Using B isotopes and B/Ca in corals from low saturation springs to constrain calcification mechanisms.

Ocean acidification is expected to negatively impact calcifying organisms, yet we lack understanding of their acclimation potential in the natural environment. Here we measured geochemical proxies (δ11B and B/Ca) in Porites astreoides corals that have been growing for their entire life under low aragonite saturation (Ωsw: 0.77-1.85). This allowed us to assess the ability of these corals to manipulate the chemical conditions at the site of calcification (Ωcf), and hence their potential to acclimate to changing Ωsw. We show that lifelong exposure to low Ωsw did not enable the corals to acclimate and reach similar Ωcf as corals grown under ambient conditions. The lower Ωcf at the site of calcification can explain a large proportion of the decreasing P. astreoides calcification rates at low Ωsw. The naturally elevated seawater dissolved inorganic carbon concentration at this study site shed light on how different carbonate chemistry parameters affect calcification conditions in corals.

Overexpression of glutamine:fructose-6-phosphate amidotransferase in transgenic mice leads to insulin resistance.

The hexosamine biosynthetic pathway has been hypothesized to be involved in mediating some of the toxic effects of hyperglycemia. Glutamine:fructose-6-phosphate amidotransferase (GFA), the first and rate limiting enzyme of the hexosamine biosynthetic pathway, was overexpressed in skeletal muscle and adipose tissue of transgenic mice. A 2.4-fold increase of GFA activity in muscle of the transgenic mice led to weight-dependent hyperinsulinemia in random-fed mice. The hyperinsulinemic-euglycemic clamp technique confirmed that transgenic mice develop insulin resistance, with a glucose disposal rate of 68.5 +/- 3.5 compared with 129.4 +/- 9.4 mg/kg per min (P < 0.001) for littermate controls. The decrease in the glucose disposal rate of the transgenic mice is accompanied by decreased protein but not mRNA levels of the insulin-stimulated glucose transporter (GLUT4). These data support the hypothesis that excessive flux through the hexosamine biosynthesis pathway mediates adverse regulatory and metabolic effects of hyperglycemia, specifically insulin resistance of glucose disposal. These mice can serve as a model system to study the mechanism for the regulation of glucose homeostasis by hexosamines.

Regulation of glycogen synthase and protein phosphatase-1 by hexosamines.

The hexosamine biosynthesis pathway has been hypothesized to be involved in mediating some of the adverse effects of high glucose. We have previously shown that glucose downregulates basal glycogen synthase (GS) activity in Rat-1 cells and that overexpressing the rate-limiting enzyme in the hexosamine biosynthesis pathway (glutamine:fructose-6-phosphate amidotransferase [GFA]) makes the cells more sensitive to these effects of glucose. GFA overexpression also leads to a reduction in insulin sensitivity of GS. Here we examine the effects of glucose and glucosamine on insulin-stimulated GS activity and on protein phosphatase-1 (PP1) activity. These activities were assayed in cytoplasmic extracts from Rat-1 fibroblasts overexpressing human GFA and cultured in varying glucose concentrations. Both maximal insulin-stimulated GS activity and insulin sensitivity decreased with increasing glucose. Overexpression of GFA leads to a further reduction in insulin sensitivity but not in maximal insulin-stimulated GS activity. Because there were no differences in total (glucose-6-phosphate-dependent) GS activity between cell lines or as a function of glucose concentration, these results most likely reflect a change in the phosphorylation state of the synthase. Activity of PP1, a potential mediator of these effects, was responsive to glucose and hexosamines. Control cells showed a 9.3 +/- 4.3% decrease in PP1 activity with increasing glucose. GFA cells showed a greater response to glucose, with PP1 activity decreasing 34.2 +/- 5.5% with increasing glucose. Glucosamine was more potent than glucose in decreasing PP1 activity in control cells. Cells overexpressing the normal human insulin receptor (HIRc-B) were used to facilitate analysis of insulin-stimulated PP1 activity. Stimulation with 1.7 mmol/l insulin led to a 37.6 +/- 9.9% increase in PP1 activity in HIRc-B cells cultured in 1 mmol/l glucose, while cells cultured in 5 mmol/l glucosamine or 20 mmol/l glucose demonstrated only 3.79 +/- 0.60 or 1.6 +/- 0.75% increases, respectively. We conclude that both basal and insulin- stimulable GS and PP1 activity are downregulated by high glucose in fibroblasts and this regulation is mediated by products of the hexosamine biosynthesis pathway.

Hexosamines and insulin resistance.

Glucose is an important regulator of cell growth and metabolism. Thus, it is likely that some of the adverse effects of hyperglycemia are reflections of normal regulation by abnormal concentrations of glucose. How the cell senses glucose, however, is still incompletely understood. Evidence has been presented that the hexosamine biosynthesis pathway serves this function for regulation of aspects of glucose uptake, glycogen synthesis, glycolysis, and synthesis of growth factors. Excess hexosamine flux causes insulin resistance in cultured cells, tissues, and intact animals. Further evidence for the possible role of this pathway in normal glucose homeostasis and disease is that the level of activity of the rate-limiting enzyme in hexosamine synthesis, glutamine:fructose-6-phosphate amidotransferase, is correlated with glucose disposal rates (GDRs) in normal humans and transgenic mice.

Regulation of insulin-stimulated glycogen synthase activity by overexpression of glutamine: fructose-6-phosphate amidotransferase in rat-1 fibroblasts.

High glucose concentrations such as are seen in diabetes mellitus are known to have deleterious effects on cells, but the pathways by which glucose induces these effects are unknown. One hypothesis is that metabolism of glucose to glucosamine might be involved. For example, it has been shown that glucosamine is more potent than glucose in inducing insulin resistance in cultured adipocytes and in regulating the transcription of the growth factor transforming growth factor alpha in smooth muscle cells. The rate-limiting step in glucosamine synthesis is the conversion of fructose-6-phosphate to glucosamine-6-phosphate by the enzyme glutamine:fructose-6-phosphate amidotransferase. To test the hypothesis that this hexosamine biosynthesis pathway is involved in the induction of insulin resistance, we have overexpressed the enzyme glutamine:fructose-6-phosphate amidotransferase in Rat-1 fibroblasts and investigated its effects on insulin action in those cells. We electroporated Rat-1 fibroblasts with expression plasmids that did and did not contain the gene for glutamine:fructose-6-phosphate amidotransferase and measured glycogen synthase activity at varying insulin concentrations. Insulin stimulation was blunted in the glutamine:fructose-6-phosphate amidotransferase-transfected cells, resulting in decreased insulin sensitivity reflected by a rightward shift in the dose-response curve for activation of synthase (ED50 = 7.5 nM vs. 3.4 nM insulin, in glutamine:fructose-6-phosphate amidotransferase and control cells, respectively). Rat-1 fibroblasts incubated with 5.- mM glucosamine for 3 days exhibited a similar shift in the dose-response curve. The rightward shift in the dose-response curve is seen as early as 2 days after poration.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of glycogen synthase by glucose, glucosamine, and glutamine:fructose-6-phosphate amidotransferase.

The hexosamine biosynthesis pathway has been hypothesized to mediate some of the regulatory as well as the deleterious effects of glucose. We have stably overexpressed the cDNA for human glutamine:fructose-6-phosphate amidotransferase (GFA), the rate-limiting enzyme in the hexosamine biosynthesis pathway, in rat-1 fibroblasts. Two cell lines expressing the human RNA were selected by Northern analysis, and they exhibited 51-95% increases in GFA activity. Insulin-stimulated glycogen synthase (GS) activity and net glycogen synthesis were assayed, and GFA cells revealed decreased insulin sensitivity for both GS and net glycogen synthesis. The ED50 for insulin stimulation of GS was 2.45 +/- 0.4 nmol/l insulin in controls and 5.29 +/- 1.01 nmol/l in GFA cells (P < 0.005). For insulin-stimulated glycogen synthesis, the ED50 was 3.43 +/- 0.88 nmol/l in controls and 5.54 +/- 0.98 nmol/l in GFA cells (P < 0.005). There were no significant differences in maximally insulin-stimulated or total GS activities, insulin binding or receptor number, or glucose uptake between GFA and control cells. We also examined the effects of glucose on GS activity. GFA cells had a twofold increase in GS activity at low glucose (0.5 mmol/l) when compared with controls (P < 0.025). Both GFA and control cells had an approximately 75-80% decrease in GS activity as glucose concentration was increased from 0.5 to 20 mmol/l. This change in GS activity was not observed until after 12 h in culture. GFA cells were more sensitive to the effects of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Hexosamine-induced fibronectin protein synthesis in mesangial cells is associated with increases in cAMP responsive element binding (CREB) phosphorylation and nuclear CREB: the involvement of protein kinases A and C.

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix protein accumulation are seen in diabetic glomerulopathy. Recent studies have demonstrated that some of the effects of high glucose (HG) on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP), in which fructose-6-phosphate is converted to glucosamine 6-phosphate by the rate-liming enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). In this study, we investigated the role of HBP on HG-stimulated fibronectin protein synthesis, a matrix component, in SV-40-transformed rat kidney MES cells. Treatment of MES cells with 25 mmol/l glucose (HG) for 48 h increases cellular fibronectin levels by two- to threefold on Western blots when compared with low glucose (5 mmol/l). Glucosamine (GlcN; 1.5 mmol/l), which enters the hexosamine pathway distal to GFA action, also increases fibronectin synthesis. Azaserine (AZA; 0.5 micromol/l), an inhibitor of GFA, blocks the HG- but not the GlcN-induced fibronectin synthesis. Fibronectin contains cAMP responsive element (CRE) consensus sequences in its promoter and the phosphorylation of CRE-binding protein (CREB) may regulate its expression. On Western blots, HG and GlcN stimulate two- to threefold the phosphorylation of CREB at Ser 133, whereas CREB protein content was unaltered by either HG or GlcN. In addition, nuclear CREB activity was increased by HG and GlcN on gel-shift assays using (32)P-CRE oligonucleotides. AZA impeded the HG-enhanced CREB phosphorylation and CRE binding but had no effect on GlcN-mediated CREB phosphorylation and CRE binding. Pharmacologic inhibition of protein kinase C (PKC) and protein kinase A (PKA), which are involved in hexosamine-mediated matrix production, blocked the CREB phosphorylation and fibronectin synthesis seen in HG and GlcN conditions. We conclude that the effects of HG on fibronectin synthesis in the mesangium are mediated by the HBP possibly via hexosamine regulation of CREB and PKC/PKA signaling pathways. These results support the hypothesis that the HBP is a sensor and regulator of the actions of glucose in the kidney.

Overexpression of glutamine: fructose-6-phosphate amidotransferase in the liver of transgenic mice results in enhanced glycogen storage, hyperlipidemia, obesity, and impaired glucose tolerance.

To examine the effect of increased hexosamine flux in liver, the rate-limiting enzyme in hexosamine biosynthesis (glutamine:fructose-6-phosphate amidotransferase [GFA]) was overexpressed in transgenic mice using the PEPCK promoter. Liver from random-fed transgenic mice had 1.6-fold higher GFA activity compared with nontransgenic control littermates (276 +/- 24 pmol x mg(-1) x min(-1) in transgenic mice vs. 176 +/- 18 pmol x mg(-1) x min(-1) in controls, P < 0.05) and higher levels of the hexosamine end product UDP-N-acetyl glucosamine (288 +/- 11 pmol/g in transgenic mice vs. 233 +/- 10 pmol/g in controls, P < 0.001). Younger transgenic mice compared with control mice had lower fasting serum glucose (4.8 +/- 0.5 mmol/l in transgenic mice vs. 6.5 +/- 0.8 mmol/l in controls, P < 0.05) without higher insulin levels (48.0 +/- 7.8 pmol/l in transgenic mice vs. 56.4 +/- 5.4 pmol/l in controls, P = NS); insulin levels were significantly lower in transgenic males (P < 0.05). At 6 months of age, transgenic animals had normal insulin sensitivity by the hyperinsulinemic clamp technique. Hepatic glycogen content was higher in the transgenic mice (108.6 +/- 5.2 pmol/g in transgenic mice vs. 32.8 +/- 1.3 micromol/g in controls, P < 0.01), associated with an inappropriate activation of glycogen synthase. Serum levels of free fatty acids (FFAs) and triglycerides were also elevated (FFAs, 0.67 +/- 0.03 mmol/l in transgenic mice vs. 0.14 +/- 0.01 in controls; triglycerides, 1.34 +/- 0.15 mmol/l in transgenic mice vs. 0.38 +/- 0.01 in controls, P < 0.01). Older transgenic mice became heavier than control mice and exhibited relative glucose intolerance and insulin resistance. The glucose disposal rate at 8 months of age was 154 +/- 5 mg x kg(-1) x min(-1) in transgenic mice vs. 191 +/- 6 mg x kg(-1) x min(-1) in controls (P < 0.05). We conclude that hexosamines are mediators of glucose sensing for the regulation of hepatic glycogen and lipid metabolism. Increased hexosamine flux in the liver signals a shift toward fuel storage, resulting ultimately in obesity and insulin resistance.

Regulation of glutamine:fructose-6-phosphate amidotransferase by cAMP-dependent protein kinase.

Glutamine:fructose-6-phosphate amidotransferase (GFA) is the rate-limiting enzyme in hexosamine biosynthesis, an important pathway for cellular glucose sensing. Human GFA has two potential sites for phosphorylation by cAMP-dependent protein kinase A (PKA). To test whether GFA activity is regulated by cAMP-dependent phosphorylation, rat aortic smooth muscle cells were treated in vivo with cAMP-elevating agents, 10 micromol/l forskolin, 1 mmol/l 8-Br-cAMP, or 3-isobutyl-1-methylxanthine. All treatments resulted in rapid and significant increases (2- to 2.4-fold) in GFA activity assayed in cytosolic extracts. Maximal effects of forskolin were observed at 10 micromol/l and 60 min. Preincubation of cells with cycloheximide did not abolish the effect of forskolin. Incubation of cytosolic extracts at 37 degrees C for 10 min in a buffer without phosphatase inhibitors led to a 79% decrease of GFA activity. This loss of activity was inhibited by the addition of phosphatase inhibitors (5 mmol/l sodium orthovanadate, 50 mmol/l sodium fluoride, or 5 mmol/l EDTA, but not 100 nmol/l okadaic acid), suggesting that GFA undergoes rapid dephosphorylation by endogenous phosphatases. Purified GFA is phosphorylated in vitro by purified PKA, resulting in a 1.7-fold increase in GFA activity. Treatment of GFA with purified protein kinase C had no effect. We conclude that GFA activity may be modulated by cAMP-dependent phosphorylation.

Overexpression of glutamine:fructose-6-phosphate amidotransferase in rat-1 fibroblasts enhances glucose-mediated glycogen accumulation via suppression of glycogen phosphorylase activity.

The hexosamine biosynthesis pathway (HBP) mediates many of the adverse effects of excess glucose. We have shown previously that glucose down-regulates basal and insulin-stimulated glycogen synthase (GS) activity. Overexpression of the rate-limiting enzyme in the HBP, glutamine:fructose-6-phosphate amidotransferase (GFA), mimics these effects of high glucose and renders the cells more sensitive to glucose. Here we examine the role of the HBP in regulating cellular glycogen content. Glycogen content and glycogen phosphorylase (GP) activity were determined in Rat-1 fibroblasts that overexpress GFA. In both GFA and controls there was a dose-dependent increase in glycogen content (approximately 8-fold) in cells cultured in increasing glucose concentrations (1-20 mM). There was a shift to the left in the glucose dose-response curve for glycogen content in GFA cells (ED50 for glycogen content = 5.80+/-1.05 vs. 8.84+/-0.87 mM glucose, GFA vs. control). Inhibition of GFA reduced glycogen content by 28.4% in controls cultured in 20 mM glucose. In a dose-dependent manner, glucose resulted in a more than 35% decrease in GP activity in controls. GP activity in GFA cells was suppressed compared with that in controls, and there was no glucose-induced down-regulation of GP activity. Glucosamine and uridine mimicked the effects of glucose on glycogen content and GP activity. However, chronic overexpression of GFA is a unique model of hexosamine excess, as culturing control cells in low dose glucosamine (0.1-0.25 mM) did not suppress GP activity and did not eliminate the glucose-mediated down-regulation of GP activity. We conclude that increased flux through the HBP results in enhanced glycogen accumulation due to suppression of GP activity. These results demonstrate that the HBP is an important regulator of cellular glucose metabolism and supports its role as a cellular glucose/satiety sensor.

Diabetic nephropathy in African Americans.

Diabetic nephropathy (DN) is the number one cause of end-stage renal disease in United States and is highly prevalent in African Americans. We have found that among African Americans in Mississippi diabetic nephropathy appears to affect females more than males, which may be related to increased rates of obesity and diabetes in African American women. Glycemic control and control of blood pressure is essential to prolong renal survival and to protect against cardiovascular events. Angiotensin-converting enzyme inhibitors reduce cardiovascular mortality in diabetics and are tolerated in advanced renal disease. The impact of glycemic control, appropriate antihypertensives, and the optimal level of blood pressure control in African Americans with advanced DN require further study. This article reviews the impact, clinical characteristics, risk factors, and treatment of diabetic nephropathy in African Americans.

Glucose-induced insulin resistance of phosphatidylinositol 3'-OH kinase and AKT/PKB is mediated by the hexosamine biosynthesis pathway.

Hyperglycemia is responsible for many of the vascular complications and metabolic derangements seen in diabetes. One potential regulator of the effects of glucose is the hexosamine biosynthesis pathway (HBP). Glutamine: fructose-6-phosphate amidotransferase (GFA), the first and rate-limiting enzyme in this pathway, catalyzes the transfer of an amino group from glutamine to fructose-6-phosphate to form glucosamine-6-phosphate. Overexpression of GFA in rat-1 fibroblasts results in insulin resistance for glycogen synthase (GS) activity, and renders these cells more sensitive to the effects of glucose. Using rat-1 cells, we examine further the mechanisms whereby hexosamines lead to insulin resistance. Insulin stimulated GS activity was found to occur via a PI-3 kinase (PI-3K)-dependent pathway as wortmannin, an inhibitor of PI-3K, blocked insulin's ability to stimulate GS activity. Subsequently, we examined the effects of hexosamines on PI-3K and Akt/PKB activity. Cells were cultured in 1 mM glucose (low glucose, LG), 20 mM glucose (high glucose, HG), or 1 mM glucose plus 3 mM glucosamine (GlcN) for 16--20 h. After treatment with insulin (100 nM) for 5 min, cell extracts were assayed for IRS-1 associated and total PI-3K activity. At LG, insulin increased PI-3K activity by 43%. There was no insulin stimulation of PI-3K activity in cells cultured in HG or GlcN. There was a trend for IRS-1 protein levels to decrease in HG but not GlcN. PI-3K protein levels were not altered by HG or GlcN. Finally PKB activity was assayed. At LG, insulin stimulated PKB activity. Again, both HG and GlcN significantly reduced insulin's ability to stimulate PKB activity. We conclude that the hexosamine-mediated insulin resistance of GS activity seen in rat-1 cells is mediated by hexosamine regulation of PI-3K and PKB.

The effects of glucose and the hexosamine biosynthesis pathway on glycogen synthase kinase-3 and other protein kinases that regulate glycogen synthase activity.

BACKGROUND: Glycogen synthase (GS) activity is determined by its phosphorylation state. We have previously demonstrated that high glucose (HG) downregulates both basal and insulin-stimulated GS activity in rat-1 fibroblasts and that the hexosamine biosynthesis pathway (HBP) may be involved in mediating some of the effects of glucose. In this study we investigate the influence of high glucose and glucosamine (GlcN) on the activity of several kinases that phosphorylate and inactivate GS. METHODS: Glycogen synthase kinase (GSK) 3, cAMP-dependent protein kinase (PKA), protein kinase C (PKC), casein kinase (CK) 1, and phosphorylase kinase (PhK) activities were assayed in cellular extracts from control rat-1 fibroblasts and those that overexpress human cDNA for glutamine:fructose 6-phosphate amidotransferase (GFA), the rate-limiting enzyme in the HBP. RESULTS: Culturing rat-1 fibroblasts in HG (20 mmol/L) or GlcN (3-5 mmol/L) for 16-20 hours increases GSK-3 activity by 23.9 and 50%, respectively, when compared to activity at low glucose (LG, 1 mmol/L). The effects of HG on GSK-3 activity are greater in cells overexpressing GFA (38.8% increase). Insulin (1.7 nmol/L) treatment leads to a 20-25% decrease in GSK-3 activity that is not affected by HG, GlcN, or GFA overexpression. Culturing control cells in HG increases PKA and CK-1 activities by 56 and 95%, respectively, and HG diminishes insulin action on CK-1 activity. GlcN inhibits insulin action on both PKA and CK-1 activities. HG, GlcN, and GFA overexpression blunted insulin's ability to downregulate PhK activity in LG conditions. PKC activity is not significantly altered in either cell line in the above conditions. CONCLUSIONS: These results suggest that HG alters both basal and insulin-regulated activity of several kinases that phosphorylate GS, and some of the effects of glucose may be mediated by its metabolism via the HBP.

Regulation of glutamine:fructose-6-phosphate amidotransferase activity by high glucose and transforming growth factor beta in rat mesangial cells.

BACKGROUND: The hexosamine biosynthesis pathway acts as a cellular glucose sensor and mediates many of the adverse effects of glucose. Increased flux through this pathway results in insulin resistance in rat fibroblasts and transgenic mice and upregulation of transforming growth factor beta (TGF-beta) transcriptional activity in rat kidney cells. The first and rate-limiting step in this pathway, which is responsible for the metabolism of glucose to glucosamine, is catalyzed by glutamine:fructose-6-phosphate amidotransferase (GFA). METHODS: Because of the known effects of hyperglycemia on mesangial cell (MC) function and growth factor regulation, we examined the regulation of GFA by glucose and TGF-beta in cultured SV40 rat MCs. GFA activity was assayed in cytosolic extracts of MCs using high-performance liquid chromatography. RESULTS: Culturing in 10 and 25 mM of glucose for 24 hours resulted in 33.4% (P < 0.025) and 43.5% (P < 0.05) decreases in GFA activity when compared with cells cultured at 1 to 5 mM of glucose. The downregulation in GFA activity by high glucose (HG) required at least 6 hours in culture and persisted for several days. HG effects were not a result of osmolar changes or glucose-induced differences in glucose uptake. Like HG, treatment of MCs with TGF-beta (2 ng/mL) for 4 hours resulted in a 30% (P < 0.05) decrease in GFA activity in cells cultured at 1 mM glucose, but the effects of TGF-beta were not additive to those of HG. TGF-beta-mediated downregulation of GFA activity was inhibited by a TGF-beta-neutralizing antibody, but HG's effects were not. Insulin-like growth factor-1 (IGF-1) had similar effects as TGF-beta, but GFA activity was not regulated by angiotensin II. CONCLUSIONS: GFA activity is downregulated by HG, TGF-beta, and IGF-1 in rat MCs. Downregulation of this cellular glucose sensor may be a protective mechanism against the harmful effects of excess glucose as seen in diabetes.

Endstage renal disease owing to diabetic nephropathy in Mississippi: an examination of factors influencing renal survival in a population prone to late referral.

BACKGROUND: Diabetic nephropathy (DN) is the leading cause of endstage renal disease (ESRD) in the United States. We reviewed our experience with DN as a cause of ESRD in a predominantly poor, African American (AA) population. METHODS: Charts of patients who entered the ESRD program through the University of Mississippi Medical Center with a primary diagnosis of DN from 1993 through 1998 were reviewed for factors that may affect renal survival. Time from initial clinic visit to entry into the ESRD program, or time to ESRD (TTE), was the primary end point. RESULTS: Five hundred sixty-two patients entered the ESRD program (85% AA), and 210 of them had DN as their primary ESRD diagnosis. DN accounted for 50.5% of ESRD cases among AA females, but for less than 20% among AA males. In contrast, hypertension was the ESRD diagnosis in 48% of AA males. Patients observed in our nephrology clinic were analyzed further (n=171). At presentation, patients had advanced disease (serum creatinine [Cr]=5.92 mg/dL), were hypertensive, obese, and not likely to be on an angiotensin-converting enzyme (ACE) inhibitor. Determinants of TTE in univariate analysis were race (AA did better), initial blood urea nitrogen and plasma serum Cr levels, starting an ACE inhibitor at the University of Mississippi Medical Center, and the level of mean arterial pressure (MAP) during the course of follow-up. On multivariate analysis only initial Cr and race remained significant The 142 AA diabetics (111 female) were analyzed separately. The only significant sex difference was body mass index (female, 33.6 vs male, 28.4 kg/m2; P=0.0069), but females tended to have relatively shorter TTE and higher blood pressure (BP). Univariate and multivariate analyses revealed the same factors as above as determinants of TTE; however, among AAs, presenting on a calcium channel blocker was negatively correlated with TTE in univariate analysis. Among the entire cohort and the AAs, patients who had MAP between 100 and 110 mm Hg during the course of follow-up did better in terms of renal survival than those who fell outside of that range. CONCLUSIONS: We conclude that AA females in Mississippi are significantly more predisposed to DN as a cause of ESRD than are AA males. Patients with DN in our population had poor BP control, presented to nephrologists with advanced disease, and often were not on an ACE inhibitor. The optimal level of BP control and which BP agents are best for this population need to be determined.

The role of hypertension, obesity, and diabetes in causing renal vascular disease.

The Jackson Heart Study will be an epidemiological study of African Americans in Jackson, Mississippi, to identify risk factors for development and progression of cardiovascular disease. One of the potential risk factors to be assessed in this study is renal vascular disease. Atherosclerotic renal vascular disease is a disease of the elderly, is predominantly seen in white people, and is strongly associated with diffuse atherosclerotic disease and high-grade hypertensive retinopathy. Patients with ischemic nephropathy may constitute up to 16% of new dialysis patients and die more quickly while on renal replacement therapy. Although often not present, hypertension is a commonly observed consequence (but probably not a cause) of renal vascular disease, and the control of blood pressure may not halt the progression of the disease. Approximately 20-25% of patients with moderate to severe renal artery stenosis will be diabetic. Diabetic patients fair less well with intervention and have a higher progression to end-stage renal disease or death. Obesity is not commonly seen in patients with renal vascular disease. The Jackson Heart Study may be able to assess the true incidence of atherosclerotic renal vascular disease in African Americans and its impact of cardiovascular morbidity and mortality.

Focal segmental glomerulosclerosis in African Americans: effects of steroids and angiotensin converting enzyme inhibitors.

BACKGROUND: Focal segmental glomerulosclerosis (FSGS) is a common primary glomerulopathy in African Americans. In this report, we present data on 40 African American patients with FSGS from our medical center. METHODS: Patients were identified from a review of all charts seen in our conservative management renal clinic in 1996, a review of renal biopsy rolls (1994-1998), and a review of patients entering the end-stage renal disease (ESRD) program with a primary diagnosis of FSGS (1993- 1997). Charts were reviewed for demographic, biopsy, and treatment data. Patients who were observed for at least 4 months (range, 4-125 months) were included. ESRD was used as the primary endpoint (n = 12). Data were analyzed using univariate and multivariate Cox hazards and Kaplan-Meier survival analysis. Twenty-four patients were treated with angiotensin-converting enzyme (ACE) inhibitors. Similarly, 24 patients were treated with corticosteroids for a mean of 8.75 +/- 2.6 months and a total dose of 9.3 +/- 2.2 g. RESULTS: On univariate analysis, factors found to be significant determinants for reaching ESRD were the initial creatinine (P = 0.0001), interstitial fibrosis (P = 0.032), the percentage of globally sclerosed glomeruli (P = 0.0018), and the mean arterial blood pressure over the course of follow-up (P = 0.05). Neither the ACE inhibitors nor the corticosteroids had a significant impact on reaching ESRD. The patients reaching ESRD (n = 12) were analyzed separately. The mean time from biopsy to ESRD was 24.7 +/- 9.8 months. ACE inhibitors prolonged renal survival (P = 0.023), but steroids did not. Initial creatinine was the only factor found to be a significant determinant for ESRD. CONCLUSIONS: We conclude that FSGS is common in African Americans. Early diagnosis and blood pressure control are important, but the beneficial effects of steroids and ACE inhibitors in this population are still unclear.

Transcriptional regulation of transforming growth factor beta1 by glucose: investigation into the role of the hexosamine biosynthesis pathway.

BACKGROUND: The hexosamine biosynthesis pathway (HBP) is hypothesized to mediate many of the adverse effects of hyperglycemia. We have shown previously that increased flux through this pathway leads to induction of the growth factor transforming growth factor-alpha (TGF-alpha) and to insulin resistance in cultured cells and transgenic mice. TGF-beta is regulated by glucose and is involved in the development of diabetic nephropathy. We therefore hypothesized that the HBP was involved in the regulation of TGF-beta by glucose in rat vascular and kidney cells. METHODS: A plasmid containing the promoter region of TGF-beta1 cloned upstream of the firefly luciferase gene was electroporated into rat aortic smooth muscle, mesangial, and proximal tubule cells. Luciferase activity was measured in cellular extracts from cells cultured in varying concentrations of glucose and glucosamine. RESULTS: Glucose treatment of all cultured cells led to a time- and dose-dependent stimulation in TGF-beta1 transcriptional activity, with high (20 mM) glucose causing a 1.4- to 2.0-fold increase. Glucose stimulation did not occur until after 12 hours and disappeared after 72 hours of treatment. Glucosamine was more potent than glucose, with 3 mM stimulating up to a 4-fold increase in TGFbeta1-transcriptional activity. The stimulatory effect of glucosamine was also dose-dependent but was slower to develop and longer lasting than that of glucose. CONCLUSIONS: The metabolism of glucose through the HBP mediates extracellular matrix production, possibly via the stimulation of TGF-beta in kidney cells. Hexosamine metabolism therefore, may play a role in the development of diabetic nephropathy.

Dignity or denial? Decisions regarding initiation of dialysis and medical therapy in the institutionalized severely mentally retarded.

Decisions regarding health care of the severely mentally retarded can be difficult. We present 2 cases of patients with severe mental retardation who lived in long-term care facilities. Both patients had progressive loss of renal function and eventually reached end-stage renal disease. In each case, the decision was made not to initiate dialysis. We discuss issues of dialysis and medical care of the severely mentally retarded and advocate using the principles of "best respect" and "best interest" in making medical decisions in this population.

"There is power in the blood": a case discussing ethical issues of utility of resources.

The allocation of medical resources is often a great concern in the United States. This article discusses a case concerning utility of resources in a patient with a terminal disease. We assert that the goals of treatment tailored to an individual patient should be made at the bedside by a fiduciary (physician) in conjunction with the patient's preferences and values. There is great responsibility in making these decisions and it is critical that they be made at the bedside with the patient and family clearly aware of the goals of treatments and informed of treatment limitations.