Responses of Hepatic and Splenic Nrf2-HO1- NF-κB pathways to Gallic Acid and Artesunate Combination Therapy in Plasmodium berghei-Infected Mice

Technical Summary: Responses of Hepatic and Splenic Nrf2-HO1-NF-κB Pathways to Gallic Acid and Artesunate Combination Therapy in Plasmodium berghei-Infected Mice

Problem Statement
Malaria pathophysiology involves a complex interplay of oxidative stress and dysregulated inflammation, driven by the generation of reactive oxygen species (ROS) and the activation of pro-inflammatory cytokines. While the host's antioxidant defense mechanisms, regulated by Nuclear Factor Erythroid 2–Related Factor 2 (Nrf2) and Heme Oxygenase-1 (HO1), are critical for maintaining redox homeostasis, they are often overwhelmed during severe infection. Concurrently, the transcription factor Nuclear Factor Kappa B (NF-κB) drives inflammatory responses that, when excessive, contribute to tissue damage and poor clinical outcomes. Although Artesunate is a primary antimalarial agent and Gallic Acid is a phytochemical with known antioxidant and immunomodulatory properties, the specific molecular mechanisms by which their combination therapy modulates the Nrf2-HO1-NF-κB signaling axis in key organs remain uncharacterized. This study addresses the gap in understanding how this combination influences gene expression dynamics in the liver (metabolic hub) and spleen (immune hub) during Plasmodium berghei infection.

Methodology
The study utilized a curative (Rane) test model with adult Swiss albino mice infected with P. berghei NK65. The experimental design included nine groups: a normal control, a negative control (infected, untreated), and seven treatment groups receiving Artesunate alone, Gallic Acid alone, or varying combinations of both (Artesunate 4 mg/kg fixed; Gallic Acid ranging from 6.25 to 100 mg/kg). Treatments were administered orally for four consecutive days post-infection.

On Day 7 post-inoculation, liver and spleen tissues were harvested, and total RNA was extracted using the TRIzol method. Complementary DNA (cDNA) was synthesized, and semi-quantitative PCR was performed to amplify target genes: HO1, Nrf2, NF-κB1, and TNF-α, with GAPDH serving as the housekeeping gene. Gene expression was analyzed via agarose gel electrophoresis and densitometric quantification using ImageJ software. Data were normalized against GAPDH and expressed as mean fold-change relative to the normal control group. Statistical significance was determined using one-way ANOVA followed by Tukey's post hoc test.

Key Contributions and Results
The study provides a comparative analysis of transcriptional responses in the liver and spleen, revealing distinct tissue-specific modulation patterns:

• Liver Response:

  • Antioxidant Pathways: Treatment with Artesunate, Gallic Acid, and their combinations generally upregulated HO1 and Nrf2 expression compared to infected controls. The highest HO1 induction was observed in the A:G50 group (1.49-fold), while Nrf2 peaked at the intermediate combination dose A:G25 (1.65-fold).
  • Inflammatory Pathways: NF-κB1 expression remained relatively stable or showed modest suppression across treatment groups compared to the negative control. In contrast, TNF-α exhibited a non-linear, dose-dependent response, with significant upregulation in the Gallic Acid monotherapy group and specific combination groups (e.g., A:G100), suggesting a context-dependent inflammatory modulation rather than uniform suppression.

• Spleen Response:

  • Antioxidant Pathways: The spleen displayed more dynamic and heterogeneous responses. Nrf2 expression showed extreme induction in the Gallic Acid monotherapy group (approx. 8.11-fold increase) and significant elevation in several combination groups. HO1 was consistently upregulated in Artesunate and combination groups, with the highest levels in the A:G50 group.
  • Inflammatory Pathways: NF-κB1 expression was markedly suppressed in most treated groups compared to the normal control, indicating a strong anti-inflammatory effect of the therapy in splenic tissue. However, TNF-α showed a divergent pattern: it was elevated in lower-dose combination groups (A:G6.25 and A:G12.5) but reduced in higher-dose groups, suggesting a reprogramming of inflammatory signaling where specific cytokine activation is preserved while upstream transcription factors are dampened.

• Fold-Change Dynamics: The analysis of fold-change relative to physiological baseline highlighted that the combination therapy induces a coordinated shift: activation of cytoprotective antioxidant pathways (Nrf2/HO1) coupled with the suppression of upstream inflammatory transcription (NF-κB1), while allowing for selective, dose-dependent modulation of effector cytokines (TNF-α).

Significance and Claims
The authors conclude that Gallic Acid and Artesunate combination therapy induces coordinated antioxidant activation and context-dependent inflammatory modulation. The study claims that this therapeutic approach offers a "balanced mechanistic framework" for malaria treatment by:

1. Enhancing Host Resilience: Promoting redox homeostasis through the upregulation of Nrf2 and HO1, thereby protecting tissues from oxidative damage.
2. Recalibrating Immune Signaling: Suppressing excessive NF-κB-mediated inflammation while selectively preserving or modulating TNF-α levels, potentially preventing immunopathology without compromising parasite clearance.
3. Tissue Specificity: Highlighting that the spleen exhibits stronger and more dynamic transcriptional responses than the liver, underscoring the organ-specific nature of malaria pathogenesis and treatment effects.

The paper posits that these findings support the potential of Artesunate-Gallic Acid combination as an immunomodulatory therapeutic strategy that targets both the parasite and host-mediated pathological processes, potentially improving treatment efficacy in the face of emerging drug resistance.