Plasma/Serum Oxidant Parameters in Systemic Lupus Erythematosus Patients: A Systematic Review and Meta-Analysis

Most published results have revealed variations in the association of serum/plasma levels of malondialdehyde (MDA), apolipoprotein B (ApoB), and oxidized low-density lipoprotein (OxLDL) and systemic lupus erythematosus (SLE). This study was performed to establish MDA, ApoB, and OxLDL levels in systemic lupus erythematosus (SLE) patients. Electronic databases were searched for the included articles up to 27th February 2023. The meta-analysis included 48 articles with 2358 SLE patients and 2126 healthy controls considered for MDA, ApoB, and OxLDL levels. There were significantly higher MDA, ApoB, and OxLDL levels in SLE patients than those in the control groups. Subgroup analysis indicated that European/American SLE patients and patients of both ages <36 and ≥36 exhibited higher MDA, ApoB, and OxLDL levels. Arab and Asian SLE patients had higher ApoB and MDA/OxLDL levels. African SLE patients recorded higher OxLDL levels than the control groups. SLE patients with a body mass index (BMI) of ≥23 and a disease duration of <10 recorded significantly higher MDA, ApoB, and OxLDL levels. Patients with systemic lupus erythematosus disease activity index (SLEDAI) ≥8 of SLE had higher MDA and ApoB levels, whereas SLE patients with SLEDAI <8 showed significantly higher ApoB levels. Patients with BMI <23 of SLE had higher MDA and OxLDL levels. This study established significantly higher MDA, ApoB, and OxLDL levels in SLE patients, suggesting a possible role of MDA, ApoB, and OxLDL in the disease.


Introduction
Systemic lupus erythematosus (SLE) is a common complex autoimmune disease that is infammatory, relapsing, and chronic.Although the exact cause of systemic lupus erythematosus (SLE) is still unknown, it is widely accepted that the autoimmune disease is marked by high autoantibody production [1], immune complexes, and compromised cellular and humoral immunity.Tese factors are most likely a result of a combination of genetic, environmental (virus, food, and UV light), and hormonal factors.In human and animal models, oxidative stress and the associated cellular damage have been implicated as key players in the etiology, development, progression, and maintenance of autoimmune disease [2][3][4][5].Lipid peroxidation produces malondialdehyde (MDA), which can form intra-and intermolecular adducts with proteins by covalent bonding [6,7].
MDA can react with nucleophilic amino acids such as cysteine and lysine, forming covalent MDA-protein adducts.MDA contains two aldehyde sets.Increased physiological disturbances, such as loss of structure and function, are brought on by oxidized proteins [8][9][10].Oxidatively altered proteins cause further sufering in autoimmune disorders because they breach B-cell tolerance, making them possible targets for the immune system [11].A prior study [12] had demonstrated that SLE patients experienced oxidative damage in addition to a markedly elevated conjugated diene and MDA production.Some studies [12,13] also discovered that the antioxidant enzymes superoxide dismutase and catalase were the targets of increased levels of circulating autoantibodies in the plasma and serum of SLE patients.
A higher sensitivity of plasma/serum lipids and lipoproteins to oxidation may, at the very least, promote atherogenesis.SLE has been linked to early atherosclerosis [14].Te production of foam cells originating from macrophages may be intimately associated with the modifcation of lowdensity lipoprotein (LDL), a sort of modifed LDL, that is triggered by scavenger receptors on macrophages rather than LDL receptors [15].Tus, OxLDL has a major role in the development and course of atherosclerosis [16,17].Furthermore, OxLDL has been demonstrated to be a cardiovascular risk factor in people with SLE [18,19].
Apolipoprotein B (ApoB) comes in two isoforms (ApoB48 and ApoB100) in human plasma and serum, and its levels are correlated with the risk of coronary heart disease.Te primary physiological ligand for both the LDL receptor and the massive monomeric protein ApoB100, which has 4563 amino acids, is found in both.Te liver produces ApoB100, which is necessary for the synthesis of extremely low-density lipoprotein.Unlike the other apolipoproteins, ApoB does not switch between lipoprotein particles; instead, it is present in LDL and intermediate density lipoprotein following the loss of ApoA, E, and C. Chylomicrons and their remnants include ApoB48.It is necessary for dietary lipids to be absorbed via the gut wall [20].
In the past years, various studies have shown plasma/ serum MDA, ApoB, and OxLDL levels in SLE patients who also have established variations in plasma/serum MDA, ApoB, and OxLDL levels in SLE patients but with a smaller sample size [21][22][23][24][25][26][27].However, the diferences in studies go far beyond the explanations of standard units, ethnicity, and varied features of control groups.A systematic review and meta-analysis are conducted to fnd a distinct estimation of the relationship between serum or plasma MDA, ApoB, and OxLDL levels and SLE.Tis is performed in order to compare the plasma/serum oxidant status of SLE patients with the control groups and also to determine the likely role of MDA, ApoB, and OxLDL in the pathophysiology of SLE.

Systematic Search.
Using PubMed, Embase, Web of Science, and ScienceDirect, a comprehensive search of published articles up to February 27, 2023, that documented the relationship between MDA, ApoB, and OxLDL levels and SLE was conducted.Malondialdehyde, MDA, Apolipoprotein, ApoB, Oxidized low-density lipoprotein, OxLDL, oxidative stress, systemic lupus erythematosus, and SLE were the search terms utilized.In order to locate other relevant papers that were not electronically collected by the aforementioned databases, the references of reviews and retrieved articles were also searched.E-mail requests for missing data were made to the respective authors.

Criteria for Inclusion.
When there was uncertainty or disagreement between the two researchers regarding the eligibility of a particular article for inclusion, a third researcher was asked to mediate.Two researchers from the research team evaluated all retrieved articles independently to determine whether each article met the requirements for inclusion.Te only human subjects, plasma/serum (MDA, ApoB, and OxLDL) levels, original data, no language or racial/ethnicity restrictions, and case-control study, crosssectional study, and cohort study were the inclusion criteria for this meta-analysis.To ensure inclusion, articles containing values in the range, median, standard error, interquartile range, and mean were transformed to mean and standard deviation [28].When the same data were provided in many articles, the most recent, thorough data were chosen.

Exclusion of Articles.
We excluded articles with insufcient data, reviews, and case reports in the metaanalysis.All original articles on animals as well as duplicate articles were excluded in the analysis.Te lack of estimates for the variables taken into account for the subgroup analysis was not the basis for the exclusion criteria.For each individual publication, a record of the reasons as to why it was excluded from the study was established.

Extraction of Data.
From the included articles, we extracted variables such as frst author, year, country, number, age (mean ± SD), gender, disease period, body mass index (BMI), systemic lupus erythematosus disease activity index (SLEDAI), MDA assay, ApoB assay, OxLDL assay, ethnicity, study type, and MDA levels (mean ± SD), ApoB levels (mean ± SD) and OxLDL levels (mean ± SD).Only data extraction from original publications was performed by two diferent researchers.Also, from the included articles, the following covariate variables: country, publication year, sample size, study type, ethnicity, measurement type, and NOS, were extracted based on literature to conduct the meta-regression.Te confounding factors were selected based on an extensive review of the literature and were chosen according to the common factors identifed across various studies.Te Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) standards [29] were followed in this analysis, and the Newcastle-Ottawa Quality Assessment Scale (NOS) [30] was used to evaluate the methodological quality of the included papers.A technique quality score of ≥5 to 9 denoted superior quality for the considered article.

Statistical Analysis.
Since we let the genuine efects to vary between studies, the random efect model was used for the analysis.To obtain the estimated values in mean and standard deviation, the conversion was performed for all data presented as either median and range or median and 2 Autoimmune Diseases interquartile range (IQR) [28].Prior to analysis, articles that provided levels of ApoB, OxLDL, and plasma/serum MDA in units other than µg/ml were converted.For every investigation, the standard mean diference (SMD) and its 95% confdence interval (CI) were used to calculate the associations between plasma/serum MDA, ApoB, and OxLDL levels and SLE.Te pooled SMD and 95% CIs were tested for signifcance using the Z-test; a value of P < 0.05 was considered statistically signifcant.Stratifed analysis was performed to successfully perform subgroup analysis.Using Cochrane's Q statistics (Q-test), heterogeneity among the included articles was assessed; P ≤ 0.01 was deemed statistically signifcant [31,32].In addition, the I 2 statistics (I 2 � (Q − df)/Q × 100%) were used to evaluate heterogeneity.According to reference [33], heterogeneity was indicated by an I 2 value of less than 25%, moderate heterogeneity by I 2 � 25 to 50%, signifcant heterogeneity by I 2 > 50 to 75%, and extreme heterogeneity by I 2 > 75%.We performed subgroup analysis to identify the sources of heterogeneity.
In addition, to identify the studies that overcontributed to the observed heterogeneity, sensitivity analysis was performed.When heterogeneity was observed, the source of the heterogeneity was found using meta-regression analysis.With Egger's linear regression and Begg's rank correlation tests, publication bias was evaluated [34].When publication bias was likely, the trim and fll analysis was applied.When P < 0.05, the publication bias was deemed statistically signifcant.Each and every analysis was conducted using STATA version 12.

Study Characteristics.
Tis meta-analysis included fortyeight articles with 2358 patients of SLE and 2126 health controls assessed for MDA (SLE: 1041 and control: 1041), ApoB (SLE: 853 and control: 834), and OxLDL (SLE: 464 and control: 834) levels.One article out of every sixteen was from a cross-sectional study, while nearly 45 percent (43.8%) of the included papers used cohort studies as their study type.In precisely half of the included papers, case-control studies were used.Te European/American ethnicity was categorized by Hungarian, North American, South American, German, Caucasian, Sweden, and mixed ethnic groups.Colorimetric assay, thiobarbituric acid reactive species, microplate reader, fuorometric assay, spectrophotometric method of lipid peroxidase LPO-586, high-performance liquid chromatography, chemiluminescent assay, immunoturbidimetric assays, nephelometric method, and radial immunodifusion were the measurement methods/types employed for plasma/serum MDA, ApoB, and OxLDL levels.Te assessment of the quality of the methodology was satisfactory for all the included articles with ratings between fve and nine.Table 1 lists the specifc characteristics of the articles that are included.

Plasma/Serum MDA, ApoB, and OxLDL Levels.
Compared to control groups, plasma/serum MDA levels were considerably higher in SLE patients (SMD � 1.292 ng/ml; 95% CI � 0.780-1.805;Z � 4.94; P < 0.001).In addition, the plasma/serum ApoB levels of SLE patients were signifcantly higher than those of the control groups (SMD � 0.808 ng/ml; 95% CI � 0.451-1.165;Z � 4.44; P < 0.001).Once more, compared to control groups, SLE patients' plasma/serum OxLDL levels were signifcantly higher (SMD � 2.266 ng/ml; 95% CI � 1.088-3.444;Z � 3.77; P < 0.001).Figures 2, 3, and 4 show the pooled results for the levels of MDA, ApoB, and Autoimmune Diseases    However, there was no signifcant publication bias shown by Egger's test in all the included articles for SLE and MDA (P > 0.05; t � 0.65; Table 2).Furthermore, trim and fll analysis was carried out for plasma/serum ApoB levels with P < 0.001, keeping the number of trials (13) the same.Tis demonstrated our consistent fndings.Again, trim and fll   Autoimmune Diseases analysis was performed for plasma/serum OxLDL levels and the results showed trimming with the number of studies changed from seven to eight.Moreover, P � 0.002 shows that our results were steady.Sensitivity analysis did not signifcantly alter the pooled results, suggesting the results to be stable (Figures 5, 6, and 7).

Meta-Regression Analysis.
A meta-regression analysis with the inclusion of covariate variables (country, publication year, sample size, study type, ethnicity, measurement type, and NOS) was carried out to fnd additional potential drivers of heterogeneity.According to the results in Table 4, all of the covariates had no efect on the overall efect size or on the correlation between plasma/serum MDA, ApoB, and OxLDL levels and SLE (all P > 0.05).

Discussion
Tis study largely evaluated a lot of literature on the association between plasma/serum MDA, ApoB, and OxLDL and SLE, in which a total of 48 articles were included.Tere was enough evidence to establish that signifcantly higher plasma/ serum MDA, ApoB, and OxLDL levels were observed in SLE patients compared to control groups even though heterogeneity existed within the included studies.We performed subgroup analysis and meta-regression to fnd the sources of heterogeneity.Numerous clinical characteristics, including lupus nephritis and tissue damage in SLE, have been linked to elevated MDA levels [54,66].In a similar vein, Koca SS et al. discovered that SLE patients had higher MDA levels than control groups.On the other hand, Tewthanom et al. reported that there was no statistically signifcant diference between the MDA levels of patients with SLE and the control groups [27].Te results of the Frosegard group's research have demonstrated that elevated levels of autoantibodies and OxLDL are risk factors for cardiovascular disease in SLE patients [67].Likewise, Kim SH et al. revealed a signifcantly higher relationship between OxLDL levels in SLE [24].However, our meta-analysis result of OxLDL levels does not support the fndings of Soep et al., who reported no statistical signifcance between SLE patients and the control group [25].
A study conducted by Du et al. is in support with our fnding that sought to indicate elevated ApoB levels in SLE patients as compared to control groups [21].Te ApoB levels of SLE patients and control groups did not difer signifcantly, according to Yuan et al. [22].Tese diferences can be related to the number of studies, the inclusion criteria, the measurement techniques, and, in the main, the sample size used in the original publications.Oxidative stress parameters play a crucial role in forecasting the consequences of oxidation and in providing the foundation for developing an appropriate Autoimmune Diseases response that can prevent or mitigate harm.Numerous studies examining MDA, ApoB, and OxLDL levels in SLE have been conducted since the disease was shown to be multigenic, with a range of results.Our research revealed a relationship with susceptibility to SLE, which was highly benefcial in elucidating the pathophysiology of SLE.MDA, ApoB, and OxLDL may represent a new SLE disease marker.
Disease activity in SLE patients is correlated with elevated plasma/serum MDA levels [12,47].Tis confrms our fndings that plasma/serum MDA levels were greater in patients with SLEDAI ≥8 of SLE.According to our research, there is a substantial correlation between SLE patients' SLEDAI scores and their plasma/serum ApoB levels.In addition, a subgroup study showed a signifcant     OxLDL levels and SLE [25].Te study's variability could be ascribed to specimen source, genetic variables, and ethnic diferences.Since majority of individual articles were written by people of Asian, European, and American ethnic backgrounds, more research from diverse geographic locations and ethnic groups or nations examining the plasma/serum levels of MDA, ApoB, and OxLDL in SLE patients compared with health controls may provide insight on the understanding of the pathophysiology of SLE.
Our research revealed a strong correlation between the BMI of SLE patients and their plasma/serum levels (MDA, ApoB, and OxLDL), which contradicts the fndings of [25,37,44,50,55,58,[62][63][64].Te primary causes of the discrepancy may be attributed to the quantity of research and the precise data extraction methods used in our investigation.Tis research also showed that, for comparison groups, individuals with SLE had signifcantly greater levels of plasma/serum MDA, ApoB, and OxLDL than patients in the control group.MDA levels and the length of the sickness were found to be signifcantly correlated by Zineldeen et al. [40].However, Tewthanom et al. [27] and Hassan et al. [44] provided evidence to the contrary.Tis study is known as the frst meta-analysis to show that plasma/serum MDA, ApoB, and OxLDL levels were examined in SLE patients relative to healthy controls.In addition, the included papers were not limited based on language, and the results were extracted accurately and validly.In comparison to the individual publications, our study's statistical power and analytical resolution were enhanced by the utilization of a sizable sample size.In addition, sensitivity analysis, trim and fll, and meta-regression were used to fnd confounding variables, heterogeneity, and publication bias.Nonetheless, certain shortcomings were noted.Certain materials, such as academic dissertations and conference abstracts, were left out and could have skewed the actual results.Once more, just a small number of components' causes of heterogeneity were examined via subgroup analysis and meta-regression.Te large degree of variability in this study may be explained by a few diferent factors, including drug use and other clinical characteristics.

Conclusion
Our research revealed that the levels of plasma/serum MDA, ApoB, and OxLDL were considerably higher in SLE patients than in the control group.Tis suggests that MDA, ApoB, and OxLDL are important factors to consider when analyzing oxidative stress and play a crucial role in the pathophysiology of SLE.Future research should examine bigger sample sizes while accounting for the environmental determinants of MDA, ApoB, and OxLDL levels in individuals with SLE.

Figure 1 :
Figure 1: Flowchart of the exclusion process of articles and the reasons.

Figure 4 :
Figure 4: Forest plots of the pooled odd ratio and 95% confdence intervals of included articles and relationship for OxLDL levels and SLE.

Figure 5 :Figure 6 :
Figure 5: Sensitivity analysis of the included articles for MDA levels.Te two vertical axes, vertical middle axis, hollow circles, and two ends of the dotted lines, respectively, represent, overall odd ratio, pooled odd ratios, and 95% confdence interval.

Figure 7 :
Figure 7: Sensitivity analysis of the included articles for OxLDL levels.Te two vertical axes, vertical middle axis, hollow circles, and two ends of the dotted lines, respectively, represent, overall odd ratio, pooled odd ratios, and 95% confdence interval.

Table 1 :
Characteristics of individual studies included in the meta-analysis: (a) MDA levels and SLE.(b) ApoB levels and SLE.(c) OxLDL levels and SLE.
3.4.Subgroup Analysis.Te variables that were taken into account for the subgroup analysis were measurement type, age, BMI, SLEDAI, disease duration, and ethnicity.Te results are shown in Table3.It was established that European/American SLE patients as well as patients of both ages <36 and ≥36 exhibited higher MDA, ApoB, and OxLDL MDA and ApoB levels compared to the controls and SLE patients with SLEDAI score of <8 showed signifcantly higher ApoB levels.Patients with a BMI of <23 of SLE had higher MDA and OxLDL levels and also with disease duration ≥10 (SMD � 2.458 ng/ml; 95% CI � 1.011-3.905;Z � 3.33; P ≤ 0.01) of SLE had signifcantly higher MDA levels.

Table 2 :
Heterogeneity and publication bias tests.Figure 2: Forest plots of the pooled odd ratio and 95% confdence intervals of included articles and relationship for MDA levels and SLE.
Figure 3: Forest plots of the pooled odd ratio and 95% confdence intervals of included articles and relationship for ApoB levels and SLE.

Table 3 :
Subgroup analysis of MDA, ApoB, and OxLDL levels in SLE.