Difficulty breathing. Late onset vitamin K deficiency bleeding

Structural Investigation of the Vitamin K Epoxide Reductase (VKORC1) Binding Site with Vitamin K

The vitamin K epoxide reductase (VKORC1) enzyme is of primary importance in many physiological processes, i.e., blood coagulation, energy metabolism, and arterial calcification prevention, due to its role in the vitamin K cycle. Indeed, VKORC1 catalyzes reduction of vitamin K epoxide to quinone and then to hydroquinone. However, the three-dimensional VKORC1 structure remains experimentally undetermined, because of the endoplasmic reticulum membrane location of this enzyme. Here we present a molecular modeling investigation of the VKORC1 enzymatic site structure and function, supported by in vitro enzymatic assays. Four VKORC1 mutants were designed in silico (F55G, F55Y, N80G, and F83G) based on a previous study that identified residues F55, N80, and F83 as being crucial for vitamin K epoxide binding. F55G, N80G, and F83G nonconservative mutants were all predicted to be inactive by molecular modeling analyses. However, the F55Y conservative mutant was expected to be active compared to wild-type VKORC1. In vitro enzymatic assays performed on recombinant proteins assessed our molecular modeling hypotheses and led us to describe the role of accurate VKORC1 active site residues with respect to VKORC1. Residues F55, N80, and F83 appeared to act in a concerted manner to keep vitamin K epoxide close to the C135 catalytic residue. Residues F55 and N80 prevent naphthoquinone head rotation away from the active site, assisted by residue F83 that prevents vitamin K from sliding outside the enzymatic pocket, through hydrophobic tail stabilization. Our results thus highlighted the specific functions of VKORC1 catalytic pocket residues and evidenced the ability of our structural model to predict biological effects of VKORC1 mutations.

Refusal of Intramuscular Vitamin K by Parents of Newborns: A Review

In 2019, the American Academy of Pediatrics made public education about intramuscular vitamin K administration at birth a public health priority, partly in response to reports of refusal of intramuscular vitamin K by parents of newborns that led to vitamin K deficiency bleeding (VKDB). We reviewed the literature on the frequency of, reported reasons for, and factors associated with refusal of intramuscular vitamin K, incidence of VKDB in newborns who did not receive intramuscular vitamin K, and use of oral vitamin K to prevent VKDB. Without prophylaxis, estimates of the incidence per 100 000 births of VKDB range from 250 to 1700 for early VKDB and from 10.5 to 80 for late VKDB. The frequency of refusal of intramuscular vitamin K by parents ranged from 0% to 3.2% in US hospitals, up to 14.5% in home births, and up to 31.0% in birthing centers. Reported reasons for refusal were concern of harm from the injection, a desire to be natural, and a belief in alternative methods of prophylaxis. Parents who refused intramuscular vitamin K were more likely to refuse immunizations. Many different regimens were used for orally administered vitamin K; it is not clear which is best, but all are less effective than intramuscular vitamin K. VKDB is rare but can result in either neurologic sequelae or death. In addition to continued surveillance of the frequency of both refusal of intramuscular vitamin K and VKDB, a renewed focus on education of and collaboration with parents is needed to address this major public health threat.

Establishment of the Variation of Vitamin K Status According to Vkorc1 Point Mutations Using Rat Models

Vitamin K is crucial for many physiological processes such as coagulation, energy metabolism, and arterial calcification prevention due to its involvement in the activation of several vitamin K-dependent proteins. During this activation, vitamin K is converted into vitamin K epoxide, which must be re-reduced by the VKORC1 enzyme. Various VKORC1 mutations have been described in humans. While these mutations have been widely associated with anticoagulant resistance, their association with a modification of vitamin K status due to a modification of the enzyme efficiency has never been considered. Using animal models with different Vkorc1 mutations receiving a standard diet or a menadione-deficient diet, we investigated this association by measuring different markers of the vitamin K status. Each mutation dramatically affected vitamin K recycling efficiency. This decrease in recycling was associated with a significant alteration of the vitamin K status, even when animals were fed a menadione-enriched diet suggesting a loss of vitamin K from the cycle due to the presence of the Vkorc1 mutation. This change in vitamin K status resulted in clinical modifications in mutated rats only when animals receive a limited vitamin K intake totally consistent with the capacity of each strain to recycle vitamin K.

Structural Insights into Phylloquinone (Vitamin K1), Menaquinone (MK4, MK7), and Menadione (Vitamin K3) Binding to VKORC1

Vitamin K family molecules-phylloquinone (K1), menaquinone (K2), and menadione (K3)-act as γ-glutamyl carboxylase (GGCX)-exclusive cofactors in their hydroquinone state, activating proteins of main importance for blood coagulation in the liver and for arterial calcification prevention and energy metabolism in extrahepatic tissues. Once GGCX is activated, vitamin K is found in the epoxide state, which is then recycled to quinone and hydroquinone states by vitamin K epoxide reductase (VKORC1). Nevertheless, little information is available concerning vitamin K1, K2, or K3 tissue distribution and preferential interactions towards VKORC1. Here we present a molecular modeling study of vitamin K1, menaquinones 4, 7 (MK4, MK7), and K3 structural interactions with VKORC1. VKORC1 was shown to tightly bind vitamins K1 and MK4 in the epoxide and quinone states, but not in the hydroquinone state; five VKORC1 residues were identified as crucial for vitamin K stabilization, and two other ones were essential for hydrogen bond formation. However, vitamin MK7 revealed shaky binding towards VKORC1, induced by hydrophobic tail interactions with the membrane. Vitamin K3 exhibited the lowest affinity with VKORC1 because of the absence of a hydrophobic tail, preventing structural stabilization by the enzyme. Enzymatic activity towards vitamins K1, MK4, MK7, and K3 was also evaluated by in vitro assays, validating our in silico predictions: VKORC1 presented equivalent activities towards vitamins K1 and MK4, but much lower activity with respect to vitamin MK7, and no activity towards vitamin K3. Our results revealed VKORC1's ability to recycle both phylloquinone and some menaquinones, and also highlighted the importance of vitamin K's hydrophobic tail size and membrane interactions.

A Blown Pupil and Intracranial Hemorrhage in a 4-Week-Old: A Case of Delayed Onset Vitamin K Deficiency Bleeding, a Rare "Can't Miss" Diagnosis

BACKGROUND

Infants are at risk for vitamin K deficiency bleeding (VKDB) because of limited stores of vitamin K (VK) at birth and a low concentration of VK in human breast milk. Therefore, the administration of intramuscular (IM) VK at birth has been recommended since 1961 in the United States. Infants who do not receive IM VK and who are exclusively breast-fed are at increased risk for VKDB. While VKDB is rare, a common presentation of late onset VKDB is intracranial hemorrhage.

CASE REPORT

We report the case of a 4-week-old infant who presented to the emergency department with lethargy and a grossly dilated right pupil. The parents denied trauma. A computed tomography scan revealed a right-sided subdural hematoma with midline shift. The infant's international normalized ratio was >10.9 and his prothrombin time PT was >120 seconds. VK was administered and the child was transferred to a tertiary care center for emergent neurosurgery. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The difficult part of making this critical diagnosis is considering it. Any bleeding in a newborn without trauma should prompt inquiry regarding neonatal VK administration and a serum prothrombin time level. Fortunately, once the diagnosis is made, therapy in the emergency department can be lifesaving and is familiar to emergency physicians. Treatment parallels usual care for the adult with excess anticoagulation caused by warfarin. Prompt intravenous VK is universally accepted. Studies to support fresh frozen plasma or prothrombin complex concentrate are lacking but make good clinical sense for life-threatening bleeding.

Reasons for Refusal of Newborn Vitamin K Prophylaxis: Implications for Management and Education

OBJECTIVE

The American Academy of Pediatrics recommends intramuscular (IM) vitamin K prophylaxis for all newborns to prevent vitamin K deficiency bleeding. Given the serious implications of late-onset vitamin K deficiency bleeding, our objective was to examine factors influencing parents' decisions to refuse IM vitamin K prophylaxis.

METHODS

Parents intending to refuse IM vitamin K prophylaxis at delivery were recruited from 5 community hospitals, 1 academic medical center, and 2 birthing centers in a single Southeastern state. Participants completed a written survey including demographics, birth and parenting decisions (eg, breastfeeding), and open-ended questions about their vitamin K information sources, concerns, and knowledge of risks.

RESULTS

The incidence of refusal was highest at the birthing centers. Fifty-four parents intending to refuse IM vitamin K completed the survey. Most were white (78%), over age 30 (57%), and college graduates (65%). All reported intention to exclusively breastfeed. Most refused hepatitis B vaccine (90%) and erythromycin eye ointment (77%). The most common source of information was the Internet (70%). Concerns included synthetic or toxic ingredients (37%), excessive dose (28%), and side effects (24%). Eighty-three percent of parents reported awareness of risks associated with vitamin K refusal. However, only 6 parents (11%) decided to accept IM prophylaxis.

CONCLUSIONS

This study provides an understanding of the concerns, mindset, and information sources used by parents refusing IM vitamin K. Educating parents about the importance of IM prophylaxis should begin in the prenatal period and must address concerns parents identify on the Internet.