Medial artery calcification of uremic patients: a histological, histochemical and ultrastructural study

Recent findings suggest that vascular calcification (VC) is an active process similar to bone mineralization, the vascular smooth muscle cells (VSMCs) undergoing phenotypic differentiation into osteoblastic cells and synthesizing calcification-regulating proteins found in bone. This study has investigated the VC process of uremic patients, with a morphologic approach. Epigastric artery samples from 49 uremic, non-diabetic patients were taken during kidney transplantation. Sections from paraffin-embedded samples were stained with hematoxylin/eosin and von Kossa. CD68 was immunohistochemically detected, and sections from frozen samples were stained with Oil Red O. Deeply calcified samples were stained with Picrosirius Red, PAS, and Alcian blue. Specimens from one patient with moderate and one with severe VC were examined under the electron microscope. None of the samples had atherosclerosis. Calcifications were found in the media of 38 patients. In 23, dot-like calcifications were irregularly scattered near the adventitia (light VC); in 11, granular calcifications formed concentric rings near the adventitia (moderate-advanced VC); in 4, zones of consolidated calcifications were found (severe VC). These zones were poor in collagen, glycoproteins and proteoglycans. In cases with moderate or severe VC, VSCMs showed necrotic changes. Matrix vesicles could be recognized in the extracellular spaces. In cases with severe VC, uncalcified or partially calcified membranous bodies were found, together with Liesegang rings. Patches of fibrin were also found. These findings point to a mainly degenerative mechanism of VC, which proceeds from the outer portion of the media. An active mechanism, however, cannot be excluded. A unifying hypothesis is suggested.

Risk factors of one year increment of coronary calcifications and survival in hemodialysis patients

Background

Heart and coronary calcifications in hemodialysis patients are of very common occurrence and linked to cardiovascular events and mortality. Several studies have been published with similar results. Most of them were mainly cross-sectional and some of the prospective protocols were aimed to evaluate the results of the control of altered biochemical parameters of mineral disturbances with special regard to serum calcium, phosphate and CaxP with the use of calcium containing and calcium free phosphate chelating agents. The aim of the present study was to evaluate in hemodialysis patients classic and some non classic risk factors as predictors of calcification changes after one year and to evaluate the impact of progression on survival.

Methods

81 patients on hemodialysis were studied, with a wide age range and HD vintage. Several classic parameters and some less classic risk factors were studied like fetuin-A, CRP, 25-OHD and leptin. Calcifications, as Agatston scores, were evaluated with Multislice CT basally and after 12-18 months.

Results

Coronary artery calcifications were observed in 71 of 81 patients. Non parametric correlations between Agatston scores and Age, HD Age, PTH and CRP were significant. Delta increments of Agatston scores correlated also with serum calcium, CaxP, Fetuin-A, triglycerides and serum albumin. Logistic regression analysis showed Age, PTH and serum calcium as important predictors of Delta Agatston scores. LN transformation of the not normally distributed variables restricted the significant correlations to Age, BMI and CRP. Considering the Delta Agatston scores as dependent, significant predictors were Age, PTH and HDL. A strong association was found between basal calcification scores and Delta increment at one year. By logistic analysis, the one year increments in Agatston scores were found to be predictors of mortality. Diabetic and hypertensive patients have significantly higher Delta scores.

Conclusions

Progression of calcification is of common occurrence, with special regard to elevated basal scores, and is predictive of survival. Higher predictive value of survival is linked to the one year increment of calcification scores. Some classic and non classic risk factors play an important role in progression. Some of them could be controlled with appropriate management with possible improvement of mortality.

"De medicina et morbis" from De rerum naturis by Rabano Mauro

De rerum naturis from the Monastery of Montecassino (MS codex 132) by Rabano Mauro, is a medieval encyclopedia issued around the year 1025, in the Abbey of Montecassino, during the period of Abbot Teobaldo. It is a copy of a more ancient text, written almost certainly in the Abbey of Fulda 2 centuries before, when Rabano Mauro was the abbot - that is, in the Carolingian age. In the Book 18 there is a chapter entitled "De medicina et morbis," in which we find related the fundamental principles on which studies of the human body, illness and the principal medicinal herbs were based. The text is not intended for teaching the medical art, but has the precise objective of helping to form the cultured Christian, trying to combine the old Greek-Roman tradition with a mystical vision, giving a moral application according to the dictates of Jewish-Christian religion. This text is indicative of the fusion of the scientific and religious worlds in the West during the Middle Ages. This interpretation of the universe will last for about a millennium, and only the Renaissance will be able to separate the 2 worlds again.

Asymmetric dimethylarginine, vascular calcifications and parathyroid hormone serum levels in hemodialysis patients

BACKGROUND

Asymmetric dimethylarginine (ADMA)is an endogenous amino acid similar to l-arginine and able to inhibit the enzyme endothelial nitric oxide synthase (eNOS). It is a factor of impaired nitric oxide (NO) synthesis. Serum levels of ADMA in chronic kidney disease (CKD) increase due to defective inactivation and excretion. High ADMA levels are associated with endothelial dysfunction and cardiovascular damage. A linkage between ADMA levels and vascular calcifications of CKD can therefore be hypothesized. This study explores also a possible relation between ADMA and parathyroid hormone (PTH) serum levels, which are known to be linked to increased rates of cardiovascular death.

METHODS

The study was carried out in 79 patients on hemodialysis (HD), mean age 59.25 +/- 12 years. In all patients, serum ADMA, PTH, Ca, P, bone alkaline phosphatase (BALP), cholesterol and albumin were measured. In addition, the patients were subjected to multislice computed tomography for heart calcification evaluation.

RESULTS

Correlation analysis of ADMA showed a significant relation with total and coronary calcium volumes, HD vintage, body mass index (BMI), cholesterol, serum albumin, PTH, natural logarithm of PTH (LnPTH) and BALP. Multiple regression analysis selected HD vintage, albumin and PTH as predictive variables for coronary calcium volume, while ADMA was excluded. With LnPTH as dependent variable, ADMA, serum calcium and BMI were predictive variables with R2 of 0.37. ADMA as dependent variable was also predicted by PTH, HD vintage, albumin and BMI.

CONCLUSIONS

Despite the results of bivariate analysis showing a linkage between ADMA and cardiac and coronary calcifications, regression analysis showed only a spurious association. The strong positive correlation between ADMA and LnPTH, validated by the regression analysis, may suggesta link between ADMA and PTH-derived vascular damage. ADMA levels could be influenced by the severity of hyperparathyroidism and contribute to cardiovascular death linked to PTH of hemodialysis patients.

Immunohistochemical localization and mRNA expression of matrix Gla protein and fetuin-A in bone biopsies of hemodialysis patients

Matrix Gla protein (MGP) and fetuin-A are inhibitors of arterial calcifications. In blood of rats, calcium-phosphate-fetuin-MGP complexes, produced in bone, have been identified. Indeed, an association between bone resorption, release of such complexes, and arterial calcifications has been reported. We have investigated the synthesis and localization of fetuin-A and MGP in bone of hemodialysis patients and the possible contribution of bone cells in arterial calcifications. Bone biopsies from 11 hemodialysis patients were used for histology, in situ hybridization of fetuin-A and MGP messenger RNA (mRNA), immunohistochemistry of fetuin-A, and total, carboxylated, and non-carboxylated MGP proteins. Patients showed various types of renal osteodystrophy, or normal bone. MGP was synthesized and expressed (total and carboxylated) by osteoblasts, osteocytes, and most osteoclasts, while fetuin-A by osteoblasts and osteocytes. Fetuin-A and carboxylated MGP proteins were positive in the calcified matrix, while total MGP was negative. Osteoid seams were negative to fetuin-A, lightly positive to carboxylated MGP, and occasionally positive to total MGP. Undercarboxylated MGP was mostly undetectable. In adult humans, fetuin-A is produced also by osteoblasts, and not only by hepatocytes, as previously believed. MGP, essentially carboxylated, is synthesized by osteoblasts and most osteoclasts. Increased bone turnover can be an important contributor to arterial calcifications.

Bone turnover, osteopenia and vascular calcifications in hemodialysis patients. A histomorphometric and multislice CT study

BACKGROUND

Several classical risk factors are at the base of vascular calcifications in hemodialysis patients. Among these, according to a general opinion, also bone turnover plays a role, which, however, requires a better definition. In addition, it has been suggested that there is a relationship between primary osteoporosis and vascular calcifications. This bone biopsy-based study on a hemodialysis patient cohort is a contribution to the evaluation of these alleged relations.

METHODS

This study has been carried out on a cohort of 32 patients on maintenance hemodialysis, who were subjected to transiliac bone biopsy for histomorphometric, histodynamic and bone aluminum deposit evaluation. The patients were also examined with multislice computerized tomography for quantitation of heart and coronary calcifications.

RESULTS

The patients were affected by renal osteodystrophy with a wide range of bone formation rate values. A significant negative correlation was found between the rate of bone turnover and log-transformed cardiac calcification score (p < 0.003). There were also negative significant correlations between the cardiac and coronary calcification score log and trabecular number (p < 0.02 and p < 0.05, respectively), while the correlations were positive with trabecular separation (p < 0.03 and p < 0.05, respectively). However, multiregression analysis, forward method, selected only age, hemodialysis age and serum Ca as predictive variables of cardiac and coronary calcification score log, while the histomorphometric and histodynamic variables were excluded.

CONCLUSIONS

In this study, in spite of the suggestive findings of the univariate statistical approach, a further multivariate analysis was indicative of a spurious association between calcification scores and both bone turnover and histomorphometric parameters of trabecular mass and connectivity. Bone turnover and trabecular mass do not appear to be prominently connected with the extent of cardiac and coronary calcifications in hemodialysis patients.

Are PTH serum levels predictive of coronary calcifications in haemodialysis patients?

BACKGROUND

Cardiac calcifications are a frequent occurrence in uraemic subjects and are probably connected to the increased cardiovascular mortality of haemodialysis patients. There is substantial support to the hypothesis that low levels of serum PTH in haemodialysis patients are associated with increased vascular and cardiac calcium deposits, due to decreased buffering capacity of bone in low turnover osteodystrophy. The present study has been carried out on a cohort of patients on haemodialysis, with exclusion of previously parathyroidectomized patients, with the aim to evaluate the association between PTH serum levels and coronary calcifications.

METHODS

The study has been carried out in a cohort of 197 haemodialysis patients. There were 133 males and 64 females. Twenty-two patients had diabetes mellitus. Average age was 58.6 +/- 12.9 years. Patients were divided into groups of intact PTH levels, 0-150 (A), 150-300 (B), 300-600 (C) and >600 (D) pg/ml.

RESULTS

The values of coronary scores in the PTH groups were as follows: (A) 624.7 +/- 939, (B) 866.4 +/- 1080, (C) 1202.8 +/- 1742.3 and (D) 1872.7 +/- 2961.9. The difference between coronary calcium scores was significant (P < 0.01). A general linear model identified serum calcium and dialysis age as independent factors of calcium deposits in the high PTH group.

CONCLUSIONS

No prominent association between low PTH serum levels and the severity of coronary calcium deposits in haemodialysis patients was found while increased levels of PTH, with special regard to very elevated levels, associated with more frequent hypercalcaemia and hyperphosphataemia, should be considered a major risk factor of coronary calcifications and cardiac events.

Renal osteodystrophy: alpha-Heremans Schmid glycoprotein/fetuin-A, matrix GLA protein serum levels, and bone histomorphometry

BACKGROUND

Fetuin-A of hepatic origin circulates in large amounts in serum, but also is expressed in bone, where it is an inhibitor of transforming growth factor beta (TGF-beta)/bone morphogenetic protein (BMP) proteins. Together with matrix GLA protein (MGP), fetuin-A is able to make up a complex with calcium and phosphate that is more soluble than calcium and phosphate alone, preventing its deposition in extraskeletal tissues. Experimental results suggested that this complex is made at bone tissue level. The aim of this study is to evaluate whether serum fetuin-A and MGP are influenced by type of renal osteodystrophy, they correlate with bone histomorphometric and histodynamic parameters, and/or serum levels may influence bone turnover.

METHODS

Thirty-eight hemodialysis patients who volunteered to undergo a bone biopsy were studied. Patients (27 men, 11 women) had a mean age of 55.2 +/- 11.8 years and dialysis vintage of 75.7 +/- 57.4 months. They were not administered vitamin D or drugs connected with mineral metabolism. They underwent transiliac bone biopsy after tetracycline labeling. Biopsies were performed for histological, histomorphometric, and histodynamic evaluation and aluminum histochemistry. Serum fetuin-A and MGP were measured by using enzyme-linked immunosorbent assay kits.

RESULTS

Serum fetuin-A levels were significantly less than normal, whereas MGP levels were less than the normal average. Fetuin-A levels in patients with hyperparathyroidism, mixed osteodystrophy, and low-turnover osteodystrophy were 0.219 +/- 0.1, 0.27 +/- 0.1, and 0.197 +/- 0.1 ng/mL, respectively (P = not significant). Fetuin-A level significantly correlated inversely with values for several histomorphometric parameters, such as osteoid volume (OV/BV), osteoblastic surface (Ob.S/BS), osteoid surface (OS/BS), and osteoclastic surface (Oc.S/BS). Logistic regression showed odds ratios of 5.3 and 4.9 for the association of high fetuin-A levels with low values for OS/BS and Ob.S/BS, respectively. Results of multiple regression analysis with intact parathyroid hormone and fetuin-A levels as independent variables and OV/BV and Ob.S/BS as dependent variables showed that independent variables correlated significantly with dependent variables, positively for intact parathyroid hormone levels and inversely for fetuin-A levels. MGP levels in patients with hyperparathyroidism, mixed osteodystrophy, and low-turnover osteodystrophy were not significantly different (3.94 +/- 0.86, 3.40 +/- 0.99, and 5.64 +/- 2.4 nmol/L, respectively). By dividing MGP serum values into tertiles, mean values for OV/BV were different (analysis of variance, P < 0.04), with a greater value in the higher MGP tertile. By exclusion of 3 extravariant cases (>3 SDs greater than the mean), 1 case for each type of osteodystrophy, a significant correlation between bone formation rate and MGP serum level was found (P < 0.05). In addition, a significant correlation was found between MGP level and trabecular thickness.

CONCLUSION

Fetuin-A and MGP levels correlated with bone formation parameters. This association could be caused by an effect of these proteins on bone formation, presumably mediated by the TGF-beta/BMP system. Fetuin-A, as opposed to MGP, is known to inhibit the TGF-beta/BMP complex, a protein-cytokine system that appears to be an important regulator of bone formation and probably a factor with an important role in renal osteodystrophy.

Cardiac calcifications: Fetuin-A and other risk factors in hemodialysis patients

Cardiac calcifications are a frequent finding in hemodialysis for chronic renal failure. Several factors may play a role in the intimal and medial calcification of coronary arteries such as age and some known atherogenetic factors. In addition, Fetuin-A has been proposed as a protective agent through solubilization of calcium phosphate salt. Fetuin-A is also a marker of inflammatory-nutritional state, and its changes could be an expression of this condition. The aim of this cross-sectional study is to evaluate the relative importance of risk factors of calcifications with special regard to Fetuin-A. The study was conducted with 132 hemodialysis patients. They were subjected to multislice computed tomography for evaluation of calcium deposits in the heart. In addition, the patients were sampled for evaluation of calcium-phosphate parameters, lipid profile, nutritional and inflammatory markers, and also Fetuin-A. There was a wide variability of the extent of calcium deposits expressed as Agatston score, with only 9.3% of patients without calcifications. Age, hemodialysis age, sex, calcium-phosphate parameters, and lipid profile were important risk factors, together with nutritional and inflammatory status of the patients. An inverse correlation between coronary calcium score and Fetuin-A emerged from a multiple regression analysis. However, there was no significant difference in serum Fetuin-A among different grades of calcium score. By dividing the patients in tertiles of serum Fetuin-A, an association between low levels of Fetuin-A and high calcification score was found. Fetuin-A as dependent variable was strictly linked to prealbumin serum levels. In addition, there was a clear link between cardiac calcification scores and inflammatory-nutritional markers. Serum calcium and treatment with calcitriol emerged as predictive variables of coronary score.Fetuin-A could be involved in the process of calcification both in the case of markedly low serum levels, due to decreased prevention of calcium phosphate precipitation, and also as a marker of inflammation, a well-known risk factor of atherogenesis. Treatment with intravenous calcitriol could marginally enhance cardiac calcifications, probably through its hypercalcemic effect.

Cardiac calcifications in hemodialysis patients assessed with spiral computed tomography

AIM

Cardiac disease is a major cause of mortality in uremic patients. The aim of this paper was to evaluate cardiac calcium content in uremic patients with multislice computed tomography (MSCT).

METHODS

The study has been carried out on 120 uremic and 28 nonuremic patients affected by cardiovascular disease. Serum calcium, phosphorus, calcium-phosphate product, intact PTH were assayed. Several lipidic and nutritional parameters were measured. Calcification values obtained with the MSCT were reported in terms of Agatson scores.

RESULTS

We found that the average score values in cohort on uremic was 10 times higher than in nonuremic patients (score values 3.389 vs 328). Cardiac calcification score was found to be correlated significantly to age (P=0.006), HD age (P=0.010), serum calcium (P=0.006), iPTH (P=0.004). Multiregression analysis (MRA) with the cardiac score as dependent variable selected the following variables (R(2) 0.612): age (P=0.002), HD age (P=0.010), serum cholesterol (P<0.000), triglycerides (P=0.001) and inversely HDL cholesterol (P=0.001) and non-HDL cholesterol (P=0.001) as predictive variables for cardiac score. By comparing patients with scores lower and higher than 400, the group with score <400 showed a significantly lower age (P=0.0001), HD vintage (P=0.01) and a significantly higher serum cholesterol (P=0.009), HDL cholesterol (P=0.05) and non-HDL cholesterol (P=0.05).

CONCLUSIONS

The MSCT could help in identifying and stratifying high-risk patients to implement preventive strategies. The control of mineral metabolism and of lipid levels is important in prevention of arterial calcification in uremic patients.

[Can cardiovascular calcifications be prevented in chronic kidney disease?]

Chronic kidney disease, with special regard to hemodialysis patients, develop frequent and widespread cardiac and vascular calcifications. In the heart calcifications are mainly located in the coronary arteries and in the valvular structures. There is a strict relation between cardiovascular mortality in CKD and the extent of cardiac and vascular calcifications. Therefore it is important to evaluate the causes of extraskeletal calcifications for the evaluation of the possibility of prevention. The importance of hyperphosphatemia, of hypercalcemia and of the increased CAxP product as a cause of cardiac calcification has been clearly underlined. However the mechanism of calcification, initially considered a physico-chemical precipitation, has been investigated with the conclusion that the process is mediated by cellular differentiation and production of factors favoring mineralization in the extracellular milieu. Increased serum phosphate levels are able to induce a transformation of vascular smooth muscle cells into osteoblast-like cells, able to produce factors known to be pro-mineralizing agents in the bone tissue. Further studies have revealed the importance of a number of inhibitors of calcification of cardiovascular structures, like Fetuin-A, MGP, Osteopontin, Osteoprotegerin. Therefore at present the calcification process of vascular tissue is considered to be linked to a balance between inducers and inhibitors of calcium-phosphate deposits. Prevention of cardiac calcifications is at present mainly based of optimal control of serum phosphate and reduction of calcium load through the use of non-calcium containing phosphate binders. Treatment with statins for prevention and treatment of atherosclerosis is also an important means of decreasing the size and number of atherosclerotic plaques, where a portion of the calcification process develops.

[Sustained low-efficiency dialysis (SLED) in patients with prevalent systolic heart failure refractory to medical treatment and with chronic renal failure]

Systolic heart failure refractory to conventional medical therapy is the principal cause of the high hospitalization rates and of high mortality risks. When this condition is associated with chronic renal failure it is necessary to treat the body liquid composition alterations, and the alterations in the hemodynamic state without creating low flow conditions, trying to achieve an electrolytic and an acid-base balance to reduce the plasmatic volume and permit refilling between the interstitium and plasm. Sustained low-efficiency dialysis (SLED) is a dialysis technique allowing the maintenance of hemodynamic stability through a reduced ultrafiltration rate, it allows an adequate clearance of small solutes, and with sustained treatment it maximizes the dialysis dose and determines a clinical improvement through the removal of the hydric overload. Our experience suggests that SLED is a substitutive treatment for acute dialysis in patients with systolic heart failure refractory to conventional medical treatment.

[Quality of life in patients with combined treatments for heart failure]

The low quality of life in patients with end-stage heart failure is correlated, above all, to frequent hospitalization and to the awareness of having an illness that limits survival. The quality of life in these patients with heart failure using treatment with sustained low efficiency dialysis (SLED) is determined through the Minnesota Living with Heart Failure (MLHF) Questionnaire. The reliability of this evaluation system has been examined through consultation with international trials. After 1 yr of this treatment, we observed an improvement in quality of life.

25-hydroxyvitamin D levels and bone histomorphometry in hemodialysis renal osteodystrophy

BACKGROUND

The importance of 25-hydroxyvitamin D (25-OHD) serum levels in hemodialysis chronic renal failure has not been so far histologically evaluated. Information still lacking relate to the effect of 25-OHD deficiency on serum parathyroid hormone (PTH) levels and on bone and its relationship with calcitriol levels.

METHODS

This retrospective study has been performed on a cohort of 104 patients on hemodialysis from more than 12 months, subjected to transiliac bone biopsy for histologic, histomorphometric, and histodynamic evaluation. The patients, 61 males and 43 females, mean age 52.9 +/- 11.7 years, hemodialysis length 97.4 +/- 61.4 months, were treated with standard hemodialysis and did not receive any vitamin D supplementation. Treatment with calcitriol was not underway at the time of the biopsy. Transiliac bone biopsies were performed after double tetracycline labels. In addition, serum intact PTH (iPTH), alkaline phosphatase, and 25-OHD were measured. Calcitriol serum levels was also measured in a subset of patients (N= 53). The patients were divided according to serum 25-OHD levels in three groups: (1) 0 to 15 (15 patients), (2) 15 to 30 (38 patients), and (3) >30 ng/mL (51 patients).

RESULTS

There was no significant difference in average age, hemodialysis age, serum PTH [490 +/- 494, 670 +/- 627, and 489 +/- 436 pg/mL, respectively (mean +/- SD)], alkaline phosphatase, and calcitriol between the three groups. The parameters double-labeled surface, trabecular mineralizing surface, and bone formation rate were significantly lower in group 1 than in the other groups (P < 0.03, < 0.03, and < 0.02, respectively). Osteoblast surface and adjusted apposition rate were borderline significantly lower in group 1 (P < 0.06 and < 0.10). There was no statistical difference in the biochemical and bone parameters between groups 2 and 3. A positive significant correlation was found between several bone static and dynamic parameters and 25-OHD levels in the range 0 to 30 ng/mL, showing a vitamin D dependence of bone turnover at these serum levels. However, actual evidence of an effect on bone of 25-OHD deficiency was found at serum levels below 20 ng/mL. With increasing 25-OHD levels beyond 40 ng/mL, a downslope of parameters of bone turnover was also observed.

CONCLUSION

Since PTH serum levels are equally elevated in low and high 25-OHD patients, while calcitriol levels are constantly low, an effect of 25-OHD deficiency (group 1) on bone, consisting of a mineralization and bone formation defect, can be hypothesized. The effect of vitamin D deficiency or bone turnover is found below 20 ng/mL. The optimal level of 25-OHD appears to be in the order of 20 to 40 ng/mL. Levels of the D metabolite higher than 40 ng/mL are accompanied by a reduction of bone turnover.

[Dialytic treatment in patients with renal insufficiency and heart failure refractory to combined drug therapy]

The incidence and prevalence of heart failure are continuously on the increase. Pharmacological therapy is not sufficient in the advanced stages of the illness to control the signs and symptoms, especially when stressing factors intervene and complicate the illness course. Dialytic treatments are always indicated more than necessary in the severe forms of heart failure, but the optimal treatment has not yet been established. In our division, 24 patients with heart failure (III-IV NYHA) and renal failure (III-IV NKF-DOQI) were treated with low flux bicarbonate dialysis, variable dialysate and limited ultra-filtration. Arrhythmia, pericarditis, ischemic cardiopathy and hyponatremia were the stressing factors that determined acute heart failure. Fifteen patients presented with diastolic failure, whereas nine patients had systolic heart failure. The first group of patients had higher arterial pressure, better ejection fraction and better prognosis regarding renal function and survival rate. The results obtained with this treatment in prevalently diastolic heart failure are satisfactory in terms of survival, as well as in renal function recovery, whereas they are not adequate in systolic failure where other approaches are being studied. Therefore, we believe that the therapeutic choice must always be determined in relation to the type of heart failure.

Inositol and phosphate regulate GIT1 transcription and glycerophosphoinositol incorporation in Saccharomyces cerevisiae

Glycerophosphoinositol is produced through deacylation of the essential phospholipid phosphatidylinositol. In Saccharomyces cerevisiae, the glycerophosphoinositol produced is excreted from the cell but is recycled for phosphatidylinositol synthesis when inositol is limiting. To be recycled, glycerophosphoinositol enters the cell through the permease encoded by GIT1. The transport of exogenous glycerophosphoinositol through Git1p is sufficiently robust to support the growth of an inositol auxotroph (ino1Delta). We now report that S. cerevisiae also uses exogenous phosphatidylinositol as an inositol source. Evidence suggests that phosphatidylinositol is deacylated to glycerophosphoinositol extracellularly before being transported across the plasma membrane by Git1p. A genetic screen identified Pho86p, which is required for targeting of the major phosphate transporter (Pho84p) to the plasma membrane, as affecting the utilization of phosphatidylinositol and glycerophosphoinositol. Deletion of PHO86 in an ino1Delta strain resulted in faster growth when either phosphatidylinositol or glycerophosphoinositol was supplied as the sole inositol source. The incorporation of radiolabeled glycerophosphoinositol into an ino1Delta pho86Delta mutant was higher than that into wild-type, ino1Delta, and pho86Delta strains. All strains accumulated the most GIT1 transcript when incubated in media limited for inositol and phosphate in combination. However, the ino1Delta pho86Delta mutant accumulated approximately threefold more GIT1 transcript than did the other strains when incubated in inositol-free media containing either high or low concentrations of P(i). Deletion of PHO4 abolished GIT1 transcription in a wild-type strain. These results indicate that the transport of glycerophosphoinositol by Git1p is regulated by factors affecting both inositol and phosphate availabilities and suggest a regulatory connection between phosphate metabolism and phospholipid metabolism.

Depletion of host-derived cyanide in the gut of the eastern tent caterpillar, Malacosoma americanum

Using a colorimetric procedure, we assessed the HCN-p of black cherry leaves (Prunus serotina) ingested by the eastern tent caterpillar, Malacosoma americanum, and the cyanide content of the bolus as it passed thorough the caterpillar's digestive tract and into the detritus pool. The mean HCN-p of leaves in our study area was 1902 +/- 174 (SE) ppm. Young leaves found at the tips of growing branches, which the caterpillars preferred, had a significantly higher HCN-p (3032 +/- 258 ppm) than older leaves found at the middle (1542 +/- 243 ppm) or base of the shoot (1131 +/- 159 ppm). Following a bout of overnight feeding on young leaves, the cyanide content of the foregut and midgut boluses of early sixth-instar caterpillars averaged 631 +/- 161 ppm, and 14 +/- 3 ppm, respectively, indicating that host-derived cyanide is rapidly depleted as the bolus transits the gut. Some cyanide, however, remains. In three studies, the mean cyanide content of fresh fecal pellets ranged from approximately 20 to 38 ppm, while the dried, compacted pellets ranged from 63 to 85 ppm. Food in the foreguts of mature caterpillars dispersing over the ground in search of pupation sites had 417 +/- 99 ppm cyanide. The potential impact of this egested and caterpillar-transported cyanide on the consumer and detritivore communities is discussed.

Calcitriol per os once, twice or three times a week: effect of different schedules of administration in hemodialysis patients

Administration of a single dose of 1,25-OH(2)D(3) can lower PTH levels for up to 4 days in chronic hemodialysis patients. Our purpose was to verify the effects of the same weekly dose of calcitriol per os given in one, two or three administrations, to patients on dialysis with secondary hyperparathyroidism. Thirty patients were studied, divided in to three groups each of 10 patients. Calcitriol therapy in group A was given as a single weekly dose of 0.08 microg/kg b.w. In group B the same total weekly dose was divided in two equal doses. In group C the same total weekly dose was divided in three times. Treatment lasted 2 months. After 8 weeks of therapy the fall in intact PTH was statistically significant in each group, respectively with one-way ANOVA: p<0.02 (A); p<0.002 (B); p<0.001 (c). Two-way ANOVA for comparison of PTH % variation among the three groups was statistically significant p<0.003. Significance was due to difference between group A and groups B and C. The present study confirms the efficacy of single dose in suppressing significantly intact PTH. However, when the same weekly dose is divided into two or in three time-spaced administrations, the suppressive effects are definitely increased.

Ischemic nephropathy in an elderly nephrologic and hypertensive population

BACKGROUND

Atherosclerotic renovascular disease is a frequent cause of end-stage renal failure leading to dialysis in the elderly population. Its prevalence is known from autopsy or retrospective arteriographic investigations. This prospective study was conducted in 133 subjects with the inclusion criteria of hypertension and/or chronic renal failure starting after 50 years of age. Renal failure was unrelated to other known causes of renal disease.

METHODS

The patients were subjected to echo-color doppler ultrasonography of renal arteries (104) and/or to renal scintigraphy (112). Thirteen of 27 patients with positivity using one or both noninvasive techniques were subjected to digital selective angiography.

RESULTS

All the patients with positivity of echo-color doppler technique were true positives, with a consequent predictive value reaching 100%. Renal scintigraphy was of markedly lower predictive value. Based on the echo-color doppler investigation, percentage positivity for hemodynamically significant stenosis (> 50%) was 3.2 (16.3% had mild nonsignificant stenosis of renal arteries) in the 50- to 59-year-old group, 20% (plus 12.5% with nonsignificant stenosis) in the 60- to 69-year-old group and 25% (plus 17.8% nonsignificant stenosis) in the > 70-year age group. Patients with significant stenosis also had a significantly higher degree of renal insufficiency and received a higher number of hypotensive drugs (p < 0.013). The percentage of hypertensive patients was not different in the stenotic and nonstenotic groups.

CONCLUSIONS

A large percentage of the elderly population is affected by renal vascular obstructive disease and is at risk of developing end-stage renal failure. Considering the wide number of cases with foreseeable renal arterial stenosis in the vast population meeting the selection criteria, it is possible to conclude that not all cases evolve to renal failure due to different rates of progression or to untimely nonrenal death.

Urinary deoxypyridinoline excretion for the evaluation of bone turnover in chronic renal failure

BACKGROUND

The urinary excretion of deoxypyridinoline (DPD) was evaluated in predialysis chronic renal failure (CRF), together with intact PTH and several classic markers of bone turnover in order to assess whether urine free and total DPD excretion are equivalent parameters of bone turnover in CRF, and to evaluate the relationship between urine DPD excretion, PTH and the other bone markers.

METHODS

The study was carried out in 94 patients with different degrees of renal failure due to various kidney diseases. Besides urinary DPD expressed as free DPD, total DPD, free/total DPD, free DPD/Cr and total DPD/Cr, the following determinations were made: intact PTH, bone alkaline phosphatase (BALP), total alkaline phosphatase (AP), osteocalcin (BGP), serum C-terminal telopeptide of collagen type I (ICTP) and hydroxyproline (OHpro). The patients were divided into 3 groups according to the increasing severity of renal failure (Ccr >40, 40-20, <20 ml/min).

RESULTS

The ratio free/total DPD decreased (NS) with advancing renal failure, and was inversely correlated with total DPD excretion. While PTH increased progressively to about four times the values observed in the Ccr >40 group, there was a parallel increase only in BGP and ICTP, parameters retained in the serum with decreasing renal function, while AP, BALP, total DPD and OHpro did not change. However, significant correlations between total DPD/Cr and PTH, BALP, BGP and ICTP were also found.

CONCLUSIONS

In CRF free DPD is an unreliable index of bone turnover due to a probable interference in its production from the peptide-bound DPD. Total DPD or total DPD/Cr are better used. In spite of the significant correlations observed in advanced renal failure between PTH and most of the parameters examined, a resistance of bone tissue to PTH action in CRF must be considered.

Bone markers in the diagnosis of low turnover osteodystrophy in haemodialysis patients

BACKGROUND

Renal osteodystrophy includes a number of low and high turnover bone histologic patterns which require a bone biopsy for their full identification. The role of intact PTH and several classical and more recent bone markers in the non-invasive diagnosis of renal bone disease in patients with CRF in HD requires further definition since available published data are limited.

METHODS

In addition to intact PTH, alkaline phosphatase (AP) and osteocalcin (BGP), bone alkaline phosphatase isoenzyme (BALP), tartrate resistant acid phosphatase (TRAP), C-terminal cross-linked peptide of collagen type 1 (ICTP) and deoxypyridinoline (DPD) were measured in the serum of 41 patients on haemodialysis, subjected at the same time to transiliac bone biopsy for histomorphometric, histodynamic and aluminium histochemical examination. Histodynamic evaluation following double tetracycline label, was carried out in 37 patients. The patients had no evidence of active cytolytic and cholestatic liver disease and a history of very limited aluminium exposure.

RESULTS

The patients had differing degrees of hyper-parathyroidism, with intact PTH ranging from normal to very elevated levels. Serum values of the markers BGP, ICTP and DPD, normally excreted through the kidneys, were on average very high. The correlation coefficients of the humoral parameters vs dynamic variables, such as BFR/BS, were high. The highest values were: intact PTH 0.798, AP 0.900, BALP 0.891, ICTP 0.807. The patients, grouped in low turnover osteodystrophy (LTO; 9), mixed osteodystrophy (MO; 9) and prevalent hyperparathyroidism (HP; 23), showed significant difference in the levels of most humoral and static and dynamic parameters (ANOVA). Bone aluminium histochemistry was negative in all cases. Discrimination of LTO patients from the other groups by humoral parameters, at the highest value of accuracy, showed 100% sensitivity and 93.7% specificity with a cut-off of 12.9 ng/ml for BALP; 88.9% sensitivity and 93.7% specificity with a cut-off of 21.5 ng/ml for DPD, and 88.9% sensitivity and 90.6% specificity with a cut-off of 79.7 pg/ml for intact PTH. The other markers had lower values. A standardized z-score approach for evaluation of all humoral parameters was also carried out. Using all variables, a correct classification of MO/HP and of LTO was possible in 93.8 and 88.9% of the cases, respectively. Predictive power was 96.8 and 80%, respectively for MO/HP and LTO. When the only variables used were intact PTH and BALP, a correct classification of MO/HP and LTO was possible in 90.6% and 88.9%, respectively. Predictive value of MO/HP was 96.7% and for LTO 72.7%. Predictive values using PTH and AP were 96.3% and 57.2%, respectively.

CONCLUSION

Intact PTH and several relatively new bone markers are of certain value in the non-invasive diagnosis of renal osteodystrophy. However some of the humoral markers carry the same quality of information and the use of intact PTH and BALP may be adequate in the discrimination of bone histologic patterns. In cases exempt from liver disease, PTH and AP may be used as a less costly alternative. Bone biopsy could be chiefly limited to cases with borderline humoral values and to all those with a suspected aluminium overload.