Coagulation and fibrinolysis proceed concomitantly, since a thrombus is formed on a damaged vessel wall and leads to the release of tPA from the intact endothelium nearby the thrombus (18
). Consequently, tPA activates the conversion of plasminogen to plasmin, inducing the so-called "thrombus-specific fibrinolysis (19
)". Venous thrombosis has many different etiologies and occurs when several risk factors are present simultaneously (20
). Risk factors in patients with acute pesticide intoxication, in addition to the traditional ones, include prolonged bed rest (21
), placement of central venous catheters (22
), and hemoperfusion (23
). This is the reason why we recruited a control group consisting of patients with non-PQ pesticide intoxication who underwent similar treatment modalities as the PQ group, including bed rest, a central venous catheter for the extracorporeal elimination of poisons, and/or the intravenous administration of a large volume of fluid.
Contrary to the previous reports (6
), we observed significantly higher levels of tPA and PAI-1 in the PQ group than in the control group (). Furthermore, the levels of tPA and PAI-1 were significantly higher in patients whose PQ levels were higher than 10 µg/mL (). We cannot explain this discrepancy, but in the previous reports (6
), the results were described from not in vivo but in vitro experiments. In another previous study (9
), they reported decreased levels of tPA after the injection of vitamin C in human subjects. With this result, they concluded that ROS may inhibit tPA production. However, their theory is open to criticism because the function of vitamin C is complicated in ROS formation, not scavenging ROS but stimulate ROS production in some situation.
In our results, there was a significant correlation between the levels of tPA and/or PAI-1 with the amount of PQ ingested (). The plasma PQ level at a given time is a function of the amount ingested and the time lag after ingestion; therefore, the PQ level does not represent the severity of intoxication in our study because the patients arrived at the ER with different time lags after ingestion. However, it has been our clinical observation that no patients survive with a plasma PQ level > 10 µg/mL during the admission period. This observation led us to divide the PQ group according to their PQ levels: greater than and lower than 10 µg/mL.
This raises the question of whether these relationships are due to PQ itself or an ROS effect generated by PQ. ROS are formed primarily in cells; however, direct measurement of ROS formation in cells is very difficult in the clinical setting. Instead, several indirect methods have been developed to measure free radicals and their metabolites, e.g., malondialdehyde (MDA; the final product of lipid peroxidation) (24
) and hydroperoxides (ROOH; intermediate products of lipid peroxidation) (25
). Recently, we reported that neither cross-sectional nor sequential measurements of plasma MDA provided reliable data on ROS formation in patients with acute PQ intoxication (24
). Given the lack of a reliable marker for ROS production, it is difficult to find a relationship between ROS levels and other parameters in acute PQ intoxication.
The plasma levels of PQ reach a peak level at 1.5 hr after PQ ingestion and decrease so rapidly that its levels are undetectable after 24 hr in the majority of patients; therefore, plasma PQ levels observed in the ER are not comparable with those from the subsequent days. Contrary to the PQ levels, the 3 measurements of tPA and PAI-1 levels taken in this study were comparable in each patient; the mean coefficient of variation was 0.42 ± 0.22 for tPA (range 0.08-1.02) and 0.39 ± 0.30 for PAI-1 (range 0.00-1.31). These results suggest that it is not the mere level of PQ that affects tPA and PAI-1 levels, but some other factor(s) activated or stimulated by PQ; therefore, we consider that ROS generated by PQ trigger the endothelium to release tPA and PAI-1.
D-dimer levels were lower in the PQ group than in the control group (). The presence of D-dimer indicates the pre-existence of fibrin formation and the concurrent formation of plasmin by tPA (26
). Coagulation and fibrinolysis are on-going physiological processes that account for the presence of D-dimer. Fibrin formation is the result of the imbalance between coagulation and anticoagulation activities in a pathological environment. Therefore, the possibility exists that some thrombogenic factor such as tissue factor could have been activated during PQ intoxication; however, changes in coagulation/anticoagulation activity were not the focus of the current study. In the PQ group, tPA and PAI-1 levels were higher, but D-dimer levels were lower than in the control group, indicating that, in this setting, PAI-1 activity overrode tPA activity.
Taken together, these results indicate that thrombosis should be a common complication in patients with acute PQ intoxication, although only 2 of the 101 PQ patients suffered from pulmonary artery thrombosis or deep vein thrombosis (, ). However, bearing in mind that venous thrombosis is often clinically silent, we believe that there must have been more patients with subclinical thrombosis complications in the PQ group.
Fig. 5 Pulmonary artery computerized tomography angiogram from a PQ-intoxicated patient who suffered pulmonary artery thrombosis. A 64-yr-old woman swallowed a mouthful of a 24.5% PQ solution. Her plasma PQ level was 0.08 µg/mL at 15 hr after PQ ingestion. (more ...)
Fig. 6 Low extremity venogram computerized tomography from a PQ-intoxicated patient who suffered deep vein thrombosis in the leg. A 50-yr-old woman swallowed 2 mouthfuls of a 24.5% PQ solution. (A) On day 21 after admission, the patient complained of left leg (more ...)
In order to verify the clinical implications of the tPA and PAI-1 levels, we performed univariate and multivariate binary logistic regression analyses. Univariate binary logistic regression analysis of the PQ group showed that age, amount of PQ ingested, plasma PQ levels, time lag after PQ ingestion, tPA levels, and PAI-1 levels were significant determinants of death (). However, multivariate binary logistic regression analysis indicated that only PQ levels were a significant independent factor predicting death ().
We have few limitations in this study. First, we had better estimate the tPA mediated fibrinolytic activity with both tPA antigen and tPA activity. Furthermore, parameters of coagulation, such as a tissue factor and its inhibitors would have enhanced the significance in the interpretation of the change in both tPA and PAI-1 levels. However, in practice, it was hard to obtain blood samples frequently in large amount because of their critical condition. The other question posed is the lack of quantitative measurement of ROS.
As we described in the introduction, it was impossible to measure ROS directly and only surrogate markers were available in clinical practice. Even with these limit, our observations imply that ROS stimulate the production of tPA and PAI-1, but PAI-1 activity overrides tPA activity in this setting. Decreased fibrinolytic activity due to increased PAI-1 activity appears to be one of the clinical characteristics of acute PQ intoxication.
In conclusion, the levels of tPA and PAI-1 were higher, but D-dimer levels were lower in the PQ group than in the control group.