Herbal Medicine after Interventional Therapy in Cardiovascular Diseases: Efficacy, Mechanisms, and SafetyView this Special Issue
Research Article | Open Access
Danhong Promotes Angiogenesis in Diabetic Mice after Critical Limb Ischemia by Activation of CSE-H2S-VEGF Axis
The aim of this paper is to investigate effect and mechanism of Danhong injection (DH) on angiogenesis in the diabetic hind limb ischemia mouse model. Thirty diabetic hind limb ischemic model mice and ten normal mice, established by intraperitoneal (i.p.) injection of streptozotocin (STZ) or PBS and ligation/excision of femoral artery, and then twenty diabetic hind limb ischemic model mice of all were evenly randomized to saline (control, ) and DH i.p. injection (2 mL/kg weight for 7 days, ) groups. Limb perfusion recovery and femoral blood hydrogen sulfide (H2S) and vessel regeneration and lower limb vascular endothelial growth factor (VEGF)/cystathionine γ-lyase (CSE) expression were evaluated during intervention and after euthanasia, respectively. DH i.p. increased ischemic limb perfusion and promoted collateral circulation generation without decreasing blood glucose level. Increased local CSE-H2S-VEGF expression contributed to beneficial effects of DH injection. In conclusion, activation of local CSE-H2S-VEGF axis might participate in proangiogenesis effects of DH injection in diabetic hind limb ischemia model mice, suggesting a potential therapy for diabetic patients with critical limb ischemia.
Current standard of care for critical limb ischemia (CLI), annually affecting estimated 500 to 1000 per million people worldwide  and particularly diabetics, includes lifestyle modification, pharmacotherapy to reduce blood cholesterol, glucose, and hypertension, and revascularization by angioplasty or bypass surgery. However, revascularization is associated with high long-term restenosis rate, does not address underlying pathology, and is not an option for all patients , who often undergo major limb amputation with 30% second amputation and 25% death rates within one year  prompting continued search for clinical and cost-effective treatments. Among traditional Chinese medicine (TCM) drugs potentially useful for therapeutic angiogenesis, Danhong injection (DH), a Chinese Materia Medica standardized product extracted from Radix Salviae miltiorrhizae and Flos Carthamus tinctorius, , has been shown in animal and clinical studies to improve angina and decrease acute and chronic cardiovascular event occurrence by modulating angiogenesis, inflammation, immunity, and oxidative stress [5–10]. This study therefore examined proangiogenesis effects and underlying mechanisms of Danhong injection in the diabetic hind limb ischemia mouse model to gain insight for potential clinical use in diabetics with CLI.
2. Materials and Methods
2.1. Preparation of DH and Quality Control
According to the production protocol of DH injection provided by Shanxi Buchang Pharmaceutical Co. (Shanxi, China), powdered Radix et Rhizoma Salviae miltiorrhizae (750 g) is twice immersed in 7.5 L of 30% ethanol in order to maximally dissolve active ingredient, and then both of the immersions are extracted for 1 h at 50°C, after filtration, and mixed with Flos Carthamus (250 g). The mixture is then twice immersed in 2.5 L of water for 1 h at 35°C and vacuum evaporated to relative density of 1.10–1.20 (65°C). The solution is filtered and stored at 4°C for 24 h. Water is added to the solution of 1.0 L; sodium chloride and sodium hydroxide are added to achieve an isotonic solution with pH of 6-7 for injection, again filtered, and then sterilized and encapsulated into ampoules (10 mL per ampoule). DH was approved over 5 years ago by the Chinese Food and Drug Administration (CFDA) as Chinese herbal patented product for coronary heart disease patients and listed in the Chinese Pharmacopoeia (Heze Buchang Pharmaceutical Co., Ltd., drug approval number Z20026866).
DH contains two herbal medicinal components, Salvia miltiorrhiza BUNGE and Carthamus tinctorius L, authenticated and standardized based on marker compounds according to Chinese Pharmacopoeia 2005. DH dose variability was minimized by strict standardization of batches, species, origin, harvest time, medicinal components, and preparation methods, which was confirmed by high performance liquid chromatography (HPLC) according to established protocol .
2.2. Chemicals and Reagents
Purified rat anti-mouse CD31 monoclonal IgG2a antibody was purchased from BD Bioscience (San Diego, CA, USA). Rabbit anti-mouse vascular endothelial growth factor (VEGF) polyclonal antibody was from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Anticystathionine γ-lyase (CSE), beta-actin antibodies, and horseradish peroxidase-linked secondary antibodies were obtained from Abcam (San Francisco, CA, USA). Mouse VEGF ELISA kits were purchased from eBioscience (San Diego, CA, USA). Sodium sulfide standard was from Alfa Aesar (cat. number 65122, Ward Hill, MA, USA). Streptozotocin (STZ) and other chemicals frequently used in our laboratory were purchased from Sigma-Aldrich Co. (St Louis, MO, USA).
2.3. Diabetic Hind Limb Ischemia Model with BALB/c Mice
Study protocol (Figure 1) was approved by Second Military Medical University’s Animal Care and Use Committee. After intraperitoneal (i.p.) injection of STZ (150 mg/kg) in BALB/c mice, blood glucose levels were continuously monitored for 2 weeks with diabetes modeling success verified when two random blood glucose levels >16 mmol/L were confirmed. At 2 weeks, hind limb ischemia model was established by ligation and excision of left femoral artery, saphenous arteries, circumflex branch of external iliac artery, and muscular branches of femoral artery . Lower limb perfusion was assessed by laser Doppler perfusion imaging (LDPI) as described below. Immediately after femoral artery ligation, blood flow in the ischemic hind limb was equally reduced in both control and diabetic mice. Consistent with previous studies [13, 14], LDPI showed significantly attenuated perfusion recovery in diabetic compared to control mice on postoperative weeks 4 and 6 (Figures 2(a) and 2(b)), confirming successful STZ-based diabetes and hind limb ischemia modeling of nude mice.
2.4. In Vivo Assessment of Limb Function
Semiquantitative assessment of ischemic limb function was performed serially using the following scoring system: 6, full and fast walking; 5, normal but slow walking; 4, walking with only mild deficit; 3, supporting weight, probability of taking 1 or 2 steps; 2, frequent and vigorous movement, no weight bearing; 1, barely perceptible movement, no weight bearing; and 0, no movement [15, 16]. Two independent observers blinded to the study evaluated scores.
2.5. Laser Doppler Perfusion Imaging
Mice were anesthetized with intraperitoneal injection of ketamine (60 mg/kg) and xylazine (8 mg/kg). Serial, noninvasive assessment of ischemic limb microvascular perfusion was performed in triplicate and in a blinded manner using a LDPI system (PeriScan PIM 3, Perimed, Sweden) after placing mice on a homoeothermic heating pad maintained at 37°C. Using LDPI image processing software (v5.0), perfusion was quantified in regions, equal in area, encompassing the distal leg (entire foot) of both ischemic and contralateral nonischemic limbs. All perfusion data were expressed as a ratio of operated ischemic to nonoperated control limb perfusion, which could minimize data variation possibly secondary to ambient temperature changes.
2.6. HPLC-FLD Analysis of H2S in Femoral Artery Blood
Animals were anesthetized with sodium pentobarbital (40 mg/kg body weight intraperitoneal injection), and a 30 G insulin syringe was inserted into the femoral vein to draw blood for H2S analysis. H2S detection was performed in duplicate for each blood sample following a modified protocol from a previous study based on the fluorescence derivation between monobromobimane (MBB) and hydrogen sulfide (H2S) contained in plasma . Briefly, 30 μL plasma was collected after centrifuging and incubated with excess MBB in 100 mM Tris-HCl buffer (pH 9.5, 0.1 mM diethylenetriamine pentaacetic acid) for 30 min in 1% oxygen at room temperature to form a stable derivation, and then the fluorescent product sulfide-dibimane (SDB) was analyzed by RP-HPLC using a Dikma-C18 Leapsil column (2.7 μm × 4.6 mm × 100 mm) with gradient elution by 0.1% (v/v) trifluoroacetic acid in acetonitrile. Using the modified protocol with new HPLC column suitable for both HPLC and UPLC system, detection time could be decreased from 12 to 5 minutes without compromising sensitivity and specificity. Standard curve was established based on different concentrations of sodium sulfide solutions prepared in a strict-control hypoxic chamber by purging with nitrogen gas to 1% O2. Retention time of SDB was 3.3 min, and detection limit was 0.5 pM.
2.7. Angiographic Assessment of Collateral Circulation
Animals were anesthetized as described above; the hearts were rapidly excised and retrogradely perfused via abdominal aorta with heparin saline (0.1% heparin in 0.9% saline). Post-mortem angiography was performed using Omnipaque (Amersham), hand infused angiographic contrast at 0.5 mL/s for 20 seconds, and a high-definition digital X-ray system (MX-20, Faxitron, USA). Recorded images of the pelvis and both hind limbs were analyzed using Image J software (NIH) to calculate angiographic score of thigh-hip joint to knee area. Specifically, a grid was laid over an image of the arterial filling phase vasculature and number of collateral vessel intersections with the grid counted over a defined, bilaterally equal area. Angiographic score was expressed as ratio of numbers of collateral vessels within operated ischemic-to-contralateral leg.
2.8. Histological Assays
After euthanasia, thigh muscles were isolated from limbs and routinely fixed overnight in 4% buffered formalin and embedded in paraffin. Four-micrometer tissue sections were subjected to immune-peroxidase biotin-avidin reaction using the labeled streptavidin biotin method to determine CD31 and VEGF expression. Sections for immunohistochemical analysis were cut and mounted on 3-aminopropyltriethoxysilane-coated (Sigma) slides, allowed to dry overnight at 37°C to ensure optimal adhesion, dewaxed, rehydrated, and treated with 0.3% H2O2 in methanol for 10 min to block endogenous peroxidase. For antigen retrieval, sections were microwave-treated in 1 mmol/L EDTA at pH 8 for 10 min and then allowed to cool for 20 min. Endogenous biotin was saturated using a biotin blocking kit (Vector Laboratories). Sections were incubated at 37°C for 30 min with the following antibodies: purified rat anti-mouse CD31 (dilution 1 : 30; monoclonal IgG2a, BD Bioscience) and rabbit anti-mouse VEGF (dilution 1 : 100, polyclonal, Santa Cruz Biotechnology). Binding was visualized using biotinylated secondary antibody (1 h incubation) and streptavidin-biotin peroxidase complex developed with diaminobenzidine. Finally, slides were counterstained with hematoxylin. Capillary density and leukocyte infiltration expressed as number of CD31+ cells per square millimeter were measured by counting six random high-power (magnification ×200) fields for a minimum of 200 fibers from each ischemic and contralateral limb. The area was measured with Image J software. Two operators analyzed the results independently.
2.9. qPCR Assay of CSE-VEGF Axis
RNA was isolated from ischemia hind limbs using the RNeasy kit (Qiagen, Hilden, Germany). Total RNA was analyzed by Nanodrop (Thermo, USA). Reverse transcription was performed with PrimeScript 1st Strand cDNA Synthesis kit (Takara, Japan) and cDNA amplified by iQ SYBR Green Real-Time PCR Supermix (Bio-rad, USA) using primers for VEGF and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in an CFX Connect real-time PCR detection system from Bio-rad. All primers were obtained from Life Technology (USA). Data were analyzed based on relative expression method with the formula , where (sample) − (calibrator = average CT values of all samples within each group), with being CT of housekeeping gene (GAPDH) subtracted from of target gene.
2.10. Statistical Analysis
Data are presented as mean ± standard deviation and were compared using paired -test with GraphPad Prism 5.01 (La Jolla, CA, USA) and SPSS for Windows 7.0. was considered statistically significant.
3.1. Protective Effects of DH Injection on Blood Flow Recovery, Collateral Vessel Formation, and Limb Function in Hind Limb Ischemia Diabetic Mouse Model
Perfusion recovery was significantly improved in mice receiving intraperitoneal DH administration at 2 mL/kg weight for 7 days as compared to control receiving equal amount of phosphate buffered saline as scheduled (Figures 3(a) and 3(b)).
Formation of collateral vessels below ligation site was examined using X-ray to ascertain whether improvement in tissue perfusion originated from increased blood flow or collateral vessel formation. At 2 weeks after ischemia induction, significantly more bridging collaterals with some degree of distal filling and originating from the internal iliac artery were visible in the thighs of mice treated with DH, in contrast to no apparent collateral vessel in the same area of controls (Figures 3(a) and 3(c)). In assessment of ischemic hind limbs using anti-mouse CD31 immunohistochemical staining, capillary density was significantly higher in DH i.p. than control group (Figures 3(a) and 3(d)).
Survival analysis showed that after femoral artery ligation DH group mice recovered not only better but also faster than controls (Figure 4).
3.2. Activation of CSE-H2S-VEGF Axis in Association with DH Protective Effects
An antihyperglycemic effect of DH was excluded by lack of significant differences in weight (time 0: versus g, week 1: versus g, and week 2: versus g) and blood glucose levels (time 0: versus mmol/L, week 1: versus mmol/L, and week 2: versus mmol/L) between saline control and DH groups, respectively, during experimental period. CD31 levels in local muscular tissue increased after DH treatment, as did VEGF mRNA and protein levels compared with controls (Figures 5(a) and 5(b)). Several studies [18, 19] suggested a key role for muscular tissue H2S system in modulating VEGF expression after different stimuli, and DH was associated with increased venous H2S levels and CSE mRNA expression (Figures 5(c)–5(e)).
This study showed that the traditional Chinese medicine herbal DH preparation improves blood flow in association with collateral vessel formation and activation of the cystathionine γ-lyase- (CSE-) hydrogen sulfide- (H2S-) vascular endothelial growth factor (VEGF) axis in a diabetic hind limb ischemia mouse model.
Ischemic vascular diseases remain a leading cause of mortality and morbidity worldwide  despite significant advances in medical and surgical intervention. Restoration of blood flow to ischemic organs is vital to prevent tissue death after arterial occlusion, and current treatment modalities are only partially efficacious. Discovery of angiogenic growth factors opened up the possibility of therapeutic angiogenesis for acute and chronic ischemia. In preclinical studies, three main approaches have been tested to deliver angiogenic agents: protein, gene, and cell therapy. In protein therapy, recombinant proteins are used directly to induce therapeutic effects , which are only transient because of the very short half-life of exogenous proteins in target tissues . In contrast, gene therapy uses nonviral or viral vectors to carry a gene construct encoding a therapeutic protein into target tissues, where it is abundantly expressed ; however, this approach is hurdled by an inability to deliver genes efficiently and to obtain sustained expression. The premise of cell therapy in its present form is that transplanted cells by functioning as factories of multiple endogenous growth factors will induce vascular growth mainly in a paracrine manner rather than directly replacing damaged cells . However, at least at the clinical level, efficacy of cell therapies has not been very satisfactory owing to poor in vivo viability of transfused cells, possibly reflecting abnormal cell microenvironment in pathological conditions.
A large body of evidence has shown the above limitations to current and developing therapeutic strategies apply to ischemic diseases associated with diabetes. Traditional Chinese medicine (TCM), widely used for centuries for ischemic diseases, has been the subject of numerous research reports elucidating effective components and their underlying mechanisms [24–28]. Exploring the effects of TCM on improvement of vascular microenvironment and functional recovery has significant clinical implications. Based on results from the present study, DH not only improved angiogenesis but also promoted ischemic organs’ function recovery [29, 30], while our data are consistent with clinical experience and encourage clinical studies in the vast spectrum of diabetic patients. Association between local CSE-H2S-VEGF system and DH protective effects opens up the possibility that DH might act similar to H2S-donor drugs, which warrants further research.
DH treatment might have potential for use in other fields of medicine. However, proper assessment of therapeutic potential warrants further studies on mechanisms underlying DH protective effects such as the role of local tissue or bone marrow stem cells and in particular intracellular signaling pathways among others.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Feng Wu, Zhiqing He, and Ru Ding contributed equally to this work.
Great thanks are for the help from editors and reviewers during the revision. Chun Liang received Grants 91539118, 31171130, 30971101, 81501523, and 81270405, Zonggui Wu received Grants 81130065, 81072981, 81473445, and 2014ZX09301307-016, Feng Wu received NSF Grant 81503371, Ru Ding received Grant 81400336 and grant from NSF and 13ZR1413600 from Shanghai Municipal Natural Science Foundation, Haiming Cui received NSF Grant 81403258, Qixia Jiang received Grant NSF 81400275, Zhigang Huang received NSF Grant 8130311, and Zhiqing He received Grant 15401931500 from Shanghai Municipal Natural Science Foundation.
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