Risk of long-term anticoagulation under sustained severe arterial hypertension: A translational study comparing warfarin and the new oral anticoagulant apixaban

Abstract

New oral anticoagulants for the prevention of stroke and systemic embolism in patients with atrial fibrillation have recently been introduced. In this translational study, we explored the risk of long-term anticoagulation on intracerebral hemorrhage under sustained severe arterial hypertension. We initiated anticoagulation with warfarin or apixaban in spontaneously hypertensive rats prone to develop severe hypertension and subsequent intracerebral bleeding complications. A non-anticoagulated group served as control. During an 11-week-study period, blood pressure, anticoagulation parameters, and clinical status were determined regularly. The incidence of histopathologically proven intracerebral hemorrhage was defined as the primary endpoint. Both warfarin and apixaban anticoagulation was fairly stable during the study period, and all rats developed severe hypertension. Intracerebral hemorrhage was determined in 29% (4/14) of warfarin rats and in 10% (1/10) of apixaban rats. Controls did not show cerebral bleeding complications (chi-square not significant). Mortality rate at study termination was 33% (2/6) in controls, 43% (6/14) in the warfarin group, and 60% (6/10) in the apixaban group. Animals died from extracerebral complications in most cases. Our study describes an experimental intracerebral hemorrhage model in the context of sustained hypertension and long-term anticoagulation. Extracerebral bleeding complications occurred more often in warfarin-treated animals compared with apixaban and control rats.

Keywords: Antithrombotics; animal model; brain ischemia; hypertension; intracerebral hemorrhage.

Figure 1.

International normalized ratio (INR) values over time as determined in rats anticoagulated with apixaban (blue) or warfarin (green) as well as in control animals (beige). Distribution of INR values is presented by means of boxplots. The box demonstrates the 25th, 50th (median), and 75th percentile, and the whiskers the 10th and 90th percentile, respectively. In the apixaban group and in the control group, INR values remained close to 1 at almost all time points. Anticoagulation was initiated during the 8th week of life.

Figure 2.

Anti-factor Xa levels (IU/ml) over time as determined in rats anticoagulated with apixaban (blue) or warfarin (green) as well as in control animals (beige). In the warfarin group and in the control group, anti-factor Xa levels remained close to 0 at almost all time points. Anticoagulation was initiated during the 8th week of life.

Figure 3.

Mean systolic blood pressure over time as determined in rats anticoagulated with apixaban (blue) or warfarin (green) as well as in control animals (beige). First measurements were performed in the 7th week of life. Salt-enriched diet to induce malignant arterial hypertension was applied in the 8th week of life. Blood pressure increased in all three groups simultaneously.

Figure 4.

Histopathological evaluation of the selected kidneys (HE-staining (upper part) and CD 13-staining (lower part)). The panels on the right side show hypertension-induced damage, the panels on the left side show normal regions for comparison. The star marks a normal-appearing glomerulus (HE-staining), the cross indicates a destroyed glomerulus. Arrows point to intact proximal tubules (CD 13-staining). Following sustained hypertension, CD 13-staining intensity is reduced, indicating structural damage to the tubules (bottom right panel). The black bar represents 200 µm in the HE-staining and 100 µm in the CD 13-staining.

Figure 5.

(a–d) Representative examples of intracerebral hemorrhages that were detected during histopathological evaluation of the rat brains (HE staining); (a) fresh intracerebral hemorrhage (estimated onset < 24 h), original magnification: 20×, warfarin group (No. 8); (b) fresh intracerebral hemorrhage (estimated onset < 24 h), original magnification: 40×, apixaban group (No. 20), (c) intracerebral hemorrhage, red blood cells pale, invasion of white blood cells, no erythrophages (estimated onset 12–24 h), original magnification 100×, warfarin group (No. 7), (d) little spot of red blood cell extravasate (approximately 60 µm in diameter) (estimated onset < 24 h), original magnification: 200×, warfarin group (No. 19)). (a′) displays a macroscopic view on the brain with the intracerebral hemorrhage shown in (a). The hemorrhage can be seen as a bluish parietal spot.

Figure 6.

Kaplan–Meier curves displaying cumulative survival rates of rats anticoagulated with apixaban (blue) or warfarin (green) as well as in control animals (beige).

Figure 7.

Mean body weight (g) over time as determined in rats anticoagulated with apixaban (blue) or warfarin (green) as well as in control animals (beige). First measurements were performed in the 7th week of life. Salt-enriched diet to induce malignant arterial hypertension was applied in the 8th week of life. Body weight increased in all three groups simultaneously. Variance increased between week 13 and 15, as some rats developed neurological symptoms. The second increase at the end of the study period results from a positive selection effect.