Iron Status of Cats with Chronic Kidney Disease

Immunometabolism, extracellular vesicles and cardiac injury

Recent evidence from our lab and others suggests that metabolic reprogramming of immune cells drives changes in immune cell phenotypes along the inflammatory-to-reparative spectrum and plays a critical role in mediating the inflammatory responses to cardiac injury (e.g. hypertension, myocardial infarction). However, the factors that drive metabolic reprogramming in immune cells are not fully understood. Extracellular vesicles (EVs) are recognized for their ability to transfer cargo such as microRNAs from remote sites to influence cardiac remodeling. Furthermore, conditions such as obesity and metabolic syndrome, which are implicated in the majority of cardiovascular disease (CVD) cases, can skew production of EVs toward pro-inflammatory phenotypes. In this mini-review, we discuss the mechanisms by which EVs may influence immune cell metabolism during cardiac injury and factors associated with obesity and the metabolic syndrome that can disrupt normal EV function. We also discuss potential sources of cardio-protective and anti-inflammatory EVs, such as brown adipose tissue. Finally, we discuss implications for future therapeutics.

Therapeutics of managing reduced red cell mass associated with chronic kidney disease - Is there a case for earlier intervention?

Reduced red cell mass is a poor prognostic indicator in chronic kidney disease (CKD) patients. Whilst overt anaemia impacts on the quality of life of patients with CKD, lowered red cell mass may also compromise oxygen delivery to proximal tubular cells and contribute to progressive kidney injury. Epidemiological data from cats with CKD support this hypothesis although controlled interventional studies involving drugs that raise red cell mass in trials designed to test this hypothesis are lacking in both human and veterinary medicine. Recombinant analogues of erythropoietin (EPO) are currently standard of care for human CKD patients where low red cell mass impacts on their quality of life. Resistance to EPO is encountered in 20% to 40% of patients treated, probably due to functional iron deficiency, reflecting the difficulties of managing iron deficiency associated with the chronic inflammation of CKD. Similar issues are likely faced in managing anaemia in feline CKD although published data on the use of human EPO analogues are limited as such treatment in cats risks antibody formation resulting in red cell aplasia and transfusion dependency and so is reserved for late stage cases only. This article reviews the recent alternative therapeutic approach to increase red cell mass using HIF-prolyl hydroxylase inhibitors and explains their mode of action and theoretical advantages over EPO analogues in the context of iron metabolism. The results of human clinical trials and the potential benefit of adopting this approach in feline CKD patients are discussed.

Diagnostic value of reticulocyte indices for the assessment of the iron status of cats with chronic kidney disease

Background

Reticulocyte indices have been suggested as alternatives to transferrin saturation (TSAT) for iron status assessment in humans and dogs but they have not been evaluated thoroughly in cats.

Objectives

To assess the value of the reticulocyte indices for the diagnosis of iron deficiency in cats with chronic kidney disease (CKD) and chronic hematuria associated with subcutaneous ureteral bypasses (SUBs).

Animals

Sixty‐four cats: 16 healthy, 14 CKD without SUB, and 34 CKD with SUB.

Methods

Prospective observational cross‐sectional study of cats presented for routine nephrology visits. Primary outcomes included assessment of the diagnostic values of erythrocyte indices (mean corpuscular volume, hemoglobin, and hemoglobin concentration: MCV, MCH, and MCHC) and reticulocyte indices (mean corpuscular volume, MCVr; corpuscular hemoglobin, CHr), using TSAT as reference.

Results

Iron deficiency was diagnosed in 9/64 cats (14%). A receiver‐operating characteristic curve analysis yielded a moderate discriminatory value for CHr in this diagnosis: area under the curve [AUC] = .75 (95% confidence interval, 0.48‐0.89); P = .006; sensitivity 67%, specificity 82% for a cutoff of 15.9 pg. This compared favorably to MCVr (AUC = .63; P = .29), MCV (AUC = .58; P = .45), MCH (AUC = .64; P = .19), and MCHC (AUC = .7; P = .03).

Conclusion and Clinical Importance

CHr added moderate value to the diagnosis of iron deficiency in cats with CKD.

Anemia, iron deficiency, and cobalamin deficiency in cats with chronic gastrointestinal disease

BACKGROUND

Iron deficiency and cobalamin deficiency, as sequelae to chronic gastrointestinal (GI) disease, could result in anemia and increased morbidity in cats with chronic enteropathies.

OBJECTIVE

To evaluate iron deficiency in cats with chronic GI disease and its relationship with hypocobalaminemia, anemia, and disease severity.

ANIMALS

Twenty client-owned cats with primary GI disease.

METHODS

Prospective, cross-sectional study. Cats were enrolled at the time of evaluation for chronic GI disease, after exclusion of comorbidities. CBC with reticulocyte indices, iron metabolism (serum iron and ferritin concentrations, total iron binding capacity [TIBC]), serum methylmalonic acid (MMA), cobalamin, and folate concentrations, pancreatic lipase and trypsin-like immunoreactivity, and disease severity were evaluated.

RESULTS

Anemia (hematocrit <30%), iron deficiency, and cobalamin deficiency were diagnosed in 4/20, 7/20, and 8/20 cats, respectively. Hematocrit (r_s = -.45; P < .05) and body condition score (r_s = -.60; P < .01) negatively correlated with MMA. Median TIBC was lower in cats with increased vs normal MMA (218 μg/mL; range, 120-466 μg/mL vs 288 μg/mL; range, 195-369 μg/mL; P = .02). Hematocrit (r_s = .51; P = .02), reticulocyte MCV (r_s = .52; P = .02), reticulocyte hemoglobin content (r_s = .71; P < .001), and percent transferrin saturation (r_s = .79; P < .0001) positively correlated with serum iron concentration.

CONCLUSIONS AND CLINICAL IMPORTANCE

Functional iron deficiency was common in cats with chronic GI disease. Associations between hypocobalaminemia, iron parameters, and hematologic parameters warrant further investigation on the impact of iron deficiency on chronic GI disease morbidity in cats.

Persistent nonregenerative anemia in a 4-year-old cat

A 4-year-old male neutered domestic shorthair cat was presented to The Ohio State University College of Veterinary Medicine for a 2-month history of severe weight loss, lethargy, anemia, and bilaterally hyperechoic kidneys with loss of corticomedullary distinction as reported by the referring veterinarian. Relevant initial laboratory results included severe non-regenerative normocytic hypochromic anemia, increased blood urea nitrogen, minimally concentrated urine, proteinuria, and an increased urine protein:creatinine ratio. Cytologic evaluation of a bone marrow aspirate revealed a markedly hypocellular marrow with abundant mucinous material. Gelatinous marrow transformation (GMT) was confirmed histologically by the presence of mucinous material in the bone marrow that stained positive for Alcian blue but negative for periodic acid-Schiff. The cat died despite repeated blood transfusions and supportive care. Gelatinous marrow transformation, immune complex-mediated membranoproliferative glomerulonephritis, and gastrointestinal hemorrhage were observed on autopsy and histology. It is likely that the development of GMT was secondary to chronic kidney disease (CKD) and that CKD, GMT, and gastrointestinal hemorrhage contributed to the cat's non-regenerative anemia.

Retrospective evaluation of serum/plasma iron, red blood cell distribution width, and nucleated red blood cells in dogs with acute trauma (2009-2015): 129 cases

OBJECTIVE

To compare the prognostic value of admission hematologic parameters serum/plasma iron, red blood cell distribution width (RDW), and nucleated red blood cells (nRBCs) in dogs presenting with acute traumatic injury.

DESIGN

Retrospective observational study (2009-2015).

SETTING

University teaching hospital.

ANIMALS

One hundred and twenty-nine clinical dogs presenting within 24 hours of acute traumatic injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

One hundred and twenty-nine dogs met the inclusion criteria and 109 (84.5%) survived, while 20 (15.5%) died or were euthanized in hospital. Patients with blunt force trauma comprised 79.8% of the patient population; dogs with penetrating trauma comprised 20.2% of cases. Hypoferremia occurred in all nonsurvivors, and the median serum/plasma iron concentration was significantly lower in nonsurvivors than survivors (P = 0.028). Normal or increased serum/plasma iron had 100% specificity and 100% positive predictive value for survival. Red blood cell distribution width was not significantly different between groups (P = 0.417). The presence of nRBCs was significantly associated with nonsurvival (P = 0.030), although the absolute nRBC concentrations were not significantly different (P = 0.070). A multiple logistic regression model found age, type of injury, presence of nRBCs, and serum/plasma iron to be independent predictors of survival with an area under the receiver operator characteristic curve of 0.813.

CONCLUSIONS

The presence of nRBCs and low serum/plasma iron are associated with mortality in patients with acute trauma; however, red blood cell distribution width was not associated with survival. Absence of hypoferremia was highly associated with a favorable prognosis in this patient population. These parameters may warrant inclusion in trauma scoring systems.

Plasma indoxyl sulfate concentration predicts progression of chronic kidney disease in dogs and cats

Indoxyl sulfate is a protein-bound uremic toxin that increases as the severity of impaired renal function increases in humans, laboratory animals, dogs and cats. An elevation of indoxyl sulfate is related to prognosis among people with chronic kidney disease. However, whether indoxyl sulfate is able to predict the progression of chronic kidney disease in dogs and cats has not been previously studied. In the present study, 58 cats and 36 dogs with chronic kidney disease were enrolled. Plasma indoxyl sulfate was measured by high performance liquid chromatography. Renal progression was defined as an increase by one International Renal Interest Society (IRIS) stage and/or a rise in serum creatinine concentration of 0.5mg/dL during the same stage within a 3-month period. Compared with the non-progression groups, across different stages of renal failure, the baseline plasma indoxyl sulfate concentration was increased in the renal progression group (P<0.05), especially for IRIS stages 2 and 3 animals. The area under the receiver operator characteristic curves of indoxyl sulfate, when predicting renal progression, was above 0.75 for both dogs and cats. Indoxyl sulfate concentrations were also correlated with the increase of blood urea nitrogen, serum creatinine, and phosphate and the decrease of hematocrit among cats; while in dogs, concentrations were only correlated with the increase of phosphate concentrations. Indoxyl sulfate served as a biomarker of progression risk in dogs and cats with chronic kidney disease.

Investigation of iron status and markers of inflammation in anaemic and non-anaemic hospitalised cats

OBJECTIVES

To measure iron parameters and markers of inflammation in anaemic cats presented for intensive care unit hospitalisation, and to compare these to cohorts of non-anaemic hospitalised cats and cats that develop hospital-acquired anaemia.

METHODS

Blood samples were collected for measurement of iron panel and serum amyloid A in addition to routine investigation in cats admitted to the intensive care unit. Medical records were reviewed to determine how many of the Systemic Inflammatory Response Syndrome criteria were met and to assign Acute Patient Physiologic and Laboratory Evaluation scores as a measure of illness severity.

RESULTS

Seventy-eight cats were enrolled. Anaemia was documented in 34·6% of cats on presentation and another 10·3% developed anaemia during hospitalisation. Compared with non-anaemic cats, animals that were anaemic on presentation had higher neutrophil and white blood cell counts, and longer hospitalisation. Iron status was consistent with anaemia of inflammation in most anaemic patients. Iron status, serum amyloid A concentration, and prevalence of systemic inflammatory response syndrome did not differ between anaemic and non-anaemic cohorts. All cause mortality was higher in anaemic cats.

CLINICAL SIGNIFICANCE

Anaemia is common in cats hospitalised in the intensive care unit. Systemic inflammation is also common in these cats. Iron status in anaemic cats suggests that anaemia of inflammatory disease may be a significant contributor to anaemia in this patient population.

Acute-Phase Proteins and Iron Status in Cats with Chronic Kidney Disease

Background

The role of inflammation in the development and progression of chronic kidney disease (CKD) in cats is not well characterized. Hepcidin is a recently discovered acute‐phase protein (APP) that plays an important role in iron metabolism and contributes to the development of anemia in humans with CKD.

Objectives

To compare serum APP concentrations, iron status, and erythropoietin (EPO) concentrations in healthy cats and cats with naturally occurring CKD.

Animals

A total of 18 healthy control cats and 38 cats with CKD.

Methods

Prospective study. After complete physical examination and routine blood analysis, the following tests were performed: serum amyloid A (SAA), haptoglobin (HAP), EPO, serum iron and ferritin concentration as well as total iron‐binding capacity (TIBC). Serum hepcidin‐25 concentration was measured by ELISA kit designed for use in humans.

Results

Mean SAA and hepcidin concentrations were significantly higher and mean total iron and TIBC were significantly lower in the CKD group (P < .05). There was a significant positive correlation between serum creatinine concentration (CRT) and 2 of the APPs (SAA and hepcidin; P < .05). Increases in SAA and hepcidin were associated with decreases in TIBC and hematocrit in the CKD group. Fourteen (37%) of the cats with CKD were anemic, and these cats had significantly lower TIBC (P < .05), suggesting a functional iron deficiency. There was no association between survival time and APP, iron status, or EPO concentrations.

Conclusions

Our data suggest that CKD in cats is associated with systemic inflammation and altered iron metabolism. With further validation in cats, hepcidin assays may help better characterize these relationships.