How Do Antihypertensive Drugs Work? Insights from Studies of the Renal Regulation of Arterial Blood Pressure

Mathematical modeling of antihypertensive therapy

Hypertension is a multifactorial disease arising from complex pathophysiological pathways. Individual characteristics of patients result in different responses to various classes of antihypertensive medications. Therefore, evaluating the efficacy of therapy based on in silico predictions is an important task. This study is a continuation of research on the modular agent-based model of the cardiovascular and renal systems (presented in the previously published article). In the current work, we included in the model equations simulating the response to antihypertensive therapies with different mechanisms of action. For this, we used the pharmacodynamic effects of the angiotensin II receptor blocker losartan, the calcium channel blocker amlodipine, the angiotensin-converting enzyme inhibitor enalapril, the direct renin inhibitor aliskiren, the thiazide diuretic hydrochlorothiazide, and the β-blocker bisoprolol. We fitted therapy parameters based on known clinical trials for all considered medications, and then tested the model's ability to show reasonable dynamics (expected by clinical observations) after treatment with individual drugs and their dual combinations in a group of virtual patients with hypertension. The extended model paves the way for the next step in personalized medicine that is adapting the model parameters to a real patient and predicting his response to antihypertensive therapy. The model is implemented in the BioUML software and is available at https://gitlab.sirius-web.org/virtual-patient/antihypertensive-treatment-modeling.

Thoroughly Calibrated Modular Agent-Based Model of the Human Cardiovascular and Renal Systems for Blood Pressure Regulation in Health and Disease

Here we present a modular agent-based mathematical model of the human cardiovascular and renal systems. It integrates the previous models primarily developed by A. C. Guyton, F. Karaaslan, K. M. Hallow, and Y. V. Solodyannikov. We performed the model calibration to find an equilibrium state within the normal vital sign ranges for a healthy adult. We verified the model's abilities to reproduce equilibrium states with abnormal physiological values related to different combinations of cardiovascular diseases (such as systemic hypertension, chronic heart failure, pulmonary hypertension, etc.). For the model creation and validation, we involved over 200 scientific studies covering known models of the human cardiovascular and renal functions, biosimulation platforms, and clinical measurements of physiological quantities in normal and pathological conditions. We compiled detailed documentation describing all equations, parameters and variables of the model with justification of all formulas and values. The model is implemented in BioUML and available in the web-version of the software.

Independent relationships between renal mechanisms and systemic flow, but not resistance to flow in primary hypertension in Africa

AIMS

Whether renal mechanisms of hypertension primarily translate into increases in systemic vascular resistance (SVR) in all populations is uncertain. We determined whether renal mechanisms associate with either increases in SVR (and impedance to flow) or systemic flow in a community of African ancestry.

METHOD

In a South African community sampled across the full adult age range (n = 546), we assessed stroke volume (SV), peak aortic flow (Q), SVR, characteristic impedance (Zc) and total arterial compliance (TAC) from velocity and diameter measurements in the outflow tract (echocardiography) and central arterial pressures. Renal changes were determined from creatinine clearance (glomerular filtration rate, GFR) and fractional Na+ excretion (FeNa+) (derived from 24-h urine collections).

RESULTS

Independent of confounders (including MAP and pressures generated by the product of Q and Zc), SV (and hence cardiac output) (P < 0.0001) and Q (P < 0.01), but not SVR, Zc or TAC (P = 0.09-0.20) were independently associated with decreases in both GFR (index of nephron number) and FeNa+. Through an interactive effect (P < 0.0001), the impact of GFR on SV or Q was strongly determined by FeNa+ and vice versa. The relationship between the GFR-FeNa+ interaction and either SV or Q was noted in those above or below 50 years of age, although neither GFR, FeNa+ nor the interaction were independently associated with SVR, Zc or TAC at any age.

CONCLUSION

Across the full adult lifespan, in groups of African ancestry, renal mechanisms of hypertension translate into increases in systemic flow rather than into resistance or impedance to flow.

Parallel generation of extensive vascular networks with application to an archetypal human kidney model

Given the relevance of the inextricable coupling between microcirculation and physiology, and the relation to organ function and disease progression, the construction of synthetic vascular networks for mathematical modelling and computer simulation is becoming an increasingly broad field of research. Building vascular networks that mimic in vivo morphometry is feasible through algorithms such as constrained constructive optimization (CCO) and variations. Nevertheless, these methods are limited by the maximum number of vessels to be generated due to the whole network update required at each vessel addition. In this work, we propose a CCO-based approach endowed with a domain decomposition strategy to concurrently create vascular networks. The performance of this approach is evaluated by analysing the agreement with the sequentially generated networks and studying the scalability when building vascular networks up to 200 000 vascular segments. Finally, we apply our method to vascularize a highly complex geometry corresponding to the cortex of a prototypical human kidney. The technique presented in this work enables the automatic generation of extensive vascular networks, removing the limitation from previous works. Thus, we can extend vascular networks (e.g. obtained from medical images) to pre-arteriolar level, yielding patient-specific whole-organ vascular models with an unprecedented level of detail.

Sir George Johnson FRCP (1818-96), high blood pressure and the continuing altercation about its origins

NEW FINDINGS

What is the topic of this review? The review takes a historical approach to examining where in the body it might be possible to identify the most common cause, or causes, of long-term hypertension. It gathers evidence from histology, human and animal physiology, and computational modelling. The burden of decades of controversy is noted. What advances does it highlight? The review highlights the distinctive pathology of the afferent renal circulation and what its consequences are for the widespread view that essential hypertension is caused by elevated peripheral vascular resistance.

ABSTRACT

The widely promulgated notion that long-term elevation in mean arterial blood pressure (MAP) can be caused by raised peripheral vascular resistance remains a subject of vigorous debate. According to the 1967 mathematical model of Guyton and Coleman, such a causal relationship is impossible, kidney function being the determining factor. We explore this altercation starting with Sir George Johnson's 19th-century renal vascular histological observations in patients with Bright's disease. We note the striking physiological measurements in hypertensives by Gómez and Bolomey in the 1950s, moving on to the mathematical modelling of the circulation from the 1960s up to the ∼100-parameter computer models of the present day. Confusion has been generated by the fact that peripheral resistance is raised in hypertension in close proportion to MAP whilst cardiac output often stays normal, an apparent autoregulation, the mechanism of which is poorly understood. All models allowing for the circulation to be an open system show that isolated changes in peripheral resistance cannot lead to long-term hypertension, but models fail so frequently to account for results from experiments such as salt loading that their credibility with regard to this key finding is compromised. Laboratory animal models of adrenergic renal actions resonate with a contemporary emphasis on the sympathetic nerve supply to the kidney as contributing to the characteristically markedly elevated renal afferent resistance that appears to be the most common cause of hypertension. Remarkably, there remains no account of the way in which the fixed structural changes in vessels observed by Johnson relate to this sympathetic overactivity, which can itself be modified by drugs in the medium term. In this account, we seek to locate the crime scene and identify a smoking gun.

Single-Cell Transcriptome Profiling of the Kidney Glomerulus Identifies Key Cell Types and Reactions to Injury

BACKGROUND

The glomerulus is a specialized capillary bed that is involved in urine production and BP control. Glomerular injury is a major cause of CKD, which is epidemic and without therapeutic options. Single-cell transcriptomics has radically improved our ability to characterize complex organs, such as the kidney. Cells of the glomerulus, however, have been largely underrepresented in previous single-cell kidney studies due to their paucity and intractability.

METHODS

Single-cell RNA sequencing comprehensively characterized the types of cells in the glomerulus from healthy mice and from four different disease models (nephrotoxic serum nephritis, diabetes, doxorubicin toxicity, and CD2AP deficiency).

RESULTS

All cell types in the glomerulus were identified using unsupervised clustering analysis. Novel marker genes and gene signatures of mesangial cells, vascular smooth muscle cells of the afferent and efferent arterioles, parietal epithelial cells, and three types of endothelial cells were identified. Analysis of the disease models revealed cell type-specific and injury type-specific responses in the glomerulus, including acute activation of the Hippo pathway in podocytes after nephrotoxic immune injury. Conditional deletion of YAP or TAZ resulted in more severe and prolonged proteinuria in response to injury, as well as worse glomerulosclerosis.

CONCLUSIONS

Generation of comprehensive high-resolution, single-cell transcriptomic profiles of the glomerulus from healthy and injured mice provides resources to identify novel disease-related genes and pathways.

The Neurochemical Effects of Prazosin Treatment on Fear Circuitry in a Rat Traumatic Stress Model

Objective

The timing of administration of pharmacologic agents is crucial in traumatic stress since they can either potentiate the original fear memory or may cause fear extinction depending on the phase of fear conditioning. Brain noradrenergic system has a role in fear conditioning. Data regarding the role of prazosin in traumatic stress are controversial.

Methods

In this study, we examined the effects of prazosin and the noradrenergic system in fear conditioning in a predator stress rat model. We evaluated the direct or indirect effects of stress and prazosin on noradrenaline (NA), gamma-aminobuytyric acid (GABA), glutamate, glycine levels and choline esterase activity in the amygdaloid complex, the dorsal hippocampus, the prefrontal cortex and the rostral pons.

Results

Our results demonstrated that prazosin might alleviate defensive behaviors and traumatic stress symptoms when given during the traumatic cue presentation in the stressed rats. However prazosin administration resulted in higher anxiety levels in non stressed rats when the neutral cue was presented.

Conclusion

Prazosin should be used in PTSD with caution because prazosin might exacerbate anxiety in non-traumatized subjects. However prazosin might as well alleviate stress responses very effectively. Stress induced changes included increased NA and GABA levels in the amygdaloid complex in our study, attributing noradrenaline a possible inhibitory role on fear acquisition. Acetylcholine also has a role in memory modulation in the brain. We also demonstrated increased choline esterase acitivity. Cholinergic modulation might be another target for indirect prazosin action which needs to be further studied.

Functional status improves in hypertensive older adults: the long-term effects of antihypertensive therapy combined with multicomponent exercise intervention

BACKGROUND

The increasing prevalence of functionally-limited hypertensive individuals highlights the need for interventions to reduce the burden of hypertension-aging-disability and to maximize the chances of healthy aging.

AIM

This study aims to compare the effects of multicomponent exercise and different pharmacological treatments on functional status and cardiovascular risk outcomes in hypertensive older adults with comorbidities.

METHODS

Participants (n = 96) engage in a 3 days/week multicomponent (aerobic + resistance) exercise program and for one of the following three conditions: (1) thiazide-related diuretics (TDs; n = 33, 69.9 ± 9.5 years); (2) calcium channel blockers (CCBs; n = 23, 67.0 ± 9.0 years); (3) and β-blockers (βBs; n = 40, 65.6 ± 7.2 years) medication. Baseline and 2-year follow-up evaluations included the Senior Fitness Test battery, anthropometrics and hemodynamic profile, health-related quality of life (HRQoL; Short-Form Health Survey 36) and health history questionnaires.

RESULTS

All groups have significantly improved the physical functional status; particularly upper and lower body strength and aerobic endurance and systolic blood pressure. The TDs and βBs groups have diminished the waist circumference and body mass. The CCBs decreased total cholesterol (P = 0.028), perceived better physical functioning, physical component score but also augmented bodily pain (P < 0.05). The βB group decreased triglycerides (P = 0.013). No group differences were found.

CONCLUSION

Multicomponent exercise training has improved functional status regardless of the antihypertensive medication options. Hypertensive older adults should add exercise training to pharmacological antihypertensive therapy to reduce the rate of physical disability.

Dynamic tissue perfusion assessment reflects associations between antihypertensive treatment and renal cortical perfusion in patients with chronic kidney disease and hypertension

PURPOSE

Renal cortical perfusion measured in noninvasive, dynamic ultrasonic method is connected with the hemodynamic cardiac properties and renal function. Antihypertensive drugs affect the functioning of the heart and kidneys. The aim of the study was to evaluate the effect of a chronic use of antihypertensive drugs on ultrasound parameters of renal cortical perfusion.

METHODS

The study included 56 consecutive patients (49 M + 7 F, age 54.0 ± 13.3) with stable chronic kidney disease and hypertension. Color Doppler dynamic tissue perfusion measurement was used to assess renal cortical perfusion.

RESULTS

Patients were treated with a mean of 2.7 ± 1.4 antihypertensive drugs, of which diuretics accounted for 25%, angiotensin-converting enzyme inhibitors (ACE-I) together with angiotensin receptor blockers (ARB) 24%, beta-blockers (BB) 23%, calcium channel blockers 16%, alpha-1 blockers (α1B) 9% and centrally acting drugs 3%. All investigated groups of drugs correlated significantly with parameters of renal perfusion. In multivariable regression analyses adjusted to age, diuretics were connected with the decrease (r = - 0.473) and ACE-I + ARB (r = 0.390) with the improvement of proximal and whole renal cortex perfusion (R² = 0.28; p < 0.001), whereas BB (r = - 0.372) and α1B (r = - 0.280) independently correlated with worsened perfusion of renal distal cortex (R² = 0.21, p < 0.01).

CONCLUSIONS

The type of antihypertensive therapy had a significant influence on the ultrasound parameters of renal cortical perfusion. Noninvasive, ultrasonic dynamic tissue perfusion measurement method appears to be an adequate tool to assess the impact of drugs on renal cortical perfusion.

Antihypertensive monotherapy or combined therapy: which is more effective on functional status?

BACKGROUND

This study aims to analyze the effects of anti-hypertensive monotherapy and combined therapy on functional status, and cardiovascular risk outcomes in older adults.

METHODS

This longitudinal non-randomized cohort study, involved hypertensive older adults (n = 440) aged 60 or more years with comorbidities. Participants underwent a community exercise training program and one of the following 2 conditions: i) use of daily mono-dose angiotensin-converting enzyme inhibitors (ACEi; n= 232); ii) combined therapy including ACEi plus other class agent (Combined; n= 208). Baseline and 2-year follow-up evaluations included the functional fitness, health-related quality of life (HRQoL), health history questionnaires, anthropometric and hemodynamic profile.

RESULTS

Both experimental groups have significantly improved physical functional status, and have significantly decreased blood pressure and waist circumference. ACEi group has significantly reduced body mass and body mass index, the Combined group significantly reduced the waist-to-hip ratio. Additionally, both groups perceived better physical HRQoL.

CONCLUSIONS

Functional status has improved with ACEi medication and exercise training, regardless the ACEi medication therapy. Exercise training plus ACEi antihypertensive therapy should be recommended into the standard prescription practice to reduce the rate of physical disability among hypertensive older adults.

Differential Interaction of Dantrolene, Glafenine, Nalidixic Acid, and Prazosin with Human Organic Anion Transporters 1 and 3

In renal proximal tubule cells, the organic anion transporters 1 and 3 (OAT1 and OAT3) in the basolateral membrane and the multidrug resistance-associated protein 4 (MRP4) in the apical membrane share substrates and co-operate in renal drug secretion. We hypothesized that recently identified MRP4 inhibitors dantrolene, glafenine, nalidixic acid, and prazosin also interact with human OAT1 and/or OAT3 stably transfected in human embryonic kidney 293 cells. These four drugs were tested as possible inhibitors of p-[³H]aminohippurate (PAH) and [¹⁴C]glutarate uptake by OAT1, and of [³H]estrone-3-sulfate (ES) uptake by OAT3. In addition, we explored whether these drugs decrease the equilibrium distribution of radiolabeled PAH, glutarate, or ES, an approach intended to indirectly suggest drug/substrate exchange through OAT1 and OAT3. With OAT3, a dose-dependent inhibition of [³H]ES uptake and a downward shift in [³H]ES equilibrium were observed, indicating that all four drugs bind to OAT3 and may possibly be translocated. In contrast, the interaction with OAT1 was more complex. With [¹⁴C]glutarate as substrate, all four drugs inhibited uptake but only glafenine and nalidixic acid shifted glutarate equilibrium. Using [³H]PAH as a substrate of OAT1, nalidixic acid inhibited but dantrolene, glafenine, and prazosin stimulated uptake. Nalidixic acid decreased equilibrium content of [³H]PAH, suggesting that it may possibly be exchanged by OAT1. Taken together, OAT1 and OAT3 interact with the MRP4 inhibitors dantrolene, glafenine, nalidixic acid, and prazosin, indicating overlapping specificities. At OAT1, more than one binding site must be assumed to explain substrate and drug-dependent stimulation and inhibition of transport activity.