Excess Dietary Lysine Increases Growth of Chicks Fed Niacin-DeficientDiets, but Dietary Quinolinic Acid Has No Niacin-Sparing Activity

N. R. Augspurger1 and D. H. Baker2

Department of Animal Sciences and Division of Nutritional Sciences,University of Illinois at Urbana-Champaign, Urbana, IL 61801

ABSTRACT Catabolism of Trp and Lys produces α-ketoadipic acid as an intermediary metabolite. An alter-nate pathway of Trp turnover leads to NAD synthesis.We hypothesized that excess Lys might improve the con-version of Trp to niacin by causing a buildup of α-ketoa-dipic acid, thereby endproduct inhibiting the main Trpcatabolic pathway and resulting in more niacin synthesisfrom Trp. Six bioassays were carried out in which 12 to20 chicks were fed each experimental diet from d 8 to d20 or 21 posthatching. The basal diet (4 mg/kg of bioavai-lable niacin) used for all assays was a semipurified corngluten meal diet fortified with crystalline amino acids to22.5% CP and 0.96% true digestible Lys. Assay 1 through3 established the requirements for digestible Trp (0.16%)and bioavailable niacin (19.5 mg/kg) and showed that0.96% digestible Lys was adequate for chick growth in

Key words: niacin, tryptophan, lysine, picolinate, quinolinate

2007 Poultry Science 86:349–355

INTRODUCTION

Tryptophan metabolism (Heine et al., 1995; Sainio etal., 1996) ultimately proceeds toward the production ofserotonin (approximately 3%), CO2 (approximately 95%),and niacin (2%; Figure 1). Krehl et al. (1945, 1950) showedthat excess Trp can be catabolized to niacin and thatdietary Trp deficiency and overall poor protein qualitycontribute to niacin deficiency (i.e., pellagra) in popula-tions subsisting on cereal-based diets. Further work inchicks revealed that under conditions of niacin deficiencyand minimal Trp adequacy, excess Trp was converted toniacin with an efficiency (wt/wt) of approximately 2%(Baker et al., 1973; Oduho and Baker, 1993; Chen et al.,1996). Further work by Oduho et al. (1994) revealed thatFe deficiency reduced the conversion efficiency of Trp toniacin from 2.4 to 1.6% (wt/wt).

Tryptophan and Lys catabolism share a common inter-mediate, α-ketoadipic acid (Figure 1). The branch point

2007 Poultry Science Association Inc.Received August 25, 2006.Accepted October 22, 2006.1Present address: JBS United Inc., Sheridan, IN 46069.2Corresponding author: dhbaker@uiuc.edu

349

the presence of adequate Trp and niacin. The fourth assaywas done to determine the effect of 1% Lys (1.25% food-grade L-Lys�HCl) on niacin utilization. Excess Lys im-proved (P < 0.01) weight gain of niacin-deficient chicks.The fifth assay showed that 1% excess food-grade Lysimproved weight gain in niacin-deficient (4 mg/kg)chicks but depressed weight gain in niacin-adequate (24mg/kg) chicks (niacin × Lys interaction, P < 0.01). In assay6, chicks fed 6 mg/kg of niacin gained faster (P < 0.01)than control chicks, but neither quinolinic acid (100 mg/kg) nor picolinic acid (4,200 mg/kg) elicited a response.These results suggest that excess Lys leads to an accumu-lation of α-ketoadipic acid, which causes endproduct inhi-bition of the main Trp catabolic pathway to CO2, thereforeincreasing flux of 2-amino-3-carboxymuconate semialde-hyde to NAD.

in Trp catabolism that leads to niacin production occursat α-amino-β-carboxymuconate semialdehyde (ACS).Approximately 95% of ACS is ultimately catabolized toCO2 and H2O, producing α-ketoadipic acid as an interme-diate 3 steps down from ACS (Lan and Gholson, 1965;Pawlak et al., 2002). The rate of ACS decarboxylation isinversely related to the amount of NAD synthesized fromTrp (Ikeda et al., 1965). Our hypothesis was that excessdietary Lys might lead to a build-up of α-ketoadipic acid,which in turn would endproduct inhibit the catabolismof ACS to α-ketoadipic acid, thus shunting more ACS(from Trp) toward NAD biosynthesis.

MATERIALS AND METHODS

Birds and Housing

All housing, feeding, and euthanasia procedures wereapproved by the University of Illinois Laboratory AnimalCare and Use Committee. Six assays were done usingNew Hampshire × Columbian Plymouth Rock color-sexed male chicks obtained from the University of IllinoisPoultry Farm. Chicks were fed a nutritionally adequatecorn-soybean meal starter diet from hatching to d 7 post-hatching. On d 8 following an overnight period of feed

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

AUGSPURGER AND BAKER350

Figure 1. Pathways involving Trp metabolism; PLP = pyridoxal phosphate.

withdrawal, chicks were weighed, wing-banded, and ran-domly allotted to form 5 replicates of 4 male chicks perpen for assays 1 to 4. Assay 5 used 4 pens of 4 chicks perdiet, and assay 6 had 4 pens of 3 chicks per diet. Chickswere housed in thermostatically controlled starter batter-ies (Petersime Incubator Co., Gettysburg, OH) with raisedwire floors in an environmentally controlled buildingwith 24-h continuous light. The experimental periodswere d 8 to 20 (assays 1, 3, 5, and 6) and d 8 to 21 (assays2 and 4). There was no mortality in any of the bioassays.

Diet Development (Assays 1, 2, and 3)

Excess dietary Trp is converted to niacin with a wt/wt efficiency of approximately 2% and a M efficiency of4% (Baker et al., 1973). Hence, tight control of dietary Trpis required in studies of niacin efficacy. A corn glutenmeal (CGM) semipurified diet (Table 1) was formulatedto meet or exceed the chick’s requirements for all nutrientsexcept niacin and Trp. This diet contained an estimated4 mg/kg of bioavailable niacin (Yen et al., 1977) and 0.06%

true digestible Trp (Baker et al., 2002). This same basaldiet (made adequate in niacin) was previously used toestimate the true digestible Lys requirement (0.96%) andtrue digestible Trp requirement (0.16%) of chicks. As aresult, the true digestible Lys level was set at 0.96% inthe basal diet shown in Table 1. With these levels of Lysand Trp, the basal diet either met or exceeded digestibleamino acid levels prescribed in the Illinois ideal protein(Baker and Han, 1994; Baker et al., 2002). Also, whenproperly fortified with niacin, Trp, Lys, and other aminoacids, the CGM diet shown in Table 1 produced weightgain and feed efficiency values that were equal to thoseobtained with a standard 23% CP corn-soybean meal diet(Peter et al., 2000).

The nutrients manipulated in the 6 bioassays presentedherein were Trp, Lys, niacin, quinolinic acid, and picolinicacid. Feed-grade (FG) L-Trp (98.5%) was used in allassays; FG Lys (98.5% L-Lys�HCl, i.e., 79% Lys) was usedin the basal diets for all 6 assays as well as in the supple-mental Lys used in assay 3. Food-grade Lys (100% L-Lys�HCl, i.e., 80% Lys), however, was used as a supple-

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

EXCESS LYSINE AMELIORATES NIACIN DEFICIENCY 351

Table 1. Composition of the niacin-deficient experimental diet1

Ingredient (%)

Corn gluten meal (62.8% CP) 18.34Cornstarch 28.92Dextrose 28.29Soybean oil 4.00Mineral premix2 5.37NaHCO3 0.50Vitamin premix3 (niacin-free) 0.20Choline chloride 0.20Gly 11.00L-Lys�HCl4 (FG) 1.02L-Trp4,5 (FG) VARL-Thr4 (FG) 0.19DL-Met4 (FG) 0.17L-Arg 0.80L-Cys 0.19L-Ile 0.28L-Val 0.37L-His�HCl�H2O 0.14Bacitracin MD premix6 0.025DL-α-tocopheryl acetate7 (20 mg/kg) +Ethoxyquin7 (125 mg/kg) +Total 100.00

1The diet contained 3,400 kcal of ME/kg and 11.52% CP furnishedby corn gluten meal; it was fortified to 22% CP with Gly and essentialamino acids. The diet was analyzed to contain 0.062% Trp (estimated0.060% digestible Trp), 0.96% digestible Lys, 0.78% digestible sulfuramino acids, and an estimated 4 mg/kg of bioavailable niacin.

2Provided the following (per kg of diet): Ca3(PO4)2, 28.0 g; K2HPO4,9.0 g; NaCl, 8.89 g; MgSO4�7H2O, 3.5 g; ZnCO3, 0.10 g; CaCO3, 3.0 g;MnSO4�H2O, 0.65 g; FeSO4�7H2O, 0.42 g; KI, 40 mg; CuSO4�5H2O, 20mg; Na2MoO4�2H2O, 9 mg; H3BO3, 9 mg; CoSO4�7H2O, 1 mg; Na2SeO3,0.22 mg.

3Provided the following (per kg of diet): thiamin�HCl, 20 mg; ribofla-vin, 10 mg; D-Ca-pantothenate, 30 mg; vitamin B12, 0.04 mg; pyridox-ine�HCl, 6 mg; D-biotin, 0.6 mg; folic acid, 4 mg; menadione dimethylpyr-imidinol bisulfate, 2 mg; cholecalciferol, 15 �g; retinyl acetate, 1,789 �g;ascorbic acid, 250 mg.

4FG = feed grade; 98.5% L-Lys�HCl, 98% L-Trp, 98.5% L-Thr, 99% DL-Met.

5In most assays, 0.10% supplemental L-Trp was contained in the niacinassay diets. This level of supplemental Trp was shown to meet the Trprequirement of chicks fed the corn gluten meal diet containing excess(20 mg/kg) supplemental niacin. VAR = variable.

6Contributed 27.5 mg/kg of bacitracin methylene disalicylate (MD).7+ = supplemented as indicated.

ment to the basal diet in assays 4 and 5. The supplementalniacin (US Biochemical Corp., Cleveland, OH), quinolinicacid (Aldrich Chemical Co. Inc., Milwaukee, WI), andpicolinic acid (Sigma Chemical Co., St. Louis, MO) werereagent grade and assumed to be 100% purity.

Assay 1 was done to confirm the requirement estimatefor true digestible Trp in the presence of excess niacin asdone previously (Baker et al., 2002). The basal diet wassupplemented with 20 mg of niacin/kg and 0.02% L-Trpto accommodate 6 graded doses of L-Trp, thus achievingfinal dietary true digestible Trp levels of 0.08, 0.10, 0.12,0.14, 0.16, and 0.18%. The results indicated that a level of0.16% true digestible Trp was adequate for maximumgrowth under conditions of niacin adequacy.

Assay 2 was done to determine the minimal require-ment for niacin in a Trp-adequate diet (0.16% true digest-ible Trp). On d 8 posthatching, chicks were allotted todietary treatments that consisted of 6 graded doses (0 to20 mg/kg) of supplemental niacin. On d 21 posthatching,

weight gain and feed intake were determined. The datarevealed a requirement of 15.5 mg/kg of supplementalniacin (19.5 mg/kg of total bioavailable niacin) to supportmaximum growth.

The objective of assay 3 was to determine the adequacyof Lys in our experimental diet that was adequate in bothTrp and niacin. The basal diet for this assay contained0.96% digestible Lys, 24 mg/kg of bioavailable niacin, and0.18% digestible Trp. Lysine adequacy was determined bycomparing the basal diet to this same diet fortified with0.10% supplemental L-Lys provided by FG L-Lys�HCl.Weight gain and feed intake were determined on d 20posthatch.

Assay 4

This assay was done to determine the effect of 1% excessLys on the biopotency of supplemental niacin and on Trpas a precursor for niacin. On d 8, chicks were assignedto dietary treatments consisting of a negative control (noadded niacin or Trp) and 2 graded levels of niacin (4 and8 mg/kg) and 2 graded levels of Trp (160 and 320 mg/kg), both in the absence and presence of 1% supplementalexcess Lys. Based on previous research (Baker et al., 1973;Oduho and Baker, 1993), linear responses were expectedto each supplement. Food-grade L-Lys�HCl was used inthis bioassay to avoid any possible contaminating niacinactivity that might have been present in the FG L-Lys�HClused in the previous assays. On d 21, weight gain andfeed intake were determined.

Assay 5

The objective of this assay was to determine the effectof excess dietary (food-grade) Lys on weight gain ofchicks fed either niacin-deficient or niacin-adequate diets.Two levels of supplemental Lys (0 and 1%) from food-grade L-Lys�HCl were fed in the presence of 0 and 20mg/kg of supplemental niacin. On d 20, weight gain andfeed intake were determined.

Assay 6

This assay was carried out to determine the effect ofquinolinic acid and picolinic acid—2 metabolites in themetabolism of Trp to niacin (Figure 1)—on weight gainof chicks fed a niacin-deficient diet. On d 8, chicks wererandomly assigned to dietary treatments that includedthe basal niacin-deficient diet supplemented with niacin(6 mg/kg), quinolinic acid (100 mg/kg), or picolinic acid(4,200 mg/kg). Quinolinic acid was added to the diet ata level isomolar to 74 mg/kg of niacin. Picolinic acid wasadded to the basal diet at a level isomolar to 5,000 mg/kg of Lys. On d 21, weight gain and feed intake were de-termined.

Statistical Analysis

Data for all assays were subjected to ANOVA appro-priate for completely randomized designs (Steel et al.,

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

AUGSPURGER AND BAKER352

Table 2. Tryptophan requirement of chicks fed niacin-adequate diets1 (assay 1)

Supplemental Bioavailable Weight FeedL-Trp2 Trp2 gain3 intake3 Gain:feed3

Diet (%) (%) (g) (g) (g/kg)

1 0.02 0.08 51 176 2902 0.04 0.10 105 242 4343 0.06 0.12 161 318 5064 0.08 0.14 201 348 5785 0.10 0.16 210 358 5876 0.12 0.18 213 353 603SEM 6 8 11

1Data are means of 5 pens of 4 male chicks during the period 8 to 20 d posthatch; average initial weight was81 g.

2All diets contained supplemental levels of niacin (20 mg/kg) and Lys (0.81%) to meet requirements for thesenutrients. Thus, diet 1 contained 24 mg/kg of bioavailable niacin, 0.96% digestible Lys, and 0.08% digestibleTrp.

3Linear (P < 0.01) response, but 0.08 through 0.12% supplemental Trp were not different (P > 0.10).

1997). Where appropriate, treatment means were sepa-rated using orthogonal comparisons. For assay 2, the re-quirement for supplemental niacin was estimated by fit-ting the data to a single-slope broken-line least-squaresmodel (Robbins et al., 1979). Assays 1, 2, and 4 usedgraded dosing of Trp, niacin, or both, and single df linearand quadratic effects were evaluated for Trp dosing(assay 1) and niacin dosing (assay 2). In assay 4, in whicha zero dose plus 2 graded levels of Trp and 2 graded levelsof niacin were evaluated in the absence and presence of1% excess Lys, linear and quadratic responses to Trp andniacin were quantified. Also, main effects of niacin, Trp,and Lys were assessed. The data of assay 4 were furthersubjected to common-intercept multiple linear regression(Finney, 1978; Oduho and Baker, 1993), and for this,weight gain (Y) was regressed on supplemental niacinintake (X1) and Trp intake (X2) in both the absence andpresence of excess Lys. Assay 5 was analyzed as a 2 × 2factorial, with main effects of niacin and Lys togetherwith the interaction of niacin × Lys.

RESULTS

Diet Development (Assays 1, 2, and 3)

As expected (Peter et al., 2000; Baker et al., 2002), theCGM basal diet was severely deficient in Trp, as shown

Table 3. Niacin requirement of chicks fed Trp-adequate diets1 (assay 2)

Supplemental Bioavailable Weight Feedniacin2 niacin2 gain3 intake3 Gain:feed3

Diet (mg/kg) (mg/kg) (g) (g) (g/kg)

1 0 4 75 156 4812 4 8 101 188 5373 8 12 153 249 6144 12 16 198 299 6625 16 20 228 342 6676 20 24 238 350 679SEM 4 7 9

1Data are means of 5 pens of 4 male chicks during the period 8 to 21 d posthatch; average initial weight was74 g.

2All diets contained supplemental levels of Trp (0.10%) and Lys (0.81%) to meet requirements for thesenutrients (assay 1). Thus, diet 1 contained 0.16% digestible Trp, 0.96% digestible Lys, and 4 mg/kg of bioavailableniacin.

3Linear (P < 0.01) response, but 16 and 20 mg of supplemental niacin/kg were not different (P > 0.10).

by a marked linear increase (P < 0.01) in weight gain(Table 2) to supplemental Trp levels up to 0.08% (0.14%true digestible Trp). To provide a safety margin, however,subsequent assays involving niacin deficiency used dietswith at least 0.16% true digestible Trp. Niacin additionto a Trp-adequate diet also resulted in a large linear in-crease (P < 0.01) in weight gain to up to 16 mg/kg ofsupplemental niacin (Table 3). Broken-line analysis (r2 =0.97) revealed a minimal supplemental niacin require-ment of 15.5 mg/kg, giving a total bioavailable niacinrequirement estimate of 19.5 mg/kg. In assay 3, supple-mentation of 0.10% Lys to the basal diet with more-than-adequate Trp and niacin did not affect (P > 0.10) chickgrowth performance (Table 4).

Assay 4

Weight gain and feed efficiency increased linearly (P< 0.05) from dietary addition of either niacin or Trp (Table5). The 1% level of supplemental food-grade Lys in-creased (P < 0.05) weight gain and gain:feed in chicksfed all of the (niacin-deficient) diets. The multiple linearregression equation of gain (Y in g) as a function of sup-plemental niacin (X1 in mg) or Trp (X2 in mg) intake wasY = 62.5 + 29.08 X1 + 0.55 X2 (r2 = 0.84) for the dietswithout excess Lys. The similar equation for the 5 diets

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

EXCESS LYSINE AMELIORATES NIACIN DEFICIENCY 353

Table 4. Lysine adequacy of the corn gluten meal basal diet containingadequate levels of Lys, Trp, and niacin1 (assay 3)

Supplemental Weight FeedL-Lys2 gain intake Gain:feed

Diet (%) (g) (g) (g/kg)

1 0 220 375 5872 0.10 219 375 584SEM 5 7 10

1Data are means of 5 pens of 4 male chicks during the period 8 to 20d posthatch; average initial weight was 80 g.

2Diet 1 contained levels of supplemental Trp (0.12%) and niacin (20mg/kg) determined to be superadequate in assays 1 and 2. It alsocontained 0.81% supplemental Lys. Thus, diet 1 contained 0.18% digest-ible Trp, 24 mg/kg of bioavailable niacin, and 0.96% digestible Lys.

containing excess Lys was Y = 72.41 + 34.13 X1 + 0.62 X2

(r2 = 0.89). The intercept value for the diets containingexcess Lys was higher (P < 0.05) than that for the dietsnot containing excess Lys, suggesting that excess Lys wasincreasing utilization of the basal diet levels of eitherniacin (4 mg/kg) or digestible Trp (0.16%).

Assay 5

There was a niacin × Lys interaction (P < 0.01) for dietintake, weight gain, and gain:feed (Table 6). Thus, excessLys (1%) improved growth performance in niacin-defi-cient chicks but decreased growth performance in niacin-adequate chicks.

Assay 6

Weight gain and gain:feed increased (P < 0.01) in re-sponse to niacin supplementation, but picolinic acid andquinolinic acid did not affect (P > 0.10) growth perfor-mance of chicks fed a niacin-deficient diet (Table 7).

Table 5. Effect of excess dietary food-grade Lys in chicks fed niacin-deficient diets containing graded levels ofsupplemental niacin or Trp1 (assay 4)

Weight Feedgain3,4 intake3,4 Gain:feed3,4

Diet Supplement2 (g) (g) (g/kg)

1 None 62 183 3392 4 mg/kg of niacin 90 231 3903 8 mg/kg of niacin 125 274 4564 160 mg/kg of Trp 83 210 3955 320 mg/kg of Trp 107 253 4236 Diet 1 + 1.0% Lys 72 201 3587 Diet 2 + 1.0% Lys 110 264 4178 Diet 3 + 1.0% Lys 159 323 4929 Diet 4 + 1.0% Lys 98 238 41210 Diet 5 + 1.0% Lys 125 278 450SEM 6 8 17

1Data are means of 5 pens of 4 male chicks during the period 8 to 21 d posthatch; average initial weight was82 g.

2The basal diet was devoid of supplemental niacin and contained supplemental Trp (0.10%) and Lys (0.81%)to meet requirements (assays 1 and 3). Thus, diet 1 contained 4 mg/kg of bioavailable niacin, 0.16% digestibleTrp, and 0.96% digestible Lys.

3Linear (P < 0.01) response to supplemental niacin or Trp in both the absence and presence of excess Lys.4The main effects of niacin (P < 0.01), Trp (P < 0.01), and excess Lys (P < 0.05) were significant.

DISCUSSION

These experiments are the first to show that excessdietary Lys increases growth performance of chicks feda niacin-deficient, Trp-adequate diet. Our hypothesis wasthat excess dietary Lys would increase the yield of niacinfrom Trp through an accumulation of α-ketoadipic acid,which would cause endproduct inhibition of the mainTrp catabolic pathway to CO2 (Figure 1), thereby increas-ing the flux of ACS to nicotinic acid mononucleotide andNAD. In assay 4 (Table 5), we did not observe an increasein the ratio of slopes (Trp:niacin) in chicks fed the dietseries with 1% excess Lys. However, the basal level ofdigestible Trp (0.16%), although adequate for chicks fedniacin at its required level, would have been in consider-able excess for chicks fed the niacin-deficient diets in thisassay, in which growth rates ranged (by design) fromabout 30 to 60% of maximal. Thus, a portion of the basallevel of Trp was likely catabolized, some of which wouldhave gone to niacin. Excess Lys did increase the interceptvalue of the multiple linear regression equations, sug-gesting that the conversion of the basal diet level of Trpto niacin was indeed enhanced by excess dietary Lys.

Pellagra is the physiological outcome of niacin defi-ciency. This condition is prevalent in populations thatdepend on cereal-based diets that are low in bioavailableniacin and poor in protein quantity and quality (Gold-smith et al., 1952, 1961). Several studies have shown thatexcess dietary Trp can provide bioavailable niacin (e.g.,approximately 50 mg of Trp is converted to 1 mg ofbioavailable niacin; Krehl et al., 1945; Baker et al., 1973;Oduho and Baker, 1993), thereby showing that a dietarydeficiency of Trp is a related factor in the etiology ofpellagra in these populations. Although Trp is severelylimiting in cereal-based diets, Lys is probably even morelimiting, and this may also play a role in the physiologicaloutcome of niacin deficiency. Our data certainly show

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

AUGSPURGER AND BAKER354

Table 6. Effect of excess dietary food-grade Lys in chicks fed dietsdeficient or adequate in niacin1 (assay 5)

Weight Feedgain3 intake3 Gain:feed3

Diet Supplement2 (g) (g) (g/kg)

1 None 58 168 3452 20 mg/kg of niacin 215 363 5923 As 1 + 1% Lys 71 203 3504 As 2 + 1% Lys 174 325 535SEM 3 9 17

1Data are means of 4 pens of 4 male chicks during the period 8 to 20d posthatch; average initial weight was 81 g.

2The basal diet was devoid of niacin and contained required levelsof supplemental Trp (0.10%) and Lys (0.81%). Thus, diet 1 contained 4mg/kg of bioavailable niacin, 0.16% digestible Trp, and 0.96% digestibleLys.

3Niacin × Lys interaction (P < 0.05).

that excess dietary Lys produces a growth response inchicks fed a niacin-deficient, Trp-adequate diet. It seemspossible that with pellagragenic diets severely deficientin Lys, very little α-ketoadipate (from Lys catabolism)would be available to endproduct inhibit the main cata-bolic pathway of Trp oxidation to CO2.

Our proposed mechanism for the Lys response in nia-cin-deficient chicks, though logical, has not been proven.Future research should be directed at measuring the activ-ity of enzymes between ACS and α-ketoadipic acid toestablish whether they have indeed been inhibited byexcess Lys ingestion. High activity of these enzymes hasbeen shown to be correlated with the poor conversion ofTrp to NAD in ducks (Chen et al., 1996) and the lack ofTrp sparing of niacin in cats (DaSilva et al., 1952; Ikedaet al., 1965). Indeed, the decarboxylation of ACS catalyzedby picolinic carboxylase that leads to α-aminomuconatesemialdehyde biosynthesis (Figure 1) is a key enzyme indetermining the yield of NAD from Trp turnover (Ikedaet al., 1965). Both cats and ducks have a very high activityof this enzyme relative to chickens, rats, and humans.Whether excess Lys by virtue of producing α-ketoadipicacid as a metabolite might inhibit this enzyme remainsto be determined. It would also be helpful to measure α-ketoadipic acid per se in tissues of chicks fed diets withand without excess Lys.

We considered other possible explanations for the Lysresponse in niacin-deficient chicks. The FG Lys used inthe basal diet might have had some niacin activity presentas a contaminant, but the food-grade Lys used as a supple-ment in assays 4 and 5 was pure L-Lys�HCl. Thus, niacinactivity contamination of our Lys product cannot explainthe Lys response in niacin-deficient chicks. We also won-dered about the HCl portion of L-Lys�HCl in terms ofa possible beneficial effect on acid-base or cation:anionbalance. However, we were able to obtain the same posi-tive Lys response in niacin-deficient chicks given 1% ex-cess Lys from L-Lys acetate (data not shown).

In assay 6, we evaluated a dietary concentration of4,200 mg/kg of picolinic acid to observe whether it, likeLys, would produce a growth response in niacin-deficientchicks. Our reasoning was that this compound, being

Table 7. Quinolinic acid and picolinic acid have no effect on growthof chicks fed niacin-deficient diets1 (assay 6)

Weight Feedgain intake Gain:feed

Diet Supplement2 (g) (g) (g/kg)

1 None 45b 128b 352b

2 6 mg/kg of niacin 104a 195a 533a

3 100 mg/kg of quinolinic acid 48b 128b 375b

4 4,200 mg/kg of picolinic acid 43b 126b 341b

SEM 4 6 12

a,bMeans within columns with different superscript letters are differ-ent (P < 0.01).

1Data are means of 4 pens of 3 male chicks during the period 8 to 20d posthatch; average initial weight was 89 g.

2All diets were devoid of supplemental niacin and contained supple-mental Trp (0.10%) and Lys (0.81%) to meet requirements. Thus, diet1 contained 4 mg/kg of bioavailable niacin, 0.16% digestible Trp, and0.96% digestible Lys.

downstream from ACS, might endproduct inhibit ACScatabolism to CO2 and thereby increase the flux of ACSconversion to NAD. However, no response was obtainedfrom this dose of picolinic acid. Perhaps the dose used(equimolar to 5,000 mg/kg of Lys) was not high enoughto elicit a response.

The lack of an effect of dietary quinolinic acid on thegrowth of chicks fed a niacin-deficient, Trp-adequate dietis puzzling. Conversion efficiencies (wt/wt) of quinolinicacid to NAD in rats have been reported to be very low(Henderson, 1949; Krehl et al., 1950; Shibata and Murata,1991). Dann et al. (1940) found that a quinolinic acid dose25 times that of niacin was totally ineffective in preventingcanine blacktongue. However, a dose 100 times greaterthan niacin gave complete protection. Krehl et al. (1950)observed that 3-hydroxyanthranilic acid was vastly supe-rior to quinolinic acid as a niacin precursor for rats. Inassay 6, we supplemented quinolinic acid at a molar ratioto niacin of 12.3:1, but no growth response occurred. Theadequacy of dietary Trp in our assay, as opposed to thedeficiency of Trp in the research referenced above, maylead to the production of nonlimiting amounts of quino-linic acid for NAD biosynthesis, the supplementation ofwhich would not lead to increased production of niacin.Additionally, quinolinate transphosphoribosylase, theenzyme required to convert quinolinic acid to niacin, hasbeen reported to be only in the liver of rats (Ikeda etal., 1965), and Ijichi et al. (1966) reported that labeledquinolinic acid penetrated into rat liver cells to a verysmall degree, indicating that, if these relationships holdtrue in poultry species, exogenous quinolinic acid wouldbe poorly available for conversion to NAD. Althoughinefficient as a precursor, in vivo studies have showngrowth responses from large quantities of oral quinoli-nate in niacin-deficient rats. Because quinolinic acid ispresent in foods (Shibata et al., 1985), the exact conversionefficiency of quinolinate to NAD needs more attention.Noteworthy, however, is that giving quinolinic acid as adietary supplement probably does not reflect the samething as quinolinic acid being synthesized from ACS inliver cells.

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from

EXCESS LYSINE AMELIORATES NIACIN DEFICIENCY 355

ACKNOWLEDGMENT

Appreciation is expressed to C. S. Scherer for techni-cal assistance.

REFERENCES

Baker, D. H., N. K. Allen, and A. J. Kleiss. 1973. Efficiency oftryptophan as a niacin precursor in the chick. J. Anim. Sci.36:299–302.

Baker, D. H., A. B. Batal, T. M. Parr, N. R. Augspurger, and C.M. Parsons. 2002. Ideal ratio (relative to lysine) of tryptophan,threonine, isoleucine, and valine for chicks during the secondand third week of life. Poult. Sci. 81:485–494.

Baker, D. H., and Y. Han. 1994. Ideal amino acid profile forchicks during the first three weeks posthatching. Poult. Sci.73:1441–1447.

Chen, B., T. Shen, and R. E. Austic. 1996. Efficiency of trypto-phan-niacin conversion in chickens and ducks. Nutr. Res.16:91–103.

Dann, W. J., H. I. Kohn, and P. L. Handler. 1940. The effect ofpyrazine acids and quinolinic acid on the V-factor contentof human blood and upon canine blacktongue. J. Nutr.20:477–490.

DaSilva, A. C., R. Fried, and R. C. DeAngeles. 1952. The domesticcat as a laboratory animal for experimental nutrition studies.III. Niacin requirements and tryptophan metabolism. J. Nutr.46:399–409.

Finney, D. J. 1978. Statistical Methods in Biological Assay. 3rded. Charles Griffen and Co., London, UK.

Goldsmith, G. A., O. N. Miller, and W. G. Unglaub. 1961. Effi-ciency of tryptophan as a niacin precursor in man. J. Nutr.73:172–176.

Goldsmith, G. A., H. P. Sarrett, U. D. Register, and J. Gibbens.1952. Studies on the niacin requirement of man. I. Experimen-tal pellagra in subjects on corn diets low in niacin and trypto-phan. J. Clin. Invest. 31:533–542.

Heine, W., M. Radke, and K. D. Wutzke. 1995. The significanceof tryptophan in human nutrition. Amino Acids 9:191–205.

Henderson, L. M. 1949. Quinolinic acid metabolism. II. Replace-ment of nicotinic acid for the growth of the rat and neuros-pora. J. Biol. Chem. 181:677–685.

Ijichi, H., A. Ichiyama, and O. Hayaishi. 1966. Studies on thebiosynthesis of nicotinamide adenine dinucleotide. III. Com-parative in vivo studies on nicotinic acid, nicotinamide, and

quinolinic acid as precursors of nicotinamide adenine dinu-cleotide. J. Biol. Chem. 241:3701–3707.

Ikeda, M., H. Tsuji, S. Nakamura, A. Ichiyama, Y. Nishizuka,and O. Hayaishi. 1965. Studies on the biosynthesis of nicotin-amide adenine dinucleotide. II. A role of picolinic carboxyl-ase in the biosynthesis of nicotinamide adenine dinucleotidefrom tryptophan in mammals. J. Biol. Chem. 240:1395–1401.

Krehl, W. A., D. Bonner, and C. Yanofsky. 1950. Utilization ofniacin precursors and derivatives by the rat and neurospora.J. Nutr. 41:159–172.

Krehl, W. A., L. J. Teply, P. S. Sarma, and C. A. Elvehjem. 1945.Growth-retarding effect of corn in nicotinic acid-low rationsand its counteraction by tryptophane. Science 101:489–490.

Lan, S. J., and R. K. Gholson. 1965. A comparative study oftryptophan catabolism. J. Biol. Chem. 240:3934–3937.

Oduho, G. W., and D. H. Baker. 1993. Quantitative efficacy ofniacin sources for chicks: Nicotinic acid, nicotinamide, NADand tryptophan. J. Nutr. 123:2201–2206.

Oduho, G. W., Y. Han, and D. H. Baker. 1994. Iron deficiencyreduces the efficacy of tryptophan as a niacin precursor. J.Nutr. 124:444–450.

Pawlak, D., A. Tankiewicz, P. Mysliwiec, and W. Buczko. 2002.Tryptophan metabolism via the kynurenine pathway in ex-perimental chronic renal failure. Nephron 90:328–335.

Peter, C. M., Y. Han, S. D. Boling-Frankenback, C. M. Parsons,and D. H. Baker. 2000. Limiting order of amino acids andeffects of phytase on protein quality in corn gluten meal fedto young chicks. J. Anim. Sci. 78:2150–2156.

Robbins, K. R., H. W. Norton, and D. H. Baker. 1979. Estimationof nutrient requirements from growth data. J. Nutr.109:1710–1714.

Sainio, E. L., K. Pulkki, and S. N. Young. 1996. L-Tryptophan:Biochemical, nutritional and pharmacological aspects.Amino Acids 10:21–47.

Shibata, K., and K. Murata. 1991. Efficiency of exogenous quino-linic acid, a metabolite of tryptophan, as a niacin precursorin rats. Pages 645–647 in Kyurenine and Serotonin Pathways.R. Schwarcz, ed. Plenum Press, New York.

Shibata, K., K. Tanaka, F. Hayakawa, and K. Murata. 1985.Efficiency of exogenous quinolinic acid as niacin, and thequinolinic acid content in food. Bull. Teikoku-Gakuen 11:1–8.

Steel, R. G. D., J. H. Torrie, and D. A. Dickey. 1997. Principlesand Procedures of Statistics: A Biometrical Approach. 3rded. McGraw-Hill Publishing Co., New York.

Yen, J. T., A. H. Jensen, and D. H. Baker. 1977. Assessment ofthe availability of niacin in corn, soybeans and soybean meal.J. Anim. Sci. 45:269–278.

at National C

hung Hsing U

niversity Library on A

pril 10, 2014http://ps.oxfordjournals.org/

Dow

nloaded from