Abstract
Background:
The leaf ethanolic extract of Etlingera hemisphaerica (LE3H) changes the levels of eight protein bands in the blood serum impacted by mercury chloride (HgCl₂), making them closer to the normal state in Rattus norvegicus.

Aim:
This study aimed to understand the effect of LE3H on restoring the intensity of serum proteins in R. norvegicus previously induced by HgCl2.

Methods:
Male R. norvegicus (rats) were categorized into four groups (K0, K1, K2, and K3), each with four rats. K1, K2, and K3 were administered an intraperitoneal injection of 5 mg/kg body weight (BW) HgCl2. After 24 h, K1 was gavaged daily with double-distilled (DD) water for 7 days, K2 was gavaged daily for 7 days at a rate of 0.27 mg/g BW LE3H, and K3 was gavaged daily for 7 days at a dose of 0.55 mg/g BW LE3H. Similarly, DD water was given to K0 as a control. On the ninth day, we used cervical dislocation to euthanize the animals and collected their blood from the heart to produce serum. Serum protein levels were quantified using the Lowry method, followed by protein isolation via two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (2-D SDS-PAGE). The 2D electropherograms were computerized comparisons, MW and pI measurements, protein digestion and peptide extraction, nano liquid chromatography-tandem mass spectrometry (nano LC-MS/MS), data processing, and protein identification.

Results:
The 2D electropherograms successfully separated 72 spot proteins. Sixteen (A,B,C,D,E,F, G,H,I,J,K,L,M,N,O, and P) presence protein spots significantly increased or decreased influenced by HgCl2 treatment, and then LE3H administration restored the presence of these proteins to close to control conditions. Four selected protein spots with National Center for Biotechnology Information (NCBI) D[gi|37805241], F[gi|295916], H[gi|155369696; gi|60551611], and K [gi|149056721], significantly increased influenced by HgCl2, then LE3H restored these proteins to close to control conditions. Four selected protein spots with NCBI L[gi|149043886; gi|116597], M[gi|121041], O[gi|231468], and P[gi|546056; gi|6981010] significantly decreased influenced by HgCl2, then LE3H on restored these proteins to close to control conditions.

Conclusion:
LE3H may serve as a potential herbal agent to mitigate mercury-induced systemic toxicity via serum protein expression modulation.

Key words: Etlingera hemisphaerica; Mercury chloride; Two-dimensional protein; Blood serum; Rattus norvegicus.