Systemic Effects of Homoarginine Supplementation on Arginine Metabolizing Enzymes in Rats with Heart Failure with Preserved Ejection Fraction.

A restoration of low homoarginine (hArg) levels in obese ZSF1 rats (O-ZSF1) before (S1-ZSF1) and after (S2-ZSF1) the manifestation of heart failure with preserved ejection fraction (HFpEF) did not affect the worsening of cardiac HFpEF characteristics. Here, potential regulation of key enzymes of arginine metabolism in other organs was analyzed. Arginase 2 (ARG2) was reduced >35% in the kidney and small intestine of hArg-supplemented rats compared to O-ZSF1. Glycine amidinotransferase (GATM) was 29% upregulated in the kidneys of S1-ZSF1. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) levels were reduced >50% in the livers of O-ZSF1 but restored in S2-ZSF1 compared to healthy rats (L-ZSF1). In the skeletal muscle, iNOS was lower in O-ZSF1 and further decreased in S1-ZSF1 and S2-ZSF1 compared to L-ZSF1. iNOS levels were lower in the liver of the S2-ZSF1 group but higher in the kidneys of S1-ZSF1 compared to L-ZSF1. Supplementation with hArg in an in vivo HFpEF model resulted in the inhibition of renal ARG2 and an increase in GATM expression. This supplementation might contribute to the stabilization of intestinal iNOS and ARG2 imbalances, thereby enhancing barrier function. Additionally, it may offer protective effects in skeletal muscle by downregulating iNOS. In the conceptualization of hArg supplementation studies, the current disease progression stage as well as organ-specific enzyme regulation should be considered.

Homoarginine in health and disease.

PURPOSE OF REVIEW: Homoarginine (hArg) is an endogenous, nonproteinogenic amino acid. It is enzymatically synthesized from L-arginine and L-lysine. Low hArg concentrations appear to be a risk factor in the renal and cardiovascular systems. This review discusses advances in-vitro and in-vivo experimental and clinical research on hArg in health and disease. RECENT FINDINGS: Recent studies indicate that low circulating and low urinary concentrations of hArg are associated with morbidity and worse outcome. Although the biological activities of hArg remain still unexplored, hArg supplementation is intensely investigated as a strategy to increase hArg concentration to reach normal levels in cases of low hArg concentrations. The greatest changes in circulating hArg concentrations are observed during pregnancy and after delivery. In healthy adults, a daily dose of 125 mg hArg seems to be optimum to normalize circulating levels. Short-term supplementation of inorganic nitrate enhances hArg biosynthesis in healthy young men. Apart from hArg supplementation, dietary L-arginine and L-citrulline appear to be a promising alternative. SUMMARY: Considerable progress has been made in recent years, but hArg remains still enigmatic. Further research is required to explore the biological activities of hArg. Supplementation of hArg or its precursors L-citrulline/L-arginine seem to be promising strategies to prevent and overcome altered hArg synthesis.

Short-Term Supplementation of Sodium Nitrate vs. Sodium Chloride Increases Homoarginine Synthesis in Young Men Independent of Exercise.

The aim of the study was to investigate the effects of short-term oral administration of inorganic nitrate (NaNO3; n = 8) or placebo (NaCl; n = 9) (each 0.1 mmol/kg body weight/d for 9 days) on plasma amino acids, creatinine, and oxidative stress in healthy young men. At baseline, the plasma concentrations of amino acids did not differ between the groups. At the end of the study, the plasma concentrations of homoarginine (hArg; by 24%, p = 0.0001), citrulline and ornithine (Cit/Orn; by 16%, p = 0.015), and glutamine/glutamate (Gln/Glu; by 6%, p = 0.0003) were higher in the NaNO3 group compared to the NaCl group. The plasma concentrations of sarcosine (Sarc; by 28%, p < 0.0001), tyrosine (by 14%, p = 0.0051), phenylalanine (by 8%, p = 0.0026), and tryptophan (by 8%, p = 0.0047) were lower in the NaNO3 group compared to the NaCl group. These results suggest that nitrate administration affects amino-acid metabolism. The arginine/glycine amidinotransferase (AGAT) catalyzes two reactions: (1) the formation of l-homoarginine (hArg) and l-ornithine (Orn) from l-arginine (Arg) and l-lysine (Lys): Arg + Lys <−> hArg + Orn, with equilibrium constant Kharg; (2) the formation of guanidinoacetate (GAA) and Orn from Arg and glycine (Gly): Arg + Gly <−> GAA + Orn, with equilibrium constant Kgaa. The plasma Kgaa/KhArg ratio was lower in the NaNO3 group compared to the NaCl group (1.57 vs. 2.02, p = 0.0034). Our study suggests that supplementation of inorganic nitrate increases the AGAT-catalyzed synthesis of hArg and decreases the N-methyltransferase-catalyzed synthesis of GAA, the precursor of creatine. To our knowledge, this is the first study to demonstrate elevation of hArg synthesis by inorganic nitrate supplementation. Remarkably, an increase of 24% corresponds to the synthesis capacity of one kidney in healthy humans. Differences in the association between plasma concentrations of amino acids in the NaNO3 and NaCl groups suggest changes in amino-acid homeostasis. Plasma concentrations of the oxidative stress marker malondialdehyde (MDA) did not change after supplementation of NaNO3 or NaCl over the whole exercise time range. Plasma nitrite concentration turned out to be a more discriminant marker of NaNO3 ingestion than plasma nitrate (area under the receiver operating characteristic curve: 0.951 vs. 0.866, p < 0.0001 each).

Expression of cardiovascular-related microRNAs is altered in L-arginine:glycine amidinotransferase deficient mice.

In humans and mice, L-arginine:glycine amidinotransferase (AGAT) and its metabolites homoarginine (hArg) and creatine have been linked to cardiovascular disease (CVD), specifically myocardial infarction (MI) and heart failure (HF). The underlying molecular and regulatory mechanisms, however, remain unclear. To identify potential pathways of cardiac AGAT metabolism, we sequenced microRNA (miRNA) in left ventricles of wild-type (wt) compared to AGAT-deficient (AGAT-/-) mice. Using literature search and validation by qPCR, we identified eight significantly regulated miRNAs in AGAT-/- mice linked to atherosclerosis, MI and HF: miR-30b, miR-31, miR-130a, miR-135a, miR-148a, miR-204, miR-298, and let-7i. Analysis of Gene Expression Omnibus (GEO) data confirmed deregulation of these miRNAs in mouse models of MI and HF. Quantification of miRNA expression by qPCR in AGAT-/- mice supplemented with creatine or hArg revealed that miR-30b, miR-31, miR-130a, miR-148a, and miR-204 were regulated by creatine, while miR-135a and miR-298 showed a trend of regulation by hArg. Finally, bioinformatics-based target prediction showed that numerous AGAT-dependent genes previously linked to CVD are likely to be regulated by the identified miRNAs. Taken together, AGAT deficiency and hArg/creatine supplementation are associated with cardiac miRNA expression which may influence cardiac (dys)function and CVD.

Homoarginine- and Creatine-Dependent Gene Regulation in Murine Brains with l-Arginine:Glycine Amidinotransferase Deficiency.

l-arginine:glycine amidinotransferase (AGAT) and its metabolites homoarginine (hArg) and creatine have been linked to stroke pathology in both human and mouse studies. However, a comprehensive understanding of the underlying molecular mechanism is lacking. To investigate transcriptional changes in cerebral AGAT metabolism, we applied a transcriptome analysis in brains of wild-type (WT) mice compared to untreated AGAT-deficient (AGAT-/-) mice and AGAT-/- mice with creatine or hArg supplementation. We identified significantly regulated genes between AGAT-/- and WT mice in two independent cohorts of mice which can be linked to amino acid metabolism (Ivd, Lcmt2), creatine metabolism (Slc6a8), cerebral myelination (Bcas1) and neuronal excitability (Kcnip3). While Ivd and Kcnip3 showed regulation by hArg supplementation, Bcas1 and Slc6a8 were creatine dependent. Additional regulated genes such as Pla2g4e and Exd1 need further evaluation of their influence on cerebral function. Experimental stroke models showed a significant regulation of Bcas1 and Slc6a8. Together, these results reveal that AGAT deficiency, hArg and creatine regulate gene expression in the brain, which may be critical in stroke pathology.

Analysis of L-arginine:glycine amidinotransferase-, creatine- and homoarginine-dependent gene regulation in the murine heart.

L-arginine:glycine amidinotransferase (AGAT) and its metabolites creatine and homoarginine (HA) have been linked to cardiovascular pathologies in both human and murine studies, but the underlying molecular mechanisms are poorly understood. Here, we report the first analysis of heart transcriptome variation using microarrays in an AGAT-deficient (AGAT-/-) mouse model to evaluate AGAT-, creatine- and HA-dependent gene regulation. Our data revealed significant differences of gene expression between AGAT-/- and wild-type (WT) mice, affecting cardiac energy metabolism (Fbp2, Ucp2), cardiac hypertrophy and fibrosis (Nppa, Ctgf), immune response (Fgl2), and the conduction system of the heart (Dsc2, Ehd4, Hcn2, Hcn4, Scn4a, Scn4b). All of these genes being expressed on WT level in creatine-supplemented mice. Using in silico analysis based on the GEO database we found that most of these candidate genes (Ctgf, Dsc2, Fbp2, Fgl2, Hcn2, Nppa)  revealed significant alterations in a WT mouse model of myocardial infarction underlining a pathophysiological relationship between AGAT metabolism and cardiovascular disease.

Muscle phenotype of AGAT- and GAMT-deficient mice after simvastatin exposure.

Statin-induced myopathy affects more than 10 million people worldwide. But discontinuation of statin treatment increases mortality and cardiovascular events. Recently, L-arginine:glycine amidinotransferase (AGAT) gene was associated with statin-induced myopathy in two populations, but the causal link is still unclear. AGAT is responsible for the synthesis of L-homoarginine (hArg) and guanidinoacetate (GAA). GAA is further methylated to creatine (Cr) by guanidinoacetate methyltransferase (GAMT). In cerebrovascular patients treated with statin, lower hArg and GAA plasma concentrations were found than in non-statin patients, indicating suppressed AGAT expression and/or activity (n = 272, P = 0.033 and P = 0.039, respectively). This observation suggests that statin-induced myopathy may be associated with AGAT expression and/or activity in muscle cells. To address this, we studied simvastatin-induced myopathy in AGAT- and GAMT-deficient mice. We found that simvastatin induced muscle damage and reduced AGAT expression in wildtype mice (myocyte diameter: 34.1 ± 1.3 µm vs 21.5 ± 1.3 µm, P = 0.026; AGAT expression: 1.0 ± 0.3 vs 0.48 ± 0.05, P = 0.017). Increasing AGAT expression levels of transgenic mouse models resulted in rising plasma levels of hArg and GAA (P < 0.01 and P < 0.001, respectively). Simvastatin-induced motor impairment was exacerbated in AGAT-deficient mice compared with AGAT-overexpressing GAMT-/- mice and therefore revealed an effect independent of Cr. But Cr supplementation itself improved muscle strength independent of AGAT expression (normalized grip strength: 55.8 ± 2.9% vs 72.5% ± 3.0%, P < 0.01). Homoarginine supplementation did not affect statin-induced myopathy in AGAT-deficient mice. Our results from clinical and animal studies suggest that AGAT expression/activity and its product Cr influence statin-induced myopathy independent of each other. The interplay between simvastatin treatment, AGAT expression and activity, and Cr seems to be complex. Further clinical pharmacological studies are needed to elucidate the underlying mechanism(s) and to evaluate whether supplementation with Cr, or possibly GAA, in patients under statin medication may reduce the risk of muscular side effects.

l-Homoarginine supplementation prevents diabetic kidney damage.

l-homoarginine is an endogenous, non-proteinogenic amino acid that has emerged as a new player in health and disease. Specifically, low l-homoarginine levels are associated with cardiovascular diseases, stroke, and reduced kidney function. However, the role of l-homoarginine in the pathogenesis of diabetic nephropathy (DN) is not known. Experiments were conducted in 6-week-old Ins2Akita mice supplemented with l-homoarginine via drinking water or mini osmotic pump for 12 weeks. Both plasma and kidney l-homoarginine levels were significantly reduced in diabetic mice compared to nondiabetic controls. Untreated Ins2Akita mice showed significant increases in urinary albumin excretion, histological changes, glomerular macrophage recruitment, the inflammatory cytokine KC-GRO/CXCL1, and urinary thiobarbituric acid reactive substances (TBARS) excretion as an indicator of oxidative stress, along with a significant reduction in kidney nitrate + nitrite levels compared to control mice at 18 weeks of age. In contrast, l-homoarginine supplementation for 12 weeks in Ins2Akita mice, via either drinking water or mini osmotic pump, significantly reduced albuminuria, renal histological changes, glomerular macrophage recruitment, KC-GRO/CXCL1 levels, urinary TBARS excretion, and largely restored kidney nitrate + nitrite levels. These data demonstrate that l-homoarginine supplementation attenuates specific features of DN in mice and could be a potential new therapeutic tool for treating diabetic patients.

Evidence by GC-MS that lysine is an arginase-catalyzed metabolite of homoarginine in vitro and in vivo in humans.

l-Homoarginine (hArg) is biosynthesized from l-arginine (Arg) and l-lysine (Lys) by arginine:glycine amidinotransferase (AGAT). AGAT also catalyzes the formation of guanidinoacetate (GAA) from Arg and glycine (Gly). GAA is converted to creatine (N-methyl guanidinoacetate) by guanidinoacetate N-methyl-transferase (GAMT). Low circulating and excretory concentrations of hArg are associated with worse cardiovascular outcome and mortality. hArg is a poor substrate of nitric oxide synthase (NOS) and a weak inhibitor of arginase. The metabolism of hArg in humans is little investigated. Previously, we found that orally administered hArg (125 mg/day) increased the plasma concentration of hArg, but not of Arg, the substrate of NOS, in healthy subjects. We newly analyzed the plasma samples collected in that study for Lys and other amino acids. Repeated measures ANOVA revealed statistically significant differences between the groups (P = 0.008) with respect to plasma Lys concentration which increased by about 8% after a 4-week hArg supplementation. In vitro, recombinant human arginase and bovine liver arginase I were demonstrated by a specific and sensitive stable-isotope GC-MS assay to hydrolyze hArg to Lys. Our results suggest that Lys is a metabolite of hArg produced by the hydrolytic activity of arginase. Arginase may play a key role in hArg homeostasis in humans.

The prognostic biomarker L-homoarginine is a substrate of the cationic amino acid transporters CAT1, CAT2A and CAT2B.

Low plasma concentration of L-homoarginine is an independent predictor of cardiovascular events and total mortality. Experimental data indicate that supplementation of L-homoarginine may have protective effects. We aimed to elucidate the mechanisms involved in the cellular uptake of L-homoarginine, which are little understood, so far. Using human embryonic kidney (HEK293) cell lines stably overexpressing the human cationic amino acid transporters CAT1 [solute carrier family 7 (SLC7A1)], CAT2A (SLC7A2A) or CAT2B (SLC7A2B) we assessed the transport kinetics of L-homoarginine and interactions with the CAT substrates L-arginine and asymmetric dimethylarginine (ADMA). Significant uptake of L-homoarginine was observed for all three CATs with apparent KM-values of 175 ± 7 µM for CAT1 and 523 ± 35 µM for CAT2B. Saturation of CAT2A-mediated L-homoarginine uptake could not be reached. Uptake of L-homoarginine by any of the three CATs could be inhibited by L-arginine and ADMA. Significant inhibition of CAT1-mediated uptake of L-homoarginine by L-arginine already occurred in the physiological concentration range. Taken together these data demonstrate that L-homoarginine is a substrate of CAT1, CAT2A and CAT2B and that CAT1 is a key site with regard to physiological relevance and interactions with related substrates such as L-arginine.

Arginine and Lysine Transporters Are Essential for Trypanosoma brucei.

For Trypanosoma brucei arginine and lysine are essential amino acids and therefore have to be imported from the host. Heterologous expression in Saccharomyces cerevisiae mutants identified cationic amino acid transporters among members of the T. brucei AAAP (amino acid/auxin permease) family. TbAAT5-3 showed high affinity arginine uptake (Km 3.6 ± 0.4 µM) and high selectivity for L-arginine. L-arginine transport was reduced by a 10-times excess of L-arginine, homo-arginine, canavanine or arginine-ß-naphthylamide, while lysine was inhibitory only at 100-times excess, and histidine or ornithine did not reduce arginine uptake rates significantly. TbAAT16-1 is a high affinity (Km 4.3 ± 0.5 µM) and highly selective L-lysine transporter and of the compounds tested, only L-lysine and thialysine were competing for L-lysine uptake. TbAAT5-3 and TbAAT16-1 are expressed in both procyclic and bloodstream form T. brucei and cMyc-tagged proteins indicate localization at the plasma membrane. RNAi-mediated down-regulation of TbAAT5 and TbAAT16 in bloodstream form trypanosomes resulted in growth arrest, demonstrating that TbAAT5-mediated arginine and TbAAT16-mediated lysine transport are essential for T. brucei. Growth of induced RNAi lines could partially be rescued by supplementing a surplus of arginine or lysine, respectively, while addition of both amino acids was less efficient. Single and double RNAi lines indicate that additional low affinity uptake systems for arginine and lysine are present in T. brucei.

Novel apidaecin 1b analogs with superior serum stabilities for treatment of infections by gram-negative pathogens.

Proline-rich antimicrobial peptides (PrAMPs) from insects and mammals have recently been evaluated for their pharmaceutical potential in treating systemic bacterial infections. Besides the native peptides, several shortened, modified, or even artificial sequences were highly effective in different murine infection models. Most recently, we showed that the 18-residue-long peptide Api88, an optimized version of apidaecin 1b, was efficient in two different animal infection models using the pathogenic Escherichia coli strains ATCC 25922 and Neumann, with a promising safety margin. Here, we show that Api88 is degraded relatively fast upon incubation with mouse serum, by cleavage of the C-terminal leucine residue. To improve its in vitro characteristics, we aimed to improve its serum stability. Replacing the C-terminal amide by the free acid or substituting Arg-17 with l-ornithine or l-homoarginine increased the serum stabilities by more than 20-fold (half-life, ∼4 to 6 h). These analogs were nontoxic to human embryonic kidney (HEK 293), human hepatoma (HepG2), SH-SY5Y, and HeLa cells and nonhemolytic to human erythrocytes. The binding constants of all three analogs with the chaperone DnaK, which is proposed as the bacterial target of PrAMPs, were very similar to that of Api88. Of all the analogs tested, Api137 (Gu-ONNRPVYIPRPRPPHPRL; Gu is N,N,N',N'-tetramethylguanidino) appeared most promising due to its high antibacterial activity, which was very similar to Api88. Positional alanine and d-amino acid scans of Api137 indicated that substitutions of residues 1 to 13 had only minor effects on the activity against an E. coli strain, whereas substitutions of residues 14 to 18 decreased the activity dramatically. Based on the significantly improved resistance to proteolysis, Api137 appears to be a very promising lead compound that should be even more efficient in vivo than Api88.

The alteration of asymmetric dimetilarginine (ADMA) levels in cardiac and gastrocnemius muscles following radioactive iodine application in guinea pigs and the effect of L-carnitine on this alteration.

PURPOSE: Tissue levels of asymmetric dimetilarginine (ADMA) and symmetric dimetilarginine (SDMA) were investigated in cardiac ventricle and gastrocnemius muscles of guinea pigs treated with radioactive iodine (RAI) alone or in combination with L-carnitine (LC). MATERIAL AND METHODS: Group 1 received no treatment (control group). Group 2 received a total dose of 30 mCi⁻¹kg⁻¹ body weight iodine-131 alone. Group 3 received 200 mg⁻¹kg⁻¹ of LC for 10 days alone. Group 4 received 200 mg⁻¹kg⁻¹ of LC plus RAI therapy. Free thyroid hormones, ADMA and SDMA concentrations were measured. RESULTS: Serum free thyroid hormone concentrations were found decreased in the RAI and LC-RAI groups after RAI application. A significant decrease in ADMA and SDMA concentration was observed in ventricle muscle following RAI application. The LC-RAI group had significantly decreased ADMA levels in ventricle muscle compared with those of the control group. Similarly, SDMA concentrations in ventricle and gastrocnemius muscles of the LC-RAI groups were significantly lower than those of the control groups. CONCLUSIONS: Our results indicated that RAI appears to exert an inhibitory effect on ADMA and SDMA levels of ventricular muscle. LC administration when given adjuvant to RAI therapy may cause a marked decrease in ADMA concentrations of both ventricular and gastrocnemius muscles.

The effect of microbial phytase on true and apparent ileal amino acid digestibilities in growing-finishing pigs.

Ten 56-d-old, 15-kg barrows were surgically fitted with a postvalvular T-cecum cannula at the ileo-cecal junction to evaluate the effect of microbial phytase on apparent and true ileal AA digestibility and N utilization. A semipurified cornstarch- and soybean meal-based diet was formulated to contain 3.4 Mcal of DE/kg, 17.0% CP, 0.8% Ca, and 0.6% P but had a low phytate-P concentration (0.13%; all on an as-fed basis). Chromic oxide and dysprosium chloride were used as indigestible markers. The basal diet was supplemented with 0 or 1,000 phytase units/kg of microbial phytase. Postprandial plasma urea N and alpha-amino N concentrations, excretion of Ca, P, and N in feces and urine, and ileal AA digestibilities were determined 3 times at 4-wk intervals beginning at 70 d of age. The homoarginine (HA) method was used to determine endogenous AA flow by replacing 50% of the basal protein with guanidinated protein. Microbial phytase had no effect on apparent ileal digestibility (AID) or on true ileal digestibilities of N and most AA but did increase AID for arginine (P = 0.006) and methionine (P = 0.037). However, in HA diets, phytase increased the AID of CP (P = 0.01) and several AA. Addition of microbial phytase had no effect on the postprandial alpha-amino N concentrations in plasma but increased overall plasma urea N concentrations (P = 0.035). Barrows fed phytase-supplemented diets had decreased P in feces (P = 0.003) and greater P in urine (P = 0.001) but comparable total P excretion compared with barrows fed no phytase-supplemented diets. In conclusion, the addition of phytase to a semi-purified soybean meal-based diet did not affect the AID of several AA. In addition, differences between the basal and HA diets in N digestibilities indicated that that guanidination may limit the use of the HA method in determining endogenous protein losses.

Synthesis and biological characterization of L-N(6)-(1-iminoethyl)lysine 5-tetrazole-amide, a prodrug of a selective iNOS inhibitor.

The 5-tetrazole amide of L-N(6)-(1-iminoethyl)lysine (L-NIL), L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide (1), has been prepared and evaluated. In contrast to L-NIL, 1 is a stable, nonhygroscopic, crystalline solid. Unlike L-NIL, 1 has minimal inhibitory activity in vitro on human inducible nitric oxide synthase (iNOS). However, it is rapidly converted in vivo to L-NIL and produces dose-dependent inhibition of iNOS in acute and chronic models of inflammation in the rodent with efficacy comparable to L-NIL. In addition, both 1 and L-NIL exhibit significant and comparable in vivo selectivity for the inhibition of iNOS vs endothelial NOS. Doses approximately 80-fold greater than those that inhibited inflammation do not elevate systemic blood pressure. In summary, both the physical properties and the pharmacological profile of 1 make it an ideal molecule for preclinical and clinical studies on the role of selective iNOS inhibitors in mediating inflammatory disease processes.

Evaluation of the homoarginine technique for measuring true ileal amino acid digestibilities in pigs fed a barley-canola meal-based diet.

The homoarginine technique has been suggested as a means to determine true ileal amino acid digestibilities in nonruminant animals fed protein-containing diets. Conditions for guanidinating lysine to homoarginine in barley and canola meal and the effect of this process on nutrient composition and ileal digestibilities in the resulting material were investigated. Conditions tested were methylisourea concentration (0.4, 0.5, or 0.6 M) and reaction time (4 or 6 d) at pH 10.5. Using 0.4 methylisourea M solution for 4 or 6 d gave guanidination rates of 72.5 and 78.5% for barley and 72.3 and 75.2% for canola meal, respectively. Using 0.5 M gave 88.0 and 84.6% guanidination rates in barley and canola meal, respectively, after a 6-d reaction time. Under these conditions, guanidination did not change the nutrient composition of barley (P > 0.10), whereas it increased CP (38.4 vs 49.0%), crude fiber (10.2 vs 16.0%), acid detergent fiber (30.0 vs 43.4%) and neutral detergent fiber (29.8 vs 49.4%) levels in canola meal (P < 0.05). Four 33.6-kg barrows fitted with a simple T-cannula at the terminal ileum were fed a 16% CP unguanidinated barley and canola meal-based diet for four consecutive 14-d periods. Ileal digesta were collected continuously for 24 h on d 12 and 14 to determine apparent nutrient digestibilities. On the morning of d 14, pigs were fed a diet in which half of the barley and canola meal was replaced with guanidinated material for determining true ileal amino acid digestibilities. Digesta samples were pooled by pig and by 24-h period to give 16 observations per diet. Apparent ileal digestibilities of DM, CP, and AA in the unguanidinated and guanidinated barley-canola meal diet were similar (P > 0.10) despite the changes observed in canola meal. Apparent ileal lysine digestibility was 73.9 and 74.5% in the unguanidinated and guanidinated diet, respectively. The true ileal lysine digestibility was 88.1%. The present results show that guanidination does not interfere with digestion and further support the use of the homoarginine method for determining true ileal amino acid digestibilities in pigs fed practical diets. A methylisourea solution of 0.5 M and a 6-d reaction time are recommended for converting lysine to homoarginine in barley and canola meal.

Dietary L-homoarginine has no lysine bioactivity in chicks.

A chick growth assay was conducted to investigate the effect of dietary L-homoarginine supplementation on performance of chicks fed a Lys-deficient corn-feather meal diet. Weight gain, feed intake, and feed efficiency increased linearly (P < .01) as Lys was added at .1 and .2% from feed-grade L-Lys.HCl. Adding homoarginine at .2% resulted in less (P < .05) weight gain and feed intake than observed in chicks fed the unsupplemented basal diet. These data suggest that dietary homoarginine had no Lys bioactivity, but may also have antagonized Lys utilization from the basal diet.