Letter to the Editor

I read with interest the article “Hemorrhagic Cardiomyopathy in Male Mice Treated with NNRTI: The role of Vitamin K” in the recent issue of Toxicologic Pathology(36:321–29, 2008). The authors present an unusual observation of hemorrhage within the myocardium and myopathy of the heart, and they investigate a theory that these observations are a consequence of vitamin K deficiency by supplementing treated animal groups with vitamin K. The authors then conclude from their observations that the hemorrhage and myopathy are a consequence of disabled clotting ability. Unfortunately, the data presented in this “mechanistic study” do not support vitamin K deficiency as the cause of the cardiac myopathy and prolonged coagulation times and only obfuscate what is an interesting observation.

The authors’ support for vitamin K deficiency as the underlying cause of the hemorrhage and cardiac myopathy is based on two types of observations. One set of observations is from one mouse in the whole study that actually developed cardiac hemorrhage and myopathy in TMC125-treated male mice not supplemented with vitamin K. The second set of observations is the PT and aPTT data and individual coagulation factor activity data in TMC125-treated groups that were either supplemented with vitamin K or not. The only mouse that developed hemorrhagic cardiomyopathy was euthanized after blood was taken for examination. The PT and aPTT were markedly prolonged in this mouse (3.9x and >100 seconds, respectively); however, all coagulation factor (II, VII, VIII, and XI) activities were reduced by more than 64%. Only coagulation factor II and VII activities depend on vitamin K for normal activity. This mouse also had hemorrhage and necrosis of the liver, as did, to varying degrees, all animals that were dosed with TMC125. Since all of the measured coagulation factors are produced by the liver, the “disabled clotting ability” may well be related to liver protein synthesis changes in general or consumption by activation of coagulation. Unfortunately, the authors did not measure TAT complexes, fibrin split products, D-dimer, or any other useful evaluation of coagulation to determine the state of coagulation activation. There is no clear reason why the coagulation times are altered in this study, and vitamin K deficiency is likely not the basic underlying cause, irrespective of the effect of vitamin K supplementation on the outcome.

The effect of vitamin K on hemostasis was not adequately tested in this report. The authors measured PT, aPTT, and coagulation factor II, VII, VIII, and IX activities to measure vitamin K coagulation factor concentrations. Even though only one mouse developed hemorrhagic cardiomyopathy, many mechanisms may cause decreased activity or prolonged coagulation times, and the authors failed to measure the one analyte in plasma that reflects vitamin K specific activity, PIVKA (proteins in vitamin K absence or antagonism). These are the uncarboxylated, inactive proteins (coagulation factors II, VII, IX, and X) circulating in plasma that are released from the liver unmodified by γ-glutamyl carboxylase, which requires vitamin K as a cofactor. Measuring PIVKA and detecting uncarboxylated coagulation factors would have said something about vitamin K’s contribution to a coagulopathy. The authors noted the decreased factor XI activities and cited a reference¹that supports not only coagulation factors II, VII, IX, and X, but also factors V, VIII, XI, and XII being decreased in vitamin K deficiency. By that logic, all coagulation defects are a result of vitamin K deficiency, and the whole of literature describing the role of vitamin K is null. The reference cited used coagulation factor activities to support their view but admitted that PIVKAs may inhibit these assays.

The authors never addressed increased coagulation factor activities with vitamin K supplementation, nor did they consider the effect other fat-soluble vitamins (such as vitamin E) may have on vascular integrity or interactions with vitamin K. The authors never questioned the notion that hemorrhage and cardiac myopathy could be a result of something else in the diet or treatment such as alteration of vitamin E or selenium metabolism or the rate of oxidative free radical production.