High fat diet enhances cardiac abnormalities in SHR rats: Protective role of heme oxygenase-adiponectin axis

Background High dietary fat intake is a major risk factor for development of cardiovascular and metabolic dysfunction including obesity, cardiomyopathy and hypertension. Methods The present study was designed to examine effect of high fat (HF) diet on cardio-vascular structure and function in spontaneously hypertensive rats (SHR), fed HF diet for 15 weeks, a phenotype designed to mimic metabolic syndrome. Results Development of metabolic syndrome like phenotype was confirmed using parameters, including body weight, total cholesterol and blood pressure levels. High fat diet impaired vascular relaxation by acetylcholine and exacerbated cardiac dysfunction in SHRs as evidenced by lower left ventricular function, and higher coronary resistance (CR) as compared to controls (p \u3c 0.05). The histological examination revealed significant myocardial and peri-vascular fibrosis in hearts from SHRs on HF diet. This cardiac dysfunction was associated with increased levels of inflammatory cytokines, COX-2, NOX-2, TxB2 expression and increase in superoxide (O2-) levels in SHR fed a HF diet (p \u3c 0.05). HO-1 induction via cobalt-protoporphyrin (CoPP,3 mg/kg), in HF fed rats, not only improved cardiac performance parameters, but also prevented myocardial and perivascular fibrosis. These effects of CoPP were accompanied by enhanced levels of cardiac adiponectin levels, pAMPK, peNOS and iNOS expression; otherwise significantly attenuated (p \u3c 0.05) in HF fed SHRs. Prevention of such beneficial effects of CoPP by the concurrent administration of the HO inhibitor stannic mesoporphyrin (SnMP) corroborates the role of HO system in mediating such effects. Conclusion In conclusion, this novel study demonstrates that up-regulation of HO-1 improves cardiac and vascular dysfunction by blunting oxidative stress, COX-2 levels and increasing adiponectin levels in hypertensive rats on HF diet

Antioxidants Condition Pleiotropic Vascular Responses to Exogenous H2O2: Role of Modulation of Vascular TP Receptors and the Heme Oxygenase System

Aims: Hydrogen peroxide (H(2)O(2)), a nonradical oxidant, is employed to ascertain the role of redox mechanisms in regulation of vascular tone. Where both dilation and constriction have been reported, we examined the hypothesis that the ability of H(2)O(2) to effect vasoconstriction or dilation is conditioned by redox mechanisms and may be modulated by antioxidants. Results: Exogenous H(2)O(2) (0.1-10.0 μM), dose-dependently reduced the internal diameter of rat renal interlobular and 3rd-order mesenteric arteries (p\u3c0.05). This response was obliterated in arteries pretreated with antioxidants, including tempol, pegylated superoxide dismutase (PEG-SOD), butylated hydroxytoluene (BHT), and biliverdin (BV). However, as opposed to tempol or PEG-SOD, BHT & BV, antioxidants targeting radicals downstream of H(2)O(2), also uncovered vasodilation. Innovations: Redox-dependent vasoconstriction to H(2)O(2) was blocked by inhibitors of cyclooxygenase (COX) (indomethacin-10 μM), thromboxane (TP) synthase (CGS13080-10 μM), and TP receptor antagonist (SQ29548-1 μM). However, H(2)O(2) did not increase vascular thromboxane B(2) release; instead, it sensitized the vasculature to a TP agonist, U46619, an effect reversed by PEG-SOD. Antioxidant-conditioned dilatory response to H(2)O(2) was accompanied by enhanced vascular heme oxygenase (HO)-dependent carbon monoxide generation and was abolished by HO inhibitors or by HO-1 & 2 antisense oligodeoxynucleotides treatment of SD rats. Conclusions: These results demonstrate that H(2)O(2) has antioxidant-modifiable pleiotropic vascular effects, where constriction and dilation are brought about in the same vascular segment. H(2)O(2)-induced oxidative stress increases vascular TP sensitivity and predisposes these arterial segments to constrictor prostanoids. Conversely, vasodilation is reliant upon HO-derived products whose synthesis is stimulated only in the presence of antioxidants targeting radicals downstream of H(2)O(2)

Decreased tubuloglomerular feedback (TGF) response in high-fat diet induced obesity

Obesity is associated with increased renal and glomerular damage and hypertension, but the mechanisms are not clear. Normally, kidneys autoregulate to keep the glomerular capillary pressure (PGC), renal blood flow and glomerular filtration rate in a steady state. In obesity, the kidney loses its autoregulatory capacity, leading to higher PGC, renal blood flow and glomerular filtration rate. Together, these may lead to glomerular damage. PGC is controlled mainly by the afferent arteriole (Af-Art) resistance. Af-Art resistance in turn is regulated by an intrinsic renal feedback mechanism known as tubuloglomerular feedback (TGF). TGF causes Af-Art constriction in response to an increase in sodium chloride (NaCl) in the macula densa, via the Na-K-2Cl cotransporter NKCC2. We previously found that in the Zucker rat model of obesity, TGF was decreased and this was associated with higher blood pressure (BP) and proteinuria. However, it is not known whether obesity induced by a high fat diet in normal Sprague Dawley (SD) rats could also affect TGF. We hypothesized that TGF would be attenuated in obesity caused by 16 weeks of high fat fed (HFD) feeding (60% fat) in SD rats. SD rats fed normal-fat diet (12% fat, NFD) served as control. HFD fed rats exhibited higher body weight (HFD: 833.7±33.3 vs. NFD: 682.3±24.8 grams, p\u3c0.05) and were hypertensive under Inactin anesthesia (mean BP HFD: 131.4±3.6 vs.115.8±3.8 mmHg, p\u3c0.05). We performed in-vivo renal micropuncture of individual rat nephrons while measuring stop-flow pressure (PSF), an index of PGC PSF decreases with an increase in Af-Art resistance. TGF response was measured as a decrease in PSF induced by changing the rate of late proximal perfusion from 0 to 40nl/min. Maximal TGF response was significantly smaller in HFD fed rats compared to the NFD rats (HFD: 4.1±0.9 vs. NFD: 10.2±0.6 mmHg, p\u3c0.05) indicating attenuation of TGF by HFD. Baseline PGC was higher in HFD rats compared to NFD rats (HFD: 41.6±0.8 vs. NFD: 38.7.2±0.5 mmHg, p\u3c0.05). We conclude that TGF is attenuated in HFD fed obese SD rats and this may contribute to increased renal blood flow and GFR observed in obesity. Hypertension, combined with an attenuated TGF response and increased PGC may explain higher renal damage caused by obesity

Expression of ALMS1 in podocytes: possible role in filtration function

Previously, we identified Alstrom Syndrome 1 (ALMS1) as an interacting partner of NKCC2 in the Thick Ascending limb of the loop of Henle (TAL). Mutations in the ALMS1 gene in humans cause Alström syndrome, characterized by progressive metabolic alterations that include obesity, hypertension, and chronic kidney disease (CDK). SNPs in ALMS1 are associated with lower GFR in GWAS. However, role of ALMS1 in glomerular filtration has not been studied. We hypothesized that ALMS1 is expressed in glomerular podocytes where it may play a role in podocyte filtration function. To begin studying this, we localized ALMS1 expression to podocytes by immunofluorescence labeling of Actinin-4, abundantly expressed in podocytes, and ALMS1. Confocal imaging showed that ALMS1 is co-localized with Actinin-4 in rat podocytes. In addition, ALMS1 was also expressed in an immortalized mouse podocyte cell line, as was Actinin-4 and nephrin, as measured by Western blot and immunofluorescence microscopy. To determine if ALMS1 plays a role in podocyte pathology we measured nephrin expression in ALMS1 KO rats. These rats were generated in the Dahl SS genetic background and are hypertensive on a normal salt diet. We found that nephrin expression in renal cortical lysates was decreased by 61±08% (p\u3c0.05, n=7) in ALMS1 KO rats. To study if ALMS1 deletion could play a role in filtration barrier function we measured albumin/creatinine ratio in urine samples from 14-16 weeks old wild type (WT) and ALMS1 KO rats. In ALMS1 KO rats, urinary albumin excretion was higher than control rats (WT: 4±2; ALMS1 KO: 26±6, n=6, p\u3c0.05). Taken together, our data show that ALMS1 is expressed in rat and mouse podocytes where it may play a role in filtration barrier function by maintaining podocyte biology

Role of connecting tubule glomerular feedback in obesity related renal damage

Zucker obese rats (ZOR) have higher glomerular capillary pressure (PGC) that can cause renal damage. PGC is controlled by afferent (Af-Art) and efferent arteriole (Ef-Art) resistance. Af-Art resistance is regulated by factors that regulate other arterioles, such as myogenic response. In addition, it is also regulated by 2 intrinsic feedback mechanisms: 1) tubuloglomerular feedback (TGF) that causes Af-Art constriction in response to increased NaCl in the macula densa and 2) connecting tubule glomerular feedback (CTGF) that causes Af-Art dilatation in response to an increase in NaCl transport in the connecting tubule via the epithelial sodium channel. Since CTGF is an Af-Art dilatory mechanism, we hypothesized that increased CTGF contributes to TGF attenuation, which in turn increases PGC in ZOR. We performed a renal micropuncture experiment and measured stop-flow pressure (PSF), which is an indirect measurement of PGC in ZOR. Maximal TGF response at 40 nl/min was attenuated in ZOR (4.47 ± 0.60 mmHg) in comparison to the Zucker lean rats (ZLR; 8.54 ± 0.73 mmHg, P \u3c 0.05), and CTGF was elevated in ZOR (5.34 ± 0.87 mmHg) compared with ZLR (1.12 ± 1.28 mmHg, P \u3c 0.05). CTGF inhibition with epithelial sodium channel blocker normalized the maximum PSF change in ZOR indicating that CTGF plays a significant role in TGF attenuation (ZOR, 10.67 ± 1.07 mmHg vs. ZLR, 9.5 ± 1.53 mmHg). We conclude that enhanced CTGF contributes to TGF attenuation in ZOR and potentially contribute to progressive renal damage

Role of connecting tubule glomerular feedback in obesity related renal damage

Zucker obese rats (ZOR) have higher glomerular capillary pressure (PGC) that can cause renal damage. PGC is controlled by afferent (Af-Art) and efferent arteriole (Ef-Art) resistance. Af-Art resistance is regulated by factors that regulate other arterioles, such as myogenic response. In addition, it is also regulated by 2 intrinsic feedback mechanisms: 1) tubuloglomerular feedback (TGF) that causes Af-Art constriction in response to increased NaCl in the macula densa and 2) connecting tubule glomerular feedback (CTGF) that causes Af-Art dilatation in response to an increase in NaCl transport in the connecting tubule via the epithelial sodium channel. Since CTGF is an Af-Art dilatory mechanism, we hypothesized that increased CTGF contributes to TGF attenuation, which in turn increases PGC in ZOR. We performed a renal micropuncture experiment and measured stop-flow pressure (PSF), which is an indirect measurement of PGC in ZOR. Maximal TGF response at 40 nl/min was attenuated in ZOR (4.47 ± 0.60 mmHg) in comparison to the Zucker lean rats (ZLR; 8.54 ± 0.73 mmHg, P \u3c 0.05), and CTGF was elevated in ZOR (5.34 ± 0.87 mmHg) compared with ZLR (1.12 ± 1.28 mmHg, P \u3c 0.05). CTGF inhibition with epithelial sodium channel blocker normalized the maximum PSF change in ZOR indicating that CTGF plays a significant role in TGF attenuation (ZOR, 10.67 ± 1.07 mmHg vs. ZLR, 9.5 ± 1.53 mmHg). We conclude that enhanced CTGF contributes to TGF attenuation in ZOR and potentially contribute to progressive renal damage

Decreased tubuloglomerular feedback response in high-fat diet-induced obesity

Obesity increases the risk of renal damage, but the mechanisms are not clear. Normally, kidneys autoregulate to keep the glomerular capillary pressure (P(GC)), renal blood flow, and glomerular filtration rate in a steady state. However, in obesity, higher P(GC), renal blood flow, and glomerular filtration rate are noted. Together, these may lead to glomerular damage. P(GC) is controlled mainly by afferent arteriole resistance, which, in turn, is regulated by tubuloglomerular feedback (TGF), a vasoconstrictor mechanism. High fat-induced obesity causes renal damage, and this may be related to increased P(GC). However, there are no studies as to whether high-fat diet (HFD)-induced obesity affects TGF. We hypothesized that TGF would be attenuated in obesity caused by HFD feeding (60% fat) in Sprague-Dawley rats. Sprague-Dawley rats fed a normal-fat diet (NFD; 12% fat) served as the control. We studied 4 and 16 wk of HFD feeding using in vivo renal micropuncture of individual rat nephrons. We did not observe significant differences in body weight, TGF response, and mean arterial pressure at 4 wk of HFD feeding, but after 16 wk of HFD, rats were heavier and hypertensive. The maximal TGF response was smaller in HFD-fed rats than in NFD-fed rats, indicating an attenuation of TGF in HFD-induced obesity. Baseline P(GC) was higher in HFD-fed rats than in NFD-fed rats and was associated with higher glomerulosclerosis. We conclude that attenuated TGF and higher P(GC) along with hypertension in HFD-fed obese Sprague-Dawley rats could explain the higher propensity of glomerular damage observed in obesity. NEW & NOTEWORTHY Reduced tubuloglomerular feedback, higher glomerular capillary pressure, and hypertension in combination may explain the higher glomerular damage observed in high-fat diet-induced obesity

FIGURE 5 in A new species of Cylloceria Schiødte, 1838 (Hymenoptera, Ichneumonidae) from the Oriental Region

FIGURE 5. Cylloceria ebbae sp. nov. ♂ (Paratype). A: head, anterior view; B: head, dorsal view; C: head and mesosoma, dorsal view; D: mesosoma, lateral view; E: posterior part of mesosoma and T1, lateral view; F: apex of metasoma and parameres, lateral view

Role of Alström syndrome 1 in the regulation of glomerular hemodynamics

Inactivating mutations in the ALMS1 gene in humans cause Alström syndrome, characterized by the early onset of obesity, insulin resistance, and renal dysfunction. However, the role of ALMS1 in renal function and hemodynamics is unclear. We previously found that ALMS1 is expressed in thick ascending limbs, where it binds and decreases Na(+)-K(+)-2Cl(-) cotransporter activity. We hypothesized that ALMS1 is expressed in macula densa cells and that its deletion enhances tubuloglomerular feedback (TGF) and reduces glomerular filtration rate (GFR) in rats. To test this, homozygous ALMS1 knockout (KO) and littermate wild-type Dahl salt-sensitive rats were studied. TGF sensitivity was higher in ALMS1 KO rats as measured by in vivo renal micropuncture. Using confocal microscopy, we confirmed immunolabeling of ALMS1 in macula densa cells (nitric oxide synthase 1 positive), supporting a role for ALMS1 in TGF regulation. Baseline glomerular capillary pressure was higher in ALMS1 KO rats, as was mean arterial pressure. Renal interstitial hydrostatic pressure was lower in ALMS1 KO rats, which is linked to increased Na(+) reabsorption and hypertension. GFR was reduced in ALMS1 KO rats. Seven-week-old ALMS1 KO rats were not proteinuric, but proteinuria was present in 18- to 22-wk-old ALMS1 KO rats. The glomerulosclerosis index was higher in 18-wk-old ALMS1 KO rats. In conclusion, ALMS1 is involved in the control of glomerular hemodynamics in part by enhancing TGF sensitivity, and this may contribute to decreased GFR. Increased TGF sensitivity, enhanced glomerular capillary pressure, and hypertension may lead to glomerular damage in ALMS1 KO rats. These are the first data supporting the role of ALMS1 in TGF and glomerular hemodynamics. NEW & NOTEWORTHY: ALMS1 is a novel protein involved in regulating tubuloglomerular feedback (TGF) sensitivity, glomerular capillary pressure, and blood pressure, and its dysfunction may reduce renal function and cause glomerular damage