Low-Grade Inflammation in Hemophilia

We previously showed that impaired clotting in hemophilia leads to a deficit in macrophage differentiation, which negatively affects critical regenerative macrophage functions such as clot infiltration and red blood cell phagocytosis. These data provide a functional basis for the delayed wound healing as well as protracted joint inflammation commonly observed in hemophiliacs and suggest that altered macrophage function is linked to the activation of the innate immune system. We, therefore, hypothesize that hemophiliacs suffer from chronic low-grade inflammation, which in turn can affect joint health, tissue regeneration and age-related ailments such as cardiovascular disease.

For this study, we collected citrated blood from 48 adult male patients with hemophilia A or B with an average age of 36 years and a body mass index (BMI) of 27.7 kg/m². The majority of patients had a residual FVIII/FIX activity < 1% (77%) and received prophylactic treatment (60%) with a recombinant or plasmatic coagulation factor concentrate. Approximately one-half of the patients had target joints or other bleeding events in the last 3 months and one-third of the patients had contracted HBV, HCV or HIV. For controls, we randomly recruited male blood donors (n = 60; age, 35.8 years; BMI, 27.0) from our blood donation center.

To assess inflammation in hemophiliacs, we analyzed platelet-poor plasma from our main collective and a BMI-adjusted cohort using commercially available ELISA kits. The results showed a significant increase of two acute-phase proteins, C-reactive protein and leptin in hemophilia patients compared to healthy controls. Further analysis demonstrated that C-reactive protein and leptin expression inversely correlated with the residual clotting activity as both parameters were high in patients with severe Hemophilia A or B and comparatively low in patients with moderate to mild hemophilia. Of note, there was neither an increase of C-reactive protein or leptin in hemophilia patients with recent bleeding (< 3 month), arthropathy, chronic viral infection nor a decrease in patients with coagulation factor activity > 10% due to prophylactic treatment or recent replacement. Therefore, these data suggest a basic link between clotting deficiencies and chronic low-grade inflammation.

Low-grade inflammation is maintained by adipokines, which originate from the adipose tissue and are modulated by a process known as adipose tissue inflammation. In addition to the upregulation of the pro-inflammatory leptin, we detected a significant down-regulation of the anti-inflammatory adiponectin in the plasma of hemophilia patients resulting in a markedly decreased adiponectin/leptin ratio. To enquire if the adipose tissue inflammation in hemophilia originates from gram-negative gut bacteria that translocate into the blood circulation, we also detected elevated plasma levels of lipopolysaccharide-binding protein and hepcidin in hemophilia patients. Together, these data support the concept that low-grade inflammation in hemophilia originates from lipopolysaccharide, which in turn causes adipose tissue inflammation.

To test the hypothesis that low-grade inflammation in hemophilia is caused by decreased clotting activity, we collected blood from hemophilia B patients before and after transition from a conventional standard-half-life factor IX concentrate to a prophylactic therapy with an elongated half-life (EHL) FIX (Albutrepennonacog alfa, Idelvion®). Following up on the enhanced factor replacement after > 6 months, we observed a return of hepcidin plasma levels back to baseline values in healthy controls. The decreased hepcidin values from EHL FXI therapy correlated with healing of target joints suggesting that EHL FIX not only controls bleeding but also inflammation.

Together, our data demonstrate a specific link between hemophilia and low-grade inflammation that appears to involve increased lipopolysaccharide levels in the blood circulation and subsequent adipose tissue inflammation. In addition, we present evidence that low-grade inflammation is the result of the underlying clotting deficit and that sustained normalization of the clotting deficit with EHL factors ameliorates inflammation.