Expression of TWEAK and its receptor Fn14 in human subcutaneous adipose tissue. Relationship with other inflammatory cytokines in obesity

TWEAK, a cytokine of the TNF family, has been found to be expressed under different inflammatory conditions but no data is available concerning the expression of this cytokine and its receptor (Fn14) in human obesity. In the present work we have evaluated the expression of many pro-inflammatory TNF system cytokines (TNF-alpha, TWEAK and their respective receptors, TNFR1, TNFR2 and Fn14) in human adipose tissue of 84 subjects some with different degree of obesity and type 2 diabetes, and its relation with inflammation by also measuring the expression of macrophage marker CD68. We detected expression of TWEAK and Fn14 in isolated mature adipocytes and in the stromovascular fraction. Additionally, we found that LPS upregulates the expression of both genes on THP-1 human monocytic cell line. TWEAK was expressed in adipose tissue of all studied subjects with no differences between obesity group, and was associated with Fn14 expression in morbid obese, mainly in women with type 2 diabetes. The data obtained here also showed that TNF-alpha and TNFR2 mRNAs were significantly more expressed in subcutaneous adipose tissue of subjects with morbid obesity compared to obese and non-obese subjects. In contrast, TNFR1 gene expression was negatively associated with BMI. Our results suggest that the expression of TNF-derived pro-inflammatory cytokines are increased in severe obesity, where macrophage infiltrate could modulate the inflammatory environment through activation of its receptors.

Tumour necrosis factor alpha in fat redistribution syndromes associated with combination antiretroviral therapy in HIV-1-infected patients: potential role in subcutaneous adipocyte apoptosis

BACKGROUND

The pathogenesis of fat redistribution syndromes (FRS) observed in the setting of highly active antiretroviral therapy (HAART) for the treatment of HIV-1-infection remains elusive. A dysregulation of the tumour necrosis factor alpha (TNF-alpha) system occurs in HIV-infected patients with FRS.

MATERIALS AND METHODS

The study looked at both the in vivo and in vitro relationship between TNF-alpha and the degree of subcutaneous adipocyte apoptosis in 60 HIV-1-infected patients on HAART with FRS, another 60 HIV-1-infected patients on HAART without FRS and 60 uninfected control patients. Apoptosis was assessed by the terminal deoxynucleotidyl transferase dUTP (deoxyuridine 5'-triphosphate)-digoxigenin Nick End Labelling (TUNEL) method. Soluble receptors of TNF-alpha were determined by the sandwich enzyme immunoassay technique. The in vitro viability was assessed by staining with 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) and apoptosis by TUNEL.

RESULTS

HIV-1-infected patients with FRS had significantly higher degrees of subcutaneous adipocyte apoptosis than those without FRS (P = 0.0001) and uninfected controls (P < 0.0001). There was a statistically significant association between serum levels of soluble TNF-alpha receptors #1 and #2 and the degree of subcutaneous adipocyte apoptosis in patients with and without FRS (P < 0.0001 for both receptors). In vitro, the addition of TNF-alpha (10 ng mL(-1)) to an adipocyte culture embedded with indinavir, either alone or in clinically relevant combinations with stavudine (d4T) and lamivudine (3TC), significantly decreased adipocyte viability (P = 0.0001) and increased adipocyte apoptosis (P < 0.0001) with respect to that observed with the addition of antiretrovirals alone.

CONCLUSIONS

TNF-alpha plays a significant role in subcutaneous adipocyte apoptosis, which occurs in the setting of FRS in HIV-1-infected patients on highly active antiretroviral therapy.

The tumour necrosis factor (TNF)-alpha system is activated in accordance with pulse pressure in normotensive subjects with type 1 diabetes mellitus

OBJECTIVE

Pulse pressure (PP) and inflammation are important predictors of cardiovascular disease (CVD), even in the normotensive. The age-related increase in PP can be diagnosed up to 20 years earlier in subjects with type 1 diabetes mellitus (T1DM) than in the general population. Some evidence suggests that PP can stimulate inflammation. Our aim was to study the relationship between PP and plasma inflammatory proteins in normotensive subjects with T1DM.

DESIGN

This was a cross-sectional study of a group of normotensive (<140/80 mmHg) subjects diagnosed with T1DM 14 years before. None of them had clinically proven CVD or inflammatory conditions or were on antiplatelet, antihypertensive, anti-inflammatory or lipid-lowering treatment.

METHODS

The following information was recorded: sex, age, body-mass index (BMI), waist-to-hip ratio (WHR), systolic blood pressure (SBP), diastolic blood pressure (DBP), PP, mean blood pressure (MBP), smoking, alcohol intake, insulin dose, lipid profile, HbA1c, microvascular complications, and plasma concentrations of soluble receptor types 1 and 2 of tumour necrosis factor (TNF)-alpha (sTNFR1 and sTNFR2, respectively), interleukin-6, C-reactive protein, adiponectin and leptin.

RESULTS

A total of 112 subjects were evaluated (aged 27.4+/-6.6 years, 52.7% women, BMI: 20.4+/-2.7 kg/m2, WHR: 0.82+/-0.09, SBP: 112+/-12 mmHg, DBP: 68+/-9 mmHg, PP: 45+/-9 mmHg, MBP: 82+/-9 mmHg, HbA1c: 8.2% (7.3-9.0%), 41.1% microvascular complications). After adjusting for potential confounders, only inflammatory markers of the TNF-alpha system correlated significantly with PP (Pearson correlation coefficient between sTNFR1 and PP: r = 0.215, P = 0.030; and between PP and sTNFR2: r = 0.238, P = 0.020).

CONCLUSION

In normotensive subjects with T1DM after 14 years of diagnosis, the activation of the TNF-alpha system is positively associated with PP levels. This finding might suggest a pathogenic role of the TNF-alpha system in the development of cardiovascular disease in T1DM.

Diabetic neuropathy is associated with activation of the TNF-alpha system in subjects with type 1 diabetes mellitus

OBJECTIVE

The development of diabetic neuropathy (DN) is predicted by cardiovascular risk factors associated with insulin resistance. As inflammation seems to be implicated in the pathogenesis of insulin resistance, we investigated whether subjects with type 1 diabetes mellitus (T1DM) and DN have an increase in plasma concentrations of inflammatory proteins involved in insulin resistance.

DESIGN

Cross-sectional. Patients One hundred twenty subjects, all diagnosed with T1DM 14 years before.

MEASUREMENTS

(1) Sex, age, body mass index, waist-to-hip ratio (WHR), blood pressure, smoking, alcohol intake, insulin dose, HbA1c and lipid profile; (2) DN (peripheral and cardiac autonomic), retinopathy and nephropathy; (3) plasma concentrations of soluble fractions of tumour necrosis factor alpha receptors 1 and 2 (sTNFR1 and sTNFR2), interleukin-6, high-sensitive C-reactive protein, adiponectin and leptin; and (4) insulin resistance (by way of a mathematical estimation of the glucose disposal rate - eGDR-).

RESULTS

Thirty-six subjects had DN and 84 did not. Subjects with DN received higher insulin doses (57.6 +/- 16.7 vs. 49.2 +/- 15.0 IU/day; P = 0.008) and had higher WHR (0.85 +/- 0.07 vs. 0.81 +/- 0.10; P = 0.007) and HbA1c values (8.5 (7.6-9.6) vs. 7.7 (7.3-8.9)%; P = 0.049) than subjects without DN. They also had higher values of sTNFR1 (2.42 +/- 0.60 vs. 1.96 +/- 0.66 microg/l; P = 0.001) and sTNFR2 (4.73 +/- 1.33 vs. 4.14 +/- 1.09 microg/l; P = 0.015), and were more insulin resistant (eGDR values: 7.28 (5.83-8.03) vs. 8.30 (7.17-9.03) mg kg(-1) min(-1); P = 0.003). The relationship between DN and either sTNFR1 or sTNFR2 remained essentially unchanged after adjusting for several confounders, including glycaemic control, WHR, lipid profile, blood pressure and other microvascular complications (OR for sTNFR1: 2.592 (1.222-5.498), P = 0.013; OR for sTNFR2: 2.124 (1.258-3.587), P = 0.005).

CONCLUSIONS

The activity of the TNF-alpha system is increased in subjects with type 1 diabetes mellitus and diabetic neuropathy, regardless of their glycaemic control and cardiovascular risk factors associated with insulin resistance. These results suggest that TNF-alpha may play a pathogenic role in the development of diabetic neuropathy.

Circulating IL-18 concentration is associated with insulin sensitivity and glucose tolerance through increased fat-free mass

AIMS/HYPOTHESIS

Knowledge of the factors which simultaneously contribute to insulin-resistance-related inflammation may contribute to early therapeutic targeting. IL-18 has recently been described as one of the factors which, in addition to insulin resistance, may also contribute to atherosclerosis. However, the source of IL-18 is not well characterised.

MATERIALS AND METHODS

We aimed to study body composition (bioelectric impedance), glucose tolerance (OGTT) and insulin sensitivity (minimal model method) in relation to serum IL-18 (ELISA) concentration in 144 otherwise healthy men aged 51.9+/-12.5 years.

RESULTS

In contrast to previous observations in women, circulating IL-18 was not significantly associated with BMI (r=0.12, p=0.1) or WHR (r=0.08, p=0.3). IL-18 was also not associated with absolute or percent fat mass (bioelectric impedance, p>0.20) but, interestingly, it was significantly linked to fat-free mass (p=0.03). Serum IL-18 increased with each quartile of fat-free mass, corresponding to values of < or = 64.2; >64.2 to < or = 71.6; >71.6 to < or = 80.9; and > or = 80.9 kg (ANOVA, p<0.0001). IL-18 was more closely associated with postload glucose during an OGTT (p=0.04) rather than with fasting glucose (p=0.1). HbA1c (p=0.03), HDL-cholesterol (p=0.04) and serum triglycerides (p=0.03) and parameters of systemic inflammation (C-reactive protein, p=0.02) were also significantly associated with circulating IL-18. Insulin sensitivity (minimal model analysis) was linked to circulating IL-18 (p=0.01). In a multiple linear regression analysis this relationship remained significant after controlling for BMI, age and glucose tolerance status. In another model, both fat-free mass and insulin sensitivity contributed to 10% of IL-18 variance.

CONCLUSIONS/INTERPRETATION

Fat mass does not seem to influence circulating IL-18, as initially proposed. In contrast, the fat-free mass compartment (a well-known confounder in the evaluation of insulin sensitivity) may significantly contribute to the relationship between IL-18 and insulin action.

Detailed molecular comparison between the inhibition mode of A/B-type carboxypeptidases in the zymogen state and by the endogenous inhibitor latexin

Treatment of advanced stages of prostate carcinoma with histone-deacetylase inhibitors entails expression of human procarboxypeptidase-A4 (hPCPA4). The three-dimensional structure of hPCPA4 has been solved and shows the features of related metallocarboxypeptidase zymogens, with a preformed alpha/beta/-hydrolase active-enzyme moiety (hCPA4) and an inhibiting pro-domain (PD). The protease moiety recalls a sphere, out of which a spherical cone has been cut. This results in a funnel-like structure, at the bottom of which the active-site cleft resides. The border of this funnel is shaped by loops, which are responsible for the interaction with the PD, characterised by a large interface area and relatively few contacts. Such an inhibitory mode is evocative of the recently reported structure of the human inhibitor latexin in its complex with hCPA4. The main contacting structure of latexin is similar to the one employed for PD inhibition. In both cases, active-site blocking relies mainly on a loop provided by the central part of a beta sheet.

Tumour necrosis factor receptors (TNFRs) in Type 2 diabetes. Analysis of soluble plasma fractions and genetic variations of TNFR2 gene in a case-control study

AIMS

We have studied the relationships between soluble fractions of tumour necrosis factor receptors (sTNFR1 and sTNFR2) in Type 2 diabetes (DM2) and its chronic microvascular complications. Likewise, we have analysed the genetic susceptibility of 196T > G exon6/CA-repeat intron 4 mutations in the TNFR2 gene in this population.

METHODS

A case-control study was conducted to examine the role of sTNFRs in 345 DM2 patients and 173 healthy subjects. The mutations were studied in all healthy subjects and in a subset of 232 patients.

RESULTS

sTNFRs levels were similar in healthy and DM2 patients. A positive correlation between age and both sTNFRs was observed in healthy subjects. In DM2 patients, sTNFR1 showed a positive correlation with age, systolic blood pressure and leptin levels (r = 0.53, P < 0.0001; r = 0.28, P = 0.005; r = 0.46, P < 0.0001, respectively) and sTNFR2 was positively correlated with age, triglycerides and leptin levels (r = 0.34, P < 0.0001; r = 0.21, P < 0.0001; r = 0.28, P = 0.002, respectively). Patients with micro- or macroalbuminuria showed higher plasma levels of sTNFR1 and sTNFR2 than normoalbuminuric patients, after adjusting for confounding variables (B = 0.85, P = 0.022, 95% CI: 0.12-1.58 for sTNFR1 and B = 1.50, P < 0.001, 95% CI: 0.67-2.33 for sTNFR2). In DM2 patients, TT-exon 6 homozygous showed lower levels of sTNFR1 [2,4 (1.1) vs. 3.4 (1.2) ng/ml], and the CA273-allele tracked with elevated plasma HDL-cholesterol [1.8 (0.7), 1.4 (0.3) and 1.3 (0.3) mm, for CA273/273, CA273/- and CA-/-, respectively]. No association was seen with other analysed variables.

CONCLUSIONS

Our findings suggest that chronic TNF activation may have some pathogenic role in diabetic nephropathy in DM2 patients. Genetic variations in exon 6/intron 4 of the TNFR2 gene do not predispose to a major risk for DM2 or its microvascular complications.

Maternal soluble tumour necrosis factor receptor type 2 (sTNFR2) and adiponectin are both related to blood pressure during gestation and infant's birthweight

OBJECTIVE

Tumour necrosis factor alpha (TNF-alpha) and adiponectin are strongly related to insulin sensitivity; insulin resistance of pregnancy is a major determinant of infant's birthweight. We aimed to study the contributions of maternal serum concentrations of soluble TNF-alpha receptors (sTNFR1 and sTNFR2) and adiponectin to infant's birthweight.

DESIGN

Cross-sectional, hospital-based study of insulin sensitivity during gestation.

PATIENTS

Fifty-one healthy women with uncomplicated pregnancy and delivery (except for elective Caesarian section) and their healthy newborn infants. measurements Maternal blood levels of glucose, insulin, glycosylated haemaglobin (HbA1c), sTNFR1, sTNFR2 and adiponectin at delivery; cord-blood levels of sTNFR1, sTNFR2 and adiponectin.

RESULTS

At delivery, maternal sTNFR2 correlated with systolic blood pressure (SBP; r = 0.38, P = 0.005). In multiple regression analyses, SBP and HbA1c were independent predictors of sTNFR2, explaining 18 and 7% of its variance, respectively; insulin resistance index (HOMA-IR), body mass index at delivery and SBP were independent predictors of adiponectin, explaining 15, 8 and 7% of its variance, respectively. Both maternal sTNFR2 and SBP were negatively correlated with infant's birthweight (r = -0.28, P = 0.04 and r = -0.36, P = 0.01 respectively, adjusted for sex and gestational age). In multivariate regression analyses, infant's sex and either maternal sTNFR2 or adiponectin were independent predictors of infant's birthweight, each explaining between 6 and 9% of birthweight variance. Further addition of maternal SBP to these models revealed that this variable was the main predictor of infant's birthweight, explaining 13% of its variance.

CONCLUSIONS

Maternal sTNFR2 and adiponectin are independently related to both maternal blood pressure and infant's birthweight in uncomplicated pregnancy. The contributions of the TNF-alpha system and adiponectin to hypertensive disorders of pregnancy and fetal growth merit further studies.

Smoking, fat mass and activation of the tumor necrosis factor-alpha pathway

OBJECTIVE

Obesity may be associated with increased markers of inflammation that could be triggered by metabolic, physical, infectious or environmental processes. As smoking significantly increases cytokine production, we aimed to study how smoking influences the relationship between fat mass and soluble tumor necrosis factor-alpha (TNF-alpha) receptors 1 and 2 (sTNFR1 and sTNFR2).

DESIGN

Cross-sectional, clinical observational study.

SUBJECTS

A total of 133 healthy men (age: 27-53 y, body mass index (BMI): 24-30.2 kg/m(2)), 80 of whom were never-smokers and 53 smokers, matched for age, BMI and waist-to-hip ratio.

MEASUREMENTS

Circulating soluble fractions of the TNF-alpha receptors sTNFR1 and sTNFR2 were measured to study their relationship with fat mass (bioelectric impedance).

RESULTS

Smokers had significantly lower fat mass, lower fasting glucose, insulin and leptin concentrations than nonsmokers. Despite lower fat mass and insulin, smokers showed significantly increased circulating sTNFR2 levels (3.7+/-0.8 vs 3.4+/-0.7 ng/ml, P=0.03). The slopes of the relationships between sTNFR1 and fat mass, and between sTNFR2 and fat mass, were significantly steeper in smokers than in nonsmokers. In a stepwise multiple linear regression analysis, both fat mass (P<0.00001) and smoking (P=0.025) independently contributed to 13% of sTNFR1 variance and to 4% of sTNFR2 variance (P=0.03).

CONCLUSION

Both fat mass and smoking are related to increased activity of the TNF-alpha axis.

Lower rate of tumor necrosis factor-alpha -863A allele and higher concentration of tumor necrosis factor-alpha receptor 2 in first-degree relatives of subjects with type 2 diabetes

Allelic variants of the tumor necrosis factor-alpha (TNF-alpha) gene seem to contribute to insulin resistance increasing the transcription rate of TNF-alpha. The TNF-alpha -863A allele is associated with a lower expression of TNF-alpha gene and less secretion of the cytokine. To investigate whether an abnormal TNF-alpha system regulation may contribute to early impairment of insulin action in first-degree relatives of patients with type 2 diabetes mellitus (DM), we studied the TNF-alpha -863C/A polymorphism and the soluble fraction of TNF-alpha receptor-2 (sTNFR2) concentration in these subjects in comparison to a control group. A total of 52% of subjects in the relatives' group showed an abnormal oral glucose tolerance (either as impaired glucose tolerance [IGT] or diabetes) and had more features of the insulin resistance syndrome, despite showing similar body composition as controls. The plasma concentration of the sTNFR2 was higher and insulin sensitivity (%S) was lower in the relatives' group than in the controls. Likewise, the TNF-alpha -863A allele was more commonly detected in the control group (10 of 41) than in the relative's group (2 of 36, P =.029). In a multivariate linear regression analysis, neither TNF-alpha -863A allele nor sTNFR2 independently determined %S. Only body mass index (BMI) and the presence of a positive family history of DM were independent determinants of insulin resistance. In summary, our study showed a lower rate of TNF-alpha -863A allele and higher concentrations of sTNFR2 in first-degree relatives of DM subjects. These findings could be included among the genetic, metabolic, and clinical heterogeneity that characterizes the pathophysiology of DM. The presence of abnormalities in the TNF-alpha pathway could predispose to the development of DM in subjects at risk for the disease.

Pro12Ala substitution in the peroxisome proliferator-activated receptor-gamma is associated with increased leptin levels in women with type-2 diabetes mellitus

OBJECTIVE

To analyze the relationship between the peroxisome proliferator-activated receptor-gamma (PPARgamma2) Pro12Ala variant and type-2 diabetes mellitus and its correlation with some cytokine determinants of insulin resistance such as tumor necrosis factor (TNF)-alpha and leptin.

METHODS

The PPARgamma2 Pro12Ala genetic polymorphism was studied in 167 type-2 diabetic patients and 63 healthy controls. Serum leptin and plasma-soluble TNF-R2 were measured.

RESULTS

Women carriers of the Pro12Ala mutation exhibited higher leptin levels than women non-carriers (median 31.4 vs. 17.5 ng/ml; p < 0.005). sTNF-R2 levels did not show differences between the two genotypes. Analysis by the multiple linear regression model of leptin-body mass index controlled by the PPARgamma2 genotype showed that leptin levels were determined by the Pro12Ala mutation in type-2 diabetic women but not in men.

CONCLUSIONS

PPARgamma2 seems to be implicated in leptin homeostasis in type-2 diabetic women.

Bone mineral mass is associated with interleukin 1 receptor autoantigen and TNF-alpha gene polymorphisms in post-menopausal Mediterranean women

Bone mass is known to be under genetic control. Interleukin-1 (IL-1), interleukin-6 (IL-6) and TNF-alpha are strong inductors of bone resorption. The estrogenic deficiency that occurs during menopause leads to an increase in the production of these cytokines. We analyzed the genetic susceptibility of several polymorphisms of the interleukin-1 receptor antagonist (IL-1ra), IL-6 and TNF-alpha genes in lumbar spine and hip bone mass in a sample of post-menopausal Caucasian Mediterranean women with osteoporosis. 104 post-menopausal osteoporotic women (58.6+/-4.8 yr) and 51 post-menopausal women without osteoporosis as the control group (57.2+/-4.5 yr) were studied. The osteoporotic group was in turn sub-classified into severe and non-severe osteoporosis. The variable number of tandem repeats IL1-ra, IL-6 SfaNI and TNF-alpha NcoI genetic polymorphisms were studied. Biochemical markers of bone turnover were measured in blood and urine. Women carrying the A2 allele (A2+) of the IL-1ra gene showed greater BMD in the lumbar spine (p=0.02) and hip (p=0.006), compared to those not carrying the allele (A2-). The IL-6 polymorphism studied in its 5' flanking region did not show any association with BMD values. The TNF-alpha gene G allele was associated with a greater bone mass in the non-severe osteoporotic subgroup, both in the lumbar spine (p=0.0007) and in the hip (p=0.02). Likewise, genotype combination A2+GG was associated to a greater hip BMD at the femoral neck and Ward triangle levels (p=0.02). We conclude that both IL-1ra and TNF-alpha can be candidate loci to be studied in the susceptibility to develop post-menopausal osteoporosis.

Crystal structure of a novel mid-gut procarboxypeptidase from the cotton pest Helicoverpa armigera

The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme.

The crystal structure of the inhibitor-complexed carboxypeptidase D domain II and the modeling of regulatory carboxypeptidases

The three-dimensional crystal structure of duck carboxypeptidase D domain II has been solved in a complex with the peptidomimetic inhibitor, guanidinoethylmercaptosuccinic acid, occupying the specificity pocket. This structure allows a clear definition of the substrate binding sites and the substrate funnel-like access. The structure of domain II is the only one available from the regulatory carboxypeptidase family and can be used as a general template for its members. Here, it has been used to model the structures of domains I and III from the former protein and of human carboxypeptidase E. The models obtained show that the overall topology is similar in all cases, the main differences being local and because of insertions in non-regular loops. In both carboxypeptidase D domain I and carboxypeptidase E slightly different shapes of the access to the active site are predicted, implying some kind of structural selection of protein or peptide substrates. Furthermore, emplacement of the inhibitor structure in the active site of the constructed models showed that the inhibitor fits very well in all of them and that the relevant interactions observed with domain II are conserved in domain I and carboxypeptidase E but not in the non-active domain III because of the absence of catalytically indispensable residues in the latter protein. However, in domain III some of the residues potentially involved in substrate binding are well preserved, together with others of unknown roles, which also are highly conserved among all carboxypeptidases. These observations, taken together with others, suggest that domain III might play a role in the binding and presentation of proteins or peptide substrates, such as the pre-S domain of the large envelope protein of duck hepatitis B virus.

Circulating interleukin 6 levels, blood pressure, and insulin sensitivity in apparently healthy men and women

There is increasing evidence that systemic inflammation and insulin resistance constitute interrelated events that contribute to atherosclerosis. We studied the effect of the association between circulating interleukin 6 (IL-6) levels, one of the major mediators of inflammation, and C-reactive protein on insulin resistance and blood pressure in 228 healthy volunteers. The plasma IL-6 concentration was significantly and similarly associated with systolic (SBP) and diastolic (DBP) blood pressure, fasting insulin, and the fasting insulin resistance index (FIRI) in all subjects. When smokers were excluded from the analysis, plasma IL-6 levels correlated with percent fat mass (r = 0.19; P = 0.02), absolute fat mass (r = 0.17; P = 0.03), SBP, DBP, fasting insulin levels, and FIRI. The latter associations persisted after controlling for body mass index (r = 0.15 and r = 0.19; P = 0.02 and P: = 0.0004 for SBP and DBP, respectively; r = 0.24 and r = 0.19, P = 0.004 and P = 0.03, for fasting insulin and FIRI, respectively). Gender and smoking status significantly influenced the results. Although IL-6 levels were significantly associated with fasting insulin and FIRI in men, these significant correlations were not observed in women. Conversely, although IL-6 levels were significantly associated with SBP and DBP in women, these coefficients were not statistically significant in men. All of these associations were lost among smokers and remained significant in nonsmokers. As IL-6 is the major mediator of the acute phase response by hepatocytes and induces the synthesis of C-reactive protein (CRP), we also controlled for the latter. Serum CRP levels correlated significantly with IL-6 in all the subjects, but mainly in nonsmokers and men. Of note was that this significant relationship was lost among smokers. CRP was associated with fasting insulin (r = 0.28; P < 0.0001) and FIRI (r = 0.25; P < 0.0001), but not with SBP or DBP (P = NS), in all subjects. Unlike IL-6, the associations between CRP and these parameters were similar in men and women and in smokers and nonsmokers. For insulin and FIRI they were stronger in women and in nonsmokers. CPR significantly correlated with the WHR only in men (r = 0.22; P = 0.01). Using multiple linear regression in a stepwise manner to predict circulating IL-6 levels, smoking status (P = 0.0059) and FIRI (P = 0.03), but not fat mass or SBP, independently contributed to 11% of its variance in men. When CRP was introduced into the model, the latter (P < 0.0001) and smoking status (P = 0.02), but not FIRI, fat mass, or SBP, contributed to 33% of the variance in IL-6 levels. In women, only SBP (P = 0.04) contributed to 5% of its variance. When CRP was introduced into the model, again only SBP (P = 0.01) contributed to 10% of the variance in IL-6 levels. In 25 of these subjects, insulin sensitivity was determined using the frequently sampled iv glucose tolerance test with minimal model analysis, and circulating IL-6 levels were strongly associated with the insulin sensitivity index (r = -0.65; P < 0.0001). Again, this relationship was even stronger in men (r = -0.75; P < 0.001) and was not significant in women (r = -0.26; P = NS). In all of these subjects, only insulin sensitivity (P = 0.0037), not fat mass, contributed to 21% of the variance of IL-6 levels in a multiple linear regression analysis. In summary, circulating IL-6 levels, by inducing either hypertension in women or insulin resistance in men, constitute a significant proatherogenic cytokine. The mechanisms of these associations should be further investigated.

Circulating interleukin 6 levels, blood pressure, and insulin sensitivity in apparently healthy men and women

There is increasing evidence that systemic inflammation and insulin resistance constitute interrelated events that contribute to atherosclerosis. We studied the effect of the association between circulating interleukin 6 (IL-6) levels, one of the major mediators of inflammation, and C-reactive protein on insulin resistance and blood pressure in 228 healthy volunteers. The plasma IL-6 concentration was significantly and similarly associated with systolic (SBP) and diastolic (DBP) blood pressure, fasting insulin, and the fasting insulin resistance index (FIRI) in all subjects. When smokers were excluded from the analysis, plasma IL-6 levels correlated with percent fat mass (r = 0.19; P = 0.02), absolute fat mass (r = 0.17; P = 0.03), SBP, DBP, fasting insulin levels, and FIRI. The latter associations persisted after controlling for body mass index (r = 0.15 and r = 0.19; P = 0.02 and P: = 0.0004 for SBP and DBP, respectively; r = 0.24 and r = 0.19, P = 0.004 and P = 0.03, for fasting insulin and FIRI, respectively). Gender and smoking status significantly influenced the results. Although IL-6 levels were significantly associated with fasting insulin and FIRI in men, these significant correlations were not observed in women. Conversely, although IL-6 levels were significantly associated with SBP and DBP in women, these coefficients were not statistically significant in men. All of these associations were lost among smokers and remained significant in nonsmokers. As IL-6 is the major mediator of the acute phase response by hepatocytes and induces the synthesis of C-reactive protein (CRP), we also controlled for the latter. Serum CRP levels correlated significantly with IL-6 in all the subjects, but mainly in nonsmokers and men. Of note was that this significant relationship was lost among smokers. CRP was associated with fasting insulin (r = 0.28; P < 0.0001) and FIRI (r = 0.25; P < 0.0001), but not with SBP or DBP (P = NS), in all subjects. Unlike IL-6, the associations between CRP and these parameters were similar in men and women and in smokers and nonsmokers. For insulin and FIRI they were stronger in women and in nonsmokers. CPR significantly correlated with the WHR only in men (r = 0.22; P = 0.01). Using multiple linear regression in a stepwise manner to predict circulating IL-6 levels, smoking status (P = 0.0059) and FIRI (P = 0.03), but not fat mass or SBP, independently contributed to 11% of its variance in men. When CRP was introduced into the model, the latter (P < 0.0001) and smoking status (P = 0.02), but not FIRI, fat mass, or SBP, contributed to 33% of the variance in IL-6 levels. In women, only SBP (P = 0.04) contributed to 5% of its variance. When CRP was introduced into the model, again only SBP (P = 0.01) contributed to 10% of the variance in IL-6 levels. In 25 of these subjects, insulin sensitivity was determined using the frequently sampled iv glucose tolerance test with minimal model analysis, and circulating IL-6 levels were strongly associated with the insulin sensitivity index (r = -0.65; P < 0.0001). Again, this relationship was even stronger in men (r = -0.75; P < 0.001) and was not significant in women (r = -0.26; P = NS). In all of these subjects, only insulin sensitivity (P = 0.0037), not fat mass, contributed to 21% of the variance of IL-6 levels in a multiple linear regression analysis. In summary, circulating IL-6 levels, by inducing either hypertension in women or insulin resistance in men, constitute a significant proatherogenic cytokine. The mechanisms of these associations should be further investigated.

Plasma soluble tumor necrosis factor-alpha receptors circulate in proportion to leptin levels during the menstrual cycle in lean but not in obese women

OBJECTIVE

In recent studies serum leptin levels were significantly higher in the luteal phase than in the follicular phase, but the mechanism of changing leptin levels are unknown. Several research lines indicate a potential role for tumor necrosis factor (TNF-alpha) in ovulation and reproductive events. As TNF-alpha appears to regulate leptin secretion, we speculated that TNF-alpha might be involved in leptin variations during the menstrual cycle.

DESIGN AND METHODS

Nine healthy never obese and ten overweight normally cycling women were studied. TNF-alpha action - through the plasma levels of the soluble fraction of the tumor necrosis factor receptors 1 and 2 (sTNFR1 and sTNFR2) - and leptin concentrations were measured in the follicular (F), peri-ovulatory (PO) and luteal phases (L) of their menstrual cycles.

RESULTS

Circulating leptin levels were significantly associated with the stage of the menstrual cycle (P<0.001), being higher in PO and L phases. However, only three of ten overweight subjects vs eight of nine lean women (Chi square P=0.014 after Fisher's exact test) showed significantly higher leptin levels in the PO and L than in the F phase (95% confidence interval (95% CI) of the differences, 3.7 to 10.2 ng/ml, paired t-test P=0.001). In these women (group 1), the changes in leptin levels parallelled the variations observed in plasma sTNFR1 (2.50+/-0.1 vs 2.11+/-0.05 ng/ml, P<0.0001, 95% CI, 0.21 to 0.56) and sTNFR2 levels (5.19+/-0.28 vs 4.55+/-0.25 ng/ml, P<0.0001, 95% CI, 0. 47 to 0.81). In the remaining women (group 2), leptin (95% CI, -1 to 9.2 ng/ml, P=not significant (NS)), sTNFR1 (95% CI, -0.3 to 0.14 ng/ml, P=NS) and sTNFR2 levels (95% CI, -0.95 to 0.39 ng/ml, P=NS) were essentially unaltered throughout the menstrual cycle. Group 2 women were similar in age (36.1+/-2.9 vs 37.3+/-1.4 years) and significantly overweight (body mass index 31+/-2.9 vs 23.9+/-1. 2 kg/m(2)) compared with group 1 women. A negative correlation was observed between leptin levels in the follicular phase and the change in plasma leptin from F to L phase in all subjects (r=-0.67, P=0.002).

CONCLUSIONS

Circulating leptin and sTNFRs levels change significantly during the menstrual cycle of most lean women. In contrast, the levels of these molecules remain essentially unaltered during the F, PO and L phases in the majority of overweight women. Obesity might be associated not only with blunted diurnal excursions and dampened pulsatility, but also with blunted excursions during the menstrual cycle.

Polymorphism of the tumor necrosis factor-alpha receptor 2 gene is associated with obesity, leptin levels, and insulin resistance in young subjects and diet-treated type 2 diabetic patients

OBJECTIVE

Mice lacking the tumor necrosis factor-alpha receptor 2 (TNFR2) gene fed a high-fat diet gain less weight and display reduced leptin and insulin levels. In humans, plasma levels of the soluble fraction of TNFR2 (sTNFR2) circulate in proportion to the degree of insulin resistance. The purpose of this study was to evaluate a polymorphism in the 3' untranslated region of the TNFR2 gene on chromosome 1 in relation to BMI, leptin levels, and insulin resistance.

RESEARCH DESIGN AND METHODS

Using single-strand conformation polymorphism, the polymorphism was analyzed in 107 nondiabetic subjects (60 women, 47 men) and in 110 consecutive patients with type 2 diabetes (79 women, 31 men). In a subset of 33 healthy subjects, insulin sensitivity (minimal model analysis) was also evaluated.

RESULTS

Four alleles of the TNFR2 gene were identified (A1, A2, A3, and A4). BMI and serum leptin levels were significantly increased in young carriers of the A2 allele. Plasma sTNFR2 levels were similar among the different TNFR2 gene variants. However, in subjects who did not carry the A2 allele, in young subjects, and in women, plasma sTNFR2 levels were proportional to BMI and leptin levels. In the study sample, carriers of the A2 allele (n = 18) showed significantly increased BMI, fat mass, waist-to-hip ratio, serum total and VLDL triglyceride levels, and leptin levels and had a lower insulin sensitivity index than noncarriers of the A2 variant (n = 15). The frequency of the different alleles among diabetic subjects was similar to that in the control population. However, diet-treated diabetic subjects (n = 49) who were carriers of the A2 allele exhibited significantly higher BMI and leptin levels than diet-treated noncarriers of the A2 allele.

CONCLUSIONS

The presence of the A2 allele in the TNFR2 gene may predispose subjects to obesity and higher leptin levels, which may in turn predispose them to insulin resistance or vice versa. The TNFR2 gene may be involved in weight-control mechanisms.

Structure of a novel leech carboxypeptidase inhibitor determined free in solution and in complex with human carboxypeptidase A2

Leech carboxypeptidase inhibitor (LCI) is a novel protein inhibitor present in the medicinal leech Hirudo medicinalis. The structures of LCI free and bound to carboxypeptidase A2 (CPA2)have been determined by NMR and X-ray crystallography, respectively. The LCI structure defines a new protein motif that comprises a five-stranded antiparallel beta-sheet and one short alpha-helix. This structure is preserved in the complex with human CPA2 in the X-ray structure, where the contact regions between the inhibitor and the protease are defined. The C-terminal tail of LCI becomes rigid upon binding the protease as shown in the NMR relaxation studies, and it interacts with the carboxypeptidase in a substrate-like manner. The homology between the C-terminal tails of LCI and the potato carboxypeptidase inhibitor represents a striking example of convergent evolution dictated by the target protease. These new structures are of biotechnological interest since they could elucidate the control mechanism of metallo-carboxypeptidases and could be used as lead compounds for the search of fibrinolytic drugs.

Metallocarboxypeptidases and their protein inhibitors. Structure, function and biomedical properties

Among the different aspects of recent progress in the field of metallocarboxypeptidases has been the elucidation of the three dimensional structures of the pro-segments (in monomeric or oligomeric species) and their role in the expression, folding and inhibition/activation of the pancreatic and pancreatic-like forms. Also of great significance has been the cloning and characterization of several new regulatory carboxypeptidases, enzymes that are related with important functions in protein and peptide processing and that show significant structural differences among them and also with the digestive ones. Many regulatory carboxypeptidases lack a pro-region, unlike the digestive forms or others in between from the evolutionary point of view. Finally, important advances have been made on the finding and characterization of new protein inhibitors of metallocarboxypeptidases, some of them with interesting potential applications in the biotechnological/biomedical fields. These advances are analyzed here and compared with the earlier observations in this field, which was first explored by Hans Neurath and collaborators.

Interleukin-6 gene polymorphism and insulin sensitivity

Type 2 diabetes and the insulin resistance syndrome have been hypothesized to constitute manifestations of an ongoing acute-phase response. We aimed to study an interleukin-6 (IL-6) gene polymorphism in relation to insulin sensitivity (IL-6 is the main cytokine involved in an acute-phase response). Subjects homozygous for the C allele at position -174 of the IL-6 gene (SfaNI genotype), associated to lower plasma IL-6 levels, showed significantly lower integrated area under the curve of serum glucose concentrations (AUCglucose) after an oral glucose tolerance test, lower blood glycosylated hemoglobin, lower fasting insulin levels, lower total and differential white blood cell count (a putative marker of peripheral IL-6 action), and an increased insulin sensitivity index than carriers of the G allele, despite similar age and body composition. A gene dosage effect was especially remarkable for AUCglucose (6.4 vs. 9.3 vs. 9.7 mmol/l in C/C, C/G, and G/G individuals, respectively). The serum concentration of fully glycosylated cortisol binding globulin (another marker of IL-6 action), suggested by concanavalin A adsorption, was lower in C/C subjects than in G/G individuals (32.6+/-2.9 vs. 37.6+/-4.6 mg/l, P = 0.03). In summary, a polymorphism of the IL-6 gene influences the relationship among insulin sensitivity, postload glucose levels, and peripheral white blood cell count.

Interleukin-6 gene polymorphism and lipid abnormalities in healthy subjects

Several lines of evidence indicate that interleukin-6 (IL-6) is involved not only in the hepatic acute phase response but also in adipose tissue metabolism, lipoprotein lipase activity, and hepatic triglyceride secretion. A polymorphism in the IL-6 gene, associated with differences in IL-6 transcription rate, has been recently described. We aimed to study whether this IL-6 gene polymorphism leads to differences in fasting and postglucose load plasma lipids in healthy subjects. Subjects with G at position -174 of the IL-6 gene were similar in age, sex, body mass index, and waist to hip ratio in comparison with carriers of the C allele. However, G carriers showed almost twice plasma triglycerides (1.5 +/- 0.9 vs. 0.90 +/- 0.37 mmol/L; P = 0.01), very low-density lipoprotein (VLDL)-triglycerides (0.97 +/- 0.69 vs. 0.42 +/- 0.2 mmol/L; P = 0.002), higher fasting (881 vs. 458 micromol/L; P = 0.01), and postglucose load free fatty acids (299 vs. 90.5 micromol/L; P = 0.03), slightly lower high-density lipoprotein-2 cholesterol (0.25 +/- 0.14 vs. 0.39 +/- 0.26 mmol/L; P = 0.058), and similar cholesterol and LDL-cholesterol levels than carriers of the C allele. Serum IL-6 levels correlated positively with fasting triglycerides, VLDL-triglycerides, and postload free fatty acids (r = 0.61, 0.65 and 0.60, respectively; P < 0.001) and negatively with high-density lipoprotein-cholesterol (r = -0.42, P < 0.05). A tendency toward higher serum IL-6 levels was observed among G carriers (9.9 +/- 6.9 vs. 6.85 +/- 1.7 pg/mL; P = 0.09). The -174G construct was recently reported to show higher expression of IL-6 in He La cells and was associated with higher plasma IL-6 levels than the -174C allele. Thus, the results of the present study suggest that subjects with the G allele, associated to higher IL-6 secretion, are prone to lipid abnormalities. Whether this polymorphism contributes to lipid alterations associated with other metabolic disorders awaits additional studies.

Crystal structure of avian carboxypeptidase D domain II: a prototype for the regulatory metallocarboxypeptidase subfamily

The crystal structure of domain II of duck carboxypeptidase D, a prohormone/propeptide processing enzyme integrated in a three repeat tandem in the natural system, has been solved, constituting a prototype for members of the regulatory metallocarboxypeptidase subfamily. It displays a 300 residue N-terminal alpha/beta-hydrolase subdomain with overall topological similarity to and general coincidence of the key catalytic residues with the archetypal pancreatic carboxypeptidase A. However, numerous significant insertions/deletions in segments forming the funnel-like access to the active site explain differences in specificity towards larger protein substrates or inhibitors. This alpha/beta-hydrolase subdomain is followed by a C-terminal 80 residue beta-sandwich subdomain, unique for these regulatory metalloenzymes and topologically related to transthyretin and sugar-binding proteins. The structure described here establishes the fundamentals for a better understanding of the mechanism ruling events such as prohormone processing and will enable modelling of regulatory carboxypeptidases as well as a more rational design of inhibitors of carboxypeptidase D.

Plasma levels of the soluble fraction of tumor necrosis factor receptors 1 and 2 are independent determinants of plasma cholesterol and LDL-cholesterol concentrations in healthy subjects

In the last few years, it has been demonstrated that tumor necrosis alpha (TNF-alpha) has important effects on whole-body lipid metabolism. TNF-alpha administration has been found to produce an increase in serum cholesterol levels and increased hepatic hydro-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase activity in mice. The purpose of this study was to test whether plasma levels of the soluble forms of the TNF-alpha receptors 1 and 2 (sTNFR1, sTNFR2) are associated with lipid abnormalities. A total of 36 healthy subjects (19 males, mean age 36.2 +/- 1.9, and 17 females, mean age 34.9 +/- 1.4) were studied. Plasma sTNFR1 levels correlated with total (r = 0.43, P = 0.01) and LDL-cholesterol (r = 0.52, P = 0.002) levels, but not with total or HDL2-HDL3 subfractions of HDL-cholesterol, total plasma triglycerides, VLDL-cholesterol or VLDL-triglycerides (all r < 0.11, P = NS). Plasma sTNFR2 levels also correlated with total (r = 0.44, P = 0.009) and LDL-cholesterol (r = 0.57, P < 0.0001) levels, and negatively with HDL2-cholesterol (r = -0.37, P = 0.029). A stepwise multiple linear regression was constructed to predict total cholesterol levels, with BMI, sex, age, sTNFR1 or sTNFR2 as independent variables. Both sTNFR1 and sTNFR2 were significantly associated with total cholesterol (P = 0.031 and 0.009), contributing to 26 and 19%, respectively, of its variance. In another model in which LDL-cholesterol was substituted for total cholesterol, sTNFR1 or sTNFR2 (P = 0.0084 and 0.0005) were significantly associated with LDL-cholesterol, contributing to 39 and 32% of its variance. In summary, plasma levels of sTNFR1 and sTNFR2 circulate in proportion to total and LDL-cholesterol in healthy subjects.

Mapping the pro-region of carboxypeptidase B by protein engineering. Cloning, overexpression, and mutagenesis of the porcine proenzyme

The proteolytic processing of pancreatic procarboxypeptidase B to a mature and functional enzyme is much faster than that of procarboxypeptidase A1. This different behavior has been proposed to depend on specific conformational features at the region that connects the globular domain of the pro-segment to the enzyme and at the contacting surfaces on both moieties. A cDNA coding for porcine procarboxypeptidase B was cloned, sequenced, and expressed at high yield (250 mg/liter) in the methylotrophic yeast Pichia pastoris. To test the previous hypothesis, different mutants of the pro-segment at the putative tryptic targets in its connecting region and at some of the residues contacting the active enzyme were obtained. Moreover, the complete connecting region was replaced by the homologous sequence in procarboxypeptidase A1. The detailed study of the tryptic processing of the mutants shows that limited proteolysis of procarboxypeptidase B is a very specific process, as Arg-95 is the only residue accessible to tryptic attack in the proenzyme. A fast destabilization of the connecting region after the first tryptic cut allows subsequent proteolytic processing and the expression of carboxypeptidase B activity. Although all pancreatic procarboxypeptidases have a preformed active site, only the A forms show intrinsic activity. Mutational substitution of Asp-41 in the globular activation domain, located at the interface with the enzyme moiety, as well as removal of the adjacent 310 helix allow the appearance of residual activity in the mutated procarboxypeptidase B, indicating that the interaction of both structural elements with the enzyme moiety prevents the binding of substrates and promotes enzyme inhibition. In addition, the poor heterologous expression of such mutants indicates that the mutated region is important for the folding of the whole proenzyme.

Tumor necrosis factor system activity is associated with insulin resistance and dyslipidemia in myotonic dystrophy

Myotonic dystrophy (MyD) is a multisystem autosomal dominant disorder associated with progressive muscle wasting and weakness. The striking metabolic abnormality in MyD is insulin resistance. The mechanism by which target tissues are insensitive to insulin action remains uncertain. In a recent study, plasma soluble tumor necrosis factor receptor (sTNFR)2 levels were found to be associated with muscle tissue mass and insulin resistance. Given these associations, we speculated that disorders of the muscle cell membrane could lead simultaneously to insulin insensitivity and sTNFR2 leakage in MyD. To test this hypothesis, we measured the levels of circulating sTNFR1 and sTNFR2 and insulin resistance in MyD patients. We studied 22 MyD patients and 24 age-, BMI-, and fat mass-matched control subjects. Both MyD men and women showed higher plasma insulin levels in the presence of comparable glucose concentrations than did control subjects. sTNFR2, but not sTNFR1, levels were approximately 1.5-fold higher in MyD patients. In parallel with these findings, the fasting insulin resistance index (FIRI) was also higher in MyD patients. In fact, in the whole population, fasting insulin and FIRI strongly correlated with sTNFR2 in both men (r = 0.77 and r = 0.81, P<0.0001, respectively) and women (r = 0.67 and r = 0.64, P = 0.001, respectively). sTNFR2 levels were also associated with the insulin sensitivity index (S(I)), calculated from an oral glucose tolerance test (OGTT) according to the method by Cederholm and Wibell (r = -0.43, P = 0.006). We constructed a multiple linear regression to predict FIRI, with BMI, waist-to-hip ratio, and sTNFR2 as independent variables. In this model, both BMI (P = 0.0014) and sTNFR2 (P = 0.0048) levels contributed independently to 46% of the variance of FIRI. In another model, in which FIRI was substituted for S(I) from the OGTT, both BMI (P = 0.0001) and sTNFR2 (P = 0.04) levels contributed independently to 48% of the variance of S(I) from the OGTT. Plasma cholesterol and triglyceride concentrations were significantly increased in MyD patients. sTNFR1 and sTNFR2 levels were found to be strongly associated with plasma cholesterol, LDL cholesterol, and triglycerides. sTNFR1 and sTNFR2 also correlated with serum creatine kinase activity in MyD patients (r = 0.57, P = 0.006; r = 0.75, P<0.0001, respectively). In conclusion, here we describe, for the first time to our knowledge, a relationship between insulin action and plasma sTNFR2 concentration in MyD patients. We have also found increased concentrations of plasma triglycerides and cholesterol levels in parallel with sTNFR1 and sTNFR2 concentrations in MyD patients. We speculate that the latter associations are dependent on, and secondary to, increased tumor necrosis factor (TNF)-alpha action. Whether TNF action is implicated in the pathogenesis of MyD or is a simple marker of disease activity awaits further studies.

A carboxypeptidase inhibitor from the medical leech Hirudo medicinalis. Isolation, sequence analysis, cDNA cloning, recombinant expression, and characterization

A novel metallocarboxypeptidase inhibitor was isolated from the medical leech Hirudo medicinalis. Amino acid sequence analysis provided a nearly complete primary structure. which was subsequently verified and completed by cDNA cloning using reverse transcriptase-polymerase chain reaction/rapid amplification of cDNA end techniques. The inhibitor, called LCI (leech carboxypeptidase inhibitor), is a cysteine-rich polypeptide composed of 66 amino acid residues. It does not show sequence similarity to any other protein except at its C-terminal end. In this region, the inhibitor shares the amino acid sequence -Thr-Cys-X-Pro-Tyr-Val-X with Solanacea carboxypeptidase inhibitors, suggesting a similar mechanism of inhibition where the C-terminal tail of the inhibitor interacts with the active center of metallocarboxypeptidases in a substrate-like manner. This hypothesis is supported by the hydrolytic release of the C-terminal glutamic acid residue of LCI after binding to the enzyme. Heterologous overexpression of LCI in Escherichia coli, either into the medium or as an intracellular thioredoxin fusion protein, yields a protein with full inhibitory activity. Both in the natural and recombinant forms, LCI is a tightly binding, competitive inhibitor of different types of pancreatic-like carboxypeptidases, with equilibrium dissociation constants Ki of 0.2-0.4 x 10(-9) M for the complexes with the pancreatic enzymes A1, A2, and B and plasma carboxypeptidase B. Circular dichroism and nuclear magnetic resonance spectroscopy analysis indicate that recombinant LCI is a compactly folded globular protein, stable to a wide range of pH and denaturing conditions.

Beta 3-adrenoreceptor gene polymorphism and leptin. Lack of relationship in type 2 diabetic patients

INTRODUCTION

The beta 3-Adrenergic receptor (beta 3AR) and leptin are molecules involved in the regulation of energy balance. Recently, a mutation in the beta 3AR gene (Trp64Arg) has been reported to be associated with features of insulin resistance, weight gain and early onset of Type 2 Diabetes Mellitus. The aim of this study was to determine the frequency and clinical characteristics of the Trp64Arg mutation in the beta 3AR gene in Type 2 diabetic patients, its relationship with leptin levels, and its role in microangiopathic complications.

SUBJECTS AND METHODS

187 Type 2 diabetic patients and 100 unrelated non-diabetic subjects were studied. There was no difference between the diabetic and nondiabetic subjects in the frequency of the Trp64 and Arg64 alleles (92.5% vs. 92.3% and 7.5% vs. 7.7%, respectively). Type 2 diabetic patients were divided into two groups according to the presence (n = 27) or absence of the mutation (n = 160).

RESULTS

Mutation of the beta 3AR gene was not associated with any differences either in the clinical and metabolic parameters or microangiopathic complications. Type 2 diabetic patients carrying the Arg64 allele tended to have a lower diabetes duration, but this was not statistically significant. Plasma leptin levels were not different according to the beta 3AR genotype.

CONCLUSIONS

The Trp64Arg mutation is not a major determinant of Type 2 diabetes and its microangiopathic complications. Moreover, this mutation was not clinically relevant in leptin regulation.

Plasma levels of the soluble fraction of tumor necrosis factor receptor 2 and insulin resistance

Recent studies have shown that the tumor necrosis factor (TNF) system is implicated in the insulin resistance of human obesity. Plasma concentrations of the soluble fraction of the TNF receptors 1 and 2 (sTNFR1 and sTNFR2) are thought to reflect the degree of activation of the TNF system. The purpose of this study was to explore whether this activation, as measured by the levels of circulating sTNFR1 and sTNFR2, is associated with insulin resistance. A total of 19 men (mean age 36.2 +/- 1.9; BMI 28.8 +/- 1.2, range 22.2-35.7) and 17 premenopausal women (age 34.9 +/- 1.4; BMI 28.1 +/- 0.8, range 19-37.9) were studied. Men showed higher levels of plasma sTNFR1 and sTNFR2 than women. However, obese men showed increased levels of sTNFR2 but similar levels of sTNFR1 in comparison with obese women. In fact, sTNFR2 levels correlated with BMI (r = 0.50, P = 0.002), fat-free mass (FFM) (r = 0.61, P < 0.0001), and waist-to-hip ratio (WHR) (r = 0.39, P = 0.02), but not with fat mass or percent fat mass. sTNFR2 levels correlated with basal glucose levels (r = 0.45, P = 0.007), area under the curve (AUC) for glucose during an oral glucose tolerance test (r = 0.42, P = 0.013), and with the quotient AUC glucose/log AUC insulin (r = 0.41, P = 0.015). sTNFR2 also correlated negatively with insulin sensitivity (S(I)), evaluated using the frequently sampled intravenous glucose tolerance test with minimal model analysis (r = -0.38, P = 0.02). Plasma sTNFR1 levels were not associated with any of these variables. Because WHR influenced both S(I) and sTNFR2 levels, we constructed a multiple linear regression to predict S(I), with WHR and sTNFR2 as independent variables. In this model, both WHR (P = 0.0078) and sTNFR2 levels (P = 0.025) contributed to 47% of the variance in S(I). In parallel with higher FFM, lean and obese men showed a lower S(I) (2.9 +/- 0.9 vs. 5.2 +/- 1.3 min(-1) x mU x l(-1), P = 0.001; and 1.15 +/- 1.1 vs. 1.8 +/- 0.8 min(-1) x mU x l(-1), P = 0.035, respectively) and higher sTNFR2 levels in comparison with lean and obese women, respectively. After controlling for FFM, the correlation between S(I) and sTNFR2 levels disappeared, indicating that FFM was significantly influencing these associations. In summary, plasma sTNFR2 levels, but not sTNFR1, were proportional to BMI, WHR, FFM (a well-known confounder in the evaluation of insulin sensitivity), basal and postload glucose levels, and insulin resistance. These findings support TNF-alpha as a system regulating insulin action in human obesity.

GLUT1 gene polymorphism in non-insulin-dependent diabetes mellitus: genetic susceptibility relationship with cardiovascular risk factors and microangiopathic complications in a Mediterranean population

OBJECTIVE

It has been suggested that the polymorphic variation of GLUT1 glucose transporter may contribute to genetic susceptibility to type 2 diabetes in some populations. We have evaluated the GLUT1-XbaI polymorphism in an association study of a Caucasian Mediterranean population and its role in the susceptibility to displaying either microangiopathic complications or any of the risk factors associated with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 193 type 2 diabetic patients (104 women and 89 men, 31-82 years of age, diabetes duration 13.2 +/- 6.2 years) and 90 healthy subjects (48 women and 42 men, 20-72 years of age) were recruited for the association study. For the evaluation of nephropathy and retinopathy, type 2 diabetic patients were matched with those not having microangiopathic complications.

RESULTS

Genotypic or allelic frequencies did not differ significantly between controls and type 2 diabetic patients. Regarding the distribution of clinical or metabolic parameters according to GLUT1 genotype, patients with X1X1 genotype tended to have higher diastolic blood pressure levels compared with the remaining genotypes (P = 0.008). There were no differences in genotypic or allelic distribution among patients for either the presence or absence of retinopathy or nephropathy.

CONCLUSIONS

We conclude that GLUT1 loci did not contribute significantly to type 2 diabetes in this cohort and is not a determinant for cardiovascular risk factors or chronic microangiopathic complications associated with type 2 diabetes. The weak association with diastolic hypertension must be confirmed in other populations.

Overexpression of human procarboxypeptidase A2 in Pichia pastoris and detailed characterization of its activation pathway

The cDNA of human procarboxypeptidase A2 has been overexpressed in the methylotrophic yeast Pichia pastoris and secreted into the culture medium by means of the alpha-mating factor signal sequence, yielding a major protein of identical size and N-terminal sequence as the wild-type form. Two other forms containing the proenzyme have also been overexpressed: one of them resulted from an incomplete processing of the signal peptide, whereas the other was a glycosylated derivative. Recombinant procarboxypeptidase A2 was purified to homogeneity, and it was shown that its mature active form displays functional properties similar to those of the enzyme directly isolated from human pancreas. The overall yield was approximately 250 mg of proenzyme or 180 mg of mature enzyme/liter of cell culture. The proteolysis-promoted activation process of the recombinant proenzyme has been studied in detail. During maturation by trypsin, the increase in activity of the enzyme is a rapid and monotonic event, which reflects the rate of the proteolytic release of the inhibitory pro-segment and the weaker nature of its interactions with the enzyme moiety compared with procarboxypeptidases of the A1 type. Three main forms of the pro-segment (96, 94, and 92 amino acids), with no inhibitory capability in the severed state, and a single mature carboxypeptidase A2 are produced during this process. No further proteolysis of these pro-segments by the generated carboxypeptidase A2 occurs, in contrast with observations made in other procarboxypeptidases (A1 and B). This differential behavior is a result of the extreme specificity of carboxypeptidase A2.

Comparative analysis of the sequences and three-dimensional models of human procarboxypeptidases A1, A2 and B

A full-length cDNA clone for preprocarboxypeptidase B from human pancreas has been isolated and sequenced. The open reading frame is 1254 bp in length, encoding a protein of 417 amino acids that includes a leader signal peptide of 15 amino acids and a 95-amino acid-long pro-segment. It contains two differences when compared to the sequence reported for pancreas-specific protein, a human serum marker for acute pancreatitis identified as procarboxypeptidase B. The main difference is a previously unreported Cys at position 138, which is needed for the formation of one of the three disulphide bridges. Sequence alignments between human procarboxypeptidases A1, A2 and B and other known forms show that the most conserved region is the enzyme moiety followed by the globular domain of the pro-segment. The maximum variability is found in the connecting region between moieties. The known three-dimensional structures of procarboxypeptidases from bovine and porcine species have been used to model all three human procarboxypeptidases and also to estimatethe interaction energies between the different parts of the molecules, in an attempt to gain insight into the structural features responsible for the differences observed in the functionality of the proenzymes, particularly in their proteolytic activation pathways. Taken together, the results obtained confirm that the main determinant for the rate and mode of activation of procarboxypeptidases is the strength of the interaction between the enzyme and the globular domain of the pro-segment, the connecting segment playing a complementary role.

Cutting at the right place--the importance of selective limited proteolysis in the activation of proproteinase E

Proteinase E is a proteolytic enzyme which belongs to a distinct subfamily of chymotrypsin-like serine endopeptidases. Its proform from the bovine pancreatic system has been structurally analyzed by X-ray crystallography for the intact native form, with a 11-residue N-terminal activation peptide, in a ternary complex with chymotrypsinogen C and procarboxypeptidase A [Gomis-Rüth, F. X., Gómez, M., Bode, W., Huber, R. & Avilés, F. X. (1995) The three-dimensional structure of the native ternary complex of bovine pancreatic procarboxypeptidase A with proproteinase E and chymotrypsinogen C, EMBO J. 14, 4387-4394]. Also for a N-terminally truncated form, lacking the first 13 residues and called subunit III, a crystal structure is available [Pignol, D., Gaboriaud, C., Michon, T., Kerfelec, B., Chapus, C. & Fontecilla-Camps, J. C. (1994) Crystal structure of bovine procarboxypeptidase A-S6 subunit III, a highly structured truncated zymogen E, EMBO J. 8, 1763-1771]. Both structures are well defined by electron density, except for the first 7 residues of subunit III. However, both structures present large deviations of up to 2 nm in several regions, indicating that they correspond to two quite distinct states of low free energy, influenced by very few contacts made via the N-terminal segment. As no structure of an active proteinase E is known so far, pancreatic porcine elastase has been chosen as a model for this enzyme and an activation mechanism for this distinct serine endopeptidase subfamily is proposed.

Characterisation and preliminary X-ray diffraction analysis of human pancreatic procarboxypeptidase A2

Human procarboxypeptidase A2 has been expressed in a Pichia pastoris heterologous system and purified by hydrophobic interaction and anion exchange chromatographies. The hydrolytic action of carboxypeptidase A2 on peptide substrates with different lengths and residues at the C-terminus was analysed, and a preference towards long substrates with aromatic amino acids in their C-terminal end, particularly tryptophan, was found; with such substrates its activity is similar or higher than that of bovine carboxypeptidase A1. Procarboxypeptidase A2 has been crystallised using a vapour diffusion approach; the crystals obtained belong to the monoclinic system, spacegroup P2(1), and present one procarboxypeptidase A2 molecule per asymmetric unit. The crystals diffract beyond 1.8 A resolution and are suitable for detailed X-ray analysis.

The three-dimensional structure of human procarboxypeptidase A2. Deciphering the basis of the inhibition, activation and intrinsic activity of the zymogen

The three-dimensional structure of human procarboxypeptidase A2 has been determined using X-ray crystallography at 1.8 A resolution. This is the first detailed structural report of a human pancreatic carboxypeptidase and of its zymogen. Human procarboxypeptidase A2 is formed by a pro-segment of 96 residues, which inhibits the enzyme, and a carboxypeptidase moiety of 305 residues. The pro-enzyme maintains the general fold when compared with other non-human counterparts. The globular part of the pro-segment docks into the enzyme moiety and shields the S2-S4 substrate binding sites, promoting inhibition. Interestingly, important differences are found in the pro-segment which allow the identification of the structural determinants of the diverse activation behaviours of procarboxypeptidases A1, B and A2, particularly of the latter. The benzylsuccinic inhibitor is able to diffuse into the active site of procarboxypeptidase A2 in the crystals. The structure of the zymogen-inhibitor complex has been solved at 2.2 A resolution. The inhibitor enters the active site through a channel formed at the interface between the pro-segment and the enzyme regions and interacts with important elements of the active site. The derived structural features explain the intrinsic activity of A1/A2 pro-enzymes for small substrates.

The TNF-alpha gene Nco I polymorphism influences the relationship among insulin resistance, percent body fat, and increased serum leptin levels

Tumor necrosis factor-alpha (TNF-alpha), acting as a modulator of gene expression in adipocytes, is implicated in the development of insulin resistance and obesity. The aim of this study was to investigate whether the Nco I polymorphism of the TNF-alpha gene influences the relationship among insulin resistance, percent body fat, and serum leptin levels. A sample of 38 subjects (19 men, mean age 36.2 +/- 1.9 years, BMI 28.8 +/- 1.2 kg/m2, range 22.2-35.7; and 19 women, age 34.9 +/- 1.4 years, BMI 28.1 +/- 0.8 kg/m2, range 19-37.9) was divided into two groups on the basis of the Nco I genotype. Twenty-three subjects were (+/+) homozygotes for the presence of the Nco I restriction site that is associated with a guanine at position -308 of the TNF-alpha promoter. Of the other subjects, 12 were (+/-) heterozygotes and 3 (-/-) homozygotes for the absence of the restriction site, resulting from a guanine-to-adenine substitution at position -308 of the TNF-alpha promoter. This substitution (termed TNF-2) leads to higher rate of transcription of TNF-alpha than the wild-type allele TNF-1 in vitro. TNF-1 (+/+) and TNF-2 (+/- and -/-) groups of subjects were comparable in sex, age, BMI, waist-to-hip ratio, and several skinfold measurements. Basal serum insulin was greater (14.2 +/- 2 vs. 9.2 +/- 0.9 mU/l, P = 0.041) in the TNF-2 group in the presence of comparable serum glucose concentration. The integrated area under the curve of serum insulin concentrations, measured in response to a 75-g oral glucose challenge, and the percent body fat, measured by bioelectric impedance, were significantly increased in TNF-2 subjects (226.8 +/- 33 vs. 139.4 +/- 17.8 mU/l, P = 0.032; 33.6 +/- 2.8 vs. 24.9 +/- 2%, P = 0.01). TNF-2 subjects also showed a decreased insulin sensitivity index, as determined by the frequently sampled intravenous glucose tolerance test with minimal model analysis (1.9 +/- 0.4 vs. 3.05 +/- 0.3 min(-1) x mU(-1) x l(-1), P = 0.03). These differences were more marked among women. Paralleling the known relationship between insulin and leptin levels, serum leptin concentration was clearly increased in the TNF-2 group (19.6 +/- 3.4 vs. 11.1 +/- 1.5 ng/ml, P = 0.03). Therefore, (+/-) heterozygotes and (-/-) homozygotes may be more susceptible to developing insulin resistance and increased percent body fat. Results of the present study suggest that TNF-alphaNco I polymorphism may exacerbate the alterations in leptin levels normally found among insulin-resistant subjects.

Angiotensin I-converting enzyme and angiotensinogen gene polymorphisms in non-insulin-dependent diabetes mellitus. Lack of relationship with diabetic nephropathy and retinopathy in a Caucasian Mediterranean population

Genotypic abnormalities of the renin-angiotensin system have been suggested as a risk factor for the development of microangiopathic complications in diabetic patients. We studied the relationship of either an insertion-deletion polymorphism in the angiotensin-converting enzyme (ACE) gene and the M235T and T174M variant polymorphisms of the angiotensinogen (AGT) gene in non-insulin-dependent diabetes mellitus (NIDDM) patients and its relationship with cardiovascular complications. A total of 193 NIDDM patients (89 men and 104 women aged 59.2 +/- 10.0 years; diabetes duration, 13.2 +/- 6.2 years) and 90 control subjects (42 men and 48 women aged 45.4 +/- 12.6 years) were recruited for the association study. Distribution of the genotype or allelic frequencies for all the studied polymorphisms did not differ significantly between controls and NIDDM patients. ACE and AGT genes did not display any difference in clinical or metabolic parameters according to each gene's genotype for either the control or the NIDDM group. For evaluation of nephropathy and retinopathy, NIDDM patients were matched with subjects not having microangiopathic complications. Thus, a total of 60 patients had diabetic nephropathy and were compared with 100 patients with normoalbuminuria. Sixty-eight NIDDM patients had diabetic retinopathy, and 92 patients presented no signs of retinopathy. There were no differences in genotypic or allelic distribution between NIDDM patients for either the presence or absence of retinopathy or nephropathy. We conclude that the ACE and AGT polymorphisms do not contribute to the genetic susceptibility to diabetic nephropathy and retinopathy in a caucasian Mediterranean population.

The TNF-beta gene Nco I polymorphism is not associated with hypertriglyceridemia or insulin resistance in lean and obese subjects

Interindividual differences in TNF-alpha monocyte responses can be accounted for by genetic polymorphisms at the TNF-beta locus defined by the Nco I restriction enzyme. Higher triglyceride levels in non-insulin-dependent diabetic patients homozygous at the 10.5-kb fragment of the TNF-beta gene have been described. The aim of this study was to investigate whether the Ncol polymorphism of the TNF-beta gene influences the relationship between insulin resistance and triglyceride levels. Thirty-eight healthy volunteers were divided into two groups according to the absence [homozygous for class 1 allele (1/1), n=16] or presence of the class 2 allele [n=22; 19 heterozygous (1/2), and 3 homozygous (2/2)]. Both groups were comparable in sex, age, BMI, waist/hip ratio, fat mass and percentage of body fat as measured by bioelectric impedance, skinfold measurements, and blood pressure (all p>0.05). There were no differences in serum cholesterol (total, or HDL and VLDL fractions) or in total or VLDL triglycerides between the groups (all p>0.05). The insulin sensitivity index (Minimal Model method) was comparable for the two groups. In summary, the 10.5-kb homozygous genotype of the TNF-beta locus does not contribute to differences in triglyceride levels or insulin sensitivity among nondiabetic subjects.

Crystal structure of an oligomer of proteolytic zymogens: detailed conformational analysis of the bovine ternary complex and implications for their activation

The pancreas of ruminants secretes a 100 kDa non-covalent ternary complex of the zymogen of a metalloexopeptidase, carboxypeptidase A, and the proforms of two serine endopeptidases, chymotrypsin C and proteinase E. The crystal structure of the bovine complex has been solved and refined to an R-factor of 0.192 using synchrotron radiation X-ray data to 2.35 A resolution. In this heterotrimeric complex, the 403 residue procarboxypeptidase A takes a central position, with chymotrypsinogen C and proproteinase E attached to different surface sites of it. The procarboxypeptidase A subunit is composed of the active enzyme part and the 94 residue prodomain, similar to the monomeric porcine homologous form. The 251 residue subunit chymotrypsinogen structure, the first solved of an anionic (acidic pI) chymotrypsinogen, exhibits characteristics of both chymotrypsinogen A and elastases, with a potential specificity pocket of intermediate size (to accommodate apolar medium-sized residues) although not properly folded, as in bovine chymotrypsinogen A; this pocket displays a "zymogen triad" characteristic for zymogens of the chymotrypsinogen family, consisting of three non-catalytic residues (one serine, one histidine, and one aspartate) arranged in a fashion similar to the catalytic residues in the active enzymes. Following the traits of this family, the N terminus is clamped to the main molecular body by a disulphide bond, but the close six residue activation segment is completely disordered. The third zymogen, the 253 residue proproteinase E, bears close conformational resemblance to active porcine pancreatic elastase; its specificity pocket is buried, displaying the second "zymogen triad". Its five N-terminal residues are disordered, although the close activation site is fixed to the molecular surface. The structure of this native zymogen displays large conformational differences when compared with the recently solved crystal structure of bovine subunit III, an N-terminally truncated, non-activatable, proproteinase E variant lacking the first 13 residues of the native proenzyme. Most of the prosegment of procarboxypeptidase A and its activation sites are buried in the centre of the oligomer, whilst the activation sites of chymotrypsinogen C and proproteinase E are surface-located and not involved in intra or inter-trimer contacts. This organization confers a functional role to the oligomeric structure, establishing a sequential proteolytic activation for the different zymogens of the complex. The large surface and number of residues involved in the contacts among subunits, as well as the variety of non-bonded interactions, account for the high stability of the native ternary complex.

Pancreatic procarboxypeptidases: oligomeric structures and activation processes revisited

The activation peptides of procarboxypeptidases of the A1 type act in a post-activation mechanism of control, limiting the expression of activity immediately after the limited proteolysis has occurred. This effect is due to structural complementarity between the enzymatic moiety and the released fragments, and is further enhanced by the occurrence of procarboxypeptidase A1 in oligomeric complexes of different type depending on the species studied. In those complexes, the activation segment has an important role in the stabilisation of the quaternary structure. The relationship between oligomeric structure and activation is reviewed here for two of the most extensively studied systems.

Diversity of patterns of improvement in confrontation naming rehabilitation: some tentative hypotheses

A previous group analysis of the effects of a computerized written naming rehabilitation program revealed global improvement with generalization of benefits to untrained items and to untreated oral naming (Deloche et al., 1992). The present multiple single-case analysis of the data indicates a variety of patterns of improvement and of generalization effects among individual patients. Patterns of relationships between written and oral naming behaviors help to explain the type of improvement that was observed.

[Apolipoprotein AI-CIII, B, and CII gene polymorphisms in patients with non-insulin dependent diabetes mellitus. Association with hyperlipemia]

BACKGROUND

Dislipidaemia is an usual feature in patients affected by non insulin dependent diabetes mellitus. Several studies show that this disease could be genetically determined. The aim of this study was to ascertain whether any of the genetic polymorphism remaining in three apolipoprotein loci (apolipoprotein AI-CIII, B100 and CII) is related with the presence of dislipidaemia in non insulin dependent diabetes mellitus patients.

PATIENTS AND METHODS

53 non insulin dependent diabetes mellitus patients with less than 5 years evolution and treated only with diet, were included. 86 healthy persons were included as the control group. The lipidic parameters analyzed were: cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, apolipoprotein AI, B and lipoprotein (a). The following polymorphic variants were analyzed: RFLP-Sacl of the apolipoprotein AI-CIII-AIV cluster, RFLP-Xbal of the apolipoprotein B100 region and the RFLP-Taql of the apolipoprotein E-CI-CII cluster.

RESULTS

There were no genetic nor allelic differences in the distribution of the genes, between controls and diabetic patients. Regarding the apolipoprotein CII gen, the diabetic patients with the T2T2 genotype had higher triglyceride levels (p < 0.01) compared with the remaining genotypes and compared with the control group having the same genotype (p < 0.01) matched for sex, age and body mass index. There was no difference in the metabolic parameters' distribution related to the genotypic distribution of the apolipoproteins AI-CIII and B100 genes.

CONCLUSIONS

The apolipoprotein CII can be related with the presence of hypertriglyceridaemia in non insulin dependent diabetes mellitus patients.

Calculation and number processing: neuropsychological assessment and daily life difficulties

One hundred unselected brain-damaged outpatients received a standardized battery of numerical tests (EC301) and, independently, a questionnaire on numerical activities in daily life (ADL). Comparisons between the two types of measurement were drawn from the scorings for different functional components of the calculation and number processing system. Results indicated high ranking correlations between the two instruments. The EC301 battery generally proved more powerful than the questionnaire in detecting the presence of mild-to-discrete impairments, but some aspects of numerical difficulties in nonaphasic patients were scored higher on the ADL questionnaire.

CD4 masking during human immunodeficiency virus type 1 infection, quantified on peripheral blood lymphocytes, is a potential marker of disease progression

In human immunodeficiency virus type 1 (HIV-1)-infected adults, the proportion of gp120-free CD4 molecules on the surface of T lymphocytes was measured by double-epitope EIA and expressed as a CD epitope concentration ratio. In 51% of these patients (n=81), CD4 T cells showed a significant decrease (up to 100%) in the accessibility of the CD4 epitope in the D1 domain remained accessible. Of interest, a significant increase in the CD4 gp120 binding site concentration, without a change in T cell counts, was observed within 10 days after initiation of zidovudine treatment. Furthermore, CD4 masking by gp120 was associated with a poor clinical patient status. The assessment of the CD4 epitope concentration ratio is proposed as a surrogate marker of disease progression in HIV-1-infected patients.

The activation pathway of procarboxypeptidase B from porcine pancreas: participation of the active enzyme in the proteolytic processing

The activation process of porcine pancreatic procarboxypeptidase B (pro-CPB) has been studied in detail by a number of complementary methodologies, and a description of the molecular events that lead to the generation of active carboxypeptidase B (CPB) has been deduced. The generated CPB participates in the degradation of its own activation segment by excising C-terminal residues from fragments produced by tryptic proteolysis. The trimming action of CPB is, however, not essential for the release of a fully functional enzyme, in contrast to what was previously reported for porcine procarboxypeptidase A (pro-CPA). In the model presented here, the activation process is solely dependent on the first tryptic cleavage, at the limit between the activation segment and the enzyme region, and the former piece loses all of its inhibitory capacity once severed from the proenzyme. The use of heterologous inhibitors of CPB activity during the study of the tryptic activation process of pro-CPB has been required for the capture of short-lived, otherwise nondetectable, intermediates. This has allowed a complete description of the process and shown that the first proteolytic action of trypsin can also take place on a second target bond. Structural considerations that take into account the three-dimensional structures of the A and B forms of the proenzymes lead us to propose that the differences in conformation at the region that connects the globular activation domain to the enzyme are the main responsible elements for the differences observed in the activation processes of both proenzymes.