Review of Herbal Traditional Chinese Medicine for the Treatment of Diabetic Nephropathy

Diabetic nephropathy (DN) is the most serious chronic complications of diabetes; 20–40% of diabetic patients develop into end stage renal disease (ESRD). However, exact pathogenesis of DN is not fully clear and we have great difficulties in curing DN; poor treatment of DN led to high chances of mortality worldwide. A lot of western medicines such as ACEI and ARB have been demonstrated to protect renal function of DN but are not enough to delay or retard the progression of DN; therefore, exploring exact and feasible drug is current research hotspot in medicine. Traditional Chinese medicine (TCM) has been widely used to treat and control diabetes and its complications such as DN in a lot of scientific researches, which will give insights into the mechanism of DN, but they are not enough to reveal all the details. In this paper, we summarize the applications of herbal TCM preparations, single herbal TCM, and/or monomers from herbal TCM in the treatment of DN in the recent 10 years, depicting the renal protective effects and the corresponding mechanism, through which we shed light on the renal protective roles of TCM in DN with a particular focus on the molecular basis of the effect and provide a beneficial supplement to the drug therapy for DN.


Introduction
Diabetic nephropathy (DN) is a widely recognized microvascular complication of diabetes and almost the leading cause of end-stage kidney failure worldwide responsible for morbidity and mortality [1]. Clinical manifestations of DN include initial increase in glomerular filtration (GFR), proteinuria, increased creatinine levels, and eventually decreased GFR [2][3][4]. Major pathological changes of DN are virtually indistinguishable in both type 1 and type 2 diabetes, including mesangial expansion, extracellular matrix (ECM) accumulations, tubulointerstitial fibrosis, and glomerular sclerosis. Hyaline arteriolosclerosis is often prominent in the established DN pathological features caused by endothelial dysfunction and inflammation [5][6][7].
Multiple factors have been implicated in the pathogenesis of DN including hyperglycemia induced activation of advanced glycation end products (AGEs) and reactive oxygen species (ROS); JAK-STAT pathways and G protein signaling; activation of the PKC, renin-angiotensin aldosterone system (RAAS), transforming growth factor -Smad-mitogenactivated protein kinase (TGF--Smad-MAPK), deregulated expression of cyclin dependent kinases (CDK), and their inhibitors; and aberrant expression of ECM proteins, ECMdegrading enzymes, metalloproteinases, and their inhibitors [8]. The abovementioned factors can induce aberrant expression of profibrotic and proinflammatory cytokines, cell-cycle genes, and ECM genes involved in DN [9]. A large number of novel treatment options has arisen from experimental studies based on the pathogenic factors of DN, including intensive glycemic control, precise blood pressure control, optimal RAAS blockade with ACEI/ARB, life style modifications such as exercise and dietary restrictions, and a lot of novel agents [10], but the portion of ESRD due to DN still remains high in spite of the widespread application of numerous therapeutic approaches focusing on the management of factors mentioned above [11][12][13]. Therefore, interventions that could effectively delay the progression of DN are greatly required.
In China, traditional Chinese medicine (TCM) has been widely used in the treatment of diabetes and its complications 2 Journal of Diabetes Research for a long time [14]; TCM has lots of advantages over the conventional medical approaches in the prevention of diabetic complications because of less toxicity and/or side effects [15][16][17]. In this review, we will explore the advance of herbal TCM treatment on DN in recent 10 years, based on the experimental and clinical studies to note the scientific basis for the therapeutic effects of TCM on DN.

Applications of TCM in DN
Plants have been widely used for medical purposes long before recorded history [18]. In China, TCM emerged and influenced the surrounding countries such as Japan and South Korea; increasing popularity of TCM caused great interests in laboratory and clinical investigations in lots of diseases on its efficiency and action mechanism. TCM manifests as herbal medicine, acupuncture, moxibustion, massage, dietary therapy, and physical exercise including shadow boxing and Qigong, and herbal remedies are the focus of TCM in mainland China [19] and acupuncture is prevalent in the United States [18]. Under the urgent need for the treatment of DN, we focus on the update of the efficient herbal TCM preparations, single herbal TCM, and/or monomers from herbal TCM in DN related clinical and experimental trials, through which we explore the effective herbal TCM for DN and clearly put forward underlying mechanism in the treatment of DN.

TCM Preparations in DN.
TCM preparations are applied as decoction, pill, and capsule in the treatment of DN. We will introduce the TCM preparations in alphabetical order about components of TCM preparations, therapeutic effects in clinical or experimental studies, and relevant mechanism. All the mentioned TCM preparations in this review are listed in Table 1. (CHYS). Chaihuang Yishen granule (CHYS, also called Qilong-Lishui granule) is composed of radix astragali, Dioscorea nipponica, radix bupleuri, Angelica sinensis, Pyrrosia petiolosa, Polyporus umbellatus, and Hirudo nipponica. A recent study in STZ plus uninephrectomized induced rats showed that CHYS could be a therapeutic agent for DN by blocking TGF-/Smad3-mediated renal fibrosis [20].

Compound Rhizoma Coptidis Capsule (CRCC).
Compound rhizoma coptidis capsule (CRCC) is composed of rhizoma coptidis, Kudzu root, dwarf lilyturf,and Loquat leaf. CRCC has been shown to protect renal function and slow down the progression of DN by the suppression of TGF-1 and type IV collagen expression in STZ induced diabetic rats [21].

Compound Shenhua Tablet (CST). Compound Shenhua
Tablet (CST), is composed of radix astragali, fructus ligustri lucidi, rhizoma zedoaria, and honeysuckle. CST treatment in STZ induced diabetic rats showed that urine mAlb, Scr, BUN, Glu, TG, and TC were significantly lower than the diabetic model group [22]. Tang (DBT). Danggui buxue tang (DBT), a preparation including radix astragaliandradix Angelica sinensis, has been shown to partially attenuate the increases in blood glucose, TG, and CHO, and DBT was supposed to retard DN progression by suppressing TGF-1 expression in STZ induced diabetic rats [23]. In the HG stimulated glomerular mesangial cells, DBT could inhibit cell proliferation and expression of LN, FN, and collagen IV indicating the renoprotective effect of DBT on DN at the early stages [24].

Fufang Xue Shuan Tong (FXST). Fufang Xue Shuan
Tong (FXST) capsule is composed of radix notoginseng, Salvia miltiorrhiza, XuanShen, and radix astragali and has been used to treat DN for many years. High dose of FXST treatment could prevent glomerular hypertrophy and mesangial matrix expansion through regulation of oxidative stress including increasing SOD activities and decreasing MDA levels in the kidney of HFD-fed plus STZ induced rats [26].

Hachimijiogan (HJG).
A most popular herbal medicine in Japanese Kampo, Hachimijiogan (HJG, Ba Wei Di Huang Wan in Chinese), is extracted from a mixture of Rehmannia radix, corni fructus, Dioscorea rhizome, Hoelen, Alismatis rhizome, Moutan cortex, Cinnamomi cortex, and Aconiti tuber. In subtotal nephrectomy plus STZ induced rats, HJG could reduce blood glucose and urinary protein excretion levels and increase Ccr; furthermore, HJG could ameliorate oxidative stress and AGEs formation associated with DN and subsequently prevent the development of renal lesions including glomerular sclerosis, tubulointerstitial lesions, mesangial expansions, and atherosclerosis [27]. In spontaneous diabetic WBN/Kob rats with DN, HJG could prevent DN progression through several established biomarkers in plasma [28] and by reducing renal oxidative injury and expression of FN and TGF-1 proteins [29]. In OLETF rats, HJG could reduce TGF-1, FN, iNOS, and COX-2 expressions in kidney cortex, urinary protein excretion was decreased, Ccr levels were improved, and serum glycosylated protein and AGEs were reduced effectively; data mentioned above suggested that HJG has beneficial effect on the DN progression [30].

Hu-Lu-Ba-Wan (HLBW).
Hu-Lu-Ba-Wan (HLBW), composed of Trigonella foenum-graecum L. (TFG) and Psoralea corylifolia L. (PC), has been shown to improve hyperglycemia, hyperlipidemia, and proteinuria in the HFD-fed plus STZ induced rats and could play renoprotective effect in attenuating renal oxidative stress via PKC-/NADPH oxidative pathway [31].   [32]. LDP treatment in type 2 diabetic patients was found to be associated with the relief of DN [33]. Liuwei Dihuang (LW) decoction has also been proven to relieve early DN abnormalities mediated by suppression of renal entothelin-1-reactive oxidative species (ET-ROS) system and escalating MMPs activity [57], and LW without fructus corni could alleviate DN by combined suppression of ET-ROS axis with modulating hypoglycemic effects in STZ induced diabetic rats [58]. SKW was reported to protect renal function by increasing NO production and decreasing TGF-1 excretion in the mesangial cells from diabetic rats [38]; in diabetic rats SKW could reduce FN expression in kidney [59] while in rat mesangial cells SKW has been shown to suppress FN secretion via TGF-1 signal way [60]. Another study showed that in STZ induced diabetic rats SKW could protect renal function and alleviate the functional and structural damage of podocytes possibly by reducing desmin and increasing podocin expression [61], and SKW could offer renal protection against DN by reducing Ang II levels in the plasma and kidney tissues and inhibiting renal AT(1)R expressions [39]. All the data supply precise mechanism of SKW treating DN.

Supplementing Qi and Activating Blood Circulation
(SQABC). Supplementing Qi and activating blood circulation (SQABC) is composed of radix astragali and Salvia miltiorrhiza and has been shown to reduce 24 h urinary protein excretion and improve tubular reabsorption function by enhancing renal tissue activity of antioxidant and upregulating megalin expression in tubular epithelial cells in STZ induced diabetic rats [40]. Another in vitro study showed that supplementing Qi and activating blood circulation could protect HG injured NRK-52E cells and improve protein uptake by increasing megalin expression [41].  [49]. In the subsequent mechanism study, XKG was proved to exert renal protective effect in DN through downregulating TGF-1 expression in rat mesangial cells [50].

Xiexin Decoction (XXD).
Xiexin decoction (XXD) is composed of three crude drugs including radix et rhizoma rhei, rhizoma coptidis, and radix Scutellaria and has been used for the treatment of DM for at least 1700 years. One study in HFD-fed plus STZ induced rats showed that XXD could attenuate albuminuria and renal pathological changes, reduce AGEs, inhibit RAGE and inflammation factors expression, suppress NF-B, and downregulate renal TGF-1. All these data suggested that renal protective potential of XXD was involved in inhibition of inflammation through downregulating NF-B pathway, reducing renal AGEs and RAGE in diabetic rats [51]. A recent study of XXD components in db/db mice showed that multicomponent herbal therapeutic formulations could be a useful approach for the treatment of DN through reducing the expression of NF-B and TGF-1 [52].

Xianzhen Tablet (XZT).
Xianzhen tablet (XZT, a Chinese patent compound recipe), is composed of astragali radix, radix Rehmannia, fructus ligustri lucidi, Scutellaria baicalensis Georgi, rhizoma coptidis, dodder weed, fairy spleen, and Salvia miltiorrhiza. XZT was reported to decrease blood glucose and HbA1c in diabetic rats, improve renal function, ameliorate proteinuria, and reduce glomerular extracellular matrix expansion and thickness of basement membrane, which was mediated by the inhibition of AGEs accumulation and RAGE mRNA levels in the kidney cortex of STZ induced diabetic rats [53].

Monomers/Single TCM in DN.
With the development of modernization of TCM preparations and applications in the treatment of DN, pharmacological complexity is difficult to be distinguished for the precise underlying mechanism, and, to avoid the toxicity and side effects, there is an increasing interest of single herbal TCM and/or monomers from herbal TCM in the treatment of DN, and they are more appropriate than TCM preparations to clarify the precise action mechanism on DN. All the single herbal TCM and monomers are listed in Table 2.

Astragalus/Radix Astragali. Astragalus (Huang Qi in
Chinese), also named as radix astragali, is a TCM from Mongolian milkvetch or membranaceus milkvetch. A metaanalysis comprising 25 studies showed that Astragalus injection had more therapeutic effect in DN patients such as decreasing BUN, Scr, and urine protein and improving Ccr and serum albumin level [63], and rebalancing TGF-/Smad signaling could be a potential mechanism to prevent DN in KK-Ay mice [64]. Astragalus may protect diabetic rats kidney mediated by downregulation of Tie-2 [110], and radix astragali was reported to upregulate c-met expression in human kidney fibroblasts to delay the progression of DN [65]. Two major isoflavonoids in radix astragali, calycosin and calycosin-7-O-beta-D-glucoside, could inhibit HG induced mesangial cell early proliferation and AGEs-mediated cell apoptosis, suggesting these two isoflavonoids have therapeutic potential to prevent the progression of DN [111]. A recent review showed that total polysaccharides, flavonoids fractions, saponins, and several isolated compounds have antidiabetic potentials, which throw light upon further investigations that should be conducted on the treatment of DN and relevant underlying mechanism [112]. Astragaloside IV (ASI) in radix astragali is considered to be an active constituents; ASI could inhibit human tubular epithelial cells apoptosis and reduce TGF-1 expression, suggesting a new   Inhibiting P-selectin [109] treatment for DN probably mediated by the inhibition of p38 MAPK pathway activation and HGF overproduction [113].

Berberine (BBR). Berberine (BBR), an effective compound of herbal TCM, includes Coptis chinensis, Hydrastis
Canadensis, Berberis aristata, Berberis aquifolium, and Arcangelisia flava. BBR treatment could restore renal functional parameters, improve glucose and lipid metabolism disorders, suppress alterations of histological and ultrastructural changes in kidney, and increase cAMP levels in HFD-fed plus STZ induced diabetic rats, and the renal protective effect is exerted by modulating the G protein-coupled receptor kinases (GRKs) in G protein-AC-cAMP signaling pathway [66]. A previous study showed that BBR-containing TCM could increase glucose uptake and lipid oxidation with insulin sensitivity in Zucker diabetic fatty rats [16].

CLL/Curcumin. Curcuma longa L. (CLL) has been
widely used to prevent diabetic vascular complications in recent years. Curcumin and demethoxycurcumin are isolated from CLL and have been shown to potentially protect DN by reducing AGE-induced oxidative stress and restoring AGEinduced mesangial cell apoptosis [68]. In the treatment of DN in db/db mice, curcumin has been shown to decrease albuminuria and attenuate glomerular sclerosis by inhibiting phosphorylation of STAT3 and degradation of I B [67]. A systemic review and meta-analysis of fourteen randomized controlled trials suggested that curcumin has protective potentials on the kidneys of diabetic rats/mice [114].

Dracorhodin Perchlorate (DP).
Dracorhodin perchlorate (DP), one of the main compositions of Dragon's blood, has been shown to prevent and retard renal fibrosis of DN partially through inhibiting SGK1 and FN expression in human mesangial cells [70].

EGB. Ginkgo biloba extract (EGB)
, taken from the leaves of Ginkgo biloba, is a mixture containing flavonoid glycosides and has been proven to ameliorate hemodynamics, suppress PAF and ACE activities, scavenge ROS, relax vascular smooth muscles, and suppress AGEs expression. In a previous study on DN patients, EGB treatment has been shown to decrease urinary mALB, 1-MG, IgG, TF, RBP, and NAG in DN patients compared with control group, which suggested that EGB has renoprotective effect on the early DN [71]. The subsequent mechanism study showed that EGB could suppress rat mesangial cells hypertrophy and ECM accumulation through decreasing Smad2/3 and TGF-1 and increasing Smad7 [73], while in DN patients EGB has been proven to retard early DN development through decreasing serum sICAM-1 and sVCAM-1 levels [72].

Flos Abelmoschus manihot. Flos Abelmoschus manihot
(Huangshukuihua in Chinese) has been widely used as the neuroprotective drug for cerebral ischemic reperfusion injury. Total flavone glycosides of flos A. manihot (TFA) contain 7 identified flavone glycosides. TFA pretreatment has been shown to prevent renal damage and podocyte apoptosis in STZ induced rats [76]. A meta-analysis of 27 randomized controlled trials showed that flos Abelmoschus manihot had significant effect on renal function in the treatment of DN deserving further investigation [115].

Genipin.
Genipin is a glycone derived from geniposide present in fruit of Gardenia jasminoides. Genipin has been proven to ameliorate body weight loss and urine albumin leakage, attenuate GBM thickness, and restore the podocyte expression of podocin and WT1 in diabetic mice; the protective effect of Genipin on DN is probably through suppressing the upregulation of mitochondrial UCP2 in STZ induced diabetic mice kidneys [77].

Houttuynia cordata Thunb. (HCT). Houttuynia cordata
Thunb. (HCT, Yu Xing Cao in Chinese), pungent in taste and cool in nature, has been reported to reduce urinary proteins in the patients with nephrotic syndrome; HCT has also been shown to protect diabetic kidney function through decreasing the expression of TGF-1 and increasing the expression of BMP-7 [78].

Icariin.
Icariin is a major constituent of flavonoid extracted from the plant herba epimedii and has been shown to relieve renal damage in STZ induced diabetic rats through inhibiting the expression of TGF-1 and collagen IV protein [79].
2.2.11. LAB. Lithospermate B (LAB), a tetramer of caffeic acid isolated from Salvia miltiorrhiza radix, was identified as antioxidant and PKC inhibitor in the renoprotective effects under diabetic conditions in vivo and in vitro [80]. In the STZ induced diabetic rats, delayed LAB treatment could inhibit renal MDA, microalbuminuria, mesangial expansion, and glomerular hypertrophy, and in mesangial cells LAB could inhibit HG and H 2 O 2 induced TGF-1 and FN secretion, HG induced intracellular PKC activation, and ROS generation, which suggested that LAB could significantly suppress the progression of diabetic renal injury. A recent study showed that LAB could prevent diabetic atherosclerosis by induction of the Nrf2-ARE-NQO1 pathway to inhibit VSMCs proliferation and migration and vascular damage [81]. All these findings suggested that LAB could be a new therapeutic agent in the treatment of DN. In the subsequent study, Salvia miltiorrhiza could protect STZ induced diabetic rats by inhibiting the overexpression of TGF-1, CTGF, PAI-1, and FN in renal cortex. has been shown to protect STZ induced diabetic kidney function via decreasing the activation of ERK1/2 through the involvement of PKC in mesangial cells [82].
2.2.14. Ligustrazine. Ligustrazine, a bioactive component of Chuangxiong, has been widely used in the treatment of vascular diseases such as myocardial and cerebral infarction in China. A meta-analysis of 25 studies showed that Ligustrazine has therapeutic effect to improve renal function and reduce urine protein excretion in DN patients [84]. Further studies should be conducted to reveal the underlying mechanism for the treatment on DN.

MC.
Moutan cortex (MC), the root bark of Paeonia suffruticosa, has been shown to have the protective effect against atherosclerosis and inflammation and inhibitory effect on the production of ROS. MC was reported to increase activity of SOD, GSH-PX, and CAT and reduce MDA in vitro or in vivo; furthermore, MC could decrease blood glucose, Scr, and urine protein in HFD-fed plus STZ induced diabetic rats, which suggested that MC has renal protective effect in AGEs-induced mesangial cell dysfunction through attenuating oxidative stress pathway [85], while, in AGEs-induced rat mesangial cells, MC could inhibit FN and collagen IV expression in matrix [86]. Apart from the abovementioned evidence of renal protective effect on DN, MC could ameliorate activity on the inflammation via target of RAGE in vitro or in vivo [87].

Morroniside.
Corni fructus, a constituent of HJG, used as a traditional medicine in China and Japan, has been shown to be superior to aminoguanidine treatment in suppressing hyperglycemia, proteinuria, renal AGE formation, and TGF-1 expression in STZ induced diabetic rats [116]. Morroniside, isolated from corni fructus, could exhibit protective effects against STZ induced renal damage by inhibiting hyperglycemia and oxidative stress [88]. Another study showed that components of corni fructus could play protective effect on early stage of DN in type 2 diabetic rats mediated by the regulation of podocytes. Loganin from corni fructus and its derivatives could inhibit the expression of FN and IL-6 in the HG stimulated mesangial cells, which supported the traditional use of corni fructus in DN and relevant kidney diseases [117].

Panax Notoginoside (PNS). Panax notoginoside (PNS)
is extracted from radix notoginseng and has been shown to protect kidney in type 1 diabetic rats at early stage through inhibiting the expression of VEGF protein and enhancing BMP-7 expression in the kidney [89]. Another report showed that the protective effect of PNS in kidney was mediated by inhibiting TGF-1 expression and enhancing the expression of Smad7 [90]. Ginsenoside Rg1, an active ingredient isolated from PNS, has been shown to improve the renal pathological changes in STZ induced diabetic rats through reducing TGF-1 expression and inflammatory reaction factors including CRP and TNF- [118]. Ginsenoside Rg1 also could effectively relieve aldosterone-induced oxidative stress through which it indirectly inhibits aldosterone-induced podocyte autophagy [119].  [101]. Another study showed that SM could ameliorate TGF-1 levels in serum and kidney and reduce the levels of collagen IV ED-1 and RAGE in the diabetic kidney [102]. Danshen injection, the aqueous extracts of SM, could protect diabetic rats associated with preservation of tubular function and structure from hyperglycemia induced oxidative stress, advanced glycation stress, and megalin expression deletion [103].

TGP.
Total glucosides of paeony (TGP), extracted from the root of Paeonia lactiflora Pall., have been shown to have the therapeutic effect in the experimental DN. TGP treatment in the STZ induced diabetic rats could prevent diabetic renal damage against oxidative stress through decreasing upregulated p-p38 MAPK and NF-B P65 expressions [104]. And, in the HFD-fed plus STZ induced rats, TGP could improve kidney damage and delay the development of DN by inhibiting Wnt/beta-catenin signaling pathway [105].

TMP. Tetramethylpyrazine (TMP) is isolated from
Ligusticum chuanxiong and has been used in the treatment of stroke and cardiovascular diseases. TMP was reported to reduce diabetic kidney damage partially by downregulating the expression of VEGF in the kidney [106].

2.2.29.
Triptolide/GTW/TwHF. Triptolide, active diterpene purified from Tripterygium wilfordii Hook. F. (TwHF), has been reported to have anti-inflammatory, antioxidative, immunosuppressive, and podocyte-protective effects. A recent study showed that triptolide could attenuate albuminuria in db/db diabetic mice accompanied with alleviated glomerular hypertrophy and podocyte injury, while inflammation and dyslipidemia were also attenuated [107]. Triptolide is one of the major active components of multiglycoside of TwHF (GTW), and GTW has been applied extensively for the treatment of CKD in China as an anti-inflammatory agent. GTW could prevent glomerular lesion in STZ induced diabetic model through decreasing urine albumin and ameliorating glomerular sclerosis [123]. A recent study showed that TwHF could prevent podocyte injury of DN patients, which may be partly mediated by downregulating the expression of OPN, CTGF, and TGF-1 [108].

Volatile Oil of Magnolia biondii Pamp. (VOMBP).
Volatile oil of Magnolia biondii Pamp. (VOMBP), extracted from herbal TCM Magnolia biondii Pamp., has been reported to protect the kidney in STZ induced diabetic rats by inhibiting the expression of P-selectin in serum and renal tissue [109].

TCMs Combined Therapy with Western Medicines in DN.
Apart from the TCM preparations and single TCM applications in DN, TCMs combined with western medicines have been indicated. Mostly used western medicines were ACEI/ARBs, and combination styles included Tangshenling (TSL) with telmisartan [124] in diabetic patients or TSL with benazepril in STZ induced rats [125], triptolide with benazepril in DN patients [126], Bailing Capsule (BC) and benazepril in DN patients [127], and safflower yellow powder injection with benazepril in DN patients [128].
Another report is about Tangshenqing (TSQ) combined with alprostadil in the treatment of DN patients [129]. All data suggested that effects of TCMs combined therapy with western medicines were superior to western medicines treatment alone.

Conclusions and Perspectives
Although there are almost no side effects mentioned in numerous scientific reports, a lot of scientific researches indicate that herbal TCM preparations have renal protective effects on DN according to respective factors, complexity, and variability of TCM preparations still presenting challenges for clinicians seeking scientific evidence to support TCM application in drug discovery. In order to avoid the toxicity and side effects of TCM formulas, there is increasing interest in studying single herbal TCM especially monomers from single herbal TCM on DN. In this review, we found that monomers such as Berberine, curcumin, Ginsenoside Rg1, Puerain, Rhein, and Ferulic acid have specific protective effect on DN. To translate the therapeutic potentials for DN into reality, placebo-controlled and randomized controlled clinical trials of single herbal TCM and/or monomers from herbal TCM are essential in the future, and prompt metaanalysis is an effective alternative.