James W. Scholey

The Effect of Cyclooxygenase-2 Inhibition on Renal Hemodynamic Function in Humans With Type 1 Diabetes

OBJECTIVE—Studies in animal models suggest that cyclooxygenase-2 (COX2) plays a role in the regulation of the renal microcirculation in diabetes. Accordingly, we examined the role of COX2 in the control of renal hemodynamic function and in the renal response to hyperglycemia in humans with uncomplicated type 1 diabetes. We hypothesized that COX2 inhibition would alleviate the hyperfiltration state and would abrogate the hyperglycemia-mediated rise in glomerular filtration rate (GFR). RESEARCH DESIGN AND METHODS—Renal function was assessed during clamped euglycemia and hyperglycemia on 2 consecutive days before and then again after 14 days of COX2 inhibition using 200 mg celecoxib once daily by mouth. For analysis, the cohort was then divided into two groups based on the baseline GFR: 9 subjects exhibited hyperfiltration (GFR ≥135 ml/min per 1.73 m2), and 12 subjects exhibited normofiltration (GFR <135 ml/min per 1.73 m2). RESULTS—Under euglycemic conditions, COX2 inhibition resulted in a significant decline in GFR in the hyperfiltration group (150 ± 5 to 139 ± 5 ml/min per 1.73 m2) but increased GFR in the normofiltration group (118 ± 5 to 138 ± 5 ml/min per 1.73 m2). COX2 inhibition did not blunt the hyperglycemia-associated rise in GFR in the normofiltration group and was instead associated with an augmented rise in GFR. CONCLUSIONS—In summary, our results support the hypothesis that COX2 is an important determinant of renal hemodynamic function in subjects with type 1 diabetes. The renal response to COX2 inhibition emphasizes that hyperfiltration and normofiltration are distinct physiological states.

Renal Hyperfiltration is a Determinant of Endothelial Function Responses to Cyclooxygenase 2 Inhibition in Type 1 Diabetes

OBJECTIVE Our aim was to examine the effect of cyclooxygenase 2 (COX2) inhibition on endothelial function in subjects with type 1 diabetes analyzed on the basis of renal filtration status. RESEARCH DESIGN AND METHODS Flow-mediated dilation (FMD) was determined in type 1 diabetic subjects and hyperfiltration (glomerular filtration rate ≥135 ml/min/1.73 m2, n = 13) or normofiltration (glomerular filtration rate ≥135 ml/min/1.73 m2, n = 11). Studies were performed before and after celecoxib (200 mg daily for 14 days) during euglycemia and hyperglycemia. RESULTS Baseline parameters were similar in the two groups. Pretreatment, FMD was augmented in normofiltering versus hyperfiltering subjects during clamped euglycemia (10.2 ± 5.3% vs. 5.9 ± 2.3%, P = 0.003). COX2 inhibition suppressed FMD in normofiltering (10.2 ± 5.3% to 5.8 ± 3.4%, P = 0.006) versus hyperfiltering subjects (ANOVA interaction, P = 0.003). CONCLUSIONS Systemic hemodynamic function, including the response to COX2 inhibition, is related to filtration status in diabetic subjects and may reflect general endothelial dysfunction.

The Effect of Direct Renin Inhibition Alone and in Combination With ACE Inhibition on Endothelial Function, Arterial Stiffness, and Renal Function in Type 1 Diabetes

OBJECTIVE Diabetes is associated with renin-angiotensin system (RAS) activation, leading to renal and systemic vascular dysfunction that contribute to end-organ injury and significant morbidity. RAS blockade with ACE inhibitors reduces, but does not abolish, RAS effects. Accordingly, our aim was to determine if direct renin inhibition alone, and in combination with an ACE inhibitor, corrects early hemodynamic abnormalities associated with type 1 diabetes. RESEARCH DESIGN AND METHODS Arterial stiffness (augmentation index), flow-mediated vasodilatation (FMD), and renal hemodynamic function (inulin and paraaminohippurate clearance) were measured at baseline under clamped euglycemic and hyperglycemic conditions (n = 21). Measures were repeated after 4 weeks of aliskiren therapy and again after aliskiren plus ramipril. RESULTS Blood pressure–lowering effects of aliskiren were similar during clamped euglycemia and hyperglycemia. Combination therapy augmented this effect under both glycemic conditions (P = 0.0005). Aliskiren reduced arterial stiffness under clamped euglycemic and hyperglycemic conditions, and the effects were augmented by dual RAS blockade (−3.4 ± 11.2 to −8.0 ± 11.5 to −14.3 ± 8.4%, respectively, during euglycemia, P = 0.0001). During clamped euglycemia, aliskiren increased FMD; dual therapy exaggerated this effect (5.1 ± 3.3 to 7.5 ± 3.0 to 10.8 ± 3.5%, repeated-measures ANOVA, P = 0.0001). Aliskiren monotherapy caused renal vasodilatation during clamped hyperglycemia only. In contrast, dual therapy augmented renal vasodilatory effects during clamped euglycemia and hyperglycemia. CONCLUSIONS In patients with uncomplicated type 1 diabetes, aliskiren-based dual RAS blockade is associated with greater arterial compliance, FMD, and renal vasodilatation.

Renal hemodynamic effect of cyclooxygenase 2 inhibition in young men and women with uncomplicated type 1 diabetes mellitus

In experimental studies, cyclooxygenase 2 (COX2)-derived vasodilatory prostaglandins play a more prominent role in arterial vasoregulation in females. The gender-dependent effect of COX2 modulation in humans with type 1 diabetes mellitus (DM) is unknown. Accordingly, we examined the renal hemodynamic role of prostaglandins by assessing the response to COX2 inhibition in young men and women with type 1 DM. We also used a graded ANG II infusion to determine whether gender-based differences were mediated by effects of COX2 inhibition on the renin angiotensin system (RAS). We hypothesized that COX2 inhibition would be associated with preferential vasoconstriction in women and would augment their response to ANG II. Baseline renal function and the response to an ANG II infusion were assessed during clamped euglycemia, and again after COX2 inhibition (200 mg celecoxib daily for 14 days) in 12 men and 9 women after 1 wk on a controlled protein and sodium diet. COX2 inhibition was associated with increases in filtration fraction (P = 0.045) and renal vascular resistance and a decline in renal blood flow (P = 0.04) in women compared with men. Before COX2 inhibition, women exhibited a decline in glomerular filtration rate in response to ANG II. COX2 inhibition abolished this effect, whereas the response was not altered in men. In summary, COX2 inhibition was associated with hemodynamic effects that differed based on gender. The ANG II response suggests that with uncomplicated type 1 DM, prostaglandins may contribute to RAS-mediated gender differences. Our results are consistent with experimental data suggesting augmented female prostanoid dependence.

Urinary markers of renal inflammation in adolescents with Type 1 diabetes mellitus and normoalbuminuria

Diabet. Med. 29, 1297–1302 (2012)

Endothelial nitric oxide synthase gene polymorphisms and the renal hemodynamic response to L-arginine

Nitric oxide is generated from L-arginine by nitric oxide synthase (NOS), an enzyme that exists in several isoforms. Some studies found that a polymorphism (G894T) in the endothelial NOS gene was associated with decreased nitric oxide bioactivity and vascular complications. However, it is not known whether the enzyme had a reduced activity. Here we measured the effect of an infusion of L-arginine on renal hemodynamic function in subjects segregated by the presence or absence of the T allele. If this polymorphism represented a functional variant, subjects with the GT/TT form should exhibit a blunted renal hemodynamic response to L-arginine compared to those with a GG allele. All subjects were given a diet controlled for sodium and protein intake. GG subjects had lower mean arterial pressure and an augmented glomerular filtration rate at baseline. In response to a graded L-arginine infusion, this group had significant changes in effective renal plasma flow, glomerular filtration rate, filtration fraction, renal vascular resistance, and renal blood flow. The renal response to L-arginine in GT/TT subjects was blunted. Circulating cGMP levels and endothelial NOS mRNA expression, measured in skin biopsies by real-time PCR, did not differ between the groups. Our study shows that the G894T allele of endothelial NOS is associated with a blunted response to L-arginine, suggesting this polymorphism may be a functional variant in humans.

Sex Differences in Renal Responses to Hyperglycemia, l-Arginine, and l-NMMA in Humans With Uncomplicated Type 1 Diabetes

OBJECTIVE Women exhibit exaggerated renal hemodynamic responses to hyperglycemia, which may promote kidney disease progression. Our aim was to determine if increased nitric oxide generation by l-arginine infusion would reverse this deleterious response to clamped hyperglycemia in women with type 1 diabetes mellitus. RESEARCH DESIGN AND METHODS Renal function, blood pressure, and plasma cyclic guanosine monophosphate (cGMP) were measured in 20 men and 15 women with type 1 diabetes mellitus during clamped euglycemia and clamped hyperglycemia. Renal function, blood pressure, and plasma cGMP responses to graded infusions of intravenous l-arginine and NG-monomethyl-l-arginine (l-NMMA) were measured during clamped hyperglycemia. RESULTS Subjects were young, normotensive, normoalbuminuric men and women who adhered to a high-sodium, moderate-protein diet. Plasma cGMP levels during euglycemia were generally lower in men compared with women, and systolic blood pressure (SBP) was higher in men. In response to hyperglycemia, cGMP levels did not change in men but did decline in women (Δ−1.10 ± 0.20 vs. Δ+0.05 ± 0.20 pmol/L, between-group effect of hyperglycemia on cGMP; P = 0.012). Hyperglycemia also was associated with an increase in SBP, glomerular filtration rate (GFR) (124 ± 6 to 143 ± 7 mL/min/1.73 m2; P = 0.003) and filtration fraction (FF) in women, but these parameters did not change in men. In response to l-arginine during hyperglycemia, the increase in cGMP was exaggerated in women versus men and GFR and FF decreased in women only, back toward baseline values observed during clamped euglycemia. l-NMMA infusion did not exaggerate changes in hemodynamic function in response to hyperglycemia. CONCLUSIONS u2002l-Arginine reversed the renal hemodynamic effects of hyperglycemia in women, suggesting that nitric oxide is an important regulator of sex-dependent vascular responses to hyperglycemia in humans.

The angiotensin II receptor type 2 polymorphism influences haemodynamic function and circulating RAS mediators in normotensive humans

BACKGROUNDnThe haemodynamic responses to angiotensin II type 1 (AT1) receptor blockade may be mediated in part by interactions between angiotensin II and the angiotensin II type 2 receptor (AT2R). An AT2R G1675A gene polymorphism has been described, but the functional effects of this polymorphism are unknown.nnnMETHODSnHaemodynamic function, circulating renin-angiotensin system mediators and norepinephrine were measured in young healthy subjects at baseline and at 2 and 4 weeks after treatment with irbesartan. Subjects were divided into two groups on the basis of the AT2R G1675A gene polymorphism: GG subjects (n = 12) and AA/GA subjects (n = 22).nnnRESULTSnAA/AG subjects exhibited hypotensive and renal vasodilatory responses to irbesartan at 4 weeks, but GG subjects did not. In accord with haemodynamic effects, circulating aldosterone levels were suppressed in AA/AG, while circulating norepinephrine levels were augmented only in GG subjects. In contrast, increases in circulating renin, angiotensin II and plasma renin activity after irbesartan were exaggerated in AA/AG subjects.nnnCONCLUSIONSnThe AT2R G1675A polymorphism is a determinant of haemodynamic responses to AT1 receptor blockade, an effect that may be due to influences on aldosterone escape.

Plasma uric acid effects on glomerular haemodynamic profile of patients with uncomplicated Type 1 diabetes mellitus

Increased plasma uric acid (PUA) levels are associated with impaired renal function in patients with Type 1 diabetes, but the mechanisms are not well understood. Our aim was to evaluate whether higher PUA levels are associated with increased afferent arteriolar resistance in patients with Type 1 diabetes vs. healthy controls, thereby influencing renal function.

Long-term hemodynamic and molecular effects persist after discontinued renin–angiotensin system blockade in patients with type 1 diabetes mellitus

Animal studies suggest temporary renin-angiotensin system (RAS) blockade enhances long-term vascular protective effects; however, this is not established in humans. Here we evaluated the long-term effects of prior RAS blockade on hemodynamic function, urinary measures of inflammation, and tissue antioxidant mRNA expression in patients with type 1 diabetes mellitus (T1DM) who participated in the 5-year Renin Angiotensin System Study (RASS). At 4 years after completing the RASS and discontinuing study medication, renal hemodynamic responses to clamped hyperglycemia were significantly greater in 18 patients in the RAS blockade group compared to 9 patients of the placebo-treated group. Individuals who had received RAS blockade also exhibited higher flow-mediated vasodilatation, reduced urinary cytokine excretion in response to hyperglycemia, and increased skin mRNA expression of superoxide dismutase-1 and catalase. Thus, patients with uncomplicated T1DM who received prior RAS blockade for 5 years maintain long-term effects on renal hemodynamic and systemic vascular function, inflammatory pathways in the kidney, and antioxidant enzyme expression in skin 4 years after discontinuation of therapy. Our findings suggest that sustained long-term protective effects of finite RAS inhibition requires further study.