Association of cell adhesion molecules levels & single nucleotide polymorphisms with vaso-occlusive crisis in sickle cell disease: A cross sectional study

Materials & Methods

This study was undertaken at the department of Genetics, ICMR-National Institute of Research in Tribal Health, Jabalpur, Madhya Pradesh, India. The study protocol was approved by the Institutional Ethical Committee.

Results

A total 140 SCD individuals (79 male and 61 female) were recruited in the present study who were admitted in a Government Medical College, Jabalpur. The mean age of the patients was 18.81±7.85 yr. There was no significant difference in occurrence of vaso-occlusive crises in last one year among different age groups (Fig. 1).

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Fig. 1.

Age group wise distribution of participants suffering from vaso-occlusive crises in sickle cell disease individuals.

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Level of CAM in SCD participants of different age group

The median and IQR of P-selectin, E-selectin, ICAM-1 and VCAM-1 levels in SCD participants were calculated. There was no significant difference in levels of P and E-selectins among different age groups of SCD participants but the levels of ICAM-1 and VCAM-1 were significantly different in different age groups (Fig. 2). P-selectin and E-selectin levels did not vary significantly with age. Although ICAM-1 levels showed a trend towards variability with age, particularly higher in the 12-18 yr group and lower in older age groups, the difference was not statistically significant. VCAM-1 levels varied significantly with age, with the highest levels observed in the 19-24 yr group. There was a significant correlation between the P-selectin levels with VCAM-I levels and ICAM-1 levels with E-selectin levels, indicating potential interplay between these molecules (Table I).

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Fig. 2.

(A) Level of cell adhesion molecules in sickle cell disease individuals of different age group. (B) Level of cell adhesion molecules in sickle cell disease individuals of different age group.

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Table I. Correlation between CAM levels

	P-selectin (r, P value)	E-selectin (r, P value)	ICAM-1 (r, P value)	VCAM-1 (r, P value)
P-selectin	-	0.189, 0.39	0.156, 0.88	0.267, 0.003
E-selectin	0.189, 0.39	-	0.177, 0.037	0.052, 0.544
ICAM-1	0.156, 0.88	0.177, 0.037	-	0.070, 0.414
VCAM-1	0.267, 0.003	0.052, 0.544	0.070, 0.414	-

Discussion

SCD patients exhibit a broad range of clinical complications, with vaso-occlusive crises being the leading cause of hospitalizations^17,18. Various environmental, non-environmental, and genetic factors are known to influence SCD severity and elevating vaso-occlusive crises. Chronic pain in sickle cell patients tends to be more persistent, and over time it might involve hospitalization. Various studies found the correlation between chronic pain and biological parameters ‘at steady state’^5,9. Recent studies have focused on identifying the genetic contributors to SCD pathophysiology. The current study focused on the SCD patients who require emergency admission due to the vaso-occlusive crises.

In this gene-centric association study, we studied on the association of selected SNPs present in four genes (SELP, SELE, ICAM1, and VCAM1) with the vaso-occlusive crises and respective soluble protein levels. Our findings showed no correlation between age groups and occurrence of vaso-occlusive crises in last one year in SCD patients. Notably, VCAM-1 levels showed a significant age-dependent increase, with the highest levels observed in the 19-24 yr group could be attributed to several factors such as immune system development and hormonal fluctuations¹⁹. It appears from the findings that during this period, the immune system is still maturing and refines its response to pathogens, which may lead to increased VCAM-1 expression. Concurrently, peak cortisol levels, lifestyle factors and developmental processes of significant physical and emotional change may contribute to enhanced VCAM-1 expression²⁰. Further investigation is, however, warranted to elucidate the relationship between age and SCD severity.

We observed a significant correlation between P-selectin levels with VCAM-1 levels, suggesting potential interactions between these molecules. ICAM-1 levels show significant correlations with E-selectin. The correlation coefficients provide valuable insights into the relationships between different adhesion molecule levels in our study population. Notably, our gender-associated analysis revealed a significantly higher frequency of heterozygotes for the SELP gene variant SELP: c.2266A>C (rs6136) in females compared to males (P=0.040). These genetic variants may impact P-selectin expression or function, leading to changes in inflammation and immune response, which can contribute to SCD complications like vaso-occlusion and organ damage^20,21. Although this variant has been linked to disease severity in cancer, its role in SCD pathophysiology is yet to be explored²¹.

The effects of SNPs can vary depending on the population being studied and other genetic and environmental factors. Several SNPs in the SELP gene, such as rs6131, rs6133, rs6127, and others, have been linked to various diseases, including SCD^22,23. Specifically, rs6127 has been associated with an increased severity of SCD in African Americans²⁴. Similarly, SNPs in the SELE gene, such as rs5361 and rs1885745, have been linked to overexpression of E-selectin, which may contribute to the adhesion of sickled red blood cells to endothelial cells, exacerbating disease severity^25,26. The ICAM-1 gene has reported to be associated with various conditions, including SCD²⁷. Notable SNPs in the ICAM-1 gene, such as rs281461 and rs5498, have been linked to increased ICAM-1 expression and severity in coronary diseases²⁸. These SNPs have also been associated with higher susceptibility to malaria and increased risk of cardiovascular disease²⁵. Furthermore, SNPs in the VCAM-1 gene, such as rs1041163 and rs3176792, may influence disease progression and severity by affecting VCAM-1’s role in inflammation, adhesion, and immune response²⁹. Expression quantitative trait locus (eQTL) studies in other genes show that SNPs can significantly influence expression.

Although several studies have investigated the role of SNPs in disease severity, no single study has examined all four genes (SELP, SELE, ICAM-1, and VCAM-1) and their 20 SNPs in conjunction. The analysis in this study revealed that patients have multiple SNPs within a single gene, which could potentially contribute to increased disease severity. However, this was not found in all patients, as some patients did not exhibit any SNPs for the genes analysed. This variability suggests that the relationship between SNPs and disease severity may be complex and influenced by individual genetic profiles. Further research is needed to fully understand the complex relationships between these genes and their impact on disease severity.

Most studies have focused on the role of SNPs in influencing the severity of diseases; however some variants in SELP gene, specifically rs6131 (T1406A), rs6127 (C1364T), rs6125 (G1354A) have been reported to reduce the SELP expression, which could lower the risk of vaso-occlusive crises³⁰. Similarly, the rs5368 (L576F) variant in SELE gene has been associated with reduced E-selectin expression, which may decrease the adhesion of sickled red blood cells to the endothelium and potentially alleviate disease severity. SNPs, rs3093030 (R241G) and rs5030359 (V310I) also found associated with reduced ICAM-1 expression and lower risk of vaso-occlusive crises in SCD. Moreover, rs3176793 (C146T) and rs11821469 (T280A) of VCAM-1 reduces VCAM-1 expression and showed lower risk of stroke in SCD patients³¹.

Some limitations in this study included patient’s disease severity could not be identified due to unavailability of previous medical records. Therefore, the association of the studied SNPs with the disease severity could not be established. Haplotype and linkage analysis could not be performed in the current study which was also one of the limitations.

Overall, the current study provides a comprehensive understanding of the genetic and molecular factors that contribute to SCD, shedding light on specific SNP associations and correlations between CAM levels. These findings offer valuable insights into disease pathophysiology and potential treatment strategies. These significant SNPs may warrant further investigation to understand their potential role in influencing vaso-occlusive crises severity. The identification of specific SNPs associated with SNP can inform personalized medicine approaches, allowing for tailored treatments based on individual genetic profiles. Furthermore, the observed correlations between CAM levels suggest potential targets for therapeutic intervention. While this study provides a significant breakthrough, further research is necessary to validate these findings across larger and more diverse patient cohorts. Functional studies are essential to elucidate the biological significance of these findings, providing a deeper understanding of how these genetic and molecular factors contribute to disease development and progression.