John C. Passmore

Hydrogen sulfide ameliorates hyperhomocysteinemia-associated chronic renal failure

Elevated level of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), is associated with end-stage renal diseases. Hcy metabolizes in the body to produce hydrogen sulfide (H(2)S), and studies have demonstrated a protective role of H(2)S in end-stage organ failure. However, the role of H(2)S in HHcy-associated renal diseases is unclear. The present study was aimed to determine the role of H(2)S in HHcy-associated renal damage. Cystathionine-beta-synthase heterozygous (CBS+/-) and wild-type (WT, C57BL/6J) mice with two kidney (2-K) were used in this study and supplemented with or without NaHS (30 micromol/l, H(2)S donor) in the drinking water. To expedite the HHcy-associated glomerular damage, uninephrectomized (1-K) CBS(+/-) and 1-K WT mice were also used with or without NaHS supplementation. Plasma Hcy levels were elevated in CBS(+/-) 2-K and 1-K and WT 1-K mice along with increased proteinuria, whereas, plasma levels of H(2)S were attenuated in these groups compared with WT 2-K mice. Interestingly, H(2)S supplementation increased plasma H(2)S level and normalized the urinary protein secretion in the similar groups of animals as above. Increased activity of matrix metalloproteinase (MMP)-2 and -9 and apoptotic cells were observed in the renal cortical tissues of CBS(+/-) 2-K and 1-K and WT 1-K mice; however, H(2)S prevented apoptotic cell death and normalized increased MMP activities. Increased expression of desmin and downregulation of nephrin in the cortical tissue of CBS(+/-) 2-K and 1-K and WT 1-K mice were ameliorated with H(2)S supplementation. Additionally, in the kidney tissues of CBS(+/-) 2-K and 1-K and WT 1-K mice, increased superoxide (O(2)(*-)) production and reduced glutathione (GSH)-to-oxidized glutathione (GSSG) ratio were normalized with exogenous H(2)S supplementation. These results demonstrate that HHcy-associated renal damage is related to decreased endogenous H(2)S generation in the body. Additionally, here we demonstrate with evidence that H(2)S supplementation prevents HHcy-associated renal damage, in part, through its antioxidant properties.

Hyperhomocysteinemic Diabetic Cardiomyopathy: Oxidative Stress, Remodeling, and Endothelial-Myocyte Uncoupling

Accumulation of oxidized-matrix (fibrosis) between the endothelium (the endothelial cells embedded among the myocytes) and cardiomyocytes is a hallmark of diabetes mellitus and causes diastolic impairment. In diabetes mellitus, elevated levels of homocysteine activate matrix metalloproteinase and disconnect the endothelium from myocytes. Extracellular matrix functionally links the endothelium to the cardiomyocyte and is important for their synchronization. However, in diabetes mellitus, a disconnection is caused by activated metalloproteinase, with subsequent accumulation of oxidized matrix between the endothelium and myocyte. This contributes to endothelial-myocyte uncoupling and leads to impaired diastolic relaxation of the heart in diabetes mellitus. Elevated levels of homocysteine in diabetes are attributed to impaired homocysteine metabolism by glucose and insulin and decreased renal clearance. Homocysteine induces oxidative stress and is inversely related to the expression of peroxisome proliferators activated receptor (PPAR). Several lines of evidence suggest that ablation of the matrix metalloproteinase (MMP-9) gene ameliorates the endothelial-myocyte uncoupling in diabetes mellitus. Homocysteine competes for, and decreases the PPARγ activity. In diabetes mellitus, endothelial-myocyte uncoupling is associated with matrix metalloproteinase activation and decreased PPARγ activity. The purpose of this review is to discuss the role of endothelial-myocyte uncoupling in diabetes mellitus and increased levels of homocysteine, causing activation of latent metalloproteinases, decreased levels of thioredoxin and peroxiredoxin, and cardiac tissue inhibitor of metalloproteinase (CIMP) in response to antagonizing PPARγ.

Reduced alpha adrenergic mediated contraction of renal preglomerular blood vessels as a function of gender and aging.

As human males age, a decline in baroreflex‐mediated elevation of blood pressure occurs due, at least in part, to a reduction in alpha‐1 adrenergic vasoconstrictor function. Alpha adrenergic constriction is mediated by guanosine triphosphate binding Protein (G Protein) coupled signaling pathways. Alpha‐1 A/C, B, and D adrenergic receptor expressions, measured by GeneChip array, are not reduced during aging in renal blood vessels of male or female rats. Alpha‐1 A GeneChip expression is greater, at all ages studied, in females than in males. Prazosin binding by alpha‐1 adrenergic receptors is greater in young adult female rats than in young adult male rats; however, it is reduced with aging in both male and female rats. G alpha q GeneChip expression declines while expression of adrenergic receptor kinase (GRK2) and tyrosine phosphatases (TyrP) increase with aging in male rats. The declines in alpha‐1 adrenergic receptor binding and G alpha q expression and also the increases in GRK2 and TyrP expression likely relate to the age‐related decline of vasoconstriction in male rats. The information that the expression of alpha‐1 A adrenergic receptors is greater in female rats and (GRK2) expression does not increase during aging could relate to the gender differences in vasoconstrictor function with aging. Gene therapy to ameliorate the age‐related decline in renal function could possibly reduce the need for renal dialysis. Signaling pathways such as those reviewed herein may provide an outline of the molecular pathways needed to move toward successful renal gene therapy for aging individuals. J. Cell. Biochem.

Effect of indomethacin on mesenteric circulation in mongrel dogs

Necrotizing enterocolitis has been attributed to the use of indomethacin (INDO) for medical closure of patent ductus arteriosus. To study the effect of INDO on cardiac output and mesenteric circulation, INDO was given by rectum (0.25 mg/kg, 0.5 mg/kg, 1.25 mg/kg--3 dogs in each group) and the control group received none. The cardiac output and organ blood flow were measured before and 1 hr after INDO with radioactive microspheres using 4 isotopes (Cr53, Ni95, Co57, Sn113). The blood flow to different parts of the GI tract was measured as percent of cardiac output using a gamma counter. Paired t test was used to calculate percent reduction in organ blood flow. During the experiment, there was no reduction in cardiac output in the entire group. Anesthesia had no effect on the control group. In the three INDO treated groups, percent reduction of mucosal blood flow of the stomach (63%, 32%, 68%, p less than 0.01), mid ileum (19%, 59%, 57%, p less than 0.05) and terminal ileum (57%, 35%, 54%, p less than 0.015) was significant. A strong trend in reduction of organ blood flow was noted in other regions. There was no significant change due to different dosages of INDO. The area of ischemia in this dog model corresponds to clinical pathology noted in necrotizing enterocolitis.

Separate hemodynamic roles for chloride and sodium in deoxycorticosterone acetate-salt hypertension.

Abstract It has been reported that both sodium and chloride ions must be injested to induce the elevated blood pressure of deoxycorticosterone acetate (DOCA)-salt-sensitive hypertension. This study was designed to determine the separate roles of the sodium and chloride ions in the altered hemodynamics underlying the high blood pressure. DOCA pellets (75 mg) were implanted in uninephrectomized rats and the animals were then fed one of four diets: (i) high sodium chloride, (ii) high sodium-low chloride, (iii) high chloride-low sodium, or (iv) low sodium chloride. Blood pressures were measured weekly by tail-cuff plethysmography for 5 weeks and the animals were then subjected to a terminal experiment to measure cardiac output by thermodilution technique, renal blood flow by electromagnetic flow probe, and direct arterial pressure. Blood pressure in the DOCA-high NaCl group was significantly greater (P<0.05) compared with that of the DOCA-low NaCl group (160 ± 3 mm Hg vs 124 ± 2 mm Hg, respectively) at 5 weeks after treatment; all other groups were not significantly different from the DOCA-low NaCl group. Cardiac output was significantly greater in DOCA-treated rats consuming diets high in sodium (44 ± 2 ml/min/100 g) or sodium chloride (40 ± 2 ml/min/100 g) compared with animals consuming low sodium chloride (31 ± 2 ml/min/100 g; P < 0.01 for each comparison). Direct intraarterial blood pressure and renal blood flow were used to calculate renal vascular resistance. Renal vascular resistance was increased in those DOCA-treated rats consuming diets high in chloride (42 ± 3 mm Hg/ml/min/100 g) and high sodium chloride (54 ± 3 mm Hg/ml/min/100 g) compared with rats consuming low sodium chloride (30 ± 3 mm Hg/ml/min/100 g; P < 0.01 for each). It appears that elevations in cardiac output are associated with increased dietary sodium and act in synergy with the elevations in renal vascular resistance associated with increased dietary chloride. Increases in both cardiac output and renal vascular resistance are involved in the maintenance of elevated blood pressure in the DOCA-salt-sensitive model of hypertension.

Mechanisms mediating canine renal vasoconstriction induced by nicotine infusion

We investigated the respective contributions of the renin-angiotensin and alpha-adrenergic systems to nicotine-induced, canine, renal vasoconstriction by using saralasin (4 micrograms/kg/min) and phentolamine (25 micrograms/kg/min) blockade respectively. Nicotine infusion (0.024 mg/kg/min) increased mean arterial blood pressure (MABP) (114 +/- 3.0 to 219 +/- 8.0 mmHg) and decreased total renal blood flow (TRBF) (3.12 +/- 0.34 to 1.60 +/- 0.37 ml/min/g). Nicotine infusion produced a significantly lesser blood flow in outer cortex (OC), inner cortex (IC), and outer medulla (OM) compared to control dogs. The intrarenal-artery infusion of saralasin or phentolamine had no effect on the nicotine-induced MABP changes. Phentolamine infusion prior to nicotine resulted in a significantly greater TRBF (P less than 0.01), OC (p less than 0.001), IC (p less than 0.001) and OM (p less than 0.01) flow than in the group that received nicotine only. Saralasin pretreatment prior to nicotine resulted only in a significantly (p less than 0.01) greater OC flow than nicotine only. Our data suggest that while angiotensin II mediates a portion of the action of nicotine on the OC renal vasculature, the alpha adrenergic system predominates as the mediator of nicotine-induced renal vasoconstriction in the first 7 minutes of nicotine infusion.

Effects of indomethacin on hemodynamics of dogs in refractory hemorrhagic shock

Abstract We examined the effects of indomethacin upon anesthetized control dogs and dogs in refractory hemorrhagic shock. Systemic arterial pressure, central venous pressure, cardiac output, and blood flow to the kidney, the heart, the brain, a small intestinal segment, and a piece of skeletal muscle were measured. Systemic vascular resistance and resistances of the vascular beds of the kidney, the heart, the brain, a small intestinal segment, and a piece of skeletal muscle were calculated. Blood flow distribution within the renal cortex was also examined. Indomethacin treatment had little effect upon dogs that were not in shock. Blood flow to the skeletal muscle was decreased. There was also a redistribution of blood flow within the renal cortex with a greater proportion of renal cortical flow going to the outer cortex. However, systemic vascular resistance, cardiac output, and blood flow to the heart, kidneys, brain, and small intestine were unchanged. The refractory shock state was characterized by low systemic arterial pressure and cardiac output with vascular resistance identical to control. Blood flow to the kidney and brain appears to be decreased while coronary flow is maintained. In addition, the ratio of outer renal cortical blood flow to inner renal cortical blood flow, which in the control dog was about 1.5, decreases to 1. Indomethacin treatment largely reversed the hypotension of refractory shock. The increase in arterial pressure following indomethacin treatment is the result of an increase in systemic vascular resistance. Indomethacin treatment had no effect upon cardiac output. The vascular resistances of the kidney, heart, brain, and small intestine increased following treatment of dogs in refractory shock with indomethacin. Renal blood flow was decreased 57%. The renal cortical blood flow distribution was shifted toward the outer cortex as in the controls. Substances dependent upon prosta glandin synthetase may be involved in the hypotension that is characteristic of refractory hemorrhagic shock and may be important in maintaining blood flow to the kidneys and gut.

Differential expression of Gs in a murine model of homocysteinemic heart failure.

High plasma homocysteine levels are a known risk factor in heart failure and sudden cardiac death. The G proteins, Gs (stimulatory) and Gi (inhibitory), are involved in calcium regulation; overexpression has pathological consequences. The aims of this study were to examine the differential expression of Gs G protein and Gi in the hearts of hyperhomocysteinemic (Hhcy) mice, and to determine if homocysteine (Hcy) acts as an agonist in cell culture to mediate the change in G protein isoforms. To create Hhcy, heterozygous cystathionine-β-synthase (CBS) knockout (KO) mice were used. Mice were sacrificed, hearts were excised, cardiac tissue homogenates were prepared, and Western blots were performed. The results suggested that Gs G protein was downregulated in cardiac tissue of heterozygous CBS KO mice to 46% that of control hearts. However, the intracellular Gi G protein content remained the same in heterozygous CBS KO mice. Transformed cardiomyocyte HL-1 cells were treated with varying concentrations of homocysteine. The results suggested no detectable differential Gs and Gi expression. This suggested that Hcy did not act as an agonist in vitro to alter G protein content, but that Hcy produced some other in vivo effects to incur these results.

Protein kinase B, P34cdc2 kinase, and p21 ras GTP-binding in kidneys of aging rats.

Renal nephropathy present in male Wistar rats more than 13 months of age was reported as an indication that the rats were in renal failure. In this study, the renal tissue damage at 14 months of age in male Munich Wistar rats was similar to that reported for Wistar rats, indicating that Munich Wistar rats could be another model for study of kidney function in the aging rat. The usual renal response to injury involves increased cell division and/or reparative processes that involve tyrosine kinase activity (TyrK) and/or guanosine triphosphate-binding (G) protein signal transduction pathways. This study reveals the presence of renal tissue damage coinciding with significantly reduced activitiy of Ras, Akt, and p34cdc2 kinase, the signaling proteins that regulate cell division and/or growth, in renal cortical tissues of aging rats compared to young rats (P < 0.005, P < 0.005, and P < 0.001, respectively). These results suggest that proteins involved in signal transduction pathways associated with cell replication are downregulated in the aging kidney cortex at a time when renal cellular damage is also present.

Effect of Human Chorionic Gonadotropin on Reproductive Organ Blood Flow in Cycling Rats

Abstract Recent characterization of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors in uterine vascular tissue, evidence that expression of these receptors is cyclic in nature, and demonstration of a correlation between hCG level and uterine vascular resistance lead us to investigate the effect of hCG administration on blood flow in reproductive organs of cycling and ovariectomized Sprague-Dawley rats. Blood flow (ml/min/g dry wt/cardiac output ± SEM) was determined by microsphere spectroscopy (57Co, 113Sn, 95Nb, 141Ce). Baseline uterine (0.5842 ± 0.1037) and cervical (0.7785 ± 0.1199) blood flows were greater in diestrus-2 rats than in every other group. Diestrus-2 (0.4530 ± 0.0584) and estrus (0.4692 ± 0.0848) rats had greater baseline ovarian blood flow than proestrus rats (0.2521 ± 0.0279). A single intraperitoneal injection of 50 IU hCG on each day of the 4-day estrus cycle decreased uterine flow by more than 30% within 20 min (P < 0.05), but did not alter uterine flow in ovariectomized rats. This dose of hCG also decreased ovarian flow in diestrus-2 rats (0.5219 ± 0.0857 to 0.4207 ± 0.0753), decreased liver flow in diestrus-2 (0.0282 ± 0.0060 to 0.0231 ± 0.0051) and estrus (0.0301 ± 0.0029 to 0.0203 ± 0.0038) rats, and increased liver flow in ovariectomized rats (0.0279 ± 0.0054 to 0.0325 ± 0.0050). Injection of 0.10 IU hCG did not alter blood flow to reproductive organs in any group, but decreased liver flow in estrus rats (0.0469 ± 0.0121 to 0.0326 ± 0.0088). Neither dose of hCG altered cervical, kidney, or skeletal muscle flow in any group. Our results indicate an organ specific, dose-dependent blood flow response to hCG in cycling rats, which appears, in the case of uterine flow, to be attenuated by removal of the ovaries. The present findings suggest high doses of hCG given clinically may decrease uterine flow and potentially lead to implantation failure. [P.S.E.B.M. 1996, Vol 211]