Evidence for Transient Acute Liver Injury in Mouse Models of Sickle Cell Disease during Steady State Health

Individuals with sickle cell disease experience episodes of acute vaso-occlusive complications interspersed by periods of feeling well and apparent health during “steady state”. It is likely that episodic and subclinical sickling and vaso-occlusion occur on an ongoing basis even during periods of steady state. In order to determine whether mice with sickle disease have acute vaso-occlusion sufficient for organ injury at apparent steady state health, we chose to study 2 mouse models of severe sickle cell disease with serial blood draws over time. Since we have shown in previous studies that the liver is highly susceptible to acute sickling/vaso-occlusion induced by hypoxia, we first examined serial ALT measurements in a total of 13 Berkeley sickle cell (BERK-SS) mice, initially from week-to-week and month-to-month, and then day-to-day time frames. Individual BERK-SS mice showed week-to-week and month-to-month variations of up to 5-fold over baseline ALT levels, followed by return to baseline levels in most mice. This suggests that BERK-SS mice, during steady state health, experience acute, yet transient, liver injury. Surprisingly, we also found day-to-day variations of up to 3-fold in ALT levels in BERK-SS mice. To determine if these changes in ALT levels were mirrored by changes in other biomarkers, we measured serum amyloid P (SAP) as a marker of acute inflammation (similar to CRP in humans) in the same plasma samples. We found up to 1.6-fold variation in SAP over baseline plasma levels over time. However, there was less overall variation in SAP levels in individual mice compared to the striking changes in ALT. In addition, we found that variations in SAP did not consistently precede, follow, or coincide with variations in ALT levels, suggesting that SAP is a marker of sickle cell-induced inflammation or vaso-occlusion independent of liver injury. We next sought to confirm our findings with daily serial ALT and SAP measurements from Townes sickle cell (TOWNES-SS) mice (n=8), a second commonly used mouse model of severe sickle cell disease. Our data showed that baseline ALT levels are higher and SAP levels are lower in TOWNES-SS as compared to BERK-SS mice, likely reflecting differences in strain background between the two models. However, we again found daily fluctuations in ALT and SAP levels in individual TOWNES-SS mice, similar to those seen in individual BERK-SS mice. We propose that these temporal variations indicate that both the Berkeley and Townes mouse models of sickle cell disease exhibit fluctuations in steady state health, similar to those seen in human individuals with sickle cell disease. In addition, the results suggest that studies in these mouse models should be designed and interpreted with these temporal fluctuations in mind.