Vitamin D Supplementation Modulates Base Excision Repair (BER) Machinery in Systemic Sclerosis: A Prospective Longitudinal Study.

Systemic sclerosis (SSc) is a chronic, autoimmune, fibrotic disorder involving immune dysregulation, vascular abnormalities and progressive fibrosis. Although oxidative stress and defective DNA repair have been implicated in its pathogenesis, the impact of vitamin D on DNA repair pathways remains unclear. This study aimed to investigate the expression of DNA repair enzymes in SSc, explore their relationship with vitamin D status and assess the effects of vitamin D supplementation on the transcriptional expression of these enzymes. Peripheral blood samples were collected from 52 female patients with SSc and 31 age-matched healthy controls (HCs). Gene expression levels of base excision repair (BER) enzymes (APE1 and OGG1) and nucleotide excision repair (NER) enzymes (XPA and XPC) were analyzed. Serum vitamin D levels were measured and correlated with disease activity scores. In a prospective arm of the study, patients received six months of vitamin D supplementation and their DNA repair capacity was evaluated pre- and post-intervention. Baseline expression of APE1 and OGG1 was significantly lower in SSc patients than in HCs, whereas expression of the NER genes remained unchanged, indicating selective impairment of the BER pathway. Vitamin D deficiency was prevalent in SSc and inversely correlated with disease severity. Supplementation significantly increased serum vitamin D levels and up-regulated APE1 and OGG1 expression; while NER genes remained unaffected. These findings are consistent with evidence of elevated oxidative DNA lesions in SSc and support a mechanistic link between BER activity and the repair of oxidative DNA damage. SSc patients exhibit reduced transcription of BER-specific enzymes associated with vitamin D deficiency andrestoration of vitamin D levels partially rescues BER enzyme expression. These findingshighlight a potentially modifiable axis linking micronutrient status, genomic stability and disease activity and provide a rationale for investigating vitamin D optimization as an adjunctive strategy to enhance DNA repair and potentially attenuate inflammatory and fibrotic processes in SSc.