Histoprotective Effect of Lepidium sativum-Loaded Solid Lipid Nanoparticles Against 6PPD-Quinone-Induced Adrenal Gland Injury in Rats

Abstract

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q), an ozonation product of the tyre antioxidant 6PPD, is now recognised as a ubiquitous environmental contaminant with demonstrable multi-organ toxicity in mammals, yet its effect on the adrenal cortex has not been characterised. The present work examined whether subchronic 6PPD-Q exposure disturbs adrenocortical structure and glucocorticoid output in adult male albino rats, and whether co-treatment with Lepidium sativum-loaded solid lipid nanoparticles (LS-SLN) confers protection. 32 rats were allocated to four groups (n = 8 per group): Control, LS-SLN only, 6PPD-Q only, and 6PPD-Q + LS-SLN, and were treated for duration 28 days. Outcomes comprised body and paired adrenal weights, adrenocortical and zonal thickness by histomorphometry, a six-item semi-quantitative histopathological injury score, zone-resolved immunohistochemical quantification of steroidogenic acute regulatory protein (StAR), and basal and adrenocorticotropic hormone (ACTH)-stimulated serum corticosterone. 6PPD-Q alone reduced total cortical thickness (698.5 ± 39.8 versus 812.4 ± 45.2 μm; p < 0.01) with the largest losses in the zona glomerulosa and zona fasciculata, produced a composite injury score four-fold above Control (8 [5–10] versus 2 [1–3]; p < 0.001), and lowered StAR immunoreactivity in all three cortical zones, most steeply in the zona fasciculata (11.2 ± 1.3 versus 18.6 ± 1.8; p < 0.001). Functionally, basal corticosterone fell to 62.4 ± 5.8 ng/mL and the ACTH-stimulated concentration to 154.2 ± 14.6 ng/mL (both p < 0.01), indicating a reduced adrenal reserve rather than an isolated basal deficit. LS-SLN alone was histologically silent but increased cortical and zonal thickness, StAR expression and both basal and stimulated corticosterone, consistent with a trophic rather than an injurious action. Co-treatment restored every morphometric, immunohistochemical and hormonal end-point to values statistically indistinguishable from Control, although the composite injury score remained modestly but significantly elevated (4 [2–6]; p < 0.05), indicating partial rather than complete rescue. Collectively, the adrenal cortex emerges as a previously unrecognised target of 6PPD-Q, with zone-selective structural damage tracking a loss of StAR-dependent steroidogenic capacity, and LS-SLN offers substantial but incomplete protection.