Aorta collagen metabolism in spontaneously hypertensive and aortic-constricted rats: variations in enzyme activities concerned with disaccharide unit synthesis and degradation according to blood pressure and age

Two enzyme activities concerned with collagen disaccharide unit metabolism (UDP-glucose: collagen glucosyltransferase and glucosyl-galactosyl-hydroxylysine glucohydrolase) have been studied in the thoracic aortic wall together with 4-prolyl hydroxylase activity and 4-hydroxyproline content in spontaneously hypertensive rats (SHR) at the prehypertensive, hypertensive and sustained hypertensive stages (respectively 32 days, 12 weeks and 19 weeks of age). They were compared with values observed in age-matched normotensive Wistar Kyoto rats (WKY). The same studies have been performed in parallel on aortic-constricted rats (ACR) 8 days after suprarenal constriction of the abdominal aorta. Negative regressions of all three specific activities as function of age were observed. The most striking difference observed between the SHR and the WKY was the increase of glucosyltransferase specific activity, already found at the prehypertensive stage and continuing thereafter; the glucohydrolase specific activity was increased only during the establishment of hypertension whereas no modification was found with prolyl hydroxylase at any stage. However, a diminution of hydroxyproline concentration was seen at all ages while total hydroxyproline mass remained unaffected. The alterations of the aortic collagen metabolism observed in the ACR recall those seen in the SHR at the prehypertensive stage: the only significant modification was that of glucosyltransferase activity. Correlation was found between glucosyltransferase activity and blood pressure level in the two animal models.

Properties of a microsomal enzyme system from Linum usitatissimum (linen flax) which oxidizes valine to acetone cyanohydrin and isoleucine to 2-methylbutanone cyanohydrin

Microsomal preparations from flax seedlings have recently been shown to convert L-valine to acetone cyanohydrin, the precursor of the cyanogenic glucoside linamarin [A. J. Cutler and E. E. Conn (1981) Arch. Biochem. Biophys. 212, 468-474]. Further details of this four-step biosynthetic sequence and also details of the analogous reactions in lotaustralin biosynthesis have been obtained. The lotaustralin precursor, 2-methylbutyraldoxime, is the best substrate for cyanide production (Vmax = 413 nmol h-1 g fresh wt-1) and inhibits the conversion of valine and isoleucine into products. Similarly, the linamarin precursor isobutyraldoxime is an excellent substrate (Vmax = 400 nmol h-1 g fresh wt-1) and also inhibits oxidation of the amino acids. The substrate specificity of the oxime-metabolizing step is low and a variety of aliphatic oximes are converted to cyanide. On the other hand, the activity of the microsomal extract is highly selective with regard to the amino acid substrate since, of the aliphatic amino acids tested, only valine and isoleucine are metabolized. We were unable to demonstrate product formation from isobutyronitrile (a linamarin precursor) but did observe detectable cyanide formation from 2-methylcyanobutane, the corresponding precursor of lotaustralin. Competition experiments showed that the biosynthesis of linamarin and lotaustralin is not likely to be catalyzed by separate enzyme systems.

Connective tissue in diabetes mellitus: biochemical alterations of the intercellular matrix with special reference to proteoglycans, collagens and basement membranes

Diabetes mellitus induces alterations in the metabolism of the macromolecules present in the intercellular matrices and particularly in the basement membranes. These contribute to the morphological changes characteristic of the disease : basement membrane thickening, skin thickening and induration. Accumulation of overglycosylated collagens and diminution of sulfated proteoglycan concentrations are the most generally reported biochemical modifications in human or animal diabetic states. More limited data are available concerning elastin, fibronectin and laminin in diabetes.

Studies on kidney sialidase in normal and diabetic rats

Rat kidney cortex sialidase was studied using alpha-sialyl-(2----3)-[3H]lactitol and alpha-sialyl-(2----6)-[3H]lactitol as substrates. The enzyme was found mainly in the lysosomal fraction. Only 23% of the sialidase activity of this fraction could be solubilized by a combination of freezing-thawing, sonication and Triton X-100 treatment. The optimal pH for the lysosomal enzyme activity was 4.2 and the enzyme's Km values for alpha-sialyl-(2----3)-lactitol and alpha-sialyl-(2----6)-lactitol were 0.28 and 0.41 mM, respectively. The specific activity was twice as high with the former substrate than with the latter. Sialidase activities in dialyzed kidney cortex homogenates of streptozotocin-diabetic rats and of age-matched control rats were compared. The specific activity was found to be significantly increased in the diabetic animals when using both substrates 5950 +/- 720 (S.E.) dpm/h per mg protein (n = 7) vs. 3970 +/- 370 in the controls (n = 8) with alpha-sialyl-(2----3)-lactitol (P less than 0.025) and 2870 +/- 300 vs. 1820 +/- 170 with alpha-sialyl-(2----6)-lactitol (P less than 0.02). The activities were also found to be increased when expressed per whole kidney cortex (P less than 0.005 and P less than 0.001, respectively). The elevated sialidase activity in diabetic kidney cortex may be related to the reported decrease in sialic acid content of the glomerular basement membrane, which lowers its negative charges and which may contribute to an increased permeability to proteins.

Cleavage of oligosaccharides by rat kidney sialidase. Influence of substrate structure

The specificity of the sialidase activity present in rat kidney cortex (12 000 X g pellet) was studied with various tritiated oligosaccharidic substrates: (i) alpha NeuAc2----3 beta Gal1----4Glc-itol[3H], alpha NeuAc2----6 beta Gal1----4Glc-itol[3H]. and alpha NeuAc2----8 alpha NeuAc2----3 beta Gal1----4Glc-itol[3H] from bovine colostrum; (ii) alpha NeuAc2----6 beta Gal1----4 beta GlcNAc-itol[3H], alpha NeuAc2----3 beta Gal1----4 beta GlcNAcl----2 alpha Man1----3 beta Man1----4 GlcNAc-itol[3H] alpha NeuAc2----6 beta Gal1----4 beta GlcNAc1----2 alpha Man1----3(beta Gal 1----4GlcNAc1----2 alpha Man 1----6)beta Man1----4GlcNAc-itol[3H]et alpha NeuAc2----6 beta Gal1----4 beta GlcNAc1----2 alpha Man1----3(alpha NeuAc2----6 beta Gal1----4 beta GlcNAc1----2 alpha Man1----6)beta Man1 4GlNAc-itol[3H] isolated from the urine of a patient with mucolipidosis I. The enzyme cleaves alpha 2----3 and alpha 2----8 linkages at a greater rate than the alpha 2----6 bonds. Its activity decreases with the length of the oligosaccharidic chain. Substitution of a glucose moiety by Nacetylglucosamine results in diminished activity. The specificity of rat kidney sialidase differs from that reported for other mammalian of viral sialidases.

Inhibition of alkaline phosphatase activity by glucose

Non-enzymatic glycosylation (NEG) of alkaline phosphatase (AP) was studied after short- and long-term incubation with glucose and other carbohydrates. Glucose and amino sugars clearly inhibited the enzyme activity; this was in contrast to reducing and non-reducing disaccharides, which had an enhancing effect. After AP had been incubated with 18 nmol/l glucose for 180 minutes (short-term incubation), a subsequent extensive dialysis revealed full recovery of the enzymatic activity. This, plus the demonstration of a [3H]sodium borohydride-reducible glucose-protein adduct, indicated that initially a labile aldimine (Schiff base) had been formed. Binding experiments with [14C]glucose and failure of dialysis to achieve a recovery of enzymatic activity after long-term incubation suggested that subsequently a stable ketoamine product had been formed. This was further confirmed by the thiobarbituric acid test, which revealed 0.65 nmol 5-hydroxymethylfurfural/mg protein for glycosylated AP compared to 0.11 for the non-glycosylated control. Preliminary results further suggest that NEG of AP also occurs in vivo. Streptozotocin diabetic rats had significantly lower serum AP activities than did non-diabetic controls (mean +/- SD: 153.7 +/- 28.4 vs. 760.5 +/- 95.7 U/l; p less than 0.001). Blood glucose levels and serum AP activity, which had been determined simultaneously during an oral glucose tolerance test, showed without exception an inverse relationship in each of 32 healthy children studied. The biological significance of these findings remains to be established.

Inhibition of the alpha-glucosidase specific for collagen disaccharide units in diabetic rat kidney by in vivo glucose levels: possible contribution to basement membrane thickening

The activity of the alpha-glucosidase specific for collagen disaccharide units has been measured in kidney cortex homogenates of streptozotocin-diabetic rats under three different conditions: (1) in dialyzed homogenates; (2) in non-dialyzed homogenates; (3) in non-dialyzed homogenates to which glucose was added to compensate for dilution due to homogenization and to reach the glucose concentration determined in kidney cortex (37.5 +/- 2.8 mmol/kg diabetic cortex versus 6.8 +/- 0.3 mmol/kg normal cortex). Under the latter condition, the enzyme activity was markedly decreased in diabetic kidney cortex when compared with that of normal age-matched controls: 4.03 +/- 0.25 versus 6.82 +/- 0.29 units/mg protein (p less than 0.001). Inhibition of enzyme activity was also significant in non-dialyzed diabetic homogenates without additional glucose. In the absence of glucose (in the dialyzed homogenates), it is confirmed that the enzyme activity is elevated in diabetic kidney. The glucose inhibition of the enzyme activity has been shown to be important under in vivo conditions. It may therefore contribute to kidney basement membrane thickening.

Studies on the alpha-glucosidase specific for collagen disaccharide units: variations associated with capillary basement membrane thickening in kidney and brain of diabetic and aged rats

The alpha-glucosidase specific for the hydroxylysine-linked disaccharide units of collagens (or 2-0-alpha-D-glucopyranosyl-5-0-beta-D-galactopyranosylhydroxy-L-lysine glucohydrolase) has been measured in kidney cortex and brain cortical tissue of streptozotocin diabetic rats after 19, 23 or 28 weeks of diabetes and of aged rats 22 months old. Increased specific activities of the enzyme have been found repeatedly in the dialyzed homogenates and the 7.2 X 10(6) g.min supernatants of kidney and brain at the various stages of diabetes when compared with age-matched controls; the specific activities returned to a normal level after insulin treatment. Similar increased specific activities were observed in kidney and brain of the aged normoglycemic rats when compared with young adult rats. In diabetic kidney cortex, beta-galactosidase and p-nitrophenyl-alpha-D-glucoside glucosidase specific activities were decreased in contrast to the increase of glucosyl-galactosyl-hydroxy-lysine glucohydrolase. In kidney cortex of the aged rats, beta-galactosidase activity was also decreased, but p-nitrophenyl-alpha-D-glucoside glucosidase was increased. In both diabetic and aged rats, thickening of the kidney glomerular basement membranes was confirmed; thickening of the brain cortical capillary basement membranes was also observed. Thus in the diabetic and aged animals, the increased glucosyl-galactosyl-hydroxylysine glucohydrolase specific activity was associated with basement membrane thickening in the kidney and the brain.

Reduced collagenolytic activity of rat kidneys with steptozotocin diabetes

Collagenolytic activity of rat kidneys with streptozotocin diabetes was estimated by means of a biological collagenase assay and compared to healthy controls. Collagenolytic activity was found significantly decreased in rat kidneys with diabetes correlating with blood glucose levels (r = -0.82, p less than 0.001). Elevated blood glucose levels seem to be responsible for the inhibition. This is supported by our experiment of incubating bacterial collagenase with several carbohydrates as glucose, galactose and saccharose: glucose and galactose significantly inhibited the collagenolytic activity, while saccharose failed to inhibit the enzymatic reaction. The interpretation of the results is that glucose is able to bind to the enzyme as Schiff base, which could be shown by tritiated sodium borohydride reduction of the Schiff base formed between collagenase and glucose. Another support of the hypothesis is that blocking of the amino group of lysine at the active site either by glucose or trifluoroacetylation of collagenase is reducing the collagenolytic activity. The biological significance could be the decreased catabolism of collageneous material of the extracellular matrix, as, e.g., the glomerular basement membrane, which was reported in a previous publication.

Aluminum phosphate visualisation of acid phosphatase activity: a biochemical and x-ray microanalysis study

A new method is described that demonstrates acid phosphatase activity in the cells of the proximal tubules of the rat kidney. The method is based on the formation of an insoluble aluminum phosphate precipitate. Microanalysis was used to demonstrate the presence of intracellular aluminum and determine the quantity present under the probe. Parallel biochemical studies showed that the aluminum precipitate was indeed due to acid phosphatase activity.

The in vitro biosynthesis of taxiphyllin and the channeling of intermediates in Triglochin maritima

The in vitro biosynthesis of the cyanogenic glucoside taxiphyllin has recently been demonstrated in Triglochin maritima (Hösel, W., and Nahrstedt, A. (1980) Arch. Biochem. Biophys. 203, 753-757). We have now studied in more detail the multistep conversion of tyrosine into p-hydroxymandelonitrile, the immediate precursor of taxiphyllin, catalyzed by microsomes isolated from dark-grown seedlings. The biosynthetic pathway involves N-hydroxytyrosine, p-hydroxyphenylacetaldoxime, and p-hydroxyphenylacetonitrile. In marked contrast to an analogous pathway in Sorghum bicolor, p-hydroxyphenylacetonitrile is the best substrate for cyanide production (Vmax = 224 nmol/h/g, fresh wt) and the physiological substrate tyrosine is the poorest (Vmax = 18.8 nmol/h/g, fresh wt). The substrates exhibit alkaline pH optima between 7.5 and 9, and all except tyrosine show pronounced substrate inhibition. We have found that p-hydroxyphenylacetonitrile generated in situ from tyrosine is free to equilibrate by diffusion with exogenous material. On the other hand, neither N-hydroxytyrosine nor p-hydroxyphenylacetaldoxime will readily exchange with exogenous intermediates. We consider both N-hydroxytyrosine and p-hydroxyphenylacetaldoxime to be channeled in T. maritima, whereas in S. bicolor N-hydroxytyrosine and p-hydroxyphenylacetonitrile are channeled and the aldoxime is freely exchangeable.

The prevalence and nature of back pain in an industrial complex: a questionnaire and radiographic and HLA analysis

A questionnaire relating to presence and nature of back pain was distributed to all 10,150 employees (59% men) of an industrial complex. The questionnaire was returned by 2892 subjects (65% men). Of these, 1880 (65% of responders or 19% of total) reported a history of back pain. One hundred twenty-four described their back pain as insidious in onset, persisting for at least three months, developing at less than 40 years of age, being associated with morning stiffness, and showing improvement with exercise. Three hundred sixty-seven subjects scored four of these five features. Pelvic radiographs of 342 persons were available for blind evaluation. Sixteen patients (12 men) were shown to have definite ankylosing spondylitis (Grade III or IV sacroiliitis or HLA B27-associated Grade II sacroiliitis). Only one of these persons was known to have spondylitis. The majority of these symptomatic patients had been seen by both medical and nonmedical practitioners.

Excretion and synthesis of basement membrane disaccharide units in Masugi nephritis

During nephrotoxic nephritis in the rat, an increased urinary excretion of glucosyl-galactosyl hydroxylysine and of galactosyl-hydroxylysine has been observed in the autologous phase of the disease. This due mainly to an elevation of the polypeptide-bound fraction of these hydroxylysyl glucosides with a molecular weight over 1,000 daltons. The levels of both urinary hydroxylysyl glucosides were correlated with proteinuria. Their increased excretion appears to originate in the lysed glomerular basement membrane. At the same stage of nephrotoxic nephritis, an increased glucosyl transferase activity could be demonstrated in the isolated glomeruli, correlated with albuminuria, attesting a higher turn-over of the disaccharide units of the glomerular basement membrane.

[Haptenic function and metabolism of the disaccharides of the glomerular basement membrane in heterologous nephrotoxic antibody-induced glomerulonephritis in rats]

The disaccharide unit Glc-gal-hyl represents 6% of dry weight of the rat glomerular basement membrane. It has been shown to be a haptenic determinant of this membrane. It appears to be one of the targets of the lesions induced by nephrotoxic antibodies in the rat: the urinary excretion of Glc-gal-hyl (as well as of Gal-hyl and Hyl which may derive from Glc-gal-hyl by degradation) during the autologous phase of the rat glomerulonephritis is significantly increased. Simultaneously the biosynthesis of Glc-gal-hyl, as measured by the glomerular glucosyltransferase activity, is elevated by 72%.

[Action of pyridinol carbamate on hetero-immune Masugi nephritis in the rat (author's transl)]

Pyridinol-carbamate (P.C.) is a new substance with various properties including an anti-inflammatory (anti-kinin) and an antiplatelet aggregation activity. Since a coagulation process has been demonstrated in Masugi nephritis in Rats, we investigated the effect of P.C. in this experimental model. P.C. (150 mg/kg/day) was given orally from day 1 to day 28. It prevented partially the G.N.: proteinuria was significantly lower than in nephritic untreated animals with a reduction of seromucoid blood levels and B.U.N. Histological examination revealed that glomerular injury was limited in treated animals specially with regards to G.B.M. alterations and deposits.