[Spinal muscular atrophy : Time for newborn screening?] / Spinale Muskelatrophie : Zeit für das Neugeborenenscreening?

The most common neurodegenerative disease in childhood is spinal muscular atrophy (SMA). The severe infantile type 1 (Werdnig-Hoffman disease) makes 60% of SMA in total. These children usually die within 18 months without ventilation. New therapeutic approaches have led from the theoretical concept to randomized controlled clinical trials in patients. For the first time, a pharmacological treatment of SMA has been approved. The early detection of the disease is decisive for the success of therapy. All previous data suggest starting treatment early and when possible prior to the onset of symptoms considerably improves the outcome in comparison to a delayed start. The goal must be the presymptomatic diagnosis in order to initiate treatment before motor neuron degeneration. Technical and ethical prerequisites for a molecular genetic newborn screening are given.

Dissection of biochemical borderline phenotypes in carriers and genetic variants of medium-chain acyl-CoA dehyrogenase deficiency: implications for newborn screening [corrected].

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) represents a potentially fatal fatty acid beta-oxidation disorder. Newborn screening (NBS) by tandem mass spectrometry (MS/MS) has been implemented worldwide, but is associated with unresolved questions regarding population heterogeneity, burden on healthy carriers, cut-off policies, false-positive and negative rates. In a retrospective case-control study, 333 NBS samples showing borderline acylcarnitine patterns but not reaching recall criteria were genotyped for the two most common mutations (c.985A>G/c.199C>T) and compared with genotypes and acylcarnitines of 333 controls, 68 false-positives, and 34 patients. c.985A>G was more frequently identified in the study group and false-positives compared to controls (1:4.3/1:2.3 vs. 1:42), whereas c.199C>T was found more frequently only within the false-positives (1:23). Biochemical criteria were devised to differentiate homozygous (c.985A>G), compound heterozygous (c.985A>G/c.199C>T), and heterozygous individuals. Four false-negatives were identified because our initial algorithm required an elevation of octanoylcarnitine (C(8)) and three secondary markers in the initial and follow-up sample. The new approach allowed a reduction of false-positives (by defining high cut-offs: 1.4 micromol/l for C(8); 7 for C(8)/C(12)) and false-negatives (by sequencing the ACADM gene of few suspicious samples). Our validation strategy is able to differentiate healthy carriers from patients doubling the positive predictive value (42-->88%) and to target NBS to MCADD-subsets with potentially higher risk of adverse outcome. It remains controversial, if NBS programs should aim at identifying all subsets of all diseases included. Because the natural course of milder variants cannot be assessed by observational studies, our strategy could serve as a general model for evaluation of MS/MS-based NBS.

Increased levels of HPV16 E6*I transcripts in high-grade cervical cytology and histology (CIN II+) detected by rapid real-time RT-PCR amplification.

OBJECTIVE: As cervical dysplasia may regress to normal cytology or progress to cervical carcinoma, it would be valuable to have a diagnostic tool to help decide whether therapeutic conization should be performed. METHODS: Cervical samples of 301 HPV16 positive women were collected in RNAlater reagent to prevent RNA degradation. Relative levels of HPV16 DNA and HPV16 E6*I mRNA in the samples were determined using real-time polymerase chain reaction. Findings were correlated with histological diagnoses and cytological follow-up. RESULTS: HPV16 E6*I mRNA levels were significantly higher in women with cytologically diagnosed severe cervical dysplasia (mean normalized ratio = 0.25) than in those with mild-to-moderate dysplasia (mean norm. ratio = 0.12), atypical squamous cells of uncertain origin (mean norm. ratio = 0.071) or normal cytology (mean norm. ratio = 0.034). Viral DNA levels were not significantly different between severe and mild-to-moderate dysplasia (mean norm. ratios, 55.8 and 63.5, respectively). The PPV for a histological diagnosis of severe cervical dysplasia [cervical intraepithelial neoplasia (CIN) II+] increased with the amounts of E6*I mRNA to more than 90% whereas the sensitivity decreased. The absence of HPV16 E6*I transcripts as well as HPV16 DNA considerably increased the negative predictive value and the specificity. However, low concentrations (or complete absence) of E6*I mRNA did not preclude a CIN II+ diagnosis. CONCLUSIONS: Although the sensitivity is low, high levels of HPV16 E6*I mRNA are indicative of CIN II+ in cytologically diagnosed cervical dysplasia of individual patients. Thus, quantification of HPV16 E6*I mRNA could be helpful in managing follow-up and treatment in a subset of HPV16 positive women.

Methionine adenosyltransferase (MAT) I/III deficiency with concurrent hyperhomocysteinaemia: two novel cases.

This study reports three novel mutations of the methionine adenosyltransferase (MAT) lA gene and confirms that hyperhomocysteinaemia may be a characteristic finding in MAT I/III deficiency. Thus, MAT I/III deficiency is important in the differential diagnoses of hyperhomocysteinaemia, which may lead to clinical complications of MAT I/III deficiency.

Supervised machine learning techniques for the classification of metabolic disorders in newborns.

MOTIVATION: During the Bavarian newborn screening programme all newborns have been tested for about 20 inherited metabolic disorders. Owing to the amount and complexity of the generated experimental data, machine learning techniques provide a promising approach to investigate novel patterns in high-dimensional metabolic data which form the source for constructing classification rules with high discriminatory power. RESULTS: Six machine learning techniques have been investigated for their classification accuracy focusing on two metabolic disorders, phenylketo nuria (PKU) and medium-chain acyl-CoA dehydrogenase deficiency (MCADD). Logistic regression analysis led to superior classification rules (sensitivity >96.8%, specificity >99.98%) compared to all investigated algorithms. Including novel constellations of metabolites into the models, the positive predictive value could be strongly increased (PKU 71.9% versus 16.2%, MCADD 88.4% versus 54.6% compared to the established diagnostic markers). Our results clearly prove that the mined data confirm the known and indicate some novel metabolic patterns which may contribute to a better understanding of newborn metabolism.

Lung function of school children with low levels of alpha1-antitrypsin and tobacco smoke exposure.

Exposure to environmental tobacco smoke (ETS) and other air pollutants has been associated with small decrements in lung function. The susceptibility to pollution exposure may, however, vary substantially between individuals. Children with an impaired protease-antiprotease balance may be particularly vulnerable. Therefore this study aimed to investigate the effects of ETS exposure on children with reduced levels of alpha1-antitrypsin (alpha1-AT). Random samples of school children (aged 9-11 yrs) (n=3,526) were studied according to the International Study of Asthma and Allergies in Childhood (ISAAC) phase II protocol, including parental questionnaires, pulmonary function and allergy testing. Blood samples were obtained to measure plasma levels of alpha1-AT and to genotype for pleomorphic protein inhibitor (Pi)Z and PiS alleles. Children with low levels of alpha1-AT (< or = 116 mg x dL(-1)) showed significant, albeit small decrements in baseline lung function. When exposed to ETS, pronounced decrements of pulmonary function, particularly in measures of mid- to end-expiratory flow rates, were seen in these children as compared to exposed children with normal levels of alpha1-AT. The mean levels of % predicted+/-SE in both groups were: maximum expiratory flow at 50% of vital capacity 79.4+/-7.2 versus 99.0+/-1.5, maximum expiratory flow at 25% of vital capacity 67.4+/-10.0 versus 100.3+/-2.1, maximal midexpiratory flow 73.7+/-8.6 versus 99.9+/-1.7. These findings suggest that school children with low levels of alpha1-antitrypsin are at risk of developing pronounced decrements in pulmonary function, particularly if they are exposed to environmental tobacco smoke. Parents of children with heterozygous alpha1-antitrypsin deficiency resulting in significantly reduced blood concentrations should be advised to prevent their children from being exposed to environmental tobacco smoke and dissuade them from taking up smoking.

Hepatic carnitine palmitoyltransferase I deficiency: acylcarnitine profiles in blood spots are highly specific.

BACKGROUND: In carnitine palmitoyltransferase I (CPT-I) deficiency (MIM 255120), free carnitine can be increased with no pathologic acylcarnitine species detectable. As inclusion of CPT-I deficiency in high-risk and newborn screening could prevent potentially life-threatening complications, we tested whether CPT-I deficiency might be diagnosed by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). METHODS: A 3.2-mm spot of whole blood dried on filter paper was extracted with 150 microL of methanol. After derivatization of carnitine and acylcarnitines to their butyl esters, the samples were analyzed by ESI-MS/MS with 37.5 pmol of L-[(2)H(3)]carnitine and 7.5 pmol of L-[(2)H(3)]palmitoylcarnitine as internal standards. RESULTS: In all dried-blood specimens from each of three patients with CPT-I deficiency, we found an invariably increased ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)]. The ratio in patients was between 175 and 2000, or 5- to 60-fold higher than the ratio for the 99.9th centile of the normal newborn population in Bavaria (n = 177 842). No overlap with the values of children that were known to be supplemented with carnitine was detected [C0/(C16 + C18), 34 +/- 30; mean +/- SD; n = 27]. CONCLUSIONS: ESI-MS/MS provides a highly specific acylcarnitine profile from dried-blood samples. The ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)] is highly specific for CPT-I deficiency and may allow presymptomatic diagnosis.

The biochemical metabolite screen in the Munich ENU Mouse Mutagenesis Project: determination of amino acids and acylcarnitines by tandem mass spectrometry.

BACKGROUND: Gene mutations often result in altered protein expression and, in turn, lead to changes in metabolite levels in one or more distinct biochemical pathways. Traditional analytical methods for metabolite determination are usually time consuming, expensive, and, thus, not suitable for high throughput analysis. However, recent developments in electrospray-tandem-mass-spectrometry allow comprehensive metabolite scanning from very small amounts of blood with high speed, cost effectiveness, and accuracy. METHODS: A blood spot from a filter paper equivalent to 3 microl of blood was punched out and transferred to a 96-well microtiter plate. After addition of a set of 14 stable isotope-labeled internal standards, amino acids and acylcarnitines were extracted with methanol. The dried residue was derivatized with butanolic hydrochloric acid and subjected to MSMS analysis. RESULTS: Acyl-carnitines were all determined by a precursor ion scan of 85 Da. Neutral loss scanning of 102 Da was suitable for the quantitation of threonine, serine, proline, histidine, alanine, aspartic acid, glutamic acid, methionine, tyrosine, phenylalanine, isoleucine/leucine and valine. Glycine was detected by a loss of a 56-Da fragment, whereas a 119-Da loss was suitable for the measurement of citrulline, ornithine, arginine, and lysine. Specific problems encountered: owing to their identical molecular weight, isoleucine and leucine could not be quantitated separately, and, owing to their instability, glutamine and asparagine were found to be decarboxylated to their respective acids. Determination was linear over the concentration range tested (20 to 1000 micromol/L), and intraassay and interassay coefficients of variation were in the range of 10-15%. CONCLUSION: ESI-MSMS proved to be a highly sensitive, linear, and sufficiently precise method for the quantitative determination of amino acids and acylcarnitines in mouse blood, allowing large-scale screening applications when speed and cost effectiveness are mandatory.

[Model project for updating neonatal screening in Bavaria: concept and initial results]. / Modellprojekt zur Neuordnung des Neugeborenen-Screenings in Bayern: Konzeption und erste Ergebnisse.

The newborn screening programme in Bavaria was confronted with several problems. Number of disorders and process quality no longer complied with screening guidelines. Mixed financing, distributed between the state (PKU, galactosaemia) and health insurances (hypothyroidism) had promoted an increasing dissipation of the system. Notified participation rates had dropped to < 80%. Increasing need for a second screening due to early discharge was an additional challenge. To overcome these problems, and considering the availability of improved screening methodology (tandem mass spectrometry) the programme was reorganised. The project, which started on Jan 1, 1999, is based on a cooperation model between laboratory (logistics, analysis), universities (treatment, scientific evaluation), and public health services (coordination, tracking). Time of blood sampling was predated to the third day of life. Screening was extended to biotinidase deficiency, congenital adrenal hyperplasia (CAH) and by introduction of tandem mass spectrometry for screening of many other disorders (besides PKU). Insurances now finance complete laboratory analysis which was transferred to the private sector. To enable all newborn to participate, the names of screened children are matched against birth lists by public health services on a regional basis. Recalls and conspicuous results are consistently followed up until disorders are either excluded or confirmed. Two clinical hotlines were established in the children's hospitals of the universities in Munich (Southern Bavaria) and in Erlangen (Northern Bavaria). Written consent is required for participation in the programme. Participation in the new programme could be continually increased; coverage is > 95% since April. In several cases screening was made up for not tested children by contacting their parents. Omitted screening was mostly due to misunderstandings regarding testing responsibility or lost samples. Altogether 52 cases of disorder were found in the 87,000 newborn screened until August 1999. Hence, the detection rate of children affected by inborn errors of metabolism was about twice as high than before changes. Among the newly screened diseases CAH was detected most often (11 cases). In 22 cases diagnosis was based on the use of tandem mass spectrometry. Among these (besides PKU, 9 cases) MCAD deficiency (6 cases) was detected most frequently. Whereas recall rates of most disorders were < 0.1%, screening for CAH still revealed a high recall rate, particularly in premature births. Second screening due to early discharge (< 48 h) was required in 1.3%. About 20% of pending recalls required contacting birth hospitals, doctors, midwives or parents. So far all affected children could be brought to treatment in time.

Quantitative measurement of different ceramide species from crude cellular extracts by electrospray ionization tandem mass spectrometry (ESI-MS/MS).

Ceramide (CER) is an important signaling molecule involved in a variety of cellular processes, including differentiation, cell growth, and apoptosis. Currently, different techniques are applied for CER quantitation, some of which are relatively insensitive and/or time consuming. Tandem mass spectrometry with its high selectivity and sensitivity is a very useful technique for detection of low abundant metabolites without prior purification or derivatization. In contrast to existing mass spectrometry methods, the developed electrospray tandem mass spectrometry (ESI-MS/MS) technique is capable of quantifying different CER species from crude cellular lipid extracts. The ESI-MS/MS is performed with a continuous flow injection and the use of an autosampler, resulting in a high throughput capability. The collision-induced fragmentation of CER produced, in addition to others, a characteristic fragment of m/z 264, making a precursor ion scan of 264 well suited for CER quantitation. Quantitation is achieved by use of a constant concentration of a non-naturally occurring internal standard C8-CER, together with a calibration curve established by spiking different concentrations of naturally occurring CER. The calibration curves showed linearity over a wide concentration range and sample volumes equivalent to 10 microg of cell protein corresponding to about 20, 000 fibroblasts were sufficient for CER analysis. Moreover this assay showed a detection limit at the subpicomole level. In summary, this methodology enables accurate and rapid analysis of CER from small samples without prior separation steps, thus providing a useful tool for signal transduction research.

High glucose-induced TGF-beta 1 regulates mesangial production of heparan sulfate proteoglycan.

Previous investigations have demonstrated that growing mesangial cells in high glucose concentration stimulates extracellular matrix synthesis and also increases the expression of transforming growth factor-beta (TGF-beta). We examined the effects of hyperglycemia on mesangial proliferation and heparan sulfate proteoglycan (HSPG) and fibronectin production. Prolonged exposure of mesangial cells to increasing glucose concentrations resulted in dose-dependent effects on growth inhibition and stimulation of matrix production. Treatment of mesangial cells with high glucose-conditioned medium or with TGF-beta 1 mimicked the effects of high-glucose incubation. Furthermore, TGF-beta 1 caused a dose-dependent increase in HSPG mRNA levels. The high-glucose effects on mesangial cells were preceded by an increase in total TGF-beta 1 protein. The presence of TGF-beta 1 antisense oligonucleotide attenuated the glucose-mediated effects on mesangial proliferation and matrix production. The data show that even moderately elevated glucose concentrations appear to affect the mesangial cells. The results indicate that 1) TGF-beta 1 protein production is necessary to obtain the high glucose-induced effects and 2) TGF-beta 1 stimulates mesangial HSPG expression and production. Because these effects may be attenuated by oligonucleotides antisense to TGF-beta 1, the results suggest a possible way for effective intervention in TGF-beta-mediated glomerulosclerosis.

Heparin induces endothelial extracellular matrix alterations and barrier dysfunction.

We investigated the influence of heparin on the composition of the subendothelial matrix and on endothelial permeability to elucidate the structure-function relationship of matrix composition and permeability. Albumin flux across the confluent endothelial monolayers was used to assess the macromolecular permeability. Lowest values were obtained when 100% serum was used as medium for permeability studies. The endothelial matrix components, fibronectin and basement membrane-associated heparan sulfate proteoglycan (HSPG), were measured by enzyme immunoassay. Treatment of proliferating endothelial cells with heparin (0-900 micrograms/ml) induced a dose-dependent decrease in endothelial HSPG content, whereas the fibronectin content was unaltered. This structural change was accompanied by an increase in albumin permeability. Both heparin effects exhibited similar dose-response curves with half-maximal effects at approximately 5 micrograms/ml heparin. Acute addition of 300 micrograms/ml heparin had no effect on permeability or HSPG content. When endothelial cells were preincubated with an HSPG antiserum, the endothelial permeability increased nearly threefold. Our results indicate that heparin-induced loss of HSPG may cause the increase in endothelial permeability. The data underline the importance of HSPG for the integrity of the endothelial barrier.

Atherogenic levels of low density lipoprotein alter the permeability and composition of the endothelial barrier.

In the present study we investigated the influence of elevated low density lipoprotein (LDL) concentration on endothelial permeability. Endothelial cells were cultured on microporous membranes until confluence and albumin, dextran and LDL transfer across endothelial monolayers was determined to assess macromolecular permeability. Exposure of proliferating aortic endothelial cells to LDL levels of more than 1 mg/ml LDL-cholesterol induced a concentration-dependent exponential increase in the permeability of confluent endothelial monolayers. Acute addition of high LDL concentration did not alter macromolecular permeability. Once elevated permeability was induced, it persisted. It was not readily reversible after addition of normal LDL levels. Change in permeability was accompanied by a selective decrease in basement membrane associated heparan sulfate proteoglycan (HSPG) content. The apparent parallel between the loss in endothelial barrier function and HSPG decrease implicates a connection between the two events. Prolonged, but not acute, incubation with antiserum directed against the core-protein of HSPG also led to increased permeability, suggesting a causal role of HSPG for the proper function of endothelium. The fact that non-atherogenic LDL-cholesterol levels had no effect indicates that a 'threshold' concentration for LDL-cholesterol may exist, leading to nondenuding injury in the endothelial barrier as an early event in development of atherosclerosis.

Upregulation of myo-inositol transport compensates for competitive inhibition by glucose. An explanation for the inositol paradox?

High glucose concentrations inhibit the uptake of myo-inositol into cells. However, whether this leads to a depletion of intracellular myo-inositol levels has been debated, because unchanged, decreased, and increased cellular myo-inositol levels all have been reported for diabetic tissues. To evaluate whether cells are capable of counterregulating impaired uptake, we have investigated myo-inositol uptake in porcine aortic endothelial cells under short- and long-term hyperglycemic conditions. Although increasing glucose concentrations inhibited acute myo-inositol uptake competitively, the uptake was increased markedly, when cells were already preincubated in a high glucose medium for > 6 h. The stimulation was maximal at 20 mM of glucose with no further increase at 40 mM glucose. The same stimulation of uptake could be induced by 5 mM of glucose plus 35 mM of raffinose, whereas 35 mM of sorbitol or mannitol, which do not compete for myo-inositol uptake, were ineffective. Lineweaver-Burk analysis revealed an increased Vmax for the induced myo-inositol transport activity, whereas the Km for myo-inositol remained constant (18 microM). The upregulated inositol transporter was still Na+ and ATP dependent, indicating that the same carrier system was operating. Uptake returned to control values when cells were again exposed to normoglycemic medium conditions for an additional 24 h. When endothelial cells were incubated with D-[U-14C]glucose and 10 microM myo-[2-3H]inositol of equal specific radioactivity for 24 h, no 14C radioactivity was found in intracellular myo-inositol, indicating that conversion of glucose to myo-inositol was rather low.

In-vitro carboxymethylation of low density lipoprotein alters its metabolism via the high-affinity receptor.

Carboxymethylation of lysine residues has been shown to result from oxidation of glycated proteins in vivo and in vitro leading to an augmentation of proteins' net negative charge. The metabolism of carboxymethylated low density lipoprotein (LDL) was studied in cultured human fibroblasts and mouse peritoneal macrophages. In vitro carboxymethylation was achieved by incubation of LDL with glyoxylic acid in the presence of Na(CN)BH3. Carboxymethylation inhibited metabolism of LDL via the high affinity receptor in fibroblasts as did methylation. The uptake of LDL into mouse peritoneal macrophages via the scavenger receptor, which was stimulated by acetylation, was not affected.

Specific glycation of albumin depends on its half-life.

Some suggest that measurements of plasma fructosamine concentration should be corrected for the plasma protein (or albumin) concentration because the extent of glycation per volume depends on both protein and glucose concentrations. Several reports, however, demonstrate a poor correlation between plasma fructosamine and albumin concentrations in diabetic patients. In vitro kinetic and in vivo studies have shown that glycation is also dependent on the half-lives of plasma proteins. Because a decrease in plasma albumin diminishes its catabolism, we speculated that low albumin concentrations are associated with a greater extent of glycation on a molar basis (specific glycation) and vice versa. To test this hypothesis, we studied plasma albumin, total protein, and fructosamine in 63 nondiabetic subjects with normal plasma fasting glucose concentrations and hemoglobin A1c between 5.1% and 5.9%. Plasma fructosamine was poorly correlated with albumin concentration (r = 0.348) but a logarithmic plot of the specific glycation of albumin vs albumin concentration showed a better correlation (r = -0.842), suggesting that the kinetic considerations were operating in vivo. Therefore, because lower specific glycation of plasma albumin "compensates" for higher concentration, correction of fructosamine for albumin content in patients will overestimate mean blood glucose when albumin is low and underestimate it when albumin is high.

Alterations of glomerular matrix proteins in the pathogenesis of diabetic nephropathy.

Diabetic late complications are characterized by morphological and biochemical alterations of the extracellular matrix. In particular, longstanding diabetes causes quantitative and qualitative changes in basement membrane structure of retinal and renal capillaries. Immunohistochemical investigations of diabetic kidneys with diffuse glomerulosclerosis show increased collagen type IV deposition in the mesangial matrix and decreased heparan sulfate proteoglycan content in the mesangial matrix and glomerular basement membrane as well. In nodular glomerulosclerosis normal basement membrane components are decreased or absent while the occurrence of collagen type III in this stage has been interpreted as an irreversible alteration of the glomerular structure. These changes seem to be the underlying cause for the alterations in renal functions like persistent albuminuria and proteinuria. Increased intra- and extracellular levels of glucose and its derivatives are thought to be responsible for diabetic tissue dysfunction although there are reports on possible genetic defects causing increased susceptibility to develop diabetic nephropathy. Recent results, however, focus on the role of glucose-induced cytokine secretion as mediator for altered metabolism of glomerular matrix proteins. In vitro studies with cultured kidney cells have shown that the glucose-induced dysregulation of the basement membrane synthesis may be mediated by a glucose dependent activation of protein kinase C. Alternatively or synergistically, the formation of AGE products formed after prolonged exposure of matrix proteins to elevated glucose may also lead to cytokine secretion subsequently inducing synthesis of extracellular matrix proteins. Studies in experimental animals confirm the diabetes induced dysregulation of the synthesis of extracellular matrix components on the molecular level.

Glomerular changes in diabetes mellitus.

Ultrastructural, immunohistochemical and biochemical studies have improved our knowledge on the events occurring during the development of diabetic late complications. Immunohistochemical investigations of diabetic kidneys, using antibodies against various components of the extracellular matrix, showed increased collagen type IV (alpha 1,alpha 2-chain) deposition in the mesangial matrix, and a decrease of heparan sulphate proteoglycan in the mesangial matrix and glomerular basement membrane. Changes in matrix components seem to be the underlying cause of the alterations in renal function, as reflected by albuminuria and proteinuria. The occurrence of collagen type III in late diffuse glomerulosclerosis has been interpreted as an irreversible change in glomerular structure. The extent of alteration of the extracellular matrix correlates to a certain extent with the severity of nephropathy of the individual subject. The studies performed to date support the hypothesis that hyperglycaemia, whatever its origin, is the primary cause of diabetic late complications, although the pathobiochemical mechanisms are not yet fully understood. Increased intra- and extracellular levels of glucose and its derivatives are thought to contribute to diabetic tissue dysfunction. Three pathobiochemical theories are favoured in the current discussion: i) the polyol pathway ii) non-enzymatic glycation of proteins iii) direct influence of hyperglycaemia on the synthesis of matrix components. The evidence for the participation of the polyol pathway in the pathogenesis of diabetic nephropathy comes mainly from animal data using aldose reductase inhibitors, but only limited data are available for humans, so that the significance of this pathomechanism cannot yet be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated glucose decreases the content of a basement membrane associated heparan sulphate proteoglycan in proliferating cultured porcine mesangial cells.

The effect of elevated glucose concentrations on the synthesis of basement membrane components was investigated in proliferating cultured porcine mesangial cells. Basement membrane associated heparan sulphate proteoglycan was determined by enzyme immunoassay with a specific antiserum recognizing the core protein of the heparan sulphate proteoglycan. When cells were exposed to increasing glucose concentrations up to 40 mmol/l, the heparan sulphate proteoglycan content was concomitantly decreased to 53% when compared to cells cultured under normal glucose concentrations or in the presence of 40 mmol/l sorbitol. The fibronectin content was essentially unchanged under these conditions. No significant effect of insulin on these basement membrane components was found. The results indicate that hyperglycaemia may be responsible for a decrease of mesangial heparan sulphate proteoglycan content in diabetes mellitus. This supports the view that loss of heparan sulphate proteoglycan may be an important step or even an initial event of mesangial alterations in diabetic glomerulopathy.