Prostaglandins and diabetic nephropathy

Role of Senescent Renal Cells in Pathophysiology of Diabetic Kidney Disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) is the leading cause of kidney failure in the USA, representing ~ 44% of all cases of kidney failure. Advancements in both glucose management and inhibitors of the renin-angiotensin system have significantly improved prognosis for individuals with DKD, yet DKD continues to affect 30-40% of people with type 2 diabetes and is still a major predictor of mortality in this population. Thus, new interventions are required to address this significant health burden.

RECENT FINDINGS

One potential target for intervention is cellular senescence. Senescence permanently arrests cell division in response to genotoxic, oncogenic, or metabolic stresses-coupled to the secretion of inflammatory cytokines, chemokines, growth factors, proteases, and other molecules that can have potent local and systemic effects. This senescence-associated secretory phenotype (SASP) explains how a relatively small number of senescent cells can promote pathology, and a growing number of degenerative conditions have been found to be caused or aggravated by senescent cells. Many SASP factors are also associated with loss of kidney function. Targeted elimination of senescent cells prevents the development of several degenerative pathologies. Since senescent cells appear in the proximal tubules and podocytes of patients with DKD, they are an appealing target for intervention in these disorders. Here, we review the current literature linking senescence to DKD and speculate on the likely routes to intervention in a clinical setting.

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

Eicosanoids and renal damage in cardiometabolic syndrome

BACKGROUND

Obesity, hypertension and Type 2 diabetes are major contributing factors to the increase in the number of patients that have chronic kidney disease. The clustering of visceral obesity and cardiovascular risk factors has been designated metabolic syndrome or cardiometabolic syndrome. Cardiometabolic syndrome is associated with a complex systemic inflammatory state that has been implicated in medically important complications, including endothelial dysfunction. Inflammation, endothelial dysfunction and insulin resistance are interrelated and have reciprocal relationships that link cardiovascular and metabolic diseases. Ultimately, cardiometabolic syndrome increases the risk for cardiovascular events and end-organ damage. Although the number of patients with cardiometabolic syndrome is escalating, therapeutic approaches have not been developed that provide protection to the kidney.

OBJECTIVE

The objective of this review is to provide an overview of the contribution of eicosanoids to renal damage in cardiometabolic syndrome.

RESULTS/CONCLUSION

Eicosanoids are altered in cardiometabolic syndrome and contribute to the progression of renal injury. The antihypertensive and anti-inflammatory actions of epoxides and soluble epoxide hydrolase inhibitors make these attractive eicosanoid therapeutic targets for chronic kidney disease in patients with cardiometabolic syndrome.

Potencial terapêutico para a prevenção e tratamento da nefropatia e neuropatia diabéticas: evidências do uso do cilostazol

O cilostazol é um inibidor seletivo da fosfodiesterase tipo III com ação vasodilatadora, antiagregante plaquetária e antitrombótica. É considerada a droga de primeira escolha na claudicação intermitente devido à doença arterial obstrutiva periférica. Vários estudos demonstraram melhora significativa na distância percorrida na caminhada sem dor e na qualidade de vida, sem aumentar o risco de sangramento. Essas ações também foram verificadas em pacientes diabéticos, pois o cilostazol não afeta o metabolismo da glicose. Estudos, principalmente experimentais, têm mostrado resultados satisfatórios na melhora do fluxo sangüíneo neural, na atividade da bomba de sódio e potássio, na resistência à insulina e na microalbuminúria. Neste artigo, apresentamos uma revisão do uso do cilostazol na prevenção e no tratamento das complicações do diabetes mellitus, como nefropatia e neuropatia. Ressalta-se a necessidade do controle adequado dos níveis glicêmicos, da hipertensão arterial sistêmica e do tabagismo. Um maior número de estudos clínicos é necessário para melhor compreensão desses efeitos benéficos.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Rofecoxib decreases renal injury in obese Zucker rats

The present study tested the hypothesis that altered vascular regulation of arachidonic acid enzymes in obese Zucker rats contributes to renal damage. Protein expression of CYP450 (cytochrome P450) and COX (cyclo-oxygenase) enzymes in renal microvessels was studied in obese and lean Zucker rats at 20–21 weeks of age. Body weight and blood glucose averaged 649±13 g and 142±10 mg/dl in obese Zucker rats compared with 437±10 g and 111±5 mg/dl in age-matched lean Zucker rats. Renal microvascular CYP4A and COX-2 protein levels were increased and CYP2C protein levels decreased in obese Zucker rats. TX (thromboxane) B2 excretion was 2-fold higher and PG (prostaglandin) E2 excretion significantly lower in obese Zucker rats. Additional studies investigated the ability of the COX-2 inhibitor, rofecoxib, to slow the progression of renal injury in obese Zucker rats. Rofecoxib treatment decreased urinary PGF2α and 8-isoprostane levels in obese Zucker rats. Renal microvessel mRNA expression of pro-inflammatory chemokines was decreased in COX-2-inhibitor-treated obese Zucker rats. Urinary albumin excretion, an index of kidney damage, averaged 95±11 mg/day in vehicle-treated and 9±1 mg/day in rofecoxib-treated obese Zucker rats. Glomerulosclerosis, characterized by mesangial expansion, tubulo-interstitial fibrosis and extracellular matrix accumulation, was prominent in obese Zucker rats compared with a lack of damage in age-matched lean Zucker rats and rofecoxib-treated obese Zucker rats. These results suggest that altered vascular arachidonic acid enzymes contribute to the renal damage, and that COX-2 inhibition decreases glomerular injury in obese Zucker rats.

Altered kidney CYP2C and cyclooxygenase-2 levels are associated with obesity-related albuminuria

OBJECTIVE

To determine cytochrome P450 (CYP450) and cyclooxygenase (COX) expression and metabolite regulation and renal damage in the early stages of obesity-related hypertension and diabetes.

RESEARCH METHODS AND PROCEDURES

Obese and lean Zucker rats at 10 to 12 weeks of age were studied. Blood pressure was measured in the conscious state using radiotelemetry. Blood glucose levels and body weight were measured periodically. Protein expression of CYP450 and COX enzymes in the kidney cortex, renal microvessels, and glomeruli was studied. The levels of CYP450 and COX metabolites in urine were measured, and urinary albumin excretion, an indicator of kidney damage, was measured.

RESULTS

Body weight and blood glucose averaged 432 +/- 20 grams and 105 +/- 5 mg/dl, respectively, in obese Zucker rats as compared with 320 +/- 8 grams and 91 +/- 5 mg/dl, respectively, in age-matched 10- to 12-week-old lean Zucker rats. Renal microvascular CYP4A and COX-2 protein levels were increased 2.3- and 17.0-fold, respectively, in obese Zucker rats. The protein expression of CYP2C11 and CYP2C23 was decreased 2.0-fold in renal microvessels isolated from obese Zucker rats when compared with lean Zucker rats. The urinary excretion rate of thromboxane B(2) was increased significantly in obese Zucker as compared with lean Zucker rats (22.0 +/- 1.8 vs. 13.4 +/- 1.0 ng/d). Urinary albumin excretion, an index of kidney damage, was increased in the obese Zucker rat at this early age.

DISCUSSION

These results suggest that increased CYP4A and COX-2 protein levels and decreased CYP2C11 and CYP2C23 protein levels occur in association with microalbuminuria during the onset of obesity-related hypertension and type 2 diabetes.

Effect of acute thromboxane A2 inhibition on the renal hemodynamics in a spontaneously non-insulin-dependent diabetic rat, Otsuka Long-Evans Tokushima Fatty rat

Thromboxane (TX) A2 plays important roles on renal injuries in streptozotocin (STZ)-induced diabetic rats, whereas its role on the renal injuries in non-insulin-dependent diabetic (NIDDM) rats remains unknown. We evaluated the effects of an intravenous infusion of TXA2 synthetase inhibitor (OKY-046, 6 mg/kg/h) on the clearances on inulin and para-aminohippurate (Cin, C(PAH)) in a spontaneously NIDDM rats, Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 8), and Long-Evans Tokushima Otsuka (LETO) rats (n = 7), served as control rats, at the age of 40-44 weeks. OLETF rats showed obesity, moderate hyperglycemia, and hyperinsulinemia. Urinary excretion of TXB2 was slightly higher and the ratio of TXB2 to 6-keto prostaglandin F1alpha (6-kPG) was significantly higher in OLETF rats (TXB2/6-kPG: 0.22 +/- 0.04 versus 0.12 +/- 0.02, P < 0.05). Both Cin and C(PAH) were significantly higher in OLETF rats than in LETO rats (Cin: 1.1 +/- 0.1 versus 0.7 +/- 0.1 mL/min/100 g BW, C(PAH): 3.1 +/- 0.2 versus 2.3 +/- 0.3 mL/min/100gBW, P < 0.01). OKY-046 did not restore Cin and C(PAH) in OLETF rats although it significantly decreased urinary excretion of TXB2, and thus ameliorated TXB2/6-kPG in OLETF rats. These data suggested that TXA2 was not involved in the renal hyperfiltration in OLETF rats at the age of 40-44 weeks, and that TXA2 might contribute to renal injuries in OLETF rats through mechanisms other than hemodynamic injury.

Effects of intravenous cilostazol on optic nerve head and choroidal blood flow in anesthetized cats

Cilostazol is one of a number of anti-platelet agents used for the treatment of thrombotic disorders, such as chronic arterial obstruction, and is a vasodilator as well. In the present study, cilostazol was intravenously administered to seven anesthetized cats, and the optic nerve head (ONH) and choroidal blood flows were continuously monitored in a noninvasive method using laser Doppler flowmetry. The systemic blood pressure dropped significantly by 4+/-4% (p<0.05) with cilostazol 0.03 microg/kg/min, although there were no significant changes in ONH and choroidal blood flows. When the drug was given at 0.1 microg/kg/min, ONH blood flow remained significantly higher than the baseline, 54+/-37% (p<0.05) at maximum, immediately after the start of administration. Soon after the start of the infusion, a significant decrease, 17+/-10% (p<0.05) at maximum, in choroidal blood flow occurred, but this was followed by a significant increase, 35+/-27% (p<0.05) at maximum. At that time, the systemic blood pressure dropped significantly by 14+/-6% (p<0.05). These findings indicate that an intravenous administration of cilostazol increases both ONH and choroidal blood flows, suggesting the potential usefulness of cilostazol for both prophylactic and therapeutic management of ophthalmic circulatory disorders.