Validating the NIH LDL-C equation for provincial implementation in Alberta

BACKGROUND

LDL-C, a cardiovascular disease risk assessment biomarker, is commonly calculated using the Friedewald equation. The NIH equation overcomes several limitations of the Friedewald equation. Consistent with the Canadian Society of Clinical Chemists (CSCC) lipid reporting recommendations, we assessed the NIH LDL-C equation in Alberta prior to its provincial implementation.

METHODS

1-year (01/01/2021-12/31/2021) of lipid results (n = 1,486,584 after data cleaning) were obtained from five analytical instrument groups used across Alberta. Analyses were performed on all data and after separating by age, analytical instrument group, and fasting status. The correlation between Friedewald- and NIH-calculated LDL-C and between Friedewald- and NIH-calculated LDL-C difference and each lipid parameter, was determined. The frequency of unreportable/inaccurate LDL-C results was compared between the two equations. The concordance between the two equations and with non-HDL-C was determined at LDL-C thresholds. Lastly, LDL-C calculated by Friedewald, NIH, and Martin-Hopkins equations was compared to density-gradient ultracentrifugation.

RESULTS

Friedewald- and NIH-calculated LDL-C exhibit the strongest correlation when triglycerides ≤ 4.52 mmol/L. The difference between Friedewald- and NIH-calculated LDL-C increases with decreasing LDL-C concentration. The NIH equation yields fewer inaccurate results (0.35 % vs. 22.0 %). The percent agreement between equations was > 96 % at all LDL-C thresholds, suggesting most patients will not require treatment changes. NIH-calculated LDL-C exhibited better agreement with non-HDL-C when triglycerides ≤ 9.04 mmol/L and better correlated with LDL-C measured by ultracentrifugation (r2 = 0.926 vs. 0.775 (Friedewald) and 0.863 (Martin-Hopkins)). Results were consistent across age, analytical instrument group, and fasting status.

CONCLUSIONS

Our findings demonstrate the benefits of implementing the NIH equation across Alberta.

Kidney injury molecule-1 inhibits metastasis of renal cell carcinoma

Metastasis is present in approximately 30% of patients diagnosed with renal cell carcinoma (RCC) and is associated with a 5-year survival rate of < 15%. Kidney injury molecule 1 (KIM-1), encoded by the HAVCR1 gene, is a proximal tubule cell-surface glycoprotein and a biomarker for early detection of RCC, but its pathophysiological significance in RCC remains unclear. We generated human and murine RCC cell lines either expressing or lacking KIM-1, respectively, and compared their growth and metastatic properties using validated methods. Surprisingly, KIM-1 expression had no effect on cell proliferation or subcutaneous tumour growth in immune deficient (Rag1^−/−) Balb/c mice, but inhibited cell invasion and formation of lung metastasis in the same model. Further, we show that the inhibitory effect of KIM-1 on metastases was observed in both immune deficient and immune competent mice. Transcriptomic profiling identified the mRNA for the pro-metastatic GTPase, Rab27b, to be downregulated significantly in KIM-1 expressing human and murine RCC cells. Finally, analysis of The Cancer Genome Atlas (TCGA) data revealed that elevated HAVCR1 mRNA expression in the two most common types of RCC, clear cell and papillary RCC, tumours correlated with significantly improved overall patient survival. Our findings reveal a novel role for KIM-1 in inhibiting metastasis of RCC and suggests that tumour-associated KIM-1 expression may be a favourable prognostic factor.

A Multicenter Assessment of the Sensitivity and Specificity for a Single High-Sensitivity Cardiac Troponin Test at Emergency Department Presentation for Hospital Admission

Background

Studies have illustrated how a low or undetectable high-sensitivity cardiac troponin (hs-cTn) concentration at emergency department (ED) presentation can rule out myocardial infarction (MI). A problem with using an undetectable hs-cTn cutoff is that this value may be defined differently among hospitals and is also difficult to monitor. In the present study, we assess the diagnostic performance of a clinical chemistry score (CCS) vs hs-cTn alone in the presentation blood sample in the ED for patient hospital admission in a multicenter setting.

Methods

From January 1 to June 30, 2018, consecutive patients with random glucose, creatinine (for an estimated glomerular filtration rate calculation), and hs-cTnI (Abbott, 2 hospitals, Hamilton, Ontario, n = 10496) or hs-cTnT (Roche, 4 hospitals, Calgary, Alberta, n = 25177) were assessed for hospital admission with the CCS (range of scores, 0–5) or hs-cTn alone. Sensitivity, specificity, predicative values, and likelihood ratios were calculated for a CCS of 0 and 5 and for hs-cTn alone (hs-cTnI cutoffs, 5 and 26 ng/L; hs-cTnT cutoffs, 6 and 14 ng/L).

Results

The CCS of 0 (CCS &lt;1) identified approximately 10% of all patients as low risk and had a sensitivity for hospital admission of nearly 98% as compared to &lt;93% when hs-cTnT (&lt;6 ng/L) or hs-cTnI (&lt;5 ng/L) cutoffs alone were used. A CCS ≥5 had a specificity for hospital admission &gt;95%, with approximately 14% of patients at high risk.

Conclusions

An ED disposition (admit or send home) using the presentation blood sample could occur in nearly 25% of all patients by use of the CCS.

Donor kidney injury molecule-1 promotes graft recovery by regulating systemic necroinflammation

Ischemia-reperfusion injury during kidney transplantation predisposes to delayed graft function, rejection, and premature graft failure. Exacerbation of tissue damage and alloimmune responses may be explained by necroinflammation: an autoamplification loop of cell death and inflammation, which is mediated by the release of damage-associated molecular patterns (eg, high-mobility group box-1; HMGB1) from necrotic cells that activate both innate and adaptive immune pathways. Kidney injury molecule-1 (KIM-1) is a phosphatidylserine receptor that is upregulated on injured proximal tubular epithelial cells and enables them to clear apoptotic and necrotic cells. Here we show a pivotal role for clearance of dying cells in regulating necroinflammation in a syngeneic murine kidney transplant model. We found persistent KIM-1 expression in KIM-1^+/+ kidney grafts posttransplantation. Compared to recipients of KIM-1^+/+ kidneys, recipients of KIM-1^-/- kidneys exhibited significantly more renal dysfunction, apoptosis and necrosis, tubular obstruction, and graft failure. KIM-1^-/- grafts also had more inflammatory cytokines, infiltrating neutrophils, and macrophages compared to KIM-1^+/+ grafts. Most significantly, passive release of HMGB1 from apoptotic and necrotic cells led to dramatically higher serum HMGB1 levels and increased proinflammatory macrophages in recipients of KIM-1^-/- grafts. Our data identify an endogenous protective mechanism against necroinflammation in kidney grafts that may be of therapeutic relevance in transplantation.

Tctex-1, a novel interaction partner of Kidney Injury Molecule-1, is required for efferocytosis

Kidney injury molecule-1 (KIM-1) is a phosphatidylserine receptor that is specifically upregulated on proximal tubular epithelial cells (PTECs) during acute kidney injury and mitigates tissue damage by mediating efferocytosis (the phagocytic clearance of apoptotic cells). The signaling molecules that regulate efferocytosis in TECs are not well understood. Using a yeast two-hybrid screen, we identified the dynein light chain protein, Tctex-1, as a novel KIM-1-interacting protein. Immunoprecipitation and confocal imaging studies suggested that Tctex-1 associates with KIM-1 in cells at baseline, but, dissociates from KIM-1 within 90 min of initiation of efferocytosis. Interfering with actin or microtubule polymerization interestingly prevented the dissociation of KIM-1 from Tctex-1. Moreover, the subcellular localization of Tctex-1 changed from being microtubule-associated to mainly cytosolic upon expression of KIM-1. Short hairpin RNA-mediated silencing of endogenous Tctex-1 in cells significantly inhibited efferocytosis to levels comparable to that of knock down of KIM-1 in the same cells. Importantly, Tctex-1 was not involved in the delivery of KIM-1 to the cell-surface. On the other hand, KIM-1 expression significantly inhibited the phosphorylation of Tctex-1 at threonine 94 (T94), a post-translational modification which is known to disrupt the binding of Tctex-1 to dynein on microtubules. In keeping with this, we found that KIM-1 bound less efficiently to the phosphomimic (T94E) mutant of Tctex-1 compared to wild type Tctex-1. Surprisingly, expression of Tctex-1 T94E did not influence KIM-1-mediated efferocytosis. Our studies uncover a previously unknown role for Tctex-1 in KIM-1-dependent efferocytosis in epithelial cells.

G protein α12 (Gα12) is a negative regulator of kidney injury molecule-1-mediated efferocytosis

Kidney injury molecule-1 (KIM-1) is a receptor for the "eat me" signal, phosphatidylserine, on apoptotic cells. The specific upregulation of KIM-1 by injured tubular epithelial cells (TECs) enables them to clear apoptotic cells (also known as efferocytosis), thereby protecting from acute kidney injury. Recently, we uncovered that KIM-1 binds directly to the α-subunit of heterotrimeric G₁₂ protein (Gα₁₂) and inhibits its activation by reactive oxygen species during renal ischemia-reperfusion injury (Ismail OZ, Zhang X, Wei J, Haig A, Denker BM, Suri RS, Sener A, Gunaratnam L. Am J Pathol 185: 1207-1215, 2015). Here, we investigated the role that Gα₁₂ plays in KIM-1-mediated efferocytosis by TECs. We showed that KIM-1 remains bound to Gα₁₂ and suppresses its activity during phagocytosis. When we silenced Gα₁₂ expression using small interefering RNA, KIM-1-mediated engulfment of apoptotic cells was increased significantly; in contrast overexpression of constitutively active Gα₁₂ (QLGα₁₂) resulted in inhibition of efferocytosis. Inhibition of RhoA, a key effector of Gα₁₂, using a chemical inhibitor or expression of dominant-negative RhoA, had the same effect as inhibition of Gα₁₂ on efferocytosis. Consistent with this, silencing Gα₁₂ suppressed active RhoA in KIM-1-expressing cells. Finally, using primary TECs from Kim-1^+/+ and Kim-1^-/- mice, we confirmed that engulfment of apoptotic cells requires KIM-1 expression and that silencing Gα₁₂ enhanced efferocytosis by primary TECs. Our data reveal a previously unknown role for Gα₁₂ in regulating efferocytosis and that renal TECs require KIM-1 to mediate this process. These results may have therapeutic implications given the known harmful role of Gα₁₂ in acute kidney injury.