Beneficial effects of fenoldopam treatment on renal function in streptozotocin-induced diabetic rats

Dopamine 1 receptor activation protects mouse diabetic podocytes injury via regulating the PKA/NOX-5/p38 MAPK axis

Diabetic nephropathy (DN) is a major microvascular complication of diabetes that can lead to end-stage renal disease. Podocytes constitute the last barrier of glomerular filtration, whose damage are the direct cause of proteinuria. Dopamine receptors are involved in the regulation of diabetes-induced glomerular hyperfiltration, and only dopamine 1 receptor (D1R) can be amplified in cultured mouse podocytes. However, the exact effect of D1R on diabetic podocytes remains unclear. This study aims to investigate the protective role of D1R activation on diabetic podocytes injury in vivo and vitro as well as its potential mechanism. We observed D1R protective effect respectively in streptozotocin (STZ)-induced type 1 diabetes (T1D) mice as well as mouse podocytes (MPC5) cultured in high glucose (HG, 40 mM) medium. It showed that D1R and podocyte-associated proteins (Podocin, CD2AP and Nephrin) expression were significantly decreased both in the T1D mice (fed for 8 and 12 weeks) and HG-cultured MPC5 cells, while the NOX-5 expression increased. In T1D mice, the levels of 24-h urine protein, serum creatinine and urinary 8-OHdG were increased in a time-dependent manner, at the same time, hematoxylin-eosin (HE) staining and electron microscope observed the kidney lesion and podocytes injury. In vitro, HG induced podocytes oxidative stress and apoptosis, which could be inhibited by SKF38393 (a D1R agonist) and N-acetyl-l-cysteine (NAC, a reactive oxygen species scavenger). Furthermore, there was a decreasing Podocin expression and a significant increasing NOX-5 expression in podocytes transfected with D1R-small interfering RNA (siRNA). More importantly, the expression of phospho-CREB (the PKA downstream transcription factor) was decreased and phospho-p38 MAPK was increased in HG-induced podocytes, which can respectively be activated or blocked by SKF38393, 8-Bromo-CAMP (a PKA activator), NAC, and SB20380 (a p38 MAPK inhibitor). In conclusion, D1R activation can protect diabetic podocytes from apoptosis and oxidative damage, in part through the PKA/NOX-5/p38 MAPK pathway.

Sorting nexin 5 and dopamine d1 receptor regulate the expression of the insulin receptor in human renal proximal tubule cells

Sorting nexin 5 (SNX5) belongs to the SNX family, which is composed of a diverse group of proteins that mediate trafficking of plasma membrane proteins, receptors, and transporters. SNX5 is important in the resensitization of the dopamine D1-like receptor (D1R). D1R is uncoupled from its effector proteins in hypertension and diabetes, and treatment of diabetes restores D1R function and insulin receptor (IR) expression. We tested the hypothesis that the D1R and SNX5 regulate IR by studying the expression, distribution, dynamics, and functional consequences of their interaction in human renal proximal tubule cells (hRPTCs). D1R, SNX5, and IR were expressed and colocalized in the brush border of RPTs. Insulin promoted the colocalization of SNX5 and IR at the perinuclear area of hRPTCs. Unlike SNX5, the D1R colocalized and coimmunoprecipitated with IR, and this interaction was enhanced by insulin. To evaluate the role of SNX5 and D1R on IR signaling, we silenced via RNA interference the endogenous expression of SNX5 or the D1R gene DRD1 in hRPTCs. We observed a decrease in IR expression and abundance of phosphorylated IR substrate and phosphorylated protein kinase B, which are crucial components of the IR signal transduction pathway. Our data indicate that SNX5 and D1R are necessary for normal IR expression and activity. It is conceivable that D1R and SNX5 may interact to increase the sensitivity to insulin via a positive regulation of IR and insulin signaling.

Dopamine D₄ receptors inhibit proliferation and migration of vascular smooth muscle cells induced by insulin via down-regulation of insulin receptor expression

Vascular smooth muscle cells (VSMCs) proliferation and migration, which are central in the development of vascular diseases, are regulated by numerous hormones and humoral factors. Activation of the insulin receptor stimulates VSMCs proliferation while dopamine receptors, via D₁ and D₃ receptors, inhibit the stimulatory effects of norepinephrine on VSMCs proliferation. We hypothesize that activation of the D₄ dopamine receptor may also inhibit the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. Our current study found that insulin increased the proliferation and migration of A10 cells, an effect that was reduced in the presence of a D₄ receptor agonist, PD168077. The negative effect of the D₄ receptor on insulin’s action may be via decreasing insulin receptor expression, because activation of the D₄ receptor inhibited insulin receptor protein and mRNA expressions, indicating that the regulation occured at the transcriptional or post-transcriptional levels. To determine whether or not the inhibition of D₄ receptor on insulin-mediated proliferation and migration of VSMCs has physiological significance, hyper-insulinemic Sprague–Dawley rats with balloon-injured carotid artery were treated with a D₄ agonist, PD168077, (6 mg/kg/d) for 14 days. We found that PD168077 significantly inhibited neointimal formation by inhibition of VSMC proliferation. This study suggests that activation of the D₄ receptor suppresses the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. The D₄ receptor may be a potential therapeutic target to reduce the effects of insulin on artery remodeling.

Synthesis and hypoglycemic activity of some new theophylline derivatives

Thirty-one new theophylline derivatives have been synthesized and evaluated for their hypoglycemic activity. Compounds 24 (56% reduction) and 31 (57% reduction) showed better hypoglycemic activity than the standard drug glibenclamide which showed 52% reduction in serum glucose level. Compound 27 remarkably reduced serum glucose level by 53%. Ten compounds showed varying degrees of hypoglycemic activity ranging from 20 to 37% reduction in serum glucose level compared to the standard drug. The aromatic amide functionality is the common feature of these theophylline hypoglycemic derivatives. However, anthranilamide and or aliphatic amides proved to be the least active compounds in the present series.

Intrarenal dopamine inhibits progression of diabetic nephropathy

The kidney has a local intrarenal dopaminergic system, and in the kidney, dopamine modulates renal hemodynamics, inhibits salt and fluid reabsorption, antagonizes the renin-angiotensin system, and inhibits oxidative stress. The current study examined the effects of alterations in the intrarenal dopaminergic system on kidney structure and function in models of type 1 diabetes. We studied catechol-O-methyl-transferase (COMT)(-/-) mice, which have increased renal dopamine production due to decreased dopamine metabolism, and renal transplantation was used to determine whether the effects seen with COMT deficiency were kidney-specific. To determine the effects of selective inhibition of intrarenal dopamine production, we used mice with proximal tubule deletion of aromatic amino acid decarboxylase (ptAADC(-/-)). Compared with wild-type diabetic mice, COMT(-/-) mice had decreased hyperfiltration, decreased macula densa cyclooxygenase-2 expression, decreased albuminuria, decreased glomerulopathy, and inhibition of expression of markers of inflammation, oxidative stress, and fibrosis. These differences were also seen in diabetic mice with a transplanted kidney from COMT(-/-) mice. In contrast, diabetic ptAADC(-/-) mice had increased nephropathy. Our study demonstrates an important role of the intrarenal dopaminergic system to modulate the development and progression of diabetic kidney injury and indicate that the decreased renal dopamine production may have important consequences in the underlying pathogenesis of diabetic nephropathy.

Synthesis and biological evaluation of some novel cyclic-imides as hypoglycaemic, anti-hyperlipidemic agents

Certain new halogenated cyclic-imides related to N-substituted phthalimide moiety were synthesized. Spacers of one or two carbon atom distances were inserted to connect the N-terminus of the cyclic-imide nuclei to the used heteroaryl groups to evaluate the effect of such alteration on biological activity. The synthesized compounds were subjected to hypoglycaemic and anti-hyperlipidemic evaluation. Some of the tested compounds proved to be more potent than the reference drugs glibenclamide and clofibrate. Compound 5e remarkably reduced serum glucose level by 55%; while 5c, 5e, 7d and 8e reduced total serum cholesterol by 58, 56, 54 and 53%, respectively. Those new cyclic-imides could be considered as useful template for future development to obtain more potent hypoglycaemic and anti-hyperlipidemic agents.

Effects ofFicus thonningii(Blume) [Morarceae] Stem-Bark Ethanolic Extract on Blood Glucose, Cardiovascular and Kidney Functions of Rats, and on Kidney Cell Lines of the Proximal (LLC-PK1) and Distal Tubules (MDBK)

Previous observations indicate that Ficus thonningii (Blume) [Moraceae] stem-bark extracts may be useful in the control of diabetes mellitus. Accordingly, we investigated in some experimental animal paradigms the effects of F. thonningii stem-bark ethanolic extract (FTE) on renal and cardiovascular functions as complications of diabetes. Oral glucose tolerance tests were conducted in separate groups of non-diabetic and STZ-treated diabetic rats given glucose load (0.86 g x kg(-1), p.o.) after 18-h fast, followed by various FTE doses (60, 120, and 240 mg x kg(-1)). Rats treated with deionized water (3 mL x kg(-1) p.o.), or metformin (500 mg x kg(-1) p.o.) acted as untreated and treated positive controls, respectively. Blood glucose was monitored at 15-min intervals for the first hour, and hourly thereafter for 3 h. Acute effects of FTE on kidney function and mean arterial blood pressure (MAP) were investigated in anaesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4 h of 1 h control, 1.5 h treatment, and 1.5 h recovery periods. FTE was added to the infusate during the treatment period. Chronic effects of FTE were studied in individually caged rats treated daily with FTE (120 mg x kg(-1), p.o.) for five weeks. Cytotoxicity of FTE was assessed by dye-reduction colorimetric (MTT) assay on MDBK and LLCPK1 kidney cell lines exposed for 24 h, 48 h, and 72 h to graded concentrations of the extract. Myocardial contractile performance was evaluated on rat isolated atrial muscle strips. FTE, like metformin, decreased blood glucose levels in non-diabetic and STZ-diabetic rats. Both acute and chronic FTE treatments did not affect renal function. In vitro studies demonstrated that FTE increased MDBK cell metabolic activity by an average of 15% (72 h), and LLCPK1 mirrored the controls. Acute intravenous infusion of FTE reduced the MAP from 119 +/- 1 mmHg to 98 +/- 4 mmHg. The MAP also was reduced throughout the five-week experimental study period. FTE also produced concentration-dependent, negative inotropic and chronotropic effects on rat isolated, electrically driven left-, and spontaneously beating right-, atrial muscle preparations. Our experimental findings suggest that FTE possesses reno- and cardio-protective effects in diabetes mellitus.

Diabetes induces changes of catecholamines in primary mesangial cells

Diabetes mellitus is a frequent cause of kidney function damage with diabetic nephropathy being predominantly related to glomerular dysfunction. Diabetes is capable of interfering with distinct hormonal systems, as well as catecholamine metabolism. Since mesangial cells, the major constituent of renal glomerulus, constitute a potential site for catecholamine production, the present study was carried out to investigate alterations in catecholamine metabolism in cultured mesangial cells from the nonobese diabetic mouse, a well-established model for type I diabetes. We evaluated mesangial cells from normoglycemic and hyperglycemic nonobese diabetic mice, as well as cells from normoglycemic Swiss mice as control. Mesangial cells from normoglycemic mice presented similar profiles concerning all determinations. However, cells isolated from hyperglycemic animals presented increased dopamine and norepinephrine production/secretion. Among the studied mechanisms, we observed an upregulation of tyrosine hydroxylase expression accompanied by increased tetrahydrobiopterin consumption, the tyrosine hydroxylase enzymatic cofactor. However, this increase in synthetic pathways was followed by decreased monoamine oxidase activity, which corresponds to the major metabolic pathway of catecholamines in mesangial cells. In addition, whole kidney homogenates from diabetic animals also presented increased dopamine and norepinephrine levels when compared to normoglycemic animals. Thus, our results suggest that diabetes alters catecholamine production by interfering with both synthesizing and degrading enzymes, suggesting a possible role of catecholamine in the pathogenesis of acute and chronic renal complications of diabetes mellitus.

Comparative evaluation of atenolol and metoprolol on cardiovascular complications associated with streptozotocin-induced diabetic rats

Recently, various clinical studies have indicated that lipophilic β-blockers reduce the coronary mortality in diabetic patients; however, systematic studies have not been reported. The objective of the present investigation was to compare the effects of chronic treatment with metoprolol and atenolol on cardiovascular complications in streptozotocin (STZ)-induced diabetic rats. Injection of STZ produced hyperglycemia, hypoinsulinemia, hyperlipidemia, increased blood pressure, cardiac hypertrophy, reduction in heart rate, and structural alterations in cardiac tissues. Metoprolol and atenolol effectively prevented the development of hypertension in diabetic rats. Metoprolol treatment produced a slight but significant reduction in serum glucose levels with elevation in serum insulin levels, while atenolol produced a slight increase in glucose levels but no effect on insulin levels. Moreover, neither metoprolol nor atenolol treatment reduced the elevated cholesterol levels in diabetic rats. Metoprolol treatment significantly prevented STZ-induced increase in triglyceride levels, but atenolol failed to produce this effect. Metoprolol exhibited a minimal improvement in STZ-induced bradycardia, whereas atenolol produced a further reduction in heart rate. Histological examination showed metoprolol treatment also prevented STZ-induced hypertrophy and some of the alterations in cardiomyocytes. In conclusion, our data suggest that metoprolol has some beneficial effects over atenolol with respect to cardiovascular complications associated with diabetes mellitus.

Fenoldopam improves corticomedullary oxygen delivery and attenuates angiogenesis gene expression in acute ischemic renal injury

BACKGROUND/AIMS

Vasoactive compounds are known to affect intrarenal hemodynamics and gene transcription, but specific effects of fenoldopam in the setting of acute renal ischemia are not known. We utilized a rat model of acute ischemic nephropathy to test the hypothesis that fenoldopam improves corticomedullary tissue oxygen tension (PtO2) and attenuates angiogenesis gene expression in acute renal ischemia.

METHODS

Rats anesthetized with 50 mg/kg urethane were divided into 4 groups (n = 6 each): (1) sham with infusion of 0.9% saline; (2) sham with infusion of 0.1 microg x kg(-1) x min(-1) fenoldopam; (3) unilateral renal ischemia followed by 6 h of reperfusion with saline, and (4) ischemia/reperfusion with fenoldopam. Renal artery blood flow (RBF), renal cortical perfusion (RCP), and PtO2 were recorded throughout. Total RNA from left kidneys was used to probe microarrays. Gene expression was measured as percent positive control (GAPDH) and confirmed using RT-PCR.

RESULTS

Fenoldopam significantly increased RBF (p < 0.05), RCP (p < 0.01) and PtO2 (p <0.01) in both non-ischemic and post-ischemic kidneys. Fenoldopam attenuated 11 of the 13 ischemia-induced genes and 44 of 78 ischemia-suppressed genes. This attenuation was statistically significant (p < 0.05) for five genes.

CONCLUSION

Data from this rat model of ischemic nephropathy suggest that fenoldopam improves intrarenal hemodynamics and attenuates ischemia-related changes in angiogenesis gene expression.

Involvement of transforming growth factor-beta in regulation of calcium transients in diabetic vascular smooth muscle cells

Altered calcium [Ca2+] transients of vascular smooth muscle cells to vasoconstrictors may contribute to altered regulation of blood flow in diabetes. We postulated that diabetes-induced transforming growth factor (TGF)-beta production contributes to impaired ANG II response of vascular smooth muscle cells in macrovessels and microvessels. Aortic vascular smooth muscle cells isolated from diabetic rats exhibited markedly impaired ANG II-induced cytosolic calcium [Ca2+] signal that was completely restored by pretreatment with anti-TGF-beta antibodies. Similar findings were noted in microvascular smooth muscle cells isolated from preglomerular vessels and cultured in high glucose. The impact of diabetes on [Ca2+] transients was replicated by addition of TGF-beta1 and -beta2 isoforms to aortic smooth muscle cells in culture and diabetic cells had enhanced production of TGF-beta2. In the in vivo condition, TGF-beta1 was increased in diabetic glomeruli, whereas TGF-beta2 was increased in diabetic aorta. The characteristic increase in glomerular filtration surface area found in diabetic rats was prevented by treatment with anti-TGF-beta antibodies, and impaired ANG II-induced aortic ring contraction in diabetic rats was completely restored by anti-TGF-beta antibodies. Impaired vascular dysfunction may be partly due to decreased inositol 1,4,5-trisphosphate receptor (IP3R), as reduced type I IP3R expression was found in diabetic aorta and restored by anti-TGF-beta antibodies. We conclude that TGF-beta plays an important role in the vascular dysfunction of early diabetes by inhibiting calcium transients in vascular smooth muscle cells.

Fenoldopam treatment improves peripheral insulin sensitivity and renal function in STZ-induced type 2 diabetic rats

Dopamine and diabetes mellitus are reported to have close link between them. We have studied the effect of six-week treatment with D1 receptor agonist fenoldopam (1 mg/kg, i.p., daily) on glucose, lipid, and renal profile in streptozotocin (STZ)-induced (non-insulin dependent) type 2 diabetic rats. Streptozotocin (90 mg/kg, i.p.) was injected to two day old Sprague-Dawley pups. Streptozotocin produced hyperglycemia, hyperinsulinemia, hyperlipidemia, hypertension, increase in serum urea and creatinine by the time animals were 10 week old. Treatment with fenoldopam significantly decreased serum glucose, insulin, cholesterol, triglyceride, urea, creatinine, and blood pressure. During oral glucose tolerance test (OGTT), diabetic rats showed increase in AUC(glucose) and AUC(insulin). Fenoldopam significantly decreased AUC(glucose) in diabetic rats. Diabetic rats showed lower insulin sensitivity index (K(TTT)) that was significantly increased by treatment with fenoldopam in diabetic rats. Diabetic rats showed decrease in urinary sodium. Fenoldopam treatment significantly increased urine output as well as urinary sodium indicating reduced sodium retention. Our data indicates fenoldopam treatment improves peripheral insulin sensitivity and renal function in STZ-induced type 2 diabetic rats.