antibodies, and other immunologic markers in individuals with occupational diseases, the interrelationship of these markers under combined exposure to different physical occupational hazards remains understudied.

The work aimed to compare and determine the interrelationships, as well as analyze the levels of cytokines and autoantibodies to neurotransmitter receptors, in individuals with VD, depending on the presence or absence of SHL and the type of vibration exposure.

METHODS

As part of a work project conducted by the East Siberian Institute of Medical and Ecological Research (Angarsk), a total of 153 men aged 41–58 years (mean age, 49.6 ± 0.88 years) with occupational diseases resulting from exposure to physical factors were examined.

Inclusion criteria: male sex, VD of occupational origin, no history of autoimmune disorders, and absence of acute respiratory infections at the time of examination. Exclusion criteria: unconfirmed diagnosis of VD or lack of informed consent.

Clinical and laboratory-immunological examinations were approved by the Local Ethics Committee of the East Siberian Institute of Medical and Ecological Research (Protocol No. 5, dated March 21, 2023) and conducted in accordance with the ethical principles of the Declaration of Helsinki. Written informed consent was obtained from all participants.

In all individuals, the diagnosis of VD was confirmed based on the classification criteria for diseases and conditions outlined in the International Classification of Diseases, 10th Revision (ICD-10). Among the participants, 67 men had an occupational disease resulting from exposure to local vibration (Group 1), and 86 men had combined exposure to local and whole-body vibration (Group 2). Group 1 included workers employed as riveters-assemblers, assembly fitters, tunnelers, loggers, installation workers, chippers, and sawmill operators. Group 2 comprised excavator, bulldozer, grader, drilling rig, and crane operators, as well as KrAZ log truck drivers, forklift drivers, and tractor operators. SHL as a second occupational disease was diagnosed in 47 individuals in Group 1 (local vibration) and in 64 individuals in Group 2 (combined local and whole-body vibration). Within each group, individuals with SHL were classified into separate subgroups.

Serum samples obtained from the participants were analyzed using enzyme-linked immunosorbent assay (ELISA) to determine the concentrations of cytokines, including interleukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), and interleukins 4, 6, and 8 (IL-4, IL-6, IL-8), using Vector-Best reagent kits. Additionally, levels of specific IgG autoantibodies were assessed using ELI-Neuro-Test kits (Immunkulus Research and Production Association). The autoantibodies studied included those targeting the following receptors: acetylcholine (nACh-R), glutamate (NMDA-R), gamma-aminobutyric acid (GABA-R), dopamine (DA-R), and serotonin (SER-R).

Statistical analysis was performed using STATISTICA 6.0 software. Normality of data distribution was assessed using the Shapiro–Wilk test. Comparisons of quantitative variables were conducted using the nonparametric Kruskal–Wallis test and the Mann–Whitney test. Associations between variables were evaluated using Spearman rank correlation and nonlinear regression analysis. The results are presented as median (Me) and interquartile range (25th and 75th percentiles, LQ–UQ). Differences were considered statistically significant at p < 0.05 for the Kruskal–Wallis test and Spearman correlation, and at p < 0.0083 for pairwise comparisons.

RESULTS

The findings revealed that in the subgroups of individuals with both VD and SHL, serum IL-1β levels were significantly higher than in individuals with VD caused by local vibration exposure without SHL (p = 0.001 and p < 0.001 for the subgroups with SHL and VD due to local and combined vibration exposure, respectively; Table 1). IL-6 levels were elevated in the subgroups with VD due to combined local and whole-body vibration exposure, both with and without SHL, as well as in individuals with SHL and VD resulting from local vibration exposure. However, these intergroup differences did not reach statistical significance and demonstrated a trend compared with the subgroup with VD from local vibration exposure without SHL (p = 0.027, p = 0.033, and p = 0.013, respectively).

 

Table 1. Cytokine levels in individuals with occupational diseases caused by exposure to physical factors, Me (LQ–UQ)

Indicator	Group with vibration disease due to local vibration exposure		Group with vibration disease due to combined local and whole-body vibration exposure		p
	Subgroup without sensorineural hearing loss	Subgroup with sensorineural hearing loss	Subgroup without sensorineural hearing loss	Subgroup with sensorineural hearing loss
IL-1β, pg/mL	1.20 (0.10–2.19)	6.10 (2.00–29.64)*	2.83 (0.95–21.61)	8.46 (2.22–30.51)*	0.001
IL-4, pg/mL	0.98 (0.72–1.63)	0.56 (0.15–2.79)	1.28 (0.03–4.22)	1.07 (0.01–3.59)	0.676
IL-6, pg/mL	2.92 (2.04–3.87)	4.37 (3.52–5.57)#	4.68 (3.35–12.34)#	4.35 (3.16–5.49)#	0.028
IL-8, pg/mL	6.73 (5.05–7.77)	8.95 (6.93–16.02)	7.89 (6.71–15.36)	7.78 (5.40–10.81)	0.087
TNF-α, pg/mL	0.44 (0.25–0.65)	0.81 (0.30–2.71)	0.50 (0.15–1.99)	0.73 (0.31–2.30)	0.337

Note. p, level of statistical significance according to the Kruskal–Wallis test; differences were considered significant at p < 0.05; * statistically significant differences compared with the subgroup of individuals with vibration disease from local vibration exposure without sensorineural hearing loss, p < 0.008; ^# trend toward significance compared to the subgroup of individuals with vibration disease from local vibration exposure without sensorineural hearing loss, 0.008 < p < 0.017.

 

Analysis of cytokine profiles across all four subgroups revealed a similar structural pattern; however, individuals with SHL as an occupational comorbidity exhibited the highest IL-1β levels. The greatest concentration of this interleukin was observed in the subgroup with SHL and VD caused by combined local and whole-body vibration exposure. Conversely, the lowest levels of both IL-1β and IL-6 were detected in the cohort with VD resulting from local vibration exposure without SHL. These findings suggest that combined exposure to noise, local, and whole-body vibration may exert a unidirectional effect on IL-1β levels and demonstrate a synergistic proinflammatory influence.

Autoantibodies play a central role in the clearance of apoptotic cells and their components during physiological cell turnover. In this context, they may exhibit protective properties and can be detected at low concentrations in the serum of healthy individuals. However, elevated autoantibody levels may either indicate or contribute to pathological processes involving increased cell death [8].

Serum test of autoantibodies targeting neurotransmitter receptors revealed no statistically significant intergroup differences (Table 2).

 

Table 2. Comparative assessment of antibody levels to neurotransmitter receptors in individuals with vibration disease and concomitant sensorineural hearing loss, Me (LQ–UQ)

Indicator	Group with vibration disease due to local vibration exposure		Group with vibration disease due to combined local and whole-body vibration exposure		p
	Subgroup without sensorineural hearing loss	Subgroup with sensorineural hearing loss	Subgroup without sensorineural hearing loss	Subgroup with sensorineural hearing loss
Antibodies to nACh-R, a.u.	0.46 (0.42–0.68)	0.50 (0.17–0.65)	0.55 (0.37–0.84)	0.55 (0.20–0.77)	0.728
Antibodies to NMDA-R, a.u.	0.40 (0.36–0.60)	0.39 (0.18–0.53)	0.41 (0.29–0.66)	0.50 (0.23–0.69)	0.480
Antibodies to GABA-R, a.u.	0.55 (0.37–0.86)	0.48 (0.15–0.59)	0.47 (0.38–0.71)	0.56 (0.21–0.70)	0.349
Antibodies to DA-R, a.u.	0.49 (0.35–0.70)	0.37 (0.20–0.52)	0.45 (0.28–0.64)	0.47 (0.24–0.64)	0.153
Antibodies to SER-R, a.u.	0.49 (0.42–0.79)	0.51 (0.21–0.62)	0.51 (0.37–0.63)	0.59 (0.27–0.71)	0.682

Note. p, level of statistical significance according to the Kruskal–Wallis test; differences were considered significant at p < 0.05; * statistically significant differences compared with the subgroup of individuals with vibration disease from local vibration exposure without sensorineural hearing loss, p < 0.008; ^# trend toward significance compared with the subgroup of individuals with vibration disease from local vibration exposure without sensorineural hearing loss, 0.008 < p < 0.017.

 

Antibody production is known to be regulated by cytokines through B-lymphocyte activation [9, 10]. Consequently, elevated levels of proinflammatory cytokines and the accompanying activation of inflammatory pathways may contribute to increased serum concentrations of autoantibodies. Accordingly, a regression test was conducted to assess associations between cytokine levels and the presence of neural tissue autoantibodies. The resulting equations describe the contribution of cytokine profiles to the development of antibody responses against neurotransmitter receptors. In the subgroup of patients with VD caused by local vibration exposure without SHL, the following models were identified: GABA-R = 1.84 − 1.44 × (IL-1β) − 6.94 × (TNF-α) + 2.54 × (IL-1β)² + 2.57 × (IL-6)² + 6.87 × (TNF-α)²(R² = 0.89, p = 0.013); DA-R = 1.37 − 3.30 × (IL-6) − 7.62 × (TNF-α) + 2.23 × (IL-1β)² + 3.48 × (IL-6)² + 7.40 × (TNF-α)²(R² = 0.86, p = 0.020). In individuals with SHL, the following model was established: NMDA-R = 1.00 − 2.49 × (IL-6) − 2.50 × (TNF-α) + 2.41 × (TNF-α)² (R² = 0.85, p = 0.029). In the subgroup with VD due to combined local and whole-body vibration exposure and comorbid SHL, the regression equation was as follows: SER-R = 0.87 + 1.28 × (IL-1β) − 1.72 × (IL-1β)²(R² = 0.66,p = 0.021), where GABA-R, DA-R, NMDA-R, SER-R, IL-1β, IL-4, IL-6 and ТNF-α represent levels of relevant autoantibodies and cytokines. No statistically significant regression models were identified for the subgroup with VD resulting from combined vibration exposure without SHL. These findings indicate that, in patients with VD due to local vibration exposure and without SHL, serum levels of autoantibodies to neurotransmitter receptors are more strongly associated with the concentrations of IL-1β, IL-4, IL-6, and TNF-α compared to individuals with combined vibration exposure or those with SHL.

DISCUSSION

It is known that IL-1β, produced by monocytes, macrophages, Kupffer cells of the liver, Langerhans cells in the epidermis, and microglial cells, exerts both local and systemic effects mediated through activation of the neuroendocrine system [9, 11]. Under normal conditions, increased IL-1β production triggers protective responses; however, it may lead to uncontrolled inflammation, tissue damage, and become part of the disease pathogenesis. Indirectly, by activating IL-6, IL-1β may promote the synthesis of antibodies of all immunoglobulin classes. In turn, IL-6 is capable of shifting the innate immune response and the development of protective mechanisms toward adaptive immunity. Elevated IL-1β and IL-6 levels in subgroups with VD and comorbid SHL may indicate the presence of chronic inflammation and autoimmune processes, as IL-6 is known to contribute to the pathogenesis of autoimmune and inflammatory conditions. The disruption of associations between cytokine levels and serum autoantibody concentrations observed in subgroups with VD caused by combined local and whole-body vibration exposure—with or without SHL—may be explained by an imbalance between pro- and anti-inflammatory cytokine production. This imbalance likely arises at a certain stage in the development of the disease under the influence of vibration and may also reflect a reduction in neuronal autoantibody levels following the clinical manifestation of the occupational disease. Previously, it was shown that patients with VD exhibit lower levels of these autoantibodies compared to experienced workers without diagnosed occupational disease [12].

In earlier studies, average serum concentrations of selected cytokines and autoantibodies were established in conditionally healthy men. For example, serum IL-1β was 3.40 (1.21–6.19), IL-4 was 0.01 (0.01–0.69), IL-8 was 5.08 (1.41–13.40), and TNF-α was 0.73 (0.01–1.47) pg/mL. Autoantibody levels were as follows (arbitrary units): nACh-R 0.34 (0.29–0.38), NMDA-R 0.27 (0.26–0.29), GABA-R 0.24 (0.22–0.28), DA-R 0.26 (0.24–0.31), and SER-R 0.46 (0.36–0.47) [3, 13]. Thus, in individuals with VD—with or without comorbid SHL—the levels of neuronal autoantibodies are approximately 1.2–2.6 times higher than those in conditionally healthy men, which is consistent with previously published data [3, 7]. Furthermore, demyelinating processes have been reported in patients with VD, along with associations between neuronal autoantibodies and impaired nerve impulse conduction in the upper and lower extremities [12].

It is well established that alterations in the levels of serotonin, glutamate, GABA, acetylcholine, and dopamine in synapses—and the resulting imbalance of these neurotransmitters within brain structures—lead to changes in the brain’s bioelectrical activity in certain neurodegenerative diseases. Glutamate, one of the primary excitatory neurotransmitters, also serves as a precursor for the synthesis of GABA, the principal inhibitory neurotransmitter in the central nervous system. Glutamate is released into the synaptic cleft via exocytosis involving voltage-gated calcium channels. From the synaptic cleft, it enters astrocytes, where it is aminated to glutamine. Alterations in the levels of this neurotransmitter—due to reduced astrocytic capacity to maintain optimal extracellular glutamate concentrations, impaired neuronal reuptake, and decreased receptor density—predispose to disrupted neurophysiological processes in the brain and play a significant role in neurodegenerative injury [14, 15]. Excessive glutamate production may be triggered by the proinflammatory cytokines IL-1β and TNF-α, which influence the expression of astrocytic transporter proteins. It has been established that in multiple sclerosis, TNF-α can stimulate glutamate release by microglia through autocrine mechanisms and by regulating glutaminase activity. Demyelinated axons may also contribute to increased glutamate synthesis and release due to altered localization of the pore-forming α1B subunit of voltage-gated Ca²⁺ channels on damaged axons. Additionally, glutamate itself can stimulate its synthesis via metabotropic glutamate receptors located on astrocytes [16]. Elevated levels of this neurotransmitter and hyperactivation of ionotropic glutamate receptors lead to increased Ca²⁺release from intracellular stores into the neuronal cytoplasm, thereby enhancing lipid peroxidation, oxidative stress, and other neurotoxic processes capable of inducing neuronal apoptosis [15]. Taken together, the existing publications suggest that glutamate receptors play a critical role in modulating cellular membrane potential, ion channel activity, and free radical formation. They also participate in the regulation of cytokine secretion by T cells and contribute to neuronal death processes, particularly affecting dopaminergic neurons in the substantia nigra [15–17]. Accordingly, NMDA receptors may represent a central link in multiple pathogenetic pathways—including autoimmune responses, inflammation, and demyelination—underlying disorders associated with neurodegenerative processes, such as VD. This is supported by the present publication’s findings, which demonstrate associations between GABA-R and NMDA-R levels and the concentrations of cytokines and autoantibodies to neurotransmitter receptors in subgroups of individuals with VD resulting from local vibration exposure, with and without SHL: NMDA-R = 1.42(SER-R) − 0.62 × (GABA-R)²(R² = 0.82,p < 0.001); GABA-R = 0.70 × (NMDA-R) − 0.62 × (NMDA-R)² + 0.75 × (DA-R)² (R² = 0.99, p < 0.001) respectively, as well as in the cohort exposed to combined local and whole-body vibration without SHL: GABA-R = 0.37 + 3.95 × (nACh-R) − 4.06 × (NMDA-R) − 4.86 × (nACh-R)² + 5.32 × (NMDA-R)²(R² = 0.93, p < 0.001).

A limitation of this work is the relatively small sample size, which restricted the use of certain statistical methods and precluded a detailed analysis of associations between cytokine and autoantibody levels across different durations of occupational exposure, disease severity and stage, and time since cessation of exposure to the harmful occupational factor.

CONCLUSION

The findings of this work confirm and extend previous evidence indicating an increased risk of neuroimmune inflammation in patients with VD resulting from combined exposure to whole-body and local vibration, compared with individuals whose VD is attributable solely to local vibration [3]. The presence of concurrent SHL exacerbates the pathological process by amplifying inflammatory changes and disrupting both cytokine profiles and neurotransmitter metabolism. Distinct features of the associations between autoantibodies to neurotransmitter receptors and cytokines were identified in individuals with VD of different etiologies and coexisting SHL. In patients with VD due to local vibration exposure without SHL, levels of autoantibodies to GABA receptors were primarily associated with IL-1β, TNF-α, and IL-6; for dopamine receptors, with IL-1β, IL-6, and TNF-α. In cases with SHL, levels of autoantibodies to glutamate receptors were associated with IL-6 and TNF-α. Among individuals with VD resulting from combined local and whole-body vibration and coexisting SHL, levels of autoantibodies to serotonin receptors were linked to IL-1β concentration.

ADDITIONAL INFORMATION

Authors’ contribution. L.B. Masnavieva — analysis and interpretation of results, literature review, preparation and writing of the article; G.M. Bodienkova — study conception and design, literature review, editing the article; E.V. Boklazhenko — data collection, analysis and interpretation of results. All authors confirm that their authorship meets the international ICMJE criteria (all authors have made a significant contribution to the development of the concept, research and preparation of the article, read and approved the final version before publication).

Funding source. The work was carried out at the expense of funds allocated within the framework of the State Task FSBSI East-Siberian Institute of Medical and Ecological Research.

Competing interests. The authors confirm the absence of obvious and potential conflicts of interest related to the publication of this article.

Patients’ consent. Written consent was obtained from all the study participants before the study screening in according to the study protocol approved by the local ethic committee.

 

¹ On the State of Sanitary and Epidemiological Well-Being of the Population in the Russian Federation in 2019: State Report. Moscow: Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing; 2020:299.

About the authors

Liudmila B. Masnavieva

East-Siberian Institute of Medical and Ecological Research

Email: Masnavieva_Luda@mail.ru
ORCID iD: 0000-0002-1400-6345
SPIN-code: 3794-7520

Dr. Sci. (Biology)

Russian Federation, Angarsk

Galina M. Bodienkova

East-Siberian Institute of Medical and Ecological Research

Author for correspondence.
Email: immun11@yandex.ru
ORCID iD: 0000-0003-0428-3063
SPIN-code: 7751-8515

MD, Dr. Sci. (Medicine), Professor

Russian Federation, Angarsk

Elena V. Boklazhenko

East-Siberian Institute of Medical and Ecological Research

Email: immun11@yandex.ru
ORCID iD: 0000-0002-2025-8303
SPIN-code: 9326-7806

MD, Cand. Sci. (Medicine)

Russian Federation, Angarsk

References

Supplementary files