Application of berberine in the treatment of nephropathy: A review

Xiao-Jiang Wang, Li-Hua Wang

Shanxi Medical University, Department of Nephrology, Second Hospital of Shanxi Medical University, Shanxi Taiyuan, China

Keywords:Berberine Ischemia reperfusion injury Diabetic kidney disease Atherosclerosis of kidney

ABSTRACT Berberine is an alkaloid extracted from traditional Chinese medicine, which has many biological effects, such as antioxidation, anti-inflammation, anti-tumor, anti-fibrosis,hypoglycemic and hypolipidemic effects. In recent years, BBR has been proved to protect kidney by alleviating various pathological changes. BBR can improve renal insufficiency and renal inflammation. In addition, BBR can inhibit renal tubular epithelial-mesenchymal transdifferentiation, glomerular mesangial cell proliferation and ECM accumulation, and alleviate renal interstitial fibrosis. BBR can play a role in protecting kidney for many kidney diseases such as renal ischemia-reperfusion injury, diabetic kidney disease and renal atherosclerosis, and is a potential drug for delaying the progress of kidney diseases.

1. Introduction

Berberine (BBR) is an isoquinoline alkaloid with various pharmacological activities isolated from Coptis chinensis and Phellodendron amurense[1]. It has antibacterial, hypoglycemic,cholesterol-lowering, anti-tumor and anti-inflammatory activities,and can be used to treat various diseases, such as type 2 diabetes,hyperlipidemia, heart disease, cancer and inflammation[2～7]. Recent studies have shown that BBR has potential clinical application value as a drug for treating nephropathy and its complications. The renal protective function of BBR is multi-target, and its mechanism is complex. This article aims to review the characteristics of BBR in treating kidney diseases and further clarify its possible molecular mechanism.

1.Berberine and ischemical reperfusion injury

Ischemical reperfusion injury (IRI) is a complicated pathological process involving cell necrosis and apoptosis[8]. Excessive reactive oxygen species (ROS) produced by IRI injured tissues of kidney can cause oxidative stress[9]. malondialdehyde (MDA) and superoxide dismutase (SOD) are sensitive indicators of oxidative stress [10],MDA is the final product of lipid peroxidation [11], and SOD can eliminate lipid peroxidation of tissues and cells and protect cells from injury[12]. Oxidative stress stimulates the activation of mitochondrial stress and endoplasmic reticulum stress pathway. In the process of mitochondrial stress, the expression levels of Bax and Bcl-2 change, and the increase of Bax/Bcl-2 ratio will change the permeability of mitochondrial membrane, resulting in the release of cytochrome C from mitochondria, the activation of caspase-3, the downstream effector of apoptosis, leading to apoptosis[13]. Similarly,oxidative stress also activates endoplasmic reticulum stress pathway.Under pathological conditions, molecular chaperones that induce endoplasmic reticulum localization are activated, including glucose regulated protein 78 (GRP78) and apoptosis-promoting transcription factor C/EBP homologous protein 12(CHOP). With the activation of these proteins, apoptosis is caused [14].

Zheng et al.[15] established IRI model in rats, and found that after berberine treatment, the expression levels of Scr and BUN decreased, Bax protein decreased and Bcl-2 protein increased.Overexpression of Bax could promote apoptosis, inhibition of Bax expression could inhibit apoptosis, and Bcl-2 could combine with Bax to form heterodimer, thus reducing Bax expression and inhibiting apoptosis. The results indicated that berberine can effectively improve the renal function of rats with renal ischemiareperfusion injury by inhibiting the expression of Bax and promoting the expression of Bcl-2. Xie et al.[16] found that serum Scr and BUN levels of IRI injured rats treated with berberine were significantly decreased, and ROS, MDA and Caspase-3 were significantly decreased compared with those of control group,which indicated that BBR protected IRI of kidney through oxidative stress and mitochondrial stress degradation. Yu et al.[17]found in the study of hypoxia/reoxygenation model of human proximal renal tubular cell line HK-2 that MDA level decreased and SOD activity increased, Bax/Bcl-2 ratio and cytochrome C decreased, and GRP78 and CHOP expression decreased in berberine treatment group, which indicated that BBR had protective effect on hypoxia/reoxygenationinduced apoptosis of human proximal renal tubular cells, and its mechanism was related to inhibition of mitochondrial stress and endoplasmic reticulum stress pathway.

To sum up, BBR can protect kidney and reduce IRI injury by antioxidation and inhibiting endoplasmic reticulum and mitochondrial stress.

2. Berberine and diabetic kidney disease

Diabetic kidney disease (DKD) is one of the main causes of endstage renal disease. It is characterized by glomerular mesangial cell proliferation, excessive accumulation of extracellular matrix (ECM),early glomerular basement membrane expansion and thickening, late glomerulosclerosis and renal interstitial fibrosis, and finally leads to the loss of renal function[18]. BBR can inhibit the accumulation of extracellular matrix in various ways, thus inhibiting mesangial thickening, glomerulosclerosis and renal interstitial fibrosis, and delaying the process of kidney injury in DKD.

Oxidative stress is involved in the kidney injury of DKD, which increases the secretion of angiotensin ⅱ, compresses the glomerulus,increases the glomerular filtration rate, forms proteinuria and leads to the thickening of glomerular basement membrane, which accelerates the progress of DKD. On the other hand, oxidative stress activates intracellular signaling pathways, such as JNK and PKC, and activates transcription factors, such as nuclear transcription factor-κ B (NF-κ B) AP- 1(activator protein 1 (AP- 1), which accelerates the deposition of ECM and reduces the degradation of extracellular matrix, leading to glomerulosclerosis and renal fibrosis. Furthermore,the sustained oxidative stress in kidney caused by hyperglycemia leads to damage of insulin receptor, insulin resistance, activation of p38 mitogen-activated protein kinases (MAPK) and extracellular signal-regulated kinase (extracellular signal-regulated kinase). ERK)signal pathway promotes the expression of transforming growth factor-beta (TGF- β), fibronectin and collagen, and leads to ECM deposition, resulting in glomerulosclerosis and tubulointerstitial fibrosis[19]. Therefore, inhibiting oxidative stress can delay the process of kidney injury in DKD.

Lipid metabolism disorder and mitochondrial bioenergy disorder can cause oxidative stress damage and interfere with the energy homeostasis of kidney, resulting in podocyte injury and glomerulosclerosis. Excessive lipid accumulation may lead to mitochondrial dysfunction and apoptosis in kidney diseases.Peroxisome proliferator-activated receptor (PPAR)γ coactivator-1α(PGC-1α) is considered as a key upstream transcriptional regulator of mitochondrial function and a key regulator of mitochondrial homeostasis. Overexpression of PGC-1α gene or stimulation of its activity by drugs can increase mitochondrial gene expression and inhibit kidney fibrosis and podocyte injury. Qin et al.[20] conducted experiments on DKD(db/db mice) model and cultured podocytes, and proved that BBR can up-regulate PGC-1α gene expression, regulate mitochondrial energy homeostasis, reduce the accumulation of extracellular matrix, alleviate glomerulosclerosis and improve the clinical symptoms of DKD.

AMPK signal pathway is a signal transduction pathway that regulates the energy metabolism of cells by controlling the production and consumption of ATP in cells. AMPK signal pathway can be activated rapidly and promote the supply of ATP in cells when the cells are damaged by low glucose, hypoxia and ischemia.Yue et al.[21] established a diabetic nephropathy rat model through high-sugar and high-fat diet combined with streptozotocin, which proved that BBR can reduce serum BUN and SCr levels, increase SOD activity in kidney tissue, reduce MDA level in kidney tissue,and increase AMPKmRNA, AMPK and p-AMPK levels in diabetic rats. Therefore, BBR can improve renal histopathological progress and apoptosis in diabetic nephropathy by activating AMPK signaling pathway.

Nuclear factor E2-related factor 2 (Nrf2) is one of the important cellular defense factors against antioxidant stress, which can neutralize ROS, thus maintaining the steady state of cell redox[22].Under normal conditions, Nrf2 exists in cytoplasm. when exposed to oxidative stress, Nrf2 is ubiquitinated and transferred to the nucleus,and then activates the transcription of antioxidant genes, such as NADPH quinone oxidoreductase -1(NQO-1) and heme oxygenase-1(HO-1), and induces the production of anti-inflammatory, antifibrosis and anti-apoptosis metabolites[23,24]. Zhang et al.[25] induced NRK-52E cells in vitro by STZ-induced diabetic mice and HG,proving that BBR can eliminate oxidative stress induced by STZ and HG, significantly increase the expression of Nrf2, increase the expression of NQO-1 and HO-1, and alleviate the process of renal interstitial fibrosis. Therefore, BBR can inhibit tubulointerstitial fibrosis of DKD by inhibiting oxidative stress mediated by Nrf2 signaling pathway.

Experimental studies show that chronic hypoxia is involved in the occurrence and development of DKD, and chronic renal hypoxia is the trigger factor for the release of various cytokines and growth factors from renal tubular epithelial cells, which may lead to phenotypic changes and apoptosis[26]. Studies have shown that-1α(Hypoxia inducible factor-1α (HIF-1α) plays an important regulatory role in hypoxia-induced apoptosis[27]. In kidney, HIF-1α is expressed in renal tubular and glomerular epithelial cells.Under hypoxia, HIF-1α is trans-activated and transferred to the nucleus to cope with hypoxia, and plays a key role in DKD kidney injury[28]. Studies have shown that phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) signaling pathway plays an important role in the regulation of HIF-1α expression[27]. Akt, as a key regulator of PI3K/Akt pathway, can induce the transcription activity of HIF-1α, lead to the shift of HIF-1α to nucleus and trigger the survival signal[28, 29].Zhang et al.[26] established the model of rat renal tubular epithelium (NRK-52E) and human renal proximal tubular cell (HK-2) induced by hypoxia/high glucose. It was proved that HIF-1α was transferred from cytoplasm to nucleus induced by hypoxia/high glucose. BBR treatment significantly enhanced HIF-1α nuclear transfer induced by hypoxia/high glucose, and activated the expression of HIF-1α and PI3K,Protect renal tubular epithelial cells from apoptosis.

The earliest detectable change in the pathogenesis of DKD is glomerular mesangial thickening, which is caused by excessive accumulation of ECM protein. In this process, TGF-β and α-SMA play an important role in ECM. TGF-β is involved in many biological processes, including cell proliferation, differentiation,apoptosis, autophagy and ECM production. Studies have shown that TGF-β levels are up-regulated in injured kidneys[30], and down-regulation of TGF-β signaling pathway may alleviate renal fibrosis[31]. Li et al.[32] proved that BBR treatment reduced the expression of TGF-β and α-SMA and improved the renal fibrosis of DKD by streptozotocin-induced DKD rats.

ECM accumulation is one of the important pathological features of diabetic renal fibrosis, and fibronectin (FN) is an important component of extracellular matrix. Previous experiments in vivo and in vitro have shown that sphingosine kinase 1/1- phosphate (SphK1/S1P) signaling pathway is activated in kidney and mesangial cells,while FN production increases, and S1P2 receptor signaling pathway participates in S1P-induced mesangial cell proliferation[33～35].Recent studies have shown that BBR can improve renal function by reducing the expression and activity of SphK1 and S1P level in diabetic mice induced by alloxan[33], and can also reduce FN expression by inhibiting S1P2 receptor in mesangial cells under diabetes[34]. S1P2 receptor is mainly involved in pathological damage, such as immunity and inflammation[36]. BBR can reverse DKD by inhibiting the activation of NF-κB inflammatory signaling pathway[37]. Zhu et al.[37] proved that BBR inhibited the activation of NF-κB, and found that PDTC, a specific inhibitor of NF-κB,significantly reduced the expression of S1P2 receptor mediated by high glucose, suggesting that the activation of NF-κB participated in the increase of S1P2 receptor mediated by high glucose. Similar to PDTC, BBR not only inhibited the nuclear translocation of NFκB, but also significantly decreased the protein expression of S1P2 receptor and FN, suggesting that BBR not only improved kidney injury through NF-κB pathway, but also had a close relationship with its inhibition of S1P2 receptor activation.

Hyperglycemia can increase the apoptosis and injury of podocytes.More and more evidences show that podocyte injury may aggravate the development of DKD by interfering with the formation of proteinuria. Podocyte and fissure membrane together constitute glomerular filtration barrier, which can prevent protein from seeping out of glomerular filtration barrier. Many studies have shown that once podocyte injury occurs, the normal structure of podoid process will be destroyed, and its function will be disordered, resulting in proteinuria, thus promoting the development of renal function injury and finally accelerating the DKD process. Ni et al.[38] used streptozotocin and high-sugar/high-fat diet to establish DKD rat model, which proved that BBR could inhibit PI3K/Akt signaling pathway to alleviate podocyte injury. Further studies on podocytes show that cell membrane protein Podoplanin(PDPN) plays an important role in maintaining the normal morphology and function of podocytes. HG can activate NF-κB signaling pathway in podocytes, thus down-regulating the expression level of podoplanin,resulting in increased apoptosis of podocytes. Yu et al.[39] proved that one of the mechanisms of BBR to improve DKD is to inhibit the activation of NF-κB signaling pathway, thereby restoring the expression of PDPN and reducing the apoptosis of foot cells induced by HG stimulation.

Renal interstitial fibrosis is the final process of DkD, and its main feature is tubular atrophy. Tubular epithelial-mesenchymal transition(EMT) is a relatively complex pathological process in the process of renal fibrosis. This pathological process involves a series of signal transduction pathways and a variety of cytokines. Notch pathway has been proved to mediate EMT in epithelial cells of DKD. snail plays an important role in regulating gene expression during cell differentiation, which is regulated by various signal pathways, the most important of which is Notch signal pathway. Notch pathway activates snail, inhibits the transcription of E-cadherin(E-Cad),down-regulates its expression, leads to the loss of adhesion of epithelial cells and promotes the occurrence of EMT. Yang et al.proved that BBR significantly reduced the mRNA expression of notch1 and snail1, suggesting that BBR down-regulated Notch1/Snail pathway at transcription level, thus inhibiting the activation of Notch1/Snail pathway, decreasing -SMA, increasing the expression of E-Cad and inhibiting renal fibrosis[40].

To sum up, BBR may inhibit renal interstitial fibrosis and delay the process of kidney injury in DKD in many ways. The pathways include degradation of oxidative stress, mitochondrial pathway,activation of AMPK signaling pathway, inhibition of Nrf2 signaling pathway, activation or inhibition of PI3K/Akt signaling pathway,inhibition of SphK1-S1P-S1P2 receptor signaling pathway,inhibition of NF-κB inflammatory signaling pathway, inhibition of TGF-β/Smad signaling pathway, inhibition of NF-κB signaling pathway and inhibition of Notch/snail pathway,and these pathways interact to inhibit the DKD fibrosis process.

3. Berberine and Atherosclerosis of kidney

Renal atherosclerosis is a chronic kidney injury caused by renal vascular diseases, which can eventually lead to end-stage renal disease (ESRD)[41]. Renal dysfunction may be the result of the interaction of atherosclerotic renal vascular stenosis with oxidative stress, inflammation and fibrosis.

When kidney is damaged by renal atherosclerosis, the main component of free radicals is superoxide, which leads to the decrease of SOD level. This highlights that oxidative stress may be the cause of kidney injury in these rats. BBR can improve blood pressure,kidney structure and function and prevent oxidative kidney injury by reducing the production of free radicals and keeping the activities of SOD and CAT[42].

Proinflammatory cytokines involved in oxidative stress in kidney can activate NF-κB and increase the production of ROS and superoxide[43]. These ROS can also increase NF-κB activity, lead to further oxidative/nitroso injury, and accelerate kidney injury[44].Once NF-κB is activated, NF-κB heterodimer p65/p50 binds to the NF-κB binding site in the promoter region of the target gene,initiating transcription and protein expression, such as TGF-β,resulting in significant inflammatory reaction[45]. The activation of NF-κB depends on the activation of inhibitor of nuclear factor kappa b kinase beta subunit (IKKβ). the kinase activity of IKK2 takes two adjacent serine residues of IKB as the target, releasing and activating NF-κB, resulting in kidney injury[46].

Wan et al.[47] proved through experimental research that BBR can effectively inhibit the activity of NF-κB, reduce the expression of phosphorylated IKK2, p65/p50 and TGF-β, which indicates that BBR can inhibit the pro-inflammatory and pro-fibrotic reactions by inhibiting the activity of NF-κB signaling pathway, improve the redox state of kidney, reduce hypercholesterolemia, and improve the inflammation and tubulointerstitial injury in kidney.

4. Conclusion and prospect

To sum up, many ways are involved in the occurrence and development of kidney diseases, so it is of great significance to find safe and effective therapeutic drugs. In recent years, a large number of studies have shown that BBR has certain potential in the treatment of kidney diseases, and has pharmacological effects such as antioxidative stress, anti-inflammatory, hypoglycemic and lipid-lowering effects. However, the mechanism of BBR in the treatment of kidney diseases is very complex, and its specific molecular mechanism has not been studied in depth at present, and most of the experiments stay in animal experiments and in vitro cell experiments, lacking specific clinical research, so we need to further explore and clarify its specific molecular mechanism in the future. To provide experimental basis for the treatment of renal fibrosis with BBR, and to combine the pharmacological effects of BBR with the characteristics of various kidney diseases, to provide clinical ideas for the formulation of clinical application programs and promote the treatment and development of kidney diseases.