The role of renin-angiotensin-aldosterone system inhibition in chronic kidney disease

Non-dialyzable uremic toxins and renal tubular cell damage in CKD patients: a systems biology approach

BACKGROUND

Chronic kidney disease presents global health challenges, with hemodialysis as a common treatment. However, non-dialyzable uremic toxins demand further investigation for new therapeutic approaches. Renal tubular cells require scrutiny due to their vulnerability to uremic toxins.

METHODS

In this study, a systems biology approach utilized transcriptomics data from healthy renal tubular cells exposed to healthy and post-dialysis uremic plasma.

RESULTS

Differential gene expression analysis identified 983 up-regulated genes, including 70 essential proteins in the protein-protein interaction network. Modularity-based clustering revealed six clusters of essential proteins associated with 11 pathological pathways activated in response to non-dialyzable uremic toxins.

CONCLUSIONS

Notably, WNT1/11, AGT, FGF4/17/22, LMX1B, GATA4, and CXCL12 emerged as promising targets for further exploration in renal tubular pathology related to non-dialyzable uremic toxins. Understanding the molecular players and pathways linked to renal tubular dysfunction opens avenues for novel therapeutic interventions and improved clinical management of chronic kidney disease and its complications.

Inhibition of G protein-coupled receptor 68 using homoharringtonine attenuates chronic kidney disease-associated cardiac impairment

Chronic kidney disease (CKD) induces cardiac inflammation and fibrosis and reduces survival. We previously demonstrated that G protein-coupled receptor 68 (GPR68) promotes cardiac inflammation and fibrosis in mice with 5/6 nephrectomy (5/6Nx) and patients with CKD. However, no method of GPR68 inhibition has been found that has potential for therapeutic application. Here, we report that Cephalotaxus harringtonia var. nana extract and homoharringtonine ameliorate cardiac inflammation and fibrosis under CKD by suppressing GPR68 function. Reagents that inhibit the function of GPR68 were explored by high-throughput screening using a medicinal plant extract library (8,008 species), and we identified an extract from Cephalotaxus harringtonia var. nana as a GPR68 inhibitor that suppresses inflammatory cytokine production in a GPR68 expression-dependent manner. Consumption of the extract inhibited inflammatory cytokine expression and cardiac fibrosis and improved the decreased survival attributable to 5/6Nx. Additionally, homoharringtonine, a cephalotaxane compound characteristic of C. harringtonia, inhibited inflammatory cytokine production. Homoharringtonine administration in drinking water alleviated cardiac fibrosis and improved heart failure and survival in 5/6Nx mice. A previously unknown effect of C. harringtonia extract and homoharringtonine was revealed in which GPR68-dependent inflammation and cardiac dysfunction were suppressed. Utilizing these compounds could represent a new strategy for treating GPR68-associated diseases, including CKD.

Potential of soluble (pro)renin receptor in kidney disease: can it go beyond a biomarker?

(Pro)renin receptor (PRR), also termed ATPase H+-transporting accessory protein 2 (ATP6AP2), is a type I transmembrane receptor and is capable of binding and activating prorenin and renin. Apart from its association with the renin-angiotensin system, PRR has been implicated in diverse developmental, physiological, and pathophysiological processes. Within the kidney, PRR is predominantly expressed in the distal nephron, particularly the intercalated cells, and activation of renal PRR contributes to renal injury in various rodent models of chronic kidney disease. Moreover, recent evidence demonstrates that PRR is primarily cleaved by site-1 protease to produce 28-kDa soluble PRR (sPRR). sPRR seems to mediate most of the known pathophysiological functions of renal PRR through modulating the activity of the intrarenal renin-angiotensin system and provoking proinflammatory and profibrotic responses. Not only does sPRR activate renin, but it also directly binds and activates the angiotensin II type 1 receptor. This review summarizes recent advances in understanding the roles and mechanisms of sPRR in the context of renal pathophysiology.

Chronopharmacology of immune-related diseases

Clock genes, circadian pacemaker resides in the paired suprachiasmatic nuclei (SCN), control various circadian rhythms in many biological processes such as physiology and behavior. Clock gene regulates many diseases such as cancer, immunological dysfunction, metabolic syndrome and sleep disorders etc. Chronotherapy is especially relevant, when the risk and/or intensity of the symptoms of disease vary predicably over time as exemplified by allergic rhinitis, arthritis, asthma, myocardial infarction, congestive heart failure, stroke, and peptic ulcer disease. Dosing time influences the effectiveness and toxicity of many drugs. The pharmacodynamics of medications as well as pharmacokinetics influences chronopharmacological phenomena. To escape from host immunity in the tumor microenvironment, cancer cells have acquired several pathways. Immune checkpoint therapy targeting programmed death 1 (PD-1) and its ligand (PD-L1) interaction had been approved for the treatment of patients with several types of cancers. Circadian expression of PD-1 is identified on tumor associated macrophages (TAMs), which is rationale for selecting the most appropriate time of day for administration of PD-1/PD-L1 inhibitors. The therapies for chronic kidney disease (CKD) are urgently needed because of a global health problem. The mechanism of the cardiac complications in mice with CKD had been related the GRP68 in circulating monocytes and serum accumulation of retinol. Development of a strategy to suppress retinol accumulation will be useful to prevent the cardiac complications of CKD. Therefore, we introduce an overview of the dosing time-dependent changes in therapeutic outcome and safety of drug for immune-related diseases.

Alteration of circadian machinery in monocytes underlies chronic kidney disease-associated cardiac inflammation and fibrosis

Dysfunction of the circadian clock has been implicated in the pathogenesis of cardiovascular disease. The CLOCK protein is a core molecular component of the circadian oscillator, so that mice with a mutated Clock gene (Clk/Clk) exhibit abnormal rhythms in numerous physiological processes. However, here we report that chronic kidney disease (CKD)-induced cardiac inflammation and fibrosis are attenuated in Clk/Clk mice even though they have high blood pressure and increased serum angiotensin II levels. A search for the underlying cause of the attenuation of heart disorder in Clk/Clk mice with 5/6 nephrectomy (5/6Nx) led to identification of the monocytic expression of G protein-coupled receptor 68 (GPR68) as a risk factor of CKD-induced inflammation and fibrosis of heart. 5/6Nx induces the expression of GPR68 in circulating monocytes via altered CLOCK activation by increasing serum levels of retinol and its binding protein (RBP4). The high-GPR68-expressing monocytes have increased potential for producing inflammatory cytokines, and their cardiac infiltration under CKD conditions exacerbates inflammation and fibrosis of heart. Serum retinol and RBP4 levels in CKD patients are also sufficient to induce the expression of GPR68 in human monocytes. Our present study reveals an uncovered role of monocytic clock genes in CKD-induced heart failure.

The Ameliorative Effect of Pectin-Insulin Patch On Renal Injury in Streptozotocin-Induced Diabetic Rats

BACKGROUND/AIMS

Renal damage and dysfunction is attributed to sustained hyperglycaemia in overt diabetes. Subcutaneous insulin injections are beneficial in delaying the progression of renal dysfunction and damage in diabetics. However, the current mode of administration is associated with severe undesirable effects. In this study, we evaluated the ameliorative effects of pectin-insulin dermal patches on renal dysfunction in diabetes.

METHODS

Pectin-insulin patches (20.0, 40.8 and 82.9 µg/kg) were applied on the skin of streptozotocin-induced diabetic rats, thrice daily for 5 weeks. Blood glucose concentration, blood pressure and urine output volume were recorded on week 5 after which the animals were sacrificed after which the kidneys and plasma were collected. Kidney nephrin expression and urinary nephrin concentration, albumin excretion rate (AER), creatinine clearance (CC) and albumin creatinine ratio (ACR) were assessed.

RESULTS

Patch application resulted in reduced blood glucose concentration and blood pressure. Furthermore, pectin-insulin patch treatment resulted in increased kidney nephrin expression and reduced urinary nephrin concentration. AER, CC ACR were also reduced post patch application.

CONCLUSIONS

The application of pectin-insulin patch limited diabetes associated kidney damaged and improved kidney function. These observations suggest that pectin-insulin patches may ameliorate kidney dysfunction that is associated with chronic subcutaneous insulin administration.

Design, synthesis and biological evaluation of renin inhibitors guided by simulated annealing of chemical potential simulations

We have applied simulated annealing of chemical potential (SACP) to a diverse set of ∼150 very small molecules to provide insights into new interactions in the binding pocket of human renin, a historically difficult target for which to find low molecular weight (MW) inhibitors with good bioavailability. In one of its many uses in drug discovery, SACP provides an efficient, thermodynamically principled method of ranking chemotype replacements for scaffold hopping and manipulating physicochemical characteristics for drug development. We introduce the use of Constrained Fragment Analysis (CFA) to construct and analyze ligands composed of linking those fragments with predicted high affinity. This technique addresses the issue of effectively linking fragments together and provides a predictive mechanism to rank order prospective inhibitors for synthesis. The application of these techniques to the identification of novel inhibitors of human renin is described. Synthesis of a limited set of designed compounds provided potent, low MW analogs (IC₅₀s<100nM) with good oral bioavailability (F>20-58%).

Lead optimization of 5-amino-6-(2,2-dimethyl-5-oxo-4-phenylpiperazin-1-yl)-4-hydroxyhexanamides to reduce a cardiac safety issue: discovery of DS-8108b, an orally active renin inhibitor

With the aim to address an undesired cardiac issue observed with our related compound in the recently disclosed novel series of renin inhibitors, further chemical modifications of this series were performed. Extensive structure-activity relationships studies as well as in vivo cardiac studies using the electrophysiology rat model led to the discovery of clinical candidate trans-adamantan-1-ol analogue 56 (DS-8108b) as a potent renin inhibitor with reduced potential cardiac risk. Oral administration of single doses of 3 and 10 mg/kg of 56 in cynomolgus monkeys pre-treated with furosemide led to significant reduction of mean arterial blood pressure for more than 12 h.

Discovery of DS-8108b, a Novel Orally Bioavailable Renin Inhibitor

A novel orally bioavailable renin inhibitor, DS-8108b (5), showing potent renin inhibitory activity and excellent in vivo efficacy is described. We report herein the synthesis and pharmacological effects of 5 including renin inhibitory activity in vitro, suppressive effects of ex vivo plasma renin activity (PRA) in cynomolgus monkey, pharmacokinetic data, and blood pressure-lowering effects in an animal model. Compound 5 demonstrated inhibitory activities toward human renin (IC50 = 0.9 nM) and human and monkey PRA (IC50 = 1.9 and 6.3 nM, respectively). Oral administration of single doses of 3 and 10 mg/kg of 5 in cynomolgus monkey on pretreatment with furosemide led to dose-dependent significant reductions in ex vivo PRA and sustained lowering of mean arterial blood pressure for more than 12 h.

Nebivolol does not protect against 5/6 ablation/infarction induced chronic kidney disease in rats - comparison with angiotensin II receptor blockade

AIMS

Nitric oxide (NO) deficiency contributes to chronic kidney disease progression. Nebivolol, a beta adrenergic receptor antagonist, may enhance endogenous NO. Here, we investigated whether Nebivolol attenuates hypertension and renal injury after 5/6 ablation/infarction (A/I). Efficacy was compared to the AT1 receptor antagonist Olmesartan.

MAIN METHODS

Kidney disease and hypertension were induced by right kidney ablation and ~2/3 infarction of the left kidney. Rats were treated orally with vehicle (placebo), Nebivolol (5mg/kg b.i.d.), or Olmesartan (2.5mg/kg/day) for 6 weeks after A/I.

KEY FINDINGS

With placebo, glomerular sclerosis and tubulointersititial fibrosis developed with increased blood pressure and proteinuria, and a fall in NO(x) excretion. Olmesartan prevented these changes, but Nebivolol had no effect on these measures but lowered heart rate. Neither treatment reduced systemic oxidative stress (urinary hydrogen peroxide and TBARS). Compared to controls, renal cortex abundance of nNOSα decreased and nNOSβ increased in rats after 5/6 A/I, with no changes in eNOS. Neither treatment restored nNOSα; however, both reduced nNOSβ. Activity of DDAH was decreased by 5/6 A/I but restored by both treatments despite no increase in DDAH protein abundance. Kidney cortex abundance of manganese SOD fell after 5/6 A/I and was restored by treatment with Olmesartan but not Nebivolol. Extracellular and copper/zinc SOD abundances were not changed.

SIGNIFICANCE

In conclusion, Nebivolol showed no benefit after 6 weeks in rapidly progressing, ANG II-dependent 5/6 A/I model of chronic kidney disease. This contrasts to the protection seen with 6 month treatment of Nebivolol in the slowly progressing 5/6 ablation model.

End-organ protection in patients with hypertension: focus on the role of angiotensin receptor blockers on renal function

The renin-angiotensin system (RAS) plays a key role in a number of pathophysiological mechanisms that are involved in the development and progression of cardiovascular and renal disease. For these reasons, pharmacological antagonism of this system, particularly the blockade of formation or the receptor antagonism of angiotensin II, has been demonstrated to be an effective and safe strategy to reduce the burden of cardiovascular disease. Among different drug classes, angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) have provided an excellent alternative to ACE inhibitors, representing a more selective and a better tolerated pharmacological approach to interfere with the RAS. Results derived from large, international, randomized clinical trials have consistently indicated that ARB-based therapeutic strategies may effectively provide cardiovascular and renal disease prevention and protection in different clinical conditions across the entire cardiovascular continuum. This article reviews the pathophysiological rationale of RAS involvement in the pathogenesis of renal diseases, focusing on the beneficial effects provided by ARBs in terms of renal protection.

Protective actions of nebivolol on chronic nitric oxide synthase inhibition-induced hypertension and chronic kidney disease in the rat: a comparison with angiotensin II receptor blockade

BACKGROUND

Nitric oxide (NO) deficiency contributes to chronic kidney disease (CKD) progression and hypertension. The β-blocker, nebivolol (N), also enhances NO production, and we studied whether N attenuates CKD and hypertension caused by chronic NO synthase inhibition (CNOSI).

METHODS

Male Sprague-Dawley rats on 6 weeks of CNOSI (L-NAME, 150 mg/L drinking water) received placebo (P), N (10 mg/kg/day), olmesartan (O, 2.5 mg/kg/day) or N + O. Blood pressure (BP) and urine protein and NOx (metabolites of NO) were monitored throughout. We measured glomerular sclerosis (GS), creatinine clearance (C(Cr)) and components of the NO and oxidant pathways in the renal cortex.

RESULTS

BP increased >50 mmHg in P by weeks 4-6, but no change occurred in N, O or N + O. P rats developed proteinuria and GS and C(Cr) was ∼30% of normal. In N, O and N + O, all values remained normal. In renal cortex of P, p22phox and nitrotyrosine abundance as well as H(2)O(2) levels were higher and extracellular superoxide dismutase (EC SOD) was lower versus normal kidneys. N, O and N + O normalized p22phox, H(2)O(2) and EC SOD and increased Mn SOD above normal. The cortical neuronal NO synthase (nNOS) β abundance increased in P and this was prevented by N, O and N + O.

CONCLUSION

We suggest that the major benefit from both N and O is reduction in oxidative stress in the renal cortex, which may potentiate residual local NO. There was no additive benefit of N + O since each drug effectively prevented injury, but a combination may be beneficial where protection is incomplete with each drug. The increased nNOSβ protein seen early in the course of the CKD may contribute to the evolving GS.

Therapeutic advantage of angiotensin-converting enzyme inhibitors in patients with proteinuric chronic kidney disease

Angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) is recommended for the treatment of hypertension in patients with chronic kidney disease (CKD). The relation of ACEI to renal prognosis was investigated in CKD patients in a retrospective cohort study. The objectives were patients with nondiabetic CKD of stage 4 or below receiving monotherapy with calcium channel blocker (CCB), ACEI, or ARB, and combination therapy. For the endpoint of progression to CKD stage 5, Cox's proportional hazards analysis was conducted with explanatory variables of age, sex, baseline estimated GFR (eGFR), and proteinuria (UP) at the start of the observation period, and final blood pressure (BP) and UP at completion of the observation period. Analyzed patients comprised 131 males and 117 females, with mean age of 47.8 years. Patients were observed for 44.2 months, and the parameters of final SBP, DBP, eGFR, and UP were 127.6 +/- 6.9 mmHg, 77.8 +/- 5.8 mmHg, 38.1 +/- 10.6 ml/min/1.73 m(2), and 1.08 +/- 0.57 g/gCr, respectively, where 42 patients progressed to CKD stage 5. Drugs of CCB, ACEI, and ARB types were administered to 93, 85, and 127 patients, respectively. In the multivariate analysis, extracted common prognostic factors included the baseline eGFR and final UP, the odds ratio of which was 0.876 (every increase by 1 ml/min of eGFR) and 2.229 (every increase by 1 g of UP), respectively. Among drugs in use, ACEI was an independent prognostic factor, whose odds ratio was 0.147. The present study suggests that ACEI is a prognostic factor independent of hypotensive action and UP in CKD patients.

Beneficial effect of all-trans retinoic acid (ATRA) on glomerulosclerosis rats via the down-regulation of the expression of alpha-smooth muscle actin: a comparative study between ATRA and benazepril

Although ATRA is a potent renoprotective agent, relatively little is known regarding the mechanisms of its action. The present study was designed to further elucidate the mechanisms of ATRA's action to GS rats and compare that with the beneficial effect of benazepril. Male SD rats weighting 160 to 200g were used in this study. GS was induced by unilateral nephrectomy and intravenous injection of adriamycin (6mg/kg). They were divided randomly 20 ones per group into GS group, GS treated with ATRA (20mg/kg/day) group, and GS treated with benazepril (10mg/kg/day) group. The other 20 ones were taken as sham-operation group, injected normal saline into caudal vein. 12weeks later, all rats were subjected to sacrifice. As expected, the GS group exhibited significant lower serum TP and Alb, and higher BUN, Cr and proteinuria than those of the sham group. Administration of ATRA or benazepril did ameliorate these above disorders of biochemical parameters in GS rats. Extensive renal damage was observed in the GS group, such as mononuclear infiltration, mesangial proliferation, focal segment glomerular sclerosis, and tubulointerstitial fibrosis. The pathological changes in both ATRA and benazepril group were alleviated remarkably. Semiquantitative GSI was used to evaluate the degree of GS in all groups. GSI was significantly higher in the GS group than in sham group. GSI decreased from 21.9+/-6.7 in the GS group to 6.9+/-2.8 in the ATRA group and 7.0+/-2.7 in benazepril group respectively. However, no significant difference in GSI between rats treated with ATRA and rats treated with benazepril was found. RT-PCR analysis revealed the renal expression of alpha-SMA mRNA was induced substantially in GS group as compared to sham group, which could be offset completely by ATRA or benazepril administration. However, expression level of alpha-SMA mRNA in GS rats treated with ATRA was identical to that in GS rats treated with benazepril. We also examined immunohistochemical staining for renal alpha-SMA, TGF-beta1, Col IV, and FN in this model. Weak staining was observed in some glomerulus, mesangial cells, and tubular interstitium of sham rats. Staining was markedly enhanced in the majority of glomerulus, mesangial cells, and tubular interstitium of untreated GS rats. Compared with untreated GS animals, intensity and extent of staining for renal alpha-SMA, TGF-beta1, Col IV, and FN were markedly reduced in glomerulus, mesangial cells, and tubular interstitium of GS rats treated with either ATRA or benazepril. However, no significant differences existed between ATRA and benazepril with respect to the glomerular and tubulointerstitial staining scores. Interestingly, our data documented some differences of therapeutic capacities between ATRA and benazepril. In comparison with benazepril, ATRA exerted no improvement in hypoproteinemia, but more significant decrease in serum Cr level in GS rats. The reasons leading to these variations are unclear. Whatever they are, the properties of down-regulate inflammatory/proliferative programs may make ATRA an attractive potential candidate for future therapeutic use in kidney disease.

Design and optimization of a substituted amino propanamide series of renin inhibitors for the treatment of hypertension

The discovery and SAR of a new series of substituted amino propanamide renin inhibitors are herein described. This work has led to the preparation of compounds with in vitro and in vivo profiles suitable for further development. Specifically, challenges pertaining to oral bioavailability, covalent binding and time-dependent CYP 3A4 inhibition were overcome thereby culminating in the identification of compound 50 as an optimized renin inhibitor with good efficacy in the hypertensive double-transgenic rat model.

Influence of T-calcium channel blocker treatment on deterioration of renal function in chronic kidney disease

Some calcium channel blockers (CCBs) have renoprotective effects. Our aim was to compare the effects of different subclasses of CCBs on the deterioration of renal function in chronic kidney disease (CKD). This is a prospective, observational cohort study in a single center. The subjects were 107 nondiabetic CKD patients. The rate of deterioration of estimated glomerular filtration rate (DeltaeGFR) was calculated by [last visit eGFR - baseline eGFR/follow-up duration]. Multivariate analysis was performed using the change in urinary protein (DeltaUP) and DeltaeGFR during follow-up as response variables. CCB subclasses were L-type in 76 patients, T- and L-type in 28 patients, and nondihydropyridines in 6 patients. Multiregression analysis indicated that higher baseline proteinuria (UP) and the use of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers were associated with the decrease of UP, while the use of L-type CCBs, prednisolone, and probucol was associated with the increase of UP. The use of T- and L-type CCBs, ACEIs and diuretics was associated with a good outcome in terms of DeltaeGFR, whereas chronic glomerulonephritis, polycystic kidney disease, and higher baseline eGFR and UP were associated with a poor outcome. It is suggested that the use of T- and L-type CCB among other subclasses may improve the outcome of patients with nondiabetic CKD in terms of renal function.

Sartan-AT1 receptor interactions: in vitro evidence for insurmountable antagonism and inverse agonism

Sartans are non-peptide AT(1) receptor antagonists used to treat hypertension and related pathologies. Their effects on the G protein-dependent responses of angiotensin II (Ang II) were the same in vascular tissues and in isolated cell systems. All are competitive but, when pre-incubated, they act surmountably (only rightward shift of the Ang II concentration-response curve) or insurmountably (also decreasing the maximal response). Insurmountable behaviour reflects the formation of tight sartan-receptor complexes; it is often partial due to the co-existence of tight and loose complexes. Their ratio positively correlates with the dissociation half-life of the tight complexes and depends on the sartan: i.e. candesartan>olmesartan>telmisartan approximately equal EXP3174>valsartan>irbesartan>>losartan. When AT(1) receptors display sufficient basal activity (in case of receptor over-expression, mutation and, especially, tissue stretching) sartans may also act as inverse agonists. This rather affects long-term, G protein-independent hypertrophic responses leading to cardiovascular remodelling.

Synergistic induction of osteopontin by aldosterone and inflammatory cytokines in mesangial cells

Hypertensive nephrosclerosis is characterized by activation of the renin-angiotensin-aldosterone system in combination with an inflammatory response characterized by an infiltration of T-cells and mononuclear cells, which release proinflammatory cytokines like IL-1beta/TNFalpha. In various models of experimental hypertensive disease the chemokine osteopontin (OPN) enhances further leukocyte infiltration. Therefore, we investigated the induction of OPN expression in renal mesangial cells (MCs) by aldosterone and the inflammatory cytokines IL-1beta/TNFalpha. Incubation with aldosterone resulted in a time- and concentration-dependent increase in OPN mRNA and protein. OPN mRNA expression followed a biphasic time course with an early increase between 4 and 8 h and the second phase starting at 14 h. The early phase was independent of protein synthesis, indicating a direct effect of aldosterone. Aldosterone-mediated induction of OPN was prevented by spironolactone, indicative of a receptor-mediated aldosterone effect. The mineralocorticoid receptor (MR) was identified in MCs by RT-PCR and immunoprecipitation, and shown to interact with a putative aldosterone-response element of the OPN promoter. The proinflammatory cytokines IL-1beta and TNFalpha only marginally affected OPN expression in MCs. However, coincubation of aldosterone and the cytokines synergistically increased OPN mRNA and protein levels. Since the synergistic effect on OPN mRNA was inhibited by diphenyleneiodonium, we assume an involvement of reactive oxygen species (ROS). We conclude that the chemokine OPN is a target gene of aldosterone in renal MCs, which is activated via the MR, and that proinflammatory cytokines enhance aldosterone-dependent OPN expression. In vivo, this may result in further leukocyte infiltration aggravating hypertensive nephrosclerosis.

Mouse models and the urinary concentrating mechanism in the new millennium

Our understanding of urinary concentrating and diluting mechanisms at the end of the 20th century was based largely on data from renal micropuncture studies, isolated perfused tubule studies, tissue analysis studies and anatomical studies, combined with mathematical modeling. Despite extensive data, several key questions remained to be answered. With the advent of the 21st century, a new approach, transgenic and knockout mouse technology, is providing critical new information about urinary concentrating processes. The central goal of this review is to summarize findings in transgenic and knockout mice pertinent to our understanding of the urinary concentrating mechanism, focusing chiefly on mice in which expression of specific renal transporters or receptors has been deleted. These include the major renal water channels (aquaporins), urea transporters, ion transporters and channels (NHE3, NKCC2, NCC, ENaC, ROMK, ClC-K1), G protein-coupled receptors (type 2 vasopressin receptor, prostaglandin receptors, endothelin receptors, angiotensin II receptors), and signaling molecules. These studies shed new light on several key questions concerning the urinary concentrating mechanism including: 1) elucidation of the role of water absorption from the descending limb of Henle in countercurrent multiplication, 2) an evaluation of the feasibility of the passive model of Kokko-Rector and Stephenson, 3) explication of the role of inner medullary collecting duct urea transport in water conservation, 4) an evaluation of the role of tubuloglomerular feedback in maintenance of appropriate distal delivery rates for effective regulation of urinary water excretion, and 5) elucidation of the importance of water reabsorption in the connecting tubule versus the collecting duct for maintenance of water balance.

Molecular characterisation of the interactions between olmesartan and telmisartan and the human angiotensin II AT1 receptor

BACKGROUND AND PURPOSE

Whereas some angiotensin II (Ang II) type 1 receptor blockers (ARBs) produce surmountable antagonism of AT(1) receptors, others such as olmesartan and telmisartan display varying degrees of insurmountability. This study compared the molecular interactions of olmesartan and telmisartan with the human AT(1) receptor, using well characterised in vitro methods and model systems.

EXPERIMENTAL APPROACH

CHO-K1 cells that stably express human AT(1) receptors (CHO-hAT(1) cells) were used in several pharmacological studies of olmesartan and telmisartan, including direct radioligand binding and inhibition of Ang II-induced inositol phosphate (IP) accumulation.

KEY RESULTS

Both ARBs were found to be competitive antagonists that displayed high affinity, slow dissociation, and a high degree of insurmountability for the AT(1) receptor (the latter greater with olmesartan). Their receptor interactions could be described by a two-step process with the initial formation of a loose complex (IR) and subsequent transformation into a tight binding complex (IR*). In washout experiments, [(3)H] telmisartan dissociated from the receptor with a half-life of 29 min and the Ang II-mediated IP accumulation response was 50% maximally restored within 24 min, whereas values for [(3)H] olmesartan were 72 min and 76 min, respectively.

CONCLUSIONS AND IMPLICATIONS

The high degree of insurmountability, slow dissociation, and high affinity of olmesartan for its receptor may relate to its ability to stabilise IR* via the carboxyl group of its imidazole core. In comparison, telmisartan displays a less potent interaction with the receptor.

Diabetes and Hypertension: Epidemiology of the Relationship and Pathophysiology of Factors Associated With These Comorbid Conditions

Diabetes and hypertension frequently coexist, leading to additive increases in the risk of life-threatening cardiovascular events. Hypertension is a common comorbid condition in patients with type 1 or type 2 diabetes when compared with the general population and occurs in 75% of patients with the more prevalent form of diabetes, type 2. Arterial blood pressure plays an important role in the development of renal damage and presents a complex relationship. It is well-known that hypertension accelerates the course of microvascular and macrovascular complications of diabetes and that hypertension often precedes type 2 diabetes and vice versa. Patients with type 1 and 2 diabetes and nephropathy frequently have circadian changes in blood pressure that correlate to nephropathy risk. Early detection of nocturnal hypertension and early intervention with angiotensin blockade may delay progression of diabetic nephropathy.

Proposal of a New Binding Orientation for Non-Peptide AT1 Antagonists: Homology Modeling, Docking and Three-Dimensional Quantitative Structure−Activity Relationship Analysis

A three-dimensional model of the AT1 receptor was constructed by means of a homology modeling procedure, using the X-ray structure of bovine rhodopsin as the initial template and taking into account the available site-directed mutagenesis data. The docking of losartan and its active metabolite EXP3174, followed by 1 ns of molecular dynamics (MD) simulation inserted into the phospholipid bilayer, suggested a different binding orientation for these antagonists from those previously proposed. Furthermore, the docking of several non-peptide antagonists was used as an alignment tool for the development of a three-dimensional quantitative structure-activity relationship (3D-QSAR) model, and the good results confirmed our binding hypothesis and the reliability of the model.

Managing the Burden of Chronic Kidney Disease

Patients with chronic kidney disease (CKD) have high rates of healthcare utilization, morbidity, and mortality. Increasing rates of obesity, diabetes, and hypertension suggest that the expected numbers of patients with CKD will rise. Managing the economic and clinical burden of CKD will be a significant challenge for the healthcare system. The burden of CKD can be considered in terms of both CKD-specific and CKD-related morbidity and mortality. CKD-specific complications include anemia and bone disease. CKD-related complications include obesity, diabetes and hypertension. CKD-specific complications tend to occur later in the course of disease and may be best treated by a nephrologist, while CKD-related complications may be most easily treated by primary care physicians. Coordinating patient care is essential to managing the burden of this growing disease.

Improving Antihypertensive Therapy in Patients with Diabetic Nephropathy

Nearly all patients with diabetic nephropathy have comorbid hypertension, which greatly elevates the risk for cardiovascular events. As patients are surviving longer, their risk of progressing to end-stage renal disease is increasing, particularly in patients with type 2 diabetes. Prevention of cardiovascular and renal events in this population requires diligent efforts to control blood pressure, serum glucose, and serum lipids. Improving antihypertensive therapy in patients with diabetic nephropathy relies on the following unified strategies: reducing blood pressure to <130/80 mm Hg, prescribing an agent that blocks the renin-angiotensin system, and designing an antihypertensive regimen that both reduces albuminuria and provides cardiovascular protection. A majority of patients will require three or more antihypertensive agents to achieve these objectives. Appropriate antihypertensive therapy in patients with diabetic nephropathy delays progression of renal disease and leads to substantial cost savings.

A Review of the Structural and Functional Features of Olmesartan Medoxomil, An Angiotensin Receptor Blocker

The angiotensin II (A-II) type 1 (AT1) receptor-mediated effects of A-II play a key role in the pathophysiology of hypertension. Effective inhibition of A-II is provided by the latest class of antihypertensive medications, the AT1 receptor blockers (ARBs). These orally available agents were developed around a common imidazole-based structural core. The most recent member of this drug class to be approved by the Food and Drug Administration, olmesartan medoxomil, contains unique features that may explain its clinical efficacy. Key structural elements of olmesartan medoxomil include a hydroxyalkyl substituent at the imidazole 4-position and a hydrolyzable ester group at the imidazole 5-position. Inter- and intramolecular hydrogen bonding involving these groups may contribute to the potentiation of antagonist activity. After oral administration, olmesartan medoxomil is deesterified in the intestinal tract to produce the active metabolite olmesartan, which undergoes no additional metabolic change. The marked antihypertensive efficacy of olmesartan medoxomil may result from a unique pharmacological interaction of the drug with the AT1 receptor, resulting in a potent, long-lasting, dose-dependent blockade of A-II. This review article characterizes the structural features of olmesartan that may be responsible for its clinical efficacy. Inferential pharmacological studies compare and contrast the effects of olmesartan to those of other ARBs in comparable preclinical animal models.