Thromboagglutination by anticardiolipin antibody complex in the antiphospholipid syndrome: a possible mechanism of immune-mediated thrombosis.

The tendency for patients with antiphospholipid syndrome (APLS) to thromboembolism and the criteria for its detection are well established, whereas the mechanism of this thrombophilic syndrome is still obscure. Using immunofluorescent techniques and a microscopic spontaneous platelet aggregation test (mSPAT), we have previously demonstrated platelet binding by antibody followed by aggregation in patients with lupus anticoagulant. In the present study, we investigated 18 anticardiolipin antibody-positive (ACLA pos.) patients, comprised of 12 primary APLS and 6 secondary APLS lupus patients. We demonstrated direct platelet microaggregate formation in 16/18 cases, whereas this finding was not present in 20 ACLA-negative (ACLA neg.) subjects (P<.001). Indirect testing revealed 10/12 cases of platelet microaggregation and none in the ACLA neg. subjects. In addition, immunofluorescent studies showed that platelet antibody complex binding occurred in 8/12 cases tested directly and in 11/12 cases in indirect testing, as compared to 1 out of 20 binding in ACLA neg. subjects (P<.001). Antibody complex binding was inhibited in two cases by prior extraction of phospholipids. Platelet aggregation could be demonstrated in two ACLA neg. individuals by the addition of exogenous ACLA to platelets in EDTA-plasma. We therefore propose a mechanism for immune-mediated thrombosis in APLS in which calcium-independent platelet aggregation, or thromboagglutination, is initiated by an ACLA-phospholipid complex present in the patients' plasma. Following the antibody complex-induced platelet agglutination, thrombosis proceeds by release, recruitment, and fibrin formation. The mechanism should have important implications in the diagnosis, management, and monitoring of APLS.

Increased D-glucaric acid excretion by jaundiced patients.

The urinary excretion of D-glucaric acid, a catabolite of glucuronic acid, is considered to be a reliable index of the state of hepatic microsomal enzyme activity. Because enzyme activity may be altered in liver disease, we examined the effect of liver disease on the excretion of this metabolite and its correlation with liver function tests. We studied 89 patients with nonhemolytic jaundice, 39 with viral hepatitis, 33 with obstructive jaundice, six with cirrhosis, and 11 patients with jaundice of mixed etiology. Glucaric acid excretion was significantly increased in all these patients as compared to controls, most pronounced in the obstructive jaundice group. No correlation was found between glucaric acid excretion and concentrations of bilirubin, albumin, globulin, aspartate aminotransferase, alkaline phosphatase, cholesterol, or gamma-glutamyltransferase in serum, even though the concentrations of these analytes did vary with the type of liver disease. We suggest that this increase in glucaric acid excretion is an indication of normal or even increased glucuronidation (UDP-glucuronosyltransferase activity), which occurs in liver disease.

Hepatic microsomal enzyme induction and its evaluation in a clinical laboratory.

We tried to determine whether short-term treatment with alpha-methyldopa, quinidine, digoxin, diazepam or furosemide--drugs in common use in hospitals--is capable of stimulating the activity of hepatic microsomal drug-metabolizing enzymes. Glucaric acid (GA) excretion and serum activity of gamma-glutamyl transpeptidase (GGT) were used as indicators of hepatic microsomal enzyme activity. Increased GA excretion was found in 45% and increased serum GGT activity in 40% of the patients on drug treatment. Only 14.3% showed an increase in both indicators. The excretion of GA rose significantly in patients who received drugs for less than 10 days, as compared with those who received drugs for less than 10 days, whereas the percentage of high GGT values did not rise significantly with increased duration of treatment. The lack of correlation between serum GGT activity and GA excretion casts doubt on the value of GGT as a consistent indicator of microsomal enzyme induction. GA excretion, on the other hand, seems to be a dependable index of microsomal enzyme induction in response to short-term treatment with standard doses of several widely used drugs.

D-Glucaric acid and gamma-glutamyltransferase as indices of hepatic enzyme induction in pregnancy.

Increased activity of hepatic microsomal enzymes can be evaluated by measuring D-glucaric acid excretion in urine and gamma-glutamyltransferase (EC 2.3.2.2) activity in serum. Aside from diverse foreign compounds, endogenous steroid hormones have been shown to be normal substrates of the microsomal enzyme system. Because there is an increase in steroid production in pregnancy, we sought to determine whether these indices of induction increase during pregnancy. In 90 women in various stages of pregnancy, all with normal kidney function, we measured glucaric acid excretion in urine and activity of the transferase in serum and in urine. Glucaric acid increased markedly during pregnancy, from 14.4 +/- 2.1 in the first trimester to 23.5 +/- 2.8 mumol of D-glucaro-1,4-lactone per gram of creatinine in the third trimester. We saw no correlation between glucaric acid excretion and the transferase activity in serum or urine. Activity of gamma-glutamyl-transferase remains within normal limits throughout pregnancy, which leaves doubt as to the value of this measurement in evaluating enzyme induction owing to endogenous steroids.