Circadian and postprandial variation in plasma citrulline concentration in healthy dogs

From Bench Top to Clinics: How New Tests Can Be Helpful in Diagnosis and Management of Dogs with Chronic Enteropathies

In this article, we review different tests that have been researched in dogs with chronic enteropathy. The usefulness of these tests either to assess etiology, to differentiate between treatment response, or to monitor treatment response is discussed. The tests are divided in those that are commercially available and those that hold promises for further development.

Plasma Cytokeratin 18 and fecal Alpha-1 Antitrypsin concentrations in dogs with osteosarcoma receiving carboplatin chemotherapy

Gastrointestinal (GI) toxicosis is a common side effect of cytotoxic chemotherapy treatment in humans and dogs. Measurement of cytokeratin 18 (CK18), an intracellular structural protein released during epithelial apoptosis, and Alpha1‐Antitrypsin (A1AT) in faeces provides a mechanism for evaluating damage to the intestinal mucosa secondary to cytotoxic chemotherapy. Our goal was to evaluate the clinical utility of plasma CK18 and faecal A1‐AT levels as non‐invasive biomarkers of cytotoxic chemotherapy induced GI toxicity. We conducted a prospective cohort study in dogs (N = 10) with osteosarcoma undergoing amputation followed by carboplatin chemotherapy. We hypothesized that plasma CK18 and faecal A1‐AT levels would increase following carboplatin administration due to drug‐induced GI epithelial damage/apoptosis, and that plasma CK18 and faecal A1‐AT levels would correlate with severity of GI toxicity. Mean baseline plasma CK18 concentration was variable amongst patients; however, CK18 concentration prior to carboplatin chemotherapy treatment was not significantly different from CK18 levels after treatment. There was significant intra and inter‐patient variability in mean faecal A1‐AT levels at baseline. Mean A1‐AT concentration did not change significantly from day 0 to day 21. Gastrointestinal toxicity was minimal; therefore, we were unable to determine the association of plasma CK18 and faecal A1‐AT concentrations with development of GI toxicosis. In this study population, plasma CK18 and faecal A1‐AT concentration were not clinically useful biomarkers for the detection of GI toxicosis secondary to carboplatin administration. Further prospective evaluation of CK18 and A1‐AT as biomarkers of drug‐induced GI toxicity is warranted in a larger cohort of dogs receiving cytotoxic chemotherapy.

AVMA clinical trial registration number: AAHSD004827.

Determining optimal therapy of dogs with chronic enteropathy by measurement of serum citrulline

Background

Serum concentration of citrulline is a useful biomarker in human intestinal disease and indicates globally reduced enterocyte mass and absorptive function in various disease states.

Objectives

To determine whether serum citrulline concentration is a biomarker in chronic enteropathy (CE) in dogs, to provide useful information regarding optimal treatment or to predict outcome.

Animals

Seventy‐four dogs with CE and 83 breed‐ and age‐matched hospital controls with no clinical signs of intestinal disease.

Methods

Retrospective study. Outcome was determined and dogs were categorized by response to treatment as having food‐responsive enteropathy (FRE), antibiotic‐responsive diarrhea (ARD), or idiopathic inflammatory bowel disease (IBD). Disease severity was quantified by the CIBDAI scoring index.

Results

Serum citrulline concentration did not differ between dogs with CE (median, 8.4 µg/mL, 5th‐95th percentile 2.0‐19.6) and controls (median, 8.1 µg/mL, 5th‐95th percentile 2.2‐19.7, P = .91). Serum citrulline concentration was similar between dogs with FRE (median, 9.1 µg/mL, 5th‐95th percentile 2.0‐18.9), ARD (median, 13.0 µg/mL, 5th‐95th percentile 1.6‐19.2), IBD (median, 8.4 µg/mL, 5th‐95th percentile 2.1‐21.0; P = .91). Serum citrulline did not correlate to CIBDAI or to serum albumin concentration.

Conclusions and Clinical Importance

In our study, serum citrulline concentration was not associated with efficacy of treatment or outcome in dogs with CE.

Plasma l-citrulline concentrations in l-arginine-supplemented healthy dogs

INTRODUCTION

To determine whether oral l-arginine increases plasma [l-citrulline] in dogs.

ANIMALS

Eleven healthy staff-owned dogs were used in this study.

MATERIALS AND METHODS

Dogs (n = 3) were given l-arginine (50mg/kg PO q8h) for 7 days, and plasma [l-arginine] and [l-citrulline] were analyzed by high performance liquid chromatography at baseline (BL), steady state trough, and 0.5, 1, 1.5, 2, 4, 6, and 8 h after final dosing on day 7. Eleven dogs were then treated with 100mg/kg l-arginine PO q8h for 7 days, and [l-arginine] and [l-citrulline] were measured at BL, steady state trough, and at peak 4 hrs after dosing (T4 hrs).

RESULTS

- Plasma [l-arginine] and [l-citrulline] peaked at T4 hrs on the 50mg/kg dosage. Target outcome, modeled after human study results, of a doubling of [l-arginine] and a 25-30% increase in [l-citrulline] from BL were not reached. After the 100mg/kg dosage, plasma [l-arginine] increased from a BL median of 160.1 μM (range, 100.2-231.4 μM) to a peak of 417.4 μM (206.5-807.3 μM) at T4 hrs, and plasma [l-citrulline] increased from a BL median of 87.8 μM (59.1-117.1 μM) to peak of 102.2 μM (47.4-192.6 μM) at T4 hrs. Ten of eleven dogs showed a doubling of plasma [l-arginine] and 4/11 dogs achieved 25-30% or greater increases in plasma [l-citrulline]. No adverse effects on heart rate or blood pressure were noted.

CONCLUSIONS

- Oral l-arginine dosage of 100mg/kg q8h doubles plasma [l-arginine] in healthy dogs, but conversion to l-citrulline is quite variable. Further evaluation of this dosage regimen in dogs with pulmonary hypertension is warranted.