Serum angiotensin-converting enzyme activity and active renin plasma concentrations in insulin-dependent diabetes mellitus

Angiotensin-converting enzyme 2 influences pancreatic and renal function in diabetic mice

Type 1 diabetes is a T-cell mediated autoimmune disease characterized by pancreatic beta cells destruction. Angiotensin-converting enzyme 2 (ACE2), a component of renin-angiotensin system (RAS) has been identified in pancreas from type 2 diabetic mice and its overexpression prevents beta cell dysfunction. We studied the effect of ACE2 deletion on pancreatic and renal function in the nonobese diabetic mice, a model that mimics type 1 diabetes. ACE2-deficient NOD mice and the respective controls were generated. Pancreas function and immunohistochemistry studies were performed. Renal function and RAS gene expression were also analyzed. Renal proximal tubular cells were obtained from these animals to dissect the effect of ACE2 deficiency in these cells. In NOD mice, ACE2 deletion significantly worsened glucose homeostasis, decreased islet insulin content, increased beta cell oxidative stress, and RIPK1-positive islets as compared with control mice. Angiotensin-converting enzyme and angiotensin II type 1 receptor (AT1R) were also increased in ACE2-deficient mice. In kidneys of 30-day diabetic mice, ACE2 deletion decreased podocyte number within the glomeruli, and altered renal RAS gene expression in tubules. ACE2 deletion influenced the expression of fibrosis-related genes in isolated primary renal proximal tubular cells before diabetes onset in NOD mice. Our findings suggest that ACE2 deletion may have a deleterious impact on beta cell and renal function, by promoting oxidative stress and increasing necroptosis mediators. In addition, this effect is accompanied by RAS alterations in both pancreas and renal proximal tubular cells, indicating that ACE2 may exert a renopancreatic protective effect on type 1 diabetes, which is activated before diabetes starts.

Circulating biomarkers in glaucoma, age-related macular degeneration, and diabetic retinopathy

Biomarkers to predict the altering physiological conditions over the period leading toward the ocular disorders are of major importance in therapeutics. Isolation and validation of the biomarkers specific to ocular diseases are a challenging task. Glaucoma is a neurodegenerative disease of the eye where the correlation of biomarkers in circulating fluid may be made specific for the eye. However, conditions such as wet age-related macular degeneration (AMD) and proliferative diabetic retinopathy (DR), circulating biomarkers might be having some degree of overlap with other conditions like cancer where a common factor such as angiogenesis is involved. Diabetes, a systemic disorder affecting the target organs such as eye, kidney, heart, and nervous system can be predicted using common circulating biomarkers. However, these markers need to be validated along with various stages of disease progression to enable the possibility of targeted pharmacological interventions apart from good glycemic control alone. This review compiles the attempts made to correlate such circulating biomarkers in the ocular conditions such as glaucoma, AMD, and DR in the search for a surrogate marker for diagnostic and prognostic value. To make biomarkers for the common convenience, genetic markers are excluded from this review.

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

Inhibition of NAD(P)H oxidase alleviates impaired NOS-dependent responses of pial arterioles in type 1 diabetes mellitus

OBJECTIVE

The goal was to identify the role of NAD(P)H oxidase in cerebrovascular dysfunction in type 1 diabetes mellitus (T1D).

METHODS

In a first series of studies, rats were assigned to nondiabetic, diabetic (streptozotocin; 50 mg/kg IP), nondiabetic-apocynin (40 mg/kg/day in drinking water)-treated and diabetic-apocynin-treated groups. Two to three months later, the authors examined in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists. Next, they used Western blot analysis to examine protein levels for subunits of NAD(P)H oxidase in cerebral microvessels and parietal cortex tissue of nondiabetic and diabetic rats. Finally, they measured superoxide production by parietal cortex tissue in nondiabetic and diabetic rats.

RESULTS

Acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared to nondiabetic rats. In addition, while apocynin did not alter responses in nondiabetic rats, apocynin alleviated T1D-induced impairment of NOS-dependent vasodilatation. In addition, p47phox and gp91phox proteins were elevated in cerebral microvessels and parietal cortex tissue, respectively, of diabetic compared to nondiabetic rats. Further, basal production of superoxide was increased in diabetic compared to nondiabetic rats and apocynin decreased this basal production.

CONCLUSIONS

The findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism related to the formation of superoxide via activation of NAD(P)H oxidase.

Diabetes-induced cerebrovascular dysfunction: role of poly(ADP-ribose) polymerase

Our goal was to identify the role of poly(ADP-ribose) polymerase (PARP) in cerebrovascular dysfunction in Type 1 diabetes mellitus (T1D). In a first series of studies, rats were assigned to nondiabetic and diabetic (streptozotocin; 50 mg/kg IP) groups. Two to three months after injection of streptozotocin, we examine in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (adenosine diphosphate (ADP), acetylcholine and histamine) and -independent (nitroglycerin) agonists. After the initial examination of reactivity to the agonists, we treated pial arterioles acutely with an inhibitor of PARP (PJ-34; 1 microM), and then we again examined responses to the agonists. In a second series of studies, we examine superoxide production (lucigenin chemiluminescence) by parietal cortex tissue in nondiabetic and diabetic rats. We found that dilation of pial arterioles in response to ADP, acetylcholine and histamine, but not to nitroglycerin, was impaired in diabetic compared to nondiabetic rats. In addition, although PJ-34 did not alter responses in nondiabetic rats, PJ-34 alleviated T1D-induced impairment of NOS-dependent vasodilation. We also found that basal production of superoxide was increased in diabetic compared to nondiabetic rats and that PJ-34 decreased this basal production of superoxide. Our findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide via activation of PARP.

Enalapril prevents impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in diabetic rats

BACKGROUND AND PURPOSE

Our goal was to identify the effects of chronic treatment with enalapril on cerebrovascular dysfunction and endothelial nitric oxide synthase (eNOS) protein in diabetic rats.

METHODS

Rats were assigned to 1 of 4 groups: nondiabetic, diabetic, nondiabetic/enalapril-treated, and diabetic/enalapril-treated groups. Rats assigned to the nondiabetic groups were injected with vehicle (sodium citrate buffer), and rats assigned to the diabetic groups were injected with streptozotocin (50 mg/kg IP). Enalapril (10 mg/kg per day) was administered in the drinking water and coincided with the injection of vehicle or streptozotocin. Two to 3 months later, we examined responses of pial arterioles to nitric oxide synthase (NOS)-dependent agonists (acetylcholine and ADP) and a NOS-independent agonist (nitroglycerin). After these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein.

RESULTS

We found that acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared with nondiabetic rats. In addition, while enalapril did not alter responses in nondiabetic rats, enalapril prevented diabetes-induced impairment of NOS-dependent vasodilatation. Furthermore, eNOS protein was higher in diabetic than in nondiabetic rats, and enalapril did not produce a further increase in eNOS protein in enalapril-treated diabetic rats compared with untreated diabetic rats.

CONCLUSIONS

These results suggest that enalapril prevents cerebrovascular dysfunction in diabetic rats. We speculate that the protective role of enalapril may be independent of an alteration in eNOS protein in cerebral microvessels.

Prognostic role of serum ACE activity on outcome of type 2 diabetic patients on chronic ambulatory peritoneal dialysis

Overexpression of the renin-angiotensin system is important in the pathogenesis of macroangiopathy (MA). Patients with diabetes with end-stage renal failure have elevated serum angiotensin-converting enzyme (ACE) activity compared with their nonuremic counterparts. Because their major cause of death is MA, the significance of serum ACE activity on outcome of this group of patients is studied. We performed a prospective cohort study of 49 patients with type 2 diabetes on continuous ambulatory peritoneal dialysis (CAPD) therapy. Baseline serum ACE activity was determined by a modified spectrophotometric method and followed up at a median of 34 months. The prevalence of MA (defined as ischemic heart disease, sudden cardiac arrest, stroke, or peripheral vascular disease) and all-cause mortality rates were studied. Risk for MA is associated with serum ACE activity (median with MA, 69.0 U/L [range, 46.0 to 100.1 U/L] versus without MA, 57.2 U/L [range, 36.3 to 81.0 U/L]; P = 0.02). At the end of follow-up, 48% of patients (24 of 49 patients) died, 70% of MA. The group that died had increased baseline serum ACE activity (nonsurvivors, 65.0 U/L [range, 33.5 to 100.0 U/L] versus survivors, 49.4 U/L [range, 36.4 to 86.5 U/L]; P < 0.05) and MA rates (nonsurvivors, 77% versus survivors, 36%; P < 0.01). Cox regression analysis performed with age, sex, mean blood pressure, body mass index, metabolic control, Kt/V, residual renal function, serum albumin level, and ACE activity showed that baseline serum ACE activity (P = 0.033) is an independent predictor for mortality in patients with type 2 diabetes on CAPD therapy. Among patients with type 2 diabetes on CAPD therapy, serum ACE activity is associated with risk for MA and is an independent predictor for mortality. Whether ACE inhibition will have a beneficial effect on the outcome of these patients needs further investigation.

Contribution of gene polymorphisms in the renin-angiotensin system to macroangiopathy in patients with diabetic nephropathy

The renin-angiotensin system is important in the control of hemodynamic status and pathogenesis of macrovascular disease, which is a major cause of morbidity and mortality in patients with type 2 diabetes with nephropathy. Serum angiotensin-converting enzyme (ACE) and angiotensinogen (Atg) levels are related to their respective gene polymorphisms. Seventy patients with type 2 diabetes with overt nephropathy (serum creatinine >/= 1.5 mg/dL) were studied. Serum ACE activity was measured by the spectrophotometric method. ACE deletion/insertion (D/I) and Atg M235T genotypes were determined by polymerase chain reaction. Patients with and without macroangiopathy were compared. Those with macroangiopathy had increased ACE activity (median, 60.9 U/L; range, 37.9 to 100 U/L versus without macroangiopathy, 47.9 U/L; range, 11.2 to 84.5 U/L; P = 0.01) and prevalence of ACE DD/DI genotypes (DD/DI:II: with macroangiopathy, 61%:39% versus without macroangiopathy, 34%:66%; P = 0.03). Multivariate analysis using age; sex; duration of diabetes; glycemic, blood pressure, and lipid level control; serum creatinine level; and presence of the ACE D allele showed that presence of the D allele (P = 0.03; odds ratio, 1.8; confidence interval, 1.1 to 3.1) and serum creatinine level (P = 0.0007) were independent risk factors for macroangiopathy. Association of the D allele became insignificant after serum ACE activity was included in the analysis in which only serum ACE activity (P = 0.004) and serum creatinine level (P = 0.01) were independent risk factors. Neither Atg M235T nor its synergistic effect with the ACE D allele showed an association with macroangiopathy. In conclusion, the ACE D allele is associated with macroangiopathy in Chinese patients with type 2 diabetes with nephropathy. The association is dependent on its effect on serum ACE activity, which is an independent risk factor for the development of macroangiopathy.

Clinical and biochemical characteristics of type 2 diabetic patients on continuous ambulatory peritoneal dialysis: relationships with insulin requirement

Although glycemic control has an important impact on the clinical outcomes of patients with diabetes undergoing dialysis, there is a paucity of data on the relationship between glucose metabolism and clinical parameters in these patients. In this study, we compared a cohort of 48 patients with type II diabetes undergoing continuous ambulatory peritoneal dialysis (CAPD) with 84 age- and sex-matched patients with type II diabetes with similar disease duration but normal renal function. Compared with those with normal renal function, patients with type 2 diabetes undergoing CAPD had greater serum angiotensin-converting enzyme activity (median, 57.4 U/L; range, 33.5 to 100.0 U/L v 46.9 U/L; range, 11.6 to 111.2 U/L; P < 0.005), fasting C-peptide (median, 9.1 ng/mL; range, 0.9 to 30.0 ng/mL v 2.2 ng/mL; range, 0.2 to 20.3 ng/mL; P < 0.0001) and triglyceride levels, and lower serum albumin concentrations. Among the patients undergoing CAPD, there was a preponderance of men in the insulin-treated group. Insulin-treated patients also had greater plasma albumin levels and body weights and lower fasting serum C-peptide levels (2.81 +/- 1.77 v 3.12 +/- 2.04 ng/mL; analysis of variance, P = 0.007 adjusted for fasting glucose concentration). Multivariate analysis showed duration of diabetes, hemoglobin A(1c) (HbA(1c)) level, and body weight were independent determinants of insulin requirement in patients undergoing CAPD. The daily insulin dosage required was related to the duration of diabetes (r = 0.5; P = 0.007). In summary, among patients with end-stage renal failure, insulin-treated patients had greater body weights and plasma albumin levels but lower cholesterol levels. Plasma C-peptide concentration and duration of diabetes were the main determinants of insulin requirement, reflecting a decrease in beta-cell reserve, whereas the daily insulin dose correlated mainly with body weight, HbA(1c) level, and duration of diabetes. Kt/V had no effect on insulin resistance or insulin requirement of the patients.

The role of angiotensin II in diabetic nephropathy: emphasis on nonhemodynamic mechanisms

Several systemic or intrarenal networks of cytokines and growth factors can be modulated by the diabetic state. We summarize the status of the renin-angiotensin system in diabetes mellitus and review the evidence of its involvement in the pathogenesis of diabetic nephropathy. Particular emphasis is placed on the nonhemodynamic properties of this vasoactive agent as both a renal growth factor and a profibrogenic peptide. Antagonizing the effects of angiotensin II with converting enzyme inhibitors is an established protective strategy in the management of diabetic nephropathy even in the absence of systemic hypertension. This and other indirect evidence from experimental animal studies suggest that the intrarenal concentration of angiotensin II may be increased as a result of increased synthesis and despite enhanced breakdown, that this peptide participates in the progression of diabetic nephropathy. However, down-regulation of angiotensin type 1 (AT1)-receptors is one of the abnormalities of both tubules and glomeruli in diabetic renal disease. A heightened bioactivation of the intrarenal angiotensin II system is therefore likely but not certain. Studies in cultured proximal tubular and glomerular mesangial cells have disclosed striking similarities between the effects of high glucose-containing medium and of treatment with angiotensin II on the growth properties and the induction of cytokines in these cells. There may also exist additive effects of angiotensin II and high glucose on signal-transduction pathways, such as activation of protein kinase C, although the contractile response to angiotensin II may be blunted by high glucose in mesangial cells. An important downstream mediator of the effects of both angiotensin II and high glucose is the activation of transforming growth factor-beta that can mediate at least some of the hypertrophic and profibrotic effects of either angiotensin II or high glucose in the diabetic kidney.