Modeling Principle

The Beagle Renal Hypertension Model adopts the classic surgical operation to construct a two-kidney one clip (2K1C) renal artery stenosis model. Based on the SCI standardized large-animal modeling system, it reproduces the complete pathological process of clinical renovascular hypertension. It accurately simulates a full set of pathological cascades induced by unilateral renal artery luminal stenosis, including insufficient perfusion of the affected kidney, glomerular ischemia and hypoxia, massive synthesis and secretion of renin, persistent hyperactivity of the RAAS system, systemic vasoconstriction, elevated peripheral resistance, progressive increase of systemic arterial pressure, and organic damage to cardiac and renal target organs such as left ventricular hypertrophy and renal interstitial fibrosis secondary to long-term high blood pressure. It remedies the experimental defects of rodent animals, which have obvious discrepancies with human renovascular hypertension in tiny kidney volume, anatomical structure of renal artery, regulatory mode of renal hemodynamics, rising process of blood pressure and time sequence of cardiac & renal target organ injury.

The renal anatomical configuration, renal artery branch course, glomerular microcirculation structure, renin secretion regulation mechanism of juxtaglomerular cells, response rule of RAAS system, post-injury renal fibrotic pathway and remodeling response of myocardium to long-term pressure load of adult Beagle dogs are highly homologous to human kidney and cardiovascular system. The unilateral renal artery is dissociated via a retroperitoneal approach, and a silver clip with fixed inner diameter is used to clamp the main renal artery to create controllable luminal stenosis, resulting in persistent hypoperfusion and ischemia of the ipsilateral kidney. Juxtaglomerular cells in ischemic kidneys compensatorily secrete abundant renin, which sequentially activates angiotensinogen to produce Ang Ⅱ. Ang Ⅱ strongly constricts systemic arterioles to raise peripheral vascular resistance, and stimulates aldosterone secretion to cause water and sodium retention, jointly driving pathological elevation of systolic and diastolic blood pressure. Under long-term hypertension, high-pressure blood flow impacts systemic vascular endothelium. Meanwhile, ischemic kidneys gradually develop tubular atrophy, renal interstitial inflammatory infiltration and collagen deposition, accompanied by compensatory myocardial hypertrophy and myocardial interstitial fibrosis in the heart, finally forming stable pathological phenotypes of renovascular hypertension combined with cardiac and renal target organ injuries. This model fully recapitulates the classic pathogenic cascade of human renal artery stenosis hypertension: mechanical stenosis of renal artery – renal ischemia – excessive activation of RAAS – vasoconstriction and water-sodium retention – sustained hypertension – organic injury of cardiac and renal target organs.

Beagle dogs possess thick renal artery lumen, the stenosis degree caused by silver clips can be accurately quantified and regulated, blood pressure rises gently with low individual dispersion, and there is no spontaneous hypertension or congenital renal lesions. Three pathological stages can be clearly distinguished: early stage of blood pressure elevation induced by renin release, middle stage of stable hypertension maintenance, and terminal stage of remodeling with cardiac and renal target organ damage. It serves as a standardized large-animal gold-standard model for translational researches including screening of new antihypertensive drugs, evaluation of renal protective preparations, intervention for hypertensive target organ damage and interventional therapy of renal vessels.

Modeling Success Criteria

In-vivo Blood Pressure and Gross Cardiac & Renal Morphological Phenotype

The blood pressure of Beagle dogs in the sham control group was maintained in the normal physiological range for a long time, bilateral kidneys were ruddy and soft in texture with normal heart size and uniform ventricular wall thickness. At Week 12 terminal point, the systolic blood pressure of animals in the model group increased by ≥40 mmHg compared with the sham group accompanied by remarkable elevation of diastolic blood pressure. Gross anatomical observation showed shrunk and pale kidneys on the stenotic side, compensatory hypertrophy of contralateral kidneys, obvious thickening of left ventricular wall and elevated heart weight index. The macroscopic phenotype of renal hypertension combined with cardiac and renal injuries was obvious with extremely significant statistical difference between groups, which could preliminarily confirm the successful construction of 2K1C renal hypertension model.

Quantitative Biochemical Gold-Standard Serum Indexes

The plasma levels of RENIN, Ang Ⅱ and ALD in the model group were extremely significantly higher than those in the sham group; slight elevation of serum Scr and BUN indicated impaired renal function; massive release of serum pro-inflammatory factors TNF-α and IL-6 was observed; the expression of TGF-β1 and type Ⅰ/Ⅲ collagen in renal and myocardial tissues was markedly upregulated, which fully conforms to the biochemical diagnostic characteristics of clinical renovascular hypertension: excessive activation of RAAS system, mild renal function damage, systemic low-grade chronic inflammation and abnormal collagen deposition & fibrosis in cardiac and renal tissues.

Cardiac and Renal Histopathological Characteristics

Sequential pathological injury changes of renal hypertension can be observed via combined staining of renal tissues with HE & Masson and myocardial tissues with WGA & Masson:

1. Pressure elevation stage at Week 4 after modeling: mild ischemic atrophy of glomeruli in stenotic kidneys, a small amount of inflammatory cell infiltration, no obvious cardiomyocyte hypertrophy and minimal collagen deposition;
2. Plateau stage at Week 8 after modeling: increased inflammatory cell infiltration in renal interstitium with initial deposition of a small amount of collagen fibers, compensatory hypertrophy of cardiomyocytes and slight collagen hyperplasia in myocardial interstitium;
3. Terminal injury stage at Week 12 after modeling: extensive atrophy of renal tubules in stenotic kidneys and large-area Masson blue-stained collagen fibrosis in renal interstitium, hypertrophic and deformed left ventricular cardiomyocytes accompanied by massive collagen deposition in myocardial interstitium to form fibrotic lesions, which perfectly recapitulates the progressive pathological changes of renal fibrosis and myocardial hypertrophic fibrosis induced by long-term renal-derived hypertension in human beings.

Gold-Standard Indexes of RAAS, Fibrosis and Inflammatory Pathways

Juxtaglomerular cells in ischemic kidneys of the model group continuously secreted high levels of renin with abnormal hyperactivity of circulating RAAS axis. The downstream TGF-β1/Smad fibrotic pathway was significantly activated to drive the activation and proliferation of fibroblasts as well as massive collagen synthesis in kidneys and myocardium. The continuously open NF-κB inflammatory pathway aggravated visceral inflammatory infiltration and fibrosis progression. Long-term high pressure load induced compensatory changes of myocardial contraction-related proteins. It accurately matches the complete pathological mechanism induced by mechanical renal artery stenosis: insufficient renal perfusion – RAAS hyperactivity – vasopressor and water-sodium retention – sustained hypertension – chronic fibrotic injury of heart and kidney, serving as the core academic basis for judging successful model formation.

Model Advantages

This model is a well-recognized exclusive large-animal gold-standard model for renovascular hypertension prepared by 2K1C surgical stenosis in the fields of hypertension pharmacology and nephrology SCI. The 12-week standardized surgical modeling can stably recapitulate complete pathological phenotypes of RAAS-hyperactive hypertension complicated with cardiac and renal interstitial fibrotic target organ injuries highly homologous to humans. The renal artery diameter, renal blood flow regulation, RAAS activation pattern and organ fibrosis progression kinetics of Beagle dogs are highly consistent with human beings. The blood pressure rising process is mild and uniform with low intra-group data dispersion, and the experimental repeatability is obviously superior to small animals such as rodents and rabbits. The modeling adopts pure physical vascular stenosis to induce endogenous blood pressure elevation without non-specific damage caused by exogenous intervention of chemical drugs and hormones, which highly simulates the pathological process of clinical essential hypertension derived from renal artery stenosis. Non-invasive blood collection and dynamic blood pressure monitoring can be carried out for many times on a single animal with abundant cardiac and renal tissue samples, which is suitable for preclinical efficacy and safety evaluation of new antihypertensive drugs, renal protective preparations, anti-myocardial fibrotic drugs and targeted preparations for hypertensive target organ protection. Experimental data are widely accepted by high-impact SCI journals of cardiovascular medicine, pharmacology and nephrology, which is applicable for National Natural Science Foundation projects, master & doctoral proposal writing, graduation theses of cardiology and nephrology, as well as translational medical researches on hypertensive organ injury repair.

Research Applications

The Beagle 2K1C Renal Hypertension Model is mainly applied to analyze the basic pathological mechanisms including renal ischemia induced by mechanical renal artery stenosis, renin release from juxtaglomerular cells, excessive activation of circulating RAAS system, sustained hypertension triggered by vasoconstriction and water-sodium retention, as well as cardiac & renal interstitial inflammatory infiltration and fibrotic remodeling induced by long-term high blood pressure. It is specially used for screening and verifying small-molecule antihypertensive drugs, active components of traditional Chinese medicine, organ-protective biological preparations and non-pharmacological intervention schemes for hypertension with functions of inhibiting excessive RAAS activation, stably reducing arterial blood pressure, alleviating renal ischemic injury, blocking activation of cardiac & renal fibroblasts, inhibiting abnormal collagen deposition, delaying visceral fibrotic lesions and protecting hypertensive target organs. It is widely adopted for excavation of pathogenic molecular targets of renovascular hypertension, elucidation of interactive regulatory network among RAAS, inflammation and fibrosis, as well as preclinical in-vivo efficacy verification of various anti-hypertensive and target organ protective drugs in large animals. It acts as an essential and scarce standardized large-animal gold-standard model in the fields of cardiovascular pharmacology, renal pathophysiology and hypertensive target organ protection.

beagle two-kidney one clip renal hypertension model, renal artery stenosis, renin-angiotensin system activation, sustained hypertension, target organ damage, antihypertensive drug & renal protection agent preclinical evaluation