Is Mitochondria Biogenesis and Neuronal Loss Prevention in Rat Hippocampus Promoted by Apigenin?

Screening of an FDA-approved compound library identifies apigenin for the treatment of myocardial injury

Apigenin is the active ingredient in Ludangshen. Although previous studies reported the cardioprotective actions of apigenin against doxorubicin (Dox)-induced cardiomyopathy, the underlying mechanisms remain incompletely understood. Since apigenin beneficially regulates various aspects of mitochondrial function and dynamics, we asked whether apigenin improves heart function in mice with Dox-induced cardiomyopathy by regulating the mitochondrial unfolded protein response (UPRmt). Co-administration of apigenin significantly restored heart function, reduced myocardial swelling, inhibited cardiac inflammation, increased cardiac transcription of UPRmt-related genes, and promoted cardiomyocyte survival in Dox-treated mice. In turn, blockade of UPRmt abolished the mito- and cytoprotective effects of apigenin, evidenced by decreased ATP production, suppressed mitochondrial antioxidant capacity, and increased apoptosis, in Dox-treated, cultured HL-1 cardiomyocytes. Furthermore, apigenin treatment prevented Dox-induced downregulation of Sirt1 and Atf5 expression, and the beneficial effects of apigenin were completely nullified in Sirt1 knockout (KO) mice or after siRNA-mediated Sirt1 knockdown in vitro. We thus provide novel evidence for a promotive effect of apigenin on UPRmt via regulation of the Sirt1/Atf5 pathway. Our findings uncover that apigenin seems to be an effective therapeutic agent to alleviate Dox-mediated cardiotoxicity.

Apigenin attenuates LPS-induced neurotoxicity and cognitive impairment in mice via promoting mitochondrial fusion/mitophagy: role of SIRT3/PINK1/Parkin pathway

RATIONALE

Alteration of the NAD⁺ metabolic pathway is proposed to be implicated in lipopolysaccharide (LPS)-induced neurotoxicity and mitochondrial dysfunction in neurodegenerative diseases. Apigenin, a naturally-occurring flavonoid, has been reported to maintain NAD⁺ levels and to preserve various metabolic functions.

OBJECTIVES

This study aimed to explore the effect of apigenin on mitochondrial SIRT3 activity as a mediator through which it could modulate mitochondrial quality control and to protect against intracerebrovascular ICV/LPS-induced neurotoxicity.

METHODS

Mice received apigenin (40 mg/kg; p.o) for 7 consecutive days. One hour after the last dose, LPS (12 µg/kg, icv) was administered.

RESULTS

Apigenin robustly guarded against neuronal degenerative changes and maintained a normal count of intact neurons in mice hippocampi. Consequently, it inhibited the deleterious effect of LPS on cognitive functions. Apigenin was effective in preserving the NAD⁺/NADH ratio to boost mitochondrial sirtuin-3 (SIRT3), activity, and ATP production. It conserved normal mitochondrial features via induction of the master regulator of mitochondrial biogenesis, peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α), along with mitochondrial transcription factor A (TFAM) and the fusion proteins, mitofusin 2 (MFN2), and optic atrophy-1 (OPA1). Furthermore, it increased phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) and parkin expression as well as the microtubule-associated protein 1 light chain 3 II/I ratio (LC3II/I) to induce degradation of unhealthy mitochondria via mitophagy.

CONCLUSIONS

These observations reveal the marked neuroprotective potential of apigenin against LPS-induced neurotoxicity through inhibition of NAD⁺ depletion and activation of SIRT3 to maintain adequate mitochondrial homeostasis and function.