Recent Insights into the Protective Mechanisms of Paeoniflorin in Neurological, Cardiovascular, and Renal Diseases

Abstract

The monoterpene glycoside paeoniflorin is the principal active constituent of the traditional Chinese herbal medicines, Radix Paeoniae Alba (RPA) and Radix Paeoniae Rubra (RPR), which have been used for millennia to treat cardiovascular diseases (e.g., hypertension, bleeding, and atherosclerosis) and neurological ailments (e.g., headaches, vertigo, dementia, and pain). Recent evidence has revealed that paeoniflorin exerts inhibitory effects on inflammation, fibrosis, and apoptosis by targeting several intracellular signaling cascades. In this review, we address the current knowledge about the pharmacokinetic properties of paeoniflorin and its molecular mechanisms of action. We also present results from recent pre-clinical studies supporting the utility of paeoniflorin for the treatment of pain, cerebral ischemic injury, and neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases. Moreover, new evidence suggests a general protective role of paeoniflorin in heart attack, diabetic kidney, and atherosclerosis. Mechanistically, paeoniflorin exerts multiple anti-inflammatory actions by targeting Toll-like receptor (TLR)-mediated signaling in both parenchymal and immune cells (in particular, macrophages and dendritic cells). A better understanding of the molecular actions of paeoniflorin may lead to the expansion of its therapeutic uses.

1. Introduction

Paeonia Lactiflora, native to China and northern Asia, is one of six famous flowering plants in China. During the Xia, Shang, and Zhou Dynasties, it was cultivated as an ornamental plant. With a stunning flower of various colors, it garnered acclaim as the “love flower.” Its roots have long been known to have substantial medicinal value. Radix Paeoniae is the dried root of Paeonia Lactiflora, which is categorized into two classes: Radix Paeoniae Alba (white peony) and Radix Paeoniae Rubra (red peony).¹

Radix Paeoniae has been used for the treatment of a variety of human disorders, such as headaches, dizziness, abdominal pain, spasmodic pain of the limbs, anemia, menstrual disorders, spontaneous sweating, and night sweats. Radix Paeoniae Alba is more widely used than Radix Paeoniae Rubra. The major bioactive component extracted from Radix Paeoniae Alba is paeoniflorin (PF), a monoterpene glycoside (Fig. 1). In past decades, PF has been observed to have a variety of pharmacological activities, such as anti-inflammation, anti-fibrosis, and anti-apoptosis in a variety of pathological conditions. PF also has been reported to kill cancer cells and suppress the growth of tumors. In addition, PF is an active component of many prescriptions in traditional Chinese medicine, such as Naoxueshuan tablets (脑血栓片),² Shaoyao-Gancao-Tang (芍药甘草汤),³ Xinnaokang capsules (心脑康胶囊),⁴ Xiongshao Capsules (芎芍胶囊),⁵ Pai Nong Powder (排脓散),⁶ and Guanjiekang (关节康),⁷ used for the treatment of stroke, dysmenorrhea, atherosclerosis, rheumatoid arthritis (RA), and other inflammatory/autoimmune diseases.

Figure 1.

Summary of the major signaling mechanisms targeted by paeoniflorin that affect apoptosis, inflammation, and oxidative stress. The structure of the terpine glucoside, paenoniflorin, ([(1R,2S,3R,5R,6R,8S)-6-hydroxy-8-methyl-3-[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy-9,10-dioxatetracyclo[4.3.1.02,5.03,8]decan-2-yl]methyl benzoate ) is presented in the inserts. Paenoniflorin has been reported to exert antiapoptic effects by attenuating the actions of the Gq protein-coupled receptors like the adenosine 1 (AT1R) and their interactions with the epithelial growth factor receptor (EGFR) by inhibiting the Gq, MAPK and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). The anti-inflammatory effects of Paeononiflorin are largely related to its ability to inhibit interleukin 6 (IL-6) and other cytokine mediated activation of the janus kinase (JAK)/signal transducer, and activator of transcription 3 (STAT3) pathway. Paeononiflorin also opposes oxidative stress by enhancing the activity of the Kelch ECH associating protein 1 (Keap1)-Nrf 2 signaling pathway which enhances the transcription and expression of antioxidative stress enzymes.

Overall, a PubMed search of the term “paeoniflorin” yielded 1,118 entries (February 12, 2021). Using Boolean operators and key search terms, we narrowly focused this review on inflammation and vascular aspects of this compound and its potential therapeutic effects for the treatment of various neurodegenerative, cardiovascular, metabolic and renal diseases, which would be of interest to the readers of Journal of Cardiovascular Pharmacology (Table 1). Our intention is to highlight recent developments in the mechanism of the protective actions of PF that might be further exploited in drug development. Additional information on the immunological actions of paeoniflorin can be found in two recent excellent reviews.^{8, 9}

Table 1.

Preclinical evidence for the protective actions of paeoniflorin in neurological, cardiovascular, and renal diseases

Protection	Condition/Disease
Neurological	Neuropathic Pain62–67
	Cerebral Ischemic Injury57,68
	Vascular Dementia47,69–72
	Alzheimer’s25,47,73,74,80,81
	Parkinson’s82,83
Cardiovascular	MI/ischemia-reperfusion injury/Heart failure85–91
	Atherosclerosis46,92
	Thrombosis93
Renal	Diabetic Nephropathy26,28,94–97,99,100
	Pancreatitis-induced renal injury98

2. Pharmacokinetics

The pharmacokinetic properties of PF have been extensively studied in rats and humans.^{3, 7, 10–13} Orally administered PF is poorly absorbed, and its bioavailability is about 3% to 4%.^{14, 15} PF is hydrophilic, absorbed mainly by passive diffusion, and is associated with a first-pass effect. It is transformed into bioactive metabolites, paeonimetabolin I (PM-I) and paeonimetabolin II (PM-II), by bacteria in the intestine.¹⁵ PF can also be digested by β-glucosidase to produce paeoniflorgenin (PG).^{16, 17} Additionally, PF is a substrate of P-glycoprotein 1 (Pgp), and co-administration of PF with inhibitors of Pgp or with other medications has been reported to alter the absorption of PF due to drug interactions.^{11, 15, 18–21} An acylated derivative, paeoniflorin-6’-O-benzene sulfonate (CP-25), was recently reported with improved absorption and distribution, lower clearance, sustained mean residence time, and increased bioavailability in rats.²²

The half-life (t½) of PF is similar in rats and humans.^{11, 23, 24} PK parameters were also determined in Chinese human volunteers.²³ The mean half-life (t½) of paeoniflorin for male and female subjects after a single IV injection of 18.3, 35.8, or 54.1 mg was 1.9, 1.9, or 1.8 h, with a clearance (CL) of 10.4, 11.3, and 11.2 L/h, respectively.²³ The apparent volume of distribution (V_ss) ranged from 16.8-18.1. Plasma maximum concentration (C_max) reached 402.2 – 1081 ng/mL when the dose increased from 18.3-54.1 mg/mL.²³

3. Molecular Mechanisms

The mechanisms by which PF exerts its biological effects are not fully defined. PF has been reported to alter the expression or activity of several nuclear transcription factors such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB),^25–27 signal transducer, and activator of transcription 3 (STAT3),^28–30 nuclear factor erythroid 2-related factor 2 (Nrf 2),^{31, 32} cAMP response element-binding (CREB),³³, and hypoxia-inducible factor-1α (HIF-1α).³⁴ It also affects mitochondrial function ³⁵ and cell survival/apoptosis of smooth muscle cells,³⁶ endothelial cells,^{34, 37} cardiomyocytes,^{38, 39} and neurons.²⁵ A summary of the major signaling pathways by which PF is thought to alter cell survival/apoptosis, inflammation, and oxidative stress is presented in Figure 1.

NF-κB plays a crucial role in the regulation of transcription, inflammatory cytokine production, and cell survival.^{40, 41} Treatment with PF in rat attenuated inflammatory NF-κB signaling in a model of collagen-induced rheumatoid arthritis, and inhibition of the NF-κB pathway was demonstrated to facilitate osteoblastogenesis in vivo and in vitro.^{42, 43} Although a direct interaction of PF with NF-κB signaling remains to be established,⁴⁴ these actions of PF would seem to be indirect, involving an upstream receptor (such as TLR4 or CB2R) or molecule (such as Rho-kinase) that impacts on IκB phosphorylation and its subsequent degradation.^{26, 45–47}

PF also attenuates the signal transducer and activator of transcription 3 (STAT3) pathway with beneficial effects in cancer, inflammation, and modulation of immune responses. In this regard, PF has been documented to exert inhibitory effects on dendritic cell function,^{29, 30} Th17 cell differentiation,^{29, 48} and pro-inflammatory M1 macrophage activation.²⁸ These actions may contribute to the beneficial therapeutic effects of PF in autoimmune encephalomyelitis or multiple sclerosis,²⁹ allergic contact dermatitis,³⁰ diabetic nephropathy,²⁸ and psoriasis.⁴⁸ The inhibitory actions of PF have been documented to impair the growth of human bladder cancer cells,⁴⁹ gastric carcinoma cells,⁵⁰ and glioma cells in vitro.⁵¹ Several mechanisms have been described for the inhibition of PF on STAT3 signaling, including the blockade of the nuclear translocation of STAT3,⁴⁹ upregulating suppressor of cytokine signaling 3 (SOCS3),³⁰ and enhancement of STAT3 degradation by the ubiquitin-proteasome pathway.⁵¹

There is also evidence that PF induces anti-oxidative stress enzymes by stimulating the Kelch ECH associating protein 1 (Keap1)-Nrf 2 signaling pathway.^{31, 32} Nrf2 is one of the most essential components of cellular antioxidant defenses, as it is a nuclear transcription factor that mediates the expression of phase II detoxification enzymes and antioxidant genes.^52–54 Inhibiting oxidative stress via the Nrf2 pathway contributes to the beneficial effects of PF in chronic kidney disease,⁵⁵ Parkinson’s disease,⁵⁶ cerebral ischemia-reperfusion injury,⁵⁷ diabetes,⁵⁸ and chronic obstructive pulmonary disease.⁵⁹ In stress settings, Nrf2 disassociates from Keap1, transits to the nucleus, and binds to the antioxidant response element (ARE) in the target gene promoters that transcribes gene, which are anti-inflammatory or anti-apoptotic.^{60, 61}

4. Role of PF in neurological protection

4.1. Pain

PF has been shown effective in analgesia. In a complete Freund’s adjuvant (CFA)-induced inflammatory pain mouse model, intrathecal injection of PF reduced the levels of pro-inflammatory cytokines (e.g., TNF-α, IL-1β, and IL-6) and inhibited spinal microglial activation, likely downstream of inhibition of Akt – NF-κB signaling.⁶² PF displayed analgesic effects in a chronic constriction injury (CCI)-induced neuropathic pain rat model by inhibiting p38 mitogen-activated protein kinase (MAPK) activation, likely due to inhibiting ASK1 activation, as well as by blunting increased NF-κB activity.^{63, 64} Moreover, suppression of NLRP3 inflammasome activation was implicated in PF-induced relief of neuropathic pain from chronic constriction injury.⁶⁵

Activation of the adenosine A1 receptor (A1R) may also contribute to the analgesic and hypnotic effects of PF. Prophylactic topical application of PF alleviated PTX-induced mechanical allodynia in mice by protecting sensory nerves from demyelination via activation of A1R.⁶⁶ Intraperitoneal injection of PF increased the mechanical threshold and prolonged thermal latency in a partial sciatic nerve ligation (PSNL) mouse model of neuropathic pain via adenosine A1 receptor activation.⁶⁷ PF inhibited c-Fos overexpression induced by PSNL in the ventrolateral periaqueductal gray and anterior cingulate cortex. These studies suggest that PF may have value in treating chronic pain and associated insomnia.

4.2. Cerebral ischemic injury

The neuroprotective actions of PF, demonstrated in middle cerebral artery occlusion (MCAO) stroke models, have been attributed to inhibition of oxidative stress, inflammation, and apoptosis. In rats, PF treatment (5 mg. kg⁻¹, i.p., twice per day) for 14 days inhibited activation of astrocytes and microglia following transient MCAO and reperfusion. In this study, PF was found to downregulate pro-inflammatory mediators (TNF-α, IL-1β, iNOS, COX-2, and 5-LOX) in plasma and brain by blocking JNK and p38 MAPK activation and NF-κB signaling but enhancing ERK activation.⁶⁸ The Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)/CREB signaling pathway plays a vital role in cell proliferation and survival, inflammation, and metabolism. In rats with transient MCAO, PF treatment decreased infarct volume and neurological deficit scores. Similarly, PF improved inhibited apoptosis of neurons, cell viability, and increased intracellular Ca²⁺ concentration in N-methyl-d-aspartic acid (NMDA)-induced excitotoxicity of primary hippocampal cells. This was associated with increased p-CREB and p-CaMKII and calmodulin (CaM) upregulation.³³ Additionally, a galloylated derivative of paeoniflorin decreased infarct volume and improved neurological deficits in rats with ischemia-reperfusion insult; and attenuated inflammation, oxidative stress, and apoptosis in PC12 cells by enhancing levels of phosphorylated Akt (p-Akt) and Nrf2, and Nrf2 nuclear translocation.⁵⁷

4.3. Neurodegenerative diseases

PF has a protective role in neurodegenerative diseases. By promoting M1 to M2 polarization of microglia/macrophages, PF attenuated morphological and ultrastructural alterations in the hippocampal CA1 area in a 4 vessel occlusion rat model of vascular dementia.⁴⁷ PF inhibited mTOR/NF-κB pro-inflammatory signaling and markedly decreased levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α, as well as increasing NO production and anti-inflammatory cytokine IL-10 and TGF-β1 expression by enhancing the PI3K/Akt anti-inflammatory pathway via cannabinoid receptor type 2 (CB2R) activation.⁴⁷ Notably, administration of PF for 4 weeks improved learning and memory abilities in a treatment mode when given a week after induction of cerebral ischemia. This study builds upon previous findings supporting PF as a potential treatment of vascular cognitive impairment and vascular dementia associated with cerebral vascular disease and ischemia, which often accompany aging.^{69, 70}

PF treatment (15 or 30 mg/kg by gavage for 4 weeks) improved cognitive function in a rat model of type 2 diabetes, as evidenced by decreased escape latency in a Morris water maze.⁷¹ These effects were associated with a reduction of phosphorylation of tau in the hippocampus.⁷² This was associated with reductions in IL-1β, TNF-α, and SOCS2 expression and elevations of insulin receptor substrate-1 (IRS-1) activity and phosphorylation of Akt and GSK-3β.⁷¹

There are several other studies in well-accepted mouse models of Alzheimer’s disease indicating that PF may be useful in the treatment of Alzheimer’s disease through its anti-inflammatory and anti-amyloidogenic effects.^{25, 73, 74} For, example, in an amyloid precursor protein (APP) and presenilin 1 (PS1) double-transgenic (APP/PS1) mouse model of Alzheimer’s disease, four-week treatment with PF (5 mg/kg, i.p., twice per day) improved cognitive function by blocking NALP3 inflammasome activation; reduced Aβ formation, glial activation, and the levels of pro-inflammatory cytokines, and increased the production of anti-inflammatory cytokines in the brain.⁷³ In another study, PF treatment decreased caspase 3 activity and inhibited cell death by increasing the Bcl2/Bax ratio and p-Akt levels and decreasing activated p38 MAPK levels.²⁵ Abnormal phosphorylation of tau due to persistent inflammation,⁷⁵ oxidative stress,⁷⁶ and excessive chemotaxis of microglia stimulated by β-amyloid (Aβ) oligomers in the brain,⁷⁷ as well as abnormal insulin signaling in the hippocampus, may promote the development of Alzheimer’s disease.^{78, 79} PF inhibited the production of IL-6, IL-1β, and TNF-α, and suppressed nuclear translocation of NF-κB subunit p65 by blocking phosphorylation of IκBα in vitro and in vivo.^{47, 73, 80} PF also reduced the release of chemokines, such as CXCL1 and CCL2, in an in vitro model. PF inhibited activation of glycogen synthase kinase 3β (GSK-3β) in the transgenic mouse model of Alzheimer’s disease ⁷³ and a tau hyperphosphorylation cell model.⁸¹ PF reduced the number of autophagosomes and stabilized microtubule structure by increasing microtubule-associated proteins MAP-2 and β III-tubulin by interfering with the calpain/Akt/GSK-3β-related pathways.⁸¹ Evidence from a transgenic mouse model of Alzheimer’s disease indicates that activation of the adenosine A₁ receptor contributes to the neuroprotective actions of PF. ⁷⁴

In the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease (PD), PF dose-dependently reduced dopaminergic cell loss. This effect may be due to preventing downregulation of dopaminergic transporter (DAT) and tyrosine hydroxylase (TH) protein levels in striatal and substantia nigra, affecting dopamine catabolism and inhibiting dopamine turnover. PF functions were also related to increased Bcl-2/Bad ratio and inhibiting caspase-9 and caspase-3 activation. In vitro, PF had neuroprotective effects against MPTP⁺-induced damage and apoptosis through the Bcl-2/Bax/caspase-3 pathwayin PC12 cells.⁸² In the 6-hydroxydopamine (6-OHDA) rat model of Parkinson’s disease, PF improved behavioral symptoms, delayed dopaminergic neuron loss, and attenuated loss of dopamine and its metabolites in the substantia nigra. PF modulated ASIC1a expression, decreased α-synuclein (α-SYN), and lessened autophagic dysfunction. Further experiments demonstrated that ASIC1a knockdown downregulated α-SYN levels and alleviated autophagic injury in 6-OHDA-treated ASIC1a-silenced PC12 cells. Thus, PF may be useful to delay the progression of Parkinson’s disease by acting on ASIC1a.⁸³

These preclinical studies support the utility of PF in the management of neuropathic pain and treatment of Alzheimer and Parkinson’s diseases. PF may have utility as well in slowing the progression of vascular dementia of various etiologies, including diabetes and aging.

5. Cardiovascular protective effects of PF

5.1. Cardiovascular diseases

Cardiovascular disease is the leading cause of death worldwide,⁸⁴ and accumulating evidence supports the therapeutic potential of PF. Recently, preconditioning protection of the heart from ischemia-reperfusion injury by PF was attributed to the reduced oxidative stress and apoptosis by regulating gene expression, including p38 MAPK.⁸⁵ Reduction of p38 activation was implicated in the actions of PF in attenuating myocardial fibrosis and improving cardiac function in a rat model of chronic heart failure.⁸⁶

PF was also shown to have protective effects on the cardiovascular system by decreasing the expression of TNF-α, IL-1β, IL-6, IL-12, IFN-γ, MCP-1, and iNOS. In an acute MI rat model, PF treatment reduced infarct size and decreased the levels of biomarkers of cell damage, such as creatine kinase (CK), lactate dehydrogenase, and cardiac troponin T. This was associated with blockade of TNF-α, IL-1β, IL-6, and NF-κB, iNOS expression, and caspase 3/9 activities.⁸⁷ In a pressure overload model of heart failure in mice, PF (20 mg/kg, i.p., 8 weeks) reduced cardiac inflammation and improved left ventricular function by decreasing protein levels of TNF-α and IL-1β, the number of infiltrating monocytes/macrophages, and phosphorylation of IκBα and NF-κB p65.⁸⁸ In mice with LPS-induced cardiac dysfunction, intraperitoneal injection of PF (15 mg/kg) reduced the levels of TNF-α, IL-1β, and IL-6 and preserved cardiac function. This was associated with inhibition of NF-κB by the activation of PI3K/Akt⁸⁹ and downregulation of the HMGB1-RAGE/TLR2 or TLR4/NF-κB pathways.⁹⁰ Finally, in diabetic mice, PF protected against myocardial ischemic injury partially via the TRPV1/CaMK/CREB/CGRP signaling pathway.⁹¹

5.2. Atherosclerosis

In a rat model of high-fat diet atherosclerosis, PF (10 or 20 mg/kg, i.g. daily for 15 weeks), decreased plasma levels of cholesterol, triglycerides, and LDL cholesterol, in the absence of changes in body weight. Further study showed that PF reduced atherosclerotic inflammation by downregulating inflammatory cytokines (IL-1β, IL-6, and TNF-α) by inhibiting the TLR4/MyD88 pathway leading to reduction of phosphorylation of IκBα and NF-κB p65.⁴⁶ Vascular smooth muscle cell (VSMC) proliferation and migration play a critical role in atherosclerosis. Upregulation of the expression of inflammatory cytokines accelerates the development of atherosclerosis. PF treatment has been shown to decrease inflammatory cytokines and chemokine expression by inhibiting p38, ERK1/2, and NF-κB activation and to arrest VSMCs in the S phase of the cell cycle by activation of heme oxygenase 1 (HO-1).⁹² Another study showed that PF decreased VSMC viability and blocked G₀/G₁ cell cycle progression, which was associated with reduced expression of cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 4, and CDK2 as well as upregulation of p21 by blocking phosphorylation of p65 and IκBα in a concentration-dependent manner. Unexpectedly, PF was shown to upregulate the expression of caspases resulting in apoptosis of VSMCs.³⁶ This observation may have relevance for the treatment of both atherosclerosis and restenosis.

Finally, PF has been reported to prevent thrombosis. In one study using the spontaneously hypertensive rat (SHR), PF (5 mg/kg, i.g., every 2 days for 2 weeks) attenuated thrombosis by increasing expression of urokinase-type plasminogen activator (uPA), whereas expression of fibrinogen, D-dimer, and thromboxane B2 was attenuated.⁹³ Further evidence attributed the increased expression of uPA to activation of the p38 and JNK MAPK signaling pathways.

In summary, there is compelling preclinical data for the utility of PF either as a cardioprotective agent or in reducing myocardial damage from ischemia-reperfusion injury, heart failure from various causes, and diabetic cardiomyopathy. PF may as well protect against atherosclerosis, restenosis, and thrombosis.

6. Inflammation in Diabetes

Several animal studies show that PF reduces albuminuria and glomerular injury in diabetic nephropathy models. PF ameliorated ER stress-related inflammation, which correlates with diabetic nephropathy by downregulating stress-related factors (GRP78/Bip and XBP-1(s)) and by reducing pro-inflammatory molecules (IL-6, MCP-1, and ICAM-1). PF also decreased phosphorylation of IRE1α and NF-κB p65, indicating that its protective mechanisms might be related to inhibition of IRE1/NF-κB.⁹⁴

TLR signaling contributes to the pathogenesis of renal inflammation. In db/db mice, intraperitoneal delivery of PF (15, 30, or 60 mg/kg) for two weeks decreased urinary albumin excretion by 50% and inhibited macrophage infiltration and activation. PF prevented macrophage activation in the mouse RAW264.7 cell line by reducing advanced glycation end product (AGE)-induced TLR2/4 activation and inflammatory responses in type 2 diabetic nephropathy by inhibiting TLR2/4 signaling.⁹⁵ PF also slowed the progression of high glucose-induced diabetic nephropathy and reduced the number of M1 macrophages, levels of inflammatory cytokines, and iNOS expression by suppressing TLR2/MyD88-dependent pathway.⁹⁶

In a streptozotocin (STZ)-induced type 1 diabetes, intraperitoneal injection of PF for 12 weeks (25, 50, or 100 mg/kg/day) decreased macrophage infiltration and expression of inflammatory factors in the kidney. This was associated with inhibition of TLR2 and JAK2/STAT3 signaling.^{28, 97} By upregulating SOCS3 and inhibiting the TLR4/NF-κB pathway, PF suppressed high glucose-induced MMP-9 expression and inflammatory response of retinal microglia in STZ-induced diabetic retinopathy.²⁶ P38 MAPK signaling regulates the expression of NF-κB in numerous inflammatory diseases, and PF provided protection against acute necrotizing pancreatitis-induced renal injury by targeting this pathway.⁹⁸ PF was also shown to reduce AGE-induced mesangial cell injury by inhibiting the RAGE/mTOR/autophagy pathway resulting from downregulating LC3II/LC3I expression and reduction of autophagosomes.⁹⁹ Recent evidence also suggests that the renal protective effects of PF in type 1 diabetes are attributable to inhibition of TLR4-mediated iNOS activation and pro-inflammatory M1 signaling in macrophages.¹⁰⁰

Thus, based on these preclinical studies, PF would seem to have utility in treating diabetic nephropathy by reducing renal inflammation, fibrosis, and glomerular/tubular injury. These actions are mediated both directly at the level of kidney cells and indirectly by modulation of the immune response, specifically macrophage polarization.

Conclusions and Future Perspectives

The therapeutic utility of paeoniflorin has long been recognized for generations in traditional Chinese medicines that have harnessed its anti-inflammatory actions. Only recently has the molecular basis for its effectiveness been revealed. Pre-clinical studies have provided evidence showing that PF blocks specific intracellular signaling pathways, often downstream of TLR activation. In this context, the exact means by which signaling is inhibited awaits to be identified. Network pharmacology analysis indicates the potential interference of PF with IL-6 signaling and TLR cascades, while molecular docking analysis supports a direct interaction of PF with the IL-6 protein.¹⁰¹ However, more rigorous investigations into the molecular underpinnings of the actions of PF are required. Studies assessing the impact of chemical modifications further to improve the pharmacokinetics of PF and its therapeutic effects are warranted. Further investigations are needed to understand the biological impact of PF on macrophages and other immune cells. Finally, multicenter randomized controlled/clinical trials are required to establish fully the potential therapeutic efficacy of PF in cardiovascular and neurodegenerative diseases fully.