Modulation of 11β-hydroxysteroid dehydrogenase functions by the cloud of endogenous metabolites in a local microenvironment: The glycyrrhetinic acid-like factor (GALF) hypothesis

11β-Hydroxysteroid dehydrogenase (11β-HSD)-dependent conversion of cortisol to cortisone and corticosterone to 11-dehydrocorticosterone are essential in regulating transcriptional activities of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Inhibition of 11β-HSD by glycyrrhetinic acid metabolites, bioactive components of licorice, causes sodium retention and potassium loss, with hypertension characterized by low renin and aldosterone. Essential hypertension is a major disease, mostly with unknown underlying mechanisms. Here, we discuss a putative mechanism for essential hypertension, the concept that endogenous steroidal compounds acting as glycyrrhetinic acid-like factors (GALFs) inhibit 11β-HSD dehydrogenase, and allow for glucocorticoid-induced MR and GR activation with resulting hypertension. Initially, several metabolites of adrenally produced glucocorticoids and mineralocorticoids were shown to be potent 11β-HSD inhibitors. Such GALFs include modifications in the A-ring and/or at positions 3, 7 and 21 of the steroid backbone. These metabolites may be formed in peripheral tissues or by gut microbiota. More recently, metabolites of 11β-hydroxy-Δ4androstene-3,17-dione and 7-oxygenated oxysterols have been identified as potent 11β-HSD inhibitors. In a living system, 11β-HSD isoforms are not exposed to a single substrate but to several substrates, cofactors, and various inhibitors simultaneously, all at different concentrations depending on physical state, tissue and cell type. We propose that this "cloud" of steroids and steroid-like substances in the microenvironment determines the 11β-HSD-dependent control of MR and GR activity. A dysregulated composition of this cloud of metabolites in the respective microenvironment needs to be taken into account when investigating disease mechanisms, for forms of low renin, low aldosterone hypertension.

Role of gut metabolism of adrenal corticosteroids and hypertension: clues gut-cleansing antibiotics give us

Intestinal bacteria can metabolize sterols, bile acids, steroid hormones, dietary proteins, fiber, foodstuffs, and short chain fatty acids. The metabolic products generated by some of these intestinal bacteria have been linked to a number of systemic diseases including obesity with Type 2 diabetes mellitus, some forms of inflammation, and more recently, systemic hypertension. In this review, we primarily focus on the potential role selected gut bacteria play in metabolizing the endogenous glucocorticoids corticosterone and cortisol. Those generated steroid metabolites, when reabsorbed in the intestine back into the circulation, produce biological effects most notably as inhibitors of 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2. Inhibition of the dehydrogenase actions of 11β-HSD, particularly in kidney and vascular tissue, allows both corticosterone and cortisol the ability to bind to and activate mineralocorticoid receptors with attended changes in sodium handling and vascular resistance leading to increases in blood pressure. In several animal models of hypertension, administration of gut-cleansing antibiotics results in transient resolution of hypertension and transfer of intestinal contents from a hypertensive animal to a normotensive animal produces hypertension in the recipient. Moreover, fecal samples from hypertensive humans transplanted into germ-free mice resulted in hypertension in the recipient mice. Thus, it appears that the intestinal microbiome may not just be an innocent bystander but certain perturbations in the type and number of bacteria may directly or indirectly affect hypertension and other diseases.

Acquired Resistance to Corticotropin Therapy in Nephrotic Syndrome: Role of De Novo Neutralizing Antibody

There is increasing evidence supporting the use of corticotropin as an alternative treatment of refractory proteinuric glomerulopathies. The efficacy of short-acting corticotropin, however, remains unknown and was tested here in an adolescent with steroid-dependent nephrotic syndrome caused by minimal change disease. After developing Cushing syndrome and recently being afflicted with severe cellulitis, the patient was weaned off all immunosuppressants, including corticosteroids. This resulted in a relapse of generalized anasarca, associated with massive proteinuria and hypoalbuminemia. Subsequently, mono-therapy with short-acting animal-derived natural corticotropin was initiated and resulted in a rapid response, marked by substantial diuresis, reduction in body weight, and partial remission of proteinuria. Ten days later, the patient developed mild skin rash and subcutaneous nodules at injection sites. A relapse followed despite doubling the dose of corticotropin, consistent with delayed-onset resistance to treatment. Immunoblot-based antibody assay revealed de novo formation of antibodies in the patient's serum that were reactive to the natural corticotropin. In cultured melanoma cells known to express abundant melanocortin receptors, addition of the patient's serum strikingly mitigated dendritogenesis and cell signaling triggered by natural corticotropin, denoting neutralizing properties of the newly formed antibodies. Collectively, short-acting natural corticotropin seems effective in steroid-dependent nephrotic syndrome. De novo formation of neutralizing antibodies is likely responsible for acquired resistance to corticotropin therapy. The proof of concept protocols established in this study to examine the anticorticotropin neutralizing antibodies may aid in determining the cause of resistance to corticotropin therapy in future studies.

An alternative explanation of hypertension associated with 17α-hydroxylase deficiency syndrome

The syndrome of 17α-hydroxylase deficiency is due to the inability to synthesize cortisol and is associated with enhanced secretion of both corticosterone and 11-deoxy-corticosterone (DOC). In humans, corticosterone and its 5α-Ring A-reduced metabolites are excreted via the bile into the intestine and transformed by anaerobic bacteria to 21-dehydroxylated products: 11β-OH-progesterone or 11β-OH-(allo)-5α-preganolones (potent inhibitors of 11β-HSD2 and 11β-HSD1 dehydrogenase). Neomycin blocks the formation of these steroid metabolites and can blunt the hypertension in rats induced by either ACTH or corticosterone. 3α,5α-Tetrahydro-corticosterone, 11β-hydroxy-progesterone, and 3α,5α-tetrahydro-11β-hydroxy-progesterone strongly inhibit 11β-HSD2 and 11β-HSD1 dehydrogenase activity; all these compounds are hypertensinogenic when infused in adrenally intact rats. Urine obtained from a patient with 17α-hydroxylase deficiency demonstrated markedly elevated levels of endogenous glycyrrhetinic acid-like factors (GALFs) that inhibit 11β-HSD2 and 11β-HSD1 dehydrogenase activity (>300 times greater, and >400 times greater, respectively, than those in normotensive controls). Thus, in addition to DOC, corticosterone and its 5α-pathway products as well as the 11-oxygenated progesterone derivatives may play a previously unrecognized role in the increased Na(+) retention and BP associated with patients with 17α-hydroxylase deficiency.

Adrenalectomy amplifies aldosterone induced injury in cardiovascular tissue: an effect attenuated by adrenally derived steroids

Aldosterone induces fibrotic changes in cardiovascular tissues but its effects have usually been demonstrated in models of pre-existing renal injury and/or hypertension. This study tests the hypothesis that aldosterone can directly induce vascular fibrotic changes in the absence of prior renal injury or hypertension. Experiments were conducted in intact or adrenalectomized (ADX) mice. Mice were divided into groups and treated for 1 week with vehicle or aldosterone (8 μg/kg/day)± inhibitor (800 μg/kg/day): CONTROLS, mice treated with aldosterone, ADX-CONTROLS, ADX+corticosterone (CORT 8 μg/kg/day), ADX with aldosterone, ADX with aldosterone plus the mineralocorticoid receptor (MR) antagonist RU-318, ADX with aldosterone+CORT (CORT inhibitor dose), and ADX with aldosterone+11-dehydro-CORT. Aortic smooth muscle to collagen ratio, aorta intimal thickness (μm), heart weight/body weight ratio (mg/gm), and left ventricular collagen (%) were measured. Prior to sacrifice, blood pressures were normal in all animals. Lower dose CORT alone had no effect on any of the variables examined. Aldosterone exposure was associated with extra-cellular matrix accumulation in cardiovascular tissues in intact mice and adrenalectomy exacerbated these effects. RU-318, CORT (inhibitor dose), and 11-deydro-CORT each attenuated the early fibrotic changes induced by aldosterone. In the heart, aldosterone exposure affected all the parameters measured and caused intimal hypercellularity with monocytes adhering to endothelial cells lining coronary vessels. Cultured endothelial cells exposed to aldosterone (10nM) released E-selectin, produced collagen, and promoted monocyte adhesion. These effects were inhibited by RU-318 and 11-deydro-CORT but not by CORT. Thus, adrenalectomy enhances aldosterone induced early fibrotic changes in heart and aorta. Aldosterone initially targets vascular endothelial cells. MR antagonists and 11-dehydro-CORT, an 11β-HSD dehydrogenase end-product, directly attenuate these effects.

Targeting activated mineralocorticoid receptor: Occam's razor revisited

Activation of mineralocorticoid receptors (MRs) classically has been associated with electrolyte transport, but we now know that MR activation can also lead to tissue inflammation and fibrosis. Aldosterone consistently activates MR, but under selected circumstances, endogenous glucocorticoids such as cortisol and corticosterone can also trigger MR. Tissue-specific safeguards such as the enzyme 11β-hydroxysteroid dehydrogenase limit glucocorticoid-induced MR activation, while the presence of reactive oxygen species may enhance the ability for glucocorticoid-induced MR activation even in the absence of aldosterone.

Aldosterone-induced fibrosis in the kidney: questions and controversies

Over the years, aldosterone has been a favorite topic of renal physiologists given its role in the maintenance of body fluids. Investigators only recently are coming to appreciate a second proinflammatory and profibrotic role for this hormone. Mineralocorticoids such as aldosterone trigger a profibrotic process that in many respects mimics the early phase of wound healing. Depending on the type of cell involved, aldosterone may activate the profibrotic process through classic mineralocorticoid receptors, nonclassic membrane-associated mineralocorticoid receptors, and/or glucocorticoid receptors. In the kidney, the actions of aldosterone can be attenuated by 11-dehydro metabolites of endogenous glucocorticoids generated by isoforms of the enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD-1 and 11β-HSD-2). Thus, the renal 11β-HSD isoforms may have 2 functions: to block the improper activation of mineralocorticoid receptors by binding endogenous glucocorticoids and to synthesize agents that limit the actions of aldosterone. Although sodium in the diet has been implicated in aggravating aldosterone-induced renal fibrotic processes, preliminary findings are consistent with the view that aldosterone alone can initiate matrix production in renal tissue even in the absence of active sodium transport. Thus, there is a growing body of laboratory and clinical evidence supporting the use of inhibitors of aldosterone action in patients with both glomerular and tubular diseases.

Direct fibrogenic effects of aldosterone on normotensive kidney: an effect modified by 11β-HSD activity

Aldosterone (Aldo) can be a profibrotic factor in cardiovascular and renal tissues. This study tests the hypothesis that prolonged Aldo exposure is able to directly induce fibrotic changes in the kidney of a normal nonhypertensive animal. Immortalized rat proximal tubule cells (IRPTC) containing 11β-hydroxysteroid dehydrogenase (11β-HSD1) but no mineralocorticoid receptors (MR) and mouse inner medullary collecting duct cells (IMCD) containing 11β-HSD2 and MR were examined. IRPTC exposed to Aldo or corticosterone (10 nM) for 48 h demonstrated no change in collagen production as assessed by Sirius red staining. In contrast, IMCD treated with Aldo exhibited a marked increase in the expression of collagen, fibronectin, and connective tissue growth factor (CTGF), whereas corticosterone alone had no effect. The Aldo-induced overexperession of collagen, fibronectin, and CTGF was substantially attenuated by the MR antagonist RU-318 and by the 11β-HSD end product 11-dehydrocorticosterone, but not by the glucocorticoid receptor antagonist RU-486. In vivo, early fibrotic changes with elevated collagen, fibronectin, and CTGF expression were observed in kidneys isolated from normotensive adrenalectomized mice receiving a continuous infusion of Aldo (8 μg·kg(-1)·day(-1)) for 1 wk. These changes were not present in corticosterone-treated mice. Aldo-induced changes were attenuated in adrenally intact mice and in mice treated with RU-318 or 11-dehydrocorticosterone. Thus, extended Aldo exposure produces fibrotic changes in cells containing MR and in normal kidneys. MR antagonists and the end products of 11β-HSD attenuate these fibrogenic effects.

Interactions of mineralocorticoids and glucocorticoids in epithelial target tissues revisited

The interplay between mineralocorticoids (MCs) and glucocorticoids (GCs) in sodium transporting epithelia is complex and only partially understood. In seminal papers published in the years soon after the discovery of aldosterone, various investigators experimentally observed that mineralocorticoid-induced renal sodium retention could only be reliably measured in adrenalectomized animals. Addition of endogenous GCs or their 11-dehydro metabolites blunted the antinatriuretic action of aldosterone and 11-dehydro-GCs decreased binding of aldosterone to mineralocorticoid receptors (MR). Under normal circumstances, endogenous GCs alone do not induce sodium transport in MC responsive epithelia yet these same GCs are able to activate MR and induce sodium transport if the enzyme 11beta-HSD2 is inhibited. Given the physiologic concentrations of both MCs and GCs, it is likely that the local epithelial cell exposure to GCs is great enough to allow GC binding to MR despite the presence of 11beta-HSD2. Thus other factors supplement the receptor selectivity role suggested for 11beta-HSD2. Why GCs bind to MR under one set of conditions and produce no effect and under different sets of conditions (11beta-HSD2 inhibition) elicit sodium transport remains a puzzle to be solved. What is clear is that a dual role for 11beta-HSD2 is emerging; first as the putative "guardian" over the MR reducing GC binding, and second as a source for 11-dehydro-GCs, which may serve as endogenously and locally produced "spironolactone-like substances", which may thus attenuate aldosterone-induced sodium transport.

Variable expression of 11beta Hydroxysteroid dehydrogenase (11beta-HSD) isoforms in vascular endothelial cells

Vascular tissue expresses two isoforms of the enzyme 11beta-Hydroxysteroid dehydrogenase, 11beta-HSD1 and 11beta-HSD2. These enzymes are responsible for the local metabolism of endogenous glucocorticoids (GCs). 11beta-HSD1 deactivates GCs to their 11keto metabolites or transforms inert 11keto metabolites back to active GCs. Although, bi-directional, vascular 11beta-HSD1 favors reactivation (reductase) over the deactivation (dehydrogenase) reaction, 11beta-HSD2 only functions as a dehydrogenase. GC deactivation by enhanced 11beta-HSD2 dehydrogenase activity or by impaired 11beta-HSD1 reductase activity correlates with lower vascular resistance. These studies were designed to demonstrate the existence and regulation of these isoforms in vascular endothelial cells and to determine whether the expression varied by species and locale. Western blots were prepared from pre-confluent and confluent cultures of human umbilical vein endothelial cells (HUVEC). 11beta-HSD1 was clearly expressed while 11beta-HSD2 was much less prominent. Cultured rat aortic and bovine glomerular endothelial cells showed a similar pattern. Using immunohistochemistry, endothelial cells from human and mouse artery preparations clearly demonstrated 11beta-HSD1. In separate experiments, pre-confluent growing HUVEC expressed more 11beta-HSD1 compared to confluent cells. Serum-deprived growth-retarded HUVEC expressed significantly less 11beta-HSD1. The enhanced expression of 11beta-HSD1 was also observed 24h following a scratch "injury" to the culture plates. Changes in 11beta-HSD1 with growth and during repair occurred at the transcription level. Thus, 11beta-HSD1 protein expression predominates in endothelial cells and varies during periods of growth.

Endogenous inhibitors (GALFs) of 11beta-hydroxysteroid dehydrogenase isoforms 1 and 2: derivatives of adrenally produced corticosterone and cortisol

Two isoforms of 11beta-HSD exist; 11beta-HSD1 is bi-directional (the reductase usually being predominant) and 11beta-HSD2 functions as a dehydrogenase, conferring kidney mineralocorticoid specificity. We have previously described endogenous substances in human urine, "glycyrrhetinic acid-like factors (GALFs)", which like licorice, inhibit the bi-directional 11beta-HSD1 enzyme as well as the dehydrogenase reaction of 11beta-HSD2. Many of the more potent GALFs are derived from two major families of adrenal steroids, corticosterone and cortisol. For example, 3alpha5alpha-tetrahydro-corticosterone, its derivative, 3alpha5alpha-tetrahydro-11beta-hydroxy-progesterone (produced by 21-deoxygenation of corticosterone in intestinal flora); 3alpha5alpha-tetrahydro-11beta-hydroxy-testosterone (produced by side chain cleavage of cortisol); are potent inhibitors of 11beta-HSD1 and 11beta-HSD2-dehydrogenase, with IC50's in range 0.26-3.0 microM, whereas their 11-keto-3alpha5alpha-tetrahydro-derivatives inhibit 11beta-HSD1 reductase, with IC50's in range 0.7-0.8 microM (their 3alpha5beta-derivatives being completely inactive). Inhibitors of 11beta-HSD2 increase local cortisol levels, permitting it to act as a mineralocorticoid in kidney. Inhibitors of 11beta-HSD1 dehydrogenase/11beta-HSD1 reductase serve to adjust the set point of local deactivation/reactivation of cortisol in vascular and other glucocorticoid target tissues, including adipose, vascular, adrenal tissue, and the eye. These adrenally derived 11-oxygenated C21- and C19 -steroidal substances may serve as 11beta-HSD1- or 11beta-HSD2-GALFs. We conclude that adrenally derived products are likely regulators of local cortisol bioactivity in humans.

Use of an immune function assay to monitor immunosuppression for treatment of post-transplant lymphoproliferative disorder

The first-line treatment for PTLD is reduction in immunosuppression, allowing partial reconstitution of cell-mediated immunity. However, there is a risk of inducing acute allograft rejection during clinical resolution of PTLD. A recently available assay, Immuknow, measures the cell-mediated immune response and could be used to monitor reduction of immunosuppression. We report a case of PTLD occurring in a pediatric kidney transplant recipient where the reduction in immunosuppression was serially followed using this assay and quantitative EBV-PCR. A rapid reduction to minimal immunosuppression was followed by resolution of PTLD. Later, when the cell-mediated immune response increased, with negative viral load, immunosuppression was gradually increased utilizing the assay to adjust dosing. Presently, there are no signs of PTLD and renal function remains normal.

Growth in adolescent hemodialysis patients: data from the Centers for Medicare & Medicaid Services ESRD Clinical Performance Measures Project

The Centers for Medicare & Medicaid Services' (CMS) end-stage renal disease (ESRD) Clinical Performance Measures (CPM) Project has collected data on all adolescent hemodialysis patients since 2000. Thus, by 2002 data were available on all adolescents on hemodialysis in the USA for 3 consecutive years. Possible associations between clinical parameters and linear growth in this cohort were evaluated. Ninety-four adolescents were on hemodialysis for the 3 study years. The mean height standard deviation score (ht SDS) fell from -1.97 to -2.36 over the 3 study years. Compared with patients with ht SDS > or =-1.88, patients with ht SDS <-1.88 in the 2002 study year (n =53) were more likely to be male (66% vs 44%, p <0.05), on dialysis longer (6.9+/-4.5 years vs 4.1+/-2.3 years, p <0.001), and had lower height SDS in the 2000 study year (-2.90+/-1.31 vs -0.772+/-1.10, p <0.001). Patients with a ht SDS <-1.88 had a lower mean hemoglobin (11.4+/-1.6 g/dl vs 12.0+/-1.1 g/dl, p <0.05), but there were no differences in other clinical parameters. Among patients with ht SDS <-1.88, 38.8% (n =20) were prescribed recombinant human growth hormone (rhGH) in the 2002 study year. There were no differences in demographic or clinical parameters between rhGH treated and untreated patients. Many adolescents who remain on hemodialysis have poor linear growth. Further evaluation is needed to delineate contributory factors and the possible underutilization of rhGH.

Effect of chenodeoxycholic acid on 11beta-hydroxysteroid dehydrogenase in various target tissues

Glucocorticoids are metabolized by isoforms of the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD). There is some controversy concerning the bile acid, chenodeoxycholic acid (CDCA), as a potential endogenously produced inhibitor of 11beta-HSD. The present experiments were designed to determine the relative specificity of CDCA for both isoforms of 11beta-HSD and to assess the biological relevance of inhibition in vascular tissue. IC(50) values (concentrations which inhibit 50% of the enzyme reaction) were calculated using rat liver microsomes as a source of 11beta-HSD1 dehydrogenase, Leydig cells for 11beta-HSD1 dehydrogenase and reductase, aorta for 11beta-HSD1 dehydrogenase and reductase, and sheep kidney for 11beta-HSD2 dehydrogenase. In each case, CDCA functioned as a potent inhibitor of 11beta-HSD1 dehydrogenase with IC(50) values of ranging from 0.2 to 7 micromol/L in contrast to 37 to 200 micromol/L for 11beta-HSD1 reductase. CDCA exhibited relatively weak inhibitory activity against 11beta-HSD2 from sheep kidney with an IC(50) of 70 micromol/L. The effect of CDCA on vascular contraction was studied in aortic rings isolated from Spague-Dawley rats incubated in medium containing corticosterone 10 nmol/L +/- CDCA (1 micromol/L) for 24 hours. Rings were stimulated with graded concentrations of phenylephrine (PE) (10 nmol/L, 100 nmol/L, and 1 micromol/L). Rings exposed to corticosterone and CDCA consistently demonstrated a greater contractile response at lower doses of PE (63% at PE 10 nmol/L, P <.001; 20% at PE 100 nmol/L, P <.025; and 10% at PE 1 micromol/L, not significant [NS]) compared to control preparations incubated with cortiosterone alone. These studies demonstrate (1) that CDCA preferentially affects 11beta-HSD1 dehydrogenase; (2) CDCA does inhibit 11beta-HSD2 dehydrogenase and 11beta-HSD1 reductase but only at high(er) concentrations exceeding 70 micromol/L and 37 micromol/L, respectively; and (3) inhibition of 11beta-HSD1 dehydrogenase in aortic rings by CDCA (1 micromol/L) enhances the contractile response of corticosterone plus PE.

Longitudinal analysis of intermediate outcomes in adolescent hemodialysis patients

In 2000 and 2001, The Centers for Medicare & Medicaid Services (CMS) End-Stage Renal Disease (ESRD) Clinical Performance Measures (CPM) project collected data on all in-center hemodialysis (HD) patients in the United States aged >or=12 and <18 years. There were 433 of 486 (89%) patients and 435 of 516 (84%) patients who had the minimum required data submitted and were included in the 2000 and 2001 study years, respectively. There were 188 patients (43%) who had data submitted in both study years, providing longitudinal data on this cohort. A comparison of clinical parameters on these 188 patients in the 2000 and 2001 study years reveals significant improvement in mean calculated spKt/V (1.50+/-0.36 vs. 1.58+/-0.30, P<0.01), mean hemoglobin (11.0+/-1.6 g/dl vs. 11.5+/-1.3 g/dl, P<0.001), mean ferritin (286+/-278 ng/ml vs. 460+/-353 ng/ml, P<0.001), mean transferrin saturation (27.8+/-15.1% vs. 31.3+/-15.0%, P<0.05), mean serum albumin as measured by the bromocresol green method (3.83+/-0.54 g/dl vs. 3.95+/-0.42 g/dl, P<0.01), and mean height standard deviation score (-1.814+/-1.756 vs. -1.699+/-1.657, P<0.05). In addition, 20 of 29 (69%) patients who had a spKt/V <1.2 in the 2000 study year had a spKt/V >1.2 in the 2001 study year. Of 68 (44%) patients who had a catheter as their HD access in the 2000 study year, 30 had an arteriovenous fistula or graft in the 2001 study year and 49 of 80 (61%) patients who had a mean hemoglobin <11 g/dl in the 2000 study year had a hemoglobin >11 g/dl in the 2001 study year. In summary, these longitudinal data demonstrate significant improvements in nearly all clinical parameters studied in these adolescent HD patients.

Anemia in pediatric hemodialysis patients: results from the 2001 ESRD Clinical Performance Measures Project

BACKGROUND

Despite improvements in dialysis care, anemia remains a problem in pediatric hemodialysis patients.

METHODS

To assess possible explanations for the anemia, clinical data were obtained from the Centers for Medicare and Medicaid Services on all hemodialysis patients ages 12 to <18 years between October and December 2000. Complete data were available for 435 of the 516 patients (84%).

RESULTS

A total of 160 (37%) patients had a mean hemoglobin of <11 g/dL (anemic). The mean (+/- SD) age for these patients was 15.5 +/- 1.8 years compared to 15.9 +/- 1.5 years for the target hemoglobin patients (P < 0.05). Mean time on chronic dialysis was similar for both the anemic and target hemoglobin patients (>/=100 g/dL) ( approximately 3 years) but patients on dialysis <6 months were more likely to be anemic (67%). While nearly all patients were treated with erythropoietin, anemic patients received greater weekly erythropoietin doses (intravenous, anemia 374 +/- 232 units/kg/week vs. target hemoglobin 246 +/- 196 units/kg/week, P < 0.001; and subcutaneous, 304 +/- 238 units/kg/week vs. 167 +/- 99 units/kg/week, P < 0.05). A total of 59% of anemic patients had a mean transferrin saturation (TSAT) >/=20% compared to 71% of patients with a target hemoglobin (P < 0.01). A mean serum ferritin >/=100 ng/mL was present in approximately two thirds of the anemic and target hemoglobin patients. Approximately 60% of all children were treated with intravenous iron. The mean Kt/V values were lower for anemic patients (1.46 +/- 0.4 vs. 1.53 +/- 0.3, P < 0.05). Anemic patients were less likely to have a normal serum albumin (29% anemic vs. 52% target hemoglobin patients, P < 0.001).

CONCLUSION

In the final multivariable regression model, dialyzing <6 months, a low albumin, and a mean TSAT <20% remained significant predictors of anemia in children.

The functional roles of 11 beta-HSD1: vascular tissue, testis and brain

Glucocorticoid hormones bind both glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) exerting a broad spectrum of actions in various tissues. The concentrations of glucocorticoid hormones in the target cells are regulated by 11 beta-hydroxysteroid dehydrogenases, type 1 (11 beta-HSD1) and type 2 (11 beta-HSD2). 11 beta-HSD2 is a unidirectional dehydrogenase, which inactivates biologically active glucocorticoid into inert metabolite, while 11 beta-HSD1 is a bi-directional oxidoreductase, which either inactivates biologically active glucocorticoid or activates inert metabolite into active forms. GRs and MRs are present in various tissues and mediate a broad spectrum of physiological actions. The co-existence of 11 beta-HSD1 with these two types of receptors plays an important role in regulation of glucocorticoid actions. This review examines the roles of 11 beta-HSD1 in vascular tissues, testis, brain and other tissues such as placental, retinal and adipose tissues.

Prevalence of protein malnutrition in children maintained on peritoneal dialysis

A paucity of outcome measures exist for children, making evidence-based treatment guidelines difficult to establish. Serum albumin has been identified as a surrogate marker for nutritional status and morbidity/mortality in patients with end-stage renal disease (ESRD). We hypothesized that the prevalence of low serum albumin (<2.9 g/dl) in children on peritoneal dialysis (PD) may be greater, making this population at risk. Patient data were collected prospectively over 24 months (1999-2000) from all children (1-18 years) maintained on either hemodialysis (HD) or PD within the six-state New England area; 64 observations were made on 39 children on PD over the 2-year period. The mean age was 11.7+/-4.7 years (mean+/-SD). The prevalence of low serum albumin in children was 35.9% (23/64 observations) compared with 19.5% (712/3,719 observations) in adult Network ESRD patients on PD ( P<0.004). None of the 32 children (47 observations) maintained on HD exhibited low serum albumin during the data collection period. The prevalence of low serum albumin in adult HD patients was 5.5%. Dietary protein intake was estimated from a calculated protein catabolic rate (PCR). PCRs in children treated with both PD and HD were similar, averaging 1.1+/-0.4 g/kg per day (mean+/-SD). Thus, children maintained on PD are at greater risk of protein malnutrition compared with peers treated with HD and adults on PD or HD. A PCR of approximately 1 g/kg per day may not be adequate to maintain nutrition.

11 beta-Hydroxysteroid dehydrogenase antisense affects vascular contractile response and glucocorticoid metabolism

Glucocorticoids (GC's) are metabolized in vascular tissue by two isoforms of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). 11 beta-HSD2 is unidirectional and metabolizes GC's to their respective inactive 11-dehydro derivatives. 11 beta-HSD1 is bi-directional, also possessing reductase activity and thus the ability to regenerate active GC from the 11-dehydro derivatives. In vascular tissue, GC's amplify the pressor responses to catecholamines and angiotensin II and may down-regulate certain depressor systems such as nitric oxide and prostaglandins. We hypothesize that both 11 beta-HSD2 and 11 beta-HSD1 regulate GC levels in vascular tissue and are part of additional mechanisms that control vascular tone. We examined the effects of specific antisense oligomers to 11 beta-HSD2 and 11 beta-HSD1 on GC metabolism and contractile response to phenylephrine (PE) in rat aortic rings. In aortic rings incubated (24 h) with corticosterone (B) (10 nmol/l) and 11 beta-HSD2 antisense (3 micromol/l), the contractile response to graded concentrations of PE (PE: 10 nmol/l - 1 micromol/l) were significantly (P < 0.05) increased compared to rings incubated with B and 11 beta-HSD2 nonsense. 11 beta-HSD1 antisense oligomers also enhanced the ability of B to amplify the contractile response to PE. In addition, 11 beta-HSD2 and 11 beta-HSD1 antisense also decreased the metabolism of B to 11-dehydro-B. 11-Dehydro-B (100 nmol/l) also amplified the contractile response to PE in aortic rings (P < 0.01), most likely due to the generation of active corticosterone by 11 beta-HSD1-reductase; this effect was significantly attenuated by 11 beta-HSD1 antisense. 11 beta-HSD1 antisense also caused a marked decrease in the metabolism of 11-dehydro-B back to B by 11 beta-HSD1-reductase. These findings underscore the importance of 11 beta-HSD2 and 11 beta-HSD1 in regulating local concentrations of GC's in vascular tissue. They also indicate that decreased 11 beta-HSD2 activity may be a possible mechanism in hypertension and that 11 beta-HSD1-reductase may be a possible target for anti-hypertensive therapy.

Clinical morbidity in pediatric dialysis patients: data from the Network 1 Clinical Indicators Project

The Health Care Financing Administration (HCFA) has gathered clinical data on end stage renal disease (ESRD) patients since 1994, but details are only available on patients >/=18 years. In this report, we present morbidity data collected prospectively over 12 months from all children (1-18 years) maintained on either hemodialysis (HD) or peritoneal dialysis (PD) within the six-state New England area. During this year, 17 observations were recorded on 14 HD patients (age 13.4+/- 11.3 years) and 36 observations were made on 25 PD patients (age 11.5+/-4.8 years; mean +/- SD). These patients were generally highly functional, attending school at least part time in nearly all cases. Dialysis adequacy index (DAI), defined as the delivered KT/V divided by DOQI guideline values, indicated that patients were well dialyzed (HD 1.41+/-0.1 and PD 1.10+/-0.1; mean +/- SE). When all dialysis patients were grouped and analyzed, the DAI did not correlate with number of hospitalizations, degree of anemia, serum albumin, or type of dialysis. The number of hospitalizations were greater the younger the patient (P<0.01). The need for antihypertensive medications was higher in the children maintained on HD (94%) compared to children on PD (58%) (P<0.01). Lastly, while serum ferritin did not correlate with serum iron, hematocrit or Epo dosage, it was inversely related to serum albumin (P<0.03). We conclude that, in children, (1) exceeding suggested dialysis adequacy may not improve patient morbidity, (2) the need for antihypertensive medications appears greater in children maintained on HD, and (3) inflammation may play a role in determining serum albumin independent of nutrition.

Insights Into Glucocorticoid-Associated Hypertension

The association between excess glucocorticoids and hypertension has been much discussed but poorly understood. From both clinical observations and laboratory studies, it is clear that glucocorticoids exert their effects at many different sites responsible for blood pressure regulation. Isoforms of the enzyme 11ss-hydroxysteroid dehydrogenase (11ss-HSD), located in steroid-responsive tissues, metabolize endogenously produced glucocorticoids. These enzymes limit steroid access to mineralocorticoid and/or glucocorticoid receptors. In the kidney, synthetic and endogenous glucocorticoids are capable of enhancing transepithelial sodium transport in the presence of 11ss-HSD inhibition. Proximal tubule reabsorption of sodium can be indirectly augmented after chronic exposure to glucocorticoids. In this segment, steroids have a permissive effect, increasing the expression of both Na(+), K(+) adenosine triphosphatase along the basolateral membrane and Na(+)-H(+) exchanger along the apical membrane of epithelial cells. Although glucocorticoids themselves produce no increase in sodium reabsorption in this segment, angiotensin II-stimulated sodium transport is significantly greater in proximal tubular cells pretreated with glucocorticoids. The increased transport in distal renal segments is more direct and stems in part from glucocorticoid cross-over binding to mineralocorticoid receptors. In vascular tissue, synthetic and endogenous glucocorticoids, after inhibition of the dehydrogenase reaction, magnify the response to circulating vasoconstrictors. The effects of glucocorticoids in vascular tissue is indirect, upregulating the expression of receptors to many vasoconstrictors and downregulating the effects of potential vasodilators. Thus, glucocorticoids have the potential to alter both circulating volume and vascular resistance.

Antisense to Both 11β-Hsd1 and 2 Increase Glucocorticoid (GC) Activity in Vascular Tissue

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GC’s amplify the pressor effects of catecholamines and Ang II in VSM. Thus, the level of vasoconstriction in vascular tissue can be influenced by local GC concentrations. GC’s are metabolized to their inactive 11-dehydro derivatives by the enzyme 11β-HSD which exists in at least two isoforms, 11β-HSD1 and 11β-HSD2. 11β-HSD2 is unidirectional, with only dehydrogenase activity (inactivating GC’s) while 11β-HSD1 is bi-directional, also possessing reductase activity and thus the ability to reactivate 11-dehydroGC’s back to the active parent steroid. The aim of the present study was to investigate the role of each isoform in the regulation of GC metabolism in vascular tissue. Aortic rings (2-3mm), from male SD rats, were incubated for 24 hrs in DMEM media with either corticosterone (B) or 11-dehydrocorticosterone (11-dehydroB)(10 -8 -10 -7 M) ± specific Antisense oligos (20 μg/ring) targeted against rat 11β-HSD1 or 11β-HSD2. The contractile responses to graded doses of phenylephrine (PE; 10 -9 - 10 -6 M)in individual rings were then measured. In aortic rings co-incubated with B and 11β-HSD2 Antisense, the contractile responses to PE were amplified 30-50% versus rings incubated with B + nonsense oligonicleotide (n = 21, p < 0.01). The co-incubation of aortic rings with B + 11β-HSD1 Antisense resulted in a 50% increase in the contractile responses to PE (n = 8, p<0.001). In parallel experiments, 11β-HSD2 Antisense caused a 25% reduction(n =16 aortic rings) and 11β-HSD1 Antisense a 12% reduction (n = 8 aortic rings)in the metabolism of B to 11-dehydroB. These results indicate that 11β-HSD1 and 11β-HSD2 are both important in the metabolism of GC’s in vascular tissue and hence in the regulation of vascular tone. Additionally, rat aortic rings incubated with 11-dehydroB have an increased contractile response to PE versus controls, an effect attenuated by 11β-HSD1 Antisense. This suggests 11-dehydroB is re-activated back to B by 11β-HSD1-reductase making this enzyme a target for possible antihypertensive therapies.

Outcome data on pediatric dialysis patients from the end-stage renal disease clinical indicators project

Network 1 (New England) initiated the Clinical Indicator Project to survey dialysis adequacy (Kt/V), nutrition (serum albumin level), and anemia management in patients maintained on chronic dialysis. Because little information is available in children, data were specifically recorded covering these variables in patients (age, 1 to 18 years) maintained on either hemodialysis (HD) or peritoneal dialysis (PD). During the 18 months of data collection, 29 observations were recorded on 23 HD patients (age, 14.3 +/- 3.6 years), and 43 observations were made on 30 PD patients (age,10.6 +/- 4.7 years). Kt/V correlated inversely with the age of the patient (HD, P < 0.004; PD, P < 0.0007). Although serum albumin level was not associated with dialysis adequacy in HD patients, there was a strong inverse relationship between albumin level and Kt/V in PD patients (P < 0.002). Hematocrit values were not significantly different in the two groups (HD, 31.0% +/- 5.5% versus PD, 32.9% +/- 4.8%) and could not be correlated with weekly erythropoietin dose. Weekly erythropoietin dose was directly related to patient age in both groups (HD, P < 0.05; PD, P < 0.02). The weekly erythropoietin dosage needed to maintain the hematocrit was greater in HD patients (HD, 11,211 +/- 7,484 U versus PD, 3,790 +/- 1,968 U; P < 0.0001). We conclude that (1) smaller children in both groups tend to have a greater Kt/V, (2) Kt/V greater than 2.75 in PD patients may not improve nutrition per se and could result in increased albumin losses, and (3) erythropoietin dosing appears to correlate best with patient size (age) rather than degree of anemia.

Interactions of mineralocorticoids and glucocorticoids in epithelial target tissues

BACKGROUND

: In Na+-transporting epithelial target tissues, such as mammalian kidney and the isolated toad bladder, glucocorticoids (GCs) do not normally elicit Na+ retention. In mammalian kidney, however, they do cause kaliuresis. The presence of 11beta-hydroxysteroid dehydrogenase isoform 2 (11beta-HSD2) in these target tissues inactivates the GCs, preventing them from accessing mineralocorticoid receptors (MRs) and stimulating Na+ transport.

RESULTS

: The usually observed Na+ retention elicited by the mineralocorticoid aldosterone was blunted when the GC corticosterone was coadministered along with aldosterone. However, when corticosterone was administered along with a 11beta-HSD2 inhibitor, a strong Na+ transport was elicited by an MR-mediated mechanism. 11-Dehydrocorticosterone also blunted aldosterone-elicited Na+ transport in these target tissues.

CONCLUSIONS

: 11beta-HSD2 appears to play two important roles in the epithelial target tissues, kidney and toad bladder. The first is to protect GC access to MR, and the second involves the product of the enzyme to regulate the magnitude of aldosterone-induced Na+ retention.

Primary laparoscopic placement of peritoneal dialysis catheters in children and young adults

BACKGROUND

Primary placement of peritoneal dialysis catheters in children often requires suturing of the catheter into the pelvis. We describe our experience with a gasless laparoscopy technique in children and young adults.

METHODS

During an 18-month period, 12 patients (mean age, 14 years) underwent primary laparoscopic placement of peritoneal dialysis catheters. A single umbilical port was used for abdominal wall elevation, telescope, and catheter. A needleholder was introduced via an accessory port at the future catheter exit site or through the umbilical port. Omentectomy was performed through the umbilical incision. The catheter was tunneled to the lateral abdominal wall. Follow-up data (>/= 15 months) included time to initiation of dialysis, hospitalization, and outcome. End points were cure, transplantation, or death.

RESULTS

Diet was started on the day of surgery and dialysis on the following day. Four patients had seven complications, including leakage and entanglement of the catheter in tubal fimbriae. Long-term revision-free catheter survival was 67% at 24 months.

CONCLUSIONS

This minimal access technique for primary placement of peritoneal dialysis catheters includes securing of the catheter tip in a dependent location and omentectomy. It allows nearly immediate use of the catheter, leads to a minimal hospital stay, and has acceptable long-term patency.

Glucocorticoid metabolism in proximal tubules modulates angiotensin II-induced electrolyte transport

The hormonal interactions that regulate electrolyte transport in the proximal tubule are complex and incompletely understood. Since endogenous glucocorticoids and angiotensin II each can affect electrolyte transport in this renal segment, we hypothesized that local metabolism of glucocorticoids by the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) might alter the response to angiotensin II. Studies were conducted in cultured origin defective SV-40 transformed immortalized renal proximal tubule cells (IRPTC) derived from weanling Wistar rat kidney. The 11beta-HSD contained in these cells uses NADP+, has an apparent Km for corticosterone of 1.6 microM, but functions only as a dehydrogenase (corticosterone --> 11-dehydro-corticosterone). When mounted in modified Ussing chambers, IRPTC generate a transmembrane current, and angiotensin II (10 pM to 10 microM) increases this sodium-dependent current. Cells incubated with corticosterone (100 nM) and the 11beta-HSD inhibitor carbenoxolone (CBX) (1 microM) for 24 hr and then acutely stimulated with angiotensin (10 nM) show a greater rise in current than do cells exposed to corticosterone alone and stimulated with angiotensin (corticosterone + CBX: 64.2% +/- 20.5% vs. corticosterone: 18.8% +/- 5.9%; P < 0.02 at 180 min)[mean +/- SE percentage above baseline, n = 8/group]. Cells exposed to corticosterone (100 nM) or CBX (1 microM) alone for 24 hr and then stimulated with angiotensin II (10 nM) had responses similar to controls. Thus glucocorticoids can enhance angiotensin II-induced electrolyte transport in proximal tubule epithelial cells when local 11beta-HSD is inhibited.

Glucocorticoids inhibit the expression of calcium-dependent potassium channels in vascular smooth muscle

Increased calcium-activated potassium channel (KCa) activity in vascular smooth muscle (VSM) cells leads to a relaxation response counteracting the effects of high blood pressure. Since chronic exposure to glucocorticoids (GC) can be associated with an increase in blood pressure, we reasoned that GCs might modify the expression of KCa channels resulting in a net rise in vascular tone. To test this hypothesis, primary cultures of rat VSM cells were exposed to (a) RU 28362 (a pure glucocorticoid receptor agonist), 1 microM; (b) corticosterone 10 nM + carbenoxolone (an inhibitor of bidirectional VSM 11beta-OH steroid dehydrogenase), 1 microM; (c) 11-dehydrocorticosterone (a biologically inactive metabolite), 10 nM + carbenoxolone; (d) carbenoxolone alone; or (e) aldosterone 10 nM for periods of up to 72 h. Proteins were then extracted and Western blots prepared. Gels were probed with a rabbit-derived polyclonal antibody directed against KCa channel protein. The experimental procedure was repeated on separate sets of VSM cells to ensure reproducibility. Expression of KCa channel protein was diminished in VSM cells incubated with corticosterone + carbenoxolone and with RU 28362 after 24 h and remained low at 72 h. Expression of KCa protein in cells exposed to 11-dehydrocorticosterone + carbenoxolone, carbenoxolone alone, and aldosterone was either similar to controls or mildly increased over the 72 h. These data are consistent with the hypothesis that GCs diminish the expression of KCa protein. Diminished KCa expression could contribute to the observed increase in vascular tone following chronic GC exposure.

Effect of serum on vascular smooth muscle function

Serum contains many biologically active factors influencing cell growth and is commonly used as a culture medium supplement. It has not generally been appreciated that serum can affect vascular tone. We have observed that the contractile response of aortic rings previously exposed to 10% fetal bovine serum (FBS) for 24 hours and then stimulated with phenylephrine (0.01-1microM) or angiotensin II (1microM) is significantly diminished compared to 1) rings incubated in FBS for only 6 hours, 2) aortic rings previously incubated in 1% FBS or 3) aortic rings incubated in 10% bovine serum albumin for 24 hours. A similar attenuated response was also seen when the vascular aortic rings were incubated in heat inactivated adult bovine serum. To test whether prostaglandins might be induced by factors contained in serum and account for the diminished stimulated contractile response, rings were incubated for 24 hours in media containing 10% FBS with either indomethacin 10microM, corticosterone 100nM or 11-dehydrocorticosterone 100nM. These agents are known to affect prostaglandin synthesis. Contractile responses were then measured accordingly. In each series, the previously attenuated contractile response to phenylephrine and to angiotensin II was fully restored with prostaglandin synthesis inhibition. Thus, factors contained in serum are capable of blunting the stimulated contractile response of rat aortic vessels. These serum factors appear to act by inducing prostaglandin synthesis in vascular tissue.

Localization of 2 11beta-OH steroid dehydrogenase isoforms in aortic endothelial cells

11Beta-hydroxysteroid dehydrogenase (11beta-HSD) is expressed in vascular smooth muscle cells (VSMC) but has not been reported to be present in vascular endothelial cells. This enzyme assists in regulating the cellular concentration of active endogenous glucocorticoids (GCs). We have observed that endothelium intact rat aortic rings express message for both Type 1 and Type 2 11beta-HSD whereas primary cultures of VSMC express only mRNA for the Type I isoform. Since GCs diminish prostacyclin synthesis in endothelial cells, we hypothesized that 11beta-HSD is present in vascular endothelial cells. In primary cultures of rat aortic endothelial (RAE) cells, mRNA from both isoforms of 11beta-HSD could be detected by RT-PCR with higher levels of the Type 1 isoform. The oxo-reductase reaction "activating" 11-dehydro metabolites back to the parent steroid is the preferred enzyme direction (12:1 after a 120 minutes steroid incubation) in intact RAE cells. When RAE cells are grown in the presence of antisense oligonucleotides specific for Type 1 11beta-HSD, oxo-reductase activity is decreased by approximately 50% but the dehydrogenase reaction, which inactivates endogenous GCs and is characteristic of the Type 2 isoform, is unaffected. Thus endothelial cells appear to express both isoforms of 11beta-HSD; the Type 1 isoform dominates functioning in the oxo-reductase mode. Inhibition of the oxo-reductase reaction may lower the local concentrations of GC and indirectly allow for increased production of prostacyclin in endothelial cells.

11BetaOH-progesterone affects vascular glucocorticoid metabolism and contractile response

Vascular smooth muscle (VSM) contains a bidirectional isoform of 11beta-hydroxysteroid dehydrogenase (11beta-HSD), the enzyme that can metabolize endogenous glucocorticoids to their respective 11-dehydro derivatives. 11BetaOH-progesterone (11betaOH-P), a compound that can be produced in vivo, is as potent or more potent than licorice derivatives in inhibiting renal and hepatic 11beta-HSD. When studied in homogenates prepared from primary cultures of rat VSM, 11betaOH-P and its derivative, 11-keto-progesterone (11-keto-P), proved to be potent, directionally specific inhibitors of vascular 11beta-HSD. 11BetaOH-P selectively inhibited the forward dehydrogenase reaction (corticosterone-->11-dehydrocorticosterone), whereas 11-keto-P selectively blocked the reverse oxidoreductase reaction. To test the physiological effects, vascular rings were prepared from rat aorta. Rings were incubated in culture media containing either a submaximal concentration of corticosterone (10 nmol/L), 11-dehydrocorticosterone (100 nmol/L), 11betaOH-P (1 micromol/L), 11-keto-P (1 micromol/L), or a combination of glucocorticoid and inhibitor for 24 hours. After the 24-hour incubation, rings were briefly stimulated sequentially with phenylephrine (10 nmol/L to 1 micromol/L) and angiotensin II (1 micromol/L). The immediate contractile response in rings incubated with both corticosterone and 11betaOH-P was greater than in rings previously incubated with either the corticosterone or 11betaOH-P alone (eg, response to 100 nmol/L phenylephrine in milligrams of force, mean+/-SE: corticosterone, 728+/-56, n=9; 11betaOH-P, 325+/-105, n=4; both, 1132+/-122, n=8; corticosterone versus both, P<.01). In contrast, the immediate contractile responses to phenylephrine and to angiotensin II were attenuated in rings exposed previously to both 11-dehydrocorticosterone and 11-keto-P. Thus, 11betaOH-P and 11-keto-P (and possibly structurally similar compounds) alter the vascular effects of glucocorticoids and may play a role in glucocorticoid-induced hypertension.

Influence of dietary sodium on the renal isoforms of 11 beta-hydroxysteroid dehydrogenase

Endogenous glucocorticoids are converted to their biologically inert 11-dehydroderivatives by isoforms of the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). The low-K(m), NAD(+)-dependent renal isoform (Type 2) identified in the distal nephron protects mineralocorticoid receptors from activation by endogenous glucocorticoids. The function of high-K(m), NADP(+)-dependent renal isoform (Type 1) is less well understood. Since glucocorticoids may modulate sodium transport in renal proximal tubules (PT), we hypothesized that Type 1 activity in this segment may be regulated by dietary Na(+)-11 beta-HSD activity was assessed in homogenates of canine PT by the conversion of cortisol to cortisone in the presence of NADP+ 200 microM. A high-Na+ diet for 4 days increased the Vmax 4-fold, with no change in the Type 1 K(m) (40 mEq/day Na+ diet: K(m) 0.959 microM, Vmax 3.40 pmoles/min/mg protein versus 150 mEq/day Na+ diet: K(m) 0.962 microM, Vmax 14.8 pmoles/min/mg protein). Type 1 mRNA also rose in the salt repleted animals. The high-Na+ diet produced no detectable change in the Type 2 isoform enzyme kinetics and mRNA level. No reverse oxo-reductase activity was noted with either renal isoform. Thus, renal Type 1 11 beta-HSD can be regulated by dietary Na+ independent of changes in the renal Type 2 isoform.

Kidney 11 beta-HSD2 is inhibited by glycyrrhetinic acid-like factors in human urine

We have previously shown that human urine contains substances that, like glycyrrhetinic acid, inhibit 11 beta-HSD1. We have named these substances "glycyrrhetinic acid-like factors" or GALFs. We now have found that human urine contains measurable quantities of both 11 beta(HSD1)- and 11 beta(HSD2)-GALF inhibitory substances. Both are markedly elevated in pregnancy. Their chemical and high-performance liquid chromatography (HPLC) characteristics suggest that several of the GALFs are steroidal. Large quantities of neutral 11 beta(HSD1)- and 11 beta(HSD2)-GALFs can be extracted directly from urine into ethyl acetate, yielding fraction EA1. Hydrolysis of the GALFs remaining in the aqueous phase by beta-glucuronidase markedly increases the total amounts of GALFs, with the majority now being ethyl acetate extractable (fraction EA2). These EA2 post-hydrolysis GALFs can be separated by HPLC resulting in at least six components with inhibitory activity against each isoenzyme. Only two GALF peaks are active against both 11 beta-HSD1 and 11 beta-HSD2. The others are peaks with specific 11 beta(HSD1)- and 11 beta(HSD2)-GALF inhibitory activity. The GALFs in the same posthydrolysis EA2 extract are also inhibitory toward the 11 beta-HSD1 that is present in vascular smooth muscle where they may play a role in the mechanisms controlling blood pressure. We have also found that 11 beta-HSD2 is selectively inhibited by 5 alpha- (but not by 5 beta-) reduced steroids. GC-MS analysis of the 11 beta(HSD2)-GALFs in EA2 is now being performed to determine whether this group includes 3 alpha,5 alpha-ring A-tetrahydro-reduced derivatives of steroids.

Effects of licorice derivatives on vascular smooth muscle function

Vascular smooth muscle contains a bidirectional form of the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) which can inactivate (dehydrogenase) endogenous circulating glucocorticoids (GCs) or activate (oxo-reductase) 11-dehydro-metabolites by their conversion back to the parent steroid. Enzyme direction in vascular smooth muscle (VSM) has potential physiological consequences since GCs may enhance the response to known vasoconstrictors. We determined that carbenoxolone is a competitive inhibitor of 11beta-HSD contained in VSM cells with a lower Ki for forward dehydrogenase reaction (0.02 microM) compared to the oxo-reductase reaction (0.41 microM). To test whether changes in enzyme directional activity can affect the contractile response, aortae from adrenally intact Sprague Dawley rats were removed and sectioned into 2.5 mm rings. Rings were incubated with corticosterone 10 nM plus carbenoxolone (CBX) 10 microM (a concentration well above the Ki for both the dehydrogenase and oxo-reductase reaction) for 24 hrs. These rings showed an enhanced dose dependent contractile response to phenylephrine (PE) 0.01 microM(-1) microM and to angiotensin II 1 microM compared to rings incubated with corticosterone alone, CBX alone, or controls: [e.g. response to PE 1 microM in mg of contractile force, mean +/- SE: corticosterone plus CBX 1495 +/- 162 (n=10) vs corticosterone 1039 +/- 64 (n=9), p<0.05]. Aortic rings preincubated with 11-dehydrocorticosterone 10(-7)M and CBX 10 microM displayed a decreased contractile response compared to 11-dehydrocorticosterone alone. Thus in situ glucocorticoid metabolism is important in mediating the constrictor responses of vascular tissue.

Glucocorticoid metabolism in the newborn rat heart

A relative cardiac hypertrophy has been observed in newborns chronically treated with dexamethasone. To test the hypothesis--that dexamethasone might alter steroid metabolism within the heart--rat pups were injected with vehicle, corticosterone (dosages 20 or 200 micrograms/pup/injection, or 1 mg/pup/injection) or dexamethasone (5 micrograms/pup/injection) on Day 2-6 and sacrificed on Day 7-8. Injections with dexamethasone in this dosage have induced the cardiac changes in this rat model. 11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) activity was assessed in hearts from these adrenally intact rat pups by incubating tissues with 3H-corticosterone 10(-8) M for 60 min. On Day 7-8, controls transformed 10.3% +/- 1.1% (mean +/- SE) of the corticosterone (Compound B) to 11-dehydrocorticosterone (Compound A) generating 1.25 +/- 0.35 x 10(-12) moles A/mg protein (n = 8). Tissues from pups pretreated with corticosterone at all three dosages were not different from controls in percent metabolized and moles A/mg generated. In contrast, hearts from dexamethasone treated pups transformed only 4.5% +/- 1.0% of the corticosterone to A generating 3.19 +/- 0.05 x 10(-13) moles A/mg protein (n = 10) (P < 0.05 versus control in moles/mg protein metabolized). Cultured cardiomyocytes exposed to dexamethasone for 4 days in vitro also decreased their expression of 11 beta-OHSD mRNA. Readily metabolized endogenous glucocorticoids produced little or no effect on developing heart muscle while treatment with dexamethasone, a potent synthetic glucocorticoid, induced relative cardiac hypertrophy and downregulated 11 beta-OHSD mRNA expression and enzyme activity.

Bidirectional activity of 11 beta-hydroxysteroid dehydrogenase in vascular smooth muscle cells

Endogenous glucocorticoids (GC) can be metabolized through the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD); in the rat, corticosterone (B) is converted to its inactive metabolite 11-dehydrocorticosterone (A). Since increased tissue concentrations of GCs may affect blood pressure by potentiating the vasoactive effects of alpha-adrenergic agonists and possibly other pressors, we studied the metabolism of corticosterone in freshly dissected aortae and cultured vascular smooth muscle cells (VSMC). Incubations were generally conducted for 60 min with 10(-8) M steroid; steroids were isolated and identified by HPLC. In aortic minces stripped of endothelium, the oxo-reductase reaction of A back to B was nearly 4 times greater than the dehydrogenase reaction of B to A (2.8 +/- 0.5 x 10(-11) versus 7.3 +/- 1.0 x 10(-12) mol/mg protein). This pattern was also seen in cultured VSMC during growth and quiescent states (growth A to B 3.2 +/- 0.4 x 10(-12) versus B to A 9.7 +/- 0.9 x 10(-13) mol/mg protein; quiescent A to B 8.8 +/- 0.1 x 10(-12) versus B to A 1.2 +/- 0.2 x 10(-12) mol/mg protein). Enzyme activity in either direction was less during growth, correlating with a decrease in mRNA for 11 beta-OHSD. In cell homogenates containing 200 microM NADP(H), the enzyme functioned equally in either direction at pH 7.4 with an apparent Km for corticosterone of approximately 2 x 10(-7) M. Carbenoxolone, an inhibitor of 11 beta-OHSD, suppressed the dehydrogenase reaction to a greater degree than the reverse oxo-reductase reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in rat renal 11 beta-hydroxysteroid dehydrogenase

11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) transforms endogenous glucocorticoids to their respective "biologically inert" 11-dehydro derivatives. A decrease in enzyme activity allows glucocorticoids to induce mineralocorticoid-like renal sodium retention. Since positive sodium balance is required for optimum growth in the newborn, we hypothesized that renal 11 beta-OHSD activity would be low in the postnatal period, a time of active growth. To test this, incubations with corticosterone were carried out using minces or homogenates prepared from kidneys of newborn, 8-day-old, and mature Sprague-Dawley rats. 11 beta-OHSD activity in renal minces, assessed by the percent of corticosterone (10(-8) M) transformed to 11-dehydrocorticosterone (compound A), was significantly lower in the newborn kidney (newborn 45.7 +/- 3.8%, 8 day 70.2 +/- 3.8%, and adult 73.4 +/- 3.1%, P < 0.001 1 vs. 8 day). Parallel studies were conducted using an antibody directed against liver 11 beta-OHSD counter stained with immunofluorescent labeled IgG. Kidneys from mature rats were brightly stained at S2 and S3 segments of proximal tubules. In contrast, staining was barely detectable in kidneys from the newborn and 8-day-old rats. When enzyme kinetics were examined in kidney homogenates (average protein concentration 2.5 mg/ml) in the presence of 200 microM NADP+, the apparent Km for corticosterone in the adult was 4.42 x 10(-6) M with a corresponding Vmax of 1.33 x 10(-9) mol/min/mg protein, while the apparent Km for corticosterone in the newborn was calculated to be 12.8 x 10(-8) M with a Vmax of 2.08 x 10(-11) mol/min/mg protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between glucocorticoids and mineralocorticoids in the regulation of renal electrolyte transport

The enzyme 11 beta-hydroxy steroid dehydrogenase (11 beta-OHSD) was described and its location in various organs noted more than 30 years ago (Mahesh and Ulrich, 1960; Jenkins, 1966). 11 beta-OHSD inactivates circulating glucocorticoids by transforming the hydroxyl group at the 11-carbon to a keto group. This chemical reaction has taken on a greater degree of physiologic and clinical significance in recent years. It has been suggested that 11 beta-OHSD, present in mineralocorticoid target tissues, can act as a 'guardian' over the mineralocorticoid receptor by transforming circulating endogenous glucocorticoids to their respective 'biologically inert' 11-dehydro derivatives (Edwards et al., 1988; Funder et al., 1988). These derivatives do not bind to mineralocorticoid receptors (MR) while both their parent compounds and mineralocorticoids bind to cloned MR with equal affinity (Arriza et al., 1987). 11 beta-OHSD has generated a growing sense of scientific excitement since this enzyme may represent one of a family of metabolic pathways or mechanisms which can regulate steroid induced renal reabsorption of sodium. Such 'protective' enzymatic pathways, present in the kidney and elsewhere, may not only control the access of glucocorticoids to MR, but control the access of glucocorticoids to glucocorticoid receptors (GR) (Teelucksingh et al., 1990; Monder, 1990) as well as access of mineralocorticoids to their own receptors. This review will focus on this concept of a family of protective enzymatic pathways and the possible physiological implications.

Activity of 11 beta-hydroxysteroid dehydrogenase in toad bladder: effects of 11-dehydrocorticosterone

11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) transforms circulating glucocorticoids to their "biologically inert" 11-dehydro derivatives. Isoforms of 11 beta-OHSD with different cofactor requirements and biochemical properties [Michaelis constant (Km) and maximal velocity (Vmax)] exist in the kidney. Since epithelial cells derived from the toad bladder also contain this enzyme, we wished to further characterize its properties in prepared cell homogenates. 11 beta-OHSD from toad bladder demonstrated a clear preference for NAD+ over NADP+ as a cofactor similar to that observed in renal cortical collecting duct (CCD) cells. Furthermore, 11 beta-OHSD had a rapid onset of action. The apparent Km for corticosterone was 16.3 x 10(-8) M, a value comparable to that observed for enzyme from CCD, and a Vmax of 4.8 x 10(-12) mol.mg protein-1.min-1. The end product, 11-dehydrocorticosterone (compound A), influenced enzyme activity; it increased 11 beta-OHSD activity at corticosterone concentrations below the apparent Km for the enzyme and inhibited 11 beta-OHSD activity at corticosterone concentrations above the Km for the enzyme. The inhibitory effects of compound A appeared noncompetitive with an apparent equilibrium constant (Ki) of 2.8 x 10(-7) M. Consistent with its inhibitory action on 11 beta-OHSD, compound A (10(-6) M) enhanced the short-circuit current response to corticosterone (10(-7) M) in the intact toad bladder (experimental 2.03 +/- 0.33 vs. control 1.40 +/- 0.17 times above baseline; n = 7, P < 0.01). Thus 11 beta-OHSD in toad bladder resembles the isoform found in CCD, and compound A may be biologically important as a regulator of 11 beta-OHSD.

Effect of carbenoxolone sodium on steroid-induced sodium transport in the toad bladder: further studies

The licorice derivative, carbenoxolone sodium, is a potent inhibitor of the enzyme 11 beta-hydroxysteroid dehydrogenase. When this enzyme is suppressed or is absent, endogenous glucocorticoids induce mineralocorticoid-like sodium retention by the kidney. Carbenoxolone sodium administered in vivo to an adrenalectomized rat has also recently been shown to enhance the mineralocorticoid response to submaximal concentrations of aldosterone, deoxycorticosterone (DOC) and 11-dehydrocorticosterone (compound A). In the present studies conducted on the urinary bladder isolated from the Dominican toad, Bufo marinus, a concentration of carbenoxolone sodium shown previously to increase glucocorticoid-induced sodium transport (2.5 x 10(-5) M) did not appear to alter the response to submaximal concentrations of aldosterone 10(-8) M, DOC 10(-7) M, or compound A 10(-5) M. These findings are consistent with the view that in the whole animal carbenoxolone sodium may modify additional steroid metabolic pathways and/or physiological processes in several organs to produce the enhanced renal response to mineralocorticoids and compound A.

Electrolyte disorders associated with respiratory distress syndrome and bronchopulmonary dysplasia

In understanding the various electrolyte disorders associated with respiratory failure, one has to appreciate how the otherwise healthy premature infant maintains extracellular fluid homeostasis. The same physiologic processes that regulate body fluids are affected to varying degrees in the infant with respiratory failure. Maintenance of sodium conservation by the kidney is of critical importance for survival and growth. The immature kidney tends to exhibit excessive sodium wasting especially early on, but appropriate positive sodium balance is achieved generally within the first week. Appropriate reduction in extracellular fluid occurring during the first week or so of life is expected and if it is not allowed to occur may result in dilutional hyponatremia and an increase in pulmonary interstitial water. Diuretics, when used to promote an increase in lung compliance, can themselves generate significant morbidity. Sodium depletion, hypokalemia, alkalosis, and calcium wasting all can either be caused by or exaggerated by the loop diuretics. Thus, one must consider the maturational state of the infant, the infant's response to pulmonary failure, and iatrogenic factors influencing the outcome.

Central nervous system and renal investigations in patients with Lowe syndrome

We describe three patients with Lowe (oculocerebrorenal) syndrome, emphasizing primarily the central nervous system and renal pathology. Using magnetic resonance imaging, we noted diffuse high T2 signals periventricularly, indicating significant white matter destruction, which may be responsible in part for the mental retardation, seizure disorder, hypotonia, and areflexia observed in the patients. In contrast to previously published reports, there was minimal renal tubular dysfunction; however, proteinuria was significantly increased in all patients. We believe that the observed proteinuria is primarily the result of glomerular pathology rather than renal tubular dysfunction and may represent a net loss of negative charges within the glomerular filter. This loss of charge may be linked to the increased excretion of glycosaminoglycans in the urine.

Primary renal lymphoma

Lymphomatous involvement of the kidneys is a common manifestation of systemic non-Hodgkin's lymphoma but associated renal dysfunction is uncommon. In contrast, lymphoma originating within the kidneys is a rare event. We report a case of primary renal lymphoma presenting with renal insufficiency and hypertension in a 10-year-old boy.

11-Dehydrocorticosterone, a glucocorticoid metabolite, inhibits aldosterone action in toad bladder

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) metabolizes glucocorticoid hormones and diminishes their ability to induce sodium transport. In these studies, we determined the location of this enzyme in toad bladder and assessed the biological role for its 11-dehydro end product. Employing a polyclonal antibody directed toward 11 beta-OHSD and immunofluorescence techniques, we located the enzyme in the epithelial cell layer of the toad bladder. Although corticosterone (10(-7) M) can partially suppress aldosterone (10(-7) M)-stimulated short-circuit current (SCC), a clear excess of corticosterone (10(-6) M) did not inhibit the aldosterone-induced induced (10(-8) M) rise in SCC (n = 6). The 11-dehydro product of corticosterone, 11-dehydrocorticosterone (compound A) added to the serosal bath suppressed aldosterone (10(-8) M) peak SCC (360 min) in a dose-dependent fashion reaching 46 +/- 5% of control values at 10(-5) M (n = 6; P less than 0.001). Compound A (10(-5) M) in the mucosal bath also was capable of partially inhibiting the peak aldosterone rise in SCC to 63 +/- 7% of control values with aldosterone at 10(-8) M (n = 6; P less than 0.01) and to 64 +/- 10% of control values with aldosterone at 10(-7) M (n = 9; P less than 0.01). Compound A alone at 10(-5) M did not have any effect on SCC. Isolated toad bladders were not able to transform compound A (at 10(-8) and 10(-5) M) back to corticosterone. Thus the 11-dehydro end product of 11 beta-OHSD (compound A) may play a biologic role by regulating a component of mineralocorticoid-induced sodium transport.