Renal angiotensin II receptors, hyperinsulinemia, and obesity

Angiotensin II and human obesity. A narrative review of the pathogenesis

Angiotensin II (Ang II) is a hormone and the main effector of the renin-angiotensin system (RAS). This peptide has crucial pathophysiologi-cal effects on hypertension, cardiac hypertrophy, endothelial proliferation, in-flammation and tissue remodelling through G protein-coupled receptors. The pro-inflammatory role of Ang II has been reported in various inflammatory pro-cesses. Obesity is linked to a chronic inflammatory process which in turn is the cause of some of its morbidities. Ang II is related to the comorbidities related to the comorbidities of obesity, which include alterations in the heart, kid-ney, hypertension and coagulation. In this regard, activation of AT1 receptors by Ang II can induce an inflammatory process mediated by the transcription factor NF-kB, triggering inflammation in various systems that are related to the comorbidities observed in obesity. The aim of this review was to highlight the pro-inflammatory effects of Ang II and the alterations induced by this hor-mone in various organs and systems in obesity. The search was done since 1990 through Medline, EMBASE and PubMed, using the keywords: angiotensin II; an-giotensin II, obesity; angiotensin II, kidney, obesity; angiotensin II, coagulation, obesity; angiotensin II, inflammation, obesity; angiotensin II, adipose tissue, obesity; angiotensin II, hypertension, obesity; angiotensin II, insulin resistance, obesity; angiotensin II, adiponectin, leptin, obesity; angiotensin II, COVID-19, obesity. Angiotensin II through its interaction with its AT1 receptor, can induce alterations in diverse systems that are related to the comorbidities observed in obesity. Therapeutic strategies to decrease the production and action of Ang II could improve the clinical conditions in individuals with obesity.

OUP accepted manuscript

Background

In living kidney transplantation there are two different individuals, a healthy donor and a renal transplant recipient. This is an excellent human model to study factors that influence kidney function in the context of reduced renal mass and the adaptation of two comparable kidneys to different metabolic demands.

Methods

We analyzed the changes in measured glomerular filtration rate (GFR, iohexol) from pretransplantation to 12 months after transplantation in 30 donor–recipient pairs. Each donor was compared with his/her recipient. We defined a priori three different groups based on GFR differences at 12 months: donor > recipient (Group A; 78 ± 8 versus 57 ± 8 mL/min), donor < recipient (Group B; 65 ± 11 versus 79 ± 11 mL/min) and donor ≈ recipient (Group C; 66 ± 7 versus 67 ± 7 mL/min). Other factors like donor/recipient mismatches in body mass index (BMI), surface area and gender were evaluated.

Results

In Group A donors were mostly male and recipients were female (75% each). Donors had a higher baseline weight than their recipients. During follow-up, weight remained stable in donors but increased 7% in recipients. In Group B donors were mostly female (60%) and recipients male. At baseline, donors had a lower weight than recipients. At 12 months, weight was stable in donors but increased in recipients. In Group C donors were mostly (75%) female and recipients male. At baseline, donors had a higher BMI than their recipients. At 12 months, BMI was stable in donors but increased 14% in recipients. In multivariable analysis, higher GFR at 12 months was associated with higher baseline weight and GFR in donors and with male gender and higher baseline weight in recipients.

Conclusions

Kidneys from living donors are more ‘plastic’ than originally thought and respond to metabolic demands and weight changes of their new host. These changes should be taken into account when assessing GFR outcomes in this population.

Obesity and metabolic syndrome induce hyperfiltration, glomerulomegaly, and albuminuria in obese ovariectomized female mice and obese male mice

OBJECTIVE

Obese patients with metabolic syndrome have a high risk of chronic kidney disease. The prevalence of obesity, metabolic syndrome, and insulin resistance increase in women after menopause, as does the risk of chronic kidney disease. This may indicate an interaction between obesity, metabolic syndrome, and menopause in the induction of renal damage. However, the pathogenesis of kidney disease in postmenopausal obese women is poorly understood.

METHODS

We investigated the interaction of an obesogenic diet and menopause on renal dysfunction in ovariectomized and non-ovariectomized lean (n = 8 and 17) and obese (n = 12 and 20) female mice. Obese (n = 12) and lean (n = 10) male mice were also studied. Glucose metabolism, insulin resistance, and kidney function were evaluated with gold standards procedures. Changes in kidney histology and lipid deposition were analyzed. Females had a lower number of glomeruli than males at baseline.

RESULTS

Only female ovariectomized obese animals developed insulin resistance, hyperglycemia, and kidney damage, evidenced as glomerulomegaly, glomerular hyperfiltration, and increased urinary albumin excretion, despite a similar increase in weight than obese non-ovariectomized female mice. Male obese mice developed hyperglycemia, insulin resistance, and hyperfiltration without major renal histological changes. Males on high fat diet showed higher renal lipid content and females on high fat diet (ovariectomized or non-ovariectomized) showed higher total cholesterol content than males.

CONCLUSIONS

In mice, there is a clear interplay between obesity, metabolic syndrome, and menopause in the induction of kidney damage.

The angiotensin type 2 receptor and the kidney

PURPOSE OF REVIEW

Angiotensin II is a main regulator of kidney function. Renal actions mediated by the angiotensin AT1 receptor have been well known for many years. In contrast, several details of angiotensin AT2 receptor actions in kidney physiology and pathophysiology were only described very recently. These findings are reviewed in this article.

RECENT FINDINGS

Regarding the role of the angiotensin AT2 receptor in kidney physiology, a major recent finding was that the AT2 receptor-mediated inhibition of Na-H exchanger-3 and Na/K-ATPase in the renal proximal tubules is caused by internalisation of these transporters, thus reducing reabsorption and increasing natriuresis/diuresis. Regarding renal pathology, several studies demonstrated an attenuation of renal injury caused by diabetes or by obesity with or without high-salt diet through anti-inflammatory, antifibrotic, and antioxidative mechanisms. Generally, AT2 receptor expression seems increased and AT2 receptor-mediated effects stronger in female and obese animals.

SUMMARY

The recent findings about the role of the angiotensin AT2 receptor in renal health and disease strongly suggest that pharmacological targeting of this receptor with selective agonists is a promising therapeutic strategy for inducing diuresis/natriuresis (also additive to established diuretics) and for the treatment of diabetic nephropathy or kidney disease of other pathogenesis.

High Na intake increases renal angiotensin II levels and reduces expression of the ACE2-AT(2)R-MasR axis in obese Zucker rats

High sodium intake is known to regulate the renal renin-angiotensin system (RAS) and is a risk factor for the pathogenesis of obesity-related hypertension. The complex nature of the RAS reveals that its various components may have opposing effects on natriuresis and blood pressure regulation. We hypothesized that high sodium intake differentially regulates and shifts a balance between opposing components of the renal RAS, namely, angiotensin-converting enzyme (ACE)-ANG II-type 1 ANG II receptor (AT(1)R) vs. AT(2)-ACE2-angiotensinogen (Ang) (1-7)-Mas receptor (MasR), in obesity. In the present study, we evaluated protein and/or mRNA expression of angiotensinogen, renin, AT(1A/B)R, ACE, AT(2)R, ACE2, and MasR in the kidney cortex following 2 wk of a 8% high-sodium (HS) diet in lean and obese Zucker rats. The expression data showed that the relative expression pattern of ACE and AT(1B)R increased, renin decreased, and ACE2, AT(2)R, and MasR remained unaltered in HS-fed lean rats. On the other hand, HS intake in obese rats caused an increase in the cortical expression of ACE, a decrease in ACE2, AT(2)R, and MasR, and no changes in renin and AT(1)R. The cortical levels of ANG II increased by threefold in obese rats on HS compared with obese rats on normal salt (NS), which was not different than in lean rats. The HS intake elevated mean arterial pressure in obese rats (27 mmHg) more than in lean rats (16 mmHg). This study suggests that HS intake causes a pronounced increase in ANG II levels and a reduction in the expression of the ACE2-AT(2)R-MasR axis in the kidney cortex of obese rats. We conclude that such changes may lead to the potentially unopposed function of AT(1)R, with its various cellular and physiological roles, including the contribution to the pathogenesis of obesity-related hypertension.

The effect of chronic candesartan therapy on the metabolic profile and renal tissue cytokine levels in the obese Zucker rat

The effect of candesartan, an angiotensin-II type-1 receptor antagonist, on the metabolic profile and renal inflammation is unclear. We evaluated this relationship by feeding male lean (LZ) and obese (OZ) Zucker rats chow or chow with candesartan (23.5 mg/kg · diet) for 14 weeks (n = 6–8/treatment/body type). Candesartan reduced serum triglycerides, plasma creatinine, urine albumin, and renal cortical collagen and glycogen deposition in the OZ. An ELISA-based cytokine array revealed that candesartan normalized elevated renal interleukin (IL) 1-β and monocyte chemoattractant protein-1 (MCP-1) levels in OZ. Nonetheless, candesartan impaired glucose tolerance, and did not lower blood insulin or glucose levels. Moreover, renal IL-1α, -2, -4, -6 and -10 tumor necrosis factor-α, interferon-γ, were significantly reduced in OZ relative to LZ, and increased by candesartan. Furthermore, candesartan increased growth-regulated oncogene, transforming growth factor-β1 and IL-18 in OZ kidneys to a level higher than LZ or untreated OZ. Candesartan did not affect renal cytokine levels in LZ. Overall, candesartan attenuated renal disease and improved renal function in OZ, despite mixed effects on metabolic factors and cytokines. Reduced plasma triglycerides and/or renal MCP-1 and IL-1β may have had a role in this protection. However, these effects were clearly independent of any improvement in glucose tolerance.

Exercise counters diet-induced obesity, proteinuria, and structural kidney alterations in rat

We studied the effects of exercise training in treating renal impairment due to hypertension and obesity in rats. Diet-induced obese and non-obese Wistar rats were assigned to four groups: Sed-Ob, Ex-Ob, Sed-C, and Ex-C (motor treadmill for 13 weeks; Ex=exercise-trained, C=control, Ob=obese, Sed=sedentary). Creatinine, proteinuria, and kidney structure were evaluated. Sed-C rats had normal and stable blood pressure (BP), while Sed-Ob rats developed hypertension. After 4 weeks of exercise, BP decreased in exercise-trained groups (less than 25% at the end of the experiment in obese rats, and less than 10% in non-obese rats). Both the body mass and retroperitoneal fat mass were lower in the exercise-trained groups than in the sedentary ones. Serum creatinine was not different among the groups, but the urinary protein excretion was significantly higher in the Sed-Ob group than in the matched non-obese group. Compared to the non-obese animals the mean glomerular volume increased by 45% in Sed-Ob rats and by 30% in Ex-Ob rats. Obese animals also showed increased mesangial volume density compared to non-obese animals. The present findings allow us to conclude that the exercise training could be an auxiliary practice to attenuate renal alterations seen in diet-induced obesity.

Angiotensin II type 1 receptor expression is increased via 12-lipoxygenase in high glucose-stimulated glomerular cells and type 2 diabetic glomeruli

BACKGROUND

Angiotensin II type 1 receptor (AT1) plays an important role in the development of diabetic nephropathy (DN). However, the roles played by 12-lipoxygenase (12-LO) in the AT1 expression in glomerular cells exposed to high glucose (HG) and diabetic glomeruli remain unclear. Our objective in the present study was to investigate the role of 12-LO in the AT1 expression in glomerular cells and glomeruli under diabetic conditions.

METHODS

Mesangial cells (MCs), podocytes and glomeruli isolated from rats were used in this study. The rats fed a high fat diet received low-dose streptozotocin to make type 2 diabetes. The 12-LO product 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] was infused to rats by osmotic mini-pump. Morphometric measurement for glomerular volume, competitive reverse transcription polymerase chain reaction for mRNA expression, western blot and immunohistochemistry for protein expression were performed, respectively.

RESULTS

Both the 12(S)-HETE and HG increased AT1 protein expression in MCs and podocytes. Furthermore, the levels of the AT1 were significantly higher in glomeruli derived from 12(S)-HETE-treated rats compared with control rats. In addition, HG-induced AT1 expression was significantly reduced by the 12-LO inhibitor cinnamyl-3,4-dihydroxy-alpha-cynanocinnamate (CDC). Compared with the non-diabetic controls, DN rats showed significant glomerular hypertrophy and albuminuria. This was associated with significant increases in AT1 protein expression. These abnormalities were prevented by treatment of the CDC.

CONCLUSIONS

These results indicate that AT1 expression is enhanced, at least in part, by 12-LO in the type 2 diabetic glomeruli, and 12-LO inhibition can ameliorate DN progression through downregulation of AT1 expression.

Preglomerular and postglomerular basal diameter changes and reactivity to angiotensin II in obese rats

AIM AND METHODS

Obesity in humans is associated with proteinuria and an increased glomerular filtration, possibly related to an increase in glomerular capillary pressure. We investigated in obese and lean Zucker rats (10-12 weeks old) whether this might be related to alterations in the diameter of preglomerular and postglomerular microvessels and their reactivity to the resistance regulator angiotensin II (AngII), using the hydronephrotic kidney model.

RESULTS

The obese rats exhibited a hyperinsulinaemic, euglycaemic state and hypertension. Urinary protein concentration and fluid intake were both increased threefold. Basal diameters of distal interlobular arteries (ILAs) and afferent arterioles (AAs) were larger in the obese rat than in the lean rat (ILA: 25.7 +/- 0.3 vs. 23.0 +/- 0.4 microm and AA: 18.8 +/- 0.3 vs. 16.7 +/- 0.5 microm, respectively; p </= 0.01), while diameters of efferent arterioles (EAs) were smaller in obese animals (14.2 +/- 1.1 vs. 18.2 +/- 1.2 microm; p </= 0.05). AngII induced a concentration-dependent constriction in ILA, AA and EA with an augmented response in the obese compared with the lean rats. Thus, at higher concentrations, AngII abolished the diameter difference between obese and lean animals in preglomerular microvessels while exaggerating that in postglomerular arterioles.

CONCLUSIONS

Our data indicate that in obese rats, a vasodilated state in small preglomerular microvessels and a vasoconstricted state in the postglomerular arterioles exist. Although AngII cancelled the former, the latter remained. Therefore, these data reveal periglomerular vascular changes that may play a role in glomerular dysfunction and renal pathology associated with obesity.

Chronic candesartan alters expression and activity of NKCC2, NCC, and ENaC in the obese Zucker rat

The obese Zucker rat reportedly has increased activity of the intrarenal renin-angiotensin-aldosterone system, which conceptually could contribute to elevated salt sensitivity and blood pressure (BP). Our aim was to determine whether there was increased angiotensin II type 1 receptor (AT(1)R)-mediated upregulation of expression or activity of the bumetanide-sensitive Na-K-2Cl cotransporter, the thiazide-sensitive Na-Cl cotransporter (NCC), and/or the epithelial sodium channel (ENaC) in obese vs. lean Zucker rats. Male obese and lean Zucker rats (10-wk old) were fed either 1) control chow (1% NaCl) or 2) chow with candesartan (CAN), an AT(1)R antagonist (25 mg/kg.diet) for 14 wk (n = 8/treatment/body type). BP measured by radiotelemetry, was markedly reduced by CAN ( approximately 20-25 mmHg) in both lean and obese rats with no body-type differences. Obese rats had significantly greater net natriuretic response to single injections of hydrochlorothiazide and benzamil, suggesting increased activity of NCC and ENaC, respectively; however, only the response to benzamil was reduced by CAN. CAN led to a significant reduction in whole kidney levels of NCC and gamma-ENaC (70-kDa band) in both lean and obese rats. However, it significantly increased alpha-ENaC and Na-K-2Cl cotransporter levels, and these increases were greater in obese rats. These studies suggest that relatively increased ENaC, but not NCC activity, in obese rats is due to enhanced AT(1)R activity. CAN attenuated the reduction of several renal transporters in the obese rat kidney. Finally, differences in intrarenal AT(1)R activity do not seem directly responsible for BP differences between lean and obese rats.

Impaired angiotensin II AT(1) receptor function and enhanced Na, K-ATPase affinity for sodium in proximal tubule of streptozotocin-treated diabetic rats

We determined angiotensin II (Ang II) AT(1) receptor function in terms of Na-K-ATPAse (NKA) stimulation in the proximal tubule (PTs) of streptozotocin-induced diabetic rats. Ang II (10 pM) stimulated NKA activity in PTs of control rats but not diabetic rats. The AT(1) receptor expression was similar, but the expression of G-proteins (G(i)alpha2 and G(i)alpha3) in the PTs was decreased in diabetic compared with control rats. Kinetic studies revealed an increase in NKA affinity, low K(0.5,) for Na, with no changes in V(max) of the enzyme in diabetic compared with control rats. Basal Ser-phosphorylation of NKA alpha1-subunit was lower in diabetic compared with control rats. This data suggest that the higher basal NKA affinity for Na, possibly due to lower Ser-phosphorylaion of alpha1-subunit and not the AT(1) receptor function, in the PTs may be responsible for increased renal Na reabsorption associated with early stage of streptozotocin-induced diabetes.

Insulin's impact on renal sodium transport and blood pressure in health, obesity, and diabetes

Insulin has been shown to have antinatriuretic actions in humans and animal models. Moreover, endogenous hyperinsulinemia and insulin infusion have been correlated to increased blood pressure in some models. In this review, we present the current state of understanding with regard to the regulation of the major renal sodium transporters by insulin in the kidney. Several groups, using primarily cell culture, have demonstrated that insulin can directly increase activity of the epithelial sodium channel, the sodium-phosphate cotransporter, the sodium-hydrogen exchanger type III, and Na-K-ATPase. We and others have demonstrated alterations in the expression at the protein level of many of these same proteins with insulin infusion or in hyperinsulinemic models. We also discuss how this regulation is perturbed in type I and type II diabetes mellitus. Finally, we discuss a potential role for regulation of insulin receptor signaling in the kidney in contributing to sodium balance and blood pressure.

Enhanced AT1receptor-mediated vasocontractile response to ANG II in endothelium-denuded aorta of obese Zucker rats

In the present study, we tested the hypothesis that ANG II causes a greater vasoconstriction in obese Zucker rats, a model of type 2 diabetes, with mild hypertension. Measurement of isometric tension in isolated aortic rings with intact endothelium revealed a modest but not significantly greater ANG II-induced contraction in obese than lean rats. Removal of endothelium or inhibition of nitric oxide (NO) synthase by NG-nitro-l-arginine methyl ester (l-NAME) enhanced 1) ANG II-induced contraction in both lean and obese rats, being significantly greater in obese rats (Emaxg/g tissue, denuded: lean 572 ± 40 vs. obese 664 ± 16; l-NAME: lean 535 ± 14 vs. obese 818 ± 23) and 2) ANG II sensitivity in obese compared with lean rats, as revealed by the pD2values. Endothelin-1 and KCl elicited similar contractions in the aortic rings of lean and obese rats. ACh, a NO-dependent relaxing hormone, produced greater relaxation in the aortic rings of obese than lean rats, whereas sodium nitroprusside, an NO donor, elicited similar relaxations in both rat strains. The expression of the ANG type 1 (AT1) receptor protein and mRNA in the endothelium-intact aorta was significantly greater in obese than lean rats, whereas the endothelium-denuded rings expressed modest but not significantly greater levels of AT1receptors in obese than lean rats. The endothelial NO synthase protein and mRNA expression levels were higher in the aorta of obese than lean animals. We conclude that, although ANG II produces greater vasoconstriction in obese rat aortic rings, enhanced endothelial AT1receptor-mediated NO production appears to counteract the increased ANG II-induced vasoconstriction, suggesting that arterial AT1receptor may not be a contributing factor to hypertension in this model of obesity.

Molecular and signaling mechanisms of atherosclerosis in insulin resistance

Although the prevalence of cardiovascular complications is increased in insulin-resistant individuals, the underlying causes of this link have been elusive. Recent work suggests that several intracellular signal transduction pathways are inappropriately activated by hyperinsulinemia, hyperglycemia, increased free fatty acids, dyslipidemia, various inflammatory cytokines and adipokines--factors that are increased in insulin resistance. Once activated, substantial cross talk occurs between these pathways, especially a self-reinforcing cascade of vascular inflammation and cell dysfunction, greatly increasing the risk and severity of atherosclerosis in the insulin-resistant individual. We review several key cell-signalling pathways, describe how they are activated in they insulin-resistant state and the damage they induce, and discusses possible therapeutic approaches to limit vascular damage.

Enhanced angiotensin II-induced activation of Na+, K+-ATPase in the proximal tubules of obese Zucker rats

Renal angiotensin II (AII) is suggested to play a role in the enhanced sodium reabsorption that causes a shift in pressure natriuresis in obesity related hypertension; however, the mechanism is not known. Therefore, to assess the influence of AII on tubular sodium transport, we determined the effect of AII on the Na+, K+-ATPase activity (NKA), an active transporter regulated by the AT1 receptor activity, in the isolated proximal tubules of lean and obese Zucker rats. Also, we determined the levels of the tubular AT1 receptor and associated signal transducing G proteins, as the initial signaling components that mediate the effects of AII on Na+, K+-ATPase activity. In the isolated proximal tubules, AII produced greater stimulation of the NKA activity in obese compared with lean rats. Determination of the AT1 receptors by Scatchard analysis of the [125I] Sar-Ang II binding and Western blot analysis in the basolateral (BLM) and brush border membrane (BBM) revealed a modest but significant increase (23%) in the AT1 receptor number mainly in the BLM of obese compared with lean rats. The AII affinity for AT1 receptors, as determined by IC50 values of AII to displace [125I] Sar-Ang II binding in BLM and BBM were similar in lean and obese rats. Western blot analysis revealed significant increases in Gialpha1, Gialpha2, Gialpha3, and Gq/11alpha in BLM and Gialpha1, Gialpha3, and Gq/11alpha in BBM of obese as compared with lean rats. The increase in the levels of the AT1 receptor and G proteins, mainly in the BLM, may be contributing to the enhanced AII-induced activation of NKA in the proximal tubules of obese rats. This phenomenon, in part, may be responsible for the increased sodium reabsorption and the development of hypertension in obese Zucker rats.