Serum laminin P1 fragment concentration in renal diseases

A chemotactic peptide from laminin alpha 5 functions as a regulator of inflammatory immune responses via TNF alpha-mediated signaling

Tissue injury triggers inflammatory responses that may result in release of degradation products or exposure of cryptic domains of extracellular matrix components. Previously, we have shown that a cryptic peptide (AQARSAASKVKVSMKF) in the alpha-chain of laminin-10 (alpha5beta1gamma1), a prominent basement membrane component, is chemotactic for both neutrophils (PMNs) and macrophages (Mphis) and induces matrix metalloproteinase-9 (MMP-9) production. To determine whether AQARSAASKVKVSMKF has additional effects on inflammatory cells, we performed microarray analysis of RNA from RAW264.7 Mphis stimulated with AQARSAASKVKVSMKF. Several cytokines and cytokine receptors were increased >3-fold in response to the laminin alpha5 peptide. Among these were TNF-alpha and one of its receptors, the p75 TNFR (TNFR-II), increasing 3.5- and 5.7-fold, respectively. However, the peptide had no effect on p55 TNFR (TNFR-I) expression. Corroborating the microarray data, the protein levels of TNF-alpha and TNFR-II were increased following stimulation of RAW264.7 cells with AQARSAASKVKVSMKF. In addition, we determined that the production of TNF-alpha and TNFR-II in response to AQARSAASKVKVSMKF preceded the production of MMP-9. Furthermore, using primary Mphis from mice deficient in TNFR-I, TNFR-II, or both TNF-alpha receptors (TNFRs), we determined that AQARSAASKVKVSMKF induces MMP-9 expression by Mphis through a pathway triggered by TNFR-II. However, TNF-alpha signaling is not required for AQARSAASKVKVSMKF-induced PMN release of MMP-9 or PMN emigration. These data suggest that interactions of inflammatory cells with basement membrane components may orchestrate immune responses by inducing expression of cytokines, recruitment of inflammatory cells, and release of proteinases.

Laminin inhibition of beta-amyloid protein (Abeta) fibrillogenesis and identification of an Abeta binding site localized to the globular domain repeats on the laminin a chain

beta-Amyloid protein (Abeta) is a major component of neuritic plaques and cerebrovascular amyloid deposits in the brains of patients with Alzheimer's disease (AD). Inhibitors of Abeta fibrillogenesis are currently sought as potential future therapeutics for AD and related disorders. In the present study, the basement membrane protein laminin was found to bind Abeta 1-40 with a single dissociation constant, K(d) = 2.7 x 10(-9) M, and serve as a potent inhibitor of Abeta fibril formation. 25 microM of Abeta 1-40 was incubated at 37 degrees C for 1 week in the presence of 100 nM of laminin or other basement membrane components, including perlecan, type IV collagen, and fibronectin to determine their effects on Abeta fibril formation as evaluated by thioflavin T fluorometry. Of all the basement membrane components tested, laminin demonstrated the greatest inhibitory effect on Abeta-amyloid fibril formation, causing a ninefold inhibition at 1 and 3 days and a 21-fold inhibition at 1 week. The inhibitory effects of laminin on Abeta fibrillogenesis occurred in a dose-dependent manner and were still effective at lower concentrations. The inhibitory effects of laminin on Abeta 1-40 fibril formation was confirmed by negative stain electron microscopy, whereby laminin caused an almost complete inhibition of Abeta fibril formation and assembly by 3 days, resulting in the appearance of primarily amorphous nonfibrillar material. Laminin also caused partial disassembly of preformed Abeta-amyloid fibrils following 4 days of coincubation. Laminin was not effective as an inhibitor of islet amyloid polypeptide fibril formation, suggesting that laminin's amyloid inhibitory effects were Abeta-specific. To identify a potential Abeta-binding site(s) on laminin, laminin was first digested with V8, trypsin, or elastase. An Abeta-binding elastase digestion product of approximately 120-130 kDa was found. In addition, a approximately 55 kDa fragment derived from V8 and elastase-digested laminin interacted with biotinylated Abeta 1-40. Amino acid sequencing of the approximately 55 kDa fragment identified a conformationally dependent Abeta-binding site within laminin localized to the globular repeats on the laminin A chain. These studies demonstrate that laminin not only binds Abeta with relatively high affinity but is a potent inhibitor of Abeta-amyloid fibril formation. In addition, further identification of an Abeta-binding domain within the globular repeats on the laminin A chain may lead to the design of new therapeutics for the inhibition of Abeta fibrillogenesis.

Serum concentrations of laminin-P1 in thrombotic microangiopathy: usefulness as an index of activity and prognostic value

Laminin is the main noncollagenous constituent of the basement membrane, and its serum levels could reflect the metabolic changes that occur in the basement membrane. Severe endothelial injury with thickening of basement membrane is a characteristic feature of thrombotic microangiopathy (TMA). With this background, the aim of the study was to investigate in a prospective way (1) the relationship among serum Lam-P1, the extent of renal histopathologic lesions, and the biochemical parameters commonly used as markers of TMA activity, and (2) the usefulness of serum Lam-P1 concentrations as a renal outcome prognostic index. To this end, 18 consecutive patients with active biopsy-proven TMA with renal involvement were studied. One hundred and twenty-one healthy control subjects, 20 patients with systemic scleroderma without renal involvement, and 35 patients with systemic lupus erythematosus (20 without nephropathy and 15 with diffuse proliferative type 4 lupus nephritis) were used as control groups. In addition, to analyze the influence of either renal failure or hemodialysis therapy on serum Lam-P1 levels, 91 patients on regular hemodialysis therapy and 81 patients with predialysis chronic renal failure of different etiologies were included in the study. Serum Lam-P1 was determined by RIA at admission, on days 10 and 30 of follow-up in all patients, and after 6 and 12 mo of follow-up in all surviving patients. Serum lactate dehydrogenase, haptoglobin, platelet count, hemoglobin, and serum creatinine were determined as markers of endothelial dysfunction and hemolysis. At admission, serum levels of Lam-P1 were significantly higher in patients with TMA than in healthy control subjects (3.39 +/- 0.56 U/ml versus 1.40 +/- 0.18 U/ml; P < 0.0001). In addition, patients with TMA had significantly higher serum Lam-P1 levels than the other groups included in the study. At the first control, Lam-P1 correlated with lactate dehydrogenase (P = 0.006) and hemoglobin (P = 0.002). During follow-up, platelet count and hemolysis indicators normalized in all patients, while serum Lam-P1 decreased only in patients with renal function recovery. In multivariate analysis, serum creatinine and Lam-P1 at day 10 were the only independent predictors of renal outcome (r2 = 0.94; P < 0.0001) and also correlated with indices of histopathologic damage (P < 0.001). Serum Lam-P1 normalized in all patients with chronic renal failure in the samples obtained at 6 and 12 mo of regular hemodialysis after solving active TMA, thus suggesting that histopathologic lesions, but not renal function itself, would be mainly responsible for the high Lam-P1 serum concentrations detected in TMA. In conclusion, serum Lam-P1 concentrations are increased in patients with active TMA. Furthermore, patients with poor renal outcome show a prolonged increase of serum Lam-P1 that is related to the extent of renal histologic lesions. Unlike the biochemical markers of hemolysis commonly used to assess TMA activity, the sequential determination of serum Lam-P1 provides valuable information about long-term renal prognosis in patients with TMA.

Levels and molecular size distribution of serum laminin in adult type I diabetic patients with and without microangiopathy

The glycoprotein laminin, a cross-shaped complex of three genetically different polypeptide chains, is a structural component of the capillary basement membrane. Serum laminin concentrations of healthy controls (n = 60) and adult type I diabetic patients (n = 170) were not age-dependent. Laminin was correlated with hemoglobin A1 (HbA1) values in normoalbuminuric patients (rs = .33, P < .0005, n = 116). Type I diabetic patients without nephropathy or retinopathy in good metabolic control had normal laminin levels. However, increasing stages of microangiopathy were associated with higher laminin levels. The molecular size distribution of serum laminin of control subjects (n = 4) and type I diabetic patients (n = 15) was analyzed by molecular-sieve chromatography. Laminin was eluted in two peaks with a molecular mass of 900 and 300 kd, most likely representing intact laminin and its P1 fragment, respectively. The areas of the two peaks were determined by two-gaussian function fitting. In patients without microangiopathy in poor metabolic control, an increase in the high-molecular weight (HMW) fraction could be detected as compared with healthy subjects and patients with acceptable metabolic control. Furthermore, the HMW laminin fraction and the ratio between the areas of the first and second peak increased with the stage of nephropathy (P < .001, Jonckheere-Terpstra test). These results provide evidence that (1) laminin concentration is increased in chronic hyperglycemia, (2) laminin may be a marker of microangiopathic lesions, and (3) elevated laminin levels may reflect an increased synthesis and/or a defective incorporation of laminin into the capillary basement membrane.

Serum concentrations of laminin-P1 in diabetes mellitus: usefulness as an index of diabetic microangiopathy

OBJECTIVE

To assess the influence of several variables on serum laminin-P1 (Lam-P1) and to evaluate its usefulness as a serum marker of diabetic microangiopathy.

MATERIAL AND METHODS

We determined Lam-P1 by serum radioimmunoassay in 121 controls and 176 diabetic patients, 58 type 1 (insulin dependent) and 118 type (non-insulin dependent), grouped according to retinal status and urinary albumin excretion. The variables evaluated were: age, gender, body mass index, blood pressure, consumption of tobacco and alcohol, type of diabetes, duration of disease, fasting blood glucose, HbA1, cholesterol, HDL-cholesterol, LDL-cholesterol, triglycerides and apolipoproteins (A1, B). Imprecision for laminin determination was: 3.6% intrassay; 5.8% interassay.

STATISTICS

Student's t-test, ANOVA, ANCOVA, and multiple regression analysis.

RESULTS

In diabetic patients Lam-P1 was higher than in controls (X = 1.63 +/- S.D. 0.36 vs. X = 1.40 +/- S.D. 0.18 U ml-1; P < 0.001) and only correlated with age (P = 0.002). Lam-P1 was higher in diabetics with proliferative retinopathy than in patients with non-proliferative retinopathy and without retinopathy (X = 2.17 +/- S.D. 0.49 U ml-1 vs. X = 1.71 +/- S.D. 0.22 U ml-1 vs. X = 1.47 +/- S.D. 0.26 U ml-1; P < 0.001). Patients with macroalbuminuria presented higher serum Lam-P1 than patients with micro or normoalbuminuria (X = 2.39 +/- S.D. 0.53 U ml-1 vs. X = 1.78 +/- S.D. 0.23 U ml-1 vs. X = 1.51 +/- S.D. 0.29 U ml-1; P < 0.001). These differences remained significative when patients were age-adjusted.

CONCLUSIONS

Lam-P1 could be useful as an index of diabetic microangiopathy but patient's age should be considered.

Serum laminin, hydrocarbon exposure, and glomerular damage

It has been postulated that occupational exposure to hydrocarbons may damage the kidney and lead to glomerulonephritis and chronic renal failure. As laminin is a ubiquitous basement membrane component that seems to play a central part in the structure and function of basement membranes and as the normal renal filtration process is highly dependent on an intact glomerular basement membrane, the serum laminin concentration was examined in a population of workers exposed to hydrocarbons. The hydrocarbon exposure was assessed by exposure surrogates (exposure duration and exposure score). An interaction between occupational exposure to hydrocarbons and hypertension increased the laminin concentration whereas the laminin concentration decreased in workers exposed for a long time probably because of a selection effect. In a subgroup of printers exposed to toluene whose hippuric acid excretion had been recorded for several years this interaction was confirmed when the hippuric acid excretion was substituted for the other exposure indices. In the exposed group, the age-related decline in creatinine clearance was accelerated. These results seem to confirm that occupational exposure to hydrocarbons is a non-specific factor that may promote a deterioration of renal function.